A thin-film transistor with a 5 nm-thick indium oxide active layer deposited by plasma-enhanced atomic layer deposition (PEALD) showed outstanding performance even with a polycrystalline phase.

Low-temperature growth of InO films was demonstrated at 70-250 °C by plasma-enhanced atomic layer deposition (PEALD) using a newly synthesized liquid indium precursor, dimethyl(N-ethoxy-2,2-dimethylcarboxylicpropanamide)indium (MeIn(EDPA)), and O plasma for application to high-mobility thin film transistors. Self-limiting InO PEALD growth was observed with a saturated growth rate of approximately 0.053 nm/cycle in an ALD temperature window of 90-180 °C. As-deposited InO films showed negligible residual impurity, film densities as high as 6.64-7.16 g/cm, smooth surface morphology with a root-mean-square (RMS) roughness of approximately 0.2 nm, and semiconducting level carrier concentrations of 10-10 cm. Ultrathin InO channel-based thin film transistors (TFTs) were fabricated in a coplanar bottom gate structure, and their electrical performances were evaluated. Because of the excellent quality of InO films, superior electronic switching performances were achieved with high field effect mobilities of 28-30 and 16-19 cm/V·s in the linear and saturation regimes, respectively. Furthermore, the fabricated TFTs showed excellent gate control characteristics in terms of subthreshold swing, hysteresis, and on/off current ratio. The low-temperature PEALD process for high-quality InO films using the developed novel In precursor can be widely used in a variety of applications such as microelectronics, displays, energy devices, and sensors, especially at temperatures compatible with organic substrates.

Atomic layer deposition (ALD) has attracted much attention, particularly for applications in nanoelectronics because of its atomic-level controllability and high-quality products. In this study, we developed a plasma-enhanced atomic layer deposition (PEALD) process to fabricate a homogeneous indium aluminum oxide (IAO) semiconductor film. Trimethylaluminum (TMA) and dimethylaluminum isopropoxide (DMAI) were used as Al precursors, which yielded different compositions. Density functional theory (DFT) calculations on the surface reactions between indium and aluminum precursors showed that while highly reactive TMA would etch In, DMAI with lower reactivity would allow indium to persist in the films, resulting in a more controlled doping of Al. The In/Al composition ratio could be further precisely controlled by adjusting the indium precursor dose time to sub-saturation. IAO based on DMAI was applied to fabricate thin-film transistors (TFTs), showing that Al can be a carrier suppressor of indium oxide. TFTs with PEALD IAO containing 3.8 atomic % Al showed a turn-on voltage of −0.4 ± 0.3 V, a subthreshold slope of 0.09 V/decade, and a field effect mobility of 18.9 cm 2 /(V s).