Gate Bias Instability under Light Irradiation in Polycrystalline Silicon Thin-Film Transistors

We have investigated the charge trapping phenomena that occur in gate insulator biased under back-light irradiation of a liquid-crystal display. Two types of gate insulators (SiO 2 and SiN x /SiO 2 ) were evaluated. In both cases, it was found that electron trapping in the insulators is caused by light irradiation under gate bias stress and that the locations of the electron trapping in gate insulator vary according to the kind of insulator and the polarity of gate bias. As for the dependence of degradation on stress time and luminance, the phenomena can be explained by an approximate equation derived from first-order rate equation. Furthermore, it was found that the analysis of the light-induced degradation is valid for evaluation of insulator quality. We confirmed that gate insulators formed in different deposition conditions have different light-induced degradation rates.