Preparation of superconducting Bi-Ca-Sr-Cu-O thin films by RF magnetron sputtering

Superconducting thin films of Bi-Ca-Sr-Cu oxide, with T _c onset of approximately 90 K were prepared by RF magnetron sputtering on sapphire with and without a CaZrO₃ buffer layer, on ZrO-coated silicon (111), and on single-crystal MgO (100). The as-deposited films were amorphous insulators which were then annealed in various ways. Zero resistance at 72 K for films on (100) MgO was achieved after annealing in air at 810°C for 2 h. However, the X-ray diffraction pattern showed that two superconducting phases, i.e., Bi₂CaSr₂Cu₂O_8+x (2122) and Bi₂Ca_xSr_2-xCuO_6+y (2021), are present, and that films have preferred orientation with c-axis normal to the substrates