DE10145728A1 - Production of dielectric capacitor ceramic, used in production of capacitor, comprises forming pourable slip from mixture containing powered barium titanate components and powdered fluxing agent, and sintering - Google Patents

Abstract

Production of a dielectric capacitor ceramic comprises forming a pourable slip from a mixture containing: (A) a powered barium titanate component having a grain diameter of less than 1 micro m, (B) a powered barium titanate component having a larger grain diameter than A and (C) a powdered fluxing agent having a grain size of less than 1 micro m; and sintering at less than 1000 deg C. Preferred Features:. Component (A) is doped with Bi, Nb, Zn and/or Nd. Component (B) is doped with Bi and/or Nb. The mixture contains up to 42.5 wt.% (A) with a grain size of 0.6 mu m, up to 42.5 wt.% (B) with a grain size of 1.2 micro m and 4 wt.% (C) with 11 wt.% dopants.

Description

State of the art

The invention is based on a method for producing dielectric capacitor ceramic according to the genus of Main claim.

Such dielectric ceramics are used in particular in Capacitors with a high dielectric constant. Because of small outer dimensions and the existing requirement after large capacitance values, these capacitors built up in layers, the capacitor electrodes for the most part come to lie within the dielectric ceramic material. As a result, the electrode material also becomes high Exposed to sintering temperatures used to manufacture the ceramic required are. So an electrode material is required, which at does not damage the given sintering temperatures. Without Measures to reduce the necessary, especially for barium titanate For this purpose, an electrode material must be used at high firing temperatures can be used that has a melting point above the  Sintering temperature. Such materials are platinum and palladium.

However, since these materials are a significant cost factor in the Manufacturing capacitors, efforts are being made to Take measures to reduce the sintering temperature of dielectric To reduce capacitor ceramic, so cheaper materials for Manufacture of lower capacitor electrodes Melting points can be used. In the present case there are efforts to reduce the palladium content of a silver Lower palladium mixture for use as an electrode paste.

A process for producing a ceramic registered in 1965 Dielectric with barium titanate components, in which one Reduction of the sintering temperature of the ceramic to values of 780 ° C can be reached up to 960 ° C is described in DE patent 16 46 941. This goal is achieved through a mixture of barium titanate, Strontium titanate, lead titanate, strontium stannate and from borates. This NDK material has a linear temperature coefficient and one DK of about 100. The use of higher proportions of lead leads this leads to a very large environmental impact.

DE patent 26 59 016 describes how the addition of 1 mol% CuO and 1 mol% GeO ₂ to barium titanate can reduce its sintering temperature to 1000 ° C. A reduction in the sintering temperature from BaTiO ₃ to 1050 ° C is possible if 0.5 mol% Cu and 0.5 mol% Ti are added to the barium titanate. And at 1030 ° C, a mixture of (Ba _0.9 Ca _0.1 ) TiO ₃ and 0.5 mol% TiO ₂ can be sintered to form a dielectric capacitor ceramic. At the same time, the temperature dependence of the DK increases above 100 ° C. In this way, however, it is only possible to reduce the palladium content of the silver-palladium mixture to approximately 25%, which is why the electrodes produced in this way are still very expensive.

Many attempts have been made to increase the salary environmentally harmful lead in barium titanate ceramics To lower the sintering temperature in order to avoid palladium as Save electrode material manufacturing costs. For example. is in the DE Patent specification 35 20 839 as described by mixtures of various Lead alloys lowered the sintering temperature to 900 ° C to 1100 ° C can be. These materials have DK values from 3500 to 19,000, but their temperature dependencies are very strong (Y5V).

DE-PS 35 29 933 also uses low sintering temperatures, however, in the case of piezoelectric materials, achieved in that Mixtures of lead oxides with non-lead oxides are used being mentioned as a non-lead metal barium. Reached sintering temperatures of 800 ° C to 1300 ° C.

DE-PS 35 41 517 describes how a reduction in Palladium content of a silver-palladium alloy by a Reduction of the firing temperature of the capacitor ceramic (DK <800 Y5V characteristics) can be achieved at values from 900 ° C to 1100 ° C can by adding a mixture of lead alloys to the barium alloy is added.

According to DE-PS 38 34 778, a waiver of palladium is said to be Reduction of the firing temperature to 950 ° C to 1050 ° C with the help of a Mixture of lead alloys can be achieved, u. a. Barium titanate is used as the starting material. This also affects electrical materials with a high DK (<4000), but also very strong temperature dependence.

Likewise in DE-PS 41 41 648 is a lead barium zirconium titanate Compound described with the low sintering temperatures (~ 1150 ° C) can be reached, so that palladium as electrode material in  reduced amount can be used.

DE 44 44 812 describes a ceramic dielectric based on BaTiO ₃ with X7R properties, which can be sintered at 900 ° C. This is achieved by applying a lead perovskite layer around the BaTiO ₃ core and embedding the core treated in this way in lead borosilicate glass. A flat temperature curve of the DK is achieved, however with DK values from 320 to 400.

Ultimately, the European patent document EP 257 653 also refers to the Use of environmentally harmful lead in bismuth-free Barium titanate ceramics based on barium titanate and lead zinc Magnesium niobate noted, thereby lowering the Sintering temperature to 1070 ° C to 1100 ° C and thus a reduction in Palladium content to 25% is achievable.

Furthermore, it is from US-PS 3,619,744, from DE-OS 32 37 571, from the DD-PS 2 58 915, from EP-publication 169 636 and from US-PS 4 499 521 known, low-sintering X7R materials based on Barium titanate with an addition of bismuth titanate or to produce bismuth-rich mixtures of glass-forming oxides. It will dielectric constant from 1800 to 2600. hereby the sintering temperature can be reduced to 1120 ° C, so that a Electrode paste made of 70% silver and 30% palladium can be used. A further lowering the sintering temperature and thus another Reduction in the palladium content of the electrode paste is due to this Way not possible.

This was done according to DE-OS 196 38 195 with a lead-free, dielectric Paste for LTCC multilayer circuits achieved from one Barium titanate nanopowder with a grain size between 0.05 µm and 0.5 µm exists at temperatures between 800 ° C and 1000 ° C can be sintered. One made with this nanopowder  However, capacitor ceramic has the disadvantage that it is high Depends on temperature and has no X7R characteristics, i.e. H., that at temperatures between -55 ° C and + 125 ° C the Capacitance deviation of capacitors made with it is significant is greater than ± 15%. The capacitor ceramic also has a Dielectric constant of little more than 200.

The invention and its advantages

The inventive method for producing dielectric Capacitor ceramic with the characteristic features of the In contrast, the main claim has the advantages of an X7R To have characteristics, d. that is, at temperatures between -55 ° C and + 125 ° C the dielectric constant of the ceramic and thus the Capacitance of the capacitors manufactured with it by less than ± 15% vary. Component A also leads to the production of Ceramics used raw materials because of their coarser Grain to a very high dielectric constant. In contrast, Component B is due to its finer grain size for a low one Sintering temperature of the ceramic of below 1000 ° C is responsible for what it allows to manufacture capacitors whose electrodes only have a very low proportion of palladium.

According to an advantageous embodiment of the invention Component A provided with dopants, and are called dopants Bismuth and / or niobium used. This will make the ferroelectric properties of component A and thus you Contribution to increasing the dielectric constant further improved.

According to a further advantageous embodiment of the invention Component 13 provided with dopants and are called dopants Bismuth, Niobium, Zinc and / or Neodyn are used, which makes the paraelectric properties of component B can be improved.  

According to a further advantageous embodiment of the invention the one to be processed into a castable slip 42.5% powder mixture from component A with a grain size of 1.2 µm, 42.5% from component B with a grain size of 0.6 µm, 4% from component C and 11% from dopants. As a result, in addition to the X7R temperature characteristic Dielectric constant of 1800 and a decrease in Sintering temperature reached 960 ° C, which makes it possible at the Manufacture of multilayer capacitors using electrodes which consist only of 10% palladium and 90% silver.

According to a further advantageous embodiment of the invention the one to be processed into a castable slip 44% powder mixture from component A with a grain size of 0.8 µm, 42% from component B with a grain size of 0.07 µm 6% from component C and 8% from dopants. This will help Maintaining the X7R temperature characteristic a further increase in Dielectric constant to 2500 and a further reduction in the Sintering temperature reached 900 ° C, so that at this Material variant is possible in the manufacture of capacitors Use electrodes that no longer contain any palladium.

Further advantageous embodiments of the invention are the following example description and the claims removable.

Description of the embodiments

Some exemplary embodiments of the method according to the invention are explained in more detail below.

The starting material used in the method according to the invention  consists of two components, namely component A, the for the ferroelectric properties of the ceramic, d. that is, for a spontaneous polarization without an external field is responsible, and out a component B, the formation of the paraelectric phases serves the ceramics, d. that is, which causes the ceramic under the Effect of an external electrical field is well polarized. moreover component B is therefore for a low sintering temperature responsible that the particle size of powder component B to extends into the nanometer range, and that they are suitable additives on low melting and recrystallizing compounds or Fluxes has.

Here, powder component A does its job for a high To care for dielectric constant, in that their Grain size is between 0.5 µm and 1.2 µm. In addition, the Component A of the barium titanate for this purpose with dopants be provided, such as with bismuth (Bi) or niobium (Nb). Otherwise it can be used for possible applications in High temperature range contain additional dopants are suitable to increase the Curie point to higher temperatures shift, such as lead (Pb).

To improve the paraelectric properties of the component B can contain dopant components, such as bismuth (Bi), Niobium (Nb), zinc (Zn) or neodyn (Nd). In addition, to achieve the grain size of component B at a low sintering temperature 0.6 µm or less.

To achieve the advantageous properties of the invention Barium titanate ceramic becomes a little less than 50% of component A used with or without dopants, such as bismuth (Bi), niobium (Ni) or lead (Pb) is provided and a grain size between 0.5 microns and 1.2 µm. Component B also becomes a little less  than 50% of with neodyn (Nd), zinc (Zn), niobium (Nb) or also with lead (Pb) doped barium titanate used, which has a grain size of very has much less than 1 µm. Finally, the third component is C a little less than 8% of a flux with a grain diameter of less than 1 µm.

To prepare the dielectric ceramic, the Barium titanate components A and B together with the dopants and the flux C in an aqueous or organic medium mixed and processed into a pourable slip. Alternatively, the barium titanate components that Dopants and the flux via a chemically adjustable Coating process homogenized and into a pourable slip be dispersed. The slip is then used to manufacture the Multi-layer capacitors used. After completion their capacity, dissipation factor, insulation resistance and the Temperature dependence of the electrical values at temperatures measured between -55 ° C and + 125 ° C.

Based on the following two exemplary embodiments The method according to the invention explained in more detail.

In Example 1, as component A, 42.5% by weight of BaTiO ₃ with a grain size of d = 1.2 μm, as component B, 42.5% by weight of BaTiO ₃ with a grain size of d = 0.6 μm, 11% dopant and used as component C 4% of a flux. Components A, B and C are mixed, ground in a 20 liter porcelain mill in an organic binder system for 90 hours. The aim of this is to achieve good enamel quality. Finally, the slurry is further processed to multilayer capacitors at a sintering temperature of 960 ° C., using an electrode paste made of 90% silver and 10% palladium. This achieves capacitors with a dielectric constant of DK = 1800, a DF value of 2%, an RC value of more than 10 ⁴ sec. At 25 ° C, an X7R temperature characteristic, a layer thickness of 13 µm after sintering and a breakdown voltage of 900 V.

In Example 2, component A contains 44% by weight of BaTiO ₃ with a grain size of d = 0.8 μm, component B contains 42% by weight of BaTiO ₃ with a particle size of d = 0.07 μm, 8% dopant and used as component C 6% of a low melting compound. The chemically homogenized material components with the finest particle sizes are dispersed over a period of 6 hours. The slip is then further processed to multilayer capacitors at a sintering temperature of 900 ° C., using an electrode paste made of 90% silver and 10% palladium. This makes it possible to achieve capacitors with a dielectric constant DK = 2500, a DF value of 2.2%, an RC value of 104 seconds at 25 ° C, an X7R temperature characteristic, a layer thickness of 6 µm and a breakdown voltage after sintering of 700 V. With this material variant it is possible to use palladium-free electrodes.

As the exemplary embodiments show, there are two principal ones Possibilities of producing the barium titanate ceramic, namely for one in the traditional way by blending the Individual components as aqueous or organic slip, which in must be ground in a mill, and secondly over one chemical manufacturing process, especially by means of a chemical regulated coating process. The one made in this way Capacitor ceramic has that over the prior art Advantages of being sintered at temperatures well below 1000 ° C can have an X7R characteristic with Dielectric constant between 1800 and 3000, a high one Reliability of materials through better mastery of grain and to achieve grain boundary chemistry and simple  Possibilities of adapting the material properties to the required ones Temperature application areas, such as high temperature applications to offer.

All in the description and in the following claims Features shown can be both individually and in any Combination with each other be essential to the invention.

Claims (5)

1. A method for producing dielectric capacitor ceramic, in which a component B made of powdered barium titanate is used, the grains of which have a diameter of less than 1 μm, characterized in that
that a further component A made of powdered barium titanate is used, the grains of which have a larger diameter than the grains of component B,
that a powdery flux whose grains have a diameter of less than 1 μm is used as further component C.
that components A, B and C are used to produce a pourable slip which consists of less than 50% of component A, less than 50% of component B and less than 8% of component C, and
that the slip is sintered at a temperature of less than 1000 ° C. 2. The method according to claim 1, characterized in that the Component A is provided with dopants, and that as dopants Bismuth and / or niobium can be used. 3. The method according to claim 1 or 2, characterized in that  component B is provided with dopants, and that as dopants Bismuth, niobium, zinc and / or neodyn can be used. 4. The method according to claim 3, characterized in that the to a pourable slurry to be processed into a powder mixture 42.5% from component A with a grain size of 1.2 µm, 42.5% from component B with a grain size of 0.6 µm, 4% Component C and consists of 11% dopants. 5. The method according to claim 3, characterized in that the to a pourable slurry to be processed into a powder mixture 44% from component A with a grain size of 0.8 µm, 42% from Component B with a grain size of 0.07 µm, 6% Component C and consists of 8% dopants.