JP2003014777A - Physical quantity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an acceleration sensor for detecting an acceleration based on the variation of distance between a movable electrode and a fixed electrode formed on a substrate in which the temperature characteristics of sensor output is prevented from deteriorating due to thermal stress caused by an electrode pad. SOLUTION: The acceleration sensor comprises a substrate 10, a detecting section comprising a movable electrode 20 formed on the substrate 10 to displace in the Y direction upon application of an acceleration and fixed electrodes 31 and 32 formed on the substrate 10 oppositely to the movable electrode 20, and electrode pads 25a, 31b and 32b formed on the outer circumference of the detecting section on the substrate 10 and connecting the movable electrode 20 and the fixed electrodes 31 and 32 electrically with the outside wherein dummy pads 61-63 are formed on the outer circumference of the detecting section on the substrate 10 and arranged symmetrically to the electrode pads with respect to the center PS of the detecting section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanical quantity sensor for detecting a mechanical quantity such as acceleration or angular velocity based on a change in distance between a movable electrode and a fixed electrode formed on a substrate.

[0002]

2. Description of the Related Art In this type of mechanical quantity sensor, a substrate is provided with a detecting portion composed of a movable electrode which can be displaced in a predetermined direction in response to the application of a mechanical quantity, and a fixed electrode which is arranged facing the movable electrode. However, when the movable electrode is displaced according to the application of the mechanical quantity, the applied mechanical quantity is detected based on the change in the distance between the movable electrode and the fixed electrode.

FIG. 5 is a diagram showing a schematic plan configuration of an acceleration sensor as a conventional general mechanical quantity sensor.
FIG. 6 is a schematic cross-sectional view taken along the line BB in FIG.
This one uses a semiconductor substrate 10 made of a silicon substrate or the like as a substrate forming a sensor. In this semiconductor substrate 10, a first semiconductor layer 11 and a second semiconductor layer 12 are provided with an insulating film 13 interposed therebetween. It is laminated. In FIG. 5, the portion showing the insulating film 13 is hatched for identification.

This sensor can be formed on the semiconductor substrate 10 by using a well-known semiconductor manufacturing technique. By forming the opening portion (rectangular shape in the illustrated example) 14 in the first semiconductor layer 11 and the insulating film 13, a base portion composed of the first semiconductor layer 11 and the insulating film 13 is formed around the opening portion 14. The frame portion 15 is formed, and the second semiconductor layer 12 is supported by the frame portion 15.

By forming a groove in the second semiconductor layer 12, the movable electrode 20 elastically supported by the opposite side of the frame 15 via the beam 22 and the frame 15 are fixed. The fixed electrodes 31 and 32 supported are formed. The movable electrode 20 is composed of a weight portion 21 and a comb-tooth electrode portion 24 protruding on both left and right sides of the weight portion 21. On the other hand, the fixed electrode 3
Reference numerals 1 and 32 have a comb-teeth shape that meshes with and faces the comb-teeth electrode portion 24 of the movable electrode 20.

In this sensor, when acceleration is applied in the Y direction in FIG. 5, the movable electrode 20 is moved by the beam 22.
Is displaced in the Y direction. At this time, the facing distance between the comb-teeth electrode portion 24 of the movable electrode and each of the fixed electrodes 31 and 32 changes.
This distance change is detected by, for example, the capacitance C1 at the detection interval 40 between the comb-teeth electrode portion 24 on the left side of the weight portion 21 and the fixed electrode 31, and the detection of the comb-teeth electrode portion 24 on the right side of the weight portion 21 and the fixed electrode 32. It is detected as a difference (C1-C2) from the capacity C2 at the interval 40. The applied acceleration can be obtained by such differential capacitance detection.

[0007]

By the way, as shown in FIG.
In the acceleration sensor shown in FIG. 6, an electrode pad 25a made of aluminum (Al) or the like for connecting an external circuit or the like to a detection portion (movable electrode, fixed electrode) of the sensor,
31b and 32b are the detection units 20, 3 on the substrate 10.
It is formed on the outer circumference of 1, 32.

However, in the prior art, as shown in FIG. 5, since the electrode pads 25a, 31b, 32b are arranged only at the portions necessary for external connection, these electrode pads are viewed from the whole sensor. Is the detection unit 2
It is asymmetric with respect to 0, 31, and 32.

Further, generally, the substrate is made of a semiconductor such as silicon, and the electrode pad is made of the above-mentioned metal such as Al. Therefore, when the temperature around the sensor changes, thermal stress is applied to the substrate due to the electrode pad that is relatively easily thermally deformed due to a difference in thermal expansion coefficient between the electrode pad and the substrate.

The thermal stress caused by the electrode pad is asymmetric because the arrangement of the electrode pad is asymmetrical and is applied non-uniformly to the detecting portion, so that the movable electrode 20 and the fixed electrodes 31 and 32 in the detecting portion have thermal stress. It is easy to displace in a large direction. Then, due to this displacement, the movable electrode 20 and the fixed electrode 3
1 and 32 (each comb-teeth electrode portion 24 and the fixed electrode 31,
The detection interval 40) with 32 changes.

Since the change in the distance between the electrodes due to such thermal stress changes due to the change in temperature, the temperature characteristics of output characteristics such as detection accuracy and offset output (output when acceleration is 0 G) deteriorates. .

In view of the above problems, it is an object of the present invention to prevent the temperature characteristics of the sensor output from deteriorating due to thermal stress caused by the electrode pads.

[0013]

In order to achieve the above-mentioned object, in the invention described in claim 1, the substrate (10) and a displacement formed in the substrate in a predetermined direction (Y) in response to the application of a mechanical quantity are applied. Possible movable electrodes (20) and fixed electrodes (31, 32) formed on the substrate and arranged to face the movable electrodes.
And a electrode pad (25a, 31b, 32b) formed on the outer periphery of the detection unit on the substrate for electrically connecting the movable electrode and the fixed electrode to the outside, In the mechanical quantity sensor that detects the applied mechanical quantity based on the change of the distance between the movable electrode and the fixed electrode when the movable electrode is displaced, dummy pads (61 to 63 ) Is formed, and the arrangement of the electrode pad and the dummy pad is symmetrical with respect to the center of the detection portion.

According to this, the thermal stress caused by the electrode pad and the dummy pad is generated symmetrically with respect to the detecting portion and is uniformly applied to the detecting portion. Therefore, even if the thermal stress changes due to the temperature change, the displacement of the movable electrode and the fixed electrode of the detection unit due to the thermal stress is suppressed.

Therefore, according to the present invention, it is possible to prevent the temperature characteristic of the sensor output from being deteriorated by the thermal stress caused by the electrode pad.

Further, in the second aspect of the invention, the electrode pads (25a, 31b, 32b) and the dummy pads (61-63) are arranged in a predetermined direction (Y) in which the movable electrode (20) in the detection section is displaced. It is characterized by being arranged along.

The predetermined direction in which the movable electrode is displaced is the direction in which the movable electrode and the fixed electrode of the sensor face each other with a detection interval. Therefore, as in the present invention, if the electrode pad and the dummy pad are symmetrically arranged with respect to the center of the detection unit along the predetermined direction, the change in the detection interval between the movable electrode and the fixed electrode due to the thermal stress, This is preferable because it can be efficiently suppressed.

The electrode pads (25a, 31b, 32)
If the b) and the dummy pads (61 to 63) are made of the same material as in the invention of claim 3 or have the same area as in the invention of claim 4, It is preferable because the thermal stress generated due to each pad can be easily made uniform.

The reference numerals in parentheses for each means described above are examples showing the correspondence with specific means described in the embodiments described later.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention shown in the drawings will be described. In the present embodiment, the present invention is applied to an acceleration sensor as the mechanical quantity sensor of the present invention. This acceleration sensor is, for example, an airbag, A
It can be applied to an acceleration sensor for automobiles for controlling the operation of BS, VSC and the like.

FIG. 1 shows a plan view of the acceleration sensor S1, and FIG. 2 shows a schematic sectional structure taken along the line AA in FIG. Note that, in FIG. 1, a portion showing the insulating film 13 is hatched for identification, but it is not a cross section.

Acceleration sensor (hereinafter simply referred to as sensor)
S1 is formed by subjecting a semiconductor substrate to well-known micromachining. Substrate 1 that constitutes the sensor S1
Reference numeral 0 denotes a semiconductor substrate, and this semiconductor substrate is, as shown in FIG. 2, insulated between a first silicon substrate 11 as a first semiconductor layer and a second silicon substrate 12 as a second semiconductor layer. Rectangular SOI having an oxide film 13 as a layer
A (silicon-on-insulator) substrate 10.

In this SOI substrate 10, the oxide film 13
The first silicon substrate 11 is removed into a rectangular shape by etching or the like to form the opening 14, and thereby a rectangular frame portion (base portion) 15 is formed. Then, on the second silicon substrate 12 supported by the frame portion 15,
By forming the groove, the movable electrode 20 and the fixed electrode 3
1 and 32, the detection part, the beam part 22, and the anchor part 23.
a and 23b are formed.

The movable electrode 20 is arranged so as to traverse over the opening 14 between the opposite side portions of the frame portion 15, and has a flat rectangular weight portion 21 and both left and right sides of the weight portion 21. And a comb-teeth electrode portion 24 that operates.

Both ends of the weight portion 21 are integrally connected to the anchor portions 23a and 23b through the beam portion 22, so that the movable electrode 20 and the beam portion 22 face the opening 14. There is. Each anchor portion 23a and 23b
Are fixedly supported by one side portion 15a of the frame portion 15 and the other side portion 15b opposite to the side portion 15a.
a and 15b, the second silicon substrate 1 around the anchor portion
2 are electrically separated from each other via a groove reaching the oxide film 13.

The beam portion 22 has a rectangular frame shape in which two beams are connected at both ends, and has a spring function of displacing in the direction orthogonal to the longitudinal direction of the beam. Specifically, when the beam portion 22 receives an acceleration including a component in the arrow Y direction in FIG. 1, the movable electrode 20 moves the movable electrode 20 in the Y direction (displacement direction of the movable portion, hereinafter referred to as displacement direction Y). It is designed to be displaced to and restored to its original state when the acceleration disappears.

As described above, the movable electrode 20 is arranged inside the frame portion 15 of the substrate 10 and is elastically supported by the beam portion 22 at the opposing portion of the frame portion 15 to apply acceleration. Accordingly, it can be displaced in the displacement direction Y.

The comb-teeth electrode portion 2 of the movable electrode 20
4 are provided integrally with the weight portion 21 on both the left and right sides of the weight portion 21, and the left and right comb tooth electrode portions 24 are respectively
In the direction orthogonal to the displacement direction Y, they are formed so as to project from the weight portion 21 in mutually opposite directions.

In the illustrated example, the comb-teeth electrode portion 24 is composed of the weight portion 21.
Each of the comb-teeth electrode portions 24 is formed in a beam shape having a rectangular cross-section and faces the opening 14. In this way, the weight 2
The comb-teeth electrode portion 24 formed integrally with 1 can be displaced in the displacement direction Y together with the weight portion 21.

The fixed electrodes 31, 32 are composed of a first fixed electrode 31 located on the left side in FIG. 1 and a second fixed electrode 32 located on the right side, and each fixed electrode 31, 32 has a weight portion. 21 side portions 15c of the frame portion 15 facing each other on the left and right sides of
It is fixedly supported by 5d.

Each of the fixed electrodes 31, 32 has a comb-teeth shape projecting from the frame portion 15 so as to mesh with the comb-teeth gap in each comb-teeth electrode portion 24, and the side portion 15c of the frame portion 15 is formed. , 15d in a state of being fixedly supported in a cantilever manner, facing the opening portion 14.

The supporting portion of each fixed electrode 31, 32 to the frame portion 15 is electrically separated from the second silicon substrate 12 around the supporting portion via a groove reaching the oxide film 13 (see FIG. 2). Thereby, the first fixed electrode 31 and the second fixed electrode 32 are electrically independent from each other.

In the illustrated example, each of the fixed electrodes 31 and 32 (four in the illustrated example) is formed in a beam shape having a rectangular cross section. The side surfaces of the individual electrodes of the fixed electrodes 31 and 32 are arranged in parallel with the side surfaces of the individual comb-teeth electrode portions 24 with a predetermined interval (detection interval) 40 therebetween.

Here, in FIG. 1, on the left side of the weight portion 21, a detection interval 40 is formed between the upper side surface of each comb-teeth electrode portion 24 and the lower side surface of the first fixed electrode 31. On the other hand, on the right side of the weight portion 21, the individual comb-teeth electrode portions 24
A detection interval 40 is formed between the lower side surface of the second fixed electrode 32 and the upper side surface of the second fixed electrode 32.

Further, the movable electrode 20 and each fixed electrode 31,
A plurality of rectangular through holes 50 penetrating from the opening 14 side to the opposite side are formed in 32. The so-called through holes 50 form a so-called ramen structure shape in which a plurality of rectangular frame portions are combined. . As a result, the movable electrode 20 and the fixed electrodes 31, 32 (detection portion) are made lighter and the torsional strength is improved.

Further, the frame portion 15 is a portion located on the outer periphery of the detection portion of the substrate 10, and one side portion of the side portions 15a and 15b facing each other in the displacement direction Y in the frame portion 15 (see FIG. An electrode pad 2 for electrically connecting the movable circuit 20 and the fixed electrodes 31 and 32 to a detection circuit 90, which will be described later, as an external circuit.
5a, 31b, 32b are formed. The sectional configurations of these electrode pads and a dummy pad described later are the same as the sectional configuration of the movable electrode pad 25a shown in FIG. 6 described above.

Of these electrode pads, 25a is a movable electrode pad for the movable electrode, 31b is a first fixed electrode pad for the first fixed electrode 31, and 32b is a second fixed electrode 32. Is a second fixed electrode pad for. Further, in the frame portion 15, these electrode pads 25 a, 3
Wiring portions 25, 31a and 32a for electrically connecting the movable electrodes 20 and the fixed electrodes 31 and 32 to the movable electrodes 1b and 32b are formed.

Each of the wiring portions 25, 31a and 32a has an oxide film 1 on the second silicon substrate 12 in the frame portion 15, respectively.
It is made by forming grooves that reach up to 3. Here, the movable electrode wiring portion 25 is connected to one anchor portion 23.
b is connected integrally with the movable electrode 20, and the fixed electrode wiring portions 31a and 32a are integrally connected to the supporting portions of the corresponding fixed electrodes 31 and 32 for supporting the frame portion 15, respectively. , 32 are connected.

Then, the wiring parts 25, 31a, 32a
Is routed from the connection with the electrodes 20, 31, 32 through the side portions 15c, 15d of the frame portion 15 to the side portion 15b of the frame portion 15. Then, each electrode pad 25a, 31
b and 32b are corresponding wiring portions 25, 31a,
A conductive metal or the like (aluminum in this example) is used to form the leading end of 32a.

Further, in the present embodiment, the substrate 10
1 which is the outer peripheral portion of the detection units 20, 31, 32 in
5, side portions 15 a, 1 facing each other in the displacement direction Y.
Dummy pads 61, 62, 63 made of a conductive metal or the like (aluminum in this example) are formed on the other side portion (upper side in FIG. 1) 15a of 5b.

The dummy pads 61 to 63 and the electrode pads 25a, 31b, 32b are arranged in the following manner.
It is symmetrical with respect to the centers of the detection units 20, 31, and 32. In the present embodiment, the center of the detection unit is the movable electrode 20.
Center point of (weight 21) (shown as a black circle in FIG. 1) PS
Is. This center point PS is also the center point of the substrate 10 in this example.

Also, the electrode pads 25a, 31b, 32b
And the dummy pads 61 to 63 are separately arranged on one side and the other side 15a, 15b facing each other in the displacement direction Y, so that the electrode pad and the dummy pad are aligned in the displacement direction Y. It has been arranged as.

Further, in this example, the electrode pads 25a, 31
The b and 32b and the dummy pads 61 to 63 are made of the same material (aluminum) and have the same shape (rectangular plate shape) and the same area.

Here, as shown in FIG. 1, each of the dummy pads 61 to 63 has wiring portions (dummy wiring portions) 61a, 62a, 6 formed in the frame portion 15 similarly to the electrode pads.
3a through the movable electrode 20 and the fixed electrode 3 respectively.
1 and 32 are electrically connected. These dummy wiring portions are wiring portions 25, 31a, 32 for the electrode pads.
Like a, it is made by forming a groove in the frame portion 15.

Then, as shown in FIG. 1, the dummy pad 6
1-63 and the dummy wiring portions 61a-63a and the electrode pads 25a, 31b, 32b and the wiring portions 25, 31a, 32a have a pattern shape that passes through the center point PS of the movable electrode 20 and in the displacement direction. It has a line-symmetrical shape with respect to a line orthogonal to Y.

Further, as shown in FIG. 2, the present sensor S1
Is bonded and fixed to the package 80 on the back surface (surface opposite to the oxide film 13) side of the first silicon substrate 11 via an adhesive agent 70 made of an adhesive film (for example, polyimide resin).

The package 80 accommodates the detection circuit (circuit means) 90. The detection circuit 90 and the electrode pads 25a, 31b, 32b described above are also provided.
Are electrically connected by a wire (not shown) formed by gold or aluminum wire bonding or the like.

In such a structure, the first detection capacitance (CS1) is formed in the detection interval 40 between the first fixed electrode 31 and the comb-teeth electrode portion 24 of the movable electrode 20, and the second fixed capacitance is formed. A second detection capacitor (CS2) is formed at a detection interval 40 between the electrode 32 and the comb-teeth electrode portion 24 of the movable electrode 20.

When subjected to acceleration, the movable electrode 20 is integrally displaced in the displacement direction Y by the spring function of the beam portion 22, the detection interval 40 is changed according to this displacement, and each of the detection capacitors CS1, CS2 changes. Then, the detection circuit 90 detects the applied acceleration based on the change in the differential capacitance (CS1-CS2) which is the difference between the first and second detection capacitances.

This acceleration detection will be specifically described with reference to FIG. FIG. 3 is a diagram (detection circuit diagram) showing a detection circuit 90 as the circuit means in the sensor S1.
In the detection circuit 90, 91 is a switched capacitor circuit (SC circuit), and this SC circuit 91 has a capacitance of C
The capacitor 92, the switch 93, and the differential amplifier circuit 94, which are f, are provided to convert the input capacitance difference (CS1-CS2) into a voltage.

An example of a timing chart for this detection circuit 90 is shown in FIG. In the sensor S1, for example, the carrier wave 1 (for example, frequency 100 kHz, amplitude 0 to 5 V) from the first fixed electrode pad 31b and the carrier wave 1 from the second fixed electrode pad 32b are 180 degrees in phase.
A carrier wave 2 (for example, a frequency of 100 kHz and an amplitude of 5 to 0 V) that has been shifted is input, and the switch 93 of the SC circuit 91 is opened and closed at the timing shown in the figure. And the applied acceleration is
As shown in the following formula 1, the voltage value V0 is output.

[0052]

## EQU1 ## V0 = (CS1-CS2) .V / Cf where V is the voltage difference between the fixed electrode pads 31b and 32b. The applied acceleration along the displacement direction Y is detected by the voltage value V0 output in this way.

Next, an example of a method of manufacturing the sensor S1 according to this embodiment will be described based on the above configuration. First, the SOI substrate 10 is prepared, aluminum is vapor-deposited on the entire surface of the second silicon substrate 12, and then the aluminum film is patterned by using a photolithography technique and an etching technique.
31b and 32b and dummy pads 61 to 63 are formed.

Next, the back surface of the SOI substrate 10 (the surface of the first silicon substrate 11) is back-polished, a plasma SiN film is deposited, and the plasma SiN film is etched to etch the opening 14. It is used as a mask when forming.

Subsequently, a PIQ (polyimide) film is applied on the surface of the SOI substrate 10 (the surface of the second silicon substrate 12), and the PIQ is etched to form the movable electrode 2 described above.
0, the fixed electrodes 31 and 32, and a pattern corresponding to the groove that defines each wiring portion are patterned.

Next, on the patterned PIQ,
Applying resist as a protective film, plasma Si on the back side
Using the N film as a mask, the SOI substrate 10 is deeply etched with, for example, a KOH aqueous solution. In this deep etching, since the etching rate of the oxide film 13 is slower than that of Si, the oxide film 13 functions as an etching stopper.

After that, the exposed oxide film 13 and the plasma SiN film are removed with an HF aqueous solution. Then S
The resist protecting the surface of the OI substrate 10 is removed,
The groove and the through hole 50 are formed in the second silicon substrate 12 by dry etching using the PIQ film as a mask. As a result, the detection units 20, 31, 32 and each wiring unit are formed. Then, the PIQ on the surface is removed by O ₂ ashing to complete the sensor S1.

By the way, according to the present embodiment, the substrate 10
Dummy pads 61 to 63 are formed on the outer periphery of the detection units 20, 31, and 32 in FIG.
The arrangement of 31b and 32b and the dummy pads 61 to 63 is symmetrical with respect to the center PS of the detection portion (hereinafter,
"Dummy pad symmetrical arrangement configuration") is the main feature.

According to this, the thermal stress caused by these electrode pads and dummy pads is detected by the detection units 20, 31, 3 and 3.
It occurs symmetrically with respect to 2 and is uniformly applied to the detection part. Therefore, even if the thermal stress changes due to the temperature change, the displacement of the movable electrode 20 and the fixed electrodes 31 and 32 of the detection unit due to the thermal stress is suppressed.

For example, in FIG. 1, the electrode pad 25
It is assumed that the thermal stress caused by a, 31b, and 32b is applied to the detection unit in the downward direction along the displacement direction Y. In that case,
Conventionally, the movable electrode 20 and the fixed electrodes 31 and 32 are displaced in the downward direction, but due to the difference in displacement between the movable electrode and the fixed electrode, the detection interval 40 on the left side of the weight portion 21 and the detection interval 40 on the right side of the weight portion 21. The difference in size causes variations in detection accuracy and offset.

However, in the case of this embodiment, the electrode pad 2
Side portion 15b of frame portion 15 in which 5a, 31b, 32b are located
The dummy pads 61 to 63 on the side portion 15a facing the
Since they are arranged symmetrically as described above, thermal stress caused by the dummy pad is applied to the detection units 20, 31, 32 in the upward direction along the displacement direction Y.

Then, on the one hand, the detecting portions 20, 31, 32 tend to be displaced downward along the displacement direction Y due to the thermal stress caused by the electrode pads, but on the other hand, they are caused by the dummy pads. Since the thermal stress tends to displace upward along the displacement direction Y, the mutual movements are canceled out, and the displacement generated in the detection unit can be suppressed.

Therefore, according to the present embodiment, by adopting the "dummy pad symmetrical arrangement configuration", even if the temperature changes, the change of the detection interval 40 in the detection units 20, 31, 32 is suppressed as much as possible. Therefore, it is possible to prevent the temperature characteristic of the sensor output from being deteriorated by the thermal stress caused by the electrode pads 25a, 31b, 32b.

Further, in the present embodiment, if the "dummy pad symmetrical arrangement configuration" is adopted, the pads may be arranged at arbitrary positions in the frame portion 15, but as shown in FIG. 1, the electrode pads 25a are formed. , 31b, 32b and the dummy pads 61 to 63 are preferably arranged along the displacement direction Y of the movable electrode 20.

The displacement direction Y of the movable electrode is a direction in which the comb-teeth electrode portion 24 of the movable electrode of the sensor S1 and the fixed electrodes 31, 32 face each other with a detection interval 40 therebetween. Therefore, while arranging the electrode pads 25a, 31b, 32b and the dummy pads 61 to 63 along the displacement direction Y,
It is preferable to adopt the “dummy pad symmetrical arrangement configuration” because the change in the detection interval 40 due to the thermal stress can be efficiently suppressed.

Further, in this example, the electrode pads 25a, 31
Since b, 32b and the dummy pads 61 to 63 are made of the same material, have the same area, and have the same shape, the thermal stress caused by each pad is
It is preferable because it can be easily made uniform.

Incidentally, the dummy pad 6 in this embodiment.
1 to 63 are, in particular, those having the above-mentioned thermal stress control action by the dummy pads themselves, even if the dummy pads 61 to 63 and the outside are not connected by bonding wires or the like. However, the electrode pad 2
5a, 31b, 32b side, not the dummy pads 61 to
The 63 side may be connected to the detection circuit 90 by wire.

Further, as shown in FIG. 1, the first fixed electrode 3
The fixed electrode wiring portion 31a for 1 and the fixed electrode wiring portion 32a for the second fixed electrode 32 have the same wiring shape including the dummy wiring portion. Therefore, the parasitic capacitance between the wiring portion and the support substrate (first silicon substrate 11) becomes the same on the first fixed electrode side and the second fixed electrode side, and the offset due to this parasitic capacitance difference can be eliminated. it can. The effect of the present invention can be obtained by forming only the dummy pads 61 to 63 without providing the dummy wiring portions 61a to 63a.

In addition to the acceleration sensor, the present invention
For example, it can be used as a sensor for detecting a mechanical quantity such as an angular velocity sensor or a pressure sensor.

[Brief description of drawings]

FIG. 1 is a schematic plan view of an acceleration sensor according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view taken along the line AA in FIG.

FIG. 3 is a detection circuit diagram of the sensor shown in FIG.

4 is a diagram showing an example of a timing chart for the detection circuit shown in FIG.

FIG. 5 is a schematic plan view of a general mechanical quantity sensor.

6 is a schematic cross-sectional view taken along the line BB in FIG.

[Explanation of symbols]

10 ... SOI substrate (substrate), 20 ... Movable electrode, 25a ...
Movable electrode pad, 31 ... First fixed electrode, 31b ... First
Fixed electrode pad, 32 ... Second fixed electrode, 32b ... Second fixed electrode pad, 61-63 ... Dummy pad.

Claims (4)

[Claims] 1. A substrate (10), a movable electrode (20) formed on the substrate and capable of being displaced in a predetermined direction (Y) in response to the application of a mechanical quantity, and a movable electrode formed on the substrate and facing the movable electrode. And a detection part composed of fixed electrodes (31, 32) arranged in parallel with each other, and an electrode pad formed on the outer periphery of the detection part on the substrate for electrically connecting the movable electrode and the fixed electrode to the outside. (25a, 31b, 32b), and when the movable electrode is displaced in response to the application of a mechanical amount, the applied mechanical amount is detected based on a change in the distance between the movable electrode and the fixed electrode. In the mechanical quantity sensor described above, dummy pads (61, 62, 63) are formed on the outer periphery of the detection unit on the substrate, and the arrangement of the electrode pad and the dummy pad is opposite to the center of the detection unit. A mechanical quantity sensor characterized by being symmetrical with respect to each other. 2. The electrode pads (25a, 31b, 32)
The dynamics according to claim 1, wherein b) and the dummy pads (61 to 63) are arranged along a predetermined direction (Y) in which the movable electrode (20) in the detection unit is displaced. Quantity sensor. 3. The electrode pads (25a, 31b, 32)
The mechanical quantity sensor according to claim 1 or 2, wherein b) and the dummy pads (61 to 63) are made of the same material. 4. The electrode pads (25a, 31b, 32)
The mechanical quantity sensor according to any one of claims 1 to 3, wherein b) and the dummy pads (61 to 63) have the same area.