Separation of the Geometric Current in Charge Pumping Measurement of Polycrystalline Si Thin-Film Transistors

In the charge pumping (CP) measurement of polycrystalline Si (poly-Si) thin-film transistors (TFTs), an experimental approach is developed to evaluate and separate the geometric current (I_geo) from the measured CP current based on a group of TFTs with different channel widths and fixed channel length. Along with the separation of I_geo, a new method is proposed to reliably characterize the trap state density of TFTs. Without the I_geo, the overestimation in CP measurement is avoided even for short CP pulse transition times. Moreover, critical transition time for the occurrence of geometry effect is determined, which agrees well with the prediction from a physical model of diffusion controlled carrier evacuation.