Acceleration sensor

Abstract

To provide an acceleration sensor capable of improving reliability and detecting acceleration accurately.SOLUTION: An acceleration sensor 1 comprises: a substrate 10; a support part 13 provided on the substrate 10; and a mass part 16 moveably supported by the support part 13 and including a first weight part 61 and a second weight part 62 with smaller mass than that of the first weight part 61. The acceleration sensor 1 further comprises: a first fixed electrode 31 and a second fixed electrode 32 of a sensor element 2 supported by the support part 13; and a first movable electrode 51 and a second movable electrode 52 of the sensor element 2 respectively provided on the first weight part 61 and the second weight part 62, and relatively moveable to the first fixed electrode 31 and the second fixed electrode 32 in a thickness direction of the substrate 10.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a capacitive MEMS (Micro Electro Mechanical System) acceleration sensor. The acceleration sensor includes a first semiconductor substrate having electrodes formed on its surface, and a second semiconductor substrate having a weight portion disposed opposite to the electrodes and bonded to the first semiconductor substrate. The acceleration sensor is configured to detect the capacitance between the electrodes and the weight portion facing each other in the thickness direction of the first and second semiconductor substrates to detect the acceleration in the thickness direction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the acceleration sensor described in Patent Document 1, since the electrodes are formed on the first semiconductor substrate, when stress is generated in the package when the substrate is molded and packaged, the capacitance between the electrodes and the weight portion is affected by the substrate, which may reduce the reliability of the sensor.

[0005] On the other hand, as a capacitive MEMS acceleration sensor, there is considered one including an inertial mass portion movably supported on a substrate, comb-shaped movable electrodes formed on the inertial mass portion, and comb-shaped fixed electrodes supported on the substrate so as to mesh with the movable electrodes, and detecting the capacitance between the movable electrodes and the fixed electrodes that are displaced in the thickness direction of the substrate in response to the displacement of the inertial mass portion to detect the acceleration in the thickness direction of the substrate. In such an acceleration sensor, it is desired to accurately detect the acceleration.

[0006] The present disclosure aims to improve the reliability of a sensor and accurately detect acceleration in an acceleration sensor that detects acceleration in the thickness direction of a substrate.

Means for Solving the Problem

[0007] The present disclosure provides an acceleration sensor including a substrate, a support portion provided on the substrate, a mass portion movably supported by the support portion and having a first weight portion and a second weight portion with a mass smaller than that of the first weight portion, a first fixed electrode and a second fixed electrode of a sensor element supported by the support portion, and a first movable electrode and a second movable electrode of the sensor element provided on the first weight portion and the second weight portion respectively and relatively movable in the thickness direction of the substrate with respect to the first fixed electrode and the second fixed electrode.

[0008] According to the present disclosure, a first and a second fixed electrode supported by a support portion and a first and a second movable electrode provided on the first and the second weight portions of a mass portion movably supported by the support portion are provided. Since two capacitors can be formed by the first and the second fixed electrode and the first and the second movable electrode supported by one support portion, the influence of the substrate can be suppressed and the reliability of the sensor can be improved. In addition, the first and the second movable electrodes can be formed on one mass portion, and the generation of noise between the first and the second movable electrodes, which are separate bodies, can be suppressed compared with the case where the first and the second movable electrodes are formed separately, and acceleration can be accurately detected. Further, by detecting the difference in capacitance between the two capacitors, the sensitivity can be increased and the noise can be reduced to improve the S / N ratio (signal-to-noise ratio) compared with the case of detecting the capacitance of one capacitor.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0011] Figure 1 is a plan view of the acceleration sensor according to the embodiment of the present disclosure. As shown in Figure 1, the acceleration sensor 1 according to the embodiment of the present disclosure is an acceleration sensor having a capacitive acceleration sensor element 2. The acceleration sensor 1 includes a substrate assembly 11 having a substrate 10 with the sensor element 2. The acceleration sensor 1 is manufactured by processing the substrate 10 using semiconductor microfabrication technology.

[0012] Hereinafter, a predetermined direction along the surface of the substrate 10 is defined as the X direction, a direction along the surface of the substrate 10 and orthogonal to the X direction is defined as the Y direction, and the thickness direction of the substrate 10 orthogonal to the X direction and the Y direction and orthogonal to the surface of the substrate 10 is defined as the Z direction. In Figure 1, the substrate assembly 11 is shown as viewed from one side in the Z direction.

[0013] The sensor element 2 is a sensor element that detects acceleration acting in the Z direction, which is a direction orthogonal to the surface of the substrate 10. Another substrate assembly having a lid substrate covering the sensor element 2 is joined to the substrate assembly 11, and the sensor element 2 can be disposed within a sealed space portion.

[0014] The substrate 10 is provided with a plurality of, specifically three, pad portions 3 spaced apart from each other in the X direction. The pad portions 3 are connected to external electronic components or the like. The pad portions 3 are adapted to input an electrical signal to the sensor element 2 or output the electrical signal of the sensor element 2. Although not shown in the figure, the substrate 10 is provided with wirings for electrically connecting the pad portions 3 and the sensor element 2.

[0015] FIG. 2 is a cross-sectional view of the acceleration sensor taken along line II-II of FIG. 1. FIG. 3 is a cross-sectional view of the acceleration sensor taken along line III-III of FIG. 1. As shown in FIGS. 2 and 3, the substrate 10 has a first main surface 10a that is the surface and a second main surface 10b that is the back surface on the opposite side of the first main surface 10a. The substrate 10 is formed in a rectangular shape in plan view as shown in FIG. 1. As the substrate 10, a conductive single crystal silicon substrate doped with impurities to impart conductivity is used as a semiconductor substrate.

[0016] As shown in FIG. 2, a cavity 12 is formed on the first main surface side corresponding to the sensor element 2, and a part of the cavity 12 is exposed on the first main surface 10a. The cavity 12 is formed by being recessed in the thickness direction of the substrate 10 from the first main surface 10a, and has a bottom wall portion 12a and side wall portions 12b extending in the thickness direction of the substrate 10 from the bottom wall portion 12a. The cavity 12 is formed at least in a portion of the bottom wall portion 12a of the substrate 10 excluding a support portion 13 described later.

[0017] As shown in FIGS. 1 to 3, the substrate 10 is formed with a first beam 20 that forms a first fixed electrode 31 and a second fixed electrode 32 of the sensor element 2, a second beam 40 that forms a first movable electrode 51 and a second movable electrode 52 of the sensor element 2, and a support portion 13 that supports the first beam 20 and the second beam 40.

[0018] As shown in FIG. 2, the support portion 13 is formed to extend in a substantially quadrangular prism shape from the bottom wall portion 12a of the cavity 12 to the first main surface 10a of the substrate 10 in the thickness direction of the substrate 10. The first beam 20 and the second beam 40 are formed to have substantially the same thickness in the thickness direction of the substrate 10, and are supported in a floating state with respect to the bottom wall portion 12a in the cavity 12 by a single support portion 13 provided on the substrate 10.

[0019] After forming a silicon oxide film on the substrate 10 by CVD method, the first beam 20 and the second beam 40 are formed by patterning the substrate 10 by photolithography and anisotropic etching to leave the support portion 13, the first beam 20 and the second beam 40, and then forming the trench deeper by isotropic etching and etching in a direction parallel to the first main surface 10a of the substrate 10, thereby forming the cavity 12.

[0020] As shown in FIG. 1, the first beam 20 forming the first fixed electrode 31 has a first portion 21 supported by the support portion 13 and extending linearly in the X direction, a second portion 22 extending linearly from the first portion 21 to both sides in the Y direction, and a first fixed electrode 31 extending linearly in the X direction spaced apart from the second portion 22 in the Y direction.

[0021] The first fixed electrode 31 is formed in a flat plate shape having a predetermined width in plan view and is formed in a comb shape. A separation portion 14 is formed in the first beam 20 for the first fixed electrode to electrically separate and mechanically connect the first fixed electrode 31 and the support portion 13. The separation portion 14 has silicon oxide and is formed by a silicon oxide film which is an insulating film.

[0022] The separation portion 14 is formed, for example, by removing a portion corresponding to the separation portion 14 on the first main surface 10a of the substrate 10 to form a trench, and then forming a silicon oxide film which is a thermal oxide film obtained by thermally oxidizing the trench. Note that the separation portion 14 described later is formed in the same manner.

[0023] The first fixed electrode 31 is provided with a deflection generating portion 35 that deflects in the Z direction with respect to the first movable electrode 51. As the deflection generating portion 35, for example, a silicon oxide film formed on the first fixed electrode 31 can be used. The first fixed electrode 31 extends substantially horizontally in the first main surface 10a of the substrate 10 in FIGS. 2 and 3, but as shown in FIG. 4 to be described later, it deflects to the other side in the Z direction with respect to the first movable electrode 51 by the deflection generating portion 35.

[0024] As shown in FIG. 1, the first beam 20 forming the second fixed electrode 32 has a first portion 21 supported by the support portion 13 and extending in the X direction, a second portion 22 linearly extending from the first portion 21 to both sides in the Y direction, and a second fixed electrode 32 linearly extending in the X direction spaced apart from the second portion 22 in the Y direction.

[0025] The second fixed electrode 32 is formed in a flat plate shape having a predetermined width in plan view and is formed in a comb shape. The first beam 20 forming the first fixed electrode 31 and the second fixed electrode 32 is formed substantially symmetrically in the X direction with the support portion 13 interposed therebetween. The first beam 20 for the second fixed electrode is formed with a separation portion 14 that electrically separates and mechanically connects the second fixed electrode 32 and the support portion 13.

[0026] The second fixed electrode 32 is provided with a deflection generating portion 35 that deflects in the Z direction with respect to the second movable electrode 52. As the deflection generating portion 35, for example, a silicon oxide film formed on the second fixed electrode 32 can be used. The second fixed electrode 32 extends substantially horizontally in the first main surface 10a of the substrate 10 in FIGS. 2 and 3, but as shown in FIG. 4 to be described later, it deflects to the other side in the Z direction with respect to the second movable electrode 52 by the deflection generating portion 35.

[0027] As shown in FIG. 1, the second beam 40 forming the first movable electrode 51 includes a pair of first portions 41 respectively supported on both sides in the Y direction of the support portion 13 and extending linearly in the Y direction, a pair of second portions 42 respectively connected to the pair of first portions 41 and extending linearly in the X direction, a first weight portion 61 connected to the pair of second portions 42, and a first movable electrode 51 spaced apart from the first weight portion 61 in the Y direction and extending linearly in the X direction.

[0028] The first weight portion 61 has a plurality of vertical straight portions 43 extending linearly in the Y direction in plan view and a plurality of horizontal straight portions 44 extending linearly in the X direction in plan view, and is formed with a substantially rectangular outer shape in plan view. The plurality of vertical straight portions 43 and the plurality of horizontal straight portions 44 are provided in a grid pattern.

[0029] The first movable electrode 51 is formed in a flat plate shape having a predetermined width in plan view and is formed in a comb shape. The first movable electrode 51 is disposed to face the first fixed electrode 31 in the Y direction orthogonal to the thickness direction of the substrate 10 so as to mesh with each other. A separation portion 14 that electrically separates and mechanically connects the first movable electrode 51 and the support portion 13 is formed in the second beam 40 for the first movable electrode, and the separation portion 14 is formed in the first portion 41 and the second portion 42 of the second beam 40.

[0030] A spring portion 45 is provided on the first portion 41 on the support portion side of the second beam 40 for the first movable electrode. The spring portion 45 is formed with a smaller width than the other portions of the first portion 41 and the second portion 42. The first weight portion 61 provided with the first movable electrode 51 is supported by the support portion 13 via the spring portion 45. Thereby, the first movable electrode 51 is made movable relative to the first fixed electrode 31 in the Z direction in response to an acceleration in the Z direction.

[0031] The second beam 40 that forms the second movable electrode 52 includes a pair of first portions 41 respectively supported on both sides of the support portion 13 in the Y direction and extending linearly in the Y direction, a pair of second portions 42 respectively connected to the pair of first portions 41 and extending linearly in the X direction, a second weight portion 62 connected to the pair of second portions 42, and a second movable electrode 52 spaced apart from the second weight portion 62 in the Y direction and extending linearly in the X direction.

[0032] The second weight portion 62 has a plurality of vertical straight portions 43 extending linearly in the Y direction in plan view and a plurality of horizontal straight portions 44 extending linearly in the X direction in plan view, and is formed with a substantially rectangular outer shape in plan view. The plurality of vertical straight portions 43 and the plurality of horizontal straight portions 44 are provided in a lattice pattern.

[0033] The second weight portion 62 is formed with a smaller mass than the first weight portion 61. In the acceleration sensor 1, the area S2 of the second weight portion 62 in plan view is smaller than the area S1 of the first weight portion 61 in plan view, and the second weight portion 62 is formed with a smaller mass than the first weight portion 61. The second weight portion 62 is set to have a mass, although not limited thereto, for example, less than 1 / 2 of the first weight portion 61.

[0034] The second movable electrode 52 is formed in a flat plate shape having a predetermined width in plan view and is formed in a comb shape. The second movable electrode 52 is disposed to face in the Y direction orthogonal to the thickness direction of the substrate 10 so as to mesh with the second fixed electrode 32. A separation portion 14 that electrically separates and mechanically connects the second movable electrode 52 and the support portion 13 is formed in the second beam 40 for the second movable electrode, and the separation portion 14 is formed in the first portion 41 and the second portion 42 of the second beam 40.

[0035] On the support portion side of the second beam 40 for the second movable electrode, a spring portion 45 is provided on the first portion 41. The spring portion 45 is formed with a smaller width compared to the other portions of the first portion 41 and the second portion 42. The second weight portion 62 where the second movable electrode 52 is provided is supported by the support portion 13 via the spring portion 45. Thereby, the second movable electrode 52 is made relatively movable in the Z direction with respect to the second fixed electrode 32 in accordance with the acceleration in the Z direction.

[0036] The second beam 40 forming the first movable electrode 51 and the second movable electrode 52 respectively is formed substantially symmetrically in the X direction with the support portion 13 interposed therebetween, excluding the first weight portion 61 and the second weight portion 62. The first fixed electrode 31 and the first movable electrode 51 are formed symmetrically with respect to the second fixed electrode 32 and the second movable electrode 52 respectively with the support portion 13 interposed therebetween in a plan view. The first portion 41 of the second beam 40 for the second movable electrode is made a common portion with the first portion 41 of the second beam 40 for the first movable electrode, and the second portion 42 of the second beam 40 for the second movable electrode is connected to the second portion 42 of the second beam 40 for the first movable electrode.

[0037] In the acceleration sensor 1, a mass portion 16 having a first weight portion 61 and a second weight portion 62 with a smaller mass than the first weight portion 61 is movably supported on the support portion 13 of the substrate 10. The mass portion 16 is constituted by the second beam 40, and the first movable electrode 51 and the second movable electrode 52 provided on the first weight portion 61 and the second weight portion 62 respectively are integrally formed. The acceleration sensor 1 includes a single support portion 13 provided on the substrate 10 and a single mass portion 16 movably supported by the support portion 13.

[0038] FIG. 4 is a diagram showing the acceleration sensor at rest and when an acceleration acts thereon. FIG. 5 is a cross-sectional view of the acceleration sensor along the V-V line in FIG. 4. FIG. 6 is a cross-sectional view of the acceleration sensor along the VI-VI line in FIG. 4. As shown by the solid line in FIG. 4, when no acceleration acts on the acceleration sensor 1 at rest, the mass portion 16 is arranged such that the surface on one side in the Z direction is substantially at the same Z-direction position as the first main surface 10a of the substrate 10, and the surfaces on one side in the Z direction of the first movable electrode 51 and the second movable electrode 52 are substantially at the same Z-direction position as the first main surface 10a of the substrate 10.

[0039] The first fixed electrode 31 and the second fixed electrode 32 are bent to the other side in the Z direction by the bending portion 35 and are arranged on the other side in the Z direction with respect to the first main surface 10a of the substrate 10 when no acceleration acts on the acceleration sensor 1 at rest. As shown in FIG. 5, the first fixed electrode 31 is arranged on the other side in the Z direction with respect to the first movable electrode 51. As shown in FIG. 6, the second fixed electrode 32 is arranged on the other side in the Z direction with respect to the second movable electrode 52.

[0040] When an acceleration acting on one side in the Z direction acts on the acceleration sensor 1, as shown by the two-dot chain line in FIG. 4, the mass portion 16 tends to keep the first weight portion 61 having a larger mass than the second weight portion 62 in place according to the acceleration, while the second weight portion 62 easily moves to one side in the Z direction, so that it tilts with respect to the first main surface 10a of the substrate 10 and the tilt angle changes according to the acceleration.

[0041] The first movable electrode 51 is displaced to the other side in the Z direction with respect to the first fixed electrode 31 as shown by the two-dot chain line in FIG. 5, and the capacitance of the first capacitor C1 formed by the first fixed electrode 31 and the first movable electrode 51 is increased. The second movable electrode 52 is displaced to one side in the Z direction with respect to the second fixed electrode 32 as shown by the two-dot chain line in FIG. 6, and the capacitance of the second capacitor C2 formed by the second fixed electrode 32 and the second movable electrode 52 is decreased.

[0042] In FIGS. 4 to 6, the acceleration acting time when the acceleration on one side in the Z direction acts on the acceleration sensor 1 is shown. However, also for the acceleration acting time when the acceleration on the other side in the Z direction acts on the acceleration sensor 1, the mass portion 16 inclines with respect to the first main surface 10a of the substrate 10 according to the acceleration, and the inclination angle changes according to the acceleration.

[0043] When the acceleration on the other side in the Z direction acts on the acceleration sensor 1, the first movable electrode 51 is displaced in the Z direction on one side with respect to the first fixed electrode 31, and the capacitance of the first capacitor C1 is reduced. The second movable electrode 52 is displaced in the Z direction on the other side with respect to the second fixed electrode 32, and the capacitance of the second capacitor C2 is increased.

[0044] The acceleration sensor 1 increases the capacitance of one of the first capacitor C1 and the second capacitor C1 and decreases the capacitance of the other according to the acceleration, and extracts the change in the capacitance of the first capacitor C1 and the second capacitor C2 as an electrical signal to detect the acceleration in the Z direction.

[0045] As shown in FIG. 1, flexible leads 15 are attached to the first movable electrode side of the second portion 42 of the second beam 40 for the first movable electrode, the second movable electrode side of the second portion 42 of the second beam 40 for the second movable electrode, and the anti-support portion side of the first portion 41 of the second beam 40 for the first movable electrode and the second movable electrode, respectively. The flexible lead 15 is supported by the second beam 40 in a state of floating with respect to the bottom wall portion 12a of the cavity 12.

[0046] The first fixed electrode 31 and the second fixed electrode 32 are electrically connected via wiring (not shown). The first fixed electrode 31 and the second fixed electrode 32, the first movable electrode 51, and the second movable electrode 52 are electrically connected to different pad portions 3 via the flexible leads 15 and the wiring, respectively. On the substrate 10, there are provided a fixed electrode wiring for electrically connecting the first fixed electrode 31 and the second fixed electrode 32 to the pad portion 3, a first movable electrode wiring for electrically connecting the first movable electrode 51 to the pad portion 3, and a second movable electrode wiring for electrically connecting the second movable electrode 52 to the pad portion 3.

[0047] FIG. 7 is a diagram showing a connection circuit of an acceleration sensor. As shown in FIG. 7, in the acceleration sensor 1, a connection circuit in which a first capacitor C1 and a second capacitor C2 are connected in series is formed. The first capacitor C1 and the second capacitor C2 are formed such that their capacitances are equal or substantially equal when no acceleration in the Z direction acts, and the capacitances of the first capacitor C1 and the second capacitor C2 change respectively when acceleration in the Z direction acts.

[0048] As shown in FIG. 7, a first input voltage V IN1 is applied to the first movable electrode 51, and a second input voltage V IN2 is applied to the second movable electrode 52. The first input voltage V IN1 and the second input voltage V IN2 are input voltages with opposite phases. In the acceleration sensor 1, when the first input voltage V IN1 and the second input voltage V IN2 are applied, the acceleration in the Z direction is detected by measuring the output voltage V OUT from the first fixed electrode 31 and the second fixed electrode 32.

[0049] In the acceleration sensor 1 configured in this way, the substrate 10 is provided with the first and second fixed electrodes 32, 32 supported by the support portion 13, and the first and second movable electrodes 52, 52 of the first and second weight portions 61, 62 of the mass portion 16 movably supported by the support portion 13.

[0050] Since two capacitors C1 and C2 can be formed by the first and second fixed electrodes 32, 32 and the first and second movable electrodes 52, 52 supported by one support portion 13, the influence of the substrate 10 can be suppressed, and the reliability of the sensor can be improved. Further, the first and second movable electrodes 52, 52 can be formed on one mass portion 16, and the generation of noise can be suppressed and the acceleration can be detected accurately as compared with the case where the first and second movable electrodes are formed separately.

[0051] FIG. 10 is a plan view of an acceleration sensor in which the first and second movable electrodes are formed separately. FIG. 11 is a cross-sectional view of the acceleration sensor taken along line XI-XI of FIG. 10. The acceleration sensor 101 shown in FIGS. 11 and 12 has the first and second movable electrodes formed separately.

[0052] On the substrate 10 of the acceleration sensor 101, a first beam 120 that forms the first fixed electrode 131 and the second fixed electrode 132 of the sensor element 102, a second beam 140 that forms the first movable electrode 151 and the second movable electrode 152 of the sensor element 102, and a support portion 113 that supports the first beam 120 and the second beam 140 are formed. The first beam 120 and the second beam 140 are supported by the support portion 113 in a state of floating with respect to the bottom wall portion 12a in the cavity 12.

[0053] The support portion 113 has a support portion 113a that supports the first beam 120 forming the first fixed electrode 131 and the second beam 140 forming the first movable electrode 151, and a support portion 113b that supports the first beam 120 forming the second fixed electrode 132 and the second beam 140 forming the second movable electrode 152. The first movable electrode 151 and the second movable electrode 152 are supported by different support portions 113a and 113b and are formed separately.

[0054] A spring portion 145 is provided on the support portion side of the second beam 140 that forms the first movable electrode 151, and the first movable electrode 151 is configured to be relatively movable in the Z direction with respect to the first fixed electrode 131 in response to an acceleration in the Z direction. A spring portion 145 is provided on the support portion side of the second beam 140 that forms the second movable electrode 152, and the second movable electrode 152 is configured to be relatively movable in the Z direction with respect to the second fixed electrode 132 in response to an acceleration in the Z direction.

[0055] The first fixed electrode 131 is provided with a deflection generating portion 135, and the first fixed electrode 131 is deflected in the other direction of the Z-axis with respect to the first movable electrode 151 by the deflection generating portion 135. The second movable electrode 152 is provided with a deflection generating portion 135, and the second movable electrode 152 is deflected in the other direction of the Z-axis with respect to the second fixed electrode 132 by the deflection generating portion 135.

[0056] When an acceleration in the Z direction acts on the acceleration sensor 101, changes in the electrostatic capacitances of a first capacitor C101 formed by the first fixed electrode 131 and the first movable electrode 151 and a second capacitor C102 formed by the second fixed electrode 132 and the second movable electrode 152 are taken out as electrical signals to detect the acceleration in the Z direction.

[0057] In the acceleration sensor 101, two capacitors C101 and C102 can be formed by the first and second fixed electrodes 131 and 132 supported by the support portion 113 and the first and second movable electrodes 151 and 152 movably supported by the support portion 113. Therefore, the influence of the substrate 10 can be suppressed to detect the acceleration. However, since the first and second movable electrodes 151 and 152 are formed separately, noise may be generated between the separate first and second movable electrodes 151 and 152.

[0058] In the acceleration sensor 1 according to the present embodiment, since the first and second movable electrodes 52 and 52 can be formed on one mass portion 16 to form the first and second movable electrodes 51 and 52 by one element, compared with the case where the first and second movable electrodes are formed separately, generation of noise between the separate first and second movable electrodes can be suppressed, and the acceleration can be detected with high accuracy.

[0059] In the acceleration sensor 1, the deflection generating portion 35 is provided on the first fixed electrode 31 and the second fixed electrode 32, and when acceleration acts, the acceleration is detected by configuring such that in the first capacitor C1 and the second capacitor C2, the capacitance of one increases and the capacitance of the other decreases. However, instead of the deflection generating portion, one may use another method to increase the capacitance of one and decrease the capacitance of the other in the first capacitor C1 and the second capacitor C2.

[0060] FIG. 8 is a diagram showing a modified example of the acceleration sensor, and shows the acceleration sensor at rest. FIG. 9 is another diagram showing a modified example of the acceleration sensor, and shows the acceleration sensor when acceleration acts. As shown in FIG. 8, by forming the first beam 20a thicker than the second beam 40a in the thickness direction of the substrate 10, the first fixed electrode 31 may be formed thicker than the first movable electrode 51 in the thickness direction of the substrate 10, and the second fixed electrode 32 may be formed thicker than the second movable electrode 52 in the thickness direction of the substrate 10.

[0061] As shown in FIG. 8, when at rest with no acceleration acting, the mass portion 16 has the surface on one side in the Z direction of the first movable electrode 51 and the second movable electrode 52 substantially at the same Z-direction position as the first main surface 10a of the substrate 10. When acceleration acting on one side in the Z direction acts, as shown in FIG. 9, the mass portion 16 is inclined with respect to the first main surface 10a of the substrate 10, and the inclination angle changes according to the acceleration.

[0062] The first movable electrode 51 is displaced to the other side in the Z direction with respect to the first fixed electrode 31, and the capacitance of the first capacitor C1 is increased. The second movable electrode 52 is displaced to one side in the Z direction with respect to the second fixed electrode 32, and the capacitance of the second capacitor C2 is decreased.

[0063] Even when an acceleration acts in the other direction in the Z direction, the mass portion 16 inclines with respect to the first main surface 10a of the substrate 10 according to the acceleration, and the inclination angle changes according to the acceleration. The acceleration sensor 1 can detect the acceleration in the Z direction by taking out, as an electric signal, the change in the capacitance of the first capacitor C1 and the second capacitor C2, in which one capacitance increases and the other capacitance decreases according to the acceleration.

[0064] In the present embodiment, the second weight portion 62 is formed to have a smaller area and a smaller mass than the first weight portion 61 in plan view. However, the mass may be made smaller than that of the first weight portion 61 by other methods, for example, by forming it thinner than the first weight portion 61 in the thickness direction of the substrate 10. The first weight portion 61 and the second weight portion 62 are formed in a substantially rectangular shape in plan view, but may be formed in other shapes.

[0065] The first beam 20 forming the first fixed electrode 31 and the second fixed electrode 32 has a first portion 21 extending in the X direction, but may be formed in other shapes. The second beam 40 forming the first movable electrode 51 and the second movable electrode 52 has a first portion 41 extending in the Y direction and a second portion 42 extending in the X direction, but may be formed in other shapes.

[0066] As described above, the acceleration sensor 1 according to the present embodiment includes a substrate 10, a support portion 13 provided on the substrate 10, a mass portion 16 movably supported by the support portion 13, the mass portion 16 having a first weight portion 61 and a second weight portion 62 having a smaller mass than the first weight portion 61, the first fixed electrode 31 and the second fixed electrode 32 of the sensor element 2 supported by the support portion 13, and the first movable electrode 51 and the second movable electrode 52 of the sensor element 2 provided on the first weight portion 61 and the second weight portion 62, respectively, and relatively movable in the thickness direction of the substrate 10 with respect to the first fixed electrode 31 and the second fixed electrode 32.

[0067] The acceleration sensor 1 includes first and second fixed electrodes 32, 32 supported by a support portion 13, and first and second movable electrodes 52, 52 provided on first and second weight portions 61, 62 of a mass portion 16 movably supported by the support portion 13. Since two capacitors C1, C2 can be formed by the first and second fixed electrodes 32, 32 and the first and second movable electrodes 52, 52 supported by one support portion 13, the influence of the substrate 10 can be suppressed, and the reliability of the sensor can be improved. Further, the first and second movable electrodes 52, 52 can be formed on one mass portion 16, and the generation of noise can be suppressed and the acceleration can be detected accurately as compared with the case where the first and second movable electrodes 52, 52 are formed separately. Further, by detecting the difference in capacitance between the two capacitors C1, C2, the sensitivity can be increased and the noise can be reduced as compared with the case of detecting the capacitance of one capacitor, and the S / N ratio (signal-to-noise ratio) can be improved.

[0068] Further, the support portion 13 is a single support portion 13 provided on the substrate 10, and the mass portion 16 is a single mass portion 16 movably supported by the support portion 13. Thereby, since a single mass portion 16 can be supported by a single support portion 13 to form two capacitors C1, C2, the difference in capacitance between the two capacitors C1, C2 can be calculated to accurately detect the acceleration.

[0069] Further, the first weight portion 61 and the second weight portion 62 are supported by the support portion 13 via spring portions 45. Thereby, the first movable electrode 51 and the second movable electrode 52 provided on the first weight portion 61 and the second weight portion 62 can be relatively moved with respect to the first fixed electrode 31 and the second fixed electrode 32, respectively.

[0070] Further, the first fixed electrode 31 and the second fixed electrode 32 are formed in a comb shape, and the first movable electrode 51 and the second movable electrode 52 are formed in a comb shape. Thereby, by detecting the capacitance between the first and second fixed electrodes 32, 32 formed in a comb shape and the first and second movable electrodes 52, 52, the acceleration in the thickness direction of the substrate 10 can be detected.

[0071] Further, the substrate 10 has a cavity 12 on its surface 10a where a part of the cavity 12 is exposed, and the first fixed electrode 31, the second fixed electrode 32, the first movable electrode 51, the second movable electrode 52, the first weight portion 61, and the second weight portion 62 are disposed within the cavity 12. Thereby, the first and second fixed electrodes 32, 32, the first and second movable electrodes 52, 52, and the first and second weight portions 61, 62 can be disposed in a floating state within the cavity 12 of the substrate 10, and the acceleration sensor 1 can be configured compactly.

[0072] Also, the first fixed electrode 31 and the first movable electrode 51 are formed symmetrically with respect to the second fixed electrode 32 and the second movable electrode 52 in a plan view, respectively. Thereby, acceleration can be accurately detected using the first fixed electrode 31 and the first movable electrode 51 and the second fixed electrode 32 and the second movable electrode 52 that are formed symmetrically with the support portion 13 interposed therebetween.

[0073] Also, the second weight portion 62 can be formed to have a smaller area than the first weight portion 61 in a plan view. Thereby, the mass of the second weight portion 62 can be made smaller relatively easily than the first weight portion 61, and when an acceleration in the thickness direction of the substrate 10 acts on the acceleration sensor, the first movable electrode 51 and the second movable electrode 52 can be tilted to detect the acceleration.

[0074] Also, the first fixed electrode 31 and the second fixed electrode 32 are respectively formed on the first beam 20 supported by the support portion 13, the first weight portion 61 and the second weight portion 62 are respectively formed on the second beam 40 supported by the support portion 13, and a spring portion 45 is formed on the second beam 40. Thereby, since the first and second movable electrodes 52, 52 formed on the first and second weight portions 62 and the first and second fixed electrodes 32, 32 are formed on the first beam 20 and the second beam 40, it is possible to suppress an adverse effect on the capacitance between the fixed electrodes 31, 32 and the movable electrodes 51, 52 even when stress occurs in the package.

[0075] Further, a separation portion 14 that electrically separates the first fixed electrode 31 and the second fixed electrode 32 from the support portion 13 is formed on the first beam 20, and a separation portion 14 that electrically separates the first movable electrode 51 and the second movable electrode 52 from the support portion 13 is formed on the second beam 40. Thereby, the first and second beams 20 and 40 can be electrically separated while being mechanically coupled to the support portion 13 by the separation portion 14, and the first and second fixed electrodes 32 and 32 and the first and second movable electrodes 52 and 52 can be formed.

[0076] Further, the substrate 10 is a silicon substrate, and the separation portion 14 has silicon oxide. Thereby, the separation portion 14 can be formed relatively easily by forming a trench in a portion of the silicon substrate corresponding to the separation portion 14 and forming an oxide film such as a thermal oxide film so as to fill the trench.

[0077] The present disclosure is not limited to the illustrated embodiments, and various improvements and design changes are possible without departing from the gist of the present disclosure.

[0078] [Appendix 1] A substrate, A support portion provided on the substrate, A mass portion movably supported by the support portion, the mass portion having a first weight portion and a second weight portion having a mass smaller than that of the first weight portion, A first fixed electrode and a second fixed electrode of a sensor element supported by the support portion, A first movable electrode and a second movable electrode of a sensor element respectively provided on the first weight portion and the second weight portion and relatively movable in the thickness direction of the substrate with respect to the first fixed electrode and the second fixed electrode, An acceleration sensor. [Appendix 2] The support portion is a single support portion provided on the substrate, The mass portion is a single mass portion movably supported by the support portion, The acceleration sensor according to Appendix 1. [Appendix 3] The first hammer portion and the second hammer portion are supported by the support portion via a spring portion. The acceleration sensor according to appended claim 1 or appended claim 2. [Appended claim 4] The first fixed electrode and the second fixed electrode are formed in a comb shape. The first movable electrode and the second movable electrode are formed in a comb shape. The acceleration sensor according to any one of appended claims 1 to 3. [Appended claim 5] The substrate has a cavity on its surface where a part of the cavity is exposed. The first fixed electrode, the second fixed electrode, the first movable electrode, the second movable electrode, the first hammer portion, and the second hammer portion are disposed in the cavity. The acceleration sensor according to any one of appended claims 1 to 4. [Appended claim 6] The first fixed electrode and the first movable electrode are symmetrically formed with respect to the second fixed electrode and the second movable electrode across the support portion in a plan view. The acceleration sensor according to any one of appended claims 1 to 5. [Appended claim 7] The second hammer portion is formed with a smaller area than the first hammer portion in a plan view. The acceleration sensor according to any one of appended claims 1 to 6. [Appended claim 8] The first fixed electrode and the second fixed electrode are respectively formed on a first beam supported by the support portion. The first hammer portion and the second hammer portion are respectively formed on a second beam supported by the support portion. A spring portion is formed on the second beam. The acceleration sensor according to any one of appended claims 1 to 7. [Appended claim 9] A separation portion for electrically separating the first fixed electrode and the second fixed electrode from the support portion is formed on the first beam. A separation portion for electrically separating the first movable electrode and the second movable electrode from the support portion is formed on the second beam. The acceleration sensor described in Supplementary Note 8. [Supplementary Note 10] The substrate is a silicon substrate, The separation part has silicon oxide. The acceleration sensor described in Supplementary Note 9.

Explanation of Reference Signs

[0079] 1,101 Acceleration sensor 10 Substrate 12 Cavity 13,113 Support part 14 Separation part 16 Mass part 20,120 First beam 31,131 First fixed electrode 32,132 Second fixed electrode 40,140 Second beam 45,145 Spring part 51,151 First movable electrode 52,152 Second movable electrode 61 First weight part 62 Second weight part

Claims

1. A substrate; A support portion provided on the substrate; a mass portion movably supported on the support portion, the mass portion having a first weight portion and a second weight portion having a mass smaller than that of the first weight portion; a first fixed electrode and a second fixed electrode of a sensor element supported by the support; a first movable electrode and a second movable electrode of a sensor element provided on the first weight portion and the second weight portion, respectively, and movable in a thickness direction of a substrate relative to the first fixed electrode and the second fixed electrode, respectively. Acceleration sensor.

2. the support portion is a single support portion provided on the substrate, The mass is a single mass movably supported on a support.

2. The acceleration sensor according to claim 1.

3. The first weight portion and the second weight portion are supported by the support portion via a spring portion.

2. The acceleration sensor according to claim 1.

4. The first fixed electrode and the second fixed electrode are formed in a comb shape, The first movable electrode and the second movable electrode are formed in a comb shape.

2. The acceleration sensor according to claim 1.

5. the substrate has a cavity, a part of which is exposed on a surface; the first fixed electrode, the second fixed electrode, the first movable electrode, the second movable electrode, the first weight portion, and the second weight portion are disposed in a cavity.

2. The acceleration sensor according to claim 1.

6. the first fixed electrode and the first movable electrode are formed symmetrically with respect to the second fixed electrode and the second movable electrode, respectively, with the support portion interposed therebetween in a plan view; 2. The acceleration sensor according to claim 1.

7. The second weight portion is formed to have a smaller area in a plan view than the first weight portion.

2. The acceleration sensor according to claim 1.

8. the first fixed electrode and the second fixed electrode are each formed on a first beam supported by the support portion; the first weight portion and the second weight portion are each formed on a second beam supported by the support portion; The second beam is formed with a spring portion.

2. The acceleration sensor according to claim 1.

9. a separation portion is formed in the first beam to electrically separate the first fixed electrode and the second fixed electrode from the support portion, a separation portion is formed in the second beam to electrically separate the first movable electrode and the second movable electrode from the support portion, 9. The acceleration sensor according to claim 8.

10. the substrate is a silicon substrate, The isolation portion includes silicon oxide.

10. The acceleration sensor according to claim 9.

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