JPH07306222A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To detect a capacitance variation signal of a capacitive acceleration sensor highly accurately while reducing the scale of electromagnetic shield and suppressing the effect of disturbance. CONSTITUTION:An acceleration detecting element 2 comprises a movable electrode 6 displaceable depending on the acceleration, and fixed electrodes 7, 8 disposed oppositely to both sides of the movable electrode respectively 6. An electronic element 2 comprises a capacitance detecting part, etc. Electromagnetic shields 20, 21 are laminated on the insulating members 10, 11 of the detecting element 2. A ground conductor pattern 31 is formed on a substrate 32 while covering the detecting element 2 and the IC 50 on the rear side thereof and bonded to the electromagnetic shield 21 through a conductive adhesive 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor for converting a physical quantity displaced according to an acceleration into an electric quantity to detect the acceleration, and more particularly to a capacitance type acceleration sensor.

[0002]

2. Description of the Related Art Conventionally, various acceleration sensors have been known which detect an acceleration by converting a physical displacement amount corresponding to the acceleration into an electric signal. For example, JP-A-63-21287
In the acceleration sensor described in Japanese Patent Application Laid-Open No. 3-6461 and Japanese Patent Application Laid-Open No. 3-6461, an electric signal is taken out by displacing a piezoelectric element according to acceleration, and in Japanese Patent Application Laid-Open Nos. 1-253657 and 4-152269, The acceleration is detected by extracting the change in the electrostatic capacitance between the movable electrode and the fixed electrode, which are displaced according to the acceleration, as an electric signal. In addition, there is also a strain gauge type.

These sensors need to be electromagnetically shielded to prevent disturbance noise. For example, (a)
In the acceleration sensor disclosed in Japanese Patent Laid-Open No. 3-6461,
The entire package case that houses the acceleration detecting element (piezoelectric element) and its circuit board is covered with a conductive member to provide an electromagnetic shield effect. (B) In the acceleration sensor disclosed in Japanese Patent Laid-Open No. 63-212873, the acceleration sensor is grounded. The conductive elastic body (package case) covers the piezoelectric element to provide an electromagnetic shield effect. (C) In the acceleration sensor disclosed in Japanese Patent Laid-Open No. 4-152269, a capacitance type acceleration detection element is made of metal. The electromagnetic shielding effect was given by covering with the package case (can package).

[0004]

By the way, of the above-mentioned electromagnetic shield systems, the system (a) has a large scale of the electromagnetic shield.

The method (b) can reduce the size of the package case as compared with the method (a), but still the entire acceleration detecting element must be wrapped in the electromagnetically shielded package case. It is costly and requires time and effort to pack the acceleration detecting element in the case.

Also, in the method (c), the acceleration detecting element is electromagnetically shielded by the can package, but the scale of the electromagnetic shield tends to be large, though not so much as in the method (a).

The present invention has been made in view of the above points, and an object thereof is to ensure noise resistance while reducing the scale of the electromagnetic shield, and to accommodate it in a general-purpose plastic package case for mass production at low cost. It is to provide an acceleration sensor having excellent properties.

[0008]

To achieve the above object, the present invention is basically constructed as follows. This will be described with reference to the reference numerals of the embodiment in FIG. 1. The present invention relates to (1) an electrostatic capacitance type acceleration sensor, which is one of the acceleration detection element 2 and its electronic circuit 50 constituting the sensor. The electromagnetic wave detecting portions 2 and 21 are provided on the acceleration detecting element 2 itself so as to form a layer with the insulating members 10 and 11 on which the fixed electrodes 7 and 8 are formed. For example, the insulating member 1 in which the fixed electrodes 7 and 8 of the acceleration detection element 2 are formed.
Electromagnetic shield portions 20 and 21 for preventing disturbance noise are formed on the outer surfaces of the outer surfaces 0 and 11 to cover the outer surfaces.

Here, the acceleration detecting element 2 includes a movable electrode 6 which is displaced according to acceleration, and fixed electrodes 7 and 8 (in other words, the movable electrode 6) which are arranged so as to face both surfaces of the movable electrode 6, respectively. It is an electrostatic capacitance type acceleration detection element having at least one pair of fixed electrodes 7, 8) which are arranged so as to face each other in a state of interposing. Further, the electronic circuit 50 electrically connected to the acceleration detection element 2 is an electronic circuit including a capacitance detection unit or the like that converts a difference ΔC between the electrostatic capacitances C1 and C2 between the fixed electrodes and the movable electrode into an electric signal. Consists of

The electromagnetic shield parts 20 and 21 are
For example, it is proposed that a conductive member is formed on the outer surface of the insulating members 10 and 11 of the acceleration detecting element 2 by vapor deposition, sputtering, plating or the like.

(2) As a mounting structure, the electronic circuit 50 is composed of an IC, and the acceleration detection is performed on the substrate 32 on which the IC 50 and the acceleration detecting element 2 with the electromagnetic shield portions 20 and 21 are mounted. Element 2 and IC50
It is proposed that the conductor pattern 31 is formed so as to cover the surface (the lower surface side in FIG. 1) facing the substrate 32, and the conductor pattern 31 is grounded.

Further, it is proposed that one of the electromagnetic shield portions 20 and 21 formed on the acceleration detecting element 2 facing the substrate 32 is bonded to the conductor pattern 31 via a conductive adhesive 30.

[0013]

According to the configuration (1), the acceleration detecting element 2
When the movable electrode 6 of the
The difference ΔC between the electrostatic capacitance C1 between the fixed electrode 7 and the movable electrode 6 facing one surface and the electrostatic capacitance C2 between the fixed electrode 8 and the movable electrode 6 facing the other surface is converted into an electric signal. To do.

In this case, since the movable electrode side or the fixed electrode side of the acceleration detecting element 2 has a high impedance in terms of a circuit, disturbance noise (high frequency radio wave, dielectric constant of the atmosphere surrounding the detecting element) is likely to be applied. If the noise is Δn even between the fixed electrode 7 and the movable electrode 6 on the one hand and between the fixed electrode 8 and the movable electrode 6 on the other hand, the capacitance difference is Δn.
C = (ΔC1 + Δn) − (ΔC2 + Δn)
Δn are offset.

However, the structure of the actual acceleration detecting element is composed of the conductive paths 33 and 22 from one fixed electrode 7 to the lead wire 80 and the conductive path 23 from the other fixed electrode 8 to the lead wire 82. Since the distance and the mode are different, the influence of noise on the acceleration detecting element is not uniform, and the disturbance noise that cannot be removed even by the differential method by ΔC detection has an influence.

On the other hand, the lead-out wiring 8 of the acceleration detecting element 2
Of 0, 81, and 82, the one with high impedance (the one connected to the input stage of the capacitance detection operational amplifier of the electronic circuit corresponds to this) is easy to get noise, but the wire drawing here is almost The target layout can be achieved, and therefore, the influence of Δn can be made almost uniform if it is limited between these wirings, so that the above cancellation can be achieved, and moreover, after the output stage of the operational amplifier is low impedance (noise). Therefore, the influence of noise is smaller on the electronic circuit 50 side than on the acceleration detecting element 2.

Therefore, according to the capacitance type acceleration sensor, the minimum necessary electromagnetic shield is provided in the acceleration detecting element 2.
In view of the above points, in the present invention, the electromagnetic shield portion 2 is formed so as to form a layer with the insulating members 10 and 11 on which the fixed electrodes 7 and 8 are formed on the acceleration detection element 2 itself.
0 and 21 are provided.

As a result, firstly, the formation area of the electromagnetic shield portion can be greatly reduced as compared with the conventional case where the electromagnetic shield portion is provided in the package case, and the formation area of the electromagnetic shield portion can be reduced. Even if it is reduced, the capacitance change signal according to the acceleration is detected with a small influence of disturbance noise and with high accuracy.

Second, in the process of this type of capacitance type acceleration sensor, a semiconductor wafer (for example, a silicon wafer) is subjected to a fine processing technique such as etching to form a large number of movable electrodes in advance, and this semiconductor wafer is formed. An insulating member (for example, Pyrex glass, a fixed electrode facing each movable electrode is formed into a thin film by vapor deposition or the like on the inner surface of the insulating member) with a layered structure, and serves as the electromagnetic shield. After the member is formed on the insulating member, these layered structures can be divided into individual products for commercialization, which enables mass production by automation.

Third, since the acceleration detecting element itself is provided with an electromagnetic shield portion, the acceleration detecting element together with other sensor parts (for example, an IC which becomes an electronic circuit) is made of a general-purpose plastic (non-conductive) package. It can be stored in a case.

Next, according to the above configuration (2), in addition to the noise resistance of the acceleration detecting element 2 being ensured by the electromagnetic shield portions 20 and 21 provided on the acceleration detecting element 2 itself, the substrate 3
The noise resistance of the detection element 2 is further improved by the grounding conductor pattern 31 provided on the wiring 2, and the electronic circuit (IC) 50 also has noise resistance by the conductor pattern 31, so that the accuracy of the sensor can be further improved.

In this case, if the electromagnetic shield portion 21 of the acceleration detecting element 2 (the electromagnetic shield portion facing the substrate 32) is bonded to the grounded conductor pattern 31 via the conductive adhesive 30, the electromagnetic wave can be easily generated. The shield portion 21 can be connected to the ground potential.

Incidentally, the electromagnetic shield portion 2 in the present invention.
Nos. 0 and 21 can exhibit a proper noise resistance function without being grounded. Further, if at least one of them is connected to the ground potential or a low impedance fixed potential, a further noise resistance function can be exhibited.

[0024]

Embodiments of the present invention will be described with reference to FIGS.

Prior to the description of the embodiments of the present invention, the operating principle of the capacitance type acceleration sensor will be described with reference to FIGS. 6 and 7.
Will be described.

FIG. 6 shows a detection circuit (electronic circuit) of the capacitance type acceleration sensor to which the present invention is applied.

The detection circuit of this sensor comprises a signal application section 1, an acceleration detection element 2, a capacitance detection section 3, and an amplification section 4.

The acceleration detecting element 2 includes a movable electrode 6 supported by a silicon beam 5, fixed electrodes 7 and 8 arranged so as to face both surfaces of the movable electrode 6 with a minute gap, and a fixed electrode 7 on the inner surface. Insulation member 1 formed with
0, the insulating member 1 also having the fixed electrode 8 formed on the inner surface
1 is the main element. Of these, the movable electrode 6 and the beam 5 are formed by finely processing the silicon plate 9 by etching or the like, and the spacers 9 (9a, 9b) are also formed. The silicon beam 5 may be composed of either a single beam or a plurality of beams, and the movable electrode 6 provided at the tip of the beam 5 has a function of a weight that is displaced according to acceleration.

On the other hand, the pair of fixed electrodes 7 and 8 facing the movable electrode 6 are made of a metal material such as aluminum, and each is a glass plate (Pyrex glass) 1 which is an insulating member.
0 and 11 are formed by vapor deposition or other appropriate method.

When manufacturing the acceleration detecting element 2, the fixed electrodes 7 and 8 and the movable electrode 6 provided on the glass plates 10 and 11 are used.
And the glass plates 10 and 11 with the spacer 9
The glass plates 10 and 11 and the spacers 9a and 9b are anodic-bonded in parallel with each other via a and 9b.

In this way, the glass plate (insulating member) 1
The acceleration detecting element 2 having a three-layer structure in which the silicon plate 9 with the movable electrode 6 is interposed between 0 and 11 is formed. An initial gap d ₀ (about several μm) is secured between the movable electrode 6 and each fixed electrode 7, 8.

The movable electrode 6 is displaced by receiving an inertial force due to the acceleration to be detected. When the movable electrode 6 is displaced, the electrostatic capacitance C1 between the movable electrode 6 and the fixed electrode 7 and the electrostatic capacitance C2 between the movable electrode 6 and the fixed electrode 8 change.

The capacitance detecting section 3 detects the difference ΔC between C1 and C2 by the rectangular wave AC voltage generated by the signal applying section 1, converts it into a voltage, and outputs it.

After the acceleration signal is converted into the voltage signal Vo by the capacitance detection unit 3, it is amplified and adjusted to a predetermined voltage value by the amplification unit 4, and a linear output voltage Vout proportional to the acceleration can be obtained. .

With such a structure, the acceleration can be detected with relatively high accuracy without using electrostatic servo control as the capacitance detection circuit of the capacitance type acceleration sensor.

FIG. 7 shows a signal applying section 1, an acceleration detecting element 2,
An embodiment of a circuit block diagram showing the capacitance detection unit 3 is shown.

The signal applying section 1 is composed of an oscillator 70 and an inverter 71. In addition, the capacitance detection unit 3 is
It is composed of an operational amplifier 72, a constant voltage 73, a capacitor 74, a switch 75, and a capacitor 76.

When the rectangular wave AC voltage Vs1 rises (Vs2 falls) by the signal applying section 1, the capacitor C1 (where the capacitance between one fixed electrode 7 and the movable electrode 6 is equivalently a capacitor) is generated. The capacitor C2 is charged and the capacitor C2 (the capacitance between the other fixed electrode 8 and the movable electrode 6 is equivalently a capacitor) is discharged. At this time, C1
To Cf (capacitance of the capacitor 74) (the charge seems to move due to the current flowing at the time of charging / discharging), and the charge Q2 moving from C2 to Cf are expressed by equations (1) and (2) It is represented by.

[0039]

## EQU1 ## Q1 = C1.Vs (1) Q2 = -C2.Vs (2) where Vs is the voltage value (peak value) of the AC voltages Vs1 and Vs2.

The charge Qf stored in the capacitor Cf is
Since it is the sum of Q1 and Q2, Qf is expressed by equation (3).

[0041]

## EQU00002 ## Qf = Q1 + Q2 = (C1-C2) Vs (3) Further, the voltage V across the capacitor Cf is expressed by the equation (4).

[0042]

## EQU3 ## V = Qf / Cf = (C1-C2) Vs / Cf (4) Since the output Vo of the operational amplifier 72 is a voltage opposite to the voltage V across the capacitor 74, the Vo is expressed by the equation (5). expressed.

[0043]

## EQU00004 ## Vo =-(C1-C2) Vs / Cf + V.alpha. (5) The switch 75 is closed almost in synchronization with the rise of the voltage Vs1, and the voltage Vo is sampled and held by the capacitor 76 and input to the amplifier 14.

In the case of the circuit of this embodiment, an oscillator 70 and an inverter 71 for generating a pulsed voltage are connected to the fixed electrodes 7 and 8 side. That is, the fixed electrode side has a low impedance circuit configuration.

On the other hand, since the movable electrode 6 side is connected to the input stage of the operational amplifier 72 which is a capacitance detector, the circuit has a high impedance. Therefore, the movable electrode 6 is a high-impedance electric wire and is easily affected by disturbance noise such as high-frequency radio waves.

Therefore, an electromagnetic shield is required to protect the movable electrode 6 from disturbance noise.

An acceleration sensor according to the first embodiment of the present invention will be described with reference to FIGS. 1, 2 and 3.

FIG. 1 is a cross-sectional view of an essential part of a capacitance type acceleration sensor according to the first embodiment, FIG. 2 is a schematic view showing only an acceleration detecting element among them, and FIG. 3 is a mounting view of this embodiment. FIG. 8 is a partially cutaway plan view showing a state, in which the same reference numerals as those used in FIGS. 6 and 7 described above indicate the same or common elements.

As shown in FIGS. 1 and 2, in this embodiment, a glass plate (insulating member) on which fixed electrodes 7 and 8 are formed with a silicon plate (silicon layer) 9 having a movable electrode 6 interposed therebetween. ) A detection element 2 of the acceleration sensor is composed of a laminated body in which 10 and 11 are arranged vertically, and this point is the same as that of FIG. The fixed electrodes 7 and 8 are electrically insulated from the silicon plate 9 via an insulating seal 34.

An electronic circuit including circuit elements other than the acceleration detecting element 2, that is, the signal applying section 1, the capacitance detecting section 3, and the amplifying section 4 in FIG. 6 are formed by an IC 50. The acceleration detecting element 2 and the IC 50 are mounted on the substrate 32, and these elements 2 and 3 are connected to the wirings 80, 81 and 8 for drawing.
It is electrically connected via 2. Here, the fixed electrode 7 is provided on the glass plate 10 and the through hole 3 with a conductive film is provided.
3, connected to the lead-out wiring 80 via a conductive path formed of a conductor pattern 22 provided on the outer surface of the glass plate 10 (this conductor pattern 22 is formed in a state of being insulated from an electromagnetic shield portion 20 described later), The fixed electrode 8 is connected to the lead-out wiring 82 via a conductive path formed of a conductor pattern 23 provided on the glass plate 11. Further, the movable electrode 6 is connected to the extraction wiring 81 via the silicon plate 9 itself.

In this embodiment, the acceleration detecting element 2 itself is
Glass plates 10, 11 on which the fixed electrodes 7, 8 are formed
The electromagnetic shield portions 20 and 21 are provided so as to form a layer. Here, the electromagnetic shields 20 and 21 are provided on the outer surfaces of the glass plates 10 and 11 so as to cover the outer surfaces.

The electromagnetic shield parts 20 and 21 are made of a conductive metal such as aluminum or nickel.
A film is formed on the outer surface (the surface opposite to the surface on which the fixed electrodes 7 and 8 are formed) of the glass plates 10 and 11 by sputtering, vapor deposition, plating or the like.

The acceleration detecting element 2 and the IC 50 are mounted on a substrate 32, respectively, and a conductor pattern 31 such as silver-palladium is printed on the substrate 32, and the conductor pattern 31 is provided on the lower side of the acceleration detecting element 2. The electromagnetic shield portion 21 (on the side facing the substrate 32) and the lower surface of the IC 50 are adhered via a conductive adhesive 30 so as to be electrically connected. The conductive adhesive 30 is made of, for example, silicon or epoxy mixed with a conductive filler such as carbon or silver. In addition, the conductor pattern 31 includes the acceleration detection element 2 and I
The lower surface of C50 (the surface facing the substrate 32) is covered so as to be connected to ground or a ground potential (a low-impedance fixed potential) such as a power supply.

According to such an electromagnetic shield structure, the movable electrode 6 for detecting the electrostatic capacitance, the silicon plate 9 serving as the wiring thereof, and the fixed electrodes 7 and 8 are the electromagnetic shield portion 2.
It is shielded from the surroundings by 0,21. for that reason,
It is possible to reduce the influence of disturbance noises (such as high frequency radio waves and changes in the dielectric constant of the surrounding atmosphere) from around the acceleration detection element. Further, the fluctuation of the stray capacitance of the acceleration detection element 2 can be reduced, and the acceleration detection accuracy can be improved.

In this embodiment, as the acceleration detecting element 2, a capacitance type of ΔC differential system is used.
Disturbance noise is ΔC = (ΔC1 + Δn) − (ΔC2 if the influence exerted between one fixed electrode 7 / movable electrode 6 and between the other fixed electrode 8 / movable electrode 6 is Δn.
It is approximated by + Δn), and Δn is canceled out, so that there is almost no influence of noise.

However, the structure of the actual acceleration detecting element is, as shown in FIG. 1, conductive paths 22 and 33 from one fixed electrode 7 to the lead wire 80 and the other lead electrode 82 to the lead wire 80. Since the distance and the form of the conductive path 23 up to are different, the influence of noise on the acceleration detection element becomes uneven, and the disturbance noise that cannot be removed even by the differential method by ΔC detection affects. In this embodiment,
The influence of such disturbance noise can be prevented.

Of the lead wires 80, 81, 82 to the electrostatic capacitance detector of the electronic circuit 50 (this capacitance detector produces the ΔC signal), the lead wire 80 on the movable electrode 6 side is also an operational amplifier. Since it is connected to the input stage of, the impedance is high and noise is apt to ride, but the wirings 80 and 82 of each fixed electrode here can be arranged almost symmetrically with respect to the movable electrode wiring 81. As long as it is between the lead wires, C1 and C
Since the influence of Δn of 2 can be made almost uniform, the above cancellation can be established, and furthermore, the impedance after the output stage of the operational amplifier is low (noise is hard to ride), so the influence of noise is small on the electronic circuit side. .

Therefore, according to the present embodiment, (1) it is sufficient to provide the minimum necessary electromagnetic shield on the acceleration detecting element 2 side, and it is possible to significantly reduce the formation region of the electromagnetic shield portion.

Further, the following effects are obtained.

(2) Since the electrostatic shield portions 20 and 21 are provided so as to cover not only the movable electrode 6 but also the fixed electrodes 7 and 8, in the case of a circuit configuration other than that shown in FIG. The same effect is obtained even in the case of a circuit configuration in which the electrode side is a high impedance circuit.

(3) In the process of the electrostatic capacitance type acceleration sensor, a semiconductor wafer (for example, a silicon wafer) is subjected to a fine processing technique such as etching to form a large number of movable electrodes 6 in advance, and the semiconductor wafer is interposed therebetween. Insulating member (for example, Pyrex glass, on the inner surface of which individual movable electrodes 6
Fixed electrodes 7 and 8 facing each other are formed into a thin film by vapor deposition or the like), and the electromagnetic shield portions 20 and 2 are joined together in a layered structure.
After forming a conductive member to be 1 on the insulating member by sputtering, plating, vapor deposition, etc., it is possible to divide these layered structures into individual ones and commercialize them, enabling mass production by automation, The cost of this kind of acceleration sensor can be reduced.

(4) Further, since the acceleration detecting element 2 itself is provided with the electromagnetic shield portions 20 and 21, the acceleration detecting element is replaced by another sensor component (for example, an electronic circuit board) 5.
It can be accommodated in a general-purpose plastic (non-conductive) package case together with 0, and the cost can be further reduced.

(5) The lower electromagnetic shield portion 21 can be easily connected to the ground potential or a ground potential (low impedance potential) such as a power source via the conductive adhesive 30 and the conductor pattern 31. The electromagnetic shield parts 20, 2
Even if one of the shield portions 21 of 1 is connected to the ground potential, noise resistance can be sufficiently achieved.

(6) Since the lower surface of the IC 50 is covered with the ground conductor pattern 31 in addition to the shield of the acceleration detecting element 2, the noise resistance of the IC 50 can be improved.

FIG. 3 shows the mounting structure of the capacitance type acceleration sensor in this embodiment.

In FIG. 3, an acceleration detecting element 2, an IC 50 in which a capacitance detecting section is integrated, a passive component 51 such as a capacitor,
Aluminum pads 52 for wiring connection are mounted on the substrate 32. The substrate 32 is mounted in a package case 54 made of plastic (may be metal) or the like. Package case 5
Reference numeral 4 is composed of a case body 54A for accommodating the substrate 32 and a cap 57. The wiring from the substrate 32 to the outside is connected to the terminal 55 from the pad 52 via the aluminum wire 55. A cap 57 is attached to the case 54. Between IC50 and substrate 32, and between IC50 and detection element 2
The spaces are electrically connected by an electric wire 53 such as a gold wire or an aluminum wire.

A conductor pattern 31 is printed on the lower side of the acceleration detecting element 2 and the IC 50 (the area of the conductor pattern is hatched in the figure for convenience), and is connected to the ground potential.

With such a structure, the IC
Since the lower side of 50 is also covered with the electrostatic shield (guard electrode) at the same time, it has a great effect on the disturbance noise.

Further, since the conductor pattern 31 is provided, it can be used as a pattern when applying an adhesive for bonding the acceleration detecting element 2 and the IC 50, as well as a pattern for position recognition and positioning for mounting. The effect is that it can also be used as a pattern.

The electromagnetic shield parts 20 and 21 need not be made of any material other than those described above as long as they can be used as conductors. For example, a conductive paste containing a conductive filler may be dispensed by a dispenser or printing. It may be applied, or it may be formed by bonding semiconductors such as silicon doped with impurities by anodic bonding, and further, the electromagnetic shield part may be composed of a film-shaped or plate-shaped conductive member.

FIG. 4 is a sectional view of the essential parts according to the second embodiment of the present invention.

In this embodiment, in addition to the structure of the first embodiment,
The electromagnetic shield 20 on the side (upper side) away from the substrate 32 is connected to an electric wire 40 such as a gold wire or an aluminum wire and a pad 4 for bonding.
1 to the ground conductor pattern 31 on the substrate side.

With such a structure, the upper and lower electromagnetic shield portions 20 and 21 can be easily connected to the ground potential by using the upper and lower electromagnetic shield portions 20 and 21 as guard electrodes, so that the structure can be made very unlikely to be affected by disturbance noise.

FIG. 5 is a cross-sectional view of essential parts according to the third embodiment of the present invention.

In addition to the structure of the first embodiment, this embodiment
The electromagnetic shield portion 21 of the acceleration detecting element 2 and the conductor pattern 31 on the substrate 32 are bonded with conductive adhesives 30a and 30b with a conductive spacer member 60 interposed therebetween.

The spacer 60 is made of metal such as iron or copper,
For example, silicon doped with impurities is used. This is used not only as a grounding wiring for the guard electrode (electromagnetic shield) 21 but also as a spacer for buffering stress.

With such a structure, it is possible to make the structure less susceptible to the influence of disturbance noise, and to reduce the influence of the stress due to the difference in thermal expansion between the detection element and the substrate and the influence of the stress from the package. is there.

[0078]

According to the present invention, the influence of external disturbances (high-frequency radio waves, changes in the dielectric constant of the surrounding atmosphere, etc.) from the outside of the package or around the acceleration detecting element is reduced while reducing the scale of electromagnetic shielding. Therefore, the acceleration can be detected with high accuracy. Further, it is possible to reduce the fluctuation of the stray capacitance of the acceleration detection element.

Moreover, the mass production is excellent, the plastic package can be formed, and the cost of this kind of acceleration sensor can be reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an acceleration sensor according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of an acceleration detection element used in the first embodiment.

FIG. 3 is a partially open plan view showing a mounting state of the acceleration sensor of the first embodiment.

FIG. 4 is a sectional view of an essential part of an acceleration sensor according to a second embodiment of the present invention.

FIG. 5 is a sectional view of an essential part of an acceleration sensor according to a third embodiment of the invention.

FIG. 6 is an explanatory diagram showing the operating principle of the capacitance type acceleration sensor.

FIG. 7 is a circuit block diagram of a capacitance type acceleration sensor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Signal application part, 2 ... Acceleration detection element, 3 ... Capacitance detection part, 4 ... Amplification part, 5 ... Beam (silicon beam), 6 ... Movable electrode, 7, 8 ... Fixed electrode, 9 ... Silicon plate, 9a, 9b
... Spacers, 10, 11 ... Glass plates (insulating members), 2
0, 21 ... Electromagnetic shield part, 30 ... Conductive adhesive, 31
... conductor pattern, 32 ... substrate, 50 ... IC (electronic circuit), 54 ... package case, 54A ... case body,
57 ... Cap.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masahiro Matsumoto Inventor Masahiro Matsumoto 7-1-1, Omika-cho, Hitachi City, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Masayoshi Suzuki Katsuta City, Ibaraki 2520 Takaba Address, Hitachi, Ltd. Automotive Equipment Division (72) Inventor Norio Ichikawa, Takada, Katsuta, Ibaraki Prefecture, Takaba 2477 Kashima Yatsu 3 Hitachi Automotive Engineering, Ltd. (72) Yukiko Sugisawa, Katsuta, Ibaraki, Ibaraki Kashima Yatsu 2477 3 Hitachi Automotive Engineering Co., Ltd. (72) Inventor Junichi Horie 2520 Takaba, Katsuta City, Ibaraki Pref., Hitachi, Ltd. Automotive Equipment Division (72) Yuji Ogasawara Katsuta Ibaraki, Ibaraki 2477 Kashima Yatsu 3 Hitachi Automotie Engineering the Corporation

Claims (8)

[Claims] 1. An electrostatic capacitance type acceleration detecting element having a movable electrode which is displaced according to acceleration and fixed electrodes which are arranged so as to face both surfaces of the movable electrode, and electrically connected to the acceleration detecting element. And an electronic circuit for converting the electrostatic capacitance difference between the fixed electrodes and the movable electrodes into an electric signal, of which the acceleration detection element itself forms a layer with the insulating member on which the fixed electrode is formed. An acceleration sensor characterized in that an electromagnetic shield is provided as described above. 2. The acceleration sensor according to claim 1, wherein the acceleration detecting element with the electromagnetic shield part and the electronic circuit are housed in a plastic package case while being mounted on a substrate. 3. The electronic circuit is composed of an IC, and a surface of the acceleration detection element and the IC facing the substrate is covered on a substrate on which the IC and the acceleration detection element with the electromagnetic shield part are mounted. 3. The acceleration sensor according to claim 1, wherein the conductor pattern is formed and the conductor pattern is grounded. 4. A movable electrode that is displaced according to acceleration, and at least one pair of fixed electrodes that are arranged to face each other with the movable electrode interposed therebetween. In an electrostatic capacitance type acceleration sensor that detects acceleration by detecting the change in electrostatic capacitance of a fixed electrode, an electromagnetic shield part for preventing disturbance noise that covers the outer surface of an insulating member formed with the fixed electrode. An acceleration sensor comprising: 5. The acceleration according to claim 1, wherein the electromagnetic shield part is formed on the outer surface of the insulating member by any one of vapor deposition, sputtering, and plating. Sensor. 6. The acceleration sensor according to claim 1, wherein the electromagnetic shield part is connected to a ground potential or a fixed potential having a low impedance. 7. An acceleration detecting element formed by integrating the movable electrode, the fixed electrode, and an insulating member with an electromagnetic shield part is mounted on a substrate, and a conductor set to a ground potential or a fixed potential on the substrate. 7. A pattern is formed, and one of the electromagnetic shield portions facing the substrate is adhered to the conductor pattern via a conductive adhesive agent. The acceleration sensor according to item 1. 8. The acceleration detecting element is adhered to the conductor pattern on the substrate with the conductive adhesive via a stress relaxation spacer made of a conductive material. 7. The acceleration sensor according to 7.