Surface Acoustic Waves in High-T_c Superconducting Thin Films on Piezoelectric PbTiO₃ Films

To generate surface acoustic waves (SAW) and to fabricate substrates for superconducting Bi-compound film, piezoelectric PbTiO₃ films with preferred c-axis orientation were prepared on MgO (100) substrates by the rf-sputtering method. By using an interdigital electrode fabricated on PbTiO₃ film for generation and detection of SAW, it has been confirmed that SAW with the frequency of 192 MHz are propagated on PbTiO₃ film/MgO substrate, as-deposited Bi-compound film/PbTiO₃/MgO substrate and heat-treated superconducting Bi-compound film/PbTiO₃/MgO substrate. The temperature dependence of the SAW attenuation coefficient has been investigated below room temperature in detail, especially in the neighborhood of the superconducting transition temperature, and found to exhibit almost monotonic decreasing behavior with decreasing temperature.