Effects of La-doping on Crystallinity and Dielectric Properties of SrAl0.5Ta0.5O3 Thin Films for High-Tc Superconductor Multilayer Structure

LaxSr1-xAl0.5Ta0.5O3 (La-SAT) thin films were prepared to examine the effects of La-doping to SrAl0.5Ta0.5O3 (SAT) as intermediate insulating films for high-T-c devices. 300-nm-thick La-SAT films were grown on approximately 10-mum-thick YBa2Cu3O7-delta (YBCO) films by metalorganic chemical vapor deposition with the La-doping ratio x of 0-0.2. The La-SAT films with x less than or equal to 0.1 exhibited good crystallinity and monotonic lattice contraction with increasing x. 300-nm-thick La0.2Y0.9Ba1.9Cu3O7-delta (La-YBCO) films deposited on these La-SAT films had good T-c and J(c) values comparable to those for the SAT films without La-doping. On the other hand, the La-SAT film with x congruent to 0.2 changed to have random orientation and a La-YBCO film on the La-SAT film showed much poorer T-c and J(c) values. These results suggest that the La solubility limit to SAT exists in the range of x = 0.1-0.2, although a monotonic decrease in the dielectric constant with increasing x was observed for all the La-SAT films in the x range of 0-0.2 and low conductance less than 10(-6) S. (C) 2003 Elsevier B.V. All rights reserved.