Microwave properties of epitaxial large-area Ca-doped YBa2Cu3O7− thin films on r-plane sapphire

Ca doping of YBa 2 Cu 3 O 7− δ (YBCO) is well known to enhance the critical current density in large-angle grain boundaries for example of bicrystals. However, up to now no data are available on microwave properties of epitaxial Ca-doped YBa 2 Cu 3 O 7− δ thin films on r -plane sapphire with CeO 2 buffer layer. Therefore, first results are presented for large-area pulsed laser deposition (PLD) grown Ca x Y 1− x Ba 2 Cu 3 O 7− δ films on 3-in. diameter sapphire wafers. The PLD process is optimised for undoped YBCO thin films and shows high reproducibility for YBCO. The microwave surface resistance R s at 8.5 GHz of Ca-doped YBCO ( x =0.1) thin films shows clear reduction (up to 20%) with respect to that of YBCO for temperatures from about 20–50 K. In addition, microwave surface resistance R s of Ca-doped YBCO is lower than that of YBCO even for enhanced microwave surface magnetic field up to about 20 mT for temperatures 20 and 40 K.