JPH04343282A - Piezoelectric effect element and electrostrictive effect element - Google Patents

Abstract

PURPOSE:To enable an element to be enhanced in reliability by a method wherein moisture is prevented from penetrating into the element through an interface between sheathing resin and ceramic. CONSTITUTION:A mounting member 10 is provided to at least one of the upper and the lower displacement generating surfaces of an element sheathed by a sheathing resin 7. The external dimension of the mounting member 10 is set larger than that of the sheathing resin in cross section vertical to the direction of displacement (in the figure, Y direction). As the side face of the mounting member 10 can be made to serve as a reference plane when the element is mounted on a certain object, the mounting of the element on the object concerned can be enhanced in accuracy. Furthermore, the mounting member 10 is threaded or a protrusion or a tenon (mortise) or a groove is provided to the mounting member 10, whereby the elements can be easily mounted on or dismounted from each other or a certain object.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric effect element and an electrostrictive effect element, and more particularly to a stacked piezoelectric effect element and an electrostrictive effect element.

0002

[Prior Art] Displacement generating elements using piezoelectric effect or electrostrictive effect include bimorph type using transverse effect,
There is a laminated type that takes advantage of the vertical effect. Among these, laminated displacement generating elements have the advantages of being small, having a large driving force, and having high energy conversion efficiency, so much applied research has been conducted on them. A conventional laminated displacement generating element will be explained using a laminated piezoelectric effect element (hereinafter referred to as an element) that utilizes a piezoelectric effect as an example. Note that, for convenience of explanation, a piezoelectric effect element will be described below, but the explanation also applies to an electrostriction effect element if "piezoelectric" is replaced with "electrostriction". This is because the only difference between a piezoelectric effect element and an electrostrictive effect element is whether the strain generated when an electric field is applied to a solid is proportional to the electric field or proportional to the square of the electric field.

FIG. 4 is a sectional view showing the structure of a conventional device. Referring to FIG. 4, in this element, piezoelectric ceramics 1 exhibiting a piezoelectric effect and internal electrodes 2 are alternately laminated. The portions of each internal electrode 2 exposed on a pair of opposing side surfaces are covered with insulating glass 3 alternately on the left and right every other layer. On the side surface described above, an external electrode 4 is formed on the insulating glass 3, and the internal electrodes 2 are connected to the external electrode 4 so that every other layer has the same potential. A lead wire 5 is attached to each of the two external electrodes 4 with solder 6. The entire four sides of this element are covered with an exterior resin 7. The two upper and lower surfaces not covered by the exterior resin 7 are displacement reference surfaces or displacement generation surfaces, and are portions that transmit displacement to other members.

In this element, the internal electrodes 2 act as opposing electrodes with the piezoelectric ceramic 1 in between, like the teeth of two combs, so when a voltage is applied to the lead wire 5 from the outside, Even at a low voltage, a large displacement occurs in the direction shown by the Y axis in the figure.

[0005]

The conventional device described above has the following drawbacks. ■Displacement generation surface (
Since the upper and lower parts of the element not covered with the exterior resin 7 in Fig. 4 are made of ceramic, the method of attaching the element to the member receiving displacement from the element (hereinafter referred to as the attached body) is by adhesive. The method is limited. Furthermore, this adhesive must meet several requirements, such as having strong adhesion to metals and ceramics, being thin enough to avoid absorbing the displacement of the element, and having a high modulus of elasticity. Difficult to choose. ■Since the dimensional accuracy of the exterior resin 7 of the element is not sufficient, this exterior resin surface cannot be used as a positional reference when attaching the element to the object to be mounted. In other words, if the element is covered
When attaching it to the mounting body, it is difficult to position it in the X-axis direction or Z-axis direction in FIG. 4. ■The upper and lower displacement generating surfaces of the element are not covered with resin and the piezoelectric ceramic 1 is exposed, so moisture in the external atmosphere can escape from the boundary between the piezoelectric ceramic 1 and the exterior resin 7 on this displacement generating surface. Easy to break into. Moreover, when the element is driven, only the piezoelectric ceramic 1 is displaced in the Y-axis direction in FIG. 4, and the exterior resin 7 tends to stay at its original position, so the adhesion between the piezoelectric ceramic 1 and the exterior resin 7 is reduced. As the temperature decreases, the moisture penetrates deeply along the boundary between the piezoelectric ceramic 1 and the exterior resin 7 on the side of the element. As a result, the reliability of the device decreases.

[0006]

[Means for Solving the Problems] In the piezoelectric effect element of the present invention, piezoelectric materials and internal electrodes are alternately laminated, and exposed portions of the internal electrodes are alternately insulated at every other layer on a pair of side surfaces parallel to the direction of displacement. A piezoelectric effect element of the type in which all sides parallel to the direction of displacement of a laminate are provided with an insulating layer that connects the internal electrodes and an external electrode that connects the internal electrodes every other layer, and all sides parallel to the direction of displacement are covered with an exterior resin. has a mounting member on at least one surface perpendicular to the direction of displacement of the mounting member, and the dimension of the cross section perpendicular to the direction of displacement of this mounting member is larger than the cross-sectional dimension of the portion covered by the exterior resin including the exterior resin. Features.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view showing the structure of a first embodiment of the present invention. This embodiment differs from the conventional element shown in FIG. 4 in that metal mounting members 10 are provided on the upper and lower displacement generating surfaces of the element. The mounting member 10 has an external dimension in a cross section perpendicular to the displacement generation direction (Y-axis direction in FIG. 1) that is larger than the external dimension in a cross section of the element including the exterior resin 7. This example was manufactured as follows.

Lead zirconate titanate (Pb(Ti, Zr)
) A small amount of organic binder is added to the powder of the piezoelectric material whose main component is O3 ), and this is dispersed in an organic solvent to make a slurry, which is then coated with a film thickness of approximately 130 μm by tape casting or the like.
A piezoelectric sheet of m was made. Next, silver and
Approximately 1 portion of electrode paste containing a 7:3 mix of palladium powder
It was formed by screen printing or the like to a thickness of 0 μm. After that, 30 piezoelectric sheets without electrode paste printed on them, 120 piezoelectric sheets with printed electrode paste on them, and 30 piezoelectric sheets without printing on them were laminated one after another, and 200 kg of piezoelectric sheets were stacked.
/cm2 by applying heat and pressure to integrate.
A sintered body was obtained by firing at a temperature of about 1100° C. for 2 hours. Through this sintering, the piezoelectric sheet described above becomes the piezoelectric ceramic 1 shown in FIG. 1, and the electrode paste becomes the internal electrode 2, which are integrated. Next, insulating glass 3 is placed alternately every other layer on the internal electrodes 2 exposed on a pair of opposing sides of the sintered body.
was formed. A paste containing silver as a main component was deposited on the side surface by screen printing or the like, dried, and then baked at 600° C. for 10 minutes to form external electrodes 4. Thereafter, the lead wire 5 was connected to the external electrode 4 with solder 6.

Metal attachment members 10 are fixed to the upper and lower displacement surfaces of this element with adhesive, and an exterior resin 7 made of epoxy resin is applied to the entire side surface of the element except for the attachment members 10 and hardened. The exterior has been applied. The type of metal for the mounting member 10 is preferably one with a small coefficient of thermal expansion. This is because the coefficient of thermal expansion of piezoelectric ceramics is much smaller than that of metals. For example, the coefficient of thermal expansion is 0
．． If the mounting member is made of super invar material with a temperature of 1×10-6/°C, the thermal expansion coefficient of the mounting member 10 and that of the piezoelectric ceramic 1 will be close to each other, so even if the temperature cycle is repeated, the mounting member 10 and the piezoelectric ceramic will remain the same. 1, and even when the temperature changes during use, fluctuations in the reference position of the displacement surface due to temperature changes are suppressed to a small extent, and good displacement characteristics are maintained. An element with this property was obtained.

Next, the device according to this embodiment was heated to a temperature of 4
A humidity resistance load life test was conducted under the conditions of 0° C., humidity 90% RH, and voltage 150 VDC. The results are shown in FIG. Figure 4
are 20 for each of the device according to this example and the conventional device.
The horizontal axis represents the test time, and the vertical axis represents the cumulative failure rate of defects that occurred over the course of the test time. Referring to FIG. 4, in the conventional element, 2
On the other hand, in the element according to this example, no defects were observed until about 500 hours, whereas defects began to occur after about 00 hours. From FIG. 4, we calculated the mean failure time, and found that the device of this example was approximately 3 times longer than the conventional device.
It turned out to be double that.

[0011] This result shows that in the conventional element, when the element is driven, only the piezoelectric ceramic 1 is displaced, so the adhesion between the piezoelectric ceramic 1 and the exterior resin 7 is reduced, and moisture easily enters from the boundary. In contrast, in the element of this example, the adhesiveness between the mounting member 10 and the exterior resin was good, so it can be considered that this is because the intrusion of moisture was suppressed.

Furthermore, in the element of this embodiment, the mounting member 1
Since the side surface of 0 protrudes outside the exterior resin 7, this side surface can be used as a reference surface when attaching the element to the object to be mounted. Therefore, in this example, it was possible to eliminate the decrease in mounting accuracy caused by variations in the exterior dimensions of the elements, and to improve the positioning accuracy.

Next, a second embodiment of the present invention will be described. FIG. 3 is a sectional view showing the structure of a second embodiment of the present invention.

This embodiment differs from the first embodiment shown in FIG. 1 in the structure of the mounting members 10a and 10b. In this embodiment, one mounting member 10a is threaded in the center, and the other mounting member 10b is provided with a hemispherical protrusion. If the mounting member has such a structure, for example, the bottom mounting member 10
Since the object to be mounted can be screwed to a, an adhesion process is not necessary and it can be easily attached or removed. In addition, the upper mounting member 10
In b, since the contact with the mounted body is made by point contact, displacement can be reliably transmitted even if the mounted body and the element are not necessarily parallel. Therefore, the processing accuracy of the mounted body and the element does not need to be as high as in the past, and processing becomes easier. Another example of processing the mounting members is, for example, if one mounting member is provided with a protrusion that serves as a tenon, and the other mounting member is provided with a mortise or groove in which the tenon is combined, two elements can be assembled. can be easily connected in series to increase displacement without using adhesive. That is, by applying appropriate processing to the mounting member, various methods can be selected for mounting the elements together or between the elements and the object to be mounted, and the mounting can be easily done in a short time.

In the first and second embodiments described above, metal such as Super Invar material was used as the material for the mounting member, but ceramic or organic polymer material may also be used. For example, if alumina (Al2O3) is used as a typical ceramic, its coefficient of thermal expansion is close to that of piezoelectric ceramics, so it not only provides the same effect as the first embodiment, but also provides an element with excellent mechanical strength. can be obtained. Furthermore, if engineering plastics such as polyethylene terephthalate (PET) are used as the organic polymer material, they can be easily processed by machining, molding, etc., and therefore the device can be manufactured at low cost.

[0016]

[Effects of the Invention] As explained above, according to the present invention,
By providing a mounting member with a cross-sectional dimension larger than the cross-sectional dimension of the element on the exterior part on at least one of the upper and lower displacement generating surfaces, moisture infiltration from the boundary between the exterior resin and ceramic is prevented and the reliability of the element is improved. can improve sex. Furthermore, since the side surface of the attachment member can be used as a reference surface when attaching to the object to be attached, attachment accuracy can be improved. Further, by processing the mounting member with threads, protrusions, mortises, grooves, etc., it is possible to easily attach and detach the elements or between the elements and the object to be mounted.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a first embodiment of the invention.

FIG. 2 is a diagram comparing the results of a moisture resistance load life test on the element according to the first embodiment of the present invention and a conventional element.

FIG. 3 is a sectional view of a second embodiment of the invention.

FIG. 4 is a cross-sectional view of a conventional element.

[Explanation of symbols]

1 Piezoelectric ceramic 2 Internal electrode 3 Insulated glass 4 External electrode 5 Lead wire 6 Solder 7 Exterior resin

Claims (4)

[Claims] [Claim 1] Piezoelectric materials and internal electrodes are alternately laminated, and on a pair of side surfaces parallel to the direction of displacement, the internal electrodes are connected to insulating layers that alternately insulate the exposed parts of the internal electrodes every other layer. In a piezoelectric effect element of a type in which all side surfaces parallel to the displacement direction of a laminate provided with an external electrode are covered with an exterior resin, an attachment member is provided on at least one surface of the laminate perpendicular to the displacement direction. A piezoelectric effect element having a cross-sectional dimension perpendicular to the displacement direction of the attachment member is larger than a cross-sectional dimension including the exterior resin of a portion covered by the exterior resin. 2. Electrostrictive materials and internal electrodes are alternately laminated, and on a pair of side surfaces parallel to the displacement direction, the internal electrodes are connected to insulating layers that alternately insulate the exposed parts of the internal electrodes every other layer. In an electrostrictive element of the type in which all side surfaces parallel to the displacement direction of a laminate including an external electrode are covered with an exterior resin, at least one surface of the laminate perpendicular to the displacement direction is covered with an exterior resin. An electrostrictive effect element comprising an attachment member, wherein a cross-sectional dimension of the attachment member perpendicular to a displacement direction is larger than a cross-sectional dimension of a portion covered by the exterior resin that includes the exterior resin. 3. The piezoelectric effect element according to claim 1 or the electrostrictive effect according to claim 2, wherein the mounting member is made of metal, ceramic, or an organic polymer material having a high elastic modulus. element. 4. The piezoelectric effect element according to claim 1, or the electrostrictive effect element according to claim 2, wherein the attachment member has a processed part for joining on a joint surface with another member.