In this letter, for both non-degenerate conduction and degenerate conduction, a new compact model of amorphous oxide semiconductor thin-film transistors is developed. The contributions of the trapped and free charges are considered in the closed-form solutions of surface potential and drain current under a degenerate regime. Furthermore, proof of the model's accuracy has been obtained by comparisons with numerical results and measured data. The proposed scheme is capable of capturing real-device dc characteristics and of maintaining high computational efficiency, which provides a better platform to develop advanced surface-potential-based model for circuit simulation.

An explicit approximation for surface potential as a function of terminal voltages is developed for partially depleted polysilicon thin-film transistors. The resulting model has taken both Gaussian deep states and exponential tail states into account, which provides a complete modeling for surface potential. Furthermore, a drain current model based on terms of surface potential is proposed. Surface potential and drain current calculations are successfully verified by comparisons with numerical and experimental ones.

A core scheme including dc and capacitance models of amorphous indium gallium zinc oxide thin-film transistors is presented based on terms of surface potential. Due to the intrinsic physical fact, carrier degeneracy is taken into account. A simpler symmetric quadrature version of charge-sheet model is adopted, which offers a new approach to deduce the expressions of current and terminal charges. Through the extensive comparisons between model results and numerical iterations or experimental data, the validity of the proposed models is strongly supported. The simplicity of algorithm and clear physical conception make the model suitable for circuit simulators.

An explicit current-voltage model for cylindrical surrounding-gate polysilicon (poly-Si) transistors with a doped poly-Si channel is presented. It is based on an intermediate parameter which is derived analytically from the 1-D Poisson's equation and satisfies the corresponding boundary conditions. The surface and midpoint potentials are described as functions of this intermediate parameter. Furthermore, the drain currents in the different operational regions are analytically integrated. Our model results show good agreement with numerical and experimental data. The use of the explicit surface potential solution results in an easy implementation into circuit simulators.

An improved model for the low-frequency noise (LFN) of amorphous indium–zinc-oxide thin-film transistors (a-IZO TFTs) is developed in this article. For a-IZO TFTs, the LFN is not only attributed to the oxide traps in the gate insulator but also affected by the discrete trap centers in the active-layer film. This makes the device has excess noise in the subthreshold region, which is obviously different from monocrystalline silicon (c-Si) MOSFETs. Therefore, we put forward an accurate and physically meaningful model to characterize this excess noise. For the subthreshold region, the charge of tail states in the channel is considered to describe the excess subthreshold noise, and the channel density of states (DOS) is extracted, confirming the effectiveness of the model. For the above-threshold region, the classic carrier number with correlated mobility fluctuation ( $\Delta N$ – $\Delta \mu $ ) mechanism has been investigated to explain the noise behavior. Furthermore, the proposed unified model is validated, and it has been successfully applied to a-IZO TFTs with different tail-state densities.