Piezoelectric vibration element and piezoelectric device

Abstract

This piezoelectric vibration element comprises a piezoelectric piece, a first excitation electrode, and a second excitation electrode. The piezoelectric piece has a first surface and a second surface. The first excitation electrode is located on the first surface. The second excitation electrode is located on the second surface. The piezoelectric piece includes a bonding portion and a vibrating portion. The bonding portion is flat at least on the first surface. In the vibrating portion, the second surface has a convex curved surface. The second surface has a curved shape having at least one inflection point in a cross section including the boundary between the bonding portion and the vibrating portion and the point at which the thickness of the vibrating portion is greatest.

Description

Click a piezoelectric vibration button and piezoelectric device

[0001] This disclosure relates to piezoelectric vibration elements and piezoelectric devices.

[0002] In response to the demand for miniaturization of piezoelectric devices, there are integrated piezoelectric devices in which a piezoelectric vibrator is sandwiched between substrates as a wafer-level package (WLP). International Publication No. 2024 / 048201 discloses a technique for confining vibration energy in such piezoelectric vibrator elements by making the shape of the piezoelectric piece a mesa type or inverted mesa type.

[0003] One aspect of the present disclosure is a piezoelectric vibrating element comprising: [1] a piezoelectric piece having a first surface and a second surface opposite to the first surface; a first excitation electrode located on the first surface; and a second excitation electrode located on the second surface, wherein the piezoelectric piece includes a joint on the first surface from which the first excitation electrode and the second excitation electrode can be electrically connected to the outside; and a vibrating portion including the area in which the first excitation electrode and the second excitation electrode are located, wherein the joint is flat at least on the first surface; the vibrating portion has a convex curved surface on the second surface; and in a cross section including the boundary between the joint and the vibrating portion and the point of maximum thickness in the vibrating portion, the second surface has a curved shape with at least one inflection point. [2] The piezoelectric vibrating element of [1], wherein the first surface is located on the same plane across the joint and the vibrating portion. [3] The piezoelectric vibrating element of [1] or [2], wherein the piezoelectric piece has a groove between the joint and the vibrating portion. [4] A piezoelectric vibrating element according to any of [1] to [3], wherein the maximum thickness of the vibrating portion is greater than the thickness of the joint and less than or equal to twice the thickness of the joint. [5] A piezoelectric vibrating element according to any of [1] to [4], wherein the vibrating portion has a rectangular shape in plan view, and the center of the set of points with the maximum thickness in the vibrating portion is further from the joint than the center of the vibrating portion. [6] A piezoelectric device comprising: a piezoelectric vibrating element according to any of [1] to [5]; a first substrate that is joined to the first surface of the joint and supports the piezoelectric vibrating element; and a second substrate that is joined to the first substrate with the piezoelectric vibrating element in between. [7] The piezoelectric device according to [6], wherein the first surface of the joint is parallel to the joining surface of the first substrate with the joint.

[0004] It is an overall perspective view showing a piezoelectric device in an embodiment. It is a perspective view of the inside with the first substrate of the piezoelectric device removed. It is a plan view of the configuration shown in FIG. 2. It is a cross-sectional view of the piezoelectric device. It is a cross-sectional view of the piezoelectric device. It is a cross-sectional view showing an enlarged piezoelectric element and its periphery. It is a cross-sectional view showing an enlarged piezoelectric element and its periphery. It is an enlarged cross-sectional view of the piezoelectric element and its periphery in another embodiment. It is an enlarged cross-sectional view of the piezoelectric element and its periphery in another embodiment. It is a plan view corresponding to FIG. 3 of a piezoelectric device having a piezoelectric element in another embodiment.

[0005] Hereinafter, embodiments will be described based on the drawings. FIG. 1 is an overall perspective view showing a piezoelectric device 1 in one embodiment. In each figure of the present disclosure, the ratio of the three direction components of the length does not necessarily reflect the actual shape for the sake of explanation. The piezoelectric device 1 has two substrates 5 and an intermediate portion 30. The two substrates 5 are the first substrate 10 and the second substrate 20. The intermediate portion 30 is sandwiched between the first substrate 10 and the second substrate 20. The direction in which the first substrate 10 and the second substrate 20 overlap is the Z-axis direction. The first substrate 10 may be located on the +Z side, that is, the upper side. Connection pads 16 and 17 are located on the upper surface, which is the surface of the first substrate 10 opposite to the second substrate 20. The connection pads 16 and 17 are made of a conductive material and may be a metal, for example, molybdenum, copper, silver, tungsten, or the like. By having such a substantially rectangular parallelepiped shape, the piezoelectric device 1 may be stacked and packaged in multiple numbers for use. Although the up and down are shown here for convenience, the up and down may be reversed for use. Further, by using wafer-level packaging (WLP) in manufacturing, the piezoelectric device 1 can be manufactured accurately by a semiconductor process.

[0006] The first substrate 10 and the second substrate 20 are silicon substrates and have an insulating layer on the surface exposed to the outside. The insulating layer may be, for example, a layer of silicon dioxide. The insulating layer only needs to have a thickness that can appropriately maintain insulation, and may be, for example, 100 nm or more. The thicknesses of the first substrate 10 and the second substrate 20 may be, for example, 30 μm or more and 200 μm or less according to the required strength and the like.

[0007] Figure 2 is a perspective view of the inside of the piezoelectric device 1 with the first substrate 10 removed. Figure 3 is a plan view of the area shown in Figure 2. The intermediate portion 30 has an annular partition wall 31 in plan view. Within the area enclosed by partition wall 31, there may be an additional annular partition wall 32 located at a predetermined distance from partition wall 31. The area enclosed by partition walls 31 and 32 is sealed by being sandwiched above and below by two substrates 5, namely the first substrate 10 and the second substrate 20. The piezoelectric vibration element 40 and connecting conductors 513 and 523 are located in this sealed internal area. The piezoelectric vibration element 40 may be, for example, an AT-cut quartz crystal vibration element, and the piezoelectric piece 41 may be a quartz crystal. The piezoelectric piece 41 may be located at a distance from the second substrate 20 in an area that overlaps with the recess 201 of the second substrate 20 in plan view. The connecting conductor 513 is positioned between insulating layers 511 and 512, and the connecting conductor 523 is positioned between insulating layers 521 and 522. The internal region may be under low pressure lower than atmospheric pressure or in a near-vacuum state, or it may be filled with an inert gas such as nitrogen.

[0008] The piezoelectric vibrating element 40 includes the piezoelectric piece 41, a first excitation electrode 42, a second excitation electrode 43, lead wires 44 and 45, and a through via conductor 46. The piezoelectric piece 41 may be, for example, rectangular in plan view, and its thickness may be appropriately determined so that it resonates at an appropriate frequency. The resonant frequency may be 100 MHz or higher, and may be even 300 MHz or higher. The plan view size of the piezoelectric piece 41 may be, for example, 1000 μm or less on each side. The first excitation electrode 42 is located on the first surface 41a of the piezoelectric piece 41 facing the first substrate 10. The second excitation electrode 43 is located on the second surface 41b of the piezoelectric piece 41 facing the second substrate 20. The first excitation electrode 42 and the second excitation electrode 43 may be in the same position in plan view from the Z direction. The first excitation electrode 42 and the second excitation electrode 43 may have the same shape, or they may be circular in plan view. The vibration of the piezoelectric vibration element 40 may be, for example, thickness-sliding vibration, but is not limited to this. The vibrating portion 412 is the +X side portion of the piezoelectric piece 41 that includes the portion where the first excitation electrode 42 and the second excitation electrode 43 are in contact, and which mainly vibrates in response to the voltage applied to the first excitation electrode 42 and the second excitation electrode 43.

[0009] The lead wire 44 is located on the first surface 41a of the piezoelectric piece 41, with one end connected to the first excitation electrode 42 and extending to the joint 411, which is the part that contacts the -X side end of the piezoelectric piece 41. The lead wire 45 is located on the second surface 41b of the piezoelectric piece 41, with one end connected to the second excitation electrode 43 and the other end connected to the through via conductor 46. That is, the X-axis may be defined along the direction in which the joint 411 and the vibrating part 412 are aligned. The Y-axis direction is perpendicular to the X-axis and the Z-axis. The X-axis direction may, but is not limited to, the longitudinal direction of the piezoelectric piece 41.

[0010] The through via conductor 46 may be positioned along the inner surface of the through hole 41c of the piezoelectric piece 41. This structure allows the wiring connected to the second excitation electrode 43 to be drawn out to the first surface 41a of the joint 411. The through via conductor 46 may have a concave shape that closes the opening of the through hole 41c to the first surface 41a. The lead wire 45 may be positioned concavely along the through via conductor 46 within the through hole 41c. The concave region within the through hole 41c may be filled with an insulating member 47, such as resin. Alternatively, the through via conductor 46 and / or the lead wire 45 may fill the through hole 41c. The through via conductor 46 may be connected to a connection pad on the first surface 41a. The lead wires 44, 45 and the through via conductor 46 allow the first excitation electrode 42 and the second excitation electrode 43 to be connected to the outside from the first surface 41a of the piezoelectric vibration element 40. The boundary between the joint 411 and the vibrating part 412 may be a straight line extending in the Y direction. Therefore, both the joint 411 and the vibrating part 412 may have a rectangular shape in plan view.

[0011] The first excitation electrode 42, the second excitation electrode 43, the lead wires 44, 45, and the through via conductor 46 are conductors made of metal or the like, for example, molybdenum, copper, silver, gold, tungsten, etc. Furthermore, some or all of the first excitation electrode 42, the second excitation electrode 43, the lead wires 44, 45, and the through via conductor 46 may have nickel plating and gold plating laminated on their surfaces. The materials of the first excitation electrode 42, the second excitation electrode 43, the lead wires 44, 45, and the through via conductor 46 may all be the same. Alternatively, some of the materials of the first excitation electrode 42, the second excitation electrode 43, the lead wires 44, 45, and the through via conductor 46 may differ from the materials of the other parts. The first excitation electrode 42, the second excitation electrode 43, and the lead wires 44, 45 may be thinner than the piezoelectric piece 41, for example, with a thickness of about 100 to 200 nm.

[0012] From the joint 411 of the piezoelectric vibration element 40, connecting conductors 513 and 523 extend outward from the recess 201 in a plan view. Connecting conductor 513 is electrically connected to the lead wire 44. Connecting conductor 523 is electrically connected to the through via conductor 46 and / or the connecting pad on the first surface 41a. The lead wire 44 and connecting conductor 513 may be connected overlapping in a plan view at the joint 411. The through via conductor 46 and / or the connecting pad on the first surface 41a and connecting conductor 523 may be connected overlapping in a plan view at the joint 411.

[0013] Figure 4A is a cross-sectional view of the piezoelectric device 1 along the cross-sectional line iva-iva in Figure 3. The cross-section in Figure 4A includes the leader wire 44 and the connecting conductor 513. Figure 4B is a cross-sectional view of the piezoelectric device 1 along the cross-sectional line ivb-ivb in Figure 3. The cross-section in Figure 4B includes the leader wire 45 and the connecting conductor 523.

[0014] The first substrate 10 has a through hole 101 in a position that overlaps with the connection pad 16 and the connection conductor 513 in a plan view. A through conductor 14 is located inside the through hole 101. The through conductor 14 electrically connects the connection pad 16 and the connection conductor 513. The first substrate 10 has a through hole 102 in a position that overlaps with the connection pad 17 and the connection conductor 523 in a plan view. A through conductor 15 is located inside the through hole 102. The through conductor 15 electrically connects the connection pad 17 and the connection conductor 523. The through conductors 14 and 15 may be coated with a metal plating or the like.

[0015] The first substrate 10 has a silicon layer 11 and insulating layers 12 and 13 covering the outer surface of the silicon layer 11. The silicon layer 11 has a recess 103 facing a part of the recess 201. The second substrate 20 has a silicon layer 21 and an insulating layer 22 covering the outer surface of the silicon layer 21. The insulating layers 12 and 22 may be, for example, silicon dioxide layers which are thermal oxide films of the silicon layer. The first substrate 10 does not have to have a two-layer structure of insulating layers 12 and 13 as insulating layers. For example, the first substrate 10 does not have to have insulating layer 12. Also, the connecting conductor 513 may be insulated from the silicon layers 11 and 21 by insulating layers 511 and 512. The connecting conductor 523 may be insulated from the silicon layers 11 and 21 by insulating layers 521 and 522. In this case, the insulating layers 511 and 521 each have openings 51a and 52a for connecting the through conductors 14 and 15 and the connecting conductors 513 and 523, respectively. The through conductor 14 may be positioned concave along the inner wall surface of the through hole 101 and the opening 51a from the upper side of the first substrate 10. The peripheral portion of the concave shape of the through conductor 14 is in contact with the connecting pad 16 on the first substrate 10, and the bottom surface of the concave shape is in contact with the connecting conductor 513. The through conductor 15 may be positioned concave along the inner wall surface of the through hole 102 and the opening 52a from the upper side of the first substrate 10. The peripheral portion of the concave shape of the through conductor 15 is in contact with the connecting pad 17 on the first substrate 10, and the bottom surface of the concave shape is in contact with the connecting conductor 523. The interior of the concave shape of the through conductor 14 may be filled with an insulating member 104, such as resin. The interior of the recessed shape of the through-conductor 15 may be filled with an insulating material 105, such as resin.

[0016] Furthermore, the bottom surface of the recessed shape of the first through conductor 14, i.e., the contact surface with the connecting conductor 513, may extend inward from the connecting conductor 513. In other words, the connecting conductor 513 may have a recess 5131 in the contact portion with the first through conductor 14, where its thickness in the Z direction is thinner than that of the portion not in contact with the first through conductor 14. Furthermore, the bottom surface of the recessed shape of the second through conductor 15, i.e., the contact surface with the connecting conductor 523, may extend inward from the connecting conductor 523. In other words, the connecting conductor 523 may have a recess 5231 in the contact portion with the second through conductor 15, where its thickness in the Z direction is thinner than that of the portion not in contact with the second through conductor 15.

[0017] Thus, the piezoelectric vibrating element 40 is supported only at the first surface 41a of the joint portion 411 of the piezoelectric piece 41 and is maintained in a one-handed state. The length of the joint portion 411 in the X direction can be set to be as short as possible to obtain the necessary support strength for the piezoelectric piece 41. This reduces the adverse effects on the vibration of the piezoelectric vibrating element 40. The piezoelectric vibrating element 40 is fixed in a state parallel to the joint surface of the first substrate 10 to which the first surface 41a of the joint portion 411 is joined.

[0018] In other words, the connecting pads 16 and 17, which are connected to the outside, are electrically connected to the first excitation electrode 42 and the second excitation electrode 43 of the piezoelectric vibration element 40, respectively. The thickness of the connecting conductors 513 and 523 may be greater than the thickness of the leader wires 44 and 45. In this case, the connecting conductors 513 and 523 may be formed by repeatedly laminating the structure of the leader wires 44 and 45 two or more times, or they may be formed by folding symmetrically with respect to the center in the Z direction. Alternatively, the connecting conductors 513 and 523 may be made of a different material from the leader wires 44 and 45.

[0019] The partition walls 31 and 32 may each have the same laminated structure made of the same material as the connecting conductor 513 sandwiched between the insulating layers 511 and 512, and the connecting conductor 523 sandwiched between the insulating layers 521 and 522, respectively. That is, partition wall 31 may have an insulating layer 311 in contact with the first substrate 10, an insulating layer 312 in contact with the second substrate 20, and a conductor layer 313 sandwiched between the insulating layers 311 and 312. The term "same material" here refers to a range that includes manufacturing variations, and does not specify the presence, amount, or ratio of trace elements that may be mixed in during manufacturing. Partition wall 32 may have an insulating layer 321 in contact with the first substrate 10, an insulating layer 322 in contact with the second substrate 20, and a conductor layer 323 sandwiched between the insulating layers 321 and 322. The thickness of the insulating layers 311 and 321 may be approximately the same as the thickness of the insulating layers 511 and 521. The thickness of the insulating layers 312 and 322 may be approximately the same as the thickness of the insulating layers 512 and 522. The thickness of the conductor layers 313 and 323 may be approximately the same as the thickness of the connecting conductors 513 and 523. Here, "approximately the same" includes manufacturing variations, and for example, there may be a difference of about ±10%. Note that Figures 4A and 4B show an example in which the conductor layers 313 and 323 of the partition wall have a two-layer structure, but the example is not limited to this. The conductor layers 313 and 323 may have a structure in which three or more layers are stacked on top of each other.

[0020] Furthermore, the insulating layers 511, 512, 521, and 522 only need to be located near the boundary where the signal paths, such as the connecting conductors 513 and 523, and the semiconductor silicon layers 11 and 21 come into contact. In other words, in areas where there are no conductors to be insulated, the insulating layers do not need to be in contact with the silicon layers 11 and 21 over an unnecessarily wide area. The insulating layers 511, 512, 521, and 522 may each be located at a distance from other insulating layers, including the insulating layers 311, 312, 321, and 322 of the partition walls 31 and 32. Although Figures 4A and 4B show examples where the connecting conductors 513 and 523 have a two-layer structure, the conductors are not limited to this. The connecting conductors 513 and 523 may have a structure in which three or more layers are stacked. The number of stacked layers, the material of each layer, and the stacking order of each material may be the same as those of the conductor layers 313 and 323, or some or all of them may be different.

[0021] As described above, the through via conductor 46 may have a recessed shape that closes one end of the through hole. The lead wire 45 may be in contact with the through via conductor 46 along the inner surface of the recessed shape. Increasing the contact area in this way reduces the possibility of disconnection. The connecting conductor 523 may be electrically connected to the bottom surface of the recessed shape of the through via conductor 46.

[0022] Figures 5A and 5B are enlarged cross-sectional views showing the piezoelectric piece 41 and its surrounding area. The piezoelectric piece 41 has a flat surface at least on the first surface 41a of the joint 411. The second surface 41b of the joint 411 may also be flat. On the other hand, at least the surface opposite to the first surface 41a, i.e., the second surface 41b, has a convex shape in the vibrating portion 412. This convex shape is a curved shape, i.e., a curved shape in any cross section parallel to the Z axis. The curved shape here may include straight sections as long as it does not have discontinuous parts such as bends. For example, the second surface 41b may include a planar area with the maximum thickness. In any cross section passing through the part with the maximum thickness, the thickness, i.e., the distance between the first surface 41a and the second surface 41b in the Z direction, increases monotonically from the edge to the point where the thickness is maximum. In each of the above cross sections, let Pm be the point on the second surface 41b where the thickness is first maximum. If, as described above, there is more than one point where the thickness is maximum, point Pm is determined linearly or annularly with respect to an arbitrary set of cross-sections. The shape of the cross-section of the vibrating section 412 that includes point Pm and is parallel to the Z direction, for example, the cross-section parallel to the XZ plane and / or the cross-sectional shape parallel to the XY plane, does not have to be symmetrical with respect to a straight line that includes point Pm and is parallel to the Z axis.

[0023] In the section of the above cross-section that includes point Pb on the boundary line between the joint 411 and the vibrating part 412, the second surface 41b is a curve having at least one inflection point Pi between point Pb and point Pm. Between point Pb and inflection point Pi, the curve is convex upwards, and the curve asymptotically approaches the second surface 41b of the joint 411, which is a straight line in cross-sectional view. That is, between the joint 411 and the set of inflection points Pi, the piezoelectric piece 41 has an inwardly concave shape. Between the inflection points Pi and point Pm, the curve is convex downwards. That is, between the set of inflection points Pi and point Pb, the piezoelectric piece 41 has an outwardly convex shape. The curves representing these cross-sections may be represented by a mathematical formula having a single term of degree three or higher, or by a polynomial combining multiple terms. Furthermore, the curve shape may differ depending on the cross-section.

[0024] The thickness of the piezoelectric piece 41 at point Pm may be greater than the thickness of the piezoelectric piece 41 at the joint 411, and may be less than or equal to twice the thickness of the piezoelectric piece 41 at the joint 411. If the piezoelectric piece 41 has a convex shape on both sides, the first surface 41a and the second surface 41b, the sum of the protrusions on both sides may be less than or equal to the size of the piezoelectric piece 41 at the joint 411. The protrusions on the first surface 41a and the protrusions on the second surface 41b may be equal or different from each other.

[0025] The center of point Pm may be located on the +X side of the center of the vibrating portion 412, that is, on the side away from the joint portion 411. In this case, there does not need to be an inflection point Pi between point Pm and the +X side tip of the piezoelectric piece 41. The +X side tip of the vibrating portion 412 may be a side surface perpendicular to the X direction, and the curve forming the cross section may be discontinuously bent between the second surface 41b and the side surface of the piezoelectric piece 41.

[0026] The first surface 41a of the vibrating part 412 may be a plane, that is, a straight line in cross-sectional view. In this case, the first surface 41a is continuous between the joint 411 and the vibrating part 412 and has no steps. That is, the first surface 41a may be located on the same plane across the joint 411 and the vibrating part 412. In this disclosure, the terms "plane" and "straight line in cross-sectional view" may include errors that may occur during manufacturing. That is, it is sufficient if there are no irregularities that can be set in the design taking into account the manufacturing process.

[0027] Figures 6A and 6B are enlarged cross-sectional views of the piezoelectric piece 41 and its surrounding area in another embodiment. The piezoelectric piece 41 has a peripheral edge 413, and in cross-sectional view, the corners of all or part of the peripheral edge of the piezoelectric piece 41 may be chamfered or rounded. The corners may be chamfered or rounded on both sides of the first surface 41a and the second surface 42b, or on only one side. If only one side is chamfered, the entire side may be chamfered and the other side may be beveled.

[0028] Figure 7 is a plan view of a piezoelectric device 1 having a piezoelectric piece 41 of another embodiment, as seen in the same state as in Figure 3. In one embodiment, the piezoelectric piece 41 may have a groove such as a slit 41d. The slit 41d is located at the boundary between the joint 411 and the vibrating part 412. The slit 41d may be cut from either of the two sides along the X-axis direction of the piezoelectric piece 41, or it may be a closed hole shape inside the piezoelectric piece 41 in plan view. The leader wires 44 and 45 wrap around the slit 41d and are led out from the first excitation electrode 42 and the second excitation electrode 43 to the joint 411, respectively, through the portion where the joint 411 and the vibrating part 412 are connected. If the portion where the joint 411 and the vibrating part 412 are connected is narrow, the leader wires 44 and 45 may have overlapping portions in plan view.

[0029] In this case, the inflection point Pi is located within cross-section vii, which passes through at least the portion where the joint 411 and the vibrating portion 412 are connected. That is, in the cross-section passing through the slit 41d, the curved surface along the second surface 41b does not necessarily have an inflection point Pi.

[0030] The groove may have a concave shape that does not penetrate the piezoelectric piece 41. In this case, the concave shape may be located on both the first surface 41a and the second surface 41b, or on only one of them, for example, the second surface 41b. The concave groove may also be located across the entire space between the joint 411 and the vibrating part 412. The leader wires 44 and 45 may extend across the concave portion. The bottom of the concave shape may be flat or a uniform curved surface in the Y direction.

[0031] As described above, the piezoelectric vibration element 40 of this embodiment comprises a piezoelectric piece 41, a first excitation electrode 42, and a second excitation electrode 43. The piezoelectric piece 41 has a first surface 41a and a second surface 41b opposite to the first surface 41a. The first excitation electrode 42 is located on the first surface 41a. The second excitation electrode 43 is located on the second surface 41b. The piezoelectric piece 41 includes a joint portion 411 on the first surface 41a that allows the first excitation electrode 42 and the second excitation electrode 43 to be electrically connected to the outside, and a vibrating portion 412 that includes the area in which the first excitation electrode 42 and the second excitation electrode 43 are located. The joint portion 411 is flat at least on the first surface 41a. The vibrating portion 412 is a convex curved surface on the second surface 41b. In a cross-section including point Pb on the boundary between the joint 411 and the vibrating part 412 and point Pm on the vibrating part 412 where the thickness is maximum, the second surface 41b has a curved shape with at least one inflection point Pi. Conventionally, with the miniaturization of piezoelectric devices, it has become difficult to contain vibration energy and reduce spurious emissions. This piezoelectric vibration element 40 can suitably contain vibration energy in the convex-shaped vibrating part 412. Furthermore, since the convex portion is a curve in cross-sectional view and the radius of curvature changes significantly, vibrations of specific frequencies are less likely to appear as spurious emissions, resulting in vibrations with less noise. In particular, even if the joint 411 is not far from the first excitation electrode 42 and the second excitation electrode 43, leakage of vibration energy to the joint 411 is reduced, making it easier to miniaturize the piezoelectric vibration element 40. In addition, since the number of angles that occur in mesa type or inverse mesa type is not increased, the resistance of the piezoelectric vibration element 40 when it is subjected to impact is improved. Furthermore, because the vibrating portion 412 is thicker than the joint portion 411, it becomes less susceptible to the effects of thermal stress originating from the joint portion 411.

[0032] Furthermore, the first surface 41a may be located on the same plane across the joint 411 and the vibrating portion 412. If the second surface 41b is a curved surface, the thickness change can be precisely determined even if the other first surface 41a is a flat surface. Also, a flat surface can be obtained more easily and accurately than a curved surface. Because the first surface 41a is a uniform flat surface and has no steps, the piezoelectric vibration element 40 reduces the reflection and coupling of vibrations in specific modes while reducing manufacturing effort and cost.

[0033] Furthermore, the piezoelectric piece 41 may have a slit 41d between the joint 411 and the vibrating part 412. Since the slit 41d separates the vibrating part 412 from the joint 411, this piezoelectric vibration element 40 can reduce the leakage of vibration energy to the joint 411 and the reflection at the joint 411, even if it is small.

[0034] Furthermore, the maximum thickness of the vibrating section 412 may be greater than the thickness of the joint section 411, and less than or equal to twice the thickness of the joint section 411. By keeping the thickness of the vibrating section 412 within a defined range relative to the thickness of the joint section 411, the increase in the planar area corresponding to the curved shape can be reduced.

[0035] Furthermore, the vibrating portion 412 may have a rectangular shape in plan view. The center of the set of points Pm where the thickness of the vibrating portion 412 is maximum may be further from the joint portion 411 than the center of the vibrating portion 412. The generation of spurious emissions is particularly susceptible to the influence of the joint portion 411. Therefore, by separating the joint portion 411 from the first excitation electrode 42 and the second excitation electrode 43, it is possible to reduce the amount of spurious emissions generated by vibration reflection at the joint portion 411.

[0036] Furthermore, the piezoelectric device 1 of this embodiment comprises one of the piezoelectric vibration elements 40 described above, a first substrate 10, and a second substrate 20. The first substrate 10 is joined to the first surface 41a of the joint 411 to support the piezoelectric vibration element 40. The second substrate 20 is joined to the first substrate 10 with the piezoelectric vibration element 40 in between. Such a piezoelectric device 1 can be obtained in a small and precise manner using a semiconductor process. In such a small piezoelectric device 1, leakage of vibration energy from the vibrating part 412 and the generation of spurious signals of a specific frequency due to reflection of vibration by the joint 411 can be effectively reduced.

[0037] Furthermore, the first surface 41a of the joint portion 411 may be parallel to the joint surface of the first substrate 10 with the joint portion 411. By having the first substrate 10 and the first surface 41a of the piezoelectric vibration element 40 that is reduced to the first substrate 10 be parallel, the piezoelectric device 1 can be miniaturized.

[0038] The above embodiment is illustrative and can be modified in various ways. For example, the inflection point of the second surface 41b in the vibrating portion 412 may be located on the ±Y side or the +X side other than the joint portion 411 side. Furthermore, there may be multiple inflection points. Also, the shape between point Pb and point Pm may be non-uniform.

[0039] Furthermore, the shapes of the first surface 41a and the second surface 41b do not need to be similar, even if the first surface 41a is not flat. The shapes of the first surface 41a and the second surface 41b may be determined separately in order to obtain an appropriate resonant frequency.

[0040] Furthermore, even if the vibrating portion 412 of the first surface 41a is substantially planar, if its position in the Z direction differs from that of the joint portion 411, these positional differences may be connected by a continuous curved surface that asymptotically approaches the vibrating portion 412 and the joint portion 411, respectively.

[0041] Furthermore, although the piezoelectric element 41 is assumed to be rectangular in plan view as described above, it is not limited to this. The piezoelectric element 41 may have rounded or blunted corners in plan view.

[0042] Further, the center position of the thickest point Pm on the second surface 41b is not limited to the +X side of the center of the vibrating portion 412 and may be determined as appropriate.

[0043] Further, the vibrating portion 412 may have a point thinner than half of the thickness of the point Pm.

[0044] Further, the piezoelectric vibrating element 40 may have a piezoelectric sheet 41 that is not a crystal sheet. In this case, the positions or shapes of the first exciting electrode 42 and the second exciting electrode 43 may be different according to the type of the piezoelectric sheet 41 or the like. In addition, specific details such as the structure, configuration, material, size, etc. shown in the above embodiments can be appropriately changed without departing from the spirit of the present disclosure. The scope of the present invention includes the scope of the invention described in the claims and its equivalent scope.

[0045] The present disclosure can be used for piezoelectric vibrating elements and piezoelectric devices.

[0046] 1 Piezoelectric device 5 Substrate 11, 21 Silicon layer 12, 13, 22 Insulating layer 14, 15 Through conductor 16, 17 Connection pad 30 Intermediate portion 31, 32 Partition wall 40 Piezoelectric vibrating element 41 Piezoelectric sheet 41a First surface 41b Second surface 41c Through hole 41d Slit 411 Joint portion 412 Vibrating portion 413 Peripheral portion 42 First exciting electrode 43 Second exciting electrode 44, 45 Lead wire 46 Through via conductor 47 Insulating member 51a, 52a Opening 101, 102 Through hole 104, 105 Insulating member 103, 201 Recess 311, 312, 321, 322 Insulating layer 313, 323 Conductor layer 511, 512, 521, 522 Insulating layer 513, 523 Connection conductor 5131, 5231 Recess Pi Inflection point

Claims

1. A piezoelectric vibrating element comprising: a piezoelectric piece having a first surface and a second surface opposite to the first surface; a first excitation electrode located on the first surface; and a second excitation electrode located on the second surface, wherein the piezoelectric piece includes a joint on the first surface that allows the first excitation electrode and the second excitation electrode to be electrically connected to the outside; and a vibrating portion that includes the area in which the first excitation electrode and the second excitation electrode are located, wherein the joint is flat at least on the first surface; the vibrating portion has a convex curved surface on the second surface; and in a cross-section including the boundary between the joint and the vibrating portion and the point on the vibrating portion where the thickness is greatest, the second surface has a curved shape with at least one inflection point.

2. The piezoelectric vibrating element according to claim 1, wherein the first surface is located on the same plane across the joint and the vibrating portion.

3. The piezoelectric vibrating element according to claim 1 or 2, wherein the piezoelectric piece has a groove between the joint and the vibrating portion.

4. The piezoelectric vibrating element according to any one of claims 1 to 3, wherein the maximum thickness of the vibrating portion is greater than the thickness of the joint portion and is no more than twice the thickness of the joint portion.

5. The piezoelectric vibrating element according to any one of claims 1 to 4, wherein the vibrating portion has a rectangular shape in plan view, and the center of the set of points with the maximum thickness in the vibrating portion is further away from the joint than the center of the vibrating portion.

6. A piezoelectric device comprising: a piezoelectric vibrating element according to any one of claims 1 to 5; a first substrate joined to the first surface of the joint and supporting the piezoelectric vibrating element; and a second substrate joined to the first substrate with the piezoelectric vibrating element in between.

7. The piezoelectric device according to claim 6, wherein the first surface of the joint is parallel to the bonding surface of the first substrate with the joint.

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