Enhanced stability in InSnO transistors via ultrathin in-situ AlOx passivation

In this study, we present the impact of an ultrathin in-situ AlOx passivation layer on the electrical performance and stability of InSnO (ITO) transistors. Devices incorporating an ultrathin (similar to 2 nm) AlOx passivation layer demonstrate satisfactory electrical performance and stability, characterized by a decent field-effect mobility, enhancement mode operation, notably reduced subthreshold swing, negligible hysteresis, and, notably, a significantly reduced threshold voltage shift under negative bias stress (NBS) and positive bias stress (PBS), respectively. The total trap density (N-tot), extracted through the sub-threshold slope, and the trap density (N-t), measured using low-frequency noise (LFN) for the AlOx-passivated ITO transistors, are significantly decreased. Those improvements can be attributed to the suppression of oxygen vacancy formation during the reactively-sputtered AlOx and subsequent annealing processes, as demonstrated by comparing the in-depth X-ray photoelectron spectroscopy (XPS) results of the AlOx-passivated and un-passivated ITO films. These results underscore the potential of in-situ reactively-sputtered ultrathin AlOx passivation layers to enhance the stability of thin-film transistors with In-rich channels.