Symposium Organizers
Stephanie P. Lacour University of Cambridge
Siegfried Bauer Johannes-Kepler Universitaet Linz
John Rogers University of Illinois, Urbana-Champaign
Barclay Morrison Columbia University
JJ1: Stretchable Bioelectrodes
Session Chairs
Thursday PM, April 08, 2010
Room 2000 (Moscone West)
9:30 AM - **JJ1.1
PDMS-based Neural Interfaces: An Integrated System Solution.
Stephen DeWeerth 1 , Liang Guo 1
1 Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractRecent trends in neural interface fabrication for prosthetic applications have shifted from the use of rigid materials to the use of soft materials in order to better match the low mechanical impedance of soft tissues. Among the many soft materials employed as substrate in neural interface fabrication, polydimethylsiloxane (PDMS) appears to offer excellent potential for better impedance matching. However, PDMS is very challenging from a fabrication perspective. Two major challenges exist: (1) although neurophysiology and neural prosthetics frequently require a high-density implementation, the density of a microelectrode array (MEA) that can be achieved on a PDMS substrate is significantly limited by the difficulties in patterning high-resolution features and in wiring high-density microelectrodes; (2) although rigid electronics is an essential part of neural interfacing technology, it has been very difficult and inefficient to package PDMS-based devices with electrical functionality, and to robustly connect these devices to external rigid electronics, such as standard silicon-based integrated circuits (amplifiers and stimulators alike in particular). As a result, the otherwise widespread application of such appealing devices has significantly been limited.In order to address the challenges associated with PDMS fabrication, we have recently developed a set of technological advances, which open the door for numerous applications that would benefit from such compliant interfaces. We have implemented conical-well microelectrodes (as small as 10 micrometers in diameter), which potentially provide an improved physical contact to soft tissue surface and a uniform current density distribution during microstimulation. We have also developed a multilayer interconnect technology within PDMS, which facilitates the implementation of high-density MEAs. Finally, we have developed a multilayer via-bonding technology that provides integrated packaging for such PDMS-based devices. With these advances, we are, therefore, able to offer an integrated system solution to applications involving PDMS-based neural interfaces (e.g., a PDMS-based MEA can be directly integrated with the silicon die of an amplifier and packaged as an integral implant for neural prostheses). We have characterized the multichannel recording and stimulation capabilities of our PDMS-based MEAs by epimysial (i.e., on the muscle surface) recording and stimulation experimentation. The device conformed to the muscle surface very well even at maximum contraction without any discontinuity of the recording signals. While these PDMS-based MEAs were initially developed for spinal cord surface stimulation, we now have multiple ongoing research projects on applications of these integrated PDMS-based MEAs (including peripheral nerve regeneration for prosthetic arm control) with an emphasis on epimysial recording and stimulation for prosthetics.
10:00 AM - JJ1.2
Electrical, Mechanical and Thermal Studies on Stretchable Electrodes.
Wenzhe Cao 1 , Oliver Graudejus 2 , Joyelle Jones 1 , Sigurd Wagner 1
1 , Princeton University, Princeton, New Jersey, United States, 2 , Arizona state university, Tempe, Arizona, United States
Show AbstractWe have been focusing on stretchable microelectrode arrays (SEMAs) for traumatic brain injury (TBI) research. SMEAs are two-dimensional arrays of thin-film gold electrodes patterned on elastomeric polydimethylsiloxane (PDMS) substrates, and encapsulated with photopoatternable silicone (PPS) insulator. We consider this as a building-block of electronic skin. We have studied two structures of electrodes—bare electrodes without top PPS layer and encapsulated electrodes with PPS layer. 5mm long and 50μm wide electrodes remain electrically conducting up to at least 80% strain. The resistance is increasing nearly linearly with strain. However, encapsulation electrodes have a lower resistance than unencapsulated electrodes, but their electrical resistance changes more with applied strain.Our gold/PDMS structure also possesses a special thermal property. The coefficient of thermal expansion (CTE) of the PDMS substrate is more than 20 times larger than that of gold. Therefore, changing the temperature causes large different thermal strain, which affects the resistance of the gold electrodes. We have measured the resistance change in a temperature-controlled environmental chamber, and observed that the resistance rises nearly linearly with the temperature. We will describe the structure and fabrication of the stretchable electrodes, and present the protocols and results of the electro-mechanical and electro-thermal experiments. This research is supported by the New Jersey Commission on Brain Injury Research.
10:15 AM - JJ1.3
Compliant Electrodes for Neural Interfaces.
Ivan Minev 1 , Pouria Moshayedi 2 , Stephanie Lacour 1
1 Nanoscience Centre, University of Cambridge, Cambridge United Kingdom, 2 Physics of Medicine Centre, University of Cambridge, Cambridge United Kingdom
Show AbstractCells are able to sense and respond to a mismatch between naturally compliant and artificially stiff implant surfaces. We are developing a soft MEMS approach that may be a suitable route for improved biocompatibility between neurons, related glial cells and electrode devices. Compliant electrodes are prepared with thin gold films (50 nm thick) deposited on polydimethylsiloxane (PDMS) substrates. The conducting tracks to the micro-electrodes are passivated with a 1µm thick layer of parylene. The electrode site is 5 x 104 µm2. In air, such composite structures remain electrically conductive when strained up to 20%. Here, we report on the electromechanical properties of parylene-gold-PDMS micro-electrodes immersed in physiological solution. We have designed a dedicated platform to probe and stretch the electrodes in a wet environment. Impedance spectra are recorded in the 1Hz to 500 kHz range and at applied strains of up to 20%. At 1 kHz, the recorded impedance is ~ 200 kΩ. The electrode impedance is little affected by the uni-axial stretch. An R,C model of the stretchable electrode is proposed. We have conducted a preliminary biocompatibility test: fibroblasts and primary astrocytes are cultured in vitro on the compliant electrodes. The cells plate and spread onto the polymeric electrode surface. Characterisation after up to 3 month exposure to physiological medium at 37°C is now required.
10:30 AM - **JJ1.4
Stretchable Bioelectrodes.
B. Ziaie 1
1 School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana, United States
Show AbstractStretchable electrodes as cell culture platforms have recently garnered particular attention for their utility in studying cellular behavior central to several important pathologies such as traumatic brain injury, cardiomyopathy, and vascular disorders. A central theme common to these diseases is the subjection of tissue to strain. The ability to record and stimulate nerve and muscle cell populations while subjecting them to mechanical strain can provide insights into mechanism of the aforementioned diseases. In addition, stretchable electrodes can be used to study stem cell differentiation since it is widely believed that mechanical cues are important in this process. Most reported stretchable electrodes are based on the evaporation of a thin gold layer on a PDMS substrate. While many of these electrodes can be stretched to tens of percent, they are not very robust [1-5]. In this work, we present a stretchable electrode array using room temperature liquid-alloy filled microchannels as interconnects and miniature gold nail-head pins as the electrodes.Stretchable electrode array which consists of two PDMS layers (25.4x25.4mm2). The top layer incorporates subsurface liquid-alloy-filled microchannels (600μm height, 500μm width) and provides a biocompatible exterior surface for cell culture. The bottom layer is bonded to the top layer, sealing the microchannels. Gold coated nailhead pins (250μm tip diameter and 1.75mm spacing) acting as electrodes are placed in the channels with their sharp head punched through the top PDMS layer and their flange-shaped nail-head bottom flush against the PDMS sealing the junction. Fusible indium alloy (liquid at room temperature) filled microchannels are used to connect the electrodes to the outside, thus providing the required stretchability. The electrode platform is biocompatible and can withstand strains of up to 40%. We tested these electrodes by repeatedly (100 times) subjecting them to 35% strain and did not notice any failure. The electrode impedance was measured between two electrodes at 1kHz with the platform stretched by 5% strain increments and decrements. Impedance measurement results showed a constant impedance of ~ 1.1kΩ with applied strains of up to 35%. We also successfully cultured mice cardiomyocytes onto the platform and performed electrical pacing. [1] S. P. Lacour, C. Tsay, S. Wagner, Y. Zhe, and B. Morrison, B., 2005 IEEE Sensors, pp. 617-620.[2] J. Blundo et al., Proceedings of the ASME 2007 BioEng. Conf., June 2007, Colorado USA.[3] D.-H. Kim et al., Science, 320 (2008), pp.507-511[4] J. Xiao et al, Appl. Phys. Lett., 93 (2008), pp013109-1-3.[5] M. Maghribi et al., 2002 IEEE-EMBS, pp. 80-83.
11:00 AM - JJ1:Bioelectrode
BREAK
JJ2: Electrode-tissue Interfaces
Session Chairs
Thursday PM, April 08, 2010
Room 2000 (Moscone West)
11:30 AM - JJ2.1
Silicon-on-Insulator (SOI)-based Integration of Neural Electrodes on Fully Flexible Parylene Substrates.
Ke Wang 1 , Marice van Deurzen 2 , Nico Kooyman 2 , Michel Decre 1
1 Healthcare Devices and Instrumentation, Philips Research Laboratories Europe, Eindhoven Netherlands, 2 MiPlaza, Philips Research Laboratories Europe, Eindhoven Netherlands
Show AbstractThe integration of MEMS and circuits on plastic substrates has received increasing interest over the past years. We present a substrate transfer technology which allows devices to be fully processed using conventional silicon-based fabrication techniques prior to their integration with parylene. A substrate transfer technology, named CIRCONFLEX, in which RF circuits fabricated on Silicon On Insulator (SOI) wafers were transferred onto ultra-thin polyimide films, was developed earlier in our organisation. The functionality of the circuits after the transfer and while bended has been demonstrated [1] [2]. This work presents an extension of the CIRCONFLEX process to integrate circuits fabricated at high temperatures onto parylene substrates.
In the substrate transfer method we have investigated, the circuits were first fabricated on standard silicon substrates using conventional processes. Parylene was then deposited at room temperature, and the substrate was glued onto a glass carrier. After the removal of the silicon substrate, processing could continue (ex. second parylene deposition, bond pad opening) before the devices were released from the glass carrier. In the final product, a metal layer is sandwiched between two stacks of oxide/nitride and parylene. The layer thicknesses are symmetric on each side in order to balance the stress in the critical (metal) layer.
A parylene-based metal microelectrode array with high-temperature silicon oxide and nitride passivation layers was realized. Unlike existing techniques which directly deposit layers on parylene [3], the devices are fully processed using conventional fabrication conditions prior to their integration with parylene. This substrate transfer technology could enable the use of high quality films (e.g. single-crystalline silicon, LPCVD silicon nitride) in parylene-based devices, thus contributes towards the realization of truly flexible, biocompatible integrated circuits. We also report measurements of the integrity and functionality of the parylene-based circuits after the transfer process and under mechanical stress.
By combining the advantages of high quality devices from well-established processes with thin, flexible and biocompatible substrates, this technology could provide exciting new opportunities, especially in biomedical applications such as implantable neural interfaces.
References
[1] R. Dekker, et al., “A 10 μm thick RF-ID tag for chip-in-paper applications”, Proceedings of the Bipolar/BiCMOS Circuits and Technology Meeting, pp. 18- 21, 2005.
[2] R. Dekker, et al., “CIRCONFLEX: an Ultra-Thin and Flexible Technology for RF-ID Tags”, EMPC 2005, June 12-15, Brugge, Belgium.
[3] D. C. Rodger, et al., “Flexible parylene-based multielectrode array technology for high-density neural stimulation and recording”, Sensors and Actuators B, 132, pp. 449-460, 2008.
11:45 AM - JJ2.2
The Stretchable Microelectrode Array: Recent Progress on a Compliant Interface for Brain Tissue.
Cezar Goletiani 1 , Zhe Yu 1 , Oliver Graudejus 2 , Wenzhe Cao 3 , Sigurd Wagner 3 , Barclay Morrison 1
1 Biomedical Engineering, Columbia University, New York, New York, United States, 2 Center for Adaptive Neural Systems, Arizona State University, Tempe, Arizona, United States, 3 Department of Electrical Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractWe continue to improve the stretchable microelectrode array (SMEA), which is a highly compliant, stretchable interface for brain tissue, in vitro. We are using the SMEA to study functional changes after in vitro traumatic brain injury (TBI). This application is especially demanding because it requires significant mechanical deformation, ~20% biaxial strain. In the current study, the fourth generation of SMEA was examined. In this generation, the electrode count was increased to 28, the electrode dimensions reduced to 50x75 μm, the packing density increased (inter-electrode distance of 100 μm), and the spatial precision of the soft photolithography improved (100x100 μm size of the vias). The SMEAs were fabricated on polydimethylsiloxane from stretchable conductive layers (2.5nm Cr/ 25-100nm Au/ 2.5nm Cr) deposited by electron beam evaporation. The metal was patterned photolithographically into an array of discrete electrodes. The metal was then encapsulated with a layer of photopatternable silicone. The SMEA were packaged in a printed circuit board so as to be compatible with a commercially available, multichannel amplifier.Brain slice cultures of rat hippocampus were placed in the center of the SMEA and grown for 12 days to ensure adhesion. To induce injury, the substrate, embedded SMEA and adherent tissue were equi-biaxially stretched using our well-characterized injury model. Injury severity was verified by high speed video to confirmed whether the tissue remained adhered to the SMEA during stretch. Both before and after injury, spontaneous and evoked electrical activity was recorded with the SMEA. A significant advantage of the SMEA is that post-injury activity can be normalized to pre-injury activity serving as a powerful internal control. Immediately after stretch, injured cultures exhibited spontaneous bursting activity, which was indicative of epileptiform activity. In response to electrical stimulation, injured cultures generated multiple spikes and bursts, whereas uninjured controls did not. We hypothesize that this bursting activity may be the result of an imbalance between inhibitory and excitatory neuronal circuits due to the mechanical injury. The SMEA are enabling ongoing studies to determine the underlying cause(s) of these functional changes. In summary, our results demonstrate that this new generation of SMEA survives large mechanical deformations and is well suited for monitoring electrophysiological consequences of TBI.
12:00 PM - **JJ2.3
Effects of Soft Neural Interfaces on Cortical Response.
Dustin Tyler 1 2 , James Harris 1 , Christian Zorman 3 2 , Christoph Weder 5 , Stuart Rowan 4 , Jeffrey Capadona 2 1
1 Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 2 Reseach, Louis-Stokes Cleveland Dept Veteran's Affairs Medical Center, Cleveland, Ohio, United States, 3 Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, Ohio, United States, 5 Polymer Chemistry and Materials, Adolphe Merkle Institute, University of Fribourg, Marly, Fribourg, Switzerland, 4 Macromolecular Science, Case Western Reserve University, Cleveland, Ohio, United States
Show AbstractThe neuroinflammatory response and preservation of neurons in proximity to neural interface devices in the cortex is affected by the mechanical properties of the device. The hypothesize is that mechanical modulus mismatch between neural interfaces and the neural tissue contribute to the inflammatory and neurodegenerative response to implanted devices within the brain. Despite significant in-vitro data about specific cell-type's response to substrate modulus, long-term in-vivo studies of soft substrates for neural interfaces have been limited by availability of compliant materials that can be chronically implanted into the brain. Recent advances with a mechanically-dynamic nanocomposite material that is stiff for insertion into the brain and then becomes soft within 14 minutes of implant have enabled these studies. The cortical tissue response to the dynamic material was compared to a Tungsten wire coated with a thin layer of the dynamic material for surfaced-matched chemistry but higher overall device modulus. The dimensions and shape of the two implants tested were similar. While active astrocytic and total microglia are increased around the softer material at 4- and 8-weeks post-implant, the activated microglia re decreased. More importantly, the number of neural cell bodies near the probe are higher for the softer material. Structure and fabrication of mechanically-dynamic neural interfaces and the neural response to these devices will be presented. This new class of material is highly promising for the next generation of neural interfaces.
12:30 PM - **JJ2.4
Improving Neural Implant Biocompatibility via Biomimetic Design.
Erdrin Azemi 1 2 , Shawn Sapp 4 , Silvia Luebben 4 , Tracy Cui 1 2 3
1 Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Center for Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 4 , TDA Research Inc, Golden, Colorado, United States, 3 McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractMicro-fabricated neural electrode array, placed in the nervous system to directly interface with neurons, have tremendous clinical and research significance. Current arrays are mostly made of stiff metal and semi-conductor materials, and they experience chronic failure due to the inflammatory tissue responses characterized by neuronal loss and glial scarring around the implant. Several biomimetic strategies are being investigated to improve their biocompatibility and long-term performance within the host brain tissue. The first strategy is immobilization of biomolecules (obtained from brain) onto the implant surface to promote attachment and growth of neurons while suppressing the adsorption of plasma protein and glia. These modifications have been characterized in vivo and showed improved neuronal health and reduced reactive glial response around the implant. The chronic neural recording performance of the modified probes is being evaluated currently. Secondly, a on-command release coating that can actively deliver anti-inflammatory or neuroprotective drugs is being developed. A number of drug molecules have been incorporated in the polymer coating and electrical stimuli can trigger the drug release repeatedly. This command driven release may be combined with a real time monitoring system so that once an onset of tissue inflammation is detected, an electrical stimulus will be given to trigger the release of the drug at a controlled dose. Thirdly, elastomeric conducting and insulating polymers that have the mechanical properties similar to those of brain tissue were synthesized for developing the new generation of soft neural electrode arrays. Soft arrays are hypothesized to cause less inflammatory tissue response. Our initial in vitro culture assays showed that soft wires made of the new materials recruited and activated less microglia in culture than the stiff tungsten wires, one of the primary elements of chronic microwire arrays. Furthermore, surface modification can be done to the soft materials to further improve their biocompatibility.
JJ3: Soft Actuators
Session Chairs
Thursday PM, April 08, 2010
Room 2000 (Moscone West)
2:30 PM - **JJ3.1
Long-lifetime All-polymer Artificial Muscle Transducers.
Roy Kornbluh 1 , Ron Pelrine 1 , Annjoe Wong-Foy 1 , Harsha Prahlad 1 , Brian McCoy 1 , Marcus Rosenthal 2 , James Biggs 2
1 , SRI International, Menlo Park, California, United States, 2 , Artificial Muscle, Inc., Sunnyvale, California, United States
Show AbstractElectroactive polymer transducers are an emerging technology with the promise of offering higher levels of performance at reduced cost compared to other transducer technologies. In particular, it has been shown that dielectric elastomers produce maximum actuation strains of over 100% and specific energy density exceeding that of any known electric-field induced technology. This performance is achieved using relatively low-cost commercially available polymer materials such as acrylic and silicone elastomers. A majority of the published data on these actuators have been at peak-performance or “over-driven” conditions which offer a relatively short operational lifetime (typically 100s or 1000s of cycles) particularly under adverse conditions such as high humidity. It has been hypothesized that, in order to produce a reliable product using dielectric elastomers, it is simply necessary to operate at reduced stress conditions and minimize stress concentration factors. Recent tests have been carried out on both acrylic and silicone material systems that do show long lifetimes at performance levels that meet specifications for commercial products – even in adverse environments. For example, we have shown lifetimes exceeding 1 billion cycles at ambient conditions and more than 10 million cycles at accelerated aging conditions of 65° C / 85% RH with actuation strains of at least 5%. In more controlled humidity and temperature controlled indoor environments, lifetimes of several million cycles and strains of more than 20% have been achieved. Such performance levels and environmental tolerance are sufficient for several applications including haptic interface devices, medical pumps (implantable and external), optical positioners, and "artificial muscle" devices for replacing small damaged muscles. These applications can exploit the unique capability of dielectric elastomers to make soft conformal devices that allow for a good transfer of energy to human tissue while minimizing discomfort and damage. Improvements in materials, actuator design and packaging may be expected to further improve the performance levels at which long operational lifetimes may be achieved.
3:00 PM - JJ3.2
Biomimetic Dielectric Elastomer Actuators Operated Under Charge and Voltage Controlled Conditions.
Xuanhe Zhao 1 , Christoph Keplinger 1 2 , Siegfried Bauer 2 , Zhigang Suo 1
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Soft Matter Physics, Johannes Kepler University Linz, Linz Austria
Show AbstractSubject to applied voltages or charges, dielectric elastomer actuators can give large strains over 100%, and vary among complex shapes. Due to its softness and versatility, dielectric elastomers are a promising material for compliant actuators and biomimetic organs. Designing such devices, however, has been challenging due to large deformation, electromechanical coupling, and diverse modes of failure. Existing computational methods, however, have only been demonstrated for relatively simple configurations.In this work, we present a method capable of solving the electromechanical coupling in dielectric elastomers with arbitrary configurations and deformations. We use the method to analyze biomimetic optical and haptic devices, i.e. an artificial eye and artificial skin. The devices can be operated under two actuation modes: charge control or voltage control. We show that the failure modes of the devices are different under different actuation modes. In addition, we prove that a charge-controlled dielectric elastomer without electrodes avoids the electromechanical pull-in failure mode.Acknowledgments: Work partially supported by the Austrian Science Funds and the Austrian Marshall Plan Foundation.
3:15 PM - JJ3.3
Aptitude of Dielectric Elastomer Transducers for Energy Harvesting Generators.
Christoph Keplinger 2 1 , Tiefeng Li 2 , Jian Zhu 2 , Zhigang Suo 2 , Philipp Maechler 1 , Martin Kaltenbrunner 1 , Reinhard Schwoediauer 1 , Nikita Arnold 1 , Siegfried Bauer 1
2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 1 Soft Matter Physics, Johannes Kepler University Linz, Linz Austria
Show AbstractDielectric elastomer actuators promise to combine high energy density at low cost and weight when used as transducer for energy harvesting generators. Only sparse research has been done on the aptitude of dielectric elastomer transducers for such energy harvesting applications. Here we present an experimental realization of an energy harvesting cycle operating between two charge reservoirs at different electrical potentials, and analyze its performance in a thermodynamic description with finite element modeling tools.Dielectric elastomer transducers consist of an elastomer membrane sandwiched between a pair of compliant electrodes. From an electrical point of view, such an arrangement is a parallel plate capacitor with variable capacitance. When the elastomer membrane is stretched mechanical energy is stored to be then transformed into electrical energy. Therefore, the system is charged with a small input voltage at the stretched state. Reducing the membrane stretch under open-circuit conditions lifts the fixed amount of charge to a higher electrical potential due to the decrease in capacitance resulting from the deformation. Thus, the fixed amount of charge times the increase in electrical potential is harvested per operation cycle of the device.In our experimental set-up of such a dielectric energy harvester, the mechanical energy is supplied via inflation of an elastomer membrane with compressed air to a balloon shape. The harvesting results are compared with a thermodynamic model of the system. To estimate the maximal harvestable energy per cycle the device is operated close to the material limits of the used elastomer. These limits include the dielectric breakdown strength limiting the maximum useable electrical field, the stretch of rupture limiting the deformation and the borderline of the electromechanical pull-in instability. Likewise, the theoretical description covers these limits as well as it pays attention to the inhomogeneous deformation in the balloon shaped operational state, taking advantage of the finite element method.The experimental results accompanied by the theoretical analysis may be used as a benchmark for the aptitude of dielectric elastomer generators in harvesting applications. Renewable energy sources like ocean wave harvesting, but also consumer electronics where dielectric elastomer generators could increase the lifetime of mobile energy sources or even make them obsolete may pave ways for using such highly compliant electronic devices.Acknowledgments: Work partially supported by the Austrian Science Funds and the Austrian Marshall Plan Foundation.
3:30 PM - **JJ3.4
Bistable Electroactive Polymers (BSEP): Rigid Polymers Actuated to Greater than 100% Strain.
Qibing Pei 1
1 Materials Science and Engineering, UCLA, Los Angeles, California, United States
Show AbstractThe ability to produce reversible, large-strain, bistable actuation has been a major challenge in the pursuit of smart materials and structures. Conducting polymers are bistable, but the achievable strain is small. Large deformations have been achieved in dielectrical elastomers at the sacrifice of mechanical strength. The gel-like soft polymers generally have elastic moduli less than 10 MPa. The deformed polymer relaxes to its original shape once the applied electric field is removed. We report new, bistable electroactive polymers (BSEP) that are capable of electrically actuated strains greater than 200%. The BSEP could be useful for constructing rigid structures. The structures can support high mechanical loads, and be actuated to large-strain deformations. We will present a few applications based on the BSEP, including Braille displays that can be quickly refreshed and maintain the displayed contents without a bias voltage.
4:00 PM - JJ3:Actuators
BREAK
JJ4: Soft Transducers
Session Chairs
Thursday PM, April 08, 2010
Room 2000 (Moscone West)
4:30 PM - **JJ4.1
Highly Stretchable Transparent Electrodes Made by Ion Implantation of Elastomers.
Herbert Shea 1
1 IMT, EPFL, Neuchatel Switzerland
Show AbstractWe report on the use of low-energy metal ion implantation by filtered cathodic vacuum arc to create highly deformable electrodes on polydimethylsiloxane (PDMS) membranes. Implantation of metal ions at energies from 2 to 10 keV in PDMS and polyurethane leads to a network of nanometer-size clusters in the first 50 nm below the surface. Unlike sputtered or evaporate metals films that cease to conduct at strains of order 3%, the implanted films conduct at strains of up to 175% because these small clusters can move relative to one another, maintaining electrical conduction when the elastomer is stretched. The nanostructure also leads to a much lower stiffness than a thin film with the equivalent amount of metal atoms.Sheet resistance vs. ion dose and vs. uniaxial strain, time stability of the resistance, and the impact of implantation on the elastomer’s Young’s modulus were investigated for gold, palladium, copper and titanium implantations. Gold electrodes have the best performance, combining low surface resistance (down to 20 ohm/square) that is very stable (unchanged after 2 years), strains of up to 175% before loss of electrical conduction, and low impact on the Young’s modulus of the underlying PDMS membrane. Lower ion doses (10^16 ions/cm^2) lead to smaller average particles size (20 nm) and allow larger maximal strains while remaining conductive, but with higher sheet resistances than films made with high ion doses. Our electrodes have been cyclically strained to 30% for more than 10^5 cycles and remain conductive. The films can also be used as sensors by exploiting the strain dependence of the resistance.Additionally, metal ion implantation allows for creating semi-transparent electrodes, with 60% optical transmission in the visible and near-IR for 30 µm-thick ion implanted PDMS membranes. When the implanted PDMS membranes were exposed to gamma and to 3.5 MeV proton irradiation at doses up to 1 Mrad, no change in electrical characteristics was observed, but a decrease by a factor of up to 2 in optical transmission did occur.The implantation technique presented here allows the rapid production of reliable stretchable electrodes for a number of applications, including dielectric elastomer actuators and foldable or rollable electronics. Application to arrays of tunable electroactive microlenses are presented.
5:00 PM - JJ4.2
Electrical Breakdown in Soft Elastomers: The Direct Influence of Stiffness in Un-prestretched Elastomers.
Matthias Kollosche 1 , Hristiyan Stoyanov 1 , Guggi Kofod 1
1 , Institut für Physik und Astronomie, Potsdam Germany
Show AbstractThe relation between electrical breakdown and mechanical properties in soft polymeric materials is a question of particular interest for multiple applications of smart materials. Typically, this relation is investigated on a single material varying the temperature. The temperature change influences the Young’s modulus, typically softening the material under study, but it also affects other factors that may influence the electrical breakdown, such as conductivity. Here, we present experiments that are performed at a constant temperature, on blends of two chemically identical tri-block thermoplastic elastomers with different stiffness, avoiding uncontrolled variation in other parameters. Stress-strain measurements proved that continuous variation in mechanical properties could be obtained, a range of 176 – 316 kPa was found. For the breakdown experiment the elastomer material was dissolved, cast and dried on a planar electrode before exposing it to a high electrical field. Measurements on the prepared film show that the breakdown field increases with Young’s modulus. The results were compared to the original Garton-Stark electro-mechanical instability theory and to a recent theory by Zhao and Suo that incorporates the effect of a mechanical load. Discrepancies between the results and the theories could be mitigated by proper adaptation of boundary conditions and the use of the Neo-Hookean constitutive equation. This study presents an approach that uses a hyperelastic material behavior and a realistic description of boundary condition of the used electrode in the experimental setup, with this model an improved description of electrical breakdown behavior of soft materials is possible.
5:15 PM - JJ4.3
Stretchable and Washable Electronics for Embedding in Textiles.
Thomas Vervust 1 , Frederick Bossuyt 1 , Fabrice Axisa 1 , Jan Vanfleteren 1
1 Elis/CMST, UGent, Ghent Belgium
Show AbstractElectronics in “wearable systems” or “smart textiles” are nowadays mainly realized on traditional interconnection substrates, like rigid Printed Circuit Boards (PCB) or mechanically flexible substrates. The electronic modules are detachable to allow cleaning and washing of the textile. The lack of technology for real integration of textile compatible electronics with high functionality is one of the factors which prevent a breakthrough of ”smart textile” products at the moment. In order to achieve a higher degree of integration and user comfort, IMEC-UGent/CMST developed a technology for flexible and stretchable electronic circuits. This submission describes the stretchable electronics technology and the method to integrate electronic systems in textiles, as well as the interconnection of stretchable modules located on different places on the textile. The electronic system is completely embedded in an elastomer material like PDMS (silicone), resulting in soft and stretchable electronic modules. The technology uses standard packaged components (IC’s) and meander shaped copper tracks, so that stretchable systems with complex functionality can be achieved. Testing methods for washability were selected and developed. First tests are showing promising results, leveling the path to washable electronics in textiles. This unique technology creates the possibility for integration of electronics in textiles with a high degree of wearing comfort, and allows washing without the need to remove the circuit. In order to show the possibilities of the technology in the field of textile applications a 7x8 single color stretchable LED-matrix was designed and integrated in textile. This LED-matrix can be applied for example in wearable signage applications.Keywords – flexible and stretchable electronics, textile-embedded systems, washability, molding, PDMS, wearable signage
5:30 PM - JJ4.4
Conformable, High Sensitivity, Large Area and Flexible Pressure Sensors Using Micro-structured Polydimethylsiloxane.
Chee-Keong Tee 1 , Stefan Mannsfeld 3 , Christopher Vicente Hsin-Hung Chen 2 , Randy Stoltenberg 2 , Zhenan Bao 2
1 Electrical Engineering, Stanford University, Stanford, California, United States, 3 , Stanford Synchrotron Radiation Lightsource, Menlo Park, California, United States, 2 Chemical Engineering, Stanford University, Stanford, California, United States
Show AbstractWe used a simple, soft lithography approach to making micro-structured thin films of polydimethylsiloxane (PDMS) on stretchable substrates. The films were molded using wet-etched silicon wafers. Such micro-structured films, when used as a dielectric material, can allow for greater pressure sensitivity as compared to unstructured films of similar thicknesses. Since it is a molding process, the mold can be designed and films for different pressure sensing regimes can be obtained. In addition to flexible substrates, such as polyethylene terephthalate (PET), the films can also be put on a stretchable and conformable substrates, such as on PDMS itself, to realize a conformable pressure sensor. By sandwiching these micro-structured films between two electrodes, capacitance change due to change in contact pressure can be measured. These films have excellent response times and returns to the uncompressed state within milliseconds. Such films can also be applied as the dielectric layer of organic field effect transistors, and hence be used in an active matrix. The facile fabrication method can be easily scaled up, and large area, conformable sensor films can be made relatively inexpensively.As we work to imbue robots with greater autonomy in a constantly changing natural environment, contact pressure sensors are vital, especially in healthcare automatons where they will come into direct touch contact with humans depending on their assigned role. Therefore, building robust pressure sensors with high sensitivity that can be operated in large pressure ranges is required and presents a challenge for the industry. Our work provides a simple, cost-effective method for enabling large area, conformable, and sensitive robust electronic skins.
5:45 PM - JJ4.5
All Solution Processed Integrated Temperature / Pressure Sensor Array.
Minkyu Kwon 1 2 , Jaewook Jeong 1 2 , Sangwoo Kim 1 2 , Donghyun Kim 1 2 , Yongtaek Hong 1 2
1 Electrical Engineering and Computer Science, Seoul National University, Seoul Korea (the Republic of), 2 Inter-University Semiconductor Research Center, Seoul National University, Seoul Korea (the Republic of)
Show AbstractWe report an integrated temperature / pressure sensor array on a flexible PET substrate using only solution processes, such as screen printing, spin coating and drop casting methods. Previously, T. Someya group has reported the integrated temperature / pressure sensor array by using organic TFTs, diodes and conducting rubber as switching and sensing elements, respectively. However, the fabrication process was relatively complicated. Therefore, to simplify fabrication process and reduce cost, we fabricated a flexible integrated temperature / pressure sensor array based on solution process methods.We used conductive carbon nanotube (CNT) ink and force sensitive resistor (FSR) ink to fabricate temperature and pressure sensors, respectively. The structure of the temperature sensor consists of two parallel in-plane silver electrodes and CNT thin film so that the resistance change of the CNT film with temperature can be measured from the two electrodes. The structure of the pressure sensor consists of two vertically–aligned silver electrodes so that the resistance change of the FSR film with pressure from the two electrodes. For integration, we used a screen printing method for making parallel in–plane silver electrodes array on the front side PET substrate and vertical electrodes array and FSR patterns on the backside PET substrate. One of parallel silver electrodes were electrically connected to the one of the vertically-aligned silver electrodes via a hole punched through the PET substrate and this electrode would perform a common electrode in the integrated sensor array. CNT thin films were spin-coated on the parallel electrodes and then encapsulated by the drop-cast PDMS films. The other of the vertically-aligned silver electrode and FSR films were finally screen printed on another PET substrate and then attached to the backside of the first PET substrate using double-side adhesive tape.CNT thin films show a typical negative temperature coefficient (NTC) characteristic for their resistance due to reaction with oxygen and other gas molecules on the CNT surface. We obtained good linear sensitivity to temperature of 1~2FS/%, which is mainly because the PDMS encapsulation regulates the rate of reaction with oxygen or other gases on the surface of the CNT thin film. The sensitivity of the temperature sensor array was quite uniform (0.17~0.18%/Centigrade). But the sensitivity of pressure sensor array was not quite uniform (0.2~1.2%/kPa). From these results, we suggest that the flexible temperature and pressure sensor integration array with passive matrix can be made only with solution process. Moreover, our fabrication process has an advantage of simple process and low cost and our device will contribute to the humanoid robotics technology.
JJ5: Poster Session
Session Chairs
Siegfried Bauer
Barclay Morrison
Friday AM, April 09, 2010
Salon Level (Marriott)
9:00 PM - JJ5.1
Interlaced Circuits for Multidirectional Stretchable Electronics.
Q. Li 1 , X. Tao 1 , T. Hua 1
1 , Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hong Kong China
Show AbstractStretchable electronic circuits have the potential to the fields where electronics have to be conformable, deformable and stretchable into three dimensional surfaces. In this work, an “interlaced” structure is developed for multidirectional stretchable circuit. The shape of the conductor is loop-like configuration. A knitted structure is employed for the elastic substrate due to its flexibility, high stretchability, low cost and simple fabrication. The electro-mechanical behavior of the interlaced circuit is investigated in three different directions, i.e., 0-degree, 45-degree, and 90-degree, respectively. A significant improvement in stretchability is achieved in 0-degree direction. Then, a preliminary theoretical analysis is made in the electro-mechanical mechanism of the interlaced circuit. From the experimental investigation and theoretical analysis, it is found that the interlaced structure gives the conductor more freedom to move in the substrate, decreasing the stress concentration in the crest and trough parts of the loop when it is stretched.
9:00 PM - JJ5.10
Pressure Sensor Array Fabrication Using Novel Magnetically Patternable Conducting Powders.
Sangwoo Kim 1 2 , Minkyu Kwon 1 2 , Junhee Cho 1 2 , Donghyun Kim 1 2 , Jaewook Jung 1 2 , Yongtaek Hong 1 2
1 Electrical Engineering and Computer Science, Seoul National University, Seoul Korea (the Republic of), 2 , Inter-University Semiconductor Research Center, Seoul National University, Seoul Korea (the Republic of)
Show AbstractWe have studied pressure sensor array for artificial skin application by using patterned conducting rubber sheet which was made with a magnetically patterning method. Conducting rubber is one of the promising candidates for detection of externally applied pressure. It has piezoresistive characteristics in which electrical resistance decreases with the applied pressure. Conducting rubber can be made with conducting particles such as carbon black, graphite or metal powder, mixed with polymer matrix like polydimethylsiloxane(PDMS). Usually, the conducting rubber is used in two forms for pressure sensor array. When it is used in the form of resistive sheet, active-matrix type switching device is required to reduce a cross talk problem. Since the conducting rubber can be patterned by using a dispensing process, it can be also used in the form of island, resulting in a reduced cross talk issue. To fabricate patterned conductive rubber in the sheet form of the polymer matrix we report a novel magnetic field based patterning method by using ferromagnetic powder as conductive filler in the PDMS matrix. Ferromagnetic materials are rearranged when it is located in a magnetic field. Using this phenomenon, we can pattern ferromagnetic materials by engineering magnetic field lines. Conducting rubber is made by mixing PDMS with curing agent and nickel powder. Before the conducting rubber is fully cured, magnets were used to apply patterned magnetic field across the conducting rubber. Nickel powder was rearranged and patterned during magnetic field exposure. The completed conducting rubber sheet is 50mm by 50mm rectangle shape and it has 0.5mm thickness. An important characteristic of this rubber sheet is that 1mm by 1mm conducting pattern was formed between top and bottom side of sheet. The periodicity of conducting pattern is 3.54mm, which corresponds to 7dpi. The resistance of the each conducting pattern varies from 1MΩ to 20Ω depending on the applied pressure. A passive matrix 8 x 8 pressure sensor array without active device was made by depositing cross Ag electrodes on top and bottom side of sheet. The proposed magnetic field based patterning method will provide a simple manufacturing process at lower cost than other existing methods.
9:00 PM - JJ5.11
Highly ductile thin metal films for flexible electronics
Noble Woo 1 , Jochen Lohmiller 2 , Ralph Spolenak 1
1 Materials, ETH Zürich, Zürich Switzerland, 2 Institut für Zuverlässigkeit von Bauteilen und Systemen, Universität Karlsruhe, Karlsruhe Germany
Show AbstractThe field of flexible and wearable electronics is new and rapidly emerging. An essential requirement for such electronic systems is having highly flexible interconnect backbone that has to be stretchable, bendable and conformable to overall shape of the device, with minimal compromise in conductivity. In this study, thin film composition spreads of Au1-xCux, where x is a function of position, hence concentration, were produced by co-sputtered deposition using two separate DC magnetron elemental sources. Films were deposited on polyimide substrates (Kapton®) for in situ tensile testing in a SEM, while films deposited on silicon wafers were used for characterization by nanoindentation, XRD and EDX. Substrate quality turned out to be extremely important in delocalizing applied macroscopic strain, which allowed high ductility. No cracking was observed up to the maximal strain of 30% for films consisting of pure Au and alloys with a low Cu content, while cracking was more prevalent in films with higher Cu contents and with applied heat treatment
9:00 PM - JJ5.2
Lifetime of Stretchable Meander-shaped Copper Conductors in PDMS Subjected to Cyclic Elongation.
Tom Sterken 1 , Frederick Bossuyt 1 , Rik Verplancke 1 , Thomas Vervust 1 , Fabrice Axisa 1 , Jan Vanfleteren 1
1 , UGent/CMST/IMEC, Zwijnaarde Belgium
Show AbstractStretchable electronics fulfill the requirements a device should have for use in wearable textile electronics and biomedical implants. They typically consist of rigid or flexible component islands interconnected with stretchable meander-shaped copper conductors embedded in a stretchable polymer e.g. PDMS. The copper meander-like interconnections are the key parts. They ensure the stretchable electrical connection between the different functional islands. However, when mechanical failure of the connections occurs, the functionality of the electronic system is not longer guaranteed. It is clear that their reliability is a major issue. To address this issue, a reliability study of these stretchable interconnections made in our stretchable electronics technology is presented. The 100 µm wide meander-like interconnections are realized in 18 µm copper. These interconnections are embedded by liquid injection molding in a 1 mm PDMS substrate. This study focuses on the determination of the maximum number of cyclic elongations before failure occurs as a function of the applied elongation (up to 20%). This approach is used to identify the different failure modes occurring during the cyclic loading and allows comparing the reliability of different variants of the technology. The use of polyimide as a support for the copper conductors has proven to increase the lifetime of the system by a factor 2.A SN-curve is deducted giving us an estimate of the number of cycles a system can survive at a certain elongation before the functionality fails. Keywords: flexible electronics, reliability, stretchable electronics, PDMS, polyimide, silicone
9:00 PM - JJ5.3
Design and Fabrication of Implantable Wireless Pressure and Oxygen Sensors for Pediatric Surgery Using PDMS Thin Films.
Goutam Koley 1 , Waliullah Nomani 1 , Jie Liu 1 , Moonbin Yim 2 , Xuejun Wen 2 , Tain-yen Hsia 3
1 Electrical Engineering, University of South Carolina, Columbia, South Carolina, United States, 2 , Clemson Univeristy, Charleston, South Carolina, United States, 3 , Medical Univeristy of South Carolina, Charleston, South Carolina, United States
Show AbstractCongenital heart defects (CHD) remain the number one cause of death from birth defects during the first year of life. Each year, more than 32,000 babies in the U.S. are born with CHD and nearly 40% of them will require a surgical intervention. In particular, during and after pediatric cardiac surgery, pressures and oxygen content in the various heart chambers provide important clinical information on the functional status of the cardiopulmonary system. Presently, intracardiac pressures are monitored by fluid-filled catheters. There are associated significant bleeding, infections, and malfunction risks and prohibits free movement of the subject. Thus, there is a clinical need to develop an integrated and miniaturized sensor system that can simultaneously, and continuously, monitor pressure and oxygenation within the cardiovascular space wirelessly. In order to develop a miniature telemetric integrated pressure and oxygen sensor, suitable for infants and children, we report the application of PDMS thin films in a novel capacitive and electrochemical sensor design. PDMS offers distinct advantages over other bio-compatible materials: (i) higher pressure sensitivity due to low young’s modulus of PDMS (<100 MPa) [3], (ii) very high permeability to O2 but not to liquids, and (iii) proven bio-compatibility. Integrating the PDMS thin film as the separation membrane in an electrochemical Clark type sensor configuration allows an O2 sensor to be realized in the same platform as the pressure sensor. PDMS thin film displacement as a result of pressure changes was transduced by a capacitive detection technique to produce quantitative measurement of absolute pressures. The best sensitivity for the pressure sensor was ~0.1 nA/KPa, with a noise limited resolution of ~0.09 KPa. Oxygen measurements were obtained by transducing the current change between a Pt and an Ag/AgCl electrode on a glass substrate, with KCl soaked filter paper as the electrolytic media that is separated from the O2 carrying fluid by a thin PDMS membrane. For testing its response, the sensor was subject to pure Ar, 10% and 30% O2. For the O2 sensor, the best sensitivity was ~2.75 microampere for 1% change in O2 content of the surrounding media, with a noise limited resolution of ~6.18 ppm O2. The sensor responses to human blood with 10% and 30% O2 were also tested and very similar responses were obtained. The integrated pressure and oxygen sensor with a passive magnetic telemetry link is able to record blood-pressure variations and oxygenation within cardiovascular system in terms of amplitude and frequency variations of the back scattered signal from the sensor. Initial results on frequency and amplitude variation with changes in capacitance were obtained, which were quite promising.
9:00 PM - JJ5.5
Stretchable Piezoelectric Sensors.
Ingrid Graz 1 , Petr Bartu 2 , Gerald Kettlgruber 2 , Christian Siket 2 , Simona Bauer-Gogonea 2 , Siegfried Bauer 2 , Stephanie Lacour 1 , Sigurd Wagner 3
1 , Nanoscience Centre, University of Cambridge, Cambridge United Kingdom, 2 , Soft Matter Physics, J. Kepler University, Linz Austria, 3 , Dept of Electrical Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractConventional pressure sensors based on piezoelectric materials rely on brittle single crystals, stiff ceramics or flexible polymers, thus resulting in only moderately conformable devices. Ferroelectrets represent a novel group of soft cellular polymer-based piezoelectrics. We prepared a highly compliant piezoelectric sensor by embedding 4x4mm2 ferroelectret foils in a PDMS matrix preliminary textured on the top and bottom faces. To enhance the pressure sensitivity multilayers of ten ferroelectret sheets were prepared. The sensor is completed by evaporating top and bottom macrotextured metallic electrodes. The obtained metal-elastomer-ferroelectret multilayer forms a reversibly stretchable piezoelectric element. We report the obtained piezoelectric coefficients of the hybrid sensor stack up to 40% uniaxial strain, and compare the results with a model, where piezoelectric layers are embedded between dielectric layers. The observed piezoelectric response is nonlinear, with a decrease from 150 pC/N at 0.20 bar to 70 pC/N at 0.9 bar for a sample subjected to 40% strain, in good agreement with the proposed model of piezoelectricity in layered hybrids. The sensitivity of the sensor hybrid is sufficient to enable signal conditioning with amorphous silicon transistors.
9:00 PM - JJ5.6
A Regenerative Scaffold Integrated With a PDMS-based Microelectrode Array for Peripheral Nerve Interfacing.
Liang Guo 1 , Isaac Clements 1 , Ravi Bellamkonda 1 , Stephen DeWeerth 1
1 Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractIn response to the increasing rate of limb amputations, significant efforts are being made in the design of prosthetics that cosmetically and functionally mimic natural limbs. Ideally, a prosthetic limb should be controlled in a natural, biomimetic manner with naturally perceived sensory inputs. However, critical challenges exist in effectively establishing a high-resolution, bi-directional nerve-electrode interface between a surviving nerve stump and an external, biomimetic prosthesis. To address some of the challenges, we have previously developed technological advances in two separate areas. In one area, a regenerative electrode scaffold (RES) has been developed with the ability to effectively bridge peripheral nerve gaps, and to guide regenerating axons within close proximity to integrated thin-film electrodes; in another area, high-density PDMS-based microelectrode arrays (MEAs) have been developed with integrated packaging.In the present work, we bring together these two pieces of technology to create a novel RES capable of establishing a stable, high-resolution peripheral nerve interface. To do this, we incorporate a chip-integrated, thin-film PDMS-based MEA into individual layers of a nanofiber scaffold to create an integrated implant for peripheral nerve interfacing. We use in vitro experimentation, including neural cell culturing, to evaluate robustness of the MEA and its capability to establish bi-directional communication between a peripheral nerve and a prosthetic device. We also test the implant in vivo by implanting it across a gap in rat sciatic nerve, such that regeneration through the implant can be histologically and functionally evaluated.
9:00 PM - JJ5.7
Flexible, Fenestrated Carbon Nanotube Electrode Arrays.
Bruce Gnade 1 , Edward Keefer 2
1 , University of Texas at Dallas, Dallas, Texas, United States, 2 , Plexon, Inc., Dallas, Texas, United States
Show AbstractChronically implanted electrode arrays for recording and stimulation of the CNS are increasingly used for both animal-based research and preclinical human testing. The most common materials used to fabricate the arrays are either metal or silicon. Both of these are inherently rigid and hard, resulting in mechanical impedance mismatch between the neural probe and the tissue in which it is implanted. The differences in material properties between brain and array presumably translate into increased inflammatory response, encapsulation of the probe by reactive cells, and a decline in the performance of the implanted electrodes with time. Given the increasing number of chronic neuropathological conditions for which brain/machine interfaces are being tested as interventional strategies, improvements in the longevity of stable neural interfaces are required. To address this issue, we have designed and tested neural electrode arrays using a novel combination of materials. We produced 16-channel electrodes using a flexible parylene substrate, lithographically defined gold electrode sites and leads on that substrate, and then insulated with another parylene layer. In addition to exposing the electrode sites with RIE, we also etched holes through the parylene substrate, resulting in a fenestrated, flexible electrode shaft with 15 µm diameter gold electrode sites separated by 100 µm vertically. We believe that the fenestrations aid in diffusion of soluble factors, as well as cell migration and subsequent incorporation of the neural probe into the brain. In order to decrease the impedance and increase charge transfer of the electrode sites, we electrochemically deposited carbon nanotubes, lowering the impedance at 1 kHz to approximately 30 kOhms. To transiently increase the axial stiffness of the arrays during insertion into the brain, we dip coated them with a thin layer of the biocompatible polymer PLGA or with PEG. We tested the mechanical characteristics of the coated probes with insertion tests in both agar gels and into the hippocampus of anesthetized rats. We also recorded neural activity from the cortex and hippocampus of rats. Despite the small size of the electrodes, (175 µm2), the carbon nanotube coatings enabled low noise, artifact-free simultaneous recordings of both single units and local field potentials. We are testing the long term stability of the recordings in chronically implanted rats, and are performing histological evaluation of the degree of tissue reaction in the vicinity of the probes. We are also conducting experiments with various neurotrophins (NGF, BDNF) incorporated into the polymer coating applied prior to insertion. As the coating degrades, elution of the active factors may decrease adverse responses and further improve neural signals.
9:00 PM - JJ5.8
Thin-film Interconnection Technology for Use in a Stretchable Cell Culture Platform.
Rik Verplancke 1 , Frederick Bossuyt 1 , Tom Sterken 1 , Jan Vanfleteren 1
1 Centre for Microsystems Technology - ELIS, Ghent University - IMEC, Gent-Zwijnaarde Belgium
Show AbstractStretchable microelectrode arrays (MEAs) have gained a lot of interest because of their ability to study cellular activity while cells are subjected to mechanical strain. Next to their advantage as a tool to study the mechanisms of pathologies such as traumatic brain injury, stretchable MEAs offer new possibilities in the area of stem cell differentiation or drug screening (e.g. in the field of cardiotoxicity).The fabrication of stretchable electrical interconnections is a key aspect for the realization of stretchable MEAs. The interconnections should not only allow for electrical conduction at a predefined strain, but also ensure reliability under cyclic loading. Ideally, a fine pitch is desired allowing routing in electrode areas with high spatial resolution.In this contribution, a new technology is presented complying with above-mentioned needs. The technology is based on the patterning of a three-layered stack into a sequence of horseshoe shapes. Therefore, a polyimide (PI2611) layer is spin-coated onto a rigid base substrate. Next, a thin film metal is sputter deposited and patterned (horseshoe shapes) on this polyimide layer. The metal consists of a TiW adhesion layer (~50nm) and a conducting Au layer (~200nm). On top of the metal, a second polyimide (PI2611) layer is spin-coated and both polyimide layers are patterned into horseshoe shapes using a dry etch process (RIE). Finally, the entire stack is embedded into an elastomeric polymer such as polydimethylsiloxane (PDMS). This allows the stack to function as a “2D spring”, where the polyimide layers are a non-elastic support for the metal conductors. As processing is done on a rigid carrier, the technology requires the use of a suitable release technique (based on KCl), allowing the transfer of this stack into PDMS.The performance of stretchable electrical interconnections when subjected to long-term cyclic uniaxial stretching was tested at an elongation of 10% and a strain rate of 10%/s, indicating a minimum lifetime of 100’000 cycles (test still ongoing at the moment of writing).In conclusion, a new technology is presented for the fabrication of an electromechanical platform for cell culturing. Key features of the technology are its biocompatibility, enhanced reliability and optical transparency (of the base substrate).
9:00 PM - JJ5.9
Design, Fabrication and Mechanical Testing of a Novel Ultra-flexible Technology for Smart Invasive Medical Instruments.
Benjamin Mimoun 1 , Vincent Henneken 2 , Ronald Dekker 1 3
1 Delft Institute of Microsystems and Nanoelectronics (DIMES), TU Delft, Delft Netherlands, 2 BioMechanical Engineering, TU Delft, Delft Netherlands, 3 , Philips Research, Eindhoven Netherlands
Show AbstractFlexible and stretchable electronics have been rapidly developing, and a large number of applications have been reported in the literature. Among these applications is an increasing trend to include electronics and/or sensing functionalities bent around the tip of invasive medical instruments, such as catheters and guidewires. The diameter of these instruments can vary from 2 mm to 300 µm.The simultaneous measurement of both dynamic blood flow and pressure in small coronary arteries has been proven to be very useful for cardiologists in the assessment of Coronary Artery Diseases (CAD). In order to achieve this, the fabrication of flexible sensors which remain functional while bent around a guidewire of 300 µm in diameter is necessary. Moreover, due to the very limited amount of space inside the guidewire for connection cables, signal processing and Analog to Digital (A/D) conversion electronic functions must also be implemented on-chip.In this paper we demonstrate a new technology for the fabrication of partially flexible miniature sensors interconnected by ultra-flexible high density interconnects and the possibility of adding top performance CMOS Application-Specific Integrated Circuits (ASIC) chip directly at the place of the sensing location. The proposed method has the advantage that it enables the fabrication of partially flexible chips of any arbitrary shape and thickness. Standard wire bonding is possible on the rigid part of the devices and the connection to other chips or components is possible via a unique “micro-flatcable” interconnect. The mechanical behavior under bending of the polyimide-based flexible part of the chip is improved by segmenting in the bending direction the layers that have to be in direct contact with the outside world. Measurements indicate that interconnects embedded in polyimide remain fully functional even while bent to a radius of 50 µm. This presented approach is based on a true post-processing procedure working on any pre-processed IC wafer. It is ideally suitable for the fabrication of miniature sensors and circuits that have to be mounted on or in catheters and others medical implantable devices such as drug delivery devices and e-pills.
Symposium Organizers
Stephanie P. Lacour University of Cambridge
Siegfried Bauer Johannes-Kepler Universitaet Linz
John Rogers University of Illinois, Urbana-Champaign
Barclay Morrison Columbia University
JJ6: Ultra-Compliant Electronic Devices
Session Chairs
Friday AM, April 09, 2010
Room 2000 (Moscone West)
9:30 AM - JJ6.1
Paper Energy Storage Devices.
Liangbing Hu 1 , Jang Wook Choi 1 , Yuan Yang 1 , Yi Cui 1
1 , Stanford, Stanford, California, United States
Show AbstractWe show that commercially available paper can be made highly conducting with a sheet resistance as low as 1 Ohm/sq by using simple solution processes to achieve conformal coating of single-walled carbon nanotube and silver nanowire films. Compared to plastics, paper substrates can dramatically improve film adhesion, greatly simplify the coating process, and significantly lower the cost. Supercapacitors based on carbon nanotube conductive paper show excellent performance with a specific capacitance of 200 F/g, a specific energy of 47 Wh/kg, which is comparable to that of rechargeable batteries, a specific power of 200,000 W/kg, and a stable cycling life over 40,000 cycles. These values are much better than those of devices on other flat substrates such as plastics. In addition, this conductive paper can be used as an excellent light-weight current collector in Li-ion batteries to replace the existing metallic counterparts. This work suggests that our conductive paper can be a highly scalable and low cost solution for high performance energy storage devices as well as flexible electronics.
9:45 AM - JJ6.2
Power and Signal Distribution and Supplies in Stretchable Electronics.
Martin Kaltenbrunner 1 , Gerald Kettlgruber 1 , Christian Siket 1 , Reinhard Schwoediauer 1 , Siegfried Bauer 1
1 Soft Matter Physics, Johannes Kepler University, Linz Austria
Show AbstractStretchable electronics is building or embedding electronic circuits and devices in a stretchable material. Substrate and interconnects must be made stretchable rather than flexible or rigid, like in flexible electronics or printed circuit boards. In stretchable electronics, sparse research has been devoted to embedded power supplies and signal distribution. Here we present concepts for ultra-compliant and mechanically robust batteries for delivering power to stretchable electronics, as well as stretchable optical interconnects for power transmission and signal distribution.The compliant battery is based on the acrylic VHB elastomer from 3M. Electrodes are based on a carbon black – silicon oil gel. Chemically active materials are Zn and MnO2, the basics of zinc carbon batteries. Active areas of approximately 1cm2 are prepared with a lateral separation of 0.3cm, to avoid intermixing of the chemicals upon stretching. The two active electrodes are closed with a Xanthan electrolyte gel. Open circuit voltages of 1.47V and short circuit currents of up to 40mA have been achieved, with a capacity of 3mAh/cm2 active cell area. The loss in open circuit voltage of the batteries is comparable to that of zinc carbon elements. Such batteries can easily be connected in series to enhance voltage or parallel to enhance current. Stretching up to 50% is demonstrated with a serial connection of two elements, driving an embedded light emitting diode.Power and signal distribution is also feasible by means of stretchable optical interconnects. First attempts towards stretchable multimode optical waveguides, directly coupled with laser and photodiodes for light generation and detection are introduced, providing alternative means to standard electrical wiring for interconnecting stretchable electronic devices.Acknowledgment: Work partially supported by the Austrian Science Funds.
10:00 AM - JJ6.3
Stretchable Supercapacitors Based on Buckled Single-walled Carbon Nanotube Macro-films.
Hanqing Jiang 1 , Bingqing Wei 2 , Cunjiang Yu 1 , Charan Masarapu 2 , Jiepeng Rong 2
1 , Arizona State University, Tempe, Arizona, United States, 2 , University of Delaware, Newark, Delaware, United States
Show AbstractStretchable electronic devices, such as p-n diodes, photovoltaic devices, transistors, and functional electronic eyes, have been fabricated using buckled single crystal (e.g., Si, GaAs) thin films supported by elastomeric substrates. Recently, carbon nanotube based highly conducting elastic composites and stretchable graphene films have been reported, which are best suitable as interconnects in a stretchable electronic device. As an indispensible component of stretchable electronics, a stretchable power source device should be able to accommodate large strains while retaining intact function. Of various power source devices, supercapacitors have attracted great interest in recent years, due to their high power and energy densities compared with lithium-ion batteries and conventional dielectric capacitors, respectively. The most active research in supercapacitors is the development of new electrode materials. Recently, carbon nanotubes (CNTs) have been studied as good candidates for electrode materials, because of several advantages, including high surface area, nanoscale dimensions, and excellent electrical conductivity.Here, we report stretchable supercapacitors, based on periodically sinusoidal single-walled carbon nanotube (SWNT) macro-films (two-dimensional network of randomly oriented SWNTs). The stretchable supercapacitors comprise two sinusoidal SWNT macro-films as stretchable electrodes, organic electrolyte and a polymeric separator. The electrochemical tests were performed and found that the fabricated stretchable supercapacitors possess comparable energy and power densities with supercapacitors using pristine SWNT macro-films as electrodes. Remarkably, the electrochemical performances of the stretchable supercapacitors are unchanged even under 30% applied tensile strain.
10:15 AM - JJ6.4
Stretchable Polymer Light Emitting Devices With Carbon Nanotubes Electrodes.
Zhibin Yu 1 , Qibing Pei 1
1 , UCLA, Los Angeles, California, United States
Show AbstractTransparent electrodes are required for a wide rang of electronic and photonic applications. The ubiquitously used indium doped tin oxide (ITO) is not suitable for highly flexible devices as ITO coatings crack at strains greater than 0.5% to 1%. Various alternative electrodes have been investigated, including conducting polymers, other metal oxides, single walled carbon nanotubes (SWNTs) and graphenes et al.SWNT thin film electrodes have been developed from solution processes onto plastic substrates with conductivity and transmittance comparable to ITO electrodes. We have shown that the SWNT electrodes are highly compliant: the electrodes remain conductive at high strains up to 700%.We report stretchable polymer light emitting devices with SWNT electrodes. SWNTs were first screen printed onto elastomeric substrates, followed by the deposition of the active layers by screen printing. The top electrode is applied by roll lamination. Such a printing and lamination process is used to fabricate a set of blue, green and red emission light emitting devices. The devices exhibited a low turn-on voltage and high efficiency and can be stretched up to 50% strain without permanently destroying the light emission characteristics.
10:30 AM - JJ6.5
A Simple Release Method for High Quality Printable III-nitride Semiconductors.
Keyan Zang 1 , Jing Hua Teng 1 , Soo Jin Chua 1
1 Materials Growth/Solid State Lighting, Institute of Materials Research and Engineering, Singapore, Singapore, Singapore
Show Abstract Transfer printable III-nitride semiconductors have attracted increasing attentions in the applications of optoelectronics and electronics on flexible substrates, such as plastic, papers, etc, due to its wide bandgap, high electron mobility and commercial applications in light emitting diodes, laser diodes and transistors. However, lack of bulk materials, III-nitrides have to be grown on dissimilar substrates. Releasing III-nitrides from their substrates, fabricating them into a printable form, while maintaining high material quality, is a challenge for transfer printing them onto flexible substrates. Here, we report a simple method to generate high quality printable gallium. The method utilizes the wet chemical etching to remove the nanopatterned SiO2 network mask which is inserted in the GaN layers and the self-release of the top GaN nanoepitaxial layers with nanostructure arrays at the interface. GaN nanoepitaxial layers is grown laterally over a nanopatterned SiO2 network mask layer fabricated on a GaN template layer on sapphire substrate by metal organic chemical vapor depostion. It has been already demonstrated by our previous study that nanoepitaxial GaN shows improved crystal quality, better surface morphology and low defect density, which benefits high efficient optoelectronic devices. A light emitting diode (LED) is fabricated on nanoepitaxial GaN showing significant improvement in the light output power. Micro-sized mesa is created by using photolithography and inductive coupled plasma etching of nanoepitaxial GaN layer. The sample is then left in HF solution. The film was found to separate from the GaN template upon the removal of SiO2 and the forming nanostructured GaN. After etching completes, the GaN mesa was observed staying at its original position by weak force, and it is ready for transfer printing. It is a reliable release method without damage to GaN films. The nanopatterned structures in the GaN film benefit to the improvement of the light extraction efficiency for LED application or to create hierarchical structures for nanophotonic applications. Meanwhile, nanoepitaxial GaN offers high and better crystal quality, beneficial to high efficient and high power applications. The application of this method can be release III-nitride based optoelectronic devices, MEMs system, microcavities and microoptics systems, or in the application of heterogeneous integration on Si or flexible substrates.
10:45 AM - JJ6.6
Layer Transfer of High Quality, Single Crystalline (110) InP for Flexible Applications.
Wayne Chen 1 , David Govea 1 , S. Lau 1 , T. Kuech 2
1 Electrical and Computer Engineering, University of California San Diego, La Jolla, California, United States, 2 Department of Chemical and Biological Engineering, University of Wisconsin, Madison, Wisconsin, United States
Show AbstractA double-flip layer transfer method has been demonstrated which enables the integration of InP with flexible substrates. This process involved ion-cutting, a well-established technology commonly used to form silicon-on-insulator, adhesive bonding as well as laser ablation. However, ion-induced damage in III-V materials is difficult to anneal out, even up to temperatures leading to material decomposition.To eliminate ion damage in critical regions of the transferred material, we have investigated an approach in (100) InP, wherein strategic areas of the implanted wafer were protected from the ion-beam. Following film transfer, a hillock/pyramidal morphology was observed in the masked (non-implanted) regions, with heights of well over 15μm for 50μm-side masked squares and increasing to over 140μm for 1mm2 square regions. Such pyramidal structures are thought to be a result of InP crack propagation along its principal cleavage plane (110), instead of parallel to the (100) wafer surface. An etch-stop epi-layer of InGaAs was grown underneath the transfer layers, which when selectively etched, undercut and removed these hillocks rendering a flat surface for device fabrication. Due to the large and nonuniform height of these hillocks, selective chemical etching time varies and can lower the resulting yield. To eliminate the need for the selectively etched etchstop layer, (110) InP was selected as the starting donor wafer, followed by ion-masking and selective implantation with the same conditions as the (100) InP. Following exfoliation, masked regions of (110) InP were observed to transfer smoothly, with crack propagation parallel to the wafer (110) surface. Pyramidal or hillock morphology was not observed in these transferred layers. These observations suggest that by selecting a crystal orientation parallel to the preferred cleavage planes of InP, large area transfer of unimplanted and therefore bulk-quality InP can result and, thus, would greatly facilitate device fabrication and enable large area transfer of bulk-quality InP onto flexible substrates.
11:00 AM - JJ6:Devices
BREAK
JJ7: Stretchable Electrodes
Session Chairs
Friday PM, April 09, 2010
Room 2000 (Moscone West)
11:30 AM - **JJ7.1
Morphology Diagram for Gold Films on Polydimethylsiloxane (PDMS).
Oliver Graudejus 1 2 , Joyelle Jones 2 , Patrick Goerrn 2 , Sigurd Wagner 2
1 Center for Adaptive Neural Systems, Arizona State University, Tempe, Arizona, United States, 2 Department of Electrical Engineering and the Princeton Institute for the Science and Technology of Materials (PRISM), Princeton University, Princeton, New Jersey, United States
Show AbstractApplications of stretchable electronics often use gold films on PDMS either as elastically stretchable interconnects or as electrodes for the stimulation of neural and muscular tissue. The electrical conductance and optical reflectance of these gold conductors depend greatly on the morphology of the film. The gold films can assume four different morphologies on PDMS: microcracked, buckled, microbuckled, and completely smooth without any distinct morphology (like gold films deposited on glass). The appearance of a particular morphology depends on the deposition temperature, the thickness of the gold film, and the elastic modulus of the PDMS substrate. We show quantitatively at which temperatures and thicknesses the transition between morphologies occurs. The transition between different morphologies is caused by the interaction of tensile and compressive stresses in the film. Most interesting is the microcracked morphology, which is widely usable for elastically stretchable electronics because they afford superior stretchability compared to films with other morphologies. We now have sufficient data to develop “morphology diagrams” of the gold films on PDMS, in deposition temperature – film thickness – substrate modulus space. These morphology diagrams serve as guide for the preparation of any of the four specific morphologies. This research is supported by the National Institute of Health and the New Jersey Commission for Brain Injury Research.
12:00 PM - JJ7.2
Multilayered Gold-elastomer Structures: Stretchable Circuit Board.
Darryl Cotton 1 , Ingrid Graz 1 , Stephanie Lacour 1
1 Nanoscience, University of Cambridge, Cambridge United Kingdom
Show AbstractWe have developed a method to fabricate multilayered gold interconnects embedded in PDMS. Four levels of metallic planes can be vertically interconnected through vias patterned in the silicone interlayers. The technique relies on the evaporation of thin gold films on PDMS and their encapsulation with positive photopatternable PDMS (PP-PDMS). The vias opened in the PP-PDMS are typically 800µm x 800µm in area and 50µm deep although openings as small as 300 µm x 300 µm have also been fabricated. This technique is a promising route to the fabrication of stretchable circuit boards that are essential to stretchable electronic circuits. 40nm x 4mm x 1mm gold thin film stripes were evaporated onto a 100µm thick PDMS substrate. Sylgard 184 is the elastomer of choice to prepare stretchable circuits. One can formulate a photo-patternable PDMS by adding photosensitive benzophenone to the polymer base and cross-linker. The layer was processed in five steps to form the vias. The PP-PDMS is spin coated on top of the gold film and substrate, exposed to UV light, soft baked at 95 deg C for 45s before being puddle developed for 60s in toluene, and finally hard baked at 60 deg C for 24 hours. The vias have side wall angles of approximately 14 ± 6 (deg) providing an excellent sloped platform for evaporating the connecting gold thin films over multiple layers. A second gold conductor (40nm x 4mm x 1mm) was evaporated through the vias and on top of the PP-PDMS to produce the multilayer connections. We have repeated this process several times to produce up to 4 levels of embedded gold interconnections. The electromechanical properties of the stacked interconnects (of effective length 5mm) were examined in a uniaxial stretcher with a maximum applied strain (e) of 20%, and over 1,000 stretch cycles. We found that after cycling the electrical conduction (from the top conductor to the bottom one) is preserved, and behaves similarly to a single layer gold conductor. The top-to-bottom resistance is 148 Ohms and 164 Ohms before and after the 1,000 cycles respectively. This technique enables the design of multilayered stretchable circuits.
12:15 PM - JJ7.3
From Single Conductive Layer to Double Conductive Layer Stretchable Electronics.
Frederick Bossuyt 1 , Tomas Podprocky 1 , Thomas Vervust 1 , Jan Vanfleteren 1
1 , UGent/CMST/IMEC, Zwijnaarde Belgium
Show AbstractStretchable electronic systems for use in textile applications or biomedical implants are currently developed based on single conductive layer technologies. These systems contain single layer stretchable copper conductors connecting different functional electronic islands. More complex systems require however more dense conductors as well as crossing conductors especially on the flexible functional islands. In this submission, a technology is presented which realizes stretchable electronic systems with two conductive layers. The technology is based on our stretchable electronics technology where polyimide is used as a mechanical support for both the stretchable interconnections and functional flexible islands supporting the SMD components. Now an extra conductor layer is added to the existing stretchable stack buildup. Again, this technology is realized by the use of standard PCB manufacturing steps and liquid injection molding techniques to achieve a robust and reliable product. The possibilities of this technology are presented based on the process flow, the used materials and the specific characteristics of the technology. Keywords: double layer, flexible electronics, stretchable electronics, PDMS, polyimide
12:30 PM - JJ7.4
Silver Electrodes on Elastomeric Substrates for Stretchable Electronics Applications.
Jaewook Jeong 1 , Junhee Cho 1 , Sangwoo Kim 1 , Yongtaek Hong 1
1 Electrical Engineering and Computer Science, Seoul National University, Seoul Korea (the Republic of)
Show AbstractRecently stretchable and rollable electrodes have been developed for the application of electrical sensors, actuators, biomedical or textile devices and flexible electronics. Among the various fabrication methods, direct deposition on compliant substrate is a preferred method because it is a simple and cost-effective process, which is compatible with a conventional semiconductor process.In addition, since both thin and thick stretchable metal electrodes are needed in practical applications such as interconnection of device element in a circuit and interconnection of integrated circuits, in this paper, we report study on mechanism of stretchable thin and thick silver electrodes on PDMS elastomeric substrates and optimized structure of stretchable thick silver electrodes by using a corrugated structure in the PDMS substrate. Although thin metal film (<10 nm) can be easily deposited on the elastomeric substrates, deposited thick metal films typically show many surface cracks, resulting in electrical disconnection even for small strain (< 1 %) similar to free standing metal electrode.Therefore, large surface roughness (1 to 1.5 μm) was introduced to reduce mechanical stress between thick metal electrode and PDMS substrate by using pre-patterned Al mold. 700nm thick silver metal on the surface roughened PDMS substrate did not show many cracks. For a thin silver electrode, 50nm thin silver metal was deposited on smooth PDMS substrate. The initial resistance (2.5cm x 1mm) of silver electrodes were 130 and 5.1 Ω for 50 and 700nm thick Ag electrodes, respectively. The prepared electrodes were subjected under tensile strain. Changes of resistance and evolution of surface cracks were monitored by Ohm meter and microscope, respectively. The stretching capability of thick silver electrode on roughened PDMS substrate was significantly improved compared to that on smooth PDMS substrate (Lmax < 1%). Interestingly, both thick and thin electrodes showed similar Rnorm changes up to 30% strain. Rnorm of both electrodes was super-linearly increased up to about 13. For thin electrode, as strain is increased, the large number of silver islands was formed and the size of silver islands depends on the maximum value of applied strain. Similarly, for thick electrode, relatively large size of silver islands were formed and evolved as strain is increased. Therefore, conduction mechanism of thick and thin silver electrodes can be explained by similar way and differ from that of gold electrode which is explained by formation of tri-branched ligand and percolation of electrical path. The stretchable capability of thick metal film was further improved by introducing wavy like corrugated structure in the substrate. The corrugated structure was also introduced by using pre-patterned Al mold. Rnorm was increased only up to 3 as strain was increased up to 40%.
12:45 PM - JJ7.5
Printed Stretchable Conductors Using Silver-based Ink on PDMS Substrates.
Adam Robinson 1 , Ivan Minev 1 , Stephanie Lacour 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractThe printing of electronic structures provides a promising alternative approach for the manufacture of stretchable and flexible devices, as it offers low-cost, relatively large-area fabrication at room temperature without the substrate compatibility problems associated with standard semiconductor fabrication processes. Stretchable substrates are usually made from elastomeric polymers such as silicones, which are hydrophobic and have ultra low surface energy. Here we demonstrate a printing technique onto PDMS membranes by employing a silver-based InkTec transparent conducting ink printed using a SonoPlot ink dispenser onto pre-patterned PDMS substrates. The patterning of the PDMS substrate, either via plasma etching or casting against a mold to produce arrays of micro-pillars, is shown to improve its hydrophilicity and reduce dewetting during ink activisation. Control of the properties of the resulting print is demonstrated by adjusting the surface morphology of the patterned PDMS substrate. Micro-cracks introduced into the conducting print by the pillars allow for out-of-plane buckling, which provides stress release during stretching. Using this technique we are able to produce printed silver conducting features of >100 nm thickness, which can be stretched up to strains of 20% over 1,000 cycles without loss of conductivity. Feature sizes down to 30 μm are demonstrated.
JJ8: Stretchable Circuits
Session Chairs
Friday PM, April 09, 2010
Room 2000 (Moscone West)
2:30 PM - **JJ8.1
Foldable and Stretchable Organic Transistor Integrated Circuits.
Takao Someya 1 , Tsuyoshi Sekitani 1
1 Electrical and Electronic Engineering and Information Systems, The University of Tokyo, Tokyo Japan
Show AbstractIn this talk, we report recent progresses of ultraflexible, foldable, and stretchable electronics based on organic field-effect transistors (FETs) for applications to large-area sensors and displays. First, low-operation (typically 2 V) driven organic FETs with self-assembled monolayer gate dielectrics are manufactured on plastic substrate. By using polyimide smoothing layers, surface smoothness of polyimide substrate is 0.3 nm of RMS in an AFM observation, which is comparable to that of silicon substrate. Organic FET ICs exhibit no detectable changes of electronic performances when they are wrapped around cylindrical bars with the diameter of 1 mm. Second, we developed elastic conductors in order to fabricate large-area stretchable integrated circuits (ICs). Millimeter-long single-walled carbon nanotubes (SWNTs) are uniformly dispersed as chemically stable dopants in a vinylidene fluoride-hexafluoropropylene copolymer matrix by using an ionic liquid. Elastic conductors are compatible with printing processes such as a screen printing. The measured value of conductivity exceeds 100 S/cm. Using printable elastic conductors, we have fabricated truly rubber-like stretchable active matrixes for sensors and displays.
3:00 PM - JJ8.2
Curvilinear Electronics Formed Using Silicon Membrane Circuits and Elastomeric Transfer Elements.
Heung Cho Ko 9 2 , Gunchul Shin 5 , Shuodao Wang 1 , Mark Stoykovich 10 2 , Jeong Won Lee 6 , Dong-Hun Kim 6 , Jeong Sook Ha 5 , Yonggang Huang 7 1 , Keh-Chih Hwang 8 , John Rogers 2 3 4
9 Materials Science and Engineering, Gwangju Institute of Science and Technology, Beijing, Gwangju, Korea (the Republic of), 2 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 5 Chemical and Biological Engineering, Korea University, Seoul Korea (the Republic of), 1 Mechanical Engineering, Northwestern University, Evanston, Illinois, United States, 10 Chemical and Biological Engineering, University of Colorado – Boulder, Boulder, Colorado, United States, 6 Materials Science and Engineering, Pohang University of Science and Technology, Pohang, Gyungbuk, Korea (the Republic of), 7 Civil and Environmental Engineering, Northwestern Universtiy, Evanston, Illinois, United States, 8 Engineering Mechanics, Tsinghua Universtiy, Beijing China, 3 Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 4 Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractAll dominant forms of electronics and optoelectronics exist exclusively in planar layouts on the flat surfaces of rigid, brittle semiconductor wafers or glass plates. Although these two dimensional configurations are well suited for many existing applications, they are intrinsically incompatible with many envisioned systems of the future. For example, they do not enable natural integration with the soft, curvilinear surfaces of living organisms (e.g. body parts), for the purposes of health monitoring or therapeutics. They also preclude the use of many interesting, often biologically inspired, non-planar device designs such as those based on curved focal plane arrays as recently demonstrated in fully functional hemispherical electronic eye cameras.[1] Such curvilinear systems cannot be achieved easily using existing technologies due to the inherently 2D nature of established device processing procedures, ranging from deposition, growth, etching and doping to photolithography. Approaches that use unusual electronic materials or patterning techniques might be useful, but they require substantial further development for high performance applications.We present in this paper advanced concepts for conformally wrapping silicon based circuits, initially fabricated in 2D layouts with conventional or moderately adapted forms of conventional techniques, onto surfaces with a range of curvilinear shapes. [2] The strategy uses structured silicon membranes with thin polymer/metal interconnects, in non-coplanar mesh layouts. Quantitative comparison of theoretical mechanics models to wrapped systems on diverse classes of substrates reveals the underlying science and establishes engineering design rules for future work.The work provides strategies for achieving electronics based on high quality, single crystalline inorganic semiconductors in geometrical layouts that are impossible using wafer-based technologies. The use of purely elastic mechanics together with hybrid plastic/inorganic circuit meshes enables predictive analysis and high strain deformations, respectively. These aspects represent important distinguishing features compared to related work. Experimental and theoretical studies of the underlying micromechanics reveal the capabilities and associated engineering design rules. The versatility of these procedures and their compatibility with established semiconductors suggest that they might be useful for applications of electronics or optoelectronics in biomedicine and other areas of application that cannot be addressed using existing technologies.[1] H. C. Ko, et al., Nature 454, 748 (2008)[2] S. Wang, et al., APL Lett. 95, issue 18 (2009)
3:15 PM - JJ8.3
Improved Stretchable Electronics Technology for Large Area Applications.
Frederick Bossuyt 1 , Thomas Vervust 1 , Fabrice Axisa 1 , Jan Vanfleteren 1
1 , UGent/CMST/IMEC, Zwijnaarde Belgium
Show AbstractA novel technology for stretchable electronics is presented which can be used for the realization of wearable textile electronics and biomedical implants. It consists of rigid or flexible component islands interconnected with stretchable meander-shaped copper conductors embedded in a stretchable polymer, e.g. PDMS. The technology uses standard PCB manufacturing steps and liquid injection molding techniques to achieve a robust and reliable product. Due to the stretchable feature of the device, conductors and component islands should be able to withstand a certain degree of stress to guarantee the functionality of the system.Although the copper conductors are meander-shaped in order to minimize the local plastic strain, the lifetime of the system is still limited by the occurrence of crack propagation through the copper, compromising the connectivity between the functional islands. In order to improve the lifetime of the conductors, the most important feature of the presented technology is the use of spin-on polyimide as a mechanical support for the stretchable interconnections and the functional flexible islands. In this way, every stretchable copper connection is supported by a 20µm layer of polyimide being shaped in the same manner as the above laying conductor. The grouped SMD components and straight copper tracks on the functional islands are also supported by a complete 20 µm polyimide layer. By use of the polyimide, the reliability of the stretchable interconnections, the straight interconnections on the flexible islands and the transitions between the stretchable and non-stretchable parts is improved. This approach results in a significant increase of the lifetime of the stretchable interconnections as it is doubled.In this contribution, the different process steps and materials of the technology will be highlighted. Initial reliability results will be discussed and the realization of some functional demonstrators containing a whole range of different components will further illustrate the feasibility of this technology. The advantages and disadvantages in terms of processability, cost and mechanical strength of the photo-definable polyimide will be covered.Keywords: flexible electronics, stretchable electronics, PDMS, polyimide
3:30 PM - **JJ8.4
Organic Thin-film Electronics on Silicone Substrates for Stretchable Electronics.
Ingrid Graz 1 , Darryl Cotton 1 , Stephanie Lacour 1
1 , Nanoscience Centre, University of Cambridge, Cambridge United Kingdom
Show AbstractStretchable electronics is a novel evolution of microelectronics where electronic circuits are designed to elongate reversibly whilst retaining full electrical functionality. Silicone elastomers are employed as the substrate material; they can elastically deform up to twice their length.Here, we present an overview of the preparation of organic thin film transistor circuits on silicone substrates. Once integrated onto rigid platforms distributed across the substrate and interconnected using stretchable metallization, reversibly stretchable circuits can be demonstrated.We have already reported the patterning of stretchable gold interconnects in detail. After a brief review of the interconnects’ electrical response to cycling 1D and 2D deformations, we focus on the fabrication and characterization of active transistor devices on silicone. The transistors are prepared using a “bottom-up” approach by successively depositing and patterning all device layers. Metal and semiconductor films are thermally evaporated whilst the dielectric is deposited at room temperature by vacuum sublimation. The overall process temperature never exceeds 100°C to prevent extensive expansion of the elastomer. Both p- and n-type field effect transistors (FETs) are realized using the small molecules pentacene and C60 respectively. The OFETs function reliably and have similar characteristics to their counterparts on plastic substrates. The pentacene FETs show saturation mobilities up to 0.3cm2/Vs, on-off current ratios of 104, and threshold voltages around -10V. The C60 devices exhibit very good performance with saturation mobilities as high as 0.8cm2/Vs, on-off current ratios of 104 and threshold voltages of around 10V.Furthermore, inverter circuits are prepared using organic semiconductors on freestanding 1mm thick elastomer (PDMS) membranes and withstand repeated bending tests without electrical failure.
4:00 PM - JJ8:Circuits
BREAK
JJ9: Mechanical Design
Session Chairs
Friday PM, April 09, 2010
Room 2000 (Moscone West)
4:30 PM - **JJ9.1
Mechanics of Electronic Eye Camera.
Yonggang Huang 1 , Jizhou Song 1
1 , Northwestern University, Evanston, Illinois, United States
Show AbstractThe human eye represents a remarkable imaging device, with many attractive design features. Prominent among these is a hemispherical detector geometry, similar to that found in many other biological systems, that enables wide field of view and low aberrations with simple, few component, imaging optics. This type of configuration is extremely difficult to achieve using established optoelectronics technologies, due to the intrinsically planar nature of the patterning, deposition, etching, materials growth and doping methods that exist for fabricating such systems. Here we report strategies that avoid these apparent limitations and we implement them to yield high performance, hemispherical electronic eye cameras based on single crystalline silicon technology. The approach uses wafer-scale optoelectronics formed in unusual, two dimensionally compressible configurations and elastomeric transfer elements capable of transforming the planar layouts in which the systems are initially fabricated into hemispherical geometries for their final implementation. In a general sense, these methods, taken together with our theoretical analyses of their associated mechanics, provide practical routes for integrating well developed planar device technologies onto the surfaces of complex curvilinear objects, suitable for diverse applications that cannot be addressed using conventional means.
5:00 PM - JJ9.2
A Taxonomy of Wrinkling and Cracking of Hardened PDMS Surfaces.
Patrick Goerrn 1 , Sigurd Wagner 1
1 Electrical Engineering, Princeton University, Princeton, New Jersey, United States
Show AbstractThe silicone elastomer poly(dimethylsiloxane) (PDMS) grows a hard surface layer when it ages in air. Similar hard surface layers, either native or deposited, also form during the fabrication of skin-like electronics on PDMS. These layers may wrinkle, crack, or both, under conditions that at times are controlled by design but more often are discovered by trial-and-error. For reproducible experimentation the conditions for wrinkle and crack formation need to be quantified. We studied the formation of native hard surface layers in plasma-enhanced oxidation by exploring the largest parameter space surveyed to date. It turns out that the biggest “phase space” of surface topographies becomes accessible when the PDMS substrate is in confined, uni-axial, tensile, prestrain. By confined we mean the result of bonding the PDMS membrane to a polyimide foil substrate, and then bending the composite: doing this stretches the PDMS in the x direction without letting it relax in the y direction. This 1-D confined stretching brings out four distinct phases: flat / wrinkled / cracked / cracked and wrinkled. These four phases of skin morphology are clearly separated in the space of plasma dose vs. plasma pressure. Of course, the most interesting phase is wrinkled, without cracks. We analyzed it, and also the cracked-and-wrinkled phase, by Atomic Force Microscopy (AFM) in the tapping mode. From wrinkle amplitude and wavelength we determined the modulus and thickness of the hard surface layer, and inferred a graded hardness, by employing a modified theoretical model. Our main result is this clear separation of the four phases, coupled with the identification of the parameters under which the technologically important pure wrinkled phase is obtained.This research is supported by the New Jersey Commission for Brain Injury Research (grant no. BIR2 08.004). P.G. thanks the Alexander von Humboldt-Foundation for a Feodor Lynen Fellowship.
5:15 PM - JJ9.3
Resistance Change of Metallic Films on Flexible Substrates During Cyclic Bending Tests.
Byoung-Joon Kim 1 , Ho-Young Lee 1 , In-Suk Choi 2 , Ji-Hoon Lee 1 , Young-Chang Joo 1
1 , Seoul National University, Seoul Korea (the Republic of), 2 , Korea Institue of Science and Technology, Seoul Korea (the Republic of)
Show AbstractThe repeating deformation have been one of the main reliability issues in the flexible electronics since metal interconnects on the flexible electronics experience bending, stretching, and twisting during their usage leading to resistance increase prior to fatigue failures. The behavior of metal thin films under cycling stretching has been studied by several research groups but the main focus was on the mechanical failure of metal thin films under uniaxial cyclic deformation. Our study has paid more attention on the resistance change during the cyclic deformation, particularly cyclic bending deformation that mimics the real failure situation of flexible electronics. We have also investigated the effect of thin film structures on the resistance change associated with different flexible substrates and deposition process. The 2um thick thin films of Cu were deposited on Bismaleimide Triazine (BT) and Polyimide (PI) using evaporation and ink-jet printing process. For comparison, the 2um Ag films on BT were prepared by evaporation process. The strain-controlled cyclic bending tests were performed up to 1.1 % strain at 1 Hz frequency. The electrical resistance monotonically increased with the increasing number of cyclic bending for all cases. However, the resistance increasing rate shows different behavior depending on the substrates and process. The resistance increasing rate of the evaporated Cu on PI is biggest; that of the evaporated Cu on BT the second biggest; and that of the inkjet processed Cu has the lowest resistance increasing rate. The evaporated Ag film was smaller than that of evaporated Cu on PI. The difference in the resistance increasing rate can be explained by the film structures. The evaporated Cu on PI has the smaller grain size than others while the evaporated Cu and Ag on BT have larger grain size and even some porous structure in Ag film. The inkjet-printed Cu films form largest porous microstructure. The grain boundary works as a vacancy sinking site so that the smaller grain size may lead to the easy vacancy annihilation due to short diffusion length of vacancy to grain boundary. The porous structure containing a lot of free-volume and large area of free surface can be a sinking site of vacancy during the cyclic deformation. The changing rate of vacancy density during the cyclic deformation may be associated with the different resistance increasing rate. In this study, the fatigue test of Sn film will be briefly mentioned in order to address the effect of different crystal structure between FCC and BCC on the cyclic bending fatigue behavior.
5:30 PM - **JJ9.4
Mimicing the Eye: Imagers Based on Hemispherical Focal Plane Arrays Using Organic Photodiodes.
Stephen Forrest 1 , Jeramy Zimmerman 1 , Xin Xu 1
1 EECS & Physics, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractThe human eye provides an example of an ideal imaging system: it is compact and lightweight while having a very wide field of view without image distortion, a very low f/number (and hence high sensitivity in low light), and has a very simple lens system. The architecture is made particularly simple since the image is formed on a nearly hemspherical surface, thereby matching the curved focal plane of the lens. Achieving this imaging system in modern cameras has been difficult since the “film plane” must be flat if conventional, brittle semiconductor sensor arrays are used. Indeed, formation of high performance organic electronic devices on three dimensionally deformed surfaces is severely constrained by the tensile stresses and shear slip that are introduced during the deformation process. Here, we demonstrate the direct transfer of metals via cold welding onto preformed, 1.0 cm radius plastic hemispheres with micrometer scale feature resolutions to realize 100x100 organic photodetector focal plane arrays that mimic the architecture of the human eye [1]. This demonstration significantly extends the ability of direct transfer patterning, previously only demonstrated on planar substrates, to advanced optical and electronic applications. The passive matrix focal plane array consists of high performance, (40µm)2 organic double heterojunction photodetectors with response extending across the visible spectrum. The dark current density of a typical detector is 2.5±¬0.1 µA/cm2 at -1V bias, and with a peak external quantum efficiency reaching 12.6±0.3% at a wavelength of 640nm. The photodetector impulse response was 20ns, making the array suitable for video recording applications.[1] “Direct Transfer Patterning on Three Dimensionally Deformed Surfaces at Micrometer Resolutions and Its Application to Hemispherical Focal Plane Detector Arrays”, X. Xu, M. Davanco, X.Qi and S. R. Forrest, Org. Electron., 9 (2008).