DE102008048051B4 - Component and method for contacting a device - Google Patents

Abstract

Component (1) comprising: - a ceramic matrix (5), - at least one inner electrode (2) arranged in the ceramic matrix (5) and exposed on a first surface (7), - at least one electrically conductive collecting contact ( 8, 10) which is electrically connected to the inner electrode (2), and - an outer layer (18), wherein the outer layer (18) exerts a compressive bias on the collecting contact (8, 10), wherein the component (1 ) further comprises an insulating layer (15) arranged between the ceramic matrix (5) and the collecting contact (8, 10), wherein the insulating layer (15) has at least one through opening (16) which forms at least a part of the inner electrode (2 ), wherein the insulating layer (15) has a thermal expansion coefficient smaller than the thermal expansion coefficient of the collecting contact (8, 10).

Description

The invention relates to a component, in particular an electroceramic component such as a piezoelectric actuator and a method for contacting a component.

Electroceramic devices such as piezoelectric actuators have a ceramic matrix with at least one inner electrode which is arranged in the ceramic body and is exposed on a surface. A piezoactuator can also be designed in the form of a multilayer piezoactuator which has a multiplicity of piezoelectrically active ceramic layers and metallic inner electrode layers which are alternately stacked on one another. In a multilayer piezoelectric actuator, the surfaces have a plurality of strip-shaped metallic inner electrodes and piezoelectrically active ceramic regions. The EP 1 835 553 A1 for example, discloses a multilayer piezoelectric actuator.

These electronic components typically have large-area metallic external contacts, which are arranged at least partially on the ceramic matrix of the component and are in electrical connection with the internal electrodes.

Piezoelectrically active components are susceptible to cracking due to the mechanical deformation of the piezoelectrically active matrix. This mechanical deformation can also lead to an additional load on the external contacts, as in the DE 199 45 934 C1 is described.

To improve the reliability of the contact between the internal electrodes and the external contact is from the DE 199 45 934 C1 known to produce the external contact of two different layers of different composition. The lower first layer has a composition which serves to improve the adhesion to the device and the upper second layer is optimized in its composition so that it has good solderability.

The DE 197 53 930 A1 discloses a piezoactuator whose surface is at least partially encapsulated by a shell under mechanical tension. The end pieces are pressed by this shell against the base or top surface.

The DE 102 25 408 A1 discloses an actuator in which the outer electrode is pressed by a shrink tube to the base metallization.

EP 1 814 169 A2 discloses a piezoelectric actuator with a metal mesh as outer electrode, which is formed from Invar and thus has a low thermal expansion.

In DE 10 2006 046 831 A1 a piezoactuator is described, which is surrounded by a flexible insulating layer with a metal foil from Invar.

However, further improvements to making more reliable bonding to a device with internal electrodes and to providing a more reliable device are desirable.

The object of the invention is therefore to provide an electronic component with a ceramic matrix and at least one inner electrode, which is more reliable. A further object of the invention is to provide a method for contacting a component with a ceramic matrix and at least one inner electrode, wherein a more reliable contact is formed.

This is solved by the subject matter of the independent claims. Advantageous developments are the subject of the respective dependent claims.

According to the invention, a component is provided which has a ceramic matrix, at least one inner electrode which is arranged in the ceramic matrix and is exposed on a first surface and at least one electrically conductive collecting contact, which is electrically connected to the inner electrode, and a further outer layer , The outer layer exerts a compressive bias on the collecting contact. The thermal expansion coefficient of the outer layer is smaller than the coefficient of thermal expansion of the collective contact.

Due to selected coefficients of thermal expansion, the outer layer exerts a compressive bias on the underlying collector contact and the inner electrode. In particular, the thermal expansion coefficient of the outer layer is smaller than the coefficient of thermal expansion of the collecting contact.

The reliability of the contact between the collecting contact and the inner electrode is improved by the outer layer, since it mechanically presses the collecting contact to the inner electrode and prevents or at least impedes the lifting of the collecting contact from the inner electrode.

The inner electrode is exposed on a first surface and is not covered by the ceramic matrix. This exposed part of the inner electrode serves as an electrically conductive contact surface. The collective contact can be directly on the Inner electrode may be arranged to establish the electrical connection between the collecting contact and the inner electrode.

The pressure bias may further improve the electrical contact between the collecting contact and the inner electrode, because of the pressure increases the contact area between the electrically conductive particles of the collecting contact and the inner electrode and the electrical contact resistance is reduced. Consequently, in a component for use as an actuator in an injection valve, a sufficiently long service life and reliability is ensured for the desired short pulse durations, high drive voltages and considerable application temperatures.

The outer layer can be arranged directly or indirectly on the collecting contact. The term indirectly is used to denote an arrangement in which another layer is disposed between the outer layer and the collecting contact. This additional layer may be electrically conductive or electrically insulating. It is also not excluded to arrange another layer on the outer layer.

In the case that the outer layer is disposed indirectly on the collecting contact, the pressure bias is transmitted to the collecting contact via the layer arranged therebetween.

The outer layer may consist of a shrunken plastic film which exerts a mechanical pressure on the collecting contact.

The difference between the coefficient of thermal expansion of the outer layer and the coefficient of thermal expansion of the collector contact is created by a suitable choice of material of the outer layer and of the collector contact. Through this material selection, the height of the pressure bias can be adjusted.

The compressive bias exerted by the outer layer can be increased at higher temperatures. At increasingly higher temperatures, the volume of the protective layer increases less than the volume of the collective contact, so that a pressure bias is applied at the application temperature. By a suitable selection of thermal expansion coefficients and their temperature dependence, this compressive stress can be further increased at elevated temperatures.

This has the advantage that the compressive bias exerted by the outer layer can be increased at higher temperatures. At increasingly higher temperatures, the volume of the protective layer increases less than the volume of the collective contact, so that a pressure bias is applied at the application temperature. By a suitable selection of thermal expansion coefficients and their temperature dependence, this compressive stress can be further increased at elevated temperatures.

In one embodiment, in a temperature range of -50 ° C to 180 ° C, the thermal expansion coefficient of the outer layer is smaller than the coefficient of thermal expansion of the collector contact. This temperature range corresponds to a conventional storage temperature range. If the coefficients of thermal expansion meet this condition, it is ensured that during the storage of the component, a compressive bias is exerted on the collecting contact of the outer layer. Consequently, it is avoided that cracks between the collecting contact and the inner electrode are formed due to relaxation of the pressure on the collecting contact during storage.

In a further embodiment, in a temperature range of -40 ° C to 150 ° C, the thermal expansion coefficient of the outer layer is smaller than the coefficient of thermal expansion of the collective contact. This temperature range corresponds to a conventional application temperature range of a piezoelectrically active actuator of an injection valve.

The outer layer may have the shape of a sleeve and be arranged only on the edge sides. It is also possible to arrange the outer layer only on the collecting contact or collecting contacts, while the other surfaces of the body remain free of the outer layer. The outer layer may comprise plastic or metal or an alloy or a glass fiber reinforced polyamide.

In a further embodiment, the device further comprises a further protective layer which is arranged between the collecting contact and the outer layer. In this case, the outer layer is disposed indirectly on the collecting contact. The protective layer serves to better protect the collecting contact from external damage, which may be caused for example by contact with a corrosive substance such as gasoline or diesel in the case of an injection valve.

The protective layer can completely encase the body at the edge sides to increase the protection. However, the end surfaces are free of the protective layer. The material of the protective layer is selected depending on the intended application, so that the protective layer can be dielectric and a potting material, for. B. may have a silicone elastomer or polyurethane.

In one embodiment, the protective layer has a thermal expansion coefficient that is greater than the thermal expansion coefficient of the outer layer. Consequently, the compressive bias exerted by the outer layer is transferred to the collecting contact via the protective layer.

The device has an additional insulating layer which is arranged between a body of the ceramic matrix and the inner electrode arranged therein and the collecting contact. This insulating layer has at least one through-opening which exposes at least a part of the inner electrode, so that the exposed inner electrode is in electrical contact with the collecting contact arranged thereon.

The insulating layer has a thermal expansion coefficient which is smaller than the thermal expansion coefficient of the collecting contact. This ratio between the thermal expansion coefficient of the insulating layer and the coefficient of thermal expansion of the collecting contact prevents expansion of the insulating layer at elevated temperatures leads to lifting of the collecting contact.

The insulating layer may also have a thermal expansion coefficient which is smaller than the thermal expansion coefficient of the further protective layer. This ratio between the thermal expansion coefficient of the insulating layer and the coefficient of thermal expansion of the collecting contact prevents expansion of the insulating layer at elevated temperatures resulting in lifting of the protective layer and its delamination from the collecting contact.

The contact between the collecting contact and the inner electrode can also be increased by a second electrically conductive layer, which is arranged between the collecting contact and the inner electrode.

This second layer can increase the mechanical strength of the connection between the inner electrode and the collecting contact and / or reduce the electrical resistance. These properties can be achieved by the selection of the materials of the second layer, the inner electrode and / or the collecting contact and / or by the structure of the second layer.

For example, the second electrically conductive layer may comprise a material that chemically reacts or alloys with the material of the inner electrode and / or the material of the collecting contact to increase the mechanical strength of the connection.

The second electrically conductive layer may also include nanoscale grains or particles which serve to increase the contact area between the second layer and the underlying inner electrode. The increased contact area leads to a lower electrical contact resistance. The term nanoscale is defined as grains or particles with a diameter of 0.1 nm up to 1000 nm, preferably 0.1 nm up to 200 nm.

The second electrically conductive layer can be formed from wet-chemically applied nanoscale grains or particles, an electrodeposited metal or by a vacuum deposition method such as PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition).

The component is in another embodiment, an electronic component such as a piezoelectric actuator, which serves for example as an actuating element of an injection valve of an engine of a motor vehicle. The device may also be a multilayer electronic device, such as a capacitor, varistor or thermistor.

The device may be a multilayer piezoelectric actuator having a plurality of piezoelectrically active layers and a plurality of electrically conductive inner electrode layers, the electrically conductive inner electrode layers each providing an electrically conductive inner electrode. The piezoelectrically active layers and the electrically conductive inner electrode layers are alternately stacked on each other in a stacking direction.

In a multilayer piezoelectric actuator, the first surface extends in the stacking direction. Each second inner electrode layer forms a region of the first surface and is electrically connected to the collecting contact, wherein the further inner electrode layers are electrically insulated from the collecting contact. The multilayer piezoelectric actuator thus has two groups of internal electrodes, which are contacted with different mutually electrically isolated collector contacts. Neighboring internal electrodes of the stack are electrically isolated from each other and independently controllable.

In one embodiment, the piezoelectrically active layers are nearly fully active. The inner electrodes extend almost completely over the surface to the edge sides of the adjacent piezoelectrically active layers.

In an alternative embodiment, the piezoelectrically active layers do not have piezoelectrically active regions. In this Embodiment, the internal electrodes do not extend to the edge of the piezoelectrically active layers.

Typically, every other inner electrode will extend to the edge side of a first surface and not to the edge side of a second opposing surface of the piezoelectric active layer. This uncovered region of the piezoelectrically active layer provides an electrical insulation of the inner electrode of the collecting contact, which is arranged on the second surface. The second group of internal electrodes extends to the edge of the second surface and not to the edge of the first surface of the piezoelectric active layer.

When the device has a second surface disposed opposite the first surface and having a plurality of the alternating piezoelectric layers and electrically conductive inner electrode layers, the inner electrode layers that are not electrically connected to the collecting contact on the first surface are at a second collecting contact electrically connected to the second surface. The first collecting contact is electrically isolated from the second collecting contact.

In a fully active stack, the second surface may also include an electrically insulating layer having openings, with an opening exposing every other inner electrode layer on the second surface that is not electrically connected to the collecting contact on the first surface. In this way, two groups of internal electrodes are provided which are independently controllable and which are alternately arranged in the stack in the stacking direction.

The invention also provides a method of contacting a device. A device is provided comprising a ceramic matrix, at least one internal electrode disposed in the ceramic matrix and exposed at a first surface, and at least one electrically conductive collector contact electrically connected to the internal electrode. The component may be a piezoactive actuator, for example a multilayer piezoelectric actuator. Another outer layer is applied to the device, this outer layer exerts a compressive bias on the collecting contact.

The outer layer may be applied in the form of a sleeve or by dipping, spraying or screen printing.

In one embodiment, after its application, the outer layer is shrunk onto the device to apply compressive bias to the collection contact.

The compressive prestress is exerted by the material selection, in particular by the selection of the thermal expansion coefficient. In one embodiment, the outer layer has a coefficient of thermal expansion that is less than the thermal expansion coefficient of the collector contact.

In one embodiment, a further protective layer is applied to the collecting contact before the application of the outer layer. This protective layer may consist of a potting material.

In a development, the material of the protective layer is selected such that it has a thermal expansion coefficient that is greater than the thermal expansion coefficient of the outer layer. The outer layer thus exerts a compressive bias on the protective layer which transfers the protective layer to the collecting contact.

When the protective layer is made of a material that is cured to produce a solid layer, the curing may be performed at temperatures lower than the application temperature of the device.

Consequently, the volume of the protective layer increases in the temperature range between the curing temperature and the application temperature. This increase in volume is hindered by the outer layer and creates a pressure bias on the collecting contact and on the connection between the collecting contact and the inner electrode.

Embodiments of the invention will now be described with reference to the drawings.

1 shows a schematic view of a multilayer piezoelectric actuator according to a first embodiment of the invention,

2 shows a schematic detailed view of the multilayer piezoelectric actuator of 1 , and

3 shows a schematic detailed view of a multilayer piezoelectric actuator according to a second embodiment of the invention.

1 and 2 show a multilayer piezoelectric actuator 1 according to a first embodiment of the invention, a plurality of internal electrode layers 2 and a plurality of piezoelectrically active layers 3 having. The 2 shows a most detailed view of part of the multilayer piezoelectric actuator of FIG 1 , The multilayer piezoelectric actuator serves in this embodiment as an actuating element in an injection valve of a motor vehicle engine. The Internal electrode layers 2 and the piezoelectrically active layers 3 are alternately on top of each other in a stacking direction 4 stacked and form a multi-layered body 5 , The multilayered body 5 can also be referred to as a composite material consisting of a ceramic matrix and internal electrodes in the form of internal electrode layers.

The internal electrode layers 2 each consist of an electrically conductive material, in particular a metal or an alloy such as Ag-Pd. The piezoelectrically active layers 3 consist of a material that shows the piezoelectric effect, ie when an electric field is applied, the material deforms mechanically. This mechanical deformation creates usable strain and / or force on the end surfaces 12 so that the stack can be used as an actuator.

In this embodiment, the piezoelectrically active layers exist 3 from a ceramic, in particular PZT (lead zirconate titanate). The internal electrode layers 2 extend over the entire area of the adjacent piezoelectrically active layers 3 as well as to the edge sides 6 of the pile and form part of it 23 the surface 7 of the body 5 of the piezo actuator 1 , The part 23 the inner electrode 2 is on the surface 7 exposed and therefore free from the ceramic matrix of the body. This arrangement of the multilayer piezoelectric actuator 1 is called a fully active piezo actuator stack.

An electrical contact to the respective internal electrodes 2 in the body 5 are arranged takes place with collective contacts 8th . 10 on the margins 6 of the body 5 are arranged. A first collective contact 8th is on a first edge side 9 of the body 5 arranged and a second collective contact 10 on the opposite edge 11 of the body 5 , The first collective contact 8th and the second collective contact 10 are electrically isolated from each other.

Each inner electrode 2 is with just one of the collective contacts 8th . 10 electrically connected so that two groups of internal electrodes 13 . 14 are provided which are electrically isolated from each other. Every second inner electrode 2 in the stacking direction 4 is with the first collecting contact 8th electrically connected and forms the first group 13 of internal electrodes 2 , The second collective contact 10 is with the internal electrodes 2 ' electrically connected, which is the second group 14 of internal electrodes 2 ' form. Neighboring internal electrodes 2 . 2 ' in the stacking direction 4 belong to different groups 13 . 14 , A voltage is applied between the adjacent internal electrodes 2 of the stack, so that the between the internal electrodes 2 arranged piezoelectrically active layers 3 react mechanically.

To make a short circuit between the two groups 13 . 14 of internal electrodes 2 . 2 ' as well as between the two collective contacts 8th . 10 To avoid is an electrically insulating layer 15 on at least the two edges 9 . 11 of the body 5 with the collective contacts 8th . 10 arranged.

The electrically insulating layer 15 has openings 16 on that the surface 23 the internal electrode layers 2 expose that part of the surface 7 of the body 5 forms. In particular, lay the openings 16 the electrically insulating layer 15 the first group 13 of internal electrodes 2 on the first edge 9 and the second group 14 of internal electrodes 2 ' on the second edge 11 free.

On the first edge side 9 is the second group 14 of internal electrodes 2 ' from the electrically insulating layer 15 covered and arranged on the first collecting contact 8th electrically isolated. On the second opposite edge side 11 is the first group 13 of internal electrodes 2 from the electrically insulating layer 15 covered and arranged by the second collecting contact 10 electrically isolated.

A protective layer 17 from a potting material is on the edge sides 5 or directly on the collective contacts 8th . 10 arranged. The protective layer 17 is dielectric, so that the collecting contacts 8th . 10 stay electrically isolated from each other. The protective layer 17 protects the underlying collective contacts 8th . 10 , the internal electrodes 2 and the piezoelectrically active layers 3 from damage to the environment, especially against corrosive media in which the piezoelectric actuator is used. In the case of an actuating element of an injection valve, the piezoelectric actuator may be in direct contact with the fuel during operation.

In a further embodiment, not shown, there is no protective layer 17 intended. This arrangement can be used when the multilayer piezoelectric actuator is not used in a corrosive environment and / or when the outer layer alone provides a sufficient protective effect.

The multilayer piezoelectric actuator 1 also has an outer layer 18 which encapsulates the multilayer piezoelectric actuator. The outer layer 18 is provided in this embodiment in the form of a sleeve which on the protective layer 17 is arranged.

The outer layer 18 has plastic in this embodiment, in particular a glass fiber reinforced polyamide. In further embodiments, the outer layer 18 a metal or alloy.

According to the invention, this outer layer exercises 18 a pressure bias on the collection contacts 8th . 10 , preferably at elevated temperatures. In this context, an elevated temperature is defined as a temperature between a typical room temperature of 20 ° C and the application temperature, which is about 100 ° C for injectors, for example.

In other embodiments, the outer layer exercises 18 a pressure on the collecting contacts 8th . 10 at temperatures in a storage temperature range, for example -50 ° C up to 180 ° C and / or in an application range, for example -40 ° C up to 150 ° C from.

This pressure bias is in one embodiment by a targeted selection of the thermal expansion coefficient of the outer layer 18 and the collective contact 8th . 10 guaranteed. In particular, the outer layer 18 a smaller thermal expansion coefficient than the collecting contacts 8th . 10 , Consequently, these expand at an elevated temperature of the collection contacts 8th . 10 further than the outer layer, so that the outer layer has a compressive bias on the collecting contacts 8th . 10 exercises. This compressive bias presses the collective contact 8th . 10 against the exposed surface 23 the internal electrodes 2 so that the mechanical and electrical connection is maintained or even improved. When the contact area between the collecting contact 8th . 10 and the exposed surface 23 the internal electrodes 2 is increased by the mechanical pressure, the electrical contact resistance is reduced and the electrical conductivity of the compound is improved.

If a protective layer 17 is provided between the outer layer 18 and the collective contact 8th . 10 is arranged, the thermal expansion coefficient of the protective layer 17 so selected that it is greater than the thermal expansion coefficient of the outer layer 18 is. This ratio allows a greater compressive bias to be applied to the collecting contact since the increase in volume of the protective layer and the collecting contact can be increased. Due to the smaller thermal expansion coefficient of the outer layer disposed thereon 18 there is a bigger difference between the volume increase of the outer layer 18 and the protective layer 17 and the collective contact layer 8th . 10 , so that the compression bias is increased.

At the insulation layer 15 between the surface 7 of the body 5 and the collective contact 8th . 10 For example, the coefficient of thermal expansion is selected to be smaller than the thermal expansion coefficient of the collector contact 8th . 10 , This ratio prevents the collecting contact from lifting because of the underlying insulation layer 15 expands further than the collective contact.

These ratios of the thermal expansion coefficients of the various layers result in more reliable bonding and a more reliable device.

The contact structure of the collective contacts 8th According to a first embodiment is in the detailed view of 2 represented, which is part of the first edge side 9 of the multilayer piezoelectric actuator 1 with four of the piezoelectrically active layers 3 as well as three internal electrode layers 2 . 2 ' shows. The contact structure of the second collective contact 10 is equal to.

2 shows that in this embodiment, the collecting contact 8th from two layers 19 . 20 consists. The collective contact 8th however, it can consist of one layer. The first shift 19 may be formed of nanoscale grains or an electrodeposited material. The nanoscale grains of the first electrically conductive layer 19 consist of an electrically conductive metal or an electrically conductive alloy, such as silver or gold and their alloys. The second layer 20 can be formed from a conductive adhesive or an electrodeposited metal.

The first lower electrically conductive layer 19 is in the openings 16 the electrically insulating layer 15 arranged and in direct contact and in electrical connection with the exposed inner electrode 2 Inside the opening 16 is arranged.

In this embodiment, the first layer is 19 completely within the respective openings 16 arranged and consists of a variety of areas 21 passing each other through the electrically insulating layer 15 are separated.

The second electrically conductive layer 20 of the collective contact 8th extends over the entire edge side 9 of the multilayer piezoelectric actuator 1 and in the openings 16 the electrically insulating layer 15 , The second layer 20 is right on the surface 22 the electrically insulating layer 15 as well as on the first electrically conductive layer 19 arranged. The second electrically conductive layer 20 connects the internal electrodes 2 the first group 13 with each other electrically.

The first electrically conductive layer 19 is between the internal electrodes 2 and the second electrically conductive collecting layer 20 arranged and can serve as a bonding agent to the mechanical strength of the connection between the common contact 8th and the body 5 of the piezo actuator 1 to improve.

The adhesion-promoting effect can be further increased if at least at the boundary between the inner electrode 2 and the first layer 19 Phases emerge, which are the products of a reaction or alloying of the material of the first layer 19 and the material of the internal electrodes 2 are. The material of the first layer 19 and the material of the inner electrode 2 can be selected and the manufacturing process adjusted so that a suitable reaction takes place.

Furthermore, the material of the first layer 19 with the material of the second layer 20 react, allowing an improved mechanical connection between the two layers 19 . 20 of the collective contact 8th arises.

The internal electrode layers 2 have a thickness of typically 2 to 3 microns and the nanoscale grains of the first layer 19 an average diameter of 2 nm to 1000 nm, preferably 2 nm to 200 nm. Thus, several nanoscale grains are in direct contact with the exposed surface 17 the inner electrode 2 ,

The contact area between the first layer 19 and the inner electrode 2 is larger than the contact area that can be achieved by using a layer with larger diameter particles, such as conductive adhesive with grains or particles with a larger diameter of 1 to 10 microns. This larger contact area provides a lower contact resistance and improved mechanical strength of the connection between the collecting contact 8th and the internal electrodes 2 in front.

The 3 shows a detailed view of a collective contact 8th' a piezoelectric actuator 1' according to a second embodiment.

At the actor 1 according to the second embodiment, the outer layer 18 ' directly on the collective contact 8th' arranged. No protective layer is provided in this embodiment. As in the first embodiment, the outer layer 18 ' a smaller thermal expansion coefficient than the collecting contact 8th' such that the outer layer exerts a compressive bias on the collecting contact.

The collective contact 8th' of the second embodiment is different from the collecting contact 8th of the first embodiment by the arrangement of the first lower electrically conductive layer 19 ' , In the second embodiment, the first layer 19 ' the shape of a closed layer that is completely and approximately compliant over the electrically insulating layer 15 extends. The first shift 19 ' extends over the inner walls as well as the bottom of the openings 16 , wherein an inner electrode 2 at least part of the bottom of each second opening 16 forms.

In this embodiment, the second upper electrically conductive layer is 20 only in direct contact with the first electrically conductive layer 19 ' and not in direct contact with the electrically insulating layer 15 , In the second embodiment, both the first layer connects 19 ' as well as the second layer 20 the exposed internal electrodes 2 the first edge side 12 electrically with each other.

The multilayer piezoelectric actuator 1 can be prepared by the following method. First, a stacked component of alternately arranged internal electrode layers 2 and piezoelectrically active layers 3 produced. After that, the surfaces can 7 of the component, for example by grinding or sandblasting, to a surface 7 from the ceramic piezoelectrically active layers 3 and the inner electrode layers 2 to shape.

An electrically insulating layer 15 will be at least on the margins 9 . 11 of the body 5 applied to which the collecting contacts 8th . 10 be applied later. This electrically insulating layer 15 can be applied as a closed layer or a structured layer. In one embodiment, all surfaces are 7 of the body 5 with the electrically insulating layer 15 coated. In the case of a closed layer, the electrically insulating layer 15 structured after application to the internal electrodes 2 to be released. In particular, on a first edge side 9 every second inner electrode 2 exposed and on the opposite edge 11 becomes every second inner electrode 2 ' uncovered, not on the first edge 9 is exposed.

The first electrically conductive layer 19 of the collective contact 8th . 10 will be in the openings 16 in the electrically insulating layer 15 applied. The first shift 19 can be applied as a suspension of nanoparticles in a solvent. The solvent is removed, for example by evaporation and a first layer 19 formed of nanoscale grains from the nanoparticles.

In the embodiment shown in the 2 is shown, the nanoparticles in the openings 16 , For example, applied by a screen printing method, so that the first electrically conductive layer 18 completely inside the openings 16 is arranged. In this case, the structured electrically insulating layer 15 be used as a mask.

In the embodiment shown in the 3 is shown, the nanoparticles as a closed layer 19 ' For example, applied by dipping, spraying or brushing, which extends over the electrically insulating layer 15 as well as the openings 16 extends.

The first shift 19 . 19 ' Both embodiments can also be applied galvanically. This galvanic process can be done with an external voltage or can be de-energized, ie no external voltage is applied to the body 5 created. Electroless galvanic methods have the advantage that an electrically conductive circuit across the body is not necessary, so that no closed electrically conductive layer on the body is necessary. The layer separates from the bath directly onto the electrically conductive surface of the submerged body. A structured layer is thus deposited directly from the solution.

If a closed first layer 19 ' on the two opposite edge sides 9 . 11 of the body 5 is applied, this is structured so that two areas of the first electrically conductive layer 19 ' , which are electrically separated from each other, on the two opposite edge sides 9 . 11 is formed.

After applying and forming the first layer 19 . 19 ' becomes a second layer 20 made of conductive adhesive at least on the edge sides 9 . 11 on which the collective contacts 8th . 10 should be arranged, applied. The second layer 20 extends between the exposed internal electrodes 2 . 2 ' one of the two groups 13 . 14 and connects the inner electrode 2 . 2 ' the group electrically with each other.

As with the first layer 19 . 19 ' becomes the second layer 20 on the two opposite edge sides 9 . 11 of the body 5 structured so that two areas and consequently two collective contacts 8th . 10 , which are electrically separated from each other. This can be achieved by the selective application of the second layer 20 or by applying a closed layer 20 respectively.

After that, a protective layer 17 made of a dielectric material on the edge sides 9 . 11 the actuator applied with dipping or spraying or screen printing and optionally cured. If the curing is carried out at a temperature lower than the application temperature of the actuator, an even higher pressure bias can be achieved.

Subsequently, an outer layer 18 on the protective layer 17 applied. This outer layer 18 is provided as a finished sleeve into which the component is molded. However, it is also possible the outer layer 18 by spraying, dipping or by screen printing. If the outer layer 18 is made of metal or an alloy, it can be applied galvanically with or without external power source.

When selecting the materials of the different layers, the following relationship is provided. The thermal expansion coefficient of the outer layer 18 is smaller than the thermal expansion coefficient of the collector contact 8th as well as the protective layer 17 if one exists. Further, the thermal expansion coefficient of the insulating layer is 15 smaller than the thermal expansion coefficient of the collective contact 8th ,

LIST OF REFERENCE NUMBERS

1

multilayer piezoelectric actuator

2

inner electrode

3

piezoelectrically active position

4

stacking direction

5

body

6

edge side

7

surface

8th

first collective contact

9

first edge side

10

second collective contact

11

second edge side

12

end face

13

first group of internal electrodes

14

second group of internal electrodes

15

insulation layer

16

by opening

17

protective layer

18

outer layer

19

first layer of the collective contact

20

second layer of the collective contact

21

Area of the first layer of the collective contact

22

Surface of the insulation layer

23

Surface of the inner electrode

Claims (13)

Component ( 1 ), which - a ceramic matrix ( 5 ), - at least one inner electrode ( 2 ) contained in the ceramic matrix ( 5 ) and at a first surface ( 7 ) is exposed, - at least one electrically conductive collecting contact ( 8th . 10 ), which is connected to the inner electrode ( 2 ) is electrically connected, and - an outer layer ( 18 ), wherein the outer layer ( 18 ) a compression bias on the collecting contact ( 8th . 10 ), wherein the component ( 1 ) an insulation layer ( 15 ) between the ceramic matrix ( 5 ) and the collective contact ( 8th . 10 ), wherein the insulating layer ( 15 ) at least one opening ( 16 ), which at least a part of the inner electrode ( 2 ), the insulation layer ( 15 ) has a thermal expansion coefficient which is smaller than the thermal expansion coefficient of the collective contact ( 8th . 10 ). Component ( 1 ) according to claim 1, characterized in that the thermal expansion coefficient of the outer layer ( 18 ) is smaller than the thermal expansion coefficient of the collective contact ( 8th . 10 ). Component ( 1 ) according to claim 1 or claim 2, characterized in that the outer layer ( 18 ) Plastic or metal or an alloy or a glass fiber reinforced polyamide. Component ( 1 ) according to one of the preceding claims, characterized in that the component ( 1 ) a further protective layer ( 17 ), which between the collecting contact ( 8th . 10 ) and the outer layer ( 18 ) is arranged. Component ( 1 ) According to claim 4, characterized in that the protective layer ( 17 ) has a thermal expansion coefficient greater than the thermal expansion coefficient of the outer layer ( 18 ). Component ( 1 ) according to claim 4 or claim 5, characterized in that the protective layer ( 17 ) comprises a potting material, for example a silicone elastomer or polyurethane. Component ( 1 ) according to one of claims 4 to 6, characterized in that the insulating layer ( 15 ) has a thermal expansion coefficient which is smaller than the thermal expansion coefficient of the further protective layer ( 17 ). Component ( 1 ) according to one of the preceding claims, characterized in that the component ( 1 ) is a multilayer piezoelectric actuator having a plurality of piezoelectrically active layers ( 3 ) and a plurality of electrically conductive inner electrode layers ( 2 ), and wherein the piezoelectrically active layers ( 3 ) and the electrically conductive inner electrode layers ( 2 ) alternately on each other in a stacking direction ( 4 ) are stacked, with the first surface ( 7 ) in the stacking direction ( 4 ) and that every second inner electrode layer ( 2 ) an area of the first surface ( 7 ) and with the collecting contact ( 8th ) is electrically connected, wherein the further inner electrode layers ( 2 ' ) from the collecting contact ( 8th ) are electrically isolated. Component ( 1 ) according to claim 8, characterized in that the component ( 1 ) a second surface ( 11 ), which are opposite the first surface ( 9 ) and a plurality of the alternating piezoelectric layers ( 3 ) and electrically conductive internal electrode layers ( 2 ' ), wherein the internal electrode layers ( 2 ' ), which does not match the collective contact ( 8th ) on the first surface ( 6 ) are electrically connected, with a second collecting contact ( 10 ) are electrically connected from the first collecting contact ( 8th ) is electrically isolated. Method for contacting a component ( 1 ), which comprises the following steps, - providing a component ( 1 ), which - a ceramic matrix ( 5 ), - at least one inner electrode ( 2 ) contained in the ceramic matrix ( 5 ) and at a first surface ( 9 ) is exposed, - at least one electrically conductive collecting contact ( 8th . 10 ) electrically connected to the inner electrode ( 2 ), - applying an insulating layer ( 15 ) between the ceramic matrix ( 5 ) and the collective contact ( 8th . 10 ) such that the insulation layer ( 15 ) at least one opening ( 16 ), which at least a part of the inner electrode ( 2 ), wherein the material of the insulating layer ( 15 ) is selected such that the insulation layer ( 15 ) has a thermal expansion coefficient which is smaller than the thermal expansion coefficient of the collective contact ( 8th . 10 ), - applying a further outer layer ( 18 ) on the device ( 1 ), the outer layer ( 18 ) a compression bias on the collecting contact ( 8th . 10 ) exercises. Method according to claim 10, characterized in that the outer layer ( 18 ) is applied in the form of a sleeve. A method according to claim 10 or claim 11, characterized in that prior to the application of the outer layer ( 18 ) another protective layer ( 17 ) on the collecting contact ( 8th . 10 ) is applied, wherein the protective layer ( 17 ) is selected to have a thermal expansion coefficient greater than the thermal expansion coefficient of the outer layer ( 18 ). A method according to claim 12, characterized in that after the application of the protective layer ( 17 ) the protective layer ( 17 ) at Curing temperatures lower than the application temperature of the device ( 1 ) are.

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