EPITAXIAL YBA2CU3O7 AND GDBA2CU3O7 THIN-FILMS GROWN INSITU BY SINGLE TARGET DC SPUTTERING

We have used single target de sputtering to grow in-situ thin films of YBa2Cu3O7 (YBCO) and GdBa2Cu3O7 (GdBCO) on substrates of (100) MgO and (100) and (110) SrTiO3 heated to about 700 °C. θ-2θ x-ray diffraction patterns show the films to be highly oriented with the c-axis perpendicular to the plane of the film. X-ray Weissenberg photographs indicate that the in-plane axes of the films are colinear with the substrate axes and thus the films are epitaxially oriented. The best films grown on SrTiO3 have resistance ratios R(290K) R(100K) between 2.5 and 2.8, superconducting onsets between 87 and 89K and zero resistance between 85 and 87K. Films grown on MgO have slightly smaller resistance ratios and lower superconducting onsets but the transition widths are comparable to those for the films grown on SrTiO3. The best films show ac susceptibilty transition widths of less than 1K and we observe clear correlations between the width of the ac transition, the film's critical current and the amount of hysteresis of the dc magnetization curves. We estimate the critical current density at 77K to be at least 106 A/cm2 for films having zero resistance above 85K. © 1990.