WO2002004379A2

WO2002004379A2 - Sintered, electrically conductive material, ceramic multilayer component comprising this material, and method for the production thereof

Info

Publication number: WO2002004379A2
Application number: PCT/DE2001/002513
Authority: WO
Inventors: Friederike Lindner; Leonore Schwegler; Alfons Kelnberger
Original assignee: Robert Bosch Gmbh
Priority date: 2000-07-11
Filing date: 2001-07-06
Publication date: 2002-01-17
Also published as: DE10033588A1; DE10033588C2; DE20022469U1; WO2002004379A3

Abstract

The invention relates to a sintered, electrically conductive material, which is made from a starting mixture containing a powdery metallic starting constituent and an organic starting constituent. After sintering, the organic starting constituent (21) encloses the powder particles (20, 20') of the metallic starting constituent in the form of a layer (21') that is at least largely carbonized into carbon. The invention also relates to a ceramic multilayer component (5), especially a piezo actuator, and to a method for the production thereof. The multilayer component (5) comprises a plurality of ceramic insulating layers (11'), which are arranged one above the other and which are separated from one another at least in areas by means of inner electrode layers (10') that are made of the electrically conductive material. The inventive method involves the preparation of the starting mixture, the preparation of a plurality of laminatable ceramic green films (11), an at least one side flat application of the starting mixture to the surface of the ceramic green films (11), the stacking of the ceramic green films (11), which are provided with the starting mixture, to form a multilayer green body, the releasing of the multilayer green body and the sintering of the multilayer green body to form the ceramic multilayer component (5).

Description

Sintered, electrically conductive material, ceramic multilayer component with this material, and method for its production

The invention relates to a sintered, electrically conductive material, in particular for use as an inner electrode material in a ceramic multilayer component, a ceramic multilayer component with such a material, and a method for producing such a ceramic multilayer component according to the preamble of the independent claims.

State of the art

Ceramic piezo actuators, which consist of a multiplicity of thin, ceramic, piezoactive layers, which are each separated from one another via inner electrode layers and can be electrically contacted and controlled via them, are widely known. For this purpose, reference is made, for example, to the application DE 199 51 016.4.

In particular, such piezo actuators often consist of a PZT ceramic, that is to say of a ceramic based on

P (Ti _x Zr ^ _ _x ) O3 with 0.4 <x <0.6, in the form of sintered piezoactive layers with inner electrodes or inner electrode layers arranged between them. The piezoactive layers experience this when an external electrical voltage is applied to the inner electrode layers the inverse piezo effect a stretching or compression. With typical control voltages from 100 volts to 300 volts, the change in length that occurs is in the range from 0.1% to 0.3%.

A material is required as the inner electrode material in a ceramic multilayer component in the form of a piezo actuator, which both debinds the ceramic green foils initially used, i.e. the burning of the organic components contained in the green foils under an oxygen or air atmosphere, as well as the subsequent sintering process withstands typical temperatures from 950 ° C to 1100 ° C. In the simplest case, this means that the inner electrode material must both be stable to oxidation and must have a melting point that is higher than the maximum sintering temperature used.

For this reason, noble metals or noble metal alloys, in particular in many cases a silver-palladium alloy with a composition of 70% by mass of silver and 30% by mass of palladium, have been used as the inner electrode material. Such an Ag-Pd alloy is less expensive than platinum and has a melting point that is still sufficiently high for sintering.

On the other hand, despite their sufficiently high melting point and controllable oxidation behavior, Ag-Pd alloys have the disadvantage that there is a diffusion of silver in the course of the cofiring process of the ceramic green sheets with the PZT ceramic and the Ad / Pd inner electrode material comes into the PZT ceramic, whereby the silver is built into the Pb positions in the PZT ceramic, which leads to an impairment of the electromechanical properties of the PZT ceramic. Another disadvantage is that when large amounts of silver are diffused into the PZT ceramic, silver secondary phases can form after silver saturation has been reached, which reduces the specific electrical resistance of the PZT material, which is electrically insulating as a whole, and ultimately leads to undesired ones electrical breakdowns in the ceramic insulation layers of the ceramic multilayer component can result. These undesirable effects become more apparent the higher the proportion of silver in the inner electrode material.

In addition, since the silver-palladium alloy used is still an expensive raw material due to the relatively high palladium content, it is desirable to either drastically reduce the noble metal content in the inner electrode material used, or to replace it entirely with a less expensive material.

Advantages of the invention

The sintered, electrically conductive material according to the invention has the advantage over the prior art that it can be used in a ceramic multilayer component, for example a piezo actuator, as the inner electrode material, it being distinguished in particular by the fact that the powdery metallic starting component contained therein can also be a base metal or a base metal alloy. The organic component added before the sintering of the starting mixture ensures that it surrounds the powder particles of the metallic starting component at least largely in the form of an at least largely carbonized layer during and after the sintering, so that the powder particles are at least largely protected against oxidation. In this respect, after the sintering of the starting mixture, the material according to the invention is in the form of a two-phase material with a metallic phase and a carbon phase at least largely surrounding this metallic phase.

The ceramic multilayer component provided with such a sintered, electrically conductive material in the form of inner electrode layers has the advantage that inner electrode layers made of this material are initially significantly cheaper than known inner electrode materials, and furthermore the problem that arises when using silver-palladium alloys the diffusion of silver into neighboring ceramic insulation layers does not occur. Thus, through the use of the material according to the invention, well-conductive inner electrode layers are formed between the ceramic insulation layers in the ceramic multilayer component, which are comparable in terms of their electrical conductivity to known inner electrode layers.

Advantageous developments of the invention result from the measures mentioned in the subclaims.

It is particularly advantageous if copper, nickel or an alloy of copper with nickel is used as the powdery metallic starting component for the electrically conductive material. The use of copper has proven to be particularly advantageous since copper is a very good conductor and at the same time relatively inexpensive.

However, it should be emphasized that in addition to copper and nickel, other metals or metal alloys are also suitable, provided that they have good electrical conductivity and, if possible, rings have a tendency to oxidize, and are compatible with the material of the ceramic insulating layers, for example PZT ceramic.

In addition, to prevent oxidation during the debinding or the subsequent sintering, it is advantageous if the powdery metallic starting component is used in the form of a highly crystalline metal powder which is already in the starting mixture with a high-temperature stable organic protective layer from the one used organic starting component has been provided. In this context, a high-temperature-stable protective layer is understood to mean a material which, in contrast to the organic constituents in the ceramic green sheets, which later form the ceramic insulation layers, is not or only slightly thermally decomposed under the process conditions prevailing during debinding.

In particular, the organic starting component which initially forms the organic protective layer around the highly crystalline metal powder is a material which is not or only slightly thermally decomposable up to a temperature of 350 ° C., in particular in an oxygen-containing gas atmosphere. It has turned out to be particularly advantageous if the organic starting component is a polyimide, a polybenzoxazole, a polyether, a polycarbonate or a polyketone.

Because the powdery metallic starting component in the starting mixture for the electrically conductive material is provided with a protective layer made of the organic starting component, this initially protects the metallic powder particles during the debinding at least against complete oxidation, and on the other hand pyrolyzes during the subsequent one Sintering process at low oxygen partial pressure or with complete exclusion of oxygen to carbon.

The use of a binder organic which can be thermally decomposed at relatively low temperatures in the ceramic

Green foils and an organic protective coating of the powder particles of the metallic starting component that can only be decomposed at significantly higher temperatures thus have the essential advantage that the metal powder is initially protected by the more heat-resistant organic coating during debinding. As soon as the debinding of the ceramic green foils is then completed, by switching to a low-oxygen or completely oxygen-free gas atmosphere, for example a nitrogen atmosphere, the organic protective coating is achieved in the following temperature range of approx. 400 ° C to 700 ° C carbonized from the organic starting component due to a lack of oxygen around the metallic powder particles, so that an electrically conductive material is formed which can be used in the ceramic multilayer component as an electrode layer made of metal and carbon.

The carbon in the inner electrode layer or in the sintered, electrically conductive layer is impaired

Material does not adversely affect the conductivity of the material obtained, and also shows no or only a negligible tendency to diffuse into adjacent ceramic layers, so that this inner electrode material does not cause any undesired contamination or no undesired doping of adjacent ceramic insulation layers.

The protective layer surrounding the metallic starting component in the form of a layer which is at least largely carbonized to carbon also has the advantage that it reduces renden character, so that in the temperature range that usually has to be run through in the sintering process, the carbon formed by coking reduces a metal oxide possibly initially formed from the metallic starting component again to metal. At the same time, this carbon only reduces lead oxide in acceptable small amounts, while titanium dioxide, barium oxide and zirconium dioxide are not reduced.

drawings

The invention is explained in more detail with reference to the drawings and in the description below. FIG. 1 shows a ceramic multilayer component with a multiplicity of ceramic insulation layers and inner electrode layers and FIG. 2 explains the production of this ceramic multilayer component starting from a multilayer green body during debinding and subsequent sintering.

embodiments

The production of the sintered electrically conductive material is explained using the example of the production of a ceramic multilayer component in the form of a piezo actuator, in which this sintered electrically conductive material forms the inner electrode layers.

For this purpose, a starting mixture is first prepared in the form of a paste, which contains a powdery metallic starting component and an organic starting component. The proportion of the metallic starting component in the starting mixture is 30% by weight to 70% by weight. The mixture of metallic and organic starting component is further a solvent such as terpineol or an alcohol and optionally other components such as long-chain ethers or ester added, so that after a final mixing, a paste-like starting mixture is formed, in which the powder particles of the metallic starting component are at least largely provided with a surface coating made of the organic starting component.

In detail, in the exemplary embodiment explained, the powdery metallic starting component is a highly crystalline copper powder with an average particle size of 100 nm to 10 μm. In the example explained, a polyimide with a thermal decomposition temperature in an oxygen atmosphere of more than 350 ° C. is used as the organic starting component. In this way it is ensured that the organic starting component is not or only slightly thermally decomposed during the debinding of the multilayer green body produced later at temperatures of up to 350 ° C.

In addition, it should be emphasized that the surface coating of the copper powder used with the polyimide can take place both before the preparation of the paste-like starting mixture and in situ during the production of the paste. Finally, instead of the copper powder used, it is also possible to use a different, preferably highly electrically conductive non-precious metal or a highly electrically conductive non-noble metal alloy whose melting point is above the temperatures that occur during the subsequent sintering. In particular, non-noble metals or non-noble metal alloys whose melting point is more than 1100 ° C. are preferred.

In addition to the starting mixture explained above as a preliminary product for the inner electrode layers in the ceramic multilayer component to be produced, a number of known, laminable ceramic green foils are also used prepared which, in addition to a binder and a solvent as ceramic component, contain a PZT ceramic of the composition Pb (Zr _x Tiι_ _x ) O3 with 0.4 <x <0.6. In addition, dopants such as rare earth metals, alkali metals and / or alkaline earth metals with a typical proportion of less than 8 mol% can also be added to these ceramic green films in a manner known per se.

Now that on the one hand the starting mixture for the inner electrode layers to be formed and on the other hand the ceramic green foils for the ceramic insulation layers to be formed have been prepared, the pasty starting mixture is applied to the surface of the prepared ceramic green foils at least on one side and at least in some areas. The ceramic green sheets thus provided with the starting mixture are then stacked to form a multi-layer green body, which is then laminated and debindered. The debinding takes place in an air atmosphere at the lowest possible temperatures of, for example, 100 ° C. to 350 ° C., in particular 100 ° C. to 200 ° C., so that organic constituents such as binders, solvents and plasticizers and / or also contained in the ceramic green sheets In addition to the organic starting component, any organic constituents that may be present in the starting mixture, in particular binders, solvents and plasticizers, at least largely volatilize and / or thermally decompose.

After the lamination and debinding of the multi-layer green body has been completed, this green body is sealing-sintered to form a ceramic multi-layer component 5 according to FIG. 1, which begins at a temperature of 400 ° C. and which ends at a temperature of 1100 ° C. This sealing sintering continues under low oxygen partial pressure, preferably, however, with the complete exclusion of oxygen, for example in a pure nitrogen atmosphere.

In this way, it is achieved that the organic starting component in the starting mixture, which has been applied to the surface of the ceramic green foils to form inner electrode layers, at least largely cokes to carbon due to lack of oxygen, which encloses the highly crystalline copper powder particles.

Overall, as shown in FIG. 1, a ceramic multilayer component 5 is formed from a regular sequence of ceramic insulating layers 11 ^angeordneten arranged one above the other, which at least in regions consist of internal electrodes 10 made of the sintered electrically conductive material produced in the manner explained.

The thickness of the insulating layers 11 according to FIG. 1 is between 50 μm and 130 μm, while the inner electrode layers 10 ^{Λ have} a thickness of 0.5 μm to 5 μm. A thickness of the inner electrode layers 10 ^Λ of approximately 1 μm to 2 μm is preferred.

The polyimide used as the organic starting component ensures that it converts to carbon in the temperature range from 400 ° C to 700 ° C by coking.

FIG. 2 once again explains the process sequence described above for producing the ceramic multilayer component 5, starting from a multilayer ceramic green body. It is shown that at a temperature of approximately 20 ° C. there is initially a multi-layer green body consisting of a sequence of stacked ceramic green foils 11 with electrode paste 10 located between them. The electrode paste 10 is the paste produced with the starting mixture for the electrically conductive material. It is further shown in FIG. 2 that the electrode paste 10 contains coated powder particles 30 which consist of a metallic powder particle 20 which is provided on the surface with an organic starting component 21, polyimide in the example explained.

FIG. 2 further shows that the debinding of the ceramic green body initially produced is completed at approximately 400 ° C. before the actual sintering process begins, which reaches a final temperature of approximately 1100 ° C. The ceramic green body produced initially shows only a slight shrinkage during debinding, but this becomes significantly larger during sintering. In addition, the ceramic green sheets 10 form at least largely organic insulating layers 11 ^Λ made of PZT ceramic during sintering, which are separated from one another by the sintered electrically conductive material via the inner electrode layers 10 ^Λ . Finally, it is indicated in FIG. 2 that the powder particles 30 initially coated at 20 ° C. can be deformed by the sintering process, so that coated sintered powder particles 30 ^λ form inside the inner electrode layers 10 ^Λ , which in their interior are made of the metal used as sintered metallic phase 20 ^Λ and a coked surface coating 21 ^Λ consist of carbon. The average thickness of this surface coating ^21λ is approximately 1 nm to 20 nm. However, it should be emphasized that after the sintering, the inner electrode layer 10 in the actual sense often no longer contains any powder particles that can be separated exactly from one another, but is designed in the form of a compact layer that has two phases, on the one hand a metallic phase and on the other hand a carbon phase.

Claims

Expectations

1.Sintered, electrically conductive material, in particular inner electrode material for a ceramic multilayer component, with an initial mixture from which, after sintering, the electrically conductive material is formed, which contains a powdered metallic initial component and an organic initial component, characterized in that the organic initial component ( 21) after sintering at least largely surrounds the powder particles (20, 20 ^Λ ) of the metallic starting component in the form of an at least largely carbonized layer (21).

2. Sintered electrically conductive material according to claim 1, characterized in that the metallic starting component is a crystalline base metal powder or a crystalline base metal alloy powder.

3. Sintered electrically conductive material according to claim 1, characterized in that the organic starting component (21) is a material which is not or only slightly thermally decomposable up to a temperature of 350 ° C, in particular in an oxygen-containing gas atmosphere.

4. Sintered electrically conductive material according to claim 1 or 3, characterized in that the organic Starting component (21) is a polyimide, a polybenzoxazole, a polyether, a polycarbonate or a polyketone.

5. Sintered electrically conductive material according to claim 1, characterized in that the powdery metallic starting component has an average particle size of 100 nm to 10 microns.

6. Sintered electrically conductive material according to at least one of the preceding claims, characterized in that the organic starting component (21) at least largely surrounds the powdery metallic starting component in the starting mixture, in particular in the form of a coating.

7. Sintered electrically conductive material according to at least one of the preceding claims, characterized in that the melting point of the metallic starting component is above the maximum sintering temperature during sintering, in particular above 1100 ° C.

8. Ceramic multilayer component, in particular piezo actuator, with a plurality of ceramic insulating layers (11 ^Λ ) arranged one above the other, which are separated from one another at least in regions by inner electrode layers (10 ^λ ) made of an electrically conductive material according to at least one of the preceding claims.

9. Ceramic multilayer component according to claim 8, characterized in that the inner electrode layers (10)

Have a thickness of 0.5 μm to 5 μm.

10. Ceramic multilayer component according to claim 8, characterized in that the ceramic insulating layers (11 ^Λ ) at least largely consist of a PZT ceramic, in particular of Pb (Ti _x Zri_ _x ) 0 ₃ with 0.40 <x <0.60, and have a thickness of 50 μm to 130 μm.

11. A method for producing a ceramic multilayer component, in particular a multilayer component according to one of claims 8 to 10, with a plurality of ceramic insulating layers (11 ^λ ) arranged one above the other, which are separated from one another at least in regions by inner electrode layers (10 ^× ) made of an electrically conductive material are, with the method steps:.. a) preparing an initial mixture as a precursor for the internal electrode layers (10 ^λ), which contains a powdery metal starting component and an organic starting component, b) preparing a plurality laminable ceramic green sheets (11), c. ) at least one-sided and at least area-wise application of the starting mixture to the surface of the ceramic green sheets (11), d.) stacking of the ceramic green sheets (11) provided with the starting mixture to form a multi-layer green body, e.) debinding of the multi-layer green body and d.) Si nternal of the multilayered green body to the Kera i- see multilayer component (5), characterized in that the binder removal and sintering of the green body is carried out such that from the starting mixture, the internal electrode layers (10 ^λ) in the ceramic multi-layer component (5), wherein the organic starting component (21) after sintering at least largely surrounds the powder particles (20, 20 ^Λ ) of the metallic starting component in the form of a layer (21 ^Λ ) at least largely carbonized.

12. The method according to claim 11, characterized in that the stacking of the ceramic green sheets (11) provided with the starting mixture is accompanied by a lamination of the green sheets (11), or that the stacking of the green sheets (11) is laminated by the green sheets (11) precedes.

13. The method according to claim 11, characterized in that a material is used as the organic starting component (21) which is at least largely thermally stable when debinding the multilayer green body, in particular in an oxygen-containing gas atmosphere.

14. The method according to claim 11, characterized in that the sintering takes place at a final temperature above 400 ° C, in particular between 900 ° C and 1150 ° C.

15. The method according to claim 11, characterized in that the starting mixture is applied in the form of a paste to the ceramic green sheets (11).

16. The method according to claim 11, characterized in that the sintering is carried out in a low-oxygen or an oxygen-free gas atmosphere, in particular a nitrogen atmosphere.

17. The method according to claim 11, characterized in that the organic starting component (21) in the temperature range from 400 ° C to 700 ° C is at least largely carbonized to carbon.