Apparent high mobility ~30 cm²/Vs of amorphous In–Ga–Zn–O thin-film transistor and its origin

Abstract

Amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs) annealed in ozone at 250°C exhibited a good subthreshold swing (S) of 123 mV/decade and a saturation mobility (μ_sat) of ~10 cm²/Vs, but a bit large threshold voltage (V_th) of 11.6 V. Further oxygen annealing at 200°C resulted in high apparent μ_sat of ~30 cm²/Vs and deteriorated characteristics such as a large S value and large hysteresis. The high apparent μ_sat values were attributed to the electrical discharge between the gate and source electrodes. Reasonably actual μ_sat values ~10 cm²/Vs were obtained using the actual capacitance calculated from the discharge characteristics.