Reseach On Fabrication And Properties Of Zinc Tin Oxide Thin Film Transisters

The display device has become more important technology in twenty-first century. Thin film transistor as a key component of the active matrix driver technology has a significant impact on the performance of display device. So far, the most mature TFT are the amorphous silicon thin film transistor and polycrystalline silicon thin film transistors. However, amorphous silicon TFT has low carrier mobility(<1 cm2/Vs), and it is difficult to meet the requirements of OLED current drive, and a-Si: H TFT has poor stability. The cost of polysilicon TFT is high and production process is relatively complex, and is difficult to have large size. The disadvantages of silicon TFT is hard to improve, while amorphous oxide thin film transistors have been rapid development. Advantages of amorphous oxide TFT are the higher carrier mobility, excellent device performance and easy to prepare. These advantages make it great value.Because of disadvantage of silicon TFT, this paper prepared ZnSn O(ZTO) films and ZTO-TFT by sol-gel method. Zinc-Tin-Oxide(ZTO) thin films were deposited on P+-Si substrate with varying Zn: Sn(9/1,7/3,5/5,2/8) atomic composition ratio. The x-ray diffraction(XRD) analysis indicates that variation of Zn/Sn atomic composition ratio in ZTO thin films induced a dramatic change in the microstructure. When Zn: Sn is 9:1, the film is polycrystalline structure. With the increasing of Sn4+, ZTO film gradually changed from polycrystalline to amorphous, and film resistivity decrease from 423.19 ? ? cm to 0.737 ? ? cm Film surface is uniform and compact; and has high transmittance in the visible region(~85%). Thermogravimetric and differential thermal analyses(TG-DTAs) were performed to investigate the chemical reactivity in the ZTO solutions in ambient air. When Zn: Sn is 5:5, TFT switch ratio is 3.85 ×105, threshold voltage is 5.5V, the subthreshold swing is 2.5 V/decade, and the saturation of the carrier mobility is 6.36 cm2/Vs.TFT has the best performance at this ratio.The effects of annealing temperatures on characteristics of ZTO film and ZTO-TFTs were investigated in this paper. Experiences indicate that with the increasing of annealing temperatures, all samples were amorphous, and surface was uniform. The ZTO thin films annealed at 400 and 500°C were highly transparent(~85%) in the visible region. When the annealing temperature increased from 300°C to 500°C, the threshold voltage of solution-processed ZTO TFTs decreased from 15.85 V to 3.7 V, and the saturation mobility increased from 0.004 cm2/Vs to 5.16 cm2/Vs. Ion/Ioff current ratio of 105 was obtained at 500°C.