NOVEL YBA2CU3O7-X AND YBA2CU3O7-X Y4BA3O9 MULTILAYER FILMS BY BIAS-MASKED ON-AXIS MAGNETRON SPUTTERING

In situ YBa2Cu3O7-x (YBCO) films have been fabricated on SrTiO3 (001) and LaAlO3 (001) substrates by on-axis biased-radio-frequency magnetro n sputtering in Ar-10% O2 at total pressures as low as 3 Pa (3 x 10(-2 ) mbar) and a deposition rate 210 nm/h. Negative oxygen ion-resputteri ng has been considerably reduced by introducing a biased copper mask b etween the substrate and target. The surface morphology and physical p roperties of the films are greatly improved on applying a positive dc substrate bias with respect to the grounded deposition chamber. We hav e obtained superconducting YBCO films with transport critical current as high as 10(6) A/cm2 at 77 K and low normal-state resistivity by thi s approach. Scanning tunneling microscopy analyses of the films with t he best superconducting properties reveal a spiral growth mechanism. H owever, films deposited by negative dc bias under identical sputtering conditions are insulating. From x-ray theta-2theta and rocking curve measurements, we identify the insulating films to be c-axis oriented Y 4Ba3O9 (YBO) films. Furthermore, YBCO films could be grown on the YBO layers without any degradation of T(C) and c-axis orientation. This no vel bias sputtering feature gives us a unique opportunity to produce s uperconductor/insulator, YBCO/YBO, multilayers from a single YBCO targ et.