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DESCRIPTION JP2007295515

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DESCRIPTION JP2007295515
The present invention provides a condenser microphone in which the vibration characteristic of a
diaphragm is improved, the parasitic capacitance is reduced, and the microphone sensitivity is
improved without complicating the manufacturing process. A diaphragm (10) has a substantially
gear shape having a central portion (12) and six arms (14), and a back plate (20) also has a
substantially gear shape having a central portion (22) and six arms (24). ing. The central portion
22 of the back plate 20 corresponds concentrically to the central portion 12 of the diaphragm
10, and the radius of the central portion 22 of the back plate 20 is smaller than the radius of the
central portion 12 of the diaphragm 10. In addition, the arm 24 of the back plate 20 is located at
a position corresponding to the notch sandwiched by the arms 14 of the diaphragm 10, and the
arm 14 of the diaphragm 10 is sandwiched by the arms 24 of the back plate 20. It is in the
position corresponding to the notch. [Selected figure] Figure 1
コンデンサマイクロホン
[0001]
The present invention relates to a condenser microphone, and more particularly to a condenser
microphone as a MEMS sensor.
[0002]
Conventionally, a condenser microphone that can be manufactured by applying a manufacturing
process of a semiconductor device is known.
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In the condenser microphone, a diaphragm vibrating by an acoustic wave forms a movable
electrode and a plate forms a fixed electrode, and the diaphragm and the plate are supported
apart from each other by an insulating spacer. That is, the diaphragm and the plate form the
counter electrode of the capacitor.
[0003]
In such a condenser microphone, when the diaphragm vibrates due to the sound wave, the
displacement of the capacitor changes due to the displacement, and the capacitance change is
converted into an electric signal and output. The sensitivity of the condenser microphone is to
increase the ratio of the displacement of the diaphragm to the distance between the opposing
electrodes, that is, by improving the vibration characteristic of the diaphragm, and by reducing
the parasitic capacitance that does not contribute to the capacitance change of the capacitor.
improves.
[0004]
Non-Patent Document 1 discloses a condenser microphone in which each of a plate and a
diaphragm is formed of a conductive thin film. However, since the entire circumference of the
diaphragm is fixed to the spacer, when sound waves propagate to the diaphragm, the
displacement due to the vibration of the diaphragm is large at the central portion but extremely
small at the outer periphery fixed to the spacer. As a result, the vibration of the diaphragm is
efficiently detected as a capacitance change mainly in the central portion of the diaphragm, and
the outer peripheral portion of the diaphragm generates almost only parasitic capacitance. And
this parasitic capacitance is a factor to which the sensitivity of a condenser microphone is
reduced.
[0005]
Patent Documents 1 and 2 disclose a condenser microphone in which the vibration characteristic
of the diaphragm is improved and the sensitivity is improved by providing a structure that acts as
a spring in the support portion of the diaphragm. Specifically, the diaphragm is provided with a
slit, and the region sandwiched by the slit is provided with a spring function. However, since the
plate corresponding to the entire diaphragm including the region having the spring function is
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2
disposed, parasitic capacitance is also generated in the region where the displacement due to the
vibration of the diaphragm is small, which causes the sensitivity reduction of the capacitor
microphone It becomes.
[0006]
In Patent Document 3, a plate opposed to a diaphragm forming a movable electrode is formed of
an insulating material, and among the opposed surfaces of the plate to the diaphragm
(hereinafter referred to as "diaphragm opposed surface"), it corresponds to the central portion of
the diaphragm. There is disclosed a condenser microphone in which sensitivity is improved by
providing a back electrode only in a part to efficiently detect a change in capacitance only in the
central part of the diaphragm and reduce parasitic capacitance in the outer peripheral part of the
diaphragm. . However, since it is necessary to provide the back electrode only on a certain
portion of the diaphragm facing surface of the plate made of an insulating material, the
manufacturing process becomes complicated, the manufacturing yield decreases, and the
manufacturing cost increases. Moreover, in the process of etching away the sacrificial layer
interposed between the diaphragm and the plate to form a void, the insulating material fixing the
back electrode of the plate is also etched not a little, so this measure is taken. The need to be
incorporated into the manufacturing process further increases the manufacturing cost.
[0007]
Electrical Society of Japan JP-A-9-508777 U.S. Pat. No. 4,776,019 JP-A-2004-506394
[0008]
An object of the present invention is to provide a condenser microphone in which the sensitivity
of the microphone is improved by improving the vibration characteristics of the diaphragm and
reducing the parasitic capacitance of the condenser without complicating the manufacturing
process.
[0009]
(1) A condenser microphone for achieving the above object has a central portion and a plurality
of arms extending radially outward from the central portion, and a conductive diaphragm that
vibrates upon receiving a sound wave, and the diaphragm A conductive plate disposed opposite
to the substrate, and a substrate provided on the opposite side of the plate with respect to the
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diaphragm, and forming a cavity in the diaphragm for relieving pressure applied from the
opposite side of the plate A support means for supporting the substrate while insulating the tip
of the arm of the diaphragm from the outer edge of the plate, and forming an air gap between
the central portion of the diaphragm and the plate; And the peripheral portion of the cavity of the
substrate and the diaphragm form an acoustic resistance higher than the acoustic resistance
between the plurality of arms It is.
In such a condenser microphone, since the diaphragm has a unique planar shape having a central
portion and a plurality of arms extending radially outward from the central portion, vibration
characteristics of the diaphragm with respect to sound waves are improved.
In addition, since there is no correspondence between at least the notches between the
diaphragm and the plate that are opposed to each other between the diaphragm and the plate,
parasitic capacitance does not occur in that portion, and parasitic capacitance as a whole is
generated. Decreases. In addition, since both the diaphragm and the plate are formed of a
conductive material, a complicated manufacturing process is not required, in which an electrode
is provided only on a certain portion of the diaphragm facing surface of the plate made of an
insulating material. Can be Furthermore, even if the diaphragm has a planar shape having a
plurality of arms, the diaphragm and the peripheral portion of the cavity of the substrate form an
acoustic resistance higher than the acoustic resistance between the plurality of arms. It is
difficult for sound waves to reach between the arms. Therefore, the diaphragm vibration
characteristic can be improved, the parasitic capacitance of the capacitor can be reduced, and the
microphone sensitivity can be improved without complicating the manufacturing process. In the
specification of the present application, "facing" the diaphragm and the plate means that the
plane including the diaphragm and the plane including the plate are in a parallel or substantially
parallel positional relationship, and also in the "corresponding" relationship. The term "meaning"
means that a certain portion of the diaphragm and a certain portion of the plate are in an
overlapping positional relationship.
[0010]
(2) In the above-mentioned condenser microphone, it is preferable that in the plate, the distance
from the center to the outer edge is shorter than the distance from the center of the central
portion of the diaphragm to the tip of the arm. In this case, even in a portion including at least a
portion of the arm of the diaphragm located outside the outer edge of the plate, no
corresponding relationship between the diaphragm and the plate occurs, so that no parasitic
capacitance occurs in that portion, and the parasitic as a whole The capacity is further reduced.
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In addition, since the planar shape of the plate can be made relatively smaller than that of the
diaphragm, the rigidity of the plate is relatively increased, and as a result, the diaphragm can be
made larger without deteriorating the stability of the microphone operation. can do. Therefore,
the microphone sensitivity can be improved by further reducing the parasitic capacitance of the
capacitor and further improving the vibration characteristic of the diaphragm.
[0011]
(3) A condenser microphone for achieving the above object has a central portion and a plurality
of arms extending radially outward from the central portion, and a conductive diaphragm that
vibrates upon receiving a sound wave, and the diaphragm An oppositely disposed conductive
plate, and a substrate provided on the opposite side of the plate to the diaphragm and forming a
cavity on the diaphragm for relieving pressure applied from the opposite side of the plate And
supporting means for insulating the tip end of the arm of the diaphragm and the outer edge of
the plate on the substrate while forming an air gap between the central portion of the diaphragm
and the plate And the plate has a distance from the center to the outer edge that is greater than
the distance from the center of the central portion of the diaphragm to the tip of the arm There.
In such a condenser microphone, since the diaphragm has a unique planar shape having a central
portion and a plurality of arms extending radially outward from the central portion, vibration
characteristics of the diaphragm with respect to sound waves are improved. In addition, since
there is no correspondence between at least the notches between the diaphragm and the plate
that are opposed to each other between the diaphragm and the plate, parasitic capacitance does
not occur in that portion, and parasitic capacitance as a whole is generated. Decreases.
Furthermore, even in a portion including at least a part of the arm portion of the diaphragm
located outside the outer edge of the plate, since there is no correspondence between the
diaphragm and the plate, no parasitic capacitance occurs in that portion, and the parasitic
capacitance as a whole Is further reduced. In addition, since the planar shape of the plate can be
made relatively smaller than that of the diaphragm, the rigidity of the plate is relatively
increased, and as a result, the diaphragm can be made larger without deteriorating the stability
of the microphone operation. can do. Therefore, the microphone sensitivity can be improved by
further reducing the parasitic capacitance of the capacitor and further improving the vibration
characteristic of the diaphragm. In addition, since both the diaphragm and the plate are formed
of a conductive material, a complicated manufacturing process is not required, in which an
electrode is provided only on a certain portion of the diaphragm facing surface of the plate made
of an insulating material. Can be Therefore, the diaphragm vibration characteristic can be
improved, the parasitic capacitance of the capacitor can be reduced, and the microphone
sensitivity can be improved without complicating the manufacturing process.
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[0012]
(4) In the above-mentioned condenser microphone, it is preferable that a portion of the plate
corresponding to the arm portion of the diaphragm is cut away. In this case, parasitic capacitance
does not occur between the plate and the arm of the diaphragm, and capacitance mainly occurs
between the plate and the central portion of the diaphragm, thereby reducing the parasitic
capacitance as a whole. Therefore, further reduction of the parasitic capacitance of the capacitor
can be realized to improve the microphone sensitivity.
[0013]
(5) In the above-mentioned condenser microphone, the support means is located between a first
support portion for supporting distal ends of a plurality of the arm portions of the diaphragm
and a plurality of the arm portions of the diaphragm; It is preferable to have the 2nd support part
which supports an outer edge part. In this case, since the tips of the arms of the diaphragm are
supported by the first support, the vibration characteristics of the diaphragm are improved as
compared to the case where the entire periphery of the diaphragm is fixed. In addition, since the
second support for supporting the outer edge of the plate is located between the arms of the
diaphragm, that is, at the notches between the arms, the planar shape of the plate is compared to
that of the diaphragm Since the rigidity of the plate is relatively increased, as a result, the
diaphragm can be enlarged without deteriorating the stability of the microphone operation.
Furthermore, since the diaphragm and the plate are directly supported on the substrate, no
complicated manufacturing process is required. Therefore, the microphone sensitivity can be
improved by further improving the vibration characteristics of the diaphragm without
complicating the manufacturing process.
[0014]
(6) In the above-mentioned condenser microphone, it is preferable that the cavity has an opening
formed along the inside of the central portion of the diaphragm. In this case, the cavity has a
sufficient volume because its opening substantially corresponds to the central portion of the
diaphragm, and as a result, the air spring constant of the cavity is sufficiently small, so that the
vibration characteristic of the diaphragm is improved. It becomes possible to maintain. In
addition, since the opening of the cavity is formed along the inside of the central portion of the
diaphragm, a passage is formed between the substrate and the diaphragm around the cavity, and
this passage causes acoustics between the plurality of arms of the diaphragm Since an acoustic
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resistance higher than the resistance is formed, it is difficult for the sound wave reaching the
diaphragm to pass between the plurality of arms.
[0015]
(7) In the above-mentioned condenser microphone, it is preferable that the cavity has an opening
formed along the inside of the outer edge of the diaphragm. In this case, since the opening of the
cavity corresponds to almost the entire diaphragm, the cavity has a sufficient volume, and the
diaphragm's vibration characteristics can be maintained better. Therefore, the microphone
sensitivity can be improved.
[0016]
(8) In the above-described condenser microphone, it is preferable that a plurality of through
holes be provided in the arm portion of the diaphragm. In this case, the rigidity of the arm is
reduced by the amount of the plurality of through holes, and the deformation of the arm in
vibration of the diaphragm is facilitated and the displacement at the central portion is increased.
Becomes even better. In addition, the plurality of through holes provided in the arms of these
diaphragms etch away the sacrificial layer interposed between the arms of the diaphragm and
the substrate in the manufacturing process of the capacitor microphone, and form a gap between
them. In addition, it functions as an entrance hole for the etching solution. Therefore, the
microphone sensitivity can be improved by further improving the vibration characteristics of the
diaphragm while simplifying the manufacturing process.
[0017]
(9) A condenser microphone for achieving the above object is provided with a conductive plate
having a central portion and a plurality of arms extending radially outward from the central
portion, and disposed so as to face the plate; A diaphragm having a conductive diaphragm that
vibrates in response to vibration, a substrate provided on the opposite side of the plate with
respect to the diaphragm, and a cavity for relieving a pressure applied to the diaphragm from the
opposite side of the plate; And supporting means for insulating the outer edge and the tip of the
arm of the plate on the substrate and forming an air gap between the diaphragm and the central
portion of the plate. In such a condenser microphone, at least a plurality of arm portions of the
plate is interposed between the diaphragm and a plate having a unique planar shape having a
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central portion and a plurality of arms extending radially outward from the central portion. Since
there is no correspondence in the notched portion, parasitic capacitance does not occur in that
portion, and the parasitic capacitance decreases as a whole. Further, since both the diaphragm
and the plate are formed of the conductive material, the manufacturing process can be simplified
as compared with the case where the electrode is provided only on a certain portion of the
diaphragm facing surface of the plate made of the insulating material. Therefore, the microphone
capacitance can be improved by reducing the parasitic capacitance of the capacitor without
complicating the manufacturing process.
[0018]
(10) In the above-mentioned condenser microphone, it is preferable that the diaphragm has a
portion corresponding to the arm portion of the plate cut out. In this case, parasitic capacitance
does not occur between the diaphragm and the arm of the plate, and capacitance mainly occurs
between the diaphragm and the central portion of the plate, so that the parasitic capacitance as a
whole is greatly reduced. Therefore, further reduction of the parasitic capacitance of the
capacitor can be realized to improve the microphone sensitivity.
[0019]
Hereinafter, embodiments of the present invention will be described based on a plurality of
examples. The components with the same reference numerals in the embodiments correspond to
the components of the other embodiments with the reference numbers. First Embodiment
Configuration FIG. 1A is a plan view schematically showing a configuration of a condenser
microphone according to a first embodiment, FIG. 1B is a cross-sectional view taken along the
line AA 'in FIG. 1A, and FIG. 1C is an enlarged view of a portion B in FIG. As shown in FIG. 1A,
FIG. 1B and FIG. 1C, the condenser microphone comprises a diaphragm 10 and a back plate 20
as a plate, which constitute an opposite electrode of the capacitor, and supporting means for
insulating and supporting these diaphragm 10 and back plate 20. It has the support substrate 30
etc. which were provided.
[0020]
The diaphragm 10 is made of, for example, a conductive thin film made of polysilicon doped with
P (phosphorus) as an impurity, and has, for example, six arms extending radially outward from
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the disk-shaped central portion 12 and the central portion 12 It has a substantially gear shape
having a portion 14. In addition, a large number of through holes 16 are continuously provided
in the six arm portions 14. Here, the thickness of the diaphragm 10 is about 0.5 μm, the radius
of the central portion 12 thereof is about 0.35 mm, and the length of the arm portion 14 is about
0.15 mm.
[0021]
The back plate 20 is disposed in parallel with the diaphragm 10 with an air gap 40 of a
predetermined distance, for example, a distance of about 4 μm. The back plate 20 is also made
of a conductive thin film made of, for example, polysilicon to which P is added, and has a diskshaped central portion 22 and, for example, six arms 24 radially extending outward from the
central portion 22. And has a substantially gear shape. A number of through holes 26 are
continuously provided in the central portion 22 and the six arms 24. These through holes 26
function as acoustic holes for passing external sound waves to reach the diaphragm 10. Here, the
thickness of the back plate 20 is about 1.5 μm, the radius of the central portion 22 is about 0.3
mm, and the length of the arm 24 is about 0.1 mm.
[0022]
The central portion 22 of the back plate 20 is disposed concentrically with the diaphragm 10,
and the radius of the central portion 22 of the back plate 20 is smaller than the radius of the
central portion 12 of the diaphragm 10. Further, the six arms 24 of the back plate 20 are located
at positions corresponding to the six notches between the six arms 14 of the diaphragm 10.
Conversely, the six arms 14 of the diaphragm 10 are located at positions corresponding to the six
notches between the six arms 24 of the back plate 20. The distance from the center of the central
portion 22 of the back plate 20 to the tip of the arm 24 is longer than the radius of the central
portion 12 of the diaphragm 10 and the tip of the arm 14 from the center of the central portion
12 of the diaphragm 10 Less than the distance.
[0023]
The tips of the six arms 14 of the diaphragm 10 are supported on the support substrate 30 by
the insulating first support 50. In addition, the front end portions of the six arms 24 of the back
plate 20 are supported by the insulating second support portions 54 positioned at six notches
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between the six arms 14 of the diaphragm 10. Supported on 30
[0024]
The first support portion 50 is made of, for example, a silicon oxide film. The second support
portion 54 includes insulating films 541 and 543 and a conductive film 542. The insulating films
541 and 543 are made of, for example, a silicon oxide film. The conductive film 542 is desirably
formed simultaneously with the diaphragm 10 which is a conductive film, and is made of, for
example, polysilicon doped with P (phosphorus) as an impurity. The conductive film 542 is set to
the same potential as the back plate 20 or the substrate 30 as described later, and functions as a
guard electrode for reducing parasitic capacitance of the condenser microphone. Note that the
conductive film 542 may be omitted.
[0025]
The supporting substrate 30 is made of, for example, a silicon substrate having a thickness of
500 to 600 μm, and a cavity 32 having an opening reaching the diaphragm 10 through the
supporting substrate 30 is provided at a position corresponding to the central portion 12 of the
diaphragm 10. There is. The cavity 32 is formed along the inside of the central portion 12 of the
diaphragm 10 and functions as a pressure buffer chamber for relieving pressure applied to the
diaphragm 10 from the opposite side of the plate. Further, the support substrate 30 around the
cavity 32 and the diaphragm 10 provide a passage 34 forming an acoustic resistance higher than
the acoustic resistance between the arms 14 of the diaphragm 10. The height H (i.e., the distance
between the diaphragm 10 and the support substrate 30) and the length L of the passage 34 (i.e.,
the most central portion of the plurality of through holes 16 of the arm 14 of the diaphragm 10).
Control the acoustic resistance by means of the distance between the through hole 16 and the
end of the cavity 32 or the distance from the end of the central portion 12 of the diaphragm 10
to the end of the cavity 32 By forming an acoustic resistance higher than the acoustic resistance,
the sound wave reaching the diaphragm 10 is prevented from leaking between the plurality of
arms 14. Here, the height H of the passage 34 is, for example, 2 μm, and its length L is, for
example, 15 μm.
[0026]
FIG. 29A is a circuit diagram for describing a detection circuit that detects a change in
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10
capacitance between the diaphragm 10 and the back plate 20 as an electrical signal. A stable bias
voltage is applied to the diaphragm 10 by a charge pump CP or the like. The capacitance change
of the back plate 20 and the diaphragm 10 is input to the amplifier A as a voltage signal. Since
the substrate 30 and the diaphragm 10 are short-circuited, parasitic capacitance is formed
between the back plate 20 and the substrate 30 if the conductive film 542 is not present.
[0027]
When the conductive film 542 is provided, the output terminal of the preamplifier A is connected
to the conductive film 542 as shown in FIG. 29B, and the conductive film 542 can function as a
guard electrode by forming a voltage follower circuit with the preamplifier A. That is, by
controlling the back plate 20 and the conductive film 542 to the same potential by the voltage
follower circuit, parasitic capacitance generated between the back plate 20 and the conductive
film 542 can be removed. Further, by shorting the substrate 30 and the diaphragm 10, the
capacitance between the conductive film 542 and the substrate 30 becomes irrelevant to the
output of the preamplifier A. By providing the conductive film 542 as described above to form
the guard electrode, parasitic capacitance of the condenser microphone can be further reduced.
[0028]
As described above, according to the condenser microphone of the first embodiment, the
diaphragm 10 and the back plate 20 both have a substantially gear shape, and the central
portion 12 of the diaphragm 10 and the central portion 22 of the back plate 20 correspond to
each other. It is in. On the other hand, the six arms 24 of the back plate 20 are positioned at six
notches between the six arms 14 of the diaphragm 10, and the six arms 14 of the diaphragm 10
are back plates The diaphragm 10 and the arms 14 and 24 of the back plate 20 do not have a
corresponding relationship because they are positioned at six notches sandwiched by twenty six
arms 24, and as a result, parasitic capacitance occurs. Absent. Therefore, as a whole, capacitance
mainly occurs between the central portions 12 and 22 of the diaphragm 10 and the back plate
20, and this capacitance becomes a signal capacitance contributing to the capacitance change of
the capacitor, while the other portions The microphone capacitance can be significantly
improved because the parasitic capacitance at the.
[0029]
The diaphragm 10 has a structure in which the tips of the six arms 14 are supported by the first
support portion 50, and the distance from the center of the central portion 12 of the diaphragm
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10 to the first support portion 50 is Since the distance from the center of the central portion 22
of the plate 20 to the second support portion 54 supporting the tips of the six arms 24 is longer
than that of the structure in which the entire circumference of the diaphragm is fixed, The
vibration characteristics of the diaphragm 10 can be improved even as compared with the case
where the planar shapes of the back plate and the back plate are substantially the same.
[0030]
Further, the back plate 20 has a radius of the central portion 22 smaller than that of the central
portion 12 of the diaphragm 10, and the distance from the center of the central portion 22 to the
second support portion 54 is the central portion 12 of the diaphragm 10. The rigidity of the back
plate 20 is higher than that in the case where the planar shapes of the diaphragm and the back
plate are almost the same, and the stability of the microphone operation is not deteriorated,
because the distance between the center of the The diaphragm can be enlarged, and the vibration
characteristic of the diaphragm 10 can be improved.
Further, by providing the plurality of through holes 16 in the six arms 14 of the diaphragm 10,
the rigidity of the arms 14 of the diaphragm 10 is reduced, and the deformation of the arms 14
in the case of vibration becomes easy. Therefore, the vibration characteristics of the diaphragm
10 can be further improved.
[0031]
The present inventors conducted the following experiment to confirm the effect of the condenser
microphone according to the first embodiment as described above. Here, FIGS. 2A and 2B are a
plan view and a cross-sectional view schematically showing the configuration of the conventional
condenser microphone, and FIGS. 3A and 3B are planes schematically showing the configuration
of the condenser microphone prepared for the experiment. It is a figure and sectional drawing.
As shown in FIGS. 2A and 2B, the condenser microphone of the conventional structure has a disklike diaphragm 100 having a radius equal to the distance from the center of the central portion
12 of the diaphragm 10 of the first embodiment to the tip of the arm 14. Is supported on the
support substrate 300 by the first support 500 all around its periphery. In addition, a diskshaped back plate 200 is disposed to cover the entire surface of the diaphragm 100, and the
entire periphery thereof is supported on the support substrate 300 by a second support portion
540.
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[0032]
In addition, as shown in FIGS. 3A and 3B, the condenser microphone of the experimental
structure has an outer periphery supported by the first support portion 500 of the diaphragm
100 at the peripheral portion of the back plate 200 of the condenser microphone of the
conventional structure. Six notches 700 for reducing parasitic capacitance are provided at
positions corresponding to the vicinity. With respect to the conventional structure shown in FIGS.
2A and 2B, the experimental structure shown in FIGS. 3A and 3B, and the condenser
microphones of the first embodiment shown in FIGS. 1A, 1B and 1C, the electrode withstand
voltage and vibration displacement The amount and the microphone sensitivity were measured,
and the results shown in the following table were obtained.
[0033]
[0034]
Here, the electrode withstand voltage means that a voltage is applied between the diaphragm and
the back plate while the sacrificial oxide film is interposed between the diaphragm and the
support substrate, that is, the entire diaphragm is fixed to the support substrate. It refers to the
voltage value when the back plate deformed by the electric force comes in contact with the
diaphragm to energize, and serves as a measure of the strength of the back plate.
The vibration displacement amount refers to the displacement amount at the central portion of
the diaphragm when a predetermined sound pressure is applied to the diaphragm. The
microphone sensitivity is an output voltage of the microphone when a predetermined sound
pressure is applied to the diaphragm, and is expressed by the following equation. Microphone
sensitivity ∝ Vibration displacement amount × applied voltage between electrodes × {signal
capacity / (signal capacity + parasitic capacitance)} In addition, the numbers in the table indicate
the electrode withstand voltage, vibration displacement amount, and microphone sensitivity in
the case of the condenser microphone of the conventional structure. Each is defined as 1.0 and
displayed as a relative value to this reference.
[0035]
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In the above table, the electrode withstand voltage of the experimental structure is reduced to
0.8 times that of the conventional structure. This is considered to be attributable to the decrease
in strength of the back plate 120 due to the provision of the notch 121 for reducing the parasitic
capacitance. Such a reduction in the electrode withstand voltage is a factor causing instability of
the microphone operation. In addition, although the back plate 20 of the first embodiment has a
substantially gear shape and has a structure equivalent to that having the notch on the outer
periphery, the electrode withstand voltage is 1.2 times that in the conventional structure. It's
getting higher. This is because the second support 54 supporting the tip of the arm 24 of the
back plate 20 according to the first embodiment is located at the notch between the arms 14 of
the diaphragm 10 and the center 22 of the back plate 20 The distance from the center of the
second support 54 to the center of the second support 54 is shorter than the distance from the
center of the diaphragm 100 of the conventional structure to the first support 500, and
accordingly the rigidity of the back plate 20 is relatively high. It is considered to be attributable.
Such an increase in electrode withstand voltage contributes to the improvement of the stability of
the microphone operation.
[0036]
Further, the amount of vibration displacement of the diaphragm 10 of the first embodiment is
2.0 times as high as that of the conventional structure. This is a structure in which the diaphragm
10 of the first embodiment has a substantially gear shape and the tip of the arm 14 is supported
by the first support 50, so the entire circumference of the diaphragm 110 is fixed. It is
considered that the vibration characteristic of the diaphragm 10 is improved as compared with
the conventional structure. In addition, the provision of a plurality of through holes 16 in the arm
portion 14 of the diaphragm 10 is also considered to contribute to an increase in the amount of
vibration displacement.
[0037]
Also, the microphone sensitivity of the first embodiment is 3.0 times higher than that of the
conventional structure. In addition to the fact that the vibration displacement amount of the
diaphragm 10 of the first embodiment is higher than that of the conventional structure, this is
mainly between the central portions 12 and 22 of the diaphragm 10 and the back plate 20 as
described above. It is considered that while capacitance is generated, no parasitic capacitance is
generated in each of the arms 14 and 24 because there is no corresponding relationship, and
therefore, the parasitic capacitance is largely reduced as a whole.
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14
[0038]
2. Manufacturing Method The condenser microphone according to the first embodiment is a
so-called silicon microphone, and is manufactured using a semiconductor manufacturing process.
Hereinafter, a method of manufacturing a condenser microphone according to the first
embodiment will be described with reference to process cross-sectional views of FIGS.
[0039]
First, as shown in FIG. 4, for example, on a supporting substrate 30 made of a semiconductor
substrate such as a single crystal silicon substrate, a first film about 2 μm thick made of a silicon
oxide film using plasma CVD (Chemical Vapor Deposition), for example. An insulating film 50a is
formed. The first insulating film 50a is removed in a later step to form a cavity in the support
substrate 30 below the diaphragm, and at the same time, a passage that generates a desired
acoustic resistance between the support substrate 30 and the diaphragm around the cavity. It
functions as a sacrificial film to be formed, and forms a first support portion for supporting the
diaphragm on the support substrate 30.
[0040]
Then, as shown in FIG. 5, a first conductive layer 10a of about 0.5 .mu.m in thickness made of a
polysilicon layer to which P is added is formed on the first insulating film 50a by using, for
example, a low pressure CVD method. At this time, the first conductive layer 10 a is also formed
on the back surface of the support substrate 30. Subsequently, as shown in FIG. 6, a photoresist
film is applied on the entire surface of the first conductive layer 10a on the first insulating film
50a, and then a photolithographic technique such as exposure and development using a
predetermined resist mask is performed. A resist pattern P1 is formed. Subsequently, as shown in
FIG. 7, the photoresist pattern P1 is used as a mask, and the first conductive layer 10a is
selectively etched away by anisotropic etching such as RIE (Reactive Ion Etching) to form a
predetermined shape. To form a diaphragm 10 having a thickness of about 0.5 .mu.m, a lead
wiring portion 18 connected to the diaphragm 10, and a plurality of through holes 16 in an arm
of the diaphragm 10. As shown in FIG. When the guard electrode is provided, a portion
corresponding to the conductive film 542 is left when the first conductive layer 10a is etched
away.
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[0041]
Next, as shown in FIG. 8, ashing with an O 2 plasma and a solution process of dipping in a mixed
solution of sulfuric acid and hydrogen peroxide solution are combined to remove the photoresist
pattern P 1. Thus, as shown in FIG. 1A, the diaphragms 10 formed by the patterning of the first
conductive layer 10a have a planar shape of a disk-shaped central portion 12 and six radially
extending outward from the central portion 12 A plurality of through holes 16 are formed in the
six arm portions 14 while forming a substantially gear shape having the arm portions 14.
[0042]
Then, as shown in FIG. 9, a second insulating film 52a of about 4 .mu.m in thickness made of a
silicon oxide film is formed on the diaphragm 10, the lead-out wiring portion 18 and the first
insulating film 50a using, for example, plasma CVD. . Here, when the second insulating film 52a
is deposited on the first insulating film 50a, the two are combined to form a laminated insulating
film 54a. The second insulating film 52a is removed in a later step to function as a sacrificial film
for forming an air gap between the diaphragm and the back plate, and the laminated insulating
film 54a is used as a sacrificial film in a later step. This is for forming a second support portion
supported on the support substrate 30.
[0043]
Next, as shown in FIG. 10, a second conductive layer 20a of about 1.5 .mu.m in thickness made of
a polysilicon layer to which P is added is formed on the second insulating film 52a by using, for
example, a low pressure CVD method. At this time, the second conductive layer 20 a is also
formed on the first conductive layer 10 a on the back surface of the support substrate 30.
Subsequently, as shown in FIG. 11, a photoresist film is coated on the entire surface of the
second conductive layer 20a on the second insulating film 52a, and then a photoresist pattern P2
is formed by photolithography. Subsequently, as shown in FIG. 12, the photoresist pattern P2 is
used as a mask, and the second conductive layer 20a is selectively etched away by anisotropic
etching technology such as RIE and processed into a predetermined shape. A back plate 20 of
about 1.5 μm and a lead wiring portion 28 connected to the back plate 20 and a plurality of
through holes 26 of a capacitance forming portion in the center of the back plate 20 are formed.
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[0044]
Next, as shown in FIG. 13, after the photoresist pattern P2 is removed by ashing treatment and
dissolution treatment with a mixed solution of sulfuric acid and hydrogen peroxide water, heat
treatment for baking is performed. Thus, as shown in FIG. 1A, the back plate 20 formed by the
patterning of the second conductive layer 20 a has six planar shapes extending radially outward
from the central portion 22 in the form of a disk and the central portion 22. A plurality of
through holes 26 are formed in the central portion 22 and the six arms 24.
[0045]
Further, as shown in FIG. 1A, the central portion 22 of the back plate 20 corresponds
concentrically to the central portion 12 of the diaphragm 10, and the radius of the central
portion 22 of the back plate 20 corresponds to the central portion 12 of the diaphragm 10. Less
than the radius of Further, the six arms 24 of the back plate 20 are located at positions
corresponding to the six notches between the six arms 14 of the diaphragm 10. Conversely, the
six arms 14 of the diaphragm 10 are located at positions corresponding to the six notches
between the six arms 24 of the back plate 20. The distance from the center of the central portion
22 of the back plate 20 to the tip of the arm 24 is longer than the radius of the central portion
12 of the diaphragm 10 and the tip of the arm 14 from the center of the central portion 12 of
the diaphragm 10 Less than the distance.
[0046]
Then, as shown in FIG. 14, a third insulating film 56 of about 0.3 μm in thickness made of a
silicon oxide film is formed on the back plate 20, the lead-out wiring portion 28 and the second
insulating film 52a using plasma CVD, for example. Form Subsequently, as shown in FIG. 15, a
photoresist film is coated on the entire surface of the third insulating film 56, and then a
photoresist pattern P3 is formed by photolithography. The photoresist pattern P 3 has an
opening above the lead-out wiring portion 18 connected to the diaphragm 10 and the lead-out
wiring portion 28 connected to the back plate 20.
[0047]
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17
Next, as shown in FIG. 16, the third insulating film 56 and the second insulating film 52a are
selectively etched away by wet etching, dry etching or an etching technique combining them,
using the photoresist pattern P3 as a mask. The electrode extraction holes 58a and 58b for
exposing the extraction wiring portions 18 and 28 are opened. Subsequently, as shown in FIG.
17, the photoresist pattern P3 is removed by ashing treatment and dissolution treatment with a
mixed solution of sulfuric acid and hydrogen peroxide solution.
[0048]
Next, as shown in FIG. 18, a metal layer 60 made of Al-Si is formed on the entire surface
including the third insulating film 56 and the lead-out interconnections 18 and 28 exposed in the
electrode extraction holes 58a and 58b using, for example, a sputtering method. Deposit.
Subsequently, as shown in FIG. 19, a photoresist film is coated on the entire surface of the metal
layer 60, and a photoresist pattern P4 covering the upper side of the electrode extraction holes
58a and 58b is formed by photolithography. Subsequently, as shown in FIG. 20, the photoresist
pattern P4 is used as a mask, and the metal layer 60 is selectively etched away by a wet etching
technique using mixed acid, for example, and processed into a predetermined shape. The first
electrode 60a and the second electrode 60b respectively connected to the lead-out wiring
portions 18, 28 via
[0049]
Then, as shown in FIG. 21, the ashing process by O 2 plasma and the dissolution process to be
immersed in the organic stripping solution are combined to remove the photoresist pattern P4.
The first electrode 60 a thus formed is connected to the diaphragm 10 via the lead-out wiring
portion 18, and the second electrode 60 b is connected to the back plate 20 via the lead-out
wiring portion 28.
[0050]
Next, as shown in FIG. 22, the second conductive layer 20a and the first conductive layer 10a on
the back surface of the support substrate 30 are ground and removed using, for example, grinder
technology, and the back surface of the support substrate 30 is further ground. The thickness is
adjusted to 500 to 600 .mu.m. Subsequently, as shown in FIG. 23, a photoresist film is applied
18-04-2019
18
thicker than usual, for example, to a thickness of 15 to 20 μm on the back surface of the
support substrate 30, and then a photoresist pattern P5 is formed by photolithography. The
photoresist pattern P5 has an opening at a position corresponding to the central portion 12 of
the diaphragm 10.
[0051]
Then, as shown in FIG. 24, using photoresist pattern P5 as a mask, support substrate 30 is
selectively etched away by anisotropic etching technology commonly referred to as deep RIE, for
example, to reach first insulating film 50a. An opening 32a is formed. The opening 32 a is
located along the inside of the central portion 12 of the diaphragm 10. Subsequently, as shown
in FIG. 25, the photoresist pattern P5 is removed by ashing treatment and dissolution treatment
with an organic stripping solution.
[0052]
Next, as shown in FIG. 26, a photoresist film is coated on the entire surface of the first electrode
60a, the second electrode 60b, and the third insulating film 56, and then a photoresist pattern P6
is formed by photolithography. The photoresist pattern P6 covers the first electrode 60a and the
second electrode 60b, and also covers the third insulating film 56 above the lead-out wiring
portions 18, 28.
[0053]
Next, as shown in FIG. 27, the third insulating film 56, the second insulating film 52a, and the
first insulating film are formed by wet etching using buffered hydrofluoric acid (Buffered HF)
using the photoresist pattern P6 as a mask. 50a is selectively etched away. At this time, the
plurality of through holes 26 formed in the central portion 22 and the arm portion 24 of the
back plate 20 are etched when the second insulating film 52 a interposed between the back plate
20 and the diaphragm 10 is etched away. It functions as a liquid entry hole. Further, the plurality
of through holes 16 formed in the arm portion 14 of the diaphragm 10 also function as an
entrance hole for the etching solution when the first insulating film 50a interposed between the
diaphragm 10 and the support substrate 30 is etched away. Do. Furthermore, the buffered
hydrofluoric acid selectively etches and removes the first insulating film 50 a and the like from
the side of the opening 32 a of the support substrate 30.
18-04-2019
19
[0054]
Thus, the second insulating film 52a between the back plate 20 and the diaphragm 10 is
removed, and the void 40 is formed in the removed trace. Further, the first insulating film 50a is
removed, and the opening 32a of the support substrate 30 is expanded until it reaches the
diaphragm 10 to form a cavity 32, and a desired space is formed between the support substrate
30 and the diaphragm 10 around this cavity 32. To form a passage 34 for forming an acoustic
resistance.
[0055]
At the same time, the first insulating film 50 a is intentionally left between the tips of the six
arms 14 of the diaphragm 10 and the support substrate 30 to form the first support 50. In
addition, the laminated insulating film 54 a is intentionally left between the tips of the six arms
24 of the back plate 20 and the support substrate 30 to form the second support 54.
[0056]
Then, as shown in FIG. 28, the photoresist pattern P6 is removed by ashing treatment and
dissolution treatment with an organic stripping solution. Thus, the condenser microphone
according to the first embodiment shown in FIGS. 1A, 1B and 1C is manufactured.
[0057]
As described above, according to the manufacturing method of the condenser microphone
according to the first embodiment, it is possible to follow the conventional manufacturing
process almost as it is, except that the pattern of the resist mask used in each photolithography
process is different. Since there is no need for steps such as providing the back electrode only on
a certain portion of the diaphragm facing surface of the plate made of the insulating material, the
manufacturing cost can be prevented from increasing.
[0058]
Second Embodiment A condenser microphone according to a second embodiment is the same as
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20
the condenser microphone according to the first embodiment shown in FIGS. 1A to 1C, in which
the entire back plate 20 has a disk shape and the radius thereof is the center of the diaphragm
10 It is longer than the radius of the portion 12 and shorter than the distance from the center of
the central portion 12 of the diaphragm 10 to the tip of the arm portion 14.
[0059]
Even in this case, since the diaphragm 10 has a substantially gear shape having the central
portion 12 and the six arm portions 14, the notch portion between the diaphragm 10 and the
back plate 20 is not formed. There is no correspondence between them, resulting in no parasitic
capacitance.
Similarly, no parasitic capacitance occurs in the arm 14 of the diaphragm 10 located outside the
outer edge of the back plate 20.
Therefore, as compared with the conventional structure shown in FIGS. 2A and 2B, the parasitic
capacitance can be reduced as a whole. However, in the arm portion 14 of the diaphragm 10, a
portion inside the outer periphery of the disk-shaped back plate 20 produces a parasitic
capacitance with the back plate 20, so compared to the case of the first embodiment, Only
parasitic capacitance increases.
[0060]
Third Embodiment A condenser microphone according to a third embodiment is a condenser
microphone according to the first embodiment shown in FIGS. 1A to 1C, in which the entire
diaphragm 10 has a disk shape. Even in this case, since the back plate 20 has a substantially gear
shape having the central portion 22 and the six arms 24, a parasitic capacitance is generated in
the notch portion sandwiched by the arms 24 of the back plate 20. It does not occur. Therefore,
as compared with the conventional structure shown in FIGS. 2A and 2B, the parasitic capacitance
can be reduced as a whole. However, in the arm portion 24 of the back plate 20, a portion on the
inner side of the outer periphery of the disk-shaped diaphragm 10 produces a parasitic
capacitance with the diaphragm 10, so compared to the case of the first embodiment Parasitic
capacitance increases.
18-04-2019
21
[0061]
Fourth Embodiment A condenser microphone according to a fourth embodiment is the same as
the condenser microphone according to the first embodiment shown in FIGS. 1A to 1C except
that the through hole 16 is eliminated and the cavity 32 is the central portion 12 of the
diaphragm 10 and It is formed along the inside of the outer periphery of the substantially gear
shape which consists of six arms 14. In this case, the opening of the cavity 32 corresponds to
substantially the entire gear-shaped diaphragm 10 except for the tip of the arm 14, and the
volume thereof is larger than that of the first embodiment. Can have better vibration
characteristics.
[0062]
1A is a plan view schematically showing the structure of a condenser microphone according to
the first embodiment, FIG. 1B is a cross-sectional view taken along the line AA 'of FIG. 1A, and
FIG. 1C is a partially enlarged view of FIG. FIG. 2A is a plan view schematically showing the
structure of a conventional condenser microphone, and FIG. 2B is a cross-sectional view thereof.
FIG. 3A is a plan view schematically showing the configuration of the condenser microphone of
the experimental structure, and FIG. 3B is a cross-sectional view thereof. It is process sectional
drawing (the 1) explaining the manufacturing method of the capacitor | condenser microphone
based on 1st Example. It is process sectional drawing (the 2) explaining the manufacturing
method of the capacitor | condenser microphone based on 1st Example. It is process sectional
drawing (the 3) explaining the manufacturing method of the capacitor | condenser microphone
based on 1st Example. It is process sectional drawing (the 4) explaining the manufacturing
method of the capacitor | condenser microphone based on 1st Example. It is process sectional
drawing (the 5) explaining the manufacturing method of the capacitor | condenser microphone
based on 1st Example. It is process sectional drawing (the 6) explaining the manufacturing
method of the capacitor | condenser microphone based on 1st Example. It is process sectional
drawing (the 7) explaining the manufacturing method of the capacitor | condenser microphone
based on 1st Example. It is process sectional drawing (the 8) explaining the manufacturing
method of the capacitor | condenser microphone based on 1st Example. It is process sectional
drawing (the 9) explaining the manufacturing method of the capacitor | condenser microphone
based on 1st Example. It is process sectional drawing (the 10) explaining the manufacturing
method of the capacitor | condenser microphone based on 1st Example. It is process sectional
drawing (the 11) explaining the manufacturing method of the capacitor | condenser microphone
based on 1st Example. It is process sectional drawing (the 12) explaining the manufacturing
method of the capacitor | condenser microphone based on 1st Example. It is process sectional
drawing (the 13) explaining the manufacturing method of the capacitor | condenser microphone
18-04-2019
22
based on 1st Example. It is process sectional drawing (the 14) explaining the manufacturing
method of the capacitor | condenser microphone concerning 1st Example. It is process sectional
drawing (the 15) explaining the manufacturing method of the capacitor | condenser microphone
based on 1st Example. It is process sectional drawing (the 16) explaining the manufacturing
method of the capacitor | condenser microphone based on 1st Example. It is process sectional
drawing (the 17) explaining the manufacturing method of the capacitor | condenser microphone
based on 1st Example. It is process sectional drawing (the 18) explaining the manufacturing
method of the capacitor | condenser microphone based on 1st Example. It is process sectional
drawing (the 19) explaining the manufacturing method of the capacitor | condenser microphone
based on 1st Example.
It is process sectional drawing (the 20) explaining the manufacturing method of the capacitor |
condenser microphone based on 1st Example. It is process sectional drawing (the 21) explaining
the manufacturing method of the capacitor | condenser microphone based on 1st Example. It is
process sectional drawing (the 22) explaining the manufacturing method of the capacitor |
condenser microphone based on 1st Example. It is process sectional drawing (the 23) explaining
the manufacturing method of the capacitor | condenser microphone based on 1st Example. It is
process sectional drawing (the 24) explaining the manufacturing method of the capacitor |
condenser microphone based on 1st Example. It is process sectional drawing (the 25) explaining
the manufacturing method of the capacitor | condenser microphone concerning 1st Example.
FIGS. 29A and 29B are circuit diagrams according to the first embodiment.
Explanation of sign
[0063]
10: diaphragm, 12: central portion (central portion of diaphragm), 14: arm portion (arm portion
of diaphragm), 16: through hole, 20: back plate, 22: central portion (central portion of back
plate), 24: Arms (arms of back plate), 26: through holes, 30: support substrate, 32: cavities, 34:
passages, 40: air gaps, 50: first supports, 54: second supports.
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