Effect of Positive Bias Stress on the Back-Gate Voltage-Modulated Threshold Voltage in Double-Gate Amorphous InGaZnO Thin-Film Transistors

In the back-end-of-line double-gate (DG) amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs), the linearity of top-gate voltage ( ${V}_{TG}$ )-swept threshold voltage ( ${V}_{T,TG}$ ) with back-gate voltage ( ${V}_{BG}$ ) is essential. In this work, the influence of positive bias stress (PBS) condition on both $\beta = \partial {V}_{T,TG}/\partial {V}_{BG}$ and $\Delta \beta = \partial \Delta {V}_{T,TG}/\partial {V}_{BG}$ is investigated in DG a-IGZO TFTs, using the subgap density-of-states (DOS) extracted before and after PBS. While $\Delta \beta $ remains almost constant in the PBS condition of ${V}_{TG}/{V}_{BG}=30$ /-30 V, the ${V}_{TG}={V}_{BG}=30$ V condition shows the complicated nonlinear relationship between $\Delta {V}_{T,TG}$ and ${V}_{BG}$ . It is found that $\lambda = \delta \Delta \beta /\delta {V}_{BG}$ , as the parametric indicator describing the PBS-induced degradation of linearity for the ${V}_{BG}$ -controlled ${V}_{T,TG}$ , is $\times 7$ larger (less linear) at ${V}_{TG}={V}_{BG}=30$ V than at ${V}_{TG}/{V}_{BG}=30$ /−30 V. The origin of this non-linearity is comprehensively explained based on the model of the excessive oxygen-related defect creation resulting from broken peroxy linkage. Our result suggests that the ${V}_{TG}/{V}_{BG}=30$ /−30 V is a more advantageous condition in the viewpoint of the $\Delta {V}_{T,TG}$ linear with ${V}_{BG}$ , in comparison with ${V}_{TG}={V}_{BG}=30$ V.