Dielectric medium, capacitor comprising same, and device provided with capacitor

Abstract

The dielectric includes a tantalum compound. The tantalum compound contains oxygen and contains a first element other than oxygen and tantalum. The first element is an element which has 4 or less valence electrons in an atom and which can become a tetravalent positive ion in an ionic state.

Description

Technical Field

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

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

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

[0004] Patent Document 2 proposes an electrode foil for a capacitor, which includes: an anode body having a porous part and containing a first metal; a first dielectric layer covering at least a part of the porous part; 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 includes: a first part having a thickness T1; and a second part having a thickness T2 smaller than the thickness T1. In Patent Document 2, the first dielectric layer is a natural oxide film, and the second dielectric layer is formed by atomic layer deposition.

[0005] In the case of forming the dielectric of a capacitor element by anodization, an aqueous phosphoric acid solution (Patent Document 3, etc.) is often used.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent No. 7122617

[0009] Patent Document 2: International Publication No. 2021 / 192607

[0010] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2011-77257 Summary of the Invention

[0011] A first aspect of the present disclosure relates to a dielectric containing a tantalum compound, the tantalum compound containing oxygen and a first element other than oxygen and tantalum, the first element being an element having 4 or less valence electrons of an atom and capable of becoming a positive ion in an ionic state.

[0012] The second aspect of the present disclosure relates to a capacitor including a first electrode, a second electrode, and the dielectric disposed between the aforementioned first electrode and the aforementioned second electrode.

[0013] The third aspect of the present disclosure relates to an apparatus including the aforementioned capacitor.

[0014] It is possible to provide a dielectric that can achieve high capacitance and high withstand voltage in a capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic cross-sectional view of a capacitor element including a dielectric according to an embodiment of the present disclosure.

[0016] Figure 2 It is a schematic cross-sectional view of a capacitor according to an embodiment of the present disclosure.

[0017] Figure 3 It is the analysis result of the negative ion mode of the outermost surface and the inside of the oxide film (dielectric) of Example 1 based on time-of-flight secondary ion mass spectrometry.

[0018] Figure 4 It is the analysis result of the positive ion mode of the outermost surface and the inside of the oxide film (dielectric) of Example 1 based on time-of-flight secondary ion mass spectrometry.

[0019] Figure 5 It is the analysis result of the negative ion mode of the outermost surface and the inside of the oxide film (dielectric) of Comparative Example 1 based on time-of-flight secondary ion mass spectrometry.

[0020] Figure 6 It is the analysis result of the positive ion mode of the outermost surface and the inside of the oxide film (dielectric) of Comparative Example 1 based on time-of-flight secondary ion mass spectrometry.

[0021] Figure 7 It is the elemental analysis spectrum of the outermost surface of the oxide films (dielectrics) of Example 1 and Comparative Example 1 based on X-ray photoelectron spectroscopy.

[0022] Figure 8 It is the elemental analysis spectrum of the outermost surface of the oxide films (dielectrics) of Example 1 and Comparative Example 1 based on X-ray photoelectron spectroscopy. DETAILED DESCRIPTION

[0023] In a capacitor, high capacitance and high withstand voltage (voltage resistance) are in a trade-off relationship and are difficult to achieve both. For example, the smaller the thickness of the dielectric or the higher the dielectric constant of the dielectric, the higher the capacitance that can be obtained, but the withstand voltage decreases.

[0024] Generally, in a capacitor using an electrode containing tantalum, from the viewpoint of increasing the surface area of the electrode to ensure a high capacitance, a porous body is used in an electrode such as an anode. Examples of the porous body include a porous molded body formed by molding particles containing tantalum or a porous sintered body obtained by sintering the same. From the viewpoint of ensuring a high capacitance, it is advantageous for the dielectric to be formed so as to thinly cover the uneven surface of the porous body. Therefore, in most cases, chemical conversion treatment using a chemical conversion solution is employed. Sometimes, the dielectric is formed by a vapor phase method such as sputtering. However, compared with the liquid phase method, it is difficult to deposit the components constituting the dielectric uniformly on the surface of the porous body without deviation, and a vacuum needs to be created in the chamber, so the cost tends to be high. Therefore, it is disadvantageous in terms of forming a dielectric with a high capacitance and high withstand voltage and mass-producing it industrially.

[0025] Generally, an aqueous phosphoric acid solution is mostly used as the chemical conversion solution. However, in the chemical conversion treatment using an aqueous phosphoric acid solution, phosphorus elements are mixed into the formed dielectric, which becomes a cause of leakage current, and it is difficult to obtain high withstand voltage. In addition, compared with alumina or the like, the dielectric constant of the oxide formed by the chemical conversion treatment of the electrode containing tantalum is high, so it is easy to obtain a high capacitance, but the withstand voltage is low.

[0026] In view of the above circumstances, (Technology 1) the dielectric of the present disclosure contains a tantalum compound. The tantalum compound contains oxygen and a first element other than oxygen and tantalum. The first element is an element having 4 or less valence electrons of an atom and capable of becoming a positive ion in an ionic state.

[0027] When the dielectric of the present disclosure is used in a capacitor, high capacitance and high withstand voltage (voltage resistance) can be ensured. It is considered that this is due to the following reasons. By making the tantalum compound constituting the dielectric contain the first element, the charge is compensated and the defect energy level of oxygen is stabilized. As a result, leakage current hardly flows, so the withstand voltage is improved. In addition, by making the dielectric contain tantalum and oxygen, a high capacitance can be obtained. Furthermore, by making the dielectric contain the first element, high withstand voltage can be ensured without increasing the thickness of the dielectric, so the high capacitance is not easily impaired.

[0028] The first element is an element having 4 or less valence electrons of an atom and capable of becoming a positive ion. However, the first element does not contain a carbon element. 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 also be in a state of being combined with other elements such as oxygen.

[0029] (Technology 2) In the above (Technology 1), the first element may be concentrated in the surface layer of the dielectric. By making the first element concentrated in the surface layer, a decrease in the dielectric constant of the entire dielectric can be suppressed, a high capacitance can be ensured, and the leakage current can be reduced by the first element concentrated in the surface layer, so a high withstand voltage can be ensured.

[0030] The surface layer of the dielectric refers to the portion from the outermost surface of the dielectric to a thickness of 0.3T from the outermost surface when the average thickness of the dielectric is set to T (in other words, the portion from the outermost surface to a depth of 0.3T). In a capacitor, the surface layer of the dielectric is, for example, the surface layer of the dielectric on the side opposite to the anode body.

[0031] The distribution of the first element in the dielectric is determined by X-ray Photoelectron Spectroscopy (XPS). More specifically, while sputtering the dielectric from the surface, XPS analysis is performed to determine the elemental content rate (atomic %) of the dielectric in the surface and the depth direction from the surface (in other words, the thickness direction) of the dielectric. The XPS analysis is performed under the following conditions.

[0032] X-ray photoelectron spectroscopy apparatus: VersaProbe (manufactured by ULVAC-PHI, Inc.)

[0033] X-ray source: monochromated-Al-Kα

[0034] Measurement diameter: diameter 100 μm

[0035] Photoelectron emission angle: 90°

[0036] The neutralization mechanism is used

[0037] Etching conditions:

[0038] Sputtering ion species: Ar +

[0039] Acceleration voltage: 2 kV

[0040] Grating area: approximately 2 mm × 2 mm

[0041] SiO2 sputtering rate based on the above conditions: 5.4 nm / min.

[0042] As a sample for XPS analysis, for example, the first electrode (more specifically, the anode) on which the dielectric is formed is used. In this case, as the first electrode, tantalum foil with a side length of 10 mm or more and 50 mm or less is used. Hereinafter, this sample will be referred to as sample A. It is also possible to use the first electrode (specifically, the anode) on which the dielectric layer is formed obtained during the production of the capacitor or capacitor element as the sample. Hereinafter, this sample will be referred to as sample B.

[0043] The thickness of the dielectric is determined from an image obtained using a Scanning Electron Microscope (SEM). The average thickness T of the dielectric is determined by measuring the thickness of the dielectric at an arbitrary number of locations (e.g., 10 locations) and averaging them. More specifically, first, for sample A or sample B, a cross-section parallel to the thickness direction is exposed, and an image is taken using SEM. For the fields of view at an arbitrary number of locations in this image, the thickness of the dielectric is determined at an arbitrary number of locations. It should be noted that the sample for taking the above cross-sectional image is obtained through the following steps. First, sample A or sample B is embedded in a curable resin, and the curable resin is cured. The cured product is wet-ground or dry-ground 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 photography.

[0044] (Technology 3) In the above (Technology 1) or (Technology 2), the content rate of the first element in the portion from the outermost surface of the surface layer of the dielectric to a thickness of 10 nm from the outermost surface can be 10 atomic % or more and 30 atomic % or less. In the dielectric, the portion from the outermost surface of the surface layer to a thickness of 10 nm from the outermost surface (in other words, the portion from the outermost surface to a depth of 10 nm) is sometimes simply referred to as the "uppermost layer portion". When the content rate of the first element in the uppermost layer portion is 10 atomic % or more, a decrease in capacitance can be suppressed and higher withstand voltage can be ensured. When the content rate of the first element in the uppermost layer portion is 30 atomic % or less, it is easy to ensure a higher capacitance. It should be noted that the content rate of the first element in the uppermost layer portion is the average value of the content rate of the first element obtained by the above XPS analysis in the portion from the outermost surface of the surface layer to a thickness of 10 nm from the outermost surface. The content rate of phosphorus in the outermost surface layer of the dielectric formed by chemical conversion treatment using a normal phosphoric acid aqueous solution is about 3 atomic %.

[0045] (Technology 4) In any one of the above (Technology 1) to (Technology 3), the content rate of the first element in the outermost surface of the surface layer of the dielectric can be 10 atomic % or more and 30 atomic % or less. In this case, higher capacitance and higher withstand voltage can be ensured. The content rate of the first element in the outermost surface is the average value of the content rate of the first element obtained by the above XPS analysis for a plurality of locations (e.g., 10 locations) on the outermost surface of the dielectric.

[0046] The uppermost layer portion of the surface layer is the uppermost layer portion of the dielectric layer. Similarly, the outermost surface of the surface layer is the outermost surface of the dielectric. In a capacitor, the uppermost layer portion and the outermost surface of the dielectric are, for example, the uppermost layer portion and the outermost surface on the side opposite to the anode body of the dielectric, respectively.

[0047] In the dielectric of the present disclosure, the first element is biased towards the surface layer. In such a dielectric, for example, in the XPS-based spectrum of the outermost surface of the surface layer of the dielectric, a peak attributed to the first element is observed. In this case, high capacitance can be ensured and leakage current can be reduced, and high breakdown voltage can be ensured. Any one of the above (Technique 1) to (Technique 4) may further have such a feature.

[0048] (Technique 5) Regarding any one of the above (Technique 1) to (Technique 4), in the XPS-based spectrum of the outermost surface of the surface layer of the dielectric, a peak of O 1s attributed to the bond between the first element and oxygen may also be observed. In this case, high capacitance can be ensured and higher breakdown voltage can be ensured.

[0049] (Technique 6) In any one of the above (Technique 1) to (Technique 5), it is preferable that the first element includes an element whose dielectric constant of the oxide is lower than that of tantalum oxide. By making the first element include such an element, higher breakdown voltage can be ensured. In addition, when included in a state where the first element is biased towards the surface layer, a decrease in the dielectric constant of the entire dielectric can be suppressed, a higher capacitance can be obtained, and higher breakdown voltage can be ensured through the surface layer.

[0050] (Technique 7) In any one of the above (Technique 1) to (Technique 6), the first element may also include at least one selected from the group consisting of Group 4 elements and Group 14 elements of the periodic table. It should be noted that the periodic table is a long-period type periodic table. When the dielectric includes such a first element, charge compensation is easy to perform, and the defect energy level of oxygen is more likely to be stabilized.

[0051] (Technique 8) In any one of the above (Technique 1) to (Technique 7), the first element preferably includes at least silicon element. In this case, in the dielectric, charge compensation is easy to perform, and the defect energy level of oxygen is more likely to be stabilized. In addition, the dielectric constant of silicon oxide is lower than that of tantalum oxide, so the breakdown voltage of the part of the dielectric containing silicon element is likely to be increased.

[0052] (Technique 9) Regarding the above (Technique 8), in the XPS spectrum of the outermost surface of the surface layer, a peak attributed to Si 2p may also be observed. In this case, it is easy to ensure high capacitance and obtain higher breakdown voltage.

[0053] (Technique 10) In any one of the above (Technique 1) to (Technique 9), it is preferable that the breakdown voltage of the surface layer is higher than that of the part other than the surface layer of the dielectric. In this case, high capacitance can be maintained and high breakdown voltage can be ensured at the surface layer.

[0054] The present disclosure also includes a capacitor including the above dielectric. (Technology 11) The capacitor includes a first electrode, a second electrode, and the dielectric according to any one of the above (Technology 1) to (Technology 10) disposed between the first electrode and the second electrode. Such a capacitor can achieve both high capacitance and high breakdown voltage resistance.

[0055] (Technology 12) In the above (Technology 11), the first electrode may contain tantalum, and the dielectric may be an oxide film of the first electrode. The first element may also be concentrated in the surface layer on the second electrode side of the dielectric. By making the dielectric an oxide film of the first electrode, it is easy to concentrate the first element in the surface layer on the second electrode side of the dielectric. Therefore, a higher capacitance can be maintained and a higher breakdown voltage can be ensured through the surface layer.

[0056] (Technology 13) In the above (Technology 11) or (Technology 12), the capacitor may also include an electrolyte disposed between the first electrode and the second electrode. In this case, a higher capacitance can be obtained.

[0057] (Technology 14) The present disclosure includes an apparatus including the capacitor according to any one of the above (Technology 11) to (Technology 13).

[0058] Hereinafter, the dielectric, capacitor, and apparatus of the present disclosure including the above (Technology 1) to (Technology 14) will be described in more detail. As long as at least one selected from the following described components can be combined technically, it can be arbitrarily combined with at least one of the above (Technology 1) to (Technology 14) of the present disclosure.

[0059] [Dielectric]

[0060] The tantalum compound contained in the dielectric contains oxygen and a first element. The first element can also be said to be a doping element doped in the tantalum compound constituting the dielectric. By making the dielectric contain the first element, the charge is compensated and the defect energy level of oxygen is stabilized, thereby suppressing the leakage current. As a result, a high capacitance can be ensured through the tantalum compound and a high breakdown voltage can be ensured through the first element.

[0061] The first element may be included in the dielectric layer in a state combined with oxygen or may be included as a single atomic ion. When the dielectric is analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS), the first element is mostly detected in the form of an oxide. The oxidation number of the first element in the oxide is not particularly limited. For example, when the first element includes silicon, silicon is detected in the form of SiO2, SiO3, SiO3H, Si2O5H, Si ions, etc. in TOF-SIMS. In the analysis, either a negative ion mode or a positive ion mode can be adopted according to the chemical species to be analyzed. The TOF-SIMS analysis is performed while etching the dielectric from the outermost surface in the depth direction (for example, from the outermost surface of the dielectric toward the first electrode side).

[0062] The withstand voltage of the surface layer of the dielectric is preferably higher than that of the portion other than the surface layer of the dielectric. High capacitance can be obtained through the portion other than the surface layer of the dielectric, and high withstand voltage can be ensured through the surface layer of the dielectric.

[0063] The first element is preferably concentrated in the surface layer of the dielectric. That is, the content ratio of the first element in the surface layer of the dielectric is higher than that of the first element in the portion other than the surface layer of the dielectric. By concentrating the first element in the surface layer, high withstand voltage can be ensured in the surface layer and a reduction in capacitance can be suppressed. In this case, it can be said that the withstand voltage of the surface layer is higher than that of the portion other than the surface layer of the dielectric.

[0064] The surface layer of the dielectric is a surface layer on one surface side of a pair of surfaces at both ends in the thickness direction of the dielectric. When the dielectric is formed so as to cover the first electrode, the surface layer of the dielectric corresponds to the surface layer of the dielectric on the side opposite to the first electrode (i.e., the second electrode side).

[0065] Let the content ratio of the first element at a position with a thickness of 0.06T from the outermost surface of the dielectric be r1, and let the content ratio of the first element at a position with a thickness of 0.50T from the outermost surface be r2. At this time, the ratio of r1 to r2 (= r1 / r2) can be 10 or more and 10000 or less, can be 50 or more and 1000 or less, can be 100 or more and 1000 or less, or can be 50 or more and 500 or less. The ratio r1 / r2 represents the degree of concentration of the first element, and the larger the value, the greater the degree of concentration. When the ratio r1 / r2 is in the above range, it is advantageous for obtaining higher withstand voltage while suppressing a reduction in capacitance caused by the entire dielectric.

[0066] From the viewpoint of ensuring higher capacitance and easily achieving higher breakdown voltage resistance, it is preferable to contain a large amount of the first element in the outermost layer of the dielectric. For example, the content ratio of the first element in the portion from the outermost surface of the dielectric surface layer to a thickness of 10 nm from the outermost surface (in other words, the outermost layer) can be 10 atomic % or more, and can also be 15 atomic % or more. From the viewpoint of more easily ensuring high capacitance, the content ratio of the first element in the outermost layer of the dielectric can be 30 atomic % or less, and can also be 25 atomic % or less. These lower limit values and upper limit values can be arbitrarily combined.

[0067] Since the outermost layer of the dielectric contains a large amount of the first element, there is a tendency that the content ratio of tantalum element in the outermost layer is lower than that of the tantalum element in the conventional dielectric containing tantalum compound. The content ratio of tantalum element in the outermost layer of the dielectric can be 3 atomic % or more and 15 atomic % or less, and can also be 5 atomic % or more and 15 atomic % or less. The content ratio of tantalum element in the outermost layer of the conventional dielectric formed by chemically converting the anode body using an aqueous phosphoric acid solution is about 18 atomic %. The content ratio of tantalum element is obtained by XPS analysis according to the case of the first element.

[0068] From the viewpoint of ensuring higher capacitance and easily achieving higher breakdown voltage resistance, the content ratio of the first element on the outermost surface of the dielectric can be 10 atomic % or more and 30 atomic % or less, and can also be 15 atomic % or more and 25 atomic % or less.

[0069] The first element can also include an element whose dielectric constant of the oxide is lower than that of tantalum oxide. In this case, the effect of improving the breakdown voltage resistance is enhanced. When a large amount of such an element is contained in the surface layer or the outermost layer of the dielectric, it is possible to suppress a decrease in the dielectric constant of the entire dielectric, stabilize the oxygen defect level while ensuring higher capacitance, and further improve the breakdown voltage resistance by making the surface layer or the outermost layer have a lower dielectric constant.

[0070] The first element may include at least one selected from the group consisting of elements of Groups 1 to 14 of the periodic table. Among them, the first element preferably includes at least one selected from the group consisting of elements of Group 4 and Group 14 of the periodic table. The Group 4 elements include titanium, zirconium, hafnium, and rutherfordium, and the Group 14 elements include carbon, silicon, germanium, tin, and lead, etc. The Group 14 element may be carbon, but from the viewpoint of easily stabilizing the defect energy level of oxygen, an element other than carbon is desired. The first element also preferably includes at least one selected from the group consisting of silicon, germanium, and hafnium. The first element may also be a Group 14 element. Among them, the first element preferably contains at least silicon element. When the first element contains such an element, for example, compared with the case of containing carbon, the effect of stabilizing the defect energy level of oxygen is high, leakage current is suppressed, and higher breakdown voltage resistance can be ensured. The dielectric constant of silicon oxide is lower than that of tantalum oxide, so when the dielectric contains silicon, the effect of improving breakdown voltage resistance is enhanced.

[0071] The outermost surface (or the outermost layer) of the surface layer of the dielectric contains a large amount of the first element. Therefore, in the XPS spectrum of the outermost surface of the surface layer, a peak attributed to the first element is observed. In addition, in the XPS spectrum of the outermost surface of the surface layer, a peak of O1s attributed to the bond between the first element and oxygen can also be observed.

[0072] For example, when the dielectric contains silicon, in the XPS spectrum of the outermost surface of the surface layer of the dielectric, a peak attributed to Si 2p can also be observed. The peak attributed to Si 2p is observed, for example, in the range of binding energy of 99 eV or more and 105 eV or less (where 102 eV or more and 104 eV or less) in the XPS spectrum. The dielectric showing such a peak contains silicon-containing ionic species at least on the outermost surface and can ensure higher breakdown voltage resistance. It should be noted that in the case of a dielectric formed using a conventional phosphoric acid aqueous solution, such a peak is not observed.

[0073] In addition, when the dielectric contains silicon, in the XPS spectrum of the outermost surface of the surface layer of the dielectric, a peak of O 1s attributed to the Si-O bond can also be observed. Such a peak is observed, for example, in the range of binding energy of 528 eV or more and 534 eV or less (where 532 eV or more and 534 eV or less) in the XPS spectrum. The dielectric showing such a peak contains silicon oxide at least on the outermost surface and can ensure higher breakdown voltage resistance. It should be noted that in the case of a dielectric formed using a conventional phosphoric acid aqueous solution, such a peak is not observed.

[0074] In the case of a dielectric formed using a conventional phosphoric acid aqueous solution, in the XPS spectrum of the outermost surface of the surface layer of the dielectric, a peak attributable to P 2p derived from a phosphorus-containing ionic species was observed. In contrast, in the XPS spectrum of the outermost surface of the surface layer of the dielectric of the present disclosure, a peak attributable to P 2p was not observed. It should be noted that such a peak is observed, for example, in the range of binding energies of 130 eV or more and 135 eV or less in the XPS spectrum.

[0075] The above XPS analysis can be performed under the same conditions as in the analysis of the first element using the above sample A or sample B.

[0076] The dielectric may also contain, as needed, elements other than oxygen, tantalum, and the first element (referred to as the second element). The dielectric may contain one second element or two or more second elements. The content rate of each second element is generally lower than the content rate of tantalum or the content rate of the first element. For example, the content rate of each second element in the outermost layer of the dielectric is lower than the content rate of tantalum. The content rate of each second element in the outermost layer of the dielectric may be 5 atomic % or less, or may be 3 atomic % or less.

[0077] The average thickness T of the dielectric may be 100 nm or more and 300 nm or less, or may be 130 nm or more and 250 nm or less. When the thickness T is in such a range, a higher capacitance can be obtained. Even when the thickness T is relatively small, such as 200 nm or less (for example, 100 nm or more and 200 nm or less, or 130 nm or more and 200 nm or less) or 175 nm or less (for example, 100 nm or more and 175 nm or less, or 130 nm or more and 175 nm or less), high breakdown voltage can be ensured by the first element, and high capacitance and high breakdown voltage can be achieved simultaneously.

[0078] The dielectric may also be formed by a vapor phase method. The dielectric is preferably formed by oxidizing the first electrode using a liquid mixture containing the first element. 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 in a state where the above liquid mixture is in contact with at least a part of the surface of the first electrode containing tantalum (for example, an anode (more specifically, an anode body)). When the dielectric is formed by oxidizing the surface of the first electrode, it is easier to form a thin oxide film so as to cover the uneven surface of the dielectric compared with the case of forming by a vapor phase method. In addition, it is easy to make the first element concentrated in the surface layer or the outermost layer of the dielectric. Therefore, it is advantageous for obtaining a higher capacitance while ensuring a higher breakdown voltage.

[0079] The liquid mixture for oxidizing the first electrode (more specifically, the anode body) is, for example, an aqueous solution containing a first element. The first element can be contained in the liquid mixture in any form. For example, the first element can be contained in the liquid mixture in the form of monatomic ions or polyatomic ions, etc.

[0080] The concentration of the first element in the liquid mixture can be 0.01% by mass or more and 5.00% by mass or less, can be 0.05% by mass or more and 0.70% by mass or less, or can be 0.08% by mass or more and 0.50% by mass or less. When the concentration of the first element is in such a range, it is easy to dope the first element in the dielectric, and it is easy to obtain higher breakdown voltage. In addition, it is easy to make the first element concentrate on the surface layer or the outermost layer.

[0081] The oxidation of the first electrode can be carried out while applying a voltage to the first electrode. The voltage applied to the first electrode (also referred to as the oxidation voltage) can be 30 V or more and 100 V or less, or can be 50 V or more and 100 V or less. The oxidation of the first electrode can be carried out at a certain voltage, can be carried out while increasing the voltage at a specified rate, or can combine them. The oxidation voltage is the voltage of the first electrode relative to the counter electrode.

[0082] The oxidation of the first electrode can be carried out at room temperature or under heating. The temperature of the liquid mixture during oxidation can be 20°C or more and 80°C or less, can be 40°C or more and 80°C or less, or can be 50°C or more and 75°C or less.

[0083] [Capacitor]

[0084] The capacitor of the present disclosure includes the above-mentioned dielectric. In the capacitor, the dielectric is disposed between the first electrode and the second electrode. The dielectric is preferably formed so as to cover at least a part of the surface of the first electrode (more specifically, the anode). Such a dielectric can also form a layer (also referred to as a dielectric layer). The capacitor can also include an electrolyte.

[0085] The capacitor can also include a capacitor element and an outer package for sealing the capacitor element. The capacitor element is composed of, for example, the first electrode, the second electrode, and the dielectric. The capacitor can include one capacitor element or can include two or more capacitor elements.

[0086] (The first electrode)

[0087] The first electrode is, for example, an anode. The first electrode includes, for example, an anode body. The anode body can also include valve-acting metals, alloys containing valve-acting metals, and compounds containing valve-acting metals, etc. The anode body can contain one of these materials or can contain two or more in combination. As valve-acting metals, for example, tantalum, aluminum, niobium, and titanium can be cited.

[0088] In the case where the dielectric is formed by the oxidation of the first electrode (in other words, when the dielectric is an oxide film of the first electrode), the first electrode contains tantalum. In the case of formation by a vapor phase method or the like, the first electrode does not necessarily need to contain tantalum. The first electrode containing tantalum may be formed of tantalum or a tantalum alloy, or may be formed of tantalum.

[0089] The anode body has a porous portion at least on the surface layer. Through such a porous portion, the anode body has a fine concavo-convex shape at least on the surface. The anode body having a porous portion on the surface layer is obtained, for example, by roughening the surface of a base material containing a valve action metal (such as a sheet-like (e.g., foil-like, plate-like) base material). The roughening can be performed, for example, by an etching treatment or the like. In addition, the anode body may be a molded body or a sintered body containing particles of a valve action metal. The molded body and the sintered body may each integrally form a porous portion. Sometimes such a molded body and a sintered body are simply referred to as a porous body. The molded body and the sintered body may each have a sheet-like shape, or may have a rectangular parallelepiped shape, a cubic shape, or a shape similar thereto.

[0090] The anode body may also be divided into a cathode forming portion facing the second electrode (specifically, the cathode) and an anode lead-out portion not facing the second electrode. In addition, the anode body may have a porous body and a wire inserted into the porous body. In this case, the wire corresponds to the anode lead-out portion. The anode lead-out portion is used, for example, for electrical connection to an external electrode or a lead terminal on the anode side.

[0091] (Dielectric)

[0092] 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.

[0093] In the case where the dielectric is an oxide film of the first electrode, the first element is concentrated in the surface layer of the dielectric on the side opposite to the first electrode (that is, the second electrode side). Since the dielectric is formed on the porous surface of the first electrode, the surface of the dielectric has a fine concavo-convex shape corresponding to the concavo-convex of the first electrode.

[0094] The present disclosure can obtain high breakdown voltage and reduce leakage current through the above dielectric. For example, compared with an anode body having a dielectric formed by a chemical conversion treatment using a normal phosphoric acid aqueous solution, the anode body having the dielectric of the present disclosure can reduce the leakage current when an electric field strength of 5.8 MV / cm is applied by about 20%. It should be noted that these anode bodies have an electrostatic capacitance of the same degree per unit area (about 1.3×10 -7 F / cm 2 ).

[0095] (Electrolyte)

[0096] The electrolyte contained in the capacitor can be a liquid electrolyte, a solid electrolyte, or both. A solid electrolyte and a liquid component can also be used in combination. The solid electrolyte can form the second electrode together with the cathode lead layer.

[0097] The liquid electrolyte contains a solvent and a solute. As the solvent, a non-aqueous solvent is preferred. As the non-aqueous solvent, for example, sulfone compounds (such as sulfolane, dimethyl sulfoxide, ethyl sulfoxide, etc.), lactone compounds (such as γ-butyrolactone, γ-valerolactone, etc.), carbonate compounds (such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, etc.), carboxylic acid ester compounds, and alcohol compounds (such as ethylene glycol, polyethylene glycol, etc.) can be cited. The liquid component can contain one solvent (such as a non-aqueous solvent) or a combination of two or more solvents.

[0098] As the solute, an acid component and a base component can be cited. A salt of an acid component and a base component can also be used as the solute. As the acid component, aromatic carboxylic acids (such as benzoic acid, salicylic acid, etc.), aromatic polycarboxylic acids (such as phthalic acid, etc.) are preferred. As the base component, organic bases (such as amines, quaternary ammonium compounds, etc.), inorganic bases (such as metal hydroxides, etc.) can be cited.

[0099] The liquid electrolyte is, for example, housed together with the capacitor element in an exterior body such as a case.

[0100] As the solid electrolyte, a gel-like electrolyte or a polymer electrolyte obtained by solidifying a liquid electrolyte using a gelling agent or a polymer can be used. In addition, as the solid electrolyte, a conductive polymer can also be used. The conductive polymer can be a conductive polymer containing a conjugated polymer and a dopant, a self-doped conductive polymer, or both of them can be used.

[0101] As the conjugated polymer, for example, a π-conjugated polymer can be cited. As the conjugated polymer, for example, polymers having a basic skeleton of polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, poly(p-phenylene vinylene), polyacene, and poly(thiophene vinylene) can be cited. Such a polymer only needs to contain at least one monomer unit constituting the basic skeleton. The monomer unit also includes a monomer unit having a substituent. The above polymers also include homopolymers and copolymers of two or more monomers. For example, polythiophene includes poly(3,4-ethylenedioxythiophene) (PEDOT), etc. The solid electrolyte can contain one conjugated polymer or a combination of two or more conjugated polymers.

[0102] As the dopant, for example, at least one selected from the group consisting of anions and polymeric anions can be cited. As the anion, for example, sulfate ion, nitrate ion, phosphate ion, borate ion, organic sulfonate ion, carboxylate ion can be cited. As the dopant, a compound capable of generating an anion can also be used. Examples of such a compound include p-toluenesulfonic acid and naphthalenesulfonic acid. As the polymeric anion, for example, polyvinylsulfonic acid, polystyrenesulfonic acid (PSS), polyallylsulfonic acid, polyacryloylsulfonic acid, polymethacryloylsulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprenesulfonic acid, polyestersulfonic acid (such as aromatic polyester sulfonic acid), phenolsulfonic acid novolak resin, and polyacrylic acid can be cited. These are only examples, and the dopant is not limited to these. The solid electrolyte may contain one dopant or may contain two or more in combination.

[0103] As the liquid component used in combination with the solid electrolyte, for example, the above non-aqueous solvent can be cited. A protic solvent such as an alcohol compound can also be used. The non-aqueous solvent can be used alone or two or more can be used in combination.

[0104] The solid electrolyte containing a conductive polymer can be formed, for example, by polymerizing a precursor (monomer, etc.) of a conjugated polymer on a dielectric in the presence of a dopant. Polymerization is carried out using chemical polymerization or electrolytic polymerization, etc. In addition, the solid electrolyte can be formed by applying a solution in which a conductive polymer is dissolved or a liquid dispersion in which a conductive polymer is dispersed to the surface of the dielectric. In a capacitor element, the solid electrolyte can form a layer. The solid electrolyte layer can be a single layer or a multi-layer.

[0105] The gel-like electrolyte is housed together with the capacitor element in an outer package such as a case. A polymer electrolyte can also be interposed between the first electrode and the second electrode to form a capacitor element.

[0106] (Second electrode)

[0107] The second electrode is, for example, a cathode. The second electrode includes an electrode lead-out layer (also referred to as a cathode lead-out layer). The second electrode can also be composed of a solid electrolyte and an electrode lead-out layer.

[0108] The electrode lead-out layer at least includes a metal-containing layer. As the metal-containing layer, a metal foil, a metal particle-containing layer, etc. can be cited.

[0109] The type of metal constituting the metal foil is not particularly limited. The metal foil may also be a valve-acting metal (such as tantalum, aluminum, niobium, etc.) or an alloy containing a valve-acting metal. The surface of the metal foil may be roughened as needed. A chemical conversion film may be provided on the surface of the metal foil, or a film of a metal (dissimilar metal) or non-metal different from the metal constituting the metal foil may be provided. As the dissimilar metal or non-metal, for example, a metal such as titanium or a non-metal such as conductive carbon can be cited. The metal foil is laminated on a layer serving as a substrate (dielectric, solid electrolyte, or carbon layer described later, etc.).

[0110] As the metal material constituting the metal particles contained in the metal particle-containing layer, silver, silver alloy, copper, copper alloy, etc. can be cited. The metal particle-containing layer is formed by coating a metal paste containing metal particles and a resin binder on a layer serving as a substrate (dielectric, solid electrolyte, or carbon layer described later, etc.) and drying or curing the coating film. As the resin binder, a thermoplastic resin may be used, or a thermosetting resin such as an imide-based resin or an epoxy resin may be used. The obtained metal particle-containing layer may contain metal particles, a resin binder, or a cured product thereof.

[0111] The electrode lead-out 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 part of the solid electrolyte and a metal-containing layer covering at least a part of the carbon layer. The carbon layer contains, for example, conductive carbon and may contain a resin binder (such as a water-soluble resin, a curable resin, etc.) or a cured product thereof as needed. As the conductive carbon, for example, graphite (artificial graphite, natural graphite, etc.) can be cited.

[0112] The carbon layer is formed, for example, by applying a conductive paste or a liquid dispersion containing conductive carbon and a resin binder as needed to the surface of a layer serving as a substrate (dielectric, solid electrolyte, etc.) and drying or curing it.

[0113] During the formation of the electrode lead-out layer, heat treatment, etc. may be performed as needed.

[0114] These configurations are merely examples of the configuration of the electrode lead-out layer, and other configurations having a current collecting function may also be used.

[0115] (Other)

[0116] The capacitor may be of a wound type, a chip type, or a multilayer type. When the capacitor includes a plurality of capacitor elements, each capacitor element may be of a wound type or a multilayer type, for example. For example, a multilayer capacitor includes a plurality of capacitor elements laminated. The configuration of the capacitor element may be selected according to the type of capacitor.

[0117] In a capacitor element, an electrode lead-out layer of a second electrode is electrically connected to, for example, one end portion of a second lead terminal. An electrode lead-out portion (e.g., an anode lead-out portion) of a first electrode is electrically connected to, for example, one end portion of a first lead terminal. The other end portions of the respective lead terminals are led out from an outer package. The other end portions of the respective lead terminals exposed from the outer package are used for soldering to a substrate on which the capacitor is to be mounted, etc., and are electrically connected to an external electrode. At least a part of the external electrode constitutes an external terminal of the capacitor. As the respective lead terminals, leads or lead frames can be used. In addition, not limited to the case of using lead terminals, the end face of an electrode lead-out portion (e.g., an anode lead-out portion) may be exposed from the outer package and connected to the external electrode. The end face of a metal foil included in the second electrode may be exposed from the outer package and connected to the external electrode. The end face of the other end portion of the second lead terminal connected to the electrode lead-out layer of the second electrode may be exposed from the outer package and connected to the external electrode.

[0118] The capacitor element is sealed with an outer package, for example. For example, the capacitor element and a resin material of the outer package (e.g., an uncured thermosetting resin and a filler) may be housed in a mold, and the capacitor element may be sealed with a resin outer package by a transfer molding method, a compression molding method, or the like. At this time, the portions on the other end portion side of the respective lead terminals led out from the capacitor element are respectively exposed from the mold. In addition, the capacitor element may be housed in a bottomed case such that the portions on the other end portion side of the respective lead terminals are located on the opening side of the bottomed case, and the opening of the bottomed case may be sealed with a sealing body to form a capacitor.

[0119] [Device having a capacitor]

[0120] The capacitor of the present disclosure has a high withstand voltage while having a high capacitance, and thus has high reliability. Therefore, it is used for various applications (devices) that require high capacitance, high withstand voltage, or high reliability, etc. As a device on which the capacitor is mounted, there is no particular limitation, and various electronic devices, various electrical devices, vehicle-mounted applications, etc. can be cited.

[0121] Figure 1 is a schematic cross-sectional view showing a capacitor element including a dielectric of one embodiment of the present disclosure.

[0122] The capacitor element 10 includes a first electrode 11 and a second electrode 13. The first electrode 11 includes a porous body 111 formed of tantalum, an electrode lead 112 erected from the porous body 111, and a dielectric 113 covering at least a part 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 a cathode lead layer. Such a capacitor element 10 is substantially cubic in shape. In the present disclosure, the dielectric 113 contains a tantalum compound containing oxygen and a first element. By making the dielectric 113 contain the first element (preferably concentrated on the surface layer of the dielectric 113), the charge compensation of the first element can be used to stabilize the defect energy level of oxygen and ensure high capacitance and high withstand voltage.

[0123] Figure 2 It is a schematic cross-sectional view showing a capacitor according to an embodiment of the present disclosure.

[0124] The capacitor 100 includes: Figure 1 a capacitor element; an outer package 20 that seals the capacitor element; and a first lead terminal 30 and a second lead terminal 40, at least a part of each of which is exposed outside the outer package 20.

[0125] The electrode lead 112 is electrically connected to the first lead terminal 30 by welding, for example. The metal particle-containing layer 133 and the second lead terminal 40 are electrically connected via an adhesive layer 50 formed of a conductive adhesive (a mixture of a thermosetting resin, carbon particles, metal particles, etc.), for example.

[0126] In Figure 2 the example, a capacitor using a solid electrolyte as the electrolyte and having the capacitor element sealed by an outer package is cited, but the capacitor of the present disclosure is not limited to such a 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.

[0127] [Examples]

[0128] Hereinafter, the present invention will be specifically described based on examples and comparative examples, but the present invention is not limited to the following examples.

[0129] 《Example 1》

[0130] Samples for evaluation were produced according to the following procedures, and their characteristics were evaluated.

[0131] (i) Preparation of the first electrode

[0132] Commercially available tantalum foil was cut into a square shape of 10 mm to 50 mm to obtain a precursor of the first electrode as a flat tantalum anode body.

[0133] (ii) Formation of Oxide Film (Dielectric)

[0134] As the chemical conversion solution, an aqueous solution containing K2SiO3 at a concentration of 0.001 to 10.00 mass% is prepared. The chemical conversion tank is filled with the chemical conversion solution, and a part of the tantalum flat plate anode body is immersed. The temperature of the chemical conversion solution is 50 to 100 °C. The upper end of the tantalum flat plate anode body not immersed in the liquid is connected to the counter electrode, and the voltage is increased at a rate of 30 V / h to 50 V / h until the chemical conversion voltage reaches 50 V to 100 V, and maintained at the specified voltage for 5 hours to 15 hours. At this time, throughout the chemical conversion process, the maximum current density is within the range of 0.10 mA / cm 2 ~10.00 mA / cm 2 and the minimum current density is within the range of 0.001 mA / cm 2 ~0.100 mA / cm 2 . In this way, an oxide film (thickness of about 100 nm to 180 nm) containing tantalum oxide with silicon as the first element is formed on a part of the surface of the tantalum flat plate anode body. A total of 10 evaluation samples of the first electrode with an oxide film formed are produced.

[0135] (iii) Formation of Upper Electrode

[0136] On the surface of the oxide film of the first electrode obtained in (ii) above, 100 to 200 dot-shaped upper electrodes with a diameter of 0.1 mm to 1 mm are formed at equal intervals using a specified metal mask and a large electron beam evaporator. In this way, a total of 4 samples for leakage current evaluation are produced.

[0137] <<Comparative Example 1>>

[0138] In (ii) of Example 1, an aqueous solution containing phosphoric acid at a concentration of 0.001 to 1.000 mass% and hydrogen peroxide at a concentration of 0.001 to 10.000 mass% is used as the chemical conversion solution instead of the aqueous solution containing K2SiO3. Except for this, the first electrode is produced in the same manner as in Example 1, and a total of 10 evaluation samples of the first electrode with an oxide film formed and a total of four samples for leakage current evaluation are produced.

[0139] [Evaluation]

[0140] (1) Analysis of Oxide Film (Dielectric)

[0141] (ii) The following analysis is performed on the evaluation samples of the obtained first electrode, and the average value is calculated.

[0142] (1-1) XPS Analysis

[0143] Elemental analysis is performed from the surface of the oxide film (dielectric) to the thickness direction (depth direction) through the above steps.

[0144] At the outermost surface of the oxide film in Example 1, the content ratios of the respective elements are O: 67 atomic %, Si: 17 atomic %, Ta: 7.8 atomic %, Al: 2.8 atomic %, K: 1.1 atomic %, and P is below the detection limit. The silicon content ratio in the portion (the outermost layer) from the outermost surface of the oxide film in Example 1 to a thickness of 10 nm from the outermost surface is approximately 17 atomic %. The ratio r1 / r2 is approximately 100.

[0145] At the outermost surface of the oxide film in Comparative Example 1, the content ratios of the respective elements are O: 64 atomic %, Ta: 18 atomic %, P: 2.7 atomic %, and Si, Al, and K are below the detection limit.

[0146] The XPS-based elemental analysis spectra of the outermost surfaces of the oxide films in Example 1 and Comparative Example 1 are shown in Figure 7 and Figure 8 . In Figure 7 and Figure 8 , Example 1 is E1 and Comparative Example 1 is C1. As shown in Figure 7 , in Example 1, in the XPS spectrum of the outermost surface of the oxide film, a peak attributed to Si2p is observed at around a binding energy of 103 eV. In contrast, in Comparative Example 1, such a peak is not observed. Further, as shown in Figure 8 , in Example 1, in the XPS spectrum of the outermost surface of the oxide film, a peak attributed to O 1s derived from the Si-O bond is observed at around a binding energy of 533 eV. In contrast, in Comparative Example 1, such a peak is not observed, and a peak of O 1s derived from the Ta-O bond is observed at around a binding energy of 531 eV. In Example 1, although a peak of O 1s derived from the Ta-O bond is also observed at around a binding energy of 531 eV, its intensity is lower than that of either the peak of O 1s derived from the Si-O bond or the peak of O 1s derived from the Ta-O bond in Comparative Example 1.

[0147] (1-2) TOF-SIMS analysis

[0148] TOF-SIMS analysis of the outermost surface and the inside of the oxide film is performed. The analysis of the oxide film is carried out under the following conditions after removing minute surface adherends with a gas cluster ion beam (GCIB).

[0149] Apparatus: TRIFTV nano TOF (manufactured by ULVAC-PHI, Inc.)

[0150] Primary ion conditions: 30Au3200 bunching mode

[0151] Use of neutralizer gun

[0152] Primary ion species: Au3+(= Au3 aggregate)

[0153] Acceleration voltage: 30 kV

[0154] Bunching mode (irradiating with a pulsed primary ion beam)

[0155] Primary ion irradiation area (= measurement area): 100 μm × 100 μm (when measuring the outermost surface)

[0156] 50 μm × 50 μm (when performing depth - direction analysis)

[0157] Sputtering conditions

[0158] Sputtering ion species:: Au3+

[0159] Continuous beam

[0160] Grating range: 150 μm × 150 μm

[0161] The analysis results of the negative - ion mode and positive - ion mode of TOF - SIMS in Example 1 are shown in Figure 3 and Figure 4 respectively. The analysis results of the negative - ion mode and positive - ion mode of TOF - SIMS in Comparative Example 1 are shown in Figure 5 and Figure 6 respectively. In the oxide film of Example 1, the part from the outermost surface to a depth (thickness) of about 50 nm from the outermost surface (the part from the outermost surface to a thickness of about 0.3T from the outermost surface (the part equivalent to the surface layer) with respect to the average thickness T of the dielectric layer) contains a large amount of chemical species containing Si. In the part other than the surface layer, the content rate of chemical species containing Si is extremely small. Thus, in Example 1, the first element is concentrated in the surface layer. In addition, among the chemical species containing Si, the content rates of SiO2 and SiO3 are particularly high. In the oxide film of Example 1, the chemical species containing phosphorus are below the detection limit in both the surface and the interior. The oxide film of Comparative Example 1 contains a large amount of chemical species containing phosphorus in the part from the outermost layer to a depth of about 10 nm, and the content rate of chemical species containing phosphorus is extremely small in the deeper part.

[0162] (2) Leakage current

[0163] Using the evaluation sample obtained in (iii), measure the leakage current value of the first electrode.

[0164] Measure a manual probe station commonly used in the evaluation of the electrical properties of thin film materials and a semiconductor parameter analyzer connected thereto. Make the unchemically converted part of the first electrode contact the positive-side probe as the lower electrode, and make the negative-side probe contact the upper electrode formed in (iii). Fix the negative-side probe at 0 V, measure the current value flowing between the electrodes when the positive-side probe is swept from 0 V to 100 V, and investigate the relationship between the electric field strength and the current value flowing through the first electrode. As a result, in Example 1, the current value when the electric field strength is 5.8 MV / cm is reduced by about 20% compared to that in Comparative Example 1. Thus, compared with Comparative Example 1, Example 1 has a reduced leakage current when a voltage is applied, indicating high breakdown voltage resistance.

[0165] (3) Capacitance

[0166] For the evaluation sample obtained in (iii), use an impedance analyzer connected to a probe at room temperature to measure the initial capacitance per unit area (F / cm 2 ) of the upper electrode on the anode body surface. Measure while changing the frequency from 1 kHz to 100 kHz. Calculate the average value of 20 capacitors for each frequency. As a result, in Example 1 and Comparative Example 1, the capacitance is almost unchanged at any frequency, and a high capacitance is obtained.

[0167] Industrial applicability

[0168] By using the dielectric of the present disclosure, high capacitance and high breakdown voltage resistance can be ensured in a capacitor. Therefore, a highly reliable capacitor with high capacitance and high breakdown voltage resistance can be obtained. Such a capacitor is suitable for applications requiring high capacitance and applications requiring high reliability. However, the uses of the dielectric and the capacitor are not limited to these.

[0169] Description of reference numerals

[0170] 100: Capacitor

[0171] 10: Capacitor element

[0172] 11: First electrode

[0173] 111: Porous body

[0174] 112: Electrode wire

[0175] 113: Dielectric

[0176] 13: Second electrode

[0177] 131: Solid electrolyte layer

[0178] 132: Carbon layer

[0179] 133: Metal particle-containing layer

[0180] 20: Outer package

[0181] 30: First lead terminal

[0182] 40: Second lead terminal

[0183] 50: Adhesive layer

Claims

1. A dielectric comprising a tantalum compound, the tantalum compound containing oxygen and a first element other than oxygen and tantalum, the first element being an element having 4 or less valence electrons in an atom and capable of becoming a positive ion in an ionic state.

2. The dielectric according to claim 1, wherein, The first element is concentrated in the surface layer of the dielectric.

3. The dielectric according to claim 2, wherein, The content of the first element in the portion from the outermost surface of the surface layer to a thickness of 10 nm from the outermost surface is 10 atomic % or more and 30 atomic % or less.

4. The dielectric according to claim 2 or 3, wherein, The content of the first element in the outermost surface of the surface layer is 10 atomic % or more and 30 atomic % or less.

5. The dielectric according to claim 2 or 3, wherein, In the spectrum based on X-ray photoelectron spectroscopy at the outermost surface of the said surface layer, a peak attributable to O 1s derived from the binding of the said first element and oxygen is observed.

6. The dielectric according to any one of claims 1 to 3, wherein, The first element includes an element whose dielectric constant of the oxide is lower than that of the oxide of tantalum.

7. The dielectric according to any one of claims 1 to 3, wherein The first element includes at least one selected from the group consisting of Group 4 elements and Group 14 elements of the periodic table.

8. The dielectric according to any one of claims 1 to 3, wherein, The first element includes at least silicon element.

9. The dielectric according to claim 8, wherein, In the spectrum based on X-ray photoelectron spectroscopy of the outermost surface of the surface layer, a peak attributable to Si was observed. 2p was observed.

10. The dielectric according to claim 2 or 3, wherein, The breakdown voltage of the surface layer is higher than that of the portion other than the surface layer of the dielectric.

11. A capacitor comprising: a first electrode, a second electrode, and the dielectric according to any one of claims 1 to 3 disposed between the first electrode and the second electrode.

12. The capacitor according to claim 11, wherein, The first electrode contains tantalum, and the dielectric is an oxide film of the first electrode, The first element is concentrated in the surface layer on the second electrode side of the dielectric.

13. The capacitor according to claim 11, comprising an electrolyte.

14. An apparatus having the capacitor according to claim 11.

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