Development of extremely low temperature processed oxide thin film transistors via atmospheric steam reforming treatment: Interface, surface, film curing

We have developed an “atmospheric steam reforming treatment” technique to obtain high-performance flexible amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs) for applications in wearable/imperceptible electronics. The oxide TFTs, using as-grown a-IGZO with low-temperature sputtering and atomic layer deposition of Al₂O₃, showed unstable electrical behavior and poor transfer characteristics, which originated from a highly defective channel, gate insulator, and channel/gate insulator interface. Surprisingly, stable a-IGZO TFTs were obtained by atmospheric steam reforming treatment at an extremely low temperature (∼90 °C), and they exhibited good TFT performance with high field-effect mobility (13.3 cm²/V·s), high on/off ratio (4.5 × 10⁸), and small SS value (0.23 V/dec). Despite the extremely low thermal budget, this steam treatment has a positive effect on the TFT characteristics because of an effective oxygen diffusion source, thereby resulting in successful healing of oxygen-related defects in the bulk oxide channel, channel/gate insulator interface, and gate insulator. Finally, by carrying out the atmospheric steam treatment at an extremely low temperature, we successfully fabricated ultrathin flexible a-IGZO TFTs with good electrical performance from a vacuum deposition system at the maximum process temperatures of 100–150 °C.