Capacitor

Abstract

To provide a capacitor with high heat resistance and capacitance. [Solution] The disclosed capacitor 10 includes a first electrode 111, a dielectric layer 112 formed on the surface of the first electrode 111, an inorganic conductive layer 120 disposed on the dielectric layer 112, and a second electrode 131 disposed on the inorganic conductive layer 120. The main component of the inorganic conductive layer 120 is an inorganic oxide containing fluorine.

Description

Technical Field

[0001] The present disclosure relates to a capacitor.

Background Art

[0002] Conventionally, various capacitors have been proposed. In claim 1 of Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2017-103412), there is described "a solid electrolytic capacitor including 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 formed using zinc oxide having a conductivity of 1 (S / cm) or more."

[0003] In claim 1 of Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2020-35890), there is described "a solid electrolytic capacitor including an anode body made of 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 formed using a p-type inorganic semiconductor."

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] By using an inorganic layer instead of a solid electrolyte layer formed using a conductive polymer, it is possible to improve the heat resistance of a capacitor. However, the capacitance of a capacitor using an inorganic layer is not sufficient, and further increase in capacitance is required. One object of the present disclosure is to provide a capacitor having high heat resistance and capacitance.

Means for Solving the Problems

[0006] One aspect of this disclosure relates to a capacitor comprising a first electrode, a dielectric layer formed on the surface of the first electrode, an inorganic conductive layer disposed on the dielectric layer, and a second electrode disposed on the inorganic conductive layer, wherein the main component of the inorganic conductive layer is an inorganic oxide containing fluorine. [Effects of the Invention]

[0007] According to this disclosure, a capacitor with high heat resistance can be obtained. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of the structure of a capacitor according to this embodiment. [Figure 2A] Figure 2A shows the results of an analysis of some of the elements fabricated in the example. [Figure 2B] Figure 2B shows a magnified view of a portion of Figure 2A. [Figure 3] Figure 3 is a schematic cross-sectional view showing an example of a capacitor according to this embodiment. [Modes for carrying out the invention]

[0009] 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.

[0010] (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 disposed on the dielectric layer, and a second electrode disposed on the inorganic conductive layer. The main component of the inorganic conductive layer is an inorganic oxide containing fluorine.

[0011] Capacitors with an inorganic conductive layer placed on a dielectric layer have high heat resistance. However, such capacitors lacked sufficient capacitance. Through investigation, the inventors of this invention discovered that it is possible to increase capacitance by adding fluorine to the inorganic conductive layer. This disclosure is based on this new finding.

[0012] 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).

[0013] 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".

[0014] 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.

[0015] When the inorganic conductive layer is mainly composed of zinc oxide, the ratio of fluorine atoms to zinc atoms (atomic ratio) F / Zn in the inorganic conductive layer, as analyzed by SEM-EDX (scanning electron microscope energy-dispersive X-ray spectroscopy), may be 0.0010 or higher, 0.0030 or higher, 0.0055 or higher, or 0.0056 or higher (or 0.00558 or higher), and may also be 0.010 or lower, 0.0080 or lower, or 0.0059 or lower (or 0.00585 or lower). The ratio F / Zn may be in the range of 0.0055 to 0.0059, or in the range of 0.0056 to 0.0059 (or in the range of 0.00558 to 0.00585). A high effect can be obtained by having the ratio F / Zn within this range. SEM-EDX analysis can be performed using the method described in the examples.

[0016] When the inorganic conductive layer is mainly composed of zinc oxide, the zinc oxide may or may not contain dopants. Adding dopants to zinc oxide can improve its conductivity.

[0017] Zinc oxide may contain a dopant. Adding a dopant to zinc oxide can increase 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.

[0018] It is preferable that the inorganic oxide, which is the main component of the inorganic conductive layer, be zinc oxide in that inexpensive and high conductivity can be obtained. On the other hand, the inorganic oxide, which is the main component of the inorganic conductive layer, may be other than zinc oxide. Examples of inorganic oxides other than zinc oxide include manganese dioxide, tin oxide, titanium oxide and the like.

[0019] The dopant may contain aluminum. In that case, the ratio (atomic ratio) Zn / Al of the number of zinc atoms to the number of aluminum atoms in the inorganic conductive layer analyzed by SEM-EDX may be 0.0010 or more, 0.0030 or more, 0.0033 or more, or 0.0050 or more, and may be 0.010 or less, 0.0070 or less, 0.0040 or less, or 0.0038 or less.

[0020] The first electrode may be an anode and the second electrode may be a cathode. Examples of the configuration of the cathode will be described later.

[0021] A valve metal may be used for 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 an aluminum foil. Another example of the first electrode is a tantalum sintered body obtained by sintering tantalum particles.

[0022] The first electrode may have a porous portion on its surface layer. In that case, the dielectric layer is formed on the surface of the porous portion, and at least a part of the inorganic conductive layer is disposed in the voids of the porous portion. By using the first electrode having a porous portion, the capacitance can be increased.

[0023] The inorganic conductive layer may be a layer formed by heating a material containing zinc. By using such an inorganic conductive layer, it is considered that the internal stress of the inorganic conductive layer can be particularly reduced. The material containing zinc may be a material containing a zinc compound (for example, a salt of zinc). Zinc oxide can be generated by heating and thermally decomposing the zinc compound. Examples of the method for forming the inorganic conductive layer will be described later.

[0024] (Capacitor manufacturing method) The manufacturing method according to this embodiment may be referred to as "manufacturing method (M)" below. Manufacturing method (M) is a method for manufacturing a capacitor. According to manufacturing method (M), a capacitor (C) can be manufactured. However, the capacitor (C) may be manufactured by methods other than manufacturing method (M). Matters described for capacitor (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 capacitor (C).

[0025] In the following example, we will explain the case where the main component of the inorganic conductive layer is zinc oxide. If the main component of the inorganic conductive layer is an inorganic oxide other than zinc oxide, you should select a material according to the type of inorganic oxide.

[0026] The manufacturing method (M) includes a first step of forming an inorganic conductive layer on a dielectric layer formed on the 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 on the dielectric layer, and a step (b) of forming the inorganic conductive layer by heating the solution.

[0027] (Step (a)) In step (a), a solution containing a zinc compound and a fluorine-containing compound is placed on a dielectric layer. The solvent of the solution is selected according to the type of zinc compound. The solvent may be water, an organic solvent, or a mixture thereof. The solvent can be a liquid in which the zinc compound and the fluorine-containing compound are dissolved and which evaporates during heating in step (b). That is, the solvent may be a liquid with a boiling point lower than the heating temperature in step (b). An example of a solvent is 2-methoxyethanol.

[0028] The zinc compound used is one in which zinc oxide is formed by heating in step (b). The zinc compound may also be a salt. Additives may be added to the solution as needed. For example, additives to increase the solubility of the zinc compound may be added to the solution.

[0029] The fluorine-containing compound may also be an organic compound containing fluorine. The organic compound containing fluorine may also be a surfactant containing fluorine. By using a surfactant containing fluorine, fluorine can be added to the formed zinc oxide. Furthermore, by using a surfactant containing fluorine, the solution can spread more easily across the surface of the dielectric layer, which has a complex shape. As a result, the contact area between the dielectric layer and the inorganic conductive layer (zinc oxide layer) can be increased, making it possible to increase the capacitance.

[0030] The fluorine-containing compound may also be a surfactant having a perfluoroalkyl group. The type of surfactant is not limited and may be anionic, nonionic, or amphoteric surfactant. Examples of surfactants having a perfluoroalkyl group include Surflon S211, Surflon S221, Surflon S233, and Surflon S243 (all manufactured by AGC Seika Chemical Co., Ltd.).

[0031] 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 also be 3.0% by mass or less, 2.0% by mass or less, or 1.5% by mass or less. By changing the concentration of the surfactant in the solution, the amount of fluorine in the inorganic conductive layer can be controlled.

[0032] (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), it is possible to produce zinc oxide by thermal decomposition of a zinc compound. For example, if the zinc compound is zinc acetate, the zinc acetate is thermally decomposed by heating to produce zinc oxide. At this time, fluorine from a fluorine-containing compound is added to the zinc oxide.

[0033] The heating conditions are selected according to the solution. The heating method is not particularly limited, and known heating methods (e.g., heating by a heater) may be used. The atmosphere in which the heating step (b) is carried out is not particularly limited, and it may be carried out in the air or in an atmosphere other than the air (e.g., in an inert gas or water vapor). Furthermore, step (b) may be carried out under reduced pressure.

[0034] In manufacturing method (M), steps (a) and (b) may be repeated. The number of cycles consisting of one step (a) and one step (b) may be 2 or more, or 5 or more, or 40 or less, or 15 or less. By repeating the cycle, it is possible to increase the thickness of the inorganic conductive layer.

[0035] 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, and mercaptopurine.

[0036] 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.

[0037] 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.

[0038] 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).

[0039] 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.

[0040] 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).

[0041] 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.

[0042] 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 portion of the first electrode, and a portion of the second electrode are sealed with a sealing resin (outer casing). These steps can be carried out by known methods.

[0043] Examples of components of a capacitor (C) are described below. The components of a capacitor (C) are not limited to the examples below. Components other than those characteristic of this disclosure may be those used in known capacitors.

[0044] (1st 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] (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.

[0049] (Inorganic conductive layer) Since the inorganic conductive layer has already been described above, I will omit any further explanation.

[0050] (2nd 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.

[0051] 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 (e.g., 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.

[0052] (Lead and outer casing) The capacitor (C) may include other components as needed. For example, the capacitor (C) may include leads and an enclosure. The leads and enclosure are not particularly limited, and known leads and enclosures may be used.

[0053] (The structure of a capacitor (C)) A capacitor (C) may contain only one capacitor element, or it may contain multiple capacitor elements. For example, a capacitor (C) may contain multiple capacitor elements connected in parallel.

[0054] 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.

[0055] (Embodiment 1) Figure 1 is a schematic cross-sectional view showing a part of a capacitor according to Embodiment 1. 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 illustration is omitted in Figure 1.

[0056] 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.

[0057] The first electrode 111 in one example shown in Figure 1 has a porous portion 111a on its surface. While the actual porous portion 111a may have a more complex shape, it is simplified in Figure 1. At least a portion of the inorganic conductive layer 120 is located within the voids of the porous portion 111a. Since the capacitor 10 can be formed without using materials with low heat resistance (such as conductive polymers or electrolytes), high heat resistance can be achieved.

[0058] Figure 3 schematically shows a cross-sectional view of another example of a capacitor (C). The capacitor 10 in Figure 3 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 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.

[0059] (Note) The following technologies are disclosed based on the above description. (Technology 1) It is a capacitor, First electrode and, A dielectric layer formed on the surface of the first electrode, An inorganic conductive layer disposed on the dielectric layer, The inorganic conductive layer includes a second electrode disposed on the inorganic conductive layer, A capacitor in which the main component of the inorganic conductive layer is an inorganic oxide containing fluorine. (Technology 2) The capacitor according to Technology 1, wherein the inorganic oxide is zinc oxide. (Technology 3) The capacitor described in Technology 2, wherein the ratio F / Zn of the number of fluorine atoms to the number of zinc atoms in the inorganic conductive layer, as analyzed by SEM-EDX, is in the range of 0.0056 to 0.0059. (Technology 4) The capacitor according to Art 2 or 3, comprising the zinc oxide dopant. (Technology 5) The capacitor according to Technology 4, wherein the dopant contains aluminum. (Technology 6) A capacitor according to any one of the techniques 1 to 5, wherein the main component of the first electrode is aluminum or tantalum. [Examples]

[0060] The capacitor (C) relating to this disclosure will be described in more detail by reference to the examples.

[0061] (Experiment 1) In Experiment 1, multiple capacitors (capacitor elements) with different inorganic conductive layers were fabricated and evaluated. A ZnO layer was used as the inorganic conductive layer.

[0062] (Capacitor A1) Capacitor A1 was fabricated using the following method. (1) Formation of tantalum sintered body and dielectric layer Tantalum powder (median diameter: 80 μm) 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. Subsequently, a rectangular parallelepiped molded body was obtained by pressure molding the tantalum powder.

[0063] 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).

[0064] (2) Formation of an inorganic conductive layer (ZnO layer) A ZnO layer (inorganic conductive layer) was formed on the dielectric layer of the surface of a tantalum sintered body using the following procedure. First, a zinc acetate solution was prepared by dissolving zinc acetate dihydrate, aluminum nitrate notahydrate, monoethanolamine, and a fluorine-containing surfactant in 2-methoxyethanol (solvent). Surflon S-243, manufactured by AGC Seikamika Co., Ltd., was used as the fluorine-containing surfactant.

[0065] 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 set to 1.0 mol / L. The concentration of monoethanolamine in the zinc acetate solution was set to 1.0 mol / L. The molar concentration of aluminum nitrate notahydrate was set to 0.01 times the molar concentration of zinc acetate dihydrate. The concentration of surfactant in the zinc acetate solution was set to 1.0% by mass.

[0066] 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.

[0067] (3) Formation of the second electrode A second electrode (cathode) was formed on the ZnO layer of element a1 using the following procedure. First, a carbon paste containing carbon particles and a dispersion medium was prepared. 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.

[0068] (Evaluation of electrical properties) The capacitance X1 and dielectric loss tangent Tanδ of the fabricated capacitor A1 were measured. Furthermore, the element a1 was immersed in the electrolyte before the formation of the second electrode, and the capacitance X0 of element a1 was measured in that state. The capacitance and dielectric loss tangent measurements were performed using the following equipment and conditions. Measuring device: LCR meter (Agilent, E4980A) AC conditions: 500mV, 120Hz (DC bias: 0)

[0069] Since the electrolyte reaches deep into the porous part, the capacitance X0 is considered to be close to the theoretical capacitance of element a1. The capacitance acquisition rate was calculated from the following formula. Capacity acquisition rate (%)=100×X1 / X0

[0070] (Analysis of inorganic conductive layers) Element a1 was cleaved to expose its cross-section. The exposed cross-section was analyzed using SEM-EDX. The analysis equipment used was a Zeiss FE-SEM (GeminiSEM560) and an Oxford Instruments EDX (windowless EDS detector: Ultim Extreme, 100mm) 2 ) was used.

[0071] SEM-EDX analysis was performed in regions where both Ta (and Ta2O5) and zinc oxide were present within the field of view. SEM-EDX analysis was conducted on regions larger than 2.2 μm × 1.6 μm. First, the elemental distribution in these regions was evaluated. The analysis was performed under the conditions of acceleration voltage = 3 kV, ap = 30 μm, and WD = 5 mm. Fluorine was more abundant in the zinc oxide region than in the Ta region. As a result, it was found that most of the fluorine was incorporated into the zinc oxide.

[0072] Next, the elemental abundance ratios in the zinc oxide layer (inorganic conductive layer) were analyzed using SEM-EDX. Based on the results, the ratio F / Zn (ratio of fluorine atoms to zinc atoms) and the ratio Al / Zn (ratio of aluminum atoms to zinc atoms) were calculated. The analysis was performed with an acceleration voltage of 4kV, ap = 30μm, and WD = 5mm. Specifically, a region containing zinc oxide was selected, and mapping analysis was performed on that region using SEM-EDX. An example of the spectrum obtained from the mapping analysis is shown in Figures 2A and 2B. The spectrum shown in Figure 2B is the spectrum of Figure 2A with the vertical axis changed (magnified). As shown in Figures 2A and 2B, the presence of Al, Zn, F, O, and C was confirmed. The vertical axis in Figures 2A and 2B represents intensity.

[0073] (Capacitors A2~A3) Element a2 and element a3 were fabricated using the same method and conditions as element a1, except that the zinc acetate solution used to form the ZnO layer was changed. Specifically, the concentration of the surfactant in the zinc acetate solution was changed as shown in Table 1. Capacitors A2 and A3 were fabricated using the same method and conditions as capacitor A1, except that elements a2 and a3 were used instead of element a1.

[0074] (Capacitor C1) Element c1 was fabricated using the same method and conditions as for element a1, except that the zinc acetate solution used to form the ZnO layer was changed. No surfactant was added to the zinc acetate solution used to fabricate capacitor C1. Capacitor C1 was fabricated using the same method and conditions as for capacitor A1, except that element c1 was used instead of element a1.

[0075] (Capacitor C2) Element c2 was fabricated using the same method and conditions as for element a1, except that the zinc acetate solution used to form the ZnO layer was changed. Polyether-modified silicone (Shin-Etsu Chemical Co., Ltd., KF-6048) was added as a surfactant to the zinc acetate solution used to fabricate element c2. This polyether-modified silicone does not contain fluorine. The concentration of zinc acetate dihydrate in the zinc acetate solution was 1.6 mol / L. The concentration of monoethanolamine in the zinc acetate solution was 1.6 mol / L. The molar concentration of aluminum nitrate nonahydrate 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. Capacitor C2 was fabricated using the same method and conditions as for capacitor A1, except that element c2 was used instead of element a1.

[0076] The fabricated elements a2, a3, c1, and c2 were evaluated in the same way as element a1. Furthermore, the fabricated capacitors A2, A3, C1, and C2 were evaluated in the same way as capacitor A1. However, capacitor C2 was not analyzed using SEM-EDX.

[0077] Some of the manufacturing conditions and evaluation results are shown in Tables 1 and 2. In Table 1, "Amount of Al added during manufacturing" indicates the molar ratio of aluminum to zinc in the zinc acetate solution. In Table 2, Tanδ indicates the measured dielectric loss tangent. A smaller Tanδ value indicates less loss. Therefore, a small Tanδ is preferable. A high capacitance acquisition rate indicates that the capacitance is close to the theoretical capacitance. Therefore, a high capacitance acquisition rate is preferable.

[0078] [Table 1]

[0079] [Table 2]

[0080] The ratio F / Zn of capacitor C2 is presumed to be zero. The ratio Al / Zn of capacitor C2 is thought to be similar to that of the other capacitors.

[0081] Capacitors A1 to A3 are capacitors (C) according to this disclosure. Capacitors C1 and C2 are comparative examples. As shown in Table 1, the capacitance and capacitance acquisition ratio of capacitors A1 to A3 were significantly larger than those of capacitors C1 and C2. The Tanδ of capacitors A1 to A3 was smaller than the Tanδ of capacitors C1 and C2. [Industrial applicability]

[0082] This disclosure can be used in capacitors. [Explanation of Symbols]

[0083] 10: Capacitor 111: 1st electrode 112: Dielectric layer 120: Inorganic conductive layer 131:Second electrode

Claims

1. It is a capacitor, First electrode and, A dielectric layer formed on the surface of the first electrode, An inorganic conductive layer disposed on the dielectric layer, The inorganic conductive layer includes a second electrode disposed on the inorganic conductive layer, A capacitor in which the main component of the inorganic conductive layer is an inorganic oxide containing fluorine.

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

3. The capacitor according to claim 2, wherein the ratio F / Zn, the number of fluorine atoms to the number of zinc atoms in the inorganic conductive layer, as analyzed by SEM-EDX, is in the range of 0.0056 to 0.0059.

4. The capacitor according to claim 2, wherein the zinc oxide comprises a dopant.

5. The capacitor according to claim 4, wherein the dopant comprises aluminum.

6. The capacitor according to any one of claims 1 to 5, wherein the main component of the first electrode is aluminum or tantalum.

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