piezoelectric elements

Abstract

The piezoelectric element (1) comprises: a piezoelectric body (2) having a first main surface (4A) and a second main surface (4B) facing each other, and a peripheral surface (5) connecting the first main surface (4A) and the second main surface (4B), and being circular when viewed from above; and an electrode (3) having at least one of the first main surface (4A) and the second main surface (4B), wherein the thickness of the outer edge portion (3a) of the electrode (3) gradually decreases toward the edge (3aa) of the outer edge portion (3a).

Description

Technical Field

[0001] This disclosure relates to a piezoelectric element. Background Technology

[0002] As an existing piezoelectric element, for example, there is the piezoelectric element described in Japanese Utility Model Publication No. 63-187358. This existing piezoelectric element has a piezoelectric element that is circular in shape when viewed from above. A pair of opposing main surfaces of the piezoelectric element are each provided with a circular electrode, which is slightly smaller than the piezoelectric element. An opening is provided in the region of one electrode, exposing the main surface of the piezoelectric element. This opening functions as a marker for identifying the polarity of the electrode. Summary of the Invention

[0003] In piezoelectric elements like those described above, to obtain the desired characteristics, it is necessary to ensure that the area that becomes the active part (mainly the area where the electrode is formed relative to the piezoelectric element) is sufficiently large. On the other hand, if the area of ​​the electrode relative to the piezoelectric element is increased, the displacement constraint caused by the electrode increases, and as a result, the vibration efficiency may decrease.

[0004] This disclosure was made to solve the above-mentioned problems, and its purpose is to provide a piezoelectric element that can achieve improved vibration efficiency.

[0005] One aspect of this disclosure relates to a piezoelectric element comprising: a piezoelectric element having a first main surface and a second main surface opposite to each other, and a peripheral surface connecting the first main surface and the second main surface, and being circular when viewed from above; and an electrode having at least one of the first main surface and the second main surface, wherein the thickness of the outer edge of the electrode gradually decreases toward the edge of the outer edge.

[0006] In this piezoelectric element, the thickness of the outer edge of the electrode disposed on at least one of the first and second main surfaces of the piezoelectric body gradually decreases towards the edge of the outer edge. This ensures that the electrode thickness in the active region at the outer edge of the electrode is adequate, while also reducing displacement constraints caused by the electrode. Therefore, this piezoelectric element achieves improved vibration efficiency.

[0007] The corner of the outer edge of the electrode, opposite to the piezoelectric element, can also be rounded. With this structure, the thickness of the electrode in the active region at the outer edge of the electrode can be ensured, while maximizing vibration efficiency.

[0008] The edge of the outer edge of the electrode can also coincide with the outer edges of the first and second main surfaces. In this case, the region that becomes the active part can be further expanded in the piezoelectric element. Even when the edge of the outer edge of the electrode is located at the outer edges of the first and second main surfaces, since the thickness of the outer edge of the electrode gradually decreases towards the edge of the outer edge, the displacement constraint of the electrode can be sufficiently reduced, thereby improving the vibration efficiency.

[0009] Alternatively, a polarity display portion can be provided on the electrode, consisting of an opening that exposes the piezoelectric element, with the thickness of the electrode gradually decreasing towards the edge of the opening. The opening, serving as the polarity display portion, is an inactive area and does not contribute to the displacement of the piezoelectric element. Therefore, by making the thickness of the electrode gradually decrease towards the edge of the opening, the uniformity of the piezoelectric element's vibration can be maintained.

[0010] The center of the opening can also be off-center relative to the center of the piezoelectric element. In this case, for example, during the inspection process of the piezoelectric element, the terminal of the inspection sensor can be brought into contact with the center of the electrode. Therefore, the operability of the process can be guaranteed.

[0011] The center of the opening can also be located near the center of the piezoelectric element. By ensuring that the opening, which does not contribute to the displacement of the piezoelectric element, is not located on the outer edge of the electrode, uniform radial diffusion vibration of the piezoelectric element can be guaranteed. Attached Figure Description

[0012] Figure 1 This is a top view of a piezoelectric element according to one embodiment of this disclosure.

[0013] Figure 2 yes Figure 1 Sectional view of line II-II.

[0014] Figure 3 It means Figure 1 An enlarged cross-sectional view of the main portion near the outer edge of the electrode of the piezoelectric element shown.

[0015] Figure 4 It means Figure 1 An enlarged cross-sectional view of the main part near the polarity indicator (opening) of the piezoelectric element shown. Detailed Implementation

[0016] Hereinafter, with reference to the accompanying drawings, a preferred embodiment of a piezoelectric element according to one aspect of this disclosure will be described in detail.

[0017] Figure 1 This is a top view of a piezoelectric element according to one embodiment of this disclosure. Additionally, Figure 2 yes Figure 1Sectional view of line II-II. Figure 1 and Figure 2 The piezoelectric element 1 shown is, for example, a component used as a structural element of an ultrasonic transducer. An ultrasonic transducer is an ultrasonic transceiver that generates ultrasonic waves through the piezoelectric element 1 or detects ultrasonic waves received by the piezoelectric element 1.

[0018] When an ultrasonic transducer emits ultrasonic waves, for example, an alternating voltage is applied to the piezoelectric element 1, causing the piezoelectric element 1 to continuously displace due to the alternating voltage. Ultrasonic waves are generated from the ultrasonic transducer based on the displacement of the piezoelectric element 1. When an ultrasonic transducer detects ultrasonic waves, for example, an electromotive force (EMF) is generated in the piezoelectric element 1 due to the displacement caused by the received ultrasonic waves. The generation of the EMF is used to detect whether ultrasonic waves are received, and the sound pressure or sound pressure level of the ultrasonic waves is detected based on the magnitude of the generated EMF.

[0019] like Figure 1 and Figure 2 As shown, the piezoelectric element 1 comprises a piezoelectric body 2 and a pair of electrodes 3, 3. The piezoelectric body 2 is generally in the shape of a thin disk. That is, the piezoelectric body 2 has a first main surface 4A and a second main surface 4B that are opposite each other, and a peripheral surface 5 connecting the first main surface 4A and the second main surface 4B, and appears circular when viewed from above.

[0020] The piezoelectric body 2 is constructed by stacking multiple piezoelectric layers (not shown). Each piezoelectric layer is made of a piezoelectric material. In this embodiment, each piezoelectric layer is made of a piezoelectric ceramic material. Examples of piezoelectric ceramic materials used include PZT [Pb(Zr,Ti)O3], PT (PbTiO3), PLZT [(Pb,La)(Zr,Ti)O3], or barium titanate (BaTiO3). Each piezoelectric layer is, for example, a sintered body of a ceramic green sheet containing the above-mentioned piezoelectric ceramic material. In the actual piezoelectric body 2, each piezoelectric layer is integrated to the extent that the boundaries between the piezoelectric layers are indistinguishable.

[0021] Electrodes 3 are respectively disposed on the first main surface 4A and the second main surface 4B of the piezoelectric element 2. The regions where the piezoelectric element 2 is located, primarily on the first main surface 4A and the second main surface 4B, function as active parts that expand and contract due to the electrostrictive effect. Electrodes 3 are made of a conductive material. Examples of conductive materials used include Ag, Cu, and Ag-Pd alloys. The electrodes are, for example, sintered bodies comprising a conductive paste containing the aforementioned conductive material.

[0022] The electrode 3 is circular when viewed from above and is concentrically arranged with the first main surface 4A and the second main surface 4B of the piezoelectric element 2. In this embodiment, the edge 3aa of the outer edge portion 3a of the electrode 3 coincides with the outer edges 4a of the first main surface 4A and the second main surface 4B. That is, in this embodiment, except for the part forming the polarity display portion P (opening portion 11) described later, the entire surface of the first main surface 4A and the entire surface of the second main surface 4B of the piezoelectric element 2 is covered by the electrode 3. The outer edge portion 3a of the electrode 3 does not extend into the peripheral surface 5 of the piezoelectric element 2, and the peripheral surface 5 is not covered by the electrode 3.

[0023] like Figure 1 As shown, a polarity display portion P is provided on the electrode 3 on the side of the first main surface 4A. The polarity display portion P is, for example, a circular opening 11 with a diameter sufficiently small relative to the electrode 3. The first main surface 4A is exposed in the opening 11. Therefore, the polarity display portion P can be easily identified based on the difference between the color of the electrode 3 and the color of the first main surface 4A exposed from the opening 11, thus performing the polarity display function of the electrodes 3.

[0024] In this embodiment, the center F2 of the opening 11 is positioned off-center from the center F1 of the piezoelectric element 2 when viewed from above. By making the center F2 of the opening 11 off-center from the center F1 of the piezoelectric element 2, for example, the terminal of the sensor used for inspecting the piezoelectric element 1 can be brought into contact with the center F1 of the piezoelectric element 2 (i.e., the center of the electrode 3), thus ensuring the operability of the inspection. Furthermore, the center F2 of the opening 11 is preferably located close to the center F1 of the piezoelectric element 2. Figure 1 In the example, the center F2 of the opening 11 is located further inward than the circular region having half the diameter of the piezoelectric element 2. In this way, by ensuring that the opening 11, which does not contribute to the radial displacement of the piezoelectric element 1, is not located on the outer edge 3a side of the electrode 3, uniform radial diffusion vibration of the piezoelectric element 1 can be guaranteed.

[0025] Next, the structure of the electrode 3 described above will be explained in further detail.

[0026] In piezoelectric element 1, such as Figure 3 As shown, the thickness of the outer edge 3a of electrode 3 gradually decreases towards the edge 3aa of the outer edge 3a. Figure 3 In the example, the corner V of the outer edge 3a of electrode 3, which is opposite to the piezoelectric element 2, has a rounded shape, and thus, the thickness of the outer edge 3a of electrode 3 gradually decreases towards the edge 3aa of the outer edge 3a. Figure 3 In the figure, only the outer edge 3a of the electrode 3 on the first main surface 4A side is shown, but the outer edge 3a of the electrode 3 on the second main surface 4B side also has the same structure.

[0027] There are no particular restrictions on the curvature of the arc at the corner V, for example, it can be 1.8 × 10⁻⁶. 5 (1 / m)~3.0×10 5 (1 / m). The curvature of the arc at the corner V can be 1.0 × 10⁻⁶. 5 (1 / m)~5.0×10 5 (1 / m), or 1.5×10 5 (1 / m)~3.5×10 5 (1 / m). Additionally, the width of the arc-shaped region at the corner V (the radial width of electrode 3) is, for example, approximately 0.067% to 0.11% of the radius of electrode 3. This width can be approximately 0.05% to 0.15% of the radius of electrode 3, or approximately 0.06% to 0.12%.

[0028] Additionally, in piezoelectric element 1, such as Figure 4 As shown, the thickness of the electrode 3 constituting the opening 11 of the polarity display section P gradually decreases towards the edge 11a of the opening 11. Figure 4 In this example, the inner wall 11b of the opening 11 becomes a gently sloping surface that slopes towards the bottom of the opening 11 (the first main surface 4A exposed from the opening 11). As a result, the thickness of the electrode 3 in the opening 11 gradually decreases towards the edge 11a of the opening 11.

[0029] The inclination angle θ of the inner wall 11b of the opening 11 relative to the bottom of the opening 11 (the first main surface 4A exposed from the opening 11) is, for example, 2.3° to 3.5°. The inclination angle θ can be 1.0° to 5.0°, or 2.0° to 4.0°. Furthermore, the thickness of the electrode 3 in the opening 11 does not necessarily have to decrease uniformly towards the edge 11a of the opening 11. For example, a gently sloping portion may exist on a part of the inner wall 11b of the opening 11.

[0030] In this embodiment, the piezoelectric ceramic material is formed, debonded, and fired. The first main surface 4A and the second main surface 4B are then ground to obtain the piezoelectric element 2. Next, the piezoelectric elements 2 are stacked in the thickness direction to form a cylindrical body. For example, the peripheral surface 5 of the piezoelectric element 2 is ground by centerless grinding. After grinding the peripheral surface 5, the cylindrical body is separated into individual piezoelectric elements 2. Then, conductive paste is printed onto the first main surface 4A and the second main surface 4B of the separated piezoelectric elements 2, and electrodes 3 are formed by sintering the conductive paste.

[0031] The conductive paste can be printed, for example, using screen printing. During screen printing, an opening 11 is formed on the electrode 3 on the first main surface 4A side. By printing and patterning the opening 11, and making the inner wall of the opening 11 a gently sloping surface that slopes towards the bottom of the opening 11, the thickness of the electrode 3 in the opening 11 gradually decreases towards the edge 11a of the opening 11. Furthermore, during the sintering of the conductive paste, surface tension is applied due to the aggregation of the conductive paste, allowing the corner V of the outer edge 3a of the electrode 3, opposite to the piezoelectric element 2, to have a rounded shape. After forming the electrodes 3, 3, they are cleaned and polarized to obtain the aforementioned piezoelectric element 1.

[0032] As explained above, in the piezoelectric element 1, the thickness of the outer edge 3a of the electrode 3 disposed on at least one of the first main surface 4A and the second main surface 4B of the piezoelectric element 2 gradually decreases towards the edge 3aa of the outer edge 3a. Therefore, the thickness of the electrode 3 in the region where it becomes the active part can be ensured even at the outer edge 3a of the electrode 3, and the displacement constraint caused by the electrode 3 can be reduced. Thus, in this piezoelectric element 1, an improvement in vibration efficiency is achieved.

[0033] In the piezoelectric element 1, the corner V of the outer edge 3a of the electrode 3, which is opposite to the piezoelectric element 2, has a rounded shape. With this structure, the thickness of the electrode 3 in the region that becomes the active part can be ensured in the outer edge 3a of the electrode 3, and the vibration efficiency can be maximized.

[0034] In the piezoelectric element 1, the edge 3aa of the outer edge portion 3a of the electrode 3 coincides with the outer edges 4a of the first main surface 4A and the second main surface 4B. This allows for a further expansion of the active region within the piezoelectric element 1. Even when the edge 3aa of the outer edge portion 3a of the electrode 3 is located at the outer edges 4a of the first main surface 4A and the second main surface 4B, the thickness of the outer edge portion 3a of the electrode 3 gradually decreases towards the edge 3aa, thereby significantly reducing the displacement constraint of the electrode 3 and improving vibration efficiency.

[0035] In the piezoelectric element 1, a polarity display portion P, consisting of an opening 11 exposing the piezoelectric element 2, is provided on the electrode 3 on the first main surface 4A side. Furthermore, the thickness of the electrode 3 in the opening 11 gradually decreases towards the edge 11a of the opening 11. The opening 11, as the polarity display portion P, is a non-active area and does not contribute to the displacement of the piezoelectric element 1. Therefore, by making the thickness of the electrode 3 in the opening 11 gradually decrease towards the edge 11a of the opening 11, the uniformity of the vibration of the piezoelectric element 1 can be maintained.

[0036] This disclosure is not limited to the embodiments described above. For example, in the embodiments described above, the edge 3aa of the outer edge portion 3a of the electrode 3 coincides with the outer edges 4a of the first main surface 4A and the second main surface 4B, but the edge 3aa of the outer edge portion 3a of the electrode 3 may also be located inwards from the outer edges 4a of the first main surface 4A and the second main surface 4B. That is, the planar shape of the electrode 3 may also be formed as a circle that is slightly smaller than the first main surface 4A and the second main surface 4B.

[0037] Furthermore, in the above embodiment, the planar shape of electrode 3 is circular, but the planar shape of electrode 3 is not limited to this; it can also be rectangular, elliptical, polygonal, or other shapes. The planar shape of electrode 3 on the first main surface 4A side and the planar shape of electrode 3 on the second main surface 4B side can also be different from each other.

[0038] In the above embodiment, the corner V of the outer edge 3a of the electrode 3, which is opposite to the piezoelectric element 2, has an arc shape. However, other methods are also possible as long as the thickness of the outer edge 3a of the electrode 3 gradually decreases towards the edge 3aa of the outer edge 3a. For example, it is also possible to form a gently sloping surface that slopes towards the edge 3aa of the outer edge 3a of the electrode 3, as in the inner wall 11b of the opening 11.

Claims

1. A piezoelectric element, wherein provided with: a piezoelectric body having a first main surface and a second main surface opposite to each other, and a peripheral surface connecting the first main surface and the second main surface, and being circular in plan view; and an electrode provided with at least one of the first main surface and the second main surface, an outer edge portion of the electrode gradually decreases in thickness toward an edge of the outer edge portion, a polarity display portion constituted by an opening portion exposing the piezoelectric body is provided at the electrode, the thickness of the electrode of the opening portion gradually decreases toward an edge of the opening portion, the opening portion is provided at one of the electrode on the first main surface side and the electrode on the second main surface side, a center of the opening portion is located at a position more inward than a circular region having a diameter of 1 / 2 of the piezoelectric body.

2. The piezoelectric element according to claim 1, wherein an angle portion of the outer edge portion of the electrode on the opposite side to the piezoelectric body is a shape with a circular arc.

3. The piezoelectric element according to claim 1 or 2, wherein an edge of the outer edge portion of the electrode coincides with an outer edge of the first main surface and the second main surface.

4. The piezoelectric element according to claim 1, wherein a center of the opening portion is eccentric with respect to a center of the piezoelectric body.

5. The piezoelectric element according to claim 4, wherein the center of the opening portion is located at a position close to the center of the piezoelectric body.

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