Improved microwave performance of Ag-doped Y₁Ba₂Cu₃O_7-δ thin film microstrip resonators

Abstract

Microwave transmission properties of undoped and Ag-doped laser ablated thin film Y₁Ba₂Cu₃O_7-δ microstrip resonators have been studied both on <100> MgO and <100> LaAlO₃ substrates at X-band frequencies. While the Q factor and microwave surface resistance, R_s, of undoped films showed better performance on LaAlO₃ as compared to that on MgO, Ag-doped films on LaAlO₃ showed far greater improvement as reflected not only by a decrease in R_s but also by a total absence of its microwave power dependence up to 13 dBm at 77 K. These results are explained as due to the influence of Ag in increasing the grain size and grain alignment and thus, significantly decreasing the density of grain boundary weak links which are known to affect the microwave transmission in high temperature superconductor films.