In-situ growth of superconducting films of Bi-Sr-Ca-Cu-O using magnetron sputtering.

摘要

Growing superconducting films of the high-temperature superconductors (HTS) in a single-step process within the vacuum system and at lower temperatures than post-annealed films has been the goal of many researchers. This has been achieved in YBa(sub 2)Cu(sub 3)O(sub 7) at a number of laboratories, but Bi and Tl-based HTS have proven more difficult. We report superconducting films of Bi(sub 2)Sr(sub 2)CaCu(sub 2)O(sub x) and Bi(sub 2)Sr(sub 2)Ca(sub 2)Cu(sub 3)O(sub x) made by magnetron sputtering from a bismuth enriched composite target, onto MgO at substrate temperatures (approx)150(degree)C lower than required for post-annealed films. These films show highly c-axis oriented growth without the need for epitaxy, which suggests that films might be grown on a variety of substrates both with and without a buffer layer. The exact mechanism of crystallization at such low temperatures is not yet known, but it can be speculated that the surface atoms are less constrained and thus have a smaller energy barrier to overcome in forming a crystal structure. There is a narrow temperature window for growth of the superconducting phase; at lower temperatures the films tend to be semiconducting, due probably to lack of sufficient thermal energy to crystallize a well-ordered phase. At higher temperatures the bismuth sticking coefficient decreases to the point where no bismuth remains and the films are insulating. 8 refs., 7 figs. (ERA citation 15:032604)