JPH06148232A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To obtain a sensor which does not require sophisticated processing accuracy by detecting the shift difference and the direction when a mass part shifts in accordance with the acceleration as the change of the capacitance between an upper and a lower electrodes. CONSTITUTION:An acceleration sensor 11 is constituted of a mass part 13 having an upper electrode 12 provided at the lower end part thereof, a spiral movable part 14 set at the upper end part of the mass part 13 and supporting the mass part 13 in an oscillatory fashion in three dimensions, a disc-like fixing part 15 for supporting and fixing the other end part of the movable part 14 and lower electrodes 16-19 below the mass part 13 and arranged in matrix on the same plane opposite to the upper electrode 12. When an acceleration works, the mass part 13 shifts in proportion to the size of the acceleration in a direction of the acceleration. The shift changes the capacitance between the upper electrode 12 and each of the lower electrodes 16-19. The shift difference and three-dimensional direction of the acceleration added to the mass part 13 can be obtained from the changing amount of the capacitance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type acceleration sensor suitable for use in automobiles, aircrafts, home electric appliances and the like.

[0002]

2. Description of the Related Art Conventionally, a wide variety of acceleration sensors using various materials such as piezoelectric ceramics, organic thin films, and silicon single crystal plates have been developed and commercialized. These acceleration sensors have no hysteresis, creep, fatigue, etc., are simple in structure, have extremely large voltage sensitivity, and can be easily amplified. Widely used in. Among them, a semiconductor acceleration sensor using a silicon single crystal has features such as being an ideal elastic body because the lattice defects of silicon itself are extremely small, and being capable of diverting the semiconductor process technology as it is, In recent years, it is a sensor that has attracted particular attention.

5 and 6 are views showing an example of the above semiconductor acceleration sensor. This semiconductor acceleration sensor 1
Is a silicon (Si) substrate (110) (semiconductor substrate) 2
The truncated pyramid-shaped mass part 3 formed in the central part, the rectangular frame part 4 formed around the mass part 3, and the mass part 3 and the frame by etching the Si substrate 2 from below. A pair of beam portions (elastic portions) 5 and 5 formed between the portion 4 and
A plurality of pairs of piezoresistors 6, 6, ... Are formed on the upper surface 5a of these beam portions 5 by impurity diffusion. The beam portions 5 and 5 may be configured such that a thin diaphragm portion is provided around the mass portion 3, and a substantially C-shaped void portion is formed in the central portion of the Si substrate 2 so that the mass portion 3 may be supported by a cantilever beam. In this semiconductor acceleration sensor 1, the magnitude of displacement when the mass part 3 is displaced in accordance with acceleration is determined by the piezoresistors 6, 6 of the beam parts 5, 5.
The displacement difference of acceleration is detected by converting into the change of the resistance value of 6, ...

[0004]

By the way, in the semiconductor acceleration sensor 1, the output due to the change in the resistance value of the piezoresistors 6, 6, ... Is determined by the thickness and size of the beam portions 5, 5 or the diaphragm portion. , And the thickness and size of the beam portions 5, 5 and the diaphragm portion must be precisely controlled in order to reduce variations in the outputs of these piezoresistors 6, 6, .... However, since the thickness of the beam portion 5 is about 5 to 50 μm and the thickness of the diaphragm portion is thinner than this, the mass portion 3 having the complicated shape, the beam portions 5, 5 or the diaphragm portion is accurately processed on the Si substrate 2. However, there is a drawback in that variations in the output due to changes in the resistance values of these piezoresistors 6, 6, ... Can not be reduced.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an acceleration sensor that does not require the use of piezoresistors and does not require high-precision machining.

[0006]

In order to solve the above problems, the present invention employs the following acceleration sensor. That is, an upper electrode is provided at a lower end portion and a mass portion that can swing in three-dimensional directions, a movable portion that supports the mass portion so as to swing in three-dimensional directions, and a lower portion of the mass electrode below the mass portion. A plurality of lower electrodes arranged facing each other on the same plane,
A displacement difference and a direction when the mass portion is displaced according to acceleration are detected as a change in capacitance between the upper electrode and a plurality of lower electrodes, and the displacement difference of the acceleration is detected from the detected value. It is characterized by determining the direction and the direction.

[0007]

In the acceleration sensor according to the present invention, when an acceleration acts on the acceleration sensor, the mass portion is displaced in the direction of the acceleration in proportion to the magnitude of the acceleration. Due to this displacement, each capacitance between the upper electrode and the plurality of lower electrodes provided on the mass portion changes, and the displacement difference of the acceleration applied to the mass portion from the magnitude of the change amount of these capacitances. And ask for the direction.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An acceleration sensor 1 according to an embodiment of the present invention will be described below.
1 will be described with reference to FIGS. 1 to 4. The acceleration sensor 11 includes a mass portion 13 having an upper electrode 12 provided at a lower end portion thereof, and an elastic spiral attached to an upper end portion of the mass portion 13 for swingably supporting the mass portion 13 in a three-dimensional direction. -Shaped movable portion 14, a circular frame portion 15 that supports and fixes the other end of the movable portion 14, a grid-shaped portion that is located below the mass portion 13 and faces the upper electrode 12, and is on the same plane. It is composed of four lower electrodes 16 to 19 arranged in a line.

A capacitor is formed between the upper electrode 12 and each of the lower electrodes 16 to 19, and the upper electrode 12 swings with respect to the lower electrodes 16 to 19 in a three-dimensional direction, whereby the upper electrode 12 is formed. And the capacitance between the lower electrodes 16 to 19 are changed. And
Lead wires 21 to 21 are respectively provided to the lower electrodes 16 to 19, respectively.
24 is connected. The mass portion 13, the movable portion 14, and the frame portion 15 are integrally formed by etching a thick silicon wafer under predetermined conditions. The mass portion 13, the movable portion 14, and the frame portion 15 are not limited to those described above, and are made of, for example, a glass substrate of borosilicate, a quartz glass substrate, or the like, polycrystalline silicon, or silicon oxide by CVD, sputter deposition, thermal oxidation, or the like. Those obtained by epitaxially growing silicon nitride, etc. are also applicable. Also,
As a material for the lead wires 21 to 24, aluminum (A
A metal such as l), polycrystalline silicon doped with phosphorus or the like is preferably used.

FIG. 4 shows an upper electrode 12 and lower electrodes 16-1.
9 shows an equivalent circuit composed of 9 and the change in capacitance between the upper electrode 12 and each of the lower electrodes 16 to 19 is equivalent to a variable capacitor.

In this acceleration sensor 11, when an acceleration acts on the acceleration sensor 11, the mass portion 13 is displaced in the direction of this acceleration in proportion to the magnitude of this acceleration.
Due to this displacement, the electrostatic capacitance between the upper electrode 12 and each of the lower electrodes 16 to 19 changes, and from the magnitude of the amount of change in these electrostatic capacitances, the displacement difference of the acceleration applied to the mass portion 13 and the three-dimensional You can find the direction.

For example, the mass portion 13 has the lower electrodes 16 to 19
When oscillating in the direction perpendicular to (Z direction) with respect to, the upper electrode 1
2 and the lower electrodes 16 to 19 have the same amount of change in each capacitance. Therefore, the displacement difference and direction of the acceleration applied to the mass portion 13 (in this case, the Z direction) can be obtained from the amount of change in these capacitances. When the mass part 13 swings in the horizontal direction (X direction) with respect to the lower electrodes 16 to 19, the upper electrode 12 and the lower electrodes 16 and 18 are moved.
The change amount of each capacitance between each of them is equal in absolute value to the change amount of each capacitance between each of the upper electrode 12 and each of the lower electrodes 17 and 19 and has the opposite sign. Therefore, the displacement difference and the direction of the acceleration applied to the mass portion 13 (in this case, the X direction) can be obtained from the amount of change in the capacitance.
The same applies when the mass unit 13 swings in the Y direction. By combining these, the mass part 13
It is possible to determine the displacement difference and the direction of the acceleration applied to the three-dimensional direction.

As described above, the above acceleration sensor 1
According to 1, the mass part 13 having the upper electrode 12 provided at the lower end, the movable part 14 that supports the mass part 13 so as to be swingable in the three-dimensional direction, and the frame that supports and fixes the movable part 14. Part 1
5 and four lower electrodes 16 to 19 arranged on the same plane below the mass unit 13 so as to face the upper electrode 12, and the upper electrode 12 is tertiary with respect to the lower electrodes 16 to 19. By swinging in the original direction, the upper electrode 12
Since the electrostatic capacitance between the upper electrode 12 and the lower electrodes 16 to 19 is changed,
.About.19, the displacement difference and direction in each of the three-dimensional directions of acceleration applied to the mass portion 13 can be obtained with high accuracy from the magnitude of the amount of change in capacitance between each of them.

Further, each of the mass portion 13 and the movable portion 14 is
Since it does not require high-precision machining accuracy as in the conventional beam portion or diaphragm portion, the manufacturing process can be simplified, the yield of the acceleration sensor 11 can be improved, and the manufacturing cost can be reduced. it can.

The mass portion 1 of the acceleration sensor 11 described above
3, the shapes of the movable portion 14 and the frame portion 15, the positional relationship between the upper electrode 12 and each of the lower electrodes 16 to 19 and the quantity thereof are not limited to the one embodiment described above, and various modifications are possible. Is. For example, the movable portion 14 may have a spring-like configuration, and the lower electrodes 16 to 19 may be arranged in a circular shape.

[0016]

As described above, according to the acceleration sensor of the present invention, the lower electrode is provided with the upper electrode, and the mass portion is swingable in the three-dimensional direction, and the mass portion is swung in the three-dimensional direction. Displacement difference when the mass part is displaced according to acceleration, comprising a movable part that supports the mass part, and a plurality of lower electrodes that are arranged on the same plane below the mass part so as to face the upper electrode. And the direction are detected as a change in capacitance between the upper electrode and the plurality of lower electrodes, and the displacement difference and the direction of the acceleration are obtained from the detected values. The displacement difference and direction in each of the three-dimensional directions of the acceleration applied to the mass portion can be obtained with high accuracy from the magnitude of the amount of change in capacitance between each of the lower electrodes.

Further, since the mass portion and the movable portion do not require the high precision processing accuracy of the conventional beam portion and diaphragm portion, the manufacturing process can be simplified and the yield of the acceleration sensor is improved. Therefore, the manufacturing cost can be reduced.

As described above, it is possible to provide a capacitance type acceleration sensor which does not require the use of a piezoresistor as in the conventional case and which does not require high precision processing.

[Brief description of drawings]

FIG. 1 is a side view showing an acceleration sensor of the present invention.

FIG. 2 is a top view showing an acceleration sensor of the present invention.

FIG. 3 is a plan view showing the arrangement of lower electrodes of the acceleration sensor of the present invention.

FIG. 4 is a diagram showing an equivalent circuit of the acceleration sensor of the present invention.

FIG. 5 is a perspective view showing a conventional semiconductor acceleration sensor.

6 is a sectional view taken along the line AA of FIG.

[Explanation of symbols]

11 ... Acceleration sensor, 12 ... Upper electrode, 13 ... Mass part,
14 ... Movable part, 15 ... Frame part, 16-19 ... Lower electrode 2
1 to 24 ... Lead wire.

Claims (1)

[Claims] 1. A mass part which is provided with an upper electrode at its lower end and is capable of swinging in three-dimensional directions, a movable part which supports the mass parts so as to be swingable in three-dimensional directions, and a portion below the mass part. A plurality of lower electrodes arranged on the same plane so as to face the upper electrode, and a displacement difference and a direction when the mass portion is displaced according to acceleration are measured between the upper electrode and the plurality of lower electrodes. Is detected as a change in the capacitance of the acceleration sensor, and the displacement difference and the direction of the acceleration are obtained from the detected value.