Microstructure and properties of superconducting sputter deposited Y–Ba–Cu–O films

Abstract

Films of Y–Ba–Cu–O have been reproducibly prepared with metal stoichiometry near 1-2-3 by sputter deposition from a single sintered target. Twenty-seven depositions resulted in films with a standard deviation in composition of 1%. For 30 samples deposited on (100) SrTiO3 and annealed, the mean and standard deviation of the critical temperature, Tc (10% above ρ = ο), was 86.2 ± 1.4 K with a transition width (10–90%) of 1.8 ± 1.1 K. The composition and Tc were independent of film thicknesses from 0.09 to 2.5 μm. Critical currents were calculated for samples as a function of thickness from transport and from magnetization measurements. Within the considerable scatter observed of ± half an order of magnitude, the two methods agreed with each other over the thickness range studied. They were both fit with an initial Jc independent of thickness, t, for films up to about 0.3 μm thick followed by a 1/t decrease in Jc for thicker films. Metallographic examination of these films indicated microstructural features consistent with this behavior. Planar TEM images of 0.10 μm thick films showed that high Jc correlated with a film which predominantly has its c-axis normal to the film plane. An alternative structure was also seen, in which regions of the firm had their c-axis along each of the three 〈100〉 SrTiO3 directions, two in the film plane, and one normal to it. This type of film has a much lower Jc.