A Multiple-Trapping-and-Release Transport Based Threshold Voltage Model for Oxide Thin Film Transistors

This article proposes a generic approach for modelling threshold voltage of oxide thin film transistors (TFTs). Threshold voltage has always been ambiguous in TFTs due to the disordered nature of semiconducting thin films, and in operation in accumulation mode. This differs from the situation with metal oxide field-effect transistors (MOSFETs), wherein strong inversion can be specifically defined. The proposed model considers double exponential distribution of deep state and tail state densities in the bandgap with the multiple-trapping-and-release (MTR) transport model. In this surface potential-based approach, pinned surface potential is defined as the surface potential at which free carrier densities exceed deep state carrier density in the deep state-dominated region. The threshold voltage is defined using pinned surface potential and carrier densities obtained at that surface potential. The model is validated using data from fabricated oxide based TFTs with silicon dioxide (SiO₂) and other dielectrics. This article develops and reports a systematic approach for fitting an oxide based TFT analytical model with experimental devices, thus ensuring the flexibility needed for compatibility with various devices.