Hybrid combinations of brittle inorganic semiconductors (e.g. silicon) and soft polymers (e.g. silicone) can yield electronic systems with excellent performance characteristics and mechanical properties matched to human tissue. We describe integrated circuits and sensors with thicknesses, effective moduli and areal mass loadings matched to the epidermis. These devices can be mounted on the surface of the skin in way that is â?~invisibleâ?T to the user, to provide various functions, including measurement of electrophysiological signals associated with activity in the heart, brain and skeletal muscles.

Layered magnetic structures providing giant magnetoresistance (GMR) are crucial components of magnetic sensor devices. Currently, GMR sensors are fabricated on rigid substrates. Successful operation of GMR devices on stretchable and flexible substrates can open up a variety of new applications for magnetic sensors due to arbitrary surface geometries possible after fabrication [1, 2]. Here, we exploit the surface wrinkling effect of thin metal layers on rubber supports to create stretchable magnetoresistive sensor elements [3]. Different GMR stacks were grown on 40 µm thick rubber films (PDMS) using magnetron sputter deposition at room temperature. The GMR layer is photolithographically structured on the PDMS surface, which qualifies the fabricated sensor elements to be fully integrated into current microelectronic fabrication processes. Due to a thermal treatment, the metal layers on top of the rubber membrane undergo a fundamental morphology transition from a smooth to a periodically wrinkled film. The investigated systems include GMR multilayers as well as top pinned spin valves. Magneto-electric measurements at room temperature reveal similar characteristics for such sensor elements on PDMS coated rigid supports and free-standing rubber membranes as on conventional silicon wafers, despite the different surface structures. The thermally induced wrinkling of the GMR layer along with the free-standing rubber membrane underneath allows for a totally elastic stretchability of the entire sensor element preventing the GMR film from cracking. Strain-dependent GMR characterizations of the sensor elements will be presented together with structural investigations. In this respect the worldâ?Ts first elastically stretchable magnetic sensors are introduced [3]. With regard to biosensor applications, an easy integration into fluidic systems is given by the mechanical flexibility of the prepared sensor elements by wrapping them around the entire circumference of a tubing. This strategy offers the following intriguing advantages: (a) sensing the magnetic stray fields in virtually all directions (isotropic sensitivity), which is unique compared to the rigid planar counterparts; (b) simplicity of the sensor integration into a fluidic circuit; (c) possibility of being reused. As magnetic stray fields to be detected in fluidics are small, we optimized the sensitivity of [Ni₈₁Fe₁₉/Cu]₃₀ GMR multilayers coupled in the 2^nd antiferromagnetic maximum fabricated on free-standing PDMS membranes. With a remarkable sensitivity of 106 T^-1 at a field of 0.8 mT we used those stretchable magnetic sensors to successfully demonstrate the in-flow detection of magnetic FeNdB particles. The work was supported in part via the German federal ministry of education and research (project Nanett; FKZ: 03IS2011). References: [1] S.S.P. Parkin et al., Jpn. J. Appl. Phys.31, L1246 (1992). [2] Y.F. Chen et al., Adv. Mater.20, 3224 (2008). [3] M. Melzer et al., Nano Lett.11, 2522 (2011).

TBD

Electronic wirings on rigid substrates, which are commonly used to connect electric components, need low electric resistance or excellent frequency characteristics. Recently, wearable, health care devices, and implant electronics techniques are attractive as next generation technology. These electronics devices have not only flexibility, which are mainly designed for flexible printed circuits, but also stretchability. In our previous study, we fabricated a polyurethane-based conductive wiring containing 56 vol% of silver flakes [1]. This wiring on polyurethane substrate stretched up to 7 times without electrical ruptures. Here, we prepared polyurethane-based wirings containing 48 vol% to 72 vol% of silver particles. Electrical properties of these wirings under cyclic tensile strain test which is up to 5 % strain were investigated. There are two electrical resistance responses against cyclic tensile strain. One response is low electrical resistance maintained, which is characterized by containing 56 vol% of silver particles. The other is correlative response between electrical resistance and strain. The stretchable wiring retaining low electrical resistance under strain during use is important for wearable and implantable applications, while the stretchable wirings relating resistance change with strain sensitivity will be applied to sensor due to correlation between resistance and strain. The authors of this paper would like to thank K. Kihara and O. Kirihara (Bayer MaterialScience Ltd.) for their valuable contributions. [1] T. Araki, et al., IEEE Electron Device Lett., 32, 1424-1426, 2011.

Wearable electronics for health monitoring and recreational purpose are an exciting prospect. These devices will have to stretch, bend and twist, requiring new substrate and active materials to accomodate these mechanics. Recent advances in making ultra thin silicon ribbons and novel architectures have enabled devices with all the above properties. For true autonomous operations, however, these devices require an equally accomodating power source. Currently commercial primary and secondary batteries are bulky, heavy and negate the advantage of the stretchable/ flexible device. In this talk, we show a technique to make stretchable battery where the electroactive material is self-assembled into the fibres of the cloth. In our previous work, we demonstrated that flexible battery electrodes of arbitrary composition can be made flexible if a supporting mesh is used to hold the electroactive particles together. We made a flexible battery with 300 micron thick electrodes which have a bend radii of 0.3 mm without and drop in the performance.We now extend this technique to stretchable sytems. In this talk, we demonstrate a technique to make a self assembled stretchable battery electrode from solution processing. An optimized electroactive ink is used such that the electroactive materials get absorbed in the fibres of the cloth due to capillary force. The architecture of the electrode ensures that the electroactive material experiences no force when stretched to up to 50%. A stretchable battery with Zn-MnO2 chemistry is made.

Organic semiconductor materials are interesting alternatives to inorganic semiconductors in applications where low cost, flexible or transparent substrates, and large area format is required. Currently they have been incorporated into organic thin-film transistors, integrated display driver circuits, photovoltaics artificial electronic skin, and radio frequency identification tags. One of our fundamental interests is to understand how we can ultimately perform rational design of organic semiconductors. In this talk, I will present recent results on understanding of molecular design rules for achieving efficient charge carrier transport and controlled growth of organic semiconductors.

We report the use of thiocyanate as a ligand for lead sulfide (PbS) nanocubes for high-performance, thin-film electronics. PbS nanocubes, self-assembled into thin films and capped with the thiocyanate, exhibit ambipolar characteristics in field-effect transistors. The nearly balanced, high mobilities for electrons and holes enable the fabrication of CMOS-like inverters with promising gains of ~22 from a single semiconductor material. The mild chemical treatment and low-temperature processing conditions are compatible with plastic substrates, allowing the realization of flexible, non-sintered quantum dot (QD) circuits.

The demand for innovative, cost effective, and more efficient optoelectronic devices has brought about a growing interest in nano-scaled hybrid materials, i.e., the combination of inorganic and organic materials. In particular, the combination of PbS quantum dots (QDs) with PET (=polyethylene terephthalate) is technologically appealing because it enables engineering of light-weight, non-brittle hosts for bright tunable light emitters that can be adjusted to match the important information transmission wavelengths in the near infrared (e.g. 1300 to 1550 nm). Unlike spun cast hybrid materials of polymers and nanoparticles, we employed a novel deposition process utilizing a centrifuge for the deposition of PbS quantum dots (diameter 4.7 nm) on PET substrates. The QD films formed did not flake off during bending and the film integrity was not disturbed with the application of an adhesive tape test. Using green laser excitation and a Fourier transform infrared (FTIR) spectrometer to collect the photoluminescence, we studied the emission of the PbS quantum dots, capped with oleic acid ligands, in the temperature range of 5 K - 300 K. The effects of using different solvents for the sample preparation were studied, as well as comparisons to results on other substrates such as glass and GaAs. Notably, the thermal characteristic of the emission linewidth of the Gaussian-like emission spectra does not follow the expected thermal broadening, which, commonly, exhibits a broader emission spectrum at ambient temperatures with respect to that observed at low temperatures. Instead, the PbS/PET sample maintains a nearly stable, temperature independent, linewidth. Since we do not observe such behavior with PbS QDs on glass or GaAs, we conclude that this observation is related to the PET substrate's unique characteristics. It is possible that colloidal PbS QDs on PET substrates are subject to photo-induced changes under light irradiation that alter the established bond linkages at the PET surface during the precipitation process. Due to the strong adhesion of the QD/oleic acid films, we conjecture that the binding forces result from covalent or hydrogen bonding, which appear to be altered under laser irradiation. The comparison of the QD film emission strength, based on the required laser intensity, with well known light emitters such as the commercially used semiconductor GaAs was also performed. The PbS/PET samples produced a surprisingly strong emission at room temperature which shows the potential for flexible inorganic light emitter applications.

A self-powered autonomous intelligent nanoscale system consists of ultrasensitive nanowire based sensors, integrated high-performance memory and logic computing components for data storage/processing as well as decision making and energy scavenging unit for sustainable, self-sufficient and independent operation. Conventional CMOS or semiconductor nanowire based logic units are electronically triggered and driven by externally applied â?ostaticâ? electrical voltages, which are separated from the dynamic mechanical actuation units in MEMS/NEMS. Notably, previous existing non-volatile resistive memories are electrically programmed and they are not suitable for direct interfacing with actuation/triggering other than electrical inputs. For applications such as human-computer interfacing, sensing/actuating in nanorobotics, and smart MEMS/NEMS, a direct interfacing of electronics with mechanical actions is required. Based on the concept of piezotronics, the piezoelectric trigged mechanical-electronic logic operation has be realized, through which the integrated mechanical electrical coupled and controlled logic computation are achieved using only ZnO NWs. By utilizing the piezoelectric potential created in a ZnO NW under externally applied deformation, strain-gated transistors (SGTs) and inverters, NAND, NOR as well as XOR gates have been demonstrated for performing piezotronic logic calculations. Meanwhile, piezoelectrically-modulated resistive switching device based on piezotronic ZnO nanowire has also been implemented, through which the write/read access of the memory cell is programmed via electromechanical modulation. Adjusted by the strain-induced polarization charges created at the semiconductor/metal interface under externally applied deformation by the piezoelectric effect, the resistive switching characteristics of the cell can be modulated in a controlled manner, and the logic levels of the strain stored in the cell can be recorded and read out, which has the potential for integrating with NEMS technology to achieve micro/nano-systems capable for intelligent and self-sufficient multi-dimensional operations. The research of piezotronics is an emerging filed in intelligent MEMS/NEMS and more functionality can be implemented based on piezotronic operations. These mechanical-electronic units can be integrated with NEMS technology to achieve advanced and complex functionalities in nanorobotics, microfluidics and micro/nano-systems on flexible substrates.

With the advent of micro fluidics, many exciting properties of fluids at the micro/nano have been uncovered and similarly many devices harnessing the uniqueness of fluids at these scales have been produced. As these devices get smaller and sample volumes get minimized, the need for greater control of these fluids increases in order to maintain the precision needed by users in industries such as biomedical devices and chemical analysis. As is typical, nature already has a solution though recreating this solution takes creative materials processing. In this talk the fabrication of inorganic nanocilia ( biological hair-like structures) sensors will be discussed with a focus on two different sensors. One sensor is designed to sense flow in micro channels and the other to sense vibrations with the potential to also harness the vibrational energy. The design is unique in that it overcomes the challenges of integrating traditional silicon based sensor with plastics while at the same time using fabrications techniques that can be easily scaled for large area production and for temperature sensitive biological applications. The sensors take advantage of magnetic field shape anisotropy of high aspect ratio (60nm diameter, 60,000nm length) HCP Co nanowires with their c-axis fabricated out of plane. The Co nanowires are suspended atop a GMR (Giant Magneto Resistance) sensor where the magnetic field of the nanowires directly interacts with the antiferromagnetic coupling of the GMR sensors as they â?oswingâ? back and forth across the sensor. Taking advantage of our groupâ?Ts expertise in anodized aluminum oxide(AAO), extremely highly ordered pores are made using a one step anodization process that utilizes a Al stamping technique we have developed using Ni coated Si stamps, and a single step removal of both the Al foil and the barrier layer through electro polishing. After contacts are sputtered on the AAO Co wires are deposited from a solution of CoSO4. For the vibration sensors, the AAO with wires were then integrated with off-the-shelf GMR SOIC chips and the wires were exposed through etching of the AAO. For the flow sensors, the nanowires were placed inside of embossed PMMA fluidic channels designed to integrate into disposable PMMA microfluidic GMR sensor packages. These packages were designed by our industry partner(Diagnostic Biosensors). From Nanowire motion was then detected as mV signals from the GMR sensors in a bridge configuration. The vibration sensor, when tested at earthquake frequencies(0-10Hz) on a shake table, showed a single- and double-frequency signal. A control sensor was fabricated in the same way but without the wires and only a 1f signal was observed due to the GMR sensors motion in the Earthâ?Ts field.

We have developed a full-color 4.1-in 121-ppi FWQVGA rollable AM-OLED display and a 13.3-in bendable 150-dpi UXGA electrophoretic display (EPD) driven by organic TFTs (OTFTs). In the OTFTs, all dielectric layers are formed from solution of polymers. For organic semiconductors, peri-Xanthenoxanthene (PXX) derivatives have been developed. The OTFT with 5-μm channel length shows apparent mobility of 0.5 cm²/Vs and current on/off ratio > 10⁶ . For the rollable OLED display, a PXX derivative is evaporated and we have developed an integrated gate-driver circuit with the OTFTs. This enables to eliminate rigid gate-driver ICs and roll up the 80 μm-thick OLED display with bending radius of 4 mm. We have also developed a soluble PXX derivative. This has been applied to high resolution backplane for a flexible EPD. The standard deviation of the field-effect mobility of the solution processed OTFTs is 5.5% to their average. The 120 μm-thick EPD can be bent with radius of 5 mm without additional failure.

Light extraction in organic light emitting diodes (OLEDs) has been an active area of research because of significant power loss due to light waveguiding in the indium tin oxide (ITO)/organic layers and the glass substrate. Although many grating structures using electron beam, holographic, and nanoimprint lithography have been used to extract the ITO/organic waveguide mode into the air mode by Bragg diffraction, the outcoupled light by those methods is strongly directional depending on the specific emission wavelength and angle.[1-5] Recently, Koo et al. reported that a spontaneously formed buckling structure with a non-directional emission profile might provide a new approach to randomize with the directionality in grating structures.[6] However, their work required inevitably an imprinting process to transfer the buckling pattern of the template to the device substrates which is not viable for the practical applications. In this study, we demonstrate a new method to incorporate a buckling structure directly to the OLED device for light extraction without any lithography and imprinting process. Buckling structures having various periodicities from several hundred nano-meters to several micro-meters have been explored. With a buckling structure having a peak periodicity at ~600 nm and the broad distribution from 400 to 900 nm, the OLED devices showed 100% enhancement in the current efficiency. Since the buckling structure is characteristic of the random orientation and broad distribution in the periodicity, the buckled OLED devices showed the enhanced EL intensity over all emission wavelengths without spectral changes and directionality. These results suggest that the buckling structure directly incorporated to the device without any lithography and imprinting process can supply a practical solution for extracting light from the OLED devices in terms of costs for mass production. Reference [1]. M. Fujita, K. Ishihara, T. Ueno, T. Asano, S. Noda, H. Ohata, T. Tsuji, H. Nakada, N. Shimoji, Jpn. J. Appl. Phys., Part 1 2005, 44, 3669. [2]. J.M. Ziebarth, A. K. Saafir, S. Fan, M. D. Mcgehee, Adv. Func. Mater. 2004, 14, 451. [3]. P. A. Hobson, J. A. E. Wasey, I. Sage, W. L. Barnes, IEEE J. Sel. Top. Quantum Electron. 2002, 8, 378. [4]. S. M. Jeong, F. Araoka, Y. Machida, Y. Takanishi, K. Ishikawa, H. Takezoe, S. Nishimura, G. Suzaki, Appl. Phys. Lett. 2008, 92, 083307. [5]. K. Ishihara, M. Fujita, I. Matsubara, T. Asano, S. Noda, H. Ohata, A. Hirasawa, H. Nakada, N. Shimoji, Appl. Phys. Lett. 2007, 90, 111114. [6]. W. H. Koo, S. M. Jeong, F. Araoka, K. Ishikawa, S. Nishimura, T. Toyooka, H. Takezoe, Nat. Photonics 2010, 4, 222.

3,5-Dipyridylphenyl-modified electron transporters, B2PyPPB, B3PyPPB and B4PyPPB, were designed and prepared. The thermal properties of BPyPPB derivatives were estimated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The glass transition temperature (Tg) was observed over 120 degree C indicating morphological stability. The weight loss of 5% (Td5) was observed around 470 degree C, indicating the thermal stability. These materials showed a deep ionization potential below 6.4 eV in the solid state. Despite the same molecular weight, physical properties greatly changed depending on the nitrogen position on peripheral pyridines. We report the influence of the nitrogen position on blue phosphorescent OLED performances as well as the results of single crystal X-ray analysis.

Metallic patterns comprising high electrical conductivity are indispensible components of many organic electronic devices, e.g. light emitting diodes (OLEDs), photovoltaic cells (OPVs), and thin film transistors. One of their most important applications is the replacement of brittle and expensive conductive oxides such as indium tin oxide (ITO) in transparent electrodes. Printing of metal containing inks or pastes on plastic foils is a convenient deposition method for these structures, especially since it is roll-to-roll (R2R) compatible and allows very high processing speeds. However, in order to achieve the high electrical conductivities which are necessary for appropriate device performance, a post-deposition sintering step is required. This process step has to be compatible with the temperature sensitive polymer substrates, which will otherwise deform. We have developed photonic flash sintering as a fast technology that allows improving the conductivities of printed silver structures on foils. Without damage to the substrate, resistivity drops of up to seven orders of magnitude are achieved within a few seconds. The operating principle is based on the selective heating of the ink by the absorption of strongly focussed visible light, for which the foil is transparent. Furthermore, exposure to short flashes (in the order of milliseconds) limits the heat flux into the substrate, so that foil deformation can be avoided. The entire process has been investigated both theoretically and experimentally. The influence of parameters such as ink type, flashing frequency, and light intensity has been studied in detail. The combination of high process velocities and mild processing conditions enabled us to construct a R2R tool that combines a rotary screen printer and an inkjet printer with a photonic flash sintering unit. We demonstrate that printed structures with a conductivity of up to 15 % of the value of bulk silver can be produced on inexpensive PET foils at a speed of up to 5 m/min on this R2R tool. These structures have a promising potential to be integrated in ITO-free organic devices such as OLEDs and OPVs on a large scale and at low production costs.

We have developed high-performance, bottom gate inkjet-printed thin-film transistors (TFTs) using oxide and organic semiconductors. N-channel oxide TFT using solution processed exhibited a field-effect mobility of 20 cm2/Vs and p-channel organic TFT had the field-effect mobility of 0.7 cm2/Vs. The process temperatures were less than 300C. The evolution of threshold voltage with bias-stress time follows a stretched exponential behavior, indicating the shift is mainly due to the carrier trapping at the interface region. The TFTs developed in this work revealed the improved characteristics such as enhanced reliability and low process temperature and thus was applied to manufacture TFT system on polyimide plastic. Inverter, shift register, ring oscillator, and logic circuits made of printed TFTs will be presented.

Organic semiconductors are an emerging technology that could potentially be used for a variety of electronic applications. However, because of the low performance and the lack of high-resolution patterning methods, their use to date has been relatively limited. Here we report on two novel fabrication paradigms that can be used for the manufacturing of high-performance nano- and micron-scale organic electronics onto rigid as well as flexible substrates. Specifically, in the first half of the talk I will discuss the development of a simple patterning method for the fabrication of advanced organic microelectronic devices such as low-voltage, self-aligned-gate (SAG) transistors onto large area substrates without the need for precise photo-mask alignment. The operating characteristics of these SAG transistors will be presented and analyzed in detail. In the second half, the use of scanning thermal nanolithography for the realisation of nano-scale organic transistors based on "on-demand" written semiconducting nanoribbons will discussed. These novel processing methods could potentially lead to demonstration of organic transistors with performance characteristics beyond current state-of-the-art devices.

The availability of n and p-channel solution-processed semiconductors enables the fabrication of complementary circuits, which have the advantages of lower power consumption and fewer transistor count compared to unipolar circuits. Here organic complementary circuits have been demonstrated by inkjet printing. With solution processing, we have demonstrated a decoder circuit required for addressing passive matrix arrays. The decoder is integrated with an array of ferroelectric capacitors for non-volatile memory applications. The decoder is currently designed to handle 3-bit address lines. The rise and fall time of the decoder output signal is =<2 ms at supply voltage of 20V. In addition to demonstrating the decoder performance, we will also discuss the challenges of device variations and stability in printed transistors.

We have demonstrated reducing the device variation in organic pseudo-CMOS inverter circuits with a floating gate structure and self-assembled monolayer (SAM) gate dielectrics. We were able to control the switching voltage of the pseudo-CMOS inverter circuits by applying programming voltage. The variation of switching voltages of 10 pseudo-CMOS inverters were reduced from 400 mV to 20 mV to apply an appropriate programming voltage. These inverters were operated below 2 V with signal gain of larger than 400. Furthermore, we were able to control the switching voltage without decreasing the signal gain.
These inverters were fabricated by vacuum evaporation and dipping processes. First, 30-nm-thick Al layer were thermally evaporated as control gate electrode using shadow mask. Second, we formed control gate dielectric layers. Then 30-nm-thick Al layer were evaporated on the control gate dielectric layers as floating gate electrode and formed floating gate dielectric layers. The control and floating gate dielectric layers were composed of 4-nm thick aluminum oxide layer which were formed by oxygen-plasma treatment and self-assembled monolayer SAMs (n-octadecylphosphonic acid) which were prepared from a 2-propanol solution at room temperature[1, 2]. Purified dinaphtho[2,3-b:2â?²,3â?²-f]thieno[3,2-b]thiophene (DNTT) were deposited in vacuum through a shadow mask to form a 30-nm-thick as p-type organic semiconductors on the floating gate dielectric layer. A 100-nm-thick Au layer was evaporated through a shadow mask to form the source and drain electrodes.
The fabricated DNTT TFTs were operated at -2 V. The mobility in the saturation regime is 3.0 cm²/Vs, while the on/off ratio is 10⁶. This work is partially supported by Special Coordination Funds for Promoting, JST and KAKENHI (Wakate S). One of the authors (T.Y.) is grateful to the research fellowships for young scientists of JSPS.
[1] H. Klauk, U. Zschieschang, J. Pflaum, and M. Halik, Nature 445, 745 (2007).
[2] T. Yokota, T. Nakagawa, T. Sekitani, Y. Noguchi, K. Fukuda, U. Zschieschang, H. Klauk, K. Takeuchi, M. Takamiya, T. Sakurai, and Takao Someya, Appl. Phys. Lett. 98, 193302 (2011).

We will describe a complementary TFT technology using p-type organic and n-type soluble oxide transistors, and show high-performance thin-film circuits made with this technology. High-performance n-type metal oxide TFTs are processed from solution and post-annealed at a temperature of only 250 °C. We use 100 nm high-k Al2O3 as gate dielectric. These TFTs have an electron mobility exceeding 2 cm2/Vs, a leakage current below 1 pA and Ion/Ioff ratios up to 108. The on-current of TFTs with a channel length of 6 micron is 0.85 microA per micron width at VGS=10V, which is ample for driving the current in active-matrix backplanes of OLED displays. We integrate p-type pentacene transistors (mobility 0.3 cm2/Vs) together with these n-type oxide transistor into a complementary TFT process. We will show how and why such complementary logic is not only more reliable but also faster than unipolar logic, and prove it by demonstrating that complementary 8-bit RFID transponder chips (about 400 TFTs) are functional for supply voltages between 2 and 20 V and operate at 25 kbit/s (at 20 V). We further use this technology to demonstrate a thin-film RFID transponder circuit that improves over unipolar circuits in that it allows for bi-directional communication at HF (i.e., using a base carrier frequency of 13.56MHz). Prior art thin-film transponder circuits were based on a â?~tag-talks-firstâ?T principle: the transponder circuit on the tag starts operating as soon as the tag is brought in the electromagnetic field of a reader. This was necessary because the TFTs on the tag were not able to decode information modulated on an HF (13.56 MHz) carrier wave. Using the fast and reliable hybrid pentacene-oxide complementary process, we made a â?~reader-talks-firstâ?T transponder circuit: the tag is now able to decode information sent by the reader, such that the read-out of the tag memory only starts when the tag has decoded a reader instruction to do so.

The purpose of this research is to develop the fabrication technique of micro structures on nonplanar substrates, investigating so called, optical softlithography. In addition, PDMS roller stamps were duplicated from these structures on curved substrates as the mold, the roll micro-contact printing was performed successfully. Micro structuring on nonplanar substrates has not been fully established yet, although several fabrication methods, such as laser direct writing and modified photolithography, were proposed. Moreover, those techniques require still expensive and complex processes. To overcome those drawbacks, optical softlithography using flexible photomasks was developed. Firstly, SU-8 micro structures were fabricated on convex substrates using PDMS flexible photomasks. Rotational UV exposure with the slit shadow mask was introduced to prevent unwanted exposures and distortions. As a result, the micro structure which has 15.6 μm line widths and 2.69 of aspect ratio was fabricated on a convex substrate. Also, experimental parameters for optical softlithography were investigated and established for further fabrications and applications. Next, the fabrication of micro structures on concave substrates was also performed using flexible photomasks. In addition, the tilting structures were confirmed due to the vertical UV exposure method. Finally, SU-8 structures with 2.5 μm line width and high aspect ratio over 7.9 were fabricated on a concave substrate. Based on these novel 3D patterning technologies, the PDMS roller stamps was fabricated and the rolling contact printing was performed as well as the roll to roll (R2R) process. The rolling microcontact printing was investigated by using the customized R2R printing apparatus. We expect this technique can provide various sized roller stamps with various micro patterns for μCP process as well as R2R process.

Large Area Electronics based on amorphous silicon thin-film transistors (a-Si:H TFTs) has enabled the development of â?osystems-on-plasticâ?. Thin-film transducers, processed at low temperatures on polyimide sheets, have been proposed for inexpensive and conformal sensor arrays capable of covering large surfaces [1] [2]. Access and control over such arrays requires integrated large-area circuits based on TFTs. For scalable control circuitry with low static power dissipation and large logic swings, despite single-carrier a-Si:H TFTs, we develop a logic style employing dynamic circuit techniques and capacitive bootstrapping. We implement this and demonstrate two passive integrated large-area platform components: (1) an a-Si TFT circuit for control logic and (2) a low-impedance sensor-access switch. These components enable circuits for controlling many sensors using a minimal number of interface signals. For the logic style, we develop key thin-film components on polyimide: (1) a-Si:H TFTs matched to appropriate circuit requirements, (2) a-Si:H diodes for efficient dynamic node charging, (3) integrated capacitors for dynamic operation and bootstrapping, (4) vias and metal-layer crossovers. The dynamic control circuit employs blanket-passivated (Silicon Nitride, SiNx), back-channel etched TFTs (deposited by PECVD at 180°C). TFT gate dielectrics are optimized for minimal gate leakage (0.1pA at Vgs=10V), essential for maintaining in-circuit dynamic nodes. Etching processes are chosen for minimal source-drain leakage at Vgs=0V (1pA), sufficient uniformity in threshold voltages as well as large on-off ratios [10^7 at 15V/0V]. TFTs are thus sufficiently off with 0V control signals. These TFT improvements are important for developing reliable SPICE models for dynamic circuit design. For the sensor readout circuit, interdigitated access TFTs are developed with large W/L [60000μm/6μm] to enable low-impedance readout of sensors. a-Si Schottky diodes are engineered to provide low-voltage drop and good forward/reverse characteristics. In-circuit metal-dielectric-metal capacitors are formed with the TFT gate dielectric used as insulator. In-circuit TFT terminal connections are designed to minimize interconnect and via resistance (10Ω) by careful choice of layer deposition sequences and via metals. Interconnect cross-over shorts are avoided by retaining selective portions of the TFT stack in between metal layers to provide adequate isolation. For wiring, Cr/Al/Cr metal layer stacks are chosen for fabrication on plastic (e.g. better-matched coefficients of thermal expansion), avoiding interconnect cracking and peeling, whilst still maintaining good TFT electrical properties. We will emphasize device- and circuit-level design choices that enable uniform device characteristics and good operation of the circuits we have implemented for a sensing system-on-plastic. [1] Someya et al. MRS Bull. 33, p. 690, 2008 [2] Wagner et al. Phys. E, vol. 25, 2-3, p. 326, 2004

High-speed printing techniques such as gravure printing have been suggested as the most appropriate printing techniques for large-area and low-cost printed electronics applications due to their high throughput and maturity at large scale. However, fully or at least partially gravure printed ring oscillators have shown relatively poor AC characteristics (at most 150 Hz) due to the low mobility and large dimensions even though devices are generally operated at high voltages (up to 100 V) that are unrealistic for practical applications. In order to meet the performance requirment for high performance applications such as printed RFID tags, further improvement of gravure printed TFTs is necessary. In this work, we present highly-scaled direct-gravure printed organic thin-film transistors (OTFTs) with unprecedented improvements in switching performance; we achieve 300 kHz operation at only 20V supply voltage. Conventional direct-gravure printing for graphic arts applications is typically used at ~50 μm resolution; we have previously demonstrated gravure printed transistors with 20 μm gate line. By adapting dramatically improved pattern engraving of the gravure printing system and optimization of ink formulation, we are able to scale down gravure-printed conductive lines to the sub-10μm regime with good conductivity while maintaining high printing speed (~1 m/s). With the highly scaled metal lines and proper electrostatic scaling, we fabricated highly-scaled direct-gravure printed OTFTs with channel lengths of 10μm with minimized overlap capacitance on plastic substrate, achieving the highest transition frequency of 300 kHz at only -20 V operation. Thus, these devices represent a dramatic improvement in the state of the art for printed organic transistors.

In this report we describe a material set and method for the fabrication of all-printed thermistors on flexible substrates. The development of these devices has been driven by concern around eventual mass production, and as such we demonstrate both scale up of the active temperature sensitive ink, and fabrication of the thermistors in an industrial environment using production class equipment. The temperature sensitive material used is a paste made from a blend of metal oxide particles and a eutectic alloy. This ink can be reliably printed using screen-printing and is processed at temperatures lower than 150 °C, making it compatible with low-cost plastic substrates. Complete devices, fabricated in air on a PET film using screen-printed conductive silver contacts, show a resistivity of about 100 kâ"¦ cm, and a greater than 1% change in resistance per degree Celsius between 20 and 70 °C. Encapsulation of these devices with a flexible film was necessary in order to prevent moisture absorption which causes the resistance values to drift over time. Remaining issues for the commercialization of such printed sensors will also be discussed, as will the incorporation of these thermistors into more complex integrated systems containing other printed electronic components.

Most organic transistors are normally-ON unipolar p-type field-effect transitors. At positive gate bias the measured current is negligible. Holes are depleted. Inversion is predicted, i.e. accumulation of electrons at the semiconductor-dielectric interface, but not observed. The question arises whether the absence of electron current is due to trapping of electrons or that the steady-state is not reached. In the first scenario electrons are injected from the contacts, but are immobilized at the semiconductor-dielectric interface. As a result, the electron current is negligible, regardless of the electron mobility in the bulk. In the second case the rate of electron injection is too low to supply the electrons required to form an inversion layer. The steady-state is then not reached within the time scale of the measurements. The electron current is negligible because there is no inversion channel. Here, we distinguish between both cases using unipolar p-type transistors based on a deliberately doped organic semiconductor. We show that the occurrence of an inversion layer can be inferred from the observation of the depletion current. We argue that on the time scale of the measurements no inversion layer is formed. Steady-state is not reached.

To realize flexible, large-area energy harvesting systems, 2-V organic transistor-based rectifiers, counters, and piezoelectric energy harvesters have been developed and integrated on thin plastics. To increase the noise margin and dependability of unipolar (p-type only) logic circuits, a pseudo-CMOS inverter [1] has been developed using dinaphtho[2,3-b:2â?²,3â?²-f]thieno [3,2-b]thiophene (DNTT) transistors [2] and a self-assembled monolayer (SAM) gate dielectric [3]. The inverter exhibits a very high gain of more than 400 for a 2-V operation. By fully utilizing the advantages of the developed organic inverters, which have very high gain, and the integration technologies for a system-on-plastic, a shoe insole pedometer has been designed. The organic insole pedometer consists of 462 transistors, and its size is 22 Ã- 7 cm^2. The energies generated by a deformed, flexible ferroelectric polymer (polyvinylidene difluoride or PVDF) film are rectified by an organic full-wave rectifier, and the number of steps is counted by an organic counter. The system concept and circuit design have been reported in the circuit conference (IEEE ISSCC2012) by our group [4]. However, this paper will focus on the materials, processes, reliability tests, and integration technologies used for systems-on-plastic. Organic digital and analog circuits are fabricated using a vacuum evaporation system. The designed pseudo-CMOS inverter comprises four p-type DNTT transistors having mobilities greater than 1 cm^2/Vs and on/off ratios exceeding 10^6. A PVDF film is used for the piezoelectric energy harvester, which can provide at least 10 µW of power during one mechanical deformation of the PVDF film. [1] T.-C. Huang, et al., IEEE TED, 58, 141 (2011). [2] T. Yamamoto and K. Takimiya, JACS, 129, 2224 (2007). [3] H. Klauk, et al., Nature, 445, 745 (2007). [4] K. Ishida, et al., 2012 IEEE ISSCC, Feb. 19-23th, 2012, San Francisco, CA, USA.

To be able to realize complex thin film circuits on foil (e.g. RFID tags, distributed sensor readouts), a robust circuit technology is required. The yield of the TFTs is herby important but even more so a narrow TFT parameter spread. There are two routes to further improve the robustness or noise margin of circuit designs that get the main attention: On the one hand, like in classical silicon technology, complementary process flows (p-type and n-type TFTs) and designs are developed. This route is especially interesting for additive process techniques like printing. A promising alternative for complementary technologies is dual-gate technology. Hereby, every TFT consists of two gates: a gate and a back gate (weaker coupled gate), requiring at least 3 metallization levels similar to process flows for active matrix backplanes. Dual-gate technology is especially relevant if the process flow shall be implemented in Flat Panel Display (FPD) like infrastructure using mainly photolithographic pattern definition. In our presentation we will show a newly developed organic dual-gate technology on foil that has a significantly better performance compared to state of the art. The process flow requires 6 mask steps and yields OTFTs with a final mobility of ~0.4cm2/Vs using evaporated pentacene. To improve the dynamic performance of the OTFT we used 100nm high-k Al2O3 as gate-dielectric whereby 2um parylene was used for the top-dielectric. The choice of dielectrics allows a higher speed and supply voltage as low as 10V but increases the required back-gate voltage. Implemented in circuits like a 19-stage ring oscillator, a stage delay of better then 5us for a channellength of 5um is achieved. Finally we will outline strategies to limit the impact of the process parameters and chemicals involved in the lithographic process onto the organic semiconductor.

Surface tension-driven self-alignment (SA) is a promising technique for heterogeneous die stacking. It can assemble a large number of dies in parallel on various substrates and at minimal cost. Since early 90â?Ts [1] the fluidic self-assembly (FSA) was thoroughly investigated and developed by numerous research groups all over the world. Many fluidic assembly case studies have been investigated: microparts [2] and RFID-tags [3], arrays of optical fibers onto an optical chip [4] and single-crystal transistors on plastic substrates [5]. To further deepen the understanding of the surface tension-driven self-alignment, the process needs to be modeled and experimentally verified. Within the past two decades researchers made a significant progress in this direction. However, most of modeling works [6-8] are based on quasi-static simulations, whereas to properly understand the self-alignment process, its dynamics needs to be investigated. Numerous research papers have been reported on the improvement of alignment accuracy and efficiency in the stacking of micron-sized chips. In the case of mm- and cm-sized systems-in-foil, however, only a few papers have been reported [9]. For successful alignment, micron-sized chips need to be pre-aligned with respect to the corresponding binding sites with high accuracy in order to sufficiently overlap a die with a corresponding fluid droplet, which is a complicated task. In case of mm- and cm-sized dies this overlap can be easily achieved without any complex machining for high precision placement. This paper reports a study on the dynamics of foil-based functional component self-alignment on big plastic substrates. We investigate the dependence of alignment time and final precision of stacking of foil dies on a number of system parameters, such as physical properties of assembly medium, size and weight of assembling dies and their initial misalignment. Using water as a medium for direct self-alignment, mm- and cm-sized square-shaped pre-marked foil dies were aligned with high accuracy (30 µm) on patterned marked carriers. High-speed camera stage and image recognition tools were used for analyzing rapid capillary-driven self-alignment processes of marked foil dies. Experimental results were successfully benchmarked with analytical and numerical modeling. It is shown that there is a definite range of initial misalignment values allowing dies to align with high accuracy and yield within the same time window, whereas both under smaller and larger initial offsets, i.e. with dies correspondingly too close or too far from their target positions, yield and alignment precision is significantly lower. Our demonstration that mm- to cm-sized functional foils can be aligned with high accuracy opens the perspective of efficiently assembling interesting new systems such as separately manufactured sensors, paper batteries and RFIDs through this direct capillary-driven self-alignment approach.

Dramatic spread is going on high frequency operation device, such as mobile phones, wireless LAN, and radio frequency identification (RFID). Especially, the antenna is the most important element in the high-frequency operation device, and has been studied around the world. In particular the printed antenna on the flexible substrate is remarkable, since that printed antenna package has more thinner, more lighter and more cheaper than conventional etching process antenna. In addition printed process has a highly efficient and eco-friendly method. So we focused on printed antenna or wiring at high frequency. The most of printed wiring were made by metal paste, a mixture of solvents and conductive filler. A lot of study about printed wiring has been relationship between metal paste and volume resistivity. That would be insufficient to know entire antenna performance about printed wiring made by metal paste. In this study, we investigated high frequency characteristics (antenna characteristics) of printed wiring made by some silver pastes at 0.5-5GHz. When the resistivity of printed wiring among several silver paste was almost the same, the return loss for the incident signal to the smooth surface wiring was slightly smaller than other wiring with rough surface. The high frequency characteristic of silver paste was affected by not only wiring resistivity but also its surface roughness. When mounted on the radio control car, silver paste antenna with smooth surface showed the good behavior, that is, low loss for the incident signal to the silver paste antenna.

Conducting polymer electrodes and transistors are being extensively studied for applications in biosensors and bioelectronics. The active conducting polymer layer can be deposited using solution or vapor-phase techniques, while the deposition on metal and insulator layers are also necessary to complete these devices. I will review a few examples of device architectures used to sense ions, metabolites such as glucose, and pathogens. I will then discuss their fabrication and compare the performance of devices fabricated using different techniques, including ink-jet printing and photolithography.

At present, Thin-Film Transistors (TFTs) research field is of high interest because of development of low cost products, such as circuits and LCDs. Low temperature deposition processes are required in order to use flexible substrates. Nevertheless, the performance of the gate insulators at temperatures below 300 °C is not as good as in CMOS technology. Thus, physical and electrical properties of semiconductor and insulator materials deposited at these low temperatures must be improved. In this work, we report the effects of curing time and dilution on properties of Spin-On Glass (SOG) as low-temperature insulator. Our SOG film was annealing at a temperature of 200°C, which is compatible to use on flexible substrates. The electrical characterization showed that the insulator breakdown field for the SiO2 films produced from SOG diluted with H2O with 1 Hr of curing time was approximately 4 MV/cm while for 6.5 Hrs of curing time the breakdown field was 21 MV/cm. Also, the refractive index and surface roughness was improved. The observed results are promising and suggest that SOG diluted with H2O is an excellent candidate to be used as insulator on flexible and large-area electronics.

Many emerging microfabrication technologies such as microfluidic devices rely on the deposition of metal features onto polymeric substrates. Au thin film metallization is particularly important for electrodes, IR reflectors and interconnects in these devices. However, due to the inert nature of Au, adhesion to polymeric substrates is generally poor. We report on the use of halogenated organic solvents as a pre-treatment onto poly(methyl methacrylate) (PMMA) substrates to improve the adhesion of an array of 121 magnetron sputter deposited 1.5 mm diameter Cr/Au dots by up to a factor of five compared to deposition on cleaned PMMA substrates. We have observed improvement by both spin-casting and vapor phase pre-treatment of the PMMA surface. Nearly 90% of the Au dots remain after a standard tape pull-test for samples pre-treated with chloroform compared with only 17% remaining on the untreated samples. The adhesion of CHCl3 and CH2Cl2 pre-treated samples is also significantly improved compared to remote O2 plasma pre-treatment (26% adhesion). Atomic force microscopy roughness data shows that this is not due to surface roughening, and we have shown through X-ray photoelectron spectroscopy and attenuated total reflection Fourier transform infrared spectroscopy studies that the chlorinated solvent molecules form a Lewis acid-base adduct with the polymer chains leaving a Cl-rich surface. A covalent bond is then formed between the Cr metal adhesion layer and the surface terminated Cl which results in the strong Au metal adhesion. Molecular modeling has been performed to understand the origin of the enhanced adhesion. DFT calculations are consistent with the presence of adduct formation having a interaction enthalpy of ~35 kJ/mol.

Fluorine-doped tin oxide(FTO) thin films are one of the most popular Transparent conducting oxides(TCO) materials. However, there have been very few investigations of FTO deposition on flexible substrates for which electrical and optical properties were high enough to be compatible with flexible electronics applications. FTO thin films are deposited on preheated polymer substrates (Kapton) by Ultrasonic Spray pyrolysis from dihydrate stannous chloride (SnCl2 .2H2O) and ammonium fluoride (NH4F) as chemical precursors. The experiments mainly focus on flexibility, optical transparency and electrical conductivity. X-ray diffraction patterns show that as deposited films are polycrystalline in nature(i.e. in the form of SnO2) with a tetragonal crystal structure. The surface morphology, optical properties and electrical conductivity are investigated by scanning electron microscopy, UV-VIS-NIR absorption spectroscopy, four point probe. A special emphasis is devoted to the stability of the thin film electrode properties under mechanical flexible tests, especially the sheet resistance change after bending cycles. The properties of FTO on flexible substrates will be described and compared with those obtained on glass substrates.

Recently, organic field effect transistors (OFETs) have been extensively studied in view of their applications to low-cost, large-area, flexible electronics. In organic semiconductors, Ï?-conjugated polymers, being quasi-one-dimensional macromolecular electronic systems, offer a number of unique properties. Poly(9,9-dioctylfluorene) (F8), which is one of liquid-crystalline semiconducting polymers, exhibits blue emission and various morphological behaviors. Fluorene-type polymers have emerged as an important class of conducting polymers due to their efficient emission, high stabilities and relatively high mobility. Fluorene-type polymers also have the potential for full color emission via energy transfer to longer wavelength emitters in blends with other emissive materials. Then, in this study, we investigated the fabrication and characteristics of top-gate type organic light-emitting transistors (OLETs) with ITO drain/source electrodes utilizing fluorene-type polymers as ambipolar organic materials. An OFET with a crystallized F8 film as an active layer, which contains only a fluorene backbone, exhibited ambipolar characteristics with hole and electron field-effect mobilities of approximately 10-3 cm2 Vâ^'1 sâ^'1. All OFETs with fluorene-type polymers exhibited ambipolar characteristics because the value of the work function of the ITO electrodes is approximately in the middle between the highest occupied molecular orbital and lowest unoccupied molecular orbital levels of fluorene-type polymers. In ambipolar OFETs, simultaneous electron and hole injection can be achieved by applying the gate voltages. Organic light-emitting diodes have achieved high luminance efficiency by using the phosphorescent emission from a triple state. Because the triplet state of the phosphorescent materials works as the electron trap sites, it is important to form the interface between the semiconducting layer and gate insulator for both the carrier conduction and phosphorescent emission for OLETs. In order to obtain phosphorescent emission from the OFETs, the concept has been verified experimentally that the thermal diffusion of phosphorescent dye at the interface between the active layer and gate insulator was controlled by utilizing the phenomenon that liquid-crystalline semiconducting polymers were self-organized due to both the reorientation of molecules and the growth of size of crystalline regions during thermal annealing process. For a top-gate type device with red emissive phosphorescent material doped in poly(alkylfluorene), the ambipolar characteristics and the red emission from the phosphorescent material were clearly observed. We demonstrate the possibility of the phosphorescent OLETs using liquid-crystalline semiconducting polymer doped with phosphorescent emissive dopants by the thermal diffusion method.

Expanding the absorption spectra is one way to achieve highly efficient dye-sensitized solar cell and many attempts have been carried out such as tandem DSCs, co-sensitized DSCs, film transfer technique and selective positioning method.[1] However, the performance of tandem DSCs is hampered by the poor p-type DSCs.[1e] Quenching effect and unfavorable competitive adsorption decrease the efficiency of co-sensitized DSCs.[2] Film loss is an unavoidable problem for film transfer technique. Although the selective positioning method could precisely control the position of different dyes, the whole process is much too complicated which makes it impossible for mass production. Here we report a pre-dyed technique to fabricate flexible DSCs containing multiple dyes in discrete layers by employing mesoporous TiO2 beads. Previous work has successfully demonstrate that dual-function mesoporous TiO2 beads improve the performance of dye-sensitized solar cells due to its high surface area, superior scattering properties.[3] Over 10% power conversion efficiency has been achieved with single film of mesoporous TiO2 beads.[3c] Different from the P25 or CCIC TiO2 nanoparticles, these TiO2 beads provide a stable structure that protect the dye molecules attached inside and make it possible for pre-dyeing the TiO2 slurry before applying onto the flexible substrate and undergoing CIP pressing. REFERENCE: [1] aD. Kuang, P. Walter, F. Nuesch, S. Kim, J. Ko, P. Comte, S. M. Zakeeruddin, M. K. Nazeeruddin, M. Gratzel, Langmuir 2007, 23, 10906-10909; bJ. H. Yum, S. R. Jang, P. Walter, T. Geiger, F. Nuesch, S. Kim, J. Ko, M. Gratzel, M. K. Nazeeruddin, Chem Commun 2007, 4680-4682; cF. Z. Huang, D. H. Chen, L. Cao, R. A. Caruso, Y. B. Cheng, Energ Environ Sci 2011, 4, 2803-2806; dY. S. Chen, Z. H. Zeng, C. Li, W. B. Wang, X. S. Wang, B. W. Zhang, New J Chem 2005, 29, 773-776; eA. Nattestad, A. J. Mozer, M. K. R. Fischer, Y. B. Cheng, A. Mishra, P. Bauerle, U. Bach, Nat Mater 2010, 9, 31-35; fQ. Miao, L. Wu, J. Cui, M. Huang, T. Ma, Adv Mater 2011; gK. Lee, S. W. Park, M. J. Ko, K. Kim, N. G. Park, Nat Mater 2009, 8, 665-671. [2] F. Inakazu, Y. Noma, Y. Ogomi, S. Hayase, Appl Phys Lett 2008, 93, 093304. [3] aD. H. Chen, L. Cao, F. Z. Huang, P. Imperia, Y. B. Cheng, R. A. Caruso, J Am Chem Soc 2010, 132, 4438-4444; bF. Z. Huang, D. H. Chen, X. L. Zhang, R. A. Caruso, Y. B. Cheng, Adv Funct Mater 2010, 20, 1301-1305; cF. Sauvage, D. H. Chen, P. Comte, F. Z. Huang, L. P. Heiniger, Y. B. Cheng, R. A. Caruso, M. Graetzel, Acs Nano 2010, 4, 4420-4425.

Recently, the inkjet printing technique has received considerable attention as one of the most promising alternatives to conventional techniques for producing conductive lines in functional electronic devices. Inkjet printing has been developed to fully or partially fabricate advanced electronic devices such as organic light-emitting diodes, organic and inorganic solar cells, organic thin-film transistors, flat panel displays, and radio-frequency identification devices. The advantages of inkjet printing include noncontact, drop-on-demand, and scale-up feasibilities. In addition, this technique allows functional materials to be positioned precisely on substrates without the need for masks. It can create precise conductive patterns approximately 30 μm in width, similar to that which can be achieved using conventional photolithographic methods. The most obvious method to minimize the line width is by reducing the nozzle diameter. However, this induces limits the choice of inks and substrates that can be printed because ejecting of ink from nozzle relies on surface tension and viscosity of the inks. Furthermore, when printing suspensions the particles should be sufficiently smaller than the nozzle diameter; otherwise nozzle clogging occurs. Therefore, much research has been done to predefine patterns on a substrate that forces material to remain in a preferred area on the surface or to modify the waveform when using piezoelectric-based DOD inkjet printers. In the present study, the authors have developed a novel process to realize narrow and well-defined conductive lines without pre-patterning of the substrate or modifying of the waveform. Thin coating layer was structured on a polyimide substrate for modifying a substrate surface. The thin coating layer brought out substantial improvement of line morphology and decreasing of line width because thin coating layer on a substrate surface suppressed spreading of ink. Furthermore, printed lines yielded excellent conductivity than on the unstructured substrate.

Observation of crystal structures at initial growth stage of organic thin films gives us valuable information about the mechanism of crystal growth of organic molecules on substrates. Because crystal structures affect the charge transport properties in organic devices such as organic thin-film transistors, control of crystal growth at the initial stage is necessary for the progress of device performances. We have so far studied the crystal structures of organic ultra-thin film by 2-dimensional grazing incidence x-ray diffraction (2D-GIXD) with bright synchrotron radiation. Recently, a portable vacuum deposition chamber for use at a synchrotron x-ray source was fabricated, and in situ real-time 2D-GIXD measurements during thin film growth has been performed. In this study, we observed the initial growth stage of pentacene thin films at the BL19B2 in SPring-8, and the dependence of substrate temperature and the effects of surface treatments were examined. During the real-time measurements, the positions of the sample and detector have been fixed, and the x-ray exposure and the deposition of molecules were continuously performed. As a result, crystal growth at the initial stage and successive polymorphic transformation from thin film phase to bulk phase are clearly observed. Additionally, a distinct orientation of bulk phase characterized by tilted (001) plane is found in the grown thin films at room temperature. This result suggests that the mechanism of the growth of bulk phase changes depending on the substrate temperature.

Ultrathin, flexible, safe energy storage devices are attractive for modern power needs. Printable ink provides high opportunity for devices on plastic. We successfully fabricated a flexible supercapacitor by printing carbon ink (multiwalled carbon nanotube) on PET film and regular printing paper. The prepared supercapacitor showed high capacity. Cyclic voltammetry was performed to evaluate the stability of the devices under the voltage ranges used (1 V for aqueous electrolyte, 1 and 3 V for organic electrolyte). Galvanostatic charge/discharge measurements were used to evaluate the specific capacitance (Cs) and the internal resistance of the devices in a two-electrode configuration. With aqueous gel electrolyte or an organic liquid electrolyte, the performances of the devices show very high energy and power densities. Furthermore, carbon ink loaded with RuO2 nanoparticles was successfully fabricated which demonstrates enhanced capacity.

Implantable biomedical devices such as implantable retina, deep brain stimulator, and implantable pacemaker have great attention for medical care and clinical applications. Integrated circuits (ICs) performed neural stimulation, neural signal processing and biomedical telemetry are essential part of implantable biomedical devices. Kim et al. have demonstrated the implantable neuroprosthetic devices using the bulk-type ICs. In those attempts, although they have made artificial retinal implant system with multifunctional ICs, there are limitations of implantable application due to the rigid and bulky properties of devices. Recently, there have been attempts to transfer the ultrathin single crystal Si membranes onto plastic substrates using the standard microfabrication and soft lithographic printing technique for integrating circuits. The thin single crystal Si semiconductors are the best way for high performance flexible electronics with excellent mobility (>550 cm2 V-1 s-1) that is same as their bulk Si equivalents. However, this transfer technology has been challenged to align a mask during the photolithographic process at tiny feature size (e.g. 2µm and below) due to the soft nature of elastomer stamp and large thermal expansion of plastic substrates. It makes hard to develop dense ICs (e.g. large scale integration). Here, we have demonstrated the implanting of the flexible nano-ICs in a live rat to apply biomedical device using the large area transistor transfer (TT) to overcome the limitation appearing in the preparation of the conventional technique. The nano size MOSFETs and RF switches (ICs) are constructed on silicon-on-insulator (SOI) wafer by standard 0.18µm CMOS process. The devices were transferred onto a liquid crystal polymer (LCP) substrate and subsequently covered with other LCP pair by thermal press bonding (LCP monolithic process). The biocompatible LCP substrates have mechanical stability and a very low degree of moisture absorption (0.04%) compared with polyimide, parylene, and etc. The electrical properties of flexible ICs, which are implanted in body of a live rat, measured in-vivo state for weeks.

Conduction type control of fullerene (C₆₀) films from n- to p-type by doping with molybdenum oxide (MoO₃) was demonstrated. The energetic value of the Fermi level, 4.60 eV, for non-doped C₆₀ films measured by the Kelvin vibrating capacitor method was positively shifted to 5.88 eV, and approached the valence band by the coevaporated doping of MoO₃ at a concentration of 3300 ppm. The existence of upward band bending of the Schottky junction formed at the interface between a metal and a p-type C₆₀ film formed by MoO₃ doping was confirmed based on its photovoltaic properties. A pn-homojunction was fabricated in a single fullerene (C₆₀) film containing MoO₃- and Ca-doped regions. The clear observation of masking effects under light irradiation to both sides of the electrode confirmed the existence of a pn-homojunction in the bulk cell. The position of the pn-homojunction was intentionally controlled by changing the thickness of the MoO₃/Ca doped regions. The present technique offers an effective method of designing suitable energetic structures for efficient organic solar cells.

Control of the energetic structure of photovoltaic co-deposited films consisting of fullerene and α-sexithiophene was demonstrated by ppm-level doping with molybdenum oxide (MoO₃). The transition from an n-type Schottky junction via a metal/insulator/metal junction to a p-type Schottky junction by increasing the MoO₃ doping concentration was verified by observing the photovoltaic properties. Direct ppm-level doping into photoactive co-deposited films could become a powerful tool for designing the appropriate built-in potential for efficient organic photovoltaic cells.

The use of microfluidics offers us a number of advantages that canâ?Tt be achieved from conventional processes. For example, high surface-to-volume ratio and small volume expedite the chemical reaction in microfluidic reactors improve the product yield. Microfluidic droplet techniques have been widely used as a novel approach to improve mixing efficiency and better control concentrations of reagents. It also offer continuous productions based on multi-step and multi reagent using designed reactors at the micro-scales integrated on a silicon wafer. The overall goal of micro total analysis system is to carry out all chemical operations on a plastic substrate, normally performed in plastic electronics for synthesis, processing, purification, and analysis on one microfluidic reactor efficiently and economically by using minute amounts of solvents and reagents. We demonstrate novel microfluidic reactors, which were employed to synthesize organics, inorganics, and hybrid materials.

Flexible circuit technology has many advantages such as reduction in package size, reduction in package weight, point to point wire replacement and wear-ability in environments needing mobility also enabling integration of devices and components and modules for wireless communication modules, sensors, home appliances, tablets requiring ultra-thin and ultra-light weight. Various commercial flexible substrates are currently available, of those LCP(Liquid crystal polymer) film is studied due to its excellent high frequency electrical properties and inherent high thermal properties. In this study LCP film was utilized to fabricate thin film capacitors for wireless device application. Bismuth niobium oxide based materials was used to fabricate thin film capacitors by RF magnetron sputtering. The fabricated thin film has a dielectric constant of 70 at 100kHz. The thin film capacitors were fabricated with achieving capacitance range of 200~1700pF. Leakage current properties and loss properties was also studied. Embedded thin film capacitors were also fabricated using LCP films and the change of capacitor properties according to bending radius was performed with regard to its flexibility.

For eventual clinical applications of brain-machine interfaces, neural stimulation and recordings must be performed over an extended period of time. In such applications, interfaces that penetrate the cortex offer substantial benefits due to their potential to access information at a higher spatial and temporal resolution[1] and increased ability to affect targeted physiological processes[2]. Current penetrating interfaces, however, are critically limited by reliability concerns. Microelectrode arrays, for example, have been observed to exhibit diminishing performance over time, leading to eventual failure, making them ill-suited for chronic recording of neural signals. Several factors are hypothesized to cause such degradation, including insertion-associated injury, mechanical mismatch causing astroglial scarring around the implanted electrodes[3], and recently, disruption of homeostatic processes regulated by the implant-affected tissue layers such as the dura mater[4]. Thus, the key to building an effective microelectrode array may lie in a combination of biocompatible, flexible, and tissue-regenerative characteristics. To improve the quality of neural recordings for in vivo microelectrode arrays, we are combining materials and technologies used in flexible electronics with collagen, a material used extensively in the field of regenerative medicine. Our microelectrode array consists of 3 main components: a flexible backplane made of copper conductors on polyimide; tungsten wire electrodes, coated with Parylene-C; and a collagen layer introduced over and around the electrodes. The electrodes are bonded to the backplane with both conductive and non-conductive epoxy. Next, a layer of PDMS is spun onto the backplane to provide both mechanical stability to the electrodes and to secure the collagen layer to the backplane. The collagen layer is critical, as the implantation of the penetrating electrode array requires an invasive surgery where skull bone and dura mater are removed[5]. The dura mater is believed to play a key role in both protective and biochemical aspects important for maintaining the metabolic processes required to ensure the viability of underlying neuronal cells. The incorporation of a collagen layer in the electrode array will help re-establish dural tissue around each electrode, forming a complete seal of the dura mater after implantation. We hope this will enable a suitable biochemical environment to maintain the physiological health of the targeted cells in the presence of the invasive electrodes. Currently, electrophysiological testing is underway, with in vivo implantation into small animal (rat) subjects. We will report device fabrication and neural recording results. References [1]Markowitz, DA et al. proc. IEEE EMBS Int. Conf. Neur. Eng. (2011) [2]Kuhn, AA et al. Jour. Neur.. 24(2008) [3]Schwartz, AB et al. Neuron 52(2006) [4]Minnikanti, S et al. Jour. Neur. Eng. 7(2010) [5]Rousche, PJ et al. Jour. Neur. Meth. 82(1998)

Recent publications [1,2] report superior moisture barrier properties for ZrO2/Al2O3 nanolaminates (NLs) compared to Al2O3, when both are deposited by atomic layer deposition (ALD) at 80 C with short cycle times directly on moisture-sensitive Ca-test coupons or OLED devices. Since there is a critical, technological need for ultra-low moisture permeation coatings on plastic substrates, in general, to enable flexible organic electronics on plastic, we have compared barrier performance of NLs with Al2O3 and ZrO2 grown by ALD at 100 C on polyester sheets. Our growth rates were ~0.09 nm/cycle for Al2O3 and 0.1 nm/cycle for ZrO2, in agreement with similar published ALD studies. In a single period for the NLs, the ratio of the number of cycles of ZrO2 to Al2O3 was varied from 5:1 to 1:1. And the number of cycles in a period was kept to fewer than 10, in order to encourage intermixing of these layers to form a â?oZr-aluminateâ? phase, which is cited as one origin of superior barrier performance of these NLs . We found that ZrO2 was a poor moisture barrier. For the NLs, with approximately the same 10 nm thickness, the moisture permeation depended on the ratio of ZrO2 to Al2O3, with better barrier properties for richer Al2O3 NLs. However, even the NL with 1:1 ratio did not outperform Al2O3, when both were directly exposed to damp heat, although we did measure slower degradation of Al2O3, when it was capped with a layer of ZrO2. What distinguishes the results of this study from previous work on the moisture permeation properties of ZrO2/Al2O3 NLs, was that our Al2O3 films were grown at the higher temperature of 100 C with longer cycle times that favor ALD versus CVD growth, and consequently films likely had less -OH defect content and were denser. The film thickness in this study was also much thinnerâ?"10 nm versus 100nm. [1]. Meyer et al.Adv. Mater. 21, 1845 (2009) [2] J. Meyer et al. Appl. Phys. Lett. 96, 243308 (2010)

Carlo Taliani, Petr Nozar, Alessandro Neri, Riccardo Lotti and Dmitry Yarmolich Organic Spintronics SrL, Italy, and Istituto ISMN, CNR, Bologna, Italy Abstract The development of flexible organic optoelectronics (flexible OLED and flexible OPV) suffers from the lack of convenient room temperature technologies for the deposition of Transparent Conducting Oxides (TCO) on flexible substrates. In fact the mechanical properties of plastic substrates are highly sensitive to temperature and lose their mechanical properties above the glass transition temperature (Tg). The lowest temperature affordable by traditional technologies like RF sputtering and CVD is the range of 150 - 200°C. The Tg of the substrate of choice for the best properties vs cost ratio, i.e. polyethylene terephtalate (PET), is only 80°C. Organic Spintronics (OS) has implemented the technology of Pulsed Plasma Deposition (PPD), based on ablation of a material by means of nanosecond pulsed electron beam that operates at room temperature without affecting the properties of the plastic substrate. Doping is achieved by oxygen vacancies giving substrates with a resistivity as low as 4 x 10-4 ohm cm2. Among the various TCO we have chosen to develop n- ZnO for the highly availability and low cost of zinc compared to indium. The PPD grown n-ZnO TCO is a stable, smooth and highly transparent ( 90% T% in the UV-VIS range) film. The T% in the near IR spectral range is definitely much superior of any TCO made by previous technologies at higher temperatures, making it a perfect match with the band gaps of thin film photovoltaics. On a glass substrates the n-ZnO sustains a high temperature treatment up to 250°C for several hours. OS has successfully developed an industrial, high rep. rate PPD source that allows the deposition at 500 nm / minute. The efficiency and the low thermal budget of the PPD deposition, associated with the low roughness and the large optical transmission of the film, allows therefore to fabricate high quality TCO on PET in the Roll to Roll configuration. Organic Spintronics is developing a 300 mm web deposition system and is looking for an industrial partner for the implementation of wider systems to the industrial scale.

The amorphous InGaZnO (a-IGZO) has been expected as a promising material of a channel layer in thin film transistors (TFTs) for next-generation displays. The large and high-resolution display can be realized by using the a-IGZO TFTs because of the higher channel mobility (μ_ch) than the traditional amorphous silicon (a-Si) TFTs. Furthermore, flexible a-IGZO devices on plastic substrates can be fabricated due to the low deposition temperature. Recently, we have reported that the μ_ch of TFTs annealed in the high-pressure water vapor (HPV) has recorded higher value than that in the typical atmosphere (AT, N₂:O₂ = 4:1) condition. However, the relationship between the electronic characteristics and the properties of the a-IGZO film is not fully clarified. The purpose of this research is to clarify the effect of the several kind of annealing process on the electronic property of a-IGZO TFTs from capacitance-voltage (C-V) characteristics.
The a-IGZO capacitors were fabricated on p-type Si substrates (resistivity = 2~4 mΩcm). The a-IGZO layer was deposited on the Si substrate having thermally oxidized SiO₂ (100 nm), by using the RF magnetron sputtering in O₂ of 5% with mixture of Ar gas ambient under 0.6 Pa at room temperature. The capacitors were annealed in AT at 300^oC for 2 h or HPV with 0.5, 0.8, and 1.2 MPa at 290^oC for 1 h. Then, ITO electrodes were formed by the sputtering and lift-off process.
The density of states (N) from the conduction band minimum (E_c) to 0.6 eV was calculated from the C-V characteristics. The N of HPV samples exhibited smaller value than that of AT samples around the region below the E_c (E_c-E = 0~0.2 eV). It is suggested that the μ_ch of TFTs after HPV increases due to the decrease of the density of the electron traps. From the cyclic C-V measurement (the voltage is applied from 0 to 20 V), the flat band shift (Î"V_FB) of HPV samples showed 1.5 V and that of AT samples reached about 4 V. Therefore, the amount of the density of the electron traps in IGZO after HPV is lower than that after AT. On the other hand, the N after HPV increased below 0.2 eV from E_c as increasing of the annealing pressure. The I_DS-V_GS characteristics of TFTs annealed in 1.2 MPa had the hump around the subthreshold region, suggesting that the increase of the N below 0.2 eV provides an energy potential to product the hump.
In conclusion, we fabricated the a-IGZO capacitors annealed in HPV or AT and performed C-V measurement analysis. From the evaluation of the N distribution and Î"V_FB of the cyclic C-V measurement, it is considered that the density of the electron traps close to E_c decreases, leading to the increase of μ_ch. This implies that the HPV process is an effective method to decrease such electron traps as compared with AT. However, the HPV under 0.8~1.2 MPa increases electron traps below 0.2 eV from E_c and has possible to cause hump into I_DS-V_GS characteristics. It is thought that the HPV into 0.5 MPa is the most promising condition.

Several advances in organic material science have accelerated the development of organic devices. While there has been rapid progress in developing organic light-emitting devices, important questions still remain regarding organic lasers. Although amplified spontaneous emission (ASE) and lasing from optically pumped organic thin films and single crystals have been observed for over a decade, electrically driven organic lasers have not yet been achieved. Recently, in addition to conventional organic LED devices, organic light-emitting field-effect transistors (LETs) have been developed. Organic single-crystal LETs (OSCLETs) with ambipolar charge transport are suitable for laser devices because they offer a high carrier mobility and a geometry that minimizes the effects of nonradiative losses. However, to achieve further spectral evolution and definitively detect electrically driven ASE, the current density must be increased. In this work, we improved the current density of ambipolar OSCLETs by the removal of carrier traps and the application of current confinement structure with laser-etched single crystals. As the results, we achieved an extremely higher current density up to 100 kA/cm2. A Si wafer with a SiO2 (500nm) layer was spin-coated with poly(methyl methacrylate) (PMMA). Grown 5,5â?-bis(biphenylyl)-2,2â?T:5â?T,2â?-terthiophene (BP3T) single crystals were laminated on to the substrates. We have tested several organic solvent for PMMA spin coating and investigated the origin of electron traps. As the results, we found that the residual organic solvent in PMMA layer is one of the origins. Finally, we successfully reduced such traps by the correct choice of solvent molecule and enough baking of PMMA layer [1]. We also removed the single-crystal absorbate by aging treatment inside inert Ar glove box and reduced the amount of traps [2]. Following these improvements, we realized very high current density (~12.3 kA/cm2). To increase the current density more, we fabricated ambipolar OSCLETs with the structure of current confinement. For the current confinement, the small area of transistor channel was narrowed by laser etching system (532nm green laser) and current was focused on a specific area. Au and Ca metals were deposited as source and drain electrodes. To achieve good n-type performance, cesium fluoride was also evaporated as an electron injection layer. As a result, ambipolar current density at the confined channel area was one or two orders of magnitude larger than previous devices and extremely high current density was realized (~100 kA/cm2). [1] Sawabe et al., Appl. Phys. Lett. 97, 043307 (2010). [2] S. Z. Bisri et al Appl. Phys. Lett. 96, 183304 (2010).

Conjugated organic molecules are promising next-generation semiconductors for use as the active materials in field-effect transistors (FETs) due to their potential for cost-effective processing and potential use in flexible applications. Traditionally, much of the research on organic semiconductors for organic FETs has traditionally focused on small molecules and polymers. These materials have anisotropic charge transport behavior meaning that the molecules require careful processing in order for the charge to propagate efficiently in the active channel of the device. The careful processing that is often required means that it is more difficult to reproducibly form the devices on practical scales. Therefore, it would be highly desirable to develop materials that allow efficient isotropic charge transport, that is, materials that are capable of achieving good transport properties without the need for specific molecular orientation in the active channel of the device. In this contribution, we present a new class of dimensionally-rich dendrimers that feature a spiro-core and a variety of fused thiophene- and carbazole-based dendrons. With charge transport in mind, the building blocks (core, branch and surface units) of the dendrimers are carefully engineered to minimise charge trapping in the film. The dendrimers were found to have excellent solubility in common organic solvents and are solution processable to give good quality films. The preparation, characterisation and OFET performance of the dendrimers will be presented. We will also discuss how computational methods can help us understand the charge transport behaviour in the dendrimers as a function of structure.

Fabricating electrical circuits on paper has gained considerable attention in the light of cost-effective roll-to-roll processing, flexible, foldable, light-weight, and environmentally friendly electronic devices comparing to the conventional printed rigid circuit boards. Therefore, the printed electronics, drop-on-demand ink-jet printing in particular that can fabricate electronic devices under the ambient conditions, like printing of newspapers or magazines, makes paper substrate possible to realize as an emerging class of materials with potential application in photovoltaics, displays, batteries, antennas, and sensors. Because the ordinary paper has a high rough surface, which is related to the featured micro-size cellulose fibers and associated voids, the nanoparticle-based conductive ink can readily permeate the paper substrate and hence the controlled printing of the narrow conductive line is impossible. Moreover, the printed lines are more easily to fail under serious strain, e.g., folding. Here, we report the ink-jet printing of narrower conductive lines on nano-structured paper, which has known to posses the comparable thermal characteristics of glass, the high tensile modulus (~13 GPa), strength (~223 MPa), and incredible low coefficient of thermal expansion (~9 ppm/k). The cellulose nanofiber paper was made using wood flour, in which cellulose nanofibrils are usually bundled together in the form of micron to macro fibers embedded within the matrix of other wood components in the wood cell wall. After the chemical treatment, the water slurry of cellulose pulp fibers was downsizing by a mechanical grinding just one time. The resulting cellulose nanofibers (10-20 nm wide) slurry was then turned into a densely packed translucent nano-structured paper (20-30 μm thick) after shear-casting on the acrylic-plates and drying in oven at 50°C. The commercially available silver nanoparticle ink was inkjetâ?"printed by using a commercial Dimatix printer. It was found that the electrical resistance of conductive lines printed on nano-structured paper was lower than those printed on plastics, like krypton and polyethylene naphthalate (PEN).

The concept of merging transparent and flexible electronics has recently been the subject of extensive research, and a key step towards its practical realization is the fabrication of appropriate memory devices for integrated circuits. We developed transparent and flexible nonvolatile memory devices based on bottom-gated organic thin-film transistors (OTFTs), which showed reliable and controllable memory properties with a large memory window of 15 V. Our devices were prepared on a plastic substrate and the source and drain electrodes were patterned using transparent indium-tin oxide (ITO) electrodes deposited at room temperature. To turn these OTFTs into memory devices, we incorporated a layer of self-assembled gold nanoparticles, fabricated via a simple colloidal solution process. The threshold voltage shift of the OTFTs, which represents the memory program/erase operation, was achieved by hole trapping/detrapping in the gold nanoparticles. The data retention time of our memory devices was more than 10⁵ s and their operation was still stable after more than 2000 bending cycles which confirms both their electrical and mechanical robustness. These results contribute towards the development of potential applications which make use of both advanced transparent/flexible electronic devices and integrated organic device circuits.

We propose a new structure for controlling threshold voltages of organic Thin Film Transistors (TFTs) in both positive and negative direction. Controlling threshold voltages is an effective way to reduce the device variation, improve the stability of Static Random Access Memory (SRAM), and increase or decrease the on-current of organic TFTs at the same operational voltage. And floating gate structure is reported as a way of controlling threshold voltages after fabrication[1], however the threshold voltages shift is only in negative direction, therefore the on-current cannot be fully controlled. In this study we report the floating gate integrated with a capacitor structure, which realizes the threshold voltage shifts in positive and negative direction.
These organic TFTs were fabricated by vacuum evaporation and chemical vapor deposition (CVD) process. First, 50-nm-thick Au layer was thermally evaporated as the control gate electrode using a metal mask on 75-μm-thick polyimide films. Second, parylene layer was deposited as the control gate dielectrics by CVD. Then 50-nm-thick Au layer was evaporated on the control gate dielectric layers as the floating gate electrode, and parylene layer was formed on them again. Purified dinaphtho[2,3-b:2�,3�-f]thieno[3,2-b]thiophene (DNTT) was thermally evaporated as a p-type organic semiconductor layer through a metal mask on the floating gate dielectric layer. Finally 50-nm-thick Au layer was evaporated through a metal mask to form the source and drain electrodes and the electrode of a capacitor.
Both of the displacement and shift direction of threshold voltages depend on the applied voltage to the capacitor, and in this study threshold voltages were controlled from -32 V to 32 V after fabrication by changing the voltage of capacitor only when we programmed. The displacement of threshold voltages is larger than that by changing the programming voltage or time of normal floating gate structure.
This work is partially supported by Special Coordination Funds for Promoting, JST and KAKENHI (Wakate S).
[1] T. Sekitani, T. Yokota, U. Zschieschang, H. Klauk, S. Bauer, K. Takeuchi, M. Takamiya, T. Sakurai, and T. Someya, Science 326, 1516-1519 (2009).

Recently, computational techniques have been widely utilized for the development of organic semiconductors. Carrier transport in respective crystals is discussed in view of the transfer integrals, and relaxation of the molecular structure accompanied by the carrier transport is obtained from the reorganization energy. Carrier mobility can be estimated from these quantities. The herringbone structure is a representative packing pattern of organic semiconductors. For a variety of organic semiconductors with the herringbone structure, we have estimated the transfer integrals between the neighboring molecules by changing the dihedral angles of the molecular planes, and the displacement along the molecular long axis on the basis of the extended Hückel calculations [1]. The transfer integrals show modulation with the sign inversion corresponding to the phase of MO, making a maximum at the eclipsed stacking. As a result, pentacene has an oscillating structure of the transfer integrals depending on the displacement, because the pentacene HOMO has nodal planes along the molecular short axis. In contrast, tetrathiafulvalene (TTF) derivatives, whose HOMO has nodal planes along the molecular long axis, show a modulation of the transfer integrals depending on the dihedral angle. The dimensionality of the carrier transport is related to the dihedral angles in the former case; two-dimensional conduction is realized at small dihedral angles, whereas one-dimensional conduction is expected for large dihedral angles, in consistent with the experimental observations. This tendency, however, does not apply to the TTF derivatives, where several peaks of transfer integrals appear in the middle dihedral angle region. Hence, significant carrier transport arises for the TTF crystals. We have explored various materials in this method and investigated thienoacene as an example. MO of thienoacene has nodal planes along the molecular short axis in the HOMO and along the molecular long axis in the LUMO. Thienoacene has been investigated principally as a p-type semiconductor so far. Perfluorophenyl(carbonyl) substitution realizes n-type characteristics but has a Ï?-stack structure [2]. Recently, dithienothiophene-dicarboximides (DTTDIs) has been synthesized, and the N-propyl DTTDI has a herringbone structure [3]. It is surprising because other diimides have mostly Ï?-stack structures. The LUMO level of N-methyl DTTDI has been estimated to be â?"3.14 eV in the B3LYP/6-31** level, and is regarded as an n-type semiconductor candidate. Notably, the LUMO of N-propyl DTTDI shows a large bandwidth (392 meV) and moderate reorganization energy (438 meV). Although there is no report of the transistor properties, we are investigating further geometrical properties of the derivatives. -- [1] H. Kojima and T. Mori, Bull. Chem. Soc. Jpn. 2011, 84, 1049. [2] M.-C. Chen et al. Chem. Commun. 2009, 1846. [3] W. Hong et al. Org, Lett. 2011, 13, 1410.

To master the electrical instabilities in zinc oxide (ZnO) semiconductor thin films, the ZnO surface is the most obvious starting-point. Using liquid processable adsorbates, additionally enables a simplified way for space-resolved conductivity tuning. We demonstrate the electrical effects of organic adsorbates on very thin solution processed ZnO films (T_max = 125°C) e.g. for application in thin film transistors (TFT). We show the tunability of the conductivity and TFT properties also with respect to the atmospheric durability of the devices and discuss the observations with respect to the density of donor and acceptor states at the ZnO surface.

All solution-processed organic thin-film transistors (TFTs) have been fabricated using room-temperature (RT) sintering silver nanoparticle ink [1] and poly(2,5-bis(3-hexadecylthiophene-2-yl)thieno[3,2-b]thiophene) (PB16TTT) [2]. The obtained silver electrode line widths were strongly affected by the surface energy of the substrates. Wide lines of about 1200 µm were formed on the glass, while fine lines of about 400 µm were formed on the plasma-treated Teflon substrate. The electrode lines exhibited a resistivity of 352 µΩcm at room temperature. The resistivity decreased to 17.9 µΩcm as increasing the sintering temperature to 100 °C. This value is very low among the silver lines prepared by silver nanoparticle inks. The all solution-processed organic TFTs exhibited good transistor characteristics with a mobility of 0.09 cm²/Vs and on/off ratio of more than 10⁵. We have found the threshold voltage shift after 10⁴ s under continuous DC bias voltage was less than 2.0 V, which was comparable to the amorphous silicon TFTs. The RT sintering silver nanoparticle ink was synthesized from silver oxalate. Mixture of silver oxalate, three kinds of amine, and oleic acid were stirred at 110 °C for 15 min to obtain the silver nanoparticles. After centrifuge process, the silver nanoparticles were dissolved in a mixed solvent of octane and butanol. Solvent ratio of octane and butanol was 3:1. The concentration of the Ag ink was 10 wt%. Fabrication process of the all solution-processed organic TFTs was as follows. First, a RT sintering silver nanoparticle ink was spin-coated on the glass substrate and sintered at 100 °C for 1 h in air to form 100-nm-thick gate electrode. The Teflon layer was formed as gate dielectric by spin-coating onto the Ag gate electrodes and dried at 150 °C for 1 h. The Teflon layer surface was treated by an oxygen-plasma to change the surface energy. The plasma power was 10 W, and the duration of plasma treatment was 10 s. The source/drain electrodes were formed by a dispenser (MUSASHI Engineering, image master 350 PC) with drawing speed of 20 mm/s. Finally, semiconducting polymer, PB16TTT layer was formed by drop-casting from 0.03 wt% solutions of toluene, and the film was annealed at 150 °C for 30 min in the nitrogen atmosphere [2]. The length and width of the channel were 40 and 2900 µm, respectively. In conclusion, our RT sintering silver nanoparticle inks gave very lower resistivity Ag electrode compared to the conventional one [3] at RT or sintering temperature of less than 100 °C. Furthermore, the organic TFTs using the Ag electrodes exhibited good electrical performance comparable to that using the evaporated Ag electrodes. These results indicate the feasibility of all-printed organic TFTs for large-area and flexible electronics. [1] M. Itoh et al., J. Nanosci. Nanotechnol. 9, 6655 (2009). [2] T. Umeda et al., J. Appl. Phys. 105, 024516 (2009). [3] J. Perelaer et al., J. Mater. Chem. 18, 3209 (2008).

Materials with a remarkable combination of high electrical conductivity and high optical transparency are important components of various optoelectronic devices such as organic light emitting diodes (OLED), solar cells, and touch screens. Doped metal oxide films such as tin doped indium oxide (ITO) have single-handedly dominated the field. However, the next generation of optoelectronic devices requires transparency and conductivity as well as flexibility, vacuum-less process, indium-less materials, and low cost. These requirements severely limit the use of ITO for transparent electrodes. Fortunately, there are several emerging alternatives to ITO, including single-walled carbon nanotubes, graphenes, PEDOT/PSS, and a random network of metal nanowires. Among these materials, a random network of silver nanowires shows excellent electrical conductivity comparable to that of ITO. Lee et al. have fabricated silver nanowires electrodes exhibiting performances that rival those of ITO, with sheet resistances approaching 16 Ω/square at a transparency of 86%. Moreover, since silver nanowires are able to be coated onto flexible substrates by cost-effective and scalable roll-to-roll manufacturing, a variety of electrical devices deposited on silver nanowire transparent electrodes have been reported including organic solar cells, OLEDs, and touch screens. Due to their inherent advantages, silver nanowire transparent electrodes are regarded as the leading candidate materials to replace ITO. Although silver nanowire transparent electrodes have such outstanding features, there is one issue to be solved. That is the application of silver nanowire transparent electrodes on heat-sensitive substrates is limited by a heat-treatment around 200 °C. The heat-sensitive plastic substrates such as PET films are easily deformed by heat-treatment at 200 °C. Thus, low-temperature fabrication of silver nanowire transparent electrodes is required. We have fabricated silver nanowire transparent electrodes at low temperature. Key factor for achieving high electrical conductivity is the achievement of formation of junctions between silver nanowires. We will report low-temperature fabrication process of silver nanowire transparent electrodes with a remarkable combination of high electrical conductivity and high optical transparency.

Recently studies on biodevices have been widely performed. One of the final goal would be the use of these inside human body as artificial organs. Inhibiting the protein adsorption is of much importance for considering the material biocompatibility. Additionally, understanding if the proteins keep their functionality or not is of much interest. However, in situ observation of protein adsorption processs and functionalities on solid/liquid interfaces is not easy because the reaction is not simple and the measurement.metohds should be high sensitive. We have invented slab optical waveguide (SOWG) spectroscopy which brings us in situ UV-vis. absorption spectra from molecules adsorbed on solid/liquid interfaces below monolayer coverage. In situ observation of adsorption process on solid/liquid interfaces, and electron transfer (ET) reaction of cytochrome c adsorbed on ITO electrodes under electrochemical condition have been carried out. Here we will show the detai results about the adsorption process and functionality of cytochrome c on solid/liquid interfaces. The SOWG system was the same as that described previously.[1,2] SOWG spectra of cytochrome c adsorbed on ITO was observed with the electrode potential sweep between 0.30 and -0.25 V vs Ag/AgCl at a scan rate of 0.1 V/sec. The adsorbed amount of cytochrom c was estimated to be about a quarter of monolayer coverage from the net charge flowed in ET reaction. The SOWG spectral change revealed cytochrome c adsorbed on ITO electrode was still active without any surface treatment nor addition of mediators, and that the redox potential of proteins after adsorption easily acquired. The effect of supporting electrolyte concentration in water on ET reaction rate is also been investigated applying pulse potential step to ITO electrode now. References [1] N. Matsuda et al., Thin Solid Films, 438-439, 403 (2003). [2] N. Matsuda et al., IEICE Trans. Electron., E94-C, 170 (2011).

Transfer printing methods can be used to assemble dissimilar materials onto a common substrate and to place high quality materials onto substrates for which they could not be directly placed such as chemical vapor deposition (CVD) grown carbon nanotubes or graphene films onto plastic substrates.[1, 2] Metallic, dielectric and semiconducting layers can be sequentially transfer printed in order to build thin-film transistors on plastic substrates.[3, 4] The primary requirement for successful transfer printing is a differential adhesion between the printable layer and both the transfer substrate and the device substrate.[5] That is, the layer to be printed must have a lower adhesion to the substrate onto which it was originally fabricated and a higher adhesion to the substrate onto which it will be printed. Therefore, the surface energy of the transfer substrate surface may need to be reduced, for example, by the application of a fluorinated self-assembled monolayer and the surface energy of the device substrate surface may need to be increased, for example, by exposure to an O¬2 plasma. For metal layers patterned using photolithography or e-beam lithography, lowering the surface energy of the processing substrate can make lift-off problematic. In the work to be presented here, it has been shown that photolithographically patterning metal films on a parylene surface allows for both good lift-off and transfer printing results. Using photolithography and lift-off, several metal films (Cr, Cu, Al) have been successfully patterned on Parylene coated Si wafers. These patterned films have then been successfully transfer printed onto plastic substrates (polyethylene naphthalene, Kapton). The fabrication method, transfer printing and characteristics of these metal films will be presented and discussed. References 1. Sangwan V. et al., Controlled growth, patterning and placement of carbon nanotube thin films SOLID-STATE ELECTRONICS 54, 1204(2010). 2. Chen Jian-Hao et al., Printed graphene circuits, ADVANCED MATERIALS 19, 3623(2007). 3. Hines D. R. et al., Nanotransfer printing of organic and carbon nanotube thin-film transistors on plastic substrates, APPLIED PHYSICS LETTERS 86, 163101 (2005). 4. Hines D. R. el al., Poly, 3-hexylthiophene. thin-film transistors with variable polymer dielectrics for transfer-printed flexible electronics, JOURNAL OF APPLIED PHYSICS 104, 024510 (2008). 5. Hines D. R. et al., Transfer printing methods for the fabrication of flexible organic electronics, JOURNAL OF APPLIED PHYSICS 101, 024503 (2007).

A series of inorganic-organic hybrid photocurable high molecular weight ladder-like structured poly(phenyl-co-methacrylate)silsesquioxanes (LPPMA) were investigated as flexible display substrates. The refractive indices were able to be tuned by controlling the Si-Phenyl ratio with respect to Si-MMA, giving rise to films with refractive indices ranging from 1.525 to 1.553. Photocured films with 50μm thickness showed high transparency (>90%), excellent thermal stability (Td >400°C), low CTE (~38ppm/K), dimensional stability, without the use of reinforced glass fibers. Furthermore, these ladder-like structured materials did not require any thermal treatment processes due to the negligible amounts of uncondensed silanol groups, thus simplifying manufacturing processing. These novel hybrid films present an alternative to organic plastics as flexible electronic device substrates.

Thin-film encapsulation with excellent permeation barrier property is highly desirable for lightweight and flexible organics devices, such as organic thin-film transistors, organic light-emitting-diodes, and organic solar cells. While alternating deposition of organic and inorganic sublayers can reach low permeation rates, the preparation process for a multilayer permeation barrier can be complicated and costly. Therefore, we are motivated to develop a flexible single-layer organic-inorganic hybrid thin film with sufficient impermeability. The single-layer organic-inorganic hybrid SiOwNxCyHz thin films are deposited from a gas mixture of hexamethyldisiloxane, hexamethyldisilazane and oxygen by plasma-enhanced chemical vapor deposition at room temperature. The oxygen to organo-silicon precursor mass flow ratio is the key parameter investigated in this study. Three types of substrates, including glass plates, polyimide foils and silicon wafers, are used. The infrared absorption spectra obtained by Fourier transform infrared spectroscopy indicate that the increase of oxygen flow leads to the increase of the number of inorganic bonds. The contact angle for a water droplet drops at high oxygen flow, which again confirms the addition of oxygen can enhance the inorganic content in the resulting film. An average optical transmittance of > 90% in the visible regime is observed by UV-VIS spectrometer. Calcium test is used to evaluate the water vapor transmission rate (WVTR) of the barrier films. WVTRs of 2.5Ã-10^-5 g/m²-day and 8.4Ã-10^-6 g/m²-day are obtained for 1-μm-thick and 3-μm-thick SiOwNxCyHz thin films, respectively, deposited at oxygen to organo-silicon precursor mass flow ratio of 2.5. The barrier properties of single-layer SiOwNxCyHz thin films with graded compositions are under study at present. Further results will be reported in the symposium.

Atmospheric plasma enhanced chemical vapor deposition is an emerging large-scale and cost-effective deposition technique. An important feature of the process is the capability to deposit a film at room temperature in the atmosphere, and thus a plastic with low glass transition temperature can be used as a substrate. In the present study, we demonstrated that thin films of zinc oxide (ZnO) and tantalum oxide (Ta₂O₅) can be deposited on plastic substrates by atmospheric plasma deposition. The integration of such ceramic oxides on plastic substrates is desirable for a wide variety of devices including photovoltaic and flexible electronics, film actuators, semiconductive lasers, hard and wear resistant coatings. Both oxides have attractive characteristics such as high transparency from visible light to infrared wave lengths, high electric conductivity (ZnO) and high electrical insulation (Ta₂O₅). Both are also piezoelectric. The micro and molecular structures of the coatings were characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and atomic force microscopy (AFM). Their interfacial adhesion was investigated by using double cantilever beam (DCB) tests. We focused on the effects of processing conditions such as substrate surface treatments, precursors and substrate temperatures. The coatings were successfully deposited and XPS surface scans were used to confirm the atomic composition. The interfacial adhesion exhibited large variation depending on the process conditions and the substrate materials (PMMA, PC, PET, PEN, and silicon). The results indicated that good quality films can be deposited. We also show that the interfacial adhesion of the oxide/plastic system is very sensitive to the deposition parameters and reveals key process factors that affect the film adhesion.

Flexible transparent conductive films are strongly demanded due to the scarcity of indium and brittleness of indium tin oxide (ITO). Flexible electronic devices are regarded as the next-generation electronic devices. In this paper, we will report highly conductive PEDOT:PSS and PEDOT:PSS/carbon nanotube composite films fabricated by solution processing. These films are highly flexible and have a conductivity of over 3000 S/cm. Their transparency and sheet resistance are comparable to ITO. We will also report their application as the transparent electrode of high-performance polymer solar cells.

We have proposed â?oWet nanotechnologyâ?, producing nano-device key-components by biomineralization and self-organization of protein supramolecules in aqueous solution, which was named â?oBio Nano Processâ? (BNP)1). In the BNP, protein supramolecules work as templates for the synthesis of homogenous nanoparticles (NPs) / nanowires (NWs) of metal-complexes and semiconductor materials 2,3). The chemically or genetically modified outer surfaces of protein supramolecules makes them self-organize into functional nano-structures on a substrate. The addition of site specific biding peptides to the protein supramolecule is very powerful method to control both protein-protein and protein-substrate interactions and used in the BNP. We have already designed and produced several kinds of protein supramolecules for the BNP and applied them to produce a floating nanodot gate memory (FNGM), a single electron transistor, a Re-RAM, bio-sensors and other electronic devices 2,4,5). Moreover, by combining the BNP and nano-etching, we fabricated arrays of silicon nanodisks 6) which functioned as ideal quantum wells and are under investigation for quantum solar cell application. We are now expanding the BNP frontier further, producing proteins which have two types of site-specific binding abilities which can catch and deliver NPs / NWs to the specific patterns on a substrate7). The BNP is a green process and environment-friendly i.e. carried out in aqueous solution, ambient pressure and room temperature, which is well suited for plastic substrate devices. The combination of conventional technologies and the BNP will produce nano-devices efficiently and economically, which could not be realized in their absence. References 1) I. Yamashita, Thin Solid Films 393, 12-18 (2001). 2) I. Yamashita et.al., Biochimica et Biophysica Acta 1800, 846â?"857, (2010), 3) M. Kobayashi, et.al., Nano Lett., 10 (3), pp 773â?"776 (2010). 4) A. Miura, et.al., Jpn. J. Appl.Phys., 45, L1-L3, (2006). 5) J. Heddle, et.al., Small 3(11), 1950-1956, (2007)., 6) C. Huang et.al., Jpn. J. of Appl. Phys., 48, 04C187-1-04C187-6 (2009). 7) B. Zheng, et.al., Nanotechnology 21, 045305, (2010)

Atmospheric plasma is an emerging large-scale, cost-efficient and low temperature surface modification and coating deposition technique. It can be applied to deposit barrier coatings for photovoltaic and flexible electronics, anti-reflection coatings with controlled transparency in PV technologies and transparent wear resistant coatings for plastic airplane windows, as well as to enhance the adhesion of multiple devices on plastic films. It is a flexible technique that can be used in industrial printing and roll-to-roll manufacturing methods. In the present work, we demonstrated low temperature deposition of dense silica and Si-C-N-O coatings on stretched poly(methyl methacrylate) and polycarbonate substrates by atmospheric plasma. The deposition rate showed a strong dependence on the delivery temperature of the precursor and the size of the precursor molecule. The dense silica coatings deposited by atmospheric plasma below 100 oC had elastic moduli from 14.4 ± 2.1 to 34.2 ± 1.2 GPa, which were comparable or even higher than the sol-gel silica coatings annealed at 400 oC. Si-C-N-O coatings were also deposited on plastics and silicon substrates with tunable carbon content from 20 atm. % to 85 atm. % and nitrogen content up to 15 atm. %. Studies was also carried out on the enhancement of the adhesion of coatings to polycarbonate and poly(methyl methacrylate) by oxygen atmopheric plasma treatment of the plastic surface. The adhesion energy of the coatings on polycarbonate increased by 5 times after a short atmospheric plasma treatment, while prolonged treatment decreased the adhesion energy gradually. Poly(methyl methacrylate) appeared to be more sensitive to atmospheric plasma treatment. To understand the trends, X-ray photoelectron spectroscopy was used to analyze the chemical states of the carbon and oxygen species on plastic surfaces after oxygen atmospheric plasma treatment. Rapid oxidation was observed for both plastics. Atomic force microscopy was also applied to characterize the surface morphology of atmospheric plasma treated plastics. It was found that oxygen atmospheric plasma treatment of plastics has double-sided effects on the adhesion of coatings to plastics: short treatment mainly resulted in rapid oxidation and enhanced the adhesion by creating more hydrophilic sites on the surface, while prolonged treatment created a thicker low-molecular-weight weak boundary layer and weakened the adhesion of coatings. The results suggested that atmospheric plasma treatment is a high-throughput and large-scale method to enhance the adhesion of multiple devices on plastics.

Blue-light phototherapy (460-490 nm) is the most usual treatment of jaundice in newborns. However, despite the fact that it is extremely simple and highly efficient, it requires some procedures to guarantee its accuracy. Among these factors, stand out the inadequate exposed body surface area, the incorrect spectrum of the lamps used and the distance from the light source to the infants are the most common problems related in literature. Accordingly, the development of sensors to control the radiation dose is an actual topic and with social and technological standpoints. In this work we evaluated the performance of a low-cost, biodegradable and flexible organic sensor for managing the radiation dose planning before treatment of jaundice of neonates. Self-adhesive films of poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene - MEH-PPV and poly(butylene adipate-co-terephthalate) â?" MEH-PPV:PBAT blends were fabricated. The results show that this system presents a gradation of color from red-orange to green under blue-light exposure. The sensors were applied on the newborns skin under phototherapy conditions. It is therefore concluded that MEH-PPV:PBAT films appear here as good candidates for an effective management of the radiation doses planning before treatment of neonatal in which the needs of the control of dose absorption of infants is extremely important. This work was supported by Fapemig, Capes and CNPq agencies from Brazil.

While flexible energy components are being considered for exciting wearable, medical, architectural and ultraportable applications, many â?omundaneâ? applications can benefit from the same features. Robust, low cost co-packaging is a desirable for many energy storage and power conversion applications. And while flexible electronics share many of the same challenges as flexible energy storage and electricity conversion, there are also significant differences: 1) Many energy storage components are already available in printable format. 2) Some devices demand a liquid component for optimal performance. 3) Areal resolution is not critical but.. 4) Device thickness must be on the order of ~10 microns or higher for area conservation. 5) Mechanical changes over both a cycle and the lifetime of the device must be considered with the flexible/stretchable parameters 6) Energy storage demands mass, thus the cost per unit mass of the energy storage components must be significantly less than that of the electronic components These constraints and opportunities demand not only new materials, but understanding of how to benefit from existing materials while systematically addressing their shortcomings, what we have dubbed â?osystem sympatheticâ? approaches. We will explain how we apply this approach to energy storage components for both wearable components as well as massive energy storage with primary batteries, secondary batteries, and solid state capacitors that leverage air stable, low cost materials.

Monolithic integration of thin film battery and electrochromic devices is reported. Both devices present a similar architecture based on two lithium insertion materials electrodes separated by an ionic conductor. This was achieved by utilising common patterned layers including current collectors and electrolyte. Common insertion materials were also utilised, with the difference of their respective thicknesses in the thin film battery and electrochromic architecture. In this study, all materials were realized by physical vapour deposition (PVD). Devices were realized on rigid (glass) and flexible (plastic) substrates. The electrolyte was a lithium phosphorus oxynitride (LiPON), the insertion materials were tungsten trioxide (WO₃) and vanadium pentoxide (V₂O₅). Current collectors consisted on ITO and ZnO:Al. The first part of the study concerns the evolution of electrochemical and optical properties of V₂O₅ and WO₃ thin films with thickness. XRD and SEM characterizations were carried out to investigate microstructural properties. Galvanostatic cycling is used to evaluate charge/discharge capacity evolution with film thickness. UV-Vis spectroscopy was used to monitor transmittance evolution with lithium insertion rate and film thickness. Lithium balancing and insertion electrodes thicknesses were then fixed for the integration in devices architecture. The second part of the study concerns the description of the monolithic integration process flow for the realization of thin film battery and the electrochromic devices simultaneously. The module surface is 25x25mm² with equal footprints on two devices, global thickness dos not exceed 5µm. Electrochemical and optical characterizations are carried out on the realized devices separately. Results on powering the electrochromic device directly from the integrated thin film battery are finally reported. As part of a flexible multifunctional electronic system, the described module would represent a cost effective solution to integrate an electrochromic display and a thin film able to store harvested energy and deliver power to display and other electronic devices.

By now, virtually all classes of silicon devices have been replicated in organic materials. One of the remaining device types for which an organic counterpart is still to be demonstrated is the charge injection device (CID) and the closely related charge coupled device (CCD). In this contribution we begin with a brief experimental and theoretical introduction to the application of the photocapacitance technique to organic metal-insulator-semiconductor (MIS) capacitors and ending with a demonstration of an organic trapped charge memory device and an organic CID. When an organic MIS capacitor based on the p-type semiconductor poly(3-hexylthiophene) is illuminated while biased into depletion, electrons photoinduced in the semiconductor depletion region migrate to and become trapped in interface or insulator states, causing a shift in the flatband voltage [1,2]. Electron trapping times depend on the nature of the insulator used in the device. We show that it can be sufficiently long (minutes to hours) to enable the off-line reading of a latent image captured in a 3 x 3 matrix of MIS capacitors. Significantly, we also show that it can be sufficiently short to enable CID action in which electrons photoinduced in the active semiconductor of one MIS capacitor are induced to migrate along the semiconductor/insulator interface to an adjacent capacitor by suitable modulation of the interfacial potential. Electron transfer is deduced from the significant hysteresis observed in the capacitance-voltage characteristic of the second capacitor [3]. Further confirmation is obtained by measuring simultaneously the temporal evolution of currents in both capacitors from which we estimate that electron transfer between the two capacitors occurs with efficiency in excess of 40%. Although lower than for silicon-based CCDs, the devices fabricated to date are not optimised either in terms of materials, device geometry or mode of operation. Significant further development is possible, suggesting that an organic CCD can be realised. Furthermore, the measurements indicate that the CID is a useful device for studying the dynamics of interfacial charge trapping and release at the organic semiconductor/insulator interface. [1] D.M. Taylor, J.A. Drysdale, I. Torres and O. Fernández, 2006 Appl. Phys. Lett. 89, 183512. [2] J. Lancaster, D. M. Taylor, P. Sayers and H.L. Gomes, 2007 Appl. Phys. Lett. 90, 103513. [3] C. P. Watson and D. M. Taylor, submitted to Appl. Phys. Lett.

A memory element is an essential component in electronics owing to its applications in data storage. The switching voltages, retention time, endurance of an industrial memory device are standardized to be about 10 V, 10 years and 10^5 cycles, respectively. Recently, organic transistor memories have been subjected to considerable attention because of their unique attractive features including mechanical flexiblility, low manufacturing cost, and low temperature processes. Floating-gate, ferroelectric, and electrets polymers have been applied in transistors to obtain memory effects. However, none of them can meet the practical requirements mentioned above. In this study, we realize a low-operation voltage and highly stable memory transistor based on a photoactive layer consisted of DPA-CM dispersed in polymethylmethacryrate (PMMA) and an electron trapping layer of poly-perfluoro-alkenyl vinyl ether (CYTOP). The dielectric layer function as an insulator under dark and a photocharge creator and/or photoconductor under photo-irradiation. This multi-functional dielectric layer brings about low voltage operation and long term retention characteristics of stored data. Under ultraviolet light irradiation, writing/erasing (W/E) processes were obtained by applying a voltage of -8 V/5 V. The observed memory characteristics indicate the practical memory devices such that a large on/off ratio of 1.48x105, the retention time >10^5 s, and reliability with more than 10^3 W/E testing cycles. The projected memory ratio remained more than 5Ã-10^3 after the operating for 10 years.

Polymer and polymer-inorganic hybrid materials organized at the nanoscale are at the heart of many devices that can be created on flexible substrates for applications in energy generation and storage, microelectronics, optoelectronics, communications and sensors. The challenge is to produce these materials using process platforms and materials sets that are environmentally and economically sustainable and can be scaled for cost-effective, high value-added manufacturing. Here we describe a resource efficient, additive approach based on roll-to-roll coating of self-assembled hybrid materials. Specifically we report that nanostructured templates with periodic spherical, cylindrical, and lamellar morphologies exhibiting sub-10 nm domains can be easily obtained through the blending of commercially available disordered polymer surfactants with commodity homopolymers that selectively associate with one segment of the surfactant. We further demonstrate that order in the surfactant systems and in block copolymer templates can be induced by nanoparticle additives that undergo multi-point hydrogen bonding with one of the segments of the polymer template. These additives, which include metal and semiconducting nanoparticles, fullerenes, and other active components, impart functionality to the device. The strong interactions further enable particle loadings of more than 40% in the target phase, resolving a crucial constraint for many applications. These systems can be scaled in our newly constructed R2R processing facility, which includes a custom microgravure coater for hybrid materials that is equipped for in-line substrate planarization and a precision R2R UV-assisted nanoimprint lithography (NIL) tool. We illustrate the capabilities of these approaches by the fabrication of floating gate field effect transistor memory devices and active layers for organic solar cells. For the memory application, the charge trapping layer is comprised of well-ordered polymer/gold NP composites prepared via additive-driven self-assembly; the addition of gold nanoparticles that selectively hydrogen bond with pyridine in poly(styrene-b-2-vinyl pyridine) copolymers yields well-ordered hybrid materials at gold nanoparticle loadings of more than 40 wt.%. The charge trapping layer is sandwiched between a dielectric layer and a poly(3-hexylthiophene) semiconductor layer. We can achieve facile control of the memory windows by changing the density of gold nanoparticles. The devices show high carrier mobility (> 0.1 cm2/Vs), controllable memory windows (0~50V), high on/off ratio (>105) between memory states and long retention times. Strategies for patterning of the device using NIL will be discussed.

A key aspect in order to fabricate thin film systems on plastic is the ability to process materials at low temperatures, possibly below 150°C. Semiconducting polymers are attractive from this point of view as they can be processed from solution at low temperature. Since they are held together by van der Waals bonds however, they suffer from having their microstructure depend heavily on processing. For instance I will show how the degree of crystallinity and intrachain order in P3HT depends on film thickness and as a result how the transport properties in a TFT depend on thickness as well. Such dependency can be mitigated by using more crystalline materials, such as PBTTT, upon thermal annealing. While weak bonding comes with disadvantages, it also allows solution-processing. I will show how taking advantage of the inherent tendency of polymers to phase separate, we can make ultra-thin body polymer FETs from solution where device non-idealities such as short channel effects are eliminated. Oxides can be solution-processed as well and are another attractive materials family for the fabrication of systems-on-plastics. A major challenge is to elicit sufficiently good properties while maintaining low processing temperatures. I will show how we have been able to make a low-temperature oxide nano-dielectric as well as oxide TFT islands that can be cured and patterned in a single step.

We demonstrated solution-processed C₆₀ single crystal field-effect transistors (FETs) with high electron mobility of 1.5 cm²/Vs, which is the highest electron mobility in solution-processed organic transistors. We adopted C₆₀ as a channel material of FETs because of the potential as high electron mobility. High quality C₆₀ thin-films are applicable to high performance n-channel organic transistors or organic photovoltaic cells. The C₆₀ FETs were fabricated as following. For preparation of C₆₀ solution, purified C₆₀ solid was resolved into anhydrous 1,2,4-trichlorobenzene (TCB) or m-xylene. Silicon wafer with 300-nm-thick thermal oxide layer was used as a substrate. The substrate was treated to phenyltrimethoxysilane (PTS) vapor, and then PTS- self-assembled monolayer (SAM) was formed on oxide layer. The C₆₀ solution was drop-casted on the PTS-SAM and dried in a dry nitrogen-filled glove box for overnight. LiF and Al were vacuum-deposited on the substrate in high vacuum chamber with thickness of 1 nm and 60 nm, respectively. Channel length and width of C₆₀ single crystal FET were 200 μm and 350 μm, respectively. Two dimensional (2D) C₆₀ single crystals with several hundreds of micrometer size were obtained from the TCB C₆₀ solution. On the other hand, one dimensional (1D) C₆₀ crystals with several-hundred-micrometer length and several-micrometer diameter were obtained from m-xylene solution. We measured X-ray diffraction (XRD) to determine the crystallinity of the C₆₀ single crystals. From the XRD patterns, the C₆₀ single crystal fabricated from TCB solution has high crystallinity as compared to that of m-xylene. The FET characteristics were measured in the glove box. One- and two-dimensional C₆₀ single crystals were used as channel layers. C₆₀ single crystal FETs from TCB has an electron field-effect mobility of 1.5 cm2/Vs in the saturation regime, a threshold voltage of 2.7 V and a subthreshold slope of 0.89 V/decade. The mobility of 1.5 cm2/Vs is the highest mobility in C₆₀ single crystal FETs including those fabricated by physical vapor transport method. On the other hand, C₆₀ single crystal FETs from m-xylene showed an electron mobility of 0.32 cm2/Vs. This is due to low crystallinity of the 1D C₆₀ single crystals. In summary, we demonstrated high performance C₆₀ single crystal FETs with an electron mobility of 1.5 cm2/Vs. XRD patterns indicated high crystallinity of fabricated 2D C₆₀ crystals. Thus the high electron mobility of C₆₀ single crystal FETs is due to the high crystallinity.

The solution processability of organic semiconductor materials is a crucial advantage for the industrial application of organic electronic devices. It is expected that solution processing under ambient conditions should permit the low-cost production of large-area, light-weight, and flexible electronic products. In such processes, the affinity of the solvent with the surface of the substrate plays a crucial role. For example, the use of spin coating becomes increasingly difficult as the hydrophobicity of the substrate increases, because the solution is readily lost before the film can grow. Meanwhile, it has been shown that the formation of semiconductor interfaces with hydrophobic gate dielectrics improves various characteristics of thin-film transistors (TFTs), such as the mobility and the currentâ?"voltage (IV) hysteresis. However, a solution process suitable for use with highly hydrophobic substrates has yet to be established. Here, we report a novel technique for manufacturing thin films of semiconducting polymers, which we call â?opush coatingâ?. In this process, a stamp of poly(dimethylsiloxane) (PDMS) elastomer is used to squash a droplet of semiconductor solution so that it is spread over the surface of a substrate. Because the thin layer of solution is confined between the substrate and the stamp, the process can, in principle, be applied to any combinations of substrate and solvent. The method allows us to produce high-performance TFTs based on both poly(3-hexylthiophene) (P3HT) thin-film transistors (TFTs) and poly(2,5-bis(3-hexadecylthiophene-2-yl)thieno[3,2-b]thiophene) (PB16TTT) TFTs. The technique uses a tiny volume of a solution of a polymeric semiconductor that is compressed by a PDMS elastomeric stamp on the substrate. Despite the higher surface free energy of PDMS compared with the substrate, the stamp can be easily peeled off from the films, leaving the polymer films adhering to the substrates. We found that the out-of-plane (100) diffractions of the push-coated films exhibit narrower linewidths than those of the spin-coated films both for P3HT and PB16TTT. The results indicate the higher crystalline nature of the push-coated films. The field-effect mobilities of polymer TFTs fabricated by push coating was estimated to be 0.47 cm2/Vs for P3HT, which was ten times as high as that fabricated by spin coating, and 0.60 cm2/Vs for PB16TTT. The technique should be quite advantageous for the production of high-performance polymer TFTs.

Organic field-effect transistors (OFETs) have attracted considerable attention because of their potential for applications in large-area, flexible, low-cost electronics. However, it is yet regarded as a serious technological challenge to achieve sufficient current for operating OFETs with the supply of practically reasonable voltages of a few volts. For the development of higher-performance devices, numbers of material combinations are being intensively tested for the layered structure of OFETs because the interfacial phenomena are crucial in determining their device performances. As one of the unique examples, there has been considerable interest in using electric double layers (EDLs) of electrolytes for efficient application of gate electric field. Since typical thickness of the EDLs is only ~ 1 nm, much higher-density carriers are accumulated at the surface of semiconductor channels than with commonly used gate dielectrics.[1] Other methods to operate OFETs with reasonably small voltages are to use gate insulator with large dielectric constant and/or with thin layer, however, such thin gate insulator always suffering from dielectric breakdown. Here we show that it is possible to reproducibly obtain OFETS with ultra-thin gate insulator (less than 50 nm) on the top of organic semiconductors by atomic layer deposition technique (ALD). The advantages of ALD technique are that we can obtain extremely uniform, ultra-thin and pinhole free gate insulator even inside pores, trenches and cavities.[2] The capacitance of this ultra-thin gate insulator becomes as high as 3 uF/cm^2. As a consequence of such high values of capacitance, it can be estimated that application of the gate voltage of 22 V (average dielectric breakdown voltage) leads the carrier density as high as 5 x 10^13 /cm^2 which is 5 times larger than the maximum carrier density that usual SiO2 devices can be reach. We show that the mobility of rubrene single-crystal transistors with ultra-thin gate insulator is ~ 1.0 cm^2/Vs is comparable to the corresponding devices with SiO2 gate insulator. We conclude that the use of ALD technique to make ultra-thin gate insulator for OFET exhibiting high mobility and ideal characteristics in air and operating at few volts. [1] S. Ono et al., Appl. Phys. Lett. 92 103313 (2008), Appl. Phys. Lett. 97 143307 (2010). [2] D. Chiba et al., Nature Mat. 10 853 (2011).

A promising approach for large-scale fabrication of flexible and stretchable electronics using carbon nanotube (CNT) networks is described. Here, we use solution-based processing to uniformly deposit semiconductor-enriched CNTs (99 %) on 4-inch flexible polyimide (PI) substrates at room temperature, and obtain field-effect transistors (FETs) with mobility as high as ~ 80 cm2V-1s-1 with high ION/IOFF of ~ 10^4, for channel lengths down to ~2 µm [1]. The PI substrate readily turns stretchable by laser cutting a honeycomb mesh structure, thereby resulting in a robust platform for large-scale fabrication of high performance, conformal electronics and sensors. The CNT network FETs are shown to exhibit excellent uniformity with a standard deviation of ~15% in key device metrics, including mobility, ION/IOFF, and threshold voltage. To demonstrate the utility of this concept, an array of 12x8 FETs is fabricated to serve as an active-matrix backplane of a pressure sensor. The device effectively functions as an artificial electronic skin, capable of mapping touch with high accuracy [1-2]. The concept of CNT network-based flexible and stretchable active matrix circuitry can be potentially expanded to achieve multifunctional sensor tapes by adding various components. The work presents an important advance towards the practical utility of carbon nanotubes. References [1] T. Takahashi, et al, Nano Letters, in press, 2011 [2] K. Takei, T. Takahashi, et al, Nature Materials, 9, 821â?"826, 2010.

Organic transistors have potential as low-cost flexible integrated circuits since they are able to fabricated using printing process such as nanoimprint, ink-jet printing etc. In order to realize low-cost flexible devices, not only active and insulating materials but also device structures suitable for printing process are important. Recently we proposed novel device structures, namely step-edge vertical channel organic field-effect transistors (SVC-OFETs) and vertically stacked OFETs. Firstly, SVC-OFETs having a short channel length show excellent device properties such as a high operational frequency approximately 1.5 MHz, etc. In addition, both p-channel and n-channel transistors can be fabricated with only one gate electrode necessary. On the other hand, the device area per stage of stacked complementary OFETs can be reduced to half the size of a conventional planar type CMOS. Such a device structure is very promising in sparing the wiring between the two complementary transistors and thus increasing the integration density. Typical inverter performances were obtained and by replacing the active materials and electrode materials with solution processable inexpensive ones, the realization of low-cost and large-area applications can be expected. From these points of view, these new devices are able to fabricate by simple process and have a potential to produce high-speed logic circuits, radio-frequency identification tags, display devices, etc.

Conjugated polymers are multichromophoric systems with chromophore consisting of a certain number of repeat units. The absorption and fluorescence spectra shift to the red upon increasing the effective conjugation length. In prototypical MEH-PPV polymer there is a bimodal distribution of fluorescence maxima that translates into a bimodal distribution of conjugation length. The relative weight of the subensembles depends on molecular weight, film preparation conditions, and the matrix in which the chains are dispersed. The essential questions are whether the emission comes from individual chains or from electronically coupled aggregates and how the more extended "red"- chains are formed. In the current work we explore the effect of aggregation of three conjugated polymers, MEH-PPV , PFO and MeLPPP, dissolved in MeTHF in the temperature range of 80K to 300K. Previous work on solutions of alkyl- or alkoxy- subsituteds oligomers of phenylenevinylenes alread indicated a continuous bathochromic shift of the absorption band and a concomitant band narrowing upon cooling. (1) This indicates that the effective conjugation length increases. Below 180 K alkoxy-derivatives adopt a fully elongated structure. We observe a similar phenomenon for MEH-PPV. The absorption spectra are a superposition of a broad ("blue") band that shifts from 2.50 eV to 2.35 eV upon cooling and a vibrationally well resolved spectrum with a 0-0 transition near 2.1 eV (the "red"-phase). The red phase appears at a critical temperatureof 190 K and grows at the expense of the blue phase. Obviously there is a temperature-induced transformation from the blue to the red phase. While this transformtation is observed in solutions of 5 x 10-6 mol/L , the red-phase is absent in a 10-7 mol/L solution. This proves that the formation of the red-phase requires aggregation. A similarly temperature dependent superposition of blue and red features can also observed for PFO, but upon dilution only the red feature survives. Finally for MeLPPP, the absorption and fluorescence spectra are mono-modal at all temperatures. The results are indicative of a rod-coil transition in the case of MEH-PPV and PFO with a temperature dependence that is characteristic of a order-disorder transition, albeit with different driving force. In the case of MEH-PPV the planarization of the chain requires chain aggregation. According to quantum chemical calculations the potential for torsional motion of the repeat units is so shallow that the motion the solvent molecules above the glass temperature is sufficient to prevent chain elongation unless chain pairing occurs. In PFO, however, the tendency towards chain planarization is obviously strong enough to facilitate the elongation of single chains and inter-chain interaction obstructs rather helps chain elongation. (1) ST Hoffmann, H Bässler, and A Köhler* J. Phys. Chem. B, 114 (2010) 17037 (2) ST Hoffmann, H Bässler, and A Köhler* Macromolecules, submitted

Organic field-effect transistors (OFETs) are vital components in the majority of small printed circuits aimed for production via roll-to-roll methods. Polyelectrolyte-gated OFETs (EGOFETs) are of particular interest because of low operating voltage requirements even when using comparatively thick and easily printed electrolyte layers. However, the wettability incompatibility between hydrophobic semiconductor and hydrophilic polyelectrolyte has been an obstacle in EGOFET printing. In this work, we use a novel block copolymer which is utilized in a surface modification treatment that renders the electrolyte layer hydrophobic, and which enables inkjet printing of the semiconductor layer without causing any considerable electrical interference in the transistor functionality. Low-voltage operation of the resulting transistor in the range of 1 V is demonstrated. This result proves that specifically tailored molecules for surface modification can provide a route towards fully printed low-voltage EGOFET circuits.

Transparent conductive oxide (TCO) materials such as indium tin oxide (ITO) have been the main technology for development of transparent electrodes in thin film solar cells, displays and touch screen thin film devices. However, ITO is brittle and costly and is often deposited through vacuum deposition at higher temperatures (>200oC), thus limiting its higher performance to glass substrates, and limiting its use on unconventional substrates such as plastic and fabric. This work presents our latest results for composite nanofiber (CNF) materials deposited by a scalable electrospinning process as transparent electrode. Electrospinning is a highly scalable process for direction deposition of a nanomesh of ultra-fine fibers from composite ink comprised of polymers and nanomaterials such as nanotubes and nanowires. The high conductance of embedded nanomaterials provide the required current carrying capability, yet the thin profile of the CNF mesh leads to its transparency. Here, we present CNF based transparent electrodes with a performance that surpass ITO by providing less than 50 Ohm/sq sheet resistance, higher than 90% transparency, high mechanical flexibility and low temperature deposition suitable for deposition on transparent plastic and fabric substrates. We demonstrate the preliminary results for development of touch screen fabrics based on these CNF materials and demonstrate preliminary results for solution processed thin film transistors fabricated based on these materials.

In this talk, the use of printed nanotubes and nanowires for multifunctional sensing of in principal any stimuli exerted on a skin-like material is discussed. The enabled electronic-skin (e-skin) is a broad concept and can be defined as a highly bendable, ultrathin material that can conformably cover any structure while providing real-time, two-dimensional mapping of an applied external stimuli. The stimuli could include pressure (e.g., touch), temperature, strain (e.g., crack formation), humidity and chemicals, and more. E-skin presents a new class of smart materials, which provides interfacing of a system to the external ambient with high fidelity. As an example system, we demonstrate a pressure-sensitive e-skin device that utilizes nanotubes and/or nanowires as the active matrix back-plane on a truly macroscale of over 7 Ã- 7 cm² in area. Uniform device networks with superb electrical properties (mobility of up to ~ 100 cm²V^-1s^-1 and I_ON/I_OFF of ~ 10⁴) are obtained. Furthermore, the ultrathin polyimide support substrate is made stretchable by laser cutting a honeycomb mesh structure, which combined with nanotube/nanowire transistors enables highly robust conformal electronic devices with minimal device-to-device stochastic variations.

Development of a high performance and low cost encapsulation solution for organic electronics is an essential technological challenge for implementation of the â?oSystems-on-plasticâ? into ubiquitous electronic displays, flexible electronic systems, and large-area, wearable electronics. Here, we report extremely efficient gas barrier films fabricated by solution processed Chemically Derived Graphene (CDG) for gas species such as H2O and O2 known to degrade the performance of organic electronics significantly. In addition to the high gas impermeability, thin films made of CDG are optically transparent and flexible, which makes it an ideal candidate for wide variety of organic devices including OLEDs and OPV. Using P3HT films as a sensor for the oxygen gas permeation, we achieved ~300% increase in the gas barrier property with CDG films that is factor of ~30 thinner compared to commercially available Cytop TM which has shown to exhibits up to an order of magnitude lower water vapor transmission rate (WVTR) than other polymer barriers, e.g. polyvinylacetate (PVAc) and polymethylmethacrylate (PMMA). Annealing of CDG film increased the lifetime by ~200% due to improved packing of the films during the reduction process, which is confirmed by the decrease of film thickness and removal of the oxygen functional groups. Detailed gas barrier property of CDG films will be discussed based on the structural analysis of the encapsulated material by Raman spectroscopy, optical analysis by UV-Vis spectroscopy, and a proposed mechanism.

Bottom-up synthetic approaches to encoding electronic functionality into nanomaterials have been extensively studied as the core to forming device elements with functions defined by synthesis. Although these efforts have led to developments of carbon nanotubes and semiconducting nanowires based functional elements, they have been limited to single to few components due to challenges in the assembly of one-dimensional nanostructures. However, encoding functionality into graphene, a two-dimensional nanomaterial, and thus producing integrated graphene devices in a chemical synthesis had not previously been explored. Here we present an unconventional approach to synthesize monolithically-integrated graphene-graphite electronic devices. Entirely integrated arrays of graphene transistors with graphitic electrodes are formed from single-step synthesis, in contrast to multiple steps required in conventional top-down processes. The synthesized, integrated arrays can be transferred to diverse substrates, and used to demonstrate real-time, multiplexed chemical sensing. In addition, three-dimensional flexible top-gate transistors can be fabricated by vertically assembling all carbon layers.

Stability of graphene thin film is one of the essential points for its real applications in modern microelectronics. A simple and versatile bar-coating method was utilized to produce a uniform protective coating layer on the tops of CVD-grown monolayer graphene films. The protective coating layer was proved to be capable of maintaining the electronic conductivity of monolayer graphene without losing the optical transmittance. The doped graphene films after top-coating presented much higher stability under the ambient condition compared with uncoated ones. The mechanical stability of polymer coated graphene film was also investigated by mechanical friction test. The results demonstrated that the polymer coating layer can enhance both the friction force and the coefficient of friction of the graphene films and protect the graphene against damage in the repeated sliding processes.

We fabricated a 10 x 10 array of carbon nanotube (CNT) transistors on a plastic film by printing methods and evaluated their electrical properties and uniformity. In the fabrication, all device geometries were defined by printing methods. At first, gate electrodes were ink-jet printed on a polyimide (PI) films with nano-Ag ink and sintered. Next, gate insulators were formed by an ink dispenser with PI ink and cured. The average thickness of printed PI was 630 nm with a standard deviation of 4.9% estimated from the capacitance-voltage characteristics measured for Ag/PI/Ag stacked structures. Then, a 30-nm-thick SiO2 layer was sputter deposited. The source and drain electrodes were ink-jet printed and sintered. An average of the channel length was 105 microns with a standard deviation of 3.7%. Then, the sample was immersed in a 3-aminopropyltriethoxysilane (APTES) solution to functionalize the SiO2 surface by amino groups. We prepared CNT ink by extracting semiconducting CNTs to purify up to more than 95%. It was an aqueous dispersion with nonionic surfactants of polyoxyethylene alkyl ether. The CNT ink was casted to the channel regions by a dispenser. We fabricated three 10 x 10 array samples. For samples 1 and 3, the casted volume of CNT ink was varied from 13.6 to 51 nl and a 17 nl droplet of CNT ink was casted to each device in sample 2. Sample 3 was fabricated without SiO2 deposition and APTES treatment. Surfactants were removed from the CNT channels by a combination of heat treatments and wet processes. The transfer characteristics measured with a gate voltage of - 20V to + 20V showed p-type behavior. For sample 1, as the CNT ink volume increased, the on current (I_on) increased. On/off ratio depended on the I_on value and a maximum on/off ratio was more than 10,000. For sample 3, a maximum on/off ratio was about 1,000 and the I_on value was less than that for sample 1 by more than an order of magnitude. The difference is due to the morphology of the CNT networks. The casted droplet of the CNT ink is stable and the edges are pinned on the surface. In this case, CNTs tend to be deposited at the droplet edge and a ring shaped condensed region so-called â?ocoffee stainâ? is formed. The â?ocoffee stainâ? deteriorated the electrical properties for sample 3. For sample 1, the amino functionalized SiO2 surface effectively adsorbed CNTs even in the middle of the droplet and homogeneous CNT network can be formed. It resulted in the good electrical properties of the printed CNT transistors. For sample 2, the relationship between I_on and on/off ratios was entirely consistent with that for sample 1. It clearly shows the good reproducibility of our print fabrication. A standard deviation of I_on for sample 2 was about 30%. It is reasonable value considering the fluctuations of the PI thickness and channel length. We also obtained a high performance printed CNT transistor that had a high mobility of 3.6 cm2/Vs with an on/off ratio of about 1,000.

Photogenerated current measurements on PLED device structures reveal that next to the known Langevin recombination also trap-assisted recombination is an important recombination channel in PLEDs. The dependence of the open-circuit voltage on light intensity enables us to determine the strength of this process. Numerical modeling of the current-voltage characteristics incorporating both Langevin and trap-assisted recombination yields a correct and consistent description of the PLED, without the traditional correction of the Langevin pre-factor. At low bias voltage the trap-assisted recombination rate is found to be dominant over the free carrier recombination rate. As a result, we show that the ideality factor in the diffusion regime of a bipolar diode is governed by the recombination of trapped electrons with free holes. As a next step we quantify the magnitude of non-radiative trap-assisted recombination and exciton quenching from the metallic cathode. The results revealed that thin devices suffer from cathode quenching although the contribution of non-radiative trap-assisted recombination is significant and increases fast with thickness. For devices thicker than 100nm non-radiative trap-assisted recombination is shown to dominate the current efficiency loss by up to 45%.

Small organic molecular semiconductors have the potential to ease fabrication and packaging constraints on organic electronic devices such as OLEDâ?Ts or organic photovoltaics due to their increased lifetimes in oxygenated environments. As the desire to print these materials in complex geometries on low temperature, flexible substrates for advanced electronic devices continues to grow, new techniques have been developed to accomplish these goals. Here we discuss a laser-based approach known as blister-actuated laser induced forward transfer (BA-LIFT), to produce conformal, high resolution patterns of small molecule organic luminescent materials onto a polymer substrate. In traditional laser transfer processes, organic molecules are especially susceptible to thermal, optical and mechanical damage during the printing process. However, our novel technique uses a thick polymer laser absorbing layer which protects the delicate organic material during the transfer process. In this non-contact method, individual droplets of solution as small as 10 um are dispensed on the surface of interest while a computer controlled manipulation stage combined with a high repetition rate pulsed laser allows for rapid pattern formation on arbitrary surfaces. We discuss the details of this technique with detailed characterization of material properties to demonstrate damage free transfers in a variety of luminescent materials. We further apply this technique to the fabrication of patterned [Ru(dtb-bpy)3]2+(PF6-)2 electroluminescent devices in ambient conditions. Devices are shown to exhibit emission spectra, luminous efficiencies, and lifetimes similar to literature values of devices fabricated in nitrogen environments.

Organic semiconductor devices are attracting considerable attention based on applicability of simple printing production processes, and mechanical flexibility, in prospect of establishing plastic and printed electronics industry. Since such solids are assemblies of van-der-Waals bonded Ï?-conjugated molecules, macroscopic transport is composed of intermolecular charge transfer of Ï?-electronic carriers, which necessarily results in its sensitivity to molecular arrangement. The effect of external pressure in such devices is fundamentally important because of vulnerability in molecular displacement against relatively small force, regarding the bending performances and even functions of pressure sensors for industrial applications. Here, we introduce a method of measuring the effect of hydrostatic pressure on the conductivity in organic semiconductor crystals inducing high-mobility charge with the application of electric field at the semiconductor surfaces. It has been established for some high-mobility organic semiconductors with the structure of field-effect transistors (FET) that band-like transport is realized for the surface charge with relatively low carrier density less than 10¹² cm^-2, artificially introduced in an intrinsic semiconductor composed of a single molecular species. The mobility in such organic single-crystal FETs already exceeds 10 cm²/Vs in several compounds. In addition to the measurement of common transfer characteristics of drain current I_D as a function of gate voltage V_G, we perform four-terminal conductivity measurement to exclude extrinsic influence of the metal/semiconductor contact resistance. Moreover, we measured Hall coefficient simultaneously to deduce the pressure coefficient estimating the change in dielectric capacitance and thickness of the gate dielectric insulators, providing a route to study "structure-property" relation. For rubrene single-crystal transistors, the size of thus deduced pressure dependence of mobility turned out to be about 7 times larger than in the typical experiments reported for silicon and other inorganic semiconductors. Interestingly, the mobility starts to decrease with further increasing pressure above 600 MPa. Noting that the organic solids are composed of molecules with peculiar shape, the application of pressure not only diminishes distance between centers of adjacent molecules but relative positions of equivalent atoms in the two molecules. It is speculated that the anomalous negative pressure effect can be caused by such additional degrees of freedom in molecular solids.

Understanding of the microscopic charge transport in organic thin-film transistors (OTFTs) still remains at a premature level although the issue attracts considerable recent attentions in a vast field of materials science. Whether in small-molecule or polymer OTFTs, the channels are usually composed of polycrystalline films that exhibit much higher mobility than amorphous ones. Although the polycrystalline films are quite useful because of the higher productivity and usability compared with single crystals, their transport properties are more or less affected by the domain boundaries. The boundaries should form trapping or scattering centers that could be a bottleneck against charge transport in OTFTs. However, the comparative evaluation of the charge transport inside crystal domains and across domain boundaries is quite difficult by the conventional transport measurements because of the nonuniform domain structures whose size is usually below a micrometer scale. Here we report the microscopic observation of the intra- and interdomain carrier dynamics in the polycrystalline OTFTs by utilizing field-induced electron spin resonance (FI-ESR) spectroscopy.^[1] We selected dinaphtho[2,3-b:2â?T,3â?T-f]thieno[3,2-b]thiophene (DNTT) and poly(2,5-bis(3- hexadecylthiophene-2-yl)thieno[3,2-b]thiophene) (PB16TTT) as small-molecule and polymer semiconductors, respectively, both of which exhibit uniaxial alignment of layered microcrystal domains on the substrates. The FI-ESR spectra were measured under applied gate voltage while the drain electrode is shorted to the source electrode.^[2,3] By measuring temperature dependence of the FI-ESR spectra at appropriate magnetic field directions, we successfully observed two types of motional narrowing effect. At the magnetic field perpendicular to the substrate, we observed the motional narrowing due to the intradomain trap-and-release carrier motion. The activation energies of the carrier motion were estimated at 5â?"21 meV. We consider that the energies should correspond to the binding energy of shallow traps inside microcrystal domains. In contrast, at the magnetic field parallel to the substrate, we observed another motional narrowing due to the carrier hopping across the domain boundaries, whose activation energies were estimated at 45â?"86 meV. We found that the activation energies coincide well with those of the effective mobilities estimated from the temperature dependence of transfer characteristics. Based on the observations and the analyses, we demonstrate that the charge transport should be limited by the potential barriers between microcrystal domains in both the small-molecule and polymer OTFTs. [1] H. Matsui et al., submitted. [2] H. Matsui et al., Phys. Rev. Lett. 100, 126601 (2008). [3] H. Matsui et al., Phys. Rev. Lett. 104, 056602 (2010).