Thermally Dependent Metastability of Indium-Tungsten-Oxide Thin-Film Transistors

Abstract Indium tungsten oxide (IWO) has been investigated as an oxide semiconductor candidate for next-generation thin-film transistors (TFTs). Bottom-gate TFTs were fabricated with a 30-nm IWO channel material sputter-deposited with oxygen partial pressure (P O2 ) ranging from 2.5% to 10% of the total ambient pressure. Annealing was conducted at temperatures ranging from 100ºC to 275ºC. Device transfer characteristic measurements revealed a pronounced interaction between the sputter P O2 setting and passivation annealing conditions. Devices annealed at 100ºC in air ambient demonstrated characteristics with a strong dependence on P O2 , attributed to differences in oxygen vacancy defects and semiconductor electronic properties. Devices annealed at 200ºC in air ambient demonstrated characteristics like those of unannealed devices, with operation far in depletion mode. Donor state passivation is possible following additional annealing at 275ºC in air, with reduced sensitivity to the initial sputter P O2 setting. A hypothesis on the mechanism of metastability is proposed.