An Investigation of Bias Temperature Instability in Hydrogenated Low-Temperature Polycrystalline Silicon Thin Film Transistors

Abstract

The instability mechanisms of the hydrogenated n-channel low-temperature polycrystalline silicon thin film transistors under on-state stress were investigated with various bias stress conditions and device channel widths. It was found that hot carrier degradation which originated from a high drain electric field and self-heating during high current operation were the two dominant mechanisms responsible for device degradation. An electrically reversible depassivation/passivation phenomenon was also found in devices under high current stress, but not in those under hot carrier stress. It was inferred that the self-heating effect would accelerate the bond breakage and diffusion of hydrogen ions, thus enhancing the rate of depassivation/passivation. Moreover, when the current in the hot carrier stress mode was sufficiently high, self-heating became the dominant degradation mechanism and hot carrier degradation phenomenon was also suppressed for devices with large channel width. Meanwhile, the electrically reversible depassivation/passivation phenomenon also occurred in this case.