Transversely-excited film bulk acoustic resonators with piezoelectric diaphragm supported by piezoelectric substrate
Acoustic resonators and filter devices, and methods for making acoustic resonators and filter devices. An acoustic resonator includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces. The back surface is attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate. A conductor pattern formed is formed on the front surface of the piezoelectric plate, including an interdigital transducer (IDT) with interleaved fingers of the IDT on the diaphragm. An insulating layer is formed between the piezoelectric plate and portions of the conductor pattern other than the interleaved fingers.
1. A filter device comprising:
at least one piezoelectric layer attached directly or via one or more intermediate layers to a substrate of a resonator of the filter device, portions of the at least one piezoelectric layer forming one or more diaphragms spanning respective cavities of the filter device;
a conductor pattern at the at least one piezoelectric layer and including a plurality of interdigital transducers (IDTs) of a respective plurality of acoustic resonators, interleaved fingers of each of the plurality of IDTs on one of the one or more diaphragms of the at least one piezoelectric layer; and
an insulating layer disposed between the at least one piezoelectric layer and portions of the conductor pattern other than the interleaved fingers,
wherein the insulating layer is not disposed on the diaphragm one or more diaphragms.
2. The filter device of claim 1 , wherein the insulating layer is not larger than the portions of the conductor pattern other than the interleaved fingers.
3. The filter device of claim 1 , wherein the insulating layer is only disposed between the at least one piezoelectric layer and portions of the conductor pattern other than the interleaved fingers.
4. The filter device of claim 1 , wherein the at least one piezoelectric layer and interleaved fingers of each of the plurality of IDTs are configured such that a radio frequency signal applied to the plurality of IDTs excites a primary shear acoustic mode in the one or more diaphragms.
5. The filter device of claim 1 , wherein:
the at least one piezoelectric layer is one of lithium niobate and lithium tantalate, and
the at least one piezoelectric layer is one of Z-cut, rotated Z-cut, and rotated YX-cut.
6. The filter device of claim 1 , wherein the insulating layer is comprised of one or both of SiO 2 and Si 3 N 4 .
7. The filter device of claim 1 , wherein the insulating layer has a thickness in a range between 1 nm and a thickness of the conductor pattern.
8. The filter device of claim 1 , wherein the insulating layer does not extend across the cavities.
9. The filter device of claim 1 , wherein the portions of the conductor pattern comprise at least one busbar, and the insulating layer is between the at least one busbar and the at least one piezoelectric layer, and wherein the insulating layer is configured to reduce acoustic coupling between the at least one busbar and the at least one piezoelectric layer.
10. The filter device of claim 1 further comprising a dielectric layer on the at least one piezoelectric layer and between the interleaved fingers.
11. A method of fabricating a filter device comprising:
attaching at least one piezoelectric layer to a substrate directly or via one or more intermediate layers, the at least one piezoelectric layer having portions that form one or more diaphragms spanning respective cavities of the filter device;
forming an insulating layer on the at least one piezoelectric layer; and
forming a conductor pattern comprising a plurality of interdigital transducers (IDTs) of a respective plurality of acoustic resonators on the at least one piezoelectric layer, interleaved fingers of each of the plurality of IDTs on the one or more diaphragms of the at least one piezoelectric layer, wherein the insulating layer is disposed between the at least one piezoelectric layer and portions of the conductor pattern other than the interleaved fingers of each of the plurality of IDTs,
wherein the insulating layer is only disposed between the at least one piezoelectric layer and portions of the conductor pattern other than the interleaved fingers.
12. The method of claim 11 , wherein the insulating layer is not larger than the portions of the conductor pattern other than the interleaved fingers.
13. The method of claim 11 , further comprising forming a dielectric layer on the at least one piezoelectric layer and between the interleaved fingers.
14. The method of claim 11 , further comprising configuring the at least one piezoelectric layer and interleaved fingers of each of the plurality of IDTs such that a radio frequency signal applied to the plurality of IDTs excites a primary shear acoustic mode in the one or more diaphragms.
15. The method of claim 11 , wherein:
the at least one piezoelectric layer is one of lithium niobate and lithium tantalate, and
the at least one piezoelectric layer is one of Z-cut, rotated Z-cut, and rotated YX-cut.
16. The method of claim 11 , wherein the insulating layer is comprised one or both of SiO 2 and Si 3 N 4 .
17. The method of claim 11 , wherein the insulating layer has a thickness in a range between 1 nm and a thickness of the conductor pattern.
18. The method of claim 11 , wherein the conductor pattern comprises at least one busbar, and the insulating layer is between the at least one busbar and the at least one piezoelectric layer, and wherein the insulating layer is configured to reduce acoustic coupling between the busbar and the at least one piezoelectric layer.
19. The method of claim 11 , wherein the insulating layer does not extend across the respective cavities.