EFFECTS OF THE SELF-BIAS VOLTAGE ON CRYSTALLINITY AND SUPERCONDUCTIVITY OF A-AXIS ORIENTED YBA2CU3O7-DELTA THIN-FILMS

Epitaxial a-axis YBa2Cu3O7-delta thin films have been grown on SrTiO3 (100) by on-axis 94.92 MHz magnetron sputtering using the YBa2Cu5Ox target at a self-bias voltage of -50 V and YBa3Cu7Ox target at a cathode voltage of -100 V adjusted by externally applying a negative dc voltage. Good crystalline quality of the films sputtered at -50 V was confirmed from a full width at half maximum, DELTAomega, of 0.04-degrees through the (100) peak by x-ray diffraction and a minimum yield, chi(min), of 4.8% by Rutherford backscattering channeling. Those films, however, have not shown superconductivity. On the other hand, the films sputtered at -100 V were characterized by a DELTAomega of 0.12-degrees and a chi(min) of 4.3%. Superconductivity occurs in the films only by shifting a self-bias voltage from -50 V on the YBa2Cu5Ox target to -100 V on the YBa3Cu7Ox target. The zero resistance temperature is 33 K at most.