High temperature superconducting films by RF magnetron sputtering

The authors have produced sputtered films of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O by RF magnetron sputtering from an oxide target consisting of loose reacted powder. The use of a large 8-in stoichiometric target in the magnetron mode permits films located above the central region to be free of negative-ion resputtering effects, and hence yields reproducible, uniform stoichiometric compositions for a wide range of substrate temperatures. Superconducting YBCO films have been obtained either by sputtering at low temperatures followed by an 850°C oxygen anneal, or alternatively by depositing onto substrates heated to ≈600-650°C and cooling in oxygen. Films prepared by the former method on cubic zirconia substrates consist of randomly oriented crystallites with zero resistance above 83 K. Those deposited on zirconia at medium temperatures without the high-temperature anneal contain smooth partially oriented crystallites, with a slightly depressed T_c≈75 K. Finally, superconducting films have been deposited on MgO using a BiSrCaCu₂O_x powder target