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DESCRIPTION JP2003125495

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DESCRIPTION JP2003125495
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
electret condenser microphone having an insulating material such as ceramic or resin as a
substrate material, and in particular, an electret condenser microphone capable of enhancing
detection sensitivity by reducing stray capacitance of the microphone portion. About.
[0002]
2. Description of the Related Art A conventional electret condenser microphone is disclosed in
Japanese Patent Application Laid-Open No. 2000-50393 and will be described below with
reference to FIGS. FIG. 4 is a cross-sectional view of an electret condenser microphone according
to a first prior art, wherein 310 is a metallic back electrode, 320 is an electret layer formed on
the upper surface of the back electrode 310, and 311 is the back electrode. An acoustic hole is
formed through the electrode 310 and the electret layer 320, and the back electrode substrate
330 is configured by the back electrode 310 and the electret layer 320. Then, in the method of
manufacturing the back electrode substrate 330, an electret layer is formed on the entire surface
of a large metal plate to be a back electrode, which is cut into a necessary size, and the acoustic
hole 311 is punched to process the back electrode substrate. It is assumed to be 330.
[0003]
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Reference numeral 340 denotes a conductive diaphragm, 350 denotes a metal support frame
fixed to the diaphragm 340, and the diaphragm 340 and the support frame 350 constitute a
diaphragm unit 360. A microphone is configured by laminating and arranging the back electrode
substrate 330 and the diaphragm unit 360 via the spacer 370. Reference numeral 400 denotes a
holder, and reference numeral 410 denotes a circuit board, on which an electronic element 420
for processing a detection signal of the microphone is mounted. 500 is a metal case which
encloses the whole and protects it electrically and mechanically.
[0004]
In the operation of the electret condenser microphone having the above configuration, the
diaphragm 370 having the vibrating film 340 having the conductive film on the surface and the
back electrode 310 having the electret layer 320 formed on the surface sandwiches the spacer
370 to form a capacitor. When the diaphragm 340 is displaced by the vibration of air applied
from the opening of the case 500, the capacitor converts the displacement into an electrical
signal, and the electrical signal is led to the circuit board 410 and processed by the electronic
element 420. After that, it is outputted from the output electrodes 430 and 440 which are led
out to the back surface of the circuit board 410. Then, due to the presence of the acoustic hole
311, the operation of the vibrating membrane 340 becomes smooth and the acoustic
characteristic is secured.
[0005]
FIG. 5 is a cross-sectional view of an electret condenser microphone mainly composed of ceramic
showing a second prior art example, and FIG. 6 is an exploded perspective view of a case portion
constituting the electret condenser microphone shown in FIG. The electret condenser
microphone shown in FIG. 5 includes a microphone unit 100 for performing acoustic conversion,
and a case unit 200 for housing the microphone unit 100. The case unit 200 is a circuit board
210 made of an insulating member, and this circuit It covers the top side with four frames
attached by laminating on the edge of the substrate 210, that is, the first frame 220, the second
frame 230, the third frame 20, the fourth frame 250 A lid 260 is provided.
[0006]
The members constituting the case portion 200 are made of ceramic, and the circuit board 210,
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the first frame 220, the second frame 230, and the third frame 240 are all made of ceramic, and
are conductive as shown by hatching in FIG. Membrane electrodes are formed, and these
electrodes are used to mount and connect the elements. Further, as will be described later, the
fourth frame 250 is made of a metal material for connection to the diaphragm.
[0007]
As shown in FIG. 5, the first frame 220, the second frame 230, the third frame 240, and the
fourth frame 250 all have the same outer shape, but the inner diameter is the first frame. The
third frame 240 is larger than the second frame 230, and the fourth frame 250 is larger than the
third frame 240. As a result, a first stepped portion 230a for mounting a back electrode substrate
described later is formed on the upper portion of the second frame 230 due to the difference in
the inner diameter shape of each frame, and the upper portion of the third frame 240 A second
step portion 240a for mounting a diaphragm unit, which will be described later, is formed on the
second step.
[0008]
Next, the microphone unit 100 includes a back electrode 110, an electret layer 120 formed on
the surface of the back electrode 110, and an acoustic hole 111 formed through the back
electrode 110 and the electret layer 120. A vibrating membrane 140 attached to a ring-shaped
conductive vibrating membrane frame 130, a lower spacer 150 interposed between the vibrating
membrane 140 and the back electrode 110, the vibrating membrane 140, and the lid And an
upper spacer 160 interposed therebetween. Then, as shown in FIG. 6, the circuit board 210 made
of ceramic, which is an insulating material, and the three frames, ie, the first frame 220, the
second frame 230, and the third frame 240, respectively. A connection electrode is formed.
[0009]
Next, an assembling procedure of the electret condenser microphone will be described with
reference to FIG. First, the first frame 220, the second frame 230, the third frame 240, and the
fourth frame 250 are stacked on the edge of the circuit board 210 on which the electric element
170 such as a semiconductor element is mounted. Install. Next, the back electrode 110 is
mounted on the first step 230 a formed on the upper portion of the second frame 230 so that
the electret layer 120 faces upward. Further, the vibrating membrane 140 is mounted on the
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second step portion 240 a formed on the upper portion of the third frame body 240 with the
lower spacer 150 and the upper spacer 160 interposed therebetween. Further, by fitting the lid
260 from above, the vibrating membrane 140 and the back electrode 110 are positioned and
fixed to the case 200, and the electret condenser microphone is completed.
[0010]
In the operation of the electret condenser microphone having the above configuration, the
diaphragm 140 having a conductive film on the surface and the back electrode 110 having the
electret layer 120 formed on the surface sandwich the lower spacer 150 to form a capacitor.
When the diaphragm 140 is displaced by the vibration of air applied from the opening of the lid
260, the capacitor converts the displacement into an electrical signal, and the electrical signal is
formed on each frame (connection electrodes (FIG. 6). And is processed by the electronic element
170 and output from an output electrode provided on the back surface of the circuit board 210.
[0011]
In the first conventional electret condenser microphone shown in FIG. 4, since the spacer 370 is
directly mounted on the back electrode substrate 330 to position the diaphragm 340, the back
electrode electrode is used. It is easy to maintain the distance between the diaphragm 310 and
the diaphragm 310 accurately. However, since the area of the back electrode 310 and the
diaphragm 340 is substantially the same size, the capacity (capacitor) formed by the back
electrode 310 and the diaphragm 340 is determined by the operable region 340 a of the
diaphragm 340. The combined capacitance of the capacitance obtained by subtracting the
capacitance lost by the acoustic hole 311 from the effective capacitance to be formed and the
stray capacitance formed by the non-operating region 340 b in which the vibrating membrane
340 is constrained by the support frame 350.
[0012]
That is, considering that the sensitivity of the microphone 300 is determined by the ratio of the
total capacitance formed by the back electrode 310 and the diaphragm 340 to the effective
capacitance formed by the operable region 340 a of the diaphragm 340, There is a problem that
the sensitivity as the microphone 300 is lowered as the floating capacitance formed by the nonoperating region 340 b of the vibrating membrane 340 and the loss capacitance lost by the
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acoustic hole 311 increase. That is, the stray capacitance is to increase the denominator, and the
loss capacitance is to decrease the numerator.
[0013]
Next, in the electret condenser microphone of the second prior art shown in FIG. 5, the ceramic
second frame 230, the third frame 240 and the fourth frame 250 constituting the case 200 are
stacked and attached The back electrode 110 is mounted on a first stepped portion 230 a formed
on the upper portion of the second frame 230, and the vibration is generated on a second
stepped portion 240 a formed on the upper portion of the third frame 240. The film 140 is
placed with the lower spacer 150 and the upper spacer 160 interposed therebetween.
[0014]
In the configuration of the electret condenser microphone according to the second conventional
example, the operation of the diaphragm 140 is performed by shifting the positions of the first
stepped portion 230a and the second stepped portion 240a and reducing the size of the back
electrode 110. Since the back electrode 110 opposes only the possible region, the capacitor
formed by the vibrating membrane 140 and the back electrode 110 becomes all effective
capacity except the loss capacity lost by the acoustic hole 111, The sensitivity of the microphone
unit 100 can be kept high.
That is, compared to the electret condenser microphone of the first embodiment shown in FIG. 4,
the sensitivity as the microphone unit 100 can be increased by the amount of the stray
capacitance although the loss capacity is the same.
[0015]
That is, although the electret condenser microphone of the second conventional example can
obtain good results in sensitivity, the back electrode substrate 110 constituting the microphone
unit 100 is positioned on the second frame 230, The vibrating membrane 140 is positioned at
the third frame 240 and configured. This results in positioning of the back electrode substrate
110 and the diaphragm 140 that constitute the microphone unit 100 in separate case members,
so that the processing accuracy of the second frame 230 and the third frame 240 Due to the
variation in the assembling system, there is a problem that the distance between the back
electrode substrate 110 and the vibrating membrane 140 can not be accurately maintained.
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[0016]
The present invention has been made in view of the above circumstances, and it is an object of
the present invention to provide an electret condenser microphone which can increase the
sensitivity as a microphone and can accurately maintain the distance between a back electrode
and a diaphragm. And
[0017]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present
invention solves the above problems by providing a back electrode substrate on which an electret
layer is formed on a back electrode, and a diaphragm unit having a diaphragm fixed to a support
frame through spacers. In the electret condenser microphone, the back electrode substrate has a
structure in which a back electrode, an electret layer, and an acoustic hole are formed on an
insulating substrate, and at least a part of the acoustic hole is the back electrode. It is
characterized in that it is provided outside the formation region.
[0018]
In addition, the acoustic hole is formed in the boundary area of the back electrode.
[0019]
Furthermore, it is characterized in that the area of the back electrode is smaller than the area
inside the support frame in the vibrating membrane unit.
[0020]
Furthermore, the upper surface of the back electrode substrate has a rectangular shape, and the
back electrode and the electret layer are formed in a circular shape on the upper surface of the
back electrode substrate, and the acoustic hole is a formation region of the back electrode It is
formed in the position corresponding to the corner part of the said back pole board | substrate
on the outer side of the above.
[0021]
DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a cross-sectional view of an
embodiment of an electret condenser microphone according to the present invention, and FIG. 2
is an exploded perspective view of each element constituting the electret condenser microphone
shown in FIG.
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[0022]
In FIG. 2, reference numeral 2 denotes a circuit board, and the circuit board 2 is formed of an
insulating substrate, and an electrode 2a for mounting an element, a connection electrode 2b,
and an output electrode 2c are film-formed.
Reference numeral 3 denotes a back electrode substrate. The back electrode substrate 3 has a
back electrode 4 formed of an electrode film formed on the upper surface side of the insulating
substrate 3a, and an electret layer 5 formed on the upper surface of the back electrode 4 An
acoustic hole 15 penetrating the insulating substrate 3 a is formed outside the back electrode 4
and the electret layer 5.
[0023]
In this embodiment, the upper surface of the back electrode substrate 3 has a rectangular shape,
and the back electrode 4 and the electret layer 5 are formed in a circular shape on the upper
surface of the back electrode substrate 3, The acoustic hole 15 is formed at a position
corresponding to the corner portion of the back electrode substrate 3 outside the formation
region of the back electrode 4, thereby efficiently using the area of the upper surface of the back
electrode substrate 3.
また6はスペーサである。
[0024]
Reference numeral 7 denotes a diaphragm unit, and the diaphragm unit 7 is integrally formed by
fixing the conductive diaphragm 10 to the diaphragm attachment electrode 9 formed on the
lower surface side of the diaphragm support frame 8 made of an insulating substrate. It has been
Reference numeral 16 denotes a metal shield case.
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[0025]
Next, the configuration of the electret condenser microphone 1 will be described with reference
to FIG.
The back electrode substrate 3, the spacer 6, and the diaphragm unit 7 are stacked on the circuit
substrate 2 in which an element such as the integrated circuit 11 is mounted on the electrode 2a,
and integrally fixed and bonded by an adhesive or the like. ing.
[0026]
In the operation of the electret condenser microphone 1 having the above configuration, the
diaphragm 6 having the vibrating film 10 having the conductive film on the surface and the back
electrode 4 having the electret layer 5 formed on the surface sandwiches the spacer 6 to form a
capacitor.
When the diaphragm 10 is displaced by air vibration, the capacitor converts the displacement
into an electrical signal, and the electrical signal is transmitted from the diaphragm attachment
electrode 9 to the circuit board 2 via the connection electrodes (not shown). After being led and
processed by the integrated circuit 11, the signal is outputted from the output electrode 2c
provided on the back surface of the circuit board 2.
Then, due to the presence of the acoustic holes 15, the operation of the vibrating membrane 10
becomes smooth and the acoustic characteristics are secured.
[0027]
In the above configuration, the operable range (not restricted by the diaphragm supporting frame
8 of the diaphragm 10) of the diaphragm 10 constituting the diaphragm unit 7 at the center of
the upper surface of the insulating substrate 3a constituting the back electrode 3 The back
electrode 4 and the electret layer 5 having an area slightly narrower than the area of the range
are formed, and the outside (back electrode 4) of the region of the insulating substrate 3a where
the back electrode 4 and the electret layer 5 are formed is further provided. And the spacer 7)).
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[0028]
As a result, the formation of the capacitance in the electret condenser microphone 1 becomes
only the effective capacitance formed in the portion where the back electrode 4 and the vibrating
membrane 10 face each other, as in the conventional example shown in FIG. Very high sensitivity
characteristics can be obtained since there will be no stray capacitance formed by the operating
region and no loss capacitance lost by the acoustic hole 15.
[0029]
FIG. 3 is a perspective view of a back electrode substrate 30 showing a second embodiment of
the present invention, and the difference from the back electrode substrate 3 shown in FIG. 2 is
that the acoustic holes 15 formed in the insulating substrate 3a are different. It is to be formed in
the boundary area of the back electrode 4.
In this case, a loss capacity is present as much as the acoustic hole 15 overlaps with a part of the
back electrode 4, but the acoustic hole 15 is used as the diaphragm 10 instead of a slight
decrease in sensitivity characteristics due to the loss capacity. It can be expected to improve the
acoustic characteristics by moving to the center side of the
[0030]
Further, in the above configuration, the back electrode substrate 3 is formed by forming the back
electrode 4 on the surface of the insulating substrate 3 a formed in a U-shaped cross section, and
further forming the electret layer 5 on the back electrode 4. Since the conductive diaphragm 10
is integrally fixed to the diaphragm supporting frame 8 made of an insulating substrate and the
diaphragm unit 7 is also integrated, the basic configuration is the circuit board 2, the back The
configuration is simplified to three bodies of the electrode substrate 3 and the diaphragm unit 7.
[0031]
Furthermore, in the above configuration, the back electrode 4 and the vibrating membrane 10
are positioned with respect to one insulating substrate 3a, whereby the distance between the
back electrode 4 and the vibrating membrane 10 can be maintained with high accuracy.
[0032]
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Furthermore, since the bottom surface of the circuit board 2 and the side surface of the back
electrode substrate 3 also serve as a case, the size and thickness can be reduced.
Further, although the materials of the insulating substrates used for the three members of the
circuit board 2, the back electrode substrate 3 and the vibrating membrane support frame 8 can
be selected arbitrarily, by using the same insulating substrate for the three members. It becomes
possible to match the whole thermal expansion coefficient, and it is possible to prevent the
deterioration of the acoustic characteristics due to the temperature change.
[0033]
The insulating substrate in the present invention is required to be a material that is easy to
process in shape and can be formed into a pattern by an electrode film including through holes,
and ceramic or a resin material is suitable, for example.
Moreover, in order to make the device smaller in size and thinner, it is desirable that the material
be high in rigidity. In this respect, the ceramic is a good material, and good results can be
obtained by using the ceramic substrate.
Further, in the resin material, it is desirable to contain glass fiber in order to enhance the rigidity,
and as a result of using the glass-filled epoxy resin, good results could be obtained.
[0034]
As described above, according to the present invention, by providing a part of the acoustic hole
outside the formation region of the back electrode on the back electrode substrate, the sensitivity
as a microphone can be increased, Further, by forming the back electrode on the insulating
substrate and positioning the spacer for supporting the vibrating film, the distance between the
back electrode and the vibrating film can be accurately maintained.
[0035]
Brief description of the drawings
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[0036]
1 is a cross-sectional view of an embodiment of the electret condenser microphone of the present
invention.
[0037]
2 is an exploded perspective view of each element constituting the electret condenser
microphone of FIG.
[0038]
3 is a perspective view of the back electrode substrate of the second embodiment of the present
invention.
[0039]
4 is a cross-sectional view of a conventional electret condenser microphone.
[0040]
5 is a cross-sectional view of a conventional electret condenser microphone.
[0041]
6 is an exploded perspective view of the case portion of the electret condenser microphone
shown in FIG.
[0042]
Explanation of sign
[0043]
1 electret condenser microphone 2, 210, 410 circuit board 3, 330 back pole board 4, 110, 310
back pole electrode 5, 120, 320 electret layer 6, 370 spacer 7, 360 vibrating membrane unit 10,
140, 340 vibrating membrane 15 , 111, 311 acoustic holes
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