Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session L19: Focus Session: Ionically Gated and Conventional OFETs and Related Devices |
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Sponsoring Units: DMP DPOLY Chair: Jun Takeya, Osaka University Room: 320 |
Tuesday, March 17, 2009 2:30PM - 2:42PM |
L19.00001: All-Printed Low Voltage Operation Polymer Transistors and Circuits Based on Ion Gel Gate Dielectrics Yu Xia, Jeong Ho Cho, Mingjing Ha, Michael Renn, C. Frisbie A key challenge in the development of organic electronics lies in the realization of high quality devices with low cost. In this presentation, we demonstrate high performance polymer transistors and circuits with all components fabricated by a commercial aerosol jet printing technique. Printing saves the device manufacturing cost through its simple procedure, fast speed, high throughput and low waste of materials. Furthermore, by employing a specially designed ion gel as the gate dielectric material, ultra-high density carrier accumulation ($>$ 10$^{14}$ cm$^{-2})$ can be achieved in the transistor channel, which results in an exceptionally large transconductance of 10 $\mu $S/$\mu $m. Our typical transistors have mobility higher than 1cm$^{2}$/Vs and frequency response up to 10 kHz. Inverters, NAND and NOR logic circuits and ring oscillators have been realized as well, with low operation voltage, fast speed and high gain. In addition, the high polarizability of the gate dielectric allows us to print the gate electrode of each single transistor along with its source and drain electrodes at the same time in a coplanar architecture, which significantly simplifies the fabrication procedure. [Preview Abstract] |
Tuesday, March 17, 2009 2:42PM - 2:54PM |
L19.00002: Non-volatile Ferroelectric Poly(vinylidene fluoride-co-trifluoroethylene) Memory based on Single Crystalline Triisopropylsilylethynyl Pentacene Field Effect Transistor Seok Ju Kang, Insung Bae, Youn Jung Park, Tae Ho Park, Jinwoo Sung, Cheolmin Park We develop a new type of non-volatile ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) memory based on Organic Thin Film Transistor (OTFT) with single crystal Triisopropylsilylethynyl pentacene (TIPS-PEN) active layer. A bottom gate OTFT was fabricated with thin P(VDF-TrFE) film gate insulator on which 1D ribbon type single crystal TIPS-PEN grown via solvent exchange method was positioned between Au source and drain electrode. As consequences a memory device exhibits substantially stable source-drain current modulation with the hysteresis ON/OFF ratio larger than 10$^{3}$, superior to a ferroelectric P(VDF-TrFE) OTFT with vacuum evaporated pentacene layer. Data retention longer than 5x10$^{4}$ seconds was achieved in ambient condition by incorporating an interlayer between gate electrode and P(VDF-TrFE) thin film. The device is environmentally stable for more than 40 days without additional passivation. [Preview Abstract] |
Tuesday, March 17, 2009 2:54PM - 3:06PM |
L19.00003: Polymer Electrolyte Gated Inorganic Transistors Anoop Singh Dhoot, Casey Israel, Xavier Moya, Stuart Wimbush, Tim Benseman, Judith MacManus-Driscoll, John Cooper, Neil Mathur, Richard Friend Electric field-induced charge at the interface between gate dielectric and semiconductor is the basis of current semiconductor technology. We report that it is possible to use polymer electrolyte to gate inorganic materials, and to achieve field-induced `doping' equivalent to a full surface coverage of charged ions per unit cell area. Very high field-induced carrier densities, $\sim $10$^{15}$~cm$^{-2}$, in the transistor channel of La$_{0.8}$Ca$_{0.2}$MnO$_{3}$ devices enable modulation of the Curie temperature of over 30~K. We have also used electrolyte gating of the superconductor YBa$_{2}$Cu$_{3}$O$_{7-x}$ to modulate the onset of superconductivity. This creates an exciting opportunity for use of the electrolyte as gate dielectric in a wide variety of inorganic materials to explore formerly inaccessible band-filling regimes without the need for chemical substitution and additional disorder. [Preview Abstract] |
Tuesday, March 17, 2009 3:06PM - 3:42PM |
L19.00004: Employing `Liquid Gap' Transistors to Examine the Mobility-Carrier Density Relation in Polymer and Single Crystal Organic Semiconductors Invited Speaker: It is generally known that the carrier mobility in organic semiconductors can depend on carrier density, but the precise relationship hinges on the degree of structural order and the dielectric polarizability at the organic/dielectric interface. We have fabricated both single crystal and polymer transistors using the PDMS stamp approach pioneered by Podzorov and Rogers [1], where we have replaced the usual `air gap' in these structures with liquids having different dielectric constants. This structure allows us to examine transport in single crystals and polymer semiconductors as a function of tunable dielectric constant and also charge density. We find striking differences in transport behavior for organic single crystals versus polymer semiconductor films using these liquid dielectric transistors. For organic single crystals such as rubrene, the carrier mobility does not seem to be a function of charge density but does strongly depend on the liquid dielectric constant, in keeping with previous results reported by Morpurgo [2] on the effects of dielectric polarizability. For polymer semiconductors, the effect of charge density is overwhelming; there is a strong increase in charge mobility with increasing carrier concentration, following a power law. These results are already largely known, but the `liquid gap' transistors provide a convenient testbed for examining these effects side-by-side for different materials in the same device. We will describe the device fabrication and the nature of our results, as well as discuss the origins of the very different behavior for single crystals versus polymer semiconductor films. 1) Sundar, V.C., \textit{et al}. \textit{Science} \textbf{303} (2004) 1643. 2) Hulea, I. N., \textit{et al. Nature Mater}. \textbf{5} (2006) 982. [Preview Abstract] |
Tuesday, March 17, 2009 3:42PM - 3:54PM |
L19.00005: Organic electrochemical transistors for sensing applications Fabio Cicoira, Sang Yoon Yang, Johm A. DeFranco, George G. Malliaras The application of organic semiconductor devices to chemical and biological sensors seems to be a great fit. A promising approach towards organic-based sensors involves the use of organic electrochemical transistors (OECTs). These devices can be operated in aqueous environment as efficient ion-to-electron converters, thus providing an interface between the worlds of biology and electronics and also a unique platform for the study of organic/organic and organic/metal interfaces in liquids. Using photolithography, surface engineering and micro fluidics we have developed several technique to fabricate OECTs having different geometries. This allows us to study the basic electronic properties and the sensing response of devices in order to understand their mechanism of operation. We studied how the dimensions of the transistors (in particular on the gate/channel area ratio) and the gate electrode material (metal or polymer) can be used to tune the device response for sensing of different species. The effect of the electrolyte on device response was evaluated studying transistors in aqueous electrolytes and ionic liquids. The detection limit of OECTs based sensors having different geometry, was analyzed for hydrogen peroxide, a species involved in glucose sensing. [Preview Abstract] |
Tuesday, March 17, 2009 3:54PM - 4:06PM |
L19.00006: Contact resistance and lifetime of organic thin film transistors Gvido Bratina, Andra\v{z} Petrovic We have used ed electric charge transport measurements coupled to Kelvin force probe microscopy of pentacene organic thin film transistors (OTFT's) to monitor the evolution of contact resistance as a function of time of exposure to ambient air. Or results demonstrate that exposure of OTFTs to ambient air for extended periods of time, results in two competitive mechanisms that are responsible for observed variation in drain-current. Initially, relatively fast oxygen doping through electronegativity-related creation of holes increases the carrier concentration and therefore increases the drain current. Slower, and persistent mechanism of water diffusion in the pentacene layer induces dipole-charge carrier interactions through the creation of energetic disorder. This results in long-term irreversible reduction of drain current. [Preview Abstract] |
Tuesday, March 17, 2009 4:06PM - 4:18PM |
L19.00007: Controlling charge carrier injection in solution processed pentacene transistors by molecular engineering of the electrodes Sangameshwar Rao Saudari, Cherie Kagan We present the device performance of pentacene transistors fabricated from a solution deposited precursor. The bottom-contact pentacene transistors are fabricated by spin-coating N-sulfinylacetamidopentacene precursor followed by thermal conversion of the precursor into pentacene. Hole mobilities $>$0.1 cm$^{2}$/Vs and I$_{on}$/I$_{off} \quad >$10$^{5}$ are repeatedly achieved by this process. The metal-semiconductor interface in organic transistors plays a very important role in charge carrier injection and the overall device performance. Here we have treated the metal surface with self-assembled monolayers having different head and tail chemistries prior to pentacene precursor deposition to tailor the interfacial electronic properties. We correlate monolayer chemistry with device contact resistance and threshold voltage. These studies are used to fabricate devices with high mobility, high I$_{on}$/I$_{off}$ and low subthreshold swing. Device hysteresis and stability issues will also be presented. [Preview Abstract] |
Tuesday, March 17, 2009 4:18PM - 4:30PM |
L19.00008: Infrared and Electro-Optic Properties of TIPS-Pentacene E.G. Bittle, J.W. Brill, J.E. Anthony We will discuss new measurements of the infrared and electro-optic properties of thin crystals of triisopropylsilylethynyl (TIPS) pentacene. As with THz studies of this class of materials, crystalline films were grown from saturated tetrahydrofuran solutions on a gold electrode mask. Square wave voltages were applied to the electrical contacts on the sample as well as a gate electrode below the sample, through an oxide dielectric. Changes in phonon frequencies were studied as functions of voltage, position between contacts, and frequency of applied voltage.~ The results are interpreted in terms of charge diffusion through the TIPS-pentacene crystals. [Preview Abstract] |
Tuesday, March 17, 2009 4:30PM - 4:42PM |
L19.00009: Crossover from recombination limited charge transport to mobility restricted charge transport in organic LED Vladimir Prigodin, Arthur Epstein The model of bipolar charge transport in organic semiconductors where the current solely is provided by e-h recombination (LEDs structures) is studied [1]. We have shown that depending on recombination rate there are two basic regimes of charge transport. For recombination rate above the critical value the current is space charge limited and the current as a function of recombination rate decreases with increasing the recombination rate. At recombination rate below the critical value the recombination takes place over the whole sample volume of sample and as a result the current is only contact limited. As a function of recombination rate the current increases with increasing recombination rate. Critical value for recombination rate depends on the thickness of sample, applied voltage and on both the hole and electron mobilities. [1] J.D. Bergeson \textit{et al.}, Phys. Rev. Lett. \textbf{100}, 067201 (2008). [Preview Abstract] |
Tuesday, March 17, 2009 4:42PM - 4:54PM |
L19.00010: Interface and bulk controlled charge transport in Pd/CuPc/Pd sandwich devices Corneliu Colesniuc, Ivan Schuller We present transport measurements in thin film devices of copper phthalocyanine sandwiched between palladium electrodes. The devices were grown in-situ using molecular beam deposition of phthalocyanine films with the thickness ranging between 30 and 600 nanometers. The I-V characteristics as a function of temperature and thickness exhibit two distinct regions - a low voltage Ohmic region with current proportional to the voltage and a high voltage region with a power law dependence. At low voltages the current shows an inverse power dependence on thickness, I$\sim $thickness $^{-n}$, with the exponent n $>$ 2, suggesting that both the interfaces and the film control the transport mechanism. The temperature dependence of the current does not show a clear activated behavior, supporting the same conclusion. On the other hand, at high voltages the power--law exponent of the I-V decreases at lower thickness for constant temperature implying also that both the interfaces and the film may control the transport. Work supported by AFOSR. [Preview Abstract] |
Tuesday, March 17, 2009 4:54PM - 5:06PM |
L19.00011: RC Transmission Line Characterization of Organic Semiconductors Daniel Lenski, Adrian Southard, Michael S. Fuhrer We have characterized thin films of organic semiconductors (pentacene and poly-3-hexylthiophene) using a 3-contact transmission line configuration, in which an AC voltage is applied between the thin film and the gate, and the phase and magnitude of the current are measured. We compare the results with those obtained from simultaneous DC measurement, and find good agreement in the sheet resistance in the ON state measured using the DC and transmission line techniques, indicating that the transmission line technique is useful for obtaining sheet resistance and mobility in the ON state. Near threshold, or at high frequencies and electric fields, we observe systematic deviations of the AC impedance from the DC values. We discuss these deviations in terms of the of frequency-dependent length scale probed by the transmission line technique, and how these measurements can shed light on the properties of the semiconductor materials as well as their interfaces with contacts and substrates. [Preview Abstract] |
Tuesday, March 17, 2009 5:06PM - 5:18PM |
L19.00012: Organic field effect transistors having single wall carbon nanotubes electrodes Fabio Cicoira, Carla M. Aguirre, Patrick Desjardins, Richard Martel Single Wall Carbon Nanotubes (SWCNTs) are of great interest as electrode materials in Organic Field Effect Transistors (OFETs). Thanks to their field emission properties, SWCNTs electrodes, in principle, are able to inject both electrons and holes into organics with low injection barriers, promoting tunneling injection. We well present recent result on the electrical properties of OFETs using \textit{hairy} SWCNTs electrodes (see Figure 1), where the CNTs are attached on the substrate by means of metallic Ti contact pads. Devices with SWCNTs electrodes show improved injection characteristics compared with devices using conventional metallic electrodes. [Preview Abstract] |
Tuesday, March 17, 2009 5:18PM - 5:30PM |
L19.00013: Electrospun tin oxide/poly(3-hexylthiophene) nanofiber p-n diodes Nicholas Pinto Electrospinning is a simple technique used to prepare nanofibers of various materials, organic and inorganic. Some advantages of this method is that the nanofibers are orders of magnitude longer than that obtained via conventional means and it is easy to isolate individual nanofibers. We have used this technique to make nanoribbons of $n$-doped tin oxide (SnO$_{2})$ and to make nanofibers of $p$-doped regio-regular poly(3hexylthiophene) (P3HT) in air and within seconds. Several $p-n$ junction nanodiodes were fabricated by crossing individual nanofibers of P3HT with individual nanoribbons of SnO$_{2}$ during the electrospinning process and electrically characterized them at room temperature. The SnO$_{2}$ nanoribbons were fabricated first by electrospinning a precursor of SnO$_{2}$ and then sintering them at 700 C to convert it to SnO$_{2}$ before crossing them with P3HT nanofibers. The devices show clear evidence of rectification in air and in vacuum with a turn-on voltage of $\sim $0.4 V and with rectification ratios $\sim $10. Exposure of the diode to UV light increases the on-state current, while removing the light restores the device to its original state making it suitable as a reusable UV light sensor as well. [Preview Abstract] |
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