An Analytical Expression for the Transfer Characteristics of a Polycrystalline Silicon Thin-Film Transistor With an Undoped Channel

An analytical model for the transfer characteristics of a polycrystalline silicon thin-film transistor (TFT) with an undoped channel is developed. While the modeling methodology is general, the analytical form is based on the observation that the trap states in a grain boundary are exponentially dispersed over the energy space defined by the energy gap of the adjacent grains. The dispersion relationship is parameterized by an energy EA. The complex mechanisms governing carrier transport in a TFT are modeled in terms of an effective ldquodriftrdquo mobility mu_eff that also accounts for the thermionic emission of charge carriers across the grain boundaries. A gate bias V _pt can be identified that roughly locates the transition from the ldquopseudo-subthresholdrdquo and the ldquoturn-onrdquo regimes of operations. Techniques for the extraction of EA and the transition voltage V _pt are proposed. A particularly simple expression of mu_eff can be obtained in terms of these and other parameters.