JP2016095177A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor capable of solving conventional problem that an electrostatic force, which is applied to a weight part when performing a self-diagnosis, causes a weight part to collide to an upper lid resulting in a chipping of the weight part, a damage of a beam or sticking of the weight part to the upper lid.SOLUTION: The acceleration sensor includes: a first electrode disposed on the weight part; a second electrode which is disposed being faced to the first electrode; and a circuit which is electrically connected to the first electrode and the second electrode. The circuit applies a voltage signal to the first electrode or the second electrode for displacing the weight part. A capacitor is disposed in parallel between the circuit and the first electrode, or between the circuit and the second electrode.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an acceleration sensor used for a vehicle or the like.

  In a conventional acceleration sensor, a self-diagnostic voltage is applied between a self-diagnostic electrode provided on the weight and a counter electrode facing the self-diagnostic electrode, so that the weight operates as if acceleration is applied. Based on this operation, whether or not the acceleration sensor is functioning normally has been diagnosed.

  As a prior art document related to the invention of this application, for example, Patent Document 1 is known.

Japanese Patent No. 3093058

  In the conventional acceleration sensor, an electrostatic force is instantaneously applied to the weight by applying a self-diagnosis voltage. Therefore, the weight is displaced larger than the balance position of the electrostatic force due to the self-diagnostic voltage and the force of the beam supporting the weight, and there is a problem that the weight or the self-diagnostic electrode collides with the counter electrode.

  Therefore, the acceleration sensor of the present invention is characterized in that a capacitor is inserted in parallel with the self-diagnosis electrode to suppress the rise of the self-diagnosis voltage.

  In the sensor of the present invention, a capacitor is inserted in parallel with the electrode for self-diagnosis, and the rapid displacement of the weight is suppressed by suppressing the rise time of the self-diagnosis voltage. Thereby, it can suppress that a weight or a self-diagnosis electrode collides with a counter electrode.

1 is an exploded perspective view of an acceleration sensor according to Embodiment 1. FIG. Top view of the detection element of the acceleration sensor (A) Cross-sectional view of the same acceleration sensor, (b) Cross-sectional view of a detection element included in the same acceleration sensor A circuit diagram showing a detection circuit provided in the acceleration sensor Characteristic diagram showing relationship between self-diagnosis voltage Vin and self-diagnosis output voltage Vout Top view of another detection element provided in the acceleration sensor of the first embodiment Cross section of the acceleration sensor Top view of a detection element provided in the acceleration sensor of the second embodiment (A) Cross-sectional view of the same acceleration sensor, (b) Cross-sectional view of a detection element included in the same acceleration sensor Cross section of contact part Another sectional view of the contact section Another sectional view of the contact part

  Hereinafter, an acceleration sensor according to the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is an exploded perspective view of the acceleration sensor 10 according to the first embodiment, FIG. 2 is a top view showing the detection element 20, FIG. ) Is an enlarged view of the detection element 20 of FIG.

  As shown in FIGS. 1, 2, and 3, the acceleration sensor 10 includes a detection element 20 that detects acceleration, an upper lid 30 that is connected to the upper surface of the detection element 20, and a lower surface that is connected to the lower surface of the detection element 20. And a lid 40. That is, the detection element 20 is sandwiched between the upper lid 30 and the lower lid 40.

  The detection element 20 includes a support portion 12, a weight portion 13, a first beam portion 14a and a second beam portion 14b, one end of which is connected to the support portion 12 and the other end of which is connected to the weight portion 13, and a weight. A first electrode 16 formed on the upper surface of the portion 13 and a ground electrode 18 formed on the support portion 12 are provided.

  The weight portion 13 is connected to the tips of the first beam portion 14a and the second beam portion 14b. The weight portion 13 is supported by the first beam portion 14a and the second beam portion 14b so as to be displaceable in the Z-axis direction in FIG.

  As shown in FIG. 3B, the detection element 20 is provided between the first silicon layer 20c, the second silicon layer 20a, and the first silicon layer 20c and the second silicon layer 20a. A first insulating layer 20b; a second insulating layer 20d provided on the first silicon layer 20c; and a first electrode 16 provided on the second insulating layer 20d. .

  As shown in FIG. 3A, the upper lid 30 includes a second electrode 17 formed at a position facing the first electrode 16. Furthermore, as shown in FIG. 2, the detection part 14c is formed on the 1st beam part 14a, and the detection part 14d is formed on the 2nd beam part 14b.

  As shown in FIG. 2, the first electrode 16 is connected to the electrode pad 19 on the support portion 12 via the wiring 15. For simplicity, the wiring is not shown in FIG.

  Next, the operation of the acceleration sensor 10 will be described with reference to FIG. FIG. 4 is a circuit diagram showing a detection circuit of the acceleration sensor 10. The piezoresistor R1 is a piezoresistor corresponding to the detector 14c, the piezoresistor R4 is a piezoresistor corresponding to the detector 14d, the piezoresistor R2 and the piezoresistor R3 are reference piezoresistors (not shown) provided in the support unit 12. ). The piezoresistor R1, piezoresistor R2, piezoresistor R3, and piezoresistor R4 are connected in a bridge form as shown in FIG. The voltage Vdd is applied to the connection point between the piezoresistor R1 and the piezoresistor R2, and the connection point between the piezoresistor R3 and the piezoresistor R4 is grounded to GND.

  When acceleration in the Z-axis direction acts on the acceleration sensor 10 configured as described above, the weight portion 13 is displaced, which causes deflection in the first beam portion 14a and the second beam portion 14b. As a result, strain is applied to the detectors 14c and 14d, and the generated strain is detected as a resistance change by the detector 14c (piezoresistor R1) and the detector 14d (piezoresistor R4), and Vout1 and Vout2 shown in FIG. As a change in the potential difference, acceleration applied to the acceleration sensor 10 can be detected.

  Next, the self-diagnosis function will be described with reference to FIGS. In the following description, an example in which the diagnostic circuit applies the self-diagnosis voltage Vin to the first electrode 16 and the second electrode 17 is grounded to GND will be described. When the self-diagnosis voltage Vin is applied to the first electrode 16, a potential difference is generated between the first electrode 16 and the second electrode 17, and an electrostatic force is generated. The electrostatic force causes the weight portion 13 to be drawn toward the upper lid 30 side. The displacement of the weight portion 13 causes deflection in the first beam portion 14a and the second beam portion 14b, and distortion occurs in the detection portion 14c and the detection portion 14d. As a result, the piezoresistor R1 and the piezoresistor R4 change, the output voltage Vout (potential difference between Vout1 and Vout2 in FIG. 3) is output from the bridge circuit, and whether or not the weight portion 13 is operating normally in the diagnostic circuit. Can be confirmed.

  In the self-diagnosis function described above, FIG. 5 is a characteristic diagram showing the relationship between the self-diagnosis voltage Vin and the output voltage Vout of the acceleration sensor (hereinafter referred to as “self-diagnosis output Vout”). As shown in FIG. 3, in the acceleration sensor 10, a capacitor is provided in parallel between the diagnostic circuit and the first electrode 16.

  One terminal of the capacitor C is between the first electrode 16 and the diagnostic circuit unit, and the other terminal is grounded to GND. For this reason, when the self-diagnosis voltage Vin is applied to the first electrode 16 from the diagnostic circuit unit, a component having a high frequency passes through the capacitor C, and the applied voltage gradually increases. The time required for the rise (rise time) at this time is determined by the capacitance value of the capacitor C and the output impedance of the diagnostic circuit, and the rise time is delayed when a capacitor having a large capacitance value is inserted. By delaying the rising time of the self-diagnosis voltage Vin, the electrostatic force between the first electrode 16 and the second electrode 17 gradually increases, and the weight portion 13 is displaced according to this electrostatic force.

  By disposing the capacitor C in this manner, the rising time of the self-diagnosis voltage Vin can be delayed, and the electrostatic force can be prevented from increasing rapidly. As a result, it is possible to prevent the weight portion 13 from colliding with the upper lid 30 due to an instantaneous increase in electrostatic force, chipping of the weight portion 13, breakage of each beam portion, Sticking can be prevented.

  Here, the capacitance value of the capacitor C to be inserted is determined by the rise time of the weight portion 13 in the acceleration sensor 10 and the output impedance R of the diagnostic circuit. As the best mode, the rise time determined by the time constant of the capacitor C and the output impedance R is longer than the rise time of the weight portion 13 and longer than the time constant of the low-pass filter in the diagnostic circuit. It is desirable to decide. This low-pass filter is a filter for removing noise included in the output voltage Vout from the bridge circuit. Here, the rise time is defined as the time required for the self-diagnosis output Vout to reach 90% of the voltage V0 from 10% of the voltage V0 when the self-diagnosis output Vout in the steady state is the voltage V0. To do. In particular, as a result of the experiment, the capacitance value of the capacitor C is about several tens of pF, and the rising time of the self-diagnosis voltage Vin is set to 20 nsec or more, thereby effectively suppressing the collision between the weight 13 and the upper lid 30 at the time of rising. I found out that I could do it.

  FIG. 6 is a top view of a detection element 110 included in the acceleration sensor 100 according to another example of the present embodiment, and FIG. 7 is a cross-sectional view of the acceleration sensor 100 taken along the line AA ′ of FIG. In FIG. 6, the detection element 110 has four weight portions 111a, a weight portion 111b, a weight portion 111c, and a weight portion 111d. 112 b 2, the beam portion 112 c 1, the beam portion 112 c 2, the beam portion 112 d 1, and the beam portion 112 d 2 are connected to the support portion 113. For example, the weight portion 111a is connected to the support portion 113 via a pair of two beam portions 112a1 and 112a2. A first electrode 114a, a first electrode 114b, a first electrode 114c, and a first electrode 114d are formed on the surfaces of the weight portions 111a, 111b, 111c, and 111d, and a pad 123 formed on the support portion 113. Are connected to each other through a wiring 122.

  As shown in FIG. 7, the acceleration sensor 100 includes a detection element 110 that detects acceleration, an upper substrate 120 connected to the upper surface of the detection element 110, and a lower substrate 130 connected to the lower surface of the detection element 110. I have. Here, the detection element 110 is sandwiched between the upper substrate 120 and the lower substrate 130. The detection element 110 includes a second silicon layer 118b and a second silicon layer 118d made of silicon. On the second silicon layers 118b and 118d, first insulating layers 117b and 117d made of a silicon oxide film are provided. On the first insulating layer 117b and the first insulating layer 117d, a first silicon layer 116b and a first silicon layer 116d made of silicon are provided. A second insulating layer 115b and a second insulating layer 115d are provided over the first silicon layers 116b and 116d. On the second insulating layers 115b and 115d, first electrodes 114b and 114d formed in a desired shape are provided. The upper substrate 120 includes a second electrode 121b and a second electrode 121d formed at positions facing the first electrodes 114b and 114d. The acceleration sensor 100 including the detection element 110 can detect acceleration in three axial directions. For example, Japanese Patent Application No. 2011-009632 is known as a document disclosing such an acceleration sensor that detects triaxial acceleration.

  The same effect can also be obtained by inserting a capacitor in parallel between the diagnostic circuit and the detection unit (variable capacitor) in the same manner with a capacitance type acceleration sensor that detects capacitance change due to acceleration. Needless to say. Even in this case, the capacitance value additionally inserted and formed has a rise time of the voltage applied to the first electrode (self-diagnosis voltage Vin) longer than the rise time of the output due to the capacitance change during the self-diagnosis. The time is set longer than the response time of the low-pass filter of the circuit unit. Here, the rise time is defined as the time required for the self-diagnosis output to reach 90% of the voltage V0 from 10% of the voltage V0 when the self-diagnosis output in the steady state is the voltage V0. To do.

  In the present embodiment, one terminal of the capacitor C is between the first electrode 16 and the diagnostic circuit unit, and the other terminal is grounded to GND. However, the present invention is not limited to this. That is, one terminal of the capacitor C may be grounded between the second electrode 17 and the diagnostic circuit unit, and the other terminal may be grounded to GND. In this case, the self-diagnosis voltage may be applied to the second electrode 17. That is, a capacitor may be provided in parallel between either the diagnostic circuit unit and the first electrode 16 or between the diagnostic circuit unit and the second electrode 17.

  Further, the inductor L may be provided in the diagnostic circuit unit. In the case of an inductor, by arranging in series between the diagnostic circuit and the first electrode 16, it is possible to block a high-frequency component and suppress the rise of the self-diagnostic voltage. At this time, the value of the inductor is 10 uH or more.

  Further, the support portion 12, the weight portion 13, the first beam portion 14a, the second beam portion 14b, the upper lid 30, and the lower lid 40 can be made of silicon, fused quartz, alumina, or the like. Preferably, by using silicon, a small acceleration sensor can be obtained by using a fine processing technique.

  Moreover, in this Embodiment, if the support part 12 is located in the outer peripheral side of the detection element 20, and if it is a shape which surrounds the weight part 13, the support part 12 is not restricted to a square shape, For example, it may be circular. Good and not limited to squares.

  In addition, regarding the first beam portion 14a and the second beam portion 14b, a structure having two beam portions in which one end is connected to the support portion 12 and the other end is connected to the weight portion 13 is shown. Not exclusively. For example, a structure in which one or three beam portions are supported on one side of the weight portion 13 may be used. In addition, a double-supported beam structure that supports the weight portion 13 with two opposing beam portions, a structure in which the weight portion 13 is supported with a beam portion from four directions, or a film-like structure such as a diaphragm, the weight portion 13 may be supported. The structure of a beam part should just be the structure which supports the weight part 13 so that the weight part 13 can be displaced according to an acceleration.

  Further, as a method for bonding the support portion 12 and the upper lid 30, bonding with an adhesive, metal bonding, room temperature bonding, anodic bonding, or the like can be used. Among these, an adhesive such as an epoxy resin or a silicon resin is used as the adhesive. By using a silicon-based resin as the adhesive, the stress due to the curing of the adhesive itself can be reduced.

  Further, an oxide film strain resistance material such as chromium oxide can be used as the piezoresistive material of the detection units 14c and 14d.

(Embodiment 2)
The acceleration sensor 10 according to the second embodiment includes a first silicon layer 20c, a second silicon layer 20a, and a first insulation provided between the first silicon layer 20c and the second silicon layer 20a. A detection element having a layer 20b, a second insulating layer 20d provided on the first silicon layer 20c, and a first electrode 16 provided on the second insulating layer 20d is provided. The first silicon layer 20c is grounded to GND, and a capacitor is formed between the first silicon layer 20c and the first electrode 16 via the second insulating layer 20d. It is characterized by suppressing the rise.

  8 is a top view showing the detection element 20 of the acceleration sensor 10 according to the second embodiment, FIG. 9A is a cross-sectional view taken along the line AA ′ of FIG. 8, and FIG. 9B is a detection of FIG. FIG. 6 is an enlarged view of the element 20.

  In FIG. 9, the detection element 20 includes a first silicon layer 20c, a second silicon layer 20a, and a first insulating layer 20b provided between the first silicon layer 20c and the second silicon layer 20a. A second insulating layer 20d provided on the first silicon layer 20c, and a contact portion 11a. Other configurations are the same as those in FIG. 3 of the first embodiment.

  FIG. 10 is a cross-sectional view of the contact portion 11a. The contact portion 11a is formed by depositing a metal layer 200a such as gold in an opening provided in the second insulating layer 20d, and the metal layer 200a is connected to the ground electrode 18 of the detection element 20 via a wiring. And are electrically connected. Therefore, since the first silicon layer 20c is grounded to GND, a capacitor C grounded to GND via the first silicon layer 20c is provided between the first electrode 16 and the diagnostic circuit unit. The formed structure. With this configuration, the capacitor C can be configured on the detection element 20, the number of parts can be reduced, wiring can be simplified, and in addition to the effects of the first embodiment, the size can be reduced.

  The self-diagnosis operation of the detection element 20 in the present embodiment is the same as that in the first embodiment, and by reducing the rise time of the self-diagnostic voltage, the electrostatic force increases instantaneously, so that the weight portion 13 can be prevented from colliding with the upper lid 30, and chipping of the weight portion 13, breakage of the beam portion, and sticking to the upper lid 30 of the weight portion 13 can be prevented.

  Furthermore, by forming the capacitor C integrally with the detection element 20, it is possible to reduce the size of the sensor and to reduce the size.

  In addition, since the first silicon layer 20c is grounded to GND, the weight portion 13 and the first silicon layer 20c are charged when a voltage is applied to an external electric field and the first electrode 16. It can be suppressed, and the self-diagnosis output is stabilized.

  Moreover, you may form a contact part as shown in FIG. FIG. 11 is another cross-sectional view of the contact portion. In the contact portion 11b, it is preferable to insert a metal layer 200b, for example, chromium or an alloy containing chromium, as an adhesion layer so that the first silicon layer 20c does not diffuse into the metal layer 200a. In this case, a third insulating layer 20e is newly provided to insulate the metal layer 200b from other layers. Thus, in the contact portion 11b when the metal layer 200b is provided, the contact hole provided in the second insulating layer 20d and the contact hole provided in the third insulating layer 20e are provided at the same position. The opening provided in the third insulating layer 20e is preferably larger than the opening provided in the second insulating layer 20d. That is, it is preferable that D1> D2. Alternatively, in another expression, the opening provided in the third insulating layer 20e is larger in width in the vertical cross section than the opening provided in the second insulating layer 20d. With this configuration, the contact resistance between the metal layer 200a and the metal layer 200b can be reduced, and the first silicon layer 20c is more efficiently grounded to GND. In addition, a capacitor C grounded to the GND via the first silicon layer 20c is formed.

  Moreover, you may form a contact part as shown in FIG. FIG. 12 is still another cross-sectional view of the contact portion. The contact portion 11c includes a metal layer 200b as an adhesion layer so that the first silicon layer 20c does not interdiffuse into the metal layer 200a, and a third insulating layer 20e newly provided to insulate the metal layer 200b from other layers. Provided. Here, in the contact portion 11c, the contact hole provided in the second insulating layer 20d and the contact hole provided in the third insulating layer 20e are provided at different positions (positions that do not overlap in a top view) and are offset from each other. In the position. That is, the vertical line L1 passing through the contact hole ridge provided in the second insulating layer 20d is shifted from the perpendicular line L2 passing through the contact hole ridge provided in the third insulating layer 20e. With this configuration, the metal layer 200b immediately above the first silicon layer 20c penetrates through etching when a contact hole is provided in the third insulating layer 20e, so that the first silicon layer 20c and the metal layer 200a are not directly joined. Can be. Accordingly, it is possible to effectively suppress the first silicon layer 20c from interdiffusing into the metal layer 200a, and the first silicon layer 20c is grounded to GND. And a capacitor C that is grounded to GND through the first silicon layer 20c.

  In the present embodiment, an example is shown in which the capacitor C formed on the detection element 20 is used. However, the capacitor C formed on the detection element 20 and the capacitor C provided separately from the detection element 20 are used. In both cases, the same effect can be obtained by increasing the rise time of the self-diagnosis voltage.

  The sensor of the present invention suppresses the displacement of the weight part by inserting a capacitor in the diagnostic circuit part and smoothing the rising of the self-diagnostic voltage, chipping the weight part, breaking the beam part, Since sticking can be prevented and stable self-diagnosis can be performed, it is useful as an acceleration sensor used in vehicles and the like.

10 acceleration sensor 11a contact part 11b contact part 11c contact part 12 support part 13 weight part 14a beam part 14b beam part 14c detection part 14d detection part 15 wiring 16 first electrode 17 second electrode 18 ground electrode 20 detection element 20a first Second silicon layer 20b First insulating layer 20c First silicon layer 20d Second insulating layer 20e Third insulating layer 30 Upper lid 40 Lower lid 100 Acceleration sensor 110 Detection element 111a Weight portion 111b Weight portion 111c Weight portion 111d Weight Part 112a1 Beam part 112a2 Beam part 112b1 Beam part 112b2 Beam part 112c1 Beam part 112c2 Beam part 112d1 Beam part 112d2 Beam part 113 Support part 114a First electrode 114b First electrode 114c First electrode 114d First electrode 115b First part Second insulating layer 115d second insulating layer 116b second Silicon layer 116d first silicon layer 117b first insulating layer 117d first insulating layer 118b second silicon layer 118d second silicon layer 120 upper substrate 121b second electrode 121d second electrode 122 wiring 123 pad 130 Lower substrate 200a Metal layer 200b Metal layer R1 Piezoresistor R2 Piezoresistor R3 Piezoresistor R4 Piezoresistor

Claims (10)

A support part;
A weight portion connected to the support portion via a beam portion;
A first electrode provided on the weight portion;
A second electrode provided opposite to the first electrode;
An acceleration sensor having a circuit portion electrically connected to the first and second electrodes,
The circuit unit applies a voltage signal for displacing the weight unit to the first electrode or the second electrode,
An acceleration sensor in which a capacitor is provided in parallel with the circuit unit between the circuit unit and the first electrode or between the circuit unit and the second electrode. The circuit unit further includes a low-pass filter,
2. The acceleration sensor according to claim 1, wherein the voltage signal is a voltage that displaces the weight portion so that a rise time thereof is longer than a response time of the low-pass filter. The rise time is a time required for the self-diagnosis output to reach 90% of the voltage V0 from 10% of the voltage V0 when the self-diagnosis output in a steady state is the voltage V0. Acceleration sensor. The acceleration sensor according to claim 2 or 3, wherein the rise time is 20 nsec or more. The support part is
A first silicon layer; a second silicon layer; a first insulating layer provided between the first silicon layer and the second silicon layer; and the first silicon layer. A second insulating layer;
The first electrode is provided on the second insulating layer;
The first silicon layer is grounded to GND;
The acceleration sensor according to claim 1, wherein the capacitor is formed by the first electrode, the second insulating layer, and the first silicon layer. The acceleration sensor according to claim 1, wherein the circuit unit performs self-diagnosis based on the displacement. A first substrate connected to the support;
The acceleration sensor according to claim 1, further comprising: a second substrate facing the first substrate and connected to the support portion. The acceleration sensor according to claim 7, wherein acceleration is detected based on a change in capacitance between the first substrate and the weight portion. It further has a detection part provided in the beam part,
The acceleration sensor according to claim 1, wherein acceleration is detected by detecting deflection of the beam portion due to acceleration. The acceleration sensor according to claim 9, wherein the detection unit is a piezoresistor or a metal oxide film.

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