Research On Active Layer Of ZnO TFT Deposited By Radio Frequency Magnetron Sputtering Technique

Zinc oxide is aⅡ-Ⅵcompound semiconductor with a wide band gap of 3.37eV and a hexagonal wurtzite structure. Zinc oxide is nontoxic, inexpensive, and it has a stable chemical characteristics. Especially, highly c-axis oriented zinc oxide thin film is an excellent photo-electric material with many advantages such as high transparency, low deposition temperature, high breakdown voltage, strong radiation tolerance, high electron saturation drift velocity and so on. Recently, a research on the field effect transistor with zinc oxide thin film as an active channel layer has been made both in and abroad. It is notable that this kind of field effect transistor can be made at a low temperature so it can be deposited on plastic or normal glass substrate. Furthermore, this kind of thin film transistor can be made entirely transparent. If zinc oxide-based thin film transistor can be applied in active-matrix liquid crystal display (AMLCD), it will simplify the processing of TFT LCD, reduce the cost, and enhance the reliability of transistors.There are many kinds of methods to deposit zinc oxide thin film, such as magnetron sputtering, MBE, sol-gel, MOCVD, and so on. Magnetron sputtering is a simple technique, films deposited in this way is compact, and they can be deposited at a low temperature, the speed of deposition is large, so Magnetron Sputtering is widely used.Zinc oxide thin films were deposited on glass substrates at a low temperature by radio frequency (RF) magnetron sputtering technique. The films grown are highly transparent and highly c-axis oriented. The optical transmission of the film in the visible part of the spectrum is more than 90%. The influence of sputtering process parameters, such as substrate temperature, Ar/O2 ratio and sputtering pressure on the film characteristics was investigated by X-ray diffraction (XRD) and scan electron microscope (SEM). The results show that when the substrate temperature is 400℃, the sputtering pressure is 1Pa, the Ar:O2 ratio is 25sccm:15sccm, the film grown is highly c-axis oriented, and the film has a good crystallinity. The grain size of the films can be as large as 50 nm. These zinc oxide thin films can be used as active layers in transparent thin film transistors (TTFT) of flat panel displays.