| With the rapid development of liquid crystal display technology,thin film transistor, as its control components, which should be required for more outstanding electrical performance.Represented by indium gallium zinc oxide of metal oxides, metal oxides had become the ideal material of thin film transistor channel layer,since they have high mobility, high transparency,low temperature preparation,and other advantages.The thin film transistor to control the pixels in the LCD were made of IGZO, which have widely used in AMOLCD, OLED display device because of the low power consumption, low cost, insensitive to visible light and other characteristics. Based on the accurate trap distribution of a-MOS TFT and the electrical characteristics, a reasonable a-IGZO TFT physical model is proposed, and the physical mechanism of drain current will provide the theoretical support for circuit simulation and device fabrication, Moreover,a satisfying and accurate model has far-reaching practical significance on the promotion and the development of integrated circuit industry.The aim of this article is to analyze the current characteristics of a-IGZO TFT with different trap distributions, put forward the surface potential-based drain current physical models for a-IGZO TFT.Trap charge distribution has a great influence on the electrical properties of thin film transistor, considering the Gaussian distribution and exponential distribution of a-IGZO density of states, respectively,using Poisson’s equation and Gaussian theorem to prove the relationship between trap state and the free carrier concentration and channel potential for a-IGZO TFT.The influence of the trap state on the drain current is discussed in detail through the numerical calculation.The results laid the foundation for a-IGZO TFT device surface potential and the research of the analytical model of drain current.Firstly,considering both the exponential band-tail and deep states continuous distributions in Poisson’s equation, the implicit equation about surface potential has been derived, this equation describes a functional relationship between the surface potential and gate voltage. Based on gradient channel approximation principle,considering the physical mechanism of carrier in the Poisson’s equation when gate voltage changes, a non-iterative algorithm and analytical surface potential of a-IGZO TFT has been developed. Compared with the calculated results of numerical iterative algorithm, the absolute error of the proposed surface potential analytic model is low to-510 orders of magnitude, and the computational efficiency also can be improved. Considering a-IGZO transmission mechanism and the Pao-Sah model, the drain current model of a-IGZOTFT can be established basing on the above surface potential analytical solution. Comparing the experimental data of a-IGZO TFT device output and transfer characteristics, and then verifies the effectiveness and accuracy of the drain current model.Secondly,based on the mathematical transformation and Lambert W function, a compact and analytical model for the surface potential of a-IGZO TFT has been derived in this paper,which considers the exponential band-tail and deep states with gaussian distribution of a-IGZO TFT.Combined with charge sheet model, the unified drain current expression of a-IGZO TFT can be deduced,which can apply to the whole work area. By comparing the output characteristic curve with the experimental data, an excellent agreement has been obtained and verifies the validity of the proposed drain current model of a-IGZO TFT.In conclusion, with a-IGZO physical mechanisms, surface-potential-based provides the method of modeling, put forward two kinds of current analytical model with different deep states distribution functions.Since the proposed current models have clear physical concept and the advantage of fewer calculations, and the models accurately describe a-IGZO TFT electrical characteristics, which are capable to fulfil circuit simulator impletment. |
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