JP4686975B2 - Multilayer piezoelectric element and manufacturing method thereof - Google Patents

Description

  The present invention relates to a multilayer piezoelectric element such as a multilayer piezoelectric actuator and a manufacturing method thereof.

  FIG. 3 shows a schematic diagram of a conventional general laminated piezoelectric actuator 1.

  In FIG. 3, reference numeral 10 denotes a laminate, which is formed by alternately laminating piezoelectric ceramic layers 11 and internal electrode layers 12. The internal electrode layers 12 are alternately connected to external electrodes 13 having different polarities provided on both side surfaces of the laminate 10. Moreover, since the upper and lower surfaces (both end surfaces in the stacking direction) of the laminate 10 are in contact with an object to be driven, a protective layer 14 is provided. A portion where the internal electrode layers 12 connected to the external electrodes 13 having different polarities are overlapped with each other is an active portion A, and the insulation between the internal electrode layers 12 having different polarities around the active portion A is ensured. The part becomes the inactive part B.

  The inactive portion B and the protective layer 14 are made of a piezoelectric material, but since an electric field is hardly applied, no distortion occurs during polarization or piezoelectric driving. On the other hand, in the active part A, an electric field is applied and distortion occurs. For this reason, stress is generated from the strain difference between the active portion A where the strain occurs and the inactive portion B where the strain does not occur and the protective layer 14 during polarization and piezoelectric driving, and the multilayer piezoelectric actuator 1 is cracked. appear.

  FIG. 10 shows a state in which the multilayer piezoelectric actuator 1 is cracked. In particular, when the height dimension T of the multilayer piezoelectric actuator 1 is 4 mm or more, cracks are likely to occur. When polarization was actually performed using the laminated piezoelectric actuator 1 having a height dimension T of 7 mm and 30 mm, cracks occurred in any case.

  Therefore, at the time of polarization, the inactive portion B and the protective layer 14 are also polarized to generate strain, thereby eliminating the strain difference generated between the active portion A and the inactive portion B and the protective layer 14. No stress is generated and cracking can be prevented.

  11 and 12 show a conventional method for manufacturing a laminated piezoelectric actuator 1 (see Patent Documents 1 and 2).

  As shown in FIG. 11, the electrodes 20 are provided on the entire upper and lower surfaces of the laminate 10 so that an electric field is applied to a place other than the active part A, so that the inactive part B and the protective layer 14 are simultaneously formed with the active part A. Is polarized. Thereafter, as shown in FIG. 12, the upper and lower electrodes 20 are removed, the external electrode 13 is formed on the side surface in the direction orthogonal to the stacking direction, and interlayer polarization is performed again. At the time of interlayer polarization, half of the piezoelectric layer in the multilayer piezoelectric actuator 1 is polarized in the direction opposite to the electric field. Therefore, once it contracts, it reverses when it exceeds the coercive electric field, and the direction of polarization is uniform throughout the actuator. . At this time, since the stretched part and the shrinking part are the same amount, they cancel each other, no strain is generated as a whole, no stress is generated between the active part A and the inactive part B or the protective layer 14, Breaking can be prevented.

Specifically, using the laminated piezoelectric actuator 1 having a height T of 7 mm, Ag paste is applied to the upper and lower surfaces, and baked at 800 ° C. to form the electrode 20. The voltage was 10 kV and the electric field strength was 2.0 kV / mm). Thereafter, the upper and lower electrodes 20 were scraped with sandpaper, and an Ag electrode film was formed on the side surfaces by sputtering film formation at room temperature, whereby the external electrode 13 was produced and polarized by an electric field. As a result, no cracks occurred.
JP-A-9-266332 JP 2000-133852 A

  However, in the manufacturing method of the multilayer piezoelectric actuator 1 shown in FIGS. 11 and 12, an electric field of 2 kV / mm is required to polarize the piezoelectric ceramic, and the height dimension (length dimension in the stacking direction) T is required. In the large multilayer piezoelectric actuator 1, a voltage of several tens of kV is required to polarize the entire multilayer piezoelectric actuator 1. For example, when the height dimension T of the multilayer piezoelectric actuator 1 is 30 mm, a voltage of 60 kV is required. Therefore, a dedicated power source is required, and further, a high withstand voltage required for the insulating oil during polarization is required, and there is a problem in that the use period is shortened and the cost is increased in order to maintain the insulation.

  Moreover, in order to polarize the whole laminated piezoelectric actuator 1, the process which attaches the electrode 20 to an upper and lower surface, removes these, and attaches the external electrode 13 to a side again is required, and a manufacturing process is complicated and becomes high-cost. There was a problem.

  Further, when the external electrode 13 is attached to the side surface, if the temperature is set higher than the Curie temperature of the piezoelectric material, the polarization applied to the whole in the step shown in FIG. 11 is removed. For this reason, there has been a problem that the treatment temperature cannot be increased to increase the adhesion of the external electrode 13.

  The present invention does not require a high voltage during polarization, can be easily oriented at low cost, prevents internal stress during polarization treatment, prevents cracks in the multilayer piezoelectric element, and is simple and inexpensive in the manufacturing process. It is another object of the present invention to provide a laminated piezoelectric element that can enhance the adhesion of external electrodes and a method for manufacturing the same.

The manufacturing method of the multilayer piezoelectric element of the present invention is formed by laminating a piezoelectric ceramic layer and an internal electrode layer, and is present around an active portion located between internal electrode layers of different polarities. The step of obtaining a laminate having an inactive part, and applying a uniform compressive stress from the entire side surface in the direction orthogonal to the laminate direction of the laminate, and extending the laminate in the laminate direction, The step of orienting the direction of the domain in any direction above or below the stacking direction and the step of applying an electric field to the stack through the internal electrode layer to polarize the active part.

  The electric field direction is, for example, the stacking direction of the stacked body.

  A pair of external electrodes having different polarities are formed by baking a conductive paste on a side surface in a direction orthogonal to the stacking direction of the stacked body, and the internal electrode layers are alternately connected to external electrodes having different polarities.

  The total length of the laminate in the stacking direction is 4 mm or more.

  In order to extend the laminated body in the laminating direction, a uniform compressive stress is applied from the entire side surface in the direction orthogonal to the laminating direction of the laminated body.

  In the manufacturing method of the multilayer piezoelectric element of the present invention, preferably, in a step after the polarization step, an electric field higher than a coercive electric field is applied to the active portion in a direction opposite to the polarization direction to reverse the polarization direction. Process.

The multilayer piezoelectric element of the present invention is formed by laminating a piezoelectric ceramic layer having pyroelectricity and an internal electrode layer, and is present around an active portion located between internal electrodes of different polarities. And a pair of external electrodes having different polarities formed by baking a conductive paste on a side surface perpendicular to the stacking direction of the stacked body, the internal electrode layers being alternately connected, Wherein the entire multilayer body is substantially oriented along the direction of the electric field applied between the internal electrode layers, and the orientation of the domains is opposite to the direction along the direction of the electric field. An aligned region is present simultaneously in the inactive portion, and a domain orientation ratio along the electric field direction is lower than that of the inactive portion and is present in the active portion .

  According to the multilayer piezoelectric element and the manufacturing method thereof of the present invention, by applying compressive stress from the side surface of the multilayer body, the multilayer body is extended in the direction of the electric field applied between the internal electrode layers of different polarities. Since the orientation of the domain is substantially aligned in the electric field direction, when applying an electric field to the laminate through the internal electrode layer to polarize the active part, no strain difference occurs between the active part and the inactive part, Internal stress can be prevented, and cracks can be prevented from occurring in the laminated piezoelectric element during polarization or during long-time piezoelectric driving.

  In particular, it is effective in a laminated piezoelectric element having a large length dimension in the lamination direction. For example, when the length dimension T in the stacking direction is 4 mm or more, when the entire polarization and the interlayer polarization are both performed by applying an electric field, the difference in stress applied to the active part and the inactive part during the interlayer polarization is generally The tensile strength of piezoelectric ceramics (PZT), which exceeds 30 to 40 MPa, may break. On the other hand, when the entire polarization is performed by applying a compressive stress from the side surface of the laminate, such a crack does not occur.

  In addition, since compressive stress is applied from the side surface of the laminate to cause mechanical polarization, it is not necessary to apply a high voltage during polarization, and the entire orientation can be easily achieved at low cost. In particular, even if the length in the stacking direction is large, it is not necessary to apply an electric field, so no high-voltage equipment is required, and conventional polarization equipment is sufficient for the polarization treatment, and it is easy and inexpensive. Overall orientation is possible.

  In addition, since the entire polarization is performed by applying compressive stress from the side surface of the laminate, there is no need to form an electrode for the entire polarization that is finally removed, and there is no need to form and remove the electrode for the entire polarization, thereby simplifying the manufacture. And cheap.

  In addition, the conductive paste is baked at a high temperature on the side surface in the direction perpendicular to the stacking direction of the multilayer body, and the entire electrode is polarized by applying compressive stress from the side surface of the multilayer body. Adhesion can be sufficiently increased.

  In addition, the polarization direction of the inactive part is parallel to the polarization direction of the active part, but it is not aligned in one direction. In this case, the currents are canceled and no current is generated, and the polarization of the inactive portion is not lowered and contracted. Therefore, it is possible to prevent the occurrence of cracks due to the pyroelectric charge generated in the internal electrode.

  In manufacturing a laminated piezoelectric element, in the process after the polarization process, an electric field equal to or greater than the coercive electric field is applied to the active part in a direction opposite to the polarization direction, thereby reversing the polarization direction. While maintaining the state in which the orientation is oriented in the direction of the electric field applied between the internal electrodes by the previous orientation process, the active part will increase the number of crystals with an increased orientation component of 90 ° domain, The elongation percentage of the piezoelectric element when the drive voltage is applied is larger than that of the piezoelectric element not subjected to the polarization inversion process.

  According to the multilayer piezoelectric element and the manufacturing method thereof of the present invention, it is not necessary to apply a high voltage at the time of polarization, it can be easily oriented at low cost, and the internal piezoelectric stress during the polarization process can be prevented to prevent cracks occurring in the multilayer piezoelectric element. In addition, the manufacturing process is simple and inexpensive, and the adhesion of the external electrode can be increased.

  An embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic diagram when a multilayer piezoelectric actuator is mechanically polarized, and FIG. 2 is a schematic diagram when the layers of the multilayer piezoelectric actuator are polarized by an electric field.

  The structure of the multilayer piezoelectric actuator 1 is the same as the example shown in FIG.

  The laminated piezoelectric actuator 1 will be described.

  First, a conductive paste to be the internal electrode layer 12 containing AgPd powder is printed on a green sheet constituting the piezoelectric ceramic layer 11 whose piezoelectric material is made of PZT (lead zirconate titanate) powder. The printed pattern of the conductive paste is such that when a plurality of green sheets are stacked to form the laminate 10, the electrode end portions can be alternately taken out from a pair of side surfaces opposed in a direction orthogonal to the lamination direction of the laminate 10. Shape. Further, the electrode end portion may be taken out at another location such as a diagonal, but a gap G that constitutes an inactive portion B for ensuring insulation is required.

  Next, after printing, the printed green sheets are stacked so that the height dimension T becomes 30 mm after firing, and then pressure is applied from both end surfaces in the stacking direction. Further, it is cut by dicing so that the cross-sectional shape perpendicular to the laminating direction after firing becomes a square of 10 mm × 10 mm. And a degreasing process (300 degreeC x 20 hours) and a baking process (1100 degreeC x 5 hours) are performed.

  The piezoelectric material may be a piezoelectric ceramic other than PZT, and the conductive paste may be another conductive material such as Ag or Cu. In addition, in order to increase the height dimension T of the multilayer piezoelectric actuator 1, low-height fired laminates may be stacked and bonded.

  Next, the external electrode 13 is attached to the side surface from which the electrode of the laminate 10 is taken out. That is, an Ag paste is printed on each of a pair of opposing side surfaces of the laminate 10 and baked at 850 ° C. The attachment of the external electrode 13 may be performed by a method that provides sufficient adhesion such as sputtering film formation or vapor deposition. The multilayer piezoelectric actuator 1 is manufactured as described above.

  Next, the polarization process will be described.

  A process of generating mechanically parallel global polarization will be described with reference to FIG.

  The laminated piezoelectric actuator 1 is housed in a mold 15 and subjected to a hydrostatic pressure treatment (injected into a container at 60 ° C. and 190 MPa for 600 seconds) through a rubber 16 as a buffer material. The mold 15 has a structure capable of preventing pressure from the height direction of the multilayer piezoelectric actuator 1 and applies a compressive stress only in a direction orthogonal to the direction without applying force in the direction to be polarized. . That is, gaps 17 are respectively formed between the protective layer 14 on the upper and lower surfaces of the multilayer piezoelectric actuator 1 and the mold 15 so as not to prevent the multilayer piezoelectric actuator 1 from extending in the vertical direction. It is configured. Moreover, the temperature at the time of compression should just be less than Curie temperature from room temperature. The hydrostatic pressure treatment is effective because it can apply compressive stress in two directions simultaneously from the side surface of the multilayer piezoelectric actuator 1, but the compressive stress from one direction using a rigid press or the like can be applied once or in a direction. You may change and perform several times.

  In this way, as a result of mechanically polarizing the whole body by applying compressive stress from the side surface of the laminate 10, the entire domain (domain) including the active part A, the inactive part B, and the protective layer 14 of the laminate 10 is obtained. ) Is oriented in a substantially laminating direction (approximately 180 ° domain) (see arrow). In addition, although the direction of polarization is substantially parallel to the stacking direction, they are not aligned on one side. That is, the point for preventing cracks that occur during polarization is that the inactive part B is distorted to the same size as the residual strain caused by the polarization of the active part A, so the direction of polarization is parallel to the strain. It does not have to be on one side.

  FIG. 2 shows a schematic diagram of the step of polarizing the active part A, that is, the step of polarizing the interlayer by an electric field.

  After the compression process of FIG. 1 is completed, the mold 15 and the rubber 16 are removed, and the positive and negative are set in a state where one of the external electrodes 13 and 13 is a positive electrode and the other is a negative electrode in a silicon oil bath at a temperature of 80 ° C. An electric field of 3 kV / mm is applied between the electrodes to polarize the layers and align the polarization direction of the active part A. In addition, the temperature in the tank at the time of polarization may be from 60 ° C. to less than the Curie temperature, and the applied electric field is changed according to the coercive electric field at that temperature.

  According to the multilayer piezoelectric element configured as described above and the manufacturing method thereof, by applying compressive stress from the side surface of the multilayer body 10, the multilayer body 10 is elongated in the stacking direction, and the domain direction of the entire multilayer body 10 is changed. Since the orientation is substantially in the stacking direction, no strain difference is generated between the active part A and the inactive part B when an electric field is applied to the stacked body 10 via the internal electrode layer 12 to cause interlayer polarization. That is, in the active part A, since the directions of polarization are aligned in both directions of polarization, no further orientation occurs during interlayer polarization, and the entire strain is canceled out by polarization in both directions. Does not occur. Note that the strain generated at the time of polarization does not have to be completely zero, but may be + 0.02% or less. In addition, there is no problem with a negative strain difference (the laminated body 10 shrinks). As described above, since no strain is generated between the active part A and the inactive part B, internal stress can be prevented, and cracks occur in the multilayer piezoelectric actuator 1 during polarization or during long-time piezoelectric driving. Can be prevented.

  Specifically, when the polarization according to the present embodiment was performed using the laminated piezoelectric actuator 1 having a height dimension T of 30 mm, no cracks occurred.

  Further, since compressive stress is applied from the side surface of the laminated body 10 to mechanically polarize, it is not necessary to apply a high voltage at the time of polarization, and the entire orientation can be easily performed at low cost. In particular, even if the length in the stacking direction is large, it is not necessary to apply an electric field, so no high-voltage equipment is required, and conventional polarization equipment is sufficient for the polarization treatment, and it is easy and inexpensive. Overall orientation is possible.

  Further, since the entire polarization is performed by applying a compressive stress from the side surface of the laminated body 10, the external electrode 13 only needs to be formed on the surface connected to the internal electrode layer 12, and it is necessary to form an electrode for total polarization to be finally removed. This eliminates the need for forming and removing the entire polarization electrode, and is simple and inexpensive to manufacture.

  In addition, in a state where the conductive paste is baked at a high temperature on the side surface in the direction orthogonal to the stacking direction of the stacked body 10, the entire electrode can be polarized by applying compressive stress from the side surface of the stacked body 10. Since the production of the external electrode 13 is completed before the treatment, an electrode production method having strong adhesion such as baking can be used, and the adhesion of the external electrode 13 can be sufficiently increased.

  In addition, since the inactive portion B exists, the insulation between the positive and negative electrodes of the internal electrode layer 12 can be sufficiently ensured. In addition, the insulating part G can be formed simultaneously with the production of the multilayer piezoelectric actuator 1 and can be produced in a simple and few process.

  Furthermore, in order to eliminate the residual stress in the electric field direction in the multilayer piezoelectric actuator 1, it is effective when driving in any of the strain directions of the vertical direction, the horizontal direction, and the sliding direction with respect to the electric field direction during the driving electric field. It is.

  If the cross section of the multilayer piezoelectric actuator 1 is rectangular, the effect of the present invention can be easily obtained by applying a force simultaneously from two directions orthogonal to the stacking direction, and when the cross section is circular, simultaneously. Further, instead of compressing from both sides, the entire polarization may be performed by pulling from the top and bottom of the laminate 10 and extending in the vertical direction.

  Further, in a state where a compressive force is applied as shown in FIG. 1, an electric field may be applied between the layers as shown in FIG. That is, a polarizable electric field may be applied only for a moment on the order of milliseconds with a compressive force applied.

  Next, for the stacked piezoelectric actuator 1 obtained through the same manufacturing process as that of the above-described embodiment, an electric field higher than the coercive electric field is applied to the active portion in the direction opposite to the polarization direction, so that the polarization direction is changed. An embodiment and an example of a method for manufacturing a laminated piezoelectric element having a reversing step will be described with reference to FIGS. FIG. 4 is a schematic diagram of a process of reversing the polarization direction by applying an electric field higher than the coercive electric field of the multilayer piezoelectric actuator in another embodiment of the present invention to the active portion. FIG. 5 is a schematic diagram showing unpolarized domains in the piezoelectric crystal grains. FIG. 6 is a schematic diagram (a) showing the domain of the polarization state in the piezoelectric crystal grains in the active part and the inactive part of the laminated piezoelectric actuator in the polarization process state of the manufacturing method according to the present invention, and the conventional or comparison. FIG. 6B is a schematic diagram (b) showing domains of polarization states in the piezoelectric crystal grains in the active part of the multilayer piezoelectric actuator of Example 1. FIG. 7 shows the activity of the stacked piezoelectric actuator after the polarization process of the manufacturing method according to the present invention and the step of reversing the polarization direction by applying an electric field higher than the coercive electric field to the active part in the direction opposite to the polarization direction. FIG. 4 is a schematic diagram (a) showing domains of polarization state in piezoelectric crystal grains in the part and a schematic diagram (b) showing domains of polarization state in piezoelectric crystal grains in the inactive part. FIG. 8 is a schematic diagram showing a domain of the polarization state in the piezoelectric crystal grains in the active portion showing a state in which a driving voltage is applied to the multilayer piezoelectric actuator shown in FIG. FIG. 9 is a graph showing the results of measuring the example of the piezoelectric element manufactured by the manufacturing method according to the present invention, the driving voltage of Comparative Examples 1 and 2, and the amount of elongation of the element due to the voltage application.

  Referring to FIG. 4, the entire multilayer body of the multilayer piezoelectric actuator 1 is extended in the direction of the electric field applied between the internal electrode layers, and the domain of the entire multilayer body is oriented in the direction of the electric field. Following the polarization step of polarizing the electrode, a triangular wave having an electric field equal to or higher than the coercive electric field of the piezoelectric material PZT of the laminate 10 with positive and negative peak values is applied to the electrodes 13 and 13 of the laminate 10. The triangular wave electric field is applied, for example, for five wavelengths. As a result, an electric field higher than the coercive electric field in the opposite direction to that during polarization is applied to the active part A. Note that even if the electric field is higher than the coercive electric field, the electric field is lower than the voltage applied during the previous polarization. This is because, when a voltage higher than the electric field at the time of polarization is applied, there is a high possibility that the laminate 10 is broken or a dielectric breakdown occurs.

  As described above, by applying an electric field equal to or higher than the coercive electric field in the opposite direction to that during polarization, the degree of domain orientation in the active part is lowered, and the effect of 90 ° domain is obtained. Hereinafter, the technical significance of applying an electric field higher than the coercive electric field in the opposite direction to the polarization step will be described.

  The domain of the active part before polarization is in an unpolarized state schematically shown in FIG. 5, and the 180 ° domain serving as an orientation component along the polarization direction and the orientation component along the direction orthogonal to the polarization direction The 90 ° domain is mixed. As schematically shown in FIG. 6 (a), in the active part, the inactive part is improved in the orientation by the whole orientation process and the polarization process of the invention according to claim 1 in the active part. Similarly, the 180 ° domain in the domain is oriented in the strain direction before application of the electric field. At this time, it was found that the film was already oriented in the 180 ° domain direction after this polarization step, that is, before application of the electric field. For this reason, the elongation of the piezoelectric element when an electric field is applied remains relatively low, and there is room for improvement in increasing the elongation. FIG. 6B schematically shows the orientation of the 180 ° domain and the 90 ° domain of the active portion when the conventional normal polarization process is performed, and many 90 ° domains remain in the active portion. Therefore, it is shown that when the drive voltage is applied, the orientation of the 90 ° domain is added to the piezoelectric strain of the 180 ° domain, and the elongation increases. By applying an electric field (voltage) equal to or higher than the coercive electric field in the opposite direction to that of polarization to the active portion in the state shown in FIG. 6A, as schematically shown in FIG. ° Domain increases. When an electric field exceeding the coercive electric field in the reverse direction is applied, if it is perfectly oriented in the same direction as the electric field, it will not return to the 90 ° domain only by a change in ion position, but it is not completely oriented in the electric field direction. Since the partial domain has a displacement component in the 90 ° direction at the time of inversion, a part of the domain returns to the 90 ° domain. In this way, when a part of the domain of the active part is 90 °, the 180 ° domain and the 90 ° domain are not largely biased to one side as in the normal polarization shown in FIG. 6B. It becomes a mixed state, and the piezoelectric constant can be increased.

  As for the inactive portion, an electric field higher than the coercive electric field opposite to that applied to the electrodes 13 and 13 is not applied (the electric field applied between the internal electrode layers changes the polarity to the inactive portion). Therefore, as shown in FIG. 7B, the degree of orientation in the strain direction of the 180 ° domain remains high.

  As a result, as shown in FIG. 6A, the elongation due to the orientation of the 90 ° domain is added to the elongation consisting of the piezoelectric strain of almost 180 ° domain. Become. Therefore, when the piezoelectric element manufactured by this manufacturing method is operated as an actuator, the elongation rate is high. FIG. 8 illustrates the state of the domain when a driving voltage is applied. During this drive, the 90 ° domain is almost gone.

  Therefore, when the polarization process of the invention according to claim 1 of the present application is performed, the degree of orientation in the 180 ° domain in the domain of the active part is high, but after the polarization process, the direction of polarization is further reversed. By applying an electric field (voltage) that is higher than the coercive electric field, the degree of domain polarization in the active part is lowered and the piezoelectric constant is increased, thereby increasing the elongation when the piezoelectric laminate is stretched. Can be increased. Therefore, by performing the steps according to claim 6 of the present application, it is possible to obtain a multilayer piezoelectric element having a good piezoelectric constant while preventing internal stress during polarization treatment and preventing cracks occurring in the multilayer piezoelectric element. . In FIG. 4, for the domain having a large piezoelectric constant, the magnitude of the polarization height direction (drive direction) component and the size of the arrow indicating the direction are displayed small.

The domain of the active part shown in FIG. 6 (a), the domain of the active part shown in FIG. 6 (b), the domain of the active part shown in FIG. 7 (a), and the domain of the active part shown in FIG. as indicating the domain and its length domain in polarization voltage application direction, respectively _{L 1, L 2, L 3} , L a, the polarization voltage applied between the front when the drive voltage is applied the piezoelectric displacement (drive voltage applied The difference in domain length in the direction) d _n (L _a −L _n ) has a relationship of d ₂ , d ₃ > d ₁ .

  In addition, as a method of applying an electric field (voltage) higher than the coercive electric field opposite to the polarization direction, a positive / negative voltage (however, a voltage opposite to the polarization direction must be higher than the coercive electric field). The voltage may be applied repeatedly, or may be applied with a voltage holding time longer than the coercive electric field with an applied voltage opposite to the polarization direction. You may set speed etc. suitably. The point is to cause one or more polarization inversions in the active part.

  After passing through the polarization step in the present invention, the laminate manufactured by the manufacturing method of the above embodiment, further comprising a step of applying an electric field higher than the coercive electric field opposite to the polarization direction in the polarization step to the active part. Examples of piezoelectric elements will be described. With respect to the multilayer piezoelectric actuator as the multilayer piezoelectric element according to the present invention, the present inventor applied a triangular wave to a 5-wavelength time electric field as in the above-described embodiment as a voltage higher than the coercive electric field opposite to the polarization direction after the polarization treatment. After that, the amount of elongation of the actuator was measured while applying a triangular wave offset to the external electrode so that only a positive voltage was applied in the direction of elongation of the actuator. The measurement result is shown by a solid line in the graph of FIG. In FIG. 9, the horizontal axis represents voltage, and the vertical axis represents the amount of elongation of the actuator. In addition, in FIG. 9, the result performed similarly to the said measurement about the laminated piezoelectric actuator of the comparative examples 1 and 2 mentioned later is shown as a graph.

  Comparative Example 1 will be described. First, the manufacturing process of the laminated piezoelectric actuator of Comparative Example 1 will be described. A conductive paste containing AgPd powder is printed on a green sheet made of the piezoelectric material PZT powder. Next, after stacking the printed green sheets so that the height is 30 mm after firing, pressure is applied from above and below the surfaces. Further, dicing is performed so that the cross-sectional side view after firing becomes a square of 10 mm × 10 mm. And a degreasing process (300 degreeC x 20 hours) and baking (1100 degreeC x 5 hours) are performed, and a laminated piezoelectric actuator is produced. In this case, the piezoelectric material may be a piezoelectric ceramic other than PZT, and the conductive paste may be another material such as Ag or Cu. The pattern at the time of printing has a shape in which the electrode short portions can be alternately taken out from the two opposing side surfaces when the actuator is used. The electrode end may be taken out at another location such as a diagonal, but a gap that constitutes an inactive portion for ensuring insulation is necessary.

  The gap shape is made only of a curve having a small gap area and no corners where stress is likely to concentrate, and the polarization split generated in the inactive portion is made as small as possible.

  An external electrode is attached to the surface from which the electrode of the actuator is taken out. The method of attaching the electrodes and the method of polarization between the internal electrodes are the same as in the example.

  In the case of this comparative example 1, it resulted in a crack in an inactive part at the time of polarization. However, the amount of displacement could be measured. However, it is determined as a defective product when cracks such as those described above occur during polarization. In addition, the state of the domain of the active part in the comparative example 1 is the same as that obtained by performing the normal polarization process shown in FIG. In Comparative Example 1 as well, as with the multilayer piezoelectric actuator of the example, the extension amount of the actuator was measured while applying a triangular wave offset to the external electrode so that only a positive voltage was applied in the extension direction of the actuator. In addition, since the substantially same result is obtained by the Example of this invention and the comparative example 1, the substantially same measurement result is obtained and the graph of FIG. 9 which shows the result has overlapped.

  Next, Comparative Example 2 will be described. First, the manufacturing process of the laminated piezoelectric actuator of Comparative Example 2 will be described. A conductive paste containing AgPd powder is printed on a green sheet made of the piezoelectric material PZT powder. Next, after stacking the printed green sheets so that the height is 30 mm after firing, pressure is applied from above and below the surfaces. Further, dicing is performed so that the cross-sectional side view after firing becomes a square of 10 mm × 10 mm. And a degreasing process (300 degreeC x 20 hours) and baking (1100 degreeC x 5 hours) are performed, and a laminated piezoelectric actuator is produced. At this time, a piezoelectric ceramic other than PZT may be used, and the conductive paste may be another material such as Ag or Cu. The pattern at the time of printing has a shape in which the electrode short portions can be alternately taken out from the two opposing side surfaces when the actuator is used. The electrode end may be taken out at another location such as a diagonal, but a gap that constitutes an inactive portion for ensuring insulation is necessary. An external electrode is attached to the surface from which the electrode of the actuator is taken out. Ag paste is printed and baked at 800 ° C. Subsequently, the actuator is housed in a mold and subjected to a hydrostatic pressure treatment (injected into a container at 60 ° C. and 190 MPa for 600 seconds) through a rubber cushioning material. At this time, a mold having a structure for preventing pressure from the height direction of the actuator is used. After the compression treatment is completed, an electric field of 3 kV / mm is applied between the positive and negative electrodes in a silicon oil bath at a temperature of 80 ° C. to polarize the layers and align the polarization direction in one direction. In addition, the state of the domain of the active part in the comparative example 2 is the same as that obtained by the polarization process shown in FIG. In Comparative Example 2, as in the multilayer piezoelectric actuator of the example, the amount of elongation of the actuator was measured while applying a triangular wave offset to the external electrode so that only a positive voltage was applied in the direction of elongation of the actuator. The result is indicated by a broken line in the graph of FIG.

  In the case of this comparative example 2, polarization cracking did not occur. Moreover, when the piezoelectric displacement was measured and the piezoelectric constant was calculated, the value was about 30 pm / V smaller than that of Comparative Example 1.

  The multilayer piezoelectric element and the manufacturing method thereof according to the present invention are useful, for example, as a multilayer piezoelectric actuator in which a large number of piezoelectric ceramics provided with internal electrodes are laminated in a layered manner and a manufacturing method thereof.

Schematic diagram of mechanical polarization process of multilayer piezoelectric actuator in an embodiment of the present invention Schematic diagram of polarization process by electric field of multilayer piezoelectric actuator in an embodiment of the present invention Schematic diagram of a typical multilayer piezoelectric actuator The schematic diagram of the process of applying the electric field more than the coercive electric field of the lamination type piezoelectric actuator in other embodiment of this invention to an active part, and reversing a polarization direction Schematic diagram showing unpolarized domains in piezoelectric crystal grains The schematic diagram (a) which shows the domain of the polarization state in the piezoelectric crystal grain in the active part of the laminated piezoelectric actuator of the manufacturing method which concerns on this invention in the state of polarization processing, and the inactive part, and lamination | stacking of the past or the comparative example 1 (B) Schematic showing domain of polarization state in piezoelectric crystal grains in active part of type piezoelectric actuator After the polarization process of the manufacturing method according to the present invention, the piezoelectric body in the active portion of the multilayer piezoelectric actuator is further subjected to a step of reversing the polarization direction by applying an electric field higher than the coercive electric field to the active portion in the direction opposite to the polarization direction. Schematic diagram showing domain of polarization state in crystal grain (a) and schematic diagram showing domain of polarization state in piezoelectric crystal grain in inactive part (b) FIG. 7A is a schematic diagram showing a domain of a polarization state in a piezoelectric crystal grain in an active portion showing a state in which a driving voltage is applied to the multilayer piezoelectric actuator shown in FIG. The graph which shows the result of having measured the Example of the piezoelectric element manufactured with the manufacturing method based on this invention, the drive voltage of Comparative Examples 1 and 2, and the elongation amount of the element by the voltage application. Schematic diagram showing the state of cracking of the multilayer piezoelectric actuator in the conventional example Schematic diagram of the multilayer piezoelectric actuator in the conventional example when the entire polarization Schematic diagram at the time of polarization between electrode layers of the multilayer piezoelectric actuator in the conventional example

Explanation of symbols

1. Multilayer piezoelectric actuator (multilayer piezoelectric element)
DESCRIPTION OF SYMBOLS 10 Laminated body 11 Piezoelectric ceramic layer 12 Internal electrode layer 13 External electrode 14 Protective layer A Active part B Inactive part

Claims (7)

A step of obtaining a laminate comprising a piezoelectric ceramic layer and an internal electrode layer laminated, and having an active part located between internal electrode layers of different polarities, and an inactive part existing around the active part; ,
Uniform compressive stress is applied from the entire side surface in a direction orthogonal to the stacking direction of the stacked body, the stacked body is extended in the stacking direction, and the orientation of the domain of the entire stacked body is any direction above or below the stacking direction. Orienting to,
Applying an electric field to the laminate through the internal electrode layer to polarize the active part;
A method for producing a laminated piezoelectric element comprising:   The method according to claim 1, wherein the total length of the stacked body in the stacking direction is 4 mm or more.   In the step of obtaining the laminated body, a pair of external electrodes having different polarities are formed by baking a conductive paste on side surfaces in a direction orthogonal to the laminating direction of the laminated body, and the internal electrodes are alternately formed into external electrodes having different polarities. 3. A method according to claim 1 or 2, characterized in that they are connected.   4. The method according to claim 1, further comprising a step of inverting the polarization direction by applying an electric field equal to or greater than a coercive electric field to the active portion in a direction opposite to the polarization direction in the step subsequent to the polarization step. The method according to any one. A laminate comprising a piezoelectric ceramic layer having pyroelectricity and an internal electrode layer, and having an active portion located between internal electrodes of different polarities and an inactive portion present around the active portion Body,
A pair of external electrodes having different polarities, formed by baking a conductive paste on side surfaces orthogonal to the stacking direction of the stacked body, the internal electrode layers being alternately connected;
A laminated piezoelectric element comprising:
A region in which the entire laminate is substantially oriented along the direction of the electric field applied between the internal electrode layers and the direction of the domain is oriented in a direction opposite to the direction along the direction of the electric field simultaneously exists in the inactive portion. The layered piezoelectric element is characterized in that an orientation ratio of domains along the electric field direction is lower than that of the inactive portion and exists in the active portion .   The multilayer piezoelectric element according to claim 5, wherein the electric field direction is a stacking direction of the stacked body.   The multilayer piezoelectric element according to claim 6, wherein the total length of the multilayer body in the stacking direction is 4 mm or more.

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