TRANSVERSELY-EXCITED FILM BULK ACOUSTIC RESONATORS WITH ELECTRODES HAVING IRREGULAR HEXAGON CROSS-SECTIONAL SHAPES

1 . An acoustic resonator comprising:

a piezoelectric layer; and

an interdigital transducer (IDT) having interleaved fingers on a surface of the piezoelectric layer,

wherein at least one finger of the interleaved fingers has an irregular hexagon cross-sectional shape, and

wherein sides of the irregular hexagon cross-sectional shape are not all a same length.

2 . The acoustic resonator of claim 1 , further comprising:

a substrate that includes a base and an intermediate layer connecting the base to the piezoelectric layer,

wherein the intermediate layer includes a cavity formed therein, and the piezoelectric layer includes a diaphragm over the cavity with the interleaved fingers on the diaphragm.

3 . The acoustic resonator of claim 2 , wherein the IDT is configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm, the primary shear acoustic mode being a bulk shear mode in which acoustic energy propagates along a direction substantially orthogonal to a surface of the piezoelectric layer and that is transverse to a direction of an electric field created by the interleaved fingers.

4 . The acoustic resonator of claim 1 , wherein the irregular hexagon cross-sectional shape comprises:

a lower portion comprising a first three sides of the irregular hexagon cross-sectional shape; and

an upper portion comprising a second three sides of the irregular hexagon cross-sectional shape,

wherein the lower portion is comprised of a different material than the upper portion, and the lower portion is between the upper portion and the piezoelectric layer.

5 . The acoustic resonator of claim 4 , wherein a thickness of the upper portion is greater than a thickness of the lower portion.

6 . The acoustic resonator of claim 4 , wherein a thickness of the lower portion is in a range from 5% to 40% of a thickness of the piezoelectric layer.

7 . The acoustic resonator of claim 4 , wherein a thickness of the upper portion is in a range from 25% to 75% of the thickness of the piezoelectric layer.

8 . The acoustic resonator of claim 4 , wherein a sidewall of the lower portion is at an angle θ 1 to the piezoelectric layer, and a sidewall of the upper portion is at an angle θ 2 , and wherein one or more of θ 1 angle and angle θ 2 is in a range from 70 degrees to less than 90 degrees.

9 . An acoustic resonator comprising:

a substrate comprising a base and an intermediate layer;

a piezoelectric layer; and

an interdigital transducer (IDT) having interleaved fingers on a portion of the piezoelectric layer over a cavity in the intermediate layer,

wherein at least one finger of the interleaved fingers has an irregular hexagon cross-sectional shape.

10 . The acoustic resonator of claim 9 , wherein the at least one finger comprises a first portion and a second portion, and wherein the first portion is disposed between the piezoelectric layer and a second portion.

11 . The acoustic resonator of claim 10 , wherein:

the first portion is a lower portion comprising a first three sides of the irregular hexagon cross-sectional shape; and

the second portion is an upper portion comprising a second three sides of the irregular hexagon cross-sectional shape that are over the lower portion, and

the lower portion is comprised of a different material than the upper portion.

12 . The acoustic resonator of claim 10 , wherein a thickness of the first portion is greater than a thickness of the second portion.

13 . The acoustic resonator of claim 10 , wherein a thickness of the first portion is in a range from 5% to 40% of a thickness of the piezoelectric layer.

14 . The acoustic resonator of claim 10 , wherein a thickness of the second portion is in a range from 25% to 75% of the thickness of the piezoelectric layer.

15 . The acoustic resonator of claim 11 , wherein a sidewall of the first portion is at an angle θ 1 to the piezoelectric layer, and a sidewall of the second portion is at an angle θ 2 , and wherein one or more of angle θ 1 and angle θ 2 is in a range from 70 degrees to less than 90 degrees.

16 . The acoustic resonator of claim 9 , wherein the irregular hexagon cross-sectional shape has at least two sides that are not a same length.

17 . The acoustic resonator of claim 9 , wherein sides of the irregular hexagon cross-sectional shape are not all a same length.

18 . The acoustic resonator of claim 9 , further comprising a dielectric layer having a thickness tfd and that is disposed on the piezoelectric layer, and wherein a total thickness defined by a thickness of the piezoelectric layer ts and the thickness tfd is between 300 nm and 500 nm.

19 . The acoustic resonator of claim 9 , wherein:

a thickness of the interleaved fingers of the IDT is greater than or equal to 0.25 times a thickness ts of the piezoelectric layer and less than or equal to 2.5 times the thickness ts of the piezoelectric layer, and

a pitch is greater than or equal to 6 times the thickness ts and less than or equal to 12.5 times the thickness ts,

the pitch is a center-to-center spacing of two adjacent interleaved fingers extending from opposing busbars, and

thickness is measured in a direction substantially orthogonal to a surface of the piezoelectric layer.

20 . A filter device comprising:

a plurality of bulk acoustic resonators that each comprise:

a piezoelectric layer; and

an interdigital transducer (IDT) having interleaved fingers on a surface of the piezoelectric layer,

wherein at least one finger of the interleaved fingers has an irregular hexagon cross-sectional shape, and

wherein sides of the irregular hexagon cross-sectional shape are not all a same length.