An Analytical Expression for Threshold Voltage of Polycrystalline-Silicon Thin-Film Transistors

A physical-based analytical expression for the threshold voltage (V_th) of polycrystalline-silicon (poly-Si) thin-film transistors (TFTs) is proposed, which is based on our previously developed analytical on-state drain-current model. The proposed V_th formula includes not only the channel inversion but also the grain-boundary (GB) potential barrier modulation effect. Furthermore, the GB barrier modulation is the dominant factor for device V_th rather than the channel inversion. The calculated V_th values agree well with the experimentally extracted ones using a constant-current or second-derivative method. The applicability of the formula is demonstrated in both n- and p-type poly-Si TFTs processed in either high or low temperature.