# US 7,745,973 B2 · Acoustic crosstalk reduction for capacitive micromachined ultrasonic transducers in immersion

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- Number: US 7,745,973 B2
- Document ID: US7745973B2
- Status: Granted
- Kind: B2
- Application number: 11/789,210
- Filed: 2007-04-23
- Published: 2008-10-23
- Granted: 2010-06-29
- Earliest claimed: 2006-05-03
- Assignees: The Board of Trustees of the Leland Stanford Junior University
- Inventors: Baris Bayram; Butrus T. Khuri-Yakub
- Web page: https://patentgrep.com/patent/US7745973B2

## CPC

- B06B 1/0292: {Electrostatic transducers, e.g. electret-type}
- 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)

## Abstract

A reduced crosstalk capacitive micromachined ultrasonic transducer (CMUT) array is provided. The CMUT array has at least two CMUT array elements deposited on a substrate, at least one CMUT cell in the array element, a separation region between adjacent CMUT array elements, and a membrane formed in the separation region. The membrane reduces crosstalk between adjacent array elements, where the crosstalk is a dispersive guided mode of an ultrasonic signal from the CMUT propagating in a fluid-solid interface of the CMUT array. Each cell has an insulation layer deposited to the substrate. A cell membrane layer is deposited to the insulation layer, where the cell membrane layer has a vacuum gap therein. The cells further have an electrode layer deposited to a portion of the membrane layer, and a passivation layer deposited to the electrode layer, the cell membrane layer and to the insulation layer.

## Claims

### Claim 1

A reduced crosstalk capacitive micromachined ultrasonic transducer (CMUT) array comprising:
a. at least two CMUT array elements deposited on a substrate;
b. at least one CMUT cell in said array element;
c. a separation region between adjacent said CMUT array elements; and
d. a membrane formed in said separation region, whereby said membrane reduces crosstalk between said adjacent array elements, whereas said crosstalk comprises a dispersive guided mode of an ultrasonic signal from said CMUT propagating in a fluid-solid interface of said CMUT array.

### Claim 2 (depends on 1)

The CMUT array of claim 1, wherein all said separation regions between said elements are substantially the same, whereby forming a substantial periodicity of said CMUT elements within said CMUT array.

### Claim 3 (depends on 2)

The CMUT array of claim 2, wherein said periodicity of said array elements is in one dimension.

### Claim 4 (depends on 2)

The CMUT array of claim 2, wherein said periodicity of said array elements is in two dimensions.

### Claim 5 (depends on 1)

The CMUT array of claim 1, wherein all said membranes in said separation regions are substantially the same, whereby forming a substantial periodicity of said CMUT elements within said CMUT array.

### Claim 6 (depends on 1)

The CMUT array of claim 1, wherein all said CMUT cells within said elements are substantially the same, whereby forming a substantial periodicity of said CMUT cells within said CMUT element.

### Claim 7 (depends on 1)

The CMUT array of claim 1, wherein said CMUT operates in a conventional mode or a collapsed mode to transmit and receive ultrasound.

### Claim 8 (depends on 1)

The CMUT array of claim 1, wherein said CMUT cell comprises:
a. an insulation layer deposited to said substrate;
b. a cell membrane layer deposited to said insulation layer, wherein said cell membrane layer has a gap therein;
c. an electrode layer deposited to said membrane layer, wherein said electrode layer covers a portion of said membrane layer; and
d. a passivation layer, wherein said passivation layer is deposited to;
i. said electrode layer;
ii. said cell membrane layer; and
iii. said insulation layer.

### Claim 9 (depends on 8)

The CMUT array of claim 8, wherein said CMUT cell has a geometry selected from a group consisting of circular, square, hexagonal and tented.

### Claim 10 (depends on 8)

The CMUT array of claim 8, wherein said insulation layer is a layer selected from a group consisting of silicon nitride and silicon oxide.

### Claim 11 (depends on 8)

The CMUT array of claim 8, wherein said membrane layer is a layer selected from a group consisting of silicon nitride and silicon oxide.

### Claim 12 (depends on 8)

The CMUT array of claim 8, wherein said electrode layer is a layer selected from a group consisting of aluminum and gold.

### Claim 13 (depends on 8)

The CMUT array of claim 8, wherein said passivation layer is a layer selected from a group consisting of silicon nitride and silicon oxide.

### Claim 14 (depends on 8)

The CMUT array of claim 8, wherein said gap is a vacuum gap.