JP6678526B2 - Electromechanical transducer - Google Patents

Description

  The present invention relates to an electret substrate, a method for manufacturing the same, and an electromechanical converter.

  2. Description of the Related Art Electromechanical converters that convert between electric power and motive power by electrostatic interaction generated by using an electret having a property of semi-permanently retaining charges are known. For example, Patent Literature 1 describes a power generation device that generates power using electrostatic induction generated by relatively moving an electret electrode and a counter electrode thereof. Further, Patent Document 2 discloses an electret driving device that drives a moving element by using an electrostatic force generated between the electrode and an electret when a voltage is applied to an electrode.

In Patent Document 3, an SiO ₂ layer containing K + ions is formed on the surface of a Si substrate by wet oxidation (thermal oxidation), and a bias voltage is applied while the upper and lower ends of the substrate are sandwiched between electrodes and heated by a heater. to, by moving the K + ions on the surface of the SiO ₂ layer, a method of manufacturing an electret substrate with an electret SiO ₂ layer containing K + ions is described.

Patent Document 4, on a Si substrate, a first SiO ₂ layer provided in contact with the base material of the Si, on the first SiO ₂ layer, in the first SiO ₂ layer an ion impermeable film provided in contact, on the ion impermeable membrane, and a second SiO ₂ layer provided in contact with the ion impermeable membrane, the alkali in the first SiO ₂ layer Electret films containing ions are described.

JP 2015-192577 A JP 2005-341675 A JP 2014-049557 A JP 2013-013256 A

In order to use an electret in an electromechanical converter, it is desirable that the surface potential of the electret (the potential difference between the base portion of the electret substrate and the charged layer) is as high as possible. Since the surface potential V of the electret is proportional to the charge density σ and the film thickness d of the charged layer (V∝σd), it is necessary to increase the charge density σ or the film thickness d in order to increase the surface potential V. There is. However, in the electrets manufactured by the methods of Patent Documents 3 and 4, since the charge density σ depends on the content of potassium, it is difficult to greatly increase the amount. Further, since the thickness d is the thickness of the thermal oxide film of the SiO ₂ layer, it takes a long time to increase the thickness, and there is a limit to the thickness. Therefore, it is difficult to increase the surface potential V.

  Therefore, an object of the present invention is to increase the potential difference between the base portion of the electret substrate and the charging layer, and to increase the output of an electromechanical converter using the electret substrate.

An electret substrate that constitutes a charging unit of an electromechanical converter that performs conversion between electric power and motive power by utilizing electrostatic interaction between the charging unit and a counter electrode, the substrate comprising Si. A base, a first SiO ₂ layer formed on the base, a Si layer formed on the first SiO ₂ layer, and a first SiO ₂ layer formed on the Si layer and containing positive ions. And an electret substrate having _two SiO ₂ layers.

In the above electret substrate, the thickness of the first SiO ₂ layer is preferably greater than the thickness of the second SiO ₂ layer.

Further, the present invention provides a method for manufacturing an electret substrate constituting an electrification portion of an electromechanical converter for performing conversion between electric power and power using an electrostatic interaction between an electrification portion and a counter electrode, comprising: A substrate having a base, a first SiO ₂ layer formed on the base, and a Si layer formed on the first SiO ₂ layer is heated in an atmosphere containing positive ions. Oxidizing to form a second SiO ₂ layer containing positive ions on the Si layer; placing a negative electrode above the second SiO ₂ layer; connecting the Si layer to the positive electrode; by applying a voltage to the SiO ₂ layer, the manufacturing method characterized in that it comprises a step of charging a second SiO ₂ layer is provided.

An electromechanical converter for converting between electric power and motive power by utilizing an electrostatic interaction between a charging unit and a counter electrode, comprising: a movable member movable with a movable supporting portion; A fixed substrate fixedly arranged facing the member, and a plurality of charging units arranged in the moving direction at intervals in the moving direction of the movable member on the same surface of one of the movable member and the fixed substrate, On the other of the movable member and the fixed substrate, on a surface facing the plurality of charged portions, there are provided a plurality of opposed electrodes arranged in the moving direction, and each of the plurality of charged portions is a base made of Si. A base, a first SiO ₂ layer formed on the base, a Si layer formed on the first SiO ₂ layer, and a _second layer formed on the Si layer and containing positive ions. electromechanical transducer, characterized in that it comprises a SiO ₂ layer is provided.

  According to the present invention, the potential difference between the base portion of the electret substrate and the charged layer becomes larger than that in the case where the present configuration is not provided, and the output of the electromechanical converter using the electret substrate becomes larger. .

It is a typical sectional view explaining the manufacturing process of electret board 50. FIG. 1 is a schematic configuration diagram of an electromechanical converter 1. FIG. 2 is a perspective view of an actuator 10 in the electromechanical converter 1. 4 is a graph showing a relationship between a thickness of a lower SiO ₂ layer 52 in the electret substrate 50 and a magnitude of a force generated in the electromechanical converter 1. FIG. 7 is a schematic configuration diagram of another electromechanical converter 2. FIG. 3 is a perspective view of a power generation unit 10 ′ in the electromechanical converter 2. FIG. 9 is a schematic configuration diagram of still another electromechanical converter 3.

  Hereinafter, the electret substrate, its manufacturing method, and the electromechanical converter will be described in detail with reference to the drawings. However, it should be understood that the invention is not limited to the drawings or the embodiments described below.

  FIGS. 1A to 1D are schematic cross-sectional views illustrating a process of manufacturing the electret substrate 50.

The electret substrate 50 is manufactured using an SOI (Silicon on Insulator) substrate 50 'shown in FIG. The SOI substrate 50 ′ is a substrate having a base 51 made of Si, a SiO ₂ layer 52 formed on the base 51, and a Si layer 53 formed on the SiO ₂ layer 52. As the SOI substrate 50 ′, a commercially available SOI substrate may be used, or a SiO ₂ layer is formed on a Si wafer by vapor deposition or sputtering, and a Si layer is formed thereon by vapor deposition or sputtering. A substrate that has been used may be used. Note that Si of the Si layer 53 does not need to be a single crystal.

When manufacturing the electret substrate 50, first, as shown in FIG. 1B, the Si layer 53 on the surface of the SOI substrate 50 'is thermally oxidized in an atmosphere containing K + ions (potassium ions) to contain K + ions. The SiO ₂ layer 54 to be formed is formed on the Si layer 53 (thermal oxidation step). In the thermal oxidation, the SOI substrate 50 'is placed in a thermal oxidation furnace, and nitrogen gas is passed through an aqueous solution of potassium hydroxide (KOH) (bubbling) to introduce KOH vapor and nitrogen gas into the furnace. It is performed by At this time, only the upper layer, not the entire thickness of the Si layer 53, is thermally oxidized to form the SiO ₂ layer 54, and the lower layer of the Si layer 53 remains Si. Thereby, an SiO ₂ layer 54, which is an oxide film into which K + ions have penetrated, is formed on the surface of the Si layer 53. The SiO ₂ layer 52 corresponds to a first SiO ₂ layer, and the SiO ₂ layer 54 corresponds to a _second SiO ₂ layer.

Subsequently, as shown in FIG. 1C, a negative electrode 55 is provided above the SiO ₂ layer 54, the Si layer 53 is connected to the positive electrode (GND), and a voltage of about 1000 V is applied while heating with a heater, for example. by applying the SiO ₂ layer 54, to charge the SiO ₂ layer 54 (charging step). Thus, K + ions in the SiO ₂ layer 54 is moved to the upper surface of the SiO ₂ layer 54, since scattered from the upper surface to the outside of the SOI substrate 50 ', the upper surface of the SiO ₂ layer 54 remains negative charge, results As a result, the SiO ₂ layer 54 is negatively charged. Since the lower SiO ₂ layer 52 is an insulating layer, the Si layer 53 above the SiO ₂ layer 52 is used as a positive electrode instead of the Si base 51 during charging. Since the Si layer 53 has a small thickness of, for example, several μm and it is difficult to apply a GND electrode terminal from the side surface, in order to apply a voltage, the upper SiO ₂ layer 54 is partially etched by etching or the like. A hole is made and an electrode terminal is applied to the Si layer 53 from above.

By the above-described thermal oxidation step and charging step, the electret substrate 50 shown in FIG. 1D is completed. The electret substrate 50 includes a base 51 made of Si, a SiO ₂ layer 52 formed on the base 51, a Si layer 53 formed on the SiO ₂ layer 52, And a SiO ₂ layer (charging layer) 54 containing K + ions. When the electret substrate 50 is used, the base 51 is grounded (connected to GND).

In the electret substrate 50, as shown in FIG. 1D, the two SiO ₂ layers 52 and 54 can be regarded as a series connection of capacitors. When the capacitance of the lower SiO ₂ layer 52 is C1 and the capacitance of the upper SiO ₂ layer 54 is C2, the surface potential V of the SiO ₂ layer 54 when the base 51 is grounded is C1. It is determined by the combined capacitance C in which C2 is connected in series. That is, since C = C1C2 / (C1 + C2), C <C2, and the surface potential V is V = Q / C> Q / C2, where Q is the charge amount of the SiO ₂ layer 54. The surface potential V2 when the electret is manufactured by directly forming the K + ion-containing SiO ₂ layer 54 on the Si substrate is V> V2 since V2 = Q / C2 when the charge amount Q is the same. is there. That is, the surface potential of the electret substrate 50 manufactured from the SOI substrate 50 ′ is higher than the surface potential of the electret manufactured from the Si substrate.

  The output when the electret is used for an electromechanical converter such as a driving device (motor) or a power generator is proportional to the magnitude of the surface potential of the electret. Therefore, if the above-described electret board 50 is used as an electret of an electromechanical converter, the power generated by the motor and the output of the power generator can be increased.

The thickness of the upper SiO ₂ layer 54 in the electret substrate 50 is, for example, about 1 μm, and in this case, the thickness of the lower SiO ₂ layer 52 may be 1 μm or more. Since the dielectric constants of both the SiO ₂ layers 52 and 54 are the same, if two insulating layers having the same thickness are used, the total combined capacitance is smaller than that when the upper SiO ₂ layer 54 is used alone. Become. The lower SiO ₂ layer 52 is preferably thicker, but if it is too thick, the manufacturing cost increases. Therefore, in practice, the upper limit of the thickness of the SiO ₂ layer 52 is about 20 μm. Therefore, the thickness of the SiO ₂ layer 52 is larger than the thickness of the SiO ₂ layer 54, preferably in the range of 1 to 20 μm, and most preferably about 5 μm in practical use. Further, the thickness of the Si layer 53 may be in the range of 2 to several tens μm, and is preferably about several μm. In addition, the thickness of the base 51 may be about 200 to 600 μm.

  Note that the positive ions for manufacturing the electret substrate do not necessarily have to be K + ions. That is, in the thermal oxidation step of the production method described above, an aqueous solution containing a positive ion or an alkali ion other than K + ions may be used instead of the aqueous potassium hydroxide solution.

The lower SiO ₂ layer 52 in the electret substrate 50 is not limited to one layer, and may be a plurality of layers. For example, the SiO ₂ layer and the Si layer may be alternately stacked on the base 51 a plurality of times, and the SiO ₂ layer 54 containing K + ions may be formed on the upper end of the electret substrate. Even in this case, the same effect as that obtained when the thickness of one SiO ₂ layer 52 is increased can be obtained, so that the surface potential of the electret can be increased as compared with the case where the electret is manufactured from the Si substrate.

  In the manufacture of the electret substrate, a SOI substrate in which a resin layer such as CYTOP (registered trademark) is formed on the SOI substrate 50 'in FIG. 1A may be used. In this case, in the charging step, the upper Si layer of the SOI substrate may be set to GND and charged by corona discharge. Even in the electret substrate manufactured in this way, if the Si base is used as GND, the surface potential becomes larger as compared with the case where the electret substrate is manufactured from the Si substrate, as in the case of the electret substrate 50. Output also increases.

  Hereinafter, an example of an electromechanical converter using the electret substrate 50 will be described.

  FIG. 2 is a schematic configuration diagram of the electromechanical converter 1. FIG. 3 is a perspective view of the actuator 10 in the electromechanical converter 1. The electromechanical converter 1 has an actuator 10 and a driving unit 20. The actuator 10 has, as main components, a rotating shaft 11, a rotating member 12, a fixed substrate 13, an electret portion 14, and opposed electrodes 15, 16. The electromechanical converter 1 uses the electrostatic force between the electret unit 14 and the counter electrodes 15 and 16 to rotate the rotating member 12 based on the electric signal input to the driving unit 20, thereby converting power from electric power. It is a driving device (motor) for taking out power.

  The rotation shaft 11 is an example of a movable support portion, and is a shaft that serves as a rotation center of the rotation member 12. The upper and lower ends are fixed to a housing of the electromechanical converter 1 (not shown) via bearings.

  The rotating member 12 is an example of a movable member, and is made of a known substrate material such as a metal, glass, or silicon substrate. The rotating member 12 has, for example, a disk shape, and is connected to the rotating shaft 11 at the center. The rotating member 12 moves around the rotating shaft 11 in a direction indicated by an arrow C in FIG. 3 by an electrostatic force generated between the electret portion 14 and the opposing electrodes 15 and 16 in response to an electric signal input to the driving portion 20 (in the direction of arrow C in FIG. That is, it can rotate clockwise and counterclockwise). A plurality of substantially trapezoidal through holes 122 are formed in the rotating member 12 at equal intervals along the circumferential direction in order to reduce the weight.

  The fixed substrate 13 is a member made of a known substrate material such as a glass epoxy substrate. The fixed substrate 13 has, for example, a disk-like shape, is arranged below the rotating member 12 so as to face the rotating member 12, and the rotating shaft 11 passes through the center thereof. However, unlike the rotating member 12, the fixed substrate 13 is not a rotatable member, but is fixed to the housing of the electromechanical converter 1.

The electret portion 14 is an example of a charging portion provided with a charging layer, and is formed on the lower surface 121 of the rotating member 12 facing the fixed substrate 13. In the actuator 10, a plurality of substantially trapezoidal electret portions 14 are provided on the lower surface 121 of the rotating member 12 with a substantially trapezoidal through-hole 122 interposed therebetween and spaced apart in the rotating direction of the rotating member 12. Are arranged at equal intervals. Each electret portion 14 is constituted by the electret substrate 50 shown in FIG. 1D, the SiO ₂ layer 54 is arranged so as to face the counter electrodes 15 and 16, and the base 51 is grounded.

  The counter electrodes 15 and 16 are formed on the upper surface 131 of the fixed substrate 13 facing the rotating member 12. In the actuator 10, the substantially trapezoidal counter electrodes 15 and 16, which are the same as the electret portions 14, are alternately arranged around the rotation axis 11 on the upper surface 131 of the fixed substrate 13. The number of the electret portions 14 and the counter electrodes 15 and the number of the electret portions 14 and the counter electrodes 16 are the same.

  Note that the electret portion 14 may be disposed on one of the rotating member 12 and the fixed substrate 13, and the counter electrodes 15 and 16 may be disposed on the other of the rotating member 12 and the fixed substrate 13. Therefore, conversely, the electret portion 14 may be disposed on the upper surface 131 of the fixed substrate 13 and the opposing electrodes 15 and 16 may be disposed on the lower surface 121 of the rotating member 12.

  The drive unit 20 is a circuit for driving the actuator 10 and includes a clock 21 and comparators 22 and 23. The driving unit 20 applies a voltage whose polarity is alternately switched to the plurality of opposed electrodes 15 and 16, and causes the rotating member 12 to generate electrostatic force generated between the plurality of electret units 14 and the plurality of opposed electrodes 15 and 16. Rotate.

  The output of the clock 21 is connected to the inputs of the comparators 22 and 23, the output of the comparator 22 is connected to the plurality of counter electrodes 15, and the output of the comparator 23 is connected to the plurality of counter electrodes 16 via electric wiring. ing. Each of the comparators 22 and 23 compares the potential of the input signal from the clock 21 with the ground potential and outputs the result in binary, but the output signals of the comparators 22 and 23 have opposite signs. When the input signal from the clock 21 is H, the counter electrode 15 has a potential of + V and the counter electrode 16 has a potential of −V. When the input signal is L, the counter electrode 15 has a potential of −V and the counter electrode 16 has a potential of + V. Become. In this manner, the driving member 20 applies the voltage whose polarity is alternately switched between the counter electrode 15 and the counter electrode 16, so that the rotating member 12 can be rotated.

FIG. 4 is a graph showing the relationship between the thickness of the lower SiO ₂ layer 52 in the electret substrate 50 and the magnitude of the force generated in the electromechanical converter 1. The horizontal axis d of the graph represents the thickness (μm) of the SiO ₂ layer 52, and the vertical axis F of the graph represents the magnitude of the force generated in the rotation direction of the rotating member 12 when the actuator 10 is driven by the driving unit 20. (MN). This graph shows the result of calculating by simulation the change in the generated force F when the thickness d of the SiO ₂ layer 52 is changed in the range of 0 to 5 μm.

As shown in FIG. 4, when the SiO ₂ layer 52 is present (the thickness d is larger than 0 μm), the K + ion-containing SiO ₂ layer 54 is directly formed on the Si substrate to produce an electret (thickness: The generated force F is larger than in the case where d is 0 μm. The generated force F is proportional to the thickness d and increases with the thickness d when the thickness d of the SiO ₂ layer 52 is in the range of 0 to 5 μm. Although not shown in detail, as the thickness of the SiO ₂ layer 52 increases, the tensile force of the actuator 10 in the direction of the rotation axis 11 also increases, and a frictional force is generated between the actuator 10 and the bearing. The relationship of F is no longer a simple proportional relationship.

  FIG. 5 is a schematic configuration diagram of another electromechanical converter 2. FIG. 6 is a perspective view of the power generation unit 10 ′ in the electromechanical converter 2. The electromechanical converter 2 has a power generation unit 10 ′ and a power storage unit 30. The power generation unit 10 ′ includes a rotating shaft 11, a rotating member 12, a fixed substrate 13, a plurality of electret units 14, a plurality of opposed electrodes 15 and 16, and a rotating weight 17 as main components. The electromechanical converter 2 is a power generation device that extracts power from power by rotating the rotating member 12 using kinetic energy of an external environment and generating static electricity by electrostatic induction in the power generation unit 10 ′.

  Among the components of the power generation unit 10 ′, the rotating shaft 11, the rotating member 12, the fixed substrate 13, the electret unit 14, and the counter electrodes 15 and 16 are the same as those of the actuator 10. A duplicate description of these components common to the electromechanical converter 1 will be omitted. The electromechanical converter 2 has a power storage unit 30 instead of the actuator 10 of the electromechanical converter 1, and the counter electrodes 15 and 16 of the electromechanical converter 2 are connected to the power storage unit 30 via electric wires, respectively. ing.

  The rotating weight 17 is a weight having a bias in weight balance, which is rotatable around the rotating shaft 11 in the direction of arrow C in FIG. 6, and is disposed above the rotating member 12. The oscillating weight 17 rotates the rotating member 12 in the direction of arrow C, for example, by being rotationally driven by the motion of a human body carrying the electromechanical transducer 2 or the vibration of a machine to which the electromechanical transducer 2 is attached. Instead of attaching the rotating weight 17 to the rotating shaft 11, a weight may be attached to the rotating member 12, and the rotating member 12 itself may be used as the rotating weight.

  When the rotary weight 17 is driven to rotate, the rotary member 12 rotates accordingly, and the overlapping area between the electret portion 14 and the opposing electrodes 15, 16 increases or decreases. For example, if a negative charge is held on the inner surface of the electret portion 14, the positive charge attracted to the counter electrodes 15 and 16 increases and decreases with the rotation of the rotating member 12, so that the space between the counter electrode 15 and the counter electrode 16 is increased. , An alternating current is generated. By generating a current in this way, the power generation unit 10 'generates power using electrostatic induction.

  The power storage unit 30 includes a rectifier circuit 31 and a secondary battery 32, and generates electric power generated by electrostatic induction between the plurality of electret units 14 and the plurality of opposed electrodes 15 and 16 according to the rotation of the rotating member 12. accumulate. Outputs from the counter electrode 15 and the counter electrode 16 are connected to a rectifier circuit 31, and the rectifier circuit 31 is connected to a secondary battery 32. The rectifier circuit 31 is a bridge-type circuit having four diodes, and rectifies the current generated between the counter electrode 15 and the counter electrode 16. The secondary battery 32 is a chargeable / dischargeable battery such as a lithium secondary battery, stores power generated by the power generation unit 10 ', and supplies the power to a circuit to be driven (not shown).

  7A to 7C are schematic configuration diagrams of still another electromechanical converter 3. The electromechanical transducer 3 has an actuator 40 and a driving unit 20 '. The actuator 40 has, as main components, a housing 41, a fixed substrate 42, a slide plate 43, a plurality of electret portions 44, and a plurality of opposed electrodes 45. The electromechanical transducer 3 uses the electrostatic force between the electret unit 44 and the counter electrode 45 to slide the slide plate 43 based on the electric signal input to the drive unit 20 ′, thereby providing power. This is a driving device that extracts power from the vehicle. FIGS. 7B and 7C are plan views showing the arrangement of the electret portion 44 and the counter electrode 45, and the moving direction of the slide plate 43. FIG.

As shown in FIG. 7A, the fixed substrate 42 is disposed on the bottom surface of the box-shaped housing 41. The slide plate 43 is an example of a movable member. The slide plate 43 is supported by a movable support (not shown) in the housing 41 and can move in a horizontal direction above the fixed substrate 42. The electret unit 44 is an example of a charging unit. As shown in FIGS. 7A to 7C, the electret unit 44 is provided on the bottom surface of the slide plate 43 at intervals in the moving direction (the direction of arrow A). It is formed in a belt shape in a direction orthogonal to the moving direction. The electret portion 44 is also composed of the electret substrate 50 shown in FIG. 1D, the SiO ₂ layer 54 is arranged so as to face the counter electrodes 15 and 16, and the base 51 is grounded. The counter electrode 45 is formed in a band shape on the upper surface of the fixed substrate 42 in parallel with each electret portion 44.

  The drive section 20 'is a circuit for driving the actuator 40, and is connected to the plurality of counter electrodes 45 via electric wiring. The drive unit 20 ′ has a configuration similar to that of the drive unit 20 of the electromechanical converter 1, and applies a voltage whose polarity is switched alternately to the plurality of counter electrodes 45, thereby forming the drive unit 20 ′ in FIG. 7B and FIG. As shown in C), the slide plate 43 is slid in the housing 41 in the horizontal direction (the direction of arrow A). The movable member of the electromechanical converter is not limited to the one that rotates like the rotating member 12 of the electromechanical converters 1 and 2, but may be one that slides like the slide plate 43 of the electromechanical converter 3. Good.

1, 2, 3 Electromechanical converter 10, 40 Actuator 10 'Power generation unit 11 Rotary shaft 12 Rotary member 13 Fixed substrate 14, 44 Electret unit 15, 16, 45 Counter electrode 20, 20' Driving unit 30 Power storage unit 50 Electret substrate 51 base 52,54 SiO ₂ layer 53 Si layer

Claims (1)

An electromechanical converter that performs conversion between electric power and power using an electrostatic interaction between a charging unit and a counter electrode,
A movable member movable with the movable support portion,
A fixed substrate fixedly arranged facing the movable member,
On the same surface of one of the movable member and the fixed substrate, a plurality of charging units arranged in the moving direction at intervals in the moving direction of the movable member,
On a surface of the other of the movable member and the fixed substrate facing the plurality of charging portions, a plurality of counter electrodes arranged in the moving direction,
Each of the plurality of charging units,
A base made of a conductive material,
A first insulating layer formed on the base and made of an insulating material;
A conductive layer formed of a conductive material and formed on the first insulating layer; and a charging layer formed on the conductive layer , wherein the conductive layer is not grounded and the base is grounded. An electromechanical converter characterized by being performed.

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