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] 2. Description of the Related Art As one of the energy harvesting technologies for harvesting energy from environmental vibrations, a method for generating power using a Micro Electro Mechanical Systems (MEMS) vibration element is known (see, for example, Patent Document 1).

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

[0004] However, the charge 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 a vacuum package to prevent deterioration of the electronic 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] JP 2018-088780 A [Patent Document 2] JP 2013-13256 A [Patent Document 3] JP 2008-182666 A [Patent Document 4] JP 2014-049557 A [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 have noticed that charging deterioration occurs even though moisture is removed, and have concluded that one of the causes is the accumulation of SiO - Hydrogen atom H in molecule + They discovered that this was due to a reaction that neutralized the charge, and that some kind of measure was needed to address this issue.

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

[0011] In order to solve the above problems, an electret device according to an 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, at least a part of an inner wall that forms 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 portion of an inner wall that forms the sealed space is water-repellent. Effect of the Invention

[0013] The present invention can provide an electret device in which deterioration due to charging of an electret sealed in a sealed space is prevented, and a method for manufacturing the same. [Brief description 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. [Diagram 2] FIG. 2 is a cross-sectional view of the electret device of FIG. [Diagram 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), (c) is a rear view of the lid member 20 of FIG 3(a). [Figure 4] FIG. 4 is a cross-sectional view of the electret device of FIG. [Diagram 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, and (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] 1 shows the results of a charging deterioration test of an electret device according to an embodiment of the present invention and a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the 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 an embodiment of the present invention, Fig. 1(b) is an exploded perspective view thereof, Fig. 1(c) is a rear view of a cover 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 cover member 20, an electret element 30, and a hydrogen getter 60. The package member 10 and the cover member 20 form a sealed space, and the electret element 30 is installed in the sealed space. Furthermore, the electret element 30 is connected to electrodes provided on the package member via wires 40 from electrode pads 31 and 32 provided 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 cover 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 cover 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, and silicon may be used. A part of the inner wall 15 of the package member 10 may be water-repellent.

[0021] (Cover material) 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, when the lid member 20 is made of a 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 substance or an alloy. A part 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 in which a voltage is applied to a heated oxide film to generate a charge is called an electret. Furthermore, maintaining the charge even after the application of the voltage is terminated is called electretization. Furthermore, an element in which an electret is used is called an electret element. Furthermore, a device including an electret element is called 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 three-layer substrate consisting of a Si support layer, a SiO2 box layer, and a Si active layer, and the support portion 51 is formed by 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 by 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 via 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 electrode of the movable comb-tooth electrode portion 53 into the comb-tooth electrode of the fixed comb-tooth electrode portion 52 changes, thereby generating power. In order 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] In the electret element 50, at least a part of one of the comb-tooth electrode portions 52 and 53 includes an electret. Furthermore, the electret element 50 may have a protective film on the electret surface.

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

[0032] (closed space) In one embodiment of the present invention, as shown in Fig. 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 between the package member 10 and the lid member 20 can be performed by a commonly used method, for example, by welding the lid member 20.

[0034] (Hydrogen getter) The hydrogen getter 60 is a material that mainly adsorbs hydrogen, and adsorbs hydrogen within the sealed space formed by the package member 10 and the cover member 20. The hydrogen getter 60 may be a material 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, even at a relatively low temperature, hydrogen atoms spread throughout the material of the hydrogen getter 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, so deterioration of the electret due to heating can be avoided, and deterioration of the electret due to charging caused by hydrogen can be prevented.

[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 in contact with the package member 10.

[0037] Furthermore, as shown in Figs. 5(a) to (c), the 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 installed 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, so that the electret device 100 can be made smaller (Figs. 6(a) to (c)). 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 in a range smaller than the distance from the lid member 20 to the surface of the fixed comb-tooth electrode portion 52. With this 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, but the hydrogen getter 60 may be attached to the package member 10 or the electret element 30. The hydrogen getter 60 may also be attached to at least a part of the package member 10, the lid member 20, or the electret element 30. The hydrogen getter 60 has a thickness smaller than the distance between the package member 10 and the electret element 30, or a thickness smaller than the distance between the lid member 20 and the electret element 30. With this configuration, the surface area of ​​the hydrogen getter 60 can be further enlarged 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 adhesion 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 part 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] Furthermore, 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-tooth chip was placed inside a ceramic packaging member, and the electrode chip was connected with a wire. Next, a lid member made of Kovar, on whose inner wall surface a hydrogen getter was placed, was welded to the packaging member in which the electret element was placed, under vacuum, to produce 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 produced 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 shown in FIG. 7, the electret device of Comparative Example 1, which did not have a hydrogen getter, showed a rapid drop in charging voltage, whereas the electret device of Example 1 did not show a significant drop in charging voltage even after more than 250 hours.

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

[0047] (1) An electret device includes a packaging member, a lid member, and an electret element. The lid member seals the packaging member to form a sealed space. The electret element is placed in the sealed space, and includes a hydrogen getter in at least a portion of the inside of the sealed space.

[0048] Since the electret device is configured in this manner, it is possible to adsorb hydrogen in the sealed space without performing high-temperature activation treatment, thereby providing an electret device with a long life that prevents deterioration of the electret element sealed in the sealed space due to charging caused by hydrogen.

[0049] (2) In an electret device, a hydrogen getter is provided in at least a part of a 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 cover 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 provided 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 opposite to 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, the electret device can be miniaturized.

[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] Because of 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 thus a longer life for 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] Because of 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 thus a longer life for the electret can be expected.

[0061] (8) In the electret device, the package member is made of a material selected from ceramics, 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 an 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] Since the electret device is configured in this manner, it is possible to adsorb hydrogen in the sealed space without performing high-temperature activation treatment, thereby providing an electret device with a long life that prevents deterioration of the electret element sealed in the sealed space due to charging caused by hydrogen.

[0065] (10) In the method for producing 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, and at least a portion of the inner wall 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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