Symposium FA
Materials Issues in Flexible and Stretchable Electronics


Session FA-1 - Materials and Fabrication Processes

FA-1:IL01  Material Challenges for Printed Electronics in the Microwave Domain
C. ARMIENTO, Alkim Akyurtlu University of Massachusetts, Lowell, MA, USA

There is growing interest in adopting additive technologies for the production of RF, microwave and wireless electronics for applications such as the Internet of Things (IoT), flexible radars and 5G telecommunications. These applications may require electronics that are flexible, conformable or embedded in 3D objects created by Fused Deposition Modeling (FDM). A printed approach to electronics requires the formulation and characterization of printable, electronic materials in the form of inks or filaments. This talk will describe research on conductive and dielectric inks including their characterization at frequencies up to 30 GHz. Work on microwave characterization of 3D, FDM-printed dielectrics will be presented. A novel ferroelectric ink, developed to print varactors and phase shifters for steerable antenna arrays and frequency-agile systems, will also be discussed. This ferroelectric ink can be tailored to have a relative permittivity as high 55 with a very low loss tangent of 0.002 at 10 GHz. Printed varactors based on this ink have demonstrated a capacitance tunability up to 10% at microwave frequencies. The ink was also used to fabricate printed phase shifters that are required for flexible, conformable radar systems.

FA-1:IL02  Soft and Flexible Bioelectronics
R.A. GREEN, J.A. Goding, Imperial College London, London, UK

Since the inception of neuroprosthetic devices and development of cardiac pacemakers, metals have been used to conduct and inject electrical charge in the body. However, metals have limitations including their high stiffness (contributes to chronic inflammatory response), low charge injection limits and potential dissolution. Conductive polymers (CPs) are a promising alternative to metallic materials for the conduction and delivery of therapeutic charge in the body. However, CPs are brittle and friable and have a limited number of compatible fabrication techniques. In this study, soft and flexible bioelectronics are developed from CPs and polyurethane (PU) to result in conductive elastomers (CE). Increasing the PEDOT content in the CE from 8 to 24 wt% corresponded to an increase in CSC from 33 to 224 Conductivity was also increased from 310 to 2857 Tensile testing of the CEs proved they are capable of significant extension with the 8 wt% PEDOT CE capable of 480% extension with an UTS of 9.1 MPa. CEs with 24 wt% PEDOT had a decreased toughness of 1.6 MPa with elongation of 90% prior to failure. CEs hold great potential for use as flexible electrode arrays and leads due to their ideal electrical and mechanical properties and MRI compatibility.

FA-1:IL05  Polymeric Solid-state Ionic Gate Dielectrics for Low-voltage Field-effect Transistors
YONG-YOUNG NOH, Department of Energy and Materials Engineering, Dongguk University, Seoul, South Korea; YOONSEUK CHOI, Department of Electronics, Hanbat National University, Daejeon, South Korea

Polymer electrolytes (e.g. ion gel) have been extensively researched for achieving high charge carrier mobility, low operation voltage and operational stability in unconventional field-effect transistors (FETs) and organic electronic devices. However, it is challenging to fabricate evaporated thin metal top gated device geometry because of the gel-like nature. Ion diffusion into the semiconducting film also interferes fundamental charge transport during operation. Here we successfully developed a new high-capacitance polymeric solid-state ionic gate dielectrics prepared by a controlled blend consisting of the high-k and low-k polymers and the ion gel based on poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP) with 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI] ionic liquid. Our engineered solid polymer electrolytes show huge capacitance values > 4 μF/cm2, which allows high drive current at low driving voltages and also allow the direct deposition of a conductive top-gate electrode by any methods such as thermal evaporation and printing. Vacuum-metalized top gate FETs with the solid-state ionic dielectrics showed excellent carrier mobilities in a range of 3-20 cm2V-1s-1 for common polymer semiconductors.

FA-1:L06  Self-organization of pi-extended Heteroacenes for Solution-processable Organic Field-effect Transistors
TATSUYA MORI, T. YASUDA, Kyushu University, Fukuoka, Japan

Organic field-effect transistors (OFETs) have attracted great interest as a promising alternative to inorganic transistors owing to their cost-effective manufacturing and high productivity. Much effort for developing organic semiconductors has led to field-effect mobilities exceeding 10 cm2V–1s–1 in OFETs. However, the majority of the reports required complex manufacturing techniques to prepare the high-quality active layers. Thus, rational materials design to realize optimum molecular organization enabling efficient charge transport in solution-processed thin films is highly desired. In this study, we focused on the arch-shaped pi-extended heteroacenes as a new type of solution-processable, high-performance organic semiconductor. A facile dip-coating process was demonstrated to produce highly molecular-oriented thin films, in which U-shaped molecules were self-organized into a bilayer lamellar structure. Moreover, OFETs based on the dip-coated films exhibited excellent charge carrier mobilities up to 3.8 cm2V–1s–1 without any post deposition treatment. These results demonstrated that less-symmetrical pi-extended core could be a novel molecular design for appropriate self-organization and resulting charge-transport property as high-performance organic semiconductors.

FA-1:L07  Realizing Flexible High-performance Silver Interconnects on Thin and Ultrathin Substrates by Inkjet-printing and Innovative Laser Treatment
M. VINNICHENKO1, D. MAKAROV2, M. FRITSCH1, T. VOITSEKHIVSKA2, V. SAUCHUK1, M. KUSNEZOFF1, 1Fraunhofer IKTS, Dresden, Germany; 2Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany

We present a study on the fabrication and thermal treatment of Ag interconnects, which are inkjet-printed on flexible substrates, i.e. thin glass, polymer foils, and paper with a thickness from 176 (special paper) down to 2.5 µm (PET foil). To enable a time efficient thermal treatment of the interconnect structures printed over large areas (75x200 mm2) we applied a novel rapid post-processing approach based on a diode laser array having a homogeneous line-shaped beam profile. Using IKTS proprietary ink, as-printed 30 mm long Ag lines after drying were electrically conducting with electrical resistivity values by a factor of ~7 (paper) to ~14 (PET, PI, thin glass) higher than those of the bulk material. Subsequent millisecond laser processing enabled silver contacts with a low electrical resistivity (~3x of bulk) on flexible substrates with thicknesses down to 2.5 µm. The contacts on paper were bendable to a radius of 4 mm with the resistivity increase of 1%; a 100 cycle test of bending to a radius of 10 mm led to negligible changes of their resistivity values. The developed interconnects were used for contacting large area flexible arrays of magnetic field sensors. The electrical and mechanical properties of the samples will be discussed in relation to their microstructure.

FA-1:IL08  Semiconducting: Insulating Polymer Blends: Towards Flexible, Robust Organic Optoelectronic Devices
N. STINGELIN, Georgia Institute of Technology, Atlanta, GA, USA

Blends and other multicomponent systems are used in various polymer applications to meet multiple requirements that cannot be fulfilled by a single material. In polymer optoelectronic devices it is often desirable to combine the semiconducting properties of the conjugated species with the properties of certain commodity polymers, such as mechanical robustness, pronounce hydrophobicity and low gas diffusion. Here we investigate bicomponent blends comprising high-mobility, polymeric semiconductors, such as diketopyrrolopyrrol derivatives (DPP-T-TT) and selected semicrystalline commodity polymers, and show that, owing to a highly favourable, crystallization-induced phase segregation of the two components, we can reach low-percolating network systems similar to poly(3-hexylthiophene):high-density polyethylene (HDPE) blends. Focus of the presentation will be on the effect of the insulator on the sub-threshold voltage, bias stress and On-Off ratio as well as long-term environmental device stability of such DPP-T-TT devices; examples in the field of organic photovoltaics and the growing bioelectronics area are also given.

FA-1:L09  Designing Novel Polymer Systems with Enhanced Dielectric Response
V. BOBNAR, Condensed Matter Physics Department, Jozef Stefan Institute, Ljubljana, Slovenia; Y. BEERAN, S. THOMAS, Mahatma Gandhi University, International University Centre for Nanoscience and Nanotechnology, Kottayam, Kerala, India; Y. GROHENS, Universite de Bretagne, Sud LIMATB Laboratory, Lorient, France; V. KOKOL, University of Maribor, Institute for Engineering Materials and Design, Maribor, Slovenia; Y. THAKUR, Q. ZHANG, Electrical Engineering Department and Materials Research Institute, The Pennsylvania State University, University Park, PA, USA

We will demonstrate that novel polymer materials with high dielectric constant, required in energy storage systems and electromechanical applications, can efficiently be developed by taking into account basic physical phenomena. In a heterogeneous system composed of dielectric matrix and electrically conductive inclusions, the charge accumulated at phase boundaries acts as a large electric dipole. Using this Maxwell-Wagner polarization we have effectively increased the dielectric constant of PVDF-based electroactive polymers and thus substantially reduced the electric field required for their giant electrostrictive response. Analogously, we have fabricated composites from graphene oxide nanoplatelets and wood-based cellulose nanofibrils. We will show that dielectric response of these flexible, eco-friendly composites is strongly enhanced already at a low filler concentration. PVDF-based polymers with strongly coupled dipoles also exhibit pronounced polarization hysteresis, which increases dielectric losses. As an alternative we will present a new class of dielectric polymer, aromatic polythiourea. We will compare the response of this amorphous, glass-phase polymer with that of commercially used systems and demonstrate its stability over broad temperature and frequency ranges.

FA-1:L12  Freestanding Utrathin and Ultraconformable PVF Capacitors
J. BARSOTTI, The Biorobotics Institute, Scuola Superiore Sant’Anna & Center for Micro-BioRobotics @SSSA, Istituto Italiano di Tecnologia,  Pontedera, Italy; I. HIRATA*, M. CAIRONI, Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia, Milano, Italy; F. GRECO**, V. MATTOLI, Center for Micro-BioRobotics @SSSA, Istituto Italiano di Tecnologia, Pontedera, Italy; *At present at Center for Micro-BioRobotics @SSSA, Istituto Italiano di Tecnologia, Pontedera, Italy; **At present at Institute of Solid State Physics, Graz University of Technology, Graz, Austria

Interest in conformable electronic devices/components - able to adhere and adapt their shape to arbitrary surfaces - is constantly increasing. Conformability is appealing when unperceivable devices are demanded, e.g. in biomedical, healthcare and sport monitoring applications, as well as in soft robotics. The main technological challenge is to achieve devices conformability and adhesion to complex surfaces without compromising functionality. We propose a novel approach to fabricate free-standing ultra-thin and ultra-conformable capacitors using nanosheets of poly (vinyl formal) (PVF) that combine extremely good conformability with excellent mechanical resistance and good dielectric properties. Capacitors have extremely low thickness and mass, down to 0.15 mg/cm^2 for a dielectric PVF layer of 10 nm. Capacitors are able to conformally adhere to virtually any surface with arbitrary topography, showing a capacitance density up to 0.4 mF/g (corresponding to 60 nF/cm^2), a wide working frequency range going from DC up to 280 kHz, with very low leakage currents and high dielectric strength. Moreover, capacitors are able to sustain bending at extremely small curvature radii, as demonstrated by conforming on complex surfaces, such has a nylon mesh with micrometric texture.

FA-1:L13  Thin Functional Dielectric Elastomer for Stretchable Devices
D.M. OPRIS1, S.J. DÜNKI1, 2, YEE SONG KO1, 2, E. PERJU1, 3, P. CASPARI1, 2, D. DAMJANOVIC2, Y. SHEIMA1, F.A. NÜESCH1, 2, 1Swiss Federal Laboratories for Materials Science and Technology Empa, Duebendorf; 2Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland; 3“Petru Poni” Institute of Macromolecular Chemistry of Romanian Academy, Romania
Soft functional materials and devices that convert one form of energy into another in response to external stimuli, produce energy on demand, can sense environment changes, and can mimic natural muscles are of great importance for future technologies. These appealing functions will be possible one day thanks to progress in dielectric elastomer transducers (DET). DET are elastic capacitors which can function as actuators, generators, or sensors. The commercialization of this technology will significantly improve if dielectric elastomer materials with better performance were available. Of the various requirements that have to be met are an increased dielectric permittivity, while maintaining all of the other dielectric and mechanical properties. This presentation gives an overview of novel materials with high dielectric permittivity which allow construction of DETs operated at unprecedentedly low voltages and of piezoelectric elastomers that generate an electric signal when mechanically stressed. High permittivity elastomers were achieved by modifying polysiloxanes with polar groups. Piezoelectric elastomers were prepared by poling specially designed silicone composites under an electric field.

Session FA-2 - Device Physics, Mechanics and Design

FA-2:IL01  Mechanical Properties of Organic Semiconductors for Stretchable and Mechanically Robust Electronics
D.J. LIPOMI, Department of NanoEngineering, University of California, San Diego, La Jolla, CA, USA

Mechanical deformability underpins many of the advantages of organic semiconductors. The mechanical properties of these materials are, however, diverse, and the molecular characteristics that permit charge transport can render the materials stiff and brittle. This review is a comprehensive description of the molecular and morphological parameters that govern the mechanical properties of organic semiconductors. Particular attention is paid to ways in which mechanical deformability and electronic performance can coexist. The review begins with a discussion of flexible and stretchable devices of all types, and in particular the unique characteristics of organic semiconductors. It then discusses the mechanical properties most relevant to deformable devices. In particular, it describes how low modulus, good adhesion, and absolute extensibility prior to fracture enable robust performance, along with mechanical “imperceptibility” if worn on the skin. A description of techniques of metrology precedes a discussion of the mechanical properties of three classes of organic semiconductors: π-conjugated polymers, small molecules, and composites. The discussion of each class of materials focuses on molecular structure and how this structure (and postdeposition processing) influences the solid-state packing structure and thus the mechanical properties. The talk concludes with applications of organic semiconductor devices in which every component is intrinsically stretchable or highly flexible.

FA-2:IL02  Mechanical Reliability of Advanced Thin Films
TAEK-SOO KIM, Department of Mechanical Engineering, KAIST, Daejeon, South Korea

Advanced thin films are ubiquitous and important in many modern technologies. Most prominent applications include microelectronic devices, fuel cells, solar cells, OLED displays for which electrical, electrochemical, and optical properties of thin films are critical. However, while significant efforts have been directed to improving those properties, mechanical integrity of the thin films has been often ignored and even sacrificed. For example, new materials with unknown mechanical properties are increasingly being used, and in many cases they turn out to have inferior mechanical reliability. To make matters worse, thin film devices are being attempted to be mounted on flexible and even stretchable substrates, and this dramatically increases film deformation and stress. All of these trends significantly sacrifice mechanical integrity of thin films and reduce device yield and reliability. This talk presents novel methods to measure and enhance mechanical properties of advanced thin films for flexible and stretchable electronics. Especially, 1) tensile testing of ultra-thin films on water surface and 2) adhesion and cohesion of advanced thin films are discussed.

FA-2:IL04  A Highly Sensitive Flexible Sensor Analog to Human Skin Via Air-assembled Motile Electronic Whiskers
J. REEDER, T. KANG, S. RAINS, W. VOIT, University of Texas at Dallas, Richardson, TX, USA

We demonstrate an assembly technique for 3D electronics for creating a sensing analog to human skin. Directed warm air heats and deforms initially planar, photolithographically-defined flexible electronics into 3D shapes by heating substrates above their glass transition temperatures and applying enough force via air flow to deform each individual, patterned whisker out of plane. Gold strain gauges patterned along each whisker are thus assembled into 3D space. Deflections of the whisker tips as small as 5 µm can be sensed, enabling a variety of distinct sensing modes including proximity, texture mapping, surface roughness, materials stiffness and temperature. An extraordinarily wide range of surface topology features can be sensed, from 50 nm changes in surface roughness to height changes up to 500 µm (four orders of magnitude). The shape memory properties of the substrate enable reversible assembly and flattening, mimicking the whisking functionality of vibrissae in nature.

FA-2:IL05  Soft Platinum-silicone Coating for the Epidural Stimulation of the Spinal Cord
G. SCHIAVONE, S.P. LACOUR, LSBI, EPFL Campus Biotech, Laboratory for Soft Bioelectronic Interfaces, School of Engineering, Geneva, Switzerland

Previous research has proven that mechanics play an important role in the interaction between implanted devices and host tissue, and substantial experimental work currently aims at replacing conventional hard materials with soft alternatives that can trade-off performance in favour of a lower immune response. In this context, we report on the performance of a soft platinum-based composite material used as coating for electrodes designed for spinal epidural stimulation. The composite material is fabricated by dispersing meso-scale platinum particles (0.27-0.47 µm average size) within a polydimethylsiloxane (PDMS) matrix, in order to create a conductive paste that offers a balance between the charge transfer properties of platinum and the mechanical properties of PDMS. In-vitro measurements taken by immersing the array under test in phosphate buffered solution (PBS) with a Pt counter electrode and an Ag|AgCl reference electrode are compared to in-vivo measurements taken post-implantation of 2 electrode arrays in the epidural space of the lumbar segment. The comparison between the in-vitro and in-vivo data highlights promising charge injection properties, as well as challenges that need to be addressed to enable the future translation of the technology to the clinic.

FA-2:IL06  Electronic and Thermoelectric Properties of High-performance Polymer Semiconductors and Conductors
M. KEMERINK, Complex Materials and Devices, Department of Physics, Chemistry and Biology (IFM), Linköping University, Sweden

There is great interest in the thermoelectric properties of organic semiconductors for application in low-cost energy harvesters. This talk addresses strategies and fundamental limitations to simultaneously achieve a high Seebeck coefficient S and a high conductivity, as needed to obtain a high figure of merit ZT. As also shown by others, tailored doping methodologies that minimize morphology disturbances allow to maintain high S while increasing the conductivity, in our case leading to a record power factor for n-doped PCBM of PF≈35 µW/m·K-2 and ZT≈0.07 at room temperature. Nevertheless, we show that the unavoidable presence of ionized dopants leads to a broadening of the density of states that translates into fundamental limits to PF and ZT. The resulting model gives a physical explanation for the often-observed power law relation between S and conductivity. Analyzing own and published data suggests that n-type organic thermoelectrics can eventually become superior to their p-type counterparts and indicates that ZT>1 should be reachable. Finally, we demonstrate a universal method to obtain record-high Seebeck coefficients while preserving reasonable conductivities in doped blends of organic semiconductors through rational design of the density of states and morphology control.

FA-2:IL07  Organic Semiconducting Crystals as Flexible, Ultra-low Voltage, Ionizing Radiation Detectors
B. FRABONI, Department of Physics and Astronomy, University of Bologna, Bologna, Italy

In the last years, the need to envisage large-area conformable and possibly flexible ionizing radiation sensor panels is rapidly growing, for applications that span from cultural heritage preservation to the security of public buildings. Organic materials have a strong potential for such applications, thanks to their mechanical flexibility and the possibility of deposition over large and bendable substrates by means of low-cost wet-technologies as printing techniques. Recent reports demonstrated how solution grown organic semiconducting single crystals (OSSCs)-based devices are excellent ionizing radiation sensors operating at room temperature [1,23] and provide a direct (i.e. the X-ray photons are directly converted into an electrical signal), stable, and linear electrical response to increasing X-rays dose rates. In particular, we reported about fully printed, direct and bendable organic thin-films X-ray detectors, with sensitivity values up to several hundreds of nC/Gy at ultra-low bias of 0.2 V. The demonstration of the first full-organic X-ray imager for real application has been provided by a 2×2 pixelated matrix printed organic detector. We developed an analytical model, based on charge accumulation and photoconductive gain, accounting for the measured signal amplitude and sensitivity values, has been developed [3,4]. These studies open the way to the development of a new class of fully flexible, real-time and low cost large area organic-based direct radiation detectors.
[1] B. Fraboni et al., Adv. Mater. 24, 2289(2012). [2] A. Ciavatti et al., Appl. Phys. Lett. 108, 153301 (2016). [6] L. Basiricò et al., Nat.Comm., 7, 13063 (2016). [4] S. Lai et al., Adv. Electron. Mater., 3, 1600409 (2017).

Session FA-3 - Applications of Flexible/Stretchable Electronics

FA-3:IL01  Ultrathin, Imperceptible Electronics
M. KALTENBRUNNER, Soft Electronics Laboratory, Linz Institute of Technology, Johannes Kepler University Linz, Austria

Electronics of tomorrow will be imperceptible and will form a seamless link between soft, living beings and the digital world. Weight and flexibility become key figures of merit for large area electronics such as robotic skin, With less than 2 μm total thickness, imperceptible electronic foils are light (≈3-5 g m-2) and unmatched in flexibility, they are highly durable and withstand severe crumpling without performance degradation. These are prerequisites for intimate contact with soft, biological tissue or organs and complex, arbitrarily shaped 3D free forms that enable applications spanning medical, safety, security, infrastructure, and communication industries. This talk introduces a technology platform for large-area, ultrathin and lightweight electronic and photonic devices, implantable organic electronics and “sixth-sense” magnetoception. These large area sensor networks build the framework for electronic foils and artificial sensor skins that are not only highly flexible but become highly stretchable and deployable when combined with engineered soft substrates such as elastomers, shape memory polymers or tissue-like hydrogels, ultimately enabling future soft electronics and soft machines.

FA-3:IL04  Wearable Strain Sensors and Power Generators
I.A. ANDERSON, Biomimetics Lab, Auckland Bioengineering Institute, University of Auckland and StretchSense Ltd., Penrose, Auckland, New Zealand

It is now possible to monitor human motion using soft stretchy sensors integrated within the clothes we wear. This can require a large number of sensors, each with its own electronics. We are seeking ways to significantly reduce this electronics burden. One solution is to electrically daisy-chain sensors so that a single electronics chip serves a sensor group. Each capacitive sensor in the chain becomes part of an electrical transmission line, for which high frequencies are attenuated more than low frequencies. Real-time analysis of the multi-frequency signal enables measurement of individual sensor stretch. The dielectric elastomer capacitor configuration used for sensing can also be used for energy harvesting from the shoe heel, for instance. We have developed a circuit for this, the self-priming circuit that manages charge delivery/ harvesting from the elastomer energy harvester. Electrical partitioning of the polymer energy harvester enables integration with its self-priming circuit so that hard capacitors within the generator self-priming circuit electronics are not required. We have demonstrated how a discrete sensor can be powered by a polymer generator. Ultimately we will combine sensor with energy harvester; developing a self-powering sensor with minimal electronics.

FA-3:L05  Metallic Nanoislands on Graphene and Machine Learning for Monitoring Swallowing Activity in Head and Neck Cancer Patients
J. RAMIREZ1, D. RODRIQUEZ1, FANG QIAO3, J. WARCHALL2, B.C. MARIN1, J. RYE1, E. AKLILE1, A.S-C. CHIANG1, P.P. MERCIER2, CK CHENG3, K.A. HUTCHESON4, E. SHINN4, D.J. LIPOMI1, 1Dept. of NanoEngineering, University of California, San Diego, La Jolla, CA, USA; Dept. of Electrical and Computer Engineering, University of California, San Diego, La Jolla, CA, USA; Dept. of Computer Science and Engineering, University of California, San Diego, La Jolla, CA, USA; 4Dept. of Behavioral Sciences, The University of Texas M.D. Anderson Cancer Center, Unit 1330, Houston, TX, USA

This presentation describes a highly sensitive, flexible strain sensor made of palladium nanoislands on single-layer graphene. These sensors, placed on the submental region of the neck, are used on 14 head and neck cancer patients. These patients exhibited various levels of swallowing function after radiation therapy: from non-dysphagic to severely dysphagic. The devices detect differences in the consistencies of food boluses when swallowed (i.e. water, cracker, etc.), and differences between dysphagic and non-dysphagic swallows. When activity from surface electromyography (sEMG) is obtained simultaneously with strain data, it is possible to differentiate swallowing vs. non-swallowing events (i.e. head turns, etc.). The major features in the plots of resistance (strain sensors) and electrical activity (sEMG) are correlated to events during the course of swallowing a barium paste as recorded by video X-ray fluoroscopy (the current standard of care). We developed a machine learning algorithm to automate the identification of boluses for a healthy subject and discriminate between swallows from either a healthy subject or a dysphagic patient. These results may lead to non-invasive and home-based systems for monitoring and diagnosis of swallowing function and improved quality of life.

FA-3:L06  Development of Lead-free Piezoelectric Ceramic Nanofiber Modules for Flexible Structural Health Monitoring Sensor Application
SANG HYUN JI, JI SUN YUN, Electronic Convergence Materials Division, Korea Institute of Ceramic Engineering and Technology, Jinju, South Korea

Lead-free piezoelectric ceramic nanofiber composites of 0.78Bi0.5Na0.5TiO2-0.22SrTiO3 (BNT-ST) ceramics and polyvinylidene fluoride (PVDF) polymer were fabricated by electrospinning. XRD, FE-SEM and EDS mapping results showed that the characteristics of ceramic and polymer coexisted in the piezoelectric nanofiber composites. The piezoelectric characteristics were analyzed by the polarization-electric field (P-E) loops, and the results confirmed that a BNT-ST content of 60 wt% had higher piezoelectric characteristics. The BNT-ST nanofiber sensor modules were prepared by a WIP (Warm Isotropic Press) process, and then poling was performed at room temperature for 1 hour at 1 kV to improve the characteristics of the BNT-ST nanofiber sensor module. After the poling process, XRD patterns of the BNT-ST nanofiber sensor modules showed the phase transition, and the higher temperature of ferroelectric-to-relaxor transition temperature was observed in the poled lead-free piezoelectric nanofiber sensor modules. For flexible structural health monitoring sensor application, the poled and unpoled lead-free piezoelectric nanofiber module was directly attached to on the structure with various shapes, and the sensor characteristics of the flexible lead-free piezoelectric nanofiber sensor modules were measured by simulating several situations. The poling process contributed greatly to the improvement of the sensing performance.

FA-3:IL07  System Design for Flexible All-organic Reflectance Oximeter
Y. KHAN, DONGGEON HAN, A. PIERRE, J. TING, XINGCHUN WANG, C.M. LOCHNER, A.C. ARIAS, Dept. of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA, USA

Existing techniques for measuring oxygen concentration in blood heavily relies on non-invasive transmission-mode pulse oximetry - a ratiometric optical sensing method, where light absorption in oxygenated and deoxygenated blood is interpreted to a person’s oxygen saturation (SpO2). Since transmitted light through tissues is used to generate the signal, transmission-mode pulse oximetry is restricted to only tissues that can be transilluminated, such as the ear and the fingers. Here, we present a reflection oximeter, which uses printed organic light-emitting diodes (OLEDs) and organic photodiodes (OPDs) to sense reflected light from tissues to determine the oxygen concentration. Using the reflection-mode, the sensor can be used beyond the conventional sensing locations. We used the reflection-mode sensor to measure SpO2 on the forehead with 1.1% mean error. We also demonstrate a method to determine oxygen saturation in the absence of pulsatile blood. Additionally, printing techniques are utilized to fabricate the sensor on flexible plastic substrates, making the sensor both comfortable to wear and efficient at extracting high-quality biosignal.

FA-3:IL08  Temporary Tattoo Ink-jet Printed Multi-Electrode Array for Electrophysiology Applicationss
F. GRECO, Institute of Solid State Physics, Graz University of Technology, Austria

The emergent field of conformable electronics can enable the development of unperceivable personal monitoring systems to be used in healthcare and sport, especially in skin contact applications. In this talk I will report about a robust, low cost and safe strategy for producing disposable ultraconformable electrodes for skin-contact electrophysiology applications, by using temporary tattoo paper as an unconventional substrate. Tattoo electrodes and multielectrode arrays based on conducting polymer PEDOT:PSS are fabricated by ink-jet printing, laser cutting/engraving and lamination. Thanks to this choice, several different configurations of arrays could be customized for different applications. They can be easily transferred on skin as temporary transfer tattoos. We demonstrated their successful performances as stable, dry electrodes for surface electromyography (sEMG), permitting the myographic control of a robotic hand. Recent advancements include high density sEMG as well as ECG and skin impedance recording with stable adhesion and operation. Long-term recording was assessed which favorably compares with state of art electrodes. Ongoing work includes EEG recording and integration of advanced devices in tattoos towards fully autonomous epidermal monitoring systems.

FA-3:L09  The Glass Transition Temperature as a Means of Kinesthetic Feedback
C.W. CARPENTER, SIEW TING M. TAN, D. RODRIQUEZ, K. SKELIL, D.J. LIPOMI, University of California, San Diego, Dept. of Nanoengineering, South Pasadena, CA, USA

Wearable kinesthetic devices, i.e. devices that stimulate the joints and muscles through the sense of touch to recreate and simulate geometry and stiffness of objects in virtual reality, are typically limited by bulky components, e.g. pulley systems and pneumatic pumps. This talk introduces a novel form of kinesthetic stimulation by manipulating the mechanical properties of a spandex-thermoplastic composite through active heating and cooling above and below its glass transition temperature, Tg, to actuate between states of high and low stiffness in a conformal form factor. To maximize the change in stiffness, when worn as a glove, a plasticizer is incorporated to raise the Tg of the spandex-thermoplastic composite to the surface temperature of the skin. Low profile peltier elements are incorporated onto the surface of a kinesthetic glove and used to actively cool or heat the surface as a means of actuation. Actuation times are determined through a psychophysical experiment, where human subjects are asked to report the onset of relative changes in stiffness in both cooling and heating modes. Finally, an integrated two-way tele-robotic proof of concept is realized to simulate the motion of tapping a finger on a surface.

FA-3:IL10  Wearable Electronic Dystem Based on Stretchable Carbon Nanotube Dlectronics and Ultrathin Organic Light Emitting Diodes
JA HOON KOO1, 2, DAE-HYEONG KIM1, 2, 3, 1Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul, South Korea; 2Interdisciplinary Program for Bioengineering, Seoul National University, Seoul, South Korea; 3School of Chemical and Biological Engineering, Institute of Chemical Processes, Seoul National University, Seoul, South Korea

Various concepts for wearable devices have been recently introduced along with remarkable advances in technologies for flexible/stretchable devices. Yet, the current wearable electronics still suffers from practical problems, mainly related to the use of inorganics for the active layers. They are subject to mechanical cracks and/or breakdown in repetitive deformations and consequent accumulation of fatigues. The mechanical mismatch between the human tissues and inorganic materials aggravates the user discomfort and fragility, since human body consists of non-flat surfaces and fine topology. Hence, electronics for wearable applications requires soft materials and deformable designs to overcome such mismatches. Here, we present carbon-based materials and device design strategies for the core elements of wearable electronics. Semiconducting carbon nanotubes were used as the channel material for electronic applications, and ultra-thin organic materials for light-emitting devices to achieve extreme wearability. Experimental and theoretical results demonstrated that the fabricated devices showed no signs of degradation after repetitive bending/stretching tests, by virtue of passivation layers and design strategies that effectively protected the active components of the devices.

FA-3:IL11  Soft and Inert Composites and Devices for Neural Interfaces
K. TYBRANDT, Laboratory of Organic Electronics, Linköping University, Norrköping, Sweden

Stretchable electronics has received significant attention in recent years due to the prospects of new exciting applications. Conformal, soft and stretchable electronic devices are especially attractive for biomedical applications, where it is important to match the mechanical properties of the interfaced tissue. To date a variety of applications have been developed, ranging from electronic skin, in vivo temperature sensors to electrode arrays for stimulation and recording. Here we report on our recent efforts in the development of soft electronics for biomedical applications in general, and for neural interfaces in particular. We discuss the whole process from materials to applications: The development of inert high performance stretchable conductors with long-term stability; Methods for fabricating biocompatible high-resolution devices based on these materials; Applications for soft electronics in biomedical engineering and neural interfaces. Finally, we comment on present challenges and opportunities.

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