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JP2007208544

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DESCRIPTION JP2007208544
In a capacitance type acoustic sensor, when an excessive sound pressure is applied or a rush
voltage is applied, short circuit between each other is prevented even when the diaphragm and
the back plate are in contact with each other, and an allowable input sound pressure higher than
before is prevented. Achieves high inrush voltage resistance. An acoustic sensor (1) has a
diaphragm (3) vibrating by sound and a back plate (4) opposite thereto, and detects a sound by
detecting a change in capacitance between the two. The diaphragm 3 is provided with an
insulating member 6 for preventing electrical contact between the plate 3 and the back plate 4.
The insulating member 6 may be provided on the opposite surface of the back plate 4 facing the
diaphragm 3. Further, the insulating member 6 may be provided in the vicinity of the central
portion of either one of the opposing surfaces of the diaphragm 3 or the back plate 4. [Selected
figure] Figure 1
Acoustic sensor
[0001]
The present invention relates to a capacitance-type acoustic sensor that detects an acoustic
sound such as an audible sound or an ultrasonic wave that transmits air or the like as a medium.
[0002]
Conventionally, an acoustic sensor is provided that acoustically vibrates one electrode of a
counter electrode type capacitor, for example, a parallel plate capacitor, and converts a change in
acoustic pressure into an electrical change in capacitance of the capacitor to perform acoustic
detection. It is known (for example, refer to patent documents 1).
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1
[0003]
Such a capacitive acoustic sensor includes, for example, a diaphragm, a back plate, a connection
portion, and a substrate.
The diaphragm and the back plate are electrically isolated from each other by a connecting
portion and separated by an air gap and held on a substrate to form a capacitive capacitor.
At least a part of each of the diaphragm and the back plate is a conductor to be a counter
electrode. The connecting portion supports the diaphragm and the back plate in the vicinity of
the diaphragm so as not to disturb the vibration of the diaphragm. A portion of the substrate may
constitute a diaphragm or back plate. In addition to converting sound into an electrical signal,
such an acoustic sensor can also convert an electrical signal into sound, and functions as a socalled bi-directional acoustoelectric transducer. JP-A-6-217396
[0004]
However, in the conventional capacitance-type acoustic sensor as disclosed in Patent Document
1, when the excessive sound pressure is applied or the rush voltage is applied, the largest
displacement portion of the diaphragm contacts the back plate and the diaphragm is And the
back plate may short circuit, and the acoustic sensor may be destroyed or noise may be mixed in
the acoustic detection signal.
[0005]
The present invention solves the above-mentioned problems, and even if the diaphragm and the
back plate are in contact with each other at the time of excessive sound pressure application or
rush voltage application due to a simple configuration, no mutual short circuit occurs. An object
of the present invention is to provide a capacitive acoustic sensor having high pressure and high
inrush voltage resistance.
[0006]
In order to achieve the above object, the invention according to claim 1 is an acoustic sensor that
has a diaphragm that vibrates by sound and a back plate that faces it, and detects the sound by
detecting a change in capacitance between the two. An insulating member for preventing
electrical contact with each other is provided on the opposing surface of at least one of the
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2
diaphragm and the back plate.
[0007]
According to a second aspect of the present invention, in the acoustic sensor according to the
first aspect, the insulating member is provided in the vicinity of a central portion of the facing
surface.
[0008]
According to the invention of claim 1, since the insulating member for preventing the electrical
contact with each other is provided on the opposite surface of at least one of the diaphragm and
the back plate, the excessive sound pressure application, rush voltage application, etc.
Sometimes, even when the diaphragm and the back plate are in contact with each other, there is
no electrical short circuit, and it is possible to provide a capacitive acoustic sensor having a high
allowable input sound pressure and a high inrush voltage resistance.
[0009]
According to the invention of claim 2, since the insulating member is provided in the vicinity of
the central portion of the diaphragm which is usually the maximum displacement portion of the
diaphragm, the insulating member for preventing electrical shorting when the diaphragm and the
back plate are in contact is minimized Performance of the acoustic sensor by minimizing the
decrease in the sensitivity of the acoustic sensor by reducing the mass added to the diaphragm as
compared to the case where the insulating member is provided on the entire diaphragm. Can be
pulled out.
[0010]
Hereinafter, a capacitive acoustic sensor according to an embodiment of the present invention
will be described with reference to the drawings.
[0011]
First Embodiment FIG. 1 shows a capacitive acoustic sensor 1 according to a first embodiment of
the present invention, FIG. 2 shows an outline of the acoustic sensor, and FIG. Shows the
disassembly state.
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The acoustic sensor 1 according to the present embodiment is a sensor that has a diaphragm 3
vibrating by sound and a back plate 4 facing it, and detects sound by detecting a change in
capacitance between the two, and vibration that opposes each other The diaphragm 3 is provided
with an insulating member 6 for preventing electrical contact between the plate 3 and the back
plate 4.
[0012]
More specifically, the acoustic sensor 1 includes a substrate 2 having a recess 21 for holding the
shape of the acoustic sensor 1 and guiding the sound, and the diaphragm 3 is formed by being
laminated on the substrate 2 and surrounding the diaphragm 3 Is held by the substrate 2 and
one surface of the diaphragm 2 faces the recess 21, and the diaphragm 3 of the portion facing
the recess 21 vibrates by sound.
Further, the back plate 4 is fixed to the diaphragm 3 so as to maintain a predetermined distance
by the insulating connection portions 5 provided at two places on the outer peripheral portion of
the diaphragm 3.
Further, for example, a recess 21 is formed on the substrate 2 by etching a silicon wafer by a
semiconductor process.
In the following, the substrate 2 is a silicon substrate, and the acoustic sensor 1 is described as
being formed using a silicon semiconductor process, but the material of the substrate 2 and the
formation process of the acoustic sensor 1 are limited thereto. is not.
[0013]
Next, each component will be described.
The diaphragm 3 is a member that forms a parallel plate capacitor with the back plate, and in the
present embodiment, the entire vibrating portion is formed of a conductor, and serves as one
counter electrode of the capacitor.
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The diaphragm 3 is formed to have a sufficiently thin thickness, for example, about 1 to 2 μm,
so as to vibrate by a minute change in sound pressure of the sound arriving from the outside.
Such a diaphragm 3 is formed using a semiconductor process. For example, a thin film having a
predetermined thickness to be the diaphragm 3 is laminated on the substrate 2 and a part of the
substrate 2 is removed by etching to form a recess 21, and the diaphragm 3 is formed on the
bottom of the recess 21. Exposed. Such a diaphragm 3 is held by the substrate 2 around its
periphery, and the portion exposed at the bottom of the recess 21 becomes a vibrating portion
that vibrates freely.
[0014]
As the thin film to be the above-described diaphragm 3, a diffusion layer formed by diffusing
high concentration impurities in the substrate 2, a deposited layer of a polysilicon film formed on
the substrate 2, or the like can be used. When the diaphragm 3 is formed of a nonconductive or
high-resistance thin film such as a polysilicon film, doping of impurities or laminating of a metal
thin film vibrates the conductivity as an electrode of a capacitor. The application to the plate 3 is
also performed. In addition, an SOI substrate having an active layer can also be used as the
substrate 2 having a thin film layer to be the diaphragm 3. The diaphragm 3 includes a
connection pad 32 for outputting an electric signal from the diaphragm 3 to the outside. For
example, wire bonding is performed on the connection pad 32.
[0015]
In the present embodiment, the back plate 4 is entirely formed of a conductor and serves as one
counter electrode of the capacitor. The back plate 4 is a fixed electrode with respect to the
diaphragm 3 and forms a parallel plate capacitor with the diaphragm 3 so that a change in sound
pressure due to sound can be detected as a change in capacity.
[0016]
Further, the back plate 4 is provided with an air flow hole for reducing air resistance between the
diaphragm 3 and the back plate 4, so-called acoustic hole 41, so that the diaphragm 3 freely
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5
vibrates without delay according to the sound. ing. Also, the back plate 4 has two portions
supported by the connection portion 5 for air circulation, and air can freely flow in or out from
the periphery of the back plate 4, and In order to suppress the occurrence of parasitic
capacitance, it has a minimum external dimension. The back plate 4 is provided with connection
pads 42 for outputting an electrical signal from the back plate 4 to the outside. For example, wire
bonding is performed on the connection pad 42.
[0017]
The back plate 4 having the above-described structure is formed by a film forming technique or
an etching technique of a semiconductor process. For example, as in the formation of the
diaphragm 3, the back plate 4 can be formed using a diffusion layer formed by performing high
concentration impurity diffusion in the substrate 2, a layer of a polysilicon film formed on the
substrate 2, or the like. . It is also performed to add impurities to a non-conductive or highresistance thin film or to stack metal thin films to give the back plate 4 conductivity as an
electrode of a capacitor.
[0018]
The connecting portion 5 is located between the diaphragm 3 and the back plate 4 and is
maintained at a constant distance in a state in which the both are electrically insulated. For
example, in the semiconductor process, a silicon oxide film, a silicon nitride film, or the like can
be used as the material of the connection portion 5.
[0019]
In the present embodiment, the insulating member 6 is formed on the entire upper surface of the
diaphragm 3, that is, the surface facing the back plate 4. As a material of the insulating member
6, for example, in a semiconductor process, a silicon oxide film, a silicon nitride film, or the like
can be used. Since such an insulating member 6 prevents the electrical contact between the
diaphragm 3 and the back plate 4, even when the excessive sound pressure is applied or the rush
voltage is applied, the diaphragm 3 and the back plate 4 are in contact with each other. The
acoustic sensor 1 having a high allowable input sound pressure and the acoustic sensor 1 having
a high inrush voltage resistance can be realized without being short-circuited with each other.
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[0020]
The acoustic sensor 1 having the above-described components and structure is, for example,
sequentially stacking material layers of the components on a silicon substrate using a
semiconductor process, and using the known patterning technique and etching technique for
each layer. Processed and formed. Further, as described above, impurity diffusion or doping may
be performed to impart conductivity. Instead of forming a film at the time of processing, it is also
possible to use an SOI substrate formed in advance.
[0021]
In addition, the connection portion 5 can be formed by a method of sacrificial layer etching. In
the sacrificial layer etching, a layer called a sacrificial layer, a part of which becomes the
connection portion 5 and the other part is etched away, is formed on the diaphragm 3 to form
the shape of the back plate 4 After that, the sacrificial layer is etched. In the etching of the
sacrificial layer, the sacrificial layer in the lower layer of the back plate 4 is etched away so that
the connection portion 5 remains, as a result, a three-dimensional three-dimensional structure in
which the back plate 4 is supported by the connection portion 5 is formed. The sacrificial layer
etching is performed by making the etching rate of the connection portion 5 higher than the
etching rates of other members, that is, the substrate 2, the diaphragm 3, the insulating member
6, and the back plate 4 (including resist protection). It is easily done by isotropic etching.
[0022]
FIG. 4 and FIG. 5 respectively show modifications of the capacitive acoustic sensor 1 according to
the third embodiment described above. Unlike the acoustic sensor 1 shown in FIG. 1, the
insulating member 6 of the acoustic sensor 1 shown in these figures is limited not to the entire
surface of the diaphragm 3 but near the central portion of the surface of the diaphragm 3 facing
the back plate 4. Is provided. The central portion of the diaphragm 3 is usually the largest
displacement portion of the diaphragm 3, and the insulating member is provided near the central
portion, so the number of insulating members can be minimized. The mass added to the
diaphragm 3 is smaller than in the case where the insulating member is provided on the whole of
the diaphragm 3, and the decrease in sensitivity of the acoustic sensor 1 can be minimized.
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[0023]
Further, the acoustic sensor 1 shown in FIG. 4 is the one in which the whole of the diaphragm 3
is conductive in the same manner as the acoustic sensor shown in FIG. 1 described above, and
the acoustic sensor 1 shown in FIG. The only central part of the diaphragm 3 is conductive. The
electrode portion of the diaphragm 3 of the acoustic sensor 1 of FIG. 5 is connected to the
connection pad 32 by a conductor pattern (not shown) or a low resistance portion doped with
impurities.
[0024]
In the acoustic sensor 1 of FIG. 5, the conductive portion of the diaphragm 3, that is, the portion
to be the electrode of the parallel plate capacitor is formed to be limited to the portion where the
amplitude of the central portion of the diaphragm 3 is large. The parasitic capacitance, in other
words, the component of the capacitance that does not contribute to the capacitance fluctuation
is small, and accordingly, the ratio of the fluctuation capacitance (signal component) to the total
capacitance is high because the parasitic capacitance is smaller than those shown in It becomes
high sensitivity.
[0025]
Second Embodiment FIG. 6 shows a capacitive acoustic sensor 1 according to a second
embodiment of the present invention.
The acoustic sensor 1 according to the first embodiment is that the insulating member 6 is
provided on the lower surface of the back plate 4, that is, the surface of the back plate 4 facing
the diaphragm 3 in this embodiment. However, the other points are the same as the acoustic
sensor 1 of the first embodiment.
[0026]
In such an acoustic sensor 1, for example, using a semiconductor process, a sacrificial layer for
forming the connection portion 5 is formed on the diaphragm 3, and further, each layer for
forming the insulating member 6 and the back plate Forming the three-dimensional threedimensional structure in which the insulating member 6 and the back plate 4 are supported at
the connection portion 5 by performing simultaneous patterning of the insulating member 6 and
the back plate 4 and then performing sacrificial layer etching of the sacrificial layer can do.
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[0027]
FIGS. 7 and 8 each show a modification of the capacitive acoustic sensor 1 according to the
second embodiment described above.
Unlike the acoustic sensor 1 shown in FIG. 6, the insulating member 6 of the acoustic sensor 1
shown in these figures is not the entire surface of the back plate 4 but near the central portion of
the back plate 4 and the maximum displacement portion of the diaphragm 3 It is limited to the
part that faces the The acoustic sensor 1 shown in FIG. 7 is the same as the acoustic sensor
shown in FIG. 6 described above in that the entire back plate 4 is conductive, and the acoustic
sensor 1 shown in FIG. Only the central part of the plate 4 is conductive.
[0028]
The electrode portion at the center of the back plate 4 of the acoustic sensor 1 of FIG. 8 is
connected to the connection pad 42 by a conductor pattern (not shown) or a low resistance
portion doped with impurities. Like the acoustic sensor 1 shown in FIG. 5, the acoustic sensor 1
shown in FIG. 8 has high sensitivity because it has less parasitic capacitance than those shown in
FIG. 6 and FIG.
[0029]
As described above, in the acoustic sensor 1 of the present invention, since the insulating
member 6 is provided on the opposing surface of the entire surface or central portion of the
diaphragm 3 or the back plate 4, when applying excessive sound pressure or applying rush
voltage, Even when the diaphragm 3 and the back plate 4 are in contact with each other, short
circuit can be prevented, and higher allowable input sound pressure and higher rush voltage
resistance can be realized.
[0030]
The present invention is not limited to the above-described configuration, and various
modifications are possible.
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For example, the connection portion 5 may be provided on a substrate, and the back plate 4 may
be held by the substrate 2. Further, instead of using the substrate 2 and the diaphragm 3 as
separate layers, the diaphragm 3 may be formed using the material of the substrate 2 itself.
Moreover, it can also be set as the acoustic sensor 1 of the structure which combined the
structure of the above-mentioned each embodiment. Further, in the above, the acoustic sensor 1
having high inrush voltage resistance is characterized in that the acoustic sensor 1 has high
resistance to inrush voltage when a bias voltage is applied between the diaphragm 3 and the
back plate 4; The characteristic in the case of using it as an electroacoustic transducer (speaker)
which converts an electric signal into sound is described.
[0031]
FIG. 1 is a cross-sectional view of a capacitive acoustic sensor according to a first embodiment of
the present invention. The perspective view of an acoustic sensor same as the above. The
disassembled perspective view of an acoustic sensor same as the above. Sectional drawing of the
modification of an acoustic sensor same as the above. Sectional drawing of the other modification
of an acoustic sensor same as the above. Sectional drawing about the electrostatic sensor of the
electrostatic capacitance type which concerns on the 2nd Embodiment of this invention.
Sectional drawing of the modification of an acoustic sensor same as the above. Sectional drawing
of the other modification of an acoustic sensor same as the above.
Explanation of sign
[0032]
1 acoustic sensor 3 diaphragm 4 back plate 6 insulating member
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