Depth profile of the microwave surface resistance of SmBa2Cu3O7-d thick films on biaxially textured Ni tapes for progressive etching processes

Abstract

Observation of a reduced critical current density J(c) for thick-film high-temperature-superconductor (HTS)-coated conductors has been an issue with regard to applications of HTS-coated conductors. We investigated the thickness dependence of the microwave surface resistance of a similar to 1.2-mu m-thick SmBa2Cu3O7-delta (SmBCO) film grown in situ on biaxially textured Ni tape by using the co-evaporation method. The microwave surface resistance and the penetration depth were measured by using a, dielectric resonator method as the SmBCO-coated conductor was etched down from similar to 1.2 mu m to similar to 0.08 mu m by using a, 0.1 vol.% Br - methyl alcohol solution. Except for the 0.08-mu m-thick bottom layer right on top of the Ni substrate, the intrinsic surface resistance R. appeared to increase continuously as the thickness increased from similar to 0.08 mu m to similar to 1.2 mu m throughout the temperature range of 7 K - 77 K. The values were similar to 380 mu Omega for the 0.3-mu m-thick top layer and similar to 1270 mu Omega for the 0.07-mu m-thick layer grown on top of the similar to 0.08-mu m-thick bottom layer at 7 K and 8.5 GHz. Interestingly, the similar to 0.08-mu m-thick bottom layer still showed strong superconductivity unlike the observation of a dead layer at the bottom by Jo et al. [10]. The penetration depth at 0 K (lambda(0)) vs. thickness data also appeared consistent with the results from the R, measurements; lambda(0) increased from 215 nm for the similar to 1.2-mu m-thick SmBCO film to 260 nm for the similar to 0.08-mu m-thick bottom layer. Our results show that the appearance of dead layers can be avoided by controlling the growth conditions, including the growth temperature and the deposition rate, and that the depth profile of microwave R. with progressive etching processes can be used as a way to assess the thickness dependence of J(c) for thick-film HTS-coated conductors in a non-invasive way.