Organic Single Crystal Transistors Gated by Electric Double Layers in Ionic Liquid
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1091-AA11-52
Organic Single Crystal Transistors Gated by Electric Double Layers in Ionic Liquid R. Hirahara1, S. Ono2, S. Seki2, Y. Tominari1, and J. Takeya1 1
Osaka University, Toyonaka, 560-0043, Japan
2
CRIEPI, Komae, 201-8511, Japan
ABSTRACT Gating organic transistors with electric double layers (EDL) of electrolytes is advantageous in injecting high-density carriers with the application of minimum gate voltage. The drawback of such devices, however, has been that commonly used polymer electrolytes suffer relatively slow ionic diffusion before forming the EDLs. In this report, we disclose a new class of EDL devices incorporating low-viscosity room temperature ionic liquid as the electrolyte layer, so that the rapid ionic diffusion allows MHz operation for the transistor performance. We fabricate a well structure using an elastomeric rubber stamp of poly-dimethylsiloxane to hold the ionic liquid 1-ethyl 3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide, known for high ionic conductivity. The transistor performs without hysteresis with the carrier mobility of 5 cm2V-1s-1, realizing the highest sheet transconductance ever achieved. INTRODUCTION Interest in room-temperature ionic liquids (RTILs) is growing at the prospect of nonvolatile “green solvents”, with the development of chemically stable, water-proof and nontoxic compounds in the recent decade [1]. Such materials have been attractive not only for technologies to produce chemicals without volatilizing organic solvents both in industry and chemistry laboratories, but also for applications to energy conversion and energy storage devices, making use of their fast ionic diffusion. They are indeed being applied to electrolytes for lithium ion batteries and fuel cells [2,3]. However, the use of the RTILs for electronic devices is not as developed as the above areas. In this proceedings, we disclose a new class of organic semiconductor devices functionalized by the fast ionic motion in the room temperature moten salts. Solid-to-liquid interfaces are formed between organic semiconductor single crystals and ionic liquids, so that the structures work as fast-switching organic field-effect transistors (OFETs) with the highest transconductance, i.e. the most efficient response of the output current to the input voltage, among the OFETs ever built.
OFETs are candidate for next generation low-cost devices producible by simple fabrication processes. Fabricating a layered structure of organic semiconductor and an electronically insulating film, carrier density Q in the organic semiconductor is controlled by gate electric field EG applied to the insulating layer, as Q = εEG. Carrier density of organic semiconductor layer is modified by the application of gate voltage VG to the insulating layer, so that current (drain current ID) is controlled from zero to finite values, giving rise to the on-off switching function. The OFETs most commonly consist of organic polycrystalline thin films and dielectric insulators such as silicon dioxide. With typical thickness of the
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