Solid electrolytic capacitor

Abstract

A solid electrolytic capacitor comprises: an anode body containing tantalum and having a porous portion on the surface thereof; a dielectric layer covering at least a part of the porous portion; and a solid electrolyte layer covering at least a part of the dielectric layer. The dielectric layer includes a first dielectric layer containing fluorine, tantalum, and oxygen. The solid electrolyte layer comprises a first conductive polymer layer, containing a first conductive polymer which is a polymer of a first monomer, on the surface of the dielectric layer. The first monomer used is EDOT to which an alkyl group R is added.

Description

Solid electrolytic capacitors Cross-reference of related applications

[0001] This disclosure claims priority rights to Japanese Patent Application No. 2024-192122, filed with the Japan Patent Office on 31 October 2024, and the entirety of the said patent application is incorporated herein by reference.

[0002] This disclosure relates to solid electrolytic capacitors.

[0003] Electrolytic capacitors are used in a variety of electronic devices because they have a low equivalent series resistance (ESR) and excellent frequency characteristics. Electrolytic capacitors typically consist of a capacitor element comprising an anode and a cathode. The anode contains a porous anode body, and a dielectric layer is formed on the surface of the anode body. The dielectric layer is in contact with the electrolyte. Solid electrolytic capacitors use a solid electrolyte such as a conductive polymer.

[0004] Patent Document 1 proposes the use of a conductive polymer containing polythiophene as a solid electrolyte for electrolytic capacitors (see, for example, Patent Document 1).

[0005] Patent Document 2 proposes "a method for manufacturing a solid electrolytic capacitor comprising an anode having a porous portion on its surface and a dielectric layer formed on at least a part of the surface of the porous portion, comprising the steps of (i) forming a first solid electrolyte layer covering at least a part of the dielectric layer and (ii) forming a second solid electrolyte layer covering at least a part of the first solid electrolyte layer, wherein the first solid electrolyte layer comprises a first conductive polymer and the second solid electrolyte layer comprises a second conductive polymer, and step (i) comprises the steps of (i-a) supplying a reaction solution containing a monomer and a silane compound to the surface of the dielectric layer and (i-b) forming the first solid electrolyte layer by polymerizing the monomer in the supplied reaction solution to form the first conductive polymer, wherein the monomer comprises a compound represented by a predetermined formula, and R in the predetermined formula is an alkyl group having 1 to 10 carbon atoms, and is a method for manufacturing a solid electrolytic capacitor." The structure of the predetermined formula is the same as the structure of formula (I) described later.

[0006] Japanese Patent Publication No. 2004-96098, International Publication No. 2023 / 145618

[0007] Currently, there is a demand for improved reliability of solid electrolytic capacitors, such as reduced leakage current and improved voltage withstand capability. In this context, one of the objectives of this disclosure is to provide solid electrolytic capacitors with superior characteristics.

[0008] In view of the above, one aspect of the present disclosure relates to a solid electrolytic capacitor. The solid electrolytic capacitor includes an anode body containing tantalum and having a porous portion, a dielectric layer covering at least a portion of the porous portion, and a solid electrolyte layer covering at least a portion of the dielectric layer, wherein the dielectric layer has a first dielectric layer containing fluorine, tantalum, and oxygen, and the solid electrolyte layer has a first conductive polymer layer on the surface of the dielectric layer, the first monomer containing a compound represented by the following formula (I). In formula (I), R represents an alkyl group having 1 to 10 carbon atoms.

[0009]

[0010] According to this disclosure, high-performance solid electrolytic capacitors can be obtained. Novel features of the present invention are described in the appended claims, but the present invention, both in terms of its structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings.

[0011] This is a schematic cross-sectional view showing a solid electrolytic capacitor according to one embodiment of the present disclosure. This is a schematic diagram showing an enlarged view of the surface of the anode in the solid electrolytic capacitor of Figure 1.

[0012] 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 "numerical value A or greater and numerical value B or less". 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 does not exceed the upper limit.

[0013] Furthermore, 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.

[0014] The solid electrolytic capacitor according to this embodiment includes an anode, a dielectric layer, and a solid electrolyte layer. The anode contains tantalum (Ta) and has a porous portion. The dielectric layer covers at least a portion of the porous portion of the anode. The solid electrolyte layer covers at least a portion of the dielectric layer. Hereinafter, the solid electrolytic capacitor may be referred to as an "electrolytic capacitor" or "capacitor."

[0015] The dielectric layer has a first dielectric layer containing fluorine (F), tantalum (Ta), and oxygen (O). The inclusion of fluorine in the first dielectric layer reduces the leakage current of the electrolytic capacitor.

[0016] The solid electrolyte layer has a first conductive polymer layer on the surface of the dielectric layer, which contains a first conductive polymer that is a polymer of the first monomer. The first monomer contains a compound represented by the above formula (I). Hereinafter, the compound represented by the above formula (I) will be referred to as "alkyl-3,4-ethylenedioxythiophene" or "alkylEDOT". AlkylEDOT has high self-healing properties, and the first conductive polymer layer containing alkylEDOT improves the long-term reliability of the electrolytic capacitor and further reduces the leakage current of the electrolytic capacitor. Furthermore, as a result of the reduction in leakage current due to the first dielectric layer containing fluorine, the self-healing properties of alkylEDOT can be maintained for a longer period of time, and reliability is synergistically improved.

[0017] The first conductive polymer layer containing alkylEDOT only needs to be positioned in a region within the solid electrolyte layer that is in contact with the dielectric layer. The first conductive polymer layer only needs to be formed on the surface of the dielectric layer.

[0018] Generally, in electrolytic capacitors using anodes containing tantalum, porous materials are used as anodes to increase the surface area of ​​the porous region and ensure high capacitance. Examples of porous materials include porous molded bodies formed from tantalum-containing particles or porous sintered bodies obtained by sintering such molded bodies. From the perspective of ensuring high capacitance, it is advantageous to form the dielectric so as to thinly cover the uneven surface of the porous material; therefore, chemical conversion treatment using a chemical conversion solution is often employed. In some cases, dielectrics are formed by vapor phase methods such as sputtering and ALD, but it is more difficult to uniformly deposit the components constituting the dielectric onto the surface of the porous material compared to liquid phase methods, and the cost tends to be higher because it is necessary to create a vacuum inside the chamber.

[0019] Generally, an aqueous solution of phosphoric acid is often used as the conversion solution. Conversion solutions containing other acids are also used. In this case, the dielectric layer formed by the conversion treatment may contain impurities derived from elements in the acid or other components such as supporting salts in the conversion solution. These elements in the dielectric layer can affect its properties, and consequently, the performance of the electrolytic capacitor.

[0020] For example, if an aqueous phosphoric acid solution is used as the chemical conversion solution, the dielectric layer formed by the chemical conversion treatment may contain the element phosphorus (P). Also, if other acids such as boric acid, silicic acid, carbonate (and carboxylic acids such as acetic acid), or salt compounds of these acids with bases are included in the chemical conversion solution, the dielectric layer formed by the chemical conversion treatment may contain the elements boron (B), silicon (Si), and carbon (C), respectively.

[0021] The first dielectric layer containing fluorine (F) can be prepared, for example, by a chemical conversion solution containing hydrogen fluoride (HF). ４ A fluorine-containing salt such as F) may be added to the chemical solution. Ammonium monohydrogen difluoride (NH ４ HF ２ An aqueous solution of ) may be used as the chemical solution, and the above is not limited to any other soluble fluorine compound.

[0022] In dielectric layers formed by chemical conversion treatment, oxygen vacancies may be formed due to the effects of uneven chemical conversion, etc. For example, when chemical conversion treatment is performed on a porous tantalum material, tantalum oxide (Ta) may be used as the dielectric layer. ２ O ５ A film of tantalum oxide is formed to cover the inner walls of the pores in the porous material, but uneven chemical formation makes it easy for oxygen vacancies to form. Oxygen vacancies in tantalum oxide can form impurity levels (e.g., donor levels), which can form current paths through which leakage current flows within the dielectric layer.

[0023] In particular, in porous materials containing tantalum, acid protons do not diffuse easily within the porous material, leading to a localized decrease in pH. This decrease in pH can locally inhibit chemical conversion, resulting in uneven conversion. Consequently, a dielectric material with many oxygen deficiencies and non-uniform quality is formed, and the dielectric's insulating properties are not uniformly exhibited, potentially leading to leakage current.

[0024] However, the inclusion of fluorine in the dielectric layer allows the fluorine (fluoride ions) to compensate for the charge at oxygen vacancy levels. As a result, the leakage current path caused by impurity levels resulting from oxygen vacancies is reduced, the leakage current flowing through the dielectric layer is decreased, and the dielectric layer maintains high insulation properties.

[0025] On the other hand, the inclusion of fluorine reduces the wettability of the first dielectric layer with respect to the anode and solid electrolyte layer, and tends to reduce adhesion between the anode and solid electrolyte layer. For this reason, a second dielectric layer may be provided on top of the first dielectric layer, with the second dielectric layer interposed between the first dielectric layer and the solid electrolyte layer. Alternatively, a third dielectric layer may be formed by a chemical conversion treatment, and then the first dielectric layer may be formed on top of the third dielectric layer by a chemical conversion treatment. The second and third dielectric layers contain tantalum (Ta) and oxygen (O), but do not necessarily have to contain fluorine (F).

[0026] That is, the dielectric layer may further have a second dielectric layer on top of the first dielectric layer, the second dielectric layer containing tantalum and oxygen elements. The second dielectric layer does not have to substantially contain fluorine. The second dielectric layer may contain at least one selected from the group consisting of phosphorus (P), boron (B), silicon (Si), and carbon (C).

[0027] Similarly, the dielectric layer may further have a third dielectric layer between the anode and the first dielectric layer. The third dielectric layer does not have to substantially contain fluorine. The third dielectric layer may contain at least one selected from the group consisting of phosphorus (P), boron (B), silicon (Si), and carbon (C).

[0028] Furthermore, the statement that the second dielectric layer (or third dielectric layer) substantially does not contain a certain element (in this case, fluorine (F)) means that the abundance ratio of the specific element in the dielectric layer is 0.1 atomic percent or less. The abundance ratio can be determined by time-of-flight secondary ion mass spectrometry (TOF-SIMS), which will be described later. Energy-dispersive X-ray analysis based on SEM images (SEM-EDX) or X-ray photoelectron spectroscopy (XPS) can also be used.

[0029] The thickness of the dielectric layer on the surface of the porous portion of the anode body is preferably greater than the thickness of the dielectric layer inside the porous portion.

[0030] The anode typically has a rectangular parallelepiped shape. On the other hand, since the anode is a porous material, the dielectric layer can be formed along the inner walls of the porous pores of the anode, from the surface layer near the outer surface of the anode (the part near the surface of the rectangular parallelepiped) to the innermost part of the anode (the part near the center (centroid) of the rectangular parallelepiped).

[0031] Since leakage current tends to occur in the surface layer near the outer surface of the anode, by making the thickness of the dielectric layer on the surface thicker than the thickness of the dielectric layer inside the anode, the leakage current can be effectively reduced while suppressing the decrease in capacitance that occurs with increasing the thickness of the dielectric layer, thereby increasing the withstand voltage.

[0032] In order to form the dielectric layer on the surface of the porous portion of the anode body thicker than the dielectric layer inside the porous portion, it is preferable that the thickness of the second dielectric layer, which is formed after the first and third dielectric layers, be thicker on the surface of the porous portion than the thickness inside the porous portion. Here, the thickness of the second dielectric layer on the surface of the porous portion of the anode body is the thickness of the second dielectric layer at a depth of 5 μm from the outer surface of the anode body. The thickness of the second dielectric layer inside the porous portion is the thickness of the second dielectric layer at a depth of 100 μm from the outer surface of the anode body. However, if the distance from the center of gravity to the outer surface calculated based on the external shape of the anode body is 100 μm or less, the thickness of the second dielectric layer at the center of gravity (when the anode wire is located at the center of gravity, the position where a straight line passing through the center of gravity and perpendicular to the outer surface intersects the boundary between the porous portion and the anode wire) is defined as the thickness of the second dielectric layer inside the porous portion.

[0033] The thickness of the first dielectric layer is, for example, about 150 to 200 nm. The thickness of the third dielectric layer is, for example, about 120 to 180 nm. The thickness of the second dielectric layer is, for example, about 200 to 250 nm at the surface of the anode.

[0034] Forming the thickness of the second dielectric layer thicker in the surface layer portion can be realized, for example, by performing a forming process by applying a high voltage (for example, 100 V or more) for a short time (for example, 30 minutes or less). Since a dense dielectric layer can be formed in a short time, it is preferable to use a forming solution containing boric acid in the forming process for forming the second dielectric layer.

[0035] The thickness of the dielectric layer formed by the forming process is generally determined by the voltage applied in the forming process after applying the voltage of the forming process for a sufficiently long time. However, there is a difference in the growth rate of the formed film within the porous body, and the growth rate of the formed film on the surface layer of the porous portion is faster than the growth rate of the formed film in the deep portion of the porous portion. For this reason, by applying a high voltage as the voltage of the forming process for a short time and stopping the forming halfway, the thickness of the dielectric layer on the surface layer of the porous portion can be formed thicker than the thickness of the dielectric layer inside.

[0036] The third dielectric layer is not particularly limited as long as it can be formed between the first dielectric layer and the anode body, is generally used, and in terms of being able to easily form a dielectric layer, in the forming process for forming the third dielectric layer, a forming solution containing phosphoric acid (aqueous phosphoric acid solution) may be used.

[0037] When the second dielectric layer contains at least one selected from the group consisting of a phosphorus element, a boron element, a silicon element, and a carbon element, the third dielectric layer may contain at least one element not contained in the second dielectric layer among the group consisting of a phosphorus element, a boron element, a silicon element, and a carbon element. For example, the second dielectric layer may contain boron and the third dielectric layer may contain a phosphorus element.

[0038] The thickness of each dielectric layer is obtained from an image by a scanning electron microscope (SEM) with respect to the cross section of the anode body on which the dielectric layer is formed. More specifically, first, for the sample, a cross section parallel to the thickness direction is exposed, and an image by SEM is taken. The thickness of the dielectric layer is obtained at an arbitrary plurality of locations (for example, 10 locations) in an arbitrary plurality of fields of this image, and the average value is obtained.

[0039] Incidentally, the sample for taking the above cross-sectional image may be obtained by the following procedure. First, a sample of the anode body on which the dielectric layer is formed is embedded in a curable resin and the curable resin is cured. The cured product is wet-polished or dry-polished to expose a cross-section parallel to the thickness direction of the dielectric (a cross-section capable of confirming the layer structure of the dielectric). By smoothing the exposed cross-section by ion milling, a sample for imaging can be obtained.

[0040] By performing depth profile analysis on the sample after resin embedding by TOF-SIMS, the abundance ratio of the elements contained in each dielectric layer can be determined. In TOF-SIMS, a Bi beam is used as the primary ion beam. As the sputtering ion species, O ２ is used.

[0041] The solid electrolyte layer may have a second conductive polymer layer containing a second conductive polymer that is a polymer of a second monomer on the first conductive polymer layer. The second monomer includes a compound (3,4-ethylenedioxythiophene) (EDOT) represented by the following formula.

[0042] The second monomer is a compound in which the alkyl group R is not substituted in the first monomer. By using the second conductive polymer, which is a polymer of the second monomer, in the solid electrolyte layer, the electrical conductivity of the solid electrolyte layer can be improved and the ESR of the electrolytic capacitor can be lowered.

[0043] The second conductive polymer layer can be formed on the first conductive polymer layer so as to cover the first conductive polymer layer. The thicknesses of the first conductive polymer layer and the second conductive polymer layer are determined by obtaining an SEM image of the cross-section of the anode body on which the solid electrolyte layer is formed and by the same method as for the thickness of the dielectric layer.

[0044] The first conductive polymer layer may be formed by a polymerization reaction of the first monomer on the dielectric layer. The polymerization of the monomer may be chemical polymerization or electrolytic polymerization.

[0045] The dielectric layer is formed to cover the inner walls of the pores of the porous body, which is the anode. When the first conductive polymer layer is formed by the polymerization reaction of the first monomer, the first monomer penetrates deep into the pores covered by the dielectric layer, and in-situ polymerization takes place on the dielectric layer. Since the molecules of the first monomer are smaller than those of the polymer after polymerization, they can easily penetrate deep into the pores located in the anode body. Therefore, it is easy to fill the pores with the first conductive polymer layer while reducing the gaps within the pores.

[0046] The surface of the first conductive polymer layer (e.g., a chemically polymerized layer) formed by polymerization has fine irregularities when viewed microscopically. These irregularities arise from uneven polymerization progress and uneven layer growth. The second conductive polymer layer is formed to fill these irregularities.

[0047] The second conductive polymer layer may be formed by coating a dispersion containing the second conductive polymer.

[0048] Furthermore, whether the conductive polymer layer is polymerized on a dielectric layer or formed by coating a dispersion of conductive polymer can be determined by identifying the components other than the conductive polymer contained in the conductive polymer layer (such as the presence or absence of oxidizing agents and additives necessary for polymerization).

[0049] The components of the solid electrolytic capacitor according to this embodiment will be described in detail below.

[0050] (Capacitor Elements) A solid electrolytic capacitor is composed of one or more capacitor elements. A capacitor element includes an anode, a dielectric layer, a solid electrolyte layer, and a cathode lead layer. The solid electrolyte layer and the cathode lead layer constitute the cathode portion of the solid electrolytic capacitor.

[0051] The anode section includes an anode body and may further include an anode wire. The anode body may be a porous sintered body or a metal foil with a porous surface. A dielectric layer is formed on at least a portion of the surface of the anode body. A solid electrolyte layer is disposed between the dielectric layer formed on the surface of the anode body and the cathode extraction layer. There are no particular limitations on the components other than the solid electrolyte layer, and components used in known solid electrolytic capacitors may be applied.

[0052] (Anode) A valve metal can be used as the material for the anode. Valve metals include tantalum (Ta). Tantalum (Ta) may be combined with other valve metals other than tantalum (Ta). Examples of other valve metals include titanium (Ti), niobium (Nb), and aluminum (Al). The valve metal may also be an alloy of these valve metals.

[0053] An anode having a porous portion may be formed by sintering material particles (for example, particles of valve metal). Alternatively, an anode having a porous portion on its surface may be formed by etching the surface of a metal foil. The dielectric layer formed on the surface of the anode may be formed by chemical conversion treatment of the anode surface. There are no limitations on the chemical conversion treatment method, and known chemical conversion treatment methods may be applied.

[0054] Capacitors using a sintered body (e.g., a sintered tantalum body) as the anode typically do not include a separator. In separator-less capacitors, the gap between the anode and the cathode lead layer is narrow, making it particularly important to suppress leakage current. For this reason, the capacitor configuration according to this disclosure is particularly preferred in separator-less capacitors. If the capacitor according to this disclosure includes a separator, there are no limitations on the separator, and known separators may be used.

[0055] (Anode Wire) When the anode body is a sintered body, the anode portion may include an anode wire. The anode wire may be a wire made of metal. Examples of materials for the anode wire include the valve metals and copper mentioned above. A portion of the anode wire is embedded in the anode body, and the remaining portion protrudes from the end face of the anode body.

[0056] (Dielectric Layer) The dielectric layer includes a first dielectric layer. The first dielectric layer contains a fluorine element, a tantalum element, and an oxygen element. That is, the first dielectric layer is a layer in which fluorine (F) is doped into a tantalum compound constituting the dielectric. By including fluorine in the tantalum compound that is the dielectric, charge compensation occurs and oxygen defect levels are stabilized. As a result, leakage current is suppressed.

[0057] The first dielectric layer can be formed by subjecting the anode body to a forming treatment (anodic oxidation) in an environment where fluoride ions (F － ) are contained in the forming solution. Examples of compounds having fluoride ions include hydrogen fluoride (HF), ammonium fluoride (NH ４ F), ammonium bifluoride (NH ４ HF ２ ), etc.

[0058] The dielectric layer may have a multilayer structure including the first dielectric layer. The dielectric layer may have a second dielectric layer on top of the first dielectric layer. The dielectric layer may have a third dielectric layer and form the first dielectric layer on top of the third dielectric layer. The first dielectric layer containing fluorine has low wettability with the anode body and the solid electrolyte layer, and the adhesiveness with the anode body and the solid electrolyte layer is likely to decrease. Therefore, it is preferable that the first dielectric layer is not in direct contact with the anode body or the solid electrolyte layer, and a second dielectric layer is interposed between the first dielectric layer and the solid electrolyte layer, and / or a third dielectric layer is interposed between the third dielectric layer and the anode body.

[0059] The second dielectric layer and the third dielectric layer preferably do not contain fluorine. The second dielectric layer and the third dielectric layer may contain at least one selected from the group consisting of phosphorus (P), boron (B), silicon (Si), and carbon (C). Among these elements, silicon (Si) and carbon (C), similar to fluorine (F), have the effect of charge compensating oxygen defects in the dielectric layer and stabilizing oxygen defect levels, contributing to a reduction in leakage current and an increase in breakdown voltage. However, the effect is smaller than that of fluorine (F).

[0060] The first to third dielectric layers may be formed on the surface of the anode body by a vapor phase method.

[0061] When forming the first to third dielectric layers by a chemical conversion treatment of the anode body, dielectric layers containing fluorine (F), phosphorus (P), boron (B), silicon (Si), and / or carbon (C) can be formed by chemical conversion treatment (anodic oxidation) of the anode body in an environment where compounds containing these elements are present in the conversion solution. The compound may be liquid at room temperature and may constitute the solvent of the conversion solution, or it may be a salt compound that dissolves in the solvent and becomes ionized.

[0062] The chemical solution may contain a buffering agent. Examples of buffering agents include bicarbonate-based buffering agents, citrate-based buffering agents, phthalate-based buffering agents, acetate-based buffering agents, phosphate-based buffering agents (such as trisodium phosphate), and MES (2-Morphorinoethylethanolamine sulfonic acid) buffering agents. One type of buffering agent may be used, or two or more types may be used in combination.

[0063] (Solid Electrolyte Layer) The solid electrolyte layer includes a first conductive polymer layer. The first conductive polymer layer is a conductive polymer layer containing a polymer (polyalkylEDOT) with alkylEDOT as the monomer. The first conductive polymer layer may also contain other conductive polymers other than polyalkylEDOT. The first conductive polymer layer may also contain a copolymer of alkylEDOT and other monomers.

[0064] Examples of conductive polymers included in the solid electrolyte layer include polypyrrole, polythiophene, polyaniline, and their derivatives. These may be used individually or in combination. The conductive polymer may also be a copolymer of two or more monomers. A derivative of a conductive polymer refers to a polymer that uses the conductive polymer as its basic skeleton. For example, an example of a derivative of polythiophene is poly(3,4-ethylenedioxythiophene).

[0065] It is preferable that a dopant is added to the conductive polymer. The dopant can be selected according to the conductive polymer, and known dopants may be used. Examples of dopants include naphthalene sulfonic acid, p-toluenesulfonic acid, polystyrene sulfonic acid, and salts thereof. A preferred example of the second solid electrolyte layer is formed using poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonic acid (PSS).

[0066] The solid electrolyte layer may be composed of two or more solid electrolyte layers. For example, the solid electrolyte layer may include a first conductive polymer layer covering the dielectric layer and a second conductive polymer layer covering the first conductive polymer layer. When the solid electrolyte layer is composed of two or more layers, the composition and formation method (polymerization method) of the conductive polymer used in each layer may be different.

[0067] (Cathode Extraction Layer) The cathode extraction layer is a conductive layer and is arranged to cover at least a portion of the solid electrolyte layer. The cathode extraction layer may include a carbon layer formed on the electrolyte layer and a metal paste layer formed on the carbon layer. The carbon layer may be formed of a conductive carbon material such as graphite and a resin. The metal paste layer may be formed of metal particles (e.g., silver particles) and a resin, and may be formed of, for example, a known silver paste.

[0068] (Cathode lead terminals and anode lead terminals) There are no particular limitations on the lead terminals (cathode lead terminals and anode lead terminals), and known lead terminals may be used. A portion of the cathode lead terminals is electrically connected to the cathode lead layer. For example, this portion may be connected to the cathode lead layer by a conductive layer (e.g., a silver paste layer).

[0069] (Outer covering) There are no limitations on the outer covering, and known outer coverings may be used. The outer covering may consist of at least one selected from the group consisting of a resin composition, a film, and a case. One example of an outer covering is arranged around the capacitor element so that the capacitor element is not exposed on the surface of the electrolytic capacitor. Furthermore, this example of an outer covering is arranged to cover a portion of the anode lead frame and a portion of the cathode lead frame. The resin composition used as the outer covering may include a resin (insulating resin) and an insulating filler.

[0070] The method for manufacturing a solid electrolytic capacitor according to this embodiment will be described below with reference to the drawings as appropriate. However, the present invention is not limited thereto. Figure 1 is a schematic cross-sectional view showing an example of a solid electrolytic capacitor according to this embodiment. Figure 2 is a schematic diagram showing an enlarged view of the surface of the anode in the solid electrolytic capacitor shown in Figure 1.

[0071] The capacitor (solid electrolytic capacitor) 100 in Figure 1 includes a capacitor element 110, an outer casing 150, an anode lead terminal 210, and a cathode lead terminal 220. The outer casing 150 is positioned to cover a portion of the anode lead terminal 210, a portion of the cathode lead terminal 220, and the capacitor element 110.

[0072] The capacitor element 110 includes an anode portion 111, a dielectric layer 114, and a cathode portion 115. The anode portion 111 includes an anode body 113 and an anode wire 112. The anode body 113 is a rectangular parallelepiped porous sintered body with a dielectric layer 114 formed on its surface. A portion of the anode wire 112 protrudes from one end face of the anode body 113 toward the front surface 100f of the electrolytic capacitor 100. The other portion of the anode wire 112 is embedded in the anode body 113.

[0073] The cathode portion 115 includes a solid electrolyte layer 116 disposed to cover at least a portion of the dielectric layer 114, and a cathode extraction layer 117 formed on the solid electrolyte layer 116. The cathode extraction layer 117 includes, for example, a carbon layer formed on the solid electrolyte layer 116 and a metal particle layer formed on the carbon layer. The metal particle layer is, for example, a metal paste layer (e.g., a silver paste layer) formed using a metal paste.

[0074] The anode lead terminal 210 includes an anode terminal portion 211 and a wire connection portion 212. The anode terminal portion 211 is exposed on the bottom surface 100b of the electrolytic capacitor 100 (see Figure 2). The wire connection portion 212 is connected to the anode wire 112. The cathode lead terminal 220 includes a cathode terminal portion 221 and a connection portion 222. The cathode terminal portion 221 is exposed on the bottom surface 100b of the electrolytic capacitor 100. The connection portion 222 is electrically connected to the cathode lead layer 117 (cathode portion 115) by a conductive layer 141.

[0075] Figure 2 schematically shows enlarged views of the anode 113, dielectric layer 114, and solid electrolyte layer 116. Since the anode 113 is a porous material, the dielectric layer 114 is formed to cover the inner walls of the pores of the porous material, and the solid electrolyte layer 116 is formed to fill the inside of the pores. However, Figure 2 omits the depiction of the internal structure of these pores and only shows the stacking of the elements constituting the dielectric layer 114 and the solid electrolyte layer 116.

[0076] The dielectric layer 114 comprises a first dielectric layer 114A, a second dielectric layer 114B, and a third dielectric layer 114C. The third dielectric layer 114C is placed on the surface (inner wall surface of the pores) of the anode body 113, and the first dielectric layer 114A is placed on top of the third dielectric layer 114C. The second dielectric layer 114B is placed on top of the first dielectric layer 114A. That is, the dielectric layers are stacked on the anode body 113 in the order of third dielectric layer 114C, first dielectric layer 114A, and second dielectric layer 114B. The dielectric layers 114A to 114C are composed of tantalum compounds (oxides). The first dielectric layer 114A contains fluorine (F). That is, the first dielectric layer 114A may be composed of a tantalum compound (oxide) doped with fluorine (F).

[0077] The solid electrolyte layer 116 comprises a first conductive polymer layer 116A and a second conductive polymer layer 116B. The first conductive polymer layer 116A is placed on the dielectric layer 114 (second dielectric layer 114B), and the second conductive polymer layer 116B is placed on top of the first conductive polymer layer 116A. That is, the conductive polymer layers are laminated on the dielectric layer 114 in the order of the first conductive polymer layer 116A and the second conductive polymer layer 116B. The first conductive polymer layer 116A contains a first conductive polymer which is a polymer with alkyl EDOT as the monomer.

[0078] (Note) The above description of embodiments discloses the following technology: (Technology 1) An anode body containing tantalum and having a porous portion; a dielectric layer covering at least a part of the porous portion; and a solid electrolyte layer covering at least a part of the dielectric layer, wherein the dielectric layer has a first dielectric layer containing fluorine, tantalum, and oxygen, and the solid electrolyte layer has a first conductive polymer layer on the surface of the dielectric layer, the first monomer having the following formula (I) A solid electrolytic capacitor comprising a compound represented by formula (I), where R represents an alkyl group having 1 to 10 carbon atoms. (Technology 2) The dielectric layer further comprises a second dielectric layer containing tantalum and oxygen on the first dielectric layer, and the thickness of the second dielectric layer formed on the surface of the porous portion is greater than the thickness of the second dielectric layer formed inside the porous portion, as described in Technology 1. (Technology 3) The solid electrolytic capacitor according to Technology 2, wherein the second dielectric layer comprises at least one selected from the group consisting of phosphorus, boron, silicon, and carbon. (Technology 4) The solid electrolytic capacitor according to any one of Technologies 1 to 3, wherein the dielectric layer further comprises a third dielectric layer between the anode and the first dielectric layer, and the third dielectric layer comprises at least one selected from the group consisting of phosphorus, boron, silicon, and carbon. (Technical 5) The dielectric layer further comprises a second dielectric layer containing tantalum and oxygen on the first dielectric layer, the dielectric layer further comprises a third dielectric layer between the anode and the first dielectric layer, the second dielectric layer comprises at least one selected from the group consisting of phosphorus, boron, silicon, and carbon, and the third dielectric layer comprises at least one element from the group consisting of phosphorus, boron, silicon, and carbon that is not included in the second dielectric layer, as described in Technical 1. (Technical 6) The solid electrolyte layer further comprises a second conductive polymer layer on the first conductive polymer layer comprising a second conductive polymer which is a polymer of a second monomer, the second monomer having the following formula A solid electrolytic capacitor according to any one of the technologies 1 to 5, comprising a compound represented by (Technology 7). The solid electrolytic capacitor according to Technology 6, wherein the second conductive polymer layer is formed by coating a dispersion containing the second conductive polymer. (Technology 8) The solid electrolytic capacitor according to any one of the technologies 1 to 7, wherein the first conductive polymer layer is formed on the dielectric layer by a polymerization reaction of the first monomer.

[0079] [Examples] The present invention will be described in detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0080] Example 1: A solid electrolytic capacitor for evaluation was fabricated according to the following procedure, and its characteristics were evaluated.

[0081] (1) Tantalum metal particles were used as the valve-acting metal for the anode body. The tantalum metal particles were formed into a rectangular parallelepiped so that one end of an anode wire made of tantalum metal was embedded in the tantalum metal particles, and then the formed body was sintered in a vacuum. This resulted in an anode section comprising an anode body made of a porous sintered tantalum body and an anode wire in which one end was embedded in the anode body and the remaining part was planted from one side of the anode body.

[0082] (2) Formation of the dielectric layer As the first conversion solution, an aqueous solution of phosphoric acid with a concentration of 0.001% by mass or more and 1.000% by mass or less was prepared. The conversion tank was filled with the first conversion solution and the anode was immersed in it. The temperature of the conversion solution was between 20°C and 95°C. The upper end of the anode wire that was not immersed in the solution was connected to the counter electrode, and a voltage of 64V was applied between the anode wire and the counter electrode for 30 minutes. In this way, an oxide film of tantalum oxide containing phosphorus (third dielectric layer) (thickness 140 nm) was formed on the surface of the anode.

[0083] Next, as the second chemical solution, NH ４ HF ２ An aqueous solution was prepared containing a concentration of 0.01% to 10.00% by mass of a substance and trisodium phosphate (buffer) at a concentration of 0.001% to 10.00% by mass. The chemical conversion tank was filled with the second conversion solution, and the anode body on which the third dielectric layer was formed was immersed in it. The upper end of the anode wire, which was not immersed in the solution, was connected to the counter electrode, and a voltage of 80V was applied between the anode wire and the counter electrode for 10 minutes. In this way, an oxide film of tantalum oxide containing fluorine (first dielectric layer) (thickness 176 nm) was formed on the surface of the anode body.

[0084] Next, an aqueous solution of phosphoric acid with a concentration of 0.01% by mass or more and 1.000% by mass or less was prepared as the third conversion solution. The conversion tank was filled with the third conversion solution, and the anode body on which the first dielectric layer had been formed was immersed in it. The upper end of the anode wire, which was not immersed in the liquid, was connected to the counter electrode, and a voltage of 100V was applied between the anode wire and the counter electrode for 30 minutes. In this way, an oxide film of tantalum oxide containing phosphorus (second dielectric layer) (thickness 220 nm) was formed on the surface of the anode body.

[0085] (3) Formation of the solid electrolyte layer A reaction solution was prepared by mixing ethanol (liquid medium), iron(III) p-toluenesulfonate (oxidizing agent), and a monomer. The monomer used was alkylEDOT in which R is a butyl group in the above formula (I).

[0086] The anode body, on which the dielectric layer was formed, was immersed in the reaction solution for about 3 to 10 seconds. Then, after removing the anode body from the reaction solution, the monomer was polymerized by heating it in air at 210°C for 3 minutes. In this way, the polymerization reaction proceeded on the oxide film, forming a first conductive polymer layer containing the first conductive polymer.

[0087] Next, the anode was immersed in an aqueous dispersion containing a second conductive polymer at a concentration of 1% to 4% by mass for about 3 to 10 seconds. After being removed from the dispersion, it was heated in air at a temperature of 60°C to 200°C for 20 minutes to form a second conductive polymer layer. The second conductive polymer used was poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrene sulfonic acid (PSS).

[0088] (4) Formation of the cathode extraction layer The tantalum sintered body on which the solid electrolyte layer obtained in (4) above was formed was immersed in a dispersion of graphite particles dispersed in water, and after being removed from the dispersion, it was dried to form a carbon layer on the surface of the solid electrolyte layer. Drying was carried out at a temperature of 180°C for a time of 10 to 30 minutes.

[0089] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of the carbon layer and dried at a temperature of 60°C to 80°C for 20 to 40 minutes. After that, the binder resin was cured by further heating at 180°C for 30 to 60 minutes, forming a metal particle-containing layer. In this way, a cathode extraction layer composed of the carbon layer and the metal particle-containing layer was formed. In this manner, a capacitor element including a cathode portion composed of a solid electrolyte layer and a cathode extraction layer was obtained.

[0090] (5) Fabrication of a solid electrolytic capacitor The cathode lead layer of the capacitor element obtained in (4) above and one end of the cathode lead terminal were joined with a conductive adhesive. The anode wire and one end of the anode lead terminal were joined by laser welding.

[0091] Next, the capacitor element was sealed with a resin casing made of insulating resin using the transfer molding method. At this time, the other end of the anode lead terminal and the other end of the cathode lead terminal were left extended from the casing. In this way, the solid electrolytic capacitor A1 according to Example 1 was manufactured.

[0092] Example 2: In Example 1, the anode body was not subjected to a chemical conversion treatment by immersion in the third conversion solution, and the second dielectric layer was not formed. That is, the dielectric layer was formed with two layers: a third dielectric layer (thickness 176 nm) and a first dielectric layer (thickness 220 nm).

[0093] Apart from the above, the solid electrolytic capacitor A2 according to Example 2 was manufactured in the same manner as in Example 1.

[0094] <Example 3> In Example 1, the conditions for the chemical conversion treatment were changed by immersing the anode in the third conversion solution. As the third conversion solution, an aqueous solution containing boric acid with a concentration of 0.01% by mass or more and 1.000% by mass or less was prepared. The conversion tank was filled with the third conversion solution, and the anode, on which the first dielectric layer had been formed, was immersed in it. The upper end of the anode wire that was not immersed in the liquid was connected to the counter electrode, and a voltage of 100V was applied between the anode wire and the counter electrode for 30 minutes. In this way, an oxide film of tantalum oxide containing boron (second dielectric layer) was formed on the surface of the anode.

[0095] Apart from the above, the solid electrolytic capacitor A3 according to Example 3 was manufactured in the same manner as in Example 1.

[0096] When the thickness of the second dielectric layer of solid electrolytic capacitor A3 was measured using the method described above, it was found to be 220 nm on the surface of the anode, and the second dielectric layer was not formed in the center (inside) of the anode.

[0097] <Comparative Example 1> In forming the solid electrolyte layer, a reaction solution was prepared by mixing ethanol (liquid medium), iron(III) p-toluenesulfonate (oxidizing agent), and 3,4-ethylenedioxythiophene (EDOT) as a monomer. Using this reaction solution, a polymerization reaction was carried out on the oxide film to form a first conductive polymer layer containing the first conductive polymer. The conditions for the polymerization reaction were the same as in Example 1.

[0098] In addition, the anode body was not subjected to a chemical conversion treatment by immersion in the second conversion solution, and the first dielectric layer was not formed. That is, the dielectric layer was formed with two layers: a third dielectric layer (thickness 176 nm) and a second dielectric layer.

[0099] Furthermore, in Example 1, the conditions for the chemical conversion treatment were changed by immersing the anode body in the third conversion solution.

[0100] Specifically, an aqueous solution of boric acid with a concentration of 0.01% by mass or more and 1.000% by mass or less was prepared as the third conversion solution. The conversion tank was filled with the third conversion solution, and the anode body on which the first dielectric layer had been formed was immersed in it. The upper end of the anode wire, which was not immersed in the liquid, was connected to the counter electrode, and a voltage of 100V was applied between the anode wire and the counter electrode for 30 minutes. In this way, an oxide film of tantalum oxide containing phosphorus (second dielectric layer) was formed on the surface of the anode body.

[0101] Apart from the above, a solid electrolytic capacitor B1 according to Example 1 was fabricated in the same manner as in Example 1. When the thickness of the second dielectric layer of the solid electrolytic capacitor B1 was measured using the method described above, it was found to be 220 nm on the surface of the anode, and the second dielectric layer was not formed in the center (inside) of the anode.

[0102] <Comparative Example 2> In Comparative Example 1, the anode body was not subjected to a chemical conversion treatment by immersion in the third conversion solution, and the dielectric layer was formed as a single layer consisting only of the third dielectric layer (thickness 220 nm).

[0103] Apart from the above, the solid electrolytic capacitor B2 according to Comparative Example 2 was manufactured in the same manner as in Comparative Example 1.

[0104] <Comparative Example 3> In Example 1, the anode body was not subjected to a chemical conversion treatment by immersing it in the second chemical conversion solution, nor was it subjected to a chemical conversion treatment by immersing the anode body in the third chemical conversion solution. Instead, the dielectric layer was formed as a single layer consisting only of the third dielectric layer (thickness 220 nm).

[0105] Apart from the above, the solid electrolytic capacitor B3 according to Comparative Example 3 was manufactured in the same manner as in Example 1.

[0106] Comparative Example 4: In forming the solid electrolyte layer, a reaction solution was prepared by mixing ethanol (liquid medium), iron(III) p-toluenesulfonate (oxidizing agent), and 3,4-ethylenedioxythiophene (EDOT) as a monomer. Using this reaction solution, a polymerization reaction was carried out on the oxide film to form a first conductive polymer layer containing the first conductive polymer. The conditions for the polymerization reaction were the same as in Example 1.

[0107] Apart from the above, the solid electrolytic capacitor B4 according to Comparative Example 4 was manufactured in the same manner as in Example 1.

[0108] (6) Evaluation The following evaluations were performed on the solid electrolytic capacitors A1 to A3 and B1 to B4.

[0109] (6-1) Leakage current (LC) For each solid electrolytic capacitor after manufacturing, a voltage of 35V was applied between the anode lead terminal and the cathode lead terminal, and the leakage current (LC) was measured after 120 seconds.

[0110] (6-2) Reliability The capacitance C0 of the solid electrolytic capacitor at a frequency of 120 Hz was measured using an LCR meter for four-terminal measurement.

[0111] Subsequently, the capacitor was placed in an environment of 125°C and maintained for 1000 hours with a voltage of 35V applied between the anode and cathode lead terminals.

[0112] After 1000 hours, the capacitance C1 of the solid electrolytic capacitor was measured using the same method as for C0. The rate of change in capacitance, ΔCap (= |C1 - C0| / C0), was evaluated as an indicator of reliability. The smaller ΔCap, the more the decrease in capacitance during long-term use is suppressed, indicating superior reliability of the solid electrolytic capacitor.

[0113] The evaluation results are shown in Table 1. In Table 1, the rate of change of leakage current LC and capacitance is shown as a relative value with the evaluation result of solid electrolytic capacitor A1 according to Example 1 set to 1.

[0114]

[0115] As shown in Table 1, capacitors A1 to A3 have a smaller initial leakage current LC and superior long-term reliability compared to the comparative example capacitors B1 to B4.

[0116] Although the present invention has been described in relation to 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.

[0117] This disclosure can be used in solid electrolytic capacitors.

[0118] 100 Electrolytic capacitor 111 Anode section 112 Anode wire 113 Anode body 114 Dielectric layer 114A First dielectric layer 114B Second dielectric layer 114C Third dielectric layer 115 Cathode section 116 Solid electrolyte layer 116A First conductive polymer layer 116B Second conductive polymer layer 117 Cathode extraction layer

Claims

1. An anode body containing tantalum and having a porous portion; a dielectric layer covering at least a portion of the porous portion; and a solid electrolyte layer covering at least a portion of the dielectric layer, wherein the dielectric layer has a first dielectric layer containing fluorine, tantalum, and oxygen, and the solid electrolyte layer has a first conductive polymer layer on the surface of the dielectric layer, the first monomer having the following formula (I) [Chemical Formula 1] A solid electrolytic capacitor comprising a compound represented by formula (I), where R represents an alkyl group having 1 to 10 carbon atoms.

2. The solid electrolytic capacitor according to claim 1, wherein the dielectric layer further comprises a second dielectric layer containing tantalum and oxygen elements on the first dielectric layer, and the thickness of the second dielectric layer formed on the surface of the porous portion is greater than the thickness of the second dielectric layer formed inside the porous portion.

3. The solid electrolytic capacitor according to claim 2, wherein the second dielectric layer comprises at least one element selected from the group consisting of phosphorus, boron, silicon, and carbon.

4. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the dielectric layer further comprises a third dielectric layer between the anode and the first dielectric layer, and the third dielectric layer comprises at least one element selected from the group consisting of phosphorus, boron, silicon, and carbon.

5. The electrolytic capacitor according to claim 1, wherein the dielectric layer further comprises a second dielectric layer containing tantalum and oxygen on the first dielectric layer, the dielectric layer further comprises a third dielectric layer between the anode and the first dielectric layer, the second dielectric layer comprises at least one selected from the group consisting of phosphorus, boron, silicon, and carbon, and the third dielectric layer comprises at least one element from the group consisting of phosphorus, boron, silicon, and carbon that is not included in the second dielectric layer.

6. The solid electrolyte layer has a second conductive polymer layer on the first conductive polymer layer, the second conductive polymer which is a polymer of the second monomer, and the second monomer is given by the following formula [Chemical Formula 2] A solid electrolytic capacitor according to any one of claims 1 to 3, comprising a compound represented by the formula.

7. The solid electrolytic capacitor according to claim 6, wherein the second conductive polymer layer is formed by coating a dispersion containing the second conductive polymer.

8. The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the first conductive polymer layer is formed on the dielectric layer by a polymerization reaction of the first monomer.

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