ZnO-based thin film transistors having high refractive index silicon nitride gate

The effect of properties of silicon nitride films on the electrical performance of zinc oxide (ZnO) thin film transistors (TFTs) has been investigated by utilizing silicon nitride films having refractive indices of 2.45 and 1.85. The ZnO TFTs having a silicon nitride with a high refractive index of 2.45 exhibited a field effect mobility of 8 cm2 V s, on/off current ratio of 106, and subthreshold slope of 0.9 V /decade. On the other hand, TFTs having a silicon nitride with a low refractive index of 1.85 showed a field effect mobility of 0.5 cm2 V s, on/off current ratio of less than 102, and subthreshold slope of 19 V /decade. The improved device performance was ascribed to a better interface between ZnO and high refractive index silicon nitride, and hydrogenation of the ZnO channel with the hydrogen originated from the high refractive index silicon nitride.