Piezoelectric element

Abstract

The present invention provides a piezoelectric element that easily utilizes piezoelectricity by converting shear deformation into tensile deformation. The piezoelectric element is characterized by including: an electret layer containing a helical chiral polymer crystal exhibiting piezoelectricity, a first electrode layer, a second electrode layer, a first connection portion provided on the side of the first electrode layer opposite to the piezoelectric body layer, and a second connection portion provided on the side of the second electrode layer opposite to the piezoelectric body layer. When viewed along the thickness direction of the piezoelectric body layer, the overlapping repeating portions of the piezoelectric body layer, the first electrode layer, and the second electrode layer are circular, and when viewed along the thickness direction of the piezoelectric body layer, the first connection portion and the second connection portion overlap with the center of the repeating portion.

Description

Technical Field

[0001] The present invention relates to a piezoelectric element. Background Art

[0002] Piezoelectric polymers are used in various forms because of the unique processability of polymer materials. For example, Patent Document 1 discloses a cord-shaped piezoelectric element formed by winding and covering a piezoelectric fiber formed of a piezoelectric polymer around the surface of a conductive fiber formed of a conductive material. In such a cord-shaped piezoelectric element, a piezoelectric fiber containing a piezoelectric polymer uniaxially oriented along the fiber axis is used. In addition, Patent Document 1 discloses that the winding angle of the piezoelectric fiber with respect to the conductive fiber is in an inclined direction of 15° or more and 75° or less. By setting the winding angle within such a range, shear stress can be generated in the piezoelectric fiber, and a large electric signal can be extracted via the conductive fiber by the piezoelectric effect.

[0003] Patent Document 1: International Publication No. 2016 / 175321

[0004] However, the structure of the cord-shaped piezoelectric element is complex and difficult to manufacture. In addition, due to the special shape of the cord-shaped piezoelectric element, there is a technical problem that it is not easy to use as a piezoelectric element. Summary of the Invention

[0005] The piezoelectric element according to an example of the present invention is characterized by including: a piezoelectric body layer having a first surface and a second surface having a front-back relationship with each other and containing a helical chiral polymer crystal showing piezoelectricity; a first electrode layer provided on the first surface of the piezoelectric body layer; a second electrode layer provided on the second surface of the piezoelectric body layer; a first connection portion provided on the side of the first electrode layer opposite to the piezoelectric body layer; and a second connection portion provided on the side of the second electrode layer opposite to the piezoelectric body layer. When viewed along the thickness direction of the piezoelectric body layer, a repeating portion where the piezoelectric body layer, the first electrode layer, and the second electrode layer overlap each other is circular, and when viewed along the thickness direction of the piezoelectric body layer, the first connection portion and the second connection portion overlap with the center of the repeating portion. Brief Description of the Drawings

[0006] Figure 1 is a perspective view showing the piezoelectric element according to the embodiment.

[0007] Figure 2 is Figure 1 a cross-sectional view of the piezoelectric element shown.

[0008] Figure 3 is Figure 1 a top view of the piezoelectric element shown.

[0009] Figure 4A It is a schematic diagram showing the molecular structure of polylactic acid crystallization.

[0010] Figure 4B It is a schematic diagram showing the molecular structure of polylactic acid crystallization.

[0011] Figure 5 It only shows Figure 1 A top view of the laminate.

[0012] Figure 6 It is an example of the laminate included in the piezoelectric element as a comparative example, and is a top view showing the laminate obtained by changing the shape of the Figure 5 laminate to a square.

[0013] Figure 7 It shows the result of simulating the displacement amount distribution of the laminate when a voltage is applied between the first electrode layer and the second electrode layer of the piezoelectric element shown in Figure 1 A diagram.

[0014] Figure 8 It is an example of a θ-2θ profile obtained by θ-2θ measurement using an X-ray diffractometer for a piezoelectric layer containing c-axis uniaxially oriented polylactic acid.

[0015] Figure 9 It is for the piezoelectric layer from which the Figure 8 shown θ-2θ profile was obtained, and is an example of a pole figure obtained by fixing the 2θ position at 16.7°.

[0016] Figure 10 A top view showing a modified example of the piezoelectric element according to the embodiment.

[0017] Figure 11 A top view showing a modified example of the piezoelectric element according to the embodiment.

[0018] Explanation of reference numerals

[0019] 10…Repeated part; 100…Piezoelectric element; 100A…Piezoelectric element; 100B…Piezoelectric element; 200…Piezoelectric body layer; 200A…Piezoelectric body layer; 201…First surface; 202…Second surface; 300…First electrode layer; 300B…First electrode layer; 400…Second electrode layer; 500…Stacked body; 500’…Stacked body; 600…First connection part; 700…Second connection part; 800…First wiring; 900…Second wiring; C1…Circle; Dc…Orientation direction; E…Outer edge; L1…Reference line; L2…Reference line; O…Center; P1…Vertex; P2…Vertex; P3…Vertex; P4…Vertex; P5…Intersection point; P6…Intersection point; P7…Intersection point; P8…Intersection point; R1…Radius; S1…Stress vector; d1…Displacement; d2…Displacement; d3…Displacement; d4…Displacement; d5…Displacement; d6…Displacement; d7…Displacement; d8…Displacement; r1…Radius; t2…Average thickness; t3…Average thickness; t4…Average thickness; t6…Thickness; t7…Thickness. Detailed implementation mode

[0020] Hereinafter, the piezoelectric element of the present invention will be described in detail based on the drawings.

[0021] Figure 1 It is a perspective view showing the piezoelectric element according to the embodiment. Figure 2 Is Figure 1 A cross-sectional view of the piezoelectric element shown. Figure 3 Is Figure 1 A top view of the piezoelectric element shown.

[0022] 1. Piezoelectric element

[0023] Figure 1 And Figure 2 The piezoelectric element 100 shown includes a stacked body 500 having a piezoelectric body layer 200, a first electrode layer 300, and a second electrode layer 400. The piezoelectric body layer 200 has a first surface 201 and a second surface 202 that have a front-back relationship with each other. The first electrode layer 300 is provided on the first surface 201 of the piezoelectric body layer 200. The second electrode layer 400 is provided on the second surface 202 of the piezoelectric body layer 200.

[0024] In addition, the piezoelectric element 100 may include components other than these components. For example, an adhesive layer or the like may be interposed between the piezoelectric body layer 200, the first electrode layer 300, and the second electrode layer 400. In addition, a protective film or the like covering the stacked body 500 may be provided.

[0025] Figure 1 And Figure 2 The top view shape of the stacked body 500 shown is as Figure 3It is shown as circular. Specifically, the piezoelectric layer 200, the first electrode layer 300, and the second electrode layer 400 are each circular in top view and have the same size as each other.

[0026] The circular shape includes, for example, a perfect circle, an ellipse, an oblong circle, etc., but a perfect circle is preferred. A perfect circle is a circular shape in which the difference between the length of the major axis and the length of the minor axis is 10% or less of the length of the major axis. The major axis is the longest axis obtainable in top view, and the minor axis is the axis that passes through the midpoint of the major axis and is orthogonal to the major axis in top view.

[0027] The first wiring 800 and the second wiring 900 are connected to the piezoelectric element 100. One end of the first wiring 800 is connected to the central portion of the circular first electrode layer 300 via the first connection portion 600. One end of the second wiring 900 is connected to the central portion of the circular second electrode layer 400 via the second connection portion 700.

[0028] The other end of the first wiring 800 and the other end of the second wiring 900 are each connected to, for example, a power supply device (not shown). Thereby, a voltage can be applied between the first electrode layer 300 and the second electrode layer 400, causing the piezoelectric layer 200 to exhibit the inverse piezoelectric effect. In this case, the piezoelectric element 100 is used by being incorporated into, for example, an actuator, a vibration generating element, an ultrasonic motor, or the like.

[0029] In addition, the other end of the first wiring 800 and the other end of the second wiring 900 can also be each connected to, for example, a charge detection device (not shown). Thereby, the charges generated by the piezoelectric effect in the piezoelectric layer 200 can be taken out from the first electrode layer 300 and the second electrode layer 400, and the charge detection device can detect the amount of charge. Based on the detected amount of charge, the force applied to the piezoelectric layer 200 can be obtained, or the electric power required for a switching operation or power generation can be generated. In this case, the piezoelectric element 100 is used by being incorporated into various force sensors such as a tactile sensor and a force sensor, various switches, a power generation element, or the like. In addition, the piezoelectric element 100 can also be connected to a voltage detection device. Thereby, the voltage generated by the piezoelectric effect can be detected by the voltage detection device.

[0030] As the constituent materials of the first electrode layer 300 and the second electrode layer 400, for example, in addition to metal materials such as monomers of metal elements such as gold, silver, platinum, copper, nickel, aluminum, indium, tin, zinc, palladium, alloys containing these metal elements, and intermetallic compounds, resin materials such as conductive polymers can also be cited.

[0031] Figure 2The average thickness t3 of the first electrode layer 300 and the average thickness t4 of the second electrode layer 400 shown are not particularly limited, but are preferably 0.05 μm or more and 500 μm or less, more preferably 0.50 μm or more and 300 μm or less, respectively.

[0032] As the first connection portion 600 and the second connection portion 700, for example, bonding metal materials such as solder and brazing filler metal, conductive paste, conductive adhesive, etc. are used. As an example, Figure 2 The first connection portion 600 shown adheres or joins to both the first electrode layer 300 and the first wiring 800, and has a shape that expands the diameter of the first wiring 800. Similarly, as an example, Figure 2 The second connection portion 700 shown adheres or joins to both the second electrode layer 400 and the second wiring 900, and has a shape that expands the diameter of the second wiring 900.

[0033] As the constituent materials of the first connection portion 600 and the second connection portion 700, for example, in addition to metal materials such as monomers of metal elements such as gold, silver, platinum, copper, nickel, aluminum, indium, tin, zinc, palladium, alloys containing these metal elements, and intermetallic compounds, resin materials such as conductive polymers can also be cited.

[0034] In addition, the constituent materials of the first connection portion 600 and the second connection portion 700 may be the same as or different from the constituent materials of the first electrode layer 300 and the second electrode layer 400.

[0035] The average thickness t2 of the piezoelectric layer 200 is not particularly limited, but is preferably 10 μm or more and 5000 μm or less, more preferably 30 μm or more and 1000 μm or less, and further preferably 50 μm or more and 500 μm or less. Thereby, the piezoelectric layer 200 has sufficient piezoelectric properties.

[0036] The piezoelectric layer 200 contains a helical chiral polymer crystal showing piezoelectricity. A helical chiral polymer refers to a polymer having a helical structure and molecular optical activity. And a helical chiral polymer crystal refers to a crystal of such a helical chiral polymer.

[0037] As the helical chiral polymer, for example, polypeptides, cellulose derivatives, polylactic acid, polypropylene oxide, poly-β-hydroxybutyric acid, etc. can be cited.

[0038] The helical chiral polymer crystal used in the present embodiment is a crystal having a helical structure in its molecular structure as described above, but is particularly preferably a crystal in which the c-axis is uniaxially oriented in the plane of the piezoelectric layer 200 when the advancing axis of the helical structure is the c-axis.

[0039] In such a piezoelectric layer 200, the c-axis of the helical chiral polymer is uniaxially oriented in the plane, and thus, a relatively large polarization can be exhibited in the thickness direction of the piezoelectric layer 200. Therefore, a piezoelectric layer 200 capable of more efficiently applying an electric field and extracting charges using the first electrode layer 300 and the second electrode layer 400 can be obtained.

[0040] The piezoelectric layer 200 containing a helical chiral polymer with a c-axis uniaxially oriented in the plane can be manufactured by an existing film manufacturing method such as a uniaxial stretching method, for example. Specifically, the piezoelectric layer 200 can be manufactured by a method having a step of forming a sheet by an extrusion molding method after melt-kneading raw materials and a step of obtaining a stretched film by uniaxially stretching the obtained sheet. According to such a method, a stretched film in which the c-axis of the helical chiral polymer is uniaxially oriented in the plane is obtained. Since this method has excellent mass productivity, cost reduction of the piezoelectric layer 200 can be easily achieved.

[0041] Among them, it is preferable that the helical chiral polymer crystallizes into polylactic acid crystals. Polylactic acid crystals have relatively high mechanical strength and excellent formability, and thus are particularly useful as the helical chiral polymer crystals contained in the piezoelectric layer 200. In other words, by including polylactic acid crystals, it is easy to improve the mechanical strength and formability of the piezoelectric layer 200.

[0042] Hereinafter, polylactic acid will be described as an example of the helical chiral polymer. As optically active polylactic acid, L-polylactic acid (PLLA) and D-polylactic acid (PDLA) are known. Here, α-phase L-polylactic acid, which is stable even in the crystalline phase of L-polylactic acid, will be described as an example. In addition, in the following description, α-phase L-polylactic acid will be simply referred to as "polylactic acid".

[0043] Figure 4A and Figure 4B are schematic views showing the molecular structure of polylactic acid crystals.

[0044] As Figure 4A and Figure 4B shown, the molecular structure of polylactic acid crystals has a helical structure. The crystal system of polylactic acid crystals is orthorhombic, the length of the a-axis of the unit cell is about 1.06 nm, the length of the b-axis is about 0.61 nm, and the length of the c-axis is about 2.88 nm. In addition, Figure 4A illustrates a plane containing the a-axis and the c-axis in polylactic acid crystals, Figure 4B illustrates a plane containing the a-axis and the b-axis in polylactic acid crystals.

[0045] The piezoelectric layer 200 may contain polylactic acid crystals, but it is preferably made mainly of polylactic acid crystals. The content rate of the polylactic acid crystals in the piezoelectric layer 200 is preferably 30% by mass or more, more preferably 50% by mass or more, and still more preferably 70% by mass or more. In addition, the piezoelectric layer 200 contains, for example, amorphous polylactic acid in addition to the polylactic acid crystals. Further, in addition to the α-phase L-type polylactic acid described above, the piezoelectric layer 200 may also contain L-type polylactic acid such as the metastable α'-phase and β-phase, or may contain D-type polylactic acid.

[0046] Figure 5 is only showing Figure 1 a plan view of the laminate 500. Figure 6 is an example of the laminate included in the piezoelectric element as a comparative example, and shows Figure 5 a plan view of the laminate 500' obtained by changing the shape of the laminate 500 into a square.

[0047] In Figure 6 the laminate 500' shown, the c-axis of the helical chiral polymer, for example, the c-axis of polylactic acid, is oriented along the orientation direction Dc. In such a laminate 500', as shown by the two arrows in Figure 6 when a shear stress parallel to the c-axis is applied, a rotational movement of the electric dipole of C=O is caused within the helical structure, and polarization appears in the direction crossing the shear plane including the two applied shear stress vectors S1. In other words, polarization appears in the direction crossing the plane where the laminate 500' expands.

[0048] If an electric field is applied to the laminate 500' showing such piezoelectricity in the direction crossing the shear plane, a shear deformation is generated in the laminate 500' by the inverse piezoelectric effect. When the laminate 500' before deformation is a square as shown by the dashed line in Figure 6 , the deformed laminate 500' becomes a parallelogram as shown by the solid line. This shear deformation is based on the stress represented by the two shear stress vectors S1, but since the action lines of the two shear stress vectors S1 are different from each other, it is not easy to utilize this deformation in the piezoelectric element having the laminate 500'. Specifically, the vertices P1, P2, P3, and P4 of the laminate 500' are displaced parallel to the shear stress vector S1 as shown by the displacements d1, d2, d3, and d4 in Figure 6 . Conventionally, a piezoelectric element utilizing shear deformation has been realized by processing into a special shape such as a string-shaped piezoelectric element, but there are technical problems from the viewpoints of structural complexity and manufacturing difficulty.

[0049] Therefore, in the piezoelectric element 100 according to the present embodiment, as shown in Figure 5As shown, the overlapping portion 10 where the piezoelectric layer 200, the first electrode layer 300, and the second electrode layer 400 overlap each other, i.e., the laminate 500, is circular. Figure 5 Among them, in particular, the laminate 500 is a perfect circle. When an electric field is applied to such a laminate 500 in a direction intersecting the shear plane, due to the inverse piezoelectric effect, shear deformation is generated based on the same shear stress vector S1 as that of the laminate 500' shown in Figure 6 At this time, since the laminate 500 is circular, the shear deformation is converted into tensile and compressive deformation.

[0050] Specifically, in the Figure 6 laminate 500', the lines of action of the displacements d1 and d4 generated at the two opposite vertices P1 and P4 are different from each other. Specifically, the directions of the displacements d1 and d4 are on different straight lines. More specifically, when extending an unillustrated reference line connecting the vertex P1 and the vertex P4, the angles formed by the direction of the displacement d1 and the reference line and the angles formed by the direction of the displacement d4 and the reference line respectively exceed 20°. In addition, the lines of action of the displacements d2 and d3 generated at the other two opposite vertices P2 and P3 are also different from each other. Specifically, the directions of the displacements d2 and d3 are on different straight lines. More specifically, when extending an unillustrated reference line connecting the vertex P2 and the vertex P3, the angles formed by the direction of the displacement d2 and the reference line and the angles formed by the direction of the displacement d3 and the reference line respectively exceed 20°.

[0051] In contrast, in the Figure 5 laminate 500, the lines of action of the displacements d5 and d8 generated at the outer edge E almost overlap each other. The displacement d5 is the displacement of the intersection point P5 of the reference line L1 and the outer edge E of the laminate 500 before deformation. The displacement d8 is the displacement of the intersection point P8 of the reference line L1 and the outer edge E of the laminate 500 before deformation. The fact that the lines of action of the displacements d5 and d8 almost overlap means that the angles formed by the direction of the displacement d5 and the reference line L1 and the angles formed by the direction of the displacement d8 and the reference line L1 are respectively 20° or less. The reference line L1 is a line that forms an angle of 45° with respect to the orientation direction Dc and passes through the center O of the laminate 500 before deformation.

[0052] In addition, in the Figure 5In the laminate 500, the lines of action of the displacements d6 and d7 generated at the outer edge E almost overlap each other. The displacement d6 is the displacement of the intersection point P6 between the reference line L2 and the outer edge E of the laminate 500 before deformation. The displacement d7 is the displacement of the intersection point P7 between the reference line L2 and the outer edge E of the laminate 500 before deformation. The fact that the lines of action of the displacements d6 and d7 almost overlap means that the angles formed by the direction of the displacement d6 and the reference line L2 and the angles formed by the direction of the displacement d7 and the reference line L2 are each 20° or less. The reference line L2 is a straight line that is orthogonal to the reference line L1 and passes through the center O of the laminate 500 before deformation.

[0053] Moreover, the displacements d5 and d8 are almost opposite to each other, and the displacements d6 and d7 are also almost opposite to each other. According to such a mechanism, in the laminate 500, shear deformation is converted into tensile deformation.

[0054] In addition, in Figure 5 the laminate 500, the top view shape is circular. Therefore, the directions of the displacements d5, d6, d7, and d8 cross the outer edge E at relatively large angles. Specifically, Figure 5 the angles formed by the directions of the displacements d5, d6, d7, and d8 indicated by the arrows and the outer edge E are preferably 70° or more and 90° or less. Thereby, when using the displacement of the laminate 500 in equipment or the like, the outer edge E of the laminate 500 is less likely to interfere with other components or the like, and the ease of use is improved.

[0055] In Figure 5 the tensile deformation shown, as Figure 5 shown, when an electric field is applied to the piezoelectric layer 200 in such a way that the displacements d5 and d8 causing the intersection points P5 and P8 to approach the center O are generated, the intersection points P6 and P7 generate the displacements d6 and d7 away from the center O. Conversely, although not shown, when an electric field is applied to the piezoelectric layer 200 in such a way that the displacements of the intersection points P5 and P8 away from the center O are generated, the intersection points P6 and P7 generate displacements approaching the center O.

[0056] On the other hand, the center O of the laminate 500 hardly displaces. Therefore, even if the center O is fixed, it hardly affects the tensile deformation of the laminate 500. Therefore, in the piezoelectric element 100 according to the present embodiment, in order to fix the laminate 500, the first connection portion 600 and the second connection portion 700 are provided at positions overlapping the center O in a top view.

[0057] The first connecting portion 600 is provided on the side of the first electrode layer 300 opposite to the piezoelectric layer 200, and is preferably a member having a higher rigidity than the first electrode layer 300. The second connecting portion 700 is also provided on the side of the second electrode layer 400 opposite to the piezoelectric layer 200, and is preferably a member having a higher rigidity than the second electrode layer 400. By sandwiching the laminate 500 with such members having a high rigidity, the laminate 500 can be fixed with a simple structure without affecting the expansion and contraction deformation.

[0058] In addition, the first connecting portion 600 electrically connects the first wiring 800 and the first electrode layer 300. The second connecting portion 700 electrically connects the second wiring 900 and the second electrode layer 400. Therefore, a voltage can be applied to the first electrode layer 300 and the second electrode layer 400 through the first wiring 800 and the second wiring 900, and the charge taken out from the first electrode layer 300 and the second electrode layer 400 can be sent to the first wiring 800 and the second wiring 900. In addition, the first connecting portion 600 and the second connecting portion 700 hardly displace as described above. Therefore, in the above structure, breakage and disconnection of the first wiring 800 and the second wiring 900 due to vibration can be reduced.

[0059] In addition, when the piezoelectric layer 200 is viewed along the thickness direction, the first connecting portion 600 is configured to overlap with the center O of the laminate 500 and is smaller than the first electrode layer 300. The first connecting portion 600 overlapping with the center O means that the center O is located inside the range of the first connecting portion 600. In addition, the first connecting portion 600 being smaller than the first electrode layer 300 means that the first connecting portion 600 is included inside the range of the first electrode layer 300.

[0060] And, when the piezoelectric layer 200 is viewed along the thickness direction, the second connecting portion 700 is configured to overlap with the center O of the laminate 500 and is smaller than the second electrode layer 400. The second connecting portion 700 overlapping with the center O means that the center O is located inside the range of the second connecting portion 700. In addition, the second connecting portion 700 being smaller than the second electrode layer 400 means that the second connecting portion 700 is included inside the range of the second electrode layer 400.

[0061] According to the above structure, the laminate 500 can be fixed at an arbitrary position in space through the first wiring 800 and the second wiring 900 via the first connecting portion 600 and the second connecting portion 700, and is electrically connected to the first wiring 800 and the second wiring 900. Thus, the piezoelectric element 100 becomes an element that is suitably used for various devices by utilizing the piezoelectricity accompanying the expansion and contraction deformation.

[0062] Here, Figure 7 It represents Figure 1The figure shows the result of simulating the displacement amount distribution of the laminate 500 when a voltage is applied between the first electrode layer 300 and the second electrode layer 400 of the piezoelectric element 100. The simulation was performed using the analysis simulation software Femtet manufactured by Murata Software Co., Ltd. In this simulation, the circular laminate 500 was fixed by the first connecting portion 600 and a second connecting portion 700 (not shown), and in this state, when an electric field was applied to the piezoelectric layer 200 containing polylactic acid crystals, the displacement amount of each point of the laminate 500 was calculated. In addition, Figure 7 in, the arrow indicates the orientation direction Dc of the piezoelectric layer 200. Additionally, Figure 7 in, the outer edge of the laminate 500 before deformation is shown by a solid line, and the displacement amount of each point of the deformed laminate 500 is shown by a shaded pattern.

[0063] As Figure 7 shown, when the c-axis of the polylactic acid is uniaxially oriented in the plane along the orientation direction Dc, the piezoelectric element 100 deforms in such a way that it extends in the direction indicated by the single-dot chain line in Figure 7 and contracts in the direction crossing this direction. Additionally, Figure 7 the shading varies along the direction obliquely crossing the orientation direction Dc, so Figure 7 the displacement amount distribution of each point shown in

[0064] is inclined along the direction obliquely crossing the orientation direction Dc.

[0065] Based on the above simulation results, it can be seen that in the piezoelectric element 100, shear deformation can be converted into tensile deformation.

[0065] In addition, the uniaxial orientation of the c-axis of the helical chiral polymer in the piezoelectric layer 200 can be determined by obtaining and analyzing the X-ray diffraction profile of the piezoelectric layer 200. Specifically, first, θ-2θ measurement using an X-ray diffractometer is performed on the piezoelectric layer 200 to obtain a θ-2θ profile.

[0066] Figure 8 is an example of a θ-2θ profile obtained by θ-2θ measurement using an X-ray diffractometer for a piezoelectric layer containing polylactic acid with c-axis uniaxial orientation. In the case of c-axis uniaxial orientation of polylactic acid, in the θ-2θ profile, as Figure 8 shown, peaks corresponding to the (200) plane and (110) plane of polylactic acid are observed. The observed peak is at 2θ = 16.7° ± 1.0°. In addition, this peak position is based on the peak position of θ-2θ measurement using characteristic X-rays of CuKα1 with a wavelength .

[0067] Next, a pole figure is obtained for this peak. Figure 9 is for the obtained Figure 8An example of a pole figure obtained by fixing the 2θ position at 16.7° for the piezoelectric layer of the θ-2θ profile shown. In this pole figure, as Figure 9 indicated by the arrow of the dashed line in Figure 9 , the contour lines indicating the diffraction intensity extend linearly in a manner passing through the center as ψ = 0°. In the pole figure shown in

[0068] , if the characteristics of such contour lines can be identified, the c-axis of polylactic acid can be determined to be uniaxially oriented in the plane of the piezoelectric layer.

[0069] Moreover, when observed along the thickness direction of the piezoelectric layer 200, the repeating portion 10 where the piezoelectric layer 200, the first electrode layer 300, and the second electrode layer 400 overlap each other, in other words, the laminate 500 is circular. Further, when observed along the thickness direction of the piezoelectric layer 200, the first connecting portion 600 and the second connecting portion 700 overlap with the center O of the laminate 500 (the center of the repeating portion 10).

[0070] According to such a structure, the shape of the repeating portion 10 is circular, and thus, the shear deformation generated by the piezoelectricity of the helical chiral polymer crystal can be converted into a telescopic deformation. Therefore, the piezoelectric element 100 that can easily utilize the piezoelectricity of the helical chiral polymer crystal can be realized.

[0071] In addition, it is preferable that when observed along the thickness direction of the piezoelectric layer 200, the first connecting portion 600 is smaller than the first electrode layer 300, and when observed along the thickness direction of the piezoelectric layer 200, the second connecting portion 700 is smaller than the second electrode layer 400.

[0072] With the first connecting portion 600 and the second connecting portion 700 having the above characteristics, the first connecting portion 600 and the second connecting portion 700 can fix the laminate 500 without hindering the telescopic deformation generated by the piezoelectric layer 200.

[0073] Such a piezoelectric element 100 is used in various devices that utilize expansion and contraction deformation. Examples of such devices include actuators, vibration generating elements, ultrasonic motors, tactile sensors, force sensors, power generation elements, various switches, and the like.

[0074] In addition, in the piezoelectric element 100, electrical connection and mechanical connection to the laminate 500 can be achieved through the first connection portion 600 and the second connection portion 700. Therefore, when the piezoelectric element 100 is incorporated into various devices, the fixing structure of the piezoelectric element 100 can be simplified. As a result, by using the piezoelectric element 100, the design freedom of the device can be easily increased.

[0075] In addition, it is preferable that the first connection portion 600 has a higher rigidity than the first electrode layer 300, and the second connection portion 700 has a higher rigidity than the second electrode layer 400. Thereby, the first connection portion 600 and the second connection portion 700 are particularly less likely to deform, and thus the laminate 500 can be fixed more stably.

[0076] The fact that the rigidity of the first connection portion 600 is higher than that of the first electrode layer 300 means that the flexural rigidity of the first connection portion 600 is greater than the flexural rigidity of the first electrode layer 300. Similarly, the fact that the rigidity of the second connection portion 700 is higher than that of the second electrode layer 400 means that the flexural rigidity of the second connection portion 700 is greater than the flexural rigidity of the second electrode layer 400. The flexural rigidity is represented by the product of Young's modulus and the moment of inertia of the cross-section. Among them, if it becomes thinner in the direction of bending, the moment of inertia of the cross-section becomes smaller. Therefore, in the present embodiment, in the thickness direction of the laminate 500, the thicknesses of the first connection portion 600 and the second connection portion 700 are made sufficiently thicker than the first electrode layer 300 and the second electrode layer 400.

[0077] Specifically, as Figure 2 shown, when the thickness of the first connection portion 600 is set to t6, the thickness t6 is preferably 2 times or more, more preferably 10 times or more and 1000 times or less, of the average thickness t3 of the first electrode layer 300. Thereby, the flexural rigidity of the first connection portion 600 can be made greater than the flexural rigidity of the first electrode layer 300.

[0078] In addition, when the thickness of the second connection portion 700 is set to t7, the thickness t7 is preferably 2 times or more, more preferably 10 times or more and 1000 times or less, of the average thickness t4 of the second electrode layer 400. Thereby, the flexural rigidity of the second connection portion 700 can be made greater than the flexural rigidity of the second electrode layer 400.

[0079] Figure 3 In, the radius of the laminate 500 (repeated portion 10) is set to R1, and a circle with a radius of r1 from the center O is set to C1. In addition, the radius r1 becomes 20% of the radius R1. As Figure 3As shown, when viewed in the thickness direction of the piezoelectric layer 200, the first connection portion 600 is preferably disposed inside the circle C1.

[0080] According to such a structure, it is possible to prevent the range occupied by the first connection portion 600 from becoming unnecessarily large. In other words, the range occupied by the first connection portion 600 can be set to a size required and sufficient for the fixed laminate 500. Thereby, the piezoelectric element 100 that can effectively utilize the piezoelectricity accompanying the expansion and contraction deformation can be realized.

[0081] In addition, although not shown, the second connection portion 700 is also preferably disposed inside the circle C1. Thereby, it is possible to prevent the range occupied by the second connection portion 700 from becoming unnecessarily large.

[0082] Furthermore, the radius r1 is preferably less than 20% of the radius R1, and more preferably less than 15% of the radius R1.

[0083] 2. Modified Example

[0084] Next, a piezoelectric element according to a modified example will be described.

[0085] Figure 10 And Figure 11 are respectively top views showing modified examples of the piezoelectric element 100 according to the embodiment.

[0086] Hereinafter, the modified example will be described. However, in the following description, the description will be centered on the differences from the above-described embodiment, and the description of the same matters will be omitted. In addition, in Figure 10 And Figure 11 structures identical to those of the above-described embodiment are denoted by the same reference numerals.

[0087] Figure 10 The piezoelectric element 100A shown is the same as the piezoelectric element 100 according to the above-described embodiment except that the shape of the piezoelectric layer 200A is different from that of the first electrode layer 300.

[0088] That is, Figure 10 the top view shape of the piezoelectric layer 200A shown is a square. In addition, the first electrode layer 300 and the second electrode layer (not shown) are respectively included inside the range of the piezoelectric layer 200A. Therefore, the overlapping repeating portion 10 of the piezoelectric layer 200A, the first electrode layer 300, and the second electrode layer is circular, the same as in the above-described embodiment. Therefore, Figure 10 the piezoelectric element 100A shown can also obtain the same effect as the above-described embodiment, that is, the effect of converting shear deformation into expansion and contraction deformation.

[0089] In this way, Figure 10The illustrated first electrode layer 300 and the second electrode layer (not shown) are each circular. Thus, the above-described effects are obtained, and Figure 10 The illustrated piezoelectric layer 200A can have any shape, and thus has the advantage of being easy to manufacture. Therefore, the shape of the piezoelectric layer 200A is not limited to a square and can be any shape.

[0090] Figure 11 The illustrated piezoelectric element 100B is the same as the piezoelectric element 100 according to the above-described embodiment, except that the shape of the first electrode layer 300B is different from that of the piezoelectric layer 200.

[0091] That is, Figure 11 The illustrated first electrode layer 300B has a square shape in plan view. In addition, although not shown, the plan view shape of the second electrode layer is also the same as that of the first electrode layer 300B. Further, the piezoelectric layer 200 is located inside the range of the first electrode layer 300B. Therefore, the overlapping portion 10 of the piezoelectric layer 200, the first electrode layer 300B, and the second electrode layer is circular, which is the same as in the above-described embodiment. Therefore, Figure 11 The illustrated piezoelectric element 100B also obtains the effect of converting shear deformation into telescopic deformation, which is the same effect as in the above-described embodiment.

[0092] Thus, Figure 11 The illustrated piezoelectric layer 200 is circular. Thus, the above-described effects are obtained, and Figure 11 The illustrated first electrode layer 300B and the second electrode layer (not shown) can have any shape, and thus have the advantage of being easy to manufacture. Therefore, the shapes of the first electrode layer 300B and the second electrode layer are not limited to a square and can be any shape.

[0093] In addition, Figure 11 Although not shown in Figure 11 the illustrated first electrode layer 300B and the second electrode layer (not shown) are insulated from each other outside the piezoelectric layer 200.

[0094] In addition, in Figure 11 the illustrated piezoelectric element 100B, the piezoelectric layer 200 is disposed inside the first electrode layer 300B and the second electrode layer, and thus is protected from external influences. Therefore, the piezoelectric element 100B has the advantages that the piezoelectric layer 200 is not easily damaged and the reliability is easily improved.

[0095] As described above, the piezoelectric element of the present invention has been described based on the illustrated embodiment. However, the piezoelectric element of the present invention is not limited to the above-described embodiment. For example, each part of the above-described embodiment can be replaced with any structure having the same function, or can be a structure obtained by adding any constituent to the above-described embodiment.

Claims

1. A piezoelectric element, characterized in that, Comprising: A piezoelectric layer having a first surface and a second surface that are related to each other as front and back, and containing a helical chiral polymer crystal exhibiting piezoelectricity; A first electrode layer provided on the first surface of the piezoelectric layer; A second electrode layer provided on the second surface of the piezoelectric layer; A first connection portion provided on the side of the first electrode layer opposite to the piezoelectric layer; And A second connection portion provided on the side of the second electrode layer opposite to the piezoelectric layer, When viewed along the thickness direction of the piezoelectric layer, the overlapping repeating portions of the piezoelectric layer, the first electrode layer, and the second electrode layer are circular; When viewed along the thickness direction of the piezoelectric layer, the first connection portion and the second connection portion overlap with the center of the repeating portion; The molecular structure of the helical chiral polymer crystal has a helical structure; The helical chiral polymer crystal is a crystal in which the c-axis is uniaxially oriented in the plane of the piezoelectric layer when the axis of the helical structure is the c-axis.

2. The piezoelectric element according to claim 1, characterized in that, The first connection portion is more rigid than the first electrode layer; The second connection portion is more rigid than the second electrode layer.

3. The piezoelectric element according to claim 1 or 2, characterized in that, When viewed along the thickness direction of the piezoelectric layer, the first connection portion is smaller than the first electrode layer; When viewed along the thickness direction of the piezoelectric layer, the second connection portion is smaller than the second electrode layer.

4. The piezoelectric element according to claim 1 or 2, characterized in that, The first connection portion is disposed inside a circle having a radius of 20% of the repeating portion; 5. The piezoelectric element according to claim 1, characterized in that, The helical chiral polymer crystal is a polylactic acid crystal.

6. The piezoelectric element according to claim 1 or 2, characterized in that, The first electrode layer and the second electrode layer are circular; 7. The piezoelectric element according to claim 1 or 2, characterized in that, The piezoelectric layer is circular.

Images