Piezoelectric device

Abstract

This piezoelectric device is provided with: a package having a recessed portion; a piezoelectric vibration element bonded to a first electrode pad via a first bonding member in the recessed portion; and a temperature-sensitive element bonded to a second electrode pad via a second bonding member below the piezoelectric vibration element in the recessed portion. The plan view area of the temperature-sensitive element is 0.2-0.9 times the plan view area of the piezoelectric vibration element. The value obtained by dividing the bonding area of the second bonding member by a distance between the bottom surface of the package and a surface including the second electrode pad is 0.7-1.3 times the value obtained by dividing the bonding area of the first bonding member by a first distance between the bottom surface of the package and a surface including the first electrode pad.

Description

Piezoelectric Devices

[0001] The present disclosure relates to piezoelectric devices.

[0002] Piezoelectric vibration elements have temperature dependency in their resonant frequency, etc. For this reason, Japanese Patent Application Laid-Open No. 2008-205938 discloses a technique in which a piezoelectric device having a piezoelectric vibration element has a thermosensitive element as a temperature sensor.

[0003] One aspect of the present disclosure is: [1] a package having a recess, in which a first electrode pad and a second electrode pad are located, a piezoelectric vibration element bonded to the first electrode pad in the recess, and a temperature-sensing element bonded to the second electrode pad below the piezoelectric vibration element in the recess, wherein the piezoelectric vibration element is bonded to the first electrode pad via a first bonding member, and the temperature-sensing element is bonded to the second electrode pad via a second bonding member, and the temperature-sensing element has a planar area of ​​1000 mm when viewed from above the recess. is 0.2 to 0.9 times the planar area of ​​the piezoelectric vibration element, and a value obtained by dividing a first planar adhesive area of ​​the first bonding member of the first electrode pad by a first distance between a bottom surface of the package and a surface of the package including the first electrode pad is 0.7 to 1.3 times the value obtained by dividing a second planar adhesive area of ​​the second bonding member of the second electrode pad by a second distance between the bottom surface of the package and a surface of the package including the second electrode pad. [2] The piezoelectric device according to [1], wherein the thickness of the temperature-sensing element is 0.1 mm or less. [3] The piezoelectric device according to [1], wherein the first bonding member and the second bonding member are made of the same material. [4] The piezoelectric device according to [1], wherein the first planar adhesive area is equal to or less than the planar area of ​​the first electrode pad, and the second planar adhesive area is equal to or less than the planar area of ​​the second electrode pad.

[0004] 1 is a plan view showing the structure of a piezoelectric device of this embodiment; FIG. 2 is a bottom view showing the structure of a piezoelectric device of this embodiment; FIG. 3 is a cross-sectional view showing the structure of a piezoelectric device of this embodiment; FIG. 4 is a diagram explaining the position of a temperature sensitive element in a piezoelectric device; FIG. 5 is a perspective view of a temperature sensitive element; FIG. 6 is a cross-sectional view explaining size setting for correlating the measured temperature of the temperature sensitive element with the temperature of a piezoelectric vibration element; FIG. 7 is a plan view explaining size setting for correlating the measured temperature of the temperature sensitive element with the temperature of a piezoelectric vibration element; FIG. 8 is a table showing parameters used when calculating the temperature tracking ability of a piezoelectric device of this embodiment by numerical simulation; FIG. 9 is a table showing the results of calculating the temperature tracking ability of a piezoelectric device of this embodiment by numerical simulation.

[0005] Hereinafter, an embodiment will be described with reference to the drawings. Figures 1A to 1C are diagrams showing the structure of a piezoelectric device 1 according to this embodiment. Figure 1A is a plan view of the inside of the piezoelectric device 1 with the lid 10 removed. Figure 1B is a bottom view of the bottom surface of the piezoelectric device 1. Figure 1C is a cross-sectional view taken along the line AA in Figure 1A.

[0006] The piezoelectric device 1 includes a package 20, a piezoelectric vibration element 30, and a temperature sensitive element 40. The package 20 has a recess 20a in the center of the top surface. The piezoelectric vibration element 30 is located within the recess 20a.

[0007] The package 20 may be a housing made of, for example, a ceramic material, a semiconductor material, a glass material, or a combination thereof. Furthermore, the package 20 has conductive signal lines inside and on its surface, which may include lines for power supply and grounding. The signal lines may be made of, for example, molybdenum, copper, silver, tungsten, or the like. Some or all of the signal lines may be nickel-plated, gold-plated, or the like. At one end of the recess 20a in the X direction along its longitudinal direction, first electrode pads 211 and 212 are positioned side by side in the Y direction perpendicular to the X direction. The first electrode pads 211 and 212 may be printed with gold or the like on the surface of the recess 20a.

[0008] Here, the piezoelectric vibration element 30 may be a quartz crystal resonator. The piezoelectric vibration element 30 has mounting electrodes 311 and 312 aligned in a direction perpendicular to the longitudinal direction at one end of the longitudinal direction of a quartz crystal blank. The mounting electrode 311 is connected to an excitation electrode 321 located on the upper surface of the piezoelectric vibration element 30. The mounting electrode 312 is connected to an excitation electrode (not shown) located on the lower surface of the piezoelectric vibration element 30, overlapping the excitation electrode 321 in a plan view.

[0009] The piezoelectric vibration element 30 may be positioned such that its longitudinal direction is parallel to the X-direction of the package 20. The mounting electrodes 311, 312 are connected to first electrode pads 211, 212 located in the recess 20a via a first bonding member 220. The piezoelectric vibration element 30 is not in contact with the package 20 except for the mounting electrodes 311, 312. Therefore, the piezoelectric vibration element 30 is in a cantilevered state. When a voltage is applied between the excitation electrodes, the crystal blank vibrates, and the voltage generated between the excitation electrodes in response to the vibration of the crystal blank is output to the outside via the mounting electrodes 311, 312 and the first electrode pads 211, 212.

[0010] Although the quartz crystal blank is shown here as having flat top and bottom surfaces, this is not limiting. For example, the quartz crystal blank may be thicker at one end where the mounting electrodes 311 and 312 are located than at other portions. Alternatively, conversely, the quartz crystal blank may be thicker at the center where the excitation electrodes 321 and the like are located than at the periphery.

[0011] The first bonding members 220 may be formed by heat-curing a first conductive adhesive. The first conductive adhesive may be, for example, a silver paste containing silver particles. The first bonding members 220 are applied to the first electrode pads 211, 212 in a substantially elliptical, e.g., circular, area. The first bonding members 220 extend within the planar view area of ​​the first electrode pads 211, 212 and the mounting electrodes 311, 312, depending on factors such as the wettability of the first electrode pads 211, 212 and the mounting electrodes 311, 312.

[0012] A recess 20b is located below the piezoelectric vibration element 30 on a portion of the bottom surface of the recess 20a. The temperature-sensing element 40 is located within the recess 20b. The temperature-sensing element 40 is a thermistor whose electrical resistance changes with temperature and may be a particularly thin film, such as a germanium telluride (GeTe) thin film. The temperature-sensing element 40 is connected to the second electrode pads 231 and 232 within the recess 20b via a second bonding member 240. The second bonding member 240 may be formed by heat-curing a second conductive adhesive and, similar to the first bonding member 220, may be applied to the second electrode pads 231 and 232 in a generally elliptical shape. The second bonding member 240 then expands within the planar view range of the second electrode pads 231 and 232, depending on the wettability of the second electrode pads 231 and 232, without extending beyond the planar view range of the second electrode pads 231 and 232. The thermal conductivity M2 of the second bonding members 240, particularly the material thereof, may be approximately the same as the thermal conductivity M1 of the first bonding members 220, particularly the material thereof, and the first bonding members 220 and the second bonding members 240 may be made of the same material. However, the first bonding members 220 and the second bonding members 240 may be different from each other.

[0013] As shown in FIG. 1B , external connection pads 251 may be located at the four corners of the bottom surface of the piezoelectric device 1. One of the external connection pads 251 is connected to one of the first electrode pads 211, 212 via wiring within the package 20 and on the surface, such as wiring 252. The other of the external connection pads 251 is connected to one of the second electrode pads 231, 232 via wiring within the package 20. The other of the first electrode pads 211, 212 and the other of the second electrode pads 231, 232 may be ground electrodes. In this case, the two ground electrodes may be connected to one of the common external connection pads 251 via wiring within the package 20. Alternatively, the first electrode pads 211, 212 and the second electrode pads 231, 232 may each be connected to one of the four external connection pads 251 in a one-to-one relationship.

[0014] As shown in Figure 1C, the second electrode pads 231, 232 and the temperature sensitive element 40 are located in a recessed portion 20b on the bottom surface of the recess 20a. The recessed portion 20b and the temperature sensitive element 40 are located on the opposite side of the package 20 from the first electrode pads 211, 212 in the X direction. The longitudinal direction of the package 20 and the longitudinal direction of the recessed portion 20b and the temperature sensitive element 40 may be the same X direction. As can be seen from Figure 1A, the temperature sensitive element 40 is located so that at least a portion thereof overlaps with the piezoelectric vibration element 30 in a planar view.

[0015] The recess 20a, including the depression 20b, is sealed by bonding a lid 10 to the upper surface of the sidewall of the recess 20a, which is the upper end of the package 20. The lid 10 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 bonding material used for sealing with the lid 10 may be heated within a temperature range that does not adversely affect the characteristics of the temperature-sensing element 40 sealed therein. For example, the lid 10 may be bonded using a brazing material or the like. A frame-shaped metallized layer may be located between the upper end of the package 20 and the lid 10. The metallized layer may be a plated layer or a conductive layer that is applied and baked.

[0016] 2A and 2B are diagrams illustrating the temperature sensitive element 40. Fig. 2A is a plan view of the inside of Fig. 1A with the piezoelectric vibration element 30 further removed. Fig. 2B is a perspective view of the temperature sensitive element 40 as seen from the bottom side.

[0017] As shown in FIG. 2A , the ratio of the planar area of ​​the recessed portion 20b to the planar area of ​​the recessed portion 20a in a plan view seen from above the package 20 in the Z direction corresponds to the ratio of the planar area of ​​the temperature sensitive element 40 to the planar area of ​​the piezoelectric vibration element 30. This planar area ratio may be, for example, 0.2 to 0.9 times. It is not expected that the size of the package 20 will be larger than necessary compared to the size of the piezoelectric vibration element 30. Therefore, the planar area of ​​the temperature sensitive element 40 may be smaller than the planar area of ​​the piezoelectric vibration element 30.

[0018] 2B, the temperature-sensing element 40 has at least a thin-film thermistor 42 whose electrical resistance is measured, and a thin-film thermistor substrate 41. The thickness of the temperature-sensing element 40 is not particularly limited, but is usually 100 μm or less, and may be, for example, about 50 μm. The material of the thin-film thermistor 42 is not particularly limited as long as the electrical resistance can be measured, but examples include MAlNO, MnCoNi, MnCoZn, and CrO, where M is at least one of Fe, Co, Mn, Cu, and Ni. ｘ N １－ｘ , GeSbTe, and GeTe. The film thickness of the thin film thermistor 42 may typically be 50 nm or more and 500 nm or less. The thin film thermistor 42 may be formed on a thin film thermistor substrate 41. The thin film thermistor substrate 41 may be, for example, an insulating film made of quartz glass, i.e., silicon dioxide. The thickness of the thin film thermistor substrate 41 is not particularly limited, but is typically 100 μm or less, and may be, for example, approximately 50 μm.

[0019] Although not particularly limited, two electrodes 43 may be located on the surface of the thin film thermistor 42 opposite the thin film thermistor substrate 41. The conductive member 44 on the electrode 43 may be obtained, for example, by heat-curing a silver paste. The electrode 43 may be joined to the second electrode pads 231 and 232 in the recess 20b via the conductive member 44.

[0020] Such a piezoelectric device 1 can be mounted on a substrate of various electronic devices. Heat is transferred from the substrate to the piezoelectric device 1 via the package 20. The heat transferred from external electrodes (not shown) located on the bottom surface of the package 20 to the package is transferred to the temperature sensor 40 and the piezoelectric vibration element 30, changing their temperatures. The temperature sensor 40 needs to measure a temperature equal to the temperature of the piezoelectric vibration element 30. However, if the area of ​​the temperature sensor 40 is large, heat may not be transferred evenly, and the temperature change of the temperature sensor 40 may not correspond to the temperature change of the piezoelectric vibration element 30.

[0021] 3A and 3B are diagrams illustrating size setting for correlating the measured temperature of the temperature sensing element 40 with the temperature of the piezoelectric vibration element 30. Fig. 3A is a cross-sectional view shown in Fig. 1C, and Fig. 3B is a plan view showing the lid 10 and the piezoelectric vibration element 30 shown in Fig. 1B without the cover 10 and the piezoelectric vibration element 30.

[0022] In the piezoelectric device 1, the distance between the bottom surface and the temperature sensing element 40 is a second distance t2. The distance between the bottom surface and the piezoelectric vibration element 30 is a first distance t1. The bonding area between the second electrode pads 231, 232 of the temperature sensing element 40, or more directly, the second bonding member 240, is bonding area S2 = s21 + s22. The bonding area between the first electrode pads 211, 212 of the piezoelectric vibration element 30, or more directly, the first bonding member 220, is bonding area S1 = s11 + s12. In the piezoelectric device 1, the first distance t1, the second distance t2, the bonding area S1, and the bonding area S2 are within an appropriate relationship range. The bonding area S1 is referred to as the first planar bonding area. The bonding area S2 is referred to as the second planar bonding area.

[0023] As described above, under the condition that the thermal conductivity M1 of the first bonding members 220 and the thermal conductivity M2 of the second bonding members 240 are equal, the first distance t1, the second distance t2, and the bonding areas S1 and S2 satisfy the condition of the following mathematical formula 1: 0.7≦(S2 / t2) / (S1 / t1)≦1.3 (Mathematical Formula 1). Note that t1>t2 holds depending on the positional relationship between the recess 20a and the dent 20b.

[0024] The larger the first distance t1 and the second distance t2, the more difficult the heat transfer. As described above, the second distance t2 from the bottom surface to the temperature sensing element 40 is shorter than the first distance t1 to the piezoelectric vibration element 30, so heat is transferred more quickly to the temperature sensing element 40 than to the piezoelectric vibration element 30. On the other hand, the larger the bonding areas S1 and S2, the more easily a large amount of heat is transferred.

[0025] Therefore, by limiting the bonding area S2 of the path that transfers heat to the temperature-sensing element 40, which is a short distance from the bottom surface, to a small value relative to the bonding area S1 of the piezoelectric vibration element 30, the piezoelectric device 1 controls the amount of heat transferred per time to the temperature-sensing element 40 and the piezoelectric vibration element 30, respectively.

[0026] Furthermore, as described above, since the temperature sensing element 40 has a small thickness and therefore a large planar size, if the bonding area S2 is small, the bonding portion of the temperature sensing element 40 becomes a bottleneck, making it easier for temperature distribution to occur within the temperature sensing element 40. In this embodiment, the bonding portions s21, s22 may be of the same size, and the bonding portions s21, s22 do not have to be significantly smaller than the planar area of ​​the temperature sensing element 40.

[0027] From the above, S / t, which is the ratio of the distance t to the bonding area S, is set to be in a roughly similar range. S2 / t2 in the temperature sensing element 40 is kept in a range of 0.7 to 1.3 times S1 / t1 in the piezoelectric vibration element 30.

[0028] 4A is a diagram showing parameters used in calculating the temperature tracking ability of the piezoelectric device 1 of this embodiment through numerical simulation. FIG. 4B is a diagram showing the results of the temperature tracking ability obtained through numerical simulation using the above parameters. The numerical simulation was performed using thermal fluid analysis software from Ansys (registered trademark).

[0029] In the numerical simulation, the package size was 0.8 mm in length along the Y direction, 1.0 mm in width along the X direction, and 0.2 mm in thickness along the Z direction. The piezoelectric vibration element was a quartz crystal chip, measuring 0.5 mm in length, 0.7 mm in width, and 0.021 mm in thickness. The thin-film thermistor 42 of the temperature sensor 40 was a GeTe film, measuring 0.3 mm in length, 0.4 mm in width, and 0.1 μmm in height. This thin-film thermistor 42 was located on a 0.05 mm-thick thin-film thermistor substrate 41. The lid 10 was 0.8 mm in length, 1.0 mm in width, and 0.04 mm in thickness. Heat was applied to the four external connection pads 251 so that the temperature rose at a rate of 3.5°C / min. The temperatures at the center of the temperature sensor 40 and the center of the piezoelectric vibration element 30 were calculated and compared.

[0030] As described above, the cover 10 is made of Kovar. The ceramic package 20 is made of alumina (Al ２ O ３) The wiring inside and on the surface of the package 20 has a nickel-plated layer and a gold-plated layer on molybdenum. The first electrode pads 211, 212 and the second electrode pads 231, 232 have the same configuration as the wiring described above. The first bonding member 220 and the second bonding member 240 may be obtained by heat-hardening a silver paste, which is a conductive adhesive. The piezoelectric vibration element 30 has a gold excitation electrode 321 and mounting electrodes 311, 312 on a quartz glass substrate on a thin-film thermistor substrate 41. The temperature sensor 40 has a GeTe thin-film thermistor 42 on a quartz glass substrate on a thin-film thermistor substrate 41.

[0031] In this piezoelectric device 1, the ratio of the second distance t2 between the bottom surface and the temperature sensor 40 to the first distance t1 between the bottom surface and the piezoelectric vibration element 30 was t2 / t1 = 75 / 105. In the comparative example, the bonding area S2 of the temperature sensor 40 was equal to the bonding area S1 of the piezoelectric vibration element 30 (S2 / S1 = 100 / 100, (S2 / t2) / (S1 / t1) = 1.4). In the example, the bonding area S2 was smaller than the bonding area S1 (S2 / S1 = 80 / 100, (S2 / t2) / (S1 / t1) = 1.12). As a result, in the example, the temperature difference between the piezoelectric vibration element 30 and the temperature sensor 40 was reduced to 44.8% of that in the comparative example.

[0032] Here, the bonding area S1 depends on the size of the crystal blank, i.e., the resonant frequency, and cannot be made larger than necessary. On the other hand, to make the bonding area S2 even smaller than in the above example, it is necessary to reduce the spread of the conductive adhesive. Also, taking into consideration the size necessary to maintain adhesive strength, the current manufacturing requirement is S2 / S1≧0.5.

[0033] As described above, the piezoelectric device 1 of this embodiment includes a package 20 having a recess 20a in which first electrode pads 211, 212 and second electrode pads 231, 232 are located, a piezoelectric vibration element 30 bonded to the first electrode pads 211, 212 within the recess 20a, and a temperature sensing element 40 bonded to the second electrode pads 231, 232 below the piezoelectric vibration element 30 within the recess 20a. The piezoelectric vibration element 30 is bonded to the first electrode pads 211, 212 via a first bonding member 220. The temperature sensing element 40 is bonded to the second electrode pads 231, 232 via a second bonding member 240. The planar area of ​​the temperature sensing element 40 when viewed from above the recess 20a is 0.2 to 0.9 times the planar area of ​​the piezoelectric vibration element 30. The value (S2 / t2) obtained by dividing the bonding area S2 of the second bonding member 240 at the second electrode pads 231, 232 by the second distance t2 between the bottom surface of the package 20 and the surface of the package 20 that includes the second electrode pads 231, 232 is 0.7 to 1.3 times the value (S1 / t1) obtained by dividing the bonding area S1 of the first bonding member 220 at the first electrode pads 211, 212 by the first distance t1 between the bottom surface of the package 20 and the surface of the package 20 that includes the first electrode pads 211, 212. As the height of the temperature sensing element 40 is reduced, a temperature sensing element 40 having an area slightly smaller than that of the piezoelectric vibration element 30 can be housed in the package 20. In this case, the bonding area S2 between the package 20 and the temperature sensitive element 40, which is closer to the bottom surface of the package 20, is made smaller than the bonding area S1 between the package 20 and the piezoelectric vibration element 30, depending on the ratio of the distances from the bottom surface of the package 20 through which heat is conducted to the piezoelectric vibration element 30 and the temperature sensitive element 40. This allows the temperature sensitive element 40 to measure a temperature corresponding to the temperature of the piezoelectric vibration element 30. In particular, by setting the ratio of (S2 / t2) to (S1 / t1) to 0.7 or more and 1.3 or 0.9 or more and 1.2 or less, the bonding area S2 of the temperature sensitive element 40 can be set to the minimum necessary for manufacturing and for maintaining adhesive strength, etc., while preventing the temperature sensitive element 40 from measuring a temperature change of the piezoelectric vibration element 30 before it actually occurs.

[0034] The thickness of the temperature sensing element 40 may be 0.1 mm or less. By using such a sufficiently thin temperature sensing element 40, the piezoelectric device 1 can be made low-profile while still being able to detect temperature appropriately using the temperature sensing element 40.

[0035] Furthermore, the first bonding member 220 and the second bonding member 240 may be made of the same material. Since the piezoelectric vibration element 30 and the temperature sensing element 40 are bonded to the package 20 with the same thermal conductivity and similar characteristics, the detected temperature of the temperature sensing element 40 can be stably brought close to the actual temperature of the piezoelectric vibration element 30 by the ratio of the bonding area to the distance from the bottom surface, as described above.

[0036] Furthermore, the bonding area S1 of the first bonding member 220 may be equal to or smaller than the planar area of ​​the first electrode pads 211, 212, and the bonding area S2 of the second bonding member 240 may be equal to or smaller than the planar area of ​​the second electrode pads 231, 232. In this way, the conductive adhesive does not extend beyond the range of the first electrode pads 211, 212 or the second electrode pads 231, 232, so that the piezoelectric device 1 can obtain a stable bonding area. Furthermore, the piezoelectric device 1 reduces the occurrence of unnecessary short circuits and the like.

[0037] The above embodiment is merely an example, and various modifications are possible. For example, the shapes of the recess 20a and the recess 20b are not limited to those shown in the above embodiment. Other shapes are possible as long as the temperature sensitive element 40 is positioned and fixed below the piezoelectric vibration element 30 within the recess 20a. Furthermore, the recess 20b may be larger than the planar area of ​​the temperature sensitive element 40 as long as the strength of the package 20 can be maintained.

[0038] Furthermore, the position of the depression 20b in the recess 20a, i.e., the position of the temperature sensing element 40 relative to the piezoelectric vibration element 30 in a plan view, is not limited to the position shown in the above embodiment. Furthermore, the longitudinal directions of these elements do not have to be in the same direction.

[0039] The first and second bonding members 220 and 240 may be formed by heat-curing a conductive adhesive containing conductive particles other than silver. The electrical conductivity of the second bonding members 240 may be lower than the electrical conductivity of the first bonding members 220.

[0040] Furthermore, the vibrating piece of the piezoelectric vibrating element 30 is not limited to a quartz crystal piece. Other materials may be used as long as they convert between electrical force and mechanical deformation. The specific details of the structure, configuration, materials, size, etc. shown in the above embodiments 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.

[0041] The present disclosure can be used in piezoelectric devices.

[0042] REFERENCE SIGNS LIST 1 Piezoelectric device 10 Lid 20 Package 20a Recess 20b Cavity 211, 212 First electrode pad 220 First bonding member 231, 232 Second electrode pad 240 Second bonding member 251 External connection pad 252 Wiring 30 Piezoelectric vibration element 311, 312 Mounting electrode 321 Excitation electrode 40 Thermosensitive element 41 Thin film thermistor substrate 42 Thin film thermistor 43 Electrode 44 Conductive member

Claims

1. A package having a recess, with a first electrode pad and a second electrode pad located within the recess; a piezoelectric vibration element bonded to the first electrode pad within the recess; and a temperature sensing element bonded to the second electrode pad below the piezoelectric vibration element within the recess, wherein the piezoelectric vibration element is bonded to the first electrode pad via a first bonding member, and the temperature sensing element is bonded to the second electrode pad via a second bonding member, and the planar area of ​​the temperature sensing element when viewed from above the recess is 0.2 to 0.9 times the planar area of ​​the piezoelectric vibration element, A piezoelectric device, wherein a value obtained by dividing a first planar adhesive area of ​​the first bonding member on the first electrode pad by a first distance between a bottom surface of the package and a surface of the package including the first electrode pad, and a value obtained by dividing a second planar adhesive area of ​​the second bonding member on the second electrode pad by a second distance between the bottom surface of the package and a surface of the package including the second electrode pad, is 0.7 to 1.3 times.

2. The piezoelectric device according to claim 1, wherein the thickness of the temperature sensing element is 0.1 mm or less.

3. The piezoelectric device according to claim 1 or 2, wherein the first bonding member and the second bonding member are made of the same material.

4. A piezoelectric device as described in any one of claims 1 to 3, wherein the first planar adhesive area is equal to or smaller than the planar area of ​​the first electrode pad, and the second planar adhesive area is equal to or smaller than the planar area of ​​the second electrode pad.

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