Effect of Moisture Exchange Caused by Low-Temperature Annealing on Device Characteristics and Instability in InSnZnO Thin-Film Transistors

Thin-film transistors (TFTs) in practical operations are inevitably impacted by moisture and temperature. An investigation on the joint effect of environmental moisture and working temperature on device characteristics and instability is becoming necessary. However, few related studies have been performed. In this work, a low-temperature (LT) annealing in air is proposed to simulate the working conditions of TFTs in display applications. The effect of moisture exchange caused by LT annealing on device characteristics and instability of InSnZnO (ITZO) TFTs is systematically investigated. Combined with X-ray photoelectron spectroscopy analysis, TCAD design simulation, and the measurement of relative humidity (RH) change on the device surface, a model considering water diffusion and water ionization is proposed. The negative shift of the transfer curve is attributed to the extra electrons released from the water ionization and the positive-bias-stress-induced instability is mainly attributed to the generation of interstitial/substitutional hydrogens and aggregation of hydrogen ions at the backchannel. The temperature and the RH on the device surface jointly determine the moisture diffusion direction. Furthermore, the model is verified by an LT vacuum annealing. The results and the model will be beneficial for the further reliable design of ITZO TFTs in commercial applications.