Processing and characterization of high temperature superconductor films formed by spin-on coating and rapid thermal annealing

A simple method has been developed to fabricate oxide high temperature superconductor (HTS) films of Y---Ba---Cu---O (YBCO) and Bi---Sr---Ca---Cu---O (BSCCO) compounds. Using spin-on coating and rapid thermal annealing (RTA), high T_c films on MgO and copper substrates have been demonstrated. Of the various solvents employed, we have achieved the best results utilizing nitric acid. The use of this solvent coupled with annealing in oxygen at 960–990 °C for 30–60 s by RTA has produced polycrystalline films with grain sizes of 5–10 μm, as indicated by scanning electron microscopy. Auger electron spectroscopy of the films shows that the stoichiometric ratio has been maintained during the transition from precursor to film. X-ray diffraction patterns of YBCO films show that the films mainly contain 123 phase. Superconductivity with zero resistance temperatures above 77 K was observed from both YBCO and BSCCO films. When copper substrates are used, a buffer layer of silver is coated between the substrate and the film so as to prevent interface reaction. The simple spin-on method combined with the short and intense heating of the RTA process may prove to be a simple and rapid method of manufacturing HTS films for large-scale electrical applications.