Transversely-excited film bulk acoustic resonator using YX-cut lithium niobate for high power applications
Acoustic resonator devices, filters, and methods are disclosed. An acoustic resonator includes a substrate and a lithium niobate (LN) plate having front and back surfaces and a thickness ts. The back surface faces the substrate. A portion of the LN plate forms a diaphragm spanning a cavity in the substrate. An interdigital transducer (IDT) is on the front surface of the LN plate with interleaved fingers of the IDT on the diaphragm. The LN plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic wave in the diaphragm. Euler angles of the LN plate are [0°, β, 0°], where 0≤β≤60°. A thickness of the interleaved fingers of the IDT is greater than or equal to 0.8 ts and less than or equal to 2.0 ts.
1. An acoustic resonator device comprising:
a substrate;
a lithium niobate plate having a front surface and a back surface facing the substrate, a portion of the lithium niobate plate forming a diaphragm that spans a cavity in the substrate; and
an interdigital transducer (IDT) on the front surface of the lithium niobate plate such that interleaved fingers of the IDT are on the diaphragm, wherein
the lithium niobate plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm,
Euler angles of the lithium niobate plate are [0°, β, 0° ], where β is greater than or equal to 0° and less than or equal to 60°, and
a thickness of the interleaved fingers of the IDT is greater than or equal to 0.8 times a thickness of the lithium niobate plate and less than or equal to 2.0 times the thickness of the lithium niobate plate.
2. The device of claim 1 , wherein β is greater than or equal to 26° and less than or equal to 34°.
3. The device of claim 1 , wherein β is about 30°.
4. The device of claim 1 , further comprising a dielectric layer between the interleaved fingers of the IDT.
5. The device of claim 4 , wherein
a thickness of the dielectric layer is less than or equal to 0.2 times the thickness of the lithium niobate plate, and
the thickness of the interleaved fingers of the IDT is greater than or equal to 1.1 times the thickness of the lithium niobate plate and less than or equal to 2.0 times the thickness of the lithium niobate plate.
6. The device of claim 4 , wherein
a thickness of the dielectric layer is greater than 0.2 times the thickness of the lithium niobate plate and less than or equal to 0.3 times the thickness of the lithium niobate plate, and
the thickness of the interleaved fingers of the IDT is greater than or equal to 1.15 times the thickness of the lithium niobate plate and less than or equal to 1.8 times the thickness of the lithium niobate plate.
7. The device of claim 4 , wherein
a thickness of the dielectric layer is less than or equal to 0.35 times the thickness of the lithium niobate plate.
8. The device of claim 1 , wherein a direction of acoustic energy flow of the primary acoustic mode is substantially orthogonal to the front and back surfaces of the diaphragm.
9. The device of claim 1 , wherein the back surface of the lithium niobate plate is attached to the substrate.
10. The device of claim 9 , wherein the back surface of the lithium niobate plate is attached to the substrate with an intermediate bonding layer.
11. A filter device, comprising:
a substrate;
a lithium niobate plate having a front surface and a back surface facing the substrate, portions of the lithium niobate plate forming one or more diaphragms spanning respective cavities in the substrate; and
a conductor pattern on the front surface, the conductor pattern including a plurality of interdigital transducers (IDTs) of a respective plurality of acoustic resonators, interleaved fingers of each of the plurality of IDTs on respective diaphragms of the one or more diaphragms, wherein
the lithium niobate plate and all of the IDTs are configured such that respective radio frequency signals applied to the IDTs excite respective primary shear acoustic modes in the respective diaphragms,
Euler angles of the lithium niobate plate are [0°, β, 0° ], where β is greater than or equal to 0° and less than or equal to 60°, and
the interleaved fingers of all of the IDTs have a common thickness greater than or equal to 0.8 times a thickness of the lithium niobate plate and less than or equal to 2.0 times the thickness of the lithium niobate plate.
12. The filter device of claim 11 , wherein β is greater than or equal to 26° and less than or equal to 34°.
13. The filter device of claim 11 , wherein β is about 30°.
14. The filter device of claim 11 , further comprising a frequency setting dielectric layer formed between the interleaved fingers of a subset of the plurality of IDTs.
15. The filter device of claim 14 , wherein
a thickness of the frequency setting dielectric layer is less than or equal to 0.2 times the thickness of the lithium niobate plate, and
the common thickness of the interleaved fingers of the IDTs is greater than or equal to 1.1 times the thickness of the lithium niobate plate and less than or equal to 2.0 times the thickness of the lithium niobate plate.
16. The filter device of claim 14 , wherein
a thickness of the frequency setting dielectric layer is greater than 0.2 times the thickness of the lithium niobate plate and less than or equal to 0.3 times the thickness of the lithium niobate plate, and
the common thickness of the interleaved fingers of the IDTs is greater than or equal to 1.15 times the thickness of the lithium niobate plate and less than or equal to 1.8 times the thickness of the lithium niobate plate.
17. The filter device of claim 14 , wherein
a thickness of the frequency setting dielectric layer is less than or equal to 0.35 times the thickness of the lithium niobate plate.
18. The filter device of claim 14 , wherein
the plurality of acoustic resonators includes one or more shunt resonators and one or more series resonator connected in a ladder filter circuit, and
the subset of the plurality of IDTs is the one or more shunt resonators.
19. The filter device of claim 11 , wherein respective directions of acoustic energy flow of all of the primary acoustic modes are substantially orthogonal to the front and back surfaces of the diaphragm.
20. The filter device of claim 11 wherein interleaved fingers of each of the plurality of IDTs are disposed on a respective diaphragm spanning a respective cavity.
21. The filter device of claim 11 , wherein the back surface of the lithium niobate plate is attached to the substrate.
22. The filter device of claim 21 , wherein the back surface of the lithium niobate plate is attached to the substrate with an intermediate bonding layer.