Reduction of Cu-rich particles in sputter deposition of Y1Ba2Cu3O7-x thin films

Y1Ba2Cu3O7-x (YBCO) thin films were deposited on MgO substrates using an unbalanced magnetron sputtering system. We studied the required pressure to produce smooth YBCO films which are free of Cu-rich surface particles and have J(c) congruent to 2.0 MA/cm(2) at 77 K. We found that the required pressure to produce these films depends on the cation ratio of the sputter target. In order to deposit such smooth YBCO films, we found that the Cu/Ba ratio of the YBCO film must be <3/2. This is achievable by optimizing the sputtering pressure of individual targets. The target, which has a lower Cu/Ba ratio, required a high sputtering pressure to obtain a similar Cu/Ba ratio on the films. For the various targets we used with different sputtering pressures, the critical current density of the smooth films was found to increase with the sputtering pressure. Crown Copyright (C) 2001 Published by Elsevier Science B.V. All rights reserved.