Capacitor and method for manufacturing the same

Abstract

The present invention provides a capacitor equipped with electrodes containing carbon nanotubes with reduced bundling. [Solution] The capacitor comprises a first electrode, a second electrode facing the first electrode, and a dielectric that covers at least a portion of the surface of the first electrode and is interposed between the first electrode and the second electrode. The first electrode comprises a first conductor containing a first metal, and a plurality of carbon nanotubes having fixed ends on the surface of the first conductor and metallic portions at their free ends. The metallic portions contain a second metal.

Description

Technical Field

[0001] The present disclosure relates to a capacitor and a method for manufacturing the same.

Background Art

[0002] Capacitors using carbon nanotubes (CNTs) as electrodes have been studied.

[0003] For example, Patent Document 1 proposes a capacitor including: a conductive substrate; a plurality of fibrous conductive members arranged on the substrate and electrically connected to the substrate; and a dielectric layer covering surfaces of the plurality of fibrous conductive members, wherein the plurality of fibrous conductive members are composed of a proximal half located proximal to a surface of the substrate and a distal half located distal to the surface of the substrate, and one of the proximal half and the distal half has a higher number density of the plurality of fibrous conductive members and a larger thickness of the dielectric layer than the other. CNTs and the like are used as the fibrous conductive members.

[0004] Non-Patent Document 1 teaches that when CNT growth occurs on a substrate surface, the CNT density becomes maximum on a side far from the substrate.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0007] In Patent Document 1 and Non-Patent Document 1, CNT growth occurs on the surface of the substrate. In this case, the density of CNTs is highest on the side furthest from the substrate. On the side furthest from the substrate, the free ends of adjacent CNTs come into contact with each other, and thereafter tend to form bundles, which shields the space on the substrate side and tends to reduce the surface area. [Means for solving the problem]

[0008] The first aspect of this disclosure is, First electrode and, A second electrode facing the first electrode, The device comprises a dielectric that covers at least a portion of the surface of the aforementioned first electrode and is interposed between the aforementioned first electrode and the aforementioned second electrode, The first electrode comprises a first conductor containing a first metal, and a plurality of carbon nanotubes having fixed ends on the surface of the first conductor and metal portions at their free ends. The aforementioned metal part relates to a capacitor, including a second metal.

[0009] The second aspect of this disclosure is, A first step involves forming a plurality of nanoparticles containing a second metal on the surface of a first conductor containing a first metal, A second step of forming a first electrode by growing carbon nanotubes on the surface of the nanoparticles and forming a plurality of carbon nanotubes between the plurality of nanoparticles and the first conductor, A third step of forming a dielectric covering at least a portion of the surface of the first electrode, The present invention relates to a method for manufacturing a capacitor, comprising a fourth step of providing a second electrode facing the first electrode and such that the dielectric material is interposed between the first electrode and the second electrode. [Effects of the Invention]

[0010] According to this disclosure, a capacitor can be obtained that uses electrodes equipped with CNTs in which bundling is reduced. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view of a capacitor according to one embodiment of the present disclosure. [Figure 2] This is a schematic cross-sectional view of section II in Figure 1, magnified. [Modes for carrying out the invention]

[0012] In conventional technology, carbon nanotubes (CNTs) grown on a substrate tend to form bundles on the side away from the substrate, resulting in a small surface area. In capacitors, it becomes necessary to form a dielectric layer on the CNT surface, but clogging on the CNT surface makes it difficult to form the dielectric layer. Therefore, the thickness of the dielectric becomes uneven, and the dielectric strength decreases. In addition, when the surface area of ​​the CNTs is small, it becomes difficult to secure sufficient capacitance. Furthermore, the high density of CNTs on the side farther from the substrate makes it difficult to embed electrodes with opposite polarity to the substrate between the CNTs. As a result, the initial equivalent series resistance (ESR) and the decrease in capacitance at high frequencies of the capacitor become large.

[0013] Technology(1) A capacitor according to one aspect of the present disclosure comprises a first electrode, a second electrode facing the first electrode, and a dielectric that covers at least a portion of the surface of the first electrode and is interposed between the first electrode and the second electrode. The first electrode comprises a first conductor containing a first metal, and a plurality of CNTs having fixed ends on the surface of the first conductor and metallic portions at their free ends. The metallic portions contain a second metal.

[0014] Said first electrode is formed by growing CNTs between the first conductor and the nanoparticles corresponding to the metal portion. Therefore, the CNT has a fixed end on the surface of the first conductor, and has a metal portion at a free end opposite to the fixed end. The presence of the metal portion at the free end allows CNTs to grow at the portion in contact with the free end of the metal portion. This enables increasing the length of the CNT. In addition, since CNTs grow on the free end side, adhesion between adjacent CNTs on the free end side to form bundles is reduced. Further, at the fixed end, since the CNTs are fixed to the first conductor, formation of bundles is suppressed. By reducing bundling of CNTs in this manner, a dielectric layer with a more uniform thickness can be formed on the surface of the first electrode. Furthermore, by reducing bundling of CNTs, the second electrode can be highly filled through the dielectric into the gaps between the plurality of CNTs formed on the surface of the first conductor. Moreover, since CNTs are directly fixed to the first conductor, high conductivity between the CNTs and the first conductor can be obtained. Therefore, high initial capacitance and low ESR of the capacitor can be obtained without forming a conventional barrier layer (such as a layer containing an insulating material such as Al₂O₃). In addition, high withstand voltage of the capacitor can be obtained by obtaining a dielectric layer formed to a more uniform thickness.

[0015] In this specification, a conductor such as the first conductor refers to a conductive member. A CNT has a fixed end and a free end. The fixed end of the CNT is the end of the CNT fixed to the surface of the first conductor. The free end of the CNT is the end that is not fixed to the first conductor in the first electrode.

[0016] Technology (2) In the above technology (1), 80% or more of the total number of the CNTs may be spaced apart from the adjacent CNTs. In other words, the number of free ends of the CNTs may be 80% or more of the number of fixed ends. In the present disclosure, bundling of CNTs in the first electrode is reduced as described above. Therefore, most of the CNTs are spaced apart from adjacent CNTs. By reducing bundling of CNTs, a dielectric layer with a more uniform thickness can be formed, and the second electrode can be highly filled into the gaps between the CNTs via the dielectric layer. Accordingly, high initial capacity and low ESR of the capacitor can be obtained. Furthermore, by forming a dielectric layer with a more uniform thickness, high voltage resistance of the capacitor can be obtained.

[0017] Technology (3) In the above technology (1) or technology (2), the average length of the CNTs is preferably 30 µm or more and 200 µm or less. In the present disclosure, since the CNT has a fixed end on the surface of the first conductor and a metal portion at the free end, the CNT can grow even during the formation of the dielectric layer, and long CNTs can be formed. In the present disclosure, bundling of CNTs is also reduced. These effects enable the specific surface area of the first electrode to be increased, and allow high filling of the second electrode. As a result, the initial capacitance can be further increased.

[0018] Technology (4) In any one of the above technologies (1) to (3), an interface based on a difference in carbon crystal structure or growth direction of the carbon nanotubes between the fixed end and the free end of the CNT may be observed. In the present disclosure, a CNT is formed between the first conductor and the metal portion, and then a dielectric layer is further formed. The CNT also grows during the formation of this dielectric layer. The CNTs formed before forming the dielectric layer and the CNTs formed during forming the dielectric layer have different carbon crystal structures and growth directions, so an interface based on this difference can be observed. Since the CNTs are formed through such a growth process, long CNTs are formed and bundling is reduced.

[0019] Technology (5) In any one of the above techniques (1) to (4), the second metal is preferably at least one selected from the group consisting of Fe, Co, and Ni. These metals have a high catalytic activity for CNT formation and facilitate the growth of CNTs at the free end. Therefore, longer CNTs can be formed.

[0020] Technology(6) In any one of the above techniques (1) to (5), it is preferable that the first metal is at least one selected from the group consisting of Ni, Cu, and Al. When CNTs are grown on a first conductor containing these first metals, the fixed ends of the CNTs are more likely to form on the surface of the first conductor, and the metallic portion is more likely to form on the free ends of the CNTs. As a result, bundling of CNTs is suppressed, and longer CNTs are more easily obtained.

[0021] Technology(7) In any one of the above techniques (1) to (6), the surface of the first conductor is preferably the surface of a conductive coating containing Al. In this case, the fixed end of the CNT is easily formed on the surface of the first conductor, and the metallic part is easily formed on the free end of the CNT. Therefore, bundling of the CNT is suppressed, and longer CNTs are more easily obtained.

[0022] Technology(8) In the above technology (7), the thickness of the coating is preferably 35 nm or less. In this case, the metal portion is more likely to form on the free end of the CNT, and bundling is more easily suppressed.

[0023] Technology(9) In any one of the above technologies (1) to (8), the average thickness of the dielectric is preferably 5 nm or more. In this case, a dielectric of more uniform thickness can be formed on the surface of the first electrode having CNTs with suppressed bundling. This results in higher dielectric strength.

[0024] Technology(10) In any one of the above techniques (1) to (9), it is preferable that the second electrode comprises a second conductor that covers at least a portion of the surface of the dielectric. In this case, it is easier to obtain a higher initial capacitance and a lower ESR of the capacitor.

[0025] Technology(11) In the above technology (10), it is preferable that the second conductor includes at least one selected from the group consisting of metals, conductive polymers, and semiconductors. In this case, it is easier to obtain a higher initial capacitance and a lower ESR of the capacitor.

[0026] Technology(12) This disclosure also includes a method for manufacturing a capacitor. The method for manufacturing a capacitor is: A first step involves forming a plurality of nanoparticles containing a second metal on the surface of a first conductor containing a first metal, A second step of forming a first electrode by growing CNTs on the surface of the nanoparticles and forming a plurality of CNTs between the plurality of nanoparticles and the first conductor, A third step of forming a dielectric covering at least a portion of the surface of the first electrode, The fourth step includes providing a second electrode facing the first electrode and such that the dielectric is interposed between the first electrode and the second electrode.

[0027] As CNTs grow on the surface of nanoparticles, fixed ends of the CNTs are formed on the surface of the first conductor, and CNTs grow in the portion that contacts the nanoparticles. This allows for an increase in the length of the CNTs. Nanoparticles are present at the end opposite the fixed end (free end), and at the fixed end, the CNTs are fixed to the first conductor. These factors reduce the adhesion and bundling of adjacent CNTs at the free end. By reducing CNT bundling, a dielectric material with a more uniform thickness can be formed on the surface of the first electrode. Furthermore, by reducing CNT bundling, the gaps between multiple CNTs formed on the surface of the first conductor can be more densely filled with the second electrode via the dielectric material. Therefore, it is easier to obtain a high initial capacitance and low ESR of the capacitor. In addition, the formation of a dielectric material with a more uniform thickness results in a high voltage withstand capability of the capacitor.

[0028] Technology(13) In the above technology (12), it is preferable to form the nanoparticles in the first step by at least one selected from the group consisting of electron beam deposition and sputtering. With these methods, the film thickness can be easily controlled and a thin film can be formed. Since nanoparticles are formed by aggregating the thin film, nanoparticles can be easily formed by using the above method. In addition, the shape of the nanoparticles is easily maintained on the surface of the first conductor. Therefore, CNTs can be grown stably and the effect of reducing CNT bundling is enhanced.

[0029] Technology(14) In the above techniques (12) or (13), it is preferable to form the dielectric by atomic layer deposition (ALD) in the third step. In this case, CNTs can be grown while the dielectric is being formed, and long CNTs can be formed. In this disclosure, the bundling of CNTs is also reduced. As a result, the specific surface area of ​​the first electrode can be increased. The second electrode can also be highly packed, which can further increase the initial capacitance.

[0030] Technology(15) In the above technology (14), the second step preferably includes a step of growing the plurality of carbon nanotubes by chemical vapor deposition (CVD). In this case, the CNT growth reaction proceeds easily on the surface of the nanoparticles, and relatively long CNTs are easily obtained.

[0031] Technology(16) In the above techniques (14) or (15), the third step preferably includes a step of further growing the plurality of carbon nanotubes in parallel with the formation of the dielectric by the ALD method. In this case, long CNTs can be formed. In this disclosure, the bundling of CNTs is also reduced. These measures make it possible to increase the specific surface area of ​​the first electrode. The second electrode can also be highly packed, which further increases the initial capacitance.

[0032] Technology(17) In the above technology (16), it is preferable to carry out the ALD method using an organometallic compound in which all organic groups bonded to the metal element are hydrocarbon groups. In this case, it is easier to grow CNTs while forming the dielectric, and longer CNTs are more easily obtained.

[0033] The capacitor and its manufacturing method described herein will be explained in more detail below, including the above-mentioned techniques (1) to (17), with reference to the drawings as necessary. To the extent that it is not technically inconsistent, at least one of the above-mentioned techniques (1) to (17) may be combined with at least one of the elements described below. Note that the figures are schematic representations, and the proportions of the dimensions (e.g., thickness) of each component may differ from those of actual components.

[0034] [capacitor] The capacitor of this disclosure comprises a first electrode, a second electrode, and a dielectric interposed between the first electrode and the second electrode. The capacitor comprises, for example, at least one capacitor element comprising a first electrode, a second electrode, and a dielectric. The capacitor may comprise two or more capacitor elements.

[0035] (1st electrode) The first electrode comprises a first conductor containing a first metal and a plurality of CNTs. Each CNT has a fixed end on the surface of the first conductor and a metal portion at its free end. The metal portion contains a second metal. The first electrode may be, for example, the anode portion of a capacitor.

[0036] (First conductor) The first conductor is a conductor that can constitute the electrodes of a capacitor. The element of the first metal is, for example, a metallic element used in the electrodes of a capacitor. Preferably, the first metal is at least one selected from the group consisting of Ni, Cu, and Al. In this case, the conductivity is relatively high, which is advantageous in achieving low ESR. The above first metal is relatively inexpensive, easy to process, and advantageous from the viewpoint of mass production by roll-to-roll manufacturing. Furthermore, when the first metal is Al, metal nanoparticles can be formed relatively easily, making it easy to grow CNTs.

[0037] The fixed end of the CNT is fixed to the surface of the first conductor. Therefore, the surface of the first conductor is preferably a conductive surface containing a metallic element that promotes the growth of CNTs. Such a metallic element is preferably the element of the first metal, and more preferably Al. The surface of the first conductor may also be the surface of a conductive coating containing the first metal (such as Al). For example, the first conductor may be formed only of a conductive coating, or it may comprise a substrate and a conductive coating formed on the surface of the substrate.

[0038] The conductive coating may be at least one selected from the group consisting of a first metal in its elemental form, an alloy containing elements of the first metal, and a conductive compound containing elements of the first metal. From the viewpoint of facilitating the formation of relatively long CNTs, the surface of the first conductor is preferably the surface of an Al coating or an Al alloy coating.

[0039] In the first conductor, the thickness of the above-mentioned coating (for example, a coating containing Al) is preferably 35 nm or less, more preferably 32 nm or less, and even more preferably 30 nm or less. When the thickness of the coating is within this range, CNTs tend to grow easily on the free end side. Therefore, the bundling of CNTs can be further reduced. The thickness of the coating is preferably 5 nm or more, more preferably 8 nm or more, and even more preferably 10 nm or more. When the thickness of the coating is within this range, nanoparticles corresponding to the metal part tend to form stably, and it is easy to form many CNTs.

[0040] The thickness of the above coating (for example, a coating containing Al) may be 5 nm or more (or 8 nm or more) and 35 nm or less, 5 nm or more (or 8 nm or more) and 32 nm or less, 5 nm or more (or 8 nm or more) and 30 nm or less, 10 nm or more and 35 nm or less (or 32 nm or less), or 10 nm or more and 30 nm or less.

[0041] If the first conductor includes a substrate, the substrate is preferably a conductive substrate used for the electrodes of a capacitor. The substrate may also include a first metal. The substrate may include, for example, at least one selected from the group consisting of Cu and Ni. The substrate may also be, for example, at least one selected from elemental metals, alloys, and conductive compounds containing these metal elements.

[0042] The shape of the first conductor is not particularly limited. The first conductor may be, for example, in the form of foil or a sheet.

[0043] The thickness of the first conductor may be between 30 μm and 1000 μm, or between 50 μm and 500 μm. When the thickness of the first conductor is within this range, high strength of the first electrode can be obtained. From the viewpoint of miniaturizing and reducing the height of the capacitor, the thickness of the first conductor is preferably 100 μm or less. Within the above range, the upper limit may be set to 100 μm.

[0044] The thickness of the coating or the first conductor is determined by measuring the thickness at any 10 points using a cross-sectional image of the capacitor element (or the first electrode or first conductor) and calculating the average value of these measurements. The above cross-sectional image is taken using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0045] (CNT) In the capacitor of this disclosure, the first electrode comprises a plurality of carbon nanotubes (CNTs) fixed to the surface of the first conductor. The CNTs are directly fixed to the surface of the first conductor. Therefore, no barrier layer (such as a layer containing an insulating material such as Al2O3), an adhesive layer including an organic binder, etc. is interposed between the end face of the CNT on the first conductor side and the first conductor.

[0046] Conventionally, there are techniques for growing carbon nanotubes (CNTs) on the surface of a conductive substrate having a barrier layer. Such techniques make it easy to form relatively long CNTs at high density. However, CNTs tend to grow on the surface of the barrier layer, and the ends of the CNTs on the opposite side of the barrier layer tend to form bundles. In the capacitor of this disclosure, by using a first conductor containing a first metal and nanoparticles containing a second metal (corresponding to the metal part), CNTs grow on the surface of the metal part located on the opposite side of the first conductor. As a result, relatively long CNTs can be obtained, and bundling is reduced.

[0047] Thus, in the first electrode, bundling at the free end of the CNTs is reduced. The number of free ends of the CNTs is preferably 80% or more of the number of fixed ends, and more preferably 90% or more. The number of free ends of the CNTs is 100% or less of the number of fixed ends. The number of free ends and fixed ends of the CNTs may be the same. In this way, in this disclosure, many CNTs are spaced apart from adjacent CNTs. Therefore, a dielectric with a more uniform thickness can be formed, and the second electrode can be highly filled in the gaps between the CNTs via the dielectric.

[0048] The average length of the CNTs is preferably 30 μm or more, more preferably 40 μm or more or 60 μm or more, and even more preferably 70 μm or more. In this disclosure, since the CNTs grow on the surface of the nanoparticles (metal part), relatively long CNTs can be formed in this way. The average length of the CNTs is preferably 200 μm or less, and more preferably 150 μm or less or 140 μm or less. When the average length of the CNTs is within this range, bending of the CNTs due to their own weight and the weight of the metal part is easily suppressed. In addition, when the average length of the CNTs is within this range, when forming the dielectric by the ALD method, it is easier to supply the organometallic compound gas, which is the raw material, to the depths of the CNTs, and the dielectric can be formed to the depths of the CNTs. The length of the CNTs is determined using the above cross-sectional image and as the average of the lengths of 10 CNTs, in accordance with the case of the thickness of the first conductor.

[0049] The average length of the CNTs may be 30 μm or more (or 40 μm or more) and 200 μm or less, 60 μm or more (or 70 μm or more) and 200 μm or less, 30 μm or more (or 40 μm or more) and 150 μm or less, 60 μm or more (or 70 μm or more) and 150 μm or less, 30 μm or more (or 40 μm or more) and 140 μm or less, or 60 μm or more (or 70 μm or more) and 140 μm or less.

[0050] The width of the CNT may be between 3 nm and 100 nm, between 10 nm and 100 nm, or between 10 nm and 50 nm. In this disclosure, CNTs with relatively large widths can be obtained. When the width of the CNT is within this range, it is easy to form long CNTs and easy to obtain high conductivity. The width of the CNT is determined using the above cross-sectional image, in accordance with the case of the thickness of the first conductor, as the average width of 10 CNTs.

[0051] The average spacing between adjacent CNTs may be between 50 nm and 1 μm, or between 100 nm and 500 nm. When the average spacing of CNTs is within this range, the bundling of CNTs is further suppressed. In addition, high conductivity, high capacitance, and low ESR are easily obtained. The average spacing of CNTs can be determined by using the cross-sectional image described above, measuring the distance between adjacent CNTs at 10 locations in the same manner as for the thickness of the first conductor, and averaging these measurements.

[0052] In carbon nanotubes (CNTs), an interface may be observed between the fixed and free ends, based on differences in the carbon crystal structure or the growth direction of the CNTs. For example, when forming a dielectric material by ALD after CNT formation by CVD, CNTs may grow in parallel with the formation of the dielectric material. In such cases, differences in the growth conditions of the CNTs lead to differences in the carbon crystal structure or the growth direction of the CNTs, and an interface may be observed based on these differences. CNTs with such interfaces tend to be longer and exhibit suppressed bundling. Therefore, a larger specific surface area of ​​the first electrode can be obtained, resulting in higher capacitance. The interface of the CNTs can be observed by cross-sectional images of the first electrode using SEM or TEM.

[0053] The carbon nanotubes (CNTs) may have a single-layer structure or a multi-layer structure. The first electrode may include both single-layer CNTs and multi-layer CNTs.

[0054] (Metal parts) The metallic portion contains a second metal. The CNTs are formed by growing between nanoparticles containing the second metal and a first conductor. In this disclosure, the growth of CNTs on the surface of the nanoparticles results in the formation of relatively long CNTs and reduces bundling. The metallic portion corresponds to these nanoparticles and is located at the free end of the CNT.

[0055] The secondary metal preferably has catalytic activity in the growth reaction of CNTs. Examples of such secondary metals include Fe, Co, and Ni. The metal portion may contain one of these secondary metals, or two or more. The metal portion contains the element of the secondary metal. The metal portion is, for example, at least one selected from the group consisting of elemental secondary metals, alloys containing the element of the secondary metal, and compounds containing the element of the secondary metal. Among these, the metal portion is preferably elemental secondary metal or an alloy containing the element of the secondary metal. Furthermore, the metal portion preferably contains at least Fe, and more preferably one selected from the group consisting of elemental Fe and Fe alloys.

[0056] The width of the metal portion may be approximately the same as the width of the CNT. The width of the metal portion may also be selected from within the range of CNT widths. Having the width of the metal portion within this range makes it easier to form relatively long CNTs with suppressed bundling. In addition, it is easier to grow the CNTs at an angle perpendicular (90°) or close to it (for example, 60° or more and less than 90°) to the surface of the first conductor. The width of the metal portion is determined using the above cross-sectional image, in accordance with the case of the thickness of the first conductor, as the average of the widths of 10 metal portions.

[0057] The height of the metal portion may be between 1 nm and 10 nm, between 1 nm and 5 nm, or between 1 nm and 3 nm. When the height of the metal portion is within this range, it is easier for it to exist stably as nanoparticles when forming CNTs, and easier to grow CNTs. The height of the metal portion is determined using the above cross-sectional image, in accordance with the case of the thickness of the first conductor, as the average height of 10 metal portions.

[0058] (dielectric) The dielectric covers at least a portion of the surface of the first electrode. More specifically, the surface of the first conductor on the CNT side and at least a portion of the surface of the CNTs are covered with the dielectric. In this disclosure, since the bundling of CNTs is reduced, the surface of the CNTs can be covered with a dielectric of a more uniform thickness. By interposing such a dielectric between the first electrode and the second electrode, high capacitance is obtained, leakage current is suppressed, and high dielectric strength is achieved.

[0059] The dielectric is composed of, for example, a metal oxide. Preferably, the dielectric is an oxide containing at least one metal element selected from the group consisting of aluminum (Al), zirconium (Zr), silicon (Si), niobium (Nb), and hafnium (Hf). The dielectric may contain, for example, aluminum oxide (Al2O3, etc.) or zirconium oxide (ZrO2, etc.). The dielectric may contain one of these oxides or two or more. When the dielectric contains two or more oxides, the two or more oxides may be mixed together, or they may be arranged in layers.

[0060] The average thickness of the dielectric is preferably 0.5 nm or more, more preferably 1 nm or more, and even more preferably 5 nm or more. When CNTs grow in parallel with the formation of the dielectric, longer CNTs are more easily formed when the average thickness of the dielectric is 5 nm or more. Furthermore, when the average thickness of the dielectric is within the above range, high dielectric strength characteristics can be obtained. From the viewpoint of easily obtaining higher capacitance, the average thickness of the dielectric may be 100 nm or less, or even 70 nm or less.

[0061] The average thickness of the dielectric material may be 0.5 nm to 100 nm (or 70 nm or less), 1 nm to 100 nm (or 70 nm or less), or 5 nm to 100 nm (or 70 nm or less).

[0062] The dielectric material can be identified as follows: A cross-sectional image of the capacitor element in the thickness direction (including the first and second electrodes) is obtained using SEM or TEM. Elemental mapping is performed using energy-dispersive X-ray spectroscopy (EDX) analysis of this image to obtain a map of metallic elements in the dielectric (e.g., oxide layer) covering the surface of the first electrode. Using this image, the regions of the microstructure constituting the first electrode and the regions of the oxide constituting the dielectric are distinguished. For example, these two regions can be distinguished by binarization of the image. The average thickness of the dielectric is determined by measuring the thickness at 10 points on the cross-sectional image and averaging the results.

[0063] (2nd electrode) The second electrode is an electrode with opposite polarity to the first electrode. The second electrode may be, for example, the cathode portion of a capacitor. The second electrode is positioned opposite the first electrode.

[0064] (Second conductor) The second electrode typically comprises a conductor (sometimes referred to as the second conductor). The second conductor covers at least a portion of the dielectric surface. In this case, a higher initial capacitance and lower ESR of the capacitor are obtained. The second electrode (more specifically the second conductor) preferably has high conductivity because higher conductivity reduces the ESR and suppresses the capacitance reduction rate under high-frequency conditions.

[0065] The second conductor preferably includes at least one selected from the group consisting of metals, conductive polymers, and semiconductors. In this case, a higher initial capacitance and lower ESR of the capacitor can be obtained. The metal or semiconductor is formed, for example, by depositing it so as to cover the surface of the dielectric by a vapor phase method. Examples of vapor phase methods include sputtering, evaporation, and ALD. These vapor phase methods may be combined as appropriate.

[0066] Examples of metals include valve metals (aluminum, tantalum, niobium, etc.), alloys containing valve metals, gold, and platinum. Examples of semiconductors include elemental semiconductors (silicon, germanium, carbon, etc.) and compound semiconductors (nitride semiconductors (titanium nitride, etc.), oxide semiconductors (zinc oxide, tin oxide, etc.), GaAs, InP, etc.).

[0067] Conductive polymers are also called solid electrolytes. Conductive polymers are composed, for example, of a conjugated polymer system and a dopant. Conductive polymers may also contain additives as needed.

[0068] Examples of conjugated polymers include π-conjugated polymers. Examples of conjugated polymers include polymers with polypyrrole, polythiophene, polyaniline, polyfuran, polyacetylene, polyphenylene, polyphenylenevinylene, polyacene, and polythiophenevinylene as their basic skeletons. Of these, polymers with polypyrrole, polythiophene, or polyaniline as their basic skeleton may be used. The above polymers only need to contain at least one monomer unit that constitutes the basic skeleton. Monomer units include monomer units having substituents. The above polymers also include homopolymers and copolymers of two or more monomers. For example, polythiophene includes poly(3,4-ethylenedioxythiophene). The conductive polymer (or conductive polymer layer) may contain one conjugated polymer or two or more conjugated polymers.

[0069] The weight-average molecular weight (Mw) of the conjugated polymer may be, for example, between 1,000 and 1,000,000.

[0070] In this specification, the weight-average molecular weight (Mw) is a polystyrene-converted value measured by gel permeation chromatography (GPC). GPC is measured, for example, using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0071] Examples of dopants include at least one selected from the group consisting of anions and polyanions.

[0072] Examples of anions include sulfate ions, nitrate ions, phosphate ions, borate ions, organic sulfonate ions, and carboxylate ions. Examples of dopants that generate sulfonate ions include benzenesulfonic acid, p-toluenesulfonic acid, and naphthalenesulfonic acid. However, anions, or dopants that generate anions, are not limited to these specific examples.

[0073] Examples of polyanions include polymer anions. The conductive polymer layer may, for example, contain a conjugated polymer containing monomer units corresponding to a thiophene compound and polymer anions.

[0074] Examples of polymer anions include polymers having multiple anionic groups. Such polymers include polymers containing monomer units having anionic groups. Examples of anionic groups include sulfo groups and carboxyl groups. It is preferable that the polymer anion has at least one sulfo group.

[0075] In the conductive polymer constituting the second electrode of the capacitor, the anionic group of the dopant may be present in free form, anionic form, or salt form, or in a form bonded to or interacting with the conjugated polymer system. In this specification, all of these forms may be simply referred to as "anionic group," "sulfo group," or "carboxyl group."

[0076] Examples of polymer anions having a sulfo group include high-molecular-weight polysulfonic acids. Specific examples of polymer anions include polyvinyl sulfonic acid, polystyrene sulfonic acid (including copolymers and substituted products), polyallyl sulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyester sulfonic acid (such as aromatic polyester sulfonic acid), and phenolsulfonic acid novolac resin. However, polymer anions are not limited to these specific examples.

[0077] The amount of dopant contained in the conductive polymer may be, for example, 10 to 1000 parts by mass, or 20 to 500 parts by mass, per 100 parts by mass of the conjugated polymer.

[0078] A layer or other element to enhance adhesion may be interposed between the dielectric and the conductive polymer.

[0079] Examples of additives include known additives added to conductive polymers (e.g., coupling agents, silane compounds), and known conductive materials other than conductive polymers (e.g., conductive inorganic materials such as manganese dioxide, TCNQ complex salts). The conductive polymer may contain one additive or a combination of two or more additives.

[0080] Conductive polymers are generally formed by using a liquid composition (such as a solution or liquid dispersion) containing the conductive polymer, or by in-situ polymerization (such as chemical polymerization or electrolytic polymerization) using a liquid composition (polymerization solution) containing a precursor and dopant of a conjugated polymer. A combination of methods utilizing in-situ polymerization and methods using a liquid composition containing the conductive polymer may also be used. In in-situ polymerization, an oxidizing agent may be used as needed.

[0081] (electrode extraction layer) The second electrode (such as the cathode) may include an electrode extraction layer (such as a cathode extraction layer) that comes into contact with the second conductor (such as a conductive polymer).

[0082] The electrode extraction layer comprises at least a first layer that is in contact with a second conductor (such as a conductive polymer). The electrode extraction layer may also comprise a first layer and a second layer covering the first layer. Examples of the first layer include a layer containing conductive particles and a metal foil. Examples of conductive particles include at least one selected from conductive carbon and metal particles. For example, the electrode extraction layer may be composed of a layer containing conductive carbon as the first layer (also referred to as a carbon layer) and a layer containing metal particles or a metal foil as the second layer. If a metal foil is used as the first layer, the electrode extraction layer may be composed of this metal foil.

[0083] Examples of conductive carbon include graphite (artificial graphite, natural graphite, etc.). The carbon layer is formed, for example, using a paste or slurry containing conductive carbon and, if necessary, a binder (such as a binder resin).

[0084] A second layer containing metal particles can be formed, for example, by laminating a composition containing metal particles (such as metal powder) onto the surface of the first layer. Examples of such a second layer include a metal particle-containing layer (for example, a metal paste layer such as a silver paste layer) formed using a composition containing metal particles such as silver particles and a resin (binder resin).

[0085] Examples of binder resins used in carbon layers and metal particle-containing layers include thermoplastic resins and thermosetting resins. Thermosetting resins such as imide resins and epoxy resins are preferably used as binder resins.

[0086] When a metal foil is used as the first layer, the type of metal is not particularly limited. Preferably, the metal foil is a valve metal (such as aluminum, tantalum, or niobium) or an alloy containing a valve metal. The surface of the metal foil may be roughened as needed. The surface of the metal foil may be coated with a chemical conversion film, or a coating of a metal different from the metal constituting the metal foil (a dissimilar metal) or a nonmetal. Examples of dissimilar metals or nonmetals include metals such as titanium and nonmetals such as carbon (such as conductive carbon).

[0087] The above-mentioned dissimilar metal or nonmetal (for example, conductive carbon) coating may be used as the first layer, and the above-mentioned metal foil may be used as the second layer.

[0088] (others) The capacitor may be either a chip type or a multilayer type. For example, the capacitor may include two or more stacked capacitor elements. The configuration of the capacitor elements is selected, for example, depending on the type of capacitor.

[0089] In a capacitor element, one end of a lead terminal is electrically connected to the electrode lead layer. The lead terminal is joined to the electrode lead layer, for example, by applying a conductive adhesive to the electrode lead layer and bonding it to the electrode lead layer via this conductive adhesive. One end of another lead terminal is electrically connected to the first conductor of the first electrode. The other end of each lead terminal is led out from the resin casing or case. The other end of each terminal exposed from the resin casing or case is used for soldering to the substrate on which the capacitor is to be mounted, etc.

[0090] The capacitor element is sealed using a resin casing or case. For example, the capacitor element and the resin material for the casing (e.g., uncured thermosetting resin and filler) may be placed in a mold, and the capacitor element may be sealed with the resin casing by a transfer molding method, compression molding method, or the like. In this case, the other end of each lead terminal drawn out from the capacitor element is exposed from the mold. Examples of thermosetting resins include epoxy resin.

[0091] Alternatively, a capacitor may be formed by housing the capacitor element in a bottomed case such that the other end of each lead terminal is located on the opening side of the bottomed case, and then sealing the opening of the bottomed case with a sealant. The material of the bottomed case can be a metal such as aluminum, stainless steel, copper, iron, or brass, or an alloy thereof.

[0092] [Capacitor manufacturing method] The capacitor of this disclosure is formed, for example, by the following manufacturing method. The method for manufacturing a capacitor is, A first step involves forming a plurality of nanoparticles containing a second metal on the surface of a first conductor containing a first metal, A second step involves growing CNTs on the surface of nanoparticles and forming multiple CNTs between multiple nanoparticles and a first conductor to form a first electrode, A third step involves forming a dielectric that covers at least a portion of the surface of the first electrode, The manufacturing method includes a fourth step of providing a second electrode facing the first electrode and with a dielectric interposed between it and the first electrode. This manufacturing method allows for the formation of relatively long CNTs and suppresses the bundling of CNTs. By suppressing the bundling of CNTs, a dielectric with a relatively uniform thickness is formed. Therefore, high capacitance, low ESR, and high withstand voltage characteristics can be obtained. Furthermore, a decrease in capacitance and an increase in ESR under high-frequency conditions can be suppressed. A step of preparing the first conductor may be performed prior to the first step.

[0093] (Preparation process for the first conductor) The first conductor may be a commercially available product or may be formed by a known method. In this step, for example, a foil or sheet-like first conductor containing a first metal is prepared.

[0094] In the case of a first conductor comprising a substrate and a coating layer, the first conductor is prepared, for example, by forming a coating layer containing a first metal on the surface of a foil-like or sheet-like substrate.

[0095] The coating layer is formed, for example, by a vapor phase method. Preferred vapor phase methods include evaporation (such as electron beam (EB) evaporation) and sputtering. One of these methods may be used, or two or more methods may be combined.

[0096] For details regarding the substrate, coating layer, and first conductor, please refer to the description of the first electrode of the capacitor.

[0097] (1st step) In the first step, multiple nanoparticles are formed on the surface of the first conductor. More specifically, a thin film containing a second metal is formed on the surface of the first conductor and heated. This causes the thin film to transform into nanoparticles, forming multiple nanoparticles on the surface of the first conductor. If the first conductor includes a coating layer, the thin film containing the second metal is formed to cover the coating layer.

[0098] Thin films are formed, for example, by a vapor phase method. Preferred vapor phase methods include vapor deposition (such as EB vapor deposition) and sputtering. One of these methods may be used, or two or more methods may be combined.

[0099] The thickness of the thin film may be between 0.1 nm and 5 nm, or between 0.5 nm and 3 nm. When the thickness of the thin film is within this range, nanoparticles are stably formed at appropriate intervals, and CNTs can be easily grown at an angle perpendicular (90°) or close to it (for example, 60° or more and less than 90°) to the surface of the first conductor.

[0100] Nanoparticle formation by heating may be carried out, for example, using a CVD apparatus. The heating temperature is selected according to, for example, the type of second metal and the composition of the thin film. The heating temperature may be 600°C to 1200°C, or 700°C to 900°C. Heating may also be carried out under increasing temperature. For example, the temperature may be increased from room temperature (such as 20°C to 35°C) to the temperature within the above range. The heating rate is determined according to, for example, the type of the underlying first conductor or the coating on the surface of the first conductor.

[0101] Heating is carried out in an atmosphere of hydrogen gas and an inert gas (such as argon gas). The heating time may be between 1 minute and 100 minutes, or between 10 minutes and 60 minutes.

[0102] (2nd process) In the second step, CNTs are grown on a portion of the surface of the nanoparticles formed in the first step. The nanoparticles preferably have catalytic activity for the CNT growth reaction, as described above. Nanoparticles containing the second element promote the dissociation of the carbon source into carbon atoms and provide nucleation sites for CNTs. The generated carbon atoms precipitate on the surface of the nanoparticles, forming CNTs at the contact surface between the nanoparticles and the first conductor. The CNT growth reaction continues on the surface of the nanoparticles on the first conductor side, thus forming CNTs between the first conductor and the nanoparticles. In this way, CNTs are formed that have a fixed end on the surface of the first conductor and a free end on the opposite side of the fixed end. The CNTs have nanoparticles (metallic parts) at their free ends. In this way, the first electrode is formed.

[0103] In the second step, the CNTs are preferably formed by the CVD method. In the CVD method, the CNTs are formed by heating the surface of the first conductor on which the nanoparticles are formed while supplying a carbon source.

[0104] As a carbon source, a gas containing the element carbon is used. More specifically, carbon sources include hydrocarbons (such as saturated or unsaturated hydrocarbons like methane, ethylene, and acetylene) and alcohols. Hydrocarbons may be aromatic or alicyclic, but aliphatic hydrocarbons are preferred from the viewpoint of ease of gasification. Aliphatic hydrocarbons such as acetylene are more preferred from the viewpoint of ease of carbon nanotube (CNT) growth. The carbon source is supplied as a gas.

[0105] The heating temperature is preferably between 600°C and 1200°C, and more preferably between 700°C and 900°C. Heating at such temperatures promotes the growth reaction of carbon nanotubes (CNTs).

[0106] The CVD method is preferably carried out under a pressure of 500 Pa to 2000 Pa, more preferably 1000 Pa to 1500 Pa. Performing the CVD method under such pressure promotes the growth reaction of carbon nanotubes (CNTs).

[0107] (3rd step) In the third step, a dielectric material is formed. Preferably, the dielectric material is formed by atomic layer deposition (ALD). In the ALD method, a dielectric material can be formed on the surface of the object by alternately supplying a raw material gas and an oxidizing agent to a reaction chamber in which the object is placed. The dielectric material may be layered (a dielectric layer may be formed).

[0108] In the ALD method, a self-limiting mechanism is at work, causing the first metal to deposit on the surface of the object in atomic layers. Therefore, one cycle consists of performing steps (1) to (4) in this order, and the thickness of the dielectric can be adjusted by the number of times this cycle is repeated. (1) Supply of raw material gas (2) Exhaust of raw material gas (purging) (3) Supply of oxidizing agent (4) Exhaust (purging) of the oxidizing agent

[0109] Examples of oxidizing agents include water, oxygen, and ozone (O3). The oxidizing agent may also be supplied to the reaction chamber as a plasma using the oxidizing agent as a raw material.

[0110] The raw material gas is the precursor gas of the dielectric. The precursor is, for example, an organometallic compound. Various organometallic compounds conventionally used in the ALD method may be used as the precursor.

[0111] Examples of precursors include those containing at least one metallic element selected from the group consisting of Al, Zr, Si, Nb, and Hf. One precursor may be used, or two or more precursors (first precursors) may be used. In addition, a second precursor may be used in combination with the first precursor. Examples of second precursors include those containing Zn.

[0112] Examples of Al-containing precursors include trialkylaluminum such as trimethylaluminum ((CH3)3Al:TMA).

[0113] Precursors containing Zr include, for example, bis(methyl-η) 5 Examples include cyclopentadienyl)methoxymethylzirconium (Zr(CH3C5H4)2CH3OCH3), tetrakis(dimethylamide)zirconium(IV) ([(CH3)2N]4Zr(TDMAZ)), tetrakis(ethylmethylamide)zirconium(IV) (Zr(NCH3C2H5)4), and zirconium(IV)t-butoxide (Zr[OC(CH3)3]4).

[0114] Examples of precursors containing Nb include niobium(V) ethoxide (Nb(OCH2CH3)5) and tris(diethylamide)(t-butylimide)niobium(V)(C 16 H 39 N4Nb) is one example.

[0115] Examples of Hf-containing precursors include hafnium tetrachloride (HfCl4), tetrakisdimethylaminohafnium (Hf[N(CH3)2]4(TDMAH)), tetrakisethylmethylaminohafnium (Hf[N(C2H5)(CH3)]4), tetrakisdiethylaminohafnium (Hf[N(C2H5)2]4), and hafnium-t-butoxide (Hf[OC(CH3)3]4).

[0116] Examples of silicon-containing precursors include N-sec-butyl(trimethylsilyl)amine (C7H19 NSi), tetrakis(dialkylamide)silanes such as tetrakis(dimethylamide)silane (TDMAS), 1,3-diethyl-1,1,3,3-tetramethyldisilazane (C8H 23 NSi2), 2,4,6,8,10-pentamethylcyclopentasiloxane ((CH3SiHO)5), pentamethyldisilane ((CH3)3SiSi(CH3)2H), tris(dimethylamino)silane ([(CH3)2N]3SiH), tris(isopropoxy)silanol ([(H3C)2CHO]3SiOH), chloropentanemethyldisilane ((CH3)3SiSi(CH3)2 Examples include (Cl), dichlorosilane (SiH2Cl2), tridimethylaminosilane (Si[N(CH3)2]4), tetraethylsilane (Si(C2H5)4), tetramethylsilane (Si(CH3)4), tetraethoxysilane (Si(OC2H5)4), dodecamethylcyclohexasilane ((Si(CH3)2)6), silicon tetrachloride (SiCl4), and silicon tetrabromide (SiBr4).

[0117] Examples of zinc-containing precursors include dialkylzinc such as diethylzinc (Zn(CH2CH3)2:DEZ), bis(6-ethyl-2,2-dimethyl-3,5-decandionato)zinc, and octadionatozinc.

[0118] In the third step, when a dielectric is formed by the ALD method, a CNT growth reaction may occur in parallel. In this case, longer CNTs are more likely to be obtained. Thus, the third step can include a step of further growing multiple CNTs in parallel with the formation of the dielectric by the ALD method. In particular, if an organometallic compound that does not contain heteroatoms such as N atoms is used as a precursor, the CNT growth reaction is more likely to occur in the third step. Examples of such organometallic compounds include organometallic compounds in which all organic groups bonded to the metal element are hydrocarbon groups. Among these, at least one selected from the group consisting of trialkylaluminum such as TMA is preferred. Furthermore, these first precursors may be used in combination with a second precursor such as dialkylzinc such as DEZ.

[0119] In the third step, the temperature at which the ALD process is performed, the time for supplying the precursor and oxidizer, and the exhaust time are adjusted according to the type of precursor and oxidizer. The temperature may be between 100°C and 300°C, or between 150°C and 200°C.

[0120] The supply time of the precursor may be between 0.1 seconds and 100 seconds, or between 1 second and 60 seconds. The exhaust time of the precursor may be between 10 seconds and 300 seconds, or between 60 seconds and 180 seconds.

[0121] The supply time of the oxidizing agent may be 0.1 seconds or more and 10 seconds or less, or 0.3 seconds or more and 5 seconds or less. The exhaust time of the oxidizing agent is preferably longer than the supply time of the oxidizing agent, and may be 1 second or more and 180 seconds or less, or 10 seconds or more and 60 seconds or less.

[0122] The number of ALD cycles is preferably 10 or more, and more preferably 20 or more. From the viewpoint of obtaining a dielectric film with a more uniform thickness and facilitating the formation of longer CNTs, the number of ALD cycles is preferably 50 or more. Furthermore, from the viewpoint of forming a dielectric film with a more uniform thickness, the number of ALD cycles is preferably 200 or more. From the viewpoint of obtaining a higher capacitance by obtaining a higher specific surface area of ​​the dielectric, the number of ALD cycles is preferably 500 or less.

[0123] (4th step) In the fourth step, a second electrode is provided. The second electrode is formed according to its configuration (such as the type of second conductor). If the second conductor contains a conductive polymer, the second electrode is formed by forming or attaching the conductive polymer to the surface of the first electrode on which the dielectric is formed, as described above. An electrode extraction layer may be formed to cover the conductive polymer. If the first conductor is a metal or a semiconductor, the second electrode is formed, for example, by a vapor phase method, as described above. For details on the fourth step, please refer to the description of the second electrode.

[0124] Figure 1 is a schematic cross-sectional view showing a capacitor according to one embodiment of the present disclosure. Figure 2 is an enlarged schematic cross-sectional view of portion II in Figure 1.

[0125] The capacitor 400 comprises a capacitor element 402, an anode lead terminal 404 and a cathode lead terminal 405 electrically connected to the capacitor element 402, and a resin casing 403 that seals the capacitor element 402. Parts of the anode lead terminal 404 and the cathode lead terminal 405 are covered by the casing 403. The casing 403 has a substantially rectangular parallelepiped shape, and the capacitor 400 also has a substantially rectangular parallelepiped shape.

[0126] The capacitor element 402 comprises an anode (first electrode) 406, a dielectric layer 407 covering the first electrode 406, and a cathode (second electrode) 408 covering the dielectric layer 407. The first electrode 406 and the second electrode 408 face each other, with the dielectric layer 407 interposed between them.

[0127] As shown in Figures 1 and 2, the first electrode 406 comprises a first conductor 460a, a plurality of CNTs 460b erected from the first conductor 460a, and a metal portion 460c that contacts the end face of the CNTs. Each CNT 460b has a first end on the side of the first conductor 460a and a second end on the opposite side of the first conductor 460a. The first end of the CNT 460b is in direct contact with the first conductor 460a. The metal portion 460c is in direct contact with the second end face of the CNT 460b. The first conductor 460a contains a first metal. The metal portion 460c contains a second metal.

[0128] The cathode portion (second electrode) 408 comprises a conductive polymer (second conductor) 409 covering the dielectric layer 407 and a cathode extraction layer 410 covering the second conductor 409. The second conductor 409 can be formed, for example, by impregnating an anode body 406 on which the dielectric layer 407 is formed into a processing solution containing a conductive polymer. The cathode extraction layer 410 has a first layer 411 such as a carbon layer and a second layer 412 such as a metal particle-containing layer (silver particle-containing layer). The carbon layer may, for example, contain conductive carbon and may further contain a binder as needed. The metal particle-containing layer may, for example, contain silver particles and a binder.

[0129] The first conductor 460a has a cathode forming portion 461a and an anode lead portion 461b. An insulating separation portion 413 is formed in the portion of the anode lead portion 406b adjacent to the second electrode (cathode portion) 408, thereby restricting contact between the second electrode 408 and the first electrode 406. The anode lead portion 461b and the anode lead terminal 404 are electrically connected by welding. The cathode lead terminal 405 is electrically connected to the second electrode (cathode portion) 408 via an adhesive layer 414 formed of a conductive adhesive.

[0130] The outer casing 403 preferably contains a cured product of a curable resin composition, and may also contain a thermoplastic resin or a composition containing the same.

[0131] Figure 1 shows a capacitor 400 having one capacitor element 402. The capacitor may also be a laminated type in which a laminate of two or more capacitor elements 402 is stacked and sealed with an outer casing 403.

[0132] [Examples] The present disclosure will be described below in detail based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0133] Examples 1-9 and Reference Example 1 A first electrode, a first electrode with a dielectric material formed on its surface, and a capacitor as shown in Figure 1 were fabricated using the following procedure.

[0134] (1) Formation of the first electrode (1-1) First step The substrate (metal foil, 100 μm thick) shown in the table was cut to match the shape of the capacitor element. An Al film with the thickness shown in the table was formed on one main surface of the substrate by EB deposition. Next, an Fe film with a thickness of approximately 2 nm was formed by EB deposition to cover the Al film. The substrate with the Al film corresponds to the first conductor. In EB deposition, deposition was started at a vacuum of 0.5 mPa or less, and the EB energy was adjusted to achieve a deposition rate of 0.5 nm / sec.

[0135] A first conductor with an Fe coating was placed in a CVD apparatus and heated in a hydrogen and argon atmosphere, increasing the temperature from room temperature to 750°C. The heating rate was adjusted according to the substrate, for example, to 10°C / min. This heating formed multiple Fe nanoparticles at intervals on the surface of the Al coating. The formation of Fe nanoparticles was confirmed by atomic force microscopy. The average particle size of the Fe nanoparticles was 20 nm.

[0136] (1-2)Second process In a CVD apparatus, the surface of a first conductor, which had Fe nanoparticles obtained in the first step on its surface, was heated at 750°C for approximately 30 minutes under a pressure of 1500 Pa while acetylene was supplied as a carbon source. As a result, carbon nanotubes (CNTs) grew with the Fe nanoparticles acting as catalysts as their tips, and CNTs were formed between the Fe nanoparticles and the first conductor. When the state of the CNTs was observed by SEM, it was found that the CNTs had a fixed end on the surface of the first conductor. The end opposite this fixed end was a free end, and this free end contained Fe nanoparticles. The Fe nanoparticles at the free end of the CNTs correspond to the metallic part containing Fe as a second metal. In this way, the first electrode was formed.

[0137] In Reference Example 1, the first electrode was formed by the second step, and the third step and subsequent steps were not performed.

[0138] (2) Third step A dielectric material with the average thickness shown in the table was formed on the surface of the first electrode using the ALD method (temperature: 150°C, precursor pulse 3 seconds, purge 180 seconds, oxidizer pulse 3 seconds, purge 180 seconds) for the number of cycles shown in the table. The components shown in the table were used as the precursor and oxidizer. The main components of the formed dielectric material are shown in the table.

[0139] (3) 4th step (3-1) Formation of conductive polymer layer An insulating separation portion was formed in a predetermined region of the first electrode, which had a dielectric material formed on its surface, as obtained in (2) above. A pre-coat layer was formed by thinly coating the first electrode with the separation portion and drying it with a conductive material.

[0140] A polymerization solution containing pyrrole (a monomer of a conjugated polymer), naphthalene sulfonic acid (a dopant), and water was prepared. Electropolymerization was performed using the obtained polymerization solution. More specifically, a pre-coated first electrode was immersed in the polymerization solution, and a conductive polymer layer was formed by electropolymerization at 25°C while applying a voltage. At this time, the conductive polymer layer was formed to fill the gaps between multiple CNTs on which the dielectric layer of the first electrode was formed, and to cover the metal parts of the CNTs. The first electrode thus obtained, with a conductive polymer layer formed on the dielectric, was washed with water and dried at 75°C for 5 minutes.

[0141] (3-2) Formation of the cathode extraction layer A dispersion of graphite particles in water was applied to the surface of the conductive polymer layer formed in (3-1) above, and the first layer (carbon layer) was formed by drying.

[0142] Next, a silver paste containing silver particles and a binder resin (epoxy resin) was applied to the surface of the first layer, and the binder resin was cured by heating to form the second layer (metal particle-containing layer). Heating was carried out at 215°C for 10 minutes. In this way, a cathode extraction layer consisting of the first layer (carbon layer) and the second layer (metal particle-containing layer) was formed, and the cathode portion (second electrode) consisting of the conductive polymer layer and the cathode extraction layer was formed. As described above, a capacitor element comprising a first electrode, a second electrode, and a dielectric layer interposed between them was fabricated.

[0143] (4) Assembly of the capacitor The second electrode of the capacitor element obtained in (3) above and one end of the cathode lead terminal were joined via an adhesive layer formed of conductive adhesive. One end of the anode lead terminal was joined to the region on the end side of the first electrode protruding from the capacitor element by laser welding.

[0144] Next, a resin casing made of insulating resin was formed around the capacitor element by molding. At this time, the other end of the anode lead terminal and the other end of the cathode lead terminal were extended from the resin casing.

[0145] A capacitor was obtained in this manner. Subsequently, the capacitor was subjected to an aging process at 130°C for 2 hours while applying the rated voltage.

[0146] (5) Evaluation The following evaluations were performed using the first electrode, or the first electrode on which the dielectric was formed (the first electrode after the third step and before the fourth step).

[0147] (5-1) Metal part position The position of the metal portion was confirmed using the first electrode on which the dielectric layer was formed, following the procedure described above. In the table, when the metal portion is located at the end (fixed end) of the CNT on the first conductor side or the coating side, it is indicated as "fixed end," and when it is located at the free end opposite the coating, it is indicated as "free end."

[0148] (5-2) Average length of CNTs Using the first electrode on which the dielectric layer was formed, the average length (μm) of the CNT portion was determined using the procedure described above. This average length is referred to as "CNT length" in the table.

[0149] (5-3) Observation of the free end Using the first electrode, we observed with a scanning electron microscope (SEM) whether adjacent CNTs were in contact and forming a bundle. When a bundle was formed, it was located on the free end side of the CNT.

[0150] (5-4) Dielectric growth The state of the dielectric layer grown on the first electrode, where the dielectric was formed, was observed using a scanning electron microscope (SEM). This state was evaluated according to the following criteria. A: A dielectric film with a relatively uniform thickness was formed on the surface of the CNT. A dielectric film was formed on the surface of B:CNTs, but its thickness was non-uniform. A dielectric layer was formed in an island-like manner on the surface of the C:CNT.

[0151] Comparative Examples 1 and 2, and Reference Examples 2 and 3 In Comparative Examples 1 and 2, an Al2O3 film was formed instead of an Al film. The Al2O3 film (barrier layer) was formed by the ALD method (temperature: 150°C, precursor pulse 0.015 seconds, purge 5 seconds, oxidizer pulse 0.015 seconds, purge 5 seconds), using TMA as the precursor and H2O as the oxidizer, by repeating the pulse and purge for 200 cycles. The average thickness of the Al2O3 film was 20 nm. Except for these, the first electrode, the first electrode with a dielectric formed on its surface, and the capacitor were fabricated and evaluated in the same manner as in Example 1 or 2.

[0152] In Reference Examples 2 and 3, an Al2O3 coating was formed instead of the Al coating, similar to Comparative Examples 1 and 2. Otherwise, the first electrode was fabricated and evaluated in the same manner as in Reference Example 1.

[0153] 《Reference example 4》 In Reference Example 4, the components shown in the table were used as the precursor and oxidizing agent in the third step of Example 1. The main component of the formed layer was ZnO (non-insulating). Except for this, the first electrode, the first electrode with a dielectric material formed on its surface, and the capacitor were fabricated and evaluated in the same manner as in Example 1.

[0154] Comparative Example 3 and Reference Example 5 In Comparative Example 3, an Al coating layer with an average thickness of 40 nm was formed. Apart from this, the first electrode, the first electrode with a dielectric material formed on its surface, and the capacitor were fabricated and evaluated in the same manner as in Example 1.

[0155] In Reference Example 5, an Al coating layer with an average thickness of 40 nm was formed. Otherwise, the first electrode was fabricated and evaluated in the same manner as in Reference Example 1.

[0156] Example 10 On the surface of a first conductor containing Fe nanoparticles, carbon nanotubes (CNTs) were grown in a region measuring 3 mm vertically and 3 mm horizontally. The dielectric and the second electrode were fabricated in the region where the CNTs were formed. Except for these, the first electrode with a dielectric formed on its surface and the capacitor were fabricated in the same manner as in Example 5. A total of 20 capacitors were fabricated. In addition to the same evaluation as in Example 5, the following evaluations (5-5) and (5-6) were performed on the capacitors. For the evaluation of the capacitors, capacitors that had undergone aging treatment in the same manner as in Example 5 were used.

[0157] (5-5) Capacitance Under 20°C conditions, the initial capacitance (μF) of each capacitor at a frequency of 120Hz was measured using a 4-terminal LCR meter (Keysight Technologies, E4980A). The average value (μF) across the 20 capacitors was then calculated and divided by the area of ​​the region where the CNTs were formed to obtain the average capacitance per unit area (μF / mm²). 2 ) was sought.

[0158] (5-6) Withstand voltage characteristics For 20 capacitors whose initial capacitance was measured, a voltage was applied while boosting it at a rate of 0.1 V / s, and the voltage at which an overcurrent of 0.01 A flowed (breakdown voltage) was determined. The breakdown voltage was used to evaluate the voltage withstand capability. A higher value indicates better voltage withstand capability.

[0159] Comparative Example 4 In Comparative Example 1, the number of ALD cycles was adjusted so that the average thickness of the Al2O3 coating was 10 nm. Furthermore, a dielectric material with the average thickness shown in the table was formed on the surface of the first electrode using the number of cycles shown in the table. Except for these steps, the first electrode, the first electrode with the dielectric material formed on its surface, and the capacitor were fabricated in the same manner as in Comparative Example 1. A total of 20 capacitors were fabricated. The same evaluation as in Example 10 was then performed.

[0160] 《Reference example 6》 Similar to Example 10, in the first step, the substrate (metal foil, 100 μm thick) shown in the table was cut to match the shape of the capacitor element. An Al film with the thickness shown in the table was formed on one main surface of the substrate by EB deposition. Then, the substrate with the Al film formed on it was used as the first electrode, and a dielectric was formed on the surface of the Al film using the procedure in the third step. Except for these steps, the capacitor was fabricated and evaluated using the same procedure as in Example 10. Of the regions where the first electrode, dielectric layer, and second electrode of the capacitor element were formed, a region of 3 mm vertically and 3 mm horizontally was evaluated.

[0161] The evaluation results for (5-1) to (5-4) for Examples 1 to 9 and Comparative Examples 1 to 3 are shown in Tables 1 to 4. The evaluation results for (5-1) to (5-3) for Reference Examples 1 to 5 are shown in Tables 1, 3, and 4. The evaluation results for (5-1) to (5-6) for Example 10, Comparative Example 4, and Reference Example 6 are shown in Table 5. In Tables 1 to 5, E1 to E10 represent Examples 1 to 10, R1 to R6 represent Reference Examples 1 to 6, and C1 to C4 represent Comparative Examples 1 to 4.

[0162] [Table 1]

[0163] As shown in Table 1, when the coating was not conductive (for example, Al2O3), the metallic portion was located on the surface of the coating, and CNTs were formed growing from the metallic portion (C1, C2, R2, and R3). In other words, in these examples, the fixed end of the CNT was fixed to the surface of the Al2O3 coating via the metallic portion. On the other hand, the free end of the CNT (the end opposite to the fixed end) was bundled together with adjacent CNTs.

[0164] In contrast, in the first electrodes of E1 and E2, the CNTs had a fixed end on the surface of the Al coating and a metallic portion on the free end opposite the fixed end. Furthermore, in E1 and E2, no bundles of CNTs were observed at the free ends of the CNTs. In E1 and E2, a dielectric with a relatively uniform thickness was formed on the surface of the CNTs compared to C1 and C2. This is thought to be because, in E1 and E2, no bundles of CNTs were formed, resulting in a more uniform state of the CNTs compared to C1 and C2.

[0165] In R1, where the first electrode was formed under the same conditions as E1, the CNT length was relatively short, ranging from 3 μm to 30 μm. In contrast, in E1 and E2, the average length of the CNTs was significantly longer than in R1, ranging from 60 μm to 140 μm. This indicates that in E1 and E2, CNTs grew even while the dielectric was being formed.

[0166] As is clear from the comparison between R2 and C1, and between R3 and C2, in the case of the Al2O3 coating, there is no difference in the length of the CNTs depending on whether a dielectric is formed or not. In these examples, the metal portion is in contact with the Al2O3 coating, and the CNT coating grows from the Al2O3 coating side. In these cases, unlike E1 and E2, it can be seen that no CNT growth is observed during the formation of the dielectric.

[0167] [Table 2]

[0168] As shown in Table 2, a dielectric layer of relatively uniform thickness was formed regardless of which precursor or oxidizing agent was used to form the dielectric. From the viewpoint of easily forming long CNTs, it is preferable that the organometallic compound of the precursor has all hydrocarbon groups bonded to the metal element (comparison of E1, E3, and E4 with E5).

[0169] [Table 3]

[0170] As shown in Table 3, when the dielectric thickness is small, the length of the CNTs formed parallel to the dielectric tends to be shorter. Therefore, from the viewpoint of forming long CNTs, an average dielectric thickness of 5 nm or more is preferable (an ALD cycle of 50 cycles or more is preferable). Also, from the viewpoint of easily forming a dielectric with more uniform thickness, an average dielectric thickness of 20 nm or more is preferable (an ALD cycle of 200 cycles or more is preferable).

[0171] [Table 4]

[0172] As shown in Table 4, as the thickness of the coating on the first conductor increases, the metal portion tends to be located on the fixed end side of the CNT, and a bundle tends to form at the free end (R4, C3). In this case, almost no CNT growth is observed during dielectric formation (comparison of R4 and C3). Therefore, the thickness of the coating on the first conductor is preferably less than 40 nm, more preferably 35 nm or less, and even more preferably 30 nm or less.

[0173] [Table 5]

[0174] As shown in Table 5, in Comparative Example 4, where CNTs were formed on the surface of the Al2O3 coating, the initial capacitance and dielectric strength were below the measurement limit. In Reference Example 5, where no CNTs were formed, high dielectric strength was obtained, but the capacitance was very low. In contrast to these, Example 11 showed high dielectric strength and a significant improvement in capacitance. [Industrial applicability]

[0175] The capacitor of this disclosure comprises a first electrode having a carbon nanotube (CNT) with reduced bundling. Therefore, the capacitor exhibits high voltage resistance and low initial ESR and capacitance reduction at high frequencies. Thus, the capacitor of this disclosure is suitable for applications requiring high voltage resistance, high capacitance, and high reliability. However, the applications of the capacitor of this disclosure are not limited to these. [Explanation of Symbols]

[0176] 400: Capacitor 402: Capacitor element 403: Exterior 404: Anode lead terminal 405: Cathode lead terminal 406: Anode body (first electrode) 460a: First conductor 461a: Cathode forming part 461b:Anode extraction part 460b: Carbon nanotubes 460c: Metal part 407: Dielectric layer 408: Cathode part (second electrode) 409: Second conductor (conductive polymer) 410: Cathode extraction layer 411: First layer (carbon layer) 412: 2nd layer (metal particle containing layer) 413: Separation part 414: Adhesive layer

Claims

1. First electrode and, A second electrode facing the first electrode, The device comprises a dielectric that covers at least a portion of the surface of the first electrode and is interposed between the first electrode and the second electrode, The first electrode comprises a first conductor containing a first metal, and a plurality of carbon nanotubes having fixed ends on the surface of the first conductor and metal portions at their free ends. The aforementioned metal part is a capacitor containing a second metal.

2. The capacitor according to claim 1, wherein 80% or more of the total number of carbon nanotubes are spaced apart from adjacent carbon nanotubes.

3. The capacitor according to claim 1 or 2, wherein the average length of the carbon nanotubes is 30 μm or more and 200 μm or less.

4. The capacitor according to claim 1 or 2, wherein an interface based on the difference in the carbon crystal structure or growth direction of the carbon nanotube is observed between the fixed end and the free end of the carbon nanotube.

5. The capacitor according to claim 1 or 2, wherein the second metal is at least one selected from the group consisting of Fe, Co, and Ni.

6. The capacitor according to claim 1 or 2, wherein the first metal is at least one selected from the group consisting of Ni, Cu, and Al.

7. The capacitor according to claim 6, wherein the surface of the first conductor is the surface of a conductive coating containing Al.

8. The capacitor according to claim 7, wherein the thickness of the coating is 35 nm or less.

9. The capacitor according to claim 1 or 2, wherein the average thickness of the dielectric is 5 nm or more.

10. The capacitor according to claim 1 or 2, wherein the second electrode comprises a second conductor that covers at least a portion of the surface of the dielectric.

11. The capacitor according to claim 10, wherein the second conductor includes at least one selected from the group consisting of metals, conductive polymers, and semiconductors.

12. A first step involves forming a plurality of nanoparticles containing a second metal on the surface of a first conductor containing a first metal, A second step involves growing carbon nanotubes on the surface of the nanoparticles and forming a plurality of carbon nanotubes between the plurality of nanoparticles and the first conductor to form a first electrode, A third step of forming a dielectric that covers at least a portion of the surface of the first electrode, A method for manufacturing a capacitor, comprising: a fourth step of providing a second electrode facing the first electrode and such that the dielectric is interposed between the first electrode and the second electrode.

13. A method for manufacturing a capacitor according to claim 12, wherein in the first step, the nanoparticles are formed by at least one selected from the group consisting of electron beam deposition and sputtering.

14. The method for manufacturing a capacitor according to claim 12, wherein the dielectric is formed by atomic layer deposition in the third step.

15. The method for manufacturing a capacitor according to claim 14, wherein the second step includes growing the plurality of carbon nanotubes by chemical vapor deposition.

16. The method for manufacturing a capacitor according to claim 14 or 15, wherein the third step includes a step of further growing the plurality of carbon nanotubes in parallel with the formation of the dielectric by the atomic layer deposition method.

17. The method for manufacturing a capacitor according to claim 16, wherein the atomic layer deposition method is carried out using an organometallic compound in which all organic groups bonded to the metal element are hydrocarbon groups.

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