JP2010161286A - Laminated piezoelectric element and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated piezoelectric element for obtaining a large displacement amount, and also reliably suppressing the generation of cracks due to displacement. <P>SOLUTION: The laminated piezoelectric element 1 includes: a laminated piezoelectric material 2 where internal piezoelectric layers 4-7 are laminated between the outermost layer piezoelectric layers 3, 8, internal electrodes 11-15 are laminated between the adjacent piezoelectric layers, and an upper surface electrode 9 and a lower surface electrode 10 are formed on the upper surface and the lower surface; and first and second external electrodes 14, 17. The adjacent piezoelectric layers are treated by polarization in opposite directions concerning a thickness direction. The polarization degree of the outermost layer piezoelectric layers 3, 8 is set lower than that of the internal piezoelectric layers 4-7. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laminated piezoelectric element used for, for example, an actuator and a manufacturing method thereof, and more specifically, a laminated piezoelectric element using a laminated piezoelectric body in which a plurality of piezoelectric layers are laminated via internal electrodes. And a manufacturing method thereof.

  Conventionally, piezoelectric actuators have been widely used to drive printer heads and magnetic disk drive heads. In the piezoelectric actuator, a driving force is obtained by displacement of the piezoelectric body. Accordingly, there is a possibility that a large stress is repeatedly applied to the piezoelectric body during driving for a long period of time and a crack is generated. In particular, in a piezoelectric actuator using a thin piezoelectric body, such a crack is likely to occur, and thus it is strongly required to suppress the crack.

  The following Patent Document 1 discloses a manufacturing method for suppressing such cracks. FIG. 13 is a schematic front cross-sectional view for explaining the method of manufacturing a piezoelectric element described in Patent Document 1. In the piezoelectric device shown in FIG. 13, a piezoelectric element 1003 is stacked on a substrate 1001 with an adhesion layer 1002 interposed therebetween. The piezoelectric element 1003 is formed by sequentially forming a first electrode layer 1004, a piezoelectric thin film layer 1005, and a second electrode layer 1006 on the adhesion layer 1002. Here, shrinkage stress is applied when the piezoelectric thin film layer 1005 is formed. Due to the difference in shrinkage between the substrate 1001 and the piezoelectric thin film layer 1005 during cooling after film formation, the tensile stress generated in the piezoelectric thin film layer 1005 is relaxed.

JP 2004-119703 A

  In the manufacturing method described in Patent Document 1, compressive stress is applied to the piezoelectric thin film layer 1005 itself upon cooling after film formation, and the tensile stress generated in the piezoelectric thin film layer 1005 is relaxed. Thereby, the occurrence of cracks is suppressed. According to such a method, it is considered that cracks when repeatedly driven are also suppressed.

  However, the method described in Patent Document 1 is only a method applicable only when the piezoelectric layer is formed by a thin film deposition method such as sputtering. That is, since the stress at the time of film formation is used, it cannot be used for a piezoelectric element using a laminated piezoelectric material obtained by laminating piezoelectric green sheets.

  In recent years, in order to obtain a larger displacement, piezoelectric actuators using a laminated piezoelectric material in which a plurality of piezoelectric layers are laminated are used in various fields. Also in the laminated piezoelectric material, in order to obtain a large displacement while being downsized and small, the piezoelectric material layer is getting thinner. Therefore, there is a possibility that cracks may occur on the surface of the laminated piezoelectric material during use. Since cracks are likely to occur as the thickness of the piezoelectric layer in the multilayer piezoelectric body becomes thinner or as the thickness of the multilayer piezoelectric body itself becomes thinner, suppression of cracks is strongly demanded.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a multilayer piezoelectric element using a multilayer piezoelectric body that eliminates the above-described drawbacks of the above-described prior art, is less likely to cause cracks in the piezoelectric layer, and has excellent reliability, and a method for manufacturing the same. .

  According to the present invention, a laminated piezoelectric body having an upper surface and a lower surface, and first and second external electrodes formed on an outer surface of the laminated piezoelectric body, the laminated piezoelectric body includes: The upper surface side outermost piezoelectric layer and the lower surface side outermost piezoelectric layer disposed on the lower surface side, the inner piezoelectric layer laminated between the upper surface side outermost layer piezoelectric layer and the lower surface side outermost layer piezoelectric layer, and An upper electrode and a lower electrode formed on the upper surface and the lower surface, respectively, and an internal electrode disposed between adjacent piezoelectric layers, and the degree of polarization of the upper surface side outermost piezoelectric layer and the lower surface side outermost piezoelectric layer is The degree of polarization of the inner piezoelectric layer is lower.

  In a specific aspect of the multilayer piezoelectric element according to the present invention, the upper surface electrode and the lower surface electrode are electrically connected to the first external electrode, and the internal electrode is electrically connected to the first external electrode. First internal electrodes connected to each other and a second internal electrode electrically connected to the second external electrode. In this structure, since the upper electrode and the lower electrode are electrically connected to the first external electrode and have the same potential, the directionality in electrical connection with the outside can be eliminated.

  In another specific aspect of the multilayer piezoelectric element according to the present invention, the upper surface side outermost piezoelectric layer and the lower surface side outermost piezoelectric layer are thicker than the inner piezoelectric layer. In this case, since the electric field having the same intensity may be applied to all the piezoelectric layers in the polarization process, the polarization process becomes easy.

  In still another specific aspect of the multilayer piezoelectric element according to the present invention, the upper surface side outermost piezoelectric layer and the lower surface side outermost piezoelectric layer have the same thickness as the inner piezoelectric layer. In this case, a laminated piezoelectric body can be easily obtained by laminating a plurality of piezoelectric green sheets having the same thickness.

  The manufacturing method of the present invention is the manufacturing method of the present invention, wherein the laminated body has an upper surface side outermost piezoelectric layer, a lower surface side outermost piezoelectric layer, first and second external electrodes, an upper surface electrode, and a lower surface electrode. Preparing a piezoelectric layer and polarizing the stacked piezoelectric body so that the polarization degree of the uppermost piezoelectric layer and the lowermost piezoelectric layer is lower than that of the inner piezoelectric layer. And a process for processing.

  In a specific aspect of the manufacturing method of the multilayer piezoelectric element according to the present invention, in the step of preparing the multilayer piezoelectric body, the thickness of the uppermost surface side outermost piezoelectric layer and the lower surface side outermost piezoelectric layer is set to the inner side. Prepare a laminated piezoelectric material that is thicker than the thickness of the piezoelectric layer, and apply an electric field of the same magnitude to the upper surface side outermost piezoelectric layer, the lower surface side outermost piezoelectric layer, and the inner piezoelectric layer to perform polarization processing. . In this case, since polarization processing can be performed by applying an electric field having the same electric field strength to all the piezoelectric layers, polarization is easy.

  In still another specific aspect of the method for manufacturing a multilayer piezoelectric element according to the present invention, in the step of preparing the multilayer piezoelectric body, the thicknesses of the upper surface side outermost layer piezoelectric material layer and the lower surface side outermost layer piezoelectric material layer are: In the step of preparing a laminated piezoelectric body having a thickness equal to the thickness of the inner piezoelectric layer and polarizing the laminated piezoelectric body, the upper surface side outermost piezoelectric layer and the lower surface side outermost piezoelectric layer are formed on the inner piezoelectric layer. It is polarized by applying a weak electric field. In this case, it is only necessary to prepare a plurality of piezoelectric green sheets having the same thickness when manufacturing the laminated piezoelectric body prior to polarization, so that the manufacturing process of the laminated piezoelectric body can be simplified.

  According to the multilayer piezoelectric element according to the present invention, the degree of polarization of the upper surface side outermost piezoelectric layer and the lower surface side outermost piezoelectric layer is lower than the degree of polarization of the inner piezoelectric layer. The polarization strain is reduced in the outermost piezoelectric layer compared to the inner piezoelectric layer. Therefore, compressive stress can be applied to the outermost piezoelectric layer, and when the laminated piezoelectric member is displaced during driving, the amount of displacement in the outermost piezoelectric layer is suppressed, thereby suppressing the occurrence of cracks. .

(A) is a typical front sectional view for explaining a polarization step in the method for manufacturing a multilayer piezoelectric element of one embodiment of the present invention, and (b) is a perspective view of the multilayer piezoelectric element of the present embodiment. . (A), (b) is each top view for demonstrating the internal electrode shape prepared in one Embodiment of this invention. It is a disassembled perspective view of the laminated piezoelectric material prepared in one embodiment of the present invention. (A), (b) is a schematic diagram which shows the state of the domain before polarization, and the state of the domain after polarization. It is a schematic diagram for demonstrating the change of the shape of the domain before and behind polarization. FIG. 5 is a schematic front view for explaining a stress relationship between an outermost piezoelectric layer and an inner piezoelectric layer of a multilayer piezoelectric body. (A) And (b) is a schematic diagram which shows each displacement state at the time of displacing so that a lamination type piezoelectric material may protrude upwards and to protrude downward. It is typical front sectional drawing for demonstrating the lamination type piezoelectric element polarization process of the 2nd Embodiment of this invention. (A)-(c) is each top view for demonstrating the internal electrode shape formed in the manufacturing method of the lamination type piezoelectric element of 2nd Embodiment, respectively. In the 2nd Embodiment of this invention, it is a perspective view which shows the state in which the electrode for polarization was formed in the laminated piezoelectric element. It is a perspective view which shows the external appearance of the lamination type piezoelectric element of the 2nd Embodiment of this invention. It is typical front sectional drawing which shows the state of the crack which arises in the conventional lamination type piezoelectric element. It is front sectional drawing for demonstrating the manufacturing method of the conventional piezoelectric element.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  FIGS. 1A and 1B are a front cross-sectional view for explaining a polarization process of a multilayer piezoelectric element according to the first embodiment of the present invention and a perspective view showing the multilayer piezoelectric element.

  The multilayer piezoelectric element 1 has a multilayer piezoelectric body 2. In the present embodiment, the laminated piezoelectric body 2 has a rectangular parallelepiped shape.

  The laminated piezoelectric body 2 has a structure in which a plurality of piezoelectric layers are laminated from the upper surface 2a to the lower surface 2b. More specifically, the upper surface side outermost piezoelectric layer 3 is disposed on the upper surface 2a side, and the lower surface side outermost piezoelectric layer 8 is disposed on the lower surface 2b side. A plurality of inner piezoelectric layers 4 to 7 are laminated between the upper surface side outermost piezoelectric layer 3 and the lower surface side outermost piezoelectric layer 8.

  An upper surface electrode 9 is formed on the upper surface 2a, and a lower surface electrode 10 is formed on the lower surface 2b.

  In the laminated piezoelectric body 2, a plurality of internal electrodes 11 to 15 are formed in order from above. The internal electrodes 11 to 15 are arranged between adjacent piezoelectric layers, and are distinguished into first internal electrodes 12 and 14 and second internal electrodes 11, 13 and 15.

  The first internal electrodes 12, 14 and the second internal electrodes 11, 13, 15 are alternately arranged in the thickness direction of the laminated piezoelectric body 2.

  The thickness of the uppermost piezoelectric layer 3 on the upper surface side and the thickness of the outermost piezoelectric layer 8 on the lower surface side, which are the outermost piezoelectric layers, are larger than the thicknesses of the inner piezoelectric layers 4-7.

  The upper surface side outermost piezoelectric layer 3, the inner piezoelectric layers 4 to 7, and the lower surface side outermost piezoelectric layer 8 are made of appropriate piezoelectric ceramics such as lead zirconate titanate ceramics, as indicated by the arrows in the figure. In addition, it is polarized in the thickness direction. In addition, the piezoelectric layers 3 to 8 are polarized so that the polarization directions of adjacent piezoelectric layers are opposite to the thickness direction.

  As shown in FIG. 1B, first and second external electrodes 16 and 17 are formed on the side surface of the laminated piezoelectric body 2. The first external electrode 16 is electrically connected to the upper surface electrode 9, the lower surface electrode 10, and the first internal electrodes 12 and 14. On the other hand, the second external electrode 17 is electrically connected to the second internal electrodes 11, 13, 15.

  In manufacturing the multilayer piezoelectric element 1, first, a first mother piezoelectric green sheet is prepared. A plurality of first internal electrodes are printed on the mother piezoelectric green sheet. Similarly, a plurality of second internal electrodes are printed on the piezoelectric green sheet of the second mother. Next, a first mother piezoelectric green sheet on which a plurality of first internal electrodes are printed and the second mother piezoelectric green sheet are alternately stacked, and a plain mother piezoelectric body is vertically stacked. Laminate green sheets to obtain a mother laminate. Only the piezoelectric green sheets constituting the outermost piezoelectric layers 3 and 8 are thicker than the piezoelectric green sheets for constituting the inner piezoelectric layers 4 to 7. The mother laminate is pressure-bonded in the thickness direction and then cut to obtain a laminate raw chip. Cutting may be performed after firing.

  The laminated green chip is fired to obtain a sintered body. The laminated piezoelectric body 2 can be obtained by forming the upper surface electrode 9 and the lower surface electrode 10 on the upper surface and the lower surface of the sintered body. The upper surface electrode 9 and the lower surface electrode 10 may be completed by printing a conductive paste at the mother laminate stage before sintering and sintering. In any case, the multilayer piezoelectric body 2 is manufactured using a well-known ceramic integrated firing technique.

  FIG. 2A is a schematic plan view for explaining a planar shape of the first internal electrode 12, and FIG. 2B is a schematic plan view for explaining the planar shape of the second internal electrode 11. It is a top view. The first internal electrode 12 has a rectangular shape smaller than the planar shape of the multilayer piezoelectric body 2, and is in a portion other than the lead portion 11 a having the lead portion 12 a led to the long side surface of the multilayer piezoelectric body 2. , Located on the inner side of the outer surface of the laminated piezoelectric body 2.

  On the other hand, as shown in FIG. 2B, the second internal electrode 11 has a rectangular shape, but is provided at a position close to one end face side of the long side surface of the laminated piezoelectric body 2. It has a drawer part 11a.

  As shown in FIG. 3, the first internal electrodes and the second internal electrodes are alternately arranged in the thickness direction. Similarly to the first internal electrode 12, the upper surface electrode 9 and the lower surface electrode 10 have extraction portions 9 a and 10 a that are extracted at the center of the long side surface of the multilayer piezoelectric body 2.

  Accordingly, the upper electrode 9, the lower electrode 10, and the second inner electrodes 11, 13, 15 are electrically connected to the first external electrode 16. The second internal electrodes 11, 13, 15 are electrically connected to the second external electrode 17.

  These electrode materials are not particularly limited, and can be formed from an appropriate metal or alloy such as Ag, Ag—Pd, Al, or Cu, for example.

  After obtaining the laminated piezoelectric material 2, as shown in FIG. 1A, a polarization process is performed by applying a voltage. A positive potential is applied to the upper surface electrode 9, the lower surface electrode 10 and the first internal electrodes 12, 14, and a negative potential is applied to the second internal electrodes 11, 13, 15. Specifically, such a potential difference may be given between the first and second external electrodes 16 and 17. As a result, as shown by the arrows in the figure, each piezoelectric layer is polarized as described above. In this case, the thickness of the uppermost piezoelectric layer 3 and the lowermost piezoelectric layer 8 is set to be larger than the thickness of the inner piezoelectric layers 4 to 7 as the remaining piezoelectric layers. The degree of polarization of the body layers 3 and 8 is lower than the degree of polarization of the inner piezoelectric layers 4 to 7.

  In the multilayer piezoelectric element 1 of the present embodiment, since the degree of polarization of the outermost piezoelectric layers 3 and 8 is relatively low, the occurrence of cracks during use can be suppressed. This will be described more specifically below.

  In use, a potential is applied between the first and second external electrodes 16 and 17. 7 can be realized by devising the shape of the internal electrode so that the connection between the internal electrode and the external electrode is partially changed between use and polarization. The vibration as shown in FIG. 7 is possible with a piezoelectric element having a bimorph structure, for example. As a result, for example, the displacement state indicated by the solid line A in FIG. 7A or the displacement state indicated by the solid line B in FIG. For example, when a positive potential is applied to the first external electrode 16 and a negative potential is applied to the second external electrode 17, as shown in FIG. 7A, the outermost piezoelectric layer 3 and the inner piezoelectric layer 5 and 6 extend in the potential direction, and the inner piezoelectric layers 6 and 7 and the lower surface side outermost piezoelectric layer 8 contract in the drawing direction, so that the displacement state A in FIG. 7A is realized.

  When the polarities of the electric fields applied to the first and second external electrodes 16 and 17 are reversed, the displacement state B shown in FIG. 7B is realized. In any case, in the laminated piezoelectric body 2, a large tensile stress is applied to the surface of the outermost piezoelectric layer 3 or the outermost piezoelectric layer 8. In this case, when all the piezoelectric layers have the same degree of polarization, a large tensile stress is applied to the surface of the outermost piezoelectric layer, so that the laminated piezoelectric material 1012 as in the conventional laminated piezoelectric material 1011 shown in FIG. Crack C tends to occur in the central region of the upper surface 1012a or the lower surface 1012b.

  On the other hand, in the multilayer piezoelectric element 1 of the present embodiment, the occurrence of such cracks C can be suppressed. This is due to the following reason. In the polarization process, a polarization electric field E is applied to the piezoelectric layer. In this case, an electric field indicated by an arrow E is applied to each domain D forming the piezoelectric layer as schematically shown in FIG. In addition, the arrow in the domain D is the polarization axis direction in each domain. When the electric field E is applied, the polarization axis direction of the domain D is changed, and the polarization axis directions of many domains D are aligned along the direction of the polarization electric field E as shown in FIG. In addition, there is also a domain D in which the polarization axis direction is not aligned with the direction of the electric field E.

  In this case, in FIG. 4A, the polarization axis direction of the domain D in which the direction of the polarization electric field E and the polarization axis direction are the same or the domain D in which the polarization electric field E direction and the polarization axis direction are not much different is When applied, the direction is substantially the same as the electric field E. On the other hand, in the case of the polarization axis direction opposite to the direction of the polarization electric field E, the polarization axis direction does not change depending on the magnitude of the polarization electric field E even if the polarization process is performed. Further, when the direction of the polarization electric field E and the polarization axis direction are at a large angle, for example, at an angle of 90 °, when the polarization electric field E is applied, the polarization axis direction changes greatly. Will be.

In the case of a domain in which the polarization axis direction changes greatly when the polarization electric field E is applied, the dimension S ₀ in the direction orthogonal to the direction of the polarization electric field E is before polarization as shown in FIG. the is, it received a polarization distortion, small and _{S 1.} This contracts in a direction orthogonal to the direction of the polarization electric field E when the domain polarization axis direction is aligned with the polarization electric field direction. That is, the greater the amount of domain rotation during polarization, in other words, the higher the degree of polarization, the greater the strain due to the polarization and the smaller the dimension in the direction orthogonal to the direction of the polarization electric field E.

  In the present embodiment, the thickness of the outermost piezoelectric layers 3 and 8 is relatively large during polarization, so that the magnitude of the electric field applied in the thickness direction during polarization is lower than that of the inner piezoelectric layers 4 to 7. Therefore, the polarization strain in the outermost piezoelectric layers 3 and 8 is relatively smaller than the polarization strain in the inner piezoelectric layers 4 and 7. As a result, as schematically shown in FIG. 6, since the degree of polarization in the outermost piezoelectric layer 3 is low and the polarization strain is small, the outermost piezoelectric layer 3 has a compressive stress F, and the inner piezoelectric layer 4 has A tensile stress G is applied.

  In this way, compressive stress in the surface direction is applied to the upper surface side outermost piezoelectric layer 3. Similarly, a compressive stress is applied to the lower surface side outermost piezoelectric layer 8 in the surface direction.

  Therefore, in the multilayer piezoelectric element 1, the displacement state A or B shown in FIG. 7A or 7B is realized when the multilayer piezoelectric body 2 is driven, and the outermost piezoelectric layer 3 or the outermost piezoelectric layer 8 is realized. Even if a large tensile stress is applied to the outer surface, the compressive stress is applied in advance, so that the displacement is suppressed, thereby suppressing the occurrence of cracks.

  Next, specific experimental examples will be described.

  In accordance with the first embodiment, a laminated piezoelectric material was manufactured with the following capacity. Using a lead zirconate titanate ceramic slurry, a piezoelectric green sheet having a thickness of 20 μm was obtained. Next, an Ag / Pd conductive paste containing Ag and Pd at a weight ratio of 8: 2 was screen-printed on a piezoelectric green sheet to a thickness of 1.0 μm. A plurality of mother piezoelectric green sheets obtained in this way are laminated according to the manufacturing method of each embodiment, but the thickness after sintering is different between the inner piezoelectric layer and the outermost piezoelectric layer. A plurality of types of piezoelectric green sheets were used. In this way, a mother laminate having 14 internal electrode layers was obtained.

  Thereafter, after performing the binder removal step, the laminate was fired at 1000 ° C. to obtain a mother sintered body. This mother sintered body was cut with a dicer to obtain a chip of 17 mm × 17 mm × thickness 0.3 mm. In this chip, the number of laminated internal electrodes was 14, the thickness of the inner piezoelectric layer was 17 μm, and the outermost piezoelectric layer was 16, 25, or 32 μm as shown in Table 1 below.

  Next, the first and second external electrodes, the upper surface electrode, and the lower surface electrode were formed of a Monel alloy containing 63 wt% or more of Ni and 30 wt% of Cu. The thickness was 0.2 μm. Thereafter, an electric field of 3.0 kV / mm was applied between the first and second external electrodes 16 and 17 for 2 minutes to perform polarization treatment.

  In this way, piezoelectric elements of sample numbers 1 to 4 shown in Table 1 below were obtained.

  In the plurality of types of laminated piezoelectric elements obtained as described above, the ratio of the polarization electric field applied to the outermost piezoelectric layer and the polarization electrolysis applied during the polarization of the inner piezoelectric layer was determined. The polarization electric field ratio is shown in Table 2 below.

  For the plurality of types of stacked piezoelectric elements, the compressive stress with respect to the polarization electric field ratio, that is, the compressive stress applied to the outermost piezoelectric layer, the failure time in the wet driving test, and the displacement amount are as follows. Asked.

1) Compressive stress Using the μ-XRD spectrum, the stress in the central portion of the sample, that is, the piezoelectric layer was measured using the 222 peak of the PZT phase. In the X-ray diffraction, the angle in the tilt direction (ψ) of the sample was changed, and each sample was measured with the tilt angle. When stress is present in the sample, the peak shifts as the tilt angle ψ increases. The stress can be obtained from this shift amount. The ratio of the compressive stress when the peak shift amount in sample number 1 is 100% is defined as the compressive stress application rate and is shown in Table 2 below.

2) Failure start time in driving test in humidity In order to evaluate the reliability, the drive frequency was set to 15 Hz in a 60 ° C. and 95% relative humidity atmosphere, and a drive voltage of 12 V was applied. Asked.

  The results are shown in Table 3.

3) Measurement of displacement amount A voltage of 12 V was applied at a driving frequency of 15 Hz, and the displacement amount was measured. The results are shown in Table 4 below.

  As is apparent from Tables 2 to 4, in Sample Nos. 2 and 3 corresponding to the examples of the present invention, a compressive stress is relatively applied to the outermost piezoelectric layer. It can be seen that the failure start time in the humidity test is much longer than that of the device, and the reliability is excellent.

  Further, in the laminated piezoelectric element of sample number 4, the upper surface electrode and the lower surface electrode were not formed, but in comparison with this sample number 4, the laminated piezoelectric element of sample numbers 2 and 3 can obtain a large amount of displacement. I understand.

  In order to make the displacement of the outermost piezoelectric layer of the multilayer piezoelectric element less than half of that of the inner piezoelectric layer, that is, in order to balance a large amount of displacement and crack prevention, The polarization degree is desirably 30% or more of the polarization degree of the inner piezoelectric layer. In this case, the reliability is greatly improved. Therefore, in the present embodiment, it is preferable that the thickness of the outermost piezoelectric layer is not more than 3.3 times the thickness of the inner piezoelectric layer. In this case, the first and second external electrodes When the electrode treatment is performed using the outermost piezoelectric layer, the degree of polarization of the outermost piezoelectric layer can surely be 30% or more of the inner piezoelectric layer.

  FIG. 8 is a front cross-sectional view for explaining a polarization method of the multilayer piezoelectric element according to the second embodiment of the present invention, and FIG. 10 shows that a polarization electrode for polarization is formed on the surface of the multilayer piezoelectric body. It is a perspective view which shows the structure made. In the present embodiment, the laminated piezoelectric body 22 has a plurality of piezoelectric layers 23 to 28 having the same thickness. That is, the outermost piezoelectric layers 23 and 28 have the same thickness as the inner piezoelectric layers 24 to 27. An upper surface electrode 29 is formed on the upper surface 22a of the multilayer piezoelectric body 22, and a lower surface electrode 30 is formed on the lower surface 22b. The plurality of internal electrodes 31 to 35 are disposed between adjacent piezoelectric layers.

  FIG. 9A is a plan view showing an electrode pattern of the upper surface electrode 29, and an extraction portion 29 a that is extracted at the center of one long side side surface of the laminated piezoelectric body 22 is provided. Similarly, the lower surface electrode 30 is also provided with a lead-out portion that is led out to the center of one long-side side surface of the multilayer piezoelectric body 22.

  As shown in FIG. 9C, the first internal electrodes 32 and 34 have a lead portion 32 a provided at a position close to one end side on one long side side surface of the laminated piezoelectric body 22. The internal electrode 34 also has a lead portion provided at the same position.

  On the other hand, as shown in FIG. 9B, the second internal electrode 31 has a lead portion 31 a provided at a position close to one end side on one long side surface of the laminated piezoelectric body 22. . The other second internal electrodes 33 and 35 also have lead portions at the same position. As shown in FIG. 10, the first polarization electrode 41 is provided so as to be electrically connected to the lead portion 29 a of the upper surface electrode 29. The first polarization electrode 41 is also electrically connected to the lower surface electrode 30. On the other hand, a second polarization external electrode 42 is formed so as to be electrically connected to the lead portion 32a of the first internal electrodes 32, 34.

  Further, the third polarization electrode 43 is formed by being brought close to the end on one long side surface of the laminated piezoelectric body 22 so as to be electrically connected to the lead portion 31 a of the second internal electrode 31. Has been.

As shown in FIG. 8, voltages V ₁ , 2V ₁ , and 0 [V] are applied to the first to third polarization electrodes 41 to 43. In this manner, the piezoelectric layers 23 to 28 are polarized as shown by arrows in FIG. In this case, a DC electric field E ₁ having a voltage V ₁ is applied to the outermost piezoelectric layers 23 and 28, and the other inner piezoelectric layers 24 to 27 correspond to a voltage of 2V ₁ −0 = 2V _1. so that the electric field E ₀ is applied. Therefore, the electric field strength E ₁ applied to the outermost piezoelectric layers 23 and 28 is half of the electric field strength E ₀ applied to the inner piezoelectric layers 24 to 27, and the degree of polarization of the outermost piezoelectric layers 23 and 28 is relatively high. Lower.

  Therefore, also in the present embodiment, as in the first embodiment, the degree of polarization of the outermost piezoelectric layers 23 and 28 is relatively low, so that the compressive stress due to the difference in polarization strain is applied to the outermost piezoelectric layers 23 and 28. Will be granted.

  Next, as shown in FIG. 11, the first external electrode 46 is formed by forming an electrode film so as to electrically connect the first and second polarization electrodes 41 and 42. Then, the third polarization electrode 43 is used as the second external electrode, and a voltage can be applied between the external electrodes to drive the same as in the first embodiment.

  Also in this embodiment, since the degree of polarization of the outermost piezoelectric layers 23 and 28 is relatively low, the displacement in the outermost piezoelectric layer is suppressed as in the stacked piezoelectric element of the first embodiment. As a result, the occurrence of cracks can be reliably suppressed.

  Also in the second embodiment, the degree of polarization of the outermost piezoelectric layers 23 and 28 only needs to be relatively low, but it is sufficient that the degree of polarization of the inner piezoelectric layers 24 to 27 is 30% or more. It is preferable in terms of suppressing cracks by the amount. Therefore, it is desirable to polarize the outermost piezoelectric layers 23 and 28 by applying an electric field strength of 3/10 or more of the electric field strength applied to the inner piezoelectric layer. As a result, it is possible to lengthen the time to failure stop in the humidity test by about 10 times.

  As is clear from the first and second embodiments, if the degree of polarization of the outermost piezoelectric layer is relatively low, the thickness of the outermost piezoelectric layer may be equal to or different from that of the inner piezoelectric layer. Good.

  In the second embodiment, since the thicknesses of all the piezoelectric layers 23 to 28 are equal, the types of piezoelectric green sheets to be prepared can be reduced, and the laminated piezoelectric body 22 can be easily obtained. On the other hand, in the first embodiment, no complicated electrical connection structure is required for polarization, and the first and second external electrodes that are finally used are directly used as the first and second polarization electrodes. Therefore, the polarization process and the manufacturing process can be simplified.

DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric element 2 ... Laminated piezoelectric body 2a ... Upper surface 2b ... Lower surface 3 ... Upper surface side outermost layer piezoelectric material layer 4-7 ... Inner piezoelectric material layer 8 ... Lower surface side outermost layer piezoelectric material layer 9 ... Upper surface electrode 9a ... Lead-out Part 10: Bottom electrode 10a ... Leader part 11, 13, 15 ... Second internal electrode 11a ... Leader part 12, 14 ... First internal electrode 12a ... Leader part 16 ... First external electrode 17 ... Second external part Electrode 22 ... Laminated piezoelectric material 22a ... Upper surface 22b ... Lower surface 23,28 ... Outermost layer piezoelectric material layer 24-27 ... Inner piezoelectric material layer 29 ... Upper surface electrode 29a ... Leader portion 30 ... Lower surface electrodes 31,33,35 ... Second Internal electrode 31a ... leader 32,34 ... first internal electrode 32a ... leader 34 ... internal electrode 41 ... first polarization electrode 42 ... second polarization external electrode 43 ... third polarization electrode 46 ... First external electrode

Claims (7)

A laminated piezoelectric body having an upper surface and a lower surface;
First and second external electrodes formed on the outer surface of the multilayer piezoelectric body,
The laminated piezoelectric material is laminated between an upper surface side outermost layer piezoelectric material layer and a lower surface side outermost layer piezoelectric material layer disposed on the upper surface side and the lower surface side, respectively, and between the upper surface side outermost layer piezoelectric material layer and the lower surface side outermost layer piezoelectric material layer. An inner piezoelectric layer, and upper and lower electrodes formed on the upper and lower surfaces, respectively, and an internal electrode disposed between adjacent piezoelectric layers,
The multilayer piezoelectric element, wherein a degree of polarization of the upper surface side outermost piezoelectric layer and a lower surface side outermost piezoelectric layer is lower than that of the inner piezoelectric layer.   The upper surface electrode and the lower surface electrode are electrically connected to the first external electrode, the internal electrode is electrically connected to the first external electrode, and the first electrode The multilayer piezoelectric element according to claim 1, further comprising: a second internal electrode electrically connected to the two external electrodes.   The multilayer piezoelectric element according to claim 1 or 2, wherein a thickness of the outermost piezoelectric layer is larger than that of the inner piezoelectric layer.   The multilayer piezoelectric element according to claim 1, wherein a thickness of the outermost piezoelectric layer is equal to a thickness of the inner piezoelectric layer. It is a manufacturing method of the lamination type piezoelectric element given in any 1 paragraph of Claims 1-4,
Preparing the multilayer piezoelectric body having an upper surface side outermost piezoelectric layer, a lower surface side outermost piezoelectric layer, first and second external electrodes, an upper surface electrode, and a lower surface electrode;
A step of polarizing the laminated piezoelectric body so that the degree of polarization of the upper surface side outermost piezoelectric layer and the lower surface side outermost piezoelectric layer is lower than the degree of polarization of the inner piezoelectric layer. A method for manufacturing a piezoelectric element. In the step of preparing the multilayer piezoelectric body, a multilayer piezoelectric body is prepared in which the upper surface side outermost piezoelectric layer and the lower surface side outermost piezoelectric layer are thicker than the inner piezoelectric layer,
6. The method of manufacturing a multilayer piezoelectric element according to claim 5, wherein polarization processing is performed by applying an electric field of the same magnitude to the upper surface side outermost piezoelectric layer, the lower surface side outermost piezoelectric layer, and the inner piezoelectric layer. In the step of preparing the laminated piezoelectric material, a laminated piezoelectric material is prepared in which the thickness of the uppermost piezoelectric layer and the lowermost piezoelectric layer is equal to the thickness of the inner piezoelectric layer,
6. In the step of polarizing the laminated piezoelectric material, polarization is performed by applying a weak electric field to the upper surface side outermost piezoelectric layer and the lower surface side outermost piezoelectric layer as compared with the inner piezoelectric layer. The manufacturing method of the lamination piezoelectric element of description.

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