Effects of crystalline structure of IGZO thin films on the electrical and photo-stability of metal-oxide thin-film transistors

In this paper, we investigated the effects of crystalline structure of indium-gallium-zinc-oxide (IGZO) thin films on the electrical and photo-stability of metal-oxide thin-film transistors (TFTs). It was found that the TFTs with c-axis aligned crystalline (CAAC) IGZO channels exhibited enhanced stability under various combinations of electrical, temperature, and light-stressed conditions compared to those with amorphous (a) and nanocrystalline (nc) IGZO channels. From various electrical and spectroscopic studies, it is suggested that the low deep-level defects in CAAC-IGZO channels allowed high electrical performance and enhanced stability. Meanwhile, the a- and nc-IGZO TFTs showed relatively poor stability owing to the higher levels of deep-level defects in the channel layers. To explain the origin of the enhanced light-stability in CAAC-IGZO TFTs, we investigated the transient photo-response characteristics and it was found that the low activation energy for recombination and/or neutralization of photo-generated carriers was responsible for the enhanced stability.