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_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.