High Performance Organic Field Effect Transistor Withanovel Top-And-Bottom Contact (TBC) Structure
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HIGH PERFORMANCE ORGANIC FIELD EFFECT TRANSISTOR WITH A NOVEL TOP-AND-BOTTOM CONTACT (TBC) STRUCTURE Manabu Yoshida, Sei Uemura, Satoshi Hoshino, Takehito Kodzasa, Satoshi Haraichi and Toshihide Kamata, Photonics Research Institute, National Institute of Advanced Industrial Science and Technology, Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, JAPAN ABSTRACT We studied the features of the newly developed Top and Bottom Contact Field Effect Transistor (TBCFET) with organic semiconductor layers. TBCFETs with ca.0.5µm channel length (L) were fabricated and their transistor properties were measured. The output drain-source currents (IDS) of TBCFET were 1 to 2 orders of magnitude higher than those of ordinary planar type FETs with 100µm channel length. On the other hand, because of the TBC structure, off current tends to become larger in the TBCFET. Therefore, in order to solve this off-current problem, we intentionally formed the Schottky junction at the top electrode/semiconductor interface. As a result, the off current became about 2 orders of magnitude smaller than before the formation of the Schottky junction. INTRODUCTION Organic thin film transistors (TFT) have received much attention in the field of flexible and printable electronics [1,2]. The most important requirements for developing an organic-TFT should be adaptability of the easy preparation process for the giant-area electronic device such as printing technique and high performance as a TFT [3]. Recently, we have developed a newly structured organic field effect transistor (FET), we called it Top-and-Bottom Contact (TBC) structure, with a purpose of developing a high performance TFT prepared by the actually easy preparation technique. In this our developed TBC structure, top and bottom contact parts are located diagonally across the semiconductor layer, thus the channel length can be controlled by the semiconductor layer thickness. This unique structure gives great advantages for the organic transistor performance. Namely, very short channel length (sub-µm order) can be easily prepared by a simple stacking process without any micromachining or related photolithography procedures. In this study, we have prepared the TBC type organic FET (TBCFET) with a channel length of 0.5µm using pentacene active layer, which has shown high performance operation. Owing to its unique structure, the transistor properties of TBCFET are very sensitive to the conditions of electrode/semiconductor interface. Finally, we have clarified the relation between transistor properties and these conditions for the TBC-FET in detail, and proposed a mechanism of such a high performance operation.
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EXPERIMENTAL Fig.1 shows the cross-sectional illustration of our newly developed TBC-FET structure that was fabricated as the following procedure. Heavily doped Si with thermally grown SiO2 (50 ~ 400 nm) was employed as a substrate and a gate electrode. Substrates were carefully UV-ozone cleaned before the fabrication of FET devices. Pentacene was train-sublimated 5 times
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