Patent ID: 10666226

Abstract:
A ladder-type filter includes: a first piezoelectric thin film resonator including a first lower electrode, a first piezoelectric film, a first upper electrode, and an insertion film inserted between the first lower and upper electrodes, the insertion film being located in an outer peripheral region of a first resonance region; a second piezoelectric thin film resonator including a second lower electrode, a second piezoelectric film, and a second upper electrode, the second piezoelectric thin film resonator having no insertion film between the second lower and upper electrodes in a second resonance region; a series resonator, at least one of the series resonator being a first resonator that is one of the first and second piezoelectric thin film resonators, and a parallel resonator, at least one of the parallel resonator being a second resonator that is another of the first and second piezoelectric thin film resonators.