An Analytical Subthreshold Model of Polycrystalline Silicon Thin-Film Transistors Based on Meyer-Neldel Rule

It is demonstrated that the subthreshold region of polycrystalline Si thin-film transistors contains both the channel full inversion and channel partial inversion regimes. Channel inversion charge sheet density is modeled based on the gate-to-channel capacitance measurement. Following the observation of the Meyer-Neldel rule for effective channel mobility (μ_eff) in the subthreshold region, a μ_eff model is constructed with the physical origin of multiphonon excited carrier thermionic emission over the grain boundary (GB) barriers. Then, by considering the carrier drift, an analytical subthreshold drain current model is developed. Subsequently, an analytical expression for subthreshold swing (SS) is derived. The gate voltage (V_g) induced GB barrier lowering effect is determined to be the key mechanism for subthreshold behavior. Besides, the V_g point of channel full inversion is demonstrated to be a key point of the subthreshold region, where SS reaches a minimum.