Investigation of the Electrical Characteristics of Bilayer ZnO/In(2)O(3) Thin-Film Transistors Fabricated by Solution Processing

Metal-oxide thin-film transistors (TFTs) have been developed as promising candidates for use in various electronic and optoelectronic applications. In this study, we fabricated bilayer zinc oxide (ZnO)/indium oxide (In(2)O(3)) TFTs by using the sol-gel solution process, and investigated the structural and chemical properties of the bilayer ZnO/In(2)O(3) semiconductor and the electrical properties of these transistors. The thermogravimetric analysis results showed that ZnO and In(2)O(3) films can be produced by the thermal annealing process at 350 °C. The grazing incidence X-ray diffraction patterns and X-ray photoemission spectroscopy results revealed that the intensity and position of characteristic peaks related to In(2)O(3) in the bilayer structure were not affected by the underlying ZnO film. On the other hand, the electrical properties, such as drain current, threshold voltage, and field-effect mobility of the bilayer ZnO/In(2)O(3) TFTs obviously improved, compared with those of the single-layer In(2)O(3) TFTs. Considering the energy bands of ZnO and In(2)O(3), the enhancement in the TFT performance is explained through the electron transport between ZnO and In(2)O(3) and the formation of an internal electric field in the bilayer structure. In the negative gate-bias stress experiments, it was found that the internal electric field contributes to the electrical stability of the bilayer ZnO/In(2)O(3) TFT by reducing the negative gate-bias-induced field and suppressing the trapping of holes in the TFT channel. Consequently, we suggest that the bilayer structure of solution-processed metal-oxide semiconductors is a viable means of enhancing the TFT performance.