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DESCRIPTION JP2007208549

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DESCRIPTION JP2007208549
The present invention provides an electrostatic capacitance type acoustic sensor that achieves
miniaturization, improvement in noise resistance, and high sensitivity, and is inexpensive. An
acoustic sensor (1) according to the present embodiment includes a diaphragm (3) formed on a
silicon substrate (2) and vibrated by sound and a back plate (4) opposed to the diaphragm (3).
Thus, the sensor is provided with a capacitance component 10 on the substrate 2 for reference,
which is a sensor for detecting sound and for receiving and amplifying a signal of capacitance
change. The capacitive component 10 for reference is made of a semiconductor structure, and is
formed of a material forming the acoustic detection portion of the main body of the acoustic
sensor 1 and a manufacturing process. [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 that vibrates one of the electrodes of a counter electrode type
capacitor, for example, a parallel plate capacitor, acoustically, converts a change in acoustic
pressure into an electrical change in the capacitance of the capacitor, and performs acoustic
detection It is known (for example, refer to patent documents 1).
[0003]
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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 with an air gap and held by the substrate to form a parallel plate capacitor.
At least a part of each of the diaphragm and the back plate is a conductor to be a counter
electrode. The connection portion supports both of 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 so-called bi-directional acoustoelectric transducer. JP-A-6-217396
[0004]
However, in the capacitive acoustic sensor as described above and shown in Patent Document 1,
when the sensor is used in a portable device, a hearing aid or the like, acoustic detection is
required to realize the required miniaturization. Because of structural limitations, it is necessary
to make the electrostatic capacitance for the small size of about 1 pF level. Therefore, the
influence of electromagnetic noise due to wiring routing and the parasitic capacitance
component generated between the signal wiring and the ground line As a result, there is a
problem that the sensitivity and the S / N ratio decrease.
[0005]
In order to detect a slight current generated by the above-described slight change in capacitance,
an amplifier circuit such as a preamplifier or an operational amplifier provided with a field effect
transistor (FET) in an input stage is used.
However, these amplifiers alone can not sufficiently eliminate the effects of noise and parasitic
capacitance, and noise reduction and elimination of parasitic components can be achieved by
using a differential amplifier or a charge amplifier type amplifier that outputs a voltage
proportional to the electric quantity. To be done. When using such an amplifier, a reference
capacitance component is used. Therefore, the performance such as noise resistance of the
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acoustic sensor is affected by the manufacturing variation of the capacitance value of the
reference capacitance component and the capacitance value fluctuation due to the temperature
change, and the acoustic sensor with stable product characteristics and good performance is
obtained. There is a problem that it is difficult to manufacture with good productivity and at low
cost.
[0006]
The present invention is intended to solve the above-mentioned problems, and it is an object of
the present invention to realize miniaturization, improvement in noise resistance, and high
sensitivity, and to provide an inexpensive capacitive acoustic sensor. .
[0007]
In order to achieve the above object, the invention according to claim 1 has a diaphragm formed
on a silicon substrate and vibrated by sound, and a back plate facing the diaphragm, and detects
a change in capacitance between the two. Thus, in the acoustic sensor for detecting the sound, a
capacitance component to be referred to by an amplification unit for receiving and amplifying
the signal of the capacitance change is provided on the substrate.
[0008]
The invention of claim 2 is the acoustic sensor according to claim 1, wherein the capacitive
component for reference comprises a semiconductor structure.
[0009]
The invention of claim 3 is the acoustic sensor according to claim 2, wherein the capacitive
component for reference is formed by inserting a high dielectric constant material between
semiconductor structures.
[0010]
The invention of claim 4 is the acoustic sensor according to claim 2, wherein the capacitive
component for reference is formed of a material forming an acoustic sensor main body.
[0011]
The invention according to claim 5 is the acoustic sensor according to any one of claims 1 to 4,
wherein the reference capacitance component is between the diaphragm and the back plate
when the amplification unit is a differential amplifier. The differential amplification input
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terminal to which the signal of capacitance change is input is connected to another differential
amplification input terminal and used.
[0012]
According to a sixth aspect of the present invention, in the acoustic sensor according to any one
of the first to fourth aspects, the capacitive component for reference is used in a feedback loop of
the amplification unit.
[0013]
According to the first aspect of the present invention, since the reference capacitive component
used by the amplification unit is provided on the substrate together with the acoustic sensor
main body, the reference capacitive component is similarly affected by the temperature
fluctuation etc. which the acoustic sensor main body receives. As a result, temperature
compensation can be performed by the capacitance component for reference, and even when the
size is reduced, it is possible to provide an acoustic sensor that realizes improvement in noise
resistance and high sensitivity.
In addition, since the capacitive component for reference can be formed simultaneously with the
formation of the capacitive component for acoustic detection consisting of a diaphragm, a back
plate, etc., the influence of dimensional variations in manufacturing, etc. affects both capacitive
components. The same effect is achieved, and therefore, the influence of dimensional variation
can be reduced as a whole of the acoustic sensor, and as a result, the output can be stabilized,
and miniaturization, improvement in noise resistance, and high sensitivity can be realized.
[0014]
According to the second aspect of the invention, since the capacitive component for reference
can be simultaneously formed by the silicon semiconductor process forming the acoustic sensor
body, the acoustic sensor can be manufactured at low cost.
[0015]
According to the invention of claim 3, by increasing the relative dielectric constant, the area for
realizing the same capacitance value can be reduced, so that the capacity component for
reference can be realized with a small area, and the acoustic sensor can be miniaturized. it can.
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[0016]
According to the invention of claim 4, since the capacitive component for reference can be
simultaneously formed by the silicon semiconductor process forming the acoustic sensor main
body, it is possible to suppress the variation of the performance of the acoustic sensor as a whole
to a certain level. There is no increase in the number, the manufacturability is good, and a highly
sensitive acoustic sensor can be realized at low cost.
[0017]
According to the invention of claim 5, since the acoustic sensor main body and the capacitive
component for reference commonly receive the influence of electromagnetic noise from the
surrounding environment as so-called common noise, the common noise component is removed
by differential amplification. Low noise, stable output acoustic sensor can be realized.
[0018]
According to the invention of claim 6, so-called charge amplifier type amplification can be
performed which amplifies only the fluctuation of the capacitance for detecting sound, so that,
for example, between the signal line and the ground (ground) It is possible to eliminate the
influence of the parasitic capacitance that occurs and to realize high sensitivity.
[0019]
Hereinafter, a capacitive acoustic sensor according to an embodiment of the present invention
will be described with reference to the drawings.
[0020]
First Embodiment FIGS. 1A and 1B show a capacitance type acoustic sensor 1 according to a first
embodiment of the present invention, and FIGS. 2 and 3 show the appearance of the acoustic
sensor 1. .
The acoustic sensor 1 of the present embodiment has a diaphragm 3 formed on a silicon
substrate 2 and vibrated by sound, and a back plate 4 opposed to the diaphragm 3, and detects a
change in capacitance between the two. The sensor is provided with a capacitance component 10
(capacitance element) for reference by an amplification unit that receives and amplifies a signal
of capacitance change.
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The capacitive component 10 for reference has a semiconductor structure, and is formed by a
material and a manufacturing process that form an acoustic sensor main body (sound pressure
detection unit) including the diaphragm 3 and the back plate 4.
[0021]
Next, each component of the acoustic sensor 1 will be described.
The manufacturing process of the acoustic sensor 1 will be described later (FIG. 4).
The silicon substrate 2 (abbreviated as the substrate 2) is a substantially square frame (frame)
having a recess 21 and a diaphragm formed in a plan view, and the frame holds the shape of the
acoustic sensor 1; The recess 21 guides the sound to the diaphragm 3.
The bottom of the recess 21 is the diaphragm 3.
That is, one surface of the diaphragm 3 is made to face the recess 21 and the substrate 2 holds
the periphery of the diaphragm 3.
The diaphragm 3 facing the recess 21 vibrates due to the sound propagating from the opening
side of the recess 21.
[0022]
The recess 21 is formed, for example, by etching a silicon wafer by a semiconductor process.
The recess 21 of the present embodiment has a quadrangular frustum shape, and is formed by
etching utilizing crystal anisotropy of silicon.
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When crystal anisotropy is not used, for example, when using a processing method such as dry
process, the shape of the recess 21 is not limited to a square, but may be a desired shape such as
a circular mask shape. be able to.
The material of the substrate 2 is silicon, and the outer size is a square having a side of about 1
mm to 2 mm, and a thickness of about 0.5 mm.
[0023]
The diaphragm 3 is a member that vibrates due to a slight change in sound pressure of the sound
arriving from the outside, and is a member that forms a parallel plate capacitor with the back
plate 4.
The diaphragm 3 has a substantially rectangular shape whose one side is about 1.0 mm in plan
view, has a sufficiently thin thickness in cross section as compared with the frame of the
substrate 2, and minute sound pressure change of the sound arriving from the outside To vibrate,
for example, about 1 to 2 .mu.m.
The substrate 2 forming the diaphragm 3 is, for example, a high resistance silicon substrate
having a resistivity of 1 × 10 <+3> (Ω · cm) or more. The central portion of the diaphragm 3
made of such a high resistance material is made conductive, and the conductor portion 31 to be
the counter electrode of the parallel plate capacitor is formed.
[0024]
The above-described conductor portion 31 is made conductive by doping an approximately
rectangular area of about 0.5 mm in the central portion of the diaphragm 3 with an impurity
element such as phosphorus by a semiconductor diffusion process. The resistivity of the
conductor portion 31 is desirably 1 × 10 <-3> (Ω · cm) or less. As a result, the difference in
resistivity with the high resistance semiconductor substrate is 10 <6> times or more, and the
area of the conductor portion 31 can be effectively limited.
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[0025]
In order to output an electrical signal to the outside from the capacitor electrode on the
diaphragm 3 side, that is, the conductor portion 31, the circuit 32 by the doping portion
extended from the conductor portion 31 and the connection pad 33 disposed at the end portion
of the circuit 32 are formed. It is done. The connection pad 33 is used as a wire bonding pad, for
example, when mounting an acoustic sensor on a mounting substrate.
[0026]
The back plate 4 has a main part in a substantially rectangular shape in plan view, is formed of a
conductive material, and serves as a fixed electrode for the vibrating plate 3 vibrating by sound,
that is, a vibrating electrode. In addition, a parallel plate condenser is formed so that a change in
sound pressure due to sound can be detected as a change in capacity. In addition, the back plate
4 has a minimum external dimension so that air can freely flow in or out from the peripheral
portion thereof, and can further suppress generation of parasitic capacitance.
[0027]
In addition, the back plate 4 releases air between the diaphragm 3 and the back plate 4 so that
the back plate 4 does not vibrate due to air pressure, and the diaphragm 3 vibrates freely
according to the sound without delay. A plurality of through holes for air circulation to reduce
resistance, so-called acoustic holes 41 are provided. The acoustic hole 41 has a substantially
square shape with a side of about 10 μm, and is formed by a semiconductor process such as
etching. The acoustic hole 41 allows the diaphragm 3 to be freely displaced with respect to the
sound pressure. Furthermore, by appropriately designing the shape and the number of the
acoustic holes 41, it is possible to suppress the excessive resonance of the diaphragm 3 and to
realize the acoustic sensor 1 having a wide band and flat sensitivity characteristics.
[0028]
The material of the back plate 4 is, for example, polysilicon deposited by a method such as CVD,
and doping of impurities is performed to impart conductivity to high-resistance polysilicon. In
addition, in order to extract an electrical signal from the back plate 4, a connection pad 42 used
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for wire bonding or the like is provided.
[0029]
In addition, the back plate 4 is configured on the substrate 2 via one or more insulating
connection portions 5. 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. The gap between the back plate
4 and the diaphragm 3 is adjusted by the height of the connection portion 5. The gap is, for
example, about 1 to 10 μm or less according to the characteristic design of the acoustic sensor
1. In the present embodiment, the connecting portions 5 are at least two places so as not to
prevent the flow of air entering and exiting from the gap.
[0030]
The capacitor component 10 for reference is laminated on the lower electrode 11 made of a
conductive layer formed by doping the silicon substrate 2 with impurities, the silicon oxide film
12 laminated on the lower electrode 11, and the silicon oxide film An upper electrode 13 is
provided to have a capacitance C2 (the circuit diagram of FIG. 5). That is, the capacitive
component 10 is configured using a so-called semiconductor structure. Further, as a dielectric
inserted between the electrodes 11 and 13, a silicon oxide film 12 which is a high dielectric
constant material having a relative dielectric constant of about four times that of air is used.
[0031]
The capacitive component 10 is provided at the end of the connection pad 14 provided on the
upper part of the upper electrode 13 and the circuit 15 by the doping part extended from the
conductive lower layer of the lower electrode 11 for connection to the external circuit. And a
connection pad 16.
[0032]
The structure of such a capacitive component 10 is simultaneously formed using the same
manufacturing process and the same material as the acoustic sensor main body provided with
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the diaphragm 3, the back plate 4, and the connection portion to detect an acoustic signal.
That is, the lower electrode 11 is formed by doping simultaneously with the formation of the
conductor portion 31, the silicon oxide film 12 is formed simultaneously with the connection
portion 5, and the upper electrode 13 is simultaneously formed with the back plate 4. Further,
the shape and arrangement of the capacitive component 10 can be easily implemented by
incorporating a mask pattern for the capacitive component 10 into an exposure mask or the like
used for forming the acoustic sensor main body. For example, a desired value can be obtained by
changing the shapes of the lower electrode 11 and upper electrode 13 pattern formation masks,
for example, for the capacitance of the capacitive component 10.
[0033]
Further, since the relative dielectric constant of the silicon oxide film 12 inserted between the
electrodes 11 and 13 is about four times that of air, the capacity component 10 can be
miniaturized. For example, when the capacitance component 10 has a capacitance value similar
to that of the capacitance C1 (FIG. 5) of the acoustic sensor main body, the area of the electrodes
11 and 13 may be about 1/4 of the area of the conductor portion 31 It will be.
[0034]
Further, although the required area is increased, a non-oscillating capacitance component 10
having a capacitance equivalent to that of the acoustic sensor main body is realized by
simultaneously forming a semiconductor structure having the same dimensions as the acoustic
sensor main body on the silicon substrate 2. Can (not shown). The capacitance component 10 in
this case is equivalent in size and structure to the acoustic sensor main body, and produces
capacitance fluctuations equal to one another with respect to environmental changes such as
temperature changes, so it is effective as a reference capacitance used for temperature
compensation etc. .
[0035]
Next, with reference to FIGS. 4A to 4D, a manufacturing process of the acoustic sensor 1
according to the first embodiment will be described. The structures of the diaphragm 3, the
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conductor 31, the connection 5, the back plate 4 and the capacitance component 10, etc., formed
on the substrate 2 described above are formed by laminating a thin film and reducing the
resistance of the high resistance The acoustic sensor 1 is formed through the steps of
conductorization, shape formation by etching, etc., to obtain a final three-dimensional shape. In
addition, a large number of acoustic sensors 1 are collectively manufactured on one wide silicon
substrate, and finally, individualization is performed by dicing the silicon substrates to obtain a
large number of acoustic sensors 1, so-called multi-cavity manufacturing Manufactured by the
method.
[0036]
The acoustic sensor 1 is manufactured in approximately two steps of a film forming process
including the doping of FIG. 4A and a subsequent etching process. First, the laminated structure
shown in FIG. 4A is formed. That is, the region to be the conductor portion 31 of the silicon
substrate 2 and the region to be the lower electrode 11 are made conductive by doping with
impurities, and the silicon oxide film 50 is formed on the entire surface of the substrate 2
including these regions. And a polysilicon layer 40 for forming the back plate 4 is formed
thereon, and further, the polysilicon layer 40 is made conductive by doping.
[0037]
As described above, the substrate 2 made of silicon has a high resistivity of 1 × 10 <+3> (Ω ·
cm) or more, and the conductor portion 31 made conductive by doping has a resistivity of 1 ×
10 <-3> (Ω · cm) or less. For doping, for example, boron (element symbol B) or phosphorus
(element symbol P) can be used as an impurity.
[0038]
A part of the silicon oxide film 50 is left as the connection part 5, but most of the silicon oxide
film 50 is removed by etching in order to form the upper polysilicon layer 40 (back plate 4)
three-dimensionally. It is.
[0039]
As shown in FIG. 4B, the above-described conductive polysilicon layer 40 is formed by removing
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the unnecessary polysilicon portion by etching, and providing the back plate 4 with the acoustic
hole 41 which is a through hole, and the upper electrode And 13 are formed.
The whole of the back plate 4 and the upper electrode 13 is a conductor, and each becomes an
electrode of a capacitor.
[0040]
Next, as shown in FIG. 4C, the recess 21 is formed on the lower surface of the substrate 2 by
etching. By this etching, the bottom surface of the recess 21 which is the upper surface of the
substrate 2 is formed as the diaphragm 3.
[0041]
Next, as shown in FIG. 4 (d), the silicon oxide film 50 is isotropically etched using an aqueous
solution such as hydrofluoric acid to form a predetermined gap between the back plate 4 and the
diaphragm 3. While securing, the three-dimensional structure which leaves the connection part 5
and the silicon oxide film 12 of the capacitive component 10 is formed (so-called sacrificial layer
etching). In isotropic etching, etching of a portion to be etched in contact with an aqueous
solution proceeds substantially uniformly. Therefore, the through holes of the acoustic holes 41
function as etching solution supply holes when the silicon oxide film 50 (sacrificial layer) in the
lower layer of the back plate 4 is removed by etching. After the sacrificial layer etching, postprocessing such as formation of connection pads 42 and 14 and separation into pieces by dicing
is performed to complete the acoustic sensor 1.
[0042]
Next, the operation of the acoustic sensor 1 will be described with reference to the amplification
circuit of FIG. The acoustic detection signal of the acoustic sensor 1 is amplified by, for example,
an amplification circuit using the operational amplifier OP shown in FIG. The capacitance
component of the acoustic sensor main body (sound pressure detection unit) and the capacitance
component 10 for reference are indicated by electrostatic capacitances C1 and C2 which are
equivalent circuits in this amplification circuit. One end (connection pad 33) of the electrostatic
capacitance C1 is connected to the inverting amplification terminal of the operational amplifier
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OP, and the other end (connection pad 42) of the electrostatic capacitance C1 is connected via
the resistor R1 and the DC power supply E connected in series. Connected to the ground. The
non-inverting amplification terminal of the operational amplifier OP is connected to one end
(connection pad 14) of the capacitance component 10 for reference, that is, the capacitance C2,
and the other end (connection pad 16) of the capacitance C2 is grounded. It is connected.
Further, a feedback resistor R2 is connected to the inverting amplification terminal of the
operational amplifier OP.
[0043]
In the above-described amplifier circuit (differential amplifier circuit), a change in capacitance C1
that changes due to the action of the sound arriving at the acoustic sensor 1 is detected and
amplified with reference to the reference capacitance C2. The reference capacitance C2 as a
reference is formed on the same silicon substrate 2 in the acoustic sensor 1 together with the
capacitance C1 of the acoustic sensor body by the same process. That is, the capacitive
component 10 is formed simultaneously with the formation of the capacitive component for
acoustic detection (that is, the acoustic sensor main body) including the diaphragm 3 and the
back plate 4.
[0044]
Therefore, the electrostatic capacitance C1 and the electrostatic capacitance C2 have the same
effect on both capacitive components due to the influence of dimensional variations in
manufacturing, etc., and the area and thickness of the electrode forming each parallel plate
capacitor, and the electrode The dimensions, such as the distance between them, are formed
under common variation factors that both grow and thin together. In the amplification circuit
shown in FIG. 5, the difference in capacitance of the electrostatic capacitances C1 and C2 formed
under the same manufacturing conditions as variation factors is amplified and taken out as the
output of the acoustic sensor 1, and therefore, based on the manufacturing variation. The cause
of the signal degradation is canceled, stable output is obtained, and the external electromagnetic
noise component can be canceled by the same effect, and the acoustic sensor 1 with a good SN
ratio can be realized, downsizing, improvement of noise resistance, and high It is possible to
realize sensitivity.
[0045]
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In addition, since the acoustic sensor 1 includes the reference capacitive component 10 used by
the amplification unit on the same substrate 2 together with the acoustic sensor main body, the
capacitive component 10 for reference is similarly affected by the temperature fluctuation and
the like that the acoustic sensor main body receives. As a result, temperature compensation can
be performed by the capacitive component 10 for reference. In addition, since the acoustic
sensor body and the capacitive component for reference commonly receive the influence of
electromagnetic noise from the ambient environment as common noise, the common noise
component is removed by differential amplification, and a low noise and stable output is
obtained. An acoustic sensor can be realized. Therefore, even when the acoustic sensor is
miniaturized, it is possible to provide the acoustic sensor 1 in which the noise resistance is
improved and the sensitivity is increased. Further, since the capacitive component 10 for
reference can be simultaneously formed by the silicon semiconductor process forming the
acoustic sensor main body, the number of processes does not increase, the manufacturability is
good, and a highly sensitive acoustic sensor can be realized at low cost.
[0046]
Second Embodiment FIGS. 6A and 6B show a capacitance type acoustic sensor 1 according to a
second embodiment of the present invention, and FIG. 7 shows an appearance of the acoustic
sensor 1. These show the example of the circuit of the amplification part which amplifies the
output of the acoustic signal of the acoustic sensor 1. FIG. In the acoustic sensor 1 according to
the second embodiment, in the acoustic sensor 1 according to the first embodiment described
above, the connection pad 33 of the acoustic sensor main body and the connection pad 16 of the
capacitive component 10 are put together in one place, The common connection pad 33 is used,
and the other points are the same as those of the acoustic sensor 1 according to the first
embodiment. The number of connection pads of the acoustic sensor 1 is smaller than that of the
acoustic sensor 1 according to the first embodiment, the number of connection steps for
mounting the acoustic sensor 1 is reduced, and the mounting reliability can also be improved.
[0047]
The acoustic detection output of the acoustic sensor 1 is amplified by an amplifier circuit using
an operational amplifier OP as shown in FIG. 8, for example. One end (connection pad 33) of the
electrostatic capacitance C1 is connected to the inverting amplification terminal of the
operational amplifier OP, and the other end (connection pad 42) of the electrostatic capacitance
C1 is connected via the resistor R1 and the DC power supply E connected in series. Connected to
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the ground. The non-inversion amplification terminal of the operational amplifier OP is
connected to the ground. The reference capacitance component 10, that is, the capacitance C2 is
used in the feedback loop of the operational amplifier OP, one end (connection pad 16) of the
capacitance C2 is connected to the inverting amplification terminal of the operational amplifier
OP, and the other end The (connection pad 14) is connected to the output side of the operational
amplifier OP.
[0048]
The output when the acoustic detection signal of the acoustic sensor 1 is amplified using the
above-described amplifier circuit is ΔC1 / C2 × V, using the bias voltage V by the DC power
supply E that drives the acoustic sensor 1 It is known to be. Here, ΔC1 is a variation of the
capacitance C1. That the output of the amplified result is represented by fluctuation ΔC1 and
does not include C1 has the following meaning. That is, the capacitance C1 used as an equivalent
circuit of the acoustic detection unit of the acoustic sensor 1 is normally between the signal line
from the acoustic sensor main body to the operational amplifier OP and the ground line close to
the signal line, etc. Contains parasitic capacitance that occurs in Such parasitic capacitances
cause the sensitivity of the acoustic sensor 1 to decrease, but since these do not fluctuate, they
are automatically eliminated from the fluctuation ΔC1. Therefore, according to such a
configuration, it is possible to amplify (so-called charge amplifier type) amplification that
amplifies the fluctuation of the capacitance C1 for detecting sound of the acoustic sensor main
body, so the influence of parasitic capacitance can be eliminated, High sensitivity can be realized.
[0049]
Further, the electrostatic capacitance C1 and the electrostatic capacitance C2 are formed on the
same substrate by the same material and the same manufacturing process, and the effect by this
can be obtained in the acoustic sensor according to the first embodiment described above.
Similar to 1.
[0050]
As described above, the capacitance-type acoustic sensor 1 of the present invention for detecting
an acoustic sound such as an audible sound or an ultrasonic wave transmitted through a medium
such as air is based on a semiconductor material such as silicon and is It can be made very small
in size using the same semiconductor process as integrated circuits) etc., and can be used for
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microphones, ultrasonic sensors, hearing aids, etc. for portable devices.
The present invention is not limited to the above-described configuration, and various
modifications are possible. For example, a circuit for amplifying an acoustic signal can also be
used in combination with the above-described differential amplifier and a charge amplifier type
amplifier. Moreover, the formation method of the capacity component 10 for a reference is not
restricted to the above-mentioned embodiment. For example, another dielectric material may be
used instead of the silicon oxide film 12 used as the dielectric material sandwiched between the
upper and lower electrodes 13 and 11, or the distance between the electrodes 13 and 11 may be
thinner than the thickness of the silicon oxide film 50. You can Further, the number, the
arrangement, the outer shape, and the like of the capacitive component 10 for reference are not
limited to the above-described embodiment, and may be plural or the outer shape may be
circular.
[0051]
(A) is the sectional view on the AA line of (b) about the capacitance type acoustic sensor
concerning a 1st embodiment of the present invention, (b) is a top view of the acoustic sensor.
The virtual disassembled perspective view of an acoustic sensor same as the above. The
perspective view of an acoustic sensor same as the above. (A)-(d) is sectional drawing which
shows the manufacturing process of an acoustic sensor same as the above in order of a main
process. The circuit diagram of the amplification part which amplifies the output of the acoustic
signal of an acoustic sensor same as the above. (A) is a BB sectional view of (b) about a capacitive
acoustic sensor concerning a 2nd embodiment of the present invention, (b) is a top view of the
acoustic sensor. The perspective view of an acoustic sensor same as the above. The circuit
diagram of the amplification part which amplifies the output of the acoustic signal of an acoustic
sensor same as the above.
Explanation of sign
[0052]
1 acoustic sensor 2 silicon substrate 3 diaphragm 4 back plate 10 capacitance component C1
capacitance (of the acoustic sensor body) C2 capacitance (of the capacitance component for
reference)
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