High-k Gated Ga₂O₃/IGZO Heterostructure TFTs With 70.9 mV/dec Subthreshold Swing Fabricated at a Low Thermal Budget of 200◦C

Ga₂O₃/In_1.0Ga_2.5Zn_0.2O_2.6 heterostructure thin-film transistors (TFTs) with high-k gate dielectrics were fabricated via sputtering at room temperature. The performances of the Ga₂O₃/IGZO TFTs gated by high-k Ta₂O₅ can be improved by modulating the oxygen content in the hetero-channel Ga₂O₃ layer. This improvement is attributed to the smoothened film surface and reduced oxygen vacancies, enhancing the passivation effect of the heterostructure Ga₂O₃ layer and forming a quasi-two-dimensional electron gas at the hetero-channel interface. Furthermore, the high-k Ta₂O₅ gate dielectric was replaced by a mixture high-k TaLaO, where the Ta and La oxides can complement with each other to improve the qualities of the high-k dielectric and interface. Finally, the Ga₂O₃/ IGZO TFT gated by TaLaO demonstrates an ultralow subthreshold swing (SS) of 70.9 mV/dec, a high field-effect mobility of 36.9 cm²/V . s, a large on/off ratio of 5.5 × 10⁸, and an excellent bias-stress stability. These results are highly competitive, especially for a low thermal budget of 200 ◦C, which paves a possible way to extend applications in low-power and high-frame-rate displays, flexible electronics and monolithic 3D integration.