JP5403170B2 - Multilayer piezoelectric actuator and piezoelectric vibration device - Google Patents

Description

  The present invention relates to a laminated piezoelectric actuator using a laminated ceramic sintered body in which a plurality of internal electrodes are laminated via a ceramic layer, and more specifically, ceramic sintered having an inactive layer as an outermost layer. The present invention relates to a laminated piezoelectric actuator using a body. The present invention also relates to a piezoelectric vibration device including a vibration plate, in which a laminated piezoelectric actuator is joined to the vibration plate.

  Conventionally, various laminated piezoelectric actuators, piezoelectric buzzers, and the like using a laminated ceramic sintered body in which a plurality of internal electrodes are laminated via a piezoelectric ceramic layer have been proposed.

  For example, Patent Literature 1 below discloses a piezoelectric buzzer in which a vibration plate made of a steel plate is bonded to the laminated ceramic sintered body. Here, the ceramic layer on the diaphragm side of the laminated ceramic sintered body is not polarized. Thereby, the ceramic layer is a relaxation layer. Therefore, it is said that the bending vibration of the vibrating body composed of the ceramic sintered body and the diaphragm can be smoothed.

  However, when the piezoelectric buzzer described in Patent Document 1 is used for a piezoelectric actuator, a ceramic layer that has not been subjected to polarization treatment becomes an inactive ceramic layer. That is, the inactive layer does not contribute to the piezoelectric effect. For this reason, the inactive layer becomes a constraining layer, and the displacement amount may be reduced.

  On the other hand, the following Patent Document 2 discloses a multilayer piezoelectric actuator 1001 having a structure shown in FIG. In the multilayer piezoelectric actuator 1001, a plurality of first internal electrodes 1003 and a plurality of second internal electrodes 1004 are alternately arranged in a stacking direction in a multilayer ceramic sintered body 1002. A first external electrode 1005 is formed on the first end face of the ceramic sintered body 1002. A second external electrode 1006 is formed on the second end face of the ceramic sintered body 1002.

  A surface electrode 1006a is formed on the upper surface of the ceramic sintered body 1002 so as to overlap the uppermost first internal electrode 1003 when viewed in plan in the stacking direction. On the other hand, no surface electrode is formed on the lower surface of the ceramic sintered body 1002. Therefore, the ceramic layer between the lowermost first internal electrode 1003 and the lower surface of the ceramic sintered body 1002, that is, the lowermost ceramic layer is an inactive layer. The thickness of this inactive layer is made thinner than the thickness of other ceramic layers that are active layers. Since the thickness of the lowermost ceramic layer, which is an inactive layer, is reduced, the displacement of the multilayer piezoelectric actuator 1001 is difficult to be restrained.

JP 61-103397 A JP 2005-285817 A

  In the multilayer piezoelectric actuator 1001 described in Patent Document 2, the first and second external electrodes 1005 and 1006 may be formed by applying or baking a conductive paste. In this case, as indicated by an arrow A in FIG. 16, the second external electrode 1006 may wrap around from the second end surface of the ceramic sintered body 1002 to the bottom surface, and a wraparound portion 1006b may be formed. When the length of the wraparound portion 1006b (the dimension from the base end, which is a portion connected to the second external electrode 1006, to the tip of the wraparound portion 1006b) is long, the wraparound portion 1006b is the largest when viewed in plan in the stacking direction. The lower first internal electrode 1003 overlaps with the lowermost ceramic layer. Therefore, as shown in FIG. 16, a part of the lowermost ceramic layer which is an inactive layer may become an active part. Since the lowermost ceramic layer, which is an inactive layer, is thin, a higher electric field is applied to the active portion than other ceramic layers, which are active layers. Therefore, the ceramic layer may be destroyed in the high electric field region X.

  Further, as shown in FIG. 15, the lengths of the first and second internal electrodes 1003 and 1004 (the first and second internal electrodes 1003 and 1004 from the base end, which is the end surface side portion, When the dimension of the second internal electrodes 1003 and 1004 to the tip) is shortened, even if the wraparound portion as shown in FIG. 16 is formed, the wraparound portion and the lowermost first internal electrode 1003 are When viewed in plan in the stacking direction, they do not overlap via the lowermost ceramic layer.

  However, in this case, the length of the active portion that is the overlapping portion when the first and second inner electrodes 1003 and 1004 are viewed in plan in the stacking direction, that is, the first and first inner portions of the ceramic sintered body 1002 The length L of the active portion in the direction connecting the two end faces is shortened. And an inactive part will exist in the said length direction both sides of this active part, and an inactive part will become large. Therefore, the displacement of the multilayer piezoelectric actuator 1001 is hindered.

  In particular, when the multilayer piezoelectric actuator 1001 is a piezoelectric actuator using a bending mode, the displacement of the multilayer piezoelectric actuator 1001 is greatly hindered when the inactive portions on the first and second end face sides are large. It becomes.

  When the lengths of the first and second internal electrodes 1003 and 1004 are increased, as shown in FIG. 16, the tip of the lowermost first internal electrode 1003 is viewed in plan view in the stacking direction. There is a possibility that the side portion overlaps with the wraparound portion 1006b via the lowermost ceramic layer.

  The object of the present invention is that the outermost ceramic layer is an inactive layer, and even if the amount of displacement is increased by reducing the thickness of the inactive layer, the ceramic sintered body is unlikely to break. Another object of the present invention is to provide a piezoelectric actuator and a piezoelectric vibration device including the multilayer piezoelectric actuator.

  The multilayer piezoelectric actuator according to the present invention is made of piezoelectric ceramics, and is formed in a ceramic sintered body having an upper surface, a lower surface and opposing first and second end surfaces, a ceramic sintered body, A plurality of first internal electrodes drawn out to the end face and formed in the ceramic sintered body, and a plurality of second internal electrodes drawn out to the second end face and formed in the ceramic sintered body A plurality of ceramic layers laminated together with the first internal electrode and the second internal electrode, a first external electrode formed on the first end face of the ceramic sintered body, and a first of the ceramic sintered body And a second external electrode formed on the end face of the second.

  In the present invention, the first internal electrode and the second internal electrode are opposed to each other through the ceramic layer in the ceramic sintered body, and are sandwiched between the first internal electrode and the second internal electrode. The ceramic layer is an active layer, and has a plurality of active layers, and in the ceramic sintered body, among the plurality of first and second internal electrodes, the uppermost internal electrode and ceramic sintered The ceramic layer between the upper surface of the body is the first inactive layer, and the ceramic layer between the lowermost internal electrode and the lower surface of the ceramic sintered body among the plurality of first and second internal electrodes Is the second inactive layer.

  Further, the thickness of the ceramic layer as the inactive layer is made thinner than the thickness of the ceramic layer as the active layer, and the length of the first or second internal electrode is set to the first or second internal electrode. Is the distance from the first or second end surface from which the first electrode is drawn to the tip of the first or second internal electrode, the length of the internal electrode located at the top and the length of the internal electrode located at the bottom At least one is made shorter than the length of the other internal electrode. Further, when viewed in plan in the stacking direction of the ceramic sintered body, the first and second external electrodes are connected to different potentials among the uppermost and lowermost internal electrodes via the inert layer. It is formed so as not to overlap with the electrode.

  In a specific aspect of the multilayer piezoelectric actuator according to the present invention, the first and second external electrodes are formed on the first and second end faces of the ceramic sintered body, and the upper surface of the ceramic sintered body And it is provided not to reach the lower surface. In this case, it is difficult to apply an electric field to the upper and lower surfaces and the inactive layers on the lower surface side of the ceramic sintered body. Therefore, destruction in the inactive layer is less likely to occur.

  In another specific aspect of the multilayer piezoelectric actuator according to the present invention, the first and second external electrodes are disposed on the end surface portion located on the first and second end surfaces of the ceramic sintered body, and on the end surface portion. And a wraparound portion that reaches at least one of the upper surface and the lower surface of the ceramic sintered body, and the wraparound portion and the uppermost portion when viewed in plan in the stacking direction of the ceramic sintered body And the internal electrodes connected to different potentials among the lowermost internal electrodes are arranged so as not to overlap with each other through the inactive layer. Thus, even when the wraparound portion exists in the first and second external electrodes, the wraparound portion and the innermost portion of the uppermost portion and the lowermost portion are viewed in plan view in the stacking direction of the ceramic sintered body. Since the internal electrodes connected to different potentials of the electrodes are arranged so as not to overlap with each other through the inert layer, the breakdown in the inert layer, which is the outermost ceramic layer as the uppermost layer or the lowermost layer, is prevented. Not likely to occur.

  In still another specific aspect of the multilayer piezoelectric actuator according to the present invention, the wraparound portion is a surface electrode for joining with another member. In this case, it can be easily mounted on a diaphragm, a substrate or the like using the surface electrode.

  In still another specific aspect of the multilayer piezoelectric actuator according to the present invention, the ceramic layers constituting the active layer have the same thickness. In this case, ceramic layers other than the inactive layer can be easily formed using the same ceramic green sheet.

  In still another specific aspect of the multilayer piezoelectric actuator according to the present invention, when the thickness of the inactive layer is L and the thickness of the active layer is H, 0 <L ≦ (1/2) H. In this case, restraint of displacement by the inert layer can be more reliably suppressed, and a larger displacement amount can be obtained with certainty.

  The piezoelectric vibration device according to the present invention includes a vibration plate, and the laminated piezoelectric actuator according to the present invention is joined to the vibration plate. In this case, according to the present invention, it is possible to provide a piezoelectric vibration device that vibrates in a bending mode and has a large amount of displacement.

  In the multilayer piezoelectric actuator according to the present invention, since the thickness of the ceramic layer that is the inactive layer is made thinner than the thickness of the ceramic layer that is the active layer, the ceramic layer that is the inactive layer is the ceramic that is the active layer. A large amount of displacement can be obtained without restraining the displacement of the layer so much. Moreover, at least one of the length of the internal electrode located at the top and the length of the internal electrode located at the bottom is shorter than the length of the other internal electrodes, and when viewed in plan in the stacking direction of the ceramic sintered body Further, the first and second external electrodes are formed so as not to overlap with the internal electrodes connected to different potentials among the uppermost and lowermost internal electrodes through the inactive layer. In a thin inactive layer, breakdown is hardly caused when an electric field is applied.

FIG. 1A is a front sectional view showing a multilayer piezoelectric actuator according to the first embodiment of the present invention, and FIG. 1B is a front sectional view showing a modification thereof. FIG. 2 is a perspective view showing the multilayer piezoelectric actuator according to the first embodiment of the present invention. FIG. 3 is a front sectional view showing a multilayer piezoelectric actuator according to the second embodiment of the present invention. FIG. 4 is a front sectional view showing the bending type piezoelectric actuator according to the first embodiment. FIG. 5 is a front cross-sectional view showing the bending type piezoelectric actuator of Comparative Example 1. FIG. 6 is a front cross-sectional view showing a bending type piezoelectric actuator of Comparative Example 2. FIG. 7 is a front cross-sectional view showing a bent piezoelectric actuator of Comparative Example 3. FIG. 8 is a front cross-sectional view showing a bending type piezoelectric actuator of Comparative Example 4. FIG. 9 is a front sectional view showing a bending type piezoelectric actuator according to a second embodiment of the present invention. FIG. 10 is a front sectional view showing a bending type piezoelectric actuator according to a third embodiment of the present invention. FIG. 11 is a front sectional view showing a modification of the piezoelectric actuator according to the present invention. FIG. 12 is a perspective view schematically showing the internal structure of the piezoelectric actuator of the modification shown in FIG. FIG. 13 is a front sectional view showing still another modification of the piezoelectric actuator according to the present invention. FIG. 14 is a front sectional view showing still another modification of the piezoelectric actuator according to the present invention. FIG. 15 is a front sectional view showing a conventional multilayer piezoelectric actuator. FIG. 16 is a front cross-sectional view for explaining problems of the conventional multilayer piezoelectric actuator shown in FIG.

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

[First Embodiment]
Fig.1 (a) is front sectional drawing which shows the laminated piezoelectric actuator 1 which concerns on the 1st Embodiment of this invention, FIG. 2 is the perspective view.

  The multilayer piezoelectric actuator 1 has a ceramic sintered body 2 made of piezoelectric ceramics. In the present embodiment, the ceramic sintered body 2 is made of a lead zirconate titanate ceramic. However, the ceramic sintered body 2 may be formed of other piezoelectric ceramics.

  The ceramic sintered body 2 has a rectangular parallelepiped shape, and has an upper surface 2a, a lower surface 2b, a first end surface 2c, and a second end surface 2d. In the ceramic sintered body 2, a plurality of ceramic layers including ceramic layers 2e, 2f, 2g are arranged. In the ceramic sintered body 2, a plurality of first internal electrodes 3a to 3d and a plurality of second internal electrodes 4a to 4d are arranged in parallel with the upper surface 2a and the lower surface 2b. The plurality of first internal electrodes 3 a to 3 d are drawn out to the first end face 2 c of the ceramic sintered body 2. The plurality of second internal electrodes 4 a to 4 d are led out to the second end surface 2 d facing the first end surface 2 c of the ceramic sintered body 2. In the ceramic sintered body 2, a plurality of ceramic layers, a plurality of first internal electrodes 3a to 3d, and a plurality of second internal electrodes 4a to 4d are laminated. In the ceramic sintered body 2, the first internal electrodes 3a to 3d and the second internal electrodes 4a to 4d are alternately arranged in the stacking direction, that is, the direction connecting the upper surface 2a and the lower surface 2b.

  A first external electrode 5 is formed on the first end face 2c. A second external electrode 6 is formed on the second end face 2d. In the present embodiment, the first external electrode 5 is connected to the end surface portion 5a located on the first end surface 2c, the wraparound portion 5b connected to the end surface portion 5a and reaching the upper surface 2a, and the end surface portion 5a. It has a wraparound portion 5c that is continuous and reaches the lower surface 2b. The second external electrode 6 is connected to the end surface portion 6a located on the second end surface 2d, the end surface portion 6a, the wraparound portion 6b reaching the upper surface 2a, the end surface portion 6a, and the lower surface. And a wraparound portion 6c leading to 2b.

  The first and second internal electrodes 3a to 3d and 4a to 4d are made of AgPd. However, the first and second internal electrodes 3a to 3d and 4a to 4d can be formed of an appropriate metal material such as Ag, Au, Cu, Ni, or an alloy thereof.

  The ceramic sintered body 2 having the first and second internal electrodes 3a to 3d and 4a to 4d is a multilayer ceramic sintered body that can be obtained by a known ceramic integrated firing technique.

  The first and second external electrodes 5 and 6 are formed by applying and baking a conductive paste. However, it may be formed by vapor deposition, sputtering, plating, or the like. In the present embodiment, the first and second external electrodes 5 and 6 are formed by a sputtering method. The first and second external electrodes 5 and 6 can be formed of an appropriate metal or alloy. In the ceramic sintered body 2, a portion sandwiched between any one of the first internal electrodes 3a to 3d and any one of the second internal electrodes 4a to 4d functions as an active layer. . Here, the active layer is a portion that expands and contracts due to the piezoelectric effect when an electric field is applied. In the ceramic sintered body 2, adjacent active layers are polarized in the opposite direction in the stacking direction.

  When driving the multilayer piezoelectric actuator 1, a voltage is applied between the first and second external electrodes 5 and 6. As a result, an electric field is applied to the plurality of ceramic layers 2e sandwiched between the first internal electrodes 3a to 3d and the second internal electrodes 4a to 4d. Therefore, when the electric field is applied, the multilayer piezoelectric actuator 1 has an appearance in which the center protrudes upward and an appearance in which the center protrudes downward at the center in the direction connecting the first and second end faces 2c and 2d. Take. That is, it is displaced in the bending mode.

  In addition, the thickness of each ceramic layer 2e which comprises the some active layer is made equal. Therefore, as will be described later, the types of green sheets necessary for forming each ceramic layer 2e can be reduced, and productivity can be increased.

  In the present embodiment, the electric field is not applied to the ceramic layer 2f that is the lowermost layer and is located below the first internal electrode 3d. Therefore, the ceramic layer 2f is an inert layer. Similarly, the electric field is not applied to the ceramic layer 2g which is the uppermost layer and is located above the second internal electrode 4a. That is, the ceramic layer 2g is an inactive layer like the ceramic layer 2f. The inactive layer is a layer to which no electric field is applied when a voltage is applied from the first and second external electrodes 5 and 6.

  The feature of the multilayer piezoelectric actuator 1 of the present embodiment is that the thickness of the ceramic layers 2f and 2g is made thinner than the thickness of the ceramic layer 2e which is an active layer. As described above, the inactive layer acts to constrain the displacement of the active layer. In this embodiment, since the ceramic layers 2f and 2g which are inactive layers are thin, the displacement of the ceramic layer 2e which is an active layer is not constrained so much. Therefore, a large amount of displacement can be obtained.

  Another feature of the multilayer piezoelectric actuator 1 of the present embodiment is that the length of the first internal electrode 3d located at the bottom of the first and second internal electrodes 3a to 3d and 4a to 4d, The length of the second internal electrode 4a located at the top is shorter than the remaining first and second internal electrodes 3a to 3c and 4b to 4d. Here, the length of the internal electrode is the dimension from the end face of the ceramic sintered body from which the internal electrode is drawn to the tip of the internal electrode, that is, the direction connecting the first and second end faces 2c, 2d of each internal electrode. The dimensions shall be said.

  In the multilayer piezoelectric actuator 1 of the present embodiment, the wraparound portion 6c of the second external electrode 6 does not overlap the first internal electrode 3d via the ceramic layer 2f when viewed in plan in the stacking direction. It is provided as follows. That is, the length of the first internal electrode 3d is shortened so as not to overlap the wraparound portion 6c via the ceramic layer 2f when viewed in plan in the stacking direction, and the length of the wraparound portion 6c is It has been shortened. The length of the wraparound portion 6c refers to the dimension from the second end surface 2d to the tip of the wraparound portion 6c, that is, the end portion on the first end surface 2c side. The wraparound portion 6c of the second external electrode 6 and the first internal electrode 3d are connected to different potentials.

  Similarly, also in the upper part of the ceramic sintered body 2, the wraparound portion 5b of the first external electrode 5 overlaps with the second internal electrode 4a via the ceramic layer 2g when viewed in plan in the stacking direction. There is no provision. That is, the length of the second internal electrode 4a is shortened so as not to overlap the wraparound portion 5b via the ceramic layer 2g when viewed in plan in the stacking direction, and the length of the wraparound portion 5a is also short. Has been. The wraparound portion 5b of the first external electrode 5 and the second internal electrode 4a are connected to different potentials.

  As shown in FIG. 16, in the conventional multilayer piezoelectric actuator 1001A, the lowermost first internal electrode 1003 and the wraparound portion 1006b of the second external electrode 1006 connected to a potential different from the internal electrode are provided. There is a possibility that a high electric field region X may be formed by applying an electric field to. For this reason, there is a possibility that the outermost thin ceramic layer is broken.

  On the other hand, in this embodiment, such a high electric field region is not formed in the ceramic layers 2f and 2g. Therefore, even if the ceramic layers 2f and 2g having relatively thin thicknesses are provided in the outermost layer and the amount of displacement is increased, the ceramic layers 2f and 2g are not easily broken.

  FIG. 1B is a front cross-sectional view showing a multilayer piezoelectric actuator 11 according to a modification of the first embodiment. In the present modification, the first and second external electrodes 5 and 6 have only the end surface portions 5a and 6a. That is, the wraparound portions 5b, 5c, 6b, and 6c in the first embodiment are not provided. Such first and second external electrodes 5 and 6 can be formed by an appropriate method such as application and baking of a conductive paste, vapor deposition, plating, or sputtering.

  In the present modification, since the wraparound portions 5b, 5c, 6b, and 6c are not provided, a high electric field is hardly applied to the ceramic layers 2f and 2g. That is, the first internal electrode 3d and the second external electrode 6 connected to a potential different from that of the first internal electrode 3d may overlap with each other through the ceramic layer 2f when viewed in plan in the stacking direction. In addition, since the distance between the tip of the first internal electrode 3d and the second external electrode 6 is longer than that in the first embodiment, it is difficult to apply a high electric field to the ceramic layer 2f.

  Similarly, the distance between the tip of the second inner electrode 4a and the first outer electrode 5 is also made larger than in the first embodiment, and a higher electric field is further applied to the ceramic layer 2g. hard. Therefore, according to this modification, dielectric breakdown is less likely to occur.

  Thus, in the present invention, the wraparound portions 5b, 5c, 6b, and 6c may not be provided.

  FIG. 3 is a front sectional view showing a multilayer piezoelectric actuator 21 according to the second embodiment of the present invention. In the second embodiment, on the lower surface 2b of the ceramic sintered body 2, the area of the wraparound portion 5c of the first external electrode 5 is made larger than in the case of the first embodiment, that is, the wraparound portion 5c is A surface electrode is formed. Similarly, the area of the wraparound portion 6c of the second external electrode 6 is made larger than that in the first embodiment, and the wraparound portion 6c also constitutes a surface electrode. Here, the surface electrode functions as a joint portion when the laminated piezoelectric actuator 21 is connected to another member, for example, a diaphragm as in the embodiments described later. The surface electrode functioning as such a joint portion needs to have a larger area than the wraparound portions 5c and 6c of the first embodiment, thereby improving the reliability of the joint.

  In the second embodiment, wraparound portions 5c and 6c that function as the surface electrodes are formed. For this reason, the length of the lowermost first internal electrode 3d is made shorter than in the first embodiment. That is, in the laminated piezoelectric actuator 21 of the present embodiment, the first internal electrode 3d and the wraparound portion 6c of the second external electrode 6 connected to a potential different from that of the first internal electrode 3d are When viewed in a plan view, they are arranged so as not to overlap with each other through the ceramic layer 2 f which is an inactive layer. In this case, since the area of the wraparound portion 6c that functions as a surface electrode is large and the length in the direction connecting the first and second end faces 2c and 2d is increased, the first internal electrode 3d is correspondingly increased. The length is shortened. Thereby, it is difficult to apply a high electric field to the ceramic layer 2f.

  As described above, in the present invention, the area of the wraparound portions 5c and 6c may be increased to improve the reliability of bonding when connecting to the diaphragm, and even in that case, the lowermost first internal electrode 3d and the wraparound portion 6c of the second external electrode 6 connected to a potential different from that of the first internal electrode 3d overlap with each other through the ceramic layer 2f which is an inactive layer when viewed in plan in the stacking direction. What is necessary is just to arrange | position so that it may not fit.

  Next, a specific example of a bending type piezoelectric actuator that is a piezoelectric vibration device in which the multilayer piezoelectric actuator 1 of the first embodiment is bonded to a vibration plate and deforms in a bending mode will be described together with a comparative example. To do.

  As Example 1, a bending type piezoelectric actuator 31 shown in FIG. In the bending type piezoelectric actuator 31, a laminated piezoelectric actuator 34 having the same structure as that of the laminated piezoelectric actuator 1 of the first embodiment described above is joined to a vibration plate 32 via an adhesive layer 33. The diaphragm 32 is passively displaced in response to the displacement of the laminated piezoelectric actuator 34. As a result, the entire bending type piezoelectric actuator 31 is displaced in the bending mode.

  In Example 1, a glass epoxy plate having a thickness of 0.8 mm was used as the diaphragm 32. Moreover, an epoxy adhesive was used as the adhesive layer 33.

  When forming the bending type piezoelectric actuator 31 using the vibration plate 32, the material of the vibration plate 32 is not limited to the glass epoxy plate. That is, the diaphragm 32 can be made of an appropriate material such as synthetic resin or metal. However, it is desirable that the thermal expansion coefficient and Young's modulus of the diaphragm 32 be close to those of the ceramic sintered body 2. Accordingly, considering the thermal expansion coefficient and Young's modulus of the piezoelectric ceramic, it is desirable that the diaphragm 32 be made of 42 nickel or low expansion glass epoxy.

  In manufacturing the ceramic sintered body 2, a well-known ceramic integrated firing technique was used. That is, a ceramic green sheet mainly composed of a piezoelectric ceramic material was prepared, and an AgPd paste was printed on the upper surface of the ceramic green sheet so as to form a mother internal electrode pattern. When printing the internal electrode pattern, the length of the internal electrode is finally reduced in the portion where the uppermost second internal electrode 4a and the lowermost internal electrode 3d are formed. Mother's internal electrode pattern was printed. In this way, a plurality of mother ceramic green sheets printed with a paste of the mother internal electrode pattern are laminated, and ceramic green sheets that are thinner than the other ceramic green sheets are laminated on top and bottom, and pressed in the lamination direction. As a result, a mother ceramic molded body was obtained.

  In Example 1, the thickness of the ceramic green sheet constituting the inactive layer was made thinner than that of the ceramic green sheet constituting the active layer. As another method, the number of ceramic green sheets constituting the active layer may be larger than the number of ceramic green sheets constituting the inactive layer.

  The mother ceramic molded body obtained as described above was cut into ceramic molded bodies of individual laminated piezoelectric actuator units. The individual ceramic molded body was fired to obtain a ceramic sintered body 2. First and second external electrodes 5 and 6 were formed on the first and second end faces 2c and 2d of the ceramic sintered body 2 by a sputtering method. Thereafter, a DC voltage was applied between the first and second external electrodes 5 and 6, and in the stacking direction, the adjacent active layers were polarized so that their polarization axes were aligned in the opposite direction in the stacking direction.

  The multilayer piezoelectric actuator 34 was obtained as described above, and the multilayer piezoelectric actuator 34 was bonded to the above-described diaphragm 32 via the adhesive layer 33. In this way, the bending type piezoelectric actuator 31 of Example 1 was obtained.

  For comparison, a bending type piezoelectric actuator 1051 of Comparative Example 1 shown in FIG. 5 was prepared. The bending type piezoelectric actuator 1051 is the same as that of the first embodiment except that the laminated piezoelectric actuator 1052 is used instead of the laminated piezoelectric actuator 34 in the bending piezoelectric actuator 31 of the first embodiment. This multilayer piezoelectric actuator 1052 has a ceramic sintered body 1053. Ceramic sintered body 1053 has an upper surface, a lower surface, a first end surface 1053c, and a second end surface 1053d. In the ceramic sintered body 1053, a plurality of first internal electrodes 1054a to 1054d and a plurality of second internal electrodes 1055a to 1055d are arranged in parallel with the upper surface and the lower surface. The plurality of first internal electrodes 1054 a to 1054 d are drawn out to the first end face 1053 c of the ceramic sintered body 1053. The plurality of second internal electrodes 1055a to 1055d are led out to a second end face 1053d facing the first end face 1053c of the ceramic sintered body 1053. In the ceramic sintered body 1053, the first internal electrodes 1054a to 1054d and the second internal electrodes 1055a to 1055d are alternately arranged in the stacking direction. Adjacent ceramic layers are polarized in the opposite direction in the stacking direction.

  The thicknesses of the ceramic layers, that is, the active layers sandwiched between the first internal electrodes 1054a to 1054d and the second internal electrodes 1055a to 1055d are all equal. Further, a first external electrode 1056 is formed on the first end face 1053c. A second external electrode 1057 is formed on the second end face 1053d. Here, the first external electrode 1056 is connected to the end surface portion 1056a located on the first end surface 1053c and the end surface portion 1056a, reaches the upper surface of the ceramic sintered body 1053, and is planar in the stacking direction. When viewed, it has a wraparound portion 1056b provided so as to overlap with the uppermost second internal electrode 1055a, and a wraparound portion 1056c connected to the end surface portion 1056a and reaching the lower surface of the ceramic sintered body 1053. . Therefore, the uppermost ceramic layer acts as an active layer. Similarly, the second external electrode 1057 includes an end surface portion 1057a located on the second end surface 1053d, a wraparound portion 1057b connected to the end surface portion 1057a and reaching the upper surface of the ceramic sintered body 1053, and an end surface. It has a wraparound portion 1057c that is continuous with the portion 1057a and reaches the lower surface of the ceramic sintered body 1053. The wraparound portion 1057c extends to the first end face 1053c side, and overlaps the lowermost first internal electrode 1054d via the ceramic layer when viewed in plan in the stacking direction. Therefore, the lowermost ceramic layer also functions as an active layer.

  In the multilayer piezoelectric actuator 1052, the outermost ceramic layer functions as an active layer, and the outermost ceramic layer has the same thickness as the other ceramic layers.

  The bending type piezoelectric actuators 31 and 1051 of Example 1 and Comparative Example 1 are driven by applying a voltage of ± 12 V in an atmosphere of a temperature of 60 ° C. and a relative humidity of 93%, and a time B10 until failure is measured. did. The results are shown in Table 1 below.

  As is apparent from Table 1, it can be seen that, according to Example 1, time B10 until failure can be increased to about four times as compared with Comparative Example 1. The reason why the failure occurred in the comparative example 1 in a relatively short time is considered that the moisture in the air reached the active layer inside under high temperature and high humidity, and the migration of Ag in the internal electrode occurred. It is done. In Example 1, the multilayer piezoelectric actuator 34 having the same structure as that of the multilayer piezoelectric actuator 1 of the first embodiment is provided, and the outermost ceramic layer is an inactive layer. For this reason, moisture in the air hardly reaches the active layer inside the multilayer piezoelectric actuator, and cracks do not easily occur in the ceramic layer as the active layer. Therefore, it is considered that the life of the multilayer piezoelectric actuator 34 has been extended.

  Next, the bending type piezoelectric actuator 31 of Example 1 and the bending type piezoelectric actuator 1061 of Comparative Example 2 shown in FIG. 6 were prepared. The bending type piezoelectric actuator 1061 of Comparative Example 2 is the same as that of Example 1 except that the laminated piezoelectric actuator 1062 is used instead of the laminated piezoelectric actuator 34 in the bending piezoelectric actuator 31 of Example 1. It is the same. The multilayer piezoelectric actuator 1062 is similar to the multilayer piezoelectric actuator 1052 of Comparative Example 1 in that the ceramic sintered body 1053, the plurality of first internal electrodes 1054a to 1054d, and the plurality of second internal electrodes 1055a to 1055a. 1055d, a first external electrode 1056, and a second external electrode 1057. The laminated piezoelectric actuator 1062 has the same structure as the laminated piezoelectric body used in the piezoelectric buzzer described in Patent Document 1 described above.

  In Comparative Example 1, on the upper surface and the lower surface of the ceramic sintered body 1053, the wraparound portion 1056b of the first external electrode 1056 and the wraparound portion 1057c of the second external electrode 1057 differ when viewed in plan in the stacking direction. The second internal electrode 1055a or the first internal electrode 1054d connected to is formed so as to overlap. Therefore, the outermost ceramic layer is the active layer.

  On the other hand, in the bending type piezoelectric actuator 1061 of Comparative Example 2, the wraparound portion 1056b and the wraparound portion 1057c are connected to the end surface portions 1056a and 1057a similarly to the wraparound portions 1056c and 1057b. It is formed so as to reach the upper surface or the lower surface. Therefore, the outermost ceramic layer is almost an inactive layer. The other points are the same as in Comparative Example 1.

  In Example 1, the thickness of the outermost ceramic layer, which is an inactive layer, is ½ of the thickness of the active ceramic layer. When a laminated piezoelectric actuator is manufactured using a ceramic layer having the same thickness as the outermost ceramic layer and the active ceramic layer, which are the inactive layers, the active layer is made of two ceramic layers and the inactive layer is made of one layer. When L = (1/2) H as the ceramic layer, the number of laminating steps is minimized compared to other conditions such as three active ceramic layers and two inactive layers. Therefore, manufacturing is easy and preferable. Furthermore, if the thickness and material of the ceramic layer are the same, the ceramic layer can be prepared in the same process, which is more preferable because the manufacturing becomes easier.

  The amount of displacement of the bending type piezoelectric actuators 31 and 1061 of Example 1 and Comparative Example 2 is bent when a voltage of ± 12 V is applied and the direction connecting the first and second end faces is the length direction. The amount of displacement at the center in the length direction of the piezoelectric actuators 31 and 1061 was determined. As a result, in Comparative Example 2, the amount of displacement was 79 μm. On the other hand, in Example 1, the displacement amount was 87 μm. Therefore, according to Example 1, it can be seen that the displacement amount can be increased by reducing the thickness of the inactive layer.

  In Comparative Example 2, there is a portion where the wraparound portion 1056b and the uppermost second internal electrode 1055a overlap with each other through part of the uppermost ceramic layer when viewed in plan in the stacking direction. To do. Similarly, when the wraparound portion 1057c and the lowermost first internal electrode 1054d are viewed in a plan view in the stacking direction, there is a portion where the wraparound portion 1057c overlaps with part of the lowermost ceramic layer. Therefore, although the outermost layer is an inactive layer, a part of the inactive layer becomes an active part.

Therefore, as described above, when a high electric field is applied to the active portion, the stress generated by the electric field applied by the piezoelectric effect in the outermost ceramic layer and the stress due to the displacement of the piezoelectric actuator, There is a possibility that the ceramic layer may be broken. In particular, if the active portion and the inactive portion are mixed in the outermost ceramic layer having a thickness smaller than that of the active layer sandwiched between the internal electrodes and having a low fracture strength, the active portion and the inactive portion to which a high electric field is applied Since the stress difference generated at the boundary between and the stress due to the displacement of the piezoelectric actuator overlap, the outermost ceramic layer having a relatively small thickness is likely to be broken.

  Next, the bending type piezoelectric actuator 31 of Example 1 and the bending type piezoelectric actuator 1071 of Comparative Example 3 shown in FIG. 7 were prepared. The bending type piezoelectric actuator 1071 of Comparative Example 3 is the same as that of Example 1 except that the laminated piezoelectric actuator 1072 is used instead of the laminated piezoelectric actuator 34 in the bending piezoelectric actuator 31 of Example 1. It is the same. The laminated piezoelectric actuator 1072 has a laminated piezoelectric actuator 1062 of the bent piezoelectric actuator 1061 of Comparative Example 2 except that the thickness of the outermost ceramic layer is ½ of the thickness of the other ceramic layers. Has the same structure. This structure is the same structure as the multilayer piezoelectric actuator described in Patent Document 2 described above.

  A DC voltage twice the coercive electric field was applied to the bending piezoelectric actuator 31 of Example 1 and the bending piezoelectric actuator 1071 of Comparative Example 3 to polarize the ceramic sintered body. That is, a voltage twice the coercive electric field was applied between the first and second external electrodes, and the ceramic layer functioning as the active layer was polarized in the stacking direction. As a result, in the laminated piezoelectric actuator 1072 used in the bending type piezoelectric actuator 1071 of Comparative Example 3, ten of the 10 samples failed, and the laminated piezoelectric actuator used in the bending type piezoelectric actuator 31 of Example 1 In 34, the number of failures in 10 samples was zero. Note that the failure means the number of short circuits that occur between adjacent electrodes during the polarization process.

  As described above, the failure of the multilayer piezoelectric actuator 1072 used in the bending piezoelectric actuator 1071 of Comparative Example 3 is considered to be due to the following reason. That is, since the thickness of the outermost ceramic layer is reduced, when the wraparound portion 1056b and the uppermost second internal electrode 1055a are viewed in plan in the stacking direction, they pass through a part of the uppermost ceramic layer. When the overlapping portion B and the wraparound portion 1057c and the lowermost first internal electrode 1054d are viewed in plan in the stacking direction, a high electric field is applied to the overlapping portion D via a portion of the lowermost ceramic layer. Is done. Therefore, it is considered that a short circuit has occurred.

  On the other hand, in Example 1, as described above, the uppermost second internal electrode 4a and the wraparound portion 5b overlap with each other through the uppermost ceramic layer when viewed in plan in the stacking direction. The lowermost first internal electrode 3d and the wraparound portion 6c do not overlap with each other through the lowermost ceramic layer when viewed in plan in the stacking direction. Therefore, a high electric field is not applied to the outermost ceramic layer, that is, the inactive layer. Therefore, it is considered that no failure has occurred during polarization.

  Next, the bending type piezoelectric actuator 31 of Example 1 and the bending type piezoelectric actuator 1081 of Comparative Example 4 shown in FIG. 8 were prepared, and the amounts of displacement were compared. The bending type piezoelectric actuator 1081 of Comparative Example 4 is the same as that of Example 1 except that a laminated piezoelectric actuator having a structure different from that of the laminated piezoelectric actuator 34 in the bending piezoelectric actuator 31 of Example 1 is used. It is the same. The laminated piezoelectric actuator of the bent piezoelectric actuator 1081 of Comparative Example 4 has a ceramic sintered body 1082. Ceramic sintered body 1082 has an upper surface, a lower surface, a first end surface 1082c, and a second end surface 1082d. In the ceramic sintered body 1082, a plurality of first internal electrodes 1083a to 1083c and a plurality of second internal electrodes 1084a to 1084c are arranged in parallel with the upper surface and the lower surface. The plurality of first internal electrodes 1083 a to 1083 c are drawn out to the first end face 1082 c of the ceramic sintered body 1082. The plurality of second internal electrodes 1084a to 1084c are led out to a second end face 1082d facing the first end face 1082c of the ceramic sintered body 1082. In the ceramic sintered body 1082, the first internal electrodes 1083a to 1083c and the second internal electrodes 1084a to 1084c are alternately arranged in the stacking direction, and when viewed in plan in the stacking direction, the ceramic layer Overlap through. Adjacent ceramic layers are polarized in the opposite direction in the stacking direction. Furthermore, first and second dummy electrodes 1085 and 1086 are disposed above the portion where the first and second internal electrodes 1083a to 1083c and 1084a to 1084c are stacked. The first and second dummy electrodes 1085 and 1086 are drawn out to the first end face 1082c and the second end face 1082d, respectively.

  The first and second dummy electrodes 1085 and 1086 are opposed to each other at the center in the length direction of the ceramic sintered body 1082. Similarly, the first and second dummy electrodes 1087 and 1088 are also connected to the first and second dummy electrodes 1085 below the portion where the first and second inner electrodes 1083a to 1083c and 1084a to 1084c are stacked. , 1086.

  Here, the portion where the first internal electrodes 1083a to 1083c and the second internal electrodes 1084a to 1084c overlap with each other through the ceramic layer when viewed in plan in the stacking direction is the active portion. When the second dummy electrode 1086 and the uppermost first internal electrode 1083a are viewed in plan in the stacking direction, the overlapping portion when viewed in plan in the stacking direction through the ceramic layer is also an active layer. Function. Similarly, a portion where the first dummy electrode 1087 and the lowermost second internal electrode 1084c overlap when viewed in plan in the stacking direction also functions as an active layer. The first and second external electrodes 1089 and 1090 are configured in the same manner as the first and second external electrodes 5 and 6 of the first embodiment.

  The displacement amount when a voltage of ± 12 V was applied to the bending piezoelectric actuator 31 of Example 1 and the bending piezoelectric actuator 1081 of Comparative Example 4 was found to be 81 μm in Comparative Example 4. According to Example 1, it was 87 μm as in the case of comparison with Comparative Example 2 described above.

  Therefore, it can be seen that the displacement amount is small in Comparative Example 4, whereas the displacement amount can be effectively increased according to Example 1. This is presumably because in Comparative Example 4, the ceramic layer below the dummy electrode 1085 and the ceramic layer above the dummy electrode 1088 also function as inactive layers, thereby restraining displacement.

[Second Embodiment]
FIG. 9 is a front sectional view showing a bending type piezoelectric actuator 51 according to the second embodiment of the present invention. In the bending type piezoelectric actuator 51 according to the second embodiment, a laminated piezoelectric actuator 53 is bonded on a vibration plate 52 via an adhesive layer 54. The diaphragm 52 has a structure in which electrode films 52b and 52c are formed on the surface of an insulating substrate 52a. A laminated piezoelectric actuator 53 is joined to the electrode films 52b and 52c via an adhesive layer 54.

  Here, similarly to the multilayer piezoelectric actuator 11 shown in FIG. 1B, the wrap portions 5c and 6c of the first and second external electrodes 5 and 6 have a larger area than the wrap portions 5b and 6b. And is formed so as to function as a surface electrode. The wraparound portions 5c and 6c are joined to the electrode films 52b and 52c, respectively. In other structures, the bending type piezoelectric actuator 51 according to the second embodiment is the same as the bending type piezoelectric actuator 31 of Example 1. Here, since the wraparound portions 5c and 6c have a large area, they can be reliably bonded to the electrode films 52b and 52c.

  Also in this embodiment, since the other structure is the same as that of Example 1, a large amount of displacement can be obtained and migration of Ag or the like can be effectively suppressed.

[Third Embodiment]
FIG. 10 is a front sectional view showing a bending type piezoelectric actuator 61 according to a third embodiment of the present invention.

  Contrary to the second embodiment, the bending type piezoelectric actuator 61 is configured such that the area of the wraparound portions 5b and 6b on the upper surface side of the ceramic sintered body 2 is relatively large and functions as a surface electrode. ing. On the other hand, the wraparound portions 5c and 6c on the lower surface side have a relatively small area and are normal wraparound portions. Other points are the same as those of the bending piezoelectric actuator 31 of the first embodiment. In the third embodiment, the upper surface side of the ceramic sintered body 2 is provided with the wrap-around portions 5b and 6b that have a relatively large area and function as surface electrodes on the upper surface side of the ceramic sintered body 2. Therefore, electrical connection with the outside can be easily performed.

  Also in this case, the wraparound portion 5b and the uppermost second internal electrode 4a that are electrically insulated from each other and connected to different potentials pass through the uppermost ceramic layer when viewed in plan in the stacking direction. And do not overlap. Therefore, as in the first embodiment, a large displacement can be obtained, and the ceramic layer of the inactive layer is hardly broken.

[Modification]
FIG. 11 is a front sectional view for explaining still another modified example of the piezoelectric actuator of the present invention, and FIG. 12 is a perspective view schematically showing the internal structure thereof.

  The piezoelectric actuator 71 of this modification has a laminated piezoelectric actuator that is bonded to the vibration plate 72 via an adhesive layer 75. The multilayer piezoelectric actuator has a ceramic sintered body 2A. In the ceramic sintered body 2A, the first internal electrodes 3a and 3b and the second internal electrodes 4a and 4b are alternately stacked via ceramic layers. As shown in FIG. 12, the first internal electrodes 3a and 3b have electrode lead portions that are extended to the end face on one end side in the length direction of the ceramic sintered body 2A. The electrode lead-out portion is narrower than the other portions of the first inner electrodes 3a and 3b. The second internal electrodes 4a and 4b also have an electrode lead portion extended to the end face on one end side in the length direction of the ceramic sintered body 2A. This electrode lead portion is also narrower than other portions of the second internal electrodes 4a and 4b. And as shown in FIG. 12, the 1st end surface electrode 73 and the 2nd end surface electrode 74 are formed in the end surface of the said one end side of the ceramic sintered compact 2A. The first end face electrode 73 is provided so as to be electrically connected to the electrode lead portions of the first internal electrodes 3a and 3b. Similarly, the second end face electrode 74 is provided so as to be electrically connected to the electrode lead portions of the second internal electrodes 4a and 4b. In the present modification, as described above, the first internal electrodes 3a and 3b and the second internal electrodes 4a and 4b are drawn out to the end face on one end side in the length direction of the ceramic sintered body 2A. At the end face, the first inner electrodes 3 a and 3 b are electrically connected to the first end face electrode 73, and the second inner electrodes 4 a and 4 b are electrically connected to the second end face electrode 74. Therefore, electrical connection with the outside can be achieved at one end in the length direction of the ceramic sintered body 2A.

  Also in this modification, the outermost ceramic layer that is an inactive layer of the ceramic sintered body 2A is made thinner than the other ceramic layers that are active layers, and the first and second internal electrodes 3a, 3b, 4a are formed. , 4b, the length of the second internal electrode 4a located at the top and the length of the first internal electrode 3b located at the bottom are made shorter than the other internal electrodes. Thus, the wraparound portion of the first end face electrode 73 is provided so as not to overlap the second inner electrode 4a via the uppermost ceramic layer when viewed in plan in the stacking direction. When the wraparound portion is provided so as not to overlap the first internal electrode 3b through the lowermost ceramic layer when viewed in plan in the stacking direction, the same effect as in the first to third embodiments can be obtained. Can do.

  FIG. 13 is a front sectional view showing still another modification of the piezoelectric actuator of the present invention. The piezoelectric actuator 81 of this modification is joined to the vibration plate 82 via an adhesive layer 83. It has a laminated piezoelectric actuator. In the present modification, like the piezoelectric actuator 71, the first internal electrodes 3a and 3b and the second internal electrodes 4a and 4b are alternately stacked via the ceramic layers in the ceramic sintered body 2A. . In the ceramic sintered body 2A, the first internal electrodes 3a and 3b and the second internal electrodes 4a and 4b are alternately stacked via ceramic layers. When viewed in plan in the stacking direction, the portion where the internal electrodes overlap through the ceramic layer constitutes the active layer. In this modification, the thickness of the inactive layer 2h, which is the lowermost ceramic layer of the ceramic sintered body 2A, is smaller than the thickness of the other ceramic layers. Further, the length of the lowermost first internal electrode 3b adjacent to the inert layer 2h is shorter than that of the first internal electrode 3a, so that the wraparound portion of the second end face electrode 6 is reduced. The uppermost second internal electrode is provided so as not to overlap the first internal electrode 3b via the inert layer 2h when viewed in plan in the stacking direction, and is adjacent to the uppermost ceramic layer. Since the length of 4a is shorter than that of the second internal electrode 4b, when the wraparound portion of the first end face electrode 5 is viewed in a plan view in the stacking direction, the second inner electrode 4b is interposed through the uppermost ceramic layer. It is provided so as not to overlap with the internal electrode 4a. Therefore, also in this embodiment, the same effect as Examples 1-3 can be acquired. However, as in the first embodiment described above, it is desirable to provide a thin inactive layer on the top and bottom.

  In FIG. 13, the inactive layer 2h is provided in the lowermost layer of the ceramic sintered body 2A. However, as in the piezoelectric actuator 91 of the modification shown in FIG. A layer 2i may be provided.

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric actuator 2, 2A ... Ceramic sintered body 2a ... Upper surface 2b ... Lower surface 2c ... 1st end surface 2d ... 2nd end surface 2e ... Ceramic layer 2f ... Ceramic layer 2g ... Ceramic layer 2h ... Inactive layer 2i ... Inactive Active layer 3a-3d ... 1st internal electrode 4a-4d ... 2nd internal electrode 5 ... 1st external electrode 5a ... End surface part 5b, 5c ... Round-around part 6 ... 2nd external electrode 6a ... End surface part 6b, 6c: wraparound part 11: laminated piezoelectric actuator 21 ... laminated piezoelectric actuator 31 ... bent piezoelectric actuator 32 ... diaphragm 33 ... adhesive layer 34 ... laminated piezoelectric actuator 51 ... bent piezoelectric actuator 52 ... diaphragm 52a ... insulation Substrate 52b, 52c ... electrode film 53 ... laminated piezoelectric actuator 54 ... adhesive layer 61 ... bent piezoelectric actuator 71 The piezoelectric actuator 73 ... first end surface electrodes 74 ... second end surface electrodes 81 ... piezoelectric actuator 82 ... diaphragm 91 ... piezoelectric actuator

Claims (7)

A ceramic sintered body made of piezoelectric ceramics, having an upper surface, a lower surface and opposing first and second end surfaces;
A plurality of first internal electrodes formed in the ceramic sintered body and led out to the first end face;
A plurality of second internal electrodes formed in the ceramic sintered body and led out to the second end face;
A plurality of ceramic layers formed in the ceramic sintered body and laminated together with the first internal electrode and the second internal electrode;
A first external electrode formed on the first end face of the ceramic sintered body;
A second external electrode formed on the second end face of the ceramic sintered body,
The first internal electrode and the second internal electrode are opposed to each other through the ceramic layer in the ceramic sintered body, and are sandwiched between the first internal electrode and the second internal electrode. The ceramic layer is an active layer, and has a plurality of active layers, and the inner electrode located on the top of the plurality of first and second inner electrodes and the ceramic firing in the ceramic sintered body. The ceramic layer between the upper surface of the bonded body is a first inactive layer, and the inner electrode located at the bottom of the plurality of first and second internal electrodes and the lower surface of the ceramic sintered body The ceramic layer is the second inert layer;
The thickness of the ceramic layer, which is the inactive layer, is made thinner than the thickness of the ceramic layer, which is the active layer, and the length of the first or second internal electrode is set to the first or second internal electrode. The length of the internal electrode located at the top and the internal electrode located at the bottom when the distance from the drawn first or second end surface to the tip of the first or second internal electrode At least one of them is shorter than the length of the other internal electrode,
When viewed in plan in the stacking direction of the ceramic sintered body, the first and second external electrodes are connected to different potentials among the uppermost and lowermost internal electrodes via an inert layer. A laminated piezoelectric actuator formed so as not to overlap with internal electrodes.   The first and second external electrodes are formed on the first and second end faces of the ceramic sintered body, and are provided so as not to reach the upper and lower surfaces of the ceramic sintered body. The multilayer piezoelectric actuator according to claim 1.   The first and second external electrodes are connected to the end surface portions located on the first and second end surfaces of the ceramic sintered body, and the upper and lower surfaces of the ceramic sintered body. A wraparound portion that reaches at least one of the wraparound portion, when viewed in plan in the stacking direction of the ceramic sintered body, the wraparound portion and the uppermost and lowermost internal electrodes have different potentials. The multilayer piezoelectric actuator according to claim 1, wherein the stacked piezoelectric actuator is arranged so that a connected internal electrode does not overlap with the inactive layer.   The multilayer piezoelectric actuator according to claim 3, wherein the wraparound portion is a surface electrode for joining to another member.   The multilayer piezoelectric actuator according to claim 1, wherein the ceramic layers constituting the active layer have the same thickness.   The multilayer piezoelectric actuator according to claim 1, wherein 0 <L ≦ (1/2) H, where L is the thickness of the inactive layer and H is the thickness of the active layer. .   A piezoelectric vibration device comprising a diaphragm, wherein the laminated piezoelectric actuator according to any one of claims 1 to 6 is joined to the diaphragm.

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