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DESCRIPTION JP2011176532

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DESCRIPTION JP2011176532
An acoustic sensor having an external vibration noise removal function improves the S / N ratio
of a signal after noise removal to improve sensor sensitivity. An acoustic detection element is
mounted on one surface of a wiring board, and a vibration detection element is mounted on the
other surface of the wiring board opposite to the element. By opening the through hole 53 in the
wiring board 22 between the hollow portion 36 a of the acoustic detection element 23 and the
hollow portion 36 b of the vibration detection element 25, the hollow portions 36 a and 36 b are
communicated with each other. A back chamber 54 of the acoustic detection element 23 is
formed by the hollow portion 36 a of the acoustic detection element 23, the through hole 53 of
the wiring substrate 22, and the hollow portion 36 b of the vibration detection element 25.
[Selected figure] Figure 3
Acoustic sensor
[0001]
The present invention relates to an acoustic sensor, and more particularly to an acoustic sensor
having a function of removing external vibration noise.
[0002]
An acoustic sensor used for a microphone or the like detects acoustic vibration using air as a
transmission medium. However, since it is usually installed in any device, it is easy to detect noise
due to an external mechanical vibration or the like.
[0003]
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In order to reduce noise (external vibration noise) due to such external mechanical vibration, the
conventional condenser microphone combines an acoustic detection unit that detects acoustic
vibration and a vibration detection unit that detects only mechanical vibration. .
An example of such a noise removing type capacitor microphone is disclosed in Patent Document
1.
[0004]
The structure of the condenser microphone disclosed in Patent Document 1 is shown in FIG.
In the condenser microphone 11, the acoustic detection unit 12 and the vibration detection unit
13 which are formed of electret condenser microphone units having substantially the same
structure are accommodated in a rigid holder 14. The acoustic detection unit 12 and the
vibration detection unit 13 both have the acoustic holes 16 opened to face the vibration film 15
for detecting the vibration, and have substantially the same structure. The sound detection unit
12 and the vibration detection unit 13 are accommodated substantially in parallel in the adjacent
delivery units 17 and 18 provided on the holder 14. The acoustic hole 16 of the acoustic
detection unit 12 housed in the delivery unit 17 is opened to the outside by the opening 19 of
the delivery unit 17. On the other hand, the acoustic hole 16 of the vibration detection unit 13
housed in the delivery unit 18 is closed by the holder 14.
[0005]
Accordingly, the acoustic vibration is detected only by the acoustic detection unit 12 through the
opening 19. Further, the external mechanical vibration is detected by the sound detection unit 12
and the vibration detection unit 13 through the holder 14. 2 (a) shows an example of a signal
waveform (acoustic vibration on which external vibration noise is applied) output from the
acoustic detection unit 12, and FIG. 2 (b) shows a signal waveform (external vibration) output
from the vibration detection unit 13. Noise)). In FIG. 2, it is assumed that the signal waveform of
the acoustic vibration is a sine wave.
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[0006]
In order to remove external vibration noise using such two types of signal waveforms, a noise
canceling circuit is generally used. In the noise canceling circuit, as shown in FIG. 2 (c), the signal
waveform output from the vibration detection unit 13 is inverted, and then the signal waveform
of the acoustic vibration on which the external vibration noise is applied as shown in FIG. 2 (a).
The inverted waveform of FIG. 2 (c) is added to. Since the output waveform of the vibration
detection unit 13 shown in FIG. 2B is the same as the noise component on the acoustic vibration
in the sound detection unit 12, the inverted waveform in FIG. 2C is output from the sound
detection unit 12 The external vibration noise is removed by adding it to the signal waveform of
FIG.
[0007]
Japanese Utility Model Application Publication No. 4-53394
[0008]
However, even with a noise canceling circuit, it has been difficult to completely remove the noise.
The acoustic vibration waveform from which the external vibration noise has been removed
using the noise canceling circuit is actually a waveform as shown in FIG. 2D, and the vibration
noise remains. The reason why the noise can not be removed as described above is that when the
signal waveform is inverted as shown in FIG. 2C, a phase delay from the original signal waveform
occurs in the inverted signal waveform. Furthermore, the noise generated inside the noise
canceling circuit is added to the inverted waveform to distort the inverted waveform, which is
also a cause of not being able to remove the noise from the synthesized waveform.
[0009]
Therefore, in the conventional condenser microphone, when mechanical vibration occurs in
addition to the acoustic vibration, the mechanical vibration is output as noise, and the S / N ratio
of the output signal is lowered.
[0010]
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On the other hand, in recent years, an acoustic sensor manufactured using MEMS (Micro Electro
Mechanical Systems) technology as a small microphone has been used.
Also in this acoustic sensor, the diaphragm of the thin film vibrates in response to the incident
acoustic vibration, and a change in capacitance between the vibrating diaphragm and the fixed
electrode is output as a detection signal. In the acoustic sensor having such a structure, when the
volume of the back chamber (space opposite to the incident side of the acoustic vibration)
formed behind the diaphragm is small, the inside of the back chamber expands or compresses by
the vibration of the diaphragm. Air dampens the vibration of the diaphragm. Therefore, in order
to obtain the detection sensitivity of acoustic vibration, it is desirable to provide a back chamber
of as large volume as possible behind the diaphragm.
[0011]
However, acoustic sensors fabricated using MEMS technology are much smaller than condenser
microphones. For example, the thickness of the MEMS chip (sound detection element) is 1 mm or
less, and the length of one side is several mm or less in plan view. Therefore, the volume of the
back chamber can not be increased. As a result, it is difficult to enhance the detection sensitivity
of acoustic vibration, and even if a noise removal method as disclosed in Patent Document 1 is
used, it is difficult to obtain a high S / N ratio.
[0012]
The present invention has been made in view of such technical problems, and an object of the
present invention is to provide an acoustic sensor having a function of removing external
vibration noise, and an S / N ratio of a signal after noise removal. To further improve the sensor
sensitivity.
[0013]
In order to achieve such an object, according to the acoustic sensor of the present invention, a
first vibration film is formed on the surface of the first substrate, facing the opening end of the
first cavity formed in the first substrate. And a second hollow portion formed in the second
substrate, facing the acoustic detection element configured to transmit external air vibration to
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the first vibrating film, A second vibration film disposed on the surface of the second substrate,
and a vibration detection element configured to prevent external air vibrations from being
transmitted to the second vibration film, and the first cavity It is characterized in that the back
chamber of the acoustic detection element is formed by communicating the part and the second
hollow part with each other.
The detection method of the acoustic detection element and the vibration detection element may
be of a capacitance type or of a piezoresistive type.
[0014]
The acoustic sensor according to the present invention includes an acoustic detection element
that detects acoustic vibration (air vibration) and a vibration detection element that detects only
an external mechanical vibration. Even when noise is generated due to the noise, it is possible to
remove or reduce the noise from the output of the acoustic detection element using the
mechanical vibration signal output from the vibration detection element. Further, in this acoustic
sensor, since the back chamber of the acoustic detection element is formed by communicating
the first hollow portion and the second hollow portion with each other, the second hollow
portion of the vibration detection element is used. The back chamber of the acoustic detection
element can be made wider than the first cavity of the acoustic detection element (the back
chamber in the case of the single acoustic detection element), and the S / N ratio of the acoustic
detection element is increased to generate acoustic vibration. Can improve the sensitivity to
[0015]
In one embodiment of the acoustic sensor of the present invention, the second vibrating
membrane of the vibration sensing element is bonded to the surface of the second substrate and
covered by a back plate having no holes. It is characterized by In this embodiment, since the
second vibrating membrane is covered with the back plate without holes and the acoustic
vibration is not transmitted to the second vibrating membrane, the vibration detection element
can be prevented from detecting the acoustic vibration. Moreover, according to such a
configuration, acoustic vibration can be prevented from being transmitted to the vibration
detection element with a simple configuration regardless of whether the vibration detection
element is disposed on the opposite side to the acoustic vibration element or on the same side .
Further, in the case of the capacitive acoustic sensor, the back plate covering the second
vibrating film can also serve as the back plate for providing the fixed electrode, so the structure
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of the acoustic sensor can be simplified.
[0016]
Another embodiment of the acoustic sensor according to the present invention is characterized in
that the second hollow portion of the vibration sensing element does not penetrate through the
front and back of the second substrate. According to this aspect, although the first cavity of the
acoustic sensing element is in communication with the second cavity of the vibration sensing
element, the acoustic vibration incident on the acoustic sensing element is not the vibration
sensing element. Vibration of the second vibrating membrane can be prevented.
[0017]
In still another embodiment of the acoustic sensor of the present invention, the acoustic
detection element is mounted on one surface of a base substrate, and the vibration detection
element is mounted on the other surface of the base substrate opposite to the acoustic detection
element. The first hollow portion and the second hollow portion may be in communication with
each other through a through hole opened in the base substrate. In this embodiment, since the
acoustic detection element and the vibration detection element mounted on both sides of the
base substrate are in the opposite direction, mechanical vibration is applied to the first vibrating
membrane and the second vibrating membrane through the base substrate. When this is done,
the signal output from the acoustic detection element and the signal output from the vibration
detection element are signals inverted to each other. Therefore, noise due to mechanical
vibration can be removed simply by adding both signals, and the S / N ratio of the acoustic
detection element can be further improved. Furthermore, according to this embodiment, the
acoustic sensor can be miniaturized to reduce the mounting area.
[0018]
Further, in such an embodiment, the vibration detection element is an acoustic member by
bonding a cover to the other surface of the base substrate and sealing the vibration detection
element in the space formed by the base substrate and the cover. Vibration can not be detected.
[0019]
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In still another embodiment of the acoustic sensor of the present invention, the acoustic sensing
element and the vibration sensing element are mounted on one surface of a base substrate, and
the first hollow portion is formed through an air passage formed in the base substrate. And the
second hollow portion communicate with each other.
In this embodiment, since the acoustic detection element and the vibration detection element are
mounted on one side of the base substrate, the acoustic sensor can be thinned. Further, since the
acoustic element and the vibration element are mounted on one side of the base substrate, the
mounting work of both elements can be simplified in the manufacturing process of the acoustic
sensor.
[0020]
In still another embodiment of the acoustic sensor of the present invention, a support plate is
mounted on the surface of a base substrate, the acoustic detection element and the vibration
detection element are mounted on the surface of the support plate, and the inside of the support
plate The first cavity and the second cavity communicate with each other through an air passage
formed in In this embodiment, since the acoustic detection element and the vibration detection
element are mounted on the support plate provided on one side of the base substrate, the
mounting operation of both elements can be simplified in the manufacturing process of the
acoustic sensor. . In addition, since the support plate is provided separately from the base
substrate to form the air passage in the support plate, the air passage can be made easier than
the air passage in the base substrate.
[0021]
In this embodiment, both the first substrate and the second substrate may be silicon substrates,
and the support plate may be made of glass, silicon or ceramic. Glass, silicon or ceramic, which is
the material of the support plate, has a small difference in linear expansion coefficient from the
silicon substrate, which is the main material of the acoustic detection element and the vibration
detection element, and therefore thermal stress generated in the acoustic detection element and
the vibration detection element And the sensitivity of the acoustic sensor can be stabilized.
[0022]
In addition, the means for solving the above-mentioned subject in the present invention has the
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feature which combined suitably the component explained above, and the present invention
enables many variations by the combination of such a component. .
[0023]
FIG. 1 is a cross-sectional view of a condenser microphone disclosed in Patent Document 1. As
shown in FIG.
Fig.2 (a) is a figure which shows the output waveform of the acoustic detection part in the
capacitor microphone of FIG. 1, FIG.2 (b) is a figure which shows the output waveform of the
vibration detection part in the capacitor microphone of FIG. 2 (b) shows an inverted waveform
obtained by inverting the output waveform of FIG. 2 (b), and FIG. 2 (d) shows a waveform
obtained by adding the output waveform of FIG. 2 (a) and the inverted waveform of FIG. is there.
FIG. 3 is a schematic cross-sectional view showing the structure of the acoustic sensor according
to Embodiment 1 of the present invention. FIG. 4 is an exploded perspective view showing an
acoustic detection element used in the acoustic sensor of the first embodiment. FIG. 5 is a crosssectional view of the acoustic sensing element of FIG. 6 (a) shows an output waveform from the
acoustic detection element of the acoustic sensor of Embodiment 1, FIG. 6 (b) shows an output
waveform from the vibration detection element of the acoustic sensor of Embodiment 1, FIG. (C)
is a figure which shows the waveform which added the output waveform of Fig.6 (a), and the
output waveform of FIG.6 (b). FIG. 7 is a schematic cross-sectional view showing the structure of
an acoustic sensor according to a modification of Embodiment 1 of the present invention. FIG. 8
is a schematic cross-sectional view showing the structure of an acoustic sensor according to
Embodiment 2 of the present invention. 9 (a) shows an output waveform from the acoustic
detection element of the acoustic sensor of Embodiment 2, FIG. 9 (b) shows an output waveform
from the vibration detection element of the acoustic sensor of Embodiment 2, FIG. (C) shows an
inverted waveform obtained by inverting the output waveform of FIG. 9 (b), and FIG. 9 (d) is a
waveform obtained by adding the output waveform of FIG. 9 (a) and the inverted waveform of
FIG. 9 (c) FIG. FIG. 10 is a schematic cross-sectional view showing the structure of an acoustic
sensor according to Embodiment 3 of the present invention. FIG. 11 is a schematic crosssectional view showing the structure of an acoustic sensor according to a modification of
Embodiment 3 of the present invention. FIG. 12 is a schematic cross-sectional view showing the
structure of an acoustic sensor according to another modification of Embodiment 3 of the
present invention. FIG. 13 is a schematic cross-sectional view showing the structure of an
acoustic sensor according to Embodiment 4 of the present invention.
[0024]
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Hereinafter, preferred embodiments of the present invention will be described with reference to
the accompanying drawings. However, the present invention is not limited to the following
embodiments, and various design changes can be made without departing from the scope of the
present invention.
[0025]
First Embodiment Hereinafter, an acoustic sensor 21 according to a first embodiment of the
present invention will be described with reference to FIGS. 3 to 6. FIG. 3 is a schematic crosssectional view of the acoustic sensor 21. As shown in FIG. A member indicated by reference
numeral 22 is a double-sided wiring board (base substrate) having a wiring pattern formed on
both sides. The acoustic detection element 23 and the circuit element 24 (IC chip) are surface
mounted on one surface of the wiring board 22, and the vibration detection element 25 and the
circuit element 26 (IC chip) are on the other surface of the wiring board 22. Surface mounted.
Further, one surface of the wiring board 22 is covered by a first cover 27 for electromagnetic
shielding, and the acoustic detection element 23 and the circuit element 24 are accommodated in
a space 28 formed by the wiring board 22 and the first cover 27 There is. Similarly, the other
surface of the wiring board 22 is covered by a second cover 29 for electromagnetic shielding,
and the vibration detecting element 25 and the circuit element 26 are accommodated in the
space 30 formed by the wiring board 22 and the second cover 29. ing. The first cover 27 and the
second cover 29 have their outer peripheral back surfaces adhered to the wiring board 22 by a
conductive adhesive, and the two covers 27 and 29 are electrically connected to the ground
pattern of the wiring board 22. Further, the gap between the covers 27 and 29 and the wiring
substrate 22 is sealed by a conductive adhesive.
[0026]
4 and 5 are diagrams for explaining the structure of the acoustic sensing element 23. FIG. 4 is an
exploded perspective view of the acoustic sensing element 23, and FIG. 5 is a cross-sectional view
thereof. The acoustic detection element 23 is a minute electrostatic capacitance type element
manufactured using MEMS technology, and a vibrating electrode plate 34a is provided on the
upper surface of a silicon substrate 32a (first substrate) via an insulating film 33a. The fixed
electrode plate 35a is provided on the electrode with a minute gap (air gap) interposed
therebetween.
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[0027]
As shown in FIGS. 4 and 5, the silicon substrate 32a has a cavity 36a (first cavity) penetrating
from the front surface to the back surface. The inner circumferential surface of the hollow
portion 36a may be vertical, or may be tapered. The size of the silicon substrate 32a may be
about 1 to 1.5 mm square (in a plan view, smaller than this). And the thickness of the silicon
substrate 32a is about 400 to 500 .mu.m. An insulating film 33a made of an oxide film (SiO2
film) or the like is formed on the upper surface of the silicon substrate 32a.
[0028]
The vibrating electrode plate 34 a is formed of a polysilicon thin film having a thickness of about
1 μm. The vibrating electrode plate 34a is a thin film having a substantially rectangular shape,
and supporting legs 37a extend outward in the diagonal direction at the four corner portions.
Furthermore, an extension 44a extends from one of the support legs 37a. The vibrating electrode
plate 34a is disposed on the upper surface of the silicon substrate 32a so as to cover the upper
surface of the hollow portion 36a, and the support legs 37a at four corners and the extending
portions 44a are fixed on the insulating film 33a. The portion of the vibrating electrode plate 34a
supported in the air above the hollow portion 36a (in this embodiment, the portion other than
the support leg 37a and the extending portion 44a) is the diaphragm 38a (first vibrating
membrane) It vibrates in response to acoustic vibration (air vibration).
[0029]
The fixed electrode plate 35a has a fixed electrode 40a made of a metal thin film provided on the
top surface of a back plate 39a made of a nitride film. As shown in FIG. 5, the fixed electrode
plate 35a covers the diaphragm 38a by opening a minute gap of about 3 μm in the area facing
the diaphragm 38a, and the fixed electrode 40a faces the diaphragm 38a to form a capacitor. ing.
The outer peripheral portion of the fixed electrode plate 35a, that is, the portion outside the
region facing the diaphragm 38a, is fixed to the upper surface of the silicon substrate 32a via the
insulating film 33a made of an oxide film or the like.
[0030]
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A lead-out portion 42a is extended from the fixed electrode 40a, and an electrode pad 43a (Au
film) electrically connected to the fixed electrode 40a is provided at the tip of the lead-out
portion 42a. Further, the fixed electrode plate 35a is provided with an electrode pad 45a (Au
film) which is joined to the extending portion 44a of the vibrating electrode plate 34a and
electrically conducted to the vibrating electrode plate 34a. The electrode pad 43a is disposed on
the upper surface of the back plate 39a, and the electrode pad 45a is located in the opening of
the back plate 39a.
[0031]
A large number of acoustic holes 41 (acoustic holes) for passing acoustic vibration are formed in
the fixed electrode 40a and the back plate 39a so as to penetrate from the upper surface to the
lower surface. The vibrating electrode plate 34a is a thin film of about 1 μm because it vibrates
in resonance with acoustic vibration and mechanical vibration, but the fixed electrode plate 35a
is an electrode that is not excited by acoustic vibration and mechanical vibration. Therefore, the
thickness is as thick as, for example, 2 μm or more.
[0032]
In the acoustic detection element 23, when the acoustic vibration is transmitted through the
acoustic hole 41, the diaphragm 38a vibrates by the acoustic vibration. When the diaphragm 38a
vibrates, the gap distance between the diaphragm 38a and the fixed electrode plate 35a changes,
thereby changing the capacitance between the diaphragm 38a and the fixed electrode 40a.
Therefore, if a direct current voltage is applied between the electrode pads 43a and 45a and this
change in capacitance is taken out as an electrical signal, acoustic vibration is converted to an
electrical signal and detected. it can.
[0033]
The vibration detection element 25 has substantially the same structure as the acoustic detection
element 23, so the detailed structure of the vibration detection element 25 is not shown.
However, in the vibration detection element 25, component parts corresponding to the respective
component parts of the sound detection element 23 are indicated by appending the subscript "b"
instead of the subscript "a" of each component part of the sound detection element 23. . For
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example, the silicon substrate of the vibration detection element 25 corresponds to the silicon
substrate 32 a of the acoustic detection element 23 and is referred to as a silicon substrate 32 b
(second substrate).
[0034]
The vibration sensing element 25 differs from the acoustic sensing element 23 in that no
acoustic hole is formed in the fixed electrode plate 35 b. In the vibration detection element 25,
since the fixed electrode plate 35b does not have an acoustic hole, the surface side of the
vibrating electrode plate 34b is closed by the fixed electrode plate 35b. Accordingly, since the
acoustic vibration is blocked by the fixed electrode plate 35b and is not transmitted to the
diaphragm 38b (second vibrating film), the vibration detection element 25 does not detect
acoustic vibration. On the other hand, since the mechanical vibration is transmitted to the
vibrating electrode plate 34b through the silicon substrate 32b as in the case of the acoustic
detection device 23, the vibration detection device 25 can detect mechanical vibration. Moreover,
the vibration detection element 25 is configured to be able to detect mechanical vibration with
the same sensitivity as the sound detection element 23.
[0035]
The entire surface of the acoustic detection element 23 is bonded to the upper surface of the
wiring substrate 22 by an adhesive 51 made of a thermosetting resin. The vibration detection
element 25 is bonded to the lower surface of the wiring substrate 22 by the adhesive 52 made of
a thermosetting resin, and the vibration detection element 25 is disposed at a position facing the
acoustic detection element 23 with the wiring substrate 22 interposed therebetween. A through
hole 53 is opened in the wiring board 22 so that the hollow portion 36a of the acoustic detection
element 23 and the hollow portion 36b (second hollow portion) of the vibration detection
element 25 communicate with each other. The hollow portions 36a and 36b The back chamber
54 of the acoustic detection element 23 is formed by the space including the through holes 53.
The space between the periphery of the cavity 36 a and the periphery of the through hole 53 is
sealed by the adhesive 51, and the space between the cavity 36 b and the periphery of the
through hole 53 is also sealed by the adhesive 52. The back chamber 54 has a volume that does
not damp the vibration of the diaphragm 38 a of the acoustic sensing element 23. Further,
between the vibrating electrode plate 34 a of the acoustic sensing element 23 and the vibrating
electrode plate 34 b of the vibration sensing element 25, the acoustic vibration entered from the
acoustic hole 41 of the acoustic sensing element 23 is attenuated in the back chamber 54 to
detect the vibration. The distance is sufficient to prevent the vibrating electrode plate 34b of the
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element 25 from vibrating.
[0036]
In the vibration detection element 25, the space formed by the hollow portions 36a and 36b and
the through hole 53 is a front chamber, and the space between the vibrating electrode plate 34b
and the fixed electrode plate 35b is a back chamber.
[0037]
A circuit element 24 for processing an output signal of the acoustic detection element 23 is
bonded to the upper surface of the wiring board 22 by a thermosetting resin, and the acoustic
detection element 23 and the circuit element 24 are bonded by bonding wires or Connected
through 22 wiring patterns.
Similarly, a circuit element 26 for processing an output signal of the vibration detection element
25 is bonded to the lower surface of the wiring board 22 by a thermosetting resin, and the
vibration detection element 25 and the circuit element 26 are bonded by a bonding wire.
Alternatively, they are connected through the wiring pattern of the wiring substrate 22.
[0038]
A part of the wiring substrate 22 protrudes from between the first cover 27 and the second cover
29, and the protruding part is a terminal portion 55. Wiring patterns for supplying power to the
circuit elements 24 and 26 and extracting output signals are formed on the upper surface and
the lower surface of the wiring board 22, and these wiring patterns are drawn out to the terminal
portion 55. .
[0039]
The first cover 27 and the second cover 29 have an electromagnetic shielding function in order
to block external electromagnetic noise. For this purpose, the first cover 27 and the second cover
29 themselves may be formed of a conductive metal, and the inner surface of the resin cover
may be covered with a metal film such as plating. Further, an opening 56 is formed in the first
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cover 27, and a space 28 between the opening 56 and the acoustic hole 41 serves as a path for
propagating the acoustic vibration, and the acoustic vibration is transmitted to the opening 56
and the acoustic hole 41. Can be led to the diaphragm 38a. On the other hand, since the second
cover 29 has no opening and the fixed electrode plate 35b also has no acoustic hole, the
diaphragm 38b of the vibration detection element 25 is doubly shielded from acoustic vibration.
[0040]
According to the acoustic sensor 21 having such a structure, the volume of the back chamber 54
of the acoustic sensing element 23 can be made larger than twice the volume of the cavity 36 a.
As the volume of the back chamber 54 is larger, the sensitivity to acoustic vibration is improved,
and the signal strength of the acoustic detection element 23 is increased. For example, if it is
assumed that the acoustic vibration waveform when using the acoustic detection element 23
alone (that is, when the cavity 36a is a back chamber) is as shown by a broken line in FIG. The
acoustic vibration waveform output from the acoustic detection element 23 at 21 has a large
signal strength as shown by the solid line in FIG. On the other hand, the external mechanical
vibration is transmitted to the vibrating electrode plate 34a through the silicon substrate 32a
and the like to vibrate the diaphragm 38a, so the magnitude of the external vibration noise is
hardly related to the volume of the back chamber. Therefore, according to the acoustic sensor
21, the S / N ratio of the signal output from the acoustic detection element 23 can be improved
by widening the back chamber 54 of the acoustic detection element 23.
[0041]
Further, when the diaphragm 38a of the acoustic detection element 23 and the diaphragm 38b
of the vibration detection element 25 vibrate due to the external mechanical vibration, the
diaphragm 38a and the diaphragm 38b are displaced in the same direction. However, since the
acoustic detection element 23 and the vibration detection element 25 are mounted in the
opposite direction, when the diaphragm 38a approaches (or separates) the vibrating electrode
plate 34a, the diaphragm 38b separates (or approaches) the vibrating electrode plate 34b ).
Therefore, the increase and decrease of the electrostatic capacitance in the acoustic detection
element 23 and the increase and decrease of the electrostatic capacitance in the vibration
detection element 25 are opposite to each other. As a result, the output waveform of the noise
component (external vibration noise) contained in the output from the acoustic detection element
23 and the mechanical vibration output from the vibration detection element 25 (FIG. 6B) is
shown. ) Is opposite to the positive or negative. Therefore, if the output waveform of the acoustic
detection element 23 and the output waveform of the vibration detection element 25 are added,
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external vibration noise is removed and only acoustic vibration can be output.
[0042]
Therefore, according to the acoustic sensor 21, (1) the S / N ratio of the signal output from the
acoustic detection element 23 is improved, (2) the output of the acoustic detection element 23
and the output of the vibration detection element 25 are added (3) Since it is not necessary to
invert the output of the vibration detection element 25 before adding it to the output of the
acoustic detection element 23, it is not necessary to invert the phase delay in the inversion
waveform as described in the above problem. There is no problem or noise from the circuit that
inverts the waveform. As a result, the S / N ratio of the output signal of the acoustic sensor 21 is
improved, and the sensitivity to acoustic vibration can be significantly improved.
[0043]
In the acoustic sensor 21 according to the first embodiment, the acoustic detection element 23
and the vibration detection element 25 are disposed so as to overlap on both sides of the wiring
board 22, and the circuit element 24 and the circuit element 26 are also overlapped on both
sides of the wiring board 22. Since the arrangement is made, the acoustic sensor 21 can be
miniaturized, and the mounting area on a circuit board or the like can be reduced.
[0044]
Further, since the acoustic detection element 23 and the vibration detection element 25 are
disposed to face each other on both sides of the wiring board 22, the position between the
mechanical vibration transmitted to the acoustic detection element 23 and the mechanical
vibration transmitted to the vibration detection element 25 The phase difference (time delay) can
be reduced, and external vibration noise can be removed more effectively.
[0045]
In this embodiment, the space 30 in which the vibration detection element 25 is housed is sealed
by the second cover 29. Therefore, as the vibration detection element 25, sound is applied to the
fixed electrode plate 35b in the same manner as the acoustic detection element 23. It is
acceptable to use one provided with the hole 41.
[0046]
(Modification of the first embodiment)
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[0047]
In the acoustic sensor 21 shown in FIG. 3, the space 30 containing the vibration detection
element 25 is sealed by the second cover 29.
Therefore, when the terminal portion 55 is mounted on a circuit board or the like by reflow
soldering or flow soldering, the heat expands the air in the space 30, and the second cover 29
peels off or floats up from the wiring board 22 to cause shielding failure. May occur.
[0048]
The acoustic sensor 61 shown in FIG. 7 is a modification of the first embodiment of the present
invention, and prevents such a problem, and can cope with mounting by reflow solder or flow
solder.
In the acoustic sensor 61, an air hole 62 is opened in the second cover 29, and air flows in and
out of the space 30 through the air hole 62.
Therefore, even when the acoustic sensor 61 is mounted by reflow soldering or flow soldering,
the expanded air can be released from the air holes 62 to the outside, and the second cover 29
can be prevented from peeling off or floating by air pressure. it can.
On the other hand, in this modification, since the fixed electrode plate 35b does not have the
acoustic hole 41 and is non-porous, acoustic vibration does not reach the vibrating electrode
plate 34b, and the vibration detection element 25 is an external machine. Only dynamic vibration
can be detected.
[0049]
Second Embodiment FIG. 8 is a schematic cross-sectional view showing an acoustic sensor 71
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according to a second embodiment of the present invention. In the acoustic sensor 71, the
acoustic detection element 23 having the acoustic hole 41, the circuit element 24, the vibration
detection element 25 having no acoustic hole, and the circuit element 26 are mounted on the top
surface of the wiring board 22. A hollow air passage 74 extending substantially horizontally is
formed inside the wiring substrate 22, and both ends of the air passage 74 are opened at the
upper surface of the wiring substrate 22. One end opening of the air passage 74 opened on the
upper surface of the wiring substrate 22 faces the lower surface of the cavity 36a, and the other
opening also faces the lower surface of the cavity 36b, and the cavity 36a and the cavity 36b are
air It is connected by the passage 74. As a result, the back chamber 54 of the acoustic detection
element 23 is configured by the hollow portion 36a, the air passage 74, and the hollow portion
36b.
[0050]
A part of the wiring pattern of the wiring board 22 is for electromagnetic shielding, and a cover
72 for electromagnetic shielding is bonded to the upper surface of the wiring board 22, and a
space formed between the wiring board 22 and the cover 72 The sound detection element 23,
the vibration detection element 25, and the circuit elements 24 and 26 are housed at 73. The
cover 72 is provided with an opening 56 for causing acoustic vibration to enter the space 73.
[0051]
Also in this acoustic sensor 71, the back chamber 54 of the acoustic detection element 23
becomes wider, so the signal intensity of the acoustic vibration is improved as shown in FIG. 9A,
and the S / N of the signal output from the acoustic detection element 23 The ratio is higher.
However, as shown in FIG. 9B, the output waveform of the mechanical vibration output from the
vibration detection element 25 is in phase with the noise component included in the output
waveform of FIG. 9A. Therefore, when noise is removed using a noise canceling circuit, the
output waveform of FIG. 9B is inverted to obtain an inverted waveform as shown in FIG. A noiseremoved signal is obtained as shown in FIG. 9 (d) by adding to the output waveform of a).
[0052]
When a noise canceling circuit is used in the second embodiment, the output signal of the
vibration detection element 25 must be inverted, so some noise may remain in the output signal
of FIG. Since the S / N ratio of the signal output from the element 23 is improved, the S / N ratio
of the output signal shown in FIG.
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[0053]
Further, in this embodiment, since the respective elements 23 to 26 are arranged on the same
plane, the acoustic sensor 71 can be thinned.
Furthermore, in the acoustic sensor 71, only the cover 72 having the opening 56 is used, so there
is no concern that the cover 72 may be peeled off or float up from the wiring board 22 due to the
expansion of the air in the space 73.
[0054]
As a method of removing noise from the output signal of FIG. 9A, the output signal of the
acoustic detection element 23 and the output signal of the vibration detection element 25 are
input to the differential amplifier without using a noise canceling circuit. You may If the ground
terminal and the signal terminal of the vibration detection element 25 are reversed from those of
the acoustic detection element 23, an inverted signal as shown in FIG. 9C can be output from the
vibration detection element 25.
[0055]
Third Embodiment FIG. 10 is a cross-sectional view showing an acoustic sensor 81 according to a
third embodiment of the present invention. In the acoustic sensor 81, the support plate 82 is
adhered to the upper surface of the wiring substrate 22, and the acoustic detection element 23
and the vibration detection element 25 are adhered to the upper surface of the support plate 82
with adhesives 51 and 52. 25 is mounted on the support plate 82.
[0056]
A hollow air passage 83 extending substantially horizontally is formed inside the support plate
82, and both ends of the air passage 83 are open at the upper surface of the support plate 82.
One end opening of the air passage 83 opened on the upper surface of the support plate 82 faces
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the lower surface of the cavity 36a, and the other opening also faces the lower surface of the
cavity 36b, and the cavity 36a and the cavity 36b are air It is connected by the passage 83. As a
result, the back chamber 54 of the acoustic detection element 23 is configured by the hollow
portion 36a, the air passage 83, and the hollow portion 36b. The other structure is the same as
that of the second embodiment, so the description will be omitted.
[0057]
This acoustic sensor 81 also exhibits the same function and effect as the acoustic sensor 71 of
the second embodiment, and can improve the S / N ratio of the acoustic sensor 81 and improve
the sensitivity to acoustic vibration. Furthermore, in the acoustic sensor 81, since the support
plate 82 is provided separately from the wiring substrate 22 to form the air passage 83 in the
support plate 82, it is possible to form the air passage in the wiring substrate 22 The air passage
83 can be easily made.
[0058]
The support plate 82 is formed of a material having a small difference in linear expansion
coefficient from the acoustic detection element 23 (silicon substrate 32a) and the vibration
detection element 25 (silicon substrate 32b), such as a glass plate, a silicon substrate, a ceramic
plate . If the support plate 82 is made of a material having a small difference in linear expansion
coefficient from the acoustic detection element 23 or the vibration detection element 25, thermal
stress associated with temperature change hardly occurs in the acoustic detection element 23
and the vibration detection element 25. The sensitivity of the element 23 and the vibration
detection element 25 can be stabilized. Moreover, it becomes possible to replace with expensive
wiring boards, such as a ceramic substrate, as wiring board 22, and to use cheap wiring boards,
such as a resin substrate.
[0059]
Modification of Third Embodiment FIG. 11 is a schematic cross-sectional view showing an
acoustic sensor 91 according to a modification of the third embodiment. In this acoustic sensor
91, a groove-like air passage 83 is formed on the lower surface of the support plate 82, and both
ends of the air passage 83 are guided to the upper surface of the support plate 82 and opened at
the upper surface of the support plate 82. Then, the lower surface of the support plate 82 is
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adhered to the upper surface of the wiring substrate 22 to close the lower surface of the air
passage 83, and the back chamber 54 of the acoustic detection element 23 is formed by the
cavity 36a, the air passage 83 and the cavity 36b. There is.
[0060]
FIG. 12 is a schematic cross-sectional view showing an acoustic sensor 101 according to another
modification of the third embodiment. In this acoustic sensor 101, a linear air passage 83 is
formed horizontally inside the support plate 82, and through holes 102, 103 are formed in the
support plate 82 so as to communicate with both ends of the air passage 83. ing. Then, the lower
surface of the support plate 82 is adhered to the upper surface of the wiring substrate 22 to
close the lower surfaces of the through holes 102 and 103, and acoustic detection is performed
by the hollow portion 36a, the through hole 102, the air passage 83, the through hole 103, and
the hollow portion 36b. The back chamber 54 of the element 23 is formed.
[0061]
Fourth Embodiment In the acoustic sensor 111 according to the fourth embodiment of the
present invention, when forming the cavity 36b by etching the silicon substrate 32b from the
back side, the silicon substrate 32b is not etched to the surface, as shown in FIG. As shown in FIG.
5, the hollow portion 36b is formed in a bag shape, leaving the lid portion 112 at the top of the
hollow portion 36b. Such an acoustic sensor 111 can prevent acoustic vibration entering from
the acoustic detection element 23 side from vibrating the vibrating electrode plate 34 b through
the back chamber 54.
[0062]
Although the structure of the first embodiment is described as an example here, the hollow
portion 36b may be formed in a bag shape in the structure of the second embodiment or the
third embodiment.
[0063]
21, 61, 71, 81, 91, 101, 111 Acoustic sensor 22 Wiring substrate 23 Acoustic sensing element
25 Vibration sensing element 24, 26 Circuit element 27, 29, 72 First cover 32 a, 32 b Silicon
substrate 34 a, 34 b Vibration electrode plate 35a, 35b fixed electrode plate 36a, 36b hollow
portion 41 acoustic hole 51 adhesive 52 adhesive 53 through hole 54 back chamber 56 opening
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62 air hole 74, 83 air passage 82 support plate
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