JP2012079814A - Piezoelectric element - Google Patents

Abstract

An object of the present invention is to prevent fatigue failure at an unselected portion of an external electrode and prevent a reinforcing plate from restraining a piezoelectric element from cracking, thereby causing selective fatigue failure at the reinforcing plate and the external electrode. Provides a piezoelectric element capable of maintaining electrical connection.
A rectangular piezoelectric element 100 in which piezoelectric layers 111 and internal electrodes 112 are alternately stacked and expands and contracts when a voltage is applied, the layer surface being formed in parallel to the stacked surface and stress that relieves stress due to expansion and contraction. A relaxation layer 117, an external electrode 115 provided on a side surface, and a metal reinforcing plate 120 bonded to the external electrode 115 and having a gap in part, the reinforcing plate 120 having a portion inside the gap. It is formed thin enough to selectively cause fatigue failure, and the portion outside the gap is not constrained by the external electrode 120 and the portion inside the gap defined by the stress relaxation layer 117 is connected.
[Selection] Figure 2

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 the active portion deforms where an electric field is applied. However, a large tensile stress is easily generated in the non-active portion where no electric field is 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. 10 is a front view showing a conventional piezoelectric element 600. The lead wire 620 is adhered and reinforced to the external electrode 615, but a crack 641 is generated at the position of the stress relaxation layer 617, and the external electrode 615 and the lead wire 620 are broken.

  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. 11 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. And a stress relieving layer that relieves stress due to expansion and contraction, an external electrode provided on a side surface, and a metal reinforcing plate that is bonded to the external electrode and has a gap in part. Is formed so thin that the portion inside the gap can be selectively damaged by fatigue, and the portion outside the gap is bound by the stress relaxation layer without being constrained by the external electrode. It is characterized by connecting.

  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 portion inside the gap can be selectively fatigued. And, since the portion outside the gap is not constrained by the external electrode and the portion inside the gap separated by the stress relaxation layer is connected, even if selective fatigue failure occurs in the reinforcing plate and the external electrode, electrical connection is made The piezoelectric element can be driven.

  (2) Further, in the piezoelectric element according to the present invention, the reinforcing plate is formed such that the gap is disposed outside the adhesion region with the external electrode in the vicinity of the layer surface of the stress relaxation layer, and the external electrode It is characterized by being glued to. As a result, a large displacement of the stress relaxation layer can selectively fatigue fracture the inner portion of the gap.

  (3) Further, in the piezoelectric element of the present invention, the gap is disposed only on one side outside the region bonded to the external electrode at each position in the stacking direction where the stress relaxation layer exists. It is a feature. Thereby, the selective fatigue failure does not propagate outside the gap on one side, and the other side propagates to the end. As a result, it is possible to connect the reinforcing plates only on one side and maintain the electrical connection.

  (4) Moreover, the piezoelectric element of the present invention is characterized in that the gaps are alternately arranged on the left and right of the region bonded to the external electrode along the stacking direction. Thereby, it is possible to balance the stress applied during expansion and contraction without deviation.

  (5) 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.

  (6) 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.

  (7) Moreover, the piezoelectric element of the present invention is characterized in that the shape of the outward recess of the gap is an arc or a gentle polygon. Thereby, since selective fatigue failure does not propagate outside the gap, the electrical connection of the external electrode can be maintained. The outward concave portion of the gap refers to the shape of the gap on the side of the element body. For example, if the void is circular, the outward concave portion is an arc.

  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.

1 is a perspective view showing a piezoelectric element according to a first embodiment. It is a front view which shows the piezoelectric element which concerns on 1st Embodiment. It is sectional drawing which shows the piezoelectric element which concerns on 1st Embodiment. It is the schematic which shows the manufacturing method of the piezoelectric element which concerns on 1st Embodiment. (A) It is a front view which shows the aspect at the time of use of the piezoelectric element which concerns on 1st Embodiment. (B) It is a front view which shows the aspect at the time of use of an element main body. (A)-(e) It is a figure which shows the example of the hole formed in the reinforcement board. (A) It is a front view which shows the piezoelectric element which concerns on 2nd Embodiment. (B) It is a front view which shows the aspect at the time of use of the piezoelectric element which concerns on 2nd Embodiment. (A) It is a front view which shows the piezoelectric element of a comparative example. (B) It is a front view which shows the element main body 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.

[First Embodiment]
(Piezoelectric element structure)
1 is a perspective view showing the piezoelectric element 100, FIG. 2 is a front view, and FIG. 3 is a cross-sectional view. 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 that connects the unit elements 105 also has a stress relieving action, it can be functionally regarded as the stress relieving 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 is bonded to the external electrode 115 to reinforce the external electrode 115. Thereby, the reinforcing plate 120 can prevent the external electrode 115 from cracking. On the other hand, the reinforcing plate 120 is formed thin and selectively causes fatigue failure at the position of the stress relaxation layer 117. Note that the fatigue failure that is selectively generated is different from the above-described crack.

  The reinforcing plate 120 has a gap in part, like the holes 121a and 121b. The hole 121a and the hole 121b are provided on the left and right when viewed from the front. The hole 121a and the hole 121b are provided on the same stress relaxation layer 117, and the reinforcing plate 120 is formed in advance so as to be arranged as such. In the reinforcing plate 120, a portion of the inner side A (external electrode 115 side, that is, the front center side of the element body 110) sandwiched between the holes 121a and 121b due to expansion and contraction of the piezoelectric element 100 is selectively fatigued. It is possible to prevent the piezoelectric element 100 from being excessively constrained by the fatigue failure of the reinforcing plate 120 and causing cracks.

  The portion B outside the holes 121a and 121b (side surface side of the element body 110, arrow B) is not bonded to the external electrode 115, and thus is not restrained by the external electrode 115 and does not fatigue. As a result, the portions outside the holes 121a and 121b are connected to the portions inside the holes 121a and 121b separated by the stress relaxation layer 117, and the electrical connection is maintained. Therefore, 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.

  Further, the reinforcing plate 120 is formed and adhered to the external electrode so that the holes 121a and 121b are disposed outside the adhesion region with the external electrode 115 at the position in the stacking direction near the layer surface of the stress relaxation layer 117. Yes. Thereby, the inner portion sandwiched between the hole 121a and the hole 121b can be selectively fatigued by a large displacement of the stress relaxation layer 117. That is, the portion inside the holes 121a and 121b (voids) can be selectively fatigued. Note that suitable shapes of the holes 121a and 121b will be described later.

  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. In addition, holes 121a and 121b are provided at the position of the stress relaxation layer 117 when attached to the element body 110 and outside the external electrodes. Positioning the holes 121a and 121b is easier to align than making a metal plate so as to avoid the stress relaxation layer 117. Moreover, although a hole may be formed by press molding or the like, it is preferable to open by etching because the operation becomes easier.

  Then, the unit elements 105 are connected, and the reinforcing plate 120 is bonded to the region 130 overlapping the external electrode 115 by soldering. The piezoelectric element 100 can be formed by adhering 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 a fatigue fracture 141 occurs in the portion sandwiched between the hole 121a and the hole 121b of the reinforcing plate 120. . 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 plate 120 reinforces the external electrode 115 and relieves stress at the position of the stress relieving layer 117. On the other hand, the reinforcing plate 120 maintains the electrical connection divided by the selective fatigue failure of the external electrode 115. That is, electricity is supplied by connecting the outer portions of the holes 121a and 121b of the reinforcing plate 120 to each other.

(Hole shape)
In the example of the piezoelectric element 100 described above, the shapes of the holes 121a and 121b are circles, but are not necessarily limited thereto. 6A to 6E are views showing examples of holes 121a formed in the reinforcing plate 120. FIG. In addition to a circle, a polygon may be considered as the shape of the holes 121a and 121b. Among these, as shown in FIGS. 6A to 6C, the shape of the outward recess 122a of the hole 121a is preferably an arc or a gentle polygon. As a result, the selective fatigue breakdown 141 as shown in FIGS. 6 (d) and 6 (e) does not propagate outward from the gap, and the electrical connection of the external electrodes can be maintained.

[Second Embodiment]
In the above embodiment, the two holes 121a and 121b of the reinforcing plate 120 are formed in parallel to the laminated surface, but may be formed in only one of them. FIG. 7A is a front view showing the piezoelectric element 200. FIG. 7B is a front view showing an aspect when the piezoelectric element 200 is used.

  As shown in FIG. 7A, the holes 221a and 221b are arranged only on one side outside the region bonded to the external electrode 115 at each position in the stacking direction where the stress relaxation layer 117 exists. Therefore, when the selective fatigue failure 241 occurs, the fatigue failure 241 does not propagate outside the hole 221a on one side and propagates to the end on the other side. As a result, it is possible to connect the reinforcing plate 220 only on one side having the hole 221a and maintain the electrical connection.

  The holes 221a and 221b are alternately arranged on the left and right of the region bonded to the external electrode 115 along the stacking direction. Thereby, it is possible to balance the stress applied during expansion and contraction without deviation. The structure of the unit element 105 is the same as that of the piezoelectric element 100.

[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. 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 510.

  FIG. 8A is a front view showing a piezoelectric element 500 of a comparative example. FIG. 8B is a front view showing the element body 110 of the comparative example. As shown in FIG. 8, when the thick reinforcing plate 520 was used, selective 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.

FIG. 9 is a table showing experimental results regarding the material and thickness of the reinforcing plate. As shown in FIG.
In the case of using a phosphor bronze or copper reinforcing plate, it was proved that the reinforcing plate can cause selective fatigue failure by preventing the damage in the unit element by setting the thickness to 0.2 mm or less. . In addition, when using a SUS reinforcing plate, it is proved that the reinforcing plate can cause selective fatigue failure by preventing the damage in the unit element by setting the thickness to 0.1 mm or less. It was.

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 Joint part 120 Reinforcing plate 121a, 121b Hole 122a Hole outward recess 130 Soldering area 141 Fatigue failure 200 Piezoelectric element 220 Reinforcing plates 221a, 221b Hole 241 Fatigue fracture A Inside B sandwiched between the holes Outside the hole

Claims (7)

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 metal reinforcing plate bonded to the external electrode and partially having a gap,
The reinforcing plate is formed so thin that a portion inside the gap can be selectively damaged by fatigue, and a portion outside the gap is bound by the stress relaxation layer without being constrained by the external electrode. A piezoelectric element characterized by connecting inner portions.   The reinforcing plate is formed so as to be disposed outside the adhesion region with the external electrode in the vicinity of the layer surface of the stress relaxation layer and bonded to the external electrode. 1. The piezoelectric element according to 1.   3. The piezoelectric element according to claim 2, wherein the void is disposed only on one side outside the region bonded to the external electrode at each position in the stacking direction where the stress relaxation layer exists.   4. The piezoelectric element according to claim 3, wherein the gaps are alternately arranged on the left and right of the region bonded to the external electrode along the stacking direction.   The piezoelectric element according to any one of claims 1 to 4, 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 claim 1, wherein the reinforcing plate is made of SUS and has a thickness of 0.1 mm or less.   The piezoelectric element according to any one of claims 1 to 6, wherein a shape of the outward concave portion of the gap is an arc or a gentle polygon.

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