Solidly-mounted transversely-excited film bulk acoustic resonator with recessed interdigital transducer fingers

1. An acoustic resonator comprising:

a substrate;

an acoustic Bragg reflector supported by the substrate;

a piezoelectric layer above the acoustic Bragg reflector and opposite the substrate, the piezoelectric layer having at least one groove extending into a surface thereof, and

an interdigital transducer (IDT) having a plurality of interleaved fingers with at least one finger disposed in the at least one groove of the piezoelectric layer,

wherein the at least one groove has a depth extending into the piezoelectric layer that is less than or equal to a thickness of the at least one finger.

2. The acoustic resonator according to claim 1 , wherein the IDT and the piezoelectric layer are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the piezoelectric layer.

3. The acoustic resonator according to claim 2 , wherein a direction of acoustic energy flow of the primary shear acoustic mode is substantially orthogonal to front and back surfaces of the piezoelectric layer.

4. The acoustic resonator according to claim 1 , wherein the acoustic Bragg reflector is sandwiched directly between the substrate and the piezoelectric layer.

5. The acoustic resonator according to claim 1 , wherein all of the plurality of interleaved fingers of the IDT are disposed in respective grooves in the piezoelectric layer.

6. The acoustic resonator according to claim 1 , wherein the piezoelectric layer is a rotated z-cut lithium niobate layer.

7. The acoustic resonator according to claim 1 , wherein the IDT is disposed on a top surface of the piezoelectric layer that is opposite to a bottom surface facing the acoustic Bragg reflector.

8. An acoustic resonator comprising:

a substrate;

an acoustic Bragg reflector supported by the substrate;

a piezoelectric layer above the acoustic Bragg reflector and opposite the substrate, the piezoelectric layer having at least one groove extending into a surface thereof; and

an interdigital transducer (IDT) having a plurality of interleaved fingers with at least one finger disposed in the at least one groove of the piezoelectric layer,

wherein the IDT is disposed on a top surface of the piezoelectric layer that is opposite to a bottom surface facing the acoustic Bragg reflector, and

wherein a dielectric layer is disposed on at least the top surface of the piezoelectric layer over and between the interleaved fingers of the IDT.

9. A filter device, comprising:

a plurality of bulk acoustic resonators, at least one of the plurality of bulk acoustic resonators comprising:

a substrate;

at least one acoustic Bragg reflector supported by the substrate;

a piezoelectric layer above the at least one acoustic Bragg reflector and opposite the substrate, the piezoelectric layer having at least one groove extending into a surface thereof; and

a conductor pattern having an interdigital transducer (IDT) that includes interleaved fingers on the piezoelectric layer,

wherein at least one finger of the IDT is disposed in the at least one groove of the piezoelectric layer, and

wherein the at least one groove has a depth extending into the piezoelectric layer that is less than or equal to a thickness of the at least one finger.

10. The filter device according to claim 9 , wherein, for the at least one bulk acoustic resonator, the IDT is configured to excite a primary shear acoustic mode in the piezoelectric layer in response to a radio frequency signal applied to the IDT.

11. The filter device according to claim 10 , wherein a direction of acoustic energy flow of the primary shear acoustic mode is substantially orthogonal to front and back surfaces of the piezoelectric layer.

12. The filter device according to claim 9 , wherein, for the at least one bulk acoustic resonator, the at least one acoustic Bragg reflector is sandwiched directly between the substrate and the piezoelectric layer.

13. The filter device according to claim 9 , wherein, for the at least one bulk acoustic resonator, all of the plurality of interleaved fingers of the IDT are disposed in respective grooves in the piezoelectric layer.

14. The filter device according to claim 9 , wherein the piezoelectric layer is a rotated z-cut lithium niobate layer.

15. The filter device according to claim 9 , wherein, for the at least one bulk acoustic resonator, the IDT is disposed on a top surface of the piezoelectric layer that is opposite to a bottom surface facing the at least one acoustic Bragg reflector.

16. The filter device according to claim 15 , wherein the at least one bulk acoustic resonator further comprises at least one dielectric layer that is disposed on at least the top surface of the piezoelectric layer over and between the interleaved fingers of the IDT.