Investigation Into ZnO Thin Film Transistors Prepared By Sol-gel Method

Thin film transistor (TFT) is a kind of insulated-gate field-effect transistors, which changed the conductivity of the semiconductors via the electric field between the source and drain electrodes. TFT is the key component in the active matrix liquid crystal display technology. ZnO is a wide-band and direct gap compound semiconductor with a high transmittance in the visible spectrum. The electron mobility in ZnO is large at room temperature, and the light sensitivity is weak; so that, the obtained device is stable.The basic properties and fabrication processes of ZnO and SiO₂ films are reviewed in this paper. The sol-gel technique is adopted to deposite the SiO₂ and ZnO films. The growth of SiO₂ film particles is basically completed at 485℃, while the growth of ZnO film grains and the formation of crystal orientations is completed at 500℃through the Differential Thermal Analysis. The influence of preheating temperature to the crystal orientations is discussed by the X-ray Diffractometer. The grain size on different substrates is compared via the Scanning Electronic Microscopic. The tranmittance of films and the optical band gap are studied by the Ultraviolet-visible Spectrophotometer.The fabrication of ZnO TFTs and the extraction of the parameters are investigated. ZnO and SiO₂ films are dip-coated on ITO/glass substrates via the sol-gel technique to serve as the channel and gate-dielectric layer, respectively, and the transmittance of the ZnO/SiO₂ films is as high as 80 %. Then, Au are sputtered on the films as drain/source electrodes. By the characterization for semiconductor devices, the TFT is operated in the enhanced mode, and the channel is n-type. The on/off current radio is about 10⁴, the threshold voltage is about 3 V, and the mobility is calculated at 6.95 cm²/Vs.