Capacitor

Abstract

In an embodiment a capacitor includes a dielectric layer including a polyamideimide, the dielectric layer being uniform and a first electrode disposed directly adjacent to the dielectric layer.

Claims

1.-25. (canceled)

26. A capacitor comprising: a dielectric layer including a polyamideimide, the dielectric layer being uniform; and a first electrode disposed directly adjacent to the dielectric layer.

27. The capacitor according to claim 26, further comprising a second electrode also arranged directly adjacent to the dielectric layer.

28. The capacitor according to claim 26, wherein the dielectric layer consists of 50% by weight or more of the polyamideimide.

29. The capacitor according to claim 26, wherein the dielectric layer is free of solid inorganic materials.

30. The capacitor according to claim 26, wherein the dielectric layer contains polyamideimide main chains comprising amide and imide groups of the polyamideimide.

31. The capacitor according to claim 30, wherein the polyamideimide main chains are partially aromatic.

32. The capacitor according to claim 30, wherein chemical crosslinks are formed in the dielectric layer between the polyamideimide main chains or within a polymer main chain.

33. The capacitor according to claim 32, wherein the crosslinks linearly link polyamideimide main chains.

34. The capacitor according to claim 33, wherein the linear linkage is formed via an imide bridge or a urethane bridge.

35. The capacitor according to claim 33, wherein, in addition to the linear linkage, three-dimensional crosslinks are formed via urea bridges.

36. The capacitor according to claim 32, wherein the chemical crosslinks are selected from urethane bridges, imide bridges or urea bridges.

37. The capacitor according to claim 36, wherein the polyamideimide has a structure according to chemical formula 1, wherein R.sup.1 is a lactam, an anhydride, a urethane bridge or an imide bridge, wherein R.sup.2 is a phenylene group, and wherein R.sup.3 is a furan, an amine, an anhydride, a urethane bridge, or an imide bridge. ##STR00003##

38. The capacitor according to claim 26, wherein the polyamideimide has phenylene groups, anhydrides and/or furan groups as functional groups.

39. The capacitor according to claim 26, wherein a plurality of first electrode layers are stacked alternately with second electrode layers, and a dielectric layer is disposed between each two adjacent electrode layers.

40. The capacitor according to claim 39, wherein all first electrode layers are electrically conductively connected to a first external contact, and all second electrode layers are electrically conductively connected to a second external contact.

41. The capacitor according to claim 39, wherein a substrate is arranged on a side surface of the capacitor which is parallel to a plane of the electrode layers.

42. The capacitor according to claim 39, wherein the capacitor is a surface mounted device (SMD).

43. The capacitor according to claim 39, further comprising wires, the wires configured for through-hole mounting.

44. The capacitor according to claim 39, wherein the capacitor is a wound capacitor.

45. A method for manufacturing a capacitor, the method comprising: forming a dielectric layer by: depositing a prepolymer polyamideimide solution on a deposition surface; drying the prepolymer polyamideimide solution on the deposition surface; and annealing the dried prepolymer polyamideimide solution.

46. The method according to claim 45, further comprising: releasing the dielectric layer from the deposition surface after formation to provide a dielectric film; metallizing the dielectric film; and winding the metallized dielectric film, wherein the deposition surface is a surface of a substrate.

47. The method according to claim 45, wherein the deposition surface is a surface of an electrically conductive substrate or a first electrode layer, and wherein the method further comprises: after, depositing the dielectric layer on the deposition surface, forming a second electrode layer on the dielectric layer, and forming a further dielectric layer on the second electrode layer by: applying the prepolymer polyamideimide solution on the second electrode layer, drying the prepolymer polyamideimide solution on the second electrode layer, and annealing the dried prepolymer polyamideimide solution.

48. The method according to claim 45, wherein the prepolymer polyamideimide solution contains polyamideimide main chains on which isocyanate groups, lactam groups, and/or anhydride groups are arranged.

49. The method according to claim 45, wherein isocyanate groups, lactam groups, and/or anhydride groups are terminally arranged on polyamideimide main chains.

50. The method according to claim 45, wherein the prepolymer polyamideimide solution is applied by doctor blade coating, slot die coating, stencil printing, spin coating or spray coating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0081] The invention is described in more detail below with reference to exemplary embodiments. These exemplary embodiments are shown in the following figures, which are not to scale. Lengths as well as relative and absolute dimensions can thus not be taken from the figures. Nor is the invention limited to the following embodiments.

[0082] FIG. 1 shows a first embodiment of a capacitor in schematic cross-section;

[0083] FIG. 2a shows the mass loss of a polyamideimide layer in a thermogravimetric analysis. FIG. 2b shows the course of the loss factor of a capacitor;

[0084] FIG. 3 shows a first multilayer capacitor as a second example of a capacitor in schematic cross-section;

[0085] FIG. 4 shows a second multilayer capacitor as a third example of a capacitor in schematic cross-section;

[0086] FIG. 5 shows a third multilayer capacitor as a fourth example of a capacitor in schematic cross-section;

[0087] FIG. 6 shows a multilayer capacitor suitable for through-hole mounting as a fifth example of a capacitor in schematic cross-section; and

[0088] FIG. 7 shows a wound capacitor as a sixth example of a capacitor in schematic cross-section.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0089] FIG. 1 shows a first embodiment example of a capacitor 1 in schematic cross-section. The capacitor 1 has an organic dielectric layer 2. The dielectric layer 2 is a uniform layer. This means that it consists of a single material and does not contain any volume regions that can be separated from one another. Thus, it is also not a composite material. At least 50% by weight of the dielectric layer 2 consists of a polyamideimide. Preferably, the polyamideimide content is higher, for example over 90%. Even more preferably, the dielectric layer 2 consists exclusively of polyamideimide.

[0090] The polyamideimide can be any polyamideimide, in particular it can be a partially aromatic polyamideimide. Particularly preferred is a polyamideimide according to structural formula 1.

##STR00002##

[0091] The polyamideimide according to structural formula 1 has a polyamideimide main chain and may have multiple functional groups. For example, phenylene groups may be included in the polyamideimide main chain as R.sup.2 of structural formula 1. The phenylene groups may adjust the flexibility of the polyamideimide main chain. For example, a biphenyl, a di- or triphenylmethane, ortho- or paradibenzylbenzene or tribenzylbenzene can be used.

[0092] Furthermore, furans can be arranged in particular terminally, for example as R.sup.3 on the polyamideimide main chain. Their polarity can thus be used to adjust the polarity of the dielectric layer. For example, benzofurans, dibenzofurans, furanones or hydroxyfuranones can be used as furans.

[0093] Alternatively, anhydrides can be used as R.sup.3.

[0094] Furthermore, crosslinks preferably exist between the various polyamideimide main chains in the dielectric layer 2.

[0095] Preferably, the polyamideimide main chains are linked to each other via urethane bridges and/or imides. These linkages may, for example, be terminally located at the position of residue R.sup.1 in structural formula 1. Alternatively, unbridged groups may still be present in the R.sup.1 position, such as lactame isocyanates, or anhydrides.

[0096] Preferably, the dielectric layer 2 was prepared from a polyamideimide resin mixture suitable for coating wires, e.g. a RESISTHERN® AI 336 L solution.

[0097] A first electrode 3 and a second electrode 4 are arranged 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.

[0098] Preferred stacking occurs over the largest areas of the flat formed layers.

[0099] The layer thickness of the electrodes can be, for example, 10 to 50 nm, preferably 20 nm. Depending on the manufacturing process, the layer thickness of the dielectric layer 2 can be set in the range between 500 nm and 10 μm.

[0100] The electrodes can be made of aluminum or silver, or preferably of an aluminum-zinc alloy. Alternatively, the electrodes may be multilayer electrodes of chromium/aluminum, chromium/silver or chromium/nickel/aluminum or chromium/nickel/silver. In addition to the elements shown here, a protective layer of hydrocarbon compounds, such as parylenes or fluorine-based hydrocarbons, may be applied to the sides of the capacitor that do not have the electrodes (not shown).

[0101] As an alternative not shown in the figures, only one electrode may be applied to the dielectric layer.

[0102] The first embodiment example of a capacitor shown in FIG. 1 can be made by any method. Preferably, it is fabricated by solvent-based processes. For example, first the first electrode 3 may be fabricated on a substrate. The substrate may 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. On a surface of the substrate, the first electrode is deposited by physical vapor deposition (PVD), such as sputtering or thermal evaporation.

[0103] Now, on the surface of the electrodes 3 as the deposition surface, the dielectric layer 2 made of a prepolymer polyamideimide solution can be deposited. The prepolymer polyamideimide solution preferably contains a polyamideimide that is largely free of crosslinking.

[0104] The prepolymer polyamideimide solution is prepared from a commercially available polyamideimide resin mixture (e.g. RESISTHERN® AI 336) by additional dilution with solvents.

[0105] The polyamideimide resin blend contains approximately 36% non-volatiles (predominantly polyamideimide main chains) in a solution of N-methylpyrolidone (NMP) and xylene. It has an initial viscosity of 4750±1750 mPa s. Furthermore, it has a density of about 1.1 g/ml.

[0106] The polyamideimide solution thus prepared is adjusted with xylene or N-methylpyrolidone to a concentration of 20% or less of the original polyamideimide concentration. For example, a polyamideimide concentration of 19% by mass or 15% by mass with respect to the original polyamideimide-resin mixture is prepared in xylene.

[0107] The concentration used depends on the layer thickness to be achieved or on the type of deposition process used.

[0108] [ono] The prepolymer polyamideimide solution prepared in this way can now be applied to the surfaces of the first electrode 3 as the deposition surface. The application can be carried out by doctor blade coating, stencil printing, spin coating or spray coating. The coating method depends on the thickness of the dielectric layer 2 to be achieved. In particular, thicker layers in the range between 500 nm and 5 μm can be applied by spin coating or spray coating, or thicker layers in the range, for example, from 1 μm to 10 μm can be applied by doctor blade coating or stencil printing.

[0109] The solution thus applied is dried at a temperature between 60 and 100° C., and preferably at 80° C. Subsequently, the dried film is annealed at temperatures above 200° C., preferably at 250° C.

[0110] During drying, most of the solvent is removed. Further amounts of volatiles are removed by annealing. In addition, crosslinking between the main chains can begin during annealing. At a temperature of 250° C., largely complete crosslinking can be achieved in 5-10 min. Preferably, isocyanate groups protected as lactams are activated, which subsequently react with hydroxy groups present, for example on furan residues, or with anhydrides.

[0111] After cooling, the second electrode 4 can be reapplied by PVD to the dielectric layer prepared in this way.

[0112] At the end of the process, the substrate can be removed to obtain the object of FIG. 1. In principle, however, it can also remain on the capacitor.

[0113] FIG. 2A shows a thermogravimetric analysis (TGA) of the polyamideimide-resin blend used. The temperature ramp is a constant 10 K/min. As the graph of FIG. 2A shows, no mass loss occurs up to a temperature of about 275° C. At a temperature above about 300° C. mass loss of less than 5% occurs. Only above 400° C. mass loss above 5% occurs.

[0114] This demonstrates the extremely high temperature stability of polyamideimide as a dielectric. In particular, a continuous temperature stability of over 200° C. can be expected for future applications.

[0115] In particular, this allows the finished capacitor to be installed, for example by soldering, without degeneration of the component or the dielectric layer being expected.

[0116] Further advantageous properties of the polyamideimide as a dielectric for a capacitor are shown in the following Tables 1 and 2 and in the graph of FIG. 2B.

[0117] Table 1 shows the dielectric loss factor (tan δ) of a polyamideimide plate capacitor similar to the structure described in FIG. 1. The dielectric layer measured here was made from the polyamideimide-resin mixture described above, which was diluted to a mass fraction of 15%, based on the original mixture with xylene as solvent (doctor blade speed 50 mm/s). The layer thickness was 3 μm, and the area of the capacitor was 50 mm.sup.2. The measurement was performed with a Keysight E4990A with cooling/heating system PHECOS from Novocontrol.

TABLE-US-00001 TABLE 1 tan δ Frequencies Temperature 1 kHz 10 kHz 100 kHz 1 MHz Room temp. 0.009 0.016 0.019 0.014 100° C. 0.009 0.009 0.010 0.017 150° C. 0.015 0.013 0.012 0.014

[0118] As Table 1 shows, the dissipation factor is always less than 2% in the frequency and temperature range studied. Remarkably, the dissipation factor even improves slightly with increasing temperature. This shows that polyamideimide as a dielectric has excellent dielectric properties.

[0119] This is also confirmed in the graph shown in FIG. 2B, which shows the dissipation factor of the dielectric layer described in reference to Table 1 at a constant temperature of 150° C. as a function of frequency. Thus, it can be observed that the dissipation factor can be considered constant in a first approximation in the investigated frequency range between 1 kHz and 1 MHz.

[0120] This constant behavior allows a wide use of polyamideimide capacitors in general and a high flexibility of the single polyamideimide capacitor in particular.

[0121] Table 2 shows the dependence of the permittivity (εr) of a polyamideimide plate capacitor corresponding to the structure shown in FIG. 1 on temperature and electrical frequency. The dielectric layer used here was prepared with a 19 wt % solution based on the polyamideimide-resin blend originally used. The layer thickness was 5 μm and the area of the capacitor was 50 mm.sup.2. The measurement was performed using a Keysight E4990A with Novocontrol's PHECOS cooling/heating system.

TABLE-US-00002 TABLE 2 ∈.sub.r Frequencies Temperature 1 kHz 10 kHz 100 kHz 1 MHz Room temp. 4.0 4.0 3.8 3.6 100° C. 4.6 4.4 4.3 4.1 150° C. 5.0 4.7 4.5 4.3

[0122] Table 2 shows that there is only a moderate variation in permittivity with respect to temperature and frequency. Although a decrease in permittivity with increasing frequency and an increase in permittivity with increasing temperature can generally be observed, the polyamideimide, with an average permittivity of 4, has almost twice the permittivity of the standard material BOPP.

[0123] This high permittivity is attributed to the partially aromatic character, as well as the polar groups, such as furan groups, of the polyamideimide. In addition, it is possible in principle to adjust the polyamideimide in such a way that the dielectric losses or other properties are optimized in a specific frequency range. This can be done both by the composition of a prepolymer polyamideimide solution from different polyamideimides, and by the specific selection of functional groups on the main chains.

[0124] For the plate capacitor described in Table 2, the breakdown voltage at room temperature is between 300 and 550 V/μm, depending on the frequency (measured with Sefelec S50). The insulation resistance at room temperature is always above 3 TΩ (measured with Novocontrolsystem Alpha A).

[0125] This shows that the polyamideimide used has excellent permittivity combined with high breakdown voltage and ohmic insulation resistance.

[0126] FIG. 3 shows a second embodiment of a capacitor 1 in schematic cross-section. The capacitor 1 has a plurality of first electrodes 3 which are alternately stacked with second electrodes 4. Both electrodes are planar electrodes.

[0127] Between the first electrodes 3 and the second electrodes 4, i.e. between two adjacent electrodes in each case, a dielectric layer 2 is always arranged, which in each case corresponds to the dielectric layer 2 from the first embodiment example in FIG. 1.

[0128] The first electrodes 3 and the second electrodes 4 have the character of internal electrodes.

[0129] Thus, the second embodiment example of a capacitor 1 is a multilayer capacitor.

[0130] First external contacts 5 and second external contacts 6 are arranged on opposite side surfaces of the multilayer capacitor.

[0131] The first electrodes 3 are electrically conductively connected to the first external contact 5. The second electrodes 4 are electrically conductively connected to the second external contact 6.

[0132] The capacitor assembled in this way can be a surface mounted device (SMD), which is very suitable for soldering due to its temperature-stable dielectric layer 2. In order to be able to use the capacitor 1 even more advantageously as an SMD capacitor, the outer contacts 5 and 6 can have a clamp-like structure. That is, the outer contacts 5 and 6 can extend a certain distance onto the two side surfaces in the stacking direction.

[0133] For example, the capacitor may be cuboidal in shape and may comprise a total of woo repeating units or more, which include a first electrode, a dielectric layer, a second electrode, and another dielectric layer. It may have a length of 3 to 4 mm, a width of 2 to 3 mm, and a height of 1 to 2 mm. The single dielectric layer 2 here may have a thickness of 500 nm to 5 μm, preferably between 500 nm and 2 μm. The inner electrodes have a thickness of 10 to 50 nm and preferably 20 nm.

[0134] However, the dimensions of the finished capacitor may also differ from those given here. Length, width, height and layer thicknesses can be adapted to different technical requirements or with regard to different technical tasks.

[0135] A manufacturing method may be similar to the manufacturing method of the first embodiment. For example, a first electrode layer 3 can be deposited on a substrate by PVD. A dielectric layer 2 can then be deposited from solution, and then a second electrode layer 4 can be deposited, again by PVD, onto which a dielectric layer 2 is again deposited from solution. This can be repeated to achieve a desired number of layers or a specific capacitance of the capacitor.

[0136] In principle, the inner electrodes can be patterned in the process. This can be done either already during deposition or after the physical vapor deposition process.

[0137] After stacking, the substrate can be removed.

[0138] Optionally, a protective layer (not shown) similar to that of the first embodiment can then be applied to the side surfaces, which remain free of external contacts, by means of a vapor deposition process and solvent-based processes or coating processes.

[0139] The external contacts 5 and 6 are applied to the finished stacked capacitor 1. These can be made, for example, of brass, copper, tin, aluminum, silver or the like and can be applied either by means of physical vapor deposition processes or other, for example, solvent-based processes.

[0140] FIG. 4 shows in schematic cross-section a third embodiment of a capacitor 1, which is also a multilayer capacitor.

[0141] The capacitor 1 in FIG. 4 corresponds in large parts to the capacitor as shown in FIG. 3 and described previously. However, in the example shown in FIG. 4, the original substrate, which in this case is the substrate 7 is shown as still being present on the component.

[0142] The substrate 7, in the case of FIG. 4, is insulating and may be, for example, a glass substrate, a semiconductor wafer, or may be a flexible substrate such as polyimide films or a release tape.

[0143] The manufacturing process for the third embodiment in FIG. 4 is the same as that for the second embodiment in FIG. 3, except for the removal of the substrate.

[0144] In FIG. 5, a fourth embodiment of a capacitor 1 (here a multilayer capacitor) is shown in schematic cross-section. The fourth embodiment shown in FIG. 5 is similar in large parts to that shown in FIG. 4.

[0145] However, here the substrate 7 is a metallic, conductive substrate, for example made of aluminum, copper or similar materials. It is present, for example, as a film. Due to its conductive character, it is not necessary to apply a conductive layer as first electrode 3 on the substrate. The substrate 7 itself can serve as a substitute for one of the first electrodes 3. The dielectric layer 2 is then applied directly to it.

[0146] 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 make electrical contact with the substrate.

[0147] The process is also similar to the embodiment example described in FIG. 4.

[0148] The fifth embodiment, which is shown in schematic cross-section in FIG. 6, is similar in almost all aspects to the second embodiment of a capacitor 1. It is therefore also a multilayer capacitor. However, this multilayer capacitor has wires 8 and 9 on its outer contacts 5 and 6, which in one application allow it to be installed in a through-hole mounting. Thus, it is a through-hole capacitor. The wires 8 and 9 create an electrical and usually a mechanical contact with connection points in an application. The wires 8 and 9 can be attached to the capacitor 1 by any method, such as bonding.

[0149] FIG. 7 shows in schematic cross-section a sixth embodiment of a capacitor 1. Here, the capacitor is a wound capacitor. In its structure, the wound capacitor is similar to the first embodiment example, that is, a dielectric layer 2 is sandwiched by a first electrode 3 and a second electrode 4. The corresponding sandwich-like structure is rolled up into a wound capacitor.

[0150] However, the manufacturing method used differs from the manufacturing method according to FIG. 1. Preferably, the dielectric layer 2 is first produced on a substrate using the deposition method described for FIG. 1. This can then be released from the substrate. It can then be post-processed by any method. Subsequently, the film thus obtained can be metallized on one side or, in the present case, on both sides by PVD. The metallized film thus obtained can be wound into a wound capacitor. Preferred film thicknesses for wound capacitor films with polyamideimide are in the range between 1 μm and 10 μm, preferably between 2 μm and 5 μm.

[0151] As an additional or alternative process for the production of various structural shapes, the formation of a polyamideimide film for a dielectric can first be carried out in a roll-to-roll process from solution by doctoring a prepolymer polyamideimide solution onto a substrate which has previously been provided with a release agent. This is followed by drying and simultaneous annealing at above 200° C., preferably at above 220° C., preferably at 250° C. This is followed by delamination or detachment of the dried and crosslinked polyamideimide film from the substrate and winding of the same. Optionally, an intermediate film can be wound along as protection. Subsequently, the electrodes are applied. This is preferably also carried out in a roll-to-roll process. The electrode layer or layers can be applied on one or both sides, depending on the technical requirements. The electrodes can be structured or remain unstructured. The thickness of the electrodes towards the edge can be adjusted or adapted. This is followed by segmentation of the roll with optional subsequent pressing to form a flat winding. Subsequently, external contacts are applied by flame spraying, PVD (e.g. sputtering, thermal evaporation) or by galvanic processes. The latter can be used to produce an SMD component. In the case of the flat winding, this is also followed by the application of the side contact and, in addition to this, also an application of wires and subsequent potting with a temperature-stable, water-repellent potting material. In the case of the SMD capacitor, a protective or barrier layer can be applied as described earlier.

[0152] However, further processing of the film produced as above can also be carried out using the sheet-to-sheet process. In this process, pieces of film are cut to a defined size, such as DIN A5 or DIN A4. These film pieces are then coated with the electrodes. This corresponds to the production of a mother stack. The electrodes are coated on both sides and structured using the PVD process. The individual film pieces are then stacked and pressed, after which the individual capacitors are cut from the mother stack, provided with a side contact, e.g. by means of flame spraying, electroplating or otherwise, and then stabilized by means of potting or a protective or barrier layer.