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 E_A. The complex mechanisms governing carrier transport in a TFT are modeled in terms of an effective "drift" mobility μ_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 "pseudo-subthreshold" and the "turn-on" regimes of operations. Techniques for the extraction of E_A and the transition voltage V_pt are proposed. A particularly simple expression of μ_eff can be obtained in terms of these and other parameters.