Transversely-excited film bulk acoustic resonator with thermally conductive etch-stop layer

1. An acoustic resonator device comprising:

a substrate;

a piezoelectric layer attached to the substrate directly or via one or more intermediate layers;

an etch-stop layer sandwiched between the substrate and the piezoelectric layer, a portion of the piezoelectric layer and the etch-stop layer forming a diaphragm over a cavity of the acoustic resonator device; and

an interdigital transducer (IDT) at the piezoelectric layer and having interleaved fingers on the diaphragm,

wherein the etch-stop layer is impervious to an etch process used to form the cavity, and the etch-stop layer is at least one of aluminum nitride, boron nitride, and diamond.

2. The acoustic resonator device of claim 1 , wherein the piezoelectric layer is one of lithium niobate and lithium tantalate.

3. The acoustic resonator device of claim 1 , further comprising a dielectric layer disposed between the piezoelectric layer and the etch stop layer, wherein the diaphragm includes the piezoelectric layer, the dielectric layer, and the etch-stop layer.

4. The acoustic resonator device of claim 3 , wherein the dielectric layer is silicon dioxide.

5. The acoustic resonator device of claim 1 , further comprising a bonding layer disposed between the etch-stop layer and the substrate, wherein the diaphragm includes the piezoelectric layer and the etch-stop layer, but not the bonding layer.

6. The acoustic resonator device of claim 5 , wherein the substrate is silicon and the bonding layer is silicon dioxide.

7. The acoustic resonator device of claim 1 , wherein a thickness of the etch-stop layer is less than or equal to 20% of a thickness of the piezoelectric layer.

8. The acoustic resonator device of claim 7 , wherein the thickness of the etch-stop layer is 4% to 6% of the thickness of the piezoelectric layer.

9. A filter device, comprising:

a plurality of acoustic resonators that include a shunt resonator and a series resonator, each of the acoustic resonators including:

a substrate;

a piezoelectric layer attached to the substrate directly or via one or more intermediate layers;

an etch-stop layer sandwiched between the substrate and the piezoelectric layer, portions of the piezoelectric layer and the etch-stop layer forming a diaphragm over a cavity of the respective acoustic resonator;

a conductor pattern at the piezoelectric layer, the conductor pattern including an interdigital transducer (IDT) that each include interleaved fingers disposed on the diaphragm; and

wherein a frequency setting dielectric layer is disposed on a surface of the piezoelectric layer and between the interleaved fingers of the IDT of the shunt resonator, and

wherein the etch-stop layer is impervious to an etch process used to form the respective cavity of each of the plurality of acoustic resonators, and the etch-stop layer is at least one of aluminum nitride, boron nitride, and diamond.

10. The filter device of claim 9 , wherein a sum of a thickness of the etch-stop layer and a thickness of the frequency setting dielectric layer is less than or equal to 35% of a thickness of the piezoelectric layer of at least one of the plurality of acoustic resonators.

11. The filter device of claim 9 , further comprising a dielectric layer between the piezoelectric layer and the etch stop layer of each of the plurality of acoustic resonators, wherein each respective diaphragm includes the piezoelectric layer, the back-side dielectric layer, and the etch-stop layer.

12. The filter device of claim 11 , wherein the dielectric layer of each of the plurality of acoustic resonators is silicon dioxide.

13. The filter device of claim 9 , further comprising a bonding layer between the etch-stop layer and the substrate of each of the plurality of acoustic resonators, wherein each respective diaphragm includes the piezoelectric layer and the etch-stop layer, but not the bonding layer.

14. The filter device of claim 13 , wherein the substrate of each of the plurality of acoustic resonators is silicon and the bonding layer is silicon dioxide.

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

forming an etch-stop layer sandwiched between a surface of a device substrate and a first surface of a piezoelectric layer having a second surface attached to a sacrificial substrate;

removing the sacrificial substrate to expose the second surface of the piezoelectric layer;

using an etch process to form a cavity in the device substrate, a portion of the piezoelectric layer and the etch-stop layer forming a diaphragm spanning the cavity; and

forming an interdigital transducer (IDT) on the second surface of the piezoelectric layer such that interleaved fingers of the IDT are disposed on the diaphragm,

wherein the etch-stop layer is impervious to the etch process used to form the cavity, and the etch-stop layer is at least one of aluminum nitride, boron nitride, and diamond.

16. The method of claim 15 , wherein the piezoelectric layer is one of lithium niobate and lithium tantalate.

17. The method of claim 15 , further comprising:

forming a dielectric layer between the piezoelectric layer and the etch stop layer,

wherein the diaphragm includes the piezoelectric layer, the dielectric layer, and the etch-stop layer.

18. The method of claim 17 , wherein the dielectric layer is silicon dioxide.

19. The method of claim 15 , further comprising forming a bonding layer between the etch-stop layer and the device substrate, wherein the diaphragm includes the piezoelectric layer and the etch-stop layer, but not the bonding layer.

20. The method of claim 19 , wherein the device substrate is silicon and the bonding layer is silicon dioxide.

21. The method of claim 15 , wherein a thickness of the etch-stop layer is less than or equal to 20% of a thickness of the piezoelectric layer.

22. The method of claim 21 , wherein the thickness of the etch-stop layer is 4% to 6% of the thickness of the piezoelectric layer.