Effect of N 2O plasma treatment on the improvement of instability under light illumination for InGaZnO thin-film transistors

Abstract

This paper investigates the impact of N 2O plasma treatment on the light-induced instability of InGaZnO thin film transistors with a SiO 2 passivation layer deposited by plasma-enhanced-chemical-vapor-deposition (PECVD). For the untreated device, because the deposition of the SiO 2 passivation layer by PECVD causes extra trap states, the anomalous subthreshold leakage current can be attributed to a lowering of the source side barrier due to trap-assisted photogenerated holes. In contrast, the N 2O plasma treatment applied to both the gate insulator and the active layer effectively suppresses the device instability under illumination. In order to clarify the influence of the N 2O plasma treatment, this study investigates a device with treatment of only the gate insulator. This device shows a slight decrease of light-induced subthreshold leakage current. This demonstrates that N 2O plasma treatment on IGZO active layer after its deposition is critical in preventing damage from the subsequent SiO 2 passivation deposition process. In addition, the instability of threshold voltage ( V T ) under negative bias illumination stress (NBIS) is significantly improved by the N 2O plasma treatment. Furthermore, a different dark recovery rate follows NBIS for untreated and N 2O plasma-treated devices, indicating different hole-trapping levels exist in the energy band.