Piezoelectric Ceramics for Filter and Resonator Applications

Piezoelectric ceramics are widely used for filter and resonator applications in the audio to UHF frequency range. The most suitable vibration mode differs for each frequency range mainly by the spurious frequency response and fabrication techniques. Many examples of filters and resonators using PZT and PbTiO3 ceramics are described hereafter. It should be noted that a ZnO thin-film is not ferroelectric but piezoelectric ceramics, and components utilizing this technique are available for transducers of LF to UHF range resonators. Also, ZnO thin-film on glass is a suitable structure for SAW filters. Using a high sonic velocity substrate, ZnO thin-film has a high SAW coupling coefficient at the third overtone.