Off-axis sputter deposition of YBa2Cu3O7 thin films for microwave applications

Thin films of superconducting YBa₂Cu₃O₇ were grown in situ by off-axis sputter deposition for microwave device fabrication. These ∼1 cm² films, which are reproducible, exhibit midpoint T_c's of 89-90.5 K as measured by ac susceptibility, ion channeling yields of 4.7%-6%, and c-axis rocking-curve half-widths of 0.5°, even with a rich microstructure as seen by scanning electron microscopy. Two films were photodefined into miniature X-band microwave bandpass filters. These narrow-band filters (0.5% bandwidth) exhibited 4.4-and 4.5-dB insertion losses at 77 K and 9.25 GHz, with little temperature dependence below 80 K.