Piezoelectric element

Abstract

To provide a piezoelectric element capable of effectively suppressing occurrence of warpage in an active region.SOLUTION: A piezoelectric element 1 incudes a laminate 2 including a plurality of piezoelectric layers on which electrodes are formed. The laminate 2 includes a first area 71A where both the piezoelectric layer and the electrode are located and a second area 71B where only the piezoelectric layer is located when viewed from the stacking direction of the piezoelectric layers. The second region 71B extends along at least part of the edge of the laminate 2 adjacent to the first region 71A, and has undulations K due to unevenness in the lamination direction.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to piezoelectric elements. [Background technology]

[0002] An example of a conventional piezoelectric element is a piezoelectric actuator described in Patent Document 1. In this conventional piezoelectric actuator, a transparent single-layer piezoelectric ceramic layer is provided on a diaphragm. An internal electrode is provided between the piezoelectric ceramic layer and the diaphragm, and a surface electrode is provided on the surface of the piezoelectric ceramic layer opposite the diaphragm. The internal electrode has a visible protruding region that protrudes from an end of the surface electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5188544 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, a technical issue with piezoelectric elements is that warpage occurs due to the difference in shrinkage stress between the piezoelectric layer and the electrode during firing of the green sheet. When such warpage occurs in the active region of the piezoelectric element, there is a problem of variation in the amount of displacement of the piezoelectric element in the warped portion and the amount of displacement of the piezoelectric element in the non-warped portion. In recent years, as devices incorporating piezoelectric elements have become smaller, piezoelectric elements have become thinner. As piezoelectric elements become thinner, the above-mentioned warpage problem has become more pronounced. Therefore, a piezoelectric element that can effectively suppress the occurrence of warpage is desired.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a piezoelectric element that can effectively suppress the occurrence of warpage in the active region. [Means for solving the problem]

[0006] A piezoelectric element according to one aspect of the present disclosure comprises a laminate including a plurality of piezoelectric layers on which electrodes are formed, and when viewed from the stacking direction of the piezoelectric layers, the laminate has a first region in which both the piezoelectric layers and the electrodes are located, and a second region in which only the piezoelectric layers are located, and the second region extends adjacent to the first region along at least a portion of the edge of the laminate and has undulations due to unevenness in the stacking direction.

[0007] This piezoelectric element has a first region where both the piezoelectric layer and the electrode are located, and a second region where only the piezoelectric layer is located. The first region functions as an active region that generates displacement in the stacking direction. Meanwhile, the second region is adjacent to the first region and extends along at least a portion of the edge of the laminate, thereby functioning as a constraint region that constrains distortion in the first region. In this piezoelectric element, the second region has undulations due to unevenness in the stacking direction, which fully demonstrates its function of constraining distortion in the first region. Therefore, in this piezoelectric element, even if a difference in shrinkage stress occurs between the piezoelectric layer and the electrode during firing of the green sheet, warping in the active region can be effectively suppressed.

[0008] The second region may be positioned so as to surround the outside of the first region when viewed from the stacking direction. By surrounding the outside of the first region with the second region as a constraint region in this way, distortion in the first region can be more reliably constrained. Therefore, the occurrence of warpage in the active region can be more effectively suppressed.

[0009] When viewed from the stacking direction, the laminate may have a pair of first edges in the longitudinal direction and a pair of second edges in the lateral direction, and the second region may extend along each of the pair of first edges and the pair of second edges. In this way, by locating the active region in the center of the laminate when viewed from the stacking direction, the electrode layout can be simplified. Furthermore, by locating the undulating second region along the first and second edges, the influence of the undulations themselves on the first region, which is the active region, can be suppressed.

[0010] In the second region along the first edge, the projections and recesses in the undulations may extend in a direction connecting the pair of first edge portions, and in the second region along the second edge, the projections and recesses in the undulations may extend in a direction connecting the pair of second edge portions. In this case, the extension directions of the projections and recesses in the undulations intersect between the first edge portion and the second edge portion, allowing the second region to function more effectively as a restraint region.

[0011] The protrusion width of the second region along the first edge from the first region may be greater than the protrusion width of the second region along the second edge from the first region, and the uneven height of the undulations in the second region along the first edge may be greater than the uneven height of the undulations in the second region along the second edge. In this case, the electrode layout can be facilitated by, for example, aligning the electrode arrangement direction with the direction in which the protrusion width is greater.

[0012] The first region may have a ripple continuing from the second region at least in a portion adjacent to the second region, in which case the restraining force of the ripple acts directly on the first region, thereby more effectively suppressing warpage in the active region.

[0013] The height of the undulations in the second region may be greater than the height of the undulations in the first region, in which case the distortion in the first region can be firmly constrained by the undulations in the second region while suppressing the strong influence of the undulations themselves on the first region, which is the active region.

[0014] The thickness of the laminate in the first region in the stacking direction may be greater than the thickness of the laminate in the second region in the stacking direction, which makes it easier to impart waviness to the second region. [Effects of the Invention]

[0015] According to the present disclosure, the occurrence of warpage in the active region can be effectively suppressed. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is an exploded perspective view showing a layer configuration of a piezoelectric element according to an embodiment of the present disclosure. [Figure 2] 2 is a plan view of a first piezoelectric layer that constitutes a laminate of piezoelectric elements shown in FIG. 1. FIG. [Figure 3] 2 is a plan view of a second piezoelectric layer that constitutes the laminate of piezoelectric elements shown in FIG. 1. FIG. [Figure 4] 2 is a plan view of a third piezoelectric layer that constitutes the laminate of piezoelectric elements shown in FIG. 1. FIG. [Figure 5] 2 is a plan view of a fourth piezoelectric layer that constitutes the laminate of piezoelectric elements shown in FIG. 1. FIG. [Figure 6] 2 is a cross-sectional view showing the layer structure of the piezoelectric element shown in FIG. [Figure 7] FIG. [Figure 8] FIG. 10 is a diagram showing an example of measurement results of the shape of a piezoelectric element according to a comparative example. [Figure 9] 10A and 10B are diagrams showing an example of measurement results of the shape of a piezoelectric element according to an example. [Figure 10] FIG. 10 is a diagram showing an example of measurement results of unevenness height of undulations. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, preferred embodiments of a piezoelectric element according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0018] FIG. 1 is an exploded perspective view showing the layer structure of a piezoelectric element according to an embodiment of the present disclosure. The piezoelectric element 1 is a so-called multi-layer piezoelectric element. As shown in FIG. 1, the piezoelectric element 1 includes a multi-layer body 2 having a flat rectangular parallelepiped shape. The multi-layer body 2 is configured to include a plurality of piezoelectric layers on which electrodes are formed. The multi-layer body 2 is configured by laminating, in this order, a first piezoelectric layer 4 (see FIG. 2), a second piezoelectric layer 6 (see FIG. 3), a third piezoelectric layer 8 (see FIG. 4), and a fourth piezoelectric layer 10 (see FIG. 5).

[0019] When viewed from the stacking direction of the piezoelectric layers, the laminate 2 has a pair of longitudinal edges (first edges) 2c, 2d and a pair of lateral edges (second edges) 2e, 2f. Here, the lateral direction is perpendicular to the longitudinal direction and perpendicular to the arrangement direction of the individual electrodes 20, 40 described below.

[0020] The first piezoelectric layer 4 to the third piezoelectric layer 8 are formed in the shape of rectangular thin plates from a piezoelectric ceramic material whose main component is, for example, lead zirconate titanate (PZT). The fourth piezoelectric layer 10 is formed in the shape of a rectangular thin plate from the above ceramic material. The thickness of the fourth piezoelectric layer 10 is smaller than the thicknesses of the first piezoelectric layer 4, the second piezoelectric layer 6, and the third piezoelectric layer 8 (see FIG. 6).

[0021] The electrodes included in the laminate 2 (individual electrodes 20, 40, dummy electrodes 22, common electrodes 30, 50, intermediate electrode 32, and connection electrodes 23, 41, which will be described later) are formed of a metal material containing silver and palladium as its main components, for example. These electrodes are patterned by screen printing, for example.

[0022] The first piezoelectric layer 4 is a layer that constitutes one end surface 2a in the stacking direction of the laminate 2. As shown in FIG. 2, individual electrodes 20, dummy electrodes 22, and connection electrodes 23 are arranged on the first piezoelectric layer 4. The first piezoelectric layer 4 has an inner region A1 in which the individual electrodes 20 are arranged, and an outer region A2 in which the dummy electrodes 22 are arranged so as to surround the inner region A1. The outer region A2 is arranged along the edge of the first piezoelectric layer 4, and the inner region A1 is arranged on the central side of the first piezoelectric layer 4.

[0023] In the inner region A1, the individual electrodes 20 are arranged in a matrix. The individual electrodes 20 are surface electrodes arranged on the surface (end face 2a) of the laminate 2. The individual electrodes 20 are arranged at predetermined intervals from each other. This achieves electrical isolation between the individual electrodes 20 on the end face 2a and prevents them from being affected by vibrations.

[0024] In the example of FIG. 2, the individual electrodes 20 are arranged in the longitudinal direction of the first piezoelectric layer 4. There are four sets of individual electrodes 20, each set consisting of two rows. Each set of individual electrodes 20 is arranged in the lateral direction of the first piezoelectric layer 4, with an interval of approximately one individual electrode 20 between them. The individual electrodes 20 have, for example, a rectangular shape. The longitudinal direction of the individual electrodes 20 is perpendicular to the longitudinal direction of the first piezoelectric layer 4, and the lateral direction of the individual electrodes 20 is perpendicular to the lateral direction of the first piezoelectric layer 4. A through-hole 21 is arranged directly below the individual electrodes 20.

[0025] A plurality of dummy electrodes 22 are arranged in the outer region A2. The dummy electrodes 22 are surface electrodes that are arranged on the surface (end surface 2a) of the laminate 2 together with the individual electrodes 20. The dummy electrodes 22 are formed, for example, in the same shape as the individual electrodes 20 and are arranged at regular intervals so as to surround the arrangement area of ​​the individual electrodes 20. No voltage is applied between the dummy electrodes 22 and the common electrode 30 of the second piezoelectric layer 6. Connection electrodes 23 are formed in the center portions of both longitudinal edge portions of the first piezoelectric layer 4. The connection electrodes 23 are arranged between the dummy electrodes 22, 22 in the outer region A2. A through hole 24 is arranged directly below the connection electrode 23.

[0026] The second piezoelectric layer 6 is a layer that constitutes the intermediate layer of the laminate 2. As shown in FIG. 3, a plurality of intermediate electrodes 32 and a common electrode 30 are arranged on the second piezoelectric layer 6. The intermediate electrodes 32 are electrodes for electrically connecting the individual electrodes 20 on the first piezoelectric layer 4 and the individual electrodes 40 on the third piezoelectric layer 8. In the example shown in FIG. 3, the plurality of intermediate electrodes 32 are arranged in the longitudinal direction of the second piezoelectric layer 6. Similar to the individual electrodes 20, the rows of the intermediate electrodes 32 are arranged in pairs, totaling four groups. The intermediate electrodes 32 are formed at positions corresponding to the through holes 21 connected to the individual electrodes 20 on the first piezoelectric layer 4. Through holes 33 are arranged directly below the intermediate electrodes 32.

[0027] The common electrode 30 is disposed on the surface of the second piezoelectric layer 6 so as to surround each row of the intermediate electrodes 32. The common electrode 30 is disposed on the entire surface of the second piezoelectric layer 6, except for the areas where each row of the intermediate electrodes 32 is disposed and the outer periphery of the second piezoelectric layer 6 (parts corresponding to second regions 71B described below). A through hole 31 is disposed directly below the common electrode 30 in the center of both longitudinal edges of the first piezoelectric layer 4.

[0028] The third piezoelectric layer 8 is a layer that, together with the second piezoelectric layer 6, constitutes an intermediate layer of the laminate 2. As shown in FIG. 4, a plurality of individual electrodes 40 are formed on the third piezoelectric layer 8. When viewed from the stacking direction of the laminate 2, the individual electrodes 40 are arranged in positions facing the individual electrodes 20 of the first piezoelectric layer 4. In the example of FIG. 4, the plurality of individual electrodes 40 are arranged in the longitudinal direction of the third piezoelectric layer 8. Similar to the individual electrodes 20, the rows of the individual electrodes 40 are arranged in pairs, for a total of four groups.

[0029] A connection electrode 41 is formed at the center of each of both longitudinal edges of the third piezoelectric layer 8. The connection electrode 41 is an electrode for electrically connecting the common electrode 30 of the second piezoelectric layer 6 and the common electrode 50 of the fourth piezoelectric layer 10. A through-hole 42 is disposed directly below the connection electrode 41.

[0030] The fourth piezoelectric layer 10 is a layer that constitutes the other end surface 2b in the stacking direction of the laminate 2. As shown in FIG. 5, a common electrode 50 is arranged on the fourth piezoelectric layer 10. In the example of FIG. 5, the common electrode 50 is arranged on the entire surface of the fourth piezoelectric layer 10 except for the outer peripheral edge portion of the fourth piezoelectric layer 10 (a portion corresponding to a second region 71B described below). The thickness of the common electrode 50 is greater than the thickness of each electrode (individual electrodes 20, 40, dummy electrode 22, common electrode 30, intermediate electrode 32, and connection electrodes 23, 41) included in the first piezoelectric layer 4 to the third piezoelectric layer 8.

[0031] In the laminate 2 described above, the individual electrodes 20, 40 are electrically connected to each other by the conductive members in the through holes 21, 33, and the common electrodes 30, 50 are electrically connected to each other by the conductive members in the through holes 231, 42. When a voltage is applied between the individual electrode 20 and the connection electrode 23, a voltage is applied between the individual electrodes 20, 40 and the common electrodes 30, 50. This generates an electric field in the regions of the first piezoelectric layer 4 to the fourth piezoelectric layer 10 that are sandwiched between the individual electrodes 20, 40 and the common electrodes 30, 50, causing these regions to displace as active regions.

[0032] Next, the configuration of the laminate 2 will be described in more detail.

[0033] Fig. 7 is an enlarged perspective view of a main portion of the laminate. For ease of explanation, Fig. 7 shows an enlarged view of the vicinity of one corner of the laminate 2 (the corner formed by the edge 2c and the edge 2f), and omits the surface electrodes (individual electrodes 20, dummy electrodes 22, and connection electrodes 23) on the end surface 2a of the laminate 2.

[0034] When viewed from the stacking direction, the laminate 2 has a first region 71A where both the piezoelectric layers and the electrodes are located, and a second region 71B where only the piezoelectric layers are located. The first region 71A is a portion that functions as an active region that generates displacement in the stacking direction. That is, the first region 71A is a region in the first piezoelectric layer 4 to the fourth piezoelectric layer 10 that includes a region sandwiched between the individual electrodes 20, 40 and the common electrodes 30, 50 (see FIG. 6). In this embodiment, the first region 71A is a rectangular region that coincides with the region where the common electrode 50 is formed on the fourth piezoelectric layer 10. The longitudinal direction of the first region 71A coincides with the longitudinal direction of the laminate 2, and the lateral direction of the first region 71A coincides with the lateral direction of the laminate 2.

[0035] The second region 71B functions as a restraining region that restrains distortion of the first region 71A. The second region 71B is adjacent to the first region 71A and extends along at least a portion of the edge of the laminate 2. The second region 71B extends along each of the edges 2c, 2d and 2e, 2f. The second region 71B is a rectangular frame-shaped region that surrounds the entire outer periphery of the first region 71A. The protrusion width W1 of the second region 71B from the first region 71A along the edges 2c, 2d is larger than the protrusion width W2 of the second region 71B from the first region 71A along the edges 2e, 2f.

[0036] The thickness of the laminate 2 in the first region 71A in the stacking direction is greater than the thickness of the laminate 2 in the second region 71B in the stacking direction. This difference in thickness is due to the fact that the first region 71A includes both piezoelectric layers and electrodes, while the second region 71B includes only piezoelectric layers. The manufacturing process of the piezoelectric element 1 includes a pressing step in which a laminate of four green sheets that will become the first piezoelectric layer 4 to the fourth piezoelectric layer 10 is pressed in the stacking direction. In this pressing step, by using an isostatic press, pressure is applied isotropically to the green sheet laminate, making it possible to more reliably create a difference in thickness between the first region 71A and the second region 71B.

[0037] 7, the second region 71B has undulations K due to unevenness in the stacking direction. The undulations K can be formed due to a difference in shrinkage stress between the first region 71A, which includes both the piezoelectric layers and the electrodes, and the second region 71B, which includes only the piezoelectric layers, during the firing process in which the green sheet stack after the pressing process is fired at a high temperature.

[0038] 7, in the second region 71B along the edges 2c and 2d, the unevenness of the swell K extends in the direction connecting the edges 2c and 2d (longitudinal direction). Also, in the second region 71B along the second edges 2e and 2f, the unevenness of the swell K extends in the direction connecting the edges 2e and 2f (transverse direction). In other words, the unevenness of the swell K in the second region 71B along the edges 2c and 2d and the unevenness of the swell K in the second region 71B along the second edges 2e and 2f are perpendicular to or intersect with each other.

[0039] The degree of the waviness K can be expressed, for example, by the height of the waviness K. The height of the waviness K is expressed, for example, by the difference in height between the highest and lowest points of the waviness in that region. In this case, the height of the waviness K depends, for example, on the width of the second region 71B extending from the first region 71A. In the example of FIG. 7, as described above, the width W1 of the second region 71B extending from the first region 71A along the edges 2c and 2d is greater than the width W2 of the second region 71B extending from the first region 71A along the edges 2e and 2f. Therefore, the height H1 of the waviness K in the second region 71B extending from the edges 2c and 2d is greater than the height H2 of the waviness K in the second region 71B extending from the edges 2c and 2d.

[0040] In this embodiment, swells K continuing from the second region 71B are also formed in the first region 71A at least in the portion adjacent to the second region 71B. In the example of FIG. 7, the swells K in the second region 71B along the edges 2c and 2d and the swells K in the second region 71B along the edges 2c and 2d each extend to the peripheral edge of the first region 71A. The uneven height of the swells K gradually decreases from the second region 71B toward the first region 71A. The uneven heights H1 and H2 of the swells K in the second region 71B are greater than the uneven height H3 of the swells K in the first region 71A.

[0041] As described above, the piezoelectric element 1 has a first region 71A where both the piezoelectric layer and the electrode are located, and a second region 71B where only the piezoelectric layer is located. The first region 71A functions as an active region that generates displacement in the stacking direction. Meanwhile, the second region 71B is adjacent to the first region 71A and extends along at least a portion of the edge of the laminate 2, thereby functioning as a restraining region that restrains the distortion of the first region 71A. In the piezoelectric element 1, the second region 71B has waviness K due to unevenness in the stacking direction, which fully exerts its function of restraining the distortion of the first region 71A. Therefore, in the piezoelectric element 1, even if a difference in shrinkage stress occurs between the piezoelectric layer and the electrode during firing of the green sheet, warping in the active region can be effectively suppressed.

[0042] In the piezoelectric element 1, the second region 71B is positioned so as to surround the outside of the first region 71A when viewed from the stacking direction. By surrounding the outside of the first region 71A with the second region 71B as a restraining region, the distortion of the first region 71A can be more reliably restrained. Therefore, the occurrence of warpage in the active region can be more effectively suppressed.

[0043] In the piezoelectric element 1, the laminate 2 has a pair of longitudinal edges 2c, 2d and a pair of lateral edges 2e, 2f when viewed in the stacking direction. The second region 71B extends along the edges 2c, 2d and the edges 2e, 2f. In this way, by locating the active region in the center of the laminate 2 when viewed in the stacking direction, the electrode layout can be simplified. Furthermore, by locating the second region 71B having the waviness K along the edges 2c, 2d and the edges 2e, 2f, the waviness itself can be prevented from excessively affecting the first region 71A, which is the active region.

[0044] In the piezoelectric element 1, in the second region 71B along the edges 2c and 2d, the unevenness of the swells K extends in the direction connecting the edges 2c and 2d, and in the second region 71B along the edges 2e and 2f, the unevenness of the swells K extends in the direction connecting the edges 2e and 2f. This causes the extending directions of the unevenness of the swells K to intersect between the edges 2c and 2d and the edges 2e and 2f, allowing the second region 71B to function more effectively as a restraining region.

[0045] In the piezoelectric element 1, the protrusion width W1 of the second region 71B along the edges 2c and 2d from the first region 71A is larger than the protrusion width W2 of the second region 71B along the edges 2e and 2f from the first region 71A. Furthermore, the unevenness height H1 of the undulations K in the second region 71B along the edges 2c and 2d is larger than the unevenness height H2 of the undulations K in the second region 71B along the edges 2e and 2f. In the piezoelectric element 1, the arrangement direction of the individual electrodes 20 and 40 is aligned with the direction in which the protrusion width is larger (the longitudinal direction), which simplifies the electrode layout. Furthermore, in the piezoelectric element 1, the unevenness height of the undulations K in the second region 71B is sufficiently ensured near the connection electrodes 23 and 41, which effectively suppresses warping near the connection electrodes 23 and 41 in the active region.

[0046] In the piezoelectric element 1, the first region 71A has ripples K that continue from the second region 71B in at least the portion adjacent to the second region 71B. This allows the restraining force of the ripples K to be exerted directly on the first region 71A, thereby more effectively suppressing the occurrence of warpage in the active region. Furthermore, in the piezoelectric element 1, the ripple heights H1 and H2 in the second region 71B are greater than the ripple height H3 in the first region 71A. This prevents the ripples K from having a strong effect on the first region 71A, which is the active region, while allowing the ripples K in the second region 71B to firmly restrain the distortion of the first region 71A.

[0047] In the piezoelectric element 1, the thickness of the laminate 2 in the stacking direction in the first region 71A is greater than the thickness of the laminate 2 in the stacking direction in the second region 71B. This makes it easier to impart undulations K to the second region 71B.

[0048] The present disclosure is not limited to the above-described embodiment. For example, in the above-described embodiment, when the laminate 2 is viewed from the stacking direction, the second region 71B is positioned so as to surround the outside of the first region 71A. However, the second region 71B does not necessarily have to surround the entire periphery of the first region 71A. For example, the second region 71B may be positioned only on one side or two opposing sides of the edge portions 2c to 2f.

[0049] Furthermore, the swell K does not necessarily have to reach the first region 71A. That is, the swell K may terminate in the second region 71B. In this case, it is possible to more reliably prevent the swell itself from affecting the first region 71A, which is the active region.

[0050] The piezoelectric element according to the present disclosure can be applied to various devices. For example, it can be applied to an ejection device that ejects ink droplets from a nozzle in an inkjet printer. It can also be applied to an acoustic device or a vibration device used as a speaker or buzzer in electronic devices that emit sound, such as televisions and smartphones.

[0051] The following describes a test to confirm the effects of the piezoelectric element according to the present disclosure.

[0052] In this test, a piezoelectric element (comparative example) consisting of only an active region (first region) and a piezoelectric element (example) in which a constraint region (second region) was formed around the active region (first region) were prepared, and the shape of the piezoelectric element in each case was measured. In forming the piezoelectric element, the sintering temperature of the green sheet laminate was set to 1100°C. A three-dimensional shape measuring machine was used to measure the shape of the piezoelectric element.

[0053] As shown in Figure 8, the piezoelectric element according to the comparative example shows warpage occurring in the outer periphery of the piezoelectric element. The warpage is particularly large near the corners of the piezoelectric element, with the maximum amount of warpage in these areas reaching approximately 1000 µm. Because the piezoelectric element according to the comparative example is composed only of an active region (first region), the warpage in the outer periphery of the piezoelectric element shown in Figure 8 directly represents warpage occurring in the active region.

[0054] In contrast, in the piezoelectric element according to the example, as shown in Figure 9, undulations due to unevenness in the stacking direction occur in the outer periphery of the piezoelectric element, while the flatness of the shape is maintained in the central portion of the piezoelectric element. The amount of warpage in the central portion of the piezoelectric element, i.e., the active region (first region), was suppressed to a maximum of approximately 500 μm. From these results, it was confirmed that the configuration of the piezoelectric element according to the present disclosure, which provides a second region having undulations due to unevenness in the stacking direction, contributes to suppressing warpage in the active region (first region).

[0055] 10 is a diagram showing an example of the measurement results of the unevenness height of the undulations in the piezoelectric element of the example. In this measurement, 12 samples of the piezoelectric element according to the example were prepared, and for each sample, the unevenness height of the undulations in the second region along the longitudinal edge of the laminate and the unevenness height of the undulations in the second region along the lateral edge of the laminate were measured. The protruding width of the second region at the longitudinal edge was set to 100 μm, and the protruding width of the second region at the lateral edge was set to 150 μm.

[0056] As shown in Figure 10, the unevenness height of the waviness in the second region along the short-side edge was 94 μm on average and 129 μm at maximum. The unevenness height of the waviness in the second region along the long-side edge was 62 μm on average and 70 μm at maximum. These results confirm that the unevenness height of the waviness in the second region can be controlled by adjusting the extension width of the second region from the first region. [Explanation of symbols]

[0057] 1...piezoelectric element, 2...laminated body, 2c, 2d...edge portion (first edge portion), 2e, 2f...(second edge portion), 4...first piezoelectric layer (piezoelectric layer), 6...second piezoelectric layer (piezoelectric layer), 8...third piezoelectric layer (piezoelectric layer), 10...fourth piezoelectric layer (piezoelectric layer), 20, 40...individual electrodes (electrodes), 22...dummy electrodes (electrodes), 23, 41...connecting electrodes (electrodes), 30, 50...common electrodes (electrodes), 32...intermediate electrodes (electrodes), 71A...first region, 71B...second region, K...waviness.

Claims

1. a laminate including a plurality of piezoelectric layers on which electrodes are formed, the laminate has, when viewed from the stacking direction of the piezoelectric layers, a first region in which both the piezoelectric layers and the electrodes are located and a second region in which only the piezoelectric layers are located; the second region is adjacent to the first region and extends along at least a part of an edge of the laminate, and has undulations due to unevenness in the laminate direction; When viewed from the stacking direction, the laminate has a pair of first edge portions in a longitudinal direction and a pair of second edge portions in a lateral direction, the second region extends along each of the pair of first edges and the pair of second edges; a protrusion width of the second region from the first region along the first edge portion is greater than a protrusion width of the second region from the first region along the second edge portion, A piezoelectric element in which the uneven height of the undulations in the second region along the first edge portion is greater than the uneven height of the undulations in the second region along the second edge portion.

2. The piezoelectric element according to claim 1 , wherein the second region is positioned so as to surround the outside of the first region when viewed in the stacking direction.

3. In the second region along the first edge portion, the unevenness in the undulations extends in a direction connecting the pair of first edge portions, 3. The piezoelectric element according to claim 1, wherein in the second region along the second edge portions, the unevenness in the undulations extends in a direction connecting the pair of second edge portions.

4. 4. The piezoelectric element according to claim 1, wherein the first region has the undulation continuing from the second region at least in a portion adjacent to the second region.

5. 5. The piezoelectric element according to claim 4, wherein the height of the undulations in the second region is greater than the height of the undulations in the first region.

6. A piezoelectric element according to any one of claims 1 to 5, wherein the thickness of the laminate in the stacking direction in the first region is greater than the thickness of the laminate in the stacking direction in the second region.

7. a laminate including a plurality of piezoelectric layers on which electrodes are formed, the laminate has, when viewed from the stacking direction of the piezoelectric layers, a first region in which both the piezoelectric layers and the electrodes are located and a second region in which only the piezoelectric layers are located; the second region is adjacent to the first region and extends along at least a part of an edge of the laminate, and has undulations due to unevenness in the laminate direction; the first region has the undulation continuing from the second region at least in a portion adjacent to the second region; The height of the undulations in the second region is greater than the height of the undulations in the first region.

8. The piezoelectric element according to claim 7 , wherein the second region is positioned so as to surround the outside of the first region when viewed in the stacking direction.

9. When viewed from the stacking direction, the laminate has a pair of first edge portions in a longitudinal direction and a pair of second edge portions in a lateral direction, 9. The piezoelectric element according to claim 7, wherein the second regions extend along the pair of first edges and the pair of second edges, respectively.

10. In the second region along the first edge portion, the unevenness in the undulations extends in a direction connecting the pair of first edge portions, The piezoelectric element according to claim 9 , wherein in the second region along the second edge portions, the unevenness in the undulations extends in a direction connecting the pair of second edge portions.

11. a protrusion width of the second region from the first region along the first edge portion is greater than a protrusion width of the second region from the first region along the second edge portion, 11. The piezoelectric element according to claim 9, wherein the height of the undulations in the second region along the first edge portion is greater than the height of the undulations in the second region along the second edge portion.

12. A piezoelectric element according to any one of claims 7 to 11, wherein the thickness of the laminate in the stacking direction in the first region is greater than the thickness of the laminate in the stacking direction in the second region.

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