A new charge pumping model and characterization of process-dependent traps in polycrystalline silicon thin film transistors

Abstract

A model is proposed to explain anomalous frequency characteristics in the charge pumping current of polycrystalline silicon thin film transistors (poly-Si TFTs). The model includes the effect Df large substrate resistance of poly-Si, by which carrier supply can be limited. The model can describe well the anomalous frequency characteristics that the charge pumping current starts to decrease with frequency above a critical frequency. Based on the model, the critical frequency can be estimated for a given device size. Process-dependence of trap characteristics can be examined by the model. For poly-Si TFTs with both oxide by electron cyclotron resonance, oxygen plasma oxidation, and chemical vapor deposition, the hole capture cross sections of traps are extracted to be 1.0 x10(-17) cm(2) from the measured dependence of the charge pumping current, but the former has lower trap density and large substrate resistance, which correspond to larger mobility, and lower subthreshold slope and leakage current.