JP2010210428A - Acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acceleration sensor capable of enhancing a strength against an impact without lowering detection sensitivity. <P>SOLUTION: The acceleration sensor includes a first electrode 400 and a second electrode 401 which are formed by dividing a first movable electrode 40 in two, a first frame 30 which surrounds the first electrode 400 and the second electrode 401 with a prescribed space left in between, and a pair of first beam parts 5a and 5b which connects each of the electrodes 400 and 401 with the first frame 30 respectively and also supports each of the electrodes 400 and 401 so that it can rock in relation to the first frame 30. The first beam parts 5a and 5b are provided respectively in the vicinity of the opposite corners of the first frame 30 and their shafts agree substantially with the direction intersecting a diagonal line of the first frame 30 perpendicularly, while the opposite ends in the axial direction are formed integrally with the first frame 30. In the substantially central portion in the axial direction of each of the beam parts 5a and 5b, each of the electrodes 400 and 401 is formed integrally the same. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a capacitance-type acceleration sensor that detects acceleration based on a change in capacitance between a movable electrode and a fixed electrode accompanying the swing of the movable electrode.

  Conventionally, a movable electrode having a rectangular shape in plan view, a pair of beam portions that swingably support the movable electrode at substantially the center of two opposite sides of the movable electrode, and a pair of beam portions on the surface of the movable electrode. A fixed electrode disposed opposite to each other with a predetermined distance from one side and the other side with a connecting straight line as a boundary line, and a static electrode between the movable electrode and the fixed electrode that accompanies the swinging of the movable electrode. A capacitance-type acceleration sensor that detects acceleration by detecting a change in capacitance is known (see, for example, Patent Document 1).

  Hereinafter, a conventional example of such an acceleration sensor will be described with reference to the drawings. In the following description, the vertical direction in FIG. 3 is defined as the vertical direction. In addition, a direction parallel to the short direction of the sensor chip 1 is defined as an x direction, a direction parallel to the longitudinal direction of the sensor chip 1 is defined as a y direction, and a direction orthogonal to the x direction and the y direction is defined as a z direction. In this conventional example, as shown in FIG. 3, a sensor chip 1 formed of an SOI (Silicon on Insulator) substrate is sandwiched between an upper fixing plate 2a and a lower fixing plate 2b. The sensor chip 1 includes a frame portion 3 having a first frame portion 30 and a second frame portion 31 that are substantially rectangular in plan view, and each frame with a gap between the side walls of the frame portions 30 and 31. The two first movable electrodes 40 and the second movable electrode 41 having a substantially rectangular shape in plan view disposed in a space surrounded by the portions 30 and 31, and two opposing sides of the upper surfaces of the movable electrodes 40 and 41. Two pairs of beam portions 5a to 5d that support the movable electrodes 40 and 41 so as to be swingable with respect to the frame portion 3 by connecting the substantially central portion and the side walls of the frame portions 30 and 31 are provided.

  The upper fixed plate 2a is formed of a glass substrate. As shown in FIG. 3, the lower surface facing the first movable electrode 40 has a straight line connecting a pair of first beam portions 5a and 5b as a boundary line. The fixed electrode 20a and the second fixed electrode 20b are provided. Further, on the lower surface facing the second movable electrode 41, a third fixed electrode 20c and a fourth fixed electrode 20d are provided with a straight line connecting the pair of second beam portions 5c and 5d as a boundary line. Yes. Each fixed electrode 20a-20d is formed from an aluminum-based alloy.

  The lower fixed plate 2b is formed of a glass substrate in the same manner as the upper fixed plate 2a. As shown in FIGS. 3 and 4, adhesion preventing films 23a and 23b are arranged at intervals from the movable electrodes 40 and 41. Yes. The adhesion preventing films 23a and 23b are made of the same material as the fixed electrodes 20a to 20d, and prevent the movable electrodes 40 and 41 from adhering to the lower fixed plate 2b during operation. In addition, when excessive acceleration exceeding the measurement range is applied, the adhesion preventing films 23a and 23b prevent the movable electrodes 40 and 41 and the lower fixed plate 2b from coming into direct contact with each other. Play.

  As shown in FIG. 3, the sensor chip 1 includes detection electrodes 6a and 6b for detecting capacitances C1 and C2 between the first movable electrode 40 and the fixed electrodes 20a and 20b, respectively, and a second Detection electrodes 6c and 6d for detecting capacitances C3 and C4 between the movable electrode 41 and the fixed electrodes 20c and 20d, respectively, and a ground electrode 7 are provided. Through holes 21a to 21d and 22 are formed through portions of the upper fixed plate 2a facing the detection electrodes 6a to 6d and the ground electrode 7, and the fixed electrodes 20a are inserted through the through holes 21a to 21d and 22, respectively. The outputs of the detection electrodes 6a to 6d and the ground electrode 7 respectively connected to ˜20d are taken out. Moreover, between the detection electrode 6a and the detection electrode 6b, between the detection electrode 6c and the detection electrode 6d, between each detection electrode 6a-6d and the flame | frame part 3, each detection electrode 6a-6d and each movable electrode 40, A gap is formed between each of the terminals 41 and 41. With this configuration, the detection electrodes 6a to 6d are electrically insulated from each other, so that parasitic capacitance of the detection electrodes 6a to 6d and crosstalk between the electrodes are reduced, and high-accuracy capacitance can be obtained. Detection can be performed.

  On one side of the lower surface of the first movable electrode 40 with a straight line connecting the pair of first beam portions 5a and 5b as a boundary line, the thickness dimension is larger than the thickness dimension on the other side as shown in FIG. A recess 40a is provided so as to be smaller. Similarly, on one side of the lower surface of the second movable electrode 41 with a straight line connecting the pair of second beams 5c and 5d as a boundary line, although not shown, the thickness dimension is smaller than the dimension on the other side. A recess is provided so as to be. As shown in FIG. 4 (only the recess 40a is shown in FIG. 4), each of the recesses is provided so that the angle θ formed by the center of gravity O of each of the movable electrodes 40 and 41 and the beam portions 5a to 5d is 45 degrees. It has been. With this configuration, when acceleration is applied, a rotational moment about the beam portions 5a to 5d is generated in each of the movable electrodes 40 and 41, and the detection sensitivity in the x direction and the z direction becomes equivalent. In this conventional example, as shown in FIG. 3, two acceleration sensors are arranged on the xy plane, and one acceleration sensor is arranged to rotate 180 degrees in the xy plane with respect to the other acceleration sensor.

  As shown in FIG. 4 (only the first movable electrode 40 is shown in FIG. 4), the surface of each movable electrode 40, 41 facing the upper fixed plate 2a and the lower fixed plate 2b is formed of silicon or a silicon oxide film. A plurality of protruding portions 40b are provided. By providing such a protrusion 40b, even if excessive acceleration exceeding the measurement range is applied to each movable electrode 40, 41, the upper fixed plate 2a and the lower portion facing each movable electrode 40, 41 are arranged. The sensor chip 1 can be prevented from being damaged without directly colliding with the fixing plate 2b. In this conventional example, the protrusions 40b are provided on the surfaces of the movable electrodes 40, 41 facing the upper fixed plate 2a and the lower fixed plate 2b. However, the movable electrodes 40 of the upper fixed plate 2a and the lower fixed plate 2b are provided. , 41 may be provided on the surface facing the projection 41b.

  Hereinafter, acceleration detection in the conventional example will be described. First, detection of acceleration in the x direction will be described. When acceleration in the x direction is applied to the first movable electrode 40, the capacitances C1 and C2 between the first movable electrode 40 and the fixed electrodes 20a and 20b are expressed by the following mathematical formulas, respectively. The The parameter C0 in the equations (1) and (2) is the distance between the first movable electrode 40 and each fixed electrode 20a, 20b in the state where no acceleration in the x direction is applied to the first movable electrode 40. The electrostatic capacity is shown.

C1 = C0−ΔC (1)
C2 = C0 + ΔC (2)
Similarly, when an acceleration in the x direction is applied to the second movable electrode 41, the capacitances C3 and C4 between the second movable electrode 41 and the fixed electrodes 20c and 20d are expressed by the following equations, respectively. It is represented by Note that the parameter C0 in the equations (3) and (4) is the same as the above, and the second movable electrode 41 and each fixed electrode 20c, when the acceleration in the x direction is not applied to the second movable electrode 41. The capacitance between 20d is shown.

C3 = C0−ΔC (3)
C4 = C0 + ΔC (4)
Thus, the capacitances C1 to C4 are detected via the detection electrodes 6a to 6d, and the difference value CA (= C1−) of the capacitances C1 and C2 is detected using an ASIC (Application Specific Integrated Circuit) or the like. C2) and the difference value CB (= C3−C4) between the capacitances C3 and C4, and the sum of the calculated difference values CA and CB (± 4ΔC) is output as the X output, whereby the capacitance From this change, the acceleration in the x direction applied to the first movable electrode 40 and the second movable electrode 41 can be detected.

  Next, detection of acceleration in the z direction will be described. When acceleration in the z direction is applied to the first movable electrode 40, the capacitances C1 and C2 between the first movable electrode 40 and the fixed electrodes 20a and 20b are expressed by the following equations, respectively. The The parameter C0 in the equations (5) and (6) is the distance between the first movable electrode 40 and each fixed electrode 20a, 20b in the state where no acceleration in the z direction is applied to the first movable electrode 40. The electrostatic capacity is shown.

C1 = C0 + ΔC (5)
C2 = C0−ΔC (6)
Similarly, when an acceleration in the z direction is applied to the second movable electrode 41, the capacitances C3 and C4 between the second movable electrode 41 and the fixed electrodes 20c and 20d are expressed by the following equations, respectively. It is represented by It should be noted that the parameter C0 in the equations (7) and (8) is the same as described above, and the second movable electrode 41 and each fixed electrode 20c, in the state where no acceleration in the z direction is applied to the second movable electrode 41. The capacitance between 20d is shown.

C3 = C0−ΔC (7)
C4 = C0 + ΔC (8)
Thus, the capacitances C1 to C4 are detected via the detection electrodes 6a to 6d, and the difference value CA (= C1−C2) between the capacitances C1 and C2 using the ASIC or the like, and the electrostatic capacitance. A difference value CB (= C3−C4) between the capacitors C3 and C4 is calculated, and the sum (± 4ΔC) of the calculated difference values CA and CB is output as a Z output. The acceleration in the z direction applied to the movable electrode 40 and the second movable electrode 41 can be detected.

US Patent Publication No. 2007-0000223

  By the way, in the acceleration sensor as described above, the strength against an impact such as excessive acceleration exceeding the measurement range is determined by the mass of the movable electrodes 40 and 41 and the rigidity of the beam portions 5a to 5d. However, in the above conventional example, when the rigidity of the beam portions 5a to 5d is increased in order to increase the strength against impact, there is a problem that the movable electrodes 40 and 41 are difficult to swing and the detection sensitivity is lowered.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an acceleration sensor that can increase the strength against impact without degrading the detection sensitivity.

  In order to achieve the above object, the first aspect of the present invention provides a first electrode portion and a second electrode portion formed by dividing the movable electrode into two parts, and the first electrode portion and the second electrode portion are arranged in a predetermined manner. A frame portion having a substantially rectangular shape in plan view and surrounding the first electrode portion, the second electrode portion, and the frame portion, and the first electrode portion and the second electrode portion are respectively frame portions. A pair of beam portions that are swingably supported, and a pair of fixed electrodes that are disposed to face the first electrode portion and the second electrode portion with a predetermined distance therebetween, An acceleration sensor that detects acceleration from a change in capacitance between a movable electrode and a fixed electrode that accompanies the swing of the movable electrode, and the beam portion of the beam portion is orthogonal to the diagonal line in the vicinity of the corner portion of the frame portion. The both ends in the axial direction are formed so as to be integrated with the frame portion in the axial direction. Wherein the portion first electrode and the second electrode portion in a substantially central portion are integrally formed, respectively.

  According to the present invention, the electrode portion obtained by dividing the movable electrode into two is supported by one beam portion whose both ends are formed integrally with the frame portion so as to be swingable. Compared with the case where the beam portion is swingably supported, the load applied to one beam portion is reduced, so that the strength against impact can be increased without degrading the detection sensitivity.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows Embodiment 1 of the acceleration sensor which concerns on this invention, (a) is a top view, (b) is an AA 'sectional view taken on the line, (c) shows the positional relationship with a fixed electrode. It is a top view. FIG. 7 is a diagram illustrating an acceleration sensor according to a second embodiment of the present invention, where (a) is a plan view of the movable electrode and the frame portion, and (b) is a bottom view of the upper fixed plate. It is a disassembled perspective view which shows the conventional acceleration sensor. It is sectional drawing in yz plane same as the above.

(Embodiment 1)
Hereinafter, a first embodiment of an acceleration sensor according to the present invention will be described with reference to the drawings. However, since the basic configuration of this embodiment is the same as that of the conventional example, common portions are denoted by the same reference numerals and description thereof is omitted. Further, in the following description, similarly to the description in the conventional example, the vertical direction in FIG. 3 is the vertical direction, the direction parallel to the short direction of the sensor chip 1 is the x direction, and the direction parallel to the long direction of the sensor chip 1 is. The directions perpendicular to the y direction, the x direction, and the y direction are defined as the z direction.

  In the present embodiment, as shown in FIGS. 1A to 1C, the first movable electrode 40 having a substantially square shape in plan view, which is divided into two parts, has a first electrode portion 400 having a substantially triangular shape in plan view and The first electrode unit 400, the first electrode unit 400, the first electrode unit 400, the first electrode unit 400, the first electrode unit 400, and the first electrode unit 400 having a substantially square shape in plan view surrounding the first electrode unit 400 and the second electrode unit 401 with a predetermined space therebetween. The second electrode part 401 and the first frame part 30 are connected to each other, and the first electrode part 400 and the second electrode part 401 are swingably supported with respect to the first frame part 30, respectively. The first fixed electrode 20a and the second fixed electrode, which are arranged to face the pair of first beam portions 5a and 5b, and the first electrode portion 400 and the second electrode portion 401 with a predetermined distance, respectively. And an electrode 20b.

  The first beam portions 5a and 5b are disposed in the vicinity of opposing corner portions of the first frame portion 30, respectively, and the shaft portions thereof substantially coincide with the direction perpendicular to the diagonal line of the first frame portion 30, and the shaft Both end portions in the direction are formed integrally with the first frame portion 30. The substantially central portion in the axial direction of one first beam portion 5a and the apex portion of the first electrode portion 400 are integrally formed, and the substantially central portion in the axial direction of the other first beam portion 5b. And the apex portion of the second electrode portion 401 are integrally formed. For this reason, each electrode part 400,401 is freely swingable about a substantially central part in the axial direction of the first beam parts 5a, 5b.

  Thus, the first electrode 400 and the second electrode 401 obtained by dividing the first movable electrode 40 into two parts of the first beam in which both end portions in the axial direction are formed integrally with the first frame portion 20. Since each of the portions 5a and 5b is swingably supported, the first movable electrode 40 is swingably supported by the pair of first beam portions 5a and 5b as in the conventional example. Thus, the load on each of the first beam portions 5a and 5b is reduced. Therefore, it is not necessary to increase the rigidity of the first beam portions 5a and 5b, and the strength against impact can be increased without degrading the detection sensitivity.

  In the configuration of the present embodiment, the center of gravity of the electrode portions 400 and 401 in the xy plane does not overlap with the first beam portions 5a and 5b, so that the center of gravity of the movable electrodes 40 and 41 is shifted as in the conventional example. There is no need to provide a recess on the surface (see FIG. 1B). Therefore, it is not necessary to manage the depth of etching that has been performed when the concave portion is provided, and the sensor can be easily manufactured as compared with the conventional example.

(Embodiment 2)
Hereinafter, an acceleration sensor according to a second embodiment of the present invention will be described with reference to the drawings. However, since the basic configuration of the present embodiment is common to that of the first embodiment, common portions are denoted by the same reference numerals and description thereof is omitted. Further, in the following description, similarly to the description in the conventional example, the vertical direction in FIG. 3 is the vertical direction, the direction parallel to the short direction of the sensor chip 1 is the x direction, and the direction parallel to the long direction of the sensor chip 1 is. The directions perpendicular to the y direction, the x direction, and the y direction are defined as the z direction.

  In the present embodiment, as shown in FIG. 2A, a first electrode portion 400 and a second electrode portion 401 each having a substantially triangular shape formed by dividing a first movable electrode 40 having a substantially square shape in plan view into two parts. And the third electrode part 410 and the fourth electrode part 411 having a substantially triangular shape formed by dividing the second movable electrode 41 having a substantially square shape in a plan view, and the electrode parts 400 and 401 at a predetermined interval. The first frame portion 30 having a substantially square shape in plan view and surrounding the electrode portions 410 and 411 with a predetermined interval and the frame portion 3 having the second frame portion 31 having a substantially square shape in plan view. A sensor chip 1 is configured (see FIG. 3 for the sensor chip 1).

  The first beam portions 5a and 5b, the first frame portion 30, the first electrode portion 400, and the second electrode portion 401 are configured in the same manner as in the first embodiment. The second beam portions 5c and 5d are respectively disposed in the vicinity of opposing corners of the second frame portion 31, and the shaft portions thereof substantially coincide with the direction perpendicular to the diagonal line of the second frame portion 31 and are Both end portions in the direction are formed integrally with the second frame portion 31. The substantially central portion in the axial direction of one second beam portion 5c and the apex portion of the third electrode portion 410 are integrally formed, and the substantially central portion in the axial direction of the other second beam portion 5d. And the apex portion of the fourth electrode portion 411 are integrally formed. For this reason, the electrode portions 410 and 411 are swingable about the substantially central portion in the axial direction of the second beam portions 5c and 5d, respectively.

  As shown in FIG. 2B, on the lower surface of the upper fixing plate 2a facing the first electrode portion 400 and the second electrode portion 401, the substantially fixed first fixed electrode 20a and the second fixed electrode 20a. Electrodes 20b are provided respectively. In addition, a third fixed electrode 20c and a fourth fixed electrode 20d are provided on the lower surface facing the third electrode portion 410 and the fourth electrode portion 411, respectively.

  Hereinafter, acceleration detection in the present embodiment will be described. When acceleration in the x-direction and y-direction is applied to the electrode portions 400, 401, 410, and 411, the capacitances C1 to C1 between the electrode portions 400, 401, 410, and 411 and the fixed electrodes 20a to 20d. C4 is as shown in the table below. The parameter C0 in the table is a static value between each electrode unit 400, 401, 410, 411 and each fixed electrode 20a to 20d in a state where no acceleration is applied to each electrode unit 400, 401, 410, 411. Indicates the electric capacity.

  Thus, the capacitances C1 to C4 are detected via the detection electrodes 6a to 6d, and difference values CA (= C1 to C2) and CB (= C3 to C4) are calculated using an ASIC or the like. By obtaining the X output and the Y output from the calculated difference values CA and CB, the biaxial acceleration in the x direction and the y direction can be detected.

  The capacitances C1 to C4 when the acceleration in the z direction is applied to the electrode portions 400, 401, 410, and 411 are as shown in the table below, and the difference values CA and CB are 0. In this embodiment, acceleration in the z direction cannot be detected. Therefore, the present embodiment is not an acceleration sensor that detects biaxial acceleration in the x direction and z direction as in the conventional example, but an acceleration sensor that detects biaxial acceleration in the x direction and y direction.

  Here, the conventional acceleration sensor is configured to detect biaxial acceleration in the x direction and the z direction by using two movable electrodes 40 and 41. However, in order to detect the acceleration in the y direction, it is necessary to further provide a movable electrode having an axis in a direction orthogonal to the axis of oscillation of the two movable electrodes 40 and 41, which increases the size of the sensor. there were. On the other hand, in the present embodiment, the movable electrodes 40 and 41 of the conventional example are each divided into two to provide four electrode portions 400, 401, 410, and 411, so that substantially four movable electrodes are utilized. It is configured to detect acceleration in the x and y directions. Thus, since there is no need to newly provide a movable electrode, acceleration in the y direction can be detected without increasing the size of the sensor.

20a 1st fixed electrode 20b 2nd fixed electrode 30 1st frame part 40 1st movable electrode 400 1st electrode part 401 2nd electrode part 5a, 5b 1st beam part

Claims (1)

  A first electrode part and a second electrode part formed by dividing the movable electrode into two parts; a frame part having a substantially rectangular shape in plan view surrounding the first electrode part and the second electrode part with a predetermined interval; A pair of beam portions that connect the first electrode portion, the second electrode portion, and the frame portion, respectively, and support the first electrode portion and the second electrode portion so as to be swingable with respect to the frame portion; A pair of fixed electrodes disposed opposite to each other with a predetermined distance from the first electrode portion and the second electrode portion, and between the movable electrode and the fixed electrode when the movable electrode swings An acceleration sensor that detects acceleration from a change in electrostatic capacitance of the beam portion, and the beam portion substantially coincides with the direction orthogonal to the diagonal line in the vicinity of the corner portion of the frame portion, and both end portions in the axial direction are frame portions. The first electrode portion and the second electrode are formed at a substantially central portion in the axial direction of each beam portion. An acceleration sensor, characterized in that integrally formed but each.

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