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JP2008252854

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DESCRIPTION JP2008252854
The present invention provides an electrostatic transducer with improved sensitivity compared to
the prior art when used as an acoustic sensor or pressure sensor, and improved output sound
pressure as compared to the prior art when used as a speaker. A fixed plate (4) has a hole (10)
penetrating in a thickness direction, and a movable plate (5) protrudes from a vibrating portion
(11) opposed to the fixed plate (4) in the thickness direction of the fixed plate (4) And a
projection 12 partially inserted into the hole 10. The movable electrode 8 is provided from the
vibrating portion 11 to the projecting portion 12, and the fixed electrode 7 integrally has a
portion along the surface facing the vibrating portion 11 in the fixed plate 4 and a portion along
the inner side surface of the hole 10 . A gap length g between a portion of the movable electrode
8 provided on the vibrating portion 11 and a portion of the fixed electrode 7 along the surface of
the fixed plate 4 facing the vibrating portion 11 is provided on the protrusion 12 of the movable
electrode 8. The gap length d between the fixed portion and the portion along the inner surface
of the hole 10 in the fixed electrode 7 is set larger. [Selected figure] Figure 1
Electrostatic transducer and method of manufacturing the same
[0001]
The present invention includes an acoustic sensor that converts vibration energy of a movable
plate into electrical energy, a pressure sensor that converts displacement of the movable plate
due to pressure change into electrical energy, and a speaker that converts electrical energy into
vibration energy of the movable plate. The present invention relates to an electrostatic
transducer used and a method of manufacturing the same.
[0002]
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1
Conventionally, as shown in FIG. 13A, the electrostatic transducer 1 is provided on the fixed plate
4 and the movable plate 5, and the fixed plate 4 and the movable plate 5, which are disposed to
face each other via the gap G. A pair of the electrodes 7, 8 (in this case, the electrode 7 provided
on the fixed plate 4 constitutes a fixed electrode, and the electrode 8 provided on the movable
plate 5 constitutes a conductive electrode) is known. (See, for example, Patent Document 1).
This type of electrostatic transducer 1 is manufactured using microfabrication technology such
as MEMS (Micro Electro Mechanical Systems) technology.
[0003]
In the example of FIG. 13A, the fixed plate 4 and the movable plate 5 are supported by the framelike support substrate 3. In this electrostatic transducer 1, a pair of electrodes 7 and 8 is opposed
via a gap G to form a capacitor between the pair of electrodes 7 and 8, and when the movable
plate 5 vibrates in the thickness direction, the pair of electrodes The distance between the
electrodes 7 and 8 changes and the capacitance of the capacitor changes. Therefore, by applying
a bias voltage between the pair of electrodes 7 and 8 and converting the change in capacitance of
the capacitor into an electric signal and taking it out, when the movable plate 5 receives a sound
wave, it corresponds to the sound wave. The vibrational energy of the movable plate 5 can be
extracted as an electrical energy (here, an electrical signal). The electrostatic transducer 1 is thus
used, for example, as an acoustic sensor. Similarly, by applying a bias voltage between the pair of
electrodes 7 and 8 and extracting the displacement of the movable plate 5 due to pressure
change as electric energy, it can also be used as a pressure sensor for detecting pressure.
[0004]
In the electrostatic transducer 1 of this type, the sensitivity (voltage sensitivity) of the output
voltage to the received sound wave is represented by: sensitivity = 20 и log 10 (E / P), where
sound pressure is P [Pa]. Here, E is the open end voltage [V] which is the voltage between the
electrodes 7 and 8 when the current supplied to the outside is 0 [A], and the capacitance between
the electrodes 7 and 8 is C [F] Assuming that the amount of change in capacitance is ?C [F] and
the DC bias voltage applied to the electrodes 7 and 8 is V0 [V], the relationship of E? (?C / C) и
V0 holds. In short, as the ?C / C (rate of change of capacitance) is larger, the sensitivity of the
electrostatic transducer 1 is higher.
04-05-2019
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[0005]
Hereinafter, when the movable plate 5 is displaced toward the fixed plate 4 along the thickness
direction from the initial state in which the DC bias voltage V0 [V] is applied between the pair of
electrodes 7 and 8, the static state is obtained. The rate of change of capacitance will be
described by focusing attention on small areas of the fixed plate 4 and the movable plate 5 in the
electrostatic transducer 1 as shown in FIG. When the movable plate 5 is displaced away from the
fixed plate 4, x [m] becomes negative. Here, it is an area shown by A in FIG. 13A, and an area in
which the cross section orthogonal to the vibration direction of the movable plate 5 is a square of
one side a [m] is a small area.
[0006]
Assuming that the distance between the electrodes 7 and 8 (in this case, the gap length of the
gap G) before displacement of the movable plate 5 is g [m], the capacitance Cparallel [F] of the
small area before displacement of the movable plate 5 is Assuming that the dielectric constant of
the gap G is ?,
[0007]
[0008]
Is represented by
Similarly, the capacitance Cparallel 'of the small area after displacement of the movable plate 5 is
[0009]
[0010]
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Is represented by
Here, since the amount of change in capacitance ?Cparallel [F] of the small area is expressed by
Cparallel??Cparallel, the rate of change in capacitance (?Cparallel / Cparallel) results in the
above-mentioned Cparallel and Cparallel ?. Using,
[0011]
[0012]
Is represented by
[0013]
By the way, it is known that the compliance of the movable plate 5 is reduced due to the residual
stress generated in the movable plate 5 when the movable plate 5 is manufactured.
Therefore, the support plate 3 is configured to support the movable plate 5 via a plurality of
arms (not shown), and the arms are distorted so that the movable plate 5 can move relative to the
support substrate 3. There is also proposed an electrostatic transducer 1 in which the residual
stress of 5 is relieved and the compliance of the movable plate 5 is improved (see, for example,
Patent Document 2).
In this configuration, the displacement x of the movable plate 5 at the time of receiving the sound
wave increases by the amount of improvement in the compliance of the movable plate 5, so that
the rate of change in capacitance (?Cparallel / Cparallel) described above becomes large. A
relatively high sensitivity can be ensured.
[0014]
In the electrostatic transducer 1 described above, when a drive voltage is applied between the
pair of electrodes 7 and 8, an electrostatic force acts between the pair of electrodes 7 and 8 and
the movable plate 5 is drawn to the fixed plate 4 side. Therefore, by changing the drive voltage
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applied between the pair of electrodes 7 and 8, the movable plate 5 can be vibrated to generate a
sound wave from the movable plate 5.
That is, the electrostatic transducer 1 described above can be used not only as an acoustic sensor
but also as a speaker that generates an acoustic wave from the movable plate 5 by converting
electric energy (drive voltage) into vibration energy of the movable plate 5 It is. Japanese Patent
Publication No. 2004-506394 (FIG. 1) Japanese Patent Publication No. 2005-535152 (Page 6-7)
[0015]
However, even the electrostatic transducer 1 described in Patent Document 2, when used as an
acoustic sensor or a pressure sensor, has lower sensitivity than commonly used electret
condenser microphones and the like, and the sensitivity is further improved. It is desired.
Moreover, when using the electrostatic transducer 1 as a speaker, the improvement of an output
sound pressure is desired.
[0016]
The present invention has been made in view of the above, and when used as an acoustic sensor
or pressure sensor, sensitivity is improved more than before, and when used as a speaker, output
sound pressure is improved more than before. And a method of manufacturing the same.
[0017]
In the first aspect of the present invention, the fixed plate and the movable plate which are
disposed to face each other via the gap, and the pair of electrodes respectively provided on the
fixed plate and the movable plate are provided, and a capacitor is formed between the pair of
electrodes. It is an electrostatic transducer, and the fixed plate has a hole opening at least on one
surface on the movable plate side, and the movable plate is vibrated with a vibrating portion
opposed to the fixed plate in the thickness direction of the fixed plate, And a protrusion which is
partially inserted into the hole at least in the initial state before the vibrating portion is displaced,
and the electrode on the movable plate extends from the vibrating portion to the protrusion. The
electrode on the fixed plate side integrally has a portion along the surface facing the vibrating
portion in the fixed plate and a portion along the inner side surface of the hole portion, and a
portion provided on the vibrating portion in the electrode on the movable plate side And the
fixed plate on the fixed plate side The distance between the vibrating portion and the portion
along the opposing surface is the distance between the portion provided on the protrusion on the
electrode on the movable plate and the portion along the inner surface of the hole on the
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electrode on the fixed plate It is characterized in that it is set larger than that.
[0018]
According to the present invention, the electrode on the movable plate side is provided from the
vibrating portion to the projecting portion, and the electrode on the fixed plate side is a portion
along the surface facing the vibrating portion in the fixed plate and a portion along the inner
surface of the hole portion And the distance between the fixed plate and the vibrating portion
changes when the movable plate is displaced, and not only the distance between the pair of
electrodes changes, but also according to the amount of insertion of the protrusion into the hole
The opposing areas of the pair of electrodes also change.
That is, when the movable plate is displaced toward the fixed plate, a portion of the movable
plate side electrode provided on the vibrating portion and a portion of the fixed plate side
electrode along the surface of the fixed plate along the opposing surface to the vibrating portion
In addition to the increase in the capacitance of the capacitor due to the reduction of the
distance, a portion of the electrode on the movable plate side provided on the protrusion and a
portion of the electrode on the stationary plate side along the inner surface of the hole portion
By increasing the facing area of the capacitor, the capacitance of the capacitor is increased.
Therefore, compared with the configuration without the hole and the protrusion, the rate of
change in capacitance can be increased even when the displacement amount of the movable
plate is the same, and the sensitivity can be improved. Moreover, the distance between the
portion of the movable plate side electrode provided on the vibrating portion and the portion of
the fixed plate side electrode along the surface of the fixed plate along the opposing surface to
the vibrating portion is a protrusion on the movable plate side electrode. Since the distance
between the provided portion and the portion along the inner surface of the hole in the electrode
on the fixed plate side is set larger, compared to the case where the distance between the pair of
electrodes is uniform over the entire area, The rate of change of capacitance increases, and
higher sensitivity can be obtained. In addition, when using it as a speaker which outputs an
acoustic wave from a movable plate by applying a drive voltage between a pair of electrodes and
applying an electrostatic force between a pair of electrodes, a comparatively big sound pressure
can be output. .
[0019]
The invention of claim 2 is characterized in that, in the invention of claim 1, the hole portion
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penetrates in the thickness direction of the fixing plate.
[0020]
According to the present invention, the vibration of the movable plate is less likely to be impeded
by passing air in the thickness direction of the fixed plate through the hole, so that the
electrostatic transducer is excellent particularly when used as an acoustic sensor in a high
frequency region. Sensitivity characteristics are obtained, and good output characteristics are
obtained when the electrostatic transducer is used as a speaker, particularly in a high frequency
region.
[0021]
The invention according to claim 3 is the method for manufacturing an electrostatic transducer
according to claim 1 or 2, wherein the fixing substrate which is the basis of the fixing plate is
opened only in one thickness direction of the fixing substrate. A fixing plate forming step of
forming the fixing plate having the hole portion and the electrode provided by forming the hole
portion in a broken state; and an opening surface side of the hole portion after the fixing plate
forming step Forming a sacrificial layer on the fixed plate by depositing a sacrificial layer on the
fixed plate to form a sacrificial layer having a recess corresponding to the hole on one surface
opposite to the fixed plate, and sacrificial layer after the sacrificial layer forming step A movable
plate forming step of forming the movable plate having the portion formed in the recess as the
projection by depositing the movable plate on the layer and forming the movable plate provided
with the electrode, and sacrificial after the movable plate forming step The fixed plate and the
movable plate are removed by removing a part of the layer Wherein said to have a sacrificial
layer removing step of forming a gap between.
[0022]
According to the present invention, by forming the sacrificial layer by the deposition method
with low step coverage, the thickness dimension of the portion of the sacrificial layer deposited
on the inner surface of the hole portion It can be easily made smaller than the thickness
dimension of the part deposited on the part of.
Thus, easily, the distance between the portion of the movable plate side electrode provided on
the vibrating portion and the portion of the fixed plate side electrode along the surface facing the
vibrating portion in the fixed plate is set to the movable plate side electrode The distance
between the portion provided on the protrusion and the portion along the inner surface of the
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7
hole in the electrode on the fixed plate side can be set larger.
[0023]
The invention according to claim 4 relates to the invention according to claim 3, wherein in the
step of forming the sacrificial layer, a plurality of the sacrificial layers are stacked on the fixing
plate, and the holes in the fixing plate in the sacrificial layer are formed. It is characterized in that
the number of layers of the portion to be deposited in other portions is set larger than the
number of layers of the portion to be deposited on the inner surface of the hole in the sacrificial
layer.
[0024]
According to the present invention, by partially increasing the number of layers of the sacrificial
layer deposited in the portion other than the hole in the fixed plate, the sacrificial layer is
deposited in the portion other than the hole in the fixed plate. The thickness dimension of the
portion can be easily made larger than the thickness dimension of the portion of the sacrificial
layer deposited on the inner surface of the hole.
Thus, easily, the distance between the portion of the movable plate side electrode provided on
the vibrating portion and the portion of the fixed plate side electrode along the surface facing the
vibrating portion in the fixed plate is set to the movable plate side electrode The distance
between the portion provided on the protrusion and the portion along the inner surface of the
hole in the electrode on the fixed plate side can be set larger.
[0025]
When used as an acoustic sensor or a pressure sensor, the present invention has an effect that
sensitivity is improved as compared with the conventional case, and output sound pressure is
improved as compared with the conventional case when used as a speaker.
[0026]
The electrostatic transducer according to the present invention includes an acoustic sensor such
as a microphone for converting vibration energy of a movable plate into electrical energy, a
pressure sensor for converting displacement of the movable plate due to pressure change into
electrical energy, and a movable plate for converting electrical energy In the following
embodiments, an electrostatic transducer is used as an acoustic sensor.
04-05-2019
8
[0027]
Embodiment 1 As shown in FIG. 1, the electrostatic transducer 1 according to the present
embodiment has a support substrate 3 formed in a rectangular frame shape, and an upper
surface of one surface side of the support substrate 3 (FIG. 1A). The fixed plate 4 formed on the
side, and the movable plate 5 disposed on the one surface side of the fixed plate 4 opposite to the
support substrate 3 with the gap G interposed therebetween.
The fixing plate 4 has a rectangular plate shape, and is formed so as to interpose the rectangular
frame-shaped insulating film 20 with the support substrate 3.
Thereby, the cavity 2 surrounded by the support substrate 3, the fixing plate 4 and the insulating
film 20 is formed on the other surface side of the support substrate 3 (lower surface side in FIG.
1A).
The insulating film 20 will be described later.
The movable plate 5 is formed in a rectangular plate shape thinner than the fixed plate 4 and is
stacked on the one surface side of the fixed plate 4 via the insulating support portion 6. The
insulating support portion 6 is interposed between the peripheral portion of the movable plate 5
and the peripheral portion of the fixed plate 4, and a gap G having a predetermined gap length
between the fixed plate 4 and the movable plate 5 by the insulating support portion 6. Is formed.
[0028]
A fixed electrode 7 is provided on the fixed plate 4, and a movable electrode 8 paired with the
fixed electrode 7 is provided at a position corresponding to the fixed electrode 7 in the movable
plate 5. A pair of electrodes (the fixed electrode 7 and the movable electrode 8) are opposed via
the gap G, and a capacitor having the fixed electrode 7 and the movable electrode 8 as an
electrode is configured. As a result, when the movable plate 5 vibrates in the thickness direction,
the distance between the fixed electrode 7 and the movable electrode 8 changes and the
capacitance of the capacitor changes, so this capacitance change is converted into an electric
04-05-2019
9
signal and taken out. Thereby, when the movable plate 5 receives a sound wave, the vibration
energy of the movable plate 5 according to the sound wave can be extracted as electric energy
(here, an electric signal). Here, in order to convert the capacitance change into an electric signal
and take it out, a bias voltage is applied between the fixed electrode 7 and the movable electrode
8 when detecting the sound wave. In the present embodiment, as shown in FIG. 1A, the pad 7a
connected to the fixed electrode 7 is provided at one end of one surface of the fixed plate 4
opposite to the support substrate 3 and connected to the movable electrode 8 By providing the
pad 8 a on one end of one surface of the movable plate 5 opposite to the fixed plate 4, a bias
voltage can be applied between the fixed electrode 7 and the movable electrode 8 from the pads
7 a and 8 a. An external circuit applying a bias voltage is connected to pads 7a and 8a by wire
bonding, for example. Here, the movable plate 5 is formed in a shape that exposes the pad 8a. In
FIG. 1B, the pads 7a and 8a and the insulating support 6 are not shown.
[0029]
The supporting substrate 3 is made of a silicon substrate and is formed in a shape that
constitutes the cavity 2 together with the fixing plate 4 and the insulating film 20 made of a
silicon oxide film by removing the central portion by etching. The cavity 2 is opened in a
rectangular shape, and here, for example, the inner side is tapered by anisotropic etching using
an alkaline solution or the like, and the area of the cross section orthogonal to the thickness
direction of the support substrate 3 is from the fixing plate 4 It forms in the shape which
becomes large as it separates, but in order to miniaturize the support substrate 3 as much as
possible, each inner side may be formed perpendicularly to the one surface of the support
substrate 3, respectively.
[0030]
The fixing plate 4 is formed in a rectangular plate shape as described above, and the upper
surface of the supporting substrate 3 is substantially parallel to each side of the supporting
substrate 3 so that each side opposed to each side of the one surface is substantially parallel. Will
be placed. The fixing plate 4 is formed of silicon (including polysilicon and amorphous silicon),
and is manufactured by deposition using a CVD method (chemical vapor deposition method) or
the like. Here, the fixing plate 4 is designed to have a predetermined rigidity, a thickness, and a
size so as to be hardly deformed even under sound pressure. Further, in the fixed plate 4, a
plurality of holes (so-called acoustic holes) 10 through which air is passed so as not to prevent
the vibration of the movable plate 5 are provided in plurality in a region to be the bottom plate of
the cavity 2. The holes 10 in the present embodiment are formed in a shape having a square
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10
opening, and are arranged in lattice points at equal intervals in a rectangular area. That is, the
area | region used as the baseplate of the cavity 2 in the stationary plate 4 is formed in grid |
lattice form. Here, the hole 10 is formed, for example, using a photolithography technique and an
etching technique.
[0031]
The insulating support portion 6 is made of a silicon oxide film, and electrically insulates the
fixed electrode 7 provided on the fixed plate 4 and the movable electrode 8 provided on the
movable plate 5. The insulating support 6 is provided over the entire circumference of one
surface of the fixing plate 4. Here, as an example, the insulating sacrificial layer fabricated
between the fixed plate 4 and the movable plate 5 in the fabrication process is partially removed,
and the remaining portion of the sacrificial layer is used as the insulating support portion 6.
[0032]
The movable plate 5 is disposed on the fixed plate 4 so that each side opposed to each side of
one surface of the fixed plate 4 is substantially parallel to each side of the fixed plate 4, and
similar to the fixed plate 4, silicon It is formed of (including polysilicon and amorphous silicon)
and manufactured by deposition using a CVD method or the like. Here, since a plurality of holes
10 are provided through the fixed plate 4 as described above, the sound wave propagated from
the other surface side of the support substrate 3 into the cavity 2 passes through the holes 10 to
move the movable plate 5. Propagated to That is, the cavity 2 formed by the support substrate 3,
the fixing plate 4 and the insulating film 20 serves as an entrance for the sound wave. Therefore,
when detecting the sound wave, the electrostatic transducer 1 is arranged to expose the opening
surface of the cavity 2 to the external atmosphere for detecting the sound wave.
[0033]
The movable plate 5 has a certain degree of compliance so as to be easily displaced (vibrated) by
receiving a sound wave, and realizes vibration characteristics such as a desired resonance
frequency or amplitude, or pull-in when a bias voltage is applied ( Material, thickness, and size
with appropriate compliance, taking into consideration that electrostatic force is too large
compared to the restoring force of the movable plate 5 and the phenomenon that the attitude of
the movable plate 5 can not be stably controlled) It is designed. At this time, the residual stress
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generated in the movable plate 5 at the time of manufacturing the movable plate 5 is also taken
into consideration.
[0034]
In the present embodiment, the fixed plate 4 itself constitutes the fixed electrode 7 by using
polysilicon doped with impurities and imparted conductivity as the material of the fixed plate 4
and poly doped with impurities and imparted conductivity. By using silicon as the material of the
movable plate 5, the movable plate 5 itself constitutes the movable electrode 8.
[0035]
By the way, the movable plate 5 according to the present embodiment includes the vibrating
portion 11 facing the region of the fixed plate 4 in the thickness direction of the fixed plate 4
with respect to the area to be the bottom plate of the cavity 2 to vibrate by receiving sound
waves. The fixing plate 4 has a plurality of protruding portions 12 provided on the surface on the
side of the fixing plate 4 so as to project at respective positions facing the opening surface of the
hole 10.
In addition, in FIG.1 (b), parts other than the projection part 12 in the movable plate 5 are shown
in figure by an imaginary line (two-dot chain line).
[0036]
The protrusion 12 is formed such that the cross section orthogonal to the protrusion direction is
smaller than the opening surface of the hole 10 and the protrusion dimension is set larger than
the gap length of the gap G between the fixed plate 4 and the vibrating portion 11 In the initial
state before the movable plate 5 vibrates, a part is inserted into the hole 10 at least. The initial
state here means a state in which a bias voltage is applied between a pair of electrodes (fixed
electrode 7 and movable electrode 8). In the present embodiment, the protrusion 12 is formed in
a square pole shape in which a cross section orthogonal to the protruding direction is a square
having a smaller size than the opening surface of the hole 10. Here, the protrusion 12 is disposed
at a central portion in the opening surface of the hole 10 so that each side surface is
substantially parallel to each inner surface of the hole 10. The protrusion 12 is formed by, for
example, removing the sacrificial layer after depositing the material of the movable plate 5 on the
one surface of the sacrificial layer having a recess on one surface in the process of
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manufacturing the movable plate 5.
[0037]
Furthermore, in the electrostatic transducer 1 of the present embodiment, the gap length of the
gap G between the facing surfaces of the fixed plate 4 and the vibrating portion 11 (that is, the
facing surface of the fixed electrode 7 with the vibrating portion 11 in the fixed plate 4). The first
gap length g, which is the distance between the portion along the line and the portion of the
movable electrode 8 provided in the vibrating portion 11, is the inner side surface of the hole 10
in the initial state before the movable plate 5 vibrates. The gap length of the gap D between the
side surface of the protrusion 12 (that is, the distance between the portion of the fixed electrode
7 along the inner surface of the hole 10 and the portion of the movable electrode 8 provided on
the protrusion 12) It is set larger than a certain second gap length d.
[0038]
In the electrostatic transducer 1 having the configuration described above, the movable electrode
8 is provided from the vibrating portion 11 to the protrusion 12, and the fixed electrode 7 is a
portion along the surface of the fixed plate 4 facing the vibrating portion 11 and a hole Since it
integrally has a portion along the inner side surface of the portion 10, when the movable plate 5
vibrates, the distance between the fixed plate 4 and the vibrating portion 11 changes, and the
distance between the fixed electrode 7 and the movable electrode 8 Not only changes the amount
of insertion of the protrusion 12 into the hole 10 but also changes the opposing area between
the inner side surface of the hole 10 and the side surface of the protrusion 12. The opposing area
also changes.
In short, not only the change of the capacitance of the capacitor due to the change of the
distance between the fixed electrode 7 and the movable electrode 8 but also the electrostatic of
the capacitor due to the change of the facing area of the fixed electrode 7 and the movable
electrode 8 There is also a change in capacity. For example, when the vibrating portion 11 is
displaced to the fixed plate 4 side, the distance between the fixed electrode 7 and the movable
electrode 8 is reduced, so that the capacitance is increased, and the inner side surface of the hole
10 and the side surface of the projection 12 are opposed The larger area further increases the
capacitance. Therefore, compared to the conventional configuration in which the hole 10 and the
protrusion 12 are not provided, the amount of change in capacitance is large even when the
displacement of the movable plate 5 is the same, and high sensitivity can be ensured. Moreover,
the first gap length g of the gap G between the opposing surfaces of the fixed plate 4 and the
vibrating portion 11 is the inner side surface of the hole 10 and the side surface of the projecting
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portion 12 in the initial state before the movable plate 5 vibrates. Because the second gap length
d of the gap D between them is set to be larger, the rate of change of capacitance compared to
the case where the distance between the fixed electrode 7 and the movable electrode 8 is
uniform over the entire area. Is larger and higher sensitivity can be obtained.
[0039]
Hereinafter, from the initial state in which the bias voltage is applied between the fixed electrode
7 and the movable electrode 8, the capacitance of the movable plate 5 is displaced toward the
fixed plate 4 by x [m] along the thickness direction. The rate of change (?C / C) will be described
by focusing attention on small areas of the fixed plate 4 and the movable plate 5 as shown in FIG.
When the movable plate 5 is displaced away from the fixed plate 4, x [m] becomes negative.
Here, it is a region shown by A in FIG. 1A, and has one hole 10 and one protrusion 12 at the
center, and a cross section orthogonal to the vibration direction of the movable plate 5 is a
square with a side a [m]. The area that is
[0040]
Before displacement of the movable plate 5, the distance between the opposing surfaces of the
fixed plate 4 and the vibrating portion 11 (that is, the first gap length) is g [m], and the side
length of the cross section of the protrusion 12 is b The amount of insertion of the protrusion 12
into the hole 10 is c [m], and the distance between the inner side surface of the hole 10 and the
side surface of the protrusion 12 (that is, the second gap length) is d [m]. Then, the electrostatic
capacitance Ccomb [F] of the small area before the displacement of the movable plate 5 is
represented by ? where the dielectric constant of the gaps G and D is ?
[0041]
[0042]
Is represented by
In the above-mentioned formula 4, the term of ? и (a <2>-(b + 2 d) <2>) / g is a part of the fixed
electrode 7 along the surface of the fixed plate 4 facing the vibrating part 11 and the movable
electrode Of the fixed electrode 7 corresponding to the electrostatic capacitance between the
04-05-2019
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portion provided in the vibrating portion 11 of 8 and the portion of the fixed electrode 7 along
the inner surface of the hole 10 and the movable portion This corresponds to the electrostatic
capacitance between the electrode 8 and the portion provided on the protrusion 12.
Similarly, the capacitance Ccomb 'of the small area after displacement of the movable plate 5 is
[0043]
[0044]
Is represented by
Here, since the amount of change in capacitance ?Ccomb [F] of the small area is expressed by
Ccomb'-Ccomb, the rate of change in capacitance (?Ccomb / Ccomb) results in the abovedescribed Ccomb and Ccomb '. Using,
[0045]
[0046]
Is represented by
[0047]
As a reference example, the values of the parameters in the above equations 4 and 5 can be
expressed as a = 10 О 10 <?6> [m], b = 2 О 10 <?6> [m], c = 1 О 10 <? Assuming that 6>
[m], d = 3 О 10 <-6> [m], g = 3 О 10 <-6> [m], the movable plate 5 has x = 5 О 10 <?9 in the
thickness direction. Assuming that the displacement is> [m], the rate of change in capacitance
(?Ccomb / Ccomb) is calculated to be ?Ccomb / Ccomb = 0.00228 from the above Equations 4,
5, and 6.
[0048]
On the other hand, in the conventional configuration in which the hole 10 and the protrusion 12
are not provided, the same condition (a = 10 О 10 <-6> [m], g = 3 О 10 <-6> [m], x = When the
04-05-2019
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rate of change of capacitance (?Cparallel / Cparallel) is calculated by 5 О 10 <?9> [m],
?Cparallel / Cparallel = 0.00167 can be obtained from the above Equations 1, 2, and 3.
[0049]
In short, in the electrostatic transducer 1 having the configuration according to the present
embodiment, the rate of change in electrostatic capacitance is increased by providing the hole 10
and the protrusion 12 as compared with the conventional electrostatic transducer 1, and the
sensitivity is increased. Will improve.
[0050]
In the present embodiment, the distance g between the portion of the fixed electrode 7 along the
surface of the fixed plate 4 facing the vibrating portion 11 and the portion of the movable
electrode 8 provided on the vibrating portion 11 is the fixed electrode Since the distance d
between the portion along the inner side surface of the hole 10 and the portion of the movable
electrode 8 provided on the protrusion 12 among 7 is set to be larger than Is set to g> d.
As an example, the value of each parameter other than d is set to the same condition as the above
reference example (a = 10 О 10 <-6> [m], b = 2 О 10 <-6> [m], c = 1 О 10 Assuming that <-6>
[m], g = 3 x 10 <-6> [m], x = 5 x 10 <-9> [m]), d = 0.5 x 10 <-6> When the rate of change in
capacitance is calculated as [m], ?Ccomb / Ccomb = 0.00282 can be obtained from the above
equations (4), (5) and (6).
Therefore, in the electrostatic transducer 1 according to the present embodiment, by setting g> d,
the change in electrostatic capacitance is more than in the reference example in which d = g (= 3
О 10 <-6> [m]). The rate is increased, and higher sensitivity can be obtained.
[0051]
Hereinafter, a method of manufacturing the electrostatic transducer 1 of the present embodiment
will be illustrated.
[0052]
04-05-2019
16
First, as shown in FIG. 3B, an insulating film 20 made of a silicon oxide film is formed by thermal
oxidation on the silicon substrate 3 'shown in FIG. A lamination step of laminating fixed substrate
4 ? made of polysilicon and serving as a base of fixing plate 4 on film 20 is performed.
The fixed substrate 4 ? is made to serve as the fixed electrode 7 by doping with an impurity (for
example, phosphorus or boron) (a region to be doped is limited if necessary).
[0053]
Next, a resist 21 is formed on one surface of the fixed substrate 4 'opposite to the insulating film
20 except for a part (a part where the hole 10 will be formed later) as shown in FIG. Formation
process).
Then, the fixed substrate 4 'is removed by dry etching with the resist 21 as an etching mask and
the insulating film 20 as an etching stopper layer, and the hole 10 is formed as shown in FIG. 3D,
from the fixed substrate 4'. A fixing plate forming step of forming the fixing plate 4 having the
holes 10 is performed.
At this time, the hole 10 is closed by the insulating film 20 at one side in the thickness direction
of the fixing plate 4 (downward in FIG. 3D).
The resist 21 is removed after the fixing plate forming process.
[0054]
Thereafter, as shown in FIG. 3E, a sacrificial layer forming step of depositing a silicon oxide film
to be the sacrificial layer 22 on the one surface (one surface opposite to the insulating film 20) of
the fixed plate 4 is performed. At this time, as described above, since the hole 10 is closed in one
of the fixing plate 4 in the thickness direction (downward in FIG. 3F), the sacrificial layer 22 is
also deposited in the hole 10. Here, the sacrificial layer 22 is deposited to such an extent that the
hole 10 does not fill, and a recess 22 a is formed in each portion corresponding to the hole 10 in
one surface of the sacrificial layer 22 opposite to the fixing plate 4. In the sacrificial layer
formation step, the step coverage is intentionally lowered by utilizing atmospheric pressure CVD
04-05-2019
17
method or the like with a short mean free path of the reactive molecules, thereby fixing the
sacrificial layer 22 to the inner surface of the hole 10 The thickness dimension d of the portion
deposited in the plane orthogonal to the thickness direction of the plate 4 is the thickness
dimension of the portion of the sacrificial layer 22 deposited in the thickness direction of the
fixed plate 4 with respect to the one surface of the fixed plate 4 Make it thinner than g. The step
coverage mentioned here represents step coverage as is well known, and if the step coverage is
lowered, holes for the thickness dimension g of the portion of the sacrificial layer 22 deposited
on the one surface of the fixed plate 4 are obtained. The ratio (that is, d / g) of the thickness
dimension d of the portion deposited on the inner surface of the portion 10 is reduced.
[0055]
Next, as shown in FIG. 3F, a movable plate forming step of forming the movable plate 5 by
depositing polysilicon 5 ? which is a material of the movable plate 5 on the sacrificial layer 22 is
performed. The polysilicon 5 'is made to serve as the movable electrode 8 by doping an impurity
(for example, phosphorus or boron) (a region to be doped is limited if necessary). Here, the
polysilicon 5 'is also deposited in the recess 22a of the sacrificial layer 22, and the hole 10 is
filled with the sacrificial layer 22 and the polysilicon 5'. The polysilicon 5 'is deposited so that
one surface opposite to the sacrificial layer 22 is substantially flat. As a result, the movable plate
5 having the portion of the polysilicon 5 'deposited in the recess 22a as the protrusion 12 is
formed. Further, in order to expose the pads 7a formed on the fixed plate 4 later, as shown in
FIG. 3G, a part of the movable plate 5 is removed by etching.
[0056]
Thereafter, as shown in FIG. 3 (h), a difference to be described later is made on both sides in the
thickness direction of the multilayer structure formed by laminating the silicon substrate 3 ', the
insulating film 20, the fixed plate 4, the sacrificial layer 22, and the movable plate 5. A silicon
nitride film 23 to be a protective mask is deposited during the anisotropic etching, and a portion
of the silicon nitride film 23 on the silicon substrate 3 'side corresponding to the opening surface
of the cavity 2 is removed by etching (mask formation step). Then, after the mask formation step,
anisotropic etching is performed using an alkaline solution (for example, an aqueous solution of
TMAH or the like) to form a supporting substrate 3 having an opening as shown in FIG. (Cavity
formation step). At this time, the insulating film 20 having a slow etching rate is used as an
etching stopper layer.
04-05-2019
18
[0057]
After the cavity formation step, the silicon nitride film 23 is removed by etching, and a sacrificial
layer removal step of removing the insulating film 20 and the sacrificial layer 22 by etching is
performed. Here, the etchant is transmitted to the sacrificial layer 22 through the holes 10 of the
fixing plate 4, and the sacrificial layer 22 is removed leaving a portion to be the insulating
support 6. Therefore, the fixed plate 4 and the vibrating portion 11 of the movable plate 5 are
separated by the thickness dimension t1 of the portion of the sacrificial layer 22 deposited on
the one surface of the fixed plate 4 (that is, the surface facing the vibrating portion 11). The
inner surface of the hole 10 and the side surface of the protrusion 12 are the same as the
thickness dimension t 2 of the portion of the sacrificial layer 22 deposited on the inner surface of
the hole 10. Opposite via a gap D having a gap length of In addition, since the thickness
dimension t1 here is equal to the gap length of the gap G in the state where the bias voltage is
not applied between the fixed electrode 7 and the movable electrode 8, the bias voltage is applied
between the fixed electrode 7 and the movable electrode 8. In the initial state in which the
movable plate 5 is drawn to the fixed plate 4 side by the electrostatic force between the fixed
electrode 7 and the movable electrode 8, the first gap length g of the gap G becomes smaller than
the thickness dimension t1 (g <T1).
[0058]
After the sacrificial layer removing step, the pads 7a and 8a made of an aluminum film are
formed by sputtering to obtain the electrostatic transducer 1 shown in FIG. 3 (j).
[0059]
In short, in the manufacturing method of the electrostatic transducer 1 shown in FIG. 3, the
sacrificial layer 22 is easily formed by forming the sacrificial layer 22 by the deposition method
(for example, atmospheric pressure CVD method) with low step coverage in the sacrificial layer
forming step. The thickness t2 of the portion of the layer 22 deposited on the inner side surface
of the hole 10 can be thinner than the thickness t1 of the portion deposited on the surface of the
fixed plate 4 facing the vibrating portion 11.
Here, the distance between the facing surface of the fixed plate 4 and the vibrating portion 11 is
determined by the thickness dimension t1 of the portion of the sacrificial layer 22 deposited on
the surface of the fixed plate 4 facing the vibrating portion 11. Since the distance between the
inner surface of the hole 10 and the side surface of the protrusion 12 is determined by the
04-05-2019
19
thickness dimension t2 of the portion deposited on the inner surface of the plate, as a result, the
opposing surface of the fixed plate 4 and the vibrating portion 11 The distance between them
can be greater than the distance between the inner side of the hole 10 and the side of the
projection 12. Further, as described above, since the first gap length g in the initial state is
smaller than the thickness dimension t1, in the present embodiment, the first gap length g in the
initial state is larger than the second gap length d. Therefore, the thickness dimensions t1 and t2
are set such that the thickness dimension t1 and t2 become larger than the thickness dimension
t2 (= d) even if the movement amount (t1-g) of the movable plate 5 due to the electrostatic force
due to the bias voltage application is subtracted from the thickness dimension t1. It is set.
[0060]
Moreover, the manufacturing method of the electrostatic transducer 1 of this embodiment is not
limited to the example of FIG. 3 mentioned above, For example, you may employ | adopt the
manufacturing method shown in FIG. The example shown in FIG. 4 is different from the abovedescribed manufacturing method of FIG. 3 in that the etching mask used in the fixing plate
forming step is used as a part of the sacrificial layer 22. The steps shown in FIGS. 4 (a) and 4 (b)
are the same as the steps described with reference to FIGS. 3 (a) and 3 (b), so the description will
be omitted.
[0061]
In the resist formation step shown in FIG. 4C, a silicon oxide film is deposited on one surface of
the fixed substrate 4 ? opposite to the insulating film 20 using the CVD method, and then a
portion of the silicon oxide film A mask 21 'is formed by patterning the silicon oxide film so as to
remove the portion where the portion 10 is to be formed.
[0062]
In the subsequent fixing plate forming step, as shown in FIG. 4D, the fixing substrate 4 'is dry
etched using the mask 21' as an etching mask to form the fixing plate 4 having the holes 10.
Since the mask 21 'is later used as part of the sacrificial layer 22, the mask 21' is not removed
immediately after the fixing plate formation process.
04-05-2019
20
[0063]
Then, in the sacrificial layer forming step shown in FIG. 4E, the mask 21 'left without being
removed after the fixing plate forming step is a part of the sacrificial layer (hereinafter referred
to as the first sacrificial layer 22a) Then, a silicon oxide film (hereinafter referred to as a second
sacrificial layer 22 b) is further deposited on the mask 21 ?. At this time, in the portion of the
sacrificial layer 22 deposited on the one surface (the one surface opposite to the insulating film
20) of the fixing plate 4, the first sacrificial layer 22a and the second sacrificial layer 22b are
stacked. On the other hand, in the portion of the sacrificial layer 22 deposited on the inner
surface of the hole 10, only the second sacrificial layer 22b is deposited. Therefore, even if the
second sacrificial layer 22b is formed to have a uniform thickness over the entire area (that is,
the step coverage is high), a portion of the sacrificial layer 22 deposited on the one surface of the
fixed plate 4 The thickness dimension t1 of the first sacrificial layer 22a is larger than the
thickness dimension t2 of the portion deposited on the inner side surface of the hole 10.
[0064]
The subsequent steps shown in FIGS. 4 (f) to 4 (j) are the same as the steps described with
reference to FIGS. 3 (f) to 3 (j), and therefore the description thereof is omitted.
[0065]
In short, according to the method of manufacturing the electrostatic transducer 1 shown in FIG.
4, the number of layers of the sacrificial layer 22 stacked on the fixed plate 4 can be easily
increased by partially increasing the number of layers facing the vibrating portion 11 The
thickness dimension t1 of the portion of the sacrificial layer 22 deposited on the surface of the
fixed plate 4 facing the vibrating portion 11 can be made thicker than the thickness dimension t2
of the portion deposited on the inner side surface of the hole 10 As a result, the distance between
the facing surfaces of the fixed plate 4 and the vibrating portion 11 can be made larger than the
distance between the inner side surface of the hole 10 and the side surface of the protrusion 12.
[0066]
The electrostatic transducer 1 described above is not limited to the arrangement in which the
opening surface of the cavity 2 is exposed to the external atmosphere in which the sound wave is
detected, and is opposite to the fixed plate 4 in the movable plate 5 in the external atmosphere in
which the sound wave is detected. It may be arranged to expose one surface of the side.
04-05-2019
21
In this case, the movable plate 5 receives an acoustic wave from the side opposite to the fixed
plate 4, so the cavity 2 functions as a back chamber.
[0067]
The specific configuration of each part of the electrostatic transducer 1 is not limited to that
described in the above embodiment.
For example, when forming the hole 10 in the fixing plate 4, the region other than the hole 10 is
formed in the fixing plate 4 is doped with an impurity, and the etching resistance is partially
improved in the region other than the hole 10. It may be formed by etching in the same state.
The fixed plate 4 and the movable plate 5 may be formed of silicon nitride or the like. The fixed
plate 4 manufactured by etching the silicon substrate different from the support substrate 3 to
form the holes 10 is bonded to the support substrate 3 and etching is further performed on the
other silicon substrate to form the protrusions 12 The movable plate 5 manufactured in the
above may be bonded to the fixed plate 4. The insulating support portion 6 may be formed of
another insulator such as a silicon nitride film.
[0068]
Further, in the above embodiment, the fixing plate 4 itself constitutes the fixed electrode 7 by
using as the material of the fixing plate 4 silicon that is doped with impurities and imparted
conductivity, but the configuration is not limited to this. The fixed electrode 7 may be formed by
forming the fixing plate 4 from a metal film having conductivity or laminating a conductive metal
film or the like on the fixing plate 4 made of an insulator. Similarly, the movable electrode 8 may
be formed by, for example, forming the movable plate 5 from a conductive metal film, or
laminating the conductive metal film or the like on the movable plate 5 made of an insulator. . In
addition, when laminating a conductive pattern on an insulator, vibration is received in the
movable plate 5 of the necessary portions of the fixed electrode 7 and the movable electrode 8,
that is, the fixed plate 4 so as to reduce parasitic capacitance. Of the movable plate 5 among the
portion (including the inner surface of the hole 10) facing the portion to be positioned, the
portion forming the connection pattern (including the pad 7a) for connecting the fixed electrode
7 to the external circuit, It is desirable to form a conductive pattern only in the part that receives
and vibrates (the vibrating part 11 and the protrusion 12) and the part that forms the connection
pattern (including the pad 8a) for connecting the movable electrode 8 to the external circuit. .
04-05-2019
22
Here, it is not essential to expose the fixed electrode 7 on the surface of the fixed plate 4 facing
the movable plate 5, and as shown in FIG. 5, the surface of the vibrating portion 11 facing the
fixed plate 4 is made of an insulating material. The insulating film 13 may be formed to prevent a
short circuit between the fixed electrode 7 and the movable electrode 8 when the movable plate
5 contacts the fixed plate 4. Similarly, it is not essential to expose the movable electrode 8 on the
surface of the movable plate 5, and the surface of the movable plate 12 may be covered with an
insulating film made of an insulating material.
[0069]
In the above embodiment, the quadrangular prism-shaped protrusion 12 is illustrated, but the
protrusion 12 is not limited to this shape, and at least a part of the hole 12 is inserted in the
initial state in which a bias voltage is applied. For example, it may have a polygonal pillar shape,
a pyramid shape, a cylindrical shape, a conical shape, or the like. The projection 12 may be
hollow as shown in FIG. Furthermore, in the above embodiment, the holes 10 are formed in a
shape having a square opening, and a plurality of the holes 10 are provided in the form of lattice
points, so that the protrusions 12 are holes 10 as shown in FIG. However, the shape and
arrangement of the holes 10 are not limited to this example, and the shape and arrangement of
the protrusions 12 may be changed appropriately in accordance with the holes 10. For example,
when making the hole 10 into an elongated slit shape, as shown in FIG. 7B, an elongated rib-like
protrusion 12 can be employed.
[0070]
Second Embodiment The electrostatic transducer 1 according to this embodiment has the same
basic configuration as that of the first embodiment, and is characterized in that a stopper is
provided to prevent the fixed plate 4 and the movable plate 5 from coming into contact with each
other. It is different from 1. In addition, about the component similar to Embodiment 1, the same
code | symbol is attached | subjected and description is abbreviate | omitted suitably.
[0071]
For example, as shown in FIG. 8, the stopper 14 is provided so as to protrude from a part of the
surface of the vibrating portion 11 facing the fixing plate 4. Thereby, the moving range
(amplitude) in the thickness direction of the vibrating portion 11 can be regulated, and damage
04-05-2019
23
to the movable plate 5 due to the displacement of the vibrating portion 11 becoming excessive
even when receiving an excessive sound pressure, for example. Also, a short circuit between the
fixed electrode 7 and the movable electrode 8 due to the movable plate 5 coming into contact
with the fixed plate 4 can be avoided. Here, when the fixed plate 4 itself constitutes the fixed
electrode 7 and the movable plate 5 itself constitutes the movable electrode 8 so that the fixed
electrode 7 and the movable electrode 8 do not short circuit through the stopper 14, or In the
case where the fixed electrode 7 and the movable electrode 8 are exposed between the facing
surfaces of the fixed plate 4 and the vibrating portion 11, at least a part of the stopper 14 (for
example, a surface or an intermediate portion in the protruding direction) is insulated It is
formed of a material to ensure the insulation between the fixed electrode 7 and the movable
electrode 8. The stopper 14 may be provided on the surface of the fixed plate 4 facing the
vibrating portion 11.
[0072]
Further, as another example, as shown in FIG. 9, the stopper 14 may be protruded on the surface
(inner side surface of the hole 10) of the fixing plate 4 facing the projection 12. Thereby, the
moving range of the movable plate 5 in the plane orthogonal to the thickness direction of the
fixed plate 4 can be restricted. For example, even when an impact is applied to the electrostatic
transducer 1, the thickness direction of the fixed plate 4 can be reduced. Avoiding breakage of
the movable plate 5 due to large movement of the movable plate 5 in the plane orthogonal to
each other and short circuit between the fixed electrode 7 and the movable electrode 8 due to
the projection 12 coming into contact with the inner surface of the hole 10 can do. Here, at least
a part of the stopper 14 (e.g., the surface, an intermediate portion in the direction of protrusion,
etc.) is formed of an insulating material to ensure the insulation between the fixed electrode 7
and the movable electrode 8. The stopper 14 may be provided on the surface of the projection
12 opposite to the inner surface of the hole 10.
[0073]
Third Embodiment The electrostatic transducer 1 of the present embodiment has the same basic
configuration as that of the first embodiment, and a plurality of pairs of electrode pairs (fixed
electrode 7 and movable electrode 8) are provided to form a plurality of capacitors. The point is
different from the first embodiment. In addition, about the component similar to Embodiment 1,
the same code | symbol is attached | subjected and description is abbreviate | omitted.
04-05-2019
24
[0074]
In the present embodiment, for example, as shown in FIG. 10, fixed plates (hereinafter referred to
as the first fixed plate 41 and the second fixed plate 42) are provided on both sides in the
thickness direction of one movable plate 5 . Here, in the movable plate 5, protrusions 12 are
respectively provided on the surfaces opposed to the first and second fixed plates 41 and 42. The
electrostatic transducer 1 includes a capacitor C1 formed between the fixed electrode 7 of the
first fixed plate 41 and the movable electrode 8 of the movable plate 5, the fixed electrode 7 of
the second fixed plate 42, and the movable plate And the capacitor C2 formed between the
movable electrode 8 and the movable electrode 8. When the movable plate 5 vibrates in the
thickness direction, the space between the first and second fixed plates 41 and 42 and the
movable electrode 8 is provided. The distance changes and the capacitance of each of the
capacitors C1 and C2 changes. Here, in order to convert each electrostatic capacitance change
into an electric signal and take it out, a bias voltage is applied to each of the capacitor C1 and the
capacitor C2 when detecting a sound wave.
[0075]
According to the configuration described above, when the movable plate 5 vibrates upon
receiving a sound wave, the electric signal extracted from the capacitor C1 and the electric signal
extracted from the capacitor C2 are in opposite phase to each other, so the difference between
the respective electric signals is If the differential amplification circuit to be taken is provided in
the latter stage, the electric signal (voltage) output to the sound wave becomes large, and the
sensitivity is improved. Furthermore, since the electrostatic transducer 1 can receive sound
waves from both sides in the thickness direction of the movable plate 5, it can be used as a socalled bi-directional acoustic sensor.
[0076]
In addition, as another example of the present embodiment, as shown in FIG. 11, movable plates
5 (hereinafter referred to as first movable plate 51 and second movable plate 52) are provided
on both sides of one fixed plate 4. You may provide. The electrostatic transducer 1 includes a
capacitor C1 formed between the movable electrode 8 of the first movable plate 51 and the fixed
electrode 7 of the fixed plate 4, and the movable electrode 8 and the fixed plate of the second
movable plate 52. And the capacitor C2 formed between the first fixed plate 7 and the fixed
electrode 7. If the first movable plate 51 vibrates, the distance between the first movable plate 51
04-05-2019
25
and the fixed plate 4 changes. While the capacitance of C1 changes, if the second movable plate
52 vibrates, the distance between the second movable plate 52 and the fixed plate 4 changes,
and the capacitance of the capacitor C2 changes. The electrostatic transducer 1 having this
configuration can receive sound waves by the first movable plate 51 and the second movable
plate 52, respectively, convert the sound waves into electric signals, and output them, so-called
bi-directional It can be used as a flexible acoustic sensor.
[0077]
Fourth Embodiment The electrostatic transducer 1 of the present embodiment has the same
basic configuration as that of the first embodiment, and the hole 10 formed in the fixing plate 4
has a thickness direction of the fixing plate 4 as shown in FIG. This embodiment differs from the
first embodiment in that it does not penetrate. The hole 10 is opened in one surface (upper
surface in FIG. 12) of the fixed plate 4 on the movable plate 5 side. In addition, about the
component similar to Embodiment 1, the same code | symbol is attached | subjected and
description is abbreviate | omitted.
[0078]
The electrostatic transducer 1 is disposed so as to expose one surface of the movable plate 5
opposite to the fixed plate 4 to an external atmosphere for detecting a sound wave, and the
support substrate 3 is omitted. In the present embodiment, in addition to the hole 10 not
penetrating, the insulating support 6 is provided over the entire circumference of the peripheral
portion of the fixed plate 4 so that between the fixed plate 4 and the movable plate 5. It forms an
airtight space. Thus, when the movable plate 5 receives a sound wave, the movable plate 5 is
deformed (vibrated) according to the pressure difference on both sides in the thickness direction
of the movable plate 5, and electrostatics between the fixed electrode 7 and the movable
electrode 8 The capacity changes.
[0079]
By the way, as a method of manufacturing the electrostatic transducer 1, after laminating the
sacrificial layer 22 (see FIG. 3) and the movable plate 5 on the fixed plate 4 as described in
Embodiment 1, the sacrificial layer 22 is etched away. When the method of forming the gap G
between the fixed plate 4 and the movable plate 5 is adopted, in the present embodiment, since
04-05-2019
26
the hole 10 does not penetrate, it is possible to transmit the etchant to the sacrificial layer 22
through the hole 10 Can not. Therefore, in the present embodiment, a plurality of inflow holes 15
penetrating in the thickness direction of the movable plate 5 are provided through the vibrating
portion 11 of the movable plate 5, and the sacrifice between the fixed plate 4 and the movable
plate 5 is performed through the inflow holes 15. It is possible to flow etchant into layer 22.
Furthermore, in order to make the space between the fixed plate 4 and the movable plate 5
airtight, a sealing plate 16 for closing the inflow hole 15 is provided. The sealing plate 16 closes
the inflow hole 15 by being laminated on one surface of the movable plate 5 opposite to the fixed
plate 4 after the sacrificial layer removing step of etching away the sacrificial layer 22. In the
case where the fixed plate 4 and the movable plate 5 are separately manufactured and attached
to each other, the inflow hole 15 and the sealing plate 16 are unnecessary.
[0080]
In the electrostatic transducer 1 of the present embodiment described above, when the movable
plate 5 vibrates in the thickness direction, the distance between the fixed plate 4 and the
vibrating portion 11 changes, and the fixed electrode 7 and the movable electrode 8 Not only the
change of the capacitance of the capacitor due to the change of the distance between, but also
the facing area of the inner side surface of the hole 10 and the side surface of the projection 12
changes, There is also a change in the capacitance of the capacitor due to the change in.
Therefore, compared to the conventional configuration in which the hole 10 and the protrusion
12 are not provided, the amount of change in capacitance is large even when the displacement of
the movable plate 5 is the same, and high sensitivity can be ensured. Moreover, the first gap
length g of the gap G between the opposing surfaces of the fixed plate 4 and the vibrating
portion 11 is the inner side surface of the hole 10 and the side surface of the projecting portion
12 in the initial state before the movable plate 5 vibrates. Because the second gap length d of the
gap D between them is set to be larger, the rate of change of capacitance compared to the case
where the distance between the fixed electrode 7 and the movable electrode 8 is uniform over
the entire area. Is larger and higher sensitivity can be obtained.
[0081]
Further, the hole 10 does not penetrate the fixed plate 4, and the space between the fixed plate 4
and the movable plate 5 is an airtight space, thereby separating the fixed plate 4 and the
movable plate 5 from the external atmosphere. Since it can be used, foreign matter can be
prevented from entering from the outside atmosphere between the fixed plate 4 and the movable
plate 5, and malfunction of the movable plate 5 and change in vibration characteristics due to the
04-05-2019
27
foreign matter can be prevented. In the case where the fixed plate 4 itself constitutes the fixed
electrode 7 and the movable plate 5 itself constitutes the movable electrode 8, or the fixed
electrode 7 and the movable electrode 8 are disposed between the opposed surfaces of the fixed
plate 4 and the movable plate 5. When exposed, it is possible to prevent a short circuit between
the fixed electrode 7 and the movable electrode 8 due to the entry of conductive foreign matter
between the fixed plate 4 and the movable plate 5. Furthermore, this electrostatic transducer 1
can also be used as a pressure sensor that detects pressure by detecting a pressure difference on
both sides of the movable plate 5 in the thickness direction, as well as detecting the sound wave.
[0082]
In the design of the material, thickness, and size of the movable plate 5, the pressure difference
and sensitivity on both sides of the movable plate 5 in the initial state (the state where no sound
pressure is acting on the movable plate 5) are considered. The fixing plate 4 is formed of a silicon
substrate having a sufficient rigidity of, for example, a thickness of several hundred ?m so as to
hardly deform under pressure.
[0083]
By the way, although the example which uses the electrostatic transducer 1 of this invention as
an acoustic sensor which converts the vibrational energy of the movable board 5 into an
electrical energy and outputs it was shown in each embodiment mentioned above, fixed electrode
7-movable electrode The electrostatic transducer 1 according to the present invention can also
be used as a pressure sensor for detecting pressure by applying a bias voltage between 8 and
extracting the displacement of the movable plate 5 due to pressure change as electric energy.
Also, as in the case of using as an acoustic sensor, high sensitivity can be obtained as compared
with the conventional configuration.
[0084]
Also, the electrostatic transducer 1 of the present invention can be used as a speaker for
converting electrical energy into vibration energy of the movable plate 5.
That is, when a driving voltage (electric energy) is applied between the pair of electrodes (the
fixed electrode 7 and the movable electrode 8), the electrostatic transducer 1 exerts an
electrostatic force between the fixed electrode 7 and the movable electrode 8 Since the movable
04-05-2019
28
plate 5 is drawn to the fixed plate 4 side, by changing the drive voltage applied between the fixed
electrode 7 and the movable electrode 8, the movable plate 5 can be vibrated to output a sound
wave from the movable plate 5. . Here, a part of the protrusion 12 is inserted into the hole 10 at
least in an initial state before the movable plate 5 vibrates (that is, in a state where a drive
voltage is not applied). When the electrostatic transducer 1 is used as a speaker, the electrostatic
force F acting between the fixed electrode 7 and the movable electrode 8 is such that the
electrostatic energy between the fixed electrode 7 and the movable electrode 8 is U, the fixed
electrode 7-the movable electrode 8 Capacitance C [F], drive voltage applied between a pair of
electrodes (fixed electrode 7 and movable electrode 8) V1 [V], displacement of the movable plate
5 from the initial state x [m] if,
[0085]
[0086]
Is represented by
Here, focusing on the small area described in the first embodiment, the electrostatic force Fcomb
of the small area in the state in which the movable plate 5 is displaced from the initial state
toward the fixed plate 4 along the thickness direction by x [m] is From the above equations 5 and
7,
[0087]
[0088]
Is represented by
The electrostatic force Fcomb is a force (so-called electrostatic attraction) in a direction to draw
the movable plate 5 toward the fixed plate 4 along the thickness direction. On the other hand, in
the conventional configuration in which the hole 10 and the protrusion 12 are not provided, the
electrostatic force of the small region in the state in which the movable plate 5 is displaced
toward the fixed plate 4 along the thickness direction from the initial state From the above
04-05-2019
29
equation 2 and equation 7, Fparallel
[0089]
[0090]
Is represented by
Therefore, as an example, the values of the parameters of the above equations 8 and 9 can be
expressed as a = 6 О 10 <-6> [m], b = 2 О 10 <-6> [m], d = 1 О 10 <? 6> [m], g = 4 О 10 <-6>
[m], electrostatic force in a small area acting on the movable plate 5 in the initial state (that is, x =
0 [m]) When the electrostatic transducer 1 of the present invention is compared with the
conventional configuration, Fcomb / Fparallel = 2.76 can be obtained from the above-mentioned
Eq. This is because, when the drive voltage V1 [V] of the same magnitude is applied between the
pair of electrodes (the fixed electrode 7 and the movable electrode 8), the electrostatic
transducer 1 of the present invention has 2.76 times the conventional configuration. It means
that electrostatic force acts between the fixed electrode 7 and the movable electrode 8.
[0091]
In short, in the electrostatic transducer 1 of the present invention, not only high sensitivity can
be obtained when used as an acoustic sensor or a pressure sensor as compared with the
conventional configuration without the hole 10 and the protrusion 12, but also as a speaker
When used, the electrostatic force acting between the fixed electrode 7 and the movable
electrode 8 is increased, and the output sound pressure is improved. When the electrostatic
transducer 1 of the present invention is used as an acoustic sensor or pressure sensor having the
same sensitivity as that of the conventional configuration, the electrostatic transducer 1 can be
miniaturized and the bias voltage can be lowered compared to the conventional configuration. In
the case where the electrostatic transducer 1 of the present invention is used as a speaker having
the same output as that of the conventional configuration, the electrostatic transducer 1 can be
miniaturized and drive voltage can be lowered compared to the conventional configuration. it
can.
[0092]
04-05-2019
30
The electrostatic transducer of Embodiment 1 of this invention is shown, (a) is a schematic
sectional drawing, (b) is the schematic perspective view which fractured | ruptured a part. It is a
schematic perspective view which shows the small area | region same as the above. It is a
schematic sectional drawing which shows the manufacturing method of an electrostatic type
transducer same as the above. FIG. 14 is a schematic cross-sectional view showing another
method of manufacturing the electrostatic transducer of the same as the above. It is a schematic
sectional drawing which shows the principal part of the other example same as the above. It is
the schematic perspective view which showed the principal part of the other example same as
the above, and was partially broken. (A) shows the principal part of the same as the above, and is
the partially broken schematic perspective view, (b) shows the principal part of another example,
and is the partially broken schematic perspective view. It is a schematic sectional drawing which
shows the principal part of the electrostatic transducer of Embodiment 2 of this invention. It is a
schematic sectional drawing which shows the principal part of the other example same as the
above. It is a schematic sectional drawing which shows the electrostatic transducer of
Embodiment 3 of this invention. It is a schematic sectional drawing which shows the other
example same as the above. It is a schematic sectional drawing which shows the electrostatic
transducer of Embodiment 4 of this invention. A prior art example is shown, (a) is a schematic
sectional view, (b) is a schematic perspective view of a small area.
Explanation of sign
[0093]
Reference Signs List 1 electrostatic transducer 4 fixed plate 4 'fixed substrate 5 movable plate 7
fixed electrode 8 movable electrode 10 hole portion 11 vibrating portion 12 protrusion 22
sacrificial layer 22a recessed portion D gap d second gap length G gap g first gap Long
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Cparallel [F] of the
small area before displacement of the movable plate 5 is Assuming that the dielectric constant of
the gap G is ?,
[0007]
[0008]
Is represented by
Similarly, the capacitance Cparallel 'of the small area after displacement of the movable plate 5 is
[0009]
[0010]
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3
Is represented by
Here, since the amount of change in capacitance ?Cparallel [F] of the small area is expressed by
Cparallel??Cparallel, the rate of change in capacitance (?Cparallel / Cparallel) results in the
above-mentioned Cparallel and Cparallel ?. Using,
[0011]
[0012]
Is represented by
[0013]
By the way, it is known that the compliance of the movable plate 5 is reduced due to the residual
stress generated in the movable plate 5 when the movable plate 5 is manufactured.
Therefore, the support plate 3 is configured to support the movable plate 5 via a plurality of
arms (not shown), and the arms are distorted so that the movable plate 5 can move relative to the
support substrate 3. There is also proposed an electrostatic transducer 1 in which the residual
stress of 5 is relieved and the compliance of the movable plate 5 is improved (see, for example,
Patent Document 2).
In this configuration, the displacement x of the movable plate 5 at the time of receiving the sound
wave increases by the amount of improvement in the compliance of the movable plate 5, so that
the rate of change in capacitance (?Cparallel / Cparallel) described above becomes large. A
relatively high sensitivity can be ensured.
[0014]
In the electrostatic transducer 1 described above, when a drive voltage is applied between the
pair of electrodes 7 and 8, an electrostatic force acts between the pair of electrodes 7 and 8 and
the movable plate 5 is drawn to the fixed plate 4 side. Therefore, by changing the drive voltage
04-05-2019
4
applied between the pair of electrodes 7 and 8, the movable plate 5 can be vibrated to generate a
sound wave from the movable plate 5.
That is, the electrostatic transducer 1 described above can be used not only as an acoustic sensor
but also as a speaker that generates an acoustic wave from the movable plate 5 by converting
electric energy (drive voltage) into vibration energy of the movable plate 5 It is. Japanese Patent
Publication No. 2004-506394 (FIG. 1) Japanese Patent Publication No. 2005-535152 (Page 6-7)
[0015]
However, even the electrostatic transducer 1 described in Patent Document 2, when used as an
acoustic sensor or a pressure sensor, has lower sensitivity than commonly used electret
condenser microphones and the like, and the sensitivity is further improved. It is desired.
Moreover, when using the electrostatic transducer 1 as a speaker, the improvement of an output
sound pressure is desired.
[0016]
The present invention has been made in view of the above, and when used as an acoustic sensor
or pressure sensor, sensitivity is improved more than before, and when used as a speaker, output
sound pressure is improved more than before. And a method of manufacturing the same.
[0017]
In the first aspect of the present invention, the fixed plate and the movable plate which are
disposed to face each other via the gap, and the pair of electrodes respectively provided on the
fixed plate and the movable plate are provided, and a capacitor is formed between the pair of
electrodes. It is an electrostatic transducer, and the fixed plate has a hole opening at least on one
surface on the movable plate side, and the movable plate is vibrated with a vibrating portion
opposed to the fixed plate in the thickness direction of the fixed plate, And a protrusion which is
partially inserted into the hole at least in the initial state before the vibrating portion is displaced,
and the electrode on the movable plate extends from the vibrating portion to the protrusion. The
electrode on the fixed plate side integrally has a portion along the surface facing the vibrating
portion in the fixed plate and a portion along the inner side surface of the hole portion, and a
portion provided on the vibrating portion in the electrode on the movable plate side And the
fixed plate on the fixed plate side The distance between the vibrating portion and the portion
along the opposing surface is the distance between the portion provided on the protrusion on the
electrode on the movable plate and the portion along the inner surface of the hole on the
04-05-2019
5
electrode on the fixed plate It is characterized in that it is set larger than that.
[0018]
According to the present invention, the electrode on the movable plate side is provided from the
vibrating portion to the projecting portion, and the electrode on the fixed plate side is a portion
along the surface facing the vibrating portion in the fixed plate and a portion along the inner
surface of the hole portion And the distance between the fixed plate and the vibrating portion
changes when the movable plate is displaced, and not only the distance between the pair of
electrodes changes, but also according to the amount of insertion of the protrusion into the hole
The opposing areas of the pair of electrodes also change.
That is, when the movable plate is displaced toward the fixed plate, a portion of the movable
plate side electrode provided on the vibrating portion and a portion of the fixed plate side
electrode along the surface of the fixed plate along the opposing surface to the vibrating portion
In addition to the increase in the capacitance of the capacitor due to the reduction of the
distance, a portion of the electrode on the movable plate side provided on the protrusion and a
portion of the electrode on the stationary plate side along the inner surface of the hole portion
By increasing the facing area of the capacitor, the capacitance of the capacitor is increased.
Therefore, compared with the configuration without the hole and the protrusion, the rate of
change in capacitance can be increased even when the displacement amount of the movable
plate is the same, and the sensitivity can be improved. Moreover, the distance between the
portion of the movable plate side electrode provided on the vibrating portion and the portion of
the fixed plate side electrode along the surface of the fixed plate along the opposing surface to
the vibrating portion is a protrusion on the movable plate side electrode. Since the distance
between the provided portion and the portion along the inner surface of the hole in the electrode
on the fixed plate side is set larger, compared to the case where the distance between the pair of
electrodes is uniform over the entire area, The rate of change of capacitance increases, and
higher sensitivity can be obtained. In addition, when using it as a speaker which outputs an
acoustic wave from a movable plate by applying a drive voltage between a pair of electrodes and
applying an electrostatic force between a pair of electrodes, a comparatively big sound pressure
can be output. .
[0019]
The invention of claim 2 is characterized in that, in the invention of claim 1, the hole portion
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penetrates in the thickness direction of the fixing plate.
[0020]
According to the present invention, the vibration of the movable plate is less likely to be impeded
by passing air in the thickness direction of the fixed plate through the hole, so that the
electrostatic transducer is excellent particularly when used as an acoustic sensor in a high
frequency region. Sensitivity characteristics are obtained, and good output characteristics are
obtained when the electrostatic transducer is used as a speaker, particularly in a high frequency
region.
[0021]
The invention according to claim 3 is the method for manufacturing an electrostatic transducer
according to claim 1 or 2, wherein the fixing substrate which is the basis of the fixing plate is
opened only in one thickness direction of the fixing substrate. A fixing plate forming step of
forming the fixing plate having the hole portion and the electrode provided by forming the hole
portion in a broken state; and an opening surface side of the hole portion after the fixing plate
forming step Forming a sacrificial layer on the fixed plate by depositing a sacrificial layer on the
fixed plate to form a sacrificial layer having a recess corresponding to the hole on one surface
opposite to the fixed plate, and sacrificial layer after the sacrificial layer forming step A movable
plate forming step of forming the movable plate having the portion formed in the recess as the
projection by depositing the movable plate on the layer and forming the movable plate provided
with the electrode, and sacrificial after the movable plate forming step The fixed plate and the
movable plate are removed by removing a part of the layer Wherein said to have a sacrificial
layer removing step of forming a gap between.
[0022]
According to the present invention, by forming the sacrificial layer by the deposition method
with low step coverage, the thickness dimension of the portion of the sacrificial layer deposited
on the inner surface of the hole portion It can be easily made smaller than the thickness
dimension of the part deposited on the part of.
Thus, easily, the distance between the portion of the movable plate side electrode provided on
the vibrating portion and the portion of the fixed plate side electrode along the surface facing the
vibrating portion in the fixed plate is set to the movable plate side electrode The distance
between the portion provided on the protrusion and the portion along the inner surface of the
04-05-2019
7
hole in the electrode on the fixed plate side can be set larger.
[0023]
The invention according to claim 4 relates to the invention according to claim 3, wherein in the
step of forming the sacrificial layer, a plurality of the sacrificial layers are stacked on the fixing
plate, and the holes in the fixing plate in the sacrificial layer are formed. It is characterized in that
the number of layers of the portion to be deposited in other portions is set larger than the
number of layers of the portion to be deposited on the inner surface of the hole in the sacrificial
layer.
[0024]
According to the present invention, by partially increasing the number of layers of the sacrificial
layer deposited in the portion other than the hole in the fixed plate, the sacrificial layer is
deposited in the portion other than the hole in the fixed plate. The thickness dimension of the
portion can be easily made larger than the thickness dimension of the portion of the sacrificial
layer deposited on the inner surface of the hole.
Thus, easily, the distance between the portion of the movable plate side electrode provided on
the vibrating portion and the portion of the fixed plate side electrode along the surface facing the
vibrating portion in the fixed plate is set to the movable plate side electrode The distance
between the portion provided on the protrusion and the portion along the inner surface of the
hole in the electrode on the fixed plate side can be set larger.
[0025]
When used as an acoustic sensor or a pressure sensor, the present invention has an effect that
sensitivity is improved as compared with the conventional case, and output sound pressure is
improved as compared with the conventional case when used as a speaker.
[0026]
The electrostatic transducer according to the present invention includes an acoustic sensor such
as a microphone for converting vibration energy of a movable plate into electrical energy, a
pressure sensor for converting displacement of the movable plate due to pressure change into
electrical energy, and a movable plate for converting electrical energy In the following
embodiments, an electrostatic transducer is used as an acoustic sensor.
04-05-2019
8
[0027]
Embodiment 1 As shown in FIG. 1, the electrostatic transducer 1 according to the present
embodiment has a support substrate 3 formed in a rectangular frame shape, and an upper
surface of one surface side of the support substrate 3 (FIG. 1A). The fixed plate 4 formed on the
side, and the movable plate 5 disposed on the one surface side of the fixed plate 4 opposite to the
support substrate 3 with the gap G interposed therebetween.
The fixing plate 4 has a rectangular plate shape, and is formed so as to interpose the rectangular
frame-shaped insulating film 20 with the support substrate 3.
Thereby, the cavity 2 surrounded by the support substrate 3, the fixing plate 4 and the insulating
film 20 is formed on the other surface side of the support substrate 3 (lower surface side in FIG.
1A).
The insulating film 20 will be described later.
The movable plate 5 is formed in a rectangular plate shape thinner than the fixed plate 4 and is
stacked on the one surface side of the fixed plate 4 via the insulating support portion 6. The
insulating support portion 6 is interposed between the peripheral portion of the movable plate 5
and the peripheral portion of the fixed plate 4, and a gap G having a predetermined gap length
between the fixed plate 4 and the movable plate 5 by the insulating support portion 6. Is formed.
[0028]
A fixed electrode 7 is provided on the fixed plate 4, and a movable electrode 8 paired with the
fixed electrode 7 is provided at a position corresponding to the fixed electrode 7 in the movable
plate 5. A pair of electrodes (the fixed electrode 7 and the movable electrode 8) are opposed via
the gap G, and a capacitor having the fixed electrode 7 and the movable electrode 8 as an
electrode is configured. As a result, when the movable plate 5 vibrates in the thickness direction,
the distance between the fixed electrode 7 and the movable electrode 8 changes and the
capacitance of the capacitor changes, so this capacitance change is converted into an electric
04-05-2019
9
signal and taken out. Thereby, when the movable plate 5 receives a sound wave, the vibration
energy of the movable plate 5 according to the sound wave can be extracted as electric energy
(here, an electric signal). Here, in order to convert the capacitance change into an electric signal
and take it out, a bias voltage is applied between the fixed electrode 7 and the movable electrode
8 when detecting the sound wave. In the present embodiment, as shown in FIG. 1A, the pad 7a
connected to the fixed electrode 7 is provided at one end of one surface of the fixed plate 4
opposite to the support substrate 3 and connected to the movable electrode 8 By providing the
pad 8 a on one end of one surface of the movable plate 5 opposite to the fixed plate 4, a bias
voltage can be applied between the fixed electrode 7 and the movable electrode 8 from the pads
7 a and 8 a. An external circuit applying a bias voltage is connected to pads 7a and 8a by wire
bonding, for example. Here, the movable plate 5 is formed in a shape that exposes the pad 8a. In
FIG. 1B, the pads 7a and 8a and the insulating support 6 are not shown.
[0029]
The supporting substrate 3 is made of a silicon substrate and is formed in a shape that
constitutes the cavity 2 together with the fixing plate 4 and the insulating film 20 made of a
silicon oxide film by removing the central portion by etching. The cavity 2 is opened in a
rectangular shape, and here, for example, the inner side is tapered by anisotropic etching using
an alkaline solution or the like, and the area of the cross section orthogonal to the thickness
direction of the support substrate 3 is from the fixing plate 4 It forms in the shape which
becomes large as it separates, but in order to miniaturize the support substrate 3 as much as
possible, each inner side may be formed perpendicularly to the one surface of the support
substrate 3, respectively.
[0030]
The fixing plate 4 is formed in a rectangular plate shape as described above, and the upper
surface of the supporting substrate 3 is substantially parallel to each side of the supporting
substrate 3 so that each side opposed to each side of the one surface is substantially parallel. Will
be placed. The fixing plate 4 is formed of silicon (including polysilicon and amorphous silicon),
and is manufactured by deposition using a CVD method (chemical vapor deposition method) or
the like. Here, the fixing plate 4 is designed to have a predetermined rigidity, a thickness, and a
size so as to be hardly deformed even under sound pressure. Further, in the fixed plate 4, a
plurality of holes (so-called acoustic holes) 10 through which air is passed so as not to prevent
the vibration of the movable plate 5 are provided in plurality in a region to be the bottom plate of
the cavity 2. The holes 10 in the present embodiment are formed in a shape having a square
04-05-2019
10
opening, and are arranged in lattice points at equal intervals in a rectangular area. That is, the
area | region used as the baseplate of the cavity 2 in the stationary plate 4 is formed in grid |
lattice form. Here, the hole 10 is formed, for example, using a photolithography technique and an
etching technique.
[0031]
The insulating support portion 6 is made of a silicon oxide film, and electrically insulates the
fixed electrode 7 provided on the fixed plate 4 and the movable electrode 8 provided on the
movable plate 5. The insulating support 6 is provided over the entire circumference of one
surface of the fixing plate 4. Here, as an example, the insulating sacrificial layer fabricated
between the fixed plate 4 and the movable plate 5 in the fabrication process is partially removed,
and the remaining portion of the sacrificial layer is used as the insulating support portion 6.
[0032]
The movable plate 5 is disposed on the fixed plate 4 so that each side opposed to each side of
one surface of the fixed plate 4 is substantially parallel to each side of the fixed plate 4, and
similar to the fixed plate 4, silicon It is formed of (including polysilicon and amorphous silicon)
and manufactured by deposition using a CVD method or the like. Here, since a plurality of holes
10 are provided through the fixed plate 4 as described above, the sound wave propagated from
the other surface side of the support substrate 3 into the cavity 2 passes through the holes 10 to
move the movable plate 5. Propagated to That is, the cavity 2 formed by the support substrate 3,
the fixing plate 4 and the insulating film 20 serves as an entrance for the sound wave. Therefore,
when detecting the sound wave, the electrostatic transducer 1 is arranged to expose the opening
surface of the cavity 2 to the external atmosphere for detecting the sound wave.
[0033]
The movable plate 5 has a certain degree of compliance so as to be easily displaced (vibrated) by
receiving a sound wave, and realizes vibration characteristics such as a desired resonance
frequency or amplitude, or pull-in when a bias voltage is applied ( Material, thickness, and size
with appropriate compliance, taking into consideration that electrostatic force is too large
compared to the restoring force of the movable plate 5 and the phenomenon that the attitude of
the movable plate 5 can not be stably controlled) It is designed. At this time, the residual stress
04-05-2019
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generated in the movable plate 5 at the time of manufacturing the movable plate 5 is also taken
into consideration.
[0034]
In the present embodiment, the fixed plate 4 itself constitutes the fixed electrode 7 by using
polysilicon doped with impurities and imparted conductivity as the material of the fixed plate 4
and poly doped with impurities and imparted conductivity. By using silicon as the material of the
movable plate 5, the movable plate 5 itself constitutes the movable electrode 8.
[0035]
By the way, the movable plate 5 according to the present embodiment includes the vibrating
portion 11 facing the region of the fixed plate 4 in the thickness direction of the fixed plate 4
with respect to the area to be the bottom plate of the cavity 2 to vibrate by receiving sound
waves. The fixing plate 4 has a plurality of protruding portions 12 provided on the surface on the
side of the fixing plate 4 so as to project at respective positions facing the opening surface of the
hole 10.
In addition, in FIG.1 (b), parts other than the projection part 12 in the movable plate 5 are shown
in figure by an imaginary line (two-dot chain line).
[0036]
The protrusion 12 is formed such that the cross section orthogonal to the protrusion direction is
smaller than the opening surface of the hole 10 and the protrusion dimension is set larger than
the gap length of the gap G between the fixed plate 4 and the vibrating portion 11 In the initial
state before the movable plate 5 vibrates, a part is inserted into the hole 10 at least. The initial
state here means a state in which a bias voltage is applied between a pair of electrodes (fixed
electrode 7 and movable electrode 8). In the present embodiment, the protrusion 12 is formed in
a square pole shape in which a cross section orthogonal to the protruding direction is a square
having a smaller size than the opening surface of the hole 10. Here, the protrusion 12 is disposed
at a central portion in the opening surface of the hole 10 so that each side surface is
substantially parallel to each inner surface of the hole 10. The protrusion 12 is formed by, for
example, removing the sacrificial layer after depositing the material of the movable plate 5 on the
one surface of the sacrificial layer having a recess on one surface in the process of
04-05-2019
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manufacturing the movable plate 5.
[0037]
Furthermore, in the electrostatic transducer 1 of the present embodiment, the gap length of the
gap G between the facing surfaces of the fixed plate 4 and the vibrating portion 11 (that is, the
facing surface of the fixed electrode 7 with the vibrating portion 11 in the fixed plate 4). The first
gap length g, which is the distance between the portion along the line and the portion of the
movable electrode 8 provided in the vibrating portion 11, is the inner side surface of the hole 10
in the initial state before the movable plate 5 vibrates. The gap length of the gap D between the
side surface of the protrusion 12 (that is, the distance between the portion of the fixed electrode
7 along the inner surface of the hole 10 and the portion of the movable electrode 8 provided on
the protrusion 12) It is set larger than a certain second gap length d.
[0038]
In the electrostatic transducer 1 having the configuration described above, the movable electrode
8 is provided from the vibrating portion 11 to the protrusion 12, and the fixed electrode 7 is a
portion along the surface of the fixed plate 4 facing the vibrating portion 11 and a hole Since it
integrally has a portion along the inner side surface of the portion 10, when the movable plate 5
vibrates, the distance between the fixed plate 4 and the vibrating portion 11 changes, and the
distance between the fixed electrode 7 and the movable electrode 8 Not only changes the amount
of insertion of the protrusion 12 into the hole 10 but also changes the opposing area between
the inner side surface of the hole 10 and the side surface of the protrusion 12. The opposing area
also changes.
In short, not only the change of the capacitance of the capacitor due to the change of the
distance between the fixed electrode 7 and the movable electrode 8 but also the electrostatic of
the capacitor due to the change of the facing area of the fixed electrode 7 and the movable
electrode 8 There is also a change in capacity. For example, when the vibrating portion 11 is
displaced to the fixed plate 4 side, the distance between the fixed electrode 7 and the movable
electrode 8 is reduced, so that the capacitance is increased, and the inner side surface of the hole
10 and the side surface of the projection 12 are opposed The larger area further increases the
capacitance. Therefore, compared to the conventional configuration in which the hole 10 and the
protrusion 12 are not provided, the amount of change in capacitance is large even when the
displacement of the movable plate 5 is the same, and high sensitivity can be ensured. Moreover,
the first gap length g of the gap G between the opposing surfaces of the fixed plate 4 and the
vibrating portion 11 is the inner side surface of the hole 10 and the side surface of the projecting
04-05-2019
13
portion 12 in the initial state before the movable plate 5 vibrates. Because the second gap length
d of the gap D between them is set to be larger, the rate of change of capacitance compared to
the case where the distance between the fixed electrode 7 and the movable electrode 8 is
uniform over the entire area. Is larger and higher sensitivity can be obtained.
[0039]
Hereinafter, from the initial state in which the bias voltage is applied between the fixed electrode
7 and the movable electrode 8, the capacitance of the movable plate 5 is displaced toward the
fixed plate 4 by x [m] along the thickness direction. The rate of change (?C / C) will be described
by focusing attention on small areas of the fixed plate 4 and the movable plate 5 as shown in FIG.
When the movable plate 5 is displaced away from the fixed plate 4, x [m] becomes negative.
Here, it is a region shown by A in FIG. 1A, and has one hole 10 and one protrusion 12 at the
center, and a cross section orthogonal to the vibration direction of the movable plate 5 is a
square with a side a [m]. The area that is
[0040]
Before displacement of the movable plate 5, the distance between the opposing surfaces of the
fixed plate 4 and the vibrating portion 11 (that is, the first gap length) is g [m], and the side
length of the cross section of the protrusion 12 is b The amount of insertion of the protrusion 12
into the hole 10 is c [m], and the distance between the inner side surface of the hole 10 and the
side surface of the protrusion 12 (that is, the second gap length) is d [m]. Then, the electrostatic
capacitance Ccomb [F] of the small area before the displacement of the movable plate 5 is
represented by ? where the dielectric constant of the gaps G and D is ?
[0041]
[0042]
Is represented by
In the above-mentioned formula 4, the term of ? и (a <2>-(b + 2 d) <2>) / g is a part of the fixed
electrode 7 along the surface of the fixed plate 4 facing the vibrating part 11 and the movable
electrode Of the fixed electrode 7 corresponding to the electrostatic capacitance between the
04-05-2019
14
portion provided in the vibrating portion 11 of 8 and the portion of the fixed electrode 7 along
the inner surface of the hole 10 and the movable portion This corresponds to the electrostatic
capacitance between the electrode 8 and the portion provided on the protrusion 12.
Similarly, the capacitance Ccomb 'of the small area after displacement of the movable plate 5 is
[0043]
[0044]
Is represented by
Here, since the amount of change in capacitance ?Ccomb [F] of the small area is expressed by
Ccomb'-Ccomb, the rate of change in capacitance (?Ccomb / Ccomb) results in the abovedescribed Ccomb and Ccomb '. Using,
[0045]
[0046]
Is represented by
[0047]
As a reference example, the values of the parameters in the above equations 4 and 5 can be
expressed as a = 10 О 10 <?6> [m], b = 2 О 10 <?6> [m], c = 1 О 10 <? Assuming that 6>
[m], d = 3 О 10 <-6> [m], g = 3 О 10 <-6> [m], the movable plate 5 has x = 5 О 10 <?9 in the
thickness direction. Assuming that the displacement is> [m], the rate of change in capacitance
(?Ccomb / Ccomb) is calculated to be ?Ccomb / Ccomb = 0.00228 from the above Equations 4,
5, and 6.
[0048]
On the other hand, in the conventional configuration in which the hole 10 and the protrusion 12
are not provided, the same condition (a = 10 О 10 <-6> [m], g = 3 О 10 <-6> [m], x = When the
04-05-2019
15
rate of change of capacitance (?Cparallel / Cparallel) is calculated by 5 О 10 <?9> [m],
?Cparallel / Cparallel = 0.00167 can be obtained from the above Equations 1, 2, and 3.
[0049]
In short, in the electrostatic transducer 1 having the configuration according to the present
embodiment, the rate of change in electrostatic capacitance is increased by providing the hole 10
and the protrusion 12 as compared with the conventional electrostatic transducer 1, and the
sensitivity is increased. Will improve.
[0050]
In the present embodiment, the distance g between the portion of the fixed electrode 7 along the
surface of the fixed plate 4 facing the vibrating portion 11 and the portion of the movable
electrode 8 provided on the vibrating portion 11 is the fixed electrode Since the distance d
between the portion along the inner side surface of the hole 10 and the portion of the movable
electrode 8 provided on the protrusion 12 among 7 is set to be larger than Is set to g> d.
As an example, the value of each parameter other than d is set to the same condition as the above
reference example (a = 10 О 10 <-6> [m], b = 2 О 10 <-6> [m], c = 1 О 10 Assuming that <-6>
[m], g = 3 x 10 <-6> [m], x = 5 x 10 <-9> [m]), d = 0.5 x 10 <-6> When the rate of change in
capacitance is calculated as [m], ?Ccomb / Ccomb = 0.00282 can be obtained from the above
equations (4), (5) and (6).
Therefore, in the electrostatic transducer 1 according to the present embodiment, by setting g> d,
the change in electrostatic capacitance is more than in the reference example in which d = g (= 3
О 10 <-6> [m]). The rate is increased, and higher sensitivity can be obtained.
[0051]
Hereinafter, a method of manufacturing the electrostatic transducer 1 of the present embodiment
will be illustrated.
[0052]
04-05-2019
16
First, as shown in FIG. 3B, an insulating film 20 made of a silicon oxide film is formed by thermal
oxidation on the silicon substrate 3 'shown in FIG. A lamination step of laminating fixed substrate
4 ? made of polysilicon and serving as a base of fixing plate 4 on film 20 is performed.
The fixed substrate 4 ? is made to serve as the fixed electrode 7 by doping with an impurity (for
example, phosphorus or boron) (a region to be doped is limited if necessary).
[0053]
Next, a resist 21 is formed on one surface of the fixed substrate 4 'opposite to the insulating film
20 except for a part (a part where the hole 10 will be formed later) as shown in FIG. Formation
process).
Then, the fixed substrate 4 'is removed by dry etching with the resist 21 as an etching mask and
the insulating film 20 as an etching stopper layer, and the hole 10 is formed as shown in FIG. 3D,
from the fixed substrate 4'. A fixing plate forming step of forming the fixing plate 4 having the
holes 10 is performed.
At this time, the hole 10 is closed by the insulating film 20 at one side in the thickness direction
of the fixing plate 4 (downward in FIG. 3D).
The resist 21 is removed after the fixing plate forming process.
[0054]
Thereafter, as shown in FIG. 3E, a sacrificial layer forming step of depositing a silicon oxide film
to be the sacrificial layer 22 on the one surface (one surface opposite to the insulating film 20) of
the fixed plate 4 is performed. At this time, as described above, since the hole 10 is closed in one
of the fixing plate 4 in the thickness direction (downward in FIG. 3F), the sacrificial layer 22 is
also deposited in the hole 10. Here, the sacrificial layer 22 is deposited to such an extent that the
hole 10 does not fill, and a recess 22 a is formed in each portion corresponding to the hole 10 in
one surface of the sacrificial layer 22 opposite to the fixing plate 4. In the sacrificial layer
formation step, the step coverage is intentionally lowered by utilizing atmospheric pressure CVD
04-05-2019
17
method or the like with a short mean free path of the reactive molecules, thereby fixing the
sacrificial layer 22 to the inner surface of the hole 10 The thickness dimension d of the portion
deposited in the plane orthogonal to the thickness direction of the plate 4 is the thickness
dimension of the portion of the sacrificial layer 22 deposited in the thickness direction of the
fixed plate 4 with respect to the one surface of the fixed plate 4 Make it thinner than g. The step
coverage mentioned here represents step coverage as is well known, and if the step coverage is
lowered, holes for the thickness dimension g of the portion of the sacrificial layer 22 deposited
on the one surface of the fixed plate 4 are obtained. The ratio (that is, d / g) of the thickness
dimension d of the portion deposited on the inner surface of the portion 10 is reduced.
[0055]
Next, as shown in FIG. 3F, a movable plate forming step of forming the movable plate 5 by
depositing polysilicon 5 ? which is a material of the movable plate 5 on the sacrificial layer 22 is
performed. The polysilicon 5 'is made to serve as the movable electrode 8 by doping an impurity
(for example, phosphorus or boron) (a region to be doped is limited if necessary). Here, the
polysilicon 5 'is also deposited in the recess 22a of the sacrificial layer 22, and the hole 10 is
filled with the sacrificial layer 22 and the polysilicon 5'. The polysilicon 5 'is deposited so that
one surface opposite to the sacrificial layer 22 is substantially flat. As a result, the movable plate
5 having the portion of the polysilicon 5 'deposited in the recess 22a as the protrusion 12 is
formed. Further, in order to expose the pads 7a formed on the fixed plate 4 later, as shown in
FIG. 3G, a part of the movable plate 5 is removed by etching.
[0056]
Thereafter, as shown in FIG. 3 (h), a difference to be described later is made on both sides in the
thickness direction of the multilayer structure formed by laminating the silicon substrate 3 ', the
insulating film 20, the fixed plate 4, the sacrificial layer 22, and the movable plate 5. A silicon
nitride film 23 to be a protective mask is deposited during the anisotropic etching, and a portion
of the silicon nitride film 23 on the silicon substrate 3 'side corresponding to the opening surface
of the cavity 2 is removed by etching (mask formation step). Then, after the mask formation step,
anisotropic etching is performed using an alkaline solution (for example, an aqueous solution of
TMAH or the like) to form a supporting substrate 3 having an opening as shown in FIG. (Cavity
formation step). At this time, the insulating film 20 having a slow etching rate is used as an
etching stopper layer.
04-05-2019
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[0057]
After the cavity formation step, the silicon nitride film 23 is removed by etching, and a sacrificial
layer removal step of removing the insulating film 20 and the sacrificial layer 22 by etching is
performed. Here, the etchant is transmitted to the sacrificial layer 22 through the holes 10 of the
fixing plate 4, and the sacrificial layer 22 is removed leaving a portion to be the insulating
support 6. Therefore, the fixed plate 4 and the vibrating portion 11 of the movable plate 5 are
separated by the thickness dimension t1 of the portion of the sacrificial layer 22 deposited on
the one surface of the fixed plate 4 (that is, the surface facing the vibrating portion 11). The
inner surface of the hole 10 and the side surface of the protrusion 12 are the same as the
thickness dimension t 2 of the portion of the sacrificial layer 22 deposited on the inner surface of
the hole 10. Opposite via a gap D having a gap length of In addition, since the thickness
dimension t1 here is equal to the gap length of the gap G in the state where the bias voltage is
not applied between the fixed electrode 7 and the movable electrode 8, the bias voltage is applied
between the fixed electrode 7 and the movable electrode 8. In the initial state in which the
movable plate 5 is drawn to the fixed plate 4 side by the electrostatic force between the fixed
electrode 7 and the movable electrode 8, the first gap length g of the gap G becomes smaller than
the thickness dimension t1 (g <T1).
[0058]
After the sacrificial layer removing step, the pads 7a and 8a made of an aluminum film are
formed by sputtering to obtain the electrostatic transducer 1 shown in FIG. 3 (j).
[0059]
In short, in the manufacturing method of the electrostatic transducer 1 shown in FIG. 3, the
sacrificial layer 22 is easily formed by forming the sacrificial layer 22 by the deposition method
(for example, atmospheric pressure CVD method) with low step coverage in the sacrificial layer
forming step. The thickness t2 of the portion of the layer 22 deposited on the inner side surface
of the hole 10 can be thinner than the thickness t1 of the portion deposited on the surface of the
fixed plate 4 facing the vibrating portion 11.
Here, the distance between the facing surface of the fixed plate 4 and the vibrating portion 11 is
determined by the thickness dimension t1 of the portion of the sacrificial layer 22 deposited on
the surface of the fixed plate 4 facing the vibrating portion 11. Since the distance between the
inner surface of the hole 10 and the side surface of the protrusion 12 is determined by the
04-05-2019
19
thickness dimension t2 of the portion deposited on the inner surface of the plate, as a result, the
opposing surface of the fixed plate 4 and the vibrating portion 11 The distance between them
can be greater than the distance between the inner side of the hole 10 and the side of the
projection 12. Further, as described above, since the first gap length g in the initial state is
smaller than the thickness dimension t1, in the present embodiment, the first gap length g in the
initial state is larger than the second gap length d. Therefore, the thickness dimensions t1 and t2
are set such that the thickness dimension t1 and t2 become larger than the thickness dimension
t2 (= d) even if the movement amount (t1-g) of the movable plate 5 due to the electrostatic force
due to the bias voltage application is subtracted from the thickness dimension t1. It is set.
[0060]
Moreover, the manufacturing method of the electrostatic transducer 1 of this embodiment is not
limited to the example of FIG. 3 mentioned above, For example, you may employ | adopt the
manufacturing method shown in FIG. The example shown in FIG. 4 is different from the abovedescribed manufacturing method of FIG. 3 in that the etching mask used in the fixing plate
forming step is used as a part of the sacrificial layer 22. The steps shown in FIGS. 4 (a) and 4 (b)
are the same as the steps described with reference to FIGS. 3 (a) and 3 (b), so the description will
be omitted.
[0061]
In the resist formation step shown in FIG. 4C, a silicon oxide film is deposited on one surface of
the fixed substrate 4 ? opposite to the insulating film 20 using the CVD method, and then a
portion of the silicon oxide film A mask 21 'is formed by patterning the silicon oxide film so as to
remove the portion where the portion 10 is to be formed.
[0062]
In the subsequent fixing plate forming step, as shown in FIG. 4D, the fixing substrate 4 'is dry
etched using the mask 21' as an etching mask to form the fixing plate 4 having the holes 10.
Since the mask 21 'is later used as part of the sacrificial layer 22, the mask 21' is not removed
immediately after the fixing plate formation process.
04-05-2019
20
[0063]
Then, in the sacrificial layer forming step shown in FIG. 4E, the mask 21 'left without being
removed after the fixing plate forming step is a part of the sacrificial layer (hereinafter referred
to as the first sacrificial layer 22a) Then, a silicon oxide film (hereinafter referred to as a second
sacrificial layer 22 b) is further deposited on the mask 21 ?. At this time, in the portion of the
sacrificial layer 22 deposited on the one surface (the one surface opposite to the insulating film
20) of the fixing plate 4, the first sacrificial layer 22a and the second sacrificial layer 22b are
stacked. On the other hand, in the portion of the sacrificial layer 22 deposited on the inner
surface of the hole 10, only the second sacrificial layer 22b is deposited. Therefore, even if the
second sacrificial layer 22b is formed to have a uniform thickness over the entire area (that is,
the step coverage is high), a portion of the sacrificial layer 22 deposited on the one surface of the
fixed plate 4 The thickness dimension t1 of the first sacrificial layer 22a is larger than the
thickness dimension t2 of the portion deposited on the inner side surface of the hole 10.
[0064]
The subsequent steps shown in FIGS. 4 (f) to 4 (j) are the same as the steps described with
reference to FIGS. 3 (f) to 3 (j), and therefore the description thereof is omitted.
[0065]
In short, according to the method of manufacturing the electrostatic transducer 1 shown in FIG.
4, the number of layers of the sacrificial layer 22 stacked on the fixed plate 4 can be easily
increased by partially increasing the number of layers facing the vibrating portion 11 The
thickness dimension t1 of the portion of the sacrificial layer 22 deposited on the surface of the
fixed plate 4 facing the vibrating portion 11 can be made thicker than the thickness dimension t2
of the portion deposited on the inner side surface of the hole 10 As a result, the distance between
the facing surfaces of the fixed plate 4 and the vibrating portion 11 can be made larger than the
distance between the inner side surface of the hole 10 and the side surface of the protrusion 12.
[0066]
The electrostatic transducer 1 described above is not limited to the arrangement in which the
opening surface of the cavity 2 is exposed to the external atmosphere in which the sound wave is
detected, and is opposite to the fixed plate 4 in the movable plate 5 in the external atmosphere in
which the sound wave is detected. It may be arranged to expose one surface of the side.
04-05-2019
21
In this case, the movable plate 5 receives an acoustic wave from the side opposite to the fixed
plate 4, so the cavity 2 functions as a back chamber.
[0067]
The specific configuration of each part of the electrostatic transducer 1 is not limited to that
described in the above embodiment.
For example, when forming the hole 10 in the fixing plate 4, the region other than the hole 10 is
formed in the fixing plate 4 is doped with an impurity, and the etching resistance is partially
improved in the region other than the hole 10. It may be formed by etching in the same state.
The fixed plate 4 and the movable plate 5 may be formed of silicon nitride or the like. The fixed
plate 4 manufactured by etching the silicon substrate different from the support substrate 3 to
form the holes 10 is bonded to the support substrate 3 and etching is further performed on the
other silicon substrate to form the protrusions 12 The movable plate 5 manufactured in the
above may be bonded to the fixed plate 4. The insulating support portion 6 may be formed of
another insulator such as a silicon nitride film.
[0068]
Further, in the above embodiment, the fixing plate 4 itself constitutes the fixed electrode 7 by
using as the material of the fixing plate 4 silicon that is doped with impurities and imparted
conductivity, but the configuration is not limited to this. The fixed electrode 7 may be formed by
forming the fixing plate 4 from a metal film having conductivity or laminating a conductive metal
film or the like on the fixing plate 4 made of an insulator. Similarly, the movable electrode 8 may
be formed by, for example, forming the movable plate 5 from a conductive metal film, or
laminating the conductive metal film or the like on the movable plate 5 made of an insulator. . In
addition, when laminating a conductive pattern on an insulator, vibration is received in the
movable plate 5 of the necessary portions of the fixed electrode 7 and the movable electrode 8,
that is, the fixed plate 4 so as to reduce parasitic capacitance. Of the movable plate 5 among the
portion (including the inner surface of the hole 10) facing the portion to be positioned, the
portion forming the connection pattern (including the pad 7a) for connecting the fixed electrode
7 to the external circuit, It is desirable to form a conductive pattern only in the part that receives
and vibrates (the vibrating part 11 and the protrusion 12) and the part that forms the connection
pattern (including the pad 8a) for connecting the movable electrode 8 to the external circuit. .
04-05-2019
22
Here, it is not essential to expose the fixed electrode 7 on the surface of the fixed plate 4 facing
the movable plate 5, and as shown in FIG. 5, the surface of the vibrating portion 11 facing the
fixed plate 4 is made of an insulating material. The insulating film 13 may be formed to prevent a
short circuit between the fixed electrode 7 and the movable electrode 8 when the movable plate
5 contacts the fixed plate 4. Similarly, it is not essential to expose the movable electrode 8 on the
surface of the movable plate 5, and the surface of the movable plate 12 may be covered with an
insulating film made of an insulating material.
[0069]
In the above embodiment, the quadrangular prism-shaped protrusion 12 is illustrated, but the
protrusion 12 is not limited to this shape, and at least a part of the hole 12 is inserted in the
initial state in which a bias voltage is applied. For example, it may have a polygonal pillar shape,
a pyramid shape, a cylindrical shape, a conical shape, or the like. The projection 12 may be
hollow as shown in FIG. Furthermore, in the above embodiment, the holes 10 are formed in a
shape having a square opening, and a plurality of the holes 10 are provided in the form of lattice
points, so that the protrusions 12 are holes 10 as shown in FIG. However, the shape and
arrangement of the holes 10 are not limited to this example, and the shape and arrangement of
the protrusions 12 may be changed appropriately in accordance with the holes 10. For example,
when making the hole 10 into an elongated slit shape, as shown in FIG. 7B, an elongated rib-like
protrusion 12 can be employed.
[0070]
Second Embodiment The electrostatic transducer 1 according to this embodiment has the same
basic configuration as that of the first embodiment, and is characterized in that a stopper is
provided to prevent the fixed plate 4 and the movable plate 5 from coming into contact with each
other. It is different from 1. In addition, about the component similar to Embodiment 1, the same
code | symbol is attached | subjected and description is abbreviate | omitted suitably.
[0071]
For example, as shown in FIG. 8, the stopper 14 is provided so as to protrude from a part of the
surface of the vibrating portion 11 facing the fixing plate 4. Thereby, the moving range
(amplitude) in the thickness direction of the vibrating portion 11 can be regulated, and damage
04-05-2019
23
to the movable plate 5 due to the displacement of the vibrating portion 11 becoming excessive
even when receiving an excessive sound pressure, for example. Also, a short circuit between the
fixed electrode 7 and the movable electrode 8 due to the movable plate 5 coming into contact
with the fixed plate 4 can be avoided. Here, when the fixed plate 4 itself constitutes the fixed
electrode 7 and the movable plate 5 itself constitutes the movable electrode 8 so that the fixed
electrode 7 and the movable electrode 8 do not short circuit through the stopper 14, or In the
case where the fixed electrode 7 and the movable electrode 8 are exposed between the facing
surfaces of the fixed plate 4 and the vibrating portion 11, at least a part of the stopper 14 (for
example, a surface or an intermediate portion in the protruding direction) is insulated It is
formed of a material to ensure the insulation between the fixed electrode 7 and the movable
electrode 8. The stopper 14 may be provided on the surface of the fixed plate 4 facing the
vibrating portion 11.
[0072]
Further, as another example, as shown in FIG. 9, the stopper 14 may be protruded on the surface
(inner side surface of the hole 10) of the fixing plate 4 facing the projection 12. Thereby, the
moving range of the movable plate 5 in the plane orthogonal to the thickness direction of the
fixed plate 4 can be restricted. For example, even when an impact is applied to the electrostatic
transducer 1, the thickness direction of the fixed plate 4 can be reduced. Avoiding breakage of
the movable plate 5 due to large movement of the movable plate 5 in the plane orthogonal to
each other and short circuit between the fixed electrode 7 and the movable electrode 8 due to
the projection 12 coming into contact with the inner surface of the hole 10 can do. Here, at least
a part of the stopper 14 (e.g., the surface, an intermediate portion in the direction of protrusion,
etc.) is formed of an insulating material to ensure the insulation between the fixed electrode 7
and the movable electrode 8. The stopper 14 may be provided on the surface of the projection
12 opposite to the inner surface of the hole 10.
[0073]
Third Embodiment The electrostatic transducer 1 of the present embodiment has the same basic
configuration as that of the first embodiment, and a plurality of pairs of electrode pairs (fixed
electrode 7 and movable electrode 8) are provided to form a plurality of capacitors. The point is
different from the first embodiment. In addition, about the component similar to Embodiment 1,
the same code | symbol is attached | subjected and description is abbreviate | omitted.
04-05-2019
24
[0074]
In the present embodiment, for example, as shown in FIG. 10, fixed plates (hereinafter referred to
as the first fixed plate 41 and the second fixed plate 42) are provided on both sides in the
thickness direction of one movable plate 5 . Here, in the movable plate 5, protrusions 12 are
respectively provided on the surfaces opposed to the first and second fixed plates 41 and 42. The
electrostatic transducer 1 includes a capacitor C1 formed between the fixed electrode 7 of the
first fixed plate 41 and the movable electrode 8 of the movable plate 5, the fixed electrode 7 of
the second fixed plate 42, and the movable plate And the capacitor C2 formed between the
movable electrode 8 and the movable electrode 8. When the movable plate 5 vibrates in the
thickness direction, the space between the first and second fixed plates 41 and 42 and the
movable electrode 8 is provided. The distance changes and the capacitance of each of the
capacitors C1 and C2 changes. Here, in order to convert each electrostatic capacitance change
into an electric signal and take it out, a bias voltage is applied to each of the capacitor C1 and the
capacitor C2 when detecting a sound wave.
[0075]
According to the configuration described above, when the movable plate 5 vibrates upon
receiving a sound wave, the electric signal extracted from the capacitor C1 and the electric signal
extracted from the capacitor C2 are in opposite phase to each other, so the difference between
the respective electric signals is If the differential amplification circuit to be taken is provided in
the latter stage, the electric signal (voltage) output to the sound wave becomes large, and the
sensitivity is improved. Furthermore, since the electrostatic transducer 1 can receive sound
waves from both sides in the thickness direction of the movable plate 5, it can be used as a socalled bi-directional acoustic sensor.
[0076]
In addition, as another example of the present embodiment, as shown in FIG. 11, movable plates
5 (hereinafter referred to as first movable plate 51 and second movable plate 52) are provided
on both sides of one fixed plate 4. You may provide. The electrostatic transducer 1 includes a
capacitor C1 formed between the movable electrode 8 of the first movable plate 51 and the fixed
electrode 7 of the fixed plate 4, and the movable electrode 8 and the fixed plate of the second
movable plate 52. And the capacitor C2 formed between the first fixed plate 7 and the fixed
electrode 7. If the first movable plate 51 vibrates, the distance between the first movable plate 51
04-05-2019
25
and the fixed plate 4 changes. While the capacitance of C1 changes, if the second movable plate
52 vibrates, the distance between the second movable plate 52 and the fixed plate 4 changes,
and the capacitance of the capacitor C2 changes. The electrostatic transducer 1 having this
configuration can receive sound waves by the first movable plate 51 and the second movable
plate 52, respectively, convert the sound waves into electric signals, and output them, so-called
bi-directional It can be used as a flexible acoustic sensor.
[0077]
Fourth Embodiment The electrostatic transducer 1 of the present embodiment has the same
basic configuration as that of the first embodiment, and the hole 10 formed in the fixing plate 4
has a thickness direction of the fixing plate 4 as shown in FIG. This embodiment differs from the
first embodiment in that it does not penetrate. The hole 10 is opened in one surface (upper
surface in FIG. 12) of the fixed plate 4 on the movable plate 5 side. In addition, about the
component similar to Embodiment 1, the same code | symbol is attached | subjected and
description is abbreviate | omitted.
[0078]
The electrostatic transducer 1 is disposed so as to expose one surface of the movable plate 5
opposite to the fixed plate 4 to an external atmosphere for detecting a sound wave, and the
support substrate 3 is omitted. In the present embodiment, in addition to the hole 10 not
penetrating, the insulating support 6 is provided over the entire circumference of the peripheral
portion of the fixed plate 4 so that between the fixed plate 4 and the movable plate 5. It forms an
airtight space. Thus, when the movable plate 5 receives a sound wave, the movable plate 5 is
deformed (vibrated) according to the pressure difference on both sides in the thickness direction
of the movable plate 5, and electrostatics between the fixed electrode 7 and the movable
electrode 8 The capacity changes.
[0079]
By the way, as a method of manufacturing the electrostatic transducer 1, after laminating the
sacrificial layer 22 (see FIG. 3) and the movable plate 5 on the fixed plate 4 as described in
Embodiment 1, the sacrificial layer 22 is etched away. When the method of forming the gap G
between the fixed plate 4 and the movable plate 5 is adopted, in the present embodiment, since
04-05-2019
26
the hole 10 does not penetrate, it is possible to transmit the etchant to the sacrificial layer 22
through the hole 10 Can not. Therefore, in the present embodiment, a plurality of inflow holes 15
penetrating in the thickness direction of the movable plate 5 are provided through the vibrating
portion 11 of the movable plate 5, and the sacrifice between the fixed plate 4 and the movable
plate 5 is performed through the inflow holes 15. It is possible to flow etchant into layer 22.
Furthermore, in order to make the space between the fixed plate 4 and the movable plate 5
airtight, a sealing plate 16 for closing the inflow hole 15 is provided. The sealing plate 16 closes
the inflow hole 15 by being laminated on one surface of the movable plate 5 opposite to the fixed
plate 4 after the sacrificial layer removing step of etching away the sacrificial layer 22. In the
case where the fixed plate 4 and the movable plate 5 are separately manufactured and attached
to each other, the inflow hole 15 and the sealing plate 16 are unnecessary.
[0080]
In the electrostatic transducer 1 of the present embodiment described above, when the movable
plate 5 vibrates in the thickness direction, the distance between the fixed plate 4 and the
vibrating portion 11 changes, and the fixed electrode 7 and the movable electrode 8 Not only the
change of the capacitance of the capacitor due to the change of the distance between, but also
the facing area of the inner side surface of the hole 10 and the side surface of the projection 12
changes, There is also a change in the capacitance of the capacitor due to the change in.
Therefore, compared to the conventional configuration in which the hole 10 and the protrusion
12 are not provided, the amount of change in capacitance is large even when the displacement of
the movable plate 5 is the same, and high sensitivity can be ensured. Moreover, the first gap
length g of the gap G between the opposing surfaces of the fixed plate 4 and the vibrating
portion 11 is the inner side surface of the hole 10 and the side surface of the projecting portion
12 in the initial state before the movable plate 5 vibrates. Because the second gap length d of the
gap D between them is set to be larger, the rate of change of capacitance compared to the case
where the distance between the fixed electrode 7 and the movable electrode 8 is uniform over
the entire area. Is larger and higher sensitivity can be obtained.
[0081]
Further, the hole 10 does not penetrate the fixed plate 4, and the space between the fixed plate 4
and the movable plate 5 is an airtight space, thereby separating the fixed plate 4 and the
movable plate 5 from the external atmosphere. Since it can be used, foreign matter can be
prevented from entering from the outside atmosphere between the fixed plate 4 and the movable
plate 5, and malfunction of the movable plate 5 and change in vibration characteristics due to the
04-05-2019
27
foreign matter can be prevented. In the case where the fixed plate 4 itself constitutes the fixed
electrode 7 and the movable plate 5 itself constitutes the movable electrode 8, or the fixed
electrode 7 and the movable electrode 8 are disposed between the opposed surfaces of the fixed
plate 4 and the movable plate 5. When exposed, it is possible to prevent a short circuit between
the fixed electrode 7 and the movable electrode 8 due to the entry of conductive foreign matter
between the fixed plate 4 and the movable plate 5. Furthermore, this electrostatic transducer 1
can also be used as a pressure sensor that detects pressure by detecting a pressure difference on
both sides of the movable plate 5 in the thickness direction, as well as detecting the sound wave.
[0082]
In the design of the material, thickness, and size of the movable plate 5, the pressure difference
and sensitivity on both sides of the movable plate 5 in the initial state (the state where no sound
pressure is acting on the movable plate 5) are considered. The fixing plate 4 is formed of a silicon
substrate having a sufficient rigidity of, for example, a thickness of several hundred ?m so as to
hardly deform under pressure.
[0083]
By the way, although the example which uses the electrostatic transducer 1 of this invention as
an acoustic sensor which converts the vibrational energy of the movable board 5 into an
electrical energy and outputs it was shown in each embodiment mentioned above, fixed electrode
7-movable electrode The electrostatic transducer 1 according to the present invention can also
be used as a pressure sensor for detecting pressure by applying a bias voltage between 8 and
extracting the displacement of the movable plate 5 due to pressure change as electric energy.
Also, as in the case of using as an acoustic sensor, high sensitivity can be obtained as compared
with the conventional configuration.
[0084]
Also, the electrostatic transducer 1 of the present invention can be used as a speaker for
converting electrical energy into vibration energy of the movable plate 5.
That is, when a driving voltage (electric energy) is applied between the pair of electrodes (the
fixed electrode 7 and the movable electrode 8), the electrostatic transducer 1 exerts an
electrostatic force between the fixed electrode 7 and the movable electrode 8 Since the movable
04-05-2019
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plate 5 is drawn to the fixed plate 4 side, by changing the drive voltage applied between the fixed
electrode 7 and the movable electrode 8, the movable plate 5 can be vibrated to output a sound
w
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