Patent Application
20090243441
A piezoelectric multiple-layer component is specified.
From publication WO 03/094252 A2, a piezoelectric actuator is known, which contains piezoelectric layers and internal electrodes arranged between these layers in a multiple-layer construction.
The task to be accomplished consists in that a piezoelectric multiple-layer component is to be prepared, which can withstand high mechanical and electrical loading.
A piezoelectric multiple-layer component described here can be constructed, for example, as a piezoceramic component with a ceramic base body, structured metal layers arranged therein, and external contacts. Electromechanical deformations of the body can take place, which lead to mechanical stress between the ceramic layers and metal layers and which can lead to the formation of cracks in metal structures accompanied with breaks in the contacts all the way up to detachment of the metallization.
A multiple-layer component is specified with at least two metal layers, which are separated from each other by a dielectric layer and which are connected to each other electrically by a contact element comprising a porous body.
A porous material is especially well suited for damping mechanical vibrations. In a porous body, the propagation of acoustic waves is largely stopped.
The porosity of the body can equal, e.g., more than 10%, in an advantageous way more than 20%. The porosity of a body is understood to be the ratio of the volume of the existing hollow spaces to the total volume of the body.
The pore size is determined, e.g., by the grain size of a material, which is used for producing the porous body, and can lie, for example, between 0.1 to 100 μm, in one variant mainly between 0.1 and 10 μm.
In a preferred variant, a piezoelectric component is specified with a base body, which comprises a stack of piezoelectric layers lying one above the other and electrode layers lying in-between. In each electrode layer there is at least one internal electrode. A contact-forming, electrically conductive contact element, which comprises a porous material, runs perpendicular to the internal electrodes.
The piezoelectric multiple-layer component is preferably a piezoceramic piezoelectric actuator or piezoelectric transformer.
The specified multiple-layer component is distinguished by high reliability and cycle stability because the formation of cracks in the porous material of the contact element is suppressed. If a crack appears, it meets a pore and is stopped in this way. In addition, over time the mechanical stress at the boundary between the ceramic and the metallization is effectively broken down through the formation of many small cracks, without negatively affecting the electrical connection.
The piezoelectric layers preferably comprise ceramic material and are sintered with each other and with the electrode layers. Preferably, first and second internal electrodes are provided one above the other in an alternating sequence. The first internal electrodes each form a contact with a first contact element and are isolated from a second contact element. Conversely, the second internal electrodes each form a contact with the second contact element and are isolated from the first contact element.
In a preferred embodiment, the contact element is constructed in the form of a pin. In one variant, the pin can be made from a porous material. Alternatively, the pin can have a porous body on which an electrically conductive layer is deposited. The electrically conductive layer can be deposited onto the porous body, e.g., in the form of a bonding agent-containing and preferably silver-containing and/or copper-containing metal paste. In this variant, the pin is pushed into a recess or opening provided for the pin in the component base body and sintered together with the piezoelectric layers and electrode layers. During sintering, the metal paste is burned into the base body producing a tight connection between the pin and the base body.
In one variant, the porous body can be electrically conductive, e.g., it is provided as a metal sponge. In another variant, an electrically conductive porous material can be organic.
In an advantageous variant, a solid pin made from an electrically conductive material, preferably a metal, is arranged in the porous body.
Several porous bodies arranged one above the other and separated from each other by an air gap can be fixed on the solid pin. The material of the porous body is preferably electrically conductive.
A contact cap made from an electrically conductive material can be provided on one end of the porous body of the contact element. In one variant, the electrically conductive material of the contact cap can be soldered. The contact cap can comprise solder or can be covered with a solder layer. The contact cap can be formed from a metal film, which covers the end of the pin-like contact element or the end of the porous body.
It is possible to insert the contact element only partially into the base body. In this case, a recess for receiving the contact element is formed on one side of the base body.
A part of the contact element preferably engages with a positive fit in this recess and is fixed in this recess, e.g., by means of a bonding agent. The bonding agent preferably represents an electrically conductive layer. The bonding agent can comprise organic components.
In another construction, it is possible to arrange the contact element for the most part in the interior of the base body, wherein the jacket surface of the contact element is preferably surrounded on all sides by the base body in cross section perpendicular to the alignment of the contact element. In the interior of the base body there is an opening for receiving the contact element.
The porous material can have an open-pore construction, i.e., most of its pores can be connected to each other.
The porous body can be made from an inorganic material, which is not electrically conductive in one variant, e.g., ceramic, whose surface is provided with an electrically conductive layer. The electrically conductive layer is preferably a metal layer.
In another variant, the electrically conductive porous material can be formed from an organic material whose surface is provided with an electrically conductive layer, e.g., made from metal.
The contact element is preferably oriented parallel to the piezoelectric axis. It is advantageous to arrange the contact element at a position of the base body, where the smallest mechanical stresses occur. This can be, for example, the middle region of the base body. Therefore, in one variant, the contact element can be arranged in the center in the interior of the base body.
The contact element arranged in the center in the interior of the base body can have a metal pin and several segments, which are made from a conductive, porous material and which are fixed to this pin and electrically connected to the metal pin. These segments are preferably arranged at a distance from each other in the axial direction. In one variant, it is also possible to fix several segments, which are spaced apart from each other in the peripheral direction and which are made from a porous material, on a pin.
In a first embodiment of the invention, the contact element can be pushed into the layer stack before decarburization and before sintering. Then it is advantageous to adjust the dimensions of the hole to the dimensions of the contact element, so that after the sintering of the layer stack, the layers are shrunk onto the contact element to a certain extent due to the shrinkage of the ceramic contained in the piezoelectric layers and thus an electrical contact between the contact element and the electrode layers can be formed.
Furthermore, here it is advantageous when the contact element consists up to at least 50% at least on its surface of the same material, from which the electrode layers are formed. This guarantees a relatively good chemical connection of the contact element to the electrode layers, which improves the electrical contact between the contact element and electrode layers.
Through suitable dimensions of the hole and contact element as well as shrinking the ceramic material onto the contact element, a positive-fit or non-positive-fit connection between the contact element and the body can be established. A positive-fit connection is advantageous for the production of the electrical contact between the contact element and the electrode layers.
In another embodiment of the invention, the contact element or the formation of the hole can be realized after the decarburization and sintering of the layer stack. In this case, if the contact element is to be used, in turn, for forming a contact for the electrode layers, it is advantageous if the dimensions of the hole and the contact element are adjusted to each other, so that in the sintered state of the layer stack, the contact element can still be pushed through the hole; that is, a certain minimum play exists between the inner wall of the layer stack and the outer wall of the contact element. To produce a reliable contact, it is then advantageous to provide, for example, the contact element on its outer side with graphite or another electrically conductive lubricant, which allows the intermediate spaces necessary for pushing in the contact element to be filled and which ensures a good contact between the contact element and the electrode layer.
Below, the invention is explained in more detail with reference to embodiments and the associated figures. The figures show different embodiments of the invention with reference to schematic and not-to-scale representations. Parts that are identical or that have identical functions are designated with the same reference symbols. Shown schematically are:
In a cut out,
The internal electrodes 3, 4 form contacts alternately with contact elements 1, 2. The associated internal electrodes—first electrode layers 3 or second electrode layers 4—are connected to each other electrically by means of the contact elements 1 or 2 insulated from the corresponding other internal electrodes. The contact elements 1, 2 extend transverse to the main surfaces of the internal electrodes.
The contact elements 1, 2 each comprise a porous body 11. An electrically conductive layer 12 is deposited onto the surface or jacket surface of the porous body 11.
In
The component according to
The contact elements 1, 2 with a porous body are preferably preformed before the sintering of the base body. The jacket surface of the porous body and/or the surface of the provided recess is covered with a bonding layer, e.g., a metal paste, and the contact element is placed in the recess. The base body is then sintered together with the contact element.
In the variant shown in
In the other variant of a piezoelectric multiple-layer component shown in
In the base body, an opening, in which the contact element preformed in the shape of a pin is pushed, is constructed transverse to the electrode layers.
In
In
The porous body 10 is preferably cylindrical, but in principle can be a porous pin with an arbitrary cross section.
An electrically conductive cap 6, which is used to make another contact between the component and, e.g., a supply line 60, is placed over one end of the porous body 10. The supply line 60 is, for example, an electrical wire.
In
In
The pin 100 is preferably, but not necessarily, made from metal. Any sufficiently stable, electrically conductive material can be used.
A solid pin can be replaced in
The invention is not limited to the presented embodiments. For producing a porous body of the contact element and also the dielectric layers of the base body of the component, any suitable materials can be used.
The porous body of the contact element can be preformed, but this is not a requirement. For example, there is the possibility of filling an opening provided for a vertical electrical connection in a dielectric layer with a filler, which comprises, in addition to electrically conductive particles, also other substances that form gases during sintering, which leads to the formation of pores in the filler.
All metals or metal alloys that are stable under sintering conditions are suitable as the electrode layers. In particular, electrode layers made from copper or from a mixture of silver and palladium in a weight ratio between 90/10 and 70/30 can be used.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 003 693.7 | Jan 2005 | DE | national |
| 10 2005 017 108.7 | Apr 2005 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE2006/000114 | 1/25/2006 | WO | 00 | 1/12/2009 |
