JP2002340928A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor easily absorbing the offset of a sensor output and its fluctuation according to the operating environment, suppressing the increase of chip size. SOLUTION: A first moving part 11 having a specific displacement direction is floatably supported to a substrate 10. A second moving part 12 having the displacement direction is supported to the first moving part 11. To the first and the second moving parts 11 and 12 (structure bodies), an alternating current voltage from an alternating current source 31 is input. A signal corresponding to the charge accumulated in a capacitor formed between the first moving part 11 and fixed electrodes 14a, 14b based on the alternating current signal is input from the fixed electrodes 14a, 14b to first detection circuits 33a, 33b, etc., and the displacement of the first moving part 11 against the substrate 10 is detected. Similarly, the displacement of the second moving part 12 against the substrate 10 is detected. To the structure bodies, a servo voltage causing electrostatic attraction suppressing the displacement is supplied by overlapping based on the detected displacement of the first moving part 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor having a movable portion floatingly supported on a substrate and detecting an acceleration based on a displacement of the movable portion according to the acceleration.

[0002]

2. Description of the Related Art Conventionally, as an acceleration sensor of this type,
For example, the structure shown in FIG. 10 is known. As shown in the figure, a silicon substrate 9 for forming an insulating layer
0 is, for example, polysilicon doped with an impurity to make it conductive (hereinafter referred to as “conductive polysilicon”).
A movable portion 91 formed of a thin film, fixed electrodes 92a and 92b for detecting acceleration, adjustment electrodes 93a and 93b, and floating body anchors a91, a92, a93, and a94 are provided. The fixed electrodes 92a and 92b and the adjustment electrode 9
3a, 93b and floating body anchors a91 to a94 are joined on a silicon substrate 90.

The movable part 91 is a movable electrode 94 for acceleration detection which extends at predetermined intervals in the longitudinal direction y and one side and the other side (right and left in FIG. 10) in the x direction.
And is formed in a substantially skeleton shape. Then, the fixed electrodes 92a and 92 are placed between the adjacent movable electrodes 94 in the y direction.
b are arranged in parallel. Note that the y direction is the direction of displacement of the movable portion 91, that is, the direction in which the acceleration is detected, and the x direction is substantially perpendicular to the y direction (displacement direction) and substantially parallel to the silicon substrate 90. .

[0004] The four corners of the movable portion 91 are the displacement directions y.
Each of the floating anchors a91 to a94 is connected to a corresponding one of the floating body anchors a91 to a94 via a conductive polysilicon spring beam 95 extending outward in the x direction so as to increase flexibility in the direction. The movable portion 91 and the spring beam 95 are formed so as to float from the silicon substrate 90 by, for example, semiconductor process processing by photolithography and etching.
5 have the same width and length as each other.

[0005] The fixed electrodes 92a and 92b are opposed to the movable electrodes 94 that are opposed on one side and the other side (upper and lower sides in FIG. 10) between adjacent movable electrodes 94 in the y direction of the movable section 91. They are formed separately from each other by a predetermined distance (however, in a stationary state). The fixed electrodes 92a and 92b are moved with respect to the silicon substrate 90 by changing the electrostatic capacitance between the movable part 91 and the movable part 91 (movable electrode 94) based on the displacement of the movable part 91 in the y direction. Used for detecting displacement in the y direction. That is, when the movable section 91 moves to one side (upper side in FIG. 10), the capacitance between the movable section 91 (the movable electrode 94) and the fixed electrode 92a decreases, and the movable section 91 (the movable electrode 91) moves. 9
The capacitance between 4) and the fixed electrode 92b increases. When the movable section 91 moves to the other side (the lower side in FIG. 10), these relations are reversed. That is, the fluctuation of the capacitance between the movable part 91 (movable electrode 94) displaced in response to the action of the acceleration and the fixed electrodes 92a and 92b is opposite to each other.

In such a structure, the fixed electrode 92
a and 92b are applied with AC voltages having opposite phases to each other via the electrode pads 96a and 96b, respectively. Then, the capacitance between the movable part 91 (the movable electrode 94) and the fixed electrode 92a and the capacitance between the movable part 91 (the movable electrode 94) and the fixed electrode 92a are determined.
For example, the difference between the capacitance between the movable beams b and the floating beam anchors a91 and a91 is determined as the electric charge stored in the movable portion 91.
It is taken out from the electrode pad 97 via 94. The charge is subjected to charge-to-voltage conversion to detect the difference in capacitance, that is, a voltage value corresponding to displacement due to acceleration. The acceleration in the y direction is detected based on this voltage value.

The adjustment electrodes 93a and 93b are
The movable portion 91 is sandwiched on the outer side of one side and the other side (the upper side and the lower side in FIG. 10), and is formed complementarily so as to extend in the x direction. When the movable portion 91 is at rest, the adjustment electrodes 93a and 93b are
From each other in the y-direction by the same distance. The individually adjusted DC voltages are applied to the adjustment electrodes 93a and 93b via the electrode pads 98a and 98b, respectively. Generally, a silicon substrate 9
The acceleration sensor formed on the silicon substrate 90
A mechanical stress is generated in the movable portion 91 due to a difference in a linear expansion coefficient between the movable portion 91 and the structure (the movable portion 91 or the like), a change in stress of the substrate fixing portion due to a temperature, and the like. Offset and its variation. Adjustment electrode 93
The a and 93b adjust the electrostatic attraction between the movable portion 91 by applying the individually adjusted DC voltage, and absorb the offset due to such an operation environment and the fluctuation thereof.

[0008]

By the way, the offset by the adjusting electrodes 93a and 93b and the absorption of the fluctuation are corrected by, for example, approximation correction for adjusting a DC voltage to be applied in accordance with a detection result by using a temperature sensing element, or the like. Or ROM
Generally, correction for adjusting the applied DC voltage based on a map corresponding to the operating environment stored in (read only memory) is common. In this case, since the offset with respect to the operating environment (temperature) and the tendency of its variation are different for each sensor, it is necessary to individually set the adjustment value of the DC voltage for each sensor, and the number of inspection steps has been increased. .

Therefore, an acceleration sensor having the shape shown in FIG. 11 has been proposed by the present applicant. As shown in the figure, a silicon substrate 10 on which an insulating layer is formed has a first
Movable part 11, second movable part 12, servo electrodes 13a, 13
b, fixed electrodes 14a, 14b for displacement detection, fixed electrodes 15a, 15b for acceleration detection, and floating body anchors a11, a
12, a13 and a14 are provided. The servo electrodes 13a, 13b, the displacement detection fixed electrodes 14a,
14b, the acceleration detection fixed electrodes 15a and 15b, and the floating body anchors a11 to a14 are joined to the silicon substrate 10.

The first movable portion 11 is formed in a substantially rectangular frame shape, and is substantially symmetric with respect to each other from the sides extending in the vertical direction (y direction) in FIG. Displacement detector 11a protruding in a square frame shape
Are formed. Then, each of these displacement detection units 11a
The interior enclosed by is equally divided into a plurality (ten in FIG. 11) in the y direction by the movable electrodes 16 for displacement detection extending in the x direction. Then, the displacement detection fixed electrodes 14a, 1 are placed between the adjacent displacement detection movable electrodes 16 in the y direction.
4b are arranged in parallel. Note that the y direction is the displacement direction of the first and second movable parts 11 and 12, that is, the acceleration detection direction (sensitivity axis), and the x direction is the y direction.
Direction (displacement direction) and substantially perpendicular to the silicon substrate 10
It is a direction substantially parallel to.

The four corners of the first movable portion 11 are made of a first conductive polysilicon thin film which is bent substantially inward in the x direction to extend in the x direction so as to have high flexibility in the y direction which is the displacement direction (detection direction). The floating body anchors a11 to a14 are respectively connected to the floating body anchors a11 to a14 via the spring beams 17. These first
The movable portion 11 and the first spring beam 17 are formed so as to float from the silicon substrate 10 by, for example, semiconductor processing by photolithography and etching, and the first spring beam 17 has the same width and length as each other. Have.

The displacement detection fixed electrodes 14a and 14b
The first and second displacement detection movable electrodes 16 adjacent to each other in the y-direction of the first movable portion 11 (displacement detection portion 11a) on one side and on the other side (upper and lower sides in FIG. 11). Each electrode is formed at a predetermined distance from the electrode 16 (however, in a neutral state in which displacement is suppressed). These displacement detection fixed electrodes 14a, 14b
Is based on the displacement of the first movable part 11 in the y direction.
When the capacitance between the first movable portion 11 and the movable substrate 11 (the movable electrode 16 for displacement detection) changes, the displacement of the first movable portion 11 with respect to the silicon substrate 10 in the y direction is detected. That is,
When the first movable part 11 moves to one side (upper side in FIG. 11), the capacitance between the first movable part 11 (displacement detection movable electrode 16) and the displacement detection fixed electrode 14a decreases. Together with the first movable part 11 (displacement detection movable electrode 16)
The capacitance between the displacement detection fixed electrode 14b and the displacement detection fixed electrode 14b increases. When the first movable portion 11 moves to the other side (the lower side in FIG. 11), these relationships are reversed. That is,
The first movable section 11 (displacement detection movable electrode 16) due to the displacement of the first movable section 11 and the displacement detection fixed electrodes 14a, 1
4b are opposite to each other.

The servo electrodes 13a and 13b extend in the x direction so as to be opposed to the first movable portion 11 on one side and the other side in the y direction of the first movable portion 11, respectively. These servo electrodes 13a and 13b are supplied with a servo voltage, which will be described later, which is generated in accordance with the detected displacement of the first movable portion 11 with respect to the silicon substrate 10 (displacement detection fixed electrodes 14a and 14b). The electrostatic attraction force in the y direction (detection direction) between the first movable portion 11 and the movable portion 11 is fluctuated, and the displacement of the first movable portion 11 is absorbed. In this conventional example, the two servo electrodes 13a and 13b arranged on both sides (upper and lower sides in FIG. 11) of the first movable portion 11 absorb the displacement of the first movable portion 11, and therefore, in a stationary state. The first movable portion 11 is supported on the silicon substrate 10 so as to be substantially symmetric with respect to the displacement detection fixed electrodes 14a and 14b. That is, the silicon substrate 1 in the neutral state is
The arrangement of the first movable part 11 on the reference numeral 0 substantially matches the arrangement in the stationary state.

The second movable part 12 is provided with the first movable part 1.
1 (displacement detecting section 11a), which is disposed at a substantially central portion of the first movable section 11 and has a smaller width and length than the first movable section 11, and is formed in a substantially square frame shape. ing. The inside of the second movable portion 12 is provided with a plurality of acceleration detection movable electrodes 18 extending in the x direction in the y direction (1 in FIG. 11).
0). The fixed electrodes 15a and 15b for acceleration detection are arranged in parallel between the adjacent movable electrodes 18 for acceleration detection in the y direction.

A support end 12a projecting outward in the y direction is formed at a substantially middle portion of the outer frame on one side and the other side (upper and lower sides in FIG. 11) of the second movable section 12 in the y direction. Have been. The second movable portion 12 extends from the support end 12a to one side in the x direction and the other side (the right side and the left side in FIG. 11) from the support end 12a so as to increase flexibility in the y direction which is the displacement direction (detection direction). Second of conductive polysilicon thin film
Displacement detecting section 1 of first movable section 11 via spring beam 19
It continues to the inside outside 1a. The second movable portion 12 and the second spring beam 19 are also formed so as to float from the silicon substrate 10 by, for example, semiconductor processing by photolithography and etching.
The spring beams 19 are formed to have the same width and length as each other.

The fixed electrodes 15a and 15b for acceleration detection
Is predetermined with respect to the acceleration detection movable electrodes 18 that are opposed to each other between the adjacent acceleration detection movable electrodes 18 in the y direction of the second movable portion 12 on one side and the other side (upper and lower sides in FIG. 11). They are formed at a distance from each other (however, in the neutral state and in a state where no acceleration is applied). These fixed electrodes 15 for acceleration detection
15a and 15b show that the capacitance between the second movable portion 12 and the second movable portion 12 (the movable electrode 18 for acceleration detection) varies based on the displacement of the second movable portion 12 in the y direction. 12 is provided for the displacement detection in the y direction with respect to the silicon substrate 10. That is, the second movable portion 12 is on one side (the upper side in FIG. 11).
When the second movable portion 12 (the movable electrode 18 for acceleration detection) decreases, the capacitance between the second movable portion 12 (the movable electrode 18 for acceleration detection) and the fixed electrode 15a for acceleration detection decreases. ) And the fixed electrode 15b for acceleration detection increase. When the second movable portion 12 moves to the other side (the lower side in FIG. 11), these relationships are reversed. That is, the variation of the capacitance between the second movable part 12 (the movable electrode for acceleration detection 18) and the fixed electrodes for acceleration detection 15a and 15b due to the displacement of the second movable part 12 is opposite to each other. I have.

The first and second movable parts 11 and 12 (the movable electrode 16 for detecting displacement and the movable electrode 18 for detecting acceleration)
And the like are electrically connected to the electrode pads 21 via the floating body anchors a13 and a14 and the wiring W11. The servo electrodes 13a and 13b are connected to the wiring W12,
It is electrically connected to the electrode pads 22a and 22b via W13. Further, the displacement detection fixed electrodes 14a, 1
4b is electrically connected to the electrode pads 23a and 23b via wirings W14 and W15, respectively. The fixed electrodes 15a and 15b for acceleration detection are respectively connected to the wiring W16,
It is electrically connected to the electrode pads 24a and 24b via W17.

Next, a description will be given of a conventional electrical configuration related to acceleration detection by the acceleration sensor. As shown in FIG. 12, the acceleration sensor can generate a first AC signal source 101 capable of generating an AC voltage having a first frequency f1, and an AC voltage having a second frequency f2 different from the first frequency f1. And a second AC signal source 102. In addition,
These first and second frequencies f1 and f2 correspond to the first movable unit 1
The resonance frequency in the displacement direction (detection direction) composed of the first and first spring beams 17, the displacement direction (detection direction) composed of the first and second movable parts 11 and 12 and the first and second spring beams 17 and 19.
Is set higher than the resonance frequency. This is to prevent oscillation of the first and second movable parts 11 and 12 and the like, and to make it possible to acquire the vibration state.

The AC voltage from the first AC signal source 101 is
Displacement detection fixed electrode 14a via electrode pad 23a
Is input to the displacement detection fixed electrode 14b via the inversion circuit 103 and the electrode pad 23b. That is, alternating voltages having the first frequency f1 and having opposite phases are input to the displacement detection fixed electrodes 14a and 14b. Accordingly, the capacitance formed by the first movable portion 11 (displacement detection movable electrode 16) and the displacement detection fixed electrode 14a and the first movable portion 11 (displacement detection movable electrode 1)
AC voltages having the first frequency f1 and having opposite phases are input to the capacitance formed by 6) and the displacement detection fixed electrode 14b.

On the other hand, the AC voltage from the second AC signal source 102 is input to the fixed electrode 15a for acceleration detection via the electrode pad 24a and to the fixed electrode 15b for acceleration detection via the inverting circuit 104 and the electrode pad 24b. Have been. That is, the acceleration detection fixed electrodes 15a, 15
AC voltages having the second frequency f2 and having opposite phases are input to b. Therefore, the second movable part 12 (the movable electrode 18 for acceleration detection) and the fixed electrode 15a for acceleration detection
And the capacitance formed by the second movable portion 12 (the movable electrode 18 for acceleration detection) and the fixed electrode 15b for acceleration detection have opposite phases having the second frequency f2. Is input.

As described above, the structures (the first and second movable portions 11, 12 and the like) which form these respective capacitances in common are formed by the first movable portion 11 and the displacement detection fixed electrode 14a. AC from the first AC signal source 101 having the first frequency f1 and being substantially proportional to the capacitance of the first movable portion 11 and the capacitance deviation of the capacitance formed by the first movable portion 11 and the displacement detection fixed electrode 14b. The electric charge substantially proportional to the voltage, the capacitance formed by the second movable portion 12 and the fixed electrode 15a for acceleration detection, and the electric charge formed by the second movable portion 12 and the fixed electrode 15 for acceleration detection
b and a charge that is substantially proportional to the capacitance deviation of the capacitance formed by the second AC signal source 102 having the second frequency f2 and that is substantially proportional to the AC voltage from the second AC signal source 102 is stored.

Structure (first and second movable parts 11 and 12)
Is connected to a detection circuit 105 such as, for example, a charge amplifier. The signal pad is converted into a voltage by the detection circuit 105 and has a voltage value corresponding to the total electric charge. Is detected.

The output signal from the detection circuit 105 is input to a synchronous detection circuit 106. An AC voltage from the first AC signal source 101 is input to the synchronous detection circuit 106, and the synchronous detection circuit 106 performs synchronous detection at the first frequency f1 using the signal as a reference timing signal, thereby obtaining the silicon substrate 1
The displacement of the first movable portion 11 in the detection direction with respect to 0 is detected.

A signal from the synchronous detection circuit 106 corresponding to the displacement of the first movable portion 11 in the detection direction is input to the servo voltage generation circuit 107,
7 generates a low frequency signal having a third frequency f3 so as to suppress the displacement of the first movable portion 11. Note that this third
The frequency f3 is, for example, higher than a frequency corresponding to a response speed corresponding to acceleration required as a sensor, and lower than the first and second frequencies f1 and f2. In other words, the displacement of the first movable portion 11 in the detection direction is suppressed faster than the response speed required as a sensor. A signal (servo voltage) obtained by inverting a low-frequency signal (servo voltage) from the servo voltage generation circuit 107 to the servo electrode 13a via an electrode pad 22a in the inversion circuit 124 and adding a predetermined bias voltage is applied to the electrode pad. 22b through the servo electrode 13b
Are entered respectively. And this servo electrode 1
With the above-described setting of the signals input to 3a and 13b, the first
The electrostatic attraction between the movable portion 11 and the like in the y direction (detection direction) is adjusted, and the first movable portion 11 with respect to the silicon substrate 10 is adjusted.
Is adjusted so as to substantially eliminate the displacement. Therefore, the displacement (offset) of the first movable portion 11 in the y direction (detection direction) due to acceleration or the displacement (offset) of the first movable portion 11 in the y direction (detection direction) due to the operating environment (temperature) and its fluctuation are suppressed. I have. And since the 2nd movable part 12 is supported with respect to the 1st movable part 11 in which the displacement of the y direction (detection direction) was suppressed in this way, the 2nd movable part 12 has the mass and the second spring. The sensitivity to the y-direction determined by only the spring constant of the beam 19, that is, the acceleration is obtained.
Therefore, by detecting the displacement of the second movable portion 12, it is possible to detect the displacement (offset) in the y direction (detection direction) due to the operating environment (temperature) and the acceleration absorbing the fluctuation thereof. In other words, the sensor output detected by the displacement of the second movable portion 12 via the first movable portion 11 is such that the offset caused by the operating environment (temperature) and its fluctuation are suppressed.

On the other hand, the output signal from the detection circuit 105 is also input to the synchronous detection circuit 108. An AC voltage from the second AC signal source 102 is input to the synchronous detection circuit 108, and the synchronous detection circuit 108 performs synchronous detection at the second frequency f2 using the signal as a reference timing signal, whereby the second movable signal with respect to the silicon substrate 10 is obtained. The displacement of the section 12 in the detection direction is detected.

A signal from the synchronous detection circuit 108 corresponding to the displacement of the second movable section 12 in the detection direction is amplified through an amplifier 109 as required, and an LPF (low-pass filter) is provided.
Only signals in the required frequency band are extracted via 110. This signal is output to, for example, a controller as an output voltage value (sensor output) corresponding to acceleration after performing a predetermined offset adjustment.

Here, this acceleration sensor adjusts the electrostatic attraction in the y direction (detection direction) between the first movable part 11 and the silicon substrate 10 in adjusting the displacement of the first movable part 11 with respect to the silicon substrate 10. Servo electrodes 13a and 13b are required. Therefore, the silicon substrate 1 of the first movable portion 11
When the adjustment of the displacement with respect to 0 is wide, the servo electrodes 13a, 13a and 13b are required to obtain a sufficient force (electrostatic attraction).
It is necessary to secure a sufficient area for the first movable portion 11b and the opposing first movable portion 11, which necessitates an increase in chip size and a reduction in productivity.

An object of the present invention is to provide an acceleration sensor capable of easily absorbing an offset of a sensor output according to an operating environment and its fluctuation while suppressing an increase in chip size.

[0029]

According to a first aspect of the present invention, there is provided a first movable portion floatingly supported on a substrate in a predetermined displacement direction, the first movable portion comprising: A second movable portion that is supported by the first movable portion with a displacement direction, and that is displaced in the displacement direction when acceleration is applied in the displacement direction; and the substrate that faces the first movable portion. An electrostatic attraction between the fixed electrode for displacement detection fixed on the substrate and fixed at a predetermined potential and the second movable portion is fixed on the substrate so as to face the second movable portion, and the electrostatic attraction between the fixed electrode and the second movable portion substantially cancels each other. Or, based on an acceleration detection fixed electrode held at a potential that does not occur, an AC signal source for inputting an AC voltage to the first and second movable parts, and an AC voltage input to the first and second movable parts. An electrostatic capacitance formed between the first movable part and the displacement detection fixed electrode; A signal corresponding to one of a current flowing through the sensor and a charge stored in the capacitance is input from the displacement detection fixed electrode to detect a displacement of the first movable portion with respect to the substrate; A servo voltage having a bias voltage adjusted based on the detected displacement of the first movable part is generated and supplied to the first and second movable parts in a superimposed manner. Applying means for applying a force so as to suppress the displacement by an electrostatic attraction between the fixed electrode for displacement detection and the second movable portion based on an AC voltage input to the first and second movable portions; A signal corresponding to either a current flowing through a capacitance formed between the acceleration detection fixed electrode and the electric charge stored in the capacitance is input from the acceleration detection fixed electrode and the second Change of the movable part with respect to the substrate And a second detecting means for detecting, and summarized in that to detect the acceleration applied on the basis of the displacement of the second movable part which is the detection.

According to a second aspect of the present invention, in the acceleration sensor according to the first aspect, the first detecting means has a negative feedback impedance in which an inverting input terminal is connected to the displacement detection fixed electrode. And the displacement detection fixed electrode connected to the operational amplifier circuit is held at a predetermined potential by a bias voltage applied to a non-inverting input terminal of the operational amplifier circuit.

The third aspect of the present invention is the first or second aspect.
4. The acceleration sensor according to claim 1, wherein the displacement detection fixed electrodes are formed in a pair having a substantially electromagnetically symmetric structure with respect to the first movable portion, and each displacement detection fixed electrode forming the pair is formed. Means that they are held at different predetermined potentials.

According to a fourth aspect of the present invention, in the acceleration sensor according to the third aspect, the first detecting means converts a signal input from each of the displacement detection fixed electrodes forming the pair into a signal obtained by subtracting the signal. The gist of the present invention is to detect the displacement of the first movable portion based on the above.

According to a fifth aspect of the present invention, in the acceleration sensor according to any one of the first to fourth aspects, the second detecting means includes a negative feedback having an inverting input terminal connected to the acceleration detecting fixed electrode. An operational amplifier circuit having impedance is provided, and the fixed electrode for acceleration detection connected to the operational amplifier circuit is configured such that the servo voltage is applied to a non-inverting input terminal of the operational amplifier circuit and the electrostatic attractive force between the servo electrode and the second movable portion. The point is that the potential is not generated.

According to a sixth aspect of the present invention, in the acceleration sensor according to any one of the first to fourth aspects, the acceleration detecting fixed electrode has an electromagnetically substantially symmetric structure with respect to the second movable portion. The fixed electrodes for acceleration detection forming the pair are held at a predetermined potential equivalent to each other, and are held at potentials at which the electrostatic attraction between the electrodes and the second movable portion substantially cancel each other. It is the gist that it is done.

According to a seventh aspect of the present invention, in the acceleration sensor according to the sixth aspect, the second detecting means has a negative input terminal connected to each of the acceleration detecting fixed electrodes forming the pair. An operational amplifier circuit having a feedback impedance is provided, and each of the fixed electrodes for acceleration detection connected to the operational amplifier circuit has an equivalent bias voltage applied to a non-inverting input terminal of the operational amplifier circuit, and is connected to the second movable portion. The gist is that the electrostatic attraction is maintained at a potential that substantially cancels out.

The invention described in claim 8 is the invention according to claim 6 or 7
In the acceleration sensor described in the above, the second detection means,
The gist is to detect the displacement of the second movable portion based on a signal obtained by subtracting a signal input from each of the acceleration detection fixed electrodes forming the pair.

(Operation) According to the first or second aspect of the present invention, the displacement of the first movable portion is based on the AC voltage input from the AC signal source to the first and second movable portions. A signal corresponding to one of a current flowing through a capacitance formed between the displacement detection fixed electrode and a charge stored in the capacitance is input to the first detection means from the displacement detection fixed electrode. Is detected.

Then, the bias voltage of the servo voltage is adjusted based on the detected displacement of the first movable portion, and the bias voltage is adjusted and supplied to the first and second movable portions. A force is applied so that the electrostatic attraction between the unit and the displacement detection fixed electrode held at the predetermined potential is adjusted to suppress the displacement.

In the state where the displacement of the first movable portion is suppressed as described above, the displacement of the second movable portion is based on the AC voltage input from the AC signal source to the first and second movable portions. A signal corresponding to one of a current flowing through a capacitance formed between the portion and the fixed electrode for acceleration detection and a signal stored in the capacitance is input from the fixed electrode for acceleration detection to the second detection means. Is detected by Then, an acceleration is detected based on the displacement of the second movable portion.

As described above, since there is no need to separately provide a servo voltage application electrode (servo electrode) for suppressing the displacement of the first movable portion, it is possible to suppress an increase in the chip size and to respond to the operating environment. The offset of the sensor output and its fluctuation are easily absorbed.

The above-mentioned fixed electrode for acceleration detection is a second electrode.
Since the electrostatic attraction between the movable portion and the movable portion is maintained at a potential that substantially cancels or does not occur, unnecessary force is applied to the second movable portion even when the servo voltage is supplied to be superimposed on the first and second movable portions. Is suppressed.

According to the third aspect of the present invention, the fixed electrodes for displacement detection form a pair having an electromagnetically substantially symmetric structure with respect to the first movable portion. The fixed electrodes for displacement detection forming a pair are held at different predetermined potentials. Therefore, for example, the reference voltage of the bias voltage of the servo voltage is set to a substantially intermediate potential between the fixed electrodes for detecting both displacements, and the bias voltage is adjusted (increase / decrease) around this potential, so that the bias voltage is adjusted in both directions in the displacement direction. An electrostatic attraction can be generated. For this reason, the displacement of the first movable portion is suppressed in a wider range, and the offset of the sensor output according to the operating environment and its fluctuation are absorbed in a wider range.

According to the fourth aspect of the invention, the displacement of the first movable portion is detected based on a signal obtained by subtracting a signal input from each of the displacement detection fixed electrodes forming the pair.
Therefore, it is possible to generate a signal in which in-phase components are canceled by disturbance or the like, and the S / N ratio of the signal is improved.

As described above, the displacement of the first movable portion with respect to the substrate is detected more accurately, the noise of the servo voltage generated based on this signal (displacement of the first movable portion) is reduced, and as a result, the first movable portion is displaced. The offset of the sensor output of the acceleration sensor due to the displacement and the variation thereof are suppressed.

According to the fifth aspect of the present invention, the fixed electrode for acceleration detection connected to the operational amplifier circuit of the second detecting means has the same servo voltage applied to the non-inverting input terminal of the operational amplifier circuit and has the same servo voltage. It is held at the voltage (bias voltage) potential. Therefore, regardless of the adjustment of the bias voltage of the servo voltage, no electrostatic attractive force is generated between the fixed electrode for acceleration detection and the second movable portion. For this reason, even if the servo voltage is supplied to the first
Unnecessary force acting on the movable part is suppressed.

According to the invention as set forth in claim 6 or 7, the fixed electrode for acceleration detection forms a pair having an electromagnetically substantially symmetrical structure with respect to the second movable portion. The fixed electrodes for acceleration detection forming a pair are held at a predetermined potential equivalent to each other. Accordingly, regardless of the adjustment of the bias voltage of the servo voltage, the potential difference between the acceleration detecting fixed electrode and the second movable portion forming the pair is equal to each other, so that the electrostatic attractive force is substantially canceled. For this reason, even if the servo voltage is supplied to the first
Unnecessary force acting on the movable part is suppressed.

According to the eighth aspect of the invention, the displacement of the second movable portion is detected based on a signal obtained by subtracting a signal input from each of the acceleration detecting fixed electrodes forming the pair. Therefore, it is possible to generate a signal in which in-phase components are canceled by disturbance or the like, and the S / N ratio of the signal is improved.

As described above, the displacement of the second movable portion with respect to the substrate is detected more accurately, and the offset of the sensor output of the acceleration sensor is suppressed.

[0049]

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS. The structure (the first and second movable parts 11, 1
Since the shapes of 2) and the like are the same as those of the above-described conventional example (see FIG. 11), the description will be omitted by appropriately quoting. As shown in FIG. 1, in the present embodiment, the servo electrode 1 according to the conventional example is used.
3a, 13b and their peripheral structures (electrode pads 22a, 2b)
2b) are omitted, and a servo voltage for suppressing the displacement of the first movable portion 11 is supplied in a manner superimposed on the structure.

Although not particularly mentioned in the conventional example,
The displacement detection fixed electrodes 14a and 14b formed at a predetermined distance from the displacement detection movable electrode 16 facing the neutral state in which the displacement is suppressed are connected to the first movable portion 11 (displacement detection movable electrode). 16) is set so as to have a substantially electromagnetically symmetrical structure. The term "electromagnetically substantially symmetrical structure" as used herein means that the opposed areas between the displacement detection fixed electrodes 14a and 14b and the first movable portion 11 (displacement detection movable electrode 16) in the neutral state and the distance between the electrodes are equal. It is set to. And the first movable part 1
That is, the capacitances between the displacement detection fixed electrodes 14a and 14b and the first movable portion 11 (displacement detection movable electrode 16) due to the displacement of 1 are set to be in opposite phases.

Similarly, the acceleration detecting fixed electrodes 15a and 15b formed at a predetermined distance from the opposing acceleration detecting movable electrode 18 in the neutral state where no acceleration is applied are also provided. 2nd movable part 1
2 (the movable electrode 18 for acceleration detection) is set to have an electromagnetically substantially symmetric structure.

Next, an electrical configuration relating to acceleration detection of the acceleration sensor will be described. As shown in FIG. 2, this acceleration sensor includes an AC signal source 31 that can generate an AC voltage centered on a GND (ground) level having a frequency f. Note that this frequency f is the resonance frequency in the displacement direction (detection direction) composed of the first movable portion 11 and the first spring beam 17, and the first and second movable portions 11, 12 and the first and second spring beams 17 , 19 in the displacement direction (detection direction). This is to prevent oscillation of the first and second movable parts 11 and 12 and the like, and to make it possible to acquire the vibration state.

The AC voltage from the AC signal source 31 is input to the adder 32. Then, a signal obtained by adding the AC voltage and a voltage (servo voltage) generated in a manner to be described later in the adder 32 is applied to the structure (the first and second movable parts 11 and 12 and the like) via the electrode pad 21. Has been entered.

Further, fixed electrodes 14a, 14b for displacement detection
Are connected to first detection circuits 33a and 33b such as charge amplifiers, for example. As shown in FIG. 9, these first detection circuits 33a and 33b constitute an operational amplifier circuit having negative feedback impedance, and each inverting input terminal is connected to one of the corresponding displacement detection fixed electrodes 14a and 14b. Have been. On the other hand, a bias voltage c is applied to a non-inverting input terminal of the first detection circuit 33a, and a bias voltage d different from the bias voltage c is applied to a non-inversion input terminal of the first detection circuit 33b. Therefore, the potential of the displacement detection fixed electrode 14a connected to the first detection circuit 33a due to a so-called virtual short circuit becomes the bias voltage c.
, And the potential of the displacement detection fixed electrode 14b connected to the first detection circuit 33b is held at the bias voltage d.

It should be noted that a substantially intermediate voltage between the bias voltages c and d is set substantially equal to the reference voltage for correcting the bias voltage for generating the servo voltage. Therefore, in the neutral state in which the displacement is suppressed, the servo voltage having the bias voltage set to the reference voltage is supplied to the structure (the first movable portion 11) via the adder 32, so that the displacement is detected. An electrostatic attractive force in the y direction (detection direction) is generated between the fixed electrodes 14a and 14b, which are equal to each other and cancel each other. This suppresses an unnecessary force (electrostatic attraction) from acting on the first movable portion 11 in the neutral state.

When the first movable portion 11 moves to one side (upper side in FIG. 1), the first movable portion 11 (displacement detecting movable electrode 16) and the displacement detecting fixed electrode 14a are separated from each other. At the same time, the first movable portion 11 (displacement detection movable electrode 16) and the displacement detection fixed electrode 14b approach each other. At this time, the bias voltage adjusted to the bias voltage d side from the reference voltage via the adder 32 is applied to the structure (first movable section 11), that is, the first movable section 11 and the displacement detection fixed electrode 14a are connected to each other. A servo voltage having a bias voltage such that the potential difference (electrostatic attraction) increases and the potential difference (electrostatic attraction) between the first movable portion 11 and the displacement detection fixed electrode 14b decreases. Thereby, the first movable portion 11
(Movable electrode 16 for displacement detection) and each fixed electrode 1 for displacement detection
4a, 14b and the first movable portion 1
1 is returned to the other side (the lower side in FIG. 1), and a force in the y direction (detection direction) is generated. When the first movable portion 11 moves to the other side (the lower side in FIG. 1), the structure (the first movable portion 11) is adjusted to the bias voltage c side from the reference voltage via the adder 32. By supplying a servo voltage having a bias voltage, these relationships are reversed. By supplying the servo voltage to the structure (the first movable portion 11) via the adder 32 in the above-described manner, the displacement of the first movable portion 11 is suppressed.

The capacitance formed by the structure (the movable electrode 16 for detecting the displacement of the first movable portion 11) and the fixed electrode 14a for detecting the displacement is substantially proportional to the capacitance. Charges are stored that are substantially proportional to the voltage between the displacement detection fixed electrodes 14a (the difference between the AC voltage and the servo voltage from the AC signal source 31 and the bias voltage c). Therefore,
The charge is subjected to charge-voltage conversion via the first detection circuit 33a, so that a signal having a voltage value corresponding to the charge is detected. In addition, the capacitance formed by the structure (the movable electrode 16 for detecting the displacement of the first movable portion 11) and the fixed electrode 14b for detecting the displacement is substantially proportional to the capacitance, and the structure and the displacement An electric charge that is substantially proportional to the voltage between the fixed electrodes for detection 14b (the difference between the AC voltage from the AC signal source 31 and the servo voltage and the bias voltage d) is stored. Accordingly, a signal having a voltage value corresponding to the charge is detected by converting the charge into a charge through the first detection circuit 33b.

The signals from the first detection circuits 33a and 33b are input to the differential amplifier 34. As described above, the fixed electrode 1 for displacement detection accompanying the displacement of the first movable portion 11
Since the fluctuations of the capacitance between the first and second movable portions 4a and 14b and the first movable portion 11 (displacement detection movable electrode 16) are set to be opposite to each other, the signals from the first detection circuits 33a and 33b are also changed. The phases are opposite to each other. Therefore, by differentially amplifying these two signals, for example, the first movable portion 11 (displacement detection movable electrode 16) and the displacement detection fixed electrode 14a,
14b, it is possible to form a signal in which the common-mode noise due to the parasitic capacitance between the electrodes 14b, electromagnetic disturbance, and the like is suppressed.
/ N ratio can be improved.

The output signal from the differential amplifier 34 is input to a synchronous detection circuit 35. This synchronous detection circuit 3
5, an AC voltage from an AC signal source 31 is input, and the signal is used as a reference timing signal to perform synchronous detection at a frequency f, whereby displacement of the first movable portion 11 in the detection direction with respect to the silicon substrate 10 is reduced. Is to be detected.

A signal from the synchronous detection circuit 35 corresponding to the displacement of the first movable portion 11 in the detection direction is input to the servo voltage generation circuit 36, and the servo voltage generation circuit 36 And a servo voltage composed of a low-frequency signal and a bias voltage adjusted in the above-described manner so as to suppress the above. The frequency of the low-frequency signal is higher than the frequency corresponding to the response speed corresponding to the acceleration required as a sensor, for example, and lower than the frequency f. In other words, the displacement of the first movable portion 11 in the detection direction is suppressed faster than the response speed required as a sensor. This servo voltage generation circuit 3
The servo voltage from No. 6 is input to the adder 32 described above.

The adder 32 adds the signals (servo voltage) to the structure (the movable electrode 16 for detecting the displacement of the first movable portion 11) and outputs the fixed electrode 14 for detecting the displacement.
As described above, the electrostatic attractive force in the y direction (detection direction) between the first and second movable members 11a and 14b is adjusted so as to substantially eliminate the displacement of the first movable portion 11 with respect to the silicon substrate 10. Therefore, the displacement (offset) of the first movable portion 11 in the y direction (detection direction) due to acceleration or the displacement (offset) of the first movable portion 11 in the y direction (detection direction) due to the operating environment (temperature) and its fluctuation are suppressed. I have. The second movable section 12 is supported by the first movable section 11 in which the displacement in the y direction (detection direction) is suppressed as described above.
The movable portion 12 has a sensitivity to the y direction, that is, acceleration, which is determined only by its mass and the spring constant of the second spring beam 19. Therefore, the second movable portion 12
, The displacement (offset) in the y-direction (detection direction) due to the operating environment (temperature) and the acceleration absorbing the fluctuation can be detected. In other words, the sensor output detected by the displacement of the second movable portion 12 via the first movable portion 11 is such that the offset caused by the operating environment (temperature) and its fluctuation are suppressed.

The electrode pad 24a connected to the fixed electrode 15a for acceleration detection is connected to a second detection circuit 37a such as a charge amplifier. This second detection circuit 37
a also constitutes an operational amplifier circuit having negative feedback impedance (see FIG. 9), and the inverting input terminal is connected to the acceleration detection fixed electrode 15a. The capacitance formed by the structure (the movable electrode 18 for acceleration detection of the second movable portion 12) and the fixed electrode 15a for acceleration detection is substantially proportional to the same capacitance, and the structure and acceleration detection are performed. An electric charge that is substantially proportional to the voltage between the fixed electrodes 15a (the difference between the AC voltage and the servo voltage from the AC signal source 31 and the bias voltage a) is stored. Therefore, this charge is equal to the second
A signal having a voltage value corresponding to the charge is detected by the charge-to-voltage conversion via the detection circuit 37a.

The bias voltage a is applied to the non-inverting input terminal of the second detection circuit 37a. Therefore, the potential of the acceleration detection fixed electrode 15a connected to the second detection circuit 37a is maintained at the bias voltage a due to a so-called virtual short. Also, a fixed electrode 1 for acceleration detection
The bias voltage a is applied to the electrode pad 24b connected to the electrode pad 5b. In the above manner, the fixed electrodes 15a and 15b for acceleration detection are set at the same potential (bias voltage a).
Is maintained even when a servo voltage having a bias voltage adjusted in the above-described manner is supplied to the structure (the second movable portion 12) with the fixed electrodes 15a and 15b for acceleration detection. Y direction (detection direction)
This is for preventing the generation of an unnecessary force (electrostatic attraction) on the second movable portion 12 by generating the electrostatic attraction of the second movable portion 12.
In other words, influences other than acceleration (electrostatic attraction) when the second movable portion 12 is displaced in the y direction (detection direction) are suppressed.

The output signal from the second detection circuit 37a is input to the synchronous detection circuit 38. An AC voltage from the AC signal source 31 is input to the synchronous detection circuit 38. The synchronous detection circuit 38 performs synchronous detection at a frequency f using the signal as a reference timing signal to detect the second movable portion 12 with respect to the silicon substrate 10. The displacement in the direction is detected.

The signal from the synchronous detection circuit 38 corresponding to the displacement of the second movable section 12 in the detection direction is amplified through an amplifier 39 as required, and only a signal in a required frequency band is extracted through an LPF 40. . This signal is output to, for example, a controller as an output voltage value (sensor output) corresponding to acceleration after performing a predetermined offset adjustment.

As described in detail above, according to the present embodiment, the following effects can be obtained. (1) In the present embodiment, the displacement of the first movable unit 11 is fixed to the first movable unit 11 for displacement detection based on the AC voltage input from the AC signal source 31 to the first and second movable units 11 and 12. A signal corresponding to the electric charge stored in the capacitance formed between the electrodes 14a and 14b is applied to the fixed electrode 14 for displacement detection.
a and 14b are input to the first detection circuits 33a and 33b, the differential amplifier 34, and the synchronous detection circuit 35, and are detected.

Then, the bias voltage of the servo voltage is adjusted based on the detected displacement of the first movable portion 11 to
And by supplying it to the second movable parts 11 and 12,
A first movable portion 11 based on the servo voltage and fixed electrodes 14 for displacement detection held at bias voltages c and d, respectively.
A force is applied so that the electrostatic attraction between the a and b is adjusted to suppress the displacement.

In the state where the displacement of the first movable portion 11 is suppressed as described above, the displacement of the second movable portion 12 is controlled by the AC input from the AC signal source 31 to the first and second movable portions 11 and 12. A signal corresponding to the electric charge stored in the capacitance formed between the second movable part 12 and the fixed electrode for acceleration detection 15a based on the voltage is supplied from the fixed electrode for acceleration detection 15a to the second detection circuit 37a and the synchronous detection circuit. 38 or the like is detected. Then, an acceleration is detected based on the displacement of the second movable portion 12.

As described above, since there is no need to separately provide an electrode for applying a servo voltage (servo electrode) for suppressing the displacement of the first movable portion 11, it is possible to suppress an increase in the chip size and to reduce the operating environment. The corresponding offset of the sensor output and its fluctuation can be easily absorbed.

The acceleration detection fixed electrodes 15a, 15a,
The servo voltage is superimposed on the first and second movable portions 11 and 12 because the potential of the first and second movable portions 11 and 12 is maintained at a potential at which the electrostatic attraction between the second movable portion 12 and the second movable portion 12 substantially cancels each other. Even when the second movable portion 12 is supplied, unnecessary force acting on the second movable portion 12 can be suppressed.

(2) In the present embodiment, the displacement detection fixed electrodes 14 a and 14 b form a pair having an electromagnetically substantially symmetric structure with respect to the first movable portion 11. The displacement detection fixed electrodes 14a, 14b forming a pair are held at different predetermined potentials (bias voltages c, d). Therefore, for example, the reference voltage of the bias voltage of the servo voltage is set to a substantially intermediate potential between the fixed electrodes 14a and 14b for displacement detection, and the bias voltage is adjusted (increased / decreased) centering on the reference voltage to thereby adjust the displacement direction. An electrostatic attractive force can be generated in both directions. For this reason, the displacement of the first movable portion 11 can be suppressed over a wider range, and furthermore, the offset of the sensor output according to the operating environment and its fluctuation can be absorbed over a wider range.

(3) In the present embodiment, the displacement of the first movable portion 11 is determined by the displacement detecting fixed electrodes 14 forming the pair.
The signals are detected based on signals obtained by subtracting signals input from the first and second detection circuits 33a and 33b from the first detection circuits 33a and 33b. Therefore, for example, the first movable portion 11 (displacement detection movable electrode 16)
And the parasitic capacitance between the fixed electrodes 14a and 14b for displacement detection,
A signal in which common-mode noise due to electromagnetic disturbance or the like is suppressed can be formed, and the S / N ratio of the signal can be improved. Also. Since the signal (AC signal) in which the common-mode noise is suppressed can be amplified with a relatively large amplification factor, the influence of the offset of the first detection circuits 33a and 33b (charge amplifier) after the synchronous detection can be reduced.

As described above, the displacement of the first movable portion 11 with respect to the silicon substrate 10 is detected more accurately, and the noise of the servo voltage generated based on this signal (displacement of the first movable portion 11) is reduced. 1 An offset of the sensor output of the acceleration sensor due to the displacement of the movable portion 11 and its fluctuation can be suppressed.

(4) In the present embodiment, the acceleration detection fixed electrodes 15 a and 15 b form a pair having a structure that is electromagnetically substantially symmetric with respect to the second movable portion 12. Each of the acceleration detection fixed electrodes 15a and 15b forming a pair is
The potentials are maintained at the same predetermined potential (bias voltage a). Therefore, regardless of the adjustment of the bias voltage of the servo voltage, the acceleration detection fixed electrodes 15 forming these pairs are formed.
Since the potential difference between the first and second movable portions 12a and 15b is equal to each other, the electrostatic attraction is substantially canceled. For this reason, even when the servo voltage is supplied to the first and second movable parts 11 and 12 in a superimposed manner, it is possible to suppress an unnecessary force from acting on the second movable part 12.

(5) In the present embodiment, the first and second movable parts 11 and 12 are provided only by a single AC signal source 31 (frequency f).
Can be detected individually, and the circuit configuration can be simplified as compared with the case where a plurality of AC signal sources (frequency) are provided.

(Second Embodiment) Hereinafter, a second embodiment of the present invention will be described with reference to FIG. In addition,
For convenience of description, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is partially omitted.

As shown in FIG. 3, in the present embodiment,
Electrode pad 2 connected to fixed electrode 15b for acceleration detection
4b is significantly different from the first embodiment in that it is connected to a second detection circuit 37b similar to the separately provided second detection circuit 37a. The capacitance formed by the structure (the movable electrode 18 for acceleration detection of the second movable portion 12) and the fixed electrode 15b for acceleration detection is substantially proportional to the capacitance, and the structure and the acceleration An electric charge that is substantially proportional to the voltage between the fixed electrodes 15b (the difference between the AC voltage from the AC signal source 31 and the servo voltage and the bias voltage a) is stored. Accordingly, a signal having a voltage value corresponding to the charge is detected by converting the charge into a charge through the second detection circuit 37b.

The signals from the second detection circuits 37a and 37b are input to the differential amplifier 41. As described above, the capacitance changes between the fixed electrodes 15a and 15b for acceleration detection and the second movable section 12 (the movable electrode 18 for acceleration detection) due to the displacement of the second movable section 12 are in opposite phases. The second detection circuits 37a, 37b
Are also out of phase with each other. Therefore, by differentially amplifying these two signals, for example, the second movable section 12
(A movable electrode 18 for acceleration detection) and a parasitic capacitance between the fixed electrodes 15a and 15b for acceleration detection, a signal in which common-mode noise due to electromagnetic disturbance or the like is suppressed, and a signal can be formed.
The S / N ratio of the signal can be improved.

The output signal from the differential amplifier 41 is input to the synchronous detection circuit 38. An AC voltage from the AC signal source 31 is input to the synchronous detection circuit 38, and this signal is used as a reference timing signal at a frequency f.
By performing synchronous detection at, the displacement of the second movable portion 12 in the detection direction with respect to the silicon substrate 10 is detected.

The signal from the synchronous detection circuit 38 corresponding to the displacement of the second movable section 12 in the detection direction is supplied to an amplifier 39, LP
The output voltage value (sensor output) corresponding to the acceleration is output to, for example, a controller via F40.

As described in detail above, according to the present embodiment, the following effects can be obtained in addition to the same effects as in the first embodiment. (1) In the present embodiment, the displacement of the second movable portion 12 is a signal obtained by subtracting the signals input from the acceleration detection fixed electrodes 15a and 15b forming the pair via the second detection circuits 37a and 37b. Is detected based on Therefore, for example, it is possible to form a signal in which common-mode noise due to the parasitic capacitance between the second movable portion 12 (the movable electrode 18 for acceleration detection) and the fixed electrodes 15a and 15b for acceleration detection, electromagnetic disturbance, and the like is suppressed. The S / N ratio of the signal can be improved. Also. Since the signal (AC signal) in which the common-mode noise is suppressed can be amplified with a relatively large amplification factor, the influence of low-frequency noise of the second detection circuits 37a and 37b (charge amplifiers) after synchronous detection can be reduced.

As described above, the displacement of the second movable portion 12 with respect to the silicon substrate 10 can be detected more accurately, and the offset of the sensor output of the acceleration sensor can be suppressed. (Third Embodiment) Hereinafter, a third embodiment of the present invention will be described with reference to FIGS. For convenience of description, the same components as those in the first and second embodiments are denoted by the same reference numerals, and the description thereof is partially omitted.

As shown in FIG. 4, in the present embodiment,
The elimination of one of the acceleration detection fixed electrode 15b and its peripheral structure (electrode pad 24b, etc.) is the first and second.
This is significantly different from the embodiment. In this embodiment, as shown in FIG. 5, the displacement of the second movable portion 12 is detected by one of the fixed electrodes 15a for acceleration detection.

That is, the non-inverting input terminal of the second detection circuit 37a connected to the fixed electrode 15a for acceleration detection via the electrode pad 24a is connected to the servo voltage generation circuit 3
6 is supplied with a servo voltage. Therefore,
The second detection circuit 37 is provided by a so-called virtual short.
The potential of the fixed electrode 15a for acceleration detection connected to a is held at the bias voltage of the servo voltage. Therefore, similarly, the structure (the first and second movable parts 11, 12 and the like) to which the servo voltage of the servo voltage generation circuit 36 is supplied and the acceleration detecting fixed electrode 15a are set to the same potential (the bias voltage of the servo voltage). Will be retained. This is the structure (second movable part 12)
Even if a servo voltage is supplied to the fixed electrode 15 for acceleration detection,
This is to prevent generation of an unnecessary electrostatic attraction in the y-direction (detection direction) between the first and second a. In other words, influences other than acceleration (electrostatic attraction) when the second movable portion 12 is displaced in the y direction (detection direction) are suppressed.

The capacitance formed by the structure (the movable electrode 18 for acceleration detection of the second movable portion 12) and the fixed electrode 15a for acceleration detection is substantially proportional to the capacitance, and these structures An electric charge that is substantially proportional to the voltage between the body and the fixed electrode 15a for acceleration detection (AC voltage from the AC signal source 31) is stored. This charge is converted into a voltage via the second detection circuit 37a to detect a signal having a voltage value corresponding to the charge, as in the first embodiment. The output signal from the second detection circuit 37a is output to, for example, a controller via the synchronous detection circuit 38, the amplifier 39, and the LPF 40.

As described in detail above, according to the present embodiment, (1) to (3) and (5) in the first embodiment are used.
In addition to the same effects as described above, the following effects can be obtained. (1) In the present embodiment, the acceleration detection fixed electrode 15a connected to the second detection circuit 37a (the operational amplifier circuit)
The servo voltage is applied to the non-inverting input terminal of the operational amplifier circuit and is maintained at the same servo voltage (bias voltage). Therefore, regardless of the adjustment of the bias voltage of the servo voltage, no electrostatic attraction is generated between the acceleration detecting fixed electrode 15a and the second movable portion 12. For this reason, even when the servo voltage is supplied to the first and second movable parts 11 and 12 in a superimposed manner, it is possible to suppress an unnecessary force from acting on the second movable part 12.

(Fourth Embodiment) Hereinafter, a fourth embodiment of the present invention will be described with reference to FIG. In addition,
For convenience of description, the same components as those in the first to third embodiments are denoted by the same reference numerals, and the description thereof is partially omitted.

As shown in FIG. 6, in the present embodiment,
The difference from the third embodiment is that the first detection circuit 33b is omitted. The bias voltage d is directly applied to the electrode pad 23b connected to the displacement detection fixed electrode 14b. In such a configuration, similarly to the first to third embodiments, the fixed electrode 1 for displacement detection is used.
4a and 14b are held at bias voltages c and d, respectively.

The first detection circuit 33a corresponds to the electric charge stored in the capacitance formed by the structure (the movable electrode 16 for detecting the displacement of the first movable portion 11) and the fixed electrode 14a for detecting the displacement. A signal having a voltage value is directly input to the synchronous detection circuit 35. An AC voltage from the AC signal source 31 is input to the synchronous detection circuit 35,
By performing synchronous detection at a frequency f using this signal as a reference timing signal, displacement of the first movable portion 11 in the detection direction with respect to the silicon substrate 10 is detected.

As described in detail above, according to the present embodiment, in addition to the effects (1), (2) and (5) in the first embodiment, and the same effects as (1) in the third embodiment. Thus, the following effects can be obtained.

(1) In the present embodiment, the first movable section 1 is constituted by only one first detection circuit 33a (charge amplifier).
1 can be detected. (Fifth Embodiment) Hereinafter, a fifth embodiment of the present invention will be described with reference to FIGS. For convenience of description, the same components as those in the first to fourth embodiments are denoted by the same reference numerals, and the description thereof is partially omitted.

As shown in FIG. 7, in the present embodiment,
It is the third and fourth points that the displacement detection fixed electrode 14b and its peripheral structure (electrode pad 23b and the like) are further omitted.
This is significantly different from the embodiment. As shown in the electrical configuration in FIG. 8, in the present embodiment, the displacement of the first movable portion 11 is detected and suppressed by one displacement detection fixed electrode 14a.

In this embodiment, the displacement of the first movable portion 11 is absorbed only by one displacement detection fixed electrode 14a disposed on one side (upper side in FIG. 7), so that the first
The movable portion 11 is supported on the silicon substrate 10 by being biased from the other side (the upper side in FIG. 7 opposite to the displacement detection fixed electrode 14a). This is to suppress displacement of the first movable portion 11 to one side (the side of the displacement detection fixed electrode 14a). In the acceleration detection, the first movable part 11 is supported in a state where the displacement of the first movable part 11 in the stationary state is absorbed. A bias voltage c that pulls back one movable portion 11 to one side (the fixed electrode 14a for displacement detection).
Is applied via the first detection circuit 33a. That is, when the servo voltage having the bias voltage set as the reference voltage is supplied to the structure (the first movable portion 11) via the adder 32, the y direction ( The electrostatic attraction in the detection direction (the detection direction)
This is generated between the movable part 11) and the displacement detection fixed electrode 14a.

As described in detail above, according to this embodiment, (1) and (5) in the first embodiment, (1) in the third embodiment, and (1) in the fourth embodiment. The same effect as the effect described above can be obtained.

The embodiment of the present invention is not limited to the above embodiment, but may be modified as follows. In the first to third embodiments, the first detection circuit 3
The detection signals from 3a and 33b are differentially amplified by the differential amplifier 34 to detect the displacement of the first movable portion 11. However, the displacement detection fixed electrodes 14a, 14b
Are applied with different bias voltages c and d via the first detection circuits 33a and 33b. For this reason, the differential amplifier 34 also amplifies the detection signal corresponding to the difference between these bias voltages c and d. In order to suppress the influence of such bias voltages c and d (DC components), an HPF (high-pass filter) may be provided between each of the first detection circuits 33a and 33b and the differential amplifier. Alternatively, another filter for cutting the bias voltages c and d (DC components) may be provided.

In each of the above embodiments, the charge accumulated in the displacement detection fixed electrodes 14a, 14b or the acceleration detection fixed electrodes 15a, 15b is charge-to-voltage converted by a charge amplifier, and the first movable portion 11 or Each displacement of the second movable part 12 is detected. On the other hand, an AC current based on a change in the electric charge accumulated in the displacement detection fixed electrodes 14a and 14b or the acceleration detection fixed electrodes 15a and 15b is converted into a current-voltage signal through an inverting amplifier circuit having a feedback resistor, for example. And the first movable part 11 or the second
Each displacement of the movable part 12 may be detected.

In each of the above embodiments, the first detection circuits 33a and 33b and the second detection circuits 37a and 37b may be replaced by switched capacitor filters instead of charge amplifiers.

In each of the above embodiments, the amplification of the signal from the synchronous detection circuit 38 in the acceleration detection (the amplifier 3
9) The order of the low pass (LPF 40) and the offset adjustment may be changed as appropriate.

In each of the above embodiments, the first and second
Movable parts 11 and 12, electrodes 14a, 14b, 15a and 15
b and the like may be formed of a conductive material such as single crystal silicon or metal other than conductive polysilicon.

The silicon substrate 1 in each of the above embodiments
0, for example, polycrystalline, single crystalline, or amorphous S
i, Ge, SiC, SixGe1-x, SixGeyC1-
A substrate formed of xy may be used.

The circuit configuration relating to the acceleration detection or the setting and supply of the servo voltage in each of the above embodiments is merely an example, and other configurations may be employed. -The shape of the structure of the first movable portion 11, the second movable portion 12, the first spring beam 17, the second spring beam 19, and the like in each of the above embodiments is an example, and other shapes may be adopted.

[0102]

As described above in detail, according to the first or second aspect of the present invention, the offset of the sensor output according to the operating environment and its variation can be easily reduced while suppressing the chip size from increasing. Can be absorbed.

According to the third aspect of the invention, the displacement of the first movable portion can be suppressed in a wider range, and the offset of the sensor output according to the operating environment and its fluctuation can be absorbed in a wider range.

According to the fourth aspect of the present invention, it is possible to generate a signal in which in-phase components due to disturbance or the like are canceled. And
The displacement of the first movable part with respect to the substrate is more accurately detected,
The noise of the servo voltage generated based on this signal (displacement of the first movable portion) is also reduced, so that the offset of the sensor output of the acceleration sensor due to the displacement of the first movable portion and its fluctuation can be suppressed.

According to the fifth aspect of the present invention, even if the servo voltage is supplied to the first and second movable portions in a superimposed manner,
Unnecessary force acting on the movable part can be suppressed. According to the invention described in claim 6 or 7, even when the servo voltage is supplied to the first and second movable portions in a superimposed manner, it is possible to suppress an unnecessary force from acting on the second movable portion.

According to the eighth aspect of the present invention, it is possible to generate a signal in which in-phase components due to disturbance or the like are canceled. And
The displacement of the second movable part with respect to the substrate is more accurately detected,
The offset of the sensor output of the acceleration sensor can be suppressed.

[Brief description of the drawings]

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

FIG. 2 is an exemplary block diagram showing the electrical configuration of the embodiment.

FIG. 3 is a block diagram showing an electrical configuration of a second embodiment of the acceleration sensor according to the present invention.

FIG. 4 is a schematic diagram showing a third embodiment of the acceleration sensor according to the present invention.

FIG. 5 is a block diagram showing an electrical configuration of the embodiment.

FIG. 6 is a block diagram showing an electrical configuration of a fourth embodiment of the acceleration sensor according to the present invention.

FIG. 7 is a schematic view showing a fifth embodiment of the acceleration sensor according to the present invention.

FIG. 8 is a block diagram showing an electrical configuration of the embodiment.

FIG. 9 is a circuit diagram showing first and second detection circuits.

FIG. 10 is a schematic diagram showing a conventional acceleration sensor.

FIG. 11 is a schematic diagram showing another conventional acceleration sensor.

FIG. 12 is a block diagram showing an electrical configuration of the acceleration sensor.

[Explanation of symbols]

 Reference Signs List 10 Silicon substrate as substrate 11 First movable portion 12 Second movable portion 14a, 14b Displacement detection fixed electrode 15a, 15b Acceleration detection fixed electrode 31 AC signal source 32 Adder 33a, 33b First detection circuit 35, 38 Synchronization Detection circuit 36 Servo voltage generation circuit 37a, 37b Second detection circuit 34, 41 Differential amplifier

Claims (8)

[Claims] A first movable portion floatingly supported on a substrate having a predetermined displacement direction; and a first movable portion supported by the first movable portion having the displacement direction and having an acceleration in the displacement direction. A second movable portion that is displaced in the direction of displacement by the addition of the first movable portion, a fixed electrode for displacement detection that is fixed on the substrate facing the first movable portion, and that is held at a predetermined potential, A fixed electrode for acceleration detection fixed on the substrate opposite to the portion and held at a potential at which an electrostatic attraction between the second movable portion and the second movable portion substantially cancels or does not occur; An AC signal source for inputting an AC voltage to the unit; and a capacitance formed between the first movable unit and the displacement detection fixed electrode based on the AC voltages input to the first and second movable units. Corresponding to the current flowing through the capacitor and the electric charge stored in the capacitance. A first detection means for detecting a displacement of the first movable portion with respect to the substrate by receiving a signal from the displacement detection fixed electrode, and a bias voltage adjusted based on the detected displacement of the first movable portion. A servo voltage is generated and supplied to the first and second movable parts in a superimposed manner, and the displacement is suppressed by an electrostatic attraction between the first movable part and the fixed electrode for displacement detection based on the servo voltage. An applying means for applying a force so as to apply a force between the second movable portion and the fixed electrode for acceleration detection based on the AC voltage input to the first and second movable portions. A signal corresponding to one of the flowing current and the charge stored in the capacitance is input from the acceleration detection fixed electrode, and a second detection unit that detects displacement of the second movable portion with respect to the substrate; The detected change of the second movable portion is detected. Acceleration sensor and detects the acceleration applied on the basis of. 2. The acceleration sensor according to claim 1, wherein the first detection unit includes an operational amplifier circuit having a negative feedback impedance and an inverting input terminal connected to the displacement detection fixed electrode, and the operational amplifier circuit includes: An acceleration sensor, wherein the connected fixed electrode for displacement detection is held at a predetermined potential by a bias voltage applied to a non-inverting input terminal of the operational amplifier circuit. 3. The acceleration sensor according to claim 1, wherein the fixed electrode for displacement detection forms a pair having an electromagnetically substantially symmetric structure with respect to the first movable portion, An acceleration sensor, wherein each of the pair of displacement detection fixed electrodes forming a pair is held at a predetermined different potential. 4. The acceleration sensor according to claim 3, wherein the first detection unit detects the first movable unit based on a signal obtained by subtracting a signal input from each of the displacement detection fixed electrodes forming the pair. An acceleration sensor for detecting displacement. 5. The acceleration sensor according to claim 1, wherein the second detection unit includes an operational amplifier circuit having a negative feedback impedance and having an inverting input terminal connected to the acceleration detection fixed electrode. The fixed electrode for acceleration detection connected to the operational amplifier circuit is held at a potential at which the servo voltage is applied to the non-inverting input terminal of the operational amplifier circuit and an electrostatic attraction between the fixed movable electrode and the second movable portion is not generated. An acceleration sensor characterized in that: 6. The acceleration sensor according to claim 1, wherein the fixed electrode for detecting acceleration forms a pair having an electromagnetically substantially symmetrical structure with respect to the second movable portion. The acceleration detecting fixed electrodes forming the pair are held at a predetermined potential equivalent to each other and are held at a potential at which an electrostatic attraction between the electrodes and the second movable portion substantially cancels each other. Acceleration sensor. 7. The acceleration sensor according to claim 6, wherein the second detection means includes an operational amplifier circuit having a negative feedback impedance, wherein an inverting input terminal is connected to each of the acceleration detection fixed electrodes forming the pair. The same bias voltage is applied to the non-inverting input terminal of the operational amplifier circuit to each of the acceleration detection fixed electrodes connected to the operational amplifier circuit, so that the electrostatic attraction between the fixed electrode and the second movable portion substantially cancels out. An acceleration sensor which is held at a potential. 8. The acceleration sensor according to claim 6, wherein the second detection unit is configured to perform the second movable operation based on a signal obtained by subtracting a signal input from each of the acceleration detection fixed electrodes forming the pair. An acceleration sensor for detecting displacement of a part.