JPH06229788A - Sense of equilibrium sensor - Google Patents

Abstract

PURPOSE:To provide a sense of equilibrium sensor for measuring the magnitude and direction of acceleration and inclination accurately. CONSTITUTION:A recess 8' is made in a silicon wafer 2 constituting an IC chip and magnetic fluid 8 is contained therein along with bubbles 9. When acceleration is imparted, the bubbles 9 migrate through the magnetic fluid 8 to cause variation of permeability. The variation is detected by a magnetoresistive element 5 (5a-5d) disposed through an oxide film 3 thus detecting the direction and magnitude of acceleration. Since the oxide film 3 can be formed very thin, the distance between the bubble 9 and the magnetoresistive elements 5a-5d can be shortened thus allowing the accurate detection even of gentle variation of acceleration or inclination without sacrifice of flux.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a balance sensation sensor for measuring the direction and magnitude of acceleration, the inclination and the magnitude thereof.

[0002]

2. Description of the Related Art Balance sensation sensors for measuring the direction and magnitude of acceleration, inclination and magnitude thereof are used in a wide range of industrial fields such as automobiles, trains and transportation robots. Conventionally,
An example of the above-described balance sensation sensor is, for example, Japanese Patent Laid-Open No. Hei 2
No. 138875 publication is known. This invention particularly detects acceleration, and a cylindrical permanent magnet is arranged in the magnetic fluid, and Hall elements are arranged on both sides of an extension line of the arrangement position of the permanent magnet. The permanent magnet moves by receiving a force in the direction opposite to the direction of acceleration, and the position (moving position) of the permanent magnet at this time is detected by the Hall element. That is, when the permanent magnet receives an acceleration and moves for a predetermined distance, a difference occurs in the magnetic force detected by the Hall elements provided on both sides, and the direction and magnitude of the acceleration received is measured by the difference in the output voltage of the Hall element. Is.

Not only the acceleration but also the inclination of an object can be similarly known by measuring the moving position of the permanent magnet in the magnetic fluid.

[0004]

However, in the conventional balanced sensation sensor (acceleration sensor), the permanent magnet moves due to acceleration or inclination, which changes the magnetic force, and this change is detected by the Hall element, which is extremely small. It detects changes in magnetic force. That is, since the permanent magnet and the Hall element are mechanically arranged, the arrangement distance between the permanent magnet and the Hall element is large (for example, on the order of several mm or tens of mm), and the magnetic force detected by the Hall element is It is extremely small. Further, the magnetic sensitivity of the Hall element is not so excellent. Therefore, the conventional acceleration sensor cannot detect a minute acceleration change or a minute inclination change, such as a case where the acceleration changes gently. That is, when the magnetic force detected by the Hall element is small, the output voltage (detection signal) of the Hall element is small and the differentiating circuit does not have sufficient meaning. Accurate acceleration or inclination data can be obtained by differentiating the detected voltage of the Hall element. I can't get it.

Further, in the conventional acceleration sensor, since the cylindrical permanent magnet is used as described above, it is possible to detect only one direction (uniaxial direction), and in order to detect the acceleration in all directions, the above-mentioned permanent magnet is used. It is necessary to arrange a large number of combinations.

This also applies to, for example, an acceleration sensor in which a strain gauge is formed on the surface of a sensing lever, and in this case, only acceleration in the direction perpendicular to the strain gauge (direction perpendicular to the sensing lever) can be detected. Therefore, also in this case, in order to detect the acceleration in any direction, it is necessary to combine a large number of the above-mentioned sensing levers.

The present invention has been made in view of the above problems, and by forming an equilibrium sensor as an IC chip, it is possible to accurately measure the magnitude and direction of acceleration and inclination. It is intended to provide a sensor.

[0008]

A magnetic fluid is accommodated in a recess formed in a silicon wafer, and bubbles or ferromagnetic particles having a magnetic permeability different from that of the magnetic fluid and movable in the magnetic fluid are moved. The movable body is housed in the recess as a body so that the movable body can move in the magnetic fluid in response to changes in acceleration and the like. Then, a plurality of magnetoresistive elements are formed on the silicon wafer through an insulating film such as an oxide film, and the plurality of magnetoresistive elements are connected to form a resistance bridge circuit by, for example, a connecting portion, and acceleration etc. The position of the moving body that changes due to is detected by the magnetoresistive element as a change in the magnetic field that changes due to the movement of the moving body.

[0009]

In the present invention, a concave portion is formed in a silicon wafer forming an IC chip, and a magnetic fluid and a moving body such as a bubble or a ferromagnetic material having a magnetic permeability different from that of the magnetic fluid are accommodated in the concave portion. The moving body moves in the magnetic fluid due to the application of acceleration or the like, and the magnetic field of the magnetic fluid that changes due to this movement is detected by the magnetic resistance element arranged via the insulating film,
The direction and magnitude of acceleration and the like are detected. By forming the balanced sensor of the present invention as an IC chip, the distance between the moving body and the magnetoresistive element can be made extremely small, and the decrease in magnetic flux is extremely small, so that even a gentle acceleration or inclination can be accurately detected. be able to.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of the balance sensation sensor of this embodiment. In the figure, the balance sensor 1
Has an oxide film (SiO ₂ ) 3 formed on a silicon wafer 2 by heating in an oxidizing atmosphere, and nickel (Ni), cobalt (Co), iron (Fe), etc. on the oxide film (SiO ₂ ) 3 The ferromagnetic thin film 4 is formed. The ferromagnetic thin film 4 is formed by a sputtering method or a vacuum deposition method, and has a thickness of about 300.
It is formed to ~ 1000Å. As shown in the figure, a part of the ferromagnetic thin film 4 constitutes a magnetoresistive element 5 described later. On the ferromagnetic thin film 4 (excluding the portion of the magnetoresistive element 5), aluminum-silicon (Al
-Si) or aluminum (Al) 6 is formed, and a protective film 7 is further formed on the magnetoresistive element 5 and the aluminum-silicon (Al-Si) or aluminum (Al) 6. Contact holes 7a and 7b are formed in a portion of the protective film 7 on the aluminum-silicon (Al-Si) or the aluminum (Al) 6.

On the other hand, on the back surface of the silicon wafer 2,
A recess 8'for enclosing the magnetic fluid 8 is formed.
The recess 8 ′ is formed by performing wet etching on the back surface of the silicon wafer 2. At this time, by using the plane orientation of the single crystal semiconductor having the mirror index of (1, 0, 0) as the silicon wafer 2 of the present embodiment, the lower surface direction (the upper surface in FIG. Direction) is fast,
A good bowl-shaped recess 8'can be formed. The magnetic fluid 8 and the bubbles 9 are stored in the recess 8 ', and the lower surface is sealed with the glass substrate 10 by so-called anodic bonding. The magnetic fluid 8 is made of a ferromagnetic material such as magnetite.
It is a colloidal solution processed into a fine powder of about 0Å and constitutes a part of the magnetic circuit. If the size of the bubble 9 enclosed in the recess 8'is too small, the bubble 9 is difficult to move in the magnetic fluid 8 due to the surface tension and the like.

A magnet (not shown) is provided on the lower surface of the glass substrate 10 to apply a magnetic force to the magnetic fluid 8 and the like. Further, the moving body enclosed together with the magnetic fluid 8 is not necessarily the bubble 9 as described later.

Although not shown in the above structure, the ferromagnetic thin film 4 and the magnetoresistive element 5 are connected. Then, contact holes 7a, 7b are formed by gold wires (not shown).
Wire-bonded via the magnetic resistance element 5 to form a resistance bridge circuit described later.

In the balance sensation sensor 1 of this embodiment, an oxide film 3 is formed between the magnetic resistance element 5 and the bubble 9 as shown in FIG. L is formed to be 50 μm or less. Therefore, the gap between the magnetoresistive element 5 and the bubble 9 is extremely narrow, and there is almost no loss of magnetic force.

FIG. 2 is a plan view of the balance sensation sensor 1 having the above-mentioned structure (note that the above-mentioned FIG. 1 is a sectional view taken along the line AA of FIG. 2, and the protective film 7 is omitted in FIG. 2). Shown).
As shown in FIG. 2, the above-mentioned magnetic resistance elements 5 are specifically formed in four pieces, and the four magnetic resistance elements 5a to 5d are bubbles 9.
Are formed at equal intervals around the center. That is, the bubbles 9
It is formed on an extension line in the XY direction that is orthogonal to each other with respect to the center, and is in a steady state (state without acceleration or inclination)
Are formed equidistant from the position of the bubble 9. However, the magnetic resistance elements 5a to 5d are not necessarily arranged at equal intervals with respect to the bubble 9, and may be provided at predetermined positions with respect to the bubble 9.

Further, FIG. 3 shows the magnetoresistive elements 5a to 5d,
A resistance bridge circuit when connected by a connection line not shown is shown. In the figure, magnetic resistance elements 5a and 5c, 5b and 5d form a series circuit, and magnetic resistance elements 5a and 5c are formed.
The terminal V1 is connected to the connection point of the magnetic resistance elements 5b and 5
The terminal V2 is connected to the connection point of d. This terminal V1
And V2 are connected to, for example, the CPU (central processing unit) of the device in which the equilibrium sensor 1 of the present embodiment is arranged, and terminals V
This is a configuration capable of detecting the voltage values of 1 and V2. Further, the other ends of the magnetic resistance elements 5a and 5b are connected to a power source and supplied with a power supply voltage V, and the other ends of the magnetic resistance elements 5c and 5d are grounded.

Next, the balance sensation sensor 1 having the above structure is
A case where the device is attached to a device and the acceleration is measured will be described. When no acceleration is applied and the device is arranged in a horizontal position, the bubble 9 in the equilibrium sensor 1 is located at the center position (steady position) of the magnetic fluid 8. But,
When acceleration is applied by moving the device, the bubbles 9 existing at the steady position move in the direction opposite to the acceleration direction. For example, as shown in (a) of FIG. 4, when an acceleration is applied in the direction of arrow X, the bubble 9 located at the center of the magnetic fluid 8 moves in the direction opposite to the direction of acceleration (direction of arrow X '), and the magnetic resistance is increased. Approach the element 5b. The moving distance P is proportional to the magnitude of the acceleration applied to the balance sensation sensor 1 (device), and the magnetic flux passing through the magnetoresistive element 5b decreases in proportion to the magnitude of the acceleration. Therefore, the resistance value of the magnetic resistance element 5b decreases (for example, -ΔR), and the potential of the terminal V2 increases as shown in (b) of the same figure. The voltage rise at this terminal V2 is
As the acceleration applied to the equilibrium sensor 1 increases, the resistance value of the magnetic resistance 5b decreases and the voltage of the terminal V2 increases because the bubble 9 approaches the magnetic resistance 5b.

On the other hand, contrary to the above, when the acceleration is applied in the direction of the arrow X'as shown in FIG. 5A, the bubble 9 moves in the direction opposite to the direction of the acceleration (direction of the arrow X). And
The moving distance P ′ is also proportional to the magnitude of the acceleration, the magnetic flux passing through the magnetic resistance element 5d decreases, and the magnetic resistance element 5c
Resistance value becomes small ((b) of FIG. 5, -ΔR). Therefore, the voltage at the terminal V1 decreases, and as the acceleration applied to the equilibrium sensation sensor 1 increases, the bubble 9 approaches the magnetoresistive element 5c, and the voltage decrease at the terminal V1 increases.

The same applies to the case where acceleration is applied in the arrow Y direction or the arrow Y'direction as shown in FIG. 6 (a). Since the magnetic resistance element 5d moves in the direction, the resistance value of the magnetoresistive element 5d decreases by ΔR, and the voltage of the terminal V2 decreases. On the contrary, when the acceleration is applied in the direction of the arrow Y, the bubble 9 moves in the direction of the arrow Y ', so that the resistance value of the magnetic resistance 5a is decreased by ΔR and the voltage of the terminal V1 is increased.

Therefore, as shown in FIG. 4, when the potential of the terminal V2 is high, acceleration is exerted in the direction of arrow X, and when the potential of the terminal V1 is low, acceleration is exerted in the direction of arrow X'as shown in FIG. When the voltage of the terminal V2 is low, as shown in arrow Y
It can be seen that acceleration is applied in the direction Y, and when the voltage at the terminal V1 is high as shown in the figure, the acceleration is applied in the direction of the arrow Y '.
That is, the direction of acceleration and its magnitude can be known by outputting the output voltages of the terminals V1 and V2 to a CPU or the like and differentiating the change in the voltage value by a differentiating circuit (not shown). When the voltage to be detected is large, the acceleration in that direction is large, and the magnitude thereof is also the terminal V1 and the terminal V in advance.
The relationship between the voltage value appearing at 2 and the magnitude of acceleration is measured, and the differential value thereof is stored in a memory or the like, so that it can be easily determined.

In this embodiment, four magnetic resistance elements 5a to 5d are arranged to measure the acceleration in four directions. However, eight magnetic resistance elements 5 are arranged around the bubble 9. If so, the detection direction of acceleration is further increased, and so-called resolution can be improved.

Further, in the above-described embodiment, the example in which the balance sensation sensor 1 is applied to the measurement of acceleration has been described, but it goes without saying that it can be applied to the measurement of the inclination of an object. Further, the concave portion formed in the substrate such as the silicon wafer 2 is not limited to the bowl-shaped concave portion, but may be a conical concave portion or the like. In addition, although an example in which a silicon wafer is used as a substrate has been described in the present embodiment, the substrate is not limited to a silicon wafer, and a substrate having a thickness of several tens of μm to
If it is possible to form a recess of several hundred μm or more, metal or resin,
Glass or the like can also be used as the substrate.

Further, although the bubble 9 (air) is contained in the magnetic fluid 8 in this embodiment, it is not limited to the bubble 9 and may be any non-magnetic material. Further, it may be a magnetic substance or a ferromagnetic substance having a magnetic permeability different from that of the magnetic fluid 8, for example. However, in this case, the resistance value of the magnetoresistive elements 5a to 5d is opposite to the above description due to the movement of the ferromagnetic body due to acceleration or the like.

Further, since the balanced sensation sensor 1 of this embodiment can be formed by a normal semiconductor manufacturing process, an amplifier for amplifying an output signal from the sensor can be formed at the same time as the sensor, and an integrated amplifier or the like can be formed. 1 including the circuit
Chips are possible.

[0025]

As described in detail above, according to the present invention, since the equilibrium sensor is formed on the IC chip, the gap between the magnetoresistive element and the bubble or the ferromagnetic material for detecting the acceleration and the inclination is detected. It can be formed in the order of several tens of μm, and the strength of the magnetic field that decreases in inverse proportion to the square of the distance can be detected by the magnetoresistive element without being decreased. Therefore, it is possible to accurately measure even the gradually changing acceleration and the inclination of the object.

Further, a large number of magnetoresistive elements can be easily formed on the oxide film by the manufacturing process of the semiconductor (IC chip), and a balance sensation sensor capable of detecting acceleration in all directions can be easily produced.

Further, since the balance sensation sensor 1 of this embodiment can be manufactured by a normal semiconductor manufacturing process, it becomes possible to manufacture a one-chip IC including an integrated circuit such as an amplifier in the balance sensation sensor.

[Brief description of drawings]

FIG. 1 is a sectional view of a balance sensation sensor according to an embodiment.

FIG. 2 is a plan view of the balance sensation sensor according to the embodiment.

FIG. 3 is a circuit block diagram of a magnetic resistance element.

4A is a configuration diagram illustrating a state of a balance sensation sensor when an acceleration is applied in an arrow X direction, and FIG. 4B is a circuit state of a magnetoresistive element when an acceleration is applied in an arrow X direction. It is a figure explaining.

5A is a configuration diagram illustrating a state of a balance sensation sensor when an acceleration is applied in an arrow X ′ direction, and FIG. 5B is a circuit of a magnetoresistive element when an acceleration is applied in an arrow X ′ direction. It is a figure explaining a state.

FIG. 6A is a configuration diagram illustrating a state of the balance sensation sensor when an acceleration is applied in the arrow Y or Y ′ direction, and FIG.
FIG. 6 is a diagram illustrating a circuit state of a magnetoresistive element when an acceleration is applied in the direction of arrow Y or Y ′.

[Explanation of symbols]

1 Balance sensor 2 Silicon wafer 3 Oxide film (SiO ₂ ) 4 Ferromagnetic thin film 5 Magnetoresistive element 5a to 5d Magnetoresistive element 6 Aluminum-silicon (Al-Si) or Aluminum (Al) 7 Protective film 8 Magnetic fluid 8'Concave 9 Bubble 10 Glass substrate

Claims (2)

[Claims] 1. A magnetic fluid housed in a recess formed in a base body, a movable body having a magnetic permeability different from that of the magnetic fluid and movable in the magnetic fluid, and an insulating film with respect to the base body. A plurality of magnetic resistance elements formed, and a connecting portion for connecting the plurality of magnetic resistance elements, wherein the magnetic resistance element is formed at a predetermined position with respect to a stationary position of the moving body. Balance sensor that is characterized by. 2. The equilibrium sensor according to claim 1, wherein the substrate is a silicon wafer.