Patent ID: 8093962

Claim:
A filter comprising a plurality of piezoelectric thin film resonators, the piezoelectric thin film resonators each comprising: a substrate; a lower electrode disposed on the substrate; a piezoelectric film disposed on the substrate and on the lower electrode; and an upper electrode disposed on the piezoelectric film so as to have a part opposing the lower electrode; wherein an electrode region where the upper electrode and the lower electrode overlap each other is shaped to be cornerless or have all of its corners rounded, and to have at least one pair of opposing perimeters that are unparallel to each other, the electrode region being further shaped to be substantially linear symmetric about a symmetric axis that is perpendicular to a direction of current flowing through the piezoelectric thin film resonator in a plan view; any one of the pair of perimeters opposes an electrode region of an adjacent piezoelectric thin film resonator; spacing between the perimeter and the opposing perimeter of the electrode region of the adjacent piezoelectric thin film resonator is constant; and the symmetric axis of one of the plurality of piezoelectric thin film resonators is substantially parallel to the symmetric axis of at least another one of the plurality of piezoelectric thin film resonators.