Industrial-scale sputter deposition of molybdenum oxide thin films: Microstructure evolution and properties

The current work investigates the microstructure and property relations of molybdenum oxide thin films synthesized by reactive dc magnetron sputtering in an industrial-scale sputter deposition plant using a rotatable molybdenum target with varying oxygen/argon gas flow ratio. The evolution of microstructure and chemical bonds as a function of oxygen partial pressure was studied by x-ray diffraction, Raman spectroscopy, and x-ray photoelectron spectroscopy. With oxygen partial pressure raising from 0% to 100%, the film growth rate decreased from 350 to 50 nm/min, while the oxygen content within the films increased up to 75 at. %. The films were dominated by MoO2, polymorphs of Mo4O11 and Mo9O26, and MoO3 phases. The electrical properties changed from electrically conductive to insulating with increasing oxygen partial pressure. The optical properties are versatile, e.g., transmittance values up to 80%, absorbance values between 50% and 80% and reflectance values up to 55%, depending on the oxygen content. In general, it can be concluded that microstructure and properties of molybdenum oxide thin films can be adjusted by varying the oxygen/argon gas flow ratio and might thus enable their use in a wide range of optical and electronic applications.