Observation of "capacitance overshoot" in the transient current measurement of polysilicon TFT's

We have observed and analyzed a new effect in the transient current measure ment of polysilicon TFT's: the presence of an "overshoot" in the transient response, which implies a time dependent gate capacitance exceeding CoxWL. We have also performed two-dimensional (2-D) transient simulations to expla in the experimental results. Our analysis indicates that a TFT circuit mode l based on lumped intranodal impedances cannot explain the observed transie nt current behavior. It follows that the "subtransistor" approach is essent ial for accurate dynamic circuit simulations.