Siegfried Bauer Johannes-Kepler Universitaet Linz
Stephanie P. Lacour University of Cambridge
Teng Li University of Maryland
Takao Someya University of Tokyo
PP1: From Flexible to Stretchable Electronic Circuits
Tuesday AM, April 14, 2009
Room 3014 (Moscone West)
9:30 AM - **PP1.1
Flexible TFT Backplanes for Displays and Image Sensors.
Robert Street 1 , W. Wong 1 , R. Lujan 1 , T. Ng 1 Show Abstract
1 , Palo Alto Research Center, Palo Alto, California, United States
Flexible electronics create new opportunities for displays, image sensors and other large area applications. We compare the properties of amorphous silicon (a-Si) and organic semiconductor devices fabricated on low temperature plastic substrates. A-Si thin film transistors (TFT) and p-i-n photodiodes can be deposited at 150-170C with modest degradation in the properties compared to conventional high temperature deposition. A larger defect density gives a slightly higher threshold voltage for TFTs and a significantly higher reverse leakage current in photodiodes. An increased rate of bias-induced threshold voltage shift is probably due to differences in the hydrogen bonding. A more significant issue with silicon on plastic is the internal mechanical stress and bending limits. In contrast, organic semiconductors are softer and therefore mechanically better suited to plastic substrates, and have low processing temperature. Again, both TFTs and photodiodes can be made with generally suitable properties for displays and image sensors. However, organic TFTs are more susceptible to electrical and chemical instability than a-Si. Organic photodiodes based on the bulk heterojunction structure have low leakage current, but lower quantum efficiency that a-Si. Various TFT backplane devices made on plastic substrates will be described to illustrate these properties.
10:00 AM - **PP1.2
Technology and Applications of Flexible and Elastic Electronics and Sensor Circuits.
Jan Vanfleteren 1 Show Abstract
1 TFCG Microsystems, IMEC, Gent-Zwijnaarde Belgium
Since more than three years IMEC-UGent/CMST (Gent, Belgium) is developing technologies for flexible and elastic electronics and sensor circuits. In the vision of CMST eventually many future wearable systems will consist of very compact component islands, which are flexible or even rigid, and which are interconnected either wirelessly, either using stretchable or elastic conductors. These component islands can be quite complex (e.g. wireless sensor nodes), or very simple (e.g. individual LED’s in a wearable LED display). Key features of the developed technologies at CMST are: (1) use of off-the-shelf packaged components, including complex chips like microcontrollers, RF chips, signal conditioning chips, etc. so that systems with complex functionality can be achieved (2) the use of meander shaped metal tracks, which form the stretchable interconnects with low (PCB-like) electrical resistance (3) the use of Liquid Injection Moulding of elastomeric materials like PDMS (silicones) or PUR (poly-urethanes), so that completely embedded circuits can be achieved, thus creating the potential for implantable or washable systems (4) the use of processing sequences which are very close to industrial standards for PCB (printed circuit board) manufacturing and component assembly : the circuits are fabricated using conventional PCB-type lithography and wet etching, components are assembled using conventional SAC (tin/silver/copper) lead-free solder processes; elastomers and circuit stretchability are introduced at the very end of the production process only (5) the use of technologies for gradual transition from mechanically rigid structures (e.g. conventionally packaged components) to flexible and from flexible to stretchable structures. This smooth transition is of utmost importance to achieve sufficient circuit reliability. Besides the presentation of the basic technologies also the integration in textiles of the fabricated circuits and several applications of wearable circuitry, under development at CMST, will be discussed. These applications include wearable signage & displays, real-time body posture tracking for applications like epileptic seizure detection, gaming, artistic performances, etc.
10:30 AM - **PP1.3
Rubber-like Stretchable Organic Transistor Integrated Circuits Using Elastic Conductors.
Tsuyoshi Sekitani 1 , Takao Someya 1 Show Abstract
1 , Univ. of Tokyo, Bunkyo-ku, Tokyo, Japan
We successfully fabricated a truly rubber-like stretchable organic transistor active matrix with integrating printed organic transistors, elastic conductors, and elastic contacts. By using an ionic liquid of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, single-walled carbon nanotubes (SWNTs) were uniformly dispersed as chemically stable conducting dopants in a vinylidene fluoride-hexafluoropropylene copolymer matrix, and manufactured SWNT composite films where the content of SWNTs was increased up to 20 wt% without sacrificing mechanical flexibility or softness of the copolymer. The SWNT composite film was coated with dimethyl-siloxane-based (PDMS) rubber to realize a rubber-like elastic conductor, which exhibited an extraordinary high conductivity of 57 S/cm and a high stretchability of 134%, simultaneously. Further, the elastic conductor was integrated with printed organic transistors to fabricate a truly rubber-like active matrix with an effective area of 20 × 20 cm^2. The active matrix sheet can be uniaxially and biaxially stretched by 70% without mechanical or electrical damages.Organic transistor array with 19 x 37 transistors was manufactured on PDMS rubber sheets using inkjet, screen printing, mechanical punching system and, vacuum evaporation with rotation mechanics. An evaluated field-effect mobility was 0.6 cm^2/Vs and on/off ratio exceeded 10^5.Taking full advantage of the SWNT elastic conductor and paste, we manufactured a printed organic transistor-based stretchable active matrix where an array of organic transistors was connected with each other by elastic conductors (bit lines for source electrodes or word lines for gate electrodes). The transistor characteristics did not change after the formation of the interconnections with the fabricated elastic conductors since the conductivity of SWNT elastic conductor was 57 S/cm, which was enough high for the integration. The SWNT elastic conductors were connected to the contact pads for gate, source, and drain electrodes using the SWNT paste.This study was partially supported by the Grant-in-Aid for Scientific Research (KAKENHI; WAKATE S), the Special Coordination Funds for Promoting and Technology. We thank Profs. Takuzo Aida, Takanori Fukushima, Takayasu Sakurai, and Makoto Takamiya, The University of Tokyo, and Kenji Hata, AIST, for invaluable discussion. We also thank Dr. Yuzou Komatsu, Daikin, and Atsuko Kosaka, ERATO-SORST /JST, for technical supports.
PP5: Poster Session: Materials for Flexible Transistors
Tuesday PM, April 14, 2009
Exhibition Hall (Moscone West)
6:00 PM - PP5.1
Characterization of Room-Temperature Deposited P-type Transparent Conducting Ca-doped Cu-Al-O Thin Films.
I-Chun Cheng 1 , Shuo-Hang Liu 1 , Mu-Rong Yang 2 , Jian Chen 3 , Hsiao-Kuan Tsai 4 Show Abstract
1 Dept. of Electrical Engineering and Graduate Institute of Photonics and Optoelectronics, National Taiwan University , Taipei Taiwan, 2 Dept. of Materials Engineering, Tatung University, Taipei Taiwan, 3 Institute of Applied Mechanics, National Taiwan University, Taipei Taiwan, 4 , Taiwan Textile Research Institute, Taipei Taiwan
Transparent conducting oxides (TCOs) are key components in many optoelectronic applications. The majority of TCOs known today are n-type. However, to realize versatile transparent electronics, p-type TCOs are desirable in conjunction with n-type TCOs. In this study, we focus on the p-type delafossite CuAlO2-based TCOs. The CuAlO2 thin films can be produced by various techniques, such as pulsed laser deposition, chemical vapor deposition, sol-gel method, evaporation, rf-sputtering, and etc. To achieve good electrical and optical properties, most of the CuAlO2 thin films reported require a post-deposition anneal at 700°C to 1000°C, which is not compatible with low-temperature organic polymer (plastic) foil substrates for flexible electronic/optoelectronic applications. Here we report a method to improve the properties of room-temperature rf-sputtered Cu-Al-O thin films by addition of small amount of Ca.The Schott B270 glass was used as the substrates. The target is prepared from powders of CuO, Al2O3 and CaO with a substitution of Ca to 10% for Al, and sintered at 1200°C. The Cu-Al-Ca-O thin films are deposited at an rf power density ranging from 3.9 to 5.9 W/cm2 and at a gas pressure of 10mTorr in the environment of oxygen and argon mixture with oxygen vol.% ranging from 0 to 66%. Films are also deposited from target without addition of Ca for comparison. Without Ca-doping, our room-temperature rf-sputtered Cu-Al-O thin films have small electrical conductivity of ~10-5 S/cm or below, which is similar to the results reported in the literatures. However, by adding small amount of Ca into the Cu-Al-O thin films, we observe a dramatic improvement (two to three orders of magnitude) on the electrical conductivity of the films, while the averaged optical transmittance in the visible light regime (400nm to 700nm) remains similar. The nature of p-type conduction in these films is confirmed by a positive Hall coefficient. In addition, the electrical conductivity increases with the oxygen vol.%, while the deposition power shows little effect when oxygen vol.% is greater than 33%. At present, our as-deposited Cu-Al-Ca-O thin films have electrical conductivities up to ~1.2×10-2 S/cm and averaged visible transmittances of ~60% for 150-nm thick films.
6:00 PM - PP5.3
Characterization of Low-Temperature Laser Annealed Sol-gel ITO Thin Films.
Chang-Pin Huang 1 , I-Chun Cheng 1 , Jian Chen 2 Show Abstract
1 Dept. of Electrical Engineering and Graduate Institute of Photonics and Optoelectronics, National Taiwan University , Taipei Taiwan, 2 Institute of Applied Mechanics, National Taiwan University, Taipei Taiwan
Indium tin oxide (ITO) is the most widely used transparent conducting oxide in optoelectronic devices. It can be prepared by various techniques, such as thermal evaporation, sputtering, pyrolysis, chemical vapor deposition, sol-gel dip coating, and etc. Among these methods, sol-gel process has the advantage of producing homogeneous thin film in a large area with easy control of doping level at low cost. However, conventional ITO sol-gel process requires a high temperature anneal at 500°C or above to convert the precursor film into crystalline phase, which is not desirable when organic polymer (plastic) substrate is used. Here we investigate an ultralow temperature ITO sol-gel process by using solid-state UV laser for post-deposition anneal. The precursor solution is prepared by dissolving anhydrous indium trichloride ( InCl3 ) in acetylacetone, followed by refluxing for 3 hrs. Then a proper amount of SnCl4 is added to achieve 10 at.% Sn dopant concentration. Corning Eagle 2000 glass substrates were dipped into the precursor solution and withdrew at a rate of 10 cm/min, followed by baking at 260°C for 1 to 5 hrs to expel the residual organic solvent in the films. A pulsed solid-state UV laser was then used for post-deposition anneal. Films prepared at the same coating and baking conditions were also thermal annealed at 500°C for comparison. We observed significant improvements on optical transparency, electrical conductivity, and surface smoothness after laser anneal. The averaged transmittance in visible light regime ( 400 nm to 700 nm ) is above 86% for a 20-nm thick film. Resistivities of 3x10-2 Ω-cm and 1.97x10-2 Ω-cm were obtained after laser anneal at a fluence of 1000 mJ/cm-2 and thermal anneal at 500°C, respectively. The comparable electrical property observed in the laser annealed samples indicates that this approach could be a replacement for high-temperature thermal anneal. At present we are modifying the precursor solutions as well as the laser anneal conditions, and will report the results at the Symposium.
6:00 PM - PP5.4
The Effect of O2 Plasma Pre-treatment on the Electrical Properties of Gallium-Doped Zinc Oxide Grown on the plastic Substrates
Seok-Jin Lee 1 , Soon-Il Kwon 1 , Seung-Beum Park 1 , Tae-Hwan Jung 1 , Jae-Hwan Park 1 , Dong Gun Lim 1 Show Abstract
1 Dept. of Electronic Engineering, Chungju National University, Chungju, Chungbuk, Korea (the Republic of)
Transparent conductive oxide (TCO) films based on zinc oxide have been studied extensively as they have a number of advantages such as non-toxicity, low cost, materials abundance, and relatively low deposition temperature compared to traditional ITO films. Recently, TCO films deposited on polymer substrates have recieved considerable attention with the advent of flexible electronics. Thus, in this work, the electrical properties of Ga-doped zinc oxide (GZO) deposited on polymer electrodes were studied. The GZO films were deposited on PEN and PET films without substrate heating by RF magnetron sputtering from a ZnO target mixed with 5 wt% Ga2O3. The effects of the O2 plasma pre-treatment on the properties of GZO films were studied. The RF power for the O2 plasma pre-treatment was fixed at 100W and the pre-treatment time was varied in the range of 60~600 sec. The GZO resistivity of 6.2×10-3 and 1.1×10-3 Ω-cm were abtained on the PET and PEN substrates. The optical transmittance was typically ca. 80%.
6:00 PM - PP5.5
Reduction of Hysteresis in Flexible Organic Thin Film Transistors using Nano-structured Gate Dielectrics.
Younggug Seol 1 , Hwa-young Noh 1 , Nae-Eung Lee 1 , Chang-Soo Lee 2 , Hyungjun Kim 2 Show Abstract
1 Materials Science and Engineering, Sungkyunkwan University, Suwon Korea (the Republic of), 2 , Pohang University of Science and Technology, Pohang Korea (the Republic of)
In this work, reduction of hysteresis in the pentacene organic thin film transistors (OTFT) employing the nano-structured gate dielectrics were investigated. Nano-structured gate dielectrics with the multi-layered or nanocomposite structures of organic PVP and atomic-layer deposited (ALD) Al2O3 layer or Al2O3 nanoparticles were fabricated and employed in the OTFT devices. For analysis of capacitance, leakage current, and hysteresis of nano-laminated PVP/Al2O3(10~30 nm-thick)/PVP and PVP-Al2O3 nanocomposite gate dielectric layers, metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) structures fabricated on flexible polyimide substrate were cyclically bended up to 100,000 times with 5 mm bending radius. For evaluation of hysteresis characteristics of fabricated devices, we also applied cyclic bending test. In case of the fabricated nano-structured gate dielectric, the leakage current and capacitance value in MIM structure was not changed even after 105 times of cyclic bending. And hysteresis characteristics of the nano-structured gate dielectrics in MIS structure were significantly reduced after cyclic bending compared to that of single PVP layer. However, hysteresis of transfer characteristics in the device with various dielectric structures showed different behavior with increasing cyclic bending. In general, hysteresis in the transfer characteristics of the device with the nano-structured gate dielectric was decreased compared to that of the device with single PVP layer. Electrical and mechanical properties of the nano-structured gate dielectrics and the devices with them will be discussed in detail.
6:00 PM - PP5.6
Patterned Transfer using Water-soluble Graphene Oxide Paper.
Young Bum Yoo 1 , Byoung Har Hwang 1 , Hyeon Seok Hwang 1 , Man Hyeop Han 1 , Jin Young Oh 1 , Hong Koo Baik 1 Show Abstract
1 , Information & Display Laboratory, Yonsei Univ., Seoul Korea (the Republic of)
Thin film deposited on graphene oxide paper successfully transferred into polymer substrate by laminating polymer film followed by dissolving graphene oxide paper in water. this concept enables transfer of high-temperature deposited thin film onto polymer substrate. In addition, this technique provide easy and simple way to pattern transfered film.
6:00 PM - PP5.7
Characterization on IGZO Nano-powder Synthesized by Using a Liquid Process for Printable Electronics.
Chul Ho Jung 1 , Yong Kyu Kang 2 , Dae Ho Yoon 1 2 Show Abstract
1 SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon, Gyeonggi-do, Korea (the Republic of), 2 School of Advanced Materials Science & Engineering, Sungkyunkwan University, Suwon, Gyeonggi-do, Korea (the Republic of)
Recently, transparent amorphous oxide semiconductors (TAOS) have attracted much attention due to lots of advantages such as low processing cost, uniformly large area deposition at room temperature. Among the TAOS, amorphous In-Ga-Zn-O (a-IGZO) thin film has been widely considered as a channel of transparent thin film transistor (TFT) device. However, it is useless to apply for low cost and simple process because all processes were carried out in vacuum system. Therefore, we have investigated an easy and simple process by using a liquid process, and report characterization on IGZO nano-powder for ink-jet printing. We have examined the size of IGZO nano-powder by field emission scanning electron microscope (FESEM) and particle size analyzer. We also carried out structural properties by a high resolution transmission electron microscope (HRTEM). Moreover, we have fabricated TFT devices by ink-jet printing process and examined the characteristic of TFT performance for samples by semiconductor characterization system.
6:00 PM - PP5.8
Separation of Carbon Nanotubes Using a Variety of Surface-Confined Functional Groups.
Justin Opatkiewicz 1 , Melbs LeMieux 1 , Zhenan Bao 1 Show Abstract
1 Chemical Engineering, Stanford University, Stanford, California, United States
It has been found that single wall carbon nanotubes (SWNTs) interact differently with a variety of functional groups. Semiconducting (sc) tubes interact preferentially with amines, whereas aromatic molecules favor metallic (met) tubes. These results have led to the discovery that amine or phenyl functionalized surfaces can be used to separate nanotubes by diameter/chirality. Reports have also shown that SWNTs adsorb onto carboxylated surfaces, however any potential chirality separation has not been reported. In this work, we characterize a variety of silane self-assembled monolayers (SAMs) with different functional groups and examine their ability to separate nanotubes. SAMs under analysis include silanes capped with cyano-, bromo-, mercapto-, carboxyl-, and epoxy- functional groups. AFM is used to observe nanotube adsorption density, length and alignment. µRaman spectroscopy and device testing are used to quantify the extent of nanotube separation. Depending on the degree of separation, these surfaces can be utilized to make flexible nanotube network sensors of varying sensitivity to a variety of molecules.
Siegfried Bauer Johannes-Kepler Universitaet Linz
Stephanie P. Lacour University of Cambridge
Teng Li University of Maryland
Takao Someya University of Tokyo
PP17: Conformable Biosensing Circuits
Thursday PM, April 16, 2009
Room 3014 (Moscone West)
4:30 PM - **PP17.1
Woven Polymer Electronics at the Interface to Neurons.
Olle Inganas 1 , Maria Asplund 2 , Mahiar Hamedi 1 , Hans von Holst 2 Show Abstract
1 IFM, Biomolecular and organic electronics, Linköping Sweden, 2 Neuronic Engineering, Royal Institute of Technology, Stockholm Sweden
The integration of electronics on woven structures with biological tissue is a preferred route to neuroelectronics, as integration of the open porous structures of a textile is better adapted to cell proliferation and supply of nutrients. Therefore soft and flexible electronic materials processed on wires are interesting candidates. We report on development of electrochemical and field effect transistors created at the intersection of thin wires (10-100 µm diameter) by interfacing electronic polymers with solid state electrolytes. Electronic polymers coat the surface of textile wires. The electrolytes can have the form of aqueous based gels, or of ionic liquids, and transistor analogues of both accumulation and depletion functions are possible. We have developed simulation tools to describe the operation of devices, and can simulate circuits. To enable addressing of neural tissue, we have further developed polymer electrodes incorporating biological macromolecules, to suppress defence reactions and scar formation in the biological host. Electroactive polymer hydrogels give adequate charge capacity to stimulate neurons in most domains of relevance, including that of the retina
5:00 PM - PP17.2
Miniaturized Implantable Pressure and Oxygen Sensors Based on Polydimethylsiloxane Thin Films.
Jie Liu 1 , Waliullah Nomani 1 , Moonbin Yim 2 , Goutam Koley 1 , Xuejun Wen 2 , Tain-Yen Hsia 2 Show Abstract
1 Electrical Engineering, University of South Carolina, Columbia, South Carolina, United States, 2 , Medical University of South Carolina, Charleston, South Carolina, United States
We demonstrate the application of polydimethylsiloxane (PDMS) thin films in highly sensitive pressure and oxygen sensors, designed for pressure and oxygen content measurements within the heart and blood vessels. PDMS thin film deflection as a result of pressure changes was transduced by a capacitive detection technique to produce quantitative measurement of absolute pressures. 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 oxygen carrying fluid by a thin PDMS membrane. Pressure sensor sensitivity was ~0.1 nA/KPa, with a noise limited resolution of 0.1 KPa. Oxygen sensor sensitivity was 2.5 micro-ampere for 1% change in oxygen content of the surrounding media, with a noise limited resolution of 0.1 % of oxygen content change. These experimental results agree with theoretical modeling predictions, and suggest that the semi-permeable and biocompatible PDMS can be successfully adopted as the contacting membrane in an integrated sensor design to quantify pressure and oxygen content in blood.
5:15 PM - PP17.3
Water-stable Organic Transistors Fabricated on a Flexible Biodegradable Substrate.
Chris Bettinger 1 , Anatoliy Sokolov 1 , Zhenan Bao 1 Show Abstract
1 Chemical Engineering, Stanford University, Stanford, Massachusetts, United States
Organic thin film transistors (OTFTs) have demonstrated a widespread of applications in low-cost and temporary-use applications. Specifically, the use of disposable transistors could have wide-ranging use in biological and environmental applications including sensors. Toward this end, recent progress in this field has focused on the development of OTFT architecture using disposable substrates such as poly(ethylene terephthalate) and cellulose. These substrate materials would not be suitable for sensors that are intended for use in a temporary resorbable medical device intended for implantation. We have previously designed a class of flexible, biodegradable elastomers that has shown to be biocompatible in vitro and in vivo (Bettinger et al, Biomaterials 2008). The physical and biological properties of these elastomers, termed poly(1,3-diamino-2-hydroxypropane-co-polyol sebacate)s (APS), provide a mechanically flexible and biodegradable material platform that is suitable substrate for the fabrication of OTFT-based technologies for expanded applications. APS substrates were cured into layers approximately 500 microns thick and processed into sol-free elastomeric substrates. After patterning gate contacts, poly(vinyl phenol) solutions were spin coated and crosslinked on APS substrates to form a high quality gate dielectric (Roberts et al, PNAS 2008). 5,5′-bis-(7-dodecyl-9H-fluoren-2-yl)-2,2′-bithiophene (DDFTTF), a p-channel semiconductor, was selected as the active layer and was evaporated onto the surface. Typical p-type field-effect transistor behavior was observed in both the dry state and in the presence of water. APS substrates exhibited significant physical degradation in the presence of bovine cholesterol esterase as assessed by mass loss and microscopy evaluation. Taken together, these results suggest that APS substrates could serve as a suitable biodegradable material platform for OTFTs with potential applications in biological and environmental sensors as well as other implantable medical devices.
5:30 PM - **PP17.4
Materials and Mechanics for Stretchable Electronics -- Electronic Eyeball Cameras and Conformal Brain Monitors.
John Rogers 1 Show Abstract
1 , University of Illinois, Urbana, Illinois, United States
Electronic circuits that involve transistors and other components on thin plastic sheets or rubber slabs offer mechanical properties (e.g. bendability, stretchability) and other features (e.g. rugged, lightweight construction) that cannot be easily replicated with technologies that use rigid, fragile semiconductor wafer or glass substrates. Device examples include personal or structural health monitors and electronic eye imagers, in which electronics must conform to complex curvilinear shapes or flex/stretch during use. This talk describes our recent work in this area, with an emphasis on the use of single crystal inorganic nanomaterials in ‘wavy’ buckled configurations on elastomeric supports. We describe key fundamental materials and mechanics aspects of these approaches, as well as engineering features of their use in individual transistors, photodiodes and integrated circuits. Cardiac and brain monitoring devices provide examples of use in biomedicine; hemispherical electronic eye cameras illustrate the capacity for bio-inspired device design.