Systematic Decomposition of the Positive Bias Stress Instability in Self-Aligned Coplanar InGaZnO Thin-Film Transistors

We propose an experimental method to decompose the positive gate-bias stress (PBS)-induced threshold voltage shift ($\Delta {V}_{\mathsf {th}})$of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) into the contributions of distinct degradation mechanisms. Top-gate self-aligned coplanar structure TFTs are used for this letter. Stress-time-divided measurements, which combine the subgap density-of-states (DOS) extraction and the analysis on recovery characteristics, are performed to separate the$\Delta {V}_{\mathsf {th}}$components. Change in excess oxygen ($\text{O}_{\mathsf {ex}})$-related DOS is clearly observed, and$\Delta {V}_{\mathsf {th}}$by PBS is quantitatively decomposed into the contributions of the active$\text{O}_{\mathsf {ex}}$, and the deep and shallow gate insulator traps. The quantitative decomposition of PBS-induced$\Delta {V}_{\mathsf {th}}$provides physical insight and key guidelines for PBS stability optimization of a-IGZO TFTs.