JP2023059607A - pressure sensor - Google Patents

Abstract

To provide a pressure sensor capable of obtaining desired electromotive force from a piezoelectric element on the basis of stress generated in a base plate.SOLUTION: A pressure sensor 1 includes a base plate 2, and a piezoelectric element 3 arranged on the main surface 2a of the base plate 2 and generating an electromotive force corresponding to the stress applied to the base plate 2. The piezoelectric element 3 includes a piezoelectric element 5, an external electrode 6A arranged on the main surface 5a side of the piezoelectric element 5 and joined to the main surface 2a of the base plate 2, and an external electrode 6B arranged on the main surface 5b side of the piezoelectric body 5 and located on the opposite side of the main surface 2a of the base plate 2. The area of the external electrode 6A and the area of the external electrode 6B are different from each other.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to pressure sensors.

2. Description of the Related Art As a piezoelectric device having a piezoelectric element, there is a piezoelectric device described in Patent Document 1, for example. This conventional piezoelectric device includes a piezoelectric element, a vibrating member to which the piezoelectric element is bonded, and a wiring member electrically connected to the piezoelectric element. One end of the wiring member is connected to another circuit member or the like via a connector or the like. The other end of the wiring member is physically connected to the vibrating member and electrically connected to the piezoelectric element.

JP-A-4-070100

The piezoelectric device of Patent Document 1 mentioned above aims to obtain vibration from a piezoelectric element. However, piezoelectric devices are used in a wide variety of applications. For example, piezoelectric devices may be applied to press sensors for the purpose of obtaining electromotive force from piezoelectric elements based on stress generated in a base plate due to contact with a finger or the like. In such a pressure sensor, it is important to obtain a desired electromotive force from the piezoelectric element based on the stress generated in the base plate from the viewpoint of sufficiently ensuring detection accuracy.

An object of the present disclosure is to provide a pressure sensor capable of obtaining a desired electromotive force from a piezoelectric element based on the stress generated in the base plate.

A pressure sensor according to one aspect of the present disclosure includes a base plate, and a piezoelectric element arranged on a main surface of the base plate and configured to generate an electromotive force in accordance with stress applied to the base plate, the piezoelectric element comprising: a piezoelectric element, a first external electrode arranged on the first surface side of the piezoelectric element and bonded to the main surface of the base plate, and a second surface of the piezoelectric element arranged on the main surface of the base plate. and a second external electrode located on the opposite side, and the area of the first external electrode and the area of the second external electrode are different from each other.

In this pressure sensor, the area of the first external electrode arranged on the first surface side of the piezoelectric element and the area of the second external electrode arranged on the second surface side of the piezoelectric element are different from each other. there is As a result, in this pressure sensor, compared to the case where the area of the first external electrode and the area of the second external electrode are made equal, the electrostatic capacitance of the piezoelectric element generated between the external electrodes can be easily adjusted. . By adjusting the area of the first external electrode and the area of the second external electrode so that the electrostatic capacitance of the piezoelectric element does not become excessive, a desired electromotive force based on the stress generated in the base plate is generated from the piezoelectric element. Obtainable.

The first external electrode may be arranged on the entire first surface of the piezoelectric body, and the area of the second external electrode may be smaller than the area of the first external electrode. In this case, since the connection resistance between the base plate and the first external electrode can be reduced, the loss when the electromotive force generated by the piezoelectric element is output to the outside can be suppressed.

The edge of the second external electrode may be located inside the edge of the second surface of the piezoelectric element when viewed from the normal direction of the main surface of the base plate. In this case, since the edge of the second external electrode is shifted inward from the edge of the second surface of the piezoelectric element, the edge of the second external electrode is short-circuited to other wiring portions. You can prevent it from happening.

The second external electrode may have a lead portion extending to the edge of the second surface of the piezoelectric element when viewed from the normal direction of the main surface of the base plate. The manufacturing process of the piezoelectric body includes, as a process before providing the base plate, a polarization process in which a predetermined voltage is applied to the piezoelectric body to impart piezoelectricity. In this step, by providing the second external electrode with a lead portion, it is possible to electrically connect a plurality of piezoelectric elements to each other via the lead portion, thereby improving the workability of the polarization step.

The second external electrode may be arranged on the entire second surface of the piezoelectric body, and the area of the first external electrode may be smaller than the area of the second external electrode. In this case, since the bonding area of the first external electrode with respect to the base plate is reduced, the binding force on the base plate due to the bonding of the first external electrode can be alleviated. Therefore, the base plate can be sufficiently distorted against the applied stress, and the electromotive force generated by the piezoelectric element can be increased.

The edge of the first external electrode may be located inside the edge of the first surface of the piezoelectric body when viewed from the normal direction of the main surface of the base plate. In this case, since the edge of the first external electrode is shifted inward from the edge of the first surface of the piezoelectric element, the edge of the first external electrode is short-circuited to other wiring portions. You can prevent it from happening.

The first external electrode may have a lead portion extending to the edge of the first surface of the piezoelectric element when viewed from the normal direction of the main surface of the base plate. The manufacturing process of the piezoelectric body includes, as a process before providing the base plate, a polarization process in which a predetermined voltage is applied to the piezoelectric body to impart piezoelectricity. In this step, by providing the second external electrode with a lead portion, it is possible to electrically connect a plurality of piezoelectric elements to each other via the lead portion, thereby improving the workability of the polarization step.

When the larger one of the area of the first external electrode and the area of the second external electrode is taken as 100%, the smaller one may be 40% to 60%. A sufficient area for electrical connection to the wiring member or the base plate by setting the smaller one of the area of the first external electrode and the area of the second external electrode to be 40% or more of the larger one. can be ensured. When the smaller one of the areas of the first external electrode and the area of the second external electrode is 60% or less of the larger area, the electrostatic capacitance of the piezoelectric element is suppressed from becoming excessive, It becomes possible to efficiently convert the distortion of the base plate into the electromotive force of the piezoelectric element.

The first external electrode may be fixed to the main surface of the base plate with an adhesive. In this case, by firmly fixing the first external electrode to the base plate with the adhesive, the connection resistance between the base plate and the first external electrode can be reduced more reliably. Therefore, it is possible to suppress the loss when outputting the electromotive force generated by the piezoelectric element to the outside.

According to the present disclosure, a desired electromotive force can be obtained from the piezoelectric element based on the stress generated in the base plate.

1 is a perspective view showing the overall configuration of a pressure sensor according to an embodiment of the present disclosure; FIG. It is a side view which shows the press sensor shown in FIG. 1 except a wiring member. 2 is a plan view showing the pressure sensor shown in FIG. 1 with wiring members removed; FIG. (a) and (b) are plan views showing another example of the second external electrode. It is a side view which shows the press sensor which concerns on a modification except a wiring member. (a) and (b) are plan views showing another example of the first external electrode.

Hereinafter, preferred embodiments of a pressure sensor according to one aspect of the present disclosure will be described in detail with reference to the drawings.

1 is a perspective view showing the overall configuration of a pressure sensor according to an embodiment of the present disclosure; FIG. As shown in FIG. 1, the pressure sensor 1 includes a base plate 2, a piezoelectric element 3 arranged on the main surface 2a side of the base plate 2, and a wiring member 4 extending toward the base plate 2 and the piezoelectric element 3. and In the pressure sensor 1, an electromotive force is obtained from the piezoelectric element 3 based on stress (distortion of the base plate 2) applied to the base plate 2 by contact with a finger or the like. The electromotive force from the piezoelectric element 3 is output outside through the wiring member 4 .

In the following description, the extending direction of the wiring member 4 is the X direction, the direction orthogonal to the X direction in the in-plane direction of the main surface 2a of the base plate 2 is the Y direction, and the normal direction of the main surface 2a of the base plate 2 is the direction. Let it be the Z direction.

The base plate 2 is made of, for example, a conductive metal material and has a rectangular shape. The base plate 2 has a pair of main surfaces 2a and 2b facing each other. The main surface 2a is a surface on which the piezoelectric element 3 is mounted. The main surface 2b is a surface on which a touch panel to which the pressure sensor 1 is applied, for example, is fixed. The planar shape of the base plate 2 is, for example, square. Examples of the constituent material of the base plate 2 include Ni—Fe alloy, Ni, brass, and stainless steel.

The piezoelectric element 3 includes a piezoelectric body 5 and a pair of external electrodes (first external electrode) 6A and external electrode (second external electrode) 6B. The piezoelectric element 5 has a rectangular parallelepiped shape that is flat in the Z direction. The rectangular parallelepiped shape includes a shape with chamfered corners and ridges, and a shape with rounded corners and ridges. The piezoelectric body 5 has a pair of main surfaces (first surface) 5a and main surface (second surface) 5b. The main surface 5a is the surface of the piezoelectric body 5 on the base plate 2 side. The main surface 5 b is the surface of the piezoelectric body 5 opposite to the base plate 2 . The main surfaces 5a and 5b have the same shape. Here, the main surfaces 5a and 5b have a square shape with one side shorter than that of the base plate 2, for example. The thickness of the piezoelectric element 5 is larger than the thickness of the base plate 2, for example. The center of the piezoelectric element 5 coincides with the center of the base plate 2 on the main surface 2 a of the base plate 2 .

The piezoelectric body 5 does not have internal electrodes and is composed of a single piezoelectric layer 7 . The piezoelectric layer 7 is made of a piezoelectric material. In this embodiment, the piezoelectric layer 7 is made of a piezoelectric ceramic material. Examples of piezoelectric ceramic materials include PZT[Pb(Zr,Ti) _O3 ], PT( _PbTiO3 ), PLZT[(Pb,La)(Zr,Ti) _O3 ], and barium titanate. The piezoelectric layer 7 is composed of, for example, a sintered body of a ceramic green sheet containing the piezoelectric ceramic material described above.

The external electrodes 6A and 6B have a rectangular parallelepiped shape flattened in the Z direction. The rectangular parallelepiped shape includes a shape with chamfered corners and ridges, and a shape with rounded corners and ridges. The thicknesses of the external electrodes 6A and 6B are approximately equal to each other, and both are sufficiently smaller than the thickness of the piezoelectric element 5. As shown in FIG. The external electrodes 6A, 6B are made of a conductive material. Examples of conductive materials include Ag, Pd, Ag--Pd alloys, and the like. The external electrodes 6A and 6B are made of, for example, a sintered conductive paste containing the conductive material described above.

The external electrode 6A is arranged on the main surface 5a of the piezoelectric body 5. As shown in FIG. The external electrodes 6A are bonded to the main surface 2a of the base plate 2 with an adhesive 8, for example. As the adhesive 8, for example, an ultraviolet curing adhesive, an anaerobic curing adhesive, a heat curing adhesive, or the like can be used. Although the adhesive 8 may wrap around between the external electrodes 6A and the main surface 2a, at least a partial region of the external electrodes 6A is in contact with the main surface 2a. Thereby, the external electrodes 6A and the base plate 2 are electrically connected to each other.

The external electrode 6B is arranged on the main surface 5b of the piezoelectric body 5. As shown in FIG. The center of the external electrode 6B coincides with the center of the main surface 5b. The four sides of the external electrode 6B are located inside the four sides of the main surface 5b when viewed in the Z direction. A region of the piezoelectric body 5 located between the outer electrode 6A and the outer electrode 6B is a piezoelectrically active region.

The wiring member 4 is configured by, for example, a flexible printed circuit board (FPC). The wiring member 4 has a structure in which a conductor 9 is covered with a cover material 10, and has a main body portion 11 extending in the X direction on the main surface 2a side of the base plate 2. As shown in FIG. The conductor 9 is made of a highly conductive material such as copper. The cover material 10 is made of non-conductive resin such as polyimide resin.

One end of the wiring member 4 (hereinafter referred to as the base end 12) can be electrically connected to a control unit or the like to which the electromotive force is output via a connecting member such as a connector. The other end of the wiring member 4 (hereinafter referred to as the tip 13) extends from one corner 2c of the base plate 2 onto the main surface 2a. The tip portion 13 branches into a first end portion 13A and a second end portion 13B. The first end portion 13A includes a first portion 14a extending in the Y direction along the edge of the base plate 2 from the body portion 11 and a second portion 14b extending in the X direction from the tip of the first portion 14a. have. The second end portion 13B extends in the X direction along the edge of the base plate 2 so as to be on the extension line of the main body portion 11 .

The first portion 14a of the first end portion 13A and the second end portion 13B are spaced apart at a constant distance in the Y direction. The position of the tip portion of the first portion 14a and the position of the tip portion of the second end portion 13B in the first end portion 13A are aligned in the X direction. At the tip of the first portion 14a and the tip of the second end 13B at the first end 13A, the conductor 9 is covered with the cover material in order to achieve electrical connection with the base plate 2 and the piezoelectric element 3. It is exposed from 10.

The pressure sensor 1 includes a first joint portion 21 that electrically joins the piezoelectric element 3 and the wiring member 4 by a conductive first joint member 24, and a conductive first joint portion 21 that connects the base plate 2 and the wiring member 4 together. A second joint portion 22 electrically joined by two joint members 25, and a third joint portion 23 physically joined to the base plate 2 and the wiring member 4 by a non-conductive third joint member 26. and

The first joint portion 21 is provided on the external electrode 6B of the piezoelectric element 3 . The first joint portion 21 is positioned on one corner 2c side of the base plate 2 in the external electrode 6B so as not to overlap the center of the base plate 2 and the center of the piezoelectric element 3 when viewed in the Z direction. are doing. In the first joint portion 21, the conductor 9 exposed at the tip portion of the first portion 14a of the first end portion 13A is joined to the external electrode 6B via the first joint member 24. As shown in FIG. Thereby, the external electrodes 6B and the wiring members 4 are electrically connected to each other. As the first joint member 24, for example, solder, conductive paste/sheet, anisotropic conductive paste/sheet, or the like can be used.

The second joint portion 22 is provided on the principal surface 2 a of the base plate 2 . The second joint portion 22 is arranged relative to the first joint portion 21 in accordance with the separation distance in the Y direction between the first portion 14a of the first end portion 13A and the second end portion 13B of the wiring member 4. are shifted in the Y direction. The second joint portion 22 is arranged close to one of the two sides forming the corner 2c of the main surface 2a of the base plate 2 along the X direction.

In the second joint portion 22, the conductor 9 exposed at the tip portion of the second end portion 13B is joined to the external electrode 6B via the first joint member 24. As shown in FIG. Thereby, the base plate 2 and the wiring member 4 are electrically connected to each other. As described above, the external electrodes 6A and the base plate 2 are electrically connected to each other. Therefore, the external electrodes 6A are electrically connected to the wiring member 4 through the base plate 2. As shown in FIG. As the second joint member 25, for example, solder, conductive paste/sheet, anisotropic conductive paste/sheet, or the like can be used.

The third joint portion 23 is provided on the main surface 2a of the base plate 2 . The third joint portion 23 is located closer to the proximal end of the wiring member 4 than the first joint portion 21 and the second joint portion 22 are. Specifically, the third joint portion 23 is arranged close to one of the two sides forming the corner 2c of the main surface 2a of the base plate 2 along the Y direction.

In the third joint portion 23, the first portion 14a of the first end portion 13A of the wiring member 4 and the base end portion 13Ba of the second end portion 13B connected to the first portion 14a are connected to the third joint portion 23. is joined to the base plate 2 via the joining member 26 of the. At the position of the third joint portion 23, the conductor 9 in the wiring member 4 is enclosed in the cover material 10, and the cover material 10 is joined to the main surface 2a of the base plate 2 via the third joint member 26. there is As a result, the wiring member 4 is physically connected to the base plate 2 at a portion closer to the proximal side than the first joint portion 21 and the second joint portion 22 . As the third joining member 26, for example, a conductive hot-melt resin containing reactive phenol resin and nitrile rubber as main components can be used.

Next, the configuration of the piezoelectric element 3 in the pressure sensor 1 described above will be described in more detail.

2 is a side view of the pressure sensor shown in FIG. 1. FIG. FIG. 3 is a plan view thereof. 2 and 3 show the base plate 2 and the piezoelectric element 3 except for the wiring member 4 and the first to third joints 21 to 23 for convenience of explanation.

As shown in FIGS. 2 and 3, in the piezoelectric element 3 of the pressure sensor 1, the area of the external electrode 6A and the area of the external electrode 6B are different from each other. More specifically, in this embodiment, the external electrodes 6A are provided over the entire main surface 5a, and the area of the external electrodes 6B is smaller than the area of the external electrodes 6A. The area of the external electrode 6A is equal to the area of the main surface 5a. On the other hand, the planar shape of the external electrode 6B is a square that is one size smaller than the main surface 5b. The area of the external electrode 6B is smaller than the area of the main surface 5b. The area of the main surface 5a and the area of the main surface 5b are equal to each other, and the area of the external electrode 6B is smaller than the area of the main surface 5a.

In the piezoelectric element 3, the edge of the external electrode 6B is located inside the edge of the main surface 5b of the piezoelectric element 5 when viewed from the normal direction (Z direction) of the main surface 2a of the base plate 2. there is In this embodiment, as described above, the external electrode 6B has a square shape slightly smaller than the main surface 5b of the piezoelectric body 5, and the center of the external electrode 6B coincides with the center of the main surface 5b. ing. As a result, each of the four sides of the external electrode 6B is located inside each of the four sides of the main surface 5b when viewed in the Z direction.

In the piezoelectric element 3, when the larger one of the areas of the external electrodes 6A and 6B is taken as 100%, the smaller area is 40% to 60%. In this embodiment, when the area of the external electrode 6A is 100%, the area of the external electrode 6B is 40% to 60% of the area of the external electrode 6A. The area of the external electrode 6B may be 55% to 60% of the area of the external electrode 6A.

As shown in FIGS. 4(a) and 4(b), the external electrode 6B is located at the edge of the main surface 5b of the piezoelectric element 5 when viewed from the normal direction (Z direction) of the main surface 2a of the base plate 2. You may have the drawer part K pulled out to the part. In the example of FIG. 4(a), lead portions K are respectively provided at the centers of two sides facing each other among the four sides of the external electrode 6B. In the example of FIG. 4B, lead portions K are provided at the centers of the four sides of the external electrode 6B.

The lead portion K extends from the center of the two sides to the edge of the main surface 5b of the piezoelectric body 5. As shown in FIG. The width of the lead portion K (the width in the direction orthogonal to the lead direction) is not particularly limited, but is, for example, equal to or smaller than the distance between the edge of the main surface 5b of the piezoelectric body 5 and the edge of the external electrode 6B. It may be In the examples of FIGS. 4A and 4B, the planar shape of the lead-out portion K is linear, but is not limited to this, and may be curved or other shape. The first joint member 24 described above is not arranged in the drawer portion K. As shown in FIG. That is, the lead-out portion K is in a state of not directly participating in the electrical connection between the piezoelectric element 3 and the wiring member 4 . Note that when the external electrode 6B is provided with the lead portion K, the area of the lead portion K may be included in the area of the external electrode 6B described above.

As described above, in the pressure sensor 1, the area of the external electrode 6A arranged on the main surface 5a side of the piezoelectric element 5 and the area of the external electrode 6B arranged on the main surface 5b side of the piezoelectric element 5 are different from each other. As a result, in the pressure sensor 1, the electrostatic capacitance of the piezoelectric element 3 generated between the external electrodes 6A and 6B can be easily adjusted compared to the case where the external electrodes 6A and 6B have the same area. . By adjusting the area of the external electrode 6A and the area of the external electrode 6B so that the electrostatic capacitance of the piezoelectric element 3 does not become excessive, a desired electromotive force based on the stress generated in the base plate 2 is obtained from the piezoelectric element 3. be able to. This makes it possible to sufficiently secure the detection accuracy of the pressure sensor.

In this embodiment, the external electrode 6A is arranged over the entire main surface 5a of the piezoelectric element 5, and the area of the external electrode 6B is smaller than the area of the external electrode 6A. With such a configuration, the connection resistance between the base plate 2 and the external electrode 6A can be reduced, so the loss when the electromotive force generated by the piezoelectric element 3 is output to the outside can be suppressed.

In this embodiment, the edge of the external electrode 6B is located inside the edge of the main surface 5b of the piezoelectric element 5 when viewed from the normal direction (Z direction) of the main surface 2a of the base plate 2. may According to such a configuration, the edges of the external electrodes 6B are shifted inwardly from the edges of the main surface 5b of the piezoelectric body 5, so that the edges of the external electrodes 6B are not in contact with other wiring portions. short circuit can be suppressed. For example, in this embodiment, the edge of the external electrode 6B contacts the second joint member 25 that electrically connects the conductor 9 of the second end 13B of the wiring member 4 and the main surface 2a of the base plate 2. It is possible to suppress

The external electrode 6B may have a lead portion K that extends to the edge of the main surface 5b of the piezoelectric element 5 when viewed from the normal direction (Z direction) of the main surface 2a of the base plate 2 . The manufacturing process of the piezoelectric body 5 includes, as a process before providing the base plate 2, a polarization process of applying a predetermined voltage to the piezoelectric body 5 to impart piezoelectricity. In this process, by providing the external electrodes 6B with the lead portions K, it becomes possible to electrically connect the plurality of piezoelectric elements 5 to each other via the lead portions K, thereby improving the workability of the polarization step. .

In this embodiment, as shown in FIGS. 4(a) and 4(b), the width of the lead portion K is determined by the distance between the edge of the main surface 5b of the piezoelectric body 5 and the edge of the external electrode 6B. It is less than or equal to the interval. Therefore, the area of the lead portion K does not become excessive, and the influence on the adjustment of the capacitance of the piezoelectric element 3 can be suppressed.

In this embodiment, when the area of the external electrode 6A is 100%, the area of the external electrode 6B is 40% to 60%. Since the area of the external electrode 6B is 40% or more of the area of the external electrode 6A, it is possible to secure a sufficient area for electrical connection to the wiring member 4 or the base plate 2 (here, the wiring member 4). becomes. Since the area of the external electrode 6B is 60% or less of the area of the external electrode 6A, the electrostatic capacitance of the piezoelectric element 3 is suppressed from becoming excessive, and the distortion of the base plate 2 is efficiently caused by the piezoelectric element 3. It can be converted into electricity.

In this embodiment, the external electrodes 6A may be fixed to the main surface 2a of the base plate 2 with an adhesive 8. FIG. By firmly fixing the external electrodes 6A to the base plate 2 with the adhesive 8, the connection resistance between the base plate 2 and the external electrodes 6A can be reduced more reliably. Therefore, it is possible to suppress the loss when outputting the electromotive force generated by the piezoelectric element 3 to the outside.

FIG. 5 is a side view showing a pressure sensor according to a modification. As in FIG. 2, FIG. 5 shows the base plate 2 and the piezoelectric element 3 except for the wiring member 4 and the first to third joints 21 to 23 for convenience of explanation. As shown in FIG. 5, the pressure sensor 31 according to the modification differs from the above embodiment in the configuration of the external electrodes 6A and 6B. Other configurations are the same as those of the above embodiment.

Specifically, in the pressure sensor 31, the external electrode 6B is arranged on the entire main surface 5b of the piezoelectric body 5, and the area of the external electrode 6A is smaller than the area of the external electrode 6B. .

In such a pressure sensor 31 as well, it is easier to adjust the capacitance of the piezoelectric element 3 generated between the external electrodes 6A and 6B than when the external electrodes 6A and 6B have the same area. Become. Therefore, a desired electromotive force based on the stress generated in the base plate 2 can be obtained from the piezoelectric element 3, and the accuracy of detection as a pressure sensor can be sufficiently ensured. Further, according to the configuration of the pressure sensor 31, the bonding area of the external electrode 6A with respect to the base plate 2 is reduced, so that the binding force on the base plate 2 due to the bonding of the external electrode 6A can be alleviated. Therefore, the base plate 2 can be sufficiently distorted against the applied stress, and the electromotive force generated in the piezoelectric element 3 can be increased.

In the pressure sensor 31, the edge of the external electrode 6A is located inside the edge of the main surface 5a of the piezoelectric element 5 when viewed from the normal direction (Z direction) of the main surface 2a of the base plate 2. are doing. Also in this modified example, as in the above-described embodiment, the external electrode 6A has a square shape that is one size smaller than the main surface 5a of the piezoelectric body 5, and the center of the external electrode 6A is the center of the main surface 5a. is consistent with As a result, the four sides of the external electrode 6A are located inside the four sides of the main surface 5a when viewed in the Z direction.

According to such a configuration, the edge of the external electrode 6A is shifted inwardly from the edge of the main surface 5a of the piezoelectric body 5, so that the edge of the external electrode 6A is not in contact with other wiring portions. short circuit can be suppressed. For example, in this modification, the edge of the external electrode 6A contacts the second joint member 25 that electrically connects the conductor 9 of the second end 13B of the wiring member 4 and the main surface 2a of the base plate 2. It is possible to suppress

In this modification, when the area of the external electrode 6B is 100%, the area of the external electrode 6A is 40% to 60% of the area of the external electrode 6B. The area of the external electrode 6A may be 55% to 60% of the area of the external electrode 6B. Since the area of the external electrode 6A is 40% or more of the area of the external electrode 6B, it is possible to secure a sufficient area for electrical connection to the wiring member 4 or the base plate 2 (here, the base plate 2). becomes. Since the area of the external electrode 6A is 60% or less of the area of the external electrode 6A, the electrostatic capacitance of the piezoelectric element 3 is suppressed from becoming excessive, and the distortion of the base plate 2 is efficiently caused by the piezoelectric element 3. It can be converted into electricity.

As shown in FIGS. 6(a) and 6(b), the external electrode 6A extends along the edge of the main surface 5b of the piezoelectric element 5 when viewed from the normal direction (Z direction) of the main surface 2a of the base plate 2. You may have the drawer part K pulled out to the part. In the example of FIG. 6(a), out of the four sides of the external electrode 6B, lead portions K are respectively provided at the centers of two sides facing each other. In the example of FIG. 6B, lead portions K are provided at the centers of the four sides of the external electrode 6B. The shape of the lead portion K is the same as in the above embodiment. By providing the external electrode 6A with the lead-out portion K, it is possible to electrically connect the plurality of piezoelectric elements 5 through the lead-out portion K in the polarization process before providing the base plate 2. workability can be improved.

The present disclosure is not limited to the above embodiments. For example, in the above-described embodiment, the planar shapes of the base plate 2 and the piezoelectric element 3 are square, but these planar shapes may be other rectangular shapes such as rectangular shapes, circular shapes, and elliptical shapes. , other shapes such as triangular.

Although the wiring member 4 is branched into the first end portion 13A and the second end portion 13B in the above embodiment, the wiring member 4 may not necessarily have such a branched portion. For example, the conductor 9 directed to the first joint portion 21 and the conductor 9 directed to the second joint portion 22 may be branched, and the cover material 10 may cover these conductors 9 and 9 integrally. Further, in the above embodiment, the first joint portion 21 is located off the center of the base plate 2 when viewed in the Z direction, but at least the first joint portion 21 is located on the base plate 2. It may overlap with the center.

DESCRIPTION OF SYMBOLS 1, 31... Pressure sensor 2... Base plate 2a... Main surface 3... Piezoelectric element 5... Piezoelectric element 5a... Main surface (first surface) 5b... Main surface (second surface) 6A... External electrode (first external electrode), 6B external electrode (second external electrode), 8 adhesive, K lead portion.

Claims (9)

a base plate;
a piezoelectric element arranged on the main surface of the base plate and generating an electromotive force corresponding to the stress applied to the base plate;
The piezoelectric element is
a piezoelectric element;
a first external electrode arranged on the first surface side of the piezoelectric element and joined to the main surface of the base plate;
a second external electrode disposed on the second surface side of the piezoelectric element and located on the side opposite to the main surface of the base plate;
A pressure sensor in which the area of the first external electrode and the area of the second external electrode are different from each other. The first external electrode is arranged over the entire first surface of the piezoelectric element,
2. The pressure sensor according to claim 1, wherein the area of said second external electrode is smaller than the area of said first external electrode. 3. The edge portion of the second external electrode is located inside the edge portion of the second surface of the piezoelectric element when viewed from the normal direction of the main surface of the base plate. pressure sensor. 4. The second external electrode according to claim 3, wherein the second external electrode has a lead portion that extends to the edge of the second surface of the piezoelectric element when viewed from the normal direction of the main surface of the base plate. pressure sensor. The second external electrode is arranged on the entire second surface of the piezoelectric body,
2. The pressure sensor according to claim 1, wherein the area of said first external electrode is smaller than the area of said second external electrode. 6. The edge portion of the first external electrode according to claim 5, wherein the edge portion of the first external electrode is located inside the edge portion of the first surface of the piezoelectric element when viewed from the normal direction of the main surface of the base plate. pressure sensor. 7. The first external electrode according to claim 6, wherein the first external electrode has a lead portion that extends to an edge of the first surface of the piezoelectric element when viewed from the normal direction of the main surface of the base plate. pressure sensor. Claims 1 to 7, wherein when the larger one of the area of the first external electrode and the area of the second external electrode is taken as 100%, the smaller one is 40% to 60%. The pressure sensor according to any one of Claims 1 to 3. The pressure sensor according to any one of claims 1 to 8, wherein the first external electrode is fixed to the main surface of the base plate with an adhesive.

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