Enhanced Electrical Performance and Low Frequency Noise of In₂O₃ Thin-Film Transistors Using Al₂O₃/CeGdO_x Bilayer Gate Dielectrics

This work reports gadolinium-doped cerium oxide (CeO ₂ ) as gate dielectric, and appropriate doping of Gd can effectively prevent oxygen vacancy-related defects in CeO ₂ thin films. Atomic layer deposition (ALD)-derived 3 nm Al ₂ O ₃ passivation layer on CeGdO _x has the advantage of further reducing the leakage current of CeGdO _x MOS capacitors due to the wide bandgap and compactness of Al ₂ O ₃ . Then, Al ₂ O ₃ /CeGdO _x bilayer dielectric-based In ₂ O ₃ thin-film transistors (TFTs) are constructed; electrical performances are systematically explored under the effect of Gd doping compared with pristine Al ₂ O ₃ /CeO ₂ -gated TFT. Al ₂ O ₃ /CeGdO _x (30 at% Gd) TFT demonstrates high performances with ${I}_{\text {ON}}/{I}_{\text {OFF}}$ ratio of 1.45 $\times 10^{{7}}$ , saturation mobility of 27.28 cm ² /V $\cdot $ s, subthreshold swing (SS) of 0.091 V/decade, interfacial trap states of $1.64\times 10^{{11}}$ cm ⁻² , as well as remarkable positive bias stress (PBS) stability. Low-frequency noise (LFN) together with X-ray photoelectron spectroscopy (XPS) illustrates that Gd doping in CeO ₂ contributes to the reduction of interface trap density, improving electrical performance. Moreover, a resistor-loading inverter based on Al ₂ O ₃ /CeGdO _x -gated TFT exhibits superior voltage transfer characteristics (VTC) with a voltage gain of 16 at 5 V, demonstrating the potential application of Al ₂ O ₃ /CeGdO _x -based TFTs for future digital circuits.