US4533795A
Expired / Lapsed
US
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Integrated electroacoustic transducer
Assignee: Nokia Bell Labs
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Filing: 1983-07-07
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Granted: 1985-08-06
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Expires: 2003-07-07
Abstract
Abstract An electroacoustic transducer, primarily in the form of a capacitive microphone, for incorporation into a semiconductor substrate. The vibrating element comprises a largely nontensioned diaphragm, such as an epitaxial layer formed on the semiconductor substrate, so as to greatly reduce its mechanical stiffness. The substrate is etched away in the desired area to define the diaphragm and form an acoustic cavity. A continuous array of microscopic holes is formed in the backplate to cut down the lateral flow of air in the gap between capacitor electrodes. Narrow gaps made possible by the hole array allow low voltage diaphragm biasing. In at least one embodiment, the acoustic input can be provided through the air hole array. An acoustic port may be added to alter the frequency response of the device, and a back closure provided to act as a rear acoustic cavity and an EMI shield.
Inventors
- 👤 John C. Baumhauer, Jr.
- 👤 Harold J. Hershey
- 👤 Tommy L. Poteat
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-02 15:30
CPC Classifications
H; H04; H04R; H04R1/00; H04R1/06; G; G01; G01L; G01L9/00; G01L9/0041; G01L9/0072; G01L9/0073; H04R19/00; H04R19/005; H04R1/20; H04R1/22; H04R1/225; Y; Y10; Y10T; Y10T29/00; Y10T29/42
Claims Analysis
Total Claims: 29
Claim 1
Independent Claim
72 words
An electroacoustic transducer formed within a semiconductor substrate comprising an essentially nontensioned diaphragm comprising a semiconductor material having a mechanical bending moment stiffness such that it vibrates in response to an input signal at audio and/or ultrasonic frequencies; and a pair of electrodes placed with respect to said diaphragm so that the electric field between the electrodes varies in relationship with the vibrating diaphragm to permit conversion between electrical and acoustic signals.
Claim 2
Dependent Claim
72 words
An electroacoustic transducer formed within a semiconductor substrate comprising an essentially nontensioned diaphragm comprising a semiconductor material having a mechanical bending moment stiffness such that it vibrates in response to an input signal at audio and/or ultrasonic frequencies; and a pair of electrodes placed with respect to said diaphragm so that the electric field between the electrodes varies in relationship with the vibrating diaphragm to permit conversion between electrical and acoustic signals.
Claim 3
Dependent Claim
39 words
The device according to claim 1 wherein the transducer is a microphone and one of the electrodes is formed to vibrate with the diaphragm such that the capacitance varies in response to an acoustic signal incident on said diaphragm.
Claim 4
Dependent Claim
23 words
The device according to claim 2 wherein the diaphragm is a single crystalline epitaxial layer formed over the surface of a semiconductor substrate.
Claim 5
Dependent Claim
19 words
The device according to claim 3 wherein the thickness of the epitaxial layer is in the range 1-5 μm.
Claim 6
Dependent Claim
19 words
The device according to claim 2 wherein the area of the diaphragm is less than 5 mm 2 .
Claim 7
Dependent Claim
28 words
The device according to claim 1 wherein the effective mechanical lumped parameter stiffness of the diaphragm, associated with the diaphragm's linearly averaged deflection, is less than 5500 N/m.
Claim 8
Dependent Claim
31 words
The device according to claim 3 wherein the epitaxial layer is formed over a surface layer in the substrate which has a higher impurity concentration than the bulk of the substrate.
Claim 9
Dependent Claim
56 words
The device according to claim 1 wherein an air gap is formed between the two electrodes and the device further comprises a continuous array of small holes extending through one of the electrodes to the air gap, said array covering essentially the entire area of that portion of the electrode which is co-extensive with the diaphragm.
Claim 10
Dependent Claim
25 words
The device according to claim 1 wherein the transducer is adapted for operation with a dc bias across the electrodes of less than 5 volts.
Claim 11
Dependent Claim
107 words
The device according to claim 1 wherein an air gap is formed between the electrodes and the device further comprises: a front acoustic cavity defined by a portion of the semiconductor substrate adjacent to the diaphragm; a rear acoustic cavity adjacent to one of the electrodes and defined by a member which also shields the transducer from electromagnetic interference; acoustic venting means comprising an array of holes connecting the air gap to the back acoustic cavity; and an acoustic port defined by an element adjacent to the front acoustic cavity, the size of the port being such as to produce a desired frequency characteristic for the transducer.
Claim 12
Dependent Claim
128 words
An electroacoustic transducer formed within a semiconductor substrate comprising: a diaphragm which vibrates in response to an input signal at audio and/or ultrasonic frequencies; a pair of electrodes placed with respect to said diaphragm so that the electric field between the electrodes varies in relation to the vibrating diaphragm to permit conversion between electrical and acoustic signals, the electrodes defining an air gap therebetween; and acoustic venting means comprising a continuous array of small holes extending through one of the electrodes to the air gap, said array covering essentially the entire area of that electrode which is co-extensive with the diaphragm, where the density of the holes in the array is at least 50 per mm 2 and the diameter of the holes is less than 100 μm.
Claim 13
Dependent Claim
128 words
An electroacoustic transducer formed within a semiconductor substrate comprising: a diaphragm which vibrates in response to an input signal at audio and/or ultrasonic frequencies; a pair of electrodes placed with respect to said diaphragm so that the electric field between the electrodes varies in relation to the vibrating diaphragm to permit conversion between electrical and acoustic signals, the electrodes defining an air gap therebetween; and acoustic venting means comprising a continuous array of small holes extending through one of the electrodes to the air gap, said array covering essentially the entire area of that electrode which is co-extensive with the diaphragm, where the density of the holes in the array is at least 50 per mm 2 and the diameter of the holes is less than 100 μm.
Claim 14
Dependent Claim
39 words
The device according to claim 11 wherein the transducer is a microphone and one of the electrodes is formed to vibrate with the diaphragm such that the capacitance varies in response to an acoustic signal incident on said diaphragm.
Claim 15
Dependent Claim
29 words
The device according to claim 11 wherein a backplate layer is included adjacent to said one of the electrodes and said array of holes is included through the layer.
Claim 16
Dependent Claim
25 words
The device according to claim 11 wherein the spacing between electrodes is less than 3.0 μm when no dc bias is supplied to the electrodes.
Claim 17
Dependent Claim
19 words
The device according to claim 11 wherein the area of the diaphragm is less than 8 mm 2 .
Claim 18
Dependent Claim
22 words
The device according to claim 1 wherein the spacing between the electrodes is uniform when no bias is supplied to the electrodes.
Claim 19
Dependent Claim
25 words
The device according to claim 11 wherein the transducer is adapted to operate with a dc bias across the electrodes of less than 5 volts.
Claim 20
Dependent Claim
26 words
The device according to claim 11 wherein the dynamic magnification factor of the output response of the transducer is greater than or equal to -3.0 dB.
Claim 21
Dependent Claim
136 words
The device according to claim 11 where the radius, r, center-to-center spacing, 2ξ, and number, N, of holes in the array satisfies the relationships: ##EQU8## where D is the minimum desirable dynamic magnification factor, ω is the highest radian frequency of the input signal to be transmitted, ω n is the natural radian frequency of vibration of the diaphragm, R a is the damping level of the air in the gap, R c is the critical damping level, X is the local radius-of-action associated with each hole, h e is the average distance between the electrodes when the desired dc bias is supplied thereto, λ is a factor relating X and ξ for the geometry of the hole array, A is the area of the diaphragm, and η is the coefficient of dynamic viscosity of air.
Claim 22
Dependent Claim
79 words
The device according to claim 11 further comprising: a front acoustic cavity defined by a portion of a semiconductor substrate adjacent to the diaphragm; a back acoustic cavity adjacent to the air hole array and defined by a member which also shields the transducer from electromagnetic interference; and an acoustic port defined by an element adjacent to the front acoustic cavity, the size of the port being such as to produce a desired frequency response characteristic for the transducer.
Claim 23
Dependent Claim
20 words
The device according to claim 12 wherein the microphone is adapted to receive the acoustic signal through the hole array.
Claim 24
Dependent Claim
156 words
An electroacoustic transducer formed within a semiconductor substrate comprising: a diaphragm which vibrates in response to an input signal at audio and/or ultrasonic frequencies; a front acoustic cavity defined by a portion of the semiconductor substrate adjacent to the diaphragm; a pair of electrodes placed with respect to said diaphragm so that the electric field between the electrodes varies in relation with the vibrating diaphragm to permit conversion between electrical and acoustic signals and so that an air gap is formed between the electrodes; a back acoustic cavity adjacent to one of the electrodes and defined by a member which also shields the transducer from electromagnetic interference; acoustic venting means comprising an array of holes connecting the air gap to the back acoustic cavity; and an acoustic port defined by an element adjacent to the front acoustic cavity, the size of the port being such as to produce a desired frequency response characteristic for the transducer.
Claim 25
Dependent Claim
156 words
An electroacoustic transducer formed within a semiconductor substrate comprising: a diaphragm which vibrates in response to an input signal at audio and/or ultrasonic frequencies; a front acoustic cavity defined by a portion of the semiconductor substrate adjacent to the diaphragm; a pair of electrodes placed with respect to said diaphragm so that the electric field between the electrodes varies in relation with the vibrating diaphragm to permit conversion between electrical and acoustic signals and so that an air gap is formed between the electrodes; a back acoustic cavity adjacent to one of the electrodes and defined by a member which also shields the transducer from electromagnetic interference; acoustic venting means comprising an array of holes connecting the air gap to the back acoustic cavity; and an acoustic port defined by an element adjacent to the front acoustic cavity, the size of the port being such as to produce a desired frequency response characteristic for the transducer.
Claim 26
Dependent Claim
40 words
The device according according to claim 22 wherein the transducer is a microphone and one of the electrodes is formed to vibrate with the diaphragm such that the capacitance varies in response to an acoustic signal incident on said diaphragm.
Claim 27
Dependent Claim
22 words
The device according to claim 22 wherein the acoustic port is defined in a carrier to which the semiconductor substrate is attached.
Claim 28
Dependent Claim
30 words
The device according to claim 22 wherein the back acoustic cavity is defined by a conductive member which covers the entire semiconductor substrate in which the integrated microphone is formed.
Claim 29
Dependent Claim
32 words
The device according to claim 22 wherein the diameter and length of the acoustic port is such as to produce a peak in the output response in the frequency range 2.8-4.5 KHz.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1988-08-05 | 1989-02-04 | 1989-08-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1992-08-05 | 1993-02-04 | 1993-08-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1996-08-05 | 1997-02-04 | 1997-08-06 | $7700.00 | Window Closed / Lapsed |