JP2018006679A - Piezoelectric element - Google Patents

Abstract

A piezoelectric element with improved connection reliability is provided. A piezoelectric element includes a pair of electrode layers, a piezoelectric layer interposed between the pair of electrode layers, and a through-hole conductor that penetrates the piezoelectric layer. The laminated body 20 which has the inactive part Sa as a part is provided. In the inactive portion Sa, there is a gap 48 close to the through-hole conductor 40. In the piezoelectric element 10, the gap 48 that is close to the through-hole conductor 40 in the inactive portion Sa relieves stress and distortion around the through-hole conductor 40. As a result, the occurrence of poor conduction or disconnection of the electrode layer 30 or the through-hole conductor 40 in the inactive portion Sa is suppressed. [Selection] Figure 3

Description

  The present invention relates to a piezoelectric element.

  Conventionally, a thin laminated piezoelectric element is known as a piezoelectric element. In such a piezoelectric element, conduction between the electrode layers such as the surface electrode and the internal electrode is achieved through a through-hole conductor penetrating the side electrode or the piezoelectric layer.

  The side electrode is generally provided on the side surface of the element body by baking, sputtering, vapor deposition, etc., but such a side electrode is exposed to the outside and is therefore damaged or deteriorated due to external factors. Easy to do. On the other hand, since the above-mentioned through-hole conductor is located inside the element body, it has high resistance against external factors. The following cited document 1 discloses an actuator in which conduction between electrodes is achieved through a through-hole conductor.

JP 2004-207340 A

  The laminated piezoelectric element described above has a laminate in which electrode layers and piezoelectric layers are alternately stacked, and the laminate is obtained by firing a laminate of electrode material and piezoelectric material. Residual stress due to the shrinkage of the film tends to occur inside the laminate. In particular, since the internal electrode and the piezoelectric layer have different constituent materials and physical properties, stress tends to concentrate on the interface and the periphery of the interface.

  And the stress which arises at the time of baking etc. causes the conduction defect and disconnection in an internal electrode or a through-hole conductor, and reduces the connection reliability of a piezoelectric element.

  Accordingly, an object of the present disclosure is to provide a piezoelectric element that is improved in connection reliability.

  A piezoelectric element according to an embodiment of the present disclosure includes a laminated body including a pair of electrode layers, a piezoelectric layer interposed between the pair of electrode layers, and a through-hole conductor penetrating the piezoelectric layer. The laminated portion has a gap close to the through-hole conductor.

  In the piezoelectric element, the gap close to the through-hole conductor in the laminated portion relieves stress and strain around the through-hole conductor. As a result, the occurrence of poor conduction or disconnection of the electrode layer or the through-hole conductor in the laminated portion is suppressed.

  In addition, there is an active part that deforms due to an electric field generated in the piezoelectric layer when a voltage is applied, and an inactive part that does not generate an electric field in the piezoelectric layer when a voltage is applied. The aspect located in may be sufficient. Since the active portion is deformed at the time of polarization or driving, the laminated portion including the through-hole conductor is located at the inactive portion in order to avoid the influence of stress and strain accompanying the deformation as much as possible.

  Moreover, the aspect of the end surface area of a through-hole conductor may be a mode smaller than the area of the cross section in the center position of the through-hole conductor in the lamination direction of a laminated body. According to the through-hole conductor having such a dimension and shape, stress and strain applied to the laminated portion are alleviated.

  According to the present disclosure, a piezoelectric element with improved connection reliability is provided.

1 is a perspective view of a piezoelectric element according to a first embodiment. It is the II-II sectional view taken on the line of the piezoelectric element shown in FIG. It is a principal part enlarged view of the inactive part of the piezoelectric element shown in FIG. It is a principal part expanded sectional view of the inactive part of the piezoelectric element which concerns on a prior art. It is a disassembled perspective view of the piezoelectric element which concerns on 2nd Embodiment. FIG. 6 is a plan view of second, fourth, sixth, and eighth piezoelectric layers of the piezoelectric element shown in FIG. 5. FIG. 6 is a plan view of third, fifth, and seventh piezoelectric layers of the piezoelectric element shown in FIG. 5. FIG. 6 is a plan view of the uppermost piezoelectric layer of the piezoelectric element shown in FIG. 5. It is the IX-IX sectional view taken on the line of the piezoelectric element shown in FIG. It is a principal part expanded sectional view of the inactive part of the piezoelectric element shown in FIG.

  Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

  First, the configuration of the piezoelectric element 10 according to the first embodiment will be described with reference to FIGS. 1 and 2.

  As shown in FIG. 1, the piezoelectric element 10 includes a stacked body 20 having a rectangular parallelepiped shape extending in one direction. The dimensions of the laminate 20 are, for example, a longitudinal length of 2.0 mm, a lateral length of 0.5 mm, and a thickness of 0.15 mm. As shown in FIG. 2, the stacked body 20 includes a plurality of electrode layers 30 and a plurality of piezoelectric layers 36 and 38, and the electrode layers 30 and the piezoelectric layers 36 and 38 are alternately stacked. Yes. In the present embodiment, the laminate 20 includes three or more electrode layers 30 and two or more piezoelectric layers 36 and 38. 1 and 2, the laminate 20 includes seven electrode layers 30 and seven piezoelectric layers 36 and 38, respectively.

  The plurality of electrode layers 30 are made of Pt, and can be made of a conductive material other than Pt (Ag—Pd alloy, Au—Pd alloy, Cu, Ni, Ag, etc.). The plurality of electrode layers 30 are patterned by screen printing or the like. The plurality of electrode layers 30 includes a first electrode layer 31, a second electrode layer 32, and a third electrode layer 33 having different electrode patterns. As shown in FIG. 2, in the plurality of electrode layers 30, the first electrode layers 31 and the second electrode layers 32 are alternately arranged in order from the top, and the lowest layer is the third electrode layer 33. It has become.

  The electrode pattern of the first electrode layer 31 includes a short pattern 31a formed near one end 20a of the stacked body 20, and a length extending from the short pattern 31a to the other end 20b of the stacked body 20 through a predetermined gap. Pattern 31b. The electrode pattern of the second electrode layer 32 is a symmetrical pattern with respect to the first electrode layer 31, and a short pattern 32a formed in the vicinity of the other end 20b of the stacked body 20 and a predetermined pattern from the short pattern 32a. And a long pattern 32b extending to one end 20a of the stacked body 20 through a gap. The third electrode layer 33 is a pattern (so-called solid pattern) formed over the entire area.

  Each of the plurality of piezoelectric layers 36 and 38 has a rectangular flat plate shape. As an example, the longitudinal length is 2.0 mm, the lateral length is 0.5 mm, and the thickness is 20 μm. Each of the piezoelectric layers 36 and 38 is made of, for example, a piezoelectric ceramic material mainly composed of lead zirconate titanate, and includes additives such as Zn and Nb. The plurality of piezoelectric layers 36, 38 include a piezoelectric layer 36 in which the electrode layer 30 is located above and below, and a lowermost piezoelectric layer 38 in which the electrode layer 30 is located only above.

  Through holes 36 a are provided in predetermined positions in the piezoelectric layer 36, and through holes for connecting the electrode layers 30 positioned above and below the piezoelectric layer 36 are formed in the regions where the through holes 36 a are formed. A conductor 40 is formed. That is, the through-hole conductor 40 is configured by filling a through-hole 36 a provided in the piezoelectric layer 36 with an electrode material.

  The through-hole conductor 40 connects the short pattern 31 a of the first electrode layer 31 and the long pattern 32 b of the second electrode layer 32 as the through-hole conductor 42 at one end 20 a of the multilayer body 20. Therefore, the short pattern 31a of the first electrode layer 31 and the long pattern 32b of the second electrode layer 32 are both external connection terminals T2 connected to the short pattern 31a of the first electrode layer 31 on the surface of the stacked body 20. And have the same polarity.

  The through-hole conductor 40 connects the short pattern 32 a of the second electrode layer 32 and the long pattern 31 b of the first electrode layer 31 as the through-hole conductor 44 at the other end 20 b of the multilayer body 20. Yes. The through-hole conductor 40 connects the short pattern 32 a of the second electrode layer 32 and the third electrode layer 33 as the through-hole conductor 44 at the other end 20 b of the multilayer body 20. Therefore, the short pattern 32a of the second electrode layer 32, the long pattern 31b of the first electrode layer 31, and the third electrode layer 33 are all long patterns 31b of the first electrode layer 31 on the surface of the stacked body 20. Are electrically connected to the external connection terminal T1 connected to each other and have the same polarity.

  In the piezoelectric element 10, a pair of external connection terminals T 1 and T 2 are provided on the surface of the multilayer body 20, and since bipolar terminals are exposed on one side, conduction can be obtained from one side.

  When a voltage is applied between the pair of external connection terminals T1 and T2, a group of electrodes connected to the one end portion 20a side of the stacked body 20 (that is, the short pattern 31a and the second electrode of the first electrode layer 31). The long pattern 32b) of the layer 32 and the electrode group connected on the other end 20b side (that is, the long pattern 31b of the first electrode layer 31, the short pattern 32a of the second electrode layer 32, and the third electrode layer). 33) has a different polarity. At this time, an electric field is generated between the long pattern 31b of the first electrode layer 31 and the long pattern 32b of the second electrode layer 32 that overlap each other between the both ends 20a and 20b of the stacked body 20, for example, near the center. As a result, the portion of the piezoelectric layer 36 located between them is deformed (elongated or contracted) in accordance with the polarization direction. Therefore, the portion sandwiched between both end portions 20a and 20b of the laminate 20 is an active portion Sb that is deformed when a voltage is applied between the pair of external connection terminals T1 and T2.

  The vicinity of one end 20a of the stacked body 20 is a stacked portion in which the electrode layer portions 31a and 32b having the same polarity are overlapped. Therefore, even if a voltage is applied between the pair of external connection terminals T1 and T2, deformation hardly occurs. Therefore, the vicinity of one end 20a of the stacked body 20 is an inactive portion Sa that does not deform even when a voltage is applied. The inactive portion Sa is suitable for installation of the above-described through-hole conductor 40 because a large displacement does not occur. The vicinity of the other end portion 20b of the stacked body 20 is also a stacked portion in which the electrode layer portions 31b and 32a having the same polarity are overlapped. ing. As described above, in the piezoelectric element 10, the inactive portion Sa and the active portion Sb are arranged along the longitudinal direction of the stacked body 20.

  Since the third electrode layer 33 is positioned only on the piezoelectric layer 38, the deformation is not caused even when a voltage is applied between the pair of external connection terminals T1 and T2, like both ends 20a and 20b of the multilayer body 20. Almost does not occur. A through-hole conductor 46 is provided through the piezoelectric layer 38. The through-hole conductor 46 can be configured by filling a through-hole provided in the piezoelectric layer 38 with an electrode material. The through-hole conductor 46 is a dummy through-hole conductor that is not intended to conduct the electrode layer 30 and can be used, for example, to identify the front and back of the component and the polarity.

  In the stacked body 20, only a portion where the deformation does not substantially occur even when a voltage is applied between the pair of external connection terminals T <b> 1 and T <b> 2 (that is, both end portions 20 a and 20 b and the lowermost piezoelectric layer 38), Through-hole conductors 42, 44, and 46 are provided.

  Next, the configuration of the electrode layer 30 and the piezoelectric layer 36 in the inactive portion Sa will be described with reference to FIG. FIG. 3 shows a cross section of the inactive portion Sa on the other end 20 b side of the stacked body 20.

  As shown in FIG. 3, in the inactive portion Sa, electrode layers 30 (more specifically, electrode layers 31 b and 32 a) having the same polarity overlap with each other via the piezoelectric layer 36. For convenience of explanation, the overlapping electrode layers 30 are also referred to as a first layer 30A, a second layer 30B, a third layer 30C, and a fourth layer 30D in order from the upper side. In addition, the piezoelectric layer 36 interposed between the first layer 30A and the second layer 30B is particularly referred to as a first piezoelectric layer 36A, and the piezoelectric body interposed between the second layer 30B and the third layer 30C. The layer 36 is specifically referred to as a second piezoelectric layer 36B, and the piezoelectric layer 36 interposed between the third layer 30C and the fourth layer 30D is specifically referred to as a third piezoelectric layer 36C.

  Adjacent layers of the first layer 30A, the second layer 30B, the third layer 30C, and the fourth layer 30D are connected by a through-hole conductor 40 penetrating the piezoelectric layer 36. For example, the first through-hole conductor 40A penetrating through the first piezoelectric layer 36A connects the first layer 30A and the second layer 30B positioned above and below. The second through-hole conductor 40B penetrating through the second piezoelectric layer 36B connects the second layer 30B and the third layer 30C positioned above and below. The third through-hole conductor 40C penetrating through the third piezoelectric layer 36C connects the third layer 30C and the fourth layer 30D positioned above and below.

  However, the through-hole conductors 40 adjacent to each other in the vertical direction do not overlap with each other when viewed from the thickness direction (the stacking direction of the multilayer body 20). Specifically, the first through-hole conductor 40A of the first piezoelectric layer 36A and the second through-hole conductor 40B of the second piezoelectric layer 36B do not overlap when viewed from the thickness direction. The laminated body 20 is arranged so as to be shifted in the longitudinal direction (left-right direction in the figure). Also, the second through-hole conductor 40B and the third through-hole conductor 40C of the third piezoelectric layer 36C do not overlap when viewed from the thickness direction, and are displaced in the left-right direction in the figure. . The third through-hole conductor 40C of the third piezoelectric layer 36C overlaps the first through-hole conductor 40A of the first piezoelectric layer 36A when viewed from the thickness direction. The amount of deviation of the through-hole conductor 40 is preferably, for example, not less than the maximum radius of the through-hole conductor 40, and more preferably not less than the maximum diameter of the through-hole conductor 40.

  Next, a procedure for manufacturing the above-described piezoelectric element 10 will be described.

  First, a binder and an organic solvent are added to the piezoelectric ceramic powder used for forming the piezoelectric layer 36 to obtain a paste. Then, a plurality of green sheets having a predetermined size are produced from the obtained paste using, for example, a doctor blade method. At this time, the ratio of the plasticizer to the binder is adjusted so as to be sufficiently deformed.

  In each green sheet, a through hole is formed at a position where the through hole conductor 40 is formed using a YAG laser.

  On each green sheet, an electrode paste (for example, Pd—Ag alloy (Pd: Ag = 3: 7)) to be the electrode layer 30 is applied and formed using the screen printing method so as to have the above-described pattern. When the electrode paste is applied, the electrode paste is filled into the through holes formed in the green sheet, but the filling rate of the electrode paste into the through holes is adjusted according to the viscosity of the electrode paste and the time until drying. .

  Subsequently, a plurality of green sheets each having an electrode paste printed thereon are superposed and further subjected to a pressing process such as warm isostatic pressing (WIP) to obtain a laminate green. In the warm isostatic press, for example, pressurization is performed at about 50 MPa at a temperature of about 80 ° C. At this time, the portion to be the electrode layer in the vicinity of the through-hole portion is bent under high temperature and constant pressure.

  And the obtained laminated body green is baked. Specifically, the laminate green is placed on a setter composed of stabilized zirconia and subjected to binder removal treatment. Further, the setter on which the laminate green is placed is placed in a stabilized zirconia mortar and about 1100. Bake at ℃.

  After firing, a predetermined polarization process is performed to complete the piezoelectric element 10. In the polarization treatment, for example, a voltage with an electric field strength of 2 kV / mm is applied at a temperature of 100 ° C. for 3 minutes.

  In the piezoelectric element 10 obtained by the above-described procedure, as shown in FIG. 3, depressions 40 a are formed at both end portions in the stacking direction of the stacked body 20 of each through-hole conductor 40. For example, the first through-hole conductor 40A penetrating the first piezoelectric layer 36A has a depression 40a that is recessed on the upper surface side (lower side in FIG. 3) of the first through-hole conductor 40A. In addition, the lower surface (the end surface on the second piezoelectric layer 36B side) has a recess 40a that is recessed on the first through-hole conductor 40A side (the upper side in FIG. 3). Similarly, the second through-hole conductor 40B and the third through-hole conductor 40C also have a recess 40a on each of the upper and lower surfaces.

  The through-hole conductor 40 is partially thinned (ie, the length in the stacking direction is short) by the recess 40a. As shown in FIG. 3, the thickness of each through-hole conductor 40 </ b> A, 40 </ b> B, 40 </ b> C in the recess 40 a is thinner than the thickness of the piezoelectric layer 36.

  Further, the protrusions 36 b of the piezoelectric layer 36 enter the recesses 40 a formed in the respective through-hole conductors 40. For example, the upward protrusion 36b of the second piezoelectric layer 36B enters the recess 40a on the lower surface of the first through-hole conductor 40A. Further, the downward protruding portion 36b of the first piezoelectric layer 36A enters the recess 40a on the upper surface of the second through-hole conductor 40B.

  The shape of the through-hole conductor 40, the shape of the electrode layer 30, and the shape of the piezoelectric layer 36 can be obtained by bending the electrode layer in the vicinity of the through-hole under high temperature and constant pressure when the piezoelectric element 10 is manufactured. Conceivable.

  In the piezoelectric element 10 obtained by the above-described procedure, a plurality of gaps 48 close to each through-hole conductor 40 are formed. More specifically, each of the plurality of gaps 48 is close to the end of each through-hole conductor 40 in the stacking direction of the multilayer body 20 and is positioned so as to enter the recess 40 a of each through-hole conductor 40. More specifically, the air gap 48 is located at the protrusion 36 b of the piezoelectric layer 36 that has entered the recess 40 a of the through-hole conductor 40. As shown in FIG. 3, each gap 48 has a cross section extending in one direction along the extending direction of the electrode layer 30. The interior of each gap 48 is filled with an inert gas.

Furthermore, in the piezoelectric element 10 obtained by the above-described procedure, the through-hole conductor 40 has a shape in which the center position in the thickness direction swells. In the through-hole conductors 40, the area S ₁ of the end face of the end portions of the through-hole conductors 40 is smaller than the area S ₂ of a cross section of the center position in the thickness direction of the through-hole conductors 40.

  As described above, the piezoelectric element 10 includes the pair of electrode layers 30 (for example, the first layer 30A and the second layer 30B in FIG. 3) and the piezoelectric layer 36 interposed between the pair of electrode layers 30. The multilayer body 20 having the inactive portion Sa as a multilayer portion including the through-hole conductor 40 (for example, the first through-hole conductor 40A in FIG. 3) penetrating the piezoelectric layer 36 is provided. In the inactive portion Sa, there is a gap 48 close to the through-hole conductor 40.

  In the piezoelectric element 10, the gap 48 close to the through-hole conductor 40 in the inactive portion Sa relieves stress and distortion around the through-hole conductor 40. As a result, the occurrence of poor conduction or disconnection of the electrode layer 30 or the through-hole conductor 40 in the inactive portion Sa is suppressed. In particular, in the above-described embodiment, the inactive portion Sa has a plurality of gaps 48, and the gaps 48 are close to each of the plurality of through-hole conductors 40. Therefore, stress and distortion are alleviated in each of the plurality of through-hole conductors 40, and the occurrence of poor conduction and disconnection in the inactive portion Sa is further suppressed.

  FIG. 4 shows an enlarged cross-sectional view of the main part of the inactive part of the piezoelectric element according to the prior art. In FIG. 4, reference numerals 52, 54, and 56 denote an electrode layer, a piezoelectric layer, and a through-hole conductor, respectively. As shown in FIG. 4, in the inactive portion of the piezoelectric element according to the related art, there is no gap that relaxes the stress and strain generated around the through-hole conductor 56. Therefore, in the piezoelectric element according to the related art, the stress and distortion in the through-hole conductor 56 are not relieved, and there is a possibility that the electrode layer 52 and the through-hole conductor 56 may be poorly connected or disconnected in the inactive portion.

  The position of the air gap 48 is not limited to the position close to the through-hole conductor 40 in the stacking direction of the multilayer body 20 (that is, the vertically aligned position), but the position close to the direction perpendicular to the stacking direction (that is, the horizontally aligned position). Position).

  In addition, in order to relieve stresses and strains with various directions and sizes, the positions (relative positions with respect to the through-hole conductors) and dimensions of the plurality of air gaps 48 are not uniform, and are not uniform and irregular. Can do. Not only the position close to the through-hole conductor 40 in the stacking direction of the multilayer body 20 (that is, the vertically aligned position) but also the position close to the direction orthogonal to the stacking direction (that is, the horizontally aligned position). Good.

  However, since the above-described air gap 48 positioned so as to enter the recess 40a of the through-hole conductor 40 can effectively relieve stress and strain, at least a part of the plurality of air gaps 48 may be present at the above position. it can.

  In addition, the piezoelectric element 10 includes an active portion Sb that deforms due to an electric field generated in the piezoelectric layer 36 when a voltage is applied, and an inactive portion Sa that does not generate an electric field in the piezoelectric layer 36 when a voltage is applied. In the piezoelectric element 10, the above-described laminated portion is located in the inactive portion Sa. As described above, the active portion Sb is deformed at the time of polarization or driving to generate internal stress or strain. Therefore, in order to avoid the influence of stress or strain accompanying the deformation as much as possible, the laminated portion including the through-hole conductor 40 is inactive. Located in the part Sa.

  In the piezoelectric element 10, internal stress generated in the inactive portion Sa during firing (ie, residual stress due to shrinkage during firing) and stress applied to the inactive portion Sa from the outside are as follows. It is alleviated by the depression 40a on the lower surface of the first through-hole conductor 40A and the depression 40a on the upper surface of the second through-hole conductor 40B. Thereby, for example, deformation or breakage of the through-hole conductor 40 is suppressed, and a situation in which the electrode layer 30 or the through-hole conductor 40 in the inactive portion Sa is poor or disconnected is suppressed.

  Further, in the inactive portion Sa, the protrusion 36 b of the piezoelectric layer 36 enters the recess 40 a of the through-hole conductor 40, so that the holding force of the piezoelectric layer 36 with respect to the through-hole conductor 40 is increased. Therefore, compared to a configuration (see FIG. 4) in which the end surface (upper and lower surfaces) of the through-hole conductor 56 is flat and the piezoelectric layer 54 does not enter (see FIG. 4), the protrusion 36b of the piezoelectric layer 36 is formed in the recess 40a of the through-hole conductor 40. In the structure which has penetrated, the displacement and deformation | transformation of the through-hole conductor 40 are suppressed or inhibited. As a result, a situation in which poor conduction or disconnection occurs in the inactive portion Sa is suppressed.

Further, in the piezoelectric element 10 described above, the through-hole conductor 40 has a shape in which the center position in the thickness direction swells, and the area S ₁ of the end faces of both end portions of the through-hole conductor 40 is equal to that of the through-hole conductor 40. It is smaller than the area S ₂ of a cross section of the center position in the thickness direction. According to the through-hole conductor 40 having such a shape, stress and strain applied to the inactive portion Sa are alleviated. In addition, since electric field concentration at the center of the through hole that can be easily disconnected when viewed from the thickness direction of the through hole conductor 40 is avoided, disconnection due to electric field concentration can be suppressed. Furthermore, since larger area S ₁ of the end face of the end portions of the cross section of the area S ₂ is through-hole conductors 40 at the center position in the thickness direction of the through-hole conductors 40, through anchor effect in the piezoelectric layer within 36 large holes As a result, unnecessary deformation of the through-hole conductor 40 is suppressed and distortion of the end face is alleviated.

  In the piezoelectric element 10, the inactive portion Sa on the one end 20 a side of the multilayer body 20 has the same electrode layer 30, piezoelectric layer 36, and through-hole conductor 40 as the inactive portion Sa on the other end 20 b side described above. Therefore, the same effect as described above can be obtained even in the inactive portion Sa on the one end portion 20a side.

  Next, the configuration of the piezoelectric element 100 according to the second embodiment will be described with reference to FIGS.

  As shown in FIG. 5, the piezoelectric element 100 includes a plurality of piezoelectric layers 103 in which individual electrodes 102 are formed and a plurality of piezoelectric layers 105 in which common electrodes 104 are formed. The piezoelectric layer 107 on which the terminal electrodes 117 and 118 are formed is configured by being laminated on the uppermost layer.

  The piezoelectric element 100 includes a laminated body 101 having a rectangular parallelepiped shape extending in one direction. The dimensions of the laminate 101 are, for example, a length in the longitudinal direction of 30.0 mm, a length in the short direction of 15.0 mm, and a thickness of 0.30 mm.

  Each of the plurality of piezoelectric layers 103 and 107 has a rectangular flat plate shape. As an example, the length in the longitudinal direction is 30.0 mm, the length in the lateral direction is 15.0 mm, and the thickness is 30 μm. Each piezoelectric layer 36 is made of, for example, a piezoelectric ceramic material mainly composed of lead zirconate titanate, and includes additives such as Nb and Sr.

  Each of the piezoelectric layers 103, 105, 107 is made of a piezoelectric ceramic material mainly composed of lead zirconate titanate, and is formed in a rectangular thin plate shape of, for example, “15 mm × 30 mm, thickness 30 μm”. The individual electrode 102, the common electrode 104, and the terminal electrodes 117 and 118 are made of an Ag—Pd alloy (Ag 70 wt%, Pd 30 wt%), and a conductive material other than the Ag—Pd alloy (Ag—Pt alloy, Au— (Pd alloy, Cu, Ni, etc.). The pattern is formed by screen printing.

  On the upper surface of the second, fourth, sixth, and eighth piezoelectric layers 103 counted from the uppermost piezoelectric layer 107, a plurality of rectangular individual electrodes are formed as shown in FIG. 102 are staggered. Each individual electrode 102 is arranged so that the longitudinal direction thereof is orthogonal to the longitudinal direction of the piezoelectric layer 103, and electrical independence is achieved between adjacent individual electrodes 102, 102 by taking a predetermined interval. And the influence by mutual vibration is prevented.

  Here, assuming that the longitudinal direction of the piezoelectric layer 3 is the column direction and the direction orthogonal to the longitudinal direction is the row direction, the individual electrodes 102 are arranged in, for example, four rows in a staggered manner. By arranging the plurality of individual electrodes 102 in a staggered arrangement, it is possible to arrange the individual electrodes 102 efficiently with respect to the piezoelectric layer 103. Therefore, while maintaining the area of the active portion contributing to deformation in the piezoelectric layer 103, the piezoelectric element 100 can be downsized or the individual electrode 102 can be highly integrated.

  Each of the individual electrodes 102 has an end facing the adjacent individual electrode as a connection end 102a, and directly penetrates the piezoelectric layer 103 as shown in FIG. 9 immediately below the connection end 102a. The through-hole conductor 114 is connected. The through-hole conductor 114 is configured by filling a through-hole 136 a provided in the piezoelectric layer 103 with an electrode material.

  Further, a relay electrode 106 for electrically connecting the common electrodes 104 of the piezoelectric layer 105 positioned above and below is formed on the edge of the upper surface of the piezoelectric layer 103. The relay electrode 106 is connected to a through-hole conductor 114 that penetrates the piezoelectric layer 103 immediately below the relay electrode 106.

  The individual electrodes 102 are also arranged in a staggered manner on the upper surface of the lowermost piezoelectric layer 103 as in the second, fourth, sixth, and eighth piezoelectric layers 103 described above. However, the lowermost piezoelectric layer 103 is different from the second, fourth, sixth, and eighth piezoelectric layers 103 in that the relay electrode 106 and the through-hole conductor 114 are not formed. Yes.

  Further, as shown in FIG. 7, the laminated body 101 is laminated on the upper surface of the third, fifth, seventh, and ninth piezoelectric layers 105 counted from the uppermost piezoelectric layer 107. A relay electrode 116 is formed to face each connection end 102a of the piezoelectric layer 103 in the direction (that is, the thickness direction of the multilayer piezoelectric element 100). As shown in FIG. 9, each relay electrode 116 is connected to a through-hole conductor 114 penetrating through the piezoelectric layer 105 as shown in FIG. The through-hole conductor 114 is configured by filling a through-hole 136 a provided in the piezoelectric layer 105 with an electrode material.

  Further, a common electrode 104 is formed on the upper surface of the piezoelectric layer 105. The common electrode 104 surrounds the set of the relay electrodes 116 in the first row and the second row and the set of the relay electrodes 116 in the third row and the fourth row with a predetermined interval, and in the stacking direction. As seen from the figure, the individual electrodes 102 overlap the portions excluding the connection end 102a. Accordingly, the entire portion of the piezoelectric layers 103 and 105 facing the portion excluding the connection end portion 102a of each individual electrode 102 is effectively used as the active portion (active portion Sb in FIG. 9) contributing to deformation. it can. In addition, the common electrode 104 is formed at a predetermined interval from the outer periphery of the piezoelectric layer 105, and is a through-hole that penetrates the piezoelectric layer 105 so as to face the relay electrode 106 of the piezoelectric layer 103 in the stacking direction. The hole conductor 114 is connected.

  Note that the relay electrode 116 and the common electrode 104 are also formed on the upper surface of the ninth piezoelectric layer 105 in the same manner as the third, fifth, and seventh piezoelectric layers 105 described above. However, the ninth piezoelectric layer 105 has a third layer, a fifth layer, and a seventh layer in that the through-hole conductor 114 facing the relay electrode 106 of the piezoelectric layer 103 is not formed in the stacking direction. Different from the piezoelectric layer 105.

  Further, as shown in FIG. 8, a terminal electrode 117 is formed on the upper surface of the uppermost piezoelectric layer 107 so as to face the connection end portion 102a of each individual electrode 102 of the piezoelectric layer 103 in the stacking direction. A terminal electrode 118 is formed so as to face the relay electrode 106 of the piezoelectric layer 103 in the stacking direction. Each of the terminal electrodes 117 and 118 is connected to a through-hole conductor 114 that penetrates the piezoelectric layer 107 immediately below.

  These terminal electrodes 117 and 118 are soldered with lead wires such as an FPC (flexible printed circuit board) for connection to a driving power source. Therefore, in order to make it easy to put solder when soldering the lead wires, in the terminal electrodes 117 and 118, in order to improve solder wettability on the base electrode layer made of a conductive material composed of Ag and Pd. A surface electrode layer made of a conductive material made of Ag is formed.

  The terminal electrodes 117 and 118 formed on the uppermost piezoelectric layer 107 are approximately 1 to 2 μm thicker than the other electrode layers 102, 104 and 116. The thicknesses of the terminal electrodes 117 and 118 are preferably 5 to 50%, more preferably 10 to 30% thicker than the thicknesses of the other electrode layers 102, 104 and 116.

  A dummy electrode pattern may be disposed on the peripheral edge of the upper surface of the uppermost piezoelectric layer 107. By disposing the dummy electrode pattern at the peripheral edge, there is an effect that the uneven pressure in pressing is reduced, and variation in green density after pressing can be reduced.

  By stacking the piezoelectric layers 103, 105, and 107 on which the electrode pattern is formed as described above, four common electrodes 104 are aligned with the relay electrode 106 in the stacking direction with respect to the uppermost terminal electrode 118. The aligned electrode layers 104 and 106 are electrically connected by the through-hole conductor 114.

  Further, with respect to each terminal electrode 117 of the uppermost layer, five individual electrodes 102 are aligned with the relay electrode 116 interposed in the stacking direction, and the aligned electrode layers 102 and 116 are arranged as shown in FIG. The through-hole conductor 114 is electrically connected.

  As shown in FIG. 9, the through-hole conductors 114 adjacent to each other when viewed from the stacking direction of the multilayer body 101 are designed so that their central axes do not overlap each other, and have a predetermined interval when viewed from the stacking direction. The piezoelectric layers 103 and 105 are formed so as to be adjacent to each other along the extending direction of the individual electrodes 102. By arranging the adjacent through-hole conductors 114 in this way, electrical connection by the through-hole conductors 114 is ensured.

  Since the multilayer piezoelectric element 100 is electrically connected as described above, when a voltage is applied between the predetermined terminal electrode 117 and the terminal electrode 118, the voltage between the individual electrode 102 and the common electrode 104 is applied. Is applied, and the active portion Sb, which is a portion where the piezoelectric layers 103 and 105 are sandwiched between the individual electrode 102 and the common electrode 104, is displaced. Therefore, by selecting the terminal electrode 117 to which the voltage is applied, among the active portions Sb corresponding to the individual electrodes 102 arranged in a matrix, the active portions Sb aligned under the selected terminal electrode 117 are arranged in the stacking direction. Can be displaced. Such a laminated piezoelectric element 100 is applied to a drive source of various devices that require minute displacement, such as valve control of a micropump.

  On the other hand, the portion where the connection end portion 102a of the individual electrode 102 and the relay electrode 116 overlap is a laminated portion where the electrode layers 31a and 32b having the same polarity overlap each other, and therefore hardly deforms even when a voltage is applied. Therefore, as shown in FIG. 9, a portion where the connection end portion 102a of the individual electrode 102 and the relay electrode 116 overlap with each other is an inactive portion Sa that does not contribute to deformation. Further, since the individual electrode 102 is positioned only below the uppermost piezoelectric layer 107, deformation hardly occurs even when a voltage is applied. In the laminated body 101, the through-hole conductor 114 is provided only in a portion where the deformation does not substantially occur even when a voltage is applied (that is, a portion where the connection end portion 102a of the individual electrode 102 and the relay electrode 116 overlap). Yes.

  As shown in FIGS. 9 and 10, in the inactive portion Sa, electrode layers 130 (more specifically, individual electrodes 102 and relay electrodes 116) having the same polarity overlap with each other via the piezoelectric layers 103 and 105. For convenience of explanation, the overlapping electrode layers 130 are also referred to as a first layer 130A, a second layer 130B, a third layer 130C, and a fourth layer 130D in order from the top. The piezoelectric layer 103 interposed between the first layer 130A and the second layer 130B is particularly referred to as a first piezoelectric layer 136A, and the piezoelectric body interposed between the second layer 130B and the third layer 130C. The layer 105 is particularly referred to as a second piezoelectric layer 136B, and the piezoelectric layer 103 interposed between the third layer 130C and the fourth layer 130D is specifically referred to as a third piezoelectric layer 136C.

  The adjacent first layer 130 </ b> A, second layer 130 </ b> B, third layer 130 </ b> C, and fourth layer 130 </ b> D are connected by a through-hole conductor 114 penetrating the piezoelectric layers 103 and 105. However, the through-hole conductors 114 adjacent to each other in the vertical direction do not overlap with each other when viewed from the thickness direction (the stacking direction of the stacked body 101). Specifically, the first through-hole conductor 114A of the first piezoelectric layer 136A and the second through-hole conductor 114B of the second piezoelectric layer 136B do not overlap when viewed from the thickness direction. These are arranged so as to be shifted in the left-right direction in the drawing (that is, the extending direction of the individual electrode 102). Further, the second through-hole conductor 114B and the third through-hole conductor 114C of the third piezoelectric layer 136C are not overlapped when viewed from the thickness direction, and are shifted in the horizontal direction in the drawing. . The third through-hole conductor 114C of the third piezoelectric layer 136C overlaps the first through-hole conductor 114A of the first piezoelectric layer 136A when viewed from the thickness direction. The amount of deviation of the through-hole conductor 114 is preferably, for example, not less than the maximum radius of the through-hole conductor 114, and more preferably not less than the maximum diameter of the through-hole conductor 114.

  The procedure for manufacturing the piezoelectric element 100 is the same as the procedure for manufacturing the piezoelectric element 10 described above. That is, green sheets coated with a predetermined pattern of electrode paste are stacked and subjected to a pressing process such as warm isostatic pressing to obtain a laminated green sheet. At this time, a portion to be an electrode layer in the vicinity of the through hole is bent under high temperature and pressure. Then, the obtained green laminate is fired and subjected to a predetermined polarization treatment, whereby the piezoelectric element 100 is completed.

  In the piezoelectric element 100 obtained by the above-described procedure, as shown in FIG. 10, depressions 114 a are formed at both ends of the through-hole conductor 114 in the stacking direction of the stacked body 101. For example, the first through-hole conductor 114A penetrating through the first piezoelectric layer 136A has a depression 114a that is recessed on the upper surface of the first through-hole conductor 114A (the lower side in FIG. 10). In addition, the lower surface (the end surface on the second piezoelectric layer 136B side) has a recess 114a that is recessed toward the first through-hole conductor 114A (upper side in FIG. 10). Similarly, the second through-hole conductor 114B and the third through-hole conductor 114C also have depressions 114a on the upper and lower surfaces.

  The through-hole conductor 114 is partially thinned (that is, the length in the stacking direction is short) by the recess 114a. As shown in FIG. 10, the thickness of each through-hole conductor 114A, 114B, 114C in the recess 114a is thinner than the thickness of the piezoelectric layers 136A, 136B, 136C.

  In addition, the protrusions 136b of the piezoelectric layers 136A, 136B, and 136C enter the recesses 114a formed in the through-hole conductors 114, respectively. For example, the upward protrusion 136b of the second piezoelectric layer 136B enters the recess 114a on the lower surface of the first through-hole conductor 114A. Further, the downward projecting portion 136b of the first piezoelectric layer 136A enters the recess 114a on the upper surface of the second through-hole conductor 114B.

  The shape of the through-hole conductor 114, the shape of the electrode layer 130, and the shape of the piezoelectric layers 103 and 105 are obtained by bending the electrode layer in the vicinity of the through-hole under high temperature and constant pressure when the piezoelectric element 100 is manufactured. It is thought that.

  The piezoelectric element 100 according to the second embodiment includes a pair of electrode layers 130 (for example, the first layer 130A and the second layer 130B in FIG. 10), and the piezoelectric layer 103 interposed between the pair of electrode layers 130. The laminated body 101 having the inactive portion Sa as a laminated portion including the through-hole conductor 114 (for example, the first through-hole conductor 114A in FIG. 10) penetrating the piezoelectric layer 103 is provided. The inactive portion Sa has a gap 148 that is close to the through-hole conductor 114.

  In the piezoelectric element 100, like the piezoelectric element 10 according to the first embodiment described above, in the inactive portion Sa, the gap 148 close to the through-hole conductor 114 relieves stress and strain around the through-hole conductor 114. This suppresses the occurrence of poor conduction or disconnection of the electrode layer 130 and the through-hole conductor 114 in the inactive portion Sa. In particular, in the above-described embodiment, the inactive portion Sa has a plurality of gaps 148, and the gaps 148 are close to the plurality of through-hole conductors 114, respectively. Therefore, stress and distortion are alleviated in each of the plurality of through-hole conductors 114, and the occurrence of poor conduction and disconnection in the inactive portion Sa is further suppressed.

  The position of the air gap 148 may be a vertically aligned position or a horizontally aligned position with respect to the through-hole conductor 114, similar to the position of the air gap 48 of the first embodiment described above. The position and size of each of the plurality of gaps 148 can also be non-uniform and irregular as with the position and dimensions of the gap 48 of the first embodiment described above. However, since the above-described gap 148 positioned so as to enter the recess 114a of the through-hole conductor 114 can effectively relieve stress and strain, at least a part of the plurality of gaps 148 may be present at the above-described position. it can.

  In addition, the piezoelectric element 100 has an active portion Sb that is deformed when an electric field is generated in the piezoelectric layers 103 and 105 when a voltage is applied, and an inactive state that does not generate an electric field in the piezoelectric layers 103 and 105 when a voltage is applied. In the piezoelectric element 100, the laminated portion described above is located in the inactive portion Sa. As described above, the active portion Sb is deformed at the time of polarization or driving to generate internal stress or strain. Therefore, in order to avoid the influence of the stress and strain accompanying the deformation as much as possible, the laminated portion including the through-hole conductor 114 is inactive. Located in the part Sa.

  In the piezoelectric element 100, the internal stress generated in the non-active portion Sa at the time of firing when the piezoelectric element 100 is manufactured (that is, the residual stress due to shrinkage during firing) and the stress applied to the non-active portion Sa from the outside are: It is alleviated by the depression 114a on the lower surface of the first through-hole conductor 114A and the depression 114a on the upper surface of the second through-hole conductor 140B. Thereby, for example, deformation or breakage of the through-hole conductor 114 is suppressed, and a situation in which the electrode layer 130 or the through-hole conductor 114 in the inactive portion Sa is poor or disconnected is suppressed.

  Further, in the inactive portion Sa, since the protrusions 136b of the piezoelectric layers 136A, 136B, and 136C enter the recess 114a of the through-hole conductor 114, the holding force of the piezoelectric layers 103 and 105 with respect to the through-hole conductor 114 is increased. ing. Therefore, compared to a configuration in which the end face of the through-hole conductor 56 is flat and the piezoelectric layer 54 does not enter (see FIG. 4), the protrusions 136b of the piezoelectric layers 136A, 136B, and 136C are formed in the recess 114a of the through-hole conductor 114. In the intruding configuration, the deformation of the through-hole conductor 114 is suppressed or inhibited. As a result, a situation in which poor conduction or disconnection occurs in the inactive portion Sa is suppressed.

  The present invention is not limited to the embodiment described above. For example, the number of electrode layers and the number of piezoelectric layers in the laminate of piezoelectric elements is the minimum number of layers required to constitute the above-described laminated portion (that is, three or more electrode layers and two or more piezoelectric layers) If it is above, it can be appropriately increased or decreased. In addition, the total thickness of the laminate, the thickness of the electrode layer, and the thickness of the piezoelectric layer can be appropriately increased or decreased. Furthermore, the thickness of the first through-hole conductor, the thickness of the second through-hole conductor, and the thickness of the third through-hole conductor are not limited to the thickness of the piezoelectric body layer. Any of the thickness of the through hole conductor, the thickness of the second through hole conductor, and the thickness of the third through hole conductor may be thinner than the thickness of the piezoelectric layer.

  DESCRIPTION OF SYMBOLS 10,100 ... Piezoelectric element, 20, 101 ... Laminated body, 30, 31, 32, 33, 102, 104, 116, 130 ... Electrode layer, 36, 38, 103, 105, 107 ... Piezoelectric layer, 36a, 136a ... through hole, 36b, 136b ... projection, 40, 42, 44, 46, 114 ... through hole conductor, 40a, 114a ... depression, 48, 148 ... gap, Sa ... inactive part, Sb ... active part.

Claims (3)

A laminate having a laminated portion including a pair of electrode layers, a piezoelectric layer interposed between the pair of electrode layers, and a through-hole conductor penetrating the piezoelectric layer;
The piezoelectric element, wherein the laminated portion has a gap close to the through-hole conductor. An active part that deforms when an electric field is generated when a voltage is applied; and an inactive part that does not generate an electric field when a voltage is applied;
The piezoelectric element according to claim 1, wherein the stacked portion is located in the inactive portion.   3. The piezoelectric element according to claim 1, wherein an area of an end face of the through-hole conductor is smaller than an area of a cross section at a center position of the through-hole conductor in a stacking direction of the multilayer body.

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