Highly reproducible large-area and double-sided pulsed laser deposition of HTSC YBCO:Ag thin films for microwave applications

Large-area pulsed laser deposition (PLD) producing high-quality YBa₂Cu₃O_7-x (YBCO) thin films on both sides of R-plane sapphire substrates with CeO₂ buffer layer is used routinely to optimize planar microwave stripline filters for satellite and mobile communication systems. A relatively simple PLD arrangement with fixed laser plume and rotating substrate, with an offset between the laser plume and the center of the substrate is employed to deposit laterally homogeneous 3-inch-diameter Ag-doped YBCO thin films. The YBCO:Ag films are about 250 nm thick and have laterally homogeneous critical current densities of more than 3.5 MA/cm² at 77 K and homogeneous maps of microwave surface resistance R_s of about 40 m Q at 145 GHz and 77 K. The R_s at 8.5 GHz and 77 K, determined in the center position of the YBCO:Ag films, remains constant at about 370 7 Q up to a microwave surface magnetic field of about 10 mT. After experience with more than 700 double-sided 3-inch-diameter films, a high degree of homogeneity and reproducibility of j_c and R_s is reached. The PLD-YBCO:Ag films are suitable for microwave applications envisaged for future communication systems.