Oxygen-Adsorption-Induced Anomalous Capacitance Degradation in Amorphous Indium-Gallium-Zinc-Oxide Thin-Film-Transistors under Hot-Carrier Stress

• Published in: Journal of the Electrochemical Society Vol. 159; no. 3; pp. H286 - H289
• Main Authors: Chung, Wan-Fang, Chang, Ting-Chang, Lin, Chia-Sheng, Tu, Kuan-Jen, Li, Hung-Wei, Tseng, Tseung-Yuen, Chen, Ying-Chung, Tai, Ya-Hsiang
• Format: Journal Article
• Language: English
• Published: The Electrochemical Society, Inc 01.01.2012
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/2.075203jes

This paper investigates anomalous capacitance-voltage (C-V) degradation in amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film-transistors (TFTs) under hot carrier stress. In vacuum hot carrier stress, both the gate-to-drain capacitance (CGD) and the gate-to-source capacitance (CGS) curves exhibited positive shifts due to electron trapping in the gate dielectric. In addition, an observed increase in capacitance value at a lower gate voltage in the CGD measurement only can be ascribed to interface state creation. However, when the hot carrier stress was performed in an oxygen-rich environment, the CGD-VG curve showed a significantly positive shift due to the electric-field-induced oxygen adsorption near the drain terminal. The degradation in the CGS-VG curve is due not only to the positive shift, but also the anomalous two step turn-on behavior. This phenomenon can be ascribed to the electron trapping in the gate dielectric and electric-field-induced oxygen adsorption on the channel layer, especially in the area adjacent to the drain terminal. The electron trapping increased the source energy barrier, with the electric-field-induced oxygen adsorption further raising the energy-band near the drain, resulting in a two-step turn-on behavior in the CGS-VG curve.