JP2000340849A - Multilayer piezoelectric actuator - Google Patents

Abstract

(57) [Problem] To provide a sufficient connection between one internal electrode and an external electrode and to insulate the other internal electrode from an external electrode even when the device is operated continuously at a high applied electric field at a high speed for a long period of time. To provide a laminated piezoelectric actuator capable of reliably securing the piezoelectric actuator. An actuator body (1) having an end portion of an internal electrode (3) exposed on two side surfaces;
An external electrode 4 is provided on one side surface. The external electrode 4 has a plurality of recesses 7 formed at predetermined intervals in the conductive plate 6, and an insulator 8 is accommodated in the recesses 7. The insulators 8 are alternately brought into contact with the ends of the internal electrodes 3, and the conductive projections 9 between the recesses 7 of the conductive plate 6 are conductively bonded to the ends of the internal electrodes 3 that are not in contact with the insulator 8. Bonded with agent 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric actuator, and more particularly, to a laminated piezoelectric actuator used for a precision positioning device such as a fuel injection valve for an automobile, an optical device, or a driving element for preventing vibration. Things.

[0002]

2. Description of the Related Art Hitherto, in order to obtain a large displacement using an electrostriction effect, a laminated piezoelectric actuator in which piezoelectric bodies and internal electrode layers are alternately laminated has been proposed. Multi-layer piezoelectric actuators are classified into two types: co-firing type and stack type in which piezoelectric ceramics and internal electrode plates are alternately laminated. Considering lower voltage and lower manufacturing cost, co-firing type Since the multilayer piezoelectric actuator is advantageous for thinning, it is showing its superiority.

As a co-firing type laminated piezoelectric actuator, for example, as described in Japanese Patent Publication No. 4-51992, a piezoelectric material exhibiting an electrostrictive effect and internal electrodes are alternately laminated and integrally fired. Actuator body consisting of a laminated sintered body, wherein the shape of each internal electrode is a cross-sectional shape perpendicular to the lamination direction of the piezoelectric body, a shape including a part including the outer peripheral portion thereof is removed, The internal electrodes are stacked so that the removed portion does not overlap between the internal electrodes adjacent to each other in the stacking direction, but overlaps between every other internal electrode. At the position corresponding to the removed part,
It is disclosed that external electrodes are formed to connect the internal electrodes every other layer.

In Japanese Patent Application Laid-Open No. Hei 4-237172, an insulating layer made of glass is coated every other end of an internal electrode exposed on a side surface of an actuator body, and an external electrode has the same pitch as the insulating layer. And a concave portion slightly larger than the cross section of the insulating layer is formed, and the insulating layer is accommodated in the concave portion, and the end of the internal electrode on which the insulating layer is not formed is formed on the convex portion between the concave portions. A multilayer piezoelectric actuator has been disclosed that secures electrical connection between an external electrode and one internal electrode by bonding with a conductive adhesive, and ensures insulation between the external electrode and the other internal electrode.

[0005]

By the way, in recent years, in order to secure a large displacement under a large pressure with a small piezoelectric actuator, a higher electric field is applied and the piezoelectric actuator is driven continuously for a long period of time. However, when continuously driven for a long period of time under a high electric field and high pressure, separation occurs between the internal electrode formed between the piezoelectric bodies and the external electrodes for the positive electrode and the negative electrode, and voltage is applied to some piezoelectric elements. There is a problem that the supply is not performed and the displacement characteristics change during driving.

In the laminated piezoelectric actuator disclosed in Japanese Patent Application Laid-Open No. 4-237172, an end portion of the internal electrode exposed on the side surface of the actuator body is covered with an insulating layer made of glass every other layer. And the piezoelectric material on both sides are firmly joined, and this insulating layer is housed in the concave portion of the external electrode to ensure insulation between the external electrode and the internal electrode. In the case of continuous driving for a long period of time, a crack occurs in the insulating layer made of glass, short-circuiting occurs between the internal electrode and the external electrode through this crack, voltage is not supplied to some piezoelectric bodies, and However, there is a problem that the displacement characteristics change.

That is, since the actuator body expands and contracts in the laminating direction of the piezoelectric body and the internal electrode, the insulating layer made of glass having a high Young's modulus provided on the end of the internal electrode and the piezoelectric body in the vicinity thereof has a long length. There is a problem that the electrode is destroyed because it cannot withstand the expansion and contraction operation due to the continuous driving for a period, and a short circuit easily occurs between the internal electrode and the external electrode through the broken portion. Note that a conductive adhesive is adhered to the ends of the piezoelectric body and the internal electrodes, but the conductive adhesive is mainly composed of a metal,
Since it has a low Young's modulus, it is less problematic than an insulating layer made of glass.

According to the present invention, it is possible to secure a sufficient connection between one internal electrode and an external electrode and to ensure insulation between the other internal electrode and the external electrode even when the device is continuously operated at a high applied electric field at a high speed for a long period of time. It is an object of the present invention to provide a laminated piezoelectric actuator which can be ensured in a compact.

[0009]

According to the present invention, there is provided a laminated piezoelectric actuator comprising a plurality of piezoelectric bodies and a plurality of internal electrodes alternately laminated, and the ends of the internal electrodes are exposed on at least two side surfaces. A laminated piezoelectric actuator comprising: an actuator main body; and external electrodes formed on two side surfaces of the actuator main body and having ends of the internal electrodes connected alternately, wherein the external electrodes are formed on a conductive plate. Are formed at predetermined intervals, and insulators are accommodated in the recesses. The insulators of the external electrodes are alternately brought into contact with the ends of the internal electrodes. Wherein the conductive projections are bonded to the ends of the internal electrodes which are not in contact with the insulator with a conductive adhesive. Here, it is desirable that an oxide film is formed on the inner surface of the concave portion.

[0010]

In the multilayer piezoelectric actuator of the present invention, the external electrodes are formed by forming a plurality of concave portions at predetermined intervals on the conductive plate and accommodating an insulator in the concave portions.
The insulator is brought into contact with the end of the internal electrode on the other layer, and the conductive projection formed between the recesses of the conductive plate is adhered to the end of the internal electrode not in contact with the insulator with a conductive adhesive. Because the insulator is in contact with the end of the internal electrode and the piezoelectric body, even if the actuator body expands and contracts in the laminating direction of the piezoelectric body and the internal electrode, almost no stress acts on the insulator, The insulator is not damaged even when driven continuously for a long time under a high electric field and high pressure. For this reason, the occurrence of a short circuit between the external electrode and the internal electrode, which should be insulated, can be prevented, and the electrical connection between one internal electrode and the external electrode and the insulation between the other internal electrode and the external electrode can be ensured. It is possible to operate for a long time even with high-speed continuous driving.

Further, by forming an oxide film on the inner surface of the concave portion, even if the insulator contained in the concave portion is broken, the discharge between the internal electrode and the external electrode is prevented by the oxide film. And high insulation between the external electrodes.

[0012]

FIG. 1 is a perspective view of a laminated piezoelectric actuator of the present invention, FIG. 2 is a cross-sectional view showing an enlarged part, and FIG. 3 is an enlarged view of a part of an external electrode. FIG.

In FIG. 1, reference numeral 1 denotes a plurality of piezoelectric bodies 2.
And a plurality of internal electrodes 3 which are alternately stacked on each other.
Are formed.

The piezoelectric body 2 is made of, for example, lead zirconate titanate Pb (Zr, Ti) O ₃ (hereinafter abbreviated as PZT) or a piezoelectric ceramic material mainly containing barium titanate BaTiO _3. However, the present invention is not limited to these, and any ceramics having piezoelectricity may be used. As the piezoelectric material, as the piezoelectric strain constant d ₃₃ it is high is preferable. Further, the thickness of the piezoelectric body 2, that is, the distance between the internal electrodes 3 is desirably 0.03 to 0.2 mm from the viewpoint of miniaturization and application of a high electric field.

The internal electrodes 3 are connected to the 4 of the actuator body 1.
Ends are exposed on all three side surfaces, and a pair of external electrodes 4
The ends of the internal electrodes 3 are connected alternately to each other, and the internal electrodes 3 having the same polarity are connected to the same external electrode 4.

The actuator body 1 is mechanically held on both end surfaces of the actuator body 1 in the stacking direction.
Inactive portions 5 for transmitting the generated power to the outside are stacked and joined.

In the piezoelectric actuator according to the present invention, the external electrode 4 is provided on the conductive plate 6 at a predetermined distance from the recess 7.
Are formed and the insulator 8 is accommodated in the concave portion 7, and the insulator 8 of the external electrode 4 is
The conductive protrusions 9 between the recesses 7 of the conductive plate 6 are adhered to the ends of the internal electrodes 3 that are not in contact with the insulator 8 by a conductive adhesive 10. I have. That is, the external electrode 4 secures electrical connection with the one internal electrode 3 and secures insulation with the other internal electrode 3.

The conductive plate 6 may be made of any metal as long as it has conductivity and can be processed. Preferably, the conductive plate 6 is made of silver alloy, copper alloy, stainless steel, Ni-Fe alloy, Ni-Fe.
-It is desirable to be formed of a Co alloy or the like.

The recess 7 is provided at a distance between an end of the internal electrode 3 exposed on the same side surface of the actuator body 1 and an end of the internal electrode 3 which is further layered, that is, a distance between the internal electrodes 3 having the same polarity. The width in the stacking direction is substantially the same as that of the piezoelectric body 2. Although the cross section of the concave portion 7 is a quadrangular prism, the cross section may be a circular shape.

The insulator 8 is made of, for example, glass, glass,
It is made of an insulating material such as an epoxy resin or a silicone rubber, and is obtained by filling the insulating material in the recess 7 of the conductive plate 6 and curing the material. As shown in FIG. 3, the insulator 8 protrudes from the surface of the conductive protrusion 9 of the conductive plate 6, and the insulator 8 contacts the end of the internal electrode 3 without joining. The insulator 8 has a rectangular cross section, but may have a circular cross section. The insulator 8
When glass is used as the material, the glass paste is filled in advance into the recess 7 of the conductor 6 to form the insulator 8, and then the conductive protrusion 9 is joined to the side surface of the actuator body 1.

The conductive adhesive 10 is, for example, 40 to 60% by weight of Ag powder and PbO—SiO ₂ —ZrO ₂ —B
It is formed using a paste from 40 to 60% by weight of a glass component containing ₂ O ₃ as a main component. It is desirable that the conductive adhesive 10 formed on the conductive protrusion 9 be a material that is easily diffused and bonded to the internal electrode material in order to firmly bond to the end of the internal electrode 3. When the internal electrode 3 is made of a material containing Ag, the main component of the conductive adhesive 10 is desirably Ag. Further, in order to strengthen the bonding, it is desirable to include a glass component of the same system as the glass component contained in the internal electrode material. By using a low Young's modulus material such as conductive silicone rubber as the conductive adhesive 10,
Damage to the conductive adhesive 10 during high-speed driving can be prevented.

The oxide film 1 is formed on the inner surface of the recess 7 of the external electrode 4.
1 may be formed. That is, by forming the oxide film 11 between the inner surface of the concave portion 7 and the insulator 8, more insulating properties can be secured.

The multilayer piezoelectric actuator configured as described above is manufactured by the following process. First,
A slurry is prepared by mixing a calcined powder of a piezoelectric ceramic such as lead zirconate titanate Pb (Zr, Ti) O ₃ , a binder made of an organic polymer, and a plasticizer, and has a thickness of 30 by slip casting. ~ 200 μm
To produce a ceramic green sheet.

On one surface of the green sheet, a conductive paste to be an internal electrode is applied by a screen printing method to a thickness of 1-10 μm.
Print to a thickness of m. After the conductive paste is dried, a predetermined number of green sheets to which the conductive paste is applied are laminated, and green sheets to which the conductive paste is not applied are laminated on both sides of the laminate.

Next, while applying pressure, 100-200 ° C.
To heat and integrate the laminate. The integrated laminate is cut into a predetermined size,
Debinding is performed for 40 hours, 900 to 1100 ° C,
The main firing is performed in 2 to 5 hours, and the actuator body 1 is manufactured. On four sides of this actuator body 1,
The end of the internal electrode 3 is exposed.

On the other hand, the external electrodes 4 are formed with a plurality of recesses 7 at predetermined intervals in the conductive plate 6, and these recesses 7 are filled with a paste of an insulating material made of, for example, glass.
The insulator 8 is accommodated by drying, and the conductive adhesive 9 is attached to the conductive protrusion 9 between the recesses 7 of the conductive plate 6.
Is applied and formed. In this state, the conductive adhesive 10 protrudes outside the insulator 8.

Then, the conductive adhesive 10 of the external electrode 4 is brought into contact with the end of the internal electrode 3, and the conductive projection 9 of the external electrode 4 is electrically connected to the end of the internal electrode 3 by heat bonding or laser welding. While being bonded through the conductive adhesive 10,
The insulator 8 of the external electrode 4 comes into contact with the end of the internal electrode 3 to which the conductive protrusion 9 is not connected.

Thereafter, although not shown, the periphery of the actuator is covered with a coating material such as silicon rubber by a method such as dipping, and leads are connected to the positive electrode external electrode and the negative electrode external electrode as shown in FIG. The line 15 is connected, a polarization voltage of 0.1 to 3 kV is applied to the positive electrode and the negative electrode, and the entire actuator is subjected to polarization processing, thereby obtaining a final laminated piezoelectric actuator.

In order to cover the corners around the actuator with a coating material such as silicon rubber, the surroundings are evacuated. At this time, the insulator 8 of the external electrode 4 is In some cases, a coating material such as silicon rubber may enter between the end of the internal electrode 3 and the piezoelectric body 2.

In the laminated piezoelectric actuator configured as described above, the insulator 8 is in contact with the end of the internal electrode 3 and the piezoelectric body 2, and the actuator body 1 is connected between the piezoelectric body 2 and the internal electrode 3. Even if the insulator 8 expands and contracts in the laminating direction, almost no stress acts on the insulator 8, and even if the insulator 8 is continuously driven under a high electric field and high pressure for a long period of time, the insulator 8 is not damaged. Can be operated for a long time.

Further, by covering the whole with an insulating coating material such as silicon rubber, it is possible to prevent moisture from entering the environment. Therefore, occurrence of electromigration between the electrode members to be used can be suppressed, and reliability of electrode connection can be ensured.

The laminated piezoelectric actuator of the present invention may have any polygonal prism shape such as a quadrangular prism, a hexagonal prism, or the like, but is preferably a quadrangular prism because of the ease of cutting.

[0033]

EXAMPLE An internal electrode paste containing Ag / Pd as a main component was printed to a thickness of 2 μm on a green sheet containing PZT as a main component and having a thickness of 0.12 mm. 300 green sheets to which the internal electrode paste is applied are laminated, and thereafter,
Green sheets to which the internal electrode paste was not applied were laminated on both surfaces, and were joined by heating and integrated.

The laminated body is 10 mm long × 10 mm wide × 3 height.
Cut to 0mm, maximum temperature 700-800
The binder was removed at 20 ° C. for 20 to 30 hours. After that, baking is performed at a maximum temperature of 900 ° C. to 1100 ° C. for 3 to 6 hours,
An actuator body was obtained.

Next, in the shape shown in FIG.
2 mm wide recesses are formed at intervals of 0.2 mm on the surface of a stainless steel conductive plate having a thickness of 0.4 mm and a thickness of 0.4 mm, and these recesses are filled with an insulating material made of borosilicate glass. Body, and A
g and a conductive adhesive composed of glass were applied to form external electrodes.

After positioning the external electrode on the side surface of the actuator body, a weight was placed on the upper portion of the external electrode, and the external electrode was heated and bonded at 600 ° C. for 30 minutes. Thereafter, silicon rubber was filled so that there was no gap between the outer peripheral portion of the piezoelectric body 2 and the external electrode 4 and the internal electrode 1. This was placed in silicon oil at 80 ° C., and a DC electric field of 3 kV / mm was applied to the positive electrode and the negative electrode for 30 minutes to perform a polarization treatment, thereby obtaining a laminated piezoelectric actuator of the present invention.

In the obtained laminated piezoelectric actuator, 20
As a result of applying a DC voltage of 0 V, a displacement amount of 40 μm was obtained. Further, as a result of applying an AC electric field of 0 to +200 V to the actuator at a frequency of 50 Hz, a displacement of 40 μm was maintained up to 5 × 10 ⁸ times. Further, ten laminated piezoelectric actuators of the present invention were subjected to a humidity of 9
In an atmosphere of 5%, an AC electric field of 0 to +200 V is applied at 50 Hz.
Even when applied at a frequency of 1 × 10 ⁸ times, no discharge occurred and no breakage occurred.

Further, the end portions of the internal electrodes are covered with a glass layer every other layer, and the external electrodes have concave portions at the same pitch as that of the glass layer. The laminated piezoelectric actuator of the comparative example, in which the alignment was performed and the projections between the depressions were bonded to the ends of the internal electrodes on which the glass layer was not formed with a conductive adhesive, was produced.

As described above, when a DC voltage of 200 V was applied, a displacement of 40 μm was obtained. Furthermore, as a result of applying an AC electric field of 0 to +200 V to the actuator at a frequency of 50 Hz, the actuator was applied up to 5 × 10 ⁸ times,
The displacement of μm was maintained. Further, 10 of these laminated piezoelectric actuators were immersed in an atmosphere of humidity of 95% to 0 to +20.
When an AC electric field of 0 V was applied 1 × 10 ⁶ times at a frequency of 50 Hz, eight were damaged due to creeping discharge. Observation of the damaged part revealed that the glass layer covering the end of the internal electrode was cracked, and the end of the internal electrode and the inner surface of the concave part of the external electrode were discharged through this crack, resulting in creeping discharge. It was confirmed.

The displacement was measured by fixing the sample on a vibration isolating table, attaching an aluminum foil to the upper surface of the sample, and averaging the values measured at the center and three peripheral portions of the element by a laser displacement meter. The value was evaluated.

[0041]

In the multilayer piezoelectric actuator of the present invention, the insulator of the external electrode is in contact with the end of the internal electrode and the piezoelectric body, and the actuator body expands and contracts in the laminating direction of the piezoelectric body and the internal electrode. However, almost no stress acts on the insulator, and even if the insulator is driven continuously for a long time under a high electric field and high pressure, the insulator is not damaged. A short circuit between them can be prevented, and a long-time operation can be performed even for a high-speed continuous drive.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a quadrangular prism-shaped laminated piezoelectric actuator of the present invention.

FIG. 2 is an enlarged sectional view showing a part of FIG. 1;

FIG. 3 is a sectional view showing an external electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Actuator main body 2 ... Piezoelectric body 3 ... Internal electrode 4 ... External electrode 6 ... Conductive plate 7 ... Concave part 8 ... Insulator 9 ... Conductive convex part 10. ..Conductive adhesive 11 ... Oxide film

Claims (2)

[Claims] 1. An actuator body comprising a plurality of piezoelectric bodies and a plurality of internal electrodes alternately laminated, and an end of the internal electrode exposed on at least two side surfaces, and two side surfaces of the actuator body, respectively. And a laminated piezoelectric actuator comprising an external electrode formed by alternately connecting ends of the internal electrode, wherein the external electrode forms a plurality of recesses in the conductive plate at predetermined intervals, and An insulator is accommodated in the recess, and the insulator of the external electrode is alternately brought into contact with the end of the internal electrode, and the conductive protrusion between the recesses of the conductive plate is not in contact with the insulator. The laminated piezoelectric actuator characterized in that the internal electrode is bonded to an end of the internal electrode with a conductive adhesive. 2. The multilayer piezoelectric actuator according to claim 1, wherein an oxide film is formed on the inner surface of the recess.