Elimination of a-axis growth in YBa2Cu3O7-delta films on CeO2-buffered Al2O3

The elimination of a-axis orientation in YBa2Cu3O7-delta (YBCO) films grown on CeO2-buffered Al2O3 for microwave devices was achieved through a two-st ep deposition process performed at different temperatures. The growth of a- axis-oriented YBCO film was considered to be due to the impediment of the a datom 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 t emperature as necessary for optimum c-axis-oriented growth. By this method, only a c-axis-oriented film was obtained. The characteristic surface resis tance R-s(T) values for this film were significantly lower than those with mixed c- and a-axis orientations.