Capacitor

Abstract

To provide a capacitor capable of suppressing peeling between an inorganic layer (conductive layer) and an electrode.SOLUTION: A disclosed capacitor includes: a first electrode 111; a dielectric layer 112 formed over the surface of the first electrode 111; a conductive layer 120 placed on the dielectric layer 112; and a second electrode 131 placed on the conductive layer 120. The conductive layer 120 has a needle-like structure of an inorganic material on the surface layer 120a of the second electrode 131 side.SELECTED DRAWING: Figure 2

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 Patent Application Laid-Open No. 2018-182106), “a laminated chip having a substantially rectangular parallelepiped shape, in which a dielectric layer mainly composed of ceramic and an internal electrode layer are alternately laminated, and a plurality of the laminated internal electrode layers are formed so as to be exposed on two end faces facing each other alternately, and external electrodes formed on the two end faces, wherein the external electrode has a structure in which a plating layer is formed on a base layer, and at least a part of the surface of the base layer includes a region in which the average interval between local peaks is 0.5 μm or less in a region where the height from the bottom to the peak is 0.4 μm or more” is described.

[0003] In claim 1 of Patent Document 2 (Japanese Patent Application Laid-Open No. 2020-35890), “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 composed of a p-type inorganic semiconductor” is described.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described in Patent Document 2, a capacitor in which an inorganic layer is placed between two electrodes is known. However, if the contact between the inorganic layer and the electrodes is insufficient, delamination occurs between the inorganic layer and the electrode layer, resulting in problems such as an increase in equivalent series resistance (ESR). In this situation, one of the objectives of this disclosure is to provide a capacitor in which delamination is less likely to occur between the inorganic layer (conductive layer) and the electrodes. [Means for solving the problem]

[0006] One aspect of this disclosure relates to a capacitor. The capacitor includes a first electrode, a dielectric layer formed on the surface of the first electrode, a conductive layer disposed on the dielectric layer, and a second electrode disposed on the conductive layer, wherein the conductive layer has a needle-like structure made of an inorganic material on the surface layer on the second electrode side. [Effects of the Invention]

[0007] According to this disclosure, a capacitor can be obtained in which delamination is less likely to occur between the inorganic layer (conductive layer) and the electrode. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic cross-sectional view showing the structure of an example capacitor according to this embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view showing a portion of the capacitor shown in Figure 1. [Figure 3] Figure 3 is a schematic cross-sectional view showing the structure of another example of a capacitor according to this embodiment. [Figure 4A] Figure 4A is a cross-sectional image of the surface layer of the zinc oxide layer of an example capacitor fabricated in Experiment 1. [Figure 4B] Figure 4B is a cross-sectional image of the surface layer of the zinc oxide layer of another example capacitor fabricated in Experiment 1. [Figure 4C] Figure 4C is a cross-sectional image of the surface layer of the zinc oxide layer of another example capacitor fabricated in Experiment 1. [Figure 4D]Figure 4D is a cross-sectional image of the surface layer of the zinc oxide layer of another example capacitor fabricated in Experiment 1. [Figure 5] Figure 5 is a cross-sectional image showing an example of the measurement results for the aspect ratio of the needle-shaped portion. [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 of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit is not greater than or equal to the upper limit.

[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, a conductive layer disposed on the dielectric layer, and a second electrode disposed on the conductive layer. The conductive layer has a needle-like structure made of an inorganic material on the surface layer on the second electrode side.

[0011] As a result of their investigation, the inventors of this application have discovered a novel method for forming a conductive layer having a needle-like structure made of inorganic material on its surface. By using a conductive layer having a needle-like structure on its surface, it is possible to suppress delamination between the needle-like surface layer (inorganic layer) and the second electrode. Therefore, it is possible to suppress the increase in ESR due to delamination.

[0012] The conductive layer can be formed of an inorganic material. Therefore, the conductive layer can be read as an inorganic layer. A preferred example of the conductive layer of the capacitor (C) does not contain an organic material (for example, a conductive polymer). By forming the conductive layer of an inorganic material, a capacitor (C) with high heat resistance can be obtained.

[0013] A part of the needle-like structure may be embedded in the second electrode. According to this configuration, the inorganic layer and the second electrode can be firmly fixed by the anchor effect.

[0014] The average value As of the aspect ratio in the cross-sectional image of the needle-like part at the end of the needle-like structure may be in the range of 4.6 to 17.2 (for example, in the range of 5 to 16). The cross-sectional image is an image of a cross-section parallel to the thickness direction Dt of the conductive layer. The average value As of the aspect ratio is obtained by the method described in the examples.

[0015] At least a part of the needle-like part at the end of the needle-like structure may be curved. According to this configuration, the anchor effect by the needle-like structure becomes particularly high. At least a part of the needle-like part may be a needle-like crystal. That is, the needle-like structure may include needle-like crystals.

[0016] The conductive layer may be made of an inorganic material containing a metal oxide. In that case, the needle-like structure may be made of the metal oxide. By using a conductive layer made of an inorganic material, a capacitor with high heat resistance can be obtained.

[0017] The metal oxide may be a conductive metal oxide having as a main component at least one selected from the group consisting of ZnO, TiO2, indium tin oxide, In2O3, SnO2, Ga2O3, MnO2, NiO2, CuInO2, CuCrO2, CuAlO2, and CuScO2, or may be a conductive metal oxide consisting of at least one of them. The metal oxide may be a conductive metal oxide having as a main component any one selected from the above group, or may be a conductive metal oxide consisting of the one. For example, the metal oxide may be a conductive metal oxide having ZnO as a main component, or may be ZnO. Although ZnO may be classified as a semiconductor, since it has conductivity, it is treated as a conductive metal oxide in this specification. Regarding the metal oxide, the main component means that the content is 50% by mass or more. The content of the main component in the metal oxide may be in the range of 80 to 100% by mass, 90 to 100% by mass, or 95 to 100% by mass.

[0018] The above conductive metal oxide may contain oxygen vacancies. By containing oxygen vacancies, it is possible to increase the conductivity of the conductive metal oxide. When the conductive metal oxide has zinc oxide (ZnO) as a main component, ZnO 1-x (0≦x≦0.25) may be used as a main component. Here, x may be greater than 0.

[0019] The above conductive metal oxide may contain an additive element for improving conductivity. When the conductive metal oxide has ZnO as a main component, at least one element selected from the group consisting of Al, Ga, B, and In may be added to ZnO so that its content is 10 atomic% or less.

[0020] When the conductive metal oxide is mainly composed of Ga2O3, at least one element selected from the group consisting of Ta and Hf may be added to the Ga2O3 so that its content is 0.1 atomic% or less. When the conductive metal oxide is mainly composed of TiO2, at least one element selected from the group consisting of Nb and Ta may be added to the TiO2 so that its content is 10 atomic% or less. When the conductive metal oxide is mainly composed of SnO2, Sb may be added to the SnO2 so that its content is 12.5 atomic% or less. When the conductive metal oxide is mainly composed of CuCrO2, Mg may be added to the CuCrO2 so that its content is 5 atomic% or less. When the conductive metal oxide is mainly composed of CuInO2, Ca may be added to the CuInO2 so that its content is 3 atomic% or less.

[0021] In capacitor (C), the first electrode may be the anode, and the second electrode may be the cathode. In capacitor (C), the first electrode may be aluminum foil or a tantalum sintered body.

[0022] In a capacitor (C), 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 a portion of the conductive layer is arranged within the voids of the porous portion. The first electrode having a porous portion on its surface may be etched aluminum foil or a sintered body of valve metal (for example, a tantalum sintered body).

[0023] The conductive layer may include a first conductive layer in contact with the dielectric layer and a second conductive layer in contact with the second electrode. The conductive layer may be composed of the first conductive layer and the second conductive layer. The second conductive layer has the needle-like structure described above on its surface. The first conductive layer and the second conductive layer may have different compositions or the same composition. The first conductive layer and the second conductive layer may be composed of the conductive metal oxide described above. If a porous portion exists on the surface of the first electrode, at least a part of the first conductive layer may be formed in the recesses of the porous portion.

[0024] The conductivity of the conductive layer may be 1 S / cm or more, or 10 S / cm or more. The conductivity of the conductive layer may be 10,000 S / cm or less, or 1,000 S / cm or less. The conductive layer may be an inorganic layer with a conductivity of 1 S / cm or more.

[0025] The thickness of the conductive layer is not particularly limited. The thickness of the conductive layer may be in the range of 0.1 μm to 100 μm (for example, in the range of 1 μm to 10 μm).

[0026] (Capacitor manufacturing method) The manufacturing method according to this embodiment 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 be manufactured by methods other than manufacturing method (M). Since the matters described for the capacitor (C) are applicable to manufacturing method (M), redundant explanations are omitted. The matters described for manufacturing method (M) may also be applied to the capacitor (C).

[0027] Manufacturing method (M) is a method for manufacturing a capacitor that includes a first electrode and a dielectric layer formed on the surface of the first electrode. Manufacturing method (M) includes steps (i) and (ii) in that order. These steps are described below.

[0028] Step (i) is a step of forming a conductive layer on a dielectric layer formed on the surface of the first electrode. The conductive layer is the conductive layer described for capacitor (C). In step (i), the conductive layer is formed such that the surface layer of the conductive layer has a needle-like structure made of inorganic material. At least the surface layer of the conductive layer can be formed by liquid phase growth. According to liquid phase growth, a conductive layer (a conductive crystalline layer) can be formed by crystal growth. At this time, by selecting the conditions of the liquid phase growth method, a surface layer having a needle-like structure can be formed.

[0029] When the surface layer is made of zinc oxide, a zinc oxide layer with a needle-like structure can be formed under the following conditions. First, a solution for liquid-phase growth (solution growth) is prepared. Examples of solutions include aqueous solutions in which zinc nitrate and other additives are dissolved. Examples of additives include hexamethylenetetramine, ammonia, citric acid, ammonium nitrate, aluminum nitrate, gallium nitrate, indium nitrate, etc. When adding the above-mentioned additive elements to ZnO, it is sufficient to dissolve a compound containing the additive elements. The pH of the solution is, for example, in the range of 6 to 11. The concentration of zinc nitrate in the solution is, for example, in the range of 0.01 mol / L to 2 mol / L. Furthermore, when forming a surface layer with a needle-like structure, the temperature of the first electrode is, for example, in the range of 65°C to 75°C. The temperature of the solution is, for example, 75°C or lower. The temperature of the solution may also be in the range of 0 to 75°C (for example, in the range of 10 to 50°C or 10 to 40°C).

[0030] When the temperature of the first electrode is high (for example, 85°C or higher), a columnar structure is formed instead of a needle-like structure. Conventionally, when forming a zinc oxide layer, conditions that form a dense columnar structure have been selected. On the other hand, the inventors of this application have found that a needle-like structure can be formed at a relatively low temperature. At least the surface layer of the conductive layer described above is formed under conditions that form a needle-like structure. The average value As of the aspect ratio of the needle-like portion at the end of the needle-like structure can be changed by changing the temperature of the first electrode, the pH of the solution, the concentration of the solution, etc.

[0031] Before forming the zinc oxide layer, a base layer made of zinc oxide may be formed beforehand. For example, the base layer made of zinc oxide may be formed by a vapor phase method. Examples of vapor phase methods include atomic layer deposition (ALD), sputtering, and chemical vapor deposition (CVD). Using a base layer makes it easier to form the zinc oxide layer by liquid phase growth. The ALD method is preferred because it makes it easy to form layers in the depressions of porous parts.

[0032] The conductive layer made of the conductive metal oxide described above can also be formed by liquid-phase growth, similar to the zinc oxide layer. In that case, a solution should be selected according to the conductive metal oxide to be formed.

[0033] The method for forming conductive layers other than the surface layer having a needle-like structure is not limited. Conductive layers other than the surface layer may be formed by a vapor phase method or a liquid phase method. Examples of vapor phase methods include the vapor phase method described above. The entire conductive layer may be formed by a liquid phase growth method, or the entire conductive layer may be formed under the same conditions as those for forming the surface layer described above. When forming the entire conductive layer by a liquid phase growth method, as described above, a base layer may be formed on the dielectric layer beforehand. Alternatively, a first conductive layer of a certain thickness may be formed on the dielectric layer by an ALD method, and then a second conductive layer may be formed by a liquid phase growth method. In either case, the surface layer of the conductive layer is formed under conditions that result in a needle-like structure. Even when forming the entire conductive layer under conditions that result in a needle-like structure, the conductive layer close to the dielectric layer may grow and not have a needle-like structure.

[0034] If the conductive layer includes a first conductive layer and a second conductive layer, the first conductive layer and the second conductive layer may be formed by the same formation method or by different formation methods. For example, the first conductive layer and the second conductive layer, which have different compositions, may be formed by the same formation method. Alternatively, the first conductive layer and the second conductive layer, which have the same composition, may be formed by different formation methods.

[0035] Step (ii) is the step of forming a second electrode on the conductive layer. At this time, the second electrode is formed on the needle-like structure on the surface layer of the conductive layer. As a result, the conductive layer and the second electrode are firmly fixed together.

[0036] The second electrode is formed using a conductive material. The material of the second electrode is not particularly limited and can be any material that can be used as an electrode for a capacitor. The method of forming the second electrode is not particularly limited, but it is preferable to use a method that firmly connects the conductive layer and the second electrode. For example, the second electrode may be formed by applying a conductive paste containing conductive particles. Alternatively, the second electrode may be formed by a vapor phase method or a plating method.

[0037] The second electrode may include a carbon layer and a silver particle layer stacked in order from the conductive layer side. In this case, first, a carbon paste containing conductive carbon particles is applied. Next, a silver paste containing silver particles is applied. Then, the carbon layer and silver particle layer are formed by heat treatment. In this way, the second electrode is formed. If necessary, heat treatment may be performed not only after the application of the silver paste but also before the application of the silver paste. The carbon paste and silver paste are not limited, and known carbon paste and silver paste may be used.

[0038] Through the above steps, a capacitor element including a first electrode, a dielectric layer, a conductive layer, and a second electrode is formed. After step (ii), lead connections and housing of the capacitor element with an outer casing are performed as needed. In this way, a capacitor (C) is obtained.

[0039] Examples of the configuration and components of a capacitor (C) are described below. Known components may be used for components other than those characteristic of this disclosure.

[0040] (1st electrode) The first electrode can be formed using valve metal, alloys containing valve metal, and compounds containing valve metal. These materials may be used individually or in combination of two or more. As valve metal, aluminum, tantalum, niobium, and titanium are preferably used. The first electrode may also be made of foil made of the above material (for example, metal foil such as aluminum foil).

[0041] A first electrode having a porous portion on its surface can be obtained, for example, by roughening the surface of a metal foil containing valve metal. Surface roughening may be performed by electrolytic etching or the like.

[0042] The first electrode may be formed by sintering particles of the above material. For example, the first electrode may be a sintered body of tantalum. When the first electrode is a sintered body, a porous portion exists on its surface. When the first electrode is a sintered body, the capacitor (C) may include an anode wire, part of which is embedded in the sintered body.

[0043] (Dielectric layer) The dielectric layer is an insulating layer that functions as a dielectric. The dielectric layer may be formed by anodizing the valve metal on the surface of the first electrode (e.g., a metal foil). The dielectric layer only needs to be formed to cover at least a portion of the first electrode. The dielectric layer is usually formed on the surface of the first electrode. 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.

[0044] A typical dielectric layer contains an oxide of the valve metal. The first electrode may be formed of the valve metal, and the dielectric layer may be formed of an oxide of the valve metal. For example, if tantalum is used as the material for the first electrode, the dielectric layer may be a tantalum oxide layer. If aluminum is used as the material for the first electrode, the dielectric layer may be an aluminum oxide layer. However, the dielectric layer is not limited to these materials; any material that functions as a dielectric layer is acceptable.

[0045] (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. Examples of metal paste include silver paste containing silver particles.

[0046] The second electrode may include a first layer formed on a 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 layer formed of metal paste.

[0047] (Lead and outer casing) The capacitor (C) may include other components as needed, such as leads and an enclosure. There are no particular limitations on the leads and enclosure, and known leads and enclosures may be used.

[0048] (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 element (C) may contain multiple capacitor elements connected in parallel. Multiple capacitor elements (C) are usually connected in parallel in a stacked configuration and covered by an outer casing.

[0049] 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 of this disclosure may be omitted. Note that the following figures are schematic and may differ from the actual configuration.

[0050] (Embodiment 1) Figure 1 is a schematic cross-sectional view showing a capacitor according to Embodiment 1. The capacitor 10 shown in Figure 1 includes a capacitor element 100, a first lead terminal 21, a second lead terminal 22, a metal paste layer 23, and an outer casing 30.

[0051] The capacitor element 100 includes a first electrode 111, a dielectric layer 112, a conductive layer 120, and a second electrode 131. The dielectric layer 112 is formed to cover at least a portion of the surface of the first electrode 111. The 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 conductive layer 120. The conductive layer 120 is the conductive layer described above.

[0052] The first lead terminal 21 is connected to the first electrode 111. The second lead terminal 22 is connected to the second electrode 131 via a metal paste layer 23. The metal paste layer 23 is formed of a metal paste (silver paste, etc.). The casing 30 is formed to cover a portion of the first lead terminal 21, a portion of the second lead terminal 22, and the capacitor element 100. A portion of the first lead terminal 21 and a portion of the second lead terminal 22 are exposed from the casing 30 and function as terminals.

[0053] Figure 2 schematically shows a cross-sectional view of an example of a portion where the conductive layer 120 exists. Figure 2 shows the thickness direction Dt of the conductive layer 120. The cross-sectional view in Figure 2 is a cross-sectional view parallel to the thickness direction Dt of the conductive layer 120. The first electrode 111 in the example in Figure 2 has a porous portion 111a on its surface. The actual porous portion 111a may have a more complex shape, but in Figure 2, the porous portion 111a is shown in a simplified form. The surface layer 120a of the conductive layer 120 has a needle-like structure. However, the needle-like structure is not shown in Figure 2.

[0054] Figure 1 shows the case where the capacitor 10 contains only one capacitor element 100. However, the capacitor 10 may contain multiple capacitor elements 100. Figure 3 schematically shows a cross-sectional view of an example of a capacitor 10 containing multiple capacitor elements 100. Note that, in order to make the figure easier to understand, some components are omitted from the illustration in Figure 3.

[0055] The capacitor 10 in Figure 3 includes multiple stacked capacitor elements 100. The multiple capacitor elements 100 are connected in parallel.

[0056] (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, A conductive layer disposed on the dielectric layer, The second electrode is disposed on the conductive layer, The conductive layer is a capacitor having a needle-like structure made of an inorganic material on the surface layer on the second electrode side. (Technology 2) A capacitor according to Technology 1, wherein a portion of the needle-shaped structure is embedded within the second electrode. (Technology 3) The capacitor according to Art 1 or 2, wherein the average aspect ratio in the cross-sectional image of the needle-shaped portion at the end of the needle-shaped structure is in the range of 4.6 to 17.2. (Technology 4) A capacitor according to any one of the technologies 1 to 3, wherein at least a portion of the needle-shaped end of the needle-shaped structure is curved. (Technology 5) The conductive layer is made of an inorganic material containing a metal oxide. The aforementioned needle-like structure is made of the metal oxide, wherein the capacitor is according to any one of the technologies 1 to 4. (Technology 6) The capacitor according to Art 5, wherein the metal oxide is a conductive metal oxide whose main component is at least one selected from the group consisting of ZnO, TiO2, indium tin oxide, In2O3, SnO2, Ga2O3, MnO2, NiO2, CuInO2, CuCrO2, CuAlO2, and CuScO2. (Technology 7) The capacitor according to Art 6, wherein the conductive metal oxide contains oxygen vacancies. (Technology 8) The capacitor according to Art 6, wherein the conductive metal oxide includes an additive element for improving conductivity. (Technology 9) A capacitor according to any one of the technologies 1 to 8, wherein the first electrode is an anode and the second electrode is a cathode. (Technology 10) The capacitor according to any one of the technologies 1 to 9, wherein the first electrode is aluminum foil or a tantalum sintered body. (Technology 11) The first electrode has a porous portion on its surface, The dielectric layer is formed on the surface of the porous portion, A capacitor according to any one of the technologies 1 to 10, wherein a portion of the conductive layer is arranged in the void of the porous portion. (Technology 12) The conductive layer includes a first conductive layer in contact with the dielectric layer and a second conductive layer in contact with the second electrode. The capacitor according to any one of the technologies 1 to 11, wherein the second conductive layer has the needle-like structure and has a composition different from that of the first conductive layer. [Examples]

[0057] The capacitor (C) relating to this disclosure will be described in more detail by reference to the examples.

[0058] (Experiment 1) In Experiment 1, conductive layers (ZnO layers) were formed and evaluated under different conditions. First, aluminum foil with a dielectric layer (aluminum oxide layer) formed on its surface was prepared. The aluminum foil used had porous areas formed on its surface by etching. The aluminum oxide layer was formed by chemical conversion treatment of the aluminum foil.

[0059] Next, a base layer made of zinc oxide was formed on the dielectric layer by the ALD method. Then, a conductive layer made of zinc oxide (ZnO) was formed on the base layer. Specifically, the aluminum foil on which the base layer was formed was immersed in a predetermined solution and held for 6 hours to form the zinc oxide layer on the base layer.

[0060] The solution used was an aqueous solution of zinc nitrate hexahydrate and hexamethylenetetramine dissolved in a 1:1 (molar ratio). The concentration of zinc nitrate hexahydrate in the solution was 0.05 mol / L. The pH of the solution was set to 6.5-7.5. The temperature of the solution was set to room temperature (approximately 24°C). During the growth of zinc oxide, a heater was placed in contact with the back side of the aluminum foil (the side opposite to the zinc oxide growth side) to heat the aluminum foil to a constant temperature. In Experiment 1, four types of zinc oxide layers were formed by changing the temperature of the aluminum foil. Figure 4A shows a cross-sectional image of the surface layer of the zinc oxide layer formed when the aluminum foil temperature was 65°C. Figures 4B-4D show cross-sectional images of the surface layer of the zinc oxide layers formed when the aluminum foil temperature was 75°C, 85°C, and 95°C. Note that the cross-sectional images in Figures 4A-4D are images of the cross-section parallel to the thickness direction Dt of the conductive layer. In other words, the cross-sectional images in Figures 4A to 4D are images of the cross-section perpendicular to the surface of the aluminum foil.

[0061] As shown in Figures 4A to 4D, when the aluminum foil temperature was in the range of 65 to 75°C, a needle-like structure was formed. On the other hand, when the aluminum foil temperature was in the range of 85 or 95°C, no needle-like structure was formed, and instead, a columnar structure was formed. As shown in Figures 4A and 4B, the needle-like portions at the ends of the formed needle-like structure were not oriented in a single direction, but extended in various directions. In addition, at least a portion of the needle-like portions at the ends of the needle-like structure was curved. Furthermore, when the aluminum foil temperature was below 50°C, the growth of zinc oxide slowed down, and no needle-like structure was formed.

[0062] The average aspect ratio As was calculated in the cross-sectional image of the needle-like portion at the end of the needle-like structure shown in Figure 4A. The average As was obtained by the following procedure. First, 22 needle-like portions were arbitrarily selected from the cross-sectional image of the end of the needle-like structure. The needle-like portion was defined as the portion at the end of the needle-like structure that did not branch. Next, the diameter D and length L of each selected needle-like portion were determined from the cross-sectional image. The diameter D was determined by measuring the diameter at any one point on the needle-like portion. If the needle-like portion was curved, the length L of the needle-like portion was determined from the total length along the curved portion. Next, the aspect ratio was calculated for each needle-like portion using the formula: aspect ratio = length L / diameter D. Then, the average As was obtained by taking the arithmetic mean of the 22 obtained aspect ratios. Figure 5 shows the aspect ratio of each needle-like portion. In Figure 5, the needle-like portions for which the aspect ratio was calculated are shown as bar shapes. As described above, the average aspect ratio As can be determined by arbitrarily selecting and measuring 20 or more (for example, 20) needle-shaped points.

[0063] The average aspect ratio As of the needle-like portion at the end of the needle-like structure shown in Figure 4A was 4.6. The average aspect ratio As of the needle-like portion at the end of the needle-like structure shown in Figure 4B was 17.2.

[0064] (Experiment 2) In Experiment 2, a second electrode was formed on a conductive layer (ZnO layer) created under different conditions. The peel resistance between the conductive layer and the second electrode was then evaluated.

[0065] First, an aluminum foil with a dielectric layer formed on its surface was prepared. The same aluminum foil with the dielectric layer formed on its surface was used as in Experiment 1. Next, a zinc oxide layer (conductive layer) was formed on the dielectric layer using the same method and conditions as described in Experiment 1. At this time, as described in Experiment 1, multiple types of zinc oxide layers were formed by changing the temperature of the aluminum foil. Next, a second electrode was formed on the zinc oxide layer. Two types of electrodes were used for the second electrode. One second electrode was formed by laminating a carbon layer and a silver particle layer on the conductive layer in that order. The other second electrode was formed by a silver particle layer only. In this way, four types of samples A1 to A4 were prepared. Furthermore, comparative examples R1 to R4 were prepared using the same method and conditions as for the preparation of samples A1 to A4, except that the substrate was changed from aluminum foil to a glass substrate.

[0066] The surface structure of the zinc oxide layer was observed in the prepared samples. Furthermore, a peel test was performed on the second electrode of the prepared samples. The peel test was performed using a method called a tape peel test. Specifically, tape was adhered to the surface of the second electrode, and then the tape was peeled off, and the presence or absence of peeling of the second electrode was observed. The sample preparation conditions and the evaluation results of the peel test are shown in Table 1.

[0067] [Table 1]

[0068] Samples A1 to A4 have the structure of the capacitor (C) according to this disclosure. In comparative examples R1 to R4, no needle-like structures were observed on the surface of the zinc oxide layer. As shown in Table 1, in samples A1 to A4, delamination of the second electrode did not occur regardless of the configuration of the second electrode. [Industrial applicability]

[0069] This disclosure can be used in capacitors. [Explanation of symbols]

[0070] 10: Capacitor 21: First lead terminal 22: Second lead terminal 30: Exterior 100: Capacitor element 111: 1st electrode 111a: Porous part 112: Dielectric layer 120: Conductive layer 120a: Surface layer 131:Second electrode

Claims

1. It is a capacitor, First electrode and A dielectric layer formed on the surface of the first electrode, A conductive layer disposed on the dielectric layer, The second electrode is disposed on the conductive layer, The conductive layer is a capacitor having a needle-like structure on the surface layer on the second electrode side, made of an inorganic material and growing from the dielectric layer side.

2. The capacitor according to claim 1, wherein a portion of the needle-shaped structure is embedded in the second electrode.

3. The capacitor according to claim 1 or 2, wherein the average aspect ratio in the cross-sectional image of the needle-shaped portion at the end of the needle-shaped structure is in the range of 4.6 to 17.

2.

4. The capacitor according to claim 1 or 2, wherein at least a portion of the needle-shaped end of the needle-shaped structure is curved.

5. The conductive layer is made of an inorganic material containing a metal oxide. The capacitor according to claim 1 or 2, wherein the needle-shaped structure is made of the metal oxide.

6. The metal oxide is ZnO, TiO ２ , indium tin oxide, In ２ O ３ , SnO ２ , Ga ２ O ３ , MnO ２ , NiO ２ , CuInO ２ , CuCrO ２ , CuAlO ２ , and CuScO ２ The capacitor according to claim 5, which is a conductive metal oxide having at least one selected from the group consisting thereof as a main component.

7. The capacitor according to claim 6, wherein the conductive metal oxide includes oxygen vacancies.

8. The capacitor according to claim 6, wherein the conductive metal oxide includes an additive element for improving conductivity.

9. The capacitor according to claim 1 or 2, wherein the first electrode is an anode and the second electrode is a cathode.

10. The capacitor according to claim 1 or 2, wherein the first electrode is an aluminum foil or a tantalum sintered body.

11. The first electrode has a porous portion on its surface, The dielectric layer is formed on the surface of the porous portion, The capacitor according to claim 1 or 2, wherein a portion of the conductive layer is arranged in the voids of the porous portion.

12. The conductive layer includes a first conductive layer in contact with the dielectric layer and a second conductive layer in contact with the second electrode. The capacitor according to claim 1 or 2, wherein the second conductive layer has the needle-like structure and has a composition different from that of the first conductive layer.

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