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-th) of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) into the contributions of distinct degradation mechanisms. Topgate 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-th components. Change in excess oxygen (O-ex)-related DOS is clearly observed, and Delta V-th by PBS is quantitatively decomposed into the contributions of the active O-ex, and the deep and shallow gate insulator traps. The quantitative decomposition of PBS-induced Delta V-th provides physical insight and key guidelines for PBS stability optimization of a-IGZO TFTs.