We investigated the synthesis of amorphous aluminum titanium oxide Al1− xTi xO y thin films from a Al(acac)3 and Ti(acac)4 mixture using CH3OH/H2O as a solvent through mist chemical vapor deposition (mist-CVD) for application as a high dielectric material. The Ti composition ratio x in the Al1− xTi xO y thin films depends on the Al(acac)3 and Ti(acac)4 mixing ratios and CH3OH/H2O volume ratio. A bandgap energy of Al1− xTi xO y films was decreased from 6.38 to 4.25 eV and the surface roughness also decreased when the Ti composition ratio was increased from 0 to 0.54. The capacitance–voltage plot revealed that the dielectric constant of Al1− xTi xO y thin films increased from 6.23 to 25.12. Consequently, Al1− xTi xO y thin films with a bandgap energy of 5.12 eV and a dielectric constant of 13.8 were obtained by adjusting the ratio x of 0.26. This Al0.74Ti0.26O y layer was applied as a gate dielectric layer for metal-oxide-semiconductor field-effect transistors (MOSFETs) using a mechanically exfoliated two-dimensional (2D) transition metal dichalcogenide (TMDC), MoSe2, and As-doped WSe2 flakes as a channel layer. The MoSe2-based MOSFETs with source/drain gold electrodes exhibit n-channel behavior with a field-effect mobility of 85 cm2/(V s), a threshold voltage of 0.92 V. On the other hand, an on/off ratio of ∼106. As-doped WSe2-based MOSFETs with source/drain platinum electrodes also showed an ambipolar behavior, which was applied for use in logic applications. These findings suggest that Al0.74Ti0.26O y by mist-CVD is promising as a high- k material for TMDC-based MOSFETs.

Molybdenum disulfide (MoS2) mono/bilayer have been systematically investigated using atmospheric-pressure mist chemical vapor deposition (mist CVD) from (NH4)2MoS4 dissolved in N-methyl-2-pyrrolidone as a precursor. Film deposition was performed by alternating MoS2 mist storage within a closed chamber and mist exhaust, i.e. sequential mist supply mode at different furnace temperatures, storage times of precursor, and repetition cycles of mist supply on thermally grown SiO2 (th-SiO2) and mist-CVD grown Al1−x Ti x O y (ATO) layers coated on p+-Si substrates. The average size of the MoS2 flake and their number of stack layers could be controlled by tuning the deposition parameters combined with substrate pretreatment. Field-effect transistors with MoS2 atomic mono/bilayer as a channel layer exhibited mobility up to 31–40 (43–55) cm2 V−1 s−1 with a threshold voltage of −1.6 (−0.5) V, subthreshold slope of 0.8 (0.11) V dec.−1, and on/off ratio of 3.2 × 104 (3.6 × 105) on th-SiO2 (ATO) layers as gate dielectric layers without mechanical exfoliation. These findings imply that mist CVD is available for the synthesis of metal transition metal dichalcogenide and metal oxide layers as channel and gate dielectric layers, respectively.

We investigated the synthesis of aluminum oxide (AlO x ) thin films using mist chemical vapor deposition (mist-CVD) from aluminum acetylacetonate (Al­(acac)3) and methanol/water (MeOH/H2O) mixture (volume ratio, 7:3). Different deposition parameters, such as the flow rate (F d) of dilution gas N2, furnace temperature (T f), solution concentration, and mesh bias (V m), were optimized via the analysis of the size distribution of mist precursors using a fast-scanning mobility particle analyzer. The film morphology, rigidity of the AlO x network, and junction property at the AlO x /n-type crystalline Si (n-Si) were dominated by the size distribution of the mist precursors determined by the deposition parameters. Further, the mesh bias supply during film growth promoted the miniaturization of the size distribution of the charged mist particles. Consequently, a marked increase in the number density of the mist particles resulted in an increased refractive index (n) of the AlO x thin films with small surface roughness values. Furthermore, such property of the AlO x films improved the junction property at the AlO x /n-Si interface. In this study, the correlation between the size distribution of mist particles, which is dependent on the deposition parameters, and the film and interface properties, is presented together with metal-oxide–semiconductor field-effect transistor (MOS-FET) performance for the AlO x thin films obtained by mist-CVD.