Ultrathin α-Bi₂O₃ Thin-Film Transistor for Cost-Effective Oxide-TFT Inverters

Electronics is advancing toward greater diversity and sustainability by prioritizing energy efficiency and cost-effectiveness. Metal oxide thin-film transistor (TFT) represents a technology at the forefront of advancing next-generation sustainable electronics, and exploring oxide channel compositions is a crucial step in opening opportunities for developing next-generation device applications. This study presents the first development of n-channel α-Bi₂O₃-TFTs using a 4 nm ultrathin channel prepared by a cost-effective vacuum-free and solvent-free liquid metal printing method in ambient air. Even the pristine device exhibited a clear TFT action but required a large negative gate bias to turn off due mainly to excess carriers from oxygen vacancy in the α-Bi₂O₃ channel. Oxygen-containing post-annealing reduced both channel carrier and subgap defect densities, enabling the development of depletion and enhancement-type α-Bi₂O₃-TFTs with the saturation mobility of 2-4 cm² V^-1 s^-1. Two types of oxide-TFT-based inverter circuits, zero-V_GS-NMOS and CMOS inverters, were fabricated by using α-Bi₂O₃-TFTs, operating in a high voltage gain of over 130. This work demonstrates the potential of oxide semiconductor materials toward the development of next-generation sustainable electronics.