DC-MAGNETRON SPUTTERING OF YBA2CU3O7-DELTA THIN-FILMS FOR MICROWAVE APPLICATIONS

High-quality YBa2Cu3O7-delta thin films with optimized surface smoothness suitable for multilayer technology have been deposited by DC-magnetron sputtering. The films not only show high critical temperatures (T(c)) up to 90 K and high critical current densities (j(c)) up to 4.2 x 10(6) A/cm2 at 77 K, but also a smooth surface with only one outgrowth of a size of more than 200 nm within an area of 150 x 150-mu-m2. The T(c) and j(c) values are slightly lower than our best values for rough films with optimized conditions for T(c) and j(c), where we reach up to 6 x 10(6) A/cm2 at 77 K and a T(c) offset up to 91.5 K on SrTiO3 and LaAlO3. Additionally, the surface resistances (R(s)) of our films were measured using coplanar resonators. We determined an R(s) of 120-mu-OMEGA at 77 K and 60-mu-OMEGA at 9 K and at 6.2 GHz for our best film. The penetration depth was evaluated to be between 160 and 200 nm for this film. A dependence of R(s) on the surface magnetic field showed a higher crystal quality of our films with increasing j(c) measured with a remanent field technique.