MEMS acceleration sensor

Abstract

To provide a MEMS acceleration sensor capable of preventing a movable electrode from abutting on a fixed electrode without reducing detection sensitivity.SOLUTION: The MEMS acceleration sensor 1 includes a substrate 10 having a cavity 11, fixed electrodes 31a, 31b, 32a, 32b disposed in the cavity 11 and fixed to the substrate 10, movable electrodes 31a, 31b disposed in parallel and opposite to the fixed electrodes 32a, 32b,, and an elastic member 50 fixed to the substrate 10 and elastically supporting the movable electrodes 41a, movably in a detection direction orthogonal to the movable electrodes,. 41b 41b 41a 41a 41b, the elastic member 50 includes a spring portion 53 having a predetermined spring constant K1, and a spring constant changing portion 54 that changes the predetermined spring constant W3 when the spring portion 53 is deformed by a predetermined deformation amount K1 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a MEMS acceleration sensor. [Background technology]

[0002] MEMS (Micro Electro Mechanical System) acceleration sensors manufactured using semiconductor microfabrication technology are known. For example, Patent Document 1 discloses a capacitance-type MEMS acceleration sensor as an example of a MEMS acceleration sensor. The capacitance-type MEMS acceleration sensor includes fixed and movable electrodes that are interdigitated with each other and formed on a semiconductor substrate, and is configured to detect acceleration by detecting changes in capacitance between the fixed and movable electrodes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2024-42442

[0004] [overview] The MEMS acceleration sensor described in Patent Document 1 has a spring as an elastic member that supports a movable electrode so that it can move in the detection direction relative to fixed electrodes aligned in the detection direction. To improve the sensitivity of this type of MEMS acceleration sensor, it is preferable to set the spring constant of the elastic member low. However, if the spring constant of the elastic member is set too low, the elastic restoring force may be insufficient, causing the movable electrode to come into contact with the fixed electrode and sticking together due to intermolecular forces (van der Waals forces).

[0005] An object of the present disclosure is to provide a MEMS acceleration sensor that can prevent the movable electrode from coming into contact with the fixed electrode without reducing detection sensitivity.

[0006] The present disclosure provides: a substrate having a cavity; a fixed electrode disposed in the cavity and fixed to the substrate; a movable electrode arranged parallel to and facing the fixed electrode; an elastic member fixed to the substrate and elastically supporting the movable electrode element so as to be movable in a detection direction perpendicular to the movable electrode element; The elastic member has a spring portion having a predetermined spring constant and a spring constant changing portion that increases the predetermined spring constant when the elastic member is deformed by a predetermined deformation amount or more. We provide MEMS acceleration sensors. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic plan view showing a MEMS acceleration sensor according to the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is an enlarged view of a main part of the portion indicated by the arrow IV in FIG. [Figure 5] FIG. 5 is a schematic plan view showing a state in which acceleration is applied to the MEMS acceleration sensor. [Figure 6A] FIG. 6A is a schematic plan view showing a first modified example of the elastic member of the MEMS acceleration sensor. [Figure 6B] FIG. 6B is a schematic plan view showing a second modified example of the elastic member of the MEMS acceleration sensor. [Figure 7] FIG. 7 is a schematic plan view showing a state in which the movable electrode of the MEMS acceleration sensor to which the elastic members of the first and second modifications are applied has moved to one side in the X direction. [Figure 8] FIG. 8 is a schematic plan view showing a state in which the movable electrode of the MEMS acceleration sensor to which the elastic members of the first and second modifications are applied has moved to the other side in the X direction.

[0008] [Detailed explanation] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the following description is merely exemplary in nature and is not intended to limit the present disclosure, its applications, or its uses.

[0009] 1 is a plan view schematically showing a MEMS acceleration sensor 1 according to an embodiment of the present disclosure. The MEMS acceleration sensor 1 is a capacitance-type acceleration sensor having a capacitance-type acceleration sensor element (hereinafter also referred to as a sensor element) 2. The MEMS acceleration sensor 1 includes a substrate 10 having a cavity 11 in which the sensor element 2 is disposed.

[0010] In the following, a predetermined direction along the surface of the substrate 10 is defined as the X direction, a direction perpendicular to the X direction is defined as the Y direction, and a thickness direction of the substrate 10 perpendicular to the X and Y directions is defined as the Z direction. Wiring formed on the substrate 10 is not shown in FIG.

[0011] The sensor element 2 is a sensor element 2 that detects acceleration acting in the X direction. However, the sensor element 2 is not limited to this, and may be a sensor element that detects acceleration acting in the Y direction or a sensor element that detects acceleration acting in the Z direction.

[0012] A plurality of pads 3 are provided on the substrate 10, spaced apart from one another in the X direction. The pads 3 are connected to external electronic components, etc. The pads 3 input electrical signals to the sensor element 2 and output electrical signals from the sensor element 2. In FIG. 1, wiring electrically connecting the pads 3 and the sensor element 2 is omitted.

[0013] As shown in FIG. 1, the MEMS acceleration sensor 1 of this embodiment includes a substrate 10 having a cavity 11, a fixed electrode 30 disposed in the cavity 11 and fixed to the substrate 10, a movable electrode 40 disposed opposite the fixed electrode 30, and an elastic member 50 fixed to the substrate 10 and elastically supporting the movable electrode 40.

[0014] For the sake of convenience, FIG. 1 shows only two pairs of fixed electrodes 31a, 31b and two pairs of movable electrodes 41a, 41b that constitute the fixed electrode 30 and the movable electrode 40, but this is not limited to this, and one or more pairs of fixed electrodes and movable electrodes may be arranged in the cavity 11 of the substrate 10.

[0015] As shown in Fig. 1, substrate 10 has a rectangular shape in plan view, with two sides extending in the X direction and two sides extending in the Y direction. As shown in Fig. 2, substrate 10 has a first main surface 10a, which is the front surface, and a second main surface 10b, which is the back surface opposite to first main surface 10a. Substrate 10 is made of a conductive single-crystal silicon substrate that has been doped with impurities to provide conductivity and has a resistivity of, for example, 1 Ω·m to 5 Ω·m. First main surface 10a of substrate 10 is formed to have a surface roughness Sa (arithmetic mean) of 1 nm or less.

[0016] 1, the substrate 10 has a cavity 11 at the center, part of which is exposed to the surface in correspondence with the sensor element 2. The cavity 11 is recessed from the surface in a thickness direction Z of the substrate 10 in a substantially rectangular parallelepiped shape, and has a bottom wall 11a and a side wall 11b extending from the periphery of the bottom wall 11a in the thickness direction Z of the substrate 10.

[0017] The substrate 10 has a support portion 15 that supports the fixed electrode 30, the movable electrode 40, and the elastic member 50. The fixed electrode 30, the movable electrode 40, and the elastic member 50 are arranged in a cavity 11 of the substrate 10 and are supported by the support portion 15 in a floating state within the cavity 11. The support portion 15 is formed in a ring shape that is approximately quadrangular in plan view so as to surround the periphery of the sensor element 2. The inner peripheral surface of the support portion 15 forms a side wall portion 11b of the cavity 11.

[0018] 1 , fixed electrode 30 has a pair of first fixed electrodes 31 located on one side in the Y direction of substrate 10 and extending in the X direction, and a pair of second fixed electrodes 32 located on the other side in the Y direction. The pair of first and second fixed electrodes 31, 32 has first fixed electrode elements 31a, 32a located on one side in the X direction and extending in the Y direction, and second fixed electrode elements 31b, 32b located on the other side in the X direction and extending in the Y direction. The outer ends in the Y direction of first and second fixed electrode elements 31a, 31b, 32a, 32b are supported by support portion 15 of substrate 10.

[0019] As shown in FIG. 2, the first and second fixed electrodes 31a, 32a, 31b, 32b are spaced apart in the Z direction from the bottom wall portion 11a of the cavity 11, and although not shown, are formed, for example, of an epitaxial growth layer stacked on a fixed electrode support portion formed by a substrate 10.

[0020] 1, movable electrode 40 has a weight portion 45 extending in the X direction in the center of substrate 10 in the Y direction, and a pair of movable electrode elements 41 in the X direction extending from weight portion 45 on both sides in the Y direction. Elastic members 50 are connected to both ends of weight portion 45 in the X direction. One end of elastic member 51 in the X direction, which is arranged on one side of weight portion 45 in the X direction, and the other end of elastic member 52, which is arranged on the other side of weight portion 45 in the X direction, are supported by support portion 15.

[0021] As shown in Figures 2 and 3, the movable electrode element 41, the weight portion 45 and the elastic member 50 are spaced apart in the Z direction from the bottom wall portion 11a of the cavity 11, and although not shown, are formed, for example, of an epitaxial growth layer stacked on a movable electrode support portion formed by a substrate 10.

[0022] 1 and 2, the movable electrode 41 has a first movable electrode 41a that faces the first fixed electrode 31a from the other side in the X direction, and a second movable electrode 41b that faces the second fixed electrode 32a from one side in the X direction. The first fixed electrode 31a and the opposing first movable electrode 41a form a first capacitor C1. The second fixed electrode 32a and the opposing second movable electrode 41b form a second capacitor C2. In a reference state in which no acceleration is applied to the MEMS acceleration sensor 1, the first and second capacitors C1 and C2 have the same inter-electrode distance W0, e.g., 2.6 μm or more and less than 3.5 μm.

[0023] Although details are omitted, an insulating layer and a contact penetrating the insulating layer are formed on the upper side in the Z direction (opposite the bottom wall portion 11a side of the substrate 10) of the fixed electrode 30 and the movable electrode 40. The contact is connected to the electrode pad 3 via a wiring layer (not shown).

[0024] 1, elastic member 50 is fixed to support portion 15 of substrate 10 and elastically supports pair of movable electrodes 41a, 41b so as to be movable in the detection direction. Elastic member 50 is disposed on both sides of pair of movable electrodes 40 in the X direction. More specifically, elastic member 50 has first elastic member 51 disposed on one side of weight portion 45 in the X direction and second elastic member 52 disposed on the other side.

[0025] As shown in Figures 3 and 4, each elastic member 51, 52 has a spring portion 53 having a predetermined spring constant K1, a spring constant changing portion 54 that changes the predetermined spring constant K1 when the spring portion 53 is deformed by a predetermined deformation amount W3 or more, a first connection portion 55 that connects the spring portion 53 to the weight portion 45 of the movable electrode 40, and a second connection portion 56 that connects the spring portion 53 to the support portion 15.

[0026] The spring portion 53 has only to have a curved portion 53b that bulges in a direction (Y direction) perpendicular to the detection direction (X direction), and in this embodiment is annular. The predetermined spring constant K1 of the spring portion 53 is set to, for example, 0.5 N / m or more and less than 1.5 N / m. The spring portion 53 is formed of, for example, a ring spring having a diameter of 70 μm or more and 100 μm or less.

[0027] 4, the spring constant change portion 54 has a plurality of protruding portions 54a that protrude from the inner circumferential surface 53a of the spring portion 53 toward the center of curvature O1 and are spaced a predetermined distance d0 apart from one another. The plurality of protruding portions 54a are arranged at equal intervals in the circumferential direction. The plurality of protruding portions 54a may be arranged in a portion where the curvature of the spring portion 53 increases when the spring portion 53 is deformed (tensioned and / or compressed) compared to the curvature before deformation (reference state) of the spring portion 53.

[0028] The portion where the curvature increases when the spring portion 53 is tensioned and / or compressed is the portion in the detection direction (X direction) and / or the direction perpendicular to the detection direction (Y direction) in which the movable electrode 40 moves relative to the fixed electrode 30, as shown in FIG. 5 (see FIG. 5).

[0029] 4, in this embodiment, the multiple protrusions 54a of the first elastic member 51 are arranged in a portion where the spring portion 53 is compressed and deformed to increase its curvature when the movable electrode 40 moves to one side in the X direction. The multiple protrusions 54a of the second elastic member 52 are arranged in a portion where the spring portion 53 is compressed and deformed to increase its curvature when the movable electrode 40 moves to the other side in the X direction. In other words, the multiple protrusions 54a are arranged on one side and the other side in the Y direction of each spring portion 53. In this embodiment, the multiple protrusions 54a are arranged in a region of ¼ of the entire circumference on each side in the Y direction of each spring portion 53.

[0030] The amount of protrusion L0 of each of the multiple protrusions 54a from the inner circumferential surface 53a of the spring portion 53 is preferably 1.2 μm or more due to manufacturing requirements. Furthermore, to prevent the protrusions 54a from contacting each other, the amount of protrusion L0 is preferably less than 30% of the radius of the spring portion 53. In this embodiment, for example, the amount of protrusion L0 is set to 1.2 μm or more and less than 15 μm. The separation distance d0 between the tips of adjacent protrusions 54a among the multiple protrusions 54a may be set so that the protrusions 54a come into contact with each other before the movable electrode elements 41a, 41b come into contact with the fixed electrode elements 31a, 31b, 32a, and 32b when the movable electrode 40 moves relative to the fixed electrode 30 (during acceleration detection).

[0031] The distance d0 between the tips of adjacent protrusions 54a among the multiple protrusions 54a is set to be less than the inter-electrode distance W0 (see FIG. 2) between the fixed electrodes 31a, 31b, 32a, 32b and the movable electrodes 41a, 41b in the reference state.

[0032] The ratio of the distance d0 between the tips of adjacent protrusions 54a among the multiple protrusions 54a to the inter-electrode distance W0 (see FIG. 2) in the reference state between the fixed electrodes 31a, 31b, 32a, and 32b and the movable electrodes 41a and 41b is preferably set to 50% or more and less than 90%. When the ratio of the distance d0 to the inter-electrode distance W0 is 90% or more, it is less likely to hinder the movement of the movable electrodes 41a and 41b when detecting acceleration, and when it is less than 50%, it is easier to prevent the movable electrodes 41a and 41b from coming into contact with the fixed electrodes 31a, 31b, 32a, and 32b. In other words, if the ratio of the separation distance d0 to the inter-electrode distance W0 is less than 50%, the protrusions 54a contact each other too quickly, excessively restricting the movement of the movable electrodes 41a, 41b. If the ratio is 90% or more, the contact between the protrusions 54a is delayed, making it difficult to prevent the movable electrodes 41a, 41b from contacting the fixed electrodes 31a, 31b, 32a, and 32b. Furthermore, if the ratio of the separation distance d0 to the inter-electrode distance W0 is 50% or more, problems such as difficulty in obtaining the desired shape of the protrusions 54a during manufacturing due to factors such as difficulty in introducing an etchant (a chemical solution or gas for etching a material) can be prevented. As a result, the protrusions 54a are prevented from contacting each other earlier than expected (the protrusions 54a contact each other, suppressing compressive deformation of the spring portion 53, i.e., the stopper is activated), and a decrease in detection sensitivity can be suppressed.

[0033] In this embodiment, the ratio of the distance d0 between the tips of adjacent protrusions 54a among the plurality of protrusions 54a to the inter-electrode distance W0 is set to 50%, for example, between 1.3 μm and 3.5 μm.

[0034] 5, when movable electrode 40 moves in the X direction, first elastic member 51 elastically deforms circular spring portion 53 into an elliptical shape having a major axis in the Y direction between support portion 15 and weight portion 45. In other words, the curvature of spring portion 53 increases on both sides in the Y direction.

[0035] When the curvature of the Y-direction portion of the spring portion 53 increases, the adjacent protrusions 54a arranged on one side and the other side in the Y direction come into contact with each other, thereby suppressing or stopping the elastic deformation of the spring portion 53. In other words, the multiple protrusions 54a function as spring constant changing portions 54 that increase the predetermined spring constant K1 of the spring portion 53 to infinity.

[0036] The elastic member 50 is configured such that when the spring portion 53 is deformed by a predetermined deformation amount W3 or more, the spring constant of the spring portion 53 approaches infinity, thereby suppressing movement of the spring portion 53 and the movable electrode 40 connected to the spring portion 53.

[0037] The ratio of the distance d0 between the tips of adjacent protrusions 54a among the multiple protrusions 54a to the amount of deformation of spring portion 53 is set to be approximately the same. In this embodiment, the amount of deformation of spring portion 53 is the difference in the distance in the X direction between the end of spring portion 53 on one side in the X direction in the reference state and the end of spring portion 53 on one side in the X direction after deformation.

[0038] When acceleration in the X direction acts on the MEMS acceleration sensor 1, the weight 45 supported by the two elastic members 50 vibrates in the X direction. As a result, the movable electrode 41 extending in the Y direction from the weight 45 also vibrates in the X direction between the adjacent pairs of fixed electrodes 31a, 31b, 32a, 32b.

[0039] When the movable electrode 40 moves to one side in the X direction, the first movable electrode 41a moves to a position closer to the adjacent first fixed electrode 31a, and the second movable electrode 41b moves to a position away from the adjacent second fixed electrode 31b. On the other hand, when the movable electrode 40 moves to the other side in the X direction, the first movable electrode 41a moves to a position away from the adjacent first fixed electrode 31a, and the second movable electrode 41b moves to a position closer to the adjacent second fixed electrode 31b. This movement of the movable electrode 40 relative to the fixed electrode 30 changes the capacitances of the first capacitor C1 and the second capacitor C2.

[0040] By detecting the change in capacitance of the first capacitor C1 and the second capacitor C2 in the MEMS acceleration sensor 1 via the electrode pad 3, the acceleration acting in the X direction can be measured.

[0041] 5, when weight 45 and movable electrode 40 move to one side in the X direction, first elastic member 51 elastically deforms circular spring portion 53 into an elliptical shape having a major axis in the Y direction between support portion 15 and weight 45. In other words, the curvature of spring portion 53 increases on both sides in the Y direction.

[0042] At this time, second elastic member 52 elastically deforms circular spring portion 53 into an elliptical shape having a major axis in the X direction between support portion 15 and weight portion 45. In other words, the curvature of spring portion 53 on one side and the other side in the Y direction decreases.

[0043] When the curvature of the Y-direction portion of the spring portion 53 of the first elastic member 51 increases, adjacent protrusions 54a arranged on one side and the other side in the Y direction come into contact with each other, thereby suppressing or stopping elastic deformation of the spring portion 53. In other words, the protrusions 54a of the first elastic member 51 function as spring constant changing portions 54 that increase the predetermined spring constant K1 of the spring portion 53 to infinity.

[0044] On the other hand, although not shown, when weight 45 and movable electrode 40 move to the other side in the X direction, circular spring portion 53 of second elastic member 52 elastically deforms into an ellipse having a major axis in the Y direction between support portion 15 and weight 45. In other words, the curvature of spring portion 53 increases on both sides in the Y direction.

[0045] At this time, first elastic member 51 elastically deforms circular spring portion 53 into an elliptical shape having a major axis in the X direction between support portion 15 and weight portion 45. In other words, the curvature of spring portion 53 on one side and the other side in the Y direction decreases.

[0046] When the curvature of the Y-direction portion of the spring portion 53 of the second elastic member 52 increases, adjacent protrusions 54a arranged on one side and the other side in the Y direction come into contact with each other, thereby suppressing or stopping elastic deformation of the spring portion 53. In other words, the multiple protrusions 54a of the second elastic member 52 function as spring constant changing portions 54 that increase the predetermined spring constant K1 of the spring portion 53 to infinity.

[0047] The MEMS acceleration sensor 1 according to the above embodiment provides the following advantageous effects.

[0048] A MEMS acceleration sensor 1 according to one embodiment of the present disclosure includes a substrate 10 having a cavity 11, fixed electrodes 31a, 31b, 32a, and 32b disposed in the cavity 11 and fixed to the substrate 10, movable electrodes 41a and 41b disposed parallel to and opposite the fixed electrodes 31a, 31b, 32a, and 32b, and an elastic member 50 fixed to the substrate 10 and elastically supporting the movable electrodes 41a and 41b so that they can move in a detection direction (X direction) perpendicular to the movable electrodes 41a and 41b. The elastic member 50 includes a spring portion 53 having a predetermined spring constant K1 and a spring constant changing portion 54 that changes the predetermined spring constant K1 when the elastic member 50 is deformed by a predetermined amount or more.

[0049] According to this configuration, the spring portion 53 is set to a predetermined spring constant K1 suited to the detection sensitivity, and when the spring portion 53 is deformed by a predetermined amount or more, the spring constant of the spring portion is increased by the spring constant changing portion 54, thereby preventing the movable electrodes 41a, 41b from contacting the fixed electrodes 31a, 31b, 32a, and 32b. This prevents the movable electrodes 41a, 41b from contacting the fixed electrodes 31a, 31b, 32a, and 32b without reducing the detection sensitivity of the MEMS acceleration sensor 1. In other words, a restoring force can be set to prevent the movable electrodes 41a, 41b from contacting the fixed electrodes 31a, 31b, 32a, and 32b without reducing the degree of freedom in designing the detection sensitivity of the MEMS acceleration sensor 1.

[0050] The spring portion 53 has a curved portion 53b that bulges at least in a direction perpendicular to the detection direction, and the spring constant changing portion 54 may have multiple protrusions 54a that protrude from the spring portion 53 toward the center of curvature O1 and are spaced apart from each other by a predetermined distance d0.

[0051] According to this configuration, when the curvature of the spring portion 53 increases as the spring portion 53 deforms in the detection direction, the adjacent protrusions 54a come into contact with each other, thereby suppressing elastic deformation of the spring portion 53. In other words, when the protrusions 54a come into contact with each other, the predetermined spring constant K1 of the spring portion 53 can be increased.

[0052] The plurality of protrusions 54a may be arranged at a portion of the spring portion 53 where the curvature increases when compressed.

[0053] According to this configuration, for example, compared to when the protrusion 54a is provided around the entire periphery of the spring portion 53, it is possible to suppress an increase in the number of processing steps for the protrusion 54a.

[0054] The elastic members 50 may be disposed on both sides of the movable electrodes 41a and 41b in the detection direction (X direction).

[0055] This configuration can prevent the movable electrodes 41a and 41b from coming into contact with the fixed electrodes 31a, 31b, 32a, and 32b when moving to one side and the other side in the X direction, while suppressing an increase in the number of processing steps for the protrusion 54a.

[0056] The distance d0 between the tips of adjacent protrusions 54a among the plurality of protrusions 54a may be set to be less than the inter-electrode distance W0 between the fixed electrodes 31a, 31b, 32a, 32b and the movable electrodes 41a, 41b in the reference state.

[0057] According to this configuration, the separation distance d0 is set to be less than the inter-electrode distance W0, so that the movable electrodes 41a and 41b can be reliably prevented from coming into contact with the fixed electrodes 31a, 31b, 32a, and 32b.

[0058] The spring constant changing portion 54 may be set so that the spring constant of the spring portion 53 becomes infinite.

[0059] According to this configuration, the spring constant change portion 54 can reliably prevent the spring portion 53 from being deformed beyond the predetermined deformation amount W3.

[0060] In this embodiment, the elastic member 50 has been described as having a configuration in which multiple protrusions 4a are arranged on one side and the other side of the spring portion 53 in the Y direction, but this is not limited to this. As in the first modified example shown in Figure 6A, the elastic member 150 may have multiple protrusions 154a arranged around the entire circumference of the spring portion 153.

[0061] According to this configuration, even if the elastic member 150 is arranged only on one side of the movable electrodes 41a, 41b in the detection direction (X direction), as shown in Figures 7 and 8, it is possible to prevent the movable electrodes 41a, 41b from contacting the fixed electrodes 31a, 31b, 32a, 32b when they move to one side and the other side in the X direction.

[0062] More specifically, as shown in FIG. 7, when the weight portion 45 and the movable electrodes 41a, 41b move to one side in the X direction, the circular spring portion 153 of the elastic member 151 elastically deforms into an ellipse having a major axis in the Y direction between the support portion 15 and the weight portion 45, and the curvature of the portions of the spring portion 153 on one side and the other side in the Y direction increases.

[0063] When the spring portion 153 of the elastic member 151 is deformed by a predetermined deformation amount W3 or more, the curvature of the Y-direction portion of the spring portion 153 increases, and the adjacent protrusions 154a arranged on one side and the other side in the Y direction come into contact with each other. This suppresses or stops the elastic deformation of the spring portion 153, and the multiple protrusions 154a arranged on one side and the other side in the Y direction function as spring constant changing portions 154 that increase the predetermined spring constant K1 of the spring portion 153 to infinity.

[0064] On the other hand, as shown in FIG. 8, when weight portion 45 and movable electrodes 41a, 41b move to the other side in the X direction, circular spring portion 153 of elastic member 151 elastically deforms into an ellipse having a major axis in the X direction between support portion 15 and weight portion 45, and the curvature of spring portion 153 on one side and the other side in the X direction increases.

[0065] When the spring portion 153 of the elastic member 151 is deformed by a predetermined deformation amount W4 or more, the curvature of the X-direction portion of the spring portion 153 increases, and the adjacent protrusions 154a arranged on one side and the other side in the X direction come into contact with each other. This suppresses or stops the elastic deformation of the spring portion 153, and the multiple protrusions 154a arranged on one side and the other side in the X direction function as spring constant changing portions 154 that increase the predetermined spring constant K1 of the spring portion 153 to infinity.

[0066] Here, the predetermined deformation amount W4 of the spring portion 153 may be the difference between the diameter D1 of the spring portion 153 in the reference state shown by the two-dot chain line in Figure 8 and the length D2 of the minor axis of the spring portion 153 after deformation.

[0067] In the present embodiment, the elastic member 50 has been described as having a configuration in which a plurality of protrusions 4a are arranged on one side and the other side of the spring portion 53 in the Y direction, but the present invention is not limited to this. For example, as in a second modified example shown in Fig. 6(b), a plurality of protrusions 254a may be arranged on the elastic member 250 in a portion where the curvature of the spring portion 253 increases during tension and compression (deformation), that is, on one side and the other side of the spring portion 253 in the X direction in addition to one side and the other side in the Y direction.

[0068] According to this configuration, as shown in FIGS. 7 and 8, even if the elastic member 250 is arranged only on one side of the movable electrodes 41a, 41b in the detection direction (X direction), as in the first modified example, it is possible to prevent the movable electrodes 41a, 41b from contacting the fixed electrodes 31a, 31b, 32a, 32b when they move to one side and the other side in the X direction.

[0069] In this embodiment, the elastic member 50 is described as being arranged on both sides of the movable electrodes 41a, 41b in the X direction, but this is not limited to this. As shown in Figures 7 and 8, the elastic member 150 may be arranged on one side or the other side of the detection direction of the movable electrodes 41a, 41b.

[0070] This configuration makes it easier to reduce the size of the MEMS acceleration sensor 1 and the number of components compared to when the electrodes are disposed on both sides of the movable electrodes 41a and 41b in the X direction.

[0071] In this embodiment, an example in which the spring portion 53 is configured in a circular ring shape has been described, but this is not limited to this, and the spring portion 53 only needs to have a curved portion that bulges out in at least the detection direction, and may be, for example, semicircular, semi-elliptical, or U-shaped.

[0072] In this embodiment, an example has been described in which one elastic member 50 is provided on each side of the movable electrode 40 in the X direction, but this is not limited to this, and multiple elastic members 50 may be provided on one side and / or the other side of the detection direction (X direction).

[0073] In this embodiment, the spring constant change portion 54 is configured to make the predetermined spring constant K1 of the spring portion 53 infinite, but the present invention is not limited to this and may have any configuration that increases the predetermined spring constant K1. For example, the spring constant change portion 54 may be elastically deformable after the protrusions 54a come into contact with each other. The spring constant of the elastic member 50 may be set to a value that can prevent the movable electrode from coming into contact with the fixed electrode when the spring portion 53 is deformed by a predetermined deformation amount W3 or more, for example, 1.5 N / m or more.

[0074] The present disclosure is not limited to the configurations described in the above embodiments, and various modifications are possible.

[0075] [Note] The present disclosure includes the following aspects.

[0076] [Aspect 1] a substrate having a cavity; a fixed electrode disposed in the cavity and fixed to the substrate; a movable electrode arranged parallel to and facing the fixed electrode; an elastic member fixed to the substrate and elastically supporting the movable electrode so as to be movable in a detection direction perpendicular to the movable electrode element; The elastic member has a spring portion having a predetermined spring constant, and a spring constant changing portion that changes the predetermined spring constant when the spring portion is deformed by a predetermined amount or more. MEMS acceleration sensor.

[0077] [Aspect 2] the spring portion has a curved portion that bulges in at least a direction perpendicular to the detection direction, The spring constant change portion has a plurality of protruding portions that protrude from the spring portion toward the center of curvature and are spaced apart by a predetermined distance. The MEMS acceleration sensor according to embodiment 1.

[0078] [Aspect 3] The spring portion is an annular member, The plurality of protrusions are arranged around the entire circumference of the annular member. The MEMS acceleration sensor according to embodiment 2.

[0079] [Aspect 4] The plurality of protrusions are disposed at a portion where the spring portion has a high curvature when tensioned and compressed. The MEMS acceleration sensor according to embodiment 2.

[0080] [Aspect 5] The elastic member is disposed on one side or the other side of the movable electrode in the detection direction. The MEMS acceleration sensor according to any one of the first to fourth aspects.

[0081] [Aspect 6] The plurality of protrusions are disposed at a portion of the spring portion where the curvature increases when the spring portion is compressed. The MEMS acceleration sensor according to any one of aspects 2 to 5.

[0082] [Aspect 7] The elastic members are disposed on both sides of the movable electrode element in the detection direction. 7. The MEMS acceleration sensor according to claim 6.

[0083] [Aspect 8] The distance between the tip ends of adjacent protrusions among the plurality of protrusions is set to be less than the inter-electrode distance between the fixed electrode and the movable electrode in a reference state. The MEMS acceleration sensor according to any one of aspects 2 to 7.

[0084] [Aspect 9] The spring constant changing portion is set so that the spring constant of the spring portion becomes infinite. The MEMS acceleration sensor according to any one of the first to eighth aspects. [Explanation of symbols]

[0085] 1 MEMS acceleration sensor 10 Substrate 11 Cavity 31a 1st fixed electrode (fixed electrode) 31b 1st fixed electrode (fixed electrode) 32a 2nd fixed electrode (fixed electrode) 32b 2nd fixed electrode (fixed electrode) 41a First movable electrode (movable electrode) 41b Second movable electrode (movable electrode) 50 Elastic member 53 Spring part 53b Curved section 54 Spring constant change part 54a Protrusion d0 Separation distance K1: Predetermined spring constant O1 center of curvature W0 Electrode distance

Claims

1. a substrate having a cavity; a fixed electrode disposed in the cavity and fixed to the substrate; a movable electrode arranged parallel to and facing the pair of fixed electrodes; an elastic member fixed to the substrate and elastically supporting the movable electrode element so as to be movable in a detection direction perpendicular to the movable electrode element; The elastic member has a spring portion having a predetermined spring constant, and a spring constant changing portion that changes the predetermined spring constant when the spring portion is deformed by a predetermined deformation amount or more. MEMS acceleration sensor.

2. the spring portion has a curved portion that bulges in at least a direction perpendicular to the detection direction, The spring constant change portion has a plurality of protrusions that protrude from the spring portion toward the center of curvature and are spaced apart by a predetermined distance. The MEMS acceleration sensor according to claim 1 .

3. The spring portion is an annular member, The plurality of protrusions are arranged around the entire circumference of the annular member. The MEMS acceleration sensor according to claim 2 .

4. The plurality of protrusions are disposed at a portion where the spring portion has a high curvature when tensioned and compressed. The MEMS acceleration sensor according to claim 2 .

5. The elastic member is disposed on one side or the other side of the movable electrode in the detection direction.

5. The MEMS acceleration sensor according to claim 3.

6. The plurality of protrusions are disposed at a portion of the spring portion where the curvature increases when the spring portion is compressed. The MEMS acceleration sensor according to claim 2 .

7. The elastic members are disposed on both sides of the movable electrode element in the detection direction. The MEMS acceleration sensor according to claim 6 .

8. The distance between the tip ends of adjacent protrusions among the plurality of protrusions is set to be less than the inter-electrode distance between the fixed electrode element and the movable electrode element in a reference state.

5. The MEMS acceleration sensor according to claim 2.

9. The spring constant changing portion is set so that the spring constant of the spring portion becomes infinite.

5. The MEMS acceleration sensor according to claim 1.

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