Transversely-excited film bulk acoustic resonators with structures to reduce acoustic energy leakage

1. An acoustic resonator device comprising:

a piezoelectric plate having front and back surfaces;

an interdigital transducer (IDT) on the front surface comprising interleaved fingers, an overlapping distance of the interleaved fingers defining an aperture of the acoustic resonator device, the back surface attached to a surface of a substrate except for a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate; and

a fast region proximate a busbar of the IDT,

wherein the piezoelectric plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode having a first frequency in the piezoelectric plate within a central portion of the aperture and a primary shear acoustic mode having a second frequency in the fast region, and

wherein the second frequency is higher than the first frequency; and

wherein a thickness of the piezoelectric plate and a thickness of the diaphragm are each less in the fast region than in the central portion of the aperture.

2. The device of claim 1 further comprising a slow region between the fast region and the central portion, wherein a radio frequency signal applied to the IDT excites a primary shear acoustic mode having a third frequency in the slow region, and wherein the third frequency is lower than the first frequency.

3. The device of claim 1 , wherein the IDT further comprises dummy fingers in the fast region.

4. The device of claim 1 , wherein the fast region is configured to reduce acoustic energy leakage as compared to an acoustic resonator device without a fast region.

5. An acoustic resonator device comprising:

a piezoelectric plate having front and back surfaces;

an interdigital transducer (IDT) on the front surface comprising interleaved fingers, an overlapping distance of the interleaved fingers defining an aperture of the acoustic resonator device;

a dielectric layer on the piezoelectric plate; and

a fast region proximate a busbar of the IDT,

wherein the piezoelectric plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode having a first frequency in the piezoelectric plate within a central portion of the aperture and a primary shear acoustic mode having a second frequency in the fast region,

wherein the second frequency is higher than the first frequency, and

wherein a thickness of the piezoelectric plate and a thickness of the dielectric layer is less in the fast region than in the central portion of the aperture.

6. The device of claim 5 further comprising a slow region between the fast region and the central portion, wherein a radio frequency signal applied to the IDT excites a primary shear acoustic mode having a third frequency in the slow region, wherein the third frequency is lower than the first frequency, and wherein one or more of a thickness of the piezoelectric plate, a thickness of the dielectric layer, and a thickness of the interleaved fingers is greater in the slow region than in the central portion of the aperture.

7. A filter device comprising:

a piezoelectric plate having front and back surfaces;

a conductor pattern on the front surface, the conductor pattern comprising a plurality of interdigital transducers (IDTs) of a respective plurality of resonators, each of the plurality of IDTs comprising interleaved fingers, an overlapping distance of the interleaved fingers defining an aperture of a respective resonator of the plurality of resonators, the back surface attached to a surface of a substrate except for portions of the piezoelectric plate forming diaphragms spanning cavities in the substrate,

wherein at least one of the plurality of resonators comprises of a fast region proximate a busbar of a respective IDT,

wherein the piezoelectric plate and the respective IDT are configured such that a radio frequency signal applied to the respective IDT excites a primary shear acoustic mode having a first frequency in the piezoelectric plate within a central portion of the aperture and a primary shear acoustic mode having a second frequency in the fast region,

wherein the second frequency is higher than the first frequency; and

wherein a thickness of the piezoelectric plate and a thickness of the diaphragms are each less in the fast region than in the central portion of the aperture.

8. The device of claim 7 , wherein the at least one resonator further comprises a slow region between the fast region and the central portion, wherein a radio frequency signal applied to the IDT excites a primary shear acoustic mode having a third frequency in the slow region, and wherein the third frequency is lower than the first frequency.

9. The device of claim 7 , wherein the respective IDT further comprises dummy fingers in the fast region.

10. The device of claim 7 wherein the fast region is configured to reduce acoustic energy leakage as compared to a resonator device without a fast region.

11. A filter device comprising:

a piezoelectric plate having front and back surfaces;

a conductor pattern on the front surface, the conductor pattern comprising a plurality of interdigital transducers (IDTs) of a respective plurality of resonators, each of the plurality of IDTs comprising interleaved fingers, an overlapping distance of the interleaved fingers defining an aperture of a respective resonator of the plurality of resonators;

a dielectric layer on the piezoelectric plate,

wherein at least one of the plurality of resonators comprises of a fast region proximate a busbar of a respective IDT,

wherein the piezoelectric plate and the respective IDT are configured such that a radio frequency signal applied to the respective IDT excites a primary shear acoustic mode having a first frequency in the piezoelectric plate within a central portion of the aperture and a primary shear acoustic mode having a second frequency in the fast region,

wherein the second frequency is higher than the first frequency, and

wherein a thickness of the piezoelectric plate and a thickness of the dielectric layer is less in the fast region than in the central portion of the aperture.

12. The device of claim 11 , wherein the at least one resonator further comprises a slow region between the fast region and the central region, wherein a radio frequency signal applied to the IDT excites a primary shear acoustic mode having a third frequency in the slow region, wherein the third frequency is lower than the first frequency, and wherein one or more of a thickness of the piezoelectric plate, a thickness of the dielectric layer, and a thickness of the interleaved fingers is greater in the slow region than in the central portion of the aperture.

13. A method of fabricating an acoustic resonator device comprising:

attaching a substrate to a back side of a piezoelectric plate except for a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate; and

forming an interdigital transducer (IDT) on a front side of the piezoelectric layer, the IDT comprising interleaved fingers, an overlapping distance of the interleaved fingers defining an aperture of the acoustic resonator device,

forming a fast region proximate a busbar of the IDT,

wherein the piezoelectric plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode having a first frequency in the piezoelectric plate within a central portion of the aperture and a primary shear acoustic mode having a second frequency in the fast region,

wherein the second frequency is higher than the first frequency; and

wherein a thickness of the piezoelectric plate and a thickness of the diaphragm are each less in the fast region than in the central portion of the aperture.

14. The method of claim 13 , wherein a slow region is between the fast region and the central portion, wherein a radio frequency signal applied to the IDT excites a primary shear acoustic mode having a third frequency in the slow region, and wherein the third frequency is lower than the first frequency.

15. The device of claim 13 further comprising a dielectric layer on the piezoelectric plate, wherein a thickness of the dielectric layer is less in the fast region than in the central portion of the aperture.