# US 11,998,950 B2 · Increased MUT coupling efficiency and bandwidth via edge groove, virtual pivots, and free boundaries

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- Number: US 11,998,950 B2
- Document ID: US11998950B2
- Status: Granted
- Kind: B2
- Application number: 17/018,304
- Filed: 2020-09-11
- Published: 2021-03-18
- Granted: 2024-06-04
- Earliest claimed: 2019-09-12
- Assignees: Exo Imaging, Inc.
- Applicants: eXo Imaging, Inc.
- Inventors: Brian Bircumshaw; Sandeep Akkaraju; Haesung Kwon
- Web page: https://patentgrep.com/patent/US11998950B2

## CPC

- B06B 1/0651: {of circular shape}
- B06B 1/0292: {Electrostatic transducers, e.g. electret-type}
- B06B 1/0662: {with an electrode on the sensitive surface}
- B06B 1/0666: {used as a diaphragm}
- H10N 30/50: having a stacked or multilayer structure
- H10N 30/871: {Single-layered electrodes of multilayer piezoelectric or electrostrictive devices, e.g. internal electrodes}
- H10N 30/708: {Intermediate layers, e.g. barrier, adhesion or growth control buffer layers}
- H10N 30/877: {Conductive materials}
- B06B: METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, {e.g.} FOR PERFORMING MECHANICAL WORK IN GENERAL (for particular applications, see the relevant subclasses, e.g. B07B1/40, B23Q17/12, B24B31/06; measurement of mechanical vibrations G01H; in direction finding, locating, distance or velocity measuring G01S; {generating seismic energy G01V1/02}; control of mechanical vibrations in general G05D; sound-producing devices, e.g. bells, sirens, whistles G10K, {e.g. methods or devices for transmitting, conducting, or directing sound in general G10K11/00}; generation of electrical oscillations H03B; electromechanical resonators in general H03H; electromechanical transducers {for communication techniques, e.g. microphones, speakers} H04R)
- H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR

## Abstract

Methods for improving the electromechanical coupling coefficient and bandwidth of micromachined ultrasonic transducers, or MUTs, are presented as well as methods of manufacture of the MUTs improved by the presented methods.

## Claims

### Claim 1

A micromachined ultrasonic transducer (MUT) comprising (i) a piezoelectric stack comprising a top electrode, a bottom electrode, and a piezoelectric layer disposed therebetween and (ii) a diaphragm disposed below the piezoelectric stack and comprising a groove that is disposed within the diaphragm and at least partially surrounds the piezoelectric stack.

### Claim 2 (depends on 1)

The MUT of claim 1, wherein the MUT is a pMUT.

### Claim 3 (depends on 2)

The MUT of claim 2, wherein the groove is within 20 diaphragm thicknesses of a diaphragm boundary, and wherein the groove has a width no larger than 10 diaphragm thicknesses, and wherein the groove has a depth of between 1% to 100% of the diaphragm thickness.

### Claim 4 (depends on 3)

The MUT of claim 3, wherein the groove has a constant width.

### Claim 5 (depends on 3)

The MUT of claim 3, wherein the groove has a variable width.

### Claim 6 (depends on 3)

The MUT of claim 3, wherein the groove is disrupted at one or more locations to allow for electrical routing.

### Claim 7 (depends on 6)

The MUT of claim 6, wherein the MUT is multimodal.

### Claim 8 (depends on 7)

A MUT array configured for ultrasound imaging, the array comprising a plurality of the MUTs of claim 7.

### Claim 9 (depends on 1)

The MUT of claim 1, wherein the MUT is a cMUT.

### Claim 10 (depends on 9)

The MUT of claim 9, wherein the groove is within 20 diaphragm thicknesses of a diaphragm boundary, and wherein the groove has a width no larger than 10 diaphragm thicknesses, and wherein the groove has a depth of between 1% to 100% of the diaphragm thickness.

### Claim 11 (depends on 10)

The MUT of claim 10, wherein the groove has a constant width.

### Claim 12 (depends on 10)

The MUT of claim 10, wherein the groove has a variable width.

### Claim 13 (depends on 10)

The MUT of claim 10, wherein the groove is disrupted at one or more locations to allow for electrical routing.

### Claim 14 (depends on 13)

The MUT of claim 13, wherein the MUT is multimodal.

### Claim 15 (depends on 14)

A MUT array configured for ultrasound imaging, the array comprising a plurality of the MUTs of claim 14.

### Claim 16 (depends on 1)

The MUT of claim 1, wherein the groove comprises one or more grooves.

### Claim 17 (depends on 16)

The MUT of claim 16, wherein all of the one or more grooves are disposed inside of a diaphragm boundary.

### Claim 18 (depends on 16)

The MUT of claim 16, wherein all of the one or more grooves are disposed outside of a diaphragm boundary.

### Claim 19 (depends on 16)

The MUT of claim 16, wherein the one or more grooves comprises at least a first groove disposed inside a diaphragm boundary and at least a second groove disposed outside of the diaphragm boundary.

### Claim 20

A micromachined ultrasonic transducer (MUT) comprising:
a substrate that forms a diaphragm, the diaphragm having a vertical thickness;
one or more electrodes located on or near the diaphragm; and
a groove cut into the diaphragm and at least partially surrounding the one or more electrodes, the groove having a depth that does not cut entirely through the vertical thickness of the diaphragm.

### Claim 21 (depends on 20)

The MUT of claim 20, wherein the MUT is a pMUT comprising a piezoelectric film.

### Claim 22 (depends on 21)

The MUT of claim 21, wherein the one or more electrodes are electrically coupled to the piezoelectric film.

### Claim 23 (depends on 20)

The MUT of claim 20, wherein the MUT is a cMUT.

### Claim 24 (depends on 23)

The MUT of claim 23, wherein the one or more electrodes are electrically coupled to the diaphragm between a gap.

### Claim 25 (depends on 21)

The MUT of claim 21, further comprising one or more anchors clamping the diaphragm.

### Claim 26 (depends on 25)

The MUT of claim 25, wherein the piezoelectric film is situated opposite the one or more anchors.

### Claim 27 (depends on 25)

The MUT of claim 25, wherein the piezoelectric film is situated on the same side as the one or more anchors.

### Claim 28 (depends on 25)

The MUT of claim 25, wherein the piezoelectric film is between the one or more anchors and the diaphragm.

### Claim 29 (depends on 20)

The MUT of claim 20, further comprising a plurality of anchors, wherein a subset of the plurality of anchors are attached to one or more vertical cantilever shells.

### Claim 30 (depends on 20)

The MUT of claim 20, wherein the groove completely surrounds the one or more electrodes without a break in the groove.

### Claim 31 (depends on 20)

The MUT of claim 20, wherein the groove is broken up to discontinuously surround the one or more electrodes.

### Claim 32 (depends on 1)

The MUT of claim 1, further comprising a substrate and an insulating layer.

### Claim 33 (depends on 32)

The MUT of claim 32, wherein the diaphragm is supported by the substrate.

### Claim 34 (depends on 32)

The MUT of claim 32, wherein the diaphragm is formed as a portion of the substrate.

### Claim 35 (depends on 32)

The MUT of claim 32, wherein the substrate comprises a cavity, the diaphragm being supported by the substrate above the cavity.

### Claim 36 (depends on 1)

The MUT of claim 1, further comprising an insulating layer disposed between the diaphragm and the piezoelectric stack.

### Claim 37 (depends on 36)

The MUT of claim 36, wherein the insulating layer comprises a dielectric layer.

### Claim 38 (depends on 1)

The MUT of claim 1, wherein the piezoelectric stack is disposed entirely within by a cylinder defined as a vertical projection of the groove upwardly from the diaphragm.

### Claim 39 (depends on 1)

The MUT of claim 1, wherein the piezoelectric stack defines a perimeter that is circumscribed by the groove when seen in a top view.

### Claim 40 (depends on 39)

The MUT of claim 39, wherein at least one of the top electrode, the bottom electrode, or the piezoelectric layer comprises a circular profile when seen in top view.

### Claim 41 (depends on 40)

The MUT of claim 40, wherein the top electrode, the bottom electrode, and the piezoelectric layer have different circular profiles compared to each other when seen in top view.

### Claim 42 (depends on 1)

The MUT of claim 1, wherein the top electrode, the bottom electrode, and the piezoelectric layer each defines a respective perimeter, the perimeter of the top electrode being circumscribed by the perimeter of the piezoelectric layer, the perimeter of the piezoelectric layer being circumscribed by the perimeter of the bottom electrode, the perimeter of the bottom electrode being circumscribed by the groove.

### Claim 43 (depends on 1)

The MUT of claim 1, wherein the groove has a depth that does not cut entirely through a vertical thickness of the diaphragm.

### Claim 44 (depends on 1)

The MUT of claim 1, wherein the groove has a depth of about 0.01% to about 100% of a vertical thickness of the diaphragm.

### Claim 45 (depends on 1)

The MUT of claim 1, further comprising a trench extending into a substrate, the groove being disposed between the trench and the piezoelectric stack when seen in a side view.

### Claim 46 (depends on 1)

The MUT of claim 1, wherein the groove completely surrounds the piezoelectric stack without a break in the groove.

### Claim 47 (depends on 1)

The MUT of claim 1, wherein the groove is broken up to discontinuously surround the piezoelectric stack.

### Claim 48

A micromachined ultrasonic transducer (MUT) comprising a piezoelectric stack and a substrate, the piezoelectric stack comprising a top electrode, a bottom electrode, and a piezoelectric layer disposed between the top and bottom electrodes, the substrate comprising an upper surface that supports the piezoelectric stack and a channel that extends into the substrate and at least partially surrounds the piezoelectric stack.

### Claim 49 (depends on 48)

The MUT of claim 48, wherein the substrate comprises a cavity cut into the substrate that forms a diaphragm located above the cavity.

### Claim 50 (depends on 49)

The MUT of claim 49, further comprising a buried insulator layer disposed immediately below the diaphragm.

### Claim 51 (depends on 49)

The MUT of claim 49, wherein the channel comprises a groove having a depth of about 0.01% to about 100% of a vertical thickness of the diaphragm.

### Claim 52 (depends on 49)

The MUT of claim 49, wherein a diaphragm boundary is defined by an edge of the cavity and a diaphragm thickness is defined by a height of the cavity.

### Claim 53 (depends on 52)

The MUT of claim 52, wherein the channel comprises a groove located within the diaphragm boundary that has a depth that is less than the diaphragm thickness.

### Claim 54 (depends on 52)

The MUT of claim 52, wherein the channel comprises a groove located outside of the diaphragm boundary that has a depth that is less than the diaphragm thickness.

### Claim 55 (depends on 52)

The MUT of claim 52, wherein the channel comprises a trench located outside of the diaphragm boundary that has a depth that is greater than or equal to the diaphragm thickness.

### Claim 56 (depends on 53)

The MUT of claim 53, wherein the channel further comprises a trench extending into the substrate outside the diaphragm boundary, the groove being disposed between the trench and the piezoelectric stack when seen in a side view.

### Claim 57 (depends on 54)

The MUT of claim 54, wherein the channel further comprises a trench extending into the substrate outside the diaphragm boundary, the groove being disposed between the trench and the piezoelectric stack when seen in a side view.

### Claim 58 (depends on 54)

The MUT of claim 54, wherein the channel further comprises a trench extending into the substrate outside the diaphragm boundary, the trench being disposed between the groove and the piezoelectric stack when seen in a side view.

### Claim 59 (depends on 53)

The MUT of claim 53, wherein the channel further comprises one or more grooves.

### Claim 60 (depends on 48)

The MUT of claim 48, wherein the channel completely surrounds the piezoelectric stack without a break in the channel.

### Claim 61 (depends on 48)

The MUT of claim 48, wherein the channel is broken up to discontinuously surround the piezoelectric stack.