High-mobility wide bandgap amorphous gallium oxide thin-film transistors for NMOS inverters

Abstract

Wide bandgap gallium oxide thin-film transistor (TFT) is promising for next-generation sustainable energy-efficient power electronics. In particular, amorphous oxide channel exhibits inherent advantages on mass productions based on a low-temperature processability compatible with cost-effective large-sized glass. Here, we developed hydrogen defect termination to produce amorphous-GaOx (a-GaOx) channel for n-channel oxide-TFT and demonstrated high-mobility a-GaOx-TFT exhibiting a high saturation mobility (μsat) of ∼31 cm2 V−1 s−1, threshold voltage (Vth) of ∼3.3 V, a current on/off ratio of ∼108, and subthreshold swing value (s-value) of ∼1.17 V·dec−1. The study found that oxygen conditions during the channel fabrication process, i.e., oxygen partial pressure during the film deposition and post-thermal annealing atmospheres, were critical for the TFT performances of gallium oxide-TFTs, and subgap defects originated from low-valence Ga+ state and excess oxygen rather than oxygen vacancy had a large responsibility for the device performances. The finding explains why the development of gallium oxide-TFTs is largely behind the other oxide-TFTs. We also fabricated depletion and enhancement-mode a-GaOx-TFTs and developed a full-swing zero-VGS-load inverter with high voltage gain ∼200 and sufficient noise margins. The present study demonstrates a high potential of gallium oxide channel for low-temperature processed n-channel oxide-TFT for next-generation electronic applications.