JPH0342884A - Laminate type piezoelectric element - 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 multilayer piezoelectric element, and relates to a full-surface electrode type structure that is excellent in reliability, particularly moisture resistance, and suitable for low voltage operation.

[Conventional technology]

Piezoelectric ceramics have the property of exchanging mechanical energy and electrical energy, and their application to sensors and actuators for detecting mechanical quantities is being actively developed. However, since the amount of displacement per applied voltage of piezoelectric ceramics is small, it is necessary to apply a very high voltage to obtain a practical amount of displacement. Therefore, a common method is to reduce the applied voltage by making the thickness of the piezoelectric ceramic as thin as possible and stacking a large number of piezoelectric ceramics. A piezoelectric element having such a structure is called a laminated piezoelectric element.

The most advanced manufacturing technology for laminated piezoelectric elements is the green sheet method. In this method, piezoelectric material powder is dispersed in a suitable solvent, the resulting slurry is formed into a sheet, a metal paste is applied as an electrode by screen printing, etc., and then a number of sheets are laminated. This manufacturing method, in which the piezoelectric element is dried and sintered, reduces the applied voltage to 10% in order to obtain a typical maximum elongation rate of 0.1% for piezoelectric elements.
It is now possible to reduce the voltage to 0v.

As a known example of a laminated piezoelectric element using the conventional green sheet method, for example, Japanese Patent Publication No. 59-32040
No. 3, No. 3, No. 12 (1983), Sensor Technology, Vol. 3, No. 12 (1983), page 31.

In addition, as an electrode structure that reduces the internal stress of the laminated piezoelectric element and improves its reliability, a full-surface electrode system in which the area of the piezoelectric ceramic and the electrode are equal was published in Japanese Patent Publication No. 63-17354.
It is stated in the No.

Cross-sectional views of the full-surface electrode type laminated piezoelectric element are shown in FIGS. 5 and 6.

[Problem to be solved by the invention]

In the former prior art, the sintering of the green sheet of the piezoelectric ceramic plate 1 shown in FIG. 5 and the lamination of the piezoelectric ceramic plate 1 with the electrode 2 are performed simultaneously at about 1300°C. Therefore, noble metals that are stable at high temperatures, particularly silver-palladium (AgPd) alloys, are often used as the material for the electrode 2.

However, the piezoelectric element using the silver-palladium alloy electrode has a problem in that the electrode shortens when operated in a humid atmosphere. This may be because water penetrates into the molding resin 5 that protects the sides of the piezoelectric element and conduction occurs between the electrodes, or a layer of water is formed between the laminate and the resin 5, and This is thought to be because silver is eluted as ions (in Ag), which are attracted by the electric field and deposited near the adjacent electrode, forming a conductive path. This phenomenon is generally called migration, and is a common problem in electrical components using silver electrodes.

On the other hand, in the latter conventional technology, which is a full-surface electrode type laminated piezoelectric element, in order to alternately connect the electrode w42 and the lead terminal 3 for external extraction, as shown in FIGS. A method of covering with an insulator 4 is used. However, in this method, insulator 4 is used to increase dielectric strength.
It is necessary to make the width and thickness of the piezoelectric ceramic plate 1 sufficiently larger than the thickness of the electrode 2.
This poses a problem in that it becomes an obstacle to reducing the thickness of the device, and as a result, it becomes difficult to reduce the operating voltage.

Further, since the lead terminal 3 is formed on the unevenness of the insulator 4, there is a problem in its reliability. Furthermore, since the process is complicated, there is also the problem that the yield is low and the production cost is high.

An object of the present invention is to provide a structure of a low-cost, all-over electrode type multilayer piezoelectric element that does not cause electrode short circuits even in a humid atmosphere, has particularly low operating voltage, and is excellent in reliability.

[Means to solve the problem]

In order to achieve the above object, the present invention uses a metal whose main component is aluminum as a metal plate serving as an electrode, and further electrically contacts only one of a pair of lead terminals on every other layer, and The other parts exposed to the sides of the laminate and the surfaces that come into contact with the other lead terminal are selectively oxidized by anodic oxidation, and then sealed by electrophoresis for electrical insulation. It is characterized by being electrochemically substituted with a chemical compound.

[Effect]

Aluminum used as an electrode material in the present invention is a very active metal when a clean surface is used, but when the surface is oxidized, it has the property of changing into a chemically stable so-called passive state. Therefore, among the aluminum electrodes exposed on the sides of the laminate, the parts that are not connected to the lead terminals are oxidized by anodic oxidation, and the remaining holes are sealed by electrophoresis to form a dense electrical insulator. ,
Even if the side surfaces of the laminate become wet with water during operation in a humid atmosphere, electrical conduction will not occur, and the electrode material will not dissolve into the water as ions and cause migration.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings. Note that the same reference numerals are given to the same structural parts as in the conventional example, and the explanation thereof will be omitted.

FIG. 1 is a perspective view of a laminated piezoelectric element according to the present invention in a state before its side surfaces are coated with molding resin. Further, FIG. 2 is a cross-sectional view of the element shown in FIG. 1 taken along plane ABC.

Dielectric ceramics that have the property of causing electric polarization when stress is applied, that is, piezoelectricity, are called piezoelectric ceramics, and are made of barium titanate (Ba T l 03).
- Lead titanate (P b T i 0a) - Lead zirconate titanate (Pb (Zr, Ti) O,) and the like are popular. A green sheet is made from a paste obtained by mixing these piezoelectric ceramic powders with a solvent, and a plurality of piezoelectric ceramic plates 1 are obtained by forming and sintering the green sheet as shown in FIGS. 1 and 2. electrode plates 2a and 2b are placed between each layer, and a laminate is obtained by heating and pressurizing. Electrode plates 2a are placed at two locations on the side of this laminate.
, 2b are formed with external lead terminals 3a and 3b,
Electrode plates 2a and 2b are alternately connected to lead terminals 3a and 3b every other layer. At this time, the end surfaces of the electrical conductors 11i2a, 2b that are not covered with the lead terminals 3a, 3b and are exposed on the side surfaces of the laminate are changed into electrically insulating compounds 4a, 4b, such as oxides or nitrides.

Furthermore, as shown in FIG. 2, the electrode 2a connected to the lead terminal 3a is coated with an electrically insulating compound 4a at its boundary to prevent electrical contact with the lead terminal 3b.
The electrode 2b connected to the lead terminal 3a is changed into an electrically insulating compound 4b at its boundary to prevent electrical contact with the lead terminal 3a. The material of each electrode plate 2a, 2b is aluminum or an alloy of aluminum with silicon, magnesium, or germanium dissolved therein. and,
A particularly desirable configuration is shown in FIG. 3, in which a skin material 22 made of an aluminum alloy having a lower melting point than the core material is formed on the screen of a core material 21 made of an aluminum alloy.

By employing the electrode material and insulating structure as described above, the following effects can be obtained.

When forming a laminate by heating and pressurizing, heating temperature 5
At 80 to 650°C, only the skin layer of the electrode becomes a liquid phase, so the oxide film on the surface of the aluminum alloy electrode is destroyed, and the active liquid phase of the aluminum alloy promotes adhesion and reaction with the piezoelectric ceramic. On the other hand, the core aluminum alloy remains in phase, forming a dense electrode and maintaining a constant thickness.

Next, an example of a method for insulating the electrode end surface will be described with reference to FIG. A piezoelectric ceramic 1 and an aluminum alloy electrode 2 having a smaller area are laminated to form an alternating laminate 6 as shown in the figure, and temporary electrodes 10 are placed on the side surfaces at positions where the end faces of the electrodes are exposed every other layer. The primary electrode to be formed is immersed in an electrolytic solution 9 with a DC power source 8 connected so that the temporary electrode 10 becomes an anode and the metal 7, which has a greater ionization tendency than the temporary electrode 10, becomes a cathode. With this device, the surface of the electrode 2 connected to the temporary electrode 10 is anodized to form a porous oxide layer. Here, as the electrolyte, for example, a dilute aqueous solution of sulfuric acid, oxalic acid, or boric acid is used.
Next, the resin is impregnated inside and on the surface of the pores of the porous oxide layer on the surface of the anodized electrode 2 by an electrophoresis method in which the electrode is immersed in a diluted electrolyte solution in which a resin is dispersed instead of an electrolyte solution. Alternatively, it adheres and is subjected to a sealing process to form a dense electrically insulating compound on the end surface of the electrode 2. This insulating layer insulates the external lead terminal and the internal electrode.

By this method, there is no restriction on the thickness of the piezoelectric ceramic plate 1 in the conventional example shown in FIG. 5, and the operating voltage can be reduced. Further, unlike the conventional example, since the side surfaces of the laminate are flat, the shape of the lead terminal 3 is smooth, and the incidence of wire breakage is reduced. Furthermore, even if water penetrates when operating in a humid atmosphere, there will be no migration or electric discharge.
2, the incidence of short circuits has decreased.

〔Effect of the invention〕

According to the present invention, the moisture resistance of the laminated piezoelectric element is improved,
This has the effect of lowering the operating voltage of the full electrode type device and improving its reliability.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a laminated piezoelectric element according to an embodiment of the present invention;
Figure 2 is a cross-sectional view of the ABC plane in Figure 1, Figure 3 is a perspective view showing the most effective structure of laminated electrodes, Figure 4 is an explanatory diagram showing the method for creating an insulator layer, and the fifth A cross-sectional view of a conventional example of a full-surface electrode type laminated piezoelectric element, FIG. 6, is the same as IV- in FIG.
It is a sectional view taken along the line IV. 1... Piezoelectric ceramic plate, 2... Electrode plate, 3...
- Lead terminal, 4... electrically insulating compound.

Claims (5)

[Claims] 1. A laminated piezoelectric element consisting of a laminated body in which piezoelectric ceramic plates and metal plates are alternately laminated, and a pair of lead terminals for external extraction formed on the side surface of the laminated body and alternately connected to the metal plates. In the metal plate, the main component is aluminum, and contact parts with lead terminals other than the lead terminals connected to the metal plate, and exposed parts exposed on the side surfaces of the laminate are selectively anodized. 1. A laminated piezoelectric element characterized in that it is electrochemically substituted with an electrically insulating compound by being oxidized and sealed by electrophoresis. 2. A laminated piezoelectric element consisting of a laminated body in which piezoelectric ceramic plates and metal plates are alternately laminated, and a pair of lead terminals for external extraction formed on the side surface of the laminated body and alternately connected to the metal plates. The piezoelectric ceramic plate and the metal plate have the same dimensions except for the thickness, and the metal plate is mainly made of aluminum, and there are no contact portions with lead terminals other than the lead terminals connected to the metal plate. , and the exposed portion exposed on the side surface of the laminate is electrochemically replaced with an electrically insulating compound by selectively oxidizing by anodic oxidation and sealing by electrophoresis. A multilayer piezoelectric element characterized by: 3. A laminated piezoelectric element consisting of a laminated body in which piezoelectric ceramic plates and metal plates are alternately laminated, and a pair of lead terminals for external extraction formed on the side surface of the laminated body and alternately connected to the metal plates. In this case, the metal plate is made of aluminum or an alloy of aluminum with silicon, magnesium, or germanium as a solid solution, and the contact portion with a lead terminal other than the lead terminal connected to the metal plate and the side surface of the laminate are A laminated type characterized in that the exposed portion exposed to the surface is electrochemically substituted with an electrically insulating compound by being selectively oxidized by anodic oxidation and sealed by electrophoresis. Piezoelectric element. 4. A laminated piezoelectric element consisting of a laminated body in which piezoelectric ceramic plates and metal plates are alternately laminated, and a pair of lead terminals for external extraction formed on the side surface of the laminated body and alternately connected to the metal plates. In the metal plate, a skin material of an aluminum alloy having a lower melting point than the core material is formed on the screen of a core material of an aluminum alloy, and the contact portion with a lead terminal other than the lead terminal connected to the metal plate is , and the exposed portion exposed on the side surface of the laminate is electrochemically replaced with an electrically insulating compound by selectively oxidizing by anodic oxidation and sealing by electrophoresis. A multilayer piezoelectric element characterized by: 5. A laminated piezoelectric element consisting of a laminated body in which piezoelectric ceramic plates and metal plates are alternately laminated, and a pair of lead terminals for external extraction formed on the side surface of the laminated body and alternately connected to the metal plates. In the metal plate, a core material of an aluminum alloy is sandwiched between aluminum alloys having a lower melting point than the core material, and the metal plate is heated at 580°C to 650°C.
The contact portions with lead terminals other than the lead terminals connected to the metal plate and the exposed portions exposed on the side surfaces of the laminate are selectively oxidized by anodic oxidation and electrophoresis. 1. A laminated piezoelectric element characterized in that it is electrochemically substituted with an electrically insulating compound by sealing using a method.