JP2014020955A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive acceleration sensor which shows no difference in detection sensitivity with regard to displacement to the plus side or to the minus side, and can measure a wide frequency range.SOLUTION: In this acceleration sensor AS, a polysilicon inertia mass body 2 is formed on a silicon substrate 1. The inertia mass body 2 is connected to four detection plates 23, 24. Detection electrodes 43a, 43b, 44a, 44b for detecting displacement of the detection plates 23, 24 are disposed below the detection plates 23, 24. An actuation electrode 5 is disposed below the inertia mass body 2. A fixed electrode 6 is arranged to face the actuation electrode 5 across the inertia mass body 2.

Description

  The present invention relates to an acceleration sensor, for example, an acceleration sensor mounted on an airbag system of an automobile.

  An example of a conventional acceleration sensor (Patent Document 1) will be described. In an acceleration sensor that detects acceleration in the out-of-plane direction of a substrate, an inertial mass body of polysilicon formed on the silicon substrate is connected to four detection plates by link beams. The four detection plates are supported by a torsion beam and further connected to the substrate by an anchor.

  A detection electrode for detecting the displacement of the detection plate is provided on the substrate below the detection plate. When acceleration is applied in the out-of-plane direction, the inertial mass body is displaced in the out-of-plane direction. The out-of-plane displacement of the inertial mass body is mechanically converted into a rotational displacement of the detection plate around the torsion beam. Due to this rotational displacement, the distance between the detection plate and the detection electrode changes, whereby the capacitance between the detection plate and the detection electrode changes.

  The detection electrode is disposed below the detection plate so as to be symmetric with respect to the torsion beam. For this reason, when one electrostatic capacity increases across the torsion beam, the other electrostatic capacity decreases and a differential capacity is formed. The capacitance is converted into a voltage proportional to the acceleration by a capacitance-voltage conversion circuit and detected as an acceleration. On the substrate below the inertial mass body, an actuation electrode is provided for diagnosing a sensor failure by displacing the inertial mass body by electrostatic attraction.

International Publication No. 2009/125510 (FIG. 19) JP 2010-66231 A (FIG. 2)

Y.Hirata, N.Konno, T.Tokunaga, M.Tsugai and H.Fukumoto “A new z-axis capacitive accelerometer with high impact durability”, Digest of Technical Papers Transducers'99, Denver, pp.1158-1161, June 21-25, 2009.

  In the conventional acceleration sensor, the distance between the inertial mass body and the actuation electrode is very narrow. For this reason, when the inertial mass body is displaced to the substrate side, a drag force is received by damping (air damping) between the substrate and the inertial mass body. On the other hand, when the inertial mass body is displaced to the side opposite to the substrate, the drag due to air damping is reduced.

  For this reason, in the relationship between the input acceleration acting on the substrate and the detected sensor output acceleration, when the upward acceleration acts on the substrate (plus side), the sensor output acceleration becomes smaller than the input acceleration. On the other hand, when downward acceleration acts on the substrate (minus side), the sensor output acceleration is the same as the input acceleration. Therefore, the conventional acceleration sensor has a problem that the displacement of the inertial mass body is different between the plus side and the minus side, and the acceleration cannot be measured accurately, particularly in a high frequency and high acceleration region where the drag due to air damping increases. There is a point.

  On the other hand, Patent Document 2 proposes a cap structure having a narrow gap, but in this cap structure, the drag due to air damping acting on the detection plate becomes excessive, and the frequency range that can be detected becomes narrow. There is a point.

  The present invention has been made to solve the above-mentioned problems, and its purpose is to measure over a wide frequency range without any difference in detection sensitivity with respect to displacement toward the plus side and displacement toward the minus side. It is possible to provide an inexpensive acceleration sensor.

  The acceleration sensor according to the present invention includes a substrate, an inertial mass body, a detection plate, a detection electrode, and a pair of damping adjustment units. The inertial mass is displaced in a direction intersecting the surface of the substrate. The detection plate and the detection electrode are arranged to detect the displacement of the inertial mass body as a change in the differential capacitance. The pair of damping adjusting portions are arranged in such a manner that the inertia mass body is sandwiched from above and below, and are arranged below and above the inertia mass body so as to be separated from each other by a first interval in a state where the inertia mass body is stationary. Adjust the mass damping.

  According to the present invention, an acceleration sensor with high detection accuracy and a wide frequency range that can be detected can be obtained.

It is a top view of the acceleration sensor which concerns on Embodiment 1 of this invention. FIG. 2 is a cross-sectional view taken along a cross-sectional line II-II shown in FIG. FIG. 6 is a cross-sectional view showing a first state for describing the operation of the acceleration sensor in the embodiment. FIG. 6 is a cross-sectional view showing a second state for describing the operation of the acceleration sensor in the embodiment. It is a top view of the acceleration sensor which concerns on a comparative example. FIG. 6 is a sectional view taken along a sectional line VI-VI shown in FIG. 5. In the same embodiment, it is a figure which shows the relationship between the sensitivity of an ideal acceleration sensor, and an input acceleration frequency. It is a figure which shows the relationship between input acceleration and the output of an acceleration sensor, and time in the acceleration sensor which concerns on a comparative example. It is a figure which shows the relationship between the sensitivity of an acceleration sensor and the input acceleration frequency in the acceleration sensor which concerns on a comparative example. In the embodiment, it is a figure which shows the relationship between the sensitivity of the acceleration sensor which concerns on the embodiment, and an input acceleration frequency with the relationship between the sensitivity of the acceleration sensor which concerns on a comparative example, and an input acceleration frequency. 3 is a block diagram showing servo control in the same embodiment. FIG. FIG. 6 is a first diagram for explaining the operation of the acceleration sensor in the same embodiment. FIG. 10 is a second diagram for illustrating the operation of the acceleration sensor in the same embodiment. In the same embodiment, it is a figure which shows the servo control of an acceleration sensor. In the same embodiment, it is sectional drawing which shows 1 process of the manufacturing method of an acceleration sensor. FIG. 16 is a cross-sectional view showing a step performed after the step shown in FIG. 15 in the same embodiment. FIG. 17 is a cross-sectional view showing a step performed after the step shown in FIG. 16 in the same embodiment. FIG. 18 is a cross-sectional view showing a step performed after the step shown in FIG. 17 in the same embodiment. FIG. 19 is a cross-sectional view showing a step performed after the step shown in FIG. 18 in the same embodiment. FIG. 20 is a cross-sectional view showing a step performed after the step shown in FIG. 19 in the same embodiment. FIG. 21 is a cross-sectional view showing a step performed after the step shown in FIG. 20 in the same embodiment. It is sectional drawing of the acceleration sensor which concerns on Embodiment 2 of this invention. It is sectional drawing of the acceleration sensor which concerns on Embodiment 3 of this invention. In the same embodiment, it is sectional drawing which shows 1 process of the manufacturing method of an acceleration sensor. FIG. 25 is a cross-sectional view showing a step performed after the step shown in FIG. 24 in the same embodiment. FIG. 26 is a cross-sectional view showing a step performed after the step shown in FIG. 25 in the same embodiment. FIG. 27 is a cross-sectional view showing a step performed after the step shown in FIG. 26 in the same embodiment. FIG. 28 is a cross-sectional view showing a step performed after the step shown in FIG. 27 in the same embodiment. FIG. 29 is a cross-sectional view showing a step performed after the step shown in FIG. 28 in the same embodiment. It is sectional drawing of the acceleration sensor which concerns on Embodiment 4 of this invention. In the same embodiment, it is sectional drawing which shows 1 process of the manufacturing method of an acceleration sensor. FIG. 32 is a cross-sectional view showing a step performed after the step shown in FIG. 31 in the same embodiment. FIG. 33 is a cross-sectional view showing a step performed after the step shown in FIG. 32 in the same embodiment. FIG. 34 is a cross-sectional view showing a step performed after the step shown in FIG. 33 in the same embodiment. FIG. 35 is a cross-sectional view showing a step performed after the step shown in FIG. 34 in the same embodiment. FIG. 36 is a cross-sectional view showing a step performed after the step shown in FIG. 35 in the same embodiment.

Embodiment 1
The acceleration sensor according to Embodiment 1 will be described. As shown in FIGS. 1 and 2, in the acceleration sensor AS, an inertia mass body 2 of polysilicon is formed on a silicon substrate 1. The inertial mass body 2 is connected to the four detection plates 21, 22, 23, and 24 by link beams 31, 32, 33, and 34. The four detection plates 21 to 24 are supported by the torsion beams 11, 12, 13, and 14 and are connected to the substrate by anchors 91, 92, 93, and 94.

  On the silicon substrate 1 below the detection plates 21 to 24, detection electrodes for detecting the displacement of the detection plates 22 to 24 are provided. Detection electrodes 41 a and 41 b are provided below the detection plate 21, and detection electrodes 42 a and 42 b are provided below the detection plate 22. Further, detection electrodes 43 a and 43 b are provided below the detection plate 23, and detection electrodes 44 a and 44 b are provided below the detection plate 24.

  On the silicon substrate 1 below the inertial mass body 2, an actuation electrode 5 is provided for diagnosing a sensor failure by displacing the inertial mass body 2 by electrostatic attraction. A fixed electrode 6 is disposed so as to face the actuation electrode 5 with the inertial mass body 2 interposed therebetween. The fixed electrode 6 is disposed along the outer peripheral portion of the inertial mass body 2 so as to cover the outer peripheral portion.

  In the acceleration sensor AS described above, when acceleration is applied in the out-of-plane direction of the silicon substrate 1, the inertial mass body 2 is displaced in an out-of-plane direction (a direction intersecting the XY plane, for example, the Z-axis direction). The out-of-plane displacement of the inertial mass body 2 is mechanically converted into rotational displacement of the detection plates 21, 22, 23, 24 around the torsion beams 11, 12, 13, 14. Due to this rotational displacement, the distance between the detection plates 21, 22, 23, 24 and the detection electrodes 41a, 41b, 42a, 42b, 43a, 43b, 44a, 44b changes, so that the detection plates 21, 22, 23, 24 The capacitance between the detection electrodes 41a, 41b, 42a, 42b, 43a, 43b, 44a, 44b changes.

  Note that the detection unit 10 and the detection unit 20 are arranged symmetrically with respect to the Y-axis direction, and the detection unit 30 and the detection unit 40 are arranged symmetrically with respect to the Y-axis direction. The sensitivity to acceleration is suppressed, and it becomes difficult to be affected by inertial forces such as angular velocity and angular acceleration.

  Further, the torsion beam 31 is arranged on one side across a line segment passing through the anchor 91 and the anchor 93, and the torsion beam 33 is arranged on the other side across the line segment. The torsion beam 32 is disposed on one side across a line segment passing through the anchor 92 and the anchor 94, and the torsion beam 34 is disposed on the other side across the line segment. As a result, when the zero point position of the detection plate is rotationally displaced from the parallel position due to warpage of the silicon substrate 1 and the like, the change in the detection capacity cancels out and becomes a constant value. Can be detected.

  The detection of acceleration due to a change in capacitance will be described in a little more detail. The detection electrodes 41 a and 41 b are arranged symmetrically with respect to the torsion beam 11, and the detection electrodes 42 a and 42 b are arranged symmetrically with respect to the torsion beam 12. The detection electrodes 43 a and 43 b are arranged symmetrically with respect to the twisted beam 13, and the detection electrodes 44 a and 44 b are arranged symmetrically with respect to the twisted beam 14.

  Thereby, for example, between the detection electrodes 41 a, 42 a, 43 a, and 44 a located on one side of the torsion beams 11, 12, 13, and 14 and the corresponding detection plates 21, 22, 23, and 24, respectively. Increase in the capacitance between the detection electrodes 41b, 42b, 43b, 44b located on the other side and the corresponding detection plates 21, 22, 23, 24, respectively. A dynamic capacity is formed.

  As shown in FIG. 3, when an upward acceleration (arrow Y1) acts on the silicon substrate 1, for example, the capacitance C2 between the detection plate 23 and the detection electrode 43a and the detection plate 24 and the detection electrode 44a. While the capacitance C2 between the detection plate 23 and the detection electrode 43b increases, and the capacitance C1 between the detection plate 24 and the detection electrode 44b decreases.

  As shown in FIG. 4, when a downward acceleration (arrow Y2) acts on the silicon substrate 1, for example, the capacitance C2 between the detection plate 23 and the detection electrode 43a and the detection plate 24 and the detection electrode 44a. While the capacitance C2 between the detection plate 23 and the detection electrode 43b decreases, and the capacitance C1 between the detection plate 24 and the detection electrode 44b increases. The change in capacitance is converted to a voltage proportional to acceleration by a capacitance-voltage conversion circuit and detected as acceleration.

  In the acceleration sensor AS described above, the actuation electrode 5 and the fixed electrode 6 are arranged in such a manner that the inertial mass body 2 is sandwiched from above and below. Thereby, an air damping effect is obtained with respect to the vertical displacement of the inertial mass body 2. This will be described with a comparative example.

  As shown in FIGS. 5 and 6, the acceleration sensor according to the comparative example is the same as the configuration of the acceleration sensor shown in FIGS. 1 and 2 except that the fixed electrode 6 is not formed. For this reason, the same reference numerals are assigned to the same members in the 100s, and the description thereof will not be repeated unless necessary.

  It is assumed that the resonance frequency of the acceleration sensor according to the comparative example is 15 KHz and the upper limit of the detection frequency has a detection frequency range of 10 KHz. First, an ideal sensitivity frequency characteristic is shown in FIG. As shown in FIG. 7, the sensitivity (detection sensitivity) is constant in the detection frequency range, and when it exceeds the detection frequency range, it is desirable to quickly attenuate in the high frequency region.

  In the acceleration sensor according to the comparative example, the distance between the inertial mass body 102 and the actuation electrode 105 (silicon substrate 101) is narrow. For this reason, when the inertial mass body 102 is displaced toward the silicon substrate 101, it receives a drag force caused by air damping between the silicon substrate 101 and the inertial mass body 102. On the other hand, when the inertial mass body 102 is displaced to the side opposite to the silicon substrate 101 side, the drag force due to air damping is relatively small.

  FIG. 8 shows the relationship between input acceleration (acting acceleration) and sensor output acceleration in this case. In FIG. 8, the positive side of the vertical axis represents a case where upward acceleration acts on the silicon substrate. At this time, the inertial mass body 102 is displaced toward the silicon substrate 101 side. On the other hand, the negative side of the vertical axis represents a case where downward acceleration acts on the silicon substrate. At this time, the inertial mass body 102 is displaced to the side opposite to the silicon substrate 101 side.

  As shown in FIG. 8, when an upward acceleration is applied to the silicon substrate, the sensor output acceleration is smaller than the input acceleration. When downward acceleration acts on the silicon substrate, the sensor output acceleration and the input acceleration are the same. Therefore, especially in the high-frequency region or high-acceleration region where the drag due to air damping is high, the acceleration is detected accurately, depending on whether the displacement of the inertial mass body is displaced to the plus side or the minus side. May not be possible.

  The inventors created an acceleration sensor in which a hole through which air passes is formed in the inertial mass body 102 in an attempt to eliminate the drag due to air damping between the silicon substrate 101 and the inertial mass body 102, and the input acceleration frequency and The relationship with sensitivity was evaluated. The result is shown in FIG. As shown in FIG. 9, when the drag due to air damping is eliminated, a peak is recognized at the elastic deformation resonance frequency of the inertial mass body 102 itself (the resonance frequency of the inertial mass body), and the detection frequency range where the sensitivity is constant becomes narrow. It turned out that. In addition, it has been found that in the vicinity of the resonance frequency of the inertial mass body, the displacement of the inertial mass body 102 becomes large and the inertial mass body 102 collides with the silicon substrate 101.

  In the acceleration sensor according to the embodiment with respect to the comparative example, the fixed electrode 6 is disposed above the inertial mass body 2, while the actuation electrode 5 is disposed below the inertial mass body 2. On the lower side of the inertial mass body 2, it receives a drag due to air damping between the inertial mass body 2 and the silicon substrate 1, and on the upper side of the inertial mass body 2, the air between the inertial mass body 2 and the silicon substrate 1. You will receive drag from damping. Thereby, the resonance of the inertial mass body as shown in FIG. 9 does not occur, and the relationship between the ideal input acceleration frequency and the sensitivity shown in FIG. 7 is obtained.

  FIG. 10 shows the result of analyzing the relationship between the input acceleration frequency and the sensitivity for the acceleration sensor in which the fixed electrode is arranged and the acceleration sensor in which the fixed electrode is not arranged. As shown in FIG. 10, in the acceleration sensor in which no fixed electrode is arranged, a peak is obtained in the vicinity of the resonance frequency of the inertial mass body, whereas in the acceleration sensor according to the embodiment, the fixed electrode is arranged. Then, it can be seen that the peak due to the resonance of the inertial mass body is suppressed by the damping effect.

  Further, in the acceleration sensor according to the embodiment, servo control can be performed so that the detection plate becomes a stationary position (zero point) of the detection plate in a state where acceleration does not act on the acceleration sensor according to the sensor output. is there. That is, by applying a predetermined potential between the inertial mass body 2 and the actuation electrode 5 and between the inertial mass body 2 and the fixed electrode 6, an electrostatic attractive force is generated between them and detected. It is possible to control so that the position of the plate becomes the zero point, and the detection accuracy can be increased. This will be described with the operation of the acceleration sensor.

  First, a block diagram of servo control is shown in FIG. In the acceleration sensor (sensor element SE), as described above, the acceleration is obtained based on a change in capacitance (differential capacitance) between the detection plate and the detection electrode. Here, as shown in FIGS. 12 and 13, the detection plates 21 to 24 (see FIG. 1) are represented by the detection plate DP, and the detection electrodes 41a, 41b to 44a and 44b (see FIG. 1) are represented as the detection electrodes DE1, Let's be represented by DE2.

  An interval (gap) between the detection plate DP and the detection electrodes DE1 and DE2 when the position of the detection plate DP is a zero point is defined as d. Then, u is the downward displacement of the inertial mass when upward acceleration acts on the silicon substrate 1. If the capacitance between the detection plate DP and the detection electrode DE1 at this time is the capacitance C1, and the capacitance between the detection plate DP and the detection electrode DE2 is the capacitance C2, the capacitance C1 and the capacitance C2 is represented by the following formulas 1 and 2.

C1 = ε · S / u · log {d / (d−u)} (Formula 1)
C2 = ε · S / u · log {(d + u) / d} (Formula 2)
Here, S is the area of the detection electrodes DE1, DE2, and ε is the dielectric constant.

  The change in capacitance shown in FIG. 11 is a change in capacitance of the capacitance C1 and the capacitance C2. The change in the differential capacitance is expressed by the following equation 3 by the capacitance-voltage conversion circuit in the circuit board CB. It is converted into a voltage Vout proportional to the displacement u.

Vout = C1 / (C1 + C2) · Vs
≈ Vs / 2 + {Vs / (4 · d)} · u (Formula 3)
The displacement u of the detection plate DP is proportional to the acceleration. As shown in FIG. 14, a predetermined servo voltage 8 is applied between the inertial mass body 2 and the actuation electrode 5 and between the inertial mass body 2 and the fixed electrode 6 to cause displacement by electrostatic attraction. It is controlled so that u does not fluctuate. That is, control is performed so that Vout does not fluctuate. The servo voltage is a function of acceleration. Therefore, the applied servo voltage is converted into acceleration, and the detected acceleration value is output (see FIG. 11).

  Next, an example of a method for manufacturing the acceleration sensor described above will be described. First, as shown in FIG. 15, an insulating film 50 such as a silicon oxide film or a silicon nitride film is formed so as to cover the surface of the silicon substrate 1. Next, a polysilicon film 80 is formed so as to cover the insulating film 50. Next, by patterning the polysilicon film 80, the actuation electrode 5, the detection electrodes 43a, 43b, 44a, 44b and the like made of the polysilicon film 80 are formed.

  Next, a first sacrificial film 51 (see FIG. 16) such as phosphate glass is formed so as to cover the actuation electrode 5, the detection electrodes 43a, 43b, 44a, 44b, and the like. Next, by performing a process such as dry etching on the portion of the first sacrificial film 51 located in the region where the fixed electrode is disposed, an opening exposing the surface of the insulating film 50 as shown in FIG. 51a is formed.

  Next, a conductive polysilicon film 81 (see FIG. 17) is formed so as to cover the first sacrificial film 51 so as to fill the opening 51a. Next, by subjecting the conductive polysilicon film 81 to a process such as dry etching, the inertia mass body 2, the detection plates 23, 24, and the like are formed as shown in FIG. In the opening 51a, the polysilicon film 81 that becomes a part of the fixed electrode is patterned.

  Next, a second sacrificial film 52 (see FIG. 18) such as phosphate glass is formed so as to cover the inertial mass body 2, the detection plates 23, 24, and the like. Next, the surface of the polysilicon film 81 is exposed as shown in FIG. 18 by performing a process such as dry etching on the portion of the second sacrificial film 52 located in the region where the fixed electrode is disposed. . Next, as shown in FIG. 19, a conductive polysilicon film 82 is formed so as to cover the second sacrificial film 52.

  Next, by patterning the conductive polysilicon film 82, the fixed electrode 6 is formed as shown in FIG. The fixed electrode 6 is formed of conductive polysilicon films 81 and 82. Next, as shown in FIG. 21, the second sacrificial film 52 and the first sacrificial film 51 are selectively removed under predetermined etching conditions. Thus, the main part of the acceleration sensor is completed.

  In the acceleration sensor manufacturing method described above, the interval (interval A) between the inertial mass body 2 and the actuation electrode 5 is adjusted by the thickness of the first sacrificial film 51. Further, the interval (interval B) between the inertial mass body 2 and the fixed electrode 6 is adjusted by the film thickness of the second sacrificial film 52. Thereby, the space | interval A and the space | interval B can be match | combined (aligned) accurately. In addition, as a manufacturing apparatus for manufacturing an acceleration sensor, a special manufacturing apparatus is unnecessary, and it can be manufactured using an existing manufacturing apparatus, and an acceleration sensor with high accuracy and a wide detection frequency range can be manufactured at low cost. Can be manufactured.

Embodiment 2
An acceleration sensor according to Embodiment 2 will be described. As shown in FIG. 22, the acceleration sensor AS is provided with an upper cap 7 that seals the inertial mass body 2, the detection plates 23 and 24, and the like. The upper cap 7 is made of glass or a silicon substrate with an insulating film. The fixed electrode 6 is disposed on the upper cap 7 facing the inertial mass 2 above the inertial mass 2. The fixed electrode 6 is disposed along the outer peripheral portion of the inertial mass body 2 so as to cover the outer peripheral portion.

  The interval (distance) between the inertial mass body 2 and the actuation electrode 5 and the interval (distance) between the inertial mass body 2 and the fixed electrode 6 are set to the same interval. The distance (distance) between the detection plates 23 and 24 and the upper cap 7 is longer than the distance (distance) between the inertial mass body 2 and the upper cap portion (the portion where the fixed electrode 6 is disposed). It is secured. As a result, the air damping effect between the detection plates 23 and 24 and the upper cap 7 is suppressed. Since the configuration other than this is the same as that of the acceleration sensor shown in FIGS.

  In the acceleration sensor described above, the fixed electrode 6 is disposed above the inertial mass body 2, while the actuation electrode 5 is disposed below the inertial mass body 2. As a result, as described in the first embodiment, resonance of the inertial mass body does not occur, and an ideal relationship between the input acceleration frequency and sensitivity (detection sensitivity) is obtained (see FIG. 7).

  Similarly to the acceleration sensor described in the first embodiment, a predetermined servo voltage 8 is applied between the inertial mass body 2 and the actuation electrode 5 and between the inertial mass body 2 and the fixed electrode 6. By performing servo control, the detection accuracy and frequency range can be expanded.

  Furthermore, the acceleration sensor described above can be manufactured by replacing the step of forming the polysilicon film for the fixed electrode with the step of processing the upper cap in the manufacturing method described in the first embodiment. It can be manufactured at low cost.

Embodiment 3
An acceleration sensor according to Embodiment 3 will be described. As shown in FIG. 23, in the acceleration sensor AS, with the inertial mass body 2 stationary, the distance between the inertial mass body 2 and the actuation electrode 5 and the distance between the inertial mass body 2 and the fixed electrode 6 are the same. The interval L is set. Further, the distance between the detection plates 23, 24 and the detection electrodes 43a, 43b, 44a, 44b, etc. is set to the distance D while the inertial mass body 2 (detection plate) is stationary. In this acceleration sensor, the interval L is set narrower than the interval D. In addition, since it is the same as that of the acceleration sensor shown in FIG.1 and FIG.2 about another structure, the same code | symbol is attached | subjected to the same member and the description is not repeated.

  In the acceleration sensor described above, since the distance L is set to be narrower than the distance D, the damping effect between the inertial mass body 2 and the actuation electrode 5 and the damping between the inertial mass body 2 and the fixed electrode 6 are achieved. The effect is enhanced compared to the damping effect when the distance L and the distance D are the same, and an acceleration sensor with a wider detection frequency range can be obtained.

  In addition, when a predetermined servo voltage is applied between the inertial mass body 2 and the actuation electrode 5 and between the inertial mass body 2 and the fixed electrode 6 to perform servo control by electrostatic attraction, the distance L Therefore, the same electrostatic attraction can be generated at a lower voltage, and the operation can be performed at a lower voltage. This eliminates the need for a control circuit that can withstand high voltages, and an inexpensive servo-controllable acceleration sensor can be obtained.

  Next, an example of a method for manufacturing the acceleration sensor described above will be described. First, after the process shown in FIG. 15, the first sacrificial film 51 such as phosphate glass is formed so as to cover the actuation electrode 5, the detection electrodes 43a, 43b, 44a, 44b, etc. (see FIG. 24). Is formed. The film thickness of the first sacrificial film 51 corresponds to the distance D (see FIG. 23) between the detection electrodes 43a, 43b, 44a, 44b and the like corresponding to the detection plates 23, 24 and the like.

  Next, the portion of the first sacrificial film 51 located in the region where the fixed electrode is disposed and the portion of the first sacrificial film 51 located in the region where the inertial mass body is disposed, such as dry etching By performing the processing, as shown in FIG. 24, an opening 51a exposing the surface of the insulating film 50 is formed, and an opening 51b exposing the actuation electrode 5 is formed.

  Next, a sacrificial film 53 (see FIG. 25) thinner than the first sacrificial film 51 is formed so as to cover the first sacrificial film 51. The thickness of the sacrificial film 53 corresponds to the distance L between the actuation electrode 5 and the inertial mass body 2 (see FIG. 23). Next, as shown in FIG. 25, the portion of the sacrificial film located in another region is removed, leaving the sacrificial film 53 located in the opening 51b.

  Next, a conductive polysilicon film 81 (see FIG. 26) is formed so as to cover the first sacrificial film 51 so as to fill the openings 51a and 51b. Next, by subjecting the conductive polysilicon film 81 to a process such as dry etching, the inertia mass body 2, the detection plates 23, 24, and the like are formed as shown in FIG. In the opening 51a, the polysilicon film 81 that becomes a part of the fixed electrode is patterned.

  Next, a second sacrificial film 52 such as phosphate glass (see FIG. 27) is formed so as to cover the inertial mass body 2, the detection plates 23, 24, and the like. Next, the surface of the polysilicon film 81 is exposed as shown in FIG. 27 by performing a process such as dry etching on the portion of the second sacrificial film 52 located in the region where the fixed electrode is disposed. . Next, a conductive polysilicon film 82 (see FIG. 28) is formed so as to cover the second sacrificial film 52.

  Next, by patterning the conductive polysilicon film 82, the fixed electrode 6 is formed as shown in FIG. The fixed electrode 6 is formed of conductive polysilicon films 81 and 82. Next, as shown in FIG. 29, the second sacrificial film 52, the sacrificial film 53, and the first sacrificial film 51 are selectively removed under predetermined etching conditions. Thus, the main part of the acceleration sensor is completed.

  In the acceleration sensor manufacturing method described above, the distance L between the inertial mass body 2 and the actuation electrode 5 is determined by the thickness of the sacrificial film 53. Further, the distance D between the detection plates 23 and 24 and the corresponding detection electrodes 43 a, 43 b, 44 a and 44 b and the like is determined by the thickness of the first sacrificial film 51. Thereby, the space | interval L and the space | interval D can be formed easily and accurately. Furthermore, as described in the first embodiment, an acceleration sensor having a wide detection frequency range and high accuracy can be manufactured at low cost using an existing manufacturing apparatus.

Embodiment 4
An acceleration sensor according to Embodiment 4 will be described. As shown in FIG. 30, in the acceleration sensor AS, with the inertial mass body 2 stationary, the distance between the inertial mass body 2 and the actuation electrode 5 and the distance between the inertial mass body 2 and the fixed electrode 6 are the same. The interval L is set. Further, the distance between the detection plates 23, 24 and the detection electrodes 43a, 43b, 44a, 44b, etc. is set to the distance D while the inertial mass body 2 (detection plate) is stationary. In this acceleration sensor AS, the interval L is set wider than the interval D. In addition, since it is the same as that of the acceleration sensor shown in FIG.1 and FIG.2 about another structure, the same code | symbol is attached | subjected to the same member and the description is not repeated.

  In the acceleration sensor described above, the interval L is set wider than the interval D. Thus, a predetermined servo voltage is applied between the inertial mass body 2 and the actuation electrode 5 and between the inertial mass body 2 and the fixed electrode 6, respectively. The servo voltage range can be set wider than when the interval L and the interval D are the same or when the interval L is set narrower than the interval D. As a result, an acceleration sensor with high detection accuracy can be obtained.

  Next, an example of a method for manufacturing the acceleration sensor described above will be described. First, after the process shown in FIG. 15, the first sacrificial film 51 such as phosphate glass is formed so as to cover the actuation electrode 5, the detection electrodes 43a, 43b, 44a, 44b, etc. (see FIG. 31). Is formed. The thickness of the first sacrificial film 51 corresponds to the distance D (see FIG. 30) between the detection plates 23, 24 and the corresponding detection electrodes 43a, 43b, 44a, 44b and the like.

  Next, the portion of the first sacrificial film 51 located in the region where the fixed electrode is disposed and the portion of the first sacrificial film 51 located in the region where the inertial mass body is disposed, such as dry etching By performing the processing, as shown in FIG. 31, an opening 51a exposing the surface of the insulating film 50 is formed, and an opening 51b exposing the actuation electrode 5 is formed.

  Next, a sacrificial film 53 (see FIG. 32) thicker than the first sacrificial film 51 is formed so as to cover the first sacrificial film 51. The thickness of the sacrificial film 53 corresponds to the distance L (see FIG. 30) between the actuation electrode 5 and the inertial mass body 2. Next, as shown in FIG. 32, the portion of the sacrificial film located in another region is removed, leaving the sacrificial film 53 protruding from the opening 51b.

  Next, a conductive polysilicon film 81 (see FIG. 33) is formed so as to cover the first sacrificial film 51 so as to fill the openings 51a and 51b. Next, by subjecting the conductive polysilicon film 81 to a process such as dry etching, the inertia mass body 2, the detection plates 23, 24, and the like are formed as shown in FIG. In the opening 51a, the polysilicon film 81 that becomes a part of the fixed electrode is patterned.

  Next, a second sacrificial film 52 (see FIG. 34) such as phosphate glass is formed so as to cover the inertial mass body 2, the detection plates 23, 24, and the like. Next, as shown in FIG. 34, the surface of the polysilicon film 81 is exposed by performing a process such as dry etching on the portion of the second sacrificial film 52 located in the region where the fixed electrode is disposed. . Next, a conductive polysilicon film 82 (see FIG. 35) is formed so as to cover the second sacrificial film 52.

  Next, by patterning the conductive polysilicon film 82, the fixed electrode 6 is formed as shown in FIG. The fixed electrode 6 is formed of conductive polysilicon films 81 and 82. Next, as shown in FIG. 36, the second sacrificial film 52, the sacrificial film 53, and the first sacrificial film 51 are selectively removed under predetermined etching conditions. Thus, the main part of the acceleration sensor is completed.

  In the acceleration sensor manufacturing method described above, the distance L between the inertial mass body 2 and the actuation electrode 5 is determined by the thickness of the sacrificial film 53. Further, the distance D between the detection plates 23 and 24 and the corresponding detection electrodes 43 a, 43 b, 44 a and 44 b and the like is determined by the thickness of the first sacrificial film 51. Thereby, the space | interval L and the space | interval D can be formed easily and accurately. Furthermore, as described in the first embodiment, an acceleration sensor having a wide detection frequency range and high accuracy can be manufactured at low cost using an existing manufacturing apparatus.

  In each of the above-described embodiments, the actuation electrode 5 and the fixed electrode 6 for use in servo control have been described as an example of the pair of damping adjustment units. The pair of damping adjusting portions is not limited to conductive members such as the actuation electrode 5 and the fixed electrode 6 as long as the damping effect in the vertical direction of the inertial mass body 2 can be obtained.

  The embodiment disclosed this time is an example, and the present invention is not limited to this. The present invention is defined by the terms of the claims, rather than the scope described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention is effectively used to detect acceleration, including an automobile airbag system.

  DESCRIPTION OF SYMBOLS 1 Board | substrate, 2 Inertial mass body, 5 Actuation electrode, 6 Fixed electrode, 7 Upper cap, 8 Servo potential, 8a Servo potential, 8b Servo potential, 10 1st detection unit, 11 1st twist beam, 12 2nd twist Beam, 13 3rd torsion beam, 14 4th torsion beam, 15 Insulating film, 20 Second detection unit, 21, 22, 23, 24 Detection plate, 30 Third detection unit, 31, 32, 33, 34 Link Beam, 40 Fourth detection unit, 41a, 41b Detection electrode, 42a, 42b Detection electrode, 43a, 43b Detection electrode, 44a, 44b Detection electrode, 50 Insulating film, 51 First sacrificial layer, 51a opening, 51b opening, 52 second sacrificial layer, 53 sacrificial layer, 80 polysilicon wiring, 81 polysilicon film, 82 polysilicon film, 91-94 Linker, AS acceleration sensor, SE sensor element, CB control circuit, DE1 detection electrodes, DE2 detection electrodes, DP detection plate, Y1, Y2 arrows.

Claims (7)

A substrate,
An inertial mass that is displaced in a direction intersecting the surface of the substrate;
A detection plate and a detection electrode arranged to detect displacement of the inertial mass body as a change in differential capacitance;
In a mode in which the inertial mass body is sandwiched from above and below, the inertial mass body is disposed below and above the inertial mass so as to be spaced apart from each other with a first interval in a stationary state, and damping of the inertial mass body An acceleration sensor comprising a pair of damping adjustment units for adjusting The pair of damping adjustment units are:
A first electrode disposed below the inertial mass body as one damping adjustment section of the pair of damping adjustment sections;
The acceleration sensor according to claim 1, further comprising: a second electrode disposed above the inertial mass body as the other damping adjustment unit of the pair of damping adjustment units. The inertial mass is electrically conductive;
The inertial mass body is brought into a stationary state by electrostatic attraction generated by applying a predetermined potential between the inertial mass body and the first electrode and between the inertial mass body and the second electrode. The acceleration sensor according to claim 2, further comprising a servo function that controls the position of the inertial mass body. The detection plate is connected to the inertial mass;
The detection electrode is disposed so as to face the detection plate, separated from the detection plate by a second interval in a state where the inertial mass body is stationary.
The acceleration sensor according to claim 1, wherein the first interval is set narrower than the second interval. The detection plate is connected to the inertial mass;
The detection electrode is disposed so as to face the detection plate, separated from the detection plate by a second interval in a state where the inertial mass body is stationary.
The acceleration sensor according to claim 1, wherein the first interval is set wider than the second interval.   The acceleration sensor according to claim 2, wherein the first electrode and the second electrode are made of polysilicon. The acceleration sensor according to claim 1, wherein the first interval is secured by removing a sacrificial film having a thickness corresponding to the first interval.

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