Preparation and non-destructive characterization of YBa2Cu3O7−δ films for microwave applications

Abstract We have deposited high-quality YBa 2 Cu 3 O 7−δ films with a thickness between 200 nm and 500 nm and a size of 1 cm 2 on YSZ, MgO and NdGaO 3 substrates. Shielding measurements show that critical temperatures T c between 89 K and 93 K and transition widths ΔT 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/cm 2 at 77 K. For the best films, values of the surface resistance R s at 87 GHz and 77 K of (16 ± 3) mΩ 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 mΩ at 4.2 K. From such high-quality YBa 2 Cu 3 O 7−δ 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.