JP3227896B2 - Stacked piezoelectric body - 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 material, and more particularly to an actuator capable of controlling the generation of mechanical driving force by controlling an applied voltage.

[0002]

2. Description of the Related Art There are two general classifications of the structure of a conventional multilayer piezoelectric body: a normal type multilayer piezoelectric body and an integral firing type multilayer piezoelectric body. First, the normal type of laminated piezoelectric body is that the molded body of the piezoelectric element is fired and ground,
After the electrodes are printed thereon, they are alternately laminated with the electrode plates. However, the thickness per layer cannot be reduced due to the processing limit due to the grinding of the element at the time of manufacturing, so that driving at a higher voltage is inevitably required as compared with the integrally formed type. In addition, since the driving is performed by using a high voltage, an extra cost is required for a circuit and a measure against electric shock.

On the other hand, a monolithic firing type laminated piezoelectric material is
An electrode is printed on a ceramic green sheet, baked integrally and, if necessary, subjected to an insulation treatment, then provided with a side electrode and provided with a means for electrical connection to the outside. The feature of this integrally fired laminated piezoelectric body is that since it is integrally fired, the thickness of the piezoelectric element per layer can be reduced, so that a relatively low voltage can be used. However, degassing during firing is difficult,
If the control is not strictly performed, a defect such as a peeling occurs between the electrode and the piezoelectric element, which causes a short circuit between the electrodes, resulting in a defective product itself and a low yield.

[0004] In addition, the improvement of the side electrode extraction technology has made it possible to manufacture a monolithically fired laminated piezoelectric body having a full-surface electrode structure, eliminating the problem of an electrically inactive portion in a single element. . However, in the adjacent element to the dummy layer located at both ends of the multilayer piezoelectric element, the adjacent element undergoes expansion and contraction distortion, but the dummy layer does not undergo expansion and contraction distortion, so that the adjacent element is sheared. There is a problem that stress concentration occurs and cracks occur.

In order to solve the above-mentioned problems, Japanese Patent Publication No. Sho 63-10596 discloses that the shear stress is reduced by slightly increasing the thickness of an element layer near an end portion. The stacked piezoelectric body is equally divided so as not to be broken. Or JP-A-4-159785
Various countermeasures have been proposed, such as reducing the shear stress by giving the electrode shape of the end element a part where the conductor is not formed on a part thereof.

[0006]

However, in the above-described integrally formed type, any effect against cracking or the like due to the concentration of shear stress has been shown, but for this purpose, the elongation inherent in the element must be sacrificed. Further, the problem of crack generation due to shear stress concentration has not been essentially solved.

Accordingly, the present invention has been made in view of the above-mentioned problems, and has a problem of generation of cracks due to concentration of shear stress, despite being a monolithic firing type laminated piezoelectric material capable of using a relatively low voltage. It is an object of the present invention to provide a laminated piezoelectric body which does not sacrifice the inherent extension of the element.

[0008]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a piezoelectric element having two opposing surfaces and an internal electrode alternately stacked, and an external electrode electrically connected to every other internal electrode. A piezoelectric body having electrodes having different poles, and a side electrode plate in which the piezoelectric bodies and thin plate-shaped electrode plates are alternately laminated, and the adjacent electrode plates are electrically connected so as to have mutually different poles And a multilayer piezoelectric element characterized by having the following.

[0009]

According to the above construction, no dummy layer is formed at both ends of a piezoelectric body in which piezoelectric elements and internal electrodes are alternately stacked. Therefore, when the expansion and contraction of the piezoelectric element is controlled, there is no influence of the dummy layer, and there is no concentration of shear stress. Also,
Since the piezoelectric body and the electrode plate are not in elemental contact but are only in physical contact with each other, the concentration of shear stress is negligibly small. Therefore, cracks hardly occur due to concentration of shear stress.

Further, in the multilayer piezoelectric body of the present invention,
To prevent the occurrence of cracks due to shear stress concentration, for example,
There is no restriction to sacrifice the inherent expansion of the element by increasing the thickness of the piezoelectric element close to the dummy layer or dividing the number of layers of the integrally fired piezoelectric body by a small number of blocks. Therefore, it is possible to drive the multilayer piezoelectric body with performance closer to the original elongation. Further, since the thickness of each piezoelectric element can be reduced, the piezoelectric element can be operated at a relatively low voltage.

[0011]

As described above, the present invention solves the problem of cracking due to concentration of shear stress even though it is a monolithic firing type laminated piezoelectric body which can use a relatively low voltage. There is an excellent effect that a laminated piezoelectric body can be provided without sacrificing the inherent elongation.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an embodiment shown in the drawings. In this embodiment, a case where the present invention is applied to a laminated piezoelectric body will be described. FIG. 1 is a cross-sectional view showing a first embodiment of the present invention, and is enlarged about 7 times in the thickness direction with respect to the radial direction for easy viewing.

In FIG. 1, a laminated piezoelectric body 1 according to this embodiment is shown.
Reference numeral 0 denotes a state in which a plurality of element units 1 each having a thin plate shape of 14 × 14 × 0.5 mm and 50 internal electrode plates 2 made of stainless steel and having substantially the same shape as the element unit 1 and having a thickness of 50 μm are alternately stacked. It is composed of FIG. 2 is a front view of the internal electrode plate 2. FIG. 3 is a structural view of the multilayer piezoelectric body of the first embodiment, and the same components as those of the multilayer piezoelectric body of the first embodiment of FIG. 1 are denoted by the same reference numerals.

Here, a projection 2a is formed on the internal electrode plate 2, as shown in FIG. This projection 2a
Is bent at a right angle at a position facing the outer peripheral edge of each element unit 1 as shown in FIG.
The projections are sequentially shifted by 180 °, and the element unit 1
Are alternately stacked, and the structure is such that the protrusions 2a are in contact with every other sheet. Further, as shown in FIG. 3, side electrode plates 3 are connected by spot welding to the protruding portions 2a which are in contact with every other one, and insulators having a thickness of 1 mm are provided at both ends of the laminated internal electrode plates 2. If the dummy portions 4a and 4b are provided, the side electrode plate 3 and the element unit 1
The laminated piezoelectric body 10 having an outer dimension of 14 × 14 × 31 mm electrically connected in parallel is obtained.

Also, lead wires (not shown) are connected to the positive and negative side electrode plates 3 by soldering or caulking, and finally, the element unit 1 and the internal electrode plate 2 are connected by a heat shrink tube (not shown). Then, the dummy parts 4a and 4b are fixed. Then, by controlling the application of a voltage to the lead wire, the expansion and contraction of the laminated piezoelectric body 10 on which the element units 1 are laminated can be controlled.

Next, the element unit 1 will be described. In FIG. 1, the element unit 1 has a configuration in which PZT elements 5 each having a thickness of 100 μm and internal electrodes 6 each having a thickness of about 2.5 μm are alternately repeated five layers. Further, external electrodes 7 having a thickness of about 10 μm are applied to the side and bottom surfaces of the element unit 1, and are formed in a pair corresponding to the positive electrode and the negative electrode of the element unit 1. In FIG. 1, the internal electrodes 6 have a partial electrode structure in which every other sheet is electrically connected to the external electrodes 7 with the internal electrodes 6 slightly recessed from the side surfaces of the element unit 1.

Therefore, a method of manufacturing the element unit 1 will be described step by step as shown in FIG. First P
The calcined ZT raw material is pulverized, and PVB (polyvinyl butyral) is added to prepare a sheet. Pt paste was printed thereon as an internal electrode 6 and punched out.
It was baked at 150 ° C. Next, an Ag paste was screen-printed as the external electrode 7 and baked at 550 ° C. to obtain an element unit 1. As described above, the general integral firing method is used. However, compared to a normal integral firing type laminated piezoelectric body, there is no dummy layer located at the end face of the piezoelectric body, and a part of the side surface of the element unit 1 is provided. The external electrode 7 is exposed on the entire bottom surface.

Next, a comparison will be made between the laminated piezoelectric body 10 having the above-described structure and a conventional integrated fired laminated piezoelectric body. As a condition for driving the laminated piezoelectric body 10 manufactured in the first embodiment, for example, when used as a driving source of a fuel injection device for an automobile, under a preset load of about 500 kgf, -30 to 110 V, 100 Hz, rectangular wave To drive.

Under the above-described conditions, 100% of the conventional integrated firing type laminated piezoelectric material can be driven for about 5 minutes (3 × 10 ⁴ times) by the generation of shear stress with the dummy portion.
Cracks are formed, and some of the internal electrodes are short-circuited by the cracks, so that the electrodes cannot be driven. On the other hand, in the multi-layer piezoelectric body 10 of the present embodiment, even when driven 5 × 10 ⁸ times, the element units 1 near the dummy units 4a and 4b and the other element units 1 are not cracked.
No short circuit or the like occurred.

Although this is an integral firing type piezoelectric body, no dummy layers are formed at both ends of the element unit 1. Therefore, when the PZT element 5 is controlled to expand and contract, no concentration of shear stress occurs due to the dummy layer having no distortion of expansion and contraction. However, the stress concentration in the radial direction in the element unit 1 should remain slightly because of the partial electrode structure. Nevertheless, it is considered that the crack was not generated because the stress concentration caused by the existence of the electrode holding distance of the internal electrode 6 did not exceed the element breaking strength under the driving conditions.

Further, the laminated element unit 1 and the internal electrode plate 2 are not joined but are only in physical contact with each other. Therefore, the element unit 1 and the internal electrode plate 2 are not connected to each other. The shear stress was also negligibly small, and it is considered that no cracks occurred. Next, a second embodiment will be described below.

FIG. 5 is an enlarged sectional view showing the laminated piezoelectric body of the second embodiment. The same components as those of the laminated piezoelectric body of the first embodiment shown in FIG. 1 are denoted by the same reference numerals. . In the first embodiment, in FIG. 3, the projection 2 a of the internal electrode plate 2 is bent at a position facing the outer peripheral edge of the element unit 1, laminated, and contacted. Therefore, in the second embodiment, as shown in FIG. 5, a spacer 8 is provided between the side electrode plate 3 and the element unit 1 in order to increase the electric gap with the opposite polarity and improve the withstand voltage. The structure has been inserted. As shown in FIG. 6, the spacer 8 may be a comb-shaped insulator, and slits are formed in accordance with the pitch of the extraction portion of the internal electrode plate 2. Further, for example, S
The insulating property may be improved by completely immersing and defoaming in the i-oil or by applying Si grease or the like. Next, a third embodiment will be described as follows.

In the first embodiment, as shown in FIG. 2, the internal electrode plate 2 in which the protrusion 2a is formed at one place is laminated. However, in the third embodiment, for example, as shown in FIG. 7, two projections 9a and 9b are provided.
Are formed in such a manner that the electrode plates 9 on which are formed are laminated. Therefore, if the four sides of the multilayer piezoelectric body are fixed by spot welding, a multilayer piezoelectric body with improved holding properties can be obtained.

Further, the multilayer piezoelectric body of the present invention has the following specific effects. In the structure of the multi-layer piezoelectric body of the present invention, the driving voltage is low because the thickness per layer is small, and can be lowered to ten and several volts if the thickness is further reduced. For example, if the thickness is 10 to 15 μm, it can be used by directly connecting to 12 V, that is, a battery of an automobile. Therefore, a large-sized piezoelectric body can be driven at a low voltage, and furthermore, a multilayered piezoelectric body having an arbitrary overall length can be obtained by simply increasing the number of stacked element units according to the required amount of elongation or the like. .

In general, in the case of the integral sintering type, the larger the size is, the more difficult it is to integrally sinter and the lower the yield. However, according to the configuration of the present invention, since the thickness of the element unit is as small as 0.5 mm, degassing or the like is easy, and even if a defect occurs, the damage is small. That is, the yield increases. In the present embodiment, the element unit 1 in FIG. 1 has a structure in which the PZT elements 5 and the internal electrodes 6 are alternately repeated. However, the present invention is not limited to this.
As shown in FIG. 8, a structure in which a piezoelectric film such as DF (polyvinylidene fluoride) is provided with electrodes by vapor deposition or the like, and has a weave shape 11 may be used.

In this embodiment, the PZT element 5 is used for the element unit 1 in FIG. 1. However, the present invention is not limited to this. For example, BaTiO ₃ or an electrostrictive material such as an electrostrictive material may be used. Any material may be used if it exists. Further, the activity of the raw material is enhanced, for example, Ag-Pd
A material that can be fired at a low temperature such that an electrode can be used may be used.

Further, in this embodiment, the laminated piezoelectric body 10
Although a heat-shrinkable tube is used to hold the piezoelectric element, the present invention is not limited to this. For example, the laminated piezoelectric element may be directly resin-molded or sealed in a metal package or the like.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view illustrating a multilayer piezoelectric body according to a first embodiment.

FIG. 2 shows an electrode plate 2 constituting the multilayer piezoelectric body of the first embodiment.
FIG.

FIG. 3 is a structural diagram of a multilayer piezoelectric body of a first embodiment.

FIG. 4 is a process chart showing a method for manufacturing the element unit 1.

FIG. 5 is an enlarged cross-sectional view illustrating a multilayer piezoelectric body according to a second embodiment.

FIG. 6 is a perspective view of a spacer 8 constituting the multilayer piezoelectric body of the second embodiment.

FIG. 7 shows an electrode plate 9 constituting the multilayer piezoelectric body of the third embodiment.
FIG.

FIG. 8 is a sectional view showing an element unit shape according to another embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Element unit 2 Internal electrode plate 3 Side electrode plate 5 PZT element 6 Internal electrode 7 External electrode

Continuation of front page (72) Inventor Hirokatsu Mukai 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (56) References JP-A-4-167579 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) H01L 41/083

Claims (1)

(57) [Claims] 1. A piezoelectric element comprising: a piezoelectric element having two opposing surfaces and an internal electrode alternately stacked, and an external electrode electrically connected to every other internal electrode and having an electrode having a different pole. And a side electrode plate which is formed by alternately stacking the piezoelectric body and the thin plate-shaped electrode plates, and which are electrically connected so that the adjacent electrode plates have mutually different poles. Stacked piezoelectric body.