JP4595864B2 - Capacitive sensor - Google Patents

Description

  The present invention relates to a capacitance sensor that detects a predetermined physical quantity by detecting a capacitance between a fixed electrode and a movable electrode.

  Conventionally, a semiconductor substrate is processed using a known semiconductor process to form a structure in which a movable electrode is supported by an elastic element on a fixed portion. There is known a capacitance type sensor that can detect various physical quantities such as acceleration and angular velocity by detecting a change in capacitance between these electrodes so as to be able to contact and separate. (For example, Patent Document 1 and Patent Document 2).

  In Patent Document 1, as a capacitive sensor, a plurality of fixed elements arranged so as to extend perpendicularly to a detection direction for detecting acceleration from one mass layer displaced by a physical quantity such as acceleration and to face each other. A semiconductor device is disclosed that detects acceleration in two axial directions perpendicular to each other by providing an electrode finger and a movable electrode finger.

In Patent Document 2, as a capacitive sensor, a fixed electrode pair is provided so as to be parallel to two opposing sides of a square annular mass member (movable electrode) that is displaced by a physical quantity such as acceleration. Thus, a solid-state accelerometer that detects acceleration in two axial directions perpendicular to each other is disclosed.
Special Table 2000-512023 JP-A-4-269659

  However, the inventions disclosed in Patent Document 1 and Patent Document 2 change the facing area between the movable electrode and the fixed electrode with respect to the acceleration in the other axis direction perpendicular to the detection direction. There is a problem that there is a high possibility of generating.

  Therefore, the present invention has been proposed in view of the above-described circumstances, and provides a capacitance type sensor that can suppress detection sensitivity in the other-axis direction and reliably detect a physical quantity in the target detection direction. The purpose is to do.

In the capacitance type sensor of the present invention, a movable electrode that operates according to a displacement of a physical quantity and a fixed electrode are arranged to face each other with a gap therebetween, and the size of the gap between the fixed electrode and the movable electrode is set. In the capacitance type sensor that detects the physical quantity based on the detected capacitance, the movable electrode surrounds the fixed electrode while maintaining an opposing arrangement relationship with the fixed electrode through the gap. together, and have a structure that surrounds the stopper portion which receives the operation of the movable electrode, parallel to the end portion of the movable electrode away maximally from the center of the movable electrode, the fixed electrode via the gap counter causes disposed, the movable electrode a square-shaped, with respect to one side of the movable electrodes and square-shaped, and is parallel opposed to the fixed electrode from the inside, the movable electrode was a square And the dynamic electrode central portion, the square detection movable electrodes surrounding the outside of the movable electrode central portion, four coupling the four corners of the detection movable electrodes extending respectively diagonally from the four corners of the movable electrode central portion The fixed electrode has a detection fixed electrode extending along the inside of the detection movable electrode, and a protrusion protruding from the center of the detection fixed electrode toward the center of the movable electrode. The stopper portion is arranged on both sides of the protruding portion, and a convex protrusion is provided on the opposing surface of the central portion of the movable electrode of the stopper portion so that the physical quantity is input. The center of the movable electrode is received by the protrusion when the protrusion is formed .

  According to the present invention, it is possible to suppress the detection sensitivity in the other axis direction and reliably detect the physical quantity in the target detection direction.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Configuration of capacitive sensor]
A configuration of a capacitance type sensor shown as an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a plan view showing a semiconductor layer 2 of a capacitive sensor. As shown in FIG. 1, the semiconductor layer 2 is formed with a frame portion 3, a beam portion 4, a movable electrode 5, a fixed electrode 6, and a stopper portion 7 by forming a gap 10 in a semiconductor substrate by a known semiconductor process. ing.

  FIG. 2 is a cross-sectional view showing a state in which the capacitive sensor 1 is cut so that the semiconductor layer 2 is cut along the line EE in FIG. As shown in FIG. 2, the capacitive sensor 1 is formed by bonding insulating layers 20 and 21 such as a glass substrate to the front and back surfaces of the semiconductor layer 2 by, for example, anodic bonding. A relatively shallow recess 22 is formed on the bonding surface between the semiconductor layer 2 and the insulating layers 20 and 21, so that insulation of each part of the semiconductor layer 2 and operability of the movable electrode 5 are ensured. As shown in FIG. 1, the capacitive sensor 1 is cut out so that the semiconductor layer 2 has a substantially square shape.

  As shown in FIG. 1, the frame portion 3 has four beams extending from the inner four corners in a spiral shape toward the center while being bent at a right angle in the middle in parallel with each side of the frame portion 3. Part 4 is provided. As shown in FIG. 1, each of the beam portions 4 extends over two sides of the frame portion 3 without interfering with each other, and is connected to a corner portion of the movable electrode 5 at the inner end portion. It functions as a spring element (spiral spring) that elastically moves and supports the movable electrode 5 with respect to the portion 3.

  Thus, in the capacitive sensor 1, the movable electrode 5 is given a function as a mass element (mass) that is movably supported by the beam unit 4 as a spring element, and the spring element and the mass element serve as a spring. It constitutes a mass system. Such a capacitance type sensor 1 detects a change in capacitance between the movable electrode 5 and the fixed electrode 6 due to a positional displacement of the movable electrode 5 as a mass element. And the capacitive sensor 1 can detect the acceleration added to the said capacitive sensor 1 from the voltage waveform obtained by carrying out CV conversion of the change of the detected electrostatic capacitance.

  Specifically, this change in capacitance is caused by four sides of the movable electrode 5 having a substantially square shape as the detection movable electrode 5a, and the detection movable electrode 5a has a center direction of the movable electrode 5, that is, the movable electrode 5 Detection is performed by detection units 8A to 8D (hereinafter collectively referred to simply as detection unit 8) in which detection fixed electrodes 6a of fixed electrode 6 are arranged to face each other. When the shape of the movable electrode 5 is substantially square, accurate acceleration detection with a good balance as a mass element can be realized.

  When acceleration is applied in the Y-axis direction shown in FIG. 1, the movable electrode 5 is displaced in the Y-axis direction, the capacitance detected by the detection movable electrode 5a and the detection fixed electrode 6a of the detection unit 8A, and the detection unit 8B. There is a difference in the capacitance detected by the detection movable electrode 5a and the detection fixed electrode 6a. The acceleration in the Y-axis direction can be detected from the difference in capacitance.

  On the other hand, when acceleration is applied in the X-axis direction shown in FIG. 1, the movable electrode 5 is displaced in the X-axis direction, and the capacitance detected by the detection movable electrode 5a and the detection fixed electrode 6a of the detection unit 8C, and detection Difference occurs in the capacitance detected by the detection movable electrode 5a and the detection fixed electrode 6a of the portion 8D. The acceleration in the X-axis direction can be detected from the difference in capacitance.

As shown in FIG. 1, the movable electrode 5 is centered on a substantially square central portion 5b (movable electrode central portion) for causing the movable electrode 5 to function as a mass element, and is detected from four corners of the central portion 5b. The movable movable electrode 5a and the central portion 5b are coupled to each other by four coupling portions 5c extending on a square diagonal line with the movable electrode 5a as one side. For such a movable electrode 5, four fixed electrodes 6 are formed in a region surrounded by a detection movable electrode 5a, a central portion 5b, and two coupling portions 5c, respectively. That is, the movable electrode 5 has a structure that surrounds the periphery of the fixed electrode 6 while maintaining the opposing arrangement relationship of the detection movable electrode 5a and the detection fixed electrode 6a.

  In the capacitance type sensor 1 of the present invention, since the fixed electrode 6 is provided inside the movable electrode 5 as described above, it is very difficult to extract a potential from the fixed electrode 6. Therefore, the surface of the central portion 6b is passed through the through-hole 24 in which the insulating layer 20 as shown in FIG. 2 is passed through the position A to the position D of the central portion 6b of the fixed electrode 6 shown in FIG. 6c, the electrode portion 23 for extracting the potential of the fixed electrode 6 is formed on the inner peripheral surface 24a of the through hole 24 and the surface 20a of the insulating layer 20 with a metal thin film so that the potential of the fixed electrode 6 is extracted. . The surface 20a of the insulating layer 20 is covered (molded) with an insulating resin layer (not shown).

  This eliminates the need for wiring from the semiconductor layer 2 so as to avoid the movable electrode 5 and the beam portion 4 to take out the potential of the fixed electrode 6 and allows the wiring to be drawn out on the insulating layer 20 at the shortest distance. In addition, it is possible to greatly reduce the parasitic capacitance generated between patterns when patterning is performed using thin film wiring. Therefore, the reliability of the capacitive sensor 1 can be improved.

  Further, since the wiring can be drawn out on the insulating layer 20 facing the region where the movable electrode 5 is formed, the capacitance type is compared with the case where the wiring is routed outside the region where the movable electrode 5 is formed. The sensor 1 can be reduced in size.

  Further, as shown in FIG. 1, the through hole 24 provided in the insulating layer 20 is positioned at positions A to D which are the centers of the fixed electrode 6 due to the symmetry of the fixed electrode 6 formed in the capacitive sensor 1. In addition to optimizing the stress balance of the entire device, the temperature characteristics can also be improved.

  Alternatively, the through hole 24 may be provided in the insulating layer 21 and the electrode portion 23 may be formed in the same manner so that the potential of the fixed electrode 6 is taken out from the back surface of the semiconductor layer 2.

  As shown in FIG. 1, the stopper portion 7 is provided to prevent the movable electrode 5 and the fixed electrode 6 from colliding and being damaged by the operation of the movable electrode 5. The stopper portion 7 is provided with a protrusion 7 a on the surface facing the movable electrode 5, thereby minimizing the influence of the collision. The stopper portion 7 is electrically insulated from the movable electrode 5 and the fixed electrode 6.

[Configuration of movable electrode 5]
Next, a detailed configuration of the movable electrode 5 will be described using a plan view in which the movable electrode 5 and the fixed electrode 6 are enlarged with the detection unit 8 of the capacitive sensor 1 shown in FIG. 3 as the center.

  As shown in FIG. 3, the detection unit 8 detects the detection movable electrode 5a and the detection using the gap 10 between the detection movable electrode 5a of the movable electrode 5 and the detection fixed electrode 6a of the fixed electrode 6 as a detection gap (electrode gap). The capacitance between the fixed electrodes 6a is detected. The detection movable electrode 5a and the detection fixed electrode 6a are arranged to face each other so as to be parallel to each other perpendicular to the main axis direction, which is the acceleration detection direction.

  Moreover, the movable electrode 5 has a structure surrounding the periphery of the fixed electrode 6 while maintaining the opposing arrangement relationship through the detection gap between the detection movable electrode 5a and the detection fixed electrode 6a.

  When the movable electrode 5 surrounds the periphery of the fixed electrode 6 as described above, the detection movable electrode 5a of the movable electrode 5 is always longer in the longitudinal direction than the detection fixed electrode 6a of the fixed electrode 6, as shown in FIG. can do.

  Thereby, even if the movable electrode 5 is displaced in the longitudinal direction of the detection fixed electrode 6a which is the other axis direction perpendicular to the main axis direction which is the acceleration detection direction, the opposing surface 6s of the detection fixed electrode 6a becomes the detection movable electrode. Since the facing relationship with the facing surface 5s of 5a is maintained without changing the facing area, a change in capacitance in the direction of the other axis is not detected. That is, the capacitive sensor 1 shown as an embodiment of the present invention is configured to be able to suppress detection sensitivity in the other axis direction while giving the movable electrode 5 a degree of freedom of displacement.

  Therefore, the detection unit 8 can greatly reduce the detection sensitivity in the other axis direction, and can always detect the acceleration in the main axis direction well. Thereby, the capacitive sensor 1 can reliably detect the acceleration generated in the target detection direction without malfunctioning.

  In addition, by surrounding the fixed electrode 6 with the movable electrode 5, the beam part 4 having the same potential as the movable electrode 5 can be formed in the vicinity of the movable electrode 5, so that the parasitic capacitance generated between the beam parts 4 is reduced. Can be suppressed. Thereby, the reliability of the capacitive sensor 1 can be improved.

  Note that the structure surrounding the fixed electrode 6 included in the movable electrode 5 does not necessarily have to be closed. In consideration of the deflection due to the operation of the movable electrode 5, the opposing area is changed by the operation of the movable electrode 5. For example, you may form so that a part of coupling | bond part 5c may be open | released. However, the movable electrode 5 has a structure in which the periphery of the fixed electrode 6 is completely surrounded as shown in FIGS. 1 and 3 rather than the structure in which the periphery of the fixed electrode 6 is substantially surrounded. There is an advantage that the strength of can be increased.

[Detection gap position]
In addition, the position of the detection gap, which is the gap 10 between the detection movable electrode 5a and the detection fixed electrode 6a, is provided at a position as far as possible from the center of the movable electrode 5 (a position farthest away).

  As described above, since the capacitance type sensor 1 hardly detects acceleration in the other axis direction, and it is guaranteed that the acceleration in the main axis direction can be detected satisfactorily, the size of the capacitance type sensor 1 is guaranteed. The distance L1 in the longitudinal direction of the detection fixed electrode 6a is maximized, and the detection movable electrode 5a and the detection fixed electrode 6a are provided at a position as far as possible from the center of the movable electrode 5 within the range defined by The opposing areas 5s and 6s facing each other can be maximized.

  A range defined by the size of the capacitive sensor 1 when the movable electrode 5 is square and the detection movable electrode 5a is each square side as in the capacitive sensor 1 shown as an embodiment of the present invention. If the square is enlarged, the position of the detection gap can be inevitably set farthest from the center of the movable electrode 5.

  Thus, since the sensitivity at the time of detecting the electrostatic capacitance in the principal axis direction can be improved by increasing the facing area, the corresponding acceleration is reliably detected even when the displacement amount of the movable electrode 5 is small. be able to.

  Further, as can be seen from “C = εS / d” which is a basic expression of the capacitance C when the capacitance is C, the facing area is S, the distance between the detection gaps is d, and the dielectric constant is ε. Since the relationship is inversely proportional, the relationship between the non-linear capacitance C and the distance d between the detection gaps is linear if there is sufficient sensitivity even if the displacement of the movable electrode 5 is small. Since it can be captured and processed, the acceleration detection process can be executed with a very simple algorithm.

[Another shape of detection movable electrode 5a and detection fixed electrode 6a]
Further, as shown in FIG. 5, each of the detection movable electrode 5a and the detection fixed electrode 6a is comb-shaped, and each detection movable electrode 5a is comb-shaped and each detection fixed electrode 6a is comb-shaped. You may make it arrange | position with a gap | interval 10 mutually by 1 to 1, respectively.

  As shown in FIG. 5, the fixed electrode 6 is formed with a band-shaped detection fixed electrode 6a extending from the central portion 6b to the left and right so as to be parallel to the detection movable electrode 5a. A plurality of detection fixed electrodes 6a are formed in a comb shape so as to be parallel to each other at a predetermined pitch.

  On the other hand, in addition to the detection movable electrode 5a that forms one side of the square movable electrode 5, the movable electrode 5 has a strip-like detection that extends in the direction parallel to the detection fixed electrode 6a toward the central portion 6b of the fixed electrode 6. The movable electrode 5a is formed. The detection movable electrode 5a has a predetermined pitch (for example, the same as the detection fixed electrode 6a) so as to face the detection fixed electrode 6a in a one-to-one parallel relationship between the plurality of comb-shaped detection fixed electrodes 6a. Are formed in a comb-teeth shape.

  Thus, since the comb-shaped detection fixed electrode 6a is formed symmetrically in the left-right direction of the central portion 6b of the fixed electrode 6, the increase or decrease in the facing area is canceled with respect to the acceleration in the other axis direction. become. Therefore, the capacitive sensor 1 can detect the acceleration in the main axis direction with little detection of the acceleration in the other axis direction as described above, while ensuring that the acceleration in the main axis direction can be satisfactorily detected. Therefore, the sensitivity when detecting the electrostatic capacitance in the main axis direction can be improved.

  Further, as described above, if there is sufficient sensitivity even when the displacement amount of the movable electrode 5 is small, the relationship between the non-linear capacitance and the distance between the detection gaps can be grasped linearly. Therefore, the acceleration detection process can be executed with a very simple algorithm.

[Configuration of Coupling Unit 5c]
In the movable electrode 5, for example, a corner 5 d is formed in the coupling portion 5 c that is a member coupling the detection movable electrode 5 a and the central portion 5 b as shown in FIG. 3. As described above, when the corner portion 5d is present, the strength of the coupling portion 5c may be reduced due to stress concentration.

  When the capacitive sensor 1 is formed by a so-called bulk micromachining technique in which the thickness of the semiconductor layer 2 is 30 μm or more, the movable electrode 5 that is a mass element becomes heavy, and the displacement of the movable electrode 5 with respect to acceleration is increased. Since the amount becomes large, the impact when it collides with the fixed electrode 6 becomes large. Therefore, when such a corner portion 5d exists, the possibility that the movable electrode 5 is damaged at the corner portion 5d becomes very high. If the movable electrode 5 is damaged, the balance of the mass elements is lost, so that the acceleration cannot be detected satisfactorily.

  Therefore, as shown in FIG. 6, the unevenness existing in the coupling portion 5c, such as the corner portion 5d, is flattened and straightened. As a result, a decrease in strength due to stress concentration can be avoided, and the possibility of damage to the movable electrode 5 can be greatly reduced.

  In addition, when the capacitive sensor 1 is formed not by the bulk micromachining technology as described above but by the surface micromachining technology in which the thickness of the semiconductor layer 2 is made thinner than 30 μm, the upper and lower layers of the semiconductor layer 2 are used. There is a high possibility that the movable electrode 5 will collide with certain insulating layers 20 and 21. In such a case, if the corner portion 5d exists in the coupling portion 5c, stress is concentrated on the corner portion 5d due to the thin thickness of the movable electrode 5 and the movable electrode 5 is likely to be damaged.

  Therefore, not only when the capacitive sensor 1 is formed by the bulk micromachining technique, but also when the capacitive sensor 1 is formed by the surface micromachining technique, the unevenness present in the coupling portion 5c such as the corner 5d. By flattening and straightening, it is possible to avoid damage to the movable electrode 5.

  The capacitance type sensor 1 shown as the embodiment of the present invention is configured to detect accelerations in two axis directions perpendicular to each other such as the X axis direction and the Y axis direction. However, the present invention can be applied to a sensor that detects acceleration in one axis direction and a sensor that detects acceleration in two or more axes.

  Moreover, although the capacitance type sensor 1 shown as embodiment of this invention detects an acceleration, this invention is not limited to this, What kind of physical quantity will be if it is a capacitance type sensor? It is applicable also to what detects.

  The above-described embodiment is an example of the present invention. For this reason, the present invention is not limited to the above-described embodiment, and according to the design or the like, as long as the technical idea according to the present invention is not deviated from other embodiments. Of course, various modifications are possible.

It is a figure shown about the structure of the semiconductor layer of the electrostatic capacitance type sensor shown as embodiment of this invention. It is a figure for demonstrating a mode that the said electrostatic capacitance type sensor was cut | disconnected by the EE line | wire shown in FIG. It is a figure for demonstrating the structure of the movable electrode of the said electrostatic capacitance type sensor, and a fixed electrode. It is a figure for demonstrating the position of the detection gap of the said electrostatic capacitance type sensor. It is a figure for demonstrating another structure of the detection movable electrode and detection fixed electrode of the said electrostatic capacitance type sensor. It is the figure which showed a mode that the coupling | bond part with which the movable electrode of the said capacitance-type sensor was equipped was planarized.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Capacitance type sensor 2 Semiconductor layer 3 Frame part 4 Beam part 5 Movable electrode 5a Detection movable electrode 5c Coupling part 5d Corner | angular part 5s Opposing surface 6 Fixed electrode 6a Detection fixed electrode 6b Center part 6s Opposing surface 8 Detection part 10 Gap 20 Insulating layer 23 Electrode 24 Through hole

Claims (3)

  A movable electrode that operates in accordance with a displacement of a physical quantity and a fixed electrode are arranged to face each other via a gap, and based on a capacitance that is detected according to the size of the gap between the fixed electrode and the movable electrode. In the capacitive sensor that detects the physical quantity,
  The movable electrode has a structure that surrounds the periphery of the fixed electrode while maintaining an opposing arrangement relationship with the fixed electrode through the gap, and surrounds a stopper portion that receives the operation of the movable electrode.And
The fixed electrode is disposed opposite to the movable electrode in parallel with the end of the movable electrode farthest from the center of the movable electrode through the gap.WithThe movable electrode is formed in a square shape, and the fixed electrode is arranged in parallel to face from one side of the square-shaped movable electrode.And
The movable electrode has a square movable electrode central portion;A square shape that surrounds the center of the movable electrodeA detection movable electrode;Four coupling portions extending diagonally from the four corners of the movable electrode central portion to couple the four corners of the detection movable electrode;Have
  The fixed electrode is formed in a T shape having a detection fixed electrode extending along the inner side of the detection movable electrode, and a protrusion protruding from the center of the detection fixed electrode toward the center of the movable electrode. And
  Place the stopper on both sides of the protrusionIn addition, a convex protrusion is provided on the opposing surface of the movable electrode central portion of the stopper portion, and the protrusion is formed when the physical quantity is input.A capacitance type sensor characterized by receiving the central portion of the movable electrode. The fixed electrode is a plurality of comb-shaped detection fixed electrodes,
The capacitive sensor according to claim 1 , wherein the movable electrode is provided with a plurality of comb-like detection movable electrodes that are arranged to face each other with a gap between the plurality of detection fixed electrodes. Providing a through hole in an insulating layer bonded to the surface of the semiconductor layer in which the fixed electrode and the movable electrode are formed;
The electrostatic capacity sensor according to claim 1 or 2 , wherein a potential of the fixed electrode is taken out on the insulating layer through the through hole.

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