Analysis on Trapping Kinetics of Stress-Induced Trapped Holes in Gate Dielectric of Amorphous HfInZnO TFT

A comprehensive study was done regarding stability under simultaneous stress of light and negative gate dc bias in amorphous hafnium–indium–zinc-oxide ( $alpha $ -HIZO) thin-film transistors. A negative threshold voltage ( $V_{mathrm{ th}})$ shift and an anomalous hump were observed in transfer characteristics after the stress, and it is explained that these phenomena are caused by the hole trapping in the SiO2 gate insulator, not by interface state generation. Furthermore, capacitance–voltage ( $C_{G}$ – $V_{G})$ measurements were performed with various frequencies to investigate the vertical distribution of the trapped holes in the gate insulator. As a result, the correlation between the vertical location of the trapped holes and the influence on $C_{G}$ – $V_{G}$ characteristics were revealed clearly. First, at the beginning of the stress, photogenerated holes are mainly trapped at the $alpha $ -HIZO/SiO2 interface and interfacial SiO2 in contact with the interface, which induces the negative $V_{mathrm{ th}}$ shift. Second, as the stress time increases, the holes start to be trapped in the spatially deeper insulator, which leads to an additional hump in the $C_{G}$ – $V_{G}$ cha- acteristics at sufficiently low frequencies.