Performance Improvement of a-In-Ga-Sn-O Thin-Film Transistor with Oxygen Doping by Reactive Sputtering Method

The thin film of indium gallium tin oxide (IGTO) was deposited by the RF magnetron sputtering system with different oxygen flow ratios, which controls the numbers of defects and free carriers to change the characteristics of thin-film transistors ((TFTs). We determined the subgap density-of-states (DOS) from the transfer characteristics curve by the unified subthreshold coupling factor technique to analyze the response of oxygen-related trap sites within the thin films fabricated under different oxygen flows. We used Python to fit the DOS data with a combination of two exponential forms, inferring that, during the increase in the oxygen flow ratio, acceptor-like oxygen-related trap sites can be gradually compensated. The IGTO TFTs exhibit optimized performance when subjected to annealing at 200 °C for 1 h with a 5% oxygen flow ratio, showing a threshold voltage (V_th) of 1.76 V, a field-effect mobility of 0.355 cm²/V s, an impressive on/off drain current ratio of 1.42 × 10⁶, and a subthreshold swing (SS) of 0.665 V/decade.