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JP2010057167

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2010057167
PROBLEM TO BE SOLVED: To provide a directional microphone excellent in directivity and
durability. SOLUTION: A base 31 having an opening 311 at a central portion, a bridge 11 bridged
over an opening 311 of the base 31, and a diaphragm elastically supported via a support shaft
321 at the central portion of the bridge 11. 32 and a plurality of fixed electrodes 13A to 13D
which are disposed opposite to the diaphragm 32 at the opening 311 with a gap and held by the
base 31, are provided at the center of the bridge 111, and the diaphragm 32 is made incident by
the sound wave. And a plurality of elastic members 32 elastically supporting the support shaft
321 of the diaphragm 32 from the side so that the incident surface of the light source tilts in
accordance with the sound source direction. Therefore, the sound collection characteristic
regarding the sound wave in the sound source direction is improved, and a microphone with high
directivity can be obtained. In addition, the pointing direction can be automatically adjusted
according to the sound source direction without changing the direction of the entire microphone.
Furthermore, since the diaphragm 32 is supported by the plurality of elastic portions 12, the
durability of the support portion can be improved. [Selected figure] Figure 1
Directional microphone
[0001]
The present invention relates to directional microphones.
[0002]
Conventionally, there is known a microphone which supports a central point of a diaphragm on
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an axis and detects a distribution of magnitudes of vibration amplitudes when the diaphragm
around the axis vibrates due to sound pressure to specify a sound source direction. .
However, when the diaphragm is vibrated for a long time, the shaft is deformed due to fatigue,
and there is a problem that the diaphragm is inclined even if the sound wave is not received.
[0003]
Therefore, in the invention described in Patent Document 1, an electrode for suppressing the
inclination of the diaphragm is provided, a voltage is applied to the electrode to suppress the
inclination, and the sound source direction is specified from the voltage.
[0004]
Unexamined-Japanese-Patent No. 2006-345130
[0005]
However, in the invention described in Patent Document 1, although the sound source direction
can be specified, there is a problem that the directivity of the microphone is hindered because
the inclination of the diaphragm is suppressed.
[0006]
The directional microphone according to the invention of claim 1 comprises a base substrate
having a void in the central portion, a beam structure bridged over the void of the base substrate,
and elasticity via a support shaft at the central portion of the beam structure. Provided at a
central portion of a beam structure, including a supported diaphragm, a fixed electrode
configured to have a plurality of divided electrodes which are disposed opposite to each other by
providing a gap with a diaphragm in a space, and held by a base substrate A plurality of elastic
members elastically supporting the support shaft of the diaphragm from the side are provided
such that the incident surface of the diaphragm is inclined according to the sound source
direction by the incidence of sound waves.
The directional microphone according to the invention of claim 2 comprises a base substrate
having a void in the central portion, a beam structure bridged over the void of the base substrate,
and a plurality of divided plates each of which is divided into a plurality of beams. A diaphragm
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which is elastically supported at a central portion of the housing, a fixed electrode configured to
have a plurality of divided electrodes which are disposed opposite to each other by providing a
split plate and a gap in a space and having a plurality of split electrodes held therein; Providing a
plurality of elastic members for elastically supporting the divided plates on the side
circumference of the support shaft provided at the central portion of the beam structure so that
the incident planes of the plurality of divided plates are inclined according to the sound source
direction It is characterized by
The directional microphone according to the invention of claim 3 is displaced according to the
direction of the sound wave incident on the base substrate having a space at the center, the
diaphragm on which the first comb electrode is formed, and the diaphragm. And a support
portion for elastically supporting the diaphragm through a plurality of elastic members above the
cavity of the base substrate, and a plurality of divided electrodes held by the base substrate,
having a first comb electrode and an air gap The second comb electrode meshing with each other
comprises a fixed electrode formed on each of the divided electrodes, and the diaphragm, the
support portion and the fixed electrode are formed by the same Si layer of an SOI (Silicon on
Insulator) substrate. I assume.
Further, as in the invention of claim 9, each of the electrostatic capacitances between the
plurality of divided electrodes and the diaphragm is individually detected by the detection unit
corresponding to each of the divided electrodes, and each detected by the detection unit The
direction of the sound source may be specified by the calculation unit based on the capacitance.
[0007]
According to the present invention, it is possible to obtain a directional microphone having
excellent directivity and durability.
[0008]
It is a front view of microphone 1 of this embodiment.
It is D1-D1 sectional drawing of FIG. It is a figure explaining the inclination generation |
occurrence | production of the diaphragm 32 by a sound source direction. It is a figure
explaining basic equation derivation of a parallel plate type microphone. It is a figure explaining
an output voltage. It is a figure which shows the equivalent circuit of FIG. It is a figure explaining
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sound source direction specification. It is a figure explaining process (a)-(d) of a manufacturing
process. It is a figure explaining the process (e) of a manufacturing process. It is a figure
explaining process (f), (g) of a manufacturing process. It is a figure explaining process (h)-(k) of a
manufacturing process. It is a figure explaining process (l)-(o) of a manufacturing process. It is a
figure which shows the microphone of 2nd Embodiment, (a) is a front view, (b) is D1-D1 sectional
drawing. It is a figure which shows the mode of the diaphragm 32 when the sound wave from a
sound source is received. It is a figure which shows the microphone of 3rd Embodiment, (a) is a
front view, (b) is D1-D1 sectional drawing. It is a figure explaining the relationship between the
direction of a sound source, and the displacement of diaphragm 32. FIG. It is a figure which
shows the modification of 3rd Embodiment, (a) shows a 1st modification, (b) shows a 2nd
modification. It is a figure which shows the modification of 3rd Embodiment, (a) shows a 3rd
modification, (b) shows a 4th modification. It is a figure which shows the modification of the
elastic part 12. As shown in FIG. It is a figure which shows the structure at the time of dividing |
segmenting the diaphragm 32 shown in FIG. 1 into four division | segmentation diaphragms
32A-32D. It is a top view which shows the modification of the microphone shown in FIG. It is a
figure which shows the modification of a comb-tooth electrode, (a) shows a 1st modification, (b)
shows a 2nd modification, respectively. It is a figure explaining a pressure difference, and (a)
shows the case where the back side of diaphragm 230 serves as a sealed space, and (b) shows
the case where the space by the side of the diaphragm back is in a semi-sealed state. It is a figure
explaining propagation of a pressure difference in a gap. It is a figure which shows the
relationship between gap width and a fluctuation | variation volume.
[0009]
Hereinafter, an embodiment of the present invention will be described with reference to the
drawings. -1st Embodiment-FIG.1, 2 is a figure which shows schematic structure of the
directional microphone of this Embodiment. FIG. 1 is a front view of the microphone 1, and FIG. 2
is a cross-sectional view taken along the line D1-D1 of FIG. The microphone 1 is manufactured by
micromachining technology or photolithography technology using an SOI (Silicon on Insulator)
substrate having a three-layer structure of a lower Si layer 30, an SiO 2 layer 20, and an upper Si
layer 10 as shown in FIG. Be done.
[0010]
In the base 31 formed by the lower Si layer 30, a circular opening 311 is formed to penetrate. On
the upper surface side of the base 31, four bridges 11 are arranged in a cross shape so as to be
bridged over the circular opening 311. One end of each bridge 11 is fixed on a base 31. At the
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other end of each bridge 11, an elastic portion 12 is provided. Each elastic portion 12 elastically
connects between the bridge 11 and the support shaft 321 provided on the diaphragm 32. The
support shaft 321 is formed to project perpendicularly from the center (that is, the center of
gravity) of the disk-like diaphragm 32. As a result, the bridge 11 elastically supports its central
portion in such a manner as to suspend the diaphragm 32.
[0011]
Four fixed electrodes 13A to 13D are provided on the upper surface of the base 31 so as to cover
the upper surface of the opening 311. Each of the fixed electrodes 13A to 13D has a fan shape
with a central angle of 90 degrees, and a wiring portion 131 and a terminal portion 132 are
provided. The bridge 11 and the fixed electrodes 13A to 13D are formed of the upper Si layer 10
of the SOI substrate, and a polycrystalline silicon film 40 and an aluminum film 50 are
sequentially formed on the upper surface of the upper Si layer 10. As described above, the
microphone 1 according to the present embodiment constitutes a condenser microphone
including the diaphragm 32 and the plurality of fixed electrodes 13A to 13D disposed opposite
to each other in parallel.
[0012]
The diaphragm 32, which is a diaphragm, vibrates when receiving a sound pressure, and the gap
between the fixed electrodes 13A to 13D and the diaphragm 32 changes according to the period
of the sound wave. Further, since the support shaft 321 and the bridge 11 are connected by the
elastic portion 12, the elastic portion 12 is bent when an external force is applied to the
diaphragm 32 by the sound pressure. For example, when the sound source is in the axial
direction of the microphone 1 (that is, in the axial direction of the circular opening 311), each
elastic portion 12 is bent substantially equally and the entire diaphragm 32 is in the axial
direction of the microphone 1 (that is, the circular opening It is displaced (oscillated) in a parallel
state to the axial direction of 311). The capacitance between each of the fixed electrodes 13A to
13D and the diaphragm 32 changes in accordance with the vibration or displacement of the
diaphragm 32.
[0013]
On the other hand, as shown in FIG. 3, when the sound source is in a direction obliquely inclined
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with respect to the central axis J of the microphone 1, the arrival time and the sound pressure of
the sound wave from the sound source differ depending on the position on the diaphragm 32.
The diaphragm 32 is inclined so that the normal of the diaphragm 32 is directed to the sound
source direction. Then, in the inclined state, the diaphragm 32 vibrates according to the output of
the sound wave.
[0014]
Here, the electrostatic capacitance C in a parallel plate is represented by following Formula (1). In
Formula (1), Q is a charge, V is a voltage, ε is a dielectric constant, S is an electrode area, and d
is an inter-electrode distance.
[0015]
In the microphone 1, the inter-electrode distance d corresponds to the distance between the fixed
electrodes 13A to 13D and the diaphragm 32. Strictly speaking, since the diaphragm 32 does not
necessarily move in parallel, the equation (1) can not be applied as it is, and it is necessary to
change the equation according to the shape of the diaphragm 32. However, as the distance
between the fixed electrodes 13A to 13D and the diaphragm 32 decreases, the capacitance
increases, and conversely, when the distance increases, the capacitance decreases, as in the case
of the parallel plate electrode. Therefore, when the sound source is in the oblique direction, the
diaphragm 32 is inclined and the distances to the fixed electrodes 13A to 13D are different from
each other, so the capacitances of the fixed electrodes 13A to 13D have different values.
[0016]
When the diaphragm 32 is inclined as shown in FIG. 3, the capacitance Ca of the fixed electrode
13A closer to the sound source is smaller, and the capacitance Cc of the fixed electrode 13C
farther from the sound source is larger. The diaphragm 32 vibrates according to the output of
the sound wave around the inclined state. Further, depending on the position of the sound
source, the period of change in capacitance also differs in each of the fixed electrodes 13A to
13D. This is because the diaphragm 32 is not rigid but rigid, so it does not always follow the
sound wave immediately, and the time difference between the change is due to the position on
the plane between the position where the sound wave first reaches and the position where it
finally reaches. Is caused.
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[0017]
Next, a signal detection method in the microphone 1 will be described. In the capacitance type
microphone as in the present embodiment, the change in capacitance value due to the fluctuation
of the diaphragm is taken out in the form of a voltage signal applied to the load resistance. With
regard to the microphone thus functioning as an electrostatic transducer, the following shows the
derivation of the basic equation of a general electrostatic transducer and its output voltage.
[0018]
[1. Derivation of Basic Formula] Here, as shown in FIG. 4, parallel plate electrodes facing
each other with a narrow gap are considered. This corresponds to the vibrating plate 32 when
the fixed electrodes 13A to 13D are one fixed electrode 100, and the electrode 101 displaced by
an external force.
[0019]
A direct-current voltage applied between the electrodes is E0, an alternating-current voltage is e,
an external force acting on the electrodes 101 is f, and an electrode distance before displacement
occurs is d0. Also, let X be a displacement of the electrode 101 when a DC voltage E 0 is applied,
x be a minute displacement, and C (x) be a capacitance generated between the electrodes. At this
time, if Lagrange's equation of motion is used for the model system shown in FIG. 4, Lagrangian
and the dissipation function become as in the following equations (2) and (3), respectively. Here,
m is a mass of the electrode 101, v is a displacement speed of the electrode 101, k is a spring
constant of a portion (corresponding to the elastic portion 12) elastically supporting the
electrode 101, and Q0 applies a DC voltage E0. It is assumed that q is a charge generated by the
alternating voltage e. Also, rf is the mechanical resistance in the system.
[0020]
Assuming that the area of the opposing surface of the parallel plate electrode is S, the equation of
capacitance generated between the parallel plate electrodes is expressed by the following
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equation (4). In addition, Lagrange's equations of motion of the mechanical system and the
electrical system are sequentially expressed by equations (5) and (6).
[0021]
By substituting the equations (2) and (3) into the equation (5) and expanding the equation, the
following equation (7) is obtained. Furthermore, the third term on the right side of Formula (7) is
expanded as Formula (8).
[0022]
Further, when the equation (8) is subjected to Taylor expansion, the following equation (9) is
obtained.
[0023]
Since the first term of equation (9) is a static term, it can be removed and put into equation (7)
and summarized to obtain final equation (10) as a basic equation of a mechanical system.
In Formula (10), A, B, and C (0) are represented by the following Formulas (11) to (13).
[0024]
Similarly, when equations (2) and (3) are substituted into equation (6) and expanded, equation
(14) is obtained.
[0025]
Taylor expansion of equation (14) yields equation (15), and elimination of Q0 = C0E0 as a static
term yields equation (16).
Therefore, the basic equation of the electrical system is equation (17). When equation (17) is
phasor-displayed, equation (18) is obtained.
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[0026]
[2. Output Voltage] In general, DC voltage Ep applied between parallel plate electrodes in a
state of actual use is supplied through some impedance as shown in FIG. This impedance usually
has a large value in applications such as condenser microphones. Therefore, when the
capacitance changes due to the displacement of the electrode 101, the DC voltage Ep also
changes. In addition, since the time constant due to the electrostatic capacitance C0 of the
parallel plate electrode and the resistance R0 is also a considerably large value, the movement of
charge is hardly performed in the frequency range used as a microphone.
[0027]
At this time, in the basic formula of the electrical system, e = −R0i (19) and the following
formula (20) holds, and by substituting the formulas (19) and (20) into the formula (18) Formula
(21) is obtained. This equivalent circuit can be written as shown in FIG. v = jω x (20)
[0028]
As described above, according to the microphone of the first embodiment, the following effects
can be obtained.
[0029]
(1) According to the microphone of the present invention, it is possible to read the change of the
capacitance according to the vibration of the diaphragm 32 by the sound wave as the voltage e
by using electrostatic conversion.
As shown in FIG. 3, the diaphragm 32 is automatically inclined such that the normal line is
directed to the sound source direction according to the direction of the sound source. Therefore,
it is possible to receive the sound wave of the sound source more efficiently, and to obtain a
highly directional microphone. In addition, it is possible to automatically adjust the pointing
direction according to the position of the sound source without changing the direction of the
entire microphone.
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[0030]
(2) In the present embodiment, a position close to the center (center of gravity) of the diaphragm
32 is supported by the plurality of elastic portions 12, so when the sound pressure acts on the
diaphragm 32, the elastic portion 12 is It is easy to deform. Therefore, in response to the sound
wave, the diaphragm 32 tilts in the sound source direction, and the directivity sensitivity is
improved. Further, by providing a plurality of elastic portions 12, the durability of the diaphragm
support structure can be improved.
[0031]
It is desirable that the positions of the elastic portions 12 be formed at equal positions on the
concentric circle from the center of the diaphragm 32. Here, the vicinity is not limited to the
position directly connected to the support shaft 321 as shown in FIG. 1, but the position of the
elastic portion 12 is approximately half or less of the radius of the diaphragm 32 when viewed
from the center of the diaphragm 32. Point to something.
[0032]
On the other hand, in the case of the microphone described in Patent Document 1, the diaphragm
is supported in the normal direction at only one central point. Therefore, when the direction of
the sound source is on the normal, no deformation in the axial direction of the support portion
can be expected, and the change in capacitance depends only on the elastic deformation of the
diaphragm. As a result, measurement is difficult because the change in capacitance is small. In
addition, when the diaphragm is not controlled so as not to tilt, the repeated stress due to the
tilting may be concentrated at one point, which may cause repeated fatigue and damage.
[0033]
In the description of the basic equation and the output voltage described above, the capacitance
change is taken out as the change of the output voltage as one capacitor with the plurality of
fixed electrodes 13A to 13D as one fixed electrode. However, assuming that four capacitors
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corresponding to the fixed electrodes 13A to 13D are connected in parallel, the change in
electrostatic capacitance of each capacitor may be taken out as a change in output voltage. In
that case, in place of the above-mentioned electrostatic capacitance C0, the electrostatic
capacitances CA0, CB0, CC0, CD0 of the respective capacitors are considered.
[0034]
As shown in FIG. 7, a resistor R0 is provided in series with each of the fixed electrodes 13A to
13D, and the voltage eA to eD of each resistor is detected by the voltage detection circuit 200 of
the sound source direction identification unit 2. The respective voltages eA to eD can be obtained
by replacing the capacitance C0 of the equation (21) with the respective capacitances CA0, CB0,
CC0, and CD0. Since the change in the capacitance of each of the fixed electrodes 13A to 13D
and the period of the change are reflected in the voltages eA to eD, the direction specifying
circuit 201 specifies the direction of the sound source based on the voltages eA to eD. For
example, when comparing the magnitude of the average value of each of the voltages eA to eD,
the average voltage increases as the distance between the electrodes is smaller, so the sound
source direction can be specified by comparing the magnitudes of those average values. Can.
[0035]
Next, the manufacturing process of the microphone shown in FIG. 1 will be described with
reference to FIGS. First, in the step (a) shown in FIG. 8A, the SOI wafer 100 having a three-layer
structure of the lower Si layer 30, the SiO2 layer 20, and the upper Si layer 10 is prepared. The
thickness of each layer 30, 20, 10 is set to, for example, 500 μm, 1 μm, 25 μm in order. In the
step (b) of FIG. 8 (b), a resist 41 is applied to the surface of the upper Si layer 10. The resist 41 is
applied, for example, by a spin coater at 3000 rpm for 30 seconds, and baked at 90 ° C. for 5
minutes.
[0036]
In the step (c) shown in FIG. 8C, the resist 41 is exposed to ultraviolet light for 4.0 seconds and
developed for 1.5 minutes using a mask having the patterns 15 corresponding to the four
corners of the support shaft 321. Then, the resist 41 in the pattern 15 portion is removed.
Thereafter, the upper Si layer 10 in the portion of the pattern 15 is etched by ICP-RIE
(inductively coupled plasma-reactive ion etching) to expose the surface of the SiO 2 layer 20. ICP-
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RIE etches a sample using a chemical reaction between ions of a process gas in a high density
plasma and the sample surface under a relatively low pressure of 0.05 to 1 Pa, and is anisotropic.
High etching process is possible. As a process gas, an oxidizing gas such as CCl2F2 or CF4 is
used.
[0037]
In the step (d) shown in FIG. 8D, the resist 41 is removed by washing with sulfuric acid hydrogen
peroxide (H 2 SO 4 + H 2 O 2) at 90 ° C. for 5 minutes, and the SiO 2 layer 20 exposed by
strong hydrofluoric acid is removed by etching. Thereafter, a polycrystalline silicon film 40 is
deposited to a thickness of 600 nm by low pressure chemical vapor deposition (LPCVD). FIG. 8D
is a view showing the cross section of the substrate after the LPCVD process, and is a cross
section corresponding to the D2-D2 cross section of FIG. 8C. A groove is formed by etching in the
Si layer 10 and the SiO 2 layer 20 of the pattern 15 portion, and a polycrystalline silicon film 40
is also formed on the surface in the groove.
[0038]
LPCVD is a film forming method in which a sample is heated under a reduced pressure of 10 to
10 <3> Pa, and a film is formed on the surface of the sample by a gas phase chemical reaction by
thermal energy. This method has the advantages of being excellent in film coverage and
obtaining a uniform film thickness. In the film formation of polycrystalline silicon, SiCl 4 + H 2 or
SiH 4 is used as a process gas. The polycrystalline silicon film 40 is formed in order to strengthen
the bond between the support shaft 321 and the diaphragm 32. Furthermore, if a contact hole is
provided at the bonding position and a polycrystalline silicon film is formed, an anchor effect can
be expected.
[0039]
After forming the polycrystalline silicon film 40, an OCD resist is applied by a spin coater at
4,000 rpm for 30 seconds, baked at 150 ° C. for 30 minutes, and then phosphorus (P) at 1000
° C. for 30 minutes. Perform thermal diffusion processing. The thermal diffusion of phosphorus
(P) into the polycrystalline silicon film 40 reduces the electrical resistance of the polycrystalline
silicon film 40. After the thermal diffusion treatment, the substrate is washed with BHF solution
for 5 minutes to remove the OCD resist.
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[0040]
In step (e) shown in FIG. 9, a resist pattern 42 is formed of a thick film resist. The thick film resist
is applied by a spin coater at 2000 rpm for 25 seconds, and then baked at 110 ° C. for 10
minutes. Then, the resist pattern 42 as shown in FIG. 9A is formed by performing ultraviolet
exposure for 60 seconds and performing development for 2 minutes. FIG.9 (b) is D3-D3 sectional
drawing.
[0041]
In the step (f) shown in FIG. 10A, the upper Si layer 10 and the polycrystalline silicon film 40 are
etched by ICP-RIE to form the fixed electrode 13 and the hole 14 of the fixed electrode 13 of the
bridge 11. In the step (g) of FIG. 10B, the thick film resist 42 is removed by washing with sulfuric
acid / hydrogen peroxide at 90 ° C. for 5 minutes. The polycrystalline silicon film 40 is present
on the outermost surface. Thereafter, in order to protect the surface etched in step (f), a thick
film resist 42 is applied again on the surface side and baked.
[0042]
In the above series of steps, the upper structure of the condenser microphone 1 is completed,
and then the lower structure is fabricated. In the step (h) of FIG. 11A, an aluminum (Al) layer 31
is formed to a thickness of 0.1 μm on the lower Si layer 30 by vacuum evaporation. In step (i) of
FIG. 11B, a resist is applied to the surface of the Al layer 31 by a spin coater under conditions of
3000 rpm and 30 seconds. After baking at 90 ° C. for 5 minutes, the resist pattern 43 is formed
by performing ultraviolet exposure for 4.0 seconds and development for 1.5 minutes. The resist
pattern 43 is a pattern in which a circular opening is formed.
[0043]
In the step (j) of FIG. 11C, the Al layer 31 is etched for forming a pattern by immersing in a
mixed acid P solution (H 3 PO 4 + HNO 3 + CH 3 COOH + H 2 O 2) for 2 minutes. , The resist 43
is removed.
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[0044]
In the step (k) of FIG. 11D, a thick film resist is applied on the surface of the lower Si layer 30
from which the Al layer 31 has been removed by a spin coater under the conditions of 2000 rpm
and 25 sec.
After baking at 110 ° C. for 5 minutes, the resist pattern 44 is formed by performing ultraviolet
exposure for 60 seconds and development for 2 minutes. The resist pattern 44 is a circular
pattern, and a ring-shaped gap region R is formed between the resist pattern 44 and the resist
pattern 43.
[0045]
In the step (l) shown in FIG. 12A, the lower Si layer 30 is etched approximately 55 μm in a ring
shape by ICP-RIE. The amount of etching determines the thickness of the diaphragm 32. In step
(m) of FIG. 12B, the thick film resist 44 is removed by a remover (resist stripping solution). At
this time, since the protective thick film resist (see FIG. 11) applied to the upper surface side of
the substrate is also peeled off, the protective thick film resist is formed again.
[0046]
In step (n) of FIG. 12C, the lower Si layer 30 is etched by about 445 μm by ICP-RIE using the Al
layer 31 as a mask. Thereby, in the circular cavity formed in the lower Si layer 30, a diaphragm
32 of Si with a thickness of 55 μm is formed. In the step (o) shown in FIG. 12 (d), the SiO 2 layer
20 is removed by strong hydrofluoric acid after washing with sulfuric acid hydrogen peroxide at
90 ° C. for 5 minutes. Thereby, the diaphragm 32 is completely separated from the fixed
electrode 13. Finally, an Al metal layer 50 is formed on the top surfaces of the bridge 11 and the
fixed electrode 13.
[0047]
In general, in a microphone (acoustic transducer element) that detects sound by vibration of a
diaphragm, a pressure difference generated between the front and back of the diaphragm as a
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diaphragm becomes important. In this embodiment, the diaphragm 32 formed of the same lower
Si layer is disposed in the circular opening 311 of the base 31 formed of the lower Si layer 30,
and the diaphragm 32 has a structure that vibrates due to sound pressure. ing. Thus, in the
structure in which the front side space and the back side space of the diaphragm 32
communicate with each other through the gap between the diaphragm 32 and the base 31, a
sufficient pressure difference is generated between the front and back of the diaphragm 32. The
gap size of the gap needs to be set to an optimal value.
[0048]
For example, as shown in FIG. 23 (a), when the back side of the diaphragm 230 is a sealed space,
and as shown in FIG. 23 (b), a hole 230a is formed in the diaphragm 230, and the space on the
diaphragm back side We consider the case where is semi-sealed.
[0049]
Since air is fluid and has viscosity, it can be considered that the velocity of air is equal to 0 at the
surface of a substance, and the velocity gradually returns to its original speed of sound as it gets
away from the surface.
The region where air is reduced to less than the speed of sound (99% or less of the speed of
sound) from the surface of the material is called the velocity boundary layer. When the surface of
an object placed in the fluid sound field is not perpendicular to the vibration velocity of the fluid
particle, a velocity boundary layer of thickness δ = (2ν / ω) ^ 0.5 is produced on the surface of
the object. Here, the velocity boundary layer is a region where the velocity of sound is slowed by
the influence of the wall. ν is the kinematic viscosity of air, ω is the angular frequency of the
sound wave.
[0050]
As shown in FIG. 23 (b), in the case of a semi-open system having a sufficiently large hole or gap
acoustically, pressure fluctuation is transmitted to the front and back at the speed of sound. And
the pressure difference between the front and back of the flat plate which received the sound
wave in one cycle of the sound wave contributes only to the thickness of the flat plate to the
degree of density of the sound, and it is very weak as a force. Assuming that the pressure
fluctuation P of air due to sound pressure is 1 Pa (at 94 dB), the pressure applied to the flat plate
03-05-2019
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is the same as in the case of a sealed or nearly closed state as shown in FIG. It shows quasisinusoidal variation up to 1 Pa. However, in the case of a semi-open system in which a
sufficiently large gap is provided as shown in FIG. 23 (b), the pressure difference between the
front and back is simply the difference by which the sound wave travels by the thickness.
[0051]
For example, if the sound pressure is 2 Pa and the frequency is 1 kHz at normal temperature and
pressure, the sound is 1 ms per period, and the pressure fluctuation advances by one wavelength,
that is, about 34 cm during that period. The time taken for the pressure fluctuation of the sound
velocity of sound to pass through the thickness 20 μm of the flat plate is 59 ns. Assuming that
the pressure fluctuation sinusoidally fluctuates, let each frequency of the density fluctuation be
ω and time be t, then the pressure difference δP on the front and back is expressed as follows:
δP = (P0 + Psinω (t + 59ns)) − (P0 + Psinωt) Be done. 59Since the value of ns is about 17000
for 1 ms and about 0.021 ° in phase, δP is less than about 2500 at most for P under this
condition, and is half open It can be seen that the pressure difference is clearly small relative to
the closed state. Therefore, in general, when a hole is open, the sensitivity is too low as a vibrator
to receive sound waves, and the reaction occurs only in a special state where the input sound
wave has a resonance frequency.
[0052]
On the other hand, if one half of the hole radius or gap spacing on the flat plate is equal to or less
than the velocity boundary layer, it can be said that the sound wave passing through the gap is
propagated later than originally expected. FIG. 24 is a view for explaining the propagation of the
pressure difference in the gap. The fixed portion 241 corresponds to the base 31 and the
movable portion 242 corresponds to the diaphragm 32. When the gap d10 is sufficiently narrow
and the thickness h of the flat plate is sufficiently thick with respect to the gap, the propagation
of the pressure difference in the gap is delayed with respect to a wide free space, so that the
pressure fluctuation Does not transmit at the speed of sound.
[0053]
Therefore, the pressure difference on the front and back of the flat plate when receiving the
sound wave can be regarded as the difference between the sound pressure of the sound wave
03-05-2019
16
itself and the equilibrium state, not the difference in thickness. At least the viscous drag
produced when air passes through the gap is larger than in the case where there is a sufficiently
large hole or gap, so the force by the acoustic wave is easily transmitted to the movable
electrode. Also, due to the squeeze film damping effect, the movable electrode does not move in
the direction parallel to the plane and moves in the perpendicular direction. Then, when the gap
is 3 μm or less and the thickness is 5 times or more, a holed flat plate as shown in FIG. 23 (b)
blocks air without a gap in a so-called audible band of 20 Hz to 20 kHz. Similar to the sealed
diaphragm, it was confirmed that it vibrated under the sound pressure.
[0054]
For example, if the acoustic boundary layer thickness is about 15.7 μm at 20 kHz and the width
of the gap is 3 μm, the propagation velocity of the sound wave passing through the gap is at
most 3.18 m / s at 25 ° C. To 1/100 or less. When the width of the gap is 1 μm, the
propagation speed of the sound wave is reduced to 0.35 m / s, which is about 1/1000. At this
speed, the arrival position of the pressure fluctuation is about 17 μm at 20 kHz per cycle, and
when the thickness of the electrode is 17 μm or more, it does not even reach the back surface.
As a result, acoustic resistance of an order that can not be practically ignored is generated.
[0055]
Furthermore, it was found that the speed of sound changes with the width of the gap, and as
shown in FIG. 25, the volume affected by pressure fluctuation of the sound wave also changes
with the width of the gap. If the range of influence of pressure fluctuations per cycle is
sufficiently larger than the volume of the original gap, the sound wave can be considered to
penetrate that gap. When the gap width d10 is 4 μm or more, the pressure fluctuation due to
the sound wave is more than doubled, and the sound wave blocking effect is reduced. Therefore,
in the present invention, the gap width at which a sufficient effect can be obtained is set to 3 μm
or less. Also, if the gap is too narrow, then there is the possibility of contact with the wall. When
general ICP-RIE processing is used, the roughness of the wall surface is about 200 nm or less, so
it is desirable that there be a gap of 0.5 μm or more if possible.
[0056]
That is, the flat plate is divided into the movable portion and the fixed portion, the gap between
03-05-2019
17
the movable portion and the fixed portion is 0.5 μm or more and 3 μm or less, and the
thickness of the edge constituting the gap between the movable portion and the fixed portion is
five times or more the gap It is desirable to improve the sensitivity. With such a structure, it is
possible to construct a sensor capable of sufficiently reading the sound pressure.
[0057]
Second Embodiment FIG. 13 is a view showing a second embodiment of the directional
microphone 1 according to the present invention. The microphone 1 shown in FIG. 1 constitutes
a parallel plate condenser microphone in which the fixed electrodes 13A to 13D and the
diaphragm 32 are disposed in parallel to face each other. On the other hand, the microphone 1
shown in FIG. 13 constitutes a comb-tooth electrode type condenser microphone. In addition, the
same code | symbol was attached | subjected to the component similar to the case of FIG.
[0058]
In FIG. 13, (a) is a plan view of the microphone 1, and (b) is a cross-sectional view taken along
the line D1-D1. In the present embodiment, the diaphragm is constituted by four substantially
sector-shaped divided diaphragms 32A to 32D, which are respectively formed by the upper Si
layer 10 of the SOI substrate, while the bridge 11 has a cross shape and a cross shape. Each tip
portion is fixed on the base 31. The bridge 11 is provided with a terminal portion 11 d. Four
elastic portions 12 are radially provided on the side surface of the central portion 111 of the
bridge 11, and the divided diaphragms 32 </ b> A to 32 </ b> D are respectively supported by
the elastic portions 12. In the arc-shaped portions of the divided diaphragms 32A to 32D, combtooth electrodes 322 and 323 formed of a plurality of concavities and convexities are formed.
[0059]
On the other hand, fixed electrodes 23A to 23C are formed on the base 31 so as to face the
comb-tooth electrodes 322 and 323, respectively. As in the case of the microphone 1 shown in
FIG. 1, the fixed electrodes 23A to 23D are formed by the upper Si layer 10. The comb-tooth
electrodes 232 and 233 are also formed on the fixed electrodes 23A to 23D. The fixed electrodes
23A to 23D are arranged such that the comb electrodes 232 and 233 and the comb electrodes
322 and 323 of the diaphragm 32 mesh with each other through a gap. A terminal portion 132
is provided on each of the fixed electrodes 23A to 23D via the wiring portion 131.
03-05-2019
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[0060]
The same applies to the gap dimensions of the comb electrodes 232 and 233 and the comb
electrodes 322 and 323 as in the case of the gap described in the first embodiment. That is, the
gap dimension between the comb-tooth electrodes 232 and 233 and the comb-tooth electrodes
322 and 323 is set to 0.5 μm or more and 3 μm or less. Further, the thickness of the combtooth electrode portion is also five times or more the gap.
[0061]
FIG. 14 is a view schematically showing the state of the diaphragm when the sound wave from
the sound source is received. As in the case shown in FIG. 3, the sound source is in a direction
obliquely inclined with respect to the central axis J of the microphone 1. When each divided
diaphragm 32A-32D receives the sound pressure by the sound wave, each elastic portion 12
bends according to the magnitude of the received sound pressure, and the divided diaphragms
32A-32D are displaced about the central portion 111 of the bridge 11 as a fulcrum And vibrate.
As a result, the pair of opposing comb electrodes shift to the upper limit, the meshing area
changes, and the capacitance changes. This corresponds to the change of the electrode area S in
the above-mentioned formula (1). In the case of the comb-tooth electrode, since the electrode
facing surface has a concavo-convex shape, the electrode area can be increased, and the
sensitivity can be improved.
[0062]
In the case shown in FIG. 14, since the divided diaphragm 32A is closer to the sound source than
the divided diaphragm 32C, the acting sound pressure is larger, and the change in capacitance is
also larger. As described above, since the capacitances of the divided diaphragms 32A to 32D
change according to the direction of the sound source, the magnitudes of changes in the
capacitances of the divided diaphragms 32A to 32D are compared with each other. The direction
can be identified. Furthermore, since the diaphragm is divided into a plurality of divided
diaphragms 32A to 32D and sound waves are independently received, sound source
identification can be performed more accurately than in the case of one diaphragm 32 as shown
in FIG. It can be carried out. In addition, it is possible to automatically adjust the pointing
direction according to the position of the sound source without changing the direction of the
03-05-2019
19
entire microphone.
[0063]
Note that the method of audio signal detection is the same as that of the first embodiment, and
the description thereof is omitted here. In the present embodiment, the diaphragm is divided into
four, but the number of divisions is not limited to four and may be plural. Although the number
of fixed electrodes is the same as the number of divided diaphragms, the number of fixed
electrodes may be equal to the number of fixed electrodes, and therefore may be larger than the
number of divided diaphragms. If the number of divided diaphragms is increased and the number
of fixed electrodes is increased, sound source direction identification can be performed more
finely.
[0064]
In the case of a parallel plate microphone in which the diaphragm and the fixed electrode are
arranged in parallel via the gap, the area of the diaphragm is increased to secure the capacitance,
and the fixed electrode and the diaphragm (diaphragm (diaphragm) It is necessary to make the
diaphragm into a thin film diaphragm in order to reduce the gap between the two) and to ensure
sensitivity. However, sticking occurs at the time of gap formation to cause deterioration in yield,
and sacrificial layer etching and cleaning techniques are required, and a large amount of masks
are required.
[0065]
On the other hand, in the second embodiment, instead of forming a parallel plate type diaphragm
structure, the capacitance portion is formed into a comb-like electrode structure, whereby the
capacitance can be reduced without forming a narrow gap structure of a thin film. It will be
possible to secure. The divided diaphragms 32A to 32D, the bridge 11, the elastic portion 12 and
the fixed electrodes 23A to 23D are simultaneously formed by the same upper Si layer 10.
Therefore, the processing process is simplified as compared to the microphone of the first
embodiment. These components are simultaneously formed by the etching process of step (c)
shown in FIG. 8C, and thereafter, the lower Si layer 30 is etched from the back surface side to
form a circular opening 31.
03-05-2019
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[0066]
Further, since the change in capacitance with respect to the inclination displacement is larger
than that in the parallel plate type, the inclination detection sensitivity is improved. In the combtooth type electrode sensor, the gap can be easily changed, the probability of occurrence of yield
defects such as sticking is lower than that of a thin film, and a narrow gap can be easily formed
by the recent development of Deep-RIE technology. It is possible to create a sensor with high
change.
[0067]
Third Embodiment In the first and second embodiments described above, when the sound source
is in the oblique direction, the diaphragm is displaced to be inclined with respect to the surface of
the base 31. On the other hand, in the present embodiment, the diaphragm is configured to be
displaced in parallel to the surface of the base 31.
[0068]
FIG. 15 is a view showing a third embodiment of the microphone, and the microphone 1
constitutes a comb-like electrode type condenser microphone as in the second embodiment.
However, the diaphragm is configured not by a divided diaphragm but by one circular diaphragm
32. Four fixed electrodes 23A to 23D having comb-tooth electrodes 232 and 233 are provided
on the base 31 so as to face the comb-tooth electrodes 322 and 323 of the diaphragm 32. The
diaphragm 32 is elastically supported on the opening 311 by the four elastic portions 12. The
elastic portion 12 has an oval beam structure so that the diaphragm 32 can be easily displaced in
parallel to the base 31.
[0069]
A groove 325 such as a Fresnel lens is formed on the sound wave incident surface of the
diaphragm 32, that is, the surface opposite to the opening 311. The cross-sectional shape of the
circular groove 325 is in the form of a saw blade, and a plurality of grooves 325 are formed
concentrically around the center of the diaphragm 32. In FIG. 15, the surface 325a on the center
03-05-2019
21
side of the groove 325 is inclined and the outer surface 325b is a vertical surface, but on the
contrary, the surface 325a on the center side is a vertical surface, the outside The surface 325b
of the may be a slope.
[0070]
When a sound wave is applied perpendicularly to the inclined surface 325a in the left side region
of the diaphragm 32 in the drawing and a sound pressure is applied, a leftward force F is applied
to the diaphragm 32. Conversely, when a sound wave is incident on the inclined surface 325 a in
the right area and a sound pressure is applied, a rightward force is applied to the diaphragm 32.
Therefore, as shown in FIG. 16A, when a sound wave is incident on the diaphragm 32 from the
sound source obliquely upward to the right with respect to the central axis J of the diaphragm
32, the diaphragm 32 receives a force in the left direction as a whole. It will be displaced to the
left. Conversely, as shown in FIG. 16B, when the light source is on the left side of the central axis,
the diaphragm 32 receives a force in the right direction as a whole and is displaced to the right.
[0071]
As a result, the gap between the comb electrode portions in the direction opposite to the sound
source direction is narrowed, and the capacitance in that region is increased. For example, in FIG.
15A, when the diaphragm 32 is displaced in the left direction, the capacitance related to the fixed
electrodes 23C and 23D increases, and conversely, the capacitance related to the fixed electrodes
23A and 23B decreases. Therefore, the capacitance change of the fixed electrodes 23C and 23D
largely depends on the sound wave from the sound source direction, and the microphone has
directivity in the sound source direction. However, since the force component due to the sound
pressure is not only in the horizontal direction but also in the vertical direction, the diaphragm
32 tilts according to the distribution state of the vertical direction component. Therefore, the
capacitance change is slightly different from that described above. Further, although the inclined
surface 325 is formed on the sound wave incident surface of the diaphragm 32 in FIG. 15, the
incident surface may be flat. That is, even if it is a flat surface, the diaphragm 32 is inclined due
to the distribution of sound pressure, and as a result, a force in the lateral direction (horizontal
direction) acts to move the diaphragm 32 in the lateral direction. In any case, the directivity is
automatically adjusted in the sound source direction. Furthermore, in the case of the comb-tooth
electrode, the change in electrostatic capacitance is larger when the comb teeth are not displaced
in the vertical direction as in the second embodiment, but are displaced in the opposite direction
as in this embodiment. . Therefore, detection sensitivity can be improved.
03-05-2019
22
[0072]
Further, the sound source direction can be specified by comparing the difference in electrostatic
capacitance among the fixed electrodes 23A to 23D. Furthermore, as in the case described above,
when the diaphragm is displaced in the opposing direction of the comb electrodes, the change in
capacitance is large, so that the directional resolution for specifying the sound source direction
can be further enhanced.
[0073]
In the example shown in FIG. 15, the elastic portion 12 elastically supports four portions of the
peripheral portion of the diaphragm 32. However, as shown in FIG. 20, the elastic portion 12
supports the portion near the center of the diaphragm 32. It is good. In FIG. 20, the elastic
portion 12 is provided at the tip end portion of the bridge 11, and the diaphragm 32 is
supported by these elastic portions 12. The other structure is the same as that shown in FIG. By
supporting the portion close to the center in this manner, not only the diaphragm 32 is moved in
parallel due to the sound pressure, but also the diaphragm 32 is easily inclined. The structure of
the elastic portion 12 may be the same as that shown in FIG. 15, or may have a structure as
shown in (a) to (d) of FIG. 19 described later.
[0074]
The planar shape of the groove 325 is not limited to the concentric shape as shown in FIG. 15,
but various forms are possible. For example, they may be arranged in a square as shown in the
first modification shown in FIG. In addition, it is also possible to direct the normal direction of the
slope 325a to a specific direction to increase the sensitivity to the sound wave from the specific
direction. The saw-tooth shaped groove can be formed by making the etching rate different by
gray mask technology. In addition, in the case of forming only slopes directed in a specific
direction, it can be formed by wet etching.
[0075]
FIG. 17B is a view showing the second modification, in which the diaphragm 32 is divided into
03-05-2019
23
four divided diaphragms 32A to 32D, which are individually supported by the elastic portion 12.
Two elastic parts 12 are connected to the divided diaphragms 32A to 32D from the cross-shaped
bridge 11, respectively. The pair of elastic portions 12 are configured such that the divided
diaphragms 32A to 32D are easily displaced in the radial direction.
[0076]
In the third modification shown in FIG. 18B, the sound wave is incident from the base 31 side,
contrary to the microphone shown in FIG. That is, the sound wave is incident on the bottom
surface 326 side of the diaphragm 32. The other configuration is the same as that of the third
embodiment described above. The bottom surface 326 is formed of a slope to enhance directivity
with respect to the sound source direction. The bottom surface 326 is convex so that the central
portion is convex. Therefore, for example, even if there is a flow of air from the bottom to the top,
the bottom shape is such that the air resistance is reduced, and the influence of the flow of air
can be reduced.
[0077]
In the third modification shown in FIG. 18A, the slope of the slope gradually increases from the
central portion to the peripheral portion, but a bottom surface 326 such as a conical surface may
be used.
[0078]
In the fourth modification shown in FIG. 18B, the bottom surface 326 is concave.
Therefore, the sound collection effect can be improved.
[0079]
As a form of the elastic portion 12, in addition to the beam structure shown in FIG. 1 and the oval
beam structure shown in FIG. 15, a beam structure as shown in FIG. 19 can be considered. The
elastic part 12 shown to Fig.19 (a) is comprised by the beam 121 of two linear form. The elastic
portion 12 is a structure that is easily bent in the y direction in the drawing. In the elastic portion
03-05-2019
24
12 shown in FIG. 19B, the thickness (dimension in the z direction) of the beam is reduced to
reduce the spring constant. In the case of this configuration, since it is easily bent in the vertical
direction (z direction), it is suitable for supporting the diaphragm 32 which is configured to be
inclined upward and downward.
[0080]
The elastic portion 12 shown in FIG. 19 (c) has a configuration in which the beams forming the
elastic portion 12 shown in FIG. 1 and the beams shown in FIG. 19 (b) are connected in series.
Therefore, it has a structure which is easy to bend in both the z direction and the y direction. The
elastic portion 12 shown in FIG. 19D has a beam structure of a bellows structure folded back in
the z direction. Therefore, it has an advantage of being easily bent in the z direction and also
being easily displaced in the x direction. When the folding direction of the bellows is the y
direction, the bellows is easily bent in the y direction and deformed in the x direction.
[0081]
The embodiment described above has the following effects. (1) The base 31 having the opening
311 at the center, the bridge 11 bridged over the opening 311 of the base 31, and the
diaphragm 32 elastically supported via the support shaft 321 at the center of the bridge 11 A
plurality of fixed electrodes 13A to 13D are provided facing the diaphragm 311 at the opening
311 so as to be opposed to the diaphragm 32 and held by the base 31, provided at the central
portion of the bridge 111. A plurality of elastic members 32 elastically supporting the support
shaft 321 of the diaphragm 32 from the side are provided such that the incident surface is
inclined according to the sound source direction. As a result, the sound collection characteristic
regarding the sound wave in the sound source direction is improved, and a microphone with high
directivity can be obtained. In addition, it is possible to automatically adjust the pointing
direction according to the position of the sound source without changing the direction of the
entire microphone. Furthermore, since the diaphragm 32 is supported by the plurality of elastic
portions 12, it is possible to improve the durability of the support portion as compared with the
conventional one-point support structure. (2) The directional microphone includes a base 31
having an opening 311 at the center, a bridge 11 bridged over the opening 311 of the base 31,
and a plurality of divided diaphragms 32A to 32D divided into a plurality of parts. 11 includes a
diaphragm 32 elastically supported at the central portion thereof, and a plurality of electrodes
13A to 13D which are disposed opposite to each other with a gap provided between the
diaphragms 32A to 32D at the opening 311 and held by the base 31 Divided by the side
circumference of the central portion 111 provided at the central portion of the bridge 11 so that
03-05-2019
25
the incident surfaces of the plurality of divided diaphragms 32A to 32D are inclined according to
the sound source direction by the incidence of sound waves. The plurality of elastic portions 12
elastically supporting the plates 32A to 32D. The directivity is further improved by tilting the
plurality of divided diaphragms 32A to 32D. (3) The comb-tooth electrodes 322 and 323 are
formed on the diaphragm 32, and the diaphragm 32 is a plurality of elastic portions on the
opening 311 of the base 31 so as to be displaced according to the direction of the incident sound
wave. It is elastically supported by 12. The fixed electrode is constituted by a plurality of divided
electrodes 23A to 23D held by the base 31, and the comb electrodes 232 and 233 meshing with
the comb electrodes 322 and 323 with an air gap are respectively divided electrodes 23A to
23D. Is formed. By using the comb-tooth electrode, the change in capacitance can be increased,
and the detection sensitivity can be improved.
Furthermore, by forming the diaphragm 32, the elastic portion 12 and the fixed electrode by the
same Si layer of the SOI (Silicon on Insulator) substrate, the etching process can be simplified and
the microphone can be miniaturized. (4) As shown in FIG. 13, the diaphragm 32 may be divided
into a plurality of parts and they may be configured to be inclined by the sound pressure, as
shown in FIG. 15 or 17 (b). 32, 32a-32d may be configured to be displaced in the surface
direction (i.e., the direction parallel to the surface). In the case of the configuration of FIG. 17B,
the directivity can be further improved by dividing the diaphragm into a plurality of divided
diaphragms 32a to 32d. (5) The diaphragm 32 is elastically supported so as to be movable in the
plane direction, and the inclined surface 325 is formed on the sound wave incident surface of the
diaphragm 32 to make the diaphragm in the opposing surface direction of the comb electrodes
by the action of sound pressure. You may make it displace. As a result, the capacitance change
with respect to the displacement of the diaphragm can be increased, and the directivity of the
microphone and the sound source direction identification performance can be improved. (6) The
electrostatic capacitance between the plurality of fixed electrodes 23A to 23D and the diaphragm
32 is individually detected as a voltage by the voltage detection circuit 200 corresponding to
each of the fixed electrodes 23A to 23D, and based on the voltage The walking identification
circuit 201 identifies the direction of the sound source. With such a configuration, the sound
source can be identified by one microphone.
[0082]
It is also possible to combine one or more of the above-described embodiment and the
modification. It is also possible to combine the variants in any way. For example, as shown in FIG.
20, the diaphragm 32 of FIG. 1 may be divided into four divided diaphragms 32A to 32D facing
the fixed electrodes 13A to 13D. In FIG. 20, in order to make the shape of the diaphragm 32 easy
to understand, the fixed electrodes 13A to 13D are omitted and the configuration of the
03-05-2019
26
microphone is shown. The central portion 111 of the bridge 11 constitutes a support shaft of the
divided diaphragms 32A to 32D, and the elastic portions 12 are radially provided on the side
circumferences thereof. The divided diaphragms 32 </ b> A to 32 </ b> D are each elastically
supported by the elastic portion 12.
[0083]
Further, the number of the bridges 11 is not limited to four, and may be two or three. The
number of divisions of the fixed electrode and the diaphragm is not limited to four, and may be
two, three or five or more. In that case, the resolution of sound source identification is improved
as the number of divisions increases.
[0084]
Furthermore, the extending direction of the comb-tooth electrodes 232, 233, 322, 323 is not
limited to the above-described one extending in the radial direction, and as shown in FIG. It may
be of the type extending to FIG. 22 is a view showing a modification of the comb electrode shape,
and a part of the diaphragm 32 and the fixed electrodes 23A to 23D, that is, the comb electrode
of the fixed electrode 23A and the comb teeth on the diaphragm 32 opposite thereto It shows an
electrode. In the example shown in FIG. 22A, two rows of comb-shaped electrodes 233 extending
in the circumferential direction are formed in the radial direction on both sides of the shaft
portion 234 extending radially from the fixed electrode 23A. A plurality of shaft portions 234 are
formed in the fixed electrode 23A.
[0085]
On the other hand, a plurality of radially extending shaft portions 324 are formed on the outer
peripheral surface of the diaphragm 32, and on both sides of each shaft portion 324, two rows of
comb-tooth electrodes 322 extending in the circumferential direction are formed in the radial
direction. The comb-tooth electrode 232 intrudes into the concave portion (comb-tooth electrode
323) on the diaphragm 32 side, and the comb-tooth electrode 322 intrudes into the concave
portion (comb-tooth electrode 233) on the fixed electrode 23A side. With such a comb-tooth
electrode structure, the change in electrostatic capacitance can be increased, and the sensitivity
of sound wave detection can be improved.
03-05-2019
27
[0086]
FIG. 22 (b) is a view showing another example, in which the shaft portions 324 of the comb
electrodes 322 and 323 extend radially from the portion near the center of the diaphragm 32
and extend in the circumferential direction 322 and 323 are provided in eight rows in the radial
direction. The comb-tooth electrode structure on the fixed electrode 23A side is the same as that
on the diaphragm side. As described above, most of the diaphragm 32 may be a comb electrode
region, and the sensitivity can be improved by increasing the capacitance change.
[0087]
The above description is merely an example, and the present invention is not limited to the
configuration of the above embodiment as long as the features of the present invention are not
impaired.
[0088]
1: Microphone, 2: Sound source direction identifying unit, 11: Bridge, 12: Elastic part, 13A to
13D, 23A to 23D: Fixed electrode, 31: Base, 32: Diaphragm, 32A to 32D: Divided diaphragm,
111: Center portion 200: voltage detection circuit 201: direction identification circuit 232, 233,
322, 323: comb-tooth electrode 311: opening 321: support shaft 325: groove 325a: sloped
surface 325b: vertical surface 326 : Bottom
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