JPH0792189A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To enhance sensitivity in the detection of acceleration by decreasing the space between the fixed electrode and the movable electrode of an acceleration sensor. CONSTITUTION:A metal film 12 is formed by electrolytic plating on the surface of each fixed part 3 of an acceleration sensor 11. A fixed electrode 12A is provided oppositely to the movable electrode 7A at a mass part 7 and the space dB between the electrodes 7A, 12A is set at a small value. This structure enhances the detection sensitivity of acceleration sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor suitable for detecting the acceleration of a vehicle or the like.

[0002]

2. Description of the Related Art Generally, an acceleration sensor used to detect the acceleration or rotation direction of a vehicle has a fixed electrode on an insulating substrate and a movable electrode arranged so as to face the fixed electrode. However, when the acceleration is applied, it is detected that the distance between the movable electrode and the fixed electrode changes according to the acceleration as a change in capacitance. As No. 263013, an acceleration sensor (hereinafter referred to as a prior art) as shown in FIGS. 6 to 8 has been proposed.

In the figure, reference numeral 1 denotes an acceleration sensor according to the prior art. The acceleration sensor 1 includes a glass substrate 2 as an insulating substrate having a recess 2A, and a recess 2 on the glass substrate 2.
It is roughly configured by a pair of fixed portions 3 and 3 provided so as to sandwich A and a movable portion 4 provided between the fixed portions 3.

Here, each of the fixed portion 3 and the movable portion 4 is separately formed by etching from a single low resistance (0.01 to 0.02 Ωcm) silicon wafer (not shown) described later. Therefore, each has conductivity. The opposed end faces of the pair of fixed portions 3 sandwiching the recess 2A are formed integrally with the fixed portions 3 as fixed electrodes 3A.

Further, the movable portion 4 has a supporting portion 5 fixed to the glass substrate 2 on the base end side to serve as a fixed end, and a beam 6 and the beam 6 on the tip side of the supporting portion 5. A mass portion 7 that is a free end that can be displaced is formed. here,
Since the movable portion 4 is also formed of the same silicon wafer as the fixed portion 3 and thus has conductivity, the mass portion 7 has opposite end surfaces on the fixed electrode 3A side as movable electrodes 7A and 7A. It is formed integrally. The mass portion 7 thus formed is located above the concave portion 2A of the glass substrate 2 and is supported by the support portion 5 and the beam 6 in a state of being displaceable in the arrow A direction between the fixed portions 3. Has been done.

The acceleration sensor 1 thus constructed is
When an external acceleration is applied in the direction of arrow A shown in FIG. 6, the mass portion 7 is displaced via the beam 6, and the mass portion 7 approaches or separates from the left and right fixing portions 3 and 3. The displacement of the separation dimension dA at this time is output as an electrostatic capacitance change between the fixed electrode 3A and the movable electrode 7A to an external signal processing circuit (not shown), and the signal processing circuit accelerates based on this electrostatic capacitance change. The signal corresponding to is output.

[0007]

By the way, in the above-mentioned prior art, the beam 6 and its supporting portion 5 and the fixing portion 3 are separately formed by anisotropic etching. In this case, the orientation of the etching mask and silicon is changed. By combining them, a groove perpendicular to the substrate can be formed. However, in order to detect with high sensitivity as the acceleration sensor 1, it is necessary to reduce the distance dA between the fixed electrode 3A and the movable electrode 7A. However, in the etching process by anisotropic etching, it is impossible to form a groove having a narrow width because the etching liquid does not enter the inside of the groove.

Therefore, the prior art acceleration sensor 1
In the above, there is an unsolved problem that the separation dimension dA between the fixed electrode 3A and the movable electrode 7A cannot be reduced and the detection sensitivity is limited.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide an acceleration sensor capable of detecting acceleration with high sensitivity.

[0010]

In order to solve the above-mentioned problems, an acceleration sensor according to the present invention is provided with an insulating substrate and a low resistance silicon plate provided on the insulating substrate and separated from each other by etching. A fixed part and a movable part formed in a fixed electrode, and a fixed electrode is integrally formed on the fixed part, and the movable part is a supporting part fixed on an insulating substrate,
A mass portion that is connected to the support portion via a beam and that is displaced so as to approach and separate from the fixed portion in response to the acceleration when an acceleration acts, and the mass portion is formed on the fixed portion. Further, it is integrally formed with a movable electrode provided so as to face the fixed electrode with a minute gap therebetween.

The features of the configuration adopted by the present invention are as follows:
The metal film is formed by electrolytic plating on the surface of at least one of the fixed electrode and the movable electrode.

[0012]

By performing electrolytic plating on either surface of the fixed electrode and the movable electrode, a relatively thick metal film can be formed between the electrodes facing each other, and as a result, the fixed electrode and the movable electrode can be formed. The distance between them can be substantially reduced.

[0013]

1 to 5 show an acceleration sensor according to an embodiment of the present invention.

First, a first embodiment of the present invention will be described with reference to FIGS. 1 to 4. In this embodiment, the same components as those of the above-mentioned prior art are designated by the same reference numerals and the description thereof will be omitted. It shall be omitted.

In the figure, reference numeral 11 denotes an acceleration sensor according to this embodiment. The acceleration sensor 11 is similar to the acceleration sensor 1 according to the prior art, and the glass substrate 2 and the glass substrate 2 are substantially the same.
It is roughly composed of a pair of fixed parts 3, 3 and a movable part 4 provided on the upper part, and the movable part 4 is composed of a support part 5, a beam 6, a mass part 7, etc. However, in the present embodiment, Unlike the prior art, the surface of the fixed portion 3 facing the mass portion 7 is not directly the fixed electrode 3A.

Reference numerals 12 and 12 denote metal films according to this embodiment. Each metal film 12 is formed by forming a material such as nickel or gold on the surface of the fixing portion 3 by a method such as an electrolytic plating process described later. .

Therefore, the surface of each metal film 12 facing the movable electrode 7A of the mass portion 7 is fixed electrode 12 according to the embodiment.
A and 12A, and the spacing dimension dB between the fixed electrode 12A and the movable electrode 7A is narrower than the spacing dimension dA of the prior art.

Here, the change ΔC in the electrostatic capacitance of the acceleration applied to the acceleration sensor 11 is expressed by the following equation 1.

[0019]

[Equation 1] However, Δd: amount of change of mass part 7 due to acceleration ε: dielectric constant S: electrode area dB: distance between fixed electrode 12A and movable electrode 7A

As can be seen from Equation 1, in order to improve ΔC (sensitivity of the acceleration sensor 11), it is sufficient to reduce the separation dimension dB between the fixed electrode 12A and the movable electrode 7A. In the sensor 11, the metal film 12
The spacing dimension dB can be adjusted by adjusting the thickness of the, and the detection sensitivity can be improved.

The acceleration sensor 11 according to this embodiment has the above-mentioned structure, and its basic operation is not different from that of the prior art.

Next, a method of forming the metal film 12 will be described.

First, the fixing portion 3 is attached to a low resistance silicon wafer.
After the movable part 4 is formed, a lead wire is connected to the fixed part 3 and a predetermined current (a current value for setting the thickness of the metal film 12) is applied to the fixed part 3 and the movable part 4 is immersed in the plating bath. As a result, the fixed part 3
Is used as a cathode, and the metal film 12 is formed on the surface of the fixed portion 3. Moreover, since no current is applied to the movable portion 4, the metal film 12 is not formed even when immersed in the plating bath.

As described above, by using low resistance silicon for the silicon wafer, the electroplating process can be easily performed, and the metal film 12 having a thickness corresponding to the current value is formed on the surface of the fixed portion 3. It is possible to surely form up to the back.

Further, compared with the film forming process such as sputtering or vapor deposition, the electrolytic plating process can surely form the film to the depth only on the single member to which the current is applied, and the film thickness can be increased. It has the advantage that it can be adjusted by the value of the applied current and that the pressure film can be easily formed.

Therefore, in this embodiment, each fixing portion 3
Since the metal film 12 is formed on the surface and the surface facing the movable electrode 7A is the fixed electrode 12A, the width of the spacing dB from the electrodes 7A, 12A can be reduced.
As can be seen from the above, the acceleration detection sensitivity can be increased and the acceleration detection accuracy can be improved.

Further, in this embodiment, since the metal film 12 is formed by the electrolytic plating process, the thickness of the metal film 12 can be easily adjusted by the strength of the electric current, and the metal film 12 is formed. It serves as a gap adjusting layer for adjusting the gap between the electrodes 7A and 12A, so that the acceleration sensor 11 can be set to have a detection sensitivity according to the purpose of use.

In the above embodiment, the metal film 12 is formed on each fixed portion 3 so that the width of the spacing dimension dB is narrowed. However, like the acceleration sensor 11 'shown in FIG. The metal film 12 ′ may be formed on the metal film 12 ′, or the metal film 12 ′ may be formed on both the fixed portion 3 and the movable portion 4.

In the above embodiment, the mass portion 7 is supported by cantilever.
Although the present invention is not limited to this, the present invention is not limited to this, and the movable portion may be constituted by supporting both ends and may be supported by a plurality of beams.

Next, a second embodiment according to the present invention will be described with reference to FIG. 5. The feature of this embodiment is that a comb-shaped electrode plate formed in a comb shape is formed on the surface of the fixed portion and is opposed to each other. This is because the comb-shaped electrode plates formed in a comb shape were respectively formed on the surface of the mass portion to be formed, and the metal film was formed on the surface of the fixed portion side by electrolytic plating.

In the figure, 21 is an acceleration sensor according to this embodiment, 22 is a glass substrate as an insulating substrate, and fixed portions 23, 23 and a movable portion 25, which will be described later, are formed on the glass substrate 22. Further, a rectangular recess 22A is formed in the glass substrate 22, and the mass portion 28 of the movable portion 25 and the movable-side comb-shaped electrode 2 located on the recess 22A are formed.
9 is displaceable in the direction of arrow B.

Reference numerals 23 and 23 denote a pair of fixing portions made of a silicon material having a low resistance.
Are spaced apart to the left and right of the glass substrate 22, and a plurality of (for example, four) thin plate-like electrode plates 24A, 24A, ... Is a fixed side comb-shaped electrode 24, 24 as a fixed electrode
Are configured respectively.

Reference numeral 25 denotes a movable portion made of a silicon material having a low resistance. The movable portion 25 is separated from the front and rear of the glass substrate 22 by a supporting portion 26 fixed to the glass substrate 22, and a supporting portion 26. The mass portion 2 which is instructed to each supporting portion 26 via the beams 27, 27 and is arranged between the respective fixing portions 3.
8 and a plurality (for example, four) of thin plate-shaped electrode plates 29A, 2 which are respectively formed to project leftward and rightward from the mass portion 28.
.., and each beam 27 is formed in a thin plate shape so that the mass portion 28 can be displaced in the arrow B direction.

Reference numerals 30 and 30 denote metal films formed on the surfaces of the fixed portions 23. The metal films 30 are formed by the electrolytic plating process described in the first embodiment, and the movable side comb-shaped electrodes 29 are provided. By reducing the distance between each electrode plate 29A and the fixed side comb-shaped electrode 24 between each electrode plate 24A,
It improves the detection sensitivity.

In the acceleration sensor 1 according to this embodiment configured as described above, the electrode plates 29A of the movable side comb-shaped electrodes 29 are the electrode plates 24 of the fixed side comb-shaped electrodes 24.
The electrode plates 24A and 29A are opposed to each other with a minute gap therebetween, and the electrode plates 24A and 29A are electrically connected in parallel. Therefore, the detection sensitivity can be increased and the acceleration detection accuracy can be improved.

Furthermore, in this embodiment, the metal film 30 is formed on the fixed side comb-shaped electrode 24, and the distance between each electrode plate 24A and the movable side comb-shaped electrode 29 can be reduced. The detection accuracy can be further improved.

Although the metal film 30 is formed on the fixed side comb-shaped electrode 24 in the above embodiment, the present invention is not limited to this, and the metal film 30 is formed on the movable side comb-shaped electrode 29 or both by electrolytic plating. You may form.

[0038]

As described above in detail, according to the present invention, in the fixed portion and the movable portion made of low resistance silicon, at least one surface of the fixed electrode and the movable electrode, which face each other, is formed. Since the metal film is formed by electrolytic plating, the metal film can be surely formed in the depth of the gap. As a result, the distance between the fixed electrode and the movable electrode can be reduced, and the acceleration detection sensitivity can be improved.

[Brief description of drawings]

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

FIG. 2 is an enlarged view of the acceleration sensor shown in FIG. 1 as seen from above.

3 is a cross-sectional view as seen from the direction of arrows III-III in FIG.

FIG. 4 is a sectional view showing an acceleration sensor according to a modification of the first embodiment as viewed from the same position as in FIG.

FIG. 5 is a cross-sectional view showing a comb-shaped electrode type acceleration sensor according to a second embodiment of the present invention.

FIG. 6 is a perspective view showing an entire acceleration sensor according to the prior art.

FIG. 7 is an enlarged view of the acceleration sensor shown in FIG. 6 seen from above.

8 is a cross-sectional view as seen from the direction of arrows VIII-VIII in FIG. 7.

[Explanation of symbols]

 2,22 Glass substrate (insulating substrate) 2A, 22A Recessed part 3,23 Fixed part 4,25 Movable part 5,26 Support part 6,27 Beam 7,28 Mass part 7A, 29 Movable electrode 11,11 ', 21 Acceleration sensor 12, 12 ', 30 Metal film 12A, 12A', 24 Fixed electrode dB Spacing size

Claims (1)

[Claims] 1. An insulating substrate, provided on the insulating substrate,
A fixed part and a movable part which are formed separately from each other by etching a low resistance silicon plate,
A fixed electrode is integrally formed on the fixed portion, and the movable portion is
A supporting portion fixed on the insulating substrate, and a mass portion connected to the supporting portion via a beam and displaced so as to approach and separate from the fixed portion in response to the acceleration when an acceleration acts. An acceleration sensor integrally formed with a movable electrode provided in the mass portion so as to face the fixed electrode formed in the fixed portion with a minute gap, wherein the fixed electrode or the movable electrode is provided. An acceleration sensor characterized in that a metal film is formed by electrolytic plating on at least one of the surfaces.