JP5369819B2 - Capacitive physical quantity detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately perform self-diagnosis even if a detecting spring has high rigidity in a capacitive acceleration sensor having a self-diagnostic function performing self-diagnosis by applying a self-diagnostic signal so as to displace the detecting spring and causing a movable electrode to generate pseudo acceleration. <P>SOLUTION: In a capacitive physical quantity detector, fixed electrodes 31, 41 are supported to a first silicon substrate 11 via springs 32, 42 for the fixed electrodes wherein the springs can be elastically displaced in a y-axial direction perpendicular to an x-axis while the springs can not be displaced elastically in an x-axial direction in which a movable electrode 23 is displaced. The physical quantity detector includes a fixed-electrode displacement means 60 for displacing the fixed electrodes 31, 41 in such a direction that facing areas between the movable electrode 23 and the fixed electrodes 31, 41 in the y-axial direction are increased by elastically displacing the springs 32, 42 for the fixed electrodes by means of an electrostatic attraction force. Self-diagnosis is performed by the fixed-electrode displacement means 60 while the facing areas between the movable electrode 23 and the fixed electrodes 31, 41 are increased as compared to a case when acceleration is detected. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention is a capacitance that displaces a movable electrode by elastic displacement of a spring portion when applying a physical quantity such as acceleration, angular velocity, pressure, etc., and performs a physical quantity in accordance with a capacitance change between the movable electrode and a fixed electrode facing the movable electrode. More particularly, the present invention relates to a device that performs a self-diagnosis by generating a pseudo physical quantity in a movable electrode.

  2. Description of the Related Art Conventionally, as a device that performs self-diagnosis in a capacitive physical quantity detection device that detects a physical quantity, for example, those described in Patent Document 1 and Patent Document 2 have been proposed. This is formed by forming each electrode and spring portion on a semiconductor substrate by a semiconductor process.

  Specifically, this is formed integrally with a support substrate, a detection spring portion supported by the support substrate and having a spring function that is displaced in a predetermined direction in response to application of a physical quantity, and a detection spring portion. The movable electrode is configured to include a movable electrode that can be displaced in a predetermined direction by the elastic displacement of the spring portion, and a fixed electrode that is supported by the support substrate and arranged to face the movable electrode.

  Furthermore, this detection device is movable by switching between a detection signal for detecting a physical quantity that is a periodically changing signal and a self-diagnostic signal that is a periodically changing signal for self-diagnosis. A signal applying means for applying between the electrode and the fixed electrode, and a CV conversion circuit for outputting a voltage corresponding to a change in capacitance composed of the movable electrode and the fixed electrode are provided.

  In this detection device, a physical quantity is detected in accordance with a change in capacitance that occurs during the application of a detection signal, and the detection spring is elastically displaced by the application of a self-diagnosis signal, thereby simulating the movable electrode. Self-diagnosis is performed by generating a physical quantity and detecting the pseudo physical quantity.

JP 2001-91535 A JP 2003-121457 A

  By the way, in the above-described conventional capacity type physical quantity detection device, it is necessary to increase the rigidity of the detection spring portion in accordance with the purpose or the like. For example, when detecting a high range of acceleration as a physical quantity, it is necessary to increase the spring rigidity of the detection spring portion.

  Here, as for self-diagnosis, the self-diagnosis was performed by applying an electrostatic force between the movable electrode and the fixed electrode and converting the displacement of the movable electrode generated thereby into a voltage. If the spring stiffness of the coil becomes high, the displacement amount of the movable electrode at the time of self-diagnosis becomes small, and the output necessary for self-diagnosis cannot be obtained.

  The present invention has been made in view of the above problems, and has a self-diagnosis function for performing a self-diagnosis by applying a self-diagnosis signal to displace the detection spring portion and generating a pseudo physical quantity in the movable electrode. It is an object of the present invention to provide a self-diagnosis that can be appropriately performed even when the rigidity of the detection spring portion is increased.

  In order to achieve the above object, according to the first aspect of the present invention, there is a periodic change between the movable electrode (23) and the fixed electrode (31, 41) formed integrally with the detection spring portion (22). A physical quantity is detected by applying a signal to output a voltage corresponding to a change in capacitance of both electrodes, and a detection signal for detecting the physical quantity and a self-diagnosis signal for performing a self-diagnosis In the capacitive physical quantity detection device in which the detection spring portion (22) is displaced by applying the self-diagnosis signal to generate a pseudo physical quantity in the movable electrode (23), the following is further applied. It features the following points.

  The fixed electrode spring portion (32, 32) that is not elastically displaced in the displacement direction (x) of the movable electrode (23) but is elastically displaceable in a direction (y) perpendicular to the displacement direction (x). 42) supporting the fixed electrodes (31, 41) on the support substrate (11) via 42).

  The opposing area of the movable electrode (23) and the fixed electrode (31, 41) in the orthogonal direction (y) by elastically displacing the fixed electrode spring (32, 42) by electrostatic attraction A fixed electrode displacing means (60) for displacing the fixed electrodes (31, 41) in the direction in which the angle increases.

  The self-diagnosis is performed with the fixed electrode displacing means (60) in a state where the facing area between the movable electrode (23) and the fixed electrodes (31, 41) is increased as compared with the case where the physical quantity is detected. The present invention is characterized by these points.

  According to this, when performing a self-diagnosis, the opposing area between the movable electrode (23) and the fixed electrode (31, 41) increases, and the capacitance between the electrodes (23, 31, 41) also increases. Even if the sensitivity is improved and the rigidity of the detection spring portion (22) is increased, the self-diagnosis can be appropriately performed.

  Here, the invention according to claim 2 and claim 3 is further characterized by the following points in the capacity type physical quantity detection device according to claim 1.

  A fixed electrode formed integrally with the movable electrode (23) and provided with a weight portion (21) that is displaced together with the movable electrode (23) in a predetermined direction (x), and is opposed to the weight portion (21). A fixed electrode support part (30a, 40a) for supporting the spring part (32, 42) for the support on the support substrate (11).

  The predetermined direction which is the displacement direction of the movable electrode (23) is the x-axis direction, the direction orthogonal to the predetermined direction, and the fixed electrodes (31, 41) are displaced by the fixed electrode spring portions (32, 42). When the direction is the y-axis direction and the x-axis direction and the direction orthogonal to the y-axis direction are the z-axis directions, the movable electrode (23) is moved from the weight part (21) to the fixed electrode support part (30a, 40a) side. The fixed electrodes (31, 41) protrude from the fixed electrode spring portions (32, 42) to the weight portion (21) side and extend along the y-axis direction. It has a columnar shape, and the side surfaces extending in the y-axis direction are opposed to each other in the movable electrode (23) and the fixed electrodes (31, 41), and a capacitor is formed between the facing side surfaces.

  In the case of the movable and fixed electrodes having the columnar shape, the planar shape of the movable electrode (23) and the fixed electrodes (31, 41) along the xy plane that is a plane including the x axis and the y axis are further defined in claim 2. These planar shapes are both elongated rectangular shapes having a constant width between the root portion and the protruding tip portion.

  This configuration is preferable when applied to a configuration of comb-like movable and fixed electrodes used for an acceleration sensor or the like, for example. During self-diagnosis, the side surfaces of both electrodes (23, 31, 41) facing each other are The facing area increases.

  Further, in the case of the movable and fixed electrodes having the columnar shape, the planar shape of the movable electrode (23) along the xy plane is narrowed from the weight (21) side to the protruding tip side as in claim 3. The planar shape of the fixed electrode (31, 41) along the xy plane is a wedge shape that becomes narrower from the fixed electrode spring portion (32, 42) side to the protruding tip portion side. Also good.

  In the case of this wedge-shaped configuration, when the facing area between the movable electrode (23) and the fixed electrode (31, 41) is increased during self-diagnosis, the movable electrode (23) and the fixed electrode ( The distance between the electrodes 31 and 41) is reduced, the capacitance between these electrodes can be increased, and the detection sensitivity of the self-diagnosis can be improved.

  In the capacitive physical quantity detection device according to claim 2 or 3, as in the invention according to claim 4, the fixed electrode spring portions (32, 42) extend along the x-axis direction. The first beams (32a, 42a) connected to the fixed electrode support portions (30a, 40a) and the first beams (32a, 42a) are arranged apart from each other in the y-axis direction and in the x-axis direction. The second beam (32b, 42b) extending along the fixed electrode (31, 41) and connected to both ends of the first and second beams in the x-axis direction (32c, 42c) ) And is elastically displaced so that the distance between the first beam (32a, 42a) and the second beam (32b, 42b) changes. There may be.

  According to this, the space occupied by the fixed electrode spring portions (32, 42) can be reduced as much as possible, which is advantageous in terms of downsizing of the apparatus.

  Further, in the capacitive physical quantity detection device according to claim 4, as in the invention according to claim 5, the fixed electrode displacement means (60) is the second of the fixed electrode spring portion (32, 42). An electrostatic attractive force generating electrode (61) is provided opposite to the beam (32b, 42b) in the y-axis direction, and a voltage is applied to the electrostatic attractive force generating electrode (61). Thus, an electrostatic attractive force is applied to the second beam (32b, 42b) to elastically displace the fixed electrode spring portion (32, 42).

  According to this, the fixed electrode displacement means (60) suitable for the structure of the fixed electrode spring portion (32, 42) of claim 4 is provided.

  In addition, the code | symbol in the bracket | parenthesis of each means described in the claim and this column is an example which shows a corresponding relationship with the specific means as described in embodiment mentioned later.

1 is a schematic plan view of a semiconductor acceleration sensor according to a first embodiment of the present invention. It is an AA schematic sectional drawing in FIG. FIG. 2 is a schematic cross-sectional view taken along line BB in FIG. 1. It is CC schematic sectional drawing in FIG. FIG. 3 is a diagram showing a schematic configuration of a fixed electrode displacement unit according to the first embodiment. It is a schematic plan view for demonstrating the action | operation of the fixed electrode displacement means shown in FIG. It is a figure which shows the specific structure of the circuit means in the sensor shown in FIG. It is a signal waveform diagram with which it uses for operation | movement description at the time of normal operation | movement of the circuit means shown in FIG. It is a signal waveform diagram with which it uses for operation | movement description at the time of the self-diagnosis of the circuit means shown in FIG. It is a figure which shows the typical structure of the fixing | fixed part and fixed electrode displacement means which concern on 2nd Embodiment of this invention. It is a schematic plan view for demonstrating the action | operation of the fixed electrode displacement means shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are given the same reference numerals in the drawings in order to simplify the description.

(First embodiment)
In the first embodiment of the present invention, the present invention is applied to a differential capacitive semiconductor acceleration sensor as a capacitive physical quantity detection device. This semiconductor acceleration sensor can be applied to, for example, an automobile acceleration sensor or a gyro sensor for performing operation control of an airbag, an ABS, a VSC, or the like.

  FIG. 1 is a diagram illustrating a schematic plan configuration of a semiconductor acceleration sensor 100 according to the present embodiment, FIG. 2 is a diagram illustrating a schematic cross-sectional structure taken along a dashed line AA in FIG. 1, and FIG. FIG. 4 is a diagram showing a schematic cross-sectional structure along the alternate long and short dash line BB in FIG. 1, and FIG. 4 is a diagram showing a schematic cross-sectional structure along the alternate long and short dash line CC in FIG.

  A semiconductor acceleration sensor (hereinafter simply referred to as a sensor) 100 is formed by subjecting a semiconductor substrate 10 to known micromachining. Here, the semiconductor substrate 10 constituting the sensor 100 is, as shown in FIG. 2, between a first silicon substrate 11 as a first semiconductor layer and a second silicon substrate 12 as a second semiconductor layer. A rectangular SOI substrate 10 having an oxide film 13 as an insulating layer. In the present embodiment, the first silicon substrate 11 is configured as a support substrate.

  The second silicon substrate 12 is formed by etching and patterning the second silicon substrate 12 to form a beam structure having a comb tooth shape including the movable portion 20 and the fixed portions 30 and 40.

  The movable portion 20 and the fixed portions 30 and 40 are provided with anchor portions 20a, 30a, and 40a that are fixed and supported by the first silicon substrate 11 as a support substrate. Here, each of these anchor portions 20a to 40a is supported by the first silicon substrate 11 via the oxide film 13 (see FIGS. 2 and 4).

  Further, in the movable portion 20 and the fixed portions 30 and 40 other than the anchor portions 20a to 40a, the oxide film 13 immediately below the portions is removed by sacrificial layer etching or the like, and is separated from the first silicon substrate 11. It is supposed to be in a state. Thus, the movable part 20 and the fixed parts 30 and 40 are supported by the first silicon substrate 11 at the respective anchor parts 20a to 40a.

  The movable portion 20 includes an elongated rectangular weight portion 21, a detection spring portion 22 connected to both ends of the weight portion 21, and a movable electrode 23 integrally connected to the weight portion 21, and includes a detection spring. The portion 22 is integrally connected to the anchor portion 20a of the movable portion 20. Thereby, the weight part 21, the detection spring part 22, and the movable electrode 23 are supported by the first silicon substrate 11 that is a support substrate and are separated from the first silicon substrate 11.

  Here, the detection spring portion 22 has an elongated frame shape in which two beams arranged in parallel are connected at both ends thereof, and is elastically displaced in a direction perpendicular to the longitudinal direction of these beams. Has a spring function.

  Specifically, the detection spring portion 22 displaces the weight portion 21 in the x-axis direction when receiving an acceleration including a component in the x-axis direction in FIG. 1, and the original state according to the disappearance of the acceleration. To restore. Thus, the weight portion 21 and the movable electrode 23 can be displaced in a predetermined direction, that is, in the displacement direction (x-axis direction) of the detection spring portion 22 in accordance with the application of acceleration.

  Here, the respective directions of the x-axis, y-axis, and z-axis shown in FIG. 1 will be described. As described above, the x-axis direction is the displacement direction of the detection spring portion 22 and also the displacement direction of the weight portion 21 and the movable electrode 23.

  The y-axis direction is in a plane parallel to the support surface (the upper surface of the first silicon substrate 11 in FIGS. 2 to 4) that supports the movable portion 20 and the fixed portion 40 of the first silicon substrate 11 that is the support substrate. , The direction perpendicular to the x-axis direction. The z-axis direction is a direction orthogonal to the support surface of the first silicon substrate 11, that is, a direction orthogonal to the xy plane as a plane including the x-axis and the y-axis.

  In the present embodiment, the movable electrode 23 protrudes in opposite directions from both side surfaces of the weight portion 21 along the y-axis direction orthogonal to the x-axis direction, which is the displacement direction of the detection spring portion 22, and the y-axis direction. It has a column shape extending to In FIG. 1, the movable electrode 23 is formed to protrude along the y-axis direction on each of the upper side and the lower side of the weight part 21.

  In the present embodiment, each movable electrode 23 is arranged on the first silicon substrate 11 apart from the first silicon substrate 11 as shown in FIG. It can be displaced in the x-axis direction, which is the displacement direction of the portion 22.

  The fixing portions 30 and 40 are respectively provided on one side and the other side in the y-axis direction of the weight portion 21 with the weight portion 21 interposed therebetween, and the first fixing portion 30 located on the upper side in FIG. It consists of the 2nd fixing | fixed part 40 located in the lower side in FIG. The two fixing portions 30 and 40 are electrically independent from each other. 3 and 4 show the second fixing portion 40, the first fixing portion 30 has the same configuration as this.

  Each of the fixed portions 30 and 40 has an anchor portion 30a and 40a, and fixed electrode spring portions 32 and 42 and fixed electrodes 31 and 41 integrally connected thereto. The fixed electrode 31 on the first fixed portion 30 side is referred to as the first fixed electrode 31, and the fixed electrode 41 on the second fixed portion 40 side is referred to as the second fixed electrode 41.

  The anchor portions 30a and 40a fix and support the fixing portions 30 and 40 on the support surface of the first silicon substrate 11, and as shown in FIG. 4, on the support surface of the first silicon substrate 11. It is supported via the oxide film 13.

  The fixed electrode spring portions 32 and 42 are connected to anchor portions 30a and 40a as fixed electrode support portions, and are supported by the first silicon substrate 11 via the anchor portions 30a and 40a. The fixed electrodes 31 and 41 have a columnar shape protruding from the fixed electrode spring portions 32 and 42 toward the weight portion 21. That is, the fixed electrodes 31 and 41 are supported in a cantilever manner by the anchor portions 30a and 40a via the fixed electrode spring portions 32 and 42.

  As shown in FIGS. 3 and 4, the oxide film 13 is removed immediately below the fixed electrodes 31 and 41 and the fixed electrode spring portions 32 and 42, and the fixed electrodes 31 and 41 and the fixed electrodes are removed. The spring portions 32 and 42 are disposed on the first silicon substrate 11 so as to be separated from the first silicon substrate 11.

  Here, the fixed electrodes 31 and 41 and the movable electrode 23 face each other with a predetermined detection interval 50, and a capacitance for acceleration detection is formed in the detection interval 50. Here, as shown in FIG. 1, the movable electrode 23 has a columnar shape that protrudes from the weight portion 21 toward the anchor portions 30 a and 40 a of the fixed portion and extends along the y-axis direction.

  On the other hand, the fixed electrodes 31 and 41 have a columnar shape protruding from the fixed electrode spring portions 32 and 42 toward the weight portion 21 and extending along the y-axis direction. As shown in FIG. 1, the planar shape of the movable electrode 23 and the planar shapes of the fixed electrodes 31 and 41 along the xy plane are both elongated rectangles having a constant width between the root portion and the protruding tip portion. It is made into a shape.

  That is, in the present embodiment, both the movable and fixed electrodes 23, 31, 41 have a straight column shape with a constant width. The side surfaces extending in the y-axis direction of the movable electrode 23 and the fixed electrodes 31 and 41 are opposed in parallel with each other with the detection interval 50 therebetween, and the acceleration detection is performed between the opposed side surfaces. A capacity is formed.

  The fixed electrode spring portions 32 and 42 are supported on the first silicon substrate 11 via the anchor portions 30a and 40a in a state where the spring portions 32 and 42 can be elastically displaced on the first silicon substrate 11. The fixed electrode spring portions 32 and 42 are not elastically displaced in the x-axis direction, which is the displacement direction of the movable electrode 23, but are elastically displaceable in the y-axis direction orthogonal to the x-axis direction. is there.

  Specifically, as shown in FIGS. 1 and 4, the fixed electrode spring portions 32 and 42 of the present embodiment are composed of two beams similar to the detection spring portion 22. This corresponds to a configuration in which the detection spring portion 22 is rotated 90 degrees in the xy plane.

  That is, the fixed electrode spring portions 32 and 42 are arranged such that two first beams 32a and 42a and second beams 32b and 42b extending along the x-axis direction are separated from each other in the y-axis direction. The first and second beams 32a, 42a, 32b, 42b have an elongated frame shape formed by connecting both end portions in the x-axis direction with connecting portions 32c, 42c. The anchor portions 30a and 40a are integrally connected to the intermediate portion of the first beams 32a and 42a, and the fixed electrodes 31 and 41 are integrally connected to the intermediate portion of the second beams 32b and 42b.

  In the fixed electrode spring portions 32 and 42, the first beams 32a and 42a, the second beams 32b and 42b, and the connecting portions 32c and 42c are elastically deformable, and are arranged in the y-axis direction. Elastic displacement is performed so that the distance between the first beams 32a and 42a and the second beams 32b and 42b is increased or decreased. By doing so, the distances along the y-axis direction between the fixed electrodes 31 and 41 and the anchor portions 30a and 40a that support the fixed electrodes 31 and 41 change.

  Thus, the fixed electrode spring portions 32 and 42 of the present embodiment are restrained from moving in the x-axis direction, which is the displacement direction of the movable electrode 23, but the fixed electrodes 31 and 41 are fixed electrode spring portions 32 and 42. The movement in the y-axis direction, which is the direction displaced by 42, exhibits an elastic force so as to have a degree of freedom.

  Further, the sensor 100 of the present embodiment is provided with a fixed electrode displacing means 60 for displacing the fixed electrodes 31 and 41 by elastically displacing the fixed electrode spring portions 32 and 42 for the respective fixed portions 30 and 40. ing. FIG. 5 is a diagram showing a schematic configuration of the fixed electrode displacement means 60 and the second fixed portion 40. The first fixing portion 30 and the fixed electrode displacement means 60 provided on the first fixing portion 30 are the same as those in FIG.

  The fixed electrode displacing means 60 includes an electrostatic attractive force generating electrode 61 provided in the vicinity of the fixed electrode spring portions 32 and 42, and an electrostatic attractive force generating circuit 62 for applying a voltage to the electrostatic attractive force generating electrode 61. It is configured with.

  As shown in FIGS. 1, 3, and 5, the electrostatic attractive force generating electrode 61 is formed on the second beams 32 b and 42 b positioned on the fixed electrodes 31 and 41 side in the fixed electrode spring portions 32 and 42. On the other hand, they are arranged opposite to each other in the y-axis direction.

  The electrostatic attractive force generating electrode 61 is formed by micromachining the second silicon substrate 12 in the same manner as the beam structures 20 to 40 in the semiconductor substrate 10, and each anchor portion 20a, 30a, 40a. Similarly, the first silicon substrate 11 is fixed and supported via the oxide film 13.

  The electrostatic attraction generating electrode 61 has a larger area facing the second beams 32b and 42b, so that the area facing the second beams 32b and 42b is larger than the area facing the fixed electrodes 31 and 41. The shape is larger than that. Here, the planar shape of the electrostatic attraction generating electrode 61 along the xy plane is a rectangle having long sides along the second beams 32b and 42b, as shown in FIGS. Yes.

  The electrostatic attraction generation circuit 62 is provided on a circuit board or the like housed in a package described later provided outside the semiconductor substrate 10, and a voltage applied to the electrostatic attraction generation electrode 61. Can be switched on and off. The electrostatic attractive force generating circuit 62 and the electrostatic attractive force generating electrode 61 are electrically connected by wire bonding, bump bonding, or the like via wirings or pads (not shown) provided on the semiconductor substrate 10.

  FIG. 6 is a schematic plan view for explaining the operation of the fixed electrode displacing means 60. FIG. 6 (a) schematically shows the entire sensor 100, and FIG. 6 (b) shows the second fixed portion 40 partially. It is enlarged to show.

  In FIG. 6A, the detection spring 22 is displaced in the left direction in the drawing along the x-axis direction. In FIG. 6, the fixed electrodes 31 and 41 and the fixed electrode spring portions 32 and 42 indicate a state before the electrostatic attraction is applied by a broken line, and indicate a state after the application by a solid line. 6B shows the second fixing portion 40, the first fixing portion 30 is the same as that shown in FIG. 6B.

  In the present embodiment, by applying a voltage to the electrostatic attractive force generating electrode 61 by the electrostatic attractive force generating circuit 62, the second beam 32b in the electrostatic attractive force generating electrode 61 and the fixed electrode spring portions 32 and 42, An electrostatic attractive force including a component in the y-axis direction acts between the terminal 42b and the element 42b.

  Then, as shown in FIG. 6, the second beams 32b and 42b are attracted to the electrostatic attractive force generating electrode 61 side, and the distance between the beams 32a and 42a and 32b and 42b is increased. The spring portions 32 and 42 are elastically displaced along the y-axis direction. At the same time, the fixed electrodes 31 and 41 are displaced in the direction approaching the weight portion 21 along the y-axis direction.

  Therefore, in the detection interval 50, the facing area between the movable electrode 23 and the fixed electrodes 31 and 41 increases after the application of the electrostatic attraction force than before the application of the electrostatic attraction. When acceleration in the x-axis direction is applied at this time, the movable electrode 23 is displaced in the x-axis direction by the action of the detection spring portion 22 while the facing area is increased.

  When the supply of voltage from the electrostatic attractive force generating circuit 62 is stopped, the electrostatic attractive force disappears, and the fixed electrode spring portions 32 and 42 are restored to the original state in accordance with the disappearance of the electrostatic attractive force. The fixed electrodes 31 and 41 are also returned to the positions before the electrostatic attractive force is applied. Thus, the fixed electrodes 31 and 41 can be displaced in the y-axis direction, which is the displacement direction of the fixed electrode spring portions 32 and 42, in accordance with the application of electrostatic attraction.

  Thus, the fixed electrode displacing means 60 is a direction in which the facing area between the movable electrode 23 and the fixed electrodes 31 and 41 increases in the y-axis direction by elastically displacing the fixed electrode spring portions 32 and 42. In addition, the fixed electrodes 31 and 41 are configured to be displaced.

  Further, although not shown in the figure, a movable electrode pad 23a (see FIG. 7 described later) electrically connected to the movable electrode 23 and the fixed electrodes 31 and 41 are electrically connected to appropriate positions of the semiconductor substrate 10. Fixed electrode pads 31a and 41a (see FIG. 7 described later) are formed. The movable electrode 23 and the fixed electrodes 31 and 41 are connected to the circuit means 200 (see FIG. 7 described later) by these pads.

  Although not shown, the semiconductor substrate 10 constituting the sensor 100 is installed in a package, and the electrostatic attraction generating circuit 62 and the circuit means 200 as the fixed electrode displacement means described above are formed in the package. A circuit board, a circuit chip, etc. are accommodated. And this circuit means 200 and each said electrode pad 23a, 31a, 41a are electrically connected by wire bonding, bump bonding, etc. FIG.

  Next, the operation of acceleration detection and self-diagnosis in the sensor 100 of this embodiment will be described. FIG. 7 is a diagram showing a configuration of the circuit means 200 provided in the sensor 100. The circuit means 200 includes a CV conversion circuit (switched capacitor circuit) 210 and a switch circuit 220.

  In the present sensor 100, the first capacitor CS <b> 1 is formed at the detection interval 50 between the first fixed electrode 31 and the movable electrode 23, and the second capacitance at the detection interval 50 between the second fixed electrode 41 and the movable electrode 23. A capacitor CS2 is formed.

  When the acceleration is received, the entire movable portion 20 excluding the anchor portion 20a is integrally displaced in the x-axis direction by the spring function of the detection spring portion 22, and each of the capacitors CS1, CS2 changes. The detection circuit 200 detects acceleration based on a change in the differential capacitance (CS1-CS2) caused by the movable electrode 23 and the fixed electrodes 31, 41.

  The CV conversion circuit 210 converts a change in the capacitances CS1 and CS2 composed of the movable electrode 23 and the fixed electrodes 31 and 41 into a voltage and outputs the voltage. The CV conversion circuit 210 includes an operational amplifier 211, a capacitor 212, and a switch 213. ing.

  The inverting input terminal of the operational amplifier 211 is connected to the movable electrode 23 via the movable electrode pad 23a, and a capacitor 212 and a switch 213 are connected in parallel between the inverting input terminal and the output terminal. In addition, either the voltage V / 2 or the voltage V1 is input to the non-inverting input terminal of the operational amplifier 211 via the switch circuit 220.

  The switch circuit 220 has either a V / 2 voltage or a V1 (different from V / 2) voltage from each voltage source (not shown) at the non-inverting input terminal of the operational amplifier 211 in the CV conversion circuit 210. , And is composed of a switch 221 and a switch 222. The switch 221 and the switch 222 are configured such that the other opens when one is closed.

  Further, the circuit means 200 has a control circuit (not shown). This control circuit inputs a carrier wave P1 that periodically changes with a fixed amplitude V from the fixed electrode pad 31a to the first fixed electrode 31 and fixes it. A carrier wave P2 that is 180 ° out of phase with the carrier wave P1 and has the same amplitude V is input to the second fixed electrode 41 from the electrode pad 41a.

  The control circuit can control the opening / closing of the switches 213, 221, and 222 at a predetermined timing. In the present embodiment, the control circuit and the switch circuit 220 constitute a signal applying unit.

  The operation of the above configuration will be described. First, a state in which a detection signal for detecting acceleration is applied (during normal operation) will be described with reference to a signal waveform diagram shown in FIG.

  As shown in FIG. 8, the carrier wave P1 (for example, frequency 100 kHz, amplitude 0 to 5 V) output from the control circuit as the signal applying means has a high level and a low level with a period φ1 as one cycle (for example, 10 μs). The rectangular wave signal has a constant amplitude that changes, and the carrier wave P2 is a rectangular wave signal whose voltage level is inverted with respect to the carrier wave P1.

  In normal operation, when the carrier waves P1 and P2 are applied to the fixed electrodes 31, 41, the switch 221 is closed and the switch 222 is open in the switch circuit 220. Thereby, a voltage of V / 2 is applied to the non-inverting input terminal of the operational amplifier 211, and a constant voltage (movable electrode signal) of V / 2 (for example, 2.5V) is applied to the movable electrode 23.

  When no acceleration is applied in this state, the potential difference between the first fixed electrode 31 and the movable electrode 23 and the potential difference between the second fixed electrode 41 and the movable electrode 23 are both V / 2, The electrostatic force between the first fixed electrode 31 and the movable electrode 23 and the electrostatic force between the second fixed electrode 41 and the movable electrode 23 are substantially equally balanced.

  Further, during normal operation, in the CV conversion circuit 220, the switch 213 is opened and closed at the timing shown in FIG. When the switch 213 is closed (period φ2), the capacitor 212 is reset. On the other hand, acceleration detection is performed when the switch 213 is opened. That is, the period other than the period φ2 in the period φ1 is a period for detecting acceleration. In this detection period, the output voltage V0 from the CV conversion circuit 220 is expressed by the following Equation 1.

(Equation 1)
V0 = (CS1-CS2) .V '/ Cf
Here, V ′ is a voltage between both pads 31 a and 41 a, that is, between both fixed electrodes 31 and 41, and Cf is a capacitance of the capacitor 212.

  When acceleration is applied, the balance between the first capacitor CS1 and the second capacitor CS2 changes. Then, a voltage corresponding to the capacitance difference (CS1−CS2) based on the above formula 1 is output as an output V0 (for example, 0 to 5V) in a form added as a bias to the output V0 when no acceleration is applied. Thereafter, the output V0 is subjected to signal processing by a signal processing circuit (not shown) including an amplifier circuit, a low-pass filter, and the like, and is detected as an acceleration detection signal.

  Next, the operation at the time of self-diagnosis will be described with reference to the signal waveform diagram shown in FIG. As shown in FIG. 9, carrier waves P <b> 1 and P <b> 2, which are rectangular wave signals having a constant amplitude V (amplitude 0 to 5 V in the illustrated example), are input by the control circuit as signal applying means. Here, in the period φ3 (for example, 100 μs), the carrier wave P1 and the carrier wave P2 are constant voltage signals (for example, the carrier wave P1 is 0V and the carrier wave P2 is 5V) whose voltage levels are inverted.

  In the period φ3, when the carrier waves P1 and P2 are applied to the fixed electrodes 31, 41, the switch 221 is open and the switch 222 is closed in the switch circuit 220. Therefore, a voltage V1 (for example, 3V) different from V / 2 is applied to the non-inverting input terminal of the operational amplifier 211, and this voltage V1 is applied to the movable electrode 23 as a movable electrode signal.

  When the voltage V1 is applied to the movable electrode 23, the balance of the electrostatic force in the normal operation is lost, and the movable electrode 23 is the fixed electrode with the larger potential difference between the fixed electrode 31 and 41 and the movable electrode 23. Be drawn to. In the example shown in FIG. 9, the detection spring portion 22 bends so that the first fixed electrode 31 is attracted, and the movable electrode 23 is pseudo-displaced integrally therewith.

  As described above, the period φ3 is a period during which pseudo acceleration is generated in the movable electrode 23. Note that in the period φ3, the switch 213 of the CV conversion circuit 220 is closed, and thus the capacitor 212 is in a reset state.

  Next, in the period φ4 (for example, 10 μs), a signal waveform similar to that in the period φ1 shown in FIG. 8 is applied between the movable electrode 23 and the fixed electrodes 31 and 41, so that the previous period φ3. This is a period for detecting the generated pseudo acceleration (physical quantity).

  That is, the switch 213 of the CV conversion circuit 220 is opened, the capacitor 212 is set in the same state as the acceleration can be detected, and the carrier waves P1 and P2 similar to those in the normal operation are applied. In the switch circuit 220, the switch 221 is closed and the switch 222 is opened, and a constant voltage of V / 2 (for example, 2.5 V) is applied to the movable electrode 23 as a drive electrode signal.

  Then, in this period φ4, for example, the movable electrode 23 that has been attracted toward the first fixed electrode 31 tends to return to the original position, so that the capacitor 212 of the CV conversion circuit 220 is changed according to this capacitance change. A pseudo acceleration generated during the period φ3 can be detected.

  As described above, the self-diagnosis signal (the carrier wave and the movable electrode signal) having the period (φ3 + φ4) as one cycle is applied between the movable electrode 23 and the fixed electrodes 31, 41, thereby enabling self-diagnosis. Yes.

  Here, in this embodiment, at the time of further self-diagnosis, as shown in FIG. 6, the opposed area between the movable electrode 23 and the fixed electrodes 31 and 41 is set larger than that when the acceleration is detected by the fixed electrode displacement means 60. Increased state. In this state, the above-described pseudo acceleration is detected.

  Specifically, in the period (φ3 + φ4), which is a period for performing the self-diagnosis, the self-diagnosis is controlled in the same manner as described above while applying a voltage from the electrostatic attraction generation circuit 62 to the electrostatic attraction generation electrode 61. To. Further, the application of the voltage is stopped in a period other than the period (φ3 + φ4). The voltage can be easily switched on / off using a general switching circuit or the like.

  As described above, according to the present embodiment, when the self-diagnosis is performed, the facing area between the movable electrode 23 and the fixed electrodes 31 and 41 is increased more than when the acceleration is detected, so that the capacitance between the electrodes 23, 31 and 41 is increased. Can also be increased. As a result, the detection sensitivity can be improved as compared with the acceleration detection.

  Therefore, the sensitivity of the self-diagnosis can be ensured even if the rigidity of the detection spring portion 22 is increased and the displacement amount of the movable electrode 23 is reduced when generating pseudo acceleration, and appropriate self-diagnosis is possible. Is possible.

  In the present embodiment, the movable electrode 23 is directly supported by the weight portion 21, and the fixed electrodes 31 and 41 are directly supported by the fixed electrode spring portions 32 and 42. These movable and fixed electrodes 23, 31, 41 are formed in a straight column shape with a constant width protruding from their own support part toward the other support part, and their side faces are opposed to each other to detect the interval. 50.

  In this case, in FIG. 1, the pair of opposed movable and fixed electrodes 23, 31, 41 is provided on each of the upper and lower sides of the weight part 21. It may be provided. In such a case, such a comb-like electrode structure in which a plurality of columnar electrodes are engaged with each other is provided. Even in this case, the same effect as described above can be obtained by providing fixed electrode displacing means.

  Further, in the present embodiment, as described above, the fixed electrode spring portions 32, 42 are formed in an elongated frame shape in which two beams 32a, 32b, 42a, 42b arranged in parallel are connected at both ends thereof. None, having a spring function of elastically displacing in the y-axis direction perpendicular to the longitudinal direction of each beam. Therefore, the space occupied by the fixed electrode spring portions 32 and 42 in the sensor 100 can be reduced as much as possible, which is advantageous in terms of size reduction.

  Further, the fixed electrode displacing means 60 of the present embodiment is opposed to the static beams springs 32 and 42 composed of two beams, and is opposed to the second beams 32b and 42b. An electrode 61 for generating an attractive force is provided, and a suitable configuration is realized in which an electrostatic attractive force is applied to the second beams 32b and 42b by applying a voltage thereto.

  In the fixed electrode spring portions 32 and 42 composed of the two beams, the second beams 32b and 42b extending long are suitable places for applying an electrostatic attractive force. Therefore, in the above example, the electrostatic attractive force generating electrode 61 has the above-described planar rectangle, the long side portion is opposed to the second beams 32b and 42b, and the short side portion is opposed to the fixed electrodes 31 and 41. By doing so, the electrostatic attractive force acting on the second beams 32b and 42b is made larger.

  In the present embodiment, it is also possible to remove foreign matters sandwiched between the detection intervals 50 by performing excitation at the resonance frequency a plurality of times for the electrodes during self-diagnosis.

(Second Embodiment)
FIG. 10 is a diagram showing a schematic plan configuration of the main part of the semiconductor acceleration sensor according to the second embodiment of the present invention. The schematic configuration of the second fixed portion 40 and the fixed electrode displacing means 60 in this sensor is shown. Show. The first fixing portion 30 is the same as that shown in FIG.

  FIG. 11 is a schematic plan view for explaining the operation of the fixed electrode displacing means 60 in the present sensor. FIG. 11A schematically shows the entire sensor, and FIG. 11B shows the second fixing portion 40. Is shown enlarged.

  11A shows a state in which the detection spring portion 22 is displaced to the left in the drawing along the x-axis direction. In FIG. 11, the fixed electrodes 31 and 41 and the fixed electrode The spring parts 32 and 42 indicate a state before application of electrostatic attraction by a broken line, and indicate a state after application by a solid line. Moreover, in FIG.11 (b), although it has shown about the 2nd fixing | fixed part 40, it is the same as that of FIG.11 (b) also about the 1st fixing | fixed part 30. FIG.

  The present embodiment is different from the first embodiment in the shapes of the movable electrode 23 and the fixed electrodes 31 and 41, and this difference will be mainly described.

  As shown in FIGS. 10 and 11, also in this embodiment, the weight portion 21 is formed integrally with the movable electrode 23 and is displaced in the x-axis direction together with the movable electrode 23. Although omitted in FIG. 11 (a), as in FIG. 1, in the sensor of this embodiment, the anchor portion 30a as the fixed electrode support portion is provided so as to face the weight portion 21 apart from the weight portion 21. The anchor portions 30 a and 40 a support the fixed electrode spring portions 32 and 42 on the first silicon substrate 11.

  10 and 11, the x-axis direction is the displacement direction of the movable electrode 23, the y-axis direction is the direction orthogonal to the x-axis, and the fixed electrodes 31, 41 are the fixed electrode spring portions 32, 42. The z-axis direction is indicated as a direction orthogonal to the x-axis direction and the y-axis direction, respectively.

  Here, in the present embodiment, the movable electrode 23 has a columnar shape protruding from the weight portion 21 toward the anchor portions 30a and 40a of the fixed portion and extending along the y-axis direction, and includes the x-axis and the y-axis. The planar shape of the movable electrode 23 along the xy plane is a wedge shape that becomes thinner from the root portion on the weight portion 21 side toward the protruding tip portion side.

  The fixed electrodes 31 and 41 have a columnar shape protruding from the fixed electrode spring portions 32 and 42 toward the weight portion 21 and extending along the y-axis direction. The fixed electrodes 31 and 41 along the xy plane are described above. The planar shape is a wedge shape that becomes narrower as it goes from the root portion on the fixed electrode spring portion 32, 42 side toward the protruding tip portion side.

  In the movable electrode 23 and the fixed electrodes 31 and 41, the side surfaces extending in the y-axis direction face each other with a detection interval 50, and a capacitance for acceleration detection is formed between the side surfaces. In the present embodiment, these side surfaces are arranged in an inclined manner with respect to the y axis and are in a parallel relationship with each other.

  Therefore, also in the present embodiment, when performing self-diagnosis, the fixed electrodes 31 and 41 are displaced in the direction approaching the weight portion 21 along the y-axis direction by application of electrostatic attraction from the fixed electrode displacement means 60. Since the facing area between the movable electrode 23 and the fixed electrodes 31 and 41 is increased as compared with the acceleration detection, the capacitance between the electrodes 23, 31 and 41 can be increased.

  Further, in this embodiment, the movable electrode 23 and the fixed electrodes 31 and 41 facing the movable electrode 23 are not formed in a straight column shape having a constant width, and both are wedges that become tapered as they go from the root portion side to the protruding tip portion side. It has a shape.

  Therefore, the distance along the x-axis direction between the movable electrode 23 and the fixed electrodes 31 and 41 is smaller in the state after the electrostatic attractive force is applied than in the state before the electrostatic attractive force is applied. That is, the detection interval 50 is shortened. As a result, the capacitance between the electrodes can be increased, and the detection sensitivity for self-diagnosis can be improved.

(Other embodiments)
In the example shown in the first embodiment, the movable electrode 23 is artificially displaced by changing the voltage applied to the movable electrode 23 during normal operation and during self-diagnosis. The movable electrode 23 may be pseudo-displaced by changing the voltage in the carrier waves P1 and P2 applied to 41 to perform self-diagnosis.

  Further, as described above, the fixed electrode spring portions 32 and 42 are not elastically displaced in the x-axis direction which is the displacement direction of the movable electrode 23 but elastically in the y-axis direction orthogonal to the x-axis direction. Any shape may be used as long as it has a displaceable spring function, and any shape other than the beam shape as shown in the above-mentioned figure may be used.

  Further, the present invention is not limited to the one applied to the semiconductor acceleration sensor, but can be similarly applied to a capacitance type physical quantity detection device such as a pressure sensor and a yaw rate sensor.

DESCRIPTION OF SYMBOLS 11 1st silicon substrate as a support substrate 21 Weight part 22 Detection spring part 23 Movable electrode 30a Anchor part of the 1st fixed part as a fixed electrode support part 31 1st fixed electrode 32 Fixed electrode of the 1st fixed part Spring portion 32a First beam 32b in the fixed electrode spring portion of the first fixed portion Second beam 32c in the fixed electrode spring portion of the first fixed portion In the fixed electrode spring portion of the first fixed portion Connecting portion 40a Anchor portion of the second fixed portion as the fixed electrode support portion 41 Second fixed electrode 42 Spring portion for fixed electrode of the second fixed portion 42a First portion of the fixed electrode spring portion of the second fixed portion Beam 42b Second beam 42c in the fixed electrode spring portion of the second fixed portion Connection portion in the fixed electrode spring portion of the second fixed portion 60 Fixed electrode displacement means 61 Electrostatic attractive force generating electrode 210 C-V conversion Circuit 220 signal applying means

Claims (5)

A support substrate (11);
A detection spring portion (22) supported by the support substrate (11) and having a spring function of displacing in a predetermined direction (x) in response to application of a physical quantity;
A movable electrode (23) formed integrally with the detection spring part (22) and displaceable in the predetermined direction (x) by elastic displacement of the detection spring part (22);
Fixed electrodes (31, 41) supported by the support substrate (11) and arranged to face the movable electrode (23);
Switching between a detection signal for detecting the physical quantity and a self-diagnosis signal for periodically performing a self-diagnosis signal, the detection signal for detecting the physical quantity, and the movable electrode (23) and the Signal applying means (220) applied between the fixed electrodes (31, 41);
A CV conversion circuit (210) that outputs a voltage corresponding to a change in capacitance composed of the movable electrode (23) and the fixed electrode (31, 41);
Detecting the physical quantity according to a change in the capacitance generated during application of the detection signal;
In the capacitive physical quantity detection device configured to generate a pseudo physical quantity in the movable electrode (23) by elastically displacing the detection spring part (22) by applying the self-diagnosis signal,
The fixed electrodes (31, 41) are not elastically displaced in the predetermined direction (x), which is the displacement direction of the movable electrode (23), but in a direction (y) orthogonal to the predetermined direction (x). Is supported on the support substrate (11) via elastically displaceable spring portions (32, 42) for fixed electrodes,
The movable electrode (23) and the fixed electrode are moved in a direction (y) perpendicular to the predetermined direction (x) by elastically displacing the fixed electrode spring (32, 42) by electrostatic attraction. Fixed electrode displacing means (60) for displacing the fixed electrode (31, 41) in a direction in which the facing area to (31, 41) increases,
The self-diagnosis is performed in a state where the opposed area between the movable electrode (23) and the fixed electrode (31, 41) is increased by the fixed electrode displacing means (60) than when the physical quantity is detected. Capacitive physical quantity detection device characterized by that. A weight portion (21) formed integrally with the movable electrode (23) and displaced in the predetermined direction (x) together with the movable electrode (23);
Fixed electrode support portions (30a, 40a) for supporting the fixed electrode spring portions (32, 42) on the support substrate (11) so as to face the weight portion (21) apart from each other,
The predetermined direction which is the displacement direction of the movable electrode (23) is the x-axis direction, the direction orthogonal to the predetermined direction, and the fixed electrodes (31, 41) are fixed by the fixed electrode spring portions (32, 42). When the direction of displacement is the y-axis direction, and the x-axis direction and the direction orthogonal to the y-axis direction are z-axis directions,
The movable electrode (23) has a columnar shape protruding from the weight (21) toward the fixed electrode support (30a, 40a) and extending along the y-axis direction,
The fixed electrodes (31, 41) project from the fixed electrode spring portions (32, 42) toward the weight portion (21) and have a column shape extending along the y-axis direction,
In the movable electrode (23) and the fixed electrode (31, 41), side surfaces extending in the y-axis direction are opposed to each other, and the capacitance is formed between the opposed side surfaces,
Both the planar shape of the movable electrode (23) and the planar shape of the fixed electrode (31, 41) along the xy plane that is a plane including the x-axis and the y-axis are between the root portion and the protruding tip portion. 2. The capacity type physical quantity detection device according to claim 1, wherein the device has a rectangular shape with a constant width. A weight portion (21) formed integrally with the movable electrode (23) and displaced in the predetermined direction (x) together with the movable electrode (23);
Fixed electrode support portions (30a, 40a) for supporting the fixed electrode spring portions (32, 42) on the support substrate (11) so as to face the weight portion (21) apart from each other,
The predetermined direction which is the displacement direction of the movable electrode (23) is the x-axis direction, the direction orthogonal to the predetermined direction, and the fixed electrodes (31, 41) are fixed by the fixed electrode spring portions (32, 42). When the direction of displacement is the y-axis direction, and the x-axis direction and the direction orthogonal to the y-axis direction are z-axis directions,
The movable electrode (23) has a columnar shape protruding from the weight (21) toward the fixed electrode support (30a, 40a) and extending along the y-axis direction,
The fixed electrodes (31, 41) project from the fixed electrode spring portions (32, 42) toward the weight portion (21) and have a column shape extending along the y-axis direction,
In the movable electrode (23) and the fixed electrode (31, 41), side surfaces extending in the y-axis direction are opposed to each other, and the capacitance is formed between the opposed side surfaces,
The planar shape of the movable electrode (23) along the xy plane that is a plane including the x-axis and the y-axis is a wedge shape that becomes thinner from the weight (21) side to the protruding tip side. Yes,
The planar shape of the fixed electrode (31, 41) along the xy plane is a wedge shape that becomes narrower from the fixed electrode spring portion (32, 42) side toward the protruding tip end side. The capacitive physical quantity detection device according to claim 1. The fixed electrode spring portions (32, 42) extend along the x-axis direction and are connected to the fixed electrode support portions (30a, 40a) and the first beams (32a, 42a). The beams (32a, 42a) are arranged apart from each other in the y-axis direction, extend along the x-axis direction, and are connected to the fixed electrodes (31, 41). And an elongated frame shape comprising the connecting portions (32c, 42c) for connecting both ends of the first and second beams in the x-axis direction,
4. The device according to claim 2, wherein the first beam (32 a, 42 a) and the second beam (32 b, 42 b) are elastically displaced so as to change a distance between them. 5. Capacitive physical quantity detection device. The fixed electrode displacing means (60) is an electrostatic attractive force that is disposed to be opposed to the second beam (32b, 42b) of the fixed electrode spring portion (32, 42) in the y-axis direction. A generating electrode (61),
By applying a voltage to the electrostatic attractive force generating electrode (61), the electrostatic attractive force is applied to the second beam (32b, 42b), and the fixed electrode spring portion (32, 42) is moved. 5. The capacity type physical quantity detection device according to claim 4, wherein the physical quantity detection device is elastically displaced.

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