Solid electrolytic capacitors

Abstract

This invention provides a solid electrolytic capacitor that can achieve high capacitance. [Solution] The solid electrolytic capacitor comprises a capacitor element containing a conductive polymer. The capacitor element comprises an anode, a first dielectric layer containing a first dielectric (excluding a composite oxide of titanium and aluminum) covering at least a portion of the surface of the anode, a second dielectric layer containing a second dielectric covering at least a portion of the surface of the first dielectric layer, and the conductive polymer covering at least a portion of the surface of the second dielectric layer. The second dielectric is an oxide containing at least one element selected from the group consisting of silicon, aluminum, and zinc. The dielectric constant D1 of the first dielectric is higher than the dielectric constant D2 of the second dielectric. The thickness T2 of the second dielectric layer is 0.003T1 or more and 0.170T1 or less with respect to the thickness T1 of the first dielectric layer.

Description

Technical Field

[0001] The present disclosure relates to solid electrolytic capacitors.

Background Art

[0002] Solid electrolytic capacitors are expected to be used in various applications because they have a low equivalent series resistance (ESR) and a high capacitance. A solid electrolytic capacitor includes, for example, an anode body, a dielectric layer covering at least a part of the surface of the anode body, and a conductive polymer covering at least a part of the surface of the dielectric layer. The dielectric layer is formed, for example, by subjecting the surface of the anode body to a forming treatment. Further, the dielectric layer may be formed using sputtering or an atomic layer deposition method or the like (Patent Documents 1 to 3).

[0003] Patent Document 4 provides an electrode foil for an electrolytic capacitor, which includes an anode body containing a valve action metal, a first dielectric layer covering at least a part of the anode body, and a second dielectric layer covering at least a part of the first dielectric layer, wherein the second dielectric layer has a higher dielectric constant than the first dielectric layer, the thickness T2 of the second dielectric layer is larger than the thickness T1 of the first dielectric layer, and the first dielectric layer is a layer that suppresses oxygen diffusion from the second dielectric layer to the anode body.

[0004] Patent Document 5 provides an electrode foil for an electrolytic capacitor, which includes an anode body containing a first metal, a first dielectric layer covering at least a part of the anode body and containing an oxide of the first metal, and a second dielectric layer covering at least a part of the first dielectric layer and containing an oxide of a second metal different from the first metal, wherein the first metal includes at least one selected from the group consisting of titanium, tantalum, niobium, and aluminum, the second metal includes at least one selected from the group consisting of silicon, zirconium, hafnium, and tantalum, and the thickness T2 of the second dielectric layer is smaller than the thickness T1 of the first dielectric layer.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2012-124347 [Patent Document 2] International Publication No. 2023 / 145920 [Patent Document 3] International Publication No. 2021 / 065356 [Patent Document 4] International Publication No. 2023 / 145920 [Patent Document 5] International Publication No. 2021 / 065356 [Overview of the project] [Problems that the invention aims to solve]

[0006] This invention provides a solid electrolytic capacitor that can achieve high capacitance. [Means for solving the problem]

[0007] One aspect of this disclosure is a solid electrolytic capacitor comprising a capacitor element containing a conductive polymer, The aforementioned capacitor element is Anode and, A first dielectric layer comprising a first dielectric (excluding a composite oxide of titanium and aluminum) covering at least a portion of the surface of the anode body, A second dielectric layer comprising a second dielectric covering at least a portion of the surface of the first dielectric layer, The conductive polymer covers at least a portion of the surface of the second dielectric layer, The second dielectric is an oxide containing at least one element selected from the group consisting of silicon, aluminum, and zinc. The dielectric constant D1 of the aforementioned first dielectric is higher than the dielectric constant D2 of the aforementioned second dielectric. This invention relates to a solid electrolytic capacitor in which the thickness T2 of the second dielectric layer is between 0.003T1 and 0.170T1 with respect to the thickness T1 of the first dielectric layer. [Effects of the Invention]

[0008] This can improve the capacitance of solid electrolytic capacitors. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic cross-sectional view showing a solid electrolytic capacitor according to one embodiment of the present disclosure. [Figure 2] This is a schematic cross-sectional view of section II in Figure 1, magnified. [Figure 3] This is a schematic cross-sectional view showing a solid electrolytic capacitor according to another embodiment of the present disclosure. [Figure 4] Figure 2 is a perspective view showing a portion of the winding used to form the solid electrolytic capacitor, unfolded. [Modes for carrying out the invention]

[0010] Solid electrolytic capacitors containing conductive polymers have lower ESR and higher capacitance compared to electrolytic capacitors using electrolytes or inorganic oxides such as manganese oxide. Therefore, solid electrolytic capacitors are expected to be used in a variety of applications. As their applications expand, even higher capacitance is required for solid electrolytic capacitors.

[0011] To increase the capacitance of solid electrolytic capacitors, the specific surface area of ​​the anode is increased by making at least the surface layer porous. As the anode, for example, an anode foil with a large specific surface area obtained by roughening the surface of a metal foil may be used as the anode. Roughening is performed by etching or the like.

[0012] The dielectric layer formed on the surface of the anode body also affects the capacitance. A general dielectric layer is formed by anodizing the anode body through a chemical conversion treatment. Such a dielectric layer contains oxides containing metal elements (such as elements of valve action metals) contained in the anode body. The dielectric layer may also be formed by sputtering, atomic layer deposition, or the like. In this case, a dielectric layer can also be formed of an oxide containing an element other than the metal element contained in the anode body. Therefore, a dielectric layer can be formed of a material having a higher dielectric constant than the dielectric layer formed by anodization.

[0013] When a dielectric layer is formed of a high dielectric constant material, a higher capacitance is expected to be obtained. In an electrolytic capacitor using an electrolytic solution, when the dielectric layer is formed of a high dielectric constant material, the capacitance is greatly improved as compared with the case where a material having a lower dielectric constant is used. However, it has been clarified that in a solid electrolytic capacitor, even when a high dielectric constant material is used, a significantly large capacitance may not be obtained.

[0014] Technology (1) A solid electrolytic capacitor according to one aspect of the present disclosure is a solid electrolytic capacitor including a capacitor element containing a conductive polymer. The capacitor element includes an anode body, a first dielectric layer including a first dielectric (excluding a composite oxide of titanium and aluminum) covering at least a part of the surface of the anode body, a second dielectric layer including a second dielectric covering at least a part of the surface of the first dielectric layer, and the conductive polymer covering at least a part of the surface of the second dielectric layer. The second dielectric is an oxide containing at least one element selected from the group consisting of silicon, aluminum, and zinc (hereinafter sometimes referred to as a second metal element). The dielectric constant D1 of the first dielectric is higher than the dielectric constant D2 of the second dielectric. The thickness T2 of the second dielectric layer is 0.003T1 or more and 0.170T1 or less with respect to the thickness T1 of the first dielectric layer.

[0015] In the above technology (1), as described above, the first dielectric layer is formed from a first dielectric with a relatively high dielectric constant, and is thinly covered with a second dielectric layer containing a second dielectric, which is an oxide containing a specific element. Because the second dielectric layer has a high affinity for conductive polymers, the adhesion between the second dielectric layer and the conductive polymer can be improved. When the surface of the second dielectric layer is covered with a conductive polymer, it is thought that there are more contact points between the conductive polymer and the dielectric layer in contact with the conductive polymer compared to when the surface of the first dielectric layer is covered with a conductive polymer. Therefore, the interfacial resistance between the conductive polymer and the dielectric layer in contact with the conductive polymer can be reduced. In addition, the proportion of the thickness of the first dielectric layer to the total dielectric layer is relatively large. As a result, the high dielectric constant of the first dielectric layer can be effectively utilized, and a high capacitance can be obtained. However, when the first dielectric is a composite oxide of titanium and aluminum, the effect of reducing leakage current is insufficient, and there is a tendency for large variations in leakage current. Therefore, it is desirable to form the first dielectric with a material other than such a composite oxide.

[0016] When the ratio of the thickness T2 of the second dielectric layer to the thickness T1 of the first dielectric layer (=T2 / T1) exceeds 0.170, the capacitance tends to be lower compared to cases where the ratio is 0.170 or higher. This is thought to be because when T2 / T1 exceeds 0.170, the thickness of the first dielectric layer becomes relatively smaller, making it difficult to obtain a high capacitance. When the T2 / T1 ratio is less than 0.003, the capacitance tends to be lower compared to cases where it is 0.003 or higher. When T2 / T1 is less than 0.003, the thickness T2 of the second dielectric layer is small, resulting in a larger exposed area of ​​the first dielectric layer. This is thought to reduce the adhesion between the dielectric layer and the conductive polymer compared to cases where T2 / T1 is 0.003 or higher, increasing the interfacial resistance and decreasing the capacitance.

[0017] In this disclosure, as described above, the dielectric layer interposed between the anode and the conductive polymer is composed of a first dielectric layer and a second dielectric layer. Therefore, since the interfacial resistance between the dielectric layer and the conductive polymer is small, the ESR of the solid electrolytic capacitor can be kept low. In addition, the two-layer structure of the dielectric layer can also keep the leakage current low.

[0018] Technology(2) In the above technology (1), the first dielectric may be an oxide containing at least one element selected from the group consisting of zirconium, niobium, and hafnium (hereinafter sometimes referred to as the first metallic element). Such a first dielectric is relatively inexpensive and readily available, and a high dielectric constant can be obtained. Therefore, by combining the first dielectric layer and the second dielectric layer, and by setting the thickness ratio T2 / T1 of each dielectric layer within the above range, the capacitance of the solid electrolytic capacitor can be further increased. In addition, ESR and leakage current can be kept low.

[0019] Technology(3) In the above techniques (1) or (2), the first dielectric may be an oxide containing at least one element selected from the group consisting of zirconium and hafnium. In this case, the capacitance of the solid electrolytic capacitor can be further increased. Also, the ESR and leakage current can be kept low.

[0020] Technology(4) In any one of the above technologies (1) to (3), the first dielectric may include a crystalline region. The first dielectric having appropriate crystallinity facilitates polarization and allows for a higher dielectric constant. The high conductivity and dielectric constant of the first dielectric, along with the second dielectric layer and its thickness ratio T2 / T1, further enhance the capacitance of the solid electrolytic capacitor. The crystallinity of the dielectric can be increased, for example, by heat treatment. For example, a first dielectric containing elements such as Zr, Hf, and Nb forms a crystalline region at a relatively lower temperature than the second dielectric.

[0021] Technology(5) In any one of the above technologies (1) to (4), the second dielectric may be amorphous. In this case, a higher capacitance and a lower ESR can be obtained compared to the case where the second dielectric has high crystallinity. The crystalline region is generally a polycrystalline state in which fine single crystals at the nanoscale are stacked. In a dielectric layer in such a polycrystalline state, pores are formed, making it easier to obtain a large surface area. Conductive polymers have difficulty penetrating these pores. Therefore, it is thought that when the second dielectric is amorphous, there are more contact points between the surface of the second dielectric layer and the conductive polymer compared to the case where it has high crystallinity. As a result, it is thought that high adhesion can be easily obtained between the second dielectric layer and the conductive polymer, and the interfacial resistance can be kept lower.

[0022] Technology(6) In any one of the above technologies (1) to (5), the anode body may be an anode foil containing aluminum. In this case, the specific surface area can be easily increased by etching or the like, which is advantageous for increasing capacity and is also cost-effective.

[0023] The solid electrolytic capacitor of this disclosure will be described in more detail below, including the above techniques (1) to (6), with reference to the drawings as necessary. To the extent that it is not technically inconsistent, at least one of the above techniques (1) to (6) may be combined with at least one of the elements described below. Note that each figure is schematic, and the proportions of the dimensions (e.g., thickness) of each component may differ from those of the actual components.

[0024] [Solid electrolytic capacitors] The solid electrolytic capacitor of this disclosure comprises a capacitor element containing a conductive polymer. The solid electrolytic capacitor has at least one capacitor element. The solid electrolytic capacitor may have two or more capacitor elements.

[0025] (Capacitor element) The capacitor element comprises an anode, a dielectric layer covering at least a portion of the surface of the anode, and a conductive polymer covering at least a portion of the surface of the dielectric layer. The dielectric layer comprises a first dielectric layer covering at least a portion of the surface of the anode, and a second dielectric layer covering at least a portion of the surface of the first dielectric layer. The conductive polymer covers at least a portion of the surface of the second dielectric layer.

[0026] (Anode) The anode may include valve metals, alloys containing valve metals, and compounds containing valve metals. The anode may contain one of these materials or a combination of two or more. As valve metals, aluminum, tantalum, niobium, and titanium are preferably used.

[0027] The anode body has a porous surface, at least. This increases the surface area of ​​the anode body, allowing for higher capacitance.

[0028] An anode body with a porous surface can be obtained, for example, by roughening the surface of a substrate containing valve-acting metal (such as a sheet-like substrate (e.g., foil-like or plate-like substrate)) by etching. Surface roughening can be performed, for example, by etching. The thickness of the sheet-like substrate (such as metal foil) is, for example, 15 μm to 300 μm.

[0029] An anode foil with a porous surface comprises, for example, a core and a porous portion integrated with the core. The porous portion may be formed on the surface of each of the two main surfaces of the anode foil. The thickness of each side of the porous portion may be, for example, 1 / 10 or more and 4 / 10 or less of the total thickness of the anode foil, from the viewpoint of securing a large surface area and maintaining the strength of the electrode foil. The thickness of the porous portion is determined by measuring the thickness at any 10 points using a cross-sectional image of the anode foil and calculating the average value. The cross-sectional image of the anode foil is taken using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0030] The anode body may be a porous molded body or a porous sintered body of particles containing valve metal. In both the porous molded body and the sintered body, the entire anode body typically has a porous structure. The molded body and the sintered body may be in sheet form, or they may be rectangular parallelepipeds, cubes, or similar shapes.

[0031] As the anode body, it is preferable to use an anode foil, and more preferably to use an anode foil whose surface layer is porous as described above. From the viewpoint of effectively utilizing the effect of the high dielectric constant of the first dielectric layer, it is preferable to use an anode foil containing aluminum.

[0032] The anode body is divided into, for example, a first part including a first end and a second part including a second end opposite to the first end. The first and second ends are the ends of the anode body in the longitudinal direction. A cathode (particularly a conductive polymer) is formed in the second part via a dielectric layer. For this reason, the second part is sometimes called the cathode-forming part. No cathode is formed in the first part. A separation section may be formed at the end of the first part on the second part side to ensure insulation between the first part and the cathode. The part of the first part in which the separation section is not formed is sometimes called the anode section (or anode lead section). Anode lead terminals may be connected to the anode section. The separation section is formed of, for example, an insulating material (such as insulating resin).

[0033] If the anode is a porous molded or sintered body, a portion of the metal lead member is embedded in the molded or sintered body.

[0034] (Dielectric layer) The dielectric layer includes a first dielectric layer and a second dielectric layer. In a solid electrolytic capacitor, the first dielectric layer covers at least a portion of the surface of the anode. The second dielectric layer covers at least a portion of the surface of the first dielectric layer.

[0035] The relative permittivity D1 of the first dielectric that constitutes the first dielectric layer and the relative permittivity D2 of the second dielectric that constitutes the second dielectric layer satisfy D1 > D2. When the dielectric layer is composed only of the first dielectric having a relatively high relative permittivity, the adhesion between the first dielectric layer and the conductive polymer is low, the interfacial resistance tends to be large, and it is difficult to effectively utilize the high relative permittivity of the first dielectric layer. When the dielectric layer is composed only of the second dielectric having a relatively low relative permittivity, it is difficult to obtain a high capacitance. Also, when D1 < D2, it is difficult to obtain a high capacitance, presumably because the adhesion between the second dielectric layer and the conductive polymer is low. In the present disclosure, a high capacitance can be obtained because D1 > D2.

[0036] The first dielectric is, for example, composed of a metal oxide. However, the composite oxide of titanium (Ti) and aluminum (Al) is excluded from the first dielectric because the effect of reducing the leakage current is insufficient and the variation is large. The first dielectric is preferably an oxide containing at least one first metal element selected from the group consisting of zirconium (Zr), niobium (Nb), and hafnium (Hf) (among them, Zr and Hf). The first dielectric may include, for example, zirconium oxide (such as ZrO) and hafnium oxide (such as HfO2). The first dielectric may contain one of these oxides or two or more of them. When the first dielectric layer contains two or more oxides, the two or more oxides may be mixed or each may be arranged in layers.

[0037] The first dielectric layer preferably contains the first metal element and substantially does not contain the second metal element. Substantially not containing the second metal element means that the second metal element is below the detection limit in energy dispersive X-ray spectroscopy (EDX) analysis.

[0038] In a solid electrolytic capacitor, the first dielectric material may be in an amorphous state. Furthermore, the first dielectric material may include crystalline regions, or it may include both crystalline and amorphous regions. When the first dielectric material includes crystalline regions and thus possesses moderate crystallinity, the capacitance of the solid electrolytic capacitor can be further improved compared to cases where the crystallinity of the first dielectric material is lower (such as when it is in an amorphous state). The moderate crystallinity of the first dielectric material facilitates polarization of the first dielectric material, resulting in a relatively high dielectric constant. Therefore, it is considered that the effect of the high dielectric constant of the first dielectric material can be more easily realized, leading to a further improvement in capacitance.

[0039] The crystallinity of the first dielectric can be improved by heat-treating at least the first dielectric layer. The crystallinity of the first dielectric may be adjusted by heat-treating an anode body having the dielectric layer, or a capacitor element or solid electrolytic capacitor having this anode body. The heat treatment temperature may be 250°C to 600°C, or 300°C to 500°C. A heat treatment temperature of 300°C to 450°C is more preferable, and 350°C to 450°C is even more preferable. When the heat treatment temperature is within this range, crystalline grains are appropriately formed in the first dielectric layer, resulting in a higher capacitance. In addition, the appropriate formation of crystalline grains suppresses crack formation and the increase in resistance due to the increase in grain boundaries, thereby keeping leakage current and ESR low.

[0040] The above heat treatment is preferably carried out under an inert gas atmosphere (for example, under an atmosphere such as nitrogen gas or argon gas). The heat treatment time may be 10 seconds to 5 minutes, 20 seconds to 3 minutes, or 30 seconds to 2 minutes.

[0041] A first dielectric, composed of a first metal element (such as zirconium or hafnium), has lower affinity for conductive polymers compared to a second dielectric. Even when a conductive polymer is formed on the surface of such a first dielectric layer, it tends to be more difficult to obtain high adhesion compared to when the conductive polymer is formed on the surface of the second dielectric layer. In other words, there are fewer contact points between the conductive polymer and the first dielectric layer than between the conductive polymer and the second dielectric layer. As a result, when the conductive polymer is in contact with the first dielectric layer, the interfacial resistance is higher compared to when it is in contact with the second dielectric layer, making it difficult to extract charge, resulting in lower capacitance and higher ESR. In this disclosure, by thinly covering the surface of the first dielectric layer with the second dielectric layer, the high dielectric constant of the first dielectric can be effectively utilized, and high capacitance can be obtained.

[0042] The second dielectric is an oxide containing at least one secondary metallic element selected from the group consisting of silicon (Si), aluminum (Al), and zinc (Zn). The second dielectric may also contain silicon oxide (SiO2, etc.), aluminum oxide (Al2O3, etc.), zinc oxide (ZnO, etc.), etc. The second dielectric may contain one of these oxides or two or more. From the viewpoint of easily obtaining higher capacitance and lower ESR, it is preferable that the second dielectric is an oxide containing at least one element selected from the group consisting of silicon and aluminum. When an oxide containing silicon or aluminum is used as the second dielectric, it is easier to further extract the high dielectric constant of the first dielectric and to obtain a higher capacitance acquisition rate. When the second dielectric layer contains two or more oxides, each oxide may be mixed together or arranged in layers. The capacitance acquisition rate indicates the utilization rate of the dielectric constant of the dielectric layer. The capacitance acquisition rate is the ratio (%) of the initial capacitance X1 of the solid electrolytic capacitor to the theoretical capacitance X0. The capacitance acquisition rate is expressed as 100(X1 / X0) (unit: %). The theoretical capacitance X0 may be calculated using the capacitance measured with an anode that has a dielectric layer formed before the conductive polymer layer is formed.

[0043] The thickness T2 of the second dielectric layer is between 0.003T1 and 0.170T1 relative to the thickness T1 of the first dielectric layer. A high capacitance can be obtained by having the thickness T2 within this range. The thickness T2 is preferably between 0.005T1 and 0.150, but may also be between 0.005T1 (or 0.025T1) and 0.100T1, or between 0.005T1 (or 0.025T1) and 0.075T1, or between 0.005T1 (or 0.025T1) and 0.050T1.

[0044] The thickness T2 of the second dielectric layer is preferably 0.05 nm or more and 3.3 nm or less, and more preferably 0.1 nm or more (or 0.10 nm or more) and 3.0 nm or less. When T2 is within this range, it is easier to ensure higher adhesion between the dielectric layer and the conductive polymer, and the effect of the low dielectric constant of the second dielectric is small, resulting in a higher capacitance.

[0045] From the viewpoint of easily ensuring higher adhesion between the second dielectric layer and the conductive polymer, the second dielectric is preferably amorphous. The second dielectric may contain crystalline regions, but it is preferable that the volume ratio of crystalline regions in the second dielectric layer is smaller than that of crystalline regions in the first dielectric layer. When heat treatment is performed to create crystalline regions in the first dielectric, if the entire dielectric layer is heat-treated, the crystallinity of the first dielectric is improved under heat treatment conditions, but the crystallinity of the second dielectric is often not improved as much. Therefore, the first dielectric layer becomes more easily polarized by heat treatment, and the adhesion with the conductive polymer is increased by the amorphous state of the second dielectric layer, resulting in a higher capacitance.

[0046] The first dielectric layer and the second dielectric layer can be identified as follows. A cross-sectional image of the anode in the thickness direction (including the porous region) is obtained by SEM or TEM, and elemental mapping is performed using energy-dispersive X-ray spectroscopy (EDX) analysis with this image to obtain a map of the first and second metal elements in the dielectric layer (e.g., oxide layer) covering the surface of the anode. Using the above image, the regions of the metallic structure constituting the anode and the regions of metal oxide constituting the first and second dielectric layers are distinguished. For example, the above two regions can be distinguished by binarization of the image. In the elemental mapping, the region where the second metal is distributed within the metal oxide region is identified and designated as the second dielectric layer. Within the metal oxide region, a region between the anode and the second dielectric layer where the first metal element is distributed and the second metal element is not distributed (below the detection limit of the second metal) is identified and designated as the first dielectric layer.

[0047] Based on the elemental mapping described above, the composition of the dielectrics forming each dielectric layer is identified from the types and relative abundances of metal elements contained in the first dielectric layer and the types and relative abundances of metal elements in the second dielectric layer. Dielectrics with the same composition are separately fabricated, and the dielectric constant of the dielectric is measured. From the measured dielectric constants, the relative magnitudes of the dielectric constant D1 of the first dielectric layer and the dielectric constant D2 of the second dielectric layer are determined. The dielectric constant is measured using a commercially available dielectric constant measuring device at 25°C, with a measurement frequency of 1 kHz and a DC bias voltage of 500 mV.

[0048] Each dielectric layer is formed, for example, by atomic layer deposition (ALD) or chemical conversion treatment. When chemical conversion treatment is used, the dielectric layer is formed from a compound (such as an oxide) of the valve metal contained in the anode. Chemical conversion treatment is performed, for example, by immersing the anode in a conversion solution such as ammonium adipate solution and applying a predetermined conversion voltage (anodic oxidation). In the case of chemical conversion treatment, the thickness T1 of the first dielectric layer can be adjusted by the conversion voltage, etc.

[0049] The ALD method allows for the formation of dielectric layers regardless of the type of valve metal contained in the anode, making it easier to adjust the dielectric constant relationship D1 > D2 between the first and second dielectric layers. In the ALD method, a raw material gas containing the first or second metal element and an oxidizer are alternately supplied to the reaction chamber where the object is placed, allowing the formation of the first or second dielectric layer on the surface of the object. In the ALD method, self-limiting action is at work, so the first metal is deposited on the surface of the object in atomic layer units. Therefore, a pattern in which steps (1) to (4) below are performed in this order constitutes one cycle, and the thickness T1 or T2 of each dielectric layer can be controlled by the number of times this cycle is repeated (number of cycles). (1) Supply of raw material gas (2) Exhaust of raw material gas (purging) (3) Supply of oxidizing agent (4) Exhaust (purging) of the oxidizing agent

[0050] Examples of oxidizing agents include water, oxygen, and ozone (O3). The oxidizing agent may also be supplied to the reaction chamber as a plasma using the oxidizing agent as a raw material.

[0051] The first or second metal element is supplied to the reaction chamber as a precursor gas containing each metal element. The precursor is, for example, an organometallic compound containing each metal element. By using a precursor in the form of an organometallic compound, each metal element can be easily chemically adsorbed onto the target material. Various organometallic compounds conventionally used in the ALD method may be used as the precursor.

[0052] Examples of precursors containing the first metal element include precursors containing Zr, Nb, and Hf. Examples of precursors containing Zr include bis(methyl-η) 5Examples of Nb-containing precursors include cyclopentadienyl)methoxymethylzirconium (Zr(CH3C5H4)2CH3OCH3), tetrakis(dimethylamide)zirconium(IV) ([(CH3)2N]4Zr(TDMAZ)), tetrakis(ethylmethylamide)zirconium(IV) (Zr(NCH3C2H5)4), and zirconium(IV)t-butoxide (Zr[OC(CH3)3]4). Examples of Nb-containing precursors include niobium(V) ethoxide (Nb(OCH2CH3)5) and tris(diethylamide)(t-butylimide)niobium(V)(C 16 H 39 Examples of Hf-containing precursors include hafnium tetrachloride (HfCl4), tetrakisdimethylaminohafnium (Hf[N(CH3)2]4(TDMAH)), tetrakisethylmethylaminohafnium (Hf[N(C2H5)(CH3)]4), tetrakisdiethylaminohafnium (Hf[N(C2H5)2]4), and hafnium-t-butoxide (Hf[OC(CH3)3]4).

[0053] The precursor may contain one primary metal element or two or more primary metal elements. Alternatively, a precursor containing one secondary metal element may be used, or a precursor containing two or more primary metal elements may be used. If necessary, the type of precursor supplied to the reaction chamber may be changed by the ALD cycle to change the type of primary metal element deposited at the atomic layer level. In this case, a primary dielectric layer (a layer of composite oxides) containing oxides of two or more primary metals is formed.

[0054] Examples of precursors containing a second metallic element include Al-containing precursors, Si-containing precursors, and Zn-containing precursors. An example of an Al-containing precursor is trimethylaluminum ((CH3)3Al). An example of a Si-containing precursor is N-sec-butyl(trimethylsilyl)amine (C7H 19 NSi), tetrakis(dimethylamide)silane (TDMAS), 1,3-diethyl-1,1,3,3-tetramethyldisilazane (C8H 23NSi2), 2,4,6,8,10-pentamethylcyclopentasiloxane ((CH3SiHO)5), pentamethyldisilane ((CH3)3SiSi(CH3)2H), tris(dimethylamino)silane ([(CH3)2N]3SiH), tris(isopropoxy)silanol ([(H3C)2CHO]3SiOH), chloropentanemethyldisilane ((CH3)3SiSi(CH3)2 Examples of zinc-containing precursors include diethylzinc (Zn(CH2CH3)2), tridimethylaminosilane (Si[N(CH3)2]4), tetraethylsilane (Si(C2H5)4), tetramethylsilane (Si(CH3)4), tetraethoxysilane (Si(OC2H5)4), dodecamethylcyclohexasilane ((Si(CH3)2)6), silicon tetrachloride (SiCl4), and silicon tetrabromide (SiBr4). Examples of zinc-containing precursors include diethylzinc (Zn(CH2CH3)2), bis(6-ethyl-2,2-dimethyl-3,5-decandionato)zinc (Zn(EDMDD)2), and octadionatozinc (Zn(OD2)).

[0055] The precursor may contain one or more secondary metal elements. Alternatively, a precursor containing one secondary metal element may be used, or a precursor containing two or more secondary metal elements may be used. If necessary, the type of secondary metal element deposited at the atomic layer level may be changed by varying the type of precursor supplied to the reaction chamber during the ALD cycle. In this case, a secondary dielectric layer (a layer of composite oxides) containing oxides of two or more secondary metals is formed.

[0056] (conductive polymer) The conductive polymer is also called a solid electrolyte. The conductive polymer covers at least a portion of the surface of the second dielectric layer. The conductive polymer may be layered. In other words, the cathode portion may include a conductive polymer layer (also called a solid electrolyte layer) that covers at least a portion of the surface of the second dielectric layer.

[0057] The conductive polymer is composed, for example, of a conjugated polymer and a dopant. The conductive polymer or conductive polymer layer may contain additives as needed.

[0058] Examples of conjugated polymers include π-conjugated polymers. Examples of conjugated polymers include polymers with polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylenevinylene, polyacene, and polythiophenevinylene as their basic skeletons. Of these, polymers with polypyrrole, polythiophene, or polyaniline as their basic skeleton may be used. The above polymers only need to contain at least one monomer unit that constitutes the basic skeleton. Monomer units include monomer units having substituents. The above polymers also include homopolymers and copolymers of two or more monomers. For example, polythiophene includes poly(3,4-ethylenedioxythiophene). The conductive polymer (or conductive polymer layer) may contain one conjugated polymer or two or more conjugated polymers.

[0059] The weight-average molecular weight (Mw) of the conjugated polymer may be, for example, between 1,000 and 1,000,000.

[0060] In this specification, the weight-average molecular weight (Mw) is a polystyrene-converted value measured by gel permeation chromatography (GPC). GPC is measured, for example, using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0061] Examples of dopants include at least one selected from the group consisting of anions and polyanions.

[0062] Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Examples of dopants that generate sulfonate ions include benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid. However, anions, or dopants that generate anions, are not limited to these specific examples.

[0063] Examples of polyanions include polymer anions. The conductive polymer layer may, for example, contain a conjugated polymer containing monomer units corresponding to a thiophene compound and polymer anions.

[0064] Examples of polymer anions include polymers having multiple anionic groups. Such polymers include polymers containing monomer units having anionic groups. Examples of anionic groups include sulfo groups and carboxyl groups. It is preferable that the polymer anion has at least one sulfo group.

[0065] In conductive polymers for solid electrolytic capacitors, the anionic group of the dopant may be present in free form, anionic form, or salt form, or in a form bonded to or interacting with the conjugated polymer system. In this specification, all of these forms may be simply referred to as "anionic group," "sulfo group," or "carboxyl group."

[0066] Examples of polymer anions having a sulfo group include high-molecular-weight polysulfonic acids. Specific examples of polymer anions include polyvinyl sulfonic acid, polystyrene sulfonic acid (including copolymers and substituted products), polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid (such as aromatic polyester sulfonic acid), and phenolsulfonic acid novolac resin. However, polymer anions are not limited to these specific examples.

[0067] The amount of dopant contained in the conductive polymer may be, for example, 10 to 1000 parts by mass, or 20 to 500 parts by mass, per 100 parts by mass of the conjugated polymer.

[0068] A layer to enhance adhesion may be interposed between the dielectric layer and the conductive polymer.

[0069] Examples of additives include known additives added to conductive polymers or conductive polymer layers (e.g., coupling agents, silane compounds), and known conductive materials other than conductive polymers (e.g., conductive inorganic materials such as manganese dioxide, TCNQ complex salts). The conductive polymer or conductive polymer layer may contain one additive or a combination of two or more additives.

[0070] Conductive polymers are generally formed by using a liquid composition (such as a solution or liquid dispersion) containing the conductive polymer, or by in-situ polymerization (such as chemical polymerization or electrolytic polymerization) using a liquid composition (polymerization solution) containing a precursor and dopant of a conjugated polymer. A combination of methods utilizing in-situ polymerization and methods using a liquid composition containing the conductive polymer may also be used. In in-situ polymerization, an oxidizing agent may be used as needed.

[0071] (Cathode extraction layer) The cathode portion may include a cathode extraction layer that comes into contact with a conductive polymer. The cathode extraction layer comprises at least a first layer in contact with a conductive polymer. The cathode extraction layer may also comprise a first layer and a second layer covering the first layer. Examples of the first layer include a layer containing conductive particles and a metal foil. Examples of conductive particles include at least one selected from conductive carbon and metal particles. For example, the cathode extraction layer may be composed of a layer containing conductive carbon as the first layer (also referred to as a carbon layer) and a layer containing metal particles or a metal foil as the second layer. If a metal foil is used as the first layer, the cathode extraction layer may be composed of this metal foil.

[0072] Examples of conductive carbon include graphite (artificial graphite, natural graphite, etc.). The carbon layer is formed, for example, using a paste or slurry containing conductive carbon and, if necessary, a binder (such as a binder resin).

[0073] A second layer containing metal particles can be formed, for example, by laminating a composition containing metal particles (such as metal powder) onto the surface of the first layer. Examples of such a second layer include a metal particle-containing layer (for example, a metal paste layer such as a silver paste layer) formed using a composition containing metal particles such as silver particles and a resin (binder resin).

[0074] Examples of binder resins used in carbon layers and metal particle-containing layers include thermoplastic resins and thermosetting resins. Thermosetting resins such as imide resins and epoxy resins are preferably used as binder resins.

[0075] When a metal foil is used as the first layer, the type of metal is not particularly limited. Preferably, the metal foil is a valve metal (such as aluminum, tantalum, or niobium) or an alloy containing a valve metal. The surface of the metal foil may be roughened as needed. The surface of the metal foil may be coated with a chemical conversion film, or a coating of a metal different from the metal constituting the metal foil (a dissimilar metal) or a nonmetal. Examples of dissimilar metals or nonmetals include metals such as titanium and nonmetals such as carbon (such as conductive carbon).

[0076] The above-mentioned dissimilar metal or nonmetal (for example, conductive carbon) coating may be used as the first layer, and the above-mentioned metal foil may be used as the second layer.

[0077] (Separator) When metal foil is used as the cathode lead layer, a separator may be placed between the metal foil and the anode (anode foil, etc.). The separator is not particularly limited, and for example, nonwoven fabrics containing fibers of cellulose, polyethylene terephthalate, vinylon, or polyamide (e.g., aliphatic polyamide, aromatic polyamide such as aramid) may be used.

[0078] (others) Solid electrolytic capacitors may be wound-wound, chip-type, or multilayer-type. For example, a solid electrolytic capacitor may include two or more multilayer-type capacitor elements. Alternatively, a solid electrolytic capacitor may include one wound-wound capacitor element or two or more wound-wound capacitor elements. The configuration of the capacitor elements is selected, for example, depending on the type of solid electrolytic capacitor.

[0079] In a capacitor element, one end of a cathode lead terminal is electrically connected to the cathode lead layer. The cathode lead terminal is joined to the cathode lead layer by, for example, applying a conductive adhesive to the cathode lead layer and bonding it to the cathode lead layer via this conductive adhesive. One end of an anode lead terminal is electrically connected to the anode portion of the anode body. The other end of the anode lead terminal and the other end of the cathode lead terminal are led out from the resin casing or case, respectively. The other ends of each terminal exposed from the resin casing or case are used for soldering to the substrate on which the solid electrolytic capacitor is to be mounted, etc.

[0080] The capacitor element is sealed using a resin casing or case. For example, the capacitor element and the resin material for the casing (e.g., uncured thermosetting resin and filler) may be placed in a mold, and the capacitor element may be sealed with the resin casing by a transfer molding method, compression molding method, or the like. In this case, the other ends of the anode lead terminal and cathode lead terminal connected to the anode lead drawn out from the capacitor element are exposed from the mold. Examples of thermosetting resins include epoxy resin.

[0081] Alternatively, a solid electrolytic capacitor may be formed by housing the capacitor element in a bottomed case such that the other ends of the anode lead terminal and cathode lead terminal are located on the opening side of the bottomed case, and then sealing the opening of the bottomed case with a sealing material. As the material for the bottomed case, metals such as aluminum, stainless steel, copper, iron, brass, or alloys thereof can be used.

[0082] Figure 1 is a schematic cross-sectional view showing a solid electrolytic capacitor according to one embodiment of the present disclosure. Figure 2 is an enlarged schematic cross-sectional view of portion II in Figure 1.

[0083] The solid electrolytic capacitor 400 comprises a capacitor element 402, an anode lead terminal 404 and a cathode lead terminal 405 electrically connected to the capacitor element 402, and a resin casing 403 that seals the capacitor element 402. Parts of the anode lead terminal 404 and the cathode lead terminal 405 are covered by the casing 403. The casing 403 has a substantially rectangular parallelepiped shape, and the solid electrolytic capacitor 400 also has a substantially rectangular parallelepiped shape.

[0084] The capacitor element 402 comprises an anode body (anode foil including valve-acting metal) 460 having a cathode forming portion 406a and an anode extraction portion 406b, a dielectric layer 407 covering the cathode forming portion 406a, and a cathode portion 408 covering the dielectric layer 407. The anode foil 406 has a porous portion on its surface, and the dielectric layer 407 is formed to cover the surface of the porous portion of the cathode forming portion 406a.

[0085] In the anode lead portion 406b, an insulating separation portion 413 is formed in the portion adjacent to the cathode portion 408, thereby restricting contact between the cathode portion 408 and the anode foil 406. The anode lead portion 406b and the anode lead terminal 404 are electrically connected by welding. The cathode lead terminal 405 is electrically connected to the cathode portion 408 via an adhesive layer 414 formed of a conductive adhesive.

[0086] The cathode section 408 comprises a solid electrolyte layer (conductive polymer layer) 409 covering the dielectric layer 407 and a cathode extraction layer 410 covering the solid electrolyte layer 409. The solid electrolyte layer 409 contains a conductive polymer. The solid electrolyte layer 409 can be formed, for example, by impregnating the anode foil 406 with a processing solution containing a conductive polymer. The cathode extraction layer 410 has a first layer 411, such as a carbon layer, and a second layer 412, such as a metal particle-containing layer (such as a silver particle-containing layer). The carbon layer may contain, for example, conductive carbon and, if necessary, a binder. The metal particle-containing layer may contain, for example, silver particles and a binder.

[0087] The outer casing 403 preferably contains a cured product of a curable resin composition, and may also contain a thermoplastic resin or a composition containing the same.

[0088] The anode foil 406 is a metal foil containing a valve metal, having a surface roughened by etching or the like. The anode foil 406 is porous, at least on its surface. As shown in Figure 2, such an anode foil 406 comprises a core portion 460a and a porous portion 460b. The porous portion 460b has a number of pits P. The dielectric layer 407 covers the outer surface of the porous portion 460b and the inner wall surfaces of the pits P. The solid electrolyte layer 409 is formed to cover at least a portion of the surface of the dielectric layer 407, including the pits P.

[0089] A first dielectric layer 407a is formed on the surface of the anode foil 406 so as to cover at least a portion of this surface. A second dielectric layer 407b is formed on the surface of the first dielectric layer 407a so as to cover at least a portion of this surface. The dielectric layer 407 is composed of the first dielectric layer 407a and the second dielectric layer 407b. The first dielectric layer 407a has a higher dielectric constant than the second dielectric layer 407b. The thickness T2 of the second dielectric layer 407b is between 0.003T1 and 0.170T1 relative to the thickness T1 of the first dielectric layer 407a.

[0090] Figure 1 shows a solid electrolytic capacitor 400 having one capacitor element 402. The solid electrolytic capacitor may also be a laminated type in which a laminate of two or more capacitor elements 402 is stacked and sealed with an outer casing 403.

[0091] Figure 3 is a schematic cross-sectional view showing a solid electrolytic capacitor according to another embodiment of the present disclosure. Figure 4 is a perspective view showing a portion of the winding used to form the solid electrolytic capacitor of Figure 3, unfolded.

[0092] The wound-type solid electrolytic capacitor 200 comprises a capacitor element. The capacitor element comprises a wound body 100 and a conductive polymer (not shown). The wound body 100 is constructed by winding an anode foil 10 and a cathode foil 20 with a separator 30 in between. The anode foil 10 has a porous surface layer at least. The anode foil 10 is an anode foil 406 as shown in Figure 2, and comprises a core portion 460a and a porous portion 460b. A dielectric layer 407 comprising a first dielectric layer 407a and a second dielectric layer 407b is formed on the surface of the anode foil 10 so as to cover at least a portion of this surface, as shown in Figure 2.

[0093] One end of lead tabs 50A and 50B is connected to the anode foil 10 and cathode foil 20, respectively. The winding body 100 is formed by winding the anode foil 10, cathode foil 20 and separator 30 while winding the lead tabs 50A and 50B. Lead wires 60A and 60B are connected to the other ends of lead tabs 50A and 50B, respectively.

[0094] A winding stopper tape 40 is placed on the outer surface of the cathode foil 20, which is located in the outermost layer of the winding body 100. The end of the cathode foil 20 is then secured by the winding stopper tape 40. If the anode foil 10 is prepared by cutting from a large sheet of foil, the winding body 100 may be further treated with a chemical conversion process to provide a dielectric layer on the cut surface.

[0095] The conductive polymer (solid electrolyte) is contained within the winding body 100 and is interposed between the anode foil 10 and the cathode foil 20 in the winding body 100. For example, the conductive polymer can be impregnated into the winding body by impregnating it with a treatment solution containing the conductive polymer. The conductive polymer may also be absorbed into the separator 30. Impregnation may be carried out under reduced pressure, for example, in an atmosphere of 10 kPa to 100 kPa.

[0096] In the solid electrolytic capacitor 200, a wound body 100 (capacitor element) containing a conductive polymer is housed in a bottomed case 211 such that the lead wires 60A and 60B are located on the opening side of the bottomed case 211. Sealing of the capacitor element is performed, for example, by the following procedure: The wound body 100 (capacitor element) containing a conductive polymer is housed in the bottomed case 211. A sealing member 212 is placed at the opening of the bottomed case 211, and the open end of the bottomed case 211 is crimped to the sealing member 212 to create a curl. This seals the wound body 100 containing the conductive polymer inside the bottomed case. Then, a base plate 213 is placed to cover the curled portion. In this way, the solid electrolytic capacitor 200 is obtained.

[0097] The sealing member 212 is formed so that the lead wires 60A and 60B pass through it. The sealing member 212 can be made of any insulating material, and an elastic material is preferred. Among these, silicone rubber, fluororubber, ethylene propylene rubber, Hypalon rubber, butyl rubber, isoprene rubber, etc., which have high heat resistance are preferred.

[0098] [Examples] The present disclosure will be described below in detail based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0099] Examples 1-10 and Comparative Examples 1-4 A solid electrolytic capacitor (rated voltage 2.50V) as shown in Figure 2 was fabricated using the following procedure.

[0100] (1) Preparation of anode foil Aluminum foil, with both main surfaces etched, was cut to match the shape of the capacitor element. The etched aluminum foil had an enlargement ratio of 300 cm² per main surface. 2 / cm 2 The total thickness was approximately 120 μm. The anode foil was prepared in this manner.

[0101] (2) Formation of dielectric layer A first dielectric layer was formed on the surface of the anode body by the ALD method (temperature: 250°C, precursor: Zr-containing precursor, oxidizing agent: O3, precursor pulse 30 seconds, purge 180 seconds, O3 pulse 0.6 seconds, purge 20 seconds). TDMAZ was used as the Zr-containing precursor to form a ZrO2 layer as the first dielectric layer.

[0102] A second dielectric layer was formed on the surface of the first dielectric layer by the ALD method (temperature: 250°C, oxidizing agent: O3, precursor pulse 3 seconds, purge 180 seconds, O3, pulse 0.6 seconds, purge 20 seconds). Trimethylaluminum, an Al-containing precursor, was used as the precursor for the second dielectric layer, and an Al2O3 layer was formed as the second dielectric layer. In Example 10, TDMAS was used as the precursor for the second dielectric layer, and an SiO2 layer was formed as the second dielectric layer.

[0103] The number of ALD cycles was adjusted so that the thicknesses T1 and T2 of each layer were the values ​​shown in the table. In this way, an anode foil having dielectric layers consisting of a first dielectric layer and a second dielectric layer on its surface was prepared (Examples 1 to 10 and Comparative Example 4).

[0104] In Comparative Example 1, the dielectric layer was formed using only the first dielectric layer. In Comparative Examples 2 and 3, the first dielectric layer was formed using Al2O3, similar to the case of the second dielectric layer in Example 1, and the dielectric layer was formed using only this first dielectric layer. In each example, the number of ALD cycles was adjusted so that the thickness T1 of the first dielectric layer was the value shown in the table. Except for these, capacitor elements and solid electrolytic capacitors were fabricated using the same procedure as in Example 1.

[0105] The first and second dielectric layers were confirmed by the method described above. The thickness T1 of the first dielectric layer and the thickness T2 of the second dielectric layer shown in Table 1 were determined by the procedure described above. The dielectric constants D1 and D2 of the dielectrics constituting each dielectric layer can be determined in accordance with the procedure described above for thin film samples prepared separately by the ALD method using the same procedure as above.

[0106] (3) Formation of conductive polymer layer A separation portion was formed in a predetermined region between the first end and the second end of the anode foil having the dielectric layer obtained in (2) above (more specifically, a predetermined region including the end of the first portion on the second portion side).

[0107] A pre-coat layer was formed by thinly coating the anode foil, which had a separation section formed on it, with a conductive material and then drying it.

[0108] A polymerization solution containing pyrrole (a monomer of a conjugated polymer), naphthalene sulfonic acid (a dopant), and water was prepared. Electropolymerization was carried out using the obtained polymerization solution. More specifically, a pre-coated anode foil was immersed in the polymerization solution, and an electropolymerization was performed at 25°C while applying a voltage to form a conductive polymer layer. The anode foil thus obtained, with the conductive polymer layer formed on the dielectric layer, was washed with water and dried at 75°C for 5 minutes.

[0109] (4) Formation of the cathode extraction layer A dispersion of graphite particles in water was applied to the surface of the conductive polymer layer of the anode foil obtained in (3) above, and the first layer (carbon layer) was formed by drying.

[0110] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of the first layer, and the binder resin was cured by heating to form the second layer (metal particle-containing layer). Heating was carried out at 215°C for 10 minutes. In this way, a cathode extraction layer consisting of the first layer (carbon layer) and the second layer (metal particle-containing layer) was formed, and a cathode portion consisting of a conductive polymer layer and a cathode extraction layer was formed. The capacitor element was fabricated in the manner described above.

[0111] (5) Assembly of solid electrolytic capacitors The cathode portion of the capacitor element obtained in (4) above and one end of the cathode lead terminal were joined via an adhesive layer formed of conductive adhesive. One end of the anode lead terminal was joined to the region on the first end side of the first portion of the anode foil protruding from the capacitor element by laser welding.

[0112] Next, a resin casing made of insulating resin was formed around the capacitor element by molding. At this time, the other end of the anode lead terminal and the other end of the cathode lead terminal were extended from the resin casing. Solid electrolytic capacitors were obtained in this manner. A total of 20 solid electrolytic capacitors were manufactured in the same way as described above. Subsequently, the solid electrolytic capacitors were subjected to an aging process at 130°C for 2 hours while applying the rated voltage.

[0113] (6) Evaluation The following evaluations were performed using solid electrolytic capacitors after aging treatment or anodes with a dielectric layer formed before the conductive polymer was formed.

[0114] (6-1) Capacitance and ESR Under 20°C conditions, the initial capacitance (μF) at 120 Hz and the initial ESR at 100 kHz of each solid electrolytic capacitor were measured using a 4-terminal LCR meter (Keysight Technologies, E4980). The average values ​​for both capacitance and ESR across 20 solid electrolytic capacitors were then calculated.

[0115] (6-2) Capacity acquisition rate The capacity acquisition rate was calculated as follows: The capacitance was measured using an anode body with a dielectric layer formed before the conductive polymer layer was formed, and the average value X0 of 20 measurements was determined. The capacitance (unit: μF) was determined by immersing the anode body with the dielectric layer formed in a beaker cell containing a simulated electrolyte, and using a 4-terminal LCR meter (Keysight Technologies, E4980) at 20°C and a frequency of 120 Hz. An aqueous solution containing ammonium adipate at a concentration of 7 mass% was used as the simulated electrolyte. In such measurements, the electrolyte reaches deep into the porous part of the anode body with the dielectric layer, so the capacitance X0 is considered to be close to the theoretical capacitance of a solid electrolytic capacitor. Using the capacitance X0 and the average value (X1) of the initial capacitance obtained in (6-1) above, the capacitance acquisition rate was calculated from the following formula. Capacity acquisition rate (%)=100×X1 / X0

[0116] (6-3) Leakage current (LC) After measuring the initial capacitance and ESR of a solid electrolytic capacitor, a 1kΩ resistor was connected in series, and a voltage of 30V to 60V was applied from a DC power supply. The leakage current (LC) value was measured 40 seconds after the start of voltage application, and the average value of 20 values ​​(unit: A) was calculated. An Agilent Technologies semiconductor parameter analyzer 4155B was used to measure the leakage current. -12 A is the upper limit of the detection limit.

[0117] Examples 11-15 An anode foil having a dielectric layer formed in the same manner as in Example 1 or Example 10 was heated under a nitrogen atmosphere under the heat treatment conditions (temperature and time) shown in the table. The heat treatment was performed using an RTA processing apparatus (infrared lamp annealing apparatus manufactured by Advanced Riko Co., Ltd.). In the first dielectric layer formed by such heat treatment, a crystalline region was formed in at least a part of the first dielectric. On the other hand, in the second dielectric layer, the second dielectric was in an amorphous state. The heated anode foil was cooled to room temperature under a nitrogen atmosphere. Capacitor elements and solid electrolytic capacitors were fabricated and evaluated in the same manner as in Example 1 or Example 10, except that an anode foil having a dielectric layer obtained in this way was used (Examples 11-14).

[0118] In Example 15, diethylzinc was used as the precursor for the second dielectric layer, and a ZnO layer was formed as the second dielectric layer. Except for this, the anode foil having a dielectric multilayer was heat-treated, and capacitor elements and solid electrolytic capacitors were fabricated and evaluated using the cooled anode foil, in the same manner as in Examples 11 to 14.

[0119] The results for Examples 1-15 and Comparative Examples 1-4 are shown in Tables 1-3. In these tables, E1-E15 represent Examples 1-15, and C1-C4 represent Comparative Examples 1-4. The "dielectric constant" shown in each table indicates the relative magnitudes of the dielectric constant D1 of the first dielectric and the dielectric constant D2 of the second dielectric.

[0120] [Table 1]

[0121] As shown in Table 1, even when a dielectric layer of high dielectric constant ZrO2 is formed in a solid electrolytic capacitor, a very high capacitance cannot be obtained (comparison of C1 and C2). C2, which has only an Al2O3 dielectric layer, has a high capacitance acquisition rate of 0.95. In contrast, C1, which has only a ZrO2 dielectric layer, has a low capacitance acquisition rate of 0.72, indicating that the high dielectric constant is not being effectively utilized. In contrast to these results, in example E1, in which a thin second dielectric layer of Al2O3 is formed on the surface of the first dielectric layer of ZrO2, a higher capacitance is obtained than both C1 and C2, and the capacitance acquisition rate is also high at 0.95. Furthermore, in Example E1, both ESR and leakage current are kept low.

[0122] On the other hand, when the capacitance of electrolytic capacitor samples using an electrolyte was measured, it was found that forming a dielectric layer of ZrO2, which has a high dielectric constant, resulted in a capacitance more than twice as high as when an Al2O3 dielectric layer was formed. When using an electrolyte, even when a thin second dielectric layer of Al2O3 was formed on the surface of the first ZrO2 dielectric layer, the capacitance decreased compared to when only the ZrO2 layer was used. In these examples, the capacitance acquisition rate was 1.00, indicating that the dielectric constant of the dielectric layer is sufficiently reflected in the capacitance.

[0123] Thus, the influence of the layer structure of the dielectric layers in solid electrolytic capacitors E1, C1, and C2 on capacitance is completely different from the case where an electrolytic solution is used. In C1, since the capacitance acquisition rate is low, when a dielectric with a relatively high dielectric constant such as ZrO2 is used, the adhesion to the conductive polymer layer is considered to be lower than when Al2O3 is in contact with the conductive polymer layer. In solid electrolytic capacitors, due to the low adhesion between the conductive polymer layer and the dielectric layer, even when a dielectric with a relatively high dielectric constant is used, the high dielectric constant cannot be fully utilized, resulting in a low capacitance acquisition rate. On the other hand, when an electrolytic solution is used, even if the adhesion between the dielectric layer and the conductive polymer layer is low, the presence of the electrolytic solution is considered to be able to maintain high conductivity between the dielectric layer and the conductive polymer layer. Therefore, when an electrolytic solution is used, a higher capacitance is considered to be obtained when the ratio of a high-dielectric-constant material such as ZrO2 is larger than that of a low-dielectric-constant material such as Al2O3.

[0124] When forming the first dielectric layer and the second dielectric layer showing the relationship D1 < D2, an effect as expected from C1 and C2 is considered to be obtained. Since the adhesion between the second dielectric layer and the conductive polymer is considered to be low and the dielectric constant of the first dielectric layer is low, it is difficult to increase the capacitance.

[0125] [Table 2]

[0126] As can be understood from Table 2, when the ratio T2 / T1 of the thickness T2 of the second dielectric layer to the thickness T1 of the first dielectric layer is 0.170 or less, a high capacitance can be obtained (comparison between C4 and E1 - E9). Also, even when T2 / T1 is extremely small at 0.003 or more, an effect of improving the capacitance can be seen (comparison between C1 and E1 - E9). Also, in the examples, a relatively high capacitance acquisition rate is obtained, and both ESR and LC are suppressed to low levels.

[0127] [Table 3]

[0128] As shown in Table 3, when the dielectric layer is heat-treated, an even higher capacitance tends to be obtained (comparison of E1 and E10 with E11-E14). In addition, ESR and LC are kept relatively low in E11-E15, where the dielectric layer is heat-treated. This is thought to be because the crystallinity of the first dielectric layer is increased by the heat treatment, making polarization more likely. Furthermore, crystallization of the second dielectric layer does not proceed easily at the above heat treatment temperatures, and it is thought that the amorphous state is maintained, thus maintaining high adhesion between the second dielectric layer and the conductive polymer layer.

[0129] From the viewpoint of obtaining a higher capacitance or capacitance acquisition rate, the second dielectric is preferably an oxide containing at least one element selected from the group consisting of silicon and aluminum.

[0130] Examples 16-23 and Comparative Examples 5-7 Corresponding to Examples 2-9 and Comparative Examples 2-4, the anode foil with a dielectric layer was heat-treated under the heat treatment conditions (heat treatment temperature and time) shown in Table 4, and the cooled anode foil was used. Otherwise, capacitor elements and solid electrolytic capacitors were fabricated and evaluated in the same manner as in Examples 2-9 and Comparative Examples 2-4. Table 4 also shows the results for Example 12, which corresponds to Example 1. In Table 4, E16-23 and E12 correspond to Examples 16-23 and 12, respectively. C5-C7 correspond to Comparative Examples 5-7.

[0131] [Table 4]

[0132] As shown in Table 4, even when the dielectric layer was heat-treated, a high capacitance was obtained with a dielectric layer thickness ratio T2 / T1 of 0.003 to 0.170, similar to the case without heat treatment (comparison of C5 with E1 to E9). Further high capacitance was obtained by heat treatment (comparison of E1 to E9 in Table 2 with E12 and E16 to E23 in Table 4). In addition, relatively high capacitance acquisition rates were obtained in the examples, and both ESR and LC were kept low.

[0133] Examples 24-26 Capacitor elements and solid electrolytic capacitors were fabricated and evaluated in the same manner as in Example 10 or Example 14, except that the thickness T2 of the second dielectric layer in Example 10 or Example 14 was changed as shown in Table 5. Table 5 shows the results for Comparative Example 1, Examples 10 and 14 together. In Table 5, E24-26, E10, and E14 are Examples 24-26, 10, and 14, respectively. C1 is Comparative Example 1.

[0134] [Table 5]

[0135] As shown in Table 5, even when the second dielectric contains Si, high capacitance can be obtained in a specific thickness ratio range T2 / T1, similar to when it contains Al (comparison of C1 with E24-E26, E10, and E14). Furthermore, when the dielectric layer is heated, even higher capacitance can be obtained (comparison of E24 and E10 with E14, E25, and E26). In addition, ESR and LC are kept low in the examples in Table 5.

[0136] Examples 27-30 and Comparative Examples 8-9 TDMAH, a precursor containing Hf, was used as the precursor for the first dielectric layer, and a layer of HfO2 was formed as the first dielectric layer. Except for this, an anode foil with a dielectric layer was formed in the same manner as in Example 6, Example 1, Example 20, Example 12, or Comparative Example 1, and capacitor elements and solid electrolytic capacitors were fabricated and evaluated using the obtained anode foil (Examples 27, 28, and 29, and Comparative Example 8).

[0137] Corresponding to Comparative Example 8, the anode foil with a dielectric layer was heat-treated under the heat treatment conditions (heat treatment temperature and time) shown in Table 6, and the cooled anode foil was used. Otherwise, the capacitor element and solid electrolytic capacitor were fabricated and evaluated in the same manner as in Comparative Example 8 (Comparative Example 9). The results for Examples 7 and 21 are also shown in Table 6. In Table 6, E27 to E30, E7 and E21 correspond to Examples 27 to 30, 7 and 21, respectively. C8 and C9 correspond to Comparative Examples 8 and 9, respectively.

[0138] [Table 6]

[0139] As shown in Table 6, even when the first dielectric contains Hf, high capacitance can be obtained in a specific thickness ratio range T2 / T1, similar to when it contains Zr (comparison of C8 and C9 with E27-30, E7 and E21). Furthermore, when the dielectric layer is heated, even higher capacitance can be obtained (comparison of E27, E28 and E7 with E29, E30 and E21). In addition, ESR and LC are kept low in the examples in Table 5. [Industrial applicability]

[0140] The solid electrolytic capacitors described herein have high capacitance and low ESR and leakage current. Therefore, they are suitable for applications requiring high capacitance and high reliability. However, the applications of solid electrolytic capacitors are not limited to these. [Explanation of Symbols]

[0141] 400: Solid electrolytic capacitor 402: Capacitor element 403: Exterior 404: Anode lead terminal 405: Cathode lead terminal 406: Anode foil 406a: Cathode forming part 406b:Anode extraction part 460a: core 460b: Porous part 407: Dielectric layer 407a: First dielectric layer 407b: Second dielectric layer 408: Cathode part 409: Solid electrolyte layer 410: Cathode extraction layer 411: First layer (carbon layer) 412: 2nd layer (metal particle containing layer) 413: Separation part 414: Adhesive layer P: Pit 200: Solid electrolytic capacitor 10: Anode foil 20: Cathode foil 30: Separator 40: Retaining tape 60A, 60B: Lead wires 50A, 50B: Lead tabs 100: Coiled body 211: Case with bottom 212: Sealing member 213: Seat board

Claims

1. A solid electrolytic capacitor comprising a capacitor element containing a conductive polymer, The aforementioned capacitor element is Anode and, A first dielectric layer comprising a first dielectric (excluding a composite oxide of titanium and aluminum) covering at least a portion of the surface of the anode body, A second dielectric layer comprising a second dielectric covering at least a portion of the surface of the first dielectric layer, The conductive polymer covers at least a portion of the surface of the second dielectric layer, The second dielectric is an oxide containing at least one element selected from the group consisting of silicon, aluminum, and zinc. The dielectric constant D1 of the first dielectric is higher than the dielectric constant D2 of the second dielectric. A solid electrolytic capacitor in which the thickness T2 of the second dielectric layer is 0.003T1 or more and 0.170T1 or less with respect to the thickness T1 of the first dielectric layer.

2. The solid electrolytic capacitor according to claim 1, wherein the first dielectric is an oxide containing at least one element selected from the group consisting of zirconium, niobium, and hafnium.

3. The solid electrolytic capacitor according to claim 1 or 2, wherein the first dielectric is an oxide containing at least one element selected from the group consisting of zirconium and hafnium.

4. The solid electrolytic capacitor according to claim 1 or 2, wherein the first dielectric includes a crystalline region.

5. The solid electrolytic capacitor according to claim 1 or 2, wherein the second dielectric material is amorphous.

6. The solid electrolytic capacitor according to claim 1 or 2, wherein the anode body is an anode foil containing aluminum.

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