Transversely-excited film bulk acoustic resonator with multi-pitch interdigital transducer

Patent metadata

Field	Value
Publication number	US-12506462-B2
Application number	US-202017093239-A
Country	US
Kind code	B2
Filing date	Nov 9, 2020
Priority date	Feb 28, 2020
Publication date	Dec 23, 2025
Grant date	Dec 23, 2025

Abstract

There are disclosed acoustic resonators. An acoustic resonator includes a single-crystal piezoelectric plate having front and back surfaces, the back surface attached to a surface of a substrate except for a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate. A conductor pattern on the front surface includes a multi-pitch interdigital transducer (IDT) with interleaved fingers of the IDT disposed on the diaphragm.

First claim

It is claimed:

1 . A filter device comprising:
a plurality of bulk acoustic wave resonators that each comprise:
a piezoelectric layer having front and back surfaces, the back surface attached to a surface of a substrate either directly or via one or more intermediate layers, the piezoelectric layer having a portion that forms a diaphragm over a cavity of the bulk acoustic wave resonator; and
a conductor pattern on the piezoelectric layer and comprising an interdigital transducer (IDT) having interleaved fingers on the diaphragm,
wherein each IDT of all of the plurality of bulk acoustic wave resonators is a multi-pitch IDT, wherein pitch is a center-to-center spacing between any adjacent interleaved fingers extending from opposing busbars of the respective IDT, wherein each of a first IDT of a first bulk acoustic wave resonator of the plurality of bulk acoustic wave resonators and a second IDT of a second bulk acoustic wave resonator of the plurality of bulk acoustic wave resonators is divided along a length of the respective IDT into at least three sections, with each of a first section, a second section, and a third section of the first IDT and the second IDT having multiple pairs of interleaved fingers, wherein the multiple pairs of interleaved fingers from each section each have a pitch that is different from respective pitches of the other sections of the at least three sections, wherein the first, second and third sections of each of the first IDT and the second IDT have essentially an equal number of interleaved fingers as each other, and a mark of the interleaved fingers in each of the first, second and third sections is constant in each section and across each of the first, second and third sections, wherein the respective pitch of the multiple pairs of interleaved fingers in each of the first, second and third sections is constant, wherein the filter device is a ladder circuit with the first IDT forming a series resonator of the ladder circuit and the second IDT forming a shunt resonator of the ladder circuit, and wherein a change in the pitch between the at least three sections of each of the plurality of bulk acoustic wave resonators has a smaller effect on a primary shear acoustic mode of all of the at least three sections of each bulk acoustic wave resonator in comparison to an effect that the change in pitch has on a spurious acoustic mode other than the primary shear acoustic mode of all of the at least three sections of each of the first IDT and the second IDT.

2 . The filter device of claim 1 , wherein the piezoelectric layer and IDTs of the plurality of bulk acoustic wave resonators are configured such that a radio frequency signal applied to each IDT excites the primary shear acoustic mode in the diaphragm, the primary shear acoustic mode being a bulk shear mode where acoustic energy propagates along a direction substantially orthogonal to the front and back surfaces of the piezoelectric layer that is lateral to a direction of an electric field generated by the IDT, and wherein atomic motions excited by the electric field are predominantly parallel to the front and back surfaces of the respective piezoelectric layer.

3 . The filter device of claim 1 , wherein a number of the at least three sections of the first IDT is different than a number of the at least three sections of the second IDT.

4 . The filter device of claim 1 , wherein, for at least one of the first IDT and the second IDT, a variance in the pitch of the at least three sections is between 7.5 times a thickness of the piezoelectric layer and 15 times a thickness of the piezoelectric layer.

5 . The filter device of claim 1 , wherein the respective IDTs of the plurality of bulk acoustic wave resonators are configured to have admittance characteristics such that the spurious acoustic mode would at least partially be canceled out if the first bulk acoustic wave resonator were placed in parallel with the second bulk acoustic wave resonator.

6 . The filter device of claim 1 , wherein the first, second and third sections of each of the first IDT and the second IDT have essentially an equal number of interleaved fingers as each other.

7 . The filter device of claim 1 , wherein a mark of each of the interleaved fingers is a width of each of the interleaved fingers within each of the first, second, and third sections of each of the first IDT and the second IDT, respectively, and wherein the mark of the interleaved fingers in each of the first, second and third sections of the second IDT is constant in each section and across each of the first, second and third sections.

8 . The filter device of claim 1 , wherein, for each of the first IDT and the second IDT, the second section is between the first and third sections along the length of the IDT, and a pitch of the first section is p(1+δ), a pitch of the second section is p, and a pitch of the third section is p(1−δ), and δ of the second IDT of the shunt resonator is greater than δ of the first IDT of the series resonator.

9 . The filter device of claim 1 , wherein the smaller effect is a smaller change in primary shear acoustic mode amplitude than a change in spurious acoustic mode amplitude.

10 . A filter device comprising:
a plurality of bulk acoustic wave resonators that each comprise:
a piezoelectric layer having front and back surfaces, the back surface attached to a surface of a substrate either directly or via one or more intermediate layers, the piezoelectric layer having a portion that forms a diaphragm over a cavity of the bulk acoustic wave resonator; and
a conductor pattern on the piezoelectric layer and comprising an interdigital transducer (IDT) having interleaved fingers on the diaphragm, wherein the interleaved fingers extend from opposing busbars,
wherein a first IDT of a first bulk acoustic wave resonator of the plurality of bulk acoustic wave resonators is a multi-pitch IDT that is divided along a length of the multi-pitch IDT into at least three sections, with each of a first section, a second section and a third section of the first IDT having at least one pair of interleaved fingers that each has a pitch that has a variation from respective pitches of the other sections, and wherein pitch is center-to-center spacing between the at least one pair of interleaved fingers, wherein the at least one pair interleaved fingers are adjacent interleaved fingers extending from opposing busbars of the first IDT, wherein a second IDT of a second bulk acoustic wave resonator of the plurality of bulk acoustic wave resonators is a multi-pitch IDT that is divided along a length of the multi-pitch IDT into at least three sections, with each of a first section, a second section and a third section of the second IDT having at least one pair of interleaved fingers that each has a pitch that has a variation from respective pitches of the other sections, and wherein pitch is center-to-center spacing between the at least one pair of interleaved fingers, wherein the at least one pair interleaved fingers are adjacent interleaved fingers extending from opposing busbars of the second IDT, wherein the filter device is a ladder circuit with the first IDT forming a series resonator of the ladder circuit and the second IDT forming a shunt resonator of the ladder circuit, wherein the respective pitch in each of the first, second and third sections of each of the first IDT and the second IDT is constant, and wherein the variation of the pitch between the at least three sections of each of the plurality of bulk acoustic wave resonators has a smaller effect on a primary shear acoustic mode of each respective bulk acoustic wave resonator in comparison to an effect that the variation of pitch

Assignees

• Murata Manufacturing Co

Inventors

• Garcia Bryant

Classifications

• H03H9/174

  Membranes · CPC title

• H03H9/564

  implemented with thin-film techniques · CPC title

• H03H9/568

  consisting of a ladder configuration · CPC title

• H03H9/02228

  Guided bulk acoustic wave devices or Lamb wave devices having interdigital transducers situated in parallel planes on either side of a piezoelectric layer · CPC title

• H03H9/132 Primary

  characterized by a particular shape · CPC title