JP2006270157A - Ultrasonic transducer and its manufacturing process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic transducer in which manufacturing process is shortened, and to provide its manufacturing process. <P>SOLUTION: The ultrasonic transducer comprises a first fixed electrode 10A having a plurality of through holes 14, a second fixed electrode 10B having a plurality of through holes 14 and paired with the first fixed electrode 10A, an oscillatory membrane 12 sandwiched by the pair of fixed electrodes 10A and 10B and having a conductive layer 121 being applied with a DC bias voltage, and a member for holding the pair of fixed electrodes 10A and 10B and the oscillatory membrane 12. All or the majority of the plurality of through holes 14 formed in the second fixed electrode 10B are located at positions opposing the plurality of through holes 14 formed in the first fixed electrode 10A through the oscillatory membrane 12, and an AC signal is applied to the pair of fixed electrodes 10A and 10B. Oscillatory membrane sandwiching portion 101 of the pair of fixed electrodes is formed of an insulating material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrostatic ultrasonic transducer that generates a constant high sound pressure over a wide frequency band and a method for manufacturing the same.

Most of conventional ultrasonic transducers are resonant types using piezoelectric ceramics.
Here, the configuration of a conventional ultrasonic transducer is shown in FIG. Most of conventional ultrasonic transducers are resonant types using piezoelectric ceramics as vibration elements. The ultrasonic transducer shown in FIG. 8 performs both conversion from an electric signal to ultrasonic waves and conversion from ultrasonic waves to electric signals (transmission and reception of ultrasonic waves) using a piezoelectric ceramic as a vibration element. The bimorph ultrasonic transducer shown in FIG. 8 includes two piezoelectric ceramics 61 and 62, a cone 63, a case 64, leads 65 and 66, and a screen 67.

The piezoelectric ceramics 61 and 62 are bonded to each other, and a lead 65 and a lead 66 are connected to a surface opposite to the bonded surface, respectively.
Since the resonance type ultrasonic transducer uses the resonance phenomenon of the piezoelectric ceramic, the transmission and reception characteristics of the ultrasonic wave are good in a relatively narrow frequency band around the resonance frequency.

Unlike the resonant ultrasonic transducer shown in FIG. 8 described above, an electrostatic ultrasonic transducer is conventionally known as a broadband oscillation ultrasonic transducer capable of generating a 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 side.
FIG. 9 shows a specific configuration of a broadband oscillation type ultrasonic transducer (Pull type).

  The electrostatic ultrasonic transducer 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 vibrating body. An upper electrode 132 formed as a metal foil such as aluminum is integrally formed on the upper surface of the dielectric 131 by a process such as vapor deposition, and a lower electrode 133 formed of brass is formed on the lower surface of the dielectric 131. It is provided so that it may contact a part. The lower electrode 133 is connected to a lead 152 and is fixed to a base plate 135 made of bakelite or the like.

  The upper electrode 132 is connected to a lead 153, and the lead 153 is connected to the DC bias power supply 150. The DC bias power supply 150 constantly applies a DC bias voltage for attracting the upper electrode of about 50 to 150 V to the upper electrode 132 so that the upper electrode 132 is attracted to the lower electrode 133 side. Reference numeral 151 denotes a signal source.

The dielectric 131, the upper electrode 132, and the base plate 135 are caulked 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 dielectric 131 side, a plurality of minute grooves of about several tens to several hundreds μm having a non-uniform shape are formed. Since this minute groove becomes a gap between the lower electrode 133 and the dielectric 131, the electrostatic capacity distribution between the upper electrode 132 and the lower electrode 133 changes minutely.

  These random minute grooves are formed by manually roughing 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 a curve Q1 in FIG. 10 by forming innumerable capacitors having different gap sizes and depths. It is broadband.

In the ultrasonic transducer having the above configuration, 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. Yes. Incidentally, as shown by a curve Q1 in FIG. 10, the frequency characteristic of the resonance type ultrasonic transducer has a center frequency (resonance frequency of the piezoelectric ceramic) of, for example, 40 kHz, and ± 5 kHz with respect to the center frequency that is the maximum sound pressure. -30 dB with respect to the maximum sound pressure at a frequency of. On the other hand, the frequency characteristics of the broadband oscillation type ultrasonic transducer having the above configuration are flat from 40 kHz to near 100 kHz, and are about ± 6 dB compared to the maximum sound pressure at 100 kHz (see Patent Documents 1 and 2). .
JP 2000-50387 A JP 2000-50392 A

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. It is known as a broadband ultrasonic transducer (Pull type).
However, as shown in FIG. 10, the maximum value of the sound pressure is lower than 120 dB in the electrostatic ultrasonic transducer, compared to 130 dB or higher (curve Q2) in the resonant ultrasonic transducer, and the sound pressure is low. Sound pressure was slightly insufficient for use as an ultrasonic speaker.

  Here, the ultrasonic speaker will be described. By applying AM modulation to an ultrasonic frequency band signal called a carrier wave with an audio signal (audible frequency band signal) and driving the ultrasonic transducer with this modulation signal, the ultrasonic wave was modulated with the audio signal of the signal source. The sound wave of the state is radiated into the air, and the original audio signal is self-regenerated in the air due to the nonlinearity of air.

  In other words, since sound waves are coarse and dense waves that propagate using air as a medium, the dense and sparse parts of air appear prominently in the process of propagation of modulated ultrasonic waves. Since the speed of sound is slow in this part, the modulation wave itself is distorted. As a result, the waveform is separated into a carrier wave (ultrasonic wave) and an audible wave (original audio signal). This is the principle that only listening can be heard, and it is generally called the parametric array effect.

In order for the above parametric effect to appear sufficiently, an ultrasonic sound pressure of 120 dB or more is required. However, it is difficult to achieve this value with an electrostatic ultrasonic transducer, and ceramic piezoelectric elements such as PZT, PVDF, etc. The polymer piezoelectric element has been used as an ultrasonic transmitter.
However, since the piezoelectric element has a sharp resonance point regardless of the material, and is practically used as an ultrasonic speaker by being driven at the resonance frequency, the frequency region where a high sound pressure can be secured is extremely narrow. That is, it can be said that it is a narrow band.

  Generally, the maximum human audible frequency band is said to be 20 Hz to 20 kHz, and has a band of about 20 kHz. That is, in an ultrasonic speaker, it is impossible to faithfully demodulate the original audio signal unless a high sound pressure is ensured over a frequency band of 20 kHz in the ultrasonic region. It can be easily understood that it is difficult to faithfully reproduce (demodulate) this 20 kHz wide band with a conventional resonance type ultrasonic speaker using a piezoelectric element.

In fact, in an ultrasonic speaker using a conventional resonance type ultrasonic transducer, (1) the reproduction frequency is narrow with a narrow band, and (2) the demodulated sound is distorted if the AM modulation degree is increased too much, so the maximum is only about 0.5. The degree of modulation cannot be increased. (3) When the input voltage is increased (when the volume is increased), the vibration of the piezoelectric element becomes unstable and the sound is broken. When the voltage is further increased, the piezoelectric element itself is liable to be destroyed, and (4) it is difficult to make an array, enlargement, and miniaturization.

On the other hand, the ultrasonic speaker using the electrostatic ultrasonic transducer (Pull type) shown in FIG. 9 can substantially solve the problems of the above-mentioned conventional technology, but can cover a wide band, but has sufficient demodulated sound. However, there was a problem that the absolute sound pressure was insufficient for the sound volume to be high.
Further, in the Pull type ultrasonic transducer, the electrostatic force works only in the direction of attracting only to the fixed electrode side, and the symmetry of vibration of the vibrating membrane (corresponding to the upper electrode 132 in FIG. 10) is not maintained. When used for an acoustic speaker, there has been a problem that the vibration of the diaphragm directly generates an audible sound.

On the other hand, in order to solve the above problem, we (the present inventors) have already proposed an ultrasonic transducer having a structure (push-pull type) shown in FIG.
However, the manufacturing method of this push-pull type ultrasonic transducer has not been studied yet.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an ultrasonic transducer and a method for manufacturing the ultrasonic transducer that can shorten the manufacturing process.

  In order to achieve the above object, an ultrasonic transducer according to the present invention includes a first fixed electrode having a plurality of through holes and a second fixed hole having a plurality of through holes paired with the first fixed electrode. A fixed electrode, a vibration 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 holding the pair of fixed electrodes and the vibration film And the plurality of through holes formed in the second fixed electrode are all or most formed at positions facing the plurality of through holes formed in the first fixed electrode through the vibrating membrane. An ultrasonic transducer in which an AC signal is applied between the pair of fixed electrodes, wherein the vibration film sandwiching portion of the pair of fixed electrodes that sandwich the vibration film is formed of an insulating material. .

  In the ultrasonic transducer of the present invention having the above-described configuration, a plurality of through holes are formed at positions where the first fixed electrode and the second fixed electrode face each other, and a DC bias voltage is applied to the conductive layer of the vibrating membrane. In this state, since the AC signal as the drive signal is applied to the pair of fixed electrodes including the first and second fixed electrodes, the vibration film sandwiched between the pair of fixed electrodes is in accordance with the polarity of the AC signal. Since the electrostatic attractive force and the electrostatic repulsive force are simultaneously received in the same direction in the direction, not only can the vibration of the vibrating membrane be sufficiently large 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.

Further, since the vibration film sandwiching portion in the pair of fixed electrodes that sandwich the vibration film is formed of an insulating material, the thickness of the insulating layer is increased by this vibration film sandwiching portion (for example, several μm to several tens μm). As a result, even a thin film having a thickness of 10 μm or less can be used as a vibrating membrane at a high voltage without any problem, and the effect of expanding the selection range of the film thickness of the vibrating membrane is obtained.
In addition, since the vibration film sandwiching portion of the pair of fixed electrodes that sandwich the vibration film is formed of an insulating material, a state occurs in which the edge of the vibration film sandwiching portion of the fixed electrode deeply penetrates into the insulating layer in the manufacturing process. However, since the thickness of the insulating layer is added to the thickness of the insulating layer of the vibrating membrane by the thickness of the vibrating membrane sandwiching portion of the fixed electrode, it is avoided that the dielectric breakdown due to the vibrating membrane is broken. effective.

In addition, even if a part of the diaphragm sandwiching part of the fixed electrode is completely in contact with the conductive layer of the diaphragm, or if the diaphragm is completely penetrated and contacted with the fixed electrode on the opposite side, the conductive parts are in contact with each other. However, it is possible to completely prevent a decrease in insulation strength and a short circuit due to structural distortion of the fixed electrode.
Furthermore, compared to the conventional case where the fixed electrode is entirely made of a conductive material, if the vibration film sandwiching portion is made of a non-conductive material, the electrostatic force acting on the vibration electrode film is not changed at all, and only the capacitance is changed. The energy efficiency can be improved by reducing the capacitance.

In the ultrasonic transducer according to the present invention, the insulating material is any one of a liquid solder resist, a photosensitive film, a photosensitive coating material, a non-conductive paint, and an electrodeposition material.
In the ultrasonic transducer of the present invention having the above-described configuration, any one of a liquid solder resist, a photosensitive film, a photosensitive coating material, a non-conductive coating material, and an electrodeposition material is used as an insulating material for forming the vibration film sandwiching portion of the fixed electrode. Since it uses, the vibration film clamping part in a fixed electrode can be formed as a permanent structure.

  The ultrasonic transducer manufacturing method of the present invention includes a first fixed electrode in which a plurality of through holes are formed, and a second fixed in which a plurality of through holes that are paired with the first fixed electrodes are formed. An electrode, a vibration 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 vibration film The plurality of through holes formed in the second fixed electrode are all or most formed at positions facing the plurality of through holes formed in the first fixed electrode through the vibrating membrane, A method of manufacturing an ultrasonic transducer in which an AC signal is applied between the pair of fixed electrodes, wherein the vibration film holding portion of the fixed electrode holding the vibration film is formed of an insulating material by a photolithography method. And

In the ultrasonic transducer manufactured by the ultrasonic transducer manufacturing method of the present invention having the above-described configuration, a plurality of through holes are formed at positions where the first fixed electrode and the second fixed electrode are opposed to each other. In the state where a DC bias voltage is applied to the conductive layer, an AC signal as a drive signal is applied to the pair of fixed electrodes formed of the first and second fixed electrodes, so that the vibration sandwiched between the pair of fixed electrodes In the direction according to the polarity of the AC signal, the membrane receives the electrostatic attractive force and the electrostatic repulsive force simultaneously in the same direction, so that not only can the vibration of the vibrating membrane be sufficiently large to obtain a parametric effect, Since the symmetry of vibration is ensured, a high sound pressure can be generated over a wide frequency band.
Further, in the method of manufacturing the ultrasonic transducer of the present invention having the above-described configuration, the vibration film holding portion in the fixed electrode that holds the vibration film is formed of an insulating material by a photolithography method. Since the process after metal electroforming can be made unnecessary, the manufacturing process can be shortened and the manufacturing cost can be reduced.
Further, a solvent or the like (mainly a strong alkali solvent) used in the residual resist peeling step is not required, and the environment can be improved.

  The ultrasonic transducer manufacturing method of the present invention covers a mask member in which a plurality of through-hole patterns are formed on a conductor plate having a predetermined thickness for forming the fixed electrode portions of the pair of fixed electrodes. Then, a first step of forming a plurality of through holes in the conductor plate by an etching process, and a conductive plate in which the plurality of through holes are formed in the first step are used as a vibration film sandwiching portion forming material. A second step of forming a conductive photosensitive resist in a predetermined thickness; and a vibration film sandwiching portion forming mask member in which a pattern of the vibration film sandwiching portion is formed on the surface of the nonconductive photosensitive resist. The method includes a third step of covering and exposing, and a fourth step of peeling off the vibration film sandwiching portion forming mask member and removing the unnecessary photosensitive resist by development.

In the method of manufacturing an ultrasonic transducer of the present invention having the above-described configuration, a mask member in which a pattern of a plurality of through holes is formed on a conductor plate having a predetermined thickness for forming a fixed electrode portion of a pair of fixed electrodes. A first step of covering and 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 as a vibration film sandwiching portion forming material A second step of forming a non-conductive photosensitive resist in a predetermined thickness; and a vibration film sandwiching portion forming mask member in which a pattern of the vibration film sandwiching portion is formed on the surface of the nonconductive photosensitive resist And a fourth step of removing the unnecessary photosensitive resist by developing and removing the mask member for forming the vibration film sandwiching portion and developing, which has been conventionally required. Processes after metal electroforming Manufacturing process is shortened since it in principal, and the manufacturing cost can be reduced.
Further, a solvent or the like (mainly a strong alkali solvent) used in the residual resist peeling step is not required, and the environment can be improved.

  In the method for manufacturing an ultrasonic transducer according to the present invention, the photosensitive resist is a photosensitive film or a photosensitive coating material.

The ultrasonic transducer manufacturing method of the present invention includes a first fixed electrode in which a plurality of through holes are formed, and a second fixed in which a plurality of through holes that are paired with the first fixed electrodes are formed. An electrode, a vibration 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 vibration film The plurality of through holes formed in the second fixed electrode are all or most formed at positions facing the plurality of through holes formed in the first fixed electrode through the vibrating membrane, A method of manufacturing an ultrasonic transducer in which an AC signal is applied between the pair of fixed electrodes, wherein the vibration film holding portion of the fixed electrode that holds the vibration film is formed of an insulating material by a screen printing method. And

In the ultrasonic transducer manufactured by the ultrasonic transducer manufacturing method of the present invention having the above-described configuration, a plurality of through holes are formed at positions where the first fixed electrode and the second fixed electrode are opposed to each other. In the state where a DC bias voltage is applied to the conductive layer, an AC signal as a drive signal is applied to the pair of fixed electrodes formed of the first and second fixed electrodes, so that the vibration sandwiched between the pair of fixed electrodes In the direction according to the polarity of the AC signal, the membrane receives the electrostatic attractive force and the electrostatic repulsive force simultaneously in the same direction, so that not only can the vibration of the vibrating membrane be sufficiently large to obtain a parametric effect, Since the symmetry of vibration is ensured, a high sound pressure can be generated over a wide frequency band.
Further, in the manufacturing method of the ultrasonic transducer of the present invention having the above-described configuration, the vibration film holding portion in the fixed electrode for holding the vibration film is formed of an insulating material by a screen printing method. The steps after metal electroforming can be eliminated, and further, the development step performed by photolithography is not required at all. Therefore, the production process can be greatly shortened and the production cost can be greatly reduced.

  The ultrasonic transducer manufacturing method of the present invention covers a mask member in which a plurality of through-hole patterns are formed on a conductor plate having a predetermined thickness for forming the fixed electrode portions of the pair of fixed electrodes. Then, a first step of forming a plurality of through holes in the conductor plate by an etching process, and forming the vibration film sandwiching portion on the surface of the conductor plate in which the plurality of through holes are formed in the first step. A second step of setting a screen printing plate in which a mask member is arranged and a liquid vibration film sandwiching portion forming material, and the screen printing plate and the liquid on the surface of the conductor plate on which the plurality of through holes are formed A third step of applying the vibration film holding portion forming material to a portion where the mask member is not applied while moving a squeegee, and setting the vibration film holding 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.

  In the method of manufacturing an ultrasonic transducer of the present invention having the above-described configuration, a mask member in which a pattern of a plurality of through holes is formed on a conductor plate having a predetermined thickness for forming the fixed electrode portions of the pair of fixed electrodes. A first step of forming a plurality of through holes in the conductive plate by etching, and the vibration film sandwiching portion on the surface of the conductive plate in which the plurality of through holes are formed in the first step. A second step of setting a screen printing plate in which mask members for forming are arranged and the liquid diaphragm holding member forming material in liquid form, and the screen printing on the surface of the conductor plate in which the plurality of through holes are formed After setting the plate and the liquid, a third step of applying the vibration film sandwiching portion forming member to a portion where the mask member is not applied while moving the squeegee, and the vibration film sandwiching portion forming material as the mask member A fourth step of removing the screen printing plate after being applied to the uncovered portion and drying the vibration film sandwiching portion forming material remaining on the surface of the conductive plate. Subsequent steps can be dispensed with, and further, a development step performed by a photolithography method is not required at all. Therefore, the production process can be greatly shortened and the production cost can be greatly reduced.

  In the method for manufacturing an ultrasonic transducer according to the present invention, the liquid vibration film holding portion forming material may be a liquid solder resist.

  The ultrasonic transducer manufacturing method of the present invention includes a first fixed electrode in which a plurality of through holes are formed, and a second fixed in which a plurality of through holes that are paired with the first fixed electrodes are formed. An electrode, a vibration 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 vibration film The plurality of through holes formed in the second fixed electrode are all or most formed at positions facing the plurality of through holes formed in the first fixed electrode through the vibrating membrane, A method of manufacturing an ultrasonic transducer in which an AC signal is applied between the pair of fixed electrodes, wherein the vibration film holding portion of the fixed electrode for holding the vibration film is formed of an insulating material by an inkjet method. To do.

  In the ultrasonic transducer manufactured by the ultrasonic transducer manufacturing method of the present invention having the above-described configuration, a plurality of through holes are formed at positions where the first fixed electrode and the second fixed electrode are opposed to each other. In the state where a DC bias voltage is applied to the conductive layer, an AC signal as a drive signal is applied to the pair of fixed electrodes formed of the first and second fixed electrodes, so that the vibration sandwiched between the pair of fixed electrodes In the direction according to the polarity of the AC signal, the membrane receives the electrostatic attractive force and the electrostatic repulsive force simultaneously in the same direction, so that not only can the vibration of the vibrating membrane be sufficiently large to obtain a parametric effect, Since the symmetry of vibration is ensured, a high sound pressure can be generated over a wide frequency band.

  Further, in the method for manufacturing an ultrasonic transducer of the present invention having the above-described configuration, the vibration film holding portion in the fixed electrode that holds the vibration film is formed of an insulating material by an ink jet method. The part can be easily formed as a permanent structure.

  In the method for manufacturing an ultrasonic transducer according to the present invention, the insulating material is a non-conductive paint.

  The ultrasonic transducer manufacturing method of the present invention includes a first fixed electrode in which a plurality of through holes are formed, and a second fixed electrode in which a plurality of through holes paired with the first fixed electrode are formed. And a vibration film sandwiched between the pair of fixed electrodes, having a conductive layer, and a DC bias voltage applied to the conductive layer, and a member holding the pair of fixed electrodes and the vibration film, The plurality of through-holes formed in the second fixed electrode are all or most formed at positions facing the plurality of through-holes formed in the first fixed electrode through the vibrating membrane, A method of manufacturing an ultrasonic transducer in which an AC signal is applied between a pair of fixed electrodes, wherein the vibration film holding portion of the fixed electrode holding the vibration film is formed of an insulating material by an electrodeposition method. To do.

  In the ultrasonic transducer manufactured by the ultrasonic transducer manufacturing method of the present invention having the above-described configuration, a plurality of through holes are formed at positions where the first fixed electrode and the second fixed electrode are opposed to each other. In the state where a DC bias voltage is applied to the conductive layer, an AC signal as a drive signal is applied to the pair of fixed electrodes formed of the first and second fixed electrodes, so that the vibration sandwiched between the pair of fixed electrodes In the direction according to the polarity of the AC signal, the membrane receives the electrostatic attractive force and the electrostatic repulsive force simultaneously in the same direction, so that not only can the vibration of the vibrating membrane be sufficiently large to obtain a parametric effect, Since the symmetry of vibration is ensured, a high sound pressure can be generated over a wide frequency band.

  Further, in the method of manufacturing an ultrasonic transducer of the present invention having the above-described configuration, the vibration film holding portion in the fixed electrode that holds the vibration film is formed of an insulating material by an electrodeposition method. The sandwiching portion can be easily formed as a permanent structure.

  In the method for manufacturing an ultrasonic transducer according to the present invention, the insulating material is an electrodeposition material.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Embodiment of Ultrasonic Transducer]
FIG. 1 shows the configuration of an ultrasonic transducer according to an embodiment of the present invention.
The ultrasonic transducer according to the embodiment of the present invention includes a first fixed electrode 10A having a plurality of through holes 14 and a second fixed hole having a plurality of through holes 14 paired with the first fixed electrode 10A. A fixed electrode 10B, a pair of fixed electrodes 10A and 10B, a conductive layer 121, a vibrating membrane 12 to which a DC bias voltage is applied to the conductive layer 121, and the pair of fixed electrodes 10A and 10B. A plurality of through-holes 14 formed in the second fixed electrode 10B and a plurality of through-holes 14 formed in the first fixed electrode 10A via the vibration film 12. All or most of the opposing positions are formed, and an ultrasonic transducer to which an AC signal is applied between the pair of fixed electrodes 10A and 10B is the vibration of the pair of fixed electrodes that sandwich the vibration film. The clamping portion 101 is characterized by the formation of an insulating material.

FIG. 1A shows a configuration of an ultrasonic transducer, and FIG. 1B 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 sandwiched between a pair of fixed electrodes 10 </ b> A and 10 </ b> B including a conductive member formed of a conductive material that functions as an electrode, and a pair of fixed electrodes, and a conductive layer 121. And a pair of fixed electrodes 10A, 10B and a member (not shown) for holding the vibration membrane.

  Each of the pair of fixed electrodes 10A and 10B includes a fixed electrode portion 100 made of a conductor and a vibration film holding portion 101 that holds the vibration film 12. The vibration film sandwiching portion 101 is made of an insulating material. As this insulating material, any of a liquid solder resist, a photosensitive film, a photosensitive coating material, a non-conductive paint, and an electrodeposition material can be used. By forming the vibration film sandwiching portion 101 with an insulating material of any one of a liquid solder resist, a photosensitive film, a photosensitive coating material, a non-conductive paint, and an electrodeposition material, the vibration film sandwiching portion in the fixed electrode has a permanent structure. It can be formed as a body.

The vibration film 12 includes an insulating layer 120 formed of an insulator and a conductive layer 121 formed of a conductive material. The conductive layer 121 is unipolar (positive polarity) by a DC bias power supply 16. DC bias voltage may be applied), and an AC signal output from the signal source 18 may be applied superimposed on the DC bias voltage. Yes.

Further, the pair of fixed electrodes 10A and 10B have the same number and a plurality of through holes 14 at positions facing each other with the vibrating membrane 12 therebetween, and a signal source 18 is provided between the conductive members of the pair of fixed electrodes 10A and 10B. An AC 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, respectively.

In the above configuration, the ultrasonic transducer 1 receives an AC signal output from the signal source 18 to the electrode layer of the vibrating membrane 12 to a DC bias voltage having a single polarity (positive polarity in this embodiment) by the DC bias power supply 16. Applied in a superimposed state.
On the other hand, an AC signal is applied from the signal source 18 to the pair of fixed electrodes 10A and 10B.

As a result, in the positive half cycle of the AC signal output from the signal source 18, since a positive voltage is applied to the fixed electrode 10A, the surface portion 12A not sandwiched between the fixed electrodes of the vibrating membrane 12 The electrostatic repulsive force acts, and the surface portion 12A is pulled downward in FIG.
Further, at this time, since a negative voltage is applied to the opposed fixed electrode 10B, an electrostatic attraction force acts on the back surface portion 12B which is the back surface side of the surface portion 12A of the vibration film 12, The back surface portion 12B is pulled further downward in FIG.

  Therefore, the membrane portion of the vibrating membrane 12 that is not sandwiched between the pair of fixed electrodes 10A and 10B receives an electrostatic repulsive force and an electrostatic repulsive force in the same direction. Similarly, also in the negative half cycle of the AC signal output from the signal source 18, the surface portion 12A of the vibration film 12 has an electrostatic attraction force upward in FIG. 1A and the back surface portion 12B. In FIG. 1B, the electrostatic repulsive force acts on the upper side, and the film portion not sandwiched between the pair of fixed electrodes 10A and 10B of the vibrating membrane 12 has the electrostatic repulsive force and the electrostatic force in the same direction. Receive repulsion. In this way, the direction in which the electrostatic force changes alternately while the vibrating membrane 12 receives the electrostatic repulsive force and the electrostatic repulsive force in the same direction according to the change in polarity of the AC signal. An acoustic signal having a sound pressure level sufficient to obtain a parametric array effect can be generated.

Thus, 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 as compared with the conventional electrostatic ultrasonic transducer (Pull type) in which only the electrostatic attraction force acts on the vibration membrane. Have the ability to meet.

  FIG. 10 shows frequency characteristics of the ultrasonic transducer according to the embodiment of the present invention. In the figure, a curve Q3 is a frequency characteristic of the ultrasonic transducer according to the present embodiment. As can be seen from the figure, a higher sound pressure level can be obtained over a wider frequency band than 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 that can obtain a parametric effect in a frequency band of 20 kHz to 120 kHz can be obtained.

  In the ultrasonic transducer 1 according to the embodiment of the present invention, the thin vibration film 12 sandwiched between the pair of fixed electrodes 10A and 10B receives both the electrostatic attractive force and the electrostatic repulsive force. In addition, since the symmetry of vibration is ensured, a high sound pressure can be generated over a wide band.

  That is, in the ultrasonic transducer of the present invention having the above-described configuration, a plurality of through holes are formed at positions where the first fixed electrode and the second fixed electrode are opposed to each other, and a DC bias voltage is applied to the conductive layer of the vibrating membrane. In this state, since an alternating current signal as a drive signal is applied to the pair of fixed electrodes including the first and second fixed electrodes, the vibration film sandwiched between the pair of fixed electrodes has the polarity of the alternating current signal. Since the electrostatic attractive force and the electrostatic repulsive force are simultaneously received in the same direction in the corresponding direction, not only can the vibration of the diaphragm be sufficiently large to obtain a parametric effect, but also the symmetry of the vibration is ensured. Therefore, a high sound pressure can be generated over a wide frequency band.

Further, since the vibration film sandwiching portion in the pair of fixed electrodes that sandwich the vibration film is formed of an insulating material, the thickness of the insulating layer is increased by this vibration film sandwiching portion (for example, several μm to several tens μm). As a result, even a thin film having a thickness of 10 μm or less can be used as a vibrating membrane at a high voltage without any problem, and the effect of expanding the selection range of the film thickness of the vibrating membrane is obtained.
In addition, since the vibration film sandwiching portion of the pair of fixed electrodes that sandwich the vibration film is formed of an insulating material, a state occurs in which the edge of the vibration film sandwiching portion of the fixed electrode deeply penetrates into the insulating layer in the manufacturing process. However, since the thickness of the insulating layer is added to the thickness of the insulating layer of the vibrating membrane by the thickness of the vibrating membrane sandwiching portion of the fixed electrode, it is avoided that the dielectric breakdown due to the vibrating membrane is broken. effective.

In addition, even if a part of the diaphragm sandwiching part of the fixed electrode is completely in contact with the conductive layer of the diaphragm, or if the diaphragm is completely penetrated and contacted with the fixed electrode on the opposite side, the conductive parts are in contact with each other. However, it is possible to completely prevent a decrease in insulation strength and a short circuit due to structural distortion of the fixed electrode.
Furthermore, compared to the conventional case where the fixed electrode is entirely made of a conductive material, if the vibration film sandwiching portion is made of a non-conductive material, the electrostatic force acting on the vibration electrode film is not changed at all, and only the capacitance is changed. The energy efficiency can be improved by reducing the capacitance.

Next, a manufacturing process in a case where the fixed electrode portion of the ultrasonic transducer according to the embodiment of the present invention is manufactured by a photolithography method by a conventional method will be described with reference to FIG. In the figure, first, a conductor plate (copper, stainless steel is used, but copper is suitable for nickel electroforming) 10 is covered with a mask member 11 in which a plurality of through hole patterns are formed. Through holes 14 are formed in the conductor plate 10 by etching (FIGS. 4A and 4B).
Next, after the through hole 14 is formed in the conductor plate 10, the mask member 11 is peeled off to obtain the conductor plate 10 having the through hole 14 (FIG. 4C).

  Here, the diameter of the through-hole 14 vacated in the conductive plate 10 by etching is limited by the relationship with 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 thickness of the through hole 14 having this diameter 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 0.25 mm-thick metal plates with through-holes 14 formed by etching are prepared in advance, and the necessary number of sheets are stacked and heated. A fixed electrode having a desired thickness is manufactured by metal bonding by pressure bonding or diffusion bonding.

Next, in order to form the vibration film sandwiching portion (step portion) constituting the fixed electrode on the conductor plate 10 with the through hole 14 formed therein, a photosensitive resist (a coating or film in the case of liquid) is used as a pretreatment material. In this case, after laminating) 20A, exposure is performed by covering the vibration film sandwiching portion forming mask member 21A (FIG. 4D).
As the photosensitive resist 20A, a liquid resist or a dry film that is generally used for forming a temporary intermediate structure by etching or plating is used. In this configuration, the through hole 14 is sealed. Therefore, it is more effective to use a dry film.

When unnecessary resist is removed by development, only the surface of the conductive plate 10 where the vibration film sandwiching portion (step portion) of the fixed electrode is formed is exposed (FIG. 4E).
Next, a metal (for example, nickel) is laminated on the exposed surface of the conductive plate 10 to a desired height by electroforming (FIG. 4F).
When the residual resist 20A ′ is removed after the electroforming process is completed, a desired fixed electrode is completed (FIG. 4G).

Problems of the fixed electrode when manufactured by the above conventional manufacturing process are shown below.
(1) A thin film cannot be used for the vibrating membrane When a fixed electrode is manufactured in the conventional manufacturing process described above, that is, when the vibrating membrane sandwiching portion of the fixed electrode is made of a conductive material, a metal vapor deposition layer (= 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.

Here, the dielectric breakdown strength of each material is as follows.
PET, PPS, PI: 200V / μm
PP: 300V / μm
The voltage applied to this transducer is several hundred volts to several kilovolts 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 vibration film, a film thickness of at least 10 μm is necessary to apply a voltage of 2 kV, and a film thinner than this cannot be used as the vibration film. Become.

(2) Easily causes 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 or the like are generated at locations where additional machining (machining) has been performed. In addition, it has been confirmed that the etched metal is easily distorted, and even when thermocompression bonding or diffusion bonding is performed, a warp of at least 10 and several μm remains.
As described above, when the vibration electrode film is securely clamped in a state where the fixed electrode is warped, the edge portion of the vibration film sandwiching portion 20 in the fixed electrode is formed on the insulating layer 120 of the vibration film 12 as shown in FIG. Bite.

In the conventional configuration, since the diaphragm sandwiching portion 20 is made 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 intrusion. The dielectric breakdown strength is reduced.
For example, when the insulating layer 120 is PET, it is difficult to apply a voltage of 200 V or more when d1 is reduced to about 1 μm.

(3) The capacitance is large, and energy is wasted.
The input power is determined by the electrostatic capacity, and as the gap between the conductive layer 121 of the vibrating membrane 12 and the fixed electrode is narrowed, that is, as the insulating layer 120 of the vibrating electrode film is thinner, the electrostatic capacity increases and the input power increases.
On the other hand, the electrostatic force acting on the vibrating membrane 12 that contributes most to the main characteristics (= sound pressure) of the ultrasonic transducer is that the area of the metal surface of the fixed electrode exposed as the vibrating membrane sandwiching portion and the level difference of the vibrating membrane sandwiching portion (= Gap between conductor and diaphragm).
Therefore, if a vibrating membrane with a thin insulating layer is used, the electrostatic force increases, but at the same time, the capacitance increases significantly, so that the energy efficiency is not good.

As described above, when the fixed electrode of the ultrasonic transducer is manufactured by the conventional manufacturing process, (1) a thin film cannot be used for the vibrating membrane, and (2) between the fixed electrode and the conductive layer of the vibrating membrane. There is a problem that dielectric breakdown is likely to occur, and (3) the capacitance formed between the conductive layer of the vibrating membrane and the fixed electrode is large, and energy is wasted.
These problems are solved by the ultrasonic transducer according to the embodiment of the present invention described above and the method for manufacturing the ultrasonic transducer described below.

[Embodiment of manufacturing method of ultrasonic transducer]
First Embodiment (Photolithography method)
Next, a first embodiment of a method of manufacturing an ultrasonic transducer according to the present invention is shown in FIG. In the method of manufacturing an ultrasonic transducer according to the first embodiment of the present invention, a first fixed electrode having a plurality of through holes and a plurality of through holes paired with the first fixed electrode are formed. A second fixed electrode; a vibration film sandwiched between the pair of fixed electrodes, having a conductive layer, and a DC bias voltage applied to the conductive layer; and a member holding the pair of fixed electrodes and the vibration film 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 through the vibrating membrane. In which an alternating current signal is applied between the pair of fixed electrodes, wherein the vibration film holding portion of the fixed electrode holding the vibration film is formed of an insulating material by a photolithography method. It is characterized by There.
That is, the ultrasonic transducer manufacturing method according to the embodiment of the present invention shown in FIG. 1 is characterized in that the vibration film holding portion of the fixed electrode for holding the vibration film is formed of an insulating material by a photolithography method. Yes.

In FIG. 2, first, a conductor plate (copper, stainless steel is used, but copper is suitable for nickel electroforming) 10 is covered with a mask member 11 in which a plurality of through hole patterns are formed. Through holes 14 are formed in the conductor plate 10 by etching (FIGS. 2A and 2B).
Next, after the through hole 14 is formed in the conductor plate 10, the mask member 11 is peeled off, and the conductor plate 10 having the through hole 14 is obtained (FIG. 2C).

Next, after applying a photosensitive resist (a coating process in the case of a liquid, a lamination process in the case of a film) 20 to form a step constituting the vibration film sandwiching portion to the conductor plate 10 in which the through hole 14 is vacant. Then, exposure is performed by covering the mask member 21 for forming the vibration film sandwiching portion (FIG. 2D).
The photosensitive resist 20 as the vibration film sandwiching portion forming material used here must be able to be permanently configured as the vibration film sandwiching portion and be non-conductive. In the case of liquid, photosensitive polyimide coating material (= photosensitive coating material used in semiconductor manufacturing, coated with a metal plate by spin coating) is used in the case of liquid, and in the case of film, the material is considered to be effective. There are a photosensitive solder resist film, a photosensitive polyimide film, and the like used for a substrate package.

  When the vibration film sandwiching portion forming mask member 21 is peeled off and unnecessary photosensitive resist 20 is removed by development, only the surface of the conductive plate 10 serving as the fixed electrode portion is exposed, and the other portions are non-conductive photosensitive. The resist 20 remains, and a desired fixed electrode is completed (FIG. 2E).

  In the ultrasonic transducer manufactured by the ultrasonic transducer manufacturing method of the present invention having the above-described configuration, a plurality of through holes are formed at positions where the first fixed electrode and the second fixed electrode are opposed to each other. In the state where a DC bias voltage is applied to the conductive layer, an AC signal as a drive signal is applied to the pair of fixed electrodes formed of the first and second fixed electrodes, so that the vibration sandwiched between the pair of fixed electrodes In the direction according to the polarity of the AC signal, the membrane receives the electrostatic attractive force and the electrostatic repulsive force simultaneously in the same direction, so that not only can the vibration of the vibrating membrane be sufficiently large to obtain a parametric effect, Since the symmetry of vibration is ensured, a high sound pressure can be generated over a wide frequency band.

Further, in the method of manufacturing the ultrasonic transducer of the present invention having the above-described configuration, the vibration film holding portion in the fixed electrode that holds the vibration film is formed of an insulating material by a photolithography method. Since the process after metal electroforming can be made unnecessary, the manufacturing process can be shortened and the manufacturing cost can be reduced.
Further, a solvent or the like (mainly a strong alkali solvent) used in the residual resist peeling step is not required, and the environment can be improved.

Second Embodiment (Screen Printing Method)

Next, FIG. 3 shows a second embodiment of a method (manufacturing process) for manufacturing an ultrasonic transducer according to the present invention.
In the method of manufacturing an ultrasonic transducer according to the first embodiment of the present invention, a first fixed electrode having a plurality of through holes and a plurality of through holes paired with the first fixed electrode are formed. A second fixed electrode; a vibration film sandwiched between the pair of fixed electrodes, having a conductive layer, and a DC bias voltage applied to the conductive layer; and a member holding the pair of fixed electrodes and the vibration film 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 through the vibrating membrane. In which an alternating current signal is applied between the pair of fixed electrodes, wherein the vibration film holding portion of the fixed electrode for holding the vibration film is formed of an insulating material by a screen printing method. It is characterized by That is, the ultrasonic transducer manufacturing method according to the embodiment of the present invention shown in FIG. 1 is characterized in that the vibration film holding portion of the fixed electrode for holding the vibration film is formed of an insulating material by a screen printing method. Yes.

In FIG. 3, first, a conductor plate (copper, stainless steel is used, but copper is suitable for nickel electroforming) 10 is covered with a mask member 11 in which a plurality of through hole patterns are formed. Through holes 14 are formed in the conductor plate 10 by etching (FIGS. 2A and 2B).
Next, after the through hole 14 is formed in the conductor plate 10, the mask member 11 is peeled off, and the conductor plate 10 having the through hole 14 is obtained (FIG. 2C).

A screen printing plate 30 and a liquid vibration film sandwiching portion forming material 32 for forming a vibration film sandwiching portion in the fixed electrode are set on the conductor plate 10 having the through holes 14 and the squeegee 31 is moved. The vibration 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. 3D).
Here, the diaphragm holding portion forming material 32 considered to be effective can be configured as a diaphragm holding section permanently and is non-conductive. For example, a liquid solder for a package generally used in a circuit board Masking ink used as a resist or a resist for sandblasting. In particular, a solder resist for a flexible printed circuit board is relatively soft (having a pencil hardness of about HB to 3H), and thus is effective for firmly holding the vibrating electrode film.

  If the screen printing plate 30 is removed after the application of the vibration film sandwiching portion forming material 32 to the portion of the screen printing plate 30 where the mask member is not applied, the conductive plate 10 is non-conductive to other portions except for the vibration film sandwiching portion. The remaining layer (= vibration film sandwiching portion forming material 32) remains, and is dried to obtain a desired fixed electrode (FIG. 3E).

  In the ultrasonic transducer manufactured by the ultrasonic transducer manufacturing method of the present invention having the above-described configuration, a plurality of through holes are formed at positions where the first fixed electrode and the second fixed electrode are opposed to each other. In the state where a DC bias voltage is applied to the conductive layer, an AC signal as a drive signal is applied to the pair of fixed electrodes formed of the first and second fixed electrodes, so that the vibration sandwiched between the pair of fixed electrodes In the direction according to the polarity of the AC signal, the membrane receives the electrostatic attractive force and the electrostatic repulsive force simultaneously in the same direction, so that not only can the vibration of the vibrating membrane be sufficiently large to obtain a parametric effect, Since the symmetry of vibration is ensured, a high sound pressure can be generated over a wide frequency band.

  Further, in the manufacturing method of the ultrasonic transducer of the present invention having the above-described configuration, the vibration film holding portion in the fixed electrode for holding the vibration film is formed of an insulating material by a screen printing method. The steps after metal electroforming can be eliminated, and further, the development step performed by photolithography is not required at all. Therefore, the production process can be greatly shortened and the production cost can be greatly reduced.

  As another method for manufacturing an ultrasonic transducer, a resist is formed in advance so that a conductive portion is exposed only in a portion to be coated (= a portion where a counter electrode forming body is formed), and a non-conductive ink (non-conductive ink) It is also possible to apply the conductive paint) by flying it with an inkjet head, or by dipping it in an electrodeposited polyimide material for electrodeposition coating and peeling the resist after application or electrodeposition.

  The ultrasonic transducer manufacturing method by the ink jet method is a manufacturing method of the ultrasonic transducer according to the embodiment of the present invention shown in FIG. 1, and includes a vibrating membrane holding portion in a fixed electrode that holds the vibrating membrane of the ultrasonic transducer. It is characterized by being formed of an insulating material by an ink jet method.

  In other words, the first fixed electrode formed with a plurality of through holes, the second fixed electrode formed with a plurality of through holes paired with the first fixed electrode, and the pair of fixed electrodes. And having a conductive layer, a vibration film to which a DC bias voltage is applied to the conductive layer, the pair of fixed electrodes, and a member for holding the vibration film, and formed on the second fixed electrode The plurality of through holes are all or most formed at positions facing the plurality of through holes formed in the first fixed electrode through the vibrating membrane, and an AC signal is transmitted between the pair of fixed electrodes. A method of manufacturing an applied ultrasonic transducer is characterized in that a vibration film holding portion in a fixed electrode for holding the vibration film is formed of an insulating material by an ink jet method.

  In the ultrasonic transducer manufactured by the ultrasonic transducer manufacturing method of the present invention having the above-described configuration, a plurality of through holes are formed at positions where the first fixed electrode and the second fixed electrode are opposed to each other. In the state where a DC bias voltage is applied to the conductive layer, an AC signal as a drive signal is applied to the pair of fixed electrodes formed of the first and second fixed electrodes, so that the vibration sandwiched between the pair of fixed electrodes In the direction according to the polarity of the AC signal, the membrane receives the electrostatic attractive force and the electrostatic repulsive force simultaneously in the same direction, so that not only can the vibration of the vibrating membrane be sufficiently large to obtain a parametric effect, Since the symmetry of vibration is ensured, a high sound pressure can be generated over a wide frequency band.

  Further, in the method for manufacturing an ultrasonic transducer of the present invention having the above-described configuration, the vibration film holding portion in the fixed electrode that holds the vibration film is formed of an insulating material by an ink jet method. The part can be easily formed as a permanent structure.

  Further, the ultrasonic transducer manufacturing method by the electrodeposition method is the ultrasonic transducer manufacturing method according to the embodiment of the present invention shown in FIG. 1, and the vibrating membrane in the fixed electrode that sandwiches the vibrating membrane of the ultrasonic transducer. The sandwiching portion is formed of an insulating material by an electrodeposition method.

    That is, in the ultrasonic transducer manufacturing method of the present invention, the first fixed electrode having a plurality of through holes and the second fixed electrode having a plurality of through holes paired with the first fixed electrode. And a vibration film sandwiched between the pair of fixed electrodes, having a conductive layer, and a DC bias voltage applied to the conductive layer, and a member holding the pair of fixed electrodes and the vibration film, The plurality of through-holes formed in the second fixed electrode are all or most formed at positions facing the plurality of through-holes formed in the first fixed electrode through the vibrating membrane, A method of manufacturing an ultrasonic transducer in which an AC signal is applied between a pair of fixed electrodes, wherein the vibration film holding portion of the fixed electrode holding the vibration film is formed of an insulating material by an electrodeposition method. To do.

  In the ultrasonic transducer manufactured by the ultrasonic transducer manufacturing method of the present invention having the above-described configuration, a plurality of through holes are formed at positions where the first fixed electrode and the second fixed electrode are opposed to each other. In the state where a DC bias voltage is applied to the conductive layer, an AC signal as a drive signal is applied to the pair of fixed electrodes formed of the first and second fixed electrodes, so that the vibration sandwiched between the pair of fixed electrodes In the direction according to the polarity of the AC signal, the membrane receives the electrostatic attractive force and the electrostatic repulsive force simultaneously in the same direction, so that not only can the vibration of the vibrating membrane be sufficiently large to obtain a parametric effect, Since the symmetry of vibration is ensured, a high sound pressure can be generated over a wide frequency band.

  Further, in the method of manufacturing an ultrasonic transducer of the present invention having the above-described configuration, the vibration film holding portion in the fixed electrode that holds the vibration film is formed of an insulating material by an electrodeposition method. The sandwiching portion can be easily formed as a permanent structure.

Forming a vibration film sandwiching portion in a fixed electrode of an ultrasonic transducer according to an embodiment of the present invention and an ultrasonic transducer manufactured by an ultrasonic transducer manufacturing method according to an embodiment of the present invention with a non-conductive material (insulating material) As a result, the following effects can be obtained.
(1) The selection range of the film thickness for forming the vibration film is expanded.
The thickness of the insulating layer is increased by the level difference (several μm to several tens of μm) of the vibration film sandwiching portion of the fixed electrode formed of a non-conductive material, and even a thin film of 10 μm or less as a vibration film is a problem. And can be used at high voltage.

For example, when a 3 μm PET film is used for the insulating layer of the vibrating electrode film, the conventional fixed electrode configuration (where the entire fixed electrode is formed of a conductive material) is an upper limit value of a voltage that can be applied with 600 V, but is not electrically conductive. By applying a conductive material, for example, even when the step of the vibration film sandwiching portion is 3 μm, the clearance between the fixed electrode surface and the conductive layer of the vibration film is 6 μm, so a voltage of 1 kV or more can be applied. It becomes.
Further, for example, when a voltage of 3 kV is applied with a step of the vibration film holding portion of the fixed electrode being 20 μm, a 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.

(2) It is possible to avoid dielectric breakdown between the fixed electrode and the conductive layer of the vibration film due to the breakage of the vibration film.
That is, when the diaphragm holding portion 20 of the fixed electrodes 10A and 10B is made of a non-conductive material, the step d2 (several μm to several tens μm) of the diaphragm holding portion 20 is added as an insulating layer in FIG. Therefore, since the minimum gap between the conductive layer 121 of the vibrating membrane 12 and the fixed electrode portion (conductive portion) 10 of the fixed electrode is (d1 + d2), insulation is achieved even if the edge portion penetrates deeply into the insulating layer 120 of the vibrating membrane 12. Breaking strength is sufficiently ensured, there is no occurrence of problems as in the prior art, and even a thin vibrating electrode film can be handled without problems.

  In addition, even when a part of the fixed electrode 10A or 10B completely contacts the conductive layer 121 of the vibration film 12, or completely penetrates the vibration film 12 and contacts the fixed electrode on the opposite side, the conductive parts contact each other. There is nothing, and a decrease in insulation strength and a short circuit due to structural distortion of the fixed electrode can be completely prevented.

(3) The energy efficiency can be improved by reducing the capacitance.
Compared to the case where the fixed electrode is entirely made of a conductive material as in the past, when the diaphragm holding part is made of a non-conductive material, the conductive part (fixed) of the fixed electrode is not changed without changing the electrostatic force acting on the diaphragm. Only the capacitance between the electrode part 100) and the electrode part 100) can be reduced.
For example, in the structure of the transducer of the present invention (FIG. 6), the insulating layer 120 of the vibration film 12 is PET (relative dielectric constant 3.2), the thickness is t1, and the vibration film sandwiching portion 20 is polyimide (relative dielectric constant). 3.5), the thickness (= step difference of the diaphragm sandwiching section 20) is t2, the outer diameter of the diaphragm sandwiching section 20 is φD1, and the inner diameter is half the outer diameter. The capacitance ratio 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 vibration film 12 becomes thinner, the effect of reducing the electrostatic capacitance by forming the vibration film holding part 20 with an insulating material becomes larger. The greater the thickness t2, the greater the capacitance reduction effect.
From the above, since only the input power can be reduced without changing the electrostatic force, an ultrasonic transducer with improved energy efficiency can be realized.

  The ultrasonic transducer according to the embodiment of the present invention and the ultrasonic transducer manufactured by the method of manufacturing the ultrasonic transducer according to the embodiment of the present invention can be used for various sensors, for example, a distance measuring sensor, etc. As described above, the present invention can be used for a sound source for a directional speaker, an ideal impulse signal generation source, and the like.

The figure which shows the structure of the ultrasonic transducer which concerns on embodiment of this invention. The manufacturing process figure which shows 1st Embodiment of the manufacturing method of the ultrasonic transducer based on this invention. The manufacturing process figure which shows 2nd Embodiment of the manufacturing method of the ultrasonic transducer based on this invention. The manufacturing process figure which shows the conventional manufacturing method of an ultrasonic transducer. Explanatory drawing which shows the problem on the structure 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 a fixed electrode and paulownia transmission of a diaphragm with the ultrasonic transducer by the conventional structure of the ultrasonic transducer which concerns on this invention. The figure which shows the structure of the conventional resonance type ultrasonic transducer. The figure which shows the specific structure of the conventional electrostatic broadband oscillation type ultrasonic transducer. The figure which showed the frequency characteristic of the ultrasonic transducer | vibrator which concerns on embodiment of this invention with the frequency characteristic of the conventional ultrasonic transducer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Ultrasonic transducer, 10 ... Conductor board, 10A, 10B ... Fixed electrode, 11 ... Mask member, 12 ... Vibration film, 14 ... Through-hole, 16 ... DC bias power supply, 18 ... Signal source, 20 ... Photosensitive resist , 21... Mask member for forming a diaphragm holding portion, 30... Screen printing plate, 31 .. squeegee, 32 .. forming member for diaphragm holding, 100 .. fixed electrode portion, 101. ... Conductive layer

Claims (12)

A first fixed electrode in which a plurality of through holes are formed;
A second fixed electrode having a plurality of through-holes paired with the first fixed electrode;
A vibrating membrane sandwiched between the pair of fixed electrodes, having a conductive layer, and a DC bias voltage applied to the conductive layer;
A pair of fixed electrodes and a member for holding the vibrating membrane;
The plurality of through-holes formed in the second fixed electrode are all or most formed at positions facing the plurality of through-holes formed in the first fixed electrode through the vibrating membrane, An ultrasonic transducer in which an AC signal is applied between a pair of fixed electrodes,
2. An ultrasonic transducer according to claim 1, wherein the vibration film sandwiching portion of the pair of fixed electrodes that sandwich the vibration film is formed of an insulating material.   The ultrasonic transducer according to claim 1, wherein the insulating material is any one of a liquid solder resist, a photosensitive film, a photosensitive coating material, a nonconductive paint, and an electrodeposition material. A first fixed electrode in which a plurality of through holes are formed;
A second fixed electrode having a plurality of through-holes paired with the first fixed electrode;
A vibrating membrane sandwiched between the pair of fixed electrodes, having a conductive layer, and a DC bias voltage applied to the conductive layer;
A pair of fixed electrodes and a member for holding the vibrating membrane;
The plurality of through-holes formed in the second fixed electrode are all or most formed at positions facing the plurality of through-holes formed in the first fixed electrode through the vibrating membrane, A method of manufacturing an ultrasonic transducer in which an AC signal is applied between a pair of fixed electrodes, wherein the vibration film holding portion of the fixed electrode holding the vibration film is formed of an insulating material by a photolithography method. A method of manufacturing an ultrasonic transducer. A mask member in which a pattern of a plurality of through holes is formed on a conductor plate having a predetermined thickness for forming a fixed electrode portion of the pair of fixed electrodes is covered, and a plurality of through holes are formed in the conductor plate by etching. A first step of forming a hole;
A second step of forming a non-conductive photosensitive resist as a vibration film sandwiching portion forming material in a predetermined thickness on the conductor plate having a plurality of through holes formed in the first step;
A third step of covering and exposing a vibration film sandwiching portion forming mask member in which the pattern of the vibration film sandwiching portion is formed on the surface of the non-conductive photosensitive resist; and
A fourth step of peeling the vibration film sandwiching portion forming mask member and removing the unnecessary photosensitive resist by development;
The manufacturing method of the ultrasonic transducer of Claim 3 characterized by the above-mentioned.   The method for manufacturing an ultrasonic transducer according to claim 4, wherein the photosensitive resist is a photosensitive film or a photosensitive coating material. A first fixed electrode in which a plurality of through holes are formed;
A second fixed electrode having a plurality of through-holes paired with the first fixed electrode;
A vibrating membrane sandwiched between the pair of fixed electrodes, having a conductive layer, and a DC bias voltage applied to the conductive layer;
A pair of fixed electrodes and a member for holding the vibrating membrane;
The plurality of through-holes formed in the second fixed electrode are all or most formed at positions facing the plurality of through-holes formed in the first fixed electrode through the vibrating membrane, A method of manufacturing an ultrasonic transducer in which an alternating current signal is applied between a pair of fixed electrodes, wherein the vibration film holding portion of the fixed electrode for holding the vibration film is formed of an insulating material by a screen printing method. A method of manufacturing an ultrasonic transducer. A mask member in which a pattern of a plurality of through holes is formed on a conductor plate having a predetermined thickness for forming a fixed electrode portion of the pair of fixed electrodes is covered, and a plurality of through holes are formed in the conductor plate by etching. A first step of forming a hole;
A screen printing plate in which a mask member for forming the vibration film sandwiching portion is arranged on the surface of the conductor plate having a plurality of through holes formed in the first step and a liquid vibration film sandwiching portion forming material are set. A second step of:
After setting the screen printing plate and the liquid vibration film sandwiching portion forming material on the surface of the conductor plate in which the plurality of through holes are formed, a mask member is applied to the vibration film sandwiching portion forming material while moving a squeegee. A third step of applying to the part that is not,
A fourth step of applying the vibration film sandwiching portion forming material to a portion where no mask member is applied, then removing the screen printing plate and drying the vibration film sandwiching portion forming material remaining on the surface of the conductive plate;
The method of manufacturing an ultrasonic transducer according to claim 6.   The method for manufacturing an ultrasonic transducer according to claim 7, wherein the liquid vibration film sandwiching portion forming member is a liquid solder resist. A first fixed electrode in which a plurality of through holes are formed;
A second fixed electrode having a plurality of through-holes paired with the first fixed electrode;
A vibrating membrane sandwiched between the pair of fixed electrodes, having a conductive layer, and a DC bias voltage applied to the conductive layer;
A pair of fixed electrodes and a member for holding the vibrating membrane;
The plurality of through-holes formed in the second fixed electrode are all or most formed at positions facing the plurality of through-holes formed in the first fixed electrode through the vibrating membrane, A method of manufacturing an ultrasonic transducer in which an AC signal is applied between a pair of fixed electrodes, wherein the vibration film holding portion of the fixed electrode for holding the vibration film is formed of an insulating material by an ink jet method. Manufacturing method of ultrasonic transducer.   The method for manufacturing an ultrasonic transducer according to claim 9, wherein the insulating material is a non-conductive paint. A first fixed electrode in which a plurality of through holes are formed;
A second fixed electrode having a plurality of through-holes paired with the first fixed electrode;
A vibrating membrane sandwiched between the pair of fixed electrodes, having a conductive layer, and a DC bias voltage applied to the conductive layer;
A pair of fixed electrodes and a member for holding the vibrating membrane;
The plurality of through-holes formed in the second fixed electrode are all or most formed at positions facing the plurality of through-holes formed in the first fixed electrode through the vibrating membrane, A method of manufacturing an ultrasonic transducer in which an AC signal is applied between a pair of fixed electrodes, wherein the vibration film holding portion of the fixed electrode holding the vibration film is formed of an insulating material by an electrodeposition method. A method of manufacturing an ultrasonic transducer. The method for manufacturing an ultrasonic transducer according to claim 11, wherein the insulating material is an electrodeposition material.

Images