FILTER, DUPLEXER USING THE SAME, AND COMMUNICATION APPARATUS USING THE DUPLEXER

摘要

Provided is a high-performance filter with low loss. The filter includes series-arm piezoelectric thin film resonators arranged in series arms and parallel-arm piezoelectric thin film resonators arranged in parallel arms. The series-arm piezoelectric thin film resonators and the parallel-arm piezoelectric thin film resonators each include a substrate (21), a lower electrode (22) formed on the substrate (21), a piezoelectric film (23) formed on the lower electrode (22), and an upper electrode (24) formed on the piezoelectric film (23). The ratio (A/B) of the length A of the major axis of a resonating section (29) to the length B of the minor axis of the same in each series-arm piezoelectric thin film resonator is higher than that in each parallel-arm piezoelectric thin film resonator.