JP2692397B2 - Electrostrictive effect element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostrictive effect element,
In particular, it relates to a laminated electrostrictive effect element.

[0002]

2. Description of the Related Art An electrostrictive effect element is a transducer that converts electric energy into mechanical energy by utilizing the electrostrictive effect of a solid. Specifically, electrodes are formed of metal or the like on two opposing surfaces of a solid having a large electrostrictive effect, and the strain of the solid generated when a potential difference is applied between the electrodes is used.

In the above electrostrictive effect, usually, the strain generated in the direction parallel to the electric field (longitudinal effect strain) is larger than the strain generated in the direction perpendicular to the electric field (lateral effect strain). It is more advantageous to use it, and the electric / mechanical energy conversion efficiency is also high.

In the electrostrictive effect element (hereinafter referred to as element) utilizing the vertical effect distortion, the amount of change per unit length of the element is almost proportional to the applied electric field strength.

Therefore, in an actual device, in order to obtain a large strain, the electric field strength is strengthened by thinning the thickness of the electrostrictive material and narrowing the interval between the electrodes, and further, a structure in which a plurality of these are laminated. , So-called laminated type elements have been considered.

FIG. 2 is a perspective view showing the structure of the above-mentioned laminated type element. In this element, as shown in the figure, internal electrodes 2a and 2b are formed inside the electrostrictive material 1 at regular intervals. The ends of the internal electrodes 2a and 2b are exposed on the four side faces of the element. On a pair of opposite side faces of the four side faces, the exposed portions of the internal electrodes exposed on the side faces are arranged on alternate layers and on the left and right sides. Alternating insulator 4a
And insulated by 4b. As the insulator, glass obtained by adhering and melting powdered glass is usually used.

External electrodes 3a and 3b are further provided on the pair of side surfaces. Therefore, when a drive voltage is applied to the external electrodes 3a and 3b, this laminated type element
Adjacent inner electrodes sandwiching the electrostrictive material 1 operate as counter electrodes.

[0008]

The conventional laminated type element as described above has an insulating material 4 as described below.
External electrodes 3a, 3b and internal electrodes 2a, a, 4b
It is in a state where it is easy to short-circuit with 2b.

First, in the manufacturing process of this element, the insulator 4 is used.
When forming a and 4b, heat treatment is performed at a temperature of about 600 to 700 ° C. in order to melt the powder glass attached to the side surface of the element. Further, after that, heat treatment is performed at a temperature of about 550 to 650 ° C. in a step of forming external electrodes. However, the material (electrostrictive material 1, internal electrode 2,
a, 2b and insulators 4a, 4b) have a different coefficient of thermal expansion, the insulator 4 is affected by the thermal history during this heat treatment.
Stress is applied to a and 4b in the stacking direction.

In terms of stress, the insulator 4a,
A stress in the stacking direction is applied to 4b even during the operation of this element. That is, when this element operates, the electrostrictive material 1 expands and contracts in the direction of the electric field (the stacking direction of the elements), whereas the insulators 4a and 4b do not expand and contract in the original manner. Try to keep the shape. Therefore, stress is applied to the insulators 4a and 4b.

As described above, the insulators 4a and 4b are subjected to the thermal stress received in the manufacturing process and the mechanical stress generated during the operation. The parts are easily damaged by microcracks.

Second, when the device operates, an insulator 4 is formed between the external electrodes 3a, 3b and the internal electrodes 2a, 2b.
A high electric field of several kV / mm is applied by narrowing a and 4b. In the presence of such a high electric field, the materials of the insulators 4a and 4b may be altered due to the addition of moisture from the environment of use to deteriorate the insulation resistance. Further, the metal components of the materials used for the external electrodes 3a, 3b and the internal electrodes 2b, 2a are ionized to cause migration along the above-mentioned microcracks, and the adjacent internal electrodes 2a and 2b are short-circuited. It becomes easy for the internal electrode 2a (2b) and the external electrode 3b (3a) to be short-circuited.

In fact, of the defects that occur when an element of this type is operating, the short circuit defect due to the insulation defect of the insulators 4a and 4b is the most common. In addition, this mode failure is one of the important factors that govern the reliability of this type of device because it is characterized in that it occurs relatively early after the start of energization.

As described above, in the conventional device, the insulator 4 is used.
It is a major issue to solve the problem of dielectric breakdown of a and 4b and to secure sufficient reliability as the entire device.

[0015]

An electrostrictive effect element according to the present invention comprises a laminated body in which layers of a material exhibiting an electrostrictive effect and layers of internal electrodes are alternately stacked, and the laminated body has a laminated direction in the laminating direction. An insulator that insulates the exposed portions of the internal electrodes for every other layer on a pair of parallel opposite sides, and an exposure to the side face of the internal electrodes on the side faces including the insulator. Part is comprises an external electrode for electrically connecting the layers not insulated, the external electrodes, and the internal electrode insulated by said insulator and its external electrodes are short-circuited
The short circuit part or near the short circuit part, the external electrode itself
It is characterized in that it has a structure of locally melting.

[0016]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of a device according to an embodiment of the present invention.

In order to manufacture this element, the internal electrodes 2a and 2b arranged at regular intervals are formed inside the lead zirconate titanate-based electrostrictive material 1 by the green sheet method. Then, powder glass is adsorbed on the pair of side surfaces where the internal electrodes 2a and 2b are exposed by an electrophoretic method for every other layer with respect to the internal electrodes, and this is baked to form the insulators 4a and 4b. .

Next, the external electrodes 3a and 3b are formed. For the external electrodes 3a and 3b, a thermosetting epoxy resin or the like containing gold powder having a low melting point is used so that the insulators 4a and 4b are completely melted by heat generated by a short-circuit current when dielectric breakdown occurs. Then, this epoxy resin is printed on the side surface of the element by screen printing, dried and cured to form the external electrodes 3a and 3b. These external electrodes 3a, 3b
As shown in FIG. 1, the shape of is such that a plurality of fine line-shaped wirings are arranged at intervals and these wirings are connected at the upper and lower portions. That is, the thin wire is connected in parallel.

The dimensions of the device shown in FIG. 1 are 5 mm × 5 mm in cross section perpendicular to the stacking direction and 20 mm in length. The external electrodes 3a and 3b have a thickness of about 30 μm,
The width of each thin wire is 0.5 mm. And this thin line is 4
Five pieces are arranged at mm intervals and are connected in parallel.

Next, 50 elements according to the present embodiment were provided with a rated DC voltage of 150 at a temperature of 40 ° C. and a humidity of 90% RH.
The results of performing a moisture resistance load life test by applying V will be described. According to the result of this test, about 10% of short-circuit defects due to dielectric breakdown of the insulator were conventionally generated in 500 hours, whereas in the element of this example, no defects were generated even in 1000 hours.

Further, when the devices which had been tested were observed, discharge marks were found in the insulators of some devices. Then, the thin wire portion of the external electrode related to the discharge was completely melted. This indicates that the thin wire-like wiring portion was surely blown by the current when the insulator was discharged, and the element itself did not cause a short circuit defect. It was confirmed that it was fulfilling. It was also confirmed that the external electrode portions of these devices that were not involved in discharge were sufficiently conductive, and the device characteristics were the same as before the test. From the above test results and observation results, it can be concluded that the element of this example was able to improve the reliability of the element without impairing the characteristics of the element.

Next, a second embodiment of the present invention will be described. This example is different from the first example in the material and method of making the external electrodes.

In this embodiment, a pure metal having a high conductivity and a low melting point such as gold, tin or aluminum is used as the external electrode. Then, a sputtering method is used as a method for forming these metal layers.

In order to manufacture the element of this embodiment, a laminated body obtained by completing the steps of forming the insulators 4a and 4b in the element shown in FIG. 1 (that is, a laminated body before forming the external electrodes 3a and 3b). A metal plate having a thin wire pattern such as the external electrode 3a in FIG. 1 previously formed is arranged on the side surface of the mask as a mask, and wiring metal (gold, tin or aluminum) is deposited by a sputtering method through the space of the mask. Then, the external electrodes 3a and 3b are formed.

This external electrode is formed by connecting ten thin wires each having a width of 0.1 mm in parallel at a pitch of 0.5 mm. The thickness of the metal layer is about 1 μm.

The shape and dimensions of the laminated body of the electrostrictive material in this embodiment are the same as those in the first embodiment.

Next, a moisture resistance load life test was conducted on the 50 elements of the second embodiment described above under the same conditions as in the first embodiment. As a result, as in the case of the first embodiment,
No short circuit failure occurred even after 1000 hours.

[0028]

As described above, in the electrostrictive effect element of the present invention, the structure of the external electrode is such that a plurality of thin wire-like wirings are connected in parallel.

As a result, in the electrostrictive effect element of the present invention, even if a discharge occurs in the insulator, only the fine line-shaped wiring related to the discharge portion is blown, and the short-circuit defect occurs in the entire element. I can do it all the time. Moreover, as the external electrodes, since a plurality of wires on a thin wire are connected in parallel, conduction is established by means other than the melted thin wire, and there is no influence on the function of the electrostrictive effect element.

That is, according to the present invention, the reliability of the electrostrictive effect element can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a perspective view of an electrostrictive effect element according to an embodiment of the present invention.

FIG. 2 is a perspective view of a conventional laminated electrostrictive effect element.

[Explanation of symbols]

 1 Electrostrictive material 2a, 2b Internal electrode 3a, 3b External electrode 4a, 4b Insulator

Claims (3)

(57) [Claims] 1. A laminated body in which a layer of a material exhibiting an electrostrictive effect and a layer of an internal electrode are alternately stacked, and a pair of side surfaces of the laminated body which face each other and are parallel to each other. An insulator that insulates the exposed portion of the internal electrode in every other layer, and electrically connects the layer on the side surface including the insulator, the exposed portion of the internal electrode to the side surface that is not insulated The external electrode comprises an external electrode, and when the external electrode and the internal electrode insulated by the insulator are short-circuited , the external electrode is provided near the short-circuited portion or the short-circuited portion.
An electrostrictive effect element having a structure in which itself melts locally . 2. The electrostrictive effect element according to claim 1, wherein:
The electrostrictive effect is characterized in that the external electrode has a structure in which a plurality of wirings arranged at intervals in a direction perpendicular to the stacking direction on the side surface on which the external electrode is provided are connected in parallel. element. 3. The electrostrictive effect element according to claim 2, wherein:
The electrostrictive effect element, wherein the external electrode is a thermosetting epoxy resin containing gold powder.