JPH08306979A - Multilayer piezoelectric device - Google Patents

Abstract

(57) [Abstract] [Purpose] Between piezoelectric elements that can prevent breakdown of electrical conduction due to increase in tensile stress at the end of the piezoelectric element during driving without reducing the thickness of the piezoelectric element and therefore without increasing the number of lamination steps. There is provided a laminated piezoelectric device having the connection structure described above. [Structure] A plurality of plate-shaped piezoelectric elements 6 polarized in the thickness direction are provided. Each piezoelectric element 6 has a film-shaped first end electrode 4 and a film-shaped second end electrode 5, which are connected to a main electrode integrally formed on the front surface and the back surface, respectively. Plural sheets are arranged such that the first end electrode 4 and the second end electrode 5 of the adjacent piezoelectric elements 6 are arranged so as to be continuous in the stacking direction, and the polarization directions of the adjacent piezoelectric elements 6 are opposite to each other. The piezoelectric element 6 is laminated. The end electrodes 4 and 5 in the same array that are continuous in the stacking direction of the piezoelectric elements 6 were connected by wire bonding. Further, the end surface of the piezoelectric material 1 was chamfered, and the end electrodes 4 and 5 in the same series were connected by a conductive adhesive.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated type structure in which a main electrode on the front and back surfaces of a plate-shaped piezoelectric material and an end electrode on the end surface are formed by a film forming technique, and these are stacked and integrally combined. The present invention relates to a piezoelectric device, and particularly to a piezoelectric actuator that utilizes the thickness effect.

[0002]

2. Description of the Related Art A piezoelectric device utilizing the thickness effect of a piezoelectric element relates to a method of laminating the piezoelectric element, and a single plate laminating method,
It is classified as an electrode integrated firing method. The most common single-plate stacking method is to stack plate-like piezoelectric materials and electrode plates made of thin metal plates alternately, make the polarization directions of adjacent piezoelectric materials opposite to each other, and place every other electrode plate. Each of the piezoelectric materials is connected in parallel with respect to the polarization direction by connecting the lead wire to the.

Of the conventional single plate stacking systems, the actual flat plate 4
In Japanese Patent Laid-Open No. 111770/1999, manufacturing costs are reduced by eliminating the need for an electrode plate to be overlaid on each layer and by eliminating the work of connecting lead wires, and there is a problem in characteristics due to the presence of a thick electrode plate. For the purpose of improving the points, as shown in FIG. 13, a piezoelectric material 1 having a plate shape is formed.
Main electrodes 2 and 3 are formed on the front and back surfaces, and a first end electrode 4 connected to the main electrode 2 on the front surface is formed on a part of the end surface of the piezoelectric material 1. A second end electrode 5 connected to the main electrode 3 on the back surface is provided at a position different from the partial electrode 4, and the first end electrode 4 and the second end electrode 5 are each provided with a piezoelectric material. Piezoelectric element 6 is formed by providing wraparound electrodes 4a and 5a on the back and front surfaces of material 1, and these wraparound electrodes 4a and 5a are stacked so that the polarization directions are alternately opposite to each other, and the piezoelectric elements are connected in parallel. The intended one is disclosed. In the figure, 6A and 6B are end piezoelectric elements stacked on the upper and lower end portions of a laminated body formed by stacking a plurality of sheets, 7 and 8 are electrode plates having signal terminals 7a and 8a, and 9 and 10 are end portions. The insulating plate 11 is an insulating resin that integrates these laminated bodies. The arrows in the piezoelectric elements 6, 6A and 6B indicate the polarization directions of the piezoelectric materials 1.

In the above structure, the wraparound electrode 4a,
It is difficult to guarantee the connection between the electrodes only by the contact between the electrodes 5a. In particular, when it is used for an actuator application that requires a large strain in the thickness direction, it is difficult to guarantee the connection between the wraparound electrodes 4a, 5a. That is, since a high voltage is applied between the main electrodes 2 and 3 on the front and back surfaces of the piezoelectric material 1, in order to ensure sufficient insulation between the two main electrodes 2 and 3, the main electrode 2 (or 3) on one surface and A sufficient gap G is required between the end electrode 5 (or 4) attached to the main electrode 3 (or 2) on the other surface and the wraparound electrode 5a (or 4a). Therefore, the peripheral portions of the end electrodes 4 and 5 deviate from the regions where the two main electrodes 2 and 3 of the piezoelectric element 6 project from each other, and the peripheral portion of the piezoelectric element 6 does not expand or contract as much as the central portion. Therefore, when driven as an actuator, a submicron-order gap is generated in the contact portion between the wraparound electrodes 4a, 5a, and the connection cannot be made.

Therefore, the end electrodes 4 belonging to the same array,
In order to ensure the connection between the five, as shown in FIG. 13, a conductive adhesive 12 having some flexibility is applied.

On the other hand, in the above-mentioned electrode integral firing system, a piezoelectric element and an electrode are integrated by firing a laminate of green sheets of piezoelectric material before firing and electrode materials which are alternately laminated. It constitutes a laminated body.

[0007]

In the electrode-integrated firing type laminated piezoelectric device, the thickness of each laminated sheet cannot be used. Therefore, the thickness of each layer becomes thin, and the laminated piezoelectric device is driven at a low voltage. Although it is suitable as an actuator, it is unsuitable for obtaining a large-sized one and has a high capacity, and therefore is unsuitable for high-speed response. Further, when trying to obtain a large displacement under high pressure (under high load), it is also disadvantageous in terms of mechanical strength.

On the other hand, the above-mentioned single-plate laminated type is unsuitable for low voltage driving because the chip made of each piezoelectric material becomes thicker than that by the sheet method, but in the application capable of high voltage driving, , Rather large and fast response is obtained,
It is characterized in that it is easy to obtain an actuator with high mechanical strength that can withstand use under high pressure. However, in the case where the electrodes 2 to 5 are not formed on the piezoelectric material 1 by a film but the electrode plate and the piezoelectric material are stacked, as described above, the number of stacked layers is, for example, several tens to one hundred and several tens. In many cases,
There is a problem that the stacking work becomes complicated and the number of lead wire connecting steps also increases.

A laminated piezoelectric device having a single-plate laminated structure without the electrode plates of the respective layers as shown in FIG. 13 is constructed to have a height of 50 mm to 80 mm, for example, -2.
Pulse driving is continuously performed at a high voltage of 00 V to 500 V, and a large displacement of, for example, −50 μm to 80 μm is set to 100, for example.
In applications to be obtained in ^{kgf / cm 2 ~200kgf / cm 2} , stretching stress of reliability on negligible magnitude is applied to the conductive adhesive 12 which connects the end electrodes 4 and 5 in the same sequence .

FIG. 14 schematically shows the situation.
Now, as shown in FIG. 14A, when a voltage is applied by the thickness t of the piezoelectric element 6, as shown in FIG. There will be different strain between the area sandwiched between the main electrodes) and the periphery,
Although it depends on the ratio between the gap G and the thickness t of the piezoelectric element 6, the thickness of the piezoelectric element 6 hardly changes at the end, so that the piezoelectric element 6 is connected to the conductive adhesive 12 connecting the ends of the piezoelectric element 6. A strain similar to the displacement Δt of is generated. As a result, tensile stress is intensively generated in the portion e connecting the ends of the piezoelectric element 6. If the thickness of each piezoelectric element of the actuator is about 0.5 mm, the displacement Δt is on the order of submicrons.

The conductive adhesive 12 is required to absorb this tensile stress and to have the flexibility not to restrain the displacement Δt of the piezoelectric element 6. However, under the above-mentioned use, the piezoelectric element 6 is not yet used. It is not possible to completely prevent the occurrence of cracks in the portion connecting the ends of the.

As one measure to alleviate the tensile stress, it is conceivable to reduce the strain Δt by reducing the thickness t per layer of the piezoelectric element 6, but this measure is advantageous for the following reasons. I don't think so. Theoretically, in the laminated piezoelectric device having the same height and the same material, the obtained displacement is limited to the same regardless of the thickness t or the number of the laminated piezoelectric elements 6. That is, the piezoelectric element 6
If the thickness per layer is halved, the number of laminated layers is required to be doubled, and the electric field that can be applied is limited by the material of the piezoelectric element 6, so the applied voltage must also be halved. The resulting displacement will not change.

Therefore, in the case where the high voltage can be used, increasing the thickness per layer of the piezoelectric element 6 to reduce the number of laminated layers is obviously advantageous in terms of manufacturing cost in order to reduce the number of steps. In addition, it is possible to avoid a problem in characteristics due to an increase in the number of layers (for example, a problem in that the load bearing characteristic is deteriorated when the number of layers increases).

In view of the above-mentioned problems, the present invention eliminates the breakage of electrical conduction due to an increase in tensile stress at the end of the piezoelectric element during driving without reducing the thickness of the piezoelectric element, and thus without increasing the number of lamination steps. An object of the present invention is to provide a laminated piezoelectric device having a connection structure between piezoelectric elements that can be prevented.

[0015]

The present invention comprises a plurality of plate-shaped piezoelectric elements polarized in the thickness direction, and each piezoelectric element has a film-shaped main electrode formed on the front and back surfaces of a molded plate-shaped piezoelectric material. And has a film-shaped first end electrode and a second end electrode formed on the end surface of the piezoelectric material by being connected to the main electrodes formed on the front surface and the back surface of the piezoelectric material, respectively. , A plurality of piezoelectric elements in which first end electrodes and second end electrodes of adjacent piezoelectric elements are arranged so as to be continuous in the stacking direction, and the polarization directions of the adjacent piezoelectric elements are opposite to each other Are laminated and the end electrodes in the same array are connected by wire bonding.

Further, the present invention is characterized in that the outer peripheral portion of the piezoelectric material is chamfered, and the end electrodes in the same array are connected by a conductive adhesive.

[0017]

Operation: The connection structure by wire bonding of the present invention,
That is, in the structure in which the end electrodes in the same series are connected by wire bonding, the wire is welded to the narrow area of the end, and the element displacement hardly occurs at the end, so when the piezoelectric device is driven. , No extra stress is applied to the welded part of the wire end electrode. Further, since the wire has sufficient flexibility to absorb a minute displacement, the displacement of the wire welding portion is absorbed by the bending of the wire, and the tensile stress due to the wire is not generated in the welding portion.

Further, when the end electrodes are connected by the conductive adhesive, the strain due to the conductive adhesive is concentrated on the minute boundary portion between the ends of the piezoelectric element in the conventional structure. In the structure of the present invention in which the outer peripheral portion is chamfered to the R surface or the like, the distance between the ends of the piezoelectric element is widened, the strain concentration is relieved, and the strain is reduced until the displacement can be sufficiently absorbed within the elastic range of the conductive adhesive. Can be made.

[0019]

1 (A) and 1 (B) are perspective views showing an embodiment of a laminated piezoelectric device according to the present invention. FIG. 1 (A) is a state before connection by a wire 13, and FIG. 1 (B) is a wire. The state after connection by 13 is shown. This laminated piezoelectric device is shown in FIG.
As shown in the exploded perspective view of FIG.
The end piezoelectric elements 6A and 6B are superposed on the upper and lower ends, the electrode plates 7 and 8 are superposed on the end piezoelectric elements 6A and 6B, and the insulating plates 9 and 10 are superposed on the electrode plates 7 and 8. As shown in FIG. 1 (A), the wires 13 are stacked as shown in FIG. 1 (B).
Thus, the end electrodes 4 and 5 in the same arrangement are connected by wire bonding, and the outside is impregnated with the insulating resin 11 leaving the end faces made of the insulating plates 9 and 10 to be integrated.

As shown in the plan view of FIG. 2B and the bottom view of FIG. 2C, the piezoelectric element 6 is formed by sputtering on the front and back surfaces of the piezoelectric material 1 formed of a plate-shaped piezoelectric ceramic. At the same time as forming the main electrodes 2 and 3, the piezoelectric material 1
A first end electrode 4 and a second end electrode 5, which are connected to the main electrodes 2 and 3, respectively, are formed on the end faces of the.
The first end electrodes 4 of this example are arranged at three locations on the outer circumference of the circular piezoelectric material 1 at intervals of 120 degrees, and the second end electrodes 5 are the first end electrodes 4 thereof. The piezoelectric material 1 is arranged between the end electrodes 4 with an interval of 120 degrees on the outer periphery of the piezoelectric material 1 and has the same shape as the front and back. They are,
As shown in FIG. 2 (D), the adjacent piezoelectric elements are stacked with a shift of 60 degrees from each other, so that the first end electrode 4 and the first piezoelectric element 6 of the adjacent piezoelectric element 6 and the first end electrode 4 are stacked as shown in FIG. 2 (A). The two end electrodes 5 are stacked so as to be continuous in the vertical direction, that is, the stacking direction.

As shown in the plan view of FIG. 3A, the piezoelectric element 6A at the upper end has a first end that overlaps in a positional relationship that is connected to the second end electrode 5 of the piezoelectric element that overlaps therebelow. The partial electrode 4 is formed continuously from the main electrode 2, and the main electrode 3 is formed on the back surface.
Only the second end electrode 5 is not provided. Further, as shown in the plan view of FIG. 3C and the bottom view of FIG. 3D, the end piezoelectric element 6B at the lower end has only the main electrode 2 which is in contact with the lower surface of the piezoelectric element 6 on the upper surface. And has a second end electrode 5 connected to the main electrode 3 on the back surface on the end surface (outer peripheral surface).

By stacking such piezoelectric elements 6A, 6 and 6B with their polarization directions opposite to each other or by polarizing after stacking, the opposing front and back surfaces of the adjacent piezoelectric elements 6A, 6 and 6B come into contact with each other, Adjacent piezoelectric elements 6A, 6,
A parallel connection state is realized in which non-opposing surfaces of 6B are connected to each other by the first end electrode 4 and the second end electrode 5, and the input / output terminals 7a and 8 formed on the electrode plates 7 and 8 are realized.
By applying a voltage from a, the amount of strain in which the strain of each piezoelectric element 6a, 6 and 6B is applied according to the voltage is obtained from the entire piezoelectric device.

FIGS. 4, 5 and 6 are cross-sectional views showing an example of the connection relationship of the end electrodes 4, 5 by the wire 13, respectively, of the end electrodes 4, 5 in the same array which are vertically arranged.
At least the end electrodes 4 and 5 attached to the main electrodes 2 and 3 on the non-opposing sides of the adjacent piezoelectric elements 6 are connected by a wire 13. In the example of FIG. 4, the adjacent piezoelectric elements 6
The main electrodes 2 and 3 facing and contacting each other maintain their electrical connection even when strain occurs, and as shown in FIG. 14B, when strain occurs, the end electrodes 4 and 5 are separated from each other. In view of the possibility of concern, the end electrodes 4 and 5 in the same series are connected to each one of the piezoelectric elements 6 by a wire 13 to reduce the number of welded portions 14.

In the example of FIG. 5, the end electrodes 4, 5 in the same series are used.
, The end electrodes 4, 5 respectively connected to the main electrodes 2, 3 of the adjacent piezoelectric elements 6 facing and contacting each other are not connected by the wire 13, and the main electrodes on the non-opposing sides of the adjacent piezoelectric elements 6 The end electrodes 4 and 5 attached to the electrodes 2 and 3 are connected by a wire 13.

In the example of FIG. 6, all the end electrodes 4 and 5 in the same series of the adjacent piezoelectric elements 6 are connected by the wires 13.

The electrodes 2 to 5 are preferably made of copper,
Nickel, aluminum or the like is used, and the wire 13 is gold thin wire, aluminum thin wire, copper thin wire or the like.

FIG. 7 (A) shows a state where no voltage is applied to the piezoelectric device, that is, no distortion is generated in the wire arrangement example of FIG. 6, and FIG. 7 (B) is generated by applying voltage. As shown in FIG. 7B, when the piezoelectric device is driven, there is almost no distortion due to the driving of the piezoelectric element due to the presence of the gap G in the welded portion 14, that is, the end face. Therefore, no extra stress is applied to the welded portion 14. In addition, since the wire 13 has sufficient flexibility with respect to a minute displacement such as a displacement caused by driving the piezoelectric element 6 which is a target of the present invention, the wire 13 sufficiently absorbs the displacement between the piezoelectric elements 6, and the welding is performed. The tensile stress of the wire 13 does not occur in the portion 14. Therefore, even when the single-plate laminated piezoelectric device is used as an actuator that continuously generates a large displacement, parallel connection between the piezoelectric elements 6 can be reliably maintained without thinning the piezoelectric material 1.

The main electrodes 2 and 3 on the front and back surfaces of the piezoelectric element 6 are also provided.
And since the end electrodes 4 and 5 are formed simultaneously and integrally by sputtering, the end electrodes 4 and 5 can be formed so as to wrap around well, and the electrodes 2 to 5 can be formed thin, the load characteristics are improved, and the surface accuracy is improved. As a result, the adhesion between the piezoelectric elements is improved. In addition, when the entire surface is preliminarily polarized by the temporary electrode before the electrodes 2 to 5 are formed, the electrodes 2 to 5 can be formed at a temperature lower than the Curie temperature of the piezoelectric material 1, so that the characteristics are not affected.

Further, when the present invention is carried out, it is possible to employ a structure in which the end piezoelectric elements 6A, 6B and the electrode plates 7, 8 are not provided, but the main electrodes 2, 3 on the front and back surfaces, and the first or the first or second main electrodes. The plate-shaped end piezoelectric elements 6A and 6B having any one of the two end electrodes 4 and 5 are arranged in a laminated body of a plurality of piezoelectric elements 6 with one of the main electrodes 2 and 3 on the front and back surfaces being outside. Overlap on both ends,
By forming insulating plates 9 and 10 on each end piezoelectric element 6A and 6B via electrode plates 7 and 8 having signal terminals 7a and 8a for inputting and outputting electric signals, respectively, the electrode plate 7 and The lead-out portion can be formed by simply overlapping 8 on the piezoelectric elements 6A and 6B, and the strength is greater than when the lead-out portion is provided on the electrode of the piezoelectric element 6.

Further, since the laminated piezoelectric device composed of the respective constituent elements 6 to 10 is integrated by impregnating it with the insulating resin 11, it is possible to increase the dielectric strength voltage and the moisture resistance.

As described above, the structure in which the end electrodes 4 and 5 are connected by the wire 13 has a plan view of FIG.
As shown in the bottom view of (F) and the cross-sectional view of (G), when the piezoelectric elements having the wrap-around electrodes 4a, 5a on the opposite side of the main electrodes 2, 3 are used as the end electrodes 4, 5, respectively. It goes without saying that it can be applied.

8 (A) and 9 show end electrodes 4, 5 attached to the main electrodes 2, 3 on the non-opposing side of the adjacent piezoelectric element 6 among the end electrodes 4, 5 in the same array. In the case where two spaces are connected by the conductive adhesive 12, the ends 1a of the piezoelectric material 1 are chamfered to prevent the conductive adhesive 12 from cracking.

Further, in FIG. 8B, the end electrodes 4 and 5 connected in the stacking direction in the same array are divided into a group consisting of a plurality of end electrodes, and the end electrodes in each group are electrically connected. The conductive adhesive 12 is applied so as to be connected.

FIG. 10 shows the end portion 1 of the piezoelectric material 1 as described above.
A is chamfered, and the conductive adhesive 12 is applied to the entire end electrodes 4 and 5 belonging to the same series.

FIG. 11 is a view showing a manufacturing process of a laminated piezoelectric device in which the end portion 1a of the piezoelectric material 1 is chamfered and the end electrodes 4 and 5 are connected by the conductive adhesive 12 as described above. First, as shown in FIG. 11A, the end portion 1a of the disk-shaped piezoelectric material 1 made of ceramic is chamfered, and
As shown in (B), the piezoelectric material 1 whose periphery is formed into an R surface
Get. This chamfer may be a C surface that forms an inclined surface in which the corner portion of the end portion 1a is shaved, but in the example, R chamfering is performed by barrel polishing for ease of manufacturing. Next, as shown in FIG. 11C, the main electrodes 2 and 3 and the end electrodes 4 and 5 are formed on the chamfered piezoelectric material 1 by sputtering. Next, as shown in FIG. 1 (A), the elements 6 to 10 are stacked, and the stacked ones are temporarily fixed with a jig or the like, and as shown in FIG. The agent 12 is applied to the end electrodes 4 and 5 of the same series. The illustrated example shows an example in which the conductive adhesive 12 is applied in a strip shape to all the end electrodes 4 and 5 belonging to the same series. The conductive adhesive 12 is cured after being applied. As shown in FIG. 11 (E), the insulating resin 11 is impregnated except for both rear end surfaces, and the whole is insulation-coated.
Adhesive and integrated. In this case, the surface accuracy of the piezoelectric device can be increased by impregnating the insulating resin 11 except the end faces of the insulating plates 9 and 10. Next, FIG. 11 (F)
As shown in, the lead wires 15 and 1 are connected to the signal terminals 7a and 8a.
Connect 6

FIG. 12 is a diagram showing the effect of chamfering the end surface of the piezoelectric material 1 in this manner, in comparison with the conventional example.
(A) is an enlarged view of the end of the piezoelectric element 6 of the conventional example and a strain distribution diagram in the Y direction (stacking direction) generated in the surface layer a of the conductive adhesive 12 at the end, (B) is the same as in the present invention And a strain distribution diagram of the surface layer d of the conductive adhesive 12,
(C) is a strain distribution chart in the X direction (radial direction of the piezoelectric element 6) in the present invention and the conventional example. In this example, the thickness of the piezoelectric material 1 is 0.5 mm, the thickness of the electrodes 2 to 5 is 1 μm, and the conductive adhesive 1 applied on the end electrodes 4 and 5 is used.
The thickness of 2 was 20 μm, and the chamfered corners of the piezoelectric material 1 were R = 0.08 mm.

When the thus constructed device is driven for use as an actuator, the maximum displacement of one piezoelectric element 6 is about 0.5 μm. If the initial point b between the piezoelectric elements 6 before driving, that is, the gap at the end face is determined by the electrode thickness, the gap at this point b is 2 μm (= 1 μm).
+1 μm). When the piezoelectric element 6 is driven, this results in 0.
Since the distortion is 5 μm, a distortion of 0.5 μm / 2 μm is generated. As described above, it is usually difficult to obtain a conductive adhesive that is flexible enough to absorb such a large amount of strain and that satisfies other requirements.

On the other hand, in the present embodiment, the end portion 1a of the piezoelectric material 1 is chamfered so that the corner portion becomes the R surface, so that at the surface layer position d of the conductive adhesive 12, as shown in FIG.
As can be seen from the comparison of the strain distribution diagrams of (A) and (B),
The strain can be reduced until the conductive adhesive 12 can be sufficiently absorbed within its elasticity range. In addition, FIG.
As shown in FIG. 4, in the conventional structure, a large strain is generated at the point b which is the joint portion, whereas in the structure of the present embodiment, the strain at the point d which is the surface layer position is at the R surface at the end of the piezoelectric element. Dispersion, the magnitude of strain is reduced, the concentration of strain on the joint is eliminated, and the occurrence of cracks in the conductive adhesive 12 is prevented.

As shown in FIG. 12B, the piezoelectric material 1
If the range for chamfering the end portion 1a of the piezoelectric material 1 is set as the thickness s for chamfering from the front and back surfaces of the piezoelectric material 1, the thickness s for performing the chamfering is relative to the thickness t of the piezoelectric material 1 (see FIG. 10).
3% to 50% (s / t = 0.03 to 0.5), preferably 10% to 30% (s / t = 0.1 to 0.3) is set to about the above-mentioned conductivity. The effect of preventing cracking of the adhesive 12 can be expected.

As shown in FIG. 8A and FIG. 9, the main electrode 2 on the surface which does not face between the two adjacent piezoelectric elements 6,
If the conductive adhesive 12 is applied so that the end electrodes 4 and 5 respectively connected to 3 are electrically connected, the application area of the conductive adhesive 12 can be reduced, and By the conductive adhesive 12, the reaction force in the direction of restraining the strain of the piezoelectric element is relaxed, cracking of the conductive adhesive 12 is better prevented, and the parallel connection of the piezoelectric elements 6 is better maintained.

Further, as shown in FIG. 8B, if the conductive adhesives 12 are applied in groups, the piezoelectric material having a reaction force in the direction of restraining the strain of the piezoelectric element 6 by the conductive adhesives 12 is applied. The concentration in the central part of the device is eased, the parallel connection of the piezoelectric elements 6 is better maintained, and
For the end electrodes of the same series for each one, the conductive adhesive 12
The application process of the conductive adhesive 12 is simplified as compared with the case of connecting by using.

Although the piezoelectric material 1 has a circular shape in the above embodiment, it may have a polygonal shape. Also, the present invention
It can be applied not only when used as an actuator but also when used as a sensor. The method of polarization of the piezoelectric material 1 includes a method of stacking pre-polarized materials and a method of stacking the piezoelectric elements in parallel and connecting them in parallel and applying a voltage higher than a normal working voltage to polarize them. Also,
In the present invention, the wire 13 and the conductive adhesive 12 may be used together to connect the end electrodes 4 and 5,
With such a combined structure, the parallel connection between the piezoelectric elements can be more reliably maintained.

[0043]

According to the first aspect of the present invention, the piezoelectric material is formed by forming the main electrodes by films on the front and back surfaces of the piezoelectric material and connecting the first and second end electrodes to the front and back main electrodes, respectively. In the laminated piezoelectric device using the element, since the end electrodes in the same array are connected by wire bonding, the single plate laminated piezoelectric device is used as an actuator for continuously generating large displacement. However, the parallel connection between the piezoelectric elements can be reliably maintained without reducing the thickness of the piezoelectric elements and thus without increasing the number of stacking steps. That is, in the single-plate stacking type piezoelectric device in which the electrodes are integrally formed by the film, the welded portion, that is, the end face, has almost no distortion due to the piezoelectric element driving due to the existence of the gap between the opposed electrodes. No extra stress is applied to the. In addition, since the wire has sufficient flexibility with respect to a minute displacement that is a target of the present invention, the wire sufficiently absorbs the displacement between the piezoelectric elements and the tensile stress of the wire is not generated in the welded portion. In addition, there is no risk of cracks or wire breakage in the welded portion, and parallel connection between the piezoelectric elements can be reliably maintained.

According to the second aspect, since the outer peripheral portion of the piezoelectric material is chamfered and the end electrodes of the same series are connected by the conductive adhesive, the strain applied to the conductive adhesive by driving the piezoelectric element is reduced. Dispersed and relaxed, the strain can be reduced until it can be sufficiently absorbed within the elastic range of the conductive adhesive, cracking of the conductive adhesive can be prevented, and a single-plate laminated piezoelectric device can be continuously Even when it is used as an actuator that generates a large displacement, parallel connection between the piezoelectric elements can be reliably maintained.

According to the third aspect, since the end electrodes are connected by using the wire bonding and the conductive adhesive together, the parallel connection between the piezoelectric elements can be more surely maintained.

According to the fourth aspect, the end electrodes connected in the stacking direction in the same array are divided into a group consisting of a plurality of end electrodes, and the end electrodes in each group are electrically connected. As described above, since the conductive adhesive is applied, the conductive adhesive alleviates the concentration of the reaction force in the direction of restraining the strain of the piezoelectric element on the central portion of the piezoelectric device, and the parallel connection of the piezoelectric elements is improved. In addition to being maintained, the application process of the conductive adhesive is simplified as compared with the case where the end electrodes of the same series are connected by the conductive adhesive for every two piezoelectric elements.

According to the fifth aspect, the conductive adhesive is applied so that the end electrodes, which are respectively connected to the main electrodes on the surfaces not facing each other between the two adjacent piezoelectric elements, are electrically connected. Therefore, in the laminated piezoelectric device in which the gaps on the front and back surfaces of the piezoelectric material exist, the electrical connection is reliably relaxed, and the application area of the conductive adhesive can be reduced. The reaction force in the direction of restraining the strain of the piezoelectric element is relaxed, cracking of the conductive adhesive is better prevented, and the parallel connection of the piezoelectric elements is better maintained.

According to the sixth aspect, since the main electrodes and the end electrodes on the front and back surfaces of the piezoelectric element are formed simultaneously and integrally by sputtering, the end electrodes can be formed so as to wrap around well.
Moreover, the electrodes can be formed thin, and the load characteristics are improved.
The surface accuracy is improved and the adhesion between the piezoelectric elements is improved.
Moreover, since the electrodes can be formed at a temperature lower than the Curie temperature of the piezoelectric material, there is no fear of affecting the characteristics.

According to the seventh aspect, the plate-shaped end piezoelectric element having the main electrodes on the front and back surfaces and either the first or the second end electrode is provided. Insulating plates are stacked on both ends of a laminated body of a plurality of piezoelectric elements with the surface having electrodes as an outer side, and through the electrode plates having signal terminals for electric signal input / output on each of the end piezoelectric elements. Since the electrodes are superposed on each other, the lead-out portion can be constructed by simply overlapping the electrode plate on the piezoelectric element, and the strength is greater than that in the case where the lead-out portion is provided on the electrode of the piezoelectric element.

According to the eighth aspect, since the laminated piezoelectric device is integrated by impregnating the insulating resin, the dielectric strength can be increased and the moisture resistance can be improved.

[Brief description of drawings]

FIG. 1A is a perspective view showing an embodiment of a laminated piezoelectric device according to the present invention in which no wire is attached, and FIG.
FIG. 4 is a perspective view showing a state in which a wire is attached in the embodiment.

2A is an exploded perspective view showing components of the embodiment, FIG. 2B is a plan view of a piezoelectric element of the embodiment, FIG. 2C is a bottom view thereof, and FIG. FIG. 3 is an exploded perspective view showing a mutual positional relationship of piezoelectric elements.

3A and 3B are respectively a plan view and a bottom view showing an end piezoelectric element at the upper end of the embodiment, and FIGS. 3C and 3D.
FIG. 3A is a plan view and a bottom view showing an end piezoelectric element at the lower end of the embodiment, and (E), (F), and (G) are a plan view, a bottom view, and a sectional view of a piezoelectric element having a wraparound electrode, respectively. .

FIG. 4 is a cross-sectional view showing an example of a wire disposition structure of the embodiment.

FIG. 5 is a cross-sectional view showing another example of the wire disposition structure of the present invention.

FIG. 6 is a cross-sectional view showing still another example of the wire disposition structure of the present invention.

7A and 7B are a cross-sectional view showing a state in which the piezoelectric element end surface portion in the example of FIG. 6 is not driven and a cross-sectional view showing a state in which distortion is generated by driving.

8A and 8B are perspective views showing another embodiment of the present invention.

FIG. 9 is a vertical cross-sectional view of FIG.

FIG. 10 is a vertical sectional view showing another embodiment of the present invention.

FIG. 11 is a manufacturing process diagram of the embodiment in FIG.

12A and 12B are cross-sectional views showing the end face structures of the piezoelectric element in the conventional example and the example of the present invention with the strain distribution in the stacking direction attached, and FIG. FIG. 5 is a diagram showing the strain distribution of the conventional example in comparison with the conventional example.

FIG. 13 is a vertical cross-sectional view showing a conventional laminated piezoelectric device.

14A and 14B are a cross-sectional view showing a state where the piezoelectric element end face structure in the conventional example of FIG. 13 is not driven and a cross-sectional view showing a state where distortion is generated by driving.

[Explanation of symbols]

1: Piezoelectric material, 1a: Edge, 2, 3: Main electrode, 4: First edge electrode, 5: Second edge electrode, 6, 6A, 6B: Piezoelectric element, 7, 8: Electrode plate , 9, 10: insulating plate, 11: insulating resin, 12: conductive adhesive, 13: wire, 14: welded part, 15, 16: lead wire

Claims (8)

[Claims] 1. A plurality of plate-shaped piezoelectric elements polarized in the thickness direction, each piezoelectric element having a film-shaped main electrode formed on the front and back surfaces of a molded plate-shaped piezoelectric material, and a surface of the piezoelectric material, A first end electrode and a second end electrode, which are film-like and are connected to the main electrodes formed on the back surface and are formed on the end faces of the piezoelectric material, respectively. End electrodes and second end electrodes are arranged so as to be continuous in the stacking direction, and a plurality of piezoelectric elements are stacked such that the polarization directions of adjacent piezoelectric elements are opposite to each other. A laminated piezoelectric device, characterized in that end electrodes in the same array extending in the same direction are connected by wire bonding. 2. A plurality of plate-shaped piezoelectric elements polarized in the thickness direction, each piezoelectric element having a film-shaped main electrode formed on the front and back surfaces of a molded plate-shaped piezoelectric material, and a surface of the piezoelectric material, A first end electrode and a second end electrode, which are film-like and are connected to the main electrodes formed on the back surface and are formed on the end faces of the piezoelectric material, respectively. End electrodes and second end electrodes are arranged so as to be continuous in the stacking direction, and a plurality of piezoelectric elements are stacked such that adjacent piezoelectric elements have opposite polarization directions. A laminated piezoelectric device, wherein the outer peripheral portion is chamfered, and end electrodes in the same array are connected by a conductive adhesive. 3. The laminated piezoelectric device according to claim 2, wherein the end electrodes in the same array are connected by a wire bonding in addition to a conductive adhesive. 4. The end electrode according to claim 2, wherein the end electrodes connected in the stacking direction in the same array are divided into a group of a plurality of end electrodes, and the end electrodes in each group are electrically connected. As described above, a laminated piezoelectric device in which a conductive adhesive is applied. 5. The conductive material according to claim 2, wherein the end electrodes that are respectively connected to the main electrodes on the surfaces that do not face each other between two adjacent piezoelectric elements are electrically connected to each other. A laminated piezoelectric device characterized by being coated with a conductive adhesive. 6. A laminated piezoelectric device according to claim 1, wherein the main electrodes and the end electrodes on the front and back surfaces of the piezoelectric element are formed simultaneously and integrally by sputtering. 7. The end-portion piezoelectric element according to claim 1, wherein the end-portion piezoelectric element is a plate having main electrodes on the front and back surfaces and one of the first and second end electrodes. With the main electrode surface on the outside, superposed on both ends of a laminated body of a plurality of piezoelectric elements, and on each end piezoelectric element, an insulating plate is superposed via electrode plates for inputting and outputting electric signals. A laminated piezoelectric device characterized by the following. 8. A laminated piezoelectric device according to claim 1, wherein the laminated piezoelectric device is integrated by impregnating the laminated piezoelectric device with an insulating resin.