JP2010210424A - Acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve shock resistance without lowering detection sensitivity. <P>SOLUTION: Beam parts 6, 7 are formed in a grid shape respectively having a plurality of strut parts 60, 70, and a plurality of bridge parts 61, 71 bridged over the plurality of strut parts 60, 70. Hereby, a tensile rigidity or a bending rigidity can be heightened furthermore than a conventional beam part formed prismatically, while maintaining a torsional rigidity of the beam parts 6, 7. Resultantly, shock resistance can be improved without lowering detection sensitivity. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a capacitance type acceleration sensor.

  Conventionally, as shown in FIG. 10, a rectangular parallelepiped weight part 100 having a movable electrode, a pair of beam parts 101 that rotatably supports the weight part 100 at a substantially center in the longitudinal direction of the weight part 100, and a pair of beams First and second fixed electrodes 102 and 103 arranged to face each other on the one side and the other side of the weight part 100 with a straight line (beam axis) connecting the parts 101 as a boundary line. An acceleration sensor provided is known. This acceleration sensor includes a movable electrode (a portion facing the fixed electrodes 102 and 103 of the weight portion 100) and the first and second fixed electrodes 102 and 103 that accompany the rotation of the weight portion 100 about the beam axis. The acceleration applied to the weight part 100 is detected by differentially detecting the change in capacitance between the two. In such an acceleration sensor, when the acceleration is applied, one side having the beam axis on the back surface of the weight part 100 as a boundary line is generated so that a moment with the beam axis as a rotation axis is generated in the weight part 100 (see FIG. 10 is formed on the one side (right side) and the other side (left side) of the weight part 100 with the beam axis as a boundary line (for example, Patent Document 1). reference).

Special table 2008-544243 gazette

  By the way, in order to increase the impact resistance of the acceleration sensor having the above-described structure, it is necessary to improve the tensile rigidity and the bending rigidity, for example, by increasing the thickness of the beam portion 101. However, when the beam portion 101 is thickened, not only the tensile rigidity and bending rigidity but also the torsional rigidity is improved, which leads to a decrease in detection sensitivity. On the other hand, if the beam section 101 is made thin with priority on detection sensitivity, the beam section 101 may be damaged when an excessive impact is applied.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an acceleration sensor capable of improving impact resistance without lowering detection sensitivity.

  In order to achieve the above object, the first aspect of the present invention provides a weight portion having a movable electrode on one surface, a frame portion surrounding the periphery of the weight portion, and the weight portion around the rotation axis. And a fixed electrode disposed opposite to the movable electrode, and the beam portion has a plurality of ends coupled to the frame portion and the other end coupled to the weight portion. It is characterized in that it is formed in a lattice shape having strut portions and a plurality of crosspieces spanned between the plurality of strut portions.

  According to the first aspect of the present invention, since the beam portion is formed in a lattice shape having a plurality of column portions and a plurality of crosspieces spanned between the plurality of column portions, the beam portion is twisted. While maintaining the rigidity, the tensile rigidity and the bending rigidity can be increased, and as a result, the impact resistance can be improved without reducing the detection sensitivity.

  The invention of claim 2 is characterized in that, in the invention of claim 1, the beam portion is formed in a ladder shape in which a plurality of crosspieces are parallel to each other.

  A third aspect of the present invention is characterized in that, in the first or second aspect of the present invention, the beam portion is formed so that the pair of column portions are not parallel to each other.

  According to invention of Claim 3, the bending rigidity of a beam part can be improved.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the beam portion is at least one of a coupling portion between the column portion and the weight portion or a frame portion or a coupling portion between the column portion and the crosspiece portion. A fillet is formed in a corner portion of either one.

  According to the invention of claim 4, the stress applied to the corners of the joint portion can be dispersed to improve the impact resistance.

  According to the present invention, the impact resistance can be improved without reducing the detection sensitivity.

1 shows an embodiment of the present invention, (a) is an exploded perspective view, (b) is a plan view of a beam portion. The same as above, (a) is a bottom view of the sensor chip, (b) is a cross-sectional view. (A)-(e) is sectional drawing for demonstrating the manufacturing method same as the above. It is explanatory drawing explaining the relationship between the vibration mode of a movable electrode (weight part), and the resonant frequency calculated by simulation. (A), (b) is a top view which shows the modification of a beam part. (A), (b) is a top view which shows the modification of a beam part. It is a top view which shows the modification of a beam part. It is a top view which shows the modification same as the above. It is a top view which shows the modification same as the above. A prior art example is shown, (a) is a sectional view and (b) is a plan view.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, in the following description, the x-axis direction in FIG. 1A is defined as the vertical direction, the y-axis direction is defined as the horizontal direction, and the z-axis direction is defined as the vertical direction.

  In the present embodiment, as shown in FIG. 1A, the sensor chip 1 whose outer shape is a rectangular flat plate, the upper fixing plate 2a fixed to the upper surface side of the sensor chip 1, and the lower surface side of the sensor chip 1 are fixed. And a lower fixing plate 2b. The sensor chip 1 has a gap with respect to the frame part 3 in which two rectangular frame parts 3a and 3b viewed in the vertical direction are arranged in the longitudinal direction (lateral direction) and the inner peripheral surface of the frame parts 3a and 3b. The rectangular parallelepiped weight parts 4 and 5 arranged in the frame parts 3a and 3b in the opened state, the inner peripheral surface of the frame parts 3a and 3b and the side surfaces of the weight parts 4 and 5 are connected to the frame part 3 A pair of beam portions 6, 6 and 7, 7 for supporting the weight portions 4, 5 so as to be rotatable about a rotation axis, and movable electrodes 4a, 5a formed on the upper surfaces of the weight portions 4, 5. It has.

  As shown in FIG. 2, the weight portions 4, 5 are integrally formed with concave portions 11, 13 opening on one surface (lower surface) and solid portions 12, 14 excluding the concave portions 11, 13. The recesses 11 and 13 are formed in a square shape in plan view when viewed from the normal direction (vertical direction) of the opening surface, and are coupled to the inner wall surface and the bottom wall surface of the recesses 11 and 13 and are diagonally viewed from the vertical direction. The two reinforcing walls 16 and 16 which are arrange | positioned and mutually cross | intersect are provided in the inside.

  The pair of beam portions 6, 6 are connected at one end to the longitudinal center portion of the inner peripheral surface of the frame portion 3 a facing in the lateral direction, and are located near the boundary between the recess portion 11 and the solid portion 12 on the side surface of the weight portion 4. The ends are connected. Similarly, a pair of beam portions 7 and 7 are connected at one end to the longitudinal center portion of the inner peripheral surface of the frame portion 3b facing in the lateral direction, near the boundary between the recess portion 13 and the solid portion 14 on the side surface of the weight portion 5. The other end is connected. That is, a straight line connecting the pair of beam portions 6 and 7 serves as a rotation shaft, and the weight portions 4 and 5 rotate around the rotation shaft. The sensor chip 1 is formed by processing a silicon substrate (silicon SOI substrate) by a semiconductor microfabrication technique as will be described later, and the portions including the upper surfaces of the weight portions 4 and 5 are movable electrodes 4a, 5a. In addition, although illustration is abbreviate | omitted in Fig.1 (a), it prevents that the weight parts 4 and 5 collide with the upper fixing board 2a and the lower fixing board 2b directly on the upper surface and lower surface of the weight parts 4 and 5. FIG. Protrusions 15a to 15g for projecting are provided (see FIG. 2B).

  The upper fixed plate 2a is made of an insulating material such as quartz glass, and on the lower surface thereof, the first fixed electrode 20a is located at a position facing the weight portion 4 (movable electrode 4a) of the sensor chip 1 along the vertical direction. And the second fixed electrode 20b are juxtaposed in the vertical direction, and the first fixed electrode 21a and the second fixed electrode 20a are positioned at positions facing the weight portion 5 (movable electrode 5a) of the sensor chip 1 along the vertical direction. Electrodes 21b are arranged in the vertical direction. Further, the upper fixing plate 2a is provided with five through holes 22a to 22e arranged side by side on one end side in the vertical direction. Further, a plurality of conductive patterns (not shown) electrically connected to the fixed electrodes 20a, 20b and 21a, 21b are formed on the lower surface of the upper fixed plate 2a.

  On the other hand, a total of four electrode portions 8 a, 8 b, 9 a, and 9 b separated from the frame portion 3 are arranged in parallel on one longitudinal end side of the sensor chip 1. The four electrode portions 8a, 8b, 9a, and 9b are formed with detection electrodes 80a, 80b, 90a, and 90b made of a metal film substantially at the center on the upper surface, and upper surfaces of end portions facing the frame portions 3a and 3b. Further, press contact electrodes 81a, 81b, 91a, 91b made of a metal film are formed respectively. A ground electrode 10 is formed between the electrode portions 8b and 9a on the upper surface of the frame portion 3. Then, when the upper fixing plate 2a is joined to the upper surface of the sensor chip 1, each of the detection is performed by press-connecting the conductive pattern formed on the lower surface of the upper fixing plate 2a and the press contact electrodes 81a, 81b, 91a, 91b. The electrodes 80a, 80b, 90a, 90b are electrically connected to the fixed electrodes 20a, 20b, 21a, 21b, and the detection electrodes 80a, 80b, 90a, 90b are connected through the through holes 22a-22d of the upper fixed plate 2a. It is exposed to the outside (see FIG. 2B). The ground electrode 10 is also exposed to the outside through the through hole 22e.

  The lower fixing plate 2b is made of an insulating material such as quartz glass like the upper fixing plate 2a, and has an adhesion preventing film on the upper surface thereof at positions facing the weight portions 4 and 5 of the sensor chip 1 along the vertical direction. 23a and 23b are formed. These adhesion preventing films 23a, 23b are made of the same material as the fixed electrodes 20a,... Such as an aluminum alloy, and prevent the lower surfaces of the rotated weight parts 4, 5 from adhering to the lower fixed plate 2b. ing.

  Here, in this embodiment, the frame part 3a, the weight part 4, the beam parts 6 and 6, the movable electrode 4a, the first and second fixed electrodes 20a and 20b, the detection electrodes 80a and 80b, the frame part 3b, the weight Part 5, beam parts 7 and 7, movable electrode 5a, first and second fixed electrodes 21a and 21b, and detection electrodes 81a and 81b each constitute an acceleration sensor, and the direction of weight parts 4 and 5 (recesses 11 and The two acceleration sensors are integrally formed in a state in which the arrangement 13 and the solid portions 12 and 14 are inverted 180 degrees.

  Next, the detection operation of this embodiment will be described.

First, consider a case where an acceleration in the x-axis direction is applied to one weight portion 4. When acceleration is applied in the x-axis direction, the weight portion 4 rotates around the rotation axis, and the distance between the movable electrode 4a and the first fixed electrode 20a and the second fixed electrode 20b changes. As a result, the capacitances C1 and C2 between the movable electrode 4a and the fixed electrodes 20a and 20b also change. Here, the capacitance between the movable electrode 4a and the fixed electrodes 20a and 20b when no acceleration in the x-axis direction is applied is C0, and the change in capacitance caused by the application of acceleration is ΔC. Then, the capacitances C1 and C2 when the acceleration in the x-axis direction is applied are
C1 = C0−ΔC (1)
C2 = C0 + ΔC (2)
It can be expressed as.

Similarly, when acceleration in the x-axis direction is applied to the other weight portion 5, the capacitances C3 and C4 between the movable electrode 5a and the fixed electrodes 21a and 21b are:
C3 = C0−ΔC (3)
C4 = C0 + ΔC (4)
It can be expressed as.

  Here, the values of the capacitances C1 to C4 can be detected by performing arithmetic processing on voltage signals taken out from the detection electrodes 80a and 80b and 81a and 81b. Then, the difference value CA (= C1-C2) between the capacitances C1, C2 obtained from one acceleration sensor and the difference value CB (= C3-C4) between the capacitances C3, C4 obtained from the other acceleration sensor. Is calculated (± 4ΔC), the direction and magnitude of the acceleration applied in the x-axis direction can be calculated based on the sum of the difference values CA and CB.

Next, consider a case where acceleration in the z-axis direction is applied to one weight portion 4. When acceleration is applied in the z-axis direction, the weight portion 4 rotates about the rotation axis, and the distance between the movable electrode 4a and the first fixed electrode 20a and the second fixed electrode 20b changes. As a result, the capacitances C1 and C2 between the movable electrode 4a and the fixed electrodes 20a and 20b also change. Here, the capacitance between the movable electrode 4a and the fixed electrodes 20a and 20b when no acceleration in the z-axis direction is applied is C0, and the change in capacitance caused by the application of acceleration is ΔC. Then, the capacitances C1 and C2 when the acceleration in the z-axis direction is applied are:
C1 = C0 + ΔC (5)
C2 = C0−ΔC (6)
It can be expressed as.

Similarly, when acceleration in the z-axis direction is applied to the other weight portion 5, the capacitances C3 and C4 between the movable electrode 5a and the fixed electrodes 21a and 21b are:
C3 = C0−ΔC (7)
C4 = C0 + ΔC (8)
It can be expressed as.

  Then, the difference value CA (= C1-C2) between the capacitances C1, C2 obtained from one acceleration sensor and the difference value CB (= C3-C4) between the capacitances C3, C4 obtained from the other acceleration sensor. Is calculated (± 4ΔC), the direction and magnitude of the acceleration applied in the z-axis direction can be calculated based on the difference between the difference values CA and CB. Since the calculation processing for obtaining the direction and magnitude of acceleration in the x-axis direction and the z-axis direction based on the sum and difference of the difference values CA and CB is well known in the art, detailed description thereof will be omitted.

  Next, the manufacturing method of this embodiment will be described with reference to FIG.

  As shown in FIG. 3A, the present embodiment is formed by processing a silicon SOI substrate including a support substrate 30a, an intermediate oxide film 30b, and an active layer 30c using a semiconductor microfabrication technique. First, a mask material 31 such as a silicon oxide film or a photoresist film is formed on both surfaces of a silicon SOI substrate, and after removing the mask material 31 at a position corresponding to the weights 4 and 5, a TMAH (tetramethyl ammonium hydroxide solution) is formed. ), KOH (potassium hydroxide solution) or other wet etching, or dry etching such as reactive ion etching (RIE), the weights 4 and 5 are displaced on the upper and lower surfaces of the silicon SOI substrate. Spaces (recesses) 32a and 32b are formed (see FIG. 3B).

  Then, protrusions 15a to 15g made of a silicon oxide film or carbon nanotube are formed at predetermined positions on the bottom surfaces of the recesses 32a and 32b. At this time, detection electrodes 80a, 80b, 90a, 90b and press-contact electrodes 81a, 81b, 91a, 91b made of a metal film are formed by using sputtering or vapor deposition (see FIG. 3C).

  Subsequently, the bottom portions of the silicon SOI substrate are etched in the order of the support substrate 30a and the intermediate oxide film 30b to form the weight portions 4 and 5 (the concave portions 11 and 13 and the solid portions 12 and 14 and the auxiliary wall 16), and then attached. The lower fixing plate 2b having the prevention films 23a and 23b formed on the upper surface is anodically bonded to the lower surface of the silicon SOI substrate (see FIG. 3D).

  Finally, the upper fixing plate 2a in which the through holes 22a to 22e and the first and second fixed electrodes 20a, 20b, 21a, and 21b are formed is anodically bonded to the upper surface of the silicon SOI substrate, thereby manufacturing the present embodiment. The process is completed (see FIG. 3 (e)).

  FIG. 4 shows the correspondence between the vibration modes of the movable electrodes 4a and 5a (weight portions 4 and 5) that vibrate due to acceleration applied from the outside and the resonance frequency calculated by simulation. Since the weight portions 4 and 5 are supported by the pair of beam portions 6 and 7 with respect to the frame portions 3a and 3b, the beam portions 6 and 7 are rotated by twisting deformation around the rotation axis (“twist” in FIG. Mode)) as well as the expansion / contraction deformation and bending deformation of the beam portions 6 and 7, "in-plane translation mode", "in-plane rotation mode", "out-of-plane translation mode", "out-of-plane translation mode" shown in FIG. Vibrates in "Rotation mode". However, only the “torsion mode” vibration is required to detect the acceleration, and the other vibration modes are unnecessary for the acceleration detection. That is, it is desirable that the weights 4 and 5 vibrate only in the torsion mode when acceleration is applied from the outside and do not vibrate as much as possible in the other vibration modes. On the other hand, it is effective to reduce the torsional rigidity of the beam portions 6 and 7 in order to improve the detection sensitivity of acceleration. That is, while suppressing the resonance frequency of the “twisting mode” to a predetermined level or less, the beam portions 6 and 7 are operated in other vibration modes (“in-plane translation mode”, “in-plane rotation mode”, “out-of-plane translation mode”. "," Out-of-plane rotation mode "), the resonance frequency may be increased.

  Therefore, in the present embodiment, as shown in FIG. 1B, a pair of support columns 60 having one end coupled to the frame portion 3 (frame portions 3a and 3b) and the other end coupled to the weight portions 4 and 5, Beam portions 6 and 7 are formed in a lattice shape having 70 and a plurality of crosspiece portions 61 and 71 spanned between the pair of column portions 60 and 70. Here, FIG. 4 shows the result of simulating the resonance frequency in each vibration mode for the beam portions 6 and 7 in the present embodiment formed in a lattice shape and the conventional beam portion formed in a prism shape. As is clear from the simulation results, according to the structure of the beam portions 6 and 7 of the present embodiment, the resonance frequency of the “twisted mode” is ensured to be equal to that of the conventional example, but in the other vibration modes, compared to the conventional example. The resonance frequency can be increased.

  Thus, according to the present embodiment, the beam portions 6 and 7 have a plurality of support columns 60 and 70 and a plurality of crosspieces 61 and 71 spanned between the support columns 60 and 70. Therefore, the tensile rigidity and bending rigidity can be increased while maintaining the torsional rigidity of the beam portions 6 and 7, and as a result, the impact resistance can be improved without degrading the detection sensitivity. . The shape of the beam portions 6 and 7 is such that the pair of column portions 60 and 70 are parallel to each other and all the beam portions 61 and 71 are perpendicular to the column portions 60 and 70 as shown in FIG. It is not limited to the shape (ladder shape). For example, as shown in FIGS. 5A and 5B, the pair of support columns 60 and 70 may have a shape (stepladder shape) that is not parallel to each other. Absent. If the beam portions 6 and 7 have the shape shown in FIG. 5A or 5B, the bending rigidity can be further increased as compared with the shape in which the column portions 60 and 70 are parallel to each other.

  Alternatively, as shown in FIGS. 6 (a) and 6 (b), the post portions 60 and 70 and the crosspiece portions 61 and 71 may not be perpendicular to each other, and a pair of crosspieces as shown in FIG. It is good also as a shape where the parts 61 and 71 cross | intersect between the support | pillar parts 60 and 70 mutually. In the beam portions 6 and 7 having the shapes shown in FIGS. 6 and 7, it is possible to particularly increase the tensile rigidity. In addition, the number of support | pillar parts 60 and 70 is not limited to two, You may be three or more.

  Here, in the beam portions 6 and 7, the coupling portion between the column portions 60 and 70 and the weight portions 4 and 5, the coupling portion between the frame portion 3 (frame portions 3a and 3b), or the column portions 60 and 70 and the crosspiece portion. If the fillets 62 and 72 are formed at the corners of at least one of the coupling portions 61 and 71 (see FIGS. 5 to 7), the stress applied to the corners of the coupling portions is dispersed to disperse the beam portions 6 and 7. Impact resistance can be improved.

  In this embodiment, the acceleration sensor that detects the acceleration in the biaxial directions of the x axis and the z axis is exemplified. However, as shown in FIG. 8, the acceleration sensor 1 described above may be arranged 90 degrees rotationally symmetrical in the xy plane. For example, an acceleration sensor that detects acceleration in the three-axis direction in which the y-axis is added to the x-axis and the z-axis can be realized. Alternatively, as shown in FIG. 9, three acceleration sensors are arranged in the same chip plane, and the second and third acceleration sensors S2 and S3 are 90 degrees in the chip plane with respect to the first acceleration sensor S1. Even if arranged 180 degrees rotationally symmetric, an acceleration sensor that detects acceleration in the three-axis direction by adding the y-axis to the x-axis and z-axis can be realized.

DESCRIPTION OF SYMBOLS 1 Sensor chip 3 Frame part 4,5 Weight part 4a, 5a Movable electrode 6 Beam part 7 Beam part 60 Post part 61 Cross part 70 Post part 71 Cross part 20a, 21a 1st fixed electrode 20b, 21b 2nd fixed electrode

Claims (4)

A weight part provided with a movable electrode on one surface, a frame part surrounding the weight part, a beam part that supports the weight part so as to be rotatable about a rotation axis with respect to the frame part, and the movable electrode. And a fixed electrode arranged
The beam portion is in a lattice shape having a plurality of support portions having one end coupled to the frame portion and the other end coupled to the weight portion, and a plurality of crosspieces spanned between the plurality of support portions. An acceleration sensor characterized by being formed.   The acceleration sensor according to claim 1, wherein the beam portion is formed in a ladder shape in which a plurality of crosspieces are parallel to each other.   3. The acceleration sensor according to claim 1, wherein the beam portion is formed so that the pair of support columns are not parallel to each other.   The beam portion has a fillet formed at a corner portion of at least one of a coupling portion between the column portion and the weight portion or the frame portion or a coupling portion between the column portion and the crosspiece portion. 4. The acceleration sensor according to any one of 3 above.

Images