crystalline and manufacturing method

Abstract

This invention provides a capacitor and manufacturing method that exhibit small ESR changes and long lifespan under high-temperature conditions. [Solution] The capacitor comprises an anode made of a valve metal, a dielectric film formed on the surface of the anode, and a cathode layer formed on the dielectric film, facing the anode with the dielectric film in between. The cathode layer comprises a semiconductor layer made of an inorganic semiconductor containing sulfur, formed on the dielectric film, and an extracted cathode formed on the semiconductor layer and facing the anode with the dielectric film and semiconductor layer in between. This capacitor is manufactured by a manufacturing method that includes an anode formation step for forming the anode, and a cathode formation step for forming the cathode layer, which includes a semiconductor layer formation step and an extracted cathode formation step. In the semiconductor layer formation step, a semiconductor layer is formed. In the extracted cathode formation step, an extracted cathode is arranged.

Description

[Technical Field]

[0001] The present invention relates to a capacitor that obtains capacitance through the dielectric polarization effect of a dielectric film and stores and discharges electric charge, and a method for manufacturing such a capacitor. [Background technology]

[0002] A capacitor is a passive element that stores and discharges electric charge by obtaining capacitance through the dielectric polarization effect of a dielectric film. In a capacitor, a dielectric film is formed on the surface of the anode body, which is made of valve-acting metal, by anodizing or other means, and the anode body and cathode layer are facing each other with this dielectric film in between.

[0003] To increase the contact area between the dielectric film and the cathode layer, and thereby increase the capacitance of the capacitor, the cathode layer comprises an extracted cathode and a solid electrolyte layer. The solid electrolyte layer is formed of electrolyte particles, and because the solid electrolyte layer fits into the irregularities of the anode body and adheres tightly, the contact area between the dielectric film and the cathode layer is increased. In other words, the solid electrolyte layer functions as a true cathode.

[0004] Known electrolyte particles include manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes. In recent years, conductive polymer particles derived from monomers with π-conjugated double bonds have attracted attention as electrolyte particles. Conductive polymer particles use acid compounds such as polyanions as dopants, and also have substructures within the monomer molecule that act as dopants. In particular, polyethylene dioxythiophene (PEDOT) doped with polystyrene sulfonic acid (PSS) has high electrical conductivity and contributes to the low ESR of capacitors, and is rapidly gaining popularity (see, for example, Patent Document 1).

[0005] Capacitors using PEDOT doped with PSS (hereinafter referred to as PEDOT:PSS) have a poorer repair function for defects in the dielectric film compared to electrolytic capacitors. Therefore, hybrid type capacitors that use PEDOT:PSS and an electrolyte in combination are also becoming popular in order to enhance the repair function of defects in the dielectric film (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2011-60980 [Patent Document 2] Japanese Patent Publication No. 2015-228424 [Overview of the project] [Problems that the invention aims to solve]

[0007] Polystyrene sulfonic acid-doped polyethylenedioxythiophene (hereinafter referred to as PEDOT:PSS) has the following problems. First, at high temperatures such as 150°C, the bonds between polyethylenedioxythiophene molecules are easily broken by oxidation. This oxidative degradation shortens the molecular chain length of PEDOT, reducing the electrical conductivity of PEDOT:PSS. Therefore, at high temperatures, capacitors using PEDOT:PSS experience increased ESR.

[0008] Furthermore, in the case of hybrid capacitors, under high-temperature environments such as 150°C, attacks on polystyrene sulfonic acid by the cationic components of the electrolyte occur frequently. This attack causes dedoping, reducing the electrical conductivity of PEDOT:PSS. Therefore, hybrid capacitors using PEDOT:PSS are further affected by increased ESR under high-temperature environments.

[0009] Capacitors intended for use in high-temperature environments are expected to exhibit small ESR changes and have a long lifespan.

[0010] This invention was proposed to solve the above problems, and its objective is to provide a capacitor with small ESR changes and long lifespan in high-temperature environments, and a method for manufacturing the same. [Means for solving the problem]

[0011] To solve the above problems, the capacitor of this embodiment comprises an anode made of a valve metal, a dielectric film formed on the surface of the anode, and a cathode layer formed on the dielectric film, facing the anode with the dielectric film in between. The cathode layer comprises a semiconductor layer made of an inorganic semiconductor containing sulfur, formed on the dielectric film, and an extraction cathode formed on the semiconductor layer, facing the anode with the dielectric film and the semiconductor layer in between.

[0012] The inorganic semiconductor may further contain copper.

[0013] The inorganic semiconductor may further contain tin.

[0014] The inorganic semiconductor may further contain zinc or aluminum.

[0015] The inorganic semiconductor may be a compound whose molecular formula is Cu2SnS3 or Cu3SnS4.

[0016] The inorganic semiconductor may be a compound represented by the molecular formula CoNi2S4.

[0017] The inorganic semiconductor may further contain zinc.

[0018] The system may further include a resistive layer interposed between the dielectric film and the semiconductor layer, which contains silicon dioxide or sorbitol.

[0019] Also, in order to solve the above problems, the method for manufacturing a capacitor according to the present embodiment includes an anode body forming step of forming an anode body made of a valve action metal and having a dielectric film formed on its surface, and a cathode layer forming step of forming a cathode layer facing the anode body with the dielectric film interposed therebetween and formed on the dielectric film. The cathode layer forming step includes a drawn cathode forming step of arranging a drawn cathode facing the anode body, and a semiconductor layer forming step of forming a semiconductor layer made of an inorganic semiconductor containing sulfur on the dielectric film.

[0020] In the semiconductor layer forming step, each material source of the inorganic semiconductor may be mixed in a solvent to prepare a mixed solution, and the mixed solution may be attached to the anode body, the drawn cathode, or both, followed by drying and firing to synthesize the inorganic semiconductor on the dielectric film.

Advantages of the Invention

[0021] According to the present invention, the change in ESR of the capacitor under a high-temperature environment is small and the capacitor has a long lifespan.

Brief Description of the Drawings

[0022] [Figure 1] It is a graph showing the relationship between the operating frequency and the capacitance. [Figure 2] It is a graph showing the relationship between the temperature and the ESR. [Figure 3] It is a graph showing the relationship between the frequency and the capacitance in the ink method and the hydrothermal synthesis slurry method. [Figure 4] It is a graph showing the relationship between the frequency and the ESR in the ink method and the hydrothermal synthesis slurry method.

Embodiments for Carrying Out the Invention

[0023] Hereinafter, the capacitor and its manufacturing method according to the embodiment will be described. Note that the present invention is not limited to the embodiments described below.

[0024] A capacitor is a passive element that stores and discharges electric charge by obtaining capacitance through the dielectric polarization effect of a dielectric film. This capacitor comprises an element. The element includes an anode, a cathode layer, and a dielectric film formed on the surface of the anode and interposed between the anode and the cathode layer. The cathode layer faces the anode with the dielectric film in between and is formed on top of the dielectric film.

[0025] The cathode layer comprises a semiconductor layer and an extracted cathode. The semiconductor layer functions as a true cathode in contact with the dielectric film of the anode. That is, the semiconductor layer is the electrolyte or a conductive polymer such as PEDOT:PSS in an aluminum electrolytic capacitor, and is used in place of these electrolytes or conductive polymers such as PEDOT:PSS. The extracted cathode is located on the opposite side of the anode, with the dielectric film and semiconductor layer in between.

[0026] This capacitor may be a hybrid capacitor that also uses an electrolyte. The electrolyte impregnates the voids in the element and adheres closely to the dielectric film, becoming a true cathode together with the semiconductor layer. When using an electrolyte, a separator may be interposed between the anode and the drawn-out cathode. The separator prevents a short circuit between the anode and the drawn-out cathode and also holds the semiconductor layer and the electrolyte together. However, a separator may be provided even when the electrolyte is not impregnated. If the semiconductor layer maintains its shape on its own and isolates the anode and the drawn-out cathode, the separator can be omitted from the capacitor configuration.

[0027] The semiconductor layer is made of an inorganic semiconductor. Unlike organic semiconductors, which are primarily carbon-based, inorganic semiconductors are composed of inorganic materials. This inorganic semiconductor also contains sulfur and is therefore a sulfide semiconductor. Hereafter, this sulfur-containing inorganic semiconductor will be referred to as a sulfide semiconductor. A capacitor with a sulfide semiconductor as the true cathode has the same capacitance as a solid electrolytic capacitor with a PEDOT:PSS solid electrolyte layer in operation across various frequency bands from low frequencies of around 120 Hz to high frequencies of around 100 kHz. Furthermore, this sulfide semiconductor is in contact with locally present defects in the dielectric film. The sulfide semiconductor in contact with the defects in the dielectric film is destroyed by leakage current and becomes an insulator. The sulfide semiconductor, now an insulator, suppresses the leakage current in the defects of the dielectric film, maintaining the insulating properties of the dielectric film. Therefore, the leakage current of the capacitor is suppressed.

[0028] Furthermore, capacitors using sulfide semiconductors as true cathodes exhibit little change in ESR over time at a temperature of 200°C. On the other hand, solid electrolytic capacitors with a PEDOT:PSS solid electrolyte layer show a more significant deterioration in ESR over time at a temperature of 200°C than capacitors using sulfide semiconductors as true cathodes. Therefore, at a temperature of 200°C, the ESR of capacitors using sulfide semiconductors as true cathodes becomes smaller at an earlier stage than that of solid electrolytic capacitors with a PEDOT:PSS solid electrolyte layer. In other words, capacitors using sulfide semiconductors as true cathodes have a longer lifespan in high-temperature environments.

[0029] As the sulfide semiconductor to be included in the semiconductor layer, a sulfide semiconductor further containing copper is preferred. More preferably, a sulfide semiconductor containing tin, zinc, aluminum, or some or all of these in addition to copper is preferred. For example, as a sulfide semiconductor, a sulfide semiconductor with the general molecular formula Cu α Sn β S γ (α=2~4, β=1, γ=3~4), or general formula Cu α Zn β S γExamples of compounds with the molecular formula (α=2, β=1.5~2.5, γ=2.5~3.5, α+β+γ=7) include those represented by the formula (α=2, β=1.5~2.5, γ=2.5~3.5, α+β+γ=7). Examples of these sulfide semiconductors include compounds with the molecular formulas Cu2SnS3, Cu3SnS4, or Cu2Zn2S3.

[0030] Sulfide semiconductors containing copper and tin may be doped with zinc. For example, Zn-Cu2SnS3 and Zn-Cu3SnS4 can also be mentioned as sulfide semiconductors. Doping with zinc reduces the initial ESR, and further reduces the ESR after being left in a 200°C environment.

[0031] Furthermore, as the sulfide semiconductor to be included in the semiconductor layer, a sulfide semiconductor containing cobalt and nickel in addition to copper is preferable. CoNi2S4 is an example of such a sulfide semiconductor. When CoNi2S4 is used in the semiconductor layer, although this is not the only possible explanation, its crystallinity improves when exposed to high-temperature environments, so the ESR at a temperature of 200°C is actually lower than before exposure to this high-temperature environment.

[0032] The semiconductor layer can be formed in the semiconductor formation process by preparing a slurry containing a sulfide semiconductor, applying the slurry to the anode or extraction cathode, and drying it. The slurry is prepared by dispersing the sulfide semiconductor in a solvent and adding a binder. Examples of binders include styrene-butadiene rubber, polyvinylidene fluoride, or polytetrafluoroethylene. A surfactant may also be used as a binder to improve the dispersibility of the sulfide semiconductor. An example of such a surfactant is 4-(1,1,3,3-tetramethylbutyl)phenyl polyethylene glycol. Solvents include methanol, alcohols such as ethanol and 2-propanol, hydrocarbon solvents, aromatic solvents, amide solvents such as N-methyl-2-pyrrolidone (NMP) and N,N-dimethylformamide (DMF), water, and mixtures thereof.

[0033] The slurry is applied to the anode or drawn-out cathode by slurry casting, doctor blade method, or spray atomization method. After application, the solvent is evaporated by drying. The sulfide semiconductor may be ground using a grinding method such as a bead mill or ball mill to adjust the particle size. Dispersion methods include using a mixer, jet mixing, ultracentrifugation, or ultrasonic treatment. In the dispersion process, the material is subdivided and homogenized and dispersed in the solution.

[0034] Preferably, the sulfide semiconductor is synthesized on the anode, the extraction cathode, or both. A mixture of each material source for the sulfide semiconductor is prepared by mixing them in a solvent. The mixture is applied to the anode, the extraction cathode, or both, and the solvent is evaporated by drying. Then, the sulfide semiconductor is synthesized by calcination. This semiconductor formation process is called the ink process.

[0035] In the ink process, methods for attaching the mixed solution to the anode, the extraction cathode, or both include impregnation, coating, and dropping. Furthermore, the semiconductor formation process that involves preparing and coating a slurry containing a sulfide semiconductor is called the hydrothermal synthesis slurry process. When a semiconductor layer is formed by the ink process, the capacitance of the capacitor is higher and the ESR of the capacitor is lower across a wide frequency range including 40 Hz to 100 kHz, compared to when a semiconductor layer is formed by the hydrothermal synthesis slurry process.

[0036] Here, a thin resistive layer may be interposed between the dielectric film and the semiconductor layer. The resistive layer may contain, for example, silicon dioxide or sorbitol. The semiconductor layer may be applied after forming the resistive layer on the dielectric film of the anode body, or the resistive layer may be formed on the dielectric film of the anode body while the semiconductor layer is applied to the extraction cathode side, and the resistive layer and the semiconductor layer are superimposed facing each other.

[0037] The anode, lead cathode, and separator used in this capacitor can be any known components, including those found in electrolytic capacitors using foil bodies made of various valve metals such as aluminum or tantalum, solid electrolytic capacitors, and conductive polymer electrolytic capacitors such as PEDOT:PSS, without any particular limitations.

[0038] In other words, the anode is a thin plate or foil made of a valve metal. The anode may be formed by stretching the valve metal, or by sintering powder of the valve metal. Furthermore, the anode may be formed by laminating powder of the same or different valve metal onto the surface of a stretched base material by sintering or vapor deposition. Examples of valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the valve metal for the anode is preferably 99.9% or higher, and it may also contain silicon, iron, copper, magnesium, zinc, etc.

[0039] An expanded surface layer is formed on one or both sides of the anode during the anode formation process. The expanded surface layer is an etched layer obtained by etching the foil body, a sintered layer obtained by sintering valve metal powder, or a vapor-deposited layer obtained by depositing valve metal particles onto the foil. In other words, the expanded surface layer has a porous structure and consists of tunnel-shaped pits, sponge-like pits, or densely packed powder or voids between particles.

[0040] Tunnel-shaped etching pits are holes carved in the direction of the foil thickness. These tunnel-shaped etching pits are typically formed by passing a direct current through an acidic aqueous solution containing halogen ions, such as hydrochloric acid. The tunnel-shaped etching pits are further expanded by passing a direct current through an acidic aqueous solution containing nitric acid, for example. Sponge-like etching pits cause the expanded layer to become a sponge-like layer with a series of fine voids. These sponge-like etching pits are formed by passing an alternating current through an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0041] The sintered layer is produced by pasteuring powder of the same or different valve metal as the foil with a binder and solvent, coating and drying it, and then heating and sintering it in a vacuum or reducing atmosphere. The vapor-deposited layer is produced, for example, by resistance heating vapor deposition or electron beam heating vapor deposition. This vapor-deposited layer is formed by heating the same or different valve metal as the foil with resistance heat or electron beam energy to evaporate it, and depositing the vapor of valve metal particles onto the surface of the foil.

[0042] The dielectric film is formed on one or both sides of the anode body where the expanding layer has been formed during the anode formation process. If an expanding layer has been formed, the dielectric film is formed on the surface of the expanding layer, following the irregularities of the expanding layer. Typically, the dielectric film is an oxide film formed on the surface of the anode body, and if the anode body is made of aluminum, it is an aluminum oxide layer formed by oxidizing the surface of the expanding layer. In the chemical conversion treatment for forming the dielectric film, a voltage is applied to the anode body in the conversion solution to achieve a desired withstand voltage. The conversion solution is a halogen-free solution, such as a phosphoric acid-based conversion solution such as ammonium dihydrogen phosphate, a boric acid-based conversion solution such as ammonium borate, or an adipic acid-based conversion solution such as ammonium adipate.

[0043] The extracted cathode of the cathode layer is a thin plate or foil made of a valve metal, or a laminate of a metal layer such as a silver layer and a carbon layer. The valve metal is preferably 99% or more in composition with respect to the extracted cathode, and may also contain silicon, iron, copper, magnesium, zinc, etc. The cathode formation process includes an extracted cathode formation process in addition to a semiconductor layer formation process, and in the extracted cathode formation process, the cathode is positioned on the opposite side from the anode body, sandwiching the dielectric film and the semiconductor layer.

[0044] The extracted cathode may be formed in a plate shape by laminating a carbon layer on a metal layer, and then stacked with the anode body with a semiconductor layer in between. Alternatively, the carbon layer may be formed by coating it onto the semiconductor layer after it has been formed on the anode body and curing it by heating. The metal layer may be formed by coating it onto the carbon layer with a paste and curing it by heating. To reduce contact resistance with the semiconductor layer, ethylene glycol or the like may be pre-applied to the surface of the semiconductor layer.

[0045] The surface of the extracted cathode is flattened or widened. An oxide film may be intentionally or naturally formed on the surface of the extracted cathode. Intentionally, a thin oxide film of about 1 to 10 Vfs may be formed by chemical conversion treatment. The naturally occurring oxide film is formed by the reaction of the cathode foil with oxygen in the air.

[0046] When separators are used, the materials include cellulose and mixed papers such as kraft, Manila hemp, esparto, hemp, cotton, and rayon; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and their derivatives; polytetrafluoroethylene resins; polyvinylidene fluoride resins; vinylon resins; polyamide resins such as aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides; polyimide resins; polyethylene resins; polypropylene resins; trimethylpentene resins; polyphenylene sulfide resins; acrylic resins; and polyvinyl alcohol resins, and these resins are used individually or in mixtures.

[0047] The separator may be fibrillated by generating thin fibers that branch out from the surface of the original fibers, such as fibrillated cellulose. Fibrillation can be achieved, for example, by beating. The fibrillated fibers intertwine using the thin fibrillated fibers, improving the strength of the separator. As a result, the separator can be made thinner. Thinning the separator allows for longer anodes and drawn-out cathodes per unit volume, improving the capacitance of the capacitor.

[0048] This capacitor may be a hybrid capacitor that includes an electrolyte as a true cathode in addition to the semiconductor layer. The solute of the electrolyte is an organic acid or its salt, an inorganic acid or its salt, or a composite compound of an organic acid and an inorganic acid or its salt, and is an ionic dissociable salt that dissociates into an anionic component and a cationic component. The solvent may be used alone or in combination of two or more.

[0049] Organic acids that act as anionic components as solutes include carboxylic acids such as oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, resorcinic acid, phloroglucic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, and pyromellitic acid, as well as phenols and sulfonic acids. Inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of complex compounds of organic and inorganic acids include borodisalicylic acid, borodisuoic acid, borodiglycolic acid, borodimalonic acid, borodisuccinic acid, borodiadipic acid, borodiazelaic acid, borodibenzoic acid, borodimaleic acid, borodilactic acid, borodimalic acid, boroditartaric acid, borodicitric acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodiresorcinic acid, borodimethylsalicylic acid, borodinafthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid.

[0050] Furthermore, examples of salts of organic acids, inorganic acids, and composite compounds of organic and inorganic acids include ammonium salts, quaternary ammonium salts, amidinium quaternary salts, amine salts, sodium salts, potassium salts, etc. Examples of quaternary ammonium ions in quaternary ammonium salts include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of amidinium quaternary salts include ethyldimethylimidazolinium and tetramethylimidazolinium. Examples of amine salts include salts of primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, and propylamine; examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine; and examples of tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine.

[0051] The solvent may be either a protic polar solvent or an aprotic polar solvent. Examples of protic polar solvents include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Examples of aprotic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and sulfoxides.

[0052] Furthermore, other additives can be added to the electrolyte. Examples of additives include complex compounds of boric acid and polysaccharides (such as mannitol and sorbitol), complex compounds of boric acid and polyhydric alcohols, boric acid esters, nitro compounds (such as o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, and p-nitrobenzyl alcohol), phosphate esters, and polymeric solvents that improve pressure resistance, such as polyols or derivatives thereof to which alkylene oxides have been added. These may be used individually or in combination of two or more.

[0053] In the electrolyte impregnation process, the device is immersed in the electrolyte to impregnate the voids inside the device. To impregnate the electrolyte into finer voids, a pressure reduction process or a pressure increase process may be performed as necessary. The electrolyte impregnation process may be repeated multiple times. For example, the interior of the device may be depressurized and the electrolyte may be injected into the interior of the device while pressurizing the electrolyte.

Example

[0054] Hereinafter, the capacitor of the example will be described in more detail. Note that the present invention is not limited to the examples described below.

[0055] (Example 1) A capacitor of Example 1 was fabricated. For the anode body, a flat aluminum foil with a purity of 99.9% or more was used. This aluminum foil is flat, and a thin piece for an external lead terminal extends from one end. This aluminum foil was subjected to formation treatment to form a dielectric film on the anode body. As a pretreatment for the formation treatment, the aluminum foil was pickled with a 60% nitric acid aqueous solution brought to room temperature, and the aluminum foil was further washed with water. Also, before the formation treatment, the boundary between the thin piece for the external lead terminal and the flat plate was masked with a silicon resin.

[0056] The area of the aluminum foil was 5.14 cm 2 Thereafter. In the formation treatment, this aluminum foil was immersed in a formation solution, and a voltage was applied while flowing a constant current until the target formation voltage was reached. The formation solution is an ammonium adipate aqueous solution with a liquid temperature of 85°C in which 150 g of ammonium adipate is dissolved in 1 liter of water. The current density of the constant current is 0.5 mA / cm 2 Thereafter. The formation voltage is 150 V.

[0057] Both sides of the aluminum foil on which the dielectric film was formed were 1.3 cm 2The surface was masked with imide tape so that it was exposed. Then, 30 μL of a slurry of sulfide semiconductor, which would form the semiconductor layer, was dropped onto this exposed area and dried. The sulfide semiconductor was Cu2SnS3, which was ground into fine particles in a mortar and pestle and dispersed in an aqueous solution to which a surfactant was added as a binder. The surfactant was 4-(1,1,3,3-tetramethylbutyl)phenyl polyethylene glycol, and the concentration of the surfactant was 5 wt%. 0.3 g of Cu2SnS3 was dispersed in 600 μL of the aqueous solution. The slurry was dried for 10 minutes at a temperature of 40°C. As a result, a semiconductor layer of Cu2SnS3 was formed on the exposed area of ​​the dielectric film on the anode.

[0058] After forming the semiconductor layer, 5 μL of ethylene glycol was dropped onto the semiconductor layer, and then a plate-shaped lead-out cathode was placed on top of it so as to be in contact with the semiconductor layer. A flat aluminum foil with a purity of 99.9% or higher was used for the plate-shaped lead-out cathode. The element was then covered by sandwiching it between bakelite plates on both sides, completing the capacitor of Example 1, in which the semiconductor layer became the true cathode.

[0059] (Comparative Example 1) To compare and verify the characteristics of Example 1, a capacitor of Comparative Example 1 was fabricated. The capacitor of Comparative Example 1 is a solid electrolytic capacitor with PEDOT:PSS as the true cathode. The anode and the drawn cathode are the same as those in Example 1, and it was fabricated using the same manufacturing method and conditions.

[0060] The solid electrolyte layer of PEDOT:PSS was formed by dropping a conductive polymer dispersion onto the exposed region of the anode and drying it. The dispersion medium of the conductive polymer dispersion was a mixture of 60 wt% water and 40 wt% ethylene glycol relative to the total volume of the dispersion medium. PEDOT:PSS was dispersed at a ratio of 1.2 wt% relative to the total volume of the conductive polymer dispersion. 106 μL of this conductive polymer dispersion was dropped and dried. The drying temperature was 110°C and the drying time was 30 minutes.

[0061] Subsequently, 5 μL of ethylene glycol was dropped onto the solid electrolyte layer, and a plate-shaped lead cathode was placed on top. The element was then covered by sandwiching it between bakelite plates on both sides, completing the capacitor of Comparative Example 1.

[0062] (Capacitance test) The capacitance of the capacitors in Example 1 and Comparative Example 1 was measured at various frequencies. Capacitance was measured using an LCR meter (Agilent ZM2376, manufactured by NF Circuit Design Block Co., Ltd.). The ambient temperature during measurement was 25°C, the DC bias was 0V, and the AC signal level was a sine wave of 1.0Vrms. The measurement frequency ranged from 50Hz to 100kHz.

[0063] The capacitance measurement results are shown in Figure 1. Figure 1 is a graph showing the relationship between operating frequency and capacitance, with frequency on the horizontal axis and capacitance on the vertical axis. In the figure, the circular plots represent the results of Example 1, and the square plots represent the results of Comparative Example 1.

[0064] As shown in Figure 1, the capacitances of Example 1 and Comparative Example 1 are equivalent across the entire frequency range, from low frequencies of 50 Hz to 100 kHz to high frequencies. In other words, it can be confirmed that capacitors using sulfide semiconductors as true cathodes are comparable to PEDOT:PSS solid electrolytic capacitors in terms of capacitance and are therefore practical.

[0065] (ESR test) The equivalent series resistance (ESR) of the capacitors in Example 1 and Comparative Example 1 was measured under various temperature conditions. ESR was measured using an LCR meter (Agilent ZM2376, manufactured by NF Circuit Design Block Co., Ltd.). The capacitors in Example 1 and Comparative Example 1 were exposed to temperature conditions of 150, 175, and 200°C for 400 hours. The DC bias was 0V, the AC signal level was a 1.0Vrms sine wave, and the measurement frequency was 100kHz.

[0066] The results of this ESR measurement test are shown in Figure 2. Figure 2 is a graph showing the relationship between the storage temperature and the ESR after 400 hours. Each ESR is shown as a percentage, with the ESR before exposure to each temperature environment, i.e., at zero elapsed time, as the baseline. In the figure, the circular plots represent the results of Example 1, and the square plots represent the results of Comparative Example 1.

[0067] As shown in Figure 2, the ESR of the solid electrolytic capacitor of Comparative Example 1 is 151% after 400 hours at 150°C (based on 0 hours), 299% after 400 hours at 175°C, and 2321% after 400 hours at 200°C. On the other hand, the ESR of the capacitor of Example 1 is 112% after 400 hours at 150°C (based on 0 hours), 140% after 400 hours at 175°C, and 222% after 400 hours at 200°C.

[0068] In other words, it can be confirmed that capacitors using sulfide semiconductors as true cathodes are less prone to ESR deterioration in the high temperature range from 150°C to 200°C. In particular, at a temperature of 200°C, the ESR of Comparative Example 1 of PEDOT:PSS increased by more than 23 times compared to before exposure to the high temperature environment, while that of Example 1 remained at about twice the original value, resulting in a lower ESR than Comparative Example 1.

[0069] (Examples 2 to 5) Capacitors of Examples 2 to 5 were fabricated. Capacitors of Examples 2 to 5 had the same configuration as those of Example 1, except for the type of sulfide semiconductor contained in the semiconductor layer, and were fabricated using the same manufacturing method and conditions as Example 1.

[0070] The sulfide semiconductor used to form the semiconductor layer in Example 2 was zinc-doped Zn-Cu2SnS3. The sulfide semiconductor used to form the semiconductor layer in Example 3 was Cu3SnS4. The sulfide semiconductor used to form the semiconductor layer in Example 4 was zinc-doped Zn-Cu3SnS4. The sulfide semiconductor used to form the semiconductor layer in Example 5 was CoNi2S4.

[0071] (Capacitance test) The capacitance of the capacitors in Examples 2 to 5 was measured at 120 Hz. The capacitance measurement method and conditions were the same as those for Example 1 and Comparative Example 1. The capacitance measurement results are shown in Table 1 below. Table 1 also shows the results for the capacitor in Example 1, which uses Cu2SnS3 as the sulfide semiconductor, and the results for the capacitor in Comparative Example 1, which has a PEDOT:PSS solid electrolyte layer instead of a semiconductor layer.

[0072] (Table 1) TIFF2026062579000002.tif71161

[0073] As shown in Table 1 above, the capacitances of Examples 2 to 5 are equivalent to those of Comparative Example 1, similar to Example 1. In other words, not only in Example 1, but capacitors using sulfide semiconductors as true cathodes are comparable to PEDOT:PSS solid electrolytic capacitors in terms of capacitance and are therefore practical.

[0074] (ESR test) The equivalent series resistance (ESR) of the capacitors of Examples 3 to 5 was measured after being exposed to a temperature environment of 200°C for 400 hours. The measurement method and conditions for ESR were the same as those for Example 1 and Comparative Example 1.

[0075] The results of this ESR measurement test are shown in Table 2. Table 2 also shows the initial ESR before exposure to a 200°C temperature environment, i.e., when the elapsed time was zero, and the ESR after 400 hours of exposure to a 200°C temperature environment, as well as the percentage change from the initial ESR after the measurement test.

[0076] (Table 2) TIFF2026062579000003.tif71161

[0077] As shown in Table 2 above, the ESR of the capacitor in Example 3 was 154% after 400 hours at 200°C, the ESR of the capacitor in Example 4 was 159% after 400 hours at 200°C, and the ESR of the capacitor in Example 5 was 85% after 400 hours at 200°C. In other words, it can be confirmed that the ESR of the capacitors in Examples 3 to 5, which use sulfide semiconductors as true cathodes, does not deteriorate easily at high temperatures.

[0078] Furthermore, Examples 3 to 5 yielded even better results than Example 1, where the ESR increase was approximately double under a 200°C temperature environment, with the ESR increase being significantly less than double. Moreover, Example 5, which used CoNi2S4 as the sulfide semiconductor, showed an ESR change rate of 85% after exposure to a 200°C temperature environment, indicating no degradation like PEDOT:PSS, and in fact, the ESR improved after exposure to the 200°C temperature environment.

[0079] Thus, it was confirmed that by replacing the solid electrolyte layer of PEDOT:PSS with a sulfur-containing semiconductor in the cathode layer and incorporating a semiconductor layer in contact with the dielectric film, the ESR change is small in high-temperature environments, resulting in a longer lifespan.

[0080] (Example 6) A capacitor was fabricated according to Example 6. The sulfide semiconductor used in Example 6 was the same Cu3SnS4 as in Example 3. However, while the semiconductor layer in Example 3 was formed by a hydrothermal synthesis slurry method, the semiconductor layer in Example 6 was formed by an ink method.

[0081] In the semiconductor formation process of Example 6, copper(II) acetate, tin(II) oxalate, and thiourea were prepared as material sources. First, oxalic acid and tin(II) oxalate were mixed in N-methylformamide solvent. Then, copper(II) acetate was added and mixed. Thiourea was then mixed in. Copper(II) acetate, tin(II) oxalate, and thiourea were added to the mixture to concentrations of 0.12 M for copper, 0.04 M for tin, and 0.6 M for sulfur.

[0082] The anode was a flat aluminum foil with a purity of 99.9% or higher. The specific surface area of ​​this aluminum foil was increased by AC etching. The conversion voltage was 65V. 500 μL of a mixture of copper(II) acetate, tin(II) oxalate, and thiourea was dropped onto the anode. After dropping the mixture onto the anode, it was dried in air at 110°C for 30 minutes, and then fired in air at 240°C for 15 minutes. This formed a semiconductor layer on the anode.

[0083] A carbon paste was applied to the semiconductor layer and dried at 110°C for 30 minutes. Furthermore, a silver paste was applied on top of the carbon layer, a copper foil was placed on top, and the process was dried at 110°C for another 30 minutes. This completed the capacitor of Example 6.

[0084] (Example 7) A capacitor was fabricated according to Example 7. The sulfide semiconductor used in Example 7 was Cu3SnS4, the same as in Example 6. However, the capacitor in Example 7 employed the same hydrothermal synthesis slurry process as in Example 3 for semiconductor formation.

[0085] 500 μL of the same slurry prepared in Example 3 was dropped onto the same anode as in Example 6, and dried at 60°C for 30 minutes. After forming the semiconductor layer, 20 μL of ethylene glycol was dropped onto the semiconductor layer, and then a 99.9% pure aluminum lead cathode was placed on top so as to be in contact with the semiconductor layer. The element was then covered by sandwiching it between bakelite plates on both sides, completing the capacitor of Example 7.

[0086] (Capacitance test) The capacitance of the capacitors in Examples 6 and 7 was measured at each frequency. The capacitance measurement method was the same as in Example 1. The capacitance measurement results are shown in Figure 3. Figure 3 is a graph showing the relationship between operating frequency and capacitance, with frequency on the horizontal axis and capacitance on the vertical axis. In the figure, the circular plots represent the results of Example 6 using the ink method process, and the square plots represent the results of Example 7 using the hydrothermal synthesis slurry method process.

[0087] As shown in Figure 3, the capacitance of Example 6 exceeded that of Example 7 across all frequency bands, from low frequencies of 40 Hz to 100 kHz to high frequencies. In particular, the difference in capacitance at 120 Hz was more than five times. This confirms that when the ink method is used in the semiconductor formation process, the capacitance of a capacitor using sulfide semiconductors as the semiconductor layer is significantly improved.

[0088] (ESR test) The ESR of the capacitors in Examples 6 and 7 was measured at each frequency. The ESR measurement method was the same as in Example 1. The results of this ESR measurement test are shown in Figure 4. Figure 4 is a graph showing the relationship between operating frequency and ESR. In the figure, the circular plots represent the results of Example 6 using the ink method process, and the square plots represent the results of Example 7 using the hydrothermal synthesis slurry method process.

[0089] As shown in Figure 4, Example 6 achieved a lower ESR than Example 7 across the entire frequency band, from low frequencies of 40 Hz to 100 kHz to high frequencies. This confirms that when an ink-based semiconductor process is used in the semiconductor formation process, the ESR of a capacitor using sulfide semiconductors as the semiconductor layer can also be kept low.

Claims

1. an anode body made of valve-acting metal, A dielectric film formed on the surface of the anode body, A cathode layer is formed on the dielectric film, facing the anode body with the dielectric film in between, Equipped with, The cathode layer is A semiconductor layer made of an inorganic semiconductor containing sulfur, formed on the dielectric film, An extraction cathode is formed on the semiconductor layer and faces the anode body with the dielectric film and the semiconductor layer in between, To be equipped, A capacitor characterized by the following:

2. The inorganic semiconductor further contains copper. The capacitor according to claim 1, characterized in that

3. The inorganic semiconductor further contains tin. The capacitor according to claim 2, characterized in that

4. The inorganic semiconductor has the molecular formula Cu ２ SnS ３ or Cu ３ SnS ４ It is a compound represented by, The capacitor according to claim 3, characterized in that

5. The inorganic semiconductor has the molecular formula CoNi ２ S ４ It is a compound represented by, The capacitor according to claim 1, characterized in that

6. The inorganic semiconductor further contains zinc. The capacitor according to claim 4 or 5, characterized by the above.

7. A process for forming an anode body made of a valve-acting metal and having a dielectric film formed on its surface, A cathode layer formation step is to form a cathode layer on the dielectric film, facing the anode body with the dielectric film in between, Includes, The cathode layer formation step is, A process of forming an extracted cathode, wherein an extracted cathode is arranged opposite to the anode body, A semiconductor layer formation step of forming a semiconductor layer made of an inorganic semiconductor containing sulfur on the dielectric film, Including, A method for manufacturing capacitors characterized by the following.

8. In the semiconductor layer formation step, the inorganic semiconductor material sources are mixed in a solvent to prepare a mixture, the mixture is applied to the anode, the extraction cathode, or both, and then dried and fired to synthesize the inorganic semiconductor on the dielectric film. A method for manufacturing a capacitor according to claim 7, characterized by the above.

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