WO2013065657A1

WO2013065657A1 - Stacked piezoelectric element, ultrasound transducer, and method of manufacturing stacked piezoelectric element

Info

Publication number: WO2013065657A1
Application number: PCT/JP2012/077934
Authority: WO
Inventors: 西江純一; 近藤親史; 太田順司
Original assignee: 株式会社村田製作所
Priority date: 2011-10-31
Filing date: 2012-10-30
Publication date: 2013-05-10

Abstract

A stacked body block is formed in which electrode patterns (22A, 22B) and piezoelectric body sheets (21A, 21B) are stacked in a prescribed stacking direction, the stacked body block is fired, a voltage is applied between the electrode patterns (22A, 22B) which are adjacent in the stacking direction, and the stacked body block is segmented, forming stacked piezoelectric elements. In the piezoelectric body sheets (21A, 21B), element forming regions (23) are dispersed so as to form a matrix with an exclusion region (24) therebetween. The measurement of the gap between the end part of the electrode pattern (22A, 22B) in each element forming region (23) and the end part of the electrode pattern (22A, 22B) facing same in an in-plane direction is greater than the thickness measurement of the piezoelectric body sheets (21A, 21B).

Description

Multilayer piezoelectric element, ultrasonic transducer, and method of manufacturing multilayer piezoelectric element

The present invention relates to a laminated piezoelectric element having a structure in which a piezoelectric layer and an electrode layer are laminated, an ultrasonic transducer that transmits or receives a sound wave using the laminated piezoelectric element, and a method for manufacturing the laminated piezoelectric element. In particular, a laminated piezoelectric element that vibrates in the thickness direction of the piezoelectric layer and the electrode layer, an ultrasonic transducer that is used as a double feed detection sensor that detects double feeding of a sheet in a printing machine, and the laminated piezoelectric element It relates to the manufacturing method.

The ultrasonic transducer is used as a double feed detection sensor for detecting double feed of a sheet by a printing machine or the like.

Ultrasonic transducers used as double feed detection sensors are required to be downsized without lowering the sound pressure level or sensitivity level. From such a viewpoint, it is preferable to configure an ultrasonic transducer that directly uses the thickness vibration of the piezoelectric element.

As a piezoelectric element that vibrates in thickness, there is a laminated piezoelectric element in which a piezoelectric layer and an electrode layer are laminated and the thickness vibrates in the laminating direction. In the laminated piezoelectric element, when a driving voltage is applied between adjacent electrode layers, the piezoelectric element vibrates by changing the thickness of the piezoelectric layer.

In stacked piezoelectric elements, drive voltages with different potentials are applied to adjacent electrode layers, so if adjacent electrode layers are exposed on the same element end face, dielectric breakdown occurs due to electromigration caused by the drive voltage. there's a possibility that. Therefore, only one of the adjacent electrode layers is exposed on at least one element end face of the multilayer piezoelectric element, and the other is not exposed, so that a driving voltage having the same potential is applied to one element end face. In some cases, a configuration is employed in which only the electrode layer is exposed and an inactive region that does not contribute to vibration is provided in the vicinity of the surface (see, for example, Patent Documents 1 and 2). The inactive region is that at least a part of the piezoelectric layer is not disposed between two electrode layers to which a driving voltage having a different potential is applied, and no deformation occurs even when a driving voltage is applied to the electrode layer. It is an area. On the other hand, at least a part of the piezoelectric layer is disposed between two electrode layers to which a driving voltage having a different potential is applied, and a region where deformation is caused by applying the driving voltage to the electrode layer is an active region. It is.

In the production of the laminated piezoelectric element, a polarization treatment step is performed in which a voltage is applied between adjacent electrode layers to align the direction of spontaneous polarization of crystals in a piezoelectric layer made of piezoelectric ceramics. In the polarization treatment step, deformation occurs in the piezoelectric layer, so that cracks may occur at the interface between the layers or in the piezoelectric layer near the interface. In particular, in a laminated piezoelectric element having an inactive region,
Since the electrode layer is embedded in the piezoelectric layer, stress concentration occurs in the vicinity of the electrode end portion, and cracks are likely to occur in the piezoelectric layer. Therefore, in a laminated piezoelectric element having an inactive region, the distance between the electrode end and the element end surface, that is, the width of the inactive region is made sufficiently larger than the thickness of the piezoelectric layer, thereby A technique for preventing the occurrence of cracks in the layer has been proposed (see, for example, Patent Document 3).

JP-A-7-135348 JP 2008-244458 A JP-A-61-69299

In the multilayer piezoelectric element disclosed in Patent Document 3, the width of the inactive region is made larger than the thickness of the piezoelectric layer in order to prevent the occurrence of cracks in the piezoelectric layer in the polarization treatment step. When the thickness dimension is made larger or the element size is made smaller, the ratio of the inactive region to the whole laminated piezoelectric element increases. That is, in the multilayer piezoelectric element, the active region that vibrates effectively is small, and the inactive region that becomes a load against the vibration of the active region becomes large, so that the vibration of the multilayer piezoelectric element is hindered, and the desired performance, For example, it becomes difficult to achieve desired sound pressure and vibration efficiency. In particular, when a multilayer piezoelectric element is used for the double feed detection sensor, it is desired to significantly reduce the element size. Therefore, it is possible to prevent cracks in the piezoelectric layer and ensure a large active area in the polarization process. There is a strong demand for it.

Accordingly, a first object of the present invention is to provide a method for manufacturing a multilayer piezoelectric element capable of realizing the desired performance of the multilayer piezoelectric element while preventing the occurrence of cracks in the piezoelectric layer in the polarization process. It is to be realized.

A second object of the present invention is to provide a multilayer piezoelectric element that realizes the desired performance of the multilayer piezoelectric element using the above-described manufacturing method.

The third object of the present invention is to generate cracks in the piezoelectric layer in the polarization process even if the element size is reduced by the multilayer piezoelectric element that achieves the desired performance using the manufacturing method described above. It is an object of the present invention to provide an ultrasonic transducer that can easily prevent both and prevent a large active area.

The method for manufacturing a laminated piezoelectric element according to the present invention includes a step of forming a laminate block in which a piezoelectric sheet and an electrode pattern are laminated in a predetermined lamination direction, a step of firing the laminate block, and a lamination direction. A polarization process step of applying a voltage between adjacent electrode patterns and a step of forming a multilayer piezoelectric element by dividing a multilayer block are performed in this order. The piezoelectric sheet is partitioned into a plurality of element formation regions and removal regions in an in-plane direction perpendicular to the stacking direction, and the element formation regions are distributed and arranged in a matrix with the removal regions in between. Yes. A part of the electrode pattern is arranged in the element formation region. In the multilayer block, at least a part of the active region in which a part of the electrode pattern adjacent in the stacking direction overlaps in the stacking direction is arranged so as to overlap the element formation region. At least a part of the inactive region in which part of the electrode pattern adjacent in the stacking direction does not overlap in the stacking direction is arranged to overlap the removal region. Here, the distance between the end of the electrode pattern in each element formation region of the multilayer block and the end of the electrode pattern facing in the in-plane direction is larger than the thickness of the piezoelectric sheet in the stacking direction. It is characterized by that.

In this method, since the polarization treatment process is performed on the laminated body block, handling facilities and processes are not required as in the case where the elements are individually polarized. Further, in the laminate block subjected to the polarization treatment step, the distance between the end of the electrode pattern in each element formation region and the end of the electrode pattern facing in the in-plane direction is the piezoelectric body in the laminate direction. Since it is larger than the thickness dimension of the sheet, the stress concentration due to the deformation of the piezoelectric sheet in the polarization treatment step is suppressed, and the generation of cracks in the piezoelectric seed in the inactive region can be suppressed. In addition, by dividing the multilayer piezoelectric element from the element formation region except for the removal region, the non-active region that partially overlaps the removal region is also removed, thereby reducing the proportion of the non-active region in the multilayer piezoelectric element. Thus, the proportion of the active region can be increased, and desired performance of the multilayer piezoelectric element, for example, high sound pressure and vibration efficiency can be realized.

In the laminated body block used in the above-described method for producing a laminated piezoelectric element, it is preferable that the width dimension of the inactive area overlapping the element forming area is smaller than the thickness dimension of the piezoelectric sheet in the laminating direction.

As a result, even if the laminated piezoelectric element is configured to reduce the proportion of the inactive region that becomes a vibration load and increase the proportion of the active region to achieve the desired sound pressure and vibration efficiency, Generation of cracks in the piezoelectric sheet can be suppressed.

The multilayer piezoelectric element according to the present invention is formed by the above-described manufacturing method, wherein a piezoelectric layer made of a piezoelectric sheet and an electrode layer made of an electrode pattern are laminated, and the piezoelectric layer and the electrode layer are laminated. A non-active region in which the electrode layer adjacent in the stacking direction does not overlap is formed on a part of the peripheral edge in the in-plane direction orthogonal to the direction, and the width dimension of the non-active region is the stacking direction. It is preferable that every other electrode layer adjacent in the laminating direction is exposed on each element end face smaller than the thickness dimension of the piezoelectric layer.

Thereby, in the laminated piezoelectric element manufactured while suppressing the occurrence of cracks in the polarization process, it is possible to achieve the desired sound pressure and vibration efficiency by increasing the area ratio of the active region. In addition, the pair of electrode layers to which the drive voltage is applied are not exposed to the end face of the element, and the occurrence of electromigration can be suppressed.

Further, an ultrasonic transducer according to the present invention includes the above-described laminated piezoelectric element, a case, and a terminal portion. The case has a bottomed cylindrical shape in which the first end surface facing the sound wave transmission / reception direction is open and has an internal space, and the second end surface facing the first end surface is closed, and the case is piezoelectric in the sound wave transmission / reception direction. The piezoelectric element is held in a state where the stacking direction of the elements is directed. The terminal portion is provided such that the first end side is in contact with the outer side surface of the piezoelectric element and the inner side surface of the case, is electrically connected to the electrode layer of the piezoelectric element, and the second end side protrudes from the case.

As a result, even ultrasonic transducers that use extremely small stacked piezoelectric elements can be manufactured while suppressing the generation of cracks in the polarization process, thereby realizing miniaturization and improved sound pressure and vibration efficiency. It becomes possible.

According to the present invention, since the polarization processing step is performed on the laminated body block, handling facilities and processes can be eliminated as in the case of individually polarizing the elements. Further, in the laminate block subjected to the polarization treatment step, the distance between the end of the electrode pattern in each element formation region and the end of the electrode pattern facing in the in-plane direction is the piezoelectric body in the laminate direction. Since it is larger than the thickness dimension of the sheet, stress concentration due to deformation of the piezoelectric layer in the polarization treatment step is suppressed, and generation of cracks in the piezoelectric layer in the inactive region can be suppressed. In addition, by dividing the multilayer piezoelectric element from the element formation region except for the removal region, the non-active region that partially overlaps the removal region is also removed, thereby reducing the proportion of the non-active region in the multilayer piezoelectric element. Thus, the proportion of the active region can be increased, and it is possible to achieve desired performance, such as high sound pressure and vibration efficiency, in the laminated piezoelectric element and the ultrasonic transducer.

It is a figure showing an example of composition of an ultrasonic transducer provided with a lamination type piezoelectric element concerning a 1st embodiment of the present invention, and a lamination type piezoelectric element concerning a 1st embodiment of the present invention. It is a figure which shows the structural example of the element part of the multilayer piezoelectric element which concerns on the 1st Embodiment of this invention. It is a figure explaining the manufacturing method of the lamination type piezoelectric element which concerns on the 1st Embodiment of this invention. It is a figure explaining the structural example of the laminated body block formed in the manufacturing process of the element part of the multilayer piezoelectric element which concerns on the 1st Embodiment of this invention. It is a figure explaining the structural example of the laminated body block formed in the manufacturing process of the element part of the multilayer piezoelectric element which concerns on the 2nd Embodiment of this invention. It is a figure explaining the structural example of the laminated body block formed in the manufacturing process of the element part of the multilayer piezoelectric element which concerns on other embodiment of this invention. It is a figure explaining the structural example of the laminated body block formed in the manufacturing process of the element part of the multilayer piezoelectric element which concerns on other embodiment of this invention.

<< First Embodiment >>
Hereinafter, a laminated piezoelectric element according to a first embodiment of the present invention will be described with reference to FIGS. The laminated piezoelectric element according to this embodiment is used for an ultrasonic transducer for a double feed detection sensor, for example. Therefore, here, the description of the multilayer piezoelectric element according to the present embodiment will be made using a configuration example of an ultrasonic transducer including the multilayer piezoelectric element.

FIG. 1A is a cross-sectional view of an ultrasonic transducer 1 including a multilayer piezoelectric element 11 according to this embodiment. FIG. 1B is a perspective view of the multilayer piezoelectric element 11. In addition, the upward direction in the paper surface in FIG. 1A and the upward direction in the paper surface in FIG. 1B are front directions in which the ultrasonic transducer 1 transmits and receives ultrasonic waves.

The ultrasonic transducer 1 includes a metal cover 2, a resin case 3, a laminated piezoelectric element 11,

external connection terminals

5 and 6, and

conductive rubbers

7 and 8.

As shown in FIG. 1B, the multilayer piezoelectric element 11 has a substantially rectangular parallelepiped shape, and includes a matching portion 11A and an element portion 11B. The matching portion 11A is located on the front side of the multilayer piezoelectric element 11 and is provided for matching the acoustic impedance between the element portion 11B and the outside (outside air). The element portion 11B is located on the back side of the multilayer piezoelectric element 11, and is configured by laminating a plurality of electrode layers and a plurality of piezoelectric layers with the direction between the front and the back as the laminating direction. The laminated piezoelectric element 11 is configured such that the thickness in the laminating direction changes (thickness vibration). In addition, the multilayer piezoelectric element 11 is configured such that two side surfaces parallel to the stacking direction (the right side surface and the left side surface positioned in the horizontal direction in FIG. 1A) are the electrode connection portions. . A more detailed configuration of the element unit 11B will be described later.

The resin case 3 is an injection-molded product of plastic resin, has a bottomed cylindrical shape with an opening on the front side, and is configured to be divided into a right side member and a left side member.
The resin case 3 holds the multilayer piezoelectric element 11 so that the end of the multilayer piezoelectric element 11 protrudes from the opening to the front side.

The metal cover 2 is made of a conductive metal material and has a cylindrical shape with an opening at the front and back. The metal cover 2 holds the resin case 3. The metal cover 2 is provided with a retaining portion 2 B, and the metal cover 2 can be detached from the resin case 3 by engaging the right side member and the left side member of the resin case 3. It is prevented.

The

external connection terminals

5 and 6 are made of a conductive metal material, and are configured in a rod shape whose longitudinal direction is the direction in which sound waves are transmitted and received. The

external connection terminals

5 and 6 have front end portions disposed in the opening of the resin case 3, and rear end portions project from the back surface of the resin case 3. The external connection terminal 5 is arranged on the left side of the multilayer piezoelectric element 11. The external connection terminal 6 is disposed on the right side surface of the multilayer piezoelectric element 11. The external connection terminal 5 has a front end formed in a meander shape, and a portion bent toward the multilayer piezoelectric element 11 faces an even number of metal layers exposed on the left side surface of the multilayer piezoelectric element 11. To do. The external connection terminal 6 has a front end formed in a meander shape, and a portion bent toward the multilayer piezoelectric element 11 faces an odd-numbered metal layer exposed on the right side surface of the multilayer piezoelectric element 11. To do.

The

conductive rubbers

7 and 8 are rubber sheets having anisotropic conductivity in the thickness direction. The conductive rubber 7 is disposed on the left side of the multilayer piezoelectric element 11, that is, between the external connection terminal 5 and the multilayer piezoelectric element 11. The conductive rubber 8 is disposed on the right side surface of the multilayer piezoelectric element 11, that is, between the external connection terminal 6 and the multilayer piezoelectric element 11. The

external connection terminals

5 and 6 are selectively electrically connected to the even-numbered metal layer or the odd-numbered metal layer of the multilayer piezoelectric element 11 through the

conductive rubbers

7 and 8.

FIG. 2 is a diagram illustrating a detailed configuration of the element portion 11B of the multilayer piezoelectric element 11. In FIG. 2A, the front surface of the element unit 11B is arranged upward in the drawing, the right side serving as the connection portion with the external connection terminal 6 is arranged in the right direction of the drawing, and the front side is arranged in the left direction of the drawing. Shows the state. 2B, the front surface of the element portion 11B is arranged upward on the paper surface, the left side surface to be connected to the external connection terminal 5 is disposed on the right hand side of the paper surface, and the rear side surface is directed to the left front side of the paper surface. It shows the state of being placed in.

The element portion 11B is a rectangular columnar member that includes six piezoelectric layers and seven electrode layers, and the piezoelectric layers and the electrode layers are alternately stacked. The piezoelectric layer is made of piezoelectric ceramics. The distance between adjacent electrode layers, that is, the thickness dimension of the piezoelectric layer is about 0.8 mm to 1.2 mm. The bottom surface is a square having a side of about 2 mm to 5 mm.

The seven electrode layers include four first electrode layers 12 and three second electrode layers 13. The first electrode layer 12 and the second electrode layer 13 are piezoelectric so that the first electrode layer 12 becomes an odd-numbered electrode layer and the second electrode layer 13 becomes an even-numbered electrode layer. The layers are alternately stacked via layers. The first electrode layer 12 and the second electrode layer 13 are configured such that their shapes coincide with each other when rotated 180 ° in plan view.

The first electrode layer 12 includes an active region portion 12A, a first exposed portion 12B, and a second exposed portion 12C. Similarly, the second electrode layer 13 includes an active region portion 13A, a first exposed portion 13B, and a second exposed portion 13C. Each of the active region portions 12A and 13A has a square shape in plan view, and is located at a position about 0.2 mm away from the end of each side of the element portion 11B, and at the center of the element portion 11B in plan view. It is formed so as to overlap in the stacking direction. The first exposed

portions

12B and 13B protrude in a convex shape from one side of the active region portions 12A and 13A (the first exposed portion 12B is a front side and the first exposed portion 13B is a back side). The tip is exposed on the side surface of the element portion 11B. The second

exposed portions

12C and 13C include one side of the active region portions 12A and 13A (the second exposed portion 12C is on the right side, the second exposed portion 13C is on the left side) and the end of the element portion 11B. The tip is exposed on the side surface of the element portion 11B. That is, in the element part 11B, the active region parts 12A and 13A overlap in plan view, the first exposed parts 12B overlap, the first exposed parts 13B overlap, and the second exposed parts 12C overlap. The second exposed portions 13C are formed so as to overlap each other.

Therefore, in the multilayer piezoelectric element 11, the active region portions 12A and 13A and the portion located between the active region portions 12A and 13A in the piezoelectric layer constitute an active region that mainly vibrates, and the portion excluding them vibrates. Therefore, a non-active region serving as a load is configured. That is, the active region is a square region having a side of 1.6 mm to 4.6 mm, which is arranged in the center when the element portion 11B is viewed in plan view. The non-active region is a rectangular annular region having a width of 0.2 mm arranged around the active region in plan view of the element portion 11B. In this embodiment, the width of the non-active region is made smaller than the distance between the first electrode layer 12 and the second electrode layer 13, that is, the thickness of each piezoelectric layer, thereby reducing the active region. The inactive area is made smaller and larger. By making the active region that mainly vibrates larger than the inactive region that becomes a vibration load of the multilayer piezoelectric element 11, the multilayer piezoelectric element 11 including the element portion 11B ensures a large sound pressure and vibration efficiency. Can do. Further, only one of the first electrode layer 12 and the second electrode layer 13 is exposed on each of the four side surfaces of the element portion 11B. Therefore, electromigration is unlikely to occur in the multilayer piezoelectric element 11 including the element portion 11B.

Next, a method for manufacturing the multilayer piezoelectric element 11 will be described. FIG. 3 is a flowchart for explaining an example of a manufacturing method of the multilayer piezoelectric element 11.

In the present embodiment, in the manufacture of the multilayer piezoelectric element 11, after manufacturing one multilayer block including the plurality of multilayer piezoelectric elements 11, the individual multilayer piezoelectric elements 11 are taken out by dicing. Specifically, first, a block-size piezoelectric sheet constituting the laminate block is formed (S1). The piezoelectric sheet is a piezoelectric ceramic green sheet made of a piezoelectric ceramic material. This piezoelectric sheet constitutes the first piezoelectric layer of the plurality of stacked piezoelectric elements 11. Then, an electrode pattern constituting the first electrode layer 12 is formed by printing on one of the two opposing surfaces of the piezoelectric sheet, and an electrode pattern constituting the second electrode layer 13 is formed on the other by printing. (S2).

Thereafter, a piezoelectric sheet constituting the second and subsequent piezoelectric layers is formed, and is laminated and bonded to the piezoelectric sheet on which the electrode pattern has been previously formed (S3). The electrode pattern positioned between the piezoelectric sheet on which the electrode pattern has been previously formed and the newly laminated piezoelectric sheet on the surface not bonded to the piezoelectric sheet on which the electrode pattern has been previously formed is different. An electrode pattern is formed by printing (S4). These are repeated until the number of stacked layers of the piezoelectric layer and the electrode layer reaches a specified number to form a stacked body block (S5).

Then, after the laminate block is fired, the laminate block is polarized by applying a voltage between adjacent electrode patterns (S6 to S7). As a result, the direction of spontaneous polarization of crystals in the piezoelectric layer made of piezoelectric ceramics can be aligned, and good piezoelectric characteristics can be expressed in the plurality of stacked piezoelectric elements 11 divided from the stacked body block. . In addition, since the polarization process is performed on the laminated body block, it is necessary to handle the individual multilayer piezoelectric elements 11 that are required when the individual multilayer piezoelectric elements 11 are polarized. No equipment or process is required. After that, the alignment block 11A is formed in the laminated body block (S8), and a plurality of laminated piezoelectric elements 11 are manufactured by being divided by dicing (S9).

FIG. 4 is a diagram for explaining the electrode pattern constituting the first electrode layer 12 and the electrode pattern constituting the second electrode layer 13 formed in each piezoelectric sheet in the above-described steps S3 to S4. 4A shows a piezoelectric sheet constituting an odd-numbered piezoelectric layer in the multilayer piezoelectric element 11, and FIG. 4B constitutes an even-numbered piezoelectric layer in the multilayer piezoelectric element 11. A piezoelectric sheet is shown.

4A has an electrode pattern 22A formed on the front side. The electrode pattern 22 A constitutes the first electrode layer 12 of the plurality of stacked piezoelectric elements 11. In the piezoelectric sheet 21B shown in FIG. 4B, an electrode pattern 22B is formed on the front side. The electrode pattern 22 B constitutes the second electrode layer 13 of the plurality of stacked piezoelectric elements 11. The piezoelectric sheets 21A and the piezoelectric sheets 21B are alternately stacked to constitute the above-described stacked body block.

Piezoelectric sheets 21 A and 21 B are each divided into a plurality of element formation regions 23 and removal regions 24. The plurality of element formation regions 23 are regions that constitute any one of the piezoelectric layers of the multilayer piezoelectric element 11, and are distributed and arranged in a matrix on the main surfaces of the

piezoelectric sheets

21A and 21B. The removal region 24 is a region excluding the plurality of element formation regions 23 in the

piezoelectric sheets

21A and 21B. The arrangement and shape of the element formation region 23 and the removal region 24 are the same in the piezoelectric sheet 21A and the piezoelectric sheet 21B.

The electrode pattern 22A includes a terminal electrode portion 22A1 and a plurality of connecting electrode portions 22A2. The terminal electrode portion 22A1 is formed in a line shape along two adjacent sides (lower side and right side in the drawing) of the four sides when the piezoelectric sheet 21A is viewed in plan. A terminal for applying a voltage to the electrode pattern 22A in the polarization processing step is connected to the terminal electrode portion 22A1. One end of each of the plurality of connecting electrode portions 22A2 is connected to the terminal electrode portion 22A1, extends from the one end to the left in the figure in a staircase shape, and a part thereof is positioned in the plurality of element formation regions 23. ing. Each connecting electrode portion 22A2 is configured such that the portion at the corner of the staircase forms the first electrode layer 12 described above. The first electrode layer 12 is formed by any one of the plurality of connecting electrode portions 22A2 in all the element formation regions 23 in the piezoelectric sheet 21A.

Similarly, the electrode pattern 22B includes a terminal electrode portion 22B1 and a plurality of connecting electrode portions 22B2. The terminal electrode portion 22B1 is formed in a line shape along two adjacent sides (upper side and left side in the drawing) of the four sides when the piezoelectric sheet 21B is viewed in plan. A terminal for applying a voltage to the electrode pattern 22A in the polarization treatment step is connected to the terminal electrode portion 22B1. One end of each of the plurality of connecting electrode portions 22B2 is connected to the terminal electrode portion 22B1, extends from the one end in a stepwise manner in a downward right direction in the drawing, and is formed so that a part thereof is positioned in the plurality of element forming regions 23. ing. Each connecting electrode portion 22B2 is configured such that the portion at the corner of the staircase forms the second electrode layer 13 described above. Note that the second electrode layer 13 is formed by any one of the plurality of connection electrode portions 22B2 in all the element formation regions 23 in the piezoelectric sheet 21B.

In the present embodiment, the connection electrode portion 22A2 and the connection electrode portion 22B2 are positioned one by one in the element formation region 23 where a part of each of the connection electrode portion 22A2 and the connection electrode portion 22B2 is located so that the electrodes do not overlap in the removal region 24. It is formed to deviate. That is, the removal region 24 is configured to be an inactive region. Further, in the

piezoelectric sheets

21A and 21B, the element forming regions 23 are arranged at intervals of the same or larger dimensions as the thickness dimensions of the

piezoelectric sheets

21A and 21B.

Therefore, in the laminated body block formed by laminating the piezoelectric sheet 21A and the piezoelectric sheet 21B, the rectangular annular region up to a position about 0.2 mm away from the end in each element forming region 23, and the removal region 24 The whole becomes the inactive region, and only the square region inside the rectangular annular inactive region in each element forming region 23 becomes the active region. That is, the dimension of the space between the adjacent active regions is at least larger than the dimension of the thickness of each piezoelectric layer (

piezoelectric sheet

21A, 21B).

In other words, the distance between the end portion of the first electrode layer 12 in each element formation region 23 and the end portion of the electrode pattern 22A facing in the in-plane direction, and the second electrode layer 13 That is, the distance between the end and the end of the electrode pattern 22B facing in the in-plane direction is larger than the thickness of the piezoelectric layer in the stacking direction.

Therefore, when the polarization process is performed on the laminated body block in the manufacturing process described above, even if the piezoelectric layer is deformed in the active region, the end portions of the first electrode layer 12 and the second electrode layer 13 are not affected. Stress concentration generated in the piezoelectric layer in the vicinity is suppressed, and generation of cracks in the piezoelectric layer can be suppressed. Therefore, even when the multilayer piezoelectric element or ultrasonic transducer is downsized for use in a double feed detection sensor, the generation of cracks in the piezoelectric layer in the polarization process is prevented and the yield rate is increased. be able to. In addition, it is possible to achieve both downsizing and large sound pressure and vibration efficiency in the multilayer piezoelectric element and the ultrasonic transducer used for the double feed detection sensor.

<< Second Embodiment >>
Next, the structure and manufacturing method of the multilayer piezoelectric element according to the second embodiment of the present invention will be described. In this embodiment, an electrode pattern shape having a configuration suitable for increasing the number of stacked piezoelectric elements from one stacked body block will be described.

FIG. 5 is a diagram for explaining an electrode pattern formed on the piezoelectric sheet in the multilayer piezoelectric element according to this embodiment. FIG. 5A shows a piezoelectric sheet constituting an odd-numbered piezoelectric layer in the multilayer piezoelectric element according to this embodiment, and FIG. 5B shows an even number in the multilayer piezoelectric element according to this embodiment. The piezoelectric sheet which comprises the piezoelectric layer of the layer is shown.

In the piezoelectric sheet 31A shown in FIG. 5A, an electrode pattern 32A is formed on the front side. The electrode pattern 32A constitutes an odd-numbered drive electrode of a plurality of stacked piezoelectric elements. An electrode pattern 32B is formed on the front side of the piezoelectric sheet 31B shown in FIG. The electrode pattern 32B constitutes an even-numbered drive electrode of a plurality of stacked piezoelectric elements. The piezoelectric sheets 31A and the piezoelectric sheets 31B are alternately stacked to constitute a stacked body block.

Piezoelectric sheets 31 A and 31 B are each divided into a plurality of element formation regions 33 and removal regions 34. In the present embodiment, in order to increase the number of stacked piezoelectric elements, the dimension of the intervals in the row direction of the plurality of element formation regions 33 arranged in a matrix is made smaller than that in the first embodiment. An example is shown in which the number of element formation regions 33 arranged in the row direction is increased by one as compared to the first embodiment.

The electrode pattern 32A includes a terminal electrode portion 32A1 and a rectangular electrode portion 32A2. The terminal electrode portion 32A1 is formed in a line shape along two adjacent sides (the lower side and the right side in the drawing) of the four sides when the piezoelectric sheet 31A is viewed in plan. A terminal for applying a voltage to the electrode pattern 22A in the polarization processing step is connected to the terminal electrode portion 32A1. One end of the rectangular electrode portion 32A2 is connected to the right side of the terminal electrode portion 32A1, extends linearly from one end to the left side, and part of the rectangular electrode portion 32A2 is positioned in the element formation region 33 arranged in two rows. Is formed. More specifically, a part of the rectangular electrode portion 32A2 is located at a portion excluding a part on the upper end side of the element formation region 33 in the first row and a part on the lower end side of the element formation region 33 in the second row. It is formed to do.

The electrode pattern 32B includes two rows of rectangular electrode portions 32B1 and 32B2. The rectangular electrode portion 32B1 is formed in a line shape along one side (upper side in the drawing) of the four sides when the piezoelectric sheet 31B is viewed in plan. The rectangular electrode portion 32B2 is formed on the lower side of the rectangular electrode portion 32B1 in parallel with the rectangular electrode portion 32B1, and the left side is connected to the rectangular electrode portion 32B1 by a connecting portion. The rectangular electrode portions 32B1 and 32B2 are formed so that parts thereof are located in the element formation regions 33 in different rows. More specifically, the rectangular electrode portion 32 B 1 is formed so that a part thereof is located in a portion excluding a part on the lower end side of the element formation region 33 in the first row. The rectangular electrode part 32B2 is formed so that a part thereof is located in a part excluding a part on the upper end side of the element formation region 33 in the second row. The rectangular electrode portion 32B1 is connected to a terminal for applying a voltage to the electrode pattern 32B in the polarization process.

In this embodiment, since the end of the electrode is separated from the end only at one side of each element forming region 33, the active region extends to the periphery of two sides perpendicular to the side. Therefore, it becomes easy to increase the ratio occupied by the active region to increase sound pressure and vibration efficiency. Further, since the number of elements to be taken increases, the manufacturing cost can be reduced. Further, by making the width dimension of the electrode non-formed portion between the electrode end portions larger than the thickness dimension of each piezoelectric layer, the piezoelectric element is subjected to the polarization process when the laminate block is subjected to the polarization process in the manufacturing process. Even when the layer is deformed, the stress concentration generated in the piezoelectric layer in the vicinity of the end portion of the electrode is suppressed, and the generation of cracks in the piezoelectric layer can be suppressed.

<< Other Embodiments >>
As described in the above embodiments, the present invention can be implemented, but the shape of the electrode pattern provided on the piezoelectric sheet is not limited to the above. For example, electrode patterns as shown in FIGS. 6 and 7 can also be cited as examples of other embodiments.

FIG. 6 is a diagram for explaining an electrode pattern formed on a piezoelectric sheet according to another embodiment of the present invention. 6A shows a piezoelectric sheet constituting the odd-numbered piezoelectric layer in the multilayer piezoelectric element, and FIG. 6B shows a piezoelectric sheet constituting the even-numbered piezoelectric layer.

A piezoelectric sheet 41A shown in FIG. 6A includes an electrode pattern in which electrode portions 42A1 and 42A2 are formed on the front side. A piezoelectric sheet 41B shown in FIG. 6B includes an electrode pattern in which electrode patterns 42B1, 42B2, and 42B3 are formed on the front side. Each of the piezoelectric sheets 41 A and 41 B is partitioned into a plurality of element formation regions 43 and removal regions 44. Each of the electrode portions 42A1, 42A2, and 42B2 includes a line-shaped electrode extending in the column direction between two element forming regions 43 arranged in the row direction, and two electrodes on both sides orthogonal to the line-shaped electrode. It consists of a rectangular electrode that covers the element formation region, and is arranged so as to be shifted from each other in the row direction. The electrode portions 42B1 and 42B3 have a shape in which the electrode portion 42B2 is divided into two at the center line along the column direction, and are arranged on both sides of the electrode portion 42B2. Even in such an electrode pattern shape, at least the width dimension of the electrode non-forming portion between the electrode end portions is made larger than the thickness dimension of each piezoelectric layer, so that the laminated block can be formed in the manufacturing process. On the other hand, even when the piezoelectric layer is deformed when the polarization treatment is performed, the stress concentration generated in the piezoelectric layer near the electrode end is suppressed, and the generation of cracks in the piezoelectric layer can be suppressed.

FIG. 7 is a diagram for explaining an electrode pattern formed on a piezoelectric sheet according to another embodiment of the present invention. FIG. 7A shows a piezoelectric sheet constituting an odd-numbered piezoelectric layer in the multilayer piezoelectric element, and FIG. 7B shows a piezoelectric sheet constituting an even-numbered piezoelectric layer.

An electrode pattern 52A is formed on the front side of the piezoelectric sheet 51A shown in FIG. In the piezoelectric sheet 51B shown in FIG. 7B, an electrode pattern 52B is formed on the front side. Each of the

piezoelectric sheets

51A and 51B is partitioned into a plurality of element formation regions 53 and removal regions 54. The

electrode patterns

52A and 52B have a shape in which connecting electrode portions are formed in a stepped manner as in the first embodiment, but the width becomes the first exposed portion of the electrode layer in the first embodiment. The difference is that the formed part is formed wide. Even in such an electrode pattern shape, at least the width dimension of the electrode non-forming portion between the electrode end portions is made larger than the thickness dimension of each piezoelectric layer, so that the laminated block can be formed in the manufacturing process. On the other hand, even when the piezoelectric layer is deformed when the polarization treatment is performed, the stress concentration generated in the piezoelectric layer near the electrode end is suppressed, and the generation of cracks in the piezoelectric layer can be suppressed.

As described in the above embodiments, the multilayer piezoelectric element and the manufacturing method thereof according to the present invention can be realized. However, the scope of the present invention is not limited to any configuration as long as it is configured as described in the claims. May be. For example, each of the above-described piezoelectric sheets may be wider, and in that case, the electrode pattern may be an electrode pattern obtained by repeating the above-described one or an extended electrode pattern. Further, the specific shapes of the multilayer piezoelectric element and the ultrasonic transducer are not limited to those described above, and for example, the matching layer is not an essential configuration.

DESCRIPTION OF SYMBOLS 1 ... Ultrasonic transducer 2 ... Metal cover 2B ... Stopping part 3 ...

Resin case

5, 6 ...

External connection terminal

7, 8 ... Conductive rubber 11 ... Laminated piezoelectric element 11A ... Matching part 11B ... Element part 12 ... No. 1st electrode layer 13 ... 2nd electrode layer 12A, 13A ...

Active region part

12B, 13B ... 1st exposed

part

12C, 13C ... 2nd exposed

part

21A, 21B, 31A, 31B, 41A, 41B, 51A, 51B:

Piezoelectric sheets

22A, 22B, 32A, 32B, 52A, 52B ... Electrode patterns 22A1, 22B1 ... Terminal electrode portions 22A2, 22B2 ...

Connection electrode portions

23, 33, 43, 53 ...

Element formation regions

24, 34, 44, 54 ... removal area

Claims

A predetermined stacking direction is partitioned into a plurality of element formation regions and removal regions in an in-plane direction perpendicular to the stacking direction, and the element formation regions are distributed and arranged in a matrix with the removal regions in between. Forming a laminate block in which a piezoelectric sheet and a plurality of electrode patterns, some of which are arranged in the element formation region, are laminated,
Firing the laminate block;
A polarization treatment step of applying a voltage between the electrode patterns adjacent to each other in the stacking direction;
Dividing the laminate block to form a laminated piezoelectric element;
Is a manufacturing method of a laminated piezoelectric element that implements in this order,
In the laminate block,
An active region in which a part of the electrode pattern adjacent in the stacking direction overlaps in the stacking direction is at least partially overlapped with the element formation region, and a part of the electrode pattern adjacent in the stacking direction is the stacked layer A non-active region that does not overlap in the direction is at least partially overlapped with the removal region, and an end portion of the electrode pattern in each element formation region is in contact with an end portion of the electrode pattern facing in an in-plane direction. A method for manufacturing a multilayer piezoelectric element, wherein a distance dimension is larger than a thickness dimension of the piezoelectric sheet in the stacking direction.
2. The multilayer piezoelectric element according to claim 1, wherein in the multilayer block, the width dimension of the inactive region overlapping the element formation region is smaller than the thickness dimension of the piezoelectric sheet in the stacking direction. Method.
A multilayer piezoelectric element formed by the method for manufacturing a multilayer piezoelectric element according to claim 1 or 2,
A piezoelectric layer made of the piezoelectric sheet and an electrode layer made of the electrode pattern are laminated, and the laminated layer is formed on a part of a peripheral portion in an in-plane direction perpendicular to the lamination direction of the piezoelectric layer and the electrode layer. A non-active region in which the electrode layers adjacent in the direction do not overlap is formed, the width of the non-active region is smaller than the thickness of the piezoelectric layer in the stacking direction, The stacked piezoelectric element, wherein every other electrode layer adjacent in the stacking direction is exposed.
A multilayer piezoelectric element formed by the multilayer piezoelectric element manufacturing method according to claim 1 or 2,
A first end face facing the sound wave transmission / reception direction is open to have an internal space, and a second end face opposite to the first end face is configured to have a bottomed cylindrical shape, and the piezoelectric element extends in the sound wave transmission / reception direction. A case for holding the piezoelectric element in a state in which the stacking direction of the elements is directed;
A first end side is provided in contact with an outer side surface of the piezoelectric element and an inner side surface of the case, and is electrically connected to an electrode layer of the piezoelectric element, and a second end side protrudes from the case; , Comprising an ultrasonic transducer.