Patent ID: 7843285

Claim:
A piezoelectric thin-film filter comprising: a substrate; a piezoelectric thin film supported by the substrate and including a portion that is acoustically separated from the substrate; a first electrode pair including at least two first electrode fingers disposed on one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate and at least two second electrode fingers disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate so as to face the first electrode fingers with the piezoelectric thin film therebetween; and a second electrode pair including at least two third electrode fingers disposed on the one main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate such that the first electrode fingers and the third electrode fingers are disposed alternately with gaps therebetween and fourth electrode fingers disposed on the other main surface of the portion of the piezoelectric thin film that is acoustically separated from the substrate so as to face the third electrode fingers with the piezoelectric thin film therebetween; wherein a filter element defined by the first electrode pair and the second electrode pair is provided between a set including a first terminal connected to each of the first electrode fingers and a second terminal connected to each of the second electrode fingers and a set including a third terminal connected to each of the third electrode fingers and a fourth terminal connected to each of the fourth electrode fingers; the piezoelectric thin-film filter include insulating films provided between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween on the one main surface of the piezoelectric thin film; each of center-to-center distances between the first electrode fingers and the third electrode fingers that are disposed alternately with the gaps therebetween is larger than a value twice the thickness of the portion of the piezoelectric thin film that is acoustically separated from the substrate; and further comprising a second insulating film provided in at least one of a first area covering the first electrode fingers, the third electrode fingers, and the insulating films; a second area covering the second electrode fingers and the fourth electrode fingers.