JP2002050804A - Laminated piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated piezoelectric actuator having improved long- term reliability by relaxing the stress concentration at the boundary part between the polarization region and the non-polarization of an inner electrode layer. SOLUTION: The laminated piezoelectric actuator is provided with a laminate 10 where a ceramic layer 11 and inner electrodes 12a and 12b are exposed alternately on the opposing end faces, and outer electrodes 13a, 13b, 13c, and 13d that are provided on both end faces being exposed to the inner electrodes 12a and 12b of the laminate 10. The inner electrodes 12a and 12b are provided with two inner electrodes 12a and 12b connected to the same outer electrodes 13a, 13b, 13c, and 13d on the same ceramic layer 11, and the lamination direction of the laminate 10 differs from the direction of flex displacement.

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 used for various electronic devices.

[0002]

2. Description of the Related Art FIG.
As shown in FIG.

First, a ceramic layer 101 and an internal electrode 102
Are alternately laminated, and a laminated body 100 in which one end of the internal electrode 102 is alternately exposed to the end faces facing each other is produced. The internal electrodes 102 are formed on one ceramic layer 101 from one end to the vicinity of the other end as shown in FIG.

[0004] Next, as shown in FIG. 7, two external electrodes 102 are provided on one of the exposed end surfaces of the internal electrodes 102 of the laminated body 100 so that the internal electrodes 102 above and below the center in the laminating direction are not short-circuited. The electrodes 103a and 103b are formed. Also, the internal electrode 1 exposed on the other end face
An external electrode 103c that can be electrically connected to all the electrodes 02 is formed.

Next, between the external electrodes 103a and 103c, 1
A DC voltage is applied between 03b and 103c to perform polarization processing on the ceramic layer 101.

By this polarization treatment, the upper ceramic layer 100 and the lower ceramic layer 100 from the center in the stacking direction are formed.
Is in the opposite direction.

[0007] When an electric field is applied in the direction of polarization, the laminated piezoelectric actuator contracts in the direction perpendicular to the direction of polarization, and expands in the direction perpendicular to the direction of polarization when an electric field is applied in the direction opposite to the direction of polarization. Therefore, the external electrodes 103a and 103b of the multilayer piezoelectric actuator having the above configuration are short-circuited, and the external electrodes 10a and 103b are short-circuited.
When a voltage is applied between 3a, 103b and 103c, elongation and contraction occur at the same time, causing bending displacement in the polarization direction.

[0008]

In such a configuration, when the number of stacked ceramic layers 101 and internal electrodes 102 increases, a step in the stacking direction that occurs at the boundary between the polarized region and the non-polarized region of the internal electrode 102 becomes larger. Become noticeable. Further, since the stacking direction and the bending displacement direction are the same direction, stress concentrates on this step. Therefore, if the actuator is driven for a long period of time, cracks may occur in the step.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a laminated piezoelectric actuator having excellent long-term reliability by reducing stress concentration on a boundary between a polarized region and a non-polarized region of an internal electrode layer. It is.

[0010]

In order to achieve this object, a laminated piezoelectric actuator according to the present invention has a ceramic layer and an internal electrode layer laminated such that the internal electrode layers are alternately exposed at end faces facing each other. Comprising a laminate, and external electrodes provided on both exposed end surfaces of the internal electrode of the laminate,
The internal electrode layer has two internal electrodes connected to the same external electrode on the same layer, and the lamination direction and the bending displacement direction of the laminate are different from each other. Can be.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is directed to a laminate in which a ceramic layer and an internal electrode layer are laminated such that the internal electrode layers are alternately exposed at end faces facing each other. External electrodes provided on both exposed end faces of the internal electrode of the laminate, wherein the internal electrode layer has two internal electrodes connected to the same external electrode on the same layer, and the lamination direction of the laminate And a bending displacement direction which are different from each other, and alleviates stress concentration on a boundary portion between a polarized region and a non-polarized region of the internal electrode layer, thereby achieving long-term reliability.

According to a second aspect of the present invention, in each of the internal electrode layers, the two internal electrodes are formed symmetrically with respect to the center line of the laminate, and the distance between the internal electrodes is made constant. Since the stray capacitance generated between the internal electrode layers becomes equal, unnecessary vibration due to non-uniform stray capacitance can be reduced.

According to a third aspect of the present invention, there is provided the multilayer piezoelectric actuator according to the first aspect, wherein the distance between the internal electrodes is larger than the thickness of the ceramic layer. And the possibility of saturation polarization even when an electric field is applied during the polarization process is low. As a result, unnecessary vibration during driving can be reduced.

According to a fourth aspect of the present invention, there is provided the multilayer piezoelectric actuator according to the first aspect, wherein a distance from an end of the internal electrode to a side surface of the multilayer body is longer than a thickness of the ceramic layer. In this case, the electric field intensity is lower than that of the ceramic layer, and the possibility of saturation polarization even when an electric field is applied during the polarization process is low. As a result, unnecessary vibration during driving can be reduced.

According to a fifth aspect of the present invention, there is provided the laminated piezoelectric actuator according to the first aspect, wherein an external electrode connected to an external electrode formed on an end surface is formed on a side surface in a direction perpendicular to the bending displacement direction. Even if unnecessary vibration occurs between the internal electrode layers, it occurs in the same direction as the bending displacement direction.
Unwanted vibration in the direction perpendicular to the bending displacement can be reduced.

According to a sixth aspect of the present invention, there is provided the laminated piezoelectric actuator according to the first aspect, wherein the ends of the internal electrodes are present on a non-coplanar plane in the laminating direction. Can be gradually reduced, so that stress concentration at the boundary portion is reduced, and the long-term reliability is improved.

According to a seventh aspect of the present invention, there is provided the multilayer piezoelectric actuator according to the first aspect, wherein the uppermost and lowermost ceramic layers of the multilayer body are thicker than the ceramic layers inside the multilayer body. The stress concentration on the boundary between the ceramic layer and the non-polarized ceramic layer is reduced, and the long-term reliability is improved.

The invention according to claim 8 is the multilayer piezoelectric actuator according to claim 1, wherein the ceramic layers on the upper and lower surfaces of the internal electrode layer are integrated by penetrating the internal electrode. Even if stress concentration occurs at the boundary with the ceramic layer, peeling of the ceramic layer can be prevented, so that long-term reliability is excellent even if the generated force is large.

According to a ninth aspect of the present invention, in the internal electrode layer, the ceramic material for forming the ceramic layer is made of a metal component of 20%.
The multilayer piezoelectric actuator according to claim 1, wherein the multilayered piezoelectric actuator is formed using a metal paste containing at least one wt% or more, and the internal electrode layer and the ceramic layers above and below the internal electrode layer can be integrated at at least one location. Even if the generation force is large, the long-term reliability is excellent.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of a laminated piezoelectric actuator according to an embodiment of the present invention, FIG. 2 is a sectional view taken along line AB of FIG. 1, FIG. 3 is a sectional view taken along line CD of FIG. 1, and FIG. 5 is a cross-sectional view showing a method of supporting the laminated piezoelectric actuator shown in FIG. 1, wherein 10 is a laminated body, 11 is a ceramic layer, 12 a and 12 b are internal electrodes, 13 a, 13 b, and 13 b.
13c and 13d are external electrodes, and 14a and 14b are supports.

First, Pb pulverized to an average particle size of about 1 μm
A predetermined amount of an organic binder, a plasticizer, and an organic solvent are mixed with a piezoelectric ceramic powder containing TiZrO ₃ as a main component to prepare a slurry. Next, a sheet is formed by a doctor blade method to obtain a ceramic sheet having a predetermined thickness to be the ceramic layer 11.

Next, the ceramic sheet and the internal electrode 12
a and a substantially rectangular parallelepiped laminated body 1 in which 12a and 12b are alternately laminated.
0 is produced. The internal electrodes 12a and 12b are formed by using a metal paste containing Ag as a main component, Pd as an auxiliary component and the piezoelectric ceramic powder in an amount of 20 wt% or more of the metal component.

As shown in FIG. 4, internal electrodes 12 of the same layer
Reference numerals a and 12b have the same shape, and are formed so as to have a predetermined interval from the same end to the vicinity of the other end on one ceramic layer 11 at a predetermined interval.

As shown in FIGS. 2 and 3, the internal electrodes 12a and 12b are alternately exposed at opposing ends of the laminated body 10, and the ceramic layers 11a and 12b are arranged in the longitudinal direction of the laminated body 10. Are provided to face each other.

Next, the laminate 10 is degreased and fired.

Next, as shown in FIGS.
0 external electrodes 13 connected to the internal electrodes 12a and 12b, respectively, on one end surface where the internal electrodes 12a and 12b are exposed.
a, 13b and the internal electrodes 12a, 12b
The external electrode 13c is formed on the entire other end surface where the is exposed, and an external electrode 13d electrically connected to the external electrode 13c is formed on one side surface following this end surface.

Thereafter, the external electrodes 13a and 13c and 13
3k per 1mm thickness of ceramic layer 11 between b and 13c
A DC voltage of V is applied in silicon oil at 100 ° C. for 30 minutes to polarize the ceramic layer 11 between the internal electrodes 12a and 12b. By this polarization treatment, a bimorph-type laminated piezoelectric actuator in which the direction of lamination of the ceramic layer 11 and the internal electrodes 12a and 12b was orthogonal to the direction of bending displacement during driving was obtained.

As shown in FIG. 5, the laminated piezoelectric actuator has one end on the side face supported by supports 14a and 14b and applies a voltage to the external electrodes 13a and 13b to cause bending displacement in the direction of the arrow. It will be. However, since the bending displacement direction and the stacking direction of the stack 10 are different from each other, the concentration of stress on the boundary between the polarized regions and the non-polarized regions of the internal electrodes 12a and 12b can be reduced. The generation is suppressed and the long-term reliability is excellent.

Hereinafter, a specific configuration of the laminated piezoelectric actuator of the present invention will be described.

(1) As shown in FIG. 3, the internal electrodes 12a,
The ends of 12b are shifted so as not to be on the same plane in the stacking direction of the stacked body 10. According to this configuration, the electric field near the ends of the internal electrodes 12a and 12b during polarization is generated not only in the internal electrodes 12a and 12b of the opposing portions via the ceramic layer 11 but also in the internal electrodes 12a and 12b of the non-opposing portions. Also occurs. As a result, when a driving voltage is applied to the laminated piezoelectric actuator, the magnitude of the generated force gradually decreases at the boundary between the polarized region and the non-polarized region, and stress concentration on this portion is reduced. Therefore, the long-term reliability of the laminated piezoelectric actuator can be improved.

(2) The internal electrodes 12a, 12a
As shown in FIG. 4, b is formed symmetrically with respect to the center line GH of the laminated body 10 and the distance between the internal electrodes 12a and 12b is made constant, so that the stray capacitance generated between the layers becomes equal. In addition, unnecessary vibration due to uneven floating capacitance can be suppressed.

(3) By making the distance between the internal electrodes 12a and 12b larger than the thickness of the ceramic layer 11,
When a driving voltage is applied, the electric field intensity is lower than that of the ceramic layer 11, and furthermore, even if an electric field is applied during the polarization process, there is a low possibility that the internal electrodes 12a and 12b are saturated with polarization. Vibration can be reduced.

(4) The distance from the end of each of the internal electrodes 12a, 12b to the end face of the multilayer body 10 is determined by the distance between the internal electrodes 12a, 12b.
By making the thickness longer than the thickness of the ceramic layer 11 interposed therebetween, the external electrodes 13a, 13b, 13
Even if an electric field is applied between the internal electrodes 12a and 12b and the internal electrodes 12a and 12b, there is a low possibility that the ceramic layer 11 is saturated and polarized from the internal electrodes 12a and 12b to the side surfaces of the multilayer body 10, and even when a driving voltage is applied. Since the electric field intensity is smaller than that of the ceramic layer 11, unnecessary vibration can be reduced.

(5) As shown in FIG. 1 and FIG.
By forming 3d on the side surface of the laminated body 10 that is perpendicular to the bending displacement direction, even if unnecessary vibration occurs between the external electrode 13d and the internal electrode 12b, the vibration occurs in the same direction as the bending displacement direction. In addition, unnecessary vibration in the direction perpendicular to the bending displacement direction can be reduced.

(6) When a drive voltage is applied by making the thickness of the uppermost and lowermost ceramic layers 11 of the laminated body 10 larger than the thickness of the ceramic layer 11 sandwiched between the internal electrodes 12a and 12b. Since the electric field intensity is lower than that of the ceramic layer 11 in the central portion compared to the uppermost and lowermost ceramic layers 11, even if an electric field is applied during the polarization process, the possibility of saturation polarization between the internal electrodes 12 a and 12 b is low, As a result, the magnitude of the generated force gradually decreases at the boundary between the polarized region and the non-polarized region via the uppermost and lowermost ceramic layers 11, and the stress concentration on this portion is reduced. Therefore, the laminated piezoelectric actuator has excellent long-term reliability.

(7) The ceramic layers 11 on the upper and lower surfaces of the internal electrodes 12a and 12b are integrated by penetrating at least a part of the internal electrodes 12a and 12b so as not to affect the electrical characteristics of the laminated piezoelectric actuator. ,
Even if stress concentration occurs at the boundary between the internal electrodes 12a and 12b and the ceramic layer 11, peeling of the ceramic layer 11 can be prevented, so that long-term reliability is excellent even when the generated force is large.

(8) The internal electrodes 12a and 12b are made of a ceramic material for forming the ceramic layer 11 using a metal component of 20 watts.
By forming and firing using a metal paste containing at least t%, the internal electrodes 12a and 12b and the upper and lower ceramic layers 11 can be integrated in at least one or more places. Excellent long-term reliability.

(9) In the above embodiment, the case where the laminated piezoelectric actuator is supported at one end has been described, but the same can be said for the case where both ends or the center is supported.

[0040]

As described above, according to the present invention, it is possible to provide a laminated piezoelectric actuator excellent in long-term reliability by relaxing stress concentration on a boundary portion between a polarized region and a non-polarized region of an internal electrode layer. .

[Brief description of the drawings]

FIG. 1 is a perspective view of a laminated piezoelectric actuator according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along a line AB in FIG.

FIG. 3 is a sectional view taken along line CD of FIG. 1;

FIG. 4 is a sectional view taken along the line EF of FIG. 1;

FIG. 5 is a sectional view showing a method of supporting the laminated piezoelectric actuator shown in FIG. 1;

FIG. 6 is a perspective view of a conventional laminated piezoelectric actuator.

FIG. 7 is a sectional view taken along line KL of FIG. 6;

FIG. 8 is a sectional view taken along the line MN in FIG. 6;

[Explanation of symbols]

 Reference Signs List 10 laminated body 11 ceramic layer 12a internal electrode 12b internal electrode 13a external electrode 13b external electrode 13c external electrode 13d external electrode 14a support 14b support

Claims (9)

[Claims] 1. A laminated body in which ceramic layers and internal electrode layers are alternately laminated on end faces where the internal electrode layers face each other, and provided on both end faces of the laminated body where the internal electrodes are exposed. A multilayer piezoelectric actuator comprising an external electrode, wherein the internal electrode layer has two internal electrodes connected to the same external electrode on the same layer, and the lamination direction and the bending displacement direction of the laminate are different. 2. The multilayer piezoelectric actuator according to claim 1, wherein two internal electrodes in each internal electrode layer are formed symmetrically with respect to a center line of the multilayer body, and the distance between the internal electrodes is made constant. 3. The multilayer piezoelectric actuator according to claim 1, wherein the distance between the internal electrodes is larger than the thickness of the ceramic layer. 4. The multilayer piezoelectric actuator according to claim 1, wherein a distance from an end of the internal electrode to a side surface of the multilayer body is longer than a thickness of the ceramic layer. 5. The laminated piezoelectric actuator according to claim 1, wherein an external electrode connected to an external electrode formed on an end face is formed on a side surface in a direction perpendicular to the bending displacement direction. 6. The multilayer piezoelectric actuator according to claim 1, wherein the ends of the internal electrodes exist on a non-coplanar plane in the laminating direction. 7. The multilayer piezoelectric actuator according to claim 1, wherein the uppermost ceramic layer and the lowermost ceramic layer of the multilayer body are thicker than the ceramic layers inside the multilayer body. 8. The multilayer piezoelectric actuator according to claim 1, wherein the ceramic layers on the upper and lower surfaces of the internal electrode layer penetrate the internal electrode and are integrated. 9. The multilayer piezoelectric actuator according to claim 1, wherein the internal electrode layer is formed using a metal paste containing 20 wt% or more of a metal component of a ceramic material for forming the ceramic layer.