JPH09162451A - Piezo-electric multilayered body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent migration without reducing the displacement. SOLUTION: An internal electrode layer 11 comprises an outer circumferential electrode 12 which is formed around the outer periphery of a substrate 10 and an inner circumferential electrode 13 which is formed on the inner circumferential side of the electrode 12, and the electrode 12 is made of conductive material superior in migration resistance than that of the electrode 13. Thanks to the electrode 12, the electrode 13 is sealed to prevent the entry of moisture and prevent migration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric laminate used as a piezoelectric actuator utilizing a piezoelectric effect, and more particularly to a technique for preventing migration of internal electrode layers.

[0002]

2. Description of the Related Art In recent years, instead of an actuator utilizing electromagnetic force, for example, Japanese Patent Laid-Open No. 62-291187,
As disclosed in Japanese Utility Model Application Laid-Open No. 64-30865, piezoelectric actuators utilizing the piezoelectric effect are widely used. Since this piezoelectric actuator generates little heat, and is small in size and can be driven at high speed, it is very promising as various mechanical drive elements. However, the mechanical displacement due to the piezoelectric effect is essentially extremely small, so in order to obtain a large amount of displacement, multiple piezoelectric plates or multiple piezoelectric plates and electrode plates were alternately laminated and covered with an insulating protective layer. It is provided as a piezoelectric laminate having a structure.

When the piezoelectric plates or the piezoelectric plates and the electrode plates are alternately laminated, it is desirable to bond the piezoelectric plates to each other or the piezoelectric plates and the electrode plates to each other in order to prevent positional displacement. It is also desired that the bond ensure electrical continuity. Therefore, Japanese Patent Application Laid-Open No. 60-121784 discloses a piezoelectric laminate in which a conductive silver paste or the like is interposed between a piezoelectric plate and an electrode plate and the bonding force of the paste is used to bond the piezoelectric laminate.

That is, for example, silver paste is attached to the entire surfaces of both surfaces of the piezoelectric plates by screen printing or the like to form internal electrode layers, and the piezoelectric plates are alternately laminated or alternately laminated with heating and heating. Press. As a result, the glass component in the silver paste melts and functions as an adhesive, and the piezoelectric plates are bonded together or the piezoelectric plate and the electrode plate are integrally bonded, and electrical conduction is secured.

[0005]

However, in the internal electrode layer formed of the silver paste, silver is likely to be ionized due to the presence of water and electrolytically deposited by an applied voltage, which is so-called migration which causes a short circuit due to movement by an electric field. There is a problem that it easily occurs. In order to prevent such a problem, it is conceivable to use a metal such as gold (Au) or platinum (Pt), which is hard to ionize and has excellent conductivity, as the material of the internal electrode layer. However, since these precious metals are expensive, the cost of the piezoelectric laminate increases, which is not practical. Also, if various silver alloys are used instead of pure silver, it becomes difficult to ionize, but the electrical characteristics are deteriorated, which causes a decrease in the displacement amount of the piezoelectric laminate.

The present invention has been made in view of such circumstances, and an object thereof is to prevent migration without a decrease in displacement amount.

[0007]

A feature of a piezoelectric laminate of the present invention that solves the above-mentioned problems is that a piezoelectric laminate is formed by laminating a plurality of piezoelectric plates, and the piezoelectric plate is a substrate made of a piezoelectric substance.
An internal electrode layer formed on at least one surface of the base body, the internal electrode layer consisting of an outer peripheral electrode formed on the outer peripheral edge of the base body and an inner peripheral electrode formed on the inner peripheral side of the outer peripheral electrode, The outer peripheral electrode is formed of a conductive material having higher migration resistance than the inner peripheral electrode.

The piezoelectric laminate according to the second aspect of the present invention is further characterized in that in the above piezoelectric laminate, the outer peripheral electrode contains a glass component, and the outer peripheral edge of the substrate is bonded to an adjacent material by heating during lamination. The inner electrode is sealed.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The piezoelectric laminate of the present invention can be formed by laminating a plurality of piezoelectric plates or by alternately laminating piezoelectric plates and electrode plates. Further, the internal electrode layers are formed on both surfaces of the piezoelectric body in the middle portion of the piezoelectric laminate, but are generally formed on only one surface at both end portions.

The piezoelectric plate is composed of a substrate and an internal electrode layer.
The body is made of a piezoelectric material that is distorted or stressed by the application of voltage.
Has been established. For example, PbT having a perovskite crystal structure
iO _Three-PbZrO_Three(PZT) -based solid solution, BaTi
O_ThreeAnd PbTiO_ThreeOr CaTiO_ThreeSuch as a solid solution with
Disc-shaped, made from piezoelectric ceramics
Similar ones are used.

The internal electrode layer is composed of an outer peripheral electrode and an inner peripheral electrode. Of these, the inner peripheral electrode occupies most of the surface area on one side of the substrate and must function as an internal electrode. Therefore, in order to secure the displacement amount as the piezoelectric laminated body,
It is necessary to use a material having excellent conductivity such as silver. The outer peripheral electrode is formed in a ring shape on the outer peripheral portion of the base body on the outer peripheral portion of the inner peripheral electrode, and is made of a conductive material having a higher migration resistance than the inner peripheral electrode. The conductive material forming the outer peripheral electrode is relatively selected according to the material of the conductive material forming the inner peripheral electrode. For example, when the inner peripheral electrode is made of silver, it is preferable to use a material having excellent conductivity after silver, such as a silver-palladium alloy, which has excellent migration resistance. As such a conductive material having excellent migration resistance, gold, platinum, etc. can be used if cost is ignored.

It is desirable that the outer peripheral electrode has a width (difference between the outer diameter and the inner diameter) as small as possible within a range in which migration of the inner peripheral electrode can be prevented. When the width of the outer peripheral electrode increases, the displacement amount of the piezoelectric laminate may decrease.
For example, when the outer peripheral electrode is made of Ag-Pd,
The width of the outer peripheral electrode is preferably 2 mm or less. The peripheral electrode preferably contains a glass component. By doing so, the glass components are melted when laminated and heated, and the opposing piezoelectric plates or the piezoelectric plates and the electrode plate are bonded in a ring shape. As a result, the inner peripheral electrode inside is sealed from moisture, and migration can be further prevented.

That is, in the piezoelectric laminate of the present invention, since the outer peripheral electrode having excellent migration resistance is exposed on the outer peripheral surface of the piezoelectric plate, migration is prevented.
If the outer peripheral electrode contains a glass component and the piezoelectric plates or the piezoelectric plate and the electrode plate, or the piezoelectric plate and the insulator are respectively joined in a ring shape, the inner peripheral electrode is reliably sealed from moisture, and thus migration resistance Is further improved.

[0014]

The present invention will be specifically described below with reference to examples. (Embodiment 1) FIGS. 1 and 2 show a piezoelectric laminate of this embodiment. This piezoelectric laminated body is a junction type PZT actuator, and is mainly composed of a plurality of laminated piezoelectric plates 1 and insulators 2, a pair of strip-shaped external electrodes 3, 3 ′, a silicon grease 4 and an insulating tube 5. ing.

As shown in FIG. 3, the piezoelectric plate 1 is composed of a base 10 made of a piezoelectric material and an internal electrode layer 11 having a thickness of about 5 μm formed on both front and back surfaces of the base 10. Of these, the substrate 10 is formed of PZT in a disk shape having a diameter of 16 mm and a thickness of 0.5 mm, and has a piezoelectric constant (d ₃₃ ) of 550 ×.
It has a characteristic of 10 ⁻¹² m / V. In addition, the internal electrode layer 1
Reference numeral 1 denotes a ring-shaped member formed on the outer peripheral edge of the base body 10 and has a width 1
The outer peripheral electrode 12 has a diameter of 15 mm and a circular inner peripheral electrode 13 having a diameter of 15 mm is formed on the inner peripheral side of the outer peripheral electrode 12 occupying most of the surface area of the substrate 10. Peripheral electrode 1
2 is formed from a paste containing a silver-palladium (Ag-Pd) alloy having excellent oxidation resistance and migration resistance and a glass component, and the inner peripheral electrode 13 is made of silver (Ag).
And a paste containing a glass component.

58 piezoelectric plates 1 are laminated, and insulators 2 are arranged at both ends thereof. As shown in FIG. 4, this insulator 2 is made up of a base body 20 similar to the piezoelectric plate 1 except that it has a thickness of 2.5 mm. An inner electrode layer 21 having an inner peripheral electrode 23 and a thickness of about 5 μm is formed. The two insulators 2 are laminated such that the surface having the internal electrode layers 21 faces the piezoelectric plate 1.

A pair of external electrodes 3, 3'in the form of strips are formed on the side peripheral surface of the laminated piezoelectric plates so as to face each other 180 degrees apart in the circumferential direction and extend parallel to the central axis. Inside the external electrode 3, an insulating layer 30 made of an epoxy resin-based insulating material is formed at every other exposed portion of the internal electrode layer 11.
Inside the outer electrode 3'on the opposite side of 180 degrees, the insulating layer 30
In the exposed portion of the internal electrode layer 11 in which the layers are not formed, every other similar insulating layer 30 ′ is formed. Further, one ends of lead wires 31, 31 'extending to the outside are connected to the external electrodes 3, 3', respectively.

Silicon grease 4 is applied to the entire side surface, and the surface thereof is covered with an insulating tube 5 contracted by heat contraction. Next, two types of methods for manufacturing the piezoelectric laminate will be described. First, the first manufacturing method will be described with reference to FIG. <Manufacturing Method 1> First, a preformed substrate 10 having a diameter of 17 mm and a substrate 20 are prepared and thoroughly washed with ethanol or acetone (step 101). Next, using paste A containing Ag powder as a conductive component and containing about 40% by weight of a glass component, the inner peripheral electrodes 13 and 23 are printed on both surfaces of the base 10 and one surface of the base 20 by screen printing and dried. . Next, using the paste B containing Ag-Pd powder as a conductive component and containing about 40% by weight of a glass component, the outer peripheral electrodes 12 and 22 were printed on both surfaces of the base 10 and one surface of the base 20 by screen printing and dried. The internal electrode layers 11 and 21 are thereby formed (steps 102 to 10).
5).

A plurality of (58) piezoelectric plates 1 are laminated, and insulators 2 are arranged at both ends of the laminated body. The insulators 2 are arranged so that the internal electrode layers 21 face the piezoelectric plate 1 (step 106). Next, the laminated body is placed in an electric furnace and heat-treated at 600 ° C. for 15 minutes while being pressed from both sides in the axial direction to be pressure-bonded (step 107). After that, the outer diameter is set to 16 mm and the axial length is set to 34 mm by grinding (steps 108 to 109).

An epoxy resin-based insulating seal is used, and every other internal electrode layer 11 or 21 exposed on the side circumferential surface is approximately 8 mm in the circumferential direction and is collinear in the axial direction. To apply. Further, the laminated body was inverted by 180 degrees, and the internal electrode layer 1 on which the insulating material was not applied first
Insulating seals are similarly applied to 1 and 21. Then 150
The insulating layers 30 and 30 'were formed by heating at 30 ° C. for 30 minutes (step 110).

Next, an Ag paste having an epoxy resin as a binder is applied so as to connect the insulating layer 30 and at the opposite side of 180 degrees, so as to connect the insulating layer 30 '. After arranging 31 ′, it was baked at 150 ° C. for 30 minutes to form the external electrodes 3 and 3 ′ (steps 111 to 113). Then, silicon grease 4 was applied to the entire side surface to perform moisture-proof treatment, and a heat-shrinkable tube was covered and heated to shrink the insulating tube 5. Then, a high voltage was applied to carry out polarization treatment to obtain a piezoelectric laminate of this example (step 11).
4-116). <Manufacturing Method 2> Next, another manufacturing method will be described with reference to FIGS.

First, a preformed substrate 1 having a diameter of 17 mm
0 and the substrate 20 are prepared and thoroughly washed with ethanol or acetone (step 201). Next, using paste A containing Ag powder as a conductive component and containing about 40% by weight of a glass component, as shown in FIGS.
The internal electrode 6 is printed on the entire surface of one of the No. 0 by screen printing and dried (steps 202 to 203). Then, a plurality of (58) piezoelectric plates 1 are laminated, and the insulators 2 are arranged at both ends of the laminated body. The insulator 2 is arranged so that the internal electrode layer 21 faces the piezoelectric plate 1 (step 204).

Next, the above-mentioned laminated body was put into an electric furnace, and while being pressed from both sides in the axial direction, it was heat-treated at 600 ° C. for 15 minutes and pressure-bonded. After that, the outer diameter was set to 16.2 mm and the axial length was set to 34 mm by grinding (steps 205 to 2).
06). Then the crimped laminate shown in FIG. 8 H ₂ O ₂ /
The electrode layer 6 is immersed in an NH ₃ mixed aqueous solution to remove the outer peripheral portion thereof to form a gap 60 as shown in FIG. 9, and then is washed and dried (steps 207 to 208). As a result, the inner peripheral electrodes 13 and 23 are formed.

Thereafter, the gap 60 is filled with a paste B containing Ag-Pd powder as a main component and containing about 40% by weight of a glass component, and baked to burn the outer peripheral electrodes 12, as shown in FIG.
22 is formed. Then, the paste B attached to the outer peripheral surface is removed by grinding and the outer diameter is set to 16 mm (steps 209 to 210). The subsequent steps (steps 211 to 218) are the same as step 109 of manufacturing method 1.
The description is omitted because it is exactly the same as that of steps 1 to 116. (Example 2) Instead of Ag-Pd paste, platinum (P
Pt containing t) as a conductive component and about 25% by weight of a glass component
The configuration is the same as that of the first embodiment except that the outer peripheral electrodes 12 and 22 are formed using a paste. (Example 3) Instead of the Ag-Pd paste, gold (A
Au containing u) as a conductive component and about 30% by weight of a glass component
The configuration is the same as that of the first embodiment except that the outer peripheral electrodes 12 and 22 are formed using a paste. (Performance Evaluation) In the above-mentioned four types of piezoelectric laminates, various piezoelectric laminates were prepared by changing the diameter dimension of the inner peripheral electrodes 13 and 23 from 0 to 16 mm, and the displacement characteristics of each were investigated. The result is shown in FIG. The investigation of displacement characteristics
The measurement was performed by measuring the displacement amount when a voltage of 600 V was applied to each piezoelectric laminate.

From FIG. 12, in the case of Pt and Au, even if the dimensions of the outer peripheral electrodes 12 and 22 are changed, the displacement amount is not affected at all, but in the case of a relatively inexpensive Ag-Pd paste, the inner periphery is changed. When the diameter of the electrodes 13 and 23 is smaller than 14 mm, the displacement characteristic is greatly reduced. Therefore, the outer peripheral electrodes 12, 23
When Ag-Pd paste is used as above, it is preferable that the diameters of the inner peripheral electrodes 13 and 23 be 14 mm or more.

Next, the diameter of the inner peripheral electrodes 13 and 23 is 15 m.
m, and Ag electrodes on the entire surface (inner peripheral electrodes 13, 2
3 having a diameter of 16 mm) was examined for durability. For durability, operating voltage is 600V, 700V,
Select three levels of 800V and repeat ON-OFF,
The number of repetitions until migration occurred was measured. FIG. 13 shows the results.

From FIG. 13, it can be seen that when the entire surface is an Ag electrode, migration occurs in a short period of time, and the higher the operating voltage, the earlier the migration occurs. However, in other cases, migration hardly occurred even after the number of repetitions of 10 ⁹ times, and there was almost no difference due to the operating voltage in this characteristic, and it was confirmed that the durability was greatly improved. It is clear that this is due to the presence of the outer peripheral electrodes 12 and 22, and the outer peripheral electrodes 12 and 22 adhere to the piezoelectric plates 1 outside the inner peripheral electrodes 13 and 23 without any gap,
It is considered that this is because the inner peripheral electrodes 13, 23 are hermetically sealed, and this excellent sealing property is achieved by the outer peripheral electrode 1.
It is considered that this is because the glass components in Nos. 2 and 22 were melted at the time of stacking and heating and adhered to the piezoelectric plate 1 and the insulator 2.

[0028]

That is, according to the piezoelectric laminate of the present invention,
Since the outer peripheral electrode has excellent migration resistance, migration is prevented from occurring and the durability is excellent.
Further, since the inner peripheral electrode occupies a sufficient area, the displacement amount does not decrease.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a piezoelectric laminate according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a piezoelectric laminate according to an embodiment of the present invention, which is a cross-sectional view taken along the line AA of FIG.

FIG. 3 is a perspective view of a piezoelectric plate used in a piezoelectric laminate according to an embodiment of the present invention.

FIG. 4 is a perspective view of an insulator used in the piezoelectric laminate according to the embodiment of the invention.

FIG. 5 is a flowchart showing a method for manufacturing a piezoelectric laminate according to an embodiment of the present invention.

FIG. 6 is a perspective view of a piezoelectric plate used in another manufacturing method according to an embodiment of the present invention.

FIG. 7 is a perspective view of an insulator used in another manufacturing method according to an embodiment of the present invention.

FIG. 8 is a cross-sectional view of a laminated body in another manufacturing method according to an embodiment of the present invention.

FIG. 9 is a cross-sectional view showing a state in which the outer peripheral portion of the internal electrode layer is removed from the laminated body in another manufacturing method according to the embodiment of the present invention.

FIG. 10 is a cross-sectional view showing a state in which an outer peripheral portion of an internal electrode layer is removed from a laminated body in another manufacturing method according to an embodiment of the present invention and a paste is filled therein.

FIG. 11 is a flowchart showing another method of manufacturing the piezoelectric laminate according to the embodiment of the present invention.

FIG. 12 is a graph showing the relationship between the diameter of the inner peripheral electrode and the displacement amount.

FIG. 13 is a graph showing the relationship between the material of the outer peripheral electrode and the number of times of durability.

[Explanation of symbols]

1: Piezoelectric plate 2: Insulator
3: External electrode 4: Silicon grease 5: Insulation tube 1
0: substrate 11: internal electrode layer 12: outer electrode 1
3: Inner circumference electrode

Claims (2)

[Claims] 1. A piezoelectric laminated body formed by laminating a plurality of piezoelectric plates, wherein the piezoelectric plate comprises a base body made of a piezoelectric body and an internal electrode layer formed on at least one surface of the base body. The electrode layer is composed of an outer peripheral electrode formed on the outer peripheral edge of the base body and an inner peripheral electrode formed on the inner peripheral side of the outer peripheral electrode, and the outer peripheral electrode is a conductive material having higher migration resistance than the inner peripheral electrode. A piezoelectric laminate, which is formed of a material. 2. The outer peripheral electrode contains a glass component, and the outer peripheral edge portions of the adjacent bases are joined to each other by heating during lamination to seal the inner peripheral electrode. Piezoelectric laminate.