Study of Josephson effects in microbridges of Bi-Sr-Ca-Cu-O films made by spray pyrolysis

Abstract

Superconducting Bi-Sr-Ca-Cu-O (22121 films were prepared by spraying stoichiometric aqueous solutions of nitrates of bismuth, strontium, calcium and copper on heated MgO (100) substrates and subsequent annealing in air. The R-T curves of the films show metallic behaviour above the superconducting transition temperature. Tc (R = 0) is observed between 80 and 85 K. Annealing temperature has a profound effect on Tc (R = 0) and on the orientation of the film. Annealing in air in near-melting region yields highly oriented films with c-axis perpendicular to the substrate. These films show a sharp superconducting transition with zero resistance at 85 K. Microbridges of the dimensions of 50/~m × 50#m have been patterned photolithographically followed with chemical etching. The I V characteristics of the microbridges show Josephson efl,~cts due to the presence of grain boundary weaklinks. The temperature dependence of the critical current for these microbridges suggest formation of superconductor-normal-superconductor type weaklinks.