Negative-Bias Light Stress Instability Mechanisms of the Oxide-Semiconductor Thin-Film Transistors Using In–Ga-O Channel Layers Deposited With Different Oxygen Partial Pressures

An In-Ga-O (IGO) semiconductor was employed as a channel layer for the oxide thin-film transistors (TFTs). The IGO composition was chosen as an In/Ga atomic ratio of 65/35 and the films were deposited by RF magnetron sputtering method. To investigate the negative-bias illumination stress (NBIS) instability mechanisms, the IGO films were prepared with various oxygen partial pressures (O₂/Ar+O₂ and P_O2). The saturation mobilities of TFTs decreased with increasing P_O2, which suggested that the increase in P_O2 reduced the carrier concentration. The NBIS characteristics of the TFTs were evaluated with the amounts of negative shifts in turn-on voltages (ΔV_ON) under the illumination of typical red, green, and blue wavelengths with a V_GS of -20 V for 10⁴ s. The X-ray photoelectron spectroscopy analysis strongly suggested that the ΔV_ON could be caused by the weakening of bonding strength between the atoms, which were analyzed as variations in the red shifts of O 1s peak. The drastic increase in the ΔV_ON of the TFT using the IGO prepared without oxygen under the NBIS using the blue illumination was well explained by the combination defect model composed of intrinsic and extrinsic defects inherent within the IGO channel layer.