Symposium Organizers
Ioannis (John) Kymissis Columbia University
Max Shtein University of Michigan
Ana Claudia Arias Palo Alto Research Center
Tsuyoshi Sekitani University of Tokyo
C1: Inorganic Electronic and Photonic Devices I
Session Chairs
Monday PM, November 30, 2009
Commonwealth (Sheraton)
9:30 AM - **C1.1
ZnO and Organic Flexible Substrate Thin Film Transistors.
Thomas Jackson 1
1 Center for Thin Film Devices and Materials Research Institute, Department of Electrical Engineering, Penn State University, University Park, Pennsylvania, United States
Show AbstractOxide semiconductor thin film transistors (TFTs) offer significantly improved performance and stability compared to hydrogenated amorphous silicon or organic semiconductor devices. Using plasma enhanced chemical vapor deposition (PEALD) to deposit ZnO and Al2O3 thin films at 200 °C we have fabricated n-channel ZnO TFTs with field-effect mobility of 20-30 cm2/V.s on glass substrates and 15-20 cm2/V.s on flexible polyimide substrates. Using a gate-self-aligned process on glass substrates we have fabricated ring oscillators with 2.5 μm channel length TFTs with propagation delay <10 nsec/stage for a supply voltage of 18 V. The layer-by-layer PEALD process is effective in reliably and uniformly coating substrates with significant surface roughness and we have demonstrated >80% yield for 8,000 cross-over test structures on flexible polyimide substrates for a 50 nm Al2O3 insulating layer and a non-clean-room fabrication process, and working TFTs on rough copper flexible printed circuit material. We have also fabricated ring oscillators with 5 μm channel length TFTs on flexible polyimide substrates with propagation delay <60 nsec/stage for a supply voltage of 18 V. Working with John Anthony (University of Kentucky) we have also investigated functionalized pentacenes and related organic semiconductors that can provide both solubility and good molecular order in deposited films. Using fluorinated 5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TES-ADT) films deposited by simple spin casting we have fabricated p-channel organic TFTs (OTFTs) with mobility >1.5 cm2/V.s. By combining ZnO TFTs with spin-cast diF-TES-ADT OTFTs, we have demonstrated a simple 4-mask CMOS process and hybrid inorganic/organic TFT ring oscillators with propagation delay <150 nsec/stage. These CMOS circuits have μA-level leakage currents limited by undesirable current flow in the unpatterned diF-TES-ADT. By using ink jet printing to deposit the diF-TES-ADT, the leakage current is reduced to sub-pA level and inverter gains >30 are easily obtained, even using lower mobility ink-jet printed OTFTs. The combination of high performance ZnO TFTs and ZnO/organic CMOS circuits provides a foundation for a wide range of flexible substrate digital and analog circuits.
10:00 AM - C1.2
Advanced Designs in Stretchable Electronics for Electronic Eyeball Cameras.
Gunchul Shin 1 , Inhwa Jung 2 3 , Viktor Malyarchuk 2 3 , Song Jizhou 5 , Heung Cho Ko 6 2 3 , Yonggang Huang 7 8 , John Rogers 2 3 4 , Jeong Sook Ha 1
1 Chemical and biological engineering, Korea University, Seoul Korea (the Republic of), 2 Materials Science and Engineering, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States, 3 Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States, 5 Mechanical and Aerospace Engineering, University of Miami, Coral Gables, Florida, United States, 6 Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of), 7 Mechanical Engineering, Northwestern University, Evanston, Illinois, United States, 8 Civil and Environmental Engineering, Northwestern University, Evanston, Illinois, United States, 4 Beckman Institute for Advanced Science and Technology, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States
Show AbstractRecent reports of hemispherical electronic eye cameras based on compressible silicon optoelectronics technology validates a new and practical route to the implementation of Si technology on complex curvilinear surfaces [1]. As a means to improve the fill factor and pixel densities in such cameras, we report new photodetector and interconnect designs, together with a reduction of the pixel size by ~90 %, in layouts guided by theoretical mechanics analysis. These systems use arrays of islands each of which supports four photodetector pixels with edge-to-edge interconnects for improved compressibility. The basic materials science and mechanics aspects will be reported. Results of high resolution color images collected with cameras that use these strategies demonstrate the practical value of these results.[1] H. C. Ko, M. P. Stoykovich, J. Song, V. Malyarchuk, W. M. Choi, C.-J. Yu, J. B. Geddes III, J. Xiao, S. Wang, Y. Huang, and J. A. Rogers, Nature 454, 748 (2008).
10:15 AM - C1.3
Stretchable Silicon Electronics and Their Integration with Rubber, Plastic, Paper, Vinyl, Leather and Fabric Substrates.
Dae-Hyeong Kim 1 , John Rogers 1
1 Materials Science and Engineering, University of Illinois at Urbana Champaign, Urbana, Illinois, United States
Show AbstractElectronic systems that offer elastic mechanical responses to high strain deformations are of growing interest, due to their ability to enable new electrical, optical and biomedical devices and other applications whose requirements are impossible to satisfy with conventional wafer-based technologies or even with those that offer simple bendability. This talk describes materials and mechanical design strategies for classes of electronic circuits that offer extremely high flexibility and stretchability over large area, enabling them to accommodate even demanding deformation modes, such as twisting and linear stretching to ‘rubber-band’ levels of strain over 100%. The use of printed single crystalline silicon nanomaterials for the semiconductor provides performance in flexible and stretchable complementary metal-oxide-semiconductor (CMOS) integrated circuits approaching that of conventional devices with comparable feature sizes formed on silicon wafers. Comprehensive theoretical studies of the mechanics reveal the way in which the structural designs enable these extreme mechanical properties without fracturing the intrinsically brittle active materials or even inducing significant changes in their electrical properties. The results, as demonstrated through electrical measurements of arrays of transistors, CMOS inverters, ring oscillators and differential amplifiers, suggest a valuable route to high performance stretchable electronics that can be integrated with nearly arbitrary substrates. We show examples ranging from plastic and rubber, to vinyl, leather and paper, with capability for large area coverage.
10:30 AM - **C1.4
Inorganic Semiconductor Nanomaterials for Unusual Format Electronics.
John Rogers 1
1 , University of Illinois, Urbana, Illinois, United States
Show AbstractSingle crystalline inorganic semiconductor nanomaterials can be used to achieve high performance electronics on diverse classes of substrates. Advanced designs allow nearly any type of mechanical property to be obtained, ranging from bendability like a thin sheet of plastic to fully elastic stretchability like a rubber band. This talk reviews the materials and mechanics approaches, and then summarizes examples of their use in unusual classes of electronics for applications in biomedicine.
11:30 AM - **C1.5
Towards Organic-based Dielectrics for Low-temperature Silicon-based Devices for Large-area Electronics.
James Sturm 1 2 , Bahman Hekmatshoar 1 2 , Lin Han 1 2 , Sushobhan Avasthi 1 2 , Grigory Vertelov 1 3 , Yabing Qi 1 2 , Jeffrey Schwartz 1 3 , Antoine Kahn 1 2 , Sigurd Wagner 1 2
1 Princeton Institute for the Science and Technology of Materials (PRISM), Princeton University, Princeton, New Jersey, United States, 2 Department of Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 3 Department of Chemistry, Princeton University, Princeton, New Jersey, United States
Show AbstractThe stability of electronic devices processed at low-temperature is a major issue for commercialization. It is scientifically a difficult problem, since deposition at low temperature using low-cost techniques tends to create materials in highly non-equilibrium and/or non-stochiometric states, which are then prone to change over time. In our work to create ultra-stable amorphous silicon TFT’s, we have found that the gate dielectric plays at least as large a role as the semiconductor, and that much of the device drift can be attributed to trapping at dangling bonds in the insulator. Thus it is of fundamental interest to consider organic insulators, since they are usually deposited from pre-formed molecules, with only van der Waals bonding between the molecules. In this talk we examine three different stages of low-temperature silicon-based devices, representing a transition towards organic-based insulators. The first work is on amorphous silicon (a-Si) TFT’s using a conventional inorganic silicon nitride insulator deposited by plasma-enhanced CVD. By using hydrogen etching during PECVD to yield an effective in-situ annealing, which reduces the density of weak and/or dangling bonds in the semiconductor and gate dielectric, the lifetime of the devices can be extended from a standard one month in DC operation to an extrapolated 1000 years. However, this requires raising the process temperature to ~300 ○C. Second, we describe such amorphous silicon TFT’s with a novel gate insulator deposited by PECVD at room temperature from a mixture of oxygen and an organo-silicon precursor, hexamethyl disiloxane. The resulting hybrid of SiO2 and silicone results in devices more stable than and with at least twice the mobility of standard a-Si devices (mobilities as high as 2 cm2/Vs). Finally, we find devices with a direct deposition of a fully organic insulator on silicon are limited by the unsaturated silicon dangling bonds on the silicon surface. The resulting interface states within the silicon bandgap cause a very high level of carrier recombination and prevent modulation of the surface Fermi level, as required in MOS capacitors and FET’s. We will show how this issue can be addressed by a heteroatomic Diels-Alder reaction between the silicon surface and 1,10-Phenanthrenequinone (PQ), a semiconducting small organic molecule (EG ~ 3.2 eV). Followed by an organic insulator, the resulting structure yields a surface recombination velocity (a measure of interface states) and MOS capacitor-voltage characteristics approaching those of high quality silicon-silicon dioxide interfaces.
12:00 PM - C1.6
Position Controlled ZnO Nanowire Arrays on p-GaN for Light Emitting Diode.
Sheng Xu 1 , Zhong Lin Wang 1
1 School of Materials Science & Technology, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractLEDs covering green to violet light are still under intensive development due to the low efficiency of the available devices. In recent years, development has begun of so-called hybrid p–n hetero-junction LEDs, which are composed of hetero-junctions between oxide-semiconductor nanowires (NWs) and thin films underneath. Among all of the known oxide semiconductors, ZnO NWs are one of the best choices for blue emission because of not only a wide band-gap (3.37 eV) and a large exciton-binding energy (60 meV), but also their easy growth via chemical and physical vapor-phase approaches. We report the fabrication of high-brightness position controlled n-ZnO NWs/p-GaN thin film hybrid hetero-junction LED devices by directly growing n-type ZnO NWs arrays using hydrothermal decomposition on p-GaN wafers [1]. The position of the ZnO NWs was readily defined by electron beam lithography, with NW size and pattern pitch controllable [2]. A UV–blue electroluminescence (EL) emission was observed from the NWs–thin film hetero-junction diodes. The emission spectrum shifted towards short wavelengths, with an increase in forward bias applied to the device, with p-GaN as anode, indicating the modification of external voltage to the band profile in the depletion region. This means that the emission color can be slightly tuned by bias voltage. In addition, the hetero-junction LED device exhibited a high sensitivity in responding to UV irradiation due to the residual charge carriers excited by UV and the change in p–n junction energy gap. The 370nm UV emission was first enhanced and then dropped after UV illumination, indicating its stronger dependence on density of charge carriers in ZnO. The 400nm blue emission was less dependent on the UV excitation.[1] Xiao-Mei Zhang, Ming-Yen Lu, Yue Zhang, Lih-J. Chen and Zhong Lin Wang, “Fabrication of a High-Brightness Blue-Light-Emitting Diode Using a ZnO-Nanowire Array Grown on p-GaN Thin Film” Adv. Mater. 2009, 21, 1-4.[2] Sheng Xu, Yaguang Wei, Melanie, Kirkham, Jin Liu, Wenjie Mai, Dragomir Davidovic, Robert L. Snyder, Zhong Lin Wang, “Patterned Growth of Vertically Aligned ZnO Nanowire Arrays on Inorganic Substrates at Low temperature without Catalyst”, J. Am. Chem. Soc. 2008, 130, 14958-14959.[3] Research supported by DARPA, DOE and NSE.[4] For more information: http://www.nanoscience.gatech.edu/zlwang/
12:15 PM - **C1.7
Paper-e: Green Electronics for the Future.
Elvira Fortunado 1
1 Materials Science, FCT-UNL, Caparica, na, Portugal
Show AbstractIn this paper we report the use of a sheet of cellulose fiber-based paper as the dielectric layer used in oxide based semiconductor thin film field effect transistors (FETs). In this new approach we are using the cellulose fiber-based paper in an “interstrate” structure since the device is build on both sides of the cellulose sheet. Such hybrid FETs present excellent operating characteristics such as high channel saturation mobility (>30 cm2/Vs), drain-source current on/off modulation ratio of approximately 104, near-zero threshold voltage, enhancement n-type operation and sub-threshold gate voltage swing of 0.8 V/ decade. The cellulose fiber-based paper FETs characteristics have been measured in air ambient conditions and present good stability. The obtained results outpace those of amorphous Si TFTs and rival with the same oxide based TFTs produced on either glass or crystalline silicon substrates. The compatibility of these devices with large-scale/large-area deposition techniques and low cost substrates as well as their very low operating bias delineates this as a promising approach to attain high-performance disposable electronics like paper displays, smart labels, smart packaging, RFID and point-of-care systems for self analysis in bio-applications, among others.
C2: Inorganic Electronic and Photonic Devices II
Session Chairs
Monday PM, November 30, 2009
Commonwealth (Sheraton)
2:30 PM - **C2.1
Expandable Silicon for Large-Area Electronics Applications.
Peter Peumans 1
1 Electrical Engineering, Stanford University, Stanford, California, United States
Show AbstractMonolithic Silicon is the electronics technology with the lowest cost per unit functionality. Unfortunately, its form factor, i.e. wafers densely packed with electronics, is not compatible with that of large-area electronics applications. We have developed a method to divide a wafer or die into miniature dies connected in a two-dimensional network via Silicon springs that also support metal interconnects. These networks can be mechanically expanded to a much larger size to cover areas up to several square meters. The expansion process results in up to tens of thousands of miniature Silicon dies, interconnected in a two-dimensional network, placed accurately in the desired location. The Silicon springs and miniature dies are formed after the circuitry has been processed with a conventional process, using a MEMS-style deep-reactive ion etch step and the subsequent release via a wet or dry etch step. The expansion step consists of translation of four or more pads to the desired end location and takes place in seconds. The application of this platform technology to smart materials, RFID, displays, focal plane arrays and solar cells, will be discussed.
3:00 PM - C2.2
Effects of Mechanical Strain on the Electrical Performance of Amorphous Silicon Thin-Film Transistors with a New Gate Dielectric.
Katherine Song 1 , Lin Han 1 , Sigurd Wagner 1
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractThe stiff SiNx gate dielectric in conventional amorphous silicon thin film transistors (TFTs) limits their flexibility by brittle fracture. We report the effect on the overall flexibility of TFTs of replacing the brittle SiNx gate dielectric with a new, resilient SiO2-silicone hybrid material. This hybrid is deposited by plasma enhanced chemical vapor deposition from a mixture of hexamethyl disiloxane and oxygen. It has been found to combine the electrical properties of SiO2 with the flexibility of silicone. Individual TFTs on a 50μm-thick polyimide foil were bent to known radii for one minute and then re-flattened for measurement of transfer characteristics. The axis of bending was perpendicular to the source-drain current path. This process was then repeated on the same TFT until the TFT failed electrically. Compared with conventional TFTs made with SiNx, TFTs made with the new hybrid material demonstrated similar flexibility when strained in compression and significantly increased flexibility when strained in tension. Under bending to compressive strain, all TFTs tested delaminated from the substrate for compressive strains greater than 2%. Conventional a-Si:H/SiNx TFTs have been previously found to delaminate at a similar compressive strain. Under bending to tensile strain, TFTs made with the new hybrid material did not exhibit significant changes in transfer characteristics up to strains of ~0.8% and remained functional up to strains of 1.6%. Conventional a-Si:H/SiNx TFTs have been found to exhibit changes in transfer characteristics at ~0.4% tensile strain and remain functional for strains of up to 0.5%, a value over 3 times less than that for TFTs made with the new hybrid material. These results suggest that TFTs made with the new dielectric material have the potential to enhance the flexibility and durability of large area electronics, such as displays and sensors. We thank Universal Display Corporation for supporting this research.
3:15 PM - C2.3
Crystallization of Patterned Nanocrystalline Micro-structures Through Self-heating.
Ali Gokirmak 1 , Gokhan Bakan 1 , Adam Cywar 1 , Kadir Cil 1 , Nicholas Williams 1 , Helena Silva 1
1 Electrical and Computer Engineering , University of Connecticut, Storrs, Connecticut, United States
Show AbstractAmorphous silicon is commonly used for conventional large area electronics applications due to its uniformity and low leakage currents. Polycrystalline (poly-) silicon offers higher performance however device to device variations are significant. Nano-crystalline (nc-) Si is a mixed phase consisting of an amorphous Si matrix containing Si nanocrystals. nc-Si offers higher performance than amorphous Si and less variability than poly-Si. nc-Si can be deposited at lower temperatures compared to poly-Si and its relatively high conductivity allows crystallization of patterned micro-structures through current annealing.Rapid current annealing of these structures through high-amplitude short duration pulses result in self-heating and melting. Growth from melt is initiated upon termination of the pulse [1] and single-crystal domains can be formed if a strong thermal gradient can be maintained during the process and the width of the structures are smaller than the thermodynamically favored grain size. Hence, this approach allows crystallization of lithographically defined structures at room temperature. Effect of the substrate and stress conditions (down to < 50 ns) on this crystallization approach will be discussed. [1] G. Bakan, A. Cywar, H. Silva and A. Gokirmak, "Melting and crystallization of nanocrystalline silicon microwires through rapid self-heating," Appl. Phys. Lett., 2009.
3:30 PM - C2.4
UV Anti-reflection Coating for Large Plastic Optics.
Yi Du 1 , Lunet Luna 1 , Wuisiew Tan 2 , Grinia Nogueira 2 , Michael Rubner 2 3 , Robert Cohen 1 3
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Center for Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract A novel thin film nanoporous coating for large-area poly(methyl methacrylate) (PMMA) Fresnel lenses has been designed to enhance the collection of UV light from cosmic ray showers at the international space station. A good coating technology should ensure a conformal coating without significant distortion of the optics. We have successfully demonstrated that a conformal antireflection (AR) coating can be achieved by the layer-by-layer (LbL) assembly method. The refractive index and film thickness can be precisely controlled by varying assembly conditions, and so the optimized AR performance can be targeted at the desired wavelength range of 300 nm to 400 nm. The AR coating design utilizes a graded index in which high- and low-refractive index regions of quarter-wave stacks were generated with commercially available oxide nanoparticles and synthesized hollow silica nanoparticles. The hollow silica nanoparticles have a diameter of 80 nm and a shell thickness of 10 nm. The refractive index of these novel nanoparticles can be as low as 1.10 and the thin film thickness can be controlled precisely to within ± 15 nm. The reflectance of the PMMA substrates was successfully reduced from 7% to 0.5% while the optimized transmission is increased from 92% to 98% at 400 nm. A spray coating LbL procedure has been employed to reduce the processing time and cost, and to scale up the AR coating to accommodate large-area PMMA lenses. The angled wedges of the Fresnel lenses are evenly coated and the optic nature is largely preserved. SEM and AFM were used to characterize the AR coating films while the refractive index and film thickness were determined by the spectroscopic ellipsometry and profilometry.
3:45 PM - C2.5
Photolithography Based Ultra-Fast Self-Assembly of Micro-Scale Particles by Open-Channel Flow.
Sun Choi 1 , Albert Pisano 1
1 Berkeley Sensor and Actuator Center (BSAC), UC Berkeley, Berkeley, California, United States
Show Abstract Micro-scale particles are crucial building blocks for numerous applications such as bio-assays, photonics and microelectronic devices. Self-assembly of micro particles is highly favorable in micro-fabrication since it provides easier, faster and more convenient way to construct micro-structures. A number of self-assembly techniques based on electrostatic force, electrochemical reactions, surface functionalization and microfluidics have been demonstrated in order to induce and control particle assembly. Especially, fluidic self-assembly is emerging as a promising pathway to guide and assemble micro structures due to its high yield and great simplicity. It is reported that particles of meso-scale, micro-scale in fluid can be assembled and structured by lateral capillary forces between particles in suspension and the mechanism of two-dimensional crystallization of micro particles was also explained. There have been several attempts to control the formation of two-dimensional micro particle-assembly from micro particle dispersed suspension, however, those approaches had drawbacks such as long assembly time and compatibility with conventional photolithography techniques. Here, we describe an ultra-fast microfluidic approach to self-assemble micro-particles in three-dimension by taking advantage of simple photolithography and capillary action of micro particles-dispersed suspensions. Theoretical aspects of fast-assembly speed have been discussed and various sizes of silica microspheres and silica gel microspheres have been successfully assembled within micro-open channel by using this approach. Also, microsphere-based line patterns have been also fabricated by releasing resist which was used for guiding open-channel flow. We anticipate the presented technique will give a huge impact on semiconductor and MEMS(Micro Electro Mechanical Systems) fields since it offers not only an fast way of controlling micro-scale particle assembly but also superb compatibility with photolithography, which can lead to an easy integration of particle assembly with existing CMOS and MEMS fabrication processes.
4:00 PM - C2:Inorganic2
break
C3: Passive Devices
Session Chairs
Monday PM, November 30, 2009
Commonwealth (Sheraton)
4:15 PM - C3.1
Wrinkling and Cracking of Gold Thin Films on PDMS.
Patrick Goerrn 1 , Oliver Graudejus 1 , Sigurd Wagner 1
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractWe have studied the wrinkling and cracking of thin gold films on poly(dimethylsiloxane) (PDMS). The gold thickness, prestrain of the substrate and its temperature during electron-beam evaporation were varied using combinatorial approaches. Typical wrinkling wavelengths lie in the range of 10 to 40µm and amplitudes up to 6µm. For high substrate temperatures the wrinkles form 50-µm to 3-mm sized domains. Interdomain wavelengths are similar but amplitudes are less. Crack sizes in the gold film range from ~ 1 µm (microcracking) to the mm range. Elastically stretchable electronic systems enable new applications beyond the reach of rigid wafer based technologies. However, the highest electrical performance is found in rigid materials such as inorganic semiconductors or metals. Therefore various approaches have been developed to integrate stiff materials and elastomeric substrates into elastically stretchable systems. In one such approach, bonding ribbons of single crystals of silicon to a prestrained elastomeric PDMSsubstrate and releasing the strain causes wrinkling of the silicon. This wrinkled composite can then be stretched much further without cracking than the silicon by itself, combining superior stretchability with desirable electrical performance. Theoretical models have been developed to describe the wrinkling amplitude and wavelength of these systems based on the Young’s moduli of the two materials. Wrinkled gold thin films are known to show improved flexibility compared to smooth layers. Recently, microcracked thin gold films on PDMS have been found to be elastically stretchable by up to 80% while remaining electrically conducting. But contrary to the first approach thin films can not be placed on the prestrained flexible susbtrate without influencing it. A growing film causes a varying strain to the substrate. The increase of the substrate temperature during that deposition also influences the mechanical properties of the substrate and leads to thermal expansion and so additional strains. Moreover some deposition technologies may alter the PDMS surface resulting in a change of its Young’s modulus. It is thus not surprising that deposition parameters have an impact on cracking and wrinkling. We found the critical prestrain for wrinkling to decrease with higher deposition temperature. When patterning a defined deposited area in the mm range via shadow masks the wrinkling wavelength is increased by around two orders of magnitude compared to identical deposition without shadow mask. Near the edges of the patterned area microcracks are found, even for thick gold layers. The results of this study enable a better understanding of the behavior of thin films on elastomeric substrates and spotlight the critical parameters for the production of elastically stretchable conductive gold thin films on PDMS.
4:30 PM - C3.2
A New Material for the Encapsulation of Plastic Foil Substrates.
Lin Han 1 , Prashant Mandlik 1 2 , Sigurd Wagner 1
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 2 , Universal Display Coporation, Ewing, New Jersey, United States
Show AbstractWe have introduced a new material to thin-film electronics. The material is a hybrid of SiO2 and silicone. It is deposited by plasma-enhanced chemical vapor deposition (PE-CVD) from a silicone monomer and oxygen. The “hybrid” has desirable properties of SiO2 but is not brittle. Its first application is as an environmental barrier for organic light-emitting diodes. We also discovered that the hybrid can replace the conventional SiNx gate dielectric in amorphous-silicon thin-film transistors (a-Si:H TFTs), where it enables an electron field-effect mobility of 2 cm2/Vs. Here we focus on use of the hybrid as the backchannel passivation layer for a-Si:H TFTs. We first encapsulate a polyimide foil substrate by depositing the hybrid on both faces. The TFTs made on this substrate have the inverted-staggered back channel-encapsulated geometry. First a Cr/Al/Cr(15/40/15nm) gate metal sandwich is thermally evaporated and patterned for gate electrodes. Then a 150-nm thick SiO2-silicone hybrid gate dielectric is deposited at room temperature by PE-CVD, followed by 150-nm i a-Si:H at Tdep of 150oC. 150-nm thick SiO2-silicone hybrid is deposited for back-channel passivation, which is patterned. 40-nm n+ a-Si:H source/drain layer is deposited at Tdep of 150oC. 15/40/15-nm Cr/Al/Cr sandwich is thermally evaporated and patterned for source/drain contacts. a-Si:H islands are separated and vias to gate electrodes are opened by etching. The TFTs adhere well to the foil substrate, have an electron field-effect mobility of 1.2 cm2/V s, subthreshold slope of 300 mV/decade, ON/OFF ratio of 107,and leakage current of 10-12A. We will discuss the TFT characteristics with focus on effects of substrate encapsulation and backchannel passivation with the new hybrid material.
4:45 PM - C3.3
Multilayer Polymer Films for Photonic Applications.
Kenneth Singer 1 2 , Joseph Lott 2 , Hyunmin Song 2 , Yeheng Wu 1 , Juefei Zhou 1 , James Andrews 3 , Eric Baer 2 , Anne Hiltner 2 , Christoph Weder 2
1 Department of Physics, Case Western Reserve University, Cleveland, Ohio, United States, 2 Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 3 Department of Physics and Astronomy, Youngstown State University, Youngstown, Ohio, United States
Show AbstractRoll-to-roll processing for low-cost production of new generations of polymeric optoelectronic devices is receiving great attention. We have been investigating continuously rolled, multilayer polymer melt co-extrusion processes for creating substrates and active devices. The process in our laboratory uses a layer multiplication scheme capable of producing hundreds or thousands of A-B layers over a wide range of thicknesses down to the nanometer scale yielding thin multilayer polymer films rolling onto a chilled take-up roll. As these multilayer polymer films are one-dimensional photonic crystals, they could find a number of applications such as lasers, optical switches, and other photonic applications. We report on our studies of optically-pumped surface-emitting lasers fabricated from co-extrusion processed multilayer films.We have fabricated all-polymer lasers both as distributed feedback lasers (DFB) and distributed Bragg reflector (DBR) lasers. As DBR lasers, a gain layer of a polymer doped with a laser dye is laminated between two multilayer polymer reflectors. The distributed Bragg mirrors are made using the layer-multiplying co-extrusion process combining poly(methyl methacrylate) (PMMA) with polystyrene (PS) with 128 layers for each Bragg reflector. Two photoluminescent dyes were incorporated into appropriate polymers as gain media dopants. Distributed feedback lasers were also fabricated by incorporating the same dyes into one of the polymers before the multilayer co-extrusion process and are processed onto a single roller. These lasers were fabricated from dye-doped SAN25 (a styrene acrylonitrile – random copolymer with 25 mol% acrylonitrile, n = 1.56), and THV 220G (a fluoroelastomer terpolymer of vinylidiene fluoride, hexafluoropropylene, and trifluoroethylene, n = 1.37). The gain species were Rhodamine 6G (R6G), a commercially available dye, and 1,4-bis-(α-cyano-4-methoxystyryl)-2,5-dimethoxybenzene (C1RG).The lasers emitted high quality spatial and temporal modes normal to the film surface. The lowest threshold for lasing for both DBR and DFB lasers was observed to be about 90 μJ/cm2, with slope efficiencies of about 5% and 19% for DFB and DBR lasers, respectively. We have studied the dependence of the threshold on the optical density of the gain layer for DBR lasers and found that the optimum optical density is about 1.1, in agreement with modeling the system as a 4-level end-pumped laser including pump absorption and emission re-absorption. Improved laser performance can be expected as the layer uniformity is improved and more stable gain media are included.
5:00 PM - C3.4
Large Area Flexible Electronics Fabrication by Selective Laser Sintering of Nanoparticles with a Scanning Mirror.
Seung Hwan Ko 1 2 , Heng Pan 1 , Daeho Lee 1 , Nico Hotz 1 , Costas Grigoropoulos 1
1 Mechanical Engineering, UC Berkeley, Berkeley, California, United States, 2 Mechanical Engineering, KAIST, Daejon Korea (the Republic of)
Show AbstractThe development of electric circuit fabrication on heat and chemically sensitive polymer substrates has attracted significant interest as a pathway to low-cost or large-area electronics. We demonstrated the large area, direct patterning of microelectronic structures by selective laser sintering of nanoparticles without using any conventional, very expensive vacuum or photoresist deposition steps. Surface monolayer protected gold nanoparticles suspended in organic solvent was spin coated on a glass or polymer substrate. Then low power continuous wave Ar-ion laser was irradiated as a local heat source to induce selective laser sintering of nanoparticles by a scanning mirror system. Metal nanoparticle possessed low melting temperature (<150°C) due to thermodynamic size effect, and high laser absorption due to surface plasmon mode. These make metal nanoparticles ideal for the low temperature, low laser energy selective laser processing, and further applicable for electronics fabrication on a heat sensitive polymer substrate. We extended our laser selective sintering of nanoparticles research to a large area (> 4” wafer) using scanning mirror to demonstrate current technology for industry level fabrication.
5:15 PM - C3.5
Maskless Large-Area Fabrication of Passive Optical Elements Through Modulated Surface Stress Lithography (MS2L).
Mathias Dietzel 1 , Sandra Troian 1
1 Applied Physics, California Institute of Technology, Pasadena, California, United States
Show AbstractOptical lithography remains the most widely used method for fabricating micro- to nanoscale structures in an efficient, parallel fashion. A major drawback of mask-based manufacturing methods, however, is the difficulty in adapting quickly to new layouts and designs, which requires insertion of new masks. Harsh developer and etchant solutions also produce highly roughened surfaces subject to significant scattering losses. Sequential methods such as ink-jet printing or dip pen lithography offer easy adaptation to new layouts but with consequent lower resolution and much slower processing speeds.In this talk, we explore through finite element simulations a promising route for large-area, maskless and adaptive fabrication of polymeric optical elements based on film patterning by modulated surface stress control. The surface tension of a nanoscale film of molten polymer is spatially modulated to induce thermocapillary stresses, leading to film elongation near cooler regions and film depressions near warmer regions. The thermocapillary stresses are purposefully tuned by the choice of the geometry and thermal gradients applied to exert a predominant effect and rapidly overcome stabilizing capillary stresses caused by the increase in surface area during structure formation. This procedure leads to positive replication of a pattern if the desired design is imposed by definition in a cooler substrate placed above the film, leaving a thin air gap between the film and the upper plate, or negative replication if the design is imposed by an array of thin film heaters from below. Successive rapid cooling of the molten polymer film to a temperature below the glass transition temperature affixes the pattern in place once the desired film shape and feature amplitudes have been achieved. As an example of this patterning process, we demonstrate the fabrication of a straight ridge waveguide by local modulation of the surface stress along the polymer film interface and analyze its optical performance through supplementary simulations of the corresponding electro-magnetic equations.Since structures fabricated by this method ultimately solidify from a melt, it is anticipated to result in specularly smooth surfaces with ultralow scattering losses. Rapid adaptation to various patterns can be achieved by simply varying the temperature distribution imposed, which can be modified in situ during the formation process. Our results indicate that this novel patterning technique can provide an important step toward truly adaptive, large-area, rapid, robust and low-cost fabrication of small-scale optical devices based on polymeric materials.
5:30 PM - C3.6
Mechanical Sintering Techniques for Printed Electrodes with Various Work-function on a Plastic Substrate.
Manabu Yoshidda 1 , Kouji Suemori 1 , Sei Uemura 1 , Satoshi Hoshino 1 , Noriyuki Takada 1 , Takehito Kodzasa 1 , Toshihide Kamata 1
1 , AIST, Tsukuba, Ibaraki, Japan
Show AbstractA print technique of an electrode on a plastic substrate is one of the most important technique for developing a printed large area device. Especially, preparation of a metal electrode with low work function by printing is very important to develop a printed active devices such as diode and transistors. However, it is well known that it is very difficult to prepare a printed metal electrode except for noble metals such as Ag and Au. Because many other kinds of metals are easily oxidized during print process owing to high temperature annealing treatment. In this study, we have examined to develop a new annealing technique on a printed electrode to reduce the process temperature during metal printing. We have newly developed a mechanical sintering technique in which mechanical forces is applied on a printed metal pattern. Control of the direction balance of applied mechanical force was effective to reduce resistivity of the printed metal without any destruction of plastic substrate. Furthermore, distribution control of metal particle in the metal ink was also effective to reduce resistivity. By using this technique, we have succeeded in the preparation of an aluminum, zinc, copper and tin electrode on a plastic substrate.On the other hand, we have tried to prepare a metal alloy ink to control the work function of printed electrode. Metal alloy ink was composed of two kinds of metal particles. Work function of the electrode was controlled by changing composition of these metal contents in a alloy ink. By applying our developed mechanical sintering technique on the printed alloy pattern, printed electrode with various work function from 3.5eV to 5eV could be prepared on a plastic substrate. These printed alloy was effective to improve the performance of printed diode and transistors.
5:45 PM - C3.7
Process Related Issues on Selective Area Patterning of Zinc Oxide by Inkjet Printing.
Yen Nan Liang 1 , Boon Keng Lok 2 , Xiao Hu 1
1 Materials Technology, Nanyang Technological University, Nanyang Avenue Singapore, 2 , Singapore Institute of Manufacturing Technology, Singapore Singapore
Show AbstractInkjet printing has been employed as a production technology to pattern inorganic functional materials such as ZnO and TiO2 etc. The influences of coffee ring profiles of inkjet printed pattern towards the process and device performance have been less described and worth investigation. In this work, selective area patterning of zinc oxide (ZnO) was carried out by inkjet printing of ZnO sol-gel precursor. The profiles of inkjet printed ZnO patterns adopted typical coffee ring profiles; which were affected by substrate’s temperature, ink concentration, ink volume deposited. It is further demonstrated the employment of inkjet printed ZnO patterns as (a) seed layers for ZnO nanorods growth and (b) active layer of thin film transistor. ZnO nanorods selectively grow on ZnO seed layer; which diameters changed at different regions of same patterns. Transistor characteristics depended very much on the morphologies of the deposited thin film. Inkjet printing was shown to be a better choice than spin-coating for thin film transistor fabrication.
Symposium Organizers
Ioannis (John) Kymissis Columbia University
Max Shtein University of Michigan
Ana Claudia Arias Palo Alto Research Center
Tsuyoshi Sekitani University of Tokyo
C4: Printing, Integration, and Packaging
Session Chairs
Tuesday AM, December 01, 2009
Commonwealth (Sheraton)
9:30 AM - **C4.1
Techniques and Materials for Making Flexible, Deformable, and Elastic Electronic Surfaces.
Sigurd Wagner 1 , Oliver Graudejus 1 , Lin Han 1 , Wenzhe Cao 1 , Patrick Goerrn 1
1 Electrical Engineering and Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, New Jersey, United States
Show AbstractDuring the past few years, new flexible electronic surfaces have been demonstrated with imaginative techniques that make use of established as well as unconventional materials. Can these exciting experiments provide guiding principles for designing flexible structures and selecting, or even designing, materials for them? In an effort to answer this question we will first review structures that have been made, and the materials that have been used. Then we will focus on a recent and fascinating development: new materials that have been introduced specifically for making electronics flexible: (i) organic polymer foils that can be processed at high temperature; (ii) organic device materials that keep functioning under plastic deformation; (iii) metal conductor/polymer composites and (iv) dispersions of carbon nanotubes in polymer films, capable of extreme plastic or even elastic deformation; and (v) inorganic-organic hybrids that combine the impermeability and high dielectric breakdown strength of brittle inorganic materials with the resilience of organic polymers. Inspection of these new materials suggests that we are entering a new field of materials science. This field is expanding through the search for optimal combinations of opto-electronic and mechanical properties. We will attempt to identify the principles by which this search proceeds.
10:00 AM - C4.2
Electronic & Mechanical Device Components Incorporating Carbon-Based, Organic and Inorganic Active Materials onto Flexible Substrates.
Daniel Hines 1 , Ellen Williams 2 , Nathan Siwak 3 4 , Reza Ghodssi 3 4
1 , Laboratory for Physical Sciences, College Park, Maryland, United States, 2 Department of Physics, University of Maryland, College Park, Maryland, United States, 3 Dept. of Electrical & Computer Engr, University of Maryland, College Park, Maryland, United States, 4 The Institute for Systems Research, University of Maryland, College Park, Maryland, United States
Show AbstractTransfer printing processes have previously been demonstrated for fabricating electronic components onto flexible substrates, using a wide variety of active layer materials, including Pentacene (Pn), poly(3-hexylthiophene) (P3HT), carbon nanotube mats (CNTM), graphene, and a variety of polymer dielectric layers including poly(hydroxystyrene) (PHS), polystyrene (PS), polycarbonate (PC) and poly(methylmethacrylate) (PMMA). The printing method has been used to fabricate transistors, resistors, capacitors, inductors and resonators onto plastic substrates in an additive process that does not require the use of chemical processing on the device substrate. Here we demonstrate the extension of the process to fabricate mechanical resonators on flexible substrates. Structures were constructed from both Si membranes and thin, Au coated polymer films transfer printed onto polycarbonate (PC) substrates. The substrates were prepatterned with cavities ranging from 100 x 100 µm to 200 x 300 µm in dimension. The structures were aligned over a cavity and printed in place. The mechanical response of the structures was measured optically in air using an AC voltage applied to a probe tip to actuate the resonator. For a Si resonator of thickness 70 nm and area 10,000 µm2 a resonant frequency of approximately 480 KHz was measured. For a 200 nm thick PC film coated with 35 nm of Au and area 10,000 µm2, a resonant frequency of approximately 520 KHz was measured. Preliminary calculations suggest a fundamental resonant frequency of 42 KHz for the Si resonator and 80 KHz for the Au coated PC film. Differences between measured and calculated frequencies are most likely related to stresses in the printed structures, which are visible in the resulting resonators. Devices, which contain less stress in the printed membrane, are being fabricated which are expected to exhibit resonant frequencies closer to the calculated values. Details of the printing methods and characteristics of the resulting devices will be presented as a function of membrane material, thickness, printing conditions and cavity dimensions.
10:15 AM - C4.3
Ink Jet Printing Devices and Circuits.
Steven Ready 1 , Ana Arias 1 , Sanjiv Sambandan 1
1 Electronic Materials and Devices Laboratory, Palo Alto Research Center, Inc., Palo Alto, California, United States
Show AbstractFor several years there have been many efforts to employ ink jet technologies in the fabrication of consumer electronics. The potential of displacing large and expensive pieces of electronic fabrication equipment and processes with seemingly appropriately scaled inexpensive alternatives is attractive. However, of course, the devil is in the details. Feature size, accuracy, registration and materials all have sever impacts on design rules, processing, performance and the types of devices appropriate to the technology. Here we present a look at some of the materials and deposition challenges along with solutions developed at PARC. The discussion will include the defining of printed features >5μm with ±1.5μm drop placement and layer to layer alignment accuracy, the materials characteristics of the generally complex functional fluids of interest required for reliable jetting and device performance. Examples of ink jet fabricated integrated circuits, working displays, imagers and microfluidic devices and RGB color filters for 15" displays will be shared.
10:30 AM - C4.4
Development of SiO2 Dielectric Thin Film Prepared by the Low-temperature Solution Process.
Takehito Kodzasa 1 , Sei Uemura 1 , Kouji Suemori 1 , Manabu Yoshida 1 , Satoshi Hoshino 1 , Noriyuki Takada 1 , Toshihide Kamata 1
1 , National Institute of Advanced Industrial Science and Technology, Tsukuba Japan
Show AbstractIt is mostly important to develop the fabrication technology of the dielectric thin film with high insulation performance and surface flatness by the solution process. We have developed a technique to fabricate a silicon dioxide (SiO2) dielectric thin film by the low temperature solution process. The thin film prepared by multi-source photo-oxidation technique below 200oC showed excellent dielectric performance with high resistivity in the order of 10 to the 16 ohm*cm and surface flatness with the same degree of thermal oxidized SiO2 thin film on the silicon wafer (RMS=0.15nm). In addition, it is showed that the production of thick film of SiO2 with high dielectric performance and surface flatness is possible by applying over-coating technique. These indicate that this SiO2 production technique is greatly useful for the large-area printed electronics technology.
10:45 AM - C4.5
Advanced Transfer Printing Modes for Heterogeneous Integration.
Andrew Carlson 1 , Paulius Elvikis 2 , Shuodao Wang 3 , Yonggang Huang 3 4 , Placid Ferreira 2 , John Rogers 1 5
1 Materials Science and Engineering, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States, 2 Mechanical Science and Engineering, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States, 3 Mechanical Engineering, Northwestern University, Evanston, Illinois, United States, 4 Civil and Environmental Engineering, Northwestern University, Evanston, Illinois, United States, 5 Chemistry, University of Illinois, Urbana-Champaign, Urbana, Illinois, United States
Show AbstractMeeting the increasing performance demands of many existing and emerging microelectronic and optoelectronic technologies often require devices fabricated by large-scale integration of disparate classes of materials into spatially organized, functional arrangements. Transfer printing, a process in which an elastomeric stamp element acts as a carrier between a prepatterned donor wafer of ‘inks’ (semiconducting nanomaterials and others) and a specified target substrate, provides a route for direct integration of diverse nanostructures and materials into single, unified systems. Transfer printing efficacy, particularly ink release from the viscoelastic transfer element (stamp) to substrate, can be enhanced by engineering the stamp/ink interface to support a variety of mechanical forces that alter its adhesive strength. We have demonstrated a series of active polydimethylsiloxane (PDMS) stamps containing small pressurized microchannels and reservoirs which can be used to locally inflate the stamp surface, providing an unprecedented level of dynamic control over stamp geometry during printing. Exploiting the well-established molding techniques of soft lithography, a variety of reservoir and channel designs were investigated to reveal critical factors influencing the printing process such as contact area manipulation of the stamp/ink interface and surface-supported shear loads. Additionally, PDMS stamps with independently programmable active regions were fabricated to demonstrate selective retrieval and printing of different ink layers onto a variety of unusual substrates such as plastic sheets and glass. Demonstration of several of heterogeneously integrated electronic devices illustrates the technologically relevant systems that can be fabricated using this approach.
11:30 AM - **C4.6
Fluidic Surface-Tension-Directed Self-Assembly of Miniaturized Semiconductor Dies Across Length Scales and 3D Topologies.
Robert Knuesel 1 , Heiko Jacobs 1
1 Electrical Engineering, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractThis talk will review recent progress in the engineered fluidic surface-tension-directed self-assembly involving liquid solder. The process is applied to the assembly of discrete inorganic semiconductor device components at different length scales producing electrically interconnected devices and systems. Prior results included the assembly with unique angular orientation and contact pad registration, parallel packaging, and the programmable assembly of various types of light emitting diodes. Recent progress on the scaling of the minimal die size from 300 to 30 µm will be presented which required the development of a new delivery system to concentrate and effectively introduce the components to solder based receptors. Specifically components are pre-oriented at a liquid-air or liquid-liquid interface and transferred onto the solder based receptors using a dynamic contact angle using a dipping process. Recent applications include the tiling of curved and 3D surfaces with single crystal semiconductors including the formation of curved 3D solar cells.
12:00 PM - C4.7
Self-aligned Nano Imprinted Organic TFTs.
Christoph Auner 1 , Herbert Gold 1 , Barbara Stadlober 1 , Ursula Palfinger 1 , Anja Haase 1 , Maria Belegratis 1 , Joachim Krenn 1 , Meltem Sezen 2 , Thomas Haber 2 , Werner Grogger 2
1 Institute of Nanostructured Materials and Photonics, Joanneum Research, Weiz Austria, 2 Institute for Electron Microscopy and Fine Structure Research, Graz University of Technology, Graz Austria
Show AbstractThe success of organic electronics depends, among others, on the speed in its applications. As smaller devices are faster, there is a major drive for downscaling the Organic Thin-Film Transistor (OTFT). Nano Imprint Lithography (NIL) is on the one hand fit for reel-to-reel-processing which is a fast, robust, and cheap industrial process, and on the other hand it maintains an excellent spatial resolution, which is limited to date by tool-making capabilities only. Our major goal is the fabrication of OTFTs with sub-micrometer channel-length using the NIL process. Downscaling of the channel length has several advantages such as higher frequencies, higher integration density, higher yield and lower operation voltages. In order to fully exploit the potential for speed increase, also the parasitic gate-to-source capacitance has to be minimized, meaning that the overlap between gate-to-source (and also gate-to-drain) electrodes has to be as small as possible, which is not trivial in submicron devicesThere have been a few approaches up to now to minimize this overlap by using self-aligned or self-assembly procedures [1]-[3], relying either on self-aligned inkjet printing of source electrodes via selective modifying the surface of the previously printed drain electrodes [1], or on a backsubstrate exposure technique using the lower electrode as a photomask and the substrate as the gate dielectric [2] or on optical patterning of a hydrophobic self-assembled monolayer by backsubstrate exposure thus defining the self-aligned position of the solution-processed upper electrodes. These examples have the disadvantage of being either very complicated in terms of introducing additional costly and error-prone wet chemical process steps [1], or impeding any reduction of the gate dielectric layer thickness below 500 nm which is necessary for sub-µm technology [2], or being limited to channel lengths not smaller than 3 µm. In this paper, we present a self-aligned process for the fabrication of NIL subµm TFTs, where the source and drain pattern is already included in the design of the gate structures and the respective stamp. As soon as the gate area is fabricated by NIL stamping, the source and drain electrodes are already defined and their position with respect to the gate is fixed. This has the additional advantage that in envisioned r2r processes misaligned transistors due to substrate shrinkage or expansion can be avoided. First results of large-area processed submicron OTFTs are presented.[1] C. W. Sele, T. V. Werne, R. H. Friend, and H. Sirringhaus, Adv. Mat. 17, 99 (2005)[2] A. Bonifiglio, F. Mamaeli, and O. Sanna, Appl. Phys. Lett. 82. 3550 (2003)[3] M. Ando, M. Kawasaki, S. Imazeki, H. Sasaki, T. Kameta, Appl. Phys. Lett. 85, 1849 (2004)
12:15 PM - C4.8
Ultrasonic Spray Deposition of Electrochromic Materials.
Robert Tenent 1 , Dane Gillaspie 1 , Anne Dillon 1
1 Materials and Computational Science, National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractWide-spread implementation of energy efficient electrochromic “smart windows” will depend critically upon the development of cost effective manufacturing techniques that can be implemented at large scale. Atmospheric pressure ultrasonic spray coating represents an excellent route to achieve this goal compared to more conventional vacuum deposition methods, such as sputtering. During the ultrasonic spray deposition process a liquid precursor material is pumped to an ultrasonically excited nozzle which leads to solution atomization. The atomized material is carried to a heated substrate by a controlled gas flow. Upon deposition on the sample surface, precursor species react in order to form the desired film. Imperative to the success of this method is the development of new chemistries that target films of the desired properties.In this presentation we will discuss our work to develop a variety of cost-effective chemistries for deposition of electrochromic metal oxide based materials. In addition to the specific chemistry, several factors related to the ultrasonic spray deposition process can impact the performance of our materials. Among these factors are substrate temperature, precursor concentration, delivery gas flow and other parameters related to solution atomization. We have already optimized deposition processes to achieve nickel oxide films that function successfully as counter electrode materials in half cell devices. These results as well as investigations for the spray deposition of tungsten oxide as an active layer and initial attempts at full device integration will be presented.
12:30 PM - C4.9
Ink-jet Printed Silver Electrodes for Organic Field-effect Transistors.
Gregory Whiting 1 , Rene Kist 1 , TseNga Ng 1 , Sanjiv Sambandan 1 , Beverly Russo 1 , Brent Krusor 1 , Ana Arias 1
1 , Palo Alto Research Center (PARC), Palo Alto, California, United States
Show AbstractInk-jet printing is a desirable manufacturing technique for electronic devices as this mask-less, additive method should allow for integration of different electronic components over large substrate areas at low cost. In order to realize entirely jet-printed devices, appropriate printed electrodes for organic semiconductor-based field effect transistors (FETs) must be chosen. Typically, printable conductive inks are silver based, which can lead to poor energy level matching with the organic semiconductor. This report will study the use of both a nanoparticle silver ink as well as a soluble silver precursor ink and will show that by modifying the surface chemistry of the printed silver contacts, though the use of self-assembly techniques (particularly thiol chemistry), the electronic and wetting characteristics of the electrodes can be tailored. Combining these modified electrodes with organic semiconductors such as 6,13-bis(triisopropyl-silylethynyl) pentacene (TIPS-pentacene) yields high performance devices with field-effect mobilities > 1 cm2 V-1 s-1.
12:45 PM - C4.10
Investigation of Electrochemically Active Printed Materials for Energy Storage in Packaging Applications.
Dan Steingart 1 , Joshua Gallaway 1 , Abhinav Gaikwad 1
1 Chemical Engineering, City College of New York, New York, New York, United States
Show AbstractPrinted electronics, from large area skins to small footprint sensor tapes, require unique energy storage capabilities to fully realize their potential as flexible, customizable devices. While innovative engineering and clever circuit design have increased the capabilities of such electronics while lowering the overall current draw, printed devices tend to require significantly higher potentials than those made through CMOS processes. Additionally some applications require flexibility that makes hermetic packaging and circuit bussing difficult. We have been investigating the use of inks that serve both as circuit busses as well as storage precursors for printed zinc-silver oxide batteries. These cells show promise in that they use existing roll-to-roll materials and processes to create high potential, flexible energy storage. Nanoparticle inks of silver were used to print single and multiple cell batteries on a variety of substrates, and the addition of ZnO/KOH solution and current creates an electrochemical storage system on first charge. Despite having organic additives that normally interfere with electrochemical processes we find that these cells are in fact electrochemically active and provide expected behavior both as a current collector for zinc anodes as well as a cathode in the form of Ag2O or AgO. Capacity and power density of these electrodes is compared to printed slurries as well as traditional silver foils. By creating microfluidic channels for the electrolyte we can begin to determine electrode strength as a function of cycle number and state of charge.
C5: Organic Electronic and Photonic Devices
Session Chairs
Tuesday PM, December 01, 2009
Commonwealth (Sheraton)
2:30 PM - **C5.1
Self-Assembled Monolayer-Based Gate Dielectrics for Large-Area Electronics.
Hagen Klauk 1
1 , Max Planck Institute for Solid State Research, Stuttgart Germany
Show AbstractOrganic thin-film transistors (TFTs) often employ relatively thick gate dielectrics with small capacitance (usually below 100 nF/cm2) und thus typically require operating voltages above 10 V. For certain applications, organic TFTs that can be operated with voltages between 2 and 3 V will be beneficial. For example, state-of-the-art organic light-emitting diodes (OLEDs) that employ doped transport layers require supply voltages between 2.5 and 3 V, reaching efficiencies between 10 cd/A (red and blue) and >70 cd/A (green) [1]. To realize flexible active-matrix displays with such OLEDs, low-voltage TFTs will be required. A second example for large-area electronics applications that will benefit from low-voltage organic TFTs are hybrid systems in which TFT arrays share signals and power with silicon-based processor units, which are typically designed to operate with a supply voltage of 2 or 3 V [2]. To realize flexible organic TFTs that can be operated with voltages of 3 V or less, a low-temperature-processed gate dielectric with a capacitance above 500 nF/cm2 is required. A promising approach are hybrid dielectrics based on a thin, plasma-grown aluminum oxide layer (with a thickness of 3.5 to 4 nm) in combination with an alkyl-phosphonic-acid self-assembled monolayer (SAM). The SAM has a thickness of about 1.5 to 2 nm, giving a total oxide/SAM dielectric thickness of 5 to 6 nm and a gate dielectric capacitance of 0.7 to 1 µF/cm2. Despite its small thickness and the low process temperature, the oxide/SAM dielectric provides leakage currents of less than 10 µA/cm2 at 3 V. This allows p-channel and n-channel organic TFTs on glass and on flexible polymeric substrates to operate with voltages between 1.5 and 3 V and with excellent static and dynamic characteristics, including large carrier mobility, large on/off current ratio, steep subthreshold slope, small gate leakage currents, and large cut-off frequency.[1]P. Wellmamm et al., J. Soc. Inf. Display, vol. 13, p. 393, 2005 (see also: www.novaled.com).[2]T. Sekitani et al., Int. Solid-State Circuits Conf. (San Francisco, February 2009).
3:00 PM - **C5.2
Fabrication of High Performance Organic Thin Film Transistor Arrays and Its Application to 5-inch Flexible Displays.
Yoshihide Fujisaki 1 , Tatsuya Takei 1 , Yoshiki Nakajima 1 , Hiroto Sato 1 , Mitsunori Suzuki 1 , Hirohiko Fukagawa 1 , Genichi Motomura 1 , Toshihiro Yamamoto 1 , Hideo Fujikake 1 , Taiichiro Kurita 1 , Shizuo Tokito 1
1 , NHK Science&Technical Research Laboratories, Setagaya-ku, Tokyo Japan
Show AbstractOrganic thin-film transistors (OTFTs), which can be fabricated at low tempeature, have attracted considerable attention for their application to low-cost large-area electron devices. Many studies have been reported that have aimed at developing a wide range of plastic electronics such as flexible displays, sensors, etc. In this talk, we will discuss the recent work, focusing on OTFT arrays and its application to flexible liquid crystal (FLC) and organic light emitting diode (OLED) displays. In order to achieve high-quality and high-resolution images, OTFT with high performances such as a high mobility, high ON/OFF ratio, low sub-threshold slope (SS) and low voltage operation, are demanded. We developed pentacene-based low-voltage operation OTFT with aTa2O5 gate insulator prepared at a low temperature process [1]. To achieve a high mobility and high ON/OFF ratio in the array structure, surface treatments of the gate insulator and patterning process of organic semiconductor films were investigated in detail. The resulting OTFT array with a short channel length of 5μm showed a high mobility of 0.3-0.4cm2/Vs, ON/OFF ratio over 107, VTH=2.7V, and low SS=0.3V/decade. On the other hand, solution-process, which offers advantages for realizing low-cost and large-area fabrication, is desirable approach. We fabricated OTFTs with solution-deposited materials such as fluoropolymer insulator and polythiophene-based semiconducting polymer. Electrical characteristics and stabilities of these devices will be also discussed. In the final section, we will demonstrate OTFT-driven flexible displays. Both of the FLC device and the OLED device were successfully integrated with pentacene-based OTFT arrays. The flexible FLC device was fabricated on the pentacene-OTFT array using printing and lamination techniques [2]. A field-sequential-color system with a flexible backlight unit was developed and used to drive the display at a high farme rate of 360Hz. 5.8-inch OLED display was also fabricated on the pentacene-based OTFT array. Phosphorescent polymer materials, which can be patterned by ink-jet printing, were used for emitting layer of OLEDs [3]. Color moving images were successively shown on the 5-inch display using an active-matrix driving technique of the OTFT at a low driving voltage of 15V. [1] Y. Iino et al., Jpn. J. Appl. Phys. 42 (2003) 299. [2] Y. Fujisaki et al., J of the SID, 15/7 (2007) 501. [3] M. Suzuki et al., IDW’08 Digest (2008) 1515.
3:30 PM - C5.3
Electrical and Mechanical Stabilities on 2V-Operational Flexible Organic Transistors with a Self-assembled Monolayer.
Kenjiro Fukuda 1 , Kazunori Kuribara 1 , Tomoyuki Yokota 1 , Shinya Takatani 1 , Tsuyoshi Sekitani 1 , Ute Zschieschang 2 , Hagen Klauk 2 , Takao Someya 1
1 Department of Electric and Electronic Engineering and Department of Applied Physics, The University of Tokyo, Tokyo Japan, 2 , Max Planck Institute for Solid State Research, Stuttgart Germany
Show AbstractWe have systematically investigated the electrical and mechanical stabilities of organic field-effect transistors (FETs) that employ self-assembled monolayer (SAM) gate dielectrics on plastic films [1]. The FETs can be operated within 2 V and exhibited excellent electrical characteristics: Mobility up to 0.7 cm2/Vs and on/off ratio exceeding 105. The change in mobility was negligible for temperatures up to 100 °C. After annealing, the threshold voltage shift originating from DC bias stress was suppressed. To demonstrate the high degree of mechanical flexibility, bending experiments were performed. We found that transistors were not damaged when bent to a radius of 4 mm, indicating excellent mechanical flexibility. High-performance organic transistors with low operating voltage were achieved within the constraints of a low-temperature, flexible-substrate-compatible, cost-effective, large-area, and simple fabrication approach. Organic transistors with SAM gate dielectrics were manufactured by vacuum evaporation and solution processes. A 25 nm thick Al layer was deposited as the gate electrodes through a shadow mask in a vacuum evaporator on a glass or plastic substrate (thickness: 75 μm). A thin aluminum oxide film with a large density of hydroxyl groups for molecular adsorption was formed by oxygen-plasma treatment (300 W, 30 min for glass, 150 W, 15 min for plastic ), and a SAM of n-octadecylphosphonic acid (2.1 nm thick) was prepared from a 2-propanol solution at room temperature. Purified pentacene was deposited to form 30 nm thick channel layers on the AlOx/SAM gate dielectric. Finally, a 50 nm thick Au layer was evaporated through a shadow mask to form the source/drain contacts. The FETs exhibited high stability to temperatures as high as 100 °C. The mobility of the transistors at 30 and 80 °C was 0.54 and 0.58 cm2/Vs, respectively, thus the change in mobility was only 7%. This result was different from the result of the temperature dependence on the mobility of pentacene FETs with polymer dielectrics, where the mobility increased dramatically with increasing temperature [2]. Furthermore, we have examined DC bias stress effects and found that the drain current decreases by about 14% when voltages of VDS=VGS= –2 V are applied for 1 h in ambient air. In FETs that are annealed after fabrication at 70 °C for 12 h in a nitrogen environment the bias stress effect is greatly suppressed, and the drain current only decreases by 5% or less even after 10 h of continuous bias stress. The electrical performance of the FETs was also characterized under mechanical bending stress. The FETs were not degraded and remained functional at the bending radius of 4 mm. [1] H. Klauk et al., Nature, 445, 745 (2007). [2] T. Sekitani et al., Appl. Phys. Lett. 85, 3902 (2004).
3:45 PM - C5.4
Semiconductor-Dielectric Interfacial Study using Spectral-Spatial Photocurrent Probes and 1/f Noise Probe in Organic Field Effect Transistors.
Zhang Jia 1 , Inanc Meric 1 , Kenneth Shepard 1 , Ioannis Kymissis 1
1 , Columbia University, New York, New York, United States
Show AbstractOrganic Field Effect Transistors (OFETs) are sensitive to the chemistry of the gate dielectric/semiconductor boundary both during and after fabrication. In particular, surface states can be introduced on polymer gate dielectrics that shift the threshold voltage if the dielectric layer is exposed to oxidizing agents prior to semiconductor deposition. To understand the interfacial properties can not only benefit practical applications but also further the understanding of transport mechanism in OFETs. Photocurrent and noise probes are well suited for investigating the properties of such process-induced interface trap states thanks to their high sensitivity to the electronic transport processes in the material. We have measured and analyzed the gate bias dependence of the photocurrent in pentacene organic field effect transistors which have been doped using a UV-ozone treatment and compared these to the response of identical devices produced in an oxygen and ozone free environment. The wavelength dependent photocurrent spectrum shows new photocurrent peaks in oxygen doped samples in the range of 350 nm to 450 nm, which corresponds to energy transitions (2.66 eV, 2.76 eV, 2.95 eV, 3.15 eV)larger than the pentacene HOMO-LUMO gap. The acceptor-like states generated by UV treatment of the dielectric layer, although outside the HOMO-LUMO gap, can free some holes into the accumulated charge pool and thus change the threshold voltage. We have also characterized the dependence of $1/f$ noise on the drain current in control OFETs fabricated with no air exposure and those whose dielectric has been exposed to UV-ozone. The noise in control devices is proportional to $I_{D}^{2}$, while noise in UV-exposed devices is proportional to $I_{D}$. This difference indicates that in the UV-exposed devices, noise is generated by acceptor-like states introduced into the HOMO, while in the control devices, interface states within the HOMO-LUMO gap are the dominant noise source. Under 405nm illumination, the change in 1/f noise is proportional to the change in $I_{D}$ for both devices implying that no additional noise-generation sites are created in the empty states which have donated charge to the channel. Spatially localized photocurrent is futher utilized to study mobility variance along the channel and preliminary results are presented.
4:30 PM - **C5.5
Materials for Unconventional Electronic Circuitry using Organic and Inorganic Building Blocks.
Tobin Marks 1
1 Chemistry, Northwestern U., Evanston, Illinois, United States
Show AbstractIn this lecture, materials synthetic approaches to the fabrication of organic and other unconventional electronic circuitry by high throughput, large area printing techniques are discussed. Issues here concern not only the rational design of high-mobility p- and n-type organic and non-organic semiconductors for CMOS electronics, but also modular high-k dielectrics with ultra-high capacitance, low leakage, high breakdown fields, and radiation hardness. It is seen that these approaches are applicable to organic, organometallic, and inorganic semiconducting materials.
5:00 PM - C5.6
Programmable Block-Copolymer Self-Assembly.
Joel Yang 1 , Yeon Sik Jung 2 , Jae-Byum Chang 2 , Caroline Ross 2 , Karl Berggren 1
1 electrical engineering and computer science, MIT, Cambridge, Massachusetts, United States, 2 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractWithout external guidance, block copolymers (BCPs) will self assemble to form complex but random nanostructures at dimensions that are currently inaccessible by conventional optical lithography. However, previous work has focused on ordering the BCP self-assembly to form periodic structures over large areas. To fully tap the potential of BCPs, we need an approach that allows a designer to guide the BCP into complex arbitrary structures. As a step in this direction, we developed a method that we call "programmable self-assembly". In this method, we information is introduced into the self-assembling system by patterning a sparse array of dots or dashes on a substrate with electron-beam lithography. These structures are made in hydrogen silsesquioxane resist and are ~10 nm in lateral dimension and ~35-nm tall. A cylindrical-morphology polystyrene-polydimethylsiloxane (PS-PDMS) BCP film that is subsequently applied interacts with these nanostructures and seeks a topology that minimizes free energy. The resultant structures are linear BCP structures that connect the HSQ nanostructures. For example, when a rectangular lattice of posts is used, the BCP would align itself either in the horizontal, vertical or diagonal directions (with various angles) to maintain an unstrained BCP natural spacing. We also show that the BCP lattice can be strained using a sparse array of dashes instead of circular posts. These effects of commensurability between the BCP and the nanostructures, and straining of the BCP lattice are useful tools that a designer could use to pattern complex structures. We demonstrated both global and local control the orientation of BCP lines, formation of cross-points, nested-elbow structures and meander patterns. These structures have potential for use in device fabrication. In comparison with an all-electron-beam-lithography process, this approach has the advantage in throughput; only a small fraction of the final desired structures are patterned lithographically leaving the missing structures for the BCP to fill-in. For comparison, a pattern that would take days of electron-beam lithography exposure will only take hours with the programmable-self-assembly approach. One potential application of this approach is in the fabrication of large-area master molds for nanoimprint lithography.
5:15 PM - C5.7
Organic Infrared Up-conversion Device.
Do Young Kim 1 , Neetu Chopra 1 , Pieter De Somer 1 , Dong Woo Song 1 , Franky So 1
1 Dept of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractAll organic light up-conversion devices are attractive because their compatibility with lightweight, rugged, or flexible plastic substrates opens up many applications that cannot be addressed using conventional inorganic technologies. Here, we demonstrated all organic NIR-to-visible up-conversion devices using tin phthalocyanine (SnPc):C60 bulk heterostructure layer as the NIR sensitizer and fac-tris(2-phenylpyridinato) iridium (III) (Irppy3) as the emitter. We have made the following device: ITO/SnPc:C60 (20 nm)/1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) (50 nm)/Irppy3:4,4-N,Ndicarbazole-biphenyl (CBP) (20 nm)/tris[3-(3-pyridyl)-mesityl]borane (3TPYMB) (50 nm)/LiF (1 nm)/Al (100 nm). The SnPc:C60 mixed layer was used as a poor hole injection layer as well as an infrared sensitizing layer, TAPC was used as a hole transport layer, CBP doped with 7% Irppy3 was used as a phosphorescent light emitting layer, and 3PTYMB was used as an electron transport layer. A control device without the infrared sensitizing layer was also fabricated. The luminance-current-voltage (LIV) characteristics were measured with and without the 830 nm infrared light irradiation. Without infrared light irradiation, emission was not observed until 13 V and the device showed a very low current efficiency of 6 cd/A compared with the controlled device with a maximum current efficiency of 80 cd/A. The low efficiency is due to poor hole injection from the SnPc:C60 layer and hence the device is extremely electron dominant. On the contrary, when the device was irradiated with infrared light, the device turned on at 2.7 V with a maximum current efficiency of 107 cd/A at a brightness of 100 cd/m2. This current efficiency is even higher than that of the control device. The higher efficiency in up-conversion device under IR laser irradiation indicate an enhanced charge balance in the up-conversion device compared to the control OLED. The maximum ON/OFF ratio of luminescence intensity was about 1400 at 12.7 V. The maximum photon-to-photon conversion efficiency (ηcon) from incident IR light photons to emitted green light photons is 2.7% at 15V.
5:30 PM - C5.8
High Sensitivity, Large Area, Flexible, Passive and Active Pressure Sensors Employing Structured Elastomeric Films.
Chee-Keong Tee 1 , Stefan Mannsfeld 3 , Randy Stoltenberg 2 , Soumen Barman 2 , Beinn Muir 2 , Zhenan Bao 2
1 Electrical Engineering, Stanford University, Stanford, California, United States, 3 , Stanford Synchrotron Radiation Lightsource, Menlo Park, California, United States, 2 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractOf all the human sense organs, the skin is the largest, continuously providing important pressure information when in contact with the surroundings while performing our daily activities, such as drinking a glass of water. The multitudinous sense receptors are both arrayed differently and have different sensitivities in various regions of the human body. In the effort to imbue robots with greater autonomy in a constantly changing natural environment, contact pressure sensors are vital, especially in healthcare automatons where they will come into direct touch contact with humans depending on their assigned role. Therefore, a robust fabrication scheme for large area pressure sensors on flexible substrates with selective sensitivity over a wide range of pressures is needed.We present a high sensitivity, capacitance-type pressure sensor using structured polydimethylsiloxane (PDMS) made using a simple soft lithography process on flexible substrates. A molding method was developed to enable films of good uniform thickness with good reproducibility to be achieved despite the high viscosity of PDMS. We evaluated and compared different micro-structures; and demonstrate that having a structured film allows for linear response with at least 10 times greater sensitivity as compared to unstructured films (1 %/kPa) of similar thickness. Contact pressures can be measured in the sub-kilopascal range. In addition, the structured film quickly returns to the ‘off’ state with a time decay constant of about two orders of magnitude less than unstructured films even at high contact pressures. The technique can be easily adapted for different sensitivity specifications by varying the film’s micro-structure. The facile production process of our pressure sensors allows for ease of scaling up for manufacturing and production. Furthermore, we are able to build active devices using organic semiconductors by utilizing the structured PDMS as the gate dielectric, modulating the current via different contact pressure on the active device. Our work provides a simple, cost-effective method for enabling large area pressure sensing.
5:45 PM - C5.9
Organic Thin Film Transistors Fabricated on Resorbable Biomaterial Substrates.
Christopher Bettinger 1 , Zhenan Bao 1
1 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractMicroelectronic systems utilizing organic materials afford many advantages over traditional silicon-based systems including the possibility of fabrication on polymeric substrates, which are suitable for a broad range of flexible electronics applications including conformal devices and displays. Recent concomitant advancements in organic electronics and biodegradable polymers processing suggest that there is the potential for the use of biodegradable polymeric systems for the development of biodegradable electronic devices for potential use in biomedical or environmental applications. We investigated the use of poly(L-lactide-co-glycolide) (PLGA) as a potential substrate material platform for organic electronic devices. We fabricated organic thin film transistors in top contact configuration using PLGA as the substrate, which composed 99.89% of the final device by mass. We used evaporated silver as the gate electrode, spin coated poly(vinyl alcohol) as the gate dielectric, evaporated 5,5′-bis-(7-dodecyl-9H-fluoren-2-yl)-2,2′-bithiophene (DDFTTF), a water stable p-channel semiconductor, as the active layer, and evaporated gold patterned using a shadow mask as the source-drain electrodes. Transistors fabricated in this manner exhibited average mobilities of approximately 0.21 cm2-sec-1-V-1 and Ion/Ioff up to 5.5x103 with threshold voltages of approximately -15.4 V. These structures performed stably under water, but failed upon exposure to phosphate buffered saline. Device degradation was simulated by submerging the device in citrate buffer at 37 oC. Mass loss degradation kinetics showed that these devices underwent 50% mass loss at 8 weeks and near complete resorption at 10 weeks. The device functionality presented in this work is the first step towards realizing more complex biodegradable and compostable electronic devices. Subsequent design, fabrication, and integration of other simple electronic components fabricated from resorbable electronically active materials could be used in the realization of temporary electronic devices such as resorbable biomedical implants.
C6: Poster Session: Large Area Processing and Patterning for Optical, Photovoltaic, and Electronic Devices
Session Chairs
Ana Arias
Ioannis Kymissis
Tsuyoshi Sekitani
Max Shtein
Wednesday AM, December 02, 2009
Exhibit Hall D (Hynes)
9:00 PM - C6.1
Preparation of Nano-Porous Polymer Films having the Smallest Size of 80nm Under High Humidity Conditions.
Takatoshi Nishio 1 , Makoto Kashiwagi 2 , Koji Miyazaki 3 , Masayuki Yahiro 4 , Chihaya Adachi 5
1 , Lintec Corporation, Saitama Japan, 2 , BEANS Laboratory, Tokyo Japan, 3 , Kyushu Institute of Technology, Fukuoka Japan, 4 , ISIT, Fukuoka Japan, 5 , Kyushu Univ., Fukuoka Japan
Show AbstractNano-porous polymer films are attractive materials with potential application in the fields of the organic electronics devices such as a substrate material of an organic photovoltaic cell and an organic thermoelectric element. The micro-patterned films can be prepared by the casting of a polymer solution under humid conditions. However, it is difficult to create a nano scale patterned porous structure by same method, since more lager porous structure was formed by the aggregation of water droplets on the surface of polymer solutions. A suitable process was found by our investigation. The nano-porous structure was obtained by dip-coater with an evaporative humidifier. Various fabrication parameters affecting the pore size such as polymer concentration, properties of solvent, coating speed, solution temperature, substrate and the coating speed of the polymer solutions are studied. The nano-porous polymer film in the range from 80 to 150 nm was obtained from 0.2 wt% of polystyrene/dichloromethane (Mw=320,000) solution at 4 degree C.
9:00 PM - C6.10
Drying with a Gas-flow Method Applied to the Phosphor Layer to Improve the Reliability of Flexible Photoluminescent Displays.
Kukjoo Kim 1 , Seung Hun Kim 1 , Cheol Jang 1 , Sung-il Ahn 1 , Kyung Cheol Choi 1
1 Department of Electrical Engineering and Computer Science, KAIST, Daejeon Korea (the Republic of)
Show AbstractAs the anticipation for flexible displays increases, reliability problems appear to be a critical issue with this product. Particularly for flexible photoluminescent displays or flexible PDPs (Plasma Display Panels) [1,2], which have merits such as self emissive display, simple structure, and easy driving, a variety of research on materials and structures is being conducted to improve the lifetime [3]. However, few studies have reported on the fabrication of phosphor layers, which is essential for flexible PDPs. Therefore, we investigate the effect of the phosphor layer on the lifetime of a flexible photoluminescence display device and suggest a new fabrication process for better reliability.First, because plastic substrates for flexible display devices cannot endure elevated temperatures, we only dried the conventional PDP phosphor paste that had been screen-printed on a rear plate. However, these fabricated panels turned off in a couple of hours because carbon and other residues become sources of gas contamination when discharges occur in panels. Therefore, we omitted polymer binders and some other ingredients from the conventional phosphor paste that need high temperatures of close to 500°C to be burned out. Fortunately, even though there are no polymer binders, we were able to use the screen-printing method in the same way that is applied to the conventional paste to fabricate phosphor layers. Therefore, we could just apply relatively low temperature to form a phosphor layer. Simple drying, however, was not enough to remove all unwanted impurities or bonds from the phosphor layer, so we dried the screen-printed phosphor layer with a gas-flow, and the effect of the gas-flow was confirmed by several measurements.TGA (Thermogravimetric analysis) and FT-IR (Fourier Transform Infrared spectroscopy) results consistently indicate that residues of fired and dried phosphor pastes made in this study have no major differences in chemical characteristics such as bonds of atoms. Rather, the dried phosphor layer shows more preferable results, if it was dried with a gas-flow, to the fired one from the perspective of reliability. It can be explained by the gas-flow activation effect.Finally, we describe the luminescence characteristic of the dried phosphor layer and discuss integration with other layers so that it can be a part of a perfect flexible photoluminescence display or a flexible PDP. References[1] R. S. Tarighat, A. Goodarzi, S. Mohajerzadeh, B. Arvan, M. R. Gaderi, and M.Fathipour, Proceedings of the IEEE 93, 7 (2005).[2] H. Hirakawa, K. Shinohe, Y. Yamazaki, M. Ishimoto, K. Awamoto, and T. Shinoda, SID 08 Digest, pp.480-483 (2008).[3] S. H. Kim, C. Jang, K. J. Kim, and K. C. Choi, ICMAP 2008, p15 (2008).
9:00 PM - C6.11
Fabrication and Characterization of Fluoride-doped Tin Oxide Films from Nanoparticles via Spray.
Talita Mazon 1 2 , Natiara Madalossi 1 , Gisele Gasparotto 3 , Maria Aparecida Zaghete 3 , Marcio Biasoli 1
1 Microsystems and Packaging Division, CTI, Campinas, SP, Brazil, 2 Energy, ABC Federal University, Santo André, SP, Brazil, 3 CDMDC, Chemistry Institute - UNESP, Araraquara, SP, Brazil
Show AbstractTransparent conductive oxides (TCO) have been increasingly important in a large variety of applications due to demands for optically-transparent conductive materials. Applications of these devices include thin-film solar cells, display devices, optoelectronic devices, polymer-inorganic composite solar-cells and gas sensors. A common TCO used is tin-doped indium oxide (ITO) due to its superior conductivity and high optical transparency. However, ITO experiences a reduction of electrical conductivity when exposed to oxygen at temperatures higher than 300 Celsius degree. Since of the above-mentioned devices undergo thermal treatments, this reduction of conductivity becomes problematic. Therefore, FTO, which is much more thermally stable, is often used as an alternative to ITO.Aming to obtain FTO films with better electrical properties, this work had the objective to prepare FTO films from nanoparticles by via spray. An ordered array of these transparent, conductive oxide nanoparticles can provide distinct advantages for devices that utilize TCO. For example, nanoparticles arrays provide far greater surface area that thin films and thus offer great advantages in applications where surface area plays a critical role.The precursors polymeric method was used to prepare fluoride-doped SnO2 films from a dispersion of crystalline nanoparticles. The nanoparticles obtained were characterized by XRD and transmission electronic microscopy (TEM). Then, undoped, 5 and 7 mol% fluoride-doped SnO2 dispersions were prepared by dispersing the nanoparticles into alcohol. The use of dispersants and other coupling agents, such as GPTS and DMS were studied as dispersion stabilizers for fluorine-doped SnO2 sol. The particles concentration and the pH of the dispersion medium were changed to assure the stability of the dispersion. Transparent conducting SnO2:F (FTO) layers have been deposited by spray on glass or silicon substrates and then annealed in air at various temperatures (300 – 800 Celsius degree). The films obtained were analyzed by scanning electronic microscopy (SEM), mechanical profilometer, electrical resistivity and optical transparency. The films prepared via spray showed homogeneous microstructure and without cracks. In the films annealed at temperatures above 800 Celsius degree, it was possible to observe particle growth and formation of sinternecks between nanoparticles aggregates or the nanoparticles itselves. The resistivity electrical and transmittance of nanoparticle FTO layers were strongly impacted by the deposition and annealing parameters.
9:00 PM - C6.12
Synthesis of Semi-Perfluoroalkyl Polyfluorenes for Orthogonal Processing in Hydrofluoroether Solvents.
Jin-Kyun Lee 1 , Hon Hang Fong 1 , Alexander Zakhidov 1 , Georgia McCluskey 2 , Priscilla Taylor 1 , Andrew Holmes 2 , George Malliaras 1 , Christopher Ober 1
1 Materials Science & Engineering , Cornell University, Ithaca, New York, United States, 2 Chemistry, University of Melbourne, Melbourne, Victoria, Australia
Show AbstractSince the discovery of electroluminescence in conjugated polymers, polymeric light-emitting devices (PLEDs) have been one of the highlights in the field of organic electronics. As with traditional displays, PLEDs require patterning to tailor emitting polymers into small, multi-layered elements. Solutions of polymers can be dispensed onto the desired area by ink-jet printing, or cast to regions a sacrificial imaging material has defined. Although the latter lithographic methods possess better resolution and higher productivity, these have not been recognized as suitable for PLEDs. There has been concern that organic solvents in photoresist deposition and stripping steps harm the quality of emitting polymers. Recently, we have identified hydrofluoroethers (HFEs) as universal, non-damaging solvents for non-fluorinated polymers. By exploiting these solvents and a fluorinated photoresist, we were able to lithographically pattern functional materials down to 5 μm resolution. This success prompted us to consider the converse combination of materials, ‘highly fluorinated functional polymers and non-fluorinated conventional photoresists and organic solvents’. Films of highly fluorinated polymers are stable upon exposure to ordinary organic solvents.In this presentation, we report the synthesis and processing of semi-perfluoroalkyl polyfluorenes. Their optical and EL properties are discussed, which are distinctive from their non-fluorinated derivatives. This fluorinated polymer is then successfully patterned with a conventional photoresist and organic solvents.
9:00 PM - C6.13
Atmospheric Pressure Chemical Vapor Deposition of Doped ZnO on Glass Substrates for Large Volume Production.
Roman Korotkov 1 , Liang Fang 2 , Alexander Salemi 1 , Robert Smith 1 , Martin Bluhm 1 , Gary Silverman 1 , Claudia Goldman 3 , Soeren Hartmann 3 , Christoph Rickers 3 , Holger Schwab 3 , Dietrich Bertram 3
1 Corporate Research, Arkema Inc., King of prussia, Pennsylvania, United States, 2 Analytical department, Arkema Inc, King of Prussia, Pennsylvania, United States, 3 OLED Lighting, Philips Technologie GlmB, Aachen Germany
Show AbstractAs the manufacturing for organic photovoltaic cells (OPV), organic light emitting diodes (OLEDs), and other electronic devices ramps up its speed, the need for large-scale transparent conductive substrates becomes more apparent. If the high volume production is to be implemented, several key parameters for the conductive coatings need to be met. These parameters are: high deposition rates, homogeneity of the opto-electronic properties, and surface morphology of the transparent conductive oxide coatings. These parameters may be varied depending on the needs of the opto-electronic devices. One of the materials that is currently considered in industry as a possible replacement for ITO thin film coatings is doped ZnO. In this work, we will present deposition of group-III doped ZnO thin films on 6x6 inch glass substrates by atmospheric pressure metalorganic chemical vapor deposition. High deposition rates of greater than 20 nm/s make chemical vapor deposition of ZnO an attractive option for large volume production. The homogeneity of optical, structural, and electrical properties as well as the root mean square (RMS) roughness of these coatings as a function of the position on the 6x6 inch substrates will be presented. The average transmittance of the ZnO/glass depends on the film thickness and typically lies at 91±2 % for 160 nm thick coatings. Electrical conductivities of 1.7x10-4 Wcm have been demonstrated. Possible application of these 6x6 inch substrates for the OLED and OPV applications will be presented.
9:00 PM - C6.14
GaN-based Light Emitting Diodes with Graded-index Layer via Nanosphere Lithography Technique.
Byung-Jae Kim 1 , Joona Bang 1 , Jihyun Kim 1
1 Department of Chemical & Biological Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractThe light extraction efficiency of Light Emitting Diodes (LEDs) was limited by total internal reflection (TIR) because the refractive index difference between GaN (n=2.5) and air (n=1) induced TIR at GaN/air interface. The photons can be extracted from GaN into air within the critical angle (~ 23.6°) according to Snell’s law. The methods for enhancing the light extraction efficiency of LEDs include photonic crystal structure, KOH-based photochemical etching and anodic aluminum oxide (AAO). However, photonic crystal structure required complex and expensive processes. Also, KOH-based photoelectrochemical wet etching had some problems such as reproducibility and controlling the etching rate. Anti-reflection (AR) layer had been used as another method to enhance the light extraction efficiency of LEDs. The refractive index of AR layer is placed between air and GaN to widen the critical angle. Usually, the materials such as SiNx, SiO2 and TiO2 were used as AR layer. To further broaden the escape angle, the simple process for Graded-Index AR layer was demonstrated in our experiments, which gradually changed the refractive index. In our experiments, we used benzocyclobutene (BCB) (n=1.55) as the starting material because BCB is highly transparent (> 90%) as well as chemically and mechanically stable. In addition, BCB layer can be deposited by spin-coating technique. We fabricated Graded-Index BCB layer by nanosphere lithography (NSL) using SiO2 nanospheres. Firstly, BCB layer with the thickness of 110nm was spin-casted on LEDs samples, followed by the hardening. Then, the second BCB layer with the thickness of 110nm was spin-casted on first BCB layer. O2 plasma treatment was employed to change the properties of BCB surface from hydrophobic to hydrophilic. Then, SiO2 nanospheres with the diameter of 300nm were spin-casted on second BCB layer, followed by heating at 160°C. SiO2 nanospheres were embedded into the second BCB layer during heating process. Nano-lens configuration was fabricated on BCB layer. Additional HF-based wet etching removed SiO2 nanospheres to increase the porosity within the second BCB layer because the refractive index of porous BCB layer was lower than that of unfabricated BCB layer. Consequently, Graded-Index BCB layer was demonstrated on LEDs samples. The refractive index from GaN to air was gradually decreased by Graded-Index BCB layer to help more photons escape into the air. The light output (EL) was also compared between LEDs with/without Graded-Index layer. The details about the experimental process and results will be presented.
9:00 PM - C6.15
Stable Aqueous Dispersions of ZnO Nanoparticles for Ink-jet Printing of Electronic Devices.
Ahmed Khalil 1 , Moazzam Ali 1 , Simon Bubel 2 , Ronald Schmechel 2 , Markus Winterer 1
1 Nanoparticle Process Technology, University Duisburg-Essen, Duisburg Germany, 2 Institute for Nanostructures and Technology , University Duisburg-Essen, Duisburg Germany
Show AbstractFor the fabrication of printable devices based on ZnO nanoparticles (ZnO NP), stable colloidal dispersions of these materials are highly desirable. In this work, ZnO NP have been synthesized by Chemical Vapor Synthesis. The particles have spherical shape with narrow size distribution. Stable aqueous dispersions of ZnO NP have been prepared successfully after the addition of a new polymeric stabilizer. The adsorption of such molecules on the surface of the particles changed completely the behavior of the zeta potential curve as a function of pH. In the pH range studied (7-10), the zeta potential values was from -30 to -45 mV. The prepared dispersions are stable for at least 2 months without observable sedimentation. The zeta potential and the size of the ZnO NP in these dispersions have been monitored for several weeks and showed constant values. Furthermore, it has been found that the optimization of the dispersion conditions (ultrasonic power and time) is very important, leading to less-aggregated particles with sizes close to the size of the primary particles (20 nm). These stable dispersions has been used to form ZnO NP films for different applications on silicon, glass and ITO-coated glass by spin-coating and ink-jet printing techniques. The viscosity and the surface tension of the dispersion as well as the printing parameters have to be optimized for forming layers with high quality. Dense and low porosity layers of ZnO NP with thickness between 100-250 nm have been fabricated on different substrates. The layers have been annealed at 200 degree for one hour. The layers are transparent and showed the characteristic PL spectrum of the ZnO NP. Using high resolution SEM analysis, it has been found that the morphology of the printed layers as well as the interface are comparable to the spin-coated layers prepared from the same dispersions. Well-defined and low roughness interfaces are needed for electronic applications. Very likely, this was the key for the realization of thin film transistors (TFTs) based on our ZnO NP layers. The TFTs have been fabricated in the bottom gate configuration. The output characteristics of the TFTs clearly show the n-type behavior of the ZnO NP. The possibilities for using the printed ZnO NP films as active layers for LEDs and gas sensors are currently under investigation.
9:00 PM - C6.16
Optical Structures Fabricared by Inkjet Etching of Polymer Surfaces for OLED Applications.
Fulvia Villani 1 , Dario della Sala 1 , Anna De Girolamo Del Mauro 1 , Immacolata Angelica Grimaldi 1 , Fausta Loffredo 1 , Carla Minarini 1 , Giuseppe Nenna 1
1 FIM-MATNANO, ENEA, Portici, Naples, Italy
Show AbstractOrganic Light Emitting Diodes (OLEDs) are a good candidate for display and lighting applications because of their low cost fabrication and flexibility. One of the most important problem of these electronic devices is the low external efficiency. Indeed, only a small fraction of the light generated in the emissive layer can be emitted outside the device, due to the total internal reflection (TIR). Several methods have been proposed in order to improve the efficiency factor of the optoelectronic devices, among which also the use of shaped substrates with mesa structures or micro-lenses arrays. Traditionally, microlenses were fabricated by means of expensive and complex process methods. In this work, we employed the ink-jet (IJ) printing technology as innovative method for manufacturing of optical structures by depositing solvent drops onto soluble polymer layer. The advantages of this technique are the accuracy, resolution and low costs, making it a versatile tool for industrial manufacturing process. When the solvent drop hits the polymer layer, the polymer is locally dissolved, carried from the centre to the edge and deposited there. As a result of this phenomenon, known as the coffee-stain effect, crater-shaped structures have been generated and used as optical structures. By IJ depositing toluene drops onto spin coated polystyrene films we performed spherical symmetrically craters, whose edges were used as optical structures. Moreover, we fabricated convex micro-lenses by spin-coating a polydimethylsiloxane film onto polystyrene optical structures used as template. Finally, we coupled OLEDs to these two different optical structures and studied how their external efficiency modifies. The optical properties of the obtained electroluminescent devices were extensively investigated and discussed.
9:00 PM - C6.19
A Scalable Spray Deposition Technique for the Fabrication of Nanocomposite Supercapactior Electrodes.
Beatriz Mendoza 1 , Xin Zhao 1 , Patrick Grant 1
1 Materials Department, University of Oxford, Oxford United Kingdom
Show AbstractSupercapacitors are energy storage devices that combine the advantages of high power density, high charge/discharge rates and high cycle efficiency. Supercapacitors have been proposed to complement or replace batteries in many energy storage applications including uninterruptible power supplies and load levelling in various technologies such as portable electronics, digital communications, and hybrid electronic vehicles. A spray deposition technique has been developed for the fabrication of large area nanostructured thin film electrodes for supercapacitors. Unlike current processing techniques such as hot moulding and pressing that produce relatively thick electrodes, the spray deposition approach allows for the fabrication of uniform films of ~250nm thickness over a 1500 cm2 area. This work reports the formulation of stable aqueous suspensions of functionalised multi-wall nanotubes (MWNTs) and their spraying into thin film meso-porous electrodes on Al coated flexible polyethylene terephthalate (PET) webs, without the use binders such as PVDF or C black commonly used in other processes. The uniformity of thickness, microstructure, meso-porosity and electrochemical properties have been shown to be reproducible over the entire area. The same approach has also been applied for the manufacture of MWNT electrodes containing pseudo-capacitive nanoparticles including Sn, Fe2O3, Fe3O4, etc by utilising in-situ hydrothermal and other synthesis routes to the nanoparticles in the presence of the MWNTs immediately prior to spraying. The microstructure and electrochemical properties of these composite electrodes in both half-cell and full-cell asymmetric configurations is reported, including performance as a function of charge/discharge cycles. Finally, the benefits and challenges of the production and performance of thin film nanocomposite electrodes produced by spray deposition will be discussed in the context of current more widely practiced process-materials combinations.
9:00 PM - C6.20
Microscopic Multi-directional Alignment of Liquid Crystalline Polymer Films Induced by Patterned Thermal Expansions of an Underlying Soft Layer.
Kyung-Woo Park 1 , Chang-sub Park 2 , Yeonjeong Han 1 , Shin-Won Kang 1 2 , Hak-Rin Kim 1 2
1 School of Electrical Engineering and Computer Science, Kyungpook National University, Daegu Korea (the Republic of), 2 Department of Sensor and Display Engineering, Kyungpook National University, Daegu Korea (the Republic of)
Show AbstractWe propose a novel alignment method of lyotropic liquid crystalline polymer (LCP) film by thermal expansion force of polymer. The lyotropic liquid crystalline polymers (LCPs) have been newly developed for display applications such as retardation films for viewing angle compensation and polarizing films for high extinction ratio in liquid crystal displays (LCDs). In general, the liquid crystalline ordering of the lyotropic LCPs is made by mechanical shearing in a gel state because of the lyotropic ordering character [1,2]. In that case, the multi-directional ordering of lyotropic LCPs is very difficult, which is essential for fabrication of complex optical films requiring micro-patterned optic axis distributions.In our method, the spin-casted lyotropic LCPs are self-aligned by the thermal expansion force of patterned poly(dimethylsiloxane) (PDMS) substrate, where the PDMS substrate is cross-linked with the benzophenone for the increase the photosensitivity of UV light in solid state [3]. The elasticity of the PDMS substrate with the cross-linked benzophenone is changed with a specific pattern according to the pattern and the dose of the UV exposure. The lyotropic LCPs is spin-coated on the patterned PDMS substrate. Then, the binary films are thermally annealed with the same temperature condition within the whole sample area. After the thermal treatment, the initially isotropic lyotropic LCPs are changed to LCPs film with a patterned ordering, where the ordering patterns depend on the geometric shapes of polymer films and the patterned UV irradiation condition. Thus, we can make microscopically patterned lyotropic LCP films with multi-directional ordering by using the patterned shearing effect induced by the patterned thermal expansion of underlying patterned soft film.AcknowledgementsThis research was financially supported by the Ministry of Education, Science Technology (MEST) and Korea Industrial Technology Foundation (KOTEF) through “the Human Resource Training Project for Regional” and the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (R11-2008-105-03003-0).References[1] G. Kwak, M. Minakuchi,T. Sakaguchi, T. Masuda, and M. Fujiki, Chem. Mater., 19, pp3654-3661(2007)[2] I. I. Smalyukh, O. V. Zribi, J. C. Butler, O. D. Lavrentovich, and G. C. L. Wong, Phys. Riew. Lett. 96, pp177801(2006)[3] Wilhelm T. S. Huck, Ned Bowden, Patrick Onck, Thomas Pardoen, John W. Hutchinson, and George M. Whitesides, Langmuir, 16, pp3497-3501(2000)
9:00 PM - C6.21
Low-Strain Fatigue Behavior of Large Area Sprayed Functional Materials.
Ali Marzban 1 , Andrew Gouldstone 1
1 Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractThermal sprayed materials are finding increased use in large-area functional materials for electronics or energy applications. This is largely due to recent advances in process reliability and precision, as well as the inherent low-cost and material flexibility of this deposition technique. In most large-area applications, coatings are mechanically cycled, within a low-strain range, and this is assumed to have little effect. Previously we reported that this assumption may be incorrect. In this abstract we describe systematic experiments to cycle different TS coatings, and incrementally measure through-thickness dielectric behavior via impedance spectroscopy. In such experiments, we observed significant changes in dielectric behavior within a few thousand cycles. In addition, we present detailed FEM models to explain such behavior, and outline the implications for operation of functional large area TS materials. Finally, we show how these measurements can yield opportunities for interfacial design of functional nano-sprayed composite materials.
9:00 PM - C6.22
Hybrid Inorganic/Organic Self-Assembled Clays Nanocomposites for Roll to Roll Fabrication in Photovoltaics.
Peter Kariuki 1 , Jasper Chiguma 1 , Jessica Gendron 1 , Michael Hagerman 2 , Wayne Jones 1
1 Chemistry and Materials Science, SUNY Binghamton, Binghamton, New York, United States, 2 Chemistry, Union College, Schenectady, New York, United States
Show AbstractThe preparation of competitive solar energy conversion technologies has been limited by the cost and efficiency of modern materials. We have been developing a new approach to layered inorganic/organic photovoltaic materials which combine the low cost and processibility of organic polymers with dye sensitized quantum dots self-assembled on layered clay materials (Laponite). The flexible thin film solar cell uses a combination of semi-conductor quantum dots/titanium dioxide nanoparticles, conducting polymer films such as polyethylenedioxythiophene (PEDOT) and polyaniline (PANI), and self-assembled layered materials of laponite coated on polyethylene terephthalate (PET) substrates. Using UV-Vis, FTIR and fluorescence spectroscopy, we have shown electron transfer, guest-guest and host-guest interactions, charge separation, spectral line broadening, and quenching of fluorescence signal indicating coupling of energy states, charge transfer and surface adsorption between [Ru(bpy)3]2+ and CdSe nanocrystals. We have also used scanning electron microscopy and atomic force microscopy to probe nanoparticle self-assembly. Initial photovoltages on assembled cells of ITO/PEDOT/CuLap/Rubpy/PANI films on glass yield photoefficiency of approximately 0.1 % when using argon ion laser excitation at 488 nm and PEDOT/TiO2(Rubpy) PANI/Ag on PET show photovoltages of up to 0.4 V.We are investigating the self-assembly of robust thin film platforms using TiO2 nanocrystals which offer a more environmentally friendly alternative to quantum dots. We have also fabricated and characterized PEDOT and PANI nanocomposites loaded with carbon nanotubes which are suitable for incorporation in solar cells by the roll to roll technique.
9:00 PM - C6.23
Depositing Ordered Arrays of Metal Sulfide Nanoparticles in Nano-Structures Using Supercritical Fluid Carbon Dioxide.
Joanna Wang 1 2 , Alexander Smetana 1 2 , Chien Wai 1 , John Boeckl 2 , Gail Brown 2
1 Department of Chemistry, University of Idaho, Moscow, Idaho, United States, 2 Materials and Manufacturing Directiorate, WPAFB, Dayton, Ohio, United States
Show Abstract Fabrication of well-defined 2 or 3 dimensional ordered arrays of nanocrystal metals and semiconductors is a challenge of nanoscience/nanotechnology in scientific communities to produce new types of optical gratings, optical filters, selective solar absorbers, data storage, and microelectronics. Metal sulfide quantum dot nanoparticles are also incorporated in sensing applications, including chemical and warfare agent detection as well as environmental monitoring and used as a photosensitizer or light detectors for photographic purposes. Nanoparticles have electric and optical properties that sensitively depend on the size. If the size of the nanoparticles can be controlled, it can be expected that new materials created from these particles will bring about new technical innovations. In this study, Ag2S and CdS nanoparticles are synthesized by chemical reactions of metal cations with freshly prepared sulfide anion solutions dissolved in the water core of water-in-oil microemulsions. Sodium bis(2-ethylhexyl)sulfosuccinate is used as an anionic surfactant with hexane as an organic solvent. Dodecanethiol is then added to the microemulsion solution to stabilize the synthesized metal sulfide nanoparticles. The alkanethiol-coated nanoparticles are easily separated from the reaction medium and dispersed in a non-polar solvent. The protected nanoparticles dispersed in an organic solution can be precipitated onto C-coated copper grids and silicon wafers to generate self-assembled 2-D arrays in supercritical fluid CO2(Sc-CO2). A unique feature of the Sc-CO2 evaporation technique is that the nanoparticles can be deposited into nano-trenches on Si wafers which cannot be achieved by traditional solvent deposition methods. Nano-scale trenches on the surface of a (111) oriented silicon wafer are milled and imaged using an FEI Strata DB235 focused ion beam with a 30 keV Ga+ ion beam. Benchtop deposition by placing the as-milled silicon wafer in the bottom of a glass vial filled with the dodecanethiol stabilized Ag2S nanoparticles in toluene would result in inhomogeneous deposition with large voids in the nano-scale trenches. When the evaporation is carried out in a Sc-CO2 cell with an as-milled Si wafer placed in the same dodecanethiol stabilized Ag2S solution, the metal sulfide nanoparticles can be deposited uniformly into the nano-scale trenches. In a similar way, stabilized CdS nanoparticles can also be deposited in small structures drilled on surface of Si wafer by the Sc-CO2 evaporation method. We show here that the metal sulfide quantum dots can be deposited in an identical manner as to the one we have used to place metal nanoparticles (Au and Pt) in nanoscale surface features. The procedure outlined here can be used to create reliable nanoparticle arrays for electronic and sensor applications without the uncertainty of evaporation from conventional solvents, which are often non-uniform over large areas due to surface tension effects and de-wetting.
9:00 PM - C6.24
Parametric CFD Optimization of an APCVD TCO Deposition Module.
Jiuan Wei 1 , Wei Zhang 1 , K. Strobl 1
1 CVD Applications Laboratory, CVD Equipment Corporation, Ronkonkoma, New York, United States
Show AbstractAPCVD (Atmospheric Pressure Chemical Vapor Deposition) thin film coating processes are one of the most cost effective large area thin film coating solutions presently available on the market and can be up to 2-2.5X lower in cost than sputtering. Several advanced materials (including transparent conductive oxides (TCO)) used for solar panel manufacturing and for energy saving (Low-E) windows have already been deposited using APCVD Tools incorporating one or more deposition modules depositing thin films such as SiO2, TiO2 and F: SnO2, etc onto glass sheets. However further improvement in material efficiencies and operational cost reductions are needed to satisfy the growing demand for such highly customized materials. It is desirable in the future to be able to cost effectively deposit other material films with targeted properties as well, i.e. those that traditionally have not yet been available on this lower cost manufacturing platform, such as ZnO.To investigate in a quantitative manner the improvement potential for the traditional APCVD deposition module design solution we performed a multidimensional CFD (Computational Fluidic Dynamics) parametric study using ANSYS FLUENT V12. As a baseline deposition module design we used a commercially available APCVD deposition module developed originally by Watkins-Johnson for SiO2 deposition for trench fill of Si wafers from TEOS, O2 and Ozone which we have located in previously published papers reporting both experimental and CFD modeling results. The CFD software enabled us to perform a full parametric APCVD deposition module design study and allowed us to quantify the efficiency and throughput gains/losses of a wide variety of design change options. The main driver for this study was to learn in a quantitative, cost efficient and time efficient manner which system design changes have the potential for significant precursor efficiency improvement and/or product throughput gains for a particular APCVD deposition process. The results of this study will be utilized to accelerate our proprietary, next generation Off-line and On-line CVDgCoat™ APCVD platform development.
9:00 PM - C6.25
Nanopatterned Bilayer Organic Solar Cell using P3HT/PCBM via Low Temperature Patterning Process.
Dae-Geun Choi 1 , Ki-Joong Lee 1 , Jun-Ho Jeong 1 , Dong Hwan Wang 2 , O Ok Park 2 , Jong Hyeok Park 3
1 Nano-Mechanical Systems Research Division, Korea Institute of Machinery & Materials, Daejeon Korea (the Republic of), 2 Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, Daejoen Korea (the Republic of), 3 Department of Chemical Engineering, Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractNanoimprint lithography (NIL) has been favored as a useful technique because NIL is a high resolution nanopatterning technique and advantageous in reducing the processing time and cost—an important requisite for mass production. Nanopatterned organic solar cell has been attracting great attention because of its scientific importatnce and is one of the useful applications of NIL nanopatterning. In this work, nanopatterned bilayer organic solar cells were prepared by using P3HT and PCMB via low temperature NIL process. Nanopatterns with 20nm, 70nm, and 100nm line was successfully fabricated and compared with bulk heterojunction and smooth nonpatterned bilayer cells.
9:00 PM - C6.26
Fabrication of Self-detoxifying Devices on Flexible Substrates with Smart Polymer Coatings for Chemical and Biological Warfare Agents.
Siqiang Zhu 1 , Von Ebron 1 , Yevgenia Ulyanova 1 , Olga Shulga 1 , Elizabeth Elliott 1 , Eve Fabrizio 1 , Patrick Kinlen 1
1 , Crosslink, St. Louis, Missouri, United States
Show AbstractWhen U.S. military operations are faced with an event involving chemical or biological warfare agents (CBWAs), the danger does not end with the passing of the event itself. Troops must then detoxify all exposed work areas and pieces of equipment, including individual and collective protection fabrics before reinstating operational access. Since most collective protection materials are passive, permeation-resistant barriers, traditional approaches to decontamination include equipment washdown with harsh neutralizing solutions and/or treatment with reactive sorbent powders. Both decontamination methods are tedious and create problems with chemical waste disposal issues. This paper introduces a new self-detoxifying, self-renewing, reactive coating technology for collective protection of structural textiles that destroys CBWAs on contact. Development of self-detoxifying polymer coatings on large-area flexible substrate will enhance CBWA protection, detoxification, and survivability of existing shelter materials, while producing no dangerous chemical waste as by-product.The multilayer reactive coating system is comprised of the following major components: (1) two flexible electrodes including an anode and an H2O2-generating cathode, (2) a supporting polymer gel electrolyte, and (3) a catalyst-containing polymer system deposited on top of the electrode/electrolyte layer. This multilayer coating yields an electro-responsive detoxifying system that generates and activates H2O2 on demand. Triggering of the active response will be accomplished by coupling to CBWA sensors. The detoxification process involves in-situ generation of H2O2 on a polymer coated fabric through the electrochemical reduction of ambient oxygen. This product concept eliminates the need for storage of H2O2 either on-site or within the material, allowing for a continuously regenerated supply of peroxide as needed. The polymer systems were coated layer-by-layer onto the shelter material fabric.Upon application of a low voltage, H2O2 is generated at the cathode electrode surface. H2O2 diffuses through the polymer gel electrolytes and interacts with H2O2-activating catalysts on the surface that enhance the rate of reaction of the H2O2 with CBWAs.Future work will focus on system optimization, live agent testing, and process scale-up to large textile areas required for collective protection shelters. AcknowledgementsWe would like to thank Don Landy (Crosslink), James Bashkin (Nanovir), Kevin Koeller (Nanovir), Paul Durham (Missouri State University, MSU), Carrie Vause (MSU), Tianying An (MSU), Julia McAdams (Natick Soldier Research Development and Engineering Center, NSRDEC), Jean Hampel (NSRDEC), Jeff Owens (Defense Threat Reduction Agency, DTRA), William Buechter (DTRA) and Charles Bass (DTRA) for their valuable contributions and support.
9:00 PM - C6.27
Patterning Functional Materials by a Combination of Soft Lithography and Gas Phase Silanization.
Antony George 1 , Dave Blank 1 , Johan ten Elshof 1
1 Inorganic Material Science Group, University of Twente, Enschede Netherlands
Show AbstractSoft lithography in combination with gas phase deposition of organosilanes is used to fabricate arrays of high aspect ratio material patterns of lateral resolution down to 70 nm with a length of 2 cm. Organosilane patterns were created either by diffusing organosilane vapor through polydimethylsiloxane (PDMS) channels bonded to silicon substrate or by using grafted water soluble polymer patterns on silicon wafer as shadow masks for vapor deposition of organosilanes. The organosilane nanopatterns were used for immobilizing functional nanoparticles, polymer nanospheres and as templates for electroless metal film deposition. The patterned materials were characterized by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). The technique enables easy, low cost and large scale nanofabrication of electronic, optoelectronic, sensing and biomedical devices using organosilane micro and nano patterns.
9:00 PM - C6.29
Reliability of Barrier Ribs in a Flexible Photoluminescent Display.
Cheol Jang 1 , Seung Hun Kim 1 , Kuk Joo Kim 1 , Sung-Il Ahn 1 , Kyung Cheol Choi 1
1 Electrical engineering, KAIST, Daejeon Korea (the Republic of)
Show Abstract The paradigm for display devices is moving from conventional displays to novel display devices such as flexible displays. Numerous groups have worked to realize flexible displays using various technologies such as liquid crystal displays, OLEDs, electrophoretic displays and plasma displays. Among those technologies, the plasma display platform is the most promising candidate for use with flexible displays [1-2] owing to feasible characteristics such as self-emission and its simple structure. In order to realize a flexible photoluminescent display, flexibility of the substrate and structure is required. Therefore, conventionally used materials for plasma display should be replaced by new materials which are flexible and reliable. The barrier rib is the most important component in the frame of the plasma display, as it sustains discharges. The reliability of barrier rib is a critical issue in the realization of a high-resolution flexible photoluminescent display. In this study the reliability of barrier ribs created from various materials is investigated in an effort to assess the potential of each material as a barrier rib for a flexible photoluminescent display. A polydimethylsiloxane (PDMS) rubber mold with a negative volume of a barrier rib structure was used in the fabrication of a barrier rib. The desired material for the barrier rib was squeezed into the PDMS mold and a glass or flexible substrate was placed on the PDMS mold. The material for the barrier rib was then cured by appropriate methods. After the molding process, a protecting layer of MgO having a thickness of 500 nm was deposited on the barrier rib by e-beam evaporation in order to protect the barrier rib from the plasma discharge. Barrier ribs were fabricated from various materials. Among those materials, UV resin, which is used as a sealant, shows good characteristics. Experimental results with glass-based test panels confirm that UV resin does not produce any outgassing problem which results in contamination of the discharge gas. To exclude the effects caused by other flexible materials, the test panels were fabricated with glass substrates and conventionally used materials for plasma displays except for the material of the barrier rib. The pixel size was 1.08 mm x 0.36 mm, and a closed-type barrier rib having a height of 150 μm was used for the test panels. Ne gas was used as a discharge gas, the pressure of which was 700 Torr. The luminance of a test panel with an MgO-coated barrier rib made of UV resin was observed for 375 hours. Even after the iterant sustain discharge, the surface of the barrier rib was not damaged due to the MgO layer. The lifetime of the UV-resin barrier rib is estimated to be more than 10,000 hours.[1] C.A. Wedding, J.W. Guy, O.M. Strbik, D.K. Wedding, R.P. Wenzlaff and W.W. Olson, SID Symposium Digest, 35, 815-819 (2004).[2] H. Hirakawa, K. Shinohe, Y. Yamazaki, M. Ishimoto, K. Awamoto and T. Shinoda, SID Symposium Digest, 39, 480-483 (2008).
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Micron-Patterning of Polydiacetylene Supramolecules using Electrohydrodynamic(EHD) Jet Printing.
Chi Ho Song 1 , Sung Yul Back 1 , Jong-Man Kim 2 , Heejoon Ahn 1
1 Fiber and Polymer Engineering, Hanyang University, Seoul Korea (the Republic of), 2 Chemical Engineering, Hanyang University, Seoul Korea (the Republic of)
Show AbstractMicron-sized polydiacetylene (PDA) patterns on silicon and glass substrates were successfully fabricated by using an electrohydrodynamic jet printing technique. The effects of applied voltage, working distance, and substrate properties on the morphology of patterns are investigated by using SEM and AFM. Heat-treatment of the solid substrate, immobilized with blue-phase PDAs, induces a blue-to-red-phase transition and results in the formation of patterned fluorescence images. This investigation has led to the development of a new strategy for the fabrication of conjugated polymer patterns on solid substrates. When combined with the novel optical properties of polydiacetylenes, this methodology should enhance the versatility of conjugated polymers in sensor and optical applications.
9:00 PM - C6.30
New Processing and Patterning Approaches Based on Photoprocessible Azo Polymers.
Xiaogong Wang 1 , Bin Liu 1 , Yaobang Li 1 , Junpeng Liu 1 , Dongrui Wang 1 , Yaning He 1
1 Department of Chemical Engineering, Tsinghua Universiy, Beijing China
Show AbstractAzobenzene-containing polymers (azo polymers for short) possess a variety of photoresponsive properties related to the photoisomerization of the azo chromophores.[1,2] One of the most well-documented properties is the photoinduced surface-relief-grating (SRG) formation.[3,4] By using the effect and combining this method with soft-lithography, new approaches can be developed to fabricate various nano/micrometer structures and patterns built up with different types of materials.[5,6] A variety of colloidal spheres and micelles were prepared from amphiphilic azo polymers and block copolymers through gradual hydrophobic aggregation. Such structures were obtained by slowly adding water into the homogeneous solutions of the polymers. One of most interesting properties of the colloidal particles is the photoinduced deformation. The colloidal spheres in the solid state can be stretched along the polarization direction of the laser beam upon the irradiation with a linearly polarized Ar+ laser single-beam or interfering beams. The deformation degree almost linearly increased with the increase of the light irradiation time before saturation. Ellipsoidal colloidal particles and particles with other shapes were prepared by this method. More complicated structures of azo polymers were prepared on the basis of this approach. New processing and patterning approaches were also explored by combining the method of SRG inscription and soft-lithographic contact printing. The approaches used photoinduced SRG on azo polymer films as masters. Elastomeric stamps of poly(dimethylsiloxane) (PDMS) were made through replica molding by using the masters. The "inks" for contact printing were prepared by dissolving different types of polymers, carbon nanotubes, and other proper materials in suitable organic volatile solvents. For contact printing, the "inked" PDMS stamps were pressed against various substrates under proper conditions. High quality patterns with high fidelity to the masters were obtained by this conformally printing method. The patterns were obtained after peeling off the stamps and dried under proper conditions. Through this soft-lithographic contact printing and other similar approaches, duplicated surface-relief-gratings, azo polymer free-standing microwires and azo polymer micro-hemisphere arrays were fabricated. Upon irradiation of a linearly polarized Ar+ laser single beam, the shapes and sizes of the azo polymer microwires and micro-hemispheres could be further modified.(1) Delaire, J. A.; Nakatani, K. Chem. Rev., 2000, 100, 1817.(2) Natansohn, A.; Rochon, P. Chem. Rev., 2002, 102, 4139.(3) Rochon, P.; Batalla, E.; Natansohn, A. Appl. Phys. Lett. 1995, 66, 136. (4) Kim, D. Y.; Tripathy, S. K.; Li, L.; Kumar, J. Appl. Phys. Lett. 1995, 66, 1166.(5) Li, Y. B.; He, Y. N.; Tong, X. L.; Wang, X. G. J. Am. Chem. Soc., 2005, 127, 2402.(6) Liu, B.; He, Y. N.; Wang, X. G. Langmuir 2006, 22, 10233.
9:00 PM - C6.31
Acceleration of Interparticle Sintering by Ag Migration in AgCu Nanoparticles.
Sukjun Kim 1 , Weili Shi 2 , Eric Stach 1 , Carol Handwerker 1
1 , Purdue University, W. Lafayette, Indiana, United States, 2 , Nanodynamics, Inc., Buffalo, New York, United States
Show AbstractThe use of PbSn solders in electronic systems has been virtually eliminated by EU and Chinese legislation. Though a range of Pb-free alloys based on the Sn-Ag-Cu system are being used commercially, they are still unsatisfactory for some applications because of the high eutectic temperature and issues associated with their anisotropic properties. Here we report on an investigation of a new solderless interconnect material – AgCu composite nanoparticles dispersed as a paste compatible with existing circuit board assemblies. Interconnects formed from Ag-Cu metal composite powders have several advantages: (1) significantly faster diffusion of Ag at low temperature than Cu; (2) high conductivity; (3) material compatibility with circuit board and component substrates; and (4) no compounds formed between Ag and Cu. Mass transport of Ag results in interparticle sintering, at temperatures where pure copper particles do not sinter. The kinetics of neck formation by Ag surface diffusion at temperatures near the typical processing temperatures of SnPn assemblies (220 °C) and the resulting electrical and mechanical properties of the sintered structures will be presented. Changes in the spatial distribution and the particle morphology were observed by TEM and energy filtered transmission electron microscopy (EFTEM) imaging, indicating that significant Ag migration occurred. These results combined with the mechanical and electrical property measurements indicate that this approach may be a viable route for creating an alternative interconnect technology.
9:00 PM - C6.32
Effect of Temperature on Thin Silicon Layer Transfer by Plasma-hydrogenation.
Zengfeng Di 1 , Yongqiang Wang 1 , Michael Nastasi 1 , Francois Rossi 2 , Phillip Thompson 3
1 , los alamos national lab, Los Alamos, New Mexico, United States, 2 European Commission, Joint Research Centre, Ispra(Va) Italy, 3 , Naval Research Laboratory, Washington, District of Columbia, United States
Show AbstractWe have developed an innovative approach without the use of ion implantation to transfer a large area high-quality thin Si layer for silicon-on-insulator fabrication. The technique is based on hydrogen diffusion and accumulation into ultra-thin strained SiGe layer in a Si/SiGe/Si heterostructure during plasma hydrogenation. The hydrogenation temperature can significantly affect the H diffusion behavior, and consequently influence the cleavage along the strained SiGe layer. At low temperature, intrinsic point defects in the molecular beam epitaxy (MBE) grown Si capping layer are found to compete with the buried strain SiGe layer for hydrogen trapping. The interaction of hydrogen with point defects affects the hydrogen long-range diffusion, and restricts the amount of hydrogen available for trapping by the SiGe layer. However, hydrogen trapping by the capping layer is attenuated with increasing hydrogenation temperature allowing more hydrogen to be trapped in the strain SiGe layer with subsequent crack formation. A potential temperature window for silicon-on-insulator fabrication by plasma hydrogenation is identified based on the combined considerations of trap-limited diffusion at low temperature and out-diffusion of H2 molecule together with the dissociation of Si-H bonds inside of H platelet at high temperature.
9:00 PM - C6.33
Development of Poly(dimethylsiloxane) Stamps for Microcontact Printing.
Hiroshi Mogi 1 2 , Atsushi Yaginuma 2 , Mikio Shiono 2 , Mitsutaka Nagae 1 3 , Hiroshi Fujita 1 3 , Takeshi Shibuya 1 4 , Masayoshi Koutake 1 5 , Hirobumi Ushijima 6 , Kiyoshi Yase 6
1 , Japan Chemical Innovation Institute, Tokyo Japan, 2 , Shin-Etsu Chemical Co.,Ltd., Annaka Japan, 3 , Dai Nippon Printing Co., Ltd., Tokyo Japan, 4 , RICOH Co., Ltd., Yokohama Japan, 5 , DIC Corporation, Chiba Japan, 6 Photonics Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan
Show AbstractMicrocontact printing method is one of the nano structure producing methods called “soft lithography” reported by A.Kumar and G.M.Whitesides*1. The method includes the following processes; making silicone rubber (PDMS: poly(dimethylsiloxane)) stamps from master patterns fabricated on Si wafer or glass, applying ink to a stamp, and finally transferring a pattern onto a glass substrate, a Si wafer, and polymer films, which can be applied to printed electronics, etc. We have already reported the development of PDMS materials for microcontact printing*2, *3. The PDMS stamps can transfer silver nanoparticle ink, organic semiconductor ink and various other inks. For the production of organic TFTs by the microcontact printing with PDMS stamps, we should further improve the PDMS materials to avoid swelling with organic solvents and soaking of lower molecular weight materials.Above problems were solved by the following methods.1)Use of the Liquid Fluoroelastomer (SHIN-ETSU SIFEL® ; SIFEL hereafter) that can suppress swelling.2)Lamination of the SIFEL onto PDMS stamps.Stamp swelling with chloroform and xylene that are used as solvents of organic semiconductor (P3HT:poly(3-hexylthiophene) ink was significantly suppressed by using the SIFEL-laminated PDMS as a stamp. The FET properties of the devices which are prepared by the microcontact printing method with SIFEL-laminated PDMS stamps are same as those of the devices prepared by using the conventional PDMS stamps.We have succeeded in transferring a solution of 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) with the “modified microcontact printing method” using SIFEL-laminated PDMS stamps in contrast to the fact that low molecular weight organic semiconductors such as TIPS pentacene soak into conventional PDMS stamps. Consequently, we can make a choice from low molecular weight organic semiconductors to high molecular weight organic semiconductors such as polymer materials.We will also report some other topics on the “modified microcontact printing method” by using the newly developed SIFEL-laminated PDMS as a stamp.This work was supported by the Project "Technological Development of Superflexible Display Components" of the Ministry of Economy, Trade and Industry (METI) and New Energy and Industrial Technology Organization (NEDO), Japan.*1)A. Kumar, G.M. Whitesides et al. Appl.Phys.Lett., 63(14) 2002-2004 (1993)*2)H.Mogi et al. 4a-D-12 JSAP The 68th Autumn Meeting (2007)*3)S.Handa et al. KK10.25 2007 MRS Fall Meeting (2007)
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Towards Large Inkjet Printing of Semicrystalline Small Molecules Organic Semiconductors.
Marie-Beatrice Madec 1 , Stephen Yeates 1
1 School of Chemistry, OMIC-Univesisty of Manchester, Manchester United Kingdom
Show AbstractPentacene based thin film devices are attractive because of the high field effect mobilities demonstrated by both vacuum deposition, 3 cm2 V-1 s-1 and in single crystals, 35 cm2 V-1 s-1 [1]. However integration in low cost large area processes is difficult as they are intractable and their crystal quality cannot be readily controlled. As an alternative, soluble pentacene derivative have been the subject of intensive recent investigation [2] attempting to combine good low cost solution processability with high performance. Although feasibility of inkjet printing of this family of compounds has been demonstrated [3]; to date it has proven difficult to control order over large areas. Additionally molecules of this class alone are not well suited for inkjet process as they reach their solubility limit before a workable viscosity can be achieved.Based on these observations, our study has been motivated by the development of robust, low cost, polymer like small molecule semiconductor ink formulations. Previously we have demonstrated that formulation with side chain aromatic insulating polymers can lead to production of thin film transistor with a saturated mobility steady at around 1cm2/Vs up to a dilution of 98% of the active semiconductor [4]. When formulated with a polymer dielectric their FET characteristics improve further, showing no hysteresis even though electrical characterisations are carried out in ambient atmosphere, demonstrating a protecting effect of the polymer host.Here we present the electronic characterisation of 1,4,8,11-Methyl-substituted 6,13-triethylsilylethynylpentacene [5] inkjet printed transistors of various architectures formulated with a range of side chain aromatic insulating polymer binders.[1] O.D. Jurchescu, J. Baas, T.M. Palstra, Appl. Phys. Lett., 84, 6, 3061[2] J. E; Anthony, Angew. Chem. Int. Ed. 2008, 47, 452-483[3] S H. Lee, M H. Choi, S H. Han, D J. Choo, J. Jang, S K. Kwon, Org. Electronics, 2008, 9 (5), 721-726[4] M-B. Madec, G. Rincon-LLorente, D.J. Crouch, S.G. Yeates, Proc. MRS 1114-G06-05, DOI: 10.1557/PROC-1114-G06-05[5] G. Rincon Llorente, Marie-Beatrice Dufourg-Madec, D. J. Crouch, R. G. Pritchard, S. Ogier and S. G. Yeates, Chem. Comm., 2009, 3059 – 3061.
9:00 PM - C6.35
Strain Field and Magnetic Field Sensors with OLED Indicators Employing Piezoelectric and Magnetoresitive Gated OFET.
Hsin-Jung Lee 1 , Shyuan Yang 1 , Yu-Jen Hsu 1 , Ioannis Kymissis 1
1 Electrical Engineering, Columbia University in the city of New York, New York, New York, United States
Show AbstractWe present an architecture for a strain field and a magnetic field sensor using organic field effect transistors (OFETs) and organic light emitting diodes (OLEDs) for charge amplification and visualization. The strain field sensor uses a piezoelectric PVDF (polyvinylidene difluoride) gate and the OFET is used to locally amplify the charge generated from the PVDF. The magnetic field sensor uses a magnetoresistive Alq3 [tris-(8-hydroxyquinoline) aluminum] as a variable resistor connected to the OFET gate. The integration of these sensors with OFETs and OLEDs enables the detection and visualization of either a local strain or magnetic field. In both of these structures, the brightness of OLED is directly proportional to the charge on the gate material, which is directly proportional to the local field strength. Finally, for both of these materials, an array of sensors is fabricated and used to produce a two-dimensional map of strain field or magnetic field strength.
9:00 PM - C6.36
High Efficient White Emitting Devices Based on Microcavity Blue Phosphorescent OLEDs with Down-conversion Phosphors.
Jaewon Lee 1 , Neetu Chopra 1 , Debasis Bera 1 , Sergey Maslov 1 , Sanghyun Eom 1 , Ying Zheng 1 , Paul Holloway 1 , Jiangeng Xue 1 , Franky So 1
1 Dept of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractThere are several approaches to generate white light from organic light emitting diodes (OLEDs). One approach is to use blue emitting OLEDs in conjunction with down-conversion phosphors. This approach requires highly efficient saturated blue emitters to provide efficient excitation for the phosphors. For blue phosphorescent emitters such as FIrpic, the emission spectrum contains too much green light and it does not excite the phosphors efficiently. In order to enhance the blue excitation for the down-conversion phosphors, we incorporated the microcavity structure and demonstrated highly efficiency white OLEDs. We previously demonstrated high efficient microcavity blue phosphorescent OLEDs (PHOLEDs) with power efficiency of 41 lm/W. With down-conversion phosphors incorporated in the blue micro-cavity PHOLEDs, a maximum luminous efficiency of 68 lm/W for the resulting white emitting device with a color rendering index (CRI) of 83 was achieved. A macrolens was also used to further extract the substrate guided modes from the phosphor film. It was done by directly attaching the macrolens on top of the phosphor film with the same index matching gel used between the OLED glass and the phosphor glass. With the macrolens attached to the phosphor film, a further enhancement of 50% in power efficiency was achieved. It is therefore expected that the resulting white emitting OLEDs should have a high luminous efficiency exceeding 100 lm/W.
9:00 PM - C6.38
Electrical and Optical Properties of Fluorine Doped Tin Oxide on PET Substrate by Dip Coating at Low Processing Temperature for Solar Cell Applications.
Gilbert Sassine 1 , Michael Ibrahim 1 2 , Mario Abdallah 1 , Mario El Tahchi 1
1 LPA-GBMI, Lebanese University, Jdeidet Lebanon, 2 LMI, University of Claude Bernard Lyon 1, Lyon France
Show AbstractResearchers have been lately working on the fabrication of transparent conducting oxide films (TCO) for use in a wide range of applications from solar cells to gas sensing and optoelectronics [1]. For the deposition of TCO films on glass substrate, many techniques are used such as spray pyrolysis, reactive magnetron sputtering, chemical vapor deposition and dip coating [2]. TCO films are then thermally treated between 400 and 600 C therefore neglecting the possibility of their deposition on plastic substrates. Fluorine doped tin oxide (FTO) is a wide band gap semiconductor ( 3.67 eV) having high transmittance in visible range and low resistivity. FTO is nowadays widely used in the electronic industry due to its low resistivity, chemical stability, thermal resistance and low costIn this study, FTO thin films are investigated for transparent electrodes applications in hybrid photovoltaic (HPV) cells. Precursor solutions are prepared using tin tetrachloride SnCl4 and NH4F or HF. Ethanol and water are used as solvents. Dip coating technique is used to fabricate SnO2:F thin films, on glass and polyethylene terephthalate PET substrates. Our choice of the dip coating technique is related to its simplicity and for the possibility of its use in industrial process for transparent electrodes fabrication. The effect of the precursor concentration, time of deposition, substrate temperature and the annealing temperature on the electrical conductivity, optical transmittance and morphology of the SnO2:F deposited layers are investigated. We should note that the FTO film is annealed at low temperatures and give a crystalline structured SnO2:F while preventing the melting of the PET substrates. Before and after dipping the PET substrate is heated at a temperature lower than 140 C in order to ensure the adhesion of the deposited film. After analyzing the electrical conductivity and optical transmittance of the films, the optimized parameters are determined for their usage as transparent electrodes in HPV.[1] J. Xu, S. Huang and Z. Wang, First principle study on the electronic structure of fluorine-doped SnO2, Solid State Communications, Vol.149, pp.527-531, 2009[2] S. Ray, M. Karanjai and D. Das Gupta, Tin dioxide based transparent semiconducting films deposited by the dip-coating technique, Surface and Coatings Technology, Vol.102, PP.73-80, 1998
9:00 PM - C6.4
NOT and NAND Logic Circuits Composed of Single GaAs Nanowire Based MESFETs on Plastic Substrates.
Changjoon Yoon 1 , Jamin Koo 1 , Sangsig Kim 1
1 Department of Electrical Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractNOT and NAND logic circuits composed of single GaAs nanowire based MESFETs were constructed on plastic substrates and their electrical characteristics were examined in this work. GaAs nanowires were obtained from a 6 inch n-type GaAs wafer using the conventional top-down approach with photolithography and anisotropic etching processes, and these nanowires were detached from the wafer and transferred onto a Si substrate. For the fabrication of MESFETs, AuGe (120nm)/Ni (20nm)/Au (200nm) layers were deposited on the GaAs nanowires after the patterning of the source and drain regions by the photolithographic process. Source and drain electrodes were formed by a lift-off process. Electrodes were annealed at 450 °c for 1 min by a rapid thermal annealing process for the formation of Ohmic contact. These source and drain patterns were transferred onto plastic substrates, and Ti (150nm)/Au (100nm) layers were deposited on the channel parts of the GaAs nanowires after the patterning of the gate region by the photolithographic process. The MESFETs exhibited nearly identical n-type depletion mode ones with Ion/Ioff ratios of ~107. With these fabrication and transfer techniques, NOT and NAND logic circuits composed of the MESFETs were constructed on plastic substrates. NOT and NAND gates operated properly as logic circuits by different input states with 3 ~ 3.5 gains. A logic swings of 0.98 V (or 98%) were obtained for the NOT and NAND logic circuits owing to the high Ion/Ioff ratios of the MESFETs.
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Formation of 100 nm-sized Nanodot Array of Low-molecular-weight Organic Semiconducting Materials in Vacuum Deposited Films.
Manabu Nakata 1 2 , Kenji Kawano 1 2 , Mao Yasumatsu 1 3 , Masayuki Yahiro 1 3 4 , Chihaya Adachi 1 3
1 , NEDO BEANS Project, Fukuoka Japan, 2 , Panasonic Electric Works Co., Ltd., Osaka Japan, 3 , Kyushu University, Fukuoka Japan, 4 , ISIT, Fukuoka Japan
Show AbstractSince the organic devices basically function in the form of ultra-thin films less than 100 nm, amorphous morphologies have been commonly used to form practical pin-hole free thin films. However, the amorphous states are not necessarily good morphologies for maximizing electrical and optical characteristics. One of unique characteristics of organic materials is an ability of self-assembly that leads a wide variety of nano-structures. In the formation of organic nano-structures, phase separation of block-co-polymors and mixed polymers have been widely studied. However, these are a few reports on the nano-structures based on small molecular weight materials.In this study, an array of the hemispherical nanostructure of low-molecular-weight organic semiconducting materials with an average diameter of around 150 nm, a height of about 60 nm, and the aspect ratio of about 3:1 was formed by using conventional vacuum deposition process on a substrate treated with a self-assembled monolayer (SAM). As deposition substrates, we used a 300 nm-thick SiO2/Si and 100 nm-thick ITO (indium thin oxide)/glass substrates, which are treated by hexamethyldisilazane (HMDS). As low-molecular-weight materials, we used two kind of materials: N, N’ – diphenyl – N, N’ – bis ( 3–methyl phenyl ) – ( 1,1’ – biphenyl ) – 4, 4’ – diamine (TPD) and N, N' – Di (1–naphthyl) – N, N' – diphenylbenzidine (a–NPD) which have a tendency to form an amorphous morphology, and pentacene, a-sexithiophene (a–6T) and fullerene (C60) which have a tendency to form a crystalline texture. The shapes of the nanostructures were mainly controlled by the underlaying SAMs, organic semiconducting materials and film thickness.
9:00 PM - C6.41
Formation of Organic Crystalline Nano-Structures and their Application to Organic Solar Cells.
Masaya Hirade 1 2 , Hajime Nakanotani 1 2 , Masayuki Yahiro 1 2 3 , Chihaya Adachi 1 2
1 Center for Future Chemistry, Kyushu Univ., Fukuoka Japan, 2 , BEANS Laboratory, Tokyo Japan, 3 , ISIT, Fukuoka Japan
Show AbstractOrganic solar cells (OSCs) are expected as a next generation energy source. They are easily prepared by low cost and low temperature device fabrication techniques. In order to enhance the device characteristics, it has been expected to introduce nano-structures into organic devices such as nano-pillar structures. These structures provide a large area of a p-n heterointerfaces, contributing efficient carrier separation and high carrier transport characteristics. In this study, we prepared OSC with organic crystalline nano-structures fabricated by annealing and vapor phase deposition (VPD) techniques. Copper phthalocyanine (CuPc) was used as a p-type material. In order to orient CuPc molecules parallel to substrates, we first deposited a 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) ultra thin layer on ITO electrodes. Then, we deposited CuPc on the PTCDA layer and annealed it, resulted in the CuPc crystalline nano-structures with 20 nm width and 20 nm height. Further, by applying VPD technique, CuPc nano-pillar structures with few hundred nano-meter length were obtained. OSCs using these structures combined with C60 as a n-type material showed improved photovoltaic characteristics with the maximum power conversion efficiencies of ~ 1.2 %.
9:00 PM - C6.42
Fabrication of High Bending Resistant Flexible Dye Sensitized Solar Cell with Well-aligned Single Crystalline ZnO-nanorod Electrode via Contact Printing Method.
Jin Ju Kim 1 , Ki Seok Kim 1 , Gun Young Jung 1
1 Materials and Sience Engineering, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Show AbstractFlexible dye sensitized solar cells(DSSCs) have three important meanings ; lightweight for portability, low cost process, and High transmittance. Recently, there is an increased interest in developing flexible DSSCs with nanostructured metal-oxide such as TiO2 or ZnO films fabricated on flexible substrates. Generally, nanoparticle base DSSCs are fabricated by connecting a mesoporous film with ITO/PET plastic substrate by low-temperature processes such as press method, hydrothermal crystallization, microwave irradiation or film transfer. However, the poor adhesion of nanoparticles arising from the low-temperature heat treatment makes the film more fragile thus limiting the bendability and efficiency of the flexible DSSCs. ZnO is a large wide band gap semiconductor with high electronic carrier mobility. ZnO-nanorod array with large surface area is a promising choice for the photoanode of DSSCs, although the power conversion efficiency PCE of DSSCs based on ZnO nanorod on indium tin oxide ITO glass is relatively low 2% due to poor dye loading and other unknown reasons. Nevertheless, the low-temperature and low-cost fabrication of ZnO nanowires by solution process hydrothermal method makes it attractive and especially suitable for flexible devices and mass production. For flexible electronics applications, orderly aligned nanowires can efficiently release the bending stress in the film through the gap between nanorods. In this presentation, we report a flexible DSSC with well-aligned single crystalline ZnO-nanorod electrode via contact printing method. The highly bendable ZnO-nanorod film on PET/ITO substrate was fabricated by low-temperature hydrothermal growth. To align the ZnO nanorod, Zinc acetate sol was used as ink and transfer the ink to the PET/ITO substrate under low pressure and low temperature.
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Fully Printed, Flexible, Integrated Organic Pyroelectric Sensors for Large-area Human-machine-interfaces.
Barbara Stadlober 1 , Martin Zirkl 1 , Gregor Scheipl 1 , Anja Haase 1 , Elke Kraker 1 , Georg Jakopic 1 , Anurak Sawatee 2 , Peter Bodo 2 , Peter Andersson 2
1 Institute of Nanostructured Materials and Photonics, Joanneum Research, Weiz Austria, 2 , Acreo AG, Norrköping Sweden
Show AbstractThe interest in the application of polymer ferroelectric thin films has continuously grown during the last decade, especially in terms of fabrication of non-volatile memory cells [1], high-performance organic thin film transistors [2], detectors for infrared radiation and temperature [3],[4], and sensors for pressure and motion [5], pointing towards full organic actuators and artificial skin [6]. With reference to human-machine interfaces successful communication often relies on the machine’s capability to recognize tactile information and distinguish humans from inanimate objects by sensing temperature and pressure. In this context semi-crystalline ferroelectric polymer materials are ideal candidates since they provide information about both, temperature and pressure changes, by exploiting the pyro- and piezoelectric effect.The flexible pyroelectric sensors presented in this work are comprised of pyroelectric PVDF-based thin film capacitor arrays integrated with high performance organic thin film transistors that operate at low voltages and act as impedance converters (or signal amplifiers). In order to enable flexible integration with diverse electronic devices or display elements large area processes such as screen printing have been used for the fabrication of the sensors. With respect to the intended purpose for detection of human-body radiation the absorbance of the impinging IR-light is dramatically increased by the application of printed carbon top electrodes, hence meeting the requirements for a cheap large area fabrication process. Besides the excellent pentacene based organic thin film transistors with high-k-nanocomposite gate dielectrics the integration of printed electrochemical transistors for large-area applications has recently been successfully realized. The latter were also fabricated by screen printing thus providing a base for direct integration of sensors and transistors on large-area flexible substrates.[1] C.G. Naber et.al., Nature Materials, vol. 4, p. 243, 2005[2] B. Stadlober et.al., Appl. Phys. Lett., vol. 86, 242902, 2005[3] D. Setiadi et.al., Sensors and Actuators, vol. 52, p. 103-109, 1996[4] M. Zirkl et al., Adv. Mat. 19, 2241 (2007)[5] S. Bauer et.al., Physics Today, vol. 37, 2004[6] R. Reston et.al., Proceedings of the 11th IEEE-Conference on Engineering in Medicine & Biology Society, 0918, 1987
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All Organic Electrochromic Spandex.
Yujie Ding 1 , Michael Invernale 1 , Gregory Sotzing 1
1 Institute of Material Science, Unversity of Connecticut, Storrs, Connecticut, United States
Show AbstractThe fabrication of all organic electrochromic spandex devices is described herein. Spandex is a common fabric having the ability to stretch to over 100% of its orginal area and ability to fit to shape. One very challenging integration of electrochromics into a solid-state device is its incorporation into a spandex, stretchable material. Some of the underlying hurdles include the ability of the conductor to remain functional as an electrode, the ability of the chromogenic material to undergo color change, and have these layers remain adherent under stress. A further challenges include construction of the multi-layered device and choice of polyelectrolyte. Spandex electrochromics could have a host of different applications, including but not limited to simple displays incorporated on wrist bands and other accessories as watches, heart-rate monitors, compasses, etc., fashion wear, and chameleonic skin. Electrochromic devices have been extensively studied for their various applications in displays, smart windows, optical shutters, e-paper, mirrors, etc. Their relatively simple architectures, low cost of fabrication and power consumption and easy control of the color transitions attract a wide industrial audience. In our present study, a fine woven stainless steel mesh fabric electrode and a conductive composite stretchable spandex (Lycra®) electrode were employed as the fabric electrodes. The spandex is coated with conducting polymer PEDOT-PSS (ORGACON®) to impart a conductivity of ~0.1 S/cm. The relatively low conductivity value of the spandex electrodes did not prevent them from functioning properly in the devices. Precursor polymers were spray-coated onto the working electrodes and assembled into devices after conversion to their electrochromic state. The processability of the polymer is critical for coating and patterning (images, letters). Although a red to blue conjugated polymer was used in the reported devices, any processable electrochromic polymer should have the ability to be incorporated, and thus various colors can be achieved in the devices. Stainless steel mesh electrodes and spandex electrodes were used in different combinations as the working and counter electrodes. All of the fabric electrode devices show fast switching speed and vivid color transitions. The spandex electrodes are highly stretchable and remain conductive. It has been proved that the spandex electrodes with coated electrochromic can function properly with up to 50% 2-way stretch in electrolyte solution. Apart from the color change induced from charge injection/removal, color intensity can be varied upon stretching of the material and may serve as a secondary mechanism for chameleonic skin applications.
9:00 PM - C6.46
Full Wafer Nano-scale Block Copolymer Patterning for Defect Reduction in Epitaxial Growth of Lattice-mismatched Materials.
Smita Jha 1 , Chi-Chun Liu 2 , T. Kuan 5 , S. Babcock 3 , J. Park 4 , L. Mawst 4 , P. Nealey 2 , T. Kuech 2
1 Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 5 Department of Physics, State University of New York, Albany, Albany, New York, United States, 3 Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 4 Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractA rapid and cost–effective full wafer approach to nanoscale patterning was used for defect reduction in heteroepitaxial growth of large lattice mismatched materials. The method is based on self-assembly in an over layer of block co-polymers PS-b-PMMA to produce full wafer patterning at the 20-nm length scale. The pattern produced in the polymer is transferred to mask layer below it by reactive ion etching. In this work, the method was used to generate a SiO2 mask layer with nanoscale holes ~ 20 nm in size on 40 nm centers over an entire GaAs wafer. Epitaxial growth, in this case of GaSb, initiates in the nanoscale holes and proceeds laterally over the SiO2 layer. Because of small separations (~20 nm) between growth windows, film coalescence occurs at nanoscopic island size. When the lattice mismatch is sufficiently large, the coalescing nanoscale islands also are fully, or nearly fully, relaxed. TEM and x-ray diffraction show that the result is a film with reduced threading dislocation density. In this work, a thin layer of SiO2 ~ 20 nm was deposited on a nominally exact (100) GaAs substrate by plasma-enhanced chemical vapor deposition. The 20 nm SiO2/GaAs substrate was pretreated with hydroxyl-terminated random polystyrene-polymethylmethacrylate random (PS-r-PMMA) copolymer brush material to generate a neutral surface. A 1% (w/w) toluene solution of PS-b-PMMA (MW: 46 kg/mol for PS and 21 kg/mol for PMMA, PDI: 1.09) diblock copolymer was spin-coated over this pretreated wafer. The coated wafer was annealed at 190°C for 24 h under vacuum to induce the formation of a hexagonal array of nanoscale PMMA cylinders with their long axis oriented perpendicular to the substrate. The PMMA cylinders were removed by acetic acid development after UV irradiation, leaving a hexagonal array of ~20nm holes on ~40 nm centers over the entire wafer surface. This pattern is transferred to the substrate by reactive ion etching of the SiO2 under the holes followed by removal of the PS matrix to generate the final mask-patterned substrate. X-ray diffraction patterns from a 200-nm thick GaSb film grown on a patterned GaAs substrate show a factor of two or more reduction in FWHM of the GaSb peak compared to a film grown to the same thickness on a non-patterned wafer. This improvement in materials structure or quality through nano-patterned growth should be applicable to a wide range of materials and lattice mismatched situations for large-area integration. This simple, spin-on cost effective technique for full wafer patterning using block copolymers followed by growth offers multiple advantages in advanced applications: 1) reduced metamorphic buffer thickness, 2) improved planarity of device structures, 3) isolation of defect bearing regions from device region and 4) ability to integrate multiple heterostructures compositions over a wafer by direct epitaxy.
9:00 PM - C6.47
Large Area Single Crystal Substrates for Production of Phovoltaics.
Meifang Li 1 , Jae Wook Shin 2 , Eric Chason 1
1 Division of Engineering, Brown University, Providence, Rhode Island, United States, 2 Metallurgy Division, B-160/224, Mail Stop 8551, National Institute of Standards and Technology, Gaithersburg, 20899, Maryland, United States
Show AbstractWe describe a method for producing large-area, inexpensive single crystal substrates through electrochemical processing. These substrates could be used for the production of photovoltaics with single crystal orientation to achieve higher performance at the cost of polycrystalline material. The method uses a sequence of electropolishing, epitaxial electrodeposition and selective etching to create freestanding foils from an initial template crystal that can then be reused to make more material. Analysis of Ni(100) samples by electron backscattering pattern (EBSP) and X-ray diffraction show that high quality foils can be produced with grain misorientations of less than 0.1 deg for both the in-plane and out-of-plane orientations. We have also shown that the starting single crystal (Ni) can be reconditioned so that we have been able to produce nine generations of ~80 mm2 freestanding films from the same starting sample with the same crystalline quality. This enables the method to be turned into a continuous process for making long ribbons or large areas of single crystal films to provide inexpensive substrates for growing large-area layers.
9:00 PM - C6.48
In situ Conversion: A Facile Method for Electrochromic Device Preparation.
Donna Marie Mamangun 1 , Michael Invernale 1 , Yujie Ding 1 , Mustafa Yavuz 2 , Gregory Sotzing 1
1 Institute of Material Science, University of Connecticut, Storrs, Connecticut, United States, 2 , Washington University in St. Louis, St. Louis, Missouri, United States
Show AbstractThe precursor polymer approach to processable electrochromics is further explored herein towards facile preparation of electrochromic devices (ECDs). Precursor polymers developed by Sotzing et al. are soluble and processable by spray-casting, ink-jetting, electrostatic spinning, doctor-blading, etc. Once processed, these polymers can be converted chemically or electrochemically to their conjugated, electrochromic forms. In situ conversion allows for this process to occur inside an already assembled ECD. Unlike electrochemical conversion, in situ conversion of precursor polymers requires no electrolyte baths. Precursor systems such as poly([dimethylpropylenedioxythiophene]-dimethylsilane), abbreviated as PProDOT-Si, poly([dimethylpropylenedioxythiophene]-tetramethylsiloxane) (PProDOT-SiOSi), and several norbornene-based pendant precursors have all been shown to undergo in situ conversion to conjugated electrochromic polymer. In this study poly(bis[3,4-ethylenedioxythiophene]-thiophene-dioctylsilane) (PBEDOT-T-Si[Octyl]2) was used to further explore this processing method. The precursor was spray-coated onto ITO substrates, followed by device assembly. In situ converted and ex situ (electrochemically in an electrolyte bath) converted devices were assembled and compared. Gel electrolyte composition and precursor film thicknesses were varied in the devices and were characterized according to their time of conversion, switching speed, long-term stability, optical memory, color coordinates, and photopic contrast. The results showed that devices converted in situ showed similar if not the same switching speeds, optical memory and device color in comparison to devices made using ex situ conversion. Using ionic liquids as the electrolyte layer was also found to support in situ conversion. With intention, dirty ITO substrates (not sonicated and with thumbprint) were used for device assembly. The conducting polymer film showed no noticeable film defects that are usually observed when films are made by electrodeposition. This further reduces the number of steps required for ECD assembly. The simplicity of this processing method shows very promising utility and value in processing and application.
9:00 PM - C6.49
Wafer-level Strained Silicon: Fabrication and Stability upon Nanoscale Patterning.
Oussama Moutanabbir 1 2 , M. Reiche 1 , A. Hahnel 1 , W. Erfurth 1 , U. Goesele 1 , M. Motohashi 2 , A. Tarun 2 , N. Hayazawa 2 , S. Kawata 2 , M. Holt 3 , J. Maser 3
1 , Max-Planck Institute of Microstructure Physics, Halle (Saale) Germany, 2 Nanophotonics Lab, RIKEN, Saitama Japan, 3 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractThe sustained scaling was the most important principle of performance enhancement in Si CMOS for more than 30 years. At the 90 nm technology node and beyond, however, performance enhancement of CMOS through device scaling such as shrinking the gate length and thinning the gate oxide has become more and more difficult, because of several physical limitations in miniaturization of MOSFETs. Thus, new channel structures and materials, which mitigate the stringent constraints regarding the device design, have recently stirred a strong interest. Strained silicon channels are one of the most important Technology Boosters for further Si CMOS developments. The mobility enhancement obtained by applying appropriate strain provides higher carrier velocity in MOS channels, resulting in higher current drive under a fixed supply voltage and gate oxide thickness. In this presentation, we describe methods for a controlled introduction of strain on the wafer level. We combine the growth of Si1-xGex virtual substrates, hydrogen implantation, direct wafer bonding, and thin layer transfer to fabricate strained silicon-on-insulator (SSOI) wafers. The amount of the strain generated can be tuned by adjusting the content of Ge in the virtual substrates, which are used as templates for the growth of strain silicon ultra thin films. We also address the stability of the strain upon nanoscale pattering – a crucial step in the fabrication of SSOI-based devices. A variety of experimental techniques were employed to quantify the strain in SSOI nanostructures with lateral dimension in 50–500 nm range. The local relaxation and strain redistribution, due to the formation of free surfaces, are investigated as a function of the lateral size, thickness, and geometry. This phenomenon is described based on detailed three-dimensional finite element simulations. The anisotropic relaxation in rectangular nanostructures is also discussed.
9:00 PM - C6.5
Complementary Logic Circuits with Chalcogenide-nanocrystals-based Transistors on Flexible Plastic Substrates.
Junggwon Yun 1 , Kyoungah Cho 1 , Sangsig Kim 1
1 , KOREA UNIV., Seoul Korea (the Republic of)
Show AbstractChalcogenide nanocrystals were used to fabricate NAND and NOR logic circuits on flexible plastic substrates. HgTe and HgSe nanocrystals were selected in this study as p- and n- type chalcogenide ones, respectively, and these nanocrystals were utilized to be channel materials for thin film transistors (TFTs). NAND gates were composed of two HgTe-p-channel TFTs in parallel and two HgSe-n-channel TFTs in serial. And NOR gates were constructed with two HgSe-n-channel TFTs in parallel and two HgTe-p-channel TFTs in serial. All channels were formed by a spin-coating method on back gate patterned plastic substrates. And cross-linked poly-4-vinlyphenol and gold were used as a gate insulator and an electrode material, respectively, in our logic circuits. The mobilities for the p- and n-channel TFTs were estimated to be 1.07 cm2/Vs and 1.98 cm2/Vs. The NAND and NOR gates operated as logic devices for different input states with 3~6 gains at room temperature in air. The electrical characteristics of NAND and NOR logics were maintained while the plastic substrates was stressed with 0.6% strain bending for 1000 cycles.
9:00 PM - C6.50
Large-area Rail-guided Self-assembly of Heterogeneous Microstructures on Flexible Substrate Using a Cross-rail Structure.
Junhoi Kim 1 , Younghoon Song 1 , Sunghoon Kwon 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractWe report large-area two-dimensional fluidic self-assembly of heterogeneous microstructures without assembly error based on unique cross-rail structures in a microfluidic channel. The guided assembly of microstructures using railed microfluidic channel shows potential for deterministic fluidic self-assembly platform. However, to construct complex assembly system with railed microfluidic channel, stable rail-to-rail transfer should be achieved. Our cross-rail structures transfer microstructures through stable rotation, just as macro-scale cross-intersection of rail ways, giving flexibility and scalability to rail-based microstructure assembly system and thereby enabling deterministic large-area self-assembly of microstructures such as light emitting diodes and photovoltaic cells.Using serial connection of cross-rail structures, we assembled 100 polymeric microstructures in a microfluidic assembly channel, which can be expanded more owing to the scalability given by the cross-rail structures. We also assembled heterogeneous microstructures by guiding and assembling two different types of microstructures with two independent cross-rail structure arrays. To construct complex functional system such as microelectronic circuit with assembled microstructures, the transfer of assembled microstructures from assembly microfluidic channel to arbitrary substrate is needed for practical applications. As a simple demonstration, we transferred the assembled structures on a flexible polyester sheet after the assembly, which promises the applications of assembling flexible display or photovoltaic modules.For rail-based high-throughput assembly, introduction of externally fabricated microstructures and filtering of flipped microstructures are required. Flipped microstructures, which stop the assembly process, are filtered out by an array of juts inside microfluidic channel. Thanks to the filtering scheme, the micron-scale components are only needed to be introduced to the microfluidic channel without additional control scheme for their assembly. With the combination of the cross-rail structure, substrate transfer method and filtering scheme, large-area rail-guided self-assembly of heterogeneous microstructures with high throughput is expected to be realized.The rotation of the microstructures at various types of cross-rail structures is investigated using three-dimensional finite element method simulation. The jut at the cross-rail structure helps guidance as well as rotation by focusing flow stream at the end of fin, which is consistent with the experimental results.We presented guiding and assembly of microstructures utilizing cross-rail structures, which gives flexibility and scalability to rail-guided assembly of microstructures. We believe that our technique is promising for various applications of high-throughput large-area assembly of heterogeneous microstructures such as biochip array assembly or microelectronic components assembly.
9:00 PM - C6.52
Characteristics of Large Area Dye-sensitized Solar Cells Improved with Glass Passivation.
Deuk Ho Yeon 1 , Oh Hyeon Kwon 1 , Yong Soo Cho 1
1 Materials Science & Engineering, Yonsei University , Seoul Korea (the Republic of)
Show AbstractA dye sensitized solar cell (DSSC) of area greater than 25 cm2 was prepared on fluorine-doped tin oxide glass (FTO-glass) substrates patterned with Ag grids and protected by a subsequent glass layer. The glass passivation of thickness about 7μm was intended to provide a critical solution for maintaining high efficiency in potential large area DSSCs. The Ag grids were prepared by printing Ag paste on the FTO-glass substrate followed by sintering at 530oC for 20 min. In the present work, we have used two types of passivation layers based on (i) bismuth borosilicate and (ii) zinc borosilicate glasses, both having low glass transition temperature less than ~480oC. Pore-free and highly visible transmitting glass passivation layers were obtained at a sintering temperature of 540oC for 20 min. The protection ability of the passivation layers was evaluated by immersing the patterned FTO-substrates in the electrolyte and subsequent measurement of resistivity of the FTO substrate, as a function of immersion time. Both the layers were found to protect the Ag patterns successfully. The lowered electrical resistance ~ 27Ωof the FTO-coated substrate was maintained over the electrolyte exposure of at least 250h when the passivation layer was sintered at 540oC. It was observed that the solar cells prepared with the Ag grid and the glass-based passivation layers have the fill-factor 30% higher than those without Ag grid and any passivation layer. The present work conclusively shows that use of the patterned Ag and a glass-based passivation layer helps maintaining efficiency of the cell in spite of increase of the cell area.
9:00 PM - C6.53
In-Fiber Nanostructured Optical Devices.
Mecit Yaman 1 , Mert Vural 1 , H. Esat Kondakci 1 2 , Mehmet Bayindir 1 2
1 UNAM, Bilkent University, Ankara Turkey, 2 Department of Physics, Bilkent University, Ankara Turkey
Show AbstractOmnidirectional reflection from dielectric quarter wave stacks (QWD) has received enormous interest from several research fields namely high-power laser delivery, fiber lasers, fiber based sensors and omnidirectional fiber reflectors [1,2]. Omnidirectional reflectors on fibers have the ability to reflect a tunable spectrum of incident radiation using a one dimensional photonic crystal structure [3]. Due to near-perfect reflection and availability of polymeric materials as a dielectric layer, these structures have found applications as optical verification items (optical bar codes) and flexible radiation barriers [4]. In this work, nanostructured composite functional fibers are fabricated by thermal drawing technique. The fibers contain omni directional photonic band gap structures with alternating polymer (PEI) and semiconducting (As2Se3) layers and a heat sensitive amorphous semiconducting cavity layer. The cavity wavelength is highly tunable by changing the environment temperature. [1] A. F. Abouraddry, M. Bayindir, et. al., Nature Mater. 6, 336 (2007).[2] M. Bayindir, et. al., Nature 431, 826 (2004).[3] Y. Fink, et. al., Science 282, 1679 (1998).[4] S. D. Hart, et. al., Science 296, 510 (2002).
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Tuning Color through Nanometer ITO Film Stretched on Compliant Substrates.
Cunjiang Yu 1 , Kevin O'brien 2 , Yong-Hang Zhang 2 , Hanqing Jiang 1 , Hongbin Yu 2
1 Mechanical Engineering, Arizona State University, Tempe, Arizona, United States, 2 Electrical Engineering, Arizona State University, Tempe, Arizona, United States
Show AbstractColor tuning ability is essential in many optical systems, and is typically achieved by mechanically rotating a grating or a prism. The tunability of devices such as grating requires complicated structure design and combined fabrication techniques. Here we describe a new and simple fabrication process of grating structure that has very large tuning range in the visible region by mechanically stretching or releasing of a film, without going through photolithography processes. The fabrication of the tunable color gratings involves depositing ultra-thin film onto pre-stretched elastomeric substrates. Specifically, a 1mm thick PDMS is stretched by a custom made stage at desired level, named pre-strain. An ultra-thin Indium Tin Oxide (ITO) film about 8 nm thick is then sputtered onto the pre-stretched substrate. Releasing the tensile strain after deposition leads a periodic sinuous buckled profile of the ITO surface due to competition between the soft and elastomeric PDMS substrates and relatively hard films. A mechanical model using energy methods is presented to predict the wavelength and amplitude of the buckled profiles, which depend on the pre-strain on the PDMS, ITO film thickness. The wavelength of 1.2 μm and amplitude given by the model agree very well with those measured by scanning electron microscopy and atomic force microscope. The optical testing of fabricated diffraction gratings is performed. The first order diffraction of incident white visible light has significant shift while stretching the grating from 0 to maximum of 30% applied strain, defined by the pre-strain of PDMS, at which level, the ITO film becomes flattened. Measurement of wavelength shift of the transmittance diffraction is performed by fixing the detector, only tuning the applied strain over the grating. The results show more than 100 nm tuning in wavelength, which clearly indicated by the color shifting from blue to orange, thus demonstrating a largely tunable color.
9:00 PM - C6.55
High Strength Metalized Fibers and Yarns.
Steven Morris 1 , Kevin Pipe 2 , Max Shtein 3
1 Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractA number of emerging applications in multifunctional composites (e.g. structurally integrated communication cables, antennas, biosensors, electronic textiles) call for lightweight fiber composites that can simultaneously provide flexibility, high electrical conductivity, and high tensile strength. Commercially available fibers such as Kevlar, Spectra, and Vectran offer tensile strengths greater than that of steel, with densities comparable to those of polymers. Creating an electrically conductive pathway on such a fiber while maintaining low weight can be accomplished by coating the fiber with a metal that has a high ratio of conductivity to density (e.g. Cu). In this work, we explore processes and conditions necessary to form metallic films on high strength monofilament fibers and multifilament yarns, through the use of vacuum thermal evaporation, electroless deposition, and electroplating. Films of copper, nickel, and silver are grown on Kevlar and Spectra yarns, as well as monofilament fibers created from Nylon and silica coated in polyimide. Pretreatment conditions, such as plasma activation of the fiber surface, are explored alongside posttreatment options such as annealing, in consideration of enhanced film adhesion and loss in fiber strength.Multifilament conductive yarns offer additional tradeoffs, as well as degrees of freedom in property optimization. For example, yarns are subject to stress concentrations that form a failure cascade, which can ultimately result in breakage. On the other hand, twisting of the yarn decreases the resistance along the composite by electrically coupling adjacent fibers, mitigating the role of parasitic resistance due to defects in the individual filament coating. Furthermore, the greater surface area of yarns also allows for thinner conductive films, which reduces the probability of film delamination when compared with the thicker films required for monofilament fibers. Performance and reliability characteristics of the coated fibers and yarns are mapped through tensile strength and conductance measurements performed under uniaxial and bending stresses. Scanning electron microscopy is used to assess film quality and wear mechanisms, through observation of variations in grain structure, thickness, and film discontinuities. Theoretical models are utilized to compare experimental results to ideal fiber composites and to suggest methods for performance and reliability improvement. Using optimized metal coating techniques, we demonstrate a high tensile strength composite offering resistance less than 0.1 Ω/inch. This composite can then easily be woven into a substrate to form a structurally integrated antenna suitable for lightweight aerial vehicles.
9:00 PM - C6.56
Water Vapor Barrier Properties of HMDSO Deposited Films on Polyethylene Terephthalate (PET) and Polyethylene Naphthalate (PEN) by Plasma Enhanced Chemical Vapor Deposition.
Moinul Choudhury 1 , Won-Ho Kim 1 , Dong-Bum Seo 1 , Sung-Ryong Kim 1
1 , Chungju National University , Chungju Korea (the Republic of)
Show AbstractThe effect of Ar and O2 flow rates on water vapor transmission rate were studied by using PET substrate in reactive ion etching mode and bias voltage effect by using PEN substrate in PECVD mode at a fixed radio frequency (RF) power of 300W. The water vapor transmission rate (WVTR) of the untreated PET and PEN were 54.56 and 6.27 g/m2/day, respectively, and it decreased after depositing the silicon oxide (SiOx) coatings. The minimum WVTR, 0.47 g/m2/day, was observed at a coating thickness of 415.44 nm in RIE mode. The intensity of the peaks for the Si-O-Si bending at 800-820 cm-1and Si-O-Si stretching at 1000-1150cm-1 varied depending on the Ar and O2 flow rates. Atomic force microscopy (AFM) revealed that the roughness of the deposited coatings increased when either the O2 or Ar flow rate was increased. Also, the effects of external negative direct current bias voltage on WVTR, coating composition and morphology were studied. The carbon content of the coatings decreased with the increase of bias voltage and increased with the increase of HMDSO flow rate at a fixed O2 flow rate. The densely packed structure and the lowest WVTR, 1.40 g/m2/day, was observed at -150 V of bias voltage.
9:00 PM - C6.57
Soft Microelectrode Arrays for High Resolution EMG Recordings.
Cinzia Metallo 1
1 , Tufts University School of Medicine, Boston, Massachusetts, United States
Show AbstractWe have designed and we are fabricating a novel implantable soft material-based microelectrode array intended for long-term electromyographic (EMG) recordings. Soft materials provide a highly biocompatible, mechanically flexible and dimensionally stable substrate that can be manipulated into unique tridimensional designs that adapt to the morphology of any biological system. Furthermore, through careful selection of materials at the tissue-electrode interface, cell responses can be maintained and the array engineered to provide optimal in vivo performance. To find the most suitable combination of materials, electronic design, and biomechanical properties, we are using the tobacco hornworm Manduca sexta as a tractable testbed. The intrinsically high spatiotemporal resolution of the array is expected to maximize the signal to noise ratio and decrease the cross talk between different muscle units. As a result, the detection of isometric and involuntary muscular activity could be significantly improved. This elevated sensitivity to change in muscular tone of our flexible arrays may have applications in the development of implanted sensors for the neuro-muscular control of prosthetics.
9:00 PM - C6.58
Amorphous High-K Hafnium Oxide Gate Dielectric Deposited at Room Temperature for Large Area Electronics.
Flora Li 1 , Andrew Flewitt 1 , William Milne 1 , Mary Vickers 2 , James Dutson 3 , Steve Wakeham 3 , Mike Thwaites 3
1 Electrical Engineering Division, University of Cambridge, Cambridge United Kingdom, 2 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 3 , Plasma Quest Ltd., Hampshire United Kingdom
Show AbstractThe structural demands of high-k hafnium oxide dielectric for large area electronics is uniquely different from that imposed by CMOS technology. In the case of CMOS technology, very thin (few nanometres) polycrystalline hafnium oxide deposited at high temperature is common. For large area electronic applications such as displays and sensors, amorphous thin films are generally preferable over polycrystalline thin films as amorphous materials can render better device uniformity and stability over large area. In this paper, we report the room-temperature deposition of amorphous hafnium oxide (HfOx) thin films with a high relative permittivity of 30, using a high target utilization sputtering (HiTUS) technique. These results represent a unique advancement for large area, flexible electronics as most research groups report HfOx thin films (over few tens of nanometre thick) deposited by sputtering at low temperatures exhibit a polycrystalline structure, and are typically characterized by a relative permittivity in the range of 10 to 22. Thus, the strength of our approach is the ability to produce higher-k, near-stochiometric, transparent amorphous HfOx gate dielectric material at high deposition rate without any intentional substrate heating. This makes it highly amenable to high volume manufacturing of TFT backplanes for displays and other large area electronic applications on flexible substrates. The application of HfOx gate dielectric in metal oxide TFTs will also be presented.
9:00 PM - C6.6
A Discussion on the Metal-assisted Etching Mechanism for the Fabrication of Si Nanowires.
Nadine Geyer 1 , Zhipeng Huang 1 , Johannes de Boor 1 , Peter Werner 1 , Ulrich Goesele 1
1 , Max Planck Institute of Microstructure Physics, Halle (Saale) Germany
Show AbstractIn recent years, a simple metal-assisted etching method using metal films as a catalyst has been developed for the controlled fabrication of vertically aligned crystalline Si nanowires on silicon wafers. This working principle, referred as the ”top-down approach”, bases on a local oxidation and dissolution of Si in a HF/H2O2 solution whereas the silver layer facilitates the etching process. In the case of hole-containing metal layers controlled nanowire arrays can be generated, where the diameters of the nanowires correlate to the diameters of the holes. Applying this method nanowire diameters in the range of several µm down to 20 nm can be achieved. Whereas the macroscopic etching is successfully applied, the etching mechanism concerning a nanowire formation is still not well understood on a microscopic range. A general question concerns the contribution of the two basic etch processes: i) a reaction process through the metal film by diffusion of Si ions or by ii) a local change of the energy/barrier of an etching reaction. In the latter case an underetching of the metal film/cluster would dominate.We have investigated etching phenomena on Si wafer surfaces in dependence of several parameters: 1) the thickness of the metal layers, 2) the existence of pores in the metal films and their diameters, 3) various types of metal, 4) the composition of the etching solution and 5) the orientation and doping/resistivity of the Si wafers. In comparison to layers also the etching behavior of metal clusters was investigated.These studies yielded to a better understanding of the etching mechanism and allow a defined formation of Si nanowires (control over diameter, length and density).
9:00 PM - C6.8
Micro-patterned Polymer Electrodes for Large Area Flexible Organic Light Emitting Diodes.
Xuhua Wang 1 , Peter Levermore 1 2 , Dong-Seok Leem 1 3 , John deMello 3 , Donal D Bradley 1
1 Department of Physics, Imperial College London, London United Kingdom, 2 , Universal Display Corporation, 375 Phillips Boulevard, Ewing, New Jersey, United States, 3 Department of Chemistry, Imperial College London, London United Kingdom
Show AbstractThe development of flexible and highly conductive transparent electrode materials is of significant scientific and commercial interest. Owing to its brittleness, indium tin oxide (ITO) – the standard transparent electrode material for rigid optoelectronic devices – is poorly suited to the emerging generation of flexible electronic devices. Vapour phase polymerised poly(3,4-ethylenedioxythiophene) (VPP-PEDOT) is a promising alternative that offers a good combination of transparency, conductivity and flexibility [1-3].VPP-PEDOT is prepared via the in-situ polymerisation of 3,4-ethylenedioxythiophene (EDOT) using an oxidant such as Fe(OTs)3 or FeCl3 alongside a complementary base, such as imidazole or pyridine, to regulate the reactivity of the oxidant. With careful optimisation, we have been able to achieve thin film conductivities in excess of 1200 S/cm, together with a work function of ~4.6 eV, a transmittance of ~89% at 550 nm, and a root-mean-square roughness of less than 2 nm [1]. In combination with an overlying hole-injection layer of poly(3,4-ethylene-dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), we have fabricated polymer light emitting diodes (pLEDs) with encouragingly high efficiencies of 10.2 cd/A at 10000 cd/m2 [2].In this work, we present a new micro-fabrication procedure for organic light sources based on optimised VPP-PEDOT transparent electrodes. The patterning technique, referred to here as in situ-micro patterning, utilises a simple masked deposition procedure that involves fewer processing steps than many comparable microscale approaches. To date we have fabricated pLED arrays with 400 μm pixels, although in principle the resolution is limited only by the dimensions of the mask. The technique, which is currently being extended to organic transistors and other optoelectronic devices, provides a simple route to the realisation of a cheap and easily patterned ITO-free electrodes for use in flexible electronic applications. References1.P. A. Levermore et al., Adv. Mater. 19, 2379-2385, 2007.2.P. A. Levermore et al., J. Mater. Chem., 2008, 18, 44142.3.P. A. Levermore et al, International Symposium of the Society-for-Information-Display (SID 2008), 1989 – 1992
9:00 PM - C6.9
Preparation of Mechanically and Chemically Durable Silica and PMMA-silica Hybrid Coating Heavily Doped with Spiropyran using Perhydropolysilazane as the Silica Source and Their Photochromic Properties.
Akihiro Yamano 1 , Hiromitsu Kozuka 2
1 Graduate School of Engineering, Department of Integrated Engineering, Kanasai University, Suita, Osaka, Japan, 2 Faculty of Chemistry, Materials and Bioengineering, Department of Chemistry and Materials Engineering, Kanasai University, Suita, Osaka, Japan
Show Abstract Spiropyran (SP) is a representative photochromic (PC) compound, and has been expected as smart window coatings and optical memories. For these applications, inorganic materials such as silica glass are desired as the matrix for PC dyes in coatings because of their greater stabilities against heat and light as well as higher mechanical and chemical resistance than organic materials. In addition, the inorganic coatings should be heavily doped with photochromic dyes so that the PC changes are visualized in spite of the small thickness. Alkoxide-based sol-gel method is a conventional technique for preparing oxide materials doped with organic PC dyes. However, mechanically and chemically durable silica coatings heavily doped with SP molecules never be achieved by conventional sol-gel technique. We focused on perhydropolysilazane (PHPS) as silica source. Previously the authors' group [1] reported that PHPS coatings prepared from xylene solutions of PHPS are converted into silica films via exposure to the vapor from aqueous ammonia at room temperature, where PHPS is an inorganic polymer consisting of Si-N bonds with Si-H terminal groups. Then, the films were found to have the hardness and the durability in hot water much higher than the alkoxide-derived silica gel films. Another benefit of PHPS is its hydrophobicity. Because PHPS and xylene are hydrophobic, the hydrophobic PC molecules are expected to be incorporated in PHPS-derived coatings in high contents. The present study aimed at the preparation of hard silica coatings heavily doped with SP molecules using PHPS as silica source at room temperature. In addition, effects of the polymethylmethacrylate (PMMA) content on those of SP-doped PMMA-silica hybrid thin films. SP-doped silica coatings were prepared from xylene solutions of PHPS, where PHPS-to-silica conversion was achieved by exposing the coatings to the vapor from aqueous ammonia at room temperature. The films could be heavily doped with SP at a SP/(SP + PHPS) mass ratio as high as 0.2. The SP-doped silica coatings showed reversible PC reaction by vis or UV light irradiation, and have extremely high pencil hardness over 9H, but the chemical durability is poor where the dyes are almost completely leached out on soaking in xylene. Because of the poor chemical durability, the coatings are practically useless in spite of their visual photochromism and high hardness. However, it was found that the introduction of PMMA in the PHPS-derived silica matrix, where the PMMA/(PHPS + PMMA) mass ratio was 0.2, greatly improved the chemical durability as well as PC sensitivity without degrading the mechanical hardness. In other words, mechanically and chemically resistant coatings heavily doped with SP could be successfully realized by employing PHPS and PMMA as the starting materials for the thin film matrix.[1] H. Kozuka, M. Fujita and S. Tamoto, J. Sol-Gel Sci. Techn., 48, 148-55 (2008).