EP2135266A1

EP2135266A1 - Method for the production of a coating of a porous, electrically conductive carrier material with a dielectric

Info

Publication number: EP2135266A1
Application number: EP08717641A
Authority: EP
Inventors: Florian Thomas
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2007-03-15
Filing date: 2008-03-12
Publication date: 2009-12-23
Also published as: US20100046141A1; KR20090122226A; JP2010521803A; TW200920825A; CN101636804A; WO2008110562A1; RU2009137942A

Abstract

The invention relates to the production of a coating of a porous, electrically conductive carrier material (1) with a dielectric (18), particularly for the use in a capacitor. The production method comprises the steps: infiltrating the carrier material (1) with a solution (2), comprising precursor compounds of the dielectric (18) and at least one solvent (12) and having a boiling temperature TS and a cross-linking temperature TN, drying the carrier material (1) infiltrated with the solution (2) at a drying temperature TT, which is lower than the boiling temperature TS and lower that the cross-linking temperature TN of the solution (2), until more than 75 wt.% of the solvent (12) is evaporated.

Description

Process for producing a coating of a porous, electrically conductive carrier material with a dielectric

description

The invention relates to a method for producing a coating of a porous, electrically conductive carrier material with a dielectric and to the use of a coating thus produced as a dielectric in a capacitor.

The storage of energy in various applications is the subject of ongoing development work. The progressive miniaturization of electrical and electronic circuits leads to the demand for ever fewer or smaller and smaller components in order to achieve this storage. For capacitors, therefore, ever higher capacitance densities are required.

After the capacitor formulas

E = ^_1/2 C »U ² and C = ε" ε _o »A / d,

where E = energy

C = capacity

U = voltage ε = dielectric constant of the dielectric ε ₀ = dielectric constant of the vacuum

A = electrode area d = electrode spacing

high capacitance densities can be achieved by the use of dielectrics with a high dielectric constant as well as by large electrode surfaces and small electrode spacings. Furthermore, the use of high dielectric strength dielectrics is desirable to achieve high operating voltages.

High capacitance ceramic capacitors require thin layers of high dielectric constant ceramic material. As ceramic materials, for example, oxides having a perovskite structure, for example, barium titanate BaTiC> ₃ , are used.

Very thin films of such ceramic materials with film thicknesses of less than 1 .mu.m can be deposited particularly advantageous as solutions. This process is known as chemical solution deposition (CSD) or sol-gel deposition. and described in detail, for example, in R. Schwartz: "Chemical Solution Deposition of Ferroelectric Thin Films" in Materials Engineering 28, Chemical Processing of Ceramics, 2nd edition 2005, pages 713 to 742. Here are solutions of the desired elements, usually of metal salts or alcoholates, in solvents such as alcohols, carboxylic acids, glycol ethers or water. These solutions are applied to suitable substrates and then thermally decomposed to the desired material.

For example, the films are subjected to a two-stage thermal treatment for the decomposition. First, in a so-called "pyrolysis" at temperatures of 250 to 400 ⁰ C in an air atmosphere, the organic components are largely removed. In the process, the dissolved inorganic components crosslink to form an amorphous preceramic material. In the second step, the so-called "calcination" or "crystallization" at temperatures of 600 to 900 ⁰ C, the remaining carbon-containing components are degraded and the resulting metal oxide sinters to a dense ceramic.

For barium titanate-containing materials, a one-step process is often preferred in which the film is heated directly to the calcination temperature. The high rate of heating is considered to be beneficial for the formation of particularly dense films.

The production of ceramic capacitors with a particularly high capacitance density is described, for example, in WO 2006/045520 A1. In these capacitors in each case a porous, electrically conductive carrier is contained on the most complete inner and outer surface of a dielectric and an electrically conductive layer are applied. The dielectric is deposited from a solution on the porous support. For this, the porous support is infiltrated with a solution containing precursor compounds of the dielectric in dissolved form, and then thermally treated to calcine the precursor compounds to the oxide. The ther- mal treatment is performed at 500 ⁰ C to 1600 ⁰ C.

In FIGS. 1a to 1d, the sequence of the thermal after-treatment according to the prior art is shown schematically.

FIG. 1a shows a detail of the pore space of a carrier material after infiltration with a coating solution. The sectioned pore 16 of the porous carrier material 1 is completely filled with a solution 2 containing precursor compounds of a dielectric and at least one solvent.

FIG. 1b shows the section according to FIG. 1a during tempering at temperatures above the boiling point T _s and above the crosslinking temperature T _{N of} the solution lie. For example, the annealing takes place at temperatures of 250 ⁰ C to 400 ⁰ C ("pyrolysis"). In the thermal treatment, above the boiling point T _s , which depends on the composition of the solution 2, boiling of the solvent occurs. Conventional boiling temperatures T _{s of} the solutions 2 used are in the range from 80 to 200 ^° C. If the infiltrated porous body 1 is then heated rapidly above the temperature, severe boiling occurs with the formation of bubbles 3 of solvent vapor, which leads to displacement of the solution 2 out of the pores 16 leads. Parts of the solution 2 are pressed out of the porous carrier material 1 and lead to deposition of material 8, 11 outside the carrier material 1 (see FIGS. 1 c and 1 d).

This material 8, 11 is lost to the coating, resulting in an increased consumption of solution 2 and the need for frequent repetitions of the coating process to the desired coating thickness.

Furthermore, above the crosslinking temperature T _N , which likewise depends on the composition of the solution 2, crosslinking of the dissolved inorganic components takes place. In the networking, it comes either to form a spatial network structure and thus for gelling the solution 2, or for the growth of particles and thus for the precipitation of solids. These reactions are known as "sol-gel" methods in the literature. If this temperature is exceeded before most of the volatile components have evaporated, the crosslinking 4 can take place in the entire volume of the pores 16, since the pores 16 are still largely filled with the solution 2. This leads to an undesired, uneven distribution of the resulting preceramic material and to a solidification 5 of material in the interior of the pores 16 (see FIG. 1 c).

FIG. 1 c shows the section according to FIGS. 1 a and 1 b after annealing (pyrolysis). There has been a cross-linking to the preceramic material 5 in a large part of the pore space 16. Within the preceramic material 5, pores 6 of different sizes are contained. A portion of the preceramic material 5 is located as a deposit 8 outside the porous substrate 1.

Figure 1 d shows the detail according to Figures 1 a, 1 b and 1 c after a final anneal ( "calcining"), for example, at 600 to 900 ⁰ C, at which the coating is finished processing methods. The walls of the pores 16 have uncoated

Areas 7 on. The ceramic film 9 covers the pore walls only incompletely.

This leads to short circuits in the desired use in a capacitor and thus to a failure of the technical component. A part of the ceramic material remains as particles 10 in the interior of the pores 16. This particulate material 10 is lost for use as a condenser, which leads to an increased consumption of Lining material and the need for more repetitions of the coating process to the desired coating thickness leads.

The object of the present invention is to avoid the disadvantages of the prior art and, in particular, to provide a method for producing a closed and defect-poor coating of a porous, electrically conductive carrier material with a dielectric.

The coating should as far as possible reach the entire inner and outer surface of the carrier material, but avoid clogging or unnecessary filling of the pores. The process should be economical and in particular suitable for the production of coatings which can be used in capacitors with high capacity density.

A further object is to provide a coating method which reduces an excess consumption of coating solution by deposition of ceramic material inside the pores and outside of the porous support material and reduces the risk of short circuits in a technical component by a more uniform coating of the pore walls.

The object is achieved according to the invention by a method for producing a coating of a porous, electrically conductive carrier material with a dielectric comprising the steps:

Infiltrating the support material with a solution containing precursor compounds of the dielectric and at least one solvent and having a boiling temperature T _s and a crosslinking temperature T _N , and

Drying the infiltrated with the solution carrier material at a drying temperature T _τ , which is less than the boiling temperature T _s and smaller than the crosslinking temperature T _{N of} the solution, to more than 75 wt .-%, preferably more than 90 wt. %, of the solvent has evaporated.

It has been found that the disadvantages of the prior art can be avoided by first treating the porous support material infiltrated with the coating solution for drying at a temperature which is both below the boiling temperature T _s and below the crosslinking temperature T _N ,

The method according to the invention comprises the infiltration of a porous, electrically conductive carrier material. The use of electrically conductive carrier materials offers the advantage that no additional coating of the carrier for metallization is necessary due to the already existing electrical conductivity of the carrier. This makes the process simpler and more economical, the capacitors become more robust and less susceptible to defects.

Suitable support materials preferably have a specific surface area (BET surface area) of from 0.01 to 10 m ² / g, particularly preferably from 0.1 to 5 m ² / g.

Such carrier materials can be prepared, for example, from powders with specific surface areas (BET surface area) of 0.01 to 10 m ² / g by pressing or hot pressing at pressures of 1 to 100 kbar and / or sintering at temperatures of 500 to 1600 ^° C. , preferably 700 to 1300 ⁰ C, produce. The pressing or sintering is advantageously carried out under an atmosphere of air, inert gas (eg argon or nitrogen) or hydrogen or mixtures thereof at an atmospheric pressure of 0.001 to 10 bar.

The pressure used for the pressing and / or the temperature used for the thermal treatment depend on the materials used and the desired material density. Desirable is a density of 30 to 50% of the theoretical value in order to ensure a sufficient mechanical stability of the capacitor for the desired application and at the same time a sufficient porosity for the subsequent coating with the dielectric.

It is possible to use powders of all metals or alloys of metals for producing the support material, which have a sufficiently high melting point of preferably at least 900 ^° C., more preferably greater than 1200 ^° C., and do not undergo any reactions with the ceramic dielectric during further processing.

Advantageously, the support material contains at least one metal, preferably Ni, Cu, Pd, Ag, Cr, Mo, W, Mn or Co and / or at least one metal alloy on the basis thereof.

Advantageously, the carrier is made entirely of electrically conductive materials.

According to a further advantageous variant, the carrier consists of at least one pulverulent non-metallic material, which is enveloped by at least one metal or at least one metal alloy, as described above. Is preferred a non-metallic material that is coated such that no reactions between the non-metallic material and the dielectric take place, which lead to a deterioration of the properties of the capacitor.

Such non-metallic materials may be, for example, Al ₂ O ₃ or graphite. However, SiO ₂ , TiO ₂ , ZrO ₂ , SiC, Si ₃ N ₄ or BN are also suitable. All materials are suitable which, by virtue of their thermal stability, prevent further reduction of the porosity by sintering of the metallic material during the thermal treatment of the dielectric.

The carrier materials used according to the invention can have a wide variety of geometries, for example cuboids, plates or cylinders. Such carriers can be produced in various dimensions, advantageously from a few mm to several dm, and thus perfectly adapted to the particular application. In particular, the dimensions can be matched to the required capacity of the capacitor.

The infiltration of the carrier material can be done by immersing the carrier in the solution, by pressure impregnation or by spraying. As far as possible, complete wetting of the inner and outer surface of the carrier material should be ensured.

According to the invention, the carrier material is infiltrated with a solution containing precursor compounds of a dielectric and at least one solvent.

In the present invention, all commonly used as dielectrics materials can be used.

The dielectric used should have a dielectric constant greater than 100, preferably greater than 500.

Advantageously, the dielectric contains oxide ceramics, preferably of the perovskite type, having a composition which can be characterized by the general formula A _x ByO ₃ . Here, A and B mean mono- to hexavalent cations or mixtures thereof, preferably Mg, Ca, Sr, Ba, Y, La, Ti, Zr, V, Nb, Ta, Mo, W, Mn, Zn, Pb or Bi, as well as x is a number from 0.9 to 1, 1 and y is a number from 0.9 to 1.1. A and B differ from each other.

Particular preference is given to using BaTiO ₃ . Further examples of suitable dielectrics are SrTiO ₃ , (Bai _-x Sr _x ) TiO ₃ and Pb (Zr _x Ti ₁ _-x ) O ₃ , where x is a number between 0.01 and 0.99. In addition, to improve specific properties such as dielectric constant, resistivity, dielectric strength or resistance to aging, the dielectric may contain dopants in the form of their oxides in concentrations between preferably 0.01 and 10 atom%, preferably 0.05 to 2 atom%. Suitable doping elements are z. B. elements of the 2nd main group, in particular Mg and Ca, and the 4th and 5th period of the subgroups, for example Sc, Y, Ti, Zr, V, Nb, Cr, Mo, W, Mn, Fe, Co, Ni, Cu, Ag and Zn of the Periodic Table and lanthanides such as La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

The dielectric is deposited according to the invention from a solution of precursor compounds of the dielectric on the support (so-called sol-gel process, also referred to as chemical solution deposition). Particularly advantageous over the use of a dispersion is the presence of a homogeneous solution, so that it can not come to a clogging of pores and an uneven coating even with larger carriers. The porous carrier material is infiltrated with the solution, which can be prepared by dissolving the corresponding elements or their salts in solvents.

Examples of suitable salts are oxides, hydroxides, carbonates, halides, acetylacets or derivatives thereof, carboxylates of the general formula M (R-COO) _x where R = H, methyl, ethyl, propyl, butyl or 2-ethylhexyl and x = 1 , 2, 3, 4, 5 or 6, alcoholates of the general formula M (RO) _x with R = methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, tert-butyl, 2-ethylhexyl, 2-hydroxyethyl , 2-aminoethyl, 2-methoxyethyl, 2-ethoxyethyl, 2-butoxyethyl, 2-hydroxypropyl or 2-methoxypropyl, and x = 1, 2, 3, 4, 5 or 6 of the above-described elements (referred to herein as M) or mixtures of these salts are used. Alcoholates and / or carboxylates of barium and titanium are advantageously used.

The solvents used may preferably be water, carboxylic acids of the general formula R-COOH where R = H, methyl, ethyl, propyl, butyl or 2-ethylhexyl, alcohols of the general formula R-OH where R = methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, isobutyl, tert-butyl or 2-ethylhexyl, glycol derivatives of the general formula R ¹ -O- (C ₂ H ₄ -O) _X- R ² with R ¹ and R ² = H, methyl, ethyl or butyl and x = 1, 2, 3 or 4, 1, 3-dicarbonyl compounds such as acetylacetone or acetoacetic ester, aliphatic or aromatic hydrocarbons, such as pentane, hexane, heptane, benzene, toluene or xylene, ethers, such as diethyl ether, dibutyl ether or tetrahydrofuran, or mixtures of these solvents are used. Glycol ethers, such as methyl glycol or butyl glycol, are particularly preferably used. Preferably, the solution of the precursor compounds of the dielectric used has a concentration of less than 10 wt .-%, preferably less than 6 wt .-%, particularly preferably 2 to 6 wt .-%, each based on the proportion of the dielectric in the total weight of Solution. The proportion of the dielectric in the total weight of the solution is calculated as the amount of material remaining after the calcination, for example BaTiO ₃ , based on the amount of the solution used.

The solution with which the porous, electrically conductive carrier material is infiltrated according to the invention has a boiling temperature T _s and a crosslinking temperature T _N , these two temperatures depending on the composition of the solution.

The boiling temperature T _s is the temperature at which a noticeable boiling of the solution occurs. Usually, this temperature corresponds to the boiling temperature of the solvent used to prepare the solution. When using solvent mixtures or by the presence of the solutes, the boiling temperature may also be higher or lower than that of the pure solvent. The determination of the boiling temperature can be carried out by heating the solution in a conventional chemical laboratory apparatus, for example in a glass flask with reflux condenser, until the solution boils under reflux. Preferably, the determination of the boiling temperature is carried out under those atmospheric conditions under which the drying process is carried out.

The crosslinking temperature T _N is the temperature at which gelation of the solution with increase in its viscosity or precipitation of solid from the solution under turbidity is observed. The determination of the crosslinking temperature can be carried out by heating the solution in a conventional chemical laboratory apparatus, for example in a glass flask with reflux condenser. The determination of the crosslinking temperature is preferably carried out under those atmospheric conditions under which the drying process is also carried out. The solution is preferably heated at a rate of at least 1 K / min, preferably at least 10 K / min, in order to minimize the time required for heating. If the heating is too slow, crosslinking may take place in the solution at a lower temperature and distort the measured value of the crosslinking temperature. The mood should be carried out with solutions which were preferably stored for no longer than 30 days. Due to aging processes, crosslinking can also take place at a lower temperature and distort the measured value of the crosslinking temperature. According to the impregnated with the solution carrier material is dried at a drying temperature T _τ , which is smaller than the boiling temperature T _s and smaller than the crosslinking temperature T _{N of} the solution.

Since this drying process at a temperature T _{τ runs} below the boiling temperature Ts, no bubbles form from solvent vapor. The solvent evaporates only slowly from the surface of the solution. Further, since the drying temperature is lower than the crosslinking temperature, crosslinking in the solution during the drying process is avoided. The infiltrated support material is dried at the drying temperature until more than 75 wt .-%, preferably more than 90 wt .-%, of the solvent contained in the solution is evaporated. The determination of the proportion of the evaporated solvent can be carried out, for example, by weighing the support material before and immediately after infiltration and at regular intervals during the drying process. After the drying process, a layer of dried solution remains, inter alia, on the pore walls of the carrier material, the interior of the pores remaining largely free of coating material.

Inert gases (for example argon, nitrogen), hydrogen, oxygen or steam or mixtures of these gases at atmospheric pressure of 0.001 to 10 bar can be used as the atmosphere during drying.

When drying in air, the solution may come into contact with atmospheric moisture during the drying process. If necessary, this can accelerate the undesirable crosslinking process during drying and reduce the crosslinking temperature T _N. Drying in air can still lead to the formation of explosive mixtures due to contact of the solvent vapors with atmospheric oxygen, which poses a safety risk. Therefore, it may be advantageous to carry out the drying process under an inert gas atmosphere, for example under nitrogen or argon.

According to a preferred embodiment of the present invention, drying takes place at a drying temperature for which the difference in the boiling temperature of the solution minus the drying temperature T _s _{-Tτ is} between 1 and 40 K, preferably between 10 and 20 K. The drying temperature T _τ should be in this temperature range in order not to let the drying process last unfavorably long. Preferably, the drying takes less than 60 minutes, more preferably 10-30 min.

If the crosslinking temperature T _{N is} below the boiling temperature T _s , it is advantageous to carry out the drying process under reduced pressure and thus

To lower Ts. According to a preferred embodiment of the present invention Therefore, the drying of the infiltrated with the solution carrier material is carried out at reduced pressure compared to standard pressure. As a result, the boiling temperature T _{s of} the solution is reduced, optionally below the crosslinking temperature T _N , SO such that the drying temperature T _{τ can be selected} as closely as possible below the boiling temperature T _s and at the same time lies below the crosslinking temperature T _N.

Alternatively or additionally, at least one additive can be added to the solution, by means of which the crosslinking temperature T _{N of} the solution is increased. For this purpose, additives can be added to the coating solution which can undergo strong coordinative interactions with the dissolved elements. These are usually compounds that are able to form chelate complexes due to the presence of multiple coordinating functional groups. Examples of such additives are 1, 3-diketo compounds such as acetylacetone or acetoacetic ester; 1,2-diols and their ethers such as, for example, methyl glycol or butyl glycol; 1, 3-diols and their ethers such as 1, 3-propanediol; 2-aminoethanol and its derivatives; 3-aminoethanol and its derivatives; Carboxylates such as acetates or propionates, diamines such as ethylenediamine.

Preferably, the at least one additive is at least one compound having the following structure:

where n = 0, 1, 2 or 3;

X, Y are independently selected from the group consisting of

CH ₂ OR, CHO, C-OR, NRR ¹ , CHNR and C-NRR ¹

R, R ¹ are independently selected from the group consisting of H, methyl, ethyl, n-propyl, iso-propyl, n-butyl, i-butyl, sec-butyl and tert-butyl.

According to one embodiment of the present invention is carried out after drying, a thermal aftertreatment of the infiltrated and dried support material at temperatures between 200 and 600 ⁰ C, preferably between 250 and 400 ⁰ C (pyrolysis). The pyrolysis is preferably carried out in an air atmosphere or a water vapor saturated air or inert gas atmosphere. This thermal aftertreatment at 200 to 600 ⁰ C is used to be removed, the organic components largely NEN. In the process, the dissolved inorganic components crosslink to form an amorphous preceramic material.

According to a preferred embodiment of the present invention, a thermal aftertreatment of the infiltrated and dried support material is carried out at temperatures between 500 and 1500 ⁰ C, preferably between 600 and 900 ⁰ C (calcination or crystallization). The remaining carbon-containing components are degraded and the resulting metal oxide sinters to a dense ceramic layer on the substrate.

Inert gases (for example argon, nitrogen), hydrogen, oxygen or water vapor or mixtures of these gases at an atmospheric pressure of 0.001 to 10 bar can be used as the atmosphere.

In this way, thin films of preferably 5 to 30 nm in thickness are obtained on the entire inner and outer surfaces of the porous support material. In so doing, as much as possible, the complete inner and outer surfaces should be included to ensure maximum capacitance of the capacitor.

After drying, a two-stage thermal post-treatment (pyrolysis and calcination) or directly a one-stage thermal post-treatment (calcination) can take place.

According to one embodiment of the present invention, the infiltration, drying and thermal aftertreatment are repeated several times.

To set the desired layer thickness of advantageously 50 to 500 nm, particularly preferably 100 to 300 nm, the infiltration and the drying process or the entire coating process (including thermal aftertreatment) are repeated several times if necessary, for example up to 20 times.

There are the following variants of the repetition:

1. the infiltration and the drying process

2. the infiltration, the drying process and the pyrolysis step at 200 to 600 ⁰ C.

3. the infiltration, the drying process, the pyrolysis step and the thermal post-treatment at 500 to 1500 ⁰ C.

The variants 2 and 3 are preferred. To save time and energy, the coating need not be fully calcined at each high temperature repeat such as 800 ^° C. A comparable quality of the coating is also achieved if the coating initially only at low temperature, for example at 200 to 600 ⁰ C, more preferably at about 400 ° C, annealed and only after completion of all repetitions of the coating process at high temperature, such as described above, is completely calcined.

To improve the electrical properties of the dielectric, it may be necessary to carry out a further temperature treatment after sintering at a temperature between 200 and 600 ⁰ C under an atmosphere with an oxygen content of 0.01% to 25%.

In an exemplary embodiment, the coating according to the invention of a porous, electrically conductive carrier material with a dielectric is carried out as follows:

The precursor compounds of the dielectric to be used according to the invention are dissolved in the usual manner at the same time or successively or first individually, optionally with cooling or with heating, in the solvent (s). The preparation of such solutions is described in the literature, for example in R. Schwartz "Chemical Solution Deposition of Ferroelectric Thin Films" in Materials Engineering 28, Chemical Processing of Ceramics, 2nd ed., 2005, pp. 713-742 Excess solvent is distilled off, if necessary by means of a rotary evaporator, until the desired concentration of the solution has been reached, and finally the solution for the removal of suspended particles is advantageously filtered.

In this solution, the porous moldings are immersed. In addition, a vacuum of 0.1 to 900 mbar, preferably of about 100 mbar, can be applied over 0.5 to 10 minutes, preferably about 5 minutes, and then re-aerated to remove trapped air bubbles. The impregnated moldings are removed from the solution and excess solution is drained off. The moldings are then dried, preferably over 5 to 60 min at 50 to 200 ⁰ C, wherein the drying temperature is below the crosslinking temperature and the boiling temperature and the time is chosen so that more than 75 wt .-% of the solvent is evaporated. Thereafter, the moldings are hydrolyzed for 5 to 60 min at 300 to 500 ⁰ C, for example, under humid nitrogen. Finally, over 10 to 120 min at the next temperatures specified above, advantageously calcined under dry nitrogen.

The sequence of impregnating / drying / calcining is repeated if necessary until the desired layer thickness is reached.

The coatings prepared by the method described above have a closed and low-defect layer of the dielectric on almost the entire inner and outer surfaces of the substrate.

For the purposes of this invention, a coating is lacking in definition if the specific resistance of the coating is more than 10 ⁸ Ω-cm, preferably more than 10 ¹¹ Ω-cm. The resistance of the coating can be determined, for example, via impedance spectroscopy. If the specific surface of the support is known (usually determined by BET measurement) and the coating layer is known (usually determined by electron microscopy), the measured resistance can be converted into resistivity in a manner known to the person skilled in the art.

The coatings of the invention can be used as a dielectric in a capacitor.

On the dielectric, a second electrically conductive layer is preferably applied as a counter electrode. In the state of the art, this can be any electrically conductive material usually used for this purpose. For example, manganese dioxide or electrically conductive polymers such as polythiophenes, polypyrroles, polyanilines or derivatives of these polymers are used. A better electrical conductivity and thus lower internal resistance (ESR, equivalent series resistance) of the capacitors is achieved by applying metal layers as a counter electrode, for example copper according to DE-A-10325243.

The contacting of the counterelectrode from the outside can likewise be carried out according to the prior art by any technique usually used for this purpose. For example, the contacting can be effected by graphitization, application of conductive silver and / or soldering. The contacted capacitor can then be encapsulated for protection against external influences.

The capacitors produced according to the invention have a porous, electrically conductive carrier, on the almost complete inner and outer surface of which a closed and defect-poor layer of a dielectric and an electrically conductive layer are applied. The capacitors produced according to the invention exhibit an improved capacitance density in comparison with the conventional tantalum capacitors or ceramic multilayer capacitors and are thus suitable for the storage of energy in a wide variety of applications, especially in those requiring a high capacitance density. Their manufacturing methods allow a simple and economical production of capacitors with significantly larger dimensions and correspondingly high capacity.

Such capacitors may be used, for example, as smooth or storage capacitors in electrical engineering, as coupling, screening or low-storage capacitors in microelectronics, as replacement for secondary batteries, as main energy storage units for mobile electrical appliances, e.g. Power tools, telecommunications applications, portable computers, medical devices, for uninterruptible power supplies, for electric vehicles, as complementary energy storage units for electric vehicles or hybrid vehicles, for electric elevators, as buffer energy storage units for covering wind power fluctuations, Solar, solar thermal or other power plants find employment.

Reference to the drawings, the invention will be explained in more detail below.

Show it:

FIGS. 2 a to 2 d schematically show the sequence of a coating method according to the invention,

2a shows a section of the pore space of a porous, electrically conductive carrier material 1. After the infiltrating of the carrier material 1 with a solution 2 containing precursor compounds of a dielectric and at least one solvent, the pores of the carrier material 1 (in particular the pore 16 shown) completely filled with the solution 2.

FIG. 2b shows a detail of the pore volume of the carrier material according to FIG. 2a during drying. According to the invention the drying of the infiltrated with the solution 2 support material 1 at a drying temperature T takes place _τ, which is less than the boiling temperature of T ₅ and the crosslinking temperature T _N of the solution. 2 Since the drying process at a temperature T _{τ is} below the boiling temperature T _s , no bubbles form from solvent vapor. The solvent 12 evaporates only slowly from the surface (from outside to inside in the pore 16). According to the invention, the drying at _T.sub.τ takes place until the major part of the material in the coating solution 2 contained solvent 12 is evaporated, preferably until more than 90% by weight of the solvent 12 is evaporated.

FIG. 2c shows the section according to FIGS. 2a and 2b after the drying process. In the pore 16 remains a film of dried coating solution 13 on the pore walls 17. The interior 14 of the pore 16 remains free of coating material.

2d shows the detail according to Figures 2a-2c, after a thermal post-treatment of the infiltrated and dried substrate 1 (calcination at temperatures between 500 ⁰ C and 1500 ⁰ C) was carried out. There remains a continuous film 15 of the ceramic material on the pore walls 17 (dielectric 18).

Examples

An example of a process according to the invention uses a solution with 1 mol of barium (II) aminoethylate 0.2 mol of 2-aminoethanol

1 mol of titanium (IV) butylate

2 moles of acetylacetone.

With the solvent butyl glycol, the solution is adjusted to a concentration of 5 wt .-% calculated on BaTiO ₃ (the product of calcination).

The crosslinking temperature T _N is 159-160 ⁰ C. The boiling point T _s is 169-171 ⁰ C.

After infiltration of the support material, a porous nickel support with a porosity of 65% and a specific surface area of 0.15 g / m ² , the samples are dried for 30 minutes at a temperature of 150 ⁰ C. This gives a uniform pore-free film.

Further examples can be found in the following table.

All solutions were adjusted to a concentration of 5% by weight, calculated on BaTiO ₃ as the calcination product.

LIST OF REFERENCE NUMBERS

I porous support 2 solution

3 bubbles

4 networking

5 solidification of material = preceramic material

6 pores in the solidified material 7 uncoated areas of the pore walls

8 deposition of material

9 ceramic film

10 particles

I 1 deposit of material 12 solvent

13 dried solution

14 Inside the pore

15 ceramic material

16 pore 17 pore walls

18 dielectric

Claims

claims

1. A method for producing a coating of a porous, electrically conductive 5 gene carrier material (1) with a dielectric (18), characterized by the

Steps:

Infiltrating the carrier material (1) with a solution (2), the precursor compounds of the dielectric (18) and at least one solvent (12)

10 holds and which has a boiling temperature T _s and a crosslinking temperature T _N , and

• drying of the solution (2) infiltrating the carrier material (1) _τ at a drying temperature T that is less than the boiling point T _s and small

15 ner than the crosslinking temperature T _{N of} the solution (2) is up to more than 75

Wt .-% of the solvent (12) is evaporated.

2. The method according to claim 1, characterized in that the solution (2) is added at least one additive through which the crosslinking temperature

20 T _{N of} the solution (2) is increased.

3. The method according to claim 2, characterized in that the at least one additive is at least one compound having the following structure:

where n = 0, 1, 2 or 3;

X, Y are independently selected from the group consisting of

CH ₂ OR, CHO, C-OR, NRR ¹ , CHNR and C-NRR ¹ oU

and R, R ^{1 are} independently selected from the group consisting of H, methyl, ethyl, n-propyl, iso-propyl, n-butyl, i-butyl, sec-butyl and tert-butyl. 35

4. The method according to any one of claims 1 to 3, characterized in that the drying takes place at reduced pressure compared to standard pressure.

5. The method according to any one of claims 1 to 4, characterized in that the drying takes place at a drying temperature for which the difference of the boiling temperature minus the drying temperature of the solution T _s - T _{τ is} between 1 and 40 K.

6. The method according to any one of claims 1 to 5, characterized in that after drying, a thermal aftertreatment of the infiltrated and dried support material (1) takes place at temperatures between 200 and 600 ⁰ C.

7. The method according to any one of claims 1 to 6, characterized in that a thermal treatment of the infiltrated and dried support material (1) takes place at temperatures between 500 and 1500 ⁰ C.

8. The method according to any one of claims 6 or 7, characterized in that the infiltration, drying and the thermal aftertreatment are repeated several times.

9. Use of the coating produced according to the method of any one of claims 1 to 8 as a dielectric (18) of a capacitor.

10. A capacitor, characterized by a porous, electrically conductive carrier (1), on the inner and outer surface of a first layer of a dielectric (18), prepared by a method according to any one of claims 1 to 8, and applied a second electrically conductive layer is.