JP6274393B2 - Piezoelectric element - Google Patents

Description

  The present invention relates to a piezoelectric element in which piezoelectric layers and internal electrodes are alternately stacked and expands and contracts by applying a voltage.

  2. Description of the Related Art Conventionally, a piezoelectric element is known in which a stress relaxation layer is provided to relieve stress generated in a piezoelectrically inactive portion with respect to a portion that is displaced when the piezoelectric element is displaced. Such a stress relaxation layer is disposed so as to surround the internal electrode basically on the same laminated surface as the internal electrode (see Patent Documents 1 and 2).

  A stress relaxation layer provided on the same laminated surface as such an internal electrode can be formed only up to the end of the internal electrode. However, if the stress relaxation layer is formed in a layer different from the internal electrode layer, it is piezoelectrically active. It can be formed up to the inside of the layer, and the stress can be relaxed.

Japanese Patent No. 2994492 Japanese Patent No. 2951129

  For example, as an example of a conventional piezoelectric element in which a stress relaxation layer is formed in a layer different from the internal electrode layer, there are piezoelectric elements as shown in FIGS. 9 and 10, (a) and (b) show a perspective view and a side sectional view, respectively. The piezoelectric element 800 shown in FIG. 9 is formed by alternately stacking piezoelectric layers 810 and internal electrodes 820 and 825. The stress relaxation layer 840 is provided between the internal electrode 820 and the internal electrode 825 having different polarities and in contact with the outer periphery of the piezoelectric element 800 over the entire periphery. The internal electrode 820 is connected to the external electrode 850 that is in contact with the stress relaxation layer 840, and the internal electrode 825 is connected to the external electrode 855 having a polarity different from that of the external electrode 850.

  On the other hand, the piezoelectric element 900 shown in FIG. 10 is formed by alternately stacking piezoelectric layers 910 and internal electrodes 920 and 925. Between the internal electrodes 925 adjacent in the stacking direction, a stress relaxation layer 940 is provided over the entire circumference of the piezoelectric element 900. Both internal electrodes 925 are connected to the same external electrode 955.

  The stress relieving layer as described above is made of a porous material or has been cracked beforehand. An external electrode is formed on the side surface of the piezoelectric element across the stress relaxation layer. Therefore, when the external electrode is formed by screen printing, there is a risk that the electrode paste enters the stress relaxation layer. Further, when cream solder is used as the solder for connecting the lead wire to the external electrode thereafter, there is a risk that the solder may enter the stress relaxation layer.

  When a conductive material enters the stress relaxation layer, the stress relaxation layer has the same polarity as that of the external electrode, and migration is likely to occur between the upper and lower internal electrodes. turn into.

  This invention is made | formed in view of such a situation, and it aims at providing the piezoelectric element which can prevent the migration from a stress relaxation layer and can prevent that there becomes a starting point of destruction.

  (1) In order to achieve the above object, the piezoelectric element of the present invention is a piezoelectric element in which piezoelectric layers and internal electrodes are alternately laminated and expands and contracts by application of voltage, and has a layer surface parallel to the laminated surface. And a stress relaxation layer that is formed in contact with the outer periphery and is provided in a ratio of one layer per a plurality of piezoelectric layers to relieve stress due to driving, and the stress relaxation layer projects all internal electrodes in the stacking direction. A part of the active region obtained in this manner, and either the nearest internal electrode having at least one overlap in the stacking direction of the stress relaxation layer or the nearest internal electrode having at least part of the other in the stacking direction. Is characterized by having the same polarity as the external electrode in contact with the stress relaxation layer.

  As a result, even if a conductive material such as electrode paste or solder enters from the external electrode in contact with the stress relaxation layer, an electric field is not applied to the nearest internal electrode, so that migration can be prevented, and that is the starting point of destruction. Can be prevented.

  According to the present invention, since an electric field is not applied between the stress relaxation layer and the nearest internal electrode, migration can be prevented, and it can be prevented that this becomes a starting point of destruction.

(A)-(c) It is the perspective view and plane sectional view which respectively show the piezoelectric element of 1st Embodiment. It is a sectional side view which shows the piezoelectric element of 1st Embodiment. It is a perspective view which shows the piezoelectric element of a reference example . (A)-(c) It is a plane sectional view which shows the piezoelectric element of a reference example , respectively. It is a sectional side view which shows the piezoelectric element of a reference example. (A)-(c) It is the perspective view and plane sectional view which respectively show the piezoelectric element of a reference example . It is a sectional side view which shows the piezoelectric element of a reference example. (A), (b) It is the table | surface which shows the average piezoelectric application time of each piezoelectric element, and the Weibull coefficient, respectively, the graph which plotted the failure probability of each piezoelectric element. (A), (b) is the perspective view and side sectional view which respectively show the conventional piezoelectric element. (A), (b) is the perspective view and side sectional view which respectively show the conventional piezoelectric element.

  Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and duplicate descriptions are omitted.

[First Embodiment]
(Configuration of piezoelectric element)
1A to 1C are a perspective view and a plan sectional view showing the piezoelectric element 100, respectively. FIG. 2 is a side sectional view showing the piezoelectric element 100. The piezoelectric element 100 is formed in a rectangular body, the piezoelectric layers 110 and the internal electrodes 120 and 125 are alternately stacked, and expands and contracts when a voltage is applied.

  The piezoelectric element 100 includes stress relaxation layers 140 and 145 for relaxing stress due to driving. The stress relaxation layers 140 and 145 are provided in a ratio of one layer per a plurality of piezoelectric layers, have a layer surface parallel to the laminated surface, and are formed in contact with the outer periphery. In addition, a lamination surface refers to a surface perpendicular | vertical to the lamination direction (stretching direction) of a piezoelectric element.

  The stress relaxation layer 140 is provided in contact with the side surface 101, and the stress relaxation layer 145 is provided in contact with the side surface 102 opposite to the side surface 101. It is preferable that the stress relaxation layers 140 and 145 have a ratio of one layer to 24 piezoelectric layers and a ratio of one layer to two piezoelectric layers. More preferably, the ratio of one layer to 24 piezoelectric layers is equal to or less than the ratio of one layer to ten piezoelectric layers.

  As shown in FIG. 1B, the internal electrode 120 is basically formed in a rectangular shape similar to the shape of the outer periphery on the inner side of the outer periphery, and is connected to the external electrode 150 on one side surface 101. Is formed. Similarly, the internal electrode 125 is basically formed in a rectangular shape similar to the shape of the outer periphery, and an extraction electrode portion for connecting to the external electrode 155 is formed on the other side surface 102.

  Moreover, as shown in FIG.1 (c), the stress relaxation layer 140 is provided along the outer periphery so that the side surface 101, the front surface 103, and the back surface 104 may be touched, and it is U shape in a plane sectional view. Similarly, the stress relaxation layer 145 is provided along the outer periphery so as to be in contact with the side surface 102, the front surface 103, and the back surface 104, and is U-shaped in a plan sectional view.

  As shown in FIG. 2, the stress relaxation layers 140 and 145 are partially included in an active region that is displaced by application of a voltage. That is, the tip portions of the stress relaxation layers 140 and 145 are inside the boundary A in FIG. The active region is a region (inner side from the boundary A in FIG. 2) obtained by projecting all the internal electrodes 120 and 125 in the stacking direction (stretching direction), and coincides with a region where internal electrodes of different potentials overlap in the stacking direction. To do.

  As shown in FIG. 2, the nearest internal electrode 120 that overlaps at least partially in one of the lamination directions of the stress relaxation layer 140 (upward direction in the drawing) has the same polarity as the external electrode 150 in contact with the stress relaxation layer 140. is there. In addition, the nearest internal electrode 120 that overlaps at least partly in the other side of the stress relaxation layer 140 in the stacking direction (the lower direction in the drawing) is also the same polarity as the external electrode 150 in contact with the stress relaxation layer.

  Thereby, even if a conductive substance such as electrode paste or solder enters from the external electrode 150 in contact with the stress relaxation layer 140, no electric field is applied to the nearest internal electrode 120, so that migration can be prevented, which is the starting point of destruction. Can be prevented. Such a structure is similarly provided for the arrangement of the stress relaxation layer 145 and the internal electrode 125 provided on the side surface 102. Thus, in the piezoelectric element 100, the stress relaxation layer is formed in the inactive layer sandwiched between the internal electrodes having the same polarity.

(Method for manufacturing piezoelectric element)
Next, a method for manufacturing the piezoelectric element 100 configured as described above will be described. First, using a slurry containing a piezoelectric material such as PZT, a green sheet is formed by a method such as pulling molding, doctor blade molding, or extrusion molding.

  A piezoelectric green sheet is prepared, and a pattern for an internal electrode and a stress relaxation layer is applied to each green sheet at a position where the internal electrode or the stress relaxation layer is provided by screen printing or the like. In that case, an electrode paste (Ag—Pd alloy or the like) is applied for an internal electrode, and then dried to form a pre-fired electrode film.

  For the stress relaxation layer, a paste of a non-sintered material (such as lead titanate) is applied. The non-sintered material is a material that does not sinter during the firing temperature process of the piezoelectric element. The non-sintered material paste is obtained by mixing a non-sintered material powder, a binder, a plasticizer, and an organic solvent in a predetermined ratio. For example, the non-sintered material includes lead titanate, the binder includes ethyl cellulose, the plasticizer includes dioctyl phthalate, and the organic solvent includes butyl carbitol. The non-sintered material includes a material such as carbon that burns away during firing to form a stress relaxation layer.

  Next, a plurality of green sheets on which an electrode film and a non-sintered material film are formed are stacked. In addition, before producing the laminated body, it is designed in advance so that the stress relaxation layer is formed at a predetermined ratio at one place in several layers of the internal electrode. In that case, the stress relaxation layer is formed by the nearest internal electrode having at least one overlap in one of the lamination directions of the stress relaxation layer and the nearest internal electrode having at least one overlap in the other of the lamination directions of the stress relaxation layer. Design to have the same polarity as the external electrode in contact with the layer.

  Next, after the laminated green sheet is press-molded, it is heated to degrease the organic components in the green sheet, the electrode paste, and the non-sintered material paste. The organic component is decomposed by heating to become a gas and escapes from the green sheet or paste film.

  The laminated body thus degreased is fired. At this time, the non-sintered material is not sintered, and the stress relaxation layers 140 and 145 are formed at locations where the non-sintered material is applied. Then, the sintered body can be appropriately processed to produce the piezoelectric element 100.

(Piezoelectric actuator)
A piezoelectric actuator can be configured using the piezoelectric element 100 as described above. The piezoelectric actuator is configured by bonding the piezoelectric element 100 in series and connecting external electrodes 150 and 155 connected to the internal electrodes 120 and 125 of the piezoelectric element 100 with lead wires. Thereby, it is possible to provide a piezoelectric actuator in which the stress relaxation layers 140 and 145 do not become a starting point of destruction.

  For example, a positioner actuator in which a plurality of piezoelectric elements 100 are bonded in the stacking direction to perform multiple treatment, polarization processing is performed on the multiple piezoelectric elements 100, and the piezoelectric elements 100 are multiplexed by covering them with a cap. Can be made.

[ Reference example ]
FIG. 3 is a perspective view showing a piezoelectric element 200 of a reference example in which a stress relaxation layer is provided in the active layer. FIGS. 4A to 4C are plan sectional views showing a piezoelectric element 200 of a reference example . FIG. 5 is a side sectional view showing a piezoelectric element 200 of a reference example . The piezoelectric element 200 is formed in a rectangular shape, and the piezoelectric layers 210 and the internal electrodes 220, 220a, 225, and 225a are alternately stacked, and expand and contract when a voltage is applied.

  As shown in FIG. 4A, the internal electrode 220 is formed in a rectangular shape basically similar to the shape of the outer periphery on the inner side of the outer periphery, and an extraction electrode portion for connecting to the external electrode 250 is formed on the side surface 201. Has been. Similarly, the internal electrode 225 is basically formed in a rectangular shape similar to the shape of the outer periphery, and an extraction electrode portion for connecting to the external electrode 255 is formed on the other side surface 202.

  As shown in FIGS. 4B and 5, the stress relaxation layer 240 is provided along the outer periphery so as to contact the side surfaces 201 and 202, the front surface 203, and the back surface 204. Is.

  On the other hand, as shown in FIGS. 4C and 5, the internal electrode 225 a is formed in a rectangular shape on the inner side of the outer periphery, and an extraction electrode portion for connecting to the external electrode 255 is formed on the side surface 202 side. . The internal electrode 225a is formed so that the end portion on the side surface 201 side is positioned inside the stress relaxation layer 240. Similarly, the internal electrode 220a is formed in a rectangular shape inside the outer periphery, and an extraction electrode portion for connecting to the external electrode 250 is formed on the side surface 201 side. The internal electrode 220a is formed so that the end on the side surface 202 side is positioned inside the stress relaxation layer 240.

  In such an arrangement, the internal electrode 225a is provided at a position on the laminated surface closest to the laminated surface of the stress relaxing layer 240 as an electrode having a polarity different from that of the external electrode 250 in contact with the stress relaxing layer 240. The internal electrode 225 a is provided at a position where an electric field generated with respect to the adjacent internal electrode 220 a when a voltage is applied is not applied to the stress relaxation layer 240. Such an arrangement is the same for the positions of the internal electrode 220a and the stress relaxation layer 240.

  Thereby, while providing the stress relaxation layer 240 in an active layer, many active layers can be provided and an efficient piezoelectric element can be comprised. Further, the electric field is not concentrated on the tip of the stress relaxation layer 240, and the breakage starting from the tip of the stress relaxation layer 240 can be prevented.

[ Reference example ]
In the above reference example , the stress relaxation layer is provided in the active layer, but is further provided as an electrode having a polarity different from that of the external electrode in contact with the stress relaxation layer at the position of the lamination surface closest to the lamination surface of the stress relaxation layer. internal electrodes that are provided in the same lamination plane and the stress relaxation layer.

6A to 6C are a perspective view and a plan sectional view showing a piezoelectric element 300 of a reference example , respectively. FIG. 7 is a side sectional view showing a piezoelectric element 300 of a reference example . The piezoelectric element 300 is formed in a rectangular body, the piezoelectric layers 310 and the internal electrodes 320 and 325 are alternately stacked, and expands and contracts when a voltage is applied.

  The piezoelectric element 300 includes stress relaxation layers 340 and 345 for relaxing stress due to driving. The stress relaxation layers 340 and 345 are provided in a ratio of one layer per a plurality of piezoelectric layers, have a layer surface parallel to the laminated surface, and are formed in contact with the outer periphery.

  As shown in FIG. 6B, the internal electrode 320 is basically formed in a rectangular shape similar to the shape of the outer periphery on the inner side of the outer periphery, and is an extraction electrode for connecting to the external electrode 350 on one side surface 301 side. The part is formed. Similarly, the internal electrode 325 is basically formed in a rectangular shape similar to the shape of the outer periphery, and an extraction electrode portion for connecting to the external electrode 355 is formed on the other side surface 302 side.

  As shown in FIG. 6C, the stress relaxation layer 340 is provided along the outer periphery so as to be in contact with the side surface 301, the front surface 303, and the back surface 304, and is U-shaped in the plan sectional view. The internal electrode 325a is formed in a rectangular shape, and an extraction electrode portion for connecting to the external electrode 355 is formed on the side surface 302 side. The internal electrode 325 a is provided on the same stacked surface as the stress relaxation layer 340, and a sufficient gap is provided between the internal electrode 325 a and the stress relaxation layer 340.

  As described above, the internal electrode 325 a provided at the position of the laminated surface closest to the laminated surface of the stress relaxing layer 340 as the electrode having a different polarity from the external electrode 350 in contact with the stress relaxing layer 340 is the same as the stress relaxing layer 340. Are provided on the laminated surface. Accordingly, it is possible to configure a piezoelectric element in which many active layers are provided and the stress relaxation layer is arranged in a well-balanced manner.

  Similarly, the stress relaxation layer 345 is provided along the outer periphery so as to be in contact with the side surface 302, the front surface 303, and the back surface 304, and is U-shaped in a plan sectional view. The internal electrode 320a is formed in a rectangular shape, and an extraction electrode portion for connecting to the external electrode 350 is formed on the side surface 301 side. The internal electrode 320 a is provided on the same laminated surface as the stress relaxation layer 345, and a sufficient gap is provided between the internal electrode 320 a and the stress relaxation layer 345.

[Examples and Comparative Examples]
Piezoelectric elements 100 and 300 having the forms shown in FIGS. 1 and 2 and FIGS. Also, piezoelectric elements 800 and 900 having the forms shown in FIGS. 9 and 10 were produced as Comparative Examples 1 and 2, respectively. Piezoelectric elements having dimensions of 6 × 6 × 10 mm and 120 internal electrodes and 11 stress relaxation layers were produced as Examples 1 and 2 and Comparative Examples 1 and 2, respectively.

  When the same voltage was applied to the produced piezoelectric element, the displacement in Example 1 was 11 μm and the displacement in Example 2 was 10 μm. On the other hand, the displacement of Comparative Example 1 was 10 μm, and the displacement of Comparative Example 2 was 11 μm.

  Each piezoelectric element was driven with a rectangular wave of 0 to 150 V at 5 Hz. FIG. 8A is a graph obtained by Weibull plotting the failure probability of each piezoelectric element. FIG. 8B is a table showing the average piezoelectric application time and the Weibull coefficient of each piezoelectric element. 8A and 8B show that the failure probability per piezoelectric application time is clearly reduced in Examples 1 and 2 compared to Comparative Examples 1 and 2. In particular, it was found that Example 2 was more difficult to break down than Example 1.

100 Piezoelectric elements 101, 102 Side surface 103 Front surface 104 Rear surface 110 Piezoelectric layer 120, 125 Internal electrode 140, 145 Stress relaxation layer 150, 155 External electrode 200 Piezoelectric element 201, 202 Side surface 210 Piezoelectric layer 220, 220a, 225, 225a Internal electrode 240 245 Stress relaxation layer 250, 255 External electrode 300 Piezoelectric element 301, 302 Side surface 303 Front surface 304 Rear surface 310 Piezoelectric layer 320, 320a, 325, 325a Internal electrode 340, 345 Stress relaxation layer 350, 355 External electrode A Active region boundary

Claims (1)

Piezoelectric elements in which piezoelectric layers and internal electrodes are alternately stacked and expand and contract by application of voltage,
A stress relief layer that has a layer surface parallel to the laminated surface, is formed in contact with the outer periphery, is provided at a rate of one layer per a plurality of piezoelectric layers, and relaxes stress due to driving;
Each of the stress relaxation layers is obtained by projecting all internal electrodes in the stacking direction, and part of the active region is an area where all the internal electrodes overlap in the stacking direction,
Both the nearest internal electrode that overlaps at least partially in one of the lamination directions of the stress relaxation layer and the nearest internal electrode that overlaps at least partially in the other of the lamination directions are both external electrodes in contact with the stress relaxation layer and A piezoelectric element having the same polarity.

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