Transversely-excited film bulk acoustic resonators with counter chirped interdigital transducers (IDTs) for mechanical and process compensation

1 . An acoustic resonator, comprising:

a piezoelectric layer having first and second surfaces that oppose each other, the second surface facing a substrate, the piezoelectric layer including a diaphragm that is over a cavity; and

a conductor pattern on at least one of the first and second surfaces, the conductor pattern comprising an interdigital transducer (IDT) having interleaved fingers on the diaphragm of the piezoelectric layer,

wherein at least one of a pitch of the interleaved fingers or a mark of the interleaved fingers varies over an area of the IDT,

wherein the pitch is a center-to-center spacing between adjacent fingers of the interleaved fingers of the IDT, and the mark is a width of at least one finger of the interleaved fingers of the IDT, and

wherein the at least one of the pitch or the mark of the interleaved fingers of the IDT varies according to p′ i =(p′ 2 −h i 2 ) 1/2 , where i is an integer representing the pitch between the adjacent fingers or the mark of the at least one finger, p′i is a counter pitch or mark variation for the at least one finger, p′ is a length along a direction of a distortion of the at least one finger, and h is a height of the distortion of the at least one finger.

2 . The acoustic resonator of claim 1 , wherein:

the piezoelectric layer and the IDT are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm, such that a direction of acoustic energy flow excited in the diaphragm is substantially orthogonal to the first and second surfaces of the piezoelectric layer, and

the pitch and the mark of the interleaved fingers vary over the diaphragm to compensate for bowing of the diaphragm due to process stress or temperature changes during use.

3 . The acoustic resonator of claim 1 , wherein:

an overlapping distance of the interleaved fingers defines an aperture of the acoustic resonator, and

at any point along a length of the IDT, the at least one of the pitch or the mark of the IDT varies across the aperture of the IDT.

4 . The acoustic resonator of claim 3 , wherein the at least one of the pitch or the mark varies across all of the interleaved fingers of the IDT.

5 . The acoustic resonator of claim 1 , wherein the at least one of a pitch of the interleaved fingers and the mark of the interleaved fingers varies in a direction tangential to a length of the interleaved fingers.

6 . The acoustic resonator of claim 5 , wherein the at least one of the pitch of the interleaved fingers or the mark of the interleaved fingers varies to compensate for a distortion of the diaphragm, which is due to one of a mechanical displacement or a stress that varies along the direction tangential to the length of the interleaved fingers of the IDT.

7 . The acoustic resonator of claim 6 , wherein the distortion of the diaphragm is divided along a length of the diaphragm into two or more sections, with each section having a distortion different from a distortion of each other section.

8 . The acoustic resonator of claim 7 , wherein the distortion of the diaphragm is p′ i =(p′ 2 −h i 2 ) 1/2 , for the two or more sections.

9 . A filter device, comprising:

a piezoelectric layer having first and second surfaces that oppose each other, the second surface facing a substrate, portions of the piezoelectric layer forming a plurality of diaphragms that are over respective cavities in an intermediate layer of the substrate;

a conductor pattern on at least one of the first and second surfaces, the conductor pattern comprising a plurality of interdigital transducers (IDTs) that each have interleaved fingers on a respective diaphragm of the plurality of diaphragms,

wherein at least one of a pitch or a mark of the interleaved fingers of each IDT varies over the respective diaphragm,

wherein the pitch is a center-to-center spacing between adjacent fingers of the interleaved fingers of at least one IDT of the plurality of IDTs, and the mark is a width of at least one finger of the interleaved fingers of the at least one IDT, and

wherein the at least one of the pitch or the mark of the interleaved fingers of the IDT varies according to p′ i =(p′ 2 −h i 2 ) 1/2 , where i is an integer representing the pitch between the adjacent fingers or the mark of the at least one finger, p′ i is a counter pitch or mark variation for the at least one finger, p′ is a length along a direction of a distortion of the at least one finger, and h is a height of the distortion of the at least one finger.

10 . The filter device of claim 9 , wherein the piezoelectric layer and the plurality of IDTs are configured such that a respective radio frequency signal applied to each IDT excites a primary shear acoustic mode in the respective diaphragm of the plurality of diaphragms, such that a direction of acoustic energy flow excited in the diaphragm is substantially orthogonal to the first and second surfaces of the piezoelectric layer.

11 . The filter device of claim 9 , wherein:

the piezoelectric layer and each of the plurality of IDTs are configured such that a radio frequency signal applied to each IDT of the plurality of IDTs excites a primary shear acoustic mode in the respective diaphragm, and

the pitch and the mark vary over the respective diaphragm to compensate for bowing of the diaphragm due to process stress or temperature changes during use.

12 . The filter device of claim 9 , wherein:

an overlapping distance of the interleaved fingers of each IDT of the plurality of IDTs defines an aperture of the respective IDT, and

at any point along a length of the IDT, the at least one of the pitch or the mark of the IDT varies across the aperture of the IDT.