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DESCRIPTION JP2014175962

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DESCRIPTION JP2014175962
Abstract: The characteristics of an acoustic transducer whose environmental resistance is
improved by opening a hole in a diaphragm are further improved. A silicon substrate has a
chamber which penetrates up and down. A diaphragm 23 is formed on the upper surface of the
silicon substrate so as to cover the upper surface of the chamber. A back plate 28 is provided
above the silicon substrate so as to cover the diaphragm 23, and a fixed electrode plate 29 is
provided on the lower surface of the back plate 28 so as to face the diaphragm 23. The back
plate 28 and the fixed electrode plate 29 are opened with a plurality of acoustic holes 31
penetrating vertically for passing acoustic vibration. A plurality of through holes 27 having a
smaller opening area than the acoustic holes 31 are formed in a region where the displacement
of the diaphragm 23 is large. [Selected figure] Figure 4
Acoustic transducer
[0001]
The present invention relates to acoustic transducers. Specifically, the present invention relates
to an acoustic transducer for converting detected acoustic vibration into an electrical signal.
[0002]
In acoustic sensors, the diaphragm may be pierced to increase the roll-off frequency. In the
acoustic sensor 11 shown in FIGS. 1A and 1B, a chamber 13 which is vertically penetrated in the
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substrate 12 is opened, and a diaphragm 14 is provided above the substrate 12 so as to cover
the upper surface of the chamber 13. A back plate 15 is provided on the upper surface of the
substrate 12 so as to cover the diaphragm 14, and a fixed electrode plate 16 opposed to the
diaphragm 14 is provided on the lower surface of the back plate 15. The back plate 15 and the
fixed electrode plate 16 have a plurality of acoustic holes 17 opened in the air gap between the
fixed electrode plate 16 and the diaphragm 14 for guiding acoustic vibration. Further, a through
hole 18 having a larger opening area than the acoustic hole 17 is opened in a large displacement
area of the diaphragm 14, that is, in the area of the diaphragm 14 facing the top opening of the
chamber 13. As such an acoustic sensor, there exists a thing described, for example in patent
document 1. FIG.
[0003]
In such an acoustic sensor 11, the acoustic vibration entering the air gap between the fixed
electrode plate 16 and the diaphragm 14 from the acoustic hole 17 is a gap between the lower
surface of the outer peripheral portion of the diaphragm 14 and the upper surface of the
substrate 12 (vent hole F) to the chamber 13). Further, when the through hole 18 is opened in
the diaphragm 14, the acoustic vibration entering the air gap from the acoustic hole 17 escapes
to the chamber 13 even through the through hole 18 of the diaphragm 14. Therefore, when the
through hole 18 is opened in the diaphragm 14, the resistance to acoustic vibration (acoustic
resistance) decreases, and the roll-off frequency of the acoustic sensor 11 increases.
[0004]
FIG. 2 is a diagram showing the sensitivity ratio of the acoustic sensor, and the horizontal axis
represents the frequency (frequency) of the acoustic vibration, and the vertical axis represents
the sensitivity ratio. A curve indicated by a broken line in FIG. 2 is a sensitivity ratio-frequency
characteristic (hereinafter referred to as a frequency characteristic) when the through hole 18 is
not opened in the diaphragm 14. )である。 On the other hand, when the through hole 18 is
opened in the diaphragm 14, the sensitivity ratio of the acoustic sensor is lowered in the low
frequency range (low frequency range) as shown by the frequency characteristic shown by the
solid line in FIG. Such lowering of the sensitivity ratio in the low frequency range is called roll-off
(effect).
[0005]
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In the acoustic sensor 11 in which the through holes 18 are opened in a large displacement
region of the diaphragm 14 and rolled off as shown in FIG. 1, environmental resistance such as
wind noise resistance, compressed air resistance and pressure fluctuation resistance can be
improved. . That is, since the diaphragm 14 is less likely to be shaken by the wind coming from
the acoustic hole 17 or the chamber 13, it becomes difficult to detect the wind as sound (wind
noise resistance). Further, for example, when the acoustic sensor 11 is dropped, wind pressure
may be applied to the chamber 13 (particularly in the case of a bottom port type microphone),
and the air pressure in the chamber 13 is compressed by the wind pressure to increase the air
pressure. Also in this case, if the through hole 18 is open in the diaphragm 14, the compressed
air is less likely to be added to the diaphragm 14, and the diaphragm 14 is less likely to be
broken by the compressed air (compressed air resistance). In addition, when the lower surface of
the chamber 13 is closed, even if the air pressure (atmospheric pressure) on the air gap side
temporarily fluctuates, the pressure escapes through the through hole 18 and the pressure
fluctuation is detected as a sound. It becomes difficult (pressure fluctuation tolerance).
[0006]
However, in the conventional acoustic sensor 11, as shown in FIG. 3, the diameter D of the
through hole 18 opened in the diaphragm 14 is equal to or larger than the diameter d of the
acoustic hole 17. In particular, in the case of a bottom port type microphone, the through hole 18
of the diaphragm 14 is larger. In such an acoustic sensor 11, since the large through hole 18 is
provided in the diaphragm 14, the sacrificial layer between the diaphragm 14 and the fixed
electrode plate 16 falls into the through hole 18 at the time of film formation, as shown in FIG. A
step δ is generated on the back plate 15 and the fixed electrode plate 16 at a location
corresponding to the edge of the through hole 18. As a result, there is a possibility that the
strength of the back plate 15 may be weakened or a partial incomplete conduction may occur in
the fixed electrode plate 16.
[0007]
Patent Document 2 also discloses an acoustic sensor having a through hole in a diaphragm.
However, in this sensor, the through holes are provided not in the area where the displacement
of the diaphragm is large but in the area (vent hole portion) facing the upper surface of the
substrate on the outer peripheral part of the diaphragm. In such a through hole, environmental
resistance such as compressed air resistance and wind noise resistance is hardly improved
because the resistance when the acoustic vibration passes through is high. Also, to increase the
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effect of roll-off, it is necessary to provide a large number of through holes, but if a large number
of through holes are provided in a vent hole portion with a limited area, the electrode area is
reduced to lower the sensitivity or mechanical strength. There is a problem such as falling.
[0008]
US Patent Application Publication 2012/0033831 (US2012 / 0033831 A1), paragraph [0043]
Japanese Patent Laid-Open Publication No. 2010-34641
[0009]
The object of the present invention is to provide an acoustic transducer in which the
environment resistance is improved by forming a through hole in the vibrating electrode plate by
making the through hole of the vibrating electrode plate smaller than the acoustic hole (acoustic
hole). It aims at the further characteristic improvement of an acoustic transducer.
[0010]
In the acoustic transducer according to the present invention, a substrate having a cavity opened
at least at the upper surface, a vibrating electrode plate formed above the substrate so as to
cover the upper surface of the cavity, and the vibrating electrode plate An acoustic transducer
comprising: a back plate formed above the substrate; and a fixed electrode plate provided on the
back plate, wherein the back plate and the fixed electrode have a plurality of acoustic holes
penetrating vertically. A plurality of through holes having a smaller opening area than the
acoustic holes are formed in a large displacement area of the electrode plate.
[0011]
In the acoustic transducer of the present invention, since a plurality of through holes having a
smaller opening area than the acoustic holes are formed in the large displacement area of the
vibrating electrode plate, the sensitivity in the low frequency range is rolled off. It is possible to
improve the environmental resistance such as wind noise resistance, compressed air resistance
and pressure fluctuation resistance.
Further, since the opening area of the through hole is small, foreign matter is less likely to
intrude into the air gap between the vibrating electrode plate and the fixed electrode plate from
the cavity side even when used in a bottom port type microphone or the like.
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Here, the region where the displacement of the vibrating electrode plate is large is a region
including the maximum displacement position of the vibrating electrode plate and the periphery
thereof.
[0012]
Since the opening area of the through hole is small, in the process of manufacturing the acoustic
transducer, the through hole is filled with a sacrificial layer for forming an air gap between the
vibrating electrode plate and the fixed electrode plate, and a step is formed on the back plate or
the fixed electrode plate. Is less likely to occur.
As a result, the strength of the back plate and the fixed electrode plate does not easily decrease
due to the level difference, and the conduction failure does not easily occur in the fixed electrode
plate. In particular, when the width of the through hole is smaller than twice the air gap, the
through hole is filled with the sacrificial layer formed for forming the air gap, and a step is hardly
generated in the back plate or the fixed electrode plate.
[0013]
In addition, because the opening area of the through holes is small, the number of through holes
must be increased to obtain the required roll-off effect, but the through holes are dispersedly
provided in a large displacement region of the vibrating electrode plate . As a result, thermal
noise in the air gap sandwiched between the vibrating electrode plate and the fixed electrode
plate can be efficiently reduced, and the S / N ratio of the acoustic transducer can be improved.
The region where the displacement of the vibrating electrode plate is large is a region where the
vibrating electrode plate is largely displaced when thermal noise occurs, so the noise of the
acoustic transducer becomes large. Therefore, the region where the displacement of the vibrating
electrode plate is large is the region where thermal noise is most desired to be reduced, and the S
/ N ratio of the acoustic transducer can be greatly improved by having holes in this region.
[0014]
As a region for forming the plurality of through holes, in particular, the central portion of the
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vibrating electrode plate is preferable. In the acoustic transducer, when the vibrating electrode
plate is disposed so as to cover the chamber, the fixed portion of the vibrating electrode plate
often becomes a peripheral portion (such as a substrate). When the diaphragm is fixed at the
periphery, the displacement of the vibrating electrode plate becomes particularly large at the
central portion. Therefore, providing a hole to reduce the thermal noise at the central portion of
the vibrating electrode plate The improvement effect is large. In particular, the displacement of
the vibrating electrode plate is large in a region of half or less from the center to the edge of the
vibrating electrode plate, and it is desirable to provide a through hole in this region.
[0015]
The vibrating electrode plate in an embodiment of the acoustic transducer according to the
present invention is characterized in that the through hole is provided at a position not
overlapping the acoustic hole when viewed from a direction perpendicular to the upper surface
of the substrate. There is. When the through holes and the acoustic holes are provided so as to
overlap with each other, the acoustic resistance is reduced and the roll-off effect is too effective,
so the number of through holes is limited. On the other hand, if the through holes are arranged
so as not to overlap with the acoustic holes, the number of the through holes can be increased
even if an appropriate roll-off effect is to be provided, and the thermal noise can be efficiently
reduced. .
[0016]
Further, in the above embodiment, the through hole is surrounded by an area between two
adjacent acoustic holes or three or more of the acoustic holes as viewed from a direction
perpendicular to the upper surface of the substrate. It is preferable to arrange in the By
arranging the through holes in this way, the through holes can be provided at locations far from
the acoustic holes, so that the roll-off effect of the acoustic sensor can be enhanced, and the
effect of reducing thermal noise is also enhanced.
[0017]
The through holes in another embodiment of the acoustic transducer according to the present
invention are characterized in that they are regularly arranged. When the acoustic holes are
regularly arranged, arranging the through holes regularly makes it easy to arrange the through
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holes and the acoustic holes so that they do not overlap. Also, if the through holes are regularly
arranged, thermal noise can be efficiently reduced in the arranged area, and the S / N ratio of the
acoustic transducer can be further improved. In particular, the pitch of the through holes is
preferably an integral multiple of the pitch of the acoustic holes. When the pitch of the through
holes is an integral multiple of the pitch of the acoustic holes, both the through holes and the
acoustic holes can be regularly arranged and arranged.
[0018]
A first microphone according to the present invention is a microphone in which an acoustic
transducer according to the present invention is mounted inside a package, and the substrate has
the cavity penetrating from the upper surface to the lower surface, and the package is an
acoustic vibration A sound introducing hole for introducing the light emitting diode into the
package is opened, and the sound introducing hole and the lower surface of the cavity are
connected. According to such a microphone, environmental resistance such as wind noise
resistance, compressed air resistance, pressure fluctuation resistance and the like can be
improved, and the strength of the acoustic transducer can be improved.
[0019]
A second microphone according to the present invention is characterized in that the acoustic
transducer according to the present invention and a circuit unit for amplifying a signal from the
acoustic transducer and outputting the signal to the outside are mounted in a package. According
to such a microphone, environmental resistance such as wind noise resistance, compressed air
resistance, pressure fluctuation resistance and the like can be improved, and the strength of the
acoustic transducer can be improved.
[0020]
In addition, the means for solving the above-mentioned subject in the present invention has the
feature which combined suitably the component explained above, and the present invention
enables many variations by the combination of such a component. .
[0021]
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FIG. 1A is a plan view showing a conventional acoustic sensor.
FIG. 1B is a cross-sectional view of a conventional acoustic sensor. FIG. 2 is a diagram for
explaining the roll-off effect of the acoustic sensor. FIG. 3 is a schematic cross-sectional view for
explaining the problem to be solved by the conventional acoustic sensor. FIG. 4A is a plan view
showing an acoustic sensor according to Embodiment 1 of the present invention. FIG. 4B is a
view showing a positional relationship among an acoustic hole, a through hole of a diaphragm,
and a stopper in the acoustic sensor of the first embodiment. FIG. 5 is a cross-sectional view of
the acoustic sensor of the first embodiment. FIG. 6 is a plan view of a diaphragm used in the
acoustic sensor of the first embodiment. 7A and 7B are diagrams for explaining the function and
effect of the acoustic sensor of the first embodiment. FIG. 8A is a schematic view showing how a
back plate is stepped in the conventional acoustic sensor. FIG. 8B is a schematic view illustrating
the reason why the back plate does not have a step in the acoustic sensor according to the first
embodiment. FIG. 9 is a schematic cross-sectional view of a microphone incorporating an
acoustic sensor according to the present invention.
[0022]
Hereinafter, preferred embodiments of the present invention will be described with reference to
the accompanying drawings. However, the present invention is not limited to the following
embodiments, and various design changes can be made without departing from the scope of the
present invention.
[0023]
Embodiment 1 Hereinafter, the structure of an acoustic transducer according to Embodiment 1 of
the present invention, that is, an acoustic sensor 21 will be described with reference to FIGS. FIG.
4A is a plan view of the acoustic sensor 21 according to Embodiment 1 of the present invention.
FIG. 4B is a plan view showing a part of the acoustic sensor 21 in an enlarged manner, and shows
the positional relationship between the acoustic hole 31, the through hole 27 of the diaphragm
23, and the stopper 32. FIG. 5 is a cross-sectional view of the acoustic sensor 21. As shown in
FIG. FIG. 6 is a plan view of the diaphragm 23.
[0024]
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The acoustic sensor 21 is a capacitive element manufactured using MEMS technology. As shown
in FIG. 5, in the acoustic sensor 21, a diaphragm 23 is provided on the upper surface of a silicon
substrate 22 (substrate) via an anchor 26 and a canopy is provided above the diaphragm 23 via a
minute air gap 30 (air gap). 24 is disposed and fixed on the upper surface of the silicon substrate
22.
[0025]
In the silicon substrate 22, a chamber 25 (cavity) penetrating from the front surface to the back
surface is opened. The diaphragm 23 is disposed on the top surface of the silicon substrate 22 so
as to cover the top opening of the chamber 25. The diaphragm 23 is formed in a substantially
disc shape by a conductive polysilicon thin film, and the diaphragm 23 itself is a vibrating
electrode plate. A plurality of anchors 26 are spaced apart on the top surface of the silicon
substrate 22 around the chamber 25. The diaphragm 23 is supported on the upper surface of the
silicon substrate 22 by the anchor 26 at the lower surface of the outer peripheral portion, and
floats from the upper surface opening of the chamber 25 and the upper surface of the silicon
substrate 22. As shown in FIG. 6, in the large displacement area of the diaphragm 23, that is, the
area facing the upper surface opening of the silicon substrate 22 (preferably, the central portion
of the diaphragm 23), It arranges regularly at a fixed pitch. Further, a lead wire 33 is drawn from
the diaphragm 23.
[0026]
As shown in FIG. 5, the canopy 24 is provided with a fixed electrode plate 29 made of polysilicon
on the lower surface of a back plate 28 made of SiN. The canopy portion 24 is formed in a dome
shape and has a hollow portion below it, and the hollow portion covers the diaphragm 23. A
minute air gap 30 (air gap) is formed between the lower surface of the canopy 24 (that is, the
lower surface of the fixed electrode plate 29) and the upper surface of the diaphragm 23. As
shown in FIG. 4A, a lead wire 34 is drawn from the fixed electrode plate 29.
[0027]
A large number of acoustic holes 31 (acoustic holes) for passing acoustic vibration are formed in
the canopy 24 (that is, the back plate 28 and the fixed electrode plate 29) so as to penetrate from
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the upper surface to the lower surface. As shown in FIG. 4A, the acoustic holes 31 are regularly
arranged. In the illustrated example, the acoustic holes 31 are arranged in a triangular shape
along three directions forming an angle of 120 ° with each other, but may be arranged in a
rectangular shape, a concentric shape, or the like. Further, stoppers 32 project from the lower
surface of the back plate 28 at appropriate intervals. The stopper 32 penetrates the fixed
electrode plate 29 and protrudes below the fixed electrode plate 29 to prevent the diaphragm 23
from sticking (sticking) to the fixed electrode plate 29.
[0028]
In addition, electrode pads 35 and 36 are provided on the top surface of the back plate 28. The
lead-out wiring 33 of the diaphragm 23 is connected to the electrode pad 35, and the lead-out
wiring 34 of the fixed electrode plate 29 is connected to the electrode pad 36.
[0029]
In the acoustic sensor 21, the fixed electrode plate 29 and the diaphragm 23 form a capacitor
structure with the air gap 30 interposed therebetween. Then, when the diaphragm 23 vibrates in
response to the acoustic vibration, the capacitance between the fixed electrode plate 29 and the
diaphragm 23 changes, and the acoustic vibration is converted into an electrical signal through
the change in capacitance.
[0030]
Here, the opening area of the through hole 27 (or the diameter if the through hole 27 is circular)
is smaller than the opening area (or diameter) of the acoustic hole 31. The through hole 27 is
disposed out of position with the acoustic hole 31 so as not to overlap with the acoustic hole 31
when viewed in a direction perpendicular to the upper surface of the silicon substrate 22. For
example, the through hole 27 is disposed at the center between two adjacent acoustic holes 31
or at the center of the area surrounded by three or more acoustic holes 31. In FIG. 4B, each
through hole 27 of the diaphragm 23 is located at the center of the area surrounded by the three
acoustic holes 31, and the arrangement pitch of the through holes 27 is equal to the
arrangement pitch of the acoustic holes 31. .
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[0031]
In the acoustic sensor 21 as described above, since the through hole 27 is opened in the large
displacement area of the diaphragm 23, as shown in FIG. 7A, the acoustic vibration s passes
through the through hole 27 and the air gap 30 from the chamber 25 side. To the chamber 25 or
to the chamber 25 from the air gap 30 side. Therefore, according to the acoustic sensor 21, it is
possible to roll off the sensitivity in the low tone range as in the conventional example, and to
improve the environmental resistance such as wind noise resistance, compressed air resistance
and pressure fluctuation resistance. . Further, in the acoustic sensor 21 of the present
embodiment, since the opening area of the through hole 27 is smaller than that of the acoustic
hole 31, the roll-off effect per one through hole 27 is small. If the number of the through holes
27 is increased while keeping the area smaller than the opening area, environmental resistance
equal to or more than that of the conventional example can be obtained.
[0032]
Further, in the acoustic sensor 21, since the opening area of the through hole 27 is small, when
used for a bottom port type microphone or the like, foreign substances such as dust and dirt are
less likely to intrude into the air gap 30 from the chamber 25 side.
[0033]
Furthermore, in the acoustic sensor 21 according to the present embodiment, since the plurality
of through holes 27 having a smaller opening area than the acoustic hole 31 can be dispersedly
provided in the region where the displacement of the diaphragm 23 is large, the heat in the air
gap 30 Noise can be reduced to improve the S / N ratio of the acoustic sensor 21.
As shown in FIG. 7B, the thermal noise in the air gap 30 causes the air molecule a to move in
brown and collide with the diaphragm 23 in the air layer in the air gap 30 sandwiched between
the diaphragm 23 and the fixed electrode plate 29. Electrical noise generated by Here, if many
small through holes 27 are provided in the diaphragm 23, air molecules a in the air gap 30 can
escape through the through holes 27 and collide with the diaphragm 23 per unit time
accordingly. The number of air molecules a is reduced and thermal noise is reduced. Moreover,
since the area where the displacement of the diaphragm 23 is large is an area where the
sensitivity of the diaphragm 23 is high, the S / N ratio of the acoustic sensor 21 is improved if
the through holes 27 are provided in this area to reduce the thermal noise. The effect is higher.
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[0034]
Further, when the through holes 27 and the acoustic holes 31 are provided so as to overlap with
each other, the acoustic resistance of the acoustic sensor becomes small and the roll-off effect is
too effective, so the number of the through holes 27 is limited. In order to improve the S / N ratio
of the acoustic sensor, many methods can be taken to further reduce the thermal noise of the air
gap 30 due to the acoustic hole 31 by increasing the ratio of the acoustic hole 31. Particularly in
such a case, the through hole 27 and the acoustic hole 31 easily overlap. On the other hand, in
the acoustic sensor 21 of the present embodiment, the through holes 27 are disposed so as not
to overlap with the acoustic holes 31. Therefore, even when an appropriate roll-off effect is to be
provided, You can increase the number. Therefore, it is possible to substantially reduce thermal
noise and improve the S / N ratio of the acoustic sensor 21.
[0035]
When the opening area of the through hole 27 is large, as in the conventional example shown in
FIG. 8A, a step is generated on the back plate 15 or the fixed electrode plate 16 at a position
corresponding to the edge of the through hole 18, and the back plate 15 or the fixed electrode
There is a possibility that the strength of the plate 16 may be reduced, or a conduction failure
may occur in the fixed electrode plate 16. On the other hand, even when the through hole 27 is
provided so as not to overlap the acoustic hole 31, as shown in FIG. 8B, the opening area
(diameter D) of the through hole 27 is the opening area (diameter d) of the acoustic hole 31. If
smaller, in the manufacturing process, the through hole 27 is filled with the sacrificial layer for
forming the air gap 30 between the diaphragm 23 and the fixed electrode plate 29, and a step is
hardly generated on the upper surface of the back plate 28 or the like. As a result, the strength of
the back plate 28 is unlikely to be reduced due to the step, and it is also less likely to cause
partial conduction in the fixed electrode plate 29.
[0036]
In the case where the through hole 27 is substantially circular, the diameter of the through hole
27 is preferably 10 μm or less. More preferably, it may be 1 μm or more and 5 μm or less. If
the diameter of the through hole 27 is 10 μm or less, it is difficult for a step to be generated in
the back plate 28 or the like, or the step is reduced.
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[0037]
Further, the portion of the diaphragm 23 facing the center between two adjacent acoustic holes
31 or the center of the region surrounded by three or more acoustic holes 31 is the farthest from
the acoustic hole 31. For this reason, if the through hole 27 is provided at a position opposite to
the center between the two adjacent acoustic holes 31 or the center of the region surrounded by
the three or more acoustic holes 31, the roll-off of the acoustic sensor 21 is performed. The
effect can be enhanced, and the effect of reducing thermal noise is also enhanced.
[0038]
When the acoustic holes 31 are regularly arranged at a constant pitch, it is desirable that the
through holes 27 be regularly arranged at a constant pitch. This is because it becomes easy to
arrange the through holes 27 so as not to overlap the acoustic holes 31. In particular, it is easy to
arrange the through holes 27 with the same pitch as the acoustic holes 31 or a multiple pitch.
[0039]
(Application to Microphone) FIG. 9 is a schematic cross-sectional view of a bottom port type
microphone 41 incorporating the acoustic sensor 21 of the first embodiment. The microphone
41 incorporates the acoustic sensor 21 and a signal processing circuit 44 (ASIC) which is a
circuit unit in a package including the circuit board 42 and the cover 43. The acoustic sensor 21
and the signal processing circuit 44 are mounted on the top surface of the circuit board 42. In
the circuit board 42, a sound introducing hole 45 for introducing acoustic vibration into the
acoustic sensor 21 is opened. The acoustic sensor 21 is mounted on the top surface of the circuit
board 42 so that the bottom opening of the chamber 25 matches the sound introduction hole 45
and covers the sound introduction hole 45. Therefore, the chamber 25 of the acoustic sensor 21
is a front chamber, and the space in the package is a back chamber.
[0040]
The electrode pads 35 and 36 of the acoustic sensor 21 and the signal processing circuit 44 are
connected by a bonding wire 46. Furthermore, the signal processing circuit 44 is connected to
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the circuit board 42 by a bonding wire 47. The signal processing circuit 44 has a function of
supplying power to the acoustic sensor 21 and a function of outputting a capacitance change
signal of the acoustic sensor 21 to the outside.
[0041]
A cover 43 is attached to the upper surface of the circuit board 42 so as to cover the acoustic
sensor 21 and the signal processing circuit 44. The package has a function of an electromagnetic
shield, and protects the acoustic sensor 21 and the signal processing circuit 44 from external
electric disturbance and mechanical impact.
[0042]
Thus, the acoustic vibration that enters the chamber 25 from the sound introduction hole 45 is
detected by the acoustic sensor 21, amplified and signal-processed by the signal processing
circuit 44, and output. In this microphone 41, since the space in the package is a back chamber,
the volume of the back chamber can be increased, and the sensitivity of the microphone 41 can
be enhanced.
[0043]
When using for such a bottom port type microphone 41, in order to improve environmental
resistance, it is necessary to enlarge the area of the through hole 27 of the diaphragm 23. In that
case, it is possible to cope with the problem by increasing the number of the through holes 27
without increasing the individual opening area of the through holes 27 or increasing the opening
area of the through holes 27 to the extent smaller Just do it.
[0044]
In the microphone 41, a sound introducing hole 45 for introducing acoustic vibration into the
package may be opened on the upper surface of the cover 43. In this case, the chamber 25 of the
acoustic sensor 21 is a back chamber, and the space in the package is a front chamber.
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[0045]
21 acoustic sensor 22 silicon substrate 23 diaphragm (fixed electrode plate) 25 chamber (cavity)
26 anchor 27 through hole 28 back plate 29 fixed electrode plate 31 acoustic hole 41
microphone 44 signal processing circuit (circuit portion) 45 sound introduction hole
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