Elimination of \mbi{a}-Axis Growth in YBa2Cu3O7-δ Films on CeO2-Buffered Al2O3

The elimination of a-axis orientation in YBa₂Cu₃O_7-δ (YBCO) films grown on CeO₂-buffered Al₂O₃ for microwave devices was achieved through a two-step deposition process performed at different temperatures. The growth of a-axis-oriented YBCO film was considered to be due to the impediment of the adatom mobility by the surface roughness of the underlying buffer layer. For the initial layer, the deposition was carried out at a high temperature to increase surface mobility. Next, the deposition was performed at a lower temperature as necessary for optimum c-axis-oriented growth. By this method, only a c-axis-oriented film was obtained. The characteristic surface resistance R_s(T) values for this film were significantly lower than those with mixed c- and a-axis orientations.