Effect of Vacuum Annealing Temperature on Optoelectrical Performance of IGZTO Films and Thin-Film Transistors

Thin-film transistors (TFTs) based on quinary indium-gallium-zinc-tin oxide (IGZTO) were fabricated via radio frequency (RF) magnetron sputtering. The impact of vacuum annealing temperatures (25–450 °C) on the microstructural and optoelectrical properties of films and TFTs was systematically investigated. All IGZTO thin films are amorphous and transparent, with optical bandgaps ranging from 3.22 eV to 3.63 eV. The one annealed at 350 °C exhibited the smoothest surface. The carrier concentrations and Hall mobilities of IGZTO films vary with the annealing temperature in the range of 7.44 × 1018 ~ 6.37 × 1019 cm−3 and 20.89~35.53 cm2·V−1·s−1, respectively. Oxygen vacancies (\({V_o^x}\)) are considered the major origin of the conductivity of IGZTO films, and their evolution with annealing temperatures was elucidated. The TFT annealed at 350 °C achieved a saturation mobility (μsat) of 19.7 cm2 V−1 s−1, threshold voltage (VTH) of 4.72 V, subthreshold swing (SS) of 0.56 V dec−1, and Ion/Ioff of 8.1 × 107, but TFTs annealed at other temperatures show no switching behaviour. TCAD simulations indicate that vacuum annealing elevates \({V_o^x}\) density, especially at the film surface; the switching failure at 150 °C and 450 °C is attributed to the pronounced structural disorder expressed by large characteristic slope energies of tail states, while the failure at 250 °C is due to excessive \({V_o^x}\) density. This work may provide useful guidance for the performance optimisation of IGZTO film and TFTs via annealing.