JP2007019420A - Multilayer piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated piezoelectric element which can be manufactured relatively easily and has excellent crack resistance.
A multilayer piezoelectric element 1 includes a multilayer body 2 in which piezoelectric bodies 3 and internal electrodes 4 are alternately laminated. Between these laminates 2, a buffer layer 5 made of a piezoelectric material having the same composition as that of the piezoelectric body 3 and having a density lower than that of the piezoelectric body 3 is interposed. The piezoelectric body 3, the internal electrode 4 and the buffer layer 5 are integrally sintered.
[Selection] Figure 1

Description

  The present invention relates to a laminated piezoelectric element having a piezoelectric body and internal electrodes.

As a conventional multilayer piezoelectric element, for example, as described in Patent Document 1, a multilayer element in which piezoelectric bodies and internal electrodes are alternately stacked is laminated via a bonding layer. It has been. In such a laminated piezoelectric element, the laminated body can be arbitrarily displaced by applying a voltage to the internal electrode and expanding and contracting the piezoelectric body sandwiched between the different polar internal electrodes that overlap in the laminating direction.
JP-A-2005-45086

  However, in the multilayer piezoelectric element as described above, a plurality of multilayer elements are formed, and these multilayer elements are bonded to each other by a bonding layer. There was a problem that it was increased and mass productivity was poor. Further, since the bonding layer is made of, for example, a glass-based material or a polymer material having a coefficient of thermal expansion different from that of the piezoelectric body, the bonding layer is inferior in crack resistance, and cracks are likely to occur in the multilayer element due to thermal shock.

  Therefore, the present invention has been made in view of such circumstances, and an object thereof is to provide a multilayer piezoelectric element that can be manufactured relatively easily and has excellent crack resistance.

  The present invention relates to a multilayer piezoelectric element including a multilayered structure in which piezoelectric bodies and internal electrodes are alternately stacked, and a piezoelectric material having the same composition system as the piezoelectric body is provided between the multilayered bodies of each layer. A buffer layer made of a material and having a density lower than that of the piezoelectric body is interposed, and the piezoelectric body, the internal electrode, and the buffer layer are integrally sintered.

  In such a laminated piezoelectric element of the present invention, a buffer layer having a density lower than that of the piezoelectric body is provided between the laminated bodies of the layers in which the piezoelectric bodies and the internal electrodes are alternately laminated. When the piezoelectric body is displaced (expanded / contracted) by applying a voltage, the stress applied to the laminated body is relaxed. Here, by integrally sintering the piezoelectric body, the internal electrode, and the buffer layer, it is not necessary to bond the laminated bodies with an adhesive. For this reason, the manufacturing process is simplified, and the multilayer piezoelectric element can be manufactured relatively easily. Furthermore, by forming the buffer layer from a piezoelectric material having the same composition system as the piezoelectric body, the piezoelectric body and the buffer layer have the same thermal expansion coefficient, so that cracks and the like extending in the stacking direction are less likely to occur during integral sintering.

  Preferably, the upper surface and the lower surface of the buffer layer are in contact with the piezoelectric body. As a result, the buffer layer having a lower density than the piezoelectric body is prevented from directly affecting the internal electrode, so that the multilayer body can be appropriately displaced. Although the buffer layer is in contact with the piezoelectric body, since these are formed of the same composition system piezoelectric material, no unnecessary reaction occurs between the piezoelectric body and the buffer layer during integral sintering.

  Preferably, the sintering temperature of the piezoelectric material forming the buffer layer is higher than the sintering temperature of the piezoelectric material forming the piezoelectric body. Thus, for example, when the piezoelectric body, the internal electrode, and the buffer layer are integrally sintered at the same temperature as the sintering temperature of the piezoelectric material forming the piezoelectric body, the piezoelectric material forming the piezoelectric body is completely sintered, Since the piezoelectric material forming the buffer layer is in an unsintered (unfired) state, the buffer layer can be formed easily and reliably.

  According to the present invention, since the multilayer piezoelectric element can be manufactured relatively easily, mass production of the multilayer piezoelectric element can be realized, and the manufacturing cost can be reduced. Moreover, since the crack resistance of the multilayer body is increased, the durability of the multilayer piezoelectric element can be improved.

  Hereinafter, preferred embodiments of a multilayer piezoelectric element according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a perspective view showing an embodiment of a multilayer piezoelectric element according to the present invention. FIG. 2 is a side view of the multilayer piezoelectric element shown in FIG. Here, the multilayer piezoelectric element 1 of the present embodiment is employed as a fuel injection device for an internal combustion engine mounted on an automobile, for example. In each figure, the multilayer piezoelectric element 1 of the present embodiment includes a quadratic element body 20. The element body 20 includes a multilayer body 2 having a plurality of layers and a buffer layer 5 interposed between the multilayer bodies 2 of each layer.

  The laminated body 2 is formed by alternately laminating piezoelectric bodies 3 and internal electrodes 4. The uppermost layer and the lowermost layer of each laminate 2 are piezoelectric bodies 3. The piezoelectric body 3 is made of a material mainly composed of ceramics such as ZnNb-based PZT (lead zirconate titanate) sintered at 950 ° C., for example, and is formed in a rectangular plate shape of “10 mm × 30 mm, thickness 30 μm”. ing.

  The internal electrode 4 is formed so as to be exposed from the inside of the side surface 2a of the multilayer body 2 to the opposite side surface 2b, and to be exposed from the inside of the side surface 2b of the multilayer body 2 to the side surface 2a. The internal electrode 4B. The internal electrodes 4A and 4B are made of a conductive material mainly composed of Ag and Pd, for example.

  The buffer layer 5 is formed so that the entire upper surface and the entire lower surface thereof are in contact with the piezoelectric body 3. The buffer layer 5 is formed of a piezoelectric ceramic material having the same composition as that of the piezoelectric ceramic material forming the piezoelectric body 3, for example, a material mainly composed of ceramics such as CoNb-based PZT. Here, the sintering temperature of the piezoelectric ceramic material forming the buffer layer 5 is higher than the sintering temperature of the piezoelectric ceramic material forming the piezoelectric body 3, for example, 1100 ° C. In order to increase the sintering temperature of PZT, for example, the composition of PZT itself may be changed, or PZT having larger powder (particles) than PZT forming piezoelectric body 3 may be used. Similarly to the piezoelectric body 3, the buffer layer 5 is also formed in a rectangular plate shape of “10 mm × 30 mm, thickness 30 μm”, for example.

  The element body 20 is formed such that the internal electrodes 4 </ b> A and 4 </ b> B are alternately stacked via the piezoelectric bodies 3 and the buffer layers 5. In the element body 20, the region where the internal electrodes 4A, 4B overlap in the stacking direction forms an active region contributing to the expansion / contraction operation (displacement) of the piezoelectric body 3, and the region where the internal electrodes 4A, 4B do not overlap (both ends). The partial region) constitutes an inactive region that does not contribute to the expansion / contraction operation of the piezoelectric body 3.

  External electrodes 6A and 6B electrically connected to the internal electrodes 4A and 4B are provided on both side surfaces of the element body 20 as described above. The external electrodes 6A and 6B are disposed outside the electrode portion 7 so as to cover a part of the side surfaces 2a and 2b of each laminated body 2, and are arranged outside the electrode portion 7 in the lamination direction. It consists of a wavy electrode portion 8 extending in a wavy shape. The corrugated electrode portion 8 is joined to the electrode portion 7 so as to be stretchable (flexible) in the stacking direction. The electrode part 7 is made of a conductive material containing, for example, one of Ag, Au, and Cu as a main component. The corrugated electrode portion 8 is made of, for example, Cu and its alloy, Ni and its alloy, a flexible substrate, or the like.

  In such a laminated piezoelectric element 1, when a voltage is applied between the external electrodes 6A and 6B, a voltage is applied between the internal electrodes 4A and 4B connected to the external electrodes 6A and 6B. As a result, an electric field is generated in the piezoelectric body 3 in the active region sandwiched between the internal electrodes 4A and 4B, and the piezoelectric body 3 is displaced in the stacking direction of the stacked body 2.

  Here, since the buffer layer 5 is formed for each predetermined layer in the element body 20, for example, when the multilayer piezoelectric element 1 is used for a long time, both sides of the element body 20 are displaced by the displacement of the piezoelectric body 3. When a crack is generated from the surface to the inside of the element body 20, the crack extends in the lateral direction along the buffer layer 5. Accordingly, since the stress applied to the element body 20 when the piezoelectric body 3 is displaced is sufficiently relaxed, no crack is generated in the stacking direction of the stacked body 2.

  Moreover, even if the electrode portion 7 of the external electrodes 6A and 6B is cut at the position due to a crack in the buffer layer 5, the electrode portion 7 is connected with the wave-like electrode portion 8, The electrical connection between the internal electrode 4A and the external electrode 6A and the electrical connection between the internal electrode 4B and the external electrode 6B remain secured.

  Next, a method for manufacturing the multilayer piezoelectric element 1 will be described with reference to FIG. First, for example, a paste in which an organic binder resin, an organic solvent, and the like are mixed with ceramic powder mainly composed of ZnNb-based PZT is prepared. Then, a plurality of ceramic green sheets 9 to be the piezoelectric bodies 3 are formed by applying the paste on a carrier film (not shown) by, for example, a doctor blade method.

  Similar to the method for forming the green sheet 9, for example, a paste in which an organic binder resin, an organic solvent, and the like are mixed with ceramic powder mainly composed of CoNb-based PZT is prepared. And the said paste is apply | coated on a carrier film (not shown), for example with a doctor blade method, and the ceramic green sheet 11 used as said buffer layer 5 is formed in multiple numbers.

  Subsequently, for example, a paste is prepared by mixing an organic binder resin, an organic solvent, and the like with a conductive material having a ratio of Ag: Pd = 85: 15. Then, the paste is screen-printed to form electrode patterns 10A corresponding to the internal electrodes 4A and electrode patterns 10B corresponding to the internal electrodes 4B on the upper surfaces of the separate green sheets 9.

  Subsequently, the green sheet 9 on which the electrode pattern 10A is printed, the green sheet 9 on which the electrode pattern 10B is printed, and the green sheet 9 on which the electrode patterns 10A and 10B are not printed are stacked in a predetermined order by a predetermined number of sheets. Then, a plurality of green laminates 12 to be the laminate 2 are produced. Further, these green laminates 12 are laminated via the green sheets 11, and the green sheets 9 on which the electrode patterns 10A and 10B are not printed are laminated on the uppermost layer and the lowermost layer, whereby the above-described element body 20 and A green laminate 13 is produced. In the green laminate 13, the number of green sheets 9 is set to 350 layers, for example, and the green sheets 11 are arranged every 30 layers, for example.

  Subsequently, the green laminate 13 is pressed in the laminating direction at a pressure of about 100 MPa while being heated at a temperature of about 60 ° C., and then the green laminate 13 is cut into a predetermined dimension by, for example, a diamond blade. Thereby, as shown in FIG. 3, the electrode patterns 10 </ b> A and 10 </ b> B are exposed on the side surface of the green laminate 13.

  Then, the cut green laminate 13 is placed on a setter, and degreasing (debinding) of the green laminate 13 is performed at a temperature of about 400 ° C. for about 10 hours, for example. Thereafter, the setter on which the degreased green laminate 13 is placed is placed in a mortar furnace, and the green laminate 13 is sintered, for example, at a temperature of about 950 ° C. for about 2 hours.

  At this time, since the buffer layer 5 is formed of a piezoelectric material having a sintering temperature higher than that of the piezoelectric body 3 and is integrally sintered at the sintering temperature of the piezoelectric body 3, the green sheet 9 is completely sintered. Nevertheless, the green sheet 11 is in an unsintered state (unfired state). Therefore, the buffer layer 5 having a sufficiently lower density than the piezoelectric body 3 can be easily and reliably formed every predetermined layer without adjusting the amount of the organic binder resin with respect to the ceramic material.

  Here, in the green laminate 12, in the region where the electrode patterns 10 </ b> A and 10 </ b> B overlap (active region), Ag, which is the material of the electrode patterns 10 </ b> A and 10 </ b> B, is diffused during sintering, thereby promoting the sintering. For this reason, the density of the buffer layer 5 in the inactive region is lower than the density of the buffer layer 5 in the active region.

  Further, since the green sheets 9 and 11 are formed of the same composition type piezoelectric material, no unnecessary reaction occurs between the green sheet 9 and the green sheet 11 during integral sintering. Thereby, the buffer layer 5 is baked cleanly as a whole.

  Subsequently, external electrodes 6 </ b> A and 6 </ b> B are formed on both side surfaces of the element body 20. Specifically, first, for example, a conductive paste containing Ag as a main component is screen-printed, and then, for example, a baking process is performed at a temperature of about 700 ° C., thereby forming the electrode portions 7 on both side surfaces of the element body 20. In addition, as a formation method of this electrode part 7, you may use sputtering method, an electroless plating method, etc. instead of baking. Then, the wavy electrode portion 8 extending in a wavy shape is joined to the electrode portion 7 at a plurality of locations, for example, by soldering.

  Finally, for example, under a temperature of 120 ° C., a polarization process is performed by applying a predetermined voltage, for example, for 3 minutes so that the electric field strength with respect to the thickness of the piezoelectric body 3 becomes 2 kV / mm. Thus, the multilayer piezoelectric element 1 is completed.

  As described above, the multilayer piezoelectric element 1 according to the present embodiment includes the buffer layer 5 having a density lower than that of the piezoelectric body 3 between the multilayer bodies 2 of each layer. Even when the piezoelectric body 3 is displaced, the stress applied to the laminated body 2 is relaxed by the buffer layer 5 when the piezoelectric body 3 is displaced, and damage such as cracks extending in the vertical direction is less likely to occur. As a result, short-circuit between the internal electrodes 4A and 4B having different polarities is prevented, so that dielectric breakdown of the element can be avoided. Furthermore, since the piezoelectric body 3 and the buffer layer 5 are formed of a piezoelectric material having the same composition, compared to the case where the laminated bodies 2 are bonded to each other with a bonding layer made of a glass-based material or a polymer material, Cracks or the like extending in the vertical direction are less likely to occur. Therefore, durability and reliability of the multilayer piezoelectric element 1 can be improved.

  Further, since the piezoelectric body 3, the internal electrode 4, and the buffer layer 5 are formed by integral sintering, the multilayer piezoelectric element 1 can be manufactured relatively easily, and the manufacturing cost can be reduced.

  The preferred embodiments of the multilayer piezoelectric element according to the present invention have been described above, but the present invention is not limited to the above embodiments. For example, in the multilayer piezoelectric element 1 of the above-described embodiment, the shape of the element body 20 is a quadrangular prism shape, but may be other polygonal column shapes or cylindrical shapes. The positions where the external electrodes 6A and 6B are provided on the side surface of the element body 20 may be positions that do not contact each other.

1 is a perspective view showing an embodiment of a multilayer piezoelectric element according to the present invention. FIG. 2 is a side view of the multilayer piezoelectric element shown in FIG. 1. It is a disassembled perspective view which shows the state after the cutting | disconnection of the green laminated body produced when manufacturing the lamination type piezoelectric element shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric element, 2 ... Laminated body, 3 ... Piezoelectric body, 4, 4A, 4B ... Internal electrode, 5 ... Buffer layer

Claims (3)

A laminated piezoelectric element comprising a multilayered structure in which piezoelectric bodies and internal electrodes are alternately laminated,
Between the laminates of the respective layers, a buffer material having a density lower than that of the piezoelectric body is interposed with a piezoelectric material having the same composition as the piezoelectric body.
The piezoelectric piezoelectric element, the internal electrode, and the buffer layer are integrally sintered. The multilayer piezoelectric element according to claim 1, wherein an upper surface and a lower surface of the buffer layer are in contact with the piezoelectric body.   3. The stacked piezoelectric element according to claim 1, wherein a sintering temperature of the piezoelectric material forming the buffer layer is higher than a sintering temperature of the piezoelectric material forming the piezoelectric body.

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