JPH06160421A - Oscillatory type acceleration sensor - Google Patents

Abstract

PURPOSE:To only detect the acceleration applied to a mass section in the detecting direction with high accuracy by means of bridges by controlling the displacement of the mass section in the vertical direction. CONSTITUTION:The main body 23 of the title sensor is constituted in such a way that a mass section 25 is supported on a supporting body by means of four beam sections 28 formed by etching a silicon substrate 24 and bridges 30 and 30 are provided across grooves 26 between the section 25 and body 27. The vibrating section 30A of each bridge 30 is always naturally vibrated at its resonance frequency by means of an external oscillation circuit and, when acceleration is applied to the section 25 in the direction shown by the arrow (a), the resonance frequencies of the bridges 30 become lower on one side and high on the other side. Therefore, the acceleration applied to the section 25 in the detecting (X-axis) direction can be accurately detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration type acceleration sensor suitable for detecting the rotation direction, posture, etc. of a vehicle or the like.

[0002]

2. Description of the Related Art First, a vibration type accelerometer disclosed in Japanese Patent Laid-Open No. 2-183167 (US Pat. No. 4,901,570) is generally known as a conventional acceleration sensor.

Here, FIGS. 12 to 14 show Japanese Patent Laid-Open No. 2-18.
An accelerometer according to Japanese Patent No. 3167 will be shown and described.

In the figure, 1 is an acceleration sensor as a vibration type accelerometer, 2 is a silicon substrate which constitutes the main body of the acceleration sensor 1, and the silicon substrate 2 is a rectangular support substrate 3 located outside. The reference mass 4 is located on the inner peripheral side of the support substrate 3.

Reference numeral 5 denotes a silicon nitride film formed on the upper surface side of the silicon substrate 2, 6 denotes a silicon nitride film formed on the lower surface side of the silicon substrate 2, and the silicon nitride film 6 has V
The restraining bridges 7, 7, ... As back beams are formed so as to support the reference mass 4 from below.

Reference numerals 8, 9, 10, and 11 denote resonance bridges formed so as to straddle between the reference mass 4 of the silicon substrate 2 and the support substrate 3, and among the bridges 8 to 11, the bridges 8 and 10 are shown. And the bridges 9 and 11 are arranged in pairs so that the longitudinal direction is coaxial with the detection direction. The bridges 8 and 10 are arranged in the X-axis direction and the bridges 9 and 1 are arranged.
1 detects the Y-axis direction.

Denoted by 12 and 12, are drive electrodes formed on the upper surface side of the support substrate 3 which are located below the bridges 8 to 11, and each drive electrode 12 is not provided outside. By applying a predetermined frequency from an oscillating device, the bridges 8 to 10 are naturally vibrated at a resonance frequency.

.. are located below the bridges 8 to 11 and indicate detection electrodes formed on the upper surface side of the support substrate 3, and each detection electrode 13 detects the voltage applied to each of the bridges 8 to 11. The deviation of the resonance frequency of each of the bridges 8 to 11 is detected by the directional acceleration.

The oscillating device individually changes the oscillating frequency of the driving electrode 12 according to the signal from each detecting electrode 13 to perform feedback control for keeping the bridges 8 to 11 in a resonance state. Further, the reference mass 4 restricts the vertical movement of the reference mass 4 by the respective restraining bridges 7, but the support substrate 3 is provided on the upper surface side of the silicon substrate 2.
A mechanical stopper fixed alternately to the reference mass 4 and the reference mass 4 is provided to prevent the reference mass 4 from moving in the vertical direction. Thereby, the natural vibration from the bridges 8 to 11 can be prevented from being transmitted to the reference mass 4, and the vertical vibration of the reference mass 4 can be prevented.

In the acceleration sensor according to the prior art configured as described above, for example, when acceleration is applied in the direction of arrow A in FIG. 12, the reference mass 4 moves in the direction of arrow A, and the bridge 8 has a compression effect. It acts, and tensile stress acts on the bridge 10. The bridge 8 has a frequency lower than the resonance frequency of natural vibration, and the bridge 10 has a frequency higher than the resonance frequency of natural vibration. Furthermore, since the detection electrode 13 detects this frequency change and feedback control is performed by the oscillating device to make the natural frequency of the resonance frequency again, the corrected frequency is applied from the drive electrode 12 and the corrected frequency is applied. The acceleration in the direction of the arrow A is detected as a large signal by adding the change amount of.

[0011]

By the way, in the above-mentioned conventional technique, the resonance bridges 8 to 11 themselves support the reference mass 4 on the support substrate 3, and the restraining bridges 7 serving as back beams also support the reference mass 4. Therefore, there is a problem in that the displacement of the acceleration of the reference mass 4 in the horizontal direction (X, Y axis direction) is reduced, and the acceleration detection sensitivity is reduced.

Further, in order to improve the detection sensitivity, if the suppression bridges 7 which are the back beams formed on the back surface side of the silicon substrate 2 are eliminated, the reference mass 4 is affected by the natural vibration of the bridges 8-11. However, there is a problem that the reference mass 4 vibrates in the vertical direction (Z-axis direction), and it becomes impossible to accurately detect the acceleration in the horizontal detection direction.

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 a vibration type acceleration sensor capable of performing acceleration detection with high sensitivity and high resolution in the detection direction. .

[0014]

In order to solve the above problems, the present invention is characterized in that the mass part and the support are integrally formed by a silicon plate, and the mass part is provided on the silicon plate. Is connected to the support body to form a beam portion that suppresses the vertical displacement of the mass portion with respect to the support body.

Further, it is desirable that the width dimension of the beam portion is sufficiently smaller than the thickness dimension.

[0016]

With the above structure, the vertical direction acceleration is restricted to the mass portion, and only the horizontal detection direction acceleration is applied. The bridge is subjected to compressive or tensile stress depending on the direction in which the acceleration is applied, and the natural vibration of the bridge is The resonant frequency can be low or high.

Further, the beam portion integrally formed on the silicon substrate can regulate the vertical movement of the mass portion and facilitate the movement in the horizontal detection direction, and the natural vibration in the vertical direction from the bridge can be prevented. It is possible to eliminate the effect on the mass part.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS. In the embodiments, the same components as those of the above-described conventional technique are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, reference numeral 21 denotes an acceleration sensor according to this embodiment, and the acceleration sensor 21 is a glass substrate 2 serving as a base.
2 and a sensor body 23, which will be described later, fixed to the upper surface of the glass substrate 22.

Reference numeral 23 denotes a sensor body, and the sensor body 2
3 is formed integrally with a silicon substrate 24 as a silicon plate, and has a rectangular mass portion 25, a rectangular support body 27 provided around the mass portion 25 through a groove 26, and the support body 27. In order to support the mass part 25, the mass part 2
5 from the four apexes toward the support 27 (see FIG. 1).
(Y-axis direction inside) beam portions 28, 28, ... And the mass portion 25
And bridges 30 provided between the support 27 and the support 27.

Here, in the sensor main body 23, the silicon substrate 24 is formed with the groove 26 by an etching process described later, so that the mass portion 25, the support 27 and each beam portion 28 are integrally formed by the silicon substrate 24. Therefore, the mass portion 25, the support body 27, and the beam portions 28 are located on the same plane. Further, as shown in FIG. 1, since the width dimension d of each beam portion 28 is smaller than the thickness dimension h, displacement is regulated even when acceleration in the Z-axis direction is applied to the mass portion 25. Has become.

Reference numeral 29 denotes a spacer provided between the glass substrate 22 and the sensor body 23. The spacer 29 is formed in the same rectangular shape as the support body 27 of the sensor body 23, and has the same mass as the glass substrate 22. A gap is formed with the portion 25.

Reference numerals 30 and 30 denote substantially U-shaped bridges made of a conductive material, and each of the bridges 30 has a vibrating portion 30A having a gap between the center and the support 27, as shown in FIG. Both ends of the vibrating portion 30A are fixed end portions 30B, 3
It becomes 0C, and the fixing end portions 30B and 30C are fixed to the mass portion 25 and the support body 27, respectively, so as to straddle between the mass portion 25 and the support body 27, that is, the groove 26. . The axes of the bridges 30 are aligned so that the longitudinal direction of each bridge 30 is located in the X-axis direction in FIG.

The mass portion 25 is supported by the support member 27 by the beam portions 28, and the bridges 30 are fixed to the mass portion 25 and the support member 27. It does not support the part 25.

Reference numerals 31, 31, 32, 32, 33, and 33 indicate the bridge electrodes, the capacitance detection electrodes, and the drive electrodes formed on the support 27, which are located below the respective bridges 30, respectively. The electrodes 31 to 33 are, as shown in FIG.
One end side of the bridge electrode 31 is connected to the fixed end portion 30C of the bridge 30, and the capacitance detection electrode 32 and the drive electrode 3 are connected.
One end side of 3 is located below the vibrating portion 30A of the bridge 30, and one end side of the drive electrode 33 is located on both sides of one end side of the capacitance detection electrode 32 in the Y-axis direction. And
Extraction electrodes 31A to 33A protruding from the silicon substrate 24 are formed on the other end side of each of the electrodes 31 to 33. It is connected through 33B.

On the other hand, the bridge electrode 31 and the drive electrode 3
3 is connected to an oscillation circuit as a vibration generating means, and the capacitance detection electrode 32 and the drive electrode 33 are connected to a signal processing circuit (neither is shown) as a detection means.

The acceleration sensor according to the present embodiment has the structure as described above, and a method of manufacturing the acceleration sensor will be described below with reference to FIGS. It should be noted that only one bridge 30 is shown in the drawings for explanation.

In the step of forming the electrode pattern and the first nitride film shown in FIG. 4, the electrodes 31, 32 and 33 as shown in FIG. 2 are photo-etched on the upper surface of the p-type (110) silicon substrate 24, and then, Each electrode 3 by diffusing phosphorus (P)
Patterns 31B to 33B of 1 to 33 are formed. After that, the fixed ends 30B and 30C of each bridge 30 are provided on the upper surface.
Are photo-etched so that a nitride film is formed except for a portion where is fixed, and a nitride film is formed on the lower surface except a portion where the groove 26 (cutout 42 'in the nitride film 42) is formed. Photoetching is performed so that Then, the first nitride films 41 and 42 are formed on the upper and lower surfaces by the low pressure CVD method.

In the sacrifice layer forming step shown in FIG. 5, in order to secure the height of the vibrating portion 30A of each bridge 30, a sacrifice layer 43 of phosphosilicate glass (PSG) is formed at the position where each bridge 30 is formed.

In the bridge and electrode forming step shown in FIG. 6, polycrystalline silicon is vapor-deposited by a low pressure CVD method from above so as to straddle the sacrificial layer 43, and phosphorus (P) is diffused in the polycrystalline silicon to reduce the resistance. After that, an etching process is performed to form the bridge 30. On the other hand, each electrode 31
~ 33 of platinum / chromium vapor-deposited to extract electrode 31
A to 33A are formed to project.

In the second nitride film forming step shown in FIG. 7, the nitride film 41 and the bridge 3 are formed from the upper side of the silicon substrate 24.
A second nitride film 44 is formed by plasma CVD so as to cover 0.

In the groove forming step shown in FIG. 8, the silicon substrate 24 is treated with an alkaline aqueous solution (for example, TMAH: tetranaphthyl ammonium hydroxide or KOH).
However, since the exposed portion of the silicon substrate 24 is only the cutout portion 42 'of the nitride film 42 on the lower surface side, the alkaline aqueous solution penetrates from this portion to melt the silicon substrate 24 and penetrate it. A groove 26 is formed to divide the silicon substrate 24 into a mass portion 25 and a support body 27.

In the oxide film forming and nitride film removing steps shown in FIG. 9, the oxide film 45 is formed on the upper side of the second nitride film 44 by the plasma CVD method. On the other hand, the portion of the first nitride film 42 on the lower surface side of the silicon substrate 24 and the portion of the nitride film 41 exposed from the groove 26 are removed by etching with hot phosphoric acid.

In the oxide film removing step shown in FIG. 10, the oxide film 45 and the PSG sacrificial layer 43 are removed by etching.

In the nitride film removing step shown in FIG. 11, the sensor film 23 is formed by removing the nitride film 41 and the nitride film 44 with CF ₄ gas.

Then, as shown in FIG. 3, the sensor body 23 formed as described above is bonded to the glass substrate 22 having the spacer 29 (alkali glass) with the adhesive S to form the acceleration sensor 21. It has become.

Also in the acceleration sensor according to the present embodiment having the above-described structure, as in the case of the acceleration sensor 1 of the prior art, an alternating current having a resonance frequency between the bridge electrode 31 and the drive electrode 33, which is a natural vibration of the bridge 30, is used. A wave is input from the oscillation circuit, and each bridge 30 is always kept in a natural vibration state.

Here, when an acceleration (indicated by an arrow a in FIG. 1) in the X-axis direction, which is the detection direction, is applied to the mass portion 25, a compressive stress acts on the bridge 30 located on the right side, and the bridge 30 located on the left side is located. Tensile stress acts on the bridge 30. As a result, the resonance frequency of the one bridge 30 becomes low, and the resonance frequency of the other bridge 30 becomes high. This frequency shift is detected by the capacitance detection electrode 32, and an AC wave corrected to return the bridge 30 to the resonance frequency of the natural vibration is output from the signal processing circuit between the bridge electrode 31 and the drive electrode 33. By calculating the difference in frequency of the corrected AC wave at this time, the influence of thermal stress due to temperature change and the influence of acceleration in the Y-axis direction can be removed, and the magnitude of acceleration applied to the mass portion 25 can be accurately determined. Can be detected.

The mass portion 25 of the sensor main body 23 is 4
Since the beam portions 28 are supported by the supporting body 27 by the beam portions 28, 28, ... And each of the beam portions 28 is formed so that the thickness dimension is smaller than the width dimension, acceleration in the Z-axis direction is applied. Even in the case of the above, the mass portion 25 is restricted from being displaced in the Z-axis direction. Further, even when the vibrating portion 30A of each bridge 30 is vibrating, the vibration can be prevented from being transmitted to the mass portion 25.

Therefore, the acceleration sensor 21 according to the present embodiment.
In the above, the mass portion 25 is X due to the shape of each beam portion 28.
Although the displacement in the axial direction is allowed, the displacement in the Y and Z axis directions is regulated, so that each bridge 30 can detect only the acceleration in the X axis direction applied to the mass portion 25 with high sensitivity. .

Further, unlike the prior art, each restraining bridge 7 as a back beam provided on the back surface of the silicon substrate can be eliminated, and the number of parts can be reduced.

In the above embodiment, four beam portions 28 supporting the mass portion 25 are formed so as to extend in the Y-axis direction so that the mass portion 25 can be easily displaced in the X-axis direction. However, the number is not limited to this, and may be two or one. The point is to support the mass portion 25 with respect to the support body 27 so that it is difficult to displace in the Z-axis direction.

In the above embodiment, two bridges 30 are provided so as to straddle the groove 26 between the mass portion 25 and the support 27 in the X-axis direction, but the present invention may be provided with one bridge 30 on one side. In this case, the detection signal becomes smaller than that in the above embodiment, and the detection accuracy is lowered due to the influence of the temperature change.

[0044]

As described above in detail, according to the present invention, a silicon plate is integrally formed, and the mass portion is supported by a support through a beam portion that suppresses vertical displacement of the mass portion. Since the bridge for detecting the acceleration applied to the mass unit is provided so as to straddle the groove with the mass unit, the vertical vibration of the bridge at the resonance frequency of the natural vibration state is always transmitted to the mass unit. In addition to preventing the above, the mass section is displaced only by the acceleration in the horizontal detection direction applied to the mass section. Therefore, the acceleration applied in the vertical direction of the mass section does not act on the bridge, and the acceleration in the detection direction is It can be detected with high accuracy.

Further, by forming the width of the beam portion to be sufficiently smaller than the thickness dimension, it is possible to regulate the displacement of the mass portion in the vertical direction and to allow only the displacement in the horizontal direction to accurately measure the acceleration. Can be detected.

[Brief description of drawings]

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

2 is a plan view showing an enlarged main part of a resonance bridge in FIG. 1. FIG.

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

FIG. 4 is a cross-sectional view showing a first nitride film forming step.

5 is a cross-sectional view showing a sacrifice layer forming step following FIG.

FIG. 6 is a cross-sectional view showing a bridge and electrode forming step following FIG.

FIG. 7 is a cross-sectional view showing a second nitride film forming step following FIG.

8 is a cross-sectional view showing a groove forming step following FIG.

FIG. 9 is a cross-sectional view showing an oxide film forming and nitride film removing step following FIG.

10 is a cross-sectional view showing an oxide film removing step following FIG.

11 is a cross-sectional view showing a nitride film removing step following FIG.

FIG. 12 is a plan view of a conventional vibration type acceleration sensor.

13 is a cross-sectional view seen from the direction of arrows XIII-XIII in FIG.

FIG. 14 is a plan view showing a back beam according to a conventional technique.

[Explanation of symbols]

 21 acceleration sensor 23 sensor body 24 silicon substrate 25 mass part 26 groove 27 support 28 beam part 30 bridge 31 bridge electrode 32 capacitance detection electrode 33 drive electrode

Claims (2)

[Claims] 1. A mass part, a support provided around the mass part with a gap, and at least one in the horizontal detection direction so as to straddle between the mass part and the support. A bridge, a vibration generating means for applying a natural frequency to the bridge by applying a predetermined frequency to the bridge, and an acceleration in a detection direction applied to the mass part are detected as a change in the natural vibration of the bridge. In a vibration type acceleration sensor including a detection means, the mass part and the support are integrally formed by a silicon plate, the mass part is connected to the support on the silicon plate, and the mass part is connected to the support. A vibration-type acceleration sensor, characterized in that a beam portion is formed to prevent displacement in the vertical direction. 2. The vibration type acceleration sensor according to claim 1, wherein the beam portion has a width dimension sufficiently smaller than a thickness dimension.