JPH07240545A - Laminated piezoelectric element - Google Patents

Abstract

PURPOSE:To provide a laminated piezoelectric element in which a ridge corner part which is parallel to the displacement direction of the element can be covered surely with an armor and which can eliminate a migration defect due to the creeping of moisture. CONSTITUTION:Conductive protrusion parts 16 are formed every other layer on the side face of a laminated body in which piezoelectric materials 11 and internal electrodes 12 are piled up alternately, and a conductive film 13 is formed so as to cover all the piezo-electric materials 11. In addition, a copper foil 15 as an external electrode is formed on the whole face on it, and the copper foil is connected electrically to the internal electrodes 12 via the conductive protrusion parts 16 every other layer. An armor 17 which is composed of a resin is conducted to the side face of an element.

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, the internal electrodes are connected every other layer by the structure shown in FIGS. 8 (a) and 8 (b).
FIG. 8A is a front view of the laminated piezoelectric element, and FIG. 8B is a cross-sectional view of the element cut in the vertical direction and shown in the horizontal direction. In FIG. 8B, on the side surface of the laminated body in which the piezoelectric material 11 and the internal electrode 12 are alternately laminated, the conductive convex portion 16 is formed on the side surface of the internal electrode 12 placed in a single layer, and All piezoelectric materials in stacking direction 1
Layer 13 containing conductive particles 31 so as to correspond to No. 1
A conductive film 13 including a and a layer 13b that does not contain a is formed. Then, a copper foil 15 is formed thereon as an external electrode, and the copper foil 15 is electrically connected to the conductive convex portion 16 and further to the internal electrode 12 via the conductive particles 31. As shown in FIG. 8A, the copper foil 15, which is an external electrode, is formed with a width considerably smaller than the width of the element. In actual use, the entire surface of the element is covered with a resin or the like to prevent ingress of moisture.

[0004]

However, according to the piezoelectric element having the structure shown in FIG. 8, at the ridge line portion parallel to the displacement direction of the element, as shown in FIG. It was difficult to reliably coat with. Since the main component of the internal electrodes used in the laminated piezoelectric element is silver, when a direct current voltage is applied in a state where water is attached, a phenomenon called so-called migration occurs, and the insulation resistance between the internal electrodes decreases. In order to prevent this phenomenon, an exterior is provided to shield the element from the outside air to prevent the ingress of moisture, that is, moisture.However, because the exterior of the corner portion is thin, it is not completely exposed to the outside air. I couldn't shut it off. If driving is continued in this state, migration gradually progresses and eventually short-circuiting occurs, and there is a problem that not only the piezoelectric element itself but also the mechanical device equipped with it becomes a defective product.

The present invention has been made in order to solve the above-mentioned problems, and the ridge line parallel to the displacement direction of the element can be surely covered with an outer package, and migration failure due to infiltration of moisture can be eliminated. It is an object of the present invention to provide a laminated piezoelectric element that can be used.

[0006]

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 in which the external electrodes are electrically connected, the external electrodes are arranged over substantially the entire side surface of the laminated body.

The external electrodes may be made of flat copper foil.

[0008] It is preferable that the outer surface of the laminate is covered with an epoxy resin or the like from the outside of the external electrode.

[0009]

According to the multi-layer piezoelectric element of the present invention having the above-mentioned structure, the external electrodes are arranged over substantially the entire side surface of the multi-layer body, so that the entire surface of the element is covered from above. Thus, when a resin or the like is applied to the exterior, the ridge line corner portion parallel to the displacement direction of the element is surely covered with the exterior and is reliably shielded from the outside air.

[0010]

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

FIG. 1 shows the appearance and cross section of the laminated piezoelectric element. FIG. 1 (a) is a perspective view of the completed element, and FIG. 1 (b) is a line B of FIG. 1 (a). FIG. 4C is an enlarged cross-sectional view taken along the line C, and FIG. 7C is an enlarged cross-sectional view taken along the line C of FIG.

In FIGS. 1B and 1C, the laminated body 10
In each of the opposite side surfaces, the conductive convex portions 16 are formed so as to be further displaced between the side surfaces and to correspond to the end portions of the internal electrodes 12 placed in each one of the side surfaces. A conductive film 13 is formed over the entire surface of each of the side surfaces on which the conductive protrusions 16 are formed, and a copper foil 15 as an external electrode is formed on the conductive film 13. The copper foil 15 is electrically connected to the internal electrodes 12 via the conductive particles 31 and the conductive protrusions 16.
The conductive film 13 is composed of an outer layer 13 a containing copper 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 electrode 12 on a green sheet formed to a predetermined thickness by the doctor blade method, and a predetermined number of punched products were stacked and integrated by hot pressing. To do. After degreasing, sintering is performed at about 1200 ° C., and as shown in FIG. 2, temporary external electrodes 22 and 23 are applied and baked onto the sintered body 21 cut at a position where the internal electrode 12 is exposed every other layer. 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 entire 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 passed for about 5 minutes in this state, the temporary external electrode 22
When the nickel plating grows on the end surface of the internal electrode 12 connected to, and the masking tape is peeled off, the conductive projections 16 made of nickel plating are formed every other layer as shown in FIG. 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 protrusion 16 is formed so as to be offset from the side surface 24 by one layer.

After cleaning, the negative electrode of the DC power supply is used as a temporary external electrode 2.
2, 23, immersed in an epoxy cation electrodeposition paint containing a predetermined pigment, and a voltage of 100 V is applied for 2 minutes. As a result, as shown in FIG. On the surface of the conductive convex portion 16, the inner electrode 12 on which the conductive convex portion 16 is not formed is electrodeposited with an epoxy cation electrodeposition coating 13c to be the inner layer 13b at the end portions thereof. It After that, when placed in an oven and subjected to heat treatment at 150 ° C. for 30 minutes, since the epoxy resin component has fluidity in the process of hardening, it is flattened as shown in FIG. 5 and becomes the inner layer 13b containing no conductive particles.

Separately from the sintered body 21, as shown in FIG. 6, the conductive particles 31 have an average particle size of 20 to 20 on the copper foil 15.
A thermosetting epoxy-based adhesive containing 30 μm copper particles uniformly applied to the thickness of about 70 μm (outer layer 13a containing conductive particles 31) is prepared. As shown in FIG. 7, the side surfaces 24 and 25 of the sintered body 21 are sized so as to cover all the conductive convex portions 16 and substantially the entire side surfaces 24 and 25. It is cut and temporarily fixed so that the inner layer 13b containing no conductive particles 31 and the outer layer 13a containing the conductive particles 31 face each other. The inner layer 13b not containing the conductive particles 31 and the outer layer 13a containing the conductive particles 31 cooperate with each other to form the conductive film 13.

When sandwiched by a pair of flat pressing jigs (not shown) heated to about 180 ° C. and thermocompression-bonded with a load of several kg, the conductive protrusions 16 cause the protrusions. As shown in Fig. 1 (b),
In this compressed portion, the conductive particles 31 penetrate through the inner layer 13 b that does not contain the conductive particles 31 and come into contact with the conductive protrusions 16. Therefore, the internal electrodes 12 placed one layer apart
The copper foil 15 and the copper foil 15 are electrically connected.

In this way, the layers are staggered on the opposite side surfaces to separate the internal electrodes 12 from each other by one layer.
7 is cut into one element at each position shown by a dotted line in FIG. 7, and then a lead wire for power supply is attached to a part of the copper foil 15, and then the lead wire is connected. A negative electrode of a direct current power source is connected to, and it is submerged in an epoxy electrodeposition paint containing a large amount of pigment, electrodeposited at a voltage of 200 V for 2 minutes, and then heat-cured at 150 ° C. to form an outer package 17. The finished product is obtained as described above.

In each completed laminated piezoelectric element, each ridge line corner portion parallel to the displacement direction of the element is surely covered with epoxy resin (see FIG. 1 (c)), and is completely shielded from the outside air.

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention. For example, the same effect can be obtained by using chrome plating or copper plating instead of nickel plating. It can also be used as an exterior by electrostatic coating or air spray coating.

[0022]

As is apparent from the above description, according to the laminated piezoelectric element of the present invention, in particular, each ridge line corner portion parallel to the displacement direction of the element can be reliably shielded from the outside air by the resin exterior. In addition, migration defects due to the intrusion of water are eliminated, and reliability and yield can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a laminated piezoelectric element according to an embodiment of the present invention.

FIG. 2 is a perspective view of a cut laminated sintered body.

FIG. 3 is a perspective view of a sintered body in which conductive protrusions are formed.

FIG. 4 is a sectional view showing a state in which an epoxy resin is electrodeposited.

FIG. 5 is a cross-sectional view showing a state in which the electrodeposition coating composition flows by heating.

FIG. 6 is a cross-sectional view showing a state in which an outer layer containing conductive particles is formed on a copper foil.

FIG. 7 is a perspective view showing a state in which a copper foil is temporarily fixed to a sintered body.

FIG. 8 is a diagram showing a configuration of a conventional laminated piezoelectric element.

FIG. 9 is a cross-sectional view of a corner portion of a conventional laminated piezoelectric element.

[Explanation of symbols]

 11 Piezoelectric Material 12 Internal Electrode 13a Outer Layer 13b Inner Layer 15 External Electrode 16 Conductive Convex Part 17 Exterior

Claims (3)

[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 multi-layer piezoelectric element, the external electrodes are electrically connected to the conductive convex portions of the one-layer-placed internal electrodes by disposing the external electrodes on the side surfaces of the external electrodes via the conductive layer. Is disposed over substantially the entire side surface of the laminated body. 2. The laminated piezoelectric element according to claim 1, wherein the external electrode is formed of a flat copper foil. 3. The laminated piezoelectric element according to claim 1, wherein an exterior of an epoxy resin or the like is provided on the entire surface of the laminated body from the outside of the external electrode.