Transversely-excited film bulk acoustic resonator with a cavity having a curved perimeter
Acoustic filters, resonators and methods are disclosed. An acoustic filter device includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate. An interdigital transducer is formed on the front surface of the piezoelectric plate with interleaved fingers of the IDT disposed on the diaphragm. At least a portion of a perimeter of the cavity is curved, and the perimeter of the cavity is corner-less.
1. An acoustic resonator device comprising:
a substrate having a surface;
a piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate; and
an interdigital transducer (IDT) formed on the front surface of the piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm, wherein
the piezoelectric 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, and
at least a portion of a perimeter of the cavity is curved, and
the perimeter of the cavity is corner-less.
2. The device of claim 1 , wherein the perimeter of the cavity is defined by an intersection of the cavity and the surface of the substrate.
3. The device of claim 1 , wherein the perimeter of the cavity is continuously curved.
4. The device of claim 1 , wherein the perimeter of the cavity is continuously convex.
5. The device of claim 1 , wherein the perimeter of the cavity is elliptical.
6. The device of claim 1 , wherein the perimeter of the cavity is a rectangle with rounded corners.
7. The device of claim 1 , wherein a least a portion of the perimeter of the cavity is concave.
8. The device of claim 1 , wherein the perimeter of the cavity is asymmetrical about one or both of a first axis that bisects a length of the IDT and a second axis that bisect an aperture of the IDT.
9. The device of claim 1 , wherein the piezoelectric plate is lithium niobate or lithium tantalate.
10. A filter device, comprising:
a substrate having a surface;
a plurality of cavities formed in the substrate, each cavity having a respective perimeter defined by an intersection of the cavity and the surface of the substrate;
a piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate, portions of the piezoelectric plate forming a plurality of diaphragms spanning respective cavities of the plurality of cavities; and
a conductor pattern formed on the front surface, the conductor pattern including a plurality of interdigital transducers (IDTs) of two or more acoustic resonators, interleaved fingers of each of the plurality of IDTs disposed on a respective diaphragm of the plurality of diaphragms, wherein
the piezoelectric 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, and
at least a portion of a perimeter of at least one cavity of the plurality of cavities is curved and
the perimeter of the at least one cavity is corner-less.
11. The device of claim 10 , wherein the perimeter of the at least one cavity is continuously curved.
12. The device of claim 10 , wherein the perimeter of the at least one cavity is continuously convex.
13. The device of claim 10 , wherein the perimeter of the at least one cavity is elliptical.
14. The device of claim 10 , wherein the perimeter of the at least one cavity is a rectangle with rounded corners.
15. The device of claim 10 , wherein at least a portion of the perimeter of the at least one cavity is concave.
16. The device of claim 10 , wherein the perimeter of the at least one cavity is asymmetrical about one or both of a first axis that bisects a length of the IDT and a second axis that bisect an aperture of the IDT.
17. The device of claim 10 , wherein the piezoelectric plate is lithium niobate or lithium tantalate.
18. A method of fabricating an acoustic resonator device, comprising:
bonding a back surface of a piezoelectric plate to a substrate such that a portion of the piezoelectric plate forms a diaphragm spanning a cavity in the substrate; and
forming an interdigital transducer (IDT) on a front surface of the piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm, wherein
the piezoelectric 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, and
at least a portion of a perimeter of the cavity is curved, and
the perimeter of the cavity is corner-less.