JPH02137281A - Electrostriction effect element - Google Patents

Abstract

PURPOSE:To improve breakdown strength, prevent the migration of inner electrode material on an element surface, and improve reliability by forming insulator on the whole layer or every other layer on inner electrodes exposed on side surfaces on which an outer electrode is not formed. CONSTITUTION:By screen printing, paste in which silver palladium powder is mixed is spread on an electrostriction sheet 1, thereby forming an inner electrode 2. Electrostriction sheets 1 on which the inner electrodes 2 are printed, and electrostriction sheets 1 on which the inner electrodes 2 are printed and further inner electrodes 2 are printed are laminated in order, and unified in a body with an electrostriction sheet 1 which has not been heated with pressure. This unified body is sintered. On inner electrodes 2 of a pair of facing side surfaces of the sintered body, glass insulator 3 is alternately formed every other layer, and conductive paste whose main component is silver powder is stuck to form an outer electrode 4. On the inner electrodes 3 exposed on a pair of the other side surfaces, glass insulator 3 is formed every other layer. A lead wire 5 is bonded to the outer electrode 4 with solder 6, and an electrostriction effect element is obtained. By this set-up, migration of inner electrode material is restrained, and breakdown strength can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an electrostrictive effect element having a laminated structure, and particularly to an insulating structure of internal electrodes thereof.

[Prior Art] Displacement generating elements using an electrostrictive effect include a bimorph piezoelectric element using a transverse effect and a laminated type element using a longitudinal effect. Among these, many applied studies have been conducted on stacked elements due to their advantages such as small size, large driving force, and high energy conversion efficiency.

The problem with this multilayer device is how to take out the internal electrodes. In an electrostrictive effect element in which electrostrictive layers and electrode layers are alternately laminated, every other internal electrode layer must be connected to a common external electrode layer, and one method for this is as shown in Figure 4. It has a similar structure to a multilayer ceramic capacitor. However, in such a structure, there are parts to which an electric field is applied and parts to which it is not applied, which not only reduces the amount of displacement of the entire element, but also has the fatal drawback of causing cranking due to stress concentration.

In order to solve these problems, there is a method of forming internal electrodes on the entire surface. Conventionally, this type of electrostrictive element has a structure as shown in FIGS. 5 and 6. That is, an internal electrode conductor layer (hereinafter referred to as internal electrode) 2 is formed on one side of a sheet 1 made of an electrostrictive material (hereinafter referred to as electrostrictive sheet), and a plurality of these layers are stacked to form a laminate. Insulators 3 are formed every other layer on internal electrodes 2 exposed on the side surfaces, and external electrodes 4 are further formed thereon. On the other hand, on the side surface opposite to the side surface, the insulator 3 is selectively formed on the exposed portion of the internal electrode 2 on which the insulator 3 was not formed, and the external electrode 4 is formed thereon. It had a structure in which lead wires 5 were connected to each other by solder 6. Therefore, external type 8i
The internal electrodes 2 are all exposed on the side surfaces where no. 4 is formed, and when actually driven, the element is used in this state or by being covered with epoxy resin or the like.

[Problems to be Solved by the Invention] The conventional electrostrictive element (FIG. 5) described above has the following drawbacks.

(1) Since it has a full-surface electrode structure and internal electrodes are exposed on the element surface, which is prone to scratches and dirt, it is easy to cause poor insulation resistance and short circuits.

(2) Also, the internal electrodes exposed at intervals of several tens to 100 μm have a withstand voltage of 1 for air! Since it is defined by the L voltage, the withstand voltage of the element is lowered.

(3) Furthermore, when silver or silver alloy, which is often used in electronic components, is used for the internal electrodes, the electrodes are exposed on the element surface, so the synergistic effect of moisture in the air and voltage application Silver migration is likely to occur.

For this reason, the insulation resistance deteriorates and short-circuit failures tend to occur, so that reliability cannot be said to be sufficient.

(4) Furthermore, even if the device is covered with resin to prevent the surface of the device from being exposed, moisture intrusion cannot be completely removed, and similar defects will occur after a long period of time. If an inorganic material such as glass is formed over the entire side surface, peeling or cracking will occur at the interface due to expansion and contraction when the element is driven, making it impossible to prevent moisture from entering.

[Means for Solving the Problems] The electrostrictive effect element of the present invention includes a laminated sintered body in which sheet-shaped piezoelectric ceramic members and internal electrodes are alternately stacked,
Two combs are formed by electrically connecting an insulating layer that insulates one end surface of the internal electrodes exposed on opposing sides of the laminated sintered body every other layer on each side surface, and the other exposed end surface of the internal electrodes. In an electrostrictive effect element including a pair of external electrodes constituting a tooth-shaped electrode, the end portions of the internal electrodes exposed on the side surfaces where the external electrodes are not formed are covered with an insulating material in all layers or every other layer. There is.

[Function] By forming an insulator in all layers or every other layer on the internal electrodes exposed on the side surfaces where no external electrodes are formed, defects do not occur at the interface between the insulator and the element or in the insulator itself. , it is possible to prevent migration of the internal electrode material on the element surface, and the reliability of the electrostrictive element is improved.

[Embodiments] Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of a first embodiment of the electrostrictive effect element of the present invention.

In this electrostrictive effect element, the end surfaces of the internal electrodes 2 exposed on the side surfaces where the external electrodes 4 of the conventional electrostrictive effect element shown in FIG. 6 are not formed are insulated with glass insulators 3 every other layer. There is.

Next, a method for manufacturing this electrostrictive element will be explained.

For example, lead zirconate titanate Pb (Ti).

Electrostrictive sheet 1 made by adding a small amount of organic binder to piezoelectric material powder containing Zr) 03 as the main component, dispersing this in an organic solvent to make a slurry, and forming the slurry to a thickness of about 130 μm by tape casting. Create. Next, electrostrictive sheet 1
A paste containing a 7:3 mixture of silver and palladium powder was applied on top by screen printing to a thickness of approximately 10 μm.
Internal electrodes 2 are formed. Next, 80 electrostrictive sheets 1 with internal electrodes 2 printed on them, 30 electrostrictive sheets 1 with no internal electrodes 2 printed on them, and 80 electrostrictive sheets 1 with internal electrodes 2 printed on them. Laminated in sequence, heated to 100℃, 25
Heat and pressurize and integrate under conditions of 0 kg/cm2, approximately 11
Sinter at a temperature of 00°C for 2 hours. Glass insulators 3 are alternately formed every other layer on the internal electrodes 2 on a pair of opposing sides of the sintered body, and a conductive paste containing silver powder as a main component is further applied to form external electrodes 4. On the other hand, glass insulators 3 are formed every other layer on the internal electrodes 2 exposed on the other pair of side surfaces. Finally, lead wires 5 are bonded onto external electrodes 4 with solder 6 to obtain the electrostrictive element shown in FIG. 1.

FIG. 2 is a perspective view of a second embodiment of the electrostrictive effect element of the present invention. This embodiment differs from the first embodiment in that the end face of the internal electrode 2 exposed on the side surface where the external electrode 4 is not formed is covered with a full-layer insulator 3.

In this embodiment, there is no need to select the internal electrodes 2 that form the insulator 3, so the method for forming the insulator 3 is easy, and there are no exposed internal electrodes 2, which has the advantage of improving reliability. be.

FIG. 3 is a diagram showing the reliability evaluation results of the elements of the first and second embodiments in comparison with the element of the conventional example (FIG. 6). 1st
A life test was conducted on 20 of the elements shown in FIG. 2, 2, and 6 in a humid atmosphere of 40° C. and 95% RH by applying a DC voltage of 150 V. As can be seen from FIG. 3, discharge defects began to occur in the conventional device after several tens of hours, whereas no defects occurred in the device of the present example even after 1000 hours. In addition, in a withstand voltage test, it was found that the withstand voltage was 1.5 times that of the conventional one.

[Effects of the Invention] As explained above, the present invention improves the internal electrode material by forming an insulator on the entire layer or every other layer at the end of the internal electrode exposed on the side surface where the external electrode is not formed. This has the effect of making it possible to suppress migration and increase the withstand voltage, making it possible to produce highly reliable electrostrictive elements.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 respectively show the first diagram of the electrostrictive effect element of the present invention.
, a perspective view showing the second embodiment, and FIG.
A graph showing the relationship between time and failure rate when a DC voltage of 50 V is applied, Figures 4 and 5 are longitudinal cross-sectional views of conventional examples of electrostrictive effect elements, and Figure 6 is the electrostrictive structure of Figure 5. It is a perspective view of an effect element. 1... Electrostrictive sheet, 2... Internal electrode, 3...
- Insulator, 4... External electrode, 5... Lead wire, 6... Solder. For 1 Figure 4 Tato @ 5 Denwari Figure 4 Confucian 5 Figure 0J Jidan (H) Ma 6 Figure

Claims (1)

[Claims] 1. A laminated sintered body in which sheet-like piezoelectric ceramic members and internal electrodes are alternately stacked, and one end surface of the internal electrodes exposed on opposing sides of the laminated sintered body is insulated every other layer on each side surface. In an electrostrictive element that includes an insulating layer and a pair of external electrodes that electrically connect the other exposed end surface of an internal electrode to form two comb-shaped electrodes, the side surface on which the external electrode is not formed is An electrostrictive effect element characterized in that exposed end portions of internal electrodes are covered with an insulating material in all layers or every other layer.