Experimental decomposition of the positive bias temperature stress-induced instability in self-aligned coplanar InGaZnO thin-film transistors and its modeling based on the multiple stretched-exponential functions

Abstract

Decomposition of the positive gate-bias temperature stress (PBTS)-induced instability into contributions of distinct mechanisms is experimentally demonstrated at several temperatures in top-gate self-aligned coplanar amorphous InGaZnO thin-film transistors by combining the stress-time-divided measurements and the subgap density-of-states (DOS) extraction. It is found that the PBTS-induced threshold voltage shift (Delta V-T) consists of three mechanisms: (1) increase of DOS due to excess oxygen in the active region; (2) shallow; and (3) deep charge trapping in the gate insulator components. Corresponding activation energy is 0.75, 0.4, and 0.9eV, respectively. The increase of DOS is physically identified as the electron-capture by peroxide. Proposed decomposition is validated by reproducing the PBTS time-evolution of I-V characteristics through the technology computer-aided design simulation into which the extracted DOS and charge trapping are incorporated. It is also found that the quantitative decomposition of PBTS-induce Delta V-T accompanied with the multiple stretched-exponential models enables an effective assessment of the complex degradation nature of multiple PBTS physical processes occurring simultaneously. Our results can be easily applied universally to any device with any stress conditions, along with guidelines for process optimization efforts toward ultimate PBTS stability.