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

摘要

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 (${rm O}_{2}/{rm Ar}+{rm O}_{2}$ and ${rm P}_{rm O2}$). The saturation mobilities of TFTs decreased with increasing ${rm P}_{rm O2}$, which suggested that the increase in ${rm P}_{rm O2}$ reduced the carrier concentration. The NBIS characteristics of the TFTs were evaluated with the amounts of negative shifts in turn-on voltages $(Delta V_{rm ON})$ under the illumination of typical red, green, and blue wavelengths with a $V_{rm GS}$ of ${-}{rm 20}~{rm V}$ for $10^{4}~{rm s}$. The X-ray photoelectron spectroscopy analysis strongly suggested that the $Delta V_{rm ON}$ 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 $Delta V_{rm ON}$ 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.