JP2005005680A - Piezoelectric actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric actuator which is suitable for injector etc. and excellent in durability and stable in its characteristics. <P>SOLUTION: The piezoelectric actuator 1 comprises a piezoelectric device unit 15 in which a ceramic layer 151 and internal electrode layers 153 and 154 are accumulated. The piezoelectric device unit 15 is formed by accumulating more than 50 layers of the piezoelectric ceramic layer 151. It includes a pair of external electrodes 5 and 6 of different potential on its sides. The internal electrodes 153 and 154, having electrode exposed parts 158 and 159 that are exposed in sides of the piezoelectric device unit 15, are connected to one of the pair of external electrodes 5 and 6 through these exposed parts and alternated their counterparts every layer. In the periphery of the internal electrode layers 153 and 154, recessed parts 155 in which these layers are recessed from the side of the piezoelectric device unit 15 are partially formed. The minimum width L of the recessed part 155 and its error W satisfy 0.1mm≤L≤1.0mm, W≤0.5mm. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a piezoelectric actuator used as a drive source such as an injector.

Conventionally, it has been proposed to use a piezoelectric element as a drive source for an injector (fuel injection device) or the like of an internal combustion engine of an automobile. In particular, since an injector needs to repeat spraying of fuel at a very high speed as many as 10 ⁸ times or more, a very severe use state is imposed on a piezoelectric element serving as a driving source. Therefore, the piezoelectric element for the injector is required to have not only excellent piezoelectric characteristics but also excellent durability.

  As such a piezoelectric element, a laminated piezoelectric actuator formed by alternately laminating a plurality of piezoelectric ceramic layers that are displaced according to an applied voltage and an internal electrode layer for supplying an applied voltage is most promising. This is because the piezoelectric actuator can generate a large driving source because the piezoelectric ceramic layers sandwiched between the internal electrode layers are displaced when a voltage is applied.

  However, the conventional piezoelectric actuator has a problem that a large stress is generated inside the actuator when a voltage is applied, and a crack is generated inside the actuator. Therefore, the conventional piezoelectric actuator is difficult to drive for a long period of time, and particularly difficult to apply to an injector or the like that is forced to use severely.

  In order to solve such a conventional problem, there has been proposed a laminated piezoelectric actuator in which end positions of the internal electrode layers that are not connected to the external electrodes are shifted in the overlapping direction of the internal electrode layers (see Patent Document 1). ). As described above, it is said that the stress generated in the actuator can be relieved by arranging the internal electrode layers so that the positions of the end portions thereof are shifted.

JP 2001-230463 A (Claims)

  However, when the conventional multilayer piezoelectric actuator is used for an injector or the like that requires harsh usage conditions, stress is increased inside the actuator by causing a shift at the end of the internal electrode as described above. There is a problem that cracks occur, and the conventional multilayer piezoelectric actuator is not sufficient in durability. There is also a problem that variations in characteristics such as capacitance and displacement characteristics increase.

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a piezoelectric actuator having excellent durability and stable characteristics suitable for applications such as injectors.

A first invention is a piezoelectric actuator having a piezoelectric element unit in which piezoelectric ceramic layers and internal electrode layers are alternately stacked.
The piezoelectric element unit is formed by stacking 50 or less piezoelectric ceramic layers, and has a pair of external electrodes having different potentials on its side surface.
The internal electrode layer has an electrode exposed portion exposed on a side surface of the piezoelectric element unit, and is connected to one of the pair of external electrodes through the electrode exposed portion, and alternately every other layer. The external electrode at the connection destination has been changed,
Further, around the internal electrode layer, a holding portion that is a region where the internal electrode layer is retreated from the side surface of the piezoelectric element unit is partially formed,
In a cross section in the stacking direction of the piezoelectric element actuator, a minimum width L that is a minimum distance from a side surface of the piezoelectric element unit to an end of each internal electrode layer in each holding portion, and the piezoelectric element unit in each holding portion The variation width W, which is the difference between the maximum and minimum distances from the side surface to each internal electrode layer, satisfies the relationship expressed by the following formula (1) (claim 1).
0.1 mm ≦ L ≦ 1.0 mm, W ≦ 0.5 mm (1)

In the piezoelectric actuator according to the first aspect of the present invention, the minimum width L of the holding portion and the variation width W satisfy the relationship of the above formula (1).
Therefore, in the piezoelectric element unit, the variation in the area of the overlapping portion of the internal electrode layers (hereinafter referred to as a piezoelectric active region as appropriate) is reduced, and characteristics such as capacitance and displacement are stabilized.

  In addition, as described above, by limiting the minimum width L and the variation width W of the storage portion, a piezoelectric ceramic layer that is in contact with the storage portion and is not easily displaced when a voltage is applied (hereinafter referred to as a piezoelectric inactive portion as appropriate). ) And the piezoelectric active region, and it is possible to prevent cracks from occurring inside the piezoelectric actuator. Therefore, the durability of the piezoelectric actuator is improved.

The piezoelectric element unit is formed by stacking 50 or less piezoelectric ceramic layers.
Thus, the stress generated in the unit when a voltage is applied is suppressed by setting the number of stacked piezoelectric element units to 50 or less. Therefore, it is possible to prevent the occurrence of cracks generated in the piezoelectric element unit.

  As described above, according to the first aspect of the present invention, it is possible to provide a piezoelectric actuator having excellent durability and stable characteristics suitable for applications such as an injector.

Next, a second invention is a piezoelectric actuator having a piezoelectric element unit in which piezoelectric ceramic layers and internal electrode layers are alternately laminated.
The piezoelectric element unit has a pair of external electrodes with different potentials on its side surface,
The internal electrode layer has an electrode exposed portion exposed on a side surface of the piezoelectric element unit, and is connected to one of the pair of external electrodes through the electrode exposed portion, and alternately every other layer. The external electrode at the connection destination has been changed,
Further, around the internal electrode layer, a holding portion that is a region where the internal electrode layer is retreated from the side surface of the piezoelectric element unit is partially formed,
One of the pair of external electrodes is a first external electrode, the other is a second external electrode, the internal electrode layer connected to the first external electrode is a first internal electrode layer, and is connected to the second external electrode. When the internal electrode layer is a second internal electrode layer,
When the first internal electrode layer and the second internal electrode layer are seen through from the laminating direction, the first internal electrode layer does not overlap with each other so that the electrode exposed portions do not overlap each other. In the portion where the electrode exposed portion is exposed, the electrode exposed portion of the second internal electrode layer is not exposed,
Further, the area of one of the first internal electrode layer and the second internal electrode layer is larger than the area of the other,
In addition, when the first internal electrode layer and the second internal electrode layer are seen through from the stacking direction, the piezoelectric activity is an area where the first internal electrode layer and the second internal electrode layer overlap The outer periphery of the region is the outer periphery A, and the outer periphery B is the portion of the outer periphery A where the larger internal electrode layer of the first internal electrode layer and the second internal electrode layer covers the outer periphery A. When the length of the outer periphery A is A and the length of the outer periphery B is B, the piezoelectric actuator is characterized by satisfying the relational expression B ≧ 0.5 × A (Claim 3).

Hereinafter, the function and effect of the second invention will be described with reference to FIG.
FIG. 10 is a view of the piezoelectric actuator as seen through the first internal electrode layer 153 and the second internal electrode layer 154 from the stacking direction.
In the piezoelectric actuator according to the second aspect of the present invention, when the first internal electrode layer 153 and the second internal electrode layer 154 are seen through from the stacking direction, the two are mutually exposed to the electrode exposed portion 158, 159 does not overlap.

The area of one of the first internal electrode layer 153 and the second internal electrode layer 154 is larger than the other area.
In addition, when the first internal electrode layer 153 and the second internal electrode layer 154 are seen through from the stacking direction, the first internal electrode layer 153 and the second internal electrode layer 154 overlap each other. The outer periphery of the piezoelectric active region is defined as an outer periphery A, and the inner electrode layer having the larger area of the first internal electrode layer 153 and the second internal electrode layer 154 covers the outer periphery A. Assuming that the portion of the outer periphery is the outer periphery B, if the length of the outer periphery A is A and the length of the outer periphery B is B, the relational expression B ≧ 0.5 × A is satisfied.

  Therefore, the variation in the area of the overlapping region (piezoelectric active region 150; the region surrounded by the dotted line in FIG. 10) of the two adjacent internal electrode layers 153 and 154 is caused when the internal electrode layers 153 and 154 are stacked. It becomes difficult to be affected by the positional deviation of the. Therefore, the piezoelectric actuator has excellent durability and can stabilize characteristics such as capacitance and displacement.

Further, the internal electrode layer in the piezoelectric element unit has an electrode exposed portion exposed on a side surface of the piezoelectric element unit. And when said 1st internal electrode layer and said 2nd internal electrode layer see through these from the lamination direction, both said 1st internal electrode layer so that the said electrode exposure part may not mutually overlap The electrode exposed portion of the second internal electrode layer is not exposed at the exposed portion of the electrode exposed portion.
That is, the electrode exposed portions of the first internal electrode layer and the second internal electrode layer are not exposed on the same side surface of the piezoelectric element unit. Therefore, an electrical short circuit due to creeping discharge on the side surface of the piezoelectric element unit can be prevented.

In the first invention (invention 1), the piezoelectric element unit is formed by stacking 50 or less piezoelectric ceramic layers.
Here, FIG. 21 shows a result obtained by simulation of the relationship between the number of stacked piezoelectric ceramic layers and the stress generated in the piezoelectric element unit.
The simulation was performed by piezoelectric analysis using a finite element method.

  As is known from FIG. 21, generally, as the number of the piezoelectric ceramic layers stacked increases, the stress generated in the unit increases. In particular, when the number of layers exceeds 50, a large internal stress is generated when a voltage is applied. As a result, cracks may occur in the piezoelectric element unit.

Further, in the cross section in the stacking direction of the piezoelectric element unit, the minimum width L and the variation width W in the holding portion satisfy the relationship of the following formula (1).
0.1 mm ≦ L ≦ 1.0 mm, W ≦ 0.5 mm (1)

Here, first, the minimum width L and the variation width W of the above-described recording portion will be described with reference to FIG.
FIG. 3 is a partially enlarged view of a cross section in the stacking direction of the piezoelectric actuator according to an example of the present invention described later. As shown in the figure, the piezoelectric actuator 1 includes piezoelectric element units 15 in which piezoelectric ceramic layers 151 and internal electrode layers 153 and 154 are alternately stacked.

At the position where the internal electrode layers 153 and 154 are stacked, a holding portion 155 which is a region where the internal electrode layers 153 and 154 recede from the side surface of the piezoelectric element unit 15 is partially formed around the internal electrode layers 153 and 154. Is formed.
Here, the minimum width L of the holding portion 155 is the distance from the side surface of the piezoelectric element unit 15 in each of the holding portions 155 to the ends of the internal electrode layers 153 and 154 in the cross section in the stacking direction of the piezoelectric actuator 1. Can be represented by the minimum value of.
The variation width W of the holding portion 155 is the maximum distance from the side surface of the piezoelectric element unit 15 to the end portions of the internal electrode layers 153 and 154 in each of the holding portions 155 in the cross section in the stacking direction of the piezoelectric actuator 1. It can be expressed by the difference between the value and the minimum value.

When the minimum width L of the storage portion is less than 0.1 mm, the occurrence of cracks may not be effectively suppressed regardless of the variation width W.
On the other hand, when the thickness exceeds 1.0 mm, the piezoelectric active region is relatively small when compared with the same size, and the characteristics of the piezoelectric element such as the displacement generating force may be deteriorated.

Further, FIG. 22 shows the result of the relationship between the variation width of the holding portion and the stress generated in the piezoelectric element unit obtained by simulation.
The simulation was performed by piezoelectric analysis using the finite element method as described above.

As is known from FIG. 22, generally, the stress generated in the unit increases as the variation width of the holding portion increases.
In particular, when the variation width exceeds 0.5 mm, a large internal stress is generated when a voltage is applied. As a result, cracks may occur in the piezoelectric element unit.

In the first aspect of the invention, it is preferable that the relationship of the following formula (2) is satisfied (claim 2).
0.2 mm ≦ L ≦ 0.6 mm, W ≦ 0.3 mm (2)
In this case, the operational effect of the first invention can be further improved. That is, variations in the area of the piezoelectric active region can be suppressed, and the characteristics of the piezoelectric element such as the displacement generating force can be stabilized. Further, it is possible to further suppress the possibility of cracks occurring in the piezoelectric element unit by suppressing the internal stress generated when a voltage is applied.

  Next, in the second invention (invention 3), when the first internal electrode layer and the second internal electrode layer are seen through from the stacking direction, the first internal electrode layer and the second internal electrode layer The outer periphery of the piezoelectric active region, which is the region where the second internal electrode layer overlaps, is defined as the outer periphery A, and the inner electrode layer having the larger area of the first internal electrode layer and the second internal electrode layer is the outer periphery A. When a portion covering the outer periphery A to the outer side is defined as an outer periphery B, the relational expression B ≧ 0.5 × A is satisfied, where A is the length of the outer periphery A and B is the length of the outer periphery B.

  Here, in the case of B <0.5 × A, the variation in the area of the overlapping piezoelectric active region (region surrounded by a dotted line in FIG. 10 described later) between two adjacent internal electrode layers is the above-described internal region. It becomes easy to be affected by a positional deviation at the time of stacking the electrode layers, and there is a possibility that the capacitance and displacement of the piezoelectric actuator cannot be stabilized.

Further, it is preferable that the relational expression B ≧ 0.6 × A is satisfied (claim 4).
In this case, variations in the area of the piezoelectric active region due to misalignment when the internal electrode layers are stacked can be further suppressed, and characteristics such as capacitance and displacement of the piezoelectric actuator can be further stabilized.

Furthermore, the relational expression B ≦ 0.75 × A is satisfied, and the electrode exposed portion of the first internal electrode layer and the electrode exposed portion of the second internal electrode layer are exposed on the same side surface. Preferably, it is not present (claim 5).
In this case, the characteristics of the piezoelectric actuator can be stabilized by satisfying 0.6 × A ≦ B ≦ 0.75 × A. Furthermore, by preventing the exposed portions of the electrodes from being exposed on the same side surface, the effect of preventing electrical short-circuiting due to creeping discharge can be further enhanced.

Next, in the first and second inventions, the internal electrode layer has a variation at an outer edge of the internal electrode layer, and a width D of the variation is within D ≦ 0.2 mm. Preferred (claim 6).
In this case, stress can be prevented from concentrating on the outer edge of the internal electrode layer, and the durability of the piezoelectric actuator is further improved.

Next, the variation width D of the outer edge of the internal electrode layer will be described with reference to FIGS.
The internal electrode layer is formed on a green sheet that becomes a piezoelectric ceramic layer after firing, for example, by screen printing or the like. 13 is a partially enlarged view of the internal electrode layer 154 formed on the piezoelectric ceramic layer 151. FIG. 14 is a partially enlarged view of the outer edge of the internal electrode layer 154 in FIG. 13 (encircled by a dotted circle in FIG. 13). FIG.

As shown in the drawing, the outer edge of the internal electrode layer 154 formed by screen printing or the like is not a straight line due to the influence of the screen mesh or the like, but has a curved shape with a certain deviation. As shown in FIG. 14, when the center of the deviation is the deviation center line 199 at the outer edge of the internal electrode layer 154, the width of the deviation across the deviation center line 199 is the variation width D. That is, the variation width D means the size of variation at the outer edge of each internal electrode layer 154.
When the variation width D exceeds 0.2 mm, a large internal stress is generated when a voltage is applied, and cracks may occur in the piezoelectric element unit.

Moreover, it is preferable that the said external electrode has covered all the said electrode exposed parts (Claim 7).
In this case, variation in the bonding area with the external electrode can be reduced, and the transient characteristics of displacement can be stabilized. Further, it is possible to block adverse effects that may affect the internal electrode layer from the external environment.

  Next, the distance between the boundary between the electrode exposed portion and the holding portion on the side surface of the piezoelectric element unit and the external electrode provided on the side surface on the holding portion side of the piezoelectric element unit is the piezoelectric element The shortest distance along the side surface of the unit is preferably 0.2 mm or more.

  When the distance between the boundary between the electrode exposed portion and the holding portion and the external electrode provided on the side surface on the holding portion side is less than 0.2 mm, creeping discharge is generated on the surface of the piezoelectric actuator. May be more likely to occur.

The piezoelectric actuator is preferably formed by stacking a plurality of the piezoelectric element units.
In this case, a larger desired displacement amount can be obtained by stacking the piezoelectric element units having a predetermined displacement amount.

Furthermore, the outermost layer of the piezoelectric element unit is preferably active (claim 10).
In this case, it is possible to increase the amount of displacement per unit length in the stacking direction of the piezoelectric actuator by stacking a plurality of the piezoelectric element units, and among the piezoelectric ceramic layers in the piezoelectric element unit, By reducing the internal stress generated at the interface between the outermost layer, which is the outermost piezoelectric ceramic layer, and the inner drive layer, the occurrence of cracks can be suppressed.

The term “activity” as used herein means that the electric field strength applied to the outermost layer during operation is greater than or equal to the coercive electric field inside the piezoelectric element unit.
Specifically, this will be described with reference to FIG.
FIG. 23 shows the result of an experiment to determine the relationship between the electric field strength applied to the piezoelectric element unit against the coercive electric field of the piezoelectric element unit and the piezoelectric constant of the piezoelectric element unit.
In the figure, the horizontal axis represents the electric field strength {(electric field strength) / (coercive electric field)} applied to the piezoelectric element unit against the coercive electric field of the piezoelectric element unit, and the vertical axis represents the piezoelectric constant of the piezoelectric element unit. .

  As can be seen from FIG. 23, when the electric field strength of the outermost layer exceeds the coercive electric field of the piezoelectric element unit, the piezoelectric constant of the outermost layer increases. That is, this indicates that the outermost ceramic layer becomes active.

Next, the coercive electric field will be described.
FIG. 24 is an explanatory diagram of the coercive electric field (Ec). In the figure, the horizontal axis represents the electric field strength applied to the piezoelectric element unit, and the vertical axis represents the amount of displacement. The electric field strength is defined as plus (+) in the same direction as the polarization direction, and (−) in the direction opposite to the polarization direction.

  Then, starting from point A, first, an electric field strength is applied to the piezoelectric element unit in the same direction as the polarization direction, and the value is gradually increased. Accordingly, the displacement amount of the piezoelectric element unit increases. In addition, the displacement amount can measure the displacement in the stacking direction when a constant voltage is applied, and the displacement per unit length in the stacking direction can be used as the displacement amount. This displacement amount can be measured using a laser displacement meter, a capacitance displacement meter, or the like.

  Next, after the electric field strength reaches point B, the electric field strength is gradually lowered. This time, the amount of displacement decreases as the electric field strength decreases. Then, even after the electric field strength becomes zero, the electric field strength is gradually decreased continuously in the direction opposite to the polarization direction. In accordance with this, the amount of displacement further decreases. Then, when the electric field intensity reaches point C, the amount of displacement suddenly starts to increase. The absolute value of the electric field strength at this point is the coercive electric field Ec in the present invention.

Then, after the electric field strength reaches point D, the electric field strength is increased again. In accordance with this, the amount of displacement decreases this time. When the electric field strength becomes 0 and the electric field strength is further increased in the polarization direction, the amount of displacement suddenly starts to increase. Since the point D and the point C may be different, in the present invention, the coercive electric field when a voltage is applied in the direction opposite to the polarization direction is Ec.
As shown in FIG. 24, by further increasing the electric field strength after that, the state finally becomes substantially the same as point B, and thereafter the same behavior is repeated.

  As a method of activating the outermost layer of the piezoelectric element unit, for example, there is a method of applying a voltage to the outermost layer without applying a normal voltage. As a result, the outermost layer can be deformed as piezoelectric activity when a voltage is applied.

Next, the piezoelectric ceramic layer is preferably made of a PZT material.
In this case, taking advantage of the excellent piezoelectric properties of the PZT-based material {Pb (Zr, Ti) O 3 -based perovskite structure oxide}, as an actuator such as an injector. Performance can be improved.

  Moreover, as said internal electrode layer, the metal of Ag, Pd, Cu, Ni, Au, Pt, or 1 or more types chosen from these metals can be used, for example.

Next, the piezoelectric actuator is preferably used for an injector.
In this case, the excellent durability of the piezoelectric actuator can be sufficiently exhibited.

(Example 1)
Next, a piezoelectric actuator according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIGS. 1 to 3, the piezoelectric actuator 1 of this example includes piezoelectric element units 15 in which piezoelectric ceramic layers 151 and internal electrode layers 153 and 154 are alternately stacked.

  The piezoelectric element unit 15 is formed by stacking 50 or less piezoelectric ceramic layers 151 and has a pair of external electrodes 5 and 6 having different potentials on its side surface. The internal electrode layers 153 and 154 have electrode exposed portions 158 and 159 that are exposed on the side surfaces of the piezoelectric element unit 15, respectively, and any of the pair of external electrodes 5 and 6 through the electrode exposed portions 158 and 159. The external electrodes 5 and 6 to be connected are alternately changed every other layer.

Further, around the internal electrode layers 153 and 154, a holding portion 155 that is a region in which the internal electrode layers 153 and 154 recede from the side surface of the piezoelectric element unit 15 is partially formed.
As shown in FIG. 3, in the cross section in the stacking direction of the piezoelectric actuator 1, the minimum width L that is the minimum value of the distance from the side surface of the piezoelectric element unit 15 to the end of each internal electrode layer 153, 154 in each holding portion 155. The variation width W, which is the difference between the maximum and minimum distances from the side surfaces of the piezoelectric element unit 15 to the respective internal electrode layers 153 and 154 in each holding portion 155, satisfies the relationship of the following formula (1).
0.1 mm ≦ L ≦ 1.0 mm, W ≦ 0.5 mm (1)

Hereinafter, the piezoelectric actuator 1 of this example will be described in detail with reference to FIGS.
As shown in FIGS. 1 to 3, the piezoelectric actuator 1 of this example is formed by stacking 20 piezoelectric element units 15 to form a joint portion 13. Each piezoelectric element unit 15 is formed by alternately laminating piezoelectric ceramic layers 151 made of PZT materials and internal electrode layers 153 and 154 made of Ag and Pd. Although not shown in detail in the drawing for convenience in drawing, the number of piezoelectric ceramic layers 151 active as piezoelectric elements in each piezoelectric element unit 15 is 20 layers.

The internal electrode layers 153 and 154 have electrode exposed portions 158 and 159 exposed on the side surfaces of the piezoelectric element unit 15. At least a part of the electrode exposed portions 158 and 159 are electrically connected alternately to the external electrodes 5 and 6 having different potentials formed so as to sandwich the side surface of the piezoelectric element unit 15 in the stacking direction. ing. Therefore, in the piezoelectric actuator 1, the two adjacent internal electrode layers 153 and 154 are connected to electrodes having different potentials. In this example, the external electrodes 5 and 6 are made of Ag, but in addition, one or more selected from Pd, Cu, Ni, Au, Pt, or these metals can be used.
In addition, the external electrode 5 and the external electrode 6 having different potentials can have different shapes so that the polarity can be easily discriminated visually.

2 and 3, the piezoelectric element unit 15 is in contact with the piezoelectric ceramic layers 151 so as not to be exposed at the side surface of the piezoelectric element unit 15 at the position where the internal electrode layers 153 and 154 are stacked. The holding part 155 in which the internal electrode layers 153 and 154 do not exist is partially included. As shown in FIG. 3, the storage portion 155 is formed on substantially the same plane as the internal electrode layers 153 and 154, and the width of each storage portion 155 varies. The minimum width L and the variation width W of the holding portion 155 satisfy the relationship of the following formula (1).
0.1 mm ≦ L ≦ 1.0 mm, W ≦ 0.5 mm (1)

Next, a method for manufacturing the piezoelectric actuator 1 of this example will be described with reference to FIGS.
The piezoelectric actuator of this example can be manufactured using a widely used green sheet method. This green sheet is prepared as follows.
That is, first, powders such as lead oxide, zirconium oxide, titanium oxide, niobium oxide, and strontium carbonate, which are main raw materials of the piezoelectric material, are weighed so as to have a desired composition by a known method. In this example, the final composition is so-called PZT (lead zirconate titanate). In consideration of the evaporation of lead, the mixture is blended so as to be 1 to 2% richer than the stoichiometric ratio of the above mixture ratio composition. These raw materials are dry-mixed in a mixer and then calcined at 800 to 950 ° C.

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

Next, the slurry is formed into a green sheet having a certain thickness by a doctor blade device.
The collected green sheet is punched out by a press machine or cut by a cutting machine to form a rectangular body having a predetermined size.

  Next, as shown in FIG. 4, for example, a pattern is formed on one surface of the green sheet 7 after forming with a silver and palladium paste (hereinafter referred to as Ag / Pd paste) having a ratio of silver / palladium = 7/3. Print molding. FIG. 4 shows an example of a green sheet after printing a metal pattern. In addition, this paste can also use the metal of Ag, Pd, Cu, Ni, Au, and Pt, or 1 or more types selected from these metals.

  On the surface of the green sheet 7, a pattern slightly smaller than this was formed on the substantially entire surface by the above Ag / Pd paste, and this was used as the internal electrode layer 153 (154). On one side of the opposite side of the surface of the green sheet 7, a non-formed part 75 of the internal electrode layer 153 (154) is provided. That is, the internal electrode layer 153 (154) does not reach one end of the opposite side of the green sheet 7, and the internal electrode layer 153 (154) reaches the other opposite end. Arranged.

  The green sheets 7 on which such internal electrode layers 153 (154) are formed are prepared for a predetermined number of stacked sheets based on the required specification of the displacement amount of the piezoelectric actuator 1. Also, the required number of green sheets 7 on which the internal electrode layer 153 (154) is not printed are prepared.

Next, as shown in FIG. 5, a green sheet 7 on which the internal electrode layer 153 (154) was printed was laminated. At this time, the non-forming portions 75 are stacked so as to be alternately positioned on the left side and the right side in the drawing.
In FIG. 5, the internal electrode layer in which the non-formed portion 75 is located on the left side in the drawing is represented as the internal electrode layer 153, and the internal electrode layer in which the non-formed portion 75 is located on the right side is represented as the internal electrode layer 154.

  In this way, 21 green sheets 7 on which the internal electrode layers 153 and 154 are formed are overlapped, and further, green sheets on which the internal electrode layers 153 and 154 are not formed are overlapped on the top and bottom. As shown, a laminate 70 composed of a total of 30 green sheets was produced. Note that FIG. 6 shows a stacked body 70 in which the number of stacked layers is omitted for convenience of drawing.

  Next, the laminated body 70 was thermocompression bonded, degreased at a temperature of 400 to 700 ° C. with an electric furnace, fired at a temperature of 900 to 1200 ° C., and polished into a desired shape. In this example, 1 mm chamfering (C chamfering) was applied to a corner of □ 7 mm, and the thickness in the stacking direction was 1.8 mm. As a result, the green sheet 7 becomes the piezoelectric ceramic layer 151, and the non-forming portion 75 is formed with the holding portion 155. As shown in FIG. 7, the piezoelectric ceramic layer 151 and the internal electrode layers 153 and 154 are alternately arranged. A stacked piezoelectric element unit 15 was obtained. In FIG. 7, the number of stacked layers is omitted for convenience of drawing, but this piezoelectric element unit 15 has 20 piezoelectric ceramic layers active as piezoelectric elements. Further, 20 piezoelectric element units 15 were produced in the same manner as described above.

Next, the 20 piezoelectric element units 15 produced as described above were stacked, and the piezoelectric actuator 1 shown in FIGS. 1 to 3 was produced as follows.
Specifically, first, external electrodes 5 and 6 made of Ag were formed so as to sandwich the side surface of the piezoelectric element unit 15.

In the piezoelectric element unit 15, the external electrode 5 is formed at a position where the internal electrode layer 153 of one pole is exposed, and the internal electrode layers 153 are electrically connected.
The external electrode 6 is formed at a position where the internal electrode layer 154 of the other electrode is exposed, and the internal electrode layers 154 are electrically connected.
Thereafter, a direct current voltage was applied from the external electrodes 5 and 6 to the internal electrode layers 153 and 154 of the piezoelectric element unit 15 in which the external electrodes 5 and 6 were formed, and polarization was performed.

  Next, as shown in FIGS. 1 to 3, the 20 piezoelectric element units 15 polarized as described above were stacked on the joint surface 156 to produce the piezoelectric actuator 1 as shown in FIGS. 1 to 3. This is designated as Sample E1.

  In the piezoelectric actuator 1 of the sample E1, the minimum width L of the retaining portion 155 was 0.3 mm, and the variation width W of the retaining portion 155 was 0.5 mm.

  Further, in this example, the piezoelectric actuators are manufactured by the same method as the sample E1 by changing the number of the piezoelectric ceramic layers stacked, the minimum width L and the variation width W of the holding portion, and these are prepared as samples E2 to E5, sample Es1 to Es4 and samples C1 to C4 were used. The details are shown in Table 1 described later.

Next, voltages were applied to the samples E1 to E5, samples Es1 to Es4, and samples C1 to C4, and the durability and stability of each sample were examined as follows.
First, 10 samples E1 to E5, 10 samples Es1 to Es4 and 10 samples C1 to C4 are prepared, and a voltage of 150 V is applied by positive voltage driving without applying a negative voltage, and an operation test is performed 4 × 10 ⁸ times. did. Then, it is checked whether or not a short circuit has occurred during operation. If no short circuit has occurred in any case, a short circuit occurs in any sample before reaching 2 × 10 ⁸ times or more and 4 × 10 ⁸ times. In the case of ◯, the case where one or more shorts occurred before reaching 2 × 10 ⁸ was determined as x. The results are shown in Table 1.

As is known from Table 1, the samples E1 to E5 and the samples Es1 to Es4 have 50 or less piezoelectric ceramic layers, and the minimum width L and variation width W of the back portion are 0.1 mm ≦ L ≦ 1. 0.0 mm and W ≦ 0.5 mm. These samples E1 to E5 and samples Es1 to Es4 did not cause a short circuit during 2 × 10 ⁸ operations, and were excellent in durability and operational stability.

In particular, the samples Es1, Es3, and Es4 in which the minimum width L and the variation width W of the holding portion are set in the ranges of 0.2 mm ≦ L ≦ 0.6 mm and W ≦ 0.3 mm, respectively, are 4 × 10 ⁸ times. Even during the operation, there was no short circuit, and the durability and stability were excellent.

  In Samples E1 to E5 and Samples Es1 to Es4, the piezoelectric element unit is composed of 50 or less piezoelectric ceramic layers. Therefore, the generation of cracks in the piezoelectric element unit can be effectively suppressed.

On the other hand, the sample C1 and the sample C2 have large piezoelectric element units exceeding 50 layers. In Sample C3 and Sample C4, the minimum width L and the variation width W of the above-described recording portion are outside the ranges of 0.1 mm ≦ L ≦ 1.0 mm and W ≦ 0.5 mm. Such samples C1 to C4 had a problem in durability and stability because a short circuit occurred during 2 × 10 ⁸ operations in any of the samples.

(Example 2)
In this example, the positional relationship and shape of the piezoelectric ceramic layer, the internal electrode layer, and the external electrode are changed, and the others are the same as in Example 1. As shown in FIG. This is an example in which two piezoelectric actuators 1 (sample E6 and sample E7 described later) formed by alternately laminating layers 153 and 154 are produced.

  8 and 9 show arrangement patterns of the internal electrode layers 153 and 154 with respect to the piezoelectric ceramic layer 151 and the external electrodes 5 and 6 in the piezoelectric actuator of this example.

  In manufacturing the piezoelectric actuator of this example, as shown in FIGS. 8 and 9, the electrode exposed portions 158 and 159 of the internal electrode layers 153 and 154 are only connected to the external electrodes 5 and 6, and the holding portion 155 The internal electrode layers 153 and 154 are formed so as to surround the internal electrode layers 153 and 154, and the piezoelectric actuator 1 as shown in FIG. 1 is manufactured in the same manner as in Example 1 except that the sample E6 and the sample E7 are formed. It was.

  In the samples E6 and E7, as shown in FIGS. 8 and 9, the internal electrode layers 153 and 154 have substantially the same shape as the piezoelectric ceramic layer 151 and are formed smaller than that.

  By covering all the electrode exposed portions 158 and 159 with the external electrodes 5 and 6 like the sample E6 and the sample E7, the variation in the joint area with the external electrode is reduced, and the transient characteristics of the displacement are stabilized. Thus, a piezoelectric actuator with further excellent stability could be obtained.

Example 3
Next, in this example, the piezoelectric actuator of the second invention will be described.
The piezoelectric actuator of this example is a piezoelectric actuator 1 having piezoelectric element units 15 in which piezoelectric ceramic layers 151 and internal electrode layers 153 and 154 are alternately stacked, as shown in FIGS. The piezoelectric element unit 15 has a pair of external electrodes 5 and 6 having different potentials on its side surface.

  The internal electrode layers 153 and 154 have electrode exposed portions 158 and 159 led to the side surfaces of the piezoelectric element unit 15, respectively, and the electrode exposed portions 158 and 159 are connected to one of the pair of external electrodes 5 and 6. The external electrodes 5 and 6 to be connected are alternately changed every other layer.

FIG. 10 shows a formation pattern of the internal electrode layers 153 and 154 when the piezoelectric actuator of this example is seen through from the stacking direction.
As shown in the figure, in the piezoelectric actuator of the present example, a holding portion 155, which is a region where the internal electrode layers 153 and 154 recede from the side surface of the piezoelectric element unit, is partially provided around the internal electrode layers 153 and 154. Is formed.

One of the pair of external electrodes is a first external electrode 5, the other is a second external electrode 6, the internal electrode layer connected to the first external electrode 5 is a first internal electrode layer 153, and the second When the internal electrode layer connected to the external electrode 6 is the second internal electrode layer 154,
When the first internal electrode layer 153 and the second internal electrode layer 154 are seen through from the stacking direction, the first internal electrode layer 153 and the electrode internal portions 158 and 159 do not overlap each other. The second internal electrode layer 154 is not exposed in the exposed portion.

The area of one of the first internal electrode layer 153 and the second internal electrode layer 154 is larger than the other area. In this example, as shown in FIG. 10, the internal electrode layer having the larger area is the second internal electrode layer 154, and the smaller internal electrode layer is the first internal electrode layer 153.
In addition, when the first internal electrode layer 153 and the second internal electrode layer 154 are seen through from the stacking direction, the first internal electrode layer 153 and the second internal electrode layer 154 overlap each other. The outer periphery of the piezoelectric active region 150 is defined as an outer periphery A, and the inner electrode layer (second internal electrode layer 154) having the larger area of the first internal electrode layer 153 and the second internal electrode layer 154 on the outer periphery A. Is the outer periphery B, and the length of the outer periphery A is A, and the length of the outer periphery B is B, the relational expression B ≧ 0.5 × A is obtained. Satisfies.

The manufacturing method of the piezoelectric actuator 1 of this example is the same as that of Example 1 except that the shape of the internal electrode layers 153 and 154 is changed as shown in FIG.
The piezoelectric actuator of this example was designated as sample E8.

In the sample E8, a portion where the first internal electrode layer 153 and the second internal electrode layer 154 overlap (region surrounded by a dotted line and filled with diagonal lines in FIG. 10), that is, a piezoelectric active region 150 active as a piezoelectric element. The first internal electrode layer 153 and the second internal electrode layer 154 are formed so as to be substantially square.
Further, when the first internal electrode layer 153 and the second internal electrode layer 154 are seen through from the stacking direction, the outer periphery of the piezoelectric active region 150 is defined as an outer periphery A (portion indicated by a dotted line in FIG. 10). In the outer periphery A, a portion of the first internal electrode layer 153 and the second internal electrode layer 154 that is covered by the internal electrode layer having the larger area (second internal electrode layer 154) extends to the outside of the outer periphery A. When the outer circumference B is A, the length of the outer circumference A is A, and the length of the outer circumference B is B, the relational expression B ≧ 0.5 × A is satisfied.

  10 and FIG. 11 and FIG. 12 to be described later show the first and second piezoelectric ceramic layers and external electrodes when the first internal electrode layer and the second internal electrode layer are seen through from the stacking direction. The arrangement patterns of the two internal electrode layers are shown respectively. In each drawing, the outer periphery B is indicated by an arrow, and this arrow originally overlaps the outer periphery A (the portion indicated by the dotted line in FIG. 10). However, they are slightly shifted for convenience of drawing.

  Further, in this example, as shown in FIGS. 11 and 12, a piezoelectric actuator having a different internal electrode layer formation pattern from that of the sample E8 is manufactured, and this is used as a sample E9 (FIG. 11) and a sample E10 (FIG. 12). It was. Sample E9 and Sample E10 are the same as Sample E8 except that the formation pattern of the internal electrode layer is changed.

In Sample E8 to Sample E10, as shown in FIGS. 10 to 12, the first internal electrode layer 153 and the second internal electrode layer 154 are arranged so that the electrode exposed portions 158 and 159 do not overlap each other. The second internal electrode layer 154 is not exposed at the portion where the internal electrode layer 153 is exposed.
In Samples E8 to E10, when the length of the outer periphery A is A and the length of the outer periphery B is B, the internal electrode layers 153 and 154 satisfy the relational expression B ≧ 0.5 × A. Is formed.

Therefore, the piezoelectric actuators of Sample E8 to Sample E10 can prevent creeping discharge from occurring on the side surfaces.
Further, the variation in the area of the piezoelectric active region 150 (the region surrounded by the dotted line in FIG. 10 to FIG. 12 and filled with the diagonal line), which is the region where the two adjacent internal electrode layers 153 and 154 overlap, is described above. It becomes difficult to be affected by misalignment when the internal electrode layers 153 and 154 are stacked. Therefore, the piezoelectric actuators of Sample E8 to Sample E10 are excellent in durability and have extremely stable characteristics such as capacitance and displacement.

  The internal electrode layer 153, 154 has a large area, and the outer periphery A of the piezoelectric active region 150 satisfies the relational expression B = 0.5 × A. If 154 is formed, it is possible to obtain an effective effect that the influence of misalignment or the like during stacking can be suppressed. That is, for example, compared to the case where the internal electrode layers 153 and 154 are formed in substantially the same shape, the influence of misalignment at the time of stacking can be reduced to about half or less.

  For example, when the internal electrode layers 153 and 154 are formed in substantially the same shape, as shown in FIG. 25, the area of the piezoelectric active region 150 is always small when the internal electrode layer 154 is misaligned with respect to the internal electrode layer 153. Become. FIG. 2A shows the piezoelectric active region 150 in an ideal laminated state in which no misalignment occurs between the internal electrode layers 153 and 154. FIGS. 5B and 5C show the piezoelectric active region 150 in the case where displacement occurs on both sides (a + side, a− side) in the diagonal line a direction of the substantially square internal electrode layers 153 and 154. It shows the area variation.

  On the other hand, in FIG. 26, as described above, the inner electrode layer 153 out of the inner electrode layers 153 and 154 has a large area, and the outer periphery B = 0.5 × A with respect to the outer periphery A of the piezoelectric active region 150. The case where the internal electrode layers 153 and 154 are formed so as to satisfy the relational expression is shown. Then, the variation of the area of the piezoelectric active region 150 due to the misalignment is illustrated. In FIG. 6A, an ideal laminated state (a substantially square internal electrode layer 153, 154 is overlapped between its internal electrode layers 153, 154 with its two sides and one vertex overlapped. The piezoelectric active region 150 in a state where they are laminated together is shown. FIGS. 5B and 5C show the piezoelectric active region 150 in the case where displacement occurs on both sides (a + side, a− side) in the diagonal line a direction of the substantially square internal electrode layers 153 and 154. It shows how the area of fluctuates.

As shown in FIG. 5B, when the internal electrode layer 154 is displaced in the a + direction, which is one direction of the diagonal line a, the area of the piezoelectric active region 150 is reduced as in the case of FIG. However, as shown in FIG. 5C, even if a stacking shift of a predetermined amount or less occurs in the a-direction which is the other direction of the diagonal line a, the area of the piezoelectric active region 150 does not vary.
That is, when any one of the internal electrode layers 153 and 154 has a large area and the internal electrode layers 153 and 154 are formed so as to satisfy the relational expression B = 0.5 × A, as described above, The stacking misalignment direction that induces the variation can be set to only one direction. That is, when the internal electrode layers 153 and 154 are formed in substantially the same shape (FIG. 25), the probability that the piezoelectric active region becomes small due to the stacking deviation can be reduced to about half or less.

  Further, FIG. 27 is an example in which the relationship between the value of (outer periphery B / outer periphery A) and the variation in characteristics of the piezoelectric actuator due to the stacking deviation between the internal electrode layers 153 and 154 is examined. In the figure, the value of (outer periphery B / outer periphery A) is defined on the horizontal axis, and the magnitude of characteristic variation is indicated on the vertical axis. As the characteristic variation, a value (%) obtained by dividing the characteristic (capacitance) when the stacking deviation occurred by the characteristic (capacitance) when there is no stacking deviation was used. Furthermore, the white alphabets in the plots in the figure indicate combinations of the shape patterns of the internal electrode layers 153 and 154 to be stacked as shown in FIGS. In the figure, the left column shows combinations of the internal electrode layers 153 and 154 in an ideal stacked state, and the right column shows a case where stacking misalignment occurs.

  As is clear from FIG. 27, the characteristic variation can be effectively suppressed as the value of (outer periphery B / outer periphery A) is increased. Particularly, in the range where the value of (outer periphery B / outer periphery A) is 0.6 or more, that is, B ≧ 0.6 × A, the characteristic variation can be suppressed to about 5% or less. Furthermore, the value of (outer periphery B / outer periphery A) is 0.6 or more and 0.75 or less, that is, 0.6 × A ≦ B ≦ 0.75 × A, and the electrode exposure of the first internal electrode layer 153 And the electrode exposed portion of the second internal electrode layer 154 are not exposed on the same side surface, the effect of preventing electrical short circuit due to creeping discharge is further enhanced while further suppressing variation in characteristics. Can do.

(Example 4)
Next, an example of a piezoelectric actuator having variations at the outer edge of the internal electrode layer will be described.
The piezoelectric actuator of this example can be manufactured by the green sheet method by the same method as in Example 1. The shape of the internal electrode layer formed on the piezoelectric ceramic layer is the same as that of the sample E6 of Example 2 (see FIG. 8).

  In this example, as in Example 1, the minimum width L and the variation width W in the holding part were changed, and six types of piezoelectric actuators were produced by screen printing, and these were designated as Samples E11 to E16. The minimum width L and the variation width W of each sample are shown in Table 2 described later.

  Further, in this example, in the green sheet method, the size of the screen mesh when the internal electrode layer is formed on the green sheet of the piezoelectric ceramic layer is changed, and the others are the same as the samples E11 to E16. Six types of piezoelectric actuators were produced, and these were designated as Sample E11a to Sample 16a.

As shown in FIGS. 13 and 14, in the samples E11 to 16 and the samples E11a to 16a, the outer edge of each internal electrode layer 154 is not linear, and has a curved shape with a certain deviation. It has become. When the width of the deviation, that is, the variation width D was measured, all of the samples E11 to 16 were 0.2 mm, and all of the samples E11a to 16a were 0.4 mm.
The variation of the outer edge of the internal electrode layer was measured by dimension measurement using a SEM (scanning electron microscope) photograph.
Table 2 shows details of the samples E11 to 16 and the samples E11a to 16a.

Further, in this example, as in Example 1, voltages were applied to the samples E11 to E16 and the samples E11a to 16a, and the operation test was performed 4 × 10 ⁸ times. Then, check if a short circuit occurred during operation, and if no short circuit occurred in any of the cases ◎ If a short circuit occurred in any of the cases before reaching 2 × 10 ⁸ times or more and 4 × 10 ⁸ times Was evaluated as x when one or more short-circuits occurred before reaching 2 × 10 ⁸ . The results are shown in Table 2.

As is known from Table 2, the samples E11 to E16 and the samples E11a to 16a were all excellent in durability because no short circuit occurred up to 2.0 × 10 ⁸ times.
However, before reaching 2.0 × 10 ⁸ times and reaching 4.0 × 10 ⁸ times, a short circuit occurred in Sample E11a and Samples E13a to E16a.
On the other hand, the sample E11 and the samples E13 to E16 having the same minimum width L and variation width W as the samples E11a and E13a to E16a but different in the variation width D are as high as 4.0 × 10 ⁸ times. In terms of the number of operations, no short circuit occurred and the durability was further improved.

In order to examine this result further, the result of Table 2 is shown in FIG.15 and FIG.16.
FIG. 15 shows the results of Samples E11 to E16 in which the variation width D of the internal electrode layers is 0.2 mm.
FIG. 16 shows the results of Sample E11a to Sample E16a in which the variation width D of the internal electrode layer is 0.4 mm.
15 and 16, the horizontal axis indicates the minimum width L of the storage portion, and the vertical axis indicates the variation width W of the storage portion. In FIGS. 15 and 16, the case where no short-circuit occurred is ◎, 2 × 10 ⁸ times or more 4 × 10 ⁸ times before short-circuit occurs, and ○ is 2 × 10 ⁸ The case where one or more shorts occurred before was plotted as x.

As can be seen from FIGS. 15 and 16, when the minimum width L and the variation width W of the stub portion are in the region surrounded by the dotted line in FIGS. 15 and 16, the operation frequency is as high as 2 × 10 ⁸ times. However, the piezoelectric actuators of the present example (the samples E11 to E16 and the samples E11a to 16a) did not cause a short circuit and had excellent durability.

However, as can be seen from FIG. 16, when the number of actuations was further increased, the samples E11a and E13a to E16a were short-circuited before reaching the number of actuations of 4 × 10 ⁸ times.

On the other hand, as can be seen from FIG. 15, the minimum width L and variation width W of the sample portion 11a, sample 14a and sample 15a are the same, but the variation width D of the internal electrode layer is 0.2 mm. Samples 11, 14 and 15 did not cause a short circuit even at a higher operation of 4 × 10 ⁸ times.

  From the above, it can be seen that the durability of the piezoelectric actuator can be further improved by setting the variation width D of the internal electrode layer within 0.2 mm.

(Example 5)
Next, the distance between the boundary between the electrode exposed portion and the holding portion on the side surface of the piezoelectric element unit and the external electrode provided on the side surface on the holding portion side of the piezoelectric element unit is determined as the piezoelectric element. An example of a piezoelectric actuator having a minimum distance of 0.2 mm along the side surface of the unit is shown.
As shown in FIGS. 17 and 18, in the piezoelectric actuator of this example, on the side surface of the piezoelectric element unit 15, a boundary portion between the electrode exposed portion 159 and the holding portion 155 that is not connected to the external electrodes 5 and 6. 8 and a distance c between the external electrodes 5 and 6 provided on the side surface of the piezoelectric element unit 15 on the side of the holding portion 155 and the shortest distance along the side surface of the piezoelectric element unit 15 is 0.2 mm or more. Thus, the piezoelectric electrode 1 shown in FIG. 1 was manufactured in the same manner as the sample E8 of Example 3 except that the internal electrode layers 153 and 154 and the external electrodes 5 and 6 were arranged. This was designated as Sample E17.

  FIG. 17 partially shows a side surface of the piezoelectric element unit 15 in the piezoelectric actuator of the sample E17. FIG. 18 shows an internal electrode layer 153 for the piezoelectric ceramic layer 151 and the external electrodes 5 and 6 in the sample E17. 154 shows an arrangement pattern of 154.

In the sample E17, as shown in FIG. 18, the internal electrode layer 153 connected to one external electrode 5 does not have the electrode exposed portion 158 except for the portion connected to the external electrode 5. The internal electrode layer 154 connected to the other external electrode 6 has an electrode exposed portion 159 other than the side surface on which the external electrodes 5 and 6 are formed.
Therefore, as shown in FIGS. 17 and 18, the internal electrode layer exposed to the side surface other than the side surface on which the external electrodes 5 and 6 are formed in the piezoelectric element unit 15 is the internal electrode layer 154 connected to the external electrode 6.

  In the sample E17, on the side surface of the piezoelectric element unit 15, the boundary portion 8 between the electrode exposed portion 159 and the retaining portion 155 that is not connected to the external electrodes 5 and 6, and the retaining portion 155 side of the piezoelectric element unit 15 are provided. The distance c to the external electrode 5 provided on the side surface is 0.2 mm or more at the shortest distance along the side surface of the piezoelectric element unit 15.

  By arranging the internal electrode layers 153 and 154 and the external electrode layers 5 and 6 in this way, it was possible to effectively prevent creeping discharge from occurring on the side surface of the piezoelectric actuator.

(Example 6)
In this example, a piezoelectric actuator in which the outermost layer of the piezoelectric element unit is active is manufactured.
First, as shown in FIG. 19, a piezoelectric element unit 15 similar to that of the first embodiment is prepared. The piezoelectric element unit 15 is formed by alternately laminating piezoelectric ceramic layers 151 and internal electrode layers 153 and 154, and on the outermost layer 152 on the outermost side of the piezoelectric ceramic layers 151 in the piezoelectric element unit 15. The internal electrode layer is not formed.

Next, as shown in FIG. 20, two external electrodes 5 and 6 having different potentials are formed so as to sandwich the side surface of the piezoelectric element unit 15, and the external electrode 5 conducts the internal electrode layer 153, and the external electrode 6 conducts the internal electrode layer 154.
The external electrode 5 includes a main body 51 disposed on the side surface of the piezoelectric actuator 1 and a branch 53 formed so as to extend from the main body 51 in a substantially right angle direction and cover the outermost layer 152 of the piezoelectric element unit 15. It consists of.

Next, the piezoelectric element units 15 are stacked so that the branch portions 53 of the external electrode 5 overlap each other, and the main body 51 and the external electrode 6 of the external electrode 5 are arranged on the same side surface after being stacked, and the piezoelectric actuator is mounted. Produced. This was designated as Sample E18.
In the sample E <b> 18, as shown in FIG. 20, the branch portion 53 of the external electrode 5 is disposed between the piezoelectric element units 15.

  In such a piezoelectric actuator, when a voltage is applied, the outermost layer 152 of the piezoelectric element unit 15 is also displaced and becomes piezoelectrically active. As a result, the amount of displacement per unit length in the stacking direction of the piezoelectric actuator can be increased, and the piezoelectric actuator can exhibit a large driving force.

FIG. 2 is an exploded explanatory view of the piezoelectric actuator according to the first embodiment. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. Explanatory drawing which shows the mode of the junction part vicinity of the piezoelectric actuator shown in FIG. FIG. 3 is an explanatory diagram illustrating a state in which an internal electrode layer is printed on a ceramic green sheet according to the first embodiment. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram showing a state in which green sheets with internal electrode layers are stacked according to Example 1; FIG. 3 is a perspective explanatory view showing a laminate according to the first embodiment. FIG. 3 is a perspective explanatory view showing a piezoelectric element unit according to the first embodiment. Explanatory drawing which shows the arrangement pattern of an internal electrode layer when it sees through the internal electrode layer in the sample E6 concerning Example 2 from the lamination direction of a piezoelectric element unit. Explanatory drawing which shows the arrangement pattern of an internal electrode layer when it sees through the internal electrode layer in the sample E7 concerning Example 2 from the lamination direction of a piezoelectric element unit. Explanatory drawing which shows the arrangement pattern of an internal electrode layer when it sees through the internal electrode layer in the sample E8 concerning Example 3 from the lamination direction of a piezoelectric element unit. Explanatory drawing which shows the arrangement pattern of an internal electrode layer when it sees through the internal electrode layer in the sample E9 concerning Example 3 from the lamination direction of a piezoelectric element unit. Explanatory drawing which shows the arrangement pattern of an internal electrode layer when it sees through the internal electrode layer in the sample E10 concerning Example 3 from the lamination direction of a piezoelectric element unit. FIG. 6 is an explanatory diagram showing a state of an end portion of an internal electrode layer formed on a piezoelectric ceramic layer according to Example 4; FIG. 14 is an enlarged view of a portion surrounded by a dotted circle in FIG. 13. Explanatory drawing which shows durability of the said piezoelectric actuator (sample E11-sample E16) concerning Example 4. FIG. Explanatory drawing which shows durability of the said piezoelectric actuator (sample E11a-sample E16a) concerning Example 4. FIG. Explanatory drawing which shows the relationship between the boundary part of an electrode exposure part and a holding | maintenance part, and an external electrode when the sample E17 concerning Example 5 is seen from a side surface. Explanatory drawing which shows the relationship between the electrode exposure part of an internal electrode layer, and an external electrode when it sees through the internal electrode layer in the sample E17 concerning Example 5 from the lamination direction of a piezoelectric element unit. Sectional explanatory drawing of the lamination direction of a piezoelectric element unit used for preparation of the sample E18 concerning Example 6. FIG. Sectional explanatory drawing of the lamination direction of the piezoelectric actuator of the sample E18 concerning Example 6. FIG. Explanatory drawing which shows the relationship between the lamination | stacking number of a piezoelectric ceramic layer, and the stress which generate | occur | produces inside a piezoelectric element unit. Explanatory drawing which shows the relationship between the dispersion | variation width W of a reservation part, and the stress which generate | occur | produces inside a piezoelectric element unit. Explanatory drawing which shows the relationship between the electric field strength of the outermost layer with respect to the coercive electric field of a piezoelectric element unit, and the piezoelectric constant of an outermost layer. Explanatory drawing which shows the relationship between the electric field strength and displacement amount of a piezoelectric element unit. FIG. 6 is an explanatory diagram for comparing and explaining the case of B = 0 × A according to the third embodiment. Explanatory drawing explaining the case concerning B = 0.5 * A concerning Example 3. FIG. The graph which shows the relationship between the value of (outer periphery B / outer periphery A) and the characteristic variation of a piezoelectric actuator concerning Example 3. FIG. FIG. 6 is an explanatory diagram showing combinations of shape patterns of internal electrode layers according to Example 3;

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric actuator 15 Piezoelectric element unit 151 Piezoelectric ceramic layer 153,154 Internal electrode layer 155 Retaining part 158,159 Electrode exposed part 5,6 External electrode

Claims (12)

In a piezoelectric actuator having a piezoelectric element unit in which piezoelectric ceramic layers and internal electrode layers are alternately laminated,
The piezoelectric element unit is formed by stacking 50 or less piezoelectric ceramic layers, and has a pair of external electrodes having different potentials on its side surface.
The internal electrode layer has an electrode exposed portion exposed on a side surface of the piezoelectric element unit, and is connected to one of the pair of external electrodes through the electrode exposed portion, and alternately every other layer. The external electrode at the connection destination has been changed,
Further, around the internal electrode layer, a holding portion that is a region where the internal electrode layer is retreated from the side surface of the piezoelectric element unit is partially formed,
In a cross section in the stacking direction of the piezoelectric element actuator, a minimum width L that is a minimum distance from a side surface of the piezoelectric element unit to an end of each internal electrode layer in each holding portion, and the piezoelectric element unit in each holding portion A piezoelectric actuator characterized in that the variation width W, which is the difference between the maximum and minimum distances from the side surface to each internal electrode layer, satisfies the relationship of the following formula (1).
0.1 mm ≦ L ≦ 1.0 mm, W ≦ 0.5 mm (1) 2. The piezoelectric actuator according to claim 1, wherein the relationship of the following formula (2) is satisfied.
0.2 mm ≦ L ≦ 0.6 mm, W ≦ 0.3 mm (2) In a piezoelectric actuator having a piezoelectric element unit in which piezoelectric ceramic layers and internal electrode layers are alternately laminated,
The piezoelectric element unit has a pair of external electrodes with different potentials on its side surface,
The internal electrode layer has an electrode exposed portion exposed on a side surface of the piezoelectric element unit, and is connected to one of the pair of external electrodes through the electrode exposed portion, and alternately every other layer. The external electrode at the connection destination has been changed,
Further, around the internal electrode layer, a holding portion that is a region where the internal electrode layer is retreated from the side surface of the piezoelectric element unit is partially formed,
One of the pair of external electrodes is a first external electrode, the other is a second external electrode, the internal electrode layer connected to the first external electrode is a first internal electrode layer, and is connected to the second external electrode. When the internal electrode layer is a second internal electrode layer,
When the first internal electrode layer and the second internal electrode layer are seen through from the laminating direction, the first internal electrode layer does not overlap with each other so that the electrode exposed portions do not overlap each other. In the portion where the electrode exposed portion is exposed, the electrode exposed portion of the second internal electrode layer is not exposed,
Further, the area of one of the first internal electrode layer and the second internal electrode layer is larger than the area of the other,
In addition, when the first internal electrode layer and the second internal electrode layer are seen through from the stacking direction, the piezoelectric activity is an area where the first internal electrode layer and the second internal electrode layer overlap The outer periphery of the region is the outer periphery A, and the outer periphery B is the portion of the outer periphery A where the larger internal electrode layer of the first internal electrode layer and the second internal electrode layer covers the outer periphery A. A piezoelectric actuator characterized by satisfying a relational expression of B ≧ 0.5 × A where A is the length of the outer periphery A and B is the length of the outer periphery B.   4. The piezoelectric actuator according to claim 3, wherein a relational expression of B ≧ 0.6 × A is satisfied.   5. The electrode according to claim 4, wherein B ≦ 0.75 × A is satisfied, and the electrode exposed portion of the first internal electrode layer and the electrode exposed portion of the second internal electrode layer are on the same side surface. Piezoelectric actuator characterized by not being exposed to.   6. The internal electrode layer according to claim 1, wherein the internal electrode layer has a variation at an outer edge of the internal electrode layer, and the variation width D is D ≦ 0.2 mm. Piezoelectric actuator.   The piezoelectric actuator according to any one of claims 1 to 6, wherein the external electrode covers all of the electrode exposed portion.   8. The external part according to claim 1, wherein a boundary portion between the electrode exposed portion and the holding portion on a side surface of the piezoelectric element unit and a side surface of the piezoelectric element unit on the side of the holding portion side. The distance from the electrode is 0.2 mm or more at the shortest distance along the side surface of the piezoelectric element unit.   9. The piezoelectric actuator according to claim 1, wherein a plurality of the piezoelectric element units are stacked.   10. The piezoelectric actuator according to claim 9, wherein the outermost layer of the piezoelectric element unit is active.   The piezoelectric actuator according to claim 1, wherein the piezoelectric ceramic layer is made of a PZT material.   The piezoelectric actuator according to any one of claims 1 to 11, wherein the piezoelectric actuator is used for an injector.

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