Capacitor

Abstract

This capacitor 10 comprises a first electrode 111, a dielectric layer 112 that is formed on the surface of the first electrode 111, an inorganic electroconductive layer 120 that is disposed on the dielectric layer 112 and contains an inorganic compound, and a second electrode 131 that is disposed on the inorganic electroconductive layer 120. The second electrode 131 includes a carbon layer 131a containing carbon particles. An intermediate layer containing an inorganic compound and carbon particles is formed between the inorganic electroconductive layer 120 and the carbon layer 131a. The thickness of the carbon layer is within the range of 25-90 µm. The carbon particles contained in the intermediate layer are spherical and have a particle diameter within the range of 30-70 nm.

Description

Capacitor

[0001] The present disclosure relates to a capacitor.

[0002] A capacitor using an inorganic layer instead of a solid electrolyte layer formed using a conductive polymer has been proposed.

[0003] Patent Document 1 describes "a solid electrolytic capacitor comprising: an anode body; a dielectric layer disposed on a surface of the anode body; and a solid electrolyte layer disposed on a surface of the dielectric layer and formed using zinc oxide having an electrical conductivity of 1 S / cm or more" (Claim 1).

[0004] Patent Document 2 describes "a solid electrolytic capacitor comprising: an anode electrode body made of a valve metal; an anodized film formed on the anode electrode body; and a solid electrolyte layer formed on the anodized film, wherein the solid electrolyte layer is connected to a cathode electrode body via a carbon layer, the solid electrolytic capacitor being characterized in that an intermediate layer in which a solid electrolyte material connected to the solid electrolyte layer and carbon particles connected to the carbon layer are mixed is provided between the solid electrolyte layer and the carbon layer" (Claim 1).

[0005] Japanese Patent Application Laid-Open No. 2017-103412, Japanese Patent Application Laid-Open No. 2001-217159

[0006] An electrolytic capacitor is exposed to many thermal loads during the manufacturing process and use. Thermal loads generate stress between materials having different coefficients of thermal expansion. In particular, when the electrolyte is formed of an inorganic material, thermal stress is likely to cause cracking in the electrolyte. As a result, the reliability of the electrolytic capacitor may be reduced, for example, an increase in ESR occurs.

[0007] One aspect of the present disclosure relates to a capacitor comprising a first electrode, a dielectric layer formed on the surface of the first electrode, an inorganic conductive layer containing an inorganic compound disposed on the dielectric layer, and a second electrode disposed on the inorganic conductive layer, wherein the second electrode includes a carbon layer containing carbon particles, and an intermediate layer containing the inorganic compound and the carbon particles is formed between the inorganic conductive layer and the carbon layer, the thickness of the carbon layer is in the range of 25 to 90 μm, and the carbon particles contained in the intermediate layer are spherical and have a particle size in the range of 30 to 70 nm.

[0008] According to this disclosure, it is possible to realize a capacitor in which the increase in ESR is suppressed in response to thermal stress.

[0009] While novel features of this disclosure are described in the attached claims, this disclosure, in conjunction with other purposes and features of this disclosure, will be better understood by the following detailed description accompanied by drawings, both in terms of its structure and content.

[0010] Figure 1 is a schematic cross-sectional view showing an example of the structure of a capacitor according to this embodiment. Figure 2 is a schematic cross-sectional view showing an example of a capacitor according to this embodiment.

[0011] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and other materials may be applied as long as they allow the invention of this disclosure to be carried out. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties or conditions are given as examples, either the given lower limit and either the given upper limit may be arbitrarily combined, as long as the lower limit does not exceed the upper limit. In the following description, when examples of components or methods are listed, unless otherwise specified, only one of the listed examples may be used, or multiple of the listed examples may be used in combination.

[0012] This disclosure encompasses any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims. In other words, any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims, is possible, provided that no technical inconsistency arises.

[0013] In the following explanation, the term "contains (or includes)" encompasses expressions such as "contains (or includes)," "substantially consists of," and "consists of."

[0014] (Capacitor) The capacitor according to this embodiment may be referred to as "capacitor (C)" below. Capacitor (C) includes a first electrode, a dielectric layer formed on the surface of the first electrode, an inorganic conductive layer containing an inorganic compound disposed on the dielectric layer, and a second electrode disposed on the inorganic conductive layer. The second electrode includes a carbon layer containing carbon particles. An intermediate layer containing an inorganic compound and carbon particles is formed between the inorganic conductive layer and the carbon layer.

[0015] Capacitors with an inorganic conductive layer placed on a dielectric layer have high heat resistance. However, the inorganic conductive layer is prone to cracking and defects due to thermal stress generated during the manufacturing process and use, which can lead to a decrease in the reliability of the capacitor, such as an increase in ESR.

[0016] The carbon layer thickness is in the range of 25 to 90 μm. The carbon particles contained in the intermediate layer are spherical and have a particle size in the range of 30 to 70 nm. By controlling the carbon layer thickness and the shape and particle size of the carbon particles within the above range, the thermal stress applied to the inorganic conductive layer is relieved by the carbon layer while suppressing a decrease in capacity density. This disclosure is based on this new finding.

[0017] The first electrode is the anode, and the second electrode is the cathode. An example of the cathode configuration will be described later.

[0018] The first electrode may have a porous portion on its surface. In this case, the dielectric layer is formed on the surface of the porous portion, and at least a portion of the inorganic conductive layer is arranged within the voids of the porous portion. By using a first electrode having a porous portion, the capacitance can be increased.

[0019] The inorganic conductive layer formed on the surface of the dielectric layer partially fills the pores of the porous portion and is also formed in a three-dimensional porous manner on the side closer to the second electrode than the apex of the convex portion closest to the second electrode on the surface of the porous portion. At this time, an intermediate layer containing carbon particles is formed to fill the depressions of the porous inorganic conductive layer. At this time, the carbon particles contained in the carbon layer can penetrate into the depressions of the inorganic conductive layer. Between the bottom of the depressions and the tops of the convex portions on the surface of the inorganic conductive layer, the inorganic compound constituting the inorganic conductive layer and carbon particles are mixed, forming an intermediate layer. In the intermediate layer, it is preferable that the carbon particles are contained in an amount of 30% to 70% by volume. The surface of the inorganic conductive layer may have irregularities of a few micrometers.

[0020] Spherical carbon particles with a particle size of 30-70 nm easily fill the depressions in the inorganic conductive layer, and their spherical shape prevents the formation of voids within the depressions that cannot be filled by carbon particles due to steric hindrance. As a result, the depressions in the inorganic conductive layer can be efficiently filled with carbon particles, improving the adhesion between the inorganic conductive layer and the carbon layer. Consequently, the ESR of the capacitor can be lowered, and the carbon particles present in the depressions of the inorganic conductive layer alleviate the thermal stress applied to the inorganic conductive layer, suppressing cracking or fracture of the inorganic compound. As a result, the increase in ESR associated with thermal stress is suppressed.

[0021] A carbon layer is formed on top of the intermediate layer. The intermediate layer improves the adhesion between the inorganic conductive layer and the carbon layer, reducing the ESR of the capacitor. In addition, by setting the thickness of the carbon layer to an appropriate thickness, the effect of mitigating the thermal stress applied to the inorganic conductive layer can be enhanced, further suppressing the rise in ESR due to thermal stress.

[0022] The carbon particles contained in the carbon layer may be the same as or different from the carbon particles contained in the intermediate layer. In other words, the type, particle size, shape, etc., of the carbon particles contained in the carbon layer may be the same as or different from the carbon particles contained in the intermediate layer.

[0023] The particle size D of the carbon particles is the average particle diameter determined by the method described later, based on electron microscope images of the cross-section of the intermediate layer.

[0024] Spherical carbon particles are those with an aspect ratio A of less than 5.0, determined by the method described later based on electron microscope images of the cross-section of the intermediate layer. Carbon particles with an aspect ratio A of 5.0 or more are flaky carbon particles. The aspect ratio of spherical carbon particles may be 3.0 or less.

[0025] The particle size D and aspect ratio A of the carbon particles are determined based on electron microscope images of the cross-section of the intermediate layer using the following method.

[0026] Image processing is performed on electron microscope images to identify the contours of carbon particles. In the cross-sectional images, 20 or more carbon particles are selected and their contours are identified. For each carbon particle, the maximum diameter D1 and the diameter D2 in the direction perpendicular to this maximum diameter D1 are measured. The aspect ratio (D1 / D2) of each particle is calculated by dividing D1 by D2. The average of the calculated aspect ratios is found and defined as the aspect ratio A of the carbon particle. In addition, for each carbon particle, the diameter D3 of a circle having the same area as the area identified from the contour is determined. The average of D3 is found and defined as the average particle diameter D of the carbon particle.

[0027] The particle size D of the carbon particles is 30 nm or more and 70 nm or less, and may be 30 nm or more and 66 nm, 30 nm or more and 60 nm, 40 nm or more and 60 nm, 39 nm or more and 60 nm, 39 nm or more and 55 nm, or 40 nm or more and 55 nm or less. The aspect ratio A of the carbon particles is less than 5.0, and may be 3.0 or less, or 2.0 or less.

[0028] The thickness of the carbon layer refers to the distance in the thickness direction from the apex of the convexity closest to the second electrode on the surface of the inorganic conductive layer, as identified based on electron microscope images, to the position closest to the second electrode on the surface of the carbon layer opposite the inorganic conductive layer. By setting the thickness of the carbon layer to 25 μm or more, a sufficient effect of mitigating the thermal stress applied to the inorganic conductive layer is obtained, and the increase in ESR due to thermal stress is suppressed. On the other hand, by setting the thickness of the carbon layer to 90 μm or less, the decrease in capacitance density that occurs with increasing the thickness of the carbon layer can be suppressed, and a capacitor (C) that achieves both high capacitance and low ESR can be realized. The thickness of the carbon layer is 25 μm or more and 90 μm or less, and may be 26 μm or more and 90 μm or less, 30 μm or more and 90 μm or less, 35 μm or more and 90 μm or less, 36 μm or more and 89 μm or less, or 36 μm or more and 73 μm or less.

[0029] The thickness of the intermediate layer refers to the distance in the thickness direction from the apex of the convexity closest to the second electrode on the surface of the porous portion (dielectric layer) to the apex of the convexity closest to the second electrode on the surface of the inorganic conductive layer opposite the porous portion. By making the thickness of the intermediate layer 20 μm or more, interfacial resistance can be reduced, and by making it 50 μm or less, the effects of thermal stress can be reduced and the decrease in capacitance density can be suppressed.

[0030] The type of carbon material constituting the carbon particles is not particularly limited. Examples of carbon materials include graphite, graphene, carbon black, soft carbon, and hard carbon. As for graphite, a carbon material having a graphite-type crystal structure is used, and either artificial graphite or natural graphite may be used. These carbon materials may be used individually or in combination of two or more types.

[0031] From the viewpoint of conductivity, it is preferable that the carbon particles have high crystallinity. Examples of carbon materials with high crystallinity include graphite, graphene, and carbon black that has been graphitized by heat treatment, etc. However, since carbon materials with high crystallinity such as graphite and graphene tend to take on a flaky form, it is preferable to use carbon black as the spherical carbon particles contained in the intermediate layer.

[0032] The inorganic oxide that is the main component of the inorganic conductive layer may be zinc oxide. Although zinc oxide is sometimes classified as a semiconductor, it can be used as a conductive material. In this specification, "main component" means a content of 50% by mass or more. The content of the main component may be in the range of 80-100% by mass, 90-100% by mass, or 95-100% by mass. The inorganic conductive layer may consist of zinc oxide containing fluorine (including zinc oxide containing a dopant).

[0033] Zinc oxide may contain oxygen vacancies. The presence of oxygen vacancies can increase the conductivity of zinc oxide. Zinc oxide is ZnO １－ｘ The material may include zinc oxide represented by (0 ≤ x ≤ 0.25), where x may be greater than 0. In this specification, unless otherwise specified, the notation "ZnO" includes zinc oxide containing oxygen vacancies. Furthermore, for the sake of simplicity, zinc oxide to which fluorine and / or dopants have been added may be referred to as "zinc oxide" or "ZnO".

[0034] The zinc oxide constituting the inorganic conductive layer may be in particulate form. Zinc oxide produced by the manufacturing method (M) described later may be in particulate form. By including particulate zinc oxide in the inorganic conductive layer, the stress generated in the inorganic conductive layer can be alleviated. As a result, the reliability of the capacitor can be improved.

[0035] When the inorganic conductive layer is mainly composed of zinc oxide, the zinc oxide may or may not contain a dopant. Adding a dopant to zinc oxide can improve its conductivity. The dopant is not particularly limited, and known dopants may be used. The dopant may be at least one element selected from the group consisting of Al, Ga, B, and In. The dopant content in zinc oxide may be 0.1 atomic% or more of Zn, or 0.5 atomic% or more, or 10 atomic% or less of Zn, or 5.0 atomic% or less.

[0036] The fact that the inorganic oxide that forms the main component of the inorganic conductive layer is zinc oxide is preferable because it allows for low cost and high conductivity. On the other hand, the inorganic oxide that forms the main component of the inorganic conductive layer may be something other than zinc oxide. Examples of inorganic oxides other than zinc oxide include manganese dioxide, tin oxide, and titanium oxide.

[0037] The dopant may contain aluminum. In that case, the ratio of the number of aluminum atoms to the number of zinc atoms in the inorganic conductive layer analyzed by SEM-EDX (atomic ratio) Al / Zn may be 0.0010 or higher, 0.0030 or higher, 0.0033 or higher, or 0.0050 or higher, and may be 0.010 or lower, 0.0070 or lower, 0.0040 or lower, or 0.0038 or lower.

[0038] Valve metal may be used as the main component of the first electrode. For example, the main component of the first electrode may be aluminum or tantalum. An example of the first electrode is aluminum foil. Another example of the first electrode is a tantalum sintered body obtained by sintering tantalum particles.

[0039] The inorganic conductive layer may be a layer formed by heating a zinc-containing material. It is believed that using such an inorganic conductive layer can particularly reduce the internal stress of the inorganic conductive layer. The zinc-containing material may be a material containing a zinc compound (e.g., a zinc salt). Zinc oxide can be produced by heating and thermally decomposing the zinc compound. Examples of methods for forming the inorganic conductive layer will be described later.

[0040] (Manufacturing Method for Capacitors) The manufacturing method according to this embodiment may be referred to as "Manufacturing Method (M)" below. Manufacturing Method (M) is a method for manufacturing capacitors. According to Manufacturing Method (M), capacitors (C) can be manufactured. However, capacitors (C) may be manufactured by methods other than Manufacturing Method (M). Matters described for capacitors (C) can be applied to Manufacturing Method (M), so redundant explanations may be omitted. Matters described for Manufacturing Method (M) may also be applied to capacitors (C).

[0041] In the following example, a case where the main component of the inorganic conductive layer is zinc oxide will be described. When the main component of the inorganic conductive layer is an inorganic oxide other than zinc oxide, a material may be selected in accordance with the type of the inorganic oxide.

[0042] The manufacturing method (M) includes a first step of forming an inorganic conductive layer on a dielectric layer formed on a surface of a first electrode, and a second step of forming a second electrode on the inorganic conductive layer. The main component of the inorganic conductive layer is zinc oxide. The first step includes a step (a) of placing a solution in which a zinc compound is dissolved onto the dielectric layer, and a step (b) of forming the inorganic conductive layer by heating the solution.

[0043] (Step (a)) In step (a), a solution in which a zinc compound is dissolved is placed onto the dielectric layer. The solvent of the solution is selected according to the type of the zinc compound. The solvent may be water, an organic solvent, or a mixed solvent thereof. A liquid that dissolves the zinc compound and the fluorine-containing compound and evaporates during heating in step (b) can be used as the solvent. That is, the solvent may be a liquid having a boiling point lower than the heating temperature in step (b). Examples of the solvent include 2-methoxyethanol.

[0044] As the zinc compound, a compound that forms zinc oxide upon heating in step (b) is used. The zinc compound may be a salt. Additives may be added to the solution as necessary. For example, an additive for increasing the solubility of the zinc compound may be added to the solution.

[0045] A fluorine-containing compound may further be added to the solution in which the zinc compound is dissolved. The fluorine-containing compound may be a fluorine-containing organic compound. The fluorine-containing organic compound may be a fluorine-containing surfactant. Fluorine can be added to the formed zinc oxide by using a fluorine-containing surfactant. Furthermore, the use of a fluorine-containing surfactant makes it easier for the solution to spread over the surface of the dielectric layer having a complex shape. As a result, the contact area between the dielectric layer and the inorganic conductive layer (zinc oxide layer) can be increased, and the capacitance can be increased.

[0046] The fluorine-containing compound may be a surfactant having a perfluoroalkyl group. The type of surfactant is not limited, and may be an anionic surfactant, a nonionic surfactant, or a zwitterionic surfactant. Examples of surfactants having a perfluoroalkyl group include Surflon S211, Surflon S221, Surflon S233, and Surflon S243 (all manufactured by AGC Seimi Chemical Co., Ltd.).

[0047] The concentration of the surfactant in the solution is not particularly limited. The concentration of the surfactant in the solution may be 0.1% by mass or more, 0.2% by mass or more, or 0.5% by mass or more, and may be 3.0% by mass or less, 2.0% by mass or less, or 1.5% by mass or less. The amount of fluorine in the inorganic conductive layer can be controlled by changing the concentration of the surfactant in the solution.

[0048] (Step (b)) In step (b), an inorganic conductive layer is formed on the dielectric layer by heating the solution on the dielectric layer. In step (b), the zinc compound can be thermally decomposed to produce zinc oxide. For example, when the zinc compound is zinc acetate, zinc acetate is thermally decomposed by heating to produce zinc oxide. At this time, fluorine from the fluorine-containing compound is added to the zinc oxide.

[0049] Heating conditions are selected according to the solution. The heating method is not particularly limited, and a known heating method (for example, heating with a heater) may be used. The atmosphere in which the heating step of step (b) is performed is not particularly limited; the step may be performed in air, or may be performed in an atmosphere other than air (for example, in an inert gas or water vapor). Step (b) may also be performed under reduced pressure.

[0050] In the production method (M), step (a) and step (b) may be repeated. The number of cycles each consisting of one step (a) and one step (b) may be 2 or more, or 5 or more, and may be 40 or less, or 15 or less. The inorganic conductive layer can be thickened by repeating the cycle.

[0051] Examples of zinc compounds include zinc acetate (e.g., zinc acetate dihydrate) and zinc nitrate (e.g., zinc nitrate hexahydrate). Examples of solvents include alcohols, acetone, acetonitrile, 2-ethoxyethyl ethyl ether acetate, tetrahydrofuran, and water. Examples of alcohols include methanol, ethanol, isopropyl alcohol, 2-methoxyethanol, 1-hexanol, cyclohexanol, 1,2-propanediol, and 1,3-propanediol. Multiple zinc compounds may be dissolved in the solution. The solvent may be a mixed solvent. Compounds containing dopants may be dissolved in the solution. Examples of compounds containing dopants include aluminum nitrate (e.g., aluminum nitrate nonahydrate). Additives may be added to the solution to increase the solubility of the zinc compounds. Examples of such additives include monoethanolamine, diethanolamine, triethanolamine, mercaptopurine, ethylenediamine, and acetylacetone.

[0052] An example of a solution is prepared by dissolving zinc acetate, aluminum nitrate, and a fluorine-containing surfactant in 2-methoxyethanol. It is preferable that monoethanolamine is added to the 2-methoxyethanol. The concentration of zinc acetate may be in the range of 0.01 to 10 mol / L (for example, 0.1 to 5 mol / L). Aluminum nitrate may be added so that the amount of dopant is within the above range. The concentration of monoethanolamine may be in the range of 0.01 to 10 mol / L (for example, 0.1 to 5 mol / L). The concentration of the fluorine-containing surfactant may be within the above range.

[0053] When zinc acetate is used as the zinc compound, the heating temperature in step (b) may be 150°C or higher, 200°C or higher, 400°C or lower, or 300°C or lower. In that case, the heating time may be 1 minute or higher, 5 minutes or higher, 30 minutes or lower, or 15 minutes or lower.

[0054] The manufacturing method (M) may include a further heat treatment step after steps (a) and (b). The heat treatment step is carried out at a higher temperature than the heating step in step (b). Heat treatment at a high temperature can improve the conductivity of the inorganic conductive layer. The heat treatment temperature in the heat treatment step may be 250°C or higher and 500°C or lower. In that case, the heat treatment time in the heat treatment step may be 10 minutes or higher and 5 hours or lower. Other conditions may be those described for step (b).

[0055] The manufacturing method (M) may include, instead of steps (a) and (b), a step (A) of placing a material containing a zinc compound on a dielectric layer, and a step (B) of forming the inorganic conductive layer by heating the material. By heating in step (B), it is possible to thermally decompose the zinc compound to produce zinc oxide.

[0056] Step (A) may be carried out by placing a solution containing a dissolved zinc compound onto a dielectric layer and then drying the solution. After performing step (a), it is possible to carry out step (A) by going through the process up to partway through step (b). The subsequent step (b) corresponds to step (B). In the same manner as steps (a) and (b), steps (A) and (B) may be repeated in manufacturing method (M).

[0057] Following the first step, a second step is performed in which a second electrode is formed on the inorganic conductive layer. This second step yields a capacitor (capacitor element). The method for forming the second electrode is not particularly limited. Examples of methods for forming the second electrode will be described later.

[0058] Subsequently, other steps may be performed as needed. In one example of a manufacturing method, first, a first lead is connected to the first electrode, and a second lead is connected to the second electrode. Next, the capacitor element, a part of the first electrode, and a part of the second electrode are sealed with a sealing resin (outer casing). These steps can be carried out by known methods.

[0059] Examples of components of a capacitor (C) are described below. The components of a capacitor (C) are not limited to the following examples. Components other than those characteristic of this disclosure may be those used in known capacitors.

[0060] (First Electrode) The first electrode contains valve metal. Examples of valve metals include aluminum (Al), titanium (Ti), tantalum (Ta), niobium (Nb), etc. The first electrode may be a foil of valve metal. Alternatively, the first electrode may be a sintered body of particles containing valve metal. These particles may be particles of valve metal, particles of an alloy containing valve metal, or particles of a compound containing valve metal. The first electrode may be aluminum foil or a sintered body of tantalum particles.

[0061] The first electrode may have a porous portion on its surface. If the first electrode is a foil, a porous portion can be formed on the surface of the foil by etching the foil.

[0062] If the first electrode is a sintered body of particles containing valve metal, a porous portion exists on the surface of the sintered body. When the first electrode is a sintered body, the capacitor (C) may include leads (e.g., lead wires) that are partially embedded in the sintered body. The leads may contain valve metal. The valve metal contained in the leads and the valve metal contained in the first electrode may be different or the same. In one example of a capacitor (C), the first electrode is a tantalum sintered body and the leads are tantalum leads.

[0063] The method for forming the sintered body (first electrode) is not particularly limited, and known methods may be used. In one example of a method for forming the sintered body, first, raw material particles are pressure-molded into a predetermined shape to obtain a molded body. At this time, a portion of the lead wire is embedded in the molded body. The median diameter (D50, volume basis) of the raw material particles may be 0.05 μm or more and 0.5 μm or less. The median diameter of the raw material particles can be determined using a laser diffraction type particle size distribution analyzer. Next, the molded body is sintered to obtain a sintered body (first electrode) in which a portion of the anode is embedded.

[0064] (Dielectric layer) The dielectric layer only needs to be formed so as to cover at least a portion of the first electrode. The dielectric layer may also be formed by chemical conversion treatment of the first electrode. By chemical conversion treatment of the first electrode, a dielectric layer (a layer of oxide of valve metal) is formed on the surface of the first electrode. For example, an aluminum oxide layer is formed by anodizing aluminum foil. A tantalum oxide layer is formed by anodizing a tantalum sintered body. If a porous portion exists on the surface of the first electrode, the dielectric layer is formed on the surface of the porous portion of the first electrode.

[0065] (Inorganic conductive layer) The inorganic conductive layer has been described above, so a redundant explanation will be omitted.

[0066] (Second Electrode) The second electrode is a conductive layer. The second electrode may be formed using conductive carbon or metal. Specifically, the second electrode may be formed using a carbon paste containing conductive carbon particles or a metal paste containing metal particles. Alternatively, the second electrode may include a layer made solely of metal (a vapor-deposited layer or metal foil). Examples of conductive carbon include graphite, carbon black, graphene flakes, and carbon nanotubes. The metal paste is a paste containing metal particles. Examples of metal pastes include silver paste containing silver particles. The carbon paste and metal paste are not particularly limited, and commercially available pastes may be used.

[0067] The second electrode may include a first layer formed on an inorganic conductive layer 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 metal particle layer (for example, a silver particle layer) formed from a metal paste. The carbon layer can be formed by heating after applying the carbon paste. The metal particle layer can be formed by heating after applying the metal paste.

[0068] (Leads and casing) The capacitor (C) may include other components as needed. For example, the capacitor (C) may include leads and a casing. The leads and casing are not particularly limited, and known leads and casings may be used.

[0069] (Structure of Capacitor (C)) A capacitor (C) may contain only one capacitor element. Alternatively, a capacitor (C) may contain multiple capacitor elements. For example, a capacitor (C) may contain multiple capacitor elements connected in parallel.

[0070] Examples of embodiments relating to this disclosure will be specifically described below with reference to the drawings. The components of the examples described below can be the components described above. Furthermore, the examples described below can be modified based on the above description. In addition, the matters described below may be applied to the embodiments described above. Furthermore, in the embodiments described below, components that are not essential to the capacitor relating to this disclosure may be omitted. Note that the following figures are schematic and may differ from the actual configuration.

[0071] Figure 1 is a schematic cross-sectional view showing a part of the capacitor according to this embodiment. The capacitor 10 shown in Figure 1 includes a first electrode 111, a dielectric layer 112, an inorganic conductive layer 120, and a second electrode 131. Actual capacitors usually include leads and an outer casing, but Figure 1 shows only the capacitor element portion. The inorganic conductive layer 120 may include inorganic particles arranged to form a layer, but the particle is not shown in Figure 1.

[0072] The dielectric layer 112 is formed to cover at least a portion of the surface of the first electrode 111. The inorganic conductive layer 120 is formed to cover at least a portion of the dielectric layer 112. The second electrode 131 is formed to cover at least a portion of the inorganic conductive layer 120. The inorganic conductive layer 120 is the inorganic conductive layer described above. The inorganic conductive layer 120 is in contact with the dielectric layer 112 and the second electrode 131.

[0073] The first electrode 111 in one example shown in Figure 1 has a porous portion on its surface. While the actual porous portion 111a may have a more complex shape, in Figure 1, the porous portion is simplified and depicted as a recess. At least a portion of the inorganic conductive layer 120 is arranged within the voids of the porous portion (along the inner surface of the recess in Figure 1).

[0074] The second electrode 131 includes a carbon layer 131a and a conductive paste layer 131b disposed on the carbon layer 131a. The carbon layer 131a contains carbon particles. The carbon layer 131a is formed on the inorganic conductive layer 120, and some of the carbon particles fill depressions on the surface of the inorganic conductive layer 120, forming an intermediate layer 128. The carbon particles are spherical and have a particle size in the range of 30 to 70 nm.

[0075] Since the capacitor 10 can be formed without using materials with low heat resistance (such as conductive polymers and electrolytes), it is possible to achieve high heat resistance. Furthermore, as described above, it is possible to suppress the rise in ESR in response to the thermal loads encountered during the manufacturing process and during use.

[0076] Figure 2 schematically shows a cross-sectional view of an example of a capacitor (C). The capacitor 10 in Figure 2 includes an anode wire 110, a first electrode (anode) 111, a dielectric layer 112, an inorganic conductive layer 120, and a second electrode (cathode) 131. The second electrode 131 includes a carbon layer 131a and a conductive paste layer (silver particle layer) 131b, which are stacked in order from the inorganic conductive layer 120 side. The capacitor 10 further includes an anode wire 110, an anode lead terminal 141, a cathode lead terminal 142, a conductive layer 143, and an outer resin 144. A portion of the anode wire 110 is embedded in the first electrode 111. The anode lead terminal 141 is connected to the anode wire 110. The second electrode 131 is connected to the cathode lead terminal 142 via the conductive layer 143. The conductive layer 143 may be formed from a metal paste or the like. The first electrode (anode) 111, the dielectric layer 112, the inorganic conductive layer 120, and the second electrode (cathode) 131 constitute a capacitor element. The capacitor element, a portion of the anode lead terminal 141, and a portion of the cathode lead terminal 142 are covered by an outer resin 144.

[0077] (Note) The above description discloses the following technologies: (Technology 1) A capacitor comprising: a first electrode; a dielectric layer formed on the surface of the first electrode; an inorganic conductive layer containing an inorganic compound disposed on the dielectric layer; and a second electrode disposed on the inorganic conductive layer, wherein the second electrode includes a carbon layer containing carbon particles; an intermediate layer containing the inorganic compound and the carbon particles is formed between the inorganic conductive layer and the carbon layer; the thickness of the carbon layer is in the range of 25 to 90 μm; and the carbon particles contained in the intermediate layer are spherical and have a particle size in the range of 30 to 70 nm. (Technology 2) The capacitor according to Technology 1, wherein the inorganic compound is zinc oxide. (Technology 3) The capacitor according to Technology 1 or 2, wherein the main component of the first electrode is aluminum or tantalum.

[0078] The capacitor (C) relating to this disclosure will be described in more detail by reference to the examples.

[0079] (Experiment 1) In Experiment 1, multiple capacitors (capacitor elements) equipped with an inorganic conductive layer were fabricated and evaluated. A ZnO layer was used as the inorganic conductive layer.

[0080] (Capacitor A1) Capacitor A1 was manufactured by the following method: (1) Formation of tantalum sintered body and dielectric layer Tantalum powder (median diameter: 80 nm) was prepared as the raw material powder for the first electrode (anode). Next, the tantalum powder was filled into a predetermined molding die and one end of the anode wire was embedded in the tantalum powder. A tantalum wire was used as the anode wire. After that, a rectangular parallelepiped molded body was obtained by pressure molding the tantalum powder.

[0081] Next, the molded body was sintered under reduced pressure at a temperature in the range of 1300 to 1400°C. In this way, a porous body (tantalum sintered body) in which a portion of the anode wire was embedded was obtained. Next, a tantalum oxide layer (dielectric layer) was formed on the surface of the tantalum sintered body by chemical conversion treatment (anodic oxidation).

[0082] (2) Formation of an inorganic conductive layer (ZnO layer) A ZnO layer (inorganic conductive layer) was formed on the dielectric layer on the surface of the tantalum sintered body by the following procedure. First, a zinc acetate solution was prepared by dissolving zinc acetate dihydrate, aluminum nitrate nonahydrate, and monoethanolamine in 2-methoxyethanol (solvent).

[0083] Aluminum nitrate notahydrate is a compound used to dope aluminum into the ZnO layer. The concentration of zinc acetate dihydrate in the zinc acetate solution was 1.5 mol / L. The concentration of monoethanolamine in the zinc acetate solution was 1.0 mol / L. The molar concentration of aluminum nitrate notahydrate was 0.01 times the molar concentration of zinc acetate dihydrate. The concentration of the surfactant in the zinc acetate solution was 1.0% by mass.

[0084] Next, the tantalum sintered body with the dielectric layer formed on it was immersed in a zinc acetate solution for 3 minutes and then removed. After that, the tantalum sintered body with the zinc acetate solution still attached was heated at 260°C for 10 minutes. This immersion and heating process was repeated 10 times. In this way, an aluminum-doped ZnO layer was formed on the surface of the dielectric layer. After that, the tantalum sintered body with the ZnO layer formed on it was heat-treated at 400°C for 1 hour. In this way, an element a1 with a ZnO layer formed on it was obtained.

[0085] (3) Formation of the second electrode The second electrode (cathode) was formed on the ZnO layer of element a1 according to the following procedure. First, a carbon paste containing carbon particles and a dispersion medium was prepared. Spherical carbon particles were used. Next, a carbon layer was formed on the ZnO layer by applying the carbon paste to the ZnO layer and then heating it. Next, a silver particle layer was formed by applying silver paste to the carbon layer and then heating it. In this way, a second electrode consisting of a carbon layer and a silver particle layer was formed. Capacitor A1 was fabricated in this manner.

[0086] (4) Evaluation of electrical characteristics The fabricated capacitor A1 was placed in an environment of 20°C, and the capacitance and initial ESR at 120 Hz were measured using an LCR meter (Agilent, E4980A). The volumetric capacitance density X0 was calculated from the capacitance.

[0087] Next, capacitor A1 was placed in a 200°C environment for 30 minutes. After that, capacitor A1 was placed back in a 20°C environment, and the ESR after heating was measured in the same manner as the initial ESR. The ratio of the ESR value R1 after heating to the initial ESR value R0, r = R1 / R0, was calculated as the ESR change rate.

[0088] (Capacitors A2-A4, Capacitors B1-B8) In the formation of the second electrode, the thickness of the carbon particles and / or carbon layer was changed as shown in Table 1. Otherwise, the same procedure as for capacitor A1 was followed, and the elements were fabricated using the same method and conditions as for element a1, and the capacitors were fabricated and their electrical characteristics were evaluated in the same manner.

[0089] In capacitors B4 to B8, flaky carbon particles were used instead of spherical carbon particles.

[0090] (Experiment 2) In Experiment 2, multiple capacitors (capacitor elements) equipped with a conductive polymer layer as a solid electrolyte layer were fabricated and evaluated.

[0091] (Capacitors C1 to C11) Instead of forming the inorganic conductive layer (ZnO layer) in Experiment 1 (2), a conductive polymer layer was formed by the following method.

[0092] A polymerization solution was prepared by mixing 3,4-ethylenedioxythiophene, p-iron(III) toluenesulfonate, and 1-butanol. After immersing the anode in the polymerization solution, the anode was removed from the polymerization solution and heat-treated in the atmosphere. In this case, p-iron(III) toluenesulfonate functions as an oxidizing agent. In this way, a conductive polymer layer containing poly(3,4-ethylenedioxythiophene) (PEDOT) was formed on the dielectric layer. The formation of the conductive polymer layer described above was repeated multiple times to form a solid electrolyte layer consisting of a conductive polymer layer of a predetermined thickness.

[0093] Aside from the above, the procedure was the same as in Experiment 1, and the elements and capacitors were fabricated and their electrical characteristics were evaluated.

[0094] In capacitors C1 to C11, the thickness of the carbon particles and / or carbon layer was changed in the formation of the second electrode as shown in Table 2. In capacitors C1 to C6, spherical carbon particles were used. In capacitors C7 to C11, flaky carbon particles were used instead of spherical carbon particles.

[0095] Tables 1 and 2 show the types (shape and particle size) of carbon particles, the thickness of the carbon layer, and the evaluation results. In Tables 1 and 2, the volumetric capacity density X0 and the ESR change rate R1 / R0 are shown as relative values ​​with the evaluation result of capacitor B2 set to 1. The particle size of the carbon particles is the average particle size determined by the method described above based on electron microscope images.

[0096]

[0097]

[0098] As shown in Table 1, when spherical carbon particles with a particle size in the range of 30 to 70 nm are used, and the thickness of the carbon layer is 25 μm or more (26 μm or more), the rate of change in ESR can be kept low. On the other hand, as the thickness of the carbon layer increases, the volumetric capacitance density decreases. In order to suppress the decrease in volumetric capacitance density, a carbon layer thickness of 90 μm or less (89 μm or less) is preferable. Capacitors A1 to A4, which use spherical carbon particles with a particle size in the range of 30 to 70 nm and a carbon layer thickness in the range of 25 to 90 μm, were able to achieve both high volumetric capacitance density and a low rate of change in ESR.

[0099] In capacitors B4 to B8, which use flaky carbon particles, there is a general tendency for the rate of change in ESR to decrease with increasing thickness of the carbon layer, but there is considerable variability.

[0100] Table 2 shows that, in the case of capacitors using conductive polymers as the solid electrolyte layer, the rate of change in ESR tends to decrease with increasing thickness of the carbon layer, similar to Table 1. However, when using conductive polymers, the decrease in the rate of change in ESR with increasing thickness of the carbon layer is slower compared to when using an inorganic conductive layer. The improvement in the rate of change in ESR by using spherical carbon particles with a particle size in the range of 30 to 70 nm and a carbon layer thickness of 25 μm or more is particularly pronounced when an inorganic conductive layer (ZnO) is used as the electrolyte.

[0101] This disclosure can be used in capacitors.

[0102] While this disclosure describes preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0103] 10: Capacitor 111: First electrode 112: Dielectric layer 120: Inorganic conductive layer 128: Intermediate layer 131: Second electrode 131a: Carbon layer 131b: Conductive paste layer

Claims

1. A capacitor comprising: a first electrode; a dielectric layer formed on the surface of the first electrode; an inorganic conductive layer containing an inorganic compound disposed on the dielectric layer; and a second electrode disposed on the inorganic conductive layer, wherein the second electrode includes a carbon layer containing carbon particles; an intermediate layer containing the inorganic compound and the carbon particles is formed between the inorganic conductive layer and the carbon layer; the thickness of the carbon layer is in the range of 25 to 90 μm; and the carbon particles contained in the intermediate layer are spherical and have a particle size in the range of 30 to 70 nm.

2. The capacitor according to claim 1, wherein the inorganic compound is zinc oxide.

3. The capacitor according to claim 1 or 2, wherein the main component of the first electrode is aluminum or tantalum.

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