Characterization of Switching Transient Behaviors in Polycrystalline-Silicon Thin-Film Transistors

Grain boundary (GB) trapping effects on switch-on and switch-off transient behaviors in polycrystalline-silicon thin-film transistors (poly-Si TFTs) are investigated. Theoretical analysis has been performed on the GB trapped charge dependence of drain current and the transient behaviors in capture and emission of carriers in the GB trap states. Transient drain current is controlled by mobility variations and a dynamic threshold voltage shift, where both are influenced by the progressive capture or emission process of carriers at the GBs within the transient time. Time derivative of the GB trapped charge in the capture process includes logarithmic time dependence in addition to t -1 time dependence of both capture and emission processes. The current variations controlled by the trapped charge and change of the trapped charge give t -α time dependence. This model has been verified by the measurements in several different types of TFTs fabricated with excimer laser annealing crystallization processes and device simulations.