JP6729100B2 - Piezoelectric element - Google Patents

Description

The present invention relates to a piezoelectric element.

Conventionally, a thin laminated piezoelectric element has been known as a piezoelectric element. In such a piezoelectric element, electrical continuity is achieved between electrode layers such as surface electrodes and internal electrodes via side-hole electrodes or through-hole conductors penetrating the piezoelectric layer.

The above-mentioned side electrode is generally provided on the side surface of the element body by baking, sputtering, vapor deposition, or the like, but since such a side electrode is exposed to the outside, it is 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 to external factors. The following Patent Document 1 discloses an actuator in which conduction between electrodes is achieved via a through-hole conductor.

JP 2004-207340 A

The above-mentioned laminated piezoelectric element has a laminated body in which electrode layers and piezoelectric layers are alternately laminated, and the laminated body is obtained by firing a stack of electrode materials and piezoelectric materials. Residual stress due to the contraction of the is easily generated inside the laminate. In particular, since the internal electrode and the piezoelectric layer have different constituent materials and physical properties, stress tends to be concentrated at the interface and the periphery of the interface.

The stress generated during firing or the like causes defective conduction or disconnection in the internal electrodes or through-hole conductors, and reduces the connection reliability of the piezoelectric element.

Therefore, it is an object of the present disclosure to provide a piezoelectric element with improved connection reliability.

A piezoelectric element according to the present disclosure is a piezoelectric element including a laminated body in which electrode layers and piezoelectric layers are alternately laminated, and the laminated body is a first piezoelectric body in which one surface of the electrode layer is laminated. A laminated portion including a first through-hole conductor penetrating the layer and a second through-hole conductor penetrating the second piezoelectric layer overlaid on the other surface of the electrode layer, In the laminated portion, the first through-hole conductor has a first recess on the end face on the second piezoelectric layer side, and a protrusion into which the second piezoelectric layer enters the first recess. The second through-hole conductor has a second recess on the end surface on the side of the first piezoelectric layer, and the first piezoelectric layer has a protrusion that enters the second recess. There is at least one void proximate at least one of the first recess of the one through-hole conductor and the second recess of the second through-hole conductor.

In the laminated portion of the piezoelectric element, the laminated portion is formed by the first depression of the first through-hole conductor on one surface side of the electrode layer and the second depression of the second through-hole conductor on the other surface side of the electrode layer. When a stress is generated inside or a stress is applied from the outside, the stress is relaxed. As a result, it is possible to prevent the occurrence of defective conduction and disconnection of the electrode layers and the through-hole conductors in the laminated portion. Moreover, in the laminated portion, the protrusion of the second piezoelectric layer is inserted into the first recess of the first through-hole conductor, and the first recess is formed in the second recess of the second through-hole conductor. Since the protrusion of the piezoelectric layer is inserted, the holding force of the piezoelectric layer for each through-hole conductor is increased. This suppresses the displacement and deformation of each through-hole conductor, and further suppresses the occurrence of defective conduction and disconnection in the laminated portion. In addition, in the above-mentioned laminated portion, the void close to the through-hole conductor relieves stress and strain around the through-hole conductor, so that the occurrence of defective conduction or disconnection of the electrode layer or the through-hole conductor is further suppressed. ..

In addition, the piezoelectric layer has an active portion where an electric field is generated and deforms when a voltage is applied, and an inactive portion where an electric field is not generated in the piezoelectric layer when a voltage is applied. And the first through-hole conductor and the second through-hole conductor are adjacent to each other along the arranging direction of the active portion and the inactive portion when viewed from the stacking direction of the stacked body. Good. The active portion is deformed at the time of polarization or driving, and stress, strain and the like due to the deformation of the active portion are added to the inactive portion. However, in the laminated portion, the first through-hole conductor has a first recess on the end surface on the side of the second piezoelectric layer, and the second through-hole conductor has an end surface on the side of the first piezoelectric layer. Since the second depression is formed in the above, the above stress and strain are alleviated, thereby suppressing the occurrence of defective conduction and disconnection in the laminated portion.

Further, it may be a mode that includes a plurality of voids and the voids are close to the first recess of the first through-hole conductor and the second recess of the second through-hole conductor. In this case, stress and strain are alleviated in each of the through-hole conductors, thereby further suppressing the occurrence of defective conduction and disconnection in the laminated portion.

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

FIG. 3 is a perspective view of the piezoelectric element according to the 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 the figure which showed the mode when the pressure of the piezoelectric element was added. It is the figure which showed the mode when the pressure of the piezoelectric element was added. FIG. 6 is an enlarged cross-sectional view of a main part of an inactive part of a piezoelectric element according to a conventional technique. It is a disassembled perspective view of the piezoelectric element which concerns on 2nd Embodiment. FIG. 8 is a plan view of second, fourth, sixth, and eighth piezoelectric layers of the piezoelectric element shown in FIG. 7. FIG. 9 is a plan view of the third, fifth, and seventh piezoelectric layers of the piezoelectric element shown in FIG. 7. FIG. 8 is a plan view of the uppermost piezoelectric layer of the piezoelectric element shown in FIG. 7. FIG. 9 is a sectional view of the piezoelectric element shown in FIG. 7, taken along line XI-XI. FIG. 8 is an enlarged cross-sectional view of a main part of an inactive part of the piezoelectric element shown in FIG. 7.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description, the same elements or elements having the same function will be denoted by the same reference symbols, without redundant description.

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 laminated body 20 having a rectangular parallelepiped outer shape extending in one direction. The dimensions of the laminated body 20 are, for example, 2.0 mm in the longitudinal direction, 0.5 mm in the lateral direction, and 0.15 mm in thickness. As shown in FIG. 2, the laminate 20 includes a plurality of electrode layers 30 and a plurality of piezoelectric layers 36 and 38, and is configured by alternately laminating the electrode layers 30 and the piezoelectric layers 36 and 38. There is. In the present embodiment, the laminated body 20 includes three or more electrode layers 30 and two or more piezoelectric layers 36 and 38. In FIGS. 1 and 2, the laminated body 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 may be made of a conductive material (Ag-Pd alloy, Au-Pd alloy, Cu, Ni, Ag, etc.) other than Pt. The plurality of electrode layers 30 are patterned by screen printing or the like. The plurality of electrode layers 30 are composed of 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, first electrode layers 31 and second electrode layers 32 are alternately arranged in order from the top, and the lowermost layer is the third electrode layer 33. Has become.

The electrode pattern of the first electrode layer 31 has a short pattern 31a formed near one end 20a of the laminate 20 and a length extending from the short pattern 31a to the other end 20b of the laminate 20 through a predetermined gap. Pattern 31b. The electrode pattern of the second electrode layer 32 is a pattern symmetrical to the first electrode layer 31, and has a short pattern 32a formed near 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 the 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, and as an example, has a longitudinal length of 2.0 mm, a lateral length of 0.5 mm, and a thickness of 20 μm. Each of the piezoelectric layers 36 and 38 is made of, for example, a piezoelectric ceramic material containing lead zirconate titanate as a main component, and contains an additive such as Zn or Nb. The plurality of piezoelectric layers 36, 38 include a piezoelectric layer 36 in which the electrode layers 30 are located above and below, and a lowermost piezoelectric layer 38 in which the electrode layers 30 are located only above.

Through holes 36a are formed at predetermined positions in the piezoelectric layer 36, and through holes that connect the electrode layers 30 located above and below the piezoelectric layer 36 are formed in the regions where the through holes 36a are formed. The conductor 40 is formed. That is, the through-hole conductor 40 is configured by filling the through-hole 36 a provided in the piezoelectric layer 36 with the 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 the one end portion 20 a of the laminated body 20. Therefore, both the short pattern 31a of the first electrode layer 31 and the long pattern 32b of the second electrode layer 32 are connected to the short pattern 31a of the first electrode layer 31 on the surface of the stacked body 20 by the external connection terminal T2. And have the same polarity.

The through-hole conductor 40 connects the short pattern 32a of the second electrode layer 32 and the long pattern 31b of the first electrode layer 31 as the through-hole conductor 44 at the other end 20b of the laminated body 20. There is. The through-hole conductor 40 connects the short pattern 32a of the second electrode layer 32 and the third electrode layer 33 as the through-hole conductor 44 at the other end 20b of the laminated 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 laminate 20. It is electrically connected to the external connection terminal T1 connected to and has the same polarity.

In the piezoelectric element 10, since a pair of external connection terminals T1 and T2 are provided on the surface of the laminated body 20 and terminals of both polarities are exposed on one surface, conduction can be established from one surface side.

When a voltage is applied between the pair of external connection terminals T1 and T2, the electrode group connected on the one end 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 near the center, for example, between the two end portions 20a and 20b of the stacked body 20. The portion of the piezoelectric layer 36 located between them is deformed (extended or contracted) according to the polarization direction. Therefore, the portion sandwiched by the both ends 20a and 20b of the stacked body 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 the one end portion 20a of the laminated body 20 is a laminated portion in which the electrode layer portions 31a and 32b having the same polarity are overlapped with each other, so that even if a voltage is applied between the pair of external connection terminals T1 and T2, there is almost no deformation. Therefore, the vicinity of the one end portion 20a of the stacked body 20 is an inactive portion Sa that is not deformed even when a voltage is applied. The non-active portion Sa is suitable for installing the above-described through-hole conductor 40 because it does not cause a large displacement. The vicinity of the other end portion 20b of the laminated body 20 is also a laminated portion in which the electrode layer portions 31b and 32a having the same polarity are overlapped with each other. 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 located only on the piezoelectric layer 38, the piezoelectric layer 38 is not deformed 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. It hardly happens. Through-hole conductors 46 are provided through the piezoelectric layer 38. The through-hole conductor 46 can be formed by filling the 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 for the conduction of the electrode layer 30, and can be used, for example, to identify the front and back of a component or the polarity.

In the laminated body 20, only the portions where the deformation does not substantially occur even when a voltage is applied between the pair of external connection terminals T1 and T2 (that is, both end portions 20a and 20b and the lowermost piezoelectric layer 38), Through-hole conductors 42, 44, 46 are provided.

Next, the configurations 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 20b side of the laminated body 20.

As shown in FIG. 3, in the inactive portion Sa, the electrode layers 30 having the same polarity (more specifically, the electrode layers 31b and 32a) overlap each other with the piezoelectric layer 36 interposed therebetween. 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 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 particularly 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 particularly referred to as a third piezoelectric layer 36C.

The layers of the first layer 30A, the second layer 30B, the third layer 30C, and the fourth layer 30D which are adjacent to each other are connected by a through-hole conductor 40 penetrating the piezoelectric layer 36. For example, the first through-hole conductor 40A penetrating the first piezoelectric layer 36A connects the upper and lower first layers 30A and 30B. The second through-hole conductor 40B penetratingly provided in the second piezoelectric layer 36B connects the second layer 30B and the third layer 30C located above and below. The third through-hole conductor 40C penetratingly provided in the third piezoelectric layer 36C connects the third layer 30C and the fourth layer 30D located above and below.

However, the through-hole conductors 40 that are vertically adjacent to each other do not overlap with each other when viewed in the thickness direction (the stacking direction of the stacked body 20) and are adjacent to each other. 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 with each other when viewed in the thickness direction. The stacks 20 are arranged so as to be displaced in the longitudinal direction (left and right direction in the drawing). Also, the second through-hole conductor 40B and the third through-hole conductor 40C of the third piezoelectric layer 36C do not overlap with each other when viewed in the thickness direction, and are arranged so as to be displaced in the left-right direction in the drawing. .. The third through-hole conductor 40C of the third piezoelectric layer 36C overlaps with the first through-hole conductor 40A of the first piezoelectric layer 36A when viewed in 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 piezoelectric element 10 described above 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 form a paste. Then, using the obtained paste, for example, a plurality of green sheets having predetermined dimensions are manufactured by using a doctor blade method. At this time, the ratio of the plasticizer to the binder is adjusted so that the binder is sufficiently deformed.

A through hole is formed in each green sheet at the position where the through hole conductor 40 is formed by using a YAG laser.

An electrode paste (for example, Pd—Ag alloy (Pd:Ag=3:7)) to be the electrode layer 30 is applied and formed on each green sheet by the screen printing method so as to have the above-described pattern. When the electrode paste is applied, the through holes formed in the green sheet are filled with the electrode paste, and the filling rate of the electrode paste into the through holes is adjusted according to the shrinkage rate of the electrode paste during drying. Further, by setting the shrinkage rate during firing to 80% or less, the recess 40a described later is efficiently formed.

Subsequently, a plurality of green sheets each having an electrode paste printed thereon are overlapped with each other, and a pressing process such as warm isostatic pressing (WIP) is performed to obtain a green laminate. In a warm isostatic press, pressure is applied at about 250 MPa at a temperature of about 80°C, for example. At this time, a portion to be an electrode layer in the vicinity of the through hole portion is curved under high temperature and constant pressure.

Then, the obtained laminated body green is fired. Specifically, the laminated green is placed on a setter made of stabilized zirconia to perform binder removal treatment, and the setter on which the laminated green is placed is placed in a stabilized zirconia-shaped casket, 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 having an electric field strength of 2 kV/mm is applied for 3 minutes at a temperature of 100°C.

In the piezoelectric element 10 obtained by the above-described procedure, as shown in FIG. 3, the recesses 40a are formed at both ends of each through-hole conductor 40 in the stacking direction of the stack 20. For example, the first through-hole conductor 40A penetratingly provided in the first piezoelectric layer 36A has an indent 40a on the upper surface side of the first through-hole conductor 40A (lower side in FIG. 3), Further, the lower surface (the end surface on the second piezoelectric layer 36B side) has a recess 40a recessed on the first through-hole conductor 40A side (upper side in FIG. 3). Similarly, the second through-hole conductor 40B and the third through-hole conductor 40C also have depressions 40a on the upper and lower surfaces, respectively.

Then, the recess 40a makes the through-hole conductor 40 partially thin (that is, the length in the stacking direction is short). As shown in FIG. 3, the thickness of each of the through-hole conductors 40A, 40B, and 40C in the recess 40a is smaller than that of the piezoelectric layer 36.

Further, the protrusions 36b of the piezoelectric layer 36 are inserted in the depressions 40a formed in each through-hole conductor 40, respectively. For example, the upward protrusion 36b of the second piezoelectric layer 36B is inserted into the recess 40a on the lower surface of the first through-hole conductor 40A. Further, the downward projection 36b of the first piezoelectric layer 36A is inserted into 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.

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

As described above, the piezoelectric element 10 is a piezoelectric element including the laminate 20 in which the electrode layers 30 and the piezoelectric layers 36 are alternately laminated, and the laminate 20 is provided on one surface of the electrode layer 30B. The first through-hole conductor 40A penetratingly provided on the first piezoelectric layer 36A that is stacked, and the second through-hole conductor 40A that is secondly provided on the second piezoelectric layer 36B that is stacked on the other surface of the electrode layer 30B. The inactive portion Sa is provided as a laminated portion including the through-hole conductor 40B. In the inactive portion Sa, the first through-hole conductor 40A has the first depression 40a on the lower surface (the end surface on the second piezoelectric layer 36B side), and the second piezoelectric layer 36B is the first The second through-hole conductor 40B has the protrusion 36b that enters the recess 40a, the second recess 40a is formed on the upper surface (the end surface on the side of the first piezoelectric layer 36A), and the first piezoelectric layer 36A has a protrusion 36b that enters the second recess 40a. Then, there are a plurality of voids 48 adjacent to the first recess 40a of the first through-hole conductor 40A and the second recess 40a of the second through-hole conductor 40B.

In the piezoelectric element 10 described above, the internal stress (that is, the residual stress due to contraction during firing) that occurs in the inactive portion Sa during firing when manufacturing the piezoelectric element 10 and the stress applied to the inactive portion Sa from outside. Are 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. As a result, for example, the deformation or breakage of the through-hole conductor 40 is suppressed, and the occurrence of defective conduction or disconnection of the electrode layer 30 or the through-hole conductor 40 in the inactive portion Sa is suppressed.

Moreover, in the inactive portion Sa, the protrusion 36b of the piezoelectric layer 36 is inserted into the recess 40a 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. Compared with the configuration in which the end surface (upper and lower surfaces) of the through-hole conductor 40 is flat and the piezoelectric layer is not inserted, in the configuration in which the protrusion 36b of the piezoelectric layer 36 is inserted in the recess 40a of the through-hole conductor 40, The displacement or deformation of the conductor 40 is suppressed or hindered. As a result, it is possible to further suppress the occurrence of defective conduction and disconnection in the inactive portion Sa.

In addition, in the non-active portion Sa, the void 48 close to the through-hole conductor 40 relieves stress and strain around the through-hole conductor 40, so that the electrode layer 30 and the through-hole conductor 40 have poor electrical continuity and disconnection. Is further suppressed. In particular, in the above-described embodiment, the inactive portion Sa has a plurality of voids 48, and the voids 48 are close to the plurality of through-hole conductors 40, respectively. Therefore, stress and strain are alleviated in each of the plurality of through-hole conductors 40, and a situation in which poor conduction or disconnection in the inactive portion Sa is further suppressed.

The position of the void 48 is not limited to a position close to the through-hole conductor 40 in the stacking direction of the stacked body 20 (that is, a vertical position), but a position close to a direction orthogonal to the stacking direction (that is, a horizontal position). Position).

It should be noted that the positions (relative positions with respect to the through-hole conductor 40) and dimensions of each of the plurality of voids 48 are not uniform, and are uneven and irregular in order to relax stresses and strains having various directions and sizes. You can The position is not limited to a position close to the through-hole conductor 40 in the stacking direction of the stacked body 20 (that is, a vertical position), but may be a position close to the through-hole conductor 40 in a direction orthogonal to the stacking direction (that is, a horizontal position). Good.

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

In addition, in the piezoelectric element 10, when stress or strain is applied from the active portion Sb to the non-active portion Sa due to deformation such as expansion or contraction or vibration of the active portion Sb, such stress or strain also occurs in the second layer 30B. And is relaxed by the third layer 30C.

Here, the stress and strain applied from the active portion Sb to the inactive portion Sa will be described with reference to FIGS. 4 and 5.

FIG. 4 shows a state of the inactive portion Sa when the active portion Sb extends in the longitudinal direction of the stacked body 20 by applying a voltage between the pair of external connection terminals T1 and T2. At this time, a compressive stress or a compressive strain is applied to the inactive portion Sa from the longitudinal direction of the stacked body 20, which is the direction in which the active portion Sb and the inactive portion Sa are arranged. Therefore, the inactive portion Sa shrinks as a whole in the longitudinal direction of the stacked body 20. However, since the through-hole conductor 40 and the piezoelectric layer 36 in the inactive portion Sa have the above-described configuration, the depth of the recess 40a is increased according to the contraction of the inactive portion Sa, so that the electrode layer 30 is compressed. Stress and compressive strain are relieved. Such deepening of the recess 40a of the through-hole conductor 40 may occur even when the inactive portion Sa is pulled from the height direction.

FIG. 5 shows a state of the inactive portion Sa when the active portion Sb contracts in the longitudinal direction of the stacked body 20 due to the voltage application between the pair of external connection terminals T1 and T2. At this time, a tensile stress or a tensile strain is applied to the inactive portion Sa from the longitudinal direction of the stacked body 20, which is the direction in which the active portion Sb and the inactive portion Sa are arranged. Therefore, the non-active portion Sa extends entirely in the longitudinal direction of the stacked body 20. However, since the through-hole conductor 40 and the piezoelectric layer 36 in the inactive portion Sa have the above-described configuration, the depth of the recess 40a is reduced according to the extension of the inactive portion Sa, so that the tensile force with respect to the electrode layer 30 is reduced. Stress and tensile strain are relieved. Such flattening of the depression 40a of the through-hole conductor 40 can occur even when the inactive portion Sa is compressed in the height direction.

FIG. 6 shows an enlarged cross-sectional view of a main part of an inactive part of a piezoelectric element according to a conventional technique. In FIG. 6, reference numerals 52, 54 and 56 represent an electrode layer, a piezoelectric layer and a through hole conductor, respectively. As shown in FIG. 6, the end surface (upper and lower surfaces) of the through-hole conductor 56 according to the related art is flat and has no depression. Therefore, in the piezoelectric element according to the related art, stress or strain applied to the inactive portion is not generated. Cannot be mitigated. As a result, the electrode layer 52 may be detached from the through-hole conductor 56 or disconnected.

In the piezoelectric element 10 described above, the stress and strain applied from the active portion Sb to the inactive portion Sa at the time of polarization or driving is also relaxed. As a result, it is possible to suppress the occurrence of defective conduction and disconnection of the electrode layer 30 and the through-hole conductor 40 in the laminated portion.

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

As shown in FIG. 7, in the piezoelectric element 100, a plurality of piezoelectric layers 103 having the individual electrodes 102 formed thereon and a plurality of piezoelectric layers 105 having the common electrode 104 formed thereon are alternately laminated. The piezoelectric layer 107 on which the terminal electrodes 117 and 118 are formed is laminated on the uppermost layer.

The piezoelectric element 100 includes a laminated body 101 having a rectangular parallelepiped outer shape extending in one direction. The dimensions of the laminated body 101 are, for example, a length in the longitudinal direction of 30.0 mm, a length in the lateral 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, and 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 containing lead zirconate titanate as a main component, and contains additives such as Nb and Sr.

Each of the piezoelectric layers 103, 105, and 107 is made of a piezoelectric ceramic material containing lead zirconate titanate as a main component, 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 Ag-Pd alloy (Ag 70 wt %, Pd 30 wt %), and conductive materials other than Ag-Pd alloy (Ag-Pt alloy, Au-). Pd alloy, Cu, Ni, etc.). The pattern is formed by screen printing.

As shown in FIG. 8, a plurality of rectangular individual electrodes are formed on the upper surface of the second, fourth, sixth, and eighth piezoelectric layers 103 counted from the uppermost piezoelectric layer 107. 102 are staggered. The individual electrodes 102 are arranged such that the longitudinal direction thereof is orthogonal to the longitudinal direction of the piezoelectric layer 103, and the individual electrodes 102, 102 adjacent to each other are electrically separated from each other by a predetermined distance. Moreover, the influence of mutual vibration is prevented.

Here, when 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 zigzag pattern. By arranging the plurality of individual electrodes 102 in a zigzag manner, it is possible to arrange them efficiently with respect to the piezoelectric layer 103. Therefore, while maintaining the area of the active portion that contributes to deformation in the piezoelectric layer 103, the piezoelectric element The miniaturization of 100 or the high integration of the individual electrodes 102 can be achieved.

Each of the individual electrodes 102 has a connection end 102a at an end facing the adjacent individual electrode, and is provided directly below the connection end 102a, as shown in FIG. 11, to penetrate the piezoelectric layer 103. It is connected to the through-hole conductor 114. The through-hole conductor 114 is configured by filling the through-hole 136a provided in the piezoelectric layer 103 with an electrode material.

Further, a relay electrode 106 for electrically connecting the common electrodes 104 of the upper and lower piezoelectric layers 105 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 is provided directly below the relay electrode 106 so as to penetrate the piezoelectric layer 103.

In addition, the individual electrodes 102 are also arranged in a staggered manner on the upper surface of the lowermost piezoelectric layer 103, similarly to the above-described second, fourth, sixth, and eighth piezoelectric layers 103. 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. There is.

Further, as shown in FIG. 9, a 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. The relay electrode 116 is formed so as to face each connection end portion 102a of the piezoelectric layer 103 in the direction (that is, the thickness direction of the laminated piezoelectric element 100). Immediately below each relay electrode 116, as shown in FIG. 11, it is connected to a through-hole conductor 114 penetrating the piezoelectric layer 105. The through-hole conductor 114 is configured by filling the through-hole 136a provided in the piezoelectric layer 105 with an electrode material.

Further, the 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 and second rows and the set of the relay electrodes 116 in the third and fourth rows with a predetermined interval and in the stacking direction. Seen from the above, it overlaps with the portion of each individual electrode 102 excluding the connection end portion 102a. As a result, it is possible to effectively use the entire portion of the piezoelectric layers 103 and 105 that faces the portion of each individual electrode 102 excluding the connection end portion 102a as an active portion (active portion Sb in FIG. 11) that contributes to deformation. it can. In addition, the common electrode 104 is formed at a predetermined distance from the outer peripheral portion of the piezoelectric layer 105, and is a through-hole provided in the piezoelectric layer 105 so as to face the relay electrode 106 of the piezoelectric layer 103 in the stacking direction. It is connected to the hole conductor 114.

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

Further, as shown in FIG. 10, 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. The 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 the through-hole conductor 114 that is provided directly below the through-hole conductor 114 that penetrates the piezoelectric layer 107.

Lead wires such as an FPC (flexible printed circuit board) are soldered to these terminal electrodes 117 and 118 for connecting to a driving power source. Therefore, in order to facilitate the placement of the solder when soldering the lead wires, the terminal electrodes 117 and 118 have good 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 composed of Ag is formed.

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

A dummy electrode pattern may be arranged on the peripheral portion of the upper surface of the uppermost piezoelectric layer 107. By arranging the dummy electrode pattern on the peripheral portion, it is possible to obtain an effect that the bias of the pressure at the time of pressing is reduced and the variation of the green density after pressing can be reduced.

By stacking the piezoelectric layers 103, 105, and 107 having the electrode patterns formed as described above, the four common electrodes 104 are aligned in the stacking direction with the relay electrode 106 interposed therebetween 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, the five individual electrodes 102 are aligned in the stacking direction with the relay electrode 116 interposed, and the aligned electrode layers 102 and 116 are arranged as shown in FIG. , And is electrically connected by the through-hole conductor 114.

The through-hole conductors 114 adjacent to each other when viewed in the stacking direction of the stacked body 101 are designed so that their central axes do not overlap each other, as shown in FIG. The piezoelectric layers 103 and 105 are formed so as to be adjacent to each other along the extending direction of the individual electrode 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 is applied between the individual electrode 102 and the common electrode 104. Is applied, 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 a voltage is applied, among the active parts Sb corresponding to the individual electrodes 102 arranged in a matrix, the active parts Sb aligned below the selected terminal electrode 117 are stacked in the stacking direction. It 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 is hardly deformed even when a voltage is applied. Therefore, as shown in FIG. 11, the portion where the connection end portion 102a of the individual electrode 102 and the relay electrode 116 overlap is an inactive portion Sa that does not contribute to deformation. Further, since the individual electrode 102 is located only below the uppermost piezoelectric layer 107, there is almost no deformation even when a voltage is applied. In the laminated body 101, the through-hole conductor 114 is provided only in a portion where 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). There is.

As shown in FIGS. 11 and 12, in the inactive portion Sa, the electrode layers 130 (more specifically, the individual electrodes 102 and the relay electrodes 116) having the same polarity are overlapped 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 upper side. Further, the piezoelectric layer 103 interposed between the first layer 130A and the second layer 130B is referred to as a first piezoelectric layer 136A in particular, 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 particularly referred to as a third piezoelectric layer 136C.

The interlayers of the first layer 130A, the second layer 130B, the third layer 130C, and the fourth layer 130D that are adjacent to each other are connected by a through-hole conductor 114 penetrating the piezoelectric layers 103 and 105. However, the vertically adjacent through-hole conductors 114 do not overlap with each other when viewed in the thickness direction (the stacking direction of the stacked body 101) and are adjacent to each other. 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 with each other when viewed in the thickness direction. , Are displaced in the left-right direction of the figure (that is, the extending direction of the individual electrode 102). Also, the second through-hole conductor 114B and the third through-hole conductor 114C of the third piezoelectric layer 136C do not overlap with each other when viewed in the thickness direction, and are arranged so as to be displaced in the left-right 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 in 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 producing the piezoelectric element 100 is the same as the procedure for producing the piezoelectric element 10 described above. That is, a green sheet coated with an electrode paste having a predetermined pattern is overlaid and subjected to a pressing process such as warm isostatic pressing to obtain a laminated green sheet. At this time, the portion to be the electrode layer near the through hole is curved under high temperature and constant pressure. Then, the obtained laminated body green is fired and subjected to a predetermined polarization treatment to complete the piezoelectric element 100.

In the piezoelectric element 100 obtained by the procedure described above, as shown in FIG. 12, the recesses 114a are formed at both ends of each through-hole conductor 114 in the stacking direction of the stack 101. For example, the first through-hole conductor 114A penetrating the first piezoelectric layer 136A has a recess 114a on the upper surface, which is recessed on the first through-hole conductor 114A side (lower side in FIG. 11). Further, the lower surface (the end surface on the second piezoelectric layer 136B side) has a recess 114a which is recessed on the first through-hole conductor 114A side (upper side in FIG. 11). Similarly, the second through-hole conductor 114B and the third through-hole conductor 114C also have depressions 114a on the upper and lower surfaces, respectively.

Then, the recess 114a partially thins the through-hole conductor 114 (that is, the length in the stacking direction is short). As shown in FIG. 11, the thickness of each of the through-hole conductors 114A, 114B, 114C at the recess 114a is thinner than the thickness of the piezoelectric layers 136A, 136B, 136C.

Further, the protrusions 136b of the piezoelectric layers 136A, 136B, 136C are respectively inserted in the depressions 114a formed in each through-hole conductor 114. For example, the upward protrusion 136b of the second piezoelectric layer 136B is inserted in the depression 114a on the lower surface of the first through-hole conductor 114A. Further, the downward protrusion 136b of the first piezoelectric layer 136A is inserted in 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 shapes of the piezoelectric layers 103 and 105 are obtained by bending the electrode layer in the vicinity of the through hole at the time of manufacturing the piezoelectric element 100 under high temperature and constant pressure. It is thought to be done.

Further, in the piezoelectric element 100 obtained by the procedure described above, a plurality of voids 148 are formed near each through-hole conductor 114. More specifically, each of the plurality of voids 148 is close to the end of each through-hole conductor 114 in the stacking direction of the stacked body 101, and is located so as to enter the recess 114 a of each through-hole conductor 114. More specifically, the void 148 is located at the protrusion 136b of the piezoelectric layer 136A, 136B, 136C that has entered the recess 114a of the through-hole conductor 114. As shown in FIG. 12, each void 148 has a cross section that extends in one direction along the extending direction of the electrode layer 130. The inside of each void 148 is filled with an inert gas.

The piezoelectric element 100 according to the second embodiment is a piezoelectric element including a laminated body 101 in which electrode layers 130 and piezoelectric layers 103 and 105 are alternately laminated, and the laminated body 101 is one of the electrode layers 130B. The first through-hole conductor 114A penetratingly provided on the first piezoelectric layer 136A stacked on the one side, and the first through-hole conductor 114A penetrating on the second piezoelectric layer 136B stacked on the other side of the electrode layer 130B. The inactive portion Sa is provided as a laminated portion including the second through-hole conductor 114B. In the inactive portion Sa, the first through-hole conductor 114A has the first depression 114a on the lower surface (the end surface on the second piezoelectric layer 136B side), and the second piezoelectric layer 136B is the first The second through-hole conductor 114B has a protrusion 136b that enters the depression 114a, the second through-hole conductor 114B has the second depression 114a on the upper surface (the end surface on the side of the first piezoelectric layer 136A), and the first piezoelectric layer 136A has a protrusion 136b that enters the second recess 114a. Then, there are a plurality of voids 148 adjacent to the first recess 114a of the first through-hole conductor 114A and the second recess 114a of the second through-hole conductor 114B.

The piezoelectric element 100 according to the second embodiment is similar to the piezoelectric element 10 according to the first embodiment described above in that the internal stress generated in the inactive portion Sa during firing when manufacturing the piezoelectric element 100 and the external stress from the outside. The stress applied to the active portion Sa is relaxed 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 114B. As a result, for example, the deformation or breakage of the through-hole conductor 114 is suppressed, and the occurrence of defective conduction or disconnection of the electrode layer 130 or the through-hole conductor 114 is suppressed.

In addition, in the inactive portion Sa, the protrusions 136b of the piezoelectric layers 103 and 105 enter the depressions 114a of the through-hole conductor 114, so that the holding force of the piezoelectric layers 103 and 105 with respect to the through-hole conductor 114 increases. There is. Compared to the configuration in which the end surface (upper and lower surfaces) of the through-hole conductor 40 is flat and the piezoelectric layer is not embedded, in the configuration in which the protrusions 136b of the piezoelectric layers 103 and 105 are embedded in the recess 114a of the through-hole conductor 114 The displacement or deformation of the through-hole conductor 114 is suppressed or hindered. As a result, it is possible to further suppress the occurrence of defective conduction and disconnection in the inactive portion Sa.

In addition, in the non-active portion Sa, the void 148 close to the through-hole conductor 114 relieves the stress and strain around the through-hole conductor 114, so that the electrode layer 130 and the through-hole conductor 114 have poor conduction or disconnection. Is further suppressed. In particular, in the above-described embodiment, the non-active portion Sa has a plurality of voids 148, and the voids 148 are close to the plurality of through-hole conductors 114, respectively. Therefore, stress and strain are alleviated in each of the plurality of through-hole conductors 114, and a situation in which conduction failure or disconnection occurs in the inactive portion Sa is further suppressed.

The position of the void 148 may be a position vertically aligned or a position horizontally aligned with the through-hole conductor 114, like the position of the void 148 of the first embodiment described above.

Further, in the piezoelectric element 100 according to the second embodiment, similarly to the piezoelectric element 10 according to the first embodiment described above, the through-hole conductor 114 and the piezoelectric layers 103 and 105 have the above-described configuration in the laminated portion of the inactive portion Sa. Therefore, the stress and strain applied from the active portion Sb to the inactive portion Sa at the time of polarization or driving can be relaxed. As a result, it is possible to suppress the occurrence of defective conduction or disconnection of the electrode layer 130 and the through-hole conductor 114 in the laminated portion.

The present invention is not limited to the above embodiment. For example, the number of layers of the electrode layers and the piezoelectric layers of the laminated body of the piezoelectric element is the minimum number of layers required to form the above-mentioned laminated portion (that is, three or more electrode layers and two or more piezoelectric layers). ) If it is above, it can increase or decrease suitably. Further, the total thickness of the laminated body, the thickness of the electrode layer and the thickness of the piezoelectric layer can be appropriately increased or decreased. Furthermore, the number of voids in the inactive portion Sa can be appropriately increased or decreased, and there is only one in the inactive portion Sa (for example, one of the first through-hole conductor and the second through-hole conductor). May be present in each through hole conductor, a plurality of holes may be provided in each through hole conductor, and a plurality of holes may be provided in each through hole 40 conductor.

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 holes, 36b, 136b... projections, 40, 42, 44, 46, 114... through hole conductors, 40a, 114a... depressions, 48, 148... voids, Sa... inactive portions, Sb... active portions.

Claims (3)

A piezoelectric element comprising a laminate in which electrode layers and piezoelectric layers are alternately laminated,
The laminated body is provided so as to penetrate the first piezoelectric layer laminated on one surface of the electrode layer and is interposed between the electrode layers adjacent to each other in the laminating direction via the first piezoelectric layer . One through-hole conductor and the second piezoelectric layer that is formed on the other surface of the electrode layer and penetrates through the second piezoelectric layer . A second through-hole conductor having a laminated portion including
In the laminated portion,
The first through-hole conductor has a first recess on the end surface on the side of the second piezoelectric layer, and also has a protrusion into which the second piezoelectric layer enters the first recess. ,
The second through-hole conductor has a second recess on the end surface on the side of the first piezoelectric layer, and the first piezoelectric layer has a protrusion that enters the second recess. Then
A piezoelectric element having at least one void adjacent at least one of the first recess of the first through-hole conductor and the second recess of the second through-hole conductor. The piezoelectric layer has an active portion where an electric field is generated and deforms when a voltage is applied, and an inactive portion where an electric field is not generated in the piezoelectric layer when a voltage is applied,
The laminated portion is located in the inactive portion,
The first through-hole conductor and the second through-hole conductor are adjacent to each other along the arrangement direction of the active portion and the inactive portion when viewed from the stacking direction of the stacked body. The piezoelectric element according to 1. The void including a plurality of the voids, wherein the void is close to each of the first recess of the first through-hole conductor and the second recess of the second through-hole conductor. The piezoelectric element according to 1.

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