Transversely-excited film bulk acoustic resonators with piezoelectric diaphragm supported by piezoelectric substrate
Acoustic resonators and filter devices. 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 spanning a cavity in the substrate. A conductor pattern formed is formed on the front surface of the piezoelectric plate, including an interdigital transducer (IDT) with interleaved fingers of the IDT on the diaphragm. The substrate and the piezoelectric plate are the same material.
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 comprising an interdigital transducer (IDT), interleaved fingers of the IDT disposed on the diaphragm,
wherein the substrate and the piezoelectric plate are the same material, and
wherein the piezoelectric plate and interleaved fingers are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm.
2. The acoustic resonator device of claim 1 further comprising a buried oxide layer between the substrate and the piezoelectric plate, wherein the substrate is attached to the piezoelectric plate via the buried oxide layer.
3. The acoustic resonator device of claim 2 , wherein the buried oxide layer is one of SiO 2 and Al 2 O 3 .
4. The acoustic resonator device of claim 2 , wherein the buried oxide layer does not extend across the cavity.
5. The acoustic resonator device of claim 2 , wherein a thickness of the buried oxide layer is in a range between 10 nm and 50 microns.
6. The acoustic resonator device of claim 1 , wherein
the substrate and piezoelectric plate are one of lithium niobate and lithium tantalate.
7. The acoustic resonator device of claim 6 , wherein
the substrate and piezoelectric plate are one of Z-cut, rotated Z-cut, and rotated YX-cut.
8. 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 piezoelectric plate forming one or more diaphragms spanning respective cavities in the substrate; 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 one of the one or more diaphragms,
wherein the substrate and the piezoelectric plate are the same material, and
wherein the piezoelectric plate and interleaved fingers are configured such that a radio frequency signal applied to the plurality of IDTs excites a primary shear acoustic mode in the one or more diaphragms.
9. The filter device of claim 8 further comprising a buried oxide layer between the substrate and the piezoelectric plate, wherein the substrate is attached to the piezoelectric plate via the buried oxide layer.
10. The filter device of claim 9 , wherein the buried oxide layer is one of SiO 2 and Al 2 O 3 .
11. The filter device of claim 9 , wherein the buried oxide layer does not extend across the cavities.
12. The filter device of claim 9 , wherein a thickness of the buried oxide layer is in a range between 10 nm and 50 microns.
13. The filter device of claim 8 , wherein
the substrate and piezoelectric plate are one of lithium niobate and lithium tantalate.
14. The filter device of claim 13 , wherein
the substrate and piezoelectric plate are one of Z-cut, rotated Z-cut, and rotated YX-cut.
15. 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;
a buried oxide layer between the substrate and the piezoelectric plate, wherein the substrate is attached to the piezoelectric plate via the buried oxide layer, and wherein the buried oxide layer does not extend across the cavity;
a conductor pattern formed on the front surface of the piezoelectric plate, the conductor pattern comprising an interdigital transducer (IDT), interleaved fingers of the IDT disposed on the diaphragm, wherein the substrate and the piezoelectric plate are the same material; and
an etch stop at an edge of the cavity.
16. 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;
a buried oxide layer between the substrate and the piezoelectric plate, wherein the substrate is attached to the piezoelectric plate via the buried oxide layer;
a conductor pattern formed on the front surface of the piezoelectric plate, the conductor pattern comprising an interdigital transducer (IDT), interleaved fingers of the IDT disposed on the diaphragm, wherein the substrate and the piezoelectric plate are the same material; and
a through hole extending through the diaphragm to the cavity.
17. 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 piezoelectric plate forming one or more diaphragms spanning respective cavities in the substrate;
a buried oxide layer between the substrate and the piezoelectric plate, wherein the substrate is attached to the piezoelectric plate via the buried oxide layer, and wherein the buried oxide layer does not extend across the cavities;
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 one of the one or more diaphragms, wherein the substrate and the piezoelectric plate are the same material; and
etch stops at respective edges of each of the cavities.
18. 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 piezoelectric plate forming one or more diaphragms spanning respective cavities in the substrate;
a buried oxide layer between the substrate and the piezoelectric plate, wherein the substrate is attached to the piezoelectric plate via the buried oxide layer;
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 one of the one or more diaphragms, wherein the substrate and the piezoelectric plate are the same material; and
through holes extending through the one or more diaphragms to each of the cavities.