Investigation of PBTS-Induced Degradation Mechanisms in SA TG Coplanar IGZO TFTs Using Low-Frequency Noise Analysis

This study investigates the degradation mechanism of self-aligned top-gate (SA TG) coplanar IGZO thin-film transistors (TFTs) under positive bias temperature stress (PBTS) using low-frequency noise (LFN) analysis. Electrical measurements revealed a positive shift in threshold voltage, increased subthreshold swing, decreased field-effect mobility, and enhanced hysteresis after PBTS. The enhanced unified LFN model, accounting for both channel trap states and gate dielectric traps, successfully explained the observed noise characteristics of fabricated SA TG coplanar IGZO TFTs before and after PBTS. From the extracted trap parameters from LFN analysis, an increase in near-interface trap density and subgap density of states near the conduction band edge was confirmed after PBTS, correlating well with the observed electrical degradation. These results demonstrate that LFN analysis based on the enhanced unified LFN model is an effective diagnostic tool for examining the electrical stress-induced degradation in IGZO TFTs.