JP2007123808A - Stacked piezoelectric element and injection apparatus using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stacked piezoelectric element, which excels in durability, capable of obtaining a large displacement value, suppressing resonance phenomena, suppressing changes in the displacement value even if continuous drive is performed for a long period under high electric field and high pressure, and suppressing delamination in the lamination part; and an injection apparatus using it. <P>SOLUTION: A lamination 13 of multiple piezoelectric layers 11 and multiple metal layers 12 (12a, 12b) composed mainly of alloys are stacked alternatively. The multiple metal layers 12 are mainly composed of alloys, and contain a plurality of higher ratio metal layers 12b in which a component composing the alloy has a higher component ration than both the adjoining metal layers 12a. <P>COPYRIGHT: (C)2007,JPO&INPIT

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, a vibration, and the like. Sensor elements mounted on drive elements (piezoelectric actuators), combustion pressure sensors, knock sensors, acceleration sensors, load sensors, ultrasonic sensors, pressure sensitive sensors, yaw rate sensors, etc. mounted on prevention devices, etc., and piezoelectric gyros, piezoelectrics The present invention relates to a laminated piezoelectric element used for a circuit element or the like mounted on a switch, a piezoelectric transformer, a piezoelectric breaker, or the like, and an injection device including the same.

  Conventionally, piezoelectric actuators in which piezoelectric bodies and metal layers are alternately stacked are known as those using stacked piezoelectric elements. In general, piezoelectric actuators are classified into two types: a co-fired type and a stack type in which piezoelectric ceramics made of one piezoelectric material and plate-like metal layers are alternately stacked. Of these, from the viewpoint of lowering the voltage and reducing the manufacturing cost, a simultaneous firing type piezoelectric actuator that is advantageous in terms of thinning and also in terms of durability is becoming more dominant.

  FIG. 7A is a perspective view showing a conventional multilayer piezoelectric element. This multilayer piezoelectric element is composed of a multilayer body 133 and a pair of external electrodes 105 formed on side surfaces facing each other. The stacked body 133 is formed by alternately stacking the piezoelectric bodies 101 and the metal layers 102. Inactive layers 104 are respectively stacked on both end surfaces of the stacked body 133 in the stacking direction. The metal layer 102 is not formed on the entire main surface of the piezoelectric body 101 and has a so-called partial electrode structure. The metal layers 102 of this partial electrode structure are laminated so as to be exposed on different side surfaces of the multilayer body 133 and are connected to the pair of external electrodes 105 every other layer.

  The manufacturing method of such a conventional multilayer piezoelectric element is as follows. That is, first, a metal paste is printed on the ceramic green sheet containing the raw material of the piezoelectric body 101 in a pattern having a predetermined metal layer structure as shown in FIG. Next, a laminate 133 having a cross-sectional structure as shown in FIG. 8 is obtained by stacking a plurality of green sheets printed with a metal paste to produce a laminate molded body and firing the laminate. Thereafter, a metal paste is applied to the opposing side surfaces of the multilayer body 133 and then fired to form a pair of external electrodes 105, thereby obtaining a multilayer piezoelectric element (see, for example, Patent Document 1).

  In general, an alloy of silver and palladium is used for the metal layer 102. Further, in order to fire the piezoelectric body 101 and the metal layer 102 at the same time, the metal composition of the metal layer 102 is set to 70% by mass of silver and 30% by mass of palladium (for example, see Patent Document 2). The reason why the metal layer 102 made of a silver-palladium alloy is used instead of the metal layer made of only silver is as follows. That is, when the metal layer 102 is composed only of silver containing no palladium, the silver in the metal layer is transferred from the positive electrode to the negative electrode in the opposing metal layer 102 when a potential difference is applied between the opposing metal layers 102. This is because a so-called ion migration phenomenon occurs that travels along the path. This phenomenon tends to occur remarkably in a high temperature and high humidity atmosphere.

  Conventionally, a metal paste prepared with substantially the same metal component ratio and metal concentration has been used for the purpose of forming a metal layer 102 having substantially the same metal filling rate. When this metal paste is screen-printed on a ceramic green sheet, the mesh density and resist thickness are set to substantially the same conditions, and the laminated body 133 is produced.

  In addition, when the ceramic green sheets are pressed and laminated, the pressed state is different between the portion where the metal layer 102 overlaps and the portion where the metal layer 102 does not overlap, so the metal layer density may be uneven even in the same plane of the metal layer 102. A method has been proposed in which a concave portion is formed in a portion of the ceramic tape where the metal layer 102 is to be formed so that the metal filling rate is uniform (for example, see Patent Document 3).

  By the way, when a conventional multilayer piezoelectric element is used as a piezoelectric actuator, a lead wire (not shown) is connected and fixed to the external electrode 105 by soldering, and is driven by applying a predetermined potential between the external electrodes 105. In recent years, multilayer piezoelectric elements have been required to ensure a large amount of displacement under a large pressure at the same time as miniaturization is promoted, so that a higher electric field is applied and the piezoelectric elements are continuously driven for a long time. It is required that it can be used under severe conditions.

  In order to meet such a demand for continuous driving for a long time under a high electric field and high pressure, Patent Document 4 proposes an element provided with a layer in which the thickness of the piezoelectric body 101 is changed. That is, stress relaxation is attempted by utilizing the fact that the amount of displacement varies with other layers due to the difference in thickness.

  Further, in the simultaneous firing type laminated piezoelectric element, it has been attempted to form a uniform metal layer so that an electric field is uniformly applied to all piezoelectric bodies. In particular, attempts have been made to make the metal composition of the metal layer uniform in order to make the conductivity of each metal layer uniform and to make the surface area of the portion in contact with the piezoelectric body uniform.

Furthermore, in the stack type multilayer piezoelectric element, the contact resistance of the interface between the electrode and the piezoelectric body is controlled to be high resistance at the center in the stacking direction of the multilayer piezoelectric element and to decrease toward both ends. It has been proposed that stress is not concentrated at the center in the stacking direction of elements (see, for example, Patent Document 5).
JP-A-61-133715 Japanese Utility Model Publication No. 1-130568 JP-A-10-199750 JP-A-60-86880 JP-A-6-326370

  However, unlike ordinary multilayer electronic components such as capacitors, the multilayer piezoelectric element continuously undergoes dimensional changes when driven, so if all piezoelectric bodies are driven in close contact via a metal layer, The type piezoelectric element is driven and deformed as a unit. For this reason, the stress due to the deformation of the element concentrates on the outer peripheral portion of the central portion of the element that expands when compressed and constricts when stretched. As a result, when driven continuously for a long time under a high electric field and high pressure, delamination may occur at the interface (lamination interface) between the piezoelectric layer and the metal layer. In particular, stress is concentrated at the interface between the active layer that is piezoelectrically displaced and the inactive layer that is not piezoelectrically displaced, and this interface is the origin of delamination.

  In addition, a resonance phenomenon in which the displacement behaviors of the piezoelectric layers coincide with each other generates a beat sound, or a harmonic signal that is an integral multiple of the drive frequency is generated to generate a noise component.

  In addition, when a laminated piezoelectric element that continuously undergoes a dimensional change is driven for a long time, the element temperature rises, and there is a problem that the amount of displacement decreases when the energy for the element temperature rise exceeds the heat dissipation amount. Accordingly, a metal layer having a small specific resistance has been demanded in order to suppress an increase in element temperature.

  Furthermore, since the amount of displacement of the piezoelectric body has a characteristic that changes depending on the environmental temperature, when the conventional multilayer piezoelectric element is used as an actuator used for a drive element such as a fuel injection device, the element temperature increases. The displacement of the piezoelectric body may change depending on the case.

  As an improvement method, methods as shown in Patent Documents 4 and 5 have been made, but at present, they are often used under severe conditions such as continuous operation for a long time under a high electric field and high pressure. Under such conditions, improvement cannot be said to be sufficient yet, and stress concentrates on the outer periphery of the central portion of the element, causing cracks or peeling, and the amount of displacement may change.

  Therefore, the present invention has been made in view of the above-described problems, and is a case where a large amount of displacement can be obtained, a resonance phenomenon can be suppressed, and continuous driving is performed for a long time under a high electric field and high pressure. Another object of the present invention is to provide a laminated piezoelectric element having excellent durability capable of suppressing a change in displacement and suppressing delamination at a laminated interface, and an injection device using the same.

  As a result of intensive research in order to solve the above problems, the present inventors have not made a plurality of metal layers mainly composed of alloys to have a uniform composition as in the prior art. As a part, a large amount of displacement can be obtained by including a plurality of high ratio metal layers in which the ratio of one component constituting the alloy is higher than the metal layers on both sides adjacent to each other, and the resonance phenomenon can be suppressed. To obtain a laminated piezoelectric element with excellent durability capable of suppressing a change in displacement and suppressing delamination of a laminated portion even when continuously driven under an electric field and high pressure for a long time. The present inventors have found a new fact that it is possible to complete the present invention.

  That is, the multilayer piezoelectric element of the present invention is a multilayer piezoelectric element in which a plurality of piezoelectric layers and a plurality of metal layers mainly composed of an alloy are alternately stacked. A plurality of high-ratio metal layers are included which are higher than the metal layers on both sides adjacent to each other.

  The plurality of high-ratio metal layers in the present invention are preferably arranged with a plurality of metal layers other than the high-ratio metal layer interposed therebetween. In addition, the alloy is a silver alloy that forms a solid solution of the entire ratio, the one component is more preferably silver, and the alloy is more preferably a silver palladium alloy.

  In the present invention, the plurality of metal layers may be formed not only from an alloy but also from a part of a metal having a single composition. That is, another multilayer piezoelectric element of the present invention is a multilayer piezoelectric element in which a plurality of piezoelectric layers and a plurality of metal layers are alternately stacked, wherein the plurality of metal layers are at least one of the metal layers. It includes a plurality of high-ratio metal layers having higher component ratios than adjacent metal layers on both sides. The plurality of high-ratio metal layers are preferably arranged with a plurality of metal layers other than the high-ratio metal layer interposed therebetween. Furthermore, it is more preferable that the one component is silver, the other metal layer is mainly composed of a silver alloy that forms a solid solution, and the high-ratio metal layer is made of silver, and the other metal layer is silver. More preferably, it consists of a palladium alloy.

  The plurality of high-ratio metal layers in the present invention are preferably arranged regularly. Further, the adhesion between the high-ratio metal layer and the piezoelectric layer is preferably lower than the adhesion between the metal layer other than the high-ratio metal layer and the piezoelectric layer. Further, the high ratio metal layer may have a Vickers hardness lower than other metal layers other than the high ratio metal layer.

  In addition, a plurality of other metal layers other than the high-ratio metal layer are disposed between the two high-ratio metal layers in the present invention, and the group of the other metal layers includes the one-component metal layer. There is preferably a gradient concentration region in which the concentration gradually decreases from the high-ratio metal layer side.

  Still another multilayer piezoelectric element of the present invention is a multilayer piezoelectric element in which a plurality of piezoelectric layers and a plurality of metal layers are alternately stacked, wherein the plurality of metal layers have at least two or more different main components. A metal layer is included, and one kind of these metal layers is arranged in a state where a plurality of other metal layers are sandwiched. The one kind of metal layer is preferably composed mainly of a silver alloy that forms a solid solution, and the other metal layer is preferably composed mainly of copper, and the one kind of metal layer is mainly composed of a silver palladium alloy. More preferred. Moreover, it is preferable that a plurality of the one kind of metal layers are regularly arranged. Further, the adhesion force between the one kind of metal layer and the piezoelectric layer is preferably lower than the adhesion force between the other metal layer and the piezoelectric layer. Further, the kind of metal layer may have a Vickers hardness lower than that of the other metal layer.

  An injection device according to the present invention is characterized in that the multilayer piezoelectric element according to any one of the above is stored in a storage container having an ejection hole.

  According to the multilayer piezoelectric element of the present invention, the plurality of metal layers include a plurality of high-ratio metal layers whose ratio of one component constituting the alloy is higher than that of both adjacent metal layers. Different metal layers can be arranged, and the stress applied to the piezoelectric element can be dispersed. Thereby, suppression of element deformation due to stress concentration is alleviated, so that the displacement amount of the entire piezoelectric element can be increased. Further, since stress concentration due to deformation of the piezoelectric element can be suppressed, delamination in the laminated portion can be suppressed even when the piezoelectric element is continuously driven for a long time under a high electric field and high pressure. Furthermore, by arranging a plurality of high-ratio metal layers, the resonance phenomenon that occurs when the displacements (dimensional changes) of the piezoelectric elements are aligned can be suppressed. Since the generation of the wave signal can be prevented, the noise of the control signal can be suppressed.

  Therefore, even if the multilayer piezoelectric element is continuously driven, the desired displacement amount does not change effectively, so that it is possible to provide a highly reliable injection device with excellent durability.

<Laminated piezoelectric element>
(First embodiment)
Hereinafter, the laminated piezoelectric element according to the first embodiment of the present invention will be described in detail. FIG. 1A is a perspective view showing a laminated piezoelectric element according to the present embodiment, and FIG. 1B is a partial perspective view showing a laminated state of a piezoelectric layer and a metal layer in FIG. FIG. FIG. 2 is a partially enlarged cross-sectional view showing the multilayer structure of the multilayer piezoelectric element according to this embodiment.

  As shown in FIGS. 1 and 2, the multilayer piezoelectric element of the present embodiment has a plurality of piezoelectric layers 11 and a plurality of metal layers 12 (12a, 12b) mainly composed of an alloy, which are alternately stacked. And a pair of external electrodes 15 are disposed on opposite side surfaces of the multilayer body 13 (one external electrode is not shown). The metal layer 12 is not formed on the entire main surface of the piezoelectric layer 11 and has a so-called partial electrode structure. The plurality of metal layers 12 of this partial electrode structure are arranged so as to be exposed on opposite side surfaces of the laminated body 13 every other layer. Thereby, the metal layer 12 is electrically connected to the pair of external electrodes 15 every other layer. The pair of external electrodes 15 may be formed on adjacent side surfaces.

  In addition, an inactive layer 14 made of a piezoelectric material is laminated on both ends of the laminated body 13 in the lamination direction. When this multilayer piezoelectric element is used as a piezoelectric actuator, the lead wires may be connected and fixed to the pair of external electrodes 15 by soldering, and the lead wires may be connected to the external voltage supply unit. By applying a predetermined voltage between the adjacent metal layers 12 through the lead wire from the external voltage supply unit, each piezoelectric layer 11 is displaced by the inverse piezoelectric effect. On the other hand, the inactive layer 14 has only the metal layer 12 disposed on one main surface side, and the metal layer 12 is not disposed on the other main surface side. Does not occur.

  In the multilayer piezoelectric element of the present embodiment, as shown in FIG. 2, the plurality of metal layers 12 are mainly composed of an alloy, and the ratio of one component constituting the alloy is higher than the adjacent metal layers 12a. It is characterized by including a plurality of high-ratio metal layers 12b. That is, since the softness (hardness) of the alloy can be freely changed depending on the composition, a part of the plurality of metal layers 12 is made to be a high-ratio metal layer 12b to be partially soft. However, different metal layers can be arranged. Thereby, since the stress applied to the piezoelectric element can be dispersed, suppression of element deformation due to stress concentration is alleviated, and the displacement of the entire element can be increased. Further, the concentration of stress due to the deformation of the element can be suppressed, and even when the element is continuously driven for a long time under a high electric field and high pressure, it is possible to suppress the occurrence of delamination and damage at the stack interface.

  As described above, the “high ratio metal layer 12b” in the present embodiment is higher in the ratio of one component constituting the alloy (for example, the ratio of silver constituting the silver palladium alloy) than the adjacent metal layers 12a. It is a metal layer. The ratio B of one component in the high ratio metal layer 12b may be set higher than the ratio A of one component in the metal layers 12a on both sides adjacent to this (B> A), but the ratio B is higher than the ratio A. Is preferably set to 0.1% by mass or more, more preferably 0.5 to 10% by mass, and still more preferably 1 to 3% by mass. When the ratio B is set to be 0.1 mass% or more higher than the ratio A, a high effect of dispersing the stress applied to the element can be obtained. In particular, when the ratio B is set higher than the ratio A by 0.5 mass% or more, the effect is high. On the other hand, when the ratio B is set higher than the ratio A in a range exceeding 10 mass%, the thermal expansion coefficient of the high-ratio metal layer 12b is different from the thermal expansion coefficients of the adjacent metal layers 12a. There is a possibility that a stress may be distributed due to a difference in thermal expansion coefficient between the body layer and the metal layer, and a location where the stress is concentrated in the multilayer piezoelectric element may occur.

  Further, in the multilayer piezoelectric element of the present embodiment, the region to be driven and deformed is that the metal layer 12 disposed on the main surface on both sides of the piezoelectric layer 11 is interposed through the piezoelectric layer 11 in the piezoelectric layer 11. This is a region overlapping in the stacking direction. Therefore, in order to obtain the effect of the present invention, the ratio B of one component in the high-ratio metal layer 12b and the ratio A of one component in the metal layer 12a are related to each other in the region overlapping with the piezoelectric layer 11 in the stacking direction. As long as you are satisfied. Thereby, suppression of element deformation due to stress concentration is alleviated, so that the displacement amount of the entire piezoelectric element can be increased. Further, since stress concentration due to deformation of the piezoelectric element can be suppressed, delamination in the laminated portion can be suppressed even when the piezoelectric element is continuously driven for a long time under a high electric field and high pressure. Furthermore, since the resonance phenomenon that occurs when the displacements (dimensional changes) of the piezoelectric elements are aligned can be suppressed, it is possible not only to prevent the generation of beat noise but also to prevent the generation of harmonic signals. Control signal noise can be suppressed.

  Furthermore, since the magnitude of displacement of the multilayer piezoelectric element 13 can be controlled by arranging a plurality of high-ratio metal layers 12b, it is not necessary to change the thickness of the piezoelectric layer 11, and the structure is effective for mass production. be able to.

  The alloy composition of the metal layer 12 can be measured as follows. That is, a part of the metal layer 12 is sampled by cutting the laminated body 13 at the interface between the metal layer 12 and the piezoelectric layer 11 so that the metal layer 12 is exposed, and ICP (inductively coupled plasma) emission is performed. It can be measured by chemical analysis such as analysis. Further, a cross section obtained by cutting the multilayer piezoelectric element in the stacking direction can be analyzed using an analysis method such as an EPMA (Electron Probe Micro Analysis) method. When the metal layer is observed with a scanning electron microscope (SEM) or metal microscope on the cut surface of the multilayer piezoelectric element, it may contain not only metal components but also elements other than metals such as voids and ceramic components. is there. In such a case, a portion composed only of metal may be analyzed by the EPMA method or the like. Thereby, the alloy ratio of the high ratio metal layer 12b and the other metal layer 12a can be specified.

  Further, the plurality of high-ratio metal layers 12b are respectively disposed with one or more metal layers 12a other than the high-ratio metal layer 12b interposed therebetween. For example, when the alloy constituting the metal layer 12 is silver-palladium and the one component is silver, the plurality of high-ratio metal layers 12b are separated from the metal layer 12a other than the high-ratio metal layer 12b for the following reason. Are preferably arranged with a plurality of layers in between. That is, when the high-ratio metal layer 12b and the other metal layers 12a are alternately arranged one by one, the stress inside the multilayer piezoelectric element 13 is uniformly distributed to all the metal layers 12. There are benefits. On the other hand, the high ratio metal layer 12b is soft because the silver ratio is higher than that of the other metal layers 12a. Therefore, the high ratio metal layer 12b has the same number of layers as the other metal layers 12a. When present, the action of reducing the drive displacement increases, and the amount of drive displacement tends to decrease. Therefore, by disposing a plurality of high-ratio metal layers 12b with a plurality of metal layers 12a other than the high-ratio metal layers interposed therebetween, the piezoelectric displacement is increased at a portion where the other metal layers 12a are sandwiched. Furthermore, since stress relaxation is possible in the portions of the plurality of high-ratio metal layers 12b, not only the displacement of the entire element can be increased, but also the concentration of stress due to deformation of the element can be suppressed, Even when driven continuously for a long time under a high electric field and high pressure, the laminated portion does not peel off.

  In addition, the alloy constituting the metal layer 12 is mainly composed of a group 8-10 metal and / or a group 11 metal in the periodic table, so that the piezoelectric body and the metal layer can be fired at the same time. In addition to strong bonding, the metal layer itself can expand and contract even when the element is displaced and stress is applied to the metal layer. Therefore, the stress does not concentrate on one point, and it is a highly reliable piezoelectric with excellent durability. An actuator can be provided. The alloy constituting the metal layer 12 is particularly a silver-palladium alloy, and the one component is preferably silver. This is not only that the multilayer piezoelectric element 13 can be obtained by firing in an oxidizing atmosphere, but because silver and palladium are all solid-dissolved metals, an unstable intermetallic compound is formed over the entire surface of the metal layer. Thus, it is possible to form the soft high-ratio metal layer 12b having a stress relaxation effect. In particular, since the metal that is a high-ratio component is silver, when a laminated piezoelectric element is sintered, silver is dissolved in the liquid phase component of the ceramic, and the liquid phase formation temperature is lowered to sinter. Can be advanced. Thereby, the mutual coupling force between the metal layer 12 and the piezoelectric layer 11 can be strengthened. Furthermore, by alloying, the metal layer 12 having a migration resistance stronger than that of a single element can be formed, and a durable laminated piezoelectric element can be obtained.

  Furthermore, it is preferable that the plurality of high-ratio metal layers 12b are regularly arranged. If the layers are irregularly arranged, the stress applied to the entire multilayer piezoelectric element concentrates on a portion where the space between the high-ratio metal layers is wide, and the effect of stress dispersion may not be sufficiently obtained. By regularly disposing the high ratio metal layer 12b, the stress applied to the multilayer piezoelectric element is effectively dispersed. Here, in the present invention, “the high ratio metal layer is regularly arranged” means that the number of other metal layers 12a existing between the high ratio metal layers 12b is between any high ratio metal layers 12b. This is a concept that includes the case where the number of other metal layers 12a existing between the high-ratio metal layers 12b is approximated to the extent that stress is not concentrated in part. Specifically, the number of other metal layers 12a existing between the high-ratio metal layers 12b is preferably within a range of ± 20% with respect to the average value of each layer number, and more preferably the average value of each layer number. On the other hand, it is preferable that they are within the range of ± 10%, more preferably the same number. When the number of other metal layers 12a existing between the high ratio metal layers 12b is within the above range, the stress applied to the multilayer piezoelectric element is more effectively dispersed.

  Moreover, it is preferable that the adhesive force between the high-ratio metal layer 12b and the piezoelectric layer 11 is set lower than the adhesive force between the metal layer 12a other than the high-ratio metal layer and the piezoelectric layer 11. As described above, since the adhesion of the high-ratio metal layer 12b is lower than that of the other metal layers 12a, when stress is applied to the multilayer piezoelectric element, the high-ratio metal layer 12b having weak adhesion is deformed and stress is applied. Alleviated. In addition, the piezoelectric layer 11 that is in contact with the high-ratio metal layer 12b having a low adhesion force has a smaller contact area with the high-ratio metal layer 12b, so that the force that restrains the piezoelectric body 11 is reduced. This also relieves the stress applied to the multilayer piezoelectric element and avoids the concentration of stress at one point, so that a multilayer piezoelectric element having excellent durability can be obtained.

  Further, the high ratio metal layer 12b is preferably set to have a Vickers hardness (Hv) lower than that of the other metal layers 12a. When the Vickers hardness (Hv) of the high-ratio metal layer 12b is lower than that of the other metal layer 12a, that is, a metal layer that is softer than the other metal layer 12a, the high-ratio metal when the piezoelectric element is driven. The force that restrains the piezoelectric layer 11 in contact with the layer 12b becomes weak, and the piezoelectric layer 11 can increase the displacement. Therefore, a laminated piezoelectric element having high durability and large displacement can be obtained.

  In the multilayer piezoelectric element according to this embodiment, since the thickness of the metal layer 12 in the stacking direction is thin, the Vickers hardness of the metal layer 12 is measured as follows. That is, when measuring the Vickers hardness, for example, a micro Vickers measuring instrument such as MVK-H3 type manufactured by Akashi Seisakusho is used. In order to measure the Vickers hardness of the metal layer 12, it is also possible to cut the laminated piezoelectric element in the vicinity of the interface between the metal layer 12 and the piezoelectric layer 11 and press the diamond indenter into the metal layer 12 portion. However, in order not to be affected by the piezoelectric layer 11 as a base, it is preferable to push a diamond indenter into the metal layer 12 from a direction perpendicular to the stacking direction of the metal layer 12. When the metal layer 12 is exposed from the side surface of the piezoelectric element, the laminated piezoelectric element is installed so that the lamination direction of the diamond indenter and the metal layer 12 is vertical, and the diamond indenter is directly pushed into the metal layer 12. Measure hardness. On the other hand, when the metal layer 12 is not exposed from the side surface of the piezoelectric element, the element is polished until the metal layer 12 is seen, and then the hardness is measured in the same manner as described above. In order to expose the metal layer 12, in addition to polishing, cutting with a dicing saw machine, use of a router or the like can be considered, but if it is a technique capable of forming a flat surface without causing cracks, etc. The method is not limited.

  In addition, a plurality of other metal layers 12a other than the high-ratio metal layer are disposed between the two high-ratio metal layers 12b, and the group consisting of the other metal layers includes one component constituting the alloy. It is preferable that there is a gradient concentration region where the concentration of selenium gradually decreases from the high ratio metal layer side. Due to the existence of such a gradient concentration region, the stress of the multilayer piezoelectric element is concentrated on the high-ratio metal layer 12b, and the stress is also distributed to the nearby metal layer 12a (the metal layer 12a in the gradient concentration region). Therefore, it is possible to obtain a laminated piezoelectric element having higher durability. Further, it is more preferable that the gradient concentration region exists between all the high-ratio metal layers 12b from the viewpoint of further improving the durability. On the other hand, if the ratio of one component constituting the alloy is extremely different between the high-ratio metal layer 12b and the metal layer 12a adjacent thereto, stress tends to concentrate on the high-ratio metal layer 12b serving as a stress relaxation layer. There is a risk.

  In the present invention, the metal layer 12 preferably has a large number of voids. When the metal layer 12 contains an insulating material other than a metal component, when the piezoelectric element is driven, there is a possibility that a portion where the voltage cannot be applied to the piezoelectric layer 11 is generated and the piezoelectric displacement cannot be increased. There is a possibility that stress during driving concentrates on this part and becomes a starting point of delamination. On the other hand, when the metal layer 12 has a large number of voids, when stress is applied to the metal portion, the presence of the void portion facilitates deformation of the metal, and the stress can be dispersed and relaxed. In addition, when the piezoelectric layer 11 in contact with the metal layer 12 is piezoelectrically displaced, the presence of the void portion causes the piezoelectric layer 11 to be partially clamped, and the piezoelectric layer 11 than when the entire surface is clamped. The force with which the material is constrained becomes smaller and the displacement becomes easier, and the amount of displacement can be increased. Thereby, the displacement amount of the piezoelectric element is larger, and a highly durable laminated piezoelectric element can be obtained.

  In particular, it is preferable that a void is provided in the metal layer 12a other than the high-ratio metal layer, and the area ratio of the void to the total cross-sectional area in the cross section of the metal layer is 5 to 70%. This is because when the void is made to occupy 5 to 70% of the area of the metal layer 12a other than the high-ratio metal layer, the amount of displacement becomes large, and a laminated piezoelectric element having excellent displacement characteristics can be obtained. Because.

  Here, the ratio (void ratio) of the void to the area of the metal layer described above is a cross section parallel to the stacking direction in the stacked piezoelectric element using, for example, a scanning electron microscope (SEM), a metal microscope, an optical microscope, or the like. Alternatively, a cross-sectional image may be obtained by observing a cross section perpendicular to the stacking direction, and the cross-sectional image may be evaluated. In the cut surface, the area of voids (voids) present in the metal layer portion is measured, and the value obtained by dividing the total sum of the void areas by the area of the metal layer is multiplied by 100.

  When the void ratio of the other metal layer 12a is smaller than 5%, the piezoelectric layer 11 is subjected to a large restraining force from the metal layer 12a when the electric field is applied and deformed, so that the deformation of the piezoelectric layer 11 is suppressed, and the laminated type There is a possibility that the amount of deformation of the piezoelectric element is reduced and the generated internal stress is also increased. On the other hand, if the void ratio of the other metal layer 12a is larger than 70%, an extremely thin portion is generated in the electrode portion, so that the strength of the metal layer itself is reduced, the metal layer 12a is likely to be cracked, and disconnection is caused. May occur. The void ratio is more preferably 7 to 70%, still more preferably 10 to 60%. By doing so, the piezoelectric layer 11 can be deformed more smoothly, and the metal layer 12 has sufficient conductivity, so that the amount of displacement of the multilayer piezoelectric element can be increased.

  Moreover, it is preferable that the area ratio which the void occupies with respect to the total cross-sectional area in the cross section of the high ratio metal layer 12b is 20 to 90%. This is because if the voids are made to occupy 20 to 90% of the area of the high-ratio metal layer 12b, the displacement amount is further increased, and a laminated piezoelectric element having an excellent displacement amount can be obtained.

  Furthermore, when the metal layer 12 is mainly composed of a metal and a void, both the metal and the void can be deformed with respect to stress, so that a laminated piezoelectric element with higher durability can be obtained. In particular, if the high-ratio metal layer 12b is mainly composed of metal and voids than other metal layers 12a other than the high-ratio metal layer, both the metal and void can be deformed with respect to stress. The relaxation effect is improved, and a laminated piezoelectric element with higher durability can be obtained.

  A specific method for measuring the void ratio is as follows. That is, there are the following two methods for measuring the void ratio. The first method is a method of observing a cross section when the stacked body 13 is cut along a plane parallel to the stacking direction, and the second method is when the stacked body 13 is cut along a plane perpendicular to the stacking direction. This is a method of observing a cross section.

  In order to measure the void ratio by the first method, for example, the following may be performed. First, the laminated body 13 is polished using a known polishing means so that a cross section parallel to the stacking direction is exposed. Specifically, for example, polishing can be performed with diamond paste using a table polishing machine KEMET-V-300 manufactured by Kemet Japan Co., Ltd. as a polishing apparatus. The cross section exposed by this polishing process is observed with, for example, a scanning electron microscope (SEM), an optical microscope, a metal microscope, an optical microscope, etc. to obtain a cross section image, and the void ratio of the metal layer is obtained by performing image processing on the cross section image. Can be measured. As a specific example, for the image of the metal layer taken with an optical microscope, the void portion is painted in black, the portion other than the void is painted in white, and the ratio of the black portion, that is, (area of the black portion) / The void ratio can be calculated by calculating (area of the black portion + area of the white portion) and expressing the percentage. For example, when the cross-sectional image is a color, it may be converted into a gray scale and divided into a black portion and a white portion. At this time, if it is necessary to set a threshold value for the boundary between the black part and the white part for binarization, the threshold value for the boundary may be set by image processing software or visually. .

  Moreover, what is necessary is just to perform as follows, for example, in order to measure a void ratio by the 2nd method. First, it polishes in the lamination direction of the laminated body 13 using a well-known grinding | polishing apparatus until the cross section (cross section perpendicular | vertical to a lamination direction) of the metal layer which wants to measure a void rate is exposed. Specifically, for example, polishing can be performed with diamond paste using a table polishing machine KEMET-V-300 manufactured by Kemet Japan Co., Ltd. as a polishing apparatus. The cross section exposed by this polishing process is observed with, for example, a scanning electron microscope (SEM), an optical microscope, a metal microscope, an optical microscope, etc. to obtain a cross section image, and the void ratio of the metal layer is obtained by performing image processing on the cross section image. Can be measured. Specifically, with respect to the image of the metal layer photographed with an optical microscope, the void portion is painted in black and the portion other than the void is painted in white, and the ratio of the black portion, that is, (area of the black portion) / ( The void ratio can be calculated by calculating the area of the black portion + the area of the white portion and expressing it as a percentage. For example, when the cross-sectional image is a color, it may be converted into a gray scale and divided into a black portion and a white portion. At this time, if it is necessary to set a threshold value for the boundary between the black part and the white part for binarization, the threshold value for the boundary may be set by image processing software or visually. . In addition, when observing the cross section of a metal layer, it is preferable to grind | polish to the position of about 1/2 of these thickness, and to observe the cross section exposed by this. However, when the thickness of the metal layer is thin and the variation in thickness is relatively large, the entire cross section of the metal layer may not be exposed by the polishing process. In such a case, when the polishing process is performed until a part of the metal layer is exposed, the exposed portion is observed to obtain a cross-sectional image, and further polishing is performed to remove other portions that have already been observed. The operation of observing the part may be repeated a plurality of times. It is only necessary that the entire cross section of the metal layer can be observed by adding together the observation images obtained by a plurality of operations.

  The high-ratio metal layer 12b is more preferably in a form in which a plurality of alloys are scattered. That is, the high-ratio metal layer 12b is preferably constituted by a plurality of conductor regions dotted in an island shape. Since the high-ratio metal layer 12b is in the form of a plurality of conductor regions interspersed, stress propagation in the high-ratio metal layer 12b can be suppressed even when the stress of the multilayer piezoelectric element 13 is applied to the metal layer 12. In the high-ratio metal layer 12b, a portion where stress is particularly concentrated is not generated, so that both stress relaxation and durability can be achieved. On the other hand, when the high-ratio metal layer 12b is composed of a single continuous layer, when the stress of the multilayer piezoelectric element 13 is concentrated on the high-ratio metal layer 12b, of the interface with the piezoelectric layer 11, Since the stress propagates and concentrates on the portion facing the side surface of the piezoelectric element, there is a possibility that a portion where the stress is concentrated is generated.

  In addition, the metal layer 12 is preferably exposed on the side surface of the stacked body 13. This is because, in the portion where the metal layer 12 is not exposed on the side surface of the element, the portion where the metal layer 12 is not exposed cannot be displaced during driving, and the region displaced during driving is confined inside the element. This is because the stress at the time of displacement tends to concentrate on the boundary, which causes a problem in durability, which is not preferable.

  The laminated body 13 is preferably a columnar body having a polygonal cross section. This is because if the laminated body 13 has a cylindrical shape, the center axis will fluctuate unless it is made into a perfect circle, so a high-precision circle must be created and stacked, and a mass-production method using simultaneous firing is used. It becomes difficult. Further, even if the outer periphery is polished and formed into a cylindrical shape after laminating a substantially circular laminate or after firing, it is difficult to align the central axis of the metal layer 12 with high accuracy. On the other hand, in the case of a polygonal columnar body, the metal layer 12 can be formed on the piezoelectric layer 11 that has determined the reference line, and can be stacked along the reference line. Since a certain central axis can be formed using a mass production type manufacturing method, a highly durable element can be obtained.

  In the present invention, when the palladium content in the metal layer 12 is M1 (mass%) and the silver content is M2 (mass%), 0 <M1 ≦ 15, 85 ≦ M2 <100, M1 + M2 It is preferable that the main component is a metal composition satisfying = 100. This is because, when palladium exceeds 15% by mass, the specific resistance increases, and when the multilayer piezoelectric element is continuously driven, the metal layer 12 generates heat, and the generated heat acts on the piezoelectric layer 11 having temperature dependency. This is because the displacement characteristics of the stacked piezoelectric element may be reduced because the displacement characteristics are reduced. Furthermore, when the external electrode 15 is formed, the external electrode 15 and the metal layer 12 are mutually diffused and joined. If palladium exceeds 15% by mass, the hardness of the portion where the metal layer component is diffused in the external electrode 15 This is because the durability of the multi-layer piezoelectric element whose dimensions change during driving may decrease. Further, in order to suppress migration of silver in the metal layer 12 to the piezoelectric layer 11, it is preferable that the palladium metal is 0.001 mass% or more and 15 mass% or less. In terms of improving the durability of the multilayer piezoelectric element, the palladium ratio is preferably 0.1% by mass or more and 10% by mass or less. Moreover, when it is excellent in heat conduction and higher durability is required, the ratio of palladium is more preferably 0.5% by mass or more and 9.5% by mass or less, and 2% by mass is required for higher durability. % To 8% by mass is more preferable.

  On the other hand, when the silver ratio is less than 85% by mass, the specific resistance of the metal layer 12 increases, and the metal layer 12 may generate heat when the multilayer piezoelectric element is continuously driven. Further, in order to suppress migration of silver in the metal layer 12 to the piezoelectric layer 11, it is preferable that silver be 85 mass% or more and 99.999 mass% or less. In terms of improving the durability of the multilayer piezoelectric element, the silver ratio is preferably 90% by mass or more and 99.9% by mass or less. Further, when higher durability is required, the silver ratio is more preferably 90.5% by mass or more and 99.5% by mass or less, and when higher durability is required, 92% by mass or more and 98% by mass. The following is more preferable. Palladium metal and silver metal showing mass% of the metal component in the metal layer 12 can be specified by an analysis method such as EPMA method.

The piezoelectric layer 11 preferably contains a perovskite oxide as a main component. For example, when the piezoelectric layer 11 is 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 is increased. Further, the piezoelectric layer 11 and the metal layer 12 can be fired simultaneously. The piezoelectric layer 11 is preferably composed mainly of a perovskite oxide made of PbZrO ₃ —PbTiO ₃ having a relatively high piezoelectric strain constant d ₃₃ .

  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 produce the dense piezoelectric layer 11. Further, when the firing temperature exceeds 1000 ° C., the bonding strength between the metal layer 12 and the piezoelectric layer 11 increases.

  Further, the metal layer 12 whose end is exposed on the side surface of the multilayer piezoelectric element of the present invention and the metal layer 12 whose end is not exposed are alternately configured, and the metal layer 12 whose end is not exposed and A groove is formed in the piezoelectric layer 11 between the external electrodes 15, and an insulator having a Young's modulus lower than that of the piezoelectric layer 11 is preferably formed in the groove. Thereby, in such a multilayer piezoelectric element, stress generated by displacement during driving can be relieved, so that heat generation of the metal layer 12 can be suppressed even when continuously driven.

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

First, 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, DBP (dibutyl phthalate), DOP (dioctyl phthalate) The slurry is mixed with a plasticizer such as). Next, a ceramic green sheet to be the piezoelectric layer 11 is produced from the slurry by a tape molding method such as a known doctor blade method or calendar roll method.

  Next, a conductive paste is produced by adding and mixing a binder, a plasticizer, and the like to the metal powder constituting the metal layer 12 such as silver-palladium. Next, this is printed on the upper surface of each of the green sheets to a thickness of 1 to 40 μm by screen printing or the like.

  Here, the conductive paste that forms the high-ratio metal layer 12b is composed of the amount of one component of the metal powder contained in the conductive paste, and the amount of one component contained in the conductive paste that forms the other metal layer 12a. More than the amount. Specifically, when the silver component of the high-ratio metal layer 12b is increased using silver-palladium as an alloy, the high-ratio metal layer 12b is formed with a metal paste having a large silver component in the alloy composition, and the alloy composition The metal layer 12a other than the high-ratio metal layer is formed with a metal paste having a small silver component. At this time, the composition may be adjusted by using a mixed powder of silver powder and palladium powder instead of the alloy powder, and the composition may be adjusted by adding silver powder or palladium powder to the silver palladium alloy. However, it is preferable to use an alloy powder having a different composition from the beginning because the metal dispersion in the paste becomes uniform and the composition distribution in the same plane of the metal layer 12 becomes uniform.

  Next, a plurality of green sheets on which conductive paste is printed are stacked in a desired arrangement, debindered at a predetermined temperature, and then fired at 900 to 1200 ° C., whereby the stacked body 13 is manufactured.

  The inert layer 14 is obtained when a metal powder constituting the metal layer 12 such as silver-palladium is added to the green sheet forming the inert layer 14 or when the green sheet forming the inert layer 14 is laminated. In addition, by printing a slurry made of a metal powder and an inorganic compound, a binder, and a plasticizer constituting the metal layer 12 such as silver-palladium on a green sheet, the shrinkage during sintering of the inert layer 14 and other portions. Since the behavior and the shrinkage rate can be matched, the dense laminate 13 can be formed.

  In addition, the laminated body 13 is not limited to what is produced by the said manufacturing method, If any laminated body 13 which laminates | stacks the several piezoelectric body layer 11 and the some metal layer 12 alternately can be produced, It may be formed by such a manufacturing method.

  Thereafter, if necessary, the metal layer 12 with the end exposed on the side surface of the multilayer piezoelectric element and the metal layer 12 with the end not exposed are alternately formed, and the metal layer 12 with no end exposed. A groove may be formed in the piezoelectric portion between the external electrodes 15, and an insulator such as a resin or rubber having a Young's modulus lower than that of the piezoelectric layer 11 may be formed in the groove. Here, the groove can be formed on the side surface of the laminate 13 with an internal dicing apparatus 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 shape, and the raw density of the dried (spattered solvent) is controlled to 6 to 9 g / cm ³ . . This sheet is transferred to the external electrode forming surface of the laminate 13, and is at a temperature higher than the softening point of the glass, at a temperature not higher than the melting point of silver (965 ° C.), and 4 / of the firing temperature (° C.) of the laminate 13. Bake at a temperature of 5 or less. Thereby, 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 15 may be baked after being laminated on the multilayer sheet, or may be baked after being laminated one by one. Baking is better for mass production. And when changing a glass component for every layer, what is necessary is just to use what changed the quantity of the glass component for every sheet, but when it wants to constitute a very thin glass rich layer on the surface most in contact with piezoelectric material layer 11 A method of laminating multilayer sheets after printing a glass-rich paste on the laminate 13 by a method such as screen printing is used. At this time, a sheet of 5 μm or less may be used instead of printing.

  In addition, the baking temperature of the silver glass conductive paste effectively forms a neck portion (portion where crystal grains are confined), diffuses and joins the silver in the silver glass conductive paste and the metal layer 12, and externally. 500 to 800 ° C. is desirable from the viewpoint that the voids in the electrode 15 are effectively left, and further, the external electrode 15 and the side surface of the columnar laminate 13 are partially joined. The softening point of the glass component in the silver glass conductive paste is preferably 500 to 800 ° C. When the neck portion is present, an excessively dense sintered body is not formed, and a network structure having a moderate gap is obtained.

  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., since the diffusion bonding is not sufficiently performed between the end portion of the metal layer 12 and the external electrode 15, the neck portion is not formed, and the metal layer 12 and the external portion are driven during driving. 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. Then, the laminated piezoelectric element of the present embodiment is completed by curing the silicone rubber filled in the groove and coated on the side surface of the laminated body 13.

  Finally, 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. A piezoelectric actuator using the multilayer piezoelectric element of the invention is completed. When a lead wire is connected to an external voltage supply unit and a voltage is applied to the metal layer 12 via the lead wire and the external electrode 15, each piezoelectric layer 11 is greatly displaced by the inverse piezoelectric effect, thereby causing, for example, an engine to It functions as an automobile fuel injection valve that injects and supplies fuel.

  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. 15 can be reduced. Thereby, it can prevent that the external electrode 15 raise | generates a local heat_generation | fever and is disconnected, and durability can be improved significantly. 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.

  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. By making the shape of the conductive particles non-spherical particles such as flakes and needles, the entanglement between the conductive particles can be strengthened, and the shear strength of the conductive adhesive can be further increased. it can.

  As described above, one embodiment of the present invention has been described. However, the multilayer piezoelectric element of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the gist of the present invention. Is possible.

  For example, in the first embodiment, the case where the metal layers are all made of an alloy has been described. However, as in the second embodiment described later, some metal layers are made of an alloy, and the remaining metal layers are single. The form which consists of these metals may be sufficient. Moreover, in the said 1st Embodiment, although the case where the metal layer contained the same component was demonstrated, from the at least 2 or more types of layer from which a metal layer differs in a main component like 3rd Embodiment mentioned later. The form which becomes may be sufficient.

(Second Embodiment)
The laminated piezoelectric element according to the second embodiment of the present invention will be described below. In the description of the second embodiment, only the configuration different from the first embodiment will be described.

  FIG. 3 is a partially enlarged cross-sectional view showing the multilayer structure of the multilayer piezoelectric element according to the second embodiment. The multilayer piezoelectric element of the present embodiment has a multilayer body 13 in which a plurality of piezoelectric layers 11 and a plurality of metal layers 12 (12c, 12d) are alternately stacked, and the plurality of metal layers 12 are metal layers. 12 includes a plurality of high-ratio metal layers 12d in which the ratio of at least one component constituting 12 is higher than that of adjacent metal layers 12c on both sides.

  By including a plurality of such high-ratio metal layers 12d, it is possible to dispose metal layers having partially different softness (hardness) in the laminate 13, so that the stress applied to the piezoelectric element is dispersed. Can do. For this reason, suppression of element deformation due to stress concentration is alleviated, so that not only can the displacement of the entire element be increased, but stress concentration due to element deformation can also be suppressed, and it is possible to maintain long periods under high electric fields and pressures. Even in the case of continuous driving for a period, peeling of the stacked portion can be suppressed.

  Furthermore, since the portion of the piezoelectric layer 11 that undergoes drive deformation is a portion that is sandwiched between the metal layers 11, it is preferable that a portion of the metal layer 12 that overlaps with the piezoelectric layer 11 has a metal composition. By forming different metal layers, the resonance phenomenon that occurs when the displacement, which is the dimensional change of the elements, can be suppressed, so that not only it can prevent beat noise but also generate harmonic signals. Therefore, noise in the control signal can be suppressed. Furthermore, since the displacement of the multilayer piezoelectric element 13 can be controlled by changing the metal composition of the metal layer 12, it is not necessary to change the thickness of the piezoelectric layer 11, which is effective for mass production. It can be a structure. Here, the metal composition of the metal layer can be measured by the same method as described above.

  The plurality of high-ratio metal layers 12d are preferably arranged with a plurality of metal layers 12c other than the high-ratio metal layer 12d interposed therebetween. When the high-ratio metal layer 12d and the other metal layers 12c are alternately arranged one by one, the stress in the multilayer piezoelectric element 13 is uniformly distributed to all the metal layers 11, but the layers are simultaneously laminated. When the type piezoelectric element is driven, the driving displacement amount is also reduced. Therefore, a plurality of high-ratio metal layers 12d are disposed with a plurality of other metal layers 12c sandwiched therebetween, respectively, so that the piezoelectric displacement can be increased at a portion sandwiching the plurality of other metal layers 12c. Stress relaxation is enabled at the portions of the plurality of high-ratio metal layers 12d. As a result, not only the displacement of the entire element can be increased, but also the concentration of stress due to the deformation of the element can be suppressed, and the laminated part can be peeled off even when driven continuously for a long time under a high electric field and high pressure. Can be suppressed.

  Specifically, it is preferable that one component constituting the metal layer 12 is silver, the other metal layer 12c is made of a silver palladium alloy, and the high ratio metal layer 12d is made of silver. This is not only that the multilayer piezoelectric element 13 can be fired in an oxidizing atmosphere, but also because the silver-palladium alloy is an alloy that dissolves completely, an unstable intermetallic compound is formed over the entire surface of the metal layer. It is possible to form a soft metal layer that has a stress relaxation effect without being formed. In particular, since the metal that is a high-ratio component is silver, when a laminated piezoelectric element is sintered, silver is dissolved in the liquid phase component of the ceramic and the liquid phase formation temperature is lowered to sinter. Can be advanced. Thereby, the mutual coupling force between the metal layer 12 and the piezoelectric layer 11 can be strengthened. Furthermore, by alloying, it becomes possible to form a metal layer having a migration resistance stronger than that of a single element, and a durable laminated piezoelectric element can be obtained.

  As described above, the high ratio metal layer 12d is mainly made of silver, and the metal layer 12c other than the high ratio metal layer is mainly made of silver palladium alloy, so that the stress relaxation effect is maximized. In the case where the high-ratio metal layer 12d mainly made of silver is adjacent to each other with the piezoelectric layer 11 interposed therebetween, insulation failure may occur due to migration of silver. In this case, the high-ratio metal layer 12d mainly made of silver is formed. Since the metal layer 12c is a metal layer 12c mainly made of a silver-palladium alloy, even if silver tries to migrate, it binds to palladium and disappears and stabilizes floating silver ions. It can be set as a highly durable laminated pressure wire element without generating.

  For the same reason as in the first embodiment, it is preferable that the plurality of high-ratio metal layers 12d are regularly arranged, and the adhesion between the high-ratio metal layer 12d and the piezoelectric layer 11 is as follows. It is preferable that the adhesion strength between the other metal layer 12c and the piezoelectric layer 11 is lower. In addition, a plurality of other metal layers 12c are arranged between the two high-ratio metal layers 12d, and the concentration of one component in the group consisting of the other metal layers 12c is from the high-ratio metal layer 12d side. It is preferred that there is a gradient concentration region that gradually decreases. Furthermore, the metal layer 12 preferably has a large number of voids, and the high-ratio metal layer 12d is preferably composed of a plurality of conductor films scattered in islands.

  In the second embodiment, when the content of palladium in the metal layer 12c is M1 (mass%) and the content of silver is M2 (mass%), 0 ≦ M1 ≦ 15, 85 ≦ M2 ≦ It is preferable that the main component is a metal composition satisfying 100 and M1 + M2 = 100. This is because, when palladium exceeds 15% by mass, the specific resistance increases, and when the multilayer piezoelectric element is continuously driven, the metal layer 12 generates heat, and the generated heat acts on the piezoelectric layer 11 having temperature dependency. This is because the displacement characteristics of the stacked piezoelectric element may be reduced because the displacement characteristics are reduced.

  Furthermore, when the external electrode 15 is formed, the external electrode 15 and the metal layer 12 are mutually diffused and joined. If palladium exceeds 15% by mass, the hardness of the portion where the metal layer component is diffused in the external electrode 15 This is because the durability of the multilayer piezoelectric element whose dimensions change during driving decreases.

  The manufacturing method of the multilayer piezoelectric element according to the second embodiment may be the same as that of the first embodiment except that silver powder is mixed in the conductive paste for forming the high ratio metal layer 12d.

(Third embodiment)
The laminated piezoelectric element according to the third embodiment of the present invention will be described below. In the description of the third embodiment, only the configuration different from the first embodiment will be described.

  FIG. 4 is a partially enlarged cross-sectional view showing a multilayer structure of the multilayer piezoelectric element according to the third embodiment. The multilayer piezoelectric element of this embodiment includes a multilayer body 13 in which a plurality of piezoelectric layers 11 and a plurality of metal layers 12 are alternately stacked, and the plurality of metal layers 12 are two kinds of metals having different main components. It consists of layers 12e and 12f, and a plurality of metal layers 12f are arranged with a plurality of other metal layers 12e sandwiched therebetween.

  The softness (hardness) of the metal layer can be freely changed depending on the composition. In the third embodiment, since the two types of metal layers 12e and 12f having different main components are arranged as described above, metal layers having partially different softness can be arranged. The stress applied to the element can be dispersed. For this reason, suppression of element deformation due to stress concentration is alleviated, so that not only can the displacement of the entire element be increased, but stress concentration due to element deformation can also be suppressed, and it is possible to maintain long periods under high electric fields and pressures. Even when driven continuously for a period, it is possible to suppress the peeling of the stacked portion.

  Specifically, it is preferable that the metal layer 12f has a silver palladium alloy as a main component and the other metal layer 12e has copper as a main component. By adopting such a form, not only can the multilayer piezoelectric element 13 be baked in a reducing atmosphere such as a nitrogen atmosphere, but also a metal in which silver, copper, and palladium are completely dissolved. Therefore, it is possible to form a soft metal layer that provides a stress relaxation effect without forming an unstable intermetallic compound over the entire surface of the metal layer. In particular, the metal layer 12f sandwiching a plurality of other metal layers 12c is mainly composed of a silver-palladium alloy, so that when the laminated piezoelectric element is sintered, silver is dissolved in the liquid phase component of the ceramic. Thus, it is possible to proceed the sintering by lowering the liquid phase formation temperature. Thereby, the mutual coupling force between the metal layer 12 and the piezoelectric layer 11 can be strengthened. Furthermore, by alloying, it becomes possible to form a metal layer having a migration resistance stronger than that of a single element, and a durable laminated piezoelectric element can be obtained.

  Furthermore, since the metal layer 12f is mainly made of silver and the other metal layer 24 is mainly made of copper, the stress relaxation effect is maximized. In the case where the metal layer 12f mainly made of silver is adjacent to the piezoelectric layer 11, the insulation failure may occur due to silver migration. However, in this embodiment, the metal layer 12f mainly made of silver is formed. Since the metal layer 12e is mainly a metal layer 12e made of copper, even if silver tries to migrate, it bonds with copper and disappears and stabilizes floating silver ions. In addition, a highly durable laminated pressure wire element can be obtained.

  Further, for the same reason as in the first embodiment, it is preferable that the plurality of high-ratio metal layers 12f are regularly arranged, and the adhesion between the high-ratio metal layer 12f and the piezoelectric layer 11 is as follows. It is preferable that the adhesion strength between the other metal layer 12e and the piezoelectric layer 11 is lower. In addition, a plurality of other metal layers 12e are arranged between the two high-ratio metal layers 12f, and the concentration of one component in the group of the other metal layers 12e is from the high-ratio metal layer 12d side. It is preferred that there is a gradient concentration region that gradually decreases. Furthermore, it is preferable that the metal layer 12 has a large number of voids. In particular, it is preferable that a void is provided in the other metal layer 12e, and the area ratio of the void to the total cross-sectional area in the cross section of the metal layer is 5 to 70%. This is because if the void is made to occupy 5 to 70% of the area of the metal layer 12e, the amount of displacement becomes large, and a laminated piezoelectric element excellent in the amount of displacement can be obtained.

  Further, if the void ratio of the metal layer 12e is less than 5%, the piezoelectric layer 11 is constrained by the metal layer when the electric field is applied and deforms, and the deformation of the piezoelectric layer 11 is suppressed, and the multilayer piezoelectric element is reduced. Since the amount of deformation is reduced and the internal stress generated is increased, the durability is also adversely affected. On the other hand, if the void ratio of the metal layer 12e is greater than 70%, an extremely thin portion is generated in the electrode portion, so that the strength of the metal layer itself is reduced, and the metal layer is liable to crack, and the worst case is disconnection or the like. This is not preferable because of fear. Furthermore, the void ratio is more preferably 7 to 70%, still more preferably 10 to 60%. By doing so, the piezoelectric layer 11 can be deformed more smoothly, and the metal layer 12 has sufficient conductivity, so that the displacement amount of the multilayer piezoelectric element can be increased.

  Furthermore, it is preferable that the area ratio of the void to the total cross-sectional area in the cross section of the metal layer 12f is 24 to 90%. This is because if the void is made to occupy 24 to 90% of the area of the high-ratio metal layer 12b, the displacement amount is further increased, and a laminated piezoelectric element having an excellent displacement amount can be obtained.

  Further, when the metal layer 12 is mainly composed of a metal and a void, both the metal and the void can be deformed with respect to stress, so that a laminated piezoelectric element with higher durability can be obtained. In particular, when the metal layer 12f is mainly composed of a metal and a void rather than the metal layer 12e, both the metal and the void can be deformed with respect to stress, so that the stress relaxation effect is improved and the durability is further improved. A high stacked piezoelectric element can be obtained.

  Furthermore, the metal layer 12f is more preferably in a form in which a plurality of metals are scattered. That is, the metal layer 12f is preferably configured by a plurality of conductor regions dotted in an island shape. Since the metal layer 12f has a configuration in which a plurality of conductor regions are scattered, even if the stress of the multilayer piezoelectric element 13 is applied to the metal layer 12, the stress propagation in the metal layer 12f can be suppressed, and the metal layer 12f In particular, it does not create places where stress is particularly concentrated. Thereby, both stress relaxation and durability can be achieved.

  In the third embodiment, when the content of palladium in the metal layer 12f is M1 (mass%) and the content of silver is M2 (mass%), 0 ≦ M1 ≦ 15, 85 ≦ M2 ≦ It is preferable that the main component is a metal composition satisfying 100 and M1 + M2 = 100. This is because, when palladium exceeds 15% by mass, the specific resistance increases, and when the multilayer piezoelectric element is continuously driven, the metal layer 12 generates heat, and the generated heat acts on the piezoelectric layer 11 having temperature dependency. This is because the displacement characteristics of the stacked piezoelectric element may be reduced because the displacement characteristics are reduced.

  Furthermore, when the external electrode 15 is formed, the external electrode 15 and the metal layer 12 are mutually diffused and joined. If palladium exceeds 15% by mass, the hardness of the portion where the metal layer component is diffused in the external electrode 15 This is because the durability of the multilayer piezoelectric element whose dimensions change during driving decreases.

  The manufacturing method of the multilayer piezoelectric element according to the third embodiment may be the same as that of the first embodiment except that the copper powder is blended with the conductive paste forming the high ratio metal layer 12e. In order to improve the bonding strength between the external electrode 15 and the metal layer 12, it is preferable to use a metal paste mainly composed of copper as the metal constituting the external electrode 15. In order to configure the external electrode 15, whether it is a silver electrode or a copper electrode, firing in a reducing atmosphere such as a nitrogen atmosphere suppresses oxidation of the metal layer 12, and a highly durable metal It can be layer 12.

  In the third embodiment, the case where the plurality of metal layers are composed of two types of metal layers having different main components has been described. However, in the present invention, at least two types of the main components of the plurality of metal layers are different. The effect of the present invention can be obtained if a plurality of such metal layers are arranged with a plurality of other metal layers sandwiched therebetween. In other words, the stress applied to the piezoelectric element is concentrated in the vicinity of the metal layer having a different metal main component, and the collected stress is further sandwiched between the piezoelectric layer around the metal layer as a stress relaxation layer, so that the collected stress is applied to the metal composition. It can be confined between two high metal layers. Thereby, the stress added to the whole piezoelectric element can be relieved. As a result, a highly reliable piezoelectric actuator having excellent durability can be provided.

<Injection device>
FIG. 5 is a schematic cross-sectional view showing an injection device according to an embodiment of the present invention. As shown in FIG. 5, in the injection device according to the present embodiment, the stacked piezoelectric element of the present invention represented by the above embodiment is stored in a storage container 31 having a 33 having an injection hole at one end. . A needle valve 35 that can open and close the injection hole 33 is provided in the storage container 31. A fuel passage 37 is disposed in the injection hole 33 so as to communicate with the movement of the needle valve 35. 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 ejected at a constant high pressure into the fuel chamber of an internal combustion engine (not shown).

  The upper end portion of the needle valve 35 has a large inner diameter, and a piston 41 slidable with a cylinder 39 formed in the storage container 31 is disposed. And in the storage container 31, the piezoelectric actuator 43 provided with the above-mentioned lamination type piezoelectric element 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 ink jet, 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 Even a circuit element other than a circuit element mounted on a gyro, a piezoelectric switch, a piezoelectric transformer, a piezoelectric breaker, or the like can be implemented as long as the element uses piezoelectric characteristics.

  The present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the present invention.

  A piezoelectric actuator composed of the multilayer piezoelectric element according to the first embodiment 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 size 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 layer 11 having a thickness of 150 μm was prepared.

  Next, 300 sheets of conductive paste obtained by adding a binder to an alloy mainly made of silver-palladium by a screen printing method so as to have the composition shown in Table 1 are laminated on one side of the ceramic green sheet, Baked. As the firing conditions, after holding at 800 ° C. for 2 hours, firing was performed at 1000 ° C. for 2 hours.

  At this time, on the portion where the high-ratio metal layer 12b is formed, printing is performed with a conductive paste in which a binder is added to a silver-palladium alloy so as to have a composition shown in Table 1 so as to have a thickness of 3 μm. The high-ratio metal layer 12b was arranged so as to be the 50th, 100th, 150th, 200th, and 250th layers.

  Next, a mixture of a flaky silver powder having an average particle size of 2 μm and an amorphous glass powder having a softening point of 640 ° C. having a balance of silicon having an average particle size of 2 μm as a main component is combined with a silver powder 8 parts by mass was added to 100 parts by mass of the total mass of the glass powder, and mixed well to prepare a silver glass conductive paste. The silver glass conductive paste thus produced was formed on a release film by screen printing, dried and then peeled off from the release film to obtain a sheet of silver glass conductive paste. In addition, the average particle diameter of the flaky powder is measured as follows. That is, a photograph of the powder was taken using a scanning electron microscope (SEM), a straight line was drawn on the photograph, and 50 lengths where the particles and the straight line intersected were measured, and the average was taken as the average particle diameter. .

  And the sheet | seat of the silver glass paste was transcribe | transferred and laminated | stacked on the external electrode 15 surface of the laminated body 13, and it baked for 30 minutes at 700 degreeC, and formed the external electrode 15. FIG.

  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 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 was obtained in the lamination direction in all piezoelectric actuators.

Furthermore, a test was performed in which the 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 results are as shown in Table 1. In addition, as shown in Table 1, the other metal layers 12a other than the high-ratio metal layer had almost the same composition.

  As shown in Table 1, in Sample No. 6 which is a comparative example, the stress applied to the laminated interface was concentrated on one point, the load increased and peeling occurred, and a beat noise and noise generation occurred.

On the other hand, Sample Nos. 1 to 5 which are embodiments of the present invention have an effective displacement amount required as a piezoelectric actuator without significantly decreasing the element displacement amount even after being continuously driven 1 × 10 ⁹ times. Thus, a piezoelectric actuator having excellent durability could be produced.

  A piezoelectric actuator composed of a multilayer piezoelectric element according to the second embodiment 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 size 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 layer 11 having a thickness of 150 μm was prepared.

  On one side of this ceramic green sheet, 300 sheets formed by screen printing with a conductive paste obtained by adding a binder to a silver-palladium alloy so as to have the composition shown in Table 2 were laminated and fired. Firing was carried out at 1000 ° C. after holding at 800 ° C.

  At this time, the portion on which the high-ratio metal layer 12d is formed is printed with a conductive paste of 100% silver so as to have a thickness of 3 μm, and the high-ratio metal layer 12b has the 50th, 100th, and 150th layers. It arranged so that it might become a layer, 200th layer, and 250th layer.

  Next, a mixture of a flaky silver powder having an average particle size of 2 μm and an amorphous glass powder having a softening point of 640 ° C. having a balance of silicon having an average particle size of 2 μm as a main component is combined with a silver powder 8 parts by mass is added to 100 parts by mass of the total mass of the glass powder, and mixed well to produce a silver glass conductive paste. The silver glass conductive paste thus produced is screen-printed on a release film. After drying, the film was peeled off from the release film to obtain a silver glass conductive paste sheet.

  And the sheet | seat of the said silver glass paste was transcribe | transferred and laminated | stacked on the external electrode 15 surface of the laminated body 13, and baked at 700 degreeC for 30 minutes, and the external electrode 15 was formed.

  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 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 was obtained in the lamination direction in all piezoelectric actuators.

Furthermore, a test was performed in which the 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 results are as shown in Table 2. In addition, as shown in Table 2, the other metal layers other than the high ratio metal layer had almost the same composition.

  As shown in Table 2, in Sample No. 6 which is a comparative example, the stress applied to the laminated interface was concentrated on one point, the load increased, peeling occurred, and a beep and noise were generated.

In contrast, Sample Nos. 1 to 5, which are examples of the present invention, have an effective displacement amount required as a piezoelectric actuator without significantly decreasing the element displacement amount even after being driven 1 × 10 ⁹ times continuously. Thus, a piezoelectric actuator having excellent durability could be produced.

  A piezoelectric actuator composed of a multilayer piezoelectric element according to the third embodiment 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 layer 11 having a thickness of 150 μm was prepared.

  On one side of this ceramic green sheet, 300 sheets formed by screen printing of conductive paste obtained by adding a binder to copper powder were laminated and fired in a nitrogen atmosphere. Firing was carried out at 1000 ° C. after holding at 800 ° C.

  At this time, printing was performed on the portion where the metal layer 12f was to be formed with a silver-palladium alloy conductive paste having the composition shown in Table 3 to a thickness of 3 μm. The metal layer 12f was arranged to be the 50th layer, the 100th layer, the 150th layer, the 200th layer, and the 250th layer.

  Next, a mixture of a flaky silver powder having an average particle size of 2 μm and an amorphous glass powder having a softening point of 640 ° C. having a balance of silicon having an average particle size of 2 μm as a main component is combined with a silver powder 8 parts by mass is added to 100 parts by mass of the total mass of the glass powder, and mixed well to produce a silver glass conductive paste. The silver glass conductive paste thus produced is screen-printed on a release film. After drying, the film was peeled off from the release film to obtain a silver glass conductive paste sheet.

  Then, the sheet of silver glass paste was transferred and laminated on the surface of the external electrode 15 of the laminate 13 and baked at 700 ° C. for 30 minutes in a nitrogen atmosphere 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 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 was obtained in the lamination direction in all piezoelectric actuators.

Furthermore, a test was performed in which the 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 results are as shown in Table 3. In addition, as shown in Table 3, the metal layers having the same main component had almost the same composition.

  As shown in Table 3, in Sample Nos. 6 and 7, which are comparative examples, the stress applied to the laminated interface was concentrated on one point, the load increased, peeling occurred, and a beat sound and noise were generated.

In contrast, Sample Nos. 1 to 5, which are examples of the present invention, have an effective displacement amount required as a piezoelectric actuator without significantly decreasing the element displacement amount even after being driven 1 × 10 ⁹ times continuously. Thus, a piezoelectric actuator having excellent durability could be produced.

The change rate of the displacement amount of each sample was measured by changing the material composition of the internal electrode 12 of the piezoelectric actuator of Sample No. 5 in Example 1. 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 4.

  As shown in Table 4, when all the internal electrodes 12 were made of 100% silver as in sample number 15, silver ion migration occurred, and the laminated piezoelectric element was damaged and could not be continuously driven. Sample Nos. 13 and 14 had a palladium content of more than 15% by mass in the metal composition in the internal electrode 12 and a silver content of less than 85% by mass. It can be seen that since the resistance is large, heat is generated when the multilayer piezoelectric element is continuously driven, and the displacement of the piezoelectric actuator is reduced.

  On the other hand, when the metal composition in the internal electrode 12 is M1 mass% for the metal composition in the internal electrode 12 and the content of the metal group 1b is 2 mass% for the metal composition in the internal electrode 12, 0 < Since the main component is a metal composition satisfying M1 ≦ 15, 85 ≦ M2 <100, and M1 + M2 = 100% by mass, the specific resistance of the internal electrode 12 can be reduced, and the internal electrode 12 is generated even when continuously driven. Since heat generation could be suppressed, it can be seen that a laminated actuator with a stable element displacement can be produced.

  In particular, Sample Nos. 6 to 8 have 2 ≦ M1 ≦ 8 when the metal composition in the internal electrode 12 has a content of Group 8-10 metal as M1 mass% and a content of Group 1b metal as M2 mass%. , 92 ≦ M2 ≦ 98 and M1 + M2 = 100% by mass as a main component, the specific resistance of the internal electrode 12 can be reduced, and the heat generated in the internal electrode 12 can be suppressed even when continuously driven. As a result, it can be seen that an extremely stable stacked actuator in which the element displacement does not change at all can be manufactured.

  One sample of each of the stacked piezoelectric elements shown in Table 1 is extracted and processed into 3 mm × 4 mm × 36 mm so that the electrode surface of the metal layer 12 is substantially perpendicular to the longitudinal direction of the test piece. The bending strength was measured by 4-point bending. At this time, a portion where the adhesive strength of the multilayer piezoelectric element was weak was identified by confirming at which portion it was broken.

  That is, it can be seen that if the piezoelectric body 11 is broken, the strength of the piezoelectric body is weak, and if it is broken in the metal layer 12, the strength of the metal layer 12 is weak, and the interface between the piezoelectric body 11 and the metal layer 12 is found. If it breaks down, it turns out that the intensity | strength of the interface of the piezoelectric material 11 and the metal layer 12 is weak.

Further, the durability when each sample functions as an actuator is shown in Table 1, but is also shown in Table 5 for comparison.

Sample No. 6 as a comparative example was broken in the piezoelectric body 11. That is, all the piezoelectric bodies 11 and the metal layers 12 are bonded with high strength. As a result, when the actuator was continuously driven 1 × 10 ⁹ times, the stress applied to the laminated interface was concentrated at one point, so that the load increased and peeling occurred.

In contrast, Sample Nos. 1 to 5 which are examples of the present invention were broken at the interface between the piezoelectric body 11 and the high-ratio metal layer. That is, the adhesion between the high-ratio metal layer and the piezoelectric layer is the weakest. From this, when a stress during continuous driving is applied, a phenomenon occurs in which the high-ratio metal layer with weak adhesion force is deformed and the stress is relaxed, and even after the actuator is continuously driven 1 × 10 ⁹ times, It is thought that it had the outstanding durability, without peeling.

One sample was extracted from the multilayer piezoelectric element shown in Table 1, and the Vickers hardness of the metal layer portion was measured. For measurement of Vickers hardness, an MVK-H3 type micro Vickers measuring instrument manufactured by Akashi Seisakusho was used. At the time of measurement, a method in which a diamond indenter was pushed into the metal layer 12 from a direction perpendicular to the stacking direction of the metal layer 12 was used so as not to be affected by the piezoelectric layer 11 as a base. The results are shown in Table 6. The durability when each sample functions as an actuator is shown in Table 1, but is also shown in Table 6 for comparison.

Sample No. 6, which is a comparative example, was found to have the same hardness because all the metal layers had the same composition. That is, all the piezoelectric bodies 11 are joined by the metal layer having the same hardness. In this sample 6, when the actuator was continuously driven 1 × 10 ⁹ times, the stress applied to the laminated interface was concentrated at one point, so that the load increased and peeling occurred.

On the other hand, the sample numbers 1-5 which are the Example of this invention resulted in the hardness of a high ratio metal layer being lower than another metal layer. That is, the high-ratio metal layer is softer than the other metal layers. As a result, when stress is applied during continuous driving, a phenomenon occurs in which the soft high-ratio metal layer is deformed and the stress is relaxed, and even after the actuator is continuously driven 1 × 10 ⁹ times, it peels off. It is thought that it had excellent durability.

  A piezoelectric actuator provided with a laminated piezoelectric element having a gradient concentration region 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 layer 11 having a thickness of 150 μm was prepared.

  Next, 300 sheets of a conductive paste obtained by adding a binder to a silver-palladium alloy (80% by mass of silver—20% by mass of palladium) by a screen printing method were laminated on one side of this ceramic green sheet and fired. As the firing conditions, after holding at 800 ° C. for 2 hours, firing was performed at 1000 ° C. for 2 hours.

  At this time, the portion where the high-ratio metal layer 12b is formed is printed with a conductive paste of silver-palladium alloy (silver 85 mass% -palladium 15 mass%) to a thickness of 3 μm. As shown in FIG. 6, the silver concentration was gradually decreased from the high-ratio metal layer 12b side. The high ratio metal layer 12b was arranged to be the 50th layer, the 100th layer, the 150th layer, the 200th layer, and the 250th layer.

  Next, a mixture of a flaky silver powder having an average particle size of 2 μm and an amorphous glass powder having a softening point of 640 ° C. having a balance of silicon having an average particle size of 2 μm as a main component is combined with a silver powder 8 parts by mass was added to 100 parts by mass of the total mass of the glass powder, and mixed well to prepare a silver glass conductive paste. The silver glass conductive paste thus produced was formed on a release film by screen printing, dried and then peeled off from the release film to obtain a sheet of silver glass conductive paste. And the sheet | seat of the silver glass paste was transcribe | transferred and laminated | stacked on the external electrode 15 surface of the laminated body 13, and it baked for 30 minutes at 700 degreeC, and formed the external electrode 15. FIG.

  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 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 was obtained in the lamination direction in all piezoelectric actuators.

A test was performed in which the 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 results are as shown in Table 7.

  From Table 7, the sample No. 3 which is a comparative example concentrated stress on the laminated interface at one point and increased the load to cause peeling, and the noise and noise were generated.

On the other hand, sample number 1, which is an embodiment of the present invention, is different from the embodiment 2, and is necessary as a piezoelectric actuator without any decrease in element displacement even after being continuously driven 1 × 10 ⁹ times. Thus, a piezoelectric actuator having an effective displacement amount and extremely excellent durability could be produced.

(a) is a perspective view showing the multilayer piezoelectric element according to the first embodiment, and (b) is a partial perspective view showing a laminated state of the piezoelectric layer and the metal layer in (a). It is a partial expanded sectional view which shows the laminated structure of the lamination type piezoelectric element concerning 1st Embodiment. It is a partial expanded sectional view which shows the laminated structure of the lamination type piezoelectric element concerning 2nd Embodiment. It is a partial expanded sectional view which shows the laminated structure of the laminated piezoelectric element concerning 3rd Embodiment. It is a schematic sectional drawing which shows the injection apparatus concerning one Embodiment of this invention. It is a graph which shows the silver composition of the metal layer of the sample number 1 of Table 7. (a) is a perspective view showing a conventional laminated piezoelectric element, and (b) is a partial perspective view showing a laminated state of a piezoelectric layer and a metal layer. It is an expanded sectional view which shows the laminated structure of the piezoelectric material and metal layer of the conventional laminated piezoelectric element.

Explanation of symbols

11 Piezoelectric body 12 Metal layer 12a Other metal layer 12b High ratio metal layer 12c Other metal layer 12d High ratio metal layer 12e, 12f Metal layer 13 Stack 14 Inactive layer 15 External electrode 31 Storage container 33 Injection hole 35 Valve 37 Fuel passage 39 Cylinder 41 Piston 43 Piezoelectric actuator

Claims (19)

  In the stacked piezoelectric element in which a plurality of piezoelectric layers and a plurality of metal layers mainly composed of an alloy are alternately stacked, the plurality of metal layers are arranged on both sides adjacent to each other in a ratio of one component constituting the alloy. A multilayer piezoelectric element comprising a plurality of high-ratio metal layers higher than the metal layer.   2. The multilayer piezoelectric element according to claim 1, wherein the plurality of high-ratio metal layers are respectively disposed with a plurality of metal layers other than the high-ratio metal layer interposed therebetween.   The multilayer piezoelectric element according to claim 1, wherein the alloy is a silver alloy that forms a solid solution of the entire ratio, and the one component is silver.   The multilayer piezoelectric element according to claim 3, wherein the alloy is a silver palladium alloy.   In the multilayer piezoelectric element in which a plurality of piezoelectric layers and a plurality of metal layers are alternately stacked, the plurality of metal layers have a higher ratio of at least one component constituting the metal layer than both adjacent metal layers. A multilayer piezoelectric element comprising a plurality of high-ratio metal layers.   The multilayer piezoelectric element according to claim 5, wherein the plurality of high-ratio metal layers are respectively disposed with a plurality of metal layers other than the high-ratio metal layer interposed therebetween.   7. The multilayer piezoelectric element according to claim 6, wherein the one component is silver, the other metal layer is mainly composed of a silver alloy that forms a solid solution, and the high-ratio metal layer is made of silver.   The multilayer piezoelectric element according to claim 7, wherein the other metal layer is made of a silver palladium alloy.   The multilayer piezoelectric element according to claim 1, wherein the plurality of high-ratio metal layers are regularly arranged.   The lamination according to any one of claims 1 to 9, wherein the adhesion between the high-ratio metal layer and the piezoelectric layer is lower than the adhesion between the metal layer other than the high-ratio metal layer and the piezoelectric layer. Type piezoelectric element.   The multilayer piezoelectric element according to claim 1, wherein the high-ratio metal layer has a Vickers hardness lower than other metal layers other than the high-ratio metal layer.   Between the two high-ratio metal layers, a plurality of other metal layers other than the high-ratio metal layer are arranged, and the group consisting of the other metal layers has the concentration of the one component in the high ratio. The multilayer piezoelectric element according to claim 1, wherein there is a gradient concentration region that gradually decreases from the metal layer side.   In the multi-layer piezoelectric element in which a plurality of piezoelectric layers and a plurality of metal layers are alternately stacked, the plurality of metal layers include at least two kinds of metal layers having different main components, and one kind of these metals A multilayer piezoelectric element, wherein a plurality of layers are arranged with a plurality of other metal layers sandwiched therebetween.   The multilayer piezoelectric element according to claim 13, wherein the one type of metal layer is mainly composed of a silver alloy that forms a solid solution of the entire percentage, and the other metal layer is mainly composed of copper.   The multilayer piezoelectric element according to claim 14, wherein the kind of metal layer is mainly composed of a silver-palladium alloy.   The multilayer piezoelectric element according to claim 13, wherein the plurality of the one type of metal layers are regularly arranged.   The multilayer piezoelectric element according to any one of claims 13 to 16, wherein an adhesion force between the one kind of metal layer and the piezoelectric layer is lower than an adhesion force between the other metal layer and the piezoelectric layer.   The laminated piezoelectric element according to claim 13, wherein the one kind of metal layer has a Vickers hardness lower than that of the other metal layer.   An injection device in which the multilayer piezoelectric element according to any one of claims 1 to 18 is stored inside a storage container having an ejection hole.

Images