JP2007127498A - Capacity detection type acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacity detection type acceleration sensor having satisfactory temperature characteristics by enhancing the internal impedance of dielectric liquid between electrodes, and by suppressing large changes in the capacitance of a capacitor between the electrodes due to temperature change. <P>SOLUTION: In this capacity detection type acceleration sensor, a moving body 4 is stored movably in a body 1, wherein liquid is enclosed, and an acceleration is detected by measuring a capacitance change between the electrodes caused by a gap change between the opposite electrodes 2a, 2c corresponding to the position of the moving body 4 that moves by receiving acceleration. By covering each surface of the electrodes 2a, 2c with insulating films 8a, 8b, leakage current can be reduced because an equivalent parallel resistance parallel to the capacitance of the dielectric liquid 3 is sufficiently high, and a direct current component, flowing in the equivalent parallel resistance, is cut significantly, and thereby, the temperature characteristic of the capacity detection type acceleration sensor can be improved. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sensor for detecting a capacitance between electrodes, and more particularly, to detect a change in capacitance according to movement of a moving body between electrodes, or to incline a sensor or a detection target attached thereto. It is related with the inclination sensor which detects.

  2. Description of the Related Art Conventionally, a moving body that receives acceleration in a main body in which liquid is enclosed is accommodated, and a capacitance between electrodes that changes due to a change in a gap between opposing electrodes according to the position of the moving body. A detection type acceleration sensor has been proposed. By measuring the changed capacitance, it is possible to detect the acceleration received by the moving body with respect to the main body, that is, the inclination or the fall of the main body.

  A capacitance type tilt sensor in which a dielectric liquid is enclosed in the body has been proposed. This capacitance type tilt sensor has a pair of differential electrodes and a common electrode facing each other in a sealed container, and a change in the liquid level of the dielectric liquid sealed in the sealed container corresponds to the tilt angle. It is a type of tilt sensor that detects as a change in capacitance. In this capacitance type tilt sensor, a pair of semicircular differential electrodes are arranged adjacent to each other in the vertical direction, and a common electrode is provided so as to face both differential electrodes with a certain gap. The pair of differential electrodes and the common electrode are housed in a sealed container, and a dielectric liquid is sealed in the sealed container. The upper and lower differential electrodes and the common electrode constitute upper or lower variable capacitors, respectively. In this type of tilt sensor, a capacitive tilt sensor that does not require temperature compensation or zero point adjustment has been proposed (Patent Document 1).

  The change in capacitance of each variable capacitor is converted into a change in DC voltage. An oscillator is connected to the common electrode plate, and each differential electrode is connected to a respective capacitance / voltage conversion circuit that converts a capacitance change into a DC voltage change. The output signal of each capacitance / voltage conversion circuit is input to a differential amplifier, and a DC signal corresponding to the tilt angle of the sensor appears at the output of the differential amplifier. The zero point adjustment circuit controls one capacitance / voltage conversion circuit so that the output voltage of the differential amplifier becomes 0 V when the sensor is in a horizontal state. The temperature compensation circuit controls the amplification factor of the differential amplifier according to the ambient temperature so that an output corresponding to the tilt angle of the sensor can be obtained regardless of the temperature.

  Further, a capacitance type tilt angle sensor that can be miniaturized while preventing performance degradation has been proposed (Patent Document 2). The tilt angle sensor according to this proposal is based on a liquid capacitive medium, a case that accommodates the capacitive medium, and a portion that is provided opposite to the opposing inner wall surface of the case and is immersed in the capacitive medium. A differential electrode and a common electrode constituting the capacitor are provided. The capacitance medium is configured by mixing fine particles having a dielectric constant higher than that of a liquid base made of an insulator. The tilt angle sensor detects the tilt based on the amount of change in the capacitance of the capacitor that changes according to the tilt of the case.

However, in a sensor filled with a liquid, particularly a dielectric liquid, between the electrodes of the capacitance detection type sensor, an electric current flows between the electrodes, and the impedance fluctuates due to a temperature change. This impedance variation has a problem that it greatly affects the capacitance change of the capacitor.
Japanese Unexamined Patent Publication No. 2000-241162 (paragraphs [0017] to [0023], FIGS. 1 to 5) JP 2005-156532 A (paragraphs [0037] to [0043], FIGS. 1 and 7)

  Therefore, paying attention to the fact that the capacitance change of the capacitor is caused by the leakage current between the electrodes, the impedance between the electrodes is increased in order to suppress the leakage current, and the influence on the capacitance due to the temperature change is mitigated. There is a problem to be solved in terms of points.

  The object of the present invention is to increase the internal impedance of the dielectric liquid between the electrodes, suppress the capacitance of the capacitor between the electrodes from greatly changing due to the temperature change, and improve the temperature characteristics. It is to provide a sensor.

  In order to solve the above-described problems, a capacitance detection type acceleration sensor according to the present invention includes a movable body that is movably accommodated in a main body in which a liquid is sealed, and corresponds to the position of the movable body that moves by receiving acceleration. In the capacitance detection type acceleration sensor that detects the acceleration by measuring the change in capacitance between the electrodes due to the change in the gap between the opposing electrodes, the electrode is covered with an insulating film. Yes.

  According to this capacitance detection type acceleration sensor, a capacitance detection type sensor that measures changes in capacitance between electrodes in a dielectric liquid by attaching an insulating film such as a silicon oxide film or a silicon nitride film to the electrodes. Temperature characteristics are improved. When an insulating film is attached to the electrode, the value of the equivalent parallel resistance parallel to the capacitance of the dielectric liquid can be reduced by selecting a basic material and manufacturing method, but it must be eliminated. I can't. However, since the equivalent circuit resistance of the insulating film is sufficiently large and leakage current can be reduced, the DC component flowing through the equivalent parallel resistance of the dielectric liquid can be substantially cut. Further, the capacitance change due to the temperature change is a phenomenon that occurs because the DC component is changed by the temperature change of the dielectric constant εr of the dielectric liquid and the parallel equivalent resistance that exists in parallel with the capacitance. Therefore, temperature characteristics can be improved by eliminating the DC component flowing through the equivalent parallel resistance.

  In this capacitance detection type acceleration sensor, the liquid may be ethyl alcohol, and the insulating film may be an oxide film.

  Since the capacitance detection type acceleration sensor according to the present invention is configured as described above, the leakage current flowing in the dielectric liquid can be reduced by attaching an insulating film to the electrode placed in the dielectric liquid. it can. As a result, there is an effect of increasing the internal impedance of the dielectric liquid, and the temperature characteristics of the capacitance detection type acceleration sensor can be improved.

  Embodiments of a capacitance detection type acceleration sensor according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a capacitance detection type acceleration sensor in which an electrode is provided in a dielectric liquid, (a) is a cross-sectional view in a plane parallel to the electrode surface, and (b) is a plane in a plane orthogonal to the electrode surface. Sectional drawing (c) is a sectional view similar to (b) showing a steady state in which no acceleration acts on the sensor.

  According to the capacitance detection type acceleration sensor shown in FIG. 1, the capacitance detection type acceleration sensor main body (hereinafter abbreviated as “main body”) 1 includes a main body first layer 1a, a main body second layer 1b, and a main body third layer. It is configured to overlap 1c. As shown in FIG. 1 (a), the main body second layer 1b is formed with a substantially triangular through hole, and the openings on both sides of the through hole are respectively the main body first layer 1a and the main body third layer 1c. Is closely overlapped with the second layer 1b of the main body, so that a sealed cavity 20 is formed.

  The main body 1 is provided with electrodes for detecting capacitance. That is, the electrodes 1a and 2b are provided on the side facing the cavity 20 on the first body layer 1a, and the electrodes 2c are provided on the side facing the cavity 20 on the side facing the cavity 20 to face the electrodes 2a and 2b. It has been. 5a and 5b are signal extraction electrodes which are electrically connected to the electrodes 2a and 2c.

  The cavity 20 in the main body 1 is usually filled with a dielectric liquid 3 so as to fill between the electrodes, and the cavity 20 is also filled with a conductive ball (hereinafter simply referred to as “ball”) 4. ing. In the steady state shown in FIG. 1, the ball 4 is stably positioned at the lowermost corner of the triangle. The electrodes 2a and 2b are arranged on each side of the sensitivity direction when the ball 4 occupying a steady state receives acceleration or gravitational acceleration and moves in the sensitivity direction of the sensor. The gap (interval) between the electrodes 2a and 2b and the electrode 2c is set to d1 as shown in FIG.

  When acceleration or gravitational acceleration is applied in the direction of sensitivity of the sensor, that is, for example, when it rotates 90 degrees counterclockwise in FIG. 1 and falls into the fall state shown in FIG. 2, it is stable that the ball 4 still occupies the lowest position. Therefore, the ball 4 enters between the electrodes 2a and 2c as shown in FIG. As a result, the gap between the electrode 2a and the ball 4 changes to d2, and the gap between the ball 4 and the electrode 2c changes to d3. As a result, the capacitance between the electrodes changes. “D2 + d3” indicates a gap between the electrodes when the ball 4 is present.

  In the capacitance detection type acceleration sensor shown in FIGS. 1 and 2, when the electrodes 2a, 2b, and 2c have no insulating film, the capacitance 6 of the dielectric liquid is compared to the capacitance 6 of the dielectric liquid as shown in the equivalent circuit shown in FIG. Therefore, there is always an equivalent parallel resistance 7 in parallel. On the other hand, in this embodiment, the surfaces of the electrodes 2a and 2b are covered with the insulating film 8a, and the surface of the electrode 2c is covered with the insulating film 8b. FIG. 4 is a cross-sectional view showing a steady state of a capacitance detection type acceleration sensor in which an electrode is covered with an insulating film, and FIG. 5 is a cross-sectional view showing an inclination state thereof, that is, an acceleration detection state. The equivalent parallel resistances 10a and 10b of the insulating films 8a and 8b have such a size as to be in an insulating state. By insulating the electrodes 2a, 2b and the electrode 2c with the insulating films 8a, 8b, an ideal capacitor having a relationship of dielectric constant, area, and distance can be formed.

  The values of the equivalent parallel resistances 10a and 10b of the insulating films 8a and 8b can be reduced by selecting a basic material and a manufacturing method, but cannot be eliminated. However, since the equivalent circuit resistance of the insulating film is sufficiently large and leakage current can be reduced, it can be regarded as the equivalent circuit on the right in FIG. Therefore, when the insulating films 8a and 8b are attached, the direct current component flowing through the equivalent parallel resistance 7 of the dielectric liquid 3 can be substantially cut.

ここで
Ｚ０ 絶縁膜付きコンデンサの内部インピーダンス
Ｒ１，Ｒ３ 絶縁膜の等価並列抵抗
Ｒ２ 誘電性液体の等価並列抵抗
Ｃ１、Ｃ３ 絶縁膜の容量
Ｃ２ 誘電性液体の容量
ω ２πｆ The capacitance change due to the temperature change is a phenomenon that occurs because the DC component is changed by the temperature change of the dielectric constant εr of the dielectric liquid and the parallel equivalent resistance that exists in parallel with the capacitance. Therefore, the temperature resistance can be improved by eliminating the DC component flowing through the equivalent parallel resistance.
The internal impedance in FIG. 6 can be obtained by the equations (1) and (2).

Z0 Internal impedance of capacitor with insulating film R1, R3 Equivalent parallel resistance of insulating film R2 Equivalent parallel resistance of dielectric liquid C1, C3 Capacitance of insulating film C2 Capacitance of dielectric liquid ω 2πf

The capacitance changes due to the temperature change is caused by the equivalent parallel resistance of the DC component. However, in consideration of canceling the influence of the equivalent parallel resistance in the equation (2), the insulating film The internal impedance marked with can be replaced by equation (3).

ここで
ε０ 真空中の誘電率
εｒ 誘電体の非誘電率
Ｓ 電極の面積
ｄ 電極間隔

表１に酸化膜、エチルアルコールによるコンデンサの容量を示す。

式（１）により、合成容量は、１４。４１６（ｐＦ）となる。
図６の容量の関係は、９ａ＝９ｂ＞６となり、９ａ，９ｂは６よりも十分大きな容量のため、９ａ，９ｂの容量は無視することができる。 For example, an insulating film is an oxide film, a dielectric liquid (ethyl alcohol, methyl alcohol, silicone oil, acetone, ethylene glycol, etc.) is ethyl alcohol,
The combined capacity when the thickness of the oxide film is 5000 mm, the area of the electrode is 10 nm2, and the gap of the electrode is 1 mm can be obtained by the equations (4) and (5).

Where ε0 dielectric constant in vacuum εr dielectric non-dielectric constant S electrode area d electrode spacing

Table 1 shows the capacitance of the capacitor using an oxide film and ethyl alcohol.

From the equation (1), the combined capacity is 14.416 (pF).
The relationship between the capacities in FIG. 6 is 9a = 9b> 6. Since 9a and 9b are sufficiently larger than 6, the capacities of 9a and 9b can be ignored.

It is sectional drawing of the capacity | capacitance detection type acceleration sensor which provided the electrode in the dielectric liquid. It is sectional drawing when the capacity | capacitance detection type acceleration sensor shown in FIG. 1 exists in a fall state. It is an equivalent circuit diagram of a capacitance detection type acceleration sensor without an insulating film. It is a figure which shows the steady state of what attached the insulating film to the electrode of the capacity | capacitance detection type acceleration sensor. It is a figure which shows the acceleration detection state of the capacity | capacitance detection type acceleration sensor shown in FIG. It is an equivalent circuit diagram of a dielectric liquid and an insulating film capacitor.

Explanation of symbols

1 Capacitance detection type acceleration sensor main body 1a First layer 1b of capacitance detection type acceleration sensor main body Second layer 1c of capacitance detection type acceleration sensor main body Third layers 2a and 2b of the capacitance detection type acceleration sensor main body are provided on the first layer Electrode 2c Electrode provided in the third layer 3 Dielectric liquid 4 Conductive balls 5a and 5b Electrode 6 Capacitance of dielectric liquid 7 Equivalent parallel resistance 8a and 8b of dielectric liquid Insulating films 9a and 9b Insulating film Capacitances 10a and 10b Equivalent parallel resistance 20 of insulating film Cavity d1 Gap between electrodes d2 when there is no conductive ball d3 Gap between electrode 2a and ball 4 d3 Gap between ball 4 and electrode 2b

Claims (2)

A moving body is movably accommodated in a main body in which a liquid is sealed, and the electrostatic capacitance between the electrodes is changed by changing a gap between opposing electrodes according to the position of the moving body that receives the acceleration and moves. In a capacitance detection type acceleration sensor that detects the acceleration by measuring a change in capacitance,
A capacitance detection type acceleration sensor comprising the electrode covered with an insulating film.   The capacitance detection type acceleration sensor according to claim 1, wherein the liquid is ethyl alcohol and the insulating film is an oxide film.

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