Theoretical Modeling of a Temperature-Dependent Threshold-Voltage Shift in Self-Aligned Coplanar IZTO Thin-Film Transistors

Abstract

Here, we investigate the effect of increasing temperature on threshold voltage (VTH) stability in self-aligned coplanar amorphous indium-zinc-tin oxide (a-IZTO) thin-film transistors (TFTs). An analytical model of the temperature dependency of VTH stability reveals the importance of device geometry and subgap density-of-state (DOS) reductions in highly stable a-IZTO TFTs. The validity of the analytical model is confirmed using experiments and technology computer-aided design simulations to predict quantitative relationships under various shifts in temperatures, subgap DOS, and VTH. The role of hydrogen impurity in performance and VTH stability is also examined. The incorporation of hydrogen in a-IZTO channels improves TFT performance and thermal stability (ΔVTH/ΔT = 3.18 mV/K) due to hydrogen’s role as a passivation center. However, excessive incorporation of hydrogen increases subgap DOS distribution, causing a slight deterioration in thermal stability (ΔVTH/ΔT = 3.31 mV/K). This suggests that hydrogen can be converted from a shallow donor to an acceptor-like deep trap state. Our findings inform future designs of stable oxide semiconductor TFTs in terms of thermal stability in emerging organic light-emitting diode, augmented and virtual reality, memory, logic, and monolithic three-dimensional applications.