WO2007137950A1

WO2007137950A1 - Fully active piezo actuator, and method for the production thereof

Info

Publication number: WO2007137950A1
Application number: PCT/EP2007/054817
Authority: WO
Inventors: Carsten Schuh; Andreas SCHÖNECKER; Bent BRÜCKNER; Sylvia Gebhardt; Morgane Radanielina; Thorsten Steinkopff
Original assignee: Siemens Aktiengesellschaft; Fraunhofer Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2006-05-31
Filing date: 2007-05-18
Publication date: 2007-12-06
Also published as: DE102006025362A1

Abstract

The invention relates to a fully active piezo actuator and a method for producing the same. The disclosed piezo actuator comprises a plurality of piezoelectric ceramic layers (10) whose faces are covered by full-area inner electrodes (20). The inner electrodes (20) can each be electrically connected to control electronics by means of one respective contact member (30). The invention further relates to a method for producing said fully active piezo actuators (1).

Description

description

Fully active piezoelectric actuator and process for its production

1. Field of the invention

The present invention relates to a fully active piezoelectric actuator, in particular a multilayer actuator, and a method for its production.

2. Background of the invention

The piezo actuators or stacks are designed as multilayers to achieve the required operating field strength of 2 kV / mm in a cost-effective system environment (drive sources, cabling). For the commonly used piezo actuators with a ceramic layer thickness of 80 microns z. B. a drive voltage of 160 V required.

The use of multilayer structures has a number of disadvantages, in particular with regard to component reliability. According to the prior art, the internal electrodes are alternately connected to the component surface by means of a collecting electrode and then connected via two leads to the drive source.

To avoid short circuits, the inner metallization of the counter-pole inner electrode in the region of the collecting electrode is not led out to the surface, ie they cover only part of the surface of the adjacent piezoelectric ceramic layer. As a result, an inactive area arises in the stack, which causes strong gradients of the electric field and thus also the mechanical stresses in the component. The manufacturers of multilayer actuators have developed special design solutions that allow reliable operation of the piezo actuators with inactive areas up to 10 ⁹ cycles.

However, the requirements from the system view are not satisfied satisfactorily. First, the partial area electrodes cause cracks in the component, which in principle can not be avoided. After the polarization of the piezoelectric actuator there is an initial damage, which is the trigger for a mechanical failure at high number of cycles. The combination of all the same-pole electrodes excludes the individual activation of individual ceramic layers. There are thus no possibilities for implementing strategies for homogenizing the mechanical and electrical loads in the stack, for introducing health monitoring or monitoring the piezoelectric layers for functional moisture, or for individually switching off faulty layers under operating conditions. Another aspect is the limitation of miniaturization, since with a cross-sectional reduction of the stack, the relative proportion of the passive volume grows and thus the efficiency of the actuator decreases.

It is therefore the problem of the present invention to provide a piezoelectric actuator that is improved in comparison with the prior art. It is another problem of the present invention to provide a manufacturing method for such a piezoactuator.

3. Summary of the Invention The above problem is solved by a fully active piezoactuator according to independent claim 1 and by a manufacturing method for this fully active piezoactuator according to independent claim 6. Advantageous embodiments and further developments of the piezoelectric actuator and its manufacturing method will become apparent from the following description, the drawings and the appended claims.

The fully active piezoactuator, in particular a multilayer actuator, has the following features: a plurality of piezoelectric ceramic layers, the opposite sides of which are oriented perpendicular to a stacking direction of the piezoactuator are covered by fully flat internal electrodes, a plurality of contacts are arranged on at least one side panel surface of the piezoelectric actuator parallel to the stacking direction, which are arranged such that each inner electrode is electrically connectable via a respective contact and / or that groups of inner electrodes are closed together via one contact in each case are electrically connected.

The piezoelectric actuator according to the invention is formed by a multilayer structure of piezoelectric layers and internal electrodes without inactive contacting zones. For this purpose, the internal electrodes are fully perpendicular to the

Stacking direction of the piezoelectric actuator arranged arranged side surfaces of the piezoceramic layers. To ensure safe actuation of the piezoelectric actuator, each inner electrode is individually connected electrically by means of a contacting. On this technical basis, the individual piezoelectric layers of the fully active piezoelectric actuator are individually controllable, each usable as a sensor within the piezoelectric actuator, in their function switched on and off and specifically regulated to optimize life and performance of the piezoelectric actuator. It is likewise preferred to electrically actuate groups of inner electrodes which are closed together via a respective contacting. Depending on the contacting of the internal electrodes, the layers of the piezoelectric actuator can thereby be controlled individually or a number of the layers individually and a different number in groups or only in different groups.

According to a further embodiment, the contacts are made of electrical leads to the individual internal electrodes or in each case a contacting pad is applied to each internal electrode.

According to one embodiment of the present invention, the plurality of contacts on the at least one side surface of the piezoelectric actuator is electrically connected via a leadframe and a plurality of contact bridges. It is further preferred that the contacts on this Leadframe individually controllable. The use of a leadframe in conjunction with the fully active piezoelectric actuator creates a constructive possibility of electrically connecting the plurality of internal electrodes without the use of a common external metallization of the piezoactuator. In addition, the leadframe provides the prerequisite that not only a group-wise control of internal electrodes but actually an individual control of each internal electrode in the fully active piezoelectric actuator is possible.

According to a further embodiment, the leadframe comprises evaluation and / or control electronics for at least one function of the piezoelectric actuator.

The production process of the fully active

Piezoactuator comprises the following steps: a) connecting a plurality of piezoelectric ceramic layers to a stack, in which perpendicular to a stacking direction of the stack o-oriented opposite sides of the piezoelectric ceramic layers are covered by full-surface internal electrodes, b) determining a respective position of the internal electrodes at least one side surface of the stack oriented parallel to its stacking direction; and c) applying one contact per inner electrode to one of the side surfaces of the stack, such that the contact and each one of the inner electrodes are electrically connected together.

4. Detailed Description of the Accompanying Drawing The preferred embodiments of the present invention will be further described with reference to the accompanying drawings. Show it:

Fig. 1 is a schematic side view of an embodiment of the fully active piezoelectric actuator with rectangular

Cross-section, 2 is a schematic sectional view along an inner electrode of the piezoelectric actuator according to FIG. 1,

3 is a schematic representation of the piezoelectric actuator of FIG. 1 with leadframe and connected electronics according to a preferred embodiment, FIG.

4 is a schematic side view of another embodiment of the fully active piezoelectric actuator with a round cross-section,

5 is a schematic sectional view along an inner electrode of the piezoelectric actuator of FIG. 4,

Fig. 6 is a schematic representation of another embodiment of the fully active piezoelectric actuator.

5. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The invention discloses a fully active piezoactuator 1, preferably a multilayer actuator, as shown schematically in a side view in FIG. The piezoelectric actuator 1 comprises a plurality of piezoceramic layers 10, which are arranged one above the other to form a stack or stack with a stacking direction 50. According to one embodiment, the piezoelectric actuator 1 seen in its upper and lower end in the stacking direction 50 inactive cover packages (not shown). The end faces of the piezoceramic layers 10 transversely to the stacking direction 50 are each completely covered by internal electrodes 20. The inner electrodes 20 each extend to the side surfaces of the stack, which are arranged parallel to the stacking direction 50. This is indicated by the dashes with the reference numeral 20 in Fig. 1. Based on this arrangement results in a fully active piezoelectric actuator without inactive areas that would represent areas of high mechanical and electrical loads of the piezoelectric actuator 1.

In order to make the majority of the above-mentioned piezoelectric ceramic layers 10 into a stack with full-surface internal electrical To connect the 20, resorted to common in the prior art manufacturing process for piezoelectric actuators. These manufacturing methods provide a piezoelectric actuator 1 with a rectangular cross-sectional area, as shown by way of example in FIGS. 1 and 2. It is also conceivable to produce piezoelectric actuators 1 with a round cross-section according to the embodiments in FIGS. 4 and 5. As further alternatives, the cross sections of piezoelectric actuators 1 are hexagonal or octagonal.

Each of the internal electrodes 20 has an individual contact or an individual electrical connection to a control, evaluation and power electronics. According to a further embodiment, in each case a plurality of internal electrodes are combined to form a group, which is then connected / driven via a group-specific contacting. In this way, piezoactuators are made with only individually contacted layers or with individual contacted layers and groups of layers or only with individual contacted groups of layers. The contacting is produced according to an embodiment directly by connecting a suitable contacting means 70 with the individual internal electrodes 20. Contacting means 70 include, for example, bonding wire, metal strand and / or electrically conductive polymers.

In addition to or instead of the direct contacting of the inner electrode 20, a contacting pad 30 is applied in each case to the inner electrode 20 to be contacted. Contacting pads 30, in adaptation to the size of the piezoactuator 1, have, for example, a surface area of 20 × 20 μm ² . Its surface is also adapted in such a way that a contacting pad 30 overlaps only one inner electrode 20 in a partial area provided for this purpose. In addition, the area and arrangement of the contacting pad 30 with respect to adjacent internal electrodes 20 or adjacent contacting pads 20 are chosen such that electrical flashovers are prevented. Contact pads 30 and thus the internal electrodes 20 which are electrically connected to them are then likewise electrically connected to the aforementioned electronics via the above-mentioned contacting means 70. The direct electrical connection of the inner electrode 20 or the connection of the inner electrode 20 via the respective contacting pad 30 takes place by means of different methods. These methods include known bonding, soldering, welding and / or gluing.

The requirements for the positional accuracy of the contacts of the internal electrodes 20 depend on the dimensions of the piezoceramic layers 10 and the internal electrodes 20 lying between them. In one embodiment, for example, the internal electrodes have a thickness of 80 ± 5 μm, while the internal electrodes 20 2 μm are thick. In order to provide a sufficient life of the piezoelectric actuator 1, moreover, the contacts must be constructed sufficiently reliable. Due to the function of the piezoelectric actuator 1 undergoes a longitudinal expansion under operating conditions, so that the contacts must be designed durable.

Taking into account the abovementioned boundary conditions, a single contacting of the internal electrodes 20 is carried out with the aid of the following steps. First, one detects the position of the inner electrodes 20 on the side surface of the piezoelectric actuator 1, which are arranged parallel to the stacking direction 50. This detection is carried out by means of optical, physical or chemical methods. After the position of the inner electrodes 20 is known, in each case one contacting pad 30 per inner electrode 20 is screen-printed, dispensed, PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition) or similar suitable method. A further alternative is to connect contacting means 70 directly to the individual internal electrodes 20 instead of the contacting pads 30. If the contact is realized via contacting pads 30, then closing still feeding and tying a suitable contact means 70 to the respective contacting pad 30th

In order to produce an efficient and space-saving electrical connection to the individual internal electrodes, a leadframe 60 known from the semiconductor industry is provided. This is shown by way of example in FIGS. 2, 3, 5 and 6. The leadframe 60 preferably consists of a structured, ie conductor tracks containing, metal frame with defined electrical connections to the internal electrodes 20. Another alternative of the leadframe 60 is to construct it similar to a known from microelectronics circuit board.

The electrical connections between inner electrode 20 and leadframe 60 are made via the aforementioned contacting means 70 or other suitable contact bridges. FIGS. 2 and 5 show an alternative of the leadframe 60, which is arranged adjacent to the piezoactuator 1. A further embodiment of the leadframe 60 is shown in FIG. 6, in which the leadframe 60 is arranged away from the piezoactuator 1.

As shown schematically in FIG. 3, the lead frame represents

60 an electrical connection 80 to the control, evaluation and power electronics (not shown) ready. A part of the control and evaluation is already arranged on the leadframe 60, if the spatial requirements of the entire arrangement of piezoelectric actuator 1 and electrical supply allow this. Such electronics on the leadframe includes, for example, chips, transistors, switches and similar electronic elements for controlling the piezoelectric actuator. 1

The control, evaluation and power electronics implemented based on the individual controllability of each individual inner electrode 20 macroscopic control and evaluation of the piezoelectric actuator 1 now in a microscopic Frame. While previously only the activation of the entire piezoelectric actuator and the evaluation of its signals or a group of piezoelectric layers 10 was possible, ie control and evaluation in the macroscopic frame, this is now done for individual piezoelectric layers 10 of the piezoactuator 1 , ie control and evaluation in a microscopic framework.

The above electronics realize the following or part of the following functions. As is shown schematically, for example, in FIGS. 3 and 6, the piezoceramic layers 10 of the piezoactuator 1 are individually controlled via the individual contacts of the internal electrodes 20. On the basis of the individual control, the representation of complex stress gradients in the piezoactuator 1 is possible. The piezoceramic layers 10 are selectively driven in the piezoelectric actuator 1 with different electrical field strengths, for example to achieve lower mechanical stresses at the transition from the active piezoceramic layers 10 to the cover package of the piezoelectric actuator 1. For this purpose, the piezoceramic layers 10 located in this boundary region are supplied, for example, with smaller electrical voltages than the piezoceramic layers 10, which are located further away from the cover plate of the piezoactuator 1.

According to a further embodiment, piezoceramic layers 10 are actuated offset in time with specific electrical voltages in order to reduce or prevent the formation and propagation of shock waves in the piezoactuator 1 in this way.

Furthermore, the individual control of the internal electrodes 20 realizes a standardization of the stress levels of the individual piezoceramic layers 10 in the piezoelectric actuator 1. Thus, for example, the clamping forces at the top and bottom of the piezoelectric actuator seen in the stacking direction 50 by controlling a different degrees of strain in the individual piezoceramic layers 10 compensated. It is further preferred to use at least one piezoceramic layer in the piezoelectric actuator 1 as a sensor layer. During the operation of the piezoelectric actuator 1, this sensor layer is exposed to mechanical stresses, as a result of which propor- tional evaluable electrical signals are generated in the sensor layer, which can be read out via the internal electrodes 20 and thus evaluated. In this way, cracks can be seen, which can be influenced by targeted regulation of the stress levels in the piezoelectric actuator 1, so that a failure of the piezoelectric actuator 1 or individual piezoceramic layers 10 is prevented. Furthermore, electrical setpoints of the piezoceramic layers 10 can be measured via the internal electrodes 20, so that, for example, switching off individual layers is possible on detection of an error. For example, voltage and current signals are read out via the inner electrodes 20 in order to determine the capacitance, and the conductivity of the piezoceramic layers 10 is detected from the small signal capacitance and the loss angle.

In order to maintain the operation of the piezoelectric actuator 1 despite switching off individual layers 10, for example, the remaining operable piezoceramic layers 10 are operated with a larger electric field, so that the required expansion behavior of the piezoelectric actuator 1 is maintained.

The monitoring of the functional moisture of the individual piezoceramic layers 10 described above is also referred to as health monitoring. The targeted shutdown of faulty layers 10 and the distribution of the force-path generation on the remaining active piezoceramic layers 10, the life of the piezoelectric actuator 1 is increased.

Another advantage is that the active volume of the piezoelectric actuator 1 and thus the power density are maximally increased by the fully active stack structure without inactive contacting zones. This has an advantageous effect on the Cost efficiency in the production of the piezoelectric actuators 1 and the later required space for installation of the piezoelectric actuator 1 from. In other words, the ever-increasing miniaturization, for example in motor vehicle construction, is supported in this way.

Overall, the above-described constructive concept allows each individual ceramic layer to be individually sensory detected and correspondingly electrically controlled. In this way, the possibility is given to even out the occurring mechanical and electrical loads in the stack to perform the health monitoring and to realize the individual shutdown or shutdown of faulty piezoceramic layers 10 under operating conditions of the piezoelectric actuator 1.

The present invention thus represents a decisive key for the increase in reliability, the increase in the control accuracy and the controllability of the piezoelectric actuator 1 as a control element. This is in particular by the full-surface inner electrodes within the ceramic multilayer component 1 and the space-saving Weiterkontaktierung on the leadframe 60 guaranteed.

Claims

claims

1. Fully active piezoelectric actuator (1), in particular a multi-layer actuator, which has the following features: a. a plurality of piezoelectric ceramic layers (10) whose opposite sides perpendicular to a stacking direction (50) of the piezoactuator (1) are covered by full-surface internal electrodes (20), b. a plurality of contacts on at least one side surface (40) of the piezoelectric actuator (1) parallel to

Stacking direction (50) arranged such that c. Each internal electrode (20) can be electrically connected via one contact each and / or that groups of internal electrodes that are closed together can be electrically connected via one contact.

2. Piezoelectric actuator (1) according to claim 1, whose contacts electrical leads to the individual internal electrodes

(20) or each a Kontaktierungspad (30) on each inner electrode (20).

3. Piezoelectric actuator (1) according to claim 1 or 2, which further comprises a leadframe (60) which is connected via a plurality of contact bridges with the contacts.

4. Piezoelectric actuator (1) according to claim 3, in which the contacting pads (30) can be controlled individually via the leadframe (60).

5. piezoelectric actuator (1) according to claim 3 or 4, in which the

Leadframe (60) evaluation and / or control electronics for at least one function of the piezoelectric actuator (1).

6. Production method of a fully active piezoelectric actuator (1), in particular a multilayer actuator, comprising the following steps: a. Bonding a plurality of piezoelectric ceramic layers (10) to a stack in which is perpendicular to one Stacking direction (50) of the stack oriented opposite sides of the piezoelectric ceramic layers (10) are covered by full-surface inner electrodes (20), b. Determining a respective position of the inner electrodes (20) on at least one side surface (40) of the

Stack oriented parallel to its stacking direction (50), and c. Producing in each case one contacting per inner electrode (20) and / or inner group of electrodes closed together so that the contacting and the respective one inner electrode (20) and / or group of inner electrodes closed together are electrically connected to one another.

7. Production method according to claim 6, with the further step:

Providing the contact in each case as an electrical supply line to the individual internal electrodes (20) or as a Kontaktierungspad (30) per inner electrode (20) on a side surface of the stack.

8. A manufacturing method according to claim 6 or 7, with the further step:

Supplying and connecting a contacting means (70) with the inner electrode (20) or directly via the contacting pad (30).

9. A manufacturing method according to claim 8, wherein the contacting means (70) is bonding wire and / or electrically conductive polymer applied by means of bonding, soldering, welding and / or gluing.

10. Manufacturing method according to claim 7, with the further step: applying the contacting pads (30) by means of screen printing, dispensing, PVD and / or CVD.