Physical Quantity Sensor

Abstract

To provide a physical quantity sensor capable of suppressing inconveniences caused by resonance of a moving part while maintaining high sensitivity. [Solution] The physical quantity sensor includes a plate-shaped cantilever having a base, a hinge portion, and a movable portion connected to the base via the hinge portion, the movable portion displacing relative to the base with the hinge portion as a fulcrum, and a physical quantity detection element fixed to the base and the movable portion and spanning the hinge portion. The movable portion is longer than the hinge portion in a second direction intersecting a first direction in which the hinge portion and the movable portion are aligned in a plan view of the cantilever, and a free end of the movable portion located opposite the hinge portion coincides with the end of the physical quantity detection element on the free end side in a plan view of the cantilever, or is located closer to the hinge portion than the end.

Description

[Technical Field]

[0001] The present invention relates to a physical quantity sensor. [Background technology]

[0002] The inertial sensor described in Patent Document 1 has a plate-like structure including a base, a cantilever having a thin constricted portion and a movable portion connected to the base via the constricted portion, an oscillator fixed to the base and the movable portion across the constricted portion, and a mass portion arranged in the movable portion.

[0003] In this type of inertial sensor, when acceleration in the Z-axis direction is applied, the movable part displaces relative to the base part, with the constricted part as the fulcrum. This displacement then applies tensile or compressive stress to the vibrator, and the resonant frequency of the vibrator changes depending on the magnitude of the applied stress. Therefore, the applied acceleration can be detected based on the change in the resonant frequency of the vibrator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2024-033901 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in an inertial sensor with such a configuration, if external vibrations with a frequency close to the resonant frequency of the cantilever are applied, problems such as output abnormalities, destruction, and an increase in vibration rectification error (VRE) may occur (hereinafter referred to as "failures due to resonance"). Therefore, to prevent such problems from occurring, it is necessary to set the resonant frequency of the cantilever sufficiently high relative to the frequency band being used so that resonance does not occur.

[0006] One method for increasing the resonant frequency of the cantilever is to reduce the mass of the moving part. However, reducing the mass of the moving part reduces the sensitivity of the inertial sensor. As such, there is generally a trade-off between increasing the resonant frequency of the cantilever and increasing the sensitivity of the physical quantity sensor, making it difficult for the inertial sensor of Patent Document 1 to achieve both. [Means for solving the problem]

[0007] The physical quantity sensor of the present invention includes a base and a plate-shaped cantilever having a hinge portion and a movable portion connected to the base portion via the hinge portion, wherein the movable portion is displaced relative to the base portion with the hinge portion as a fulcrum; a physical quantity detection element that straddles the hinge portion and is fixed to the base portion and the movable portion, the movable portion is longer than the hinge portion in a second direction intersecting a first direction in which the hinge portion and the movable portion are aligned in a plan view of the cantilever, The free end of the movable part located on the opposite side to the hinge part is coincident with the end of the physical quantity detection element on the free end side in a planar view of the cantilever, or is located closer to the hinge part than the end. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a top view showing the inside of the physical quantity sensor according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 2 is a top view showing a physical quantity sensor element. [Figure 4] FIG. 10 is a top view showing a physical quantity sensor element according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A physical quantity sensor according to the present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings.

[0010] First Embodiment Fig. 1 is a top view showing the inside of the physical quantity sensor according to the first embodiment, Fig. 2 is a cross-sectional view taken along line AA in Fig. 1, and Fig. 3 is a top view showing a physical quantity sensor element.

[0011] For ease of explanation, the physical quantity sensor will be defined below as having three mutually orthogonal axes: an X-axis, a Y-axis, and a Z-axis. The direction along the X-axis will be referred to as the X-axis direction, the direction along the Y-axis as the Y-axis direction, and the direction along the Z-axis as the Z-axis direction. The arrowed side of each axis will be referred to as the "plus side," and the opposite side as the "minus side." The plus side of the Z-axis direction will be referred to as the "upper side," and the minus side as the "lower side." A planar view from the Z-axis direction, i.e., a planar view of the cantilever 42 described below, will be simply referred to as a "planar view."

[0012] 1 is an acceleration sensor that detects acceleration in the Z-axis direction. Such physical quantity sensor 1 has a package 2 and a physical quantity sensor element 3 housed in the package 2.

[0013] First, the package 2 will be described. As shown in Fig. 1, the package 2 has a base 21 having a recess 211 that opens on the top surface, and a plate-shaped lid 22 that is joined to the top surface of the base 21 via a joining member so as to close the opening of the recess 211. Inside the package 2, an airtight internal space S is formed by the recess 211, and the physical quantity sensor element 3 is housed in this internal space S.

[0014] For example, the base 21 is made of a ceramic such as alumina, and the lid 22 is made of a metal material such as Kovar. This results in a package 2 with excellent mechanical strength. Furthermore, the difference in linear expansion coefficients between them can be kept small, thereby suppressing the occurrence of thermal stress. However, the materials constituting the base 21 and the lid 22 are not particularly limited. Furthermore, the internal space S is in a reduced pressure state, preferably a state closer to a vacuum. This reduces viscous resistance and improves the vibration characteristics of the physical quantity sensor element 3. However, the atmosphere in the internal space S is not particularly limited.

[0015] As shown in FIG. 1 , the base 21 has three first seats 212a, 212b, and 212c and one second seat 213 that protrude from the bottom surface of the recess 211. The physical quantity sensor element 3 is joined to the first seats 212a, 212b, and 212c via joining members (not shown). Internal terminals 214a and 214b are disposed on the second seat 213. The internal terminals 214a and 214b are electrically connected to the physical quantity sensor element 3 via conductive wires W. Although not shown, two external terminals are disposed on the underside of the base 21. These two external terminals are electrically connected to the internal terminals 214a and 214b via internal wiring (not shown) formed in the base 21. This enables electrical connection to the physical quantity sensor element 3 via the external terminals.

[0016] The above has described the package 2. Next, we will describe the physical quantity sensor element 3. As shown in Fig. 1, the physical quantity sensor element 3 has a substrate structure 4 supported by first pedestals 212a, 212b, and 212c, and a physical quantity detection element 5 arranged on the upper surface of the substrate structure 4.

[0017] The substrate structure 4 is a plate-like monolithic structure formed from a quartz substrate, and is flat along the XY plane perpendicular to the Z axis. The cut angle of the quartz substrate is not particularly limited as long as it functions as a sensor element using the piezoelectric effect, but in this embodiment, it is a Z-cut with the optical axis aligned along the thickness direction. The X-axis, Y-axis, and Z-axis shown in each figure correspond to the crystal axes of the quartz substrate, with the X-axis coinciding with the electrical axis of the quartz substrate, the Y-axis coinciding with the mechanical axis, and the Z-axis coinciding with the optical axis.

[0018] The substrate structure 4 has a base 41, a cantilever 42 connected to the base 41 and displaceable in the Z-axis direction, and an arm 43 supporting the base 41.

[0019] The arm portion 43 has three arms 431, 432, and 433. The arms 431, 432, and 433 are arranged around the base portion 41 and are each connected to the base portion 41. The substrate structure 4 is joined at the tip of each of the arms 431, 432, and 433 to the first pedestals 212a, 212b, and 212c of the base 21 via joining members (not shown). This allows the substrate structure 4 to be supported by the base 21.

[0020] The cantilever 42 is plate-shaped and has a hinge portion 421 and a movable portion 422 connected to the base portion 41 via the hinge portion 421. As shown in FIG. 2, the hinge portions 421 of the substrate structure 4 are formed on both main surfaces of the cantilever 42, overlap each other in a plan view from the Z-axis direction, and are defined as two grooves each extending along the Y-axis direction. Therefore, the hinge portion 421 has a smaller thickness (length in the Z-axis direction) than the base portion 41 and the movable portion 422 located on either side of it. In the cantilever 42 configured in this manner, the movable portion 422 is displaced in the Z-axis direction relative to the base portion 41, with the hinge portion 421 as a fulcrum.

[0021] As shown in FIG. 1, the physical quantity detection element 5 is a double-ended tuning fork vibration element formed from a quartz substrate. By forming the physical quantity detection element 5 from the same material as the substrate structure 4, the linear expansion coefficients of the physical quantity detection element 5 and the substrate structure 4 can be made equal. This makes it difficult for thermal stress to occur between them. Therefore, thermal stress caused by the difference in linear expansion coefficients between the physical quantity detection element 5 and the substrate structure 4 does not substantially occur, and forces other than the acceleration in the Z-axis direction, which is the detection target, are unlikely to be applied to the physical quantity detection element 5. This results in a physical quantity sensor 1 with high acceleration detection accuracy.

[0022] 1, the physical quantity detection element 5 has two vibrating beams 51 and 52, a first end 53 terminating one end of the two vibrating beams 51 and 52, and a second end 54 terminating the other end of the two vibrating beams 51 and 52. In the physical quantity detection element 5, the vibrating beams 51 and 52 are arranged along the X-axis, and the first end 53 is joined to the movable part 422 via a joining member (not shown), and the second end 54 is joined to the base part 41 via a joining member (not shown). In other words, the physical quantity detection element 5 is fixed to the base part 41 and the movable part 422 across the hinge part 421.

[0023] The physical quantity detection element 5 also has a pair of excitation electrodes (not shown) provided on the vibrating beams 51 and 52. When an AC voltage drive signal is applied between these excitation electrodes, the vibrating beams 51 and 52 flexurally vibrate so as to move away from or towards each other in the Y-axis direction. The pair of excitation electrodes is electrically connected to the internal terminals 214a and 214b via wires W.

[0024] Here, we will first explain a method for detecting acceleration in the Z-axis direction using the physical quantity sensor element 3. When acceleration in the Z-axis direction is applied to the physical quantity sensor 1, the movable part 422 is displaced in the Z-axis direction relative to the base part 41, with the hinge part 421 as the fulcrum. This displacement applies tensile stress or compressive stress to the physical quantity detection element 5, and the resonant frequency of the physical quantity detection element 5 changes depending on the magnitude of the applied stress.

[0025] Specifically, when acceleration is applied to the positive side in the Z axis direction, the movable part 422 is displaced to the negative side in the Z axis direction relative to the base part 41, which applies tensile stress to the physical quantity detection element 5 and increases the resonant frequency of the physical quantity detection element 5. Conversely, when acceleration is applied to the negative side in the Z axis direction, the movable part 422 is displaced to the positive side in the Z axis direction relative to the base part 41, which applies compressive stress to the physical quantity detection element 5 and decreases the resonant frequency of the physical quantity detection element 5. Therefore, the physical quantity sensor 1 can detect acceleration based on a change in the resonant frequency of the physical quantity detection element 5. The resonant frequency of the physical quantity detection element 5 can be detected by detecting the potential of detection electrodes (not shown) provided on the surfaces of the vibrating beams 51 and 52.

[0026] The above is a brief description of the overall configuration of the physical quantity sensor 1. Next, the cantilever 42, which is a feature of the physical quantity sensor 1, will be described in detail.

[0027] FIG. 3 is a top view of the physical quantity sensor element 3. As shown in FIG. 3, the movable part 422 is longer than the hinge part 421 in the Y-axis direction in a plan view. In other words, the length L1 of the movable part 422 in the Y-axis direction is longer than the length L2 of the hinge part 421 in the Y-axis direction. Furthermore, in a plan view, the free end 422a of the movable part 422, i.e., the end located opposite the hinge part 421, coincides with the end 53a of the first end 53 of the physical quantity detection element 5, i.e., the end on the same side as the free end 422a. Note that the phrase "the free end 422a of the movable part 422 coincides with the end 53a of the physical quantity detection element 5" means not only that the free end 422a and the end 53a coincide with each other in a plan view, but also that the free end 422a and the end 53a are spaced apart from each other to the extent that there is not enough space on the top surface of the movable part 422 for disposing a separate member such as a weight between them.

[0028] According to this configuration, compared to conventional configurations, the movable part 422 can be made thicker and shorter while suppressing a decrease in the mass of the movable part 422. By making the movable part 422 thicker and shorter in this way, the center of gravity G of the movable part 422 can be brought closer to the hinge part 421, that is, the base end (fixed end) of the movable part 422, and the resonant frequency of the cantilever 42 can be increased accordingly. As described above, according to the cantilever 42 of this embodiment, the resonant frequency of the cantilever 42 can be increased while ensuring a sufficient mass of the movable part 422. Therefore, the resonant frequency of the cantilever 42 can be increased while sufficiently increasing the sensitivity of the physical quantity sensor 1.

[0029] 3, the center of gravity G of the movable part 422 is located inside the physical quantity detection element 5 in plan view. In particular, in the physical quantity sensor 1 of this embodiment, the center of gravity G overlaps with the central axis J of the physical quantity detection element 5 in plan view. With this configuration, the physical quantity detection element 5 is less likely to be twisted when subjected to acceleration in the positive Z-axis direction. Therefore, it is possible to effectively suppress a decrease in the detection accuracy of acceleration.

[0030] Furthermore, in plan view, the center O1 of the hinge portion 421 is located closer to the free end 422a than the center O2 of the physical quantity detection element 5. With this configuration, the movable portion 422 becomes shorter, and the resonant frequency of the cantilever 42 can be increased accordingly.

[0031] The above has described the physical quantity sensor 1. As described above, the physical quantity sensor 1 includes the plate-shaped cantilever 42 having the base 41, the hinge 421, and the movable part 422 connected to the base 41 via the hinge 421, with the movable part 422 displacing relative to the base 41 around the hinge 421 as a fulcrum, and the physical quantity detection element 5 fixed to the base 41 and the movable part 422, straddling the hinge 421. The movable part 422 is longer than the hinge 421 in the Y-axis direction, which is a second direction intersecting the X-axis direction, which is a first direction in which the hinge 421 and the movable part 422 are aligned, in a planar view of the cantilever 42. The free end 422a of the movable part 422, located on the opposite side to the hinge 421, coincides with the end 53a of the physical quantity detection element 5 on the side of the free end 422a, in a planar view of the cantilever 42. According to this configuration, the movable part 422 can be made thick and short while suppressing a reduction in the mass of the movable part 422. Therefore, the sensitivity of the physical quantity sensor 1 can be sufficiently increased while the resonance frequency of the cantilever 42 can be increased.

[0032] Furthermore, as described above, in a plan view of the cantilever 42, the center of gravity G of the movable part 422 is located inside the physical quantity detection element 5. With this configuration, the physical quantity detection element 5 is less likely to be twisted when subjected to acceleration in the positive Z-axis direction. Therefore, it is possible to effectively suppress a decrease in the detection accuracy of acceleration.

[0033] Furthermore, as described above, in a plan view of the cantilever 42, the center O1 of the hinge portion 421 is located closer to the free end 422a than the center O2 of the physical quantity detection element 5. With this configuration, the movable portion 422 becomes shorter, and the resonant frequency of the cantilever 42 can be increased accordingly.

[0034] Second Embodiment FIG. 4 is a top view showing the physical quantity sensor element according to the second embodiment.

[0035] The physical quantity sensor 1 according to this embodiment is similar to the physical quantity sensor 1 of the first embodiment described above, except for the configuration of the physical quantity sensor element 3. Therefore, in the following description, the physical quantity sensor 1 of this embodiment will be described mainly with reference to the differences from the first embodiment described above, and a description of similar points will be omitted. Furthermore, in the drawings of this embodiment, the same reference numerals are used to designate similar components to those of the above-described embodiment.

[0036] 4, in the physical quantity sensor element 3 of this embodiment, in plan view, the free end 422a of the movable part 422 is located closer to the hinge part 421 than the end 53a of the first end part 53 of the physical quantity detection element 5. According to this configuration, the center of gravity G of the movable part 422 can be moved further toward the base end part compared to the first embodiment described above, and therefore the resonance frequency of the cantilever 42 can be further increased.

[0037] The above has described the physical quantity sensor 1. In such physical quantity sensor 1, as described above, the free end 422a of the movable part 422 located on the opposite side to the hinge part 421 is located closer to the hinge part 421 than the end 53a of the physical quantity detection element 5 on the free end 422a side in a plan view of the cantilever 42. With this configuration, the center of gravity G of the movable part 422 can be moved further towards the base end part compared to the first embodiment described above, and therefore the resonance frequency of the cantilever 42 can be further increased.

[0038] The second embodiment can also achieve the same effects as the first embodiment described above.

[0039] The physical quantity sensor of the present invention has been described above based on the illustrated embodiment, but the present invention is not limited to this, and the configuration of each part can be replaced with any configuration having a similar function. Also, any other configuration may be added to the present invention. For example, a weight may be disposed on the movable part 422. [Explanation of symbols]

[0040] 1...physical quantity sensor, 2...package, 21...base, 211...recess, 212a...first base, 212b...first base, 212c...first base, 213...second base, 214a...internal terminal, 214b...internal terminal, 22...lid, 3...physical quantity sensor element, 4...substrate structure, 41...base, 42...cantilever, 421...hinge portion, 422...movable portion, 422a...free end, 43...arm portion, 431...arm portion, 432...arm portion, 433...arm portion, 5...physical quantity detection element, 51...vibrating beam, 52...vibrating beam, 53...first end portion, 53a...end, 54...second end portion, J...central axis, L1...length, L2...length, G...center of gravity, O1...center, O2...center, S...internal space, W...wire

Claims

1. A base and a plate-shaped cantilever having a hinge portion and a movable portion connected to the base portion via the hinge portion, wherein the movable portion is displaced relative to the base portion with the hinge portion as a fulcrum; a physical quantity detection element that straddles the hinge portion and is fixed to the base portion and the movable portion, the movable portion is longer than the hinge portion in a second direction intersecting a first direction in which the hinge portion and the movable portion are aligned in a plan view of the cantilever, a free end of the movable part located on the opposite side of the hinge part, which is coincident with the end of the physical quantity detection element on the free end side in a planar view of the cantilever, or which is located closer to the hinge part than the end.

2. The physical quantity sensor according to claim 1 , wherein the center of gravity of the movable part is located inside the physical quantity detection element in a plan view of the cantilever.

3. The physical quantity sensor according to claim 1 , wherein the center of the hinge portion is located closer to the free end than the center of the physical quantity detection element in a plan view of the cantilever.

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