Impact of Hydrogenation of ZnO TFTs by Plasma-Deposited Silicon Nitride Gate Dielectric

Plasma-enhanced chemical vapor deposition grown silicon nitride gate insulator with high refractive index of 2.39 was employed as the source of hydrogen to hydrogenate zinc oxide (ZnO) thin-film transistors (TFTs) with bottom-gate configuration. The hydrogenated TFTs exhibited a field-effect mobility of 7.8 cm²/Vmiddots, an on/off current ratio of 10⁶, and a subthreshold slope of 1.2 V/dec. In comparison, TFTs using silicon nitrides with lower refractive indices of 2.26, 1.92, and 1.80 showed relatively poor performance. Dynamic secondary ion mass spectroscopy study showed that the amount of hydrogen present in the ZnO TFT structures using high refractive index silicon nitride gate dielectric is higher than that in the TFT samples using low-refractive index silicon nitride, which indicate the evidence of hydrogenation of ZnO TFTs by high refractive index silicon nitride gate dielectric. The enhanced performance of the hydrogenated TFTs is attributed to the passivation of ZnO/dielectric interface states and doping of the channel by hydrogenation effect.