Instability of amorphous hafnium-indium-zinc-oxide thin film transistors under negative-bias-illumination stress

In this study, the degradation mechanism and location of defect creation (whether the source or the drain side) of amorphous hafnium-indium-zinc-oxide thin film transistors under negative-bias-illumination stress was investigated. Most of the electrical characteristics - such as threshold voltage, subthreshold slope, and mobility - deteriorated remarkably due to defects generated in the deep-level and tail bands of the semiconductor bandgap. (The extent of hysteresis due to damage reflects the amount of defects generated.) As the drain voltage was increased - whilst under stress and with the gate voltage fixed - the electrical properties of thin film transistors got progressively worse. This indicates that the drain region was more seriously affected (compared to the source region), most likely because the drain region was placed under a higher negative field in the active layer.