Piezoelectric element

Abstract

To provide a piezoelectric element capable of improving the reliability of electrical connection at a conductor.SOLUTION: A piezoelectric element PD1 comprises: an element body 1; an external electrode arranged on an outer surface of the element body 1; and an internal electrode connected with the external electrode and arranged in the element body 1. The internal electrode has an internal conductor 31 and an internal conductor 32 opposed to each other. The internal conductor 32 includes a conductor portion 32b extending in a first direction D1 and connected with the internal conductor 31. The conductor portion 32b is formed with a cavity 50.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] A known piezoelectric element includes a plurality of conductors arranged on a piezoelectric body (see, for example, Patent Document 1). The plurality of conductors includes, for example, an external electrode arranged on the outer surface of the piezoelectric body, and an internal electrode connected to the external electrode and arranged inside the piezoelectric body. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6747111 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of each aspect of the present invention is to provide a piezoelectric element that improves the reliability of electrical connections in conductors. [Means for solving the problem]

[0005] The present inventors have conducted research into piezoelectric elements that improve the reliability of electrical connections in conductors. As a result, the present inventors have newly obtained the following findings, which have led to the present invention. The plurality of conductors arranged in the piezoelectric element may include a first conductor and a second conductor that face each other. In this case, the second conductor includes a connecting portion that extends in the direction in which the first conductor and the second conductor face each other and is connected to the first conductor. In a configuration in which the piezoelectric element includes an external electrode and an internal electrode, for example, the internal electrode may have a first internal conductor that includes the first conductor, and a second internal conductor that includes the second conductor and a connecting portion and faces the first internal conductor. In a piezoelectric element, as the piezoelectric element deforms, stress from the piezoelectric element may act on the conductor. The stress acting from the piezoelectric element may concentrate at the connection part. If the stress acting from the piezoelectric element concentrates at the connection part, cracks may occur at the connection part. If cracks occur at the connection part, the reliability of the electrical connection in the conductor decreases. A conductor with a reduced reliability of the electrical connection makes it difficult to achieve stable transmission of drive signals. According to the inventors' investigations, in a configuration in which the connection portion is deformable, even if stress from the piezoelectric element acts on the connection portion, the connection portion reduces the risk of cracks occurring at the connection portion. Reducing the risk of cracks occurring at the connection portion increases the resistance of the conductor to stress acting from the piezoelectric element. This improves the reliability of the electrical connection in the conductor.

[0006] A piezoelectric element according to one aspect of the present invention includes a piezoelectric body, an external electrode disposed on the outer surface of the piezoelectric body, and an internal electrode connected to the external electrode and disposed within the piezoelectric body. The internal electrode has a first internal conductor and a second internal conductor that face each other. The second internal conductor includes a connection portion that extends in the direction in which the first internal conductor and the second internal conductor face each other and is connected to the first internal conductor. A cavity is formed in the connection portion.

[0007] In the above aspect, the internal electrode has a first internal conductor and a second internal conductor facing each other. The second internal conductor includes a connection portion connected to the first internal conductor. A cavity is formed in the connection portion. The connection portion with the cavity formed is more easily deformed than a connection portion without the cavity. Therefore, when stress from the piezoelectric element acts on the connection portion as the piezoelectric element deforms, cracks are less likely to occur in the connection portion. As a result, the resistance of the internal electrode to stress acting from the piezoelectric element is increased. The reliability of the electrical connection in the internal electrode is improved.

[0008] In the above-mentioned one aspect, in a cross section obtained by cutting the connection portion along a plane extending in the above-mentioned direction, which cross section includes a cavity, the circle-equivalent diameter of the cavity at the cross section may be 50% or less of the width at the cross section of the connection portion. In a configuration in which the equivalent circular diameter of the cavity at the cross section is 50% or less of the width at the cross section of the connection part, electrical disconnections due to the formation of a cavity at the connection part are unlikely to occur, realizing stable transmission of drive signals through the connection part and further improving the reliability of the electrical connection at the internal electrodes.

[0009] In the above aspect, the cross section of the cavity may be polygonal. In a configuration in which the cross section of the cavity is polygonal, the surfaces defining the cavity have multiple corners and edges, so the connection portion is more likely to deform in response to deformation of the piezoelectric element. Cracks are less likely to occur in the connection portion. As a result, the resistance of the internal electrodes to stress acting from the piezoelectric element is further increased. This further improves the reliability of the electrical connection at the internal electrodes.

[0010] In the above aspect, the first internal conductor may include a first conductor portion and a second conductor portion that are continuous with each other. The second internal conductor may further include a third conductor portion that faces the first conductor portion in the above direction. The connection portion may have a first region connected to the second conductor portion, and a second region that is continuous with the first region and also with the third conductor portion. The piezoelectric element may include an element body portion located between the first internal conductor and the second internal conductor. A through hole may be formed in the element body portion, penetrating the element body portion in the above direction. The connection portion may be located within the through hole. The thickness of the connection portion in the above direction may increase toward the center line of the through hole. In a configuration in which the connection portion is continuous with the third conductor portion and the thickness of the connection portion in the above direction increases toward the center line of the through hole, the shape of the internal electrode gradually changes where the connection portion and the third conductor portion are continuous with each other. Stress acting on the conductor from the piezoelectric element due to deformation of the piezoelectric element is less likely to concentrate at the continuous portion. At the continuous portion, a decrease in the reliability of the electrical connection due to stress concentration is suppressed. As a result, the reliability of the electrical connection at the internal electrode is further improved.

[0011] In the above aspect, the cavity may be formed in at least one of the first region and the second region. In a configuration in which a cavity is formed in at least one of the first region and the second region, at least one of the first region and the second region is easily deformed. Cracks are less likely to occur in the first and second regions. As a result, the resistance of the internal electrodes to stress acting from the piezoelectric element body is further increased. The reliability of the electrical connection in the internal electrodes is further improved.

[0012] In the above aspect, the degree of increase in thickness of the second region in the above direction may be smaller than the degree of increase in thickness of the first region in the above direction. When the second region has a smaller increase in thickness in the above direction than the first region, the shape of the internal electrode changes more gradually at the continuous portion. Stress acting on the internal electrode from the piezoelectric element due to deformation of the piezoelectric element is less likely to concentrate at the continuous portion. As a result, the reliability of the electrical connection at the internal electrode is improved.

[0013] In the above aspect, the directions may include a first direction from the first internal conductor to the second internal conductor and a second direction from the second internal conductor to the first internal conductor. Taking a plane that is orthogonal to the above directions and that includes the third conductor portion as a reference plane, the second region may include a region having a thickness in the first direction from the reference plane and a region having a thickness in the second direction from the reference plane. The thicknesses of the region portions included in the second region in the above directions may increase toward the center line. In a configuration in which the thickness of each region included in the second region in the above direction increases toward the center line, the shape of the internal electrode changes more gradually at the continuous portion. Stress acting on the internal electrode from the piezoelectric element due to deformation of the piezoelectric element is less likely to concentrate at the continuous portion. As a result, the reliability of the electrical connection at the internal electrode is further improved.

[0014] In the above aspect, the entire outer edge of the second conductor portion may be located inside the outer edge of the second region when viewed from the above direction. In a configuration in which the entire outer edge of the second conductor portion is located inside the outer edge of the second region when viewed from the above direction, the outer edge of the second region is located farther from the center line when viewed from the above direction, and the degree of increase in thickness of the second region in the above direction is reduced. The shape of the internal electrode changes more gradually at the continuous portion. Stress acting on the internal electrode from the piezoelectric element due to deformation of the piezoelectric element is even less likely to concentrate at the continuous portion. As a result, the reliability of the electrical connection at the internal electrode is further improved.

[0015] In the above aspect, the second region may have a recess formed at an end portion thereof that is distant from the first region in the above direction. In a configuration in which a recess is formed in the second region at an end away from the first region in the above direction, the thickness of the fourth conductor portion in the above direction is reduced by the amount of the recess formed in the second region. This reduction in thickness allows the fourth conductor portion to more easily follow the contraction and expansion of the third conductor portion that accompanies deformation of the piezoelectric element body. Therefore, a decrease in the reliability of the electrical connection in the above-mentioned continuous portion is further suppressed. As a result, the reliability of the electrical connection in the internal electrodes is further improved.

[0016] In the above aspect, the cavity may be formed in a region within the second region that includes the surface that defines the recess. In a configuration in which the cavity is formed in a region within the second region that includes the surface defining the recess, peeling between the recess and the piezoelectric element can be suppressed, thereby further improving the reliability of the electrical connection at the internal electrodes.

[0017] In the above aspect, the depth of the recess may increase as it approaches the center line. In a configuration in which the depth of the recess increases toward the center line, the thickness of the fourth conductor portion in the above direction decreases toward the center line, and the fourth conductor portion more easily follows the contraction and expansion of the third conductor portion that accompanies deformation of the piezoelectric element. Therefore, deterioration in the reliability of the electrical connection in the continuous portion is further suppressed. As a result, the reliability of the electrical connection in the internal electrodes is further improved.

[0018] In the above aspect, the second conductor portion may be located inside the outer periphery of the recess when viewed from the above direction. In a configuration in which the second conductor portion is located inside the outer periphery of the recess when viewed from the above direction, the formation of the recess further expands the range in which the thickness of the fourth conductor portion in the above direction is reduced. This reduction in thickness over a wider range allows the fourth conductor portion to more easily follow the contraction and expansion of the third conductor portion that accompanies deformation of the piezoelectric element. Therefore, deterioration in the reliability of the electrical connection in the continuous portion is further suppressed. As a result, the reliability of the electrical connection in the internal electrodes is further improved.

[0019] In the above aspect, the second region and the depression may have a circular shape when viewed from the above direction. In a configuration in which the second region and the recess have a circular shape when viewed from the above direction, the fourth conductor portion is more likely to follow the contraction and expansion of the third conductor portion in a direction intersecting the above direction that accompanies deformation of the piezoelectric element body. Therefore, deterioration in the reliability of the electrical connection in the continuous portion is further suppressed. As a result, the reliability of the electrical connection in the internal electrode is further improved.

[0020] In the above aspect, the length of the first region in the above direction may be smaller than the length of the bottom of the recess and the second conductor portion in the above direction. In a configuration in which the length of the first region in the above-mentioned direction is shorter than the length between the bottom of the recess and the second conductor portion in the above-mentioned direction, the fourth conductor portion is more likely to follow the contraction and expansion of the third conductor portion that accompanies deformation of the piezoelectric element body. Therefore, deterioration in the reliability of the electrical connection in the continuous portion is further suppressed. As a result, the reliability of the electrical connection in the internal electrodes is further improved.

[0021] In the above aspect, the connecting portion may have a recess formed therein that opens to an outer peripheral surface of the connecting portion. A configuration in which a recess that opens onto the outer periphery of the connecting portion is formed in the connecting portion is less likely to reflect vibrations transmitted from the piezoelectric element than a configuration in which no recess is formed, and therefore vibrations caused by deformation of the piezoelectric element are more easily transmitted within the piezoelectric element, improving the resonance characteristics of the piezoelectric element.

[0022] A piezoelectric element according to another aspect of the present invention includes a piezoelectric body, an external electrode disposed on the outer surface of the piezoelectric body, and an internal electrode connected to the external electrode and disposed within the piezoelectric body. The internal electrode has a first internal conductor and a second internal conductor facing each other. The second internal conductor includes a connection portion extending in the direction in which the first internal conductor and the second internal conductor face each other and connected to the first internal conductor. The connection portion has a recess formed in the outer peripheral surface of the connection portion.

[0023] In another aspect of the invention, the internal electrode has a first internal conductor and a second internal conductor facing each other. The second internal conductor includes a connection portion connected to the first internal conductor. The connection portion has a recess formed therein that opens to the outer circumferential surface of the connection portion. The connection portion with the recess formed therein is more easily deformed than the connection portion without the recess formed therein. Therefore, when stress from the piezoelectric element acts on the connection portion as the piezoelectric element deforms, cracks are less likely to occur in the connection portion. As a result, the resistance of the internal electrode to stress acting from the piezoelectric element is increased. The reliability of the electrical connection in the internal electrode is improved.

[0024] A piezoelectric element according to yet another aspect of the present invention includes a piezoelectric body, a first conductor disposed on the piezoelectric body, and a second conductor connected to the first conductor and disposed on the piezoelectric body so as to face the first conductor. The second conductor includes a connection portion extending in the direction in which the first conductor and the second conductor face each other and connected to the first conductor. A cavity is formed in the connection portion. In yet another aspect of the present invention, a cavity is formed in the connection portion. A connection portion with a cavity formed therein is more easily deformed than a connection portion without a cavity formed therein. Therefore, when stress from the piezoelectric element acts on the connection portion as the piezoelectric element deforms, cracks are less likely to occur in the connection portion. As a result, the resistance of the conductor to stress acting from the piezoelectric element is increased. This improves the reliability of the electrical connection in the conductor.

[0025] A piezoelectric element according to yet another aspect of the present invention includes a piezoelectric body, a first conductor disposed on the piezoelectric body, and a second conductor connected to the first conductor and disposed on the piezoelectric body so as to face the first conductor. The second conductor includes a connection portion extending in the direction in which the first conductor and the second conductor face each other and connected to the first conductor. The connection portion has a recess formed in the outer circumferential surface of the connection portion. In another aspect of the present invention, the connection portion has a recess formed in the outer circumferential surface of the connection portion. The connection portion with the recess formed is more easily deformed than the connection portion without the recess formed. Therefore, when stress from the piezoelectric element acts on the connection portion as the piezoelectric element deforms, cracks are less likely to occur in the connection portion. As a result, the resistance of the conductor to stress acting from the piezoelectric element is increased. The reliability of the electrical connection in the conductor is improved. [Effects of the Invention]

[0026] Each aspect of the present invention provides a piezoelectric element that improves the reliability of electrical connections with conductors. [Brief explanation of the drawings]

[0027] [Figure 1]FIG. 1 is a perspective view illustrating a piezoelectric element according to an embodiment. [Figure 2] 1 is a diagram showing a cross-sectional configuration of a piezoelectric element according to an embodiment of the present invention. [Figure 3] FIG. 10 is a diagram showing an arrangement of through holes. [Figure 4] FIG. 2 is a diagram showing the configuration of an internal conductor. [Figure 5] FIG. 2 is a diagram showing the configuration of an internal conductor. [Figure 6] FIG. 2 is a diagram showing the configuration of an internal conductor. [Figure 7] FIG. 2 is a diagram showing the configuration of an internal conductor. [Figure 8] FIG. 2 is a diagram showing the configuration of an internal conductor. [Figure 9] FIG. 2 is a diagram showing the configuration of an internal conductor. [Figure 10] FIG. 2 is a diagram showing the configuration of an internal conductor. [Figure 11] FIG. 2 is a diagram showing the configuration of an internal conductor. [Figure 12] FIG. 2 is a diagram showing the configuration of an internal conductor. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description, the same elements or elements having the same functions will be denoted by the same reference numerals, and redundant description will be omitted.

[0029] The configuration of the piezoelectric element PD1 according to this embodiment will be described with reference to Figs. 1 to 12. Fig. 1 is a perspective view showing the piezoelectric element according to this embodiment. Fig. 2 is a diagram showing the cross-sectional configuration of the piezoelectric element according to this embodiment. Fig. 3 is a diagram showing the arrangement of through holes. Figs. 4 to 12 are diagrams showing the configuration of the internal conductor. Hatching has been omitted in Figs. 4 to 12 to clearly show each part.

[0030] As shown in FIGS. 1 and 2, the piezoelectric element PD1 includes an element body 1, external electrodes 10 and 20, and internal electrodes 30 and 40. The external electrodes 10 and 20 are disposed on the outer surface of the element body 1. The internal electrodes 30 and 40 are disposed within the element body 1. The internal electrodes 30 and 40 are connected to the external electrodes 10 and 20. The internal electrodes 30 and 40 are connected to corresponding ones of the external electrodes 10 and 20. The internal electrodes 30 and 40 are physically and electrically connected to corresponding ones of the external electrodes 10 and 20. For example, voltages of opposite polarities are applied to the external electrodes 10 and 20. For example, if the external electrodes 10 and 20 constitute a first conductor, the internal electrodes 30 and 40 constitute a second conductor. For example, if the external electrodes 10 and 20 constitute a second conductor, the internal electrodes 30 and 40 may constitute a first conductor.

[0031] In this embodiment, the element body 1 is a piezoelectric element body having a rectangular parallelepiped shape. The element body 1 has a pair of principal surfaces 1a and 1b facing each other, a pair of side surfaces 1c and 1d facing each other, and a pair of side surfaces 1e and 1f facing each other. The principal surfaces 1a and 1b, the side surfaces 1c and 1d, and the side surfaces 1e and 1f form the outer surface of the element body 1. The principal surfaces 1a and 1b, the side surfaces 1c and 1d, and the side surfaces 1e and 1f have a rectangular shape.

[0032] The principal surfaces 1a and 1b face each other in the first direction D1. The principal surfaces 1a and 1b define both ends of the element body 1 in the first direction D1. The side surfaces 1c and 1d are adjacent to the principal surfaces 1a and 1b and face each other in a second direction D2 intersecting the first direction D1. The side surfaces 1c and 1d define both ends of the element body 1 in the second direction D2. The side surfaces 1e and 1f are adjacent to the principal surfaces 1a and 1b and the side surfaces 1c and 1d and face each other in a third direction D3 intersecting the first direction D1 and the second direction D2. The side surfaces 1e and 1f define both ends of the element body 1 in the third direction D3. In this embodiment, the first direction D1, the second direction D2, and the third direction D3 are orthogonal to each other. In this specification, the term "rectangular parallelepiped shape" includes a rectangular parallelepiped shape with chamfered corners and ridges, and a rectangular parallelepiped shape with rounded corners and ridges. In this specification, the term "rectangular" includes, for example, a shape in which each corner is chamfered and a shape in which each corner is rounded.

[0033] The principal surfaces 1a and 1b extend in the second direction D2 to connect the side surface 1c and the side surface 1d. The principal surfaces 1a and 1b extend in the third direction D3 to connect the side surface 1e and the side surface 1f. The side surfaces 1c and 1d extend in the first direction D1 to connect the principal surfaces 1a and 1b. The side surfaces 1c and 1d extend in the third direction D3 to connect the side surfaces 1e and 1f. The side surfaces 1e and 1f extend in the first direction D1 to connect the principal surfaces 1a and 1b. The side surfaces 1e and 1f extend in the second direction D2 to connect the side surfaces 1c and 1d. The principal surfaces 1a and 1b, the side surfaces 1c and 1d, and the side surfaces 1e and 1f may be indirectly adjacent to each other. In this case, ridges are located between the main surfaces 1a and 1b, the side surfaces 1c and 1d, and the side surfaces 1e and 1f.

[0034] The length of the element body 1 in the first direction D1, i.e., the thickness of the element body 1, is, for example, 0.2 to 0.5 mm. The length of the element body 1 in the second direction D2 is, for example, 20 mm. The length of the element body 1 in the third direction D3 is, for example, 10 mm. In the element body 1, the second direction D2 is, for example, the long side direction.

[0035] The element body 1 includes, for example, multiple piezoelectric layers 3a, 3b, 3c, 3d, and 3e. In this embodiment, the element body 1 includes five piezoelectric layers 3a, 3b, 3c, 3d, and 3e. The piezoelectric layers 3a, 3b, 3c, 3d, and 3e are stacked, for example, in a first direction D1. The piezoelectric layer 3a has a main surface 1a. The piezoelectric layer 3e has a main surface 1b. The piezoelectric layers 3b, 3c, and 3d are located between the piezoelectric layer 3a and the piezoelectric layer 3e. In this embodiment, the piezoelectric layers 3a, 3b, 3c, 3d, and 3e have the same thickness. In this specification, "same" does not necessarily mean that the values ​​are the same. The thicknesses may be considered to be equal even if there are slight differences, manufacturing errors, or measurement errors within a predetermined range. In this embodiment, the piezoelectric element PD1 is a so-called stacked piezoelectric element.

[0036] The piezoelectric layers 3a, 3b, 3c, 3d, and 3e are made of a piezoelectric material. In this embodiment, the piezoelectric layers 3a, 3b, 3c, 3d, and 3e are made of a piezoelectric ceramic material. The piezoelectric ceramic material includes, for example, PZT [Pb(Zr,Ti)O3], PT (PbTiO3), or barium titanate (BaTiO3). The piezoelectric layers 3a, 3b, 3c, 3d, and 3e are made of, for example, a sintered ceramic green sheet containing the above-mentioned piezoelectric ceramic material. In the actual element body 1, the piezoelectric layers 3a, 3b, 3c, 3d, and 3e are integrated to the extent that the boundaries between the piezoelectric layers 3a, 3b, 3c, 3d, and 3e are indistinguishable.

[0037] The external electrode 10 is disposed on the main surface 1b, for example. When viewed from the first direction D1, the external electrode 10 is spaced apart from all edges (four sides) of the main surface 1b, for example. The external electrode 20 is disposed on the main surface 1b, for example. When viewed from the first direction D1, the external electrode 20 is spaced apart from all edges (four sides) of the main surface 1b, for example. In this embodiment, when viewed from the first direction D1, the external electrodes 10 and 20 have a rectangular shape. When viewed from the first direction D1, the external electrodes 10 and 20 have, for example, the same shape as each other. When viewed from the first direction D1, the long side direction of the external electrodes 10 and 20 coincides with, for example, the second direction D2, and the short side direction of the external electrodes 10 and 20 coincides with, for example, the third direction D3. The external electrodes 10 and 20 contain a conductive material. For example, Ag, Pd, Cu, Pt, an Au—Pd alloy, or an Ag—Pd alloy is used as the conductive material of the external electrodes 10, 20. The external electrodes 10, 20 are formed, for example, as a sintered body of a conductive paste containing the above-mentioned conductive material.

[0038] The internal electrode 30 is connected to, for example, the external electrode 10. The internal electrode 30 has an internal conductor 31, an internal conductor 32, an internal conductor 33, and an internal conductor 34. The internal conductors 31, 32, 33, and 34 are arranged at different positions (layers) in the first direction D1. The internal conductors 31, 32, 33, and 34 face each other at an interval in the first direction D1. The internal conductors 31, 32, 33, and 34 are, for example, arranged in this order in the first direction D1. The internal conductor 34 faces the external electrode 10 in the first direction D1. The internal conductors 31, 32, 33, and 34 are not exposed on the outer surface of the element body 1. Therefore, the internal conductors 31, 32, 33, and 34 are spaced apart from all edges (four sides) of the main surfaces 1a and 1b. The internal conductors 31, 32, 33, and 34 are also spaced apart from the side surfaces 1c, 1d, 1e, and 1f. For example, when the internal conductor 31 constitutes the first internal conductor, the internal conductor 32 constitutes the second internal conductor. For example, when the internal conductor 32 constitutes the first internal conductor, the internal conductor 33 constitutes the second internal conductor. For example, when the internal conductor 33 constitutes the first internal conductor, the internal conductor 34 constitutes the second internal conductor.

[0039] The element body 1 includes, for example, a plurality of element body portions 5a, 5b, 5c, 5d, and 5e. The element body portion 5a is located between the main surface 1a and the internal conductor 31. The element body portion 5a includes, for example, the piezoelectric layer 3a. The element body portion 5b is located between the internal conductors 31 and 32. The element body portion 5b includes, for example, the piezoelectric layer 3b. The element body portion 5c is located between the internal conductors 32 and 33. The element body portion 5c includes, for example, the piezoelectric layer 3c. The element body portion 5d is located between the internal conductors 33 and 34. The element body portion 5d includes, for example, the piezoelectric layer 3d. The element body portion 5e is located between the internal conductor 34 and the main surface 1b. The element body portion 5e includes, for example, the piezoelectric layer 3e. The internal conductor 31 is located between the element body portions 5a and 5b. The inner conductor 32 is located between the element body portion 5b and the element body portion 5c. The inner conductor 33 is located between the element body portion 5c and the element body portion 5d. The inner conductor 34 is located between the element body portion 5d and the element body portion 5e.

[0040] In this embodiment, through holes 35b, 35c, 35d, and 35e are formed. The element body portion 5b has a through hole 35b that penetrates the element body portion 5b in the first direction D1. The element body portion 5c has a through hole 35c that penetrates the element body portion 5c in the first direction D1. The element body portion 5d has a through hole 35d that penetrates the element body portion 5d in the first direction D1. The element body portion 5e has a through hole 35e that penetrates the element body portion 5e in the first direction D1.

[0041] As shown in FIG. 3, the through holes 35b, 35c, 35d, and 35e are arranged, for example, in a matrix when viewed from the first direction D1. In the example shown in FIG. 3, the through holes 35b, 35c, 35d, and 35e are arranged in a matrix of two rows and two columns when viewed from the first direction D1. The through holes 35b and 35d, for example, overlap each other when viewed from the first direction D1. The through holes 35c and 35e, for example, overlap each other when viewed from the first direction D1. The through holes 35b and 35d and the through holes 35c and 35e are arranged, for example, at equal intervals when viewed from the first direction D1. The through holes 35b and 35d and the through holes 35c and 35e are arranged, for example, at the intersections of a lattice drawn at equal intervals, i.e., a square lattice. The arrangement interval of the through holes 35b, 35d in the second direction D2 is, for example, equal to the arrangement interval of the through holes 35c, 35e in the second direction D2. The arrangement interval of the through holes 35b, 35d in the third direction D3 is, for example, equal to the arrangement interval of the through holes 35c, 35e in the third direction D3. When viewed from the first direction D1, the through holes 35c, 35e are shifted in parallel with the through holes 35b, 35d by, for example, half the arrangement interval of the through holes 35b, 35c, 35d, 35e in the second direction D2 and the third direction D3. When viewed from the first direction D1, the through holes 35c, 35e may be shifted in parallel with the through holes 35b, 35d by, for example, half the arrangement interval of the through holes 35b, 35c, 35d, 35e in only one of the second direction D2 and the third direction D3. The through holes 35b, 35c, 35d, and 35e may be arranged in a matrix of, for example, 3 rows and 3 columns when viewed from the first direction D1.

[0042] The internal electrode 40 is connected to, for example, the external electrode 20. The internal electrode 40 has an internal conductor 41, an internal conductor 42, an internal conductor 43, and an internal conductor 44. The internal conductors 41, 42, 43, and 44 are arranged at different positions (layers) in the first direction D1. The internal conductors 41, 42, 43, and 44 face each other at an interval in the first direction D1. The internal conductors 41, 42, 43, and 44 are, for example, arranged in this order in the first direction D1. The internal conductor 44 faces the external electrode 20 in the first direction D1. The internal conductors 41, 42, 43, and 44 are not exposed on the outer surface of the element body 1. Therefore, the internal conductors 41, 42, 43, and 44 are spaced apart from all edges (four sides) of the main surfaces 1a and 1b. The internal conductors 41, 42, 43, and 44 are also spaced apart from the side surfaces 1c, 1d, 1e, and 1f. For example, when the internal conductor 41 constitutes the first internal conductor, the internal conductor 42 constitutes the second internal conductor. For example, when the internal conductor 42 constitutes the first internal conductor, the internal conductor 43 constitutes the second internal conductor. For example, when the internal conductor 43 constitutes the first internal conductor, the internal conductor 44 constitutes the second internal conductor.

[0043] The element body portion 5a is located between the principal surface 1a and the internal conductor 41. The element body portion 5a includes, for example, the piezoelectric layer 3a. The element body portion 5b is located between the internal conductors 41 and 42. The element body portion 5b includes, for example, the piezoelectric layer 3b. The element body portion 5c is located between the internal conductors 42 and 43. The element body portion 5c includes, for example, the piezoelectric layer 3c. The element body portion 5d is located between the internal conductors 43 and 44. The element body portion 5d includes, for example, the piezoelectric layer 3d. The element body portion 5e is located between the internal conductor 44 and the principal surface 1b. The element body portion 5e includes, for example, the piezoelectric layer 3e. The internal conductor 41 is located between the element body portion 5a and the element body portion 5b. The internal conductor 42 is located between the element body portion 5b and the element body portion 5c. The inner conductor 43 is located between the element body portion 5c and the element body portion 5d, and the inner conductor 44 is located between the element body portion 5d and the element body portion 5e.

[0044] In this embodiment, through holes 45b, 45c, 45d, and 45e are formed. A through hole 45b is formed in the element body portion 5b, penetrating the element body portion 5b in the first direction D1. A through hole 45c is formed in the element body portion 5c, penetrating the element body portion 5c in the first direction D1. A through hole 45d is formed in the element body portion 5d, penetrating the element body portion 5d in the first direction D1. A through hole 45e is formed in the element body portion 5e, penetrating the element body portion 5e in the first direction D1.

[0045] The through holes 45b to 45e are arranged, for example, in a matrix when viewed from the first direction D1. For example, when viewed from the first direction D1, four through holes 45b to 45e are arranged in a matrix of two rows and two columns. The through holes 45b, 45d and the through holes 45c, 45e are arranged, for example, at equal intervals when viewed from the first direction D1. The through holes 45b, 45d and the through holes 45c, 45e are arranged, for example, at the intersections of a lattice drawn at equal intervals, i.e., a square lattice. The arrangement of the through holes 45b to 45e is, for example, the same as the arrangement of the through holes 35b to 35e illustrated in FIG. 3.

[0046] In the example shown in FIG. 2, the internal conductor 31 and the internal conductor 42 face each other in the first direction D1. The internal conductor 31 and the internal conductor 42 sandwich the element body portion 5b therebetween. The internal conductor 42 and the internal conductor 33 face each other in the first direction D1. The internal conductor 42 and the internal conductor 33 sandwich the element body portion 5c therebetween. The internal conductor 33 and the internal conductor 44 face each other in the first direction D1. The internal conductor 33 and the internal conductor 44 sandwich the element body portion 5d therebetween.

[0047] In the element body 1, the region of the element body portion 5b sandwiched between the internal conductors 31 and 42, the region of the element body portion 5c sandwiched between the internal conductors 42 and 33, and the region of the element body portion 5d sandwiched between the internal conductors 33 and 44 constitute piezoelectrically active regions. Active regions are formed between the internal conductors 31 and 42, between the internal conductors 42 and 33, and between the internal conductors 33 and 44. When viewed from the first direction D1, the outer edges of the regions where the internal conductors 31 and 42, the internal conductors 42 and 33, and the internal conductors 33 and 44 overlap in the element body portions 5b, 5c, and 5d define boundaries between the active regions and piezoelectrically inactive inactive regions. In the element body 1, the element body portion 5a and the element body portion 5e constitute inactive regions.

[0048] The internal electrodes 30, 40 contain, for example, an Ag-Pd alloy. The internal electrodes 30, 40 are formed, for example, by co-firing with the element body 1, and are configured as a sintered body of a conductive paste containing particles of Ag and Pd. In addition to the Ag-Pd alloy, the internal electrodes 30, 40 contain, for example, a conductive material made of Pt, Ag, Pd, Au, Cu, or an alloy thereof. The internal electrodes 30, 40 may be configured as a sintered body of a conductive paste containing these conductive materials.

[0049] 4 and 5 are diagrams showing the configuration of the internal conductors 31 and 32. As shown in FIGS. 4 and 5, the internal conductor 31 includes a conductor portion 31a and a conductor portion 31b. The conductor portion 31a and the conductor portion 31b are continuous with each other. The conductor portion 31a and the conductor portion 31b are continuous with each other, for example, in the second direction D2 and the third direction D3. For example, when the conductor portion 31a constitutes a first conductor portion, the conductor portion 31b constitutes a second conductor portion.

[0050] The internal conductor 32 includes a conductor portion 32a and a conductor portion 32b. The conductor portion 32a faces the conductor portion 31a in the first direction D1. The conductor portion 32b extends in the first direction D1 and is connected to the internal conductor 31. The conductor portion 32b includes a region 32c and a region 32d. The region 32c is connected to the conductor portion 31b. The region 32c is, for example, physically and electrically connected to the conductor portion 31b. The region 32d is continuous with the region 32c and with the conductor portion 32a. In this embodiment, the region 32d is continuous with the region 32c in the first direction D1 and with the conductor portion 32a in the second direction D2 and the third direction D3. The conductor portion 32b is located within the through hole 35b. For example, when the conductor portion 32a constitutes the third conductor portion, the conductor portion 32b constitutes the fourth conductor portion. For example, when conductor portion 32a constitutes the third conductor portion, conductor portion 32b constitutes the connecting portion. For example, when region 32c constitutes the first region, region 32d constitutes the second region. The thickness of conductor portion 31a and conductor portion 32a is, for example, 2 μm.

[0051] 5, the thickness of the conductor portion 32b in the first direction D1 increases toward the center line CL1 of the through hole 35b. Therefore, the thicknesses of the regions 32c and 32d in the first direction D1 increase toward the center line CL1. The total thickness of the regions 32c and 32d in the first direction D1 increases toward the center line CL1 in the direction from the conductor portion 32a toward the conductor portion 31a. For example, the center line CL1 extends in the first direction D1.

[0052] In this embodiment, the rate at which the thickness of region 32d increases in the first direction D1 is different from the rate at which the thickness of region 32c increases in the first direction D1. For example, the rate at which the thickness of region 32d increases in the first direction D1 is smaller than the rate at which the thickness of region 32c increases in the first direction D1. Therefore, the rate at which the thickness of conductor portion 32b increases in the first direction D1 decreases, for example, at the boundary between region 32d and region 32c. The rate at which the thickness of region 32d increases in the first direction D1 may be greater than the rate at which the thickness of region 32c increases in the first direction D1. The rate at which the thickness of region 32d increases in the first direction D1 may be substantially the same as the rate at which the thickness of region 32c increases in the first direction D1.

[0053] In this embodiment, the first direction D1 includes a direction D1a from the internal conductor 31 toward the internal conductor 32 and a direction D1b from the internal conductor 32 toward the internal conductor 31. The region 32d includes a region portion 32d1 and a region portion 32d2. The reference plane SP1 is a plane that is perpendicular to the first direction D1 and includes the conductor portion 32a. The region 32d includes a region portion 32d2 having a thickness in the direction D1a from the reference plane SP1 and a region portion 32d1 having a thickness in the direction D1b from the reference plane SP1. The thicknesses of the region portions 32d1 and 32d2 in the first direction D1 increase toward the center line CL1. For example, if the direction D1a constitutes the first direction, the direction D1b constitutes the second direction.

[0054] When viewed from the first direction D1, the region 32d has, for example, a circular shape. When viewed from the first direction D1, the region 32c and the conductor portion 31b also have, for example, a circular shape. When viewed from the first direction D1, the region 32d extends outside the conductor portion 31b around the entire circumference of the conductor portion 31b. Therefore, when viewed from the first direction D1, for example, the circular shape of the region 32d includes the circular shape of the conductor portion 31b and extends outside the circular shape of the conductor portion 31b. In this specification, the term "circular shape" includes, for example, a perfect circle shape or an ellipse shape.

[0055] A recess 36 is formed in the region 32d at an end 32f away from the region 32c in the first direction D1. The recess 36 has, for example, a circular shape when viewed from the first direction D1. The recess 36 is filled with, for example, the element portion 5c. The recess 36 opens in a direction from the conductor portion 31a toward the conductor portion 32a. The recess 36 is formed, for example, by an opening edge 36a, a bottom 36b, and an inclined portion 36c connecting the opening edge 36a and the bottom 36b. The depth of the recess 36 increases from the opening edge 36a toward the bottom 36b. The opening edge 36a defines the outer periphery of the recess 36 when viewed from the first direction D1. The conductor portion 31b is located inside the outer periphery of the recess 36 when viewed from the first direction D1. The bottom 36b has, for example, a circular shape when viewed from the first direction D1. The width of the bottom 36b is smaller than the width of the opening edge 36a, i.e., the opening width W1. The inclined portion 36c is formed, for example, so that the width of the bottom 36b is smaller than the opening width W1. The bottom 36b intersects, for example, with the center line CL1. The central axis of the recess 36, for example, substantially coincides with the center line CL1.

[0056] In this embodiment, the entire outer edge of the conductor portion 31b is located, for example, inside the outer edge of the region 32d when viewed from the first direction D1. Therefore, the opening width W1 is, for example, larger than the width W2 of the conductor portion 31b. Therefore, the recess 36 extends outside the conductor portion 31b around the entire periphery of the conductor portion 31b when viewed from the first direction D1. The opening width W1 may be smaller than the width W2 of the conductor portion 31b or may be approximately the same as the width W2 of the conductor portion 31b.

[0057] The length H1 of the region 32c in the first direction D1 is smaller than, for example, the length H2 between the bottom 36b and the conductor portion 31b in the first direction D1. Therefore, the position where the rate of increase in the thickness of the conductor portion 32b changes is closer to the conductor portion 31b in the first direction D1 than to the bottom 36b. The length H1 may be greater than the length H2 or may be approximately the same as the length H2. The thickness of the conductor portion 32b in the first direction D1 is reduced by the amount corresponding to the formation of the recess 36.

[0058] As shown in Figures 4 and 5, the conductor portion 32b has a region 32p and a region 32q. The region 32p includes a first material having electrical conductivity. The region 32q includes a second material different from the first material. The linear expansion coefficient of the second material is different from the linear expansion coefficient of the first material. The linear expansion coefficient of the second material is, for example, smaller than the linear expansion coefficient of the first material. In this specification, the "linear expansion coefficient" represents the rate at which the length of a material changes with temperature. This "linear expansion coefficient" is defined, for example, as the rate of change in length per 1°C change in temperature.

[0059] The first material includes, for example, the same conductive material as the material included in the internal electrode 30 other than the conductive portion 32b. In this embodiment, the first material includes, for example, an Ag-Pd alloy, or a conductive material made of Pt, Ag, Pd, Au, Cu, or an alloy thereof. The conductive portion 32b may be configured as a sintered body of a conductive paste containing such a conductive material.

[0060] The second material includes, for example, a ceramic material. The ceramic material included in the second material is, for example, the same as the ceramic material included in the element body 1. The ceramic material included in the second material includes, for example, copper oxide.

[0061] Conductor portion 32b has, for example, a plurality of regions 32q. The plurality of regions 32q are distributed within region 32p. The plurality of regions 32q are, for example, uniformly distributed within region 32p. In this case, region 32p does not have an area where the plurality of regions 32q are distributed unevenly compared to other regions.

[0062] Region 32q has, for example, a protruding portion 32r that protrudes toward element body 1. Therefore, region 32q is in contact with, for example, element body 1. Region 32q may be integrated with element body 1, for example.

[0063] Region 32q is located in at least one of region 32c and region 32d. Therefore, region 32q is located in both region 32c and region 32d, for example. Region 32q is located in region 32c, but not in region 32d, for example. Region 32q is located in region 32d, but not in region 32c, for example.

[0064] Region 32q is located, for example, in region 32d, in region 32s including the surface that defines recess 36. In this embodiment, region 32q is located, for example, in regions 32c, 32d, and 32s. Region 32q is located, for example, in regions 32c and 32s, but not in region 32d. Region 32q is located, for example, in regions 32d and 32s, but not in region 32c. Region 32q does not have to be located in region 32s. In regions 32c, 32d, and 32s, when region 32q is located, for example, portion 32r may protrude toward the element body 1.

[0065] As shown in Figures 4 and 5, a cavity 50 is formed in the conductor portion 32b. In this embodiment, one or more cavities 50 are formed. Figures 4 and 5 show an example in which multiple cavities 50 are formed. The cavity 50 contains, for example, an inert gas. The inert gas contained in the cavity 50 is, for example, N2 or CO2, and the concentration of the inert gas is, for example, dilute. The cross section of the cavity 50 has a polygonal shape.

[0066] The cavities 50 are formed so as to be distributed within the conductor portion 32b. For example, the cavities 50 are formed so as to be uniformly distributed within the conductor portion 32b. In this case, the conductor portion 32b does not have an area where the cavities 50 are distributed unevenly compared to other areas.

[0067] The cavity 50 is formed in at least one of the region 32c and the region 32d. Therefore, for example, the cavity 50 is formed in both the region 32c and the region 32d. For example, the cavity 50 is formed in the region 32c but not in the region 32d. For example, the cavity 50 is formed in the region 32d but not in the region 32c.

[0068] The cavity 50 is formed, for example, in the region 32c, in the region 32s including the surface that defines the recess 36. In this embodiment, the cavity 50 is formed, for example, in the region 32c, the region 32d, and the region 32s. The cavity 50 is formed, for example, in the region 32c and the region 32s, but is not formed in the region 32d. The cavity 50 is located, for example, in the region 32d and the region 32s, but is not formed in the region 32c. The cavity 50 does not have to be formed in the region 32s.

[0069] The conductor portion 32b has a recess 51 formed therein that opens to the outer peripheral surface of the conductor portion 32b. For example, a plurality of recesses 51 are formed. The element body 1 is filled in the recess 51. In the example shown in FIGS. 4 and 5, the element body portions 5b and 5c are filled in the recess 51.

[0070] Fig. 6 is a diagram showing the configuration of the internal conductors 33 and 34. As shown in Fig. 6, the internal conductor 33 includes a conductor portion 33a and a conductor portion 33b. The conductor portion 33a and the conductor portion 33b are continuous with each other. The conductor portion 33a and the conductor portion 33b are continuous with each other, for example, in the second direction D2 and the third direction D3. For example, when the conductor portion 33a constitutes a first conductor portion, the conductor portion 33b constitutes a second conductor portion.

[0071] The internal conductor 34 includes a conductor portion 34a and a conductor portion 34b. The conductor portion 34a faces the conductor portion 33a in the first direction D1. The conductor portion 34b extends in the first direction D1 and is connected to the internal conductor 33. The conductor portion 34b includes a region 34c and a region 34d. The region 34c is connected to the conductor portion 33b. The region 34c is, for example, physically and electrically connected to the conductor portion 33b. The region 34d is continuous with the region 34c and with the conductor portion 34a. In this embodiment, the region 34d is continuous with the region 34c in the first direction D1 and with the conductor portion 34a in the second direction D2 and the third direction D3. The conductor portion 34b is located within the through hole 35d. For example, when the conductor portion 34a constitutes the third conductor portion, the conductor portion 34b constitutes the fourth conductor portion. For example, when conductor portion 34a constitutes the third conductor portion, conductor portion 34b constitutes the connecting portion. For example, when region 34c constitutes the first region, region 34d constitutes the second region. The thickness of conductor portion 33a and conductor portion 34a is, for example, 2 μm.

[0072] 6, the thickness of the conductor portion 34b in the first direction D1 increases toward the center line CL1 of the through hole 35d. Therefore, the thicknesses of the regions 34c and 34d in the first direction D1 increase toward the center line CL1. The total thickness of the regions 34c and 34d in the first direction D1 increases toward the center line CL1 in the direction from the conductor portion 34a toward the conductor portion 33a. For example, the center line CL1 extends in the first direction D1.

[0073] In this embodiment, the rate at which the thickness of region 34d increases in the first direction D1 is different from the rate at which the thickness of region 34c increases in the first direction D1. For example, the rate at which the thickness of region 34d increases in the first direction D1 is smaller than the rate at which the thickness of region 34c increases in the first direction D1. Therefore, the rate at which the thickness of conductor portion 34b increases in the first direction D1 decreases, for example, at the boundary between region 34d and region 34c. The rate at which the thickness of region 34d increases in the first direction D1 may be greater than the rate at which the thickness of region 34c increases in the first direction D1. The rate at which the thickness of region 34d increases in the first direction D1 may be substantially the same as the rate at which the thickness of region 34c increases in the first direction D1.

[0074] In this embodiment, the first direction D1 includes a direction D1a from the internal conductor 33 toward the internal conductor 34 and a direction D1b from the internal conductor 34 toward the internal conductor 33. The region 34d includes a region portion 34d1 and a region portion 34d2. The reference plane SP1 is a plane that is perpendicular to the first direction D1 and includes the conductor portion 34a. The region 34d includes a region portion 34d2 having a thickness in the direction D1a from the reference plane SP1 and a region portion 34d1 having a thickness in the direction D1b from the reference plane SP1. The thicknesses of the region portions 34d1 and 34d2 in the first direction D1 increase toward the center line CL1. For example, if the direction D1a constitutes the first direction, the direction D1b constitutes the second direction.

[0075] When viewed from the first direction D1, the region 34d has, for example, a circular shape. When viewed from the first direction D1, the region 34c and the conductor portion 33b also have, for example, a circular shape. When viewed from the first direction D1, the region 34d extends outside the conductor portion 33b around the entire circumference of the conductor portion 33b. Therefore, when viewed from the first direction D1, for example, the circular shape of the region 34d includes the circular shape of the conductor portion 33b and extends outside the circular shape of the conductor portion 33b.

[0076] A recess 36 is formed in the region 34d at an end 34f away from the region 34c in the first direction D1. When viewed from the first direction D1, the recess 36 has, for example, a circular shape. The recess 36 is filled with, for example, the element portion 5e. The recess 36 opens in a direction from the conductor portion 33a toward the conductor portion 34a. The recess 36 is formed, for example, by an opening edge 36a, a bottom 36b, and an inclined portion 36c connecting the opening edge 36a and the bottom 36b. The depth of the recess 36 increases from the opening edge 36a toward the bottom 36b. When viewed from the first direction D1, the opening edge 36a defines the outer periphery of the recess 36. When viewed from the first direction D1, the conductor portion 33b is located inside the outer periphery of the recess 36. When viewed from the first direction D1, the bottom 36b has, for example, a circular shape. The width of the bottom 36b is smaller than the width of the opening edge 36a, i.e., the opening width W1. The inclined portion 36c is formed, for example, so that the width of the bottom 36b is smaller than the opening width W1. The bottom 36b intersects, for example, with the center line CL1. The central axis of the recess 36, for example, substantially coincides with the center line CL1.

[0077] In this embodiment, the entire outer edge of the conductor portion 33b is located, for example, inside the outer edge of the region 34d when viewed from the first direction D1. Therefore, the opening width W1 is, for example, larger than the width W2 of the conductor portion 33b. Therefore, the recess 36 extends outside the conductor portion 33b around the entire periphery of the conductor portion 33b when viewed from the first direction D1. The opening width W1 may be smaller than the width W2 of the conductor portion 33b or may be approximately the same as the width W2 of the conductor portion 33b.

[0078] The length H1 of the region 34c in the first direction D1 is smaller than, for example, the length H2 between the bottom 36b and the conductor portion 33b in the first direction D1. Therefore, the position where the rate of increase in the thickness of the conductor portion 34b changes is closer to the conductor portion 33b in the first direction D1 than to the bottom 36b. The length H1 may be greater than the length H2 or may be approximately the same as the length H2. The thickness of the conductor portion 34b in the first direction D1 is reduced by the amount corresponding to the formation of the recess 36.

[0079] As shown in FIG. 6, the conductor portion 34b has a region 34p and a region 34q. The region 34p includes a first material. The region 34q includes a second material. The linear expansion coefficient of the second material is different from the linear expansion coefficient of the first material. The first material included in the region 34p is, for example, the same as the first material included in the region 32p. The second material included in the region 34q is, for example, the same as the second material included in the region 32q.

[0080] Conductor portion 34b has, for example, a plurality of regions 34q. The plurality of regions 34q are distributed within region 34p. The plurality of regions 34q are, for example, uniformly distributed within region 34p. In this case, region 34p does not have an area where the plurality of regions 34q are distributed unevenly compared to other regions.

[0081] Region 34q has, for example, a protruding portion 34r that protrudes toward element body 1. Therefore, region 34q is in contact with, for example, element body 1. Region 34q may be integrated with element body 1, for example.

[0082] Region 34q is located in at least one of region 34c and region 34d. Therefore, region 34q is located in both region 34c and region 34d, for example. Region 34q is located in region 34c, but not in region 34d, for example. Region 34q is located in region 34d, but not in region 34c, for example.

[0083] Region 34q is located, for example, in region 34d, in region 34s including the surface that defines recess 36. In this embodiment, region 34q is located, for example, in regions 34c, 34d, and 34s. Region 34q is located, for example, in regions 34c and 34s, but not in region 34d. Region 34q is located, for example, in regions 34d and 34s, but not in region 34c. Region 34q does not have to be located in region 34s. In regions 34c, 34d, and 34s, when region 34q is located, for example, portion 34r may protrude toward the element body 1.

[0084] As shown in FIG. 6, a cavity 50 is formed in the conductor portion 34b. In this embodiment, one or more cavities 50 are formed. FIG. 6 shows an example in which multiple cavities 50 are formed. The cavity 50 contains, for example, the same inert gas as the cavity 50 formed in the conductor portion 32b. The concentration of the inert gas is, for example, low. The cross section of the cavity 50 has a polygonal shape.

[0085] The cavities 50 are formed so as to be distributed within the conductor portion 34b. For example, the cavities 50 are formed so as to be uniformly distributed within the conductor portion 34b. In this case, the conductor portion 34b does not have an area where the cavities 50 are distributed unevenly compared to other areas.

[0086] The cavity 50 is formed in at least one of the region 34c and the region 34d. Therefore, for example, the cavity 50 is formed in both the region 34c and the region 34d. For example, the cavity 50 is formed in the region 34c but not in the region 34d. For example, the cavity 50 is formed in the region 34d but not in the region 34c.

[0087] The cavity 50 is formed, for example, in the region 34c, in the region 34s including the surface that defines the recess 36. In this embodiment, the cavity 50 is formed, for example, in the region 34c, the region 34d, and the region 34s. The cavity 50 is formed, for example, in the region 34c and the region 34s, but is not formed in the region 34d. The cavity 50 is located, for example, in the region 34d and the region 34s, but is not formed in the region 34c. The cavity 50 does not have to be formed in the region 34s.

[0088] The conductor portion 34b has a recess 51 formed therein that opens to the outer peripheral surface of the conductor portion 34b. For example, a plurality of recesses 51 are formed. The recess 51 is filled with the element body 1. In the example shown in FIG. 6, the recess 51 is filled with element body portions 5d and 5e.

[0089] FIG. 7 is a diagram showing the configuration of the internal conductors 41 and 42. As shown in FIG. 7, the internal conductor 41 includes a conductor portion 41a and a conductor portion 41b. The conductor portion 41a and the conductor portion 41b are continuous with each other. The conductor portion 41a and the conductor portion 41b are continuous with each other, for example, in the second direction D2 and the third direction D3. For example, when the conductor portion 41a constitutes a first conductor portion, the conductor portion 41b constitutes a second conductor portion.

[0090] The internal conductor 42 includes a conductor portion 42a and a conductor portion 42b. The conductor portion 42a faces the conductor portion 41a in the first direction D1. The conductor portion 42b extends in the first direction D1 and is connected to the internal conductor 41. The conductor portion 42b includes a region 42c and a region 42d. The region 42c is connected to the conductor portion 41b. The region 42c is, for example, physically and electrically connected to the conductor portion 41b. The region 42d is continuous with the region 42c and with the conductor portion 42a. In this embodiment, the region 42d is continuous with the region 42c in the first direction D1 and with the conductor portion 42a in the second direction D2 and the third direction D3. The conductor portion 42b is located within the through hole 45b. For example, when the conductor portion 42a constitutes the third conductor portion, the conductor portion 42b constitutes the fourth conductor portion. For example, when conductor portion 42a constitutes the third conductor portion, conductor portion 42b constitutes the connecting portion. For example, when region 42c constitutes the first region, region 42d constitutes the second region. The thickness of conductor portion 41a and conductor portion 42a is, for example, 2 μm.

[0091] 7, the thickness of the conductor portion 42b in the first direction D1 increases toward the center line CL1 of the through hole 45b. Therefore, the thicknesses of the regions 42c and 42d in the first direction D1 increase toward the center line CL1. The total thickness of the regions 42c and 42d in the first direction D1 increases toward the center line CL1 in the direction from the conductor portion 42a toward the conductor portion 41a. For example, the center line CL1 extends in the first direction D1.

[0092] In this embodiment, the rate at which the thickness of the region 42d increases in the first direction D1 is different from the rate at which the thickness of the region 42c increases in the first direction D1. For example, the rate at which the thickness of the region 42d increases in the first direction D1 is smaller than the rate at which the thickness of the region 42c increases in the first direction D1. Therefore, the rate at which the thickness of the conductor portion 42b increases in the first direction D1 decreases, for example, at the boundary between the region 42d and the region 42c. The rate at which the thickness of the region 42d increases in the first direction D1 may be greater than the rate at which the thickness of the region 42c increases in the first direction D1. The rate at which the thickness of the region 42d increases in the first direction D1 may be substantially the same as the rate at which the thickness of the region 42c increases in the first direction D1.

[0093] In this embodiment, the first direction D1 includes a direction D1a from the internal conductor 41 to the internal conductor 42 and a direction D1b from the internal conductor 42 to the internal conductor 41. The region 42d includes a region portion 42d1 and a region portion 42d2. The reference plane SP1 is a plane that is perpendicular to the first direction D1 and includes the conductor portion 42a. The region 42d includes a region portion 42d2 having a thickness in the direction D1a from the reference plane SP1 and a region portion 42d1 having a thickness in the direction D1b from the reference plane SP1. The thicknesses of the region portions 42d1 and 42d2 in the first direction D1 increase toward the center line CL1. For example, if the direction D1a constitutes the first direction, the direction D1b constitutes the second direction.

[0094] When viewed from the first direction D1, the region 42d has, for example, a circular shape. When viewed from the first direction D1, the region 42c and the conductor portion 41b also have, for example, a circular shape. When viewed from the first direction D1, the region 42d extends outside the conductor portion 41b around the entire circumference of the conductor portion 41b. Therefore, when viewed from the first direction D1, for example, the circular shape of the region 42d includes the circular shape of the conductor portion 41b and extends outside the circular shape of the conductor portion 41b.

[0095] A recess 46 is formed in the region 42d at an end 42f away from the region 42c in the first direction D1. The recess 46 has, for example, a circular shape when viewed from the first direction D1. The recess 46 is filled with, for example, the element portion 5c. The recess 46 opens in a direction from the conductor portion 41a toward the conductor portion 42a. The recess 46 is formed, for example, by an opening edge 46a, a bottom 46b, and an inclined portion 46c connecting the opening edge 46a and the bottom 46b. The depth of the recess 46 increases from the opening edge 46a toward the bottom 46b. The opening edge 46a defines the outer periphery of the recess 46 when viewed from the first direction D1. The conductor portion 41b is located inside the outer periphery of the recess 46 when viewed from the first direction D1. The bottom 46b has, for example, a circular shape when viewed from the first direction D1. The width of the bottom 46b is smaller than the width of the opening edge 46a, i.e., the opening width W1. The inclined portion 46c is formed, for example, so that the width of the bottom 46b is smaller than the opening width W1. The bottom 46b intersects, for example, with the center line CL1. The central axis of the recess 46, for example, substantially coincides with the center line CL1.

[0096] In this embodiment, the entire outer edge of the conductor portion 41b is located, for example, inside the outer edge of the region 42d when viewed from the first direction D1. Therefore, the opening width W1 is, for example, larger than the width W2 of the conductor portion 41b. Therefore, the recess 46 extends outside the conductor portion 41b around the entire periphery of the conductor portion 41b when viewed from the first direction D1. The opening width W1 may be smaller than the width W2 of the conductor portion 41b or may be approximately the same as the width W2 of the conductor portion 41b.

[0097] The length H1 of the region 42c in the first direction D1 is smaller than, for example, the length H2 between the bottom 46b and the conductor portion 41b in the first direction D1. Therefore, the position where the rate of increase in the thickness of the conductor portion 42b changes is closer to the conductor portion 41b in the first direction D1 than to the bottom 46b. The length H1 may be greater than the length H2 or may be approximately the same as the length H2. The thickness of the conductor portion 42b in the first direction D1 is reduced by the amount corresponding to the formation of the recess 46.

[0098] As shown in FIG. 7, the conductor portion 42b has a region 42p and a region 42q. The region 42p includes a first material. The region 42q includes a second material. The linear expansion coefficient of the second material is different from the linear expansion coefficient of the first material. The first material included in the region 42p is, for example, the same as the first material included in the region 32p. The second material included in the region 42q is, for example, the same as the second material included in the region 32q.

[0099] Conductor portion 42b has, for example, a plurality of regions 42q. The plurality of regions 42q are distributed within region 42p. The plurality of regions 42q are, for example, uniformly distributed within region 42p. In this case, region 42p does not have an area where the plurality of regions 42q are distributed unevenly compared to other regions.

[0100] Region 42q has, for example, a protruding portion 42r that protrudes toward element body 1. Therefore, region 42q is in contact with, for example, element body 1. Region 42q may be integrated with element body 1, for example.

[0101] Region 42q is located in at least one of region 42c and region 42d. Therefore, region 42q is located in both region 42c and region 42d, for example. Region 42q is located in region 42c, but not in region 42d, for example. Region 42q is located in region 42d, but not in region 42c, for example.

[0102] Region 42q is located, for example, in region 42d, in region 42s including the surface that defines recess 46. In this embodiment, region 42q is located, for example, in regions 42c, 42d, and 42s. Region 42q is located, for example, in regions 42c and 42s, but not in region 42d. Region 42q is located, for example, in regions 42d and 42s, but not in region 42c. Region 42q does not have to be located in region 42s. In regions 42c, 42d, and 42s, when region 42q is located, for example, portion 42r may protrude toward the element body 1.

[0103] As shown in FIG. 7, a cavity 50 is formed in the conductor portion 42b. In this embodiment, one or more cavities 50 are formed, and FIG. 7 shows an example in which multiple cavities 50 are formed. The cavity 50 contains, for example, the same inert gas as the cavity 50 formed in the conductor portion 32b. The concentration of the inert gas is, for example, low. The cross section of the cavity 50 has a polygonal shape.

[0104] The cavities 50 are formed so as to be distributed within the conductor portion 42b. For example, the cavities 50 are formed so as to be uniformly distributed within the conductor portion 42b. In this case, the conductor portion 42b does not have an area where the cavities 50 are distributed unevenly compared to other areas. One cavity 50 is formed, for example, in the center of the conductor portion 42b.

[0105] The cavity 50 is formed in at least one of the region 42c and the region 42d. Therefore, for example, the cavity 50 is formed in both the region 42c and the region 42d. For example, the cavity 50 is formed in the region 42c but not in the region 42d. For example, the cavity 50 is formed in the region 42d but not in the region 42c.

[0106] The cavity 50 is formed, for example, in the region 42c, in the region 42s including the surface that defines the recess 46. In the present embodiment, the cavity 50 is formed, for example, in the region 42c, the region 42d, and the region 42s. The cavity 50 is formed, for example, in the region 42c and the region 42s, but is not formed in the region 42d. The cavity 50 is located, for example, in the region 42d and the region 42s, but is not formed in the region 42c. The cavity 50 does not have to be formed in the region 42s.

[0107] Conductor portion 42b has recesses 51 formed therein that open to the outer peripheral surface of conductor portion 42b. For example, a plurality of recesses 51 are formed. Element body 1 is filled inside recess 51. In the example shown in FIG. 7, element body portions 5b and 5c are filled inside recess 51.

[0108] FIG. 8 is a diagram showing the configuration of the internal conductors 43, 44. As shown in FIG. 8, the internal conductor 43 includes a conductor portion 43a and a conductor portion 43b. The conductor portion 43a and the conductor portion 43b are continuous with each other. The conductor portion 43a and the conductor portion 43b are continuous with each other, for example, in the second direction D2 and the third direction D3. For example, when the conductor portion 43a constitutes a first conductor portion, the conductor portion 43b constitutes a second conductor portion.

[0109] The internal conductor 44 includes a conductor portion 44a and a conductor portion 44b. The conductor portion 44a faces the conductor portion 43a in the first direction D1. The conductor portion 44b extends in the first direction D1 and is connected to the internal conductor 43. The conductor portion 44b includes a region 44c and a region 44d. The region 44c is connected to the conductor portion 43b. The region 44c is, for example, physically and electrically connected to the conductor portion 43b. The region 44d is continuous with the region 44c and with the conductor portion 44a. In this embodiment, the region 44d is continuous with the region 44c in the first direction D1 and with the conductor portion 44a in the second direction D2 and the third direction D3. The conductor portion 44b is located within the through hole 45d. For example, when the conductor portion 44a constitutes the third conductor portion, the conductor portion 44b constitutes the fourth conductor portion. For example, when conductor portion 44a constitutes the third conductor portion, conductor portion 44b constitutes the connecting portion. For example, when region 44c constitutes the first region, region 44d constitutes the second region. The thickness of conductor portion 43a and conductor portion 44a is, for example, 2 μm.

[0110] 8, the thickness of conductor portion 44b in the first direction D1 increases toward the center line CL1 of through hole 45d. Therefore, the thicknesses of regions 44c and 44d in the first direction D1 increase toward the center line CL1. The total thickness of regions 44c and 44d in the first direction D1 increases toward the center line CL1 in the direction from conductor portion 44a toward conductor portion 43a. For example, center line CL1 extends in the first direction D1.

[0111] In this embodiment, the rate at which the thickness of region 44d increases in the first direction D1 is different from the rate at which the thickness of region 44c increases in the first direction D1. For example, the rate at which the thickness of region 44d increases in the first direction D1 is smaller than the rate at which the thickness of region 44c increases in the first direction D1. Therefore, the rate at which the thickness of conductor portion 44b increases in the first direction D1 decreases, for example, at the boundary between region 44d and region 44c. The rate at which the thickness of region 44d increases in the first direction D1 may be greater than the rate at which the thickness of region 44c increases in the first direction D1. The rate at which the thickness of region 44d increases in the first direction D1 may be substantially the same as the rate at which the thickness of region 44c increases in the first direction D1.

[0112] In this embodiment, the first direction D1 includes a direction D1a extending from the internal conductor 43 to the internal conductor 44 and a direction D1b extending from the internal conductor 44 to the internal conductor 43. The region 44d includes a region portion 44d1 and a region portion 44d2. The reference plane SP1 is a plane perpendicular to the first direction D1 and including the conductor portion 44a. The region 44d includes a region portion 44d2 having a thickness extending from the reference plane SP1 to the direction D1a and a region portion 44d1 having a thickness extending from the reference plane SP1 to the direction D1b. The thicknesses of the region portions 44d1 and 44d2 in the first direction D1 increase toward the center line CL1. For example, if the direction D1a constitutes the first direction, the direction D1b constitutes the second direction.

[0113] When viewed from the first direction D1, the region 44d has, for example, a circular shape. When viewed from the first direction D1, the region 44c and the conductor portion 43b also have, for example, a circular shape. When viewed from the first direction D1, the region 44d extends outside the conductor portion 43b around the entire circumference of the conductor portion 43b. Therefore, when viewed from the first direction D1, for example, the circular shape of the region 44d includes the circular shape of the conductor portion 43b and extends outside the circular shape of the conductor portion 43b.

[0114] A recess 46 is formed in the region 44d at an end 44f away from the region 44c in the first direction D1. The recess 46 has, for example, a circular shape when viewed from the first direction D1. The recess 46 is filled with, for example, the element portion 5c. The recess 46 opens in a direction from the conductor portion 43a toward the conductor portion 44a. The recess 46 is formed, for example, by an opening edge 46a, a bottom 46b, and an inclined portion 46c connecting the opening edge 46a and the bottom 46b. The depth of the recess 46 increases from the opening edge 46a toward the bottom 46b. The opening edge 46a defines the outer periphery of the recess 46 when viewed from the first direction D1. The conductor portion 43b is located inside the outer periphery of the recess 46 when viewed from the first direction D1. The bottom 46b has, for example, a circular shape when viewed from the first direction D1. The width of the bottom 46b is smaller than the width of the opening edge 46a, i.e., the opening width W1. The inclined portion 46c is formed, for example, so that the width of the bottom 46b is smaller than the opening width W1. The bottom 46b intersects, for example, with the center line CL1. The central axis of the recess 46, for example, substantially coincides with the center line CL1.

[0115] In this embodiment, the entire outer edge of the conductor portion 43b is located, for example, inside the outer edge of the region 44d when viewed from the first direction D1. Therefore, the opening width W1 is, for example, larger than the width W2 of the conductor portion 43b. Therefore, the recess 46 extends outside the conductor portion 43b around the entire periphery of the conductor portion 43b when viewed from the first direction D1. The opening width W1 may be smaller than the width W2 of the conductor portion 43b or may be approximately the same as the width W2 of the conductor portion 43b.

[0116] The length H1 of the region 44c in the first direction D1 is smaller than, for example, the length H2 between the bottom 46b and the conductor portion 43b in the first direction D1. Therefore, the position where the rate of increase in the thickness of the conductor portion 44b changes is closer to the conductor portion 43b in the first direction D1 than to the bottom 46b. The length H1 may be greater than the length H2 or may be approximately the same as the length H2. The thickness of the conductor portion 44b in the first direction D1 is reduced by the amount corresponding to the formation of the recess 46.

[0117] As shown in FIG. 8, the conductor portion 44b has a region 44p and a region 44q. The region 44p includes a first material. The region 44q includes a second material. The linear expansion coefficient of the second material is different from the linear expansion coefficient of the first material. The first material included in the region 44p is, for example, the same as the first material included in the region 32p. The second material included in the region 44q is, for example, the same as the second material included in the region 32q.

[0118] Conductor portion 44b has, for example, a plurality of regions 44q. The plurality of regions 44q are distributed within region 44p. The plurality of regions 44q are, for example, uniformly distributed within region 44p. In this case, region 44p does not have an area where the plurality of regions 44q are distributed unevenly compared to other regions.

[0119] Region 44q has, for example, a protruding portion 44r that protrudes toward element body 1. Therefore, region 44q is in contact with, for example, element body 1. Region 44q may be integrated with element body 1, for example.

[0120] Region 44q is located in at least one of region 44c and region 44d. Therefore, region 44q is located in both region 44c and region 44d, for example. Region 44q is located in region 44c, but not in region 44d, for example. Region 44q is located in region 44d, but not in region 44c, for example.

[0121] Region 44q is located, for example, in region 44d, in region 44s including the surface that defines recess 46. In this embodiment, region 44q is located, for example, in regions 44c, 44d, and 44s. Region 44q is located, for example, in regions 44c and 44s, but not in region 44d. Region 44q is located, for example, in regions 44d and 44s, but not in region 44c. Region 44q does not have to be located in region 44s. In regions 44c, 44d, and 44s, when region 44q is located, for example, portion 44r may protrude toward the element body 1.

[0122] As shown in FIG. 8, a cavity 50 is formed in the conductor portion 44b. In this embodiment, one or more cavities 50 are formed, and FIG. 8 shows an example in which multiple cavities 50 are formed. The cavity 50 contains, for example, the same inert gas as the cavity 50 formed in the conductor portion 32b. The concentration of the inert gas is, for example, low. The cross section of the cavity 50 has a polygonal shape.

[0123] The cavities 50 are formed so as to be distributed within the conductor portion 44b. For example, the cavities 50 are formed so as to be uniformly distributed within the conductor portion 44b. In this case, the conductor portion 44b does not have an area where the cavities 50 are distributed unevenly compared to other areas. One cavity 50 is formed, for example, in the center of the conductor portion 44b.

[0124] The cavity 50 is formed in at least one of the region 44c and the region 44d. Therefore, for example, the cavity 50 is formed in both the region 44c and the region 44d. For example, the cavity 50 is formed in the region 44c but not in the region 44d. For example, the cavity 50 is formed in the region 44d but not in the region 44c.

[0125] The cavity 50 is formed, for example, in the region 44c, in the region 44s including the surface that defines the recess 46. In this embodiment, the cavity 50 is formed, for example, in the region 44c, the region 44d, and the region 44s. The cavity 50 is formed, for example, in the region 44c and the region 44s, but is not formed in the region 44d. The cavity 50 is located, for example, in the region 44d and the region 44s, but is not formed in the region 44c. The cavity 50 does not have to be formed in the region 44s.

[0126] Conductor portion 44b has recesses 51 formed therein that open to the outer peripheral surface of conductor portion 44b. For example, a plurality of recesses 51 are formed. Element body 1 is filled inside recess 51. In the example shown in FIG. 8, element body portions 5d and 5e are filled inside recess 51.

[0127] FIG. 9 shows a cavity 50 formed in the conductor portion 32b. In this embodiment, one or more cavities 50 are formed, and FIG. 9 shows an example in which one cavity 50 is formed. One cavity 50 is formed, for example, in the center of the conductor portion 32b. The cavity 50 contains, for example, an inert gas. The inert gas contained in the cavity 50 is, for example, N2 or CO2, and the concentration of the inert gas is, for example, dilute. The cross section of the cavity 50 has a polygonal shape.

[0128] 9, in a cross section including the cavity 50, the equivalent circle diameter R1 of the cross section of the cavity 50 is, for example, 50% or less of the width R2 of the cross section of the conductor portion 32b. In this embodiment, the equivalent circle diameter R1 of the cross section of the cavity 50 is, for example, 20% or more of the width R2 of the cross section of the conductor portion 32b.

[0129] FIG. 10 shows a cavity 50 formed in the conductor portion 34b. In this embodiment, one or more cavities 50 are formed, and FIG. 10 shows an example in which one cavity 50 is formed. One cavity 50 is formed, for example, in the center of the conductor portion 34b. The cavity 50 contains, for example, the same inert gas as the cavity 50 formed in the conductor portion 32b. The cross section of the cavity 50 has a polygonal shape.

[0130] 10, in a cross section including the cavity 50, the equivalent circle diameter R1 of the cross section of the cavity 50 is, for example, 50% or less of the width R2 of the cross section of the conductor portion 34b. In this embodiment, the equivalent circle diameter R1 of the cross section of the cavity 50 is, for example, 20% or more of the width R2 of the cross section of the conductor portion 34b.

[0131] FIG. 11 shows a cavity 50 formed in the conductor portion 42b. In this embodiment, one or more cavities 50 are formed, and FIG. 11 shows an example in which one cavity 50 is formed. One cavity 50 is formed, for example, in the center of the conductor portion 42b. The cavity 50 contains, for example, the same inert gas as the cavity 50 formed in the conductor portion 32b. The cross section of the cavity 50 has a polygonal shape.

[0132] 11, in a cross section including the cavity 50, the equivalent circle diameter R1 of the cross section of the cavity 50 is, for example, 50% or less of the width R2 of the cross section of the conductor portion 42b. In this embodiment, the equivalent circle diameter R1 of the cross section of the cavity 50 is, for example, 15% or more of the width R2 of the cross section of the conductor portion 42b.

[0133] FIG. 12 shows a cavity 50 formed in the conductor portion 44b. In this embodiment, one or more cavities 50 are formed, and FIG. 12 shows an example in which one cavity 50 is formed. One cavity 50 is formed, for example, in the center of the conductor portion 44b. The cavity 50 contains, for example, the same inert gas as the cavity 50 formed in the conductor portion 32b. The cross section of the cavity 50 has a polygonal shape.

[0134] 12, in a cross section including the cavity 50, the equivalent circle diameter R1 of the cross section of the cavity 50 is, for example, 50% or less of the width R2 of the cross section of the conductor portion 44b. In this embodiment, the equivalent circle diameter R1 of the cross section of the cavity 50 is, for example, 15% or more of the width R2 of the cross section of the conductor portion 44b.

[0135] An example of a method for manufacturing the piezoelectric element PD1 will be described. The order of the steps in the manufacturing method may be reversed. In this example of the manufacturing method, first, piezoelectric ceramic powder, for example, PZT powder, is made into a paint. Next, a plurality of green sheets are formed by, for example, a doctor blade method. The plurality of green sheets are used to form piezoelectric layers 3a to 3e. The piezoelectric layers 3a to 3e correspond to, for example, element portions 5a to 5e, respectively.

[0136] In the method for manufacturing the piezoelectric element PD1, the green sheet is then irradiated with, for example, laser light to form openings for forming the through holes 35b-35e and 45b-45e. The laser light irradiation is performed, for example, in two stages. For example, the first irradiation with laser light forms openings for inserting the regions 32c, 34c, 42c, and 44c, and the second irradiation with laser light forms openings for inserting the regions 32d, 34d, 42d, and 44d. The openings for inserting the regions 32c, 34c, 42c, and 44c and the openings for inserting the regions 32d, 34d, 42d, and 44d are continuous with each other. The green sheet is irradiated with the laser light such that the rate of increase in thickness of the regions 32d, 34d, 42d, and 44d in the first direction D1 is smaller than the rate of increase in thickness of the regions 32c, 34c, 42c, and 44c in the first direction D1. The first irradiation of the laser light may form openings for inserting the regions 32d, 34d, 42d, and 44d, and the second irradiation of the laser light may form openings for inserting the regions 32c, 34c, 42c, and 44c. The green sheet may be irradiated with the laser light only once. The laser light may be, for example, a YAG laser light.

[0137] In this embodiment, the internal electrodes 30 and 40 are then formed. For example, an electrode pattern for forming the internal conductors 31 and 41 is formed on a first green sheet for forming the piezoelectric layer 3a. Next, a second green sheet for forming the piezoelectric layer 3b, in which openings are formed by laser irradiation, is laminated on the first green sheet on which the electrode pattern is formed. A conductive paste for forming the conductor portions 32b, 34b, 42b, and 44b is also filled into the openings of the second green sheet. In this embodiment, while the conductive paste is filled into the openings, an electrode pattern for forming the internal conductors 32 and 42 is formed on the second green sheet. The electrode pattern for forming the internal conductors 31, 32, 41, and 42 is formed by screen printing using a conductive paste.

[0138] The conductive paste for forming the conductor portions 32b, 34b, 42b, and 44b may contain, for example, a first material and a second material. In this case, the conductor portions 32b, 34b, 42b, and 44b have regions 32p, 34p, 42p, and 44p and regions 32q, 34q, 42q, and 44q. The content of the first material in the conductive paste for forming the conductor portions 32b, 34b, 42b, and 44b is, for example, 55% by mass. The content of the second material in the conductive paste is, for example, 10% by mass.

[0139] The filled conductive paste is dried at a low temperature, for example, 60°C to 75°C. The drying time is, for example, 5 minutes. In this case, at least one of cavities 50 and depressions 51 is formed in the conductor portions 32b, 34b, 42b, and 44b. While drying at a low temperature, the conductive paste for forming the conductor portions 32b, 34b, 42b, and 44b maintains, for example, a low viscosity, and can form an outer peripheral surface that conforms to the shape of the through-hole 35b. The printed electrode pattern is dried at a high temperature, for example, 90°C or higher. The drying time is, for example, 1 minute. Because the printed electrode pattern is dried at a high temperature for a short time, it is difficult for the outer peripheral surface to conform to the shape of the through-holes 35b, 35d, 45b, and 45d.

[0140] In this embodiment, similar steps are then followed to fill the openings of the green sheets for forming the piezoelectric layers 3c to 3e with conductive paste and form electrode patterns on the green sheets. The green sheets after filling the openings with conductive paste and forming electrode patterns on the green sheets are then stacked on top of each other.

[0141] Next, the stacked green sheets are pressed, for example, by isostatic pressing. The green sheets are pressed in a first direction D1, which is the stacking direction. In isostatic pressing, a pressure of 100 MPa is applied, for example. The temperature during pressing is, for example, about 70°C. The pressing time is, for example, 5 minutes. After pressing the stacked green sheets, a laminate is formed.

[0142] Next, for example, the laminate is subjected to a binder removal process. The temperature during the binder removal process is, for example, 450°C. The binder removal process takes, for example, about 24 hours. Next, the laminate is fired to form a laminate substrate. The temperature during firing the laminate is, for example, 1100°C. The firing time is, for example, 18 hours.

[0143] When at least one of the cavities 50 and the recesses 51 is formed in the conductor portions 32b, 34b, 42b, and 44b, the temperature for firing the laminate is, for example, about 940°C. The firing time is, for example, 16 hours. The temperature rise rate is, for example, 450°C / hour. By firing the laminate at the above temperature, aggregation of the metal material in the conductor portions 32b, 34b, 42b, and 44b is suppressed. Therefore, inert gas remaining in the conductor portions 32b, 34b, 42b, and 44b can be sealed within the conductor portions 32b, 34b, 42b, and 44b. In this embodiment, the internal electrodes 30 and 40 are configured as, for example, sintered bodies of a conductive paste. The conductive paste for forming the internal electrodes 30 and 40 contains, for example, Ag, Pd, Pt, or an Ag-Pd alloy.

[0144] Next, the external electrodes 10, 20 are formed, for example, together with the internal electrodes 30, 40, as a sintered body of conductive paste. Therefore, to form the external electrodes 10, 20, for example, a conductive paste is applied to stacked green sheets. The stacked green sheets integrated with the conductive paste are pressed, for example, by a hydrostatic press. The pressed laminate is then subjected to, for example, a binder removal process and firing. The external electrodes 10, 20 are formed by firing the laminate.

[0145] In this embodiment, the external electrodes 10, 20 may be formed by firing a conductive paste applied to the outer surface of the laminate substrate. Therefore, for example, a conductive paste for forming the external electrodes 10, 20 is applied to the outer surface of the laminate substrate, and the laminate substrate integrated with the conductive paste is fired. The external electrodes 10, 20 are formed by firing the laminate substrate. The conductive paste is applied to the laminate substrate by, for example, screen printing. The conductive paste applied to the outer surface of the laminate substrate contains, for example, Ag, Pd, or an Ag-Pd alloy. The temperature for firing the external electrodes 10, 20 is, for example, 850°C. The firing time is, for example, 2 hours.

[0146] Next, the element body 1 on which the external electrodes 10, 20 have been formed is subjected to a polarization treatment. The temperature during the polarization treatment is, for example, 100 to 110°C. The voltage applied to the element body 1 is, for example, 3 kV / mm. The polarization treatment time is about 5 minutes. After the polarization treatment, the piezoelectric element PD1 is produced.

[0147] As described above, the piezoelectric element PD1 according to this embodiment includes the element body 1, the external electrodes 10 and 20, and the internal electrodes 30 and 40. The internal electrodes 30 and 40 have the internal conductors 31, 33, 41, and 43 and the internal conductors 32, 34, 42, and 44 that face each other. The internal conductors 32, 34, 42, and 44 extend in the first direction D1 and include conductor portions 32b, 34b, 42b, and 44b that are connected to the internal conductors 31, 33, 41, and 43. Cavities 50 are formed in the conductor portions 32b, 34b, 42b, and 44b.

[0148] In the piezoelectric element PD1, the internal electrodes 30 and 40 have internal conductors 31, 33, 41, and 43 and internal conductors 32, 34, 42, and 44 that face each other. The internal conductors 32, 34, 42, and 44 include conductor portions 32b, 34b, 42b, and 44b that are connected to the internal conductors 31, 33, 41, and 43. Cavities 50 are formed in the conductor portions 32b, 34b, 42b, and 44b. Due to the presence of the cavities 50, the conductor portions 32b, 34b, 42b, and 44b in which the cavities 50 are formed are less likely to form dense sintered bodies overall than the conductor portions 32b, 34b, 42b, and 44b in which the cavities 50 are not formed. The conductor portions 32b, 34b, 42b, and 44b in which the voids 50 are formed are more easily deformed than the conductor portions 32b, 34b, 42b, and 44b in which the voids 50 are not formed. Therefore, when stress from the element body 1 acts on the conductor portions 32b, 34b, 42b, and 44b as the element body 1 deforms, cracks are less likely to occur in the conductor portions 32b, 34b, 42b, and 44b. As a result, the resistance of the internal electrodes 30 and 40 to stress acting from the element body 1 is increased.

[0149] As described above, when the thicknesses of the conductor portions 32b, 34b, 42b, and 44b in the first direction D1 increase toward the center lines CL1 of the through holes 35b, 35d, 45b, and 45d, the reliability of the electrical connection in the internal electrodes 30 and 40 improves. When a cavity 50 is formed in the conductor portions 32b, 34b, 42b, and 44b, cracks are less likely to occur in the conductor portions 32b, 34b, 42b, and 44b than in the conductor portions 32b, 34b, 42b, and 44b in which the cavity 50 is not formed. As a result, the risk of cracks occurring in the conductor portions 32b, 34b, 42b, and 44b is reliably reduced, and the resistance of the internal electrodes 30 and 40 to deformation of the element body 1 is further increased. As a result, the reliability of the electrical connection in the internal electrodes 30 and 40 improves.

[0150] In the piezoelectric element PD1, in a cross section obtained by cutting the conductor portions 32b, 34b, 42b, 44b by a plane extending in the first direction D1 and including the cavity 50, the circle equivalent diameter R1 at the cross section of the cavity 50 is 50% or less of the width R2 at the cross section of the conductor portions 32b, 34b, 42b, 44b. In this case, electrical disconnection due to the formation of the cavity 50 in the conductor portions 32b, 34b, 42b, 44b is unlikely to occur. Stable transmission of the drive signal by the conductor portions 32b, 34b, 42b, 44b is realized, and the reliability of the electrical connection in the internal electrodes 30, 40 is further improved.

[0151] In the piezoelectric element PD1, the cross section of the cavity 50 has a polygonal shape. In this case, since the surfaces defining the cavity 50 have multiple corners and edges, the conductor portions 32b, 34b, 42b, and 44b are more likely to deform in response to deformation of the element body 1. Cracks are less likely to occur in the conductor portions 32b, 34b, 42b, and 44b. As a result, the resistance of the internal electrodes 30 and 40 to stress acting from the element body 1 is further increased. The reliability of the electrical connection at the internal electrodes 30 and 40 is further improved.

[0152] In the piezoelectric element PD1, the cavity 50 is formed in at least one of the regions 32c, 34c, 42c, and 44c and the regions 32d, 34d, 42d, and 44d. In this case, at least one of the regions 32c, 34c, 42c, and 44c and the regions 32d, 34d, 42d, and 44d is easily deformed. Cracks are less likely to occur in the regions 32c, 34c, 42c, 44c, 32d, 34d, 42d, and 44d. As a result, the resistance of the internal electrodes 30 and 40 to stress acting from the element body 1 is further increased.

[0153] In the piezoelectric element PD1, the cavity 50 is formed in the regions 32s, 34s, 42s, and 44s that are within the regions 32d, 34d, 42d, and 44d and that include the surfaces that define the recess 50. In this case, it is possible to prevent the recesses 36, 46 from peeling off from the element body 1. As a result, the reliability of the electrical connection at the internal electrodes 30, 40 is further improved.

[0154] In the piezoelectric element PD1, the conductor portions 32b, 34b, 42b, and 44b are formed with recesses 51 that open to the outer circumferential surfaces of the conductor portions 32b, 34b, 42b, and 44b. In this case, the outer peripheral surface on which the recesses 51 are formed is less likely to reflect vibrations transmitted from the element body 1 than an outer peripheral surface on which the recesses 51 are not formed. Therefore, vibrations caused by deformation of the element body 1 are more easily transmitted within the element body 1, improving the resonance characteristics of the piezoelectric element PD1.

[0155] The piezoelectric element PD1 includes an element body 1, external electrodes 10 and 20, and internal electrodes 30 and 40. The internal electrodes 30 and 40 have internal conductors 31 and 32 facing each other. The internal conductors 32, 34, 42, and 44 extend in the first direction D1 and include conductor portions 32b, 34b, 42b, and 44b connected to the internal conductors 31, 33, 41, and 43. Recesses 51 are formed in the conductor portions 32b, 34b, 42b, and 44b.

[0156] In the piezoelectric element PD1, the internal electrodes 30 and 40 have internal conductors 31, 33, 41, and 43 and internal conductors 32, 34, 42, and 44 that face each other. The internal conductors 32, 34, 42, and 44 include a conductor portion 32b connected to the internal conductors 31, 33, 41, and 43. The conductor portions 32b, 34b, 42b, and 44b have depressions 51 that open to the outer surfaces of the conductor portions 32b, 34b, 42b, and 44b. The conductor portions 32b, 34b, 42b, and 44b with the depressions 51 formed therein are less susceptible to cracking than the conductor portions 32b, 34b, 42b, and 44b without the cavities 50 formed therein. The resistance of the internal electrodes 30 and 40 to stress acting from the element body 1 is increased. The reliability of the electrical connection in the internal electrodes 30 and 40 is improved.

[0157] In this embodiment, when at least one of the recesses 51 and the voids 50 is formed in the conductor portions 32b, 34b, 42b, and 44b and the conductor portions 32b, 34b, 42b, and 44b also have regions 32q, 34q, 42q, and 44q containing the second material, the reliability is further improved. When the conductor portions 32b, 34b, 42b, and 44b have regions 32q, 34q, 42q, and 44q containing the second material, the conductor portions 32b, 34b, 42b, and 44b have a lower sintering temperature. Therefore, cracks are less likely to occur in the conductor portions 32b, 34b, 42b, and 44b than in the conductor portions 32b, 34b, 42b, and 44b without the voids 50. This improves the reliability of the electrical connection at the internal electrodes 30 and 40.

[0158] According to the inventor's research, in a piezoelectric element, as the piezoelectric element deforms, stress from the piezoelectric element may act on the conductor, and the stress acting from the piezoelectric element tends to concentrate at the location where the shape of the conductor changes. The shape of the conductor changes at the connection location where the fourth conductor portion and the second and third conductor portions are connected or continuous with each other, and the stress acting from the piezoelectric element tends to concentrate at the connection location. The concentration of stress reduces the reliability of the electrical connection at the connection location. A conductor with reduced reliability of the electrical connection makes it difficult to achieve stable transmission of a drive signal. The conductor corresponds to, for example, the internal electrodes 30 and 40. The connection portion corresponds to, for example, the conductor portions 32b, 34b, 42b, and 44b. Therefore, the internal electrodes 30, 40, which have reduced changes in shape at the connection points, suppress the concentration of stress acting from the element body 1 on the conductor portions 32b, 34b, 42b, 44b. Suppressing stress concentration further improves the reliability of the electrical connection at the internal electrodes 30, 40.

[0159] The piezoelectric element PD1 according to this embodiment includes an element body 1, external electrodes 10 and 20, and internal electrodes 30 and 40. The internal electrodes 30 and 40 have internal conductors 31, 33, 41, and 43 and internal conductors 32, 34, 42, and 44 that face each other. The internal conductors 31, 33, 41, and 43 include conductor portions 31 a, 33 a, 41 a, and 43 a and conductor portions 31 b, 33 b, 41 b, and 43 b that are continuous with each other. The internal conductors 32, 34, 42, 44 include conductor portions 32a, 34a, 42a, 44a facing the conductor portions 31a, 33a, 41a, 43a in the first direction D1, regions 32c, 34c, 42c, 44c connected to the conductor portions 31b, 33b, 41b, 43b, and regions 32d, 34d, 42d, 44d continuous with the regions 32c, 34c, 42c, 44c and with the conductor portions 32a, 34a, 42a, 44a. The element body 1 includes element body portions 5b, 5d located between the internal conductors 31, 33, 41, 43 and the internal conductors 32, 34, 42, 44. The conductor portions 32b, 34b, 42b, and 44b are located in through holes 35b, 35d, 45b, and 45d that penetrate the element portions 5b and 5d in the first direction D1. The thicknesses of the conductor portions 32b, 34b, 42b, and 44b in the first direction D1 increase toward the center lines CL1 of the through holes 35b, 35d, 45b, and 45d.

[0160] In the piezoelectric element PD1, the mutually opposing internal conductors 31, 33, 41, 43 and 32, 34, 42, 44 are connected to each other by conductor portions 32b, 34b, 42b, 44b. The conductor portions 32b, 34b, 42b, 44b are continuous with the conductor portions 32a, 34a, 42a, 44a of the internal conductors 32, 34, 42, 44, and the thicknesses of the conductor portions 32b, 34b, 42b, 44b in the first direction D1 increase toward the center lines CL1 of the through holes 35b, 35d, 45b, 45d. Therefore, the shapes of the internal electrodes 30, 40 change gradually at the locations where the conductor portions 32b and 32a, 34a, 42a, 44a are continuous with each other. The stress acting on the internal electrodes 30, 40 from the element body 1 as the element body 1 deforms is less likely to concentrate at the continuous area. This prevents a decrease in the reliability of electrical connection due to stress concentration at the continuous area. As a result, the reliability of electrical connection at the internal electrodes 30, 40 is further improved.

[0161] In the piezoelectric element PD1, the degree of increase in the thickness of the regions 32d, 34d, 42d, and 44d in the first direction D1 is smaller than the degree of increase in the thickness of the regions 32c, 34c, 42c, and 44c in the first direction D1. In this case, the shapes of the internal electrodes 30, 40 change more gradually at the continuous portion. The stress acting on the internal electrodes 30, 40 from the element body 1 as the element body 1 deforms is less likely to concentrate at the continuous portion. As a result, the reliability of the electrical connection at the internal electrodes 30, 40 is further improved.

[0162] In the piezoelectric element PD1, the first direction D1 includes a direction D1a from the internal conductors 31, 33, 41, 43 toward the internal conductors 32, 34, 42, 44, and a direction D1b from the internal conductors 32, 34, 42, 44 toward the internal conductors 31, 33, 41, 43. With a plane that is orthogonal to the first direction D1 and includes the conductor portions 32a, 34a, 42a, 44a as a reference plane SP1, the regions 32d, 34d, 42d, 44d include region portions 32d2, 34d2, 42d2, 44d2 that have a thickness in the direction D1a from the reference plane SP1, and region portions 32d1, 34d1, 42d1, 44d1 that have a thickness in the direction D1b from the reference plane SP1. The thicknesses of the region portions 32d1, 34d1, 42d1, 44d1, 32d2, 34d2, 42d2, and 44d2 included in the regions 32d, 34d, 42d, and 44d in the first direction D1 increase toward the center line CL1. In this case, the shapes of the internal electrodes 30, 40 change more gradually at the continuous portion. The stress acting on the internal electrodes 30, 40 from the element body 1 as the element body 1 deforms is less likely to concentrate at the continuous portion. As a result, the reliability of the electrical connection at the internal electrodes 30, 40 is further improved.

[0163] In the piezoelectric element PD1, the entire outer edges of the conductor portions 31b, 33b, 41b, and 43b are located inside the outer edges of the regions 32d, 34d, 42d, and 44d when viewed from the first direction D1. In this case, when viewed from the first direction D1, the outer edges of the regions 32d, 34d, 42d, and 44d are located farther away from the center line CL1, and the degree of increase in thickness of the regions 32d, 34d, 42d, and 44d in the first direction D1 is reduced. The shapes of the internal electrodes 30 and 40 change more gradually at the continuous portions. Stress acting on the internal electrodes 30 and 40 from the element body 1 as the element body 1 deforms is less likely to concentrate at the continuous portions. As a result, the reliability of the electrical connection at the internal electrodes 30 and 40 is further improved.

[0164] In the piezoelectric element PD1, recesses 36 and 46 are formed in the regions 32d, 34d, 42d, and 44d at end portions 32f, 34f, 42f, and 44f that are distant from the regions 32c, 34c, 42c, and 44c in the first direction D1. In this case, the thicknesses of the conductor portions 32b, 34b, 42b, and 44b in the first direction D1 are reduced by the amount of the recesses 36 and 46 formed in the regions 32d, 34d, 42d, and 44d. This reduction in thickness allows the conductor portions 32b, 34b, 42b, and 44b to more easily follow the contraction and expansion of the conductor portions 32a, 34a, 42a, and 44a that accompany deformation of the element body 1. This further reduces the deterioration in the reliability of the electrical connection in the continuous portion. As a result, the reliability of the electrical connection in the internal electrodes 30 and 40 is further improved.

[0165] In the piezoelectric element PD1, the depth of the recesses 36, 46 increases as they approach the center line CL1. In this case, the thicknesses of the conductor portions 32b, 34b, 42b, and 44b in the first direction D1 decrease toward the center line CL1, and the conductor portions 32b, 34b, 42b, and 44b are more likely to follow the contraction and expansion of the conductor portions 32a, 34a, 42a, and 44a that accompany deformation of the element body 1. This further suppresses deterioration in the reliability of electrical connection in the continuous portion. As a result, the reliability of electrical connection in the internal electrodes 30 and 40 is further improved.

[0166] In the piezoelectric element PD1, the conductor portions 31b, 33b, 41b, and 43b are located inside the opening edges of the recesses and 46 when viewed from the first direction D1. In this case, the formation of the recesses 36, 46 further expands the range in which the thickness of the conductor portions 32b, 34b, 42b, 44b in the first direction D1 is reduced. This reduction in thickness over a wider range allows the conductor portions 32b, 34b, 42b, 44b to more easily follow the contraction and expansion of the conductor portions 32a, 34a, 42a, 44a that accompany deformation of the element body 1. This further suppresses the deterioration of the reliability of the electrical connection in the continuous portion. As a result, the reliability of the electrical connection in the internal electrodes 30, 40 is further improved.

[0167] In the piezoelectric element PD1, the regions 32d, 34d, 42d, 44d and the recesses 36, 46 have a circular shape when viewed from the first direction D1. In this case, the regions 32d, 34d, 42d, and 44d are more likely to follow the contraction and expansion of the conductor portions 32a, 34a, 42a, and 44a in the direction intersecting the first direction D1 that accompanies deformation of the element body 1. This further suppresses deterioration in the reliability of electrical connection in the continuous portion. As a result, the reliability of electrical connection in the internal electrodes 30 and 40 is further improved.

[0168] In the piezoelectric element PD1, the lengths of the regions 32c, 34c, 42c, and 44c in the first direction D1 are smaller than the lengths of the bottoms 36b and 46b of the recesses 36 and 46 and the conductor portions 31b, 33b, 41b, and 43b in the first direction D1. In this case, the conductor portions 32b, 34b, 42b, and 44b are more likely to follow the contraction and expansion of the conductor portions 32a, 34a, 42a, and 44a that accompany deformation of the element body 1. This further suppresses deterioration in the reliability of electrical connection in the continuous portion. As a result, the reliability of electrical connection in the internal electrodes 30 and 40 is further improved.

[0169] According to the inventor's research, in a piezoelectric element, the piezoelectric element expands and contracts and deforms in response to a drive signal applied to the conductor. The deformation of the piezoelectric element may also cause deformation of the connection portion. When the connection portion deforms, cracks may occur in the connection portion. When cracks occur in the connection portion, the reliability of the electrical connection in the conductor decreases. A conductor with a reduced reliability of the electrical connection makes it difficult to achieve stable transmission of the drive signal. Therefore, if the connection portion can deform similarly to the piezoelectric element, the connection portion reduces the risk of cracks occurring at the connection portion. The reduced risk of cracks increases the resistance of the conductor to deformation of the piezoelectric element.

[0170] The piezoelectric element PD1 according to this embodiment includes an element body 1, external electrodes 10 and 20, and internal electrodes 30 and 40. The internal electrodes 30 and 40 include internal conductors 31, 33, 41, and 43 and internal conductors 32, 34, 42, and 44 that face each other. The internal conductors 32, 34, 42, and 44 include conductor portions 32b, 34b, 42b, and 44b that extend in a first direction D1 and are connected to the internal conductors 31, 33, 41, and 43. The conductor portions 32b, 34b, 42b, and 44b include regions 32p, 34p, 42p, and 44p that include a first material having conductivity, and regions 32q, 34q, 42q, and 44q that include a second material different from the first material and that has a linear expansion coefficient different from that of the first material.

[0171] In the piezoelectric element PD1, the internal electrodes 30 and 40 have mutually opposing internal conductors 31, 33, 41, and 43 and internal conductors 32, 34, 42, and 44. The internal conductors 32, 34, 42, and 44 include conductor portions 32b, 34b, 42b, and 44b connected to the internal conductors 31, 33, 41, and 43. The conductor portions 32b, 34b, 42b, and 44b have regions 32p, 34p, 42p, and 44p containing a first material and regions 32q, 34q, 42q, and 44q containing a second material, and the linear expansion coefficient of the second material is different from the linear expansion coefficient of the first material. Therefore, the linear expansion coefficient of the conductor portions 32b, 34b, 42b, 44b having the regions 32q, 34q, 42q, 44q containing the second material can be closer to, for example, the linear expansion coefficient of the element body 1 compared to the linear expansion coefficient of the conductor portions 32b, 34b, 42b, 44b consisting of the regions 32p, 34p, 42p, 44p containing the first material. The deformation of the conductor portions 32b, 34b, 42b, 44b accompanying deformation of the element body 1 approaches the deformation of the element body 1. As a result, the risk of cracks occurring in the conductor portions 32b, 34b, 42b, 44b is reduced, and the resistance of the internal electrodes 30, 40 to deformation of the element body 1 is further increased. When the thicknesses of the conductor portions 32b, 34b, 42b, and 44b in the first direction D1 increase toward the center lines CL1 of the through holes 35b, 35d, 45b, and 45d, the reliability of the electrical connection in the internal electrodes 30 and 40 is further improved. That is, as described above, stress acting on the internal electrodes 30 and 40 from the element body 1 due to deformation of the element body 1 is less likely to concentrate on the conductor portions 32b, 34b, 42b, and 44b. Furthermore, the deformation of the conductor portions 32b, 34b, 42b, and 44b due to deformation of the element body 1 approaches the deformation of the element body 1 due to the large linear expansion coefficients of the conductor portions. This reliably reduces the risk of cracks occurring in the conductor portions 32b, 34b, 42b, and 44b, and further increases the resistance of the internal electrodes 30 and 40 to deformation of the element body 1. As a result, the reliability of the electrical connection in the internal electrodes 30 and 40 is further improved.

[0172] In the piezoelectric element PD1, the conductor portions 32b, 34b, 42b, 44b have a plurality of regions 32q, 34q, 42q, 44q containing the second material, and the plurality of regions 32q, 34q, 42q, 44q containing the second material are distributed within the regions 32p, 34p, 42p, 44p containing the first material. In this case, the linear expansion coefficients of the conductor portions 32b, 34b, 42b, 44b can be closer to the linear expansion coefficient of the element body 1, for example, than the linear expansion coefficient of the conductor portions 32b, 34b, 42b, 44b consisting of the regions 32p, 34p, 42p, 44p containing the first material. The deformation of the conductor portions 32b, 34b, 42b, 44b accompanying deformation of the element body 1 becomes closer to the deformation of the element body 1. As a result, the risk of cracks occurring in the conductor portions 32b, 34b, 42b, 44b is further reduced, and the resistance of the internal electrodes 30, 40 to deformation of the element body 1 is further increased. The reliability of the electrical connection at the internal electrodes 30, 40 is further improved.

[0173] In the piezoelectric element PD1, the regions 32q, 34q, 42q, 44q containing the second material have protruding portions 32r that protrude toward the element body 1. In this case, the conductor portions 32b, 34b, 42b, 44b can be in contact with the element body 1 via the protruding portions 32r of the regions 32q, 34q, 42q, 44q containing the second material. This improves adhesion between the conductor portions 32b, 34b, 42b, 44b and the element body 1. As a result, the risk of cracks occurring in the conductor portions 32b, 34b, 42b, 44b is further reduced, and the resistance of the internal electrodes 30, 40 to deformation of the element body 1 is further increased. This further improves the reliability of electrical connection at the internal electrodes 30, 40.

[0174] In the piezoelectric element PD1, the regions 32q, 34q, 42q, and 44q containing the second material are located in at least one of the regions 32c, 34c, 42c, and 44c and the regions 32d, 34d, 42d, and 44d. In this case, the linear expansion coefficient of at least one of the regions 32c, 34c, 42c, 44c and the regions 32d, 34d, 42d, 44d can be closer to the linear expansion coefficient of the element body 1 than the linear expansion coefficient of the conductor portions 32b, 34b, 42b, 44b consisting of the regions 32p, 34p, 42p, 44p containing the first material. The deformation of the regions 32c, 34c, 42c, 44c and the regions 32d, 34d, 42d, 44d due to deformation of the element body 1 approaches the deformation of the element body 1. As a result, the risk of cracks occurring in the regions 32c and the regions 32d, 34d, 42d, 44d is reduced, and the resistance of the internal electrodes 30, 40 to deformation of the element body 1 is further increased. The reliability of the electrical connection of the internal electrodes 30, 40 is further improved.

[0175] In the piezoelectric element PD1, the regions 32q, 34q, 42q, 44q containing the second material are located in the regions 32s, 34s, 42s, 44s which include the surfaces that define the recesses 36, 46 within the regions 32d, 34d, 42d, 44d. In this case, it is possible to prevent the recesses 36, 46 from peeling off from the element body 1. As a result, the reliability of the electrical connection at the internal electrodes 30, 40 is further improved.

[0176] Although the embodiments of the present invention have been described above, the present invention is not necessarily limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention.

[0177] In the piezoelectric element PD1, the rate of increase in the thickness of the regions 32d, 34d, 42d, and 44d in the first direction D1 does not have to be smaller than the rate of increase in the thickness of the regions 32c, 34c, 42c, and 44c in the first direction D1. In a configuration in which the rate of increase in the thickness of the regions 32d, 34d, 42d, and 44d in the first direction D1 is smaller than the rate of increase in the thickness of the regions 32c, 34c, 42c, and 44c in the first direction D1, as described above, the shape of the internal electrodes 30 and 40 changes more gradually at the location where the fourth conductor portion and the third conductor portion are connected to each other. Stress acting on the internal electrodes 30 and 40 from the element body 1 as the element body 1 deforms is less likely to concentrate at the connected location. As a result, the reliability of the electrical connection between the internal electrodes 30 and 40 is improved. In the piezoelectric element PD1, the thicknesses of the respective region portions 32d1, 34d1, 42d1, 44d1, 32d2, 34d2, 42d2, and 44d2 included in the regions 32d, 34d, 42d, and 44d in the first direction D1 do not need to increase toward the center line CL1. In a configuration in which the thicknesses of the respective region portions 32d1, 34d1, 42d1, 44d1, 32d2, 34d2, 42d2, and 44d2 included in the regions 32d, 34d, 42d, and 44d in the first direction D1 increase toward the center line CL1, as described above, the shape of the internal electrodes 30 and 40 changes more gradually at the location where the fourth conductor portion and the third conductor portion are connected to each other. As the element body 1 deforms, stress acting on the internal electrodes 30 and 40 from the element body 1 is less likely to concentrate at the connected location. As a result, the reliability of the electrical connection between the internal electrodes 30, 40 is further improved. In the piezoelectric element PD1, the entire outer edges of the conductor portions 31b, 33b, 41b, and 43b do not have to be located inside the outer edges of the regions 32d, 34d, 42d, and 44d as viewed from the first direction D1. In a configuration in which the entire outer edges of the conductor portions 31b, 33b, 41b, and 43b are located inside the outer edges of the regions 32d, 34d, 42d, and 44d as viewed from the first direction D1, the outer edges of the regions 32d, 34d, 42d, and 44d are located farther from the center line CL1 as viewed from the first direction D1, and the degree of increase in thickness of the regions 32d, 34d, 42d, and 44d in the first direction D1 is reduced. The shape of the internal electrodes 30 and 40 changes more gradually at the point where the fourth conductor portion and the third conductor portion are connected to each other. The stress acting on the internal electrodes 30, 40 from the element body 1 as the element body 1 deforms is even less likely to concentrate at the continuous portion, thereby further improving the reliability of the electrical connection at the internal electrodes 30, 40. In the piezoelectric element PD1, the regions 32d, 34d, 42d, 44d do not necessarily have to have the recesses 36, 46 at the ends 32f, 34f, 42f, 44f that are distant in the first direction D1 from the regions 32c, 34c, 42c, 44c. In a configuration in which the regions 32d, 34d, 42d, 44d have the recesses 36, 46 at the ends 32f, 34f, 42f, 44f that are distant in the first direction D1 from the regions 32c, 34c, 42c, 44c, as described above, the thicknesses of the conductor portions 32b, 34b, 42b, 44b in the first direction D1 are reduced by the amount corresponding to the recesses 36, 46 formed in the regions 32d, 34d, 42d, 44d. The reduced thickness allows the conductor portions 32b, 34b, 42b, and 44b to more easily follow the contraction and expansion of the conductor portions 32a, 34a, 42a, and 44a that accompany deformation of the element body 1. This further suppresses deterioration in the reliability of electrical connection at the location where the fourth conductor portion and the third conductor portion are connected to each other. As a result, the reliability of electrical connection at the internal electrodes 30 and 40 is further improved. In the piezoelectric element PD1, the depths of the recesses 36, 46 do not necessarily increase toward the center line CL1. In a configuration in which the depths of the recesses 36, 46 increase toward the center line CL1, as described above, the thicknesses of the conductor portions 32b, 34b, 42b, and 44b in the first direction D1 decrease toward the center line CL1. This allows the conductor portions 32b, 34b, 42b, and 44b to more easily follow the contraction and expansion of the conductor portions 32a, 34a, 42a, and 44a that accompany deformation of the element body 1. This further suppresses deterioration in the reliability of the electrical connection in the continuous portion. As a result, the reliability of the electrical connection in the internal electrodes 30 and 40 is further improved. In the piezoelectric element PD1, the conductor portions 31b, 33b, 41b, and 43b do not necessarily need to be located inside the opening edges of the recesses 36 and 46 as viewed in the first direction D1. In a configuration in which the conductor portions 31b, 33b, 41b, and 43b are located inside the opening edges of the recesses 36 and 46 as viewed in the first direction D1, the formation of the recesses 36 and 46 further expands the range in which the thickness of the conductor portions 32b, 34b, 42b, and 44b in the first direction D1 is reduced. This reduction in thickness over a wider range allows the conductor portions 32b, 34b, 42b, and 44b to more easily follow the contraction and expansion of the conductor portions 32a, 34a, 42a, and 44a that accompany deformation of the element body 1. This further suppresses the deterioration of the reliability of the electrical connection in the continuous portion. As a result, the reliability of the electrical connection within the internal electrodes 30 and 40 is further improved. In the piezoelectric element PD1, the regions 32d, 34d, 42d, and 44d and the recesses 36 and 46 do not necessarily have a circular shape when viewed from the first direction D1. In a configuration in which the regions 32d, 34d, 42d, and 44d and the recesses 36 and 46 have a circular shape when viewed from the first direction D1, as described above, the regions 32d, 34d, 42d, and 44d are more likely to follow the contraction and expansion of the conductor portions 32a, 34a, 42a, and 44a in a direction intersecting the first direction D1 due to deformation of the element body 1. Therefore, the deterioration of the reliability of the electrical connection in the continuous portion is further suppressed. As a result, the reliability of the electrical connection in the internal electrodes 30 and 40 is further improved. In the piezoelectric element PD1, the lengths of the regions 32c, 34c, 42c, and 44c in the first direction D1 do not have to be shorter than the lengths of the bottoms 36b and 46b of the recesses 36 and 46 and the conductor portions 31b, 33b, 41b, and 43b in the first direction D1. In a configuration in which the lengths of the regions 32c, 34c, 42c, and 44c in the first direction D1 are shorter than the lengths of the bottoms 36b and 46b of the recesses 36 and 46 and the conductor portions 31b, 33b, 41b, and 43b in the first direction D1, as described above, the conductor portions 32b, 34b, 42b, and 44b are more likely to follow the contraction and expansion of the conductor portions 32a, 34a, 42a, and 44a that accompany deformation of the element body 1. This further suppresses deterioration in the reliability of the electrical connection in the continuous portion. As a result, the reliability of the electrical connection between the internal electrodes 30, 40 is further improved.

[0178] In the piezoelectric element PD1, the conductor portions 32b, 34b, 42b, and 44b may not have the regions 32q, 34q, 42q, and 44q containing the second material. As described above, a configuration in which the conductor portions 32b, 34b, 42b, and 44b have the regions 32q, 34q, 42q, and 44q containing the second material further improves the reliability of the electrical connection in the internal electrodes 30 and 40.

[0179] In the piezoelectric element PD1, the conductor portions 32b, 34b, 42b, and 44b do not necessarily have to have the cavities 50. The configuration in which the cavities 50 are formed in the conductor portions 32b, 34b, 42b, and 44b further improves the reliability of the electrical connection between the internal electrodes 30 and 40, as described above.

[0180] In piezoelectric element PD1, conductor portions 32b, 34b, 42b, and 44b do not necessarily have to have recesses 51 that open to the outer circumferential surfaces of conductor portions 32b, 34b, 42b, and 44b. In a configuration in which conductor portions 32b, 34b, 42b, and 44b have recesses 51 that open to the outer circumferential surfaces of conductor portions 32b, 34b, 42b, and 44b, as described above, vibrations caused by deformation of element body 1 are easily transmitted within element body 1, improving the resonance characteristics of piezoelectric element PD1.

[0181] As can be understood from the above-described embodiments and modifications, this specification includes the following disclosures. Specifically, the piezoelectric element PD1 includes a piezoelectric body, a first conductor disposed on the piezoelectric body, and a second conductor connected to the first conductor and disposed on the body so as to face the first conductor. The second conductor includes a connection portion extending in the direction in which the first conductor and the second conductor face each other and connected to the first conductor. A cavity is formed in the connection portion. In a configuration in which the piezoelectric element PD1 includes an external electrode disposed on the outer surface of the piezoelectric body and an internal electrode connected to the external electrode and disposed within the piezoelectric body, the internal electrode may have an internal conductor facing the external electrode. The internal conductor facing the external electrode may include a connection portion extending in the direction in which the external electrode and the internal conductor face each other and connected to the external electrode. A cavity may be formed in the connection portion.

[0182] The piezoelectric element PD1 includes a piezoelectric body, a first conductor disposed on the piezoelectric body, and a second conductor connected to the first conductor and disposed on the piezoelectric body so as to face the first conductor. The second conductor includes a connection portion extending in the direction in which the first conductor and the second conductor face each other and connected to the first conductor. The connection portion has a recess formed in its outer circumferential surface. In the piezoelectric element PD1, the connection portion has a recess formed in the outer circumferential surface of the connection portion. The connection portion with the recess formed is more easily deformed than the connection portion without the recess formed. Therefore, when stress from the piezoelectric element acts on the connection portion as the piezoelectric element deforms, cracks are less likely to occur in the connection portion. As a result, the resistance of the conductor to the stress acting from the piezoelectric element is increased. The reliability of the electrical connection in the conductor is improved. [Explanation of symbols]

[0183] 1...element body, 5b...element body portion, 10...external electrode, 20...external electrode, 30...internal electrode, 31...internal conductor, 31a...conductor portion, 31b...conductor portion, 32...internal conductor, 32a...conductor portion, 32b...conductor portion, 32c...region, 32d...region, 32d1...region portion, 32d2...region portion, 32f...end, 32p...region, 32q...region, 33...internal conductor, 33a...conductor portion, 33b...conductor portion, 34...internal conductor, 34a...conductor portion, 34b...conductor portion, 34c...region, 34d...region, 34d1...region portion, 34d2...region portion, 34f...end, 35b...through hole, 35c...through hole, 36...recess, 40...internal electrode, 41...internal conductor , 41a...conductor portion, 41b...conductor portion, 42...internal conductor, 42a...conductor portion, 42b...conductor portion, 42c...region, 42d...region, 42d1...region portion, 42d2...region portion, 42f...end, 42p...region, 42q...region, 43...internal conductor, 43a...conductor portion, 43b...conductor portion, 44...internal conductor, 44a...conductor portion, 44b...conductor portion, 44c...region, 44d...region, 44d1...region portion, 44d2...region portion, 44f...end, 45b...through hole, 45c...through hole, 46...recess, 50...cavity, 51...recess, CL1...center line, D1...first direction, D1a...direction, D1b...direction, PD1...piezoelectric element, SP1...reference plane.

Claims

1. a piezoelectric element; an external electrode disposed on the outer surface of the piezoelectric element; an internal electrode connected to the external electrode and disposed within the piezoelectric element; Equipped with The internal electrode has a first internal conductor and a second internal conductor facing each other, the second inner conductor includes a connection portion extending in a direction in which the first inner conductor and the second inner conductor face each other and connected to the first inner conductor, A cavity that is a closed space is formed within the connection portion, the first inner conductor includes a first conductor portion and a second conductor portion that are continuous with each other; the second inner conductor further includes a third conductor portion facing the first conductor portion in the direction; the connection portion has a first region connected to the second conductor portion, and a second region continuous with the first region and continuous with the third conductor portion, the piezoelectric element includes an element portion located between the first internal conductor and the second internal conductor, a through hole penetrating the element body portion in the direction is formed in the element body portion, the connection portion is located within the through hole, the thickness of the connection portion in the direction increases toward the center line of the through hole, the directions include a first direction from the first inner conductor toward the second inner conductor and a second direction from the second inner conductor toward the first inner conductor; a plane orthogonal to the direction and including the third conductor portion is defined as a reference plane, and the second region includes a region portion having a thickness in the first direction from the reference plane and a region portion having a thickness in the second direction from the reference plane; A piezoelectric element, wherein the thickness of each of the region portions included in the second region in the direction increases as it approaches the center line.

2. 2. The piezoelectric element of claim 1, wherein in a cross section obtained by cutting the connection portion along a plane extending in the direction, the cross section including the cavity, the circle-equivalent diameter of the cavity at the cross section is 50% or less of the width of the connection portion at the cross section.

3. The piezoelectric element according to claim 1 , wherein the cavity has a cross section that is polygonal.

4. 4. The piezoelectric element according to claim 1, wherein the cavity is formed in at least one of the first region and the second region.

5. The piezoelectric element according to any one of claims 1 to 4, wherein the degree of increase in thickness of the second region in the direction is smaller than the degree of increase in thickness of the first region in the direction.

6. 6. The piezoelectric element according to claim 1, wherein the entire outer edge of the second conductor portion is located inside the outer edge of the second region when viewed from the direction.

7. 7. The piezoelectric element according to claim 1, wherein the connecting portion further has a recess formed therein that opens onto an outer peripheral surface of the connecting portion.

8. 8. The piezoelectric element according to claim 1, wherein the cavity contains an inert gas.

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