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 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 with 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 has a first spring portion 53 having a first spring constant K1, and a second spring portion 54 connected in series to the first spring portion 53 and having a second spring constant K1 larger than the first spring constant K2.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] One aspect of the present disclosure is 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 first spring portion having a first spring constant and a second spring portion connected in series with the first spring portion and having a second spring constant greater than the first spring constant. 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] 1 is a glove showing the relationship between the displacement amount and the restoring force of an elastic member. [Figure 6] FIG. 6 is a schematic plan view showing a state in which acceleration is applied to the MEMS acceleration sensor. [Figure 7A] FIG. 7A is a schematic plan view showing a first modified example of the elastic member of the MEMS acceleration sensor. [Figure 7B] FIG. 7B is a schematic plan view showing a second modified example of the elastic member of the MEMS acceleration sensor. [Figure 7C] FIG. 7C is a schematic plan view showing a third modified example of the elastic member of the MEMS acceleration sensor. [Figure 7D] FIG. 7D is a schematic plan view showing a fourth modified example of the elastic member of the MEMS acceleration sensor.

[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 electrode elements 41a, 41b so that they can move in the detection direction. Elastic members 50 are arranged on both sides of movable electrode 40 in the X direction. More specifically, elastic member 50 has a first elastic member 51 arranged on one side of weight portion 45 in the X direction and a second elastic member 52 arranged on the other side.

[0025] Each of the elastic members 51, 52 has a first connection portion 55 that connects 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. Each of the elastic members 51, 52 is disposed between the support portion 15 and the weight portion 45 at its natural length.

[0026] Each elastic member 51, 52 has a zigzag shape with continuous waves in the X direction. That is, each elastic member 51, 52 has multiple beams 53a, 54a extending in the Y direction and multiple connecting portions 53b, 54b connecting adjacent beams 53a, 54a. Each elastic member 51, 52 is a spring that utilizes a restoring force generated by elastically deforming each beam 53a, 54a and each connecting portion 53b, 54b. Because each elastic member 51, 52 is formed of multiple beams 53a, 54a extending in the Y direction, it has a structure that easily elastically deforms in the X direction. Each elastic member 51, 52 has lower rigidity in the X direction than in the Y and Z directions.

[0027] As shown in Figures 3 and 4, each elastic member 51, 52 has a first spring portion 53 having a first spring constant K1, and a second spring portion 54 connected in series to the first spring portion 53 and having a second spring constant K2 greater than the first spring constant K1.

[0028] More specifically, the first spring portion 53 has a plurality of first beam portions 53a extending in a direction perpendicular to the detection direction (Y direction) and a plurality of first connection portions 53b connecting ends of adjacent first beam portions 53a in series in the detection direction. The second spring portion 54 has a plurality of second beam portions 54a extending in a direction perpendicular to the detection direction and a plurality of second connection portions 54b connecting ends of adjacent second beam portions 54a in series in the detection direction.

[0029] The first spring constant K1 and the second spring constant K2 are set to different values ​​by varying a first pitch P1, which is the distance between the first beam portions 53a in the detection direction, and a second pitch P2, which is the distance between the second beam portions 54a in the detection direction. In this embodiment, the first pitch P1 is set to be larger than the second pitch P2. Each pitch P1, P2 is formed to be smaller than the inter-electrode distance W0 between the movable electrodes 41a, 41b and the fixed electrodes 31a, 31b, 32a, 32b.

[0030] Generally, the spring constant K of a cantilever beam is inversely proportional to the cube of the effective length L of the beam, as shown in the following equation 1. In this specification, if the effective length L is one cycle of a wave, the effective length L is the sum of the length L0 of each beam portion 53a, 54a and the lengths L1, L2 of each connecting portion 53b, 54b.

[0031] [Number 1] K∝(E·I / L 3 ) E: Young's modulus I: Moment of inertia L: Effective length of one wave cycle L (length of beam L0 + lengths of connecting parts L1, L2)

[0032] 3 and 4, in this embodiment, the Z-direction thicknesses t0 of the first and second beam portions 53a, 54a and the first and second connecting portions 53b, 54b are approximately the same, and the widths W1 of the first and second beam portions 53a, 54a in the detection direction (X-direction) and the widths W2 of the first and second connecting portions 53b, 54b in the Y-direction are approximately the same. Furthermore, the Y-direction lengths L0 of the first and second beam portions 53a, 54a are approximately the same, but the X-direction lengths of the first and second connecting portions 53b, 54b are different. Therefore, the relationship between the first spring constant K1 and the second spring constant K2 depends on the X-direction lengths L1, L2 of the first and second connecting portions 53b, 54b of each spring portion 53, 54.

[0033] In this embodiment, the lengths L1 and L2 of the connecting portions 53b and 54b of the spring portions 53 and 54 are approximately equal to the pitches P1 and P2. Therefore, since the first pitch P1 is set larger than the second pitch P2, the first spring constant K1 is smaller than the second spring constant K2. In this embodiment, the first spring constant K1 is set to be equal to or greater than 0.5 N / m and smaller than 1.5 N / m, and the second spring constant K2 is set to be equal to or greater than 1.5 N / m.

[0034] As the first spring portion 53 and the second spring portion 54 begin to be displaced from their free length to the predetermined displacement amount W3, the first spring portion 53, which has a smaller spring constant, deforms more than the second spring portion 54. In this embodiment, the displaceable amount (compressible amount) of the first spring portion 53 roughly matches the predetermined displacement amount W3.

[0035] Since the first spring portion 53 and the second spring portion 54 are connected in series, the overall spring constant of each elastic member 51, 52 is a so-called combined series spring constant Kt, which is smaller than the first spring constant K1 and the second spring constant K2, as shown in the following equation 2. In the following equation 2, a is a predetermined constant that depends on the amount of displacement of the first spring portion 53, and b is a predetermined constant that depends on the amount of displacement of the first spring portion 53.

[0036] [Number 2] 1 / Kt=a(1 / K1)+b(1 / K2)

[0037] The greater the difference between the first spring constant K1 and the second spring constant K2, the smaller the displacement of the second spring portion 54 becomes relative to the displacement of the first spring portion 53. Therefore, depending on the settings of the first spring constant K1 and the second spring constant K2, the overall spring constant of the elastic members 51, 52 until the predetermined displacement amount W3 is reached may be considered to be the first spring constant K1. The second spring constant K2 may be any value as long as it is larger than the first spring constant K1, and in this embodiment, the ratio of the second spring constant K2 to the first spring constant K1 is set to 200% (the second spring constant K2 is twice the first spring constant K1).

[0038] Furthermore, when each of the elastic members 51, 52 reaches a predetermined displacement W3, that is, when the displacement reaches or exceeds the predetermined displacement W3 (when the compression of the first spring portion 53 is almost complete), the second spring portion 54, which has a larger spring constant, begins to compress. In other words, when the displacement reaches or exceeds the predetermined displacement W3, the displacement range of the first spring portion 53 disappears, so essentially only the second spring portion 54 is deformed, and the combined spring constant Kt of the entire elastic members 51, 52 roughly matches the second spring constant K2.

[0039] The overall spring constant of each elastic member 51, 52 is the combined spring constant Kt of the first spring constant K1 and the second spring constant K2 until the compression of the first spring portion 53 is almost complete, and when the compression of the second spring portion 54 begins after the compression of the first spring portion 53 is almost complete, it can be considered to be the second spring constant K2.

[0040] The predetermined displacement amount W3 may be smaller than the inter-electrode distance W0 between the movable electrodes 41a, 41b and the fixed electrodes 31a, 31b, 32a, 32b.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] The set values ​​of the first spring constant K1 and the second spring constant K2 will be described with reference to Figures 5 and 6. In Figure 5, line A is a line showing the relationship between the displacement and restoring force of the first spring portion 53 and the second spring portion 54 up to a predetermined deformation amount W3, and line B is a line showing the relationship between the displacement and restoring force of the first spring portion 53 and the second spring portion 54 after the predetermined deformation amount W3 is exceeded. Note that in Figure 5, the inclination angle of line A corresponds to the spring constant (composite spring constant) Kt of the entire elastic members 51, 52 up to the predetermined displacement amount W3, and the inclination angle of line B corresponds to the spring constant (second spring constant K2) of the entire elastic members 51, 52 at or above the predetermined displacement amount W3.

[0045] As described above, a restoring force proportional to the composite spring constant Kt acts from the time when the elastic member 50 starts to be compressed until the compression of the first spring portion 53 is almost complete. When the second spring portion 54 starts to be compressed from the time when the compression of the first spring portion 53 is almost complete, a restoring force substantially proportional to the spring constant K2 of the second spring portion 54 acts in addition to the restoring force when the compression of the first spring portion 53 is almost complete.

[0046] 5, in range C where the movable electrode 40 is below a predetermined displacement W3, the compression of the first spring portion 53 is not nearly complete, and a restoring force acts according to the deformation of the first spring portion 53 and the second spring portion 54. The first spring constant K1 and the second spring constant K2 are set so that in range C, the combined spring constant Kt of the elastic members 51, 52 as a whole becomes a value suitable for the detection sensitivity of the acceleration detected by the MEMS acceleration sensor 1.

[0047] In range D where the movable electrode 40 exceeds the predetermined displacement amount W3, compression of the first spring portion 53 is almost completed, and in addition to the restoring force at displacement amount W3, a restoring force substantially corresponding to the displacement amount of the second spring portion 54 acts, and the combined spring constant Kt of the entire elastic members 51, 52 substantially becomes the second spring constant K2. Furthermore, the second spring constant K2 is set to a value such that, in range D, a restoring force is obtained that can prevent the movable electrodes 41a, 41b from contacting the fixed electrodes 31a, 31b, 32a, 32b.

[0048] 6, when acceleration is input to the MEMS acceleration sensor 1, in the range (area C in FIG. 5) until the movable electrode 40 reaches a predetermined displacement amount W3 in the X direction, the first spring portion 53 and the second spring portion 54 elastically deform between the weight portion 45 and the support portion 15. As shown in FIG. 5, the composite spring constant Kt is set to a restoring force (less than σ1) that provides a desired detection sensitivity until the movable electrode 41a reaches the predetermined displacement amount W3.

[0049] In the range where the movable electrode 40 is displaced in the X direction by a predetermined amount W3 or more (area D in FIG. 5), the first spring portion 53 elastically deforms and compression is almost completed, and the second spring portion 54 continues to deform elastically between the first spring portion 53 and the support portion 15. As shown in FIG. 5, the second spring constant K2 is set so as to obtain a restoring force (σ1 or more) that prevents displacement of the movable electrode element 41a by the predetermined amount W3 or more.

[0050] The elastic member 50 is configured such that when it is deformed by a predetermined displacement amount W3 or more, the spring constant of the elastic member 50 increases from the composite spring constant Kt to a second spring constant K2, thereby preventing movement of the movable electrode 40 connected to the elastic member 50.

[0051] The MEMS acceleration sensor 1 according to the above embodiment provides the following advantageous effects.

[0052] 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 arranged in the cavity 11 and fixed to the substrate 10, movable electrodes 41a and 41b arranged 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 as to be movable in a detection direction (X direction) perpendicular to the movable electrodes 41a and 41b. The elastic member 50 includes a first spring portion 53 having a first spring constant K1 and a second spring portion 54 connected in series to the first spring portion 53 and having a second spring constant K2 greater than the first spring constant K1.

[0053] According to this configuration, the combined spring constant Kt of the first spring constant K1 and the second spring constant K2 is set to a value suitable for detection sensitivity, and the second spring constant K2 is set to a value that provides a restoring force that can prevent the movable electrodes 41a, 41b from contacting the fixed electrodes 31a, 31b, 32a, and 32b. Therefore, it is possible to prevent 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.

[0054] The first spring portion 53 has a plurality of first beam portions 53a extending in a direction (Y direction) perpendicular to the detection direction (X direction) and a plurality of first connection portions 53b that connect the ends of adjacent first beam portions 53a among the plurality of first beam portions 53a in series in the detection direction, and the second spring portion 54 has a plurality of second beam portions 54a extending in a direction perpendicular to the detection direction and a plurality of second connection portions 54b that connect the ends of adjacent second beam portions 54a among the plurality of second beam portions 54b in series in the detection direction.

[0055] This configuration makes it possible to realize a MEMS acceleration sensor having a composite spring constant Kt of the first spring constant K1 and the second spring constant K2 that is suitable for the detection sensitivity described above, and a second spring constant K2 for a restoring force that can prevent the movable electrodes 41a, 41b from contacting the fixed electrodes 31a, 31b, 32a, 32b.

[0056] A first pitch P1, which is the distance between adjacent first beam portions 53a of the first spring portion 53, is larger than a second pitch P2, which is the distance between adjacent second beam portions 54a of the second spring portion 54.

[0057] According to this configuration, by making the pitch of the first spring portion 53 and the second spring portion 54 different, it is possible to achieve the desired first spring constant K1 and second spring constant K2.

[0058] The first pitch P1 and the second pitch P2 are smaller than the inter-electrode distance W0 between the fixed electrodes 31a, 31b, 32a, 32b and the movable electrodes 41a, 41b before the movable electrodes 41a, 41b are displaced.

[0059] According to this configuration, even when the first spring portion 53 is almost completely compressed, a gap remains between the fixed electrodes 31a, 31b, 32a, 32b and the movable electrodes 41a, 41b, thereby preventing the movable electrodes 41a, 41b from coming into contact with the fixed electrodes 31a, 31b, 32a, 32b.

[0060] The elastic members 50 are disposed on both sides of the movable electrode elements 41a and 41b.

[0061] This configuration makes it possible to prevent the movable electrodes 41a and 41b from coming into contact with the fixed electrodes 31a, 31b, 32a, and 32b when they move to one side and the other side in the detection direction (X direction).

[0062] In the present embodiment, the first spring portion 53 and the second spring portion 54 have substantially the same length L0 in the direction (Y direction) perpendicular to the detection direction (X direction), but the present invention is not limited to this. As in a first modified example of elastic member 150 shown in Fig. 7A, the length L1 of first spring portion 153 in the direction perpendicular to the detection direction (X direction) may be greater than the length L2 of second spring portion 154 in the direction perpendicular to the detection direction (X direction).

[0063] According to this configuration, by making the lengths L1, L2 of the first spring portion 153 and the second spring portion 154 in the direction perpendicular to the detection direction different, it is possible to achieve the desired first spring constant K1 and second spring constant K2.

[0064] In the present embodiment, the configuration has been described in which the widths W1 of the first spring portion 53 and the second spring portion 54 in the detection direction (X direction) are approximately the same, but this is not limited to this. As in a second modified example of elastic member 250 shown in Fig. 7B, the width W21 of the first spring portion 253 in the detection direction may be smaller than the width W22 of the second spring portion 254 in the detection direction.

[0065] According to this configuration, by making the widths W21, W22 of the first spring portion 253 and the second spring portion 254 different, it is possible to achieve the desired first spring constant K1 and second spring constant K2.

[0066] In the present embodiment, the elastic member 50 includes the first spring portion 53 and the second spring portion 54, but the present invention is not limited to this. As in a third modified example of the elastic member 350 shown in FIG. 7C , the elastic member 350 may include a third spring portion 357 having a third spring constant K3 that is different from the first spring constant K1 and the second spring constant K2. For example, the third spring portion 357 may have a pitch P33 that is smaller than the pitch P31 of the first spring portion 353 and smaller than the pitch P32 of the second spring portion 354.

[0067] 7D , the elastic member 450 may have a third spring portion 457 having a third spring constant K3 different from the first spring constant K1 and the second spring constant K2. For example, the third spring portion 457 may have a Y-direction length L13 that is smaller than the Y-direction length L11 of the first spring portion 453 and smaller than the Y-direction length L12 of the second spring portion 454.

[0068] According to this configuration, in addition to the first spring portions 353, 453 and the second spring portions 354, 454, the third spring portions 357, 457 are provided. Therefore, for example, the third spring constant K3 can be set to a value greater than the first spring constant K1 and less than the second spring constant K2, and the spring constant of the elastic member can be changed continuously compared to when the spring constant is set in two stages, which makes it easier to improve the controllability of the MEMS acceleration sensor 1.

[0069] In this embodiment, a configuration has been described in which the Z-direction thickness t0 of the first spring portion 53 and the second spring portion 54 is roughly the same, but this is not limited to this. Although not shown in the drawings, the Z-direction thickness of the first spring portion may be smaller than the Z-direction thickness of the second spring portion 254. By making the thicknesses of the first spring portion and the second spring portion 254 different, the desired first spring constant K1 and second spring constant K2 can be achieved.

[0070] It should be noted that the first spring portion, the second spring portion and / or the third spring portion may be arranged in any manner, for example, the second spring portion may be arranged between the first spring portions, or the first spring portion may be arranged between the second spring portion and the third spring portion.

[0071] Since the spring constant depends on the pitch, Y-direction length, X-direction width, and Z-direction thickness of the elastic member, the spring constant of the elastic member may be set to obtain a desired spring constant by combining these.

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

[0074] [Note] The present disclosure includes the following aspects.

[0075] [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 element so as to be movable in a detection direction perpendicular to the movable electrode element; The elastic member has a first spring portion having a first spring constant and a second spring portion connected in series with the first spring portion and having a second spring constant greater than the first spring constant. MEMS acceleration sensor.

[0076] [Aspect 2] the first spring portion has a plurality of first beam portions extending in a direction perpendicular to the detection direction, and a plurality of first connection portions connecting ends of adjacent first beam portions among the plurality of first beam portions in series in the detection direction, The second spring portion has a plurality of second beam portions extending in a direction perpendicular to the detection direction, and a plurality of second connection portions that connect ends of adjacent second beam portions among the plurality of second beam portions in series in the detection direction. 2. The MEMS acceleration sensor according to claim 1.

[0077] [Aspect 3] A first pitch, which is a distance between adjacent first beam portions of the first spring portion in the detection direction, is larger than a second pitch, which is a distance between adjacent second beam portions of the second spring portion in the detection direction. The MEMS acceleration sensor according to embodiment 2.

[0078] [Aspect 4] The length of the first beam portion of the first spring portion in the direction perpendicular to the detection direction is greater than the length of the second beam portion of the second spring portion in the direction perpendicular to the detection direction. The MEMS acceleration sensor according to embodiment 2 or 3.

[0079] [Aspect 5] The width of the first beam portion of the first spring portion in the detection direction is smaller than the width of the second beam portion of the second spring portion in the detection direction. The MEMS acceleration sensor according to any one of aspects 2 to 4.

[0080] [Aspect 6] The first pitch and the second pitch are smaller than the inter-electrode distance between the fixed electrode element and the movable electrode element before the movable electrode element is displaced. The MEMS acceleration sensor according to any one of aspects 2 to 5.

[0081] [Aspect 7] The elastic members are disposed on both sides of the movable electrode element. The MEMS acceleration sensor according to any one of the first to sixth aspects.

[0082] [Aspect 8] The resilient member further includes a third spring portion having a third spring constant different from the first spring constant and the second spring constant. The MEMS acceleration sensor according to any one of the first to seventh embodiments. [Explanation of symbols]

[0083] 1 MEMS acceleration sensor 10 Substrate 11 Cavity 31a Fixed electrode 31b Fixed electrode 32a Fixed electrode 32b Fixed electrode 41a Movable electrode 41b Movable electrode 50 Elastic member 53 First spring part 53a 1st beam part 53b First connection part 54 Second spring part 54a 1st beam section 54b 2nd beam section 357 Third spring part K1 First spring constant K2 Second spring constant K3 Third spring constant L1 length L2 length P1 First pitch P2 2nd pitch W0 Distance between electrodes W1 width W21 width W22 width

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 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 first spring portion having a first spring constant and a second spring portion connected in series with the first spring portion and having a second spring constant greater than the first spring constant. MEMS acceleration sensor.

2. the first spring portion has a plurality of first beam portions extending in a direction perpendicular to the detection direction, and a plurality of first connection portions connecting ends of adjacent first beam portions among the plurality of first beam portions in series in the detection direction, The second spring portion has a plurality of second beam portions extending in a direction perpendicular to the detection direction, and a plurality of second connection portions connecting ends of adjacent second beam portions among the plurality of second beam portions in series in the detection direction. The MEMS acceleration sensor according to claim 1 .

3. A first pitch, which is a distance between adjacent first beam portions of the first spring portion in the detection direction, is larger than a second pitch, which is a distance between adjacent second beam portions of the second spring portion in the detection direction. The MEMS acceleration sensor according to claim 2 .

4. The length of the first beam portion of the first spring portion in the direction perpendicular to the detection direction is greater than the length of the second beam portion of the second spring portion in the direction perpendicular to the detection direction. The MEMS acceleration sensor according to claim 2 .

5. The width of the first beam portion of the first spring portion in the detection direction is smaller than the width of the second beam portion of the second spring portion in the detection direction. The MEMS acceleration sensor according to claim 2 .

6. The first pitch and the second pitch are smaller than the inter-electrode distance between the fixed electrode and the movable electrode before the movable electrode is displaced. The MEMS acceleration sensor according to claim 3 .

7. The elastic members are disposed on both sides of the movable electrode element.

6. The MEMS acceleration sensor according to claim 2.

8. The resilient member further includes a third spring portion having a third spring constant different from the first spring constant and the second spring constant.

6. The MEMS acceleration sensor according to claim 2.

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