JP2019161560A - Capacitive sound wave generator and capacitive speaker - Google Patents

Abstract

To provide a technique capable of improving the reliability of a capacitive sound wave generator by suppressing the occurrence of pull-in in the capacitive sound wave generator.SOLUTION: A capacitive sound wave generator includes a fixed electrode (11) having a through hole (11a) provided to penetrate in the thickness direction, two vibrating electrodes (12, 13) arranged so as to face and sandwich the fixed electrode (11) and movable relative to the fixed electrode (11), and a connecting member (14) that connects the two vibrating electrodes (12, 13) through the through hole (11a), and further includes a dielectric layer (15) on at least a part of the surface on both sides of the fixed electrode (11) facing the two vibrating electrodes (12, 13).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a capacitive sound wave generator and a capacitive speaker.

  Among sound wave generators, those that are generally used as speakers that output sound waves in the audible range include dynamic speakers, balanced armature speakers, capacitance speakers, and the like. The dynamic type speaker vibrates the cone by electromagnetic driving and has a characteristic that the sound range is wide. On the other hand, the dynamic type speaker has a disadvantage of low response because the mass of the cone to be vibrated is large. In particular, a small speaker such as an earphone has a problem that the responsiveness is further deteriorated because the inertial force of the diaphragm is relatively large. In addition, the balanced armature type speaker vibrates an iron piece by electromagnetic driving, and is characterized in that it is easy to miniaturize and consumes less power, but has a disadvantage that the sound range is narrow.

  On the other hand, an electrostatic speaker that solves such a problem is used (see, for example, Patent Documents 1-5). In this capacitive speaker, two fixed electrodes are arranged so as to sandwich the diaphragm. The electrostatic attraction generated between the diaphragm and each fixed electrode is used by charging the diaphragm positively or negatively and charging each fixed electrode by sending an electric signal of the opposite polarity to the diaphragm. Then, the diaphragm is vibrated to output sound waves. Since this capacitance type speaker does not have a coil or the like attached to the diaphragm, high response can be realized. In addition, there is an advantage that the structure is simple and power consumption is low.

Iman Shahoseni, et al, “Electromagnetic MEMS micropeaker for portable electronics”, Microsystem Technologies, June 2013, Volume 19, 6, 19 879-886 A-S Roller, et al, “The stability and pull-in voltage of electrostatic parallel-plate actuators and liquid solutions, Junalof Microechanics in Ml. 794-801

US Pat. No. 6,842,964 European Patent Application No. 2410768 European Patent Application No. 2464142 European Patent Application Publication No. 2582156 Japanese Patent No. 3281887 Japanese Patent No. 5801475

The capacitance type speaker as described above has low power consumption, but it is necessary to apply a high voltage (100 to 200 V) between the vibration electrode and the fixed electrode in order to output a sufficient sound pressure. In addition, in a battery-driven application, a booster circuit that boosts voltage from a low battery voltage (within several volts) is required, which may increase device cost and power consumption. In addition to increasing the voltage between the electrodes, as a means of securing the sound pressure of the capacitive speaker, a method of increasing the electrode area can be considered, but in mobile devices and wearable devices where the speaker size is limited, the area of the speaker There were constraints and cost issues. For the reasons described above, it has been difficult to mount a capacitive speaker in mobile devices and wearable devices that have restrictions on both power consumption and speaker size.

  And in order to solve the above problems, to reduce the driving voltage of the capacitive sound wave generator or the capacitive speaker, and to suppress the power consumption, the penetration provided through the thickness It is composed of a fixed electrode having a hole, a vibration electrode that is arranged so as to face the fixed electrode and is movable with respect to the fixed electrode, and a connecting member that connects the two vibration electrodes through the through hole. Capacitance-type speakers that have been adapted are also proposed.

By the way, in the above capacitive speaker, when the displacement d of the vibrating electrode becomes equal to or more than 1/3 of the initial distance (d ₀ ) between the vibrating electrode and the fixed electrode, the displacement becomes unstable and faces each other. It is known that a phenomenon of colliding with a fixed electrode occurs. This phenomenon is called pull-in. When the above pull-in occurs, the vibrating electrode collides with the opposing fixed electrode, but since there is a strong electrostatic attraction, the vibrating electrode sticks to the fixed electrode, or the vibrating electrode is In some cases, it was destroyed.

  The present invention has been made in view of the prior art as described above, and an object of the present invention is to suppress the occurrence of pull-in in the capacitive sound wave generator, and thereby to improve the reliability of the capacitive sound wave generator. It is to provide technology that can improve performance.

The present invention has been made to solve the above-described problem, and has a plate-like shape and a fixed electrode having one or a plurality of through holes provided so as to penetrate in the thickness direction;
Two sheets having a plate-like or film-like shape, arranged so as to face the fixed electrode, with the fixed electrode interposed therebetween, and at least a central portion of the fixed electrode being provided so as to be movable in the thickness direction A vibrating electrode,
A connecting member for connecting the two vibrating electrodes through the through hole;
With
A capacitance-type sound wave generator, wherein a dielectric layer is provided in at least a part of a region on both surfaces of the fixed electrode facing the two vibrating electrodes.

  According to this, the two vibrating electrodes can be vibrated as a unit based on the electrostatic force between the fixed electrode not provided with the sound hole and the two vibrating electrodes disposed with the fixed electrode interposed therebetween. it can. In the present invention, the area of the electrode for generating an electrostatic force can be increased as compared with a conventional sound wave generator in which a plurality of sound holes are provided in the fixed electrode, and the vibrating electrode is vibrated more efficiently. be able to. Here, the fixed electrode has a through-hole through which the connecting member is passed. The area of the through-hole is significantly larger than the total area of the sound holes of the fixed electrode in a normal capacitive sound wave generator. Since it can be made smaller, there is no problem.

  In the present invention, a dielectric layer is provided in at least a part of the regions on both sides of the fixed electrode facing the two vibrating electrodes. As a result, by appropriately setting the dielectric constant and thickness of the dielectric layer, and the distance between the dielectric layer and the vibrating electrode, the position of the vibrating electrode where the pull-in occurs in principle can be theoretically determined. Can be set to As a result, it is possible to suppress the occurrence of pull-in.

In the present invention, the thickness of the dielectric layer is t ₁ , the dielectric constant of the dielectric layer is ε ₁ , the distance between the vibrating electrode and the dielectric layer is g, the vibrating electrode and the dielectric When the dielectric constant of the space between the layers is ε,

You may make it satisfy | fill. According to this, the position of the vibrating electrode where pull-in occurs can be theoretically set inside the dielectric layer. As a result, it is possible to more reliably prevent pull-in.

  Further, in the present invention, the fixed electrode and the two vibrating electrodes are each moved or deformed in the same direction by an electrostatic attractive force generated between the two vibrating electrodes and the fixed electrode. An acoustic signal input means for applying a voltage between the two may be further provided. As a result, sound waves can be generated more efficiently, the applied voltage of the sound wave generator can be reduced, and power consumption can be reduced.

  In the present invention, at least one of the fixed electrode and the two vibrating electrodes may be fixed at the peripheral edge thereof. According to this, the positions and movements of the fixed electrode and the vibration electrode can be further stabilized, and the quality of the sound wave generated by the sound wave generator can be improved.

In the present invention, the acoustic signal input means is
Applying a positive or negative bias voltage to the fixed electrode;
The acoustic signal is converted into an analog signal based on one of an inverted bias voltage obtained by inverting the polarity of the bias voltage, the bias voltage, or a voltage between the inverted bias voltage and the bias voltage, and the polarity of the analog signal Inverted analog signals may be generated, and the analog signal and the inverted analog signal may be applied to the two vibrating electrodes, respectively.

  According to this, it is possible to control the two vibrating electrodes so as to move in the same direction by the electrostatic attractive force generated between the two vibrating electrodes. As a result, sound waves can be generated more efficiently, the applied voltage of the sound wave generator can be reduced more reliably, and power consumption can be reduced.

  Further, the present invention is characterized by comprising the above-described capacitance-type sound wave generator and configured to be able to generate sound waves in the audible range by the vibration of the two vibration electrodes by the acoustic signal input means. A capacitive speaker may be used. According to this, it is possible to provide a highly reliable electrostatic capacity type speaker that can be mounted on a mobile device or a wearable device in which both power consumption and speaker size are restricted and pull-in does not occur.

  In addition, the means for solving each of the above-described problems can be used in combination as much as possible.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to suppress generation | occurrence | production of a pull in in a capacitive sound wave generator, and to improve the reliability of a capacitive sound wave generator.

It is the schematic which shows the sound wave generation part of the electrostatic capacitance type speaker used as the premise of this invention. It is a figure for demonstrating the action | operation of the sound wave generation part used as the premise of this invention. It is the schematic which shows the sound wave generation part of the electrostatic capacitance type speaker which concerns on the application example of this invention. It is the schematic of an electrostatic capacitance type speaker including the acoustic signal input part in the Example of this invention. It is a figure for demonstrating the pull-in phenomenon of the electrostatic capacitance type speaker in the Example of this invention. It is a graph for demonstrating the pull-in phenomenon of the electrostatic capacitance type speaker in the Example of this invention. It is a figure which shows the principle of the sound wave generation part of the capacitive speaker in the Example of this invention. It is a graph which shows the principle of the sound wave generation part of the capacitive speaker in the Example of this invention. It is a 2nd graph which shows the principle of the sound wave generation part of the capacitive speaker in the Example of this invention. It is a 3rd graph which shows the principle of the sound wave generation part of the capacitive speaker in the Example of this invention. It is a graph which shows the position of the balance point in case the drive voltage of the capacitive speaker in the Example of this invention is below a pull-in voltage. It is a graph which shows the position of the balance point in case the drive voltage of the capacitive speaker in the Example of this invention is higher than a pull-in voltage. It is a 1st figure which shows the manufacturing process of the sound wave generation part of the capacitive speaker in the Example of this invention. It is a 2nd figure which shows the manufacturing process of the sound wave generation part of the capacitive speaker in the Example of this invention. It is a 3rd figure which shows the manufacturing process of the sound wave generation part of the capacitive speaker in the Example of this invention. It is a 4th figure which shows the manufacturing process of the sound wave generation part of the capacitive speaker in the Example of this invention. It is a 5th figure which shows the manufacturing process of the sound wave generation part of the capacitive speaker in the Example of this invention.

[Application example]
Hereinafter, application examples of the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic diagram of a capacitive speaker 10 configured to generate audible sound waves as an example of a capacitive sound wave generator to which the present invention is to be applied. In the capacitance type speaker 10, the vibrating body 12 and the vibrating electrode 13 are arranged as two vibrating electrodes so as to sandwich the fixed electrode 11. The vibrating body 12 and the vibrating electrode 13 are the same as the fixed electrode 11. It is connected by the connecting member 14 through the through hole 11a. In the example of FIG. 1, the end of the fixed electrode 11 and the end of the vibrating body 12 are fixed, and the end of the vibrating electrode 13 is free. As shown in FIG. 2A, the capacitance type speaker 10 applies a voltage to the vibrating body 12 in a state where a voltage is applied to the fixed electrode 11 and the fixed electrode 11 is negatively charged. By sending an electric signal having a polarity opposite to that of the fixed electrode 11 to the vibrating body 12 and positively charging it, an electrostatic attractive force is generated between the vibrating body 12 and the fixed electrode 11, and the vibrating body 12 is moved to the fixed electrode 11 side. To deform.

  Similarly, as shown in FIG. 2B, a voltage is applied to the vibrating electrode 13, and an electric signal having a polarity opposite to that of the fixed electrode 11 is sent to the vibrating electrode 13 so as to be positively charged. An electrostatic attractive force is applied between the electrode 13 and the fixed electrode 11 to move the vibration electrode 13 to the fixed electrode 11 side. At this time, since the vibrating body 12 and the vibrating electrode 13 are coupled by the connecting member 14, the vibrating body 12 and the vibrating electrode 13 move in the same direction. As a result, the vibrating body 12 is deformed to the opposite side to the fixed electrode 11. Thus, by applying a voltage related to an acoustic signal to the vibrating body 12 and the vibrating electrode 13, the vibrating body 12 can be vibrated and a sound wave can be output.

  In the capacitive speaker 10, the vibrating body 12 and the vibrating electrode 13 are disposed so as to sandwich the fixed electrode 11, and the vibrating body 12 and the vibrating electrode 13 disposed on the outside vibrate. Therefore, it is not necessary to provide a sound hole in any of the fixed electrode 11, the vibrating body 12, and the vibrating electrode 13. As a result, dust, water, moisture, and the like are placed between the fixed electrode 11 and the vibrating body 12 or the vibrating electrode 13 as compared with a conventional capacitive speaker in which a sound hole is provided in each outer fixed electrode. Hard to invade. For this reason, it can suppress that a foreign material adheres to the vibrating body 12, the vibrating electrode 13, and the fixed electrode 11, and generation | occurrence | production of discharge can be suppressed and the reliability and durability of the vibrating body 12 can be improved.

  In the capacitance type speaker 10, the through hole 11 a provided in the fixed electrode 11 is used only for passing the connection member 14, and therefore, compared to the sound hole for passing sound waves, the fixed electrode 11. The ratio with respect to the surface area can be reduced. For this reason, even when the through hole 11a is provided, the amount of decrease in electrostatic force due to the through hole 11a is small. In addition, since the vibrating body 12 and the vibrating electrode 13 are disposed outside the fixed electrode 11, the waveform of the capacitive speaker 10 is disturbed by interference due to the sound wave output from the vibrating body 12 or the vibrating electrode 13. It can be propagated to the outside without increasing the sound quality.

  Here, in the capacitive speaker 10, a voltage is applied between the fixed electrode 11 and the vibrating body 12 or the vibrating electrode 13, and the vibrating body 12 and the vibrating electrode 13 are vibrated by the generated electrostatic force. By this vibration, air is vibrated to generate sound waves. Such a mechanism for working by electrostatic force is also called an electrostatic actuator, and is used in various devices in addition to the capacitive speaker 10. Here, it is known that when the vibrating electrode approaches the fixed electrode facing the electrostatic actuator more than a certain amount, the displacement becomes unstable and a phenomenon of colliding with the fixed electrode occurs. This phenomenon is called pull-in.

  When the pull-in occurs, the vibrating body 12 or the vibrating electrode 13 collides with the opposing fixed electrode 11, and a strong electrostatic attraction is acting on the vibrating body 12 or the vibrating electrode 13, so that the vibrating body 12 or the vibrating electrode 13 contacts the fixed electrode 11. In some cases, the vibrating body 12 or the vibrating electrode 13 may be damaged due to sticking or an impact at the time of collision. Therefore, it is necessary to prevent pull-in when using an electrostatic actuator.

In order to prevent the above pull-in from occurring, in the capacitive speaker 10, the interval between the vibrating body 12 or the vibrating electrode 13 and the fixed electrode 11 is set to be three times the vibration displacement of the vibrating body 12 or the vibrating electrode 13. It was necessary to set above. Here, the size and vibration displacement of the vibration electrode necessary for obtaining a sound pressure of 80 dB at a distance of 1 cm from the capacitive speaker 10 are as follows, for example.
1. Diameter of vibration electrode and fixed electrode: 4 mm
2. Vibrating electrode thickness / Young's modulus: 5 μm / 2.8 GPa
3. Displacement of vibrating electrode: 27μm

  In this case, in order to prevent pull-in from occurring, it is necessary to make the interval between the fixed electrode 11 and the vibrating body 12 or the vibrating electrode 13 larger than 81 μm, which is three times the vibration displacement. When the distance between the fixed electrode 11 and the vibrating body 12 or the vibrating electrode 13 is set to 81 μm, the driving voltage is 130V. Thus, in order to suppress pull-in in the capacitive speaker 10, the drive voltage had to be very high.

  To deal with this problem, in this application example, as shown in FIG. 3, a dielectric having a predetermined thickness and dielectric constant between the fixed electrode 11 of the capacitive speaker 10, and the vibrating body 12 and the vibrating electrode 13. It was decided to install. Thereby, pull-in can be suppressed in the capacitive speaker 10. The dielectric 15 is completely different in technical significance from a stopper or a spacer for preventing the vibrating body 12 and the vibrating electrode 13 from colliding with the fixed electrode 11. When a simple stopper or spacer that does not have an appropriate thickness and dielectric constant is inserted into the capacitive speaker 10, as a result, the vibrating body 12 or the vibrating electrode 13 can be prevented from colliding with the fixed electrode 11, This is because it may be difficult for the vibrating body 12 or the vibrating electrode 13 to adhere to the dielectric 15 or behave stably in the space between the dielectric 15.

  In this application example, by installing the dielectric 15 having an appropriate thickness and dielectric constant between the fixed electrode 11 and the vibrating body 12 or the vibrating electrode 13, the vibrating body 12 or the vibrating electrode 13 is It has become possible to suppress sticking to the dielectric 15 and unstable operation.

  In FIG. 3, the dielectric 15 is provided over the entire surface on both sides of the fixed electrode 11, but the dielectric 15 is not necessarily provided over the entire surface of both surfaces of the fixed electrode 11. You may provide in the one part area | region of the surface facing the vibrating body 12 or the vibrating electrode 13. FIG. For example, on the surface on the vibration body 12 side, the vibration body 12 may be provided only in the central portion where the displacement of the vibration body 12 becomes larger. In the above application example, the fixed electrode 11 is provided with the single through hole 11a, and the vibration member 12 and the vibration electrode 13 are connected by the single connection member 14. Of course, a plurality of holes 11a and connecting members 14 may be provided.

<Example 1>
Next, Embodiment 1 of the present invention will be described with reference to FIG. Here, first, the capacitive speaker system 20 including the capacitive speaker 10 and the acoustic signal input device 16 as acoustic signal input means in the present embodiment will be described. As described above, the capacitive speaker system 20 includes the capacitive speaker 10 including the fixed electrode 11, the vibrating body 12, the vibrating electrode 13, the connection member 14, and the dielectric 15, and the acoustic signal input device 16. ing.

  Here, in the capacitive speaker 10, the fixed electrode 11 has a disk shape, for example, and is provided with a through hole 11 a provided in the center in the thickness direction. The vibrating body 12 has a thin disk shape with a diameter smaller than that of the fixed electrode 11, for example. The vibrating body 12 is disposed so as to face the fixed electrode 11. The vibrating electrode 13 has a disk shape having the same diameter and thickness as the vibrating body 12, and is disposed so as to face the fixed electrode 11 on the side opposite to the vibrating body 12 with respect to the fixed electrode 11. .

  The connecting member 14 has an elongated rod shape, and connects the vibrating body 12 and the vibrating electrode 13 through the through hole 11 a of the fixed electrode 11. Both ends of the connecting member 14 are fixed to the central portion of the vibrating body 12 and the central portion of the vibrating electrode 13, respectively. Thereby, the vibrating body 12 and the vibrating electrode 13 can vibrate in the thickness direction with respect to the fixed electrode 11. At that time, the vibrating body 12 and the vibrating electrode 13 are moved by the same distance in the same direction by the connecting member 14 and are vibrated simultaneously.

  The acoustic signal input device 16 includes a bias generator 31 and a voltage converter 32. The bias generator 31 generates positive and negative bias voltages and supplies the positive bias voltage to the fixed electrode 11. In addition, the bias generator 31 supplies a negative bias voltage to the voltage converter 32. The voltage conversion unit 32 receives an acoustic signal from the acoustic input terminal 32a, and uses the acoustic signal as a reference from a negative bias voltage supplied from the bias generation unit 31 as a positive voltage or bias potential higher than the bias potential. Convert to analog signal with low negative voltage. The voltage conversion unit 32 supplies the converted analog signal to the vibrating body 12 and supplies an inverted signal obtained by inverting the polarity of the analog signal to the vibrating electrode 13. Accordingly, the capacitive speaker 10 vibrates using the electrostatic force acting between the vibrating body 12 and the fixed electrode 11 and between the vibrating electrode 13 and the fixed electrode 11 in accordance with the principle described with reference to FIGS. 1 and 2. The body 12 and the vibrating electrode 13 are vibrated to generate sound waves. Note that the bias generator 31 may supply the voltage converter 32 with a positive bias voltage or a voltage between the negative bias voltage and the positive bias voltage instead of the negative bias voltage. In this case, the voltage conversion unit 32 uses the positive bias voltage supplied from the bias generation unit 31 or a voltage between the negative bias voltage and the positive bias voltage as a reference, or a voltage higher than that potential. You may make it convert into the analog signal of a low voltage.

Next, the principle of occurrence of pull-in will be described. FIG. 5 is a diagram schematically showing the relationship between the fixed electrode 11 and the vibrating body 12. In FIG. 5, the fixed electrode 11 is represented as a rigid frame. The vibrating body 12 is represented as a plate hung by a helical spring having a spring constant k. FIG. 5A shows a case where no voltage is applied between the fixed electrode 11 and the vibrating body 12. In FIG. 5A, the vibrating body 12 is located at a distance d ₀ from the fixed electrode 11. At this height, the weight of the plate and the spring force are in balance. In the following description of the present specification, the vibrating body 12 is selected as an example of the vibrating electrode. However, the same description also applies to the vibrating electrode 13.

FIG. 5B shows a case where a relatively low voltage V ₁ is applied between the fixed electrode 11 and the vibrating body 12. As shown in FIG. 5 (b), in this case, between the fixed electrode 11 and the vibrating body 12, the electrostatic attraction caused by the voltage V _1, the vibrating body 12 is pulled to the fixed electrode 11. Then, in balance with the spring force in the second balancing position lowered by x ₁ from the balanced position. FIG. 5C shows a case where a voltage V ₂ higher than V ₁ is applied between the fixed electrode 11 and the vibrating body 12. As shown in FIG. 5 (c), between the fixed electrode 11 and the vibrating body 12, the electrostatic attraction caused by the voltage V _2, the vibrating body 12 is pulled to the fixed electrode 11, stuck on colliding End up.

  FIG. 6 shows the relationship between the spring force Fs and the electrostatic attractive force Fe. The solid line represents the spring force Fs, and the solid curve represents the electrostatic attractive force Fe. In FIG. 6, it can be seen that the electrostatic attractive force Fe and the spring force Fs are acting in opposite directions. In order to show the relationship between the absolute value of the spring force Fs and the electrostatic attractive force Fe, a broken line obtained by vertically inverting the spring force Fs is shown.

In FIG. 6, it can be seen that the electrostatic attractive force Fe and the spring force Fs when the voltage V ₁ is applied intersect at x = x ₁ . This point is the balance point when a voltage is applied to V _1. When the voltage V ₁ is applied, even if x is slightly larger than x ₁ , the spring force Fs is larger than the electrostatic attractive force Fe, so that the position of the vibrating body 12 is stable at the balance point. There is no pull-in. However, as the moving distance x increases, the spring force Fs increases linearly in proportion to x, whereas the electrostatic attractive force Fe increases in inverse proportion to the square of (d ₀ −x). Therefore, when x increases and exceeds the threshold value at which pull-in occurs, the electrostatic attractive force Fe exceeds the spring force Fs, and the vibrating body 12 further approaches the fixed electrode 11. Then, since the difference between the electrostatic attractive force Fe and the spring force Fs becomes larger, the vibrating body 12 approaches the fixed electrode 11 at an accelerated speed, and as a result, the vibrating body 12 collides with and adheres to the fixed electrode 11. .

Further, as can be seen from FIG. 6, when a higher voltage V ₂ is applied between the fixed electrode 11 and the vibrating body 12, the electrostatic attractive force Fe regardless of the distance between the fixed electrode 11 and the vibrating body 12. Since the spring force Fs is satisfied, there is no balance point, and the vibrating body 12 and the fixed electrode 11 collide and stick in an instant.

On the other hand, in this embodiment, as shown in FIG. 7, the dielectric 15 is provided on the fixed electrode 11. Hereinafter, the principle of the present embodiment will be described. In the system shown in FIG. 7, a voltage V is applied between the fixed electrode 11 and the vibrating body 12 to generate an electrostatic attractive force Fe between the electrodes, so that the vibrating body 12 moves by x and the spring force Fs. The electrostatic force Fe acting on this system when balanced with is expressed as the following equation (1).

Here, ε ₀ is the dielectric constant of vacuum, ε is the dielectric constant of the space between the vibrating body 12 and the dielectric 15, and ε
₁ is the dielectric constant of the dielectric 15. Further, S is the area of the fixed electrode 11, the vibrating body 12 and the dielectric 15, V is an applied voltage between the fixed electrode 11 and the vibrating body 12, and g is a balanced position when there is no applied voltage (hereinafter also referred to as an initial position). ), The distance between the vibrating body 12 and the dielectric 15, t ₁ represents the thickness of the dielectric 15, and x represents the displacement of the vibrating body 12 from the initial position.

The following equation (2) is established at a position where the electrostatic attractive force Fe when the voltage V is applied is balanced with the spring force Fs based on the spring constant k.

And the following formula | equation (3) is obtained by deform | transforming Formula (2).

In Equation (3), the change in the values of the right side and the left side with respect to x can be expressed as shown in FIG. Since the left side of Equation (3) is a cubic function for x, the value of x is from 0 to (t ₁ ε / ε
_It has a peak at x = (t ₁ ε / ε ₁ + g) / 3 while changing to ₁ + g). On the other hand, the right side of Expression (3) is a constant value determined by the value of the voltage V regardless of the change of x. In FIG. 8, the value of x at the intersection of the cubic function on the left side of Equation (3) and the straight line on the right side of Equation (3) is the balanced position, which is the solution of Equation (2).

In FIG. 8, since the straight line by the right side of Formula (3) rises by increasing the voltage V, when the voltage V exceeds a fixed value, the curve by the left side of Formula (3) and the straight line by the right side of Formula (3) No longer has an intersection. Since the peak of the curve on the left side of the equation (3) exists at x = (t ₁ ε / ε ₁ + g) / 3, if the value of the straight line on the right side of the equation (3) becomes larger than the peak, it is balanced. The point disappears. Such a state can be considered as pull-in. In the following description, the voltage V at which pull-in occurs, that is, the voltage V in a state where the value of the straight line on the right side of Equation (3) in FIG. 8 is in contact with the peak is also referred to as a pull-in voltage.

In the present invention, the dielectric 15 layer is formed on the fixed electrode 11 to suppress the occurrence of pull-in. More specifically, the peak shown in FIG. 8 is made to exist inside the dielectric 15, and the vibration body 12 can be stably operated in the movable range of the vibration body 12. For this purpose, the following equation (4) should be satisfied.

Equation (4) is transformed into Equation (5).

If Expression (5) is satisfied, as shown in FIG. 9, the peak on the left side of Expression (3) always exists in the dielectric 15, so that the intersection with the straight line on the right side of Expression (3) The balance point is not to reach the peak on the left side of Equation (3). Therefore, the pull-in state does not appear in the movable range (x <g) of the vibrating body 12, and a stable operation is performed.

  As described above, the layer of the dielectric 15 of the present invention is completely different from the spacers and stoppers often used in the electrostatic actuator in terms of operation and effect. For example, in Patent Document 6, a spacer is provided in the air gap of the electrostatic actuator. This prevents the electrodes from sticking directly when a pull-in operating voltage is applied. The dielectric constant and dimensions are not associated with the operation of the electrostatic actuator and do not suppress pull-in.

  Here, as the material of the dielectric 15, for example, a photosensitive resin formed by dispersing an inorganic material in a polymer may be used. In this case, examples of the inorganic material to be dispersed include high dielectric constant inorganic particles (e.g., about ε≈50) such as barium titanate. Further, as the material of the dielectric 15, a resin material for photoresist having a dielectric constant of about 3 to 4 such as SU-8 may be used. By using these, shape processing can be performed by a photolithography technique, and the dielectric 15 can be formed integrally with the fixed electrode 11 by a semiconductor manufacturing process.

When pull-in does not occur according to the present invention, it is possible to suppress the inconvenience of the vibrating body 12 and the vibrating electrode 13 sticking to the fixed electrode 11 or colliding with and being damaged by the pull-in. And the range which can control the vibrating body 12 and the vibration electrode 13 stably can be expanded. 10A shows an example of the relationship between the voltage V and the displacement of the vibrating body 12 when the present embodiment is not applied, and FIG. 10B shows the case where the present embodiment is applied. In the vicinity of the pull-in voltage V ₀ , the displacement of the vibrating body 12 increases rapidly.

Therefore, as shown in FIG. 10A, when the peak on the left side of Equation (3) exists in the movable range of the vibrating body 12, the operation of the vibrating body 12 becomes unstable near the pull-in voltage V ₀ . Therefore, this area cannot actually be used. On the other hand, in FIG. 10B, the pull-in generation point is outside the movable range of the vibrating body 12 (inside the dielectric 15), and therefore, in the movable range of the vibrating body 12, the displacement of the vibrating body 12 is abrupt. There is no increase. Therefore, the operation of the vibrating body 12 is stable, and it is possible to use the entire region of the space between the vibrating body 12 and the dielectric 15.

  Next, the relationship between the applied voltage and the operation of the vibrating body 12 according to the present embodiment will be described from another viewpoint with reference to FIGS. 11 and 12. 11 and 12, the horizontal axis indicates x, that is, the position of the vibrating body 12. The vertical axis represents the force acting on the vibrating body 12. More specifically, the straight line that increases in proportion to x is the absolute value of the spring force Fs. The curve having a convex shape below is the electrostatic force Fe. 11 and 12, the left unhatched part indicates the movable region of the vibrating body 12, and the right hatched part indicates the inside of the dielectric 15. In the curve indicating the electrostatic force Fe, a solid line indicates a portion where the dielectric 15 is provided, and a broken line indicates a portion where the dielectric 15 is not provided and is different from the case where the dielectric 15 is provided.

FIG. 11A shows a case where the applied voltage V is smaller than the pull-in voltage V ₀ . In this case, the electrostatic force Fe is generally small, and the balance point, which is the intersection of the straight line indicating the spring force Fs and the curve indicating the electrostatic force Fe, is in a place where x is relatively small in the movable region of the vibrating body 12. Existing. Therefore, even when the voltage V is applied, regardless of the presence or absence of the dielectric 15, the vibrating body 12 moves to the balance point and stabilizes, and pull-in does not occur.

Next, FIG. 11B shows a case where the applied voltage V is equal to the pull-in voltage V ₀ . In this case, the curve indicating the electrostatic force Fe when the dielectric 15 is not provided is in contact with the straight line indicating the spring force Fs. On the other hand, the curve indicating the electrostatic force Fe when the dielectric 15 is provided intersects with a straight line indicating the spring force Fs. In this case, when the dielectric 15 is not provided, a balance point exists, but the electrostatic force Fe is larger than the spring force Fs at a position other than the balance point, so that the operation of the vibrating body 12 becomes unstable. Pull-in is likely to occur. On the other hand, when the dielectric 15 is provided, there is a balanced point at the intersection of the curve indicating the electrostatic force Fe and the straight line indicating the spring force Fs, and the operation of the vibrating body 12 is stable. In this case, since the vicinity of the surface of the dielectric 15 serves as a balance point, the vibrating body 12 may come into contact with the dielectric 15, but there is no inconvenience such as damage to the vibrating body 12 due to a collision.

Next, FIG. 12A shows a case where the applied voltage V is greater than the pull-in voltage V ₀ . In FIG. 12A, the curve indicating the electrostatic force Fe when the dielectric 15 is not provided does not touch the straight line indicating the spring force Fs. And pull-in occurs. In this case, since the electrostatic force Fe is always greater than the spring force Fs, the vibrating body 12 may collide with the fixed electrode 11. On the other hand, the curve indicating the electrostatic force Fe when the dielectric 15 is provided intersects the straight line indicating the spring force Fs, and there is still a balance point, and the operation of the vibrating body 12 is stable. Actually, since the balance point exists inside the dielectric 15, the vibrating body 12 may contact the dielectric 15, but the difference between the electrostatic force Fe and the spring force Fs is small. There will be no inconvenience such as damage.

It shows a case where the applied voltage V is much greater than the pull-in voltage V ₀ in FIG. 12 (b). In FIG. 12B, the curve indicating the electrostatic force Fe when the dielectric 15 is not provided does not contact the straight line indicating the spring force Fs, and the gap is larger than that in FIG. In this case, pull-in occurs, and there is a risk that the vibrating body 12 may collide with the fixed electrode 11 with further momentum. On the other hand, the curve indicating the electrostatic force Fe when the dielectric 15 is provided is in contact with the straight line indicating the spring force Fs, and in this case, there is an entanglement point. Actually, since the balance point exists inside the dielectric 15, it is possible that the vibrating body 12 abuts on the dielectric 15, but even in this case, the difference between the electrostatic force Fe and the spring force Fs is small. There is no inconvenience such as breakage of the vibrator 12.

Next, an example of a manufacturing method of the capacitive speaker 10 in the present embodiment will be described. The capacitive speaker 10 according to the present embodiment can be manufactured by the following semiconductor manufacturing process. That is, as shown in FIG. 13A, a silicon substrate 50 comprising silicon (Si) 51 having a thickness of 300 μm and insulating layers 52 and 53 of silicon oxide (SiO 2) having a thickness of 0.8 μm provided on both surfaces. On the other hand, as shown in FIG. 13B, the lower insulating layer 53 in the drawing is entirely removed by dry etching, and the upper insulating layer 52 in the drawing forms a contact hole 54 by photolithography and dry etching.

  Next, as shown in FIG. 13C, a parylene vibrating film 55 that becomes the vibrating body 12 of the capacitive speaker 10 is formed on the insulating layer 52 in which the contact holes 54 are formed by a CVD (chemical vapor deposition) method. To form a thickness of 5 μm. A Ti / Au bilayer film (Ti 0.3 μm / Au 1 μm) 56 is formed as an electrode on the back surface of the surface on which the parylene vibration film 55 is formed by sputtering. Then, as shown in FIG. 13D, a carbon thin film 57 having a thickness of 100 nm is formed on the parylene vibration film 55 by sputtering.

  Next, as shown in FIG. 14A, for the purpose of forming a gap in the capacitive speaker 10 on the parylene vibration film 55, SU-8 (2000) is formed by a roll coat method, and a photolithography technique is used. As a result, a SU-8 (2000) gap forming portion 58 having a height of 27 μm is formed around the parylene vibration film 55 in a band shape. Further, a diaphragm connecting portion 59 having a diameter of 0.5 mm and a height of 27 μm is formed in the central portion of the parylene vibrating membrane 55 to form the connecting member 14. Further, as shown in FIG. 14B, a P-type silicon 60 having a thickness of 200 μm and a resistivity of 1 to 50 Ωcm is prepared as the fixed electrode 11.

  Then, the dielectric layers 61 and 62 of SU-8 (2000) are formed to a thickness of 100 μm by roll coating to form the dielectric 15 on both surfaces. In addition, slits (inner diameter 0.51 mm, width 50 μm) 63 and 64 for connecting the parylene vibration film 55 are formed in the dielectric layers 61 and 62 by a photolithography technique. A Ti / Au bilayer film (Ti 0.3 μm / Au 1 μm) 65 is formed as an electrode on the silicon 60 by sputtering. Next, as shown in FIG. 14C, the gap forming portion 58 and the diaphragm connecting portion 59 and the silicon 60 for the fixed electrode 11 are pressed through the dielectric layer 62 of SU-8 (2000). / Adhere by heating.

  Next, as shown in FIG. 15A, the silicon 60 for the fixed electrode 11 is through-etched along the slits of the dielectric layers 61 and 62 by anisotropic dry etching. Then, as shown in FIG. 15B, the silicon 51 is bonded to the parylene vibrating film 55 so that the parylene vibrating film 55 that becomes the vibrating body 12 and the insulating layer 52 of silicon oxide (SiO 2) remain by the anisotropic dry etching technique. Etching away from the back side of the insulating layer 52 of silicon oxide (SiO2) into a circle having a diameter of 4 mm. And as shown in FIG.15 (c), the vibration electrode unit 63 which should become the another vibrating body 12 formed by the process of the said Fig.13 (a)-FIG.14 (a) is prepared.

As shown in FIG. 16A, another vibrating electrode unit 63 and the silicon 60 for the fixed electrode 11 are bonded by pressing / heating through a dielectric layer 61 of SU-8 (2000). Then, as shown in FIG. 16B, the silicon 67 is subjected to parylene vibration so that the parylene vibration film 68 to be the vibrating body 12 and the insulating layer 66 of silicon oxide (SiO 2) remain by an anisotropic dry etching method. The film 68 and the silicon oxide (SiO 2) insulating layer 66 are etched away into a circle having a diameter of 4 mm from the back side. Then, as shown in FIG. 17, the insulating layers 52 and 66 of silicon oxide (SiO 2) formed in contact with the parylene vibration films 55 and 68 are removed by a method of oxide film dry etching, and the electrostatic capacity in this embodiment is thus obtained. The type speaker 10 is completed. In the present embodiment, since the capacitive speaker 10 is formed by such a semiconductor manufacturing process, the capacitive speaker 10 can be manufactured more easily and with high reliability.

  In the present embodiment, the capacitive speaker 10 has been described as an example of the capacitive sound wave generator, but the present invention is a capacitive sound wave generator other than the capacitive speaker 10. It is also applicable to. For example, an ultrasonic generator or a low-frequency generator corresponds to this. Further, in this embodiment, it has been described that the capacitive speaker 10 is manufactured by the semiconductor manufacturing process shown in FIGS. 13 to 17, but the capacitive speaker 10 is limited to such a MEMS device. I can't. The present invention is also applicable to a capacitance type speaker other than the MEMS type manufactured in a larger and general assembly process.

In the following, in order to make it possible to compare the configuration requirements of the present invention with the configuration of the embodiment, the configuration requirements of the present invention are described with reference numerals in the drawings.
<Invention 1>
A fixed electrode (11) having a plate-like shape and having one or a plurality of through-holes (11a) provided so as to penetrate in the thickness direction;
It has a plate-like or film-like shape, and is arranged with the fixed electrode (11) sandwiched so as to face the fixed electrode (11), and at least the central part of the fixed electrode (11) is in the thickness direction Two vibrating electrodes (12, 13) movably provided on the
A connecting member (14) for connecting the two vibrating electrodes (12, 13) through the through hole (11a);
With
A dielectric layer (15) is provided in at least a part of the surface on both sides of the fixed electrode (11) facing the two vibrating electrodes (12, 13). Capacitance type sound wave generator.
<Invention 2>
The thickness of the dielectric layer (15) is t ₁ , the dielectric constant of the dielectric layer (15) is ε ₁ , the distance between the vibrating electrodes (12, 13) and the dielectric layer (15) is g, When the dielectric constant of the space between the vibrating electrode (12, 13) and the dielectric layer (15) is ε,

The electrostatic capacity type sound wave generator according to claim 1, wherein:
<Invention 3>
The fixed electrode (11) and the two vibrating electrodes (12, 13) are moved and deformed in the same direction by electrostatic attraction generated between the two vibrating electrodes (12, 13) and the fixed electrode (11). The capacitive sound wave generator according to claim 1 or 2, further comprising acoustic signal input means (16) for applying a voltage between the vibrating electrodes (12, 13).
<Invention 4>
The at least one of the fixed electrode (11) and the two vibrating electrodes (12, 13) is fixed at the peripheral edge thereof, according to any one of claims 1 to 3, Capacitance type sound wave generator.
<Invention 5>
The acoustic signal input means (16)
Applying a positive or negative bias voltage to the fixed electrode (11);
The acoustic signal is converted into an analog signal based on one of an inverted bias voltage obtained by inverting the polarity of the bias voltage, the bias voltage, or a voltage between the inverted bias voltage and the bias voltage, and the polarity of the analog signal Are generated, and the analog signal and the inverted analog signal are respectively converted into the two vibrating electrodes (12
13) The capacitive sound wave generator according to claim 3, wherein the capacitive sound wave generator is configured to be applied to the capacitor 13).
<Invention 6>
The capacitive sound wave generator according to any one of claims 1 to 5, wherein the acoustic signal input means (16) causes an audible range due to vibration of the two vibrating electrodes (12, 13). A capacitive speaker configured to generate sound waves.

DESCRIPTION OF SYMBOLS 10 ... Capacitance type speaker 11 ... Fixed electrode 11a .. Through-hole 12 ... Vibrating body 13 ... Vibrating electrode 14 ... Connection member 16 ... Acoustic signal input part 20 ... Capacitance type speaker system 31... Bias generator 32... Voltage converter 32 a.

Claims (6)

A fixed electrode having a plate-like shape and having one or a plurality of through holes provided so as to penetrate in the thickness direction;
Two sheets having a plate-like or film-like shape, arranged so as to face the fixed electrode, with the fixed electrode interposed therebetween, and at least a central portion of the fixed electrode being provided so as to be movable in the thickness direction A vibrating electrode,
A connecting member for connecting the two vibrating electrodes through the through hole;
With
A capacitance-type acoustic wave generator, wherein a dielectric layer is provided in at least a part of a region on both surfaces of the fixed electrode facing the two vibrating electrodes. The thickness of the dielectric layer is t ₁ , the dielectric constant of the dielectric layer is ε ₁ , the distance between the vibrating electrode and the dielectric layer is g, and the dielectric of the space between the vibrating electrode and the dielectric layer If the rate is ε,

The electrostatic capacity type sound wave generator according to claim 1, wherein:   A voltage is applied between the fixed electrode and the two vibrating electrodes so that each of the two vibrating electrodes is moved or deformed in the same direction by an electrostatic attractive force generated between the two vibrating electrodes. The capacitive sound wave generator according to claim 1, further comprising an acoustic signal input unit.   4. The capacitive sound wave generator according to claim 1, wherein at least one of the fixed electrode and the two vibrating electrodes is fixed at a peripheral edge thereof. 5. . The acoustic signal input means includes
Applying a positive or negative bias voltage to the fixed electrode;
The acoustic signal is converted into an analog signal based on one of an inverted bias voltage obtained by inverting the polarity of the bias voltage, the bias voltage, or a voltage between the inverted bias voltage and the bias voltage, and the polarity of the analog signal 4. The capacitance-type electrostatic capacitor according to claim 3, wherein an inverted analog signal is generated by inverting the analog signal, and the analog signal and the inverted analog signal are applied to the two vibrating electrodes, respectively. Sound wave generator.   6. The capacitive sound wave generator according to claim 1, wherein the sound wave is generated in an audible range by vibration of the two vibrating electrodes by the acoustic signal input unit. Capacitance type speaker characterized by that.