JP2000323762A - Piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric actuator capable of securing high migration- resistant of an insulation layer between an internal electrode and an external electrode, and further improving dielectric strength. SOLUTION: A piezoelectric actuator comprises a piezoelectric moving part consisting of a laminate alternately laminated and integrally joined by a piezoelectric element 1 and an internal electrode 2, the pairs of continued external electrodes 5 and 5 respectively arranged in the direction of lamination on an opposite flank of the piezoelectric moving part to apply an electric potential of reversed polarity to the both sides in the lamination direction of each piezoelectric element 1, the internal electrode 2 with its external edge connected to one and insulated to the other of the pairs of the external electrodes 5 and 5 every one layer, and an insulation layer 3 lying between the external edge of the internal electrode 2 and the external electrode 5. The insulation layer 3 consists of an inner layer 31 directly joined to the external edge of the internal electrode 2, and an outer layer 32 directly joined to the external electrode 5. The migration resistant to the material of an internal electrode 2 of the inner layer 31 is larger than that of the outer layer 32 and the elasticity of the outer layer 32 is lower than that of the inner layer 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator in which piezoelectric elements and internal electrodes are alternately stacked.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 1, there has been known a piezoelectric actuator in which a piezoelectric operation section 10 is constituted by a laminate in which piezoelectric elements 1 and internal electrodes 2 are alternately laminated and integrally joined. I have. This type of piezoelectric actuator has a pair of opposing external electrodes continuous in the laminating direction on the opposing side surfaces of the piezoelectric operating portion 10 in order to apply opposite potentials to both sides of the piezoelectric element 1 in the laminating direction. 5, 5 are provided, and the outer edge of the internal electrode 2 is connected every other layer to one of the pair of external electrodes 5, 5 to be insulated from the other, and the outer edge of the internal electrode 2 and the outer An insulating layer 3 interposed between the electrodes 5 and 5 is provided.

The insulating layer 3 is required to have high withstand voltage and also to have migration resistance for preventing electromigration of the internal electrode material (Ag or the like). In particular, when the operating voltage of the actuator is high,
Migration resistance becomes important. High withstand voltage,
As a typical insulating resin having excellent migration resistance, a polyimide resin is used. If a higher operating voltage is required, it is necessary to further increase the thickness of the insulating layer in order to ensure insulation in the thickness direction of the insulating layer. However, since polyimide resin also has high mechanical strength and elastic modulus, when formed thick, a large internal stress is generated due to cure shrinkage, and the insulating layer may peel off during operation of the actuator. Therefore, there is a limit in further increasing the withstand voltage while ensuring high migration resistance of the insulating layer between the internal electrode and the external electrode.

As a measure for preventing the occurrence of cracks in the insulating layer between the internal electrode and the external electrode, Japanese Patent Application Laid-Open No. 7-169999 discloses
A method has been proposed in which a stress relaxation layer directly bonded to the outer edge of an internal electrode is formed with a release agent such as a silicon-based or fluorine-based material, and an elastic epoxy resin layer is formed thereon. However, in this method, a silicon-based or fluorine-based stress relaxation layer cannot obtain high migration resistance against migration of the material of the internal electrode.

[0005]

SUMMARY OF THE INVENTION The present invention provides an internal electrode /
It is an object of the present invention to provide a piezoelectric actuator capable of securing high migration resistance of an insulating layer between external electrodes and further increasing withstand voltage.

[0006]

In order to achieve the above object, a piezoelectric actuator according to the present invention has a piezoelectric operation section composed of a laminate in which piezoelectric elements and internal electrodes are alternately laminated and integrally joined. Then, in order to apply potentials of opposite polarities to both sides of the individual piezoelectric elements in the laminating direction, a pair of external electrodes continuous in the laminating direction are provided on the opposing side surfaces of the piezoelectric operation part, and the internal electrodes are provided. The outer edge of every other layer is connected to one of the pair of external electrodes and insulated from the other,
In a piezoelectric actuator having an insulating layer interposed between the outer edge of the internal electrode and the external electrode for this insulation, the insulating layer is directly bonded to the inner layer directly connected to the outer edge of the internal electrode and directly connected to the external electrode. The inner layer has a higher migration resistance to the material of the inner electrode than the outer layer, and the outer layer has a lower elastic modulus than the inner layer.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A piezoelectric actuator according to the present invention
The insulating layer between the inner electrode and the outer electrode is composed of an inner layer directly bonded to the outer edge of the inner electrode and an outer layer directly bonded to the outer electrode. The inner layer has higher migration resistance to the material of the inner electrode than the outer layer, and the outer layer has elasticity. The ratio was lower than that of the inner layer.

When increasing the operating voltage of the actuator,
The thickness of the insulating layer required to prevent the migration of the internal electrode material may be smaller than the thickness required to ensure a withstand voltage in the thickness direction of the insulating layer. That is, migration resistance can be ensured without forming the inner layer too thick. A polyimide resin is suitable as the material of the inner layer imparting migration resistance.

On the other hand, in order to ensure a withstand voltage in the thickness direction of the insulating layer, an outer layer having a lower elastic modulus than the inner layer is formed thicker. When the cure shrinkage occurs, the internal stress generated in the low elastic material of the outer layer is smaller than the internal stress generated in the high elastic material of the inner layer. Therefore, compared to the conventional case where the entire insulating layer is formed of the same material as the inner layer, the outer layer is formed of a material having a low elastic modulus according to the present invention, thereby reducing the internal stress generated in the insulating layer due to cure shrinkage. Since the insulating layer can be prevented from peeling off during the operation of the actuator, the thickness of the insulating layer can be increased, and the withstand voltage in the insulating layer thickness direction can be increased.

[0010] In contrast to the polyimide resin having high migration resistance and forming the high elastic modulus inner layer, polyether amide resin is used as a material for forming the low elastic modulus outer layer.
Silicone resin and tetrafluoroethylene resin are suitable. Hereinafter, the present invention will be described in more detail with reference to examples.

[0011]

EXAMPLE A PZT piezoelectric element (diameter φ14 mm, thickness 0.5)
mm) and FIG. 1 with an Ag internal electrode and an Ag external electrode.
A piezoelectric actuator having a piezoelectric operation section having the structure described above was manufactured. However, as shown in Table 1, the insulating layer 3 interposed between the internal electrode 2 and the external electrode 5 had a conventional one-layer structure or a two-layer structure according to the present invention.

The insulating layer having a two-layer structure according to the present invention is, as shown in FIG. 2, an inner layer 3 in which the insulating layer 3 is directly bonded to the internal electrode.
1 and an outer layer 32 directly bonded to an external electrode. A piezoelectric actuator having a two-layer insulating layer according to the present invention was manufactured by the following procedure. First, the outer edge of the internal electrode 2 and the P on both sides thereof are placed on the side surface of the laminate of the piezoelectric element 1 and the internal electrode 2.
Apply polyimide to cover a part of ZT element surface,
After drying at 80 ° C., curing was performed at 340 ° C. to form an inner layer 31 made of a polyimide resin having a thickness of 10 μm.

Next, polyetheramide is applied so as to cover the entire inner layer 31 and dried at 80 ° C.
By curing at 80 ° C., an outer layer 32 made of a polyetheramide resin having a thickness of 20 μm was formed. Thereafter, the external electrode 5 was formed by applying, drying, and baking an Ag paste.

A conventional piezoelectric actuator having an insulating layer having a one-layer structure was formed by the following procedure. Polyimide is applied to the side surface of the laminated body of the piezoelectric element 1 and the internal electrode 2 so as to cover the outer edge of the internal electrode 2 and a part of the surface of the PZT element on both sides thereof, dried at 80 ° C., and then cured at 340 ° C. Thus, an insulating layer 3 made of a polyimide resin having a thickness of 10 μm or 20 μm was formed. After applying polyetheramide instead of polyimide and drying at 80 ° C,
By curing at 180 ° C., an insulating layer 3 made of a polyetheramide resin having a thickness of 20 μm was formed.

Thereafter, an external electrode 5 was formed by applying, drying, and baking an Ag paste. A high-temperature operation test was performed on each of the manufactured piezoelectric actuators under the following conditions. [High-temperature operation test conditions] Atmosphere: 120 ° C Applied voltage: -200 V to +400 V Frequency: 100 Hz [Evaluation item] The number of operations in which a short circuit occurred.

The test results are also shown in Table 1.

[0017]

[Table 1] As shown in Table 1, according to the present invention, a piezoelectric actuator having an insulating layer composed of an inner layer made of polyimide resin having a thickness of 10 μm and an outer layer made of polyetheramide having a thickness of 20 μm is 1 × 10 ^8. No short circuit occurred even with the number of operations.

On the other hand, short-circuit occurred in any of the conventional piezoelectric actuators having an insulating layer having a single-layer structure. That is, in Conventional Example 1, an insulating layer having a one-layer structure made of a polyimide resin having a thickness of 10 μm was formed. However, since the withstand voltage was insufficient due to an insufficient thickness of the insulating layer, the number of operations was 2 ×.
At ¹⁰⁷ times, a short circuit occurred in the path from the outer edge of the internal electrode to the external electrode through the insulating layer in the thickness direction.

[0019] Conventional Example 2 has formed the insulating layer of the one-layer structure having a thickness of 20μm of polyimide resin, since a large internal stress is generated when the polyimide cure shrinkage, in operating cycle 3 × 10 ⁷ times, the insulating layer The interface between the electrode and the outer edge of the internal electrode and the piezoelectric element on both sides peeled off, and a short circuit occurred using the peeled portion as a path. In Conventional Example 3, an insulating layer having a single-layer structure made of polyetheramide having a thickness of 20 μm was formed. However, migration resistance of Ag, which is an internal electrode material, occurred due to insufficient migration resistance of polyetheramide, and the outer edge of the internal electrode was damaged. A short circuit occurred in the path from the substrate to the external electrode through the insulating layer in the thickness direction.

As a comparative example, a combination of a polyether amide inner layer / polyimide outer layer in which the order of the constituent materials of the layers is reversed with respect to the combination of the polyimide inner layer / polyether amide outer layer according to the present invention can be assumed. However, in practice, only the sequence of curing the polyimide with the higher cure temperature first and then the polyetheramide with the lower cure temperature is feasible, and vice versa.

[0021]

As described above, according to the present invention,
Provided is a piezoelectric actuator capable of securing high migration resistance of an insulating layer between an internal electrode and an external electrode and further increasing the withstand voltage.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a piezoelectric actuator of a piezoelectric actuator.

FIG. 2 is an enlarged sectional view showing an insulating layer having a two-layer structure interposed between an internal electrode and an external electrode of a piezoelectric actuator according to the present invention, and its periphery.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 piezoelectric element 2 internal electrode (or conductive paste for forming internal electrode) 3 insulating layer 31 inner layer of insulating layer 3 32 outer layer of insulating layer 3 5 external electrode 10 piezoelectric actuator

Claims (2)

[Claims] 1. A piezoelectric actuator comprising a laminated body in which piezoelectric elements and internal electrodes are alternately laminated and integrally joined, and potentials of opposite polarities are applied to both surfaces of each of the piezoelectric elements in the laminating direction. To this end, a pair of external electrodes continuous in the laminating direction are provided on the opposing side surfaces of the piezoelectric operation section, and the internal electrodes are connected to one of the pair of external electrodes at the outer edges of the other and insulated from the other. A piezoelectric actuator having an insulating layer interposed between the outer edge of the internal electrode and the external electrode for this insulation, wherein the insulating layer is directly connected to the inner layer and the external electrode directly joined to the outer edge of the internal electrode. A piezoelectric actuator, wherein the inner layer has higher migration resistance to the material of the inner electrode than the outer layer, and the outer layer has a lower elastic modulus than the inner layer. Data. 2. The method according to claim 1, wherein the high-modulus layer is made of a polyimide resin, and the low-modulus layer is made of one selected from the group consisting of a polyetheramide resin, a silicone resin and a tetrafluoroethylene resin. The piezoelectric actuator according to claim 1, wherein