Effects of deposition rate and thickness on the properties of YBCO films deposited by pulsed laser deposition

YBCO films with various thicknesses from 100 nm to 1.6 μm were deposited on single crystal SrTiO₃ substrates by pulsed laser deposition (PLD). The effects of thickness and deposition rate - by means of controlling the pulsed laser frequency - on the critical current density (J_c) were studied. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to examine the orientation, crystallization and surface quality. The amount of a-axis YBCO component evaluated from the ratio of XRD chi-scan intensities of the α-axis and c-axis for the YBCO (102) plane increased as the YBCO film became thicker. SEM was used to analyse the surface of YBCO film, and it was shown that the surface of YBCO film became rougher with increasing thickness. There were many large singular outgrowths and networks of outgrowths on the surface of the YBCO films with thickness greater than 0.4 μm. The increased amount of a-axis YBCO component and the coarse microstructure of the thick YBCO film caused degradation of J_c with increasing thickness.