JPH07226542A - Multilayered piezoelectric element - Google Patents

Abstract

PURPOSE:To provide a multilayered piezoelectric element wherein the contraction amount of a propective layer part is relieved, by forming inner electrodes isolated in a non-conducting state on both sides of a laminate, and the imperfect insulation can be surely prevented, by surely connecting original inner electrodes and outer electrodes together in a specified relation. CONSTITUTION:Piezoelectric material 11 and inner electrodes 12 are alternately laminated to form a laminate 10. On the side surface of the laminate 10, conductive protruding parts 16 are exposed so as to correspond with the inner electrodes 12 arranged every other layer. An outer electrode 15 is arranged, via a conducting layer 13, on the side surface of the laminate 10 where the conductive protruding parts 16 are exposed. Thereyby the outer electrode 15 is electrically connected with each of the conductive protruding parts 16 of the inner electrodes 12 arranged every other layer. Non-conducting inner electrodes 17 which are isolated in a non-conducting state in the laminate 10 are formed on both of the end portions in the laminate direction of the laminate 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric element in which a large number of thin films of piezoelectric material are laminated and a longitudinal displacement can be obtained by applying a voltage.

[0002]

2. Description of the Related Art Conventionally, in the case of manufacturing a laminated piezoelectric element mainly used as an actuator, the side surface of a single-layer internal electrode is connected to an external electrode. When the conventional multilayer capacitor method is used in the manufacture, the internal electrode area is smaller than the cross-sectional area of the element,
There is a fatal defect that an electric field is not generated on the entire surface, the displacement is hindered, stress concentration occurs in a non-uniform portion, and finally the material is broken. In addition, positioning at the time of stacking is difficult, and the number of stacked layers is limited to several tens at most. For the same applied voltage, the displacement amount of the element is proportional to the number of stacked layers. It was difficult to manufacture. In order to solve this drawback, a method of printing and laminating electrodes on the entire surface of the piezoelectric sheet, that is, a structure in which the area of the internal electrode and the area of the element are made equal is common.

In this case, a method as shown in FIG. 1 has been considered to connect the internal electrodes placed on one layer to the external electrodes. That is, on each side surface on the opposite side of the laminated body, the side surfaces are further displaced from each other, and a conductive convex portion is exposed and formed at each end portion of each internal electrode on each side surface. By uniformly pressing the external electrode with a flat plate through the conductive film to the side surface of the laminate in which the conductive protrusions are formed, the pressure applied to the portion corresponding to each conductive protrusion is increased. The internal electrode corresponding to the portion is electrically connected to the external electrode. In this case, when the conductive film has a two-layer structure of a layer containing conductive particles and a layer not containing the same particles, the conductive particles break through the layer not containing the same particles by the pressure. The conductive protrusion and the external electrode are brought into contact with each other, so that the conductive protrusion and the external electrode are electrically connected.

Further, since this kind of piezoelectric element utilizes the vertical effect, both ends in the displacement direction protect only a portion of the piezoelectric material having a thickness several to several tens of times thicker than the piezoelectric material film of the laminated portion. It is often provided as a layer. In this case, cracking or peeling occurs due to the difference in shrinkage amount during sintering between the piezoelectric material of the laminated layer and the piezoelectric material of the protective layer that alternately overlap with the internal electrodes. Layers printed with internal electrodes that do not contribute to the are gradually laminated to reduce the difference in shrinkage and prevent cracking and peeling.

[0005]

However, the flat plate used for the pressurizing has a certain cushioning property on its surface in order to cope with the variation in the height of the conductive convex portion. As shown in (3), when the arrangement interval of the internal electrodes becomes large at both ends of the laminated body, the ends of the internal electrodes, which should be originally insulated, become conductive, and the piezoelectric element does not function. That is, since there is no problem because the distance between the conductive protrusions is small in the middle portion of the laminated body, the distance between the conductive protrusions becomes wide at both ends, so that the flat plate to be pressed does not reach the internal electrodes without the conductive protrusions. The same pressure is applied. As a result, since the internal electrode is connected to the external electrode on the opposite side surface, all the layers that should originally be insulated are brought into conduction, and there is a problem that the piezoelectric element has no function at all.

The present invention has been made to solve the above-mentioned problems, and provides internal electrodes separated in a non-conducting state at both ends of the laminate to reduce the amount of contraction of the protective layer portion. At the same time, it is an object of the present invention to provide a multilayer piezoelectric element capable of surely connecting the original internal electrodes and external electrodes in a predetermined relationship and reliably preventing insulation failure thereof.

[0007]

In order to achieve this object, a laminated piezoelectric element of the present invention has a layered structure in which piezoelectric materials and internal electrodes are alternately laminated on a side surface of the laminated body. Correspondingly, by exposing the conductive convex portion, and by disposing the external electrode via the conductive layer on the side surface of the laminate in which the conductive convex portion is exposed, the conductive convex portions of the one-layer-placed internal electrodes are formed. In the laminated piezoelectric element configured to electrically connect the external electrodes, at least one internal electrode arranged at both end portions in the laminating direction of the laminated body is separated into a non-conducting state inside the laminated body. It is a thing.

Further, the internal electrodes separated in a non-conducting state inside the laminated body can be formed by a printed pattern in which a plurality of conductive portions are intermittently arranged in a substantially lattice pattern or a wavy pattern.

[0009]

According to the multi-layer piezoelectric element of the present invention having the above-mentioned structure, since the internal electrodes which are separated in a non-conventional state are provided at both ends of the laminate, when the external electrodes are arranged in pressure contact with the side surface of the laminate. , Even if the end of the non-conducting internal electrode is connected to the external electrode, since the internal electrode is interrupted inside the laminated body, it is electrically connected to the external electrode on the opposite side surface. Never. Further, the internal electrode separated in the non-conducting state, by forming a plurality of conductive portions in a printing pattern that is intermittently arranged in a grid or wavy form, the contraction of the protective layer portion at both ends of the laminate becomes uniform, There is no need for positioning during stacking.

[0010]

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view of a laminated piezoelectric element.
(A) of the same figure is a sectional view of the whole laminated piezoelectric element shown by breaking the intermediate part, and (b) of the same figure is an enlarged sectional view within the dotted line frame of (a) of the same figure. In the figure, a laminated body 10 in which a film-shaped piezoelectric material 11 and internal electrodes 12 are alternately laminated
An internal electrode (hereinafter referred to as a non-conductive internal electrode) 17 and two protective layers 18 for shrinkage relaxation are formed at both ends in the stacking direction. Each of the non-conducting internal electrodes 17 has a laminated body 10
As shown in FIG. 2, the conductive portions 17A are separated from each other in a non-conducting state in a plan view, and each of the conductive portions 17A is formed by a printing pattern in which the conductive portions 17A are intermittently arranged in a dimple shape. Other forms of the intermittent arrangement may be a lattice shape or a wave shape. The non-conducting internal electrode 17 may be provided in only one layer or in three or more layers. However, it is desirable to provide at least two to three layers in order to surely perform the shrinkage relaxation.

Further, on the opposite side surfaces of the laminated body 10, the side surfaces are further displaced from each other, and any side surface thereof is made to correspond to the end portion of the internal electrode 12 of each layer, and the side surface is electrically conductive. The convex portion 16 is formed. further,
A conductive film 13 is formed over the entire surface of each of the side surfaces on which the conductive convex portions 16 are formed, and a copper foil 15 is formed thereon as an external electrode. That copper foil 1
Reference numeral 5 denotes the internal electrode 1 via the conductive portion 14 and the conductive convex portion 16.
2 is electrically connected. The conductive film 13 is composed of an outer layer 13 a containing conductive particles 31 and an inner layer 13 b containing no conductive particles 31.

A method of manufacturing the laminated piezoelectric element will be described below.

First, after the piezoelectric material 11 containing PZT (lead zirconate titanate) as a main component is mixed to a desired composition,
To the powder calcined at 850 ° C., 5 parts by weight of a binder, a small amount of a plasticizer and a defoaming agent are added, and dispersed in an organic solvent to form a slurry. This slurry was screen-printed on the entire surface with a Pd paste as the internal electrodes 12 on a green sheet formed into a predetermined thickness by the doctor blade method, and as shown in FIG. A non-conducting internal electrode 17 is prepared.

After that, 150 sheets each having a predetermined size punched and printed on the entire surface are laminated, and several green sheets on which electrodes are not printed are stacked on both ends thereof, and the non-conductive internal electrodes 17 printed in a dimple shape are sandwiched therebetween. Further, several unprinted sheets are stacked and integrated by hot pressing. After degreasing, sintering is performed at about 1200 ° C., and as shown in FIG. 3, temporary external electrodes 22 and 23 are applied and baked onto a sintered body 21 cut at a position where the internal electrodes 12 are exposed in alternate layers. Then, further cutting is performed so that another pair of side surfaces 24, 25 is exposed.

Next, on one side surface 24 of the sintered body 21, a side surface portion other than the end surface portion of the internal electrode 12 forming the conductive convex portion 16 and the other side surface 25 are masked with tape. Then, the negative electrode of the DC power source is connected to the temporary external electrode 22 and immersed in the nickel plating bath. If a current of 50 mA is applied for about 15 minutes in this state, the temporary external electrode 2
When nickel plating grows on the end surface of the internal electrode 12 connected to 2 and the masking tape is peeled off, as shown in FIG.
The conductive protrusions 16 made of nickel plating are formed in alternate layers. Similarly, in order to form the conductive convex portion 16 on the end surface of the internal electrode 12 which is further shifted on the opposite side surface 25, the entire side surface 24 on which the conductive convex portion 16 has already been formed and a part of the side surface 25 are formed. Is masked with a tape to protect it, and then the negative electrode is connected to the temporary external electrode 23 to grow nickel plating. As a result, even on the side surface 25,
The conductive protrusions 16 are formed so as to be offset from the side surfaces 24 one by one. At this time, since the non-conducting internal electrodes 17 for relaxing shrinkage at the upper and lower ends of the sintered body 21 are printed in a dimple shape,
Since no current flows, the conductive protrusion 16 is not formed at the end of the non-conducting internal electrode 17.

After cleaning, the negative electrode of the DC power supply is used as a temporary external electrode 2.
2, 23, and immersed in an epoxy cation electrodeposition paint containing a predetermined pigment, and a voltage of 100 V was applied for 2 minutes. As a result, as shown in FIG. In the inner electrode 12 where the conductive protrusion 16 is not formed on the surface of the conductive protrusion 16, the epoxy cation electrodeposition coating 13c to be the inner layer 13b is electrodeposited on the end portion thereof. . After that, when placed in an oven and subjected to heat treatment at 150 ° C. for 30 minutes, the epoxy resin component has fluidity in the process of curing, so that it is flattened as shown in FIG. 6 and becomes the inner layer 13b containing no conductive particles.

Separately from the sintered body 21, as shown in FIG. 7, conductive particles 31 are formed on the copper foil 15 and have an average particle size of 20 to 3
A thermosetting epoxy-based adhesive containing 0 μm copper particles uniformly applied to a thickness of about 50 μm (outer layer 13a containing conductive particles 31) is prepared. As shown in FIG. 8, the side surfaces 24 and 25 of the sintered body 21 are cut into a size so as to cover the respective conductive protrusions 16, and the inner layer 13b containing no conductive particles 31 and the conductive layer 31b are electrically conductive. Temporary fixing is performed so that the outer layer 13a containing the particles 31 faces each other. Inner layer 13 containing no conductive particles 31
b and the outer layer 13a containing the conductive particles 31 cooperate with each other to form the conductive film 13.

Then, it is sandwiched by a pair of flat pressing jigs 53 (only one side is shown in FIG. 8) heated to approximately 180 ° C., and a load of several kg is applied to perform thermocompression bonding.
Due to the presence of 6, only the vicinity of the convex portion is compressed, and FIG.
As shown in FIG. 5, in this compressed portion, the conductive particles 31 penetrate the inner layer 13b that does not contain the conductive particles 31, contact the conductive protrusions 16 and also contact the copper foil 15 that is an external electrode. Thus, the conductive portion 14 is formed, and the internal electrodes 12 and the copper foils 15 are electrically connected every other layer. In this case, even if the non-conducting internal electrode 17 for shrinkage relaxation conducts at the end that should be originally insulated, the non-conducting internal electrode 17 is interrupted inside the laminated body 10 and therefore short-circuited. Can be avoided.

In this way, the layers are staggered on the opposite side surfaces to separate the internal electrodes 12 from each other by one layer.
After the sintered body 21 connected to is cut into one element,
A lead wire for power supply is attached to a part of the copper foil 15, and a resin sheath and polarization treatment are applied to complete the product.

[0021]

As is apparent from the above description, according to the laminated piezoelectric element of the present invention, the internal electrodes at both ends of the laminated body in the laminating direction are separated from each other inside the laminated body to be in a non-conducting state. Therefore, it is possible to reliably connect the original internal electrode and external electrode while maintaining the effect of alleviating the amount of contraction of the protective layer portions at both ends of the laminate, and reliably prevent the insulation failure. be able to.

[Brief description of drawings]

FIG. 1 is a sectional view of a piezoelectric element.

FIG. 2 is a printed pattern of internal electrodes for shrinkage relaxation.

FIG. 3 is a perspective view of a cut laminated sintered body.

FIG. 4 is a perspective view of a laminated sintered body in which conductive protrusions are formed.

FIG. 5 is a cross-sectional view showing a state of an element surface layer on which electrodeposition coating is applied.

FIG. 6 is a cross-sectional view showing a state in which an electrodeposition coating composition is cured while flowing by heat.

FIG. 7 is a cross-sectional view showing a state in which a layer containing conductive particles is formed on a copper foil.

FIG. 8 is a cross-sectional view showing a state in which a copper foil having an electrodeposition layer and a conductive film is pressed.

FIG. 9 is an explanatory diagram showing a state in which a conductive portion is formed by applying pressure.

[Explanation of symbols]

 11 piezoelectric material 12 internal electrode 13 conductive film 13a outer layer 13b inner layer 14 conductive portion 15 copper foil 16 conductive convex portion 17 non-conductive internal electrode

Claims (2)

[Claims] 1. A laminated body in which a conductive convex portion is exposed on a side surface of a laminated body in which piezoelectric materials and internal electrodes are alternately laminated so as to correspond to internal electrodes placed one layer apart, and the conductive convex portions are exposed. In the multilayer piezoelectric element, the external electrodes are electrically connected to the conductive protrusions of the one-layer-placed internal electrodes by disposing external electrodes on the side surfaces of the multilayer body. 2. A laminated piezoelectric element, wherein at least one internal electrode arranged at both end portions in the stacking direction is separated in a non-conductive state inside the stacked body. 2. The internal electrode separated in a non-conducting state inside the laminated body is formed by a printing pattern in which a large number of conductive portions are intermittently arranged in a substantially lattice shape, a wavy shape, or the like. 1. The laminated piezoelectric element according to 1.