Ag-doped large-area double-sided YBaCuO and GdBaCuO thin films for microwave applications

The influence of Ag-doping was investigated on structural, electrical and microwave properties of pulsed laser deposited YBaCuO thin films on 3-inch diameter sapphire wafers. Up to now, no significant improvement of microwave surface resistance R-s, was found due to Ag-doping. However, Ag-doped YBCO films show a reduced surface roughness, improved homogeneity and reproducibility of R-s and critical current density, and no residues after wet chemical etching of stripline structures. Therefore, the pulsed laser deposition process seems to be assisted by Ag-doping of YBaCuO. The microwave surface resistance correlates with the degree of in-plane epitaxy of the YBCO:Ag thin films as measured by polarized Raman spectroscopy, and with the size of laser droplets in the films. Up to now, R-2 of PLD-YBCO thin films remains constant at about 500 mu Omega (8.5 GHz, 77 K) and 180 mu Omega(19 GHz, 4.2 K) up to surface magnetic field of about 7 mT.