Suppression of degradation induced by negative gate bias and illumination stress in amorphous InGaZnO thin-film transistors by applying negative drain bias.

The effect of drain bias (V(DS)) on the negative gate bias and illumination stress (NBIS) stability of amorphous InGaZnO (a-IGZO) thin-film transistors was investigated using a double-sweeping gate voltage (V(GS)) mode. The variation in the transfer characteristics was explored using current-voltage and capacitance-voltage characteristics. In the initial stage (<1000 s) of NBIS with grounded V(DS) (V(GS) = -40 V and V(DS) = 0 V), the transfer characteristics shifted negatively with an insignificant change in the subthreshold swing (SS) because of hole trapping at an IGZO/gate insulator interface. On the other hand, on-current degradation was observed and was accelerated in the forward measurement as the NBIS duration increased. The results indicated that NBIS induced donor-like defects near the conduction band; however, the transfer curves in the reverse measurement shifted positively without on-current and SS degradations. It was found that the degradations were enhanced by applying a positive V(DS) bias (V(GS) = -40 V and V(DS) = 40 V); in contrast, they could be reduced by applying a small negative V(DS) of V(DS) > V(GS) (V(GS) = -40 V and V(DS) = -20 V). Furthermore, it was confirmed that the NBIS degradations could be suppressed by applying a large negative V(DS) bias of V(DS) < V(GS) (V(GS) = -40 V and V(DS) = -60 V) during NBIS.