Photo-bias instability of metal oxide thin film transistors for advanced active matrix displays

Metal oxide optoelectronics is an emerging field that exploits the intriguing properties of the ns orbital-derived isotropic band structure as a replacement for traditional silicon-based electronics in advanced active-matrix information displays. Although the device performance of metal oxide thin film transistors (TFTs) has been substantially improved, the device reliability against external light and gate bias stress remains a critical issue. This paper provides a literature review of light-induced gate bias stress instability in metal oxide TFTs and explain the importance of photo-bias instability in the applications of metal oxide TFTs to optoelectronic device. The rationale of threshold voltage (Vth) instability under the negative bias illumination stress (NBIS) condition is discussed in detail. The charge trapping/injection model, oxygen vacancy photoionization model, and ambient interaction model are described as plausible degradation mechanisms. Finally, the possible approaches to prevent NBIS-inducedVthinstability are proposed based on an understanding of the NBIS instability.