Enhanced Thermal Stability of Elevated-Metal Metal-Oxide Thin-Film Transistors via Low-Temperature Nitrogen Post-Annealing

Effects of low-temperature annealing in nitrogen atmosphere on elevated-metal metal-oxide (EMMO) thin-film transistors (TFTs) are investigated and reported in this article. Compared with the short-circuit behavior of EMMO TFTs after annealing in nitrogen atmosphere at 300 °C, it is found that TFTs received annealing in nitrogen atmosphere at 200 °C prior to that at 300 °C not only remain the transfer characteristics, but also exhibit improved on-state current and subthreshold characteristics. Both the results of X-ray photoelectron spectroscopy (XPS) and persistent photoconductivity (PPC) confirmed the reduction of oxygen vacancies in the a-IGZO after annealing in nitrogen atmosphere at 200 °C, indicating that the passivation of oxygen vacancy with nitrogen is dominant rather than the generation of oxygen vacancy. Furthermore, the thermal stability improvement could not be realized when the annealing in nitrogen atmosphere at 200 °C was performed before the source/drain formation annealing at 400 °C, which emphasizes the importance of annealing procedures during device fabrication.