Dielectric substance, capacitor including same, and device comprising capacitor

Abstract

A dielectric substance according to the present disclosure contains a tantalum compound. The dielectric substance contains: oxygen; and a first element other than oxygen and tantalum. The first element is an element which has an atomic valence electron number of 3 or 4 and can be a positive ion in an ion state. The abundance ratio of the first element in an outermost layer of the dielectric substance is less than 10 at%.

Description

Dielectric, capacitor including same, and device including capacitor

[0001] The present disclosure relates to a dielectric, a capacitor including the same, and a device including the capacitor.

[0002] The capacitor element includes, for example, a first electrode, a second electrode, and a dielectric interposed between these electrodes. The anode body included in the anode serving as the first electrode is, for example, a metal foil or porous body containing a valve metal. Examples of the valve metal include tantalum, niobium, and aluminum. The dielectric is formed by, for example, a vapor phase method (such as sputtering or atomic layer deposition) or chemical conversion treatment so as to cover at least a portion of the surface of the anode body.

[0003] Patent Document 1 proposes a dielectric material containing an amorphous tantalum compound containing fluorine and oxygen, in which the dielectric material is formed by RF magnetron sputtering or anodization using an aqueous solution containing NaF and NaOH.

[0004] Patent Document 2 discloses an anode body having a porous portion and containing a first metal, a first dielectric layer covering at least a part of the porous portion, and a second dielectric layer covering at least a part of the first dielectric layer and containing an oxide of a second metal, the first dielectric layer having a thickness T １ a first portion having a thickness T １ a thickness T smaller than ２ In Patent Document 2, the first dielectric layer is a native oxide film, and the second dielectric layer is formed by atomic layer deposition.

[0005] When the dielectric of a capacitor element is formed by anodic oxidation, an aqueous solution of phosphoric acid is often used (see, for example, Patent Document 3).

[0006] Japanese Patent No. 7122617 (Claim 1, Examples) International Publication No. 2021 / 192607 (Claim 1, Examples) Japanese Patent Application Laid-Open No. 2011-77257

[0007] Dielectrics containing tantalum compounds (eg, capacitors having such dielectrics) exhibit large variations in initial leakage current (LC).

[0008] A first aspect of the present disclosure relates to a dielectric containing a tantalum compound, the dielectric containing oxygen and a first element other than oxygen and tantalum, the first element having an atomic number of 3 or 4 valence electrons and capable of becoming a positive ion in an ionized state, and an abundance ratio of the first element in an outermost layer of the dielectric being less than 10 atomic %.

[0009] A second aspect of the present disclosure relates to a capacitor including: a first electrode; a second electrode; and the above-described dielectric disposed between the first electrode and the second electrode.

[0010] A third aspect of the present disclosure relates to a device including the above capacitor.

[0011] According to the present disclosure, variations in the initial leakage current in the dielectric can be reduced.

[0012] 1A and 1B are cross-sectional views schematically illustrating a capacitor element including a dielectric according to an embodiment of the present disclosure, and a capacitor according to an embodiment of the present disclosure.

[0013] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0014] In general, in capacitors using electrodes containing tantalum, porous bodies are used for electrodes such as anodes to increase the surface area of ​​the electrodes and ensure high capacitance. Examples of porous bodies include porous compacts formed from tantalum-containing particles and porous sintered compacts formed by sintering such compacts. To ensure high capacitance, it is advantageous to form a dielectric so that it thinly covers the irregular surface of the porous body, and therefore chemical conversion treatment using a chemical conversion solution is often used. Dielectrics can also be formed by gas-phase methods such as sputtering, but this method makes it more difficult to deposit the components that make up the dielectric uniformly and evenly on the surface of the porous body than liquid-phase methods, and the need to evacuate the chamber tends to increase costs.

[0015] Phosphoric acid aqueous solution is commonly used as the chemical conversion solution. However, when using a phosphoric acid aqueous solution, phosphorus is mixed into the dielectric formed, contributing to leakage current. Furthermore, when using a chemical conversion solution containing other acids, elements contained in the acid may be doped into the dielectric. In chemical conversion, protons from the acid diffuse and are neutralized. However, in porous bodies containing tantalum, protons are difficult to diffuse internally, making the pH prone to localized decreases. A decrease in pH can result in the formation of precipitates of elements contained in the acid or localized inhibition of chemical conversion, resulting in uneven chemical conversion. As a result, dielectrics of non-uniform quality are formed, and the insulating properties of the dielectric are not uniformly exhibited, resulting in leakage current. This results in large variations in leakage current, impairing the stability of quality (also known as reliability). Consequently, when the dielectric is used in capacitors and other applications, its performance deteriorates.

[0016] (Technology 1) In view of the above, the dielectric of the present disclosure is a dielectric containing a tantalum compound. The dielectric contains oxygen and a first element other than oxygen and tantalum. The first element has an atomic number of 3 or 4 valence electrons and can become a positive ion when in an ionic state. The abundance ratio of the first element in the outermost layer of the dielectric is less than 10 atomic %.

[0017] By keeping the abundance ratio of the first element in the outermost layer of the dielectric relatively low, less than 10 atomic %, precipitation of compounds containing the first element is suppressed, and uneven chemical conversion is also suppressed. Therefore, a dielectric of relatively uniform quality is formed. As a result, variation in the initial leakage current in the dielectric can be suppressed.

[0018] The first element is an element whose atomic number of valence electrons is 3 or 4 and which can become a positive ion. However, the first element does not include carbon. The first element does not necessarily have to be in the state of a positive ion of the first element in the dielectric. In the dielectric, the first element may be in a state of being bonded to another element such as oxygen.

[0019] The outermost layer of a dielectric is the outermost layer on one of a pair of surfaces located at both ends of the dielectric in the thickness direction. The outermost layer is a portion of the dielectric up to 10 nm thick. In other words, it is a portion of the dielectric up to 10 nm deep from the outermost surface. When a dielectric is formed to cover a first electrode, the outermost layer of the dielectric corresponds to the outermost layer on the side of the dielectric opposite the first electrode (i.e., the second electrode side). In a capacitor, the outermost surface of the dielectric is, for example, the surface of the dielectric opposite the anode body. The abundance ratio (corresponding to the content) of the first element in the outermost layer is determined using X-ray photoelectron spectroscopy (XPS). The abundance ratio of the first element is the average abundance ratio of the first element determined for the outermost layer of the dielectric. The phosphorus content in the outermost layer of a dielectric formed by a typical chemical conversion treatment using a phosphoric acid aqueous solution is approximately 3 atomic %.

[0020] In this specification, the distribution of elements in a dielectric, including the abundance ratio of the first element, is determined by XPS. More specifically, by performing XPS analysis while sputtering the dielectric from the surface, the abundance ratio (content) (unit: atomic %) of the elements in the dielectric at the surface and in the depth direction from the surface (in other words, the thickness direction) is determined. The XPS analysis is performed under the following conditions: X-ray photoelectron spectrometer: VersaProbe (manufactured by ULVAC-PHI, Inc.) X-ray source: monochromated-Al-Kα Measurement diameter: 100 μm diameter Photoelectron take-off angle: 90° Neutralization mechanism used Etching conditions: Sputter ion species: Ar ＋ Acceleration voltage: 2 kV Raster area: approx. 2 mm x 2 mm SiO under the above conditions ２ Sputtering rate: 5.4 nm / min.

[0021] As a sample for XPS analysis, for example, a first electrode (more specifically, an anode) on which a dielectric is formed is used. In this case, a tantalum foil or sintered body with a side length of 10 mm or more and 50 mm or less is used as the first electrode. Hereinafter, this sample will be referred to as Sample A. A first electrode (specifically, an anode) on which a dielectric is formed, obtained in the process of manufacturing a capacitor or capacitor element, may also be used as the sample. Hereinafter, this sample will be referred to as Sample B.

[0022] (Technology 2) In the above (Technology 1), the outermost layer may further contain a second element. The second element is an element other than oxygen, tantalum, and the first element. The second element is an element whose atomic number of valence electrons is one or two and which can become a positive ion when in an ionic state. By including the second element in the outermost layer, it is easy to adjust the abundance ratio of the first element to less than 10 atomic %. Therefore, precipitation of compounds containing the first element and chemical conversion unevenness in the dielectric are easily suppressed. As a result, variation in initial leakage current in the dielectric can be further suppressed.

[0023] The second element is an element whose atomic number of valence electrons is 1 or 2 and which can become a positive ion. The second element does not necessarily have to be in the form of a positive ion of the second element in the dielectric. In the dielectric, the second element may be in a state of being bonded to another element such as oxygen.

[0024] (Technology 3) In the above-mentioned (Technology 2), the abundance ratio of the first element in the dielectric decreases with increasing distance from the outermost layer, and when the penetration depth of the first element at a maximum depth at which the abundance ratio of the first element is 0.5 atomic % or more is D nm, the penetration depth of the second element may be 0.2 D nm or more. In this way, when the outermost layer contains the second element, the second element also exists in the dielectric in a state of having penetrated to a certain depth. By having the second element penetrate to a certain depth in the dielectric, it is easy to adjust the abundance ratio of the first element in the outermost layer.

[0025] In the dielectric, the abundance ratio of the first element decreases with increasing distance from the outermost layer (or the surface of the outermost layer). This means that the abundance ratio of the first element tends to decrease with increasing distance from the outermost layer (or the surface of the outermost layer), and as long as the abundance ratio of the first element tends to decrease overall, it also includes cases where the abundance ratio of the first element increases locally.

[0026] The penetration depth D (unit: nm) of the first element refers to the deepest position from the surface of the dielectric (in other words, the surface of the outermost layer) among positions where the abundance ratio of the first element is 0.5 mass % or more. The penetration depth D has almost the same meaning as the thickness of the second layer described below. Similarly to the case of the first element, the penetration depth of the second element refers to the deepest position from the surface of the dielectric (in other words, the surface of the outermost layer) among positions where the abundance ratio of the second element is 0.5 mass % or more.

[0027] (Technology 4) In any one of (Technology 1) to (Technology 3) above, the dielectric may include a first layer and a second layer covering the first layer. The second layer includes the outermost layer and is a region where the abundance ratio of the first element is 0.5 atomic % or more. The first layer is a region where the abundance ratio of the first element is less than 0.5 atomic %. The first layer and the second layer are distinguished by the difference in the abundance ratio of the first element. As such, the second layer contains a larger amount of the first element than the first layer. The dielectric contains tantalum and oxygen, and oxygen defects are likely to occur. By having the dielectric have the above layer structure, leakage current in the first layer can be suppressed to a certain extent, and oxygen defects can be compensated for by the first element, thereby ensuring high voltage resistance. Furthermore, as described above, the outermost layer has a relatively low abundance ratio of the first element, which suppresses precipitation of compounds containing the first element, thereby making the quality of the dielectric relatively uniform and reducing leakage current variation.

[0028] (Technology 5) In the above (Technology 4), when the total thickness of the first layer and the second layer is T (unit: nm) and the thickness of the second layer is D (unit: nm) of the penetration depth of the first element, the thickness D of the second layer may be equal to or less than 0.33 T. By setting the thickness D of the second layer in this range, precipitation of the compound containing the first element can be further suppressed, chemical conversion unevenness can be suppressed, and a more homogeneous dielectric can be obtained.

[0029] (Technology 6) In the above (Technology 4) or (Technology 5), the thickness D of the second layer may be equal to or less than 0.15 T. By setting the thickness of the second layer in this range, precipitation of the compound containing the first element can be further suppressed, chemical conversion unevenness can be suppressed, and a more homogeneous dielectric can be obtained.

[0030] The thicknesses of the dielectric and the first and second layers constituting the dielectric are determined from images taken with a scanning electron microscope (SEM). The average thickness of the dielectric is determined by measuring the thickness of the dielectric at multiple arbitrary locations (e.g., 10 locations) and averaging the measurements. More specifically, a cross section parallel to the thickness direction of sample A or sample B is exposed, and an SEM image is taken. The thickness of the dielectric is determined at multiple arbitrary locations in the field of view of the image. The sample for capturing the cross-sectional image is obtained by the following procedure: First, sample A or sample B is embedded in a curable resin, and the curable resin is cured. The cured product is wet- or dry-polished to expose a cross section parallel to the thickness direction of the dielectric (a cross section where the layer structure of the dielectric can be confirmed). The exposed cross section is smoothed by ion milling to obtain a sample for imaging. The thicknesses (average thicknesses) of the first and second layers are also determined in the same manner as the thickness of the dielectric.

[0031] (Technology 7) In any one of the above (Technology 1) to (Technology 6), the first element may include at least silicon. In this case, precipitation of compounds including the first element can be more effectively suppressed, and a more homogeneous dielectric can be obtained.

[0032] (Technology 8) In any one of the above (Technology 1) to (Technology 7), the second element may include at least one element selected from the group consisting of sodium and potassium. By introducing such a second element into the dielectric, it is easy to adjust the amount of the first element introduced and to adjust the abundance ratio of the first element in the outermost layer, the first layer, and the second layer. This makes it easy to suppress precipitation of compounds containing the first element, and makes the dielectric more homogenous.

[0033] (Technology 9) The present disclosure also encompasses a capacitor including the above-described dielectric. The capacitor of the present disclosure includes a first electrode, a second electrode, and the dielectric according to any one of (Technology 1) to (Technology 8) above, disposed between the first and second electrodes. In such a capacitor, variations in initial leakage current can be suppressed.

[0034] (Technology 10) In the above (Technology 9), the first electrode may contain tantalum, and the dielectric may be an oxide film of the first electrode. The abundance ratio of the first element in the outermost layer of the dielectric on the second electrode side may be less than 10 atomic %. When the dielectric is an oxide film of the first electrode, it is easy to adjust the abundance ratio of the first element in the outermost layer of the dielectric on the second electrode side.

[0035] (Technology 11) In the above (Technology 9) or (Technology 10), the capacitor may contain an electrolyte, which can provide a higher capacitance.

[0036] (Technology 12) The present disclosure also includes a device including the capacitor according to any one of (Technology 9) to (Technology 11) above.

[0037] The dielectric, capacitor, and device of the present disclosure will be described in more detail below, including the above (Technology 1) to (Technology 12). At least one selected from the components described below can be arbitrarily combined with at least one of the above (Technology 1) to (Technology 12) of the present disclosure, as long as such combination is technically possible. Note that each figure is a schematic illustration, and the dimensional ratios (e.g., thickness) of each component may differ from the actual ratios.

[0038] In the following, embodiments of the present disclosure may be described using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In the following description, when lower and upper limits of numerical values ​​related to specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more of the materials may be used in combination.

[0039] [Dielectric] The tantalum compound contained in the dielectric contains oxygen and a first element. The first element can also be considered a doping element that is doped into the tantalum compound that constitutes the dielectric. The first element is an element that has three or four valence electrons and can become a positive ion when in an ionic state. When the dielectric contains such a first element, charge compensation is achieved and the oxygen defect level is stabilized, thereby suppressing leakage current.

[0040] In the present disclosure, the abundance ratio of the first element in the outermost layer of the dielectric is less than 10 atomic %. By having the abundance ratio of the first element in the outermost layer in this range, precipitation of compounds containing the first element and uneven chemical conversion are suppressed, resulting in the formation of a relatively homogeneous dielectric. This suppresses variations in leakage current and maintains high capacitance in reliability tests. The abundance ratio of the first element in the outermost layer of the dielectric may be 8 atomic % or less, 5 atomic % or less, or 2 atomic % or less. The abundance ratio of the first element in the outermost layer of the dielectric layer may be greater than 0 atomic %.

[0041] The probability of the presence of tantalum element in the outermost layer of the dielectric may be 0 atomic % or more and 36 atomic % or less, or may be 1 atomic % or more and 30 atomic % or less.

[0042] The outermost layer of the dielectric may further contain a second element. The second element is an element other than oxygen, tantalum, and the first element. The second element has one or two valence electrons and can become a positive ion when in an ionic state. When the outermost layer contains the second element, it is easy to adjust the abundance ratio of the first element to within the above range.

[0043] The abundance ratio of the second element in the outermost layer of the dielectric may be 0.5 atomic % or more and 15 atomic % or less, or may be 1 atomic % or more and 10 atomic % or less. When the abundance ratio of the second element in the outermost layer is in such a range, it is easier to adjust the existence probability of the first element in the outermost layer.

[0044] Each of the first element and the second element may be contained in the dielectric in a state of being bonded to oxygen, or may be contained as a monoatomic ion.

[0045] In a dielectric, the abundance ratio of the first element may decrease with increasing distance from the outermost layer (more specifically, the surface of the outermost layer). In a dielectric, when the penetration depth of the first element is D (unit: nm), the penetration depth of the second element may be 0.2D (unit: nm) or more. When the outermost layer contains the second element, the second element penetrates relatively deeply. In this case, it is easy to adjust the abundance ratio of the first element in the outermost layer. The penetration depth of the second element may be 0.5D (nm) or more, or may be 0.8D (nm) or more. The penetration depth of the second element may be 2.0D (nm) or less.

[0046] The dielectric may include a first layer and a second layer covering the first layer. The second layer includes the outermost layer of the dielectric. The second layer is a layer formed by chemical conversion using an acid aqueous solution containing the first element. Therefore, the abundance ratio of the first element is higher in the second layer than in the first layer. The second layer includes the outermost layer and is a region where the abundance ratio of the first element is 0.5 atomic % or more. The first layer is a region where the abundance ratio of the first element is less than 0.5 atomic %. The dielectric has the above-mentioned layer structure, which makes it easier to suppress leakage current in the first layer to a certain extent and ensure high voltage resistance by allowing the first element to compensate for oxygen defects with electric charge. The first layer may be a layer formed by chemical conversion using an aqueous phosphoric acid solution.

[0047] The abundance ratio of the first element in the dielectric, the outermost layer, the first layer, and the second layer is determined by the XPS analysis described above. The abundance ratios of other elements such as the second element are also determined by XPS analysis in the same manner as for the first element.

[0048] The thickness of the second layer has the same meaning as the penetration depth of the first element and is expressed in D (unit: nm). When the total thickness of the first layer and the second layer is T (unit: nm), the thickness D (unit: nm) of the second layer may be 0.33 T or less, 0.20 T or less, 0.15 T or less, or 0.14 T or less. When the thickness of the second layer is in this range, a more homogeneous dielectric can be obtained and the variation in leakage current can be further suppressed. From the viewpoint of further suppressing the leakage current, the thickness D of the second layer may be 0.01 T or more or 0.02 T or more. The total thickness T of the first layer and the second layer can also be referred to as the thickness (average thickness) T of the dielectric.

[0049] The thickness D of the second layer may be 0.01T or more (or 0.02T or more) and 0.33T or less, 0.01T or more (or 0.02T or more) and 0.20T or less, 0.01T or more (or 0.02T or more) and 0.15T or less, or 0.01T or more (or 0.02T or more) and 0.14T or less.

[0050] The average thickness T of the dielectric may be 100 nm or more and 300 nm or less, or 130 nm or more and 250 nm or less. When the thickness T is in such a range, a higher capacitance can be obtained.

[0051] The first element may include at least one element selected from the group consisting of Groups 3 to 14 of the periodic table. In particular, the first element preferably includes at least one element selected from the group consisting of Groups 4 and 14 of the periodic table. Examples of Group 4 elements include titanium, zirconium, hafnium, and rutherfordium. Examples of Group 14 elements include carbon, silicon, germanium, tin, and lead. The Group 14 element may be carbon, but an element other than carbon is preferred from the viewpoint of facilitating stabilization of oxygen defect levels. It is also preferable for the first element to include at least one element selected from the group consisting of silicon, germanium, and hafnium. The first element may be a Group 14 element. In particular, it is preferable for the first element to include at least silicon. When the first element includes such an element, the effect of stabilizing oxygen defect levels is greater than, for example, when the first element includes carbon, thereby suppressing leakage current and ensuring higher voltage resistance. Since the dielectric constant of silicon oxide is lower than that of tantalum oxide, when the dielectric contains silicon, the effect of improving the voltage resistance is enhanced.

[0052] The first element contained in the outermost layer of the dielectric can be observed in the XPS spectrum. In the XPS spectrum of the outermost layer, a peak attributed to the first element is observed. In addition, in the XPS spectrum of the outermost layer, O 2 derived from the bond between the first element and oxygen is observed. １ｓ A peak attributed to may be observed.

[0053] For example, when the dielectric contains silicon, the XPS spectrum of the outermost layer of the dielectric contains Si ２ｐ A peak attributed to Si may be observed. ２ｐ The peak attributed to is observed, for example, in the binding energy range of 99 eV to 105 eV (particularly, 102 eV to 104 eV) in the XPS spectrum. Dielectrics exhibiting such a peak contain silicon-containing ionic species at least in the outermost layer. Note that such a peak is not observed in dielectrics formed using conventional phosphoric acid aqueous solutions.

[0054] Furthermore, when the dielectric contains silicon, the XPS spectrum of the outermost layer of the dielectric shows O derived from Si—O bonds.１ｓ A peak attributed to may be observed. Such a peak is observed, for example, in the binding energy range of 528 eV or more and 534 eV or less (particularly, 532 eV or more and 534 eV or less) in the XPS spectrum. A dielectric exhibiting such a peak contains silicon oxide at least in the outermost layer. Such a peak is not observed in the case of a dielectric formed using a conventional phosphoric acid aqueous solution.

[0055] In the case of a dielectric formed using a conventional phosphoric acid aqueous solution, the XPS spectrum of the outermost surface of the dielectric shows P derived from phosphorus-containing ion species. ２ｐ In contrast, in the XPS spectrum of the outermost layer of the dielectric material of the present disclosure, a peak attributed to P ２ｐ Such a peak is observed, for example, in the binding energy range of 130 eV to 135 eV in the XPS spectrum.

[0056] The second element may include at least one element selected from the group consisting of elements of Groups 1 to 14 of the periodic table. In particular, the second element preferably includes at least one element selected from elements of Group 1 of the periodic table. The Group 1 element is preferably at least one element selected from the group consisting of sodium and potassium.

[0057] The dielectric may optionally contain an element (referred to as a third element) other than oxygen, tantalum, the first element, and the second element. The dielectric may contain one or more third elements. The content of each third element in the outermost layer of the dielectric may be 5 atomic % or less, or may be 3 atomic % or less.

[0058] The dielectric may be formed by forming a film (first layer) by a gas phase method, and then further forming a film (second layer) containing the first element (and the second element). Alternatively, the dielectric may be formed by oxidizing the first electrode using a phosphoric acid aqueous solution, and then further oxidizing the formed oxide film (first layer) and the first electrode using a liquid mixture (such as an acid aqueous solution) containing the first element to form an oxide film (second layer). That is, the dielectric is preferably an oxide film of the first electrode. Such a dielectric is formed, for example, by oxidizing the surface of the first electrode (and the oxide film formed by the phosphoric acid aqueous solution) with the phosphoric acid aqueous solution or liquid mixture in contact with at least a portion of the surface of the first electrode containing tantalum (e.g., an anode (more specifically, an anode body) or an anode body having an oxide film formed by the phosphoric acid aqueous solution). When the dielectric is formed by oxidizing the surface of the first electrode, a thin oxide film is more likely to be formed to cover the uneven surface of the dielectric than when the dielectric is formed by a gas phase method.

[0059] Examples of the phosphoric acid aqueous solution used for oxidizing the first electrode (more specifically, the anode body) include phosphoric acid aqueous solutions used in general chemical conversion treatments. The concentration of phosphoric acid in the phosphoric acid aqueous solution may be 0.001% by mass or more and 10.000% by mass or less, 0.001% by mass or more and 1.000% by mass or less, or 0.010% by mass or more and 1.000% by mass or less. By chemical conversion using the phosphoric acid aqueous solution, an oxide film (first layer) is formed on the surface of the first electrode (more specifically, the anode body). The first layer formed in this manner contains elemental phosphorus.

[0060] The phosphoric acid aqueous solution may contain hydrogen peroxide. The concentration of hydrogen peroxide in the phosphoric acid aqueous solution may be 0.001% by mass or more and 15,000% by mass or less, or 0.001% by mass or more and 10,000% by mass or less.

[0061] The liquid mixture used for further oxidation of the first electrode (more specifically, the anode body) having the oxide film is, for example, an aqueous solution (such as an acid aqueous solution) containing the first element. The first element may be contained in the liquid mixture in any form. For example, the first element may be contained in the liquid mixture in the form of monoatomic ions or polyatomic ions. The second layer is formed using such a liquid mixture.

[0062] The liquid mixture may contain a buffer. Examples of the buffer include bicarbonate-based buffers, citrate-based buffers, phthalate-based buffers, acetate-based buffers, phosphate-based buffers (such as trisodium phosphate), and MES (2-morpholinoethane sulfonic acid) buffers. One type of buffer may be used, or two or more types may be used in combination.

[0063] Buffers are often composed of salts of an acid and a base. Therefore, buffers may contain elements of Group 1 of the periodic table, such as sodium and potassium, derived from the base. These elements are doped into the oxide film as second elements together with the first element by chemical conversion using a liquid mixture.

[0064] The concentration of the first element in the liquid mixture is 2.00 × 10 －４ The concentration of the first element may be from 0.01% to 2.50% by mass, or from 0.05% to 1.00% by mass. When the concentration of the first element is in this range, the first element is easily doped into the dielectric and the abundance ratio of the first element in the outermost layer is easily adjusted, which makes it easy to suppress variations in leakage current.

[0065] The concentration of the second element in the liquid mixture is 5.00 x 10 －４ The concentration of the second element may be from 0.02% by mass to 8.00% by mass, or from 0.05% by mass to 3.00% by mass. When the concentration of the second element is in this range, the dielectric is easily doped with the second element and the first element, and it is easy to adjust the abundance ratio of the first element in the outermost layer.

[0066] The oxidation of the first electrode (oxidation using the phosphoric acid aqueous solution and the liquid mixture) may be performed with a voltage applied to the first electrode. The voltage applied to the first electrode (also referred to as oxidation voltage) may be 30 V or more and 100 V or less, 50 V or more and 100 V or less, or 70 V or more and 100 V or less. The oxidation of the first electrode may be performed at a constant voltage, may be performed while increasing the voltage at a predetermined rate, or a combination of these. For example, oxidation may be performed by increasing the voltage at a predetermined rate and maintaining the increased voltage constant for a predetermined period of time. The oxidation voltage is the voltage of the first electrode relative to the counter electrode. The rate of increase in voltage may be, for example, 0.5 V / h or more and 15 V / h or less, or 1 V / h or more and 10 V / h or less. The voltage maintained after the increase in voltage may be within the above oxidation voltage range. The time for which the constant voltage is maintained may be 5 hours or more and 50 hours or less, or 10 hours or more and 30 hours or less.

[0067] The oxidation of the first electrode may be performed at room temperature or under heating. The temperature of the liquid mixture during oxidation may be 20°C or higher and 100°C or lower, 35°C or higher and 100°C or lower, or 50°C or higher and 100°C or lower. The temperature of the phosphoric acid aqueous solution during oxidation may be within the range described above for the temperature of the liquid mixture, and may be 30°C or higher and 70°C or lower, or 30°C or higher and 50°C or lower.

[0068] [Capacitor] The capacitor of the present disclosure includes the above-described dielectric. In the capacitor, the dielectric is disposed between a first electrode and a second electrode. The dielectric is preferably formed so as to cover at least a portion of the surface of the first electrode (more specifically, the anode). Such a dielectric may form a layer (also referred to as a dielectric layer). The capacitor may also include an electrolyte.

[0069] The capacitor may include a capacitor element and an exterior body that seals the capacitor element. The capacitor element may be configured, for example, with a first electrode, a second electrode, and a dielectric. The capacitor may include one capacitor element or two or more capacitor elements.

[0070] (First Electrode) The first electrode is, for example, an anode. The first electrode includes, for example, an anode body. The anode body may include a valve metal, an alloy containing a valve metal, or a compound containing a valve metal. The anode body may include one of these materials or a combination of two or more of them. Examples of valve metals include tantalum, aluminum, niobium, and titanium.

[0071] When the dielectric is formed by oxidation of the first electrode (in other words, when the dielectric is an oxide film of the first electrode), the first electrode contains tantalum. When the first electrode is formed by a vapor phase method or the like, it does not necessarily have to contain tantalum. The first electrode containing tantalum may be formed of tantalum or a tantalum alloy, or may be formed of tantalum itself.

[0072] The anode body has a porous portion at least on its surface. Such a porous portion provides the anode body with a finely textured shape at least on its surface. An anode body having a porous portion on its surface can be obtained, for example, by roughening the surface of a substrate containing a valve metal (such as a sheet-like (e.g., foil-like, plate-like) substrate). The roughening may be performed, for example, by etching. The anode body may also be a compact or sintered body of particles containing a valve metal. The compact and sintered body may each entirely constitute a porous portion. Such a compact and sintered body may be simply referred to as a porous body. The compact and sintered body may each be in the form of a sheet, a rectangular parallelepiped, a cube, or a similar shape.

[0073] The anode body may be divided into a cathode-forming portion facing the second electrode (specifically, a cathode) and an anode lead portion that does not face the second electrode. The anode body may also have a porous body and a wire inserted into the porous body. In this case, the wire corresponds to the anode lead portion. The anode lead portion is used, for example, for electrical connection to an external electrode or a lead terminal on the anode side.

[0074] (Dielectric) The dielectric is formed, for example, so as to cover at least a part of the surface of the anode body. The dielectric layer is an insulating layer that functions as a dielectric.

[0075] When the dielectric is an oxide film of the first electrode, the dielectric is formed on the porous surface of the first electrode, and therefore the surface of the dielectric has a finely uneven shape corresponding to the unevenness of the first electrode. In the present disclosure, the above-mentioned dielectric suppresses variations in initial leakage current.

[0076] (Electrolyte) The electrolyte contained in the capacitor may be a liquid electrolyte, a solid electrolyte, or both. A combination of a solid electrolyte and a liquid component may also be used. The electrolyte may be interposed between the first electrode and the second electrode. The solid electrolyte may constitute the second electrode together with the cathode extraction layer.

[0077] The liquid electrolyte contains a solvent and a solute. A non-aqueous solvent is preferable as the solvent. Examples of the non-aqueous solvent include sulfone compounds (sulfolane, dimethyl sulfoxide, ethyl sulfoxide, etc.), lactone compounds (γ-butyrolactone, γ-valerolactone, etc.), carbonate compounds (ethylene carbonate, propylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, etc.), carboxylic acid ester compounds, and alcohol compounds (ethylene glycol, polyethylene glycol, etc.). The liquid component may contain one type of solvent (such as a non-aqueous solvent) or a combination of two or more types.

[0078] The solute may be an acid component or a base component. A salt of an acid component and a base component may also be used as the solute. Preferred examples of the acid component include aromatic carboxylic acids (e.g., benzoic acid, salicylic acid), aromatic polycarboxylic acids (e.g., phthalic acid), etc. The base component may include organic bases (e.g., amines, quaternary ammonium compounds), and inorganic bases (e.g., metal hydroxides).

[0079] The liquid electrolyte is housed, for example, together with the capacitor element in an exterior body such as a case.

[0080] The solid electrolyte may be a gel electrolyte or a polymer electrolyte obtained by solidifying a liquid electrolyte with a gelling agent or a polymer. Alternatively, a conductive polymer may be used as the solid electrolyte. The conductive polymer may be a conductive polymer containing a conjugated polymer and a dopant, or a self-doped conductive polymer, or both.

[0081] Examples of conjugated polymers include π-conjugated polymers. Examples of conjugated polymers include polymers with a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylene vinylene, polyacene, and polythiophene vinylene. Such polymers may contain at least one monomer unit constituting the basic skeleton. The monomer unit may also include a monomer unit having a substituent. The above polymers include homopolymers and copolymers of two or more monomers. For example, polythiophenes include poly(3,4-ethylenedioxythiophene) (PEDOT). The solid electrolyte may contain one type of conjugated polymer or a combination of two or more types.

[0082] Examples of dopants include at least one selected from the group consisting of anions and polymeric anions. Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Compounds capable of generating anions may also be used as dopants. Examples of such compounds include paratoluenesulfonic acid and naphthalenesulfonic acid. Examples of polymeric anions include polyvinylsulfonic acid, polystyrenesulfonic acid (PSS), polyallylsulfonic acid, polyacrylicsulfonic acid, polymethacrylicsulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyestersulfonic acids (such as aromatic polyestersulfonic acids), phenolsulfonic acid novolac resin, and polyacrylic acid. These are merely examples, and the dopants are not limited thereto. The solid electrolyte may contain one type of dopant or a combination of two or more types.

[0083] Examples of liquid components used in combination with the solid electrolyte include the non-aqueous solvents described above. Protic solvents such as alcohol compounds may also be used. The non-aqueous solvents may be used alone or in combination of two or more.

[0084] A solid electrolyte containing a conductive polymer may be formed, for example, by polymerizing a precursor (such as a monomer) of a conjugated polymer on a dielectric in the presence of a dopant. Chemical polymerization or electrolytic polymerization may be used for the polymerization. Alternatively, the solid electrolyte may be formed by applying a solution in which the conductive polymer is dissolved or a liquid dispersion in which the conductive polymer is dispersed to the surface of the dielectric. In a capacitor element, the solid electrolyte may form a layer. The solid electrolyte layer may be a single layer or multiple layers.

[0085] The gel electrolyte is housed together with the capacitor element in an exterior body such as a case. The capacitor element may be formed by interposing a polymer electrolyte between the first electrode and the second electrode.

[0086] (Second Electrode) The second electrode is, for example, a cathode. The second electrode includes an electrode extraction layer (also referred to as a cathode extraction layer). The second electrode may be composed of a solid electrolyte and the electrode extraction layer.

[0087] The electrode extraction layer includes at least a metal-containing layer, such as a metal foil or a metal particle-containing layer.

[0088] The type of metal constituting the metal foil is not particularly limited. The metal foil may be a valve metal (tantalum, aluminum, niobium, etc.) 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 provided with a chemical conversion coating, or a coating of a metal (dissimilar metal) or nonmetal different from the metal constituting the metal foil. Examples of dissimilar metals or nonmetals include metals such as titanium and nonmetals such as conductive carbon. The metal foil is laminated on an underlying layer (such as a dielectric, solid electrolyte, or carbon layer, as described below).

[0089] Examples of metal materials constituting the metal particles contained in the metal particle-containing layer include silver, silver alloys, copper, and copper alloys. The metal particle-containing layer is formed by applying a metal paste containing metal particles and a resin binder to a base layer (such as a dielectric, solid electrolyte, or carbon layer described below) and drying or solidifying the coating. The resin binder may be a thermoplastic resin, or a thermosetting resin such as an imide resin or an epoxy resin. The resulting metal particle-containing layer may contain metal particles and a resin binder or a cured product thereof.

[0090] The electrode extraction layer may include a carbon layer and a metal-containing layer covering the carbon layer. For example, when the second electrode includes a solid electrolyte, the second electrode may further include a carbon layer covering at least a portion of the solid electrolyte and a metal-containing layer covering at least a portion of the carbon layer. The carbon layer may include, for example, conductive carbon and, if necessary, a resin binder (such as a water-soluble resin or a curable resin) or a cured product thereof. Examples of conductive carbon include graphite (such as artificial graphite or natural graphite).

[0091] The carbon layer is formed, for example, by applying a conductive paste or liquid dispersion containing conductive carbon and, if necessary, a resin binder to the surface of an underlying layer (dielectric, solid electrolyte, etc.), and then drying or solidifying it.

[0092] In the process of forming the electrode extraction layer, a heat treatment or the like may be carried out as necessary.

[0093] These configurations are merely examples of the configuration of the electrode extraction layer, and other configurations having a current collecting function may also be used.

[0094] (Other) The capacitor may be of a wound type, chip type, or stacked type. When a capacitor includes multiple capacitor elements, each capacitor element may be of a wound type or stacked type. For example, a stacked capacitor includes multiple stacked capacitor elements. The configuration of the capacitor elements may be selected depending on the type of capacitor.

[0095] In the capacitor element, for example, one end of a second lead terminal is electrically connected to the electrode lead layer of the second electrode. For example, one end of a first lead terminal is electrically connected to the electrode lead portion (e.g., anode lead portion) of the first electrode. The other end of each lead terminal is respectively led out from the exterior housing. The other end of each lead terminal exposed from the exterior housing is used for solder connection with a substrate on which the capacitor is to be mounted, and is electrically connected to an external electrode. At least a portion of the external electrode constitutes an external terminal of the capacitor. Each lead terminal may be a lead wire or a lead frame. Furthermore, without being limited to the use of lead terminals, an end face of the electrode lead portion (e.g., anode lead portion) may be exposed from the exterior housing and connected to an external electrode. An end face of a metal foil included in the second electrode may be exposed from the exterior housing and connected to an external electrode. An end face of the other end of the second lead terminal connected to the electrode lead layer of the second electrode may be exposed from the exterior housing and connected to an external electrode.

[0096] The capacitor element is sealed with, for example, an exterior body. For example, the capacitor element and the resin material of the exterior body (e.g., uncured thermosetting resin and filler) may be placed in a mold, and the capacitor element may be sealed with the resin exterior body by transfer molding, compression molding, or the like. At this time, the other end portions of each lead terminal drawn from the capacitor element are exposed from the mold. Alternatively, the capacitor element may be housed in a bottomed case such that the other end portions of each lead terminal are positioned on the opening side of the bottomed case, and the opening of the bottomed case may be sealed with a sealant to form a capacitor.

[0097] [Devices Including Capacitors] The capacitors of the present disclosure have reduced variations in initial leakage current and are highly reliable. The initial leakage current is also kept low. Therefore, the capacitors are used in a variety of applications (devices) that require high reliability. Devices in which the capacitors are mounted include, but are not limited to, various electronic devices, various electrical devices, and in-vehicle applications.

[0098] FIG. 1 is a cross-sectional view schematically illustrating a capacitor element including a dielectric according to an embodiment of the present disclosure. The capacitor element 10 includes a first electrode 11 and a second electrode 13. The first electrode 11 includes a porous body 111 made of tantalum, an electrode wire 112 extending from the porous body 111, and a dielectric 113 covering at least a portion of the porous body 111. The second electrode 13 includes a solid electrolyte layer 131, a carbon layer 132, and a metal particle-containing layer 133. The carbon layer 132 and the metal particle-containing layer 133 function as cathode extraction layers. The capacitor element 10 has a generally cubic shape. In the present disclosure, the dielectric 113 includes a tantalum compound containing oxygen and a first element. The abundance ratio of the first element in the outermost layer of the dielectric 113 is less than 10 atomic %. This distribution of the first element suppresses precipitation of the compound containing the first element in the dielectric and also suppresses uneven chemical conversion. This allows the dielectric to be formed with relatively uniform quality, thereby suppressing variations in the initial leakage current in the capacitor.

[0099] 2 is a cross-sectional view schematically illustrating a capacitor according to an embodiment of the present disclosure. Capacitor 100 includes the capacitor element of FIG. 1, an exterior body 20 that seals the capacitor element, and first and second lead terminals 30 and 40, at least a portion of which is exposed to the outside of exterior body 20.

[0100] The electrode wire 112 and the first lead terminal 30 are electrically connected by, for example, welding. The metal particle-containing layer 133 and the second lead terminal 40 are electrically connected via an adhesive layer 50 formed of, for example, a conductive adhesive (such as a mixture of a thermosetting resin with carbon particles or metal particles).

[0101] 2 illustrates a capacitor in which a solid electrolyte is used as the electrolyte and the capacitor element is sealed in an exterior case, but the capacitor of the present disclosure is not limited to this combination. For example, the capacitor of the present disclosure may be a capacitor in which a capacitor element and a liquid electrolyte are housed in a case.

[0102] EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0103] Example 1 Evaluation samples were prepared in the following manner, and their properties were evaluated.

[0104] (i) Preparation of First Electrode Tantalum metal particles were used as the valve metal. Tantalum metal particles were molded into a rectangular parallelepiped so that one end of an anode wire made of tantalum metal was embedded in the tantalum metal particles, and the molded body was then sintered in a vacuum. This resulted in an anode part including an anode body made of a porous tantalum sintered body and an anode wire with one end embedded in the anode body and the remaining portion embedded in one surface of the anode body.

[0105] (ii) Formation of Oxide Film (Dielectric) An aqueous solution containing phosphoric acid at a concentration of 0.001% by mass to 1.000% by mass and hydrogen peroxide at a concentration of 0.001% by mass to 10.000% by mass was prepared as a chemical conversion solution (first chemical conversion solution). A chemical conversion tank was filled with the first chemical conversion solution, and the anode body was immersed in the first chemical conversion solution. The chemical conversion solution had a temperature of 50°C to 100°C. The upper end of the wire not immersed in the solution was connected to a counter electrode, and the chemical conversion voltage was increased at a rate of 1 V / h to 10 V / h until the chemical conversion voltage reached 50 V to 100 V, and the increased voltage was maintained for 10 hours to 30 hours. In this way, a phosphorus-containing tantalum oxide oxide film (first layer) was formed on a portion of the surface of the anode body.

[0106] Next, as a chemical conversion solution (second chemical conversion solution), Na ２ SiO ３ An aqueous solution containing 0.001% by mass or more and 10.00% by mass or less of the above-mentioned compound and trisodium phosphate (a buffer agent) at a concentration of 0.001% by mass or more and 10.00% by mass or less was prepared. A chemical conversion tank was filled with the second chemical conversion solution, and the anode body on which the first layer had been formed was immersed therein. The chemical conversion voltage was set to 70 V or more and 100 V or less. Except for this, an oxide film (second layer) of tantalum oxide containing silicon as the first element and sodium as the second element was formed in the same manner as above. In this manner, a first electrode having a dielectric with a first layer and a second layer and an evaluation sample of the first electrode were produced.

[0107] (iii) Formation of a Solid Electrolyte Layer A dispersion was prepared by mixing 3,4-ethylenedioxythiophene, iron(III) p-toluenesulfonate, and 1-butanol. The anode element was immersed in the dispersion, then removed from the dispersion and subjected to heat treatment in the air at a temperature of 60°C or higher and 200°C or lower. In this case, iron(III) p-toluenesulfonate functions as an oxidizing agent. In this way, a polymerization reaction was carried out on the oxide film, and a first solid electrolyte layer containing poly(3,4-ethylenedioxythiophene) (PEDOT) was formed.

[0108] The tantalum sintered body on which the first solid electrolyte layer was formed was immersed in an aqueous dispersion containing a conductive polymer (PSS-doped PEDOT) at a concentration of 1% by mass to 4% by mass for approximately 30 to 60 seconds, and then the tantalum sintered body was pulled out of the aqueous dispersion. The tantalum sintered body pulled out of the liquid dispersion 2A was then dried by heating at a temperature of 140°C to 180°C for 10 to 20 minutes, thereby forming a solid electrolyte. The second solid electrolyte layer was formed by repeatedly immersing in the aqueous dispersion and drying. In this way, a solid electrolyte layer composed of a first solid electrolyte layer and a second solid electrolyte layer was formed.

[0109] (iv) Formation of Cathode Extraction Layer The tantalum sintered compact on which the solid electrolyte layer formed in (iii) above was formed was immersed in a dispersion liquid in which graphite particles were dispersed in water, and then removed from the dispersion liquid and dried to form a carbon layer on the surface of the solid electrolyte layer. The drying was carried out at a temperature of 180°C for 10 minutes to 30 minutes.

[0110] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of the carbon layer and dried at a temperature of 60°C to 80°C for 20 to 40 minutes. The binder resin was then cured by heating at 180°C for 30 to 60 minutes, forming a metal particle-containing layer. In this way, a cathode extraction layer composed of the carbon layer and the metal particle-containing layer was formed.

[0111] In this way, a capacitor element including a cathode portion composed of a solid electrolyte layer and a cathode extraction layer was fabricated.

[0112] (v) Assembly of a solid electrolytic capacitor The cathode extraction layer of the capacitor element obtained in (iv) above was joined to one end of a cathode lead terminal with a conductive adhesive, and the wire protruding from the capacitor element was joined to one end of an anode lead terminal by laser welding.

[0113] Next, a resin outer casing made of insulating resin was formed around the capacitor element by transfer 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 outer casing. In this way, a total of 20 solid electrolytic capacitors were completed.

[0114] Example 2 Anodization using a first chemical conversion solution was carried out under the conditions of a temperature of the chemical conversion solution of 30° C. to 50° C. and a chemical conversion voltage of 70 V to 100 V. Anodization using a second chemical conversion solution was carried out under the conditions of a temperature of the chemical conversion solution of 50° C. to 100° C. and a chemical conversion voltage of 70 V to 100 V. The second chemical conversion solution contained Na ２ SiO ３ The aqueous solution used contained 0.001% by mass or more and 10.000% by mass or less of sodium hydroxide and trisodium phosphate (a buffer agent) at a concentration of 0.001% by mass or more and 10.000% by mass or less. A first electrode and a total of 20 solid electrolytic capacitors were fabricated in the same manner as in Example 1, except for the above.

[0115] Comparative Example 1: Only chemical formation using the first chemical formation solution was performed. The chemical formation was performed under conditions of a chemical formation solution temperature of 50° C. to 100° C. and a chemical formation voltage of 70 V to 100 V. Other than these, a first electrode, an evaluation sample of the first electrode, and a total of 20 solid electrolytic capacitors were fabricated in the same manner as in Example 1.

[0116] [Evaluation] (1) Analysis of oxide film (dielectric) The evaluation sample of the first electrode obtained in (ii) was subjected to XPS analysis to evaluate the distribution of elements and measure the thicknesses of the first and second layers.

[0117] (1-1) XPS Analysis Elemental analysis was performed from the surface of the oxide film (dielectric) in the thickness direction (depth direction) using the procedure described above. The penetration depth of the first element, Si, and the second element, Na, were also measured. In the outermost layer of the oxide film of Example 1, the abundance ratios of each element were O: 71.8 atomic %, Si: 4.9 atomic %, Ta: 14.7 atomic %, Na: 7.2 atomic %, and P: 1.4 atomic %. In the outermost layer of the oxide film of Comparative Example 1, the abundance ratios of each element were O: 69.9 atomic %, Ta: 28.6 atomic %, and P: 1.5 atomic %, with Si and Na being below the detection limit.

[0118] (1-2) SEM Analysis The thickness (nm) of each of the first and second layers in the oxide film (dielectric) was determined using the procedure described above. The total thickness of the first and second layers was defined as T (nm), and the ratio of the thickness of the second layer to the total thickness T was calculated.

[0119] (2) Evaluation of Solid Electrolytic Capacitors The following evaluations were carried out using 20 solid electrolytic capacitors.

[0120] (2-1) Initial Leakage Current (LC) A 1 kΩ resistor was connected in series to 20 solid electrolytic capacitors, and a voltage of 30 V to 60 V was applied from a DC power supply. The leakage current value (μA) was measured 40 seconds after the start of voltage application, and the median and standard deviation of the 20 solid electrolytic capacitors were calculated. The median and standard deviation of the examples are shown as relative values ​​when the respective values ​​in Comparative Example 1 were set to 1.

[0121] The results of the Examples and Comparative Examples are shown in Table 1. In Table 1, C1 is Comparative Example 1, and E1 and E2 are Example 1 and Example 2, respectively.

[0122]

[0123] As shown in Table 1, C1, in which the dielectric (such as the outermost layer) does not contain the first element, exhibits a large variation in the initial LC value. Compared to C1, E1 and E2 exhibit significantly reduced variation in the initial LC value. When the abundance ratio of the first element in the outermost layer is 10% by mass or more, the initial LC value is larger than E1 and the variation is also larger compared to E1 and E2. Therefore, it is believed that the above-described effects are achieved in E1 and E2 because the outermost layer contains the first element at a specific abundance ratio.

[0124] Furthermore, a comparison of E1 and E2 reveals that when the penetration depth of the first element (thickness of the second layer) (or the abundance ratio of the first element in the outermost layer) is small, the initial LC value also tends to be lower than when it is large.

[0125] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0126] The use of the dielectric of the present disclosure can reduce variations in initial leakage current in capacitors, but the applications of the dielectric and capacitor are not limited to these.

[0127] 100: Capacitor 10: Capacitor element 11: First electrode 111: Porous body 112: Electrode wire 113: Dielectric 13: Second electrode 131: Solid electrolyte layer 132: Carbon layer 133: Metal particle-containing layer 20: Outer casing 30: First lead terminal 40: Second lead terminal 50: Adhesive layer

Claims

1. A dielectric containing a tantalum compound, the dielectric containing oxygen and a first element other than oxygen and tantalum, the first element having an atomic number of 3 or 4 valence electrons and capable of becoming a positive ion when in an ionic state, and the abundance ratio of the first element in the outermost layer of the dielectric being less than 10 atomic %.

2. The dielectric according to claim 1, wherein the outermost layer further contains a second element, the second element being an element other than oxygen, tantalum, and the first element, the number of valence electrons of the atom being one or two, and the second element being an element that can become a positive ion when in an ionic state.

3. The dielectric according to claim 2, wherein the abundance ratio of the first element in the dielectric decreases with increasing distance from the outermost surface layer, and when the penetration depth of the first element is D nm, the penetration depth of the second element is 0.2 D nm or more, wherein the penetration depth of the first element is the maximum depth at which the abundance ratio of the first element is 0.5 atomic % or more.

4. The dielectric according to claim 1 or 2, wherein the dielectric includes a first layer and a second layer covering the first layer, the second layer includes the outermost layer and is a region where the abundance ratio of the first element is 0.5 atomic % or more, and the first layer is a region where the abundance ratio of the first element is less than 0.5 atomic %.

5. The dielectric according to claim 4, wherein the thickness D of the second layer is 0.33T or less, where T nm is the total thickness of the first layer and the second layer, and D nm is the penetration depth of the first element.

6. The dielectric according to claim 5, wherein the thickness D of said second layer is 0.15T or less.

7. The dielectric according to claim 1 or 2, wherein the first element includes at least silicon.

8. The dielectric according to claim 2, wherein the second element includes at least one element selected from the group consisting of sodium and potassium.

9. A capacitor comprising: a first electrode; a second electrode; and a dielectric material according to claim 1 or 2 disposed between the first electrode and the second electrode.

10. The capacitor according to claim 9, wherein the first electrode contains tantalum, the dielectric is an oxide film of the first electrode, and the abundance ratio of the first element in the outermost layer of the dielectric on the second electrode side is less than 10 atomic %.

11. The capacitor of claim 9, including an electrolyte.

12. A device comprising the capacitor according to claim 9.

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