抄録
The superconducting YBa2Cu3O7-x (YBCO) thin films on MgO (100) substrates were successfully fabricated by a reactive evaporation method under the oxygen plasma condition. In this paper, we described the details of the reactive evaporation method and the optimum preparation conditions. The superconducting transition temperature, surface morphology and crystal quality were examined as a function of the substrate temperature (Tsub) and the oxygen partial pressure (PO2). The oxygen was introduced into the film by the injection nozzle. After deposition, the films were allowed to cool with the same pressure as in the deposition under the reactive O2 plasma. The as-grown films showed Tczero=83K with Tconset=88K under the preparation conditions of Tsub=620°C and PO2=1.4×10-3Torr. The XRD analysis showed preferentially c-axis oriented superconducting phases perpendicular to the film surface. The crystal quality and degree of preferred orientation of the films were improved as the substrate temperature increased. The as-grown films were post-annealed at a various temperature and the changes of Tczero and lattice parameter c were examined. As a result, the values of Tczero were not affected by the post-annealing, although the lattice parameter c was shortened at the annealing of above 750°C. This results may be related to the deficiency of oxygen in the CuO2 plane of the YBCO perovskite structure.
