EP1949465A1

EP1949465A1 - Piezoelectric actuator and method for producing the same

Info

Publication number: EP1949465A1
Application number: EP06807430A
Authority: EP
Inventors: Martin Schröder; Manfred Weigl
Original assignee: Continental Automotive GmbH
Current assignee: Continental Automotive GmbH
Priority date: 2005-10-26
Filing date: 2006-10-20
Publication date: 2008-07-30
Also published as: WO2007048756A1; DE102005051289B3; CN101356661B; US20110062830A1; US20080315717A1; CN101356661A; US8132304B2

Abstract

The invention relates to a piezoelectric actuator and to a method for producing the same having the following steps: providing a plurality of piezoelectric material layers (2) which can be assembled into a stack; applying electrode layers (3) each having a recess (4, 4') to the plurality of piezoelectric material layers, such that an alternating sequence of piezoelectric material layers and electrode layers is formed in the stack, wherein electrode layers with a recess (4) in a first recess zone and electrode layers with a recess (4') in a second recess zone which differs from the first recess zone are alternatingly formed in the stack; and providing a stress-relieving material (5) in the first and second recesses, the stress-relieving material exhibiting electrically insulating properties after the stack is sintered, and preventing the individual material layers from adhering to one another.

Description

description

Piezoelectric actuator and method for producing the same

The present invention relates to a piezoelectric actuator, preferably in monolithic multilayer construction, and a method for producing the same.

Piezo actuators usually consist of a plurality of piezo elements arranged in a stack. Each of these elements in turn consists of a piezoelectric ceramic layer that is both ^¬ sides with metallic electrodes. If a voltage is applied to these electrodes, then the piezo ^¬ ceramic layer reacts with a grid consumption, which leads along a major axis to a usable length expansion. Since this in turn is less than 2 parts per thousand of the layer thickness along the main axis, a correspondingly higher layer thickness of active piezoceramic must be provided to achieve a desired absolute length expansion. However, with increasing layer thickness of the piezoelectric ceramic layer of a single piezoelectric element and the surfaces to attrac ^¬ increases the piezoelectric element required voltage. In order to keep these within manageable limits, the thicknesses of piezo-individual elements are usually between 20 and 200 μm. A piezoelectric actuator in a multi-layer design must therefore have a corresponding number of individual elements or layers for a desired linear expansion.

Known piezoelectric actuators in multilayer construction therefore generally consist of a large number of individual layers. For their preparation, piezoelectric ceramic layers are alternately arranged with electrode material to form a stack and laminated ge ^¬ jointly to form a monolithic composite and sintered. Such a method is known, for example, from European Patent EP 0 894 340 B1. Here piezoceramic green films are printed with an electrode material be ^¬. The printing is done according to a pattern which includes printed areas and unprinted free areas. The electrode layers are stacked alternately such that over each unprinted area in a first electrode layer an area printed with electrode material is arranged in the next adjacent second electrode layer. Due to the alternating arrangement, every second electrode layer is congruent with respect to its electrode pattern. In the intervening likewise to each other congruent electrode layers, the unprinted free remaining area are diagonally offset.

In this approach according to the prior art, however, the fact has proven to be disadvantageous that in a sintering internal pressure and volume compensation takes place, for example, the unprinted spare areas ^¬ che in the electrode pattern are completely filled by ceramic material of the adjacent ceramic layers. When electrically contacting the electrode layers, all the ceramic layers undergo expansion, with the exception of the corner regions comprising the unprinted regions, since no effective electric field strength can be built up in these two diagonally opposite corner regions. In contrast to the rest of the ceramic areas, these corner areas therefore do not experience any expansion during activation, which results in mechanical stresses between the active areas and the inactive areas. These mechanical stresses cause the formation of cracks, which can lead from the inactive corner regions into the active ceramic regions. Such cracks can propagate uncontrolled through the ceramic in the longitudinal direction and significantly limit the life of the piezoelectric actuator.

It is known to the Applicant to integrate relief layers into the stack according to a predetermined alternating sequence of ceramic and electrode layers in order to avoid agreed to create separation areas to reduce mechanical stresses.

In this approach, however, the fact has been found to be disadvantageous in that the introduction of additional Entlas ^¬ tung layers with an additional manufacturing expense and additional production costs associated. In addition, these relief layers increase the stack construction adversely.

Moreover, the Applicant further measures are known in order to reduce mechanical stresses in the piezoelectric actuator, which, however, not but prevent cracking in general, single ^¬ Lich a formation of cracks in the longitudinal direction of the piezoelectric actuator, thereby maintaining the function of the piezoelectric actuator far ^¬ continuously remains , Nevertheless, these measures continue to pose the risk of uncontrolled crack propagation due to residual transverse cracks, which may reduce or even destroy the performance of the piezoelectric actuator.

The present invention is thus based on the object of specifying a piezoactuator and a production method for the same, wherein poling cracks are reduced or minimized despite inactive regions in the electrode layers.

According to the invention, this object is achieved by the method having the features of patent claim 1 and by the piezoelectric actuator having the features of patent claim 7.

The to the present invention idea underlying be ^¬ is the fact that the piezoelectric actuator of several zusammenfügbarer to a stack of piezo-electric material layers is produced, said electrode layers are applied, each egg ner recess to the plurality of piezoelectric material layers such that in the stacking egg ^¬ ne alternating sequence of piezoelectric material layers and electrode layers results, wherein electrode layers are provided with a recess in a first recess region and electrode layers with a recess in a second, different from the first recess region recess region in the stack alternately. Furthermore, a relief material is respectively provided in the first and second recesses, which after sintering of the stack has electrically insulating properties that do not stick together to the individual material layers.

Thus, the present invention over the known approaches has the advantage that the proposed free-lying areas or recesses of the electrode layers are not completely filled with Kera ^¬ mikmaterial in a sintering of the stack, but due to the non-adherent properties of the relief material Mecha ^¬ nische separation point or create a relief recess between two successive ceramic layers in the region of the recesses. For the case of diffusion of a high permeability material having relief ^¬ currency rend sintering the separating points are formed as voids between adjacent ceramic layers. Thus, there is no adhesion between the ceramic layers in this area, so that in these inactive areas no significant mechanical stresses can arise. The mechanical stresses, if any, are no longer sufficient to cause damaging cracks.

Furthermore, the present invention has the advantage that in the areas of the recesses due to the electrically insulating properties of the relieving material electrically isolated areas arise, the ßenmetallisierung the piezoelectric actuator for an electrical on ^¬ control every other electrode layer to simple and inexpensive Guarantee the way. In addition, for the production of the piezoelectric actuator according to the invention no new technology must be introduced, ie it can be the usual and previously known manufacturing equipment and manufacturing processes with minor modifications, ie only the application of the relief material in the recesses used. Thus, in a simple and cost-effective manner, harmful cracks in the ceramic layers can be prevented or minimized.

Advantageous embodiments and modifications of the invention are the subject of the other dependent claims and the description with reference to the figures of the drawing.

According to a preferred refinement, a noble metal-containing metallization paste having a low diffusion capability of the electrically conductive particles is printed on each of the piezoelectric material layers as electrode layers during sintering of the stack. For example, a silver-palladium-containing paste verwen ^¬ det, wherein the palladium content a retention of the silver in the paste and the silver content ensure good electrical Leitfä ^¬ ability of the paste.

According to a further preferred embodiment, a noble metal-containing paste is printed with a very high diffusivity of the electrically conductive particles during sintering of the stack as a relief material on ^¬ into the recesses. For example, a silver-containing paste is comparable turns, wherein the silver during sintering in the ^¬ be adjacent electrode regions diffuses.

According to a further preferred embodiment, each second electrode layer in the stack is provided with a recess in a first corner region and each electrode layer provided therebetween has a recess in a second corner region opposite the first corner region. det. In this way, an inexpensive and simple external contact can be ensured in such a way that a metallisation over the whole longitudinal extension of the Piezoak- gate is provided in the corner areas, with only every second electrode layer contacts and is thus driven elekt ^¬ driven.

According to a further preferred development of the piezoelectric actuator is formed with at least two longitudinally extending bores, wherein the first recess region in the region of a bore and the second recess region in the region of the other bore in the stack are provided in alternating sequence. For example, the single ^¬ NEN electrode layers can be coupled via the bores with an elec- contacting step such that, in turn, per well, only every second electrode layer is contacted elekt ^¬ driven. The two holes are typically, but not necessarily a similarly relatively large ^¬ SEN diameter in the mm range, since because of too large Stei- stiffness not simply a massive wire can be soldered, but rather a lot of fine wires wire comprising (eg a bottle brush ) can be used.

The invention will be explained in more detail with reference to the exemplary embodiments shown in the schematic figures of the drawing. It shows:

Figure 1 is an exploded view of several attached to a Sta ^¬ pel zusammenfügbarer ceramic layers with electrode layers listed a preferred embodiment of the present invention according to;

Figure 2 shows the exploded view of Figure 1 with the initial discharge savings deposited material in accordance with a preferred embodiment of the constricting vorlie ^¬ invention; and 3 shows a perspective view of a piezoelectric actuator in assembled monolithic multilayer construction according to a preferred embodiment of the present invention.

In the figures, same reference characters designate the same or functionally similar components, unless otherwise indicated Converse ^¬ sat.

The piezoelectric actuator according to the invention and its construction method are generally independent of the materials used. As a piezoelectric material layers may beispielswei ^¬ se any PZT (lead zirconate titanate) ceramics. For example, so genann ^¬ te green sheets are drawn or molded from this material having a thickness of microns, for example 20 to 200 after drying.

After drying the green sheets, they are provided with electrode layers, for example printed with a suitable silver-palladium paste. The paste contains preference ^¬, the particles of a silver / palladium alloy in a binder with a total printable consistency. This screen printing paste has, for example, in addition to organic excipients fine-grained silver powder and palladium powder. The silver content in the paste ensures the good electrical conductivity of the electrode layer after sintering, whereas the palladium content ensures that, despite the high diffusibility of the silver at the temperatures occurring during sintering, it remains in the printed electrode layer. This corresponds in the paste ^¬ preserved silver achieved at a diffusion during sintering in the presence of palladium uniform Kon ^¬ zentrationsverteilung in the palladium. The diffusibility of palladium is so low that it is not to be taken into account. Figure 1 illustrates an exploded view of four piezo-electric ceramic layers 2 ^¬ that lektrodenschicht with an E in each case 3, for example from the above-described ^¬ NEN silver-palladium paste is printed on one side. Although only four ceramic layers are illustrated by way of example in Figures 1 and 2, it is open ^¬ clear for a skilled person that any number of piezoelectric ceramic layers can be bonded in a stack with each other in an analogous manner.

As can also be seen in FIG. 1, the ceramic layers 2 are printed according to a pattern in such a way that a printed electrode region 3 and an unprinted, free recess region 4 or 4 ^{λ are} provided on each ceramic layer. For example, one side palladium paste silver-3 printed as much of the associated ceramic layers 2 for the electrode layers ^¬ that after sintering a 2-3 micron thick contiguous Elect ^¬ clear layer 3 is obtained.

The printed with electrode material piezoceramic layers 2 are optionally dried and then stacked in ge ^¬ suitable manner one above the other, wherein a ^¬ al ternierende arrangement of piezoelectric ceramic layers 2 and electronics clear layers 3 is obtained.

Arranged at the electrode layers 3 is also alternately stacked so that on each recess 4 and 4 ^λ in a first electrode layer, the clear areas of the unprinted elec- 4 or 4 ^λ corresponding to a printed with electrode material surface in the next adjacent Elect ^¬ clear layer is, as can be seen in Figure 1. In the embodiment shown in Figure 1, the recesses 4 and 4 ^{λ are provided} alternately in diagonally opposite corner regions. However, it is obvious to one skilled in the art, that the recesses 4 and 4 ^λ at any other point in alternating render sequence on the ceramic layers can be provided.

By the alternating arrangement of every second layer is congruent with respect to its electrode pattern with pre ^¬ provided recesses 4. In the intervening likewise mutually congruent layers, the recesses 4 ^λ with respect to the recesses 4 are arranged offset.

In this way, a stack of so many superimposed individual layers is formed that a desired Ge ^¬ total height of the piezoelectric actuator is achieved.

Subsequently, according to an exemplary embodiment of the present invention, in addition to each silver-palladium print, an additional printing operation is carried out in which a silver paste 5 is printed in the recesses 4 or 4 ^λ , as schematically illustrated in FIG. Thus ^¬ with, only the recesses 4 and 4 ^λ of approximately Ausspa- areas having the silver paste 5 printed, whereas the other production processes remain unchanged. Consequently, each layer consists of an electrode portion 3 printed with a silver-palladium paste and a recess portion 5 printed with a silver paste 5.

After a suitable aligning and stacking of the individual layers, sintering is carried out for example, under light pressure in an oxidizing atmosphere for a predetermined time and at a predetermined sintering temperature which may be, for example, to more than 1000 ⁰ C. Currency ^¬ rend sintering reaches the silver in the silver-palladium paste by diffusion due to the presence of the palladium a uniform concentration distribution in the palladium. Thus, the silver remains in the Elektrodenbe- areas 3, which have a palladium content. In contrast, the silver diffuses into the Silberpas ^¬ te ^λ 5 in the recesses 4 and 4 due to its high diffusivity almost completely out of the recess ^¬ areas 4 and 4 ^λ and into the adjacent silver-palladium electrode regions 3 into it. Due to the diffusion of silver from the recessed portions 4 and 4 ^λ into the adjacent electrode layers 3 are relief recesses 6 and 6 ^λ in the areas of the recesses 4 and formed ^λ 4, as is schematically indicated in Figure 3 by the dashed lines.

The recesses 4 and 4 ^λ comprising recess portions have due to the diffusion of the electrically conductive silver particles on an electrically insulating or electrically non-conductive property, which is required for a connecting ^¬ de external contact only every second layer. This allows the time-tested Kontak- tierungstechnologie of the piezoelectric actuator to be retained unchanged upright ^¬.

Furthermore adhere two adjacent electrode layers in the recessed portions 4 and 4 ^λ due to the generated discharge recesses 6 and 6 ^λ in these fields not to each other, since according to the present embodiment, in each of the two corner portions diagonally opposite to each second layer has a separating point by from ^¬ diffused silver paste is done. It can successfully ^¬ sparungsbereichen Lich at a polarization of the piezoelectric actuator 1 no material ^¬ union stresses between the inactive training ^λ 4 or 4 and the active, the electrode layers to build 3-bearing areas of the piezoceramic.

FIG. 3 illustrates a perspective view of a finished piezoactuator 1, which is contacted with an outer metallization 8 in strip form for electrical contacting at opposite corners. Due to the Cell layer to single layer alternating electrode structure reaches such an external contact 8 only each second electrode layer, while the attached to the gegenüberlie ^¬ ing edge outer contact 8 contacts the respective dazwi lying electrode layers. Thus, an electrically parallel interconnection of the piezoelectric material layers lying between the electrode layers is possible, which enables optimum operation of the piezoelectric actuator 1.

Accordingly, the present invention provides a piezoactuator and a method for producing the same, wherein due to the separation points or relief recesses achieved during the sintering in the areas of the recesses 4 and 4, ^λ electrically non-conductive regions as well as mechanically relieved areas for preventing mechanical stresses become. The method according to the invention ensures that no new technology has to be introduced and no new production facilities are required. Furthermore, due to the use of the silver paste and the silver-palladium paste, no new chemical compounds or elements are added to the chemical system of the piezoactuator, which could lead to unknown effects. Furthermore, silver compared to palladium inexpensive so that additional material costs are unwesent ^¬ Lich. The additional screen printing process for printing the silver paste is compared to additional manufacturing ^¬ steps in previous measures to avoid cracks easy and inexpensive to accomplish.

Although the present invention has been described with reference to preferred embodiments, it is not limited thereto, but modify in many ways ^¬ bar.

For example, instead of the silver-palladium paste, another precious metal-containing metallizing paste with a low diffusivity of the electrically conductive particles are used in a sintering of the stack. Furthermore, the can also be used instead of the silver paste as a material relief ^¬ another precious metal-containing paste or a suitable res On the other relief material with a very high Dif ^¬ fusion capability of the electroconductive particles during sintering of the stack can be used. In general, any relief material is suitable which ensures an electrically non-conductive region in the recess ^regions and adhesion between adjacent layers for

Forming a relief recess or a discharge area prevented.

Further, the recessed portions can be used instead of diagonally opposite corner regions within the layer surface can be provided, for example such that hole ^¬ holes in the longitudinal direction of the piezoelectric actuator in each case through each recess pattern extend. Thus, a contact from the outside of the piezoelectric actuator to the inside can be advantageously laid. For example, geeig ^¬ items contacting means in the at least two bores are made in such a way that only every second turn E- lektrodenschicht electrically contacts and the intermediate layers due to the intended Aussparungsbe- not rich are contacted. In addition, adjacent layers do not adhere to each other in these recessed areas because of the relief recesses.

Claims

claims

1. A method for producing a piezoelectric actuator (1), with fol ^¬ ing method steps:

Providing a plurality of piezoelectric material layers (2) which can be joined together to form a stack;

Applying in each case one cutout (4; 4 ^λ ) of the electrode layers (3) to the plurality of piezoelectric material layers (2) such that an alternating sequence of piezoelectric material layers (2) and electrode layers (3) results in the stack, wherein electrode layers (3) with a recess (4) in a first recess region and electrode layers (3) with a recess (4 ^λ ) are alternately provided in a second recess region, which differs from the first recess region, in the stack; and

- Provision of a relief material (5) in the first and second recesses (4, 4 ^λ ), which after sintering the stack electrically insulating and the individual Mate ^¬ rialschichten (2) non-adherent properties.

2. Ve rfahren according to claim 1., characterized in that the plurality of piezoelectric material layers (2) each having a noble metal-containing metallization (3) having a low diffusion ability of the electrically lei ^¬ Tenden particles during sintering of the stack, Example ^¬ as a silver -Palladium-containing paste is printed as electrode ^¬ layers.

3. Method according to at least one of the preceding claims, characterized in that that a precious metal-containing paste (5) with a very high diffusivity of the electrically conductive particles during sintering of the stack, for example a silver containing paste ^¬, in the recesses (4; 4 ^λ) is printed as a relief material.

4. The method according to at least one of the preceding claims, characterized in that are used as piezoelectric material layers (2) ceramic green sheets.

5. The method according to at least one of the preceding claims, characterized in that each second electrode layer (3) in the stack with a recess (4) in a first corner region and each provided therebetween electrode layer (3) with a recess (4 ^λ ) in a the first corner region opposite the second corner region are formed.

6. The method according to at least one of the preceding claims, characterized in that the piezoelectric actuator (1) is formed with at least two longitudinally extending bores, wherein the Ausspa ^¬ ments (4) of the first recess region in the region of a bore and the recesses (4 ^λ ) of the second recess region (4 ^λ ) in the region of the other bore in the stack are provided in alternating sequence, wherein the bores are each coupled to an electrical contact.

7. Piezo actuator (1),

with a plurality of piezoelectric material layers (2) assembled into a stack; and

with electrode layers (3) which are applied to the plurality of piezoelectric material layers (2) in each case in such a way were introduced, that in the stack results in an alternating sequence of piezoelectric material layers (2) and electrode layers (3);

wherein electrode layers (3) with a relief Ausspa ^¬ tion (6) in a first recess region and electrode layers (3) with a relief recess (6 ^λ ) in a second, different from the first recess region recess portion (4 ^λ ) in the stack provided alternately are.

8th . Piezoelectric actuator (1) according to claim 7, characterized in that the electrode layers (3) consist of a precious metal-containing metallization with a low diffus ^¬ onsfähigkeit the electrically conductive particles in a sintering of the stack, for example, a silver-palladium-containing paste.

9. piezoelectric actuator according to at least one of claims 7 or 8, characterized in that the plurality of piezoelectric material layers (2) are formed as ceramic green sheets.

10. piezoelectric actuator according to at least one of claims 7 to 9, characterized in that each second electrode layer (3) in the stack a Ent ^¬ lastungsaussparung (6) in a first corner portion and each provided therebetween electrode layer (3) a dismissal tung recess (6 ^λ ) in a second corner region opposite the first corner region.

11. piezoelectric actuator according to at least one of claims 7 to 10, characterized in that the piezoelectric actuator (1) has at least two longitudinally extending bores, wherein relief reliefs (6) in the region of a bore and relief Ausspungsausspa- ments (6 ^λ ) are provided in the region of the other bore in the stack in an alternating sequence, wherein the bores can be coupled with an electrical contact.