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.