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Electrical evaluation of scaled organic thin-film transistors with submicron-gap electrodes fabricated by focused ion beam sputtering

Yoshihiro Tada, Katsuhiro Uesugi, Hisashi Fukuda

Submicron-gap electrodes were fabricated using focused ion beam (FIB) sputtering and applied as source/drain to scaled organic thin-film transistors (OTFTs). Fully focused Ga ions emitted fromliquid ion source in a FIB system were irradiated onto a target metal surface for the etching of a defined area. A comparison of long-channel OTFTs indicates that with decreasing channel length toward submicron region, marked reduction of mobility and a threshold voltage shift were observed in submicron-channelOTFTs. A0.25 m-channelOTFTs fabricated by the FIBprocess showed a threshold voltage of -0.5 V and a carrier mobility three orders of magnitude smaller than that of the 5-m-channel conventional OTFT. The 0.25 m-channel OTFTs exhibit also a nonsaturating drain current in the output characteristics owing to short-channel effect. It was concluded that large contact resistance at the metal/organic interface provides the degradation ofmobility of scaled OTFTs.