JP5643561B2 - Piezoelectric element and manufacturing method thereof - 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 application of a voltage, and a method for manufacturing the same, and particularly relates to relaxation of generated stress.

  A piezoelectric element is an element in which piezoelectric layers and internal electrodes are alternately stacked and displacement due to application of voltage is used. In the piezoelectric element, the piezoelectrically active piezoelectric layer is displaced, and the inactive portion is not displaced. Therefore, stress is generated in the piezoelectric element when the piezoelectric element is displaced. As one method of relieving such stress, a method of disposing a stress relieving layer is known. The stress relaxation layer is disposed so as to surround the periphery of the internal electrode on the same plane as the internal electrode, and relieves stress generated during driving (see Patent Documents 1 and 2).

Japanese Patent No. 2994492 Japanese Patent No. 2951129

  However, the stress relaxation layer as described above can be a starting point of fracture against a lateral load as a material mechanical defect. In particular, the corners of the piezoelectric element are vulnerable to load. Therefore, the malfunction which may break by the handling of the adhesion process which connects a piezoelectric element to a lamination direction may generate | occur | produce. On the other hand, in a piezoelectric element structure without a stress relaxation layer, stress may be generated during the operation of the piezoelectric element, and the direction and size of cracks due to the stress may not be controlled.

  The present invention has been made in view of such circumstances, and provides a piezoelectric element that can maintain strength in a manufacturing process and can sufficiently relieve stress during operation after manufacturing, and a manufacturing method thereof. With the goal.

  (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. Is formed by opening the quasi-stress relaxation layer with respect to the outer periphery, which is closed with respect to the outer periphery around the overlapping active region and formed of a non-sintered material or voids. And a stress relaxation layer that relaxes.

  Thereby, since the quasi-stress relaxation layer is closed with respect to the outer periphery, the piezoelectric element has strength against a load in a direction perpendicular to the stacking direction. Moreover, the stress relaxation layer can relieve the stress generated in a state where a voltage is applied to the piezoelectric element. As a result, in the manufacturing process up to the polarization treatment, the strength can be maintained by the quasi-stress relaxation layer, and then the stress can be relaxed by the stress relaxation layer opened to the outer periphery.

  (2) In the piezoelectric element of the present invention, the ratio of the stress relaxation layer region to the total region of the quasi-stress relaxation layer and the stress relaxation layer is 8% or more. Thereby, when a voltage is applied to the piezoelectric element and the piezoelectric element operates, the stress relaxation layer functions, and the stress can be sufficiently relaxed.

  (3) In the piezoelectric element of the present invention, the thickness of the outer peripheral wall closing the quasi-stress relaxation layer with respect to the outer periphery is 0.05 mm or more and 0.35 mm or less. Thereby, the quasi-stress relaxation layer can be opened during the polarization treatment while maintaining the strength in the manufacturing process. That is, since the thickness of the outer peripheral wall is 0.05 mm or more, the strength is maintained until the middle of the manufacturing process, and since it is 0.35 mm or less, the wall can be taken and the stress can be relaxed.

  (4) 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. Including a step of degreasing and firing the molded body and a step of polarizing the fired fired body, and when the non-sintered material becomes a fired body, projections in the stacking direction of the internal electrodes overlap. Printing is performed in a region that does not reach the outer periphery around the active region.

  Thereby, in a manufacturing process, intensity | strength is maintained with an outer peripheral wall, and malfunctions, such as breakage, can be prevented. Moreover, stress can be relieved by a stress relieving layer whose outer peripheral wall is broken by polarization treatment thereafter.

  According to the present invention, strength can be maintained in the manufacturing process, and stress can be sufficiently relaxed during operation after manufacturing.

BRIEF DESCRIPTION OF THE DRAWINGS (a) Perspective view, (b) Plan sectional view, (c) Plan sectional view showing a piezoelectric element according to the present invention. It is a sectional side view which shows the piezoelectric element which concerns on this invention. It is a perspective view which shows the sintered body in one scene of a manufacturing process. (A1), (a2) perspective view, (b1), (b2) sectional view, (c1), (c2) sectional view showing a piezoelectric element of a comparative example.

  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.

  FIGS. 1A to 1C are a perspective view showing the piezoelectric element 100, a sectional view of the quasi-stress relaxation layer 140, and a sectional view of the stress relaxation layer 140, respectively. In the piezoelectric element 100, the piezoelectric layers 110 and the internal electrodes 120 are alternately stacked in the stacking direction Z, and are formed in a rectangular shape. The piezoelectric layer 110 is made of, for example, a piezoelectric material such as PZT, and is polarized in alternate directions in the thickness direction. 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 is distorted and the entire piezoelectric element expands and contracts. In addition, although the piezoelectric element 100 is demonstrated as a piezoelectric actuator, this invention is not necessarily limited to this. In addition, the piezoelectric element 100 is not limited to a rectangular shape and can take various forms.

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

  The piezoelectric element 100 has a quasi-stress relaxation layer 140 and a stress relaxation layer 150. FIG. 2 is a side sectional view showing the piezoelectric element 100. The cross section shown in FIG. 2 corresponds to the cross section A in FIGS. The quasi-stress relaxation layer 140 is closed with respect to the outer periphery by the outer peripheral wall 141 around the active region, and is formed of a non-sintered material or a void. In principle, the outer peripheral wall 141 is continuously formed along the outer periphery. However, a part of the outer periphery may be closed and the remaining part may be opened.

  The thickness of the outer peripheral wall 141 is preferably 0.05 mm or more and 0.35 mm or less. Thereby, for example, 8% or more of the outer peripheral wall 141 in the outer peripheral wall 141 formed at the time of firing is broken in the polarization step, and the quasi-stress relaxation layer 140 for 8% can be changed to the stress relaxation layer 150. When the piezoelectric element 100 has 120 quasi-stress relaxation layers 140, it is sufficient that about 10 of the quasi-stress relaxation layers 140 become the stress relaxation layers 150.

  When the thickness of the outer peripheral wall 141 is greater than 0.35 mm, the outer peripheral wall 141 may be broken only by 8% or less in the polarization step, and a sufficient number of stress relaxation layers 150 may not be formed. In that case, a large crack may enter the active region starting from the stress relaxation layer 150, and the piezoelectric element 100 may be destroyed.

  The quasi-stress relaxation layer 140 is changed to the stress relaxation layer 150 when the outer peripheral wall 141 is broken and opened with respect to the outer periphery in the manufacturing process of the piezoelectric element 100. Since the quasi-stress relaxation layer 140 is closed with respect to the outer periphery until the middle of the manufacturing process, the strength of the piezoelectric element 100 that can withstand the lateral load applied in the process is maintained. Usually, the piezoelectric element 100 is sufficient if the strength is maintained until the polarization treatment step, and the outer peripheral wall 141 is preferably designed to be broken in the polarization treatment step.

  The stress relaxation layer 150 is formed in a region around the active region. The stress relaxation layer 150 is formed when the quasi-stress relaxation layer 140 is broken and opened with respect to the outer periphery, and relieves stress due to driving. Each stress relaxation layer 150 is formed in contact with the outer periphery on a cross section 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 ratio of the stress relaxation layer region to the total region of the quasi-stress relaxation layer 140 and the stress relaxation layer 150 is 8% or more. Accordingly, when a voltage is applied to the piezoelectric element 100 and the piezoelectric element 100 is operated, the stress relaxation layer 150 functions and the stress can be sufficiently relaxed.

(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. A pattern for the internal electrode 120 and the stress relaxation layer 150 is applied to the green sheet 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 quasi-stress relaxation layer 140. 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 quasi-stress relaxation layer 140.

  Each region on which the paste of the non-sintered material is printed is printed in a region that does not reach the outer periphery around the active region when it becomes a fired body. It is preferable to print from 0.05 mm to 0.35 mm from the position that becomes the outer periphery after firing. The region up to the remaining outer peripheral position becomes the outer peripheral wall 141 by firing.

  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, lead titanate is not sintered, and a quasi-stress relaxation layer 140 is formed at a location where a non-sintered material is applied. The non-sintered material is a material that does not sinter at the firing temperature of the piezoelectric element 100. FIG. 3 is a perspective view showing the fired body 200 in one scene of the manufacturing process. By appropriately processing after firing, the fired body 200 before polarization is obtained. And the sintered compact 200 is processed suitably, and it adhere | attaches on the end surface of the lamination direction Z, and is made in multiples. And the actuator for positioners can be produced by polarization-processing the baked body 200 made into multiple.

  At that time, since a voltage is applied between the internal electrodes 120 and distortion occurs, the outer peripheral wall 141 of a part of the quasi-stress relaxation layer 140 is broken, and the quasi-stress relaxation layer 140 is changed to the stress relaxation layer 150. In this way, the piezoelectric element 100 is obtained as a multiple actuator as a positioner actuator.

  The piezoelectric elements 800 and 900 of Comparative Examples 1 and 2 and the piezoelectric element 100 of Example 1 were manufactured. At that time, each of the six fired bodies was made into multiples by the bonding process, and the occurrence of defects was observed. In addition, it was confirmed that there was no problem with the amount of displacement by operating a piezoelectric element that had been subjected to polarization treatment and connected in multiples.

  4 are (a1) and (a2) perspective views, (b1) and (b2) cross-sectional views, and (c1) and (c2) cross-sectional views showing the piezoelectric elements 800 and 900 of Comparative Examples 1 and 2. FIG. The piezoelectric element 800 is formed by alternately stacking piezoelectric layers 810 and internal electrodes 820. The piezoelectric layers 810 are polarized in alternate directions. The piezoelectric element 800 has an external electrode 830 on the side surface as an extraction electrode of the internal electrode 820, and the displacement can be controlled by applying a voltage between the internal electrodes 120 using these electrodes. In addition, the piezoelectric element 800 has a stress relaxation layer 850 over one circumference around the internal electrode 820.

  Similarly, the piezoelectric element 900 is formed by alternately stacking piezoelectric layers 910 and internal electrodes 920. The piezoelectric layers 910 are polarized in alternating directions. The piezoelectric element 900 has an external electrode 930 on the side surface as an extraction electrode of the internal electrode 920, and the displacement can be controlled by applying a voltage between the internal electrodes 120 using these electrodes. In addition, the piezoelectric element 900 has a stress relaxation layer 950 over a half circumference (two sides of the side surface) around the internal electrode 920. Reference examples 1 and 2 were produced by a method for producing a piezoelectric element having a normal stress relaxation layer.

In Example 1, the electrode pattern and the non-sintered material pattern were arranged so that the quasi-stress relaxation layer 140 was not exposed on the element surface. A 6 mm × 6 mm cross section has a 5.4 mm × 5.4 mm active region where the internal electrodes overlap, and the periphery is surrounded by a 0.3 mm wide quasi-stress relaxation layer 140. The quasi-stress relaxation layer 140 was not exposed on the surface of the device after processing. When this was polarized at 3 kV / mm, it was confirmed that the outer peripheral wall 141 was peeled in 10 to 20 layers of the 120 quasi-stress relaxation layers 140. Regarding the piezoelectric elements of Comparative Examples 1 and 2 and Example 1 manufactured as described above, Table 1 in which a plurality of piezoelectric elements were connected in series by an adhesion process and the amount of displacement was measured is a table showing the experimental results. is there. As the amount of change, the amount of displacement when the amount of displacement of Cited Example 1 is taken as 100% is displayed in%.

  The main cause of the defect in the bonding process is a defect that breaks during work after bonding. By using the structure as in the example, almost no defects were broken. Moreover, the amount of displacement was almost the same. It is considered that during the polarization process after the bonding process, stress was applied to the peeled portion due to the displacement of the active portion, and peeling occurred due to the stress relaxation layer hidden inside the element. Although there were few stress relaxation layers with peeling as 10-20 layers, displacement was not restrained.

DESCRIPTION OF SYMBOLS 100 Piezoelectric element 110 Piezoelectric layer 120 Internal electrode 130 External electrode 140 Quasi stress relaxation layer 141 Outer peripheral wall 150 Stress relaxation layer 200 Firing body A Section Z Lamination direction

Claims (3)

Piezoelectric elements in which piezoelectric layers and internal electrodes are alternately stacked and expand and contract by application of voltage,
A quasi-stress relaxation layer formed of a non-sintered material or a void, which is closed with respect to the outer periphery of the piezoelectric element around the active region where projections in the stacking direction of the internal electrodes overlap;
The quasi-stress relaxation layer is formed by opening with respect to the outer periphery of the piezoelectric element , and includes a stress relaxation layer that relaxes stress due to driving ,
The thickness of the outer peripheral wall closing the quasi stress relieving layer with respect to the outer periphery of the piezoelectric element, the piezoelectric element characterized der Rukoto than 0.35mm below 0.05 mm.   2. The piezoelectric element according to claim 1, wherein a ratio of a region of the stress relaxation layer to a total region of the quasi-stress relaxation layer and the stress relaxation layer is 8% or more. 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,
The non-sintered material is printed in a region that does not reach the outer periphery of the fired body around the active region where the projections in the stacking direction of the internal electrodes overlap when it becomes a fired body ,
In the manufactured piezoelectric element, the thickness of the outer peripheral wall closing the quasi-stress relaxation layer formed of the non-sintered material or the gap with respect to the outer periphery of the piezoelectric element is 0.05 mm or more and 0.35 mm or less. method for manufacturing a piezoelectric element characterized der Rukoto.

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