JPH06323940A - Capacitance-type sensor - Google Patents

Abstract

PURPOSE:To provide an electrostatic-force servo-type pressure sensor whose structure is simplified and whose manufacturing process is simple. CONSTITUTION:A single-crystal silicon wafer is etched anisotropically, and a frame 3 which supports a diaphragm 4 so as to be capable of being freely rocket is made. A movable electrode 7 is formed in the center of the diaphragm 4, and an electrode 9 for electrostatic-force generation is formed to be a frame shape at its outer circumference. A cover 2 in which a hollow 11 is formed in such a way that the diaphragm 4 can be micro-scopically deformed freely in its thickness direction is made of another single-crystal silicon wafer. A fixed electrode 8 is formed in the center of the hollow 11 so as to face the movable electrode 7, and another electrode 10, for electrostatic-force ] generation, so as to face the electrode 9, for electrostatic-force generation, on the diaphragm 4 is formed at its outer circumference. In addition, introduction ports 5 which introduce a fluid such as air or the like are made in the cover 2, the frame 3 is bonnet to the surface of the cover 2 by a low-temperature bonding technique or the like, and a pressure sensor 1 is manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type sensor. More specifically, the present invention relates to a capacitance sensor used to detect a change in capacitance that occurs in proportion to the displacement of a detection unit and to measure the acceleration of a vehicle or the gauge pressure of air or the like.

[0002]

2. Description of the Related Art Conventionally, for example, "Thechnical Digest of the
11th Sensor Symposium, 1992, p.47-50 ”. This acceleration sensor 51
As shown in FIG. 4, a mass portion 53 is arranged at the center of a frame 52 made of a silicon substrate and having a rectangular frame shape. The mass portion 53 is formed within the frame 52 by a large number of shaft-bar-shaped beams 54. It is fully supported. The mass portion 53 can be freely minutely displaced in the thickness direction of the mass portion 53 by the elasticity of the beam 54, and a movable electrode 55 is formed on the upper surface thereof.

A glass substrate 5 is provided on the upper and lower surfaces of the frame 52.
6, 57 are stacked, and the peripheral portions of the glass substrates 56, 57 are bonded to the frame 52 by anodic bonding. A fixed electrode 58 is provided on the inner surface of the glass substrate 56 on the upper side of the frame 52 with a small gap from the movable electrode 55 of the mass portion 53, and the movable electrode 55 and the fixed electrode 58 constitute a detection capacitor. ing. Also, the mass section 5
Electrodes 59 and 60 for electrostatic force generation are provided on the lower surface of 3 and the inside of the glass substrate 57 below the frame 52, respectively.

In the acceleration sensor 51, the capacitance of the detection capacitor is detected by a detection circuit 61 integrated on the frame 52, and the detection circuit 61 converts the magnitude of the capacitance into a frequency. -Frequency conversion (C-
f conversion) is performed and a frequency signal corresponding to the capacitance of the capacitor is output. Next, the electrostatic force generation circuit 62 integrated on the frame 52 compares the frequency of the output frequency signal and the reference frequency, and the bottom surface of the mass portion 53 so that the frequency of the frequency signal matches the reference frequency. Also, a voltage is applied to the electrostatic force generating electrodes 59 and 60 provided on the inner surface of the glass substrate 57 below the frame 52 to move the mass portion 53.
Is adjusted so that it is always at a constant position in the center of the frame 52.

However, when acceleration is applied to the acceleration sensor 51, the mass portion 53 is displaced, the gap amount between the movable electrode 55 and the fixed electrode 58 is changed according to the displacement amount of the mass portion 53, and the capacitance is changed. Will change. When the electrostatic capacitance changes, the voltage applied by the electrostatic force generating circuit 62 to the electrostatic force generating electrodes 59 and 60 also changes. Therefore, by detecting the voltage applied to the electrostatic force generating electrodes 59, 60, the magnitude of the acceleration applied to the acceleration sensor 51 can be known.

However, in the capacitance type acceleration sensor 51 having such a configuration, the electrostatic force generating electrode 5 is used.
In order to provide 9, 60, it is necessary to provide a glass substrate 57 in addition to the glass substrate 56 provided with the fixed electrode 58 to form a three-layer structure of glass-silicon-glass, resulting in high cost. Further, since the movable electrode 55 and the electrostatic force generating electrode 59 for forming the detection capacitor have to be formed on the upper and lower surfaces of the mass portion 53, respectively, the mass portion 53 needs to be accurately formed from both sides. Therefore, the manufacturing process of the mass portion 53 was very difficult. Further, since the acceleration sensor 51 has a three-layer structure, the glass substrates 56 and 57 have to be bonded to the frame 52 twice, and thus the process of manufacturing the acceleration sensor 51 is troublesome.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of conventional examples, and an object of the present invention is to provide two substrates constituting an electrostatic capacitance type sensor. The purpose is to simplify the structure of the capacitance type sensor and simplify the manufacturing process.

[0008]

According to another aspect of the present invention, there is provided a capacitance type sensor, wherein a detecting portion is elastically supported by a supporting substrate, and a fixed substrate is bonded to one surface of the supporting substrate. In the capacitance type sensor in which a fixed electrode is provided on the inner surface of the fixed substrate so as to face the movable electrode provided on the inner surface of the fixed substrate, and the movable electrode and the fixed electrode constitute a detection capacitor, the electrostatic capacitance of the detection capacitor An electrostatic force generating electrode for generating an electrostatic force for holding the capacitance at a constant capacity is provided on the inner surface of the detection unit, and is opposed to the electrostatic force generation electrode provided on the detection unit to form a pair on the inner surface of the fixed substrate. It is characterized in that an electrostatic force generating electrode is provided.

Further, the object of measurement is the pressure of a fluid such as air, and an inlet for introducing a fluid such as air may be provided in the fixed substrate.

[0010]

According to the electrostatic capacity sensor of the present invention, the electrostatic force generating electrode for generating the electrostatic force for holding the electrostatic capacity of the detecting capacitor at a fixed capacity is fixed to the detecting portion having the movable electrode. Since the electrodes are provided so as to face the inner surface of the fixed substrate on which the electrodes are formed, the electrostatic force servo type capacitive sensor, which is conventionally composed of three substrates, is used as a support substrate and a fixed substrate. It can be configured by the substrate. Therefore, the structure of the electrostatic force servo type sensor can be simplified.

Further, since the electrostatic force generating electrode and the movable electrode only have to be formed on one of the surfaces of the supporting substrate and the supporting substrate and the fixed substrate can be joined at once, the manufacturing process can be performed. It can be simplified, and the electrostatic force servo sensor can be manufactured by the same process as the conventional non-electrostatic force servo capacitive sensor.

Also, a fixed substrate having an inlet for introducing a fluid can be bonded to a supporting substrate to manufacture a pressure sensor whose measurement target is the pressure of a fluid such as air.

[0013]

1 is a sectional view of an electrostatic force servo type pressure sensor according to an embodiment of the present invention, and FIG. 2 is a plan view thereof.
The pressure sensor 1 includes a frame 3 in which a thin film diaphragm 4 is slidably supported on the entire surface of a rectangular frame on the upper surface of a cover 2 provided with an inlet 5 for introducing air to be measured. And the peripheral portion of the cover 2 is joined to the frame 3 by a low temperature joining technique or the like.

The frame 3 and the diaphragm 4 are integrally formed from a single crystal silicon wafer by anisotropic etching with a potassium hydroxide solution, and the diaphragm 4 is accurately manufactured to an arbitrary thickness by an electrochemical etching stop technique. . Frame 3 and diaphragm 4
Has an oxide film 6 for surface protection, a movable electrode 7 is formed in the center of the diaphragm 4, and an electrostatic force generating electrode 9 is formed in a frame shape on the outer periphery of the movable electrode 7 by sputtering aluminum or the like. Has been formed.

The cover 2 is produced by dry etching a single crystal silicon wafer, and a recess 11 is provided on the inner surface of the cover 2 so that the diaphragm 4 can be elastically deformed and freely displaced in the thickness direction. ing. The inlet 5 is formed in the cover 2 by anisotropic etching with a potassium hydroxide solution. A fixed electrode 8 is formed in the recess 11 with a small gap from the movable electrode 7 of the diaphragm 4 by sputtering of aluminum or the like, and a detection capacitor is formed between the movable electrode 7 and the fixed electrode 8. . Further, another electrostatic force generating electrode 10 is similarly formed on the outer periphery of the fixed electrode 8 so as to face the electrostatic force generating electrode 9 of the diaphragm 4, and the fixed electrode 8 and the electrostatic force generating electrode 10 are It is drawn out to the electrode pads 12a and 13a provided on the upper surface of the cover 2 via conductive paths (not shown) formed in the cover 2 by an ion implantation method or the like.

A connection pad 14 is provided in the recess 11 of the cover 2.
Are provided so as to project, and the connection pad 14 is connected to the p ⁺ region 16
Is electrically connected to another electrode pad 13b on the upper surface of the cover 2. Another connection pad 15 is provided on the lower surface of the frame 3, and the connection pad 15 is connected to the electrostatic force generating electrode 9. The connection pads 14 and 15 are covers 2
And the frame 3 are pressure-bonded to each other by the bonding of the frame 3, and the connection pads 14 and 15 are electrically connected. In this way, the electrostatic force generating electrode 9 of the diaphragm 4 is pulled out to the electrode pad 13b on the upper surface of the cover 2. In addition, the movable electrode 7 of the diaphragm 4 is similarly drawn to another electrode pad 12b on the upper surface of the cover 2.

FIG. 3 is a diagram for explaining the operation of the pressure sensor 1. The operation of the pressure sensor 1 will be described below with reference to FIG. In the pressure sensor 1, the capacitance of the capacitor is detected by the oscillation circuit 21 connected to the electrode pads 12a and 12b on the upper surface of the cover 2. Oscillator circuit 21
Is a capacitance-frequency conversion (Cf conversion) circuit that converts the magnitude of the capacitance into a frequency, and outputs a frequency signal according to the capacitance of the capacitor to the comparator 22. Next, the comparator 22 compares the frequency of the input frequency signal with the frequency (reference frequency) of the frequency signal corresponding to the capacitance of the pressure sensor 1 in the stationary state, and inputs the frequency signal and the reference frequency. Between the movable electrode 7 and the fixed electrode 8 so as not to change the electrostatic capacitance between the movable electrode 7 and the fixed electrode 8 via the filter amplifier 23 and the driver circuit 24. An appropriate voltage is applied to.

When air is introduced into the depression 11 from the inlet 5, the pressure of the introduced air causes the diaphragm 4 to be displaced, and the displacement of the diaphragm 4 changes the capacitance of the capacitor. . This change in capacitance is detected by the comparator 22 as the difference between the frequency of the frequency signal output by the oscillation circuit 21 and the reference frequency, and is applied between the electrostatic force generating electrodes 9 and 10 through the filter amplifier 23 and the driver 24. The applied voltage is changed.
Therefore, the pressure of the air applied to the pressure sensor 1 can be known by detecting the change in this voltage.

The electrostatic force servo pressure sensor 1 having such a structure can be easily manufactured by bonding two silicon wafers, and the manufacturing process thereof can be simplified. Moreover, since the change in the detected voltage does not depend on the spring constant of the diaphragm 4, the measurement accuracy of the pressure sensor 1 is not affected by variations in the shape of the diaphragm 4 and the reliability of the pressure sensor 1 is improved. You can

[0020]

According to the capacitance type sensor of the present invention, the capacitor is constituted by the electrostatic force generating electrode for generating the electrostatic force for keeping the electrostatic capacitance of the detecting capacitor constant. Since it is provided on the supporting substrate and the fixed substrate made of silicon, the sensor can be configured with two silicon substrates, the supporting substrate and the fixed substrate, and the structure of the electrostatic force servo type sensor, which conventionally required three substrates, is provided. Can be easy.

Further, since it is composed of two substrates, the bonding is required only once, and furthermore, the electrostatic force generating electrode is formed on one surface of the supporting substrate at the same time as the movable electrode, and the fixed substrate is fixed electrode. At the same time, the electrostatic force generating electrode can be formed, so that the manufacturing process can be simplified, and the electrostatic force servo type sensor is manufactured in the same process as the conventional non-electrostatic force servo type capacitive sensor. It will be possible.

Further, a fixed substrate provided with a hole-shaped inlet for introducing a fluid may be bonded to the upper surface of the support substrate to manufacture a pressure sensor whose measurement target is the pressure of a fluid such as air. it can.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a pressure sensor that is an embodiment of the present invention.

FIG. 2 is a plan view of the above pressure sensor.

FIG. 3 is an operation explanatory view of the above pressure sensor.

FIG. 4 is a cross-sectional view of a conventional pressure sensor.

[Explanation of symbols]

 4 Diaphragm 5 Inlet 7 Movable Electrode 9,10 Electrostatic Force Generation Electrode 14,15 Connection Pad 22 Comparator

Claims (2)

[Claims] 1. A detection substrate is elastically supported on a support substrate,
A fixed substrate is bonded to one of the surfaces of the supporting substrate,
In the electrostatic capacitance type sensor in which a fixed electrode is provided on the inner surface of the fixed substrate so as to face the movable electrode provided on the inner surface of the detection unit, and the movable electrode and the fixed electrode constitute a detection capacitor, the detection capacitor An electrostatic force generating electrode for generating an electrostatic force for holding the electrostatic capacity of the fixed capacity is provided on the inner surface of the detection unit, and the inner surface of the fixed substrate is opposed to the electrostatic force generation electrode provided on the detection unit. An electrostatic capacitance sensor, which is provided with an electrode for generating electrostatic force to form a pair. 2. The electrostatic capacitance according to claim 1, wherein the object of measurement is the pressure of a fluid such as air, and an inlet port for introducing a fluid such as air is provided in the fixed substrate. Capacitive sensor.