Wide bandwidth temperature-compensated transversely-excited film bulk acoustic resonator

1. An acoustic resonator device comprising:

a substrate having a surface;

a lithium niobate (LN) plate having front and back surfaces, the back surface attached to the surface of the substrate except for a portion of the LN plate forming a diaphragm that spans a cavity in the substrate;

an interdigital transducer (IDT) formed on the front surface of the LN plate such that interleaved fingers of the IDT are disposed on the diaphragm, the LN plate and the IDT configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode in the diaphragm; and

a half-lambda dielectric layer formed on one of the front surface and the back surface of the diaphragm, wherein

Euler angles of the LN plate are [0°, β, 0°], where 20°≤β≤25°.

2. The acoustic resonator device of claim 1 , wherein

Euler angles of the LN plate are substantially equal to [0°, 23°, 0°].

3. The acoustic resonator device of claim 1 , wherein

the dielectric layer is SiO 2 , and

a thickness is of the LN plate and a thickness td of the dielectric layer are related as follows:

0.875ts≤td≤1.25ts.

4. The acoustic resonator device of claim 1 , wherein

the dielectric layer is one or more of SiO 2 , Si 3 N 4 , Al 2 O 3 , and AlN.

5. The acoustic resonator device of claim 1 , wherein the LN 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. A filter device, comprising:

a substrate;

a lithium niobate (LN) plate having front and back surfaces, the back surface attached to the substrate except for portions of the LN plate forming a plurality of diaphragms that span respective cavities in the substrate;

a conductor pattern formed 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, interleaved IDT fingers of each of the plurality of IDTs disposed on respective diaphragms;

a first dielectric layer having a thickness tds deposited on one of the front surface and the back surface of the diaphragm of the series resonator; and

a second dielectric layer having a thickness tdp deposited one of the front surface and the back surface of the diaphragm of the shunt resonator, wherein

tdp is greater than tds, and

Euler angles of the LN plate are [0°, β, 0°], where 20°≤β≤25°.

7. The filter device of claim 6 , wherein

Euler angles of the LN plate are substantially equal to [0°, 23°, 0°].

8. The filter device of claim 6 , wherein

the first dielectric layer and the second dielectric layer are SiO 2 , and

tdp, tds, and a thickness ts of the LN plate are related by the equation:

0.875ts≤tds<tdp≤1.25ts.

9. The filter device of claim 6 , wherein

the first dielectric layer and the second dielectric layer are one or more of SiO 2 , Si 3 N 4 , Al 2 O 3 , and AlN.

10. The filter device of claim 6 , wherein the LN plate and all of the IDTs are configured such that a radio frequency signal applied to each IDT excites a respective shear primary acoustic mode within the respective diaphragm.

11. A filter device, comprising:

a substrate;

a lithium niobate plate having front and back surfaces and a thickness ts, the back surface attached to the substrate;

a conductor pattern formed on the front surface, the conductor pattern including a plurality of interdigital transducers (IDTs) of a respective plurality of resonators including a series resonator and a shunt resonator, interleaved fingers of each of the plurality of IDTs disposed on respective portions of the LN plate suspended over one or more cavities formed in the substrate;

a first SiO 2 layer having a thickness tds deposited on one of the front surface and the back surface of the diaphragm of the series resonator; and

a second SiO 2 layer having a thickness tdp deposited on one of the front surface and the back surface of the diaphragm of the shunt resonator, wherein

ts, tds, and tdp are related by the equation:

0.875ts≤tds<tdp≤1.25ts.

12. The filter device of claim 11 , wherein

Euler angles of the LN plate are [0°, β, 0°], where 20°≤β≤25°.

13. The filter device of claim 12 , wherein

Euler angles of the LN plate are substantially equal to [0°, 23°, 0°].

14. A method of fabricating an acoustic resonator device on a single-crystal lithium niobate (LN) plate having front and back surfaces, the back surface attached to a substrate, the method comprising:

forming a cavity in the substrate such that a portion of the LN plate forms a diaphragm spanning the cavity;

forming an interdigital transducer (IDT) on the front surface of the LN plate such that interleaved IDT fingers of the IDT are disposed on the diaphragm, the LN plate and the IDT configured such that a radio frequency signal applied to the IDT excites a shear primary acoustic mode within the diaphragm; and

forming a half-lambda dielectric layer on one of the front surface and the back surface of the diaphragm, wherein

Euler angles of the LN plate are [0°, β, 0°], where 20°≤β≤25°.

15. The method of claim 14 , wherein

Euler angles of the LN plate are substantially equal to [0°, 23°, 0°].

16. The method of claim 14 , wherein

the dielectric layer is SiO 2 , and

a thickness is of the LN plate and a thickness td of the dielectric layer are related as follows:

0.875ts≤td≤1.25ts.

17. The method of claim 14 , wherein

the dielectric layer is one or more of SiO 2 , Si 3 N 4 , Al 2 O 3 , and AlN.

18. The method of claim 14 , wherein the LN 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.