JP2539560B2 - Semiconductor acceleration sensor and airbag system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor acceleration sensor formed of a semiconductor single crystal and an airbag system using the same.

[0002]

2. Description of the Related Art Conventional semiconductor acceleration sensors include, for example, Japanese Patent Laid-Open Nos. 56-133877 and 63-16907.
As disclosed in Japanese Patent Publication No. 8, a thick portion (rigid body, mass portion) that responds to acceleration is provided in the center, and the central thick portion is surrounded by a thick fixing portion around the thin portion (diaphragm portion). A piezoresistive element is supported on the diaphragm by diffusion, and an elastic beam is used instead of the diaphragm to support the mass part, and the piezoresistive element is provided on the beam. The acceleration is captured by detecting the displacement of the mass portion in response to the acceleration by twisting the diaphragm or the beam through a strain gauge (piezoresistive element).

Further, in place of the strain gauge, the mass portion is used as a movable electrode, and a fixed electrode is arranged to face the movable electrode with a minute gap therebetween, and a change in the gap between the electrodes is replaced with a capacitance to take out acceleration. Various things to be caught have been proposed.

[0004]

By the way, as for the above-mentioned acceleration sensor, the development of an acceleration sensor for vehicle body control is progressing at present, and there are many documents about the acceleration sensor of about 1 to 2 G. At present, there is a delay in the development of an acceleration sensor capable of sufficiently satisfying all the conditions of detection up to ± (plus or minus) 50 G, impact resistance, and mass productivity required for collision detection.

For example, when the mass portion is supported only by the diaphragm, the response is much smaller than the collision acceleration, and when the mass portion is supported by the beam, the single crystal semiconductor has a wall cleaving property. For this reason, there is a concern about impact resistance, and there is a process for processing the gap between the beams, so the number of precision processing steps increases, and mass productivity tends to be poor.

The present invention has been made in view of the above points, and an object thereof is an acceleration sensor that can sufficiently detect a large acceleration such as a vehicle collision and that satisfies both conditions of impact resistance and mass productivity. Is to provide a reliable airbag system.

[0007]

In order to achieve the above object, the present invention basically proposes the following problem solving means.

One is that a mass part for converting acceleration into an inertial force is supported by a frame part (fixed part) arranged around the mass part through a diaphragm part, and the mass part, the frame part and the diaphragm part are made of a single crystal semiconductor. In the acceleration sensor integrally formed by, the beam part connecting the frame part and the mass part is configured by thickly forming a part of the diaphragm part, and the beam part and the diaphragm part are integrally combined structure. In the case of the strain gauge type, a piezoresistive element is formed on this beam portion or diaphragm, and in the case of the capacitance type, the mass portion is used as a movable electrode, and a fixed electrode is formed through a minute gap with this movable electrode. Are opposed to each other (this is the first problem solving means).

Another proposal is to reverse the positional relationship between the mass portion and the fixed portion. That is, a fixed part fixed to an acceleration detection target is arranged in the center, and a mass part for converting acceleration into inertial force is arranged around the fixed part while supporting it via a diaphragm part. , The mass part is integrally formed of a single crystal semiconductor, and the beam part connecting the fixing part and the mass part is formed by thickly molding a part of the diaphragm part to integrally form the beam part and the diaphragm part. (This is a second means for solving problems).

[0010]

When the elastic support for supporting the mass part is constructed by integrally combining the diaphragm part and the beam part, the mass part is focused on a relatively large acceleration (for example, up to ± 50 G). Responsive. In addition, the shock resistance is greatly improved, and it can withstand a shock of about ± 50G.

Further, the semiconductor portion (gauge portion) can be manufactured by directly using the process of the mass-produced diaphragm type semiconductor pressure sensor. In other words, if the mask design for the acceleration sensor is done, the process of diaphragm processing and diffusion technology of piezoresistive element can be processed exactly the same as the existing process, and more time-consuming precision processing work such as providing a gap between beams is required. Since it is unnecessary, mass productivity can be improved.

In the above structure, the mass portion changes in accordance with the acceleration at the time of collision in both the first and second problem solving means, but in the case of the first problem solving means, the mass portion responds within the frame portion. On the other hand, in the case of the second problem solving means, the center serves as a fixed portion, and the mass portion performs a response operation (a so-called staggered movement with the center serving as a fulcrum) outside the fixed portion. To do. In the latter case, there are advantages that the degree of freedom in designing the mass part is large and that three-dimensional acceleration can be detected. The change of the mass part in response to the acceleration is the change of the value of the piezoresistive element arranged on the beam or the diaphragm part, or when the mass part is the movable electrode, the capacitance is generated by the cooperation with the fixed electrode facing it. Is detected as a change in the value of.

[0013]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a gauge portion of an acceleration sensor 100 according to the first embodiment of the present invention.

In this embodiment, the single crystal silicon 1 is processed to integrally form the frame portion 2, the mass portion 3, the beam portion 4 connecting them, and the diaphragm portion 6. The beam portion 4 is formed by thickening a part of the diaphragm portion 6. The mass portion 3 has a square shape, and the beam portions 4 are arranged on the four sides thereof. In this embodiment, four beam portions 4 are arranged with the center of gravity of the mass portion 3 as the center. At least one of the beam portions 4 is provided with a piezoresistive element 5 serving as a bridge resistance circuit element. The beam portion 4 is used in combination with the diaphragm portion 6 to balance when the mass portion 3 moves in response to acceleration and to react to a relatively large acceleration of about ± 50 G. It is not necessary to provide the piezoresistive element 5. The strain amount of the beam portion 4 in response to the acceleration is detected by the piezoresistive element 5 having a bridge structure, and a detection signal is taken out from the terminal 7.

FIG. 2 shows various aspects of the structure in which the diaphragm portion 6 and the beam portion 4 are integrally combined as described above.

FIG. 2A shows a so-called H shape, which has a structure in which two beam portions 4 are provided on each of opposite sides of a pair of mass portions 3, and the balance in a fixed direction is obtained. We made a prototype as something that can be taken. It is a structure that operates in a well-balanced manner with respect to a movement to which acceleration is applied.

FIG. 2B is intended to secure the sensitivity as well as the balance, and it is a so-called π type arrangement structure, in which two beam portions 4 are arranged on each side, one on each side. The beam portion 4 is provided. Two beam parts 4 are provided on the side opposite to the terminal 7 side to secure the operation of a single beam and support the mass part 3 together with the diaphragm part 6, but the beam parts on both sides adjacent to that side. By arranging 4 closer to the terminal 7, the operation after the acceleration is applied is corrected as a whole to form a balanced structure.

FIG. 2C relates to the embodiment shown in FIG. 1 and has a so-called cross-shaped beam portion 4 and diaphragm portion 6.
The optimum balance is provided to support the mass part 3 in combination with.

FIG. 2D is a so-called cross H type in which two beam portions 4 are arranged on each side of the mass portion 3, and one beam is arranged on each side of (C). Against
This is intended to obtain better balance characteristics.

In each of the structures (a) to (d), the beam portion 4
And the arrangement of the piezoresistive elements 5 do not match. This is because the arrangement of each beam portion and the position to be detected are different, and therefore the arrangement of the piezoresistive element 5 must be examined for each structure.

FIG. 3 shows the output characteristics of the piezoresistive element with respect to each beam arrangement shown in FIG.
Although the shape is output, the non-linearity (Non-lineality) is large, and the cross in (C) has the smallest non-linearity and is suitable for mass production.

FIGS. 4 to 7 are characteristic diagrams of acceleration detection axis component-non-linear error of the beam arrangement corresponding to FIGS. 2 (A) to 2 (D). 5] [corresponding to FIG. 2]
(B)] and FIG. 7 [corresponding to FIG. 2D] are acceleration G
It can be seen that there is a large difference in the way of adding, that is, clockwise and counterclockwise. On the other hand, as shown in FIG.
In the structure in which the cross-shaped beam portion 4 is combined with the diaphragm 6 to support the mass portion 3 shown in (corresponding to (c)), the data is almost the same in both clockwise and counterclockwise directions.

In view of the above, the acceleration sensor has a small non-linearity error, and its variation shows a value that is almost the same for both clockwise and counterclockwise accelerations. The structure was judged to be most suitable. However, when the non-linear error is ignored and the sensitivity is emphasized, it goes without saying that the π shape shown in (b) of FIG. When the support structure is required, the cross H-shaped structure of FIG. 2D is preferable, and when the acceleration from one direction is detected, the cross H-shaped structure of FIG.
H type is good, and you can select the most suitable one according to various applications.

In the sensor for detecting acceleration in the structure that supports the mass part 3 by combining the beam part 4 and the diaphragm part 6, the cross-shaped structure of FIG. 2C, which has the best total characteristics, is preferable. In the airbag system of FIG. 8, this sensor is applied as an acceleration sensor (G sensor).

In FIG. 8, 100 is a G sensor, 101
Is a DC power supply, 102 is a diagnostic circuit, 103 is an amplification / temperature correction circuit, 104 is an acceleration detection circuit, and 105 is a determination circuit for determining whether or not there is a collision based on the acceleration detection value. When the vehicle is installed at a certain place and a large acceleration of 50 to 100 G or the like is applied due to the collision, the airbag module 107 is operated via the circuit elements 103, 104 and 105 to protect an occupant in the case of the collision. The diagnostic device 102 periodically diagnoses whether or not this system is healthy. In this embodiment, in addition to operating the airbag module 107, the G sensor 100
The alarm lamp 106 is configured to be turned on in advance by using a signal from the above, and a buzzer may be emitted instead.

9A and 9B show another embodiment of the acceleration sensor according to the present invention. FIG. 9A is a partially cutaway perspective view and FIG. 9B is a sectional view taken along the line aa. The same reference numerals as those of the above-described embodiments indicate the same or common elements. 1 is different from the embodiment of FIG. 1 in that the center is fixedly mounted on a substrate 8 as a fixed portion 2 ', and an integral combination body (elastic support) of the diaphragm portion 6 and the beam portion 4 is provided on the outer side (periphery) thereof. The frame-shaped mass part 3 is arranged. The beam portion 4 is configured by thickly forming a part of the diaphragm portion 6 as in the other embodiments described above.
As shown in FIG. 9B, the outer mass portion 3 is floated from the substrate 8 via the minute gap G, that is, the so-called mass portion 3 is arranged in four directions around the fixing portion 2 ′. In this state, the displacement of each part of the mass part 3 is different with respect to the acceleration component in each direction in three dimensions. This means that the amount of strain of each beam 3 is also different.

A piezoresistive element 5 is formed on the beam portion 4 by diffusion, and three-dimensional acceleration is detected by knowing the amount of strain of each beam portion 4 described above.

Also in this embodiment, the elastic support member for supporting the mass portion 3 is constructed by integrally combining the beam portion 4 and the diaphragm portion 6, and thereby the same effect as that of the first embodiment is obtained. Moreover, in the present embodiment, the mass portion 3 is arranged on the outer side. However, in this case, the mass W is slightly increased or decreased as compared with the case where the mass portion is provided in the frame as in the first embodiment. Since the part 3 can be adjusted to be increased / decreased greatly, the design of the mass part 3 can be given flexibility without being restricted by space. Further, there is an advantage that one sensor can detect three-dimensional acceleration.

FIG. 10 is a partially cutaway perspective view showing a gauge portion of a capacitance type acceleration sensor according to another embodiment of the present invention, and FIG. 11 is a view showing the fixed electrode side substrate from the movable electrode (mass portion) side. It is a top view.

In this embodiment as well, as in the embodiment of FIG. 9, the central portion is the fixed portion 2 ', and the mass portion 3 is arranged around the fixed portion 2', and these elements 2'and 3 are connected to the beam portion 4 and the diaphragm. Part 6
It is connected by an integrated combination structure (elastic support). The mass portion 3 is used as a movable electrode, and the fixed electrodes 10 facing the movable portion 3 are arranged at four positions with a minute gap G therebetween. The fixed electrode 10 is formed on the insulating substrate 9.
The fixed electrode 10 may be arranged on one side of the mass part 3 or may be arranged so as to face both sides.

This embodiment also has the same effect as that of the embodiment of FIG. 9, but the determination in the three-dimensional direction is made by recognizing the change in the electrostatic capacitance between each fixed electrode 10 and the movable electrode 3. That is, as described above, since the displacement of each part of the mass part 3 is different with respect to the acceleration component in each of the three-dimensional directions, the displacement of each part is measured between the fixed electrode 10 and the movable electrode (mass part) 3. The three-dimensional acceleration is detected by capturing the value of the electrostatic capacitance.

The mass portion 3 in the embodiment shown in FIGS. 9 to 11 has a series of frame-shaped forms, and as shown in FIG. 12, a plurality of mass portions 3 are fixed by cutting the frame-shaped corners. ´
It may be a mode in which it is arranged around the center.

Further, in the acceleration sensor having the mass part, the diaphragm part / beam part, and the frame part as shown in FIG. 1, the mass part is used as the movable electrode instead of the strain gauge method, and the fixed electrode is arranged opposite to this. It is also possible to use a capacitance type.

[0035]

As described above, according to the present invention, the support of the mass portion that responds to acceleration is constructed by an integral combination of the diaphragm portion and the beam portion, so that a large acceleration such as a vehicle collision is generated. Therefore, it is possible to provide an acceleration sensor which can sufficiently cope with the above-mentioned detection, and which satisfies both conditions of shock resistance and mass productivity, and a reliable airbag system using the acceleration sensor.

[Brief description of drawings]

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

FIG. 2 is an explanatory view showing various supporting modes of a mass part used in the above-mentioned embodiment.

FIG. 3 is an explanatory diagram showing the output characteristics (non-linear error) of the acceleration sensor of various aspects in (A) to (D) of FIG.

FIG. 4 is an output characteristic diagram corresponding to the acceleration sensor of FIG.

FIG. 5 is an output characteristic diagram corresponding to the acceleration sensor of FIG.

FIG. 6 is an output characteristic diagram corresponding to the acceleration sensor shown in FIG.

FIG. 7 is an output characteristic diagram corresponding to the acceleration sensor shown in FIG.

FIG. 8 is an explanatory view showing an example of the airbag system of the present invention.

FIG. 9 is a partially cutaway perspective view of an acceleration sensor according to another embodiment of the present invention and a sectional view taken along the line aa.

FIG. 10 is a partially cutaway perspective view of an acceleration sensor according to another embodiment of the present invention.

11 is a plan view of a substrate on the fixed electrode side of the acceleration sensor of FIG. 10 viewed from the movable electrode side.

FIG. 12 is a partially cutaway perspective view of an acceleration sensor according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Single crystal silicon, 2 ... Frame part (fixed part), 2 '... Fixed part, 3 ... Mass part, 4 ... Beam part, 5 ... Piezoresistive element, 6 ...
Diaphragm part, 7 ... Terminal, 001 ... DC power supply, 100
... G sensor (semiconductor acceleration sensor), 101 ... DC power supply, 102 ... Diagnostic circuit, 103 ... Amplification / temperature correction circuit, 104 ... Acceleration detection circuit, 105 ... Judgment circuit, 1
06 ... Alarm lamp, 107 ... Airbag module.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-3-94168 (JP, A) JP-A-63-222464 (JP, A) JP-A-63-169078 (JP, A) JP-A-56- 133877 (JP, A) JP 63-70529 (JP, A) JP 2-95265 (JP, A)

Claims (10)

(57) [Claims] 1. A mass part for converting an acceleration into an inertial force is supported by a frame part arranged around the mass part through a diaphragm part, and the mass part, the frame part, and the diaphragm part are integrally molded of a single crystal semiconductor. In the acceleration sensor, a beam portion connecting the frame portion and the mass portion is formed by thickly forming a part of the diaphragm portion to form a combined structure of the beam portion and the diaphragm portion, and the beam portion or A semiconductor acceleration sensor comprising a piezoresistive element formed on a diaphragm. 2. A mass part for converting an acceleration into an inertial force is supported by a frame part arranged around the mass part through a diaphragm part, and the mass part, the frame part and the diaphragm part are integrally molded of a single crystal semiconductor. In the acceleration sensor, a beam portion connecting the frame portion and the mass portion is formed by thickly forming a part of the diaphragm portion to form a combined structure of the beam portion and the diaphragm portion, and the mass portion is A semiconductor acceleration sensor comprising a movable electrode, and a fixed electrode facing the movable electrode with a minute gap therebetween. 3. A fixed part fixed to an acceleration detection target is arranged at the center, and a mass part for converting acceleration into inertial force is arranged around this fixed part while supporting it via a diaphragm part. , The diaphragm part and the mass part are integrally molded from a single crystal semiconductor, and the beam part connecting the fixing part and the mass part is formed by thickly molding a part of the diaphragm part to form the beam part and the diaphragm part. And a piezoresistive element formed on the beam portion or the diaphragm. 4. A fixed part fixed to an acceleration detection target is arranged in the center, and a mass part for converting acceleration into an inertial force is arranged around this fixed part while supporting it via a diaphragm part. , The diaphragm part and the mass part are integrally molded from a single crystal semiconductor, and the beam part connecting the fixing part and the mass part is formed by thickly molding a part of the diaphragm part to form the beam part and the diaphragm part. And an integral combination structure, and the mass portion is a movable electrode, and a fixed electrode is arranged so as to face the movable electrode with a minute gap therebetween. 5. The beam portion according to any one of claims 1 to 4, wherein the beam portion is arranged around the center of gravity of the mass portion while supporting the four sides of the mass portion. Semiconductor acceleration sensor. 6. The semiconductor acceleration sensor according to claim 1, wherein a plurality of the beam portions are arranged on each side of the mass portion. 7. The semiconductor acceleration sensor according to claim 1, wherein a plurality of the beam portions are arranged on opposite sides of the pair of mass portions, respectively. 8. The beam part according to claim 1, wherein two beam parts are arranged on one side of the mass part, and one beam part is arranged on each side of the mass part to form a π-type arrangement. A semiconductor acceleration sensor characterized by being presented. 9. An elastic support body in which a mass portion for converting acceleration into an inertial force by a semiconductor single crystal, a diaphragm portion and a beam portion are integrally combined with each other in a part of a vehicle, and the elastic support body is used to interpose the elastic support body. A vehicle collision is provided by providing an acceleration sensor for vehicle collision detection, which is integrally formed with a fixed portion that supports the mass portion, and detects displacement of the mass portion from a resistance value of a piezoresistive element provided on the elastic support. An air bag system, characterized in that it is provided with means for detecting an air conditioner and operating the air bag. 10. A part of a vehicle, an elastic support body in which a mass part for converting an acceleration into an inertial force by a semiconductor single crystal, a diaphragm part and a beam part are integrally combined, and the elastic support body is interposed therebetween. An acceleration sensor for vehicle collision detection, which is integrally formed with a fixed portion that supports the mass portion, is provided, and displacement of the mass portion is replaced with a change in capacitance to detect a vehicle collision and operate an airbag. An airbag system comprising means for causing the airbag system.