JP2000106461A - Laminated piezoelectric device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated piezoelectric device where delamination is prevented from occurring in an interface between an inner electrode and a piezoelectric body or between a laminate and an electric insulating film layer or an outer electrode without using special material. SOLUTION: Openings 11 are provided to a piezoelectric body 41 penetrating through it in the direction of lamination, and a joint 90 that is high in electric insulting properties and elasticity is provided between the piezoelectric body 41 and an inner electrode 50, whereby delamination can be prevented from occurring in an interface between the inner electrode 50 and the piezoelectric body 41 or between a laminate and an electric insulating film layer or an outer electrode without using special material.

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, and more particularly to an element structure capable of preventing separation at an interface between an internal electrode and a piezoelectric body, and at an interface between a laminated body and an electrically insulating coating layer or an external electrode.

[0002]

2. Description of the Related Art FIG. 6 shows the structure of a conventional laminated piezoelectric element to which the present invention is applied. The laminated piezoelectric element is composed of a piezoelectric body 40 which is a thin sheet of a composite oxide having a lead-based perovskite structure such as lead zirconate titanate (PZT) and a metal layer such as silver palladium (Ag / Pd) or platinum (Pt). After cutting out a small piece from the laminate obtained by laminating and integrating the internal electrodes 50, an electric insulating coating layer 60 is formed, and the internal electrodes 5 are formed.
0 is electrically connected by an external electrode 70 to produce the semiconductor device.
The electric insulating coating layers 60 are alternately provided on two opposing side surfaces of the four side surfaces on which the internal electrodes 50 are exposed, on the exposed portions of the internal electrodes and on the piezoelectric body 40 in the vicinity thereof. The electrically insulating coating layer 60 is formed at a desired position by a glass powder having a softening point at 500 ° C. to 700 ° C. by an electrophoresis method or a screen printing method using the glass powder as a paste-like substance. The internal electrodes and the external electrodes are also formed by a screen printing method using the electrode material as a paste-like substance.

[0003] When a voltage is externally applied to a laminated piezoelectric element, a predetermined amount of displacement can be obtained in the laminating direction by a piezoelectric effect. At this time, a desired vertical displacement is obtained, and at the same time, a horizontal displacement is generated. In other words, if the piezoelectric body induces a lateral displacement and cannot follow this displacement, lateral distortion occurs in the electric insulating coating layer and the external electrode,
Separation may occur at each interface due to this distortion. For this reason, there have been problems such as a decrease in the yield at the time of manufacturing the device and a low reliability during the operation of the device.

As a technique for preventing separation at the interface between the laminate and the electric insulating coating layer or the external electrode, for example, Japanese Patent Application Laid-Open No. 7-16999
A multilayer piezoelectric actuator described in Japanese Patent Application Laid-Open No. 8-108 is known. This is because the electric insulating coating layer is made of a mixture of the elastic member and the substantially spherical beads, so that the electric insulating coating layer follows the displacement of the piezoelectric body, and the element life when the actuator is repeatedly driven is improved. As another known technique, an electrostrictive element described in JP-A-61-216368 is known. By providing a hollow portion penetrating the element stacking direction in the electrostrictive effect element, distortion in the horizontal direction with respect to expansion and contraction during operation of the element is reduced by the hollow portion, and the life of the element is improved.

[0005]

The piezoelectric actuator described in Japanese Patent Application Laid-Open No. 7-169998 uses special materials and shapes for the external electrodes and the electrically insulating coating layer, which may increase the manufacturing cost. is there. Also, JP-A-61-2163
In the case of the electrostrictive effect element described in JP-A-68-68, when the distortion in the lateral direction with respect to the expansion and contraction of the element is large, stress is concentrated on the hollow part, and there is a possibility that the element is broken at the interface between the piezoelectric body and the internal electrode.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laminated piezoelectric element which can prevent separation at the interface between an internal electrode and a piezoelectric material, the interface between a laminate and an electrically insulating coating layer or an external electrode without using a special material. is there.

[0007]

A first means for achieving the above object (first invention) is located at a position facing a laminated body in which a plate-like piezoelectric body and internal electrodes are alternately laminated and integrated. On the pair of laminated end surfaces, an electrically insulating coating layer for insulating the laminated internal electrodes every other layer is provided in an asymmetric shape deviated in the laminating direction, and two external electrodes are provided to enable electrical conduction every other layer. In a laminated piezoelectric element provided with electrodes,
The object is to provide a plurality of openings penetrating in the laminating direction of the piezoelectric body, and to provide an electrically insulating and elastic joint between the piezoelectric body and the internal electrode.

According to a second aspect of the present invention, there is provided a multi-layer piezoelectric element according to the first aspect, wherein a plurality of openings penetrate in the laminating direction of the internal electrodes, and a plurality of openings are provided. And the position of the opening of the internal electrode.

A third means (third invention) for achieving the above object is the laminated piezoelectric element according to the first or second aspect, wherein all of the openings in the opening provided in the piezoelectric body or the internal electrode are provided. Alternatively, an electrically insulating elastic body is provided in a part.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below. FIG. 1 is an external view of a multilayer piezoelectric element showing a first embodiment of the present invention. The material of the piezoelectric body 41 is lead titanate (PbT
A piezoelectric material mainly composed of a lead-based composite oxide of iO ₃ ) -lead zirconate (PbZrO ₃ ), barium titanate (Ba)
TiO ₃ ) -based piezoelectric materials, other piezoelectric materials having a perovskite structure, and the like. The manufacturing method of the piezoelectric body 41 is shown in FIG.
Add a trace amount of binder to the raw material powder as shown in (a)
A slurry is prepared by mixing and dispersing this in a solvent, and a film-shaped piezoelectric sheet 20 is prepared by a green sheet method using a doctor blade device, and cut into a desired area. Also, based on the raw material powder, the bulk body 3 shown in FIG.
0 may be produced and sliced to a desired area and thickness. The bulk body 30 is a sintered body or a crystal. FIG.
The internal electrode 50 is a thin plate-shaped electrode mainly composed of Ag / Pd, Pt, Ni or the like.

Next, a plurality of openings 11 are provided to penetrate the piezoelectric body 41 in the laminating direction.
Are bonded by an electrically insulating elastic joint 90 to form a laminate. The shape of the opening 11 is not limited to a fixed shape such as a cylinder and a square tube, and may be any shape. The holes may be punched using a punching machine or drilled using a drill. Alternatively, an opening may be provided through a needle-like material. If the diameter of the aperture exceeds half the thickness of the piezoelectric body required for the actuator, usually 0.01 mm to 1 mm,
Even if a voltage is applied, the lines of electric force wrap around into the hole become remarkable, and a large displacement of the piezoelectric body cannot be obtained. Therefore, the thickness of the piezoelectric body must be 以下 or less of the thickness of the piezoelectric body. Further, the total hole cross-sectional area, which is the sum of the areas of the holes, is preferably not more than 以下 of the cross-sectional area of the piezoelectric body because the strength in the direction perpendicular to the laminating direction decreases as the number of holes increases.

Thereafter, the internal electrode 50 is provided on the laminated end face of the laminated body.
Is formed in an asymmetric shape shifted in the laminating direction so as to insulate every other layer, and the two external electrodes 70 are connected to enable the internal electrodes 50 to be electrically connected every other layer. The manufacturing process of the multilayer piezoelectric element is completed. Here, the electrically insulating coating layer 60 is made of a thermosetting resin such as an epoxy resin, an acrylic resin, or a phenol resin, an ultraviolet-curable resin, glass, or the like. The external electrode 70 is made of the same electrode material as the internal electrode 50 described above.

FIG. 3 is an exploded view of the multilayer body of the multilayer piezoelectric element of the first embodiment. Note that the exploded view of FIG.
Electrically insulative elastic joint 90 between the electrode and the internal electrode 50
Is omitted. In the case of these configurations, it is usually difficult to simultaneously fire the piezoelectric body and the electrically insulating elastic joint due to a difference in the firing temperature. Therefore, the piezoelectric body cut out from the bulk body shown in FIG. Devices are often assembled. At the time of producing a bulk body, a laminate composed only of a piezoelectric body was produced using the piezoelectric sheet 20 of FIG. 2A, and if an opening 11 was provided at this time, an organic substance contained in the binder was vaporized. Since it serves as a vent, the time required for degreasing can be reduced. Therefore, a bulk body can be manufactured in a shorter time than before, and the time required for the element manufacturing process can be reduced.

As an example, the cross-sectional area of the piezoelectric body is 5 mm × 5 m
m, thickness is 200 ~ 240μm, internal electrode thickness is 2 ~ 2
For a sample obtained by laminating 20 layers with a thickness of 5 μm, a conventional structure and a laminate having openings (hole diameter: about 100 μm, total hole cross-sectional area: about 5 mm ² ) were degreased.
While the amount of residual carbon is in the order of 100 ppm by degreasing over time, the laminated body provided with holes can achieve the amount of residual carbon in the order of 100 ppm in 20 hours.

With this structure, when a voltage is applied to the piezoelectric body, the aperture absorbs a vertical displacement that occurs vertically in addition to a displacement that occurs in the stacking direction, and the piezoelectric body absorbs a lateral displacement. As a result, lateral strain stress applied to the entire element can be dispersed as compared with an element having a hollow portion penetrating in the element stacking direction.

Further, when the piezoelectric body 41 having the opening 11 and the internal electrode 50 are bonded together by an electrically insulating elastic joint 90, the electrically insulating elastic joint 90 in the opening serves as a cushioning material. The strength in the direction perpendicular to the stacking direction can be reinforced. When an element manufactured from the above laminate was operated and an interface between the laminate and the electric insulating coating layer after 500 hours was observed with an optical microscope, there was an element in which the conventional structure had cracks at the interface from around 500 hours. On the other hand, in the element provided with the holes, no crack was generated at the interface after 500 hours, and the crack was less generated even after 1000 hours. Thus, it has been found that the present invention can prevent peeling occurring near the interface without using a special material.

Next, a second embodiment of the present invention will be described. The external view of the multilayer piezoelectric element of the second embodiment is the same as FIG. FIG. 4 is an exploded view of the multilayer body of the multilayer piezoelectric element of the present invention.
In the exploded view of FIG. 4, the electrically insulating elastic joint 90 between the piezoelectric body 41 and the internal electrode 51 is omitted. This is because, in the multilayer piezoelectric element of the first embodiment, the internal electrode 51
This is a laminated piezoelectric element in which a plurality of openings 12 penetrating in the stacking direction are provided, and the positions of the openings 11 of the piezoelectric body 41 and the openings 12 of the internal electrodes 51 are shifted. In addition, the laminated body shown in FIG. 4 may use a mesh-shaped electrode material without processing the opening 12 of the internal electrode 51.

With this structure, when the piezoelectric body 41 provided with the opening 11 and the internal electrode 51 provided with the opening 12 are bonded to each other by an electrically insulating elastic joint portion 90, the opening is formed. The electrically insulating elastic joint portion 90 functions as a cushioning material, and can reinforce the strength in the direction perpendicular to the lamination direction.
In addition, when a voltage is applied to the piezoelectric body, there is an aperture in the internal electrode which is a non-moving body during operation of the element because there is a hole for absorbing a vertical displacement that is generated separately from a displacement generated in the stacking direction. It can have its own flexibility.

Further, since the positions of the openings provided in the piezoelectric body and the internal electrode are shifted, the portion of the piezoelectric body which becomes an immovable body near the opening of the internal electrode increases, so that the accumulation is made in the openings of the internal electrode. The residual stress can be dispersed and reduced. Second
When the multilayer piezoelectric element shown in the example was operated and the interface between the laminate and the electric insulating coating layer after 500 hours was observed with an optical microscope, cracks and peeling were observed in the same manner as in the element of the above-described example. No evidence was seen. Thus, it has been found that the present invention can prevent peeling occurring near the interface without using a special material.

Next, a third embodiment of the present invention will be described. The external view of the multilayer piezoelectric element of the third embodiment is the same as FIG. This is the multilayer piezoelectric element of the first or second embodiment,
This is a laminated piezoelectric element in which an electrically insulating elastic body is provided in all or a part of an opening provided in a piezoelectric body or an internal electrode. The electrically insulating elastic body 80 is preferably made of a rubber-based material. FIG. 5A shows an example in which the electrically insulating elastic body 80 is provided in the entire opening 13 formed in the piezoelectric body 41, and the electrically insulating elastic body 80 is partially provided in the opening 13. FIG. 5B shows examples of the provision. The electrically insulating elastic body 80 may have an adhesive function. When making a laminate, it is not necessary to make a laminate with the same type of piezoelectric body or internal electrode,
For example, the piezoelectric body shown in FIG. 5A and the piezoelectric body shown in FIG.

According to this structure, an electrically insulating elastic material or an adhesive enters into the opening provided in the piezoelectric body or the internal electrode, and these serve as a cushioning material. Vertical strength can be reinforced. Third
When the multilayer piezoelectric element shown in the example was operated and the interface between the laminate and the electric insulating coating layer after 500 hours was observed with an optical microscope, cracks and peeling were observed in the same manner as in the element of the above-described example. No evidence was seen. Thus, it has been found that the present invention can prevent peeling occurring near the interface without using a special material.

[0022]

According to the multi-layer piezoelectric element of the present invention, it is possible to prevent the interface between the internal electrode and the piezoelectric body and the interface between the multi-layer body and the electric insulating coating layer or the external electrode without using a special material. This is effective in reducing the cost of the device, improving the yield, and extending the life of the device.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the appearance of a multilayer piezoelectric element showing a first embodiment of the present invention.

FIGS. 2A and 2B are perspective views of a piezoelectric sheet and a piezoelectric body showing an example of a method for manufacturing a piezoelectric body.

FIG. 3 is an exploded perspective view showing an appearance of a multilayer body of the multilayer piezoelectric element according to the first embodiment of the present invention.

FIG. 4 is an exploded perspective view showing the appearance of a multilayer body of a multilayer piezoelectric element according to a second embodiment of the present invention.

FIGS. 5A and 5B are top views of a piezoelectric body of a multilayer piezoelectric element according to a third embodiment of the present invention.

FIG. 6 is a perspective view showing the appearance of a conventional laminated piezoelectric element.

[Explanation of symbols]

11-13: Opening, 20: Piezoelectric sheet, 30: Bulk body, 40, 41: Piezoelectric body, 50, 51: Internal electrode, 60
... electric insulating coating layer, 70 ... external electrode, 80 ... electric insulating elastic body, 90 ... electric insulating elastic joint.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mitsuo Hayashibara 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Motoyuki Miyata 7, Omikamachi, Hitachi City, Ibaraki Prefecture No. 1 in the Hitachi Research Laboratory, Hitachi, Ltd.

Claims (3)

[Claims] An electrically insulating coating layer for insulating the laminated internal electrodes every other layer on a pair of laminated end faces opposite to a laminated body in which a plate-shaped piezoelectric body and internal electrodes are alternately laminated and integrated. Is provided in an asymmetric shape shifted in the stacking direction,
In a laminated piezoelectric element provided with two external electrodes that enable electrical conduction every other internal electrode, a plurality of openings penetrating in the laminating direction of the piezoelectric body are provided, and the piezoelectric body and the internal electrode are provided. Characterized in that an electrically insulating and elastic joint is provided between the piezoelectric element and the piezoelectric element. 2. The multilayer piezoelectric element according to claim 1, wherein a plurality of openings penetrating in the stacking direction of the internal electrodes are provided, and the positions of the openings of the piezoelectric body and the openings of the internal electrodes are shifted. A multilayer piezoelectric element characterized by the presence of: 3. The multilayer piezoelectric element according to claim 1, wherein an electrically insulating elastic body is provided in all or a part of an opening formed in the piezoelectric body or the internal electrode. Type piezoelectric element.