Ultrahigh field-effect mobility of 147.5 cm²/Vs in ultrathin In₂O₃ transistors via passivating the surface of polycrystalline HfO₂ gate dielectrics

This study presents considerable improvements in the electrical characteristics of atomic-layer-deposited 3-nm-thick In₂O₃ thin-film transistors (TFTs), which were achieved by introducing a 2-nm-thick amorphous Al₂O₃ interfacial layer to passivate the surface of a polycrystalline HfO₂ gate dielectric. The resulting devices exhibited exceptional electrical characteristics, including an ultrahigh field-effect mobility (μ_FE) of approximately 147.5 ± 16.6 cm²/V s, subthreshold swing of 103.7 ± 9.1 mV/dec, and threshold voltage (V_TH) of 0.5 ± 0.1 V. These enhancement-mode devices represent increases of more than threefold in μ_FE compared to devices without an amorphous passivation layer. This is despite all the fabrication processes being identical, except for the introduction of the Al₂O₃ interfacial layer. This improvement can be primarily attributed to the reduced electron scattering through suppressed remote Coulomb interactions. Furthermore, the In₂O₃ TFTs exhibited enhanced operational stability, showing minimal V_TH shifts of 0.15 and −0.01 V under positive and negative bias-stress conditions, respectively. The findings of this study emphasize the critical role of the surface passivation of polycrystalline HfO₂ dielectrics in improving the electrical performance of ultrathin In₂O₃ TFTs.