capacitor

Abstract

This capacitor includes: a positive electrode body (111) having a dielectric layer (112) formed on a surface thereof; and a conductive layer (120) which comprises a metal oxide and which is formed on the dielectric layer (112). The conductive layer (120) includes: a first conductive layer (121) formed on the dielectric layer (112); and a second conductive layer (122) formed on the first conductive layer (121). The average thickness of the second conductive layer (122) is greater than the average thickness of the first conductive layer (121).

Description

[Technical Field]

[0001] The present disclosure relates to capacitors. [Background technology]

[0002] Various capacitors have been proposed in the past. Patent Document 1 (JP 2017-103412 A) discloses "a solid electrolytic capacitor comprising an anode body, a dielectric layer disposed on the surface of the anode body, and a solid electrolyte layer disposed on the surface of the dielectric layer and made of zinc oxide having a conductivity of 1 (S / cm) or more."

[0003] Patent Document 2 (JP 2020-35890 A) discloses "a solid electrolytic capacitor comprising an anode body made of a valve metal, a dielectric layer formed on the surface of the anode body, a semiconductor layer formed on the dielectric layer, and a cathode layer formed on the semiconductor layer, wherein the semiconductor layer is composed of a p-type inorganic semiconductor." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-103412 [Patent Document 2] Japanese Patent Application Publication No. 2020-35890 Summary of the Invention [Problem to be solved by the invention]

[0005] Currently, there is a demand for capacitors with high resistance to high temperatures. In this situation, one of the objects of the present disclosure is to provide a novel capacitor with high resistance to high temperatures. [Means for solving the problem]

[0006] One aspect of the present disclosure relates to a capacitor including an anode body having a dielectric layer formed on a surface thereof, and a conductive layer made of a metal oxide formed on the dielectric layer, the conductive layer including a first conductive layer formed on the dielectric layer and a second conductive layer formed on the first conductive layer, the second conductive layer having an average thickness greater than that of the first conductive layer. [Effects of the Invention]

[0007] According to the present disclosure, a capacitor with high resistance to high temperatures can be obtained. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view schematically illustrating the structure of an example capacitor according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view schematically showing a part of the capacitor shown in FIG. [Figure 3] FIG. 10 is a cross-sectional view schematically illustrating the structure of another example of a capacitor according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and other materials may be applied as long as the invention of the present disclosure can be implemented. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." In the following description, when lower and upper limits of numerical values ​​related to specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not greater than the upper limit.

[0010] (Capacitor) The capacitor according to this embodiment includes an anode body having a dielectric layer formed on its surface, and a conductive layer made of a metal oxide formed on the dielectric layer. Hereinafter, the capacitor and the conductive layer may be referred to as a "capacitor (C)" and a "conductive layer (L)." The conductive layer (L) includes a first conductive layer formed on the dielectric layer and a second conductive layer formed on the first conductive layer. The average thickness of the second conductive layer is greater than the average thickness of the first conductive layer.

[0011] In the capacitor (C), the thin first conductive layer can relieve stress, so that the conductive layer (L) can be prevented from peeling off from the dielectric layer even when exposed to high temperatures.

[0012] The capacitor (C) may further include a cathode extraction layer containing an inorganic conductive material formed on the conductive layer. The capacitor (C) having this configuration does not include a solid electrolyte layer containing a conductive polymer, and therefore has particularly high resistance to high temperatures.

[0013] The average thickness T1 of the first conductive layer may be 1 nm or more, or 5 nm or more, or may be 1 μm, 500 nm or less, 100 nm or less, or 50 nm or less. The average thickness T1 of the first conductive layer may be in the range of 1 nm to 1 μm, or in the range of 5 nm to 1 μm. Within any of these ranges, the upper limit may be 500 nm, 100 nm, or 50 nm.

[0014] The average thickness T2 of the second conductive layer may be 50 nm or more, or 100 nm or more, and may be 50 μm or less, 20 μm or less, or 1 μm or less.

[0015] The ratio T2 / T1 of the average thickness T2 of the second conductive layer to the average thickness T1 of the first conductive layer may be greater than 1, 10 or more, 100 or more, or 1000 or more, and may be 100,000 or less, or 10,000 or less.

[0016] The average thickness T1 of the first conductive layer can be measured as follows. First, a cross section of the first conductive layer is exposed, and an image of the cross section is obtained using an electron microscope. Next, ten arbitrary points are selected in the image, and the thickness of the first conductive layer is measured. The average thickness T1 is then determined by arithmetically averaging the ten measurements. The average thickness T2 of the second conductive layer can be determined in a similar manner. Note that if the boundary between the first and second conductive layers is unclear in the scanning electron microscope image, the boundary can be identified using EDS (energy dispersive X-ray analysis) or electron beam diffraction using a STEM (scanning transmission electron microscope) or TEM (transmission electron microscope).

[0017] The anode body may include a porous portion on its surface, in which case the dielectric layer is formed in the porous portion.

[0018] The conductivity of the second conductive layer may be 1 S / cm or more, or 10 S / cm or more. The conductivity of the second conductive layer may be in the range of 1 S / cm to 10,000 S / cm. By making the conductivity of the second conductive layer 1 S / cm or more, a reduction in the ESR of the capacitor can be expected. It is also preferable that the conductivity of the first conductive layer is in the range exemplified here.

[0019] The conductive layer may be composed of at least one selected from the group consisting of ZnO, TiO2, indium tin oxide (ITO), In2O3, SnO2, MnO2, NiO2, CuInO2, CuCrO2, CuAlO2, and CuScO2. Among these, ZnO, indium tin oxide (ITO), In2O3, CuInO2, and CuCrO2 are preferred because of their high conductivity.

[0020] Although ZnO and the like are sometimes classified as conductors and sometimes as semiconductors, they are treated as conductors in this specification.

[0021] The materials of the first conductive layer and the second conductive layer may be different or the same. To improve adhesion between the first conductive layer and the second conductive layer, it is preferable that both are formed of the same material. In a preferred example, the materials of the first conductive layer and the second conductive layer are both ZnO or indium tin oxide.

[0022] The conductive layer may contain an impurity element to improve the conductivity of the conductive layer. The concentration of the impurity element may be in the range of 0.1 to 15 atomic %. The impurity element is selected depending on the material of the conductive layer. Only the first conductive layer may contain the impurity element, or only the second conductive layer may contain the impurity element. Alternatively, both the first and second conductive layers may contain the impurity element.

[0023] (Capacitor manufacturing method) An example of a method for manufacturing a capacitor will be described below. This manufacturing method may be referred to as "manufacturing method (M)" below. According to manufacturing method (M), a capacitor (C) can be manufactured. However, the capacitor (C) may also be manufactured by a manufacturing method other than manufacturing method (M).

[0024] The manufacturing method (M) includes steps (i) and (ii). Step (i) is a step of forming a conductive layer (L) on a dielectric layer formed on the surface of an anode body. Step (i) includes step (ia) of forming a first conductive layer on the dielectric layer and step (ib) of forming a second conductive layer on the first conductive layer.

[0025] The method for forming the first and second conductive layers is not particularly limited, and they may be formed by known methods. Examples of these formation methods include vapor-phase methods in which a layer is formed in a vapor phase and liquid-phase methods in which a layer is formed in a liquid phase. Examples of vapor-phase methods include evaporation, sputtering, atomic layer deposition (ALD), and chemical vapor deposition (CVD). Examples of liquid-phase methods include sol-gel methods, chemical solution deposition, hydrothermal synthesis, flux methods, coating methods, electrolytic plating, and electroless plating. It is preferable to select these methods taking into consideration the material of the conductive layers.

[0026] The first conductive layer is preferably formed by a method that provides high coverage even when the surface is uneven. In particular, when the anode body has a porous portion on its surface, the first conductive layer is preferably formed by a method that provides high coverage. Examples of methods that provide high coverage include ALD.

[0027] A preferred example of a method for forming the second conductive layer is a liquid phase method, which is preferred in terms of low cost and ease of forming a film even inside a porous material.

[0028] In a preferred example, the first conductive layer is formed by an ALD method, and the second conductive layer is formed by a liquid phase method. In a preferred example of the conductive layer, the first conductive layer is made of ZnO formed by an ALD method, and the second conductive layer is made of ZnO formed by a liquid phase method.

[0029] Step (ii) is a step of forming a cathode extraction layer on the second conductive layer. A capacitor element is obtained by steps (i) and (ii). After step (ii), if necessary, a step of connecting leads to the capacitor element and a step of covering the capacitor element with an outer casing are performed. In this manner, a capacitor (C) is manufactured. Note that when the capacitor (C) includes multiple capacitor elements, manufacturing method (M) includes a step of connecting the multiple capacitor elements.

[0030] Examples of the configuration and constituent members of the capacitor (C) are described below. Known constituent members may be used for constituent members other than those characteristic of the present disclosure.

[0031] (anode body) The anode body can be formed using a valve metal, an alloy containing a valve metal, a compound containing a valve metal, or the like. These materials may be used alone or in combination of two or more. Examples of valve metals that are preferably used include aluminum, tantalum, niobium, and titanium. The anode body may be formed using a foil of the above materials (e.g., a metal foil such as aluminum foil).

[0032] An anode having a porous surface can be obtained by roughening the surface of a metal foil containing a valve metal, for example. The roughening may be performed by electrolytic etching or the like.

[0033] Alternatively, the anode body may be formed by sintering particles of the above material. For example, the anode body may be a sintered body of tantalum. When the anode body is a sintered body, a porous portion exists on the surface. When the anode body is a sintered body, the capacitor (C) may include an anode wire partly embedded in the sintered body.

[0034] (dielectric layer) The dielectric layer is an insulating layer that functions as a dielectric. The dielectric layer may be formed by anodizing a valve metal on the surface of the anode body (e.g., a metal foil). The dielectric layer may be formed so as to cover at least a portion of the anode body. The dielectric layer is usually formed on the surface of the anode body. When a porous portion is present on the surface of the anode body, the dielectric layer is formed on the surface of the porous portion of the anode body.

[0035] A typical dielectric layer contains an oxide of a valve metal. For example, when tantalum is used as the valve metal, a typical dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, a typical dielectric layer contains Al2O3. However, the dielectric layer is not limited to these and may be any material that functions as a dielectric.

[0036] (Cathode extraction layer) The cathode extraction layer is a conductive layer. The cathode extraction layer may be formed using conductive carbon or metal. Specifically, the cathode extraction layer may be formed using a carbon paste containing conductive carbon particles or a metal paste containing metal particles. Alternatively, the cathode extraction layer may include a layer made of metal only (a vapor deposition layer or a metal foil). Examples of conductive carbon include graphite, carbon black, graphene flakes, and carbon nanotubes. Examples of metal pastes include a silver paste containing silver particles.

[0037] The cathode extraction layer may include a first layer formed on the conductive layer (L) and a second layer formed on the first layer. In this case, the first layer may be a carbon layer containing conductive carbon, and the second layer may be a layer formed of a metal paste.

[0038] (Lead material and exterior body) There are no particular limitations on the lead members and the exterior body, and known lead members and exterior bodies may be used.

[0039] (Capacitor (C) structure) The capacitor (C) may include only one capacitor element. Alternatively, the capacitor (C) may include multiple capacitor elements. For example, the capacitor element (C) may include multiple capacitor elements connected in parallel. The multiple capacitor elements (C) are typically connected in parallel in a stacked state and covered with an exterior body.

[0040] Examples of embodiments according to the present disclosure will be described in detail below with reference to the drawings. The components described above can be applied to the components of the examples described below. The examples described below can be modified based on the above description. The matters described below may also be applied to the above embodiments. In the embodiments described below, components that are not essential to the capacitor of the present disclosure may be omitted. Note that the following drawings are schematic and may differ from the actual configuration.

[0041] (Embodiment 1) 1 is a cross-sectional view schematically illustrating a capacitor according to embodiment 1. Capacitor 10 shown in FIG.

[0042] Capacitor element 100 includes anode body 111, dielectric layer 112, conductive layer 120, and cathode extraction layer 131. Dielectric layer 112 is formed so as to cover at least a portion of the surface of anode body 111. Conductive layer 120 is formed so as to cover at least a portion of dielectric layer 112. Cathode extraction layer 131 is formed so as to cover at least a portion of conductive layer 120. Conductive layer 120 is the conductive layer (L) described above.

[0043] Anode lead 21 is connected to anode body 111. Cathode lead 22 is connected to cathode extraction layer 131 via metal paste layer 23. Metal paste layer 23 is formed of metal paste (silver paste) or the like. Exterior body 30 is formed to cover part of anode lead 21, part of cathode lead 22, and capacitor element 100. Part of anode lead 21 and part of cathode lead 22 are exposed from exterior body 30 and function as terminals.

[0044] A cross-sectional view of an example of a portion where conductive layer 120 is present is shown schematically in Figure 2. Anode body 111 of the example in Figure 2 has porous portion 111a on its surface. As shown in Figure 2, conductive layer 120 includes first conductive layer 121 formed on dielectric layer 112 and second conductive layer 122 formed on first conductive layer 121. The average thickness of second conductive layer 122 is greater than the average thickness of first conductive layer 121.

[0045] FIG. 1 shows a case where capacitor 10 includes only one capacitor element 100. However, capacitor 10 may include multiple capacitor elements 100. FIG. 3 is a schematic cross-sectional view of an example of capacitor 10 including multiple capacitor elements 100. Note that, to make the drawing easier to understand, some components are omitted from FIG. 3.

[0046] 3 includes a plurality of stacked capacitor elements 100. The plurality of capacitor elements 100 are connected in parallel.

[0047] (Example) An aluminum foil with a porous surface was prepared as an anode. A conductive layer was formed on this aluminum foil using two methods. In the first method, a thick ZnO layer was formed solely by liquid-phase deposition. In the second method, a thin ZnO layer (first conductive layer) was formed by ALD, followed by a thick ZnO layer by liquid-phase deposition. SEM-EDS measurements were performed on the cross-sections of the porous portions of the conductive layers formed by the first and second methods. The intensity ratio Zn / Al was calculated from the measurement results. The Zn / Al intensity ratio for the conductive layer formed by the first method was 0.04, and the Zn / Al intensity ratio for the conductive layer formed by the second method was 0.18. This result suggests that forming the first conductive layer by ALD improves the coverage of the conductive layer in the porous portion. [Industrial Applicability]

[0048] The present disclosure can be used for capacitors. While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention. [Explanation of symbols]

[0049] 10: Capacitor 21: Anode lead 22: Cathode lead 30: Exterior body 100: Capacitor element 111: Anode body 111a: Porous part 112: Dielectric layer 120: Conductive layer 121: First conductive layer 122: Second conductive layer 131: Cathode extraction layer

Claims

1. A capacitor, an anode body having a dielectric layer formed on its surface; a conductive layer made of a metal oxide formed on the dielectric layer, the conductive layer includes a first ZnO layer formed on the dielectric layer and a second ZnO layer formed on the first ZnO layer; The average thickness of the second ZnO layer is greater than the average thickness of the first ZnO layer.

2. The first ZnO layer is a layer formed by atomic layer deposition, The capacitor according to claim 1 , wherein the second ZnO layer is a layer formed by a liquid phase method.

3. 3. The capacitor according to claim 1, further comprising a cathode extraction layer formed on the conductive layer and containing an inorganic conductive material.

4. 3. The capacitor according to claim 1, wherein the average thickness of the first ZnO layer is in the range of 1 nm to 1 μm.

5. the anode body includes a porous portion on the surface, 3. The capacitor according to claim 1, wherein the dielectric layer is formed in the porous portion.

6. 3. The capacitor according to claim 1, wherein the second ZnO layer has a conductivity of 1 S / cm or more.

7. 3. The capacitor according to claim 1, wherein the conductive layer contains an impurity element for improving the conductivity of the conductive layer.

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