JPH04303978A - Laminated piezoelectric actuator - Google Patents

Abstract

PURPOSE:To prevent the water content in an atmosphere from being diffused from an exterior finishing resin surface to a piezoelectric ceramic surface and the dielectric breakdown phenomenon from occurring between an internal electrode and an external electrode or between the internal electrodes by providing a metal foil layer which covers surfaces of four sides within an exterior finishing resin. CONSTITUTION:A multilayered ceramic body is formed into one piece by superposing a plurality of ceramic sheets with a piezoelectric effect where a conductive internal electrode 4 is clad and formed on an entire surface and furthermore by laminating a piezoelectric sheet which becomes a protection layer 2 on the upper and lower surfaces. Also, an electrical insulation layer 5 which is provided at each other layer on an exposed portion of an internal electrode and a ceramic near it, a conductive external electrode 6 which is formed on its side surface, and an exterior finishing resin 9 which covers surfaces of four sides are provided. A metal foil layer 10 exists in the exterior finishing resin 9, covers the surfaces of four sides, and prevents water contents which are diffused from a surface of the exterior finish resin 9 from reaching a surface of a piezoelectric ceramic 3, thus preventing an insulation breakdown phenomenon from occurring between the internal electrode 4 and the external electrode 6 or the internal electrodes 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric actuator, and more particularly to a highly reliable laminated piezoelectric actuator in which dielectric breakdown phenomenon in an electrically insulating layer portion is improved.

0002

2. Description of the Related Art FIG. 4 is a sectional view showing the structure of a conventional laminated piezoelectric actuator to which the present invention is applied. In the figure, 2 is a protective layer, 3 is a piezoelectric ceramic, and 4 is an internal electrode.On two opposing sides of the four sides where the internal electrode 4 is exposed,
Electrical insulating layers 5 are alternately provided on the exposed portions of the internal electrodes 4 and on the piezoelectric ceramic 3 in the vicinity thereof. The internal electrodes 4 are electrically connected to every other layer by external electrodes 6, and are connected to lead wires 7 via solder 8. Furthermore, the two side surfaces provided with the electrical insulating layer 5 and the two exposed side surfaces of the internal electrodes 4 are covered with an exterior resin 9.

Conventionally, the piezoelectric ceramic 3 is made of a lead-based perovskite composite oxide such as lead zirconate titanate (PZT), and the electrical insulating layer 5 is made of glass powder having a softening point of 500 to 700° C. by electrophoresis. It is made of a glass body that is formed by adhering it to a desired position and then firing it at 600 to 800°C. The external electrode 6 is made by applying a paste-like material prepared by dispersing and mixing metal powder such as silver or silver-palladium mixed powder in a vehicle with glass powder to a desired position using a screen printing method, and then
It is made of a sintered body of metal powder fired at 800°C. The exterior resin is made by electrostatically coating epoxy resin powder and curing it at a temperature of 150 to 200°C.

0004

[Problems to be Solved by the Invention] The conventional laminated piezoelectric actuator shown in FIG.
m) at 150V in an atmosphere of 40°C and 90-95% RH.
Figure 3 shows the results of a life test. As can be seen from this figure, if a laminated piezoelectric actuator with a conventional structure is used continuously in a high humidity atmosphere, it will break down after an average lifespan of several hundred hours. The reason for this is as follows. Moisture in the atmosphere diffuses from the surface of the exterior resin 9 to the inside, and the piezoelectric ceramic 3
When it reaches the surface, the electrical insulating layer 5 is subjected to stress corrosion, causing cracks, and the silver in the internal electrodes 4 on the side surfaces where the electrical insulating layer 5 is not provided is migrated. As a result, the insulation between the internal electrodes 4 and the external electrodes 6 is broken, or the insulation between the internal electrodes 4 is broken, causing the laminated piezoelectric actuator 1 to become short-circuited and become defective.

FIG. 3 shows the results of evaluations made by changing the thickness of the exterior resin into three types. according to this,
It can be seen that increasing the thickness of the exterior resin 9 improves the life of the conventional laminated piezoelectric actuator 1 to some extent, but since it is not possible to prevent the diffusion of moisture in the exterior resin 9, it is essential to extend the life. It turns out that there are limits to.

As described above, in the laminated piezoelectric actuator of the conventional structure, water in the atmosphere diffuses from the surface of the outer resin 9 to the inside, which causes the inner electrode 4
There is a problem in that dielectric breakdown occurs between the external electrode 6 and the internal electrode 4, resulting in failure in a short period of time.

An object of the present invention is to prevent moisture in the atmosphere from diffusing from the exterior resin surface to the piezoelectric ceramic surface, and to prevent dielectric breakdown from occurring between the internal and external electrodes or between the internal electrodes. The object of the present invention is to provide a laminated piezoelectric actuator with significantly improved reliability.

[0008]

[Means for Solving the Problems] The laminated piezoelectric actuator of the present invention has a plurality of ceramic sheets exhibiting a piezoelectric effect each having a conductive internal electrode adhered to the entire surface thereof, and a piezoelectric actuator serving as a protective layer on the top and bottom surfaces of the piezoelectric actuator. A laminated ceramic body made by laminating and integrating body sheets, and electrical insulating layers alternately provided every other layer on the exposed parts of the internal electrodes and the ceramic in the vicinity on two opposing sides of the four sides where the internal electrodes are exposed. , a conductive external electrode formed on the side surfaces, an exterior resin covering the four sides, and moisture in the exterior resin that covers the four sides and diffuses from the exterior resin surface to the piezoelectric ceramic surface. It has a metal foil layer that prevents it from reaching.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be explained with reference to the drawings. FIG. 1 is a sectional view showing the structure of a laminated piezoelectric actuator according to an embodiment of the present invention. In this example, the protective layer 2
And the piezoelectric ceramic 3 is Pb(Ni1/3 Nb2/
3) Perovskite structure composite oxide represented by 0.5 Ti0.35Zr0.15O3, internal electrode 4 is silver 7
A silver-palladium mixed electrode containing 0% palladium and 30% palladium was used. The electrical insulating layer 5 was made of zinc-based glass containing 60.0% ZnO, 25% B2 O3, and 15% other oxides. The external electrode 6 was made of silver as a conductor, and the firing temperature was 700.degree. Furthermore, the lead wire 7 is soldered to the external electrode 6, and an epoxy powder resin is applied by electrostatic coating so that the thickness will be about 200 μm after curing.
Temporarily harden at 0°C for about 3 minutes. Further, an aluminum foil is wrapped around the exterior resin so as to cover all of the four sides, and an overlapping portion is created to form the aluminum foil layer 10. This situation is shown in FIG. The above-mentioned epoxy powder resin is further applied to a thickness of about 200 μm on top of this aluminum foil layer 10 by electrostatic coating.
Cure at 50°C for about 2 hours.

[0010] A prototype laminated piezoelectric actuator according to an embodiment of the present invention was manufactured and its reliability test was conducted. The results are shown in FIG. 3 together with the test results of a laminated piezoelectric actuator having a conventional structure in which the thickness of the outer resin was changed. . The prototype device has a piezoelectric ceramic 3 with a thickness of 105 μm and an internal electrode 4 with 1 layer.
There were 26 layers, the thickness of the protective layer 2 was 2 mm and 4 mm, the cross section of the element was 5 mm x 5 mm, and the thickness of the exterior resin including the aluminum foil 10 was about 450 μm. The test conditions are 4
0°C-90%RH, 150VDC. It can be seen that by implementing the present invention, diffusion of moisture to the surface of the piezoelectric ceramic 3 is prevented, and the life of the laminated piezoelectric actuator is improved several times.

[0011]

As explained above, the present invention provides a metal foil layer in the exterior resin 9 to prevent moisture in the atmosphere from diffusing from the surface of the exterior resin 9 to the surface of the piezoelectric ceramic 3, thereby preventing internal electrodes from dispersing. 4 and the external electrode 6 or between the internal electrode 4 and the reliability of the laminated piezoelectric actuator is greatly improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a perspective view showing the process of forming an aluminum foil layer in the exterior resin, which is the main part of an embodiment of the present invention.

FIG. 3 is a diagram showing reliability test results (relationship between reliability test time and defective rate) of a laminated piezoelectric actuator having an embodiment of the present invention and a conventional structure.

FIG. 4 is a cross-sectional view of an example of a conventional laminated piezoelectric actuator.

[Explanation of symbols]

1 Laminated piezoelectric actuator 2 Protective layer 3 Piezoelectric ceramic 4 Internal electrode 5 Electrical insulation layer 6 External electrode 7 Lead wire 8 Solder 9 Exterior resin 10 Aluminum foil layer

Claims (1)

[Claims] Claim 1: A multilayer ceramic in which a plurality of ceramic sheets exhibiting a piezoelectric effect are laminated with conductive internal electrodes formed on the entire surface, and piezoelectric sheets serving as protective layers are further laminated on the top and bottom surfaces of the ceramic sheets. Electrical insulating layers are provided alternately every other layer on the exposed parts of the internal electrodes and the ceramic in the vicinity on two opposing sides of the body where the internal electrodes are exposed, and conductive layers are further provided on the side surfaces. A laminated piezoelectric actuator formed by forming an external electrode and further coating the four side surfaces with a resin, the laminated piezoelectric actuator comprising a metal foil layer covering the four side surfaces in the coating resin.