Ag-doped double-sided PLD-YBCO thin films for passive microwave devices in future communication systems

Pulsed laser deposited (PLD) Ag-doped YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin films on both sides of 3-inch diameter sapphire wafers are used routinely for development of microwave filters for future communication systems. The reproducibly deposited YBCO:Ag films of about 250 nm thickness show critical current densities of 4 MA/cm/sup 2/ at 77 K and laterally homogeneous maps of microwave surface resistance R/sub s/ of about 45 m/spl Omega/ at 145 GHz and 77 K measured by an open resonator technique. The R/sub s/ at 8.4 GHz and 77 K determined in the center position of the YBCO:Ag films with a sapphire resonator technique remains constant at about 380 /spl mu//spl Omega/ up to a microwave surface magnetic field of 7-10 mT. Correlations of transport and microwave properties to the film microstructure are shown in terms of in-plane epitaxy, size of particulates on the films, and composition ratios Cu/O and Y/O, and growth defects like stacking faults as shown by Raman spectroscopy, SEM, and SNMS depth profiling, and TEM cross sections, respectively. The optimum Ag-content of the PLD-YBCO target was determined to be about 4 weight -%. The results demonstrate that Ag-doping supports the PLD process for YBCO in terms of reliability and cost effectiveness.