Threshold voltage, field effect mobility, and gate-to-channel capacitance in polysilicon TFTs

Based on experimental and theoretical studies of n- and p-channel polysilicon thin film transistors with gate W/L ratios from 0.3 to 3.3, we have demonstrated that the threshold voltage extracted from gate to channel capacitance data results in field effect mobility parameters which are independent of device geometry. The parameters extracted using this V_t allow us to reproduce the I-V characteristics of the n- and p channel TFTs over wide ranges of bias voltages and gate sizes. The C_gc-V_GS characteristics of polysilicon TFTs are strongly affected by the trapping and de-trapping of carriers. As a result, the measured C_gc characteristic is a function of measurement frequency and gate length. However, we demonstrate that to the first order, the frequency dispersion of the C_gc curve can be related to the effective carrier transit time determined using the V_GS dependent field effect mobility