Film thickness dependence of microwave surface resistance and microstructure in YBa2Cu3O7-δ thin films

Abstract

Film thickness dependence of microwave surface resistance, morphology and microstructures of YBa2Cu3O7-δ thin films were studied by X-ray diffraction (XRD), AFM and transmission electron microscopy (TEM). There was no direct correlation between the microwave surface resistance and film thickness, although full width at half maximum of XRD rocking curve of (0 0 5) peak increased with increase in film thickness. AFM morphology investigation showed no significant difference on film surface roughness and particulate density. Through the TEM cross-section microstructure analysis, it was found that the c-axis film became more regular from the bottom to the top, which could explain the abnormal phenomenon observed. It was very interesting to note that the c-axis films contained few stacking faults and tilting c-axis grains with a-axis grains occurring immediately. We have proposed that the occurrence of small volume fractional a-axis grains with high-angle grain boundary might benefit microwave dissipation loss.