Study On Improving The Performance Of Amorphous IGZO TFT With SiN_x Insulating Layer

Oxide Semiconductor Thin Film Transistor(AOS TFT) has been attracting widespread attentions of academia and industry due to their excellent electrical and optical characteristics for display applications. Especially, amorphous indium-gallium-zinc thin film transistor(a-IGZO TFT) has been increasingly been stuided for driving/switching devices in Active Matrix Organic Light Emitting Diode(AMOLED) and Active Matrix Liquid Crystal Display(AMLCD) backplanes because of its advantages, such as a lowcost and room temperature fabrication process, fast response speed, a large area uniform integration, a good short-range uniformity,transparency, a high field-effect mobility(μFE), etc. Therefore, as displays toward large-size, flexible and lightweight, a-IGZO TFT is considered to be the most promising backplane technology.However, there are many issues still to be resolved, such as the defect states between the active layer and the insulating layer and device stability. In this paper,top-contact thin-film transistors were fabricated using Si Nx as the gate insulator and In Ga Zn O as the channel layer so as to investigate the effect of Al2O3 buffer layer on the performance of a-IGZO TFT. Detail works are as follows:(1) We report on the electrical properties of bottom-gate IGZO thin film transistors with different channel layer thicknesses and different temperature of annealing. Studied the influence of the active layer thickness and temperature of annealing on the device performances. Obtained good performance of IGZO TFT by optimize the active layer thickness of the devices and the temperature of annealing.When the active layer thickness was 40 nm, temperature of annealing was 250℃,we get the optative device performances;(2)Analyzed the effects of Si Nx as the gate insulator materials, poor TFT performance due to Si Nx gate insulator will be damage when in sputter deposition process, resulting in the addition of maximum density of surface states at the channel-insulator interface.After using 5nm Al2O3 thin layer as an buffer layer,compared to the unmodified devices, electrical performance have improved.Moreover,obtained a good performance of TFT device by optimize the buffer layer thickness,the results show that the device with 4nm thick Al2O3 exhibits the best electrical performance. Under 1 hour bias stress, the threshold voltage shift is 1.41V/dec;(3)Analyse the unmodified devices and the devices with 4nm thick Al2O3 buffer layer, the time dependence of ΔVTH is in agreement with a stretched-exponential equation.After all stress experiments, both the unmodified device and the device with4 nm thick Al2O3 buffer layer were spontaneously recover their initial states after a period of relaxation of 1h.Indicating the cause of the positive threshold voltage drift is charge injection model, that carriers were captured by states at the channel-insulator interface. Contrasting to the TFT without buffer layers, the device with 4nm thick Al2O3 buffer layer density of surface states at the channel–insulator interface was reduced from 2.79×1012cm-2 to 2.31×1012cm-2.