JPH095353A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an acceleration sensor having simple structure in which the temperature dependency is eliminated and the failure is minimized. SOLUTION: The acceleration sensor comprises a weight part 22 displaceable with acceleration, and a part 21 for supporting the weight part 22 through a beam part 23 wherein the weight part 22 is made of a translucent material. Means 5 for making a luminous flux irradiate the weight part 22 and means 6 for receiving the light emitted from the light emitting means 5 and transmitted through the weight part 22 are disposed while being spaced apart from the weight part 22 thus obtaining a light transmitting acceleration sensor. Preferably, the weight part 22 and the beam part 23 are applied with covers 3, 4 and the light emitting and receiving means 5, 6 are mounted on the covers 3, 4. Alternatively, the weight part 22 may be shaped to condensate the light or may be a return transmission type for transmitting the light a plurality of times.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor for detecting acceleration by optical means.

[0002]

2. Description of the Related Art Conventionally, many types of acceleration sensors are known to be mounted on automobiles and the like. For example, there is a cantilever type acceleration sensor using a piezoresistor as shown in FIG. This acceleration sensor is a small sensor having a 3 × 2 mm plane. The weight portion, the beam portion, and the support portion are integrally made of silicon, and are formed by etching (etching) using potassium hydroxide. A piezoresistor is arranged on the beam portion of this sensor. In this acceleration sensor, since the resistance of the piezoresistor changes as the beam part bends as the weight part is displaced by acceleration, the change in resistance is detected as acceleration.

Further, as an acceleration sensor using light,
A device as shown in FIG. 8 has been proposed (JP-A-6-5).
0984). In this acceleration sensor, the end portion of the first optical fiber a is fixed to the weight portion d from the frame b through the beam portion c, and the second optical fiber e faces the first optical fiber a on the frame b. It is arranged. In this acceleration sensor, when acceleration is applied to the weight part d, the first optical fiber a is also displaced by an amount according to this acceleration. Therefore,
If the light is emitted from the first optical fiber a, the fluctuation of the light can be detected as the acceleration by the second optical fiber e on the light receiving side.

[0004]

However, in the acceleration sensor using the piezoresistor, the temperature of the resistor itself of the piezoresistor is high, and the influence of expansion and contraction of the beam component material due to heat is high. There is a problem in that it is easy to receive and correction by temperature is necessary.

Further, in the acceleration sensor using the above light, since the first optical fiber a is arranged so as to lie from the beam portion c to the weight portion d, the first optical fiber a adversely affects the bending of the beam portion c. In addition to the problem that high sensitivity detection of acceleration is impeded, there is also the problem that adjustment is difficult when the positional deviation between the first optical fiber a and the second optical fiber e occurs.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a highly sensitive acceleration sensor which has no temperature dependence, has a simple structure, and has few failures.

[0007]

The present invention can be applied to an acceleration sensor having a weight portion that is displaced by acceleration and a support portion that supports the weight portion through a beam portion. In order to solve the above-mentioned problems of the prior art and achieve the above object,
In the acceleration sensor of the present invention, a weight portion made of a light transmissive material and displaced by acceleration is interposed in the optical path from the light emitting means to the light receiving means. That is, according to the present invention, the weight portion is made of a light-transmissive material, and a light emitting means for irradiating light toward the weight portion, and a light transmitted from the light emitting means and transmitted through the weight portion. It is characterized in that the light receiving means for detecting the light and the light receiving means are arranged separately from the weight portion.

In the acceleration sensor having such a structure, the incident angle of the light to the weight portion changes with the displacement of the weight portion, which changes the position of the reaching point (light spot) of the transmitted light, the light amount, and the like. Therefore, this change in transmitted light is detected as acceleration. Since such a light transmission type acceleration sensor uses light, it is not affected by environmental temperature. Further, since it is not necessary to dispose any additional parts on the weight portion and the beam portion, the movement of the weight portion is not restricted,
The sensitivity is good, and the structure is simple and there are few failures.

Silicon can be selected as a constituent material of the weight portion. In this case, since silicon is transparent to infrared rays, the light from the light emitting means needs to include infrared rays. When the beam portion and the support portion are made of silicon in addition to the weight portion, these can be formed by etching from a silicon single crystal wafer. This allows
The size of the sensor can be reduced by using the semiconductor microfabrication technology.
Reliability is further improved.

In such an acceleration sensor, the weight part and the beam part may be enclosed by a cover. Accordingly, the light emitting means and the light receiving means can be arranged on the cover, and the structure is simpler and the reliability is higher, and the light emitting means and the light receiving means are easily positioned, which is preferable in this sense. In this case, if the cover is made of silicon, the CCD as the light receiving means can be built in advance in the silicon, and the reliability is further increased. Further, if the light emitting means or the light receiving means is embedded or externally attached from the outside of the cover, assembly and lead-out of the lead wire are facilitated.

The weight portion can be configured to collect light. For example, the displacement of the weight can be detected more easily by forming the weight in the shape of a convex lens and condensing the transmitted light of the weight on the light receiving means.
On the other hand, a return transmission type acceleration sensor in which the optical path from the light emitting means is bent may be used. This increases the arbitrariness of the arrangement such as aligning the light emitting means and the light receiving means on one side. In this case, another feature of the light emitting means is that the emitted light is angled at a predetermined angle so that the emitted light can obliquely enter the weight portion. In addition, the light receiving unit is a position where light can be received at least once after being obliquely transmitted through the weight portion, after being repeatedly reflected by a predetermined portion (for example, the inner surface of the cover) and re-incident and transmitted to the weight portion. Another feature is that the light receiving means is arranged. Providing a reflective film on the inner surface of the cover or the like where light is reflected is preferable in terms of light utilization efficiency.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an acceleration sensor according to the present invention will be specifically described with reference to the drawings. 1A and 1B show an example of the configuration of an acceleration sensor of the present invention. FIG. 1A is a schematic sectional structural view, and FIG. 1B is a plan view (bottom view) of a sensor body.

The acceleration sensor 1 includes a sensor body 2 and
It is provided with an upper cover 3 and a lower cover 4 which cover the upper cover 3 from above and below. The sensor body 2 is an operating portion of a cantilever type sensor integrally formed of, for example, silicon single crystal. Specifically, the sensor body 2 includes a support portion (for example, the upper cover 3
And a frame-shaped frame 21 to which the lower cover 4 can be attached)
And a weight portion 22 located inside the frame 21, and a beam portion 23 that supports the weight portion 22 by connecting the weight portion 22 to the inner peripheral wall of the frame 21.

The weight portion 22 is a mass body that is displaced in the thickness direction (vertical direction in FIG. 1A) about the support portion (frame 21) as a fulcrum due to acceleration. The material of the weight portion 22 is not particularly limited, except that it has optical transparency. The size and support position of the beam portion 23 that supports the weight portion 22 so as to be elastically deformable, in consideration of the material and the mass of the weight portion 22, the beam portion 23.
Is designed so that the displacement of the weight portion 22 is as large as possible within the range where there is no problem in the mechanical strength of the. In the present embodiment, as illustrated, the beam portion 23 supports the weight portion 22 on the upper end side in the thickness direction at the center of one side of the weight portion 22.

The inner central portions of the upper cover 3 and the lower cover 4 are
Recesses are formed so that the weight portions 22 do not hit when displaced. The upper and lower covers 3 and 4 are fixed to the frame 21 from the thick portions around them. As a result, the weight portion 22 and the beam portion 23 are enclosed by the upper and lower covers 3 and 4.

A light emitting means 5 is provided inside the upper cover 3 so as to irradiate the lower weight portion 22 with infrared rays and the like. On the other hand, inside the lower cover 4,
A light receiving unit 6 for detecting the transmitted light emitted from the light emitting unit 5 and transmitted through the weight portion 22 is provided.

As the light emitting means 5, various light sources such as recent small semiconductor lasers and light emitting diodes can be used. In addition, the end portion of the optical fiber that guides and emits light from another light source can be provided in the upper cover 3 or the lower cover 4. In this case, as the other light source, a light source utilizing a photoelectron emission effect such as a photoelectric tube can be used. When the weight portion 22 is made of a silicon single crystal, since the silicon single crystal does not pass visible light but infrared rays, it is necessary to select the light emitting means 5 that emits light having a wavelength of about 1 μm or more.

As the light receiving means 6, various photodetectors, for example, photodiodes, phototransistors, those utilizing a photoconductive effect such as CdS and CdSe, and image pickup devices typified by CCD (charge coupled device) are widely used. Can be used.

If the upper and lower covers 3 and 4 are made of silicon, the photodiodes, phototransistors, CCDs, etc. of the light receiving means 6 can be directly built in the silicon in advance. In this case, instead of forming the recesses in the upper and lower covers 3 and 4 later, the silicon pieces cut out from the substrate in which these light receiving elements are formed are raised by the spacers in the frame 21 portion to secure the operation space of the weight portion 22. A method such as doing is possible.

Next, a method of measuring the displacement of the weight portion 22 with the transmission type acceleration sensor of the present invention will be specifically described. As shown in FIG. 2, in the non-acceleration state (indicated by the solid line) in which the weight portion 22 is not displaced, the light flux L from the light emitting / emission means 5 is generated.
Passes through the weight portion 22 at a right angle and reaches P1. When acceleration is applied in this state, the weight portion 22 is displaced and the incident angle to the weight portion 22 is changed, as shown by the one-dot chain line in the figure, and the arrival point of transmitted light (hereinafter referred to as the light point) is changed from P1 to P2. It shifts. If the shift of the light spot is detected by the light receiving means 6,
The displacement of the weight 22 can be measured.

More specifically, a predetermined amount of light from the light emitting means 5 is irradiated toward the weight portion 22, and the transmitted light at this time is received by the light receiving means so that the maximum amount of light can be obtained in a non-accelerated state, for example. By disposing 6 and detecting a decrease in the amount of light received by the light receiving means 6 due to the shift of the light spot, the displacement of the weight portion 22 can be measured. It is also possible to dispose the light receiving means 6 so that the transmitted light crosses with the displacement of the weight portion 22 and measure the displacement of the weight portion 22 based on the amount of received light and the increasing / decreasing direction thereof.

When the deviation of the light spot is large, it is preferable to arrange a plurality of light receiving means 6 in that direction. In this case, if the light receiving position in the non-acceleration state is set at the midpoint of the light receiving means 6 arranged in plural, it is possible to cope with both vertical displacements of the weight portion 22. When the light receiving means 6 is a photodiode or a phototransistor, the same effect can be obtained by arranging a plurality of photodiodes or phototransistors in a pattern within the single light receiving means 6.

With an image pickup device, such as a CCD, in which a large number of small light receiving elements are integrated, the position of the light spot can be directly measured and the amount of deviation thereof can be detected. In this case, it is preferable to use a semiconductor laser as the light emitting means 5 because the beam diameter thereof is relatively small and therefore the position can be accurately detected.

On the other hand, as shown in FIG. 3, the light shielding portions 22a and the light transmitting portions 22b are alternately formed corresponding to the upper and lower surfaces of the weight portion 22, respectively, and the transmitted light A transmitted through the upper and lower light transmitting portions 22b. There is also a method of detecting the amount of light. When the weight portion 22 is displaced and tilted with respect to the light flux, the light shielding portion 22a on the upper side overlaps with the light transmitting portion 22b on the lower side, so that the light amount of the transmitted light A is reduced. The displacement of the weight portion 22 can be measured by detecting this decrease in the amount of light.

Next, a method of manufacturing the sensor main body 2 will be briefly described by taking as an example the case of integrally forming a silicon single crystal. This sensor main body 2 is formed by etching a silicon wafer using a silicon wafer and a weight portion 2
2, it can be manufactured by creating the beam portion 23 and the support portion (frame 21). For example, using a (100) plane wafer, a portion to be the beam portion 23 is previously doped with boron at a high concentration. After that, after forming an etching mask in which a window is opened by patterning the boundary portion between the frame 21 and the weight portion 22, wet etching such as potassium hydroxide is performed. Then, at this boundary, 54.74 from the horizontal position.
° Angled grooves can be formed. At this time, the beam portion 23 remains because it is not selectively etched due to the doping. Further, when the light shielding portion 22a is provided on the weight portion 22 as shown in FIG. 3, it can be formed by patterning a metal film of gold, chromium or the like by using an ordinary lithography technique.

The upper and lower covers 3 and 4 can be made of silicon, glass or the like, and a recess is formed in the center of these wafers by etching or the like according to a conventional method. Then, the upper and lower covers 3 and 4 are joined to the sensor body 2 by joining the thick-walled portions remaining in the peripheral portions to the frame 21 by means such as anodic joining.

In the acceleration sensor 1 shown in FIG. 4, the upper and lower covers 3 and 4 are made of a light transmissive material such as glass and silicon, and the light emitting means 5 and the light receiving means 6 are arranged on the outer surfaces of the covers 3 and 4. The light emitted from the light emitting means 5 is
The light is transmitted through the upper cover 3, the weight portion 22, and the lower cover 4, and reaches the light receiving means 6.

According to the acceleration sensor 1 as described above, since it is not necessary to provide any holes for passing a waveguide such as a conductive wire or an optical fiber in the upper and lower covers 3 and 4, the structure is simpler and the cost is lower. And is highly reliable, and in addition, the degree of freedom in selecting the light emitting means 5 and the light receiving means 6 is high.

In the acceleration sensor 1 shown in FIG. 5, the weight portion 22 is formed in the shape of a convex lens, and the weight portion 2 is emitted from the light emitting means 5.
The transmitted light that has passed through 2 is focused on the light receiving means 6, which makes it easier to measure the shift amount or the light amount of the light spot by the light receiving means 6. Instead of forming the weight portion 22 in the shape of a convex lens, it is also possible to form fine unevenness on the light incident surface of the weight portion 22 on the light source side to form a Frenelli lens shape. Further, in the acceleration sensor 1, the light receiving means 6 such as a CCD is used as the lower cover 4 made of a silicon substrate.
It has a structure in which it is directly formed on the inner surface and is joined to the frame 21 via the spacer 7, and the light receiving means 6 such as a CCD can be easily assembled.

In the acceleration sensor 1 shown in FIG. 6, the light emitting means 5 and the light receiving means 6 are arranged on one of the upper and lower covers 3 and 4,
It is a return transmissive type in which a reflective film 8 of Au or the like is provided on the other inner side surface and the like. In this case, as shown, the light emitting means 5
It is necessary to give an angle to the emission direction of. According to the acceleration sensor 1 as described above, not only the light emitting means 5 and the light receiving means 6 are provided on one side, but it is easy to take out the lead wire.
An optical component in which the light emitting means 5 is angled in advance and the light receiving means 6 is integrally incorporated can be used, and the detection accuracy and reliability can be improved.

In this acceleration sensor 1, the number of times the optical path is returned is not limited, and of course, as described above,
The light emitting means 5 can be externally attached. In this case, as a method of angling the light emitting means 5, as shown in an enlarged view of the end portion of the optical fiber in FIG. 6B, a transparent angling member 9 for facilitating the angulation is used. By using the transparent member 9, the optical fiber end 5 can be fixed to the outer flat surface of the upper cover 3. The transparent member 9 has in advance an oblique groove into which the optical fiber end 5 having a vertical cross section can be inserted. Although not particularly shown, if there is no problem of light loss or durability due to joining, the optical fiber end portion 5 may be brought close to the outer plane at a predetermined angle and the periphery may be fixed with a fixing material.

Further, as shown in FIG. 3C, an inclined surface for forming an angle is provided in advance on the outer surface of the upper cover 3 or the like,
The concave inclined surface 3a of FIG. 3A may be used, or a concave portion or a convex portion having an inclined surface may be formed inside the upper cover 3 although not particularly shown.

The present invention is not limited to the above description. For example, in the above example, the acceleration sensor is shown as a single device, and therefore the upper and lower covers 3 and 4 are provided as a member for protecting the sensor body 2 and attaching the light emitting means 5 and the light receiving means 6. However, the weight portion 2 in the present invention
2, the beam portion 23, and the support portion 21 can be provided as a part of a high-performance sensor, for example. In this case, the upper and lower covers 3 and 4 may be omitted, and the light emitting means 5 and the light receiving means 6 or the return transmissive reflection film 8 of FIG. 6 may be provided on other parts of the high-performance sensor. When the other portion has a high reflectance, the reflection film 8 can be omitted.

In the above example, the sensor body 2 is made of silicon.
, But may be made of other material such as quartz or MgO. Further, a film of silicon nitride, silicon oxide or the like may be formed on a silicon wafer, and this film may be left as the beam portion 23. Good. Further, the light emitting means 5 and the light receiving means 6 are not limited to the above example, and the cantilever has been described in the above example, but needless to say, the invention is not limited to this. Various changes can be made without departing from the spirit of the invention.

[0035]

As described above, according to the acceleration sensor of the present invention, since it is of the transmission type, it is not necessary to attach any part to the beam portion and the bending of the beam portion is not obstructed. , High sensitivity. Further, it is not affected even if the environmental temperature becomes high or low, and is excellent in accuracy.
Further, the structure is simple, the semiconductor can be miniaturized by using the fine processing technology, and the number of failures is small. Therefore, it is particularly suitable for an automobile with a lot of vibration.

[Brief description of drawings]

FIG. 1 shows an example of an acceleration sensor of the present invention,
(A) is a schematic sectional structural view, and (B) is a plan view (bottom view) of the sensor body.

FIG. 2 is an explanatory diagram showing a state in which displacement of a weight portion is detected.

FIG. 3 is a schematic diagram showing a state in which light-shielding portions are alternately formed on the weight portion.

FIG. 4 is a schematic sectional structural view showing another embodiment of the acceleration sensor of the present invention.

FIG. 5 is a schematic sectional structural view showing still another embodiment of the acceleration sensor of the present invention.

FIG. 6A is a schematic sectional structural view showing still another embodiment of the acceleration sensor of the present invention. FIG.
FIG. 6C is an enlarged view of a main part showing an example of a fixing method when the light emitting means is externally attached.

7A and 7B show an example of a conventional acceleration sensor using a piezoresistor, where FIG. 7A is a plan view and FIG. 7B is a sectional view.

FIG. 8 is a perspective view showing an example of a conventional optical acceleration sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Acceleration sensor, 2 ... Sensor main body, 21 ... Frame (supporting part), 22 ... Weight part, 23 ... Beam part, 3 ... Upper cover (cover), 3a ... Recessed inclined surface, 4 ... Lower cover (cover), 5 ... Light emitting means, 6 ... Light receiving means, 7 ... Spacer, 8 ... Reflective film, 9 ... Transparent member.

Claims (10)

[Claims] 1. An acceleration sensor comprising a weight portion that is displaced by acceleration and a support portion that supports the weight portion through a beam portion, wherein the weight portion is made of a light-transmissive material, and the weight portion is formed. A light emitting means for irradiating light toward the portion and a light receiving means for detecting transmitted light emitted from the light emitting means and transmitted through the weight portion are arranged separately from the weight portion. And an acceleration sensor. 2. The acceleration sensor according to claim 1, wherein the weight portion is made of silicon, and the light emitted from the light emitting means includes infrared rays. 3. The weight portion, the beam portion and the support portion are integrally formed by etching from a silicon single crystal substrate.
The acceleration sensor according to any one of the preceding claims. 4. The acceleration sensor according to claim 1, wherein the weight portion and the beam portion are enclosed by a cover, and the light emitting means and the light receiving means are provided on the cover. 5. The acceleration sensor according to claim 4, wherein the light receiving unit is a charge-coupled device integrally formed with the cover made of silicon. 6. The cover is made of a light transmissive material,
The acceleration sensor according to claim 4 or 5, wherein the light emitting means and the light receiving means are embedded in or externally attached to the cover, respectively. 7. The weight portion is shaped to collect light,
The acceleration sensor according to any one of claims 1 to 6, wherein transmitted light from the weight portion is condensed on the light receiving means. 8. The light emitting means is angled at a predetermined angle so that the emitted light can be obliquely incident on the weight portion, and the light receiving means is at least once after obliquely transmitted through the weight portion. The acceleration sensor according to any one of claims 1 to 6, wherein the acceleration sensor is arranged at a position capable of receiving light after repeating reflection at a predetermined portion and re-incident and transmission to the weight portion. 9. The acceleration sensor according to claim 8, wherein the predetermined portion is an inner surface of the cover, and a reflective film is provided on the inner surface of the cover including a light reflection position. 10. The displacement of the weight section is obtained from the change of the position or the light amount of the light spot at which the transmitted light impinges on the light receiving section for the light emitted by the light emitting means and transmitted through the weight section,
The acceleration is detected by this.
The acceleration sensor according to the item.