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 measurement of polysilicon TFT's: the presence of an "overshoot" in the transient response, which implies a time dependent gate capacitance exceeding C/sub ox/ WL. We have also performed two-dimensional (2-D) transient simulations to explain the experimental results. Our analysis indicates that a TFT circuit model based on lumped intranodal impedances cannot explain the observed transient current behavior. It follows that the "subtransistor" approach is essential for accurate dynamic circuit simulations.