Electrode, solid electrolytic capacitor, and method for manufacturing electrode

Abstract

This electrode for a solid electrolytic capacitor comprises: a substrate containing a valve action metal; a first dielectric layer covering at least a portion of a surface of the substrate; and a second dielectric layer covering at least a portion of a surface of the first dielectric layer. The first dielectric layer includes a composite oxide containing titanium. The second dielectric layer includes at least one selected from a group consisting of aluminum oxide and hafnium oxide. The thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer.

Description

Electrode, solid electrolytic capacitor, and method for manufacturing an electrode Cross-reference of related applications

[0001] This disclosure claims the benefit of priority with respect to Japanese Patent Application No. 2024-229185, filed with the Japan Patent Office on 25 December 2024, and the entirety of the said patent application is incorporated herein by reference.

[0002] This disclosure relates to electrodes, solid electrolytic capacitors, and methods for manufacturing electrodes.

[0003] The electrodes used in a solid electrolytic capacitor comprise a substrate containing a valve-acting metal and a dielectric layer covering at least a portion of the surface of the substrate. The solid electrolytic capacitor comprises electrodes and a conductive polymer covering at least a portion of the surface of the dielectric layer of the electrodes.

[0004] Patent Document 1 proposes "an electrode foil for electrolytic capacitors, comprising a substrate containing a valve-acting metal and a dissimilar metal composite layer covering the surface of the substrate, wherein the dissimilar metal composite layer includes a mixed region in which a first metal and a second metal different from the first metal are mixed, the mixed region constitutes at least 50% of the thickness direction of the dissimilar metal composite layer, and the content M1 of the first metal and the content M2 of the second metal relative to the total metal in the mixed region are each 1 atomic percent or more."

[0005] Furthermore, Patent Document 2 states, "The step of forming a storage electrode, and placing ZrO on the storage electrode." ２ Thin film and Al ２ O ３ A method for forming a capacitor for a semiconductor device has been proposed, characterized by including the steps of forming a multidielectric film made of a thin film and forming a plate electrode on the multidielectric film.

[0006] International Publication No. 2022 / 024772, Japanese Patent Publication No. 2006-135339

[0007] In recent years, there has been a growing demand for further improvements in the performance and reliability of solid electrolytic capacitors.

[0008] One aspect of the present disclosure relates to an electrode for a solid electrolytic capacitor, comprising a substrate containing a valve-acting metal, a first dielectric layer covering at least a portion of the surface of the substrate, and a second dielectric layer covering at least a portion of the surface of the first dielectric layer, wherein the first dielectric layer contains a composite oxide containing titanium, and the second dielectric layer contains at least one selected from the group consisting of aluminum oxide and hafnium oxide, and the thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer.

[0009] Another aspect of this disclosure relates to a solid electrolytic capacitor comprising the electrodes described above and a conductive polymer covering at least a portion of the second dielectric layer of the electrodes.

[0010] A further aspect of this disclosure relates to a method for manufacturing electrodes for solid electrolytic capacitors, comprising the steps of: preparing a substrate containing a valve-acting metal; forming a first dielectric layer covering at least a portion of the surface of the substrate; and forming a second dielectric layer covering at least a portion of the surface of the first dielectric layer, wherein the first dielectric layer comprises a composite oxide containing titanium, and the second dielectric layer comprises at least one selected from the group consisting of aluminum oxide and hafnium oxide, and the thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer.

[0011] According to this disclosure, the performance and reliability of solid electrolytic capacitors can be improved.

[0012] While novel features of the present invention are described in the appended claims, the present invention, both in terms of its structure and content, will be better understood by the following detailed description in conjunction with the drawings, in conjunction with other objects and features of the present invention.

[0013] This is a schematic cross-sectional view of a main part showing an example of an electrode for a solid electrolytic capacitor according to one embodiment of the present disclosure. This is a schematic cross-sectional view showing a solid electrolytic capacitor according to an embodiment of the present disclosure.

[0014] 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 materials may be applied as long as the effects of this disclosure are obtained. 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 are given as examples for numerical values ​​of specific physical properties or conditions, 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. When multiple materials are given as examples, one of them may be selected and used alone, or two or more may be used in combination.

[0015] [Electrodes for Solid Electrolytic Capacitors] An electrode according to the embodiment of this disclosure is used in a solid electrolytic capacitor and comprises a substrate containing a valve-acting metal, a first dielectric layer covering at least a portion of the surface of the substrate, and a second dielectric layer covering at least a portion of the surface of the first dielectric layer. The first dielectric layer contains a composite oxide containing titanium (Ti) (hereinafter also referred to as a Ti-based composite oxide). The second dielectric layer contains at least one selected from the group consisting of aluminum (Al) oxide and hafnium (Hf) oxide. The thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer. Hereinafter, when the substrate is a metal foil containing a valve-acting metal, the electrode may be referred to as an "electrode foil" or "electrode body". When the substrate is a porous body (sintered body) containing a valve-acting metal, the electrode may be referred to as an "electrode body".

[0016] To increase capacity, the dielectric layer material is made of Ti oxide (TO), which has a high relative permittivity. ｘ While it is conceivable to use ), in the case of Ti oxide, leakage current (LC) tends to increase in both low-temperature and high-temperature environments. By using a Ti-based composite oxide as the dielectric layer material, it is possible to increase the capacity and reduce leakage current in low-temperature environments (near room temperature), but leakage current may still increase in high-temperature environments (for example, above 80°C or 90°C).

[0017] In contrast, this disclosure makes it possible to simultaneously achieve increased capacitance and reduced leakage current in high-temperature environments in a solid electrolytic capacitor by forming the second dielectric layer on the surface of the first dielectric layer containing a Ti-based composite oxide. This significantly improves the performance and reliability of the solid electrolytic capacitor.

[0018] The detailed reasons for the suppression of leakage current increase under high-temperature conditions described above are unclear, but the following is speculated. In the case of Ti-based composite oxides, compared to Ti oxides, crystallization is difficult and the interatomic distance is large (bond energy is small), so oxygen vacancies are easily generated. Under normal temperature conditions, water is adsorbed at the vacancy sites, but under high-temperature conditions, water is released from the vacancy sites, causing oxygen vacancies to become apparent on the surface of the dielectric layer, thus increasing the leakage current under high-temperature conditions. In this disclosure, by forming the above-mentioned second dielectric layer on the surface of the first dielectric layer containing a Ti-based composite oxide, the generation of oxygen vacancies on the surface of the first dielectric layer is suppressed, and therefore the increase in leakage current under high temperatures is presumed to be significantly suppressed. It is presumed that the second dielectric layer is less permeable to water, has high insulating properties, or has short interatomic distances and is dense, which contribute to the suppression of leakage current increase under high temperatures.

[0019] (First Dielectric Layer) The first dielectric layer contains a Ti-based composite oxide. This allows for increased capacity. The Ti-based composite oxide is a composite oxide of Ti and another metal element M other than Ti (Ti-M-O ｘ In Ti-based composite oxides, Ti and the metal element M are mixed together, and the oxide of Ti (TiO ｘ ) and oxides of metal element M (MO ｘ ) and are mixed together. Metal element M (oxide of metal element M) may be one type or two or more types. Ti-M-O ｘ The molar ratio of Ti / M in the composite oxide may be, for example, 1.5 or more and 15 or less, 2 or more and 10 or less, or 1.5 or more and 8 or less.

[0020] By appropriately selecting the metal element M, the capacitance, breakdown voltage resistance, etc. can be further enhanced, and the CV index described later can be improved. From the viewpoints of increasing the capacitance, improving the breakdown voltage resistance, and reducing the leakage current, the Ti-based composite oxide preferably contains at least one selected from the group consisting of zinc (Zn), silicon (Si), and aluminum (Al). That is, the metal element M is preferably at least one selected from the group consisting of Zn, Si, and Al. From the viewpoint of improving the relative permittivity, Zn is more preferable. From the viewpoint of improving the breakdown voltage resistance, Si is more preferable.

[0021] Examples of the composite oxide include a composite oxide of Ti and Zn (Ti-Zn-O ｘ ), a composite oxide of Ti and Si (Ti-Si-O ｘ ), a composite oxide of Ti and Al (Ti-Al-O ｘ ), etc. For example, a composite oxide in which TiO ２ and at least one oxide selected from the group consisting of ZnO, SiO ２ , and Al ２ O ３ are mixed may also be used.

[0022] (Second dielectric layer) The second dielectric layer contains at least one selected from the group consisting of an oxide of Al (AlO ｘ ) and an oxide of Hf (HfO ｘ ). Thereby, an increase in the leakage current in a high-temperature environment when a dielectric layer containing a Ti-based composite oxide is provided is significantly suppressed. From the viewpoints of cost reduction, improvement of breakdown voltage resistance, etc., an oxide of Al is preferable. From the viewpoint of improving the relative permittivity, an oxide of Hf is preferable. The second dielectric layer may contain both an oxide of Al and an oxide of Hf. In this case, the oxide of Al and the oxide of Hf may be mixed with each other, or may be formed in layers respectively.

[0023] From the viewpoint of reducing the leakage current at high temperatures, the second dielectric layer preferably does not substantially contain Ti (an oxide of Ti). Not substantially containing Ti means that the amount of Ti is less than the detection limit in energy dispersive X-ray spectroscopy (EDX) analysis.

[0024] The thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer. This allows for simultaneous and efficient achievement of high capacitance using the first dielectric layer and low LC (electrical capacitance) in high-temperature environments using the second dielectric layer.

[0025] From the viewpoint of reducing LC, T2 / T1 may be 0.05 or more, 0.1 or more, or 0.15 or more. From the viewpoint of increasing capacity, T2 / T1 may be less than 1, 0.8 or less, 0.6 or less, 0.4 or less, 0.25 or less, or 0.15 or less. For example, T2 / T1 may be 0.05 or more, less than 1, 0.1 or more, or 0.8 or less.

[0026] The thickness T1 of the first dielectric layer may be, for example, 1 nm or more and 20 nm or less, or greater than 4 nm and 20 nm or less.

[0027] The thickness T2 of the second dielectric layer is preferably 1 nm or more and 4 nm or less. When the thickness T2 is 1 nm or more, LC is easily reduced in high-temperature environments. When the thickness T2 is 4 nm or less, the thinness of the second dielectric layer makes it easier to increase the capacitance of the first dielectric layer.

[0028] The first dielectric layer and the second dielectric layer can be identified as follows: A cross-sectional image (including the porous portion) of the area near the surface of the electrode foil is obtained using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Elemental mapping is performed using energy-dispersive X-ray spectroscopy (EDX) analysis with this image. Using the above image, the regions of the metallic structure constituting the substrate (metal foil) and the regions of the metal oxide constituting the first dielectric layer and the second dielectric layer are distinguished. For example, the two regions can be distinguished by binarization of the image. In the elemental mapping, a region of the metal oxide where Ti and the metal element M are mixed and distributed along the surface of the substrate is identified and designated as the first dielectric layer. A region where at least one of Al and Hf is distributed along the surface of the first dielectric layer is identified and designated as the second dielectric layer.

[0029] The thickness T1 of the first dielectric layer is determined by measuring the thickness at any 10 locations on the first dielectric layer as confirmed above and calculating the average value of these measurements. The thickness T2 of the second dielectric layer is determined in the same manner.

[0030] Figure 1 is a schematic cross-sectional view of a key part of an example of an electrode for a solid electrolytic capacitor according to an embodiment of the present disclosure. Figure 1 shows a cross-section of the surface portion of the electrode foil. In the figure, P is a pit (or pore) of the porous portion 112, D is the thickness of the porous portion 112, T1 is the thickness of the first dielectric layer 121, and T2 is the thickness of the second dielectric layer 122. The electrode according to the embodiment of the present disclosure is not limited thereto.

[0031] The electrode foil 100 (anodic foil) comprises a substrate 110 containing a valve-acting metal and a dielectric layer 120 covering at least a portion of the substrate 110. The first dielectric layer 121 comprises a first dielectric layer 121 covering at least a portion of the surface of the substrate 110 and a second dielectric layer 122 covering at least a portion of the surface of the first dielectric layer 121. The first dielectric layer 121 contains a composite oxide including titanium. The second dielectric layer 122 contains at least one selected from the group consisting of aluminum oxide and hafnium oxide. The thickness T2 of the second dielectric layer 122 is smaller than the thickness T1 of the first dielectric layer 121.

[0032] The substrate 110 is a metal foil having a surface roughened by etching or the like, and has a core portion 111 and a porous portion 112. The porous portion 112 has a large number of pits P. The first dielectric layer 121 and the second dielectric layer 122 are formed to cover the outer surface of the porous portion 112 and the inner wall surface of the pits P.

[0033] [Method for Manufacturing Electrodes for Solid Electrolytic Capacitors] A method for manufacturing electrodes for solid electrolytic capacitors according to the embodiment of the present disclosure includes the steps of: preparing a substrate containing a valve-acting metal; forming a first dielectric layer covering at least a portion of the surface of the substrate; and forming a second dielectric layer covering at least a portion of the surface of the first dielectric layer. The first dielectric layer contains a composite oxide containing titanium, and the second dielectric layer contains at least one selected from the group consisting of aluminum oxide and hafnium oxide, and the thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer.

[0034] (Preparation process for the base material) The base material contains a valve metal. The valve metal may include, for example, at least one selected from the group consisting of tantalum, niobium, and aluminum. The base material may include an alloy containing a valve metal, or a compound containing a valve metal.

[0035] The substrate is, for example, foil, and may be a metal foil. The thickness of the metal foil is, for example, 15 μm or more and 300 μm or less. At least a part of the surface of the metal foil may be roughened by etching or the like. The metal foil with a roughened surface comprises a porous portion and a core portion continuous with the porous portion. In this case, the dielectric layer is formed to cover the metal skeleton constituting the porous portion. The porous portion has a large number of pits. The most frequent pore diameter of the pits is not particularly limited, but is, for example, 50 nm or more and 2000 nm or less, as it is easy to obtain a large surface area and the dielectric layer is easily formed deep in the pits. The most frequent pore diameter of the pits is the most frequent pore diameter in the volume-based pore diameter distribution measured by a mercury porosimeter. The thickness D per side of the porous portion is not particularly limited, but from the viewpoint of securing a large surface area and maintaining the strength of the electrode foil, it may be, for example, 1 / 10 or more and 4 / 10 or less of the total thickness of the metal foil. The thickness D on one side of the porous portion can be determined by measuring the thickness at any 10 points using a cross-sectional image of the metal foil taken with a SEM or TEM, and calculating the average value of those measurements.

[0036] Alternatively, a porous body (sintered body) obtained by sintering particles containing a valve-acting metal (e.g., tantalum) may be used as the base material. A portion of a metal lead member (e.g., an anode wire connected to an anode lead terminal) is embedded in the porous body.

[0037] (Dielectric layer formation process) The dielectric layer may be formed by a vapor phase method. Examples of vapor phase methods include atomic layer deposition (ALD), chemical vapor deposition (CVD), and physical vapor deposition (PVD). Alternatively, the dielectric layer may be formed by a liquid phase method. Examples of liquid phase methods include the sol-gel method. The method for forming the first dielectric layer may be the same as or different from the method for forming the second dielectric layer. The first and second dielectric layers may each be formed by a vapor phase method (e.g., ALD).

[0038] Among the various methods for forming the dielectric layer, the ALD method is preferred. The ALD method facilitates the formation of a Ti-based composite oxide film and allows for easy control of the molar ratio of Ti to the metal element M contained in the film. Furthermore, it facilitates easy control of film thickness and the formation of a dense film. When the substrate has a porous surface, it is easy to form the dielectric film deep into the pits (pores) of the porous portion.

[0039] In the ALD method, a dielectric layer can be formed on the surface of the object by alternately supplying a raw material gas containing metal element A and an oxidizer to a reaction chamber where the object is placed. In the ALD method, self-limiting action is at work, so metal element A is deposited on the surface of the object in atomic layer units. Therefore, the thickness T of the dielectric layer can be easily controlled by the number of cycles, which consists of supplying the raw material gas, purging the raw material gas, supplying the oxidizer, and purging the oxidizer.

[0040] Examples of oxidizing agents include water, oxygen, and ozone. The oxidizing agent may also be supplied to the reaction chamber as a plasma using the oxidizing agent as a raw material.

[0041] Metal element A is supplied to the reaction chamber as a precursor gas (raw material gas) containing metal element A. The precursor is, for example, an organometallic compound containing metal element A, which makes metal element A more readily adsorbed onto the target material. Various organometallic compounds conventionally used in the ALD method can be used as precursors.

[0042] Metal element A may be used alone or in combination of two or more types. When using a combination of two or more types of metal element A, the type of precursor supplied to the reaction chamber may be changed depending on the cycle, thereby changing the type of metal element A deposited at the atomic layer level. In this case, a precursor containing two or more types of metal element A may also be used. In this case, a dielectric layer (a layer of composite oxide) containing oxides of two or more types of metal element A can be formed.

[0043] When forming the first dielectric layer, for example, a precursor containing Ti and a precursor containing a metal element M (e.g., Zn, Si, or Al) may be prepared, and the type of precursor supplied to the reaction chamber may be changed by changing the type of metal deposited at the atomic layer level depending on the cycle. In this case, a dielectric layer (a composite oxide layer) in which Ti oxide and metal element M oxide are mixed can be formed. In the ALD method, the mixing ratio of Ti oxide and metal element M oxide in the composite oxide layer is easy to control.

[0044] When forming the second dielectric layer, it is sufficient to prepare at least one of a precursor containing Al and a precursor containing Hf.

[0045] Examples of Ti-containing precursors include bis(t-butylcyclopentadienyl)titanium(IV) dichloride(C) 18 H 26 C l2Examples include titanium (Ti), tetrakis(dimethylamino)titanium (IV) ([(CH3)2N]4Ti), tetrakis(diethylamino)titanium (IV) ([(C2H5)2N]4Ti), tetrakis(ethylmethylamino)titanium (IV) (Ti[N(C2H5)(CH3)]4), titanium (IV) (diisopropoxide-bis(2,2,6,6-tetramethyl-3,5-heptanedionate(Ti[OCC(CH3)3CHCOC(CH3)3]2(OC3H7)2), titanium tetrachloride (TiCl4), titanium (IV) isopropoxide (Ti[OCH(CH3)2]4), titanium (IV) ethoxide (Ti[O(C2H5)]4), etc.

[0046] Examples of precursors containing Zn include diethylzinc (Zn(CH4)). ２ CH ３ ) ２ ), bis(6-ethyl-2,2-dimethyl-3,5-decandionato) zinc (Zn(EDMDD) ２ ), octadiona zinc (Zn(OD ２ )) is one example of an Al-containing precursor. For example, trimethylaluminum ((CH4) ３ ) ３ Examples include Al.

[0047] Examples of silicon-containing precursors include N-sec-butyl(trimethylsilyl)amine (C ７ H １９ NSi), 1,3-diethyl-1,1,3,3-tetramethyldisilazane (C ８ H ２３ NSi ２ ), 2,4,6,8,10-pentamethylcyclopentasiloxane ((CH ３ SiHO) ５ ), pentamethyldisilane ((CH ３ ) ３ SiSi (CH ３ ) ２ H), tris(dimethylamino)silane ([(CH ３ ) ２ N] ３ SiH), Tris(isopropoxy)silanol ([(H ３ C) ２ CHO]３ SiO), chloropentanemethyldisilane ((CH ３ ) ３ SiSi (CH ３ ) ２ Cl), dichlorosilane (SiH ２ Cl ２ ), tridimethylaminosilane (Si[N(CH ３ ) ２ ] ４ ), tetraethylsilane (Si(C ２ H ５ ) ４ ), tetramethylsilane (Si(CH ３ ) ４ ), tetraethoxysilane (Si(OC ２ H ５ ) ４ ), dodecamethylcyclohexasilane ((Si(CH ３ ) ２ ) ６ ), silicon tetrachloride (SiCl ４ ), silicon tetrabromide (SiBr ４ Examples include:

[0048] Examples of Hf-containing precursors include hafnium tetrachloride (HfCl ４ ), tetrakisdimethylaminohafnium (Hf[N(CH ３ ) ２ ] ４ ), tetrakisethylmethylaminohafnium (Hf[N(C) ２ H ５ ) (CH ３ )] ４ ), tetrakisdiethylaminohafnium (Hf[N(C) ２ H ５ ) ２ ] ４ ), hafnium-t-butoxide (Hf[OC(CH) ３ ) ３ ] ４ Examples include:

[0049] [Solid Electrolytic Capacitor] A solid electrolytic capacitor according to the embodiment of this disclosure comprises the above-mentioned electrodes and a conductive polymer (solid electrolyte) covering at least a portion of the second dielectric layer. The conductive polymer (solid electrolyte) may be in layer form. The above-mentioned electrodes are, for example, electrode foils or electrode bodies and can be used as anode foils or anode bodies. The method for forming the conductive polymer covering the dielectric layer can be a known method and is not particularly limited.

[0050] Examples of conductive polymers include π-conjugated polymers. Examples of conductive polymers include polypyrrole, polythiophene, polyfuran, and polyaniline. Conductive polymers may be used individually, in combination of two or more types, or as copolymers of two or more monomers. The weight-average molecular weight of the conductive polymer is, for example, 1,000 to 100,000.

[0051] In this specification, polypyrrole, polythiophene, polyfuran, polyaniline, etc., refer to polymers that have polypyrrole, polythiophene, polyfuran, polyaniline, etc. as their basic skeletons. Therefore, polypyrrole, polythiophene, polyfuran, polyaniline, etc., may also include their respective derivatives. For example, polythiophene includes poly(3,4-ethylenedioxythiophene) (PEDOT), etc.

[0052] The conductive polymer may be doped with a dopant. Examples of dopants include polystyrene sulfonic acid (PSS). The solid electrolyte may further contain additives as needed.

[0053] (Capacitor element) A solid electrolytic capacitor comprises a capacitor element. The capacitor element may comprise, for example, the above-mentioned electrode (anode foil or anode body), a conductive polymer layer (solid electrolyte layer), and a cathode lead layer. The cathode lead layer may comprise, for example, a carbon layer covering at least a portion of the surface of the solid electrolyte layer and a silver paste layer covering at least a portion of the surface of the carbon layer.

[0054] Furthermore, the capacitor element may also comprise an electrode group including the above-mentioned electrode foil (anode foil) and cathode foil, and a conductive polymer. The electrode group may be a wound body in which the anode foil and cathode foil are wound. For example, a metal foil (or a metal foil having a dielectric layer on its surface) as exemplified in the above-mentioned substrate can be used for the cathode foil. A separator may be placed between the anode foil and the cathode foil. The separator is not particularly limited, and for example, a nonwoven fabric containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid) may be used.

[0055] Figure 2 is a schematic cross-sectional view showing an example of a solid electrolytic capacitor according to one embodiment of the present disclosure.

[0056] The solid electrolytic capacitor 1 comprises a capacitor element 2, an outer casing 3 that encloses the capacitor element 2, and an anode lead terminal 4 and a cathode lead terminal 5, each at least partially exposed to the outside of the outer casing 3. The outer casing 3 has a substantially rectangular parallelepiped shape, and the solid electrolytic capacitor 1 also has a substantially rectangular parallelepiped shape. The capacitor element 2 comprises an anode portion 6 (metal foil), a dielectric layer 7 covering the anode portion 6, and a cathode portion 8 covering the dielectric layer 7. The anode portion 6, which has the dielectric layer 7 on its surface, is the electrode described above. The dielectric layer 7 has the first dielectric layer and the second dielectric layer described above.

[0057] The anode portion 6 includes a region facing the cathode portion 8 and a region that does not face it. In the region of the anode portion 6 that does not face the cathode portion 8, an insulating separation layer 13 is formed in a band-like manner to cover the surface of the anode portion 6 adjacent to the cathode portion 8, thereby restricting contact between the cathode portion 8 and the anode portion 6. In the other portion of the region of the anode portion 6 that does not face the cathode portion 8, it is electrically connected to the anode lead terminal 4 by welding. The surface of the anode portion 6 (metal foil) is usually roughened, but the surface of the region that does not face the cathode portion 8 does not need to be roughened.

[0058] The cathode section 8 comprises a solid electrolyte layer 9 covering at least a portion of the dielectric layer 7, and a cathode extraction layer 10 covering the solid electrolyte layer 9. The cathode extraction layer 10 has a carbon layer 11 and a silver paste layer 12. The cathode lead terminal 5 is electrically connected to the cathode section 8 via an adhesive layer 14 formed of a conductive adhesive.

[0059] The carbon layer 11 includes, for example, carbon particles and silver. The silver paste layer 12 includes, for example, silver particles and a binder. The binder is not particularly limited, but a cured product of a curable resin is preferred. Examples of curable resins include thermosetting resins such as epoxy resins.

[0060] The solid electrolyte layer 9 contains a conductive polymer and may optionally contain a dopant or the like. Examples of conductive polymers that can be used include polypyrrole, polythiophene, polyaniline, and their derivatives. The solid electrolyte layer 9 can be formed, for example, by coating or impregnating the surface of the anode portion 6 (dielectric layer 7) with a processing solution (solution or dispersion of the conductive polymer) containing the conductive polymer.

[0061] The outer casing 3 is a resin outer casing, which preferably contains a cured product of a curable resin composition, and may also contain a thermoplastic resin or a composition containing the same. Examples of curable resins include thermosetting resins such as epoxy resins.

[0062] [Note] The above description of embodiments discloses the following technologies. (Technology 1) An electrode used in a solid electrolytic capacitor, comprising: a substrate containing a valve-acting metal; a first dielectric layer covering at least a portion of the surface of the substrate; and a second dielectric layer covering at least a portion of the surface of the first dielectric layer, wherein the first dielectric layer contains a composite oxide containing titanium, and the second dielectric layer contains at least one selected from the group consisting of aluminum oxide and hafnium oxide, and the thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer. (Technology 2) The electrode according to Technology 1, wherein the composite oxide contains at least one selected from the group consisting of zinc, silicon, and aluminum. (Technology 3) The electrode according to Technology 1 or 2, wherein the ratio of the thickness T2 of the second dielectric layer to the thickness T1 of the first dielectric layer: T2 / T1 is 0.05 or more and less than 1. (Technology 4) The electrode according to any one of Technology 1 to 3, wherein the thickness T2 of the second dielectric layer is 1 nm or more and 4 nm or less. (Technology 5) A solid electrolytic capacitor comprising an electrode according to any one of Technologies 1 to 4, and a conductive polymer covering at least a portion of the second dielectric layer of the electrode. (Technology 6) A method for manufacturing an electrode used in a solid electrolytic capacitor, comprising the steps of: preparing a substrate containing a valve-acting metal; forming a first dielectric layer covering at least a portion of the surface of the substrate; and forming a second dielectric layer covering at least a portion of the surface of the first dielectric layer, wherein the first dielectric layer contains a composite oxide containing titanium, and the second dielectric layer contains at least one selected from the group consisting of aluminum oxide and hafnium oxide, and the thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer. (Technology 7) A method for manufacturing an electrode according to Technology 6, wherein the first dielectric layer and the second dielectric layer are formed by a vapor phase method. (Technology 8) A method for manufacturing an electrode according to Technology 6 or 7, wherein the composite oxide contains at least one selected from the group consisting of zinc, silicon, and aluminum.(Technical 9) The method for manufacturing an electrode according to any one of Technical 6 to 8, wherein the ratio of the thickness T2 of the second dielectric layer to the thickness T1 of the first dielectric layer: T2 / T1 is 0.05 or more and less than 1. (Technical 10) The method for manufacturing an electrode according to any one of Technical 6 to 9, wherein the thickness T2 of the second dielectric layer is 1 nm or more and 4 nm or less.

[0063] [Examples] The present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to these examples.

[0064] 《Anode Foil a1-a3》 (Preparation of Anode Foil) (First Step: Preparation of Substrate) An Al foil with a thickness of 130 μm was prepared, and the surface of the Al foil was roughened by etching to form a porous portion (thickness D per side: 50 μm). In this way, a substrate was obtained.

[0065] (Second step: Formation of the first dielectric layer) ALD method (Temperature: 150°C, Precursor: Ti-containing precursor and Zn-containing precursor, Oxidizing agent: O ３ A first dielectric layer (Ti-Zn-O) is formed on the surface of the substrate by a pressure of 1 Pa. ｘ It formed a layer.

[0066] As a Ti-containing precursor, tetrakis(dimethylamino)titanium (IV) is used, and as a Zn-containing precursor, diethylzinc (Zn(C) ２ H ５ ) ２ A composite oxide (Ti-Zn-O) was used. Six cycles constituted one set, with five cycles in each set supplied with a Ti-containing precursor and one cycle supplied with a Zn-containing precursor. In this way, a composite oxide (Ti-Zn-O) in which Ti and Zn are mixed in a molar ratio of 5:1 was obtained. ｘ A layer of the first dielectric layer was formed. The number of cycles (number of sets) was adjusted as appropriate to obtain the thickness T1 of the first dielectric layer as shown in Table 1.

[0067] (Third step: Formation of the second dielectric layer) ALD method (Temperature: 150°C, Precursor: Al-containing precursor, Oxidizing agent: O ３ At a pressure of 1 Pa, Al oxide (AlO2) is formed on the surface of the first dielectric layer as a second dielectric layer. ｘA layer of ( ) was formed. Trimethylaluminum was used as the precursor containing Al. The cycle number was appropriately adjusted so that the thickness T2 of the second dielectric layer was the value shown in Table 1.

[0068] A substrate having a first dielectric layer and a second dielectric layer on its surface was cut into a predetermined size to obtain anode foils a1 to a3.

[0069] 《Anode foil b1》 In the second step, by the ALD method (temperature: 150 °C, precursor: a precursor containing Al, oxidant: O ３ , pressure: 1 Pa), a layer of aluminum oxide (AlO ｘ ) was formed as the first dielectric layer on the surface of the substrate. Trimethylaluminum was used as the precursor containing Al. The cycle number was appropriately adjusted so that the thickness T1 of the first dielectric layer was the value shown in Table 1. The third step was not performed and the second dielectric layer was not formed.

[0070] Except as described above, an anode foil b1 was produced in the same manner as the anode foil a1.

[0071] 《Anode foil b2》 An anode foil b2 was produced in the same manner as the anode foil a1, except that the third step was not performed and the second dielectric layer was not formed.

[0072] 《Anode foil b3》 In the second step, by the ALD method (temperature: 150 °C, precursor: a precursor containing Al, oxidant: O ３ , pressure: 1 Pa), a layer of aluminum oxide (AlO ｘ ) was formed as the first dielectric layer on the surface of the substrate. Trimethylaluminum was used as the precursor containing Al. The cycle number was appropriately adjusted so that the thickness T1 of the first dielectric layer was the value shown in Table 1.

[0073] In the third step, by the ALD method (temperature: 150 °C, precursor: a precursor containing Ti and a precursor containing Zn, oxidant: O ３ , pressure: 1 Pa), a second dielectric layer (Ti-Zn-O ｘ layer) was formed on the surface of the first dielectric layer.

[0074] Tetrakis(dimethylamino)titanium(IV) was used as the precursor containing Ti, and diethylzinc (Zn(C ２ H５ ) ２ ) was used. Taking 6 cycles as one set, 5 cycles per set were supplied with a precursor containing Ti, and 1 cycle was supplied with a precursor containing Zn. In this way, a composite oxide (Ti-Zn-O ｘ ) in which Ti and Zn are mixed at a molar ratio of 5:1 was formed. The cycle number (number of sets) was appropriately adjusted so that the thickness T2 of the second dielectric layer was the value shown in Table 1.

[0075] Except for the above, an anode foil b3 was produced in the same manner as the anode foil a1.

[0076] [Evaluation] Using each of the anode foils produced above, a simple dry evaluation was performed. Specifically, carbon was applied to the surface of the anode foil and fired to form a carbon layer, silver paste was applied to the surface of the carbon layer and fired to form a silver paste layer. In this way, a cathode lead-out layer (C / Ag electrode) was formed on the surface of the anode foil, and a device for evaluation was constructed. For this device, IV measurement was performed using a semiconductor parameter analyzer. Note that A1 to A3 and B1 to B3 in the table are devices including anode foils a1 to a3 and b1 to b3, respectively. The voltage was applied while increasing the voltage at a rate of 1 V / second in an environment of 20°C or 100°C.

[0077] (Capacitance) In an environment of 20°C, the capacitance C at a frequency of 120 Hz was measured using an LCR meter for four-terminal measurement.

[0078] (Breakdown voltage) In an environment of 20°C, a voltage was applied while increasing the voltage at a rate of 1 V / second, and the voltage at which an overcurrent of 0.5 A flows was measured as the breakdown voltage V.

[0079] (CV index) The CV index was obtained by multiplying the capacitance C by the breakdown voltage V.

[0080] (Leakage current) In an environment of 20°C, a voltage was applied while increasing the voltage at a rate of 1 V / second, and the current at the time when the voltage reached 1 V was measured, and the current value was obtained as the leakage current (room temperature LC). Also, in an environment of 100°C, the current was measured in the same manner as above, and the current value was obtained as the leakage current (high temperature LC).

[0081] (LC Index) The ratio of high-temperature LC to room-temperature LC: (high-temperature LC / room-temperature LC) was calculated as the LC index.

[0082] The evaluation results are shown in Table 1. In Table 1, the CV index and LC index are expressed as relative values ​​with the CV index and LC index of device B1 set to 100. In Table 1, anode foils a1 to a3 are electrode foils of the example, and anode foils b1 to b3 are electrode foils of the comparative example.

[0083]

[0084] Devices A1 to A3 (anodic foils a1 to a3) yielded a capacitance approximately 1.2 to 1.7 times higher than that of device B1, resulting in a high CV index and a low LC index.

[0085] In device B2 (anodic foil b2), the formation of a first dielectric layer containing a high dielectric constant Ti-containing composite oxide resulted in higher capacitance and CV index compared to device B1 (anodic foil b1). However, the absence of a second dielectric layer led to a significant increase in the LC index.

[0086] In device B3 (anodic foil b3), which forms an AlOx layer as the underlayer of a composite oxide layer containing Ti, the capacitance and breakdown voltage were lower than in device B2 (anodic foil b2), and the CV index was lower. Furthermore, the improvement in the LC index for device B3 (anodic foil b3) compared to device B2 (anodic foil b2) was also smaller.

[0087] For anode foils a1, b1, and b2, a polypyrrole layer (solid electrolyte layer) was formed on the surface of the anode foil, and a cathode layer was formed on the surface of the solid electrolyte layer to constitute a solid electrolytic capacitor. When the same evaluation as above was performed, it showed the same trend as devices A1, B1, and B2.

[0088] The electrode according to this disclosure is suitably used in a solid electrolytic capacitor that includes a capacitor element containing a conductive polymer.

[0089] 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.

[0090] 1: Solid electrolytic capacitor, 2: Capacitor element, 3: Outer casing, 4: Anode lead terminal, 5: Cathode lead terminal, 6: Anode section, 7: Dielectric layer, 8: Cathode section, 9: Solid electrolyte layer, 10: Cathode lead layer, 11: Carbon layer, 12: Silver paste layer, 13: Separation layer, 14: Adhesive layer, 100: Electrode foil, 110: Substrate, 120: Dielectric layer, 121: First dielectric layer, 122: Second dielectric layer

Claims

1. An electrode used in a solid electrolytic capacitor, comprising: a substrate containing a valve-acting metal; a first dielectric layer covering at least a portion of the surface of the substrate; and a second dielectric layer covering at least a portion of the surface of the first dielectric layer, wherein the first dielectric layer contains a composite oxide containing titanium, and the second dielectric layer contains at least one selected from the group consisting of aluminum oxide and hafnium oxide, and the thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer.

2. The electrode according to claim 1, wherein the composite oxide comprises at least one selected from the group consisting of zinc, silicon, and aluminum.

3. The electrode according to claim 1, wherein the ratio of the thickness T2 of the second dielectric layer to the thickness T1 of the first dielectric layer: T2 / T1 is 0.05 or more and less than 1.

4. The electrode according to claim 1, wherein the thickness T2 of the second dielectric layer is 1 nm or more and 4 nm or less.

5. A solid electrolytic capacitor comprising an electrode according to any one of claims 1 to 4, and a conductive polymer covering at least a portion of the second dielectric layer of the electrode.

6. A method for manufacturing electrodes used in solid electrolytic capacitors, comprising the steps of: preparing a substrate containing a valve-acting metal; forming a first dielectric layer covering at least a portion of the surface of the substrate; and forming a second dielectric layer covering at least a portion of the surface of the first dielectric layer, wherein the first dielectric layer contains a composite oxide containing titanium, and the second dielectric layer contains at least one selected from the group consisting of aluminum oxide and hafnium oxide, and the thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer.

7. The method for manufacturing an electrode according to claim 6, wherein the first dielectric layer and the second dielectric layer are formed by a vapor phase method.

8. The method for manufacturing an electrode according to claim 6, wherein the composite oxide comprises at least one selected from the group consisting of zinc, silicon, and aluminum.

9. The method for manufacturing an electrode according to claim 6, wherein the ratio of the thickness T2 of the second dielectric layer to the thickness T1 of the first dielectric layer, T2 / T1, is 0.05 or more and less than 1.

10. The method for manufacturing an electrode according to claim 6, wherein the thickness T2 of the second dielectric layer is 1 nm or more and 4 nm or less.

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