JP2012028410A - Piezoelectric element and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element capable of reducing the defective rate in a manufacturing process of a product utilizing a piezoelectric element and also relaxing the stress inside of the piezoelectric element during driving and a method of manufacturing the same.SOLUTION: A piezoelectric element 100 in which piezoelectric layers 110 and internal electrodes are alternately stacked and which expands and contracts by applying a voltage includes a plurality of stress relaxation layers 150 that relax the stress caused by driving and are formed in contact with an outer periphery on a series of cross-sections vertical to a stacking direction Z around an active region 145 where projections of the internal electrodes in the stacking direction Z overlap. The length of each of the stress relaxation layers 150 along the outer periphery is shorter than the length of one side of the outer periphery. With this configuration, the stress relaxation layers 150 can reduce the stress applied in the piezoelectric element 100 when stress is generated by expansion and contraction of the piezoelectric element 100, and thus the destruction of the piezoelectric element 100 can be prevented. In addition, as the length of each of the stress relaxation layers 150 is shorter than that of one side of the outer periphery, the stress relaxation layers 150 do not cause the destruction and defects hardly occur.

Description

  The present invention relates to a piezoelectric element in which piezoelectric layers and internal electrodes are alternately stacked and expands and contracts by application of a voltage, and a method for manufacturing the same, and particularly relates to relaxation of generated stress.

  The piezoelectric element has a structure in which piezoelectric ceramics and electrodes are laminated. When a voltage is applied, the active part is deformed, but the inactive part is not deformed. Therefore, stress is generated inside the element.

  As one of methods for relieving such stress, a method of providing a stress relieving layer is known (see, for example, Patent Documents 1 and 2). In Patent Documents 1 and 2, a stress relaxation layer that relieves stress generated in a piezoelectrically inactive portion when displaced is arranged so as to surround the internal electrode on the same plane as the internal electrode. A piezoelectric element is disclosed.

  FIG. 9 is a (a) perspective view, (b) (c) cross-sectional view, and (d) a perspective view after use of such a conventional piezoelectric element 1000. In the cross section of the piezoelectric element 1000, the stress relaxation layer 1050 is arranged so as to surround the internal electrode 1020. When a voltage is applied to the external electrode 1030, the stress generated by the deformation of the piezoelectric element is relaxed by the stress relaxation layer 1050.

Japanese Patent No. 2994492 Japanese Patent No. 2951129

  However, as shown in FIG. 9D, the stress relaxation layer 1080 may open more than necessary during firing. The stress relaxation layer 1080 becomes a material mechanical defect, and can become a starting point of destruction with respect to a lateral load. In particular, the corners of the piezoelectric element 1000 are vulnerable to load. In the case of the stress relaxation layer 1050 formed by integral firing, the stress relaxation layer 1050 is often non-uniform, and stress concentrates on the corner portions of the stress relaxation layer 1050 and is easily broken. Therefore, it is weak against the force in the direction perpendicular to the stacking direction, and defects such as breakage may occur in the manufacturing process of products using piezoelectric elements.

  The present invention has been made in view of such circumstances, and provides a piezoelectric element capable of reducing a defect rate in a manufacturing process of a product using a piezoelectric element and relieving internal stress during driving, and a method for manufacturing the same. It is intended.

  (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 stacked and expands and contracts by application of voltage, and the internal electrodes are projected in the stacking direction. A plurality of stress relaxation layers that are formed in contact with the outer periphery on a series of cross-sections perpendicular to the stacking direction around the overlapping active region, and have a length along the outer periphery of each of the stress relaxation layers. Is characterized by being shorter than one side of the outer periphery.

  Thereby, when a stress is generated due to expansion and contraction of the piezoelectric element, the stress applied in the piezoelectric element can be reduced by the stress relaxation layer, and the destruction of the piezoelectric element can be prevented. On the other hand, since the stress relaxation layer is shorter than one side of the outer periphery, the stress relaxation layer does not serve as a starting point of breakdown and hardly causes a failure.

  (2) In addition, the piezoelectric element of the present invention is characterized in that the total sum of projected areas obtained by projecting the plurality of stress relaxation layers in the stacking direction is continuous. Thereby, it can prevent that stress concentrates locally and can relieve stress uniformly.

  (3) In the piezoelectric element of the present invention, the stress relaxation layers are arranged in the stacking direction between the stress relaxation layers closest to each other in a series of cross sections on which the stress relaxation layers are formed. The projected areas overlap each other. Thereby, the stress which arises in the lamination direction can be relieved efficiently.

  (4) Further, the piezoelectric element of the present invention is characterized in that a ratio of the length along the outer periphery of each stress relaxation layer to the length of one side of the outer periphery is 12.5% or more and 33% or less. As a result, it is possible to prevent defects while appropriately balancing stress relaxation and mechanical strength and maintaining the function of the piezoelectric element.

  (5) A method for manufacturing a piezoelectric element according to the present invention is a method for manufacturing a piezoelectric element in which piezoelectric layers and internal electrodes are alternately stacked and expands and contracts by application of a voltage, and the electrode paste is applied to a green sheet of piezoelectric ceramics. And a step of printing a non-sintered material that does not sinter in a predetermined firing temperature process, a step of laminating and pressing a piezoelectric ceramic green sheet including the printed green sheet, and the pressure bonding. A step of degreasing and firing the molded body, and a step of polarizing the fired fired body. When the non-sintered material becomes a fired body, the projection of the internal electrodes in the stacking direction is performed. It is characterized in that it is printed so as to occupy an area shorter than one side of the outer periphery around the overlapping active area and to touch the outer periphery. Thereby, the stress concerning an inside can be reduced and the piezoelectric element which cannot be destroyed easily can be manufactured.

  According to the present invention, it is possible to reduce a defect rate in a manufacturing process of a product using a piezoelectric element and relieve internal stress during driving.

It is a perspective view which shows the piezoelectric element which concerns on this invention. (A) (b) It is a perspective view which shows the piezoelectric element which concerns on this invention. (A) (b) It is a plane sectional view showing the piezoelectric element concerning the present invention. It is a perspective view which shows a green sheet. It is a perspective view which shows the piezoelectric element which concerns on this invention. (A1), (a2) perspective view, (b1), (b2) sectional view, (c1), (c2) sectional view of a conventional piezoelectric element. It is (a1)-(a3) perspective view, (b1)-(b3) sectional drawing, (c1)-(c3) sectional drawing of the piezoelectric element which concerns on this invention. (A4), (a5) perspective view, (b4), (b5) sectional view, (c4), (c5) sectional view of the piezoelectric element according to the present invention. It is (a) perspective view, (b) sectional view, (c) sectional view, (d) perspective view of a 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.

(Configuration of piezoelectric element)
FIG. 1 is a perspective view showing the piezoelectric element 100. 2A and 2B are perspective views showing the piezoelectric element 100. FIG. The piezoelectric element 100 is formed in a rectangular shape. In the piezoelectric element 100, the piezoelectric layers 110 and the internal electrodes 120 are alternately stacked in the stacking direction Z, and the piezoelectric layers 110 are polarized in alternate directions in the thickness direction. The piezoelectric layer 110 is made of a piezoelectric material such as PZT. The internal electrode 120 is taken out to the external electrode 130 on the opposite side surface, and is formed so that a different voltage can be applied to the adjacent internal electrode 120. By applying a voltage to the internal electrode 120, each piezoelectric layer 110 expands and contracts, and the entire piezoelectric element expands and contracts. Although the piezoelectric element 100 has been described as a piezoelectric actuator, the present invention is not necessarily limited to this. Further, the piezoelectric element 100 is not limited to a rectangular shape, and can take various forms.

  The piezoelectric element 100 can be divided into protective layers 141 and 143 provided at both ends in the stacking direction Z as processing allowances and an active layer 142 driven by application of voltage. Further, the active layer 142 can be divided into a central active region 145 where projections of the internal electrodes 120 in the stacking direction Z overlap and a surrounding region 146 provided so that the internal electrodes 120 do not short-circuit with the outside. The active region 145 is a region that is actually driven in the piezoelectric element 100. The active region 145 is driven by voltage, but the surrounding region 146 is not deformed by the application of voltage, and stress is generated.

  A plurality of stress relaxation layers 150 are formed in a region 146 around the active region 145 so as to be partitioned. Each stress relaxation layer 150 is in contact with the outer periphery on a series of cross sections perpendicular to the stacking direction Z. As a result, the stress is released to the outside, and the stress caused by driving the piezoelectric element 100 can be relaxed.

  The length Wr along the outer periphery of each stress relaxation layer 150 is shorter than the length W of one side (side width) of the outer periphery, and the stress relaxation layer 150 is finely divided on a cross section perpendicular to the stacking direction Z. Multiple areas exist. As a result, even if the stress relaxation layer 150 is opened to the outside as a result of firing, it is unlikely to be a starting point of failure as a failure.

  As shown in FIG. 2B, the plurality of stress relaxation layers 150 are intermittently present around the active region on the cross section 147 perpendicular to the stacking direction Z. Since the region 160 where the piezoelectric layers are connected between the stress relaxation layers 150 is three-dimensionally continuous, the piezoelectric element 100 can maintain mechanical strength. The ratio between the length Wr along the outer periphery of each stress relaxation layer 150 and the length W of one side of the outer periphery is preferably 12.5% or more and 33% or less. As a result, the stress relaxation layer 150 is less likely to be a starting point of fracture, and the balance between the stress relaxation effect and the mechanical strength can be appropriately realized.

  FIG. 2B shows a projection of the stress relaxation layer 150 and its stacking direction Z. As shown in FIG. 2B, the total area 170 of the projection areas obtained by projecting the plurality of stress relaxation layers 150 in the stacking direction Z is continuous. Regarding one cross section 147 perpendicular to the stacking direction Z, the area occupied by each stress relaxation layer 150 is intermittent, but the total area 170 obtained by superimposing projections on a plurality of cross sections is continuous.

  In addition, among a series of cross sections that are continuous in the stacking direction in which the stress relaxation layer 150 is formed, projection regions in the stacking direction Z of the stress relaxation layer 150 overlap each other between the stress relaxation layers that are closest to each other on adjacent cross sections. Yes. For example, the length d of the overlapping region of the projections of adjacent cross sections is preferably designed so that d / Wr is 0.1 or more with respect to the length Wr of the stress relaxation layer 150. Thereby, even if the several stress relaxation layer 150 is provided intermittently, stress is fully relieved. FIG. 1 shows the length d of the overlapping region of adjacent cross-sectional projections, the length Wr of the stress relaxation layer, and the length W of one side of the outer periphery.

  3A and 3B are plan sectional views showing the piezoelectric element 100. FIG. Each is a view showing a cross section in which the internal electrode 120 is provided. As shown in FIGS. 3A and 3B, an internal electrode 120 is provided at the center, and regions 160 where the stress relaxation layers 150 and the piezoelectric bodies are connected are alternately provided in the surrounding region. In the figure, the region of the stress relaxation layer 150 is indicated by a low-density pointillistic pattern.

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

  FIG. 4 is a perspective view showing a part of the manufacturing process of the piezoelectric element. A piezoelectric green sheet 200 as shown in FIG. 4 is prepared, and a pattern for the internal electrode 120 and the stress relaxation layer 150 is applied to the green sheet 200 by screen printing or the like. An electrode paste (Ag—Pd alloy or the like) is applied for the internal electrode 120 and then dried to form a pre-fired electrode film.

  Further, a paste of a non-sintered material (such as lead titanate) is applied for the stress relaxation layer 150. The non-sintered material is a material that does not sinter during the firing temperature process of the piezoelectric element 100. 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 out during firing to form the stress relaxation layer 150.

  The paste of non-sintered material is applied to a region finely divided around the region 220 to which the electrode paste is applied. Each region 250 on which the paste of the non-sintered material is printed is provided so as to be shorter than one side of the outer periphery and in contact with the outer periphery when it becomes a fired body.

  Next, a plurality of green sheets on which an electrode film and a non-sintered material film are formed are laminated, press-molded, and then 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 layer 150 is formed at the location where the non-sintered material is applied. Then, the sintered body is appropriately processed, and a plurality of processed sintered bodies are bonded in the stacking direction to be multiple. An actuator for a positioner in which the piezoelectric elements 100 are connected in series can be manufactured by performing polarization treatment on the fired bodies that are connected in series and covering the caps.

  In addition, as a result of firing, the piezoelectric element 100 may open the stress relaxation layer 150 more than necessary. FIG. 5 is a perspective view showing the piezoelectric element 100 with some stress relaxation layers open. Some of the stress relaxation layers 180 of the piezoelectric element 100 as shown in FIG. However, unlike the stress relaxation layer 1080 as shown in FIG. 9, since the length of the stress relaxation layer is small with respect to one side of the outer periphery, the opened stress relaxation layer 180 does not serve as a starting point of destruction.

  A plurality of types of fired bodies were produced with designs having different stress relaxation layer lengths, and six fired bodies for each type were bonded in multiple layers by adhering end faces in the stacking direction. Then, the fired bodies that were serialized were polarized and covered with a cap, and the displacement amount of the obtained positioner was measured, and the defect rate in the process was recorded.

(Comparative Examples 1 and 2)
6 (a1) to (a2), (b1) to (b2), and (c1) to (c2) are perspective views showing Comparative Example 1 and Comparative Example 2, respectively, a cross-sectional view of a left side extraction electrode position, and a right side It is sectional drawing of a surface extraction electrode position. The piezoelectric element 1100 of Comparative Example 1 has a continuous stress relaxation layer 1150 around the entire periphery of the internal electrode 1120. The stress relaxation layer 1150 is provided so that the ratio of the stress relaxation layer length to the side surface length is 1. Other configurations are the same as those in the above embodiment. Such a piezoelectric element 1100 was bonded in the displacement direction to form a multiple positioner. And the amount of displacement was measured and the defective rate in the adhesion process was recorded.

  On the other hand, the piezoelectric element 1200 of Comparative Example 2 has a stress relaxation layer 1150 continuous on two sides around the internal electrode 1220. The stress relaxation layer 1150 is provided so that the ratio of the stress relaxation layer length to the side surface length is 0.9. Other configurations are the same as those in the above embodiment. Such a piezoelectric element 1200 was also subjected to multiple connection by an adhesion process to produce a positioner. And the amount of displacement was measured and the defective rate in the adhesion process was recorded.

(Examples 1-5)
7 (a1) to (a3), (b1) to (b3), (c1) to (c3), FIGS. 8 (a4) to (a5), (b4) to (b5), (c4) to (c5) ) Are a perspective view of Examples 1 to 5, a cross-sectional view of a left side extraction electrode position, and a cross-sectional view of a right side extraction electrode position, respectively.

  The piezoelectric element 300 according to the first embodiment includes a plurality of stress relaxation layers 350 around the internal electrode 320. The stress relaxation layer 350 is provided so that the ratio of the stress relaxation layer length to the side surface length is 12.5%. Further, adjacent cross-sections provided with the stress relaxation layers 350 do not overlap in the stacking direction of the stress relaxation layers 350 and are alternately arranged. Other configurations are the same as those in the above embodiment. A plurality of such piezoelectric elements 300 were manufactured, and bonded in the displacement direction to form multiple positioners. And the amount of displacement was measured and the defective rate in the adhesion process was recorded.

  The piezoelectric element 400 of Example 2 has a plurality of stress relaxation layers 450 around the internal electrode 420. The stress relaxation layer 450 is provided so that the ratio of the stress relaxation layer length to the side surface length is 25%. In addition, the adjacent cross-sections provided with the stress relaxation layers 450 are arranged in a staggered manner without overlapping the projections in the stacking direction of the stress relaxation layers 450. Other configurations are the same as those in the above embodiment. A plurality of such piezoelectric elements 400 were produced, adhered in the displacement direction, and connected in multiples to produce a positioner. And the amount of displacement was measured and the defective rate in the adhesion process was recorded.

  The piezoelectric element 500 of Example 3 has a plurality of stress relaxation layers 550 around the internal electrode 520. The stress relaxation layer 550 is provided so that the stress relaxation layer length to side length ratio is 33%. In addition, the adjacent cross sections provided with the stress relaxation layers 550 are arranged in a staggered manner without overlapping the projections in the stacking direction of the stress relaxation layers 550. Other configurations are the same as those in the above embodiment. A plurality of such piezoelectric elements 500 were manufactured, adhered in the displacement direction, and connected in multiples to prepare a positioner. And the amount of displacement was measured and the defective rate in the adhesion process was recorded.

  The piezoelectric element 600 of Example 4 has a plurality of stress relaxation layers 650 around the internal electrode 620. The stress relaxation layer 650 is provided so that the ratio of the stress relaxation layer length to the side surface length is 17%. Further, the adjacent cross sections provided with the stress relaxation layer 650 are arranged so that the projections in the stacking direction of the stress relaxation layer 650 overlap each other by 17%. Other configurations are the same as those in the above embodiment. A plurality of such piezoelectric elements 600 were produced, adhered in the displacement direction, and connected in multiples to produce a positioner. And the amount of displacement was measured and the defective rate in the adhesion process was recorded.

  The piezoelectric element 700 of Example 5 has a plurality of stress relaxation layers 750 around the internal electrode 720. The stress relaxation layer 750 is provided such that the ratio of the stress relaxation layer length to the side surface length is 19%. Further, the adjacent cross sections provided with the stress relaxation layer 750 are arranged so that the projections in the stacking direction of the stress relaxation layer 750 overlap each other by 25%. Other configurations are the same as those in the above embodiment. A plurality of such piezoelectric elements 700 were manufactured, and bonded in the displacement direction to form multiple positioners. And the amount of displacement was measured and the defective rate in the adhesion process was recorded.

Table 1 shows the shape and arrangement of the stress relaxation layer, the ratio of the amount of displacement, and the defective rate of the bonding process for Comparative Examples 1 and 2 and Examples 1 to 5.

  The main cause of the defect in the bonding process is a defect that breaks during the work after bonding the fired body. In Comparative Examples 1 and 2, defects occurred 0.5% and 0.25%, respectively, in the bonding process. On the other hand, as in Examples 1 to 5, by setting the stress relaxation layer length to 33% or less of the side length, the defect rate in the bonding process was less than 0.1%, and defects were almost eliminated. Furthermore, when the stress relaxation layer length was designed to be 25% or less of the side surface length, there were no defects broken in the bonding process.

  The displacement amount when the displacement amount of the positioner of Comparative Example 1 was taken as 100% was measured. The displacement amounts of Comparative Example 2, Example 3, and Example 5 were almost the same as those of Comparative Example 1 and were 100%. In Example 1, the amount of displacement was reduced by about 5%, and in Examples 2 and 4, the amount of displacement was reduced by about 2%. This is considered to be because when the stress relaxation layer is shortened, the displacement is hindered by the restraint of the portion where there is no stress relaxation layer.

  On the other hand, in Example 5, it is considered that the above-described constraint can be relaxed by projecting the stress relaxation layers of adjacent cross sections in the stacking direction, and the displacement is not hindered. Thereby, the projection area | region to the lamination direction of a stress relaxation layer mutually overlaps between the stress relaxation layers nearest on an adjacent cross section among a series of cross sections in which the stress relaxation layer was formed. Therefore, it is conceivable that not only the defective rate is reduced in the bonding process, but also the amount of displacement is secured.

  Thus, it has been confirmed that the defect rate can be reduced by setting the stress relaxation layer length to the side surface length to 12.5% or more and 33% or less. It was also confirmed that a sufficient amount of displacement could be ensured by setting the overlap length corresponding force relaxation length to 25% or more.

100, 300, 400, 500, 600, 700 Piezoelectric element 110 Piezoelectric layer 120, 320, 420, 520, 620, 720 Internal electrode 130 External electrode 141 Protective layer 142 Active layer 145 Active region 146 Surrounding region 147 Cross section 150, 350 , 450, 550, 650, 750 Stress relaxation layer 160 Area where piezoelectric bodies are connected 170 Total area of projection area 180 Open stress relaxation layer 200 Green sheet 220 Area where electrode paste is applied 250 Paste of non-sintered material Each printed area Z Lamination direction

Claims (5)

Piezoelectric elements in which piezoelectric layers and internal electrodes are alternately stacked and expand and contract by application of voltage,
Provided with a plurality of stress relaxation layers formed in contact with the outer periphery on a series of cross sections perpendicular to the stacking direction around the active region where the projections in the stacking direction of the internal electrodes overlap,
The length along the outer periphery of each said stress relaxation layer is shorter than one side of an outer periphery, The piezoelectric element characterized by the above-mentioned.   2. The piezoelectric element according to claim 1, wherein the plurality of stress relaxation layers have a total sum of projection areas obtained by projecting in the stacking direction.   The projected regions of the stress relaxation layers in the stacking direction overlap each other between the stress relaxation layers closest to each other in a series of cross sections in which the stress relaxation layers are formed. Item 3. The piezoelectric element according to item 1 or 2.   The ratio of the length along the outer periphery of each of the stress relaxation layers and the length of one side of the outer periphery is 12.5% or more and 33% or less, according to any one of claims 1 to 3. Piezoelectric element. Piezoelectric layers and internal electrodes are alternately stacked, and a piezoelectric element manufacturing method that expands and contracts by applying a voltage,
Printing an electrode paste and a non-sintered material that does not sinter in a predetermined firing temperature process on a piezoelectric ceramic green sheet;
Including the green sheet on which the printing has been performed, a step of laminating and pressing the piezoelectric ceramic green sheet; and
Degreasing and firing the molded body obtained by the pressure bonding; and
A step of polarizing the fired fired body,
When the non-sintered material becomes a fired body, the non-sintered material is printed so as to occupy a region shorter than one side of the outer periphery around the active region where the projections in the stacking direction of the internal electrodes overlap, and touch the outer periphery. A method of manufacturing a piezoelectric element characterized by the above.

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