Improved microwave performance of Ag-doped Y<SUB>1</SUB>Ba<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7-&#948;</SUB> thin film microstrip resonators

Microwave transmission properties of undoped and Ag-doped laser ablated thin film Y1Ba2Cu3O7-&#948; microstrip resonators have been studied both on &lt;100&gt; MgO and &lt;100&gt; LaAlO3 substrates at X-band frequencies. While the Q factor and microwave surface resistance, Rs, 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 Rs 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