Hydrogen and oxygen induced abnormal reliability degradation in flexible top-gate amorphous In-Ga-Zn-O thin-film transistors under negative bias thermal illumination stress

Ensuring device stability under various stress factors is critical for the long-term operation of flexible amorphous InGaZnO thin-film transistors (a-IGZO TFTs) for market-ready display applications. Here, we report the abnormal threshold voltage (V_th) shift behavior in flexible top-gate a-IGZO TFTs under negative-bias temperature illumination stress (NBTIS). Under NBTIS, an initial negative V_th shift occurred. However, with an extended stress duration, an unexpected positive V_th shift occurred, deviating from the expected charge-trapping model. Our results show that this phenomenon is strongly correlated with the thickness of the a-IGZO active layer, with thicker films exhibiting more pronounced reverse V_th shifts. Photo-excited charge collection spectroscopy and X-ray photoelectron spectroscopy analyses revealed that the density of hydrogen/oxygen-related defect states near the valence band maximum increased with increasing a-IGZO thickness, facilitating the enhanced photo and thermal excitation of charge carriers under illumination and thermal stresses. We demonstrate that the optimization of the a-IGZO channel thickness can effectively suppress the observed abnormal reliability degradation under NBTIS, providing valuable insights into optimizing a-IGZO TFTs for enhanced long-term stability in next-generation flexible and transparent electronic applications.