JP2994492B2 - Multilayer piezoelectric actuator and method of manufacturing the same - Google Patents

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 a method of manufacturing the same, and more particularly, to a piezoelectric actuator having a portion for relaxing insulation and internal stress when alternately connecting internal electrodes and external electrodes alternately. And a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 5, a ceramic laminated element 10 such as a laminated ceramic capacitor generally has a ceramic layer 11 and an internal electrode layer 12 alternately laminated, and an internal electrode layer 12 and an external electrode 14 are formed. It is structured to connect every other layer. At the same time, in the case of a multilayer piezoelectric actuator element, if the structure shown in FIG.
Since the internal stress is generated in the ceramic layer 11 to which the second electrode 2 and the external electrode 14 are not connected, the displacement amount is restricted. In addition, since stress is concentrated on the portion of the ceramic layer 11 that is not connected, there is a problem that a crack is formed.

For this reason, in a laminated piezoelectric actuator element 20, a piezoelectric ceramic layer 21 and an internal electrode layer 22 are generally alternately laminated as shown in FIG. Has been proposed. In such a method, as can be understood from FIG. 6, in the multilayer piezoelectric actuator element 20, an insulator 25 is formed every other layer on the internal electrode layer 22 exposed on the side surface before forming the external electrode 24. There is a need.

Conventionally, such an insulator 25 is formed by an electrophoresis method or a screen printing method. However, in any of the methods, if the interval between the internal electrode layers of the laminate is smaller than about 70 microns, it becomes impossible to form an insulator. On the other hand, if the multilayer piezoelectric actuator element is downsized and driven at a low voltage, the interval between the internal electrode layers of the multilayer body needs to be 70 μm or less. There is a need for a method that can securely connect every other layer.

[0005]

In order to solve the above-mentioned problems, a conductor paste for internal electrodes is printed on the ceramic green sheets to be laminated, and when the internal electrodes and the external electrodes are connected one by one, A method of simultaneously printing and laminating a carbon paste for forming pores for maintaining insulation between an internal electrode and an external electrode which are not connected is disclosed in, for example, JP-A-61-142780 and JP-A-62-24747.
No. 5, JP-A-63-174380.

In these methods, as a method for maintaining the insulation between the internal electrodes and the external electrodes, instead of providing an insulator outside the piezoelectric actuator element as shown in FIG. This is a method in which insulating portions are provided inside the actuator element, and these insulating portions are vacated to fill the insulator. However, in the method of providing such holes, when the thickness of the ceramic layer is as thin as 100 μm or less, there is a problem that the holes are fused at the time of firing, and the side surface on which the holes are provided becomes brittle. And other problems.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a laminated piezoelectric actuator made by laminating and integrally sintering green sheets in order to solve such a conventional problem. And a method of manufacturing the same. In particular, the internal electrode spacing is 7
Ultra-compact laminated piezoelectric actuator of 0 μm or less, laminated piezoelectric actuator in which internal electrode layers and external electrode layers are connected alternately even in a laminated sintered body having an internal electrode lamination interval of 70 μm or less, and method of manufacturing the same Is to provide.

[0008]

Therefore, in order to achieve the above-mentioned object, according to the present invention, a laminated piezoelectric actuator comprises a piezoelectric ceramic layer and an internal electrode layer alternately laminated, and the internal electrode layer is formed of an external electrode layer. In a laminated piezoelectric actuator connected to every other electrode, a portion for maintaining insulation between the external electrode and the internal electrode layer and relaxing internal stress between an end of the internal electrode layer not connected to the external electrode and the external electrode. Is formed separately from the piezoelectric ceramics layer to maintain this insulation.
In addition, the portion that relieves internal stress is formed of lead titanate that breaks down into fine particles due to phase transition in the process of cooling after sintering.

Further, according to the present invention, a method of manufacturing a laminated piezoelectric actuator is provided in which a conductor paste is printed on each of a plurality of piezoelectric ceramic green sheets to form internal electrode layers, and the temperature is reduced after sintering. An insulating paste consisting of an insulator mainly composed of lead titanate, which is degraded into fine particles by phase transition, is printed so as to be adjacent to the conductor paste, and these piezoelectric ceramic green sheets are printed on the insulating paste. Laminated so as to be located alternately, crimping, degreasing, firing to form a laminated sintered body,
An external electrode is formed on a side surface of the laminated sintered body, and the internal electrode layer and the external electrode are connected alternately.

[0010] Lead titanate (PbTiO ₃ ) is used as lead zirconate titanate (PbTiO ₃ ) used in a multilayer piezoelectric actuator.
It is a perovskite compound similar to ZT) and has a Curie temperature around 500 ° C. Pure lead titanate
Even when sintering at high temperatures, the change in axial ratio due to the phase transition that occurs when passing through the Curie temperature around 500 ° C is large,
A large internal stress is generated, it is broken finely and does not sinter.
The present invention focuses on this phenomenon, and is configured by using lead titanate as a portion for relaxing the insulation and internal stress on the non-connected side when connecting the internal electrode to the external electrode every other layer. I have.

That is, lead titanate used as a portion for relaxing insulation and internal stress is a compound having the same perovskite-type crystal structure as lead zirconate titanate in a ceramic layer which induces displacement. As the part to relax, familiarity with the ceramic layer is good. In addition, in the process of raising the temperature during firing, the ceramic layer is sintered in the same manner as lead zirconate titanate (PZT), and in the process of lowering the temperature during firing, it is refined by a phase transition at a Curie point around 500 ° C. This is based on characteristics. Since the formed insulation and the part that relieves internal stress contain lead titanate that breaks down into fine particles due to phase transition in the process of cooling after sintering, it shows sufficient insulation, and voltage is applied to the laminated piezoelectric actuator. Does not restrict displacement when applied, and it is possible to prevent a crack in the laminated piezoelectric actuator element due to stress concentration at the time of displacement.

As described above, most of the ceramics for inducing displacement used in the multilayer piezoelectric actuator element are lead zirconate titanate compounds having a perovskite structure. This compound contains lead (Pb) at the A site, but if the lead atmosphere is not adjusted during firing, there is a problem that the lead at the A site evaporates and adversely affects the properties of the ceramic. Therefore, in the present invention, the lead titanate used for the portion for relaxing the insulation and the internal stress is also the same perovskite compound in that respect, and the lead is contained in the A site, so that the evaporation of the lead in the ceramic layer is suppressed. I can do it. In addition, lead titanate is a stable compound among lead compounds, particularly as compared with lead zirconate titanate (PZT) which induces displacement.
There is little adverse effect on the property of inducing displacement by reacting with the ceramic layer.

The lead titanate used as a portion for relaxing insulation and internal stress must not react with the piezoelectric ceramics which induces displacement during firing, and the phase in the cooling process after sintering. Desirably, the purity is such that the change in axial ratio occurs sufficiently so that crushing due to displacement occurs. For this purpose, it is important that the lead titanate has high purity and is sufficiently crystallized.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The laminated piezoelectric actuator of the present invention and a method of manufacturing the same will be described in more detail with reference to the drawings. First, Pb (Zr, Ti) which is suitable as a material for a laminated piezoelectric actuator that can be integrally fired
A composite perovskite compound is added as a third component to O ₃ , and the ceramic powder modified with strontium is pulverized with a sand mill to a particle size of 1 μm or less. A binder, a dispersing agent, an activator, and an antifoaming agent are added to the pulverized powder, followed by vacuum defoaming, and then a green sheet is produced using a doctor blade method. The thickness of the obtained green sheet was 55 microns. An internal electrode layer 5 of platinum was printed on the green sheet 4 using a screen printing method (FIG. 1). Next, an insulating paste made of lead titanate, that is, a portion 6 for relaxing insulation and internal stress is printed on the same green sheet 4 so as to be adjacent to the internal electrode layer 5 (FIG. 2). The portion 6 made of this insulating paste for relaxing the insulation and internal stress is 99.9%
Solid content (70% by weight), and ethyl cellulose as a binder, butyl carbitol,
α-Tervineol is used as a solvent. It is necessary to determine the printing thickness of the portion 6 where the insulation of the insulating paste and the internal stress are relieved in consideration of the printing thickness of the internal electrode layer 5. That is, the thickness must be the same when the laminate is sintered. If there is a difference in thickness at the time of lamination and pressure bonding or sintering, it causes delamination and cracks. In the illustrated example, the paste printing thickness of the internal electrode layer 5 was 18 μm, and the insulating paste printing thickness of the portion 6 for relaxing the insulation and internal stress was 8 μm. Next, 30 green sheets on which the internal electrode layer 5 has not been printed and 120 green sheets on which a portion composed of the internal electrode layer and lead titanate have been printed are used.
Sheets, and further, 30 sheets of the green sheet on which the internal electrode layer is not printed are laminated, heat-pressed, and degreased.
It was fired at 00 ° C. to obtain a laminated sintered body 2 as shown in FIG. The thickness of the ceramic layer 3 of the laminated sintered body 2 is 25
The thickness of the portion composed of the internal electrode layer 5 and the lead titanate, that is, the portion 6 for relaxing insulation and internal stress was 5 μm.

Next, the four side surfaces of the laminated sintered body 2 are polished to form a portion composed of the internal electrode layer 5 and lead titanate,
That is, the external electrodes 7 are formed by baking silver paste on the exposed opposite side surfaces of the portions 6 for relaxing the insulation and internal stress. A lead wire is soldered to the external electrode 7, and a sheath is applied to the external electrode 7 so as to have a width 2 × a diameter 3 × height 5 mm as shown in FIG.
Was obtained.

The insulation resistance of the laminated piezoelectric actuator element manufactured as described above was measured to be 100 MΩ or more, indicating that the element was sufficiently insulated. When the displacement was measured, the laminated piezoelectric actuator element was displaced by 3 μm or more at 70 V. It turned out that it functions sufficiently as an actuator element. Also,
70V to The multilayer piezoelectric actuator device, by applying a sine wave voltage of 1kHz to drive the multilayer piezoelectric actuator device was subjected to life test, be displaced 10 ⁸ times without causing destruction also sufficiently durable It was understood that there was.

[0017]

As described above, in the laminated piezoelectric actuator manufactured according to the present invention, 70
Even in the case of a laminated sintered body with an internal electrode spacing of less than μm, the internal electrode layer and the external electrode layer can be connected securely every other layer, and a small, low voltage drive laminate with an internal electrode spacing of 70 μm or less The effect that a piezoelectric actuator element can be manufactured can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a first stage of a manufacturing process of a multilayer piezoelectric actuator of the present invention.

FIG. 2 is an explanatory view showing a second stage of the manufacturing process according to the present invention.

FIG. 3 is an explanatory view showing a third stage of the manufacturing process according to the present invention.

FIG. 4 is an explanatory view showing a final fourth stage of the manufacturing process according to the present invention.

FIG. 5 is an explanatory view showing an example of a conventional laminated piezoelectric actuator element.

FIG. 6 is an explanatory view showing another example of a conventional laminated piezoelectric actuator element.

[Description of Signs] 1 Multilayer piezoelectric actuator element 2 Multilayer sintered body 3 Ceramic layer 4 Green sheet 5 Internal electrode layer 6 Insulation and internal stress relaxing portion 7 External electrode

Claims (2)

(57) [Claims] In a laminated piezoelectric actuator in which a piezoelectric ceramic layer and an internal electrode layer are alternately laminated, and the internal electrode layer is connected to an external electrode every other layer, an end of the internal electrode layer not connected to the external electrode and an external electrode are connected. A portion for maintaining insulation between the external electrode and the internal electrode layer and relaxing internal stress between the electrode and the electrode is formed separately from the piezoelectric ceramic layer.
Wherein the portion for maintaining internal stress and relaxing internal stress is formed of lead titanate which breaks down into fine particles due to a phase transition in a cooling process after sintering. 2. A conductive paste is printed on each of a plurality of piezoelectric ceramic green sheets to form an internal electrode layer, and lead titanate having a purity that collapses into fine particles due to a phase transition during a cooling process after sintering is mainly used. Printing an insulating paste made of an insulator to be adjacent to the conductor paste,
The plurality of piezoelectric ceramic green sheets are laminated so that the printed portions of the insulating paste are alternately positioned, pressed, degreased, and fired to form a laminated sintered body, and external electrodes are formed on the side surfaces of the laminated sintered body. A method for manufacturing a laminated piezoelectric actuator, comprising forming and connecting an internal electrode layer and an external electrode every other layer.