Transversely-excited film bulk acoustic resonator with reduced spurious modes
Acoustic filters, resonators and methods are disclosed. An acoustic resonator device includes a substrate having a surface. A back surface of a single-crystal piezoelectric plate 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. A conductor pattern is formed on the front surface of the piezoelectric plate, the conductor pattern including an interdigital transducer (IDTs), interleaved fingers of the IDT disposed on the diaphragm. A pitch of the interleaved fingers and a mark of the interleaved fingers are set in combination such that a resonance frequency of the acoustic resonator is equal to a predetermined target frequency.
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 piezoelectric plate forming a diaphragm that spans a cavity in the substrate; and
a conductor pattern formed on the front surface of the piezoelectric plate, the conductor pattern including an interdigital transducer (IDTs), interleaved fingers of the IDT disposed on the diaphragm,
wherein a pitch of the interleaved fingers and a mark of the interleaved fingers are set in combination such that a resonance frequency of the acoustic resonator is equal to a predetermined target frequency, and
a ratio of the mark of the interleaved fingers to the pitch of the interleaved fingers is greater than or equal to 0.2 and less than or equal to 0.3.
2. The device of claim 1 , wherein
a ratio of the mark of the interleaved fingers to the pitch of the interleaved fingers is greater than or equal to 0.235 and less than or equal to 0.265.
3. The device of claim 1 , wherein the diaphragm is contiguous with the piezoelectric plate around at least 50% of a perimeter of the cavity.
4. The device of claim 1 wherein the interleaved fingers of the IDT are aluminum with a thickness greater than or equal to 50 nm and less than or equal to 150 nm.
5. The device of claim 1 , wherein the single-crystal piezoelectric plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode within the diaphragm.
6. The device of claim 1 , wherein the single-crystal piezoelectric plate is lithium niobate.
7. An acoustic 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 except for portions of the piezoelectric plate forming a plurality of diaphragms spanning respective cavities in the substrate; and
a conductor pattern formed on the front surface of the piezoelectric plate, the conductor pattern including interdigital transducers (IDTs) of a plurality of acoustic resonators, interleaved fingers of each IDT disposed on a respective diaphragm from the plurality of diaphragms,
wherein, for each of the IDTs, a pitch of the interleaved fingers and a mark of the interleaved fingers are set in combination such that a resonance frequency of the respective acoustic resonator is equal to a respective predetermined target frequency, and
for one or more of the IDTs, a ratio of the mark of the interleaved fingers to the pitch of the interleaved fingers is greater than or equal to 0.2 and less than or equal to 0.3.
8. The device of claim 7 , wherein
for one or more of the IDTs, a ratio of the mark of the interleaved fingers to the pitch of the interleaved fingers is greater than or equal to 0.235 and less than or equal to 0.265.
9. The device of claim 7 , wherein the single-crystal piezoelectric plate is lithium niobate.
10. The device of claim 7 , wherein each of the plurality of diaphragms is contiguous with the piezoelectric plate around at least 50% of a perimeter of the cavity.
11. The device of claim 7 wherein the interleaved fingers of all of the IDTs are aluminum with a thickness greater than or equal to 50 nm and less than or equal to 150 nm.
12. The device of claim 7 , wherein the single-crystal piezoelectric plate and the plurality of IDTs are configured such that respective radio frequency signals applied to the plurality of IDTs excite respective shear primary acoustic modes within the respective diaphragms.
13. A method of fabricating an acoustic resonator device, comprising:
bonding a back surface of a single-crystal piezoelectric plate to a surface of a substrate, a portion of the piezoelectric plate forming a diaphragm that spans a cavity in the substrate; and
forming a conductor pattern on a front surf ace of the piezoelectric plate, the conductor pattern comprising an interdigital transducers (IDT), interleaved fingers of the IDT disposed on the diaphragm; and
wherein a pitch of the interleaved fingers and a mark of the interleaved fingers are set in combination such that a resonance frequency of the acoustic resonator is equal to a predetermined target frequency, and
a ratio of the mark of the interleaved fingers to the pitch of the interleaved fingers is greater than or equal to 0.2 and less than or equal to 0.3.
14. The method of claim 13 , wherein
a ratio of the mark of the interleaved fingers to the pitch of the interleaved fingers is greater than or equal to 0.235 and less than or equal to 0.265.
15. The method of claim 13 , wherein the single-crystal piezoelectric plate and the IDT are configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode within the diaphragm.
16. The method of claim 13 , wherein the single-crystal piezoelectric plate is lithium niobate.
17. The method of claim 13 , wherein the diaphragm is contiguous with the piezoelectric plate around at least 50% of a perimeter of the cavity.
18. The method of claim 13 , wherein the interleaved fingers of the IDT are aluminum with a thickness greater than or equal to 50 nm and less than or equal to 150 nm.