SUPERCONDUCTIVITY OF BI-SR-CA-CU-O THIN-FILMS PREPARED BY MOCVD

The superconducting properties of 5 to 300 nm thick Bi-Sr-Ca-Cu-O films prepared by MOCVD have been investigated. The zero resistance temperature (T(CO)) and critical current density (J(C)) at 4.2 K in zero applied field for all samples were about 70 K and 1 x 10(10) A/m2, respectively. The temperature dependences of J(C) varied with film thickness. J(C)(T) for a film with intermediate thickness could be modeled as a weighted average of the critical current densities for thicker and thinner films. This suggested the existence of a distinct layer in the films containing different junctions by the annealing effect during deposition. Both T(CO) and J(C) were nearly independent of magnetic fields up to 6 T when the fields were apllied parallel to the film surface. This results were thought to be due to the effect of the film thinness. By the calculation of the free energy for the thin film with high Ginzburg-Landau parameter, the effective lower critical field in fields parallel to the film surface (H(c1)parallel-to) was shown to become larger than that for a bulk superconductor. In addition, it is difficult for a vortex to move through the film because of the potential barrier near the surface of the film.