Performance Enhancement of Channel-Engineered Al–Zn–Sn–O Thin-Film Transistors with Highly Conductive In–Ga–Zn–O Buried Layer via Vacuum Rapid Thermal Annealing

Abstract

In this study, we propose, fabricate, and examine the electrical characteristics of high-performance channel-engineered amorphous aluminum-doped zinc tin oxide (a-AZTO) thin-film transistors (TFTs). Amorphous indium gallium zinc oxide (a-IGZO) film with improved conductivity (obtained via rapid thermal annealing in vacuum) is applied as the local conductive buried layer (LCBL) of the channel-engineered a-AZTO TFTs. The optical transmittance of the a-IGZO and a-AZTO films in the visible region is >85%. The a-IGZO LCBL reduces the resistance of the a-AZTO channel, thereby resulting in increased drain current and improved device performance. We find that our fabricated channel-engineered a-AZTO TFTs with LCBLs are superior to non-channel-engineered a-AZTO TFTs without LCBLs in terms of electrical properties such as the threshold voltage, mobility, subthreshold swing, and on–off current ratios. In particular, as the a-IGZO LCBL length at the bottom of the channel increases, the channel resistance gradually decreases, eventually resulting in a mobility of 22.8 cm2/V · s, subthreshold swing of 470 mV/dec, and on–off current ratio of 3.98×107. We also investigate the effect of the a-IGZO LCBL on the operational reliability of a-AZTO TFTs by measuring the variation in the threshold voltage for positive gate bias temperature stress (PBTS), negative gate bias temperature stress (NBTS), and negative gate bias temperature illumination stress (NBTIS). The results indicate that the TFT instability for temperature and light is not affected by the LCBL. Therefore, our proposed channel-engineered a-AZTO TFT can form a promising high-performance high-reliability switching device for next-generation displays.