(Digital Presentation) Liquid-Metal-Printed Ultra-Thin ITO-Thin-Film Transistor

Indium oxide is one of the promising materials for the n-channel layer for high-mobility oxide-TFT because of its high electron mobility characteristics due to the nature of spatially spread-In 5s orbital. However, excess carrier electrons in In-based channels cancel field-effect gate modulation and causes the formation of a short depletion layer. Moreover, it is challenging to reduce the electron density without the degradation of electron transport. Therefore, developing fully-depletion operated TFT using an ultra-thin channel is a straightforward strategy to demonstrate the high potential of In-based materials for TFT applications. In this work, we developed an ultra-thin tin-doped Indium oxide (ITO) channel (~ 1.9 nm-thick.) and demonstrated a fully-depleted ITO-TFT exhibiting high mobility of 27 cm2/Vs. The ITO channel was grown by a cost-effective vacuum-free liquid-metal-printing route at the maximum process temperature of ~ 200 oC in an ambient atmosphere. Post-thermal annealing in air made significant improvement of device characteristics originating from the reduction of shallow acceptor-like in-gap defects in the ITO channels, and high-performance n-channel ITO-TFT with a large on/off-current ratio of 109 and a sharp threshold slope was achieved. By controlling air-annealing temperature, we also successfully fabricated both enhancement and depletion-mode devices and developed a full signal swinged-oxide-NMOS inverter composed of a depletion-load structure.