Improvement of the microwave properties of Y-Ba-Cu-O films with artificial defects

In this paper, the potential of defects for optimizing the microwave properties of YBa₂Cu₃O₇ (YBCO) thin films is demonstrated. On one hand, microscopic Y₂O₃ precipitates, which can be created in YBCO thin films by modification of the deposition process, serve as ideal scattering centres for quasiparticles and, thus, lead to a considerable reduction of the microwave surface resistance R_s. The modification R_s(T) can be explained in terms of the two-fluid model. Data for the quasiparticle scattering rate can be obtained from the measurements. On the other hand, the impact of artificial defects, so called antidots, upon the microwave properties is analyzed. R_s measurements demonstrate that the ion beam etching creates a -20 nm broad damaged area at the edge of the antidots. First measurements of the power handling capability of YBCO thin film resonators indicate that the magnetic contribution to the nonlinear behavior can be reduced by antidots. The implementation of antidots, which have been proven to be an ideal and easy tool to improve active YBCO thin film devices, might be of use for microwave applications as well