JP2014110295A - Laminated piezoelectric element and piezoelectric actuator - Google Patents

Abstract

The present invention provides a laminated piezoelectric element that can achieve both securing strength and improving displacement.
SOLUTION: Internal electrodes 27a and 27b stacked with a piezoelectric layer 26 interposed therebetween, and formed on side surfaces extending in the stacking direction, are electrically connected to the internal electrodes 27a and 27b. A first portion 29a and a second portion 29b having different cross-sectional areas in a direction perpendicular to the stacking direction, and the first portion 29a is arranged in the stacking direction. It is arranged so that both sides in the stacking direction are sandwiched by the second portion 29b having a cross-sectional area in the direction perpendicular to the first portion 29a that is larger than the first portion 29a.
[Selection] Figure 2

Description

  The present invention relates to a multilayer piezoelectric element and a piezoelectric actuator including the same.

  A piezoelectric element is an element that mutually converts mechanical displacement and electrical displacement using a piezoelectric effect and an inverse piezoelectric effect. Such a piezoelectric element is manufactured, for example, by forming and firing piezoelectric ceramics to obtain an element body, forming an electrode on the element body, and further performing a polarization treatment.

  The piezoelectric element is suitably used as a part of an actuator that requires precise and accurate control, for example. More specifically, it can be used for lens driving, HDD head driving, inkjet printer head driving, fuel injection valve driving, and the like.

  In addition, a laminated piezoelectric element having a laminated structure of an electrode and a piezoelectric layer can increase the displacement amount and driving force per unit volume as compared with a non-laminated piezoelectric element. For example, a small actuator Etc. (see Patent Document 1).

International Publication No. 2007-052599

  However, recently, from the viewpoint of improving the performance of actuators and the like, there is a demand for the development of a multilayer piezoelectric element that can obtain a larger amount of displacement. In addition, the multilayer piezoelectric element used for the actuator is required to have higher strength and reliability so that the displacement generated in the multilayer piezoelectric element can be transmitted to other members.

  An object of the present invention is to provide a multilayer piezoelectric element that can achieve both securing of strength and improvement of displacement.

  In order to solve the above-described problems, a multilayer piezoelectric element according to the present invention is formed on internal electrodes stacked with a piezoelectric layer in between and side surfaces extending in the stacking direction. A pair of external electrodes electrically connected to each other, and having a first portion and a second portion having different cross-sectional areas in a direction perpendicular to the stacking direction, and the first portion is The cross-sectional area in a direction orthogonal to the stacking direction is arranged so that both sides of the stacking direction are sandwiched between the second portion larger than the first portion.

  The multilayer piezoelectric element according to the present invention has a first portion and a second portion having different cross-sectional areas in a direction perpendicular to the stacking direction, and the first portion having a small cross-sectional area is the second portion having a large cross-sectional area. It is sandwiched between. In the vicinity of the first portion, the ratio of the piezoelectric inactive portion to the piezoelectric active portion is smaller than that in the second portion. Therefore, the multilayer piezoelectric element having such a first portion is displaced more greatly. In addition, the second portion having a large cross-sectional area supplements the strength, so that the multilayer piezoelectric element according to the present invention can achieve both securing of strength and improvement of displacement.

  For example, the piezoelectric layer and the internal electrode that are stacked between both end faces in the stacking direction may be integrally fired.

  It is preferable that all the piezoelectric layers and internal electrode layers included in the multilayer piezoelectric element are integrally fired. Such a multilayer piezoelectric element is easy to manufacture and exhibits good strength. .

  For example, the multilayer piezoelectric element according to the present invention may include a plurality of the first portions.

  By adopting a structure in which the first portion and the second portion are repeated along the stacking direction, it is possible to effectively secure the strength while reducing the volume of the piezoelectric inactive portion and improving the displacement. .

  Further, for example, a resin adhering portion in which a resin adheres to the surface of the external electrode in the second portion may be formed.

  A multilayer piezoelectric element having a resin adhesion portion formed on the surface of the external electrode can easily form the first portion and the second portion by barrel polishing or the like, and is easy to manufacture.

A piezoelectric actuator according to the present invention includes any one of the above laminated piezoelectric elements,
A connecting member attached to at least one of both end faces in the stacking direction;
A drive unit electrically connected to the external electrode and applying a drive signal to the external electrode;
According to the driving by the driving unit, a vibration node is generated closer to the second part than to the first part.

  In the piezoelectric actuator, it is considered that a larger load is applied to the position of the vibration node than the other parts. However, the piezoelectric actuator in which the vibration node is generated near the second part having a large cross-sectional area is particularly suitable for durability. Play.

FIG. 1 is a conceptual diagram showing a lens driving device using a laminated piezoelectric element according to an embodiment of the present invention. FIG. 2 is an enlarged perspective view of the multilayer piezoelectric element included in the lens driving device shown in FIG. 3A and 3B are cross-sectional views taken along a cross section in a direction orthogonal to the stacking direction of the stacked piezoelectric element shown in FIG. FIG. 4 is a conceptual diagram showing the position of a vibration node generated by driving the lens driving device shown in FIG. FIG. 5 is a plan view showing a multilayer piezoelectric element according to the second embodiment of the present invention. FIG. 6 is a plan view showing a multilayer piezoelectric element according to the third embodiment of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment FIG. 1 is a conceptual diagram showing a lens driving device 60 using a laminated piezoelectric element 20 according to an embodiment of the present invention. The lens driving device 60 includes a laminated piezoelectric element 20, a weight 42, a shaft 44, and first and second resin portions 52 and 54 that connect them. The lens driving device 60 further includes a drive circuit 58 that applies a drive signal to the multilayer piezoelectric element 20, a wiring portion 32 that electrically connects the multilayer piezoelectric element 20 and the drive circuit 58, and the like.

  A weight 42 is fixed to a first end surface 22 that is one end surface in the stacking direction of the multilayer piezoelectric element 20 via a first resin portion 52. Further, a shaft 44 is connected to the second end surface 24, which is the other end surface in the stacking direction of the multilayer piezoelectric element 20, via a second resin portion 54.

  The lens driving device 60 has a moving member 56 that is movably engaged with the shaft 44. The moving member 56 holds a lens, and the moving member 56 and the lens held by the moving member 56 can relatively move along the shaft 44.

  The laminated piezoelectric element 20 is deformed by being applied with a voltage by the drive circuit 58. Accordingly, the shaft 44 connected to the multilayer piezoelectric element 20 reciprocates in the direction indicated by the arrow 34. The voltage waveform output by the drive circuit 58 is not particularly limited. For example, the drive circuit 58 outputs a voltage waveform having a sawtooth waveform, thereby exceeding the deformation amount of the stacked piezoelectric element 20 and the displacement amount of the shaft 44 associated therewith. A moving amount can be generated in the moving member 56.

  In the present embodiment, an example in which the multilayer piezoelectric element 20 is applied to the lens driving device 60 will be described as an example. However, the apparatus to which the multilayer piezoelectric element 20 is applied is not limited to this, and the multilayer piezoelectric element 20 is not limited thereto. The piezoelectric element 20 can also be applied to other driving devices.

  As shown in FIGS. 1 and 2, the multilayer piezoelectric element 20 included in the lens driving device 60 has a substantially prismatic shape (a quadrangular prism in the present embodiment), and includes a piezoelectric layer 26, First and second internal electrodes 27a and 27b, and first and second external electrodes 28a and 28b are provided. The external shape of the multilayer piezoelectric element 20 is not limited to a prismatic shape, and may be a cylindrical shape, an elliptical columnar shape, or other shapes.

  In the multilayer piezoelectric element 20, the first internal electrodes 27 a and the second internal electrodes 27 b are alternately stacked with the piezoelectric layers 26 interposed therebetween. The first external electrode 28 a and the second external electrode 28 b are formed on the side surface of the surface of the multilayer piezoelectric element 20 that extends along the stacking direction. As shown in FIG. 2, the first external electrode 28a is formed on the first side surface 25a extending along the stacking direction Z, and the second external electrode 28b faces in the direction opposite to the first side surface 25a. It is formed on the second side surface (not shown).

  As shown in FIGS. 1 and 2, the first internal electrode 27a is electrically connected to the first external electrode 28a, and the second internal electrode 27b is electrically connected to the second external electrode 28b. Yes. As shown in FIG. 2, among the side surfaces of the multilayer piezoelectric element 20, the third side surface 25c and the fourth side surface (not shown) where the first and second external electrodes 28a and 28b are not formed Although the electrode 27a and the second internal electrode 27b are exposed, a resin layer for preventing migration may be formed on the third side surface 25c and the fourth side surface.

  As shown in FIG. 2, the stacked piezoelectric element 20 has a shape in which a ridge line portion 21 extending along the stacking direction Z is curved toward the center at the center in the stacking direction. It has a constricted outer shape. Therefore, the multilayer piezoelectric element 20 includes the first portion 29a and the second portion 29b having different cross-sectional areas in the direction orthogonal to the stacking direction.

  3A is a cross-sectional view in the direction perpendicular to the stacking direction Z in the first portion 29a shown in FIG. 2, and FIG. 3B is perpendicular to the stacking direction Z in the second portion 29b shown in FIG. It is sectional drawing of the direction to do. The ridge line portion 21a in the first portion 29a is closer to the element center than the ridge line portion 21b in the second portion 29b. Further, the ridge line portion 21 (including the ridge line portions 21a and 21b) has an R shape, and the curvature radius of the ridge line portion 21a in the first portion 29a is larger than the curvature radius of the ridge line portion 21b in the second portion 29b. However, the ridge line portion 21 does not necessarily have an R shape, and may have another curve and a straight line shape.

  As shown in FIGS. 3A and 3B, the cross-sectional area Sb of the second portion 29b is larger than the cross-sectional area Sa of the first portion 29a, and the first portion 29a having a small cross-sectional area as shown in FIG. However, it is arrange | positioned so that both sides of the lamination direction Z may be pinched | interposed by the 2nd part 29b with a large cross-sectional area. Further, from the comparison between FIG. 3A and FIG. 3B, in the first portion 29a corresponding to the constricted portion, the piezoelectric inactive region in the piezoelectric layer 26 that is particularly close to the external electrodes 28a and 28b. It can be seen that 26b is smaller than the second portion 29b corresponding to the bulging portion.

  On the other hand, in the piezoelectric layer 26, the piezoelectric active region 26a located at a position away from the external electrodes 28a and 28b (near the center) is approximately the same size in the first portion 29a and the second portion 29b. It is. The piezoelectric active region 26a is a portion of the piezoelectric layer 26 that is sandwiched between the first internal electrode 27a and the second internal electrode 27b having different polarities along the stacking direction Z, and the piezoelectric inactive region 26b. Is a portion other than the piezoelectric active region 26a.

  Since the ratio of the piezoelectric inactive region 26b occupying the piezoelectric layer 26 is smaller than that of the second portion 29b, the first portion 29a can be displaced more than the second portion 29b. This is because the piezoelectric inactive region 26b has an action of suppressing the amount of displacement of the piezoelectric layer 26, so that if the piezoelectric active region 26a has the same size, the smaller the piezoelectric inactive region 26b is larger. This is because displacement can occur.

  On the other hand, since the second portion 29b has a large cross-sectional area in the direction orthogonal to the stacking direction Z, it contributes to improving the strength of the stacked piezoelectric element 20. The multilayer piezoelectric element 20 according to the present embodiment is arranged so that the first portion 29a having a small cross-sectional area is sandwiched on both sides in the stacking direction Z by the second portion 29b having a large cross-sectional area. Improvement in displacement can be achieved at the same time.

  FIG. 4 is a conceptual diagram showing a position P of a vibration node generated by driving the lens driving device 60 shown in FIG. The lower graph in FIG. 4 represents the displacement generated at each position of the lens driving device 60, the solid line represents the displacement when the stacked piezoelectric element 20 extends in the stacking direction Z, and the chain line represents the stack. The displacement when the piezoelectric element 20 contracts along the stacking direction Z is shown. The positions of the first portion 29a and the second portion 29b in the multilayer piezoelectric element 20 are not particularly limited, but as shown in FIG. 4, a vibration node is generated near the second portion 29b rather than the first portion 29a. Is preferred. Since a larger load is applied near the vibration node position P than the other portions, the lens driving device 60 in which the vibration node is generated near the second portion 29b having a large cross-sectional area has particularly suitable durability.

  In the multilayer piezoelectric element 20 shown in FIG. 2, as the conductive material constituting the first internal electrode 27a and the second internal electrode 27b, for example, noble metals such as Ag, Pd, Au, Pt and alloys thereof (Ag—Pd) Etc.), or base metals such as Cu and Ni, and alloys thereof, but are not particularly limited. The conductive material constituting the first external electrode 28a and the second external electrode 28b is not particularly limited, and the same material as the conductive material constituting the internal electrode can be used. It should be noted that the above-mentioned various metal plating layers or sputtered layers may be formed on the outermost surfaces of the first external electrode 28a and the second external electrode 28b.

The material of the piezoelectric layer 26 is not particularly limited as long as it is a material exhibiting a piezoelectric effect or an inverse piezoelectric effect, and examples thereof include PbZr _x Ti _1-x O ₃ and BaTiO ₃ . Moreover, the component for characteristic improvement etc. may contain, The content should just determine suitably according to a desired characteristic.

  The material of each member attached to the multilayer piezoelectric element 20 is not particularly limited. For example, the shaft 44 can be made of a metal material such as SUS so that the moving member 56 can be suitably supported. Further, the weight 42 preferably includes a metal material having a relatively large specific gravity such as tungsten so as to function suitably as an inertial body for giving displacement to the shaft 44, but the material of the weight 42 is not particularly limited. .

  The materials of the first resin portion 52 and the second resin portion 54 that connect the multilayer piezoelectric element 20 and the weight 42 or the shaft 44 are not particularly limited. For example, the first resin portion 52 and the second resin portion 54 are thermosetting. It is comprised by the adhesive material hardening part which the adhesive agent hardened.

  Hereinafter, an example of a method for manufacturing the multilayer piezoelectric element 20 and the lens driving device 60 will be described with reference to FIGS. 4 and 5.

  In the manufacturing process of the multilayer piezoelectric element 20, first, a green sheet on which an internal electrode paste film having a predetermined pattern to be the first internal electrode 27 a and the second internal electrode 27 b is formed after firing and a green having no internal electrode paste film. Prepare a sheet.

  The green sheet is produced by the following method, for example. First, a binder is added to the calcined powder containing the raw material of the material constituting the piezoelectric layer 26 to form a slurry. Next, the slurry is formed into a sheet by means such as a doctor blade method or a screen printing method, and then dried to obtain a green sheet having no internal electrode paste film. Furthermore, by applying the internal electrode paste containing the above-described conductive material onto the green sheet by means such as a printing method, a green sheet on which an internal electrode paste film having a predetermined pattern is formed is obtained. Note that the raw material of the material constituting the piezoelectric layer 26 may contain inevitable impurities.

  After preparing each green sheet, the prepared green sheets are superposed, pressure is applied and pressure-bonded, and after passing through necessary steps such as a drying step, it is cut to obtain a laminate.

  Next, after the obtained laminated body is fired under a predetermined condition to obtain a sintered body, the sintered body is cut into a strip shape using a dicing saw or the like. Further, the first external electrode 28a and the second external electrode 28b are formed in portions corresponding to the first side surface 25a and the second side surface of the sintered body, and a DC voltage is applied to these electrodes to polarize the piezoelectric layer 26. I do. Thereafter, the strip-shaped sintered body after the polarization treatment is cut into individual element bodies, and then barrel polishing is performed to obtain a multilayer piezoelectric element 20 as shown in FIG. Barrel polishing is performed using a medium having a predetermined diameter with respect to the multilayer piezoelectric element 20, and the multilayer piezoelectric element 20 having the curved ridge line portion 21 is prevented while preventing generation of cracks and chips during manufacturing. It is preferable from a viewpoint of manufacturing appropriately. For example, the media diameter of barrel polishing is larger than the maximum width of the multilayer piezoelectric element 20 by the projection plane perpendicular to the lamination direction, and smaller than twice the length of the multilayer piezoelectric element 20 in the lamination direction. Is particularly preferred.

  Note that the ridge line portion perpendicular to the stacking direction Z and the corner portion 72 of the stacked piezoelectric element 20 may also have an R shape as in the ridge line portion 21 (see FIG. 2) parallel to the stack direction (see FIG. 2). 5). By making the corners and ridges of the multilayer piezoelectric element 20 into an R shape, it is possible to prevent the external electrodes from peeling off. It is also preferable to form a resin layer on the third side surface 25c and the fourth side surface.

  In the manufacturing process of the lens driving device 60 shown in FIG. 1, first, the wiring portion 32 is connected to the laminated piezoelectric element 20 by soldering or the like. Next, a weight 42 and a shaft 44 are attached to the first end surface 22 and the second end surface 24 of the multilayer piezoelectric element 20 using a thermosetting adhesive or the like, respectively. At this time, the resin portions 52 and 54 are formed by curing the thermosetting adhesive. Finally, the lens driving device 60 is obtained by attaching the moving member 56 to the shaft 44. In the above description, a thermosetting adhesive is used as an adhesive for connecting the laminated piezoelectric element 20 to the weight 42 and the shaft 44 as connecting members connected thereto. The adhesive used for manufacture is not limited to this.

  As shown in FIG. 2, the multilayer piezoelectric element 20 according to the present embodiment has a first portion 29a that has a small cross-sectional area in a direction orthogonal to the stacking direction and is constricted with respect to the peripheral second portion 29b. The multilayer piezoelectric element 20 expands the displacement by the first portion 29a and increases the strength by the second portions 29b disposed on both sides of the first portion 29a, so that both improvement of displacement and securing of the strength can be achieved. . Further, the laminated piezoelectric element 20 having a constricted shape by the first portion 29a and the second portion 29b is also used when the assembly apparatus or the like performs chucking with the ridge line portion 21 located on the diagonal line of the laminated piezoelectric element 20 interposed therebetween. Accurately chucked.

  Further, as described in the manufacturing method, it is preferable that the piezoelectric layer 26 and the internal electrodes 27a and 27b stacked between both end faces 22 and 24 in the stacking direction Z are integrally fired. Such a laminated piezoelectric element 20 is easy to manufacture and is advantageous for downsizing.

Second Embodiment FIG. 5 is a plan view showing a laminated piezoelectric element 70 according to a second embodiment of the present invention. The laminated piezoelectric element 70 according to the second embodiment is the first embodiment in that not only the ridge line part 71 parallel to the lamination direction Z but also the ridge line part 73 and the corner part 72 perpendicular to the lamination direction Z are R-shaped. Although different from the multilayer piezoelectric element 20 according to the embodiment, other configurations are the same as those of the multilayer piezoelectric element 20.

  The multilayer piezoelectric element 70 can be manufactured by the same method as the multilayer piezoelectric element 20 except that the polishing conditions (polishing time, media, etc.) in barrel polishing are changed.

  As shown in FIG. 5, in the multilayer piezoelectric element 70, as in the multilayer piezoelectric element 20 (see FIG. 2), the first portion 79a having a small cross-sectional area in the direction perpendicular to the stacking direction has a large cross-sectional area. It arrange | positions so that it may be pinched | interposed into the 2 part 79b. Thereby, the multilayer piezoelectric element 70 has the same effect as the multilayer piezoelectric element 20 described above.

Third Embodiment FIG. 6 is a plan view showing a multilayer piezoelectric element 80 according to a third embodiment of the present invention. In the multilayer piezoelectric element 80, a plurality of constricted portions are formed on a ridge line portion 81 parallel to the stacking direction, and a resin adhering portion 84 is formed on the surface having the plurality of first portions 89a and on the surface of the first external electrode 28a. However, the other configuration is the same as that of the multilayer piezoelectric element 70 according to the second embodiment.

  As shown in FIG. 6, in the multilayer piezoelectric element 80, first portions 89 a having a small cross-sectional area in a direction orthogonal to the stacking direction Z and second portions 89 b having a large cross-sectional area are alternately arranged along the stacking direction Z. Is arranged. The multilayer piezoelectric element 80 having a plurality of first portions 89a can improve displacement in the same manner as the multilayer piezoelectric element 70 having one first portion 79a (see FIG. 5), and has three second portions. The strength can be effectively secured by 89b.

  The laminated piezoelectric element 80 is the laminated piezoelectric element except that the resin adhesion portion 84 is formed by adhering resin to the surface of the external electrode 28a after the formation of the external electrode 28a and before barrel polishing. It can be manufactured by the same method as 70. In barrel polishing, the resin adhering portion 84 is less likely to be polished than the peripheral portion, and thus the second portion 89 b is formed around the resin adhering portion 84. Thus, by providing the resin adhesion portion 84 on the surface of the external electrode 28a, the first portion 89a and the second portion 89b can be formed at an arbitrary position.

Other Embodiments Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and can be implemented in various modes without departing from the scope of the present invention. Of course.

  For example, the number of first parts included in the multilayer piezoelectric element is not limited to 1 or 2 described in the embodiment, and the multilayer piezoelectric element may include three or more first parts. Further, the formation of the constricted portion is not limited to the ridge line portions 21, 71, 81. For example, even if the constricted portion is formed on the first side face 25a or the second side face where the external electrodes 28a, 28b are formed. good. Further, not only an aspect in which all of the ridge lines parallel to the stacking direction Z are curved, but also an aspect in which only a part of the ridge lines are constricted and an aspect in which the ridge lines are constricted asymmetrically are carried out. Included in the form.

20, 70, 80 ... stacked piezoelectric elements 21, 21a, 21b, 71, 81 ... ridge line part 22 ... first end face 24 ... second end face 25a ... first side face 25c ... third side face 26 ... piezoelectric layer 26a ... piezoelectric Active region 26b ... piezoelectric inactive region 27a ... first internal electrode 27b ... second internal electrode 28a ... first external electrode 28b ... second external electrode 29a, 79a, 89a ... first portion 29b, 79b, 89b ... second portion DESCRIPTION OF SYMBOLS 32 ... Wiring part 42 ... Weight 44 ... Shaft 52 ... 1st resin part 54 ... 2nd resin part 56 ... Moving member 58 ... Drive circuit 60 ... Lens drive device 72 ... Corner | angular part 84 ... Resin adhesion part

Claims (5)

Internal electrodes stacked with a piezoelectric layer in between,
A pair of external electrodes formed on side surfaces extending along the stacking direction and electrically connected to the internal electrodes;
A first portion and a second portion having different cross-sectional areas in a direction perpendicular to the stacking direction, wherein the first portion has a cross-sectional area in a direction orthogonal to the stacking direction greater than the first portion; 2. A laminated piezoelectric element characterized in that the two parts are arranged so as to sandwich both sides in the laminating direction.   2. The multilayer piezoelectric element according to claim 1, wherein the piezoelectric layer and the internal electrode that are stacked between both end faces in the stacking direction are integrally fired.   The multilayer piezoelectric element according to claim 1, further comprising a plurality of the first portions.   The multilayer piezoelectric element according to any one of claims 1 to 3, wherein a resin adhesion portion to which a resin is adhered is formed on a surface of the external electrode in the second portion. The multilayer piezoelectric element according to any one of claims 1 to 4,
A connecting member attached to at least one of both end faces in the stacking direction;
A drive unit electrically connected to the external electrode and applying a drive signal to the external electrode;
The piezoelectric actuator according to claim 1, wherein a vibration node is generated closer to the second part than the first part by driving by the driving unit.

Images