JP2006351602A - Multilayer piezoelectric actuator device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer piezoelectric actuator device having a highly reliable element structure where insulation performance is not deteriorated even under a severe driving environmental condition where large displacement is repeated for long time. <P>SOLUTION: Slit-like air gaps 2 are previously formed inside a piezoelectric ceramic layer 1a at prescribed intervals. Connections of inner electrode layers 1b and outer electrodes 3 are performed at the prescribed interval so that they become the same poles. Electric connections of the adjacent inner electrodes 1b and the outer electrodes 3 are arranged and laminated across the piezoelectric ceramic layer 1a having the slit-like air gaps 2 so that they become the same poles. The outer electrode 3 and the slit-like air gaps 2 are covered with flexible and insulating resin. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piezoelectric actuator, and more particularly to an insulating structure of a laminated piezoelectric actuator element suitable for applications requiring a large amount of displacement and repeated durability performance.

  A laminate in which a thin plate-like or film-like piezoelectric ceramic layer and an internal electrode layer having approximately the same area as the piezoelectric ceramic layer are laminated, and an insulating material layer and a conductive material layer respectively formed on the side surface portion of the laminate. The laminated piezoelectric element is known as a highly reliable element with large displacement (see Patent Document 1).

  However, in the multilayer piezoelectric element disclosed in Patent Document 1, it is very difficult to electrically insulate different internal electrodes from each other. Therefore, a method in which an insulating material is formed on and near every other internal electrode layer by electrophoresis (see Patent Document 2) or a photosensitive resin film is formed on the side end surface of the laminated body and removed every other layer by etching. (Patent Document 3) was proposed.

  However, the multi-layer piezoelectric element based on the electrophoresis method of Patent Document 2 has a problem that the insulating material has a low density, and further shrinks due to the sintering process, so that a necessary insulation distance cannot be secured, resulting in a decrease in insulation. .

  In addition, the multilayer piezoelectric element by etching disclosed in Patent Document 3 cannot use a photosensitive resin, so that the processing temperature cannot be increased, and a material having a baking temperature of 800 ° C. or higher cannot be used for the external electrode layer coated with paste. Therefore, there was a problem that reliability could not be improved.

  A technique that solves such problems of insulation is disclosed in Patent Document 4. The multilayer piezoelectric element of Patent Document 4 is formed on a laminated body in which a thin plate-like or film-like piezoelectric ceramic layer and an internal electrode layer having substantially the same area as the piezoelectric ceramic layer are laminated, and on a side surface portion of the laminated body. In the laminated piezoelectric element having the insulating material layer and the conductive material layer, the insulating material layer has a notch removal portion where the end portions of the internal electrodes that are not exposed at the side surface portion of the laminated body are exposed every other layer, and is electrically conductive. The material layer is formed by embedding the incision removal portion exposed every other layer with a conductive material such as silver paste, and integrating the connecting portion that is electrically connected to the internal electrode that is not exposed on the side surface portion of the laminate. A laminated piezoelectric element. This technology can secure a large amount of displacement, but because the expansion and contraction in the vicinity of the adhesive layer is large, a severe distortion is generated in the piezoelectric ceramic layer immediately below and immediately above the adhesive layer, and it is repeated over a long period of severe driving environment conditions There was a problem that sufficient durability could not be secured.

  A technique for improving a large displacement amount and repeated durability performance is disclosed in Patent Document 5. In the multilayer piezoelectric actuator element of Patent Document 5, a material having an electrostrictive effect and internal electrode layers are alternately laminated, and a laminate in which every other internal electrode layer is connected to a pair of external electrodes has an adhesive layer. In the connected laminated piezoelectric actuator elements connected in series via a plurality of layers, the external electrodes between the laminated bodies are electrically connected by a conductive wire fixed to a portion excluding the adhesive layer. .

  Furthermore, Patent Document 6 discloses a technique of a multilayer actuator that is less likely to fail despite a larger displacement than in the past. The multilayer actuator of Patent Document 6 is a multilayer piezoelectric actuator element composed of a multilayer body in which piezoelectric layers composed of piezoelectric materials having a relative dielectric constant of less than 3000 and internal electrode layers are alternately stacked. A laminated piezoelectric actuator element configured such that a stress relaxation layer sandwiched between adjacent piezoelectric layers and having a smaller elastic modulus than the piezoelectric layer is provided on a side surface portion of the stacked body so that the edges of adjacent internal electrode layers do not overlap. It is.

JP-A-58-196074 JP 59-175176 JP 58-196071 A JP-A-5-259524 JP-A-8-250777 JP 2001-156348 A

  In the internal electrode structure of the multilayered piezoelectric actuator element of Patent Document 4 described above, it is inactive that does not expand or contract even when a voltage is applied to the outer edge portion in three directions excluding the area range corresponding to the external electrode on the surface from which the internal electrode is extracted. Since the portion exists, the boundary portion is distorted, and the insulating portion is cracked due to the internal stress caused by the strain. This crack also affected the internal electrode surface when driving the multilayer piezoelectric actuator element. As a result, there is a problem in that a discharge failure occurs due to voltage application and insulation is lowered due to the influence of humidity in the atmosphere.

  In the multilayer piezoelectric actuator element of Patent Document 5 described above, there is no inactive portion that does not expand or contract even when a voltage is applied to the outer edge portion in three directions excluding the area range corresponding to the external electrode on the surface from which the internal electrode is extracted. As described above, the upper limit of the number of “unit cells” in the multilayer piezoelectric actuator element is limited. Further, the “unit cell” is laminated by bonding the “unit cell” with an adhesive, thereby obtaining a large displacement. A lead wire for connecting another external electrode is provided so that there is no problem even if the external electrode breaks due to expansion and contraction in the vicinity of the adhesive layer. In this case, due to the introduction of the adhesive layer, the expansion and contraction in the vicinity of the adhesive layer is locally increased, and there is a problem that the repeated durability performance deteriorates.

  In the multilayer piezoelectric actuator element of Patent Document 6 described above, by providing a stress relaxation layer or groove on the side surface portion of the multilayer body, the edges of the adjacent internal electrode layers (the edges of the positive and negative electrodes do not overlap each other). In this case, a highly reliable stacked piezoelectric actuator element that does not easily cause failure due to a structure in which stress due to internal strain does not occur is realized. There was a problem that it could not be obtained.

  The present invention has been made to solve the above-described problems, and its technical problem is that it is highly reliable with no failure or deterioration in insulation performance even under severe driving environment conditions in which a large displacement is repeated over a long period of time. It is to provide a laminated piezoelectric actuator element having an element structure.

  A first invention for achieving the above object comprises a laminate in which piezoelectric ceramic layers and internal electrode layers configured using piezoelectric ceramics are alternately laminated, and a main surface from which the internal electrode layers are exposed; In a stacked piezoelectric actuator element in which a pair of external electrodes provided on the other main surface and the internal electrode layers are connected every other layer, in a direction perpendicular to the main surface and the other main surface In this multilayer piezoelectric actuator element, slit-like voids are formed at predetermined intervals so as to enter the inside of the piezoelectric ceramic layer on the outer peripheral portion of the side surface of the laminate.

  A second invention for achieving the above object is a multilayer piezoelectric actuator element in which the electrical connection between the internal electrode layer and the external electrode is continuously made to have the same polarity by a predetermined interval.

  According to a third aspect of the present invention for achieving the above object, at least two or more of the internal electrode layers adjacent to each other with the piezoelectric ceramic layer formed with the slit-shaped voids are electrically connected to the external electrode. This is a stacked piezoelectric actuator element in which various connections are made continuously at the same pole.

  According to a fourth aspect of the invention for achieving the above object, the material in which the slit-shaped gap is burned and scattered at a temperature lower than the sintering temperature of the piezoelectric ceramic is printed on the surface of the piezoelectric ceramic green sheet, and sintered after lamination. The laminated piezoelectric actuator element in which the slit-shaped gap formed in this way and the external electrode are covered with an insulating resin.

  According to the present invention, in order to absorb and relieve the stress generated by the expansion and contraction of the multilayer piezoelectric actuator element due to voltage application and the difference in the thickness of the internal electrode layer, slit-like voids are previously formed in the ceramic layer at predetermined intervals. To form. In addition, by connecting the internal electrode layer and the external electrode so as to be the same pole at a predetermined interval, continuous strain accumulation can be divided, and the maximum stress at the center of the multilayer piezoelectric actuator element And stress applied to the piezoelectric ceramic layer can be relaxed.

  In addition, by placing and laminating the piezoelectric ceramic layers having slit-like voids so that the electrical connection between adjacent internal electrodes and external electrodes is the same pole, the tip of the slit-like voids Insulation resistance (IR), since cracks generated from the vicinity of the part propagate in an oblique direction with respect to the stacking direction and reach the internal electrode layer, no electric field is applied between the internal electrode layers stacked on the same electrode. Can be suppressed.

  Furthermore, the durability against humidity environment can be improved by covering the external electrode and the slit-shaped gap with a flexible insulating resin.

  As described above, it is possible to provide a stacked piezoelectric actuator element having a highly reliable element structure that does not deteriorate in failure or insulation performance even under severe driving environment conditions in which a large displacement is repeated over a long period of time.

  The multilayer piezoelectric actuator element of the present invention shown in FIG. 1 includes a laminated body 1 formed by laminating a plurality of plate-like piezoelectric ceramic layers 1a and a plurality of plate-like internal electrode layers 1b, and the internal electrode layer 1b. Are provided as a pair of external electrodes 3 connected on opposite sides of the laminate 1. Slit-shaped gaps 2 are formed at predetermined intervals in the stacking direction, and the external electrode surfaces and the exposed surfaces of the internal electrodes are all externally covered except for the upper and lower end surfaces shown in FIG. Covered with resin 4. Further, the internal electrode layer and the external electrode are connected so as to have the same pole at a predetermined interval.

  In the best mode for carrying out the present invention, slits are formed in advance at predetermined intervals in order to absorb and relieve stress generated by the expansion and contraction of the multilayer piezoelectric actuator element due to voltage application and the difference in internal electrode thickness in the gap. Are formed in the piezoelectric ceramic layer 1a. The slit-shaped gap 2 formed here can relieve the stress generated by the expansion and contraction of the laminated piezoelectric actuator element that occurs during the polarization process or driving, but the tip of the formed slit-shaped gap 2 is the internal electrode layer 1b. Therefore, the thickness of the piezoelectric ceramic layer 1a where the slit-like gap 2 is introduced is made as thick as possible within the range of displacement required for the multilayer piezoelectric actuator element.

  By connecting the internal electrode layer 1b and the external electrode 3 so as to have the same pole at a predetermined interval, accumulation of continuous strain can be divided, and the maximum is near the center of the multilayer piezoelectric actuator element. Stress can be reduced and stress applied to the piezoelectric ceramic layer 1a can be relaxed. In the best mode for carrying out the present invention, the positions of the electrically identical poles are 1 / 2L, 1 / 4L, 3 / 4L (however, the length of the active portion of the laminated piezoelectric actuator element is If it is arranged at a position where L is set, the effect becomes greater.

  In addition, the internal electrode layer 1b adjacent to the piezoelectric ceramic layer 1a having the slit-shaped gap 2 and the external electrode 3 are arranged so that the electrical connection is the same pole, and laminated, Even when a crack generated from the vicinity of the tip of the gap 2 propagates in an oblique direction with respect to the stacking direction and reaches the internal electrode layer 1b, it is formed between the internal electrode layers stacked so as to be electrically the same pole. Since no electric field is applied, there is no possibility of causing migration or the like of the electrode material, and a decrease in insulation resistance (IR) can be suppressed. Here, the reason why the internal electrode layer 1b laminated so as to be electrically the same pole is made to be two or more layers is to make the structure in which the migration of the electrode material is less likely to occur even if a crack occurs. is there.

  A slit-shaped gap can be easily formed by inserting a green sheet printed in a predetermined pattern into a paste of resin or carbon powder that burns below the sintering temperature of piezoelectric multilayer ceramics. (See FIGS. 1 and 3).

  Furthermore, the durability against the humidity environment can be improved by covering the external electrode and the slit-shaped gap with a flexible insulating resin.

  The production method of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a view showing a multilayer piezoelectric actuator element (Embodiment 1) according to the present invention. FIG. 1 (a) is a perspective view, FIG. 1 (b) is a sectional view, and FIG. 1 (c) shows an electrode pattern. FIG. The first embodiment is an example in which the same polarity arrangement as the slit introduction is performed. 2A and 2B are diagrams showing a multilayer piezoelectric actuator element (Embodiment 2) according to the present invention. FIG. 2A is a perspective view, FIG. 2B is a sectional view, and FIG. 2C is an electrode pattern. FIG. The second embodiment is an example in which the same polarity is arranged. Moreover, FIG. 3 is a figure which shows the example of three types of carbon printing patterns inserted for the slit introduction of this invention. 3A shows an example in which slits are introduced on two sides, FIG. 3B shows an example in which slits are introduced on four sides, and FIG. 3C shows an example in which slits are introduced on four corners. FIG. FIG. 3 is a typical example of the slit introduction of FIG.

  In the present invention, a piezoelectric ceramic powder mainly composed of nickel / lead niobate was dispersed in a solvent, and a binder was added to prepare a slurry. This mud was formed on a carrier tape to obtain a green sheet having a thickness of 90 to 130 μm. After printing the Ag / Pd internal electrode paste on this sheet, it was dried, punched into a predetermined shape, laminated in a mold, filled, and then a laminated body integrated by thermocompression bonding was produced. In this case, a film on which paste-like carbon powder was printed was inserted at predetermined intervals in the stacking direction so that slit-like voids 2 could be arranged on the outer peripheral portion of the internal electrode pattern.

  In addition, it was set as the space | interval which inserts the slit-shaped space | gap 2 every time 20-60 layers of active internal electrode layers 1b are laminated | stacked. Further, the internal electrode layers were arranged and laminated so that the printed films of the internal electrodes adjacent to the upper and lower sides of the carbon printed film were electrically the same pole.

  The laminated body 1 of the piezoelectric ceramic layer 1a including the carbon printing layer and the internal electrode layer 1b thus produced was cut so as to have a cross-sectional shape of 5 × 5 mm in the dimension at the time of the sintered body. The cut multilayer piezoelectric actuator element was heated to 450 ° C. in the air to remove the resin component, and then sintered at a temperature of 1050 to 1150 ° C. for 2 to 6 hours.

  After lapping the surface where the internal electrode layer 1b of the sintered body of the obtained laminate 1 is exposed, a silver electrode for conduction with the internal electrode layer 1b is printed on the processed surface and applied, I baked it.

  Next, the laminated piezoelectric actuator element on which the external electrode is formed is electrostatically coated with an epoxy powder, subjected to a baking treatment at 150 ° C. for 30 to 60 minutes, and an insulating resin is formed on the outer peripheral surface excluding the upper and lower end surfaces in the laminating direction. Layer 4 was coated. A multilayer piezoelectric actuator element was fabricated by applying an electric field of 2 kV / mm or more in the atmosphere to the multilayer piezoelectric actuator element subjected to the resin exterior, and applying a polarization treatment.

  In addition, a gap of 5 to 25 μm in width was formed in the outer peripheral portion of the multilayer piezoelectric actuator element after the polarization treatment in the surface of the multilayer piezoelectric actuator element into which the pasty carbon printed film was inserted.

  Finally, the manufactured laminated piezoelectric actuator element (Embodiment 1 and Embodiment 2) was subjected to a moisture resistance load test of DC 150 V in an atmosphere of 40 ° C. and 90% RH, and the change in insulation resistance with time was measured with a conventional laminated piezoelectric element. Comparison was made with an actuator element (see FIG. 4).

  The change of the insulation resistance with time was determined by determining the number of defects after 250 hours from the failure of the stacked piezoelectric actuator element having an insulation resistance lower than 1 MΩ. In the multilayer piezoelectric actuator element having the conventional structure (see FIG. 4), 12 defects out of 50 occurred, whereas in the multilayer piezoelectric actuator element having the structure of the present invention [Embodiment 1 and Embodiment 2]. The occurrence of defects was zero among the 50 pieces (see FIGS. 1 and 2).

  As described above, the multilayer piezoelectric actuator element according to the present invention is a highly reliable multilayer piezoelectric actuator element that does not deteriorate in failure or insulation performance even under severe driving environment conditions in which a large displacement is repeated over a long period of time. It has a structure.

The figure which shows the lamination type piezoelectric actuator element (Embodiment 1) of this invention. FIG. 1A is a perspective view. FIG.1 (b) is sectional drawing. FIG. 1C shows an electrode pattern. The figure which shows the lamination type piezoelectric actuator element (Embodiment 2) of this invention. FIG. 2A is a perspective view. FIG. 2B shows an electrode pattern. The figure which shows the example of three types of carbon printing patterns inserted for slit introduction of this invention. 3A is a diagram showing an example in which slits are introduced on two sides, FIG. 3B is a diagram showing an example in which slits are introduced on four sides, and FIG. 3C is a diagram showing slits on four corners. FIG. The perspective view which shows the lamination type piezoelectric actuator element of a conventional structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laminated body 1a Piezoelectric ceramic layer 1b Internal electrode layer 2 Slit-shaped space | gap
3 External electrode (baked silver)
4 Insulating resin

Claims (4)

  A pair of external electrodes provided on a main surface from which the internal electrode layer is exposed and the other main surface, comprising a laminate in which piezoelectric ceramic layers and internal electrode layers configured using piezoelectric ceramics are alternately stacked. And the internal electrode layer are connected to every other layer, the piezoelectric element on the outer peripheral portion of the side surface of the multilayer body in a direction perpendicular to the main surface and the other main surface. A laminated piezoelectric actuator element characterized in that slit-like voids are formed at predetermined intervals so as to enter the inside of the ceramic layer.   2. The multilayer piezoelectric actuator element according to claim 1, wherein electrical connection between the internal electrode layer and the external electrode is made the same pole continuously by a predetermined interval.   At least two or more of the internal electrode layers adjacent to each other with the piezoelectric ceramic layer formed with the slit-like voids are continuously connected to the external electrode with the same polarity. The multilayer piezoelectric actuator element according to claim 2.   The slit-shaped gap formed by printing the material on which the slit-shaped gap burns and scatters below the sintering temperature of the piezoelectric ceramic on the surface of the green sheet of the piezoelectric ceramic, and sintering after lamination. 4. The multilayer piezoelectric actuator element according to claim 1, wherein the laminated piezoelectric actuator element is covered with an insulating resin.

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