JP2006005314A - Multilayer piezoelectric element and injector using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer piezoelectric element which has good electrical continuity between side electrodes and internal electrodes, and to provide an injector using the multilayer piezoelectric element. <P>SOLUTION: A multilayer piezoelectric element 1 has a ceramic laminate 10 with alternating piezoelectric layers 11 made of a piezoelectric material and layered internal electrodes 21 and 22 having conductivity. Side faces 101 and 102 of the ceramic laminate 10 are provided with a first side electrode 31 and a second side electrode 32 respectively. The internal electrodes 21 and 22 consist of alternating first internal electrodes having electrical continuity to the first side electrode 31 and second internal electrodes having electrical continuity to the second side electrode 32. Each of the side electrodes 31 and 32 is made of a conductive adhesive having conductive particles suspended in a resin material with adhesiveness. The conductive particles have an average particle diameter which is smaller than the thickness of each internal electrode in the laminating direction and is between or equal to 1 nm and 100 nm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laminated piezoelectric element having excellent electrical reliability and excellent quality, and an injector for fuel injection using the laminated piezoelectric element.

  Conventionally, as a laminated piezoelectric element, for example, a pair of side electrodes electrically connected to every other internal electrode on the side of a ceramic laminate in which layered internal electrodes and piezoelectric layers are alternately laminated There is what formed. The multilayer piezoelectric element is configured to generate a piezoelectric displacement by a driving voltage applied between a pair of external electrodes electrically connected to the side electrodes.

  As the side electrode for electrically connecting an external electrode and a predetermined internal electrode, for example, a conductive adhesive in which conductive particles such as silver are dispersed in a resin adhesive having an electrical insulation property is used. It may be formed by using (see, for example, Patent Document 1). Further, for example, the side electrode may be formed from baked silver in which silver powder is dispersed in a glass substrate (see, for example, Patent Document 2).

JP 2001-102647 A JP 2001-307548 A

  However, the conventional multilayer piezoelectric element has the following problems. That is, in the side electrode made of the above conductive adhesive, electrical conduction is only ensured by only point contact between the outer peripheral end of the internal electrode and the conductive particles contained in the conductive adhesive. . Therefore, if the layer thickness of the internal electrode is reduced, the number of contact points between the outer peripheral end of the internal electrode and the conductive particles cannot be secured sufficiently, and the electrical resistance between the internal electrode and the side electrode may be excessive. On the other hand, side electrodes made of fired silver require heating at a high temperature of 800 ° C. or higher when formed, and thus there is a problem that damage to the ceramic laminate such as thermal stress is not small.

  The present invention has been made in view of such conventional problems, and provides a multilayer piezoelectric element having excellent electrical conductivity between a side electrode and an internal electrode, and an injector using the multilayer piezoelectric element. It is what.

The first invention has a ceramic laminate formed by alternately laminating a plurality of piezoelectric layers made of a piezoelectric material and a plurality of conductive internal electrodes, and is provided on a side surface of the ceramic laminate. The external electrodes are joined via the first side electrode and the second side electrode, respectively, and the internal electrode is electrically connected to the first internal electrode connected to the first side electrode and the second side electrode. In the laminated piezoelectric element formed by alternately arranging the second internal electrodes,
Each of the side electrodes is formed of a conductive adhesive in which conductive particles are dispersed in an adhesive resin material. The conductive particles have an average particle diameter in the stacking direction of the internal electrodes. A multilayer piezoelectric element having a thickness smaller than the thickness and not smaller than 1 nm and not larger than 100 nm (Claim 1).

  Each side electrode of the multilayer piezoelectric element of the first invention is formed of the conductive adhesive in which conductive particles are dispersed in an adhesive resin material. Here, the conductive particles have an average particle size smaller than the thickness of the internal electrodes in the stacking direction, and the average particle size is 1 nm or more and 100 nm or less.

  Thus, in the said conductive adhesive, the average particle diameter of the said electroconductive particle is made smaller than the thickness of the lamination direction of the said internal electrode. Therefore, the conductive particles can be brought into contact with high reliability with the outer peripheral end of the internal electrode exposed on the side surface of the ceramic laminate. Therefore, according to the conductive adhesive, electrical connection with the internal electrode can be ensured with high reliability.

  Furthermore, in the conductive particles having an average particle diameter of 1 nm or more and 100 nm or less, a so-called necking phenomenon (a phenomenon that occurs between metal particles that are refined to the nanometer order and have high surface energy, and forms metal particles). This is a phenomenon in which metal particles are welded and fixed to each other at a temperature lower than the original melting point of the metal material. This is because this necking phenomenon generally occurs remarkably for metal particles of 100 nm or less. And according to this necking phenomenon, the point contact state of metal particles can be changed to a surface contact state.

  And, according to the conductive adhesive in which conductive particles having an average particle diameter of 1 nm or more and 100 nm or less are dispersed, the above necking phenomenon can be actively utilized, and the original melting point of the metal material forming the conductive particles can be increased. The side electrode can be formed by welding the conductive particles or the conductive particles and the internal electrode at a low temperature. And in the side electrode which produced the necking phenomenon of electroconductive particle, while being able to reduce the internal resistance, the electrical connection state between a side electrode and an internal electrode can be improved markedly. Further, if each side electrode is formed using the above necking phenomenon, the temperature required to form the side electrode having excellent electrical characteristics is lower than the melting point temperature of the main body of the conductive particles. it can. Therefore, it is possible to manufacture a multilayer piezoelectric element having excellent electrical characteristics while suppressing thermal damage acting on the multilayer piezoelectric element.

  When the particle diameter of the conductive particles exceeds 100 nm, the above necking phenomenon does not occur sufficiently, and the electrical characteristics between the internal electrode and the side electrode may not be sufficiently improved. On the other hand, when the particle size of the conductive particles is less than 1 nm, the particles are likely to aggregate, and thus the conductive particles may not be dispersed with high uniformity in the resin material.

  Therefore, the multilayer piezoelectric element according to the first aspect of the invention can efficiently apply the driving voltage applied between the pair of side electrodes to the internal electrode, and has excellent piezoelectric efficiency.

A second invention is an injector configured to open and close a valve body using displacement of a piezoelectric actuator to perform fuel injection control.
The piezoelectric actuator is an injector comprising the multilayer piezoelectric element according to the first aspect of the invention (claim 7).

  The injector according to the second aspect of the present invention utilizes a piezoelectric actuator including the above-described multi-layer piezoelectric element having excellent quality. This multilayer piezoelectric element has good electrical conductivity between the internal electrode and the side electrode. Therefore, the injector has good injection characteristics.

  In the first invention, epoxy, phenol, silicone, polyimide, or the like can be used as the resin material forming the conductive adhesive. Furthermore, in addition to the conductive particles, a metal filler made of silver, copper, nickel, etc. having a larger diameter than the conductive particles may be dispersed in the resin material. In this case, the conductive particles can be welded to the outer periphery of the metal filler by a necking phenomenon. In addition, silver, copper, platinum, or an alloy thereof can be used as the internal electrode.

The conductive particles preferably have an average particle size of 1 nm or more and 50 nm or less (claim 2).
In this case, the necking phenomenon can be generated more remarkably, thereby further improving the electrical conductivity between the side electrode and the internal electrode and further suppressing the internal resistance of the side electrode. it can. Therefore, the piezoelectric characteristics of the multilayer piezoelectric element can be further improved.

Further, it is preferable that 10% by weight or more and 90% by weight or less of the conductive particles are contained in 100% by weight of the conductive adhesive.
In this case, by making the content ratio of the conductive particles appropriate, the adhesive force exerted by the conductive adhesive and the electrical conductivity between the side electrode to be formed and the internal electrode are balanced in a balanced manner. Can do. Here, if the content ratio of the conductive particles is less than 10% by weight, the electrical conductivity between the side electrode and the internal electrode and the size of the internal resistance of the side electrode may not be sufficient. On the other hand, when the content ratio of the conductive particles exceeds 90% by weight, the content ratio of the resin material is relatively insufficient, and the adhesive force by the conductive adhesive may be insufficient.

The thickness of the internal electrode in the stacking direction is preferably 0.1 μm or more and 10 μm or less.
If the layer thickness of the internal electrode is reduced, the piezoelectric performance of the multilayer piezoelectric element can be further enhanced. On the other hand, in this case, the contact area between the thin-film internal electrode and the side electrode is reduced, so that the effect of the first invention is particularly effective.

Moreover, it is preferable that the said electroconductive particle consists of at least any one of gold | metal | money, silver, copper, tin, and platinum.
In the conductive particles made of the metal material, the necking phenomenon is likely to occur. For this reason, the effect of the first invention of improving the electrical characteristics of the multilayer piezoelectric element by actively utilizing the necking phenomenon of the conductive particles is more effectively exhibited.

In addition, an insulating member that covers an outer peripheral end portion of the second internal electrode is exposed on a side surface of the ceramic laminate in which the first side electrode is provided, and on a side surface in which the second side electrode is provided, It is preferable that an insulating member covering the outer peripheral end of the first internal electrode is exposed, and each of the insulating members is made of an organic material.
In general, the insulating member made of an organic material cannot be said to have sufficient heat resistance. Therefore, by utilizing the necking phenomenon, the effect of the first invention in which the side electrode on which the conductive particles are welded at a temperature lower than the melting point temperature of the main body of the conductive particles can be formed is particularly effective. .

Example 1
This example is an example related to the multilayer piezoelectric element 1 that exhibits the piezoelectric effect. The contents will be described with reference to FIGS.
The laminated piezoelectric element 1 of this example has a ceramic laminate 10 in which a plurality of piezoelectric layers 11 made of a piezoelectric material and a plurality of layered internal electrodes 21 and 22 having conductivity are alternately laminated. The external electrode 7 is joined to the side surfaces 101 and 102 of the ceramic laminate 10 via the first side electrode 31 and the second side electrode 32, respectively, and the first side electrode 31 is used as the internal electrodes 21 and 22. A first internal electrode (hereinafter referred to as the first internal electrode 21 as appropriate) and a second internal electrode (hereinafter referred to as the second internal electrode 22 as appropriate) connected to the second side electrode 32. Are arranged alternately.
As shown in FIG. 2, each of the side electrodes 31 and 32 is formed of a conductive adhesive 30 in which conductive particles 302 are dispersed in an adhesive resin material 301. Here, the conductive particles 302 have an average particle diameter smaller than the thickness W in the stacking direction of the internal electrodes 21 and 22, and the average particle diameter is 1 nm or more and 100 nm or less.
Hereinafter, this content will be described in detail.

  As shown in FIGS. 1, 4, and 5, the multilayer piezoelectric element 1 of the present example includes a piezoelectric layer 11 that expands and contracts in response to an applied voltage, and a layered interior for applying the applied voltage to the piezoelectric layer 11. It has an octagonal columnar ceramic laminate 10 in which electrodes 21 and 22 are alternately laminated. The first side electrode 31 and the second side electrode 32 are provided on the pair of side surfaces 101 and 102 among the side surfaces, and the external electrode 7 is joined via the side electrodes 31 and 32. In this example, dummy layers 18 and 19 that do not produce a piezoelectric effect are provided at the upper and lower ends of the ceramic laminate 10 in the stacking direction. In addition, the laminated body shape may be a cylinder, a triangle, a quadrangular prism, or the like other than the octagonal shape of this example. Further, the pair of side surface electrodes 31 and 32 are not necessarily arranged to face each other. The external electrode 7 may be bonded not only on the ceramic laminate 10 but over the entire region in the stacking direction.

  As shown in FIGS. 1 and 8, the first internal electrode 21 has an outer peripheral end exposed on the side surface 101 and is in direct contact with the first side electrode 31. On the other hand, the first internal electrode 21 is exposed at the bottom 420 of the second concave groove portion 42 on the side surface 102 facing the side surface 101, and is covered with the insulating filler 5 filling the second concave groove portion 42. The second side electrode 32 is disposed so as to be in contact with the outer peripheral side of the insulating filler 5.

  Similarly, the second inner electrode 22 has an outer peripheral end exposed at the side surface 102 and is in direct contact with the second side electrode 32. On the other hand, the second internal electrode 22 is exposed at the bottom portion 410 of the first concave groove portion 41 on the side surface 101 facing the side surface 102, and is covered with the insulating filler 5 filled in the first concave groove portion 41. The first side electrode 31 is disposed so as to be in contact with the outer peripheral side of the insulating filler 5.

  Further, as shown in FIGS. 1 and 8, each of the first and second groove portions 41 and 42 is provided so that the bottom surfaces of the bottom portions 410 and 420 are substantially parallel to the side surfaces 101 and 102, and the depth of the grooves. The length D is about 100 μm. For the piezoelectric layer 11 having a thickness L = 80 μm, the groove width W of each of the first groove portions 41 and the second groove portions 42 is set to 80 μm.

  Each first groove portion 41 and second groove portion 42 are filled with an insulating filler 5 made of polyimide. The insulating filler 5 may be made of a material such as silicone, epoxy, or polyamideimide instead.

  As described above, the first side surface electrode 31 and the second side surface electrode 32 are formed from the conductive adhesive 30 in which conductive particles 302 are dispersed in an electrically insulating resin material 301 as shown in FIG. Formed. In this example, epoxy is used as the resin material 301, and the conductive particles 302 are made of Ag having an average particle diameter of 20 nm. In this example, the content ratio of the conductive particles 302 with respect to 100% by weight of the conductive adhesive 30 is 80% by weight. As the material of the conductive particles 302, gold, copper, platinum, or the like can be used in addition to Ag in this example.

Next, a method for manufacturing the multilayer piezoelectric element 1 having the above configuration will be briefly described.
First, a piezoelectric layer firing step is performed in which a ceramic green sheet serving as a piezoelectric material is fired to obtain the piezoelectric layer 11.
In this example, a green sheet was produced as follows in order to employ PZT as the piezoelectric layer 11. First, powders such as lead oxide, zirconium oxide, titanium oxide, niobium oxide, and strontium carbonate, which are main raw materials of the piezoelectric material, are weighed so as to have a desired composition. In consideration of the evaporation of lead, the mixture is blended so as to be 1 to 2% richer than the stoichiometric ratio of the mixing ratio composition. This is dry-mixed in a mixer and then calcined at 800 to 950 ° C.

  Next, pure water and a dispersant are added to the calcined powder to form a slurry, which is wet pulverized by a pearl mill. After this pulverized product is dried and powdered and degreased, a solvent, a binder, a plasticizer, a dispersant and the like are added and mixed by a ball mill. Thereafter, this slurry is subjected to vacuum defoaming and viscosity adjustment while stirring with a stirrer in a vacuum apparatus.

  Next, the slurry is formed into a green sheet having a constant thickness by a doctor blade device. Then, the green sheet was punched out with a press machine or cut with a cutting machine to obtain a 7 mm square sheet piece. Depending on the shape of the multilayer piezoelectric element to be obtained, a sheet piece such as a quadrangle, an ellipse, or a barrel can be formed.

Next, the green sheet is degreased and then fired to obtain the piezoelectric layer 11. The degreasing treatment was performed by holding the green sheet at a temperature of 400 to 700 ° C. for a predetermined time with an electric furnace. The firing process was performed by holding the green sheet at a temperature of 900 to 1200 ° C. for a predetermined time. In this way, in this example, the sintered piezoelectric layers 11 each having a thickness of 80 μm and mainly made of PZT, which is an oxide of a Pb (Zr, Ti) O ₃ perovskite structure, were formed separately one by one. .

Next, as shown in FIG. 3, a laminate manufacturing process was performed in which the obtained piezoelectric layers 11 and the layered electrode material 20 were alternately stacked to prepare a laminate.
In this example, a copper foil having a thickness of 5 μm was used as the electrode material 20. Further, as shown in FIG. 3, the shape of the copper foil was a 7 mm square and the same as that of the piezoelectric layer 11. And the piezoelectric layer 11 and the electrode material 20 were laminated | stacked alternately, and the laminated body was produced so that the lamination | stacking number of the piezoelectric layers 11 might be 250 layers. In addition, dummy layers 18 and 19 were formed on the upper and lower ends in the stacking direction of the stacked body by stacking the piezoelectric layer 11 without the electrode material 20 interposed therebetween.

Next, the laminate is placed in a furnace with a load of about 3 MPa applied from the lamination direction, and the atmosphere in the furnace is evacuated to a vacuum of 1 × 10 ⁻² Pa, and then the pressure in the furnace is set. N ₂ gas as an inert gas was introduced into the furnace so that was maintained at 10 Pa. And the heating joining process which joins the internal electrodes 21 and 22 which consist of the said electrode material 20, and the piezoelectric layer 11 was implemented by hold | maintaining for 10 minutes at the temperature of 960 degreeC.

As a result, as shown in FIG. 4, the substantially quadrangular prism-shaped ceramic laminate 10 having the four side surfaces 101 to 104 and having the internal electrodes 21 and 22 with the end portions exposed on the entire side surfaces is obtained.
Next, as shown in FIG. 5, the corners of the quadrangular prism shape are subjected to surface grinding, and four side surfaces 105 to 108 are newly provided to form the substantially octagonal prism-shaped ceramic laminate 10.

Next, as shown in FIG. 6, a groove was formed by irradiating a laser along the end of the second internal electrode 22 exposed on the side surface 101 of the ceramic laminate 10 to form the first concave groove 41. Similarly, the second concave groove portion 42 was formed by irradiating a laser along the end portion of the first internal electrode 21 exposed on the side surface 102 of the ceramic laminate 10 to form a groove. In this example, a CO ₂ laser was used as the laser, and the respective groove portions 41 and 42 were processed by scanning a laser spot using a galvano optical scanner. In addition, this groove processing can also be performed using grinding with a grindstone, shot blasting, etc. instead of the processing method by laser irradiation. In this example, the cross-sectional shapes of the first groove portion 41 and the second groove portion 42 are the groove depth D = 100 μm and the groove width W = 80 μm (see FIG. 1) as described above.

  Next, as shown in FIG. 7, the first groove portion 41 and the second groove portion 42 are supplied with the insulating filler 5 made of polyimide by using a dispenser and then evacuated to thereby form the first groove portion. The insulating filler 5 was filled into the inner peripheral surfaces of 41 and the second concave groove portion 42 without a gap. Other coating methods such as screen printing and metal mask printing are also possible.

  Next, the conductive adhesive 30 was printed on the side surfaces 101 and 102 of the ceramic laminate (in this example, printed by a metal mask method), and the external electrode 7 was disposed thereon. Thereafter, it was cured at a temperature of 150 ° C. for 60 minutes. In this example, this causes a necking phenomenon in the conductive particles 302. Therefore, in the multilayer piezoelectric element 1 of the present example, electrical conduction between the first side electrode 31 and each first internal electrode 21 and between the second side electrode 32 and each second internal electrode 22 are performed. Electrical continuity is high and reliable. The multilayer piezoelectric element shown in FIG. 1 is manufactured by the above procedure.

Next, the function and effect of the multilayer piezoelectric element 1 of this example will be described.
As described above, the side electrodes 31 and 32 in the multilayer piezoelectric element 1 of the present example are conductive adhesives in which the conductive particles 302 made of silver are dispersed in the resin material 301 made of epoxy as described above. 30. Here, the conductive particles 302 have an average particle diameter of 20 nm, which is smaller than the thickness t = 5 μm in the stacking direction of the internal electrodes 21 and 22.

  When the average particle diameter of the conductive particles 302 is sufficiently small as described above, the conductive particles 302 or the conductive particles 302 and the internal electrodes 21 and 22 are welded due to a so-called necking phenomenon. In this example, by actively utilizing the necking phenomenon, the conductive particles 302 are welded at 150 ° C. lower than the melting point (950 ° C.) of Ag forming the conductive particles 302, and the side electrodes 31, 32 are formed. Formed. Accordingly, the side electrodes 31 and 32 can be formed while suppressing the possibility of thermal damage to the ceramic laminate 10 such as the insulating filler 5 filled in the concave groove portions 41 and 42.

  In the side electrodes 31 and 32 of this example, the conductive particles 302 are welded to each other, and the electrical conductivity is excellent. Further, at the contact interface between the side electrode 31 (32) and the internal electrode 21 (22) or the contact interface between the side electrode 31, 32 and the external electrode 7, the surface of the end of the internal electrodes 21, 22 made of copper or The conductive particles 302 are welded to the surface of the external electrode 7. Therefore, the side electrode 31 (32) and the internal electrode 21 (22) and the side electrodes 31, 32 and the external electrode 7 are electrically connected with high reliability. Further, in the laminated piezoelectric element 1 of this example in which the conductive particles 302 in the side electrodes 31 and 32 are welded to the surfaces of the internal electrodes 21 and 22 made of copper, the side surface at the outer peripheral end of the internal electrode 21 (22). The contact surface with the electrode 31 (32) is less likely to be oxidized. Therefore, even if the multilayer piezoelectric element 1 is heated during production processing or use, there is no possibility that the contact surface is oxidized, and the electrical connection between the internal electrode 21 (22) and the side electrode 31 (32). Stable contact state is maintained.

  FIG. 9 shows the connection resistance value, which is the magnitude of the electrical resistance between the side electrode 31 (32) and the internal electrode 21 (22) in the multilayer piezoelectric element 1, and the multilayer piezoelectric element 1 of this example. This is an example comparing a conventional multilayer piezoelectric element. As in the present example, the side electrode in the conventional multilayer piezoelectric element uses a conductive adhesive in which conductive particles made of silver are dispersed in an epoxy resin material at the same formation temperature as in this example. It is cured at a certain 150 ° C. However, the average particle diameter of the conductive particles 302 in the conventional multilayer piezoelectric element is 5 μm, which is larger than the average particle diameter 20 nm of the conductive particles 302 of this example.

  As can be seen from FIG. 9, in the laminated piezoelectric element 1 of this example, the connection resistance value between the internal electrode and the side electrode is remarkably improved as compared with the conventional one. The reason for this is that the large-diameter conductive particles used in the conventional multilayer piezoelectric element are less susceptible to necking at the above forming temperature and are only dispersed inside the side electrodes. Therefore, in the conventional multilayer piezoelectric element, since the conductive particles are only in point contact with the outer peripheral end portion of the internal electrode, the connection resistance value is high. On the other hand, in the multilayer piezoelectric element 1 of the present example, the conductive particles 302 of the side electrode 31 (32) are welded to the outer peripheral end of the internal electrode 21 (22), so the connection resistance value is low. Yes.

  In this example, the example of the multilayer piezoelectric element 1 having the entire surface electrode structure has been described. Instead, the multilayer piezoelectric element having the partial electrode structure having the side electrodes 31 and 32 of this example is formed. You can also Further, in this example, the end portions of the internal electrodes 21 and 22 are exposed to the bottom portions 410 and 420 of the concave groove portions 41 and 42 and the concave groove portions 41 and 42 are filled with the insulating member 5, but instead, As shown in FIG. 10, the insulating member 51 can be formed on the side surfaces 101 and 102 of the ceramic laminate 10.

  In this example, silver particles are used as the conductive particles 302, but instead, particles made of copper, gold, nickel, platinum, or the like can be used. Furthermore, in this example, copper was used as the internal electrodes 21 and 22 in particular, but an internal electrode containing silver or a silver-palladium alloy that is generally used may be used. Etc. can also be used.

  Furthermore, as shown in FIG. 11, a conductive adhesive 30 in which conductive fillers 303 having an average particle diameter of 5 μm and conductive particles 302 having an average particle diameter of 20 nm are dispersed in a resin material 301 made of epoxy is used. The side electrodes 31 and 32 can also be formed. In this case, the conductive adhesive 30 contains a conductive filler 303 having a diameter larger than that of the conductive particles 302, thereby melting the conductive filler 303 and the internal electrodes 21 and 22 with the conductive particles 302. Effects such as resistance stabilization by adhesion (welding) and cost reduction by reducing the content of the conductive particles 302 can be obtained. As the conductive filler 303, silver, copper, tin, an alloy thereof, or the like can be used.

(Example 2)
In this example, the plating filler 305 obtained by plating the conductive particles 302 based on the conductive adhesive of the first embodiment is included. The contents will be described with reference to FIG.
The conductive adhesive 30 used in this example includes a plating filler 305 in which conductive particles 302 having an average particle diameter of 20 nm are attached to the outer periphery of a conductive filler 303 having an average particle diameter of 5 μm. The conductive adhesive 30 is obtained by dispersing the plating filler 305 in a resin material 301 made of epoxy. In this example, silver particles are used as the conductive particles 302, and silver particles are used as the conductive filler 303.

  The plating filler 305 of this example can be obtained by the following procedure, for example. A metal salt solution mixed with conductive filler 303 (in this example, silver nitrate) is prepared, and a reducing agent is put into the metal solution to deposit silver. Then, the deposited silver adheres to the outer peripheral surface of the conductive filler 303, and the above-described plating filler 305 is obtained. According to this procedure, the conductive particles 302 having an average particle diameter of 5 μm can be efficiently attached to the outer peripheral surface of the conductive filler 303.

  The side electrodes 31 and 32 made of the conductive adhesive 30 cause a necking phenomenon in the conductive particles 302 on the outer periphery of the plating filler 305 during the thermosetting process. Then, the plating fillers 305 are welded to each other via the conductive particles 302 in which the necking phenomenon has occurred. Furthermore, the plating filler 305 is welded to the outer peripheral ends of the internal electrodes 21 and 22 or the external electrodes through the conductive particles 302 that have caused the necking phenomenon.

Therefore, the plating fillers 305 are welded to each other, and in the side electrodes 31 and 32 of this example in which the plating filler 305 is welded to the internal electrodes 21 and 22, the internal resistance is sufficiently suppressed, Electrical continuity between the electrodes 21 and 22 is sufficiently ensured. Therefore, the multilayer piezoelectric element 1 of the present example having the side electrodes 31 and 32 has excellent electrical characteristics.
Other configurations and operational effects are the same as those in the first embodiment.

Example 3
In this example, the multilayer piezoelectric element 1 of the first embodiment is used as a piezoelectric actuator of an injector 6. This injector 6 is used for a common rail injection system of a diesel engine.
As shown in FIG. 13, the injector 6 includes an upper housing 62 in which the laminated piezoelectric element 1 serving as a drive unit is accommodated, and a lower housing 63 that is fixed to the lower end of the injector 6 and in which an injection nozzle portion 64 is formed. have.

The upper housing 62 has a substantially cylindrical shape, and the laminated piezoelectric element 1 is inserted and fixed in a vertical hole 621 that is eccentric with respect to the central axis.
A high-pressure fuel passage 622 is provided in parallel to the side of the vertical hole 621, and an upper end portion thereof communicates with an external common rail (not shown) through a fuel introduction pipe 623 protruding to the upper side of the upper housing 62. .

A fuel lead-out pipe 625 communicating with the drain passage 624 protrudes from the upper portion of the upper housing 62, and the fuel flowing out from the fuel lead-out pipe 625 is returned to the fuel tank (not shown).
The drain passage 624 passes through a gap 60 between the vertical hole 621 and the drive unit (piezoelectric element) 1, and further, a three-way valve, which will be described later, by a passage (not shown) extending downward from the gap 60 in the upper and lower housings 62 and 63. It communicates with 651.

  The injection nozzle section 64 has a nozzle needle 641 that slides in the vertical direction in the piston body 631, and an injection hole 643 that is opened and closed by the nozzle needle 641 and injects high-pressure fuel supplied from a fuel reservoir 642 into each cylinder of the engine. I have. The fuel reservoir 642 is provided around the middle portion of the nozzle needle 641, and the lower end portion of the high-pressure fuel passage 622 is opened here. The nozzle needle 641 receives the fuel pressure in the valve opening direction from the fuel reservoir 642 and receives the fuel pressure in the valve closing direction from the back pressure chamber 644 provided facing the upper end surface, and the pressure in the back pressure chamber 644 is reduced. When lowered, the nozzle needle 641 is lifted, the nozzle hole 643 is opened, and fuel is injected.

  The pressure in the back pressure chamber 644 is increased or decreased by the three-way valve 651. The three-way valve 651 is configured to selectively communicate with the back pressure chamber 644 and the high pressure fuel passage 622 or the drain passage 624. Here, a ball-shaped valve body that opens and closes a port communicating with the high-pressure fuel passage 622 or the drain passage 624 is provided. The valve body is driven by the drive unit 1 through a large-diameter piston 652, a hydraulic chamber 653, and a small-diameter piston 654 disposed below the valve body.

In this example, the multilayer piezoelectric element 1 shown in the first embodiment is used as a drive source in the injector 6 having the above-described configuration. As described above, this multilayer piezoelectric element 1 has a high reliability of the insulation structure between the internal electrode layers 21 and 22 and the side electrodes 31 and 32 and is excellent in durability. Therefore, even in the injector 6 used in a harsh state under a high-temperature atmosphere, the occurrence of cracks during operation can be suppressed, durability can be improved, and the performance and reliability of the injector 6 as a whole are improved. Can be achieved.
Other configurations and operational effects are the same as those in the first embodiment.

FIG. 3 is an explanatory diagram showing the structure of a multilayer piezoelectric element in Example 1. Explanatory drawing which shows the contact state of an internal electrode and a side electrode in Example 1 ((B) is the figure which expanded the A part in (A).). FIG. 3 is an explanatory diagram showing a stacking order of ceramic laminates in Example 1. FIG. 3 is an explanatory diagram showing a quadrangular prism-shaped ceramic laminate in Example 1. FIG. 3 is an explanatory diagram showing an octagonal prism-shaped ceramic laminate in Example 1. Explanatory drawing which shows the state which formed the 1st ditch | groove part and the 2nd ditch | groove part in Example 1. FIG. Explanatory drawing which shows the state which filled the insulating filler in the 1st ditch | groove part and the 2nd ditch | groove part in Example 1. FIG. FIG. 3 is an explanatory diagram illustrating a cross section orthogonal to the stacking direction of the stacked piezoelectric elements in Example 1. The graph which shows the connection resistance value of an internal electrode and a side electrode in Example 1. FIG. FIG. 3 is an explanatory view showing the structure of another multilayer piezoelectric element in Example 1. Explanatory drawing which shows the contact state of the other side surface electrode and internal electrode in Example 1. FIG. Explanatory drawing which shows the contact state of a side electrode and an internal electrode in Example 2. FIG. Explanatory drawing which shows the structure of the injector in Example 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Multilayer piezoelectric element 10 Ceramic laminated body 11 Piezoelectric layer 21 1st internal electrode 22 2nd internal electrode 30 Conductive adhesive 301 Resin material 302 Conductive particle 303 Conductive filler 305 Plating filler 31 1st side electrode 32 2nd Side electrode 41 1st groove part 42 2nd groove part 5 Insulating filler 6 Injector

Claims (7)

A ceramic laminate formed by alternately laminating a plurality of piezoelectric layers made of a piezoelectric material and a plurality of layered internal electrodes having conductivity; a first side electrode provided on a side surface of the ceramic laminate; External electrodes are respectively joined via second side electrodes, and the internal electrodes include a first internal electrode that conducts to the first side electrode and a second internal electrode that conducts to the second side electrode. In the laminated piezoelectric element arranged alternately,
Each of the side electrodes is formed of a conductive adhesive in which conductive particles are dispersed in an adhesive resin material. The conductive particles have an average particle diameter in the stacking direction of the internal electrodes. A multilayer piezoelectric element having a thickness smaller than the thickness and not smaller than 1 nm and not larger than 100 nm.   The multilayer piezoelectric element according to claim 1, wherein the conductive particles have an average particle diameter of 1 nm to 50 nm.   3. The multilayer piezoelectric element according to claim 1, wherein 10% by weight to 90% by weight of the conductive particles are contained in 100% by weight of the conductive adhesive.   4. The multilayer piezoelectric element according to claim 1, wherein a thickness of the internal electrode in the stacking direction is 0.1 μm or more and 10 μm or less.   5. The multilayer piezoelectric element according to claim 1, wherein the conductive particles are made of at least one of gold, silver, copper, tin, and platinum.   In any 1 paragraph of Claims 1-5, the insulating member which covers the perimeter end part of the 2nd internal electrode is exposed to the side which provided the 1st side electrode in the ceramic layered product, The above-mentioned An insulating member covering an outer peripheral end of the first internal electrode is exposed on a side surface provided with two side electrodes, and each of the insulating members is made of an organic material.   The multilayer piezoelectric element according to any one of claims 1 to 6, wherein the piezoelectric actuator is configured to perform fuel injection control by opening and closing a valve body using displacement of a piezoelectric actuator. Injector characterized by having.

Images