JP2012079816A - Piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element capable of preventing fatigue breakdowns at spots of an external electrode which are not selected, preventing cracks from occurring in the piezoelectric element by being constrained by a reinforcing plate, and maintaining electrical connection even if selective fatigue breakdowns occur in the reinforcing plate and the external electrode.SOLUTION: A rectangular piezoelectric element 100, which expands and contracts by applying voltage, comprises: piezoelectric layers 111 and internal electrodes 112 alternately laminated; layer surfaces formed in parallel to laminate surfaces; stress relaxation layers 117 to relax stresses caused by expansion and contraction; external electrodes 115 disposed on the side face; reinforced parts 121, which are bonded to the external electrodes 115, to reinforce the external electrodes 115; connecting parts 122 to connect the reinforced parts 121 which are divided by the stress relaxation layers 117 without being constrained by the external electrodes 115; and a metal reinforcing plate 120 formed in such a thickness that fatigue breakdowns occur selectively at the reinforced parts 121 near the stress relaxation layers 117.

Description

  The present invention relates to a rectangular piezoelectric element in which piezoelectric layers and internal electrodes are alternately stacked and expands and contracts when a voltage is applied.

  A laminated piezoelectric element can be expanded and contracted by applying a voltage to internal electrodes alternately laminated with piezoelectric layers, and is applied to, for example, positioning a stage holding a silicon wafer. During expansion and contraction, the internal electrode overlaps and deformation of the active part to which an electric field is applied is likely to cause a large tensile stress in the non-active part to which an electric field is not applied, which may cause destruction. For this reason, a structure has been proposed in which a stress relaxation layer is provided in the inactive portion to relieve stress.

  However, since a large deformation occurs in the stress relaxation layer portion, the external electrode connecting the internal electrodes can cause fatigue failure. As countermeasures, techniques have been proposed in which lead wires are embedded in external electrodes, wavy lead wires are attached using a stretchable conductive adhesive, or a plurality of lead wires are attached.

  For example, the multilayer piezoelectric element described in Patent Document 1 relieves stress applied in the vicinity of the external electrode while reinforcing the external electrode with a plate having a groove cut in advance. In addition, the multilayer piezoelectric element described in Patent Document 2 connects a plurality of electric wires so that a voltage is supplied even if fatigue failure occurs at a planned crack position.

JP 2010-74033 A JP 2010-109057 A

  As described above, the conventional multilayer piezoelectric element has a problem that the external electrode in the stress relaxation layer portion can cause fatigue failure. FIG. 8 is a front view showing a conventional piezoelectric element 600. The lead wire 620 is bonded to the external electrode 615 for reinforcement, but the external electrode 615 and the lead wire 620 are broken at the position of the stress relaxation layer 617.

  However, if this is dealt with using a thick lead wire, cracks may occur in the vicinity of the external electrode due to the restraint of the lead wire. FIG. 9 is a front view showing a conventional piezoelectric element 700. Although the thick lead wire 720 is bonded to the external electrode 715, a crack 741 is generated near the external electrode 715 due to the restraint of the lead wire 720.

  As in the piezoelectric element described in Patent Document 1, it is conceivable to cut a groove in a plate that reinforces the external electrode in advance to relieve the stress applied to the vicinity of the external electrode. Since it does not exist, fatigue fracture can occur from that point and break. Moreover, although it is conceivable to connect the lead wires so that a voltage is supplied as described in Patent Document 2, the manufacturing work becomes complicated.

  The present invention has been made in view of such circumstances, and prevents fatigue destruction of unselected locations in the external electrode and prevents the reinforcing plate from restraining the piezoelectric element from causing cracks, An object of the present invention is to provide a piezoelectric element that can maintain electrical connection even when selective fatigue failure occurs in a reinforcing plate and external electrodes.

  (1) In order to achieve the above object, a piezoelectric element of the present invention is a rectangular piezoelectric element in which piezoelectric layers and internal electrodes are alternately stacked and expands and contracts by application of a voltage, and the layer surface is parallel to the stacked surface. Is formed, a stress relaxation layer that relieves stress due to expansion and contraction, an external electrode provided on a side surface, a reinforcing portion that is bonded to the external electrode and reinforces the external electrode, and is not restrained by the external electrode. A metal reinforcing plate having a connecting portion that connects the reinforcing portions separated by a stress relaxation layer, and is formed thin enough to selectively fatigue breakage of the reinforcing portion in the vicinity of the stress relaxation layer; It is characterized by providing.

  As described above, since the reinforcing plate is bonded to the external electrode, it is possible to prevent fatigue failure of a non-selected portion of the external electrode. On the other hand, generation of cracks in the element body caused by restraint of the reinforcing plate can be prevented because the reinforcing portion can selectively undergo fatigue failure. And since a connection part connects a reinforcement part without being restrained by an external electrode, even if a selective fatigue failure arises in a reinforcement board and an external electrode, an electrical connection can be maintained and a piezoelectric element can be driven.

  (2) Further, the piezoelectric element of the present invention is characterized in that each of the connecting portions is formed in an arch shape and is formed integrally with the reinforcing portion. Since each of the connecting portions is formed in an arch shape and is not bonded to the external electrode in this way, the connecting portion does not suffer fatigue failure.

  (3) Moreover, the piezoelectric element of the present invention is characterized in that the connecting portions are alternately arranged on the left and right of the reinforcing portions along the stacking direction. Thereby, it is possible to balance the stress applied during expansion and contraction.

  (4) Moreover, the piezoelectric element of the present invention is characterized in that the reinforcing plate is made of phosphor bronze or copper and has a thickness of 0.2 mm or less. Thereby, the reinforcing plate can cause selective fatigue failure, and can prevent the element body from being destroyed.

  (5) Moreover, the piezoelectric element of the present invention is characterized in that the reinforcing plate is made of SUS and has a thickness of 0.1 mm or less. Thereby, the reinforcing plate can cause selective fatigue failure, and can prevent the element body from being destroyed.

  According to the present invention, the fatigue failure of the non-selected portion of the external electrode is prevented, and the reinforcement plate restrains the piezoelectric element from being cracked. Even if this occurs, electrical connection can be maintained.

It is a perspective view which shows the piezoelectric element which concerns on this invention. It is a front view which shows an element main body. It is sectional drawing which shows the piezoelectric element which concerns on this invention. It is the schematic which shows the preparation methods of the piezoelectric element which concerns on this invention. (A) It is a front view which shows the aspect at the time of use of the piezoelectric element which concerns on this invention. (B) It is a front view which shows the aspect at the time of use of a piezoelectric material. (A) It is a front view which shows the piezoelectric element of a comparative example. (B) It is a front view which shows the piezoelectric material of a comparative example. It is a table | surface which shows the experimental result about the material and thickness of a reinforcement board. It is a front view which shows the conventional piezoelectric element. It is a front view which shows the conventional piezoelectric element.

  Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and duplicate descriptions are omitted.

(Piezoelectric element structure)
FIG. 1 is a perspective view showing the piezoelectric element 100, FIG. 2 is a front view showing the element body 110, and FIG. 3 is a cross-sectional view showing the piezoelectric element 100. In FIG. 1 and FIG. 3, an arrow F indicates a direction toward the front. FIG. 3 shows a cross section taken along the plane S shown in FIG. In the drawings, the piezoelectric element 100 is shown by omitting both end sides in the longitudinal direction.

  As shown in FIGS. 1 to 3, the piezoelectric element 100 has a rectangular shape in which piezoelectric layers 111 and internal electrodes 112 are alternately stacked. And it expands and contracts by applying a voltage to the internal electrode 112. The piezoelectric element 100 includes a piezoelectric layer 111, an internal electrode 112, an external electrode 115, a stress relaxation layer 117, and a reinforcing plate 120.

  The piezoelectric element 100 is formed by adhering a reinforcing plate 120 to an element body 110 to which a unit element 105 in which a piezoelectric layer 111 and an internal electrode 112 are integrally fired is connected. The unit elements 105 are connected by an adhesive, but are not necessarily limited. Alternatively, the piezoelectric element 100 may be formed by only a single unit element 105 without being connected.

  The piezoelectric layer 111 is formed of a piezoelectric material such as PZT. The piezoelectric body sandwiched between the series of internal electrodes 112 is polarized by a polarization process. One layer of the piezoelectric layer 111 is actually about 30 μm to 100 μm and is very thin, but is schematically shown in the drawing.

  The internal electrodes 112 are alternately stacked with the piezoelectric layers 111 and are embedded in the piezoelectric body. The piezoelectric element 100 can be driven by applying a voltage to the internal electrode 112 and applying an electric field to the piezoelectric body.

  The external electrode 115 is connected to the lead-out portion of the internal electrode 112 on the side surface of the piezoelectric element 100. The external electrode 115 can be formed by printing and baking a paste such as Ag or Ag / Pd. A voltage is applied to the internal electrode 112 via the external electrode 115.

  The stress relaxation layer 117 has a layer surface in a region around the active region that is parallel to the laminated surface, that is, perpendicular to the expansion and contraction direction. As a result, stress due to expansion and contraction of the piezoelectric element 100 is relieved. In addition, since the coupling portion 117a of the unit element 105 also has a stress relaxation function, it can be functionally regarded as the stress relaxation layer 117.

  The piezoelectric element 100 can be divided into a protective layer provided at both ends in the stacking direction and an active layer that is driven by application of a voltage as a processing allowance. Further, the active layer can be divided into a central active region where projections in the stacking direction of the internal electrodes overlap and a peripheral region provided so that the internal electrodes do not short-circuit with the outside. The active region is a region that is actually driven in the piezoelectric element 100. The active region is driven by a voltage, but the surrounding region is not deformed by the application of the voltage and a stress is generated. Therefore, the stress relaxation layer 117 is necessary.

  The reinforcing plate 120 is made of metal and includes a reinforcing portion 121 and a connecting portion 122. The reinforcing portion 121 is formed in a band shape and is bonded to the external electrode 115 to reinforce the external electrode 115. As described above, since the reinforcing portion 121 is bonded to the external electrode 115, the external electrode 115 can be prevented from cracking. The reinforcing portion 121 is formed in the vicinity of the stress relaxation layer 117 so as to be thin enough to selectively cause fatigue failure. On the other hand, since the reinforcing portion 121 selectively fatigues and breaks, the reinforcing plate 120 does not restrain the element main body 110 and can prevent the element from being broken. Note that the fatigue failure that is selectively generated is different from the above-described crack.

  The connecting part 122 connects the reinforcing part 121 separated by the stress relaxation layer 117 without being constrained by the external electrode 115. Thereby, even if selective fatigue failure occurs in the reinforcing plate 120 and the external electrode 115, electrical connection can be maintained and the piezoelectric element 100 can be driven. Each of the connecting portions 122 is formed in an arch shape and is formed integrally with the reinforcing portion 121. Since the structure is not bonded to the external electrode 115, the connecting portion 122 is not damaged by fatigue.

  It is preferable that the connection part 122 is arrange | positioned alternately at the right and left of the reinforcement part 121 along the lamination direction. As a result, stress is applied evenly during expansion and contraction. In addition, the shape of the connection part 122 does not necessarily need to be an arch shape, it swells outside, and the space | gap 123 should just exist between the reinforcement parts 121. FIG. Due to the voids, fatigue failure does not extend to the outer edge.

  The reinforcing plate 120 is preferably made of phosphor bronze or copper. In that case, the reinforcing plate can cause selective fatigue failure by setting the thickness to 0.2 mm or less. The reinforcing plate 120 may be made of SUS. In this case, the thickness is preferably 0.1 mm or less in order to cause fatigue failure.

(Production method)
Next, a method for manufacturing the piezoelectric element 100 having the above configuration will be described. FIG. 4 is a schematic view showing a method for manufacturing the piezoelectric element 100.

  The unit element 105 is formed by laminating and baking the piezoelectric layer 111 and the internal electrode 112. On the other hand, the metal plate used as the material of the reinforcing plate 120 is selected to have a suitable thickness, and is processed so as to be wider than the external electrode 115 and have the length of the element body 110 to which the unit elements 105 are connected. Further, the connecting portion 122 is provided so as to swell outward (side surface side) at the position of the stress relaxation layer 117 when it is attached to the element body 110. The reinforcing plate 120 is preferably produced by etching.

  Then, the unit elements 105 are connected, and the reinforcing portion 121 is bonded to the region 130 that overlaps the external electrode 115 by soldering. In this way, the piezoelectric element 100 can be formed by bonding the reinforcing plate 120 to a predetermined position of the element body 110 obtained by connecting the unit elements 105. Note that, instead of solder, a conductive adhesive may be used for bonding.

(Usage mode)
Next, a mode when the piezoelectric element 100 is actually used will be described. FIG. 5A is a front view showing an aspect when the piezoelectric element 100 is used. FIG. 5B is a front view showing the element body 110 in use.

  As shown in FIG. 5A, when the piezoelectric element 100 is expanded and contracted, the displacement of the stress relaxation layer 117 increases, and the fatigue failure 141 occurs in the reinforcing portion 122 of that portion. The fatigue failure 141 may be generated in advance. Further, at that time, as shown in FIG. 5B, the fatigue failure 142 occurs also in the portion of the external electrode 115 that overlaps the stress relaxation layer 117.

  By selectively causing fatigue failure 141, the reinforcing portion 121 reinforces the external electrode 115 and relieves stress at the position of the stress relieving layer 117. On the other hand, the connecting portion 122 maintains the electrical connection that is disconnected due to fatigue failure of the external electrode 115. That is, it is energized because the connecting part 122 is connected.

[Example]
Experiments were conducted on the material and thickness of the reinforcing plate of the piezoelectric element. The material of the reinforcing plate was phosphor bronze, copper, or SUS304. Thicknesses of 0.05 mm, 0.1 mm, 0.15 mm, 0.2 mm, and 0.3 mm were prepared. Moreover, the thing of the width of the reinforcement part 0.2mm and the thing of 0.4mm were each prepared. A piezoelectric element was manufactured using such a reinforcing plate. The phosphor bronze and copper reinforcing plates were bonded to the external electrodes by soldering, and the SUS reinforcing plates were bonded to each other with a conductive adhesive.

  When the piezoelectric element manufactured in this way is expanded and contracted, in the piezoelectric element 100 of the embodiment using the thin reinforcing plate, the fatigue failure 141 occurs in the reinforcing plate 120, the stress is relieved, and the element body 110 includes No destruction occurred. On the other hand, as described below, the piezoelectric element 500 of the comparative example using a thick reinforcing plate was broken inside the element body 110.

  FIG. 6A is a front view showing a piezoelectric element 500 of a comparative example. FIG. 6B is a front view showing the element body 110 of the comparative example. As shown in FIG. 6, when the thick reinforcing plate 520 was used, fatigue failure did not occur in the vicinity of the stress relaxation layer 117 of the reinforcing plate 520. In addition, a crack 541 was generated from the vicinity of the end of the external electrode 115, which could be generated when the external electrode 115 was peeled off. For example, in the case of a 0.3 mm reinforcing plate made of phosphor bronze, element destruction occurred. Therefore, a reinforcing plate having a shape in which the reinforcing portion is divided for each unit element 105 was also tried, but element destruction could not be prevented. Further, a reinforcing plate having a sine curve as a whole without a reinforcing portion was also tested, but element destruction occurred in the same manner.

FIG. 7 is a table showing experimental results regarding the material and thickness of the reinforcing plate. As shown in FIG.
When using a phosphor bronze or copper reinforcing plate 120, it is proved that the reinforcing plate can cause selective fatigue failure by preventing the destruction in the unit element 105 by setting the thickness to 0.2 mm or less. It was done. In addition, when the SUS reinforcing plate 120 is used, the reinforcing plate can cause selective fatigue failure by preventing the damage in the unit element 105 by setting the thickness to 0.1 mm or less. Proven. The width of the reinforcing part did not affect the experimental results.

DESCRIPTION OF SYMBOLS 100 Piezoelectric element 105 Unit element 110 Element main body 111 Piezoelectric layer 112 Internal electrode 115 External electrode 117 Stress relaxation layer 117a Connection part 120 Reinforcement plate 121 Reinforcement part 122 Connection part 130 Soldering area 141, 142 Fatigue failure

Claims (5)

Piezoelectric layers and internal electrodes are alternately stacked, and are rectangular piezoelectric elements that expand and contract by application of voltage,
A layer surface is formed in parallel to the laminated surface, and a stress relaxation layer that relieves stress due to expansion and contraction,
An external electrode provided on the side surface;
A reinforcing portion that is bonded to the external electrode and reinforces the external electrode; and a connecting portion that connects the reinforcing portion that is bound by the stress relieving layer without being constrained by the external electrode, and near the stress relieving layer A piezoelectric element comprising: a metal reinforcing plate formed so thin that the reinforcing portion can be selectively fatigued.   2. The piezoelectric element according to claim 1, wherein each of the connecting portions is formed in an arch shape and is formed integrally with the reinforcing portion.   3. The piezoelectric element according to claim 1, wherein the connecting portions are alternately arranged on the left and right of the reinforcing portions along the stacking direction.   The piezoelectric element according to any one of claims 1 to 3, wherein the reinforcing plate is made of phosphor bronze or copper and has a thickness of 0.2 mm or less.   The piezoelectric element according to any one of claims 1 to 3, wherein the reinforcing plate is made of SUS and has a thickness of 0.1 mm or less.

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