Study On Fabrication And Properties Of Thin Film Transistors Based On PI Optical Orientation Layer

Amorphous oxide semiconductor thin film transistor（AOS TFT）has more and more application space in electronic fields such as flat panel display due to its advantages of high optical transparency,high current switching ratio and low temperature technology.The cation Sn⁴⁺and In³⁺in amorphous indium gallium tin oxide（a-IGTO）have the same electronic configuration,which can greatly help the formation of conductive channels and improve the electrical performance of devices.In this thesis,the electrical characteristics of a-IGTO TFT devices are further improved by adding a polyimide（PI）optical orientation layer between the device insulation layer and the active layer.The main research contents are as follows:First,Silvaco is used to simulate the effect of different insulation layer thickness on device performance.According to the experimental results,the thickness of insulation layer is selected as 100 nm to prepare for subsequent research.Then the mechanism of a-IGTO TFT device based on optical orientation layer is simulated and explored.The effect of orientation layer on the active layer material is studied by simulating the change of carrier concentration in the active layer.The experiments show that the high concentration carrier region presents a gradient distribution.This diffusion lowers the carrier concentration in the top portion of the active layer and raises it in the bottom region,which has an impact on the device’s electrical performance.Next,the preparation process of devices based on silicon oxide insulation layer is explored,and the effects of different oxygen/argon flow ratio,sputtering power and annealing atmosphere on the electrical properties of devices are explored.The experiment shows that the device has high saturated carrier mobility(μ_sat)of 7.68cm²/V·s when the oxygen/argon flow ratio is 15:70 and the sputtering power is 180 W.The device current switching ratio is up to 2.26×10⁶when the sputtering power is 60 W.In addition,the experiment shows that the device annealed in vacuum sputtering chamber has the best performance,and the device annealed in air has the worst performance.Finally,the preparation process of a-IGTO TFT device based on optical orientation layer is explored.The experiment shows that the PI alignment layer irradiated by ultraviolet polarized light presents an ordered channel structure,and the device irradiated by ultraviolet polarized light has better electrical characteristics.Among them,the change trend of electrical parameters such as threshold voltage is consistent with the simulation.The experiment shows that the film thickness becomes thinner and the flatness is better with the increase of spin coating speed within a certain range of rotational speed,and the device performance is improved.It has the best performance when the rotational speed is 5000 rpm.The orientation layer film at the rotational speed of 6000 rpm is too thin,and the orderly channel structure may not be formed after illumination,or the channel structure is not obvious,which will reduce the device performance.The experiment shows that when the sputtering power is 60 W,the low power sputtering has little effect on the surface morphology of the alignment layer,and the device has the minimum off state current of 2.39×10^-9A and the maximum open state current is 3.42×10^-3A.Maximum saturated carrier mobility of TFT based on optical orientation layerμ_satis 9.56 cm²/V·s,which is 24%higher than 7.68 cm²/V·s of TFT devices based on silicon oxide insulation.