rf Power dependence on the chemical and structural properties of copper oxide thin films obtained at various oxygen fractions

Copper oxide (CuOx) thin films were deposited on flexible polyethyleneterephthalate (PET) substrates by rf magnetron sputtering and the effects of the rf power and the O2 fraction on the physical and chemical properties of the films were examined. The obtained films were characterized with a surface profiler, X-ray diffraction (XRD), scanning electron microscopy (SEM), four points probe, and X-ray photoelectron spectroscopy (XPS). The trend of surface resistance of CuOx films was almost identical as rf power varied from 200 to 300 W. The surface resistance of the films increased as the O2 fraction increased up to 14.3%. After this point it decreased. The propensity of surface resistance of the films, however, monotonically increased as a function of O2 fraction at 400 W of rf power. XRD study revealed that the preferential phase of CuOx changed from metallic cubic Cu(1 1 1) through cubic Cu2O(1 1 1) to monoclinic CuO(image) as the O2 fraction increased. The compositional ratio of Cu species with different oxidation state in CuOx films was investigated by X-ray induced Auger electron spectroscopy (XAES). XAES study revealed that the compositional ratio of Cu was dependent with the rf power. The higher rf power applied, the more Cu+ species and less Cu2+ species formed in CuOx films.