JPH0312974A - Laminated piezoelectric actuator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a piezoelectric element that converts electrical energy into mechanical energy in the form of displacement or force proportional to the electrical energy, and particularly relates to a piezoelectric element that converts electrical energy into mechanical energy in the form of displacement or force proportional to the electrical energy. This invention relates to a multilayer piezoelectric actuator.

[Conventional technology] Conventionally, electromagnetic actuators such as voice coil motors and pulse motors have been used as actuators for precision positioning devices and precision X-Y tables, but in recent years, electromagnetic actuators such as voice coil motors and pulse motors have Laminated piezoelectric actuators, which are superior to the electromagnetic actuators, are being used.

A laminated piezoelectric actuator has piezoelectric ceramic plates and internal electrode plates alternately laminated to form a ceramic laminate.

In the laminated piezoelectric actuator, concentrated stress can be eliminated by making the cross-sectional area of the piezoelectric ceramic plate orthogonal to the direction of displacement coincide with the cross-sectional area of the internal electrode plate. With the progress of
It is possible to increase the amount of distortion that occurs.

Referring to FIG. 2, the conventional laminated piezoelectric actuator 2 has a pair of internal electrodes 12 facing each other on its side surfaces.
It has a structure in which the edges of and 12 are exposed. In addition, in FIG. 2, 13 is a glass insulating part, 14 is an external electrode, and 15 is a lead wire. As mentioned above, in this laminated piezoelectric actuator 2, the internal electrodes 12 and 12' are exposed from the side surfaces, so in order to ensure electrical insulation from other devices, an insulator must be formed on the side surfaces. There must be. For this reason, it is common practice to cover the side surfaces with an organic resin layer (not shown).

[Problems to be Solved by the Invention] However, even if the side surfaces of the laminated piezoelectric actuator are covered with an organic resin layer, it is difficult to prevent moisture from entering or passing through.

Moreover, if the laminated piezoelectric actuator is used for a long time in a high temperature environment, the insulation resistance between the pair of internal electrodes 12 and 12- will decrease, and even lead to a short circuit.

Therefore, the technical problem of the present invention is to provide a laminated piezoelectric actuator that prevents moisture from entering and passing through and does not cause a decrease in insulation resistance between internal electrodes even when used for a long time in a high temperature environment. That's true.

[Means for Solving the Problems] According to the present invention, there is provided a laminated piezoelectric actuator having a piezoelectric ceramic portion and at least a pair of internal electrodes disposed substantially parallel to each other in the piezoelectric ceramic portion. In the multilayer piezoelectric actuator, the pair of internal electrodes have edges exposed to the outside from the side surfaces of the multilayer piezoelectric actuator, and the pair of internal electrodes are made of copper oxide, nickel oxide, tin oxide, zinc oxide, chromium oxide, or copper oxide. A laminated piezoelectric actuator is obtained, characterized in that the laminated piezoelectric actuator is made of at least one type of iron and has a coating layer that covers at least the side surfaces of the laminated piezoelectric actuator.

Also, a laminated piezoelectric actuator having a piezoelectric ceramic portion and at least a pair of internal electrodes arranged substantially parallel to each other in the piezoelectric ceramic portion, one of the pair of internal electrodes being connected to the laminated piezoelectric actuator. The laminated piezoelectric actuator has an edge exposed to the outside from one of the pair of mutually opposing side surfaces, and the other of the pair of internal electrodes has an edge exposed to the outside from the other of the pair of side surfaces of the laminated piezoelectric actuator. The laminated piezoelectric actuator has a coating layer formed on each of the pair of side surfaces of the laminated piezoelectric actuator, and each of the coating layers is made of platinum, palladium, ruthenium, rhodium, or gold. A laminated piezoelectric actuator comprising at least one of the following can be obtained.

Furthermore, a laminated piezoelectric actuator having a piezoelectric ceramic portion and at least a pair of internal electrodes disposed substantially parallel to each other in the piezoelectric ceramic portion, wherein one of the phantom internal electrodes is The laminated piezoelectric actuator has an edge exposed to the outside from one of a pair of opposing side surfaces, and the other of the pair of internal electrodes is
The laminated piezoelectric actuator has an edge exposed to the outside from the other of the pair of side surfaces of the laminated piezoelectric actuator, further comprising a coating layer formed on each of the pair of side surfaces of the laminated piezoelectric actuator. However, a laminated piezoelectric actuator is obtained in which each of the coating layers is made of at least one of copper, nickel, tin, zinc, chromium, and iron.

[Function] The reason for the low insulation resistance between a pair of internal electrodes when the conventional laminated piezoelectric actuator 2 is continuously used in a high humidity environment is that moisture permeates through the organic resin layer and the internal electrodes It is presumed that this is due to the ionization of silver contained in the internal electrodes.

Positive side of the surface-exposed internal electrode: Ag-+Ag"+e Negative side of the surface-exposed internal electrode: Ag" 10e→Ag In other words, the above reaction progresses, and silver grows in a dendritic shape on the surface of the surface-exposed internal electrode on the negative side. , the substantial distance between the positive side and negative side of the surface-exposed internal electrodes is shortened, and the insulation resistance between the pair of internal electrodes is reduced. the result,
The insulation resistance between the external electrodes 15 decreases.

The present invention has a structure in which the surfaces of the internal electrodes and external electrodes exposed to the surface are covered with a layer of a material that does not contain silver and has good water corrosion resistance, thereby preventing silver migration and preventing high humidity. It is possible to provide a laminated piezoelectric actuator whose insulation resistance does not decrease under environmental conditions.

Table 1 F Examples Examples of the present invention will now be described with reference to the drawings.

Referring to FIG. 1, the multilayer piezoelectric actuator according to the present invention is composed of Pb t (Ni-Nb) l Ti-
Using Zr)03-based piezoelectric ceramics 11 as a starting material,
A laminated piezoelectric actuator with dimensions of 5 x 5 mm in cross section and 18 mm in length was prototyped using the thick film lamination method. The material of the internal electrode 12 is a silver-palladium alloy.
The distance between 2 and 12 is 115 μm, and the number of stacked internal electrodes is 150. The glass insulating portion 13 functions to prevent the internal electrodes 12 and 12' from being exposed to the side surface of the laminated piezoelectric actuator. The external electrode 14 was formed by baking silver paste. Next, at least one metal oxide selected from copper oxide, nickel oxide, tin oxide, zinc oxide, chromium oxide, and iron oxide is applied to the surfaces of the internal electrodes and external electrodes exposed in the laminated piezoelectric actuator 1 by electroplating. thing,
The coating layer 26 was coated with at least one metal among platinum, palladium, ruthenium, rhodium, and gold, and at least one metal among copper, nickel, tin, zinc, chromium, and iron. Note that in order to form a metal oxide film, a metal layer formed by plating is heat-treated at 250° C. in oxygen gas. A commercially available bright plating bath is used as the plating bath, and the plating thickness is several μm. After that, the outside was coated with Epoquine resin.

Referring to Table 1, the comparative example is a conventional laminated piezoelectric actuator 2, in which the side surface of the laminated piezoelectric actuator 2 is coated with an organic resin layer.

Except for the comparative example, the laminated piezoelectric actuator 1 of the present invention is coated with a coating layer 26 on the side surface of the laminated piezoelectric actuator 1. In order to investigate the reliability of the prototype laminated piezoelectric actuator 1 in a high humidity environment,
0 'C1 DC voltage 100 in an atmosphere of 95% relative humidity
Aging was performed by continuously applying V. The number of samples subjected to aging was 100 for each example, and if the insulation resistance between the external electrodes 14 of each example decreased by one digit or more, it was considered defective1. Expressed as defective rate. The results are shown in Table 1.

As is clear from Table 1, in the laminated piezoelectric actuator 2 of the conventional structure, the insulation resistance between the laminated layers of the piezoelectric ceramic 11 decreases due to the ingress of moisture over time. insulation resistance decreases,
Either all of the piezoelectric actuators become defective in 500 hours, or the laminated piezoelectric actuator 1 according to the embodiment of the present invention fails at maximum 3 in 240 hours.
%, and the defective rate was 1 to 8% after 500 hours, which shows that the moisture resistance performance is much better than that of the conventional structure.

[Effects of the Invention] As explained above, the present invention provides a highly reliable multilayer piezoelectric actuator in which the insulation resistance between internal electrodes does not decrease even when used for a long time in a high humidity environment. There is an effect that it can be done.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a laminated piezoelectric actuator according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of a conventional laminated piezoelectric actuator. 1... Laminated piezoelectric actuator according to an embodiment of the present invention, 2... Conventional layered piezoelectric actuator, 11
...Piezoelectric ceramics, 12 and 12'...Internal electrode, 13...Glass insulation part, 14...External electrode, 1
5... Lead wire, 26... Coating layer. 3

Claims (3)

[Claims] 1. A laminated piezoelectric actuator comprising a piezoelectric ceramic portion and at least a pair of internal electrodes arranged substantially parallel to each other in the piezoelectric ceramic portion, the pair of internal electrodes being arranged on a side surface of the laminated piezoelectric actuator. The layered piezoelectric actuator has an edge portion exposed to the outside from the layered piezoelectric actuator, wherein the layered piezoelectric actuator is made of at least one of copper oxide, nickel oxide, tin oxide, zinc oxide, chromium oxide, and iron oxide; A laminated piezoelectric actuator characterized by having a coating layer covering at least the side surface. 2. A laminated piezoelectric actuator comprising a piezoelectric ceramic portion and at least a pair of internal electrodes disposed substantially parallel to each other in the piezoelectric ceramic portion, one of the pair of internal electrodes being connected to the laminated piezoelectric actuator. The actuator has an edge exposed to the outside from one of the pair of mutually opposing side surfaces, and the other of the pair of internal electrodes has an edge exposed to the outside from the other of the pair of side surfaces of the laminated piezoelectric actuator. The laminated piezoelectric actuator has a coating layer formed on each of the pair of side surfaces of the laminated piezoelectric actuator, and each of the coating layers is made of one of platinum, palladium, ruthenium, rhodium, and gold. A laminated piezoelectric actuator comprising at least one type of piezoelectric actuator. 3. A laminated piezoelectric actuator comprising a piezoelectric ceramic portion and at least a pair of internal electrodes disposed substantially parallel to each other in the piezoelectric ceramic portion, one of the pair of internal electrodes being connected to the laminated piezoelectric actuator. The actuator has an edge exposed to the outside from one of the pair of mutually opposing side surfaces, and the other of the pair of internal electrodes has an edge exposed to the outside from the other of the pair of side surfaces of the laminated piezoelectric actuator. The laminated piezoelectric actuator has a coating layer formed on each of the pair of side surfaces of the laminated piezoelectric actuator, and each of the coating layers includes copper, nickel, tin, zinc, chromium, and iron. A laminated piezoelectric actuator comprising at least one of the following.