XBAR resonators with non-rectangular diaphragms
Acoustic resonator devices, filter devices, and methods of fabrication are disclosed. An acoustic resonator includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces. The back surface is 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, the diaphragm having an edge about a perimeter of the cavity. An interdigital transducer (IDT) is formed on the front surface of the single-crystal piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. The IDT is configured to excite a primary acoustic mode in the diaphragm in response to a radio frequency signal applied to the IDT. At least a portion of the edge of the diaphragm is at an oblique angle to the fingers and to an X crystalline axis of the piezoelectric plate.
1. An acoustic resonator device comprising:
a substrate having a surface;
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 single-crystal piezoelectric plate forming a diaphragm that spans a cavity in the substrate, the diaphragm having an edge about a perimeter of the cavity; and
an interdigital transducer (IDT) formed on the front surface of the single-crystal piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm, the IDT configured to excite a primary acoustic mode in the diaphragm in response to a radio frequency signal applied to the IDT, wherein at least a portion of the edge of the diaphragm is at an oblique angle to the fingers, and wherein the at least a portion of the edge of the diaphragm is also at the oblique angle to an X crystalline axis of the single-crystal piezoelectric plate.
2. The device of claim 1 , wherein a direction of acoustic energy flow of the excited primary shear acoustic mode is substantially normal to the front and back surfaces of the single-crystal piezoelectric plate.
3. The device of claim 1 , wherein a Z-axis of the single-crystal piezoelectric plate is normal to the front and back surfaces.
4. The device of claim 1 , wherein the interleaved fingers are substantially parallel to each other and extend in a first direction, and an electric field generated by the interleaved fingers extends in a second direction normal to the first direction.
5. The device of claim 4 , wherein the at least a portion of the edge of the diaphragm is at an angle in a range from 5 degrees to 25 degrees to the second direction.
6. The device of claim 4 , wherein the at least a portion of the edge of the diaphragm is at an angle of 20 degrees to the second direction.
7. The device of claim 1 , wherein the single-crystal piezoelectric plate is formed of lithium niobate.
8. The device of claim 1 , wherein the IDT comprises a busbar and the interleaved fingers of the IDT extend at the oblique angle from the busbar.
9. A method of fabricating a filter device on a piezoelectric plate having front and back surfaces, the back surface attached to a substrate, the method comprising:
forming one or more cavities in the substrate such that respective portions of the piezoelectric plate form one or more diaphragms suspended over the one or more cavities, each diaphragm having a respective edge about a perimeter of a respective cavity; and
forming a conductor pattern on the front surface, the conductor pattern including a plurality of interdigital transducers (IDTs) of a respective plurality of resonators including a shunt resonator and a series resonator, wherein interleaved fingers of each of the plurality of IDTs are disposed on a respective diaphragm of the one or more diaphragms, wherein the piezoelectric plate and all of the plurality of IDTs are configured such that radio frequency signals applied to the IDTs excite respective primary shear acoustic modes in the respective diaphragms, wherein at least a portion of the edge of at least one diaphragm is at an oblique angle to the respective fingers, and wherein the at least a portion of the edge of the at least one diaphragm is also at the oblique angle to an X crystalline axis of the piezoelectric plate.
10. The method of claim 9 , wherein the interleaved fingers disposed on the at least one diaphragm are substantially parallel to each other and extend in a first direction, and an electric field generated by said interleaved fingers extends in a second direction normal to the first direction.
11. The method of claim 10 , wherein the at least a portion of the edge of the at least one diaphragm is at an angle in a range from 5 degrees to 25 degrees to the second direction.
12. The method of claim 10 , wherein the at least a portion of the edge of the at least one diaphragm is at an angle of 20 degrees to the second direction.
13. A filter device comprising:
a substrate having a surface;
a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to the surface of the substrate, portions of the single-crystal piezoelectric plate forming one or more diaphragms spanning respective cavities in the substrate, each diaphragm having a respective edge about a perimeter of the respective cavity; 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, interleaved fingers of each of the plurality of IDTs disposed on a diaphragm of the one or more diaphragms, the single-crystal piezoelectric plate and all of the IDTs configured such that respective radio frequency signals applied to each IDT excite respective shear primary acoustic modes in the respective diaphragms, wherein at least a portion of the edge of at least one diaphragm is at an oblique angle to the respective fingers, and wherein the at least a portion of the edge is also at the oblique angle to an X crystalline axis of the piezoelectric plate.
14. The filter device of claim 13 , wherein a Z-axis of the single-crystal piezoelectric plate is normal to the front and back surfaces.
15. The filter device of claim 13 , wherein the interleaved fingers disposed on the at least one diaphragm are substantially parallel to each other and extend in a first direction, and an electric field generated by said interleaved fingers extends in a second direction normal to the first direction.
16. The filter device of claim 15 , wherein the at least a portion of the edge of the at least one diaphragm is at an angle in a range from 5 degrees to 25 degrees to the second direction.
17. The filter device of claim 15 , wherein the at least a portion of the edge of the at least one diaphragm is at an angle of 20 degrees to the second direction.
18. The filter device of claim 13 , wherein the IDT disposed on the at least one diaphragm comprises a busbar and the interleaved fingers of said IDT extend at the oblique angle from the busbar.