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JP2006270157

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2006270157
PROBLEM TO BE SOLVED: To provide an ultrasonic transducer and a method of manufacturing
an ultrasonic transducer in which the manufacturing process is shortened. SOLUTION: A first
fixed electrode 10A in which a plurality of through holes 14 are formed, a second fixed electrode
10B in which a plurality of through holes 14 paired with the first fixed electrode 10A are formed,
and a pair of Vibrating film 12 held between fixed electrodes 10A and 10B and having
conductive layer 121 to which a DC bias voltage is applied to the conductive layer 121, and a
member for holding the pair of fixed electrodes 10A and 10B and vibrating film 12 And the
plurality of through holes 14 formed in the second fixed electrode 10B are all or at positions
opposed to the plurality of through holes 14 formed in the first fixed electrode 10A with the
vibrating membrane 12 interposed therebetween. It is an ultrasonic transducer in which many
are formed and an alternating current signal is applied between a pair of fixed electrodes 10A
and 10B, and the diaphragm sandwiching portion 101 of the pair of fixed electrodes sandwiching
the diaphragm is formed of an insulating material Do. [Selected figure] Figure 1
Ultrasonic transducer and method of manufacturing the same
[0001]
The present invention relates to an electrostatic ultrasonic transducer that generates constant
high sound pressure over a wide frequency band and a method of manufacturing the same.
[0002]
Conventional ultrasonic transducers are mostly resonant type using piezoelectric ceramic.
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Here, the configuration of a conventional ultrasonic transducer is shown in FIG. Conventional
ultrasonic transducers are mostly resonant type using piezoelectric ceramic as a vibrating
element. The ultrasonic transducer shown in FIG. 8 uses piezoelectric ceramic as a vibrating
element to perform both conversion from an electrical signal to ultrasonic waves and conversion
from ultrasonic waves to electrical signals (transmission and reception of ultrasonic waves). The
bimorph ultrasonic transducer shown in FIG. 8 is composed of two piezoelectric ceramics 61 and
62, a cone 63, a case 64, leads 65 and 66, and a screen 67.
[0003]
The piezoelectric ceramics 61 and 62 are bonded to each other, and the lead 65 and the lead 66
are connected to the surface opposite to the bonding surface, respectively. Since the resonance
type ultrasonic transducer utilizes the resonance phenomenon of piezoelectric ceramic, the
transmission and reception characteristics of the ultrasonic wave become good in a relatively
narrow frequency band around the resonance frequency.
[0004]
Unlike the resonance type ultrasonic transducer shown in FIG. 8 described above, the
electrostatic type ultrasonic transducer is conventionally known as a broadband oscillation type
ultrasonic transducer capable of generating high sound pressure over a high frequency band.
This electrostatic ultrasonic transducer is called a pull type because it works only in the direction
in which the vibrating membrane is attracted to the fixed electrode. FIG. 9 shows a specific
configuration of the broadband oscillation type ultrasonic transducer (Pull type).
[0005]
The ultrasonic transducer of the electrostatic type shown in FIG. 9 uses a dielectric 131
(insulator) such as PET (polyethylene terephthalate resin) having a thickness of about 3 to 10
μm as a vibrator. For the dielectric 131, the upper electrode 132 formed as a metal foil such as
aluminum is integrally formed on the upper surface thereof by a process such as evaporation,
and the lower electrode 133 formed of brass is the lower surface of the dielectric 131 It is
provided to contact the part. The lower electrode 133 is connected to the lead 152 and fixed to a
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base plate 135 made of Bakelite or the like.
[0006]
Further, a lead 153 is connected to the upper electrode 132, and the lead 153 is connected to a
DC bias power supply 150. A DC bias voltage for attracting the upper electrode of about 50 to
150 V is constantly applied to the upper electrode 132 by the DC bias power supply 150 so that
the upper electrode 132 is attracted to the lower electrode 133 side. 151 is a signal source.
[0007]
The dielectric 131 and the upper electrode 132 and the base plate 135 are crimped by the case
130 together with the metal rings 136, 137 and 138 and the mesh 139. On the surface of the
lower electrode 133 on the side of the dielectric 131, a plurality of microgrooves of
approximately several tens to several hundreds of μm having an uneven shape are formed. Since
this minute groove serves as an air gap between the lower electrode 133 and the dielectric 131,
the distribution of capacitance between the upper electrode 132 and the lower electrode 133
changes minutely.
[0008]
The random minute grooves are formed by manually roughening the surface of the lower
electrode 133 with a file. In the electrostatic ultrasonic transducer, the frequency characteristics
of the ultrasonic transducer shown in FIG. 9 are as shown by curve Q1 in FIG. 10 by thus forming
an infinite number of capacitors having different sizes and depths of the air gaps. It is broadband.
[0009]
In the ultrasonic transducer configured as described above, a rectangular wave signal (50 to 150
Vp-p) is applied between the upper electrode 12 and the lower electrode 133 in a state where a
DC bias voltage is applied to the upper electrode 132. There is. Incidentally, as shown by a curve
Q1 in FIG. 10, the frequency characteristic of the resonance type ultrasonic transducer has a
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center frequency (resonance frequency of the piezoelectric ceramic) of, for example, 40 kHz, ± 5
kHz with respect to the center frequency which is the maximum sound pressure. At a frequency
of -30 dB relative to the maximum sound pressure. On the other hand, the frequency
characteristic of the broadband oscillation type ultrasonic transducer of the above configuration
is flat from 40 kHz to 100 kHz, and is about ± 6 dB at 100 kHz as compared to the maximum
sound pressure (see Patent Documents 1 and 2) . Japanese Patent Laid-Open No. 2000-50387
Japanese Patent Laid-Open No. 2000-50392
[0010]
As described above, unlike the resonant ultrasonic transducer shown in FIG. 8, the electrostatic
ultrasonic transducer shown in FIG. 9 can generate a relatively high sound pressure over a wide
frequency band conventionally. It is known as a broadband ultrasound transducer (Pull type).
However, as shown in FIG. 10, the sound pressure of the electrostatic ultrasonic transducer is as
low as 120 dB or less, as shown in FIG. 10, compared with the resonance ultrasonic transducer of
130 dB or more (curve Q2). The sound pressure was a bit short to use as an ultrasonic speaker.
[0011]
Here, the ultrasonic speaker will be described. An ultrasonic wave is modulated by an audio
signal of a signal source by AM-modulating a signal in an ultrasonic frequency band called a
carrier wave with an audio signal (a signal in an audible frequency band) and driving an
ultrasonic transducer with this modulation signal. The sound waves of the state are emitted into
the air, and the non-linearity of the air causes the original audio signal to self-reproduce in the
air.
[0012]
That is, since the sound wave is a compression wave propagating through the air as a medium, in
the process of propagation of the modulated ultrasonic wave, the dense part and the sparse part
of the air appear prominently. As the speed of sound is slowed, the modulation wave itself is
distorted, so that the waveform is separated into the carrier wave (ultrasonic wave) and the audio
wave (original audio signal), and we human beings the audible sound below 20 kHz (original
audio signal) The principle is that you can hear only, and is generally called parametric array
effect.
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[0013]
Although ultrasonic sound pressure of 120 dB or more is necessary for the above-mentioned
parametric effect to fully appear, it is difficult to achieve this value with electrostatic ultrasonic
transducers, and ceramic piezoelectric elements such as PZT and PVDF, etc. are exclusively used.
Polymer piezoelectric elements have been used as ultrasound transmitters.
However, since the piezoelectric element has a sharp resonance point regardless of the material
and is driven at the resonance frequency and put into practical use as an ultrasonic speaker, the
frequency range where high sound pressure can be secured is extremely narrow. That is, it can
be said that it is a narrow band.
[0014]
Generally, the maximum audio frequency band of human beings is said to be 20 Hz to 20 kHz,
and has a band of about 20 kHz. That is, in the ultrasonic speaker, it is impossible to faithfully
demodulate the original audio signal unless a high sound pressure is secured over the 20 kHz
frequency band in the ultrasonic region. It will be easily understood that it is difficult to faithfully
reproduce (demodulate) this wide band of 20 kHz at the very bottom of a conventional resonance
type ultrasonic speaker using a piezoelectric element.
[0015]
In fact, in the ultrasonic speaker using the conventional resonance type ultrasonic transducer, (1)
the band is narrow and the reproduction sound quality is bad, (2) if the AM modulation degree is
too large, the demodulation sound is distorted, so the maximum is only about 0.5. (3) When the
input voltage is raised (when the volume is raised), the vibration of the piezoelectric element
becomes unstable and the sound breaks. When the voltage is further increased, the piezoelectric
elements themselves are easily broken. (4) It is difficult to achieve array formation, upsizing,
downsizing, and thus cost increase.
[0016]
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On the other hand, the ultrasonic speaker using the electrostatic ultrasonic transducer (Pull type)
shown in FIG. 9 can almost solve the problems of the above-mentioned prior art, but it can cover
a wide band but the demodulation sound is sufficient. There was a problem that the absolute
sound pressure was insufficient to achieve a good volume. Further, in the Pull-type ultrasonic
transducer, the electrostatic force works only in the direction of attracting the electrode to the
fixed electrode side, which corresponds to a vibrating film (corresponding to the upper electrode
132 in FIG. 10). When used in an ultrasonic speaker, there is a problem that the vibration of the
vibrating membrane directly generates an audible sound, since the symmetry of the vibration of
(a) is not maintained.
[0017]
On the other hand, in order to solve the above problem, we (the present inventors) have already
proposed an ultrasonic transducer of a structure (push-pull type) shown in FIG. However, the
method of manufacturing this push-pull ultrasonic transducer has not been studied yet.
[0018]
The present invention has been made in view of such circumstances, and it is an object of the
present invention to provide an ultrasonic transducer in which the manufacturing process is
shortened and a method of manufacturing the same.
[0019]
In order to achieve the above object, according to an ultrasonic transducer of the present
invention, a first fixed electrode in which a plurality of through holes are formed, and a second in
which a plurality of through holes paired with the first fixed electrode are formed. A vibrating
membrane held between the pair of fixed electrodes, having a conductive layer, to which a DC
bias voltage is applied to the conductive layer, and a member for holding the pair of fixed
electrodes and the vibrating membrane, And the plurality of through holes formed in the second
fixed electrode are all or most formed at positions opposed to the plurality of through holes
formed in the first fixed electrode via the vibrating membrane. An ultrasonic transducer to which
an alternating current signal is applied between the pair of fixed electrodes, wherein the
diaphragm sandwiching portion in the pair of fixed electrodes sandwiching the diaphragm is
formed of an insulating material. .
[0020]
In the ultrasonic transducer according to the present invention having the above configuration, a
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plurality of through holes are formed at positions facing the first fixed electrode and the second
fixed electrode, and a DC bias voltage is applied to the conductive layer of the diaphragm. In the
state, since an AC signal which is a drive signal is applied to the pair of fixed electrodes
consisting of the first and second fixed electrodes, the vibrating film sandwiched between the
pair of fixed electrodes is in accordance with the polarity of the AC signal. In the direction, the
electrostatic attraction force and the electrostatic repulsion force are simultaneously received in
the same direction, so that not only the vibration of the vibrating membrane can be made large
enough to obtain a parametric effect, but also the symmetry of the vibration is ensured. High
sound pressure can be generated over a wide frequency band.
[0021]
Further, since the diaphragm sandwiching portion in the pair of fixed electrodes sandwiching the
diaphragm is formed of an insulating material, the thickness of the insulating layer is increased
by the diaphragm sandwiching portion (for example, several μm to several tens of μm) As a
result, even a thin film of 10 μm or less as a vibrating membrane can be used with high voltage
without any problem, and the effect of expanding the selection range of the thickness of the
vibrating membrane can be obtained.
Further, since the diaphragm sandwiching portion of the pair of fixed electrodes sandwiching the
diaphragm is formed of an insulating material, a state occurs in which the edge of the diaphragm
sandwiching portion of the fixed electrode bites deeply into the insulating layer in the
manufacturing process. However, the thickness of the insulating layer is added to the thickness
of the insulating layer of the vibrating film by the thickness of the vibrating film pinching portion
in the fixed electrode, so that the dielectric breakdown due to the breakage of the vibrating film
is avoided effective.
[0022]
In addition, even when a part of the diaphragm sandwiching portion in the fixed electrode
completely contacts the conductive layer of the diaphragm, or completely breaks the diaphragm
and contacts the fixed electrode on the opposite side, the conductive parts contact with each
other. It is possible to completely prevent the decrease in insulation strength and the occurrence
of short circuit due to the structural distortion of the fixed electrode.
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Furthermore, compared to the case where the fixed electrodes are all made of a conductive
material as in the prior art, when the vibrating film sandwiching portion is made of a
nonconductive material, only the capacitance is changed without changing the electrostatic force
acting on the vibrating electrode film at all. Can be reduced, and energy efficiency can be
improved by reducing the capacitance.
[0023]
In the ultrasonic transducer according to the present invention, the insulating material is any of a
liquid solder resist, a photosensitive film, a photosensitive coating material, a nonconductive
paint, and an electrodeposition material.
In the ultrasonic transducer according to the present invention having the above configuration,
any one of a liquid solder resist, a photosensitive film, a photosensitive coating material, a
nonconductive paint, and an electrodeposition material is used as an insulating material for
forming the vibrating film sandwiching portion in the fixed electrode. Since it is used, the
vibrating film pinching portion in the fixed electrode can be formed as a permanent structure.
[0024]
Further, in the method of manufacturing an ultrasonic transducer according to the present
invention, a first fixed electrode having a plurality of through holes formed therein, and a second
fixed member having a plurality of through holes forming a pair with the first fixed electrode are
formed. It has an electrode, a vibrating film sandwiched between the pair of fixed electrodes,
having a conductive layer, to which a DC bias voltage is applied to the conductive layer, and a
member for holding the pair of fixed electrodes and the vibrating film The plurality of through
holes formed in the second fixed electrode are all or most formed at positions opposed to the
plurality of through holes formed in the first fixed electrode via the vibrating film, A method of
manufacturing an ultrasonic transducer in which an alternating current signal is applied between
the pair of fixed electrodes, wherein the vibrating film sandwiching portion in the fixed electrode
sandwiching the vibrating film is formed of an insulating material by photolithography. I assume.
[0025]
In the ultrasonic transducer manufactured by the method of manufacturing an ultrasonic
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transducer according to the present invention having the above-described configuration, a
plurality of through holes are formed at positions facing the first fixed electrode and the second
fixed electrode. In a state in which a DC bias voltage is applied to the conductive layer, an
alternating current signal, which is a drive signal, is applied to the pair of fixed electrodes
consisting of the first and second fixed electrodes. The film can not only make the vibration of
the vibrating film sufficiently large to obtain a parametric effect, because the electrostatic
attraction and electrostatic repulsion are simultaneously received in the same direction in the
direction according to the polarity of the AC signal. Since the symmetry of vibration is ensured,
high sound pressure can be generated over a wide frequency band.
Further, in the method of manufacturing an ultrasonic transducer according to the present
invention having the above-described configuration, the vibrating film sandwiching portion in the
fixed electrode sandwiching the vibrating film is formed of an insulating material by
photolithography. Since the process after metal electroforming can be omitted, the
manufacturing process can be shortened and the manufacturing cost can be reduced. In addition,
the solvent (mainly a strong alkali solvent) used in the peeling process of the residual resist is not
necessary, and the environment can be improved.
[0026]
In the method of manufacturing an ultrasonic transducer according to the present invention, a
mask member in which a pattern of a plurality of through holes is formed on a conductor plate of
a predetermined thickness for forming a fixed electrode portion of the pair of fixed electrodes is
covered. And a first step of forming a plurality of through holes in the conductor plate by
etching, and a conductor plate having a plurality of through holes formed in the first step. A
second step of forming a conductive photosensitive resist to a predetermined thickness, and a
mask member for forming a diaphragm holding portion in which a pattern of the diaphragm
holding portion is formed on the surface of the nonconductive photosensitive resist It has a third
step of covering and exposing, and a fourth step of peeling the mask member for forming a
diaphragm sandwiching portion and removing an unnecessary photosensitive resist by
development.
[0027]
In the method of manufacturing an ultrasonic transducer according to the present invention
having the above configuration, a mask member in which a pattern of a plurality of through holes
is formed on a conductor plate of a predetermined thickness for forming a fixed electrode
portion of a pair of fixed electrodes A first step of coating and forming a plurality of through
04-05-2019
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holes in the conductor plate by etching treatment, and a conductor forming plate in which a
plurality of through holes are formed in the first step A second step of forming a nonconductive
photosensitive resist to a predetermined thickness, and a mask member for forming a diaphragm
holding portion having the pattern of the diaphragm holding portion formed on the surface of
the nonconductive photosensitive resist And the fourth step of peeling the mask member for
forming the vibrating film sandwiching portion and removing the unnecessary photosensitive
resist by development, which is conventionally required. Process after metal electroforming
Manufacturing process is shortened since it in principal, and the manufacturing cost can be
reduced.
In addition, the solvent (mainly a strong alkali solvent) used in the peeling process of the residual
resist is not necessary, and the environment can be improved.
[0028]
In the method of manufacturing an ultrasonic transducer according to the present invention, the
photosensitive resist is a photosensitive film or a photosensitive coating material.
[0029]
Further, in the method of manufacturing an ultrasonic transducer according to the present
invention, a first fixed electrode having a plurality of through holes formed therein, and a second
fixed member having a plurality of through holes forming a pair with the first fixed electrode are
formed. It has an electrode, a vibrating film sandwiched between the pair of fixed electrodes,
having a conductive layer, to which a DC bias voltage is applied to the conductive layer, and a
member for holding the pair of fixed electrodes and the vibrating film The plurality of through
holes formed in the second fixed electrode are all or most formed at positions opposed to the
plurality of through holes formed in the first fixed electrode via the vibrating film, A method of
manufacturing an ultrasonic transducer in which an alternating current signal is applied between
the pair of fixed electrodes, wherein the vibrating film sandwiching portion in the fixed electrode
sandwiching the vibrating film is formed of an insulating material by a screen printing method. I
assume.
[0030]
In the ultrasonic transducer manufactured by the method of manufacturing an ultrasonic
transducer according to the present invention having the above-described configuration, a
plurality of through holes are formed at positions facing the first fixed electrode and the second
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fixed electrode. In a state in which a DC bias voltage is applied to the conductive layer, an
alternating current signal, which is a drive signal, is applied to the pair of fixed electrodes
consisting of the first and second fixed electrodes. The film can not only make the vibration of
the vibrating film sufficiently large to obtain a parametric effect, because the electrostatic
attraction and electrostatic repulsion are simultaneously received in the same direction in the
direction according to the polarity of the AC signal. Since the symmetry of vibration is ensured,
high sound pressure can be generated over a wide frequency band.
Further, in the method of manufacturing an ultrasonic transducer according to the present
invention having the above configuration, the diaphragm sandwiching portion in the fixed
electrode sandwiching the diaphragm is formed of the insulating material by the screen printing
method. Since the process after metal electroforming can be made unnecessary and the process
such as the development performed by the photolithography method is not required at all, the
manufacturing process can be greatly shortened and the manufacturing cost can be significantly
reduced.
[0031]
In the method of manufacturing an ultrasonic transducer according to the present invention, a
mask member in which a pattern of a plurality of through holes is formed on a conductor plate of
a predetermined thickness for forming a fixed electrode portion of the pair of fixed electrodes is
covered. And forming the vibrating film sandwiching portion on the surface of the conductor
plate on which the plurality of through holes are formed in the first step of forming the plurality
of through holes in the conductor plate by the etching process. Step of setting a screen printing
plate in which mask members are arranged and a liquid vibrating film holding portion forming
material, and the screen printing plate and liquid on the surface of the conductor plate on which
the plurality of through holes are formed A third step of applying the vibrating membrane
pinching portion forming material to a portion not covered with the mask member while moving
the squeegee after setting the vibrating membrane pinching portion forming material, and the
vibrating membrane pinching portion forming member trout After coating the portion member is
not applied, removing the screen printing plate, and having a fourth step of drying the oscillation
Makukyo sandwiching member forming material remaining on the conductive plate surface.
[0032]
In the method of manufacturing an ultrasonic transducer according to the present invention
having the above configuration, a mask member having a pattern of a plurality of through holes
formed on a conductor plate of a predetermined thickness for forming a fixed electrode portion
of the pair of fixed electrodes. And forming the plurality of through holes in the conductor plate
by etching, and the vibrating film pinching portion on the surface of the conductor plate on
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which the plurality of through holes are formed in the first step. A screen printing plate in which
mask members to be formed are arranged, a second step of setting the liquid diaphragm film
forming portion forming material, and the screen printing on the surface of the conductor plate
on which the plurality of through holes are formed After setting the plate and the liquid, a third
step of applying the vibrating membrane holding portion forming member to a portion where the
mask member is not applied while moving the squeegee, and the vibrating membrane holding
portion forming material as the mask member After the application to the non-applied portion,
the screen printing plate is removed, and the fourth step of drying the vibrating membrane
sandwiching portion forming material remaining on the surface of the conductive plate is
provided. Since the subsequent steps can be omitted and the steps of development by
photolithography are not required at all, the manufacturing process can be greatly shortened and
the manufacturing cost can be significantly reduced.
[0033]
Further, in the method of manufacturing an ultrasonic transducer according to the present
invention, the material for forming the diaphragm sandwiching portion in a liquid state is a liquid
solder resist.
[0034]
Further, in the method of manufacturing an ultrasonic transducer according to the present
invention, a first fixed electrode having a plurality of through holes formed therein, and a second
fixed member having a plurality of through holes forming a pair with the first fixed electrode are
formed. It has an electrode, a vibrating film sandwiched between the pair of fixed electrodes,
having a conductive layer, to which a DC bias voltage is applied to the conductive layer, and a
member for holding the pair of fixed electrodes and the vibrating film The plurality of through
holes formed in the second fixed electrode are all or most formed at positions opposed to the
plurality of through holes formed in the first fixed electrode via the vibrating film, A method of
manufacturing an ultrasonic transducer in which an alternating current signal is applied between
the pair of fixed electrodes, wherein the vibrating film sandwiching portion in the fixed electrode
sandwiching the vibrating film is formed of an insulating material by an inkjet method. Do.
[0035]
In the ultrasonic transducer manufactured by the method of manufacturing an ultrasonic
transducer according to the present invention having the above-described configuration, a
plurality of through holes are formed at positions facing the first fixed electrode and the second
fixed electrode. In a state in which a DC bias voltage is applied to the conductive layer, an
alternating current signal, which is a drive signal, is applied to the pair of fixed electrodes
consisting of the first and second fixed electrodes. The film can not only make the vibration of
04-05-2019
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the vibrating film sufficiently large to obtain a parametric effect, because the electrostatic
attraction and electrostatic repulsion are simultaneously received in the same direction in the
direction according to the polarity of the AC signal. Since the symmetry of vibration is ensured,
high sound pressure can be generated over a wide frequency band.
[0036]
Further, in the method of manufacturing the ultrasonic transducer according to the present
invention having the above configuration, the vibrating film pinching portion in the fixed
electrode sandwiching the vibrating film is formed of an insulating material by the inkjet method.
The part can be easily formed as a permanent structure.
[0037]
In the method of manufacturing an ultrasonic transducer according to the present invention, the
insulating material is a nonconductive paint.
[0038]
Further, in the method of manufacturing an ultrasonic transducer according to the present
invention, a first fixed electrode having a plurality of through holes formed therein, and a second
fixed electrode having a plurality of through holes forming a pair with the first fixed electrode
are formed. And a vibrating film sandwiched between the pair of fixed electrodes, having a
conductive layer, to which a DC bias voltage is applied to the conductive layer, and a member for
holding the pair of fixed electrodes and the vibrating film, The plurality of through holes formed
in the second fixed electrode are all or most formed at positions opposed to the plurality of
through holes formed in the first fixed electrode via the vibrating film, A manufacturing method
of an ultrasonic transducer in which an alternating current signal is applied between a pair of
fixed electrodes, wherein a vibrating film sandwiching portion in the fixed electrode sandwiching
the vibrating film is formed of an insulating material by an electrodeposition method. Do.
[0039]
In the ultrasonic transducer manufactured by the method of manufacturing an ultrasonic
transducer according to the present invention having the above-described configuration, a
plurality of through holes are formed at positions facing the first fixed electrode and the second
fixed electrode. In a state in which a DC bias voltage is applied to the conductive layer, an
alternating current signal, which is a drive signal, is applied to the pair of fixed electrodes
consisting of the first and second fixed electrodes. The film can not only make the vibration of
the vibrating film sufficiently large to obtain a parametric effect, because the electrostatic
attraction and electrostatic repulsion are simultaneously received in the same direction in the
04-05-2019
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direction according to the polarity of the AC signal. Since the symmetry of vibration is ensured,
high sound pressure can be generated over a wide frequency band.
[0040]
Further, in the method of manufacturing an ultrasonic transducer according to the present
invention having the above configuration, the vibrating membrane sandwiching portion in the
stationary electrode sandwiching the vibrating membrane is formed of an insulating material by
an electrodeposition method. The sandwiching portion can be easily formed as a permanent
structure.
[0041]
In the method of manufacturing an ultrasonic transducer according to the present invention, the
insulating material is an electrodeposition material.
[0042]
Hereinafter, embodiments of the present invention will be described in detail with reference to
the drawings.
Embodiment of Ultrasonic Transducer A configuration of an ultrasonic transducer according to
an embodiment of the present invention is shown in FIG.
The ultrasonic transducer according to the embodiment of the present invention has a first fixed
electrode 10A in which a plurality of through holes 14 are formed, and a second in which a
plurality of through holes 14 paired with the first fixed electrode 10A are formed. Of the fixed
electrode 10B and the pair of fixed electrodes 10A and 10B, having the conductive layer 121, to
which a DC bias voltage is applied to the conductive layer 121, and the pair of fixed electrodes
10A and 10B The plurality of through holes 14 formed in the second fixed electrode 10B have a
plurality of through holes 14 formed in the first fixed electrode 10A with the diaphragm 12
interposed therebetween. An ultrasonic transducer in which all or most of the electrodes are
formed at opposite positions, and an alternating current signal is applied between a pair of fixed
electrodes 10A and 10B, in which vibration in the pair of fixed electrodes sandwiching the
vibrating membrane The clamping portion 101 is characterized by the formation of an insulating
material.
04-05-2019
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[0043]
FIG. 1 (A) shows the configuration of the ultrasonic transducer, and FIG. 1 (B) shows a plan view
in which a part of the ultrasonic transducer is broken.
In FIG. 1, the ultrasonic transducer 1 according to the present embodiment is held between a pair
of fixed electrodes 10A and 10B including a conductive member formed of a conductive material
functioning as an electrode, and a pair of fixed electrodes. , A pair of fixed electrodes 10A and
10B, and a member (not shown) for holding the vibrating film.
[0044]
Each of the pair of fixed electrodes 10A and 10B includes a fixed electrode portion 100 formed
of a conductor and a vibrating film sandwiching portion 101 sandwiching the vibrating film 12.
The diaphragm sandwiching portion 101 is formed of an insulating material.
As the insulating material, any of a liquid solder resist, a photosensitive film, a photosensitive
coating material, a nonconductive paint, and an electrodeposition material can be used.
The vibrating film pinching portion in the fixed electrode is permanently structured by forming
the vibrating film pinching portion 101 with an insulating material of liquid solder resist,
photosensitive film, photosensitive coating material, nonconductive paint, or electrodeposition
material. It can be formed as a body.
[0045]
The vibrating film 12 has an insulating layer 120 formed of an insulator and a conductive layer
121 formed of a conductive material. The conductive layer 121 has a single polarity (positive
polarity) by the DC bias power supply 16. However, any one of negative polarity may be used.
04-05-2019
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The DC bias voltage of (1) is applied, and an AC signal output from the signal source 18 is
applied in addition to the DC bias voltage.
[0046]
Further, the pair of fixed electrodes 10A and 10B have the same number and a plurality of
through holes 14 at the positions facing each other through the vibrating film 12, and the signal
source 18 is used between the conductive members of the pair of fixed electrodes 10A and 10B.
An alternating current signal is applied.
The fixed electrode 10A and the conductive layer 121, and the fixed electrode 10B and the
conductive layer 121 form a capacitor.
[0047]
In the above configuration, the ultrasonic transducer 1 outputs an alternating current signal
output from the signal source 18 to the electrode layer of the vibrating membrane 12 to a single
polarity (in the present embodiment, a positive polarity) DC bias voltage by the DC bias power
supply 16. It is applied in the superimposed state.
On the other hand, an alternating current signal is applied from the signal source 18 to the pair
of fixed electrodes 10A, 10B.
[0048]
As a result, in the positive half cycle of the alternating current signal output from the signal
source 18, a positive voltage is applied to the fixed electrode 10A, so the surface portion 12A of
the diaphragm 12 which is not sandwiched by the fixed electrodes is The electrostatic repulsive
force acts, and the surface portion 12A is pulled downward in FIG. 1 (a).
At this time, since a negative voltage is applied to the opposing fixed electrode 10B, an
04-05-2019
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electrostatic attraction force acts on the back surface portion 12B which is the back surface side
of the surface portion 12A of the vibrating film 12, The back surface portion 12B is pulled
further downward in FIG. 1 (b).
[0049]
Therefore, the film portion of the vibrating film 12 which is not held by the pair of fixed
electrodes 10A and 10B receives electrostatic repulsion and electrostatic repulsion in the same
direction.
Similarly, for the negative half cycle of the alternating current signal output from the signal
source 18, the surface portion 12A of the vibrating membrane 12 has an electrostatic attraction
force upward in FIG. 1A and the back surface portion 12B. In FIG. 1 (b), electrostatic repulsion
acts on the upper side, and the membrane portion of the diaphragm 12 which is not held by the
pair of fixed electrodes 10A and 10B has electrostatic repulsion and electrostatic force in the
same direction. Receive repulsion.
In this manner, as the vibrating film 12 receives electrostatic repulsion and electrostatic
repulsion in the same direction in accordance with the change in polarity of the AC signal, the
direction in which the electrostatic force acts alternately changes, so that large film vibration, ie,
An acoustic signal of a sound pressure level sufficient to obtain a parametric array effect can be
generated.
[0050]
As described above, the ultrasonic transducer 1 according to the embodiment of the present
invention is called a push-pull type because the vibrating membrane 12 vibrates by receiving a
force from the pair of fixed electrodes 10A and 10B. The ultrasonic transducer 1 according to the
embodiment of the present invention has a wide band and high sound pressure at the same time
compared with the conventional ultrasonic transducer (Pull type) of which only the electrostatic
attraction acts on the vibrating film. Have the ability to meet.
[0051]
04-05-2019
17
The frequency characteristic of the ultrasonic transducer according to the embodiment of the
present invention is shown in FIG. In the same figure, curve Q3 is the frequency characteristic of
the ultrasonic transducer which relates to this execution form. As is clear from the figure, it can
be seen that high sound pressure levels can be obtained over a wider frequency band as
compared to the frequency characteristics of the conventional broadband electrostatic ultrasonic
transducer. Specifically, it can be seen that a sound pressure level of 120 dB or more at which a
parametric effect can be obtained in a frequency band of 20 kHz to 120 kHz can be obtained.
[0052]
In the ultrasonic transducer 1 according to the embodiment of the present invention, the
vibrating membrane 12 of the thin film sandwiched between the pair of fixed electrodes 10A and
10B receives both electrostatic attraction and electrostatic repulsion, so that only large vibration
occurs. Because the symmetry of vibration is secured, high sound pressure can be generated over
a wide band.
[0053]
That is, in the ultrasonic transducer according to the present invention having the above
configuration, a plurality of through holes are formed at positions facing the first fixed electrode
and the second fixed electrode, and a DC bias voltage is applied to the conductive layer of the
diaphragm. Since the AC signal which is a drive signal is applied to the pair of fixed electrodes
consisting of the first and second fixed electrodes in the above state, the vibrating film
sandwiched between the pair of fixed electrodes has the polarity of the AC signal. In the
corresponding direction, the electrostatic attraction force and the electrostatic repulsion force
are simultaneously received in the same direction, so that not only the vibration of the vibrating
membrane can be made large enough to obtain a parametric effect, but also the symmetry of the
vibration is ensured Therefore, high sound pressure can be generated over a wide frequency
band.
[0054]
Further, since the diaphragm sandwiching portion in the pair of fixed electrodes sandwiching the
diaphragm is formed of an insulating material, the thickness of the insulating layer is increased
by the diaphragm sandwiching portion (for example, several μm to several tens of μm) As a
result, even a thin film of 10 μm or less as a vibrating membrane can be used with high voltage
without any problem, and the effect of expanding the selection range of the thickness of the
vibrating membrane can be obtained.
04-05-2019
18
Further, since the diaphragm sandwiching portion of the pair of fixed electrodes sandwiching the
diaphragm is formed of an insulating material, a state occurs in which the edge of the diaphragm
sandwiching portion of the fixed electrode bites deeply into the insulating layer in the
manufacturing process. However, the thickness of the insulating layer is added to the thickness
of the insulating layer of the vibrating film by the thickness of the vibrating film pinching portion
in the fixed electrode, so that the dielectric breakdown due to the breakage of the vibrating film
is avoided effective.
[0055]
In addition, even when a part of the diaphragm sandwiching portion in the fixed electrode
completely contacts the conductive layer of the diaphragm, or completely breaks the diaphragm
and contacts the fixed electrode on the opposite side, the conductive parts contact with each
other. It is possible to completely prevent the decrease in insulation strength and the occurrence
of short circuit due to the structural distortion of the fixed electrode.
Furthermore, compared to the case where the fixed electrodes are all made of a conductive
material as in the prior art, when the vibrating film sandwiching portion is made of a
nonconductive material, only the capacitance is changed without changing the electrostatic force
acting on the vibrating electrode film at all. Can be reduced, and energy efficiency can be
improved by reducing the capacitance.
[0056]
Next, a manufacturing process in the case of manufacturing the fixed electrode portion of the
ultrasonic transducer according to the embodiment of the present invention by the
photolithography method according to the conventional method will be described with reference
to FIG. In the figure, first, a conductor plate (copper or stainless steel is used, but copper is
suitable for nickel electroforming. The mask member 11 in which a plurality of through hole
patterns are formed is placed on the substrate 10, and the through holes 14 are formed in the
conductor plate 10 by etching (FIGS. 4A and 4B). Then, after the through holes 14 are formed in
the conductor plate 10, the mask member 11 is peeled off to obtain the conductor plate 10
having the through holes 14 (FIG. 4 (c)).
04-05-2019
19
[0057]
Here, the diameter of the through hole 14 formed in the conductive plate 10 by etching is
restricted in relation to the thickness of the conductive plate 10. For example, the minimum
diameter of the through hole 14 used in the ultrasonic transducer according to the embodiment
of the present invention is 0.25 mm, and the plate thickness at which the through hole 14 of this
diameter is opened is 0.25 mm or less. Therefore, when a fixed electrode with a thickness of 0.25
mm or more is required, several sheets of metal plate with a thickness of 0.25 mm with the
through holes 14 prepared by etching are prepared in advance, and the necessary number of
these are stacked to obtain heat. Metal bonding is performed by pressure bonding or diffusion
bonding to fabricate a fixed electrode of a desired thickness.
[0058]
Next, in order to form a vibrating film sandwiching portion (step portion) which constitutes a
fixed electrode on the conductor plate 10 in which the through hole 14 is opened, a
photosensitive resist (a coating or a film in the case of liquid) is used as a pretreatment material.
In this case, after laminating 20A, a mask member 21A for forming a diaphragm holding portion
is covered and exposed (FIG. 4D). As the photosensitive resist 20A, a liquid resist or a dry film
generally used to form a temporary intermediate structure by etching, plating or the like is used,
but in the present component, the through hole 14 is sealed. It is more effective to use a dry film
in order to
[0059]
When the unnecessary resist is removed by development, only the surface of the conductive
plate 10 in the portion where the diaphragm sandwiching portion (step portion) of the fixed
electrode is to be formed is exposed (FIG. 4 (e)). Next, a metal (for example, nickel) is laminated
on the exposed surface of the conductive plate 10 by electroforming to a desired height (FIG. 4
(f)). After completion of the electroforming process, the remaining resist 20A 'is peeled off to
complete the desired fixed electrode (FIG. 4 (g)).
[0060]
04-05-2019
20
The problems of the fixed electrode when manufactured by the above conventional
manufacturing process are shown below. (1) The thin film can not be used for the vibrating film
When manufacturing the fixed electrode by the above-mentioned conventional manufacturing
process, that is, when the vibrating film sandwiching portion of the fixed electrode is made of a
conductive material, the metal deposition layer of the vibrating film (= conductive The maximum
clearance between the layer) and the fixed electrode is the thickness of the insulating layer of the
vibrating membrane. Here, the insulating layer of the vibrating electrode film used in the
ultrasonic transducer according to the embodiment of the present invention is made of
polyethylene terephthalate (PET), polyethylene sulfide (PPS), polypropylene (PP), polyimide (PI)
or the like.
[0061]
Here, the dielectric breakdown strength of each material is as follows. PET, PPS, PI: 200 V / μm
PP: 300 V / μm Further, the voltage applied to the present transducer is several hundred V to
several kV for both the fixed electrode and the vibrating electrode film. Therefore, in the
conventional configuration, for example, when PET is used for the insulating layer of the
vibrating film, a film thickness of at least 10 μm is required to apply a voltage of 2 kV, and a
film thinner than this can not be used as the vibrating film. Become.
[0062]
(2) It is easy to cause the dielectric breakdown. The edge portion of the fixed electrode formed by
the etching process is very sharp. In addition, burrs of several to several tens of microns are
generated at locations where additional machining (machining) is performed. In addition, it has
been confirmed that the metal which has been subjected to the etching process is easily
distorted, and a warp of at least 10 several μm remains even when thermocompression bonding
or diffusion bonding is performed. As described above, when it is intended to reliably sandwich
the vibrating electrode film in a state in which the fixed electrode is warped, the edge portion of
the vibrating film sandwiching portion 20 in the fixed electrode is the insulating layer 120 of the
vibrating film 12 as shown in FIG. Bite.
[0063]
04-05-2019
21
In the conventional configuration, since the diaphragm sandwiching portion 20 is formed of a
conductive material, the minimum gap between the conductive layer 121 of the diaphragm 12
and the conductive portion of the fixed electrode is d1 in the figure, and the gap is narrowed by
the amount of biting. , Dielectric breakdown strength is reduced. For example, in the case where
the insulating layer 120 is PET, when d1 decreases to about 1 μm, it becomes difficult to apply a
voltage of 200 V or more.
[0064]
(3) The capacitance is large, and energy is consumed wastefully. The input power is determined
by the capacitance, and the smaller the gap between the conductive layer 121 of the vibrating
film 12 and the fixed electrode, ie, the thinner the insulating layer 120 of the vibrating electrode
film, the larger the capacitance and the higher the input power. On the other hand, the
electrostatic force acting on the vibrating film 12 which contributes most to the main
characteristics (= sound pressure) of the ultrasonic transducer is the difference in area of the
metal surface of the fixed electrode exposed as the vibrating film sandwiching part and the step
difference of the vibrating membrane sandwiching part It is determined by (the gap between the
conductor and the vibrating membrane). Therefore, although the electrostatic force is increased
if a thin vibrating film of the insulating layer is used, the capacitance is also greatly increased at
the same time, so the energy efficiency is not good.
[0065]
As described above, when the fixed electrode of the ultrasonic transducer is manufactured by the
conventional manufacturing process, (1) a thin film can not be used for the vibrating film, (2)
between the fixed electrode and the conductive layer of the vibrating film There is a problem that
(3) the electrostatic capacitance formed between the conductive layer of the vibrating film and
the fixed electrode is likely to cause dielectric breakdown, and energy is consumed wastefully.
These problems are solved by the ultrasonic transducer according to the embodiment of the
present invention described above and the method of manufacturing the ultrasonic transducer
described below.
[0066]
Embodiment of Method of Manufacturing Ultrasonic Transducer First Embodiment
04-05-2019
22
Photolithographic Method Next, a first embodiment of a method of manufacturing an ultrasonic
transducer according to the present invention is shown in FIG. In a method of manufacturing an
ultrasonic transducer according to a first embodiment of the present invention, a first fixed
electrode in which a plurality of through holes are formed, and a plurality of through holes that
form a pair with the first fixed electrode are formed. A second fixed electrode, a pair of fixed
electrodes, a conductive layer, a vibrating film to which a DC bias voltage is applied to the
conductive layer, a member for holding the pair of fixed electrodes and the vibrating film And the
plurality of through holes formed in the second fixed electrode are all or most at positions facing
the plurality of through holes formed in the first fixed electrode via the vibrating membrane. Is a
manufacturing method of an ultrasonic transducer in which an alternating current signal is
applied between the pair of fixed electrodes, wherein the vibrating film sandwiching portion in
the fixed electrode sandwiching the vibrating film is formed of an insulating material by
photolithography. It is characterized by There. That is, in the method of manufacturing an
ultrasonic transducer according to the embodiment of the present invention shown in FIG. 1, the
vibrating film sandwiching portion in the fixed electrode sandwiching the vibrating film is formed
of an insulating material by photolithography. There is.
[0067]
In FIG. 2, first, a conductor plate (copper or stainless steel is used, but copper is suitable for
nickel electroforming. The mask member 11 in which a plurality of patterns of through holes are
formed is covered on the surface 10), and the through holes 14 are formed in the conductor
plate 10 by etching (FIGS. 2A and 2B). Then, after the through holes 14 are formed in the
conductor plate 10, the mask member 11 is peeled off to obtain the conductor plate 10 in which
the through holes 14 are opened (FIG. 2 (c)).
[0068]
Next, after applying a photosensitive resist (coating treatment in the case of liquid, lamination
treatment in the case of film) 20 to the conductor plate 10 having the through holes 14 to form a
step constituting the vibrating film sandwiching portion The mask member 21 for forming a
diaphragm sandwiching portion is covered and exposed (FIG. 2D). The photosensitive resist 20 as
a vibrating film sandwiching part forming material used here must be a material that can be
permanently configured as a vibrating membrane sandwiching part and is nonconductive.
Materials considered to be effective include photosensitive polyimide coating material (=
photosensitive coating material used in semiconductor manufacture, used by coating a metal
plate by spin coating method in the case of a liquid), and circuit in the case of a film There are
04-05-2019
23
photosensitive solder resist films and photosensitive polyimide films that are used for packaging
of substrates.
[0069]
When the mask member 21 for forming a vibrating film sandwiching portion is peeled off and
the unnecessary photosensitive resist 20 is removed by development, only the surface of the
conductor plate 10 serving as a fixed electrode portion is exposed, and the other portion is
nonconductive photosensitive. The resist 20 remains to complete the desired fixed electrode (FIG.
2 (e)).
[0070]
In the ultrasonic transducer manufactured by the method of manufacturing an ultrasonic
transducer according to the present invention having the above-described configuration, a
plurality of through holes are formed at positions facing the first fixed electrode and the second
fixed electrode. In a state in which a DC bias voltage is applied to the conductive layer, an
alternating current signal, which is a drive signal, is applied to the pair of fixed electrodes
consisting of the first and second fixed electrodes. The film can not only make the vibration of
the vibrating film sufficiently large to obtain a parametric effect, because the electrostatic
attraction and electrostatic repulsion are simultaneously received in the same direction in the
direction according to the polarity of the AC signal. Since the symmetry of vibration is ensured,
high sound pressure can be generated over a wide frequency band.
[0071]
Further, in the method of manufacturing an ultrasonic transducer according to the present
invention having the above-described configuration, the vibrating film sandwiching portion in the
fixed electrode sandwiching the vibrating film is formed of an insulating material by
photolithography. Since the process after metal electroforming can be omitted, the
manufacturing process can be shortened and the manufacturing cost can be reduced.
In addition, the solvent (mainly a strong alkali solvent) used in the peeling process of the residual
resist is not necessary, and the environment can be improved.
[0072]
Second Embodiment Screen Printing Method
04-05-2019
24
[0073]
Next, FIG. 3 shows a second embodiment of the method for manufacturing an ultrasonic
transducer (manufacturing process) according to the present invention.
In a method of manufacturing an ultrasonic transducer according to a first embodiment of the
present invention, a first fixed electrode in which a plurality of through holes are formed, and a
plurality of through holes that form a pair with the first fixed electrode are formed. A second
fixed electrode, a pair of fixed electrodes, a conductive layer, a vibrating film to which a DC bias
voltage is applied to the conductive layer, a member for holding the pair of fixed electrodes and
the vibrating film And the plurality of through holes formed in the second fixed electrode are all
or most at positions facing the plurality of through holes formed in the first fixed electrode via
the vibrating membrane. Is a manufacturing method of an ultrasonic transducer in which an
alternating current signal is applied between the pair of fixed electrodes, wherein the vibrating
film sandwiching portion in the fixed electrode sandwiching the vibrating film is formed of an
insulating material by a screen printing method. It is characterized by
That is, in the method of manufacturing an ultrasonic transducer according to the embodiment of
the present invention shown in FIG. 1, the vibrating film sandwiching portion in the fixed
electrode sandwiching the vibrating film is formed of an insulating material by screen printing.
There is.
[0074]
In FIG. 3, first, a conductor plate (copper or stainless steel is used, but copper is suitable for
nickel electroforming. The mask member 11 in which a plurality of patterns of through holes are
formed is covered on the surface 10), and the through holes 14 are formed in the conductor
plate 10 by etching (FIGS. 2A and 2B). Then, after the through holes 14 are formed in the
conductor plate 10, the mask member 11 is peeled off to obtain the conductor plate 10 in which
the through holes 14 are opened (FIG. 2 (c)).
[0075]
04-05-2019
25
A screen printing plate 30 and a liquid diaphragm holding portion forming material 32 for
forming a diaphragm holding portion in the fixed electrode are set on the conductor plate 10
having the through holes 14 and the squeegee 31 is moved. The vibrating film sandwiching
portion forming material 32 is applied to the portion of the screen printing plate 30 where the
mask member is not applied (FIG. 3 (d)). Here, the vibrating membrane pinching portion forming
material 32 considered to be effective can be permanently configured as a vibrating membrane
pinching portion and is non-conductive, and for example, a liquid solder for a package generally
used for a circuit board It is a masking ink used as a resist or a resist for sandblasting. In
particular, since a solder resist for a flexible printed circuit is relatively soft (approximately HB to
3H in hardness of pencil), it is effective for firmly holding a vibrating electrode film.
[0076]
When the screen printing plate 30 is removed after the application of the vibrating membrane
pinching portion forming material 32 to the portion of the screen printing plate 30 on which the
mask member is not applied, the other portion of the conductive plate 10 excluding the vibrating
membrane pinching portion is nonconductive. The property layer (= the vibrating film
sandwiching portion forming material 32) remains, and it is dried to obtain the desired fixed
electrode (FIG. 3 (e)).
[0077]
In the ultrasonic transducer manufactured by the method of manufacturing an ultrasonic
transducer according to the present invention having the above-described configuration, a
plurality of through holes are formed at positions facing the first fixed electrode and the second
fixed electrode. In a state in which a DC bias voltage is applied to the conductive layer, an
alternating current signal, which is a drive signal, is applied to the pair of fixed electrodes
consisting of the first and second fixed electrodes. The film can not only make the vibration of
the vibrating film sufficiently large to obtain a parametric effect, because the electrostatic
attraction and electrostatic repulsion are simultaneously received in the same direction in the
direction according to the polarity of the AC signal. Since the symmetry of vibration is ensured,
high sound pressure can be generated over a wide frequency band.
[0078]
Further, in the method of manufacturing an ultrasonic transducer according to the present
invention having the above configuration, the diaphragm sandwiching portion in the fixed
electrode sandwiching the diaphragm is formed of the insulating material by the screen printing
method. Since the process after metal electroforming can be made unnecessary and the process
such as the development performed by the photolithography method is not required at all, the
04-05-2019
26
manufacturing process can be greatly shortened and the manufacturing cost can be significantly
reduced.
[0079]
In addition, as another method of manufacturing an ultrasonic transducer, a resist is formed in
advance so that the conductive portion is exposed only in the portion to be coated (= the portion
forming the counter electrode forming body). Alternatively, the conductive paint may be applied
by spraying with an ink jet head, or may be dipped in an electrodeposition polyimide material for
electrodeposition coating, and the resist may be peeled off after application or electrodeposition.
[0080]
The method of manufacturing an ultrasonic transducer by the inkjet method is a method of
manufacturing an ultrasonic transducer according to the embodiment of the present invention
shown in FIG. 1, which comprises: a vibrating film sandwiching portion in a fixed electrode
sandwiching a vibrating film of the ultrasonic transducer It is characterized in that it is formed of
an insulating material by an inkjet method.
[0081]
That is, it is held between a first fixed electrode having a plurality of through holes, a second
fixed electrode having a plurality of through holes forming a pair with the first fixed electrode,
and the pair of fixed electrodes. A vibrating film to which a conductive layer is applied, to which a
DC bias voltage is applied, and a member for holding the pair of fixed electrodes and the
vibrating film, the conductive film being formed on the second fixed electrode A plurality of
through holes are all formed at positions opposed to the plurality of through holes formed in the
first fixed electrode through the vibrating film, or most of them are formed, and an alternating
current signal is generated between the pair of fixed electrodes. A method of manufacturing an
ultrasonic transducer to be applied, wherein the vibrating membrane pinching portion in the
fixed electrode pinching the vibrating membrane is formed of an insulating material by an inkjet
method.
[0082]
In the ultrasonic transducer manufactured by the method of manufacturing an ultrasonic
transducer according to the present invention having the above-described configuration, a
plurality of through holes are formed at positions facing the first fixed electrode and the second
fixed electrode. In a state in which a DC bias voltage is applied to the conductive layer, an
alternating current signal, which is a drive signal, is applied to the pair of fixed electrodes
consisting of the first and second fixed electrodes. The film can not only make the vibration of
04-05-2019
27
the vibrating film sufficiently large to obtain a parametric effect, because the electrostatic
attraction and electrostatic repulsion are simultaneously received in the same direction in the
direction according to the polarity of the AC signal. Since the symmetry of vibration is ensured,
high sound pressure can be generated over a wide frequency band.
[0083]
Further, in the method of manufacturing the ultrasonic transducer according to the present
invention having the above configuration, the vibrating film pinching portion in the fixed
electrode sandwiching the vibrating film is formed of an insulating material by the inkjet method.
The part can be easily formed as a permanent structure.
[0084]
In addition, the method of manufacturing an ultrasonic transducer by electrodeposition is a
method of manufacturing an ultrasonic transducer according to the embodiment of the present
invention shown in FIG. 1, which is a vibrating membrane in a fixed electrode sandwiching a
vibrating membrane of the ultrasonic transducer. It is characterized in that the holding portion is
formed of an insulating material by an electrodeposition method.
[0085]
That is, in the method of manufacturing an ultrasonic transducer according to the present
invention, the first fixed electrode in which the plurality of through holes are formed, and the
second fixed electrode in which the plurality of through holes paired with the first fixed electrode
are formed. And a vibrating film sandwiched between the pair of fixed electrodes, having a
conductive layer, to which a DC bias voltage is applied to the conductive layer, and a member for
holding the pair of fixed electrodes and the vibrating film, The plurality of through holes formed
in the second fixed electrode are all or most formed at positions opposed to the plurality of
through holes formed in the first fixed electrode via the vibrating film, A manufacturing method
of an ultrasonic transducer in which an alternating current signal is applied between a pair of
fixed electrodes, wherein a vibrating film sandwiching portion in the fixed electrode sandwiching
the vibrating film is formed of an insulating material by an electrodeposition method. Do.
[0086]
In the ultrasonic transducer manufactured by the method of manufacturing an ultrasonic
transducer according to the present invention having the above-described configuration, a
plurality of through holes are formed at positions facing the first fixed electrode and the second
fixed electrode. In a state in which a DC bias voltage is applied to the conductive layer, an
alternating current signal, which is a drive signal, is applied to the pair of fixed electrodes
04-05-2019
28
consisting of the first and second fixed electrodes. The film can not only make the vibration of
the vibrating film sufficiently large to obtain a parametric effect, because the electrostatic
attraction and electrostatic repulsion are simultaneously received in the same direction in the
direction according to the polarity of the AC signal. Since the symmetry of vibration is ensured,
high sound pressure can be generated over a wide frequency band.
[0087]
Further, in the method of manufacturing an ultrasonic transducer according to the present
invention having the above configuration, the vibrating membrane sandwiching portion in the
stationary electrode sandwiching the vibrating membrane is formed of an insulating material by
an electrodeposition method. The sandwiching portion can be easily formed as a permanent
structure.
[0088]
An ultrasonic transducer according to an embodiment of the present invention and a method of
manufacturing an ultrasonic transducer according to an embodiment of the present invention
form a vibrating film sandwiching portion in a fixed electrode of an ultrasonic transducer with a
nonconductive material (insulating material) By doing so, the following effects can be obtained.
(1) The selection range of the film thickness forming the vibration film is expanded.
The thickness of the insulating layer is increased by the step difference (several μm to several
tens of μm) of the vibrating film sandwiching portion in the fixed electrode formed of the
nonconductive material, and the thin film of 10 μm or less as a vibrating film has a problem. Can
be used at high voltage.
[0089]
For example, when a 3 μm PET film is used for the insulating layer of the vibrating electrode
film, the conventional fixed electrode configuration (the entire fixed electrode is formed of a
conductive material) is the upper limit of the voltage to which 600 V can be applied. By applying
the insulating material, for example, even when the step of the diaphragm sandwiching portion is
3 μm, the clearance between the fixed electrode surface and the conductive layer of the
04-05-2019
29
diaphragm becomes 6 μm, so that a voltage of 1 kV or more can be applied. It becomes.
Also, for example, if it is desired to apply a voltage of 3 kV with a step of the diaphragm holding
portion at the fixed electrode of 20 μm, the conventional fixed electrode configuration requires
a 15 μm insulating layer (PET). If a non-conductive material is used to form the part, a 1 μm
PET film (clearance: 21 μm) is sufficient.
[0090]
(2) It is possible to avoid the occurrence of dielectric breakdown between the fixed electrode and
the conductive layer of the vibrating membrane due to the breakage of the vibrating membrane.
That is, when the vibrating membrane pinching portion 20 of the fixed electrodes 10A and 10B
is made of a nonconductive material, in FIG. 5, the step d2 (several μm to tens of μm) of the
vibrating membrane pinching portion 20 is added as an insulating layer. Therefore, the minimum
gap between the conductive layer 121 of the vibrating film 12 and the fixed electrode portion
(conductive portion) 10 of the fixed electrode is (d1 + d2). The breaking strength is sufficiently
secured, and the conventional failure does not occur, and even a thin vibrating electrode film can
be handled without any problem.
[0091]
In addition, even when part of the fixed electrode 10A or 10B completely contacts the conductive
layer 121 of the vibrating film 12 or completely breaks the vibrating film 12 and contacts the
fixed electrode on the opposite side, the conductive parts contact with each other. There is
nothing wrong with this, and it is possible to completely prevent the decrease in insulation
strength and short circuit due to the structural distortion of the fixed electrode.
[0092]
(3) The energy efficiency can be improved by reducing the capacitance.
When the vibrating membrane sandwiching portion is formed of a non-conductive material as
compared to the conventional case where the stationary electrode is entirely made of a
04-05-2019
30
conductive material, the conductive portion of the stationary electrode (fixing is performed
without changing the electrostatic force acting on the vibrating membrane) It is possible to
reduce only the capacitance between the electrode unit 100).
For example, in the structure of the transducer according to the present invention (FIG. 6), the
insulating layer 120 of the vibrating film 12 is PET (relative dielectric constant 3.2), its thickness
is t1, and the vibrating film sandwiching part 20 is polyimide (relative dielectric constant 3.5),
the thickness (= step of the diaphragm holding portion 20) is t2, the outer diameter of the
diaphragm holding portion 20 is φD1, and the inner diameter is half the outer diameter, as
compared to the conventional fixed electrode configuration The ratio of capacitance is shown in
FIGS. 7 (a) and 7 (b).
As is clear from the figure, as the thickness t1 of the insulating layer 120 of the vibrating
membrane 12 becomes thinner, the reduction effect of the electrostatic capacity by forming the
vibrating membrane pinching portion 20 with the insulating material is larger, and As the
thickness t2 increases, the effect of reducing the capacitance increases.
From the above, only the input power can be reduced without changing the electrostatic force, so
that an ultrasonic transducer with improved energy efficiency can be realized.
[0093]
The ultrasonic transducer according to the embodiment of the present invention and the
ultrasonic transducer manufactured by the method of manufacturing an ultrasonic transducer
according to the embodiment of the present invention can be used as various sensors, for
example, a distance measuring sensor, etc. As described above, it can be used as a sound source
for directional speakers, an ideal impulse signal generation source, and the like.
[0094]
The figure which shows the structure of the ultrasonic transducer which concerns on
embodiment of this invention.
BRIEF DESCRIPTION OF THE DRAWINGS The manufacturing-process figure which shows 1st
Embodiment of the manufacturing method of the ultrasonic transducer which concerns on this
04-05-2019
31
invention.
The manufacturing-process figure which shows 2nd Embodiment of the manufacturing method
of the ultrasonic transducer which concerns on this invention.
The manufacturing-process figure which shows the conventional manufacturing method of an
ultrasonic transducer.
Explanatory drawing which shows the structural problem of the ultrasonic transducer
manufactured by the manufacturing method of the ultrasonic transducer shown in FIG.
Explanatory drawing which shows the characteristic improvement of the ultrasonic transducer by
this invention.
Explanatory drawing which shows the ratio of the electrostatic capacitance between the fixed
electrode and the weir transmission of a vibrating membrane with the ultrasonic transducer by
the conventional structure of the ultrasonic transducer based on this invention. The figure which
shows the structure of the conventional resonance type ultrasonic transducer. FIG. 8 is a diagram
showing a specific configuration of a conventional electrostatic broadband ultrasonic transducer.
The figure which showed the frequency characteristic of the ultrasonic transducer which
concerns on embodiment of this invention with the frequency characteristic of the conventional
ultrasonic transducer.
Explanation of sign
[0095]
DESCRIPTION OF SYMBOLS 1 ... Ultrasonic transducer, 10 ... Conductor board, 10A, 10B ... Fixed
electrode, 11 ... Mask member, 12 ... Vibrating film, 14 ... Through hole, 16 ... DC bias power
supply, 18 ... Signal source, 20 ... Photosensitive resist , 21: mask member for forming a
diaphragm sandwiching part, 30: screen printing plate, 31: squeegee, 32: forming material for
diaphragm sandwiching part, 100: fixed electrode part, 101: diaphragm diaphragm sandwiching
part, 120: insulating layer, 121 ... Conductive layer
04-05-2019
32
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