Acceleration sensor

Abstract

This acceleration sensor comprises: a device layer that is provided with a weight portion, an elastic portion, a first vibrator, and a second vibrator each of which is disposed on an intersection surface intersecting with a sensitivity axis direction; an application mechanism that applies rotational force to the weight portion; a lower lid that is provided below the device layer in the sensitivity axis direction; and an upper lid that is provided above the device layer in the sensitivity axis direction, and is for detecting an acceleration in the sensitivity axis direction. The weight portion has a rotary shaft that is orthogonal to the sensitivity axis direction, a first rotating portion that extends from the rotary shaft, and a second rotating portion that extends from the rotary shaft to the opposite side from the first rotating portion. The elastic portion is connected to the rotary shaft of the weight portion, and holds the weight portion so as to enable the weight portion to be translated in the sensitivity axis direction. The first vibrator is connected to the first rotating portion of the weight portion, and is configured to have a resonance frequency which changes according to the displacement of the first rotating portion. The second vibrator is connected to the second rotating portion of the weight portion, and is configured to have a resonance frequency which changes according to the displacement of the second rotating portion. In detecting an acceleration in the sensitivity axis direction, the weight portion is inclined with respect to an orthogonal surface orthogonal to the sensitivity axis direction due to rotational force applied by the application mechanism, and undergoes acceleration in the sensitivity axis direction while being kept inclined, and is thus translated in the sensitivity axis direction. The acceleration in the sensitivity axis direction is detected on the basis of the difference between the resonance frequency of the first vibrator and the resonance frequency of the second vibrator.

Description

Acceleration sensor

[0001] The present invention relates to an acceleration sensor.

[0002] Examples of acceleration sensors that are used include capacitance-type acceleration sensors that detect acceleration based on changes in the capacitance formed by a moving part, and frequency-modulation-type acceleration sensors that detect acceleration based on changes in the resonant frequency of a vibrator connected to a moving part.

[0003] For example, Patent Document 1 discloses a vibration-type piezoelectric acceleration sensor having a frame, a pair of diaphragms arranged opposite each other in a straight line on the frame, supports that hold the adjacent ends of each diaphragm, and an element consisting of a holding part that holds the supports so that they can slide freely in a straight line, in which the diaphragm expands and contracts due to acceleration transmitted to the supports via the holding part of the element, and acceleration is detected from changes in the natural vibration frequency of the diaphragm.

[0004] Japanese Patent Application Laid-Open No. 2005-249446

[0005] According to the acceleration sensor described in Patent Document 1, when acceleration is applied in the in-plane direction, tensile strain occurs in one of the pair of diaphragms and compressive strain occurs in the other, resulting in so-called out-of-phase deformation. Therefore, by reading the difference in the change in natural vibration frequency, the acceleration in the in-plane direction of the element can be detected with high sensitivity. It is also possible to cancel out other-axis sensitivities and environmental factors such as temperature changes. However, when acceleration is applied in the out-of-plane direction, tensile strain occurs in both of the pair of diaphragms, resulting in so-called in-phase deformation. Therefore, there is a problem in that the frequency changes of the pair of diaphragms cancel each other out in the difference in the change in natural vibration frequency, making it impossible to detect acceleration in the out-of-plane direction.

[0006] The present invention has been made in view of the above circumstances, and has as its object to provide an acceleration sensor capable of detecting acceleration in an out-of-plane direction.

[0007] An acceleration sensor according to one aspect of the present invention includes a device layer including a weight portion, an elastic portion, a first oscillator, and a second oscillator, each of which is arranged on an intersecting plane intersecting a sensitivity axis direction; an applying mechanism that applies a rotational force to the weight portion; a lower lid provided below the device layer in the sensitivity axis direction; and an upper lid provided above the device layer in the sensitivity axis direction, and detects acceleration in the sensitivity axis direction. The weight portion has a rotation axis perpendicular to the sensitivity axis direction, a first rotating portion extending from the rotation axis, and a second rotating portion extending from the rotation axis on the opposite side to the first rotating portion. The elastic portion is connected to the rotation axis of the weight portion, and rotates the weight portion in the sensitivity axis direction. the first vibrator is connected to a first rotating part of the weight part and is configured so that its resonant frequency changes in response to the displacement of the first rotating part; the second vibrator is connected to a second rotating part of the weight part and is configured so that its resonant frequency changes in response to the displacement of the second rotating part; when detecting acceleration in the sensitivity axis direction, the weight part is tilted with respect to an orthogonal plane perpendicular to the sensitivity axis direction by the rotational force applied from the application mechanism, and is subjected to acceleration in the sensitivity axis direction while inclined, thereby translating in the sensitivity axis direction, and the acceleration in the sensitivity axis direction is detected based on the difference between the resonant frequency of the first vibrator and the resonant frequency of the second vibrator.

[0008] According to the present invention, it is possible to provide an acceleration sensor capable of detecting acceleration in an out-of-plane direction.

[0009] 1 is a plan view of a device layer in an acceleration sensor according to a first embodiment. FIG. 1 is a cross-sectional view of the acceleration sensor taken along line A-A in a basic state. FIG. 2 is a cross-sectional view of the acceleration sensor taken along line B-B in a basic state. FIG. 3 is a cross-sectional view of the acceleration sensor taken along line C-C in a basic state. FIG. 4 is a cross-sectional view of the acceleration sensor taken along line A-A in a preparatory state. FIG. 5 is a cross-sectional view of the acceleration sensor taken along line C-C in a preparatory state. FIG. 6 is a cross-sectional view of the acceleration sensor taken along line D-D in a preparatory state. FIG. 7 is a cross-sectional view of the acceleration sensor taken along line A-A in a detecting state. FIG. 8 is a cross-sectional view of the acceleration sensor taken along line B-B in a detecting state. FIG. 9 is a cross-sectional view of the acceleration sensor taken along line D-D in a detecting state. FIG. 10 is a plan view of a device layer in an acceleration sensor according to a second embodiment. FIG. 11 is a cross-sectional view of an acceleration sensor according to a second embodiment. FIG. 12 is a plan view of a device layer in an acceleration sensor according to a third embodiment. FIG. 13 is a cross-sectional view of an acceleration sensor according to the third embodiment. FIG. 14 is a plan view of a device layer in an acceleration sensor according to a fourth embodiment. FIG. 15 is a cross-sectional view of an acceleration sensor according to the fourth embodiment. FIG. 16 is a cross-sectional view of an acceleration sensor according to a fifth embodiment. FIG. 17 is a cross-sectional view of an acceleration sensor according to a sixth embodiment. FIG. 18 is a cross-sectional view of an acceleration sensor according to a seventh embodiment.

[0010] Hereinafter, embodiments of the present invention will be described. In the following description of the drawings, the same or similar components are denoted by the same or similar reference numerals. The drawings are illustrative, and the dimensions and shapes of each part are schematic. The technical scope of the present invention should not be interpreted as being limited to the embodiments.

[0011] In order to clarify the relationship between the drawings and to aid in understanding the positional relationship of each component, each drawing may be accompanied by an orthogonal coordinate system consisting of X, Y, and Z axes, which correspond to each other in each drawing.

[0012] In the following description, the direction parallel to the X-axis is referred to as the "X-axis direction," the direction parallel to the Y-axis as the "Y-axis direction," and the direction parallel to the Z-axis as the "Z-axis direction." The directions of the arrows on the X-axis, Y-axis, and Z-axis are referred to as "positive" or "+ (plus)," and the directions opposite the arrows are referred to as "negative" or "- (minus)." For convenience, the +Z-axis direction will be referred to as the upward direction and the -Z-axis direction as the downward direction, but the up and down orientations of the acceleration sensor 1 are not limited to these. The plane specified by the X-axis and Z-axis is referred to as the ZX-plane, and the direction parallel to the ZX-plane is referred to as the ZX-plane direction. The same applies to planes specified by the other axes.

[0013] First Embodiment

[0014] First, the configuration of the acceleration sensor 1 according to the first embodiment in its basic state will be described with reference to FIGS. 1 to 4. FIG. 1 is a plan view of the device layer 100 in the acceleration sensor 1 according to the first embodiment. FIG. 2 is a cross-sectional view of the acceleration sensor 1 taken along line A-A in the basic state. FIG. 3 is a cross-sectional view of the acceleration sensor 1 taken along line B-B in the basic state. FIG. 4 is a cross-sectional view of the acceleration sensor 1 taken along line C-C in the basic state. The "basic state" refers to a state in which no rotational force is being applied to the weight section 110 (described later) by the application mechanism 190 (described later).

[0015] The acceleration sensor 1 is a frequency modulation type acceleration sensor. The sensitivity axis of the acceleration sensor 1 is the Z axis, and the acceleration sensor 1 detects acceleration in the Z axis direction. The Z axis is an example of the sensitivity axis of the acceleration sensor 1, the X axis and the Y axis are examples of orthogonal axes perpendicular to the sensitivity axis, and the XY plane is an example of an orthogonal plane perpendicular to the sensitivity axis. A plane intersecting the sensitivity axis is referred to as an intersecting plane. The intersecting plane includes an orthogonal plane, and is, for example, a plane that forms an angle with the sensitivity axis of 45 degrees or more and 135 degrees or less (90 degrees ±45 degrees). The angle formed between the intersecting plane and the sensitivity axis is preferably 60 degrees or more and 120 degrees or less (90 degrees ±30 degrees), more preferably 70 degrees or more and 110 degrees or less (90 degrees ±20 degrees), and even more preferably 80 degrees or more and 100 degrees or less (90 degrees ±10 degrees).

[0016] The acceleration sensor 1 includes a device layer 100 , an application mechanism 190 , a lower cover 170 , and an upper cover 180 .

[0017] The device layer 100 includes a weight portion 110, an elastic portion 120, a first vibrator 150, and a second vibrator 160. The weight portion 110, the elastic portion 120, the first vibrator 150, and the second vibrator 160 are each disposed on an intersecting plane.

[0018] Plummet 110 is a plate-like member having a pair of main surfaces. In the base state, the main surfaces of plummet 110 extend in the XY plane. Plummet 110 has a first rotating portion 111, a second rotating portion 112, and a rotation axis 113. Plummet 110 is held rotatably around rotation axis 113. When viewed from a plane in the Z-axis direction, which is the sensitivity axis (hereinafter simply referred to as "planar view"), plummet 110 in the base state has a rectangular shape (hereinafter referred to as "planar shape") with short sides extending in the Y-axis direction and long sides extending in the X-axis direction. Furthermore, the shape of a cross section of plummet 110 perpendicular to the main surfaces (hereinafter referred to as "cross-sectional shape") is a flat plate with a uniform thickness.

[0019] The planar shape of the weight portion is not limited to a rectangular shape having long sides extending in the X-axis direction. For example, the planar shape of the weight portion may be a rectangular shape having long sides extending in the Y-axis direction, or a square shape having sides extending in the X-axis and Y-axis directions. The planar shape of the weight portion may be such that the width of at least one of the end portions on the positive X-axis direction and the negative X-axis direction is larger than or smaller than the width of the central portion in the X-axis direction. The planar shape of the weight portion may be such that the width of at least one of the end portions on the positive Y-axis direction and the negative Y-axis direction is larger than the width of the central portion in the Y-axis direction. The planar shape of the weight portion may be polygonal, circular, elliptical, or a combination thereof.

[0020] Furthermore, the cross-sectional shape of the mass portion is not limited to a flat plate with a uniform thickness. For example, the cross-sectional shape of the mass portion in the X-axis direction may be a normal mesa structure in which the thickness of the central portion is greater than the thickness of the ends, or an inverted mesa structure in which the thickness of the central portion is smaller than the thickness of the ends. The cross-sectional shape of the mass portion in the X-axis direction may be a convex structure in which the amount of change in thickness changes continuously, or a bevel structure in which the amount of change in thickness changes discontinuously. The cross-sectional shape of the mass portion in the Y-axis direction may be a normal mesa structure, an inverted mesa structure, a convex structure, or a bevel structure. The mass portion may be provided with at least one through-hole or recess opening in the Z-axis direction.

[0021] The first rotating part 111 extends from the rotating shaft 113 toward the negative side of the X-axis. The second rotating part 112 extends from the rotating shaft 113 toward the positive side of the X-axis, opposite the first rotating part 111. The first rotating part 111 and the second rotating part 112 are formed as a continuous flat plate. In the basic state, the area of ​​the first rotating part 111 is smaller than the area of ​​the second rotating part 112 when viewed from above. The dimension of the first rotating part 111 in the Y-axis direction is equal to the dimension of the second rotating part 112 in the Y-axis direction, and the dimension of the first rotating part 111 in the X-axis direction is smaller than the dimension of the second rotating part 112 in the X-axis direction. The weight of the first rotating part 111 is smaller than the weight of the second rotating part 112. The center of gravity of the first rotating part 111 is located closer to the rotating shaft 113 than the center of gravity of the second rotating part 112.

[0022] Rotation axis 113 is the center of rotation of rotatably configured weight portion 110. Rotation axis 113 extends in the Y-axis direction. When first rotating portion 111 rotates around rotation axis 113 in the positive or negative direction of the Z-axis, second rotating portion 112 rotates around rotation axis 113 in the opposite direction of the Z-axis.

[0023] Elastic portion 120 is connected to rotation shaft 113 of weight portion 110 and holds weight portion 110 so that it can translate in the Z-axis direction. Elastic portion 120 has a restoring force that acts to return weight portion 110, which has translated in response to acceleration, to its original position. Elastic portion 120 has a first spring portion 121 connected to the Y-axis positive side of rotation shaft 113 and a second spring portion 122 connected to the Y-axis negative side of rotation shaft 113.

[0024] The first spring portion 121 is connected to a side surface of the weight portion 110 on the positive side of the Y-axis via a rod-shaped connecting portion 131, and is connected to a side wall portion 172 of the lower cover 170 (described later) via a rod-shaped connecting portion 133. The second spring portion 122 is connected to a side surface of the weight portion 110 on the negative side of the Y-axis via a rod-shaped connecting portion 132, and is connected to a side wall portion 172 of the lower cover 170 (described later) via a rod-shaped connecting portion 134. The first spring portion 121 and the second spring portion 122 have their longitudinal direction in the X-axis direction and their transverse direction in the Y-axis direction. This suppresses changes in the posture of the connecting portions 131 and 132 when the weight portion 110 translates in the Y-axis direction. In other words, when the weight portion 110 translates in the Y-axis direction, tilting of the connecting portions 131 and 132 with respect to the rotation axis 113 is suppressed, thereby suppressing deflection of the weight portion 110.

[0025] First oscillator 150 is connected to first rotating portion 111 of weight portion 110 and is configured such that its resonant frequency changes in response to the displacement of first rotating portion 111. First oscillator 150 has two oscillators 151 and 152. Oscillator 151 is connected to a side surface of first rotating portion 111 on the positive Y-axis side at the end portion on the negative X-axis side. Oscillator 152 is connected to a side surface of first rotating portion 111 on the negative Y-axis side at the end portion on the negative X-axis side. Oscillators 151 and 152 are each connected to first rotating portion 111 via a rod-shaped connecting portion and to a side wall portion 172 of bottom cover 170 (described later) via a rod-shaped connecting portion. The resonant frequency of first oscillator 150 is calculated, for example, as the average value of the resonant frequency of oscillator 151 and the resonant frequency of oscillator 152. The amount of change in the resonant frequency of the first oscillator 150 is calculated as the average value of the amount of change in the resonant frequency of the oscillator 151 and the amount of change in the resonant frequency of the oscillator 152 .

[0026] The vibrators 151 and 152 are provided in a frame shape with a through-hole formed in the center that opens in the Z-axis direction. This makes the vibrators 151 and 152 susceptible to elastic deformation. In other words, tensile strain or compressive strain is likely to occur in the vibrators 151 and 152 in response to the displacement of the first rotating part 111. The ease of elastic deformation of the vibrator 151 is equal to the ease of elastic deformation of the vibrator 152. Note that "equal" means that they are designed to be equal, and includes cases where slight differences occur due to manufacturing errors.

[0027] Vibrator 151 is arranged symmetrically with vibrator 152, with the ZX plane as the plane of symmetry. Vibrators 151 and 152 are aligned in the Y-axis direction. The distance from the connection portion of first rotating part 111 with vibrator 151 to rotation axis 113 of weight part 110 is equal to the distance from the connection portion of first rotating part 111 with vibrator 152 to rotation axis 113 of weight part 110. The dimensions, shape, and Young's modulus of the piezoelectric body of vibrator 151 are equal to the dimensions, shape, and Young's modulus of the piezoelectric body of vibrator 152. The resonant frequency of vibrator 151 is equal to the resonant frequency of vibrator 152. The rate of change of the resonant frequency of vibrator 151 with respect to strain is equal to the rate of change of the resonant frequency of vibrator 152 with respect to strain.

[0028] Second oscillator 160 is connected to second rotating portion 112 of weight portion 110 and is configured such that its resonant frequency changes in response to the displacement of second rotating portion 112. Second oscillator 160 has two oscillators 161 and 162. Oscillator 161 is connected to a side surface of second rotating portion 112 on the positive Y-axis direction side at the end portion of second rotating portion 112 on the positive X-axis direction side. Oscillator 162 is connected to a side surface of second rotating portion 112 on the negative Y-axis direction side at the end portion of second rotating portion 112 on the positive X-axis direction side. Oscillators 161 and 162 are each connected to second rotating portion 112 via a rod-shaped connecting portion and to a side wall portion 172 of bottom cover 170 (described later) via a rod-shaped connecting portion. The resonant frequency of second oscillator 160 is calculated, for example, as the average value of the resonant frequencies of oscillators 161 and 162. The amount of change in the resonant frequency of the second oscillator 160 is calculated as the average value of the amount of change in the resonant frequency of the oscillator 161 and the amount of change in the resonant frequency of the oscillator 162 .

[0029] The vibrators 161 and 162 are provided in a frame shape with a through-hole formed in the center that opens in the Z-axis direction. This makes the vibrators 161 and 162 prone to elastic deformation. In other words, tensile strain or compressive strain is likely to occur in the vibrators 161 and 162 depending on the displacement of the second rotating part 112. The ease of elastic deformation of the vibrator 161 is equal to the ease of elastic deformation of the vibrator 162.

[0030] Vibrator 161 is arranged symmetrically with vibrator 162, with the ZX plane as the plane of symmetry. Vibrators 161 and 162 are aligned in the Y-axis direction. The distance from the connection portion of second rotating unit 112 with vibrator 161 to rotation axis 113 of weight unit 110 is equal to the distance from the connection portion of second rotating unit 112 with vibrator 162 to rotation axis 113 of weight unit 110. The dimensions, shape, and Young's modulus of the piezoelectric body of vibrator 161 are equal to the dimensions, shape, and Young's modulus of the piezoelectric body of vibrator 162. The resonant frequency of vibrator 161 is equal to the resonant frequency of vibrator 162. The rate of change of the resonant frequency of vibrator 161 with respect to strain is equal to the rate of change of the resonant frequency of vibrator 162 with respect to strain.

[0031] Oscillator 161 is provided in plane symmetry with oscillator 151, with the YZ plane passing through rotation axis 113 as the plane of symmetry. Similarly, oscillator 162 is provided in plane symmetry with oscillator 152. The distance from the connection portion of second rotating unit 112 with oscillator 161 to rotation axis 113 of weight unit 110 is equal to the distance from the connection portion of first rotating unit 111 with oscillator 151 to rotation axis 113 of weight unit 110. The distance from the connection portion of second rotating unit 112 with oscillator 162 to rotation axis 113 of weight unit 110 is equal to the distance from the connection portion of first rotating unit 111 with oscillator 152 to rotation axis 113 of weight unit 110. The number of oscillators 161 and 162 of second oscillator 160 is equal to the number of oscillators 151 and 152 of first oscillator 150.

[0032] The ease of elastic deformation of vibrator 161 is equal to the ease of elastic deformation of vibrator 151, and the ease of elastic deformation of vibrator 162 is equal to the ease of elastic deformation of vibrator 152. The dimensions, shape, and Young's modulus of the piezoelectric body of vibrator 161 are equal to the dimensions, shape, and Young's modulus of the piezoelectric body of vibrator 151, and the dimensions, shape, and Young's modulus of the piezoelectric body of vibrator 162 are equal to the dimensions, shape, and Young's modulus of the piezoelectric body of vibrator 152. The resonant frequency of vibrator 161 is equal to the resonant frequency of vibrator 151, and the resonant frequency of vibrator 162 is equal to the resonant frequency of vibrator 152. The rate of change of the resonant frequency of vibrator 161 with respect to strain is equal to the rate of change of the resonant frequency of vibrator 151, and the rate of change of the resonant frequency of vibrator 162 with respect to strain is equal to the rate of change of the resonant frequency of vibrator 152.

[0033] In the above description, piezoelectrically driven (piezo type) vibrators 151, 152 and vibrators 161, 162 are used as examples of the first and second vibrators, but the drive method of the first and second vibrators is not limited as long as the resonant frequency varies based on the displacement of the weight portion. For example, the first and second vibrators may be electrostatically driven vibrators or electromagnetically driven vibrators.

[0034] The applying mechanism 190 applies a rotational force to the mass section 110. The applying mechanism 190 applies, for example, an electrostatic attraction force to the mass section 110 as the rotational force. The applying mechanism 190 has an upper electrode 192 that applies an electrostatic attraction force to the second rotating section 112 of the mass section 110. The upper electrode 192 is provided on the side of the top lid 180 that faces the device layer 100. The upper electrode 192 faces the second rotating section 112 in the Z-axis direction, which is the sensitivity axis direction.

[0035] The applying mechanism is not limited to an electrode that applies electrostatic attraction as a rotational force, as long as it can apply a rotational force to the weight portion. The applying mechanism may be, for example, a magnet, a bimetal, a piezoelectric element, etc. In this embodiment, the applying mechanism can switch the application of the rotational force on and off, but the application of the rotational force may be always on.

[0036] The lower lid 170 is provided below the device layer 100 in the Z-axis direction. The lower lid 170 has a bottom wall 171 that faces the device layer 100 at a distance in the Z-axis direction, and a side wall 172 that extends from the outer edge of the bottom wall 171 toward the upper lid 180. The side wall 172 surrounds the spindle portion 110 of the device layer 100 at a distance in the XY plane direction. The lower lid 170 is made of an insulating material.

[0037] The upper lid 180 is provided above the device layer 100 in the Z-axis direction. The upper lid 180 faces the device layer 100 with a gap therebetween in the Z-axis direction. The outer edge of the upper lid 180 is joined to the side wall 172 of the lower lid 170. The upper lid 180 is made of an insulating material.

[0038] The lower lid 170 and the upper lid 180 correspond to a container that forms an internal space that accommodates the device layer 100. For example, an inert gas is injected into the internal space sealed by the lower lid 170 and the upper lid 180 in order to obtain a damping effect that suppresses vibration of the weight part 110. The internal space may be a vacuum.

[0039] Next, the configuration of acceleration sensor 1 in the preparation state according to the first embodiment will be described with reference to Figures 5 to 7. Figure 5 is a cross-sectional view of acceleration sensor 1 taken along line A-A in the preparation state. Figure 6 is a cross-sectional view of acceleration sensor 1 taken along line C-C in the preparation state. Figure 7 is a cross-sectional view of acceleration sensor 1 taken along line D-D in the preparation state. Note that the "preparation state" refers to a state in which weight section 110 is tilted from the XY plane, which is a plane orthogonal to the sensitivity axis, by the rotational force applied from application mechanism 190, and acceleration sensor 1 is not receiving acceleration in the sensitivity axis direction.

[0040] 5, in the preparation state, voltage V is applied to upper electrode 192, and second rotating unit 112 is attracted toward upper cover 180 by electrostatic attraction. Plummet 110 rotates about rotation axis 113 and is tilted with respect to the orthogonal XY plane. The posture of plummet 110 is maintained constant.

[0041] As shown in Fig. 6, the first rotating part 111 is displaced toward the lower cover 170. Tensile strain is generated in the vibrators 151 and 152. As shown in Fig. 7, the second rotating part 112 is displaced toward the upper cover 180. Tensile strain is generated in the vibrators 161 and 162. The resonance frequency of the first vibrator 150 and the second vibrator 160 in the basic state is defined as f0, and the change in the resonance frequency caused by the tensile strain when the first vibrator 150 and the second vibrator 160 change from the basic state to the ready state is defined as Δf ｒｅａｄｙ The resonance frequency of the first oscillator 150 in the standby state is set to f1 ｒｅａｄｙ , the resonance frequency of the second oscillator 160 in the standby state is f2 ｒｅａｄｙ When this is done, the resonant frequency f1 ｒｅａｄｙ , f2 ｒｅａｄｙ are expressed by the following equations: ｒｅａｄｙ = f0 + Δf ｒｅａｄｙ f2 ｒｅａｄｙ = f0 + Δf ｒｅａｄｙ

[0042] At this time, the difference f between the resonance frequency of the first vibrator 150 and the resonance frequency of the second vibrator 160 ｄｅｔｅｃｔ is expressed by the following formula: ｄｅｔｅｃｔ = f1 ｒｅａｄｙ -f2 ｒｅａｄｙ = (f0 + Δf ｒｅａｄｙ ) - (f0 + Δf ｒｅａｄｙ ) = 0

[0043] Next, the configuration of the acceleration sensor 1 according to the first embodiment in a detection state will be described with reference to Figs. 8 to 11. Fig. 8 is a cross-sectional view of the acceleration sensor 1 taken along line A-A in the detection state. Fig. 9 is a cross-sectional view of the acceleration sensor 1 taken along line B-B in the detection state. Fig. 10 is a cross-sectional view of the acceleration sensor 1 taken along line C-C in the detection state. Fig. 11 is a cross-sectional view of the acceleration sensor 1 taken along line D-D in the detection state. Note that the "detection state" refers to a state in which the mass section 110 is subjected to acceleration in the sensitivity axis direction and is thereby translated in the sensitivity axis direction.

[0044] 8 , in the detection state, acceleration sensor 1 is subjected to acceleration Acc in the negative Z-axis direction with voltage V applied to upper electrode 192. At this time, mass 110 translates in the negative Z-axis direction, which is the sensitivity axis direction, while maintaining its tilt with respect to the orthogonal XY plane, and approaches lower cover 170.

[0045] As shown in Fig. 9, the rotating shaft 113 is displaced toward the lower cover 170. As shown in Fig. 10, the first rotating part 111 is displaced further toward the lower cover 170 than in the ready state. Tensile strain is generated in the vibrators 151 and 152 in the detection state relative to the vibrators 151 and 152 in the ready state. As shown in Fig. 11, the second rotating part 112 is displaced toward the lower cover 170, inversely to the change from the base state to the ready state. Compressive strain is generated in the vibrators 161 and 162 in the detection state relative to the vibrators 161 and 162 in the ready state. In other words, strains of opposite phases are generated in the first vibrator 150 and the second vibrator 160.

[0046] The change in resonance frequency due to the tensile strain when the first oscillator 150 changes from the ready state to the detection state, and the change in resonance frequency due to the compressive strain when the second oscillator 160 changes from the ready state to the detection state are defined as Δf ａｃｃ＿Ｚ When the resonance frequency of the first oscillator 150 in the detection state is f1 and the resonance frequency of the second oscillator 160 in the detection state is f2, the resonance frequencies f1 and f2 are respectively expressed by the following equations: f1=f1 ｒｅａｄｙ +Δf ａｃｃ＿Ｚ = (f0 + Δf ｒｅａｄｙ ) + Δf ａｃｃ＿Ｚ f2 = f2 ｒｅａｄｙ -Δf ａｃｃ＿Ｚ = (f0 + Δf ｒｅａｄｙ ) -Δf ａｃｃ＿Ｚ

[0047] At this time, the difference f between the resonance frequency of the first vibrator 150 and the resonance frequency of the second vibrator 160 ｄｅｔｅｃｔ is expressed by the following formula: ｄｅｔｅｃｔ =f1-f2 =(f0+Δf ｒｅａｄｙ +Δf ａｃｃ＿Ｚ ) - (f0 + Δf ｒｅａｄｙ -Δf ａｃｃ＿Ｚ ) = 2Δf ａｃｃ＿ＺThat is, differential detection can be performed by taking the difference between the resonance frequency of the first oscillator 150 and the resonance frequency of the second oscillator 160, thereby improving sensitivity. Furthermore, when in-phase distortion occurs in the first oscillator 150 and the second oscillator 160 due to acceleration on another axis, f ｄｅｔｅｃｔ In the same way, when an in-phase distortion occurs in the first oscillator 150 and the second oscillator 160 due to an environmental factor such as a temperature change, the changes in f1 and f2 caused by the in-phase distortion are canceled out, so that noise due to the other axis sensitivity can be suppressed. ｄｅｔｅｃｔ Since the changes in f1 and f2 caused by the in-phase distortion are cancelled out in this case, noise due to environmental factors can be suppressed.

[0048] As described above, this embodiment includes device layer 100 including weight section 110, elastic section 120, first oscillator 150, and second oscillator 160 arranged on an intersecting plane, and applying mechanism 190 that applies a rotational force to weight section 110. Weight section 110 has first rotating section 111, second rotating section 112, and rotation shaft 113, and elastic section 120 is connected to rotation shaft 113 and holds weight section 110 so that it can translate in the sensitivity axis direction. When detecting acceleration Acc in the sensitivity axis direction, weight section 110 is tilted with respect to the orthogonal plane by the rotational force applied from applying mechanism 190, and receives acceleration Acc while in the tilted state, thereby translating in the sensitivity axis direction, and a difference f between resonant frequency f1 of first oscillator 150 and resonant frequency f2 of second oscillator 160 is detected. ｄｅｔｅｃｔ The acceleration Acc is detected based on the above.

[0049] This allows the device layer extending in the intersecting plane to detect acceleration along the sensitivity axis, and differential detection improves the sensitivity to acceleration along the sensitivity axis, while offsetting acceleration along the orthogonal axis to correct other-axis sensitivity.

[0050] In this embodiment, the applying mechanism 190 applies an electrostatic attractive force to the weight part 110 as a rotational force.

[0051] This allows for the application of a rotational force only when detecting acceleration, thereby suppressing the accumulation of damage to device layer 100, for example, at the connection between weight section 110 and elastic section 120. Furthermore, the electrostatic attraction can be easily controlled because it can be switched on and off by applying a voltage.

[0052] In addition, in this embodiment, the second rotating part 112 is larger than the first rotating part 111, and the application mechanism 190 has an upper electrode 192 provided on the upper cover 180, and the upper electrode 192 faces the second rotating part 112 in the sensitivity axis direction.

[0053] According to this, because the first rotating part 111 and the second rotating part 112 are asymmetrical, even if a rotational force is applied to the mass part 110 by one upper electrode 192, it is possible to suppress the translation of the mass part 110 due to the electrostatic attractive force of the upper electrode 192. Furthermore, because the applying mechanism 190 applies the electrostatic attractive force by the upper electrode 192 so as to pull the mass part 110 upward, it is possible to suppress the drooping of the mass part 110 due to gravity.

[0054] In addition, in this embodiment, the number of oscillators 161, 162 of the second oscillator 160 is equal to the number of oscillators 151, 152 of the first oscillator 150, and the distance from the rotation axis 113 to the second oscillator 160 is equal to the distance from the rotation axis 113 to the first oscillator 150.

[0055] According to this, the difference f between the resonance frequency f1 of the first oscillator 150 and the resonance frequency f2 of the second oscillator 160 is smaller than when the number or distance of the first oscillator 150 and the second oscillator 160 is different. ｄｅｔｅｃｔ This simplifies the calculation of

[0056] The number of second oscillators may be different from the number of first oscillators, and the distance of the second oscillators from the rotation axis may be different from the distance of the first oscillators from the rotation axis.

[0057] Other embodiments will be described below. Note that components that are the same as or similar to those in the first embodiment are denoted by the same or similar reference numerals, and descriptions thereof will be omitted as appropriate. Furthermore, similar effects resulting from similar components will not be mentioned one after another.

[0058] Second Embodiment Next, the configuration of an acceleration sensor 2 according to a second embodiment will be described with reference to Fig. 12 and Fig. 13. Fig. 12 is a plan view of the device layer 100 in the acceleration sensor 2 according to the second embodiment. Fig. 13 is a cross-sectional view of the acceleration sensor 2 according to the second embodiment. Fig. 13 shows a cross-section of the acceleration sensor 2 in a preparation state, which corresponds to a cross-section of the acceleration sensor 1 taken along line A-A.

[0059] The applying mechanism 290 of the acceleration sensor 2 further has a lower electrode 291. The lower electrode 291 is provided on the side of the bottom wall portion 171 of the lower lid 170 that faces the device layer 100. The lower electrode 291 faces the first rotating portion 111 in the Z-axis direction, which is the sensitivity axis direction. The shape and dimensions of the lower electrode 291 are different from the shape and dimensions of the upper electrode 192. Furthermore, in the basic state and the preparation state, the distance of the lower electrode 291 from the rotation axis 113 is different from the distance of the upper electrode 192 from the rotation axis 113. The voltage V1 applied to the upper electrode 192 and the voltage V2 applied to the lower electrode 291 are adjusted as appropriate so that the weight portion 110 can be maintained in a suitable posture.

[0060] According to this embodiment, the translation of the weight part 110 due to the electrostatic attractive force applied by the applying mechanism 290 can be further suppressed.

[0061] Third Embodiment Next, the configuration of an acceleration sensor 3 according to a third embodiment will be described with reference to Fig. 14 and Fig. 15. Fig. 14 is a plan view of a device layer 300 in the acceleration sensor 3 according to the third embodiment. Fig. 15 is a cross-sectional view of the acceleration sensor 3 according to the third embodiment. Fig. 15 shows a cross-section of the acceleration sensor 3 in a preparation state, which corresponds to a cross-section of the acceleration sensor 1 taken along line A-A.

[0062] The spindle portion 310 of the device layer 300 is provided in plane symmetry with respect to a plane perpendicular to the main surface of the spindle portion 310 that passes through the rotation axis 113. The dimensions and shape of the second rotating portion 312 are equal to those of the first rotating portion 311. The upper electrode 392 and the lower electrode 391 are provided in point symmetry with respect to the rotation axis 113 in the basic state and the preparatory state. The shape and dimensions of the lower electrode 391 are equal to those of the upper electrode 392. In the basic state and the preparatory state, the distance from the rotation axis 113 of the lower electrode 391 is equal to the distance from the rotation axis 113 of the upper electrode 392. The voltage V1 applied to the lower electrode 391 is equal to the voltage V2 applied to the upper electrode 392.

[0063] According to this embodiment, the weight portion 310 and the applying mechanism 390 are provided symmetrically, so that the translation of the weight portion 310 due to the electrostatic attractive force can be further suppressed.

[0064] In order to prevent the weight 310 from sagging due to gravity, the voltage V2 may be set to be greater than the voltage V1.

[0065] Fourth Embodiment Next, the configuration of an acceleration sensor 4 according to a fourth embodiment will be described with reference to Fig. 16 and Fig. 17. Fig. 16 is a plan view of a device layer 400 in the acceleration sensor 4 according to the fourth embodiment. Fig. 17 is a cross-sectional view of the acceleration sensor 4 according to the fourth embodiment. Fig. 17 shows a cross-section of the acceleration sensor 4 in a preparation state, which corresponds to a cross-section of the acceleration sensor 1 taken along line A-A.

[0066] First oscillator 450 is connected to the side surface of first rotating part 311 on the negative X-axis direction side at the end portion on the negative X-axis direction side. Second oscillator 460 is connected to the side surface of second rotating part 312 on the positive X-axis direction side at the end portion on the positive X-axis direction side. In the basic state, first oscillator 450 and second oscillator 460 are provided in plane symmetry with a plane that is perpendicular to the main surface of weight part 410 and passes through rotation axis 113 as the plane of symmetry. In the basic state and the preparatory state, first oscillator 450 and second oscillator 460 are provided in point symmetry with rotation axis 113 as the point of symmetry.

[0067] According to this embodiment, it is possible to improve the symmetry of the first oscillator 450 and the second oscillator 460 with respect to the rotation axis 113. If the symmetry of the first oscillator and the second oscillator is lost, f1 ｒｅａｄｙ and f2 ｒｅａｄｙ Since f does not match ｄｅｔｅｃｔ In f1 ｒｅａｄｙ and f2 ｒｅａｄｙ However, according to the present embodiment, the symmetry of the first oscillator 450 and the second oscillator 460 can be increased, and therefore noise caused by the symmetry of the first oscillator 450 and the second oscillator 460 can be suppressed. Furthermore, since the structure of the first oscillator and the second oscillator is simpler than a configuration in which each of the first oscillator and the second oscillator includes multiple oscillators, the occurrence of defective products can be suppressed and the yield can be improved.

[0068] Fifth Embodiment Next, the configuration of an acceleration sensor 5 according to a fifth embodiment will be described with reference to Fig. 18. Fig. 18 is a cross-sectional view of the acceleration sensor 5 according to the fifth embodiment. Fig. 18 shows a cross-section of the acceleration sensor 5 in a ready state, which corresponds to a cross-section of the acceleration sensor 1 taken along line A-A.

[0069] The applying mechanism 590 has a first lower electrode 591, a second lower electrode 594, a first upper electrode 593, and a second upper electrode 592. The first lower electrode 591 and the first upper electrode 593 face the first rotating part 311 in the Z-axis direction, which is the sensitivity axis direction. The second lower electrode 594 and the second upper electrode 592 face the second rotating part 312 in the Z-axis direction, which is the sensitivity axis direction. The first lower electrode 591 and the second lower electrode 594 are arranged symmetrically with respect to the YZ plane. The first upper electrode 593 and the second upper electrode 592 are arranged symmetrically with respect to the YZ plane. The first lower electrode 591 and the first upper electrode 593 are arranged symmetrically with respect to the XY plane. The second lower electrode 594 and the second upper electrode 592 are arranged symmetrically with respect to the XY plane. In the basic state and the preparation state, the first lower electrode 591 and the second upper electrode 592 are provided in point symmetry with respect to the rotation axis 113. In the basic state and the preparation state, the second lower electrode 594 and the first upper electrode 593 are provided in point symmetry with respect to the rotation axis 113. The first lower electrode 591, the second lower electrode 594, the first upper electrode 593, and the second upper electrode 592 have the same dimensions and shapes.

[0070] According to this embodiment, the weight 310 can be translated, rotated, and deformed by adjusting the voltages applied to the first lower electrode 591, the second lower electrode 594, the first upper electrode 593, and the second upper electrode 592. This makes it possible to correct the effects of warping of the device layer 400 that occurs during the manufacturing process.

[0071] Sixth Embodiment Next, the configuration of an acceleration sensor 6 according to a sixth embodiment will be described with reference to Fig. 19. Fig. 19 is a cross-sectional view of the acceleration sensor 6 according to the sixth embodiment. Fig. 19 shows a cross-section of the acceleration sensor 6 in a ready state, which corresponds to a cross-section of the acceleration sensor 1 taken along line A-A.

[0072] The first lower electrode 691 is composed of a plurality of electrodes 691 a and 691 b, which are aligned in the X-axis direction. Similarly, the second lower electrode 694 is composed of a plurality of electrodes 694 a and 694 b, the first upper electrode 693 is composed of a plurality of electrodes 693 a and 693 b, and the second upper electrode 692 is composed of a plurality of electrodes 692 a and 692 b.

[0073] According to this embodiment, the degree of freedom in designing the electrodes is improved, and it is possible to more precisely translate, rotate, and deform the weight portion 310. Therefore, the influence of warpage of the device layer 400 can be more effectively corrected.

[0074] As described above, the present invention is not limited to the embodiment in which all of the first lower electrode, second lower electrode, first upper electrode, and second upper electrode are composed of multiple electrodes, as long as at least one of the first lower electrode, second lower electrode, first upper electrode, and second upper electrode is composed of multiple electrodes. Furthermore, in each embodiment, the upper electrode or the lower electrode may be composed of multiple electrodes. For example, in the first embodiment, the upper electrode 192 may be composed of multiple electrodes, and in the second embodiment, at least one of the upper electrode 192 and the lower electrode 291 may be composed of multiple electrodes.

[0075] Seventh Embodiment Next, the configuration of an acceleration sensor 7 according to a seventh embodiment will be described with reference to Fig. 20. Fig. 20 is a cross-sectional view of the acceleration sensor 7 according to the seventh embodiment. Fig. 20 shows a cross-section of the acceleration sensor 7 in a ready state, which corresponds to a cross-section of the acceleration sensor 1 taken along line A-A.

[0076] The acceleration sensor 7 includes two sensor structures 701 and 702. The sensor structures 701 and 702 are provided adjacent to each other in the X-axis direction. The sensor structures 701 and 702 are provided symmetrically with respect to the boundary surface between the sensor structures 701 and 702.

[0077] The change in the resonant frequency of the vibrators of the sensor structures 701 and 702 when subjected to acceleration in the X-axis direction is defined as Δfａｃｃ＿Ｘ The difference f of the resonant frequency in the sensor structure 701 is ７０１ and the difference f of the resonant frequencies in the sensor structure 702 ７０２ are expressed by the following equations: ７０１ = (f0 + Δf ｒｅａｄｙ +Δf ａｃｃ＿Ｘ ) - (f0 + Δf ｒｅａｄｙ -Δf ａｃｃ＿Ｘ ) = 2Δf ａｃｃ＿Ｘ f ７０２ = (f0 + Δf ｒｅａｄｙ -Δf ａｃｃ＿Ｘ ) - (f0 + Δf ｒｅａｄｙ +Δf ａｃｃ＿Ｘ ) = -2Δf ａｃｃ＿Ｘ

[0078] Therefore, the difference f of the resonant frequencies in the sensor structure 701 ７０１ and the difference f between the resonant frequencies of the sensor structure 702 ７０２ The difference fcross-axis is expressed by the following formula: fcross-axis=f ７０１ -f ７０２ = 2Δf ａｃｃ＿Ｘ -2Δf ａｃｃ＿Ｘ =0

[0079] According to this embodiment, it is possible to make fcross-axis = 0. That is, it is possible to cancel out the influence of acceleration in the X-axis direction. Therefore, it is possible to suppress other-axis sensitivity and improve the detection accuracy of acceleration in the out-of-plane direction.

[0080] Some or all of the embodiments of the present invention will be described below, but the present invention is not limited to the following descriptions.

[0081] <1> An acceleration sensor comprising: a device layer including a weight portion, an elastic portion, a first oscillator, and a second oscillator, each disposed on an intersecting plane intersecting a sensitivity axis direction; an applying mechanism that applies a rotational force to the weight portion; a lower lid provided below the device layer in the sensitivity axis direction; and an upper lid provided above the device layer in the sensitivity axis direction, the acceleration sensor detecting acceleration in the sensitivity axis direction, wherein the weight portion has a rotation axis perpendicular to the sensitivity axis direction, a first rotating portion extending from the rotation axis, and a second rotating portion extending from the rotation axis on an opposite side to the first rotating portion; the elastic portion is connected to the rotation axis of the weight portion and holds the weight portion translatable in the sensitivity axis direction; the first oscillator is connected to the first rotating portion of the weight portion and configured to change its resonance frequency in response to displacement of the first rotating portion; and the second oscillator is connected to the second rotating portion of the weight portion and configured to change its resonance frequency in response to displacement of the second rotating portion. When detecting acceleration in the sensitivity axis direction, the weight section is tilted with respect to an orthogonal plane perpendicular to the sensitivity axis direction due to the rotational force applied from the application mechanism, and is subjected to acceleration in the sensitivity axis direction while inclined, thereby causing the weight section to translate in the sensitivity axis direction, and the acceleration in the sensitivity axis direction is detected based on the difference between the resonant frequency of the first vibrator and the resonant frequency of the second vibrator.

[0082] <2> The acceleration sensor according to <1>, wherein the applying mechanism applies an electrostatic attractive force to the weight portion as the rotational force.

[0083] <3> The acceleration sensor according to <2>, wherein the second rotating part is larger than the first rotating part, the applying mechanism has an upper electrode provided on the upper cover, and the upper electrode faces the second rotating part in the sensitivity axis direction.

[0084] <4> The acceleration sensor according to <3>, wherein the applying mechanism further includes a lower electrode provided on the lower cover, and the lower electrode faces the first rotating part in the sensitivity axis direction.

[0085] <5> The acceleration sensor according to <2>, wherein the second rotating part has dimensions and a shape equal to those of the first rotating part, the applying mechanism has an upper electrode provided on the top cover and a lower electrode provided on the bottom cover, and the lower electrode and the upper electrode are arranged symmetrically with respect to the rotation axis when not receiving acceleration in the sensitivity axis direction.

[0086] <6> The acceleration sensor according to any one of <2> to <5>, wherein the applying mechanism has a first upper electrode and a second upper electrode provided on the top cover, and a first lower electrode and a second lower electrode provided on the bottom cover, the first upper electrode and the first lower electrode facing the first rotating part in the sensitivity axis direction, and the second upper electrode and the second lower electrode facing the second rotating part in the sensitivity axis direction.

[0087] <7> The acceleration sensor according to <6>, wherein at least one of the first upper electrode, the second upper electrode, the first lower electrode, and the second lower electrode is configured by a plurality of electrodes.

[0088] <8> The acceleration sensor according to any one of <1> to <7>, wherein a basic state is when no rotational force is being applied to the weight section by the application mechanism, a standby state is when the weight section is tilted with respect to the orthogonal plane by the rotational force applied by the application mechanism and is not receiving acceleration in the sensitivity axis direction, and a detection state is when the weight section is receiving acceleration in the sensitivity axis direction and is translating in the sensitivity axis direction, a tensile strain occurs in the first oscillator and the second oscillator in the standby state compared to the first oscillator and the second oscillator in the basic state, a tensile strain occurs in the first oscillator in the detection state compared to the first oscillator in the standby state, and a compressive strain occurs in the second oscillator in the detection state compared to the second oscillator in the standby state.

[0089] <9> The acceleration sensor according to any one of <1> to <8>, wherein the number of the second vibrators is equal to the number of the first vibrators, and when viewed in a plan view from the sensitivity axis direction, the distance from the rotation axis to the second vibrators is equal to the distance from the rotation axis to the first vibrators.

[0090] <10> The acceleration sensor according to any one of <1> to <9>, comprising two sensor structures provided adjacent to each other in an orthogonal axis direction perpendicular to a sensitivity axis direction, the two sensor structures being provided in plane symmetry with respect to a boundary surface between the two sensor structures.

[0091] As described above, according to one aspect of the present invention, an acceleration sensor capable of detecting acceleration in an out-of-plane direction can be provided.

[0092] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the scope of the present invention. The present invention may be modified or improved without departing from its spirit, and equivalents are also included within the scope of the present invention. In other words, designs modified by those skilled in the art as appropriate to the embodiments and / or modifications are also encompassed within the scope of the present invention as long as they incorporate the characteristics of the present invention. For example, the elements and their arrangements, materials, conditions, shapes, sizes, etc. of the embodiments and / or modifications are not limited to those illustrated and can be modified as appropriate. Furthermore, the embodiments and modifications are merely examples, and it goes without saying that partial substitutions or combinations of the components shown in different embodiments and / or modifications are possible. These are also encompassed within the scope of the present invention as long as they incorporate the characteristics of the present invention.

[0093] DESCRIPTION OF SYMBOLS 1...Acceleration sensor 100...Device layer 110...Plummet portion 111...First rotating portion 112...Second rotating portion 113...Rotation axis 120...Elastic portion 121...First spring portion 122...Second spring portion 131, 132, 133, 134...Connecting portion 150...First oscillator 151, 152...Oscillator 160...Second oscillator 161, 162...Oscillator 170...Lower cover 180...Upper cover 190...Applying mechanism 192...Upper electrode

Claims

1. An acceleration sensor for detecting acceleration in the sensitivity axis direction, comprising: a device layer including a weight portion, an elastic portion, a first vibrator, and a second vibrator, each disposed on an intersecting plane intersecting the sensitivity axis direction; an applying mechanism for applying a rotational force to the weight portion; a lower lid provided below the device layer in the sensitivity axis direction; and an upper lid provided above the device layer in the sensitivity axis direction, wherein the weight portion has a rotation axis perpendicular to the sensitivity axis direction, a first rotating portion extending from the rotation axis, and a second rotating portion extending from the rotation axis on the opposite side to the first rotating portion; the elastic portion is connected to the rotation axis of the weight portion and holds the weight portion translatable in the sensitivity axis direction; the first vibrator is connected to the first rotating portion of the weight portion and configured to have a resonant frequency that changes in response to displacement of the first rotating portion; and the second vibrator is connected to the second rotating portion of the weight portion and configured to have a resonant frequency that changes in response to displacement of the second rotating portion. when detecting acceleration in the sensitivity axis direction, the weight portion is tilted with respect to an orthogonal plane perpendicular to the sensitivity axis direction by the rotational force applied from the applying mechanism, and receives acceleration in the sensitivity axis direction while remaining in the tilted state, thereby translating in the sensitivity axis direction, and the acceleration in the sensitivity axis direction is detected based on the difference between the resonant frequency of the first vibrator and the resonant frequency of the second vibrator.

2. The acceleration sensor according to claim 1, wherein the applying mechanism applies an electrostatic attractive force to the weight portion as the rotational force.

3. The acceleration sensor according to claim 2, wherein the second rotating portion is larger than the first rotating portion, the applying mechanism has an upper electrode provided on the top cover, and the upper electrode faces the second rotating portion in the sensitivity axis direction.

4. The acceleration sensor according to claim 3, wherein the applying mechanism further has a lower electrode provided on the lower cover, the lower electrode facing the first rotating part in the sensitivity axis direction.

5. An acceleration sensor as described in claim 2, wherein the second rotating part has the same dimensions and shape as the first rotating part, the applying mechanism has an upper electrode provided on the top cover and a lower electrode provided on the bottom cover, and the lower electrode and the upper electrode are arranged symmetrically with respect to the rotation axis when no acceleration is applied in the sensitivity axis direction.

6. An acceleration sensor as described in any one of claims 2 to 5, wherein the applying mechanism has a first upper electrode and a second upper electrode provided on the top cover, and a first lower electrode and a second lower electrode provided on the bottom cover, the first upper electrode and the first lower electrode facing the first rotating part in the sensitivity axis direction, and the second upper electrode and the second lower electrode facing the second rotating part in the sensitivity axis direction.

7. The acceleration sensor according to claim 6, wherein at least one of the first upper electrode, the second upper electrode, the first lower electrode and the second lower electrode is composed of a plurality of electrodes.

8. An acceleration sensor according to any one of claims 1 to 7, wherein: a basic state is when the weight is not being applied with the rotational force from the application mechanism; a ready state is when the weight is tilted with respect to the orthogonal plane by the rotational force applied from the application mechanism and is not receiving acceleration in the sensitivity axis direction; and a detection state is when the weight is receiving acceleration in the sensitivity axis direction and is translating in the sensitivity axis direction, wherein tensile strain occurs in the first and second vibrators in the ready state compared to the first and second vibrators in the basic state, tensile strain occurs in the first vibrator in the detection state compared to the first vibrator in the ready state, and compressive strain occurs in the second vibrator in the detection state compared to the second vibrator in the ready state.

9. An acceleration sensor as described in any one of claims 1 to 8, wherein the number of second vibrators is equal to the number of first vibrators, and when viewed in a planar view from the sensitivity axis direction, the distance from the rotation axis to the second vibrators is equal to the distance from the rotation axis to the first vibrators.

10. An acceleration sensor according to any one of claims 1 to 9, comprising two sensor structures arranged adjacent to each other in an orthogonal axis direction perpendicular to the sensitivity axis direction, and the two sensor structures are arranged in plane symmetry with respect to the boundary surface between the two sensor structures.

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