PREPARATION AND NONDESTRUCTIVE CHARACTERIZATION OF YBA2CU3O7-DELTA FILMS FOR MICROWAVE APPLICATIONS

We have deposited high-quality YBa2Cu3O7-delta films with a thickness between 200 nm and 500 nm and a size of 1 cm2 on YSZ, MgO and NdGaO3 substrates. Shielding measurements show that critical temperatures T(c) between 89 K and 93 K and transition widths DELTAT(c) between 0.7 K and 0.2 K can be obtained reproducibly on all of these substrates. A contactless inductive j(c) measurement technique, based on the detection of the 3rd harmonic, has given critical current densities up to (5.1 +/- 0.5) MA/cm2 at 77 K. For the best films, values of the surface resistance R(s) at 87 GHz and 77 K of (16 +/- 3) mOMEGA have been derived from measurements in a copper host cavity. Furthermore, these films show a significant reduction of the residual microwave losses at temperatures below 60 K, leading to R(s) values below 3 mOMEGA at 4.2 K. From such high-quality YBa2Cu33O7-delta films on MgO, we have started to fabricate and optimize the design of microwave devices by use of standard patterning techniques. As an example, a narrow nonlinear coplanar-line device is presented. We have observed ''fast'' and ''slow'' nonlinear response, which limits the output power.