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.