JP2015190863A - Pressure detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a pressure detector having a bimorph and a pressing surface of glass or other members to have an increased detection sensitivity.SOLUTION: A pressure detector 110 includes a supporting substrate 1 having an input surface 1a on which pressures act and a back surface 1b having a supported edge. A first piezoelectric sheet 3a is arranged in the center part of the back surface 1b of the supporting substrate 1, and a second piezoelectric sheet 3b is arranged on the side of the first piezoelectric sheet 3a opposite to the supporting substrate 1 to face the first piezoelectric sheet 3a. A first detection electrode 4a is arranged on the side of the first piezoelectric sheet 3a opposite to the second piezoelectric sheet 3b, and a second detection electrode 4b is arranged on the side of the second piezoelectric sheet 3b opposite to the first piezoelectric sheet 3a. An intermediate adhesive layer 8 is arranged between the first and second piezoelectric sheets 3a and 3b and has an elastic coefficient of smaller than 10 MPa.

Description

  The present invention relates to a pressure detection device, and more particularly to a pressure detection device using a bimorph obtained by bonding two piezoelectric sheets.

  A pressure sensor using a piezoelectric sheet is known as a device for detecting the amount of pressure on the touch panel (see, for example, Patent Document 1). In the touch input device shown in Patent Document 1, the pressure-sensitive sensors are stacked on the plane of the flexible touch panel so as to be in close contact with each other.

JP 05-61592 A

As a piezoelectric material used for the piezoelectric sheet, there are lead zirconate titanate (PZT), polyvinylidene fluoride (PVDF), and a polymer thereof. However, since these typical piezoelectric materials have pyroelectricity, it is difficult to accurately detect the pressing force.
Therefore, the inventor of the present application has focused on adopting a so-called bimorph structure in which two piezoelectric sheets are bonded to each other with the polarization directions reversed to improve this problem. The bimorph structure mainly has a rectangular or circular bimorph composed of two upper and lower piezoelectric elements. Detection electrodes are provided on both sides of the piezoelectric element. The bimorph structure further includes a frame-like support member attached around the lower surface of the bimorph. The bimorph structure may further have a glass or other member as a protective material on the top surface of the bimorph in order to improve the strength of the piezoelectric element (scratch prevention, crack prevention).

Hereinafter, a mechanism for detecting the pressing force by the bimorph structure will be described. When the upper and lower two piezoelectric elements are bent by the pressing force acting on the central portion, stress σ _u and stress σ _l proportional to the pressing force are generated in the respective upper and lower piezoelectric elements.
In a bimorph structure without glass, the stress σ _u is a negative value because it is a compressive stress, and the stress σ _l is a positive value because it is a tensile stress. In that case, the potential difference appearing between the detection electrodes is proportional to the difference between the stress σ _u and the stress σ _l .
On the other hand, in the bimorph structure to which glass is attached, both the stress σ _u and the stress σ _l are tensile stresses. In this case, since the stress σ _l is larger than the stress σ _u , a potential difference corresponding to the difference appears.

As described above, the inventor of the present application reduces the potential difference between the detection electrodes due to the small difference between the tensile stress σ _u and the tensile stress σ _{l in} the bimorph structure provided with glass (that is, detection) Focusing on the problem of low sensitivity, we invented a means to solve this problem.

  An object of the present invention is to increase detection sensitivity in a pressure detection device having a bimorph and glass or another member as a pressing surface.

  Hereinafter, a plurality of modes will be described as means for solving the problems. These aspects can be arbitrarily combined as necessary.

A pressure detection device according to an aspect of the present invention is a pressure detection device for detecting pressure based on a potential difference between two piezoelectric sheets generated by pressure applied from the outside. The pressure detection device includes a sheet member, a first piezoelectric sheet, a second piezoelectric sheet, a first detection electrode, a second detection electrode, and an elastic body.
The sheet member has a first surface on which pressure acts and a second surface on which the edge is supported.
The first piezoelectric sheet is disposed at the center of the second surface of the sheet member.
The second piezoelectric sheet is disposed opposite the first piezoelectric sheet on the side opposite to the sheet member of the first piezoelectric sheet.
The first detection electrode is disposed on the opposite side of the first piezoelectric sheet from the second piezoelectric sheet.
The second detection electrode is disposed on the opposite side of the second piezoelectric sheet from the first piezoelectric sheet.
The elastic body is disposed between the first piezoelectric sheet and the second piezoelectric sheet. The elastic body has an elastic modulus of less than 10 MPa.

  In this apparatus, when the central portion of the first surface of the sheet member is pressed, the sheet member bends while the edge portion is supported by another member. As a result, the first piezoelectric sheet and the second piezoelectric sheet are also bent. At this time, since the elastic coefficient of the elastic body disposed between the first piezoelectric sheet and the second piezoelectric sheet is less than 10 MPa, the tensile stress of the second piezoelectric sheet is smaller than the tensile stress of the first piezoelectric sheet. . As a result, the amount of charge generated at the first detection electrode becomes larger than the amount of charge generated at the second detection electrode, and the potential difference between the first detection electrode and the second detection electrode becomes sufficiently large. As a result, the pressure detection sensitivity of the pressure detection device is increased.

The elastic coefficient of the elastic body may be 1 MPa or less.
In this apparatus, since the elastic coefficient of the elastic body is 1 MPa or less, the potential difference between the first detection electrode and the second detection electrode becomes sufficiently large.

The thickness of the elastic body may be 5 μm or more.
In this apparatus, since the thickness range is sufficiently wide, the potential difference between the first detection electrode and the second detection electrode is sufficiently large.

The thickness of the elastic body may be 25 to 100 μm.
In this apparatus, since the thickness of the elastic body is set large, the potential difference between the first detection electrode and the second detection electrode is further increased.

The elastic body may be an adhesive that bonds the first piezoelectric sheet and the second piezoelectric sheet.
In this apparatus, the above effects can be obtained by selecting the type of adhesive.

The pressure detection device may further include a second sheet member. The second sheet member is disposed on the side opposite to the sheet member of the second piezoelectric sheet and has an elastic coefficient of 10 GPa or more.
In this apparatus, the potential difference between the first detection electrode and the second detection electrode is further increased by applying a member having a high elastic coefficient as the second sheet member. As a result, the pressure detection sensitivity of the pressure detection device is further increased.

The pressure detection device may further include an adhesive layer. The adhesive layer is disposed between the sheet member and the first and second piezoelectric sheets. The adhesive layer has an elastic coefficient that is 10 times or more the elastic coefficient of the elastic body.
In this apparatus, the potential difference between the first detection electrode and the second detection electrode is further increased by setting the elastic coefficient of the adhesive layer large. As a result, the pressure detection sensitivity of the pressure detection device is further increased.

  In the pressure detection device according to the present invention, since the elastic coefficient of the elastic body disposed between the first piezoelectric sheet and the second piezoelectric sheet is less than 10 MPa, the tensile stress of the second piezoelectric sheet is less than that of the first piezoelectric sheet. It becomes smaller than the tensile stress. This increases the potential difference between the first detection electrode and the second detection electrode. As a result, the pressure detection sensitivity of the pressure detection device is increased.

It is a perspective view of an electronic device. It is sectional drawing of the II-II cross section in FIG. It is sectional drawing of a pressure detector. It is sectional drawing of a pressure detector. It is sectional drawing of a pressure detector (2nd Embodiment). It is sectional drawing of a pressure detector (3rd Embodiment). It is sectional drawing of a touchscreen (4th Embodiment). It is an expanded view of an electrode (4th Embodiment).

1. First Embodiment (1) Outline of Pressure Detector A pressure detector 100 as an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view of an electronic device. 2 is a cross-sectional view taken along the line II-II in FIG.
The pressure detector 100 is a device for measuring the magnitude of the pressing force (load) when pressed by a finger or a pen. In the following description, the front side (upper side in FIG. 2) viewed from the user during use is referred to as the “input surface side” of the pressure detector 100, and the rear side (lower side in FIG. 2) viewed from the user is the pressure. This is referred to as the “back side” of the detector 100.

  As shown in FIG. 1, the electronic device 110 mainly includes a housing 6 and a pressure detector 100. The housing 6 has a rectangular frame shape and is made of synthetic resin. The pressure detector 100 is accommodated in the housing 6.

More specifically, the housing 6 has a recess 6a that opens in a rectangular shape toward the input surface. The recess 6a is formed to have a step, and this step is a support portion 6b. The support portion 6b corresponds to the shape of the recess 6a, that is, is formed in a rectangular frame shape. The support portion 6b corresponds to an edge portion of the back surface 1b of the support substrate 1 to be described later, and has a structure for supporting pressure acting on the support substrate 1. In the recess 6a, a support substrate 1 (to be described later) is accommodated in a first region on the input surface side of the support portion 6b, and a pressure detector 100 is accommodated in a second region on the back side.
In the recess 6 a, the side surface of the first region is in contact with the support substrate 1 with a slight gap, and the side surface of the second region is in contact with the pressure detector 100 with a slight gap. A space 7 is provided between the bottom surface of the housing 6 and the pressure detector 100.

The pressure detector 100 mainly includes a support substrate 1, a piezoelectric sheet 3, and a detection electrode 4. As a basic operation of the pressure detector 100, when the support substrate 1 is pressed, the pressure detector 100 bends, a tensile stress is applied to the piezoelectric sheet 3, and an electric charge is generated. And the pressing force applied to the pressure detector 100 can be detected by the two detection electrodes 4 detecting the electric charge.
More specifically, the pressure detector 100 includes the support substrate 1, the adhesive layer 2, the first detection electrode 4a, the first piezoelectric sheet 3a, the intermediate adhesive layer 8, and the second piezoelectric sheet from the input surface side to the back surface side. 3b and a second detection electrode 4b. Each configuration will be described below. 2 and the like, the position and thickness of each layer are appropriately adjusted for convenience of explanation.

(2) Support substrate The support substrate 1 (an example of a sheet member) is a sheet-like member, and is disposed on the support portion 6 b of the housing 6. The pressure detector 100 has an input surface 1a (first surface). The support substrate 1 has a back surface 1b (second surface) on the side opposite to the input surface 1a. The edge portion of the back surface 1b of the support substrate 1 is fixed so as to be supported by the support portion 6b.
The support substrate 1 preferably has transparency, scratch resistance, antifouling property and the like as a protective plate. Examples of the material for the support substrate 1 include general-purpose resins such as polyethylene terephthalate and acrylic resins, general-purpose engineering resins such as polyacetal resins and polycarbonate resins, super engineering resins such as polysulfone resins and polyphenylsulfide resins, and glass. There is.
In addition, the thickness of the support substrate 1 is 0.4 mm-1.0 mm, for example.
The support substrate 1 has higher rigidity than other members described later.

(3) Piezoelectric Sheet The piezoelectric sheet 3 is fixed to the back surface 1 b of the support substrate 1 through the adhesive layer 2. The piezoelectric sheet 3 is disposed at the center of the back surface 1 b of the support substrate 1.
For example, a transparent optical adhesive is used for the adhesive layer 2. An example of this is a pressure sensitive adhesive (hereinafter referred to as “PSA”). The thickness A of the adhesive layer 2 is 5 μm to 300 μm.
The elastic modulus of the adhesive layer 2 is not limited, but is about 10 MPa, preferably about 10 MPa or more and about 1 GPa. The material of the adhesive layer 2 is, for example, an acrylic, silicone, or epoxy adhesive. The adhesive layer 2 is preferably cured by UV curing or heat curing after bonding the adhesive.

  The piezoelectric sheet 3 is a sheet that generates a potential difference in accordance with the pressing force applied to both sides when the deflection caused by the pressing force is generated. The piezoelectric sheet 3 includes a first piezoelectric sheet 3a and a second piezoelectric sheet 3b. Both sheets have the same shape and face each other. The first piezoelectric sheet 3a is disposed on the back surface 1b side of the support substrate 1, and the second piezoelectric sheet 3b is disposed on the back surface side of the first piezoelectric sheet 3a (the side opposite to the support substrate 1 of the first piezoelectric sheet 3a). . The first piezoelectric sheet 3a and the second piezoelectric sheet 3b are bonded to each other via an intermediate adhesive layer 8 made of PSA. The intermediate adhesive layer 8 will be described later.

(4) Detection electrode The detection electrode 4 includes a first detection electrode 4a and a second detection electrode 4b. The first detection electrode 4a is disposed between the support substrate 1 (specifically, the adhesive layer 2) and the first piezoelectric sheet 3a (that is, the side opposite to the second piezoelectric sheet 3b of the first piezoelectric sheet 3a), The two detection electrodes 4b are arranged on the back side of the first piezoelectric sheet 3a (that is, the side opposite to the first piezoelectric sheet 3a of the second piezoelectric sheet 3b).
Note that the first detection electrode 4a and the second detection electrode 4b are made of a conductive material. Examples of the conductive material include transparent conductive oxides such as indium-tin oxide (ITO), tin-zinc oxide (TZO), and polyethylenedioxythiophene. A conductive polymer such as (Polyethylenedioxythiophene, PEDOT) can be used. In this embodiment, the detection electrode 4 is directly formed on the surface of the piezoelectric sheet 3 by using, for example, vapor deposition or screen printing.
In addition, the thickness of the detection electrode 4 can be 1 nm-30,000 nm, for example.

Alternatively, a conductive metal such as copper or silver may be used as the conductive material. In this case, the detection electrode may be formed on the piezoelectric sheet by vapor deposition, or may be formed using a metal paste such as a copper paste or a silver paste. Note that the detection electrode made of metal may have a mesh structure in order to improve translucency.
The detection electrode formed on the surface of a resin film or the like using vapor deposition or screen printing may be fixed to a support substrate or a piezoelectric sheet with an adhesive (for example, the third embodiment).

  Furthermore, as a material having conductivity, a material in which a conductive material such as carbon nanotube, metal particle, or metal nanofiber is dispersed in a binder may be used.

(5) Detector A detector (not shown) is a device that detects the pressing amount from the voltage signal detected by the detection electrode. The detector includes a charge amplifier using an operational amplifier.

(6) Pressing means Note that the pressing means for applying pressure to the pressure detector 100 is not particularly limited as long as it can apply pressure. Examples of the pressing means include a finger and a stylus ben.

(7) Detailed Description of Piezoelectric Sheet As the material of the first piezoelectric sheet 3a and the second piezoelectric sheet 3b, a sheet obtained by forming a ferroelectric material into a sheet shape and then polarizing it in the thickness direction can be used. Examples of the ferroelectric material include PVDF, copolymers such as PVDF and TrFE, ETFE, and PZT. The first piezoelectric sheet 3a and the second piezoelectric sheet 3b are laminated so that the polarization directions are opposite to each other.
A combination of materials of the first piezoelectric sheet 3a and the second piezoelectric sheet 3b is not particularly limited. However, it is preferable that the material which has the same characteristic is used for both sheets. This is because the output from the piezoelectric sheet caused by the thermal stress due to temperature change and the pyroelectric effect can be canceled.

  A mechanism for canceling the output due to the pyroelectric effect in the piezoelectric sheet will be described with reference to FIG. FIG. 3 is a cross-sectional view of the pressure detector.

When the 1st piezoelectric sheet 3a and the 2nd piezoelectric sheet 3b are comprised from a ferroelectric material, the 1st piezoelectric sheet 3a and the 2nd piezoelectric sheet 3b are comprised so that the polarization direction in a non-pressing state may become a mutually reverse direction It is preferable that With the above configuration, when a temperature change occurs in the pressure detector 100 and a pyroelectric effect occurs in the piezoelectric sheet 3, as shown in FIG. 3, the input of the first piezoelectric sheet 3a is performed. The same positive and negative charges are generated on the surface side and the back side of the second piezoelectric sheet 3b.
When the first piezoelectric sheet 3a and the second piezoelectric sheet 3b are made of a material having a sufficiently small thickness (for example, 5 μm to 50 μm) and the same characteristics, the back surface of the first piezoelectric sheet 3a and the second piezoelectric sheet are formed. Between the surfaces on the input surface side of the sheet 3b, the potentials are substantially equal. As a result, between the surface on the input surface side of the first piezoelectric sheet 3a and the surface on the back surface side of the second piezoelectric sheet 3b, It is derived that the potentials are equal.

  Therefore, when configured as described above, when the piezoelectric sheet 3 is affected by the pyroelectric effect, the potential of the surface on the input surface side of the first piezoelectric sheet 3a generated due to the pyroelectric effect and the second piezoelectric sheet The potentials on the back side of 3b are substantially equal. Then, in the pressure detector 100, when the first piezoelectric sheet 3a and the second piezoelectric sheet 3b are affected by the pyroelectric effect, the potential difference due to the pyroelectric effect as the piezoelectric sheet 3 detected by the detection electrode 4 is It becomes almost “0”. Therefore, even if the pyroelectric effect is generated in the first piezoelectric sheet 3a and the second piezoelectric sheet 3b, the piezoelectric sheet 3 as a whole hardly detects a potential difference due to the pyroelectric effect. That is, when the piezoelectric sheet 3 (the first piezoelectric sheet 3a and the second piezoelectric sheet 3b) is made of a ferroelectric material, the piezoelectric sheet 3 and the detection electrode 4 are configured as described above, so that the temperature changes. The accompanying malfunction (particularly malfunction due to the pyroelectric effect) hardly occurs.

(8) Intermediate adhesive layer As described above, the intermediate adhesive layer 8 is disposed between the first piezoelectric sheet 3a and the second piezoelectric sheet 3b. For the intermediate adhesive layer 8, for example, PSA is used.

The intermediate adhesive layer 8 is made of a softer material than the conventional one and has an elastic modulus of less than 10 MPa. The elastic modulus of the intermediate adhesive layer 8 is preferably 1 MPa or less. More specifically, the elastic modulus of the intermediate adhesive layer 8 is preferably in the range of 0.05 MPa to 1 MPa, more preferably in the range of 0.1 MPa to 0.3 MPa. As described above, in this embodiment, the intermediate adhesive layer 8 functions as an elastic body having a relatively low elastic coefficient between the first piezoelectric sheet 3a and the second piezoelectric sheet 3b.
The intermediate adhesive layer 8 only needs to realize the above elastic modulus, and the type of material is not particularly limited. However, the intermediate adhesive layer 8 is made of, for example, an acrylic adhesive or a silicone adhesive. This is because any of the pressure-sensitive adhesives has a low elastic modulus because it has a low molecular weight and a low crosslinking density.

  The thickness of the intermediate adhesive layer 8 is 5 μm or more. More preferably, the thickness of the intermediate adhesive layer 8 is in the range of 25 to 100 μm.

The charge generation mechanism when pressure is applied to the pressure detector 100 will be described with reference to FIG. FIG. 4 is a cross-sectional view of the pressure detector.
As shown in FIG. 4, when the pressure detector 100 is pressed, the support substrate 1 has higher rigidity than the piezoelectric sheet 3 and the detection electrode 4, so that the piezoelectric sheet 3 (first piezoelectric sheet 3 a And a tensile stress is generated in the second piezoelectric sheet 3b). At this time, a tensile stress σ _u is generated in the first piezoelectric sheet 3a, and a tensile stress σ _l is generated in the second piezoelectric sheet 3b. As a result, charges corresponding to the tensile stress are respectively generated on the input surface side surface and the back surface surface of the first piezoelectric sheet 3a and the second piezoelectric sheet 3b. Due to the generated charges, a potential difference is generated between the input surface side and the back surface of each of the first piezoelectric sheet 3a and the second piezoelectric sheet 3b. The potential difference V ₁ ′ generated between the first piezoelectric sheets 3a is the difference between the potential on the input surface side of the first piezoelectric sheet 3a and the potential on the back surface side, and the potential difference V ₁ ′ is the magnitude of the tensile stress σ _u. It is proportional. The potential difference V ₂ ′ generated between the second piezoelectric sheets 3b is a difference between the potential on the input surface side and the potential on the back surface side of the second piezoelectric sheet 3b, and the potential difference V ₂ ′ is the magnitude of the tensile stress σ _l . It is proportional to

In this embodiment, the tensile stress σ _l is smaller than the tensile stress σ _u , so that the absolute value of the potential difference V ₂ is smaller than the absolute value of the potential difference V ₁ . Therefore, the detection sensitivity of the pressure detector 100 is high. Such an effect was obtained because the intermediate adhesive layer 8 having the above characteristics was newly provided.

In addition to the above configuration, when the thickness of the intermediate adhesive layer 8 exceeds 5 μm, the above effect is further enhanced. The intermediate adhesive layer 8 preferably has a thickness of about 25 μm.
In addition to the above configuration, when the elastic modulus of the adhesive layer 2 is 10 times or more the elastic modulus of the intermediate adhesive layer 8, the above effect is further enhanced. Specifically, the elastic modulus of the adhesive layer 2 is 10 MPa or more, and preferably about 1 GPa. In this case, it is preferable that the elastic modulus of the adhesive layer 2 is 10 times or more that of the intermediate adhesive layer.

  In the first embodiment, only the intermediate adhesive layer 8 is disposed between the first piezoelectric sheet 3a and the second piezoelectric sheet 3b. However, the configuration is not limited to the adhesive layer alone as long as the elastic body satisfies the above characteristics. For example, the elastic body may be composed of a core sheet and an adhesive on both sides. In addition, a sheet that realizes optical characteristics may be used for a part of the elastic body.

  The simulation results performed to show the principle and effect of the first embodiment will be described below. The simulation has the same structure as that of the above embodiment, and a bimorph (corresponding to the piezoelectric sheet 3) is pasted on glass (corresponding to the support substrate 1), and the four sides are both surfaces on the base (corresponding to the casing 6 of the electronic device 110). A pressure detector (corresponding to the pressure detector 100) fixed with a tape was assumed. In this pressure detector, the condition of applying a force of 1 N to the central portion of the glass was adopted. The piezoelectric sheet assumed a film-like PVDF copolymer. The glass size is, for example, 120 mm × 60 mm, and the thickness is, for example, 0.55 mm. FEM simulation software was used for the simulation.

表１において、２枚の圧電シート（第１圧電シート３ａ及び第２圧電シート３ｂに相当）を弾性体（中間接着層８に相当）によって接着してなるバイモルフを、接着剤（接着層２に相当）でガラスに貼り合せた場合のシミュレーション結果である。Ｘ方向とＹ方向はそれぞれ上面図の長辺方向と短辺方向であり、上側の第１圧電シート（ＰＩＥＺＯ Ｕ）と下側の第２圧電シート（ＰＩＥＺＯ Ｌ）からなる圧電シートに加わる応力をＸとＹ方向について算出した。

In Table 1, a bimorph formed by bonding two piezoelectric sheets (corresponding to the first piezoelectric sheet 3a and the second piezoelectric sheet 3b) with an elastic body (corresponding to the intermediate adhesive layer 8) is used as an adhesive (adhering to the adhesive layer 2). It is a simulation result at the time of pasting together on glass. The X direction and the Y direction are the long side direction and the short side direction in the top view, respectively, and stress applied to the piezoelectric sheet composed of the upper first piezoelectric sheet (PIEZO U) and the lower second piezoelectric sheet (PIEZO L). Calculations were made in the X and Y directions.

  Simulation No. A3, A4, A5, A6, A7, A10, A11, A12, A13, and A14 are examples that satisfy the minimum conditions of this embodiment. A1, A2, A8, and A9 are reference examples that do not satisfy the minimum conditions of this embodiment. A1 to A7 are cases where the elastic coefficient of the elastic body between the glass and the piezoelectric sheet is low (10 MPa), and A8 to A14 are high and the elastic coefficient of the elastic body between the glass and the piezoelectric sheet is high. (1 GPa).

  When the elastic body does not exist as in Reference Example A1, that is, when bonded with an extremely thin and very hard adhesive, the tensile stress generated in the second piezoelectric sheet is greater than the tensile stress generated in the first piezoelectric sheet. Further, the difference (σux−σlx, σuy−σly) is not so large. On the contrary, when the elastic body is interposed (elastic coefficient 1 MPa) as in Example A4, the tensile stress generated in the second piezoelectric sheet is the first piezoelectric sheet, contrary to the case where the elastic body is not present. It is smaller than the generated tensile stress, and the difference (σux−σlx, σuy−σly) is larger than that of Reference Example A1.

When the elastic body is further softened or thickened, the difference (σux−σlx, σuy−σly) between the tensile stress generated in the second piezoelectric sheet and the tensile stress generated in the first piezoelectric sheet increases. Examples in which the elastic modulus of the example A4 is further reduced are examples A5, A6, and A7. Example A6 is an example in which the elastic modulus is the same as Example A5 but the thickness is increased. In either case, more preferable results are obtained.
Example A3 and Example A4 have the same elastic modulus, but the thickness of Example A4 is larger. As a result, the difference in tensile stress generated in Example A4 is larger than that in Example A3. The relationship between Example A5 and Example A6, the relationship between Example A10 and Example A11, and the relationship between Example A12 and Example A13 are the same.
As described above, it is understood that the pressure detection sensitivity of the pressure detector can be increased by forming an elastic body between the piezoelectric sheets and making it softer or thicker.

  When Examples A3 to A7 (the adhesive layer between the glass and the piezoelectric sheet is soft) and Examples A10 to A14 (the adhesive layer between the glass and the piezoelectric sheet are hard) are compared, the latter is more It can be seen that a large difference in tensile stress is obtained. From this fact, when the adhesive that bonds the glass and bimorph is hardened, the tensile stress generated in the second piezoelectric sheet becomes smaller than the tensile stress generated in the first piezoelectric sheet, and the pressure detection sensitivity of the pressure detector is increased. You can see that

2. Second Embodiment A pressure detector 100A according to a second embodiment will be described with reference to FIG.
The basic structure of the pressure detector 100A is the same as the pressure detector 100 of the first embodiment. Therefore, only different points will be described here.

The pressure detector 100A includes a display device 5 (an example of a second sheet member) in addition to the structure of the first embodiment. The display device 5 is fixed to the back side of the second detection electrode 4b through the adhesive layer 9. The display device 5 is composed of an LCD or an organic EL. The display device 5 has higher rigidity than the piezoelectric sheet 3.
In this way, the pressure detector 100A includes the support substrate 1, the adhesive layer 2, the first detection electrode 4a, the first piezoelectric sheet 3a, the intermediate adhesive layer 8, and the second piezoelectric sheet from the input surface side toward the back surface side. 3b, the second detection electrode 4b, the adhesive layer 9, and the display device 5.

Also in this embodiment, the tensile stress σ _l is smaller than the tensile stress σ _u by lowering the elastic modulus of the intermediate adhesive layer 8, and thereby the potential difference V ₁ is larger than the potential difference V ₂ . Therefore, the detection sensitivity of the pressure detector 100B is high.
Further, by providing the display device 5 on the back side of the piezoelectric sheet 3, the tensile stress generated in the second piezoelectric sheet is further smaller than the tensile stress generated in the first piezoelectric sheet as compared with the first embodiment. The pressure detection sensitivity of the pressure detector can be increased.

Also, if the elastic body is further softened or thickened under these conditions, the tensile stress generated in the second piezoelectric sheet 3b becomes negative (that is, compressive stress is generated). As a result, the pressure detection sensitivity of the pressure detector can be further increased.
Further, by providing the display device 5, the bending rigidity of the pressure detector 100A is also improved. That is, a pressure detector with less deflection even when pressure is applied.
Note that the same effect can be obtained by providing a separate hard material such as glass instead of the display device. However, in any case, it is preferable that the elastic coefficient of the member attached to the lowermost surface of the pressure detector is 10 GPa or more.

  The simulation results performed to show the principle and effect of the second embodiment will be described below.

表２において、２枚の圧電シート（第１圧電シート３ａ及び第２圧電シート３ｂに相当）を弾性体（中間接着層８に相当）によって接着してなるバイモルフ（圧電シート３に相当）を、接着剤（接着層２に相当）でガラス（支持基板１に相当）に貼り合せ、さらにガラス（ディスプレイ装置５に相当）を圧電シートの背面側に設けた場合のシミュレーション結果である。Ｘ方向とＹ方向はそれぞれ上面図の長辺方向と短辺方向であり、上側の第１圧電シート（ＰＩＥＺＯ Ｕ）と下側の第２圧電シート（ＰＩＥＺＯ Ｌ）からなる圧電シートに加わる応力をＸ方向とＹ方向について算出した。

In Table 2, a bimorph (corresponding to the piezoelectric sheet 3) formed by bonding two piezoelectric sheets (corresponding to the first piezoelectric sheet 3a and the second piezoelectric sheet 3b) with an elastic body (corresponding to the intermediate adhesive layer 8), It is a simulation result in the case of bonding to glass (corresponding to the support substrate 1) with an adhesive (corresponding to the adhesive layer 2) and further providing glass (corresponding to the display device 5) on the back side of the piezoelectric sheet. The X direction and the Y direction are the long side direction and the short side direction in the top view, respectively, and stress applied to the piezoelectric sheet composed of the upper first piezoelectric sheet (PIEZO U) and the lower second piezoelectric sheet (PIEZO L). Calculations were made for the X and Y directions.

Simulation No. B3 to B7 are examples that satisfy the minimum conditions of this embodiment. B1 to B2 are reference examples that do not satisfy the minimum conditions of this embodiment.
When Examples B3 to B7 are compared with Examples A3 to A7 of the first embodiment in which the elastic modulus and thickness conditions of the elastic body are the same, Examples B3 to B7 are different from Examples A3 to A7. In comparison, the difference between the generated tensile stresses is larger. From the above, it can be seen that the detection sensitivity of the pressure detector can be further enhanced by fixing a highly rigid sheet to the back side of the piezoelectric sheet.

3. Third Embodiment A pressure detector 100B as a third embodiment will be described with reference to FIG. FIG. 6 is a cross-sectional view of the pressure detector.
The pressure detector 100B has the same basic structure as the first embodiment. Therefore, only different points will be described here.

  In this embodiment, the detection electrode is formed on the surface of the resin film using vapor deposition or screen printing. Specifically, the first detection electrode 4 a is formed on the back surface of the resin film 11. The resin film 11 is fixed to the piezoelectric sheet 3 through the adhesive layer 12. Further, the resin film 11 is fixed to the support substrate 1 through the adhesive layer 2. The second detection electrode 4 b is formed on the input side surface of the resin film 13. The resin film 13 is fixed to the back surface of the piezoelectric sheet 3 through the adhesive layer 14.

In this manner, the pressure detector 100B includes the support substrate 1, the adhesive layer 2, the resin film 11 (including the first detection electrode 4a), the adhesive layer 12, and the first piezoelectric sheet from the input surface side toward the back surface side. 3a, intermediate adhesive layer 8, second piezoelectric sheet 3b, adhesive layer 14, and resin film 13 (including second detection electrode 4b).
Also in this embodiment, the tensile stress σ _l is smaller than the tensile stress σ _u by lowering the elastic modulus of the intermediate adhesive layer 8, and thereby the potential difference V ₁ is larger than the potential difference V ₂ . Therefore, the detection sensitivity of the pressure detector 100B is high.
Furthermore, the above effect can be further enhanced by increasing the thickness of the intermediate adhesive layer 8.

  Furthermore, when the elastic modulus of the adhesive layer 2, the adhesive layer 12, and the adhesive layer 14, which are adhesive layers other than the intermediate adhesive layer 8, is 10 times or more the elastic modulus of the intermediate adhesive layer 8, the above effect is further enhanced. Become. Specifically, the elastic modulus of these adhesive layers is 10 MPa or more, preferably about 1 GPa.

  The simulation results performed to show the principle and effect of the third embodiment will be described below.

表３は、２枚の圧電シート（第１圧電シート３ａ及び第２圧電シート３ｂに相当）を弾性体（中間接着層８に相当）によって接着してバイモルフ（圧電シート３に相当）とし、第１検出電極（第１検出電極４ａに相当）を形成した樹脂フィルム（樹脂フィルム１１に相当）及び第２検出電極（第２検出電極４ｂに相当）を形成した樹脂フィルム（樹脂フィルム１３に相当）をバイモルフに固定し、さらに接着剤（接着層２に相当）でガラス（支持基板１に相当）に貼り合わせた場合のシミュレーション結果である。Ｘ方向とＹ方向はそれぞれ上面図の長辺方向と短辺方向であり、上側の第１圧電シート（ＰＩＥＺＯ Ｕ）と下側の第２圧電シート（ＰＩＥＺＯ Ｌ）からなる圧電シートに加わる応力をＸ方向とＹ方向について算出した。

Table 3 shows that two piezoelectric sheets (corresponding to the first piezoelectric sheet 3a and the second piezoelectric sheet 3b) are bonded by an elastic body (corresponding to the intermediate adhesive layer 8) to form a bimorph (corresponding to the piezoelectric sheet 3). A resin film (corresponding to the resin film 11) on which one detection electrode (corresponding to the first detection electrode 4a) is formed and a resin film (corresponding to the resin film 13) on which the second detection electrode (corresponding to the second detection electrode 4b) is formed. Is a simulation result in a case where is fixed to bimorph and further bonded to glass (corresponding to the support substrate 1) with an adhesive (corresponding to the adhesive layer 2). The X direction and the Y direction are the long side direction and the short side direction in the top view, respectively, and stress applied to the piezoelectric sheet composed of the upper first piezoelectric sheet (PIEZO U) and the lower second piezoelectric sheet (PIEZO L). Calculations were made for the X and Y directions.

  Simulation No. C3 to C7 and C10 to C14 are examples in which the minimum conditions of this embodiment are satisfied. C1-C2 and C8-C9 are reference examples that do not satisfy the minimum conditions of this embodiment.

  Examples C3 to C7 (adhesive layer between glass and piezoelectric sheet, and adhesive layer between each resin film and piezoelectric sheet are soft) and Examples C10 to C14 (adhesive layer between glass and piezoelectric sheet) And the adhesive layer between each resin film and the piezoelectric sheet are harder), it can be seen that a greater difference in tensile stress is obtained in the latter. Accordingly, when the elastic modulus of the adhesive other than the elastic body is increased, the difference between the tensile stress generated in the second piezoelectric sheet and the tensile stress generated in the first piezoelectric sheet is further increased, thereby pressing the pressure detector. It can be seen that the detection sensitivity can be increased.

  Next, using Table 4, the result of measuring the output of the actually manufactured pressure detector is shown below. The layer structure of the pressure detector is the same as in the third embodiment. PSAmid (corresponding to the intermediate adhesive layer 8), which is a soft adhesive layer, was provided between the bimorph (corresponding to the piezoelectric sheet 3) piezoelectric sheets (corresponding to the first piezoelectric sheet 3a and the second piezoelectric sheet 3b). Further, a bimorph (corresponding to the piezoelectric sheet 3) is sandwiched between ITO films (corresponding to the resin film 11 and the resin film 13) from both sides, and further, PSA1 (corresponding to the adhesive layer 2) is placed on the glass (corresponding to the support substrate 1). A pressure detector (corresponding to the pressure detector 100b) having a structure adhered to the above was made as a prototype. The ITO film was attached to the bimorph via PSA2 (corresponding to the adhesive layer 12) and PSA3 (corresponding to the adhesive layer 14). And the electric power which came out by applying a press was detected with the charge amplifier (not shown) as an electric charge.

参考例としてのセンサ１では、ＰＳＡ１，ＰＳＡ２、ＰＳＡ３及びＰＳＡｍｉｄ（中間接着層８に相当）に薄くて硬いものを採用した。この場合、各ＰＳＡは、貼合せを行った後、ＵＶ硬化させており、硬化後の弾性係数は約３ＧＰａであった。この場合、５００ｇの加圧で０．５２ｎＣの電荷出力が観察された。

In the sensor 1 as a reference example, thin and hard PSA1, PSA2, PSA3, and PSAmid (corresponding to the intermediate adhesive layer 8) were used. In this case, each PSA was UV cured after pasting, and the elastic modulus after curing was about 3 GPa. In this case, a charge output of 0.52 nC was observed at a pressure of 500 g.

  In the sensor 2 as an example, thin and hard PSA1, PSA2 and PSA3 were used, but soft PSAmid (corresponding to the intermediate adhesive layer 8) was used. The elastic modulus of ordinary PSA in PSAmid was about 0.1 MPa. The charge having the opposite sign to that of the sensor 1 was detected, and the amount thereof was 1.55 nC, which is three times that of the sensor 1, and an effect was seen.

4). Fourth Embodiment In the first to third embodiments, the bimorph of the pressure detector is fixed to the support substrate 1, but the present invention is not limited to these embodiments. The bimorph of the pressure detector may be fixed to the back surface of the touch panel. In this case, not only the pressing force but also the pressing position can be detected.
Examples of the touch panel include a capacitance method, a resistance film method, and an optical method. The case of the electrostatic capacity method will be described below.

Hereinafter, the touch panel 110 </ b> C will be described with reference to FIGS. 7 and 8. FIG. 7 is a cross-sectional view of the touch panel. FIG. 8 is a development view of the electrodes.
The basic structure of the pressure detector 100C included in the touch panel 110C is the same as in the first to third embodiments. Therefore, description of common parts is omitted. However, the pressure detector 100C has the display device 5 on the rearmost side as in the second embodiment. In the pressure detector 100, the first detection electrode 4a and the second detection electrode 4b are formed on the resin film 11 and the resin film 13, respectively, as in the third embodiment.

  As shown in FIGS. 7 and 8, the touch panel 110C includes a touch sensor 51 in addition to the pressure detector 100C. The touch sensor 51 mainly has an upper electrode 53 and a lower electrode 55.

  A plurality of upper electrodes 53 are formed on the input side surface of the resin film 11. The plurality of upper electrodes 53 are arranged in parallel to each other so as to be arranged at a predetermined interval in the Y-axis direction. In the present embodiment, the upper electrode 53 is formed in a stripe shape (a linear shape having a constant width). The upper electrode 53 may be formed in, for example, a wave shape or a zigzag shape. In any case, each of the upper electrodes 53 is formed so as to extend along the X-axis direction as a whole.

  Moreover, it is preferable that the upper electrode 53 is configured using a material having excellent transparency. Examples of materials that satisfy such requirements include metal oxides such as tin oxide, indium oxide, antimony oxide, zinc oxide, cadmium oxide, and ITO (Indium Tin Oxide), silver nanowires, carbon nanotubes, and conductive polymers. First class is exemplified. The upper electrode 53 is a transparent conductive film formed using these materials, and the thickness thereof can be set to, for example, 5 nm to 5000 nm. In the present embodiment, the upper electrode 53 is composed of an ITO thin film. In this case, the upper electrode 53 is formed on the input side surface of the resin film 11 using vapor deposition or screen printing, and is fixed to the support substrate 1 with the adhesive layer 2. The upper electrode may be directly formed on the back surface of the support substrate 1 using vapor deposition, screen printing, or the like. The thickness of the upper electrode 53 is, for example, 1 nm to 20 μm.

In the present embodiment, a plurality of lower electrodes 55 are formed on the back side of the upper electrode 53. The plurality of lower electrodes 55 are arranged in parallel to each other so as to be arranged at a predetermined interval in the X-axis direction. In the present embodiment, the lower electrode 55 is formed in a stripe shape (a linear shape having a constant width). The lower electrode 55 may be formed in a wave shape or a zigzag shape, for example. In any case, each of the lower electrodes 55 is formed so as to extend along the Y-axis direction as a whole. Thereby, the upper electrode 53 and the lower electrode 55 are arranged so as to intersect with each other (in this example, orthogonal) in plan view. As with the upper electrode 53, the lower electrode 55 is preferably made of a material having excellent transparency. The material and thickness of the lower electrode 55 are the same as those of the upper electrode 53. The method for forming the lower electrode 55 is the same as that for the upper electrode 53.
In this embodiment, the lower electrode 55 is formed on the surface of the resin film 13 using vapor deposition, screen printing, or the like, and is fixed to the first piezoelectric sheet 3a via the adhesive layer 12.
The upper electrode 53 and the lower electrode 55 may have a mesh structure made of a conductive metal such as silver or copper, like the detection electrode.

  Each of the plurality of upper electrodes 53 is connected to a detection circuit (not shown) via a lead wiring. The plurality of lower electrodes 55 are also connected to the detection circuit via routing wires. Note that the routing wiring is configured using a metal such as gold, silver, copper, and nickel, or a conductive base such as carbon.

  In this embodiment, the lower electrode 55 is also used as the first detection electrode 4a of the pressure detector 100C. This eliminates the need for a separate layer for insulating both electrodes, thus reducing the weight and thickness of the device. Also, the electrode material is reduced.

  The touch panel 110C includes a control unit (not shown) including an arithmetic processing unit such as a CPU, and the control unit is configured to perform position detection calculation and pressing force detection calculation. Specifically, when the user's finger or the like is touched on the touch panel 110C (input surface 1a), the capacitance between the upper electrode 53 and the user's finger or the like, the lower electrode 55 and the user's finger or the like The capacitance between them changes. The control unit can determine the pressing position in the XY coordinate system on the input surface 1a based on the change in capacitance obtained from the detector. When the user's finger or the like is touched on the touch panel 110C, the potential difference between the piezoelectric sheets 3 changes according to the magnitude of the applied pressing force as described above. The control unit can determine the magnitude of the pressing force applied in the direction (Z direction) orthogonal to the input surface 1 a by detecting the potential difference change of the piezoelectric sheet 3.

In addition, when using a pressure detector and a touch panel in combination, it is not always necessary to share the electrodes.
Further, the layer configuration of the above-described device is one embodiment, and the present invention is not limited to this.

5. Common Items of Embodiments The first to fifth embodiments have the following configurations and functions in common.
The pressure detection devices (for example, pressure detectors 100, 100A, 100B, and 100C) are pressure detection devices for detecting pressure based on a potential difference between two piezoelectric sheets generated by pressure applied from the outside. . The pressure detection device includes a sheet member, a first piezoelectric sheet, a second piezoelectric sheet, a first detection electrode, a second detection electrode, and an elastic body.
The sheet member (for example, support substrate 1, touch panel) has a first surface (for example, input surface 1a) on which pressure acts and a second surface (for example, back surface 1b) on which the edge is supported.
The first piezoelectric sheet (for example, the first piezoelectric sheet 3a) is disposed at the center of the second surface of the sheet member.
The second piezoelectric sheet (for example, the second piezoelectric sheet 3b) is disposed to face the first piezoelectric sheet on the side opposite to the sheet member of the first piezoelectric sheet.
The first detection electrode (for example, the first detection electrode 4a) is disposed on the opposite side of the first piezoelectric sheet from the second piezoelectric sheet.
The second detection electrode (for example, the second detection electrode 4b) is disposed on the opposite side of the second piezoelectric sheet from the first piezoelectric sheet.
The elastic body (for example, the intermediate adhesive layer 8) is disposed between the first piezoelectric sheet and the second piezoelectric sheet. The elastic body has an elastic modulus of less than 10 MPa.

In this apparatus, when the central portion of the first surface of the sheet member is pressed, the sheet member bends while the edge portion is supported by the support portion (see FIG. 4). As a result, the first piezoelectric sheet and the second piezoelectric sheet are also bent. At this time, since the elastic coefficient of the elastic body disposed between the first piezoelectric sheet and the second piezoelectric sheet is less than 10 MPa, the tensile stress (for example, σ _l ) of the second piezoelectric sheet is the first piezoelectric sheet. Less than the tensile stress (for example, σ _u ). As a result, the amount of charge generated at the first detection electrode becomes larger than the amount of charge generated at the second detection electrode, and the potential difference between the first detection electrode and the second detection electrode becomes sufficiently large. As a result, the pressure detection sensitivity of the pressure detection device is increased.

6). Other Embodiments Although a plurality of embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. In particular, a plurality of embodiments and modifications described in this specification can be arbitrarily combined as necessary.

  The present invention can be widely applied to a pressure detection device, particularly a pressure detection device using a bimorph obtained by bonding two piezoelectric sheets.

1: support substrate 1a: input surface 2: adhesive layer 3: piezoelectric sheet 3a: first piezoelectric sheet 3b: second piezoelectric sheet 4: detection electrode 4a: first detection electrode 4b: second detection electrode 5: display device 6: Housing 6a: Recess 6b: Support 7: Space 8: Intermediate adhesive layer 9: Adhesive layer 11: Resin film 12: Adhesive layer 13: Resin film 14: Adhesive layer 100: Pressure detector 100A: Pressure detector 100B: Pressure detector 110: electronic equipment 110C: touch panel? uj: tensile stress Shigumaeru: tensile stress _{V 1:} a potential difference _{V 2:} potential difference

Claims (7)

A pressure detection device for detecting the pressure based on a potential difference between two piezoelectric sheets generated by pressure applied from the outside,
A sheet member having a first surface on which the pressure acts and a second surface on which an edge is supported;
A first piezoelectric sheet disposed in the center of the second surface of the sheet member;
A second piezoelectric sheet disposed opposite to the first piezoelectric sheet on a side opposite to the sheet member of the first piezoelectric sheet;
A first detection electrode disposed on the opposite side of the first piezoelectric sheet from the second piezoelectric sheet;
A second detection electrode disposed on the opposite side of the first piezoelectric sheet to the second piezoelectric sheet;
An elastic body having an elastic coefficient of less than 10 MPa, disposed between the first piezoelectric sheet and the second piezoelectric sheet;
A pressure detection device.   The pressure detection device according to claim 1, wherein an elastic coefficient of the elastic body is 1 MPa or less.   The pressure detection device according to claim 1, wherein the elastic body has a thickness of 5 μm or more.   The pressure detection device according to claim 3, wherein the elastic body has a thickness of 25 to 100 μm.   The pressure detection device according to claim 1, wherein the elastic body is an adhesive that bonds the first piezoelectric sheet and the second piezoelectric sheet.   The pressure detection device according to claim 1, further comprising a second sheet member that is disposed on a side opposite to the sheet member of the second piezoelectric sheet and has an elastic coefficient of 10 GPa or more.   The adhesive layer which has an elastic coefficient 10 times or more of an elastic coefficient of the elastic body arranged between the sheet member, the first piezoelectric sheet, and the second piezoelectric sheet is further provided. The pressure detection device according to any one of 6.

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