JP2010210416A - Acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To supply an acceleration sensor which can be miniaturized, while suppressing deterioration in the detection sensitivity. <P>SOLUTION: Weight parts 4 and 5 have recessed parts 11 and 13 opened in the underside and solid parts 12 and 14, excluding the recessed parts 11 and 13, which are formed integrally. In the recessed parts 11 and 13, an embedded part 17, consisting of a material having a specific gravity twice or higher that of a material forming the solid parts 12 and 14, is formed in each section divided by two reinforcing walls 16 and 16. Thus, the dimensions can be lessened, without changing the weight of the weight parts 4 and 5, and as a result, miniaturization can be attained, while suppressing deterioration in the detection sensitivity. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a capacitance type acceleration sensor.

  Conventionally, as shown in FIG. 7, 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. 7 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, when the size of the weight part 100 is reduced in the conventional example, the weight of the weight part 100 is also reduced, and when the acceleration is applied, the moment with the beam axis as the rotation axis is reduced and the detection sensitivity may be lowered. was there.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an acceleration sensor that can be downsized while suppressing a decrease in detection sensitivity.

  In order to achieve the above object, the invention according to claim 1 is a weight portion having a movable electrode provided on one surface thereof, a beam portion for rotatably supporting the weight portion around a rotation shaft, and the movable electrode. The weight portion is formed of a material having a specific gravity that is twice or more that of other portions excluding the portion.

  According to the first aspect of the present invention, since at least a part of the weight part is formed of a material having a specific gravity that is twice or more that of other parts excluding the part, for example, the weight of the weight part is not changed. The size can be reduced. As a result, downsizing can be achieved while suppressing a decrease in detection sensitivity.

  According to a second aspect of the present invention, in the first aspect of the invention, the weight portion is formed such that a portion formed of the material and a portion having a weight less than the portion are aligned along the rotation direction. It is characterized by being.

  According to the present invention, downsizing can be achieved while suppressing a decrease in detection sensitivity.

1 shows an embodiment of the present invention, (a) is a bottom view of a sensor chip, and (b) is a cross-sectional view. It is an exploded perspective view same as the above. (A)-(e) is sectional drawing for demonstrating the manufacturing method same as the above. (A), (b) is sectional drawing which shows another structure of the weight part in the same as the above. 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. In the following description, however, the x-axis direction in FIG. 2 is defined as the vertical direction, the y-axis direction as the horizontal direction, and the z-axis direction as the vertical direction.

  In this embodiment, as shown in FIG. 2, the sensor chip 1 whose outer shape is a rectangular flat plate, the upper fixing plate 2 a fixed to the upper surface side of the sensor chip 1, and the lower portion fixed to the lower surface side of the sensor chip 1 And a fixed 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 And a pair of beam portions 6a, 6b and 7a, 7b that support 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. 1, 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. Further, in each of the sections of the recesses 11 and 13 separated by the two reinforcing walls 16 and 16, an embedded portion made of a material having a specific gravity more than twice that of the material forming the solid portions 12 and 14. 17 is formed.

Here, in the present embodiment, since the solid portions 12 and 14 are formed of silicon (specific gravity: 2.33 [g / cm ³ ]), the material for forming the embedded portion 17 is nickel (specific gravity: 8. 90 [g / cm ³ ]), tungsten (specific gravity: 19.3 [g / cm ³ ]), chromium (specific gravity: 7.87 [g / cm ³ ]), palladium (specific gravity: 12.02 [g / cm ³ ]), platinum (specific gravity: 21.45 [g / cm ³ ]), manganese (specific gravity: 7.43 [g / cm ³ ]), or the like may be used.

  One end of the pair of beam portions 6a and 6b is connected to the central portion in the vertical direction on the inner peripheral surface of the frame portion 3a facing in the horizontal direction, and the other is near the boundary between the concave portion 11 and the solid portion 12 on the side surface of the weight portion 4. The ends are connected. Similarly, one pair of beam portions 7a and 7b is connected at one end to the longitudinal center portion of the inner peripheral surface of the frame portion 3b facing in the lateral direction, and near the boundary between the concave 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 6a and 6b and 7a and 7b 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. Although not shown in FIG. 2, the weights 4 and 5 are prevented from directly colliding with the upper fixing plate 2a and the lower fixing plate 2b on the upper and lower surfaces of the weights 4 and 5, respectively. Protrusions 15a to 15g are projected.

  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 passed through the through holes 22a-22d of the upper fixed plate 2a. It is exposed to the outside (see FIG. 1B). 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 the present embodiment, the frame portion 3a, the weight portion 4, the beam portions 6a and 6b, the movable electrode 4a, the first and second fixed electrodes 20a and 20b, the detection electrodes 80a and 80b, the frame portion 3b and the weight. Part 5, beam parts 7a and 7b, 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 recess portions 11 and 13 and the solid portions 12 and 14 and the auxiliary wall 16). After the formation of the embedded portion 17 by embedding a material having a specific gravity more than twice that of silicon, such as tungsten, chromium, palladium, platinum, and manganese, into the recesses 11 and 13 defined by the auxiliary wall 16, the adhesion prevention is performed. The lower fixing plate 2b having the 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)).

  Thus, according to the present embodiment, at least a part of the weight parts 4 and 5 (embedded part 17) has a specific gravity more than twice that of other parts (solid parts 12 and 14) excluding the part. Since it is made of a material, for example, it is possible to reduce the size without changing the weight of the weight portions 4 and 5, and as a result, it is possible to reduce the size while suppressing a decrease in detection sensitivity.

  Here, instead of embedding a material whose specific gravity is twice or more larger than that of the material of the solid portions 12 and 14 in the recesses 11 and 13, as shown in FIG. The portion 18 may be formed at a portion where the concave portions 11 and 13 were formed. Alternatively, as shown in FIG. 4B, the auxiliary walls 16 and the inner walls of the recesses 11 and 13 are removed, and the solid portions 12 and 14 have a specific gravity 2 higher than that of the material (silicon) forming the movable electrodes 4a and 5a. It may be made of a material that is twice or more larger.

  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. 5, 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 z-axis can be realized. Alternatively, as shown in FIG. 6, three acceleration sensors are arranged in the same chip surface, and the second and third acceleration sensors S2 and S3 are 90 degrees in the chip surface 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 4,5 Weight part 4a, 5a Movable electrode 6a, 6b Beam part 7a, 7b Beam part 11,13 Recessed part 12,14 Filling part 17 Embedded part 20a, 21a 1st fixed electrode 20b, 21b 2nd Fixed electrode

Claims (2)

  A weight portion provided with a movable electrode on one surface, a beam portion that rotatably supports the weight portion around a rotation axis, and a fixed electrode disposed to face the movable electrode, the weight portion, An acceleration sensor, characterized in that at least a part is formed of a material having a specific gravity twice or more that of other parts excluding the part.   2. The acceleration sensor according to claim 1, wherein the weight portion is formed so that a portion formed of the material and a portion having a weight less than the portion are aligned along a rotation direction.

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