We investigated the effect of simultaneous mechanical and electrical stress on the electrical characteristics of flexible indium-gallium-zinc oxide (IGZO) thin-film transistors (TFTs). The IGZO TFTs exhibited a threshold voltage shift (∆VTH) under an application of positive-bias-stress (PBS), with a turnaround behavior from the positive ∆VTH to the negative ∆VTH with an increase in the PBS application time, whether a mechanical stress is applied or not. However, the magnitudes of PBS-induced ∆VTH in both the positive and negative directions exhibited significantly larger values when a flexible IGZO TFT was under mechanical-bending stress than when it was at the flat state. The observed phenomena were possibly attributed to the mechanical stress-induced interface trap generation and the enhanced hydrogen diffusion from atomic layer deposition-grown Al2O3 to IGZO under mechanical-bending stress during PBS. The subgap density of states was extracted before and after an application of PBS under both mechanical stress conditions. The obtained results in this study provided potent evidence supporting the mechanism suggested to explain the PBS-induced larger ∆VTHs in both directions under mechanical-bending stress.
Keywords: Al2O3 gate dielectric; Flexible IGZO TFTs; hydrogen; simultaneous mechanical and electrical stress.