Effects of drain-bias and ambient on hump formation in the transfer curves of positively gate-biased MgZnO thin film transistors

This study investigates the effects of drain-bias and atmosphere on the hump formation in the transfer curves for RF-sputtered bottom-gate Mg0.05Zn0.95O thin film transistors (TFTs) after the gate-bias stressing at an elevated temperature (80 °C). TFTs with two different annealing conditions are tested: one is 200 °C for 5 h; the other is 350 °C for 30 min. Both 200 °C and 350 °C-annealed TFTs exhibit typical shift of transfer curves when stressed at 25 °C. However, we observe a hump shape in the subthreshold region of the transfer curve for the 200 °C-annealed TFT after positive gate-bias stressing at 80 °C; yet a hump is not identified for the TFT annealed at 350 °C. This suggests that the hump formation in the transfer curves should relate to the material properties of TFTs, modified by the annealing condition. The formation of the hump in the transfer curves is not much influenced by the additional application of the drain-bias (5 V) to the positive gate-bias (20 V). However, TFTs stressed under dry O2 or N2 atmosphere show some mitigation or deferring effects on the development of humps in the transfer curves, yet humps still form.

► Humps show in the transfer curves for stressed MgZnO thin film transistors (TFTs).
► The hump is suppressed for the MgZnO TFT annealed at 350 °C for 30 min.
► The hump is related to both the testing ambient and the quality of active-layer.