JP2018107251A - Piezoelectric element and piezoelectric actuator including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element capable of suppressing breakdown in high voltage driving and a piezoelectric actuator including the piezoelectric element.SOLUTION: A piezoelectric element 1 according to the present disclosure includes a plate-like piezoelectric body 11 and a surface electrode 12 having a lattice-like protrusion 121 or a surface electrode 13 having a lattice-like recess 131 on the main surface of the piezoelectric body 11, and further includes a plate-like laminate in which a piezoelectric body and an internal electrode are laminated and a surface electrode having a lattice-shaped protrusion or a surface electrode having a lattice-like recess on the main surface of the laminate.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a piezoelectric element used for, for example, an acoustic transducer, precise positioning for correcting displacement of a magnetic head, shutter driving of a camera, needle selection driving of a knitting machine or a loom, or a relay switch, and a piezoelectric actuator including the piezoelectric element. It is about.

  Piezoelectric actuators with a piezoelectric element bonded to a thin metal plate (shim plate), for example, precise positioning to correct magnetic head displacement, camera shutter drive, knitting machine or loom needle selection drive or relay switch, etc. Widely used in

Here, it is known that the displacement amount and lifetime of the piezoelectric actuator can be improved by using a Cu—Sn—Fe based alloy plate having a longitudinal elastic modulus of, for example, 17 to 18 × 10 ⁶ psi as the metal plate ( For example, see Patent Document 1).

Japanese Patent Laid-Open No. 08-097480

  In recent years, piezoelectric actuators are sometimes driven at a high voltage in order to satisfy higher generated force and displacement. However, when the piezoelectric actuator is driven at a high voltage, the piezoelectric element may be broken by the high voltage.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a piezoelectric element that can suppress breakage during high-voltage driving and a piezoelectric actuator including the piezoelectric element.

  A piezoelectric element of the present disclosure includes a plate-like piezoelectric body or a plate-like laminate in which a piezoelectric body and an internal electrode are laminated, and a surface electrode provided on the main surface of the piezoelectric body or the laminate. The surface electrode has a grid-like convex part or a grid-like concave part.

  A piezoelectric actuator according to the present disclosure includes the piezoelectric element and a shim plate to which the main surface of the piezoelectric element is bonded.

  According to the piezoelectric element of the present disclosure, it is possible to suppress the breakdown of the piezoelectric element during high voltage driving. Further, according to the piezoelectric actuator of the present disclosure, since the piezoelectric element in which the breakdown in the high voltage driving is suppressed is used, the piezoelectric actuator can be driven at a higher voltage and the generated force and the displacement amount can be improved.

It is a schematic perspective view which shows an example of embodiment of a piezoelectric element. FIG. 2A is a plan view of a part of the piezoelectric element shown in FIG. 1, and FIG. 2B is a cross-sectional view taken along line ii-ii shown in FIG. It is a schematic perspective view which shows the other example of embodiment of a piezoelectric element. FIG. 4A is a plan view of a part of the piezoelectric element shown in FIG. 3, and FIG. 4B is a side view of the piezoelectric element shown in FIG. It is the side view seen from the longitudinal direction which shows the other example of embodiment of a piezoelectric element. It is a schematic perspective view which shows an example of embodiment of a piezoelectric actuator.

  Hereinafter, an example of an embodiment of a piezoelectric element will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

  FIG. 1 is a schematic perspective view showing an example of an embodiment of a piezoelectric element, FIG. 2 (a) is a plan view of a part of the piezoelectric element shown in FIG. 1, and FIG. 2 (b) is an ii-ii shown in FIG. It is sectional drawing cut | disconnected by the line. 3 is a schematic perspective view showing another example of the embodiment of the piezoelectric element, FIG. 4A is a plan view of a part of the piezoelectric element shown in FIG. 3, and FIG. 4B is FIG. It is the side view seen from the longitudinal direction of the piezoelectric element shown.

  The piezoelectric element 1 shown in FIGS. 1 and 2 includes a plate-like piezoelectric body 11 and a surface electrode 12 provided on the main surface of the piezoelectric body 11, and the surface electrode 12 has a lattice-like convex portion 121. doing.

  The piezoelectric element 1 shown in FIGS. 3 and 4 includes a plate-like piezoelectric body 11 and a surface electrode 13 provided on the main surface of the piezoelectric body 11, and the surface electrode 13 has a lattice-shaped recess 131. Have.

The piezoelectric body 11 is provided with ceramics having piezoelectric characteristics. As such ceramics, lead-free piezoelectric materials such as lead zirconate titanate (PbZrO ₃ -PbTiO ₃ ), lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), Bi layered compounds, tungsten bronze structure compounds, etc. Conventionally used piezoelectric ceramics such as materials can be used.

  The shape of the piezoelectric body 11 is a rectangular plate shape (cuboid shape) in the example shown in FIGS. The shape of the piezoelectric body 11 is not particularly limited, and may be a polygonal shape other than a rectangle, or a circular shape or an elliptical shape. The dimensions of the piezoelectric body 11 can be, for example, 20 mm to 45 mm in length, 5 mm to 10 mm in width, and 0.01 mm to 3.0 mm in thickness.

  Further, the surface electrode 12 and the surface electrode 13 apply a driving voltage to the piezoelectric body 11, and both main surfaces of one main surface (upper main surface) and the other main surface (lower main surface) of the piezoelectric body 11. Are provided respectively. The main surface here means a surface having a larger area than other surfaces.

  The surface electrode 12 and the surface electrode 13 can be formed, for example, by baking on the piezoelectric body 11. As the material of the surface electrode 12, for example, a conductor that can be fired at a low temperature, a conductor mainly composed of silver, a silver-palladium alloy, nickel, copper, platinum, or the like can be used. Moreover, in addition to these conductor materials, you may contain a ceramic component and a glass component.

  The surface electrode 12 shown in FIGS. 1 and 2 has a grid-like convex portion 121. The surface electrode 12 is provided with recesses 122 arranged vertically and horizontally, and a portion other than the recesses 122 is a lattice-like protrusion 121. That is, the grid-like convex portion 121 is a relatively thick portion, and the concave portion 122 is a relatively thin portion.

  On the other hand, the surface electrode 13 shown in FIGS. 3 and 4 has a lattice-shaped recess 131. The surface electrode 13 is provided with convex portions 132 arranged in the vertical and horizontal directions, and a portion other than the convex portions 132 is a lattice-shaped concave portion 131. That is, the lattice-shaped concave portion 131 is a relatively thin portion, and the convex portion 132 is a relatively thick portion.

The surface electrode 12 has a grid-like convex portion 121 as shown in FIGS. 1 and 2.
Further, as the surface electrode 13 has the lattice-shaped recess 131 as shown in FIGS. 3 and 4, a relatively thick part and a thin part are regularly provided. By this shape effect, a compressive stress is applied in the vicinity of the surface of the piezoelectric body 11 facing the relatively thick portion.

  Specifically, when the surface electrodes 12 and 13 are formed by baking and are cooled, the surface electrodes 12 and 13 contract and the compression of the surface electrodes 12 and 13 generates a compressive stress near the surface of the piezoelectric body 11. And the compressive stress concerning the piezoelectric material 11 becomes so large that the thickness of the surface electrodes 12 and 13 is thick. Therefore, compressive stress is applied near the surface of the piezoelectric body 11 facing the relatively thick portion.

  Compressive stress applied to the piezoelectric body 11 due to the shape effect of the surface electrodes 12 and 13 is regularly generated along a direction parallel to the main surface of the piezoelectric body 11. For this reason, generation | occurrence | production and extension of the crack to the piezoelectric material 11 are suppressed, and the destruction in the high voltage drive of the piezoelectric element 1 can be suppressed.

  If the entire thickness of the surface electrodes 12 and 13 is increased, compressive stress is applied to the entire area of the piezoelectric body 11, but if the entire thickness is increased in this way, bending vibration is hindered. Therefore, by having the lattice-like convex portions 121 or the lattice-like concave portions 131 as described above, it is possible to suppress the generation and extension of cracks in the piezoelectric body 11 while maintaining the flexibility of the piezoelectric element 1. .

  The size of each of the concave portions 122 shown in FIGS. 1 and 2 and the convex portions 132 shown in FIGS. 3 and 4 may be different, but they should be substantially uniform. 1 and 2 and the lattice-shaped recess 131 shown in FIGS. 3 and 4 have a plurality of linear portions extending in the longitudinal direction of the piezoelectric body 11 having a rectangular shape in plan view. It is preferable that the linear portions extending in the short direction perpendicular to each other are parallel to each other and have substantially the same width and spacing.

  By adopting such a configuration, the region where the compressive stress is applied to the piezoelectric body 11 is uniformly distributed throughout the entire area of the piezoelectric body 11, so that the progress of the crack can be suppressed regardless of the position where the crack is generated. 1 destruction can be suppressed.

  Here, as the shape of the concave and convex portions 122 arranged in the vertical and horizontal directions, a triangular shape, a pentagonal or higher polygonal shape, a circular shape, or the like can be adopted in addition to the rectangular shape in plan view as shown in FIGS. Similarly, as the shape of the convex portions 132 arranged in the vertical and horizontal directions, a triangular shape, a pentagonal or higher polygonal shape, a circular shape, or the like can be adopted in addition to the rectangular shape in plan view as shown in FIGS.

  Further, the maximum thickness of the surface electrodes 12 and 13 (distance to the surface farthest from the main surface of the piezoelectric body 11) is set to 2 to 30 μm, for example.

  Also, the width w1 of the grid-like convex portion 121 and the width w2 of the grid-like concave portion 131 are set to 0.01 mm to 0.20 mm, for example.

  In addition, the width of the concave and convex portions 122 arranged in the vertical and horizontal directions is set to, for example, 0.01 mm to 0.20 mm with respect to the longitudinal direction and the width direction of the piezoelectric body 11. Similarly, the width of the convex portions 132 arranged in the vertical and horizontal directions is also set to, for example, 0.01 mm to 0.20 mm with respect to the longitudinal direction and the width direction of the piezoelectric body 11.

Further, a thickness difference t1 between the grid-like convex portion 121 and the concave portion 122 (depth of the concave portion 122 when the grid-like convex portion 121 is used as a reference plane) is set to 1 to 10 μm, for example. Similarly, the thickness difference t2 between the lattice-shaped concave portion 131 and the convex portion 132 (the height of the convex portion 132 when the lattice-shaped concave portion 131 is used as a reference surface) is set to 1 to 10 μm, for example.

  Further, in the case where the concave portions 122 or the convex portions 132 have a square shape of 0.1 mm square in plan view, the surface electrode 12 or the surface electrode 13 can be provided with 50 rows in the width direction and 200 rows in the length direction.

  The sizes of the concave portions 122 shown in FIGS. 1 and 2 and the convex portions 132 shown in FIGS. 3 and 4 may be different from each other, but they should be substantially uniform. 1 and 2 and the lattice-shaped recess 131 shown in FIGS. 3 and 4 have a plurality of linear portions extending in the longitudinal direction of the piezoelectric body 11 having a rectangular shape in plan view. The linear portions extending in the short direction perpendicular to each other in parallel with each other and having the same width and spacing are parallel to each other to form a lattice having substantially the same width and spacing. However, such a configuration is preferable. .

  By adopting such a configuration, the region where the compressive stress is applied to the piezoelectric body 11 is uniformly distributed throughout the entire area of the piezoelectric body 11, so that the progress of the crack can be suppressed regardless of the position where the crack is generated. 1 destruction can be suppressed.

  Alternatively, the corners of the lattice-shaped convex portions 121 or the lattice-shaped concave portions 131 may be curved. FIG. 5 shows an example in which corners of the lattice-shaped recess 131 shown in FIGS. 3 and 4 are curved. Here, the corner means both the ridge on the opening side and the ridge on the bottom side.

  With such a configuration, when the piezoelectric element 1 is displaced, the stress generated at the corners of the surface electrodes 12 and 13 can be dispersed, and the occurrence of cracks in the surface electrodes 12 and 13 can be suppressed.

  Further, although not shown, a plate-like laminated body in which a piezoelectric body and internal electrodes are laminated may be used instead of the piezoelectric body 11 shown in FIGS. In other words, a plate-like laminate in which a piezoelectric body and internal electrodes are laminated, and a surface electrode provided on the main surface of the laminate, the surface electrode having a lattice-like convex portion or a lattice-like concave portion. It is good also as composition which is doing.

  In this case, the thickness of one layer of the piezoelectric body constituting the laminated body can be set to, for example, 0.01 to 0.1 mm in order to drive with a low voltage. The number of stacked layers can be, for example, 2 to 300 layers. Moreover, in order to obtain a large flexural vibration, it can have a piezoelectric constant d31 of 200 pm / V or more.

  In addition, the internal electrodes constituting the laminated body are alternately laminated with piezoelectric bodies, and internal electrodes with different poles are arranged in the order of lamination so that a driving voltage is applied to the piezoelectric bodies sandwiched between them. It is. As a material constituting the internal electrode, various metal materials can be used. For example, a conductor containing silver or silver-palladium as a main component that can be fired at a low temperature, or a conductor containing copper, platinum, or the like can be used. However, a ceramic component or a glass component may be contained therein. When the internal electrode layer is made of a material containing a metal component composed of silver and palladium and a ceramic component that constitutes the piezoelectric layer, the stress due to the shrinkage difference during firing between the piezoelectric layer and the internal electrode layer Therefore, it is possible to obtain a piezoelectric element free from stacking faults.

  The structure of the laminate may be either a unimorph type or a bimorph type.

Although not shown, as a wiring member for inputting an electrical signal to the piezoelectric element 1, a lead wire, a flexible substrate (FPC), or the like whose outer periphery is covered with an insulating film can be used.

  Next, a method for manufacturing the piezoelectric element 1 of the present embodiment will be described.

  First, a binder, a dispersant, a plasticizer, and a solvent are kneaded with the raw material powder of the piezoelectric material to produce a slurry. As the piezoelectric material, any of lead-based and non-lead-based materials can be used.

  Next, the obtained slurry is formed into a sheet shape to obtain a green sheet (molded body). When producing a laminate, an internal electrode paste is printed on this green sheet to form an internal electrode pattern, and, for example, four green sheets on which this electrode pattern is formed are stacked, and only the green sheet is the uppermost layer. Lamination is performed to produce a laminated molded body. Thereafter, the molded body or laminated molded body is degreased and fired, cut into a predetermined size, and then processed into an outer peripheral portion as necessary to obtain a piezoelectric body or laminated body.

  After that, after the surface electrode paste is printed by screen printing or the like over the entire predetermined range of the main surface of the piezoelectric body or the laminate, and then dried, the surface electrode paste is again used with a plate making provided with a mask having a convex portion at a predetermined position. After being printed, the images are baked at a predetermined temperature. In the case of a laminate, after printing the surface electrode paste, the paste of the external electrode that is electrically connected to the internal electrodes may be printed on both sides of the laminate, for example, in the longitudinal direction, and baked.

  In addition to the above-described method, the surface electrode is provided with a predetermined shape by, for example, printing the surface electrode paste over the entire predetermined area of the main surface by screen printing or the like, and then printing the resist in a predetermined shape by an etching method. It is also possible to use a method of forming and a method of printing by adjusting the viscosity of the surface electrode paste using a plate making composed of a mesh having a predetermined shape, for example.

  Thereafter, in order to impart piezoelectricity to the piezoelectric element, a desired piezoelectric element 1 is obtained by applying a DC voltage through the surface electrode or the external electrode to polarize the piezoelectric body.

  Next, an example of an embodiment of the piezoelectric actuator 10 will be described. In addition, this invention is not limited by embodiment shown below.

  FIG. 6 is a schematic perspective view showing an example of the piezoelectric actuator of the present embodiment. A piezoelectric actuator 10 shown in FIG. 6 includes a piezoelectric element 1, a shim plate 2 to which the main surface of the piezoelectric element 1 is bonded, and an adhesive 3 that bonds the piezoelectric element 1 and the shim plate 2.

  As described above, the piezoelectric element 1 includes the surface electrodes 12 and 13 on both main surfaces of the piezoelectric body 11 or the laminated body (not shown), and the surface electrode 12 has the lattice-shaped convex portions 121 or the lattice-shaped concave portions 131. It is a thing of the structure which has. In addition, the structure which has the surface electrode 12 is shown in the figure.

  The shim plate 2 is bonded to one main surface of the piezoelectric element 1 with an adhesive 3. In other words, in order to join the piezoelectric element 1 and the shim plate 2, the adhesive 3 is interposed therebetween.

  Examples of the material of the shim plate 2 include metals such as 42 alloy, brass, and stainless steel, carbon fiber reinforced epoxy resin, and glass fiber reinforced epoxy resin.

  The dimensions of the shim plate 2 can be, for example, 20 mm to 50 mm in length, 5 mm to 12 mm in width, and 0.05 mm to 3.0 mm in thickness.

  The shim plate 2 can be larger in width and length than the piezoelectric element 2. At this time, the shim plate 2 may protrude from both ends in the longitudinal direction of the piezoelectric element 1 or may protrude from both ends in the width direction of the piezoelectric element 2. In addition, as shown in FIG. 6, the shim plate 2 may protrude in both the length direction and the width direction of the piezoelectric element 1. Further, the protruding length of the shim plate 2 from the piezoelectric element 1 is different between the longitudinal direction and the width direction of the piezoelectric element 1 even if the length is the same in the longitudinal direction and the width direction of the piezoelectric element 1. Also good.

  The portion of the shim plate 2 that protrudes from the piezoelectric element 1 can be used as a mounting portion for the piezoelectric actuator 10. The shim plate 2 can also be used as a terminal electrode for connecting a lead wire or the like for applying a voltage to the piezoelectric element 1. The dimensions of the shim plate 2 may be set according to the ease of attachment of the piezoelectric actuator 1 and connection of lead wires or the like.

  As the adhesive 3, for example, an ultraviolet curable adhesive can be used, and usually used adhesives such as epoxy, acrylate, and polyester can be used. If the ultraviolet curable adhesive has anaerobic curability, the area to be cured can be increased.

  Then, when a voltage is applied to the piezoelectric element 1, the piezoelectric body 11 of the piezoelectric element 1 expands and contracts. The piezoelectric actuator 10 bends because the piezoelectric element 1 that expands and contracts and the shim plate 2 that does not expand and contract are bonded together. The piezoelectric element 1 at this time is a unimorph type. Moreover, when the piezoelectric element 1 includes a laminated body, the piezoelectric element 1 can be a bimorph type. In this case, the piezoelectric element 1 itself bends and also bends as the piezoelectric actuator 10 together with the shim plate 2.

  In the piezoelectric actuator 10 having such a structure, the magnitude of bending becomes the displacement amount, and the function of bending displacement in the thickness direction is applied to various devices.

  Here, when driving at a high voltage in order to improve the generated force and displacement, the piezoelectric element 1 may be destroyed, whereas according to the piezoelectric actuator 10 of the present embodiment, the piezoelectric body 11 or the laminated body Since the surface electrodes 12 and 13 provided on the main surface have the lattice-shaped convex portions 121 or the lattice-shaped concave portions 131, the destruction of the piezoelectric element is suppressed. Therefore, it is possible to obtain the piezoelectric actuator 10 that is improved in generated force and displacement by higher voltage driving.

  Further, since the surface electrodes 12 and 13 have the lattice-shaped convex portions 121 or the lattice-shaped concave portions 131, the bonding area with the adhesive 3 increases, so that the bonding strength between the piezoelectric element 1 and the shim plate 2 And the peeling between the piezoelectric element 1 and the shim plate 2 is suppressed even during long-term high-voltage driving.

  Although an example in which one piezoelectric element 1 is bonded to one side of the shim plate 2 as the piezoelectric actuator 10 is shown, the piezoelectric actuator 10 has the piezoelectric element 1 on both sides of the shim plate 2 with the shim plate 2 interposed therebetween. It may be joined.

DESCRIPTION OF SYMBOLS 1 Piezoelectric element 11 Piezoelectric body 12, 13 Surface electrode 121 Grid-shaped convex part 122 Concave part 131 Grid-shaped concave part 132 Convex part 2 Shim plate 3 Adhesive

Claims (4)

A plate-like piezoelectric body, and a surface electrode provided on the main surface of the piezoelectric body,
The surface electrode has a lattice-shaped convex portion or a lattice-shaped concave portion. A plate-like laminate in which a piezoelectric body and internal electrodes are laminated, and a surface electrode provided on the main surface of the laminate,
The surface electrode has a lattice-shaped convex portion or a lattice-shaped concave portion.   3. The piezoelectric element according to claim 1, wherein a corner portion of the lattice-shaped convex portion or the lattice-shaped concave portion is a curved surface. A piezoelectric actuator comprising: the piezoelectric element according to any one of claims 1 to 3; and a shim plate to which the main surface of the piezoelectric element is bonded.

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