Electret Device

Abstract

To provide an electret device which has a long service life and in which an electrostatic property of an electret element enclosed in a sealed space can be prevented from deteriorating.SOLUTION: Provided is an electret device including a package member, a lid member, and an electret element. The lid member seals the package member to form a sealed space. The electret element is disposed in the sealed space. In the package member, at least a portion of an inner wall forming the sealed space is water-repellent.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an electret device and a method for manufacturing an electret device. [Background technology]

[0002] BACKGROUND ART One known energy harvesting technique for harvesting energy from environmental vibrations is a technique for generating power using a micro-electro-mechanical systems (MEMS) vibration element (see, for example, Patent Document 1).

[0003] The vibrating element may use an electret, i.e., a member that maintains a charge by applying a voltage to a dielectric. Electrets are produced by a method of injecting charge into an insulating film by corona discharge, or by a method described in Patent Document 2.

[0004] However, the charge amount of the electret decreases over time. This is called charge deterioration. It is known that charge deterioration occurs mainly when the electret comes into contact with moisture in the outside air (see Patent Document 3, etc.).

[0005] Generally, electronic elements are sealed in vacuum packages to prevent deterioration of the elements due to moisture. Furthermore, an adsorbent material called a getter is placed inside the vacuum package to maintain the vacuum state inside the vacuum package (see Non-Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-088780 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-13256 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-182666 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-049557 [Patent Document 5] Patent No. 4662666 [Non-patent literature]

[0007] [Non-Patent Document 1] "Mounting Technology for Small Bio-Measurement Sensors," Eiji Higurashi et al., Journal of the Japan Society for Precision Engineering, Vol. 73, No. 11, P. 1190 (2007) Summary of the Invention [Problem to be solved by the invention]

[0008] However, because the surface of the vacuum getter material is covered with adsorbed gas molecules, it must be heated in a vacuum (for example, to 400°C or higher) to activate it, and such heating treatment may reduce the charge of the electret.

[0009] Furthermore, the inventors noticed that charging deterioration occurs even though moisture is removed, and found that one of the causes is the SiO in the silicon oxide film that stores electric charges. - The molecule contains a hydrogen atom, H + We discovered that this was due to the reaction of the two metals, neutralizing the charge, and found that some kind of countermeasure was necessary.

[0010] Therefore, an object of the present invention is to provide an electret device having a long life in which hydrogen, which causes deterioration, is removed without high-temperature treatment and charging deterioration of an electret element sealed in a sealed space is prevented. [Means for solving the problem]

[0011] In order to solve the above problem, an electret device according to one embodiment of the present invention is an electret device including a package member, a lid member, and an electret element, the lid member seals the package member to form a sealed space, The element including the electret is placed in the sealed space, The package member is an electret device in which at least a part of an inner wall forming the sealed space is water-repellent.

[0012] Another embodiment of the present invention is an electret device including a package member, a lid member, and an electret element, the lid member seals the package member to form a sealed space, The electret element is installed in the sealed space, The cover member is an electret device in which at least a part of an inner wall that forms the sealed space is water-repellent. [Effects of the Invention]

[0013] The present invention can provide an electret device that prevents deterioration of an electret sealed in a sealed space due to charging, and a method for manufacturing the same. [Brief explanation of the drawings]

[0014] [Figure 1] 1(a) is a perspective view showing an electret device according to an embodiment of the present invention, (b) is an exploded perspective view of the electret device of FIG. 1(a), and (c) is a rear view of the lid member 20 of FIG. [Figure 2] FIG. 1(b) is a cross-sectional view of the electret device of FIG. [Figure 3] 3(a) is a perspective view showing an electret device according to a modified example of the embodiment of the present invention, (b) is an exploded perspective view of the electret device of FIG. 3(a), and (c) is a rear view of the lid member 20 of FIG. [Figure 4] FIG. 3(b) is a cross-sectional view of the electret device of FIG. [Figure 5] (a) An example of mounting a hydrogen getter according to a modified embodiment of the present invention. (b) An example of mounting a hydrogen getter according to a modified embodiment of the present invention. (c) An example of mounting a hydrogen getter according to a modified embodiment of the present invention. [Figure 6] 5(a) is a cross-sectional view of an electret device to which the lid member of Fig. 5(a) is attached, (b) is a cross-sectional view of an electret device to which the lid member of Fig. 5(b) is attached, and (c) is a cross-sectional view of an electret device to which the lid member of Fig. 5(c) is attached. [Figure 7] 10 shows the results of a charging deterioration test of an electret device according to one embodiment of the present invention and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to these.

[0016] <Configuration of electret device> Fig. 1(a) is a perspective view showing an overview of an electret device according to one embodiment of the present invention, Fig. 1(b) is an exploded perspective view thereof, Fig. 1(c) is a rear view of a lid member, and Fig. 2 is a cross-sectional view of the electret device of Fig. 1(a).

[0017] In one embodiment of the present invention, the electret device 100 includes a package member 10, a lid member 20, an electret element 30, and a hydrogen getter 60. The package member 10 and the lid member 20 form a sealed space, and the electret element 30 is installed in this sealed space. Furthermore, the electret element 30 is connected to electrodes installed in the package member via wires 40 from electrode pads 31 and 32 installed on the element, and is connected to an external circuit (not shown). A hydrogen getter 60 is installed inside the sealed space.

[0018] Although details will be described later, in this embodiment, by providing a hydrogen getter 60 in at least a part of the package member 10, the lid member 20, or the electret element 30 that form the sealed space, it is possible to adsorb hydrogen in the sealed space without performing high-temperature activation treatment. This makes it possible to provide an electret device with a long life that prevents charging deterioration due to hydrogen of the electret element sealed in the sealed space.

[0019] (Packaging material) The package member 10 is a member in which the electret element 30 is installed and which forms a sealed space together with the lid member 20 described later. The package member 10 has electrodes connected to the electret element 30 via wires 40, and can connect the electret element 30 to an external circuit.

[0020] The material used for the package member 10 may be any material generally used for sealing electronic elements. For example, ceramics such as alumina, metal, resin, glass, or silicon may be used. A portion of the inner wall 15 of the package member 10 may be treated to be water-repellent.

[0021] (Cover member) The cover member 20 is a member that forms a sealed space together with the package member 10 .

[0022] The material used for the lid member 20 may be a material generally used for sealing electronic elements. For example, if the lid member 20 is made of metal, the lid member 20 can be sealed by welding, which is preferable. The metal used for the lid member 20 may be a simple metal or an alloy. A portion of the inner wall surface 25 of the lid member 20 may be water-repellent.

[0023] (electret element) The electret element 30 is an electronic element including an electret, and may be, for example, a vibration element that converts vibration energy into electrical energy.

[0024] In this specification, a member that has been charged by applying a voltage to a heated oxide film is referred to as an electret. Furthermore, maintaining the charge even after the application of the voltage is terminated is referred to as electretization. Furthermore, an element that uses an electret is referred to as an electret element. Furthermore, a device that includes an electret element is referred to as an electret device.

[0025] The electret can be produced by a method known in the art. For example, it is formed by carrying out a known charging treatment described in Patent Document 4. The electret element 30 may have a protective film on the electret surface.

[0026] The electret element 30 is connected to the package member 10 via a wire 40, and can be connected to an external circuit (not shown).

[0027] In a modified embodiment of the present invention, the electret element may be an electret element 50 having comb-tooth electrode portions 52 and 53 (see FIGS. 3(a) to 4). In this embodiment, the electret element 50 has a fixed comb-tooth electrode portion 52 formed on a support portion 51 and a movable comb-tooth electrode portion 53 elastically supported on the support portion 51 via an elastic support portion. The electret element 50 can be formed, for example, by a general MEMS processing technique using an SOI (Silicon On Insulator) substrate. The SOI substrate is a substrate with a three-layer structure consisting of a Si support layer, a SiO2 box layer, and a Si active layer, and the support portion 51 is formed from the support layer, and the fixed comb-tooth electrode portion 52, the movable comb-tooth electrode portion 53, and the elastic support portion are formed from the active layer.

[0028] The comb-tooth electrodes of the fixed comb-tooth electrode portion 52 and the movable comb-tooth electrode portion 53 are arranged to mesh with each other with a gap in the y-axis direction, and when the movable comb-tooth electrode portion 53 vibrates in the x-axis direction, the insertion amount of the comb-tooth electrodes of the movable comb-tooth electrode portion 53 into the comb-tooth electrodes of the fixed comb-tooth electrode portion 52 changes, thereby generating power. To increase the vibration and improve power generation efficiency, a pair of weights 70a and 70b may be fixed to both the front and back surfaces of a portion of the movable comb-tooth electrode portion 53.

[0029] The fixed comb-tooth electrode portion 52 is connected to the package member 10 via a wire 40, and can transmit electricity obtained by vibration of the movable comb-tooth electrode portion 53 to an external circuit (not shown).

[0030] The electret element 50 includes an electret in at least a part of one of the comb-tooth electrode portions 52 and 53. The electret element 50 may also have a protective film on the electret surface.

[0031] The following description will be given using the electret element 30, but the same applies to the case where the electret element 50 is used as the electret element.

[0032] (closed space) 2, a package member 10 having an electret element 30 therein is sealed with a lid member 20 to form a sealed space. The sealing can be performed in the atmosphere, in the presence of an inert gas such as nitrogen or argon, or in a vacuum.

[0033] The sealing of the package member 10 and the lid member 20 can be carried out by a commonly used method, for example, by welding the lid member 20.

[0034] (hydrogen getter) The hydrogen getter 60 is a substance that mainly adsorbs hydrogen, and adsorbs hydrogen in the sealed space formed by the package member 10 and the cover member 20. The hydrogen getter 60 may be a substance known in the art as a hydrogen adsorbent, and for example, the hydrogen getter described in Patent Document 5 may be used.

[0035] As described in Patent Document 5, hydrogen atoms spread throughout the material of the hydrogen getter even at relatively low temperatures to form an initial solid solution, and as the hydrogen concentration increases, hydrides such as ZrH2 can be formed, so the hydrogen adsorption capacity is high even at low temperatures. Therefore, the hydrogen getter 60 can adsorb hydrogen in the sealed space without high-temperature activation treatment, which avoids deterioration of the electret due to heating and can prevent charging deterioration of the electret due to hydrogen.

[0036] The hydrogen getter 60 can be installed anywhere in the sealed space formed by the package member 10 and the lid member 20, as long as it does not interfere with the operation of the electret device 100. For example, as shown in FIG. 3(c), the hydrogen getter 60 may be installed so as to cover the inner wall surface 25 of the lid member 20 except for the edge portion that contacts the package member 10.

[0037] Furthermore, as shown in FIGS. 5(a) to 5(c), a hydrogen getter 60 may be provided on the inner wall surface 25 of the lid member 20 in a shape that avoids the portion facing the weight 70a placed on the movable comb-tooth electrode portion 53. With this configuration, the distance between the lid member 20 and the electret element 50 can be reduced without interfering with the movement of the movable comb-tooth electrode portion 53, thereby making it possible to miniaturize the electret device 100 (FIGS. 6(a) to 6(c)). Also, in FIGS. 6(a) to 6(c), the hydrogen getter 60 may extend in the Z-axis direction from the inner wall surface 25 of the lid member 20 toward the electret element 50 so as to fill the space adjacent to the weight 70a without interfering with the movement of the movable comb-tooth electrode portion 53. The hydrogen getter 60 has a thickness that is smaller than the distance from the lid member 20 to the surface of the fixed comb-tooth electrode portion 52. By adopting such a configuration, the surface area of ​​the hydrogen getter 60 can be increased and the processing capacity of the hydrogen getter can be improved, so that the life of the electret can be expected to be extended.

[0038] In the above embodiment, the hydrogen getter 60 is attached to the lid member 20. However, the hydrogen getter 60 may be attached to the package member 10 or the electret element 30. Alternatively, the hydrogen getter 60 may be attached to at least a portion of the package member 10, the lid member 20, or the electret element 30. The hydrogen getter 60 has a thickness that is smaller than the distance between the package member 10 and the electret element 30, or a thickness that is smaller than the distance between the lid member 20 and the electret element 30. This configuration allows the surface area of ​​the hydrogen getter 60 to be increased without interfering with the movement of the movable comb-tooth electrode portion 53. The hydrogen getter 60 can be attached by, for example, a welding method such as resistance welding, or by bonding using an adhesive.

[0039] <Method of manufacturing an electret device> Next, a method for manufacturing the electret device 100 according to one embodiment of the present invention will be described.

[0040] A package member 10 and a lid member 20 are provided, and a hydrogen getter 60 is installed on at least a portion of the inner wall 15 of the package member 10 or the inner wall surface 25 of the lid member 20. Next, an electret element 30 is installed inside the package member 10, and the package member 10 is sealed with the lid member 20.

[0041] The sealing of the package member 10 with the lid member 20 can be carried out in the atmosphere, in the presence of an inert gas such as nitrogen or argon, or in a vacuum.

[0042] <Performance test of electret devices> Example 1 An electret element having a comb-shaped chip was placed inside a ceramic package member, and the electrode chip was connected with a wire. Next, a kovar lid member with a hydrogen getter placed on its inner wall surface was welded to the package member with the electret element placed in a vacuum, to create a sealed electret device.

[0043] (Comparative Example 1) A sealed electret device was produced in the same manner as in Example 1, except that no hydrogen getter was provided on the lid member.

[0044] (Charge retention test) The electret devices prepared in Example 1 and Comparative Example 1 were heated to 100° C., and the charging voltage was measured. The results are shown in FIG.

[0045] As can be seen in FIG. 7, the electret device of Comparative Example 1, which did not have a hydrogen getter, showed a sudden drop in charging voltage, but the electret device of Example 1 did not show a significant drop in charging voltage even after 250 hours.

[0046] According to the embodiment described above, the following advantageous effects are achieved.

[0047] (1) An electret device includes a package member, a lid member, and an electret element, the lid member sealing the package member to form a sealed space, the electret element being installed in the sealed space, and a hydrogen getter being provided in at least a portion of the interior of the sealed space.

[0048] With this configuration, the electret device can adsorb hydrogen in the sealed space without performing high-temperature activation treatment, thereby providing an electret device with a long life that prevents charging deterioration due to hydrogen in the electret element sealed in the sealed space.

[0049] (2) In the electret device, the hydrogen getter is disposed in at least a part of the package member.

[0050] With this configuration, the hydrogen getter can be installed without significantly affecting the space inside the electret device.

[0051] (3) In the electret device, the hydrogen getter is disposed in at least a part of the lid member.

[0052] With this configuration, the hydrogen getter can be installed without significantly affecting the space inside the electret device.

[0053] (4) In an electret device, a hydrogen getter is disposed on at least a portion of an electret element.

[0054] With this configuration, the hydrogen getter can be installed without significantly affecting the space inside the electret device.

[0055] (5) The electret element has a movable weight, and a hydrogen getter is provided in an area other than the area facing the movable area of ​​the weight.

[0056] With this configuration, the distance between the cover member 20 and the electret element 50 can be reduced without interfering with the movement of the movable comb-tooth electrode portion 53, thereby making it possible to miniaturize the electret device 100.Since the distance between the cover member and the electret element can be reduced without interfering with the movement of the movable part of the electret element, it is possible to miniaturize the electret device.

[0057] (6) In an electret device, the hydrogen getter has a thickness that is smaller than the distance between the packaging member and the electret element.

[0058] With this configuration, the electret device can expand the surface area of ​​the hydrogen getter 60 so as to fill the space adjacent to the weight 70a without interfering with the movement of the movable comb-tooth electrode portion 53, improving the processing capacity of the hydrogen getter, and therefore, a longer lifespan of the electret can be expected.

[0059] (7) In the electret device, the hydrogen getter has a thickness that is smaller than the distance between the lid member and the electret element.

[0060] With this configuration, the electret device can expand the surface area of ​​the hydrogen getter 60 so as to fill the space adjacent to the weight 70a without interfering with the movement of the movable comb-tooth electrode portion 53, improving the processing capacity of the hydrogen getter, and therefore, a longer lifespan of the electret can be expected.

[0061] (8) In the electret device, the package member is made of a material selected from ceramic, metal, resin, glass, and silicon.

[0062] With this configuration, the electret device can be sealed simply and sufficiently, and deterioration of the electret can be suppressed.

[0063] (9) A method for manufacturing an electret device including a packaging member, a lid member, and an electret element includes the steps of providing a packaging member, placing the electret element in the packaging member, and sealing the packaging member with the lid member to form an airtight space, and includes the step of providing a hydrogen getter on at least a portion of the packaging member, the lid member, and the electret element that form the inner wall of the airtight space before the sealing step.

[0064] With this configuration, the electret device can adsorb hydrogen in the sealed space without performing high-temperature activation treatment, thereby providing an electret device with a long life that prevents charging deterioration due to hydrogen in the electret element sealed in the sealed space.

[0065] (10) In the method for manufacturing an electret device, sealing is performed under vacuum.

[0066] By configuring in this manner, it is possible to prevent moisture and the like from entering the sealed space from the outside during the sealing process, prevent deterioration of the electret, and suppress a decrease in the output of the electret device.

[0067] (11) In the method for producing an electret device, sealing is performed in an inert gas atmosphere.

[0068] By configuring in this manner, it is possible to prevent moisture and the like from entering the sealed space from the outside during the sealing process, prevent deterioration of the electret, and suppress a decrease in the output of the electret device.

[0069] Although various embodiments and modifications have been described above, the present invention is not limited to these. Other embodiments that are conceivable within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention.

[0070] Furthermore, one or more of the above-described embodiments and modifications may be combined as appropriate. [Explanation of symbols]

[0071] 10. Packaging materials 15 Inner wall 20 Cover member 25 Inner wall surface 30 Electret element 40 wire 50 Electret element containing interdigitated electrodes 51 Support part 52 Fixed comb-shaped electrode part 53 Movable comb-shaped electrode part 60 Hydrogen Getter 70a weight 70b weight

Claims

1. An electret device including a package member, a lid member, and an electret element, the lid member seals the package member to form a sealed space, The electret element is installed in the sealed space, The electret device has an inner wall of the package member that forms the sealed space, at least a part of which is water-repellent.

2. An electret device including a package member, a lid member, and an electret element, the lid member seals the package member to form a sealed space, The electret element is installed in the sealed space, The lid member is an electret device in which at least a portion of an inner wall that forms the sealed space is water-repellent.

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