Fully Sputtered a-IGZO TFTs with Ultrathin Al2O3 Passivation and Low-Thermal-Budget Annealing for Enhanced Logic Circuit Performance

Abstract

Developing low-temperature sputtering for gate dielectrics is crucial for simple, flexible oxide TFT fabrication. However, such films suffer from low capacitance, high leakage, and high interfacial defects. This work proposes a synergistic strategy using an ultrathin alumina passivation layer combined with ultraviolet-assisted oxygen ambient rapid thermal annealing (UV-ORTA) to enable fully low-temperature sputtered high-performance amorphous indium gallium zinc oxide (a-IGZO) TFTs. The UV-ORTA process significantly improves the gate dielectric by reducing oxygen vacancies, increasing optical bandgap, and boosting capacitance density. The sputtered alumina layer effectively optimizes the dielectric/active layer interface, reducing defect density comparably to atomic layer deposition. TFTs fabricated entirely by sputtering at 200 °C demonstrate high performance: saturation mobility of 14.5 cm²·V⁻¹·s⁻¹, on/off ratio of 8.6 × 10⁶, subthreshold swing of 0.09 V/dec, and good bias stability. Resulting inverters show full-swing operation, sensitive dynamic response, excellent frequency stability, and a voltage gain exceeding 12. This strategy provides a promising solution for low-temperature, fully-sputtered all-oxide TFTs compatible with flexible displays.