JP2010283141A - Laminated piezoelectric element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated piezoelectric element which has superior stress relaxing performance and does not have conductivity in a ceramic layer to have no decrease in displacing performance of the laminated piezoelectric element. <P>SOLUTION: The laminated piezoelectric element 10 includes a piezoelectric layer 3, a ceramic laminate 4 having conductive internal electrode layers 1, 2 laminated alternately, and a pair of external electrodes 5, 5 formed on outer peripheral surfaces of the ceramic laminate 4. The one internal electrode layer 1 and the other internal electrode layer 2 stay in the ceramic laminate 4 such that the internal electrode layer 1 has one end 1' in contact with one external electrode 5 and the other end 1" at an interval t<SB>0</SB>with the other external electrode 5; and slits 7 extending from the pair of external electrodes 5, 5 to the inside of the ceramic laminate 4 are formed between the one internal electrode layer 1 and the other internal electrode layer 2, and filled with conductive resin bodies 8. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a laminated piezoelectric element used for a piezoelectric actuator or the like.

  Piezo-actuators are generally used as devices that enable precise positioning in the range of nanometers to several hundreds of micrometers using a piezoelectric effect, and that have rapid response. A microphone can be mentioned. In addition, from the viewpoint of promoting reduction of environmental impact load, in order to improve the fuel efficiency of a vehicle, application to an injector drive source for fuel injection of an engine or the like is currently under intensive investigation.

  The piezoelectric effect is a phenomenon in which charges are generated in proportion to the mechanical pressure applied to a crystal. Conversely, the reverse piezoelectric effect in which the piezoelectric body itself is deformed by the application of an electric field is also this phenomenon. It is included in the piezoelectric effect, and a general piezo actuator applies this inverse piezoelectric effect.

  The piezoelectric actuator described above includes a laminated piezoelectric element in which a plurality of ceramic layers and an internal electrode layer for supplying an applied voltage are alternately laminated, and the voltage generated in the piezoelectric element is two. The value can be as large as discharge occurs between the two electrodes. The electric field applied in parallel to the polarization direction of the multilayer piezoelectric element generates a rotational force in the electric dipoles arranged in a straight line, and as a result, a high torque can be generated. A change in length occurs, causing the crystal to stretch. As this material, titanic acid, zirconic acid, lead oxide or the like is used.

By the way, in the multilayer piezoelectric element constituting the conventional piezoelectric actuator, when the portion where the displacement due to the piezoelectric effect described above is displaced, the stress is concentrated on the portion where the piezoelectric displacement does not occur. Cracks due to this stress concentration occur between the piezoelectric elements, and this is one major factor that determines the durability of the multilayer piezoelectric element.
Therefore, in order to effectively suppress the occurrence of the cracks described above, a multilayer piezoelectric element having a slit that exerts a stress relaxation action at an appropriate position in the multilayer piezoelectric element is disclosed in Patent Document 1.

Certainly, it is possible to relieve stress by providing slits at appropriate positions inside the multilayer piezoelectric element, and the generation of cracks can be effectively suppressed. However, since this slit is provided, there is a concern about another problem this time.
This is because, when an electric field is applied to a slit provided inside the multilayer piezoelectric element, a substance that causes a reduction reaction is generated in the slit, and the reducing substance is formed from a metal oxide present at a grain boundary in the ceramic layer. This is a problem that the displacement performance of the multilayer piezoelectric element is reduced as a result of reduction and electrical conductivity in the ceramic layer.

  More specifically, when these laminated structures are formed by integrally sintering an internal electrode layer made of Ag and a ceramic layer, Ag is contained in the grain boundary in the ceramic layer during the sintering. It has been confirmed that it diffuses, and furthermore, it has been found that this Ag has a very high diffusion coefficient, and an oxide of Ag is likely to intervene in the ceramic layer.

  In general, in the case of PTZ ceramics (PTZ: lead zirconate titanate), it is also known that lead decomposes during firing, and PbO forms a liquid layer and exists at grain boundaries.

  In order to maximize the stress relaxation effect of the slit, it is preferable to form the slit from the end of the internal electrode to the inside, and in this case, an electric field is applied above and below the slit. It has been specified by the present inventors that when the electric field acts above and below the slit and the electric field is applied for a long period of time, the insulating properties of the ceramic layer at the periphery of the portion gradually decrease.

According to the present inventors, reducing as the cause, the water present in the slit is decomposed to produce a high reducing property H ^+, an oxide of Ag and Pb of the H ⁺ are present in the ceramic layer And it has been specified to metallize. This metallization causes conductivity in the ceramic layer, which leads to a decrease in the displacement performance of the multilayer piezoelectric element described above.

  In addition, in Patent Document 2, which is a separate published technique related to the multilayer piezoelectric element, there is a description of an example in which an adhesive is interposed in the slit described above, but this slit is in contact with the internal electrode, Therefore, Ag of the internal electrode is now deposited inside the adhesive of the slit, and the distance between the portion where Ag is deposited in the slit and the adjacent internal electrode is relatively shorter than other portions. As a result, there is a fear of another problem that local electric field concentration occurs at a portion where the distance is short or in the vicinity thereof. In addition, this structure has a structure in which dissimilar materials of ceramics and adhesive are sandwiched up to a part of the electrode, so there is a concern that a crack is likely to occur at the end of the adhesive.

  Therefore, development of a multilayer piezoelectric element that obtains the stress relaxation effect of the technique disclosed in Patent Document 1 and that does not cause conductivity in the ceramic layer and thus cannot cause a reduction in displacement performance of the multilayer piezoelectric element. However, this is an urgent development issue in this field.

JP 2008-66391 A JP 2007-243066 A

  The present invention has been made in view of the above-described problems, and is a multilayer type that is excellent in stress relaxation performance and that does not cause conductivity in the ceramic layer, so that the displacement performance of the multilayer piezoelectric element cannot be reduced. An object is to provide a piezoelectric element.

  In order to achieve the above object, a multilayer piezoelectric element according to the present invention includes a ceramic laminate in which piezoelectric layers made of a piezoelectric material and conductive internal electrode layers are alternately laminated, and an outer periphery of the ceramic laminate. A pair of external electrodes formed on an outer peripheral surface perpendicular to the stacking direction of the ceramic laminate, and in one internal electrode layer and the other internal electrode layer adjacent in the stacking direction, One end of one internal electrode layer is in contact with one external electrode constituting the pair of external electrodes, and the other end of the one internal electrode layer is spaced from the other external electrode constituting the pair of external electrodes The other internal electrode layer is in contact with the other external electrode constituting the pair of external electrodes, and the other end of the other internal electrode layer The pair of external It is stopped inside the ceramic laminate in a posture spaced apart from one external electrode constituting the pole, and among the ceramic laminate, between the one internal electrode layer and the other internal electrode layer, A slit extending from each of the pair of external electrodes into the ceramic laminated body is formed, and a conductive resin body closes the inside of the slit.

  The multilayer piezoelectric element of the present invention is a ceramic laminate in which piezoelectric layers and internal electrodes are alternately laminated, and slits for imparting stress relaxation to the multilayer piezoelectric element as in the prior art. However, the slit is disposed at a position that is not continuous with the internal electrode, and an electric field (potential) is generated in the slit because the slit is closed with a conductive resin body. Thus, the deterioration of the insulating properties of the ceramic laminate is effectively suppressed.

  Here, the material of the conductive resin body is not particularly limited. However, the conductive resin body has conductivity so as not to generate an electric field above and below the opened slit, and the inside of the slit. Both the slit and the area of the conductive resin body have hardness or deformation performance (flexibility) that can provide stress relaxation when the multilayer piezoelectric element is operated. Any material can be used as long as the material satisfies the above performance. For example, it is a material in which Ag, Cu, Ni or the like, which is a conductive filler, is mixed with polyethylene resin, soft polyvinyl chloride, silicone resin (including silicone rubber), or the like.

  As a preferred embodiment, the slit may have a length equal to or longer than the distance between the end of the internal electrode and the external electrode.

  When the slit is shorter than the interval between the end of the internal electrode and the external electrode, i.e., does not reach between the alternately stacked internal electrodes, when the piezoelectric layer located between the internal electrodes is displaced, This is because stress at the time of displacement tends to concentrate on the surrounding non-displaced portion, and high stress relaxation action cannot be expected. Moreover, even when the slit is extended into the internal electrode, the electric field (potential) acts above and below the slit by adopting a configuration in which the conductive resin body is closed in the slit, which is the configuration of the present invention. Therefore, the problem of the multilayer piezoelectric element disclosed in Patent Document 1 cannot occur.

  According to the piezoelectric actuator including the multilayer piezoelectric element according to the present invention described above, the stress relaxation performance is excellent, and since the electric field is not applied above and below the formed slit, the insulating property of the ceramic laminate gradually decreases. Therefore, it is possible to obtain a piezoelectric actuator composed of a highly durable laminated piezoelectric element.

  As can be understood from the above description, according to the multilayer piezoelectric element of the present invention, a multilayer piezoelectric element having extremely high durability can be obtained by simply changing the structure of the prior art.

It is the longitudinal cross-sectional view explaining the lamination type piezoelectric element of this invention. It is the figure which showed the endurance test result of the lamination type piezoelectric element (Example) of this invention, and the lamination type piezoelectric element (conventional example) of a conventional structure, and the graph which showed the relationship between the frequency | count of driving of a lamination type piezoelectric element, and insulation resistance It is.

  Embodiments of the present invention will be described below with reference to the drawings. In the illustrated multilayer piezoelectric element, the internal electrodes 1 and 2 are not shown in the middle, but the radix of the internal electrodes 1 and 2 depends on the total length of the ceramic laminate, the desired amount of deformation, etc. It is set accordingly.

  In the laminated piezoelectric element 10 shown in FIG. 1, the piezoelectric layer 3 and the internal electrode layers 1 and 2 (one internal electrode layer 1 and the other internal electrode layer 2) adjacent to each other with the piezoelectric layer 3 interposed therebetween are alternately arranged. The ceramic laminate 4 is generally composed of a laminate, and a pair of external electrodes 5 and 5 attached to the outer peripheral surface of the ceramic laminate 4 via a conductive adhesive layer 6.

  The shape of the ceramic laminate 4 can be arbitrarily set depending on the application, and can be formed into a cylindrical shape, a prismatic shape, a pyramid shape, a conical shape, a barrel shape, or the like. A protective layer 3 ′ is provided on the upper and lower ends of the ceramic laminate 4.

  Here, the piezoelectric layer 3 and the protective layer 3 ′ are made of, for example, piezoelectric ceramics made of lead zirconate titanate (PZT), and the internal electrode layers 1 and 2 are made of Ag or Ag—Pd. It is formed from an alloy or the like. The conductive adhesive layer 6 is made of a material in which a filler such as Ag is contained in an epoxy resin. The conductive adhesive layer 6 is an adhesive made of the same material as the conductive resin body 8 that closes the slit 7 described later. Also good.

One end 1 ′ of one internal electrode layer 1 is in contact with one external electrode 5 constituting the pair of external electrodes 5 and 5, and the other end 1 ″ is spaced from the other external electrode 5: t It is stopped inside the ceramic laminate 4 with the posture _0. Similarly, one end 2 'of the other internal electrode layer 2 is in contact with the other external electrode 5 constituting the pair of external electrodes 5 and 5. in contact, and the other end 2 ", one of the intervals to the external electrode 5: has stopped inside the ceramic laminate 4 in a posture placing the t _0. By exhibiting such a structure, the electrical insulation in the outer peripheral surface of the ceramic laminated body 4 is ensured.

  In the ceramic laminate 4, the piezoelectric layer 3 in a region where both internal electrodes 1 and 2 are wrapped in the stacking direction is a deformation region (X direction) that is deformed when the piezoelectric actuator is driven. And all the piezoelectric layers 3 and the internal electrode layers 1 and 2 which comprise the ceramic laminated body 4 are laminated | stacked alternately, and these are comprised integrally by baking, Between the internal electrode layers 1 and 2, All the provided piezoelectric layers 3 are displaced during driving, and the amount of displacement of the entire ceramic laminate 3 is improved. This is synonymous with improvement in output of the multilayer piezoelectric element 10.

Here, in the ceramic laminate 4, slits 7 having a length: t ₁ longer than the above-described interval: t ₀ are at positions corresponding to the pair of external electrodes 5, 5, and one end of each slit is the external electrode 5. , 5 so as to communicate with the external electrodes (strictly speaking, the external electrodes 5 and 5 are indirectly communicated with each other through the conductive adhesive layer 6).

  Furthermore, the conductive resin body 8 is filled and cured in the slit 7 and the inside thereof is closed.

  This conductive resin body 8 is a material in which Ag, Cu, Ni or the like, which is a conductive filler, is mixed with polyethylene resin, soft polyvinyl chloride, silicone resin, etc., which is relatively soft in the curing posture among the resins. Formed from. Among them, it is preferable to apply a silicone rubber mixed with an Ag filler having a hardness (durometer A) of 80 or less and a volume resistivity of 1.0 × 10 −3 Ω · m or less.

As shown in the figure, the slit 7 is completely cut off from the internal electrodes 1 and 2 (not energized), and the conductive resin body 8 is closed in the slit 7. No potential is generated above and below the slit 7 provided to impart stress relaxation performance to the element 10. Further, since it is possible to suppress the moisture that becomes the source of H ⁺ that can reduce the oxides of Ag and Pb present in the piezoelectric layer from being present in the slit 7, the piezoelectric layer becomes conductive, and the laminated type A reduction in the displacement performance of the piezoelectric element is effectively suppressed.

  In addition, the relatively soft conductive resin body 8 is interposed in the slit 7, and the slit 7 and the end of the conductive resin body 8 inside the slit 7 reach the wrap region of the adjacent internal electrodes 1 and 2. Due to the extension, the stress relaxation action can be sufficiently expected. That is, a plurality of soft conductive resin bodies 8 provided in the slits 7 are provided, for example, at regular intervals in the laminating direction of the ceramic laminated body 4. It is possible to effectively relieve the stress generated in. Thereby, generation | occurrence | production of defects, such as a crack, in the ceramic laminated body 4 can be suppressed, and it becomes possible to improve the durability and reliability of the multilayer piezoelectric element 10.

[Durability Test and Results of Multilayer Piezoelectric Element of the Present Invention (Example) and Conventionally Structured Multilayer Piezoelectric Element (Conventional Example)]
The inventors of the present invention have a piezoelectric actuator test body including the multilayer piezoelectric element (example) having the configuration shown in FIG. 1, and a laminate in which the slit and the conductive resin body that closes the inside of this example do not exist. Piezo actuator test specimens each having a piezoelectric element (conventional example), both of which are driven in a temperature atmosphere of 150 ° C. under conditions of an applied voltage of 150 V and a cycle frequency of 150 Hz. While measuring the corresponding insulation resistance as needed, an experiment was conducted to compare the degree of decrease. The result of this experiment is shown in FIG.

FIG. 2 shows that the number of times of driving up to 5 × 10 ⁸ shows a similar decrease in insulation resistance in both the example and the conventional example (both there is almost no decrease in insulation resistance). As a result, the degree of resistance decrease is significantly different.

In the conventional example, when the number of times of driving is about 1 × 10 ⁹ times and the insulation resistance becomes zero and the insulation resistance becomes zero, the durability of the multilayer piezoelectric element (durability period) The number of times of driving is the durability number of the comparative example.

On the other hand, in the embodiment, 2 × 10 ⁹ times about hardly decreased insulation resistance to actuation number, 3 × 10 has a ^nine times the insulation resistance zero driving number has exceeded even durable 3 times It has been demonstrated that a longer period can be realized.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

DESCRIPTION OF SYMBOLS 1 ... One internal electrode layer, 2 ... The other internal electrode layer, 3 ... Piezoelectric layer, 4 ... Ceramic laminated body, 5 ... External electrode, 6 ... Adhesive layer, 7 ... Slit, 8 ... Conductive resin body, 10 ... Multilayer piezoelectric element

Claims (2)

A ceramic laminate in which piezoelectric layers made of a piezoelectric material and conductive internal electrode layers are alternately laminated;
The outer peripheral surface of the ceramic laminate, and a pair of external electrodes formed on the outer peripheral surface perpendicular to the stacking direction of the ceramic laminate,
In one internal electrode layer and the other internal electrode layer adjacent in the stacking direction, one end of the one internal electrode layer is in contact with one external electrode constituting the pair of external electrodes, and the one internal electrode The other end of the layer is stopped inside the ceramic laminate in a posture spaced apart from the other external electrode constituting the pair of external electrodes, and one end of the other internal electrode layer is connected to the pair of external electrodes The other internal electrode layer is in contact with the other external electrode, and the other end of the other internal electrode layer is stopped inside the ceramic laminate in a posture spaced apart from the one external electrode constituting the pair of external electrodes. ,
Between the one internal electrode layer and the other internal electrode layer of the ceramic laminate, a slit extending from the pair of external electrodes to the inside of the ceramic laminate is formed.
A laminated piezoelectric element in which a conductive resin body is closed inside the slit.   The multilayer piezoelectric element according to claim 1, wherein the slit has a length equal to or longer than the distance between an end of the internal electrode and the external electrode.

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