A computationally efficient simulation model for the drain current characteristics of long-channel amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) is developed. This model uses numerical solutions of the one-dimensional Poisson equation to significantly reduce the calculation time compared to a widely used two-dimensional approach. Moreover, for accurate simulation, the model takes into account the influence of trap states in the band gap, which makes it possible to reproduce the gradual increase of the drain current in the subthreshold region. The model also includes both drift and diffusion components of the drain current and so can describe the drain current in all regions of device operation, i.e., the subthreshold, linear, and saturation regions, by using a unified current equation without introducing the threshold voltage as an input parameter. Calculations using the model provide results that are in good agreement with the measured drain current characteristics of a-IGZO TFTs over a wide range of gate and drain voltages. The presented model is expected to enable faster and accurate characteristic analysis and structure design for a-IGZO TFTs.
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