Study of Solid/Liquid Interfaces in Organic Field-Effect Transistors with Ionic Liquids
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1154-B05-15
Study of Solid/Liquid Interfaces in Organic Field-Effect Transistors with Ionic Liquids Ono, Shimpei1, Miwa, Kazumoto1; Seki, Shiro1; Takeya, Jun2 1
Central Research Institute of Electric Power Industry, Materials Science Research Laboratory, Komae, Tokyo, Japan 2 Osaka University, Graduate School of Science, Toyonaka, Osaka, Japan ABSTRACT We report high-mobility rubrene single-crystal field-effect transistors with ionic-liquid electrolytes used for gate dielectric layers. As the result of fast ionic diffusion to form electric double layers, their capacitances remain more than 1.0 µF/cm2 even at 0.1 MHz. With high carrier mobility of 9.5 cm2/Vs in the rubrene crystal, pronounced current amplification is achieved at the gate voltage of only 0.2 V, which is two orders of magnitude smaller than that necessary for organic thin-film transistors with dielectric gate insulators. The results demonstrate that the ionic-liquid/organic semiconductor interfaces are suited to realize low-power and fastswitching field-effect transistors without sacrificing carrier mobility in forming the solid/liquid interfaces. INTRODUCTION Organic field-effect transistors (OFETs) have attracted much attention because of their potential applications in large-area, flexible, and low-cost electronics [1]. For the development of higher-performance devices, numbers of material combinations are being intensively tested for the layered structure of organic FETs because the interfacial phenomena are crucial in determining their device performances [2]. As one of the unique examples, there has been considerable interest in using electric double layers (EDLs) of electrolytes for efficient application of gate electric field. Since typical thickness of the EDLs is only ~ 1 nm, much higher-density carriers are accumulated at the surface of semiconductor channels than with commonly used 100-500 nm thick SiO2 or polymer gate dielectrics. Therefore, such devices realize excellent current amplification even at small gate voltage VG less than 1 V [3]. Recently it has been reported by several groups that the EDL gating technique is indeed useful for high performance OFETs [4-11]. Furthermore, it is also demonstrated for oxide compounds that the high-density carriers introduced by the EDL gating provoke electronic phase transitions from insulating to metallic or even to superconducting phases [12,13], further testifying importance of the electrolyte-gating technique. However, there has not been any detailed study on microscopic mechanisms of the charge transport taking place in the very vicinity of the interfaces to the electrolytes. Since both the transistor performances and properties of the electric phase transitions should be critically influenced by polarization effects of the electrolytes adjacent to the semiconductors, experiments of varying electrolyte materials are desired to develop a detailed description of the electronic states of the interfacial carriers, which is absolutely necessary for both of the above subjects. In this work we intr
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