Analysis of frequency dispersion in amorphous In–Ga–Zn–O thin-film transistors

It is shown in this paper that the finite resistance of the accumulation channel in amorphous In–Ga–Zn–O thin-film transistors (a-IGZO TFTs) is the main cause of the frequency dispersion of the capacitance–voltage curves in these devices. A transmission line model, accounting for the distributed nature of channel resistance, is used to explain this. Multi-frequency analysis techniques for trap density distribution use a lumped series resistance model and attribute dispersion solely to the charging and discharging of trap states. As the resistance–capacitance (RC) time constant values of the IGZO TFTs are in the range of 10–100 µs, a distributed RC network is better suited for the measured frequency range (1 kHz–1 MHz).