Patent ID: 8421560

Claim:
A boundary acoustic wave resonator comprising: a piezoelectric substrate; a first dielectric layer laminated on the piezoelectric substrate; an IDT electrode provided at an interface between the piezoelectric substrate and the first dielectric layer; and a pair of reflectors disposed at the interface on both sides of the IDT electrode in a boundary acoustic wave propagating direction; wherein the IDT electrode includes: a first busbar; a second busbar; a plurality of first electrode fingers extending from the first busbar toward the second busbar; a plurality of second electrode fingers extending from the second busbar toward the first busbar; first dummy electrodes that face ends of the plurality of first electrode fingers with gaps therebetween and are connected to the second busbar; and second dummy electrodes that face ends of the plurality of the second electrode fingers with gaps therebetween and are connected to the first busbar; the IDT electrode is apodization weighted such that an intersecting width of an electrode finger decreases closer to both ends of the IDT electrode in the boundary acoustic wave propagating direction from a location at which a maximum intersecting width of the electrode finger is obtained; a side of the first busbar to which the plurality of first electrode fingers and the second dummy electrodes are connected includes an inclined portion that is inclined with respect to the boundary acoustic wave propagating direction so that the side of the first busbar is disposed a predetermined distance from an envelope obtained by having been apodization weighted; a side of the second busbar to which the plurality of second electrode fingers and the first dummy electrodes are connected includes an inclined portion that is inclined with respect to the boundary acoustic wave propagating direction so that the side of the second busbar is disposed a predetermined distance from the envelope obtained by having been apodization weighted; a length of an electrode finger of each of the pair of reflectors that is adjacent to an outermost electrode finger of the IDT electrode is substantially equal to a sum of a length of the outermost electrode finger of the IDT electrode and a length of a dummy electrode facing an end of the outermost electrode finger; and a sum N of numbers of electrode fingers and dummy electrodes that a straight line extending from an end of at least one of electrode fingers of the IDT electrode in the boundary acoustic wave propagating direction crosses before reaching one of the sides of the first busbar and the second busbar is equal to or greater than 5, and the number of electrode fingers included in one of the pair of reflectors is approximately N.