Vertically coupled SAW resonators
Aspects of the disclosure relate to devices, wireless communication apparatuses, methods, and circuitry implementing filters with electroacoustic vertical coupling. One aspect is a filter comprising a piezoelectric substrate having a first piezoelectric surface and a second piezoelectric surface opposite the first piezoelectric surface. The filter further comprises a first electroacoustic resonator comprising a first interdigital transducer (IDT) disposed on or over the first piezoelectric surface of the piezoelectric substrate and a second electroacoustic resonator comprising a second IDT disposed on or over the second piezoelectric surface of the piezoelectric substrate. The second electroacoustic resonator is electrically coupled to the first electroacoustic resonator in series or in parallel.
1. A radio frequency (RF) filter, comprising:
a piezoelectric substrate having a first piezoelectric surface and a second piezoelectric surface opposite the first piezoelectric surface;
a first electroacoustic resonator comprising a first interdigital transducer (IDT) disposed over the first piezoelectric surface of the piezoelectric substrate;
a second electroacoustic resonator comprising a second IDT disposed over the second piezoelectric surface of the piezoelectric substrate; and
a silicon substrate, wherein the silicon substrate has a cavity formed in a portion of a surface of the silicon substrate,
wherein the second piezoelectric surface of the piezoelectric substrate shares a boundary with the surface of the silicon substrate, aligned such that the second IDT fits within the cavity without contacting the silicon substrate, and
wherein the second electroacoustic resonator is electrically coupled to the first electroacoustic resonator.
2. The RF filter of claim 1 , wherein a thickness of the piezoelectric substrate is less than 20 times a minimum of a pitch of the first IDT and a pitch of the second IDT.
3. The RF filter of claim 2 , wherein the thickness of the piezoelectric substrate is greater than 0.1 times the minimum of the pitch of the first IDT and the pitch of the second IDT.
4. The RF filter of claim 1 , wherein the piezoelectric substrate comprises a first piezoelectric layer, the first piezoelectric layer comprising the first piezoelectric surface.
5. The RF filter of claim 4 , wherein the first piezoelectric layer further comprises the second piezoelectric surface; and
wherein a thickness of the first piezoelectric layer is between 0.4 times of a minimum of a pitch of the first IDT and a pitch of the second IDT and 2 times the minimum of the pitch of the first IDT and the pitch of the second IDT.
6. The RF filter of claim 4 , wherein the piezoelectric substrate further comprises:
a second piezoelectric layer comprising the second piezoelectric surface; and
a spacer layer positioned between and in contact with the first piezoelectric layer and the second piezoelectric layer.
7. The RF filter of claim 6 , wherein a thickness of the piezoelectric substrate is less than 20 times a minimum of a pitch of the first IDT and a pitch of the second IDT.
8. The RF filter of claim 7 , wherein a thickness of the spacer layer is less than 10 times the minimum of the pitch of the first IDT and the pitch of the second IDT.
9. The RF filter of claim 8 , wherein the first piezoelectric layer and the second piezoelectric layer are made from a same piezoelectric material.
10. The RF filter of claim 7 , wherein a thickness of the spacer layer is greater than 10 times a maximum of the pitch of the first IDT and the pitch of the second IDT.
11. The RF filter of claim 7 ,
wherein a thickness of the spacer layer is less than 1.2 times the minimum of the pitch of the first IDT and the pitch of the second IDT.
12. The RF filter of claim 6 , further comprising a third electroacoustic resonator comprising a third IDT formed within the spacer layer on a surface of the first piezoelectric layer opposite the first piezoelectric surface.
13. The RF filter of claim 12 , further comprising a fourth electroacoustic resonator comprising a fourth IDT formed within the spacer layer on a surface of the second piezoelectric layer opposite the second piezoelectric surface.
14. The RF filter of claim 13 , wherein a thickness of the second piezoelectric layer is between 0.4 times a minimum of a pitch of the second IDT and a pitch of the fourth IDT and 2 times the minimum of the pitch of the second IDT and the pitch of the fourth IDT.
15. The RF filter of claim 12 , wherein a thickness of the first piezoelectric layer is between 0.4 times a minimum of a pitch of the first IDT and a pitch of the third IDT and 2 times the minimum of the pitch of the first IDT and the pitch of the third IDT.
16. The RF filter of claim 6 , wherein the spacer layer comprises a dielectric material.
17. The RF filter of claim 1 , further comprising:
an antenna; and
processing circuitry, wherein the antenna and the processing circuitry are communicatively coupled via the RF filter, and wherein the RF filter is configured to filter RF signals traveling between the antenna and the processing circuitry.
18. The RF filter of claim 1 , further comprising:
a plurality of spacers positioned on the first piezoelectric surface of the piezoelectric substrate; and
a cap mounted on the plurality of spacers, such that the first IDT is positioned in a gap between the first piezoelectric surface of the piezoelectric substrate and the cap.
19. The RF filter of claim 1 , wherein the first electroacoustic resonator and the second electroacoustic resonator are part of a ladder filter.
20. The RF filter of claim 1 , wherein the RF filter is integrated into an RF front-end circuit of a transceiver.
21. The RF filter of claim 1 , wherein a filter characteristic of the RF filter is based on electroacoustic coupling between the first electroacoustic resonator and the second electroacoustic resonator through the piezoelectric substrate.
22. The RF filter of claim 21 , wherein the first IDT and the second IDT overlap in a vertical direction such that a vertical projection across the piezoelectric substrate of an area on the first piezoelectric surface that includes the first IDT overlaps with an area on the second piezoelectric surface that includes the second IDT.
23. An acoustic wave (AW) filter comprising:
a piezoelectric substrate comprising:
a first piezoelectric layer having a first piezoelectric surface and a second piezoelectric surface opposite the first piezoelectric surface;
a second piezoelectric layer having a third piezoelectric surface and a fourth piezoelectric surface opposite the third piezoelectric surface; and
a spacer layer between the first piezoelectric layer and the second piezoelectric layer, wherein the second piezoelectric surface is opposite the third piezoelectric surface across the spacer layer;
a first interdigital transducer (IDT) disposed over the first piezoelectric surface of the first piezoelectric layer; and a second IDT disposed over the second piezoelectric surface of the first piezoelectric layer, wherein the first IDT and the second IDT do not overlap in a vertical direction such that a vertical projection of the first IDT projection across the first piezoelectric substrate does not overlap with an area on the second piezoelectric surface that includes the second IDT;
a third IDT disposed over the third piezoelectric surface of the second piezoelectric layer;
a fourth IDT disposed over the fourth piezoelectric surface of the second piezoelectric layer.
24. The AW filter of claim 23 , wherein a first filter characteristic of the AW filter is based on electroacoustic coupling between the first IDT and the second IDT across the first piezoelectric layer, and wherein a second filter characteristic of the AW filter is based on electroacoustic coupling between the third IDT and the fourth IDT across the second piezoelectric layer.
25. The AW filter of claim 23 , wherein the spacer layer comprises a dielectric material.
26. A radio frequency (RF) filter, comprising:
a piezoelectric substrate comprising:
a first piezoelectric layer comprising a first piezoelectric surface;
a second piezoelectric layer comprising a second piezoelectric surface opposite the first piezoelectric surface; and
a spacer layer positioned between and in contact with the first piezoelectric layer and the second piezoelectric layer;
a first electroacoustic resonator comprising a first interdigital transducer (IDT) disposed over the first piezoelectric surface of the piezoelectric substrate;
a second electroacoustic resonator comprising a second IDT disposed over the second piezoelectric surface of the piezoelectric substrate, wherein the second electroacoustic resonator is electrically coupled to the first electroacoustic resonator in series or in parallel; and
a third electroacoustic resonator comprising a third IDT formed within the spacer layer on a surface of the first piezoelectric layer opposite the first piezoelectric surface.
27. The RF filter of claim 26 , further comprising a fourth electroacoustic resonator comprising a fourth IDT formed within the spacer layer on a surface of the second piezoelectric layer opposite the second piezoelectric surface.
28. A method of fabricating an acoustic wave (AW) filter package, the method comprising:
forming one or more via holes through a piezoelectric substrate, wherein the piezoelectric substrate has a first piezoelectric surface and a second piezoelectric surface opposite the first piezoelectric surface;
fabricating one or more conductive vias from the first piezoelectric surface to the second piezoelectric surface using the one or more via holes;
fabricating a first acoustic layer over the first piezoelectric surface of the piezoelectric substrate, wherein the first acoustic layer comprises one or more first interdigital transducers (IDTs) and one or more connections from the one or more first IDTs to the one or more conductive vias;
depositing one or more spacers on the first piezoelectric surface of the piezoelectric substrate, using a resist layer to protect the one or more first IDTs;
bonding the one or more spacers to a silicon substrate to mount the piezoelectric substrate on the silicon substrate using the one or more spacers;
thinning the piezoelectric substrate to a selected thickness by removing material from the second piezoelectric surface of the piezoelectric substrate; and
fabricating a second acoustic layer over the second piezoelectric surface of the piezoelectric substrate, wherein the second acoustic layer comprises one or more second IDTs connected to the one or more first IDTs via the one or more conductive vias.
29. The method of claim 28 , wherein a projection of the one or more first IDTs onto the second piezoelectric surface in a perpendicular direction from the first piezoelectric surface does not overlap with the one or more second IDTs.
30. The method of claim 29 , wherein a filter characteristic of the AW filter package filter is based on electroacoustic coupling between the one or more first IDTs and the one or more second IDTs through the piezoelectric substrate; and
wherein the electroacoustic coupling through the piezoelectric substrate is based on an overlap between the one or more first IDTs and the one or more second IDTs in a vertical direction across the piezoelectric substrate.