Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/80—Constructional details
  • H10N30/87—Electrodes or interconnections, e.g. leads or terminals
  • H10N30/871—Single-layered electrodes of multilayer piezoelectric or electrostrictive devices, e.g. internal electrodes
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/01—Manufacture or treatment
  • H10N30/06—Forming electrodes or interconnections, e.g. leads or terminals
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/50—Piezoelectric or electrostrictive devices having a stacked or multilayer structure
  • H10N30/503—Piezoelectric or electrostrictive devices having a stacked or multilayer structure having a non-rectangular cross-section in a plane orthogonal to the stacking direction, e.g. polygonal or circular in top view
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/80—Constructional details
  • H10N30/87—Electrodes or interconnections, e.g. leads or terminals
  • H10N30/872—Interconnections, e.g. connection electrodes of multilayer piezoelectric or electrostrictive devices
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N30/00—Piezoelectric or electrostrictive devices
  • H10N30/80—Constructional details
  • H10N30/87—Electrodes or interconnections, e.g. leads or terminals
  • H10N30/875—Further connection or lead arrangements, e.g. flexible wiring boards, terminal pins

Definitions

• the present invention relates to a fully active piezoelectric actuator, in particular a multilayer actuator, and a method for its production.
• 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).
• drive sources 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.
• 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.
• 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.
• 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.
• the requirements from the system view are not satisfied satisfactorily.
• 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.
• 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.
• 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.
• the internal electrodes are fully perpendicular to the
• each inner electrode is individually connected electrically by means of a contacting.
• 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.
• 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.
• 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.
• 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.
• the leadframe comprises evaluation and / or control electronics for at least one function of the piezoelectric actuator.
• 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.
• 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,
• FIG. 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
• FIG. 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.
• 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.
• 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.
• piezoelectric actuators 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.
• a plurality of internal electrodes are combined to form a group, which is then connected / driven via a group-specific contacting.
• 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.
• 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 ⁇ m 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.
• 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.
• the internal electrodes have a thickness of 80 ⁇ 5 ⁇ m, while the internal electrodes 20 2 ⁇ m are thick.
• the contacts 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.
• a single contacting of the internal electrodes 20 is carried out with the aid of the following steps.
• 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
• 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.
• FIGS. 2 and 5 show an alternative of the leadframe 60, which is arranged adjacent to the piezoactuator 1.
• FIG. 6 shows a further embodiment of the leadframe 60 in which the leadframe 60 is arranged away from the piezoactuator 1.
• the lead frame represents
• 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
• 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 piezoceramic layers 10 of the piezoactuator 1 are individually controlled via the individual contacts of the internal electrodes 20.
• 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.
• 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.
• 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.
• 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.
• 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.
• at least one piezoceramic layer in the piezoelectric actuator 1 is used 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.
• 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.
• 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.
• each individual ceramic layer to be individually sensory detected and correspondingly electrically controlled.
• 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-savingmanntitle réelle on the leadframe 60 guaranteed.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• General Electrical Machinery Utilizing Piezoelectricity, Electrostriction Or Magnetostriction (AREA)

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Citations (5)

• 2006
  • 2006-05-31 DE DE102006025362A patent/DE102006025362A1/de not_active Withdrawn
• 2007
  • 2007-05-18 WO PCT/EP2007/054817 patent/WO2007137950A1/de active Application Filing

Patent Citations (5)

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