Acoustic wave device and method of fabricating the same, filter, and multiplexer

1. An acoustic wave device comprising:

a support substrate;

a single piezoelectric substrate that is located on the support substrate and is single-crystal;

first electrodes located on a first surface of the piezoelectric substrate;

second electrodes located on a second surface of the piezoelectric substrate; and

an acoustic mirror that is located on the support substrate, is located between the support substrate and the first electrodes in resonance regions where the first electrodes and the second electrodes face each other across at least a part of the piezoelectric substrate, is not located between the support substrate and the first electrodes in at least a part of a region between the resonance regions, and reflects an acoustic wave propagating through the piezoelectric substrate,

wherein an air gap is located between the support substrate and the piezoelectric substrate in the at least a part of the region between the resonance regions.

2. The acoustic wave device according to claim 1 , wherein

the piezoelectric substrate is a lithium tantalate substrate or a lithium niobate substrate.

3. The acoustic wave device according to claim 1 , wherein

the piezoelectric substrate includes a first substrate and a second substrate that are stacked, polarization directions of the first substrate and the second substrate being opposite to each other.

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

piezoelectric thin film resonators corresponding to the resonance regions, wherein

a part of the first electrodes located on the first surface of the piezoelectric substrate and/or a part of the second electrodes located on the second surface of the piezoelectric substrate electrically connects between the piezoelectric thin film resonators, and

the piezoelectric thin film resonators include one or more series resonators connected in series between an input terminal and an output terminal and one or more parallel resonators connected in parallel between the input terminal and the output terminal.

5. The acoustic wave device according to claim 4 , wherein

at least one of the one or more series resonators and the one or more parallel resonators is divided into a first resonator and a second resonator in series or in parallel between two nodes, and

when the first resonator and the second resonator are viewed from one of the two nodes, a polarization direction of the piezoelectric substrate of the first resonator is opposite to a polarization direction of the piezoelectric substrate of the second resonator.

6. The acoustic wave device according to claim 4 , wherein

at least one of the one or more series resonators and the one or more parallel resonators is divided into a first resonator and a second resonator in series between two nodes,

when the first resonator and the second resonator are viewed from one of the two nodes, a polarization direction of the piezoelectric substrate of the first resonator is opposite to a polarization direction of the piezoelectric substrate of the second resonator,

all the input terminal, the output terminal, and a ground terminal connected to the one or more parallel resonators are located on the second surface, and

a through electrode penetrating through the piezoelectric substrate and connecting at least one of the first electrodes and at least one of the second electrodes is not provided.

7. An acoustic wave device comprising:

a support substrate;

a single piezoelectric substrate that is located on the support substrate and is single-crystal;

first electrodes located on a first surface of the piezoelectric substrate;

second electrodes located on a second surface of the piezoelectric substrate;

an acoustic mirror that is located on the support substrate, is located between the support substrate and the first electrodes in resonance regions where the first electrodes and the second electrodes face each other across at least a part of the piezoelectric substrate, is not located between the support substrate and the first electrodes in at least a part of a region between the resonance regions, reflects an acoustic wave propagating through the piezoelectric substrate, and includes a first film and a second film alternately stacked, an acoustic impedance of the second film being higher than an acoustic impedance of the first film,

an insulator film that is located between the support substrate and the piezoelectric substrate in the at least a part of the region between the resonance regions, is made of a different material from the acoustic mirror, and has a Young's modulus less than Young's modulus of the first film and the second film.

8. The acoustic wave device according to claim 7 , wherein:

the piezoelectric substrate is a lithium tantalate substrate or a lithium niobate substrate.

9. The acoustic wave device according to claim 7 , wherein:

the piezoelectric substrate includes a first substrate and a second substrate that are stacked, polarization directions of the first substrate and the second substrate being opposite to each other.

10. The acoustic wave device according to claim 7 , further comprising:

piezoelectric thin film resonators corresponding to the resonance regions, wherein

a part of the first electrodes located on the first surface of the piezoelectric substrate and/or a part of the second electrodes located on the second surface of the piezoelectric substrate electrically connects between the piezoelectric thin film resonators, and

the piezoelectric thin film resonators include one or more series resonators connected in series between an input terminal and an output terminal and one or more parallel resonators connected in parallel between the input terminal and the output terminal.

11. The acoustic wave device according to claim 10 , wherein

at least one of the one or more series resonators and the one or more parallel resonators is divided into a first resonator and a second resonator in series or in parallel between two nodes, and

when the first resonator and the second resonator are viewed from one of the two nodes, a polarization direction of the piezoelectric substrate of the first resonator is opposite to a polarization direction of the piezoelectric substrate of the second resonator.

12. The acoustic wave device according to claim 10 , wherein

at least one of the one or more series resonators and the one or more parallel resonators is divided into a first resonator and a second resonator in series between two nodes,

when the first resonator and the second resonator are viewed from one of the two nodes, a polarization direction of the piezoelectric substrate of the first resonator is opposite to a polarization direction of the piezoelectric substrate of the second resonator,

all the input terminal, the output terminal, and a ground terminal connected to the one or more parallel resonators are located on the second surface, and

a through electrode penetrating through the piezoelectric substrate and connecting at least one of the first electrodes and at least one of the second electrodes is not provided.

13. A filter comprising the acoustic wave device according to 7 .

14. An acoustic wave device comprising:

a support substrate;

a single piezoelectric substrate that is located on the support substrate and is single-crystal;

first electrodes located on a first surface of the piezoelectric substrate;

second electrodes located on a second surface of the piezoelectric substrate; and

an acoustic mirror that is located on the support substrate, is located between the support substrate and the first electrodes in resonance regions where the first electrodes and the second electrodes face each other across at least a part of the piezoelectric substrate, is not located between the support substrate and the first electrodes in at least a part of a region between the resonance regions, and reflects an acoustic wave propagating through the piezoelectric substrate,

wherein the first surface in a first region where the first electrodes are located and the first surface in a second region where the first electrodes are not located are flat.

15. The acoustic wave device according to claim 14 , wherein the piezoelectric substrate is a lithium tantalate substrate or a lithium niobate substrate.

16. The acoustic wave device according to claim 14 , wherein the piezoelectric substrate includes a first substrate and a second substrate that are stacked, polarization directions of the first substrate and the second substrate being opposite to each other.

17. The acoustic wave device according to claim 14 , further comprising:

piezoelectric thin film resonators corresponding to the resonance regions, wherein:

a part of the first electrodes located on the first surface of the piezoelectric substrate and/or a part of the second electrodes located on the second surface of the piezoelectric substrate electrically connects between the piezoelectric thin film resonators, and

the piezoelectric thin film resonators include one or more series resonators connected in series between an input terminal and an output terminal and one or more parallel resonators connected in parallel between the input terminal and the output terminal.

18. The acoustic wave device according to claim 17 , wherein:

at least one of the one or more series resonators and the one or more parallel resonators is divided into a first resonator and a second resonator in series or in parallel between two nodes, and

when the first resonator and the second resonator are viewed from one of the two nodes, a polarization direction of the piezoelectric substrate of the first resonator is opposite to a polarization direction of the piezoelectric substrate of the second resonator.

19. The acoustic wave device according to claim 17 , wherein:

at least one of the one or more series resonators and the one or more parallel resonators is divided into a first resonator and a second resonator in series between two nodes,

when the first resonator and the second resonator are viewed from one of the two nodes, a polarization direction of the piezoelectric substrate of the first resonator is opposite to a polarization direction of the piezoelectric substrate of the second resonator,

all the input terminal, the output terminal, and a ground terminal connected to the one or more parallel resonators are located on the second surface, and

a through electrode penetrating through the piezoelectric substrate and connecting at least one of the first electrodes and at least one of the second electrodes is not provided.

20. A filter comprising the acoustic wave device according to 14 .