JPH03155178A - Laminated displacement element - Google Patents

Abstract

PURPOSE:To prevent migration and reduce cost by making only the peripheral part of an internal electrode which becomes an anode or an entire internal electrode consist of a high melt-point metal where no migration occurs. CONSTITUTION:A plurality of thin plates 1, 1' consisting of an electromechanical conversion material are laminated alternately through internal electrodes 2, 2' consisting of a conductive metal material. A pair of external electrodes 3 to be connected alternately at every other layer with the internal electrodes 2, 2' are provided at the side surface, where all or a peripheral part of the internal electrodes 2, 2' to be connected to an anode side external electrode 3 consists of a non-silver conductive material. One type or two types or more of Au, Pt, Pd, Ir, Rh, Os, and Ru or their alloy are used as a high melt-point non-silver material. Also, it is desirable to use a piezoelectric material or a electrostriction material as an electromechanical conversion material.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an electromechanical transducer used in actuators of industrial robots, ultrasonic motors, etc. The present invention relates to an improvement of a laminated displacement element in which the amount of displacement is increased by laminating a plurality of displacement elements with electrodes interposed therebetween.

[Prior Art] Conventionally, laminated piezoelectric elements used as displacement elements used in X-Y stage positioning mechanisms and brakes, etc., are made by attaching electrodes to a thin plate made of piezoelectric ceramic material processed into a predetermined shape. After the electrodes are provided and polarized, they are bonded directly or via a thin metal using an organic adhesive. However, when laminated using adhesive as described above, depending on the usage conditions, the adhesive layer may absorb the displacement caused by the vibration of the piezoelectric element, or the adhesive may deteriorate due to high-pitched environments or long-term use. There are drawbacks.

For this reason, recently, multilayer piezoelectric elements having a multilayer chip capacitor structure have been put into practical use. That is, for example, as described in Japanese Patent Publication No. 59-32040, a paste-like piezoelectric ceramic material obtained by adding a binder to raw material powder and kneading is formed into a thin plate of a predetermined thickness, and one side of this thin plate or Internal electrodes are formed by coating both sides with a conductive material such as silver-palladium. A predetermined number of the above thin plates are laminated and pressed together, further processed into a predetermined shape, and then fired to form a ceramic, and external electrodes are formed on both sides of the laminate. The laminated piezoelectric element with the above structure has excellent adhesion between the thin plate made of piezoelectric ceramic material and the internal electrode, and has stable thermal properties, so it can be used satisfactorily even in high-temperature environments, and can be used for long periods of time. It has the advantage of extremely little deterioration over time.

[Problems to be Solved by the Invention] In the laminated piezoelectric element having the above structure, when used in an electronic component where a direct current high voltage is continuously applied between the electrodes to obtain displacement, S is used as the electrode material. When such materials are used, there is a problem that so-called migration occurs in a high-humidity atmosphere, eventually leading to dielectric breakdown. In other words, although Ag, which constitutes the electrode, is an element that is easily oxidized,
In a high humidity atmosphere, ionized (A g '') L is attracted to the negative electrode by the applied voltage and deposited on the negative electrode side.

These deposits grow in the shape of cedar leaves over time, lowering the insulation resistance between the electrodes and eventually causing a short circuit. As a means to prevent such migration, it may be possible to form the electrodes from a noble metal material with a high melting point, such as Pt or Pci, but this is not preferable since it results in a rise in cost, even though it improves performance. .

In addition, the exposed part of the internal electrode made of silver thread material is
It has been proposed to coat the metal with a film made of a metal having a migration property smaller than that of silver (see, for example, Japanese Patent Application Laid-Open No. 62-62571).

However, the work of covering the exposed parts after forming a laminate is extremely complicated, and it is not always possible to completely cover the exposed parts with the metal film, allowing moisture to enter from the outside through, for example, pinholes. There is,
There are still some unsatisfactory points in terms of reliability.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems existing in the above-mentioned prior art and to provide a laminated displacement element that can completely prevent migration without causing a rise in cost.

[Means for Solving the Problems] In order to achieve the above object, in the present invention, a plurality of thin plates made of an electromechanical conversion material are alternately laminated via internal electrodes made of a conductive metal material. In a laminated displacement element that is a laminated body and has a pair of external electrodes on its side surfaces that are to be connected to the internal electrodes alternately every other layer, the entire or peripheral portion of the internal electrodes connected to the anode-side external electrode is raised. We adopted a technical method of using a non-silver-based conductive material with a melting point.

In the present invention, the high melting point non-silver material includes Au,
It is preferable to use one or more of Pt, Pd%Ir, Rh%Os, Ru, or an alloy thereof.

Further, as the electromechanical conversion material, it is desirable to use a piezoelectric material or an electrostrictive material.

[Effect] Migration occurs in a high humidity atmosphere.

This is because the metal forming the anode is ionized by a chemical reaction with water and is attracted to the negative electrode by the applied voltage.

By making only the peripheral edge of the internal electrode, which serves as the anode, or the entire internal electrode from a high-melting metal that does not cause migration, ionization of the metal does not occur, so migration can be completely suppressed.

[Embodiment] FIG. 1 is a front view of essential parts showing an embodiment of the present invention. In the figure, reference numerals 1 and 1' denote thin plates, which are made of piezoelectric ceramic material and are formed into a square shape with a side of 10 mm and a thickness of 1001 m, for example. Reference numeral 2.2' denotes an internal electrode, which is made of a conductive material to be described later and is provided on the surface of the thin plate 1.

Next, 3 is an external electrode, which is formed of a conductive material.
A pair of internal electrodes 2 are provided on both side surfaces of a laminate formed by laminating, for example, 100 of the thin plates 1, with the insulating material 4 as a base, so as to connect the edge portions of the internal electrodes 2 every other layer.

Next, FIG. 2 is a plan view showing the internal electrode 2 connected to the anode-side external electrode in FIG. 1, and FIG. 3 is a sectional view taken along the line A--A in FIG. 2. In both figures, 2a is the intermediate member and 2b is the edge member. That is, the intermediate member 2a
is formed, for example, from a conventionally used silver-palladium alloy, and has one side of 9M, and the edge member 2b
is formed into a frame shape with a width of 0.5 no. by, for example, PL so as to surround the peripheral edge of the intermediate member 2a, and
It is provided integrally with the intermediate member 2a.

Figure 4 shows the internal electrode 2' connected to the negative external electrode.
FIG. 2 is a plan view showing an electrode member 2a made of, for example, a conventionally used inexpensive silver-palladium alloy.

The internal electrodes 2 can be provided on the surface of the thin plate 1 shown in FIG. 1 by, for example, screen printing means. That is, first, Pb(Zr.

A thin plate 1 having a thickness of 100 mm is formed by, for example, a doctor blade method using a raw material obtained by adding and mixing an organic binder, a plasticizer, an organic solvent, etc. to Ti)O powder. Next, a silver-palladium paste is printed on the surface of this thin plate 1 by screen printing to form an intermediate member 2a shown in FIGS. 2 and 3.

Furthermore, an edge member 2b is formed on the peripheral edge of this intermediate member 2a, but in this case it is preferable to mask the intermediate member 2a. Note that the intermediate member 2a and the edge member 2
The formation order of b may be reversed. Next, a silver-palladium paste is printed on the surface of the thin plate 1' by screen printing.

For example, 100 thin plates 1 and 1' formed as described above are alternately laminated and pressed together, and then fired at 1000 to 1200°C for 1 to 5 hours to obtain a sintered laminate with a side of 10 mm square. Can be done. The external electrodes 3 to be provided on both sides of this sintered laminate are formed by, for example, N1 plating or a combination of Ni and Au plating after the insulating layer 4 is formed.

By using the external electrode connected to the thin plate 1 of the laminated displacement element configured as described above as the anode and the external electrode connected to the thin plate 1' as the negative electrode, the anode peripheral portion is completely blocked or sealed by the peripheral member 2b. This prevents metal ionization of the internal electrode, which serves as the anode, and therefore completely prevents the occurrence of migration, which is characteristic of silver thread materials.

FIG. 5 shows a second configuration example of the present invention, and shows the internal electrode 2 connected to the anode-side external electrode. In this configuration, the entire internal electrode 2 is made of a high melting point non-silver material such as platinum or palladium, and the internal electrode 2 is connected to the negative external electrode.
' is shown in FIG. 4, which is the same as in the previous embodiment, and has a structure that is even more reliable than the first embodiment.

FIG. 6 shows a third embodiment of the present invention, and the same parts are designated by the same reference numerals as in FIGS. 1 to 3. In the figure, the internal electrodes 2 are not provided on the entire surface of the thin plate 1;
It is formed into a so-called alternating electrode type with a blank section provided near one side surface.

Next, FIG. 7 is a plan view showing the internal electrode 2 connected to the anode side external electrode in FIG. 6, and FIG.
It is a sectional view taken along the B line. In both figures, the edge member 2b is formed in a U-shape in plan view, with one edge portion open. Note that the opposite side distance Q' on the side where the edge part is opened is:
It is formed to be smaller than other opposite side distances Ω, for example, to have a dimensional difference corresponding to the width W of the insulating member 2b. That is, Q'≦2
-W is preferable.

FIG. 9 shows the internal electrode 2' connected to the negative external electrode. FIG. To,
The thin plates 1 are arranged so that the insulating material 2b is connected to the external electrode which becomes the anode, and the thin plates 1' are laminated and crimped alternately so that they can be connected to the external electrode which becomes the negative electrode. After sintering in the same manner as described above,
As shown in FIG. 1, external electrodes 3 are provided to form a laminated piezoelectric element.

Strictly speaking, due to the above structure, a gap corresponding to the thickness of the internal electrode 2 is created in a part of the side surface of the thin plate 1, but the thickness of the internal electrode 2 is usually extremely small, 2 to 3. The gap is substantially closed due to the thickness, compression of the thin plate 1 before firing, partial expansion during firing, and the like. Therefore, the occurrence of migration due to intrusion of outside air is hardly recognized. However, if strict specifications are required, a spacer corresponding to the thickness of the internal electrode 2 may be interposed and sandwiched.

In this embodiment, the planar outer diameter contour shape of the thin plate and the internal electrode is square.

A circular, rectangular, or other geometric shape other than a square can be arbitrarily selected. Note that it is preferable that the width of the edge member constituting the internal electrode be as small as possible. Further, in the case of an alternating electrode type, the above-mentioned edge member may be formed into a frame shape instead of a U-shape. However, in this case, by making the width of the edge of the - smaller or by forming the width of the internal electrodes to be different on the left and right sides, when the thin plates are stacked, the edges of the internal electrodes will not touch the sides of the laminate. It is necessary to make it appear every other layer. Next, the material constituting the internal electrode or its edge member, which will become the anode, needs to be a material with low migration characteristics, but it must also have oxidation resistance and a high melting point that will not change in quality even when fired together with a thin plate. Requires characteristics. Therefore, it is preferable to use a high melting point material as described above. In addition, the electromechanical transducer material forming the thin plate is not limited to piezoelectric ceramic materials such as lead zirconate titanate shown in this example, but also other piezoelectric materials.
A laminated displacement element using an electrostrictive material, which has characteristics such as having a Curie temperature lower than room temperature and having characteristics such as no need for polarization, a large amount of displacement, and little hysteresis, has exactly the same effect as described above. You can expect it. Examples of such electrostrictive materials include (Pb@41@La1.@$4) (Zr@+llTl@
, ms) @, lff! 011 (Pb, 1., Sr
. , 1i) (Zr., 5ITl@, 54Zn., *+a
aNle, 5stsNb, 1. ,)O,.

(Pb*, 5sSr*, +j(Zr., 5Jie, 5e
zn*, ms[. ,.

Nb,,,,)O.

etc. can be used.

[Effects of the Invention] Since the present invention has the above-described configuration and operation, it is possible to suppress metal ionization of the internal electrode serving as an anode and completely prevent migration.

In addition, the cost of the electrode material when only the anode side internal electrode is made of a non-silver-based conductive material is half the cost when all the internal electrodes are made of a non-silver thread conductive material, and the edge material of the anode internal electrode is small. Therefore, it becomes possible to manufacture highly reliable laminated displacement elements without migration at extremely low cost.

[Brief explanation of the drawing]

FIG. 1 is a front view of essential parts showing an embodiment of the present invention, FIG. 2 is a plan view showing the anode-side internal electrode in FIG. 1, FIG. FIG. 4 is a plan view showing the negative internal electrode in FIG. 1, and FIG. 5 is a plan view showing the negative internal electrode in FIG.
FIG. 6 is a front view of main parts showing the third embodiment of the present invention; FIG. 7 is a plan view showing the anode-side internal electrode in FIG. 6; 8 is a sectional view taken along the line BB in FIG. 7, and FIG. 9 is a plan view showing the negative internal electrode in FIG. 6. 1.1°; thin plate, 2. 2': Internal electrode, 2a:
Intermediate member, 2b: Edge member, 3: External electrode second

Claims (2)

[Claims] (1) A laminate in which a plurality of thin plates made of electromechanical conversion material are alternately laminated with internal electrodes made of conductive metal material interposed therebetween, and the inner electrodes are connected to the side surfaces of the thin plates alternately every other layer. A laminated displacement element provided with a pair of external electrodes, characterized in that the periphery of the internal electrode connected to the anode-side external electrode or the entire internal electrode is made of a high melting point non-silver-based conductive material. displacement element. (2) The above-mentioned high melting point non-silver material is Au, Pt, Pd, I
2. The laminated displacement element according to claim 1, which is one or more of r, Rh, Os, Ru, or an alloy thereof.