Simulation Of IGZO Flexible Semiconductor Device

Due to its flexible ability, low cost, low power consumption, simplicity of manufacturing process and large-area production, the flexible semiconductor has achieved broad prospects in future application of surface displays, intelligent IDs, small computer chips,wearable devices and so on, which can bring customers a fresh experience.The flexible semiconductor is made by flexible materials. And Indium Gallium Zinc Oxide(IGZO) is one of the most widely used materials for the flexible semiconductor.Although flexible IGZO Thin Film Transistors(TFT) has not been mass produced, the process of its fabrication is compatible with CMOS process. And IGZO TFT also has widely application in many fields. So, international researches of IGZO TFT have been made broadly and thoroughly.It is necessary to do thorough researches in the characteristics of IGZO TFTs for a better utilization of it in diverse products. Generally speaking, there is a capacitance between the gate electrode and the drain electrode in a Metal-Oxide-Semiconductor(MOS)structure. The value of the capacitance can be changed with the variation of gate voltage. The relationship of the capacitance value and gate voltage can be described by the Capacitance-Voltage(C-V) curve. The C-V measurement can characterize the distribution of carriers’ density, the location of traps, the time constant of traps, the energy level of traps, and the frequency character of amplifiers. The IGZO TFT is similar with MOSFET. However, due to its lack of carriers, there is no inversion region in the C-V curve of IGZO TFTs. So, the C-V profile of IGZO TFTs should be researched thoroughly.In this Master Thesis, the structure of IGZO TFTs has been simulated. And the simulation includes below items. Firstly, the electronic character of the flexible IGZO materials has been analyzed, especially for the density of carriers. The simulation results indicate that the density of the intrinsic carriers is 10-15cm-3in the material, which is much lower than other semiconductor materials. According to this, the relationship between the bias voltage and the carrier density is achieved, and the model of the simulation has been built. Secondly, a detail discussion of the normal structure of IGZO TFTs, the back gate structure, has been made in the thesis. Owing to its symmetry, the structure has been simplified. And the simulated device is divided by finite difference method. Thirdly, the Matrix form of Poisson’s equation is solved by using the Singular Value Decomposition. Then, the two dimensional distributions of electric potential and electric field are achieved. For a further discussion of the C-V profile, Poisson’s equation with exponential time-included alternating electric potential has been solved to get the two dimensional distribution of electric potential in the device within a certain frequency of a small signal. At last, the C-V profile is achieved by using the resistance model of the capacitance. The results show the nearly the same as the experimental C-V profile.And according to the solved two dimensional distributions of the amplitude and the phase angle of the alternating electric potential, the difference between the high frequency and low frequency capacitance in accumulation region is due to low density of carriers and high resistance in the IGZO material.