JP2019040948A - Stacked piezoelectric element - Google Patents

Abstract

To provide a stacked piezoelectric element in which deterioration of drive accuracy, due to significant deformation of an external electrode at a specific site caused by long term driving, is restrained.SOLUTION: A stacked piezoelectric element 1 includes a laminate 10 having an active part 13 where multiple piezoelectric layers 11 and internal electrode layers 12 are laminated, and an inactive part 14 connected with at least one end of the active part 13 in the lamination direction, a conductor layer 15 provided on the lateral face of the laminate 10 so as to extend in the lamination direction, and an external electrode 17 bonded onto the surface of the conductor layer 15 via a conductive bonding material 16, so as to extend in the lamination direction. A stress relaxation region 18, where the piezoelectric layer 11 is thicker than the central part of the active part 13 exists in the active part 13 near the boundary with the inactive part 14, and when viewing from the lateral face of the laminate 10, the external electrode 17 does not overlap the stress relaxation region 18, but overlaps the active part 13 excepting the stress relaxation region 18.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a piezoelectric element used as, for example, a piezoelectric actuator.

  As a multilayer piezoelectric element, a multilayer body having an active portion in which a plurality of piezoelectric layers and internal electrode layers are stacked, an inactive portion connected to at least one end in the stacking direction of the active portion, and a side surface of the multilayer body, A conductor layer that extends along the laminating direction and is electrically connected to the internal electrode layer, and is joined to the surface of the conductor layer via a conductive bonding material, and extends along the laminating direction. One provided with an external electrode provided is known (see, for example, Patent Document 1).

JP 2002-61551 A

  Here, since the active portion expands and contracts by driving the multilayer piezoelectric element, the inactive portion does not expand and contract, and stress is applied to these boundaries. Therefore, a stress relaxation region in which the thickness of the piezoelectric layer is thicker than the central portion in the stacking direction of the active portion may be provided in a region located near the boundary between the active portion and the inactive portion. As a result, in the vicinity of the boundary between the active portion and the inactive portion (stress relaxation region), the amount of displacement (stretching amount) is smaller than the central portion in the stacking direction of the active portion. This can contribute to suppressing the occurrence of cracks at the boundary.

  However, since the external electrode is joined from the central portion in the stacking direction of the active portion having a large expansion and contraction to the stress relaxation region having a small expansion and contraction, a load is applied near the boundary of the region having a different displacement amount due to long-term driving. The external electrode may be deformed at the portion, and the driving accuracy of the multilayer piezoelectric element may be lowered.

  The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a multilayer piezoelectric element that suppresses a reduction in driving accuracy due to deformation of an external electrode at a specific portion due to long-term driving.

  A multilayer piezoelectric element of the present disclosure includes a multilayer body having an active portion in which a plurality of piezoelectric layers and internal electrode layers are stacked, an inactive portion connected to at least one end in the stacking direction of the active portion, and the multilayer body. A conductor layer provided on a side surface along the laminating direction and electrically connected to the internal electrode layer is bonded to the surface of the conductor layer via a conductive bonding material, along the laminating direction. A stress relaxation region in which the piezoelectric layer is thicker than the central portion of the active portion in the vicinity of the boundary of the active portion with the inactive portion. The external electrode does not overlap the stress relaxation region as viewed from the side surface of the laminate, and is provided to overlap the active portion excluding the stress relaxation region.

  According to the multilayer piezoelectric element of the present disclosure, it is possible to suppress a reduction in driving accuracy due to the external electrode being deformed at a specific portion by long-term driving.

It is a schematic perspective view which shows an example of embodiment of the lamination type piezoelectric element of this indication. It is a schematic perspective view which shows the other example of embodiment of the lamination type piezoelectric element of this indication. It is a schematic perspective view which shows the other example of embodiment of the lamination type piezoelectric element of this indication. It is a schematic perspective view which shows the other example of embodiment of the lamination type piezoelectric element of this indication. It is a schematic perspective view which shows the other example of embodiment of the lamination type piezoelectric element of this indication. It is a schematic perspective view which shows the other example of embodiment of the lamination type piezoelectric element of this indication.

  Hereinafter, an example of the multilayer piezoelectric element of the present embodiment will be described with reference to the drawings.

  FIG. 1 is a schematic perspective view illustrating an example of an embodiment of a multilayer piezoelectric element of the present disclosure. 1 includes an active portion 13 in which a plurality of piezoelectric layers 11 and internal electrode layers 12 are stacked, and an inactive portion 14 connected to at least one end of the active portion 13 in the stacking direction. A laminated body 10 having a conductive layer 15 extending along the laminating direction on the side surface of the laminated body 10 and electrically connected to the internal electrode layer 12, and conductive on the surface of the conductive layer 15. And an external electrode 17 which is joined through a joining material 16 and extends along the laminating direction. In the vicinity of the boundary between the active part 13 and the inactive part 14, the active part 13 is more piezoelectric than the central part. There is a stress relaxation region 18 in which the thickness of the body layer 11 is increased. The external electrode 17 does not overlap the stress relaxation region 18 when viewed from the side surface of the stacked body 10, and the active portion 13 excluding the stress relaxation region 18. It is provided to overlap.

  A laminated body 10 constituting the laminated piezoelectric element 1 is formed by laminating piezoelectric layers 11 and internal electrode layers 12. For example, an active portion in which a plurality of piezoelectric layers 11 and internal electrode layers 12 are alternately laminated. 13 and an inactive portion 14 composed of the piezoelectric layer 11 connected to at least one end in the stacking direction of the active portion 13, for example, 0.5 mm to 10 mm in length, 0.5 mm to 10 mm in width, and 5 mm to 100 mm in height. It is formed in a rectangular parallelepiped shape. In the example shown in the figure, the inactive portions 14 are provided at both ends of the active portion 13 in the stacking direction.

The piezoelectric layer 11 constituting the laminated body 10 is formed of ceramics having piezoelectric characteristics. As such ceramics, for example, a perovskite oxide made of lead zirconate titanate (PbZrO ₃ -PbTiO ₃ ), Lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or the like can be used. The thickness of the piezoelectric layer 11 is, for example, 3 μm to 250 μm.

  The internal electrode layers 12 constituting the multilayer body 10 are formed by simultaneous firing with the ceramics forming the piezoelectric layer 11, and are alternately laminated with the piezoelectric layers 11. As this material, for example, a conductor mainly composed of a silver-palladium alloy that can be fired at a low temperature, or a conductor containing copper, platinum, or the like can be used. In the example shown in the figure, the positive electrode and the negative electrode (or the ground electrode) are alternately led to a pair of side surfaces facing each other of the laminate 10. The thickness of the internal electrode layer 12 is, for example, 0.1 μm to 5 μm.

  In the vicinity of the boundary between the active portion 13 and the inactive portion 14 in the stacked body 10, there is a stress relaxation region 18 in which the piezoelectric layer 11 is thicker than the central portion of the active portion 13. As a result, the displacement (stretching amount) in the vicinity of the boundary between the active portion 13 and the inactive portion 14 (stress relaxation region 18) is smaller than the central portion of the active portion 13 in the stacking direction. This can contribute to suppressing the occurrence of cracks at the boundary with the active portion 14.

The thickness of the piezoelectric layer 11 in the stress relaxation region 18 is set within the range of, for example, 1.2 times to 3.0 times the thickness of the central portion of the active portion 13 in the stacking direction. Further, in the stress relaxation region 18, it is preferable that the thickness of the piezoelectric layer 11 increases as it goes from the central side in the stacking direction to the outside. At this time, the relationship between the thicknesses of the piezoelectric layers 11 adjacent to each other is such that the thickness of the piezoelectric layer 11 located outside is 1.2 times to 2 times the thickness of the piezoelectric layer 11 located on the center side in the stacking direction. It should be set to 0 times.

  A conductor layer 15 is provided on the side surface of the multilayer body 10 so as to extend in the stacking direction, and is electrically connected to the internal electrode layer 12. Specifically, the conductor layers 15 are respectively provided on a pair of opposing side surfaces of the multilayer body 10, and are electrically connected to the internal electrode layers 12 that are alternately led to the pair of opposing side surfaces of the multilayer body 10. Yes. The conductor layer 15 is formed by applying and baking a paste made of, for example, silver and glass, and has a thickness of, for example, 5 μm to 500 μm. Since the conductor layer 15 is electrically connected to all the internal electrode layers 12 led out to the side surface on which the conductor layer 15 is provided, the conductor layer 15 is formed longer than the external electrode 17 described later.

  An external electrode 17 is provided on the surface of the conductor layer 15 via a conductive bonding material 16. Examples of the conductive bonding material 16 used here include a conductive adhesive made of an epoxy resin or a polyimide resin containing a metal powder having good conductivity such as Ag powder or Cu powder. The conductive bonding material 16 has a thickness of 5 μm to 500 μm, for example.

  The external electrode 17 is made of a plate-like body such as copper, iron, stainless steel, phosphor bronze, etc., and has a width of 0.5 mm to 10 mm and a thickness of 0.01 mm to 1.0 mm, for example.

  As shown in FIG. 1, the external electrode 17 is provided so as not to overlap the stress relaxation region 18 as viewed from the side surface of the stacked body 10 and to overlap the active portion 13 excluding the stress relaxation region 18. By joining the external electrode 17 so as to avoid the stress relaxation region 18 with a small amount of displacement, the movement of the external electrode 17 becomes substantially uniform, and the external electrode 17 is caused by stress concentration during expansion and contraction near the boundary where the amount of displacement is different. It is possible to suppress large deformation at this portion, and it is possible to suppress a decrease in driving accuracy even when driven for a long time.

  Here, as shown in FIG. 2, the external electrode 17 has an extending portion 171 that extends in the width direction at the end in the stacking direction, and extends when the side surface of the stacked body 10 is viewed from the front. The portion 171 may extend in the width direction from the conductor layer 15. At this time, the portion of the extending portion 171 that extends in the width direction from the conductor layer 15 is preferably not bonded to the conductor layer 15 by the conductive bonding material 16. Then, for example, a lead member may be bonded to the distal end portion of the extending portion 171 that is a portion not bonded by the conductive layer 15 and the conductive bonding material 16 and connected to an external circuit.

  With this configuration, the external electrode 17 and the lead are connected to each other by the expansion and contraction of the multilayer body 10 as compared with the configuration in which the lead member is directly joined to the end without having an extension at the end in the stacking direction of the external electrode 17 The load of stress applied to the joint with the member can be reduced. In addition, the stress is dispersed and the stress applied to the joint between the external electrode 17 and the lead member as compared with the configuration in which the extension member extending in the stacking direction is provided and the REIT member is joined through the extension. Can reduce the load.

  In particular, when the side surface of the laminate 10 is viewed from the front, the extending portion 171 preferably extends and projects in the width direction from the side surface. Since the position of the joint portion of the lead member moves away from the active portion where the laminate 10 expands and contracts, the stress load applied to the joint portion becomes smaller and breakage can be suppressed. In addition, it is possible to suppress the peeling of the external electrode 17 due to the inrush current and the influence on the laminated body 10, and it is possible to suppress the thermal influence on the joint due to the self-heating of the laminated body 10.

Here, the external electrode 17 is not limited to a flat plate as shown in FIGS. 1 and 2, but as shown in FIG. 3, slits 172 cut out alternately from both sides in the width direction along the stacking direction.
The metal plate which has can be employ | adopted. Thereby, it has followability when the laminated body 10 is displaced, and the displacement amount of the laminated piezoelectric element 1 can be stabilized over a long period of time.

  Here, the slits 172 extend alternately from one side and the other side in the width direction, and are formed to have a width of 0.05 mm to 1 mm and a length of 0.3 mm to 9.5 mm, for example. The slit 172 extending from one side in the width direction and the slit 172 extending from the other side are usually the same length. The slit 172 may have a flat tip or may be rounded. Further, the tip of the slit 172 may be formed wider than the width of the other part, may be tapered such that the width gradually decreases toward the tip of the slit 172, and toward the tip of the slit 172. The taper shape which a width | variety becomes gradually wide may be sufficient. In this way, there are various variations. In addition, as the external electrode 17, what was processed into mesh shape (not shown) etc. is employable.

  In addition, the external electrode 17 shown in FIGS. 1 to 3 has a length from the side surface of the multilayer body 10 until the external electrode 17 is close to the stress relaxation region 18, but may be shorter than this. . For example, as shown in FIG. 4, when the active portion 13 has a plurality of planned fracture layers 19 that are more likely to fracture than other portions, the external electrode 17 is located in the stress relaxation region 18 when viewed from the side surface of the laminate 10. It may be shorter as long as it is provided up to a position overlapping with the nearest planned fracture layer 19.

  It should be noted that, in order to suppress the occurrence of a large influence on the driving of the multilayer piezoelectric element 1 such as a crack that cuts the internal electrode layer 12 due to the stress due to the expansion and contraction of the multilayer body 10, a plurality of schedules are likely to be broken in advance. The rupture layer 19 is provided, and the plurality of planned rupture layers 19 are cracked to an extent that there is no problem, and the stress is dispersed throughout the laminate 10. Here, since the external electrode 17 is provided up to a position overlapping the planned fracture layer 19 closest to the stress relaxation region 18 when viewed from the side surface of the multilayer body 10, a crack generated in the planned fracture layer 19 progresses and the multilayer body. It can suppress that 10 breaks.

  Further, as shown in FIG. 5, the conductive bonding material 16 may be provided along the stacking direction at a position corresponding to the center portion in the width direction perpendicular to the stacking direction of the external electrodes 17. Here, the central portion in the width direction of the external electrode 17 means an inner halved region when the external electrode 17 is divided into four equal parts in the width direction. With such a configuration, the external electrode 17 easily expands and contracts, and easily follows the expansion and contraction of the laminate 10.

  Moreover, as shown in FIG. 6, it is good to provide to the position which protrudes from the both ends of the direction along the lamination direction of the external electrode 17. As shown in FIG. Since the conductive bonding material 16 is provided longer than the external electrode 17, the external electrode 17 is not easily peeled off from the end in the stacking direction, and the conductor layer 15 is protected and reinforced.

  Note that the laminated piezoelectric element 1 is not limited to the above-described embodiment, and various modifications and combinations of the respective configurations are possible.

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

First, a ceramic green sheet to be the piezoelectric layer 11 is produced. Specifically, a ceramic slurry is prepared by mixing a calcined powder of piezoelectric ceramic, a binder made of an organic polymer such as acrylic or butyral, and a plasticizer. And a ceramic green sheet is produced using this ceramic slurry by using tape molding methods, such as a doctor blade method and a calender roll method. As the piezoelectric ceramic, any material having piezoelectric characteristics may be used. For example, a perovskite oxide made of lead zirconate titanate (PbZrO ₃ —PbTiO ₃ ) can be used. As the plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.

  Next, a conductive paste to be the internal electrode layer 12 is produced. Specifically, a conductive paste is prepared by adding and mixing a binder and a plasticizer to a silver-palladium alloy metal powder. This conductive paste is applied on the ceramic green sheet in the pattern of the internal electrode layer 12 using a screen printing method. Furthermore, after laminating a plurality of ceramic green sheets printed with this conductive paste, and performing a binder removal treatment at a predetermined temperature, firing at a temperature of 900 ° C. to 1200 ° C., and using a surface grinder or the like The laminated body 10 including the piezoelectric body layers 11 and the internal electrode layers 12 that are alternately laminated is manufactured by performing a grinding process so as to have the shape of

  At this time, the multilayer body 10 includes the active portion 13 in which a plurality of piezoelectric layers 11 and internal electrode layers 12 are alternately stacked, and the piezoelectric layer 11 at least at one end in the stacking direction of the active portion 13, preferably at both ends. It is fabricated so as to have an inactive portion 14. Also, in the vicinity of the boundary between the active portion 13 and the inactive portion 14 in the active portion 13 constituting the multilayer body 10, there is a stress relaxation region 18 in which the thickness of the piezoelectric layer 11 is thicker than the central portion of the active portion 13. Produced. Here, in order to increase the thickness of the piezoelectric layer 11, the thickness of the ceramic green sheet may be increased.

  The laminate 10 is not limited to the one produced by the above manufacturing method, and any laminate 10 can be produced as long as the laminate 10 formed by laminating a plurality of piezoelectric layers 11 and internal electrode layers 12 can be produced. It may be produced by a manufacturing method.

  Thereafter, a silver glass-containing conductive paste prepared by adding a binder, a plasticizer, and a solvent to a mixture of conductive particles mainly containing silver and glass is used to form a side surface of the laminate 10 in the pattern of the conductor layer 15. After printing by a screen printing method or the like, after drying, a baking process is performed at a temperature of 650 to 750 ° C. to form the conductor layer 15.

  Next, the external electrode 17 is bonded onto the surface of the conductor layer 15 via the conductive bonding material 16.

  Here, the conductive bonding material 16 uses a paste of a conductive adhesive made of an epoxy resin or a polyimide resin containing a metal powder having good conductivity such as Ag powder or Cu powder, and has a predetermined thickness by, for example, a dispensing method. It is formed by controlling the width and length.

  The external electrode 17 is prepared by adjusting the length as long as it does not reach the stress relaxation region 18, and by preparing a conductor layer having slits that are alternately cut from both sides in the width direction as necessary. What is necessary is just to join to 15 desired positions.

  The multilayer piezoelectric element 1 can be produced by the above method.

DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric element 10 ... Laminated body 11 ... Piezoelectric layer 12 ... Internal electrode layer 13 ... Active part 14 ... Inactive part 15 ... Conductor layer 16 ... Conductive bonding material 17 ... external electrode 171 ... extension 172 ... slit 18 ... stress relaxation region 19 ... expected fracture layer

Claims (7)

  A laminated body having an active part in which a plurality of piezoelectric layers and internal electrode layers are laminated, an inactive part connected to at least one end in the laminating direction of the active part, and a side surface of the laminated body extending along the laminating direction A conductive layer electrically connected to the internal electrode layer, and an external electrode bonded to the surface of the conductive layer via a conductive bonding material and extending along the laminating direction; A stress relaxation region in which the thickness of the piezoelectric layer is thicker than the central portion of the active portion, in the vicinity of the boundary between the active portion and the inactive portion; A laminated piezoelectric element that does not overlap the stress relaxation region as viewed from the side of the substrate but is overlapped with the active portion excluding the stress relaxation region.   The multilayer piezoelectric element according to claim 1, wherein the external electrode has slits that are alternately cut from both sides in the width direction along the stacking direction.   The active part has a plurality of planned fracture layers that are more likely to fracture than other parts, and the external electrode is provided up to a position that overlaps with the planned fracture layer closest to the stress relaxation region when viewed from the side of the laminate. The multilayer piezoelectric element according to claim 1 or 2, wherein the multilayer piezoelectric element is provided.   4. The conductive bonding material according to claim 1, wherein the conductive bonding material is provided along the laminating direction at a position corresponding to a central portion in a width direction perpendicular to the laminating direction of the external electrode. The laminated piezoelectric element according to 1.   5. The multilayer piezoelectric element according to claim 1, wherein the conductive bonding material is provided to a position that protrudes from both ends of the external electrode in a direction along the stacking direction. 6.   The external electrode has an extending portion extending in the width direction at an end portion in the stacking direction, and when the side surface of the stacked body is viewed from the front, the extending portion extends in the width direction from the conductor layer. The multilayer piezoelectric element according to any one of claims 1 to 5. The multilayer piezoelectric element according to claim 6, wherein when the side surface of the multilayer body is viewed from the front, the extension portion extends and projects in the width direction from the side surface.

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