CN100517789C - Laminated piezoelectric element and method for manufacturing the same - Google Patents

Abstract

The present invention provides a stacked piezoelectric element, comprising: the multilayer body, it has active part, this active part is laminated at least 1 piezoelectrics and formed by a plurality of internal electrodes formed by first internal electrode and second internal electrode alternately, the active part expands and contracts with the voltage that is applied between first internal electrode and second internal electrode, and external electrode, it forms on 2 sides of the multilayer body separately, one of them links with first internal electrode, another one links with second internal electrode, each external electrode is the layer more than 3 including the 1 st layer that forms with the side of the multilayer body and 2 nd layers that form on the 1 st layer. Therefore, the stacked piezoelectric element is excellent in durability.

Description

Multilayer piezoelectric element and manufacturing method thereof

technical field

The present invention relates to a multilayer piezoelectric element (hereinafter also simply referred to as "element"), for example, to a fuel injection device mounted in an automobile engine, a liquid injection device such as an ink jet, a precision positioning device such as an optical device, or a vibration prevention device, etc. Drive elements in combustion pressure sensors, shock sensors, acceleration sensors, load sensors, ultrasonic sensors, pressure sensitive sensors, yaw rate sensors, etc., and sensor elements mounted in piezoelectric gyroscopes, piezoelectric switches, piezoelectric Multilayer piezoelectric elements used as circuit elements in electric transformers, piezoelectric circuit breakers, etc.

Background technique

Conventionally, a multilayer piezoelectric actuator in which piezoelectric bodies and internal electrodes are alternately laminated is known as a multilayer piezoelectric element. Multilayer piezoelectric actuators are classified into two types, the simultaneous firing type and the lamination type in which piezoelectric ceramics composed of one piezoelectric body and internal electrodes of plate-shaped bodies are alternately stacked, but for the purpose of facilitating low-voltage electrification, In terms of manufacturing cost reduction, layer thinning, and durability considerations, the fired-type laminated piezoelectric actuator is excellent.

FIG. 7 is a diagram showing a conventional multilayer piezoelectric element disclosed in Patent Document 1. As shown in FIG. This multilayer piezoelectric element is composed of a multilayer body 20 and external electrodes 54 formed on a pair of side surfaces facing each other. The laminated body 20 has piezoelectric bodies 51 and internal electrodes 52 stacked alternately. However, the internal electrodes 52 are not formed on the entire main surface of the piezoelectric bodies 51, but have a so-called partial electrode structure. In this partial electrode structure, the internal electrodes 52 are stacked differently on the left and right sides, so that every other layer of the internal electrodes 52 is exposed to different side surfaces of the stacked body 20 . Furthermore, external electrodes 54 are formed on a pair of side surfaces of the laminated body 20 facing each other so as to conduct with the internal electrodes 52 exposed every other layer.

In addition, inert layers 104 are laminated on both end surfaces of the laminated body 20 in the lamination direction. The inert layer 62 is also called a protective layer, and the protective layer generally does not contain the electrode 51 . However, in such a configuration, a shrinkage difference may occur between the portion including the internal electrode layer 52 and the inert layer 62 during firing, resulting in stress or cracks. In order to prevent this, Patent Document 3 discloses a method in which, as shown in FIG. 8 , an electrode 61 identical to an active layer 63 is laminated on an inert layer 62 to prevent cracks after firing. In addition, since the portion including the internal electrode layer 52 connected to the external electrode expands and contracts in response to an applied voltage, it is called an active layer.

Such a multi-layer piezoelectric element is manufactured by the following method. First, an internal electrode paste is printed in a pattern to form a predetermined electrode structure on a ceramic green sheet containing a raw material of the piezoelectric body 51, and a laminated molded body obtained by laminating a plurality of green sheets coated with the internal electrode paste is produced. Then, the laminated body 20 is manufactured by firing this. Then, external electrodes 54 are formed by firing on a pair of side surfaces of the laminate 20 to obtain a multilayer piezoelectric element (for example, refer to Patent Document 1).

In addition, an alloy of silver and palladium is used as the internal electrode 52, and in order to simultaneously fire the piezoelectric body 51 and the internal electrode 52, the metal composition of the internal electrode 52 is set to 70% by mass of silver and 30% by mass of palladium (for example, refer to Patent Document 2).

In this way, instead of using the internal electrode 52 composed of only silver, the internal electrode 52 composed of a metal composition containing silver-palladium alloy (containing palladium) is used because: in a composition containing only silver, When a potential difference is applied between a pair of opposing internal electrodes 52 , silver in the pair of internal electrodes 52 propagates and moves along the surface of the element from the positive electrode to the negative electrode, that is, a so-called silver migration phenomenon occurs. This silver migration phenomenon is particularly evident in a high-temperature, high-humidity environment.

When a conventional multilayer piezoelectric element is used as a piezoelectric actuator, lead wires are further fixed to the external electrodes 54 (not shown) with solder, and a predetermined potential is applied between the external electrodes 54. And drive. In particular, in recent years, small multi-layer piezoelectric elements have been required to be driven continuously for a long time by applying a higher electric field because they are required to ensure a large displacement under a high pressure.

Patent Document 1: Japanese Patent Application Laid-Open No. 61-133715

Patent Document 2: Japanese Patent Application Publication No. 1-130568

Patent Document 3: Japanese Patent Application Laid-Open No. 9-270540

However, in the multi-layer piezoelectric element, as described above, the active layer is stretchable, but the external electrodes and the inert layer formed around it are not stretchable, and thus the following problems arise.

First, since the active layer undergoes repeated dimensional changes during driving, in the case of continuous driving under high electric field and high pressure for a long period of time, the external electrode and the piezoelectric body may peel off, or the external electrode itself may be cracked. Contact failure may occur at the connection portion between the external electrode and the internal electrode. Accordingly, voltage cannot be supplied to some piezoelectric bodies, and when used for a long time, the displacement characteristics will change, sparks will be generated, and the drive will stop.

In recent years, in order to obtain a large displacement, a higher electric field is applied to a small multi-layer piezoelectric element, and it is driven continuously for a long period of time, so such a problem becomes apparent.

In addition, in the inert layer disclosed in Patent Document 3, although the shrinkage difference between the active layer and the inert layer is alleviated, when a high voltage is applied, especially in the case of continuous driving for a long time, the electrodes forming the inert layer 62 Cracks are generated at the interface between 61 and the piezoelectric layer (active portion) 63 , and there is a problem in terms of durability.

Contents of the invention

Therefore, the present invention is made in view of the above-mentioned problems, and its object is to provide a piezoelectric actuator that can increase the displacement of the piezoelectric actuator under high voltage and high pressure, and the displacement can be reduced even when it is driven continuously for a long time. Multilayer piezoelectric element with excellent durability that does not change.

In order to achieve the above object, the first multilayer piezoelectric element of the present invention is characterized in that it has a laminated body having an active part in which at least one piezoelectric body and the first internal electrode and a plurality of internal electrodes composed of a second internal electrode, the active part expands and contracts in response to the voltage applied between the first internal electrode and the second internal electrode, and the external electrode, which respectively formed on two side surfaces of the laminate, one of which is connected to the first internal electrode and the other of which is connected to the second internal electrode,

Each of the external electrodes is composed of three or more layers including a first layer formed in contact with a side surface of the laminate and a second layer formed on the first layer,

The first layer contains more metal oxide than the second layer.

In addition, the first multi-layer piezoelectric element of the present invention is characterized by having:

A laminated body, which has an active part and an inert layer made of a piezoelectric material at both ends of the active part, the active part is an alternate stack of at least one piezoelectric body and a first internal electrode and a second internal electrode. composed of a plurality of internal electrodes, the active part expands and contracts in response to the voltage applied between the first internal electrode and the second internal electrode,

external electrodes respectively formed on two side surfaces of the laminate, one of which is connected to the first internal electrode and the other of which is connected to the second internal electrode,

The inert layer of the laminate contains dispersed metal.

Furthermore, the manufacturing method of the laminated piezoelectric element of the present invention is characterized in that it includes:

Piezoelectric material layers are formed on both ends of the raw laminate formed by alternately laminating piezoelectric green sheets and conductor layers;

forming a metal layer over the piezoelectric material layer;

After firing the green laminate in which the piezoelectric material layer and the metal layer are formed, the metal layer is removed.

(invention effect)

In the first multilayer piezoelectric element of the present invention constituted as described above, each of the external electrodes includes a first layer formed in contact with the side surface of the laminate and a second layer formed on the first layer. There are three or more layers including three or more layers, so the interface of three or more layers can be used to block cracks (prevent cracks from expanding to upper or lower layers), and prevent cracks from penetrating the entire external electrode.

Accordingly, it is possible to prevent external electrode cracks due to dimensional changes of the multilayer body, and the displacement amount does not change even in the case of continuous driving for a long period of time, thereby improving the durability of the multilayer piezoelectric element.

In addition, in the first multi-layer piezoelectric element of the present invention, since the inert layer of the laminate contains dispersed metal, it is possible to relax (homogenize) the gap between the inert layer and the active layer during firing shrinkage. Stress can increase the displacement of the piezoelectric actuator under high voltage and high pressure, and the displacement will not change even if it is driven continuously for a long time, which can improve the performance under high voltage and long-term continuous use. durability.

In addition, in the method for manufacturing a multilayer piezoelectric element of the present invention, the metal layer is removed after firing the green laminate in which the metal layer is formed on the piezoelectric material layer. Therefore, It is possible to manufacture a multilayer piezoelectric element in which metal is easily dispersed in the inert layer.

Description of drawings

1A is a perspective view showing the configuration of a multilayer piezoelectric element according to Embodiment 1 of the present invention.

1B is a perspective development view showing a stacked state of piezoelectric layers and internal electrode layers in the multi-layer piezoelectric element according to Embodiment 1. FIG.

2 is an enlarged cross-sectional view showing a stacked structure of external electrodes formed on side surfaces of piezoelectric bodies in the multi-layer piezoelectric element according to Embodiment 1. FIG.

3A is a perspective view showing the configuration of a multilayer piezoelectric element according to Embodiment 2 of the present invention.

3B is a cross-sectional view of a multi-layer piezoelectric element according to Embodiment 2. FIG.

FIG. 4A is a perspective view when a conductive auxiliary member is further formed in the multi-layer piezoelectric element of Embodiment 2. FIG.

FIG. 4B is a cross-sectional view of FIG. 4A.

5 is a cross-sectional view of a laminate before firing in the manufacturing process of the laminated piezoelectric element according to Embodiment 2. FIG.

Fig. 6 is a sectional view of the spraying device of the present invention.

FIG. 7 is a perspective view showing the structure of a conventional multilayer piezoelectric element.

FIG. 8 is a cross-sectional view showing the configuration of a conventional multilayer piezoelectric element different from FIG. 7 .

In the figure: 1-piezoelectric body, 2-internal electrode, 3-groove, 4, 15-external electrode, 6-wire, 7-conductive auxiliary part, 8-electrode layer, 10-multilayer piezoelectric element , 10a-raw laminate, 11-active part, 12-inert layer, 14-metal, 15a-the first layer of external electrodes, 15b-intermediate layer, 15c-outermost layer of external electrodes, 31-accommodating container, 33- Injection hole, 35-valve, 43-piezoelectric actuator.

Detailed ways

Hereinafter, the multi-layer piezoelectric element according to the embodiment of the present invention will be described in detail.

Implementation mode 1.

1A and B are diagrams showing the configuration of a multilayer piezoelectric element according to Embodiment 1 of the present invention, wherein FIG. 1A is a perspective view, and FIG. 1B is a three-dimensional development showing a stacked state of a piezoelectric layer and an internal electrode layer. picture. In addition, FIG. 2 is an enlarged cross-sectional view showing a multilayer structure of external electrodes formed on the side surfaces of the piezoelectric body of the multilayer piezoelectric element of the present invention.

The multilayer piezoelectric element of Embodiment 1 is formed on a pair of opposing side surfaces of a laminated body 13 formed by alternately laminating piezoelectric bodies 1 and internal electrodes 2 as shown in FIGS. 1A and 1B . The external electrodes 15 expose the ends of the internal electrodes 2 every other layer on the side surfaces of the laminated body 13 where the external electrodes 15 are formed, and the external electrodes 15 are connected to the exposed internal electrodes 2 .

In addition, inert layers 12 a formed of piezoelectric bodies 1 are provided at both ends in the stacking direction of the stacked body 13 . Here, when using the multilayer piezoelectric element of Embodiment 1 as a multilayer piezoelectric actuator, the lead wires may be connected and fixed to the external electrodes 15 with solder, and the lead wires may be connected to External voltage supply part.

Internal electrodes 2 are arranged between the piezoelectric layers 1, and the internal electrodes 2 are formed of a metal material such as silver-palladium, for example. In the multi-layer piezoelectric element, a predetermined voltage is applied to each piezoelectric body 1 via an internal electrode 2, thereby causing displacement of the piezoelectric body 1 by the inverse piezoelectric effect.

Conversely, since the inert layer 12a is composed of a plurality of layers of the piezoelectric body 1 not provided with the internal electrodes 12, displacement does not occur even when a voltage is applied.

Here, in particular, the multilayer piezoelectric element of the first embodiment is characterized in that three or more external electrodes 15 are laminated as shown in FIG. 2 . In this way, the external electrode 15 is formed of three or more layers in order to improve the durability of the multi-layer piezoelectric element.

That is, in the case of driving a multilayer piezoelectric element in which the external electrode 15 is composed of a single layer or two layers, there may be cracks generated starting from the surface of the external electrode 15 and the interface between the external electrode 15 and the piezoelectric body 1. The cracks generated at the starting points are joined together, and the external electrodes 15 are disconnected. Furthermore, when the external electrode 15 has two layers, if the multilayer piezoelectric element is driven to continuously and repeatedly cause dimensional changes in the piezoelectric body, there is a problem of peeling between the two layers. In particular, in order to increase the adhesion strength between the external electrode 15 and the piezoelectric body 1, the external electrode layer to which glass is added is used as the external electrode layer in contact with the piezoelectric body 1, and the external electrode layer with less glass is provided as the external electrode layer. In the case where a two-layer structure is formed on the outer side, the above-mentioned peeling problem is more likely to occur.

Therefore, the external electrodes 15 of the multilayer piezoelectric element, which continuously and repeatedly change in size during driving, are required to ensure close contact with the piezoelectric body 1 and to be able to expand and contract while the dimension of the multilayer piezoelectric element changes. In order to meet this requirement, in the first embodiment, the external electrode 15 has a multilayer structure as follows. That is, the external electrode 15 is composed of three or more layers including the first external electrode layer 15a, the outermost external electrode layer 15c, and the intermediate layer.

In this external electrode 15, the first layer 15a of the external electrode layer, which is a layer in contact with the piezoelectric body 1, is a layer having a high bonding strength with the piezoelectric body, and the outermost layer 15c stacked farthest from the piezoelectric body 1 is An electrode layer having a small Young's modulus and a low resistivity. Furthermore, the intermediate layer located in the middle is a layer for relieving stress caused by dimensional changes when the multilayer piezoelectric element is driven, and is also an external electrode layer in contact with the piezoelectric body. The first layer 15a and the outermost layer The outermost layers 15 c of the outer external electrode layers are all layers having an adhesive force.

In addition, in order to prevent the peeling between the piezoelectric body 1 and the external electrode 15 due to the dimensional change during continuous driving of the multi-layer piezoelectric element, or the peeling within the external electrode layer, or the external electrode 15 during driving, Cracks cause disconnection, and it is preferable that each layer of external electrodes 15 in which three or more layers are stacked is continuously connected. Furthermore, in consideration of the smoothness and mass productivity of the external electrodes 15, five or fewer layers are more preferable.

In addition, the conductive material constituting the external electrode 15 is preferably a metal with low resistivity and low hardness (in view of sufficiently absorbing stress due to expansion and contraction of the actuator). Gold, silver or copper are preferred. Copper or silver is more preferable to obtain a durable multilayer piezoelectric element. Silver is most preferred, so that a more durable multilayer piezoelectric element can be obtained.

Furthermore, in the present invention, it is preferable that the thickness of the first external electrode layer 15 a of the external electrode 15 that is in contact with the piezoelectric body 1 is 10 μm or less. Here, the thickness of the first external electrode layer 15a is an average value of the thicknesses of the first external electrode layers that can be confirmed by observing the cross-section of the multilayer piezoelectric element with a microscope such as a SEM. When driving a multi-layer piezoelectric element with a thickness exceeding 10 μm, the first layer of the external electrode in contact with the piezoelectric body changes with the size of the element, especially when the element is elongated, tensile stress is applied, and it is easy to generate Cracked. Therefore, by setting the thickness to 10 μm or less, it is possible to obtain a durable external electrode that does not generate cracks even if the element size changes. It is preferably 5 μm or less, and more preferably 3 μm or less, so that the durability can be further improved. In addition, it is most preferable to set the thickness of the first external electrode layer 15a to be 0.5 μm or more and 2 μm or less to greatly improve durability.

Furthermore, it is preferable that the thickness of each external electrode layer other than the first layer 15a is thicker than that of the first layer 15a, so that the propagation of cracks generated in the outermost layer of the external electrode 15 can be effectively suppressed. In order to suppress the above-mentioned crack propagation, the thickness of each layer other than the first layer 15 a is preferably 5 μm or more, more preferably 10 μm or more, and most preferably 15 μm or more. Accordingly, the durability of the external electrode 15 as a whole increases. In addition, if the entire thickness of the external electrode 15 in the stacking direction is 15 μm or more, the multi-layer piezoelectric element can withstand continuous driving. In addition, when the thickness is 20 μm or more, preferably 30 μm or more, disconnection due to crack propagation can be prevented, and since the resistance value of the external electrode 15 can be reduced, heat generation of the external electrode 15 can be suppressed.

On the other hand, when the overall thickness exceeds 100 μm, since the external electrode 15 cannot follow the piezoelectric body 1 , the amount of displacement is significantly reduced. Therefore, the overall thickness is more preferably 30 to 100 μm.

Furthermore, in the present invention, it is preferable that the first external electrode layer 15a contains more metal oxide than the second external electrode layer 15b covering the first external electrode layer 15a. This is because: when the metal oxide of the first layer 15a in contact with the piezoelectric body 1 is less than that of the second layer 15b, the resistivity of the first layer 15a is smaller than that of the second layer 15b. In the case of electrical components, the current flows to the first layer 15a with a small resistivity, so that the first layer 15a is overheated, causing peeling between the piezoelectric body 1 and the first layer 15a, or increasing the temperature of the multi-layer piezoelectric element to generate heat. out of control.

Here, as the metal oxide, any oxide of Groups 1 to 15 in the periodic table of elements can be used, and Si, B, Bi, Pb, Zn, Al, and Ca, which can form glass at a temperature below 1000°C, are preferable. , Ba, Ti, Zr, rare earth oxides. Furthermore, if it is an oxide of Si, B, Bi, Pb, or Zn, since it can form an amorphous substance at a low temperature, it is more preferable. According to this, the first layer 15a and the piezoelectric body 1 are firmly in close contact with each other under the heat treatment conditions for forming the external electrodes of the multi-layer piezoelectric element. In particular, in order to obtain a highly durable multilayer piezoelectric element, the amount of metal oxide in the first layer of the external electrode is preferably 30 vol% or more, more preferably 50 vol% or more, and most preferably 70 vol% or more.

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. Accordingly, the Young's modulus of the outermost layer 15c can be reduced. Therefore, even if the multilayer piezoelectric element is driven continuously, the external electrodes expand and contract according to the size change of the element, and cracks generated in the external electrodes can be easily suppressed. Also, since an electrode with low resistivity can be made, the element will not overheat even if it is continuously driven, so there is no thermal runaway. In addition, by increasing the metal component, soldering or welding becomes easy, and contact resistance can be reduced even when joining is performed with a conductive resin.

Here, if the metal oxide of the external electrode layers other than the first layer 15a is less than that of the electrode layers of the first layer 15a, although the heat generation of the element can be suppressed, in order to improve the adhesion force of the external electrode layers, it will not be in the layer. Peeling occurs, and it is more preferable that the metal oxide gradually decreases from the first layer 15 a to the outer electrode layer. That is, the content of metal oxide in each layer of the external electrode 15 is controlled stepwise in such a manner that the content of the metal oxide in each layer of the external electrode 15 is first layer>second layer>third layer>...>outermost layer, so that the adjacent external electrode layers The coefficients of thermal expansion are close to each other, and the adhesion strength between the layers can be improved.

In addition, the amount of the composition of the external electrode 15 is specified by an analysis method such as the EPMA (Electron Probe MicroAnalysis) method. In particular, in order to produce a multilayer piezoelectric element with high durability, the amount of metal oxide in the outermost layer 15c of the external electrode 15 is preferably 30% by volume or less, more preferably 10% by volume or less, and most preferably 5% by volume or less. .

Also, in the present invention, it is preferable that the metal oxide is mainly glass. According to this, it is possible to suppress the problem of embrittlement of the electrodes due to the formation of intermetallic compounds in the external electrodes 15 . Furthermore, the glass component diffuses into the intergranular space of the metal component constituting the external electrode 15 , so that the external electrode 15 can be firmly brought into close contact with the piezoelectric body 1 .

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

In this method, first, calcined powder of piezoelectric ceramics of perovskite type oxides composed of PbZrO ₃ -PbTiO ₃ and the like, and adhesives composed of organic polymers such as acrylic and butyral Mixture, DBP (dibutyl phthalate), DOP (dioctyl titanate) and other plasticizers are mixed to make a slurry. Then, the slurry is produced into a ceramic green sheet of the piezoelectric body 1 by a known tape forming method such as a doctor blade method or a calender roll method.

Next, add and mix metal oxides such as silver oxide, binders, and plasticizers to the metal powder that constitutes the internal electrode 2 such as silver-palladium, etc. to make a conductive paste, and then use methods such as screen printing to coat it with a thickness of 1 to 40 μm. A thickness is printed on the upper surface of each of the green sheets.

Then, a plurality of green sheets on which the conductive paste was printed on the upper surface are laminated, and the laminate is debonded at a predetermined temperature, and then fired at 900 to 1200° C. to obtain the laminate 13 .

At this time, as described in detail in Embodiment 2, by adding silver-palladium or other metal powder constituting the internal electrodes 2 to part of the green sheet of the inert layer 12a, the contraction action of the inert layer 12a and other parts during sintering can be controlled. The state and shrinkage are consistent, and a dense laminate can be formed.

In addition, the laminated body 13 is not limited to the manufacturing method described above, as long as the laminated body 13 in which a plurality of piezoelectric bodies 1 and a plurality of internal electrodes 2 are alternately laminated can be manufactured, it may be formed by any manufacturing method. can be.

Then, internal electrodes 2 whose ends are exposed and internal electrodes 2 whose ends are not exposed are alternately formed on the side surfaces of the multilayer piezoelectric element.

Next, add a binder to the glass powder to make a silver glass conductive paste, shape it into a sheet, control the original density of the sheet after drying (to volatilize the solvent) to 6-9g/cm ³ , and then transfer the sheet On the external electrode forming surface of the columnar laminate 13, at a temperature higher than the softening point of glass and below the melting point of silver (965° C.), and 4/5 of the firing temperature (° C.) of the laminate 13 Baking is carried out at a temperature below to disperse the binder component in the sheet made of the silver glass conductive paste, thereby forming the external electrode 15 made of a porous conductor having a three-dimensional network structure.

At this time, the paste constituting the external electrodes may be laminated into a multilayer sheet and then fired, or may be fired every time a layer is laminated. superior. In addition, in the case of changing the glass composition for each layer of the external electrode layer, although it is possible to change the amount of the glass composition for each sheet, if it is desired to form an extremely thin glass-rich layer on the surface closest to the piezoelectric body , then it is also possible to use screen printing and other methods to print glass-enriched paste on the laminate, and then laminate multiple sheets. In this case, a sheet having a thickness of 5 μm or less may be used without printing.

In addition, in order to effectively form the neck, the silver in the silver glass conductive paste and the internal electrode 2 are diffusely bonded, and the voids in the external electrode 15 are effectively left, and the external electrode 15 and the side surface of the columnar laminate 13 are partially formed. In consideration of bonding, the firing temperature of the silver glass conductive paste is preferably 500-800°C. In addition, the softening point of the glass component in the silver glass conductive paste is preferably 500 to 800°C.

When the firing temperature is higher than 800° C., the silver powder of the silver glass conductive paste is excessively sintered, and a porous conductor with an effective three-dimensional network structure cannot be formed, and the external electrodes 15 will be too dense. As a result, the Young's modulus of the external electrodes 15 is too high, and the stress at the time of driving cannot be sufficiently absorbed, and the external electrodes 15 may be disconnected. It is best to fire at a temperature within 1.2 times the softening point of the glass.

On the other hand, when the firing temperature is lower than 500° C., since the diffusion bonding between the end of the internal electrode 2 and the external electrode 15 is not sufficiently performed, the neck is not formed, and there is a possibility that there is a gap between the internal electrode 2 and the external electrode 15 during driving. A spark is generated between the electrodes 15 .

Next, by immersing the laminated body 13 on which the external electrodes 15 were formed in a silicone rubber solution and vacuum-degassing the silicone rubber solution, the grooves of the laminated body 13 were filled with silicone rubber, and then, The laminated body 13 was lifted up, and silicone rubber was applied to the side of the laminated body 13 . Then, the multilayer piezoelectric element of the present invention is obtained by curing the silicone rubber filled in the groove and coated on the side surface of the columnar laminate 13 .

Furthermore, lead wires are connected to the external electrodes 15, and a direct current voltage of 0.1 to 3 kV/mm is applied to the pair of external electrodes 15 through the lead wires, and the laminated body 13 is subjected to polarization treatment, thereby achieving a laminated structure utilizing the present invention. Multilayer piezoelectric actuators with piezoelectric elements. The lead wires are connected to an external voltage supply unit, and when a voltage is applied to the internal electrodes 2 via the lead wires and the external electrodes 15, each piezoelectric body 1 is greatly displaced due to the inverse piezoelectric effect. Accordingly, it is possible to function, for example, as an automotive fuel injection valve that injects and supplies fuel to an engine.

Implementation mode 2.

Next, a multilayer piezoelectric element according to Embodiment 2 of the present invention will be described.

The basic structure of the active part 11 in the laminated body 10 of the multilayer piezoelectric element according to the second embodiment is the same as that of the multilayer piezoelectric element according to the first embodiment, and is characterized by the configuration of the inert layer 12 .

3A and 3B are diagrams showing the configuration of a multilayer piezoelectric element according to Embodiment 2 of the present invention, wherein FIG. 3A is a perspective view, and FIG. Cross-sectional view of the lamination state of the protective layer.

In addition, as shown in FIGS. 3A and 3B , in the multilayer piezoelectric element according to the second embodiment, on the side surface of the active part 11 in which the piezoelectric body 1 and the internal electrode 2 are alternately laminated, there is formed a There are insulating grooves every other layer between the electrode 4 and the internal electrode 2 , so that the external electrode 4 is formed in such a way that the internal electrode 2 and the external electrode are electrically connected every other layer.

Hereinafter, the inert layer 12 having the characteristic configuration of the second embodiment will be mainly described.

In the multilayer piezoelectric element according to the second embodiment, the inert layer 12 is composed of the same piezoelectric body as the piezoelectric body 1, and is characterized in that the inert layer 12 further contains metal 14 dispersed therein.

That is, the invention of the multilayer piezoelectric element according to Embodiment 2 was achieved based on the inventor's unique discovery that, as shown in FIG. 3B , metal 14 is dispersed in inert layer 12 so 1) When firing the laminated body 10, the difference in firing shrinkage between the inert layer 12 and the active part 11 is alleviated, and a laminated piezoelectric element with very little residual stress is obtained; (2) In addition, the dispersed metal 14 is The sintering is promoted when the laminated body 10a is fired, and the dense laminated body 10 is obtained, which can withstand the stress generated by the vibration when the multilayer piezoelectric element is continuously driven.

Therefore, the multi-layer piezoelectric element of Embodiment 2 having the inert layer 12 in which the metal 14 is dispersed has excellent durability, does not deteriorate even if it is used for a long time, and has high reliability.

Here, "the metal is dispersed" means, for example, that the active layers of piezoelectric bodies and internal electrodes are alternately formed to contain layered metals, and typically refers to piezoelectric elements in which a metal element is diffused into the inert layer 12. in vivo. In addition, the metal element may be diffused from the surface of the inert layer 12 to the inside of the inert layer 12 . The dispersion of the metal 14 can be specified by an analytical method such as the EPMA (Electron Probe Micro Analysis) method. Specifically, when an arbitrary cross section of the inert layer is analyzed by EPMA, the distribution state of the metal can be confirmed.

In addition, the melting point of the metal 14 dispersed in the inert layer 12 is preferably 1.6 times or less the firing temperature of the multi-layer piezoelectric element. This is because the diffusion efficiency of the metal in the inert layer 12 deteriorates for the metal 14 having a melting point higher than the above-mentioned melting point. When the melting point of the metal 14 is not more than 1.6 times the firing temperature of the multi-layer piezoelectric element, the metal element can be easily transferred from the surface of the inert layer 12 to the inside of the inert layer 12 .

In addition, when two or more metals 14 are added, or when an alloy composed of two or more metals is added, it is preferable that the melting point of each metal is 1.6 times or less than the firing temperature of the multi-layer piezoelectric element. . However, it goes without saying that the metal that is not conducive to dispersing into the inert layer 12 does not need to be below the above-mentioned melting point.

Furthermore, in the present invention, the metal 14 dispersed in the inert layer 12 is preferably at least one of Ag, Pd, Cu, Ca, Na, Pb, and Ni. This is because the melting points of these metals are near or lower than the firing temperature of the laminated body 10a, and therefore, during the firing process of the laminated body 10a, the diffusion into the inert layer 12 becomes active, promoting Metal 14 is uniformly dispersed in inert layer 12 .

In addition, the amount of the metal 14 dispersed in the inert layer 12 is preferably 0.001 to 1.0% by mass of the inert layer 12 . This is because: when it is 0.001 mass % or less, the shrinkage difference or shrinkage curve of the inert layer 12 and the active part 11 are different during firing, and a large strain occurs between the two, and in the worst case, delamination occurs after firing. Or prone to delamination after long-term use.

In addition, when the dispersed metal 14 is larger than 1.0% by mass, the insulation of the inert layer 12 deteriorates, impairing the function of the inert layer. In addition, in order to further reduce the residual stress after the firing of the inert layer 12, so as not to cause defects in the multi-layer piezoelectric element after firing, it is more preferable that the content of the metal 14 relative to the passive layer 12 is 0.05% by mass to 1.0% by mass. %. In addition, in order to have high reliability even against stress caused by vibration during continuous driving of the multilayer piezoelectric element, the content of the metal 12 is most preferably 0.1% by mass to 1.0% by mass. In addition, the content of the metal 14 relative to the inert layer 12 can be quantitatively measured by ICP (Inductively Coupled Plasma Atomic) emission analysis.

In addition, the thickness of the inert layer 12 is preferably 0.1 mm to 2.0 mm. When the thickness is 0.1 mm or less, the inert layer 12 is thin, and therefore the inert layer 12 may be broken due to the stress generated by the vibration during continuous driving of the multi-layer piezoelectric element. In addition, when it is thicker than 2.0 mm, it is difficult for the metal 14 to disperse into the inert layer 12 . Here, if the degree of dispersion of the metal 14 in the inert layer 12 is poor, the portion with more metal dispersion and the portion with less metal dispersion will have a difference in shrinkage or shrinkage curve during firing. Therefore, a larger shrinkage occurs during firing. Large strain, delamination after firing or easy delamination after long-term use. In addition, the inert layer 12 is disposed on both end faces of the stacked body 10 in the stacking direction, and the thickness of the inert layer 12 refers to the thickness of the inert layer 12 disposed on one of the end faces.

In addition, the metal 14 dispersed in the inert layer 12 is preferably a metal composition constituting the internal electrode 2 . This is because when a metal other than the metal constituting the internal electrodes 2 is used, the firing shrinkage curves of the inert layer 12 and the active portion 11 including the internal electrodes 2 are different when the laminate 10a is fired, and may be caused by firing shrinkage. stress.

Requirements other than the inert layer of Embodiment 2 will be described below.

In the multilayer piezoelectric element according to Embodiment 2, the internal electrodes 2 exposed at the ends of the side surfaces of the laminate and the internal electrodes 2 not exposed at the ends are alternately formed, and the internal electrodes 2 not exposed at the ends are connected with A groove 3 is formed in a portion of the piezoelectric body 1 between the external electrodes 4 . In the present invention, it is preferable to form an insulator having a Young's modulus lower than that of the piezoelectric body 1 in the groove. In this way, in such a multi-layer piezoelectric element, since the stress due to the displacement during driving can be relaxed, heat generation of the internal electrodes 2 can be suppressed even when the driving is continued.

In addition, in the present invention, the firing temperature of the laminate is preferably 900°C or higher and 1200°C or lower. This is because when the firing temperature is 900° C. or lower, the firing temperature is low and the firing is insufficient, making it difficult to produce a dense piezoelectric body 1 . In addition, this is because: when the firing temperature exceeds 1200°C, the stress caused by the deviation between the shrinkage of the internal electrode 2 and the shrinkage of the piezoelectric body 1 during firing becomes large, and there is a possibility of continuous driving of the multi-layer piezoelectric element. Create cracks.

Also, in the multi-layer piezoelectric element of the second embodiment, the same effect as that of the first embodiment can be obtained when external electrodes having three or more layers as described in the first embodiment are used.

Furthermore, the external electrode 4 is preferably formed of a porous conductor having a three-dimensional network structure. If the external electrode 4 is not made of a porous conductor with a three-dimensional network structure, the external electrode 4 is not flexible and cannot follow the expansion and contraction of the multilayer piezoelectric actuator. The contact between electrode 4 and internal electrode 2 is poor.

Here, the three-dimensional network structure does not mean the state in which so-called spherical voids exist in the external electrodes 4, but implies a three-dimensional connection and joining state of the conductive material powder and the glass powder constituting the external electrodes 4 as follows, that is, In order to bake the conductive material powder and the glass powder constituting the external electrodes 4 at a relatively low temperature, the voids exist in a connected state to some extent without preventing the progress of sintering.

The porosity of such holes in the external electrode 4 is preferably 30 to 70% by volume. Here, the porosity refers to the proportion of voids in the external electrodes 4 . This is because: if the porosity in the external electrode 4 is smaller than 30% by volume, the external electrode 4 cannot withstand the stress caused by the expansion and contraction of the laminated piezoelectric actuator, and the external electrode 4 may be disconnected; When the porosity exceeds 70% by volume, since the resistance value of the external electrode 4 becomes large, the external electrode 4 may locally generate heat when a large current flows, which may lead to disconnection.

Furthermore, it is preferable that a glass-rich layer is formed on the surface layer portion of the external electrode 4 on the piezoelectric body 1 side. This is because, in the absence of the glass-rich layer, bonding with the glass component in the external electrode 4 is difficult, and therefore, the external electrode 4 may not be easily bonded to the piezoelectric body 1 firmly.

In addition, it is preferable that the softening point (° C.) of the glass constituting the external electrodes 4 is 4/5 or less of the melting point (° C.) of the conductive material constituting the internal electrodes 2 . This is because when the softening point of the glass constituting the external electrodes 4 exceeds 4/5 of the melting point of the conductive material constituting the internal electrodes 2, since the softening point of the glass constituting the external electrodes 4 and the melting point of the conductive material constituting the internal electrodes 2 become Therefore, the temperature for firing the external electrodes 4 must be close to the melting point of the internal electrodes 2. Therefore, when the external electrodes 4 are fired, the conductive materials of the internal electrodes 2 and the external electrodes 4 aggregate to prevent diffusion bonding, or cannot The firing temperature is set at a temperature at which the glass component of the external electrode 4 is sufficiently softened, and thus sufficient bonding strength of the softened glass may not be obtained.

Furthermore, it is preferable that the glass constituting the external electrodes 4 is amorphous. This is because, in crystalline glass, the external electrodes 4 cannot absorb the stress caused by the expansion and contraction of the multi-layer piezoelectric actuator, and therefore cracks may occur.

In addition, the thickness of the external electrode 4 is preferably thinner than the thickness of the piezoelectric layer 1 . This is because if the thickness of the external electrode 4 is thicker than the thickness of the piezoelectric layer 1, the strength of the external electrode 4 increases, so when the laminated body 10 expands and contracts, the joint portion between the external electrode 4 and the internal electrode 2 becomes weaker. When the load increases, contact failure may occur.

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

In this method, first, as in the first embodiment, a ceramic green sheet to be the piezoelectric body 1 is produced.

Next, this green sheet is cut into an arbitrary size and fixed to a frame.

Then, add and mix binders, plasticizers, etc. to the silver-palladium metal powder constituting the internal electrodes 2 to make a conductive paste, and then print it on each of the green sheets with a thickness of 1 to 40 μm by screen printing or the like. On the surface, a green sheet for the active part 11 is prepared.

Next, a green sheet on which no conductive paste is printed on the inert layer 12 is prepared.

Then, a plurality of green sheets for the active part 11 and green sheets for the inert layer 12 are stacked so that the laminated portion of the green sheet for the inert layer 12 is placed on the laminated layer of the green sheet for the active part 11 on which the conductive paste is printed on the upper surface. Part up and down, at the same time, apply pressure to make it tight. Here, a plurality of portions serving as the inert layer 12 are stacked on the top and bottom of the active portion 11 with a thickness of 0.1 to 2.0 mm.

Then, the laminated green sheet is cut into an appropriate size, and as shown in FIG. 5 , a conductive paste ( For example, Ag, Pd, Cu, Ca, Na, Ni, Pb, etc.) form the metal layer 8 . After that, binder removal is performed at a predetermined temperature, followed by firing at a temperature of 900 to 1200° C., and after firing, the metal layer 8 is removed by a surface grinder or the like to obtain a fired laminate 10 .

Here, the thickness of the formed metal layer 8 is preferably 5 mm or less. This is because if the thickness of the metal layer 8 exceeds 5 mm, cracks may occur in the metal layer 8 due to the difference in firing shrinkage between the metal layer 8 and the inert layer 12 when the laminate 10 a is fired.

Next, internal electrodes 2 with exposed end portions and internal electrodes 2 with non-exposed end portions are alternately formed on the side surface of the laminated body 10a, and grooves 3 are formed at portions of the piezoelectric body 1 between the internal electrodes 2 with non-exposed end portions and the external electrodes 4. An insulator such as resin or rubber having a Young's modulus lower than that of the piezoelectric body 1 is formed in the groove 3 . Here, the groove 3 is formed on the side of the active part 11 by an internal slicing device or the like. In order to sufficiently absorb the stress generated by the expansion and contraction of the multilayer piezoelectric element, the conductive material constituting the external electrode 4 preferably has a low Young's modulus. silver or silver-based alloys.

Next, add a binder to the glass powder to make a silver glass conductive paste, shape it into a sheet, control the original density of the sheet after drying (to volatilize the solvent) to 6-9g/cm ³ , and then transfer the sheet On the external electrode forming surface of the active part 11, the firing is performed at a temperature higher than the softening point of glass and at a temperature not higher than the melting point of silver (965° C.), and at a temperature not higher than 4/5 of the firing temperature (° C.), By dispersing the binder component in the sheet made of silver glass conductive paste, external electrodes 4 made of a porous conductor having a three-dimensional network structure can be formed.

In addition, in order to effectively form the neck between the particles, the silver in the silver glass conductive paste and the internal electrode 2 are diffusely bonded, and the voids in the external electrode 4 are effectively left, and the external electrode 4 and the laminated body side surface In consideration of local bonding, the firing temperature of the silver glass conductive paste is preferably 500-700°C. In addition, the softening point of the glass component in the silver glass conductive paste is preferably 500 to 700°C.

When the calcination temperature is higher than 700° C., the silver powder of the silver glass conductive paste is excessively sintered, and a porous conductor with an effective three-dimensional network structure cannot be formed, and the external electrodes 4 will be too dense. As a result, the Young's modulus of the external electrodes 4 is too high, and the stress at the time of driving cannot be sufficiently absorbed, and the external electrodes 4 may be disconnected. It is best to fire at a temperature within 1.2 times the softening point of the glass.

On the other hand, when the firing temperature is lower than 500°C, since the diffusion bonding between the end of the internal electrode 2 and the external electrode 4 is not sufficiently performed, the neck between the particles is not formed, and there is a possibility that the internal electrode may be damaged during driving. A spark is generated between 2 and the external electrode 4.

In addition, it is preferable that the thickness of the silver glass conductive paste sheet is thinner than that of the piezoelectric body 1 . From the viewpoint of following the expansion and contraction of the actuator, it is more preferably 50 μm or less.

Next, by immersing the active part 11 on which the external electrodes 4 were formed in the silicone rubber solution and vacuum-degassing the silicone rubber solution, the groove 3 of the active part 11 was filled with silicone rubber, and then lifted from the silicone rubber solution. The active part 11 is coated with silicone rubber on the side of the active part 11 . Then, the multilayer piezoelectric element of the present invention is obtained by curing the silicone rubber filled inside the groove 3 and coated on the side surface of the active part 11 .

Furthermore, a lead wire 6 is connected to the external electrodes 4, and a DC voltage of 0.1 to 3 kV/mm is applied to the pair of external electrodes 4 through the lead wire 6 to polarize the active part 11, thereby achieving a multilayer structure utilizing the present invention. Multilayer piezoelectric actuators with piezoelectric elements. The lead wire 6 is connected to an external voltage supply unit, and when a voltage is applied to the internal electrode 2 via the lead wire and the external electrode 4, each piezoelectric body 1 is greatly displaced due to the inverse piezoelectric effect. Accordingly, it is possible to function, for example, as an automotive fuel injection valve that injects and supplies fuel to an engine.

More preferable forms of the internal electrodes and the like in Embodiments 1 and 2 will be described below.

(internal electrode)

In the present invention, the metal composition in the internal electrodes 2 preferably contains Group 8 to Group 10 metals and/or Group 11 metals as main components. This is because the piezoelectric body 1 and the internal electrodes 2 can be fired simultaneously at the firing temperature because the metal composition has high heat resistance. Therefore, since the sintering temperature of the external electrodes can be lower than the sintering temperature of the piezoelectric body, intense mutual diffusion between the piezoelectric body and the external electrodes can be suppressed.

In addition, when the content of Group 8 to Group 10 metals is M1 (mass %) and the content of Group 11 metals is M2 (mass %), it is preferable that the metal composition in the internal electrode 2 satisfies 0<M1≦15 , 85≤M2<100, M1+M2=100 metal composition is the main component. This is because when the metal of Groups 8 to 10 exceeds 15% by mass, the resistivity becomes large, and when the multilayer piezoelectric element is driven continuously, the internal electrodes 2 may generate heat, and this heat acts on the temperature-dependent voltage. The electric body 1 reduces the displacement characteristic, so the displacement of the multi-layer piezoelectric element becomes small; and, when the external electrode 15 is formed, although the external electrode 15 and the internal electrode 2 are mutually diffused and bonded, the group 8 to 10 metal exceeds When it is 15% by mass, the hardness of the portion of the external electrode 15 in which the internal electrode component is diffused becomes high, and the durability of the multilayer piezoelectric element in which dimensional changes occur during driving decreases. In addition, in order to suppress migration of the Group 11 metal in the internal electrode 2 to the piezoelectric body 1 , it is preferable that the Group 8 to 10 metal is 0.001% by mass or more and 15% by mass or less. In addition, from the viewpoint of improving the durability of the multi-layer piezoelectric element, it is preferably not less than 0.1% by mass and not more than 10% by mass. In addition, when heat conduction is excellent and higher durability is required, it is more preferably 0.5% by mass or more and 9.5% by mass or less. In addition, when pursuing higher durability, it is more preferably not less than 2% by mass and not more than 8% by mass.

This is also because when the Group 11 metal is less than 85% by mass, the resistivity of the internal electrodes 2 becomes large, and the internal electrodes 2 may generate heat when the multilayer piezoelectric element is continuously driven. In addition, in order to suppress migration of the Group 11 metal in the inner metal 2 to the piezoelectric body 1, the Group 11 metal is preferably 85% by mass or more and 99.999% by mass or less. In addition, from the viewpoint of improving the durability of the multi-layer piezoelectric element, it is preferably 90% by mass or more and 99.9% by mass or less. Moreover, when higher durability is required, 90.5 mass % or more and 99.5 mass % or less are more preferable. In addition, when achieving higher durability, it is more preferably 92% by mass or more and 98% by mass or less.

The above-mentioned metal components in the internal electrode 2 can be specified by an analysis method such as the EPMA (Electron Probe Micro Analysis) method, which shows group 8 to 10 metals and group 11 metals in mass %.

In addition, the metal components in the internal electrode 2 of the present invention are preferably at least one or more of Ni, Pt, Pd, Rh, Ir, Ru, and Os for group 8-10 metals, and at least one of Cu, Ag, and Au for group 11 metals. 1 or more. This is because they are metal compositions that are superior in mass productivity in alloy powder synthesis technology in recent years.

Furthermore, the metal components in the internal electrodes 2 are preferably at least one of Pt and Pd as the group 8 to 10 metal, and at least one or more of Ag and Au as the group 11 metal. Accordingly, it is possible to form the internal electrodes 2 having excellent heat resistance and low resistivity.

In addition, the metal in the internal electrode 2 or a subgroup 8-10 metal is preferably Ni. Accordingly, the internal electrodes 2 excellent in heat resistance can be formed.

In addition, it is more preferable that the metal component in the internal electrode 2 is that the Group 11 metal is Cu. Accordingly, internal electrodes 2 having low hardness and excellent thermal conductivity can be formed.

Furthermore, it is preferable to add oxides, nitrides, or carbides to the internal electrodes 2 together with the above-mentioned metal composition. Accordingly, the strength of the internal electrodes increases, and the durability of the multilayer piezoelectric element improves. In particular, it is more preferable that the oxide and the piezoelectric body interdiffuse to increase the adhesion strength between the internal electrodes and the piezoelectric body. Furthermore, it is preferable that the said inorganic composition is 50 volume% or less. Accordingly, the bonding strength between the internal electrodes 2 and the piezoelectric body 1 can be made smaller than the strength of the piezoelectric body 1 . More preferably, it is 30% by volume or less, so that the durability of the multi-layer piezoelectric element can be improved.

Preferably, the oxide is a perovskite-type oxide composed of PbZrO ₃ -PbTiO ₃ as a main component. In addition, the content of the added oxide and the like can be calculated from the composition area ratio in the internal electrodes of the cross-sectional SEM image of the multilayer piezoelectric element.

(piezoelectric body)

In the present invention, the piezoelectric body 1 preferably has a perovskite-type oxide as its main component. In this way, for example, when it is formed of a perovskite type piezoelectric ceramic material represented by barium titanate (BaTiO ₃ ), since the piezoelectric strain constant d ₃₃ expressing its piezoelectric characteristics is high, the amount of displacement can be increased. In addition, the piezoelectric body 1 and the internal electrodes 2 can also be fired at the same time. As the piezoelectric body 1 shown above, it is preferable that the main component is a perovskite-type oxide composed of PbZrO ₃ -PbTiO ₃ having a relatively high piezoelectric strain constant d ₃₃ .

In addition, the firing temperature is preferably not less than 900°C and not more than 1000°C. This is because: when the firing temperature is below 900°C, the firing temperature is low and the firing is insufficient, making it difficult to produce a dense piezoelectric body 1; The bonding strength with the piezoelectric body 1 is increased.

In addition, the internal electrodes 2 exposed at the end portions of the multilayer piezoelectric element of the present invention and the internal electrodes 2 not exposed at the end portions are alternately configured. When grooves are formed on the side surfaces, it is preferable to form an insulator having a Young's modulus lower than that of the piezoelectric body 1 in the grooves. Accordingly, in such a multi-layer piezoelectric element, the stress caused by the displacement during driving can be relaxed, and thus heat generation of the internal electrodes 2 can be suppressed even when the driving is continued.

(Conductive auxiliary part 7 on external electrode 4)

Furthermore, in the present invention, it is preferable to provide a conductive auxiliary member 7 made of a conductive adhesive embedded with a metal mesh or a mesh metal plate on the outer surface of the external electrode 4 as shown in FIG. 4B . If the conductive auxiliary member 7 is not provided on the outer surface of the external electrode 4, when the multilayer piezoelectric element is driven by passing a large current, the external electrode 4 cannot withstand the large current and locally generates heat, which may lead to disconnection. In addition, since the conductive adhesive is embedded with a metal mesh or mesh metal plate, cracks in the conductive raw adhesive can be prevented.

In addition, the metal mesh refers to a structure in which metal wires are woven, and the mesh metal plate refers to a mesh-like structure in which holes are formed on a metal plate.

In addition, if no metal mesh or mesh metal plate is used on the outer surface of the external electrode 4, the stress generated by the expansion and contraction of the multilayer piezoelectric element will directly act on the external electrode 4, and the external electrode 4 may be damaged due to fatigue during driving. Easy to peel off from the side of the multi-layer piezoelectric element.

In addition, it is preferable that the conductive adhesive is composed of polyimide resin in which conductive particles are dispersed. This is because: by using a polyimide resin, it is possible to have relatively high heat resistance even when driving a multilayer piezoelectric element at a high temperature, and by using such a polyimide having relatively high heat resistance Resins and conductive adhesives are also easy to maintain high bond strength. Moreover, it is preferable that electroconductive particle is silver powder. This is because it is easy to suppress local heating of the conductive adhesive by using silver powder with a relatively low resistance value for the conductive particles. Also, by dispersing silver powder with low resistance value in polyimide resin with high heat resistance, it is possible to form conductive auxiliary member 7 with low resistance value and maintain high adhesive strength even when used at high temperature.

In addition, the conductive particles used here are preferably non-spherical particles such as flakes or needles. This is because by forming the shape of the electroconductive particles into non-spherical particles such as flakes or needles, the aggregation between the electroconductive particles can be strengthened, and the shear strength of the electroconductive adhesive can be further increased.

The multilayer piezoelectric elements of Embodiments 1 and 2 have been described in detail above. However, the multilayer piezoelectric element and its manufacturing method of the present invention are not limited thereto. Various changes can be made within the scope. For example, when the metal 14 is dispersed in the inert layer, the metal layer 8 is printed on both ends of the laminate 10 on which the inert layer 12 is arranged as described above, and the metal 14 is dispersed in the inert layer 12 by firing, but it may also be The metal 14 is preliminarily added to the green sheet forming the inert layer 12 . In addition, in the case of dispersing the metal 14 whose melting point is lower than the firing temperature of the laminated body 10, for example, the laminated body 10a may be arranged in a crucible, and the metal 14 may be placed in its vicinity while firing, thereby, The metal vapor volatilized from the metal 14 is vapor-deposited and dispersed in the inert layer 12 .

In addition, although the example in which the external electrodes 4 are formed on the opposite side surfaces of the active portion 11 has been described above, the present invention may also form a pair of external electrodes 4 on adjacent side surfaces, for example.

Implementation mode 3.

Hereinafter, the injection device of the present invention will be described. This injection device is constructed using the multi-layer piezoelectric element of the present invention.

FIG. 6 shows the spraying device of the present invention. A spray hole 33 is provided at one end of a container 31. In addition, a needle valve 35 capable of opening and closing the spray hole 33 is housed in the container 31.

A fuel passage 37 is provided so as to communicate with the injection hole 33 , and the fuel passage 37 is connected to an external fuel supply source, and fuel is normally 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 injected at a constant high pressure into a fuel chamber (not shown) of the internal combustion engine.

In addition, the diameter of the upper end portion of the needle valve 35 is enlarged, and it is configured as a piston 41 slidable with a cylinder 39 formed in the storage container 31 . Furthermore, the above-mentioned piezoelectric actuator 43 is housed in the housing container 31 .

In such an injection device, when the piezoelectric actuator 43 is extended by applying a voltage, the piston 41 is pushed, the needle valve 35 closes the injection hole 33, and the supply of fuel is stopped. In addition, when the voltage application is stopped, the piezoelectric actuator 43 contracts, the disk spring 45 pushes back the piston 41, and the injection hole 33 communicates with the fuel passage 37 to perform fuel injection.

In addition, the ejection device of the present invention is not limited to the above-mentioned embodiments, and, for example, other than drive elements mounted in fuel injection devices for automobile engines, liquid ejection devices such as ink jets, precision positioning devices such as optical devices, or vibration prevention devices, etc. , or sensor elements mounted in combustion pressure sensors, shock sensors, acceleration sensors, load sensors, ultrasonic sensors, pressure sensitive sensors, yaw rate sensors, etc., as well as sensor elements mounted in piezoelectric gyroscopes, piezoelectric switches, piezoelectric transformers , Piezoelectric circuit breakers, etc., as long as it is an element that utilizes piezoelectric characteristics, it is of course applicable.

【Example】

Hereinafter, examples of the present invention will be described.

(Example 1)

As Example 1, a multilayer piezoelectric actuator composed of the multilayer piezoelectric element according to Embodiment 1 of the present invention was manufactured as follows.

First, a slurry of calcined powder of piezoelectric ceramics, a binder, and a plasticizer mixed with lead zirconate titanate (PbZrO ₃ -PbTiO ₃ ) having an average particle size of 0.4 μm as the main component was prepared, A ceramic green sheet of the piezoelectric body 1 having a thickness of 150 µm was produced by a doctor blade method.

On one side of the ceramic green sheet, a conductive paste with a thickness of 3 μm is formed by screen printing, and the conductive paste is formed by adding a binder to a silver-palladium alloy (silver 95% by mass-palladium 5% by weight), 300 sheets on which the conductive paste was formed were stacked and fired. The firing was carried out at 1000°C after holding at 800°C.

Then, grooves with a depth of 50 μm and a width of 50 μm were formed every other layer at the end of the internal electrodes on the side of the laminate by a slicing device.

Next, as in the composition shown in Table 1, flaky silver powder with an average particle diameter of 2 μm and the remainder mainly composed of silicon with an average particle diameter of 2 μm are amorphous glass powders with a softening point of 640° C. 8 mass parts of binders were added to the mixture of silver powder and glass powder with respect to the total weight of 100 mass parts of silver powder, and it mixed well, and the silver glass conductive paste was produced. The thus-produced silver glass conductive paste was formed on a release film by screen printing, and after drying, it was peeled off from the release film to obtain a sheet of the silver glass conductive paste.

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

Afterwards, wires were connected to the external electrodes 15, and a DC electric field of 3 kV/mm was applied to the positive and negative external electrodes 15 via the wires for 15 minutes to perform polarization treatment, and a stacked layer as shown in FIGS. 1A and B was made. Multilayer piezoelectric actuators with piezoelectric elements.

A DC voltage of 170 V was applied to the obtained multilayer piezoelectric element, and as a result, all the multilayer piezoelectric actuators obtained a displacement of 45 μm in the stacking direction. In addition, at room temperature, the multilayer piezoelectric element was subjected to a drive test with an AC voltage of 0 to +170V applied at a frequency of 150 Hz, and the test was carried out until the continuous drive was 1×10 ⁹ times,

In addition, the layer thickness and glass amount of the external electrode 15 were measured by SEM measuring a cross section. The thickness is calculated from the average value of 5 points in the SEM image, the amount of glass is calculated from the area of the electrode layer by SEM and EPMA, and then the area of the glass part is calculated, and the area ratio of the calculated area is taken as volume %. The results are shown in the table 1.

Table 1-1

In Table 1-1, the amount of glass is expressed in volume %.

Table 1-2

No. Initial displacement A(μm) The maximum displacement B after continuous driving (μm) Change rate of displacement (%) *1 45.0 The external electrode is cracked, peeled off and destroyed - *2 45.0 The external electrode is cracked, peeled off and destroyed - 3 45.0 44.7 0.7 4 45.0 44.8 0.4 5 45.0 44.9 0.2 6 45.0 45.0 0.0 7 45.0 45.0 0.0 8 45.0 44.8 0.4 9 45.0 44.7 0.7 10 45.0 44.7 0.7 11 45.0 44.6 0.9 12 45.0 45.0 0.0 *13 45.0 The external electrode is cracked, peeled off and destroyed -

In Table 1-2, the initial displacement A represents the displacement (μm) in the initial state, and the maximum displacement B after continuous driving represents the maximum displacement (μm) after continuous driving (1×10 ⁹ times).

In addition, in Table 1-2, the rate of change of displacement represents the rate of change (%) of the displacement after continuous driving relative to the displacement of the initial state, which is taken as A and B, and expressed as |(A-B)/A×100| To represent.

As can be seen from Table 1, for sample numbers 1, 2, and 13 of the comparative example, since the number of layers constituting the external electrode 15 is two or less, when the multilayer piezoelectric actuator is continuously driven, the size of the piezoelectric body 12 changes, the load on the interface between the piezoelectric body 12 and the external electrode 15 increases, and cracks occur from the interface to the external electrode 15, and peeling occurs at the interface.

In contrast, in sample numbers 3 to 12 of the examples of the present invention, since they are multilayer piezoelectric actuators with three or more layers of external electrodes, the displacement of the element after continuous driving 1×10 ⁹ times is also the same. It does not decrease significantly, and has the effective displacement required as a multilayer piezoelectric actuator. In addition, it is possible to manufacture a multilayer piezoelectric actuator with excellent durability without thermal runaway and malfunction.

(Example 2)

The material composition of the internal electrode 2 of the multilayer piezoelectric actuator of sample No. 7 in Example 1 was changed, and the rate of change of the displacement of each sample was measured. Here, the rate of change in displacement is the difference between the displacement (μm) when the multilayer piezoelectric element of each sample was driven 1× ¹⁰⁹ times and the initial state of the multilayer piezoelectric element before continuous driving was started. The displacement (μm) is obtained by comparison. The results are shown in Table 2.

Table 2

In Table 2, the metals in the internal electrodes represent the ratio of each metal in the internal electrodes to the total amount of the metals in % by mass. In addition, the rate of change in the amount of displacement indicates the rate of change (%) of the amount of displacement after continuous driving with respect to the amount of displacement in the initial state, and destruction indicates damage due to migration.

It is found from Table 2 that: in sample No. 1, when the internal electrode 2 is set to 100% silver, the multilayer piezoelectric element is damaged due to silver migration and cannot be driven continuously; in addition, sample No. 18, due to the internal electrode In the metal composition in 2, the content of group 8 to 10 metals exceeds 15% by mass, and the content of group 11 metals is less than 85% by mass, so the resistivity of the internal electrode 2 is large, and in the case of continuous drive multilayer type When the piezoelectric element generates heat, the displacement of the multi-layer piezoelectric actuator decreases.

On the other hand, it was also found that in samples Nos. 2 to 14, since the metal composition in the internal electrode 2 contained M1 mass % of Group 8 to Group 10 metals and M2 mass % of Group 11 metals, When the metal composition satisfying 0<M1≤15, 85≤M2<100, M1+M2=100% by mass is the main component, the resistivity of the internal electrode 2 can be reduced, and the resistivity of the internal electrode 2 can be suppressed even if it is driven continuously. 2 Since heat is generated, it is possible to manufacture a multilayer actuator with stable element displacement.

In addition, it was found that Sample Nos. 15 to 17 also reduced the resistivity of the internal electrodes 2 and suppressed the generation of heat in the internal electrodes 2 even after continuous driving. Therefore, it was possible to produce a multilayer actuator with stable element displacement.

In addition, this invention is not limited to the said Example, Various changes are possible to some extent in the range which does not deviate from the summary of this invention.

(Example 3)

In Example 3, a multilayer piezoelectric actuator composed of the multilayer piezoelectric element of the present invention was produced as follows.

First, prepare a slurry obtained by mixing calcined powder of piezoelectric ceramics mainly composed of lead zirconate titanate (PbZrO ₃ -PbTiO ₃ ), a binder, and a plasticizer, and make a slurry with a thickness of 150 μm by the doctor blade method. The ceramic green sheet that becomes the piezoelectric body 11.

A conductive paste was printed on one side of the ceramic green sheet by a screen printing method to form a sheet having a thickness of 3 μm, and 300 sheets of this sheet were stacked to prepare for the active layer. In addition to this, green sheets with a thickness of 100 μm (with no conductive paste) for constituting the inert layer 12 were prepared, and 5 to 20 green sheets for the inert layer, 300 green sheets for the active layer, and 300 green sheets for the inert layer were sequentially laminated. Press with 5 to 20 sheets. Among them, the conductive paste is obtained by adding a binder to a silver-palladium alloy formed at an arbitrary composition ratio.

Next, a conductive paste was printed with a thickness of 5 μm by a screen printing method on both end surfaces of the laminate 10 a having the inert layer 12 , that is, on the end surfaces of the inert layer 12 , to form the metal layer 8 . Afterwards, after firing at 1000°C for a certain period of time, the metal layer 8 is removed by a surface grinder, etc., wherein the conductive paste is obtained by adding a binder to Pd, Ni, Cu, Ag, Na, Pb, W, or Mo Conductive paste, or a conductive paste obtained by adding a binder to silver-palladium alloy.

Then, grooves 3 having a depth of 50 μm and a width of 50 μm were formed every other layer at the end of the internal electrodes on the side of the laminate by a slicing device, and the grooves 3 were filled with silicone rubber and cured.

Next, in a mixture of 90% by volume of flaky silver powder with an average particle size of 2 μm and 10% by volume of amorphous glass powder whose main component is silicon with an average particle size of 2 μm and a softening point of 640° C. 8 mass parts of binders were added with respect to 100 mass parts of total weights of silver powder and glass powder, and it mixed well, and the silver glass conductive paste was produced. The thus-produced silver glass conductive paste was formed on a release film by screen printing, and after drying, it was peeled off from the release film to obtain a sheet of the silver glass conductive paste. The original density of the sheet was measured by the Archimedes method to be 6.5 g/cm ³ .

Next, a sheet of silver glass paste was transferred onto the external electrode surface of the laminate, and fired at 650° C. for 30 minutes to form an external electrode composed of a porous conductor having a three-dimensional network structure. In addition, the porosity of the external electrodes at this time was 40% as a result of analyzing a cross-sectional photograph of the external electrodes by an image analysis device. In addition, K ₂ CO ₃ or Na ₂ CO ₃ powder is added to the raw materials of the piezoelectric body 1 , the internal electrode 2 , and the external electrode 4 . The alkali metal contained in the piezoelectric body, internal electrodes, and external electrodes of the obtained sintered body was detected by an ICP analysis method.

In addition, as a comparative example, a multilayer piezoelectric element in which an electrode not electrically connected to an external electrode was provided in an inert layer as shown in FIG. 8 was fabricated. Here, the piezoelectric body of the multi-layer piezoelectric element is the same as the above-mentioned composition of the present invention, and the ratio of silver to palladium in the internal electrodes of the comparative example is constituted at 95:5. In Table 3-1, in Sample No. 1 of the comparative example, since no metal is dispersed in the inert layer, the columns of the melting point ratio of the dispersed metal and the composition of the dispersed metal are shown as blank (-). And, after laminating sequentially 10 sheets for the inert layer, 300 sheets for the active layer, and 10 sheets for the inert layer, external electrodes, wires, etc. were provided by the same method as the above-mentioned present invention to produce a multilayer piezoelectric element (Table 3 The sample number 1).

Afterwards, the wire 6 is connected to the external electrode 4, and a DC electric field of 3 kV/mm is applied to the positive and negative external electrodes 4 via the wire 6 for 15 minutes to perform polarization treatment, and the electrode shown in Fig. 3A and B is made. Multilayer piezoelectric actuator for multilayer piezoelectric elements.

A DC voltage of 170 V was applied to the obtained multilayer piezoelectric element, and as a result, a displacement of 45 μm was obtained in the lamination direction. Further, a drive test was performed at room temperature by applying an AC voltage of 0 to +170 V at a frequency of 150 Hz to the multilayer piezoelectric element.

Furthermore, the multilayer piezoelectric element was subjected to a continuous driving test up to 1×10 ⁹ times, and the number of occurrences of defects at this time was expressed as a defect rate. In addition, with respect to the metal 14 dispersed in the inert layer 12 , EPMA analysis was carried out at three points on an arbitrary cross section of the inert layer 12 to investigate whether or not the metal was dispersed. On the other hand, the content of the metal 14 in the inert layer 12 is obtained by taking samples from any three positions of the inert layer 12, and performing ICP emission analysis on each sample, and taking the average value of the calculated contents. The results are shown in Table 3. In addition, the ratio of the melting point of the dispersed metal to the firing temperature shown in Table 3 represents the ratio of the melting point of the dispersed metal to the firing temperature of the laminate 10a.

Table 3-1

No. metal dispersion The ratio of the melting point of the dispersed metal to the firing temperature (%) Composition of dispersed metals *1 none - 2 have 218 W 3 have 282 Mo 4 have 130 Pd 5 have 120 Ni 6 have 90 Cu 7 have 80 Ag 8 have 73 Na 9 have 27 Pb 10 have 80, 130 99.99Ag-0.01Pd 11 have 80, 130 95Ag-5Pd 12 have 80, 130 90Ag-10Pd 13 have 80, 130 85Ag-15Pd 14 have 80, 130 95Ag-5Pd 15 have 80, 130 95Ag-5Pd 16 have 80, 130 95Ag-5Pd 17 have 80, 130 95Ag-5Pd 18 have 80, 130 95Ag-5Pd 19 have 80, 130 95Ag-5Pd 20 have 80, 130 95Ag-5Pd twenty one have 80, 130 95Ag-5Pd

Table 3-2

No. Composition of internal electrodes Dispersion amount of metal (mass%) The thickness of the inert layer (mm) Defect rate after continuous durability test (%) *1 95Ag-5Pd 0 0.5 9 2 95Ag-5Pd 0.0001 0.5 3 3 95Ag-5Pd 0.0002 0.5 4 4 95Ag-5Pd 0.03 0.5 0.7 5 95Ag-5Pd 0.03 0.5 0.8 6 95Ag-5Pd 0.08 0.5 0.8 7 95Ag-5Pd 0.06 0.5 0.4 8 95Ag-5Pd 0.09 0.5 0.6 9 95Ag-5Pd 0.03 0.5 0.9 10 99.99Ag-0.01Pd 0.1 0.5 0.07 11 95Ag-5Pd 0.1 0.5 0.05 12 90Ag-10Pd 0.1 0.5 0.06 13 85Ag-15Pd 0.1 0.5 0.07 14 95Ag-5Pd 0.001 0.5 0.5 15 95Ag-5Pd 0.01 0.5 0.3 16 95Ag-5Pd 0.1 0.5 0.05 17 95Ag-5Pd 1.2 0.5 1.2 18 95Ag-5Pd 0.1 0.1 0.06 19 95Ag-5Pd 0.1 0.1 0.05 20 95Ag-5Pd 0.1 1.0 0.05 twenty one 95Ag-5Pd 0.1 2.0 0.05

From Table 3, it is found that in the multilayer piezoelectric actuator of Sample No. 1 of the comparative example, since the electrodes are provided on the inert layer, the stress generated by the vibration of the multilayer piezoelectric element during the continuous driving test Cracks are generated at the interface between the electrodes in the inert layer and the active part, resulting in a high defect rate.

In contrast, in the multilayer piezoelectric actuators of sample numbers 2 to 21 in Example 3 of the present invention, since the metal is dispersed in the inert layer 12, the gap between the inert layer 12 and the active part 11 can be reduced during firing shrinkage. The stress generated between them can be relaxed and homogenized, and cracks in the inert layer 12 can be suppressed even under high voltage and long-term continuous use, and the durability is excellent, so the defective rate is reduced.

In addition, in sample numbers 2 and 3, since the melting point of the metal constituting the electrode layer 8 is significantly higher than the firing temperature of the laminate 10a, it is difficult to disperse the metal 14 in the inert layer 12, and it is difficult to exert the above-mentioned effect.

In addition, in Sample No. 17, since the dispersion amount of the metal 14 exceeds 1.0 mass % with respect to the inert layer 12 , the insulation of the inert layer 12 deteriorates, causing dielectric breakdown, and the defective rate becomes somewhat higher.

On the other hand, in the sample numbers 4 to 16 and 18 to 21, since the dispersion amount of the metal 14 is 0.001 to 1.0 mass % with respect to the inert layer 12, the above-mentioned effect is easily exhibited. In particular, sample numbers 11 to 13, 16, and 18 to 21 in which the above dispersion amount is 0.1% by mass and the metal 14 is composed of silver and palladium, that is, the metal 8 contains the metal constituting the internal electrode 2, because the stability of the inert layer 12 is ensured. Insulation, and the metal 14 is easy to diffuse to the inert layer 12, so it can suppress cracks in the inert layer 12 under high voltage and long-term continuous use, and has excellent durability, so the defect rate is significantly reduced.

Claims (16)

1. laminate type piezoelectric element is characterized in that having:

Laminated body, it has active portion, this active portion is that at least 1 piezoelectrics of alternative stacked form with a plurality of internal electrodes that are made of first internal electrode and second internal electrode, described active portion be added to voltage between described first internal electrode and described second internal electrode corresponding stretch and

Outer electrode, it is respectively formed on 2 sides of described laminated body, and one of them is connected with described first internal electrode, wherein another is connected with described second internal electrode,

Described each outer electrode is to comprise join the 1st layer of forming and be formed on the 1st layer the 2nd layer at the interior layer more than 3 layers of side with described laminated body,

Described the 1st layer contains more metal oxide compared with described the 2nd layer.

2. laminate type piezoelectric element according to claim 1 is characterized in that:

Described the 1st layer thickness is below the 10 μ m.

3. laminate type piezoelectric element according to claim 1 and 2 is characterized in that:

The amount of the outermost metal oxide of described outer electrode is minimum in described layer more than 3 layers.

4. laminate type piezoelectric element according to claim 1 is characterized in that:

Described metal oxide is a glass.

5. laminate type piezoelectric element according to claim 1 and 2 is characterized in that:

Described laminated body has the inert layer that is made of piezoelectric respectively at both ends,

Described inert layer comprises dispersed metal.

6. laminate type piezoelectric element according to claim 1 is characterized in that:

Metal constituent in the described internal electrode is a principal component with 8～10 family's metals and/or 11 family's metals.

7. laminate type piezoelectric element according to claim 6 is characterized in that:

When the amount that the amount of 8～10 family's metals in described internal electrode is made as M1 quality %, 11 family's metals is made as M2 quality %, satisfy 0＜M1≤15,85≤M2＜100, M1+M2=100.

8. according to claim 6 or 7 described laminate type piezoelectric elements, it is characterized in that:

Described 8～10 family's metals be among Ni, Pt, Pd, Rh, Ir, Ru, the Os more than at least a kind, 11 family's metals be among Cu, Ag, the Au more than at least a kind.

9. according to claim 6 or 7 described laminate type piezoelectric elements, it is characterized in that:

Described 8～10 family's metals be among Pt, the Pd more than at least a kind, 11 family's metals be among Ag, the Au more than at least a kind.

10. according to claim 6 or 7 described laminate type piezoelectric elements, it is characterized in that:

Described 8～10 family's metals are Ni.

11., it is characterized in that according to claim 6 or 7 described laminate type piezoelectric elements:

Described 11 family's metals are Cu.

12., it is characterized in that according to claim 6 or 7 described laminate type piezoelectric elements:

In described internal electrode, oxide, nitride or carbide have been added with described metal constituent.

13. laminate type piezoelectric element according to claim 12 is characterized in that:

Described oxide is with by PbZrO ₃-PbTiO ₃The perofskite type oxide that constitutes is a principal component.

14. laminate type piezoelectric element according to claim 1 is characterized in that:

Described piezoelectrics are principal component with the perofskite type oxide.

15. laminate type piezoelectric element according to claim 14 is characterized in that:

Described piezoelectrics are with by PbZrO ₃-PbTiO ₃The perofskite type oxide that constitutes is a principal component.

16. laminate type piezoelectric element according to claim 1 is characterized in that:

Be formed with groove between described second internal electrode on the side in described 2 sides of described laminated body and the described outer electrode, between described first internal electrode on another side and described outer electrode, be formed with groove,

In described groove, be filled with the Young's modulus insulator lower respectively than described piezoelectrics.

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