JPH03155180A - Laminated displacement element - Google Patents

Abstract

PURPOSE:To enable an internal electrode to be completely sealed, prevent migration, improve moisture resistance, and prevent occurrence of crack of a film by laminating films each consisting of an inorganic material on the side surface of the laminated body while polymerizing a plurality of films and by shutting off an interlayer connection state of a pin hole and/or fine crack which exist on the film. CONSTITUTION:Internal electrodes 2a and 2b are formed on the entire surface of a thin plate 1. After performing lamination and contact bonding the thin plate 1 with the internal electrodes 2a and 2b thus formed alternately, it is fired and a laminated body 5 is formed. Then, films 7a an 7b consisting of an insulation material are provided on the side surface which is adjacent to this laminated body 5 so that they cross the internal electrodes 2a and 2b. Then, a film 9 is clad onto the side surface of the laminated body 5, avoiding external electrodes 3a and 3b. With the film 9, a fine powder consisting of an inorganic material such as for example SiO2, Al2O3, and glass is dried and coated twice similarly. Since the side surface of the laminated body 5 is clad with the film 9 consisting of a plurality of layers which are made of the inorganic material, interlayer connection of water contents due to a pin hole and/or a fine crack can be prevented.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electromechanical transducer used in actuators, ultrasonic motors, etc. of industrial robots.
In particular, 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 three plates made of electromechanical conversion material via internal electrodes.

[Conventional technology]

Conventionally, laminated piezoelectric elements used as displacement elements used in X-Y stage positioning mechanisms and brakes are polarized by providing electrodes on a yi plate made of piezoelectric ceramic material processed into a predetermined shape. After that, a method is adopted in which they are joined directly or through a thin metal using an organic adhesive. However, when stacking layers using adhesive as described above, depending on the usage conditions, the adhesive layer may absorb displacement due to vibration of the piezoelectric element, or the adhesive may deteriorate due to high temperature environment 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, 1, for example, as described in Japanese Patent Publication No. 59-32040, a paste-like piezoelectric ceramic material made by adding a binder to raw material powder and kneading is formed into a thin plate of a predetermined thickness, and one of the thin plates is An internal electrode is formed by applying a conductive material such as silver-palladium to one or both surfaces. 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.

FIG. 4 shows an example of the structure of the laminated piezoelectric element, which is so-called an alternating electrode type. In FIG. 4, a thin plate 1 is made of a piezoelectric ceramic material, and positive and negative internal electrodes 2a and 2b are alternately sandwiched and stacked to form a laminate 5. The internal electrodes 2a, 2b are each formed so that one end edge protrudes or is exposed to the outside, and are connected to external electrodes 3a, 3b each extending in the stacking direction, and the lead wire 6 is connected thereto.

With the above configuration, when positive and negative voltages are applied to the external voltages 13a and 3b, an electric field is generated between the internal molds tM2a and 2b, and the thin plate 1 is extended in the thickness direction due to the longitudinal effect of the piezoelectric ceramic material, causing displacement. .

Next, the one shown in FIG. 5 is an example of another laminated piezoelectric element, which is a so-called full electrode type with improved piezoelectric displacement efficiency (see, for example, Japanese Patent Application Laid-Open No. 58196068, etc.). In FIG. 5, the same parts are indicated by the same reference numerals as in FIG. 4, but the internal electrodes 2a, 2b are formed so as to cover the entire surface of the thin plate 1, and the required number of internal electrodes are laminated in the same manner as described above. Next, on one side of the laminate 5 formed as described above, the edges of the internal electrodes 2a, 2b are lined with (
For example, a coating 4 made of an insulating material is provided only on the internal electrode 2b, and an external electrode 3a made of a conductive material is applied over the coating 4. On the other hand, on the other side of the laminate 5, an internal electrode (for example 2a
) is provided with a coating 4 in the same manner as described above, and an external electrode 3b is applied thereon. The effect of the above configuration is similar to that shown in FIG. 4 above.

[Problem to be solved by the invention]

In the laminated piezoelectric element having the above structure, when used in electronic parts where a high direct current voltage is continuously applied between the electrodes to obtain displacement, if a silver-based material is used as the electrode material, high humidity There is a problem in that so-called migration occurs in the atmosphere, eventually leading to dielectric breakdown. In other words, although Ag, which constitutes the electrode, is an element that is easily oxidized,
It is ionized (Ag+) in a high humidity atmosphere, 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 is also conceivable to form the poles from a noble metal material with a high melting point, such as Pt or Pd, but this does not improve performance.

This is not preferable because it results in an increase in costs.

In addition, the exposed parts of the internal electrodes made of silver-based material are
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 the 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. However, there are still some unsatisfactory points in terms of reliability.

In addition to the above, there are other means for preventing the intrusion of moisture in a high-humidity atmosphere, such as coating means with a film made of a resin material (for example, see JP-A-62-88382 and JP-A-1-137686), metal Attempts have been made to seal the inside of the container. However, even when coated with a film made of a resin material, the film is not necessarily completely impermeable to water, and may also cause small racks or gaps at the interface with the lead wires due to the operation of the element. Moisture may enter through the

In addition, in the method of further interposing a metal layer in order to prevent moisture from entering (see Japanese Patent Laid-Open No. 1-137686), the formation of the coating becomes complicated.

This has the disadvantage of suppressing the amount of displacement of the element. Moreover, when the device is sealed in a metal container, there is a drawback that not only the amount of displacement of the device is suppressed, but also the overall volume increases, which further increases the cost.

Furthermore, means for covering the side surfaces of the element with a glass film (
There are also proposals for forming an inorganic insulating layer directly only on the exposed portions of internal electrodes and the electrostrictive material in the vicinity (see Japanese Patent Application Laid-open No. 1-164080). However, simply coating the sides of the element with a layer made of inorganic material such as glass may not be able to completely prevent the intrusion of moisture from the outside air due to the presence of pinholes and/or minute cranks, or In an element having a large value, there are problems in that the amount of displacement is suppressed and that cracks are formed in the layer made of the inorganic material due to the expansion and contraction action of the element. In any case, it is difficult to completely prevent migration with the conventional structure described above, and there is a problem that the service life is extremely short.

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 and has high moisture resistance without causing a rise in cost. .

[Means to solve the problem]

In order to achieve the above object, the present invention has the following features.

A laminate is formed by alternately stacking a plurality of thin plates made of an electromechanical transducer material and internal electrodes made of a conductive material, which are formed to have substantially the same planar contour and contact area, and the internal electrodes are placed on the side surface of this laminate. In a laminated displacement element provided with a pair of external electrodes to be connected to every other layer.

A plurality of coatings made of an inorganic material are formed on the side surface of the laminate by polymerizing multiple layers to block communication between pinholes and/or microcracks existing in the coating between the layers. A technical method was adopted.

In the present invention, in the middle part of the coating in the stacking direction, the thickness is approximately parallel to the surface of the thin plate having a thickness of t, and the gap is less than 2.

A slit preferably having a width of less than t may be provided.

[Function] With the above configuration, the communication between the side surface of the laminate and the outside air is completely cut off, so that it is possible to completely prevent moisture from entering the outside air.

[Embodiment] FIGS. 1(a) to d) are perspective views showing embodiments of the present invention, and the same parts are designated by the same reference numerals as in FIGS. 4 and 5. First, in FIG. 1(a), for example, Pb(Zr,Ti)03 powder is used.

PVB as an organic binder, BPBG as a plasticizer,
Trichlene was added as an organic solvent and mixed, and this mixed material was made into a thickness of 100I! using a doctor blade method. m
A sheet-like thin plate 1 is formed.

Next, a silver-palladium paste is screen printed over the entire surface of this thin plate 1 to form internal molds 8ii2a, 2b. Internal electrode 2a formed as described above.

For example, 100 thin plates 1 having 2b are alternately laminated and crimped, and then cut into a predetermined size and shape to form a laminate, 1
The laminated body 5 is formed by firing at 050-1200°C for 1 to 5 hours. The dimensions of this laminate 5 are, for example, 5 x 5 x 101
01 (WI or 10xlOxlOffi (am)
It is. Next, the adjacent side surfaces of this laminate 5 are coated with an insulating material. a and 7b are provided so as to cross the internal electrodes 2a and 2b. 8a in FIG. 1(b).

Reference numeral 8b indicates a groove, and the covering 7a,
7b at positions corresponding to the internal electrodes 2a and 2b.

Is the external electrode 3a3b covered in FIG. 1(C)? a,?
If it is provided on the grooves 8a and 8b so as to cross the grooves 8a and 8b,
The external electrodes 3a, 3b and the internal electrodes 2a, 2b can be connected in a corresponding manner. Next, in FIG. 1(d), 9 is a coating, and external electrodes 3a,
3b is avoided and deposited. The coating 9 is made of, for example, 5iOzAl.
Fine powder made of an inorganic material such as TOS or glass is mixed with a liquid binder to form a paste.

It is preferable to apply several micrometers of the coating, dry it, and then apply the coating two more times in the same manner to polymerize three layers.

Next, after soldering lead wires (not shown) for voltage supply to the external electrodes 3a and 3b, the entire side surface of the laminate 5 was further covered with an epoxy resin.

The laminate 5 configured as above was heated to 40'C, 9
Table 0 shows the relationship between the test time and the cumulative number of defective pieces, in which a durability test was carried out by applying 150 square meters of direct current in an atmosphere of 0 to 95% RH, and is for one sample of 20 pieces. In the table, the comparative example has a conventional structure in which the coating 9 is not deposited on the side surface of the laminate 5.

As is clear from the table, in the comparative example, 10% of the samples became defective after 25 hours from the start of the test, 55% (more than half) after 70 hours, most 95% after 125 hours, and all of the samples failed after 350 hours. It is defective. This is a result of moisture in the atmosphere penetrating into the laminate 5 in a high humidity environment, causing so-called migration.

It is recognized that it causes dielectric breakdown. On the other hand, in the examples, there were no defects even after 500 hours, indicating that the moisture resistance was extremely high. This is presumed to be due to the effect of coating the side surfaces of the laminate 5 with a plurality of layers of the coating 9 made of inorganic material, which prevents interlayer communication of moisture due to pinholes and/or minute racks.

FIG. 1(e) is a perspective view showing a modification of the coating 9 in FIG. 1(d). In FIG.
It is applied to substantially the entire side surface of the laminate 5. It was confirmed that with this configuration, manufacturing becomes easier and the moisture resistance effect is further improved.

FIG. 2 is a perspective view of main parts showing another embodiment of the present invention.

In FIG. 2, 10 is a slit.

A part of the coating 9 in the middle part of the laminate 5 in the stacking direction is provided so as to be divided.

3 (al is an enlarged cross-sectional view showing the state near the slit 10 in FIG. 2. In FIG. 3 (al), the slit 10 is provided parallel to the surface of the thin plate 1 and has a width of t
is formed so that Ls<2L, preferably us<L, where t is the thickness of the thin plate l. Note that the slit 10 is provided along the (-) side internal electrode (for example, 2b).

By configuring as described above, especially when the number of laminated thin plates 1 in the laminate 5 is large, that is, when the amount of displacement is large, it is possible to prevent cracking of the coating 9 and to prevent the amount of displacement. It is effective in preventing the inhibitory effect of In this case, a part of the internal electrode 2b on the (-) side is exposed, but the Ag' ions contributing to one migration are (
Since it occurs in the internal electrode (for example, 2a) on the +) side, there is no particular problem. In other words, the internal electrode on the (+) side (e.g. 2a
) is completely covered by the coating 9,
Inconveniences caused by migration migration can be completely prevented.

FIG. 3 (bl is an enlarged sectional view showing a modified example of the slit 10. In FIG. 3(b), the slit 10 is formed with a part of the coating 9 remaining.
For example, this occurs when the coating 9 is formed by screen printing, and the effect is shown in FIG.
This is similar to that shown in a).

In this example, the entire surface of TaWt having the configuration shown in FIG.
Although an example of the type has been described, it is of course applicable to the alternating electrode type shown in FIG. 4 and the all-over electrode type shown in FIG. 5. In addition, the plane projection shape of the thin plate and internal electrodes is not only rectangular but also square, three circular,
It can be oval or other geometric shape. In the above embodiment, an example was described in which screen printing was used as a means of forming the internal electrodes and external electrodes, but the same effect can be obtained by other methods such as plating, vapor deposition, and coating. It is. Furthermore, in the above embodiments, the case where the electromechanical transducer material is a piezoelectric material was described, but since the Chierie temperature is lower than room temperature,
No need for polarization.

Furthermore, an electrostrictive material having characteristics such as a large amount of displacement and little hysteresis can be expected to have exactly the same effect as described above. Examples of such electrostrictive materials include 9.

(Pbo, q+b Lao, owJ(Zro, as T
io, zs) o, vtq Os + (Pbo, ss
Sro, +s) (Zro, 5lTi, o, 34
Zno, o+zs)fig, o3tSNbo,
+a) 03(Pbo, as Sro, +s) (
Zro, so Tie, so Zno, asNi
o, os Nbo, to) O! etc. can be used.

Furthermore, although an example has been described in which three layers of a coating made of an inorganic material are polymerized, it is sufficient to polymerize at least two or more layers of the coating. In addition to paste coating, other known means such as sputtering, spraying, and screen printing can be used to form the film.

〔Effect of the invention〕

Since the present invention has the structure and operation as described above,
The internal electrodes can be completely sealed, completely preventing migration, and dramatically improving moisture resistance. Furthermore, even in an element with a large amount of displacement, it is possible to exhibit the inherent stretching function without suppressing the amount of displacement (and without causing cracks in the coating).

2nd concave Akira 5

[Brief explanation of the drawing]

1(a) to d) are perspective views showing embodiments of the present invention, FIG. 1(e) is a perspective view showing a modification of the coating in FIG. 1(b), and FIG. FIG. 3(a) is an enlarged sectional view of the main part showing the state near the slit in FIG. 2; FIG. 3(b) shows a modification of the slit. The enlarged sectional view, FIG. 4, and FIG. 5 are side views each schematically showing an example of a conventional laminated displacement element. 1: thin plate, 5: laminate, 9: film, 10 varnish slint. Figure 4, Figure 5 (2)

Claims (2)

[Claims] (1) A laminate is formed by alternately stacking a plurality of thin plates made of an electromechanical transducer material and internal electrodes made of a conductive material, which are formed to have approximately the same planar contour and contact area, and the side surfaces of this laminate are In the laminated displacement element which is provided with a pair of external electrodes to be connected to the internal electrodes every other layer, a plurality of coatings made of an inorganic material are formed on the side surface of the laminate by polymerizing multiple layers, and the pinholes present in the coating are removed. and/or a laminated displacement element configured to block interlayer communication of microcracks. (2) The laminated displacement device according to claim (1), wherein a slit is provided in the intermediate portion of the coating in the lamination direction, the slit being substantially parallel to the surface of the thin plate having a thickness of t and having a width of less than 2t, preferably less than t. element.