A piezoelectric resonant filter includes a group of series resonators and a group of parallel resonators for forming a ladder-type filter circuit. Each of the resonators has a piezoelectric thin film having piezoelectric characteristic, and lower and upper electrodes disposed on opposite surfaces of...http://www.google.fr/patents/US6989723?utm_source=gb-gplus-shareBrevet US6989723 - Piezoelectric resonant filter and duplexer
