Variations in the structural, morphological and microwave properties of YBa2Cu3O7-δ films on etching

Various etching techniques have been used for making high-temperature superconductor (HTS) circuits and devices for electronic applications and to reduce the film thickness for investigating the thickness dependence of the critical current density J(c) of HTS-coated conductors. We studied the effects of wet-chemical etching and Ar-ion milling on the structural, morphological and microwave properties of YBa2Cu3O7-delta (YBCO) films grown on LaAlO3 substrates. Br-2 in methanol (Br-2-MeOH), nitric acid and disodium ethylenediaminetetraacetic acid (EDTA) were used as the etchants for the wet etching process. The lattice constant and the surface roughness of the YBCO films were measured before and after etching along with the microwave surface resistance (R-S) at similar to 8.5GHz. Variations in the YBCO film thickness oil etching were considered to compare the intrinsic R-S values of YBCO films before and after etching with the effects of finite film thickness taken into account. Both disodium EDTA and Br-2-MeOH appeared to be suitable as etchants with the observed increases in the c-axis constant, the rms surface roughness and the intrinsic RS being less than 0.04 %, 19 % and 5 %, respectively, after etching. Meanwhile, YBCO films etched with Ar-ion milling and nitric acid showed significant degradation in the properties with variations of 55 % and 25 % in the intrinsic RS observed after etching, respectively. A small, but nevertheless enhanced, intrinsic RS was consistently observed for YBCO films etched by either Br-2-MeOH or disodium EDTA throughout the measured temperatures.