Origin of the Thickness Dependence of Critical Current Densities in YBCO Films Prepared by Pulsed Laser Deposition

Introducing porosity allows us to increase film thickness of the YBa(2)Cu(3)O(7-x) (YBCO) films on sapphire substrates without microcracking. However, we have observed that porous films possess relatively low values of J(c), especially in thick film region (>500 nm). In order to find out the cause of the degradation of J(c), we examined the depth profiles of the magnetic-field angular dependence of critical current density J(c)(t, theta) and other properties for YBCO films (t <= 1550 nm). The YBCO films were deposited by a large-area pulsed laser deposition system on CeO(2)-buffered r-cut sapphire. Depth profiles were obtained for YBCO films successively milled with an Ar ion beam irradiation. In the as-grown film, the J(c)(theta) exhibits a broad J(c) peaks at H//c, and smaller one centered at H//ab. After the milling, the J(c) (H//ab)/J(c) (H//c) ratio increases with decreasing film thickness. The YBCO (005) peak of x-ray diffraction shifts towards higher angle with decreasing film thickness. The depth profiles reveal that the oxygen deficit is one of the causes of the decrease of the J(c) of the large-area PLD YBCO/CeO(2)/Al(2)O(3) films with increasing film thickness.