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DESCRIPTION JP2014179685

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DESCRIPTION JP2014179685
Abstract: The present invention provides a capacitance type sensor which has a wide dynamic
range, small mismatch between sensing parts, and can be miniaturized and reduced in noise. In a
silicon substrate 12, a chamber 15 penetrating in the vertical direction is opened. A diaphragm
13 is disposed on the top surface of the silicon substrate 12 so as to cover the top opening of the
chamber 15. The diaphragm 13 is divided by a slit 17 into a region (first diaphragm 13 a)
located above the chamber 15 and a region (second diaphragm 13 b) located above the upper
surface of the silicon substrate 12. A fixed electrode plate 19 is disposed above the first
diaphragm 13a, and the first diaphragm 13a and the fixed electrode plate 19 form a first
acoustic sensing unit 23a for small volume. Further, the second diaphragm 13b and the upper
surface (conductive layer 21) of the silicon substrate 12 form a second acoustic sensing unit 23b
for large volume. [Selected figure] Figure 5
Capacitive sensor, acoustic sensor and microphone
[0001]
The present invention relates to a capacitive sensor, an acoustic sensor and a microphone.
Specifically, the present invention relates to a capacitance type sensor constituted by a capacitor
structure comprising a vibrating electrode plate (diaphragm) and a fixed electrode plate. The
present invention also relates to an acoustic sensor (acoustic transducer) that converts acoustic
vibration into an electrical signal and outputs the signal, and a microphone using the acoustic
sensor. In particular, the present invention relates to a micro-sized electrostatic capacitance type
sensor or an acoustic sensor manufactured using MEMS (Micro Electro Mechanical System)
technology.
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1
[0002]
Until now, Electret Condenser Microphones have been widely used as small-sized microphones
mounted on mobile phones and the like. However, electret condenser microphones are weak to
heat, and are inferior to MEMS microphones in terms of digitalization, miniaturization, high
functionality and multifunctionality, and power saving. Therefore, MEMS microphones are now in
widespread use.
[0003]
A MEMS microphone detects an acoustic vibration and converts it into an electrical signal
(detection signal), an acoustic sensor (acoustic transducer), a drive circuit applying a voltage to
the acoustic sensor, amplification of a detection signal from the acoustic sensor, etc. And a signal
processing circuit that performs signal processing and outputs the signal to the outside. The
acoustic sensor used for the MEMS microphone is a capacitive acoustic sensor manufactured
using MEMS technology. Further, the drive circuit and the signal processing circuit are integrally
manufactured as an application specific integrated circuit (ASIC) using a semiconductor
manufacturing technology.
[0004]
Recently, microphones are required to detect sounds from small sound pressure to high sound
pressure with high sensitivity. In general, the maximum input sound pressure of a microphone is
limited by the total harmonic distortion. This is because, if it is attempted to detect a sound with
a large sound pressure by the microphone, harmonic distortion occurs in the output signal and
the sound quality and accuracy are lost. Therefore, if the harmonic distortion rate can be
reduced, the maximum input sound pressure is increased to detect the sound pressure range of
the microphone (hereinafter referred to as the dynamic range. ) Can be broadened.
[0005]
However, in a general microphone, there is a trade-off between improvement in detection
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sensitivity of acoustic vibration and reduction in harmonic distortion rate. For this reason, in a
high sensitivity microphone capable of detecting a small volume (small sound pressure), the
harmonic distortion rate of the output signal becomes large when a large volume of sound comes
in, and hence the maximum detected sound The pressure is limited. This is because a high
sensitivity microphone has a large output signal and is prone to harmonic distortion. On the
other hand, if it is attempted to increase the maximum detected sound pressure by reducing
harmonic distortion of the output signal, the sensitivity of the microphone becomes worse, and it
becomes difficult to detect low-volume sound with high quality. As a result, it has been difficult
for a general microphone to have a wide dynamic range from low volume (low sound pressure)
to high volume (high sound pressure).
[0006]
Under such technical background, as a method of realizing a microphone having a wide dynamic
range, a microphone using a plurality of acoustic sensors having different detection sensitivities
is being studied. As such a microphone, there exist some which were disclosed by patent
document 1-4, for example.
[0007]
Patent Documents 1 and 2 disclose microphones provided with a plurality of acoustic sensors
and switching or fusing a plurality of signals from the plurality of acoustic sensors in accordance
with the sound pressure. In such a microphone, for example, a high sensitivity acoustic sensor
having a detectable sound pressure level (SPL) of about 30 dB to 115 dB and a low sensitivity
acoustic sensor having a detectable sound pressure level of about 60 dB to 140 dB By switching
and using it, it is possible to construct a microphone whose detectable sound pressure level is
about 30 dB-140 dB. Patent Documents 3 and 4 disclose one in which a plurality of independent
acoustic sensors are formed on one chip.
[0008]
FIG. 1A shows the relationship between the harmonic distortion rate and the sound pressure in
the high sensitivity acoustic sensor of Patent Document 1. FIG. 1B shows the relationship
between the harmonic distortion rate and the sound pressure in the low-sensitivity acoustic
sensor of Patent Document 1. Further, FIG. 2 shows the relationship between the average
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displacement of the diaphragm and the sound pressure in the high sensitivity acoustic sensor
and the low sensitivity acoustic sensor of Patent Document 1. Now, if the allowable harmonic
distortion rate is 20%, the maximum detection sound pressure of the high sensitivity acoustic
sensor is about 115 dB. Further, in the high sensitivity acoustic sensor, if the sound pressure
becomes smaller than about 30 dB, the S / N ratio is degraded, so the minimum detection sound
pressure is about 30 dB. Therefore, the dynamic range of the high sensitivity acoustic sensor is
approximately 30 dB to 115 dB as shown in FIG. 1A. Similarly, if the allowable harmonic
distortion rate is 20%, the maximum detection sound pressure of the low sensitivity acoustic
sensor is about 140 dB. Further, the low sensitivity acoustic sensor has a smaller diaphragm area
than the high sensitivity acoustic sensor, and as shown in FIG. 2, the average displacement of the
diaphragm is smaller than that of the high sensitivity acoustic sensor. Therefore, the minimum
detection sound pressure of the low sensitivity acoustic sensor is larger than that of the high
sensitivity acoustic sensor, which is about 60 dB. As a result, the dynamic range of the low
sensitivity acoustic sensor is approximately 60 dB to 140 dB as shown in FIG. 1B. When such a
high sensitivity acoustic sensor and a low sensitivity acoustic sensor are combined, the detectable
sound pressure range becomes as wide as about 30 dB-140 dB as shown in FIG. 1C.
[0009]
The harmonic distortion rate is defined as follows. The waveform shown by a solid line in FIG. 3A
is a sine waveform of the basic frequency f1. When this basic sinusoidal waveform is subjected to
Fourier transform, spectral components appear only at the position of frequency f1. Suppose that
the basic sine waveform of FIG. 3A is distorted as shown by the broken line in FIG. 3A for some
reason. When this distortion waveform is subjected to Fourier transform, it is assumed that a
frequency spectrum as shown in FIG. 3B is obtained. That is, it is assumed that distortion
waveforms have FFT intensities (fast Fourier transform intensities) of V1, V2,..., V5 at frequencies
f1, f2,. At this time, the harmonic distortion rate THD of the distortion waveform is defined by the
following Equation 1.
[0010]
U.S. Patent Application Publication No. 2009/0331616 U.S. Patent Application Publication No.
2010/0183167 Japanese Patent Application Publication No. 2008-245267 U.S. Patent
Application Publication No. 2007/0047746
[0011]
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However, in the microphones described in Patent Documents 1-4, even if the plurality of acoustic
sensors are formed on separate chips, the plurality of acoustic sensors are integrally formed on
one chip (substrate). Even in the case, each acoustic sensor has a capacitor structure independent
of each other.
Therefore, in these microphones, variation and mismatching occur in acoustic characteristics.
Here, the variation in acoustic characteristics refers to the difference between the acoustic
characteristics of the acoustic sensors among the chips. Further, the mismatching of the acoustic
characteristics refers to the difference between the acoustic characteristics of a plurality of
acoustic sensors in the same chip.
[0012]
Specifically, in the case where each acoustic sensor is formed on a separate chip, the variation in
chip-related detection sensitivity occurs due to the warpage of the manufactured diaphragm and
the variation in thickness. As a result, the variation between chips with respect to the difference
in detection sensitivity between acoustic sensors becomes large. In addition, even when the
individual acoustic sensors are integrally formed on a common chip, the gap distance between
the diaphragm and the fixed electrode varies when producing the capacitor structure of each
acoustic sensor using MEMS technology. Is likely to occur. Furthermore, since the back chamber
and the vent hole are separately formed, acoustic characteristics such as frequency
characteristics and phase influenced by the back chamber and the vent hole will be mismatched
in the chip.
[0013]
The present invention has been made in view of the above technical problems, and the object of
the present invention is to widen the dynamic range by integrally forming a plurality of sensing
units having different sensitivities, and thus to be performed between the sensing units. It is an
object of the present invention to provide a capacitance type sensor and an acoustic sensor
which can be reduced in mismatch and can be miniaturized and reduced in noise.
[0014]
A capacitive sensor according to the present invention comprises a substrate having a cavity
opened at least on the upper surface, a vibrating electrode plate formed above the substrate so as
to cover the upper surface of the cavity, and the vibrating electrode plate Thus, in the
capacitance type sensor provided with the back plate formed above the substrate and the fixed
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electrode plate provided on the back plate, the vibrating electrode plate includes a region located
above the cavity A first sensing unit is formed by a region located above the upper surface of the
substrate and located above the cavity of the vibrating electrode plate and the fixed electrode
plate, and the substrate of the vibrating electrode plate A second sensing portion is formed by
the region located above the top surface of the substrate and the top surface of the substrate.
[0015]
A region of the vibrating electrode plate that constitutes the first sensing unit (that is, a region
located above the cavity) and a region that constitutes the second sensing unit (that is, a region
that is located above the upper surface of the substrate) Is divided by, for example, a slit formed
in a vibrating electrode plate.
Further, in order to use the upper surface of the substrate as an electrode of the second sensing
unit, the upper surface of the substrate may be made conductive by ion implantation or the like,
or the upper surface of the substrate may be made of the vibrating electrode plate The substrate
electrode may be formed so as to face the region constituting the second sensing unit.
[0016]
According to the capacitance type sensor of the present invention, since the vibrating electrode
plate is separated, a plurality of sensing parts (variable capacitor structure) are formed between
the vibrating electrode plate and the fixed electrode plate.
Therefore, an electrical signal is output from each of the separated sensing units, and pressure
changes such as acoustic vibration can be converted into a plurality of electrical signals and
output. According to such a capacitance type sensor, for example, the detection area and
sensitivity of each sensing unit are made different by changing the area for each vibrating
electrode plate or changing the displacement amount for each vibrating electrode plate. By
switching or combining the signals, the detection area can be expanded without reducing the
sensitivity.
[0017]
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Further, since the plurality of sensing units are formed by separating the vibrating electrode
plate or the fixed electrode plate simultaneously manufactured, compared with the prior art
having a plurality of sensing units which are separately manufactured and are independent of
each other. And the characteristic variation among the sensing units is reduced. As a result, the
characteristic variation due to the difference in detection sensitivity between the sensing units
can be reduced. In addition, since each sensing unit shares the vibrating electrode plate and the
fixed electrode plate, it is possible to reduce mismatching regarding characteristics such as
frequency characteristics and phase.
[0018]
Further, in the capacitance type sensor of the present invention, since the second sensing unit is
disposed so as to surround the first sensing unit, comparison with the case where the first
sensing unit and the second sensing unit are disposed side by side is compared Thus, the
capacitive sensor can be miniaturized.
[0019]
In one embodiment of the capacitance type sensor according to the present invention, the fixed
electrode plate is formed at a position not overlapping with a region constituting the second
sensing portion of the vibrating electrode plate as viewed from above the substrate. It is
characterized by being.
According to this aspect, it is possible to reduce parasitic capacitance between the fixed electrode
plate and the region that constitutes the second sensing portion of the vibrating electrode plate.
[0020]
In another embodiment of the capacitance type sensor according to the present invention, the
area in which the first sensing unit is formed at a position where the vibrating electrode plate is
shifted to the inside of the cavity than the edge of the upper surface opening of the cavity. And
the second sensing unit is divided into regions. According to this aspect, it is possible to reduce
the parasitic capacitance between the region constituting the first sensing portion of the
vibrating electrode plate and the upper surface of the substrate. In addition, since the influence
of the Brownian motion of the air molecules between the area forming the first sensing unit and
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the upper surface of the substrate is reduced, the noise of the signal of the first sensing unit is
reduced.
[0021]
In still another embodiment of the capacitance type sensor according to the present invention, a
region of the vibrating electrode plate that constitutes the first sensing unit and a region that
constitutes the second sensing unit are partially continuous. ing. In this embodiment, since the
first sensing unit and the second sensing unit are electrically connected, the electrical wiring of
the capacitive sensor is simplified. In addition, by supporting the vibrating electrode plate with
the fixing portion at a place where the first sensing portion and the second sensing portion are
connected, the first sensing portion and the second sensing portion can be supported at one time.
[0022]
In still another embodiment of the capacitance type sensor according to the present invention,
the region constituting the second sensing portion of the vibrating electrode plate is supported at
its lower peripheral edge by a fixing portion provided on the upper surface of the substrate.
There is. According to this embodiment, since the second sensing unit can be firmly supported,
the independence of the vibration of the region constituting the first sensing unit of the vibrating
electrode plate and the region constituting the second sensing unit is maintained. Thus, the
interference between the signals of the first sensing unit and the second sensing unit can be
prevented.
[0023]
In still another embodiment of the capacitive sensor according to the present invention, the area
of the region constituting the second sensing portion of the vibrating electrode plate is the same
as that of the region constituting the first sensing portion of the vibrating electrode plate. It is
smaller than the area. According to this embodiment, the first sensing unit is a high sensitivity
sensing unit, and the second sensing unit is a low sensitivity sensing unit.
[0024]
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In still another embodiment of the capacitive sensor according to the present invention, the area
constituting the second sensing portion of the vibrating electrode plate is further divided into an
area having a relatively large area and an area having a relatively small area. ing. According to
such an embodiment, the dynamic range of the capacitive sensor can be further extended.
[0025]
An acoustic sensor according to the present invention is an acoustic sensor using the capacitance
type sensor according to the present invention, wherein the back plate and the fixed electrode
plate are formed with a plurality of holes for passing acoustic vibration. And outputting signals
with different sensitivities from the first sensing unit and the second sensing.
[0026]
In an acoustic sensor which shares a thin film and divides electrodes and has a plurality of
sensing parts, when acoustic vibration with a large sound pressure is applied, the vibrating
electrode plate collides with the back plate in the first sensing part with high sensitivity.
Distortion vibration is likely to occur.
However, since the second sensing unit of the acoustic sensor according to the present invention
has a structure that is less susceptible to the strain vibration of the back plate, harmonics of the
second sensing unit on the low sensitivity side due to the strain vibration generated on the high
sensitivity side. Distortion can be prevented from increasing, and the dynamic range of the
acoustic sensor can be prevented from narrowing.
[0027]
A microphone according to the present invention includes the acoustic sensor according to the
present invention, and a circuit unit that amplifies the signal from the acoustic sensor and
outputs the signal to the outside. According to the microphone of the present invention, it is
possible to prevent the harmonic distortion of the sensing part on the low sensitivity side from
becoming large due to the distortion vibration generated on the high sensitivity side, and to
prevent the dynamic range of the microphone from being narrowed.
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[0028]
In an embodiment of the microphone according to the present invention, a circuit for phase
inversion in which the circuit section inverts the phase of one of the output signal of the first
sensing section and the output signal of the second sensing section. Is equipped. In the acoustic
sensor (capacitance sensor) having the structure as in the present invention, the phase of the
signal is inverted between the signal output from the first sensing unit and the signal output
from the second sensing unit. However, in this embodiment, the phase inversion circuit can
invert the phase of one of the output signal of the first sensing unit and the output signal of the
second sensing unit. The phases of the output signal of the unit and the output signal of the
second sensing unit can be aligned and handled.
[0029]
In addition, the means for solving the above-mentioned subject in the present invention has the
feature which combined suitably the component explained above, and the present invention
enables many variations by the combination of such a component. .
[0030]
FIG. 1A is a diagram showing the relationship between the harmonic distortion rate and the
sound pressure in the high-sensitivity acoustic sensor of Patent Document 1.
FIG. 1B is a view showing the relationship between the harmonic distortion rate and the sound
pressure in the low sensitivity acoustic sensor of Patent Document 1. FIG. 1C is a diagram
showing the relationship between the harmonic distortion rate and the sound pressure when the
high sensitivity acoustic sensor and the low sensitivity acoustic sensor of Patent Document 1 are
combined. FIG. 2 is a view showing the relationship between the average displacement amount of
the diaphragm and the sound pressure in the high sensitivity acoustic sensor and the low
sensitivity acoustic sensor of Patent Document 1. As shown in FIG. FIG. 3A is a diagram showing
a basic waveform and a waveform including distortion. FIG. 3B is a frequency spectrum diagram
of the waveform shown in FIG. 3A. FIG. 4 is an exploded perspective view of the acoustic sensor
according to Embodiment 1 of the present invention. FIG. 5 is a cross-sectional view of an
acoustic sensor according to Embodiment 1 of the present invention. FIG. 6A is a plan view
showing a state in which the back plate is removed from the acoustic sensor according to
Embodiment 1 of the present invention. FIG. 6B is a plan view showing the acoustic sensor
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according to Embodiment 1 of the present invention from which the back plate and the fixed
electrode plate are removed. FIG. 7 is a schematic cross-sectional view showing a comparative
example in which a fixed electrode plate is also provided at a position facing the second
diaphragm. FIG. 8A is a partially broken plan view of a microphone in which the acoustic sensor
and the signal processing circuit according to Embodiment 1 of the present invention are housed
in a casing. FIG. 8B is a longitudinal sectional view of the microphone. FIG. 9 is a circuit diagram
of a microphone according to Embodiment 1 of the present invention. FIG. 10 is a plan view
showing an acoustic sensor of a reference example. FIG. 11 is a schematic cross-sectional view
showing how the diaphragm on the high sensitivity side collides with the back plate in the
acoustic sensor of the reference example. FIG. 12A is a view showing vibration generated in the
high sensitivity side back plate when the high sensitivity side diaphragm collides with the back
plate in the acoustic sensor of FIG. FIG. 12B is a diagram showing vibration propagating to the
low sensitivity side back plate when the high sensitivity side diaphragm collides with the back
plate in the acoustic sensor of FIG. FIG. 12C is a diagram showing the vibration of the diaphragm
on the low sensitivity side. FIG. 12D is a view showing a change in the gap between the high
sensitivity side diaphragm and the fixed electrode plate when the high sensitivity side diaphragm
collides with the back plate in the acoustic sensor of FIG. FIG. 13 is a schematic cross-sectional
view showing that the diaphragm on the high sensitivity (small volume) side collides with the
back plate in the acoustic sensor according to the first embodiment of the present invention. 14A
and 14B are plan views showing different arrangement examples of the anchor.
FIG. 15 is a plan view showing yet another example of arrangement of anchors. FIG. 16 is a crosssectional view showing a part of an acoustic sensor provided with a conductive layer formed of a
substrate electrode. FIG. 17 is a plan view showing a state in which the back plate is removed
from the acoustic sensor according to Embodiment 2 of the present invention. FIG. 18 is a plan
view showing a state in which the back plate is removed from the acoustic sensor according to
Embodiment 3 of the present invention. FIG. 19 is a plan view showing a state in which the back
plate is removed from the acoustic sensor according to Embodiment 4 of the present invention.
FIG. 20 is a plan view showing a state in which the back plate is removed from the acoustic
sensor according to Embodiment 5 of the present invention. 21A and 21B are schematic plan
views showing different arrangement examples of the anchor in the acoustic sensor of the fifth
embodiment.
[0031]
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
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present invention. In particular, although an acoustic sensor and a microphone will be described
below as an example, the present invention can be applied to a capacitive sensor such as a
pressure sensor as well as the acoustic sensor.
[0032]
(Structure of Embodiment 1) Hereinafter, the structure of the acoustic sensor according to
Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 4 is an
exploded perspective view of the acoustic sensor 11 according to the first embodiment of the
present invention. FIG. 5 is a cross-sectional view of the acoustic sensor 11, and also shows a
part of the acoustic sensor 11 in an enlarged manner. FIG. 6A is a plan view of the acoustic
sensor 11 excluding the back plate 18, and shows a state in which the diaphragm 13 (vibrating
electrode plate) and the fixed electrode plate 19 overlap above the silicon substrate 12
(substrate). FIG. 6B is a plan view of the acoustic sensor 11 excluding the back plate 18 and the
fixed electrode plate 19 and shows the arrangement of the diaphragm 13 on the upper surface of
the silicon substrate 12.
[0033]
The acoustic sensor 11 is a capacitive element manufactured using MEMS technology. As shown
in FIGS. 4 and 5, the acoustic sensor 11 is provided with a diaphragm 13 on the upper surface of
a silicon substrate 12 (substrate) via an anchor 16 (fixing portion), and a minute air gap 20
(above The canopy 14 is disposed via the air gap and fixed to the upper surface of the silicon
substrate 12.
[0034]
A chamber 15 (cavity) penetrating from the front surface to the back surface is opened in the
silicon substrate 12 made of single crystal silicon. In the illustrated chamber 15, a wall surface is
formed by an inclined surface formed by the (111) surface and the surface equivalent to the
(111) surface of the (100) silicon substrate, but the wall surface of the chamber 15 is a vertical
surface. May be Further, the upper surface of the silicon substrate 12 is given conductivity by ion
implantation, and becomes a conductive layer 21. The conductive layer 21 is connected to an
electrode pad 33 provided on the top surface of the back plate 18.
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[0035]
As described above, when the conductive layer 21 is formed on the upper surface of the silicon
substrate 12 by ion implantation and used as a substrate side electrode for the second acoustic
sensing unit 23 b described later, a wiring pattern by a metal film is formed on the upper surface
of the silicon substrate 12. As in the case of forming the wiring, it is not necessary to arrange the
wiring, and the process for manufacturing the acoustic sensor 11 can be simplified.
[0036]
The diaphragm 13 is disposed on the top surface of the silicon substrate 12 so as to cover the
top opening of the chamber 15.
As shown in FIGS. 4 and 6B, the diaphragm 13 is formed in a substantially rectangular shape.
The diaphragm 13 is formed of a conductive polysilicon thin film, and the diaphragm 13 itself is
a vibrating electrode plate. The diaphragm 13 is simultaneously and integrally manufactured,
and then divided into two regions by the slits 17 extending substantially in parallel with each
side of the outer periphery thereof. However, the diaphragm 13 is not completely divided into
two by the slit 17, but is mechanically and electrically connected near the end of the slit 17 (the
corner of the diaphragm 13). In the following, of the two areas divided by the slits 17, a
substantially rectangular area having a large area located at the central portion is referred to as a
first diaphragm 13a (an area forming a first sensing portion of the vibrating electrode plate). A
region formed to surround the one diaphragm 13a is referred to as a second diaphragm 13b (a
region constituting a second sensing portion of the vibrating electrode plate).
[0037]
It is also possible to completely separate the first diaphragm 13a and the second diaphragm 13b
or the second diaphragms 13b on each side mechanically and electrically, in which case each
portion is an anchor. It must be supported, and each part must be connected by a wiring pattern.
Therefore, in the present embodiment, the first diaphragm 13a and the second diaphragm 13b
are separated by the slits 17 and connected at the corner portion, thereby simplifying the
support structure and eliminating the need for connection by the wiring pattern. .
[0038]
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The diaphragms 13, ie, the first diaphragm 13a and the second diaphragm 13b, are supported on
the upper surface of the silicon substrate 12 by the anchors 16 of the leg pieces 26 provided at
each corner, and the upper surface opening of the chamber 15 and the silicon substrate 12
Supported from the top of the Further, a lead wire 27 is drawn from the diaphragm 13, and the
lead wire 27 is connected to an electrode pad 31 provided on the top surface of the back plate
18.
[0039]
As shown in FIG. 5, the canopy portion 14 is provided with a fixed electrode plate 19 made of
polysilicon on the lower surface of a back plate 18 made of SiN. The canopy portion 14 is formed
in a dome shape and has a hollow portion below it, and the hollow portion covers the diaphragm
13. A minute air gap 20 (air gap) is formed between the lower surface of the canopy 14 (that is,
the lower surface of the fixed electrode plate 19) and the upper surface of the diaphragm 13. A
lead wire 28 is drawn from the fixed electrode plate 19, and the lead wire 28 is connected to an
electrode pad 32 provided on the top surface of the back plate 18.
[0040]
A large number of acoustic holes 24 (acoustic holes) for passing acoustic vibration are formed in
the canopy 14 (that is, the back plate 18 and the fixed electrode plate 19) so as to penetrate from
the upper surface to the lower surface. As shown in FIGS. 4 and 6A, the acoustic holes 24 are
regularly arranged. In the illustrated example, the acoustic holes 24 are arranged in a triangular
shape along three directions forming an angle of 120 ° with each other, but may be arranged in
a rectangular shape, a concentric shape, or the like.
[0041]
In the acoustic sensor 11, the fixed electrode plate 19 and the first diaphragm 13a form a
capacitor structure with the air gap 20 interposed therebetween, and form a first acoustic
sensing unit 23a (first sensing unit). Similarly, the second diaphragm 13 b and the surface
(conductive layer 21) of the silicon substrate 12 form a capacitor structure with the air gap 22
interposed therebetween, and form a second acoustic sensing unit 23 b (second sensing unit).
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[0042]
Here, as shown in FIGS. 5 and 6A, the fixed electrode plate 19 is provided in a region facing the
first diaphragm 13a, and when viewed from a direction perpendicular to the upper surface of the
silicon substrate 12, the fixed electrode plate 19 is 19 is disposed so as not to overlap with the
second diaphragm 13b. When the fixed electrode plate 19 is provided at a position facing the
second diaphragm 13b as in the comparative example shown in FIG. 7, a parasitic capacitance Cs
is generated between the fixed electrode plate 19 and the second diaphragm 13b. The signal of
the first acoustic sensing unit 23a and the signal of the second acoustic sensing unit 23b
interfere with each other. On the other hand, if the fixed electrode plate 19 is provided only at
the position facing the first diaphragm 13a as in the present embodiment, the parasitic
capacitance between the fixed electrode plate 19 and the second diaphragm 13b is reduced.
Interference between the signals of the one acoustic sensing unit 23a and the second acoustic
sensing unit 23b can be prevented.
[0043]
Further, as shown in FIGS. 5 and 6B, the slit 17 is shifted to the inside of the chamber 15 more
than the edge of the top opening of the chamber 15 except for the both ends thereof.
[0044]
(Operation of Embodiment 1) In the acoustic sensor 11, when acoustic vibration enters the
chamber 15 (front chamber), the diaphragms 13a and 13b, which are thin films, vibrate in the
same phase by the acoustic vibration.
When the diaphragms 13a and 13b vibrate, the capacitances of the acoustic sensing units 23a
and 23b change. As a result, in the first acoustic sensing unit 23a, the acoustic vibration (change
in sound pressure) sensed by the first diaphragm 13a becomes a change in electrostatic
capacitance between the first diaphragm 13a and the fixed electrode plate 19, and Output as a
static signal. Further, in the second acoustic sensing unit 23 b, the acoustic vibration (change in
sound pressure) sensed by the second diaphragm 13 b is a change in electrostatic capacitance
between the second diaphragm 13 b and the conductive layer 21 of the silicon substrate 12. , Is
output as an electrical signal. Also, in the case of a use form in which the chamber 15 is a back
chamber, acoustic vibration passes through the acoustic hole 24 and enters the air gap 20 in the
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canopy 14, and the diaphragms 13a and 13b are thin films. Vibrate.
[0045]
In addition, since the area of the second diaphragm 13b is smaller than the area of the first
diaphragm 13a, the second acoustic sensing unit 23b is a low sensitivity acoustic sensor for the
sound pressure range from medium volume to large volume. The first acoustic sensing unit 23a
is a high sensitivity acoustic sensor for a sound pressure range from small volume to medium
volume. Therefore, the dynamic range of the acoustic sensor 11 can be expanded by hybridizing
both the acoustic sensing units 23a and 23b and outputting a signal by a processing circuit
described later. For example, if the dynamic range of the first acoustic sensing unit 23a is
approximately 30 to 120 dB and the dynamic range of the second acoustic sensing unit 23b is
approximately 50 to 140 dB, the dynamic range can be increased by combining both acoustic
sensing units 23a and 23b. It can be spread to about 30-140 dB. In addition, if the output of the
acoustic sensor 11 is switched by the first acoustic sensing unit 23a for small volume to medium
volume and the second acoustic sensing unit 23b for medium volume to large volume, the output
of the first acoustic sensing unit 23a is The output can not be used at high volume. As a result,
even if harmonic distortion increases in a large sound pressure region, the first acoustic sensing
unit 23a does not output from the acoustic sensor 11, and therefore the performance of the
acoustic sensor 11 is not affected. As a result, the sensitivity to the small volume of the first
acoustic sensing unit 23a can be increased.
[0046]
Furthermore, in the acoustic sensor 11, the first acoustic sensing unit 23a and the second
acoustic sensing unit 23b are formed on the same substrate. Moreover, the first acoustic sensing
unit 23 a and the second acoustic sensing unit 23 b use the first diaphragm 13 a and the second
diaphragm 13 b obtained by dividing the diaphragm 13 simultaneously and integrally
manufactured by the slits 17. That is, what is originally one sensing unit is divided into two, and
the first acoustic sensing unit 23a and the second acoustic sensing unit 23b are hybridized.
Therefore, the first acoustic sensing unit 23a and the second acoustic sensing unit 23b are
different from the prior art in which two independent sensing units are provided on one
substrate or the prior art in which sensing units are provided on separate substrates. Variations
in detection sensitivity will be similar. As a result, the variation in detection sensitivity between
the two acoustic sensing units 23a and 23b can be reduced. Moreover, since both acoustic
sensing parts 23a and 23b share the diaphragm, the mismatching regarding the acoustic
characteristics, such as a frequency characteristic and a phase, can be suppressed.
11-04-2019
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[0047]
(Application to Microphone) FIG. 8A is a partially broken plan view of the microphone 41
incorporating the acoustic sensor 11 of the first embodiment, and shows the inside by removing
the upper surface of the cover 43. FIG. FIG. 8B is a longitudinal sectional view of the microphone
41. As shown in FIG.
[0048]
The microphone 41 incorporates the acoustic sensor 11 and a signal processing circuit 44 (ASIC)
which is a circuit unit in a package including the circuit board 42 and the cover 43. The acoustic
sensor 11 and the signal processing circuit 44 are mounted on the top surface of the circuit
board 42. A sound introduction hole 45 for introducing acoustic vibration into the acoustic
sensor 11 is opened in the circuit board 42. The acoustic sensor 11 is mounted on the top
surface of the circuit board 42 so that the bottom opening of the chamber 15 is aligned with the
sound introduction hole 45 and covers the sound introduction hole 45. Therefore, the chamber
15 of the acoustic sensor 11 is a front chamber, and the space in the package is a back chamber.
[0049]
The electrode pads 31, 32 and 33 of the acoustic sensor 11 are connected to the pads 47 of the
signal processing circuit 44 by bonding wires 46 respectively. A plurality of terminals 48 for
electrically connecting the microphone 41 to the outside are provided on the lower surface of the
circuit board 42, and on the upper surface of the circuit board 42 are provided respective
electrode portions 49 electrically connected to the terminals 48. The pads 50 of the signal
processing circuit 44 mounted on the circuit board 42 are connected to the electrode unit 49 by
bonding wires 51, respectively. The pad 50 of the signal processing circuit 44 has a function of
supplying power to the acoustic sensor 11 and a function of outputting a capacitance change
signal of the acoustic sensor 11 to the outside.
[0050]
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17
A cover 43 is attached to the upper surface of the circuit board 42 so as to cover the acoustic
sensor 11 and the signal processing circuit 44. The package has a function of an electromagnetic
shield, and protects the acoustic sensor 11 and the signal processing circuit 44 from external
electric disturbance and mechanical impact.
[0051]
Thus, the acoustic vibration entering the chamber 15 through the sound introducing hole 45 is
detected by the acoustic sensor 11 and amplified and signal-processed by the signal processing
circuit 44 and output. In this microphone 41, since the space in the package is a back chamber,
the volume of the back chamber can be increased, and the sensitivity of the microphone 41 can
be enhanced.
[0052]
In the microphone 41, a sound introducing hole 45 for introducing acoustic vibration into the
package may be opened on the upper surface of the cover 43. In this case, the chamber 15 of the
acoustic sensor 11 is a back chamber, and the space in the package is a front chamber.
[0053]
FIG. 9 is a circuit diagram of the MEMS microphone 41 shown in FIG. As shown in FIG. 9, the
acoustic sensor 11 includes a first acoustic sensing unit 23a on the high sensitivity side and a
second acoustic sensing unit 23b on the low sensitivity side.
[0054]
Further, the signal processing circuit 44 includes a charge pump 52, a low sensitivity amplifier
53, a high sensitivity amplifier 54, a ΣΔ (Δ () type ADC (Analog-to-Digital Converter) 55, 56, a
reference voltage generator 57, and a buffer 58. And a phase inversion circuit 59.
[0055]
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18
The charge pump 52 applies a high voltage HV to the first acoustic sensing unit 23a and the
second acoustic sensing unit 23b, and the electric signal output from the second acoustic sensing
unit 23b is amplified by the low sensitivity amplifier 53, The electrical signal output from the
first acoustic sensing unit 23a is amplified by the high sensitivity amplifier 54.
However, the first acoustic sensing unit 23a outputs the capacitance between the upper surface
of the first diaphragm 13a and the fixed electrode plate 19, and the second acoustic sensing unit
23b is between the lower surface of the second diaphragm 13b and the conductive layer 21.
Capacitance is output. Therefore, when the air gap 20 of the first acoustic sensing unit 23 a
becomes narrow (wide), the air gap 22 of the second acoustic sensing unit 23 b becomes wide
(narrow), and the output of the first acoustic sensing unit 23 a and the second The output of the
acoustic sensing unit 23b is inverted in phase (phase is shifted by 180 °). Therefore, the output
of the second acoustic sensing unit 23b is input to the low sensitivity amplifier 53 in a state in
which the phase is reversed by the phase inversion circuit 59 and the phase difference from the
output of the first acoustic sensing unit 23a is eliminated. . Of course, the phase inversion circuit
59 may be inserted between the first acoustic sensing unit 23 a and the high sensitivity amplifier
54.
[0056]
The signal amplified by the low sensitivity amplifier 53 is converted into a digital signal by the
ΔΔ type ADC 55. Similarly, the signal amplified by the high sensitivity amplifier 54 is converted
into a digital signal in the ΔΔ type ADC 56. The digital signals converted by the ΔΔ type ADCs
55 and 56 are output to the outside on one data line as a PDM (pulse density modulation) signal
through the buffer 58. Although not shown, the first acoustic sensing unit 23a and the second
acoustic sensing unit 23b can be automatically switched according to the sound pressure by
selecting digital signals mixedly mounted on one data line according to the signal strength. .
[0057]
In the example of FIG. 9, the two digital signals converted by the ΔΔ type ADCs 55 and 56 are
mixed and output on one data line, but the two digital signals are output on separate data lines.
You may
[0058]
11-04-2019
19
Furthermore, according to the structure like the acoustic sensor 11, the acoustic sensor 11 can
be miniaturized.
The applicant of the present invention proposes a structure as shown in FIG. 10 as an acoustic
sensor in which the dynamic range is expanded by hybridizing the two acoustic sensing units and
the mismatch between acoustic sensing units is reduced. (For example, Japanese Patent
Application No. 2012-125526). In the acoustic sensor 61 (reference example) of FIG. 10, the
diaphragm 64 provided on the upper surface of the silicon substrate 62 is divided into right and
left by the slits 63 to form a large first diaphragm 64a and a small second diaphragm 64b. There
is. A fixed electrode plate 65a having a large area is provided above the first diaphragm 64a so
as to face the first diaphragm 64a, and the first diaphragm 64a and the fixed electrode plate 65a
constitute a first acoustic sensing portion 66a for high sensitivity. ing. Similarly, a fixed electrode
plate 65b having a small area facing the second diaphragm 64b is provided above the second
diaphragm 64b, and a second acoustic sensing unit 66b for low sensitivity is provided by the
second diaphragm 64b and the fixed electrode plate 65b. Are configured. In such an acoustic
sensor 61, since the first acoustic sensing unit 66a and the second acoustic sensing unit 66b are
arranged side by side, the size as viewed from above becomes large, and the occupied area when
mounted on a wiring board or the like is large. Become.
[0059]
On the other hand, in the acoustic sensor 11 of the present embodiment, since the first acoustic
sensing unit 23a and the second acoustic sensing unit 23b are formed in the central portion and
the outer circumferential portion, the conventional acoustic sensor 11 has a single acoustic
sensing unit. Almost the same size as the acoustic sensor. Therefore, according to the acoustic
sensor 11 of the present embodiment, the sensor size can be made smaller than that of the
acoustic sensor 61 of the reference example.
[0060]
Further, in the acoustic sensor 61 as shown in FIG. 10, the low sensitivity side is caused by the
interference between the high sensitivity side (small volume side) first acoustic sensing unit 66a
and the low sensitivity side (high volume side) second acoustic sensing unit 66b. The harmonic
distortion of the acoustic sensor is increased, and as a result, the maximum detection sound
pressure of the acoustic sensor may be reduced to narrow the dynamic range. According to the
acoustic sensor 11 according to the first embodiment of the present invention, such an increase
11-04-2019
20
in harmonic distortion can be prevented. The reason is as follows.
[0061]
First, the case of the acoustic sensor 61 will be described. The first diaphragm 64a on the high
sensitivity side has a larger area and is flexible than the second diaphragm 64b on the low
sensitivity side. Therefore, when acoustic vibration of high sound pressure is applied to the
acoustic sensor 61, as shown in FIG. 11, the first diaphragm 64a may collide with the back plate
67a. FIG. 11 shows that in the acoustic sensor 61, the first diaphragm 64a collides with the back
plate 67a due to high sound pressure.
[0062]
When the first diaphragm 64a collides with the back plate 67a as shown in FIG. 11, the shock
causes the vibration of the back plate 67a to be distorted, resulting in strained vibration as
shown in FIG. 12A. The back plate vibrates by acoustic vibration as well as the diaphragm, but
since the amplitude of the back plate is about 1/100 of the amplitude of the diaphragm, the
acoustic vibration is not shown in FIG. Since the strain vibration generated in the back plate 67a
is transmitted to the back plate 67b, the strain vibration as shown in FIG. 12B occurs in the back
plate 67b due to the collision of the first diaphragm 64a. On the other hand, since the second
diaphragm 64b has a smaller displacement than the first diaphragm 64a, the second diaphragm
64b does not collide with the back plate 67b, and performs, for example, sinusoidal vibration as
shown in FIG. 12C. When strain vibration of the back plate 67b is added to the sine wave
vibration of the second diaphragm 64b, the gap distance between the back plate 67b and the
second diaphragm 64b in the second acoustic sensing unit 66b changes as shown in FIG. 12D.
Become. As a result, the output signal from the second acoustic sensing unit 66b is distorted, and
the harmonic distortion rate of the second acoustic sensing unit 66b is degraded. For this reason,
in the acoustic sensor 61, a configuration for preventing distortion vibration generated on the
first acoustic sensing unit side from being transmitted to the second acoustic sensing unit side is
required.
[0063]
On the other hand, in the case of the acoustic sensor 11 according to the first embodiment, as
shown in FIG. 13, even if the first diaphragm 13 a collides with the back plate 18 due to the large
11-04-2019
21
sound pressure and distortion vibration occurs, the distortion vibration is generated. Is unlikely
to affect the second acoustic sensing unit 23b, and the harmonic distortion rate of the second
acoustic sensing unit 23b is unlikely to deteriorate. That is, since the second acoustic sensing
unit 23 b does not include the back plate 18 or the fixed electrode plate 19, the output of the
second acoustic sensing unit 23 b is not affected by the strain vibration of the back plate 18. As a
result, it is possible to prevent the dynamic range of the acoustic sensor 11 from being narrowed
due to strain vibration in the first acoustic sensing unit 23a.
[0064]
In the acoustic sensor 11 of the first embodiment, as shown in FIG. 5, the slit 17 is shifted to the
inside of the chamber 15 rather than the edge of the top opening of the chamber 15 except for
the both ends. As a result, when viewed in a direction perpendicular to the upper surface of the
silicon substrate 12, the first diaphragm 13 a does not overlap with the upper surface
(conductive layer 21) of the silicon substrate 12, and parasitics between the first diaphragm 13 a
and the conductive layer 21. The capacity can be reduced, and the signal interference of the first
acoustic sensing unit 23a can be reduced.
[0065]
In addition, since air is trapped between the diaphragm 13 and the upper surface of the silicon
substrate 12, the Brownian motion of air molecules trapped here may cause acoustic noise.
However, in the acoustic sensor 11 according to the first embodiment, the slit 17 is provided
between the first diaphragm 13a and the second diaphragm 13b, and the slit 17 is shifted to the
inside of the chamber 15 rather than the edge of the top opening of the chamber 15. . For this
reason, the air captured between the first diaphragm 13a and the upper surface of the silicon
substrate 12 can be eliminated, and the air sensor is not affected by the acoustic noise due to the
air molecules captured here. Acoustic noise can be reduced.
[0066]
(Different Arrangement Example of Anchor) In the first embodiment, the diaphragm 13 supports
the leg pieces 26 provided at the corner portions by the anchor 16, but the support structure of
the diaphragm 13 is shown in FIGS. 14A, 14B and 15. Thus, various forms are conceivable.
[0067]
11-04-2019
22
In FIG. 14A, anchors 16 are added to the outer peripheral edge of each side of the second
diaphragm 13b.
In FIG. 14B, the anchor 16 is provided on the entire outer peripheral edge of the second
diaphragm 13b. In FIG. 15, anchors 16 are provided to fly along the outer peripheral edge of the
second diaphragm 13b. According to these modifications, the diaphragm 13, particularly the
second diaphragm 13b, can be firmly supported by the anchor 16, so that the independence of
the vibration of the first acoustic sensing unit 23a and the second acoustic sensing unit 23b can
be maintained. Signal interference can be mutually prevented.
[0068]
(Different Structure of Conductive Layer) The conductive layer 21 on the surface of the silicon
substrate 12 may be a substrate electrode formed by patterning a metal thin film on the upper
surface of the silicon substrate 12 as shown in FIG. . In such a modification, since the area of the
conductive layer 21 is determined by the patterning region of the metal thin film, the variation in
the area of the conductive layer 21 is reduced.
[0069]
Second Embodiment FIG. 17 is a schematic plan view of an acoustic sensor 71 according to a
second embodiment of the present invention from which a back plate is removed. In this
embodiment, the first diaphragm 13 a and the four second diaphragms 13 b on each side are
completely separated from each other by the slits 17. The first diaphragm 13a is connected to
the electrode pad 31a on the back plate by a lead wire 27a drawn from the first diaphragm 13a.
The four second diaphragms 13 b are drawn out from the lead wires 27 b, and each lead wire 27
b is connected to the electrode pad 31 b on the back plate by a wire 72.
[0070]
According to this embodiment, the electrical wiring of the first diaphragm 13a of the first
acoustic sensing unit 23a and the electrical wiring of the second diaphragm 13b of the second
acoustic sensing unit 23b can be performed separately and independently. The parasitic
capacitance between the acoustic sensing unit 23a and the second acoustic sensing unit 23b can
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23
be reduced, and signals can not easily interfere with each other.
[0071]
Third Embodiment FIG. 18 is a schematic plan view of an acoustic sensor 74 according to a third
embodiment of the present invention from which a back plate is removed.
In this embodiment, the first diaphragm 13 a and the second diaphragm 13 b are completely
separated from each other by the slit 17. On the other hand, the second diaphragms 13 b on
each side are connected mechanically and electrically at the corner portions of the diaphragms
13. The first diaphragm 13a is connected to the electrode pad 31a on the back plate by a lead
wire 27a drawn from the first diaphragm 13a. The second diaphragm 13b is connected to the
electrode pad 31b on the back plate by a lead wire 27b drawn from the second diaphragm 13b.
[0072]
According to this embodiment, the electrical wiring of the first diaphragm 13a of the first
acoustic sensing unit 23a and the electrical wiring of the second diaphragm 13b of the second
acoustic sensing unit 23b can be performed separately and independently. The parasitic
capacitance between the acoustic sensing unit 23a and the second acoustic sensing unit 23b can
be reduced, and signals can not easily interfere with each other. And since it is not necessary to
connect the 2nd diaphragms 13b of each side, wiring can be simplified.
[0073]
Fourth Embodiment FIG. 19 is a schematic plan view of an acoustic sensor 76 according to a
fourth embodiment of the present invention from which a back plate is removed. In this
embodiment, the first diaphragm 13 a and the four second diaphragms 13 b on each side are
completely separated from each other by the slits 17. In any two second diaphragms 13ba and
13bb of the four second diaphragms 13b, the area of one second diaphragm 13bb is larger than
the area of the other second diaphragm 13ba. Thus, the capacitance between the first diaphragm
13a and the fixed electrode plate 19 constitutes a first acoustic sensing unit 23a (first sensing
unit) for small volume (high sensitivity). The second acoustic sensing unit 23c (second sensing
unit) for medium volume (medium sensitivity) is configured by the capacitance between the
11-04-2019
24
second diaphragm 13bb and the upper surface of the silicon substrate 12, and the second
diaphragm 13ba and the silicon substrate The second acoustic sensing unit 23 b (second sensing
unit) for high sound volume (low sensitivity) is configured by the electrostatic capacitance
between the upper surfaces of the twelve. The first diaphragm 13a is connected to the electrode
pad 31a on the back plate by a lead wire 27a drawn from the first diaphragm 13a. The second
diaphragm 13bb is connected to the electrode pad 31bb on the back plate by the lead wire 27bb.
The second diaphragm 13ba is connected to the electrode pad 31ba on the back plate by the lead
wire 27ba. The fixed electrode plate 19 is connected to the electrode pad 32 on the back plate by
the lead wire 28, and the upper surface (conductive layer 21) of the silicon substrate 12 is
connected to the electrode pad 33.
[0074]
According to this embodiment, since the first sound sensing unit 23a for small volume, the
second sound sensing unit 23c for medium volume, and the second sound sensing unit 23b for
large volume are configured, the acoustic sensor It is possible to further expand the sound
pressure range (dynamic range) of 76.
[0075]
Fifth Embodiment FIG. 20 is a schematic plan view of an acoustic sensor 81 according to a fifth
embodiment of the present invention from which a back plate is removed.
In this embodiment, the circular diaphragm 13 is divided by the slits 17 into an arc-shaped
second diaphragm 13 b located on the outer peripheral side and a circular first diaphragm 13 a
located inside thereof. Further, a fixed electrode plate 19 is formed on the lower surface of the
back chamber so as to face the first diaphragm 13a.
[0076]
The first diaphragm 13a is supported in a cantilevered manner above the chamber 15 by fixing
the lead wire 27a with the silicon substrate 12 or the like. The first diaphragm 13 a and the fixed
electrode plate 19 constitute a first acoustic sensing unit 23 a for small volume.
[0077]
11-04-2019
25
The second diaphragm 13 b is supported by a substantially arc-shaped anchor 16 at the outer
peripheral portion of the lower surface of the second diaphragm 13 b. The second diaphragm 13
b and the conductive layer 21 of the silicon substrate 12 constitute a second acoustic sensing
unit 23 b for large volume.
[0078]
In addition, as shown to FIG. 21A, the anchor 16 may be provided in a line along the lower
surface outer peripheral part of the 2nd diaphragm 13b.
[0079]
Further, as shown in FIG. 21B, a part of the upper surface of the silicon substrate 12 is projected
toward the inside of the circular chamber 15, and a crescent-shaped anchor 82 is provided
thereon, and the end of the first diaphragm 13a is The anchor 82 may support in a cantilever
manner.
If such an anchor 82 is used, the strength of the first diaphragm 13a can be improved.
[0080]
Although the acoustic sensor and the microphone using the acoustic sensor have been described
above, the present invention can also be applied to a capacitance sensor other than the acoustic
sensor such as a pressure sensor.
[0081]
11, 71, 74, 76, 81 Acoustic sensor 12 Silicon substrate 13 Diaphragm 13 a First diaphragm 13 b
Second diaphragm 15 chamber 16, 82 Anchor 17 Slit 18 Back plate 19 Fixed electrode plate 21
Conductive layer 23 a First acoustic sensing unit 23 b First 2 Acoustic sensing unit 24 Acoustic
hole 41 Microphone 44 Signal processing circuit 45 Sound introduction hole 59 Circuit for phase
reversal
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26
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