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

Abstract
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 Tc’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.