Bias-Temperature-Stress Characteristics of $\hbox {ZnO/HfO}_{2}$ Thin-Film Transistors

Positive and negative bias temperature instabilities (PBTI and NBTI) of ZnO/HfO₂ thin-film transistors are investigated by the bias-temperature-stress test method. PBTI results show a linear shift in threshold voltage in the positive voltage direction with a magnitude that semilogarithmically increases with time. This is indicative of dielectric charge trapping. Trends with stress voltage and temperature also support this conclusion. NBTI characteristics include threshold voltage shifts in the negative voltage direction, reduced channel mobility, and an increased subthreshold slope with temperature. The observed behavior suggests that defect state creation at the interface is the dominant mechanism responsible for NBTI.