An analytical model of the influence of grain size on the mobility and transfer characteristics of polysilicon thin-film transistors (TFTs)

Influence of the grain size oil the effective carrier mobility (mu(eff)) and transfer characteristics of a polycrystalline silicon thin-film transistor (poly-Si TFT) has been theoretically investigated by developing analytical model. The dependence of mu(eff) is studied as function of doping concentration and gate voltage for different values of-rain size. It is observed that at low as well as at high doping concentrations, the effective carrier mobility (mu(eff)) increases with increasing grain size, whereas the observed dip at the intermediate doping concentration is confirmed. The effect of the grain size on transfer characteristics of poly-Si TFT in its linear region is also presented. It is found that at low gate voltages. mu(eff) and I-D increase rapidly with the increase in V-G for all grain sizes due to the grain boundary barrier lowering effect. At high gate voltage the grain boundary barrier lowering effect becomes insignificant and causes the saturation of mu(eff) and I-D. The model was found to account correctly for the experimentally observed mobility variation and yield a reasonably good agreement.