JP2008064603A - Acceleration sensor and acceleration detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To miniaturize an acceleration sensor, and achieve a triaxial acceleration detection. <P>SOLUTION: First and second main faces are disposed so as to be perpendicular to a substrate. The first main face is fixed to the substrate. The second main face is supported so as to be integrally and three-dimensionally displaced. The first and second main faces are provided each of which has a length larger in the direction of a substrate's main face than in the direction perpendicular to the substrate. At each capacitor, the first and second main faces are disposed so as to shift centroids of the first and second main face perpendicularly to the main face of the substrate. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a capacitance type acceleration sensor manufactured by a so-called surface micromachining technique, and an acceleration detection apparatus including the acceleration sensor.

  In recent years, an acceleration detection apparatus having an acceleration sensor capable of detecting an acceleration acting three-dimensionally has attracted attention as a highly functional acceleration detection apparatus. At the same time, there is a tendency to further downsize the acceleration sensor. In the production of an acceleration sensor, a MEMS (Micro Electro Mechanical System) technology is introduced for miniaturization.

Accelerometers incorporating MEMS technology can be broadly classified into those using piezoresistive elements and those using capacitive elements, and those using piezoresistive elements have been the mainstream from the history of development. However, there is a structural limit to the demand for miniaturization, and from the viewpoint of reducing power consumption, a device using a capacitive element is now emerging.
The MEMS technology for manufacturing a small acceleration sensor is roughly classified into a bulk micromachining technology and a surface micromachining technology. An acceleration sensor manufactured using a bulk micromachining technology has been proposed that can detect acceleration components in three axial directions (see Patent Document 1). However, the bulk micromachining technology can reduce the size. Since it is difficult, the thing which can detect each acceleration component of a triaxial direction using the surface micromachining technique from the viewpoint of the further size reduction is searched.

Conventionally, a capacitance type acceleration sensor manufactured by surface micromachining technology can detect an acceleration component in one axis direction (refer to Patent Document 2) or a two-axis acceleration component in a substrate main surface direction. What can be detected (see Patent Document 3) has been proposed. Therefore, in order to detect acceleration acting in a three-dimensional manner, it is considered that these three or two may be simply combined. .
Japanese Patent Laying-Open No. 2005-017216 JP 2003-337138 A Special Table 2000-512023

  However, if three or two acceleration sensors using the conventional surface micromachining technique are combined to detect acceleration acting in three dimensions, is one substrate provided so as to be orthogonal to another substrate? There may be a need to arrange two sensor structures on a substrate, or to produce a sensor with a very complicated structure, and it may not be possible to meet the demand for miniaturization.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an acceleration sensor capable of detecting an acceleration that can be reduced in size and acting three-dimensionally, and an acceleration detection device including the acceleration sensor. To do.

  In order to achieve the above object, the acceleration sensor according to the present invention comprises a substrate and a swinging body swingable in the X, Y, and Z axis directions with respect to the substrate. And at least one movable electrode is formed on each of a total of four swing rod members extending in opposite directions around the intersection of both swing rods. The fixed electrode that faces each of the movable electrodes is formed on the substrate side to form at least four electrode pairs, and the movable members of the pair of rocking rod members constituting the first rocking rod are movable. A pair of the electrode pairs formed by the electrodes and the fixed electrodes opposed to the electrodes is contracted with respect to the longitudinal swing (X-axis direction) of the first swing rod so that the gap between the one electrode pair is reduced. The pair of the above-mentioned rocking members constituting the second rocking rod is set so that the gap between the other electrode pair is widened. A pair of the electrodes formed by the movable electrodes of the flange member and the fixed electrode opposed to the movable electrode is set to one electrode with respect to the swing in the longitudinal direction (Y-axis direction) of the second swing rod. The gap between the pair of electrodes is set so that the gap between the other electrode pair is widened, and the change in the facing area of the electrode pair of the first rocking rod and the second rocking movement are further performed when the rocking body moves in the Z-axis direction. The relationship between the fixed electrode and the movable electrode was set so that the change in the facing area of the electrode pair of the palpit was reversed.

  As described above, the acceleration sensor according to the present invention includes the substrate and the oscillating body that can oscillate in the X, Y, and Z axis directions with respect to the substrate, and the oscillating body includes the first oscillating rod and the first oscillating rod. A crossing second rocking rod, and extending in opposite directions around the intersection of the two rocking rods, and forming at least one movable electrode on each of a total of four rocking rod members, A fixed electrode facing each of the movable electrodes is formed on the substrate side to form at least four electrode pairs, and each of the movable electrodes of the pair of rocking rod members constituting the first rocking rod The pair of the electrode pairs formed by the fixed electrodes opposed to the first electrode pair is contracted with respect to the longitudinal swing (X-axis direction) of the first swinging hook portion, and the gap between the first electrode pair is reduced. The gap between the other pair of electrodes is set so that the gap between the other electrode pair is widened, and the pair of the above-mentioned rocking rods constituting the second rocking rod A pair of the electrode pairs formed by the movable electrode and the fixed electrode opposed to the movable electrode has a gap between one electrode pair with respect to the longitudinal oscillation (Y-axis direction) of the second oscillation rod. It set so that it might shrink and the gap of the other electrode pair might expand.

Specifically, in the acceleration sensor according to the present invention, a plurality of the movable electrodes of the two oscillating rods and a plurality of the fixed electrodes on the substrate are provided, and the arrangement order thereof is set to the two oscillating electrodes. When viewed from the crossing part of the scissors, the above functions can be exhibited if they are in the same order in the direction along any of the swing scissors members.
Therefore, in the acceleration sensor according to the present invention, when the acceleration is applied, the change in the gap between one electrode pair and the change in the gap between the other electrode pair are compared in each of the first swing rod and the second swing rod. When the signs of each other are reversed, and the amount of change in the capacitance of one capacitor is compared with the amount of change in the capacitance of the other capacitor when acceleration acts and each electrode pair functions as a capacitor In addition, the sign of the component due to the displacement in the X-axis direction or the Y-axis direction is reversed.

In addition, with respect to the rocking motion of the rocking body in the Z-axis direction, the change in the facing area of the electrode pair of the first rocking rod and the change in the facing area of the electrode pair of the second rocking rod is reversed. The relationship between the electrode and the movable electrode was set.
Specifically, in the acceleration sensor according to the present invention, each movable electrode formed on each of the first swing rod and the second swing rod is formed in a long shape in parallel with the substrate. The opposed fixed electrodes are elongated and parallel to the substrate, and the fixed electrode and the movable electrode are opposed to each other so that their respective axes are parallel to each other. The order of the centroid of the opposing surface on the movable electrode side in the opposing surface and the centroid of the opposing surface on the fixed electrode side in the Z-axis direction is the same as that on the movable electrode side in the opposing surface of the electrode pair of the second swing rod. If the order of the centroid of the opposing surface and the centroid of the opposing surface on the fixed electrode side in the Z-axis direction is reversed, the above function can be exhibited.

Therefore, in the acceleration sensor according to the present invention, when the electrode pair of the first swing rod and the electrode pair of the second swing rod are compared, the capacitance change of the capacitor when the electrode pair functions as a capacitor. In the quantity, the sign of the component due to the displacement in the Z-axis direction is reversed.
In the acceleration sensor according to the present invention, by adopting the above configuration, a component resulting from the displacement in the X-axis direction, the Y-axis direction, and the Z-axis direction is included in the change in capacitance of each capacitor. Therefore, by performing arithmetic processing such as a Gaussian elimination method based on the measured capacitance value of each capacitor, the three-axis directions (the X-axis direction, the Y-axis direction, and the Z-axis direction), respectively. It is possible to extract a component due to the displacement of. It is preferable to make these X-axis, Y-axis, and Z-axis coincide with the orthogonal coordinate system because the usability of each displacement component after extraction is improved.

  Here, in the acceleration sensor, the capacitance of each capacitor when acceleration is not acting on all the electrode pairs, that is, if the initial capacitance Co is made equal, the equation of the capacitance of each capacitor described later is obtained. The term of the initial capacitance can be eliminated by taking the difference by appropriately combining, and the sum of the electrode gaps of each pair of electrode pairs under the action of acceleration for each pair of electrodes of the swing rod, If it is made equal to the sum of the electrode gaps of the pair of electrodes in a state where no acceleration is applied, the absolute values of the terms ΔX and ΔY can be made equal in the capacitance equation of each capacitor described later. If the distance between the centroids of the opposing principal planes in the Z-axis direction is made equal in all the electrode pairs, the absolute value of the term ΔZ can be calculated in the capacitance formula of each capacitor described later. Equalize Door can be. When both the movable electrode and the fixed electrode are formed in a long shape parallel to the main surface of the substrate and the extending direction thereof is orthogonal to the longitudinal direction of each swing rod, each electrode is X Since it is orthogonal to the axial direction or the Y-axis direction, even if the relative position of the movable electrode and the fixed electrode is displaced in the extending direction of each electrode, the amount of change in the capacitance of the capacitor is almost negligible. No longer affect. Therefore, the amount of change in the capacitance of the capacitor includes almost no component in the direction perpendicular to the X-axis direction or the Y-axis direction and parallel to the main surface of the substrate.

Then, in the acceleration sensor, each of the pair of electrode pairs formed by the movable electrodes of the pair of swinging rod members constituting the first swinging rod and the fixed electrode facing the movable electrodes, Each of the pair of electrode pairs formed by the movable electrodes of the pair of rocking rod members constituting the second rocking rod and the fixed electrodes opposed to them is expressed by the following formula (1). Or the relationship of (4) is satisfied.
(1) C1 = Co + PΔX + RΔZ
(2) C2 = Co−PΔX + RΔZ
(3) C3 = Co + QΔY-RΔZ
(4) C4 = Co-QΔY-RΔZ
Here, C1 is the capacitance of one of the pair of electrodes on the first swinging hook side, and C2 is the other electrode pair of the pair of electrodes on the first swinging hook side. , C3 is the capacitance of one of the pair of electrodes on the second swinging hook side, and C4 is the other of the pair of electrodes on the second swinging hook side. Represents the capacitance of the electrode pair.

If the operation of Expression (1) -Expression (2) is executed, the term of ΔX can be extracted, and if the operation of Expression (3) -Expression (4) is executed, the term of ΔY can be extracted. 1) + Expression (2)}-{Expression (3) + Expression (4)} is executed, the term of ΔZ can be extracted.
Therefore, in order to extract each term of ΔX, ΔY, ΔZ from the above formulas (1) to (4), the capacitors C1 to C4 are connected in parallel as shown in FIG. When the circuit is constructed and the following equations (5) to (7) are executed by the arithmetic processing unit, the arithmetic processing unit executes a differential operation, and each axis direction included in the above equation is executed. An output value corresponding to the displacement component can be output, and acceleration in each axis direction can be detected.
(5) (Co + PΔX + RΔZ) · (−Vr) + (Co−PΔX + RΔZ) · (+ Vr) = Cf · Vx
(6) (Co + QΔY−RΔZ) · (−Vr) + (Co−QΔY−RΔZ) · (+ Vr) = Cf · Vy
(7) (Co + PΔX + RΔZ), (+ Vr) + (Co−PΔX + RΔZ), (+ Vr) + (Co + QΔY−RΔZ), (−Vr) + (Co−QΔY −RΔZ) · (−Vr) = Cf · Vz
Co: Capacitance (initial capacity) of each variable capacitor when acceleration is not applied
P, Q, R: Coefficients ΔX, ΔY, ΔZ: Displacement in each axial direction + Vr, −Vr: Input voltage to the acceleration detection device Vx, Vy, Vz: Output voltage from the acceleration detection device Cf: Negative Therefore, if the acceleration sensor according to the present invention is connected to the arithmetic processing unit, the acceleration can be detected three-dimensionally when the acceleration is applied to the acceleration sensor. it can.

Since any of the above acceleration sensors can be manufactured by surface micromachining technology, it can be manufactured by a general-purpose MEMS process, and has a structure that can simplify the manufacturing process compared to acceleration sensors manufactured by conventional bulk machining technology. ing.
The acceleration sensor according to the present invention is a conventional bulk micromachining as compared with the case where two or three conventional so-called uniaxial or biaxial acceleration sensors produced by using surface micromachining technology are combined. The acceleration sensor can be reduced in size by thinning the structure of the acceleration sensor while detecting the acceleration three-dimensionally as compared with the acceleration sensor manufactured by the technology.

  In a state where no acceleration is applied, the capacitance of a pair of electrodes composed of the movable electrode formed on the first swing rod and the fixed electrode on the substrate, and the second swing When the capacitances of a pair of electrode pairs composed of the movable electrode formed in a moving manner and the fixed electrode on the substrate are set equal to each other, the X-axis direction, the Y-axis direction, and the Z-axis direction When an output value corresponding to the displacement of each direction component is output, a compensation capacitor or offset adjustment circuit for canceling the difference in initial capacitance is not necessary, which is preferable.

  Specifically, each of the first swing rod and the second swing rod is supported by the spring member at both ends thereof, and the movable electrode provided on each flange member in a state where no acceleration is applied. And the fixed gap on the substrate opposite to this, the capacitances can be set to be equal as described above, and the compensation capacitance or the offset adjustment circuit is not necessary.

Further, if the plurality of movable electrodes provided on each swing rod member and the fixed electrode on the substrate opposed thereto are configured so that the electrode length is increased in proportion to the distance from the intersection, A large opposing area can be secured and sensitivity can be increased.
When the movable electrode and the fixed electrode are arranged in this way, the movable electrode and the fixed electrode can be arranged so as to be line-symmetric with respect to the axis of the rocking rod. Even if the movable electrode swings in the longitudinal direction of the movable electrode, the sensitivity to displacement in the direction can be eliminated, and the number of terms that are subject to differential calculation processing can be reduced by one in the differential calculation as described above. This is preferable because it can suppress the burden of arithmetic processing. Further, since at least one of the spring members also serves as an external extraction circuit for the movable electrode, the external extraction circuit for the fixed electrode is connected to the end of the fixed electrode that does not face the movable electrode. Can be separated from the external extraction circuit of the movable electrode and the external extraction circuit of the fixed electrode on the substrate surface, the planar wiring becomes easy, and the structure of the acceleration sensor can be thinned. ,preferable.

(Embodiment 1)
A three-axis acceleration detection apparatus according to Embodiment 1 of the present invention will be described with reference to the drawings as appropriate.
<Schematic configuration of detection device>
FIG. 1A is a schematic cross-sectional view of the triaxial acceleration detection device according to the present embodiment, and FIG. 1B is a plan view of the main part in the detection device.

As shown in FIG. 1A, in the three-axis acceleration detecting device 10 according to the present embodiment, an acceleration sensor unit 12 and the sensor are formed on an insulating mold body 11 formed of an insulating resin such as an epoxy resin. The calculation processing unit 13 for calculating the output value output from the unit 12 is included.
Specifically, the sensor unit 12 and the arithmetic processing unit 13 are die-bonded to the main surface of the die pad 14 placed on the inner bottom of the mold body 11 via a conductive member 15. For example, a semiconductor element such as an ASIC is employed for the arithmetic processing unit 13. In the detection device 10, a detection circuit (see FIG. 5B) is constructed by the sensor unit 12, the arithmetic processing unit 13 including the sequence control circuit 36, and a power source (not shown).

Then, as shown in FIG. 1 (b), the lead 16 penetrating the mold body 11 and electrically connecting the inside and outside of the mold body 11 and the bonding pad portion 17 of the arithmetic processing unit 13 are wire-bonded, A bonding pad portion 18 different from the bonding pad portion 17 and a bonding pad portion 19 of the sensor portion 12 are wire-bonded.
In the sensor unit 12, a cover plate 21 is placed so as to cover the main surface of the sensor structure 20. The covering plate 21 is formed with, for example, a glass material as a main component. A through hole 22 is formed in the cover plate 21. A wiring layer (not shown) is provided so as to close the through hole 22, and the wiring layer is integrated with the bonding pad portion 19. Therefore, the potential extraction unit 26 (see FIG. 2) of the sensor structure 20 is electrically connected to the arithmetic processing unit 13 through the wiring layer, and a signal from the sensor structure 20 described below is input to the arithmetic processing unit 13. Is output.

<Schematic configuration of sensor structure 20>
FIG. 2 is a schematic plan view of the sensor structure 20 according to the present embodiment.
As shown in FIG. 2, in the present embodiment, a plurality of fixed electrode units 24 are fixed to the main surface of the substrate 23, and when the movable electrode unit 25 is accelerated on the substrate 23, the acceleration is in the direction of the acceleration. It is supported by a spring portion 33 so that it can swing three-dimensionally in proportion to the size of. In each fixed electrode unit 24, fixed electrode fingers 29 are arranged in a comb shape in a fixed direction along the main surface of the substrate 23. The movable electrode unit 25 is provided with comb-like movable electrode fingers 31 arranged in parallel with the fixed electrode fingers 29. Within the illustrated range, four fixed electrode units 24 are provided, of which one of the pairs is provided with the fixed electrode fingers 29 along the X-axis direction, and the other pair is provided with the fixed electrode fingers 29 along the Y-axis direction. Yes. One movable electrode unit 25 is provided on the main surface of the substrate 23, and the fixed electrode unit 24 and the movable electrode unit 25 are electrically insulated from each other. That is, for example, if the sensor structure 20 is manufactured using an SOI (Silicon On Insulator) substrate, each fixed electrode unit 24 and the movable electrode unit 25 are provided with a gap in the main surface direction of the substrate 23. Therefore, the fixed electrode units 24 and the fixed electrode unit 24 and the movable electrode unit 25 can be electrically insulated. Of course, the fixed electrode unit 24 may be integrally provided by being connected to each other by an insulator.

The potential extracting portions 26 of the fixed electrode unit 24 and the movable electrode unit 25 are arranged in a line on the main surface of the substrate 23.
In the sensor structure 20, a frame body 27 is disposed on the periphery of the substrate 23 on the main surface of the substrate 23 so as to surround the fixed electrode unit 24 and the movable electrode unit 25, and the frame body 27 is grounded (GND). Is arranged so as to be included in the row of the potential extraction units 26.

  FIG. 3 is a perspective view of a main part of the sensor structure 20 in the present embodiment, and shows the A part and the B part shown in FIG. FIG. 4 is a perspective view of a main part of the sensor structure 20 in the present embodiment, and shows the C part and the D part shown in FIG. All of the A part to the D part are shown in a state in which the arrangement positions shown in FIG. 2 are maintained in any of FIGS. Hereinafter, description will be made with reference to FIGS. 2 and 3 and 4.

<Schematic configuration of fixed electrode unit 24>
Each of the fixed electrode units 24 includes a wall portion 28 and a fixed electrode finger 29 (see FIGS. 3 and 4).
The wall portion 28 has a contour that is substantially isosceles triangular or a combination of a substantially isosceles triangle and a rectangle so that the main surface of the substrate 23 is equally divided into four. However, the said wall part 28 is opened in the part applicable to the intersection of an isosceles side. The wall portion 28 is arranged in a state where the openings are brought into contact with each other. In the present embodiment, the contour of the wall portion 28 has a substantially isosceles triangle shape, but is not limited thereto, and may be an equilateral triangle shape.

  A plurality of fixed electrode fingers 29 of the fixed electrode unit 24 are arranged so as to extend from the inner side wall of the isosceles portion of the substantially isosceles triangular wall portion 28 and to be parallel to the base of the isosceles triangle. ing. The number of fixed electrode fingers 29 in one fixed electrode unit 24 is not limited to a plurality, and may be one. It is preferable to provide a plurality of fixed electrode fingers 29 extending from the wall portion 28 because the sensitivity of the sensor structure 20 is improved.

3 and 4, the fixed electrode finger 29 of the fixed electrode unit 24 is in a state of floating with respect to the substrate 23, but the wall of the fixed electrode unit 24 that supports the fixed electrode finger 29. The portion 28 is fixed to the substrate 23 so as not to move, and therefore, the fixed electrode finger 29 is supported so as not to move in principle with respect to the substrate 23.
As shown in FIGS. 3 and 4, in this embodiment, the length of the fixed electrode finger 29 of the fixed electrode unit 24 is the same in the portion A and the portion B in the direction perpendicular to the main surface of the substrate 23. And the same for the C part and the D part, but when the A part or the B part is compared with the C part or the D part, they are different. Specifically, in the direction perpendicular to the main surface of the substrate 23, the length of the fixed electrode fingers 29 of the fixed electrode unit 24 in the A part and the B part is equal to the fixed electrode unit 24 in the C part and the D part. This is larger than the length of the fixed electrode finger 29.

<Schematic configuration of movable electrode unit 25>
The movable electrode unit 25 includes a mass section 30 and movable electrode fingers 31 (see FIGS. 3 and 4).
The mass portion 30 is arranged in a cross shape so that the ridge member is extended in all directions so that the linear ridge is orthogonal to the centroid of the main surface of the substrate 23 within the range shown in the figure ( (See FIG. 2). Each of the flange members of the mass portion 30 is arranged so as to enter the region on the main surface of the substrate 23 surrounded by the wall portion 28 from the opening portion of the wall portion 28 of the fixed electrode unit 24.

  The movable electrode fingers 31 of the movable electrode unit 25 are fixed to the fixed electrode fingers of the fixed electrode unit 24 in a state of extending from the flange members of the mass portion 30 toward the isosceles portion of the wall portion 28 of the fixed electrode unit 24. A plurality are arranged so as to enter between 29 and parallel to the fixed electrode fingers 29 of the fixed electrode unit 24. The number of movable electrode fingers 31 of the movable electrode unit 25 is not limited to this, and may be one. It is preferable that a plurality of movable electrode fingers 31 extending from the mass part 30 is provided because the sensitivity of the sensor structure 20 is improved.

By adopting the above configuration, the movable electrode finger 31 of the movable electrode unit 25 and the fixed electrode finger 29 of the fixed electrode unit 24 are arranged in parallel in principle as shown in the partial enlarged views of FIGS. .
The anchor portion 32 connected to the movable electrode unit 25 via the spring portion 33 is fixed to the main surface of the substrate 23 in a region surrounded by the wall portion 28 of the fixed electrode unit 24 in the main surface of the substrate 23. (See FIG. 2). The mass portion 30 of the movable electrode unit 25 and the anchor portion 32 are connected to the spring portion 33.

As shown in FIGS. 3 and 4, in the movable electrode unit 25, the mass part 30 is basically in a state of floating away from the substrate 23. 3 and 4, the movable electrode finger 31 formed integrally with the mass portion 30 is also lifted from the substrate 23 in principle, and although not shown, the spring portion 33 is not shown. Is also floating from the substrate 23 in principle.
By adopting this configuration, when the acceleration that is the sum of the three axial components or the direction components of these axial components is applied to the sensor structure 20, the mass unit 30. The plurality of movable electrode fingers 31 extended from the support are supported so as to be displaceable three-dimensionally with respect to the substrate 23 via the anchor portion 32 and the spring portion 33.

<Configuration of counter electrode>
As shown in FIG. 2, the fixed electrode finger 29 of the fixed electrode unit 24 and the movable electrode finger 31 of the movable electrode unit 25 in all of the A part to the D part of the sensor structure 20 have respective principal surfaces on the X axis. It arrange | positions so that it may oppose in a direction or a Y-axis direction. When a voltage is applied from a power source (not shown) to the fixed electrode finger 29 of the fixed electrode unit 24 and the movable electrode finger 31 of the movable electrode unit 25 is maintained at the ground potential (GND), the opposing main surface is the capacitor. Demonstrate the function.

Since the movable electrode finger 31 of the movable electrode unit 25 is configured to extend from the mass unit 30 supported so as to be three-dimensionally displaceable with respect to the substrate 23, the fixed electrode unit 24 fixed to the substrate 23 When acceleration is applied to the sensor structure 20 between the fixed electrode fingers 29, the principal surfaces facing each other can exhibit the function of a variable capacitor (variable capacitor).
[Features of counter electrode in Z-axis direction]
As shown in the partial enlarged view of FIG. 3, in the Z-axis direction perpendicular to the main surface of the substrate 23, the movable electrode finger 31 and the fixed electrode finger 29 are opposed to each other at the A part and the B part in the sensor structure 20. The centroids of the main surfaces are arranged so as to be shifted from each other. Similarly, the electrode fingers 29 and 31 are arranged so that the centroids of the opposing main surfaces are shifted from each other in the C portion and the D portion.

When the A part, the B part, the C part, and the D part are compared, the centroid mc of the opposed main surface of the movable electrode finger 31 in the Z-axis direction and the centroid of the opposed electrode of the fixed electrode finger 29 fc The deviation is reversed.
That is, in the A part and the B part of the sensor structure 20, the centroid mc of the opposing main surface of the movable electrode finger 31 is closer to the main surface of the substrate 23 than the centroid fc of the opposing main surface of the fixed electrode finger 29. The fixed electrode finger 29 and the movable electrode finger 31 are arranged on the center (see FIG. 6), and the centroid mc of the opposed main surface of the movable electrode finger 31 is the opposed main finger of the fixed electrode finger 29 in the C part and the D part. A fixed electrode finger 29 and a movable electrode finger 31 are arranged so as to be farther from the main surface of the substrate 23 than the centroid fc of the surface (see FIG. 7).

  In the sensor structure 20 according to the present embodiment, when acceleration is applied and the movable electrode finger 31 of the movable electrode unit 25 has a displacement component in the Z-axis direction, The component caused by the displacement in the Z-axis direction and the component caused by the displacement in the Z-axis direction among the change in the capacitance of the variable capacitor in the B portion have the same sign, and the change in the capacitance of the variable capacitor in the C portion Among them, the component due to the displacement in the Z-axis direction and the component due to the displacement in the Z-axis direction among the change in capacitance of the variable capacitor at the D portion have the same sign.

  As described above, when the A part, the B part, the C part, and the D part are compared, the centroid mc of the opposing main surface of the movable electrode finger 31 in the Z-axis direction and the fixed electrode finger 29 Since the deviation of the counter electrode from the centroid fc is reversed, the component resulting from the displacement in the Z-axis direction and the capacitance at the C and D portions among the change in capacitance at the A and B portions. Of these changes, the component resulting from the displacement in the Z-axis direction has the opposite sign.

  That is, in the sensor structure 20, when both the portions caused by the displacement in the Z-axis direction increase in the capacitance change of the variable capacitors in the A portion and the B portion, the static capacitance of the variable capacitors in the C portion and the D portion is increased. Of the change in capacitance, the portion due to the displacement in the Z-axis direction decreases, and conversely, the portion due to the displacement in the Z-axis direction among the change in capacitance of the variable capacitor in the A portion and the B portion decreases. At this time, the portion due to the displacement in the Z-axis direction among the capacitance changes of the variable capacitors in the C part and the D part increases.

  Specifically, in part A and part B of sensor structure 20, the length of movable electrode finger 31 of movable electrode unit 25 is longer than the length of fixed electrode finger 29 of fixed electrode unit 24 in the Z-axis direction. It is getting smaller. 4, the length of the movable electrode finger 31 of the movable electrode unit 25 is fixed in the C part and the D part of the sensor structure 20 in the direction perpendicular to the main surface of the substrate 23. It is larger than the length of the fixed electrode finger 29 of the electrode unit 24.

In all of the A part to the D part of the sensor structure 20, the fixed electrode finger 29 of the fixed electrode unit 24 and the movable electrode finger 31 of the movable electrode unit 25 have the same distance from the main surface of the substrate 23. Is arranged.
It is not limited to the said structure, When the said electrode finger 29 and the said electrode finger 31 are contrasted, the separation distance from the main surface of the board | substrate 23 may differ. When the separation distance is the same, it is preferable because the sensor structure 20 can be easily manufactured using an SOI (Silicon On Insulator) substrate as compared with the case where the separation distances are different.
[Characteristics of counter electrode in X-axis direction and Y-axis direction]
As shown in the partial enlarged view of FIG. 3, in the A part of the sensor structure 20, the movable electrode disposed so as to be sandwiched between the fixed electrode fingers 29 of the fixed electrode unit 24 in the direction along the main surface of the substrate 23. The movable electrode fingers 31 of the unit 25 are not equidistant from the fixed electrode fingers 29 of the adjacent fixed electrode units 24. Specifically, the movable electrode fingers 31 of the movable electrode unit 25 and the movable electrode fingers The gap distance between the fixed electrode unit 24 of the fixed electrode unit 24 positioned in the negative direction of the X axis with respect to 31 and the positive electrode of the X axis with respect to the movable electrode finger 31 of the movable electrode unit 25 and the movable electrode finger 31 is It is shorter than the gap distance between the fixed electrode unit 24 positioned in the direction of the fixed electrode finger 29 and the fixed electrode finger 29.

  Similarly, in part B of the sensor structure 20, the movable electrode finger 31 of the movable electrode unit 25 arranged so as to be sandwiched between the fixed electrode fingers 29 of the fixed electrode unit 24 in the direction along the main surface of the substrate 23. It is not located at the same distance from the fixed electrode fingers 29 of the adjacent fixed electrode units 24. Specifically, the movable electrode finger 31 of the movable electrode unit 25 and the movable electrode finger 31 are negative in the X axis. The fixed electrode unit 24 is located in the positive direction of the X axis with respect to the movable electrode finger 31 of the movable electrode unit 25 and the gap distance between the fixed electrode unit 24 and the fixed electrode finger 29 of the movable electrode unit 25. It is longer than the distance between the 24 fixed electrode fingers 29.

That is, when the A portion and the B portion of the sensor structure 20 are compared, the positions of the fixed electrode fingers 29 and the movable electrode fingers 31 in the respective portions are determined by the cross-shaped mass portion 30 of the movable electrode unit 25. The mirror surface is symmetrical with respect to a virtual plane passing through the orthogonal point and orthogonal to the main surface of the substrate 23.
Since the movable electrode finger 31 of the movable electrode unit 25 and the fixed electrode finger 29 of the fixed electrode unit 24 are arranged at the positions described above, the sensor structure 20 according to the present embodiment is movable with acceleration. When the movable electrode finger 31 of the electrode unit 25 has a displacement component in the X-axis direction, the component resulting from the displacement in the X-axis direction among the change in capacitance of the variable capacitor when comparing the A portion and the B portion. Even when the C part and the D part are compared, acceleration is applied and the movable electrode finger 31 of the movable electrode unit 25 has a displacement component in the Y-axis direction. Sometimes, the structure has a similar relationship.

  Specifically, when the A part and the B part in the sensor structure 20 are compared, when the component due to the displacement in the X-axis direction increases in the capacitance change of the variable capacitor in the A part, The component caused by the displacement in the X-axis direction among the change in capacitance of the variable capacitor in the B portion decreases, and conversely, the change in capacitance caused by the variable capacitor in the A portion results from the displacement in the X-axis direction. When the component decreases, the component resulting from the displacement in the X-axis direction among the capacitance change of the variable capacitor in the B portion increases.

Further, as shown in the partially enlarged view of FIG. 4, the C portion and the D portion of the sensor structure 20 are also arranged so as to be sandwiched between the fixed electrode fingers 29 of the fixed electrode unit 24 in the direction along the main surface of the substrate 23. The movable electrode fingers 31 of the movable electrode unit 25 thus formed are not located at the same distance from the fixed electrode fingers 29 of the adjacent fixed electrode units 24.
Specifically, in the direction along the main surface of the substrate 23, the portion C of the sensor structure 20 is positioned in the negative direction of the Y axis with respect to the movable electrode finger 31 of the movable electrode unit 25 and the movable electrode finger 31. The fixed electrode finger of the fixed electrode unit 24 that is positioned in the positive direction of the Y axis with respect to the movable electrode finger 31 of the movable electrode unit 25 and the gap between the fixed electrode unit 24 and the fixed electrode finger 29 It is shorter than the gap distance with 29.

  Then, in the direction along the main surface of the substrate 23, in the portion D of the sensor structure 20, the movable electrode finger 31 of the movable electrode unit 25 and the fixed electrode positioned in the negative Y-axis direction with respect to the movable electrode finger 31. The gap distance between the unit 24 and the fixed electrode finger 29 is such that the movable electrode finger 31 of the movable electrode unit 25 and the fixed electrode finger 29 of the fixed electrode unit 24 positioned in the positive direction of the Y axis with respect to the movable electrode finger 31 Longer than the gap distance.

That is, when the C part and the D part of the sensor structure 20 are compared, the arrangement positions of the fixed electrode fingers 29 and the movable electrode fingers 31 in the respective parts are the positions of the cross-shaped mass part 30 of the movable electrode unit 25. The mirror surface is symmetrical with respect to a virtual plane passing through the orthogonal point and orthogonal to the main surface of the substrate 23.
When the C part and the D part in the sensor structure 20 are compared, when the component due to the displacement in the Y-axis direction among the capacitance change of the variable capacitor in the C part increases, the D part The component due to the displacement in the Y-axis direction of the capacitance change of the variable capacitor decreases, and conversely, the component due to the displacement in the Y-axis direction among the capacitance change of the variable capacitor at the C portion decreases. In this case, the component due to the displacement in the Y-axis direction increases in the capacitance change of the variable capacitor in the D portion.

<Configuration as a circuit>
FIG. 5A is a schematic diagram showing the sensor structure 20 according to the present embodiment in an electric equivalent circuit, and FIG. 5B shows the detection circuit 34 according to the present embodiment as an electric equivalent circuit. FIG. 5C is a schematic diagram showing an on / off timing chart of voltage application to the detection circuit 34.

In FIG. 5B, the portion surrounded by the broken line corresponds to the sensor structure 20 according to the present embodiment, and the capacitors C1 to C4 are respectively connected to the electrode fingers 29, Each main surface of 31 corresponds to a variable capacitor constructed facing each other.
As shown in FIG. 5A, when the sensor structure 20 according to the present embodiment is viewed as an electrical equivalent circuit, each of the variable capacitor C1 to C4 has each of the movable electrode fingers 31 of the movable electrode unit 25. The main surface is a flat plate electrode having the same potential, the main surface of the fixed electrode finger 29 of the fixed electrode unit 24 is a flat plate electrode having a potential different from that of the main surface of the movable electrode finger 31, and the fixed electrode fingers 29 have different potentials. The sensor structure 20 is constructed so as to be a settable plate electrode.

The sensor structure 20 having the above structure becomes a part of the detection circuit 34 shown in FIG. 5 (b), and is supplied from the power source (not shown) to the detection circuit 34 based on the timing chart shown in FIG. 5 (c). When the detection circuit 34 is driven by applying a voltage, the displacement component in each axial direction can be output as a voltage.
<Operation of detection device>
6 and 7 are schematic cross-sectional views of the variable capacitor according to the present embodiment. FIG. 6 schematically shows a cross section of the variable capacitor at the A portion and the B portion, and FIG. 7 schematically shows a cross section of the variable capacitor at the C portion and the D portion. 6 corresponds to FIG. 3 and FIG. 7 corresponds to FIG.

[Variable capacitors C1 to C4]
In the variable capacitors C1 and C2, the movable electrode fingers 31 of the movable electrode unit 25 constituting the counter electrode are provided so as to be integrally and three-dimensionally displaced as shown in FIG. When acceleration is applied to 20, all the movable electrode fingers 31 are displaced in the same direction as shown by the broken line in FIG. Specifically, all the movable electrode fingers 31 are displaced in the same direction in a direction including a displacement component in the X-axis direction and a displacement component in the Z-axis direction.

  Similarly, the variable capacitors C3 and C4 are provided so that the movable electrode fingers 31 of the movable electrode unit 25 constituting the counter electrode are integrally and three-dimensionally displaced as shown in FIG. When acceleration is applied to the structure 20, all the movable electrode fingers 31 are displaced in the same direction as indicated by broken lines in FIG. 7. Specifically, all the movable electrode fingers 31 are displaced in the same direction in a direction including a displacement component in the Y-axis direction and a displacement component in the Z-axis direction.

  When the movable electrode finger 31 of the movable electrode unit 25 constituting each of the variable capacitors C1 and C2 has a displacement component in any axial direction, the initial capacitance of the variable capacitors C1 and C2 is Co, and the variable capacitors C1 and C2 ΔC1, ΔC2, the dielectric constant of vacuum, εo, the dielectric constant of the insulator between the fixed electrode finger 29 and the movable electrode finger 31, εr, the fixed electrode finger 29, the movable electrode finger 31, the length in the main surface direction of the substrate 23 at the portion where the variable capacitors C1, C2 are constructed is l, and the substrate 23 at the portion where the variable capacitors C1, C2 are constructed among the fixed electrode fingers 29 and the movable electrode fingers 31. Theoretically, when the length in the vertical length direction is h, the displacement amount of the electrode finger 31 of the movable electrode unit 25 in the X-axis direction, and the displacement amount in the Z-axis direction are ΔX and ΔZ, respectively, the capacitance is theoretically. C is

と表され、したがって、静電容量の変化量は、

Therefore, the amount of change in capacitance is

と、表せるので、変位後の可変キャパシタＣ１，Ｃ２の静電容量Ｃ１，Ｃ２について以下の関係式が成立する。
すなわち、可動電極ユニット２５の可動電極指３１がＺ軸の正方向の変位成分を有するとき、

Therefore, the following relational expression is established for the capacitances C1 and C2 of the variable capacitors C1 and C2 after displacement.
That is, when the movable electrode finger 31 of the movable electrode unit 25 has a displacement component in the positive direction of the Z axis,

また、可動電極ユニット２５の可動電極指３１がＺ軸の負の方向の変位成分を有するとき、

When the movable electrode finger 31 of the movable electrode unit 25 has a displacement component in the negative direction of the Z axis,

式３、式４においてＺ軸変位成分が表れていないが、理論上、可動電極ユニット２５の可動電極指３１がＺ軸の正の方向に変位成分を有するときには、可変キャパシタＣ１，Ｃ２それぞれにおける対向電極面積が変化しないためである。

Although the Z-axis displacement component does not appear in Equations 3 and 4, theoretically, when the movable electrode finger 31 of the movable electrode unit 25 has a displacement component in the positive direction of the Z-axis, it is opposed to each of the variable capacitors C1 and C2. This is because the electrode area does not change.

  However, in reality, due to the end effect, even when the movable electrode finger 31 of the movable electrode unit 25 has a displacement component in the positive direction of the Z axis, the variable capacitor is caused by the displacement in the positive direction of the Z axis. The capacitances C1 and C2 of C1 and C2 change. Specifically, within a certain range in the positive direction of the Z-axis, the change component resulting from the displacement in the Z-axis direction among the amount of change in capacitance increases.

  In view of the end effect and the above expressions 3, 4, 5, and 6, when the movable electrode finger 31 is displaced, the following relational expressions can be derived for the variable capacitors C1 and C2.

上記いずれの式にもＹ軸方向の変位に起因する成分が含まれていない（△Ｙの項がない）のは、各固定電極指２９，可動電極指３１において互いに他の固定電極指２９，可動電極指３１と対向する面での基板２３の主面方向の長さｌが当該面での基板２３に垂直な方向の長さｈと比べて大きいため、静電容量変化のうちＹ軸方向の変位に起因する成分が無視できるほどに小さいからである。

None of the above formulas includes a component due to the displacement in the Y-axis direction (there is no term of ΔY) that each fixed electrode finger 29 and the movable electrode finger 31 have other fixed electrode fingers 29, Since the length l in the main surface direction of the substrate 23 on the surface facing the movable electrode finger 31 is larger than the length h in the direction perpendicular to the substrate 23 on the surface, the Y-axis direction among the capacitance changes. This is because the component due to the displacement of is so small that it can be ignored.

  When the movable electrode finger 31 of the movable electrode unit 25 constituting each of the variable capacitors C3 and C4 has a displacement component in any axial direction, the initial capacitance of the variable capacitors C3 and C4 is Co, and the variable capacitor C3 , C4 capacitance change amount ΔC3, ΔC4, vacuum dielectric constant εo, dielectric constant dielectric between the fixed electrode finger 29 and movable electrode finger 31 εr, fixed electrode finger 29, operation The length of the electrode finger 31 in the direction of the principal surface of the substrate 23 at the portion where the variable capacitors C3 and C4 are constructed is l, and the substrate at the portion of the fixed electrode finger 29 and the movable electrode finger 31 where the variable capacitors C3 and C4 are constructed. When the length in the length direction perpendicular to 23 is h, the displacement amount of the electrode finger 31 of the movable electrode unit 25 in the Y-axis direction, and the displacement amount in the Z-axis direction are ΔY and ΔZ, respectively, the variable after the displacement Capacitors C3 and C4 The following relational expressions are theoretically established for the capacitances C3 and C4.

  That is, when the movable electrode finger 31 of the movable electrode unit 25 has a displacement component in the positive direction of the Z axis,

また、可動電極ユニット２５の可動電極指３１がＺ軸の負の方向の変位成分を有するとき、

When the movable electrode finger 31 of the movable electrode unit 25 has a displacement component in the negative direction of the Z axis,

式１１、式１２においてＺ軸変位成分が表れていないが、理論上、可動電極ユニット２５の可動電極指３１がＺ軸の負の方向に変位成分を有するときには、可変キャパシタＣ３，Ｃ４それぞれにおける対向電極面積が変化しないためである。

Although the Z-axis displacement component does not appear in Equations 11 and 12, theoretically, when the movable electrode finger 31 of the movable electrode unit 25 has a displacement component in the negative direction of the Z-axis, it is opposed to each of the variable capacitors C3 and C4. This is because the electrode area does not change.

  However, in reality, even when the movable electrode finger 31 of the movable electrode unit 25 has a displacement component in the negative direction of the Z axis due to the end effect, the variable capacitor is caused by the displacement in the negative direction of the Z axis. The capacitances C3 and C4 of C3 and C4 change. Specifically, within a certain range in the negative direction of the Z-axis, the change component resulting from the displacement in the Z-axis direction among the amount of change in capacitance increases.

  In view of the end effect and the above expressions 9, 10, 11, and 12, when the electrode finger 31 is displaced, the following relational expressions can be derived for the variable capacitors C3 and C4.

上記いずれの式にもＸ軸方向の変位に起因する成分が含まれていない（△Ｘの項がない）のは、各固定電極指２９，可動電極指３１において互いに他の固定電極指２９，可動電極指３１と対向する面での基板２３の主面方向の長さｌが当該面での基板２３に垂直な方向の長さｈと比べて大きいため、静電容量変化のうちＸ軸方向の変位に起因する成分が無視できるほどに小さいからである。

None of the above formulas includes a component due to the displacement in the X-axis direction (the term of ΔX is not present) because each of the fixed electrode fingers 29 and the movable electrode fingers 31 has another fixed electrode finger 29, Since the length l in the main surface direction of the substrate 23 on the surface facing the movable electrode finger 31 is larger than the length h in the direction perpendicular to the substrate 23 on the surface, the X-axis direction of the capacitance change This is because the component due to the displacement of is so small that it can be ignored.

What should be noted when comparing the above Expression 7 and Expression 8 is that the sign of the change component caused by the displacement in the X-axis direction, that is, the term of ΔX is reversed and the sign of the term of ΔZ is the same. This is the point.
The points to be noted when comparing the above Expression 13 and Expression 14 are that the change component caused by the displacement in the Y-axis direction, that is, the sign of the term ΔY is reversed and the sign of the term ΔZ Is the same.

In addition, when the above formulas 13 and 14 are compared with the above formulas 7 and 8, the change component caused by the Z-axis direction displacement, that is, the sign of the term ΔZ is reversed. Is a point.
The reason why such a sign relationship is established in each of the terms ΔX, ΔY, and ΔZ is due to the electrode structure described above.

Hereinafter, the operation of the detection circuit 34 will be specifically described.
[Detection operation of acceleration component in X axis direction]
As shown in FIG. 5C, when the switching elements s1b and s2a of the detection circuit 34 are turned on and the other switching elements are turned off in the period p1, the fixed electrode finger of the fixed electrode unit 24 of the variable capacitor C1 is turned off. A voltage −Vr is applied from the power supply to the power supply 29, and a voltage + Vr is applied from the power supply to the movable electrode finger 29 of the fixed electrode unit 24 in the variable capacitor C2.

  At this time, between the variable capacitors C1 and C2 and the negative feedback capacitor Cf, the capacitance of the variable capacitor C1 is C1, the capacitance of the variable capacitor C2 is C2, and the capacitance of the negative feedback capacitor Cf is Cf. The following relational expression holds.

式１５と上記の式７、式８とから、以下の関係式を導き出せる。

From Equation 15 and Equations 7 and 8 above, the following relational expression can be derived.

式１６を整理すると、電源から各可変キャパシタＣ１，Ｃ２の固定電極指２９に印加される電圧が逆極性であることから式１６の左辺において初期容量Ｃｏおよび△Ｚの項が消えて、以下の関係式が導出される。

By rearranging Expression 16, since the voltage applied from the power source to the fixed electrode fingers 29 of the variable capacitors C1 and C2 has a reverse polarity, the terms of the initial capacitance Co and ΔZ disappear on the left side of Expression 16, and A relational expression is derived.

式１７から分かるように、出力電圧Ｖｘは、△Ｘの項のみで表され、すなわち、可動電極ユニット２５の可動電極指３１のＸ軸方向の変位成分にのみ依存する。
この出力電圧Ｖｘがオペアンプ（ＯＰＡ）３５から出力され、期間ｐ１においてスイッチＳｘがｏｎされるとキャパシタＣｘに出力電圧Ｖｘが蓄積され、出力電圧Ｖｘを検出できる。

As can be seen from Expression 17, the output voltage Vx is expressed only by the term of ΔX, that is, depends only on the displacement component in the X-axis direction of the movable electrode finger 31 of the movable electrode unit 25.
When the output voltage Vx is output from the operational amplifier (OPA) 35 and the switch Sx is turned on in the period p1, the output voltage Vx is accumulated in the capacitor Cx, and the output voltage Vx can be detected.

When the switch S5 is turned on after the lapse of the period p1, the negative feedback capacitor Cf is short-circuited, so that charges are injected into the movable electrode finger 31 of the movable electrode unit 25 and at the same time, the fixed electrode unit 24 is connected through a line (not shown). The charge on the fixed electrode finger 29 side is also moved, and the potential difference maintained in the variable capacitors C1 and C2 due to the input voltage Vr is erased.
Therefore, only the displacement component in the X-axis direction of the movable electrode finger 31 of the movable electrode unit 25 can be detected by the electrode structure and the arithmetic processing.

[Detection operation of acceleration component in Y-axis direction]
As shown in FIG. 5C, when the switching elements s3b and s4a of the detection circuit 34 are turned on and the other switching elements are turned off in the period p2, the fixed electrode finger of the fixed electrode unit 24 of the variable capacitor C3 is turned off. A voltage −Vr from the power source is applied to 29, and a voltage + Vr from the power source is applied to the fixed electrode finger 29 of the fixed electrode unit 24 in the variable capacitor C4.

  At this time, between the variable capacitors C3 and C4 and the negative feedback capacitor Cf, the capacitance of the variable capacitor C3 is C3, the capacitance of the variable capacitor C4 is C4, and the capacitance of the negative feedback capacitor Cf is Cf. The following relational expression holds.

式１８と上記の式１３、式１４とから、以下の関係式を導き出せる。

From the equation 18 and the above equations 13 and 14, the following relational expression can be derived.

式１９を整理すると、電源から各可変キャパシタＣ３，Ｃ４の固定電極指２９に印加される電圧が逆極性であることから式１９の左辺において初期容量Ｃｏおよび△Ｚの項が消えて、以下の関係式が導出される。

By rearranging Equation 19, since the voltage applied from the power source to the fixed electrode fingers 29 of the variable capacitors C3 and C4 has a reverse polarity, the terms of the initial capacitance Co and ΔZ disappear on the left side of Equation 19, and A relational expression is derived.

式２０から分かるように、出力電圧Ｖｙは、△Ｙの項のみで表され、すなわち、可動電極ユニット２５の可動電極指３１のＹ軸方向の変位成分にのみ依存する。
この出力電圧Ｖｙがオペアンプ（ＯＰＡ）３５から出力され、期間ｐ２においてスイッチＳｙがｏｎされるとキャパシタＣｙに出力電圧Ｖｙが蓄積され、出力電圧Ｖｙを検出できる。

As can be seen from Equation 20, the output voltage Vy is expressed only by the term ΔY, that is, depends only on the displacement component of the movable electrode finger 31 of the movable electrode unit 25 in the Y-axis direction.
When this output voltage Vy is output from the operational amplifier (OPA) 35 and the switch Sy is turned on in the period p2, the output voltage Vy is accumulated in the capacitor Cy, and the output voltage Vy can be detected.

When the switch S5 is turned on after the period p2 elapses, the negative feedback capacitor Cf is short-circuited, so that charges are injected into the movable electrode finger 31 of the movable electrode unit 25 and at the same time, the fixed electrode unit 24 The electric charge on the electrode finger 29 side is also moved, and the potential difference maintained in the variable capacitors C3 and C4 due to the input voltage Vr is erased.
Therefore, only the displacement component in the Y-axis direction of the movable electrode finger 31 of the movable electrode unit 25 can be detected by the electrode structure and the arithmetic processing.

[Detection operation of acceleration component in the Z-axis direction]
As shown in FIG. 5C, when the switching elements s1a, s2a, s3b, and s4b of the detection circuit 34 are turned on and the other switching elements are turned off in the period p3, each of the variable capacitors C1 and C2 is fixed. A voltage of + Vr is applied from the power source to the fixed electrode finger 29 of the electrode unit 24, and a voltage of −Vr is applied from the power source to the fixed electrode finger 29 of the fixed electrode unit 24 among the variable capacitors C3 and C4. The

  At this time, between the variable capacitors C1, C2, C3, and C4 and the negative feedback capacitor Cf, the capacitance of the variable capacitor C1 is C1, the capacitance of the variable capacitor C2 is C2, and the capacitance of the variable capacitor C3. Is C3, the capacitance of the variable capacitor C4 is C4, and the capacitance of the negative feedback capacitor Cf is Cf, the following relational expression is established.

式２１と上記の式７、式８、式１３、式１４とから、以下の関係式が導き出せる。

The following relational expressions can be derived from Expression 21 and Expressions 7, 8, 13, and 14 described above.

式２２を整理すると、可変キャパシタＣ１と可変キャパシタＣ２とを対比したとき、固定電極指２９に電源から印加される電圧は、その絶対値が同じでかつ同極性であり、かつＸ軸方向の変位に起因する静電容量の変化成分、すなわち△Ｘの項が異符号であるので、△Ｘの項が消える。そして、可変キャパシタＣ３と可変キャパシタＣ４とを対比したとき、固定電極指２９に電源から印加される電圧は、その絶対値が同じでかつ同極性であり、かつＹ軸方向の変位に起因する静電容量の変化成分、すなわち△Ｙの項が異符号であるので、△Ｙの項が消える。

To summarize Equation 22, when the variable capacitor C1 and the variable capacitor C2 are compared, the voltage applied from the power source to the fixed electrode finger 29 has the same absolute value and the same polarity, and the displacement in the X-axis direction. The component of change in capacitance caused by, that is, the term of ΔX has a different sign, so the term of ΔX disappears. When the variable capacitor C3 and the variable capacitor C4 are compared, the voltage applied from the power source to the fixed electrode finger 29 has the same absolute value and the same polarity, and the static voltage caused by the displacement in the Y-axis direction. Since the change component of the capacitance, that is, the term of ΔY has a different sign, the term of ΔY disappears.

  When the variable capacitor C1 and the variable capacitor C2 are compared with the variable capacitor C3 and the variable capacitor C4, the voltage applied from the power source to the fixed electrode finger 29 has the same absolute value and different polarity, and Since the initial capacity Co has the same sign, the term of the initial capacity Co disappears. In the comparison, the ΔZ term of the variable capacitor C1 and the ΔZ term of the variable capacitor C2 have the same sign, and the ΔZ term of the variable capacitor C3 and the ΔZ term of the variable capacitor C4 have the same sign. Therefore, when combined with the polarity relationship of the applied voltage, the following relational expression is derived.

式２３から分かるように、出力電圧Ｖｚは、△Ｚの項のみで表され、すなわち、可動電極ユニット２５の可動電極指３１のＺ軸方向の変位成分にのみ依存する。
この出力電圧Ｖｚがオペアンプ（ＯＰＡ）３５から出力され、期間ｐ３においてスイッチＳｚがｏｎされるとキャパシタＣｚに出力電圧Ｖｚが蓄積され、出力電圧Ｖｚを検出できる。

As can be seen from Equation 23, the output voltage Vz is expressed only by the term ΔZ, that is, depends only on the displacement component in the Z-axis direction of the movable electrode finger 31 of the movable electrode unit 25.
When the output voltage Vz is output from the operational amplifier (OPA) 35 and the switch Sz is turned on in the period p3, the output voltage Vz is accumulated in the capacitor Cz, and the output voltage Vz can be detected.

  When the switch S5 is turned on after the period p3 elapses, the negative feedback capacitor Cf is short-circuited, so that charges are injected into the movable electrode finger 31 of the movable electrode unit 25 and at the same time, the fixed electrode unit 24 The electric charge on the fixed electrode finger 29 side is also moved, and the potential difference maintained in the variable capacitors C1, C2, C3, C4 due to the input voltage Vr is erased.

Therefore, only the displacement component in the Z-axis direction of the movable electrode finger 31 of the movable electrode unit 25 can be detected by the electrode structure and the arithmetic processing.
<< Effect of Acceleration Detection Device According to Embodiment 1 >>
In the present embodiment, when the sensor structure 20 compares the A part and the B part by having the above-described configuration of the fixed electrode finger 29 of the fixed electrode unit 24 and the movable electrode finger 31 of the movable electrode unit 25, The variable capacitors C1 and C2 are arranged so as to cause a capacitance change of opposite sign in the X-axis direction, and when the C part and the D part are compared, the variable capacitors C3 and C4 are reversed in the Y-axis direction. It arrange | positions so that the electrostatic capacitance change of a code | symbol may be caused.

In addition, when comparing the A part and the B part with the C part and the D part, the variable capacitors C1 and C2 and the variable capacitors C3 and C4 are arranged so as to cause a capacitance change of opposite sign in the Z-axis direction. Yes.
Therefore, if the sensor structure 20 is incorporated in the arithmetic processing unit and the output value when the acceleration is applied to the sensor structure 20 according to the timing, the acceleration that can detect the acceleration in the three-axis direction can be detected. A detection device can be realized.

  That is, in the sensor structure 20, when three conventional sensor structures capable of detecting one axis are combined, a conventional sensor structure capable of detecting one axis acceleration and a sensor capable of detecting two axes acceleration. When combined with a structure or compared with an acceleration sensor manufactured by bulk micromachining technology, it is possible to detect triaxial acceleration without increasing the mounting area, and to detect triaxial acceleration. Miniaturization can be realized while being possible.

If the sensor structure 20 is incorporated in an acceleration detection device, the detection device can be reduced in size.
And since the acceleration sensor in this Embodiment can be manufactured with a surface micromachining technique, it can be manufactured with a general purpose MEMS process, and a manufacturing process is simple compared with the triaxial acceleration sensor manufactured with the conventional bulk micromachining technique. It has a structure.

  In the acceleration sensor according to the present embodiment, the movable electrode unit 25 is supported at a predetermined reference position by the spring portion 33, and the electrode pair functioning as a capacitor in the A portion to D portion in a state where no acceleration is applied. Since the initial capacitance Co is the same, the initial capacitance Co can be eliminated without using a reference capacitance when performing the above-described calculation by differential detection, compared to a conventional so-called bulk type triaxial acceleration sensor. Further downsizing of the sensor structure 20 can be achieved.

  In the present embodiment, as shown in FIG. 2, the wall portion 28 is arranged in an isosceles shape on the main surface of the substrate 23, and the fixed electrode finger 29 is combed from there toward the bowl-shaped mass portion 30 orthogonal to the comb. Since the movable electrode fingers 31 are extended in a comb shape from the mass portion 30 toward the wall portion 28, the movable electrode fingers 31 and the fixed electrode fingers 29 are limited to the substrate 23. A large area can be provided within the area, the opposing area of the capacitor formed in each of the A region and D region can be secured large, and the movable electrode finger 31 and the fixed electrode finger 29 can be secured in each of the A region and D region. It is preferable that the sensitivity can be improved as compared with the case where each of them is one.

Since each of the comb-like movable electrode finger 31 and the fixed electrode finger 29 is arranged in line symmetry with respect to the axis of the cross-shaped mass portion 30, the movable electrode is extended in the extending direction of these electrode fingers. Even if the unit 25 swings, the sensitivity in the direction can be erased, which is preferable because the calculation burden can be reduced in the calculation processing described above.
In addition, as shown in FIG. 2, the energization path to the fixed electrode finger 29 is routed through the isosceles wall portion 28 at its end, more specifically, each of the ridges constituting the cross-shaped mass portion 30. Assuming a square as a symmetric axis, the corner of the virtual square is connected to the potential extraction unit 26 formed on the main surface of the substrate 23, and the energization path to the movable electrode finger 31 is the same as that of the virtual square. The spring portion 33 positioned in the middle of each side also serves as an energization path, passes through the mass portion 30 and the spring portion 33, passes through the anchor portion 32, and is different from the potential extraction portion 26 on the fixed electrode finger 29 side. 26, the wiring in the sensor structure 20 can be easily formed in a planar shape, and the sensor structure 20 can be thinned.
<Others>
In the present embodiment, the first main surface and the second main surface are arranged so as to be perpendicular to each axial direction (X-axis direction and Y-axis direction) of the orthogonal coordinate system in the substrate 23 main surface direction. However, the present invention is not limited to this, and may not be perpendicular to the X-axis direction and the Y-axis direction.

By disposing at a right angle, the number of capacitors formed by the first main surface and the second main surface can be reduced.
This is because, as described above, the capacitance of each capacitor when subjected to triaxial acceleration includes a displacement component in a direction perpendicular to the opposing main surface of each capacitor and a displacement component in a direction perpendicular to the substrate 23. Therefore, if three capacitors are prepared, displacement components in each direction can be extracted by executing appropriate arithmetic processing, and the mounting area on the main surface of the board 23 can be reduced. can do.

However, if the first main surface and the second main surface are arranged so as to be perpendicular to the X-axis direction and the Y-axis direction, the arithmetic processing unit performs arithmetic processing in the orthogonal coordinate axis direction. This is preferable in that it can detect the displacement and reduce the burden on the arithmetic processing in the arithmetic processing unit.
That is, depending on the arithmetic processing unit having a simple configuration used in the above embodiment, if a sensor structure including three capacitors is employed, arithmetic processing cannot be performed, whereas the four arithmetic capacitors according to the present embodiment are included. If the sensor structure 20 is used, arithmetic processing can be performed.

In the present embodiment, the mass part 30 has a cross shape, and specifically, the movable electrode finger 31 is arranged so as to be line symmetric from the collar member constituting the mass part 30 to the axis of the collar member. However, the present invention is not limited to this, and the mass part 30 may not be in the shape of the bowl, and the movable electrode finger 31 may not be arranged symmetrically with respect to the axis of the bowl of the mass part 30.
However, it is preferable that the mass portion 30 has a cross-shaped outer shape orthogonal to each other, since it is geometrically stable. Therefore, it is preferable that the stability of sensitivity can be improved, and the movable electrode finger 31 further has a shaft of the flange member. If they are arranged symmetrically to each other, the stability of the sensitivity can be further improved in terms of geometric stability.

  In the present embodiment, the A part and the D part occupy the sensor structure 20 evenly within the range shown in the figure, but the present invention is not limited to this, and the A part and the D part include the sensor structure 20. May not be evenly occupied. However, if the A part or the D part occupies the sensor structure 20 evenly, the so-called initial capacity can be made equal in the A part or the D part, and compared with the conventional so-called bulk type triaxial acceleration detecting device. This is preferable because a reference capacity is not necessary.

  In the present embodiment, each of the fixed electrode finger 29 and the movable electrode finger 31 is disposed so as to surround the other, so that each of the opposing main surfaces of the fixed electrode finger 29 and the movable electrode finger 31 is a substrate. Although the end effect when moving in the direction of the principal surface of 23 is negligible, when a configuration other than the present embodiment is adopted, that is, one electrode finger is placed between the fixed electrode finger 29 and the movable electrode finger 31. When adopting a configuration that does not surround the other electrode finger, in the main surface direction of the substrate 23, the total length of the main surfaces on the movable electrode finger 31 side of the main surfaces facing each other between the fixed electrode fingers 29 and the movable electrode fingers 31. Is set to be larger than the total length of the main surfaces on the fixed electrode finger 29 side, and the distance between the end of the fixed electrode finger 29 and the end of the movable electrode finger 31 is set to be equal to each other. For example, the fixed electrode finger 29 and the movable electrode finger 31 Each of the opposed main surfaces can be removed the displacement components in the change in electrostatic capacitance when moved in the main surface direction of the substrate 23.

  Further, in the present embodiment, in the sensor structure 20, the variable capacitor constituted by the fixed electrode finger 29 and the movable electrode finger 31 is arranged in four directions along the main surface of the substrate 23. The present invention is not limited to this, and variable capacitors may be arranged in four or more directions along the main surface of the substrate 23.

  The present invention can be widely applied to devices that will be further miniaturized in the future, such as portable information terminals, digital cameras, and external HDDs, and its industrial applicability is very wide and large.

(A) is a schematic sectional drawing of the triaxial acceleration detection apparatus which concerns on Embodiment 1, The figure (b) is a principal part top view in the said detection apparatus. 1 is a schematic plan view of a sensor structure according to Embodiment 1. FIG. 3 is a perspective cross-sectional view of a main part of the sensor structure according to Embodiment 1. FIG. 3 is a perspective cross-sectional view of a main part of the sensor structure according to Embodiment 1. FIG. (A) is the schematic schematic diagram which showed the sensor structure based on Embodiment 1 with the electrical equivalent circuit, (b) is the schematic schematic diagram which showed the detection circuit based on Embodiment 1 with the electrical equivalent circuit FIG. 4C is a schematic diagram illustrating a timing chart of on / off of voltage application to the detection circuit according to the first embodiment. 1 is a schematic cross-sectional view of a variable capacitor according to a first embodiment. 1 is a schematic cross-sectional view of a variable capacitor according to a first embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Acceleration detection apparatus 11 Insulation mold body 12 Sensor part 13 Arithmetic processing part 14 Die pad 15 Conductive member 16 Lead 17, 18, 19 Bonding pad part 20 Sensor structure 21 Covering plate 22 Through hole 23 Substrate 24 Fixed electrode unit 25 Movable electrode unit 26 Potential Extraction Unit 27 Frame 28 Wall 29 Fixed Electrode Finger 30 Mass (Mass) Unit 31 Movable Electrode Finger 32 Anchor Unit 33 Spring Unit 34 Detection Circuit 35 Operational Amplifier 36 Sequence Control Circuit 37 Detection Circuit Unit

Claims (8)

A substrate and a swinging body swingable in the X, Y, and Z axis directions with respect to the substrate;
The rocking body includes a first rocking rod and a second rocking rod crossing the first rocking rod.
At least one movable electrode is formed on each of the four rocking rod members extending in opposite directions around the intersection of the two rocking rods, and fixed on the substrate side facing each of the movable electrodes. Electrodes are formed to form at least four electrode pairs;
A pair of the electrode pairs formed by the movable electrodes of the pair of rocking rod members constituting the first rocking rod and the fixed electrodes opposed thereto are in the longitudinal direction of the first rocking rod. With respect to the oscillation in the (X-axis direction), the gap between one electrode pair is reduced, and the gap between the other electrode pair is increased.
A pair of the electrode pairs formed by the movable electrodes of the pair of rocking rod members constituting the second rocking rod and the fixed electrodes opposed to the movable electrodes are in the longitudinal direction of the second rocking rod ( Y axis direction) is set such that the gap between one electrode pair is reduced and the gap between the other electrode pair is increased,
Further, with respect to the rocking movement of the rocking body in the Z-axis direction, the change in the facing area of the electrode pair of the first rocking rod and the change in the facing area of the electrode pair of the second rocking rod are reversed. An acceleration sensor characterized in that a relationship between an electrode and a movable electrode is set.   In a state where no acceleration is applied, the capacitance of a pair of electrodes composed of the movable electrode formed on the first swing rod and the fixed electrode on the substrate, and the second swing 2. The acceleration according to claim 1, wherein the capacitances of a pair of electrodes formed by the movable electrode formed in a moving manner and the fixed electrode on the substrate are set to be equal to each other. Sensor.   A plurality of the movable electrodes of the two oscillating rods and the fixed electrode on the substrate are respectively provided, and the arrangement order thereof is any of the oscillating plates when viewed from the intersection of the two oscillating rods. 3. The acceleration sensor according to claim 1, wherein the acceleration sensor is in the same order in a direction along the swinging member. Each of the movable electrodes formed on each of the first swing rod and the second swing rod is long and parallel to the substrate, and the fixed electrode facing them is long. Parallel to the substrate, the fixed electrode and the movable electrode are opposed so that their respective axes are parallel,
The order of the centroid of the opposed surface on the movable electrode side and the centroid of the opposed surface on the fixed electrode side in the opposed surface of the electrode pair of the first rocking rod in the Z-axis direction is The order in the Z-axis direction of the centroid of the opposing surface on the movable electrode side and the centroid of the opposing surface on the fixed electrode side in the opposing surface of the electrode pair is reversed. 4. The acceleration sensor according to any one of 3.   The first swing rod and the second swing rod are configured to be swingable by supporting both ends of each rod with spring members provided on the substrate. 2. The acceleration sensor according to 1.   The plurality of movable electrodes provided on each swing rod member and the fixed electrode on the substrate opposed thereto are configured such that the electrode length is increased in proportion to the distance from the intersection. The acceleration sensor according to claim 4. During acceleration action, the electrode pair of the first swinging hook part is formed as a capacitor that causes a change in capacitance that satisfies the relationship of the following expression (1) or (2), and the second swinging hook part: The acceleration sensor according to any one of claims 1 to 6, wherein each of the electrode pairs is formed as a capacitor that causes a change in capacitance satisfying a relationship of the following expression (3) or (4).
(1) C1 = Co + PΔX + RΔZ
(2) C2 = Co−PΔX + RΔZ
(3) C3 = Co + QΔY-RΔZ
(4) C4 = Co-QΔY-RΔZ
However, C1, C2, C3, C4: Capacitance of each variable capacitor when acceleration acts Co: Capacitance (initial capacity) of each variable capacitor when acceleration does not act
P, Q, R: Coefficients △ X, △ Y, △ Z: Displacement in each axis direction The acceleration sensor according to claim 7, and an arithmetic processing unit that outputs the axial direction component values of the X, Y, and Z according to the action of acceleration,
The said arithmetic processing part performs the following formula | equation (5) to (7) according to the effect | action of acceleration, The acceleration detection apparatus characterized by the above-mentioned.
(5) (Co + PΔX + RΔZ) · (−Vr) + (Co−PΔX + RΔZ) · (+ Vr) = Cf · Vx
(6) (Co + QΔY−RΔZ) · (−Vr) + (Co−QΔY−RΔZ) · (+ Vr) = Cf · Vy
(7) (Co + PΔX + RΔZ), (+ Vr) + (Co−PΔX + RΔZ), (+ Vr) + (Co + QΔY−RΔZ), (−Vr) + (Co−QΔY −RΔZ) · (−Vr) = Cf · Vz
Co: Capacitance (initial capacity) of each variable capacitor when acceleration is not applied
P, Q, R: Coefficients ΔX, ΔY, ΔZ: Displacement in each axial direction + Vr, −Vr: Input voltage to the acceleration detection device Vx, Vy, Vz: Output voltage from the acceleration detection device Cf: Negative Capacitance of feedback capacitor

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