JP2010212315A - Multilayer piezoelectric ceramic element and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer piezoelectric ceramic actuator which has high-reliability and high-performance driving characteristics and actuator characteristics, and to provide a multilayer piezoelectric ceramic element using the same and a method of manufacturing the same. <P>SOLUTION: The multilayer piezoelectric ceramic element 1 has a driving part 2 formed by stacking piezoelectric units each composed of piezoelectric ceramic and an internal electrode alternately, and dummy parts 3, 4 fixed to the driving part 2, wherein the dummy parts 3, 4 are provided with at least one layer of a dummy internal electrode 16 and formed in a part not in contact with an external electrode 5. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an improvement of a laminated piezoelectric ceramic element and a method for manufacturing the same, and more specifically includes a laminated piezoelectric ceramic actuator and a laminated piezoelectric ceramic, and has particularly high reliability and high performance drive characteristics. Moreover, it is related with the manufacturing method.

  Conventionally, the multilayer piezoelectric ceramic actuator is disclosed in Patent Documents 1 to 5 and the like. The outline of the configuration is shown in FIGS. 14 and 15 as perspective views. 14A and 14B are structural views of a conventional multilayer piezoelectric ceramic actuator, FIG. 14A is a side perspective view, and FIG. 14B is a side perspective view of a piezoelectric unit 15 that is stacked by changing the direction of internal electrodes. FIG. 15 is a side perspective view showing a state of an external electrode portion of a conventional multilayer piezoelectric ceramic actuator. As shown in FIG. 14B, the driving unit 2 of the laminated piezoelectric ceramic actuator 1 is formed by laminating piezoelectric units 15. The piezoelectric unit 15 has an internal electrode 6 formed on a piezoelectric ceramic. More specifically, the internal electrode 6 includes a margin electrode 6 and a portion 7 where the margin electrode 6 is not formed on the upper surface of the piezoelectric ceramic.

  FIG. 14B is a state diagram before the four units of the piezoelectric unit 15 are overlapped with the ends of the margin electrode 6 being repeatedly reversed in order from right to left. In this state, the external electrode 15 collects the part where the internal electrode appears at the left end and the part where the internal electrode appears at the right end, and is connected to the left external electrode 5 and the right external electrode 5 (not shown). As the piezoelectric output of the laminated piezoelectric ceramic actuator, the actuator piezoelectric output generated between the left external electrode and the right external electrode 5 can be taken out. In this way, the piezoelectric unit 15 functions as the driving unit 2 of the actuator 1 by stacking portions made of alternately stacked piezoelectric ceramics.

  On the other hand, as a practical example, Non-Patent Document 1 shows “Manufacturing process of laminated PA” of “NEC TOKIN piezoelectric device”. Among these, in order to relieve the stress generated in the gap between the electrode and the ceramic, a technique of applying an insulating glass to the surface and relieving the internal stress is adopted.

However, these documents still have the following problems to be solved.
In Patent Documents 1 to 5, dummy portions 3 and 4 are provided on an upper part and a lower part made of laminated piezoelectric ceramics as a countermeasure against insulation and as a countermeasure against an impact against a load. However, the upper and lower dummy parts are composed only of ceramics, and there is a difference in Young's modulus between the drive part 2 (piezoelectric part) containing the internal electrodes and the dummy part, resulting in a large error in the output of the generated force. There was a problem that would occur.

  There are two types of internal electrodes of the laminated element: a type in which a metal plate and piezoelectric ceramic are bonded, and a type in which the internal electrode is applied and integrally sintered. However, since the former is a type using an adhesive, there is a problem that an accurate displacement amount cannot be obtained and the cost is high. Further, in the case of a laminated ceramic element that is fixed with an adhesive using a metal plate as an internal electrode and a sintered ceramic element, there is a problem that the manufacturing accuracy is low and the cost is high. In addition, there is a problem that the shape of the laminated element is at most φ8 mm or less and height is 5 mm or less.

  For the latter type in which the internal electrode is applied, for example, a method of alternately laminating piezoelectric ceramic sheets is disclosed (Patent Document 1). According to this, regarding the dummy part and the ceramic part (driving part) at the time of firing, the ceramic of the dummy part uses base metal and uses reducing atmosphere sintering. Further, there is a disclosure that the lead zirconate titanate (PZT) composition constituting the dummy part adjusts the shrinkage by changing the density of the ceramic sheet. However, this method requires a special sheet in the dummy part to which the base metal is added, and it is necessary to sinter in a reducing atmosphere, so a dedicated furnace must be secured and a dedicated sintering temperature pattern is essential, making the manufacturing process complicated. There was a problem.

  The multilayer actuator disclosed in Patent Document 2 discloses that the pattern of the internal electrode near the upper part is changed and the vicinity of the center is displaced from the surroundings. However, the multilayer actuator is required to have various shapes depending on the application, but cannot be applied thereto. Further, since there is a non-electrode portion inside, there is a portion that does not stretch, and there remains a problem in reliability for continuous driving and driving in a no-load environment.

  Patent Document 3 discloses a method of making holes using laser light every other layer in order to connect the internal electrode and the external electrode. According to this, a dedicated device is necessary, and problems remain in practicality in terms of manufacturing. For example, it is difficult to maintain the drilling accuracy with a sheet of 100 μm or less. Sintering conditions that match the shrinkage of the drilled hole and the shrinkage accuracy of the sheet are required, but there is no disclosure thereof. As a result, it is necessary to set for each shape of the laminated actuator, and there remains a problem in terms of manufacturing cost in a variety of laminated actuators.

  The multilayer piezoelectric actuator disclosed in Patent Document 4 provides a multilayer piezoelectric actuator with excellent durability that is resistant to stress destruction. Therefore, the center portion of the element is displaced compared to the outer peripheral portion, resulting in displacement variation. ing. As a solution to this problem, the displacement variation control means only discloses that manganese or the like contained in the dope paste is diffused into a part of the ceramic when the piezoelectric actuator is fired. However, such a method is not practical, and there is a problem that the composition of the contact surface changes due to diffusion after firing.

  Patent Document 5 discloses a structure in which stress concentration in the vicinity of the boundary between the piezoelectric driving portion and the protective layer portion is relaxed by the stress absorption layer. In the piezoelectric drive unit, it is mentioned that the occurrence of dielectric breakdown is suppressed at a portion close to the protective layer portion.

  According to this, the shape of the internal electrode layer in the piezoelectric drive unit is set to a so-called annular rectangle (Table 1). Further, “curvature R1” in Table 1 indicates the curvature provided at the four corners of the rectangular internal electrode layer, and no curvature is provided in the comparative example and Examples 1 and 2, and Example In 3-5, the description that the curvature of 2 mm is provided is recognized. Then, the curvature R1 suppresses charge concentration at the four corners of the internal electrode layer, making it difficult for dielectric breakdown to occur, and providing the curvature R2 at the joint can reduce stress concentration. Is allowed.

  However, this is for the occurrence of dielectric breakdown in the piezoelectric drive section and the protective layer section, and internal strain occurs with respect to the load in the laminated piezoelectric actuator, and the problem about the cause of the breakdown has not been solved. Furthermore, since the lamination actuator is sintered from the silver portion in the outer peripheral portion, there is a problem that non-uniform sintering at the sintering temperature may occur between the central portion and the silver internal electrode as a whole.

  In order to ensure insulation between layers, as shown in FIG. 14, an electrode portion having a margin electrode 6 (in Patent Document 5, it is connected to the external electrode 13 only by a small connecting portion from the internal electrode 12; see FIG. 2). Is required. However, Patent Document 5 does not suggest a problem with respect to the point that tensile stress concentrates on the margin electrode 6 and leads to damage or cracks during driving. On the other hand, Non-Patent Document 1 uses an internal electrode without a margin, and a glass coating is used for taking out the electrode. However, such a method is expensive, and it is difficult to cope with a device using many laminated elements.

  In general, the piezoelectric ceramics constituting the piezoelectric actuator have variations in characteristics, but in the laminated state, the entire displacement amount is also averaged. On the other hand, the displacement characteristics vary greatly depending on the number of stacked layers and shapes, and depending on the composition, there are many problems such as different proper firing temperatures, differences in shrinkage, cracks, delamination, etc. It was.

  Thus, Patent Documents 1 to 5 do not disclose that the edge portion is processed on the peripheral surface portion of the piezoelectric ceramic. For this reason, according to the confirmation of the present inventors, chipping (debris) is likely to occur in the process of manufacturing the piezoelectric ceramic element, and good characteristics could not be obtained in the final durability driving test. Pressure distortion at the time of deformation occurs in the upper and lower parts of the multilayer piezoelectric ceramic actuator. For this reason, it is considered that an accurate displacement amount cannot be output due to a reaction force from an external fixed portion (installation portion) during driving. As a problem in manufacturing, distortion occurs due to a difference in shrinkage between the internal electrode and the ceramic during firing of the laminated element. Since the internal electrode exerts a large strain force in the in-plane shear direction, it has been necessary to solve problems such as delamination and cracks often occurring during firing.

JP 2002-314156 A Japanese Patent Laid-Open No. 2003-23186 JP 2004-111718 A JP 2004-158494 A JP 2006-286774 A

http://www.nec-tokin.com/product/piezodevice1/piezo_actuator.html

  The present invention has been made in view of such circumstances, and relates to an improvement of a multilayer piezoelectric ceramic actuator, and in particular, a multilayer piezoelectric ceramic actuator having high reliability and high performance drive characteristics and actuator characteristics, and a multilayer piezoelectric using the same. An object is to provide a ceramic element.

  In order to solve the above-described problems, the present invention provides a laminated piezoelectric ceramic element including a driving unit in which piezoelectric units made of piezoelectric ceramics and internal electrodes are alternately stacked, and a dummy unit fixed to the driving unit. The dummy portion is provided with a laminated piezoelectric ceramic element, wherein the dummy portion is provided with at least one layer of dummy inner electrode and formed in a portion not in contact with the external electrode.

Further, the piezoelectric ceramic is selected from lead-free piezoelectric ceramics including lead zirconate titanate (PZT) composition using lead, bismuth sodium titanium (Bi Na) TiO ₂ and potassium sodium niobium (Na K) NbO ₃ system. It is provided by the laminated piezoelectric ceramic element, which is any material.

The internal electrode has a resistance value of 10 ohms or less when driven, and is silver-nickel-copper (Ag, Ni, Cu), cobalt-nickel-iron alloy (Co-Ni-Fe alloy, Kovar, KOVAR ( Provided by the multilayer piezoelectric ceramic element described above, wherein the laminated piezoelectric ceramic element is any material selected from ceramics such as base metals such as (registered trademark) plate) and conductive transition metals such as lanthanum copper oxide (La ₂ CuO ₄ ). Is done.
Furthermore, A> 0.05 mm between the thickness A (mm) of the dummy part added to the upper part and the lower part of the driving part and the overall length L (mm) of the laminated piezoelectric ceramic element, and The multilayer piezoelectric ceramic element is provided with the relationship 2A <0.5L.

Furthermore, the dummy part fixed to the driving part is provided by the laminated piezoelectric ceramic element, which is added to the upper part and the lower part of the driving part.
In addition, the multilayer piezoelectric ceramic element is provided with the drive unit having the drive unit in which a chamfer is formed by a straight cut or a cut by a curvature R at a peripheral corner portion of the drive unit.

The cut with the curvature R satisfies the relationship of R ≧ W / 2 and R <3W with the width W (W1, W2), and the unevenness of the cut processing surface is processed to a maximum of 10 μm or less. It is provided by the laminated piezoelectric ceramic element described above.
Further, the dummy part is provided by the multilayer piezoelectric ceramic element, wherein the dummy part is fixed to only one of the drive parts, and at least one internal electrode in the dummy part is included.

Furthermore, the internal electrode in the dummy portion is a full surface electrode having no margin portion, and is provided by the multilayer piezoelectric ceramic element.
In addition, a non-electrode printed portion is applied to the central portion of the internal electrode in order to reduce the tensile stress of the silver electrode, and the non-electrode printed portion is 2% or less of the total area of the internal electrode. Effectively provided by ceramic elements.

Furthermore, the non-electrode printed part having a diameter of 0.5 to 3 μm is applied, and the non-electrode printed part is arranged on the diagonal line and uniformly in the central part. It is effectively provided by the above-mentioned laminated piezoelectric ceramic element.
The multilayer piezoelectric ceramic element according to any one of the above, wherein the multilayer piezoelectric ceramic element is a multilayer piezoelectric ceramic actuator.
The multilayer piezoelectric ceramic element according to any one of the above-mentioned features, wherein the multilayer piezoelectric ceramic element is a multilayer piezoelectric ceramic.

  Piezoelectric ceramic powder and organic binder components, dispersing agent, plasticizer, etc. are mixed and defoamed with an organic solvent, viscosity is adjusted to produce a sheet molding slurry, and a tape is formed using the slurry to form a sheet And printing and laminating internal electrodes on the molded sheet, pressing the molded sheet together with a dummy portion provided with at least one dummy inner electrode, cutting the laminated piezoelectric ceramic element, collecting the inner electrode side, It is provided by a method for manufacturing a laminated piezoelectric ceramic element, characterized in that a driving section is formed and polarized.

Further, the present invention is provided by the method for manufacturing a laminated piezoelectric ceramic element, wherein a plurality of unsilvered portions 8 are formed on the internal electrode.
Further, the present invention is effectively provided by the method for manufacturing a laminated piezoelectric ceramic element, wherein a chamfering is formed at a peripheral corner portion of the driving portion by a straight cut or a cut by a curvature R.

  The present invention is intended to improve the reliability of laminated piezoelectric ceramic actuators, laminated piezoelectric ceramics, production yield, durability, and the like. Due to such improved reliability and durability, the actuator can be applied to automobiles and used in structures. In general, improvement in characteristics can be expected by using laminated piezoelectric ceramic actuators and laminated piezoelectric ceramics as developments of lead-free piezoelectric ceramic materials that do not use lead, which has inferior piezoelectric characteristics compared to PZT.

FIG. 1 is a side perspective view of a multilayer piezoelectric ceramic actuator. FIG. 2 is a side perspective view showing a state of the dummy inner electrode of the multilayer piezoelectric ceramic actuator of FIG. FIG. 3 shows one embodiment of a piezoelectric unit to which an internal electrode 6 on a piezoelectric ceramic is added. FIGS. 3A and 3B are plan views in which the position of the non-electrode portion 8 is changed. FIG. 4 is a plan view of the piezoelectric unit showing that the unsilvered portions 8 of the internal electrodes 6 are distributed when the piezoelectric units are stacked. 5A and 5B are structural views of the laminated piezoelectric ceramic actuator, wherein FIG. 5A is a side perspective view, FIG. 5B is a top view, and FIG. 5C is a side view. 6A and 6B are structural views of the laminated piezoelectric ceramic actuator, in which FIG. 6A is a side perspective view and FIG. 6B is a top view. (A) is a top view. FIG. 7 is a relationship diagram between the driving voltage and the displacement amount of the laminated piezoelectric ceramic actuator. FIG. 8 is a diagram showing the relationship between the amount of displacement and the generated force of the laminated piezoelectric ceramic actuator. FIG. 9 is a continuous durability test graph of the laminated piezoelectric ceramic actuator. FIG. 10 is a time schedule diagram during sintering of the laminated piezoelectric ceramic actuator. FIG. 11 is a time schedule diagram of the polarization operation of the laminated piezoelectric ceramic actuator. FIG. 12 is a histogram of dielectric constant for the multilayer piezoelectric ceramic actuator of the present invention and a conventional product. Figure 13 is a histogram showing the thickness direction of the piezoelectric constant d ₃₃ of the present invention and the conventional products. 14A and 14B are structural views of a conventional multilayer piezoelectric ceramic actuator, FIG. 14A is a side perspective view, and FIG. 14B is a side perspective view of a state where the orientation of internal electrodes is changed and stacked. FIG. 15 is a side perspective view showing a state of an external electrode portion of a conventional multilayer piezoelectric ceramic actuator.

  The laminated piezoelectric ceramic element of the present invention is provided as a laminated piezoelectric ceramic actuator and a laminated piezoelectric ceramic, and the basic configuration has the same structure in principle. Hereinafter, the present invention will be specifically described with reference to FIGS. 1 to 13 by taking a laminated piezoelectric ceramic actuator as an example.

FIG. 1 is a side perspective view showing the structure of a laminated piezoelectric ceramic actuator 1 according to an embodiment of the present invention. The drive unit 2 has a structure in which piezoelectric ceramics and piezoelectric units composed of internal electrodes described later are laminated. Further, an external electrode 5 is provided on a side surface of the laminated piezoelectric ceramic actuator 1 at a position called a drive unit 2 connected to an internal electrode (not shown). Dummy parts 3 and 4 are added to the upper and lower parts of the laminated piezoelectric ceramic actuator 1. One or two layers of dummy inner electrodes 16 are arranged in the dummy portions 3 and 4. Further, the multilayer piezoelectric ceramic actuator 1 was provided with an exterior such as a case (not shown), and the output from the internal electrode was taken out and completed. In the figure, 9 indicates the total length L of the laminated piezoelectric ceramic including the dummy portions 3 and 4.
Further, the drive unit may be referred to as a piezoelectric unit by paying attention to the piezoelectric output generated between each piezoelectric ceramic of the laminated piezoelectric ceramic and the internal electrode.

  One embodiment of the multilayer piezoelectric ceramic actuator and the manufacturing method thereof of the present invention will be described. The laminated piezoelectric ceramic element is generally composed of a lead-free piezoelectric ceramic such as a PZT composition using lead, and not using lead, for example, bismuth sodium titanium (Bi Na) TiO3, potassium sodium niobium (Na K) NbO3 based composition. .

  Piezoelectric ceramic powder having an average particle size of 1 μm or less, an organic binder component, a dispersant, a plasticizer, and the like were mixed and defoamed with an organic solvent, the viscosity was adjusted, and a sheet forming slurry was prepared. Using this slurry, a tape is formed to form a sheet. The formed sheet is cut, internal electrodes are printed, laminated and pressure-bonded, and element cutting (dicing) is performed. The material for the laminated piezoelectric ceramic actuator of the present invention can be selected from a dielectric material and a piezoelectric material, and will be described hereinafter using a piezoelectric material.

As shown in FIG. 10, the firing conditions in PZT were as follows.
The temperature is raised to 500 ° C. in 25 hours and held at 500 ° C. for 5 hours to remove the binder. For sintering, the temperature is raised from a maximum temperature of 1100 to 1150 ° C. in 5 hours and held at the maximum temperature for 2 hours. Then cool down. In total, the binder was decomposed and fired for approximately 45 hours.
Furthermore, the laminated body side surface (C surface) was polished smoothly, and as will be described later, the internal electrode 6 side in the piezoelectric unit 15 shown in FIG. 3 was gathered to form the external electrode 5 there. Furthermore, a metal cover was applied, and the coating was completed by polarization.
As shown in FIG. 11, the polarization condition was such that the ramp time to the maximum voltage was 1 minute, the electric field was 500 V / mm (applied 0.04 kV when the thickness of the piezoelectric unit was 80 μm), and the holding time was 20 minutes.

  Moreover, the sheet | seat formation used for the piezoelectric unit 15 was performed with the following method. In forming the sheet, the slurry was coated on a polyethylene terephthalate (PET) film using a doctor blade method, and the coated surface was wound up in a roll while drying with hot air. The coating speed was 10 mm / min. The thermocompression bonding in the lamination of the piezoelectric bodies was performed by uniaxial press molding and CIP processing by CIP molding (molded under a pressure of 49 MPa to 98 MPa by a cold isostatic pressing method).

  The internal electrode 6 of the piezoelectric unit 15 was formed as follows. It is essential that the internal electrode material of the laminated piezoelectric material does not melt at the sintering temperature, and high crystal platinum Pt, silver / palladium (Ag / Pd) alloy, etc. can be used, but high crystal Pt is generally expensive. In the present invention, an Ag / Pd alloy was used, and the coating thickness was about 1 to 7 μm. Moreover, it is preferable to add a dispersant and a ceramic powder in order to increase the peel strength of the Ag / Pd electrode and increase the fluidity at the time of application.

  Next, the internal electrode 6 of the piezoelectric unit 15 will be described with reference to FIG. The internal electrode of the conventional method has applied the said Ag / Pd alloy to the surface of piezoelectric ceramics, and was heat-dried (refer FIG.14 (b)). In the present invention, a plurality of unsilvered portions 8 are formed in the internal electrode 6. In the embodiment, as shown in FIG. 3, one of the piezoelectric units 15 is in the form of an upward triangle at the center of the internal electrode shown in FIG. 3A, and the other of the piezoelectric units 15 is in the form of a downward triangle shown in FIG. An unsilvered portion 8 as a non-electrode was applied to the electrode surface. The piezoelectric units 15 shown in FIGS. 3A and 3B are alternately stacked on the left and right sides of the drawing. The purpose of this is to provide the effect of preventing the delamination and cracks by applying the unsilvered portion 8 to reduce the shrinkage of the internal electrodes by the holes.

  As shown in FIG. 1, a laminated piezoelectric ceramic element is generally formed into a quadrangular prism with, for example, a rectangular top surface and an outer dimension of 9.5 mm × 9.5 mm. The laminated piezoelectric ceramic element 1 was formed by alternately stacking the piezoelectric units 15 of FIG. Also, the piezoelectric unit 15 shown in FIG. 3 is composed of piezoelectric ceramics and internal electrodes 6 formed on the surface thereof, of which the surface unsilvered portion 8 has a favorable diameter of about 0.5 mm to 3 mm. The diameter. As a result, the shrinkage of the internal electrode was relaxed by this hole, and the effect of preventing delamination and cracks was obtained. The reason for this is that by applying an unsilvered portion having a diameter of about 1 mm at the center of the internal electrode 6, the shrinkage of the internal electrode relaxes the tensile stress of the silver electrode through this hole and prevents delamination and cracks. It is done.

  Similarly, the piezoelectric unit 15 was formed with a non-internal electrode 7 in which FIG. 3A was on the upper side, FIG. FIG. 4 is a conceptual diagram showing a state in which the unsilvered portion 8 is arranged when the piezoelectric units 15 are superposed with (a) on top and (b) not shown on the bottom. In short, since the three round non-internal electrodes 8 are provided for each of FIGS. 3A and 3B, the total number is 6 in FIG. Note that the number of round non-internal electrodes 8 is not limited to three, but due to the function as a piezoelectric body, it may be arranged in a balanced manner as shown in FIG. It is effective. If it exceeds the above range, it may cause performance variation due to non-uniform displacement and deterioration of actuator characteristics. It is desirable that the arrangement of the non-electrode portions has a target property with the non-electrode portions arranged in the same manner on the entire surface of the electrode application with different polarity when they are positioned at the center of the electrode application front surface and overlapped as shown in FIG.

  The dummy parts 3 and 4 will be described. FIG. 15 shows a piezoelectric ceramic actuator structure having a conventional dummy portion 3. In the present invention, as shown in FIG. 1, when the dummy portions 3 and 4 are made of only ceramics, it is possible to obtain a result that a large error is likely to occur in output such as generated force and displacement. For this reason, the upper and lower dummy parts 3 and 4 need to be thicker than one ceramic layer and have a certain relationship with the length L of the laminated piezoelectric ceramic element actuator 1. This solves the problem that an accurate displacement amount can be obtained even if the reaction force from the upper part and the lower part (displacement transmission part) is received. The dummy parts 3 and 4 can use the piezoelectric unit 15 or the like in addition to the ceramic alone.

  The relationship between the thickness A of the dummy portion 3 and the length L (including the dummy portion) of the laminated piezoelectric ceramic element actuator 1 is such that A> 0.05 mm or more in the range of 2A <0.5L. This is because when A is 0.05 mm or less, the strength of the dummy portion 3 is lowered and it is difficult to take out the external electrode. In addition, although the dummy part 3 was made into the upper and lower dummy parts on both sides of the drive part 2, it does not necessarily deny only one dummy part. In this case, as a condition, the surface of the dummy portion 3 must always have a ceramic surface.

  Moreover, the further improvement method of the dummy parts 3 and 4 is demonstrated. As shown in FIG. 1, one or more dummy inner electrodes 16 are laminated in parallel with the piezoelectric unit 15 in the dummy portions 3 and 4. As the material of the dummy inner electrode, the same material as that of the inner electrode 6 can be used. In the present invention, the dummy portion 3 has a structure in which not only the piezoelectric ceramic layer but also an internal electrode is included. As an inherent number, about 2 to 3 is desirable.

  The internal electrode in the dummy part 3 has the effect of uniforming the Young's modulus of the entire laminated element, and specifically, a very remarkable effect was found in reducing the variation in the displacement amount and the generated force value when not present. . Further, the improvement in performance and reliability of the actuator characteristics could be confirmed as described later, such as the amount of displacement and the generated force, by making the Young's modulus uniform. These will be clarified with reference to FIGS. 12, 13 and 7 to 9 described later.

  Furthermore, the distortion due to the difference in shrinkage between the internal electrode 6 and the piezoelectric ceramic during sintering becomes a factor that causes cracks and delamination. In order to reduce and mitigate the shrinkage difference, the sintering time schedule according to FIG. 10 is effective. In contrast to the conventional method, the sintering conditions were dealt with by extending the binder removal time and firing temperature.

Silver Suitable electrode materials in the internal electrode - nickel - base metals such as copper (Ag-Ni-Cu), cobalt - nickel - iron (Co-Ni-Fe, Kovar plate), further conductive such as _La 2 CuO ₄ There is no particular problem if transition metal ceramics can be used and the value measured by an insulation resistance meter is 10 ohms or less. La 2 _{CuO 4,} when utilizing a lanthanum nickel oxide (La 2 _{NiO 4)} or the like in the internal electrode can be applied with the addition of a binder such as ethyl cellulose should be a paste like silver electrodes Likewise screen printing.

Furthermore, as Example 2, the method for forming the peripheral surface of the laminated piezoelectric ceramic actuator was improved. Hereinafter, a description will be given with reference to FIGS. 5 and 6. FIG. 5 is a structural diagram of a laminated piezoelectric ceramic actuator having a C-plane linear shape, FIG. 5 (a) is a side perspective view thereof, FIG. 5 (b) is a top view thereof, and the corner portion 10 is subjected to a linear cut.
6A and 6B are structural views of the laminated piezoelectric ceramic actuator, FIG. 6A is a side perspective view, FIG. 6B is a top view, and FIG. 6C is a side view.
A linear shape cut 10 or a curved shape cut 11 having a curvature was applied to the peripheral edge portions (four corner portions of the piezoelectric ceramics constituting the quadrangular piezoelectric unit 15 in the plan view). The shape of the cut surface was 0.3 mm in a straight cut (the cut length of the C surface in FIG. 5B is a straight shape).

Although it is possible to obtain a highly reliable value even with a straight cut as shown in FIG. 5, a curved cut as shown in FIG. 6 was further implemented as an improvement. 6A and 6B are structural diagrams in which the C-plane of the multilayer piezoelectric ceramic actuator has a curved shape, FIG. 6A is a side perspective view thereof, FIG. 6B is a top view, and FIG.
The range of the linear cut amount (C-plane is linear shape) in FIG. 5B is preferably about 0.3 mm to 0.9 mm when the outer dimensions of the laminated piezoelectric ceramic actuator are W1 = 7 mm and W2 = 7 mm. understood. When it is 0.3 mm or less, the durability is lowered, and when it is 0.9 mm or more, there is a possibility of insulation failure and it cannot be used.

Next, 12 in FIG. 6 (b) is a top view of the laminated piezoelectric ceramics, a distance r from the center of the drawing to the curved cut portion, 13 is a side length W1 of the laminated piezoelectric ceramic element, and 14 is a side length of the laminated piezoelectric ceramic element. Let W2.
The curvature R having a curved C surface will be described. Similarly to FIG. 5, when the outer dimensions of the multilayer piezoelectric ceramic actuator are W1 = 7 mm and W2 = 7 mm, the curvature R of the curved surface C in FIG. 6B is in the range of 3.6 to 4.8 mm. Higher reliability can be obtained. If it is 3.2 mm or less, the appearance of debris and deterioration of durability are caused, and if it is 4.8 mm or more, the actuator characteristics such as displacement and generated force are deteriorated.

  FIG. 7 shows the relationship between the driving voltage and the displacement when the driving voltage of the laminated piezoelectric ceramic actuator is changed. The displacement was measured using a laser Doppler displacement meter. A displacement of 15 μm was obtained with a drive voltage of about 50 V, and when the drive voltage was increased to 150 V, the displacement amount was 40 μm.

  Further, when the drive voltage was decreased, a linear decrease in displacement was observed. As a result, the degree of hysteresis was small and a large amount of displacement could be obtained. By stacking, it can be used even when the driving voltage is low. Further, regarding the generated force, the characteristics of the laminated actuator can be drawn out at 1500N. Furthermore, it has been confirmed that the device can be sufficiently used as a highly reliable device with reproducibility of characteristics even in repeated driving.

The relationship between the amount of displacement and the generated force of the laminated piezoelectric ceramic actuator obtained in Example 1 and Example 2 of the present invention is shown in the graph of FIG. The generated force was measured using a tensile tester, and the displacement was measured using a strain gauge.
As a result, the generated force was about 1500 N when the displacement amount was 0, about 900 N when the displacement amount was 15 μm, and about 0 N when the displacement amount was 45 μm. The characteristics were that the generated force was large, the sensitivity was high, and the relationship between the displacement and the generated force was highly responsive, and stability and linearity were recognized. The measured values are reproducible, and it was confirmed that they can be used sufficiently as highly reliable elements.

  FIG. 9 shows the durability test results of the laminated piezoelectric ceramic actuator of the present invention. As a comparative example, a multilayer element manufactured by a conventional technique was used. The test method was carried out using a pulse receiver and function generator with a built-in laminated actuator in a dedicated jig. In the durability test method, a laminated piezoelectric ceramic actuator was fixed to a jig, held at 500 N as a preload, applied with a voltage of 0 to 150 V, and driven at a frequency of 10 kHz.

  Weibull failure probability method was used to verify the failure probability of laminated piezoelectric ceramic actuators. The horizontal axis represents the logarithm of the number of times of driving (for example, “1E + 05” corresponds to 100,000 times, “1E + 07” corresponds to 10 million times), and the vertical axis represents the logarithm ln (1 / (1-F)) of the fracture probability distribution function. (For example, “1E-02” corresponds to 0.01% and “1E + 01” corresponds to 10%).

  According to FIG. 9, the destruction probability of the multilayer element manufactured by the conventional technique started to break when the number of driving was about 150,000 times, and the result was that all were destroyed after 400,000 times (sample display number: 11). The laminated element of the present invention started to break at about 3 million times, and resulted in a failure probability of all destruction at 8 million times (11 samples displayed). From this result, it was confirmed that the multilayer element of the present invention was about 20 times as durable as the multilayer element produced by the prior art, and a significant improvement in durability was obtained compared to the conventional element.

  The laminated piezoelectric ceramic actuator obtained in Example 1 (Example 2) can also be used as a laminated piezoelectric ceramic, and will be specifically described as Example 3 below. The structure is the same as that shown in FIGS. 1 to 6 used for the laminated piezoelectric ceramic actuator, and the manufacturing method of the laminated piezoelectric ceramic actuator can be applied in the same manner. A laminated piezoelectric ceramic having the same basic structure was obtained.

  The characteristics of the obtained laminated piezoelectric ceramic are shown in FIG. 7, FIG. 8, FIG. 12, and FIG. The graphs of FIGS. 7 and 8 show the characteristics of the laminated piezoelectric ceramic actuator. In the laminated piezoelectric ceramics, FIG. 7 shows a relationship diagram between the input voltage to the laminated piezoelectric ceramics and its displacement amount, and FIG. It should be read as "Relationship diagram of piezoelectric output generation force with respect to displacement".

As shown in FIG. 12 and FIG. 13, a histogram of specific dielectric constant and piezoelectric constant d _{33 in} the thickness direction with respect to the variation between lots is a result of comparing the product of the present invention with the conventional product. In FIG. 12, the horizontal axis represents the dielectric constant, and the vertical axis represents the frequency. Here, the cumulative number of frequencies in the histogram is displayed as 100% (the same applies to FIG. 13). As shown in FIG. 12, the center value of the dielectric constant is about 1.9 μF, and the variation state of the product of the present invention is concentrated, the distribution form is almost normal distribution, and there is no distant state. It was confirmed that the characteristics of the product of the present invention were extremely excellent since the variation was wide and the distribution form lacked a normal distribution.

Also, as shown in FIG. 13, the piezoelectric constant d ₃₃ characteristics in the thickness direction are similarly concentrated in the variation state of the present invention as in FIG. 12, the distribution form is close to the normal distribution, and there is no separated state. Obtained. Compared to this, the variation of the conventional product is larger than that of FIG. 12, and the peak is distributed in two, and a single normal distribution was not recognized. It was confirmed that the characteristics of the product of the present invention were extremely excellent as well as the dielectric constant. It can be understood that these can be obtained by the piezoelectric characteristics of the piezoelectric ceramics constituting the piezoelectric unit 15 in the present invention, and particularly high reliability and high performance drive characteristics, and multilayer piezoelectric ceramic actuators and multilayer piezoelectric ceramics are suitably used as piezoelectric characteristic elements. It was recognized that it could be provided. Furthermore, it was confirmed that the fact that the variation between lots is small is more effective for productivity on a mass production scale, and that a laminated piezoelectric ceramic element capable of maintaining stable characteristics can be provided.

On the other hand, conductive ceramics can be used as the internal electrodes used in the laminated piezoelectric ceramic element. For example, a conductive transition metal compound such as La ₂ CuO ₄ type, for example, (La Sr) ₂ CuO ₄ or La ₂ NiO ₄ can be used as the conductive ceramic. In this case, conventionally used platinum, palladium, silver palladium, and base metal become unnecessary. Since conductive ceramics used for the laminated piezoelectric ceramic element are not made of different materials such as metals, it is possible to expect an effect that the bonding force is high and cost reduction. In general, if the melting point of the metal used for the internal electrode and the ceramic are different, it is essential to lower the temperature of the ceramic in order to match the shrinkage temperature. However, by using conductive ceramics having the same structure (perovskite structure), shrinkage and diffusion occur at the same temperature, so that an effect of increasing the bonding force can be expected.

  The multilayer piezoelectric ceramic element of the present invention can be used not only for multilayer piezoelectric ceramic actuators and multilayer piezoelectric ceramics, but also for diesel engine injection multilayer elements and positioning actuators, as well as for opening and closing valves, and for inkjet printers. It can be used as an actuator, and can be used as a laminated piezoelectric ceramic element that can be used as a drive motor for precision equipment or the like. Further, in the future, it can be expected that the laminated piezoelectric ceramic element will be used for various purposes using the effects of the present invention.

  In addition, the laminated piezoelectric ceramics of the present invention can be expected to increase the amount of displacement and generated force due to lamination compared to conventional piezoelectric ceramics or laminated piezoelectric ceramics, and application to valve opening and closing, positioning actuators, and new motors is considered. This enables applications that could not be achieved with a single piezoelectric ceramic.

DESCRIPTION OF SYMBOLS 1 Laminated piezoelectric ceramic element 2 Drive part 3 Dummy part 4 Dummy part 5 External electrode 6 Internal electrode 7 Non-internal electrode 8 Non-silvered part 9 Total length L of laminated piezoelectric ceramics
10. Cut section 11 on the peripheral surface 11 Cut section 12 on the peripheral surface Distance r from the center of the drawing to the curved cut portion in the top view of the laminated piezoelectric ceramic
13 Side length W1 of laminated piezoelectric ceramic element
14 Side length W2 of multilayer piezoelectric ceramic element
15 Piezoelectric unit 16 Dummy inner electrode

Claims (17)

  In a laminated piezoelectric ceramic element including a drive unit in which piezoelectric units each including piezoelectric ceramics and internal electrodes are alternately stacked and a dummy unit fixed to the drive unit, the dummy unit includes at least one dummy inner electrode. A laminated piezoelectric ceramic element, characterized in that it is formed at a portion that is provided and is not in contact with an external electrode. The piezoelectric ceramic is any one selected from lead-free piezoelectric ceramics including lead zirconate titanate (PZT) composition using lead, bismuth sodium titanium (Bi Na) TiO ₂ and potassium sodium niobium (Na K) NbO ₃ based composition. 2. The laminated piezoelectric ceramic element according to claim 1, wherein the laminated piezoelectric ceramic element is made of any of the above materials. The internal electrode has a resistance value of 10 ohms or less when driven, and is selected from ceramics such as base metals such as Ag, Ni, and Cu, Co—Ni—Fe alloys, and conductive transition metals such as La ₂ CuO ₄ . 2. The laminated piezoelectric ceramic element according to claim 1, wherein the laminated piezoelectric ceramic element is any one of the materials.   2. The laminated piezoelectric ceramic element according to claim 1, wherein the piezoelectric ceramic and the internal electrode are either an integral sintering method or an adhesion method.   Between the thickness A (mm) of the dummy part added to the upper part and the lower part of the driving part and the overall length L (mm) of the laminated piezoelectric ceramic element, A> 0.05 mm and 2A < 2. The laminated piezoelectric ceramic element according to claim 1, which has a relationship of 0.5L.   2. The multilayer piezoelectric ceramic element according to claim 1, further comprising: the drive unit in which a chamfer is formed by a straight cut or a cut by a curvature R at a peripheral corner portion of the drive unit.   The cut with the curvature R satisfies the relationship of R ≧ W / 2 and R <3W with the width W (W1, W2), and the unevenness of the cut processing surface is processed to a maximum of 10 μm or less. The multilayered piezoelectric ceramic element according to claim 1.   2. The multilayer piezoelectric ceramic element according to claim 1, wherein the dummy part is fixed to only one of the driving parts, and at least one electrode in the dummy part is included.   2. The multilayer piezoelectric ceramic element according to claim 1, wherein the dummy part internal electrode is a full-surface electrode having no margin part.   The laminate according to claim 1, wherein a non-electrode printed portion is applied to the central portion of the internal electrode in order to relieve the tensile stress of the silver electrode, and the non-electrode printed portion is 2% or less of the total area of the internal electrode. Piezoelectric ceramic element.   The non-electrode printed portion is coated with a non-electrode printed portion having a diameter of 0.5 to 3 μm, and the non-electrode printed portion is arranged on the diagonal line and uniformly in the central portion. The laminated piezoelectric ceramic element according to claim 10.   The multilayer piezoelectric ceramic element according to any one of claims 1 to 11, wherein the multilayer piezoelectric ceramic element is a multilayer piezoelectric ceramic actuator.   The multilayer piezoelectric ceramic element according to claim 1, wherein the multilayer piezoelectric ceramic element is a multilayer piezoelectric ceramic element.   Piezoelectric ceramic powder and organic binder components, dispersing agent, plasticizer, etc. are mixed and defoamed with an organic solvent, the viscosity is adjusted to prepare a sheet forming slurry, and the slurry is formed into a tape by using the slurry. A method for producing a laminated piezoelectric ceramic element, comprising: forming, cutting the molded sheet, printing an internal electrode, laminating and pressing, and polarizing the element after cutting.   Piezoelectric ceramic powder and organic binder components, dispersing agent, plasticizer, etc. are mixed and defoamed with an organic solvent, viscosity is adjusted to produce a sheet molding slurry, and a tape is formed using the slurry to form a sheet And printing and laminating internal electrodes on the molded sheet, pressing the molded sheet together with a dummy portion provided with at least one dummy inner electrode, cutting the laminated piezoelectric ceramic element, collecting the inner electrode side, A method for manufacturing a laminated piezoelectric ceramic element, characterized in that a driving section is formed and polarized.   The method for manufacturing a laminated piezoelectric ceramic element according to claim 15, wherein a plurality of unsilvered portions 8 are formed on the internal electrode.   16. The method for manufacturing a laminated piezoelectric ceramic element according to claim 15, wherein a chamfer is formed by a straight cut or a cut by a curvature R at a corner portion of the peripheral surface of the drive unit.

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