Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-12-22
2001-05-15
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S364000, C310S369000, C310S320000
Reexamination Certificate
active
06232701
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to piezoelectric components and, more specifically, piezoelectric components including multiple layers of ceramic piezoelectric materials and electrode layers sandwiched between the ceramic layers. The present invention is also directed toward a method of manufacturing such a piezoelectric component.
BACKGROUND OF THE INVENTION
A piezoelectric component is composed, for example, of a piezo ceramic layer that has both sides provided with a metallic electrode layer. When a different electrical voltage is applied to these electrode layers, then the piezo ceramic layer reacts with a lattice distortion. As a result thereof, the component expands and contracts in a direction that is defined by the arrangement of the piezo ceramic layer and of electrode layers.
DE 196 15 694 discloses a piezoelectric component in the form of a piezo actuator in monolithic multilayer structure. The piezo actuator comprises a stack of alternating electrodes and piezo ceramic layers. One electrode layer serves each neighboring piezo ceramic layer as electrode. To that end, an electrical contacting of the electrode layers ensues in an alternating polarity. The alternating polarity is achieved with the assistance of two metalization strips that are laterally applied to the stack. One metalization strip extends over a height that derives from piezoelectrically active layers of the stack stacked on top of one another. The stack has a quadratic base area. The electrical contacting of the electrode layers ensues at opposite comers of the stack. The spacing from electrode to electrode of different polarity amounts to approximately 80 &mgr;m. One of the metalization strips is electrically conductively connected to each second eletrode layer and is insulated from each first electrode layer lying there between. By contrast thereto, the second metalization strip is insulated from every second electrode layer and is electrically conductively connected to each first electrode layer. An insulation of an electrode layer relative to a metalization is achieved in that the electrode layer comprises a recess in a region in which the metalization is applied. The piezo actuator is piezoelectrically inactive in this region since no lattice distortion can be produced here by applying a voltage.
It is important for the functionability of the described piezo actuator that each electrode layer is electrically contacted in the piezoelectrically inactive region. At the same time, it is important that an electrical arc-over or a short-circuit is avoided in a piezoelectrically active area. A lattice distortion occurs in the piezoelectrically active area by applying a voltage. An arc-over can occur between neighboring electrode layers or an electrode layer and an arbitrary electrode of the piezo actuator. A short-circuit can be produced, for example, by mechanical damage, contamination and an influence of atmospheric humidity and/or a fuel (diesel, oil, etc.).
SUMMARY OF THE INVENTION
An object of the invention is to disclose how, given a piezoelectric component, a reliable electrical contacting of every electrode layer can be produced and how an electrical arc-over between electrodes of different polarity can be avoided at the same time.
A piezoelectric component is provided for achieving this object. According to this solution, the component comprises a stack comprising at least two ceramic layers and: an electrode layer arranged between two ceramic layers, characterized in that an interspace that comprises an electrically insulating material is present between the ceramic layers.
The component is, for example, a piezo actuator comprising a stack that comprises a monolithic multi-layer composite of ceramic and electrode layers.
The underlying idea of the invention is comprised in specifying a piezoelectric component having an optimally large piezoelectrically active cross sectional area. A lattice distortion of the piezo ceramic occurs over this cross sectional area. At the same time, however, an electrical arc-over between electrode layers of different polarity should be avoided. This succeeds with the assistance of a recited interspace. The interspace is therefore preferably arranged in a piezoelectrically active region of the stack. The interspace increases an effective distance from electrode layer to electrode layer of different polarity. As a result thereof, for example, the probability is decreased that an electrical short will occur between the electrodes due to dirt.
In an embodiment, the interspace is open at one side. The interspace is located at one side of the stack, particularly at a side of the piezoelectrically active region of the stack.
In an embodiment, the interspace is arranged at a hole of the stack. The hole passes through the stack, particularly perpendicular to the layers of the stack. The hole can entirely or only partially pass through the stack.
The material of the interspace comprises, for example, a gas, particularly a dry gas.
In an embodiment, the material of the interspace comprises a plastic. The entire lateral surface of the stack is preferably provided with a protective layer of plastic. The material of the interspace is thereby a component part of the protective layer. The protective layer has the job of protecting the sensitive, piezoelectrically active surface of the piezo actuator against damage, contamination and the influence of atmospheric humidity and fuels. At the same time, the protective layer functions as insulator in an interspace.
A silicone elastomer is particularly suited as plastic. An elasticity of the protective layer in a wide temperature range from −40° C. through +150° C. is required, for example, for a use of the piezo actuator in a diesel injection system. This specification is met by a silicone elastomer.
In an embodiment, the stack has a ceramic layer that comprises a lead zirconate titanate (PZT, PbZr
x
Ti
1-x
O
3
). An electrode layer thereby particularly comprises a substance that is selected from the group of palladium and/or silver. An alloy of said substances having a ratio of palladium to silver of 30 to 70 is particularly advantageous. An electrode is also conceivable that comprises copper and/or nickel.
For achieving the object, a method for manufacturing a piezoelectric component is recited in addition to a piezoelectric component. Ceramic layers and electrode layers are arranged such to form a stack given the component to be manufactured that the layers terminate flush at a lateral surface of a piezoelectrically inactive region of the stack. The method is characterized by the following method steps: a) sintering a stack of at least two glean ceramic foils and an electrode layer arranged there between, and b) removing a material of a ceramic layer and/or of electrode layer at a lateral surface of the inactive region of the stack.
In an embodiment of the invention, the removal ensues by grinding. The grinding is implemented, for example, with a diamond grinding tool. A relative direction of the grinding can be freely selected with reference to a position of the layers of the stack.
In an embodiment, a lateral surface of the piezoelectrically active region remains in a condition as it was present after the sintering (as fired). This surface of the active region is thus not ground.
Before the sintering, a stack of green ceramic foils and electrode layers arranged there between is produced. A manufacture of this stack advantageously occurs in the panel [or: blank] (multi space up). Larger green ceramic foils and electrode layers are thereby arranged above one another to form a panel [or blank] stack. The individual stacks to be sintered are separated from this panel [or blank] stack. This ensues, for example, by cutting, punching or sawing. A smearing of electrode material at the lateral surfaces of the stack can thereby occur.
A combination of lead zirconate titanate ceramic and an electrode material is the form of an alloy of palladium and silver is especially
Cramer Dieter
Lubitz Karl
Schuh Carsten
Addison Karen
Ramirez Nestor
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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