Effect of Channel Layer Thickness on Electrical and Thermal Stabilities of High-Mobility Zinc Oxynitride Thin-Film Transistors

We investigated the effect of channel layer thickness (tch) on the electrical and thermal stabilities of high-mobility zinc oxynitride (ZnON) thin-film transistors (TFTs). ZnON TFTs with various tch values of 11, 16, 21, and 26 nm were prepared for experiments. The drain current was barely modulated by the gate-to-source voltage in the ZnON TFT with a tch of 26 nm. When tch was less than 21 nm, both the electrical and thermal stabilities of the ZnON TFTs improved with an increase in tch. To explain this phenomenon, the chemical composition and bonding states of the ZnON thin-films with different thicknesses were characterized using X-ray photoelectron spectroscopy (XPS). The XPS results indicated that more oxygen exists in the bulk of the 11-nm-thick ZnON thin-film than in the bulk of the 21-nm-thick ZnON thin-film. In addition, the number of defective ZnXNY bonds decreased in the ZnON with an increase in the distance from the back surface to the characterized layer. Because the excess oxygen and defective ZnXNY bond generate subgap states in ZnON, the observed tch-dependence of the electrical/thermal stability in the ZnON TFT could be mainly attributed to the decrease in the subgap states in ZnON with the increase in tch.