Investigation of Low-Temperature Processed Amorphous ZnO TFTs Using a Sol-Gel Method

Abstract

In this paper, ZnO Thin Film Transistors (TFTs) were fabricated by a sol-gel method using a low-temperature process, and their physical and electrical characteristics were analyzed. To lower the process temperature to 200℃, we used a zinc nitrate hydrate (Zn(NO3)2·xH2O) precursor. Thermo Gravimetric Analyzer (TGA) analysis showed that the zinc nitrate hydrate precursor solution had 1.5% residual organics, much less than the 6.5% of zinc acetate dihydrate at 200℃. In the sol-gel method, organic materials in the precursor disrupt formation of a high-quality film, and hightemperature annealing is needed to remove the organic residuals, which implies that, by using zinc nitrate hydrate, ZnO devices can be fabricated at a much lower temperature. Using an X-Ray Diffractometer (XRD) and an X-ray Photoelectron Spectrometer (XPS), 200℃ annealed ZnO film with zinc nitrate hydrate (ZnO (N)) was found to have an amorphous phase and much more oxygen vacancy (Vo) than Zn-O bonds. Despite no crystallinity, the ZnO (N) had conductance comparable to that of ZnO with zinc acetate dihydrate (ZnO (A)) annealed at 500℃ as in TFTs. These results show that sol-gel could be made a potent process for low-cost and flexible device applications by optimizing the precursors.