capacitor

Abstract

The disclosed capacitor includes: an anode body (111) that has a dielectric layer (112) formed on a surface thereof; a cathode extraction layer (131); and an n-type semiconductor layer (120) that is disposed between the dielectric layer (112) and the cathode extraction layer (131) and that contacts the cathode extraction layer (131). The work function of an n-type semiconductor that forms the n-type semiconductor layer (120) is greater than or equal to the work function of an inorganic conductive material that forms the cathode extraction layer (131).

Description

[Technical Field]

[0001] The present disclosure relates to capacitors. [Background technology]

[0002] Various capacitors have been proposed in the past. Patent Document 1 (JP 2017-103412 A) discloses "a solid electrolytic capacitor comprising an anode body, a dielectric layer disposed on the surface of the anode body, and a solid electrolyte layer disposed on the surface of the dielectric layer and made of zinc oxide having a conductivity of 1 (S / cm) or more."

[0003] Patent Document 2 (JP 2020-35890 A) discloses "a solid electrolytic capacitor comprising an anode body made of a valve metal, a dielectric layer formed on the surface of the anode body, a semiconductor layer formed on the dielectric layer, and a cathode layer formed on the semiconductor layer, wherein the semiconductor layer is composed of a p-type inorganic semiconductor."

[0004] Patent Document 3 (WO 2015 / 059913) discloses "an electrolytic capacitor including an anode body having a dielectric layer formed on its surface, a cathode body having a nickel layer formed on its surface, and a solid electrolyte formed between the anode body and the cathode body and containing a conductive polymer, wherein the nickel layer contains nickel crystal particles having a length of 50 nm or more in a direction perpendicular to the thickness direction in a cross section cut in the thickness direction of the nickel layer." Furthermore, Patent Document 3 discloses an electrolytic capacitor in which the work function of the nickel layer is greater than the work function of the conductive polymer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2017-103412 [Patent Document 2] Japanese Patent Application Publication No. 2020-35890 [Patent Document 3] International Publication No. 2015 / 059913 Summary of the Invention [Problem to be solved by the invention]

[0006] Currently, there is a demand for capacitors with low ESR. In this situation, one of the objectives of the present disclosure is to provide a capacitor capable of reducing equivalent series resistance (ESR). [Means for solving the problem]

[0007] One aspect of the present disclosure relates to a capacitor including an anode body having a dielectric layer formed on a surface thereof, a cathode extraction layer, and an n-type semiconductor layer disposed between the dielectric layer and the cathode extraction layer and in contact with the cathode extraction layer, wherein the work function of the n-type semiconductor constituting the n-type semiconductor layer is equal to or greater than the work function of an inorganic conductive material constituting the cathode extraction layer.

[0008] Another aspect of the present disclosure relates to another capacitor including an anode body having a dielectric layer formed on a surface thereof, a cathode extraction layer, and a p-type semiconductor layer disposed between the dielectric layer and the cathode extraction layer and in contact with the cathode extraction layer, wherein a work function of a p-type semiconductor constituting the p-type semiconductor layer is equal to or lower than a work function of an inorganic conductive material constituting the cathode extraction layer.

[0009] Another aspect of the present disclosure relates to another capacitor including an anode body having a dielectric layer formed on a surface thereof, a cathode extraction layer, and a conductive polymer layer disposed between the dielectric layer and the cathode extraction layer and in contact with the cathode extraction layer, the conductive polymer layer being made of a conductive polymer that exhibits p-type semiconductor properties, and the conductive polymer having a work function equal to or lower than the work function of an inorganic conductive material constituting the cathode extraction layer. [Effects of the Invention]

[0010] According to the present disclosure, a capacitor capable of reducing ESR is obtained. 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. [Brief explanation of the drawings]

[0011] [Figure 1] 1A and 1B are diagrams illustrating examples of band structures of components of a capacitor. [Figure 2] 4 is a diagram schematically illustrating an example of a contact state between an n-type semiconductor layer and a cathode extraction layer in a first capacitor. FIG. [Figure 3] 10 is a diagram schematically illustrating an example of a contact state between a p-type semiconductor layer and a cathode extraction layer in a second capacitor. FIG. [Figure 4] 10A and 10B are diagrams illustrating another example of the band structure of the constituent members of the capacitor. [Figure 5] FIG. 4 is a diagram schematically illustrating an example of a state of contact between a conductive polymer layer and a cathode extraction layer in a second capacitor. [Figure 6] 1 is a cross-sectional view schematically illustrating the structure of an example capacitor according to an embodiment of the present invention. [Figure 7] FIG. 10 is a cross-sectional view schematically illustrating the structure of another example of a capacitor according to the present embodiment. [Figure 8] FIG. 2 is a cross-sectional view schematically illustrating an evaluation method of an example. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following describes embodiments of the present disclosure 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 other materials may be applied as long as the invention of the present disclosure can be implemented. In this specification, the expression "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or more and numerical value B or less." 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 greater than the upper limit.

[0013] As the capacitor according to the present disclosure, three types of capacitors (first to third capacitors) will be described below. Hereinafter, the first to third capacitors may be collectively referred to as capacitor (C).

[0014] (First capacitor) The first capacitor includes an anode body having a dielectric layer formed on its surface, a cathode extraction layer, and an n-type semiconductor layer disposed between the dielectric layer and the cathode extraction layer and in contact with the cathode extraction layer, the n-type semiconductor constituting the n-type semiconductor layer having a work function equal to or greater than the work function of the inorganic conductive material constituting the cathode extraction layer.

[0015] The cathode extraction layer is positioned opposite the dielectric layer on the anode body. The n-type semiconductor layer is typically in contact with the dielectric layer on the anode body. That is, the first capacitor has a laminated structure of anode body / dielectric layer / n-type semiconductor layer / cathode extraction layer. This laminated structure does not include a polymer such as a conductive polymer layer, resulting in a capacitor with high heat resistance. However, other layers may be positioned between the dielectric layer and the n-type semiconductor layer. For example, another n-type semiconductor layer or a conductive polymer layer may be positioned between them.

[0016] Figure 1 shows a schematic diagram of the band diagrams of n-type semiconductors, p-type semiconductors, semimetals (conductive carbon), and metals. Figure 1 also shows the band gap Eg1, Fermi level Ef1, and work function Wn of n-type semiconductors. Figure 1 also shows the band gap Eg2, Fermi level Ef2, and work function Wp2 of p-type semiconductors. Figure 1 also shows the Fermi level Efc and work function Wc of conductive carbon, a semimetal. Figure 1 also shows the Fermi level Efm and work function Wm of metals. For each material, the work function is calculated as the difference between the vacuum level and the Fermi level.

[0017] Consider the case where the work function Wn of the n-type semiconductor constituting the n-type semiconductor layer is equal to or greater than the work function Wi1 of the inorganic conductive material constituting the cathode extraction layer. For example, consider the case where a metal with a work function Wm (where Wm≦Wn) is used as the inorganic conductive material constituting the cathode extraction layer. In this case, when the two are joined, their band structures become as shown in Figure 2. As shown in Figure 2, when Wm≦Wn (Wi1≦Wn), there is no barrier to the flow of electrons, and the two are in ohmic contact. Therefore, it is possible to reduce the ESR of a capacitor having this configuration. Note that in this specification, ohmic contact may include contact that can be considered substantially ohmic contact.

[0018] The thickness of the n-type semiconductor layer is not particularly limited and may be 1 nm or more, 10 nm or more, 100 nm or more, or 1 μm or more, or 100 μm or less, 10 μm or less, or 1 μm or less. The thickness may be in the range of 1 nm to 100 μm (for example, in the range of 10 nm to 10 μm).

[0019] There are no particular limitations on the n-type semiconductor as long as it satisfies Wi1≦Wn. The n-type semiconductor may be a metal oxide, such as ZnO, indium tin oxide (ITO), In2O3, or Ga2O3. These may be doped with a dopant or may have an oxygen deficiency or excess.

[0020] The work function Wn of the n-type semiconductor may be 4.65 eV or more. The work function Wn varies depending on the material of the n-type semiconductor. Furthermore, Wn may be varied depending on the manufacturing method. Wn may be 4.93 eV or more. There is no particular upper limit for Wn, but it may be 6.00 eV or less.

[0021] In the first capacitor, examples of combinations of the n-type semiconductor that constitutes the n-type semiconductor layer and the inorganic conductive material that constitutes the cathode extraction layer will be described later.

[0022] (Second capacitor) The second capacitor includes an anode body having a dielectric layer formed on its surface, a cathode extraction layer, and a p-type semiconductor layer disposed between the dielectric layer and the cathode extraction layer and in contact with the cathode extraction layer. The work function of the p-type semiconductor constituting the p-type semiconductor layer is equal to or less than the work function of the inorganic conductive material constituting the cathode extraction layer.

[0023] The cathode extraction layer is positioned opposite the dielectric layer on the anode body. The p-type semiconductor layer is typically in contact with the dielectric layer on the anode body. That is, the second capacitor has a laminated structure of anode body / dielectric layer / p-type semiconductor layer / cathode extraction layer. This laminated structure does not include a polymer such as a conductive polymer layer, resulting in a capacitor with high heat resistance. However, other layers may be positioned between the dielectric layer and the p-type semiconductor layer. For example, another p-type semiconductor layer or a conductive polymer layer may be positioned between them.

[0024] Consider the case where the work function Wp2 of the p-type semiconductor that makes up the p-type semiconductor layer is equal to or less than the work function Wi2 of the inorganic conductive material that makes up the cathode extraction layer. For example, consider the case where a metal with a work function Wm (where Wp2 ≦ Wm) is used as the inorganic conductive material that makes up the cathode extraction layer. In this case, when the two are joined, their band structures become as shown in Figure 3. As shown in Figure 3, when Wp2 ≦ Wm (Wp2 ≦ Wi2), there is no barrier to the flow of holes, and the two form an ohmic contact. Therefore, it is possible to reduce the ESR of a capacitor with this configuration.

[0025] The thickness of the p-type semiconductor layer is not particularly limited and may be 1 nm or more, 10 nm or more, 100 nm or more, or 1 μm or more, or 100 μm or less, 10 μm or less, or 1 μm or less. The thickness may be in the range of 1 nm to 100 μm (for example, in the range of 10 nm to 10 μm).

[0026] There are no particular limitations on the p-type semiconductor as long as it satisfies Wp2≦Wi2. The p-type semiconductor may be a metal oxide, such as NiO, MnO2, or CuInO2. These may be doped with a dopant or may have an oxygen deficiency or excess.

[0027] The work function Wp2 of the p-type semiconductor may be 4.90 eV or less. The work function Wp2 varies depending on the material of the p-type semiconductor. Furthermore, Wp2 may be varied by the manufacturing method. Wp2 may be 4.80 eV or less, or 4.40 eV or less. There is no particular lower limit for Wp2, but it may be 2.10 eV or more.

[0028] In the second capacitor, examples of combinations of the p-type semiconductor constituting the p-type semiconductor layer and the inorganic conductive material constituting the cathode extraction layer will be described later.

[0029] The first and second capacitors may contain a conductive polymer. However, as described above, the first and second capacitors can be constructed without using a conductive polymer, resulting in a capacitor with high heat resistance.

[0030] (Third capacitor) The third capacitor includes an anode body having a dielectric layer formed on its surface, a cathode extraction layer, and a conductive polymer layer disposed between the dielectric layer and the cathode extraction layer and in contact with the cathode extraction layer. The conductive polymer layer is composed of a conductive polymer exhibiting p-type semiconductor properties. Hereinafter, this conductive polymer may be referred to as a "p-type conductive polymer." The work function of this conductive polymer is equal to or less than the work function of the inorganic conductive material that constitutes the cathode extraction layer. From one perspective, the conductive polymer layer can also be considered a p-type semiconductor layer.

[0031] The cathode extraction layer is disposed opposite the dielectric layer on the anode body. The conductive polymer layer is typically in contact with the dielectric layer on the anode body. That is, the first capacitor has a laminated structure of anode body / dielectric layer / conductive polymer layer / cathode extraction layer. However, other layers may be disposed between the dielectric layer and the conductive polymer layer. For example, another p-type conductive polymer layer may be disposed between them.

[0032] Figure 4 shows a schematic diagram of the band diagrams of p-type conductive polymers, semimetals (conductive carbon), and metals. Figure 4 also shows the work function Wp3, band gap Eg3, Fermi level Ef3, and ionization potential Ip of p-type conductive polymers. Similarly to Figure 1, Figure 4 also shows the band structures of semimetals and metals. Z in Figure 4 is the difference between the Fermi level Ef3 and the highest occupied molecular orbital (HOMO) energy level (HOMO level).

[0033] The ionization potential Ip is determined by the difference between the vacuum level and the energy level of the highest occupied molecular orbital (HOMO). The band gap Eg3 is determined by the difference between the energy level of the lowest unoccupied molecular orbital (LUMO) and the HOMO level. The work function Wp3 is determined by Wp3 = (Ip - Z). The ionization potential Ip of the conductive polymer and the work function of the semiconductor layer can be measured by the methods described in the examples.

[0034] Consider the case where the work function Wp3 of the conductive polymer that makes up the conductive polymer layer is equal to or less than the work function Wi3 of the inorganic conductive material that makes up the cathode extraction layer. For example, consider the case where a metal with a work function Wm (where Wp3 ≦ Wm) is used as the inorganic conductive material that makes up the cathode extraction layer. In this case, when the two are joined, their band structures become as shown in Figure 5. As shown in Figure 5, when Wp3 ≦ Wm (Wp3 ≦ Wi3), there is no barrier to the flow of holes, and the two form an ohmic contact. Therefore, it is possible to reduce the ESR of a capacitor with this configuration.

[0035] Considering the ionization potential Ip and the above Z, if (Ip-Z)≦Wi3, then ohmic contact is achieved. In other words, if (Ip-Wi3)≦Z, then ohmic contact is achieved. For example, if Z is 0.2 eV or more, then ohmic contact is achieved if (Ip-0.2)≦Wi3 (i.e., (Ip-Wi3)≦0.2) is satisfied. The value of Z can be changed by the dopant content, etc. By increasing the dopant content, the value of Z can be reduced.

[0036] The thickness of the p-type conductive polymer layer is not particularly limited and may be 1 nm or more, 10 nm or more, 100 nm or more, or 1 μm or more, or 100 μm or less, 10 μm or less, or 1 μm or less. The thickness may be in the range of 1 nm to 100 μm (for example, in the range of 10 nm to 10 μm).

[0037] As long as Wp3≦Wi3 is satisfied, there are no particular limitations on the p-type conductive polymer. Examples of p-type conductive polymers include polypyrrole, polythiophene, polyaniline, and derivatives thereof. These may be used alone or in combination. The conductive polymer may also be a copolymer of two or more monomers. Note that a conductive polymer derivative refers to a polymer having a conductive polymer as its basic skeleton. For example, an example of a polythiophene derivative is poly(3,4-ethylenedioxythiophene) (PEDOT). The p-type conductive polymer may be a polypyrrole-based polymer. Examples of polypyrrole-based polymers (polypyrroles) include polypyrrole and its derivatives. The p-type conductive polymer may be at least one polymer selected from the group consisting of polypyrrole and polypyrrole derivatives. Examples of polypyrrole derivatives include poly(alkylpyrrole). The alkyl group is bonded to a nitrogen atom or carbon atom constituting a five-membered ring. The number of carbon atoms in the alkyl group may be in the range of 1 to 3.

[0038] The conductive polymer layer may contain a dopant. The dopant is selected depending on the conductive polymer. There are no particular limitations on the dopant, and known dopants may be used. Examples of dopants include sulfuric acid, sulfonates, and the like. For example, examples of dopants include benzenesulfonic acid, alkylbenzenesulfonic acid, naphthalenesulfonic acid, alkylnaphthalenesulfonic acid, polystyrenesulfonic acid (PSS), and salts thereof. The conductive polymer layer may contain PEDOT doped with PSS. The conductive polymer constituting the conductive polymer layer may contain PEDOT doped with PSS or may be PEDOT doped with PSS.

[0039] The p-type conductive polymer may be a conductive polymer in which a sulfonate is added as a dopant to a polypyrrole-based polymer. Examples of polypyrrole-based polymers include polypyrrole and its derivatives. Examples of sulfonates include sodium naphthalenesulfonate-based compounds. Examples of sodium naphthalenesulfonate-based compounds include sodium naphthalenesulfonate and its derivatives. The sodium naphthalenesulfonate-based compound may be at least one selected from the group consisting of sodium naphthalenesulfonate and its derivatives. Examples of sodium naphthalenesulfonate-based compounds include sodium propyl naphthalenesulfonate, sodium octafluoropentyl naphthalene polysulfonate, etc. The p-type conductive polymer may be polypyrrole doped with a sulfonate (e.g., a sodium naphthalenesulfonate-based compound).

[0040] The ionization potential of the p-type conductive polymer may be 5.11 eV or less.

[0041] The p-type conductive polymer layer may be composed of only one type of conductive polymer, or may be composed of multiple types of conductive polymers. When the p-type conductive polymer layer is composed of multiple conductive polymers, the conductive polymer that is the main component (the component with the highest content) among the multiple conductive polymers satisfies the above relationship. It is preferable that all of the multiple conductive polymers satisfy the above relationship.

[0042] In the first to third capacitors, the inorganic conductive material constituting the cathode extraction layer is selected depending on the work function or ionization potential of the materials constituting the adjacent layers (the n-type semiconductor layer, p-type semiconductor layer, and conductive polymer layer). The inorganic conductive material may be conductive carbon. Alternatively, the inorganic conductive material may be silver, copper, gold, platinum, or an alloy containing at least one of these. The inorganic conductive material constituting the cathode extraction layer may include at least one selected from the group consisting of conductive carbon, silver, copper, gold, and platinum, or may be at least one selected from the group consisting of these. Examples of conductive carbon include graphite, carbon black, graphene flakes, and carbon nanotubes.

[0043] The inorganic conductive material constituting the cathode extraction layer may be composed of only one type of material, or may contain multiple types of materials. When the inorganic conductive material contains multiple types of conductive materials, the main component (the component with the highest content) among the multiple conductive materials satisfies the above relationship. It is preferable that all of the multiple conductive materials satisfy the above relationship.

[0044] (Method of manufacturing capacitor (C)) There are no particular limitations on the method for manufacturing the capacitor (C), and components other than the p-type semiconductor layer of the first capacitor, the n-type semiconductor layer of the second capacitor, and the p-type conductive polymer layer of the second capacitor may be formed by known methods.

[0045] The method for forming the p-type semiconductor layer of the first capacitor and the n-type semiconductor layer of the second capacitor is not limited, and they may be formed by known methods. Examples of these formation methods include a vapor-phase method in which a layer is formed in a vapor phase and a liquid-phase method in which a layer is formed in a liquid phase. Examples of vapor-phase methods include evaporation, sputtering, atomic layer deposition (ALD), and chemical vapor deposition (CVD). Examples of liquid-phase methods include a sol-gel method, chemical solution deposition, liquid-phase deposition, hydrothermal synthesis, flux deposition, coating, electrolytic plating, and electroless plating. These methods are preferably selected taking into consideration the material of the semiconductor layer and the desired work function.

[0046] The method for forming the conductive polymer layer of the third capacitor is not particularly limited, and may be formed by a known method. For example, the conductive polymer layer may be formed using a dispersion containing a p-type conductive polymer. The dispersion may contain a dopant as needed. Alternatively, the conductive polymer layer may be formed by electrolytic polymerization.

[0047] Examples of the configuration and constituent members of the capacitor (C) are described below. Known constituent members may be used for constituent members other than those characteristic of the present disclosure.

[0048] (anode body) The anode body can be formed using a valve metal, an alloy containing a valve metal, a compound containing a valve metal, or the like. These materials may be used alone or in combination of two or more. Examples of valve metals that are preferably used include aluminum, tantalum, niobium, and titanium. The anode body may be formed using a foil of the above materials (e.g., a metal foil such as aluminum foil).

[0049] An anode having a porous surface can be obtained by roughening the surface of a metal foil containing a valve metal, for example. The roughening may be performed by electrolytic etching or the like.

[0050] Alternatively, the anode body may be formed by sintering particles of the above material. For example, the anode body may be a sintered body of tantalum. When the anode body is a sintered body, a porous portion exists on the surface. When the anode body is a sintered body, the capacitor (C) may include an anode wire partly embedded in the sintered body.

[0051] (dielectric layer) The dielectric layer is an insulating layer that functions as a dielectric. The dielectric layer may be formed by anodizing a valve metal on the surface of the anode body (e.g., a metal foil). The dielectric layer may be formed so as to cover at least a portion of the anode body. The dielectric layer is usually formed on the surface of the anode body. When a porous portion is present on the surface of the anode body, the dielectric layer is formed on the surface of the porous portion of the anode body.

[0052] A typical dielectric layer contains an oxide of a valve metal. For example, when tantalum is used as the valve metal, a typical dielectric layer contains Ta2O5, and when aluminum is used as the valve metal, a typical dielectric layer contains Al2O3. However, the dielectric layer is not limited to these and may be any material that functions as a dielectric.

[0053] (Cathode extraction layer) The cathode extraction layer is a layer having electrical conductivity. As described above, the cathode extraction layer contains an inorganic conductive material. The cathode extraction layer may be formed using particles of an inorganic conductive material (such as conductive carbon particles or metal particles). Specifically, the cathode extraction layer may be formed using a carbon paste containing conductive carbon particles or a metal paste containing metal particles. Alternatively, the cathode extraction layer may include a layer made only of conductive carbon or a layer made only of metal (a vapor deposition layer or a metal foil). Examples of metal pastes include pastes containing the above-mentioned metal particles.

[0054] At least one other conductive layer may be formed on the cathode extraction layer. In this case, the cathode extraction layer can be considered to include a first cathode extraction layer disposed on the surface facing the anode body and a second cathode extraction layer (another conductive layer) formed on the first cathode extraction layer. In this case, the first cathode extraction layer is in contact with the n-type semiconductor layer of the first capacitor, the p-type semiconductor layer of the second capacitor, or the conductive polymer layer of the third capacitor. Therefore, the inorganic conductive material constituting the first cathode extraction layer is selected to have a work function that satisfies the above-mentioned condition. The material of the other conductive layer (second cathode extraction layer) is not particularly limited, and any of the materials exemplified for the cathode extraction layer (first cathode extraction layer) may be used.

[0055] The cathode extraction layer may contain components other than the inorganic conductive material. Examples of such components include a resin that functions as a binder. However, the conductivity of the cathode extraction layer is provided by the inorganic conductive material. Typically, the content of the inorganic conductive material in the cathode extraction layer is 50 mass % or more (for example, in the range of 70 to 100 mass %).

[0056] (Lead material and exterior body) There are no particular limitations on the lead members and the exterior body, and known lead members and exterior bodies may be used.

[0057] (Capacitor (C) structure) The capacitor (C) may include only one capacitor element. Alternatively, the capacitor (C) may include multiple capacitor elements. For example, the capacitor element (C) may include multiple capacitor elements connected in parallel. The multiple capacitor elements (C) are typically connected in parallel in a stacked state and covered with an exterior body.

[0058] Examples of embodiments according to the present disclosure will be described in detail below with reference to the drawings. The components described above can be applied to the components of the examples described below. The examples described below can be modified based on the above description. The matters described below may also be applied to the above embodiments. In the embodiments described below, components that are not essential to the capacitor of the present disclosure may be omitted. Note that the following drawings are schematic and may differ from the actual configuration.

[0059] (Embodiment 1) In the first embodiment, an example of a first capacitor will be described. Fig. 6 is a cross-sectional view schematically showing an example of the first capacitor. The capacitor 10 shown in Fig. 6 includes a capacitor element 100, an anode lead 21, a cathode lead 22, a metal paste layer 23, and an outer casing 30. The metal paste layer 23 is the conductive layer (L) described above.

[0060] Capacitor element 100 includes an anode body 111, a dielectric layer 112, an n-type semiconductor layer 120, and a cathode extraction layer 131. Dielectric layer 112 is formed so as to cover at least a portion of the surface of anode body 111. N-type semiconductor layer 120 is formed so as to cover at least a portion of dielectric layer 112. Cathode extraction layer 131 is formed so as to cover at least a portion of n-type semiconductor layer 120. The work function of the n-type semiconductor that constitutes n-type semiconductor layer 120 is equal to or greater than the work function of the inorganic conductive material that constitutes cathode extraction layer 131.

[0061] Anode lead 21 is connected to anode body 111. Cathode lead 22 is connected to cathode extraction layer 131 via metal paste layer 23. Metal paste layer 23 is formed of metal paste (silver paste) or the like. Exterior body 30 is formed to cover part of anode lead 21, part of cathode lead 22, and capacitor element 100. Part of anode lead 21 and part of cathode lead 22 are exposed from exterior body 30 and function as terminals.

[0062] FIG. 6 shows a case where the capacitor 10 includes only one capacitor element 100. However, the capacitor 10 may include multiple capacitor elements 100. FIG. 7 is a schematic cross-sectional view of an example of a capacitor 10 including multiple capacitor elements 100. Note that, to make the drawing easier to understand, some components are not shown in FIG. 7.

[0063] 7 includes a plurality of stacked capacitor elements 100. The plurality of capacitor elements 100 are connected in parallel.

[0064] In the case of the second capacitor, the n-type semiconductor layer 120 may be replaced with a p-type semiconductor layer. In the case of the third capacitor, the n-type semiconductor layer 120 may be replaced with a conductive polymer layer made of a p-type conductive polymer. In these cases, the inorganic conductive materials that make up the p-type semiconductor layer, the p-type conductive polymer, and the cathode extraction layer 131 are selected so as to satisfy the above-mentioned relationship. [Example]

[0065] The capacitor (C) will be described in more detail below using examples. In the following examples, layers made of various materials were formed by various methods. The work function or ionization potential of the formed layers was measured by the following method.

[0066] In measuring the work function of the semiconductor (semiconductor layer), a semiconductor thin film was first formed on a glass substrate, and then the work function of the formed semiconductor thin film was measured using an ultraviolet photoelectron spectrometer (UPS) (AC-2, manufactured by Riken Keiki Co., Ltd.).

[0067] To measure the ionization potential of the conductive polymer (conductive polymer layer), a conductive polymer film was first formed by electrolytic polymerization. Then, the ionization potential of the formed conductive polymer film was measured using an ultraviolet photoelectron spectrometer (UPS) (AC-2, manufactured by Riken Keiki Co., Ltd.).

[0068] Example 1 In Example 1, the contact between the n-type semiconductor and the cathode extraction layer in the first capacitor was investigated. Table 1 shows the work function Wn of the n-type semiconductor, the work function Wi1 of the cathode extraction layer material, and the type of contact formed by the combination of the n-type semiconductor and various cathode extraction layer materials.

[0069] [Table 1]

[0070] In Table 1, the work functions of In2O3, Ga2O3, gold, and platinum are not actual measurements but values ​​obtained from literature. The other work functions are values ​​measured by the method described above. In ITO, the atomic ratio of In to Sn was In:Sn=9:1. Graphite (particle size 0.5-1.0 μm) was used as the carbon.

[0071] Al-ZnO is ZnO doped with Al. The Al-ZnO (liquid phase growth method) in Table 1 was formed by liquid phase growth (liquid phase method). Specifically, an aqueous solution containing zinc nitrate, aluminum nitrate, and hexamethylenetetramine was prepared. A glass substrate was immersed in the aqueous solution at 85°C until an Al-ZnO layer with a predetermined thickness was formed. After immersion, the formed Al-ZnO layer was dried at 120°C for 10 minutes. The ZnO (liquid phase growth method) in Table 1 was formed by liquid phase growth (liquid phase method). Specifically, an aqueous solution containing zinc nitrate and hexamethylenetetramine was prepared. A glass substrate was immersed in the aqueous solution at 85°C until a ZnO layer with a predetermined thickness was formed. After immersion, the formed ZnO layer was dried at 120°C for 10 minutes. The Al-ZnO (sputtering) and ITO (sputtering) in Table 1 were formed by sputtering.

[0072] In Table 1, when 0≦Wn−Wi1 (i.e., Wi1≦Wn), the n-type semiconductor layer and the cathode extraction layer are in ohmic contact. In the first capacitor, the materials of the n-type semiconductor and the cathode extraction layer are selected so that the contact between them is ohmic.

[0073] As shown in Table 1, when an Al-ZnO layer is formed by sputtering, a Schottky contact is formed when the conductive materials shown in Table 1 (commonly used conductive materials) are used for the cathode extraction layer. This fact was not previously known. It is preferable to form the Al-ZnO layer and ZnO layer by a liquid phase method, as this makes it easier to satisfy the relationship Wi1≦Wn.

[0074] The Al-ZnO (sputtering), Al-ZnO (liquid phase growth), and ZnO (liquid phase growth) layers were analyzed by X-ray diffraction (XRD). The lattice constant C of the ZnO in the c-axis direction was 5.1762 Å for Al-ZnO (sputtering), 5.1308 Å for Al-ZnO (liquid phase growth), and 5.1302 Å for ZnO (liquid phase growth). The lattice constant C of the ZnO formed by liquid phase growth was small, while the lattice constant C of the ZnO formed by sputtering was large.

[0075] Furthermore, stacked structures corresponding to A1 to A3 and A16 to A18 in Table 1 were formed, and resistance values ​​were measured. Specifically, as shown in FIG. 8, a first layer 201 made of an n-type semiconductor was formed on a glass substrate 200, and two second layers 202a and 202b were formed on the first layer 201 at a distance from each other. The second layers 202a and 202b were formed from the material of the cathode extraction layer. The resistance value between the second layer 202a and the second layer 202b was then measured. The measurement results are shown in Table 2.

[0076] [Table 2]

[0077] As shown in Table 2, the combinations of A1 to A3 and A18, which form Schottky contacts, had high resistance values, while the combination of A16 and A17, which form ohmic contacts, had low resistance values.

[0078] Example 2 In Example 2, the contact between the p-type semiconductor and the cathode extraction layer in the second capacitor was investigated. Table 3 shows the work function Wp2 of the p-type semiconductor, the work function Wi2 of the cathode extraction layer material, and the type of contact formed by the combination of the p-type semiconductor and various cathode extraction layer materials.

[0079] [Table 3]

[0080] The work functions of NiO, MnO2, CuInO2, gold, and platinum are not measured but are taken from the literature. The other work functions are measured using the method described above.

[0081] In Table 3, when Wp2-Wi2≦0 (i.e., Wp2≦Wi2), the p-type semiconductor layer and the cathode extraction layer are in ohmic contact. In the second capacitor, the materials of the p-type semiconductor and the cathode extraction layer are selected so that the contact between them is ohmic.

[0082] Example 3 In Example 3, the contact between the p-type conductive polymer layer and the cathode extraction layer in the third capacitor was investigated. Table 4 shows the ionization potential Ip of the conductive polymer, the work function Wp3 of the conductive polymer, the work function Wi3 of the cathode extraction layer material, and the type of contact resulting from the combination of a conductive polymer layer formed using a p-type conductive polymer and various cathode extraction layer materials. The value of the work function Wp3 is based on the assumption that the value of Z is 0.2 eV.

[0083] [Table 4]

[0084] Polymer 1 in Table 4 is polypyrrole doped with sodium propyl naphthalene sulfonate. Polymer 2 in Table 4 is polypyrrole doped with sodium octafluoropentyl naphthalene polysulfonate.

[0085] When the contact state of the combinations of C1, C6, and C7 was actually measured, C1 and C6 were in ohmic contact, and C7 was in Schottky contact.

[0086] In Table 4, when Wp3 - Wi3 ≦ 0 (i.e., Wp3 ≦ Wi3), the conductive polymer layer and the cathode extraction layer are in ohmic contact. In the third capacitor, the materials of the conductive polymer and the cathode extraction layer are selected so that the contact between them is ohmic.

[0087] Assuming that the value of Z is 0.2 eV, ohmic contact occurs if Wp3 = (Ip - 0.2) ≦ Wi3 is satisfied. In other words, if (Ip - 0.2) ≦ Wi3 (i.e., (Ip - Wi3) ≦ 0.2) is satisfied, ohmic contact occurs if 0.2 ≦ Z is satisfied. [Industrial Applicability]

[0088] The present disclosure can be used for capacitors. 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. [Explanation of symbols]

[0089] 10: Capacitor 100: Capacitor element 111: Anode body 112: Dielectric layer 120: n-type semiconductor layer 131: Cathode extraction layer

Claims

1. A capacitor, an anode body having a dielectric layer formed on its surface; a cathode extraction layer; an n-type semiconductor layer disposed between the dielectric layer and the cathode extraction layer and in contact with the cathode extraction layer; a work function of the n-type semiconductor constituting the n-type semiconductor layer is equal to or greater than a work function of the inorganic conductive material constituting the cathode extraction layer;

2. The n-type semiconductor is ZnO, indium tin oxide, In ２ O ３ , and Ga ２ O ３ The capacitor according to claim 1, wherein the capacitor is any one of the following:

3. 2. The capacitor according to claim 1, wherein the work function of the n-type semiconductor is 4.65 eV or more.

4. A capacitor, an anode body having a dielectric layer formed on its surface; a cathode extraction layer; a p-type semiconductor layer disposed between the dielectric layer and the cathode extraction layer and in contact with the cathode extraction layer; a work function of a p-type semiconductor constituting the p-type semiconductor layer is equal to or lower than a work function of an inorganic conductive material constituting the cathode extraction layer;

5. The p-type semiconductor is NiO, MnO ２ , and CuInO ２ The capacitor according to claim 4, wherein the capacitor is any one of the following:

6. 5. The capacitor of claim 4, wherein the work function of the p-type semiconductor is 4.90 eV or less.

7. 7. The capacitor according to claim 1, wherein the inorganic conductive material comprises at least one selected from the group consisting of conductive carbon, silver, copper, gold, and platinum.

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