JP2014217178A - Electret device - Google Patents

Abstract

To improve the charge retention stability of an electret device. An electret element 100 includes a substrate 108, an electret film 103 formed on the substrate 108, and a conductive electrode 104 formed in a region where the electret film 103 is not formed on the substrate 108. By providing the concave structure 105 between the film 103 and the conductive electrode 104, it is possible to prevent the electric charge held in the electret film 103 from flowing out to the conductive electrode 104. [Selection] Figure 1

Description

  The present invention relates to an electret element.

  2. Description of the Related Art Conventionally, a vibration power generator has been proposed that uses an electret, which is a dielectric that holds a charge semipermanently, and uses electrostatic induction generated in a conductor approaching the electret to convert vibration energy into electrical energy.

  In FIG. 12, the cross-sectional schematic of the vibration electric power generator 10 described in patent document 1 is shown. The vibration power generator 10 includes a first substrate 11 having a plurality of current collecting electrodes 13 and a second substrate 16 having a plurality of electret films 15. The first substrate 11 and the second substrate 16 are arranged at a predetermined interval from each other. The second substrate 16 is fixed, springs 19 are connected to both side surfaces of the first substrate 11, and the springs 19 are connected to the fixing structure 17. The first substrate 11 moves laterally by external vibration and returns to a fixed position by the spring force of the spring 19. Due to this movement, the overlapping area between the electret element 15 and the opposing collector electrode 13 increases or decreases, and the charge induced in the collector electrode 13 changes. The electrostatic induction vibration power generator generates power by taking out the change in the electric charge as electric energy.

  FIG. 13 is a cross-sectional view of the electret element 30 included in the energy conversion element including the fixed substrate 32 and the movable substrate 31 described in Patent Document 2. The electret element 30 includes an electret 38 including a base electrode 37 formed on a fixed substrate 32 and a guard electrode 39. The electret 38 and the guard electrode 39 are covered with an insulating film 33. By providing the guard electrode 39, when the relative positional relationship between the fixed substrate 32 and the movable substrate 31 changes, the electrostatic capacity when the electret 38 and the counter electrode completely overlap with each other and when both do not overlap at all The difference in electrostatic capacity between the two increases, and the power generation output can be increased.

Japanese translation of PCT publication No. 2005-529574 (FIG. 4) JP 2010-136598 A (FIG. 4)

  The present invention provides an electret element that can improve the charge retention stability of the electret, and in particular can prevent the outflow of charges around the electret.

One embodiment of the present invention
A substrate,
An electret film formed on at least one surface of the substrate;
A conductive electrode formed in a region where the electret film is not formed on the at least one surface of the substrate;
And at least one non-flat structure selected from a concave structure, a convex structure, or a combination thereof, formed on the at least one surface of the substrate,
The surface of the substrate on which the electret film is formed is insulative,
The non-flat structure is located in a region where neither the electret nor the conductive electrode is formed.
It is an electret element.

  According to the electret device according to the embodiment of the present invention, the charge retention stability of the electret film can be improved, and in particular, the outflow of charge around the electret film can be prevented. Therefore, if the electret element which concerns on one Embodiment of this invention is used, the vibration power generator excellent in stability of electric power generation output can be provided.

Sectional drawing of the electret element 100 which concerns on embodiment of this invention. The top view of the electret element 100 which concerns on embodiment of this invention Sectional drawing of a vibration power generator using electret element 100 concerning an embodiment of the invention Sectional drawing of the 1st modification of the electret element which concerns on embodiment of this invention Sectional drawing of the 2nd modification of the electret element which concerns on embodiment of this invention Sectional drawing of the 3rd modification of the electret element which concerns on embodiment of this invention Sectional drawing of the 4th modification of the electret element which concerns on embodiment of this invention Sectional drawing of the 5th modification of the electret element which concerns on embodiment of this invention Sectional drawing of the 6th modification of the electret element which concerns on embodiment of this invention Sectional drawing of the 7th modification of the electret element which concerns on embodiment of this invention Sectional drawing of the 8th modification of the electret element which concerns on embodiment of this invention Cross-sectional view of a conventional vibration generator Cross-sectional perspective view of an electret element included in a conventional energy conversion element Sectional drawing which shows the movement path | route of the electric charge in the electret element 100 which concerns on embodiment of this invention Sectional drawing of the 9th modification of the electret element which concerns on embodiment of this invention Sectional drawing of the 10th modification of the electret element which concerns on embodiment of this invention

(Background to the embodiment of the present invention)
The charges held in the electret are diffused over time from a region having a high charge density to a region having a low charge density by mutual electrostatic repulsion. Charge diffusion leads to charge discharge from the electret, which leads to a decrease in the power output of the vibration generator. Further, in the electret element 30 described in Patent Document 2, although the power generation output is increased by the installation of the guard electrode 39, the electric charge held in the electret 38 is attracted to the conductive electrode, so that the outflow of electric charge is accelerated.

  As described above, in the electret, due to the diffusion of the charges and the movement of the charges toward the guard electrode, the outflow of the charges occurs with time, and this causes, for example, a decrease in the power generation output of the vibration power generator with time. The present inventors have studied a configuration that suppresses the outflow of electric charge in consideration of the direction of the electric field acting on the electric charge when the electric charge flows out of the electret and moves on the substrate surface. As a result, it has been found that the outflow of electric charge from the electret can be reduced by forming a concave structure, a convex structure, or a combination thereof on the substrate surface between the electret and the guard electrode.

(Aspect of the present invention)
The first aspect of the present invention is:
A substrate,
An electret film formed on at least one surface of the substrate;
A conductive electrode formed in a region where the electret film is not formed on the at least one surface of the substrate;
And at least one non-flat structure selected from a concave structure, a convex structure, or a combination thereof, formed on the at least one surface of the substrate,
The surface of the substrate on which the electret film is formed is insulative,
The non-flat structure is located in a region where neither the electret nor the conductive electrode is formed.
It is an electret element.

  Here, “electret” means a dielectric capable of holding a charge semipermanently, “electret film” means a film made of an electret, and “electret element” means an electret ( Or the thing containing the board | substrate which supports an electret film | membrane, an electrode, etc. is meant. The electret (or electret film) may be composed of a plurality of dielectrics, and a charge may be held in some or all of the plurality of dielectrics.

  The substrate constituting the electret element generally has a flat and wide surface (main surface), and an electret film and a conductive electrode (guard electrode) are formed on the surface. The “concave structure” is a structure having a surface (or portion) lower than the flat surface (approximately the same height (or level) as the bottom surface of the electret film or the conductive electrode), The “convex structure” is a structure having a surface (or portion) higher than the flat surface. The combination of the concave structure and the convex structure refers to a structure in which a part of the concave structure is continuous with a part of the convex structure, for example, as shown in FIG.

  In the first aspect, the non-flat structure is formed on the insulating surface of the substrate (the surface on which the electret film is formed) and is located in a region where neither the electret film nor the conductive electrode is formed. It can be said that the non-flat structure is formed between the electret film and the conductive electrode. This non-flat structure can reduce the outflow of charges from the electret film to the conductive electrode. More specifically, the non-flat structure increases the distance of charge movement when the charge flowing out of the electret film moves toward the conductive electrode along the insulating surface of the substrate, thereby Runoff can be reduced. In a non-planar structure, an electric field in which a conductive electrode draws a charge with respect to an electric charge is a portion connecting a portion lower than the surface of the substrate and the surface of the substrate (the portion is also referred to as a “side wall”). A different direction, for example, a path perpendicular to the electric field, is provided, so that the influence of the electric field serving as a driving force for charge transfer can be reduced, and the outflow of charges to the conductive electrode can be reduced.

  A second aspect is the electret element according to the first aspect, wherein the substrate has an insulating layer and a conductive layer, and the electret film is formed on one surface of the insulating layer.

  A third aspect is the electret element according to the second aspect, wherein the non-flat structure is formed in the insulating layer.

  According to a fourth aspect, in the substrate, at least one non-flat structure for forming the non-flat structure is formed in the conductive layer, and a surface on which the non-flat structure formed in the conductive layer is located is formed. It is the electret element of the 2nd aspect covered with the said insulating layer.

  A fifth aspect is the electret element according to any one of the first to fourth aspects, further including a moisture-proof layer, wherein the moisture-proof layer covers at least a surface of the electret film.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, repeated description of substantially the same configuration may be omitted. The same reference numerals appearing in several drawings indicate the same element or member.

(Embodiment)
FIG. 1 is a cross-sectional view of an electret element 100 according to an embodiment of the present invention. FIG. 2 is a plan view of the electret element 100, and FIG. 1 shows a cross section cut along AB in FIG. The electret element 100 includes an insulating substrate 108, an electret film 103 formed on the surface of the insulating substrate 101, a conductive electrode 104 formed on the surface of the insulating substrate 108, and a surface of the insulating substrate 108. It is comprised from the concave structure 105 located in the area | region in which neither the electret film | membrane 103 and the electroconductive electrode 104 are formed.

  Since the insulating substrate (hereinafter also simply referred to as “substrate”) 108 is a substrate made of an insulating material, the surface on which the electret film 103 is formed (the upper surface in the drawing) has an insulating property. In this embodiment, the non-flat structure is a concave structure 105 having a lower portion than the surface of the substrate 108, and is located between the electret film 103 and the conductive electrode 104 on the surface of the substrate 108.

The concave structure 105 has a bottom surface 105a, a side wall 105b, and a top surface 105c (the top surface 105c is also the surface of the substrate 108). In the illustrated form, the bottom surface 105 a and the top surface 105 c of the recess are surfaces parallel to the surface of the substrate 108. A part of the bottom surface 105a and the top surface 105c may be curved, for example. Further, the sidewall 105b may be perpendicular to the surface of the insulating substrate 108 or may have an inclination. Alternatively, the side walls 106b may be curved, for example, be a quadratic curve as represented by f (x) = x ² in the cross section shown in FIG. Alternatively, the concave structure 105 may be a structure that does not have a flat portion at the bottom and does not clearly distinguish between the bottom surface and the side wall. Specifically, the cross section of the concave structure 105 may have, for example, a V shape.

  As shown in FIG. 2, the electret films 103 and the conductive electrodes 104 are both rectangular when viewed from the z direction, and are alternately arranged so as to be parallel to each other in the x direction. The electret film 103 has, for example, a width (dimension in the x direction) 250 μm, a length (dimension in the y direction) 1 cm, and a thickness (dimension in the z direction) 1000 nm. The conductive electrode 104 has, for example, a width (x The dimension (direction dimension) is 200 μm, the length (dimension in the y direction) is 1 cm and the thickness (dimension in the z direction) is 300 nm. The distance between the electret film 103 and the conductive electrode 104 (the dimension in the x direction of the region where both are not formed) is, for example, 25 μm.

  The concave structure 105 is also rectangular (or linear) when viewed from the z direction, and is formed in parallel. In the illustrated form, the concave structure 105 has, for example, a width (dimension in the x direction) of 5 μm, a length (dimension in the y direction) that is the same as those of the electret film 103 and the conductive electrode 104, and a depth ( The dimension in the z direction) is 100 nm. The concave structure 105 is necessarily located between the electret film 103 and the conductive electrode 104 in the x direction. The concave structure 105 formed in this way lengthens the path of charge from the electret film 103 to the conductive electrode 104, and advances the charge in a direction different from the electric field exerted on the charge by the conductive electrode 104. . As a result, charge outflow is reduced.

  Charge injection into the electret film 103 is performed by corona discharge or the like. The electret film 103 is made of a dielectric. The electret film 103 may have a single layer structure or a laminated structure composed of a plurality of dielectrics. Or the electret film | membrane 103 consists of two types of dielectric materials, for example, the structure where the other dielectric material has coat | covered one dielectric material may be sufficient. When the electret film 103 is composed of a plurality of dielectrics, the charge may be injected into all the dielectrics, or may be injected only into one or a plurality of specific dielectrics (ie, the charge is injected). There may be no dielectric). The electret film 103 may be composed of either an inorganic material or an organic material, or a combination of both. The polarity of the charge injected into the electret film may be positive or negative.

  FIG. 3 shows a cross-sectional view of a vibration power generator 600 provided with the electret element 100 of the present invention. The vibration power generator 600 is composed of a plurality of electret films 103a to 103c and conductive electrodes 104a to 104b and a substrate 603 on which current collecting electrodes 607a to 607c are provided facing each other at a predetermined interval. The Both ends of the insulating substrate 108 are connected to the fixed structure 610 through the elastic structure 609. The elastic structure 609 may be a spring or may be made of a material (for example, rubber) that pushes back the insulating substrate 108 by repulsion.

  When an external vibration 608 is applied, the elastic structure 609 expands and contracts, whereby the insulating substrate 108 is displaced relative to the substrate 603. At this time, the overlapping area of the electret films 103a to 103c and the collecting electrodes 607a to 607c on the substrate 603 increases and decreases, and the amount of charge induced in the collecting electrodes 607a to 607c increases and decreases. Electricity is generated by taking out the increase and decrease of this electric charge as electric energy. The vibration power generator 600 may be used in, for example, a low-power wireless communication module and other electronic devices.

  According to the electret device 100 according to the embodiment of the present invention, an effect of improving the charge retention stability of the electret can be obtained. This effect will be described in detail below.

  The charges injected and held in the electret element 100 diffuse and flow out over time from the inside of the electret film 103 having a high charge density to the outside having a low charge density due to the electrostatic repulsion between the held charges. To do. Furthermore, the charge held in the electret film 103 is attracted to the conductive electrode 104 having a lower potential by electrostatic attraction. At this time, since the electric charge flowing out from the electret film 103 easily passes through a region having low insulating properties, the electric charge moves along the surface of the insulating substrate 108 and is likely to flow out to the conductive electrode 104.

  In the electret device 100 shown in FIGS. 1 and 2, a path in which the electric charge held by the electret film 103 flows out of the electret film 103 and travels toward the conductive electrode 104 is shown in FIG. 14. In FIG. 14, the electric charge is indicated by a white circle. The charges exiting the electret film 103 move along the surface of the substrate 108 in the direction indicated by the arrows in the figure.

  As shown in FIG. 14, the surface area of the insulating substrate 108 is increased by providing the concave structure 105 on the surface of the insulating substrate 108. More specifically, the charge movement path is longer by a distance corresponding to the two side walls 105b than the movement path when the concave structure 105 is not present. By increasing the charge transfer path, the time required for the charge flowing out toward the conductive electrode 104 to move can be increased, and the rate of charge discharge can be reduced.

  In addition, the direction in which the charge moves along the side wall 105b of the concave structure 105 (z direction in FIG. 14) and the direction of the electric field in which the charge is attracted to the conductive electrode 104 (x direction in FIG. 14) are vertical. Therefore, the influence of the electric field serving as the driving force for charge transfer can be reduced. Thereby, the outflow speed of charges can be reduced, and the charge retention of the electret element 100 can be stabilized. This is also true when the conductive electrode 104 is connected to a ground potential or a floating potential. This is also the case where the conductive electrode 104 is connected to a potential having the same polarity as the electric charge held by the electret film 103 and whose absolute value is smaller than the absolute value of the surface potential of the electret film 103, or conductive This is the case even when the conductive electrode 104 is connected to a potential having a polarity different from the charge held by the electret film 103.

  In the present embodiment, the insulating substrate 108 is a substrate made of only an insulating material such as a glass substrate. In the first modification, as shown in FIG. 4, the substrate on which the electret film and the conductive electrode are formed is a substrate having a conductive substrate 111 as a conductive layer and an insulating layer 112. The insulating layer 112 is formed on the surface of the two main surfaces of the conductive substrate 111 on the side where the electret film 103 is formed. Thus, the substrate on which the electret film is formed may have a conductive portion as long as the surface on which the electret film is formed is insulative. When the substrate includes a conductive substrate and an insulating layer, the insulating layer and the non-flat structure are formed on the surface on which the electret element is formed so that the conductive portion is not exposed. In the modification shown in FIG. 4, since the concave structure 105 is formed in the insulating layer 112 and the depth (dimension in the z direction of the side wall) is smaller than the thickness of the insulating layer 112, the conductive portion is exposed on the surface. Never do.

  In this variation, the conductive substrate 111 may be connected to ground potential. In this case, since the electric charge flowing out from the electret film 103 and moving toward the conductive electrode 104 is stabilized at the bottom surface of the concave structure 105, according to this modification, the charge retention stability is further improved. be able to. Specifically, the charge moving to the bottom surface of the concave structure 105 is attracted to the conductive substrate 111 connected to the ground potential by electrostatic attraction. Therefore, even if the electric charge moves along the side wall 105b of the concave structure 115 in a direction away from the conductive substrate 111 (upward in the z direction in FIG. 4), the electrostatic attractive force attracted to the conductive substrate 111 acts on the charge. For this reason, the electric charge hardly moves from the bottom surface of the concave structure 105. Thereby, the movement of the charge to the conductive electrode 104 can be prevented, and the charge is stably held on the bottom surface of the concave structure 105.

  This is when the conductive substrate 111 has a potential of the same polarity as the electric charge held by the electret film 103 and the absolute value thereof is connected to a potential smaller than the absolute value of the surface potential of the electret film 103, or the conductive substrate This applies even when 111 is connected to a potential having a polarity different from the charge held by the electret film 103.

  Alternatively, the conductive substrate 111 may be connected to a potential having the same polarity as the electric charge held by the electret film 103 and having an absolute value larger than the absolute value of the surface potential of the electret film 103. In this case, even if the electric charge flowing out from the electret film 103 tries to move in the direction approaching the conductive substrate 111 (downward in the z direction in FIG. 4) along the side wall 105 b of the concave structure 105, it repels from the conductive substrate 111. Since the electrostatic repulsive force that acts on the charge, the charge cannot move toward the bottom surface of the concave structure 105. Such electrostatic repulsion also contributes to the prevention of charge outflow.

  In the first modification, the conductive substrate 111 is, for example, a single crystal silicon substrate doped with impurities, and the insulating layer 112 is formed by oxidizing the conductive substrate 111 by a thermal oxidation method, and has a thickness of 1 μm. This is a silicon oxide film. The electret film 103 is, for example, a laminated film in which a silicon nitride film having a thickness of 300 nm is formed on the surface of a silicon oxide film having a thickness of 1000 nm formed by LPCVD (Low pressure chemical vapor deposition). The conductive electrode 104 is, for example, a 300 nm thick polycrystalline silicon film doped with impurities, formed by LPCVD. The concave structure 115 formed in the insulating layer 112 may be formed by dry etching.

  In the electret element shown in FIG. 1 and FIG. 4, the width (the dimension in the x direction) of the bottom surfaces of the concave structures 105 and 115 is smaller than the distance between the electret film 103 and the conductive electrode 104 in the x direction. In the second modified example, as shown in FIG. 5, the width of the bottom surface of the concave structure 125 of the electret element 120 and the interval between the electret film 103 and the conductive electrode 104 are the same, and the entire interval is a recess. It matches the bottom. Therefore, in the element 120, the presence or absence of the concave structure 125 may not be immediately recognized when viewed from the z direction, but it is immediately understood that the concave structure 125 exists when the cross section is viewed. Such a concave structure 125 can be formed by using overetching when the electret film 103 and the conductive electrode 125 are patterned. Therefore, the electret element 120 can be manufactured with reduced process man-hours.

  An electret element 130 of a third modification is shown in FIG. The electret element 130 has a plurality of concave structures 135. Assuming that the depth of the concave structure 135 is the same as the depth of the concave structure 105 shown in FIG. 1, the greater the number of concave structures, the more the electric charge that flows out of the electret film 103 and travels toward the conductive electrode 104 becomes the substrate ( In FIG. 6, the distance traveled on the surface of the insulating layer 112) is longer. Thereby, the time until the electric charge reaches the conductive electrode 104 can be made longer, and the charge retention stability is further improved.

  An electret element 140 according to a fourth modification is shown in FIG. The electret element 140 has a convex structure 145 as a non-flat structure. The convex structure 145 has a top surface 145a and a side wall 145b. In the illustrated form, the top surface 145a is a surface parallel to the surface of the substrate (insulating layer 112). A part of the top surface 145a may be curved, for example. Further, the side wall 145b may be curved. Alternatively, the convex structure 145 may have a structure that does not have a flat portion at the highest portion and does not clearly distinguish between the top surface and the side wall. Specifically, the cross section of the convex structure 145 may have an arch shape.

  In the illustrated modification, the dimension (height) in the z direction of the side wall 145 b of the convex structure 145 is the same as that of the conductive electrode 104. Also in the convex structure 145, the direction in which the electric charge moves along the side wall 145b (z direction in FIG. 7) is completely relative to the direction of the electric field attracted to the conductive electrode 104 (x direction in FIG. 7). It becomes vertical. Therefore, the convex structure 145 can also increase the charge movement distance and reduce the influence of the electric field serving as the driving force for charge movement, thereby improving the charge retention stability.

  An electret element 150 of a fifth modification is shown in FIG. This modification has a structure (concavo-convex structure) 155 that combines a concave structure and a convex structure as a non-flat structure. In the concavo-convex structure 155, the side wall of the concave structure and the side wall of the convex structure are continuous. The uneven structure 155 can efficiently increase the distance of charge movement on the surface of the insulating layer 112 and can further improve the charge retention stability. In the concavo-convex structure, the shape of the side wall of the concave portion (side wall of the convex portion), the bottom surface of the concave portion, and the top surface of the convex portion is not limited to that illustrated, but as described with reference to FIGS. It may be a shape.

  An electret element 160 according to a sixth modification is shown in FIG. In this modification, after forming a concave structure on the conductive substrate 161, an insulating layer 162 is formed to make the surface of the substrate insulating. The shape and size of the concave structure 165 formed as a non-flat structure that suppresses the outflow of charges are substantially the same as the concave structure formed in the conductive substrate 161, but the insulating layer 162 is formed on the surface thereof. Therefore, the size and depth of the bottom surface are smaller than those of the concave structure formed on the conductive substrate 161.

  In the sixth modified example, unlike the first modified example, a concave structure having a larger depth can be formed without being limited by the film thickness of the insulating layer 162. By increasing the depth of the concave structure 165, the movement distance of the charge is lengthened, the time for the charge to reach the conductive electrode 104 from the electret film 103 is lengthened, and the charge retention stability is further increased. Can be improved. For example, when the insulating layer 162 is a silicon oxide film formed by a thermal oxidation method, the maximum film thickness is about 2 μm. Therefore, when a concave structure is formed in this film, the distance (depth) from the top surface to the bottom surface of the concave structure needs to be less than 2 μm. However, when the concave structure 165 is formed by the method of forming the insulating layer 162 after forming the concave structure on the conductive substrate 161 (for example, a silicon substrate), the depth is the thickness of the silicon substrate (for example, several hundred μm). It is possible to form a concave structure 165 substantially corresponding to.

  In the above, the silicon oxide film by the thermal oxidation method is given as an example of the insulating layer. Even when the insulating layer is formed by the LPCVD method or the spin coating method, the thickness of the obtained insulating layer is limited, and it is generally difficult to make it larger than the thickness of the conductive substrate 161. Therefore, the sixth modification is useful as a configuration for obtaining a deeper concave structure when the insulating layer is formed by any method.

  An electret element 170 according to a seventh modification is shown in FIG. This modification is the same as the fourth modification except that a conductive embedded electrode 176 is formed inside the electret film 173. In the illustrated element 170, the embedded electrode 176 is formed on the surface of the insulating layer 112. In this modification, when the charge is injected into the electret film 173 by corona discharge, the buried electrode 176 is connected to the ground potential, whereby the charge can be more efficiently drawn into the electret film 173 and injected. After the charge is injected into the electret film 173, the embedded electrode 176 may be at a floating potential or may be connected to a ground potential.

  The embedded electrode 176 attracts the electric charge held in the electret film 173 by electrostatic attraction like the conductive electrode 104, but the embedded electrode 176 is covered by the electret film 173, so that the electric charge hardly flows out. It tends to flow out to the conductive electrode 104 more easily. Therefore, the outflow of charges can be reduced by the concave structure 105 also in this modification.

  An electret element 190 according to an eighth modification is shown in FIG. In this modification, a moisture-proof layer 197 is formed, and the moisture-proof layer 197 covers the surfaces of the insulating layer 112, the electret film 103, the conductive electrode 104, and the concave structure 105. The moisture-proof layer 197 prevents the charges in the electret film 103 and the charges that flow out of the electret film 103 and exist on the surfaces of the insulating layer 112 and the concave structure 105 from diffusing into the atmosphere due to humidity in the air. In addition, the charge retention stability can be further improved. By combining the moisture-proof monk 197 and the effect of preventing electric charge outflow by the concave structure 195, electric charge outflow from the electret film 197 can be further prevented. The moisture-proof layer 197 may cover only the surface of the electret film 103. As shown in the figure, the moisture proof layer 197 covers the surfaces of the concave structure 105 and the insulating layer 112, so that the outflow of charges is further suppressed.

  The moisture-proof layer 197 is made of HMDS (hexamethyldisilane), BCB (benzocyclobutene), or an inorganic material having a high gas barrier property (for example, a silicon oxide film, a silicon nitride film, or an aluminum oxide film) that prevents water adsorption by a hydrophobic group ).

  In the above, the electret element in which the electret film and the conductive electrode that are rectangular when viewed in the z direction are arranged in parallel to each other in the x direction has been described. The present embodiment can be applied regardless of the shape and arrangement of the electret film and the conductive electrode. For example, as shown in FIG. 15, in the electret element 200 in which the wedge-shaped electret films 203 and the conductive electrodes 204 are alternately arranged on the disk-shaped substrate, the electret films 203 are disposed between the conductive electrodes 204. A non-flat structure (concave structure 205 in the figure) extending in the diameter direction may be located.

  Alternatively, as shown in FIG. 16, in the electret element 210 in which the electret film 213 and the conductive electrode 214 are arranged on the substrate 208 in a checkered pattern (or checkered pattern), a non-flat structure (concave structure 215 in the figure) is used. Alternatively, it may be formed in a frame shape surrounding the periphery of the conductive electrode 214. In a further modification of the electret element 210 shown in FIG. 16, the non-flat structure may be formed in a frame shape surrounding the electret film 214.

  In any illustrated electret element, the non-flat structure is continuous with a relatively large dimension in one direction (eg, the element shown in FIG. 1 has a large y-direction dimension), but is non-flat. The structure may be point-like or island-like. For example, in FIG. 2, the concave structure 105 may not be continuous in the y direction but may be dotted. Alternatively, the non-flat structure may be formed so as to surround the electret film or the conductive electrode when the substrate surface is viewed.

Each of the illustrated forms is an example of the present embodiment, and the number, shape, size and depth of the concave structure, the thickness of the dielectric layer, the amount of charge held in the dielectric layer, and the conductive electrode The shape and number are not limited to specific ones. Even if these are arbitrarily selected, the effects of the present embodiment can be obtained.
The above-described embodiments are for illustrating the present invention, and various changes, substitutions, additions, omissions, and the like can be made within the scope of the claims and the equivalents thereof.

  The electret device of the present invention has improved charge retention stability and is useful as an electret electrode of a vibration power generator.

100 electret element 103 electret film 104 conductive electrode 105 concave structure (non-flat structure)
108 Insulating substrate 111 Conductive substrate 112 Insulating layer 145 Convex structure (non-flat structure)
155 Uneven structure (non-flat structure)
176 Embedded electrode 197 Moisture-proof layer

Claims (5)

A substrate,
An electret film formed on at least one surface of the substrate;
A conductive electrode formed in a region where the electret film is not formed on the at least one surface of the substrate;
And at least one non-flat structure selected from a concave structure, a convex structure, or a combination thereof, formed on the at least one surface of the substrate,
The surface of the substrate on which the electret film is formed is insulative,
The non-flat structure is located in a region where neither the electret nor the conductive electrode is formed.
Electret element.   The electret device according to claim 1, wherein the substrate has an insulating layer and a conductive layer, and the electret film is formed on one surface of the insulating layer.   The electret element according to claim 2, wherein the non-flat structure is formed in the insulating layer.   In the substrate, at least one non-flat structure for forming the non-flat structure is formed in the conductive layer, and a surface on which the non-flat structure formed in the conductive layer is located is covered with the insulating layer. The electret device according to claim 2, wherein   The electret device according to any one of claims 1 to 4, further comprising a moisture-proof layer, wherein the moisture-proof layer covers at least a surface of the electret film.

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