Solidly-mounted transversely-excited film bulk acoustic resonator with recessed interdigital transducer fingers
Acoustic resonator devices, filters, and methods are disclosed. An acoustic resonator includes a substrate, a piezoelectric plate having front and back surfaces, and an acoustic Bragg reflector between a surface of the substrate and the back surface of the piezoelectric plate. An interdigital transducer (IDT) is formed on the front surface of the piezoelectric plate. The IDT is configured to excite a shear primary acoustic mode in the piezoelectric plate in response to a radio frequency signal applied to the IDT. All fingers of the IDT are disposed in a respective grooves in the piezoelectric plate.
1. An acoustic resonator device comprising:
a substrate having a surface;
a piezoelectric plate having front and back surfaces;
an acoustic Bragg reflector between the surface of the substrate and the back surface of the piezoelectric plate; and
an interdigital transducer (IDT) formed on the front surface of the piezoelectric plate, the IDT and the piezoelectric plate configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode in the piezoelectric plate,
wherein all fingers of the IDT are disposed in respective grooves in the piezoelectric plate.
2. The device of claim 1 , wherein a direction of acoustic energy flow of the shear primary acoustic mode is substantially orthogonal to the front and back surfaces of the piezoelectric plate.
3. The device of claim 1 , wherein a depth of the grooves is less than or equal to a thickness of the piezoelectric plate.
4. The device of claim 1 , wherein a depth of the grooves is less than a thickness of the finger.
5. The device of claim 1 , wherein a depth of the grooves is equal to a thickness of the finger.
6. The device of claim 1 , wherein the piezoelectric plate is a rotated z-cut lithium niobate plate.
7. A filter device, comprising:
a substrate;
a piezoelectric plate having front and back surfaces;
an acoustic Bragg reflector between the surface of the substrate and the back surface of the piezoelectric plate; and
a conductor pattern formed on the front surface, the conductor pattern including a plurality of interdigital transducers (IDTs) of a respective plurality of acoustic resonators, wherein all of the IDTs are configured to excite respective shear primary acoustic modes in the piezoelectric plate in response to respective radio frequency signals applied to each IDT,
wherein all fingers of at least one of the plurality of IDTs are disposed in respective grooves in the piezoelectric plate.
8. The filter device of claim 7 , wherein directions of acoustic energy flow of all of the shear primary acoustic modes are substantially orthogonal to the front and back surfaces of the piezoelectric plate.
9. The filter device of claim 7 , wherein a depth of the grooves is less than or equal to a thickness of the piezoelectric plate.
10. The filter device of claim 7 , wherein a depth of the grooves is less than a thickness of the finger.
11. The filter device of claim 7 , wherein a depth of the grooves is equal to a thickness of the finger.
12. The filter device of claim 7 , wherein the piezoelectric plate is a rotated z-cut lithium niobate plate.
13. 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 back surface of a piezoelectric plate having a front surface attached to a sacrificial substrate;
bonding the piezoelectric plate to the device substrate such that layers of the acoustic Bragg reflector are between the back surface of the piezoelectric plate and the surface of the device substrate;
removing the sacrificial substrate to expose the front surface of the piezoelectric plate; and
forming an interdigital transducer (IDT) on the front surface of the piezoelectric plate such that interleaved fingers of the IDT are configured to excite a shear primary acoustic mode in the piezoelectric plate in response to a radio frequency signal applied to the IDT, wherein all fingers of the IDT are disposed in respective grooves in the piezoelectric plate.
14. The method of claim 13 , wherein a depth of the grooves is less than or equal to a thickness of the piezoelectric plate.
15. The method of claim 13 , wherein a depth of the grooves is less than a thickness of the fingers of the IDT.
16. The method of claim 13 , wherein a depth of the grooves is equal to a thickness of the fingers of the IDT.
17. The method of claim 13 , wherein the piezoelectric plate is a rotated z-cut lithium niobate plate.