Phase-Composite InOx Semiconductors for High-Performance Flexible Thin-Film Transistors

Indium oxide (InO_x) offers high electron mobility and optical transparency, making it a promising material for advanced thin-film transistors (TFTs). However, challenges related to the high carrier concentration, crystallization control, and instability limit its performance. In this study, we demonstrate the fabrication of amorphous/nanocrystal phase-composite InO_x films using high-pressure atomic layer deposition (ALD) using InCA-1 and H₂O₂ as the metal precursor and oxidant, respectively. The amorphous matrix in the phase-composite structure enables resonant hybridization, facilitating efficient electron transport by forming delocalized states via wave function overlap between nanocrystalline and amorphous regions. The systematic investigation of the deposition temperature and channel thickness allowed precise control over carrier concentration and fine-tuning of the phase-composite structure. The optimized InO_x films, deposited at 110 °C with a 7.0 nm thick InO_x channel, exhibited outstanding electrical properties, including a field-effect mobility of 61.1 cm² V^-1 s^-1, an on/off ratio of ∼0.9 × 10⁶, and a subthreshold swing of 0.45 V dec^-1. The films also demonstrate high reproducibility, high optical transmittance (>87% in the visible range), and smooth surface morphology with a root-mean-square roughness of 3.03 Å. Moreover, the devices exhibited remarkable mechanical flexibility, maintaining stable operation after 10,000 bending cycles with a bending radius of 3 mm, and excellent environmental stability, retaining performance after 60 days of ambient air exposure. This study addresses key limitations of conventional InO_x-based TFTs by improving the phase control, carrier concentration regulation, and mechanical durability, offering a promising pathway for next-generation electronic and optoelectronic applications.