Facile diffusion of sulfur and fluorine into a-IGTO thin films for high-performance and reliability of transparent amorphous oxide semiconductor thin-film transistors

Plasma treatment with fluoro-containing gases is widely studied to improve the electrical performance of amorphous oxide semiconductor-based thin-film transistors (TFTs). However, given its research solely focuses on improving electrical performance, its practical use faces limitations due to an insufficient comprehension of its influence on device reliability – a pivotal factor for optimal, long-term device operation. Herein, improvements in the electrical performance and reliability of highly transparent amorphous indium-gallium-tin-oxide (a-IGTO) TFTs through SF₆ plasma treatment, a facile and straightforward approach with high applicability, are thoroughly investigated. Furthermore, the addition of oxygen gas, a widely used supplementary gas in plasma treatment, is analyzed. The diffusion of S and F by SF₆ plasma treatment breaks the weak bonds between the metal ions and oxygen atoms and reduces the number of oxygen vacancies in a-IGTO thin films. Despite the decrease in the oxygen vacancies, the carrier concentration is increased, as F acts as a donor-like defect. This diffused S and F effect increased the field-effect mobility (μ, 19.4 cm²/V·s) by a factor of about two and also greatly reduced the threshold voltage (V_th) shifts under various bias stress tests. The high performance and reliability of SF₆ plasma-treated a-IGTO TFTs demonstrate the feasibility of transparent TFT-based next-generation transparent electronics.