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JP2008259061

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2008259061
The present invention provides an electrostatic transducer which can be miniaturized as
compared with the prior art. An electrostatic transducer (1) includes a supporting substrate (10),
a fixing plate (20) formed on one surface side of the supporting substrate (10), and one fixing
surface of the fixing plate (20) in the thickness direction. And a movable plate portion 30
supported by the fixed plate portion 20 via a spring structure portion 40 displaceable in the
thickness direction of the portion 20. The fixed plate portion 20 is provided with a plurality of
holes 21 communicating with the space 60 between the fixed plate portion 20 and the movable
plate portion 30, and the fixed plate portion 20 also serves as the fixed electrode 25. The fixed
electrode 25 extends along the inner surface of the hole 21. Further, in the movable plate portion
30, a plurality of projections 31 loosely inserted one by one in each hole portion 21 of the fixed
plate portion 20 are provided continuously and integrally, and the movable plate portion 30
doubles as the movable electrode 35. Therefore, the movable electrode 35 extends to the
protrusion 31. [Selected figure] Figure 1
Electrostatic transducer
[0001]
The present invention relates to electrostatic transducers.
[0002]
Conventionally, electrostatic transducers formed using micromachining technology and the like
are known (see, for example, Patent Documents 1 and 2).
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1
[0003]
Here, as shown in FIG. 9, the electrostatic transducer 1 ′ disclosed in Patent Document 1
includes a support substrate 10 ′ having an insulating film 10b ′ formed of a silicon oxide film
formed on a silicon substrate 10a ′. A fixed plate portion 20 'supported by the support
substrate 10' on one surface side of the support substrate 10 '; a movable plate portion 30'
disposed opposite to the fixed plate portion 20 'and also serving as a movable electrode 35'; 20
'and a fixed electrode 25' formed of a metal thin film formed on the movable plate 30 'side, and
the fixed plate 20' communicates with a space between the fixed plate 20 'and the movable plate
30'. A plurality of small holes 21 'are formed in a penetrating manner, and an opening 11'
communicating with a space 60 'between the fixed plate 20' and the movable plate 30 'is formed
in the support substrate 10'.
The fixed plate portion 20 'is designed to be high in rigidity, and the movable plate portion 30' is
designed to be low in rigidity.
[0004]
In the above-described electrostatic transducer 1 ′, a capacitor having the fixed electrode 25 ′
and the movable electrode 35 ′ as an electrode is formed. Therefore, the movable plate portion
30 ′ receives the sound wave to move the fixed electrode 25 ′ and the movable electrode The
distance to the electrode 35 'changes, and the capacitance of the capacitor changes.
Therefore, if a DC bias voltage is applied between the fixed electrode 25 'and the movable
electrode 35', a minute voltage change between the fixed electrode 25 'and the movable
electrode 35' according to the sound pressure of the sound wave. Therefore, it can be used as an
acoustic sensor that converts the vibrational energy of the movable plate 30 'generated by the
sound pressure of the sound wave into an electrical signal.
[0005]
In addition, when the voltage is applied between the fixed electrode 25 ′ and the movable
electrode 35 ′, the electrostatic transducer 1 ′ described above is moved by the electrostatic
attractive force generated between the fixed electrode 25 ′ and the movable electrode 35 ′.
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Since the plate portion 30 'is displaced in the direction approaching the fixed plate portion 20',
the voltage applied between the fixed electrode 25 'and the movable electrode 35' is changed to
vibrate the movable plate portion 30 '. Since a sound wave can be generated, it can be used as a
speaker. Here, in order to increase the sound pressure to be output, the displacement amount of
the diaphragm portion 30 'may be increased.
[0006]
By the way, in an electrostatic transducer which applies a DC bias voltage and is used as an
acoustic sensor, the open end voltage (open end output voltage) is E [V], and the sound pressure
of the sound wave received by the movable plate portion 30 ' Assuming that Pa], voltage
sensitivity [dB] is known to be expressed by the following equation (1).
[0007]
[0008]
Here, the open end voltage E is a capacitor in an initial state in which a prescribed DC bias
voltage applied between the fixed electrode 25 'and the movable electrode 35' is Vb [V] and a
prescribed DC bias voltage Vb is applied. Capacitance (hereinafter, also referred to as sensor
capacitance) C [F], the amount of change in capacitance when the distance between the fixed
electrode 25 ′ and the movable electrode 35 ′ changes (hereinafter, sensor capacitance
fluctuation The relationship between the open end voltage E and the DC bias voltage Vb can be
expressed by the following equation 2.
[0009]
[0010]
As a means to improve the voltage sensitivity when using an electrostatic transducer as an
acoustic sensor from the above-described Equation 1 and Equation 2, increasing the ratio of
sensor capacitance fluctuation to sensor capacitance (that is, ΔC / C) It turns out that it is
effective.
[0011]
Here, in order to simplify the description of the above-mentioned capacitor, it is considered as a
minute element having a square shape in plan view (parallel plate capacitor), and as shown in
FIG. 10, the length of one side of the minute element is a. [M] The distance between the fixed
04-05-2019
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electrode 25 'and the movable electrode 35' in the initial state in which a prescribed DC bias
voltage is applied is g [m], and the fixed electrode 25 'of the movable electrode 35' from the
initial state The displacement amount of the movable electrode 35 'is x [m] when the
displacement direction toward the direction toward the direction is a positive direction, and the
displacement amount of the medium (air) existing in the space between the fixed electrode 25'
and the movable electrode 35 ' The capacitance of the microelement in the displacement state
where the dielectric constant is ε, the capacitance of the microelement in the initial state
(hereinafter also referred to as sensor capacitance) is C1 [F], and the displacement of the
movable electrode 35 'is x C1 Assuming that '[F], the capacitances C1 and C1' Following
Expression 3, represented by the number 4.
[0012]
[0013]
[0014]
From Equations 3 and 4 described above, the ratio of the sensor capacity fluctuation to the
sensor capacity is represented by the following Equation 5.
[0015]
[0016]
From the above-described Equations 3, 4 and 5, it can be seen that as the displacement amount x
becomes larger, the ratio of the sensor capacity fluctuation to the sensor capacity becomes
larger.
[0017]
By the way, in this type of electrostatic transducer, it is important to reduce the residual stress of
the movable plate portion to increase the compliance of the movable plate portion. There is
disclosed an electrostatic transducer in which residual stress of a movable plate portion is
reduced to increase compliance by supporting the support substrate via a plurality of arms
juxtaposed in the outer peripheral direction.
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JP-A 2004-506394 (paragraphs [0021]-[0022] and FIG. 1) JP-A-2005-535152 (paragraphs
[0015]-[0023] and FIG. 1-FIG. 2)
[0018]
However, in the case of using the electrostatic transducer 1 ′ having the configuration shown in
FIG. 9 disclosed in Patent Document 1 or the electrostatic transducer disclosed in Patent
Document 2 as an acoustic sensor, the size is further reduced. Although voltage sensitivity is
lower than commercially available electret condenser microphones, and miniaturization is limited
by desired voltage sensitivity, improvement in voltage sensitivity is desired.
Further, even when the above-described electrostatic transducer is used as a speaker,
improvement of the sound pressure of the sound wave to be output is desired in order to achieve
further miniaturization.
[0019]
The present invention has been made in view of the above-described problems, and an object
thereof is to provide an electrostatic transducer which can be miniaturized as compared with the
prior art.
[0020]
The invention of claim 1 includes a fixed plate portion and a movable plate portion opposed to
one surface side in the thickness direction of the fixed plate portion, and provided on the fixed
electrode and the movable plate portion provided on the fixed plate portion. The movable plate
portion is supported by the fixed plate portion via a spring structure portion displaceable in the
thickness direction of the fixed plate portion, and the fixed plate portion is And a hole
communicating with a space between the fixed plate and the movable plate is provided, and the
fixed electrode extends along the inner surface of the hole, and the movable plate is formed in
the hole of the fixed plate. A protrusion to be loosely inserted is provided, and the movable
electrode is extended to the protrusion.
[0021]
According to the present invention, since the movable plate portion is supported by the fixed
plate portion via the spring structure portion which can be displaced in the thickness direction of
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the fixed plate portion, the residual stress of the movable plate portion can be reduced and the
movable plate portion The fixed plate portion is provided with a hole communicating with the
space between the fixed plate portion and the movable plate portion, and the fixed electrode
extends along the inner surface of the hole portion. Since the movable plate portion is provided
with a protrusion which is loosely inserted into the hole portion of the fixed plate portion and the
movable electrode extends to the protrusion, the planar size of the fixed plate portion and the
movable plate portion is increased As to the capacitor formed between the fixed electrode and
the movable electrode, the capacitance can be increased, and the amount of change in
capacitance with respect to the displacement of the movable plate can be increased. It can be
miniaturized compared to the
[0022]
According to a second aspect of the present invention, in the first aspect of the present invention,
the spring structure portion is disposed in a plane perpendicular to the thickness direction so as
to surround the movable plate portion over the entire circumference, and formed in a corrugated
plate shape. It is characterized by being.
[0023]
According to the present invention, it is possible to form the spring structure at the same time as
the projection, and cost reduction can be achieved by simplification of the manufacturing
process.
[0024]
The invention according to claim 3 is characterized in that, in the invention according to claim 1
or 2, the hole portion is a through hole which is provided in the thickness direction of the fixing
plate portion.
[0025]
According to this invention, the space between the fixed plate portion and the movable plate
portion can be communicated with the space on the opposite side of the movable plate portion
side of the fixed plate portion through the hole portion. Since air can flow in the thickness
direction of the fixed plate portion, sensitivity characteristics in the case of using as an acoustic
sensor for high frequency, for example, can be improved, and output characteristics in the case
of using as a speaker for high frequency can be improved.
[0026]
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According to the first aspect of the present invention, there is an effect that downsizing can be
achieved as compared with the prior art.
[0027]
Embodiment 1 Hereinafter, an electrostatic transducer 1 of the present embodiment will be
described with reference to FIGS. 1 to 3.
[0028]
The electrostatic transducer 1 of the present embodiment includes a fixed plate portion 20, and a
movable plate portion 30 opposed to one surface side (upper surface side in FIG. 1A) of the fixed
plate portion 20 in the thickness direction. The capacitor is formed of the fixed electrode 25
provided on the fixed plate portion 20 and the movable electrode 35 provided on the movable
plate portion 30. For example, it can be used as an acoustic sensor, but other uses (For example,
it can be used as a speaker, a pressure sensor, etc.).
[0029]
Here, the electrostatic transducer 1 according to the present embodiment includes the support
substrate 10, the above-described fixed plate portion 20 formed on the one surface side of the
support substrate 10, and one surface side in the thickness direction of the fixed plate portion
20. And a movable plate portion 30 supported by the fixed plate portion 20 via a spring
structure portion 40 which is disposed so as to face each other and displaceable in the thickness
direction of the fixed plate portion 20, and the fixed plate portion 20 doubles as the fixed
electrode 25 described above The movable plate portion 30 doubles as the movable electrode 35
described above.
[0030]
Further, in the electrostatic transducer 1 according to the present embodiment, the fixed plate
portion 20 is provided with a plurality of holes 21 communicating with the space 60 between the
fixed plate portion 20 and the movable plate portion 30 and fixed. Since the plate 20 also serves
as the fixed electrode 25, the fixed electrode 25 extends along the inner surface of the hole 21.
Further, in the electrostatic transducer 1 of the present embodiment, a plurality of projections 31
loosely inserted one by one into the holes 21 of the fixed plate portion 20 are continuously and
integrally provided on the movable plate portion 30, and Since the movable plate portion 30
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doubles as the movable electrode 35 as in the above, the movable electrode 35 extends to the
protrusion 31.
In addition, the electrostatic transducer 1 of the present embodiment includes the pads 26 and
36 electrically connected to the fixed electrodes 25 and 35, respectively.
Therefore, the electrostatic transducer 1 of the present embodiment can electrically connect the
fixed electrode 25 and the movable electrode 35 to an external circuit provided on a circuit
board or the like via a bonding wire or the like.
[0031]
The supporting substrate 10 is configured of a silicon substrate 10 a and an insulating film 10 b
made of a silicon oxide film formed on the silicon substrate 10 a.
By the way, the holes 21 of the fixing plate portion 20 described above are penetrated in the
thickness direction, and in the supporting substrate 10, one opening portion 11 penetrating in
the thickness direction and communicating with each hole 21 of the fixing plate portion 20. Is
formed.
Here, the portion of the opening 11 formed on the silicon substrate 10 a is formed by anisotropic
etching using an alkaline solution (for example, an aqueous solution of TMAH, an aqueous
solution of KOH, etc.). The opening area gradually increases with distance.
The opening 11 may be formed by dry etching using, for example, an inductively coupled plasma
etching apparatus, and it may be other than the support substrate 10 as compared to the case
where the opening 11 is formed by anisotropic etching using an alkaline solution. Since the
opening area on the surface can be reduced, the planar size of the support substrate 10 can be
reduced.
Here, the outer peripheral shape of the support substrate 10 is rectangular.
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[0032]
The fixed plate portion 20 is formed of a polysilicon film to which conductivity is imparted by
doping an impurity (for example, boron or the like), and the impurity on the one surface side of
the support substrate 10 by using, for example, a CVD method. After forming a doped polysilicon
film, the above-mentioned hole 21 may be formed using photolithography technology and
etching technology.
Here, the fixing plate portion 20 is not limited to the polysilicon film, but may be made of an
amorphous silicon film to which conductivity is imparted by doping an impurity.
Further, in the present embodiment, the fixed plate portion 20 also serves as the fixed electrode
25. However, when the fixed plate portion 20 and the fixed electrode 25 are formed of different
materials, for example, the fixed plate portion 20 is non-doped The fixed electrode 25 may be
formed of a metal film (for example, a laminated film of a platinum film and a chromium thin
film), and in this case, the fixed electrode 25 may be formed of a polysilicon film, a non-doped
amorphous silicon film or a silicon nitride film. The fixed electrode 25 formed on one surface
side facing the movable plate portion 30 in the thickness direction of the fixed plate portion 20
may be extended to the inner surface of each hole 21.
In short, the fixed electrode 25 may be formed across the one surface of the fixed plate portion
20 and the inner surface of each hole 21.
Here, the material of the metal film constituting the fixed electrode 25 is not limited to platinum
or chromium, and for example, aluminum, nickel, titanium, tungsten, gold or the like may be
adopted.
Since it is desirable to increase the rigidity of the fixing plate portion 20, a silicon substrate
having a thickness of several hundred μm different from the above-mentioned silicon substrate
10a may be used to be bonded to the supporting substrate 10 .
[0033]
In the fixing plate portion 20, the opening shape of each hole 21 described above is a rectangular
shape (in the present embodiment, a square shape), and the plurality of holes 21 are arranged in
04-05-2019
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a two-dimensional array. The opening shape and the arrangement of the holes 21 are not
particularly limited, and the opening shape of the holes 21 may be, for example, polygonal (for
example, hexagonal) or circular.
[0034]
In the present embodiment, since the fixed plate portion 20 also serves as the fixed electrode 25
as described above, the above-described pad 26 electrically connected to the fixed electrode 25 is
formed on the fixed plate portion 20.
When the fixed plate portion 20 and the fixed electrode 25 are formed of materials different
from each other as described above, the fixed electrode 25 and the pad 26 may be appropriately
patterned through metal wiring in order to reduce parasitic capacitance. Electrical connection is
desirable.
[0035]
The movable plate portion 30 is formed of a polysilicon film to which conductivity is imparted by
doping an impurity (for example, boron or the like), and for example, using a film forming
technique such as a CVD method, a sacrificial layer etching technique, or the like. It should be
formed.
Here, the movable plate portion 30 is not limited to the polysilicon film, but may be made of an
amorphous silicon film to which conductivity is imparted by doping an impurity.
Further, in the present embodiment, the movable plate portion 30 doubles as the movable
electrode 35. However, in the case where the movable plate portion 30 and the movable
electrode 35 are formed of different materials, the movable plate portion 30 is, for example, nondoped The movable electrode 35 may be formed of a metal film (for example, a laminated film of
a platinum film and a chromium thin film), and in this case, the movable electrode 35 may be
formed of a polysilicon film, a non-doped amorphous silicon film or a silicon nitride film. The
movable electrode 35 formed on one surface side facing the fixed plate portion 20 in the
thickness direction of the movable plate portion 30 may be extended to the outer peripheral
surface of each protrusion 31.
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In short, the movable electrode 35 may be formed across the one surface of the movable plate
portion 30 and the outer peripheral surface of each protrusion 31.
Here, the material of the metal film constituting the movable electrode 35 is not limited to
platinum or chromium, and for example, aluminum, nickel, titanium, tungsten, gold or the like
may be adopted.
Although a silicon substrate different from the above-mentioned silicon substrate 10a may be
used as the movable plate portion 30, the movable plate portion 30 needs to be deformed by a
pressure difference on both sides in the thickness direction of the movable plate portion 30.
Therefore, it is desirable to reduce the thickness to reduce the rigidity.
[0036]
The protrusion 31 in the movable plate portion 30 is formed in a square pole shape whose cross
section orthogonal to the thickness direction of the movable plate portion 30 is rectangular (in
the present embodiment, square).
Here, when forming the polysilicon film for movable plate portion 30 on the one surface side of
fixed plate portion 20 via a sacrificial layer formed of, for example, a silicon oxide film or a
silicon nitride film, protrusion 31 is a sacrificial layer. Recesses corresponding to the respective
protrusions 31 are formed on the surface, and a polysilicon film can be formed on the surface
side of the sacrificial layer by the CVD method or the like.
The sacrificial layer may be etched through the openings 11 of the support substrate 10 and the
holes 21 of the fixed plate 20 after depositing the polysilicon film to be the movable plate 30. In
this embodiment, the sacrificial layer is used. The sacrificial layer is etched so as to leave a
portion of the insulating layer 50 as an insulating portion 50 interposed between the spring
structure 40 and the fixed plate 20.
Therefore, the distance between the fixed plate portion 20 and the movable plate portion 30 can
be defined by the thickness of the insulating portion 50. In addition, since the protrusion
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dimension of the protrusion 31 in the movable plate part 30 is set larger than the thickness
dimension of the insulation part 50, it corresponds to each protrusion 31 in the sacrificial layer
formation process of forming the above-mentioned sacrificial layer. For example, the support
substrate 10 before the opening 11 is formed so that the depth of the recess is larger than the
thickness of the portion of the sacrificial layer formed on the one surface of the fixed plate 20.
After the fixed plate portion 20 having the respective holes 21 is formed on the one surface side
of the above, a sacrificial layer made of a silicon oxide film may be formed by a film forming
method with low step coverage such as atmospheric pressure CVD. .
[0037]
Here, the protrusion dimension of the protrusion 31 of the movable plate portion 30 does not
necessarily have to be set larger than the thickness dimension of the insulating portion 50. For
example, the protrusion 31 is a hole due to deformation of the movable plate portion 30 due to
its own weight or residual stress. The protrusion 31 may be set so as to be loosely inserted in the
portion 21 or in a state in which a prescribed DC bias voltage is applied between the fixed
electrode 25 and the movable electrode 35 using the pads 26 and 36 described above. It may be
set to be loosely inserted in the hole 21.
[0038]
In addition, the shape of the protrusion 31 is not limited to the shape of a quadrangular prism,
for example, a polygonal prism (for example, hexagonal prism), a column, a pyramid, a cone, a
truncated pyramid, a truncated cone, or the like. The flat plate may have a thin plate shape (a
linear shape in plan view) as shown, or may have a thin plate shape (a curved shape in plan view)
which is curved as shown in FIG. You may form in the shape of a square pole which has a hollow
as shown to the figure (c).
However, the shape of the protrusion 31 needs to be formed in a shape corresponding to the
shape of the hole 21.
[0039]
By the way, the above-mentioned spring structure part 40 is a leaf spring which can be displaced
to the thickness direction of fixed board part 20, and outer periphery shape is continuously
formed integrally with movable board part 30 of circular shape. In short, in the present
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embodiment, four spring structures 40 are continuously and integrally formed on the movable
plate portion 30. Here, the four spring structure portions 40 are arranged to have rotational
symmetry with respect to the central axis along the thickness direction of the movable plate
portion 30, one end portion is connected to the movable plate portion 30, and the other The end
is connected with the above-mentioned insulating part 50. Here, after forming a polysilicon film
which is a basis of the spring structure portion 40 and the movable plate portion 30, the spring
structure portion 40 patterns the polysilicon film using a photolithography technique, an etching
technique, or the like. By doing so, the movable plate portion 40 can be formed at the same time,
so the dimensions and the planar shape may be designed to increase the compliance of the
spring structure portion 40. In the present embodiment, as described above, the movable plate
portion 30 is formed of the polysilicon film to which conductivity is imparted, and the spring
structure portion 40 is also formed of the polysilicon film to which conductivity is imparted. The
above-mentioned pad 36 is formed on a portion overlapping the insulating portion 50 at the
other end of the spring structure 40.
[0040]
Here, in order to simplify the description of the above-mentioned capacitor, it is considered as a
minute element having a square shape in plan view, and as shown in FIG. 3, the length of one
side of the minute element is a [m], The length of each side in the square cross section of the
portion 31 is b [m], the insertion dimension of the protrusion 31 into the hole 21 is c [m], and
the fixed electrode in the thickness direction of the fixed plate portion 20 in the initial state The
distance between the movable electrode 35 and the movable electrode 35 (hereinafter referred
to as the first gap length) is g [m], and the distance between the inner surface of the hole 21
facing each other and the outer surface of the projection 31 (hereinafter referred to as Let d [m]
be the second gap length), and x [m] be the displacement of the movable electrode 35 when the
displacement direction of the movable electrode 35 from the initial state toward the fixed
electrode 25 is positive. Of the medium (air) present in the space 60 between the fixed electrode
25 and the movable electrode 35 by ε Let Ccomb [F] be the capacitance of the microelement in
the initial state (hereinafter also referred to as sensor capacitance), and Ccomb '[F] be the
capacitance of the microelement when the displacement of the movable electrode 35 is x. The
electrostatic capacitances Ccomb and Ccomb 'are represented by the following equations 6 and
7, respectively.
[0041]
[0042]
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[0043]
From the above equations (6) and (7), the ratio of the sensor capacity fluctuation to the sensor
capacity is expressed by the following equation (8).
[0044]
[0045]
Here, as an example, the values of the respective parameters in the above equations 6 and 7 are,
for example, a = 10 × 10 <-6> [m], b = 2 × 10 <-6> [m], c = 1 Assuming that × 10 <-6> [m], d =
3 × 10 <-6> [m], g = 3 × 10 <-6> [m], x = 5 × 10 <-9> [m] The ratio of the sensor capacitance
fluctuation to the sensor capacitance is ΔCcomb / Ccomb = 0.00228.
[0046]
On the other hand, when the hole 21 and the protrusion 31 do not exist, the size of the minute
element is the same, and the value of each parameter in the above equations 3 and 4 is a = 10 ×
10 <-6> [m , G = 3 × 10 <-6> [m], x = 5 × 10 <-9> [m], the ratio of the sensor capacity
fluctuation to the sensor capacity is ΔC1 / C1 = 0.00167 .
[0047]
In short, in the electrostatic transducer 1 having the configuration according to the present
embodiment, the fixed plate portion 20 is provided with the hole 21 and the fixed electrode 25
extends along the inner surface of the hole 21 and protrudes from the movable plate 30
Regarding the capacitor formed between the fixed electrode 25 and the movable electrode 35 by
extending the movable electrode 35 to the protrusion 31 loosely inserted in the hole 21 of the
fixed plate portion 20, compared to the prior art, The capacitance can be increased, and the
amount of change in capacitance with respect to the amount of displacement of the movable
plate 30 can be increased, and the voltage sensitivity is improved. Therefore, the planar size (chip
size) can be reduced. be able to.
[0048]
In the above example, the first gap length g and the second gap length d are illustrated as being
in the relationship of g = d, but the relationship between both gap lengths g and d is such that g>
d. Design, a = 10 × 10 <-6> [m], b = 2 × 10 <-6> [m], c = 1 × 10 <-6> [m], g = 3 × 10 <-6
Assuming that> [m], d = 0.5 × 10 <-6> [m] and x = 5 × 10 <−9> [m]), ΔCcomb / Ccomb =
04-05-2019
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0.00282.
Therefore, in the electrostatic transducer 1 according to the present embodiment, by setting g> d,
the amount of change in capacitance with respect to the amount of displacement of the movable
plate portion 30 is greater than in the case where d = g is designed. It can be made large and the
voltage sensitivity can be further enhanced.
[0049]
In the electrostatic transducer 1 of the present embodiment described above, the movable plate
portion 30 is supported by the fixed plate portion 20 via the spring structure portion 40 which
can be displaced in the thickness direction of the fixed plate portion 20. The residual stress of the
plate portion 30 can be reduced to increase the compliance of the movable plate portion 30, and
the fixed plate portion 20 communicates with the space 60 between the fixed plate portion 20
and the movable plate portion 30. While the hole 21 is provided, the fixed electrode 25 extends
along the inner surface of the hole 21, and the movable plate 30 is provided with the protrusion
31 loosely inserted in the hole 21 of the fixed plate 20, and is movable Since the electrode 35
extends to the projection 31, the capacitor formed between the fixed electrode 25 and the
movable electrode 35 can be made quiet without increasing the planar size of the fixed plate
portion 20 and the movable plate portion 30. Increasing the capacitance As well as being able to
increase the amount of change in capacitance with respect to the amount of displacement of the
movable plate 30, it is possible to improve the sensitivity when used as an acoustic sensor or
pressure sensor, etc. When using as a speaker, output sound pressure Therefore, miniaturization
and cost reduction can be achieved as compared with the prior art.
[0050]
Further, in the electrostatic transducer 1 according to the present embodiment, since the hole 21
of the fixed plate 20 is a through hole penetrating in the thickness direction of the fixed plate 20,
the fixed plate 20 and the movable plate 30 The space 60 between them and the space on the
opposite side to the movable plate 30 side of the fixed plate 20 (in the present embodiment, the
opening 11 of the support substrate 10) can be communicated through the hole 21. Since the air
can flow in the thickness direction of the fixed plate portion 20, the hole 21 functions as an
acoustic hole, and the sensitivity characteristic can be improved when used as an acoustic sensor
for high frequency, for example, a speaker for high frequency Output characteristics when used
as
[0051]
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Here, in the case where the electrostatic transducer 1 of the present embodiment is used as a
speaker, if a drive voltage is applied between the fixed electrode 25 and the movable electrode
35 via the above-described pads 26 and 36, the fixed electrode 25 is obtained. Electrostatic force
(electrostatic attraction) acts between the movable electrode 35 and the movable plate portion
30 so as to displace the movable plate portion 30 in the direction toward the fixed plate portion
20. Therefore, the drive applied between the fixed electrode 25 and the movable electrode 35 By
changing the voltage, the movable plate portion 30 can be vibrated to output a sound wave.
When the electrostatic transducer 1 of the present embodiment is used as a speaker, the
electrostatic force F acting between the fixed electrode 25 and the movable electrode 35 is such
that the electrostatic energy between the fixed electrode 25 and the movable electrode 35 is U,
The electrostatic capacitance between the fixed electrode 25 and the movable electrode 35 is C
[F], the drive voltage applied between the fixed electrode 25 and the movable electrode 35 is V1
[V], and the movable plate portion 30 from the initial state. Assuming that the displacement
amount is x [m], it is expressed by the following equation 9.
[0052]
[0053]
Here, considering the above-mentioned minute element, the electrostatic force in the minute
element in a state where the movable plate portion 30 is displaced toward the fixed plate portion
20 along the thickness direction of the fixed plate portion 20 from the initial state Fcomb is
represented by the following equation 10 from the above equations 7 and 9.
[0054]
[0055]
On the other hand, when the hole 21 and the protrusion 31 do not exist, the size of the minute
element is the same, and from the initial state, the movable plate portion 30 moves to the fixed
plate portion 20 side along the thickness direction The electrostatic force F1 in the microelement
in the state of being displaced by x [m] is represented by the following equation 11 from the
above equations 4 and 10.
[0056]
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[0057]
Here, as an example, the values of the parameters of the above equations 10 and 11 can be
expressed as a = 6 × 10 <-6> [m], b = 2 × 10 <-6> [m], d = 1 × 10 < Assuming that −6> [m]
and g = 4 × 10 <−6> [m], Fcomb / F1 = Fcomb / F1 = in the initial state (that is, x = 0 [m]) in
terms of the electrostatic force acting on the microelements. It becomes 2.76.
Therefore, in the electrostatic transducer 1 of the present embodiment, when the drive voltage
V1 [V] is applied between the fixed electrode 25 and the movable electrode 35, the static
electricity acting between the fixed electrode 25 and the movable electrode 35 The power can be
increased compared to the conventional case, and the output sound pressure can be improved.
[0058]
By the way, in the electrostatic transducer 1 of the present embodiment, as described above, the
fixed plate portion 20 doubles as the fixed electrode 25, and the movable plate portion 30
doubles as the movable electrode 35. For example, as shown in FIG. 5A, the insulating film 80
may be formed over the entire surface of the movable plate 30 on the side of the fixed plate 20
as shown in FIG. The insulating film 80 may be formed on one surface of the fixed plate portion
20 on the periphery of the movable plate portion 30 as shown in FIG. 7B, or the fixed plate
portion 20 as shown in FIG. An insulating film 80 may be formed on the inner side surface of the
hole 21 in FIG.
The insulating film 80 in FIGS. 5A to 5C can also have a function as a stopper that regulates
excessive displacement of the movable plate portion 30 by appropriately setting the thickness
dimension.
[0059]
Second Embodiment The basic configuration of the electrostatic transducer 1 of the present
embodiment is substantially the same as that of the first embodiment, and as shown in FIG. 6, the
fixed plate 20 is provided on each side of the movable plate 30 in the thickness direction. Are
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opposed to each other, and the projecting portions 31 are provided to project from both sides in
the thickness direction of the movable plate portion 30.
In addition, the same code | symbol is attached | subjected to the component similar to
Embodiment 1, and description is abbreviate | omitted.
[0060]
The electrostatic transducer 1 according to this embodiment includes a fixed electrode
(hereinafter referred to as a first fixed electrode) 25 provided on the upper fixed plate portion 20
in FIG. 6 and a movable electrode 35 provided on the movable plate portion 30. , A fixed
electrode (hereinafter referred to as a second fixed electrode) 25 provided on the lower fixed
plate portion 20 in the same figure, and a movable electrode 35 provided on the movable plate
portion 30. And the movable capacitor 30 is displaced in the thickness direction to change the
distance between the first fixed electrode 25 and the movable electrode 35 in the thickness
direction of the movable plate 30. Then, the capacitance of the first capacitor is changed, and the
distance between the second fixed electrode 25 and the movable electrode 35 is changed, and
the capacitance of the second capacitor is changed.
Here, in the case where the electrostatic transducer 1 of the present embodiment is used as, for
example, an acoustic sensor, in order to convert the capacitance change of each of the first
capacitor and the second capacitor into an electric signal and take it out, Apply a bias voltage to
each of the capacitors.
[0061]
In the electrostatic transducer 1 of the present embodiment, when the movable plate portion 30
receives a sound wave and vibrates, the electrical signal extracted from the first capacitor and the
electrical signal extracted from the second capacitor are in opposite phase to each other.
Therefore, if a differential amplifier circuit that takes the difference between the respective
electric signals is provided in the subsequent stage, the electric signal (voltage) output to the
sound wave becomes large, and the sensitivity is improved.
Further, since the electrostatic transducer 1 of the present embodiment can receive sound waves
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from both sides in the thickness direction of the movable plate portion 30, it can be used as a socalled acoustic sensor having bi-directionality.
[0062]
Third Embodiment The basic configuration of the electrostatic transducer 1 of the present
embodiment is substantially the same as that of the first embodiment, and as shown in FIG. 7, the
movable plate 30 is provided on each side of the fixed plate 20 in the thickness direction. Are
opposite to each other.
In addition, the same code | symbol is attached | subjected to the component similar to
Embodiment 1, and description is abbreviate | omitted.
[0063]
The electrostatic transducer 1 according to the present embodiment is fixed to a movable
electrode (hereinafter referred to as a first movable electrode) 35 provided on the upper movable
plate portion (hereinafter referred to as a first movable plate portion) 30 in FIG. A first capacitor
constituted by the fixed electrode 25 provided on the plate portion 20, and a movable electrode
provided on the lower movable plate portion (hereinafter referred to as a second movable plate
portion) 30 in the figure , And the second capacitor constituted by the fixed electrode 25
provided on the fixed plate portion 20, when the first movable plate portion 30 is displaced in
the thickness direction. The distance between the fixed electrode 25 and the first movable
electrode 35 changes in the thickness direction of the fixed electrode 25 to change the
capacitance of the first capacitor, while the second movable plate 30 is in the thickness direction.
In the thickness direction of the fixed electrode 25 Capacitance of the second capacitor is varied
by changing the distance between the 25 and the second movable electrode 35.
[0064]
Here, in the case where the electrostatic transducer 1 of the present embodiment is used as, for
example, an acoustic sensor, in order to convert the capacitance change of each of the first
capacitor and the second capacitor into an electric signal and take it out, If a bias voltage is
applied to each of the capacitors, the first movable plate portion 30 and the second movable
plate portion 30 can receive the sound waves, convert the respective sound waves into electric
signals, and output them. It can be used as a so-called bi-directional acoustic sensor.
04-05-2019
19
[0065]
(Fourth Embodiment) The basic configuration of the electrostatic transducer 1 of the present
embodiment is substantially the same as that of the first embodiment, and as shown in FIG. 8, a
fixing plate portion 20 is formed using a silicon substrate, The thickness dimension of the fixed
plate portion 20 is larger than that of the first embodiment, and the depth dimension of the hole
portion 21 provided in the fixed plate portion 20 so as to communicate with the space 60
between the fixed plate portion 20 and the movable plate portion 30 is The point is smaller than
the thickness dimension of the fixing plate portion 20, the shape of the spring structure portion
40, and the like are different.
In addition, the same code | symbol is attached | subjected to the component similar to
Embodiment 1, and description is abbreviate | omitted.
[0066]
The fixed plate portion 20 forms the fixed electrode 25 by doping the portion on the movable
plate portion 30 side with a high concentration of impurities (for example, boron) to impart
conductivity, but the fixed electrode 25 is made of metal. It may be formed of a film.
[0067]
The spring structure portion 40 is disposed so as to surround the entire periphery of the
movable plate portion 30 in a plane orthogonal to the thickness direction of the fixed plate
portion 20, is formed in a corrugated plate shape, and has a high compliance structure. ing.
Here, the spring structure 40 is formed continuously and integrally with the movable plate 30.
In the present embodiment, the insulating portion 50 is formed in a ring shape.
[0068]
By the way, in order to prevent interference of the spring structure 40, a plurality of annular
04-05-2019
20
escape recesses 22 are formed on the surface of the fixed plate 20 on the movable plate 30 side,
and the spring structure 40 is formed of the fixed plate 20 can be prevented from colliding or
being absorbed.
Here, the opening width (width dimension) of the relief recess 22 is set larger than the opening
width of the hole 21.
[0069]
Therefore, after forming the sacrificial layer on the surface side of the fixed plate portion 20
where the hole 21 and the relief recess 22 are formed in forming the above-described spring
structure portion 40, the movable plate portion is formed on the surface side of the sacrificial
layer. If a manufacturing process is employed in which a polysilicon film to be the basis of the
structure 30 and the spring structure 40 is formed and then an unnecessary portion of the
sacrificial layer is etched away, the spring structure 40 is formed simultaneously with the
protrusion 31. It is possible to reduce costs by simplifying the manufacturing process.
The spring structure 40 in the embodiment may be applied to the other embodiments 1 to 3.
[0070]
Further, in the electrostatic transducer 1 according to the present embodiment, the holes 21 of
the fixed plate 20 do not penetrate in the thickness direction of the fixed plate 20, so the holes in
the fixed plate 20 as described above are produced during manufacture. After forming a
sacrificial layer on the surface side where the portion 21 and the relief concave portion 22 are
formed, a polysilicon film to be a basis of the movable plate portion 30 and the spring structure
portion 40 is formed on the surface side of the sacrificial layer In order to adopt the
manufacturing process of etching away the unnecessary portion of the sacrificial layer, a
plurality of fine holes 37 penetrating in the thickness direction of the movable plate portion 30
in the movable plate portion 30 after forming the polysilicon film. An etchant for etching the
sacrificial layer is introduced from the fine holes 37, as shown in FIG. 8 (a).
Further, in order to make the space 60 between the fixed plate portion 25 and the movable plate
portion 35 an airtight space, sealing is performed to close each micro hole 37 on the surface side
04-05-2019
21
of the movable plate portion 30 opposite to the fixed plate portion 20 side. A section 38 is
provided.
When using a manufacturing process in which the movable plate portion 30 and the fixed plate
portion 20 formed by processing different silicon substrates individually are joined without using
the sacrificial layer etching technology, fine holes are used. 37 and the seal 38 are unnecessary.
The inside of the space 60 may be, for example, an inert gas atmosphere or a vacuum
atmosphere.
[0071]
Therefore, when using the electrostatic transducer 1 of the present embodiment as a pressure
sensor, when the movable plate portion 30 receives pressure, the movable plate portion 30 is
displaced according to the pressure difference between both sides in the thickness direction of
the movable plate portion 30. The capacitance between the fixed electrode 25 and the movable
electrode 35 changes.
[0072]
In the electrostatic transducer 1 of the present embodiment described above, the movable plate
portion 30 is supported by the fixed plate portion 20 via the spring structure portion 40
displaceable in the thickness direction of the fixed plate portion 20 as in the first embodiment.
Since the residual stress of the movable plate portion 30 can be reduced and the compliance of
the movable plate portion 30 can be increased, the fixed plate portion 20 can be formed between
the fixed plate portion 20 and the movable plate portion 30. The fixed electrode 25 extends
along the inner surface of the hole 21 and the movable plate 30 is a protrusion that is loosely
inserted in the hole 21 of the fixed plate 20. Since 31 is provided and the movable electrode 35
is extended to the protrusion 31, it is formed between the fixed electrode 25 and the movable
electrode 35 without increasing the planar size of the fixed plate portion 20 and the movable
plate portion 30. Capacitance with regard to the When it is used as an acoustic sensor or a
pressure sensor, sensitivity can be improved, and when it is used as a speaker. In addition, since
the output sound pressure can be improved, downsizing and cost reduction can be achieved as
compared with the prior art.
[0073]
Further, in the electrostatic transducer 1 according to the present embodiment, since the space
60 between the fixed plate portion 20 and the movable plate portion 30 is an airtight space,
04-05-2019
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foreign matter, moisture, and the like may enter the space 60 from the outside. This can prevent
the short circuit between the fixed electrode 25 and the movable plate portion 35, the operation
failure of the movable plate portion 30, and the change of the vibration characteristic, so that the
reliability can be improved.
[0074]
Of course, in the second to fourth embodiments, the insulating film 80 described in FIGS. 5A to
5C may be provided.
[0075]
1st Embodiment is shown, (a) is a schematic sectional drawing, (b) is the schematic perspective
view which fractured partially.
It is the schematic perspective view which showed the principal part in the same as the above,
and was partially broken.
FIG.
It is explanatory drawing of the other structural example of the principal part in same as the
above.
It is explanatory drawing of the other structural example of the principal part in same as the
above.
5 is a schematic cross-sectional view showing Embodiment 2. FIG.
FIG. 10 is a schematic cross-sectional view showing Embodiment 3. The Embodiment 4 is shown,
(a) is a schematic sectional drawing, (b) is the principal part schematic perspective view which
fractured | ruptured partially. It is a schematic sectional drawing which shows a prior art
example. FIG.
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Explanation of sign
[0076]
DESCRIPTION OF SYMBOLS 1 electrostatic transducer 10 support substrate 11 aperture part 20
fixed plate part 21 hole part 25 fixed electrode 30 movable plate part 31 protrusion 35 movable
electrode 40 spring structure part 50 insulation part 60 space
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