Information
-
Patent Grant
-
6741709
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Patent Number
6,741,709
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Date Filed
Wednesday, December 20, 200023 years ago
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Date Issued
Tuesday, May 25, 200420 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
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CPC
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US Classifications
Field of Search
US
- 381 173
- 381 174
- 381 175
- 381 191
- 367 172
- 367 173
- 367 174
- 367 181
- 367 188
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International Classifications
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Abstract
A microphone assembly comprising a housing, the housing including an upper lip, a silicon backplate having a top portion, a bottom portion, an annular side portion, a silicon spacer integrally formed with the backplate and comprising at least one protrusion extending from and integral to the top portion of the silicon backplate, the spacer further comprising an insulating layer, such as silicon dioxide or a fluoropolymer. A plurality of openings extend from the top portion of the backplate to the bottom portion of the backplate. A single diaphragm, comprised of metallized polymer film, acts as both a protective environmental barrier and a sensing electrode of a capacitive electroacoustic sensing transducer. A metal ring is positioned against the upper lip of the metal housing. The diaphragm is adhesively affixed to the ring, and the ring, in cooperation with the upper lip and a spring, secure the diaphragm against the insulating layer of the spacer.
Description
FIELD OF THE INVENTION
The present invention relates to microphones, and more particularly to condenser microphone assemblies, such as a backplate with integral spacer made from semiconductor components.
BACKGROUND OF THE INVENTION
Condenser or capacitance microphones are widely used in the audio, electronics and instrumentation industries. Condenser microphones include a flexible diaphragm or membrane and a rigid backplate that may contain one or more openings. Together, the membrane and the backplate of the microphone form a capacitor, which is also known as a condenser. When a sound wave hits the membrane, the membrane moves, causing a variation in height of the air gap between the membrane and the backplate. This gap variation results in a change in the capacitance of the condenser formed by the membrane and the backplate. If a fixed or controlled charge Q is maintained on the capacitor, a voltage will be formed across the capacitor that will then vary proportionally to the change in the height of the air gap. As is known in the art, conventional diaphragms may be constructed from metal films or metallized polymer films.
For a variety of applications, it is desirable to manufacture small, high quality condenser microphones. As is known in the art, openings in the backplate may be created by drilling or punching holes. Controlling the precise size and location of such holes, which can be critical, becomes more difficult as the holes become smaller.
As is also known in the art, entire condenser microphones, including diaphragms, can be formed on silicon substrates through MicroElectroMechanical Systems (MEMS) fabrication methods, which is the formation of mechanical components based on silicon integrated circuit manufacturing processes. For example, U.S. Pat. No. 5,889,872 discloses a capacitive microphone formed with semiconductor processing techniques. A diaphragm is formed as part of the fabrication by applying a polysilicon layer on a silicon nitride layer. The polysilicon layer is patterned or etched to form a diaphragm.
U.S. Pat. No. 5,870,482 explains challenges associated with maintaining highly compliant and precisely positioned diaphragms fabricated from a silicon wafer. That patent discloses an alternative solid state condenser microphone with a semiconductor support structure.
U.S. Pat. No. 6,075,867 discloses a micromechanical microphone with multiple diaphragms. To address problems of humidity, dust and dirt, the microphone includes two sealing membranes on either side of a transducer. However, an environmental membrane in front of a sensing transducer may affect audio characteristics, such as signal to noise ratio, frequency response, and sensitivity.
The formation of complete condenser microphones through MEMS processing is extremely difficult and expensive. Moreover, condenser microphones constructed entirely from MEMS processing often exhibit inferior audio and reliability characteristics.
SUMMARY OF THE INVENTION
The present invention solves many of the aforementioned problems by a microphone assembly comprising a housing, a semiconductor backplate mounted in the housing and a flexible diaphragm located above the backplate. The semiconductor spacer is integrally formed with the backplate and intermediate the backplate and the diaphragm. The backplate and spacer is not integrally formed with the diaphragm, the diaphragm frame, or the housing.
The diaphragm is stretched over and adhesively affixed to the diaphragm frame. The diaphragm frame maintains tension in the diaphragm. The diaphragm is comprised of a metal film or metallized polymer film, and the diaphragm is both a protective environmental barrier and a sensing electrode of a capacitive electroacoustic transducer. The housing may be made of metal, and the backplate made of silicon. The spacer may further comprise an electrically insulating layer, such as silicon dioxide or a fluoropolymer.
The backplate includes a top portion, a bottom portion, and a side portion and a plurality of openings extending from the top portion of the backplate to the bottom portion of the backplate. In one embodiment, the plurality of openings are located along the side portion of the backplate and are radially outward of the spacer. The backplate may be circular, rectangular or another desirable shape. The spacer may consist of an annular wall, a series of arcuate walls, a series of arcuate extensions or a rectangular wall.
The housing comprises an upper lip, and the diaphragm frame comprises a metal ring positioned against the upper lip. The assembly may further comprise a metal contact on the bottom portion of the backplate. Furthermore, the invention may include a spring positioned between the backplate and a lower portion of the housing.
In addition, the invention may comprise a transistor coupled to the housing or the backplate. The microphone assembly may also comprise an application specific integrated circuit (ASIC) coupled to the backplate, and the ASIC may include a transistor.
These as well as other novel advantages, details, embodiments, features and objects of the present invention will be apparent to those skilled in the art from following the detailed description of the invention, the attached claims and accompanying drawings, listed herein, which are useful in explaining the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
In the following text and drawings, wherein similar reference numerals denote similar elements throughout the several views thereof, the present invention is explained with reference to illustrative embodiments, in which:
FIG. 1
is a perspective view of a first embodiment of a microphone assembly made in accordance with the present invention;
FIG. 2
is a perspective view of a portion of the microphone assembly made in accordance with the present invention
FIG. 3
is a plan view of a first embodiment of a backplate made in accordance with the present invention;
FIG. 4
is a plan view of a second embodiment of a backplate made in accordance with the present invention;
FIG. 5
is a plan view of a third embodiment of a backplate made in accordance with the present invention;
FIG. 5A
is an enlargement of the area shown by the region
104
in
FIG. 5
; and
FIG. 6
is a plan view of a fourth embodiment of a backplate made in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to
FIGS. 1 and 2
, in a preferred embodiment, the present invention includes a membrane or diaphragm
10
that is separated from a backplate
12
. The diaphragm
10
is flexible and is exposed to the air. A protective grille (not shown) may be mounted above the diaphragm
10
. The diaphragm
10
is made of a known material for constructing microphone diaphragms, such as metal film or metallized polymer film.
The backplate
12
is rigid or fixed. Integrally formed with the backplate
12
are spacers, shown for example at
14
in
FIG. 1 and 15
in FIG.
2
. The diaphragm
10
is separated from the backplate
12
by a narrow air gap
13
(shown only in
FIG. 2
) defined by the spacers
14
,
15
. The backplate
12
and spacer
14
are fabricated, for example, from semiconductor material, such as silicon, by batch processing techniques. Referring to
FIG. 1
, a top region
28
of the spacer
14
includes a layer of electrically insulating material, such as silicon dioxide or a fluoropolymer, such as TEFLON. Similarly, referring to
FIG. 2
, a top region
30
of the spacer
15
includes a similar insulating layer. The spacer may take the form of many shapes, such as a wall or a ridge.
The membrane
10
and the backplate
12
form a capacitor, also known as a condenser. When a sound wave hits the membrane
10
, the membrane moves, causing a variation in height of the air gap
13
between the membrane
10
and the backplate
12
. This gap variation results in a change in the capacitance of the condenser formed by the membrane
10
and the backplate
12
. If a fixed or controlled charge Q is maintained on the capacitor, a voltage will be formed across the capacitor that will then vary proportionally to the change in the height of the air gap
13
.
The diaphragm
10
is stretched over a diaphragm frame
16
and glued or adhesively affixed to the diaphragm frame
16
. The diaphragm frame
16
maintains tension in the diaphragm
16
. The diaphragm frame
16
is positioned between the spacer
14
and an upper edge
18
of a housing
20
. The housing
20
is a known housing not manufactured from batch processing techniques, and is preferably made of metal, not silicon. The housing
20
serves as an electrical ground.
The backplate
12
may include openings or holes indicated by arrows
22
,
24
and
26
. These openings allow air to pass from the area above the backplate
12
to the area below the backplate
12
.
The backplate
12
shown in
FIG. 1
is rectangular or square. The backplate is situated in the housing
20
by a nest
32
. An opening
34
between the backplate
12
and the nest
32
also allows air to pass from the area above the backplate
12
to the area below the backplate
12
. In one embodiment, materials, such as metal, could be selectively deposited in the circular portion indicated by the numeral
40
.
Referring to
FIG. 2
, a spring
42
is used to mechanically bias the backplate
12
against a bottom portion
44
of the housing
20
, which is a PC board. The spring
42
causes the spacer
15
of the backplate
12
to be pushed into the diaphragm
10
and the diaphragm frame or ring
16
, which consequently press against the upper edge or lip
18
of the housing
20
. In this manner, the diaphragm is coupled to the spacer
15
. Thus, together, the spring
42
, the diaphragm frame
16
, the upper lip
18
of the housing
20
, the housing
20
and the PC board
44
cooperate to secure the diaphragm
10
against the insulating layer
30
of the spacer
15
. The diaphragm
10
is not integrally formed with the spacer
15
.
The microphone assembly preferably employs a single diaphragm
10
that serves as both a protective environmental barrier and a sensing electrode of a capacitive electroacoustic transducer. In contrast, prior art systems of silicon fabricated condenser microphones employ either no protective environmental barrier or more than one diaphragm or membrane, one of which serves as an environmental barrier and one of which does not.
A variety of shapes and configurations may be used for the diaphragm
10
and backplate
12
. For example in
FIG. 1
the diaphragm frame
16
is round and in the form of an annular ring and the backplate
12
is square. One skilled in the art will appreciate that the diaphragm frame
16
and backplate
12
could include other shapes depending on the shape of the housing
20
and the other components of the invention.
Because the diaphragm
10
is not fabricated or processed as part of the backplate
12
, the diaphragm is free from stress associate with fabricating and mounting the backplate
12
. In addition, the tension on the diaphragm
10
is independent of the internal stresses in the backplate
12
. As is recognized in the art, these uncontrolled internal stresses are a common undesirable consequence of semiconductor fabrication processing. Thus, the diaphragm
10
is free floating relative to stress parallel to the face of the backplate
12
or the face of the diaphragm
10
. By mounting the diaphragm
10
on a suitable diaphragm frame
16
that is independent from the backplate
12
and spacer
15
, the tensile stress of the diaphragm
10
is free from influences from the packaging and the backplate.
FIGS. 3-6
illustrate alternative embodiments with different arrangements of the spacers and holes on a backplate. As would be appreciated by one of ordinary skill in the art, the location, number and size of holes affects the audio characteristics of the microphone. MEMS will allow improved control of the hole size and placement, which will enhance the ability to control frequency response and sensitivity.
Referring to
FIG. 3
, holes
80
may be located radially inward of spacers
82
. Spacers
82
may be small circular protrusions.
Alternatively,
FIG. 4
shows holes
90
and notches
92
along a side of a backplate
95
that allow air to pass from above to below the backplate.
FIG. 4
also shows an annular spacer wall
94
.
FIG. 5
shows a backplate with no holes radially inward of a series of arcuate spacer portions
100
. Instead, air passes from above the backplate to below the backplate via openings
102
. Arrows
106
,
108
and
110
in
FIG. 5A
, which is an enlargement of the area
104
in
FIG. 5
, depict the flow of air from the top of a backplate
112
to the underside of the backplate
112
.
FIG. 6
further illustrates a rectangular or square backplate
130
with a square or rectangular spacer wall and grid or holes, one of which is shown by
134
. As will be appreciated by one of ordinary skill in the art, the spacers may also be or arcuate portions of a wall sufficient to support the diaphragm
10
and diaphragm frame
16
.
Referring again to
FIG. 2
, the backplate
12
is externally biased at output
140
with a voltage bias. The backplate could be externally biased with direct current (DC) voltage or a radio frequency (RF) bias. In one embodiment, a transistor or FET (not shown) is mounted to the PC board
44
within the area defined by the PC board
44
and the housing
20
. The FET could also be located outside the housing
20
or directly on the bottom of the backplate
12
. Generally, locating the FET closer to the backplate should improve noise characteristics of the invention. The unit could also be biased by an electret, for example, a charged or polarized layer on the backplate
12
(not shown).
The underside of the backplate
12
may include contact regions
142
, which are preferably metal, that can be deposited by chemical vapor deposition (CVD) techniques. The spring
42
may provide an electrical contact from the contact region
142
to the region
140
.
Referring again to
FIG. 1
, an integrated circuit (IC) or application specific integrated circuit (ASIC)
180
could be mounted beneath the PC board (not shown). The ASIC could contain a transistor, such as a FET. The ASIC could also include a preamplifier to increase the electrical output of the microphone and/or modify the response of the microphone.
The ASIC could also include an analog to digital converter (A/D). The purpose of the A/D is to convert the analog output of the microphone, or microphone preamplifier, to a digital signal that can either be used as a direct digital output from the microphone, or a feed to digital signal processing (DSP) circuitry. The purpose of the DSP is to modify the output of the microphone after an A/D. The output can either be a digital or analog or both. Specific applications can include equalization, signal compression, frequency dependent signal compression, and self-calibration.
A voltage step up circuit could also be used to allow a readily available compact battery source (e.g. a 9 v battery) to provide an elevated voltage (e.g. 200 v) for externally DC biasing a condenser.
Another embodiment of the invention would include a radio frequency (RF) biasing circuit to provide a bias voltage that oscillates with an RF wavelength. A further purpose for such a circuit is to allow the microphone to output a RF modulated signal for wireless transmission.
Thus, different backplates and different ASIC circuits that could be combined in the housing
20
would permit a variety of potential operations and functions of the microphone.
In the foregoing specification, the present invention has been described with reference to specific exemplary embodiments thereof. Although the invention has been described in terms of a preferred embodiment, those skilled in the art will recognize that various modifications, embodiments or variations of the invention can be practiced within the spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, therefore, to be regarded in an illustrated rather than restrictive sense. Accordingly, it is not intended that the invention be limited except as may be necessary in view of the appended claims.
Claims
- 1. A microphone assembly comprising:a housing, wherein the housing is metal; a semiconductor backplate mounted in the housing, wherein the backplate is silicon, wherein the backplate includes a top portion, a bottom portion, and a side portion and a plurality of openings extending from the top portion of the backplate to the bottom portion of the backplate, and wherein the plurality of openings are located along the side portion of the backplate and are radially outward of the spacer; a flexible diaphragm located above the backplate, the flexible diaphragm acting as both a protective environmental barrier and a sensing electrode of a capacitive electroacoustic sensing transducer, wherein the diaphragm is comprised of a material consisting of the group metal film or metallized polymer; a semiconductor spacer integral to the backplate and intermediate the backplate and the diaphragm wherein the spacer further comprises an insulating layer from the group consisting of silicon dioxide or a fluoropolymer; and a diaphragm frame, the diaphragm stretched over and adhesively affixed to the diaphragm frame, the diaphragm frame maintaining tension in the diaphragm.
- 2. A microphone assembly as in claim 1 wherein the backplate is circular.
- 3. A microphone assembly as in claim 1 wherein the backplate is rectangular.
- 4. A microphone assembly as in claim 2 wherein the spacer is comprised of the group consisting of an annular wall, a series of arcuate walls, a series of arcuate extensions or a rectangular wall.
- 5. A microphone assembly as in claim 4 wherein the housing comprises an upper lip and the diaphragm frame comprises a metal ring positioned against the upper lip.
- 6. A microphone assembly as in claim 5 further comprising a metal contact on the bottom portion of the backplate.
- 7. A microphone assembly as in claim 6 further comprising a spring positioned between the backplate and a lower portion of the housing.
- 8. A microphone assembly as in claim 7 further comprising a transistor coupled to the housing.
- 9. A microphone assembly as in claim 7 further comprising a transistor coupled to the backplate.
- 10. A microphone assembly as in claim 7 further comprising an integrated circuit coupled to the backplate, the integrated circuit having a transistor.
- 11. A microphone assembly as in claim 7 further comprising an integrated circuit coupled to the backplate, the integrated circuit having a voltage step up circuit.
- 12. A microphone assembly as in claim 7 further comprising an integrated circuit coupled to the backplate, the integrated circuit having an RF biasing circuit.
- 13. A microphone assembly as in claim 12 wherein the RF biasing circuit generates an RF modulated output and the RF modulated output is used for RF wireless transmission.
- 14. A microphone assembly as in claim 7 further comprising an integrated circuit coupled to the backplate, the integrated circuit having a digital signal processor.
- 15. A microphone assembly as in claim 7 further comprising an integrated circuit coupled to the backplate, the integrated circuit having an analog to digital converter.
- 16. A microphone assembly comprising:a housing, the housing including an upper lip; a silicon backplate having a top portion, a bottom portion, an annular side portion; a silicon spacer integrally formed with the backplate and comprising at least one protrusion extending from and integral to the top portion of the silicon backplate, the spacer further comprising an insulating layer from the group consisting of silicon dioxide or a fluoropolymer; a plurality of openings extending from the top portion of the backplate to the bottom portion of the backplate; a single diaphragm comprised of metallized polymer film, the single diaphragm acting as both a protective environmental barrier and a sensing electrode of a capacitive electroacoustic sensing transducer; and a metal ring positioned against the upper lip of the housing, the diaphragm adhesively affixed to the ring, the ring in cooperation with the upper lip and a spring securing the diaphragm against the insulating layer of the spacer.
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Number |
Name |
Date |
Kind |
4887248 |
Griebeler |
Dec 1989 |
A |
4910840 |
Sprenkels et al. |
Mar 1990 |
A |
5745438 |
Hill et al. |
Apr 1998 |
A |
6243474 |
Tai et al. |
Jun 2001 |
B1 |