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A simple method of making low-resistivity contacts ( approximately 10-7 Omega cm2) is reported for the first time on Bi-Sr-Ca-Cu-O films. The method basically involves the laying of silver-paste pads on the surface of as-deposited film, their annealing and the subsequent attachment of copper leads. The annealing step thus serves a dual purpose. It not only renders the film superconducting with requisite oxygenation but also helps in the preparation of low-resistivity contacts. The contacts on the film are quite rugged and could withstand several thermal cyclings between 4.2 and 300 K over a period of one month.

Superconducting films of YBa2Cu3O7-x with thickness ranging from 5 to 15 mu m have been grown on MgO(100) substrate by the spray pyrolysis technique followed by suitable annealing in flowing oxygen. A systematic study of the temperature dependence of Ic of the microbridges patterned on these films indicates that the grain boundary weak links behave as S/N/S junctions in microbridges having high Jc, while they behave as S/I/N/S or S/I/S junctions as the Jc of the microbridge is gradually decreased. Shapiro steps in I-V curves as well as SQUID behaviour in V- Omega curves are clearly observed in microbridges having low Jc but not in microbridges having high Jc.

Superconducting thick films of YBaCuO are made by spray pyrolysis technique on single crystal SrTiO 3 and MgO substrates. The thickness of the film is about 10 µm. The best film shows T c (R = 0) of the order of 86 K. No marked degradation in superconducting transition temperature is observed when the films are thermally cycled between room temperature and 4.2 K inside a closed liquid helium container. Temperature dependence of the critical current of microbridges fabricated on this film indicates the presence of SNS type weak links. dc SQUID configuration has been made in this film by scribing two bridges in parallel. V - Φ curves show periodic behavior superposed with additional structures.

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