Acoustic wave device

1. An acoustic wave device comprising:

a support substrate; and

a first resonant section and a second resonant section that are adjacent to each other on the support substrate; wherein

each of the first resonant section and the second resonant section includes:

a piezoelectric thin film;

an interdigital transducer electrode on the piezoelectric thin film; and

a support layer surrounding the piezoelectric thin film in a plan view of the acoustic wave device, and having a different linear expansion coefficient from the piezoelectric thin film;

the piezoelectric thin film in the first resonant section and the piezoelectric thin film in the second resonant section are divided by the support layer between the first resonant section and the second resonant section; and

a projection projecting in a first direction toward the support substrate from the first resonant section and the second resonant section is provided in an edge portion of a surface of the support layer, the surface being located on a side closer to the support substrate.

2. The acoustic wave device according to claim 1 , further comprising an intermediate layer between at least one of the first resonant section and the second resonant section and the support substrate.

3. The acoustic wave device according to claim 2 , wherein a portion of the intermediate layer between the piezoelectric thin film and the support substrate in the first resonant section and a portion of the intermediate layer between the piezoelectric thin film and the support substrate in the second resonant section are divided by the support layer between the first resonant section and the second resonant section.

4. The acoustic wave device according to claim 2 , wherein the intermediate layer includes a high acoustic velocity layer through which an acoustic bulk wave propagates at a higher velocity than an acoustic wave propagating through the piezoelectric thin film.

5. The acoustic wave device according to claim 2 , wherein the intermediate layer includes a multilayer body including a first layer with a first acoustic impedance and a second layer with a second acoustic impedance higher than the first acoustic impedance that are alternately laminated.

6. The acoustic wave device according to claim 5 , further comprising a protective layer provided in a boundary region between the second layer and the support layer in the intermediate layer.

7. The acoustic wave device according to claim 6 , wherein the protective layer is provided by oxidizing or nitriding the second layer.

8. The acoustic wave device according to claim 2 , wherein

the projection is provided in the intermediate layer.

9. The acoustic wave device according to claim 2 , wherein

the support substrate is a silicon substrate;

the support layer is made of polyimide;

a layer in the intermediate layer in contact with the support substrate is made of silicon dioxide;

a charge generation layer is provided at an interface between the support substrate and the intermediate layer; and

a lower surface of the support layer is located on a side away from the interface between the support substrate and the intermediate layer in a first direction toward the support substrate from the first resonant section and the second resonant section.

10. The acoustic wave device according to claim 2 , further comprising a protective layer between the intermediate layer and the support layer.

11. The acoustic wave device according to claim 2 , further comprising a protective layer covering the piezoelectric thin film and the support layer.

12. The acoustic wave device according to claim 2 , wherein

the acoustic wave device is a ladder filter including a serial arm circuit including the first resonant section and a parallel arm circuit including the second resonant section;

a metal film is provided in at least a portion of the intermediate layer;

the acoustic wave device further includes a wiring portion provided on the support layer and connected to the second resonant section; and

at least a portion of the wiring portion and the metal film do not overlap with each other in the plan view of the acoustic wave device.

13. The acoustic wave device according to claim 2 , wherein

the acoustic wave device is a ladder filter including a serial arm circuit including the first resonant section and a parallel arm circuit including the second resonant section;

the acoustic wave device further includes a bridging capacitance portion connected to the first resonant section in parallel;

the bridging capacitance portion includes a piezoelectric thin film and an IDT electrode disposed on the piezoelectric thin film;

the intermediate layer is further provided between the bridging capacitance portion and the support substrate;

a metal film is provided in at least a portion of the intermediate layer; and

the bridging capacitance portion and the metal film overlap with each other in the plan view of the acoustic wave device.

14. The acoustic wave device according to claim 2 , wherein

the acoustic wave device is a ladder filter including a serial arm circuit and a parallel arm circuit;

the serial arm circuit includes the first resonant section and the second resonant section;

a metal film is provided in at least a portion of the intermediate layer;

the acoustic wave device further includes first to fourth wiring portions provided on the support layer;

the first wiring portion is connected to a busbar on an input side of the IDT electrode in the first resonant section;

the second wiring portion is connected to a busbar on an output side of the IDT electrode in the first resonant section;

the third wiring portion is connected to a busbar on an input side of the IDT electrode in the second resonant section;

the fourth wiring portion is connected to a busbar on an output side of the IDT electrode in the second resonant section; and

in the plan view of the acoustic wave device, an area where the first wiring portion and the second wiring portion overlap with the metal film is different from an area where the third wiring portion and the fourth wiring portion overlap with the metal film.

15. The acoustic wave device according to claim 1 , wherein the projection is provided in the support substrate.

16. The acoustic wave device according to claim 1 , wherein a portion of the support layer is located on a surface of each of the piezoelectric thin films in the first resonant section and the second resonant section.

17. The acoustic wave device according to claim 1 , wherein a thickness of a portion of the support layer other than an outer peripheral portion of the acoustic wave device is thicker than a thickness of the support layer in the outer peripheral portion of the acoustic wave device.