# US 11,909,381 B2 · Transversely-excited film bulk acoustic resonators with two-layer electrodes having a narrower top layer

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- Number: US 11,909,381 B2
- Document ID: US11909381B2
- Status: Granted
- Kind: B2
- Application number: 17/133,498
- Filed: 2020-12-23
- Published: 2021-04-29
- Granted: 2024-02-20
- Earliest claimed: 2018-06-15
- Assignees: Murata Manufacturing Co., Ltd.
- Applicants: Murata Manufacturing Co., Ltd
- Inventors: Viktor Plesski; Patrick Turner; Robert Hammond; Bryant Garcia; Ventsislav Yantchev; Neal Fenzi; Julius Koskela
- Web page: https://patentgrep.com/patent/US11909381B2

## CPC

- H03H 9/174: {Membranes}
- H03H 9/547: {Notch filters, e.g. notch BAW or thin film resonator filters}
- H03H 3/02: for the manufacture of piezoelectric or electrostrictive resonators or networks (H03H3/08 takes precedence)
- H03H 3/04: for obtaining desired frequency or temperature coefficient
- H03H 9/02015: {Characteristics of piezoelectric layers, e.g. cutting angles}
- H03H 9/02062: {Details relating to the vibration mode}
- H03H 9/02228: {Guided bulk acoustic wave devices or Lamb wave devices having interdigital transducers situated in parallel planes on either side of a piezoelectric layer}
- H03H 9/02559: {of lithium niobate or lithium-tantalate substrates}
- H03H 9/131: {consisting of a multilayered structure}
- H03H 9/132: {characterized by a particular shape}
- H03H 2003/023: {the resonators or networks being of the membrane type}
- H03H: IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS (waveguides, resonators, lines or other devices of the waveguide type H01P)

## Abstract

An acoustic resonator device, filter devices, and methods of making the same. An acoustic resonator device includes a substrate having a surface and a single-crystal piezoelectric plate having front and back surfaces, where the back surface is 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. The device further includes an interdigital transducer formed on the front surface of the piezoelectric plate, where interleaved fingers of the IDT disposed on the diaphragm are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm. The interleaved fingers include a first layer adjacent the diaphragm and a second layer over the first layer, the second layer having a narrower width than the first layer.

## Claims

### Claim 1

An acoustic resonator device comprising:
a substrate having a surface;
a single-crystal 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 formed on the front surface of the piezoelectric plate, interleaved fingers of the IDT disposed on the diaphragm configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the diaphragm,
wherein the interleaved fingers comprise a first layer adjacent the diaphragm and a second layer over the first layer, the second layer having a narrower width than the first layer.

### Claim 2 (depends on 1)

The device of claim 1, wherein the first layer is a different material than the second layer.

### Claim 3 (depends on 2)

The device of claim 2, wherein the first layer comprises a low transverse acoustic impedance metal.

### Claim 4 (depends on 2)

The device of claim 2, wherein the second layer comprises a high transverse acoustic impedance metal.

### Claim 5 (depends on 2)

The device of claim 2, wherein the first layer comprises aluminum or titanium.

### Claim 6 (depends on 2)

The device of claim 2, wherein the second layer comprises chromium or tungsten.

### Claim 7 (depends on 1)

The device of claim 1, wherein a thickness of the first layer is less than a thickness of the second layer.

### Claim 8 (depends on 1)

The device of claim 1, wherein the second layer has an irregular shape.

### Claim 9 (depends on 1)

The device of claim 1, wherein a direction of acoustic energy flow of the primary acoustic mode is substantially normal to the front and back surfaces of the diaphragm.

### Claim 10

A filter device comprising:
a substrate having a surface;
a single-crystal 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 comprise a first layer adjacent the one or more diaphragms and a second layer over the first layer, the second layer having a narrower width than the first layer.

### Claim 11 (depends on 10)

The device of claim 10, wherein the first layer is a different material than the second layer.

### Claim 12 (depends on 11)

The device of claim 11, wherein the first layer comprises a low transverse acoustic impedance metal.

### Claim 13 (depends on 11)

The device of claim 11, wherein the second layer comprises a high transverse acoustic impedance metal.

### Claim 14 (depends on 11)

The device of claim 11, wherein the first layer comprises aluminum or titanium.

### Claim 15 (depends on 11)

The device of claim 11, wherein the second layer comprises chromium or tungsten.

### Claim 16 (depends on 10)

The device of claim 10, wherein a thickness of the first layer is less than a thickness of the second layer.

### Claim 17 (depends on 10)

The device of claim 10, wherein the second layer has an irregular shape.

### Claim 18 (depends on 10)

The device of claim 10, wherein a direction of acoustic energy flow of the primary acoustic mode is substantially normal to the front and back surfaces of the one or more diaphragms.

### Claim 19 (depends on 10)

The device of claim 10, 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.

### Claim 20

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 primary acoustic mode in the diaphragm in response to a radio frequency signal applied to the IDT,
wherein the interleaved fingers comprise a first layer adjacent the diaphragm and a second layer over the first layer, the second layer having a narrower width than the first layer.

### Claim 21 (depends on 20)

The method of claim 20, wherein the first layer is a different material than the second layer.

### Claim 22 (depends on 21)

The method of claim 21, wherein the first layer comprises a low transverse acoustic impedance metal.

### Claim 23 (depends on 21)

The method of claim 21, wherein the second layer comprises a high transverse acoustic impedance metal.

### Claim 24 (depends on 21)

The method of claim 21, wherein the first layer comprises aluminum or titanium.

### Claim 25 (depends on 21)

The method of claim 21, wherein the second layer comprises chromium or tungsten.

### Claim 26 (depends on 20)

The method of claim 20, wherein a thickness of the first layer is less than a thickness of the second layer.

### Claim 27 (depends on 20)

The method of claim 20, wherein the second layer has an irregular shape.

### Claim 28 (depends on 20)

The method of claim 20, wherein a direction of acoustic energy flow of the primary acoustic mode is substantially normal to the front and back surfaces of the diaphragm.