Reduction of contact resistance in pentacene thin-film transistors by direct carrier injection into a-few-molecular-layer channel

We found an abrupt reduction of contact resistance, Rc, in pentacene bottom-contact thin-film transistors (TFTs) with Au/Ti source/drain (S/D) electrodes when Ti thickness is below ∼3nm. Our results suggest that the direct ohmic contact with a few molecular layer channel is a key to reduce the Rc of the S/D electrodes. We propose a Au/self-assembled monolayer electrode structure enabling direct ohmic contact with these few molecular layer channels, and achieved high-performance bottom-contact TFTs with an extrinsic mobility of 1.1cm2∕Vs, an on/off ratio of 106, and a subthreshold swing of 0.3 V/decade.