Transversly-excited film bulk acoustic resonators and filters
Acoustic resonator devices and filters are disclosed. An acoustic resonator includes a substrate and a single-crystal piezoelectric plate. A back surface of a supported portion of the piezoelectric plate is attached to a surface of the substrate. A portion of the piezoelectric plate forms a diaphragm that spans a cavity in the substrate. An interdigital transducer (IDT) is formed on a front surface of the piezoelectric plate. The IDT includes first and second busbars, and interleaved fingers extending alternately from the first and second busbars. Overlapping portions of the interleaved fingers are disposed on the diaphragm. At least portions of both the first and second busbars are disposed on the supported portion of the piezoelectric plate.
1. An acoustic resonator, comprising:
a substrate;
a single-crystal piezoelectric layer comprising a supported portion and a diaphragm, wherein a surface of the supported portion is attached to a surface of the substrate directly or via one or more intermediate layers and the diaphragm is over a cavity of the acoustic resonator;
an interdigital transducer (IDT) at the piezoelectric layer, the IDT comprising a first busbar, a second busbar, and interleaved fingers extending alternately from the first and second busbars,
wherein overlapping portions of the interleaved fingers are disposed on the diaphragm, and
wherein at least portions of both the first and second busbars are disposed on the supported portion of the piezoelectric layer.
2. The device of claim 1 , wherein the piezoelectric layer is one of lithium niobate and lithium tantalate.
3. The device of claim 2 , wherein the piezoelectric layer is one of Z-cut, rotated Z-cut, and rotated Y-cut.
4. The device of claim 1 , wherein a thickness of the piezoelectric layer is greater than or equal to 200 nm and less than or equal to 800 nm.
5. The device of claim 4 , wherein a pitch of the fingers of the IDT is greater than or equal to 2.5 times the thickness of the piezoelectric layer and less than or equal to 25 times the thickness of the piezoelectric layer.
6. The device of claim 5 , wherein:
the fingers of the IDT have a width, and
the pitch is greater than or equal to 2 times the width and less than or equal to 20 times the width.
7. The device of claim 1 , further comprising:
a dielectric layer on the piezoelectric layer and between the fingers of the IDT,
wherein a resonant frequency of a primary acoustic mode is based, in part, by a thickness of the dielectric layer.
8. The device of claim 7 , wherein the dielectric layer comprises at least one of silicon dioxide and silicon nitride.
9. The device of claim 7 , wherein a thickness of the dielectric layer is greater than zero and less than or equal to a thickness of the piezoelectric layer.
10. The device of claim 1 , further comprising:
a dielectric layer disposed on the diaphragm,
wherein a resonant frequency of a primary shear acoustic mode is based, in part, by a thickness of the dielectric layer.
11. The device of claim 10 , wherein the dielectric layer comprises at least one of silicon dioxide and silicon nitride.
12. The device of claim 1 , wherein the IDT comprises one or more layer of aluminum, an aluminum alloy, copper, a copper alloy, beryllium, titanium, tungsten, chromium, molybdenum, and gold.
13. A radio frequency filter, comprising:
a plurality of acoustic resonators that each comprise:
a substrate;
a piezoelectric layer comprising a supported portion and a diaphragm, wherein a surface of the supported portion is attached directly or via one or more intermediate layers to a surface of the substrate and the diaphragm is over a cavity of the respective acoustic resonator; and
a conductor pattern at the piezoelectric layer, the conductor pattern comprising an interdigital transducer (IDT) that includes:
a first busbar and a second busbar, at least portions of both the first and second busbars being disposed on the supported portion of the piezoelectric layer, and
interleaved fingers extending alternately from the first and second busbars, overlapping portions of the interleaved fingers disposed on the respective diaphragm of the acoustic resonator.
14. The filter of claim 13 , wherein the piezoelectric layer of each of the plurality of acoustic resonators is one of lithium niobate and lithium tantalate.
15. The filter of claim 14 , wherein the piezoelectric layer of each of the plurality of acoustic resonators is one of Z-cut, rotated Z-cut, and rotated Y-cut.
16. The filter of claim 13 , wherein a thickness of the piezoelectric layer of each of the plurality of acoustic resonators is greater than or equal to 200 nm and less than or equal to 800 nm.
17. The filter of claim 16 , wherein a pitch of the interleaved fingers of each of the IDTs is greater than or equal to 2.5 times the thickness of the piezoelectric layer and less than or equal to 25 times the thickness of the piezoelectric layer.
18. The filter of claim 1 , wherein
the plurality of acoustic resonators includes one or more shunt resonators and one or more series resonators, and
the conductor pattern of the plurality of acoustic resonators includes conductors to connect the one or more shunt resonators and the one or more series resonators in a ladder filter circuit.
19. The filter of claim 18 , further comprising:
a first dielectric layer having a first thickness formed between the IDT fingers of the one or more shunt resonators, and
a second dielectric layer having a second thickness formed between the IDT fingers of the one or more series resonators,
wherein the first thickness is greater than the second thickness.
20. The filter of claim 19 , wherein first thickness is less than or equal to a thickness of the piezoelectric layer and the second thickness is greater than or equal to zero.
21. The filter of claim 19 , wherein a difference between an average resonance frequency of the series resonators and an average resonance frequency of the shunt resonators is based, in part, by a difference between the first thickness and the second thickness.
22. The filter of claim 13 , wherein the conductor pattern of each of the plurality of acoustic resonators comprises one or more layer of aluminum, an aluminum alloy, copper, a copper alloy, beryllium, titanium, tungsten, chromium, molybdenum, and gold.