JP2011112389A - Acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acceleration sensor improving precision of temperature characteristics of output and reducing a difference in capacitance between each fixed electrode and each movable electrode. <P>SOLUTION: The acceleration sensor includes two sensor units comprising weight units 4, 5 where recesses 41, 51 and full units 40, 50 are formed integrally, a pair of beam units 6a, and the like, movable electrodes 4a, 5a, first fixed electrodes 20a, 21a and second fixed electrodes 20b, 21b, and electrode units 8a, and the like including respective detection electrodes 80a, and the like. The respective electrode units 8a, and the like are disposed along one direction so that the sensor chip 1 is divided into half, the respective weight units 4, 5 are disposed so that the respective weight units 4, 5 are symmetrical with respect to a point with nearly the center of the arrangement of the respective electrode units 8a, and the like as a center, and the respective beam units 6a, and the like are disposed so that a straight line connecting the respective beam units 6a, and the like are orthogonal to the arrangement directions of the respective electrode units 8a, and the like. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a capacitance type acceleration sensor.

  Conventionally, a rectangular parallelepiped weight portion having a movable electrode, a pair of beam portions that rotatably support the weight portion at a substantially center in the longitudinal direction of the weight portion, and a straight line connecting the pair of beam portions as a boundary line An acceleration sensor is known that includes a pair of fixed electrodes that are arranged to face each other on the one side and the other side of the surface of the weighted portion with a predetermined distance therebetween (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. 4 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 longitudinal direction of the sensor chip 1 is the y direction, x direction, and y direction. The directions orthogonal to each other are defined as the z direction. In this conventional example, as shown in FIG. 4, the sensor chip 1 whose outer shape is a rectangular plate, the upper fixing plate 2 a 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 state in which a gap is formed between a frame portion 3 in which two rectangular frame portions 3a and 3b as viewed in the vertical direction are arranged in parallel in the longitudinal direction and an inner peripheral surface of the frame portions 3a and 3b. The weights 4 and 5 having a rectangular parallelepiped shape arranged in the frame portions 3a and 3b and the inner peripheral surface of the frame portions 3a and 3b and the side surfaces of the weight portions 4 and 5 are connected to the frame portion 3 to be weighted. A pair of beam portions 6a, 6b and 7a, 7b for rotatably supporting the portions 4, 5 and movable electrodes 4a, 5a formed on the upper surfaces of the weight portions 4, 5 are provided.

  The weight portions 4 and 5 are integrally formed with a recess (not shown) that opens to one surface (lower surface) and a solid portion (not shown) excluding the recess. The concave portion is formed in a square shape in plan view when viewed from the normal direction (vertical direction) of the opening surface, and a reinforcing wall (not shown) that divides the concave portion into two is formed integrally with the weight portions 4 and 5. ing.

  The pair of beam portions 6a and 6b connects the frame portion 3a and the substantially central portion in the x direction of the side surface facing the frame portion 3a of the weight portion 4. Similarly, the pair of beam portions 7a and 7b connects the frame portion 3b and the substantially central portion in the x direction of the side surface facing the frame portion 3b of the weight portion 5. Thus, a straight line connecting the pair of beam portions 6a and 6b and a straight line connecting the pair of beam portions 7a and 7b serve as a rotation axis, and the weight portions 4 and 5 rotate around the rotation axis. It is like that.

  The sensor chip 1 is formed by processing an SOI (Silicon on Insulator) substrate by a semiconductor microfabrication technique, and the portions including the upper surfaces of the weight portions 4 and 5 become the movable electrodes 4a and 5a. Further, protrusions 43a, 43b, 53a, 53b for preventing the weights 4, 5 from directly colliding with the upper fixing plate 2a and the lower fixing plate 2b protrude from the upper and lower surfaces of the weights 4, 5, respectively. It is installed.

  The upper fixed plate 2a is made of an insulating material such as glass, for example, and the lower surface thereof has the first fixed electrode 20a and the first fixed electrode 20a at a position facing the weight portion 4 (movable electrode 4a) of the sensor chip 1 along the vertical direction. The second fixed electrode 20b and the second fixed electrode 20b are arranged side by side in the x direction, and the first fixed electrode 21a and the second fixed electrode 20a are arranged at positions facing the weight portion 5 (movable electrode 5a) of the sensor chip 1 along the vertical direction. The fixed electrode 21b is juxtaposed in the x direction. Further, five through holes 22a to 22e are arranged side by side in the y direction on one end side in the x direction of the upper fixing plate 2a. 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, 9 b separated from the frame portion 3 are juxtaposed on one end side in the x direction 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. In addition, a pressure contact electrode (not shown) made of a metal film is formed. 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, the conductive pattern formed on the lower surface of the upper fixing plate 2a and the press contact electrode are connected by press contact, whereby each of the detection electrodes 80a, 80b, 90a and 90b are electrically connected to the fixed electrodes 20a, 20b, 21a and 21b, and the detection electrodes 80a, 80b, 90a and 90b are exposed to the outside through the through holes 22a to 22d of the upper fixed plate 2a. To do. 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 glass like the upper fixing plate 2a, and the upper surface of the lower fixing plate 2b is respectively attached to the sensor chip 1 at positions facing the weight portions 4 and 5 along the vertical direction. , 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 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 90a and 90b each constitute a sensor part, and the direction of weight parts 4 and 5 (the solid part and The two sensor portions are integrally formed in a state where the arrangement of the recesses is inverted 180 degrees.

Next, the detection operation of the conventional example will be described. First, consider a case where an acceleration in the x direction is applied to one weight portion 4. When acceleration is applied in the x direction, the weight 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 each fixed electrode 20a, 20b when no acceleration in the x direction is applied is C0, and the change in capacitance caused by the application of acceleration is ΔC. For example, the capacitances C1 and C2 when the acceleration in the x direction is applied are:
C1 = C0−ΔC (1)
C2 = C0 + ΔC (2)
It can be expressed as.

Similarly, when an acceleration in the x 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 from the detection electrodes 80a and 80b and 90a and 90b. Then, the difference value CA (= C1-C2) between the capacitances C1, C2 obtained from one sensor unit and the difference value CB (= C3-C4) between the capacitances C3, C4 obtained from the other sensor unit. Is calculated (± 4ΔC), the direction and magnitude of the acceleration applied in the x direction can be calculated based on the sum of the difference values CA and CB.

Next, consider a case where an acceleration in the z direction is applied to one weight portion 4. When acceleration is applied in the z 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 z direction is applied is C0, and the change in capacitance caused by the application of acceleration is ΔC. For example, the capacitances C1 and C2 when the acceleration in the z direction is applied are:
C1 = C0 + ΔC (5)
C2 = C0−ΔC (6)
It can be expressed as.

Similarly, when acceleration in the z direction is applied to the other weight portion 5, the capacitances C3 and C4 between the movable electrode 5a and the fixed electrodes 21 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 sensor unit and the difference value CB (= C3-C4) between the capacitances C3, C4 obtained from the other sensor unit. Is calculated (± 4ΔC), the direction and magnitude of the acceleration applied in the z direction can be calculated based on the difference between the difference values CA and CB. Note that calculation processing for obtaining the direction and magnitude of the acceleration in the x direction and the z direction based on the sum and difference of the difference values CA and CB is well known in the art, and detailed description thereof is omitted here.

Special table 2008-544243 gazette

  By the way, in the acceleration sensor as in the conventional example, the difference in thermal expansion coefficient between the material (here, silicon) constituting the sensor chip 1 and the material (here, glass) constituting each of the fixing plates 2a and 2b. There is a risk of distortion due to the resulting thermal stress. Further, when the sensor chip 1 is die-bonded to a package (not shown) with a resin material, the sensor chip 1 may be distorted. When the sensor chip 1 is thus distorted and twisted, the stress is concentrated on the diagonal line of the sensor chip 1. Here, the sensor chip 1 of the above-described conventional example has a substantially symmetrical structure with respect to an axis parallel to the x direction passing through the approximate center in the y direction, but passing through the approximate center in the x direction and the y direction. It is not a line-symmetric structure with respect to an axis parallel to the axis. For this reason, a difference arises in the stress which concentrates by the solid part of each weight part 4 and 5, and a recessed part. Therefore, there is a problem that the accuracy of the temperature characteristic of the output such as the temperature characteristic of the detection sensitivity and the offset temperature characteristic deteriorates.

  In the conventional example, the distance between the first fixed electrodes 20a, 21a and the electrode portions 8a, 8b, 9a, 9b and the second fixed electrodes 20b, 21b and the electrode portions 8a, 8b in each sensor unit. , 9a, 9b are different from each other. For this reason, since the wiring lengths of the conductive patterns connecting the electrodes are different from each other, the parasitic capacitances of the conductive patterns are also different. Therefore, the electrostatic capacitance between the fixed electrodes 20a,... And the movable electrodes 4a, 5a is different. There was a problem in that there was a difference in capacity.

  The present invention has been made in view of the above points, and can improve the accuracy of output temperature characteristics and reduce the difference in capacitance between each fixed electrode and each movable electrode. An object is to provide an acceleration sensor.

  In order to achieve the above object, the first aspect of the present invention is such that the concave portion opening on one surface and the weight portion integrally formed with the solid portion excluding the concave portion, and the concave portion and the solid portion are aligned along the rotation direction. A pair of beam portions that rotatably support the weight portion, a movable electrode provided across the concave portion and the solid portion on the other surface different from the one surface where the concave portion opens, and the concave portion side of the movable electrode; A first fixed electrode disposed at a position facing the second fixed electrode; a second fixed electrode disposed at a position facing the solid portion side of the movable electrode; and a detection electrode electrically connected to each fixed electrode. A change in capacitance between the movable electrode and the fixed electrode that accompanies the rotation of the weight portion with a straight line connecting the pair of beam portions as a rotation axis. Acceleration sensor for detecting acceleration, and the sensor unit is 2 on the same chip. Each electrode part is arranged along one direction so as to divide the chip in half, and each weight part is arranged so as to be symmetric about the center of the arrangement of each electrode part, and each Each beam part is arranged so that a straight line connecting the beam parts is along a direction orthogonal to the arrangement direction of each electrode part.

  The invention of claim 2 is characterized in that, in the invention of claim 1, the acceleration in the first direction applied to the weight portion and the acceleration in the second direction orthogonal to the first direction are detected. .

  The invention of claim 3 is characterized in that, in the invention of claim 2, one of the sensor parts is arranged to rotate 180 degrees in the same plane with respect to the other sensor part.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, a protrusion is formed on a surface of each fixed electrode facing the movable electrode or a surface facing each fixed electrode of the movable electrode. It is characterized by that.

  According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the protrusion is formed of silicon or a silicon oxide film.

  The invention of claim 6 is characterized in that, in the invention of claim 4, the surface of the protrusion is formed of a carbon material.

  The invention of claim 7 is characterized in that, in the invention of claim 6, the carbon material is a carbon nanotube.

  The invention according to claim 8 is the invention according to any one of claims 1 to 7, further comprising a fixing plate disposed at a predetermined distance from a surface opposite to the opposite side of the weight fixed electrode. The surface of the fixing plate facing the weight portion is provided with an adhesion preventing film for preventing the weight portion from adhering.

  The invention according to claim 9 is the invention according to claim 8, wherein the adhesion preventing film is made of the same material as that of the fixed electrode.

  The invention of claim 10 is characterized in that, in the invention of claim 8 or 9, the adhesion preventing film is formed simultaneously with the fixed electrode.

  According to an eleventh aspect of the present invention, in the invention according to any one of the eighth to tenth aspects, the adhesion preventing film is formed using a semiconductor manufacturing process.

  A twelfth aspect of the invention is characterized in that, in the invention of any one of the eighth to eleventh aspects, the adhesion preventing film is formed of an aluminum alloy.

  According to a thirteenth aspect of the present invention, in the invention according to any one of the eighth to twelfth aspects, the first and second fixed electrodes and the movable electrode are generated by generating a suction force between the fixed electrode and the movable electrode. It is characterized by detecting a change in capacitance between the two.

  The invention of claim 14 is characterized in that, in the invention of claim 13, a thin film made of an organic material is provided on the surface of the adhesion preventing film.

  The invention of claim 15 is the invention of claim 14, characterized in that the thin film is a polyimide thin film.

  The invention according to claim 16 is the invention according to any one of claims 1 to 15, wherein the angle formed between the perpendicular line drawn from the center of gravity of the weight portion to the rotation shaft and the surface of the movable electrode is approximately 45 degrees. As described above, the beam portion is arranged to be shifted to the concave portion side.

  According to the present invention, since the symmetry of the entire sensor is increased, even when distortion occurs due to thermal expansion or the like, the entire sensor is also distorted, and the overall balance is not impaired. Therefore, it is possible to improve the accuracy of the temperature characteristic of the output. Also, as the distance between each electrode part and each weight part becomes equal, the distance between each electrode part and each fixed electrode also becomes equal, so the wiring length of each conductive pattern that connects the electrodes is reduced. Can be equal to each other. Therefore, the difference in parasitic capacitance of each conductive pattern is reduced, and the difference in capacitance between each movable electrode and each fixed electrode can also be reduced. Further, since the distance from the beam portion to each end of the weight portion, that is, the turning radius of the weight portion can be increased, the same detection sensitivity can be obtained as compared with the conventional acceleration sensor having the same size as the chip. Therefore, the required rotational displacement can be reduced. For this reason, since the bending rigidity of a beam part can be made high, even if a movable electrode adheres to a fixed electrode, a movable electrode can be peeled from a fixed electrode with the restoring force of a beam part.

It is a disassembled perspective view which shows embodiment of the acceleration sensor which concerns on this invention. It is the top view which looked at the sensor chip same as the above from the lower side. It is sectional drawing same as the above. It is a disassembled perspective view which shows the conventional acceleration sensor.

  Hereinafter, embodiments 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. In the following description, the vertical direction in FIG. 1 is the vertical direction, the direction parallel to the longitudinal direction of the sensor chip 1 is the x direction, and the direction parallel to the short direction of the sensor chip 1 is the y direction, x direction, and y direction. The directions orthogonal to each other are defined as the z direction.

  In the present embodiment, as shown in FIG. 1, the electrode portions 8a, 8b, 9a, 9b, and 10a are arranged linearly along the x direction at substantially the center in the short direction (y direction) of the sensor chip 1. ing. That is, the electrode portions 8a,... Are arranged so as to divide the sensor chip 1 in half. A ground electrode 10 is provided on the upper surface of the electrode portion 10a. Further, the weights 4 and 5 are arranged so as to be point-symmetric about the approximate center of the arrangement of the electrode parts 8a, and a straight line connecting the beam parts 6a, 6b, 7a, and 7b is provided for each electrode. Each beam part 6a, 6b, 7a, 7b is arrange | positioned along the direction (y direction) orthogonal to the arrangement direction of the part 8a, 8ab, 9a, 9b. Further, the electrode portion 8a and the first fixed electrode 20a, the electrode portion 8b and the second fixed electrode 20b, the electrode portion 9a and the first fixed electrode 21a, and the electrode portion 9b and the second fixed electrode 21b each have a conductive pattern. Is electrically connected. In the present embodiment, as shown in FIG. 2, in the concave portions 41 and 51 of the weight portions 4 and 5, two reinforcing walls 42 and 52 are respectively provided so that the inside of the concave portions 41 and 51 is divided into three parts. It is formed integrally with the parts 4 and 5.

  By configuring as described above, in this embodiment, the sensor chip 1 has a point-symmetric structure with the ground electrode 10 as the center. For this reason, the symmetry of the whole sensor increases, and even when distortion occurs due to thermal expansion or the like, the whole sensor is also distorted, and the overall balance is not lost. Therefore, it is difficult for the stresses concentrated in the solid portions 40 and 50 and the concave portions 41 and 51 of the weight portions 4 and 5 and the beam portions 6a and 6b and 7a and 7b to occur, and the temperature characteristic of the output is improved. be able to.

  Further, in the present embodiment, as the distance between each electrode portion 8a,... And each weight portion 4, 5 becomes equal, the distance between each electrode portion 8a,... And each fixed electrode 20a,. Since the distances are also equal, the wiring lengths of the conductive patterns connecting the electrodes can be made equal to each other. Therefore, the difference in parasitic capacitance of each conductive pattern is reduced, and the difference in capacitance between each movable electrode 4a, 5a and each fixed electrode 20a,.

  Further, in the present embodiment, the distance from the beam portions 6a, 6b, 7a, 7b to the end portions in the longitudinal direction of the weight portions 4, 5, that is, the turning radius of the weight portions 4, 5 can be increased. Therefore, the rotational displacement necessary for the sensor chip 1 to obtain the same detection sensitivity as compared with the conventional acceleration sensor having the same dimensions can be reduced. Therefore, since the bending rigidity of the beam portions 6a, 6b, 7a, 7b can be increased, the beam portions 6a, 6b, 7a even if the movable electrodes 4a, 5a are attached to the fixed electrodes 20a,. , 7b, the movable electrodes 4a, 5a can be peeled off from the fixed electrodes 20a,.

  Incidentally, in this embodiment, as shown in FIG. 3, the protrusions 43a, 43b, 53a, and 53b are provided in the same manner as the acceleration sensor of the conventional example, but the protrusions 43a, 43b, 53a, and 53b are made of silicon. Alternatively, the protrusions 43a, 43b, 53a, 53b can be easily manufactured when formed from the main material of the sensor chip such as a silicon oxide film. Moreover, you may coat the surface layer of protrusion part 43a, 43b, 53a, 53b with a carbon material. In this case, the mechanical strength of the protrusions 43a, 43b, 53a, 53b is increased, and the protrusions 43a, 43b, 53a, 53b can be prevented from being damaged by the collision with the upper fixing plate 2a and the lower fixing plate 2b. it can. Furthermore, if carbon nanotubes are used as the carbon material, the thickness of the coating can be reduced, so that the protrusions 43a, 43b, 53a, 53b can be easily adjusted to the desired height.

  Further, in the present embodiment, as shown in FIG. 1, the adhesion preventing films 23a and 23b are provided in the same manner as the conventional acceleration sensor, but the adhesion preventing films 23a and 23b are the same as the fixed electrodes 20a,. By forming with a material, the adhesion preventing films 23a and 23b can be easily formed. At this time, if the adhesion preventing films 23a, 23b are formed simultaneously with the fixed electrodes 20a,..., Between the weight portions 4, 5 and the fixed electrodes 20a,... And between the weight portions 4, 5 and the lower fixed plate 2b. The accuracy of the distance can be increased.

  When the adhesion preventing films 23a and 23b are formed by a semiconductor manufacturing process, minute irregularities are formed on the surfaces of the adhesion preventing films 23a and 23b, so that the weight portions 4 and 5 adhere to the lower fixing plate 2b. Can be more suitably prevented. Here, when the adhesion preventing films 23a and 23b are formed of an aluminum alloy, the etching process becomes easy. Further, by forming an organic material thin film such as a polyimide thin film having good consistency with the semiconductor manufacturing process and easy to process on the surface of the adhesion preventing films 23a and 23b, the adhesion preventing films 23a and 23b and the weight part 4 are formed. , 5 may be prevented from being short-circuited.

  In the present embodiment, as shown in FIG. 1, between the adjacent electrode portions 8 a,..., Between each electrode portion 8 a,... And the frame portion 3, each electrode portion 8 a,. , 5 are respectively provided with gaps. With this configuration, the detection electrodes 80a, 80b, 90a, and 90b are electrically insulated from each other, thereby reducing parasitic capacitance of the detection electrodes 80a, 80b, 90a, and 90b and crosstalk between the electrodes. Highly accurate capacitance detection can be performed.

  In the present embodiment, as shown in FIG. 3, the beam portions 6a, 6b, 7a, 7b (only the beam portion 6a is shown in the figure) are recessed from the approximate center in the longitudinal direction of the weight portions 4, 5. By shifting to the side (left side of the figure), the angle θ formed by the perpendicular line drawn from the center of gravity of the weights 4 and 5 to the rotation axis and the surfaces of the movable electrodes 4a and 5a becomes approximately 45 degrees. I am doing so. Thus, the angle θ can be maintained at about 45 degrees simply by shifting the beam portions 6a, 6b, 7a, 7b, so that the thickness dimensions of the weight portions 4, 5 are increased, or the weight portion 4 , 5 can be improved without reducing the weight.

  In the present embodiment, the operation of the acceleration sensor can be confirmed by following the following procedure. That is, an attractive force is generated between the first fixed electrode 20a or the second fixed electrode 20b and the movable electrode 4a, or between the first fixed electrode 21a or the second fixed electrode 21b and the movable electrode 5a. Thus, the weight parts 4 and 5 are rotated. Whether the acceleration sensor is operating normally by detecting a change in capacitance between the fixed electrodes 20a,... And the weights 4 and 5 that occur as the weights 4 and 5 rotate. You can check whether or not. The same operation confirmation may be performed by generating a suction force between the adhesion preventing films 23a and 23b and the movable electrodes 4a and 5a.

DESCRIPTION OF SYMBOLS 1 Sensor chip 20a, 21a 1st fixed electrode 20b, 21b 2nd fixed electrode 4, 5 Weight part 40, 50 Solid part 41, 51 Recessed part 4a, 5a Movable electrode 6a, 6b Beam part 7a, 7b Beam part 8a, 8b, 9a, 9b Electrode portion 80a, 80b, 90a, 90b Detection electrode

Claims (16)

  A pair of beam portions that rotatably supports the weight portion so that the concave portion and the solid portion excluding the concave portion are integrally formed, and the weight portion and the solid portion are aligned along the rotation direction. And a movable electrode provided across the concave portion and the solid portion on the other surface different from the one surface where the concave portion opens, a first fixed electrode disposed at a position facing the concave portion side of the movable electrode, A sensor unit including a second fixed electrode disposed at a position facing the solid portion side of the movable electrode and a pair of electrode units having a detection electrode electrically connected to each fixed electrode; An acceleration sensor that detects acceleration from a change in capacitance between a movable electrode and a fixed electrode that accompanies rotation of a weight portion with a straight line connecting a pair of beam portions as a rotation axis. Two are formed on the chip, and each electrode part divides the chip in half Arranged in one direction, the weights are arranged so as to be point-symmetric about the center of the arrangement of the electrode parts, and the straight line connecting the beam parts is orthogonal to the arrangement direction of the electrode parts. An acceleration sensor characterized in that each beam portion is arranged along a direction to be moved.   2. The acceleration sensor according to claim 1, wherein an acceleration in a first direction applied to the weight part and an acceleration in a second direction orthogonal to the first direction are detected.   The acceleration sensor according to claim 2, wherein the one sensor unit is rotated 180 degrees in the same plane with respect to the other sensor unit.   The acceleration according to any one of claims 1 to 3, wherein a protrusion is formed on a surface of each of the fixed electrodes facing the movable electrode or on a surface of the movable electrode facing the fixed electrode. Sensor.   The acceleration sensor according to claim 4, wherein the protrusion is formed of silicon or a silicon oxide film.   The acceleration sensor according to claim 4, wherein the protrusion has a surface layer formed of a carbon material.   The acceleration sensor according to claim 6, wherein the carbon material is a carbon nanotube.   A fixing plate disposed at a predetermined distance from a surface opposite to a surface of the weight portion opposite to the fixed electrode; and preventing the weight portion from adhering to the surface of the fixing plate facing the weight portion. An acceleration sensor according to any one of claims 1 to 7, further comprising an adhesion preventing film.   The acceleration sensor according to claim 8, wherein the adhesion preventing film is made of the same material as the fixed electrode.   10. The acceleration sensor according to claim 8, wherein the adhesion preventing film is formed simultaneously with the fixed electrode.   The acceleration sensor according to claim 8, wherein the adhesion preventing film is formed using a semiconductor manufacturing process.   The acceleration sensor according to claim 8, wherein the adhesion preventing film is made of an aluminum alloy.   9. A change in electrostatic capacitance between the first and second fixed electrodes and the movable electrode is detected by generating an attractive force between the fixed electrode and the movable electrode. The acceleration sensor according to any one of 12.   The acceleration sensor according to claim 13, wherein a thin film made of an organic material is provided on a surface of the adhesion preventing film.   The acceleration sensor according to claim 14, wherein the thin film is a polyimide thin film.   The beam portion is arranged so as to be shifted to the concave portion side so that an angle formed by a perpendicular drawn from the center of gravity of the weight portion to the rotation shaft and the surface of the movable electrode is approximately 45 degrees. The acceleration sensor according to any one of 1 to 15.

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