The Influence of In/Zn Ratio on the Performance and Negative-Bias Instability of Hf–In–Zn–O Thin-Film Transistors Under Illumination

The performance and stability of hafnium–indium–zinc–oxide (HIZO) thin-film transistors (TFTs) are evaluated with respect to the relative content in In and Zn cations. While devices that incorporate an active layer with an In-rich composition exhibit higher field-effect mobility values, they undergo larger negative shifts in$V_{\rm th}$upon negative-bias illumination stress (NBIS). Density-of-states analyses suggest that a higher In/Zn ratio in the semiconductor results in larger defect states in the vicinity of the semiconductor/gate-insulator interface. Accordingly, these defect states may act as carrier traps that accelerate the degradation of HIZO TFTs upon NBIS.