Piezoelectric device

Abstract

This piezoelectric device comprises: a package having a recess, with an electrode pad positioned within the recess; and a piezoelectric vibration element joined to the electrode pad by a joining member. The piezoelectric vibration element is substantially rectangular when observed in plan view, and comprises: a vibrating unit: and a thick part that is thicker than the vibrating unit and that is arranged, with the vibrating unit, in an X direction, the X direction extending along the longitudinal direction of at least the piezoelectric vibration element. The joining member joins the thick part and the electrode pad at at least two locations. The center position of the joining member in plan view, from a side surface on the thick part side in the X direction, is located within a range from 0.21 to 0.61 times a first length which extends in the X direction of the piezoelectric vibration element.

Description

Piezoelectric Devices

[0001] The present disclosure relates to piezoelectric devices.

[0002] Conventionally, there are cantilever-shaped piezoelectric devices in which one end of a piezoelectric vibration element, which is approximately rectangular in plan view and extends along its long side, is fixed to a package or the like, and the opposite end is open. An electrode located near the fixed end is electrically connected and fixed to an electrode pad on the package using a conductive adhesive. In the crystal element described in JP 2018-56861 A, the thickness of the crystal element decreases from the fixed portion toward the flat portion at the tip. This shape reduces the mixing of vibrations other than the desired vibration mode into the crystal element's vibration.

[0003] One aspect of the present disclosure is a piezoelectric device comprising: (1) a package having a recess, with electrode pads located in the recess; and a piezoelectric vibration element joined to the electrode pads by a bonding member, wherein the piezoelectric vibration element is substantially rectangular in a plan view and has a vibrating portion and a thick portion that is aligned with the vibrating portion at least in a first direction along the longitudinal direction of the piezoelectric vibration element and is thicker than the vibrating portion, the bonding member bonds the thick portion to the electrode pad at least in two locations, and the planar view center position of the bonding member is located in a range from 0.21 to 0.61 times a first length of the piezoelectric vibration element in the first direction, from an end face on the thick portion side in the first direction. (2) The piezoelectric device of (1), wherein the planar view center position of the bonding member is located farther from the end face of the piezoelectric vibration element in the first direction than a center position of the thick portion. (3) The piezoelectric device according to (1) or (2), wherein the piezoelectric vibration element has a pair of mounting electrodes to which the bonding member is bonded, and the center positions of the bonding members in a planar view are located closer to the outer edge of the piezoelectric vibration element than the center positions of the mounting electrodes in a planar view in a second direction perpendicular to the first direction in a planar view. (4) The piezoelectric device according to any one of (1) to (3), wherein the resonant frequency of the piezoelectric vibration element is 75 MHz or higher.

[0004] 1A and 1B are an overall perspective view and a cross-sectional view of a piezoelectric device according to an embodiment of the present invention; FIG. 1C are a plan view and a cross-sectional view of a package; FIG. 1D are views illustrating bonding positions by bonding members;

[0005] Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is an overall perspective view of a piezoelectric device 1 according to this embodiment. This FIG. 1 shows a state in which a lid 30 is removed. Note that in the drawings of this disclosure, the ratio of height in the Z-axis direction to size in the XY-axis plane perpendicular to the Z-axis is for illustrative purposes only and does not necessarily reflect actual values. The piezoelectric device 1 according to one embodiment, which is a piezoelectric vibrator, includes a package 10, a piezoelectric vibrating element 20, and a lid 30.

[0006] The package 10 may be a housing made of, for example, a ceramic material, a semiconductor material, a glass material, or a combination of these. Furthermore, the package 10 may have a conductive signal line inside or on the surface of the above material. The signal line may include a portion related to power supply and grounding. The signal line may be made of, for example, molybdenum, copper, silver, tungsten, or the like. Nickel plating, gold plating, or the like may be laminated on a portion or all of the signal line. The package 10 has a recess 10a that opens to the top surface, which is the +Z side surface. The piezoelectric vibration element 20 is housed in the recess 10a.

[0007] In one embodiment, the piezoelectric vibration element 20 may be a quartz vibration element. The piezoelectric vibration element 20 is located inside the recess 10a. The piezoelectric vibration element 20 has a generally rectangular shape in a planar view. The generally rectangular shape may include, for example, a rectangle with rounded corners or a rectangle with chamfered corners. Meanwhile, in one embodiment, the piezoelectric vibration element 20 may not have a notch, cutout, or through-hole in a planar view. Depending on the shape of the piezoelectric vibration element 20, the recess 10a may have a rectangular shape in a planar view. The X-axis direction in each drawing is equal to the X-axis direction of the quartz vibration element and corresponds to the first direction of the present disclosure. The Y-axis direction in each drawing represents the Z'-axis direction of the quartz vibration element and corresponds to the second direction of the present disclosure. The longitudinal direction of the piezoelectric vibration element 20 is parallel to the X-axis, and the direction perpendicular to the longitudinal direction is parallel to the Y-axis.

[0008] The lid 30 is joined to the periphery of the opening of the package 10, i.e., to the upper end of the sidewall surrounding the recess 10a in a plan view seen from the +Z side, thereby sealing the recess 10a. The lid 30 is a flat plate of a metal conductor, and may be, for example, a metal containing iron, copper, nickel, cobalt, molybdenum, or tungsten, or an alloy thereof, such as Kovar. The lid 30 may be joined to the package 10, for example, by a brazing material. A frame-shaped metallization layer may be located between the upper end of the package 10 and the lid 30. The metallization layer may be a plated layer or a conductor layer that is applied and baked.

[0009] Fig. 2A is a plan view of the piezoelectric device 1. Fig. 2B is a cross-sectional view of the piezoelectric device 1 taken along the cross-sectional line AA in Fig. 1. The plan view of Fig. 2A shows the inside of the recess 10a with the lid 30 removed.

[0010] The piezoelectric device 1 has a crystal blank 21 in which a vibrating portion 211 and a thick portion 212 that is thicker than the vibrating portion 211 are aligned in the X direction. In one embodiment, the width of the thick portion 212 in the X direction, i.e., a second length A2 described below, may be 31% to 68% of the length of the piezoelectric vibration element 20 in the X direction, i.e., a first length A1 described below. When the thin vibrating portion 211 has a length within this range, the center of gravity of the piezoelectric vibration element 20 can be located on the thick portion 212 side.

[0011] An excitation electrode 23 is located approximately in the center of the vibrating part 211 on each of the ±Z sides. The excitation electrode 23 may be rectangular in a plan view. Alternatively, the excitation electrode 23 may be elliptical, for example. The excitation electrodes 23 on each side may be positioned so as to overlap each other in a plan view. When a voltage is applied to the excitation electrode 23, a displacement occurs in the vibrating part 211. Alternatively, a voltage is generated between the excitation electrodes 23 in response to the displacement of the vibrating part 211. When a voltage is applied at a frequency corresponding to the resonant frequency of the vibrating part 211, the vibrating part 211 resonates. In one embodiment, the resonant frequency of the vibrating part 211 may be 75 MHz or higher, or even 150 MHz or higher.

[0012] The thick portion 212 is thicker than the vibrating portion 211. Specifically, the thick portion 212 may be three times thicker than the vibrating portion 211, and may even be approximately seven to ten times thicker. As described above, the length of the thick portion 212 in the X direction is approximately one-third to two-thirds of the first length, and therefore, 70% or more of the mass of the crystal blank 21, and depending on the structure, 90% or more, is the thick portion 212. The thick portion 212 may protrude upward from the top surface of the vibrating portion 211 on the +Z side, and may protrude downward from the bottom surface of the vibrating portion 211 on the -Z side.

[0013] A set of mounting electrodes 24 is arranged in the Y direction on the thick portion 212. For example, the mounting electrode 241 on the +Y side may be connected to the excitation electrode 23 on the upper surface, and the mounting electrode 241 on the -Y side may be connected to the excitation electrode 23 on the lower surface. The mounting electrodes 24 and the excitation electrodes 23 are connected by connection wiring 25. The vibration of the vibrating portion 211 that is transmitted to the thick portion 212 is negligible compared to the vibration of the vibrating portion 211 itself.

[0014] The upper and lower surfaces of the mounting electrode 24 are connected via the side surfaces. In one embodiment, the upper and lower surfaces of the mounting electrode 24 may be connected along the side surface 20a on the -X side. The lower surface of the mounting electrode 24 is bonded to the electrode pad 11 via a bonding member 40. The mounting electrode 241 is bonded to the electrode pad 11 via a bonding member 41. The mounting electrode 242 is bonded to the electrode pad 11 via a bonding member 42.

[0015] The bonding member 40 is conductive and electrically connects the two mounting electrodes 24 to the corresponding electrode pads 11. The bonding member 40 may be, for example, a conductive adhesive. The conductive adhesive hardens under predetermined conditions, such as heating. That is, the mounting electrodes 24 are placed in a predetermined positional relationship with respect to the conductive adhesive applied to the electrode pads 11, and the predetermined conditions are met in this state to bond and fix the electrode pads 11 and the mounting electrodes 24. The planar area of ​​the bonding member 40 is a size that allows for stable and reliable fixation, and may be, for example, a circle or an equivalent circle with a radius of approximately 35 μm to 80 μm.

[0016] The bonding member 40 before hardening may have viscosity, but does not generate enough stress to resist a force due to gravity acting in a direction other than downward on the piezoelectric vibration element 20 including the mounting electrode 24. In other words, when the piezoelectric vibration element 20 is bonded with the bonding member 40, the piezoelectric vibration element 20 may tilt or become displaced from its original position.

[0017] External connection pads 12 are located on the bottom surface of the package 10 .

[0018] 3 is a plan view of the package 10. The electrode pads 11 are positioned side by side in the Y direction on the bottom surface of the recess 10a of the package 10. A signal wiring 13 extends inside the package 10 from one of the electrode pads 11 toward the lower side of the vibrating section 211, i.e., in the +X direction. The signal wiring 13 may extend in the vertical direction at a position where it connects to the external connection pad 12 in a plan view, thereby electrically connecting the electrode pad 11 and the external connection pad 12.

[0019] Furthermore, the signal wiring 14 extends inside the package 10 and connects the wiring conductors 15 located along the inner side surface of the recess 10a to the external connection pads 12. The wiring conductors 15 contact the lid 30, thereby electrically connecting the lid 30 and the external connection pads 12. When the external connection pads 12 are grounded, the lid 30 is also grounded.

[0020] The electrode pad 11 different from the one mentioned above may extend in the −X direction on the bottom surface of the recess 10a. The external connection pad 12 that overlaps the −X side end of this electrode pad 11 in a plan view may be electrically connected to this electrode pad 11 by a wiring conductor 15 that connects between this electrode pad 11 and the external connection pad 12 and passes through the package 10. This electrode pad 11 may also be located inside the package 10, except for the portion that is actually joined to the mounting electrode 24 by the joining member 40.

[0021] FIG. 4 is a plan view of the piezoelectric vibration element 20 illustrating the bonding position by the bonding member 40. The first length A1 of the piezoelectric vibration element 20 in the X direction, the second length A2 of the thick portion 212 in the X direction, the third length A3 of the mounting electrode 24 in the X direction, and the fifth length A5 of the mounting electrode 24 in the Y direction are reference lengths. The first length A1 is longer than the second length A2. In one embodiment, the first length A1 is 450 μm or more and 750 μm or less. As described above, when the second length A2 is 31% or more of the first length A1, the second length A2 is 139 μm or more. Furthermore, depending on manufacturing conditions, the second length A2 may be 240 μm or more. The second length A2 is equal to or greater than the third length A3.

[0022] A central position C1, which is the center position of the bonding member 41 in a planar view, is a position that is a fourth length A4 from the side surface 20a, which is the end face on the -X side of the piezoelectric vibration element 20, and is a position that is a sixth length A6 from the side surface 20b on the +Y side of the piezoelectric vibration element 20. Furthermore, a central position C2, which is the center position of the bonding member 42 in a planar view, may be a position that is the fourth length A4 from the side surface 20a on the -X side of the piezoelectric vibration element 20, or may be a position that is a sixth length A6 from the side surface 20c on the -Y side. Alternatively, the central position C2 may be shifted from the above-mentioned position.

[0023] Here, the central positions C1 and C2 may be the center of gravity positions of the respective joining members 40 in a planar view. In other words, the distribution of mass and thickness of the joining members 40 does not need to be taken into consideration. When the joining members 40 are circular in a planar view, the central positions C1 and C2 coincide with the center position of the circle. The planar view of the joining members 40 may be a shape other than a circle, and may further be an asymmetric shape.

[0024] The fourth length A4 may be determined so as to balance the weight of the piezoelectric vibration element 20 and prevent it from tilting significantly toward the -Z direction due to the influence of its own weight or the shrinkage of the adhesive when bonded by the bonding member 40. Therefore, the fourth length A4 may be greater than half the second length A2, i.e., the center positions C1 and C2 may be located farther from the side surface 20a than the center position of the thick portion 212. Furthermore, the fourth length A4 may be greater than half the third length A3, i.e., the center positions C1 and C2 may be located farther from the side surface 20a than the center position of the mounting electrode 24. In this embodiment, the fourth length A4 is greater than or equal to 0.21 and less than or equal to 0.61 of the first length A1. Furthermore, the ratio of the fourth length A4 to the first length A1 may be greater than or equal to 0.23, greater than or equal to 0.25, or greater than or equal to 0.27. On the other hand, the ratio of the fourth length A4 to the first length A1 may be 0.50 or less, 0.45 or less, 0.40 or less, or 0.35 or less. In particular, taking into consideration the ratio between the thickness of the thick portion 212 and the thickness of the vibrating portion 211, and the ratio between the first length A1 and the second length A2, the center positions C1 and C2 may be set on the +X side in a plan view of the center of gravity of the piezoelectric vibration element 20. This further reduces the possibility that the piezoelectric vibration element 20 will tilt when bonding the piezoelectric vibration element 20, causing the vibrating portion 211 to come into contact with the package 10.

[0025] If the bonding member 40 adheres to the vibrating portion 211, it will adversely affect the vibration of the vibrating portion 211. Therefore, the bonding member 40 does not overlap with the vibrating portion 211 in a plan view. For this reason, the fourth length A4 is shorter than the second length A2. The bonding member 40 also connects the mounting electrode 24 and the electrode pad 11. In other words, it is preferable that the bonding area of ​​the bonding member 40 with the mounting electrode 24 is large. Therefore, the fourth length A4 may be shorter than the third length A3.

[0026] Furthermore, in order to reduce the possibility that the bonding member 40 will flow to the excitation electrode 23, the center positions C1 and C2 may be located near the side surface 20b or the side surface 20c, which are both edges of the piezoelectric vibration element 20, in the Y direction. In one embodiment, the sixth length A6 may be shorter than half the fifth length A5. That is, the center positions C1 and C2 may be located closer to the outer edge of the piezoelectric vibration element 20 in the Y direction than the center position of the mounting electrode 24 in a planar view. Note that the bonding member 40 may extend outside the range of the piezoelectric vibration element 20 in a planar view.

[0027] As described above, the piezoelectric device 1 of this embodiment includes a package 10 having a recess 10a with electrode pads 11 located within the recess 10a, and a piezoelectric vibration element 20 bonded to the electrode pads 11 by a bonding member 40. The piezoelectric vibration element 20 is generally rectangular in plan view and includes a vibrating portion 211 and a thick portion 212 that is aligned with the vibrating portion 211 at least in the X direction along the longitudinal direction of the piezoelectric vibration element 20 and is thicker than the vibrating portion 211. The bonding member 40 bonds the thick portion 212 to the electrode pad 11 at at least two locations. Center positions C1 and C2 of the bonding member 40 in plan view are located within a range of 0.21 to 0.61 times the first length A1 of the piezoelectric vibration element 20 in the X direction from the side surface 20a, which is the end face on the thick portion 212 side in the X direction. As described above, in the piezoelectric device 1 of this embodiment, the piezoelectric vibration element 20 is fixed and held by the bonding member 40 near the center of the thick portion 212. This allows the piezoelectric vibration element 20 to be balanced during bonding, reducing tilt until the bonding material 40 hardens. Therefore, the piezoelectric device 1 can reduce the possibility that the vibrating part 211 of the piezoelectric vibration element 20 will come into contact with the wall surface of the package 10 or the like, adversely affecting vibration.

[0028] Furthermore, the center positions C1 and C2 of the bonding member 40 in a plan view may be located farther away from the side surface 20a of the piezoelectric vibration element 20 than a position half the second length A2 from the side surface 20a, which is the center position of the thick portion 212 in the X direction. This allows the piezoelectric vibration element 20 to be fixed closer to the center than the center of gravity of the thick portion 212. This further reduces the possibility that the piezoelectric vibration element 20 will tilt when fixed and the vibration portion 211 will come into contact with the wall surface of the package 10, etc.

[0029] The piezoelectric vibration element 20 also has a pair of mounting electrodes 24 to which the bonding member 40 is bonded. The center positions C1 and C2 of the bonding member 40 in a plan view may be located toward the outer edge of the piezoelectric vibration element 20 in the Y direction, from positions that are half the fifth length A5 from the side surfaces 20b and 20c, which are the center positions of the mounting electrodes 241 and 242 in a plan view. This reduces the possibility that the bonding member applied to the electrode pad 11 will flow and adhere to the excitation electrode 23 before hardening.

[0030] Furthermore, the resonant frequency of the piezoelectric vibration element 20 may be 75 MHz or higher. In the vibration part 211 that vibrates in a high frequency band of 75 MHz or higher, the vibration does not extend significantly beyond the periphery of the excitation electrode 23. Therefore, the area of ​​the vibration part 211 can be made smaller than that of the crystal blank 21. In other words, since the thick part 212 can easily be expanded to near the center, it is easy to stably bond the thick part 212 and the electrode pad 11.

[0031] The above embodiment is merely an example, and various modifications are possible. For example, the center positions C1 and C2 of the joining member 40 in a plan view may not be the same in the X direction and / or the Y direction. In this case, both positions in the X direction are within a range that satisfies the condition for the first length A1. Either one of the positions in the Y direction may be within a range that satisfies the condition for the fifth length A5, or both may or may not satisfy the condition.

[0032] Furthermore, the piezoelectric device 1 does not necessarily have to include the lid 30 .

[0033] Furthermore, the vibrating portion 211 does not have to be located at the center of the thick portion 212 in the Z direction. In other words, the vibrating portion 211 may be located offset above or below the center of the thick portion 212 in the Z direction.

[0034] Furthermore, vibrating portion 211 may be surrounded by a frame that is thicker than vibrating portion 211 and thinner than thick portion 212. That is, crystal blank 21 may have three thickness levels. Alternatively, the boundary between vibrating portion 211 and thick portion 212 may have an inclined portion where the thickness changes continuously.

[0035] Furthermore, the connection between each electrode pad 11 and the mounting electrode 24 by the bonding member 40 does not have to be at one location. The bonding member 40 may be connected at two separate locations. In this case, it is sufficient that the bonding member 40 at the connection location farthest from the side surface 20 a satisfies the condition of the fourth length A4 described above.

[0036] Furthermore, the upper and lower surfaces of the mounting electrode 24 may be connected via the side surfaces 20b and 20c, rather than the side surface 20a.

[0037] Furthermore, the piezoelectric vibration element 20 may not have the crystal blank 21 but may have another piezoelectric material. Alternatively, the piezoelectric vibration element 20 may be a combination of a crystal blank and another ceramic material. The specific details of the structure, configuration, materials, size, etc. shown in the above embodiment may be modified as appropriate without departing from the spirit of this disclosure. The scope of the present invention includes the scope of the invention described in the claims and their equivalents.

[0038] The present disclosure can be used in piezoelectric devices.

[0039] REFERENCE SIGNS LIST 1 Piezoelectric device 10 Package 10a Recess 11 Electrode pad 12 External connection pad 13, 14 Signal wiring 15 Wiring conductor 20 Piezoelectric vibration element 20a to 20c Side surface 21 Crystal blank 211 Vibration portion 212 Thick portion 23 Excitation electrode 24, 241, 242 Mounting electrode 25 Connection wiring 30 Lid 40 to 42 Joint members C1, C2 Center position

Claims

1. A piezoelectric device comprising: a package having a recess with an electrode pad located within the recess; and a piezoelectric vibration element joined to the electrode pad with a bonding material, wherein the piezoelectric vibration element is approximately rectangular in a plan view and has a vibration portion and a thick portion that is aligned with the vibration portion in at least a first direction along the longitudinal direction of the piezoelectric vibration element and is thicker than the vibration portion, the bonding material bonds the thick portion to the electrode pad in at least two locations, and the center position of the bonding material in a plan view is located in a range of 0.21 to 0.61 times the first length of the piezoelectric vibration element in the first direction from the end face on the thick portion side in the first direction.

2. A piezoelectric device as claimed in claim 1, wherein the central position of the joining member in a plan view is located farther away from the end face of the piezoelectric vibration element than the central position of the thick portion in the first direction.

3. A piezoelectric device as described in claim 1 or 2, wherein the piezoelectric vibration element has a set of mounting electrodes to which the joining member is joined, and the center positions of the joining members in a planar view are located closer to the outer edge of the piezoelectric vibration element than the center positions of the mounting electrodes in a planar view in a second direction perpendicular to the first direction in a planar view.

4. A piezoelectric device according to any one of claims 1 to 3, wherein the resonant frequency of the piezoelectric vibration element is 75 MHz or higher.

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