JPH07306224A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To provide an acceleration sensor strong against temperature variation and excellent in linearity. CONSTITUTION:A mass part 3 is cantilevered swingably by a frame 4 through an elastic beam 2. The center of gravity G of the mass part 3 is set between the fixed part 8 of the beam 2 and a mass supporting part 9 (preferably, in the center thereof) in the axial direction of the beam 2. Since the mass part 3 translates with respect to a substrate 6 without inclining upon application of an acceleration, the capacitance between a movable electrode and a fixed electrode 7 varies in proportion to the acceleration thus enhancing the linearity of an acceleration sensor. Furthermore, since the mass part 3 is cantilevered through the beam 2, influence of temperature variation, e.g. thermal expansion of the beam 2, can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor.
Specifically, the present invention relates to an acceleration sensor that detects displacement of a mass portion caused by acceleration or vibration as a change in acceleration.

[0002]

2. Description of the Related Art FIG. 34 shows a conventional acceleration sensor 101. FIG. 34A shows the acceleration sensor 1.
01 is a plan view and FIG. 34 (b) is a cross-sectional view thereof. In the acceleration sensor 101, the mass portion 103 is supported by the frame 104 in a cantilevered manner by the elastic beam 102. Part 103 and beam 1
02 can be formed integrally with, for example, a silicon substrate. The lower surface of the mass portion 103 has conductivity,
It is the movable electrode 105. A substrate 106 made of, for example, glass is bonded to the lower surface of the frame 104, and the fixed electrode 1 faces the movable electrode 105 with a minute gap from the movable electrode 105 on the upper surface of the substrate 106.
07 are formed.

However, when acceleration is applied to the acceleration sensor 101, the mass portion 103 is displaced by the elastic deformation of the beam 102, and the movable electrode 10 is displaced according to the displacement amount of the mass portion 103.
The amount of the gap between 5 and the fixed electrode 107 changes. When the gap amount changes, the electrostatic capacitance between the movable electrode 105 and the fixed electrode 107 changes, and therefore the acceleration can be detected by outputting the change in the electrostatic capacitance as an electric signal.

However, such an acceleration sensor 1
In No. 01, since the center of gravity of the mass portion 103 is closer to the mass portion 103 side than the mass supporting portion 108 of the beam 102, when acceleration is applied, as shown in FIG.
3 cannot move in parallel, resulting in an inclination ω. Therefore, the capacitance between the movable electrode 105 and the fixed electrode 107 does not change in direct proportion to acceleration, and the linearity of the acceleration sensor 101 is poor.

In order to solve such a problem, there is one in which the displacement of the mass portion 103 is moved in parallel.
FIG. 36 shows a sectional view of the acceleration sensor 110. In the acceleration sensor 110, the mass portion 103 is supported by the beam 102 having elasticity in a cantilevered manner.

However, since the acceleration sensor 110 has a two-sided support, the acceleration sensor 110
Had a problem in that Further, the temperature characteristics are poor, and the thermal expansion of the beam 102 causes a change in the tension of the beam 102, causing a change in the sensitivity and offset of the acceleration sensor 110. Further, in the case where the temperature change is remarkable, such as when the frame 104 and the substrate 106 are joined, the beam 102 is damaged, and the yield and reliability of the acceleration sensor 110 are reduced.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the drawbacks of the above conventional examples, and an object thereof is to provide an acceleration sensor which is resistant to temperature changes and has high linearity. is there.

[0008]

A first acceleration sensor of the present invention is an acceleration sensor in which a mass portion is supported by a support substrate in a cantilever manner by an elastic beam, and the center of gravity of the mass portion is the beam. It is characterized in that it is located closer to the substrate fixing portion side than the free end of the beam farthest from the substrate fixing portion in the axial direction.

The second acceleration sensor of the present invention is an acceleration sensor in which a mass portion is supported by a supporting substrate in a cantilevered manner by an elastic beam, and the center of gravity of the mass portion is in the axial direction of the beam. It is characterized in that it is located between the substrate fixing portion of the beam and the mass supporting portion of the beam.

In these acceleration sensors, the mass portion can be a movable electrode, or the movable electrode can be formed on at least a part of the upper surface or the lower surface of the mass portion.

Further, it is preferable to dispose the mass portion on the upper surface or the lower surface of the beam.

The mass portion may be supported by the two beams on the side surface of the mass portion, or a beam supporting portion for supporting the beam may be provided on the side surface of the mass portion so as to project therefrom.

Further, the beam may be provided with at least one folding portion, and the mass supporting portion of the beam or the folding portion may be provided with a rigid portion thicker than the thickness of the beam, or the central portion of the beam. It is preferable that the beam is formed so that the thickness increases from the side toward the mass support portion or the folded portion.

Further, the mass portion may be formed of two or more kinds of materials, and the thickness of the mass portion may not be uniform. Further, the mass portion may have an asymmetrical shape in the beam axis direction, and a depression, a groove, or
A center of gravity adjusting portion having a hole or a hollow shape may be provided.

[0015]

In the acceleration sensor according to the first aspect of the present invention, in the acceleration sensor cantilevered by the beam, the center of gravity of the mass portion is the maximum from the substrate fixing portion of the beam in the axial direction of the beam. Since it is located closer to the substrate fixing portion side than the far free end, when acceleration is applied to the acceleration sensor, the mass portion can move in parallel in the thickness direction of the mass portion without tilting. Therefore, the electrostatic capacitance between the movable electrode formed on the upper surface or the lower surface of the mass portion and the fixed electrode facing the movable electrode changes in direct proportion to the acceleration. Therefore, the linearity of the acceleration sensor can be improved while taking advantage of the advantage of the cantilever type acceleration sensor having good temperature characteristics.

According to the second acceleration sensor of the present invention,
It shows a special case of the first acceleration sensor, in which the mass portion is supported at the free end farthest from the fixed end of the beam, and in this case as well, the mass portion does not tilt and the mass portion does not tilt. It can be translated in the thickness direction of the part.

At this time, in the acceleration sensor using the entire mass portion as the movable electrode, the mass portion can be easily made of, for example, semiconductor or metal. If the movable electrode is formed on at least a part of the upper surface or the lower surface of the mass portion, for example, the mass portion can be made of a material having a low specific gravity such as resin, and the mass portion can be made lightweight. It is possible to reduce the weight of the acceleration sensor as a whole.

Further, by disposing the mass portion also on the upper surface or the lower surface of the beam, the electrode area of the movable electrode formed on the mass portion can be increased, so that the sensor sensitivity can be improved.

Further, when the mass portion is supported by the two beams on the side surface of the mass portion, the mass portion is unlikely to be displaced in the width direction even when a lateral acceleration is applied, and the influence of the sensitivity of the other axis of the acceleration sensor. Can be reduced.

At this time, if the beam supporting portion for supporting the beam on the side surface of the mass portion is provided so as to project from the mass portion, the mass portion can be easily supported, and the beam shape is formed into, for example, a flat plate shape. It is possible to further reduce the displacement in the twisting direction, further improve the linearity, and reduce the influence of the sensitivity of another axis.

If at least one turn-back portion is provided on the beam, the acceleration sensor does not need to be large, and
Since the substantial length of the beam can be increased, the displacement amount of the mass portion is increased, and the sensitivity of the acceleration sensor can be increased.

If a rigid portion thicker than the thickness of the beam is provided in the mass supporting portion or the folding portion of the beam, the twisting of the beam in the mass supporting portion or the folding portion can be reduced, so that the linearity can be further improved. The improvement can be achieved, and the influence of acceleration other than the thickness direction can be reduced. Further, the same effect can be obtained by forming the beam so that the beam thickness increases from the central portion of the beam toward the mass supporting portion or the folded portion of the beam.

In these acceleration sensors, the center of gravity of the mass portion can be easily adjusted by forming the mass portion with two or more kinds of materials. Further, the center of gravity of the mass portion can be easily adjusted by making the thickness of the mass portion not uniform. Further, the shape may be asymmetric in the beam axis direction.

Further, the center of gravity of the mass portion is located closer to the substrate fixing portion side than the free end farthest from the substrate fixing portion of the beam by providing the mass portion with a center of gravity adjusting portion such as a depression, a groove, a hole, or a cavity. Alternatively, it may be located between the substrate fixing portion and the mass supporting portion.

[0025]

1 and 2 show an acceleration sensor 1 according to an embodiment of the present invention. 1 is a perspective view showing the acceleration sensor 1, FIG. 2 (a) is a plan view thereof, and FIG. 2 (b) is a sectional view thereof. The acceleration sensor 1 is swingably supported by a frame 4 by a beam 2 whose mass portion 3 has elasticity. For example, the mass portion 3, the beam 2 and the frame 4 are made of metal, semiconductor or the like, and the mass portion 3 and the frame 4 are joined to the frame portion 4 by the beam 2 by joining the end portion of the beam 2 to the mass portion 3 and the frame 4.
It is swingably supported by. Since the entire mass portion 3 is electrically conductive, the lower surface of the mass portion 3 has a function as the movable electrode 5, a substrate 6 made of glass or the like is attached to the lower surface of the frame 4, and the upper surface of the substrate 6 is movable. A fixed electrode 7 is formed so as to face the movable electrode 5 with a small gap from the electrode 5. The mass portion 3 is formed in a substantially U-shape in a plane symmetrically with respect to the central axis of the beam 2, and the center of gravity G of the mass portion 3 is an end portion of the beam 2 on the frame 4 side in the axial direction of the beam 2. That is, it is located between the fixed portion 8 of the beam 2 and the end of the mass 2 on the side of the mass 3 supporting the mass 3, that is, the mass support 9, and the mass 3 is supported by the beam 2. The mass portion 3 is supported by the upper end surface of the mass portion 3 so that the upper surface of the beam 2 and the upper surface of the mass portion 3 are flush with each other.

However, when acceleration is applied to the acceleration sensor 1, the mass portion 3 is displaced according to the acceleration, and the movable electrode 5
The capacitance between the fixed electrode 7 and the fixed electrode 7 changes. By detecting this electrostatic capacitance with a detection circuit or the like connected to the electrode pad 10, the magnitude of the acceleration applied to the acceleration sensor 1 can be known.

In the acceleration sensor 1, the mass portion 3
Since the center of gravity G is located between the fixed portion 8 of the beam 2 and the mass support portion 9, the mass portion 3 has a smaller inclination as compared with the conventional acceleration sensor 101, and the mass portion 3 can move in parallel. Therefore, the linearity of the acceleration sensor 1 can be improved, and since the mass portion 3 is supported in a cantilever manner, the influence of temperature change is small. Hereinafter, the principle of the present invention will be described according to the model shown in FIG.

As shown in FIG. 3A, in the conventional acceleration sensor in which the beam length is L and the distance from the beam mass supporting portion to the center of gravity G of the mass portion is a, the case where a load P is applied is shown. Think The following equation holds at the position of the distance x from the fixed portion on the beam. ^{d 2 y / dx 2 = -M} / (EI) = P (L-x) / (EI) + P × a / (EI) ...... However, M is the bending moment, EI is the stiffness of the beam. When the formula is integrated with respect to x, dy / dx = (P / EI) × {L × x + a × x− (1/2) x ² + c} (c is an integration constant). Here, the boundary condition is dy / dx = 0 at x = 0, so that c = 0, and dy / dx = (P / EI) × {L × x + a × x− (1/2) x ² } It can be expressed as ... Since the inclination ω of the mass portion is equal to the deflection dy / dx of the beam in the mass support portion, x = L is substituted into the equation, and ω = dy / dx = (P / EI) × {(1/2) L ² + a × L} ... Therefore, according to the equation, in the conventional acceleration sensor, the load P increases as the acceleration increases, and the inclination of the mass portion increases.

On the other hand, as shown in FIG. 3B, in the case of the acceleration sensor according to the present invention in which the center of gravity G of the mass portion is on the fixed portion side by the distance a from the mass supporting portion of the beam, FIG.
Similarly to (a), the inclination ω ′ of the mass portion is ω ′ = dy / dx = (P / EI) × {(1/2) L ² −a × L}.

Therefore, as can be seen from the equation, the inclination ω'of the mass portion becomes smaller by positioning the center of gravity G of the mass portion closer to the fixed portion side than the mass supporting portion of the beam. Further, the difference between the inclination ω ′ of the mass portion of the acceleration sensor of the present invention and the inclination ω of the mass portion of the acceleration sensor of the conventional example is ω′−ω = −2P × a × L / (EI) <0. The inclination of the mass portion can be made smaller than that of the conventional acceleration sensor.

Those shown in FIGS. 4 (a) and 4 (b) are, respectively,
FIG. 6 is a plan view of a frame 4 of an acceleration sensor 51 according to another embodiment of the present invention and a cross-sectional view of the acceleration sensor 51. In the acceleration sensor 51, a mass portion 3 is arranged at the center of an opening 4a of a frame 4 having a rectangular frame shape, and is supported by a beam 2 so as to be swingable. Similar to the acceleration sensor 1, the mass portion 3 is formed in a generally U-shaped plane so that the center of gravity G is located closer to the fixed portion 8 side of the beam 2 than the mass support portion 9 of the beam 2. The upper end surface of the portion 3 is supported.

The mass portion 3 is made of, for example, silicon, and the entire mass portion 3 has conductivity by ion implantation or the like, and the upper and lower surfaces of the mass portion 3 are movable electrodes 5. Of course, the mass portion 3 may be made of metal. Substrates 6 made of glass or the like are adhered to the upper and lower surfaces of the frame 4, respectively, and fixed electrodes 7 are formed on the inner surface of the substrate 6 with a movable electrode 5 and a minute gap therebetween. A space 11 around the mass portion 3 surrounded by the substrate 6 and the frame 4 is filled with a liquid having a reduced pressure or a constant pressure.

Even in the acceleration sensor 51, since the center of gravity G of the mass portion 3 is located closer to the fixed portion 8 than the mass supporting portion 9 of the beam 2, the linearity can be improved. Although it is needless to say, the linearity of the acceleration sensor 51 can be further improved by taking the difference between the changes in the electrostatic capacities of the two capacitors formed above and below the mass portion 3, and the beam 2 due to the temperature change can be further improved. Since it is possible to eliminate the influence of the flexure, the temperature characteristic of the acceleration sensor 51 can be improved.

Further, since the space 11 around the mass portion 3 is maintained in a decompressed state or the like, for example, exhaust gas does not enter from the outside of the sensor, and the corrosion of the mass portion 3 and the beam 2 can be prevented, The durability can be improved. At this time, by reducing the pressure, the vibration of the mass portion 3 is less attenuated by air and the frequency characteristics of the acceleration sensor 51 can be improved. Further, by filling the space 11 with the liquid, the acceleration sensor 51 is activated by the buffering force of the liquid.
It is possible to prevent the beam 2 and the like from being damaged due to the impact applied to it, and it is possible to improve the impact resistance.

FIGS. 5A and 5B are a plan view and a sectional view showing an acceleration sensor 52 which is still another embodiment of the present invention. The mass portion 3 of the acceleration sensor 52 is made of resin or the like. The mass part 3 is made of a material with a low specific gravity.
The movable electrode 5 is formed on the lower surface of the metal thin film such as aluminum. By thus forming the mass portion 3 with resin or the like, it is possible to reduce the weight of the acceleration sensor 52 as a whole. Further, the electric resistance of the movable electrode 5 can be reduced as compared with the case where the mass portion 3 is made of a semiconductor such as silicon. Therefore, it is possible to improve the temperature characteristics by reducing the change in the capacitance due to the change in temperature.

6A and 6B are a plan view and a sectional view showing an acceleration sensor 53 which is still another embodiment of the present invention, in which the center of gravity G of the mass portion 3 is the beam 2. The beam 4 is formed to be short by projecting the frame 4 toward the mass support portion 9 so as to be positioned in the middle of the fixed portion 8 and the mass support portion 9. In the acceleration sensor 53, a = 1 / 2L in the above equation,
The inclination ω ′ of the mass portion 3 is ω ′ = P / (EI) × {(1/2) L ² −a × L} = 0, and the inclination of the mass portion 3 can be completely eliminated.
Therefore, the mass unit 3 can move in parallel regardless of the magnitude of the acceleration, the magnitude of the electrostatic capacitance changes in proportion to the acceleration applied to the acceleration sensor 53, and the linearity of the acceleration sensor 53 is further improved. Can be improved. The center of gravity G of the mass portion 3 may be located at the center between the fixed portion 8 of the beam 2 and the mass support portion 9 without projecting the frame 4 toward the mass support portion 9. .

Further, FIG. 7 is a plan view and a sectional view of an acceleration sensor 54 which is still another embodiment of the present invention.
Shown in (a) and (b). In the acceleration sensor 54, the mass portion 3 is also formed on the lower surface of the beam 2,
Are arranged along the depressions 12 provided on the upper surface of the mass portion 3, and the mass portion 3 is supported by the beam 2. In this acceleration sensor 54, since the electrode area of the movable electrode 5 on the lower surface of the mass portion 3 can be increased, the fixed electrode 7
Capacitance between and becomes large, and the sensitivity of the sensor can be improved.

8 (a) and 8 (b) are a plan view and a sectional view of an acceleration sensor 55 which is still another embodiment of the present invention.
The frame 4 is integrally formed. In this way, by integrally forming the beam 2 and the frame 4,
Damage to the fixing portion 8 of the beam 2 is reduced, and the shock resistance of the acceleration sensor 55 can be improved. At this time, as shown in FIG.
Is formed, the stress generated in the fixed portion 8 is dispersed,
Beam 2 is less likely to be damaged even after repeated use,
The life of the acceleration sensor 55 can be extended.

Further, like the acceleration sensor 56 shown in FIG. 9, by integrally molding the beam 2 and a part of the mass portion 3, it is possible to reduce damage to the mass support portion 9 of the beam 2. Further, if the mass support portion 9 of the beam 2 is formed with the radius 13, the stress generated in the mass support portion 9 is dispersed, and the beam 2 is less likely to be damaged. Further, like the acceleration sensor 57 shown in FIG. 10, at least a part of the frame 4, the beam 2 and the mass portion 3 may be integrally molded. Of course, even if the upper and lower surfaces of the beam 2 of the fixed portion 8 and the mass support portion 9 are formed with the radius 13, the same effect can be obtained.

In the acceleration sensor 58 shown in FIG. 11, the beam 2 is provided with the frame mounting portion 14, and the mass portion 3, the beam 2 and the frame mounting portion 1 are provided.
4 is integrally formed of metal or the like. The frame mounting portion 14 is provided with a hole 15. The frame 4 formed of resin or the like is provided with a beam attachment portion 16 including a recessed portion and a protrusion portion 16a to be accommodated in the hole 15. The frame attachment portion 14 is attached to the beam by attaching the protrusion portion 16a to the hole 15. It is fitted and joined to the concave portion of the portion 16. As described above, the sensor detection portion including the mass portion 3, the beam 2 and the frame mounting portion 14 is integrally molded to reduce the number of parts, and the frame 4 is made of an inexpensive resin or the like to manufacture the acceleration sensor 58. The cost can be reduced.

FIG. 12 shows an acceleration sensor 59 which is another embodiment of the present invention. 12A is an exploded perspective view of the acceleration sensor 59, and FIG. 12B is a sectional view thereof. In the acceleration sensor 59, the mass portion 3 is swingable on the inner surface of the box-shaped mass portion 3. A recess 17 is provided so as to be displaceable, and an elastic beam 2 is disposed in the recess 17. The mass portion 3 is supported by one end of the beam 2, and a columnar support portion 18 is provided at the other end of the beam 2.
The support portion 18 is placed on the substrate, and the mass portion 3 is swingably supported by the beam 2. The mass portion 3 is formed so that the center of gravity G of the mass portion 3 is located between the mass support portion 9 and the fixed portion 8 of the beam 2 in the axial direction of the beam 2. The mass portion 3 is made of, for example, a semiconductor, and the movable electrode 5 is formed at least in the outer peripheral area of the depression 17 on the lower surface of the mass portion 3. Of course, the entire mass portion 3 may have conductivity. This movable electrode 5 is a beam 2,
It is electrically connected to the movable electrode lead-out wiring 19 formed on the upper surface of the substrate 6 through the supporting portion 18. Also, the substrate 6
A fixed electrode 7 is formed above the movable electrode 5 of the mass portion 3 so as to face the movable electrode 5. In this acceleration sensor 59, since it is not necessary to dispose the frame 4 supporting the beam 2 around the mass portion 3, the size of the acceleration sensor 59 can be reduced.

13A and 13B are a plan view and a side view, respectively, showing an acceleration sensor 60 according to still another embodiment of the present invention. In the acceleration sensor 60, the mass of the tip of the beam 2 is shown. The supporting portion 9 is supported on the side surface of the mass portion 3 by bending the supporting portion 9 into a plane L shape. As described above, since the side surface of the mass portion 3 is supported by the two beams 2, the mass portion 3 is not displaced in the width direction due to the lateral acceleration, and the detection axis direction of the beam 2 (mass portion 3 It is less likely to be affected by accelerations other than the thickness direction), and the acceleration in the desired direction can be accurately measured. Further, by supporting the mass portion 3 with the two beams 2 on both side surfaces of the mass portion 3, the surface of the mass portion 3 can be increased, and the electrode area of the movable electrode 5 can be increased. Therefore, the movable electrode 5 and the fixed electrode 7
The capacitance between and becomes large, and the sensitivity of the acceleration sensor 60 can be increased.

FIG. 14 shows an acceleration sensor 61 according to still another embodiment of the present invention, in which the beam supporting portions 20 are provided on the mass portion 3 so as to project from both sides of the mass supporting portion 20. The mass portion 3 is supported by the two beams 2. Even in this case, the surface of the mass portion 3 can be enlarged, and the sensitivity of the acceleration sensor 61 can be increased. Further, since the beam 2 can have a simple shape, for example, a long plate shape, the mass portion 3 is less likely to be displaced in the lateral direction, and the influence of the sensitivity of the other axis can be reduced.

FIG. 15 shows an acceleration sensor 62 which is another embodiment of the present invention. The beam 2 gradually increases in thickness from the fixed portion 8 side in the vicinity of the mass support portion 9 of the beam 2. It is formed, and the rigidity of the mass support portion 9 is high. Therefore, even when acceleration in a direction other than the detection axis direction is applied to the acceleration sensor 62, the beam 2 is not twisted and is less likely to be affected by acceleration in a direction other than the detection axis direction. Of course, the acceleration sensor 6 shown in FIG.
The same effect can be obtained by gradually increasing the thickness as shown in FIG.

FIG. 17 shows still another embodiment of the present invention. 17A is a plan view of the acceleration sensor 64, and FIG.
(B) is a side view thereof, in which the beam 2 pulled out from the fixed portion 8 is folded back toward the fixed portion 8 near the tip of the mass portion 3 and is reciprocated once in the beam axis direction. Is supported. In the acceleration sensor 64, the center of gravity G of the mass portion 3 is located at the free end farthest from the fixed portion 8 of the beam 2, that is, between the folded portion 21 of the beam 2 and the fixed portion 8. When acceleration is applied to the acceleration sensor 64, the mass portion 3 can move in parallel with the substrate 6 without tilting. Further, since the length of the beam 2 is substantially the same as that of the beam 2, the displacement amount of the mass portion 3 can be approximately doubled without increasing the size of the acceleration sensor 64. Yes, acceleration sensor 64
The sensitivity of can be almost doubled. Further, as shown in FIG. 18, if the beam 2 is folded a plurality of times, for example, twice or three times, the displacement amount of the mass portion 3 can be obtained in proportion to the number of times the beam is folded back. The sensitivity of can be improved.

Further, by forming the rigid portion 22 thicker than the thickness of the beam 2 in the folded portion 21 of the beam 2 as in the acceleration sensor 66 shown in FIG. 19, deformation in the twisted direction of the folded portion 21 is reduced, and the acceleration is increased. The linearity of the sensor 66 can be improved. Further, even in the mass supporting portion 9 of the beam 2, by forming the rigid portion 22 thicker than the thickness of the beam 2, the deformation in the twisting direction of the mass supporting portion 9 is reduced, which is more effective. Of course, as in the acceleration sensor 67 shown in FIG. 20, a rigid portion 22 thicker than the beam 2 may be formed in each folded portion 21 of the beam 2 that is folded back a plurality of times.

Further, as in the acceleration sensor 68 shown in FIG. 21, instead of providing the rigid portion 22, the rigidity of the folded portion 21 of the beam 2 is increased by gradually increasing the thickness of the beam 2 toward the folded portion 21. May be made higher, or the beam 2 may be formed so that the thickness of the beam 2 is increased stepwise like an acceleration sensor 69 shown in FIG.

In the acceleration sensor of each of the above embodiments,
The center of gravity G of the mass portion 3 is located closer to the fixed portion 8 side than the mass support portion 9 of the beam 2, or between the fixed portion 8 of the beam 2 and the free end farthest from the fixed portion 8, that is, the folded portion 21 of the beam 2. Need to be located. There are various possible methods for this. Description will be made below with reference to FIGS. 23 to 33.

First, in the acceleration sensor 70 shown in FIG. 23, the entire mass portion 3 is composed of two types of members 3a and 3b having different specific gravities. Therefore, by appropriately combining the members 3a and 3b, the mass portion 3
The center of gravity G of the beam 2 can be located between the fixed portion 8 and the mass support portion 9 of the beam 2 (the center thereof is particularly desirable). Also, like the acceleration sensor 71 of FIG.
It is also possible to replace a part of the above with a member 3c having a different specific gravity, and by further providing a hole-like center of gravity adjusting portion 23 with a drill or the like in this part, fine adjustment of the center of gravity position may be performed.

In the acceleration sensor 72 shown in FIG. 25, the thickness of the mass portion 3 is changed by providing the taper 24 on the upper surface of the mass portion 3 by polishing the mass portion 3 or the like. The position of the center of gravity of can be adjusted. It is also possible to provide a taper 24 on the lower surface of the mass portion 3, but in this case the movable electrode 5 of the mass portion 3 and the fixed electrode 7 on the upper surface of the substrate 6 cannot be made parallel to each other. Taper 24 on the upper surface of the mass part 3
Is provided and the lower end of the mass portion 3 is supported by the beam 2, there is an advantage that the fixed electrode 7 and the movable electrode 5 can be maintained in parallel. Of course, even when the lower end of the mass portion 3 is supported, there is no inconvenience in detecting the acceleration.

Further, the position of the center of gravity can be easily adjusted also by forming the mass portion 3 so as to be asymmetrical in the beam axis direction by partially cutting it off. In the acceleration sensor 73 shown in FIG. 26, the notches 25 are provided at both corners of the mass portion 3 and are formed asymmetrically in the beam axis direction. Alternatively, like the acceleration sensor 74 of FIG. 27, the notch 25 may be provided on the central axis of the beam 2.

Further, in the acceleration sensor 75 shown in FIG. 28, the center of gravity adjusting portion 23 composed of a plurality of grooves is provided on the upper surface of the mass portion 3. In this acceleration sensor 75,
The position of the center of gravity can be freely changed by changing the number of grooves, the position of the groove, or by providing a wide groove-shaped center-of-gravity adjusting portion 23 like the acceleration sensor 76 of FIG. 29 and changing the width and depth of the groove. be able to.

Further, as in the acceleration sensor 77 shown in FIG. 30, a large number of hole-shaped center-of-gravity adjusting portions 23 may be provided in the mass portion 3 to adjust the center of gravity G of the mass portion 3. Also by this method, the position of the center of gravity can be freely adjusted by changing the size, depth and number of the holes. In this case, the resistance of air or the like received due to the displacement of the mass portion 3 is reduced, and in particular, as in the acceleration sensor 51 of the second embodiment shown in FIG. 4, a liquid or the like is enclosed in the space 11 around the mass portion 3. In this case, vibration damping due to the liquid can be reduced, which is particularly preferable from the viewpoint of frequency characteristics of the acceleration sensor 77. Of course, one large hole-shaped center-of-gravity adjusting portion 23 may be used as in the acceleration sensor 78 shown in FIG.

Further, FIG. 32 shows an acceleration sensor 79 provided with another gravity center adjusting portion 23. The mass portion 3 of the acceleration sensor 79 has a hollow center of gravity adjusting portion 2 in the width direction of the mass portion 3.
3 is provided. When the hollow center of gravity adjusting section 23 is provided, the electrode area of the mass section 3 does not decrease, so that the center of gravity position can be adjusted without lowering the sensor sensitivity.

Further, in the acceleration sensor 80 shown in FIG. 33, the hollow center of gravity adjusting portion 23 provided in the mass portion 3 is used.
An opening 26 connected to is provided on the upper surface of the mass portion 3, and a low melting point substance 27 such as wax is filled in the cavity. In this case, the low-melting substance 27 such as wax is previously filled in the center-of-gravity adjusting portion 23 having a hollow shape, and the low-melting substance 27 is melted by heating and taken out from the opening 26, and the low-melting substance in the cavity is removed. The amount of 27 can be adjusted freely. Therefore, the center of gravity of the mass portion 3 can be freely adjusted by changing the amount of the low melting point substance 27 to be taken out. Further, even if the adjustment is unsuccessful, the center of gravity can be readjusted again by putting the low melting point substance 27 in the cavity, so that the yield of the acceleration sensor 80 can be improved. It should be noted that it is conceivable to fill the cavity with liquid, but the number of parts increases and the structure of the mass portion 3 becomes complicated because it is necessary to prevent liquid leakage. In this respect, it is preferable to fill the low-melting point substance 27 in the solid state during normal use since the low-melting point substance 27 does not leak from the opening 26 and the structure of the mass portion 3 is facilitated.

[0056]

According to the acceleration sensor of the present invention, the center of gravity of the mass portion is located closer to the substrate fixing portion than the free end of the beam farthest from the substrate fixing portion in the axial direction of the beam. Alternatively, since it is positioned between the substrate fixing portion of the beam and the mass supporting portion of the beam, the mass portion cantilevered by the beam can be translated in the thickness direction of the mass portion. For example, the electrostatic capacitance between the movable electrode provided on the mass portion and the fixed electrode provided so as to face the movable electrode changes in proportion to the magnitude of acceleration. Therefore, it is possible to improve the linearity of the acceleration sensor in which the mass portion having excellent temperature characteristics is supported in a cantilever manner.

Further, since the entire mass portion is the movable electrode, the mass portion can be easily made from a semiconductor or metal. Further, if the movable electrode is formed on the upper surface or the lower surface of the mass portion, the mass portion can be made lighter by making the mass portion with resin or the like, and the acceleration sensor as a whole can be made lighter.

Further, by disposing the mass portion also on the upper surface or the lower surface of the beam, the electrode area of the movable electrode formed on the mass portion can be increased, so that the sensor sensitivity can be improved.

When the mass portion is supported by the two beams on the side surface of the mass portion, the displacement of the mass portion in the lateral direction is reduced, and the sensitivity of the other axis of the acceleration sensor can be lowered.

At this time, if the beam supporting portion for supporting the beam on the side surface of the mass portion is provided so as to project from the mass portion, the mass portion can be easily supported, and the beam shape is formed into, for example, a flat plate shape. It is possible to further reduce the displacement in the twisting direction, further improve the linearity, and reduce the influence of the sensitivity of another axis.

If at least one turn-back portion is provided on the beam, the acceleration sensor does not need to be large, and
Since the substantial length of the beam can be increased, the displacement amount of the mass portion is increased, and the sensitivity of the acceleration sensor can be increased.

If a rigid portion thicker than the thickness of the beam is provided on the mass supporting portion or the folded portion of the beam, twisting of the beam at the mass supporting portion or the folded portion can be reduced, so that the linearity can be further improved. The improvement can be achieved, and the influence of acceleration other than the thickness direction can be reduced. Further, the same effect can be obtained by forming the beam so that the beam thickness increases from the central portion side of the beam toward the mass supporting portion or the folded portion of the beam.

In these acceleration sensors, the center of gravity of the mass can be easily adjusted by forming the mass with two or more kinds of materials. Further, the thickness of the mass portion may not be uniform. Furthermore, it may be asymmetric in the beam axis direction.

Further, the center of gravity of the mass portion is positioned closer to the substrate fixing portion side than the free end farthest from the substrate fixing portion of the beam by providing the mass portion with a center of gravity adjusting portion such as a depression, a groove, a hole, or a cavity. Alternatively, it may be located between the substrate fixing portion and the mass supporting portion.

[Brief description of drawings]

FIG. 1 is a perspective view showing an acceleration sensor according to an embodiment of the present invention.

FIG. 2A is a plan view showing an acceleration sensor of the above.
(B) is the sectional view.

FIG. 3A is an explanatory diagram showing displacement of a mass portion in a conventional acceleration sensor, and FIG. 3B is an explanatory diagram showing displacement of a mass portion in the acceleration sensor of the present invention.

4A and 4B are a plan view and a sectional view, respectively, showing an acceleration sensor according to another embodiment of the present invention.

5A and 5B are a plan view and a sectional view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

6A and 6B are a plan view and a sectional view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

7A and 7B are a plan view and a sectional view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

8A and 8B are a plan view and a sectional view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

9A and 9B are a plan view and a sectional view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

10A and 10B are a plan view and a sectional view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

11A and 11B are a plan view and a sectional view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

12A is an exploded perspective view of an acceleration sensor according to still another embodiment of the present invention, and FIG. 12B is a sectional view thereof.

13A and 13B are a plan view and a side view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

14A and 14B are a plan view and a side view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

15A and 15B are a plan view and a side view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

FIG. 16 is a side view showing an acceleration sensor according to still another embodiment of the present invention.

17A and 17B are a plan view and a side view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

FIG. 18 is a plan view showing an acceleration sensor which is still another embodiment of the present invention.

19 (a) and 19 (b) are respectively a plan view and a side view showing an acceleration sensor according to still another embodiment of the present invention.

FIG. 20 is a plan view showing an acceleration sensor according to still another embodiment of the present invention.

21 (a) and 21 (b) are respectively a plan view and a side view showing an acceleration sensor according to still another embodiment of the present invention.

FIG. 22 is a side view showing an acceleration sensor according to still another embodiment of the present invention.

23A and 23B are a plan view and a sectional view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

FIG. 24 is a perspective view in which an acceleration sensor according to still another embodiment of the present invention is partially omitted.

25A and 25B are a plan view and a sectional view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

FIG. 26 is a plan view showing an acceleration sensor that is still another embodiment of the present invention.

FIG. 27 is a perspective view in which an acceleration sensor according to still another embodiment of the present invention is partially omitted.

FIG. 28 is a sectional view showing an acceleration sensor according to still another embodiment of the present invention.

FIG. 29 is a perspective view in which an acceleration sensor according to still another embodiment of the present invention is partially omitted.

30A and 30B are a plan view and a sectional view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

FIG. 31 is a perspective view in which an acceleration sensor according to still another embodiment of the present invention is partially omitted.

32A and 32B are a plan view and a sectional view, respectively, showing an acceleration sensor according to still another embodiment of the present invention.

FIG. 33 is a perspective view in which an acceleration sensor according to still another embodiment of the present invention is partially omitted.

34A and 34B are a plan view and a sectional view, respectively, showing an acceleration sensor of a conventional example.

FIG. 35 is an explanatory diagram showing displacement of a mass portion in the above acceleration sensor.

FIG. 36 is a cross-sectional view showing another conventional acceleration sensor.

[Explanation of symbols]

 1, 51, 52, ..., 80 Acceleration sensor 2 Beam 3 Mass part 8 Fixed part 9 Mass support part 21 Folded part 22 Rigid part 23 Center of gravity adjustment part 27 Low melting point substance

Claims (14)

[Claims] 1. An acceleration sensor in which an elastic beam supports a mass portion on a supporting substrate in a cantilever manner, wherein a center of gravity of the mass portion is farthest from a substrate fixing portion of the beam in the axial direction of the beam. An acceleration sensor, characterized in that the acceleration sensor is located closer to the substrate fixing portion side than the free end thereof. 2. An acceleration sensor in which an elastic beam supports a mass portion on a supporting substrate in a cantilevered manner, wherein a center of gravity of the mass portion has a substrate fixing portion of the beam and the beam with respect to an axial direction of the beam. An acceleration sensor, characterized in that it is located between the mass support part of the. 3. The acceleration sensor according to claim 1, wherein the mass portion is a movable electrode. 4. The acceleration sensor according to claim 1, wherein a movable electrode is formed on at least a part of an upper surface or a lower surface of the mass portion. 5. The acceleration sensor according to claim 1, wherein the mass portion is provided on the upper surface or the lower surface of the beam. 6. The mass member is supported by the two beams on the side surface of the mass member.
The acceleration sensor according to 2, 3, 4 or 5. 7. The acceleration sensor according to claim 6, wherein a beam supporting portion for supporting a beam is provided on the side surface of the mass portion so as to project therefrom. 8. The beam according to claim 1, 2, 3, 4, 5, wherein at least one folded portion is provided.
The acceleration sensor according to 6 or 7. 9. A rigid portion thicker than the thickness of the beam is provided at the mass supporting portion or the folded portion of the beam, or 8
The acceleration sensor according to. 10. The beam is formed so that the thickness thereof increases from the central portion side of the beam toward the mass support portion or the folded portion. The acceleration sensor according to 5, 6, 7, 8 or 9. 11. The mass portion is formed of two or more kinds of materials, 1, 2, 3, 4, 5, 6,
The acceleration sensor according to 7, 8, 9, or 10. 12. The thickness of the mass portion is not uniform, 1, 2, 3, 4, 5, 6, 7, 8,
The acceleration sensor according to 9, 10, or 11. 13. The mass portion has an asymmetric shape in the beam axis direction, as claimed in claim 1.
The acceleration sensor according to 5, 6, 7, 8, 9, 10, 11 or 12. 14. The mass center is provided with a center-of-gravity adjusting part such as a depression, a groove, a hole, or a hollow shape, and the mass part is provided with a center of gravity adjusting part. 10, 11, 1
The acceleration sensor according to 2 or 13.