Acoustic wave device
An acoustic wave device includes a piezoelectric substrate, and an IDT electrode on the piezoelectric substrate, and the IDT electrode includes an intersection region in which first and second electrode fingers overlap each other in an acoustic wave propagation direction, the intersection region includes a central region and first and second low acoustic velocity regions outside the central region on respective sides in an extending direction of the first and second electrode fingers, first and second busbars include first and second cavities, respectively, first and second inner busbar portions on one side of the first and second cavities, and first and second outer busbar portions on another side are connected by first and second connecting portions, and at least one of the first connecting portions and at least one of the second connecting portions are a first wide width connecting portion and a second wide width connecting portion having a width wider than that of each of remaining first and second connecting portions.
1 . An acoustic wave device comprising:
a piezoelectric substrate; and
an IDT electrode on the piezoelectric substrate; wherein
the IDT substrate includes a first busbar and a second busbar facing each other, a plurality of first electrode fingers extending toward the second busbar from the first busbar, and a plurality of second electrode fingers extending toward the first busbar from the second busbar;
an intersection region in which the first electrode fingers and the second electrode fingers overlap each other in an acoustic wave propagation direction includes a central region at a center in an extending direction of the first electrode fingers and the second electrode fingers, and a first low acoustic velocity region and a second low acoustic velocity region outside the central region on respective sides in the extending direction of the first electrode fingers and the second electrode fingers;
acoustic velocities in the first low acoustic velocity region and the second low acoustic velocity region are lower than an acoustic velocity in the central region;
the first busbar and the second busbar each include a plurality of cavities arranged in the acoustic wave propagation direction;
a portion on an intersection region side of the plurality of cavities in the first busbar and a portion on an intersection region side of the plurality of cavities in the second busbar are a first inner busbar portion and a second inner busbar portion, respectively;
a portion on a side opposite to the intersection region of the plurality of cavities in the first busbar and a portion on a side opposite to the intersection region of the plurality of cavities in the second busbar are a first outer busbar portion and a second outer busbar portion, respectively;
the first inner busbar portion and the second inner busbar portion are connected to the first outer busbar portion and the second outer busbar portion by a plurality of connecting portions; and
at least one of the plurality of connecting portions is a wide width connecting portion with a dimension in the acoustic wave propagation direction larger than a dimension of each of remaining ones of the plurality of connecting portions.
2 . The acoustic wave device according to claim 1 , wherein the wide width connecting portion includes a plurality of wide width connecting portions in the first busbar and the second busbar.
3 . The acoustic wave device according to claim 2 , wherein the plurality of wide width connecting portions include a pair of wide width connecting portions in at least one of the first busbar and the second busbar.
4 . The acoustic wave device according to claim 3 , wherein the pair of wide width connecting portions are located at respective ends in the acoustic wave propagation direction in at least one of the first and second busbars.
5 . The acoustic wave device according to claim 1 , wherein the wide width connecting portion has a dimension, extending in the acoustic wave propagation direction, in a range of about 1λ to about 10λ, when a wavelength λ is determined by electrode finger pitches of the first and the second electrode fingers of the IDT electrode.
6 . The acoustic wave device according to claim 1 , wherein in the first and second low acoustic velocity regions, mass adding films laminated on the first electrode fingers and the second electrode fingers are provided.
7 . The acoustic wave device according to claim 1 , wherein the first electrode fingers and the second electrode fingers in the first and second low acoustic velocity regions have widths larger than widths of the first electrode fingers and the second electrode fingers in the central region.
8 . The acoustic wave device according to claim 1 , wherein the piezoelectric substrate includes a piezoelectric film and a high acoustic velocity material layer made of a high acoustic velocity material in which an acoustic velocity of a bulk wave that propagates through the high acoustic velocity material is higher than an acoustic velocity of an acoustic wave that propagates through the piezoelectric film.
9 . The acoustic wave device according to claim 8 , further comprising a low acoustic velocity material layer that is laminated between the high acoustic velocity material layer and the piezoelectric film and is made of a low acoustic velocity material in which an acoustic velocity of a bulk wave that propagates through the low acoustic velocity material is lower than an acoustic velocity of a bulk wave that propagates through the piezoelectric film.
10 . The acoustic wave device according to claim 7 , wherein the high acoustic velocity material layer is a high acoustic velocity supporting substrate made of the high acoustic velocity material.
11 . The acoustic wave device according to claim 1 , wherein the piezoelectric substrate is a piezoelectric substrate made of a piezoelectric monocrystal.
12 . The acoustic wave device according to claim 1 , wherein the acoustic wave device is a one-port acoustic wave resonator.
13 . The acoustic wave device according to claim 1 , further comprising reflectors at both sides of the IDT electrode on the piezoelectric substrate.
14 . The acoustic wave device according to claim 6 , wherein the mass adding films are made of metals or dielectrics.
15 . The acoustic wave device according to claim 6 , wherein the mass adding films are on lower surface sides of the first and second electrode fingers.
16 . The acoustic wave device according to claim 1 , wherein the mass adding films are dielectric films and extend to a region between the first and second electrode fingers.
17 . The acoustic wave device according to claim 2 , wherein a pair of the plurality of wide width connecting portions in the first busbar is separated in the acoustic wave propagation direction, and a pair of the plurality of wide width connecting portions in the second busbar is separated in the acoustic wave propagation direction.
18 . The acoustic wave device according to claim 2 , wherein a width of each of the plurality of wide width connecting portions is equal to or more than about 10 μm and equal to or less than about 30 μm.
19 . The acoustic wave device according to claim 13 , wherein the reflectors are grating reflectors.
20 . The acoustic wave device according to claim 9 , wherein
the piezoelectric film is made of a piezoelectric monocrystal;
the low acoustic velocity material layer is made of glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum pentoxide, or a material containing compounds obtained by adding fluorine, carbon, or boron to silicon oxide as principal components; and
the high acoustic velocity material layer is made of silicon, aluminum oxide, silicon carbide, silicon oxynitride, sapphire, lithium tantalate, lithium niobate, crystal, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesia, a diamond-like carbon (DLC) film or diamond.