JP2012247204A - Acceleration sensor and method for measuring acceleration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor reducing a difference in sensitivity due to a so-called air damping effect that is an effect of an air layer becoming a cushioning material for cushioning a shock while the difference depends on an acceleration application direction, and to provide a method for measuring the acceleration.SOLUTION: A correction circuit 24 includes a function that inputs, in a correction table 25, a displacement signal of an inertial mass body 3 that is an output signal of a capacitance-voltage conversion circuit 22, and a speed signal of the inertial mass body 3 that is an output signal of a differentiating circuit 23, and corrects the output signal by detecting electrodes 81 and 82 that is the output signal of the capacitance-voltage conversion circuit 21 on the basis of a sensor output correction amount obtained from the correction table 25.

Description

  The present invention relates to an acceleration sensor and an acceleration measuring method, and more particularly to a capacitance type acceleration sensor and an acceleration measuring method.

  2. Description of the Related Art Conventionally, there is known an acceleration sensor that detects acceleration based on a change in capacitance between electrodes accompanying application of acceleration. In this capacitance type acceleration sensor, as a sensor that detects acceleration in a direction perpendicular to the substrate, an acceleration sensor that converts the displacement of the inertial mass body into a rotational displacement and detects the rotational displacement as a capacitance change, For example, International Publication No. 2010/055716 pamphlet (Patent Document 1) has been proposed.

  Patent Document 1 proposes an acceleration sensor made of polycrystalline silicon on a silicon substrate, which includes an inertial mass body, a detection frame, a link beam, a torsion beam, an anchor portion, and a detection electrode. The anchor portion and the detection frame are connected by a torsion beam, and the detection frame and the inertia mass body are connected by a link beam. The detection electrode is provided on the substrate so as to face the detection frame.

  When acceleration in a direction perpendicular to the substrate (out-of-plane direction) is applied to the acceleration sensor, the inertial mass body is displaced in the out-of-plane direction. Due to the displacement of the inertial mass body in the out-of-plane direction, the detection frame is rotationally displaced about the axis of the torsion beam via the link beam. That is, the displacement in the out-of-plane direction of the inertial mass body is converted into the rotational displacement of the detection frame. Since the interval between the detection frame and the detection electrode changes due to this rotational displacement, the capacitance formed between the detection frame and the detection electrode changes. By converting the difference between the capacitances of the two detection electrodes arranged so that the interval is increased or decreased with respect to the application of the acceleration into a voltage by the capacitance-voltage conversion circuit, a voltage corresponding to the acceleration is obtained, Acceleration can be detected.

  In addition, the effect of the air layer in the gap between the detection frame and the substrate acting as a cushioning material to mitigate the impact, the so-called air damping effect, makes it difficult for the detection frame and the substrate to contact even when an impact is applied. Can be hard to break.

International Publication No. 2010/055716 Pamphlet

  However, in the acceleration sensor shown in Patent Document 1, drag is generated in the air layer in the gap between the inertial mass body and the substrate when the inertial mass body is displaced in a direction approaching the substrate due to the air damping effect. This drag increases as the inertial mass body is closer to the substrate and as the speed at which the inertial mass body approaches the substrate is larger. For this reason, the subject that the sensitivity differs depending on whether the inertial mass body is displaced in a direction approaching the substrate or in a direction away from the substrate, that is, depending on the direction in which the acceleration is applied.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an acceleration sensor and an acceleration measurement method capable of reducing the difference in sensitivity depending on the direction in which the acceleration is applied.

  The acceleration sensor of the present invention includes a substrate, an inertial mass body, a first fixed electrode, and a correction unit. The inertial mass body is supported on the surface of the substrate so that it can be displaced in the thickness direction of the substrate. The 1st fixed electrode is arrange | positioned on the surface of a board | substrate so that an electrostatic capacitance may be comprised between inertial mass bodies. The correcting unit detects a displacement signal of the inertial mass body and a velocity signal of the inertial mass body based on a capacitance between the inertial mass body and the first fixed electrode, and detects the displacement signal and the velocity detected. The displacement of the inertial mass body is corrected on the basis of the above signal.

  According to the acceleration measuring method of the present invention, an electrostatic capacity is configured between a substrate, an inertial mass body supported on the surface of the substrate so as to be displaceable in the thickness direction of the substrate, and the inertial mass body. An acceleration measurement method using an acceleration sensor including a fixed electrode disposed on a surface of a substrate, and includes the following steps.

  A capacitance between the inertial mass and the fixed electrode is detected. A displacement signal of the inertial mass body and a speed signal of the inertial mass body are output based on the capacitance between the inertial mass body and the fixed electrode. The displacement of the inertial mass body is corrected based on the displacement signal and the velocity signal of the inertial mass body.

  As described above, according to the present invention, by detecting the displacement signal and the velocity signal of the inertial mass body, it is possible to correct the difference in sensitivity depending on the acceleration application direction caused by the air damping effect. .

It is a schematic plan view which shows the structure of the sensor element structure of the acceleration sensor in Embodiment 1 of this invention. It is a schematic sectional drawing in alignment with the II-II line of FIG. It is a schematic sectional drawing which follows the III-III line of FIG. It is a figure for demonstrating electrostatic capacitance C1-C4. It is a functional block diagram which shows roughly the structure of the acceleration sensor in Embodiment 1 of this invention. FIG. 6 is a circuit diagram showing a configuration of a capacitance-voltage conversion circuit 21 in FIG. 5. FIG. 6 is a circuit diagram showing a configuration of a capacitance-voltage conversion circuit 22 in FIG. 5. It is a circuit diagram which shows the structure of the differentiation circuit 23 of FIG. It is a figure which shows the relationship between the magnitude | size of the clearance gap d, and the drag D by an air damping. It is a figure which shows the relationship between the time change ∂d / ∂t of the size of gap d, and drag D by air damping. It is a schematic sectional drawing which shows the 1st process of the manufacturing method of the sensor element structure of the acceleration sensor in Embodiment 1 of this invention. It is a schematic sectional drawing which shows the 2nd process of the manufacturing method of the sensor element structure of the acceleration sensor in Embodiment 1 of this invention. It is a schematic sectional drawing which shows the 3rd process of the manufacturing method of the sensor element structure of the acceleration sensor in Embodiment 1 of this invention. It is a schematic sectional drawing which shows the 4th process of the manufacturing method of the sensor element structure of the acceleration sensor in Embodiment 1 of this invention. It is a schematic sectional drawing which shows the 5th process of the manufacturing method of the sensor element structure of the acceleration sensor in Embodiment 1 of this invention. It is a schematic sectional drawing which shows the 6th process of the manufacturing method of the sensor element structure of the acceleration sensor in Embodiment 1 of this invention. It is a schematic sectional drawing which shows the 7th process of the manufacturing method of the sensor element structure of the acceleration sensor in Embodiment 1 of this invention. It is a schematic sectional drawing which shows the 8th process of the manufacturing method of the sensor element structure of the acceleration sensor in Embodiment 1 of this invention. It is a figure which shows a displacement when the downward acceleration in a figure is applied to the sensor element structure of the acceleration sensor in Embodiment 1 of this invention, and is a schematic sectional drawing shown in the cross section corresponding to FIG. It is a figure which shows the displacement when the upward acceleration in a figure is applied to the sensor element structure of the acceleration sensor in Embodiment 1 of this invention, and is a schematic sectional drawing shown in the cross section corresponding to FIG. It is a figure which shows that a difference arises in the displacement of an inertial mass body according to the application direction of acceleration resulting from the drag by air damping. It is a flowchart which shows the measuring method of the acceleration using the acceleration sensor of Embodiment 1 of this invention. It is a schematic sectional drawing shown in the cross section corresponding to FIG. 3 which shows the modification of the layout of the fixed electrode of Embodiment 1 of this invention. It is a functional block diagram which shows the modification of the acceleration sensor in Embodiment 1 of this invention. It is a top view which shows the modification of the sensor element structure of the acceleration sensor in Embodiment 1 of this invention. FIG. 26 is a schematic sectional view taken along line XXVI-XXVI in FIG. 25. It is a functional block diagram which shows the modification of the acceleration sensor in Embodiment 1 of this invention. It is a functional block diagram which shows the modification of the acceleration sensor in Embodiment 1 of this invention. It is a functional block diagram which shows roughly the structure of the acceleration sensor in Embodiment 2 of this invention. It is a schematic sectional drawing which shows the structure of the sensor element structure of the acceleration sensor in Embodiment 2 of this invention. It is a figure which shows the correction value required in order to correct | amend the error with respect to the displacement and speed shown in FIG. It is a figure which shows the relationship of the electrostatic capacitance with respect to the clearance gap between an inertial mass body and a 3rd fixed electrode. It is a figure which shows the relationship between a displacement and the "displacement signal of an inertial mass body" in FIG. It is a circuit diagram which shows the structure of a HPF circuit. It is a figure which shows the frequency characteristic of the output signal Vout4 with respect to the input signal Vin4 shown in FIG. FIG. 36 is a diagram showing the relationship between the speed of an inertial mass body and the magnitude of an output signal in which the characteristics shown in FIG. 35 have been rewritten focusing on the speed and output magnitude of the inertial mass body. It is a figure which shows the relationship between the displacement and the magnitude | size of an output signal which rewritten the characteristic shown in FIG. 35 paying attention to the magnitude | size of the displacement of an inertial mass body, and an output. It is a characteristic view obtained by multiplying the characteristic of FIG. 33 and the characteristic of FIG. FIG. 30 is a functional block diagram illustrating a configuration in which an amplifier 51 is omitted from the functional block diagram of FIG. 29.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
First, the configuration of the acceleration sensor according to the first embodiment of the present invention will be described with reference to FIGS.

  1 to 5, the acceleration sensor according to the present embodiment includes a sensor element structure 10 and a circuit unit 20 (FIG. 5). 1 to 4, the sensor element structure 10 includes a substrate 1, an insulating film 9, an anchor 5, a torsion beam 6 (FIG. 1), a detection frame 7, and a link beam 4 (FIG. 1). 1), an inertial mass body 3, a first fixed electrode 13, a second fixed electrode 14, and detection electrodes 81 and 82. As illustrated in FIG. 5, the circuit unit 20 mainly includes capacitance-voltage conversion circuits 21 and 22, a differentiation circuit 23, a correction circuit 24, and a correction table 25.

  Referring mainly to FIG. 2, as substrate 1 of sensor element structure 10, for example, a silicon substrate can be used. An insulating film 9 is formed on the surface of the substrate 1. As the insulating film 9, for example, a silicon nitride film or a silicon oxide film can be used.

  An anchor 5 is provided on the surface of the insulating film 9. The anchor 5 is composed of, for example, two conductive layers 5a and 5b. A first fixed electrode 13, a second fixed electrode 14, and detection electrodes 81 and 82 are formed on the surface of the substrate 1 with an insulating film 9 interposed therebetween.

  Referring mainly to FIG. 3, when viewed from the thickness direction of substrate 1 (viewed from the detection axis direction), detection electrodes 81 and 82 are arranged on both sides of conductive layer 5a so as to sandwich conductive layer 5a. Further, the first fixed electrode 13 and the second fixed electrode 14 are arranged on both sides of the detection electrodes 81 and 82 so as to sandwich the detection electrodes 81 and 82. The first fixed electrode 13 is disposed adjacent to the detection electrode 81, and the second fixed electrode 14 is disposed adjacent to the detection electrode 82. Each of the detection electrodes 81 and 82, the first fixed electrode 13, and the second fixed electrode 14 extends, for example, linearly in the same direction (up and down direction in the drawing).

  Referring mainly to FIG. 1, a detection frame 7 is connected to the conductive layer 5b of the anchor 5 with a torsion beam 6 interposed. The torsion beam 6 is configured to be twisted about a virtual torsion axis along the extending direction of the torsion beam 6. Accordingly, the detection frame 7 is supported by the torsion beam 6 so as to be rotatable about the torsion axis, and can be inclined with respect to the surface of the substrate 1 by the torsion of the torsion beam 6. The detection frame 7 has a frame shape surrounding the outer periphery with a gap between the detection frame 7 and the outer periphery of the conductive layer 5 b when viewed from the thickness direction of the substrate 1.

  The inertia mass body 3 is connected to the detection frame 7 via the link beam 4. The link beam 4 is supported by the detection frame 7 so as to extend on an imaginary line shifted from the twist axis when viewed from the thickness direction of the substrate 1. The inertia mass body 3 is supported by the link beam 4 so as to be displaceable in the thickness direction of the substrate 1 with respect to the substrate 1. The inertial mass body 3 has a frame shape that surrounds the outer periphery of the detection frame 7 with a gap as seen from the thickness direction of the substrate 1.

  The anchor 5, the torsion beam 6, the detection frame 7, the link beam 4, and the inertia mass body 3 are electrically connected so as to be equipotential to each other. The substrate 1 is electrically insulated from the detection electrodes 81 and 82, the first fixed electrode 13, and the second fixed electrode 14 by the insulating film 9.

  Referring mainly to FIGS. 2 and 4, the lower surface of detection frame 7 faces the upper surface of detection electrode 81 and the upper surface of detection electrode 82 with a gap therebetween. As a result, a capacitance C2 is formed between the detection frame 7 and the detection electrode 81, and a capacitance C1 is formed between the detection frame 7 and the detection electrode 82. The detection frame 7 and the detection electrodes 81 and 82 constitute a sensor unit that detects acceleration information.

  The lower surface of the inertial mass 3 is opposed to the upper surface of the first fixed electrode 13 and the upper surface of the second fixed electrode 14 with a gap. Thus, a capacitance C3 is formed between the inertial mass body 3 and the first fixed electrode 13, and a capacitance C4 is formed between the inertial mass body 3 and the second fixed electrode 14. The second fixed electrode 14 is configured to generate an electrostatic force between the second fixed electrode 14 and the inertial mass body 3 by applying a voltage to the second fixed electrode 14 and to displace the inertial mass body 3. .

  Each of the anchor 5, the torsion beam 6, the detection frame 7, the link beam 4, the inertia mass body 3, the conductive layers 5a and 5b, the first fixed electrode 13, the second fixed electrode 14, and the detection electrodes 81 and 82 is, for example, It is made of a conductive polycrystalline silicon film, and it is desirable that this polycrystalline silicon film has low stress and no stress distribution.

  Referring mainly to FIG. 5, the circuit unit 20 includes a capacitance-voltage conversion circuit 21 and correction units 22 to 25. The capacitance-voltage conversion circuit 21 has a function of outputting a voltage corresponding to the difference between the capacitances C1 and C2 as an output signal (output signal of the sensor unit) from the detection electrodes 81 and 82.

  The correction unit detects and detects a displacement signal of the inertial mass body 3 and a speed signal of the inertial mass body 3 based on the capacitance C3 between the inertial mass body 3 and the first fixed electrode 13. It has a function of correcting output signals from the detection electrodes 81 and 82 based on the displacement signal and the velocity signal. The correction unit includes a capacitance-voltage conversion circuit 22, a differentiation circuit (time change calculation unit) 23, a correction circuit 24, and a correction table 25.

  The capacitance-voltage conversion circuit 22 has a function of outputting a voltage corresponding to the capacitance C3 as a displacement signal of the inertial mass body 3. The differentiation circuit 23 is electrically connected to the capacitance-voltage conversion circuit 22. The differentiation circuit 23 differentiates the displacement signal of the inertial mass body 3 converted by the capacitance-voltage conversion circuit 22 and outputs a velocity signal of the inertial mass body 3 as a time change of the input signal (that is, electrostatic capacitance). C3).

  The correction circuit 24 is electrically connected to each of the capacitance-voltage conversion circuits 21 and 22, the differentiation circuit 23, and the correction table 25. The correction table 25 has a function of outputting a sensor output correction amount corresponding to the displacement and the speed by using the displacement signal and the speed signal of the inertial mass body 3 as inputs. Thus, the correction circuit 24 inputs the displacement signal and velocity signal of the inertial mass body 3 to the correction table 25, and corrects the output signals from the detection electrodes 81 and 82 based on the sensor output correction amount obtained from the correction table 25. It has a function to do. Thus, the signal corrected by the correction circuit 24 is output as a sensor output.

  As shown in FIG. 6, the capacitance-voltage conversion circuit 21 is configured together with capacitances C <b> 1 and C <b> 2 formed by the sensor element structure 10. The capacitance-voltage conversion circuit 21 is configured to obtain an output Vout1 by applying a voltage Vd that is a constant voltage. This output Vout1 is expressed by the following equation 1.

  Further, the capacitance-voltage conversion circuit 22 is configured together with a capacitance C3 formed by the sensor element structure 10 as shown in FIG. The capacitance-voltage conversion circuit 22 is configured to obtain an output Vout2 corresponding to the capacitance C3 by a configuration known as a switched capacitor circuit.

  Further, the differentiating circuit 23 is configured by a general differentiating circuit as shown in FIG. 8, and is configured to output a time differential signal Vout3 with respect to the input Vin3.

The correction table 25 is determined as follows.
As is generally known, the drag force due to air damping corresponds to the viscosity term (C · ∂x / 運動 t) of the equation of motion (Formula 2 below) with respect to the displacement x.

  Further, when the gap is extremely small, the coefficient C itself of the viscosity term in Equation 2 also changes depending on the gap d and its time change ∂d / ∂t. Therefore, the drag due to air damping depends on the gap d and its time variation ∂d / ∂t. In general, the drag increases exponentially as the gap d becomes smaller when the time variation ∂d / 図 t of the gap is constant as shown in FIG. 9, and when the gap d is constant as shown in FIG. The larger the time change ∂d / ∂t of the gap, the larger the gap. The drag is uniquely determined by the gap and the time change of the gap.

  Therefore, when the acceleration is applied to the sensor element structure 10, the drag D acting on the inertial mass body 3 becomes closer as the inertial mass body 3 approaches the substrate 1 side, and the speed of the inertial mass body 3 increases. It gets bigger. As the drag D increases, the displacement of the inertial mass body 3 decreases, and as a result, the acceleration sensitivity as a sensor decreases.

  The drag D is uniquely determined by the displacement and speed of the inertial mass 3. Therefore, if the sensor output corresponding to the displacement and speed of the inertial mass body 3 is determined in advance by actual measurement or the like, the output correction amount due to the influence of the drag D can be determined. That is, the amount of decrease in the sensor output due to the drag D determined by the displacement and speed of the inertial mass body 3 can be determined as the output correction amount. Thereby, the correction table 25 which outputs the output correction amount uniquely determined according to the displacement and speed of the inertial mass body 3 can be determined.

  The correction circuit 24 is a circuit that performs output correction based on the correction table 25 as described above.

  In using the acceleration sensor of the present embodiment, it is necessary to electrically connect the sensor element structure 10 and the circuit unit 20 in order to convert the capacitance into a voltage or to apply a voltage to the electrodes. There is. As this electrical connection, the anchor 5 of the sensor element structure 10, the detection electrodes 81 and 82, the first fixed electrode 13, the second fixed electrode 14, and the like are connected to the circuit unit 20 by a wiring pattern or a bonding wire on the substrate 1. Connection is possible.

  Next, a method for manufacturing the sensor element structure 10 of the acceleration sensor according to the present embodiment will be described with reference to FIGS.

  The sensor element structure 10 according to the present embodiment is manufactured by a so-called semiconductor microfabrication technology or MEMS (Micro Electro Mechanical Systems) device manufacturing technology in which processes such as film formation, patterning, and etching are repeatedly performed on a substrate 1 made of silicon, for example. can do.

  Referring to FIG. 11, an insulating film 9 made of silicon oxide is formed on a substrate 1 made of silicon, for example, by LPCVD (Low Pressure Chemical Vapor Deposition).

  Referring to FIG. 12, conductive polycrystalline silicon film 101 is formed on insulating film 9. The conductive polycrystalline silicon film 101 is patterned by a normal photolithography technique and etching technique.

  Referring to FIG. 13, conductive layer 5a made of conductive polycrystalline silicon film, first fixed electrode 13, second fixed electrode 14, and detection electrodes 81 and 82 are formed by the above patterning.

  Referring to FIG. 14, a PSG (Phosphosilicate Glass) film 102 is formed on insulating film 9 so as to cover conductive layer 5a, first fixed electrode 13, second fixed electrode 14, and detection electrodes 81 and 82. Is done.

  Referring to FIG. 15, PSG film 102 is patterned by a normal photolithography technique and etching technique. As a result, a hole 102 a reaching the conductive layer 5 a is formed in the PSG film 102.

  Referring to FIG. 16, conductive polycrystalline silicon film 103 is formed on PSG film 102 so as to be in contact with conductive layer 5a through hole 102a. The conductive polycrystalline silicon film 103 is patterned by a normal photolithography technique and etching technique.

  Referring to FIG. 17, by the above patterning, conductive layer 5b made of a conductive polycrystalline silicon film, torsion beam (not shown), detection frame 7, link beam (not shown), and inertial mass 3 are formed. It is formed. Thereafter, the PSG film 102 is removed by etching, and the sensor element structure 10 of the acceleration sensor according to the present embodiment shown in FIG. 18 is manufactured.

Next, the operation of the acceleration sensor according to the present embodiment will be described with reference to FIGS.
In the sensor element structure 10 of the acceleration sensor according to the present embodiment, as shown in FIG. 19, when downward acceleration (positive direction) is applied in the figure, the inertial mass body 3 is displaced in a direction away from the substrate 1. In this case, the detection frame 7 connected to the inertial mass body 3 and the anchor 5 by the link beam 4 and the torsion beam 6 is rotationally displaced around the torsion axis by the deformation of the link beam 4 and the torsion beam 6. Due to this rotational displacement, the gap intervals between the detection electrodes 81 and 82 and the detection frame 7 change, the capacitance C1 increases, and the capacitance C2 decreases. Since the displacement of the inertial mass body 3 changes in proportion to the magnitude of the applied acceleration, and (C1 / (C1 + C2)) changes in proportion to the displacement of the inertial mass body 3, the capacitance-voltage The applied acceleration can be detected by the output of the conversion circuit 21.

  On the other hand, as shown in FIG. 20, when an upward acceleration (negative direction) is applied, the inertial mass body 3 is displaced in a direction approaching the substrate 1. In this case, the detection frame 7 is rotationally displaced to the opposite side to the case of FIG. Due to this rotational displacement, the gap intervals between the detection electrodes 81 and 82 and the detection frame 7 change, the electrostatic capacity C1 decreases, and the electrostatic capacity C2 increases. Since the displacement of the inertial mass body 3 changes in proportion to the magnitude of the applied acceleration, and (C1 / (C1 + C2)) changes in proportion to the displacement of the inertial mass body 3, FIG. Similarly to the case, the applied acceleration can be detected by the output of the capacitance-voltage conversion circuit 21.

  However, in the case shown in FIG. 20, drag due to the air damping effect occurs. For this reason, as shown in FIG. 21, as the displacement increases in the negative direction (that is, as the inertial mass 3 approaches the substrate 1 or the velocity of the inertial mass 3 increases), the change in displacement becomes smaller. As a result, an error occurs in the sensor output, resulting in a difference in sensitivity depending on the acceleration application direction.

  Here, when the gap between the inertial mass body 3 and the second fixed electrode 14 changes due to the application of acceleration, the capacitance C3 monotonously increases or decreases with respect to the acceleration. A capacitance C3 between the inertial mass body 3 and the second fixed electrode 14 is measured (step S1: FIG. 22). The distance between the inertial mass body 3 and the second fixed electrode 14, that is, the displacement of the inertial mass body 3 can be detected by the output of the capacitance-voltage conversion circuit 22 having the capacitance C3. Furthermore, the speed of the inertial mass body 3 can be detected from the output of the differentiation circuit 23. In this manner, the displacement signal and the velocity signal of the inertial mass 3 are detected based on the capacitance C3 (step S2: FIG. 22).

  The drag due to the air damping effect is uniquely determined by the displacement and speed of the inertial mass body 3 with reference to the above equation 2. Therefore, the displacement of the inertial mass body 3 is corrected using the correction table 25 from the obtained displacement signal and velocity signal (step S3: FIG. 22). That is, the output signal from the detection electrodes 81 and 82 is corrected by correcting the decrease in the displacement of the inertial mass body 3 using the correction table 25 from the obtained displacement signal and velocity signal. Thereby, it is possible to obtain a sensor output signal having no difference in sensitivity depending on the acceleration application direction.

Next, the effect of this Embodiment is demonstrated.
As described above, according to the present embodiment, the deformation of the torsion beam 6 and the link beam 4 gives the inertial mass 3 a displacement corresponding to the acceleration applied in the thickness direction of the substrate 1, and A rotational displacement corresponding to the acceleration applied in the thickness direction can be applied to the detection frame 7. Accordingly, acceleration information can be output by the detection frame 7, and a displacement signal and a speed signal of the inertial mass body 3 can be detected. As a result, the acceleration information output from the detection frame 7 and the detection electrodes 81 and 82 is corrected based on the displacement and speed signals of the inertial mass body 3, thereby depending on the direction in which the acceleration is applied due to the air damping effect. Sensitivity differences can be corrected.

  In addition, the sensor element structure 10 according to the present embodiment receives a drag due to the air damping effect regardless of whether the sensor output is corrected or the direction in which the acceleration is applied. For this reason, even when an impact is applied, the contact between the detection frame 7 and the substrate 1 hardly occurs, and the sensor element structure 10 is hardly broken.

  Moreover, an electrostatic force can be generated between the inertial mass body 3 by applying a voltage to the second fixed electrode 14, and the inertial mass body 3 can be displaced. Thereby, by generating an electrostatic force between the inertial mass body 3 and the second fixed electrode 14, the inertial mass body 3 can be displaced regardless of the application of acceleration, and whether the structure is destroyed or not. Can self-diagnose.

  In the present embodiment, as shown in FIG. 3, each of the first fixed electrode 13 and the second fixed electrode 14 is disposed only on one side of the anchor 5 (conductive layer 5a) when viewed from the thickness direction of the substrate 1. The case of (asymmetrically arranged) has been described. However, as shown in FIG. 23, when viewed from the thickness direction of the substrate 1, each of the first fixed electrode 13 and the second fixed electrode 14 surrounds the anchor 5 (conductive layer 5a). It may be configured symmetrically with respect to a virtual line AA passing through 5a). What is necessary is just to form the electrostatic capacitance C3 between the 1st fixed electrode 13 and the inertial mass body 3 in order to detect the displacement of the inertial mass body 3, and the position and arrangement | positioning of the 1st fixed electrode 13 are not restrict | limited in particular. Moreover, the 2nd fixed electrode 14 should just generate | occur | produce an electrostatic force between the inertial mass bodies 3, and the position and arrangement | positioning of the 2nd fixed electrode 14 are not restrict | limited in particular.

  FIG. 23 shows the case where the first fixed electrode 13 is on the inner peripheral side and the second fixed electrode 14 is on the outer peripheral side. However, the first fixed electrode 13 is on the outer peripheral side and the second fixed electrode 14 is on the inner peripheral side. May be located.

  Further, in the present embodiment, the first fixed electrode 13 and the second fixed electrode 14 are individually provided. However, correction of the sensor output is always necessary at the time of self-diagnosis as to whether the structure is destroyed. is not. On the other hand, a self-diagnosis function is not necessary when detecting acceleration. For this reason, as shown in FIG. 24, by providing only one electrode (first fixed electrode) as an electrode facing the inertial mass body 3 and switching from the outside with switches (switching switches) SW1, SW2, etc. The two functions of detection and generation of electrostatic force by voltage application may be switched.

  Further, in the present embodiment, as shown in FIG. 1, one inertia mass body 3 surrounds one detection frame 7 when viewed from the thickness direction of the substrate 1, but as shown in FIGS. One inertial mass 3 may surround two detection frames 7. In this configuration, when viewed from the thickness direction of the substrate 1, in the detection frame 7 on the left side in the figure, the virtual line is located on the left side in the figure of the virtual twist axis, whereas the detection frame 7 on the right side in the figure. Then, the virtual line is located on the right side in the figure of the virtual twist axis. In this way, the detection frames 7, the torsion beams 6, the link beams 4, and the inertial mass body 3 on the left and right sides in the figure are configured symmetrically with respect to a virtual line BB passing between the two detection frames 7. Has been. As shown in FIG. 26, the detection electrodes 81 and 82 face the detection frame 7 on the left side in the drawing, and the detection electrodes 83 and 84 face the detection frame 7 on the right side in the drawing.

  Thus, in the line-symmetric configuration, when the inertial mass body 3 is displaced in the thickness direction of the substrate 1, each of the two detection frames 7 is rotationally displaced in directions opposite to each other. However, when the inertial mass 3 is inclined or displaced in the in-plane direction of the substrate 1, the two detection frames 7 are rotationally displaced in the same direction. Therefore, the detection electrodes 81 and 84 are electrically connected to each other so that the sensitivity of each of the two detection frames 7 is high only in the rotational displacements in the opposite directions, and the capacitance C1 is formed. By configuring the capacitance C2 by electrically connecting the terminals 82 and 83 to each other, it is possible to suppress the sensitivity to accelerations other than the detection axis direction and to be less susceptible to the effects of angular velocity and angular acceleration.

  As shown in FIG. 27, voltage signals after the capacitance-voltage conversion circuits 21 and 22 are converted from analog to digital by analog-to-digital converters (A / D) 31 and 32, whereby analog-to-digital conversion is performed. The signal processing after the devices 31 and 32 may be digital processing. By using digital processing, circuit temperature characteristics can be suppressed, noise resistance can be improved, manufacturing variations can be eliminated, circuit wiring can be miniaturized, cost can be reduced, and correction table 25 can be easily updated. There is an advantage of being able to plan.

  Further, as in the configuration shown in FIG. 28, the processing units (circuit unit 20) after the capacitance-voltage conversion circuits 21 and 22 may be formed as one circuit as an ASIC (application-specific integrated circuit).

(Embodiment 2)
Next, the configuration of the acceleration sensor according to the present embodiment will be described with reference to FIGS. 29 and 30. FIG.

  Referring to FIG. 29, the configuration of this embodiment is an HPF circuit including a capacitance C5 in sensor element structure 10 instead of differentiation circuit 23 and correction circuit 24 of the first embodiment shown in FIG. (High-pass filter, high-pass filter), an amplifier 51, and an adder are different from the configuration of the first embodiment.

  As shown in FIG. 30, the capacitance C5 is between the inertial mass body 3 and the third fixed electrode 15 provided on the substrate 1 with the insulating film 9 interposed so as to face the inertial mass body 3. It consists of The third fixed electrode 15 is formed by patterning the same conductive layer as the detection electrodes 81 and 82 and the first fixed electrode 13, and is made of, for example, a conductive polycrystalline silicon layer. In FIG. 30, the second fixed electrode for constituting the capacitance C4 is not shown, but the second fixed electrode may be formed in a portion not shown in FIG.

  The HPF circuit has the above-described capacitance C5 and a resistor R connected to the capacitance C5. An amplifier 51 is connected to this HPF circuit. An adder is connected to both the amplifier 51 and the capacitance-voltage conversion circuit 21.

  Since the configuration of the present embodiment other than the above is substantially the same as the configuration of the first embodiment, the same elements are denoted by the same reference numerals and description thereof is not repeated.

  Next, the operation of the acceleration sensor according to the present embodiment will be described with reference to FIGS. 29 and 31 to 33.

  In order to correct the error with respect to the displacement and speed shown in FIG. 21 in the present embodiment, correction values as shown in FIG. 31 are required. On the other hand, the capacitance C3 increases as the inertial mass 3 approaches the substrate 1 as shown in FIG. Therefore, by the capacitance-voltage conversion circuit 22 (switched capacitor circuit) shown in FIG. 7, the “displacement signal of the inertial mass body” in FIG. 29 generally has the characteristics shown in FIG.

  In general, in the HPF circuit, the frequency characteristic of the output signal Vout4 with respect to the input signal Vin4 shown in FIG. 34 is substantially as shown in FIG. The frequency characteristic of the output signal Vout4 of the HPF circuit increases as the frequency increases on the low frequency side, and the HPF circuit has a characteristic as a differentiating circuit (time change calculation unit). Further, as the capacitance C constituting the HPF circuit is increased, the signal passband is expanded toward the low frequency side, and as a result, the output signal is increased for the input signal having the same frequency F.

  The characteristics shown in FIG. 35 can be redrawn generally as shown in FIG. 36 when attention is paid to the speed and output magnitude of the inertial mass body 3, and further attention is paid to the displacement of the inertial mass body 3 and the output magnitude. Then, it can be rewritten generally as shown in FIG. That is, the physical quantity corresponding to the velocity and displacement of the inertial mass body can be obtained from the characteristics shown in FIG.

  Therefore, the characteristic after the “displacement signal of the inertial mass body” passes through the HPF circuit and passes through the amplifier 51 is obtained by multiplying the characteristic of FIG. 33 and the characteristic of FIG. 37, as shown in FIG. Characteristics. Thus, the necessary correction value signal characteristics shown in FIG. 31 can be obtained. Thereafter, the sensor output correction is performed by subtracting the “output signal from the detection electrode” and the correction value signal by an adder. In general, it is considered that the signal size needs to be adjusted even if the characteristics tend to be the same. For this adjustment, an amplifier 51 is added to the final stage.

  As a result of the above, according to the configuration of FIG. 29, the same effect as that of the correction circuit in the first embodiment can be obtained, and the sensor output in which the decrease in displacement is substantially corrected and the difference in sensitivity depending on the acceleration application direction is reduced. A signal can be obtained.

  In the acceleration sensor according to the present embodiment, each of the first fixed electrode 13 and the third fixed electrode 15 may form a capacitance with the inertial mass body 3 in order to detect the displacement of the inertial mass body 3. Well, their position and arrangement are not limited. Moreover, the 2nd fixed electrode should just generate | occur | produce an electrostatic force between the inertial mass bodies 3, and there is no restriction | limiting also in the position and arrangement | positioning.

  In the present embodiment, the amplifier 51 is used to uniformly adjust the magnitude of the correction signal. However, by adjusting the capacitances C3 and C5 formed in the sensor element structure 10 or the resistance component R constituting the HPF circuit, a configuration not using the amplifier 51 as shown in FIG. 39 is adopted. May be. Specifically, the magnitude of the correction signal can be uniformly adjusted by increasing or decreasing the areas of the first fixed electrode 13 and the third fixed electrode 15.

  Further, in the acceleration sensor according to the present embodiment, the first fixed electrode 13 and the second fixed electrode 14 or the third fixed electrode 15 and the second fixed electrode 14 are formed as in the acceleration sensor according to the first embodiment. The two functions of capacitance detection and generation of electrostatic force due to voltage application may be switched by being provided as one electrode instead of being individually provided and being switched from the outside by a switch or the like.

  In addition, the configuration of the present embodiment may be a configuration in which one detection frame 7 is surrounded by one inertial mass body 3, and as shown in FIG. The structure surrounded by the inertia mass body 3 may be sufficient.

  The torsion beam 6, the detection frame 7, the link beam 4, and the inertia mass body 3 constitute a displacement member. Further, the torsion beam 6, the detection frame 7, and the link beam 4 may constitute a beam member included in the displacement member.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention can be advantageously applied to a capacitance type acceleration sensor.

  DESCRIPTION OF SYMBOLS 1 Substrate, 3 Inertial mass body, 4 Link beam, 5 Anchor, 5a, 5b Conductive layer, 6 Torsion beam, 7 Detection frame, 9 Insulating film, 10 Sensor element structure, 13 First fixed electrode (displacement detection electrode) , 14 2nd fixed electrode (electrode for self-diagnosis), 15 3rd fixed electrode, 20 circuit part, 21, 22 capacity-voltage conversion circuit, 23 differentiation circuit, 24 correction circuit, 25 correction table, 31, 32 analog- Digital converter, 51 amplifier, 81, 82, 83, 84 detection electrode, SW1, SW2 switch.

Claims (9)

A substrate,
An inertial mass supported on the surface of the substrate so as to be displaceable in the thickness direction of the substrate;
A first fixed electrode disposed on the surface of the substrate to form a capacitance with the inertial mass;
Detecting a displacement signal of the inertial mass body and a velocity signal of the inertial mass body based on the capacitance between the inertial mass body and the first fixed electrode, and detecting the displacement signal detected And a correction unit that corrects the displacement of the inertial mass body based on the velocity signal.   The acceleration sensor according to claim 1, wherein the correction unit includes a time change calculation unit that calculates a time change of the capacitance between the inertial mass body and the first fixed electrode.   The correction unit receives either the displacement signal and the velocity signal of the inertial mass body, or a physical quantity corresponding to the displacement and velocity of the inertial mass body, and outputs a sensor output correction amount. The acceleration sensor according to claim 1 or 2, comprising a correction table.   The acceleration sensor according to claim 1, further comprising a beam member that supports the inertial mass body on the substrate so as to be displaceable in the thickness direction with respect to the substrate. A torsion beam supported by the substrate and twisted about a virtual torsion axis; and
A detection frame supported by the torsion beam so as to be rotatable about the torsion axis;
A link beam supported by the detection frame on an imaginary line deviated from the torsion axis when viewed from the thickness direction and supporting the inertial mass body so as to be displaceable in the thickness direction with respect to the substrate. The acceleration sensor according to claim 1.   The acceleration sensor according to claim 5, further comprising a detection electrode disposed on the surface of the substrate so as to face the detection frame and forming a capacitance with the detection frame.   The apparatus further comprises a second fixed electrode disposed on the surface of the substrate so as to face the inertial mass body and generating an electrostatic force between the inertial mass body and a voltage application. The acceleration sensor in any one of -6.   The acceleration sensor according to claim 1, further comprising a changeover switch that enables voltage application for generating an electrostatic force between the first fixed electrode and the inertial mass body. A capacitance is formed between the substrate, an inertial mass supported on the surface of the substrate so as to be displaceable in the thickness direction of the substrate, and the inertial mass on the surface of the substrate. A method of measuring acceleration using an acceleration sensor comprising a fixed electrode disposed,
Detecting a capacitance between the inertial mass body and the fixed electrode;
Outputting a displacement signal of the inertial mass body and a velocity signal of the inertial mass body based on the capacitance between the inertial mass body and the fixed electrode;
And a step of correcting the displacement of the inertial mass body based on the displacement signal and the velocity signal of the inertial mass body.

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