JP2005322691A - Multilayer piezoelectric element and fuel injector employing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance durability of a multilayer piezoelectric element by employing an external electrode of three layers or more. <P>SOLUTION: In the multilayer piezoelectric element comprising a multilayer body formed by laying at least one piezoelectric and a plurality of internal electrodes alternately in layers, and a pair of external electrodes connected alternately with every other internal electrode on the side face of the multilayer body and being driven by applying an electric field to the external electrode, the external electrode is formed by laying three or more layers. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a laminated piezoelectric element (hereinafter, also simply referred to as “element”) and an injection device, for example, a fuel injection device for an automobile engine, a liquid injection device such as an ink jet, a precision positioning device such as an optical device, and a vibration. Drive elements mounted on prevention devices, etc., and sensor elements mounted on combustion pressure sensors, knock sensors, acceleration sensors, load sensors, ultrasonic sensors, pressure sensitive sensors, yaw rate sensors, etc., and piezoelectric gyros, piezoelectric switches, piezoelectric elements The present invention relates to a multilayer piezoelectric element and a jetting device used for circuit elements mounted on transformers, piezoelectric breakers, and the like.

  2. Description of the Related Art Conventionally, a multilayer piezoelectric actuator in which piezoelectric bodies and internal electrodes are alternately stacked is known as a multilayer piezoelectric element. Multi-layer piezoelectric actuators are classified into two types: simultaneous firing type and stack type in which piezoelectric ceramics made of a single piezoelectric body and plate-like internal electrodes are stacked alternately. Low voltage and low manufacturing costs. In view of the above, the simultaneous firing type laminated piezoelectric actuator is showing superiority because it is advantageous for thinning and advantageous for durability.

  FIG. 3 shows a conventional multilayer piezoelectric element shown in Patent Document 1, and is composed of a multilayer body 20 and external electrodes 23 formed on a pair of side surfaces facing each other. The laminated body 20 is formed by alternately laminating piezoelectric bodies 21 and internal electrodes 22 constituting the laminated body 20, but the internal electrodes 22 are not formed on the entire main surface of the piezoelectric body 21 but have a so-called partial electrode structure. . The internal electrodes 22 of this partial electrode structure are alternately stacked on the left and right sides so as to be exposed on the side surfaces of different stacked bodies 20. Inactive layers 24 are stacked on both end surfaces of the stacked body 20 in the stacking direction. And the external electrode 23 is formed so that the said exposed internal electrodes 22 may be connected to a pair of mutually opposing side surfaces of the laminated body 20, and the internal electrodes 22 can be connected every other layer.

  As a conventional method for manufacturing a laminated piezoelectric element, an internal electrode paste is printed on a ceramic green sheet containing a raw material of the piezoelectric body 21 in a pattern having a predetermined electrode structure as shown in FIG. A laminated body obtained by laminating a plurality of coated green sheets is produced, and the laminated body 20 is produced by firing this. Thereafter, external electrodes 23 are formed on the pair of side surfaces of the laminated body 20 by firing to obtain a laminated piezoelectric element (see, for example, Patent Document 1).

  As the internal electrode 22, an alloy of silver and palladium is used. Further, in order to simultaneously fire the piezoelectric body 21 and the internal electrode 22, the metal composition of the internal electrode 22 is 70% by mass of silver and 30% by mass of palladium. (See, for example, Patent Document 2).

  As described above, the internal electrode 22 made of a metal composition containing a silver-palladium alloy containing palladium is used instead of the internal electrode 22 made of a metal composition containing only silver. This is because when a potential difference is applied between the opposing internal electrodes 22, a so-called silver migration phenomenon occurs in which silver in the electrode moves along the element surface from the positive electrode to the negative electrode of the pair of internal electrodes 22. This phenomenon occurred remarkably in a high temperature and high humidity atmosphere.

When a conventional multilayer piezoelectric element is used as a piezoelectric actuator, a lead wire is further fixed to the external electrode 23 by solder (not shown), and can be driven by applying a predetermined potential between the external electrodes 23. . In particular, in recent years, there is a demand for a small multilayer piezoelectric element to ensure a large amount of displacement under a large pressure, and therefore, a higher electric field is applied and driven continuously for a long time.
JP-A-61-133715 Japanese Utility Model Publication No. 1-130568

  In the conventional co-fired multilayer piezoelectric element, in order to form an external electrode, a metal powder added with a glass component is pasted and printed and fired on the side surface of the laminate 20.

  However, unlike ordinary multilayer electronic components such as capacitors, the multilayer piezoelectric element continuously undergoes dimensional changes when driven, so when driven continuously for a long time under a high electric field and high pressure, If the piezoelectric bodies are peeled off or cracks occur in the external electrodes themselves, contact failure occurs at the connection between the external electrodes and the internal electrodes, and voltage is not supplied to some of the piezoelectric bodies, resulting in displacement characteristics during driving. There was a problem of changing or sparking and stopping driving.

  That is, in recent years, in order to ensure a large amount of displacement with a small multilayer piezoelectric element, a higher electric field is applied and the continuous driving is performed for a long period of time. The external electrode and the internal electrode are not sufficiently bonded to each other only when applied and baked, and the external electrode peels off from the side surface of the laminate and the end of the internal electrode when continuously driven with a high electric field. There is a problem that a contact failure occurs and the displacement characteristics deteriorate. In addition, when a laminated piezoelectric element that continuously undergoes dimensional changes is driven for a long time, the element temperature rises, and if the element temperature exceeds the heat dissipation, a thermal runaway phenomenon occurs, causing destruction, and the displacement amount deteriorates rapidly. There was a problem to do. Therefore, an internal electrode having a small specific resistance has been demanded in order to suppress an increase in element temperature.

  Furthermore, when a conventional multilayer piezoelectric element is used as an actuator used for a drive element such as a fuel injection device, the desired displacement amount gradually changes, causing a problem that the device malfunctions. There has been a demand for suppression of change in displacement and improved durability during operation.

  The present invention has been made in view of the above-described problems. The displacement amount of the piezoelectric actuator is increased even when the displacement amount of the piezoelectric actuator is increased under a high voltage and a high pressure and the piezoelectric actuator is continuously driven for a long period of time. It is an object of the present invention to provide a laminated piezoelectric element and a jetting device which are excellent in durability and have excellent durability.

  The multilayer piezoelectric element of the present invention has a multilayer body in which at least one piezoelectric body and a plurality of internal electrodes are alternately stacked, and the internal electrodes are alternately connected to the side surface of the multilayer body every other layer. A laminated piezoelectric element that includes a pair of external electrodes and is driven by applying an electric field to the external electrodes, wherein the external electrodes are formed by laminating three or more layers.

  Moreover, the thickness of the 1st layer which contact | connected the said piezoelectric material among the said external electrodes is 10 micrometers or less, It is characterized by the above-mentioned.

  Further, the external electrode first layer contains more metal oxide than the external electrode second layer covering the external electrode first layer.

  Further, the outermost layer of the external electrode contains less metal oxide than any other external electrode layer.

The metal oxide is mainly glass. The group 8-10 metal is at least one of Ni, Pt, Pd, Rh, Ir, Ru, and Os. The metal is at least one of Cu, Ag, and Au.

  Further, the Group 8-10 metal is at least one of Pt and Pd, and the Group 11 metal is at least one of Ag and Au. Alternatively, the Group 8-10 metal is Ni, and the Group 11 metal is Cu.

  Furthermore, an oxide, a nitride or a carbide is added to the internal electrode together with the metal composition.

The oxide is mainly composed of a perovskite oxide composed of PbZrO ₃ —PbTiO ₃ .

Further, the piezoelectric body is mainly composed of a perovskite oxide. Further, the piezoelectric body is mainly composed of a perovskite oxide made of PbZrO ₃ —PbTiO ₃ .

  Moreover, the firing temperature of the laminate is 900 ° C. or higher and 1000 ° C. or lower.

  Further, the internal electrodes whose end portions are exposed on the side surfaces of the laminate and the internal electrodes whose end portions are not exposed are alternately configured, and the internal electrodes between which the end portions are not exposed and the external electrodes are formed. A groove is formed in the piezoelectric body portion, and the groove is filled with an insulator having a Young's modulus lower than that of the piezoelectric body.

  The injection device of the present invention includes a storage container having an injection hole, a stacked piezoelectric element stored in the storage container, and a valve that ejects liquid from the injection hole by driving the stacked piezoelectric element. It is characterized by becoming.

  According to the multilayer piezoelectric element of the present invention, the external electrodes are continuously laminated in three or more layers, so that when the multilayer piezoelectric element is driven, the dimensional change of the element continuously occurs. Also, the adhesion strength between the external electrode and the piezoelectric body can be increased. Even if a crack occurs from the outside of the external electrode due to the stress caused by the dimensional change of the element, or even if a crack occurs in the external electrode starting from between the external electrode and the piezoelectric body, the external electrode layer has three or more layers. By being present, the cracks that penetrate the external electrodes can be prevented by blocking the cracks at the interfaces of the external electrode layers.

  Further, by increasing the metal oxide component in the first layer of the external electrode, the adhesion strength between the piezoelectric body and the external electrode is improved, so that the external electrode can be prevented from peeling off. Furthermore, by reducing the metal oxide component in the outermost layer of the external electrode farthest from the piezoelectric body, the hardness of the external electrode is reduced, and even if the multilayer piezoelectric element is driven and continuously changes in size, it becomes an external electrode. It is possible to provide a highly reliable piezoelectric actuator that is less likely to crack and is excellent in durability with a constant displacement during driving. Furthermore, since the outermost layer contains a small amount of metal oxide component in the outermost layer of the external electrode, the outermost layer contains a large amount of metal component, so when connecting a lead wire or the like to the external electrode, solderability, weldability, etc. The connectivity will be excellent.

  Furthermore, since the thickness of the external electrode first layer in contact with the piezoelectric body among the external electrodes is 10 μm or less, the external electrode first layer becomes rich in ductility, so that it is easy to follow the dimensional change of the piezoelectric body. Thus, even if a dimensional change occurs in the multilayer piezoelectric element, a durable external electrode that does not crack can be obtained.

Therefore, even if the multilayer piezoelectric element is continuously driven, the desired displacement amount does not change effectively, so that the device does not malfunction, and a highly reliable injection device having excellent durability is provided. it can.

  The multilayer piezoelectric element of the present invention will be described in detail below. 1A and 1B show an embodiment of a laminated piezoelectric element according to the present invention. FIG. 1A is a perspective view, and FIG. 1B is a perspective development view showing a laminated state of a piezoelectric layer and an internal electrode layer. FIG. 2 is an enlarged sectional view showing a laminated structure of external electrodes in contact with the piezoelectric body of the laminated piezoelectric element of the present invention.

  As shown in FIG. 1, the multilayer piezoelectric element of the present invention has end portions where the internal electrodes 12 are exposed on a pair of opposing side surfaces of a multilayer body 13 in which piezoelectric bodies 11 and internal electrodes 12 are alternately laminated. The external electrodes 15 that are electrically conductive are joined every other layer. In addition, an inactive layer 14 formed of the piezoelectric body 11 is stacked on both ends of the stacked body 13 in the stacking direction. Here, when the multilayer piezoelectric element of the present invention is used as a multilayer piezoelectric actuator, a lead wire may be connected and fixed to the external electrode 15 by soldering, and the lead wire may be connected to an external voltage supply unit.

  An internal electrode 12 is arranged between the piezoelectric bodies 11. Since the internal electrode 12 is made of a metal material such as silver-palladium, a predetermined voltage is applied to each piezoelectric body 11 through the internal electrode 12. The piezoelectric body 11 has a function of causing displacement due to the reverse piezoelectric effect.

On the other hand, since the inert layer 14 is a layer of a plurality of piezoelectric bodies 11 in which the internal electrode 12 is not disposed, no displacement occurs even when a voltage is applied.

  As shown in FIG. 2, the present invention is characterized in that the external electrode 15 is formed by laminating three or more layers. Here, the reason why three or more external electrodes 15 are laminated is that the durability of the laminated piezoelectric element is enhanced.

  That is, when the external electrode 15 is driven by a single-layer or two-layer laminated piezoelectric element, the crack is generated starting from the surface of the external electrode 15 and the interface between the external electrode 15 and the piezoelectric body 11 is generated. As a result, the external electrode 15 is disconnected. At the same time, when the external electrode 15 has two layers, there is a problem of peeling between the two layers when the multilayer piezoelectric element is driven to continuously change the size of the piezoelectric body. In particular, an external electrode layer to which glass is added in order to increase the adhesion strength between the external electrode 15 and the piezoelectric body 11 is provided as an external electrode layer in contact with the piezoelectric body 11, and an external electrode layer having a small amount of glass is provided outside the two layers. Occurs when constructing a structure.

  Therefore, what is required of the external electrode 15 of the multilayer piezoelectric element that continuously changes in size when driven is to ensure close contact with the piezoelectric body 11 and to expand and contract simultaneously with the dimension change of the multilayer piezoelectric element. Since the external electrode 15 can be formed, the external electrode 15 itself has a multilayer structure, and a layer in contact with the piezoelectric body 11 forms a layer having a high bonding strength with the piezoelectric body, and is laminated farthest from the piezoelectric body 11. The outermost layer 15c of the external electrode 15 constitutes an electrode layer having a low Young's modulus and a low resistivity, and is an intermediate layer that relieves stress generated by a dimensional change during driving of the multilayer piezoelectric element. The external electrode layer first layer 15a in contact with the piezoelectric body and the external electrode layer outermost layer 15c located on the outermost side constitute an adhesive layer.

  In order to prevent disconnection due to cracks generated in the external electrode 15 during driving or peeling between the piezoelectric body 11 and the external electrode 15 due to dimensional changes during continuous driving of the multilayer piezoelectric element. It is preferable that each layer of the external electrode 15 laminated in three or more layers is continuously connected. Furthermore, when the smoothness and mass productivity of the external electrode 15 are taken into consideration, 5 layers or less are more preferable. The conductive material constituting the external electrode 15 is desirably a metal having a low specific resistance and a low hardness from the viewpoint of sufficiently absorbing the stress generated by the expansion and contraction of the actuator, and is preferably gold, silver or copper. More preferably, it is a durable laminated piezoelectric element by using copper or silver. More preferably, silver is used to provide a more durable laminated piezoelectric element.

  Furthermore, the present invention is characterized in that the thickness of the external electrode first layer 15a in contact with the piezoelectric body 11 in the external electrode 15 is 10 μm or less. Here, the thickness of the external electrode first layer 15a is an average value of the thickness of the external electrode first layer that can be confirmed when a cross section of the multilayer piezoelectric element is observed with a microscope such as SEM. When the laminated piezoelectric element is driven when the thickness exceeds 10 μm, the dimensional change occurs. Therefore, the external electrode first layer in contact with the piezoelectric body is subject to a dimensional change of the element. There was a problem of cracking. Therefore, by setting the thickness to 10 μm or less, it is possible to obtain a durable external electrode that does not crack even when the element size changes. It is preferable that the thickness is 5 μm or less because durability is further improved. 3 μm or less is more preferable because durability is further improved. Further, it is more preferable that the thickness is 0.5 μm or more and 2 μm or less because durability is further improved.

  If the thickness of each external electrode layer other than the first layer 15a is thicker than that of the first layer 15a, the propagation of cracks occurring in the outermost layer of the external electrode 15 can be effectively suppressed. In order to suppress the propagation of the cracks described above, the thickness of each external electrode layer other than the first layer 15a is preferably 5 μm or more, and more preferably 10 μm, preferably 15 μm or more. Increased durability. Further, if the total thickness of the external electrodes 15 in the stacking direction is 15 μm or more, it can withstand continuous driving of the stacked piezoelectric element. Furthermore, if it is 20 μm, preferably 30 μm or more, it is possible to prevent cracks from propagating and disconnection, and the resistance value of the external electrode 15 can be reduced, so that heat generation of the external electrode 15 can be suppressed. On the other hand, if the total thickness exceeds 100 μm, the external electrode 15 cannot follow the piezoelectric body 11 and the amount of displacement is significantly reduced. Therefore, the total thickness is more preferably 30 to 100 μm.

  Further, in the present invention, it is preferable that the external electrode first layer 15a contains more metal oxide than the external electrode second layer 15b covered with the external electrode first layer 15a. This is because when the metal oxide of the first layer 15a in contact with the piezoelectric body 11 is smaller than that of the second layer 15b, the specific resistance of the first layer 15a is smaller than that of the second layer 15b. When the current flows toward the first layer 15a having a small specific resistance, the first layer 15a is overheated, and the piezoelectric body 11 and the first layer 15a are separated from each other or the temperature of the multilayer piezoelectric element is increased. It is because of thermal runaway. Here, the metal oxide is an oxide of any one of groups 1 to 15 in the periodic table, and can form glass at 1000 ° C. or less, and can be formed of Si, B, Bi, Pb, Zn, Al, and Ca. Ba, Ti, Zr, and rare earth oxides are preferable. Furthermore, Si, B, Bi, Pb, and Zn oxides are more preferable because an amorphous state can be formed at a lower temperature. As a result, the first layer 15a is firmly adhered to the piezoelectric body 11 under the heat treatment conditions for forming the external electrode in the multilayer piezoelectric element. In particular, in order to obtain a multi-layer piezoelectric element with high durability, the amount of the metal oxide of the external electrode first layer is preferably 30% by volume or more, more preferably 50% by volume or more, and even more preferably 70% by volume or more. preferable.

  Furthermore, in the present invention, it is preferable that the outermost layer 15c of the external electrode 15 contains less metal oxide than any other external electrode layer. As a result, the outermost layer 15c is configured to have a low Young's modulus. Therefore, even if the multilayer piezoelectric element is continuously driven and the external electrode expands and contracts as the element size changes, cracks generated in the external electrode are suppressed. It becomes easy to do. Furthermore, since the electrode can have a low resistivity, the element does not overheat even if the element is continuously driven, and thermal runaway does not occur. Moreover, it goes without saying that by increasing the metal component, it is possible to facilitate soldering and welding, or to reduce the contact resistance even when joining with a conductive resin.

  Here, if any of the external electrode layers other than the first layer 15a has less metal oxide than the electrode layer of the first layer 15a, the heating of the element can be suppressed, but the adhesion of the external electrode layer is improved, In order to prevent peeling in the layer, it is more preferable that the metal oxide decreases in order from the first layer 15a toward the outer electrode layer. That is, if the content is controlled step by step so that the content of the metal oxide in each layer of the external electrode 15 is first layer> second layer> third layer>. Thus, the thermal expansion coefficients of the external electrode layers can be made closer to each other, and the adhesion strength between the respective layers can be improved. The amount of the composition of the external electrode 15 can be specified by an analysis method such as an EPMA (Electron Probe Micro Analysis) method. In particular, in order to obtain a laminated piezoelectric element with high durability, the metal oxide content of the outermost layer 15c in the external electrode 15 is preferably 30% by volume or less, more preferably 10% by volume or less, and 5% by volume or less. More preferably.

  Furthermore, in this invention, it is preferable that a metal oxide is mainly glass. As a result, it is possible to suppress the formation of an intermetallic compound in the external electrode 15 and the electrode becoming brittle. Then, the glass component diffuses into the grain boundary of the metal component constituting the external electrode 15 so that the external electrode 15 can be firmly adhered to the piezoelectric body 11.

  In the present invention, it is desirable that the metal composition in the internal electrode 12 is mainly composed of a group 8-10 metal and / or a group 11 metal. This is because the above metal composition has high heat resistance, so that the piezoelectric body 11 and the internal electrode 12 having a high firing temperature can be fired simultaneously. For this reason, since the sintering temperature of the external electrode can be made lower than the sintering temperature of the piezoelectric body, severe interdiffusion between the piezoelectric body and the external electrode can be suppressed.

  Furthermore, when the content of the group 8-10 metal in the internal electrode 12 is M1 (mass%) and the content of the group 11 metal is M2 (mass%), 0 <M1 ≦ 15, 85 ≦ It is preferable that the main component is a metal composition satisfying M2 <100 and M1 + M2 = 100. This is because when the group 8-10 metal exceeds 15% by mass, the specific resistance increases, and when the laminated piezoelectric element is continuously driven, the internal electrode 12 generates heat, and the generated heat has temperature dependence. This is because the amount of displacement of the multilayer piezoelectric element may be reduced because the displacement characteristic is reduced by acting on the substrate 11. Further, when the external electrode 15 is formed, the external electrode 15 and the internal electrode 12 are mutually diffused and joined. However, when the group 8-10 metal exceeds 15 mass%, the internal electrode component diffuses into the external electrode 15. This is because the durability of the laminated piezoelectric element whose dimensions change during driving is reduced because the hardness of the above-described portions becomes high. Moreover, in order to suppress the migration of the group 11 metal in the internal electrode 2 to the piezoelectric body 11, the group 8 to 10 metal is preferably 0.001% by mass to 15% by mass. Moreover, 0.1 mass% or more and 10 mass% or less are preferable at the point of improving the durability of a laminated piezoelectric element. Moreover, when it is excellent in heat conduction and needs higher durability, 0.5 mass% or more and 9.5 mass% or less are more preferable. In addition, when higher durability is required, it is more preferably 2% by mass or more and 8% by mass or less.

  Here, when the Group 11 metal is less than 85% by mass, the specific resistance of the internal electrode 12 increases, and the internal electrode 12 may generate heat when the stacked piezoelectric element is continuously driven. Further, in order to suppress migration of the Group 11 metal in the internal metal 12 to the piezoelectric body 11, the Group 11 metal is preferably 85 mass% or more and 99.999 mass% or less. Moreover, 90 mass% or more and 99.9 mass% or less are preferable at the point of improving the durability of a laminated piezoelectric element. Moreover, when higher durability is required, 90.5 mass% or more and 99.5 mass% or less are more preferable. Moreover, when higher durability is calculated | required, 92 to 98 mass% is further more preferable.

  The 8-10 group metal and 11 group metal which show the mass% of the metal component in the internal electrode 12 can be specified by an analysis method such as EPMA (Electron Probe Micro Analysis) method.

  Furthermore, the metal component in the internal electrode 12 of the present invention is that the Group 8-10 metal is at least one of Ni, Pt, Pd, Rh, Ir, Ru, Os, and the Group 11 metal is Cu, Ag, Preferably, at least one of Au is used. This is because the metal composition has excellent mass productivity in recent alloy powder synthesis techniques.

  Furthermore, as for the metal component in the internal electrode 12, it is preferable that a group 8-10 metal is at least 1 or more types among Pt and Pd, and a group 11 metal is at least 1 type or more among Ag and Au. Thereby, there is a possibility that the internal electrode 12 having excellent heat resistance and small specific resistance can be formed.

  Furthermore, as for the metal component in the internal electrode 12, it is preferable that a 8-10 group metal is Ni. Thereby, the internal electrode 12 excellent in heat resistance may be formed.

  Furthermore, as for the metal component in the internal electrode 12, it is preferable that group 11 metal is Cu. Thereby, there is a possibility that the internal electrode 12 having a low hardness and excellent thermal conductivity can be formed.

  Furthermore, it is preferable to add an oxide, nitride, or carbide to the internal electrode 12 together with the metal composition described above. Thereby, the strength of the internal electrode is increased, and the durability of the multilayer piezoelectric element is improved. In particular, an oxide is more preferable because it interdiffuses with the piezoelectric body and increases the adhesion strength between the internal electrode and the piezoelectric body. Furthermore, it is preferable that the said inorganic composition is 50 volume% or less. Thereby, the bonding strength between the internal electrode 12 and the piezoelectric body 11 can be made smaller than the strength of the piezoelectric body 11. More preferably, the durability of the multilayer piezoelectric element can be improved by setting the volume to 30% by volume or less.

It is preferable that the oxide contains a perovskite oxide composed of PbZrO ₃ —PbTiO ₃ as a main component. The content of the added oxide or the like can be calculated from the area ratio of the composition in the internal electrode in the cross-sectional SEM image of the multilayer piezoelectric element.

Furthermore, it is preferable that the piezoelectric body 11 has a perovskite oxide as a main component. This is because, for example, when formed of a perovskite type piezoelectric ceramic material typified by barium titanate (BaTiO ₃ ) or the like, the piezoelectric strain constant d ₃₃ indicating the piezoelectric characteristics is high, so that the amount of displacement can be increased. Further, the piezoelectric body 11 and the internal electrode 12 can be fired simultaneously. The piezoelectric body 11 described above preferably contains a perovskite oxide composed of PbZrO ₃ —PbTiO ₃ having a relatively high piezoelectric strain constant d ₃₃ as a main component.

  Furthermore, it is preferable that a calcination temperature is 900 degreeC or more and 1000 degrees C or less. This is because when the firing temperature is 900 ° C. or lower, the firing temperature is low, so firing is insufficient, and it becomes difficult to manufacture the dense piezoelectric body 11. Further, when the firing temperature exceeds 1000 ° C., the bonding strength between the internal electrode 12 and the piezoelectric body 11 increases.

  In addition, the internal electrodes 12 whose end portions are exposed on the side surfaces of the multilayer piezoelectric element of the present invention and the internal electrodes 12 whose end portions are not exposed are alternately configured, and the internal electrodes 12 whose end portions are not exposed and It is preferable that a groove is formed in the piezoelectric portion between the external electrodes 15 and an insulator having a Young's modulus lower than that of the piezoelectric body 11 is formed in the groove. As a result, in such a multilayer piezoelectric element, stress generated by displacement during driving can be relieved, so that heat generation of the internal electrode 12 can be suppressed even when continuously driven.

  Next, a method for producing the multilayer piezoelectric element of the present invention will be described.

The multilayer piezoelectric element of the present invention includes a calcined powder of a perovskite oxide piezoelectric ceramic made of PbZrO ₃ —PbTiO ₃ or the like, a binder made of an organic polymer such as acrylic or butyral, and DBP (phthalate). A ceramic green sheet that is made into a piezoelectric body 11 by mixing a slurry with a plasticizer such as dibutyl acid or DOP (dioctyl phthalate), and producing the slurry by a tape molding method such as a known doctor blade method or calendar roll method. Is made.

  Next, a metal paste such as silver-palladium and the like constituting the internal electrode 12 is mixed with a metal oxide such as silver oxide, a binder, a plasticizer, and the like to prepare a conductive paste. Printing on the upper surface to a thickness of 1 to 40 μm by screen printing or the like.

  Then, a plurality of green sheets with conductive paste printed on the upper surface are laminated, the binder is debindered at a predetermined temperature, and then fired at 900 to 1200 ° C., whereby the laminate 13 is produced.

  At this time, when the metal powder constituting the internal electrode 12 such as silver-palladium is added to the green sheet of the inert layer 14 or when the green sheet of the inert layer 14 is laminated, the silver- By printing on the green sheet a slurry composed of metal powder and inorganic compound constituting the internal electrode such as palladium, a binder and a plasticizer, the shrinkage behavior and shrinkage rate of the inert layer 14 and other parts during sintering can be reduced. Since they can be matched, a dense laminate can be formed.

  In addition, the laminated body 13 is not limited to what is produced by the said manufacturing method, What is necessary if the laminated body 13 which laminates | stacks alternately the several piezoelectric body 11 and the some internal electrode 12 is producible. It may be formed by any manufacturing method.

  Thereafter, the internal electrodes 12 whose ends are exposed and the internal electrodes 12 whose ends are not exposed are alternately formed on the side surfaces of the multilayer piezoelectric element, and the internal electrodes 12 and the external electrodes 15 whose ends are not exposed are formed alternately. A groove is formed in the piezoelectric portion, and an insulator such as resin or rubber having a Young's modulus lower than that of the piezoelectric body 11 is formed in the groove. Here, the groove is formed on the side surface of the laminate 13 by an internal dicing device or the like.

Next, a binder is added to the glass powder to produce a silver glass conductive paste, which is formed into a sheet and dried (the solvent is scattered), and the raw density of the sheet is controlled to 6 to 9 g / cm ³ . Then, this sheet is transferred to the external electrode formation surface of the columnar laminate 13, and is a temperature higher than the softening point of the glass, a temperature not higher than the melting point of silver (965 ° C.), and the firing temperature (° C. of the laminate 13). ) At a temperature of 4/5 or less, the binder component in the sheet produced using the silver glass conductive paste is scattered and disappeared, and the external electrode 15 made of a porous conductor having a three-dimensional network structure. Can be formed.

  At this time, the paste constituting the external electrode may be baked after being laminated on the multilayer sheet, or may be baked by laminating the layers one by one. Baking is better for mass production. And when changing the glass component for each layer of the external electrode layer, it is only necessary to have a glass component whose amount is changed for each sheet, but it forms a very thin glass-rich layer on the surface most in contact with the piezoelectric body. In order to achieve this, it is used to laminate a multilayer sheet after printing a glass-rich paste on the laminate by a method such as screen printing. At this time, a sheet of 5 μm or less may be used instead of printing.

  The baking temperature of the silver glass conductive paste effectively forms a neck portion, diffuses and joins silver in the silver glass conductive paste and the internal electrode 12, and effectively creates voids in the external electrode 15. The temperature is preferably 500 to 800 ° C. from the standpoint of remaining and further partially bonding the external electrode 15 and the side surface of the columnar laminate 13. The softening point of the glass component in the silver glass conductive paste is preferably 500 to 800 ° C.

  When the baking temperature is higher than 800 ° C., the silver powder of the silver glass conductive paste is sintered too much to form a porous conductor having an effective three-dimensional network structure. May become too dense, and as a result, the Young's modulus of the external electrode 15 may become too high to absorb the stress during driving sufficiently and the external electrode 15 may be disconnected. Preferably, baking should be performed at a temperature within 1.2 times the softening point of the glass.

  On the other hand, when the baking temperature is lower than 500 ° C., the diffusion electrode is not sufficiently bonded between the end portion of the internal electrode 12 and the external electrode 15, so that the neck portion is not formed and the internal electrode 12 and the external electrode are externally driven. There is a possibility of causing a spark between the electrodes 15.

  Next, the laminated body 13 on which the external electrode 15 is formed is immersed in a silicone rubber solution, and the silicone rubber solution is vacuum degassed to fill the groove of the laminated body 13 with silicone rubber. The laminated body 13 is pulled up, and the side surface of the laminated body 13 is coated with silicone rubber. Thereafter, the silicone rubber filled in the groove and coated on the side surface of the laminated body 13 is cured to complete the laminated piezoelectric element of the present invention.

  Then, a lead wire is connected to the external electrode 15, a direct current voltage of 0.1 to 3 kV / mm is applied to the pair of external electrodes 15 via the lead wire, and the laminate 13 is subjected to polarization treatment. When a multilayer piezoelectric actuator using the multilayer piezoelectric element is completed, a lead wire is connected to an external voltage supply unit, and a voltage is applied to the internal electrode 12 via the lead wire and the external electrode 15, each piezoelectric The body 11 is largely displaced by the inverse piezoelectric effect, and thereby functions as an automobile fuel injection valve that injects and supplies fuel to the engine, for example.

  Furthermore, a conductive auxiliary member made of a conductive adhesive in which a metal mesh or a mesh-like metal plate is embedded on the outer surface of the external electrode 15 may be formed. In this case, even when a large current is input to the actuator by providing a conductive auxiliary member on the outer surface of the external electrode 15 and the actuator is driven at a high speed, a large current can flow through the conductive auxiliary member. For the reason that the current flowing through 15 can be reduced, the external electrode 15 can be prevented from causing local heat generation and disconnection, and the durability can be greatly improved. Furthermore, since a metal mesh or a mesh-like metal plate is embedded in the conductive adhesive, it is possible to prevent the conductive adhesive from cracking.

  The metal mesh is a braided metal wire, and the mesh metal plate is a mesh formed by forming holes in a metal plate.

  Furthermore, the conductive adhesive constituting the conductive auxiliary member is preferably made of a polyimide resin in which silver powder is dispersed. That is, by dispersing silver powder having a low specific resistance in a polyimide resin having high heat resistance, a conductive auxiliary member having a low resistance value and maintaining a high adhesive strength can be formed even when used at high temperatures. . More preferably, the conductive particles are non-spherical particles such as flakes or needles. This is because the entanglement between the conductive particles can be strengthened by making the shape of the conductive particles non-spherical particles such as flakes and needles, and the shear strength of the conductive adhesive can be further increased. This is because it can be increased.

  The multilayer piezoelectric element of the present invention is not limited to these, and various modifications can be made without departing from the gist of the present invention.

  Moreover, although the example which formed the external electrode 15 in the side surface which the laminated body 13 opposes above was demonstrated, in this invention, you may form a pair of external electrode in the side surface provided adjacently, for example.

  FIG. 4 shows an injection device of the present invention. An injection hole 33 is provided at one end of the storage container 31, and a needle valve 35 that can open and close the injection hole 33 is stored in the storage container 31. Has been.

  A fuel passage 37 is provided in the injection hole 33 so as to be able to communicate. The fuel passage 37 is connected to an external fuel supply source, and fuel is always supplied to the fuel passage 37 at a constant high pressure. Therefore, when the needle valve 35 opens the injection hole 33, the fuel supplied to the fuel passage 37 is formed to be injected into a fuel chamber (not shown) of the internal combustion engine at a constant high pressure.

  Further, the upper end portion of the needle valve 35 has a large diameter, and serves as a piston 41 slidable with a cylinder 39 formed in the storage container 31. In the storage container 31, the piezoelectric actuator 43 described above is stored.

  In such an injection device, when the piezoelectric actuator 43 is extended by applying a voltage, the piston 41 is pressed, the needle valve 35 closes the injection hole 33, and the supply of fuel is stopped. When the application of voltage is stopped, the piezoelectric actuator 43 contracts, the disc spring 45 pushes back the piston 41, and the injection hole 33 communicates with the fuel passage 37 so that fuel is injected.

  Further, the present invention relates to a multilayer piezoelectric element and an injection device, but is not limited to the above-described embodiments. For example, a fuel injection device for an automobile engine, a liquid injection device such as an inkjet, an optical device, etc. Drive elements mounted on precision positioning devices, vibration prevention devices, etc., or sensor elements mounted on combustion pressure sensors, knock sensors, acceleration sensors, load sensors, ultrasonic sensors, pressure sensors, yaw rate sensors, and piezoelectric elements Needless to say, the present invention can be applied to elements other than circuit elements mounted on a gyroscope, a piezoelectric switch, a piezoelectric transformer, a piezoelectric breaker, or the like as long as the elements use piezoelectric characteristics.

  Example 1 A laminated piezoelectric actuator comprising the laminated piezoelectric element of the present invention was produced as follows.

First, a slurry in which a calcined powder of a piezoelectric ceramic mainly composed of lead zirconate titanate (PbZrO ₃ -PbTiO ₃ ) having an average particle diameter of 0.4 μm, a binder, and a plasticizer is prepared, and a doctor blade method is used. A ceramic green sheet to be the piezoelectric body 11 having a thickness of 150 μm was produced.

  On one side of this ceramic green sheet, 300 sheets of a conductive paste prepared by adding a binder to a silver-palladium alloy (silver 95% by mass-palladium 5% by weight) to a thickness of 3 μm by a screen printing method are laminated and fired. did. Firing was carried out at 1000 ° C. after holding at 800 ° C.

  Thereafter, a groove having a depth of 50 μm and a width of 50 μm was formed at every other end of the internal electrode on the side surface of the laminate by a dicing apparatus.

  Next, an amorphous glass powder having a softening point of 640 ° C. mainly composed of flaky silver powder having an average particle diameter of 2 μm and silicon having an average particle diameter of 2 μm as the main component so as to have the composition shown in Table 1. 8 parts by mass of the binder is added to the total mass of 100 parts by mass of the silver powder and the glass powder, and mixed well to prepare a silver glass conductive paste. The conductive paste was formed on the release film by screen printing, dried, and then peeled off from the release film to obtain a silver glass conductive paste sheet.

  Then, the silver glass paste sheet was transferred and laminated on the surface of the external electrode 15 of the laminate 13 so as to satisfy the lamination conditions shown in Table 1, and baked at 700 ° C. for 30 minutes to form the external electrode 15.

  Thereafter, a lead wire is connected to the external electrode 15, a 3 kV / mm direct current electric field is applied to the positive and negative external electrodes 15 through the lead wire for 15 minutes, and polarization is performed. As shown in FIG. A multilayer piezoelectric actuator using a piezoelectric element was produced.

When a DC voltage of 170 V was applied to the obtained multilayer piezoelectric element, a displacement amount of 45 μm in the stacking direction was obtained in all the multilayer piezoelectric actuators. Further, a test was performed in which the multilayer piezoelectric actuator was continuously driven up to 1 × 10 ⁹ times by applying an AC voltage of 0 to +170 V at a frequency of 150 Hz at room temperature.

The layer thickness of the external electrode 15 and the amount of glass were measured by measuring the cross section with an SEM. The thickness is calculated from the average value of 5 points in the SEM image, the amount of glass is calculated by calculating the area of the electrode layer from SEM and EPMA, and calculating the area of the glass portion in the area ratio as volume% Calculated. The results are as shown in Table 1.

  From Table 1, since sample numbers 1, 2, and 13 as comparative examples had two or less layers constituting the external electrode 15, when the multilayer piezoelectric actuator was continuously driven, the dimensional change of the piezoelectric body 12 As a result, the load applied to the interface between the piezoelectric body 12 and the external electrode 15 increased, cracks occurred in the external electrode 15 from the interface, and peeling occurred at the interface.

On the other hand, in Sample Nos. 3 to 12, which are the examples of the present invention, since the external electrode was a laminated piezoelectric actuator composed of three or more layers, the element was continuously driven 1 × 10 ⁹ times. A multi-layer piezoelectric actuator having an effective displacement required for a multi-layer piezoelectric actuator and having excellent durability without causing thermal runaway or malfunction could be produced without significantly reducing the displacement.

(Example 2) Sample No. The change rate of the displacement amount of each sample was measured by changing the material composition of the internal electrode 12 of the multilayer piezoelectric actuator 7. Here, the change rate of the displacement amount is the displacement amount (μm) when the multilayer piezoelectric element of each sample reaches 1 × 10 ⁹ times of driving, and the initial value of the multilayer piezoelectric element before starting the continuous driving. This is a comparison with the amount of displacement (μm) in the state. The results are shown in Table 2.

  From Table 2, Sample No. When one internal electrode 12 was made of 100% silver, the laminated piezoelectric element was damaged by silver migration, and continuous driving became impossible. Sample No. 18 is a metal composition in the internal electrode 12, the group 8-10 metal content exceeds 15 mass%, and the group 11 metal content is less than 85 mass%. It can be seen that because the resistance is large, heat is generated when the multilayer piezoelectric element is continuously driven, and the displacement amount of the multilayer piezoelectric actuator decreases.

  In contrast, sample no. 2 to 14, when the metal composition in the internal electrode 12 is 8% to 10% of the metal content and 1% of the metal group content is 2% by mass, 0 <M1 ≦ 15, 85 ≦ M2 <100, M1 + M2 = In order to have a metal composition that satisfies 100% by mass as a main component, the specific resistance of the internal electrode 12 can be reduced, and heat generated in the internal electrode 12 can be suppressed even when continuously driven. It can be seen that a laminated actuator with a stable element displacement can be produced.

  Sample No. 15 to 17 can reduce the specific resistance of the internal electrode 12 and suppress the heat generation generated in the internal electrode 12 even when continuously driven, so that it can be understood that a laminated actuator with a stable element displacement can be manufactured.

  It should be noted that the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the scope of the present invention.

1A and 1B show a laminated piezoelectric element of the present invention, in which FIG. 1A is a perspective view, and FIG. It is an expanded sectional view which shows the laminated structure of the external electrode which touches the piezoelectric material of the multilayer piezoelectric element of this invention. It is a perspective view which shows the conventional lamination type piezoelectric element. It is sectional drawing which shows the injection apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11, 21 ... Piezoelectric body 12, 22 ... Internal electrode 13, 20 ... Laminated body 14, 24 ... Inactive layer 15, 23 ... External electrode 31 ... Storage container 33 ... -Injection hole 35 ... Valve 37 ... Fuel passage 39 ... Cylinder 41 ... Piston 43 ... Piezoelectric actuator

Claims (18)

It has a laminate formed by alternately laminating at least one piezoelectric body and a plurality of internal electrodes, and has a pair of external electrodes in which the internal electrodes are alternately connected to every other side surface of the laminate, A multilayer piezoelectric element that is driven by applying an electric field to the external electrode, wherein the external electrode is laminated in three or more layers. 2. The multilayer piezoelectric element according to claim 1, wherein a thickness of a first external electrode layer in contact with the piezoelectric body of the external electrodes is 10 μm or less. 3. The multilayer piezoelectric element according to claim 1, wherein the first external electrode layer contains more metal oxide than the second external electrode layer covering the first external electrode layer. 4. 4. The multilayer piezoelectric element according to claim 1, wherein the outermost layer of the external electrode contains less metal oxide than any other external electrode layer. The multilayer piezoelectric element according to claim 1, wherein the metal oxide is mainly glass. The multilayer piezoelectric element according to claim 1, wherein the metal composition in the internal electrode contains a group 8-10 metal and / or a group 11 metal as a main component. When the content of the group 8-10 metal in the internal electrode is M1 (mass%) and the content of the group 11 metal is M2 (mass%), 0 <M1 ≦ 15, 85 ≦ M2 <100, M1 + M2 = The multilayer piezoelectric element according to claim 6, wherein 100 is satisfied. The Group 8-10 metal is at least one of Ni, Pt, Pd, Rh, Ir, Ru, and Os, and the Group 11 metal is at least one of Cu, Ag, and Au. The multilayer piezoelectric element according to claim 6 or 7. The group 8-10 metal is at least one of Pt and Pd, and the group 11 metal is at least one of Ag and Au. Multilayer piezoelectric element. 9. The multilayer piezoelectric element according to claim 6, wherein the group 8-10 metal is Ni. The multilayer piezoelectric element according to claim 6, wherein the group 11 metal is Cu. 12. The multilayer piezoelectric element according to claim 6, wherein an oxide, a nitride, or a carbide is added to the internal electrode together with the metal composition. 13. The multilayer piezoelectric element according to claim 12, wherein the oxide contains a perovskite oxide composed of PbZrO ₃ —PbTiO ₃ as a main component. The multilayer piezoelectric element according to claim 1, wherein the piezoelectric body contains a perovskite oxide as a main component. 15. The multilayer piezoelectric element according to claim 14, wherein the piezoelectric body contains a perovskite oxide composed of PbZrO ₃ —PbTiO ₃ as a main component. 16. The multilayer piezoelectric element according to claim 1, wherein a firing temperature of the multilayer body is 900 ° C. or higher and 1000 ° C. or lower. The internal electrodes whose ends are exposed on the side surfaces of the laminate and the internal electrodes whose ends are not exposed are alternately configured, and the internal electrodes between which the ends are not exposed and the external electrodes are formed. The multilayer piezoelectric element according to any one of claims 1 to 16, wherein a groove is formed in the piezoelectric body portion, and the groove is filled with an insulator having a Young's modulus lower than that of the piezoelectric body. . A storage container having an injection hole, the stacked piezoelectric element stored in the storage container, and a valve that ejects liquid from the injection hole by driving the stacked piezoelectric element. An injection device comprising:

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