Capacitor

Abstract

To provide an electrical capacitor that uses polyamideimide as a capacitor material having excellent temperature stability as well as a high or customized dielectric constant.SOLUTION: A capacitor (1) has a single dielectric layer (2) that is free of solid inorganic materials, the dielectric layer (2) includes polyamideimide, and a first electrode (3) disposed directly adjacent to the dielectric layer (2).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an electric capacitor. [Background technology]

[0002] Polymer dielectrics are used in a wide variety of applications in power electronics, particularly in passive components such as electrolytic capacitors.

[0003] As a capacitor dielectric, for example, a dielectric film containing polyimide, such as the polyetherimide described in Patent Document 1, has already been proposed.

[0004] Polyamide-imide has been known primarily through its use as a heat-resistant coating for enameled wires and the like.

[0005] For capacitor applications, these have so far been proposed primarily in relation to inorganic components as dielectric layers.

[0006] Patent document 2 discloses that polyamide-imide can be a matrix component for inorganic particles in a capacitor dielectric.

[0007] Patent Document 3 discloses that polyamide-imide can be used in a capacitor having a non-uniform dielectric layer consisting of an organic polymer material as the first dielectric layer and an inorganic material as the second dielectric layer. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] U.S. Patent Application Publication No. 2007 / 0258190 Specification [Patent Document 2] Japanese Patent Publication No. 2000-338667 [Patent Document 3] U.S. Patent Application Publication No. 2010 / 0259865 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, the use of polyamide-imide as a capacitor material possessing both exceptional temperature stability and a high or customized dielectric constant has not been previously known. [Means for solving the problem]

[0010] According to a first embodiment, a capacitor having a single dielectric layer is presented. In this case, the dielectric layer comprises polyamide-imide, and at least one first electrode is disposed directly adjacent to the dielectric layer.

[0011] Directly adjacent electrodes can be placed on top of the layer. Preferably, direct contact exists at the molecular level, as can be achieved by the coating method described below.

[0012] The second electrode is preferably also part of the capacitor. Optionally or as required by technical requirements, the second electrode is also preferably located directly adjacent to the dielectric layer. In this case, the dielectric layer is sandwiched between the first and second electrodes.

[0013] A single dielectric layer may be, for example, homogeneous and may contain polyamide-imide. Homogeneity here may mean, in particular, that the dielectric layer does not contain additives that would make the layer heterogeneous. It is especially preferable that the dielectric layer does not contain micromaterials or nanomaterials or any additional solids. The dielectric layer preferably does not contain hybrid materials. Since the electrodes are located directly adjacent to the single dielectric layer, there is no further layer between the single dielectric layer and the electrodes that is different from the single dielectric layer, for example.

[0014] A single dielectric layer containing polyamideimide has the advantage of having temperature stability up to approximately 300 °C compared to other polymer-based dielectric layers. Furthermore, a dielectric layer containing polyamideimide can have a high dielectric constant over a wide input frequency range. In that case, preferably, a high breakdown voltage is also maintained.

[0015] Thus, polyamideimide as a polymer material for a dielectric layer in capacitor applications can simultaneously satisfy two conflicting requirements: high temperature stability and customized or stable dielectric properties.

[0016] Thus, a single dielectric containing polyamideimide can be a substitute for biaxially oriented polypropylene (BOPP), one of the most widely used materials for capacitor dielectrics. This can be advantageous because BOPP, which has a normal operating temperature of up to 105 °C and a low dielectric constant in the region of 2.2, has reached its performance limits with respect to temperature stability while simultaneously maintaining electrical or electronic parameters for current development.

[0017] Thus, a polyamideimide-containing dielectric layer according to the present invention can have higher temperature stability up to 150 °C. Furthermore, a dielectric constant almost twice that of BOPP can be achieved even at higher temperatures.

[0018] Thus, it may even meet the requirements for future applications such as those in aerospace engineering, where operating temperatures above 150 °C and in some cases above 200 °C may be achieved.

[0019] According to a preferred embodiment of the capacitor, the dielectric layer consists of at least 50% by weight of polyamideimide.

[0020] Such a high polyamideimide content in a single dielectric layer can ensure that the excellent dielectric properties of polyamideimide prevail over any other possible components.

[0021] Preferably, the dielectric layer has a weight ratio of 90% or more polyamide-imide, and more preferably, the dielectric layer consists solely of polyamide-imide.

[0022] The inventors have recognized that polyamide-imides can be readily functionalized chemically. Therefore, they can be flexibly customized to possess outstanding electrical or electronic properties, which, depending on the application, should be satisfied, for example, solely by organic components. Accordingly, the capacitor is manufactured such that the dielectric layer, which is preferably a single dielectric layer, does not contain any additional solid materials such as inorganic materials. The dielectric layer is preferably not a hybrid material.

[0023] Dielectric layers that do not contain inorganic materials may be easier to manufacture than mixed layers made of inorganic-organic hybrid materials.

[0024] Preferably, the dielectric layer of the capacitor comprises a polyamideimide main chain containing amide groups and imide groups of polyamideimide.

[0025] This specifically means that the main chain of the polyamide-imide polymer is formed solely via amide or imide bonds. This does not preclude the possibility of additional chemical functional groups being bonded to or within the main chain.

[0026] Polyamide-imide compounds, or the chemical bonds contained therein, are stable at high temperatures, which is an advantage for dielectric layers used under high-temperature conditions.

[0027] In a more preferred embodiment, the polyamide-imide main chains contained in the dielectric layer may be chemically crosslinked with each other, that is, they may have crosslinks.

[0028] By using a customized number of crosslinks, the mechanical and electronic properties of polyamide-imide, as well as its temperature properties in particular, can be precisely tuned.

[0029] In principle, the term “crosslinking” as used in this application includes any type of covalent chemical bond present between polyamide-imide backbone chains or between different points on a polyamide-imide backbone chain. Crosslinking is a chemical bond formed in addition to the chemical bonds between repeating units of a polyamide-imide backbone chain. In this case, preferably, the number of crosslinks is selected so as to form a thermoplastic polyamide-imide.

[0030] Preferably, the crosslinking involves linear bonds that connect terminal units of one polyamideimide backbone to terminal units of another polyamideimide backbone, thereby creating a series chain linkage. Preferably, the linear bonds between backbones are different from the type of bonds within the polyamideimide backbone. That is, the crosslinking preferably does not have amideimide motifs. However, the crosslinking can be amide bonds or imide bonds. In that case, such bonds can interrupt the repeating motif of polyamideimide motifs that are repeated within the polyamideimide backbone. Multiple polyamideimide backbones can be linearly linked in series.

[0031] The number of crosslinks can be controlled by the annealing temperature. The higher the temperature, the more polyamide-imide main chains are bonded to each other in series. Therefore, the polymer chains become longer as the annealing temperature increases. This can increase the mechanical stability of the dielectric layer. Furthermore, it can reduce the dissipation rate. This method of controlling the degree of crosslinking by temperature is particularly preferred for linear bonding.

[0032] Preferably, the chemical crosslinking is formed via urethane crosslinking.

[0033] Urethane crosslinks can preferably be formed via isocyanate groups on the main chain, which react with other hydroxyl groups on the main chain to form urethane bonds.

[0034] Lactams can also be present as functional groups in the starting material because they function as protecting groups to control the reaction between isocyanate groups and hydroxyl groups. Such lactams can be ring-opened, for example, by the action of temperature, to form an isocyanate group, which then reacts, for example, with hydroxyl groups in other main chains. That is, isocyanate groups and / or lactam functional groups may be present in the starting material. However, preferably, only lactams are present in the starting material because very long durability can be achieved even at room temperature. Furthermore, it is possible to extend the applicable dropping time during the fabrication of the dielectric layer, for example.

[0035] Preferably, imide crosslinks can be formed between polyamide-imide main chains, instead of or in addition to other crosslinks such as urethane crosslinks.

[0036] Imide crosslinks can be formed between two polyamide-imide main chains by a reaction in which, for example, an anhydride group reacts with a suitable group on the other polyamide-imide main chain, such as an amine, to form an imide crosslink. Preferably, the anhydride group is a phthalic anhydride group. Such a reaction can also form bonds between different points on the polyamide-imide main chains.

[0037] Both urethane crosslinking and imide crosslinking are particularly suitable for the technically simple formation of linear bonds. Furthermore, the degree of linear bonding with these groups can be precisely controlled by controlling the annealing temperature.

[0038] Furthermore, crosslinks can also be formed via urea crosslinks. These can be formed with the involvement of amine groups on the polyamide-imide main chain. When three-dimensional crosslinks are formed by this, it is particularly preferable that linear bonds are formed rather than exclusively by this bonding motif. Even more preferably, only such crosslinks that are not linear bonds can be formed via urea crosslinks. Particularly preferably, these can coexist with linear bonds. For example, polymer materials three-dimensionally crosslinked via urea crosslinks, as well as polymer materials linearly crosslinked via imide crosslinks or urethane crosslinks, can be formed or formed for dielectric layers.

[0039] In principle, urethane crosslinks can exist in addition to imide crosslinks. However, it is preferable to have only one linear bonding motif because this facilitates process control.

[0040] An example of a suitable starting material is, for instance, commercially available REISTHERN® AI 336 L.

[0041] As an example of such a starting material, a polyamide-imide resin solution can be used, which can be used, in particular, for insulating coatings of wires or electrodes. An example of such a polyamide-imide resin solution is, for example, the commercially available REISTHERN® AI 336 L.

[0042] In a further preferred embodiment of a single dielectric layer of a capacitor, the dielectric layer may be formed such that the polyamide-imide main chain is partially aromatic.

[0043] Partially aromatic polyamide-imide backbone chains contribute, in particular, to a balanced relationship between flexibility and temperature stability. Therefore, fully aromatic polyamide-imide backbone chains can be too rigid. However, partial aromaticity, i.e., the aromaticity of the imide component, allows for the desired temperature stability to be obtained simultaneously with flexibility.

[0044] In a preferred embodiment, the polyamide-imide may contain a phenylene group and / or a furan group as functional groups.

[0045] For example, the introduction of phenylene groups into a polyamide-imide main chain may be related to obtaining the necessary flexibility of the main chain. For instance, the length and flexibility of the repeating units are adapted depending on the selection from one or more different phenylene groups within the main chain. For example, biphenyl, diphenylmethane and triphenylmethane, orthodibenzylbenzene and paradibenzylbenzene or tripenzylbenzene can be used as possible phenylene groups. In principle, multiple different types of these or other phenylene groups can exist within a polyamide-imide main chain; that is, various types of phenylene groups can exist within a polyamide-imide main chain. However, in many cases, only one type of phenylene group is present in the main chain.

[0046] Because furan itself has high polarity, the polarity of the dielectric layer can be adjusted by selecting different furans. For example, benzofuran, dibenzofuran, furanone, or hydroxyfuranone can be used for this purpose. For example, hydroxyfuranone or other furan derivatives may have one or more hydroxyl groups, which are required as reaction partners for forming urethane crosslinks, for example, via isocyanate groups that can be formed from lactam groups.

[0047] According to another preferred embodiment, the polyamide-imide may have a structure according to the chemical formula (Chemical Formula 1), where R 1 This is an unreacted group such as a lactam, anhydride, or amine, or a urethane crosslink or imide crosslink. Preferably, R 1 This is a urethane crosslink or imide crosslink. Here, R 2 is a phenylene group, R 3 It can be franc. Alternatively, R 3This can be urethane crosslinked or imide crosslinked. In this case, the polyamide-imide main chain is bonded at both ends to two other polyamide-imide main chains.

[0048] [ka]

[0049] In principle, as already mentioned above, lactams are formed by, for example, the R in the polymer chain in the starting material. 1 It is a preferred group bonded to the terminal. Crosslinking to other polyamide-imide main chains, for example in the form of urethane crosslinking, can be formed in principle via the isocyanate group formed from the lactam. The lactam can be, for example, β, γ, δ, or ε lactam. Of these, δ and ε lactam are particularly preferred.

[0050] Urethane crosslinks can be formed from terminal lactams and terminal furans in the starting material along with hydroxyl groups, thereby linking the main chain in series and thus extending it. This reaction allows the main chain to be crosslinked such that the formed polyamide-imide layer has thermoplastic properties. In this case, the number of crosslinks is adjusted so that the dielectric layer of the capacitor does not become too hard and brittle.

[0051] As explained above, linearly bonded imide bridges can be formed via an anhydride, such as phthalic anhydride, which reacts with an amine. Alternatively, isocyanate groups react with anhydride groups to form imides, in which case CO2 is separated.

[0052] In the starting material, that is, before the formation of crosslinks including linear bonds, the functional group suitable for the corresponding bond is R in chemical formula (Chemical Formula 1). 3 or R 1 It is located in that position.

[0053] In a preferred embodiment of the capacitor, a number of first electrode layers are stacked alternately with second electrode layers. A dielectric layer is placed between each pair of adjacent electrode layers.

[0054] In other words, a capacitor can be a multilayer capacitor.

[0055] Alternatively, a multilayer capacitor can be disconnected from the coil, for example. In this case, a structured layer of a conductive or preferably metallic material can be used as an electrode, the layer having at least two electrically isolated regions and thus functioning as a capacitor electrode.

[0056] In a further preferred embodiment, the entirety of the first electrode layer can be electrically connected to the first external contact, and the entirety of the second electrode layer can be electrically connected to the second external contact.

[0057] External contacts can be coated by flame spraying, PVD process, or other methods.

[0058] Multilayer capacitors with corresponding external contacts enable their use in a variety of technical applications.

[0059] In a further embodiment, the substrate can be placed on the side of the capacitor, parallel to the plane of the electrode layer.

[0060] As mentioned above, such substrates can be conductive, that is, they can function as electrodes, but they can also be insulating and remain on the component after the manufacturing process.

[0061] In particular, the capacitors mentioned above can be surface-mount devices (SMDs).

[0062] Furthermore, as mentioned above, the capacitor can also be a through-hole capacitor (Durchsteck kondensator), meaning it has wires for through-hole mounting. These wires allow the capacitor to be attached to external contacts both electrically and mechanically.

[0063] The capacitor may be a wound capacitor. In particular, in this case, the capacitor may have only a single metallization as the electrode in direct contact with the dielectric layer. A structure with two electrodes in direct contact with the dielectric layer is also possible.

[0064] In a further aspect of the present invention, a method for manufacturing a capacitor is presented, which includes the production of a dielectric layer. The dielectric layer is produced by coating a prepolymer-polyamide-imide solution onto a deposition surface, subsequently drying the prepolymer-polyamide-imide solution on the deposition surface, and annealing the dried prepolymer-polyamide-imide solution.

[0065] The deposition surface can be the surface of an electrode or electrode layer. The deposition surface may also be the surface of a substrate. The substrate may be the substrate of a completed capacitor, or it may simply be an intermediate carrier from which a coated and possibly crosslinked polyamide-imide film is peeled off again.

[0066] This method allows for the manufacture of the aforementioned capacitors.

[0067] In this way, a single dielectric layer can also be manufactured. The prepolymer polyamide-imide solution may be a resin that is particularly suitable as an insulating coating, such as a solution of REISTHERN® AI 336 L dissolved in an organic solvent.

[0068] Polyamide-imides are essentially soluble in many solvents and can be applied at various concentrations to form closed layers or films. Therefore, they are suitable for a wide range of deposition methods and flexible use with various layer thicknesses, as will be described in more detail below.

[0069] During the drying of the prepolymer / polyamide-imide solution, the solvent can be largely or completely removed.

[0070] During annealing of the dried prepolymer / polyamide-imide solution, the material becomes denser, and crosslinking via lactams, for example, can be used within the layer thus formed.

[0071] The rate of the crosslinking reaction can be determined by the annealing temperature.

[0072] Preferably, the degree of crosslinking is determined by the number of linker groups (e.g., lactam-protected isocyanate groups) on the polyamideimide main chain in the prepolymer-polyamideimide solution, and the annealing temperature is selected so that all linker groups form crosslinks.

[0073] Preferably, the linker group is located at the end of the polyamide-imide main chain. Basically, but especially in this case, the degree of crosslinking can be affected or adjusted by the annealing temperature. The higher the annealing temperature selected, the more crosslinks are formed within a given time. This allows more polyamide-imide main chains to be bonded together.

[0074] In a further embodiment, the method can be modified as described above, such that the deposition surface is the surface of the substrate, the dielectric layer is peeled off from the deposition surface after its manufacture to produce a dielectric film, the dielectric film is metallized, and finally the metallized dielectric film is wound.

[0075] Therefore, the method described above can be used to manufacture wound capacitors. This has the advantage that the dielectric layer or film thus formed, which is provided on the first and second electrodes by metallizing, can be further processed before metallizing. For example, methods such as foil stretching can be applied to optimize the material properties.

[0076] In a further embodiment, the manufacture of the capacitor may include the following: a conductive substrate, or alternatively, a substrate on which a first electrode layer is formed on its surface, is used. Thus, the deposition surface may be the surface of a conductive substrate or the first electrode layer. After coating a dielectric layer on the deposition surface, a second electrode layer may be formed on the dielectric layer, and a further dielectric layer may be formed on this second electrode layer by coating a prepolymer polyamide-imide solution onto the second electrode layer, drying it, and then annealing it.

[0077] In the case of a conductive substrate, this substrate can function as an electrode, for example, as a first electrode. A second electrode layer can be coated on top of this. In this case, of course, to obtain a multilayer capacitor, another dielectric layer, followed by the first electrode layer, can be coated on top of the second electrode layer.

[0078] Alternatively, as mentioned above, the substrate can be, for example, non-conductive, i.e., electrically insulating. In that case, the electrode layer is first applied before any further layers are applied or placed on top of the substrate. In either case, this is a method for constructing a stacked multilayer capacitor from a solution, in contrast to a wound capacitor or a multilayer capacitor cut from a wound body.

[0079] The method described above is preferable if the prepolymer-polyamideimide solution contains a polyamideimide backbone in which isocyanate groups and / or more preferably lactam groups protected as isocyanate groups are arranged in the polyamideimide backbone.

[0080] These have the advantages mentioned above.

[0081] Preferably, the method can be carried out such that the prepolymer / polyamide-imide solution is applied by a doctor blade, rotary coating (spin coating), nozzle coating (slot die coating), or spray coating (spray coating).

[0082] The present invention will be described in detail below with respect to exemplary embodiments. These exemplary embodiments are shown in the following drawings, which are not to scale. Therefore, lengths and relative and absolute dimensions cannot be read from the drawings. The present invention is also not limited to the following description. [Brief explanation of the drawing]

[0083] [Figure 1] A schematic cross-sectional view shows a first embodiment of the capacitor. [Figure 2a] This shows the mass loss of the polyamide-imide layer in thermogravimetric analysis. [Figure 2b] This shows the trend in the dissipation rate of the capacitor. [Figure 3] A schematic cross-sectional view shows the first multilayer capacitor, which is a second embodiment of the capacitor. [Figure 4] A second multilayer capacitor, representing a third embodiment of the capacitor, is shown in a schematic cross-sectional view. [Figure 5] A third multilayer capacitor, representing a fourth embodiment of the capacitor, is shown in a schematic cross-sectional view. [Figure 6] A fifth embodiment of the capacitor, a multilayer capacitor suitable for through-hole mounting, is shown in a schematic cross-sectional view. [Figure 7] A wound capacitor, as a sixth embodiment of the capacitor, is shown in a schematic cross-sectional view. [Modes for carrying out the invention]

[0084] Figure 1 shows a first embodiment of a capacitor in a schematic cross-sectional view. The capacitor 1 has an organic dielectric layer 2. The dielectric layer 2 is a single layer. This means that it consists of a single material and does not contain any volume regions separable from each other. Therefore, it is not a composite material. The dielectric layer 2 consists of at least 50% by weight of polyamideimide. Preferably, the polyamideimide content is higher, for example, exceeding 90%. More preferably, the dielectric layer 2 consists only of polyamideimide.

[0085] The polyamideimide can be any polyamideimide, and in particular, it can be a partially aromatic polyamideimide. The polyamideimide according to Structural Formula (Chemical Formula 2) is particularly preferred.

[0086]

Chemical Formula

[0087] The polyamideimide according to Structural Formula (Chemical Formula 2) has a polyamideimide main chain and can have a plurality of functional groups. For example, within the polyamideimide main chain, a phenylene group can be included as R in Structural Formula (Chemical Formula 2). The flexibility of the polyamideimide main chain can be adjusted by the phenylene group. For example, biphenyl, diphenylmethane or triphenylmethane, orthodibenzylbenzene or paradibenzylbenzene, or tribenzylbenzene can be used. 2 Furthermore, furan can be arranged on the polyamideimide main chain, especially at the ends, for example, as R. Therefore, the polarity of the dielectric layer can be adjusted by its polarity. For example, as furan, benzofuran, dibenzofuran, furanone or hydroxyfuranone can be used.

[0088] 3

[0089]

[0090] Alternatively, an anhydride can be used as R. 3

[0090] Furthermore, crosslinking is preferably present between the various polyamide-imide main chains in the dielectric layer 2.

[0091] Preferably, the polyamide-imide main chains are linked to each other via urethane crosslinks and / or imides. These bonds are, for example, R in structural formula (Chemical Formula 2). 1 It can be located at the terminal position of the residue. Alternatively, an uncrosslinked group, such as lactam isocyanate or anhydride, can also be R 1 It can exist in that location.

[0092] Preferably, the dielectric layer 2 was prepared from a polyamide-imide resin mixture suitable for coating the wire, for example, a solution of RESISTERN® AI 336 L.

[0093] A first electrode 3 and a second electrode 4 are positioned above and below the dielectric layer 2. Both the first electrode 3, the dielectric layer 2, and the second electrode 4 can be formed flat.

[0094] The preferred lamination is carried out across the largest surface of the flatly formed layer.

[0095] The electrode layer thickness can be, for example, 10 to 50 nm, preferably 20 nm. Depending on the manufacturing method, the thickness of the dielectric layer 2 can be set in the range of 500 nm to 10 μm.

[0096] The electrodes may be made of aluminum or silver, or preferably an aluminum-zinc alloy. Alternatively, the electrodes may be multilayer electrodes made of chromium / aluminum, chromium / silver, chromium / nickel / aluminum, or chromium / nickel / silver. In addition to the elements shown herein, a protective layer made of a hydrocarbon compound, such as parylene or a fluorinated hydrocarbon, may be applied to the side surface of the capacitor without electrodes (not shown).

[0097] As an alternative example not shown, the dielectric layer may be in contact with only one electrode.

[0098] The first embodiment of the capacitor shown in Figure 1 can be manufactured by any method. Preferably, it is manufactured by a solvent-based process. For example, the first electrode 3 may first be formed on a substrate. The substrate can be a rigid substrate such as glass or a semiconductor wafer. It may be a metal film such as aluminum or copper, or a flexible polymer film such as polyimide or a release tape. The first electrode is coated onto the surface of the substrate by physical vapor deposition (physical vapor deposition, PVD), such as sputtering or thermal deposition.

[0099] Here, a dielectric layer 2, consisting of a prepolymer-polyamide-imide solution, can be coated onto the surface of the electrode 3, which serves as the deposition surface. The prepolymer-polyamide-imide solution preferably contains mostly uncrosslinked polyamide-imide.

[0100] Prepolymer polyamide-imide solutions are prepared by further dilution of commercially available polyamide-imide resin mixtures (e.g., REISTHERN® AI 336) with a solvent.

[0101] The polyamide-imide resin mixture contains approximately 36% non-volatile substances (mainly polyamide-imide main chains) in a solution of N-methylpyrrolidone (NMP) and xylene. It has an initial viscosity of 4750 ± 1750 mPa·s. Furthermore, it has a density of approximately 1.1 g / ml.

[0102] The polyamide-imide solution thus provided is adjusted to a concentration of 20% or less of the initial polyamide-imide concentration using xylene or N-methylpyrrolidone. For example, a polyamide-imide concentration of 19% by mass or 15% by mass is produced relative to the initial polyamide-imide resin mixture in xylene.

[0103] The concentration used depends on the layer thickness to be achieved or the type of deposition method used.

[0104] Here, the prepolymer-polyamide-imide solution thus produced is applied to the surface of the first electrode 3, which serves as the deposition surface. The application can be carried out by doctor blade, stencil printing, rotary coating, or spray coating. The coating method depends on the thickness of the dielectric layer 2 to be achieved. For example, relatively thick layers, particularly in the range of 500 nm to 5 μm, can be applied by rotary coating or spray coating, while relatively thick layers, for example, in the range of 1 μm to 10 μm, can be applied by doctor blade or stencil printing.

[0105] The applied solution is dried at a temperature of 60-100°C, preferably 80°C. Subsequently, the dried film is annealed at a temperature exceeding 200°C, preferably 250°C.

[0106] During drying, most of the solvent is removed. The remaining volatile substances are removed by annealing. Furthermore, crosslinking between the main chains may be used during annealing. At a temperature of 250°C, nearly complete crosslinking can be achieved in 5-10 minutes. Here, preferably, the isocyanate group protected as a lactam is activated, which then reacts with an existing hydroxyl group or an anhydride present, for example, on a furan residue.

[0107] After cooling, the second electrode 4 can be coated again onto the dielectric layer prepared in this manner by PVD.

[0108] At the end of the method, the substrate can be removed to obtain the item shown in Figure 1. However, it can also essentially remain on the capacitor.

[0109] Figure 2a shows the thermogravimetric analysis (TGA) of the polyamide-imide resin mixture used. The temperature gradient is constant at 10 K / min. As the graph in Figure 2a shows, no mass loss occurs up to a temperature of approximately 275°C. A mass loss of less than 5% occurs for the first time at temperatures above approximately 300°C. Only above 400°C does the mass loss exceed 5%.

[0110] This demonstrates the extremely high temperature stability of polyamide-imide as a dielectric material. In particular, long-term temperature stability exceeding 200°C can be expected for future applications.

[0111] This allows the completed capacitor to be mounted, for example, by soldering, without having to anticipate any degradation of the components or dielectric layers.

[0112] Further advantages of polyamide-imide as a dielectric for capacitors are shown in Tables 1 and 2 and the graph in Figure 2b below.

[0113] Table 1 shows the dissipation rate (tanδ) of a polyamide-imide plate capacitor with a structure similar to that shown in Figure 1. The dielectric layer measured here was obtained from the above polyamide-imide resin mixture diluted to a 15% mass fraction relative to the initial mixture with xylene as a solvent (squeegee speed 50 mm / s). The layer thickness was 3 μm, and the capacitor area was 50 mm². 2 The measurements were performed using a Keysight E4990A equipped with Novocontrol's PHECOS cooling / heating system.

[0114] [Table 1]

[0115] As shown in Table 1, the dissipation rate is consistently less than 2% across the tested frequency and temperature ranges. Notably, the dissipation rate even slightly improves with increasing temperature. This indicates that polyamide-imide, as a dielectric, possesses outstanding dielectric properties.

[0116] This is also confirmed by the graph shown in Figure 2b, which displays the dissipation rate of the dielectric layer as a function of frequency, as explained with reference to Table 1 at a constant temperature of 150°C. Therefore, it can be seen that the dissipation rate in the tested frequency range of 1 kHz to 1 MHz can be considered constant under a first-order approximation.

[0117] This consistent behavior generally enables the wide use of polyamide-imide capacitors, and in particular, allows for the high flexibility of individual polyamide-imide capacitors.

[0118] Table 2 shows the dielectric constant (ε) of the polyamide-imide plate capacitor corresponding to the structure shown in Figure 1. r This shows the dependence of the voltage on temperature and electrical frequency. The dielectric layer used here was fabricated using a 19 wt% solution of the polyamide-imide resin mixture used initially. The layer thickness was 5 μm, and the capacitor area was 50 mm². 2 The measurements were performed using a Keysight E4990A equipped with Novocontrol's PHECOS cooling / heating system.

[0119] [Table 2]

[0120] Table 2 shows that the dielectric constant exhibits only slight variations with respect to temperature and frequency. Basically, we can observe a decrease in dielectric constant with increasing frequency or an increase in dielectric constant with increasing temperature. However, polyamide-imide with an average dielectric constant of 4 has almost twice the dielectric constant of the standard material BOPP.

[0121] This high dielectric constant is due to the partially aromatic properties of polyamide-imides and polar groups such as furan groups. Furthermore, it is essentially possible to adjust polyamide-imides so that dielectric loss or other properties are optimized in a specific frequency range. This can be done by adjusting the composition of a prepolymer-polyamide-imide solution consisting of various polyamide-imides, or by specially selecting functional groups on the main chain.

[0122] For the flat plate capacitors listed in Table 2, the dielectric breakdown voltage at room temperature is 300-550 V / μm, depending on the frequency (measured with Sefelec S50). The insulation resistance at room temperature is always greater than 3 TΩ (measured with Novocontrolsystem Alpha A).

[0123] This indicates that the polyamide-imide used possesses both a high dielectric breakdown voltage and ohmic insulation resistance, as well as an excellent dielectric constant.

[0124] Figure 3 shows a schematic cross-sectional view of a second embodiment of capacitor 1. Capacitor 1 has a number of first electrodes 3 stacked alternately with a second electrode 4. The two electrodes are flat electrodes.

[0125] A dielectric layer 2 is always placed between the first electrode 3 and the second electrode 4, that is, between each pair of adjacent electrodes, and these correspond to the dielectric layer 2 in the first embodiment shown in Figure 1.

[0126] The first electrode 3 and the second electrode 4 have the properties of internal electrodes.

[0127] Therefore, the second embodiment of capacitor 1 is a multilayer capacitor.

[0128] On the opposite side of the multilayer capacitor, the first external contact 5 and the second external contact 6 are located.

[0129] The first electrode 3 is electrically connected to the first external contact 5. The second electrode 4 is electrically connected to the second external contact 6.

[0130] The capacitor assembled in this manner can be a surface-mount device (SMD), which is very suitable for soldering due to its temperature-stable dielectric layer 2. To make capacitor 1 more advantageous as an SMD capacitor, the external contacts 5 and 6 can be configured in a clamp-like manner. That is, the external contacts 5 and 6 can extend slightly in the stacking direction on both sides.

[0131] The capacitor can be, for example, rectangular and may have a total of 1000 or more repeating units, including a first electrode, a dielectric layer, a second electrode, and further dielectric layers. It can have a length of 3-4 mm, a width of 2-3 mm, and a height of 1-2 mm. Each dielectric layer 2 can have a thickness of 500 nm to 5 μm, preferably 500 nm to 2 μm. The internal electrode has a thickness of 10-50 nm, preferably 20 nm.

[0132] However, the dimensions of the finished capacitor may differ from those presented here. The length, width, height, and layer thickness can be adapted to various technical requirements or to various technical tasks.

[0133] The manufacturing method may be the same as that of the first embodiment. For example, a first electrode layer 3 can be coated onto the substrate by PVD. Subsequently, a dielectric layer 2 can be coated from a solution, and then a second electrode layer 4 can be coated again by PVD. On top of this, another dielectric layer 2 is coated from a solution. This can be repeated to achieve a desired number of layers or a specific capacitance of the capacitor.

[0134] In principle, the internal electrodes can be structured in the method. This can be done either during deposition or after physical vapor deposition.

[0135] The substrate can be removed after lamination.

[0136] Optionally, a protective layer (not shown) similar to that of the first embodiment may then be applied to the side surface that remains without external contacts by a vapor deposition process, a solvent-based process, or a coating process.

[0137] External contacts 5 and 6 are mounted on the completed capacitor 1. These can be made of, for example, brass, copper, tin, aluminum, or silver, and can be applied by either a physical vapor deposition process or another process, such as a solvent-based process.

[0138] Figure 4 is a schematic cross-sectional view showing a third embodiment of capacitor 1, which is also a multilayer capacitor.

[0139] Capacitor 1 in Figure 4 largely corresponds to the capacitor shown in Figure 3 and described above. However, in the example shown in Figure 4, the original circuit board, which is now circuit board 7, is still present on the component.

[0140] In the case of Figure 4, the substrate 7 is insulating and can be, for example, a glass substrate, a semiconductor wafer, or a flexible substrate such as a polyimide film or release tape.

[0141] The manufacturing method of the third embodiment in Figure 4 corresponds to the manufacturing method of the second embodiment in Figure 3, except that the substrate is removed.

[0142] Figure 5 shows a schematic cross-sectional view of a fourth embodiment of capacitor 1 (in this case, a multilayer capacitor). The fourth embodiment shown in Figure 5 is largely similar to that in Figure 4.

[0143] However, here, the substrate 7 is a metallic conductive substrate made of, for example, aluminum, copper, or a similar material. It exists, for example, as a film. Due to its conductivity, it is not necessary to provide a conductive layer as the first electrode 3 on the substrate. The substrate 7 itself can function as a substitute for one of the first electrodes 3. A dielectric layer 2 is then directly coated on it.

[0144] Since the substrate preferably extends across the entire width and length of the capacitor, care must be taken to ensure that the second external contact 5 does not come into electrical contact with the substrate.

[0145] This method is also similar to the embodiment shown in Figure 4.

[0146] The fifth embodiment, shown in a schematic cross-sectional view in Figure 6, is similar in almost all respects to the second embodiment of capacitor 1; that is, it is also a multilayer capacitor. However, this multilayer capacitor has wires 8 and 9 at its external contacts 5 and 6, which allow for through-hole mounting in one application; that is, it is a through-hole capacitor. Wires 8 and 9 create electrical and, in most cases, mechanical contact with the connection point in one application. Wires 8 and 9 can be fixed to capacitor 1 by any method, such as bonding.

[0147] Figure 7 is a schematic cross-sectional view showing a sixth embodiment of capacitor 1, which is a wound capacitor. In its structure, the wound capacitor is similar to that of the first embodiment, namely, the dielectric layer 2 is sandwiched between the first electrode 3 and the second electrode 4. The corresponding sandwich structure is wound to form a wound capacitor.

[0148] However, the manufacturing method used is different from the manufacturing method corresponding to Figure 1. Therefore, preferably, a dielectric film 2 is first formed on the substrate by the deposition method described with respect to Figure 1. This can then be peeled off from the substrate. It can then be post-processed by any method. Subsequently, the film thus obtained can be metallized by PVD on one side or, in this case, both sides. The metallized film thus obtained can be wound to form a wound capacitor. The preferred layer thickness of the wound capacitor film having polyamide-imide is in the range of 1 μm to 10 μm, preferably 2 μm to 5 μm.

[0149] As an additional or alternative method for manufacturing various structures, first, a polyamide-imide film for dielectrics is formed from a solution by a roll-to-roll process using a doctor blade of a prepolymer polyamide-imide solution onto a substrate pre-treated with a release agent. Subsequently, drying and, simultaneously, annealing at over 200°C, preferably over 220°C, and best 250°C are performed. This is followed by peeling of the dried and crosslinked polyamide-imide film from the substrate and winding it. Optionally, an interlayer for protection may be wound together. Next, electrodes are coated. This is preferably also performed by a roll-to-roll process. The electrode layer may be coated on one side or both sides, depending on technical requirements. The electrodes may or may not be structured. The thickness of the electrodes toward the edges may or may not be adapted. This is followed by segmentation of the roll, with optional subsequent pressing into a flat coil. Next, the external contacts are coated by flame spraying, PVD (e.g., sputtering, thermal deposition), or by an electrical process. The latter allows for the manufacture of SMD components. In the case of flat coils, similarly, the side contacts are coated, followed by the attachment of wires, and then the injection of a temperature-stable, water-repellent grout. In the case of SMD capacitors, as already mentioned, a protective layer or barrier layer may be applied.

[0150] However, further processing of the films manufactured as described above can also be carried out by the sheet-to-sheet method. Here, the film pieces are cut to a specified size, such as DIN A5 or DIN A4 size. These film pieces are then coated with electrodes. This corresponds to the manufacture of a motherstack. The electrode coating is done on both sides and structured by a PVD process. The individual film pieces are then stacked and pressed, and then the individual capacitors are cut out from the motherstack, and side contacts are provided by methods such as flame spraying or electroplating, followed by grout injection or stabilization with a protective or barrier layer. [Explanation of symbols]

[0151] 1 Capacitor 2 Dielectric layers 3. First electrode 4. Second electrode 5. First external contact 6. Second external contact 7 circuit boards 8. First wire 9. Second wire

Claims

1. A capacitor (1) having a single dielectric layer (2) that does not contain solid inorganic material, wherein the dielectric layer (2) contains polyamide-imide, a first electrode (3) is disposed directly adjacent to the dielectric layer (2), the dielectric layer (2) contains a polyamide-imide main chain containing amide groups and imide groups of the polyamide-imide, and chemical crosslinks are formed within the dielectric layer (2) between the polyamide-imide main chains or within the polymer main chains.

2. The capacitor (1) according to claim 1, wherein the second electrode (4) is similarly disposed directly adjacent to the dielectric layer (2).

3. The capacitor (1) according to claim 1 or 2, wherein the dielectric layer (2) is made of polyamide-imide in an amount of 50% by weight or more.

4. The aforementioned crosslinking is a capacitor (1) according to claim 1, wherein the polyamide-imide main chains are linearly bonded to each other.

5. The capacitor (1) according to claim 4, wherein the linear coupling is formed via imide crosslinks or urethane crosslinks.

6. The capacitor (1) according to claim 4, wherein, in addition to linear coupling, a three-dimensional crosslink is formed via urea crosslinking.

7. A capacitor (1) having a single dielectric layer (2) that does not contain solid inorganic material, wherein the dielectric layer (2) contains polyamide-imide, and a first electrode (3) is disposed directly adjacent to the dielectric layer (2), The polyamide-imide is a capacitor (1) containing an anhydride as a functional group.

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