JPH0627134A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To improve the detecting accuracy, reliability and the like in detection of acceleration by detecting the displacement of a movable part highly accurately with a displacement detecting part. CONSTITUTION:A displacement detecting part 26 is formed of a piezoelectric body 27, which is provided on a supporting part 25A of a cantilever 25 as a movable part, and a displacement detecting circuit 29, which is provided at the side of the protruding end of the supporting part 25A in adjacent to the piezoelectric body 27. The charge signal, which is outputted from the piezoelectric body 27 through an electrode 28, is converted into the voltage value in the displacement detection circuit 29. The driving voltage signals are outputted from an electrostatic drive circuit 34 of a driving part 32 into electrodes 32 and 33. Specified static electricity is generated between each of the electrodes 32 and 33 and a mass part 25B. Thus, the position of the cantilever 25 is controlled with the driving part 31. In this way, the displacement of the cantilever 31 caused by vibration is detected as the charge signal with the piezoelectric body 27. The charge signal is converted into the voltage signal with the displacement detection circuit 29.

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 moving body such as an automobile, and more particularly to a servo which feedback-controls a signal of a drive unit according to a displacement of a movable unit. Type acceleration sensor.

[0002]

2. Description of the Related Art Generally, as an acceleration sensor, a movable portion formed of a silicon material, the base end side of which is a fixed end and the tip end side of which is a mass portion, a displacement detecting portion for detecting displacement of the movable portion, and the displacement Based on the displacement detection signal from the detector,
The displacement detecting unit detects the displacement of the movable unit based on a change in capacitance, and the driving unit uses an electrostatic force to move the movable unit so that the displacement of the movable unit becomes zero. It is known that the movable part is returned.

On the other hand, in an acceleration sensor using electrostatic force (electrostatic capacity) for both this type of detection system and drive system, signal interference is likely to occur due to parasitic capacitance between the detection system and drive system. Since the detection accuracy of acceleration is low, an acceleration sensor that uses a piezoresistive element for the displacement detecting section and detects the displacement of the movable section based on the resistance change of the piezoresistive element is disclosed in, for example, Japanese Patent Laid-Open No. 1-240865. Have been proposed by.

Therefore, an acceleration sensor disclosed in Japanese Patent Laid-Open No. 1-240865 will be described with reference to FIG. 2 as an acceleration sensor according to this type of prior art.

In the figure, reference numeral 1 denotes a sensor body of an acceleration sensor, and the sensor body 1 constitutes an acceleration sensor together with a switching circuit 9 and the like which will be described later.

Reference numeral 2 denotes a lower substrate made of an insulating material such as a glass material, and 3 is provided on the lower substrate 2 via a cantilever 5 described later, and made of an insulating material such as a glass material. The upper substrate is shown, and a space 4 in which a cantilever 5 is displaceably provided is defined between the substrates 2 and 3.

Reference numeral 5 denotes a cantilever which is provided between the substrates 2 and 3 and is made of a single crystal silicon material as a movable portion. The cantilever 5 has a base end side between the substrates 2 and 3. A support portion 5A having a thick fixed end sandwiched and a free end extending into the space 4 and a support portion 5A integrally formed on the front end side of the support portion 5A and formed to have a predetermined mass And a mass part 5B that is formed. The cantilever 5 is grounded. When an acceleration is applied to the cantilever 5, the mass portion 5B vibrates (displaces) in the space 4 in the upward and downward directions according to the acceleration.

Reference numeral 6 denotes a displacement detecting portion provided on the support portion 5A of the cantilever 5, and the displacement detecting portion 6 is composed of a piezoresistive element and is connected to a phase advance circuit 8 described later. The displacement detector 6 detects the displacement of the cantilever 5 that vibrates according to the acceleration as a resistance value change due to the strain of the support 5A, and outputs this to the phase advance circuit 8.

Reference numeral 7 is an amplifier connected to the displacement detector 6, and 8
Is a phase lead circuit connected to the displacement detector 6 via the amplifier 7, and 9 is a switching circuit connected to the phase lead circuit 8, respectively. The amplifier 7, the phase lead circuit 8 and the switching circuit 9 serve as servo circuits. A circuit is formed. When the displacement detection signal based on the resistance value change from the displacement detection unit 6 is input to the switching circuit 9 via the amplifier 7 and the phase advance circuit 8, the switching circuit 9 drives based on this displacement detection signal. The voltage signal is selectively output to either the lower drive electrode 10 or the upper drive electrode 11 described later.

Reference numeral 10 is a lower drive electrode which is located below the mass portion 5B of the cantilever 5 and which is provided on the upper surface side of the lower substrate 2.
Are upper drive electrodes which are provided on the lower surface side of the upper substrate 3 so as to face the lower drive electrodes 10 and which constitute an electrostatic drive unit together with the lower drive electrodes 10, respectively. 11 are connected to the switching circuit 9, respectively. The electrodes 10 and 11 generate an electrostatic force between the electrodes 10 and 11 and the mass portion 5B of the grounded cantilever 5 by the drive voltage signal selectively output from the switching circuit 9, and the electrostatic force causes the electrodes 10 and 11 to move. The displacement of the cantilever beam 5 is returned to zero, that is, the vibration-free state (origin).

Reference numeral 12 denotes an arithmetic processing circuit connected to the switching circuit 9. The arithmetic processing circuit 12 controls externally on the basis of a drive voltage signal which is a feedback signal output from the switching circuit 9 to each of the electrodes 10 and 11. An acceleration detection signal is output to a unit (not shown) or the like.

The acceleration sensor according to the prior art has the above-mentioned structure, and when acceleration is applied to the sensor body 1, the mass portion 5B of the cantilever 5 is supported by the support portion 5A while moving up and down in the space 4. The support portion 5A of the cantilever 5 is distorted by this vibration. When the displacement detector 6 detects a change in resistance value due to this distortion and outputs a displacement detection signal for the cantilever 5, the displacement detection signal is passed through the amplifier 7 and the phase advance circuit 8 to the switching circuit 9
The switching circuit 9 outputs a drive voltage signal corresponding to the displacement detection signal to each of the electrodes 10 and 11 in order to make the displacement of the cantilever 5 zero. As a result, each electrode 10,
11 and the mass portion 5B of the cantilever 5, an electrostatic force is generated,
The electrostatic force causes the cantilever beam 5 to return, and its position is controlled.

[0013]

By the way, in the acceleration sensor according to the above-mentioned prior art, a piezoresistive element is used for the displacement detecting section 6, and the displacement of the cantilever 5 is detected based on the resistance change of the piezoresistive element. Since the structure is such that the cantilever 5 is returned by the electrostatic force generated by the electrodes 10 and 11,
Detection system (displacement detection unit 6) and drive system (each electrode 10, 11)
The signal types of and are different, and it is possible to prevent signal interference due to parasitic capacitance.

However, in general, since the piezoresistive element has low sensitivity, the displacement of the cantilever 5 cannot be detected with high accuracy, and there is a problem that the detection accuracy and reliability of acceleration detection are low.

The present invention has been made in view of the above-mentioned problems of the prior art, and it is possible to detect the displacement of the movable part with high accuracy by the displacement detection part, and to improve the detection accuracy and reliability of acceleration detection. It is an object of the present invention to provide an acceleration sensor having the above structure.

[0016]

In order to solve the above-mentioned problems, the structure adopted by the present invention is such that a silicon material or a part thereof is made of a silicon compound material, and the base end side is a fixed end and the tip end side is an acceleration. A displacement detection section configured to detect displacement of the movable section, the displacement detection section including a movable section serving as a mass section that is displaced in response to the movable section, and a piezoelectric body provided on the base end side of the movable section. And a drive unit that controls the position of the movable unit by generating an electrostatic force so that the displacement of the movable unit becomes zero based on the signal.

[0017]

When the acceleration is applied, the movable portion is displaced by this acceleration, and the displacement detecting portion detects the displacement of the movable portion based on the electric charge generated in the piezoelectric body. Then, the drive unit generates an electrostatic force so that the displacement of the movable unit becomes zero based on the displacement detection signal from the displacement detection unit, and controls the position of the movable unit.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

In the figure, reference numeral 21 denotes a sensor main body of the acceleration sensor according to this embodiment, and the sensor main body 21 constitutes an acceleration sensor together with an electrostatic drive circuit 34 and the like which will be described later.

Reference numeral 22 denotes a lower substrate made of an insulating material such as glass, and 23 denotes a cantilever 25 to be described later on the lower substrate 22.
And an upper substrate formed of an insulating material such as glass, respectively, and a space 24 in which a cantilever 25 is displaceably provided is defined between the substrates 22 and 23. Further, one end side (the left side in the drawing) of the lower substrate 22 projects to the outside to form a protrusion 22A, and a displacement detection circuit 29 described later is formed on the protrusion 22A.

Reference numeral 25 denotes a cantilever which is provided between the substrates 22 and 23 and is made of a single crystal silicon material as a movable portion. The cantilever 25 has a base end side between the substrates 22 and 23. A thin flat plate-shaped support portion 25A having a fixed end sandwiched and a free end extending into the space 24 is integrally formed on the front end side of the support portion 25A, and is thick so as to have a predetermined mass. And the formed mass portion 25B,
Moreover, the cantilever 25 is grounded. Further, the projecting end side of the cantilever 25 extends on the projecting portion 22A of the lower substrate 22, and a displacement detecting circuit 29 is formed. When the sensor body 21 is subjected to acceleration, the cantilever 25 causes the mass portion 25B to vibrate upward and downward in the space 24 in response to the acceleration.

Reference numeral 26 denotes a displacement detector according to this embodiment,
The displacement detecting section 26 is provided on the supporting section 25A of the cantilever 25, a piezoelectric body 27 formed in a flat plate shape from a piezoelectric material such as a ZnO thin film, and an electrode provided on the upper surface side of the piezoelectric body 27. 28 and the supporting portion 2 of the cantilever 25 adjacent to the piezoelectric body 27.
5A is provided on the protruding end side, and the piezoelectric body 2 is provided through the electrode 28.
7 and a displacement detection circuit 29 composed of a field effect transistor (FET) or the like. Here, the displacement detection circuit 29 is integrally formed on the supporting portion 25A of the cantilever 25 made of a silicon material by using a semiconductor manufacturing technique such as an etching technique.
The electric charge output from the device is converted into a voltage value. Then, the displacement detector 26 determines the displacement of the cantilever 25 that vibrates up and down in the space 24 based on the electric charge generated in the piezoelectric body 27 by the strain generated in the support portion 25A of the cantilever 25. It detects and outputs the displacement detection signal which is the electric charge signal to the signal processing circuit 30 through the displacement detection circuit 29.

Reference numeral 31 denotes a drive unit according to the present embodiment. The drive unit 31 is located below the mass portion 25B of the cantilever 25 and is provided on the upper surface side of the lower substrate 22 on the lower drive electrode 32.
An upper drive electrode 33 provided on the lower surface of the upper substrate 23 so as to face the lower drive electrode 32, and the electrodes 32, 3
3 and the electrostatic drive circuit 34 connected to the electrostatic drive circuit 34. Then, the drive unit 31
On the basis of the displacement detection signal output from the displacement detection unit 26 via the signal processing circuit 30, selectively outputs a drive voltage signal to each of the electrodes 32 and 33 in order to reduce the displacement of the cantilever 25 to zero. As a result, a predetermined electrostatic force is generated between the mass portion 25B of the cantilever 25 and each of the electrodes 32 and 33, and the position of the cantilever 25 is controlled.

Reference numeral 35 denotes an arithmetic processing circuit connected to the electrostatic drive circuit 34. The arithmetic processing circuit 35 is based on a drive voltage signal, which is a feedback signal output from the electrostatic drive circuit 34, and is connected to an external control unit ( (Not shown)
Etc. to output an acceleration detection signal.

The acceleration sensor according to this embodiment has the above-mentioned structure. When acceleration is applied to the sensor body 21, the mass portion 25B of the cantilever 25 is supported by the support portion 25A and moves upward in the space 24. The support portion 25A vibrates downward, and stress (strain) is generated in the support portion 25A. Then, the stress generated in the support portion 25A is converted into a charge signal according to the displacement of the cantilever 25 by the piezoelectric body 27, and the displacement detection signal as the charge signal is a displacement detection circuit 29.
After being converted into a voltage value by, the signal is output to the signal processing circuit 30, and then output from the signal processing circuit 30 to the electrostatic drive circuit 34.

Next, the electrostatic drive circuit 34 constituting the drive unit 31 selectively outputs a drive voltage signal corresponding to the displacement detection signal from the displacement detection unit 26 to each of the electrodes 32 and 33, and each of the electrodes 32 and 33. A predetermined electrostatic force is generated between 32 and 33 and the mass portion 25B, and the drive portion 31 restores the displacement of the cantilever 25 to the vibration-free state (origin).

As a result, the arithmetic processing circuit 35 outputs an acceleration detection signal to the control unit or the like based on the drive voltage signal output from the electrostatic drive circuit 34.

Thus, according to this embodiment, the cantilever 25
Of the piezoelectric body 27 provided on the supporting portion 25A of the
Since the displacement detecting unit 26 is configured by the displacement detecting circuit 29 which is provided adjacent to the supporting portion 25A and converts the charge signal output from the piezoelectric body 27 through the electrode 28 into a voltage value, the piezoelectric body 27 is formed. It is possible to detect the displacement of the cantilever 25 with high sensitivity by utilizing the excellent electric quantity-mechanical quantity conversion characteristic of.

As a result, based on the highly sensitive displacement detection signal from the displacement detection unit 26, the drive unit 31 accurately causes the cantilever 25.
The position can be controlled, and the accuracy of acceleration detection, reliability, etc. can be greatly improved.

Further, the base end side of the supporting portion 25A of the cantilever 25 is extended to above the projecting portion 22A of the lower substrate 22, and the supporting portion 2
Since the displacement detection circuit 29 including an FET or the like is integrally formed on the protruding end side of the 5A by using semiconductor manufacturing technology,
The charge signal from the piezoelectric body 27 can be quickly converted into a voltage value. As a result, noise generated in the displacement detection signal can be effectively reduced, acceleration detection accuracy can be significantly improved, and acceleration detection up to low frequencies can be accurately performed, resulting in improved performance and reliability. Can be improved.

Further, since the displacement detecting section 26 is composed of the piezoelectric body 27 and the like and the driving section 31 is composed of the electrodes 32 and 33 and the like as an electrostatic force type driving section, it is parasitic between the detection system and the driving system. Surely prevent signal interference due to capacity,
Acceleration detection accuracy can be significantly improved.

In the above embodiment, the piezoelectric body 27 is made of Zn.
Although the present invention is described as being formed from an O piezoelectric thin film, the present invention is not limited to this, and a piezoelectric thin film such as a PZT thin film or a lead titanate thin film, or a piezoelectric ceramic thin piece such as PZT, lead titanate, or ZnO is used. It may be configured.

Further, in the above embodiment, each of the substrates 22 and 23 is
However, the present invention is not limited to this, and each substrate and the cantilever may be formed of a silicon material. In this case, an insulating film may be formed between each electrode and the substrate.

Further, although the cantilever 25 has been described as being formed of a silicon material, the present invention is not limited to this, and the whole or one portion of the cantilever 25 excluding the portion forming the displacement detection circuit 29 is used. The portion may be formed of a silicon compound material such as silicon nitride or silicon oxide. in this case,
A conductive thin film for forming a ground electrode is formed on the surface of a silicon compound material.

Furthermore, in the above embodiment, the case where only the displacement detection circuit 29 is integrally formed on the cantilever 25 has been described as an example, but the present invention is not limited to this, and in some cases, the signal processing circuit 30 or the static circuit. Other circuits such as the electric drive circuit 34 cantilever 2
It may be configured to be integrally formed on the protruding end side of 5. Also,
When the lower substrate and the upper substrate are made of a silicon material, these displacement detection circuits 29 and the like may be integrally formed on the surface of each substrate.

[0036]

As described above in detail, according to the present invention, the movable portion, which is made of a silicon material and has a base end side which is a fixed end and a distal end side which is a mass portion which is displaced in accordance with acceleration, and the movable part of the movable portion. A displacement detection section that is composed of a piezoelectric body provided on the base end side and detects the displacement of the movable section, and an electrostatic force so that the displacement of the movable section becomes zero based on a displacement detection signal from the displacement detection section. And a drive unit that controls the position of the movable unit by generating an electric field. Therefore, when acceleration is applied, the movable unit is displaced by this acceleration, and the displacement detection unit causes the displacement of the movable unit to occur in the piezoelectric body. The drive unit can control the position of the movable unit by generating an electrostatic force so that the displacement of the movable unit becomes zero based on the displacement detection signal from the displacement detection unit. As a result, the displacement of the movable part can be detected with high sensitivity by utilizing the excellent electric quantity-mechanical quantity conversion characteristic of the piezoelectric body, and the position of the movable part can be accurately controlled by the driving part. The acceleration detection accuracy and reliability can be improved.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an acceleration sensor according to an embodiment of the present invention.

FIG. 2 is an overall configuration diagram showing an acceleration sensor according to a conventional technique.

[Explanation of symbols]

 25 cantilever (movable part) 25A support part 25B mass part 26 displacement detection part 27 piezoelectric body 31 drive part 32 lower drive electrode 33 upper drive electrode

Claims (1)

[Claims] 1. A movable part, which is made of a silicon material or a part of which is made of a silicon compound material, has a base end side as a fixed end and a tip end side as a mass part which is displaced according to acceleration, and a base end side of the movable part. A displacement detection unit that is provided with a piezoelectric body and detects displacement of the movable unit, and generates an electrostatic force so that the displacement of the movable unit becomes zero based on a displacement detection signal from the displacement detection unit. An acceleration sensor including a drive unit that controls the position of the movable unit.