Transversely-excited film bulk acoustic resonator with optimized electrode thickness, mark, and pitch
Acoustic resonators and filter devices. An acoustic resonator includes a piezoelectric plate having front and back surfaces, a portion of the piezoelectric plate forming a diaphragm, and a conductor pattern on the front surface, the conductor pattern including an interdigital transducer (IDT), fingers of the IDT on the diaphragm. A thickness of the interleaved fingers is greater than or equal to 0.85 times a thickness of the piezoelectric plate and less than or equal to 2.5 times the thickness of the piezoelectric plate. The IDT comprises a first portion having a first pitch and a first mark and a second portion having a second pitch and a second mark not equal to the first pitch and first mark.
1. An acoustic resonator comprising:
a substrate;
a piezoelectric layer attached to the substrate either directly or via at least one intermediate layer and including a diaphragm over a cavity of the acoustic resonator; and
an interdigital transducer (IDT) at the piezoelectric layer and having interleaved fingers that are on the diaphragm,
wherein a thickness of at least one of the interleaved fingers of the IDT is less than 0.375 times the thickness of the diaphragm, and
wherein the IDT comprises a first portion including a first plurality of interleaved fingers having a first pitch and a second portion including a second plurality of interleaved fingers having a second pitch that is not equal to the first pitch.
2. The acoustic resonator of claim 1 , wherein the thickness of the interleaved fingers and the thickness of the diaphragm are measured in a direction predominantly orthogonal to a surface of the diaphragm.
3. The acoustic resonator of claim 1 , wherein the piezoelectric layer and the IDT are configured such that a radio frequency signal applied to the IDT laterally excites a primary shear acoustic mode in the diaphragm.
4. The acoustic resonator of claim 1 , wherein a ratio of the first pitch of the interleaved fingers is between 2 and 20 times a first mark of the interleaved fingers in the first portion, and a ratio of the second pitch of the interleaved fingers is between 2 and 20 times a second mark of the interleaved fingers in the second portion.
5. The acoustic resonator of claim 1 , wherein the piezoelectric layer is one of lithium niobite and lithium tantalate.
6. The acoustic resonator of claim 1 , wherein the piezoelectric layer is one of Z-cut, rotated Z-cut, and rotated Y-cut.
7. The acoustic resonator of claim 1 , wherein the substrate is one or more of silicon, sapphire, and quartz, and the at least one intermediate layer is a dielectric layer.
8. The acoustic resonator of claim 7 , wherein the cavity is disposed within the dielectric layer.
9. The acoustic resonator of claim 1 , wherein the first and second pitches are measured as a center-to-center distance of adjacent fingers of the first and second portions, respectively.
10. The acoustic resonator of claim 1 , wherein the first and second portions each have a plurality of interleaved fingers having a different mark from each other, wherein the respective marks are measured as a width of at least one of the interleaved fingers of the first and second portions, respectively, and the interleaved fingers within each portion of the first and second portions have a constant pitch and mark.
11. The acoustic resonator of claim 1 , wherein the IDT includes at least three portions, which includes the first portion and the second portion, and the at least three portions each have a plurality of interleaved fingers having a different pitch from each other, and the interleaved fingers within each separate portion of the at least three portions have a constant pitch.
12. A filter device, comprising:
a plurality of resonators, each resonator comprising:
a substrate;
a piezoelectric layer attached to the substrate either directly or indirectly via one or more intermediate layers; and
a conductor pattern at the one or more piezoelectric layers layer, the conductor pattern including an interdigital transducer (IDT) having interleaved fingers at the piezoelectric layer,
wherein at least one interleaved finger of the IDT of each of the plurality of resonators has a thickness that is less than 0.375 times a thickness of the piezoelectric layer, and
wherein the IDT of each of the plurality of resonators comprises a first portion including a first plurality of interleaved fingers having a first pitch and a second portion including a second plurality of interleaved fingers having a second pitch not equal to the first pitch.
13. The filter device of claim 12 , wherein, for at least one resonator of the plurality of resonators, the thickness of the at least one interleaved finger and the thickness of the piezoelectric layer are measured in a direction predominantly orthogonal to a surface of the respective piezoelectric layer.
14. The filter device of claim 12 , wherein, for at least one resonator of the plurality of resonators, the piezoelectric layer and the IDT are configured such that a radio frequency signals applied to the IDT laterally excites a primary shear acoustic mode in the piezoelectric layer.
15. The filter device of claim 12 , wherein, for at least one resonator of the plurality of resonators, a ratio of the first pitch of the interleaved fingers is between 2 and 20 times a first mark of the interleaved fingers, and a ratio of the second pitch of the interleaved fingers is between 2 and 20 times a second mark of the interleaved fingers.
16. The filter device of claim 12 , wherein, for at least one resonator of the plurality of resonators, the substrate is one or more of silicon, sapphire, and quartz, and the one or more intermediate layers is a dielectric layer.
17. The filter device of claim 16 , wherein, for the at least one resonator of the plurality of resonators, a cavity is disposed within the dielectric layer.
18. The filter device of claim 17 , wherein, for the at least one resonator of the plurality of resonators, the first and second pitches are measured as a center-to-center distance of adjacent fingers within each portion of the IDT, respectively.
19. The filter device of claim 12 , wherein, for the at least one resonator of the plurality of resonators, the first and second portions each have a plurality of interleaved fingers having a different mark from each other, wherein mark is measured as a width of at least one of the interleaved fingers of the first and second portions, respectively, and the interleaved fingers within each portion of the first and second portions have a constant pitch and mark.
20. The filter device of claim 12 , wherein the plurality of resonators comprises at least one series resonator and one shunt resonator in a ladder filter circuit, and wherein a difference between pitch in the first portion and the second portion of the at least one series resonator and the at least one shunt resonator respectively is different.