Acoustic wave device

1. An acoustic wave device comprising:

a piezoelectric substrate a reverse-velocity surface of which is convex;

an interdigital transducer electrode disposed on the piezoelectric substrate; and

a mass addition film stacked above a portion of the interdigital transducer electrode; wherein

the interdigital transducer electrode includes a first busbar and a second busbar that face each other, first electrode fingers each of which includes an end connected to the first busbar, and second electrode fingers each of which includes an end connected to the second busbar, the second electrode fingers being interdigitated with respect to the first electrode fingers;

an intersection region is defined as a region in which the first electrode fingers and the second electrode fingers overlap in a first direction, where the first direction is a direction in which an acoustic wave propagates, and a second direction is a direction perpendicular or substantially perpendicular to the first direction;

the intersection region includes a central region located at a center or approximate center in the second direction, a first edge region located between the central region and the first busbar, and a second edge region located between the central region and the second busbar;

the interdigital transducer electrode includes a first gap region located between the first edge region and the first busbar, and a second gap region located between the second edge region and the second busbar;

the first busbar includes a first inner busbar region located adjacent the first gap region and a first outer busbar region located outside the first inner busbar region in the second direction, and the second busbar includes a second inner busbar region located adjacent the second gap region and a second outer busbar region located outside the second inner busbar region in the second direction;

the mass addition film is stacked in at least the first edge region, the second edge region, the first inner busbar region, and the second inner busbar region;

an acoustic velocity in the first edge region and the second edge region is lower than an acoustic velocity in the central region;

an acoustic velocity in the first gap region and the second gap region is higher than the acoustic velocity in the central region;

an acoustic velocity in the first inner busbar region and the second inner busbar region is lower than the acoustic velocity in the central region; and

an acoustic velocity in at least a portion of the first outer busbar region and at least a portion of the second outer busbar region is higher than the acoustic velocity in the central region.

2. The acoustic wave device according to claim 1 , wherein the piezoelectric substrate includes only a piezoelectric layer and is made of lithium niobate.

3. The acoustic wave device according to claim 1 , wherein the piezoelectric substrate includes a high acoustic velocity member, a low acoustic velocity film disposed on the high acoustic velocity member, and a piezoelectric layer disposed on the low acoustic velocity film;

an acoustic velocity of a bulk wave that propagates through the high acoustic velocity member is higher than an acoustic velocity of an acoustic wave that propagates through the piezoelectric layer; and

an acoustic velocity of a bulk wave that propagates through the low acoustic velocity film is lower than the acoustic velocity of the bulk wave that propagates through the piezoelectric layer.

4. The acoustic wave device according to claim 3 , further comprising:

a support substrate; wherein

the high acoustic velocity member is a high acoustic velocity film disposed between the support substrate and the low acoustic velocity film.

5. The acoustic wave device according to claim 3 , wherein the high acoustic velocity member is a support substrate.

6. The acoustic wave device according to claim 3 , wherein the piezoelectric layer is made of lithium tantalate.

7. The acoustic wave device according to claim 1 , wherein the first outer busbar region of the interdigital transducer electrode includes a first cavity formation region in which cavities are arranged in the first direction, and the second outer busbar region includes a second cavity formation region in which cavities are arranged in the first direction.

8. The acoustic wave device according to claim 1 , wherein the first busbar and the second busbar of the interdigital transducer electrode include no cavity.

9. The acoustic wave device according to claim 1 , wherein the mass addition film is stacked in the first gap region and the second gap region of the interdigital transducer electrode.

10. The acoustic wave device according to claim 1 , wherein the piezoelectric substrate, the interdigital transducer electrode, and the mass addition film are stacked in this order.

11. The acoustic wave device according to claim 1 , wherein the piezoelectric substrate, the mass addition film, and the interdigital transducer electrode are stacked in this order.

12. The acoustic wave device according to claim 1 , wherein a dielectric film is disposed on the piezoelectric substrate and covers the interdigital transducer electrode.

13. The acoustic wave device according to claim 12 , wherein the dielectric film is made of silicon oxide.

14. The acoustic wave device according to claim 1 , wherein widths of the first gap region and the second gap region are about 0.2λ or less, wherein λ is a wavelength that is defined by an electrode finger pitch of the interdigital transducer electrode, and the widths of the first gap region and the second gap region are dimensions of the first gap region and the second gap region in the second direction.

15. The acoustic wave device according to claim 1 , further comprising:

a first reflector on a first side of the interdigital transducer electrode in the direction in which the acoustic wave propagates; and

a second reflector on a second side of the interdigital transducer electrode opposite to the first side in the direction in which the acoustic wave propagates.

16. The acoustic wave device according to claim 1 , wherein the mass addition film is stacked above entire or substantially entire portions extending in the first direction in the first inner busbar region and the second inner busbar region.

17. The acoustic wave device according to claim 1 , wherein the mass addition film is not stacked in the first outer busbar region and the second outer busbar region.

18. The acoustic wave device according to claim 1 , wherein the mass addition film is made of a dielectric material.

19. The acoustic wave device according to claim 1 , wherein the mass addition film is made of metal.