Transversely-excited film bulk acoustic resonators with electrodes having irregular hexagon cross-sectional shapes
Acoustic resonators and filter devices, and method of making acoustic resonators and filter devices. An acoustic resonator includes a substrate having a surface and 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. An interdigital transducer (IDT) is formed on the front surface of the piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm. The interleaved fingers have an irregular hexagon cross-sectional shape.
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,
wherein interleaved fingers of the IDT are disposed on the diaphragm and configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm, and
wherein the interleaved fingers have an irregular hexagon cross-sectional shape.
2. The device of claim 1 , wherein the irregular hexagon cross-sectional shape comprises:
a lower layer comprising three sides of the irregular hexagon cross-sectional shape that is adjacent the diaphragm; and
an upper layer comprising the other three sides of the irregular hexagon cross-sectional shape that is over the lower layer opposite the diaphragm.
3. The device of claim 2 , wherein a thickness of the upper layer is greater than a thickness of the lower layer.
4. The device of claim 3 , wherein the thickness of the lower layer is in a range from 5% to 40% of a thickness of the diaphragm, and the thickness of the upper layer is in a range from 25% to 75% of the thickness of the diaphragm.
5. The device of claim 2 , wherein the lower layer comprises a different material than the upper layer.
6. The device of claim 2 , wherein the lower layer is titanium, platinum or molybdenum.
7. The device of claim 2 , wherein a sidewall of the upper layer is at an angle in a range from 70 degrees to 90 degrees to the diaphragm.
8. The device of claim 2 , wherein a sidewall of the lower layer is at an angle in a range from 90 degrees to 120 degrees to the diaphragm.
9. A filter 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, 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, the 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 diaphragm,
wherein the interleaved fingers have an irregular hexagon cross-sectional shape.
10. The device of claim 9 , wherein the irregular hexagon cross-sectional shape comprises:
a lower layer comprising three sides of the irregular hexagon cross-sectional shape that is adjacent a respective one of the one or more diaphragms; and
an upper layer comprising the other three sides of the irregular hexagon cross-sectional shape that is over the lower layer opposite the respective one of the one or more diaphragms.
11. The device of claim 10 , wherein a thickness of the upper layer is greater than a thickness of the lower layer.
12. The device of claim 11 , wherein the thickness of the lower layer is in a range from 5% to 40% of a thickness of a respective one of the one or more diaphragms, and the thickness of the upper layer is in a range from 25% to 75% of the thickness of the respective one of the diaphragm.
13. The device of claim 10 , wherein the lower layer comprises a different material than the upper layer.
14. The device of claim 10 , wherein the lower layer is titanium.
15. The device of claim 10 , wherein a sidewall of the upper layer is at an angle in a range from 70 degrees to 90 degrees to the respective one of the one or more diaphragms.
16. The device of claim 10 , wherein a sidewall of the lower layer is at an angle in a range from 90 degrees to 120 degrees to the respective one of the one or more diaphragms.
17. The device of claim 9 , wherein the plurality of acoustic resonators comprises at least one first acoustic resonator and at least one second acoustic resonator, wherein a front side dielectric layer is deposited over the at least one first acoustic resonator and not deposited over the at least one second acoustic resonator.
18. A method of fabricating an acoustic resonator device, comprising:
bonding a piezoelectric plate to a substrate;
forming a cavity in the substrate, before or after bonding the piezoelectric plate to the substrate, such that a portion of the piezoelectric plate forms a diaphragm spanning the cavity; and
forming an interdigital transducer (IDT) on the front surface of the piezoelectric plate such that interleaved fingers of the IDT are disposed on the diaphragm, the IDT configured to excite a shear primary acoustic mode in the diaphragm in response to a radio frequency signal applied to the IDT,
wherein the interleaved fingers have an irregular hexagon cross-sectional shape.