Impact of Drain Bias on Degradation of Amorphous-InGaZnO Thin-Film Transistors

초록

In this work, the drain stress voltage (V-DS)-dependent reliability degradation behavior in amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) is investigated at a fixed positive gate stress voltage (V-GS) of 30 V. As V-DS increases from 0 to 5 V, the V-DS-induced weakened vertical electric field alleviates positive threshold voltage shift (Delta V-th), whereas a further increase in V-DS toward 15 V accelerates degradation due to enhanced thermionic injection. The degradation results of the gate-to-source and gate-to-drain capacitance (C-GS and C-GD) under CCS at 5 V-V-DS reveal suppressed electron trapping near the drain region due to the V-DS-induced reduction in the vertical electric field. AC C-CS measurements at 15 V-V-DS show strong mitigation of Delta V-th with decreasing stress duty ratio, confirming that SHE-induced thermionic injection becomes significant at high V-DS. Notably, Delta V(th )under AC stress with a 5% duty ratio becomes smaller at 15 V-V-DS than at 5 V-V-DS confirming that the V-DS-induced vertical electric field reduction becomes dominant when SHE is alleviated. Furthermore, the stress-time-divided technique employed to analyze the energy distribution of predominant trap sites demonstrates that thermionic injection promotes electron trapping into deeper states. In summary, the dominant degradation mechanism evolves with increasing V-DS from degradation mitigation induced by vertical electric field reduction to enhanced deep-level electron trapping driven by SHE-induced thermionic injection.

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