JP2004274030A - Unit joint laminated piezoelectric element and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a unit joint laminated piezoelectric element of which ceramic materials are fired and internal electrodes are reduced sufficiently regardless of the size of a laminated material and excellent in durability and performance, and provide its manufacturing method. <P>SOLUTION: The unit joint stacked piezoelectric element 1 comprises two or more laminated piezoelectric element units 15 in which piezoelectric ceramic layers 151 and internal electrodes 153 are layered alternatively. Its manufacturing method is also provided. The internal electrode 153 is made of a conductive base metal of which standard Gibbs free energy of the formation of a metal oxide at firing temperature is larger than that of a ceramic material of the piezoelectric ceramic layer 151. When an average potential difference between respective internal electrodes 153 of the laminated piezoelectric element unit 15 is provided as V1, a potential difference V between adjacent internal electrodes 153 that sandwich a joint part 17 of the laminated units 15 has the relationship of V<(1/2)V1. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a unit-bonded laminated piezoelectric element in which two or more laminated piezoelectric element units in which piezoelectric ceramic layers and internal electrode layers are alternately laminated, and a method of manufacturing the same.

2. Description of the Related Art Conventionally, a laminated piezoelectric element formed by alternately laminating a piezoelectric ceramic layer made of a PZT-based material having various excellent piezoelectric and dielectric properties and an internal electrode layer made of a base metal such as copper is an actuator or a capacitor. Widely used for such purposes.
As a method of manufacturing such a laminated piezoelectric element, for example, usually, a plurality of steps as described below are performed.

First, a green sheet made of a ceramic material such as PZT is prepared, and an electrode paste material made of a metal oxide or a metal and a metal oxide is applied to the green sheet by screen printing or the like. Subsequently, a desired number of green sheets to which the electrode paste material has been applied are laminated to form a laminate, and the laminate is degreased.
Next, by heating the degreased laminate in a heating furnace under reducing conditions, the metal oxide in the electrode paste material is reduced to form a conductive internal electrode layer (electrode reduction step). . Thereafter, the laminated body is fired to densify the ceramic material, and a final stacked piezoelectric element is obtained (firing step).

It is preferable that the ceramic material and the electrode paste material be co-fired in order to improve the bonding state at the boundary and the durability thereof.
However, in the firing step, the electrode paste material and the ceramic material require contradictory atmosphere conditions. That is, for example, a ceramic material such as PZT is an oxide, and thus is preferably fired in an oxidizing atmosphere. It is preferable to perform firing in an atmosphere.

  In the firing step, when firing is performed in an oxidizing atmosphere in order to sufficiently fire the ceramic material, the internal electrode layer made of copper or the like previously reduced in the electrode reduction step is oxidized again, and the conductivity is reduced. There is a risk of doing it. On the other hand, when firing is performed in a reducing atmosphere, there is a problem that the ceramic material is reduced, and the characteristics of the fired laminate deteriorate.

  In order to solve such a problem, after the conductive paste material is reduced in an atmosphere containing hydrogen gas, in the subsequent firing step, the above-mentioned laminate is removed under an atmosphere in which the oxygen partial pressure is controlled to a specific range. There is a firing method (see Patent Document 1).

In addition, the conductive paste material is reduced at a temperature lower than the firing temperature, and in the subsequent firing step, an N ₂ -H ₂ -H ₂ O-O ₂ mixed gas is used to control the O ₂ partial pressure to a specific range. There is a method in which the above-mentioned laminate is fired in a reduced atmosphere (see Patent Document 2).

  According to such a conventional method, the ceramic material can be densified without substantially oxidizing the internal electrode layer made of copper or the like reduced in the electrode reduction step in the firing step.

  However, in the above-mentioned conventional method, it is difficult to balance the reduction / oxidation reaction amount between the central part and the outer peripheral part of the laminated body, particularly when producing a laminated body having a large number of laminated layers. Is extremely difficult. Furthermore, if the shape of the laminate is large, an enormous amount of time is spent removing the binder in the degreasing step before firing or before firing and reducing the electrode.

  On the other hand, if the time required for the degreasing step is reduced, a part of the binder remains in the center of the laminate. Since the remaining substance such as carbon easily reacts with oxygen or the like, the oxygen partial pressure in the firing or firing / electrode reduction step is likely to be non-uniform at the central portion of the laminate and at the outer peripheral portion and surface of the laminate. As a result, the performance of the multilayer piezoelectric element obtained after firing is reduced.

  Further, in Patent Document 3 below, in a unit-to-unit conveyed product, two opposing internal electrodes adjacent to a joint surface have the same electrical polarity, and an insulative insulating layer as a piezoelectric body is formed. It is described that by making the thickness of the insulating layer twice or less than the other thickness, displacement of the unit laminated product due to the piezoelectric effect is efficiently obtained.

However, although excellent in initial characteristics such as displacement, it was found that as a result of an examination including durability of the initial characteristics, as shown in Example 3 described later, a problem may occur.
In addition, as shown in Patent Document 3, if two adjacent layers sandwiching the bonding surface are extremely thin, even if they are connected to the same side electrode, some products happen to be used as internal electrodes during mass production. In the case where there is a break, the internal electrode layer next to the broken internal electrode layer as viewed from the joint surface of the unit where the internal electrode is broken, and the electrode of the other unit facing the joint surface were not broken at the joint surface It is assumed that an electric field is formed between the internal electrodes. In this case, the load on the unit joint surface may be rather large and the durability may be deteriorated.

  The interruption of the internal electrode as described above is considered to be a phenomenon peculiar to a base metal electrode that must form a reducing atmosphere during firing or the like, such as Cu or Ni, apart from the expensive Ag-Pd electrode. When the reducing atmosphere is deviated to the oxidizing side from the optimum atmosphere conditions, the internal electrode may be oxidized, causing a eutectic reaction with the ceramic layer made of oxide, melting and diffusing. Further, when the ceramic material is deviated from the optimum atmosphere to the reduction side, a part of the ceramic layer is reduced, causing a eutectic reaction with the metal of the internal electrode layer, and the electrode material may be melted and diffused. Eutectic reactions tend to occur between metals and metals or oxides and oxides, and eutectic reactions are extremely rare in combinations of metals and oxides.

  Therefore, the optimum atmosphere condition is formed by adjusting the reducing atmosphere, the ceramic layer is present in an oxide state, and the internal electrode layer is required to be present in a metal state. For example, the internal electrode is likely to be interrupted due to the melting of the electrode material due to the above-mentioned eutectic reaction, and unlike the case of a noble metal electrode which does not require the formation of a reducing atmosphere, each type represented by firing in a reducing atmosphere. For base metal electrodes that require treatment, reducing the thickness of two adjacent layers sandwiching the bonding surface was not always effective in consideration of not only initial characteristics but also mass productivity and durability.

JP-A-5-82387 Japanese Patent Publication No. 7-34417 JP-A-64-33980

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and enables the firing of a ceramic material and the reduction of an internal electrode layer to be sufficiently performed irrespective of the size of a laminated body, and the durability and performance are improved. An object of the present invention is to provide an excellent unit-bonded laminated piezoelectric element and a method for manufacturing the same.

According to a first aspect of the present invention, there is provided a unit-joined laminated piezoelectric element comprising two or more laminated piezoelectric element units in which piezoelectric ceramic layers and internal electrode layers are alternately laminated.
The internal electrode layer is mainly composed of a conductive base metal material having a larger standard Gibbs free energy for generating metal oxides at the firing temperature than the ceramic material constituting the piezoelectric ceramic layer,
Assuming that the average potential difference between the respective internal electrode layers of the multilayer piezoelectric element unit is V1, the potential difference V between two adjacent internal electrode layers sandwiching the joint between the multilayer piezoelectric element units is V <(1 (2) A unit-bonded laminated piezoelectric element having a relationship of V1.

Next, the operation and effect of the present invention will be described.
In the unit-bonded laminated piezoelectric element of the present invention, the internal electrode layer is mainly composed of a conductive base metal material having a larger standard Gibbs free energy of metal oxide generation at a firing temperature than the ceramic material constituting the piezoelectric ceramic layer. I do.
Therefore, in the laminated piezoelectric element unit constituting the unit-bonded laminated piezoelectric element, it is easy to adjust the atmosphere during firing, the internal electrode layer is sufficiently reduced, and the piezoelectric ceramic layer is sufficiently oxidized. It will be in the state of being in a state.
In the internal electrode layer, a part of the conductive base metal material may be oxidized as long as the conductivity is not hindered.

In the unit-bonded laminated piezoelectric element, as the ceramic material, for example, a PZT-based material ｛Pb (Zr, Ti) O ₃ -based oxide having a perovskite structure is used, and Pb, Zr, and Ti are partially substituted. The same applies to the following. In this case, the unit-bonded laminated piezoelectric element can be used as a high-performance piezoelectric element. As the ceramic material, a material that does not contain Pb as a component element, such as KNbO ₃ or BaTiO _3, can also be used.
In many cases, the PZT-based material contains PbO having a property of being more easily reduced than PZT in its composition. When PbO is reduced to Pb, the eutectic melting reaction easily occurs with the conductive base metal material. The internal electrode layer cannot be formed continuously. Therefore, when a PZT-based material is used as the ceramic material, it must be fired without oxidizing the conductive base metal material and reducing PbO as well as the PZT-based material. Setting becomes very difficult.

  In the present invention, the conductive base metal material used has a higher standard Gibbs free energy of metal oxide generation at the firing temperature than the ceramic material constituting the piezoelectric ceramic layer. The conductive base metal material is hardly oxidized, and the atmospheric conditions can be easily set.

Further, the unit-bonded laminated piezoelectric element of the present invention is formed by laminating two or more laminated piezoelectric element units in which piezoelectric ceramic layers and internal electrode layers are alternately laminated.
Therefore, at the time of manufacturing the unit-bonded laminated piezoelectric element, first, a plurality of laminated piezoelectric element units each having a small number of layers and a relatively small shape are manufactured by firing, and then two or more laminated piezoelectric element units are laminated. Thus, a desired number of unit-bonded laminated piezoelectric elements can be manufactured.

  During firing, the stacked piezoelectric element unit with a small number of stacked layers can be fired, so there is little need to consider the reduction and oxidation reaction balance between the inside and the surface of the stacked piezoelectric element unit. Adjustment of oxygen partial pressure and the like during reduction and firing is simplified. Therefore, firing of the piezoelectric ceramic layer and reduction of the internal electrode layer can be sufficiently performed. As a result, each of the laminated piezoelectric element units can exhibit excellent properties with almost no problem in the piezoelectric ceramic layer and the internal electrode layer. In particular, this effect appears more remarkably in a PZT-based material containing PbO.

  And since the final unit-bonded laminated piezoelectric element is manufactured by laminating the above-mentioned laminated piezoelectric element units, it is apparent that the same laminated body with the same number of layers as when integrally laminated and co-fired is used. Obtainable. In addition, since it is more uniformly fired, it has better performance.

  Further, in the unit-bonded laminated piezoelectric element of the present invention, when the average potential difference between the internal electrode layers of the laminated piezoelectric element unit is set to V1, two adjacent piezoelectric elements sandwiching the joint portion where the laminated piezoelectric element units are joined to each other. The potential difference V between the two internal electrode layers has a relationship of V <(1/2) V1.

Therefore, in the unit-bonded laminated piezoelectric element, the electric field applied to the bonding portion is relatively small. Therefore, non-resonance and displacement transmission hardly occur due to the mismatch (discontinuity) of the bonding surfaces between the stacked piezoelectric element units. As a result, the generation of stress in the direction perpendicular to the stacking direction of the unit-bonded laminated piezoelectric element is reduced, and the probability of occurrence of stress is reduced. It can be tempered. Therefore, even when a side electrode is formed on the side surface of the unit-joined laminated piezoelectric element or when the unit-joined laminated piezoelectric element is fixed with a shrink tube, the side electrode, the shrink tube and the like can be prevented from being damaged. Even when the laminated piezoelectric element units are joined to each other with a resin or the like, heat or the like due to dielectric loss hardly occurs at the joints, so that the resin hardly deteriorates due to the heat.
Therefore, in the unit-bonded laminated piezoelectric element of the present invention, the same or higher durability can be maintained as that obtained by integrally and simultaneously firing the same number of laminated bodies as the unit-bonded laminated piezoelectric element.
In the present invention, the average potential difference V1 between the internal electrode layers of the multilayer piezoelectric element unit is determined by calculating the internal electrode in the multilayer piezoelectric element unit excluding the outermost piezoelectric ceramic layer in the multilayer piezoelectric element unit. This is the average potential difference between layers.

  As described above, according to the present invention, firing of the ceramic material and reduction of the internal electrode layer can be sufficiently performed irrespective of the size of the laminated body, particularly, the length in the laminating direction, and the durability and performance are improved. An excellent unit-bonded laminated piezoelectric element can be provided.

According to a second aspect of the present invention, there is provided a unit-bonded laminated piezoelectric element comprising two or more laminated piezoelectric element units in which piezoelectric ceramic layers and internal electrode layers are alternately laminated.
The internal electrode layer is mainly composed of a conductive base metal material having a larger standard Gibbs free energy for generating metal oxides at the firing temperature than the ceramic material constituting the piezoelectric ceramic layer,
Assuming that the average electric field strength between the internal electrode layers of the laminated piezoelectric element unit is E1, the electric field strength E between two adjacent internal electrode layers sandwiching a joint portion where the laminated piezoelectric element units are joined is E <E < A unit-bonded laminated piezoelectric element having a relationship of (1/2) E1 is provided (claim 3).

In the unit-bonded multi-layer piezoelectric element of the second invention, when an average electric field strength between the internal electrode layers of the multi-layer piezoelectric element unit is E1, an adjacent electric field sandwiching a bonding portion at which the multi-layer piezoelectric element units are bonded is sandwiched. The electric field strength E between two matching internal electrode layers has a relationship of E <(1/2) E1.
Therefore, in the unit-bonded laminated piezoelectric element, the load on the bonding portion is reduced.
That is, in general, the displacement of the piezoelectric element due to the electric field intensity changes continuously, and in many cases, monotonically increases as the electric field intensity increases. However, if the electric field strength is reduced to less than half of the electric field strength required for efficient displacement, the displacement does not decrease in proportion to the reduction ratio of the electric field strength. Is reduced, and the displacement can be kept small.
In the present invention, as described above, the electric field strength E between two adjacent internal electrode layers sandwiching the bonding portion is set to be smaller than half the average electric field strength E1 between the internal electrode layers of the multilayer piezoelectric element unit. I'm making it smaller. Therefore, the displacement at the joint is significantly reduced, and the load on the joint can be reduced.

Further, the region of the electric field intensity where the displacement is significantly reduced can be specified by the type of the material. An example of the identification method will be described.
That is, first, the displacement when the electric field strength (proportional to the value obtained by dividing the potential difference between the two electrodes by the distance between the two electrodes) is measured, the electric field strength is plotted on the horizontal axis, and the displacement is plotted on the vertical axis. The amount of displacement at each electric field strength is plotted on a graph. In this plotted graph, a tangent line at a point where the electric field intensity has increased by a small amount Δ from zero, or a straight line obtained by linearly approximating a point where the electric field intensity has increased a small amount from zero, is defined as a tangent line 1. In the plotted graph, a tangent at a point where the rate of increase in displacement is the highest is drawn, and this is designated as tangent 2. If the intersection of the tangent 1 and the tangent 2 is defined as a critical point, the load on the joint can be reduced by not applying an electric field strength above this critical point to the joint.
However, since the critical point of the electric field strength changes depending on the material of the piezoelectric ceramic layer or its constituent substances and constituent elements, as in the present invention, the electric field strength between two adjacent internal electrode layers sandwiching the joint is determined by the above-mentioned laminated type. The average electric field intensity E1 between the internal electrode layers of the piezoelectric element unit may be less than half.

Further, in the unit-bonded laminated piezoelectric element according to the second aspect of the invention, similarly to the first aspect, the electric field applied to the junction is relatively small. Therefore, non-resonance and displacement transmission hardly occur due to the mismatch (discontinuity) of the bonding surfaces between the stacked piezoelectric element units. As a result, the generation of stress in the direction perpendicular to the stacking direction of the unit-bonded laminated piezoelectric element is reduced, and the probability of occurrence of stress is reduced. It can be tempered. Therefore, when the side electrode is formed on the side surface of the unit-joined laminated piezoelectric element, or when the unit-joined laminated piezoelectric element is fixed by the shrink tube, it is possible to prevent the side electrode and the shrink tube from being damaged. Even when the laminated piezoelectric element units are joined to each other with a resin or the like, heat or the like due to dielectric loss hardly occurs at the joints, so that the resin hardly deteriorates due to the heat.
Therefore, the unit-bonded laminated piezoelectric element of the second aspect of the present invention can maintain the same or higher durability as that obtained by integrally firing the same number of laminated bodies as the unit-bonded laminated piezoelectric element. it can.
Other functions and effects are the same as those of the first invention.

According to a third aspect of the present invention, there is provided a method of manufacturing a unit-bonded laminated piezoelectric element comprising two or more laminated piezoelectric element units in which piezoelectric ceramic layers and internal electrode layers are alternately laminated.
An electrode printing step of applying an electrode paste material to at least one surface of a ceramic green sheet formed of a ceramic material into a sheet shape;
A crimping step of laminating and crimping the ceramic green sheets coated with the electrode paste material to form a laminate;
A degreasing step of degreasing the laminate,
A firing step of firing the laminated body in a reducing atmosphere to produce a laminated piezoelectric element unit;
A superimposing step of forming a joint by laminating two or more of the laminated piezoelectric element units on the joint surfaces with the outermost surface in the laminating direction of the laminated piezoelectric element unit as a joint surface. ,
The paste material for an electrode is made of a conductive base metal material and / or an oxide thereof having a larger standard Gibbs free energy for forming a metal oxide at a firing temperature than the ceramic material constituting the ceramic green sheet,
Assuming that the average potential difference between the internal electrode layers of the multilayer piezoelectric element unit is V1, the potential difference V between two adjacent internal electrode layers sandwiching the bonding portion is such that V <(1/2) V1. There is provided a method of manufacturing a unit-bonded laminated piezoelectric element, characterized in that:

In the third aspect of the invention, after the laminate is fired in a reducing atmosphere to produce a multilayer piezoelectric element unit (firing step), the outermost surface in the stacking direction of the multilayer piezoelectric element unit is bonded to a bonding surface. As described above, two or more of the laminated piezoelectric element units are overlapped with each other at the joint surfaces to form a joint (overlapping step).
Therefore, in the above-described firing step, a stacked body having a small number of stacked layers can be fired.

  By reducing the number of stacked layers, it is less necessary to consider the balance between the reduction and oxidation reactions between the inside and the surface of the stacked piezoelectric element unit. The adjustment of the partial pressure and the like is simplified. Therefore, the firing of the piezoelectric ceramic layer and the reduction of the internal electrode layer can be sufficiently performed. As a result, each of the laminated piezoelectric element units can exhibit excellent performance with almost no defect in the piezoelectric ceramic layer and the internal electrode layer.

In general, in a method of manufacturing a laminated body having a base metal electrode inside, for example, after degreasing, the electrode is reduced or fired in a reducing atmosphere, or, for example, degreasing in a reducing atmosphere and firing in a reducing atmosphere. Production methods involving reduction treatment are the mainstream. However, in the reduction process, the reduction reaction reacts in order from the outer surface of the laminate, which is the sample to be reduced, toward the center, so that the larger the sample to be reduced, the difference in the reduction state between the outer surface and the center. Will occur. The difference in the reduction state does not necessarily affect the performance and the like, but if the difference in the reduction state is extremely large, there occurs a problem that, for example, a part of the internal electrode layer is cut off and the performance is adversely affected. May be caused.
In the present invention, as described above, since the laminate is degreased and fired in a plurality of units, there is little difference in the reduction state between the outer surface and the center.

Further, in the manufacturing method of the present invention, the above-mentioned overlapping step is performed after the above-mentioned firing step.
Therefore, even if the number of the laminated bodies is reduced and the firing is performed after the firing step, the desired number of laminated layers is finally obtained by stacking the laminated piezoelectric element units in the overlapping step. Can be.

  Then, the final unit-bonded laminated piezoelectric element has the same appearance as that obtained by integrally firing the same number of laminated bodies. In addition, since it is more uniformly fired, it has better performance.

  Further, in the manufacturing method of the present invention, when the average potential difference between the internal electrode layers of the multilayer piezoelectric element unit is V1, the potential difference V between two adjacent internal electrode layers sandwiching the bonding portion is V <( (1/2) V1.

Therefore, in the unit-bonded laminated piezoelectric element, the electric field applied to the bonding portion is relatively small. Therefore, non-resonance and displacement transmission hardly occur due to the mismatch (discontinuity) of the bonding surfaces between the stacked piezoelectric element units. As a result, the generation of stress in the direction perpendicular to the stacking direction of the unit-bonded laminated piezoelectric element is reduced, and the probability of occurrence of stress is reduced. It can be tempered. Therefore, when the side electrode is formed on the side surface of the unit-joined laminated piezoelectric element, or when the unit-joined laminated piezoelectric element is fixed by the shrink tube, it is possible to prevent the side electrode and the shrink tube from being damaged. Even when the laminated piezoelectric element units are joined to each other with a resin or the like, heat or the like due to dielectric loss hardly occurs at the joints, so that the resin hardly deteriorates due to the heat.
As a result, the unit-bonded laminated piezoelectric element can maintain durability equal to or higher than that obtained by integrally and simultaneously firing the same number of laminated bodies as the unit-bonded laminated piezoelectric element.

The electrode paste material is made of a conductive base metal material and / or an oxide thereof having a larger standard Gibbs free energy for forming a metal oxide at a firing temperature than the ceramic material forming the piezoelectric ceramic layer.
Therefore, in the firing step, the internal electrode layer can be sufficiently reduced while suppressing the reduction of the ceramic material.

  As described above, according to the present invention, regardless of the size of the laminated body, it is possible to sufficiently perform firing of the ceramic material and reduction of the internal electrode layer, and furthermore, a unit-bonded laminated piezoelectric element having excellent durability and performance. Can be provided.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a unit-bonded laminated piezoelectric element comprising two or more laminated piezoelectric element units in which piezoelectric ceramic layers and internal electrode layers are alternately laminated.
An electrode printing step of applying an electrode paste material to at least one surface of a ceramic green sheet formed of a ceramic material into a sheet shape;
A crimping step of laminating and crimping the ceramic green sheets coated with the electrode paste material to form a laminate;
A degreasing step of degreasing the laminate,
A firing step of firing the laminated body in a reducing atmosphere to produce a laminated piezoelectric element unit;
A superimposing step of forming a joint by laminating two or more of the laminated piezoelectric element units on the joint surfaces with the outermost surface in the laminating direction of the laminated piezoelectric element unit as a joint surface. ,
The paste material for an electrode is made of a conductive base metal material and / or an oxide thereof having a larger standard Gibbs free energy for forming a metal oxide at a firing temperature than the ceramic material constituting the ceramic green sheet,
Assuming that the average electric field strength between the internal electrode layers of the multilayer piezoelectric element unit is E1, the electric field strength E between two adjacent internal electrode layers sandwiching the bonding portion is such that E <(1/2) E1. The present invention provides a method for manufacturing a unit-bonded laminated piezoelectric element, characterized in that:

In the manufacturing method according to the fourth aspect of the present invention, when the average electric field strength between the internal electrode layers of the multilayer piezoelectric element unit is E1, the electric field strength E between two adjacent internal electrode layers sandwiching the bonding portion is expressed by: E <(1/2) E1.
Therefore, in the unit bonded multilayer piezoelectric element obtained by the manufacturing method of the present invention, the load on the bonded portion is reduced.
That is, in general, the displacement of the piezoelectric element due to the electric field intensity changes continuously, and in many cases, monotonically increases as the electric field intensity increases. However, if the electric field strength is reduced to less than half of the electric field strength required for efficient displacement, the displacement does not decrease in proportion to the reduction ratio of the electric field strength. Is reduced, and the displacement can be kept small.
In the present invention, as described above, the electric field strength E between two adjacent internal electrode layers sandwiching the bonding portion is set to be smaller than half the average electric field strength E1 between the internal electrode layers of the multilayer piezoelectric element unit. It is configured to be small. Therefore, the displacement at the joint is significantly reduced, and the load on the joint can be reduced.

Further, in the unit-bonded laminated piezoelectric element obtained by the manufacturing method of the present invention, similarly to the third invention, the electric field applied to the bonding portion is relatively small. Therefore, non-resonance and displacement transmission hardly occur due to the mismatch (discontinuity) of the bonding surfaces between the stacked piezoelectric element units. As a result, the generation of stress in the direction perpendicular to the stacking direction of the unit-bonded laminated piezoelectric element is reduced, and the probability of occurrence of stress is reduced. It can be tempered. Therefore, when the side electrode is formed on the side surface of the unit-joined laminated piezoelectric element, or when the unit-joined laminated piezoelectric element is fixed by the shrink tube, it is possible to prevent the side electrode and the shrink tube from being damaged. Even when the laminated piezoelectric element units are joined to each other with a resin or the like, heat or the like due to dielectric loss hardly occurs at the joints, so that the resin hardly deteriorates due to the heat.
Therefore, the unit-bonded laminated piezoelectric element can maintain the same or higher durability as that obtained by integrally firing the same number of laminated bodies as the unit-bonded laminated piezoelectric element.
The other effects are the same as those of the third invention.

According to a fifth aspect of the present invention, there is provided a method of manufacturing a unit-bonded laminated piezoelectric element comprising two or more laminated piezoelectric element units in which piezoelectric ceramic layers and internal electrode layers are alternately laminated.
An electrode printing step of applying an electrode paste material to at least one surface of a ceramic green sheet formed of a ceramic material into a sheet shape;
A crimping step of laminating and crimping the ceramic green sheets coated with the electrode paste material to form a laminate;
A degreasing step of degreasing the laminate,
A firing step of firing the laminated body in a reducing atmosphere to produce a laminated piezoelectric element unit;
A superimposing step of forming a joint by laminating two or more of the laminated piezoelectric element units on the joint surfaces with the outermost surface in the laminating direction of the laminated piezoelectric element unit as a joint surface. ,
The paste material for an electrode is made of a conductive base metal material and / or an oxide thereof having a larger standard Gibbs free energy for forming a metal oxide at a firing temperature than the ceramic material constituting the ceramic green sheet,
The laminated piezoelectric element unit has n rotational symmetry (where n is a natural number of 3 or more), and one or more and n-1 or less of n corners of the laminated piezoelectric element unit. A method for manufacturing a unit-bonded laminated piezoelectric element, characterized in that the corner is chamfered so as to have a shape different from the remaining corners (claim 27).

In the manufacturing method according to the fifth aspect of the present invention, the multilayer piezoelectric element unit has n rotational symmetry, and one or more and n−1 or less of n corners of the multilayer piezoelectric element unit. Bevel the corner so that it has a different shape than the other corners.
Therefore, it is easy to stack the above-mentioned stacked piezoelectric element units with, for example, a certain direction. That is, by chamfering as described above, the directionality of the laminated piezoelectric element unit can be easily understood, so that the stacking step can be performed easily.

In the manufacturing method according to the fifth aspect of the invention, the overlapping step is performed after the firing step, as in the third and fourth aspects. Therefore, in the firing step, a laminate having a small number of stacked layers can be fired, and as described above, the firing of the piezoelectric ceramic layer and the reduction of the internal electrode layers can be sufficiently performed.
Also, even if the number of the laminated bodies is reduced and the firing is performed after the firing step, the desired number of laminated layers is finally obtained by stacking the laminated piezoelectric element units in the overlapping step. Can be.

The electrode paste material is made of a conductive base metal material and / or an oxide thereof having a larger standard Gibbs free energy for forming a metal oxide at a firing temperature than the ceramic material forming the piezoelectric ceramic layer.
Therefore, similarly to the third and fourth inventions, the internal electrode layer can be sufficiently reduced while suppressing the reduction of the ceramic material in the firing step.

In the first to fifth inventions, a conductive base metal material having a larger standard Gibbs free energy for forming a metal oxide at a firing temperature than the ceramic material is used.
“Large standard Gibbs free energy for metal oxide formation” means “not easily oxidized”. For example, at 1000 ° C., the Gibbs free energy of Cu oxide formation is −40, the oxidation of Pb is −15, and the oxidation of Ni is −60. Cu, Pb, and Ni are obtained.

Further, in the first invention (claim 1), when the average potential difference between the internal electrode layers of the multilayer piezoelectric element unit is V1, the adjacent piezoelectric element unit sandwiches a joining portion where the multilayer piezoelectric element units join. The potential difference V between two matching internal electrode layers has a relationship of V <(1/2) V1.
Further, in the second invention (claim 3), when the average electric field strength between the internal electrode layers of the multilayer piezoelectric element unit is E1, a bonding portion where the multilayer piezoelectric element units join is sandwiched. The electric field intensity E between two adjacent internal electrode layers has a relationship of E <(1/2) E1.
The average potential difference V1 and the average electric field strength E1 are respectively the average of the potential difference and the electric field strength between each of the internal electrode layers other than the two adjacent internal electrode layers sandwiching the junction.

In the case of V ≧ (又 は) V1 or E ≧ (１ ／) E1, displacement as a piezoelectric body occurs in the above-mentioned joint at the same level as other parts. There is a possibility that non-resonance may occur or displacement transmission may be deteriorated due to the disagreement (discontinuity) at the interface between the two. As a result, the stress in the direction perpendicular to the stacking direction of the unit-joined laminated piezoelectric element increases, and the probability of occurrence of the stress increases, so that the load on the outer peripheral portion of the unit-joined laminated piezoelectric element increases. . Therefore, when a side electrode is formed on the side surface of the unit-joined laminated piezoelectric element, or when the unit-joined laminated piezoelectric element is fixed with a shrink tube, the side electrode or the shrink tube may be damaged. In addition, when the laminated piezoelectric element units are joined to each other by a resin or the like, heat or the like is generated at the joined portion due to dielectric loss, and the resin may be deteriorated by the heat.
Preferably, the average potential difference V1 between the internal electrode layers of the laminated piezoelectric element unit and the potential difference V between two adjacent internal electrode layers sandwiching the joint portion further have a relationship of V ≦ (１ ／) V1. It is desirable to have (claim 2).
Preferably, the average electric field strength E1 between the internal electrode layers of the laminated piezoelectric element unit and the electric field strength E between two adjacent internal electrode layers sandwiching the joint are further expressed as E ≦ (（). It is preferable to have a relationship of E1 (claim 4).

A method in which the potential difference V between two adjacent internal electrode layers sandwiching the above-described junction is V <(1/2) V1, or the electric field strength E between two adjacent internal electrode layers sandwiching the above-described junction is expressed as E < As a method of setting (1/2) E1, for example, when the two internal electrode layers are connected to side electrodes having positive and negative potentials, respectively, of the two internal electrode layers adjacent to each other sandwiching the above-mentioned junction. There is a method in which either one of them is not connected to the side electrode and the respective potentials are made positive and zero or zero and negative. Specifically, for example, there is a method of providing a portion that is electrically disconnected from the side surface electrode on at least one of two adjacent internal electrode layers sandwiching the above-mentioned joint.
In addition, for example, a method of electrically connecting two adjacent internal electrode layers sandwiching the above-mentioned joint to the same side electrode or a method of electrically connecting the two inner electrode layers to a side electrode having substantially the same potential, There is a method of making the potential difference applied between two matching internal electrode layers smaller than the potential difference between the other internal electrode layers. Further, in particular, as a method of setting the electric field strength E between two adjacent internal electrode layers sandwiching the joint portion to be E <(1/2) E1, other than the above, for example, the piezoelectric ceramic layer sandwiching the joint portion may be used. To make the thickness larger than the thickness of other piezoelectric ceramic layers.
Each of these methods can be performed alone or in combination. However, it is only necessary to satisfy the above expressions of V <(1/2) V1 and E <(1/2) E1, and the present invention is not limited to these methods.

  Further, as described above, when one of the two adjacent internal electrode layers sandwiching the bonding portion is not connected to the side electrode, the internal electrode layer not connected to the side electrode has an electric field. If the potential is not the potential of an electrode to which is directly applied (for example, a side surface electrode or the like), the potential may have substantially some potential. The above-mentioned “case where the potential is not caused by an electrode to which an electric field is directly applied” is, for example, a case where a part of the piezoelectric ceramic layer is reduced and the insulating property is reduced, and as a result, the internal electrode layer has a small potential. is there.

Further, as described above, it is preferable to satisfy V ≦ (１ ／) V1 and E ≦ (１ ／) E1.
In this case, the load on the outer peripheral portion can be further reduced.
More preferably, the potential difference V and the electric field intensity E between two adjacent internal electrode layers sandwiching the above-mentioned junction are preferably substantially zero.
In this case, displacement and heat generation at the joint can be further reduced and furthermore can be almost eliminated.

Next, the unit-bonded laminated piezoelectric element has one or more side electrodes sandwiching the side surface of the unit-bonded laminated piezoelectric element, and two adjacent internal electrode layers sandwiching the joint. Is preferably electrically connected to side electrodes having substantially the same potential (claim 5).
In this case, two adjacent internal electrode layers sandwiching the junction are connected to the same type of electrode (positive and positive or negative and negative), and the above V <(1/2) V1 or E <(1 / 2) The relationship of E1 can be easily realized, and the potential difference and the electric field intensity applied to the junction can be substantially reduced to zero. Therefore, non-resonance does not occur or displacement transmission is hardly caused by the mismatch (discontinuity) of the bonding surfaces between the stacked piezoelectric element units. As a result, the generation of stress in the direction perpendicular to the stacking direction of the unit-bonded laminated piezoelectric element is further alleviated, and the probability of generation of stress is further reduced. The load is further reduced. Therefore, when the side electrodes are formed on the side surfaces of the unit-joined laminated piezoelectric element, or when the unit-joined laminated piezoelectric elements are fixed by the shrinkable tube, the damage to the side electrodes and the shrinkable tube can be further prevented. Even when the laminated piezoelectric element units are joined to each other with a resin or the like, heat or the like due to dielectric loss hardly occurs at the joints, so that the resin hardly deteriorates due to the heat.

In this case, one or more of the side electrodes may be formed on the side surface of the unit-bonded laminated piezoelectric element. In the case where a plurality of side electrodes are formed, even if all the side electrodes are not connected, it suffices that the two internal electrode layers sandwiching the bonding portion have substantially the same potential. Further, the two internal electrode layers sandwiching the joint may be connected to the same side electrode.
Note that although the resistance value of the ceramic piezoelectric layer is very large although it is electrically limited, the electric potential between the two internal electrode layers sandwiching the above-mentioned joint is not exactly the same, and even if there is a slight difference, it is substantially equal. Can be regarded as having the same potential. In particular, in the case of a unit-bonded laminated piezoelectric element having a base metal electrode, a gas having an oxidizing power (reducing power) represented by oxygen is adjusted in order to suppress reduction of the piezoelectric ceramic layer while suppressing oxidation of the base metal during manufacturing. Therefore, 100% suppression of oxidation (suppression of reduction) cannot always be achieved. Therefore, there is a possibility that the difference in potential is larger than when noble metals are used for the electrodes. However, the difference in potential at this time, or the potential difference or electric field strength caused by the difference in potential at this time, is the difference in potential between the electrically different side electrodes or the potential difference or electric field strength caused by the difference in potential. Since it is extremely small compared to, it can be regarded as substantially zero.

  The side electrode may be made of a conductive material such as Ag, Fe, Ni, Cu, or a mixed metal material of Ag and Pd.

It is preferable that the total thickness of the two adjacent piezoelectric ceramic layers sandwiching the bonding portion and the thickness of the bonding portion exceeds twice the thickness of the piezoelectric ceramic layer inside the multilayer piezoelectric element unit. ).
As described above, when only two internal electrode layers adjacent to each other sandwiching the above-mentioned junction are electrically connected to side electrodes having substantially the same potential, one of the internal electrode layers is interrupted and the electrical polarity cannot be controlled. In addition, an electric field is formed by the internal electrode layer next to (adjacent to) the internal electrode layer interrupted from the junction and the other internal electrode layer facing the interrupted internal electrode layer at the junction. If the distance between the two internal electrode layers formed with is not sufficiently large, an electric field larger than the reference electric field strength is formed at the junction, and the load on the junction may be increased. As a result, the durability of the unit-bonded laminated piezoelectric element may be reduced.
As described above, when the sum of the thicknesses of two adjacent piezoelectric ceramic layers sandwiching the joint portion is configured to exceed twice the thickness of the piezoelectric ceramic layer inside the multilayer piezoelectric element unit, Such risks can be avoided. Further, in this case, the electric field strength between two adjacent internal electrode layers sandwiching the joint is determined without complicating the configuration of the side electrode and the internal electrode. The average electric field strength can be made smaller than １ ／, and the load on the joint can be easily reduced.

The thickness of the piezoelectric ceramic layer inside the multilayer piezoelectric element unit is the average thickness of the piezoelectric ceramic layer inside the multilayer piezoelectric element unit. If a thick or thin portion or layer is accidentally formed, The thickness can be arbitrarily calculated at 10 or more places (each point is selected from a different layer), excluding the accidentally formed portion or layer, and the average can be calculated. Here, the accidentally formed portion means a portion formed 10% or more thicker or thinner in the same layer, and the accidentally formed layer means 10% or more thicker or thinner than other layers. It shall mean a layer formed thinly (even if it is different from the sheet stage, it does not contribute at all, and can be used as the above standard).
The total thickness of two adjacent piezoelectric ceramic layers sandwiching the joint and the thickness of the joint is a thickness obtained by adding the thickness of the piezoelectric ceramic layer adjacent to the joint and the thickness of the joint. For example, when the laminated piezoelectric element unit is joined via a resin material at the joint, the thickness includes the thickness of the resin material.

Further, even if the total thickness of the adjacent piezoelectric ceramic layers sandwiching the joint and the joint is apparently less than twice the thickness of the piezoelectric ceramic layer inside the multilayer piezoelectric element unit, If the electrode layer is no longer an electrically effective electrode due to electrical interruption, the invalid internal electrode layer is not regarded as an electrode, but is replaced with the adjacent piezoelectric ceramic layer sandwiching the above joint. The total thickness of the above-mentioned joints may be calculated, and the total thickness may be more than twice the thickness of the piezoelectric ceramic layer inside the multilayer piezoelectric element unit.
Further, the adjustment of the electric field intensity near the joint is not limited to the thickness of the adjacent piezoelectric ceramic layers sandwiching the joint and the thickness of the joint. For example, the electric field strength may be adjusted by adjusting the potential difference between two internal electrode layers sandwiching the joint, and furthermore, the total of the two adjacent piezoelectric ceramic layers sandwiching the joint and the joint may be adjusted. The electric field strength may be adjusted by adjusting the thickness and the potential difference between the two internal electrode layers sandwiching the joint. This is because the electric field strength is determined by the potential difference between the two electrodes and the distance between the two electrodes.

Further, it is preferable that the laminated piezoelectric element units are joined to each other via a resin material at the joint portion.
In this case, the laminated piezoelectric element units can be uniformly fixed at the joint.
Examples of the resin material include an epoxy-based resin material, polyamide, polyester-based, isocyanate, polyimide-based, silicon-based, and urethane-based adhesives.

Further, it is preferable that the resin material contains a ceramic material and / or a metal material.
In this case, the elasticity at the joint is improved, and the attenuation of displacement due to the presence of the joint can be reduced. In this case, the acoustic impedance of the unit-bonded laminated piezoelectric element can be increased. Therefore, the unit-bonded laminated piezoelectric element can be made suitable for an ultrasonic piezoelectric element or the like.
The same ceramic material as the piezoelectric ceramic layer can be used as the ceramic material contained in the resin material. The metal material may be the same as the base metal material of the internal electrode layer, or a metal having the same sound speed (for example, Ni for Cu).

It is preferable that the resin material has conductivity at least in part, and electrically connects adjacent piezoelectric ceramic layers sandwiching the bonding portion.
In this case, it is possible to make the potentials of the adjacent piezoelectric ceramic layers sandwiching the bonding portion substantially equal. Therefore, even if the piezoelectric ceramic layer is reduced at the time of manufacture and the insulating property is reduced, the risk of increasing the load on the joint can be avoided.
As a method of giving the above-mentioned conductivity to the above-mentioned resin material, for example, there is a method of making the above-mentioned resin material contain a conductive material such as a metal material so as to partially penetrate the resin material.

Further, the stacked piezoelectric element units may be directly contacted with each other and joined at the joint portion.
In this case, it is possible to prevent the joint portion from deteriorating due to heat generation.
As a specific example, there is a method in which side electrodes and lead wires are attached to the unit-bonded laminated piezoelectric element, and then the laminated piezoelectric element units are joined to each other by, for example, covering and shrinking a shrinkable tube or the like. .

Next, the ceramic material preferably contains a PZT-based material.
In this case, the characteristics of the unit-bonded laminated piezoelectric element are improved by taking advantage of the excellent characteristics of the PZT-based material as a piezoelectric body.

Preferably, the conductive base metal material is Cu.
In this case, it is possible to reduce the cost of the unit-bonded laminated piezoelectric element, and it is easier to reduce or maintain the reduced state of the internal electrode layer during manufacturing.

Next, in the third invention (claim 13), when the average potential difference between the respective internal electrode layers of the multilayer piezoelectric element unit is V1, the potential difference between two adjacent internal electrode layers sandwiching the bonding portion is set. V is configured such that V <(1/2) V1.
Further, in the fourth invention (claim 15), when the average electric field strength between the internal electrode layers of the multilayer piezoelectric element unit is E1, a bonding portion where the multilayer piezoelectric element units are joined is sandwiched. The electric field strength E between two adjacent internal electrode layers is configured to satisfy E <(1/2) E1.
The average potential difference V1 and the average electric field strength E1 are respectively the average of the potential difference and the electric field strength between each of the internal electrode layers other than the two adjacent internal electrode layers sandwiching the junction.

When V≥1 / 2V1 or E≥ (1/2) E1, the displacement as a piezoelectric body occurs equally at the joint, as in the first and second inventions. Non-resonance may occur or displacement transmission may be deteriorated due to mismatch (discontinuity) at the interface between the piezoelectric element units. As a result, the stress in the direction perpendicular to the stacking direction of the unit-joined laminated piezoelectric element increases, and the probability of occurrence of the stress increases, so that the load on the outer peripheral portion of the unit-joined laminated piezoelectric element increases. . Therefore, when a side electrode is formed on the side surface of the unit-joined laminated piezoelectric element, or when the unit-joined laminated piezoelectric element is fixed with a shrink tube, the side electrode or the shrink tube may be damaged. In addition, when the laminated piezoelectric element units are joined to each other by a resin or the like, heat or the like is generated at the joined portion due to dielectric loss, and the resin may be deteriorated by the heat.
Preferably, the relationship between the average potential difference V1 between the internal electrode layers of the multilayer piezoelectric element unit and the potential difference V between two adjacent internal electrode layers sandwiching the joint is V ≦ (１ ／) V1. It is preferable to satisfy the requirement (claim 14).
Preferably, the average electric field strength E1 between the internal electrode layers of the laminated piezoelectric element unit and the electric field strength E between two adjacent internal electrode layers sandwiching the bonding portion further satisfy E ≦ (１ ／). It is preferable to configure so as to satisfy the relationship of E1 (claim 16).

A method in which a potential difference V between two adjacent internal electrode layers sandwiching the above-mentioned junction is set to V <(1/2) V1, or an electric field strength E between two adjacent internal electrode layers sandwiching the above-mentioned junction is expressed by E < The method of setting (1/2) E1 can be realized by the same method as the first and second inventions.
More preferably, it is preferable that the potential difference V and the electric field strength E between two adjacent internal electrode layers sandwiching the above-mentioned junction are substantially zero. In this case, displacement and heat generation at the joint can be almost eliminated.

Next, side electrodes are provided on each side surface of the laminated piezoelectric element unit after the firing step or the unit-bonded laminated piezoelectric element after the overlapping step so as to sandwich the laminated piezoelectric element unit or the unit-bonded laminated piezoelectric element. It is preferable to provide one or more (claim 17).
In this case, a voltage can be easily applied to the internal electrode layer.
As the side electrode, a conductive material such as Ag, Fe, Ni, Cu, or a mixed metal material of Ag and Pd can be used.

Next, in the superposing step, it is preferable that two adjacent internal electrode layers sandwiching the joint between the laminated piezoelectric element units are stacked so as to be electrically connected to side electrodes having substantially the same potential ( Claim 18).
In this case, two adjacent internal electrode layers sandwiching the junction are connected to the same type of electrode (positive and positive or negative and negative) or an electrode of substantially the same potential, and the above V <(1/2) The relationship of V1 and the relationship of E <(1/2) E1 can be easily realized, and the potential difference and the electric field intensity applied to the junction can be made substantially zero.
Therefore, non-resonance does not occur or displacement transmission is hardly caused by the mismatch (discontinuity) of the bonding surfaces between the stacked piezoelectric element units. As a result, the generation of stress in the direction perpendicular to the stacking direction of the unit-bonded laminated piezoelectric element is further alleviated, and the probability of generation of stress is further reduced. The load is further reduced. Therefore, when the side electrodes are formed on the side surfaces of the unit-joined laminated piezoelectric element, or when the unit-joined laminated piezoelectric elements are fixed by the shrinkable tube, the damage to the side electrodes and the shrinkable tube can be further prevented. Even when the laminated piezoelectric element units are joined to each other with a resin or the like, heat or the like due to dielectric loss hardly occurs at the joints, so that the resin hardly deteriorates due to the heat.

In addition, it is preferable that the total thickness of two adjacent piezoelectric ceramic layers sandwiching the bonding portion and the thickness of the bonding portion exceed twice the thickness of the piezoelectric ceramic layer inside the multilayer piezoelectric element unit. (Claim 19).
As described above, by merely electrically connecting two adjacent internal electrode layers sandwiching the bonding portion to side electrodes having substantially the same potential, for example, the eutectic of the ceramic material and the electrode paste material in the firing step. When a reaction or the like occurs and one of the two internal electrode layers adjacent to the joint portion is interrupted and the electrical polarity cannot be controlled, the internal electrode layer that has been interrupted as viewed from the joint portion is disconnected. An electric field is formed by the next (adjacent) internal electrode layer and the other internal electrode layer facing the broken internal electrode layer at the junction, and the distance between the two internal electrode layers that formed the electric field is sufficient. If the distance is not large, an electric field larger than the reference electric field intensity is formed by the joint, and the load on the joint may be increased. As a result, the durability of the unit-bonded laminated piezoelectric element may be reduced.
Therefore, if the total thickness of two adjacent piezoelectric ceramic layers sandwiching the above-mentioned joint portion is set to be larger than twice the thickness of the piezoelectric ceramic layer inside the multilayer piezoelectric element unit, the above risk is avoided. can do. Further, in this case, the electric field strength between two adjacent internal electrode layers sandwiching the joint is determined without complicating the configuration of the side electrode and the internal electrode. The average electric field strength can be made smaller than １ ／, and the load on the joint can be easily reduced.

Next, in the overlapping step, it is preferable that the laminated piezoelectric element units are joined with a resin material.
In this case, the laminated piezoelectric element units can be uniformly fixed at the joint.
As the resin material, the same material as in the first and second inventions can be used.

Next, the resin material preferably contains a ceramic material and / or a metal material.
In this case, the elasticity at the joint is improved, and the attenuation of displacement due to the presence of the joint can be reduced. In this case, the acoustic impedance of the unit-bonded laminated piezoelectric element can be increased. Therefore, the unit-bonded laminated piezoelectric element can be made suitable for an ultrasonic piezoelectric element.
As the ceramic material contained in the resin material, the same material as the ceramic green sheet can be used. The metal material may be the same as the base metal material of the electrode paste material, or a metal having the same sound speed (for example, Ni for Cu).

Next, it is preferable that the resin material has conductivity at least in part, and electrically connects adjacent piezoelectric ceramic layers sandwiching the joint.
In this case, it is possible to make the potentials of the adjacent piezoelectric ceramic layers sandwiching the bonding portion substantially equal. Therefore, even if the piezoelectric ceramic layer is reduced and the insulating property is reduced, the risk of increasing the load on the joint can be avoided.
As a method of giving the above-mentioned conductivity to the above-mentioned resin material, for example, there is a method of making the above-mentioned resin material contain a conductive material such as a metal material so as to partially penetrate the resin material.

Further, in the superposing step, the laminated piezoelectric element units can be brought into direct contact with each other and joined.
In this case, it is possible to further prevent non-resonance from occurring at the joint.
In this case, the unit-bonded laminated piezoelectric element can be fixed, for example, by covering a shrink tube after attaching the side electrodes and the lead wires.

Next, the piezoelectric ceramic layer preferably contains a PZT-based material.
In this case, a unit-bonded laminated piezoelectric element having excellent characteristics can be manufactured by taking advantage of the excellent characteristics of the PZT-based material as a piezoelectric material.

Further, the PZT-based material often contains PbO having a property of being more easily reduced than PZT in its composition, and when PbO is reduced to Pb, a eutectic melting reaction occurs with the conductive base metal material. This makes it difficult to form the internal electrode layer continuously. Therefore, when a PZT-based material is used as the ceramic material, it must be fired without oxidizing the conductive base metal material and reducing PbO as well as the PZT-based material. Setting becomes very difficult.
However, in the present invention, the conductive base metal material has a larger standard Gibbs free energy of metal oxide generation at the firing temperature than the ceramic material constituting the piezoelectric ceramic layer. Thus, the conductive base metal material is hardly oxidized, and the atmospheric conditions can be easily set.
That is, as described above, when a PZT-based material is used, the internal electrode layer can be sufficiently reduced while suppressing the reduction of the ceramic material during the firing step in the third and fourth inventions. The effect can be obtained more remarkably.

Next, it is preferable that the conductive base metal material is Cu.
In this case, the unit-bonded laminated piezoelectric element can be manufactured at low cost, and the reduction of the electrode or the maintenance of the reduced state of the electrode becomes easier.
Further, when the ceramic material contains a PZT-based material, as described above, PbO having the property of being easily reduced often exists. In the firing step, an oxide of a conductive base metal that is reduced without reducing PbO, or a conductive base metal that can maintain a reduced state without reducing PbO (not oxidized) is almost equal to an oxide of Cu or Cu. Limited.

Next, the multilayer piezoelectric element unit has n rotational symmetry (where n is a natural number of 3 or more), and one or more of n corners of the multilayer piezoelectric element unit and n− Preferably, one or less corners are chamfered so as to have a shape different from the remaining corners.
In this case, it is possible to simplify the step of stacking the stacked piezoelectric element units in a desired arrangement in the overlapping step, thereby improving productivity.

  In particular, as shown in an embodiment to be described later, a partial electrode is formed as the internal electrode layer, and in the overlapping step, two adjacent internal electrode layers sandwiching a joint between the laminated piezoelectric element units are, for example, the same. When controlling the orientation of the internal electrode layers, such as when stacking them so that they are electrically connected to the side electrodes, the orientation of the stacked piezoelectric element units when stacking the stacked piezoelectric element units is important. Therefore, it is effective to perform the above chamfering.

  Further, the fifth invention (claim 27) is not limited to the first to fourth inventions, and is effective when it is desired to have the desired orientation and to superimpose the laminated piezoelectric element units. I do.

  The above-mentioned n-rotational symmetry means that the above-mentioned laminated piezoelectric element unit encounters the same shape as the original state n times while it is rotated 360 degrees around the central axis in the laminating direction. is there. For example, when the cross-sectional shape of the laminated piezoelectric element in a plane perpendicular to the laminating direction is a square, the shape becomes almost the same as the original state every time it is rotated by 90 degrees. , 4 times rotational symmetry (n = 4). Naturally, if the chamfered shape is changed, strictly speaking, the shape will not be the same during rotation. In the above, the reason why they are described as being substantially the same is to evaluate whether or not the chamfered shapes are the same, omitting differences in the chamfered shapes.

  At this time, by chamfering one corner of the square into a shape different from the other corners, for example, when a partial electrode is formed as the internal electrode layer, it is possible to visually determine which side the partial electrode is facing. it can. Therefore, in the superposing step, when the multi-layer piezoelectric element units are stacked while adjusting the orientation of the internal electrode layers, there is no need to use a microscope or the like, and the manufacturing method is simplified.

  The above-mentioned "chamfering so as to have a different shape" means, for example, that the size of the chamfer may be changed in the same flat chamfer as well as the flat chamfer and the curved chamfer, Is also good. Also, the presence or absence of chamfering can be changed. The shape of the chamfer is not limited to these.

  As an example of the above-mentioned chamfering, as described above, the case where one corner of the square is formed in a different shape from the other corners is illustrated. However, even if there are two or more corners having different shapes, the visual direction Anything that assists in gender determination may be used. That is, in the laminated piezoelectric element unit having n rotation symmetry, the chamfered shape of one or more and n-1 or less corners may be made different from the chamfered shape of the remaining corners.

The step of chamfering can be performed before the overlapping step, for example, after the pressure bonding step, after the degreasing step, or after the firing step.
Preferably, it is performed after the above-mentioned firing step. This is because before the firing step, the ceramic material is not sintered and is brittle, so that it becomes difficult to chamfer a desired shape.

It is preferable that the number of corners for performing the chamfering and the shape of the chamfering be uniform for the whole stacked piezoelectric element units.
In this case, the shape of the unit-bonded laminated piezoelectric element becomes uniform as a whole. For example, when the unit-bonded laminated piezoelectric element is used as a medium and the medium is used in an injector or the like, it can be incorporated into an injector or the like. Easy.

  Further, in this specification, an electrode having two polarities may have positive and negative polarities, or may be composed of positive and zero, and zero and negative. Even when the potential is large (positive (negative)) and small (negative), the same effect can be obtained as long as a potential difference or electric field strength is formed due to the difference in potential between the two electrodes.

(Example 1)
Next, a unit-bonded laminated piezoelectric element and a method of manufacturing the same according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, the unit-bonded laminated piezoelectric element of this embodiment is a unit-bonded laminated piezoelectric element formed by laminating two or more laminated piezoelectric element units 15 in which piezoelectric ceramic layers 151 and internal electrode layers 153 are alternately laminated. It is one.

The internal electrode layer 153 is made of a conductive base metal material having a larger standard Gibbs free energy for forming a metal oxide at a firing temperature than the ceramic material forming the piezoelectric ceramic layer 151.
Assuming that the average potential difference between the internal electrode layers 153 of the laminated piezoelectric element unit 15 is V1, the potential difference V between two adjacent internal electrode layers sandwiching a joint portion where the laminated piezoelectric element units 15 are joined is: V <(1/2) V1.

Hereinafter, the unit-bonded laminated piezoelectric element of this example will be described in detail with reference to FIG.
As shown in FIG. 1, the unit-bonded laminated piezoelectric element 1 has a laminated piezoelectric element unit 15 joined at a joint 17. The unit-stacked piezoelectric element 1 of this embodiment is formed by joining ten stacked-type piezoelectric element units 15. In FIG. 1, the illustration is omitted for convenience of drawing. As shown in the figure, each laminated piezoelectric element unit 15 is formed by alternately laminating a piezoelectric ceramic layer 151 made of a PZT material and an internal electrode layer 153 made of Cu.

The internal electrode layer 153 is formed so as to reach only one side surface of the piezoelectric ceramic layer 151, and a non-formed portion 159 having no internal electrode layer 153 is provided on the other side surface.
Further, two side electrodes 19 are formed on the side surface of the unit-bonded laminated piezoelectric element 1 so as to sandwich the same. The side electrodes are made of Ag. In this example, Ag was used as the side electrode, but other conductive materials such as Fe, Ni, Cu, or a mixed metal material of Ag and Pd can be used.

  As shown in FIG. 1, in the laminated piezoelectric element unit 15 constituting the unit-bonded laminated piezoelectric element 1, the internal electrode layers 153 are alternately connected to different side electrodes 19. Are connected to the same side electrode 19.

The method for manufacturing the unit-bonded laminated piezoelectric element 1 according to the present invention includes an electrode printing step, a pressure bonding step, a degreasing step, a firing step, and a laminating step, which will be described later.
In the electrode printing step, as shown in FIG. 2, an electrode paste material 253 is applied to at least one surface of a ceramic green sheet 251 formed of a ceramic material in a sheet shape.
In the above-mentioned pressing step, as shown in FIGS. 3 and 4, the ceramic green sheets 251 coated with the electrode paste material 253 are laminated and pressed to form the laminate 25.

Next, in the degreasing step, the laminate 25 is degreased.
In the firing step, the multilayer body 25 is fired in a reducing atmosphere to produce the multilayer piezoelectric element unit 15 as shown in FIG.
In the superimposing step, as shown in FIGS. 1 and 5, the outermost surface of the multilayer piezoelectric element unit 15 in the laminating direction is set as the bonding surface 157, and the multilayer piezoelectric element unit 15 is At least two are overlapped to form the joint 17.

  The electrode paste material is made of a conductive base metal material and / or an oxide thereof having a larger standard Gibbs free energy for forming a metal oxide at a firing temperature than the ceramic material constituting the ceramic green sheet. When the average potential difference between the internal electrode layers 153 of the multilayer piezoelectric element unit 15 is V1, the potential difference V between two adjacent internal electrode layers 153 sandwiching the joint 17 is represented by V ≦ (1/2). ) V1.

Hereinafter, the manufacturing method of this example will be described in detail with reference to FIGS.
First, a ceramic material is manufactured as follows.
83.5 mol% and 16.5 mol% of lead oxide and tungsten oxide were respectively weighed and dry-mixed, and then baked at 500 ° C. for 2 hours, thereby causing a part of the lead oxide and tungsten oxide to react. oxide powder (chemical _{formula:... Pb0 835 W0 165} O 1 33) was prepared. Next, this auxiliary oxide powder was atomized by a medium stirring mill and dried to increase the reactivity.

On the other hand, metal oxides of PbO, SrCO ₃ , ZrO ₂ , TiO ₂ , Y ₂ O ₃ , Nb ₂ O ₅ , and Mn ₂ O ₃ are mixed, and these are dry-mixed and then fired at 850 ° C. for 7 hours. As a result, a piezoelectric calcined powder was produced.

  Next, 5.5 L of water was added to 4.7 kg of the piezoelectric calcined powder, and D134 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a dispersant was added to the piezoelectric calcined powder in an amount of 5 wt. %, And mixed for 1 hour to prepare a slurry for pulverizing the piezoelectric calcined powder.

  This pulverizing slurry was pulverized by a medium stirring mill for 8 hours to reduce the median diameter to 0.2 μm or less. Further, the pulverized slurry was dried at 220 ° C. by a spray drier to obtain a pulverized powder of a piezoelectric preliminarily calcined powder. Since the dispersant remains in the pulverized powder, the pulverized powder was further heat-treated at 650 ° C. for 5 hours to degrease the dispersant and obtain a calcined piezoelectric substance powder.

  Next, 7 g of the auxiliary oxide prepared in advance as described above was added to 700 g of the piezoelectric preliminarily fired powder to prepare a raw material powder. 16% by weight of butanol, 16% by weight of isoamyl acetate, 0.6% by weight of sorbitan triolate as a dispersing agent, 5% by weight of BBP (benzyl butyl phthalate, Wako Pure Chemical Industries, Ltd.) as a plasticizer, and a binder 7.5 wt% (made by Denki Kagaku Kogyo KK) was added and mixed by a ball mill for 72 hours to obtain a slurry of a ceramic material.

  Next, the slurry of the ceramic material was formed into a sheet having a thickness of 150 μm by a doctor blade method. Thereafter, the sheet was dried at 80 ° C. and cut into 100 mm × 100 mm with a sheet cutter to obtain a ceramic green sheet.

Next, an electrode paste material is prepared as follows.
An organic vehicle obtained by dissolving ethylcellulose with terpineol and a resin material (acrylic resin, arachid resin, ethocell resin, etc.) are mixed with CuO powder (average particle size of 1 to 2 μm, approximately spherical) and Cu powder (average particle size of 0. An electrode paste material was prepared by kneading 5 μm, approximately spherical powder into a plate-like material in a mixing ratio shown in Table 1 below.

  Next, as shown in FIG. 2, the electrode paste material 253 is applied to a plurality of ceramic green sheets 251. At this time, the electrode paste material 253 is applied to one surface of the ceramic green sheet 251 so as to reach only one side surface of the ceramic green sheet 251. At this time, the non-formed portion 159 is provided on the other side. The printing thickness of the electrode paste material 253 was set to 20 μm. FIG. 11 shows an example of the ceramic green sheet 251 after printing.

Subsequently, as shown in FIG. 3, the ceramic green sheets 251 on which the electrode paste material 253 is printed are laminated. At this time, the electrode paste materials 253 were laminated such that they alternately reached the left and right side surfaces.
In this manner, the ceramic green sheets 251 were sequentially laminated, and as shown in FIG. 4, a laminate 25 in which a total of 25 ceramic green sheets 251 were laminated was produced. When laminating the ceramic green sheets 251, two ceramic green sheets each having a thickness of 10 μm smaller than the others and having a thickness of 130 μm are prepared. These thin ceramic green sheets were laminated. In the two ceramic green sheets laminated on both ends of the laminated body 25, the ceramic green sheet disposed at the lowermost stage of the laminated body 25 is the same as that described above, on which the paste material for electrodes is printed. As the ceramic green sheet disposed in the upper stage, a sheet on which no electrode paste material was printed was used. Similarly, a total of ten laminates 25 were produced.

Then, the ten laminates 25 obtained as described above were each fixed to a crimping jig, and thermocompression-bonded at 110 ° C. for 1 minute at 16 MPa. The laminated body 25 subjected to thermocompression bonding was cut into a size of 86 mm in length and 86 mm in width by a sheet cutter, and then flattened by applying a pressure of 7.8 MPa in the laminating direction at room temperature.
Subsequently, each laminate 25 was placed in a gas circulation type degreasing furnace and heated at a temperature of 550 ° C. for 10 hours to perform degreasing.

Next, the electrode paste material 253 applied on the ceramic green sheets 251 constituting each of the laminates 25 is reduced. In the reduction of the electrode paste material 253, CuO contained in the electrode paste material 253 is reduced to Cu.
Specifically, the laminate 25 is heated in a reducing atmosphere.

In this example, since the ceramic green sheet 251 contains lead and the electrode paste material 253 contains Cu, the temperature immediately below or near 326 ° C., which is the eutectic point of lead and copper, was used as the heating temperature. . Specifically, the temperature is 320 ° C. ± 5 ° C. Note that ± 5 ° C is the fluctuation range of the actually measured value.
By this heating, the electrode paste material 253 applied to each ceramic green sheet 251 is reduced to form the internal electrode layer 153.

Next, the laminated body 25 is fired to produce the laminated piezoelectric element unit 15 shown in FIG.
The firing temperature during firing was 950 ° C., and the atmosphere was adjusted to an atmosphere in which Cu in the internal electrode layer was not oxidized as much as possible and oxides in the element portion were not reduced as much as possible. Specifically, the oxygen partial pressure at a firing temperature of 950 ° C. was adjusted to be 10 ⁻³ hPa (10 ⁻⁶ atm).

During this firing, the ceramic green sheets 251 in the laminate 25 are sintered to form the piezoelectric ceramic layers 151.
In this way, as shown in FIG. 5, a laminated piezoelectric element unit 15 in which the piezoelectric ceramic layers 151 and the internal electrode layers 153 were alternately laminated was obtained. At this time, the height of the laminated piezoelectric element unit 15 was 2 mm.

Next, as shown in FIGS. 5 and 6, the outermost surface of the laminated piezoelectric element unit 15 in the laminating direction is set as a bonding surface 157, and the laminated piezoelectric element unit 15 is overlapped with the bonding surfaces 157 and bonded. The part 17 was formed. At this time, as shown in FIG. 6, the stacked piezoelectric element units 15 were overlapped so that two adjacent internal electrode layers 153 sandwiching the joint 17 were both directed to the same side surface. In this way, a total of ten laminated piezoelectric element units 15 were superimposed, and their bonding surfaces 157 were bonded to each other with epoxy resin, thereby producing a unit bonded laminated piezoelectric element 1 as shown in FIG.
This was designated as Sample E1.

  In this example, a unit-bonded laminated piezoelectric element 1 in which the bonding surfaces 157 of ten laminated piezoelectric element units 15 are bonded with a mixed resin material of 90 parts by weight of an epoxy resin and 10 parts by weight of a ceramic material is used. It was fabricated and used as a sample E2. The ceramic material in the mixed resin material used had the same composition as the ceramic material used for producing the ceramic green sheet.

  Further, in this example, a unit-bonded laminated piezoelectric element in which the bonding surfaces of the laminated-type piezoelectric element unit were brought into direct contact with each other without any material being interposed therebetween was produced, and this was designated as Sample E3.

In this example, as shown in FIG. 7 to be described later, when the laminated piezoelectric element units 15 are overlapped with each other, two adjacent internal electrodes sandwiching the joint 17 are used for comparison with the samples E1 to E3. The unit-bonded laminated piezoelectric element 9 in which the laminated piezoelectric element units 15 were overlapped with each other such that the layers 153 face the opposite side faces was produced, and these were used as samples C1 to C3.
Sample C1, sample C2, and sample C3 are samples for comparison with sample E1, sample E2, and sample E3, respectively.

  That is, the sample C1 is obtained by bonding the bonding surfaces of the laminated piezoelectric element units to each other with the epoxy resin similarly to the sample E1. Sample C2, like Sample E2, was obtained by joining the bonding surfaces of the multilayer piezoelectric element unit with a mixed resin material of 90 parts by weight of epoxy resin and 10 parts by weight of ceramic material. Sample C3 was obtained by directly joining the joining surfaces of the stacked piezoelectric element units without interposing any material therebetween.

6 and 7 show differences in the arrangement of the internal electrode layers in the vicinity of the joint between Samples E1 to E3 and Samples C1 to C3, respectively.
As is known from FIG. 6, in the samples E1 to E3, the two adjacent internal electrode layers 153 sandwiching the joint 17 are formed so as to face the same side surface.
On the other hand, as is known from FIG. 7, in the samples C1 to C3, the two adjacent internal electrode layers 153 sandwiching the joint 17 are formed so as to face opposite side surfaces.

  Next, of the four side surfaces of the samples E1 to E3 and the samples C1 to C3, side electrodes 19 were formed on two side surfaces where the internal electrode layers alternately reached the side surfaces so as to sandwich the side surfaces. . The side electrode 19 was made of baked silver and was prepared by baking an Ag paste. The composition of the baked silver was 97% by weight of Ag and 3% by weight of the glass frit component.

  This side electrode was prepared for comparing the characteristics of the samples E1 to E3 and the characteristics of the samples C1 to C3, and did not significantly affect the superiority of the unit-bonded laminated piezoelectric element itself. Therefore, the material of the side electrode is not limited to Ag, and a side electrode containing any one or more of Fe, Cu, Pt, Ni, Pd and the like can also be used.

Next, the characteristics of the samples E1 to E3 and the samples C1 to C3 are evaluated as follows.
A voltage consisting of a rectangular wave having a peak-to-peak intensity of 0 to 180 V was applied intermittently to the side electrodes of Samples E1 to E3 and Samples C1 to C3, one of which was a positive electrode and the other was a negative electrode. At this time, the occurrence of noise and the occurrence of peeling and cracking of the joints in the samples E1 to E3 and the samples C1 to C3 were examined.

In the sample C1 and the sample C2, when the voltage application time (total time) reached 8 hours and 24 hours, respectively, peeling occurred in the joined portion, and the displacement amount instantaneously decreased.
In addition, in the sample C3, before the voltage application time (total time) was less than one hour, a problem that the degree of adhesion of the joint was reduced and a gap was formed in the joint occurred, and the displacement amount was reduced. Dropped instantly.

  On the other hand, in Samples E1 to E3, even if the voltage application time (total time) exceeded 100 hours, no peeling or cracking was observed at the joint, and no noise due to non-resonance was observed.

  As shown in FIG. 1, in the above-mentioned samples E1 to E3, two adjacent internal electrodes 153 sandwiching the joint 17 are connected to the same side electrode 19. Therefore, the voltage between two adjacent internal electrodes 153 sandwiching the joint 17 is substantially zero. That is, when the average potential difference between the internal electrode layers 153 of the multilayer piezoelectric element unit 15 is V1 and the potential difference between two adjacent internal electrode layers 153 sandwiching the joint 17 is V, V ≦ (１ ／) The relationship of V1 is satisfied.

  Therefore, non-resonance does not occur or displacement transmission is hardly deteriorated due to mismatch (discontinuity) of the bonding surfaces of the stacked piezoelectric element units 15. Further, even when the laminated piezoelectric element units 15 are joined to each other with a resin or the like (samples E1 and E2), the influence of the heat resistance (deterioration due to heat) of the resin can be reduced.

  For this reason, the unit-bonded laminated piezoelectric elements of Samples E1 to E3 can be driven for a long time of 100 hours or more as described above without causing noise due to peeling, cracking, and non-resonance at the bonding portion. It is considered.

(Example 2)
In the present embodiment, the four corners of the laminated piezoelectric element unit similar to the first embodiment are chamfered so that one corner has a shape different from the remaining three corners, and the unit is joined. This is an example of manufacturing a laminated piezoelectric element.

  First, as shown in FIG. 4, a laminate 25 similar to that of Example 1 was prepared. As shown in FIG. 4, this laminate 25 is formed by stacking 24 ceramic green sheets 251 coated with the electrode paste material 253 as in the first embodiment, and the electrode paste material is not coated on the uppermost portion. It is a stack of ceramic green sheets. The thicknesses of the ceramic green sheet 251 and the electrode paste material 253, and the dimensions of the laminate 25 are the same as in the first embodiment.

Subsequently, as shown in FIG. 8, four corners of the laminate 25 were chamfered in a shape in which the length of two sides of a right-angled isosceles triangle was 1 mm. This is designated as Sample C4.
Also, of the four corners of the laminate, only one specific point viewed from the internal electrode is chamfered in a shape in which the length of two sides of the right-angled isosceles triangle is 1.5 mm, and the other three corners are chamfered. Each prepared a sample chamfered in such a shape that the length of two sides of a right-angled isosceles triangle was 1 mm, and this was designated as Sample E4.

  Further, ten samples E4 and C4 each were prepared, and degreased and fired as in Example 1. Further, in the same manner as in Example 1, ten pieces of each of the fired samples E4 and C4 were superposed. At the time of the superposition, the superposition was performed by visual observation so that the two internal electrodes sandwiching the bonding portion both face the same side surface as in Example 1.

  As for the sample E4, since one specific corner is chamfered in a shape different from the other corners as described above, the direction can be sufficiently discriminated visually, and the two corners sandwiching the joined portion can be determined. The internal electrodes could be stacked so that they both face the same side.

  On the other hand, for sample C4, it was difficult to determine the direction because all four corners were chamfered in the same shape. As a result, in the two internal electrodes sandwiching the joint, substantially the same number of portions facing the same side surface and portions facing the opposite side surface were formed.

(Example 3)
This example is an example in which a unit-bonded laminated piezoelectric element in which the electric field strength at the joint of the laminated-type piezoelectric element unit is reduced was manufactured, and its driving durability was evaluated.
As shown in FIG. 9, the multilayer piezoelectric element unit of this embodiment is a unit-bonded multilayer piezoelectric element in which two or more multilayer piezoelectric element units 35 in which piezoelectric ceramic layers 351 and internal electrode layers 353 are alternately laminated are stacked. 3. The internal electrode layer 353 is mainly composed of a conductive base metal material having a larger standard Gibbs free energy for generating a metal oxide at a firing temperature than the ceramic material constituting the piezoelectric ceramic layer 351. When the average electric field strength between the internal electrode layers 353 of the multilayer piezoelectric element unit 35 is E1, the distance between two adjacent internal electrode layers 353 sandwiching the joint 37 at which the multilayer piezoelectric element units 35 join is sandwiched. The electric field strength E has a relationship of E <(1/2) E1.

As shown in FIG. 9, the unit-bonded laminated piezoelectric element 3 of the present embodiment has a laminated piezoelectric element unit 35 joined at a joint 37 as in the first embodiment. The unit-bonded laminated piezoelectric element 3 of this example is formed by bonding 20 laminated piezoelectric element units 35. In each laminated piezoelectric element unit 35, 20 piezoelectric ceramic layers 351 are laminated. In FIG. 9, the number of stacked piezoelectric element units 35 and the number of stacked piezoelectric ceramic layers 351 in the stacked piezoelectric element unit 35 are omitted for convenience of drawing. Each laminated piezoelectric element unit 35 is formed by alternately laminating a piezoelectric ceramic layer 351 made of a PZT-based material and an internal electrode layer 353 made of Cu.
Further, as in the first embodiment, the internal electrode layer 353 is formed so as to reach only one side surface of the piezoelectric ceramic layer 351. Further, two side electrodes 39 are formed on the side surfaces of the unit-bonded laminated piezoelectric element 3 so as to sandwich the same.

As in the first embodiment, the method of manufacturing the unit-bonded laminated piezoelectric element 3 of the present embodiment includes an electrode printing step, a pressure bonding step, a degreasing step, a firing step, and an overlapping step. Each step is the same as in Example 1.
Further, in the manufacturing method of this example, as a paste material for an electrode to be printed on a ceramic green sheet, a conductive base metal having a larger standard Gibbs free energy for forming a metal oxide at a firing temperature than the ceramic material constituting the ceramic green sheet is used. A material composed of a material and / or an oxide thereof is used. When the average electric field strength between the respective internal electrode layers of the multilayer piezoelectric element unit is E1, the electric field strength E between two adjacent internal electrode layers sandwiching the joint is E <(1/2) E1. To do.

Hereinafter, a method of manufacturing the multilayer piezoelectric element unit of the present example will be described with reference to FIGS.
First, the same ceramic material as in Example 1 was prepared, formed into a sheet by a doctor blade method, dried at 80 ° C., cut into 100 mm × 100 mm by a sheet cutter, and a ceramic green sheet having a thickness of 150 μm was obtained. Produced.
Further, in the same manner as in Example 1, an electrode paste material was produced. In this example, the paste material for the electrode has a weight ratio of Cu and CuO of 50:50, and the weight of Cu and CuO is 65% by weight of the total weight of the paste material for the electrode. Using.

Next, as in Example 1, this electrode paste material was applied to a plurality of ceramic green sheets. At this time, similarly to the first embodiment, the electrode paste material is applied to one surface of the ceramic green sheet so as to reach only one side surface of the ceramic green sheet, and the other side surface is covered with the crocodile. A non-formed portion was provided.
Next, the ceramic green sheets on which the electrode paste material was printed were laminated. At this time, as in the case of Example 1, the electrode paste materials were laminated such that they reached the left and right side surfaces alternately.

In this way, the ceramic green sheets were sequentially laminated, and as shown in FIG. 10, a total of 20 ceramic green sheets 451 were laminated to produce a laminate 45. As shown in the figure, in the laminate 45, ceramic green sheets 451 and electrode paste materials 453 are alternately laminated. The electrode paste material 453 printed on each ceramic green sheet 451 reaches only one side surface of the multilayer body 45, and the non-formed portion 359 is provided on the other side.
In this example, when the ceramic green sheets 451 are stacked to form the laminate 45, two ceramic green sheets having a large thickness of 330 μm are prepared, and as shown in FIG. That is, these thick ceramic green sheets 455 were laminated on the lowermost and uppermost stages. In the two ceramic green sheets 455 laminated on both ends of the laminated body 45, the ceramic green sheet disposed at the lowermost stage of the laminated body 45 is the one printed with the electrode paste material in the same manner as described above. As the ceramic green sheet disposed on the uppermost stage, the one on which the electrode paste material was not printed was used. Similarly, a total of 20 laminates 45 were produced.

Each of the twenty laminates 45 obtained above was fixed to a crimping jig, and thermocompression-bonded at 110 ° C. for 1 minute at 16 MPa. The thermocompression-bonded laminate 45 was cut into a size of 86 mm in length and 86 mm in width by a sheet cutter, and then flattened by applying a pressure of 7.8 MPa in the laminating direction at room temperature.
Subsequently, each of the laminates 45 was placed in a gas circulation type degreasing furnace and heated at a temperature of 550 ° C. for 10 hours to perform degreasing.

  Next, the electrode paste material 453 applied on the ceramic green sheets 451 constituting the respective laminates 45 is reduced. In the reduction of the electrode paste material 453, CuO contained in the electrode paste material 453 is reduced to Cu. Specifically, the laminate 45 is heated in a reducing atmosphere.

In this example, since the ceramic green sheet 451 contains lead and the electrode paste material 453 contains Cu, the temperature immediately below or near 326 ° C., which is the eutectic point of lead and copper, was used as the heating temperature. . Specifically, the temperature is 320 ° C. ± 5 ° C. Note that ± 5 ° C is the fluctuation range of the actually measured value.
By this heating, the electrode paste material 453 applied to each ceramic green sheet 451 is reduced to form an internal electrode layer.

Next, the laminated body 45 is fired as described below to produce a laminated piezoelectric element unit 35 as shown in FIG.
The firing temperature during firing was 950 ° C., and the atmosphere was adjusted to an atmosphere in which Cu in the internal electrode layer was not oxidized as much as possible and oxides in the element portion were not reduced as much as possible. Specifically, the firing was performed while adjusting the oxygen partial pressure at a firing temperature of 950 ° C. to be 10 ⁻³ hPa (10 ⁻⁶ atm).

During this firing, the ceramic green sheets in the laminate are sintered to form a piezoelectric ceramic layer.
In this way, as shown in FIG. 11, 20 laminated piezoelectric element units 35 in which the piezoelectric ceramic layers 351 and the internal electrode layers 353 were alternately laminated were obtained. In the laminated piezoelectric element unit 35, as expected from the thickness of the ceramic green sheet before firing, the thickness of the piezoelectric ceramic layer 351 is about 90 μm, and the thickness of the internal electrode layer 353 is about 7 μm. It has a thickness of about 97 μm (about 100 μm). The outermost piezoelectric ceramic layer 355 of each laminated piezoelectric element unit 35 has a thickness about 2.2 times that of the internal piezoelectric ceramic layer 351. The laminated piezoelectric element unit 35 is formed by stacking a total of 20 piezoelectric ceramic layers 351 and 355.

  Next, Ag was baked on the side surfaces of these twenty stacked piezoelectric element units 35 at a temperature of 550 ° C. to 600 ° C., and the capacitance was measured to determine whether or not a particularly abnormal value was shown. did. At this time, the impedance at the resonance point of the multilayer piezoelectric element unit 35 can be measured in some cases.

Next, as shown in FIGS. 11 and 12, the twenty stacked piezoelectric element units 35 are overlapped with each other by forming the outermost surface in the stacking direction as a bonding surface 357 to form a bonding portion 37. did. At this time, as shown in FIG. 12, the stacked piezoelectric element units 35 were overlapped so that two adjacent internal electrode layers 353 sandwiching the joint 37 face different side surfaces. In this way, a total of 20 laminated piezoelectric element units 35 were overlapped on the joint surface 357, and as shown in FIG. Thereafter, a side electrode 39 made of Cu is attached with resin silver so as to sandwich the side surface of the unit-bonded laminated piezoelectric element 3, and the side electrode 39 is fixed to the unit-bonded laminated piezoelectric element 3 by heating at a temperature of 150 ° C. to 170 ° C. did.
Next, a lead wire was attached to the side surface electrode 39, and the lead wire was taken out from the upper part of the unit-bonded laminated piezoelectric element 3, and a contraction tube was put thereon to fix each laminated piezoelectric element unit 35. The unit-bonded laminated piezoelectric element 3 thus obtained was used as a sample E5. Note that, for convenience of drawing, FIG. 9 does not show a lead wire or a shrinkable tube.

  As shown in FIG. 12, in the unit-bonded laminated piezoelectric element of sample E5, adjacent internal electrode layers 353 sandwiching the bonding portion 37 are electrically connected to different side electrodes 39, respectively. The sum of the thickness of the two adjacent piezoelectric ceramic layers 355 sandwiching the joint 37 and the thickness of the joint 37 exceed twice the piezoelectric ceramic layer 351 inside the multilayer piezoelectric element unit 35.

Next, of the two side electrodes 39 of the unit-bonded laminated piezoelectric element 3 of the sample E5, a potential of 150 V was applied to one side electrode, and the other side electrode was grounded, and a voltage of about 150 V was applied to the sample E5. .
Next, the potential difference between two adjacent internal electrode layers 353 of the sample E5 was measured. The potential difference between the internal electrode layers was arbitrarily measured at 10 points excluding the potential difference between the two internal electrode layers sandwiching the joint. When the average potential difference was determined from all the measured potential differences, the average potential difference was 151 V.
In addition, in the sample E5, the thickness of the piezoelectric ceramic layer 351 was arbitrarily measured at ten places, and the average value was obtained. The average thickness was 90 μm. When the thickness of the piezoelectric ceramic layer is arbitrarily measured, the thickness of the piezoelectric ceramic layer 351 inside the laminated piezoelectric element unit 35 excluding the thickness of two adjacent piezoelectric ceramic layers 355 sandwiching the joint 37 is excluded. Was measured.

From the average potential difference calculated above and the average thickness of the piezoelectric ceramic layers, the average electric field strength E1 between the internal electrode layers of the multilayer piezoelectric element unit was determined as follows.
In general, the electric field strength is ideally measured by measuring the thickness of the piezoelectric ceramic layer and the potential difference between the internal electrode layers at the same position. It was calculated by dividing the potential difference by the average thickness of the piezoelectric ceramic layer. As a result, the average electric field intensity E1 was 1.68 V / μm.

The potential difference between two adjacent internal electrode layers 353 sandwiching the joint 37 in the sample E5 was 152 V, and the thickness of the two adjacent piezoelectric ceramic layers 355 sandwiching the joint 37 was equal to the thickness of the joint. It was 381 μm including the thickness. Therefore, the electric field strength E between two adjacent internal electrode layers 353 sandwiching the joint 37 was 0.40 V / μm.
Therefore, in the sample E5, the electric field strength E between the two adjacent internal electrode layers 353 sandwiching the joint 37 is about ４ of the average electric field strength between the internal electrode layers 353 inside the multilayer piezoelectric element unit 35. Had become one.

  The thickness of the two adjacent piezoelectric ceramic layers 355 sandwiching the joint 37 in the sample E5 (or the thickness of the portion sandwiched between the two internal electrodes sandwiching the joint) is 381 μm as described above. It is smaller than 330 (μm) × 90 (μm) / 150 (μm) × 2 (layer) = 396 (μm) (or 396 μm + thickness of the joint) expected from the thickness ratio of the ceramic green sheet in the previous stage. Has become. It is considered that the reason for this is that the two piezoelectric ceramic layers 355 adjacent to the joining portion 37 are on the surface of the laminated piezoelectric element unit 35 at the time of firing, so that the reaction occurs quickly and the thickness is reduced. However, there is no problem in thickness comparison.

Further, in this example, as shown in FIG. 13, two adjacent internal electrode layers 153 sandwiching the joint 17 are both electrically connected to the same side electrode 19, similarly to the samples E1 to E3 of the first embodiment. As a result, the unit-bonded laminated piezoelectric element 1 in which the laminated piezoelectric element units 15 were overlapped was manufactured. This was designated as Sample E6. Therefore, in the sample E6, almost no voltage is applied to the junction, and the electric field intensity E at the junction becomes almost equal to zero.
Further, as shown in the figure, in the unit-bonded laminated piezoelectric element 1 of the sample E6, the thickness of each of the two adjacent piezoelectric ceramic layers 151 sandwiching the joint 17 is the same as the thickness of the piezoelectric ceramic in the laminated piezoelectric element unit 15. It is the same as the thickness of the layer 151.
Further, the sample E6 is formed by stacking twenty laminated piezoelectric element units 15 each composed of 20 piezoelectric ceramic layers 151 in the same manner as the sample E5. Other configurations are the same as those of the sample E5.

Further, in this example, as shown in FIG. 14, the thickness of the outermost piezoelectric ceramic layer 755 of the multilayer piezoelectric element unit 75 is set to be larger than that of the inner piezoelectric ceramic layer 751 for comparison between the sample E5 and the sample E6. The laminated piezoelectric element unit 7 manufactured by stacking the reduced laminated piezoelectric element units 75 was prepared. This was designated as Sample C5.
That is, as shown in FIG. 14, in the sample C5, the thickness of the outermost piezoelectric ceramic layer 755 of the multilayer piezoelectric element unit 75 is 83 μm, and the thickness of the internal piezoelectric ceramic layer 751 is 90 μm. The total thickness of the two adjacent piezoelectric ceramic layers 755 sandwiching 77 (about 7 μm) and the thickness of the bonding portion 77 is about 173 μm, which is twice (180 μm) the thickness of the piezoelectric ceramic layer 751 inside the multilayer piezoelectric element unit 75. Less than.
In the sample C5, two adjacent internal electrode layers 753 sandwiching the joint 77 are electrically connected to different side electrodes 79.
Therefore, in the sample C5, the electric field strength E between two adjacent internal electrode layers sandwiching the joint 77 is larger than half the average electric field strength E1 between the internal electrode layers 753 of the multilayer piezoelectric element unit 75. .

Next, a driving durability test was performed on the samples E5, E6, and C5 in order to examine their durability.
Specifically, first, a rectangular wave current having a low current value of 0 A, a high current value of 13 A, a frequency of 60 kHz, and a duty ratio of 50% was passed through the samples E5, E6, and C5 for 150 μs. The battery was charged and the voltage reached 150 V. After maintaining the charged state for 2 ms, the battery was discharged with a rectangular wave current having a low current value of -13 A, a high current value of 0 A, a frequency of 50 kHz, and a duty ratio of 50%, and the voltage value reached 0 V. A drive endurance test in which such charge / discharge was applied to each sample at a cycle of 20 Hz was performed. In addition, the current at the time of discharge in which the current value is indicated by minus means that the current has flowed in the opposite direction to that at the time of charging.

In the above driving durability test, each time charging and discharging were repeated 0.5 × 10 ⁸ times (the number of times converted from the durability driving time and the frequency of 20 Hz), the resonance characteristics were measured as shown in FIG. 15 and the change was observed. .
In FIG. 15, the horizontal axis represents frequency, and the vertical axis represents impedance. Here, the resonance characteristic means a value obtained by measuring the impedance mainly at every 1 kHz and plotting the frequency dependence of the impedance by a measured value in the range of 1 kHz to 100 kHz. In this measurement, in the vicinity of the resonance point where the impedance shows the minimum value (arrow A in the figure) and near the anti-resonance point where the impedance shows the maximum value (arrow B in the figure), the measurement was performed by narrowing the frequency division to 0.1 kHz. , Plotted on a graph.
In FIG. 15 and FIGS. 16 to 19 to be described later, a frequency region that is less involved in resonance / semi-resonance is omitted.
FIG. 15 shows the resonance characteristics (initial characteristics) of the sample E5 at the start of charging and discharging. Although not shown in the figure, Sample E6 and Sample C5 also exhibited the same initial characteristics as Sample E5 shown in FIG.

As a result of the above driving durability test, in the sample C5, after driving 1.5 × 10 ⁸ times, as shown in FIG. 16, the resonance point and the anti-resonance point peculiar to the piezoelectric characteristics did not appear. Then, the shrinkable tube was removed from the sample C5, and the multilayer piezoelectric element unit of the sample C5 was visually observed.
Next, the side electrode of the sample C5 was removed, and a new side electrode was attached again. At this time, the method of attaching the side electrodes is the same as the method of attaching the side electrodes before removal.
Thereafter, when the resonance characteristics of the sample C5 were measured again, at least the anti-resonance point (arrow C in the figure) was reproduced as shown in FIG. The resonance point, that is, the frequency at which the impedance has a minimum value, is hard to identify because the increase and decrease of the impedance appears fine as shown by the arrow D in FIG. 17, but since the impedance has decreased and the anti-resonance point has been reached. It is considered that a resonance point exists.
As described above, in the sample C5, the resonance characteristics were reproduced by replacing the side electrodes. Therefore, as shown in FIG. 16, the reason why the resonance characteristics disappeared after driving 1.5 × 10 ⁸ times is that a larger load was applied to the side surface electrode and the multilayer piezoelectric element in the unit-bonded multilayer piezoelectric element. It is considered that the variation at the junction of the element units is a factor.

On the other hand, when the same drive endurance test was performed on sample E5, as shown in FIG. 18, the resonance characteristics changed after 8.5 × 10 ⁸ times of drive. FIG. 18 shows the resonance characteristic (measured value after driving 8.0 × 10 ⁸ times) of the sample E5 after driving 8.5 × 10 ⁸ times and the resonance characteristic after driving 8.5 × 10 ⁸ times. The characteristics are also shown.
As can be seen from FIG. 18, in the sample E5, the resonance characteristic was obtained even after driving 8.5 × 10 ⁸ times. However, after driving 8.5 × 10 ⁸ times, the impedances were not constantly measured, and the data after driving 8.5 × 10 ⁸ times in FIG. 9 is a plot of instantaneous readings in a state where the width is relatively large. Therefore, the reliability of the resonance characteristics is low.

Further, as is known from the figure, the minimum value (arrow E 'in the figure) and the maximum value (arrow F' in the figure) of the impedance after driving the sample E5 8.5 × 10 ⁸ times are 8.5. minimum value of the impedance before driving × 10 ⁸ times are shifted respectively to the low frequency side as compared with (in the arrow E) and maximum values (in the arrow F). That is, after driving 8.5 × 10 ⁸ times, the resonance point and the anti-resonance point are shifted to the lower frequency side. From this, it can be seen that in the sample E5, after driving 8.5 × 10 ⁸ times, a change occurs in the medium that resonates. Also, comparing FIG. 18 with FIG. 15, the resonance point and the anti-resonance point after driving 8.5 × 10 ⁸ times are much lower than the resonance point and the anti-resonance point at the start of charging and discharging. It can be seen that it is shifted to the frequency side.

Next, when the side electrode of the sample E5 after driving 8.5 × 10 ⁸ times was observed with a microscope in the same manner as in the case of the sample C5, the side electrode was partially broken. Then, like the sample C5, the side electrode was replaced with a new side electrode. As a result, the sample E5 showed a resonance point near the frequency of 22 to 24 kHz and an anti-resonance point near the frequency of 26 to 27 kHz, similarly to the start of charge / discharge (at the time of initial characteristics). That is, by replacing the side electrodes, the resonance characteristics were restored to the same as the initial characteristics at the start of charging / discharging (see FIG. 15).

In addition, as for the sample E6, as a result of the above-mentioned driving durability test, the resonance characteristics disappeared as shown in FIG. 19 after driving at 10.5 × 10 ⁸ . After the disappearance of the resonance characteristic, when the side electrode of the sample E6 was visually observed, a break occurred in the side electrode as in the case of the sample C5. Also in the sample E6, as in the case of the sample C5, the resonance characteristics were reproduced when the side electrodes were replaced.
It should be noted that Sample E5, Sample E6, and Sample C5 in the state where the side electrode was replaced did not show any deterioration in displacement with respect to the initial characteristics before the side electrode was replaced.

As described above, in the drive durability test of the unit-bonded laminated piezoelectric elements (samples E5, E6, and C5), sample C5, which is considered to have a relatively large load (electric field strength) on the bonding portion, is 1. With a relatively short drive count of 5 × 10 ⁸ times, the side electrodes were interrupted, and the resonance characteristics peculiar to the piezoelectric element were impaired.
On the other hand, in the samples E5 and E6, the resonance characteristics could be maintained up to the relatively long driving times of 8.5 × 10 ⁸ times and 10.5 × 10 ⁸ times, respectively.
That is, it can be seen that the samples E5 and E6 have better durability than the sample C5.

FIG. 2 is an explanatory view showing the entire unit-bonded laminated piezoelectric element according to the first embodiment. FIG. 2 is an explanatory view showing a state in which a paste material for an electrode is applied to a ceramic green sheet according to the first embodiment. FIG. 4 is an explanatory diagram showing a state in which ceramic green sheets are laminated in a pressure bonding step according to the first embodiment. FIG. 2 is an explanatory view showing a laminate after a pressure bonding step according to the first embodiment. FIG. 2 is an explanatory view showing the entire multilayer piezoelectric element unit according to the first embodiment. FIG. 3 is an explanatory diagram showing an arrangement pattern of internal electrode layers near a joint in a unit-bonded laminated piezoelectric element (samples E1 to E3) according to the first embodiment. FIG. 3 is an explanatory diagram showing an arrangement pattern of internal electrode layers near a joint in a unit-bonded laminated piezoelectric element (samples C1 to C3) according to the first embodiment. FIG. 7 is an explanatory diagram showing the entire chamfered laminate according to the second embodiment. FIG. 9 is an explanatory view showing the entire unit-bonded laminated piezoelectric element (sample E5) according to a third embodiment. FIG. 11 is an explanatory view showing a laminate after a pressure bonding step according to the third embodiment. FIG. 9 is an explanatory view showing the entire multilayer piezoelectric element unit according to a third embodiment. FIG. 9 is an explanatory diagram showing a configuration near a joint in a unit-joined laminated piezoelectric element (sample E5) according to a third embodiment. FIG. 9 is an explanatory diagram showing a configuration near a bonding portion in a unit bonded laminated piezoelectric element (sample E6) according to a third embodiment. FIG. 9 is an explanatory diagram showing a configuration near a bonding portion in a unit bonded laminated piezoelectric element (sample C5) according to a third embodiment. 13 is a graph showing resonance characteristics (initial characteristics) at the start of charging and discharging of the unit-bonded laminated piezoelectric element (sample E5) according to Example 3. 9 is a graph showing the dependence of impedance on the frequency of sample C5 when a break occurs in a side electrode of a unit-bonded laminated piezoelectric element (sample C5) according to Example 3. 11 is a graph showing the resonance characteristics of the sample C5 after replacing the side electrodes of the unit-bonded laminated piezoelectric element (sample C5) according to the third embodiment. 9 is a graph showing the dependence of impedance on the resonance characteristic or frequency of sample E5 before and after the side electrode of the unit-bonded laminated piezoelectric element (sample E5) according to the third embodiment. 11 is a graph showing the dependence of impedance on the frequency of sample E6 when a break occurs in the side electrode of the unit-bonded laminated piezoelectric element (sample E6) according to Example 3.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Unit bonding laminated piezoelectric element 15 Laminated piezoelectric element unit 151 Piezoelectric ceramic layer 153 Internal electrode layer 159 Non-formed part 17 Joint part 19 Side electrode

Claims (28)

In a unit-bonded laminated piezoelectric element comprising two or more laminated piezoelectric element units in which piezoelectric ceramic layers and internal electrode layers are alternately laminated,
The internal electrode layer is mainly composed of a conductive base metal material having a larger standard Gibbs free energy for generating metal oxides at the firing temperature than the ceramic material constituting the piezoelectric ceramic layer,
Assuming that the average potential difference between the respective internal electrode layers of the multilayer piezoelectric element unit is V1, the potential difference V between two adjacent internal electrode layers sandwiching the joint between the multilayer piezoelectric element units is V <(1 / 2) A unit-bonded laminated piezoelectric element having a relationship of V1.   2. The device according to claim 1, wherein the average potential difference V1 between the internal electrode layers of the multilayer piezoelectric element unit and the potential difference V between two adjacent internal electrode layers sandwiching the joint portion are further expressed as V ≦ (３) V1. A unit-bonded laminated piezoelectric element having a relationship. In a unit-bonded laminated piezoelectric element comprising two or more laminated piezoelectric element units in which piezoelectric ceramic layers and internal electrode layers are alternately laminated,
The internal electrode layer is mainly composed of a conductive base metal material having a larger standard Gibbs free energy for generating metal oxides at the firing temperature than the ceramic material constituting the piezoelectric ceramic layer,
Assuming that the average electric field strength between the internal electrode layers of the laminated piezoelectric element unit is E1, the electric field strength E between two adjacent internal electrode layers sandwiching the joint portion where the laminated piezoelectric element units are joined is E <E < (1/2) A unit bonded laminated piezoelectric element having a relationship of E1.   In claim 3, the average electric field strength E1 between each internal electrode layer of the multilayer piezoelectric element unit and the electric field strength E between two adjacent internal electrode layers sandwiching the joint portion are further expressed as E ≦ (１ ／). A unit-bonded laminated piezoelectric element having a relationship of E1.   5. The unit-joined laminated piezoelectric element according to claim 1, wherein the unit-joined laminated piezoelectric element has one or more side electrodes sandwiching the side surface of the unit-joined laminated piezoelectric element, and the joining part includes A unit-joined laminated piezoelectric element characterized in that two adjacent internal electrode layers sandwiching the same are electrically connected to side electrodes having substantially the same potential.   6. The piezoelectric ceramic layer according to claim 1, wherein the total thickness of two adjacent piezoelectric ceramic layers sandwiching the joint and the thickness of the joint is two times the thickness of the piezoelectric ceramic layer inside the multilayer piezoelectric element unit. 7. A unit-bonded laminated piezoelectric element characterized by more than double.   7. The unit-bonded laminated piezoelectric element according to claim 1, wherein the laminated piezoelectric element units are joined to each other at a joint portion via a resin material.   8. The unit-joined laminated piezoelectric element according to claim 7, wherein the resin material contains a ceramic material and / or a metal material.   9. The unit bonding laminate according to claim 7, wherein the resin material has conductivity at least in part, and electrically connects adjacent piezoelectric ceramic layers sandwiching the bonding portion. Piezoelectric element.   7. The unit-bonded laminated piezoelectric element according to claim 1, wherein the laminated piezoelectric element units are directly contacted and joined to each other at the joint.   11. The unit-bonded laminated piezoelectric element according to claim 1, wherein the ceramic material contains a PZT-based material.   The unit-bonded laminated piezoelectric element according to any one of claims 1 to 11, wherein the conductive base metal material is Cu. In a method of manufacturing a unit-bonded laminated piezoelectric element in which two or more laminated piezoelectric element units in which piezoelectric ceramic layers and internal electrode layers are alternately laminated are laminated.
An electrode printing step of applying an electrode paste material to at least one surface of a ceramic green sheet formed of a ceramic material into a sheet shape;
A crimping step of laminating and crimping the ceramic green sheets coated with the electrode paste material to form a laminate;
A degreasing step of degreasing the laminate,
A firing step of firing the laminated body in a reducing atmosphere to produce a laminated piezoelectric element unit;
A superimposing step of forming a joint by laminating two or more of the laminated piezoelectric element units on the joint surfaces with the outermost surface in the laminating direction of the laminated piezoelectric element unit as a joint surface. ,
The paste material for an electrode is made of a conductive base metal material and / or an oxide thereof having a larger standard Gibbs free energy for forming a metal oxide at a firing temperature than the ceramic material constituting the ceramic green sheet,
When the average potential difference between the internal electrode layers of the laminated piezoelectric element unit is V1, the potential difference V between two adjacent internal electrode layers sandwiching the bonding portion is such that V <(1/2) V1. A method for manufacturing a unit-bonded laminated piezoelectric element, comprising:   14. The device according to claim 13, wherein the average potential difference V1 between the internal electrode layers of the multilayer piezoelectric element unit and the potential difference V between two adjacent internal electrode layers sandwiching the bonding portion are further expressed as V ≦ (１ ／) V1. A method of manufacturing a unit-bonded laminated piezoelectric element, characterized in that the relationship is satisfied. In a method of manufacturing a unit-bonded laminated piezoelectric element in which two or more laminated piezoelectric element units in which piezoelectric ceramic layers and internal electrode layers are alternately laminated are laminated.
An electrode printing step of applying an electrode paste material to at least one surface of a ceramic green sheet formed of a ceramic material into a sheet shape;
A crimping step of laminating and crimping the ceramic green sheets coated with the electrode paste material to form a laminate;
A degreasing step of degreasing the laminate,
A firing step of firing the laminated body in a reducing atmosphere to produce a laminated piezoelectric element unit;
A superimposing step of forming a joint by laminating two or more of the laminated piezoelectric element units on the joint surfaces with the outermost surface in the laminating direction of the laminated piezoelectric element unit as a joint surface. ,
The paste material for an electrode is made of a conductive base metal material and / or an oxide thereof having a larger standard Gibbs free energy for forming a metal oxide at a firing temperature than the ceramic material constituting the ceramic green sheet,
Assuming that the average electric field strength between the internal electrode layers of the multilayer piezoelectric element unit is E1, the electric field strength E between two adjacent internal electrode layers sandwiching the bonding portion is such that E <(1/2) E1. A method for manufacturing a unit-bonded laminated piezoelectric element, characterized in that:   16. The electric field strength E1 between the internal electrode layers of the laminated piezoelectric element unit and the electric field strength E between two adjacent internal electrode layers sandwiching the joint portion according to claim 15, wherein E ≦ (１ ／). A method for manufacturing a unit-bonded laminated piezoelectric element, wherein the method is configured to satisfy a relationship of E1.   17. The multilayer piezoelectric element unit or the unit-bonded multilayer piezoelectric element according to claim 13, wherein the multilayer piezoelectric element unit or the unit-bonded multilayer piezoelectric element is sandwiched between the multilayer piezoelectric element unit after the firing step or the unit-bonded multilayer piezoelectric element after the overlapping step. Wherein one or more side electrodes are provided on each side surface.   18. The method according to claim 17, wherein in the overlapping step, two adjacent internal electrode layers sandwiching a joint between the stacked piezoelectric element units are stacked so as to be electrically connected to side electrodes having substantially the same potential. A method for producing a unit-bonded laminated piezoelectric element, which is characterized in that:   20. The piezoelectric ceramic layer according to claim 13, wherein a total thickness of two adjacent piezoelectric ceramic layers sandwiching the joint and the thickness of the joint is two times the thickness of the piezoelectric ceramic layer inside the multilayer piezoelectric element unit. A method of manufacturing a unit-bonded laminated piezoelectric element, characterized in that the piezoelectric element is configured to exceed the number of times.   20. The method according to any one of claims 13 to 19, wherein in the overlapping step, the multilayer piezoelectric element units are joined with a resin material.   21. The method according to claim 20, wherein the resin material contains a ceramic material and / or a metal material.   22. The unit bonding laminate according to claim 20, wherein the resin material has conductivity at least in part, and electrically connects adjacent piezoelectric ceramic layers sandwiching the bonding portion. A method for manufacturing a piezoelectric element.   20. The method of manufacturing a unit-bonded laminated piezoelectric element according to claim 13, wherein in the overlapping step, the laminated piezoelectric element units are brought into direct contact with each other and joined.   24. The method according to claim 13, wherein the piezoelectric ceramic layer contains a PZT-based material.   The method according to any one of claims 13 to 24, wherein the conductive base metal material is Cu.   26. The multi-layer piezoelectric element unit according to claim 13, wherein the multi-layer piezoelectric element unit has n rotational symmetry (where n is a natural number of 3 or more). A method of manufacturing a unit-bonded laminated piezoelectric element, comprising chamfering one or more corners and n-1 or less corners so as to have a shape different from other remaining corners. In a method of manufacturing a unit-bonded laminated piezoelectric element in which two or more laminated piezoelectric element units in which piezoelectric ceramic layers and internal electrode layers are alternately laminated are laminated.
An electrode printing step of applying an electrode paste material to at least one surface of a ceramic green sheet formed of a ceramic material into a sheet shape;
A crimping step of laminating and crimping the ceramic green sheets coated with the electrode paste material to form a laminate;
A degreasing step of degreasing the laminate,
A firing step of firing the laminated body in a reducing atmosphere to produce a laminated piezoelectric element unit;
A superimposing step of forming a joint by laminating two or more of the laminated piezoelectric element units on the joint surfaces with the outermost surface in the laminating direction of the laminated piezoelectric element unit as a joint surface. ,
The paste material for an electrode is made of a conductive base metal material and / or an oxide thereof having a larger standard Gibbs free energy for forming a metal oxide at a firing temperature than the ceramic material constituting the ceramic green sheet,
The laminated piezoelectric element unit has n rotational symmetry (where n is a natural number of 3 or more), and one or more and n-1 or less of n corners of the laminated piezoelectric element unit. Characterized in that the corners are chamfered so as to have a shape different from the remaining corners.   28. The method according to claim 26, wherein the number of corners to be chamfered and the shape of the chamfers are standardized in the entire stacked piezoelectric element unit to be stacked.

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