Systematic Study on the Amorphous, C-Axis-Aligned Crystalline, and Protocrystalline Phases in In–Ga–Zn Oxide Thin-Film Transistors

In an effort to fabricate In–Ga–Zn oxide (IGZO) thin-film transistors (TFTs) that combine high performance and high stability, we optimize sputtering conditions to create devices based on different IGZO phases: amorphous, c-axis-aligned crystalline (CAAC), and a transition between them, which is introduced here as protocrystalline IGZO. For this, we study the performance of TFTs based on thin films of IGZO sputtered at different substrate temperatures Tsub and oxygen flow ratios RO2. While Tsub is the principal phase-determining parameter, RO2 can be further optimized to enhance IGZO TFT characteristics. For both amorphous IGZO and CAAC IGZO, the best TFT performance and the best TFT bias stress stability are found under different sputtering conditions. In contrast, the protocrystalline IGZO shows a convergence of the highest TFT performance and the best bias stress stability, observed for an IGZO film sputtered at Tsub = 200 °C and RO2 = 20%.