Solidly-mounted transversely-excited film bulk acoustic resonator with recessed interdigital transducer fingers using rotated y-x cut lithium niobate
Acoustic resonator devices, filters, and methods are disclosed. An acoustic resonator includes a substrate, a lithium niobate plate having front and back surfaces, wherein 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 an acoustic Bragg reflector between the surface of the substrate and the back surface of the lithium niobate plate. An interdigital transducer (IDT) is formed on the front surface of the piezoelectric plate. At least one finger of the IDT is disposed in a groove in the lithium niobate plate.
1. An acoustic resonator device comprising:
a substrate having a surface;
a lithium niobate plate, wherein 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°;
an acoustic Bragg reflector between the surface of the substrate and the lithium niobate plate; and
an interdigital transducer (IDT) at the lithium niobate plate, wherein at least one finger of the IDT extends in a groove in the lithium niobate plate,
wherein the groove has a depth in the lithium niobate plate that is less than or equal to a thickness of the at least one finger of the IDT.
2. The device of claim 1 , wherein the IDT and the lithium niobate plate are configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode within the lithium niobate plate, wherein a direction of acoustic energy flow of the shear primary acoustic mode is substantially orthogonal to front and back surfaces of the lithium niobate plate.
3. The device of claim 1 , wherein the IDT comprises a plurality of fingers that all extend in respective grooves in the lithium niobate plate.
4. The device of claim 1 , wherein a depth of the groove is less than or equal to a thickness of the lithium niobate plate.
5. The device of claim 1 , wherein is greater than or equal to 26° and less than or equal to 34°.
6. The device of claim 1 , wherein the acoustic Bragg reflector comprises a plurality of layers alternating between high acoustic impedance layers and low acoustic impedance layers, wherein the high acoustic impedance layers are one of silicon nitride and aluminum nitride, and the low acoustic impedance layers are carbon-containing silicon oxide.
7. The device of claim 1 , further comprising a front-side dielectric layer at the lithium niobate plate over and/or between the fingers of the IDT.
8. A filter device, comprising:
a substrate;
a lithium niobate plate, wherein 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°;
an acoustic Bragg reflector between the substrate and the lithium niobate plate; and
a conductor pattern at the lithium niobate plate, the conductor pattern including a plurality of interdigital transducers (IDTs) of a respective plurality of acoustic resonators that each have interleaved fingers at the lithium niobate plate,
wherein at least one finger of at least one of the plurality of IDTs extends in a groove in the lithium niobate plate, and
wherein the groove has a depth in the lithium niobate plate that is less than or equal to a thickness of the at least one finger.
9. The device of claim 8 , wherein the each of the plurality of IDTs and the lithium niobate plate are configured such that a radio frequency signal applied to the each of the plurality of IDTs excites a shear primary acoustic mode within the lithium niobate plate, wherein a direction of acoustic energy flow of the shear primary acoustic mode is substantially orthogonal to front and back surfaces of the lithium niobate plate.
10. The device of claim 8 , wherein the at least one of the plurality of IDTs comprises a plurality of fingers that all extend in respective grooves in the lithium niobate plate.
11. The device of claim 8 , wherein a depth of the groove is less than or equal to a thickness of the lithium niobate plate.
12. The device of claim 8 , wherein β is greater than or equal to 26° and less than or equal to 34°.
13. The device of claim 8 , wherein the acoustic Bragg reflector comprises a plurality of layers alternating between high acoustic impedance layers and low acoustic impedance layers, wherein the high acoustic impedance layers are one of silicon nitride and aluminum nitride, and the low acoustic impedance layers are carbon-containing silicon oxide.
14. The device of claim 8 , further comprising a front-side dielectric layer at the lithium niobate plate over and/or between the fingers of at least one of the plurality of IDTs.
15. A method of fabricating an acoustic resonator device, comprising:
forming an acoustic Bragg reflector by depositing material layers on one or both of a surface of a device substrate and a lithium niobate plate attached to a sacrificial substrate, wherein 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°;
bonding the lithium niobate plate to the device substrate such that layers of the acoustic Bragg reflector are between the lithium niobate plate and the surface of the device substrate;
removing the sacrificial substrate to expose the lithium niobate plate; and
forming an interdigital transducer (IDT) at the lithium niobate, wherein at least one finger of the IDT extends in a groove in the lithium niobate plate,
wherein the groove has a depth in the lithium niobate plate that is less than or equal to a thickness of the at least one finger of the IDT.
16. The method of claim 15 , wherein the IDT and the lithium niobate plate are configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode within the lithium niobate plate, wherein a direction of acoustic energy flow of the shear primary acoustic mode is substantially orthogonal to front and back surfaces of the lithium niobate plate.
17. The method of claim 15 , further comprising forming the IDT to comprise a plurality of fingers that all extend in respective grooves in the lithium niobate plate.
18. The method of claim 15 , wherein a depth of the groove is less than or equal to a thickness of the lithium niobate plate.
19. The method of claim 15 , wherein is greater than or equal to 26° and less than or equal to 34°.
20. The method of claim 15 , wherein the acoustic Bragg reflector comprises a plurality of layers alternating between high acoustic impedance layers and low acoustic impedance layers, wherein the high acoustic impedance layers are one of silicon nitride and aluminum nitride, and the low acoustic impedance layers are carbon-containing silicon oxide.
21. The method of claim 15 , further comprising forming a front-side dielectric layer at the lithium niobate plate over and/or between the fingers of the IDT.