JP2014106082A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acceleration sensor which can achieve the improvement of accuracy of detecting acceleration by reducing a difference of fluctuation of capacitance, which is generated during the rotation of a weight part due to a difference of gaps between fixed electrodes and movable electrodes.SOLUTION: In a first sensor 21, connections 28B, 29B provided to each of pairs of first and second fixed electrodes 28, 29, which are surrounded by a movable electrode 30, are placed on end sides in a manner to alternately differ with respect to each of the fixed electrodes 28, 29 arrayed in a Y direction.

Description

  The technology disclosed in the present application relates to an acceleration sensor configured as MEMS (Micro Electro Mechanical Systems).

  Conventionally, some acceleration sensors manufactured using MEMS technology use capacitance. For example, a capacitor is composed of a fixed electrode fixed to the substrate and a movable electrode provided on a weight portion that can swing relative to the substrate, and acceleration is caused by a change in capacitance of the capacitor. There is an acceleration sensor to detect (for example, Patent Document 1). In the acceleration sensor disclosed in Patent Document 1, the acceleration is calculated from the amount of change in capacitance according to the change in the distance between the fixed electrode and the movable electrode that occurs when the weight portion changes in the detection direction (X direction). It is configured as a uniaxial acceleration sensor for detection. Further, there are three-axis acceleration sensors capable of detecting acceleration acting in the three detection directions of XYZ with respect to the above-described one-axis acceleration sensor (for example, Patent Documents 2 to 7).

  In the acceleration sensor described above, each fixed electrode is connected to the substrate in order to output the amount of change in capacitance to a processing circuit that calculates acceleration, for example. For example, in the acceleration sensor disclosed in Patent Literature 1, connection portions (support portions in the literature) for connecting to a substrate are provided on fixed electrodes provided on both sides of the weight portion. In this acceleration sensor, the fixed electrode extends from the connection portion toward one side in the Y direction, and the movable electrode extends from the weight portion toward the other side in the Y direction so as to face the fixed electrode.

  Further, for example, in the acceleration sensor disclosed in Patent Document 2, movable electrodes are provided on the outer peripheral portion of the weight portion at intervals along the X and Y directions. In a region sandwiched between adjacent movable electrodes, first and second fixed electrodes are provided adjacent to each other so as to face each movable electrode. The first and second fixed electrodes are connected to the substrate at a connection portion (terminal in the literature), and the capacitance between the first and second fixed electrodes and the movable electrode that changes as the weight portion swings. The amount of change is output and processed from the connection to a processing circuit (such as a differential amplifier circuit), and acceleration is detected. This acceleration sensor is also configured so that the movable electrode extending from the weight portion faces the fixed electrode extending from the connection portion, as in Patent Document 1 described above.

Japanese Patent Laid-Open No. 11-344507 Japanese Patent Application Laid-Open No. 07-245413 JP 2005-534016 A Japanese Patent Laid-Open No. 06-258340 JP 05-340960 A Japanese Patent No. 2773495 Japanese Patent No. 3327595

  Incidentally, for example, a configuration of an acceleration sensor 401 shown in FIG. FIG. 15 is a schematic diagram of the acceleration sensor. A movable portion 414 is provided on the weight portion 411 having a square shape in plan view so as to surround the pair of first and second fixed electrodes 412 and 413. A plurality of sets of first and second fixed electrodes 412 and 413 are arranged side by side along one direction (Y direction in the figure) in the central portion. The acceleration sensor 401 is electrostatically charged according to the distance between the movable electrode 414 and the first and second fixed electrodes 412 and 413 as the weight portion 411 held by a spring (not shown) swings in the Y direction. The capacitance changes and the acceleration in the Y direction is detected.

  On the other hand, the movable electrode 414 of the acceleration sensor 401 is formed so as to surround the first and second fixed electrodes 412 and 413, and not only in the acceleration detection direction (Y direction in this case) but also in the X direction orthogonal to the Y direction. It faces each fixed electrode 412, 413. The first fixed electrode 412 is provided with a connecting portion 412B at one end portion in the X direction (left end portion in the figure), and the second fixed electrode 413 has the other end portion in the X direction (right end portion in the figure). ) Is provided with a connecting portion 413B. In the connection portions 412B and 413B, through-holes connected to a substrate (not shown) are formed for each of the plate-like first and second fixed electrodes 412 and 413, for example, and each fixed electrode 412 in plan view is formed. The thickness of 413 is increased compared to other portions.

  The connecting portion 412B is formed to be widened to the adjacent second fixed electrode 413 side so that the first fixed electrode 412 and the movable electrode 414 are flush with each other. Further, the connecting portion 413B is formed to be widened to the adjacent first fixed electrode 412 side so that the second fixed electrode 413 and the movable electrode 414 are flush with each other. The first and second fixed electrodes 412 and 413 are configured such that the connection portion 412B faces the movable electrode 414 at one end in the X direction and the connection portion 413B faces the movable electrode 414 at the other end.

  Here, the weight portion 411 is disposed between the first and second fixed electrodes 412 and 413 (including the connection portions 412B and 413B) and the movable electrode 414 so as not to come into contact with the swing in the X direction. A gap (gap) is provided. For example, the distance between the connection portion 412B and the movable electrode 414 is a width 415A, and the distance between the connection portion 413B and the movable electrode 414 is a width 416B. The gaps of the widths 415A and 416B are formed in the same process of etching the first and second fixed electrodes 412 and 413, for example.

  In a state where the shock sensor 411 is rotated due to a large impact applied to the acceleration sensor 401, as shown in FIG. 16, the gap between the fixed electrodes 412 and 413 including the connecting parts 412B and 413B and the movable electrode 414 is removed. The distance is different in both the X and Y directions. For example, the widths 415A and 416B (see FIG. 15) are different distances at positions in the Y direction. The electrostatic capacitance between the fixed electrodes 412 and 413 and the movable electrode 414 varies due to the weight portion 411 swinging in a direction different from the detection direction due to rotation or the like. For this reason, it is preferable to configure a bridge circuit including, for example, the fixed electrodes 412 and 413 and the movable electrode 414 so as to cancel the amount of change due to the fluctuation so that the fluctuation does not affect the detection accuracy of the acceleration.

  At this time, the widths 415A and 416B shown in FIG. 15 are set to the same distance in order to cancel the fluctuation due to the rotation of the weight portion 411 with respect to the capacitance between the connection portions 412B and 413B and the movable electrode 414. preferable. However, the widths 415A and 416B are set to the same distance from the limit of accuracy (for example, μm order accuracy) in the manufacturing process such as position adjustment (alignment) of the photomask for forming the resist for etching and control on the etching amount. That is extremely difficult. As a result, when rotation occurs in the weight part 411, due to the difference between the widths 415A and 416B, different displacement amounts are generated in the capacitances of the connection parts 412B and 413B and the movable electrode 414 in the X direction. It is conceivable that fluctuations will occur. Originally, the capacitance between the connection portions 412B and 413B and the movable electrode 414 changes according to the swing of the weight portion 411 in the non-detection direction (X direction) orthogonal to the detection direction, so that acceleration is detected. Although this does not contribute to this, a change in capacitance is detected also in this portion, which causes a problem of adversely affecting the detection accuracy of acceleration.

  In addition to the configuration shown in FIGS. 15 and 16, for example, the configuration of an acceleration sensor 401A shown in FIG. 17 is conceivable. The acceleration sensor 401A shown in FIG. 17 is provided with six pairs of first and second fixed electrodes 412 and 413. The first fixed electrode 412 is provided with a connection portion 412B on one end side in the X direction (the upper three in the drawing are the left side and the lower three are the right side). In addition, the second fixed electrode 413 is provided with a connecting portion 413B on one end side in the X direction opposite to the first fixed electrode 412 (the upper three in the drawing are the right side and the lower three are the left side). Yes. Therefore, in the acceleration sensor 401A, the positions of the connection portions 412B and 413B provided on the fixed electrodes 412 and 413 are different between one set (upper side) and the other set (lower side) in the Y direction. Thereby, the change amount with respect to the displacement in the non-detection direction (X direction) is canceled.

  However, in the acceleration sensor 401A, for example, when the weight portion 411 rotates counterclockwise, the width 415A (see FIG. 15) of the gap between the connection portion 412B and the movable electrode 414 is equal to the gap between the connection portion 413B and the movable electrode 414. It will be arranged in a portion that is larger than the width 416B. Therefore, in the acceleration sensor 401A, the difference in capacitance variation between the fixed electrodes 412 and 413 and the movable electrode 414 is further increased.

  The technology disclosed in the present application has been proposed in view of the above problems. Regarding capacitance-type acceleration sensors, it is possible to reduce the difference in capacitance fluctuation that occurs when the weight rotates due to the difference in gap between the fixed electrode and the movable electrode, and to improve the detection accuracy of acceleration. It is an object of the present invention to provide an acceleration sensor that can be used.

  An acceleration sensor according to a technique disclosed in the present application includes a substrate, a weight portion that is provided so as to be swingable by being separated from the substrate, a movable electrode that is provided on the weight portion, a fixed surface of the substrate, and a plane of the substrate. A first fixed electrode and a second fixed electrode whose distance in the detection direction with the movable electrode varies according to the acceleration in the detection direction parallel to the direction, and whose capacitance with the movable electrode varies according to the distance; Provided at one end in a direction orthogonal to the detection direction of the electrode, the first connection portion for connecting the first fixed electrode to the substrate, and the other side opposite to the one end in the direction orthogonal to the detection direction of the second fixed electrode A second connection portion provided at the end portion for connecting the second fixed electrode to the substrate, and the first and second fixed electrodes are disposed adjacent to each other in a region surrounded by the movable electrode The first and second fixed electrodes sandwich the movable electrode along the detection direction. Several sets are arranged side by side, and one end of the plurality of sets and another set adjacent to each other in the detection direction are different from each other at one end and the other end where the first and second connection portions are provided. .

  In the acceleration sensor, a plurality of pairs of first and second fixed electrodes arranged adjacent to each other in a region surrounded by the movable electrodes are arranged side by side along the detection direction with the movable electrodes interposed therebetween. . The first connection portion is provided at one end of the first fixed electrode in a direction orthogonal to the detection direction. The second connection portion is provided at an end of the second fixed electrode opposite to the first connection portion in a direction orthogonal to the detection direction. Here, the first and second connection portions are opposed to the movable electrode at both ends in the direction orthogonal to the detection direction, but the gap between each connection portion and the movable electrode is the same due to the accuracy limit in the manufacturing process. It is difficult to be a distance. In this case, if rotation occurs in the weight portion, the displacement between the connecting portions and the movable electrode varies in different amounts of displacement, which may adversely affect acceleration detection accuracy.

  Therefore, in the acceleration sensor, the end where the first and second connection portions are provided is different between one set of the plurality of sets of the first and second fixed electrodes and another set adjacent in the detection direction. The configuration. That is, in the first connection portion, the positions of the end portions provided with respect to the first fixed electrode are alternately different end portions with respect to the first fixed electrodes arranged in the detection direction. Similarly, in the second connection portion, the positions of the end portions provided with respect to the second fixed electrode are alternately different end sides with respect to the second fixed electrodes arranged in the detection direction. In such a configuration, the movable electrode has a similar variation in the capacitance generated between each of the first and second connection portions during rotation. As a result, it is possible to improve acceleration detection accuracy by reducing the difference in fluctuation caused by rotation with respect to the capacitance of the movable electrode and each of the first and second fixed electrodes.

  Further, in the acceleration sensor according to the technology disclosed in the present application, the first connection portion is formed to be widened at a position facing one end portion of the adjacent second fixed electrode, and the second connection portion is adjacent to the first first electrode. The pair of first and second fixed electrodes are formed so as to be widened at a position facing the other end of the fixed electrode. It is good also as a structure which is either of 2 connection parts.

  In the acceleration sensor, the first and second fixed electrodes are provided so that the first and second connection portions provided at the end portions are widened to the other electrode side adjacent to each other, and the end portions in the direction orthogonal to the detection direction are provided. Any one of the connection portions faces the movable electrode. As a result, each connection portion in which the width of the electrode increases is provided on a different end side of the pair of fixed electrodes and arranged so as to be staggered, and the fixed electrodes are occupied by arranging both fixed electrodes closer to each other. The area can be reduced and the apparatus can be downsized.

  Further, in the acceleration sensor according to the technique disclosed in the present application, the pair of first and second fixed electrodes and the movable electrode are detected at a central portion of a region surrounded by the outer peripheral edge of the weight portion in a plan view of the substrate. It is good also as a structure arrange | positioned along with a line in a line.

  In the acceleration sensor, the pair of fixed electrodes and movable electrodes are alternately arranged in a line along the detection direction at the center of the region surrounded by the outer periphery of the weight portion. In such a configuration, by disposing each fixed electrode and the movable electrode in the central part where the fluctuation of the weight part due to the rotation is small, the difference in fluctuation caused by the rotation can be more effectively reduced.

  According to the technology disclosed in the present application, it is possible to reduce the difference in capacitance variation that occurs when the weight portion rotates due to the difference in gap between the fixed electrode and the movable electrode, and to improve the acceleration detection accuracy. It is possible to provide an acceleration sensor capable of

It is a perspective view which shows schematic structure of the acceleration sensor of embodiment. (A) is a top view of a sensor, (b) is an AA line end view of FIG. 2 (a), (c) is a BB line end view of FIG. 2 (a). It is a figure which shows the electrical connection of a sensor. It is a schematic diagram for demonstrating arrangement | positioning of an electrostatic capacitance part. It is a schematic diagram for demonstrating the gap of a fixed electrode and a movable electrode. It is a schematic diagram for demonstrating the gap of the fixed electrode and movable electrode at the time of rotation. It is a schematic perspective view for demonstrating the shape of a movable electrode. (A) The schematic diagram for demonstrating the spring of this embodiment, (b) (c) is a schematic diagram for demonstrating the spring of a comparative example. It is a graph which shows the relationship between the frequency | count of folding and a spring constant. (A)-(c) is an end elevation for demonstrating the manufacturing process of a sensor. (A)-(c) is an end elevation for demonstrating the manufacturing process of a sensor. It is a schematic diagram for demonstrating arrangement | positioning of the electrostatic capacitance part of another acceleration sensor. It is a schematic diagram for demonstrating arrangement | positioning of the electrostatic capacitance part of another acceleration sensor. It is a top view for demonstrating another acceleration sensor. It is a schematic diagram for demonstrating the gap of the fixed electrode and movable electrode in the sensor of a comparative example. It is a schematic diagram for demonstrating the gap of the stationary electrode and movable electrode at the time of rotation in the sensor of a comparative example. It is a schematic diagram for demonstrating the gap of the stationary electrode and movable electrode at the time of rotation in the sensor of a comparative example.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of the invention will be described with reference to the accompanying drawings. Note that, for convenience of explanation, the accompanying drawings include portions that are illustrated differently from actual dimensions and scales.
FIG. 1 shows a schematic configuration of a chip in which a capacitance type acceleration sensor according to the present embodiment is manufactured using a MEMS (Micro Electro Mechanical Systems) technology. As shown in FIG. 1, the acceleration sensor 10 includes a substrate 12 formed in a substantially rectangular plate shape in plan view. In the acceleration sensor 10, a first sensor 21 and a second sensor 31 are formed in each of two chip regions arranged in parallel in the direction along the long side of the substrate 12. In the following description, as shown in FIG. 1, the direction along the long side of the acceleration sensor 10 (the direction in which the first and second sensors 21 and 31 are arranged side by side) is the X direction and the X direction. A direction perpendicular to the acceleration sensor 10 along the short side is referred to as a Y direction, and a direction perpendicular to both the X direction and the Y direction (a direction perpendicular to the substrate plane of the substrate 12) is referred to as a Z direction. explain.

  The first sensor 21 includes a frame part 23, a weight part 24, a pair of spring parts 26, and a capacitance part 27. As shown in FIG. 2A, the frame portion 23 is formed in a square frame shape in plan view, and a weight portion 24 is provided on the enclosed inner portion. The weight portion 24 is formed in a plate shape having a substantially square shape in plan view. The weight portion 24 has a plurality of through holes 24 </ b> A penetrating in the Z direction, and the through holes 24 </ b> A are formed in a matrix with respect to the weight portion 24. Incidentally, the through-hole 24A functions as a vent hole for reducing resistance when the weight portion 24 moves in the Z direction and as an inlet for an etching solution when etching a sacrificial layer described later.

  Further, the first sensor 21 is provided with spring portions 26 on both side portions in the Y direction. The spring portion 26 includes a beam portion 41 provided at a substantially central portion in the X direction and a pair of springs 43 provided on both sides of the beam portion 41 in the X direction. The beam portion 41 is formed in a plate shape having a substantially rectangular shape in plan view, and a long side is provided along the Y direction. The weight portion 24 and the beam portion 41 are connected via respective springs 43. The spring 43 has a meandering shape in plan view, the fixed end 43A on one end side is fixed to the side surface of the beam portion 41, and the movable end 43B on the other end side is connected to the weight portion 24. Although the details will be described later, the meandering shape of the spring 43 is such that the short side and the long side that are perpendicular to each other are alternately connected, the short side is provided along the X direction, and the long side is the Y direction. It is formed in a zigzag shape provided along. The spring 43 is configured such that the distance between the fixed end 43A fixed to the beam portion 41 and the movable end 43B connected to the weight portion 24 is longer than the long side, and the rigidity in the X direction is increased. It has a structure in which expansion and contraction is restricted.

  2B is an end view taken along line AA in FIG. 2A, and FIG. 2C is an end view taken along line BB in FIG. 2A. As shown in FIG. 2B, the beam portion 41 is integrally formed and fixed with an anchor portion 45 erected on the substrate 12. For this reason, as shown in FIG. 2C, the weight portion 24 is held in a state of floating on the substrate 12 by being supported by the fixed beam portion 41 via the spring 43. ing. Further, the weight part 24 and the frame part 23 surrounding the weight part 24 are separated from each other.

  As shown in FIG. 2A, the capacitance unit 27 includes first and second fixed electrodes 28 and 29 and a movable electrode 30. The electrostatic capacitance part 27 is provided at the center of the first sensor 21 and the weight part 24. The first sensor 21 includes a plurality of pairs (in this embodiment, five pairs) of a pair of first and second fixed electrodes 28 and 29. The first and second fixed electrodes 28 and 29 are formed in a substantially rectangular plate shape whose main surface is along the Z direction, and long sides are provided along the X direction. The first and second fixed electrodes 28 and 29 are alternately provided along the Y direction so that their main surfaces face each other. In other words, the first and second fixed electrodes 28 and 29 are juxtaposed along the Y direction.

  The first fixed electrode 28 is provided with a through hole 28A on one end side in the X direction, and is electrically connected to a wiring (not shown) formed on the substrate 12. The second fixed electrode 29 is electrically connected to a wiring (not shown) formed on the substrate 12 with a through hole 29A provided on one end side in the X direction opposite to the first fixed electrode 28. . The thickness (width in the Y direction) of the first fixed electrode 28 is larger at the connection portion 28B where the through hole 28A is formed than at other portions. Similarly, the thickness (width in the Y direction) of the second fixed electrode 29 is larger at the connection portion 29B where the through hole 29A is formed than at other portions.

  The first and second fixed electrodes 28 and 29 are different from each other in end portions where the connection portions 28B and 29B are provided in each set. More specifically, for example, the first fixed electrode 28 included in one set on one end side in the Y direction (uppermost side in the figure) is provided with a connecting portion 28B on one end side in the X direction (left side in the figure). The second fixed electrode 29 is provided with a connecting portion 29B on the other end side in the X direction (right side in the drawing). In addition, in the first set (second set from the top in the figure) adjacent to the first set of fixed electrodes 28 and 29 in the Y direction, the first fixed electrode 28 has an X direction in the X direction. A connection portion 28B is provided on one end side (right side in the drawing), and the second fixed electrode 29 is provided with a connection portion 29B on the other end side in the X direction (left side in the drawing). That is, the first and second fixed electrodes 28 and 29 are one end of the plurality of sets and another end adjacent in the Y direction, and end portions where the connection portions 28B and 29B are provided are different from each other. It has become. In other words, the connection portion 28B has end portions that are alternately provided to the first fixed electrodes 28 that are arranged in the Y direction at the positions of the end portions provided with respect to the first fixed electrodes 28. Similarly, in the connection portion 29B, the position of the end provided with respect to the second fixed electrode 29 is on the end side that is alternately different with respect to the second fixed electrode 29 arranged in the Y direction.

  Further, as shown in FIG. 2B, the first and second fixed electrodes 28 and 29 are formed such that portions excluding the end portions where the through holes 28A and 29A are provided are separated from the substrate 12. . Note that the first and second fixed electrodes 28 and 29 may be configured such that the entirety including the end portions is connected to the substrate 12.

  The movable electrode 30 includes a frame-shaped electrode portion 30A formed so as to surround the outer peripheral portions of the first and second fixed electrodes 28, 29 in plan view, and the Y-direction of each of the first and second fixed electrodes 28, 29. And a flat plate electrode portion 30B provided therebetween. The frame-shaped electrode portion 30 </ b> A has a rectangular frame shape formed integrally with the central portion of the weight portion 24, and is separated from each of the first and second fixed electrodes 28 and 29. The plate electrode portion 30B extends from the weight portion 24 so as to face the first and second fixed electrodes 28 and 29, has a main surface formed in a substantially rectangular plate shape along the Z direction, and has a long side in the X direction. It is provided along. Each plate electrode portion 30B is integrally formed with the weight portion 24 at both ends in the X direction.

  Further, the first and second fixed electrodes 28 and 29 are disposed adjacent to each other in a region sandwiched between the plate electrode portions 30B adjacent in the Y direction. The connecting portion 28B is formed to be widened to the adjacent second fixed electrode 29 side so that the first fixed electrode 28 and the plate electrode portion 30B are flush with each other. Further, the connecting portion 29B is formed to be widened to the adjacent first fixed electrode 28 side so that the second fixed electrode 29 and the plate electrode portion 30B are flush with each other.

  As shown in FIG. 2B, the substrate 12 includes a core substrate 51, an insulating layer 53 formed so as to cover the upper surface of the core substrate 51, and a third fixed electrode 55 formed on the insulating layer 53. With. The anchor portion 45 formed integrally with the beam portion 41 is connected to the pad 58, and the weight portion 24 is electrically connected to an external terminal via wiring (not shown). As shown in FIG. 3, in the first sensor 21, parallel plate capacitors C <b> 1 and C <b> 2 are configured by the movable electrode 30 of the weight portion 24 and the first and second fixed electrodes 28 and 29. The parallel plate capacitors C1 and C2 are provided between each of the first and second fixed electrodes 28 and 29 and the plate electrode portion 30B according to the acceleration acting in the Y direction (detection direction) with respect to the first sensor 21. The capacitance varies with the distance. For example, the capacitance of the parallel plate capacitor C1 decreases while the capacitance of the parallel plate capacitor C2 increases as the weight portion 24 changes in one direction in the Y direction (upward in the figure). By measuring the capacitance of the parallel plate capacitor that changes with the variation in the distance between the movable electrode 30 (plate electrode portion 30B) and the first and second fixed electrodes 28 and 29, the Y direction can be measured. It is possible to detect acceleration.

  For example, the voltage at the measurement point 61 connected to the weight portion 24 is output from the external terminal to the processing circuit, the potential difference (capacitance difference) between the capacitors C1 and C2 is detected, and the acceleration is calculated. As shown in FIG. 3, the first sensor 21 includes a bridge circuit including capacitors C1 and C2 in order to increase the output of the difference in capacitance and improve the sensitivity. In addition, by configuring this bridge circuit, it is possible to cancel the change in the capacitance of each of the capacitors C1 and C2 with respect to the X direction, which is the non-detection direction, and to reduce so-called other-axis sensitivity. The first sensor 21 may include a correction circuit for canceling the offset voltage at the measurement point 61 when no load is applied without acceleration.

  Also, the third fixed electrode 55 shown in FIG. 2B is formed to extend over the entire upper surface of the insulating layer 53 so as to face the weight portion 24 in the Z direction. The first sensor 21 includes a parallel plate capacitor that is opposed to the weight portion 24 and the third fixed electrode 55 in the Z direction. The capacitance of the parallel plate capacitor changes according to the acceleration acting on the first sensor 21 in the Z direction. In the first sensor 21, the acceleration in the Z direction is detected by measuring the capacitance of the parallel plate capacitor that changes as the distance between the weight portion 24 and the third fixed electrode 55 varies.

  As described above, the first sensor 21 detects the acceleration acting in the Y direction and the Z direction, while the spring 43 (see FIG. 2A) is configured to restrict expansion and contraction in the X direction. The weight portion 24 is not bent in the X direction. Therefore, the first sensor 21 is configured as a biaxial acceleration sensor that can detect accelerations in the Y direction and the Z direction. As shown in FIG. 1, the second sensor 31 included in the acceleration sensor 10 has the same configuration as the first sensor 21, and includes a frame portion 23, a weight portion 24, a pair of spring portions 26, First and second fixed electrodes 28 and 29 and a third fixed electrode (not shown) are provided. The second sensor 31 has a structure in which the first sensor 21 is rotated 90 degrees with the Z direction as a rotation axis. That is, the second sensor 31 detects acceleration acting in the X direction and the Z direction, while the spring 43 of the spring portion 26 is restricted from expanding and contracting in the Y direction so that the weight portion 24 does not flex in the Y direction. It has become. Therefore, the second sensor 31 is configured as a biaxial acceleration sensor that can detect accelerations in the X direction and the Z direction.

  In the acceleration sensor 10 configured as described above, accelerations in three directions are detected based on the outputs of the first and second sensors 21 and 31. Further, the acceleration sensor 10 measures the change in capacitance according to the variation in the distance between the weight portion 24 of each of the first and second sensors 21 and 31 and the third fixed electrode 55 in the acceleration in the Z direction. To detect. That is, the acceleration sensor 10 is configured to detect the acceleration in the Z direction using a value obtained by combining the outputs of both the first and second sensors 21 and 31.

  Next, the arrangement of the capacitance unit 27 will be described with reference to FIG. FIG. 4 is a schematic diagram for illustrating the arrangement of the capacitance unit 27, in which each member included in the first sensor 21 is omitted as appropriate. As shown in FIG. 4, the capacitance part 27 is provided in the center of the weight part 24 and arranged in a line. More specifically, the electrostatic capacity portion 27 is located at the center of the electrostatic capacitance portion 27 at the midpoint (center of gravity 70) of the diagonal line in the weight portion 24 having a square outer periphery in plan view. The center of the capacitance part 27 here is the center when the capacitance part 27 including the first and second fixed electrodes 28 and 29 and the plate electrode part 30B is viewed in three dimensions. Position. The center of the capacitance unit 27 is appropriately set according to the configuration of the capacitance unit 27 and the like. In the first sensor 21 of the present embodiment, the center of the electrostatic capacitance portion 27 coincides with the center of gravity 70 of the weight portion 24, and not only in a plan view but also in a three-dimensional view, The positions that are the centers of are consistent. In the present embodiment, the second sensor 31 has the same configuration as that of the first sensor 21, and each sensor 21, 31 has the center of the electrostatic capacity portion 27 aligned with the center of gravity 70 of the weight portion 24. ing.

  Here, in the first and second fixed electrodes 28 and 29, the electrode thickness 71 of the connection portions 28B and 29B in which the through holes 28A and 29A are formed is increased as compared with the other portions. FIG. 12 shows an arrangement of the electrostatic capacity portion 27 of the first sensor 21A as a comparative example. The first sensor 21A shown in FIG. 12 has a capacitance portion 27A in which the capacitance portion 27 is divided into two (two rows) in the longitudinal direction (X direction) of the first and second fixed electrodes 28 and 29. , 27B. The electrostatic capacitance parts 27A and 27B are arranged in a distributed manner at positions symmetrical with respect to the position of the center of gravity 70 of the weight part 24 in plan view. In such a configuration, the capacitance units 27 corresponding to one detection direction (Y direction) are arranged in a distributed manner in the two capacitance units 27A and 27B. Connection portions 28B and 29B are provided on the first and second fixed electrodes 28 and 29 of 27A and 27B.

  On the other hand, in the first sensor 21 shown in FIG. 4, the electrostatic capacitance portion 27 corresponding to the detection direction is provided in a row in the central portion of the weight portion 24 and is provided in the Y direction at the central portion of the weight portion 24. The first and second fixed electrodes 28 and 29 and the movable electrode 30 are alternately arranged in parallel. Therefore, when compared with the first sensor 21A shown in FIG. 12, the first sensor 21 can be reduced in size by the number of connections 28B and 29B omitted. More specifically, for example, when the first sensor 21 is compared with the first sensor 21A in the X direction, if the length in the X direction of the connection portions 28B and 29B is 72, the connection portion 28B, It is possible to shorten the length in the X direction by the length of 29B (the width 72 is two). Therefore, in such a configuration, the capacitance portions 27 corresponding to one detection direction are concentrated in one place, so that the arrangement of the connection portions 28B and 29B provided in the fixed electrodes 28 and 29 can be optimized. It is possible to reduce the size of the apparatus by reducing the number of the sections 28B and 29B.

  Further, the first and second fixed electrodes 28 and 29 are separated from the weight portion 24. Therefore, for example, when the first sensor 21 is compared with the first sensor 21A in the X direction, the width of the gap in the X direction between the connection portions 28B and 29B and the weight portion 24 is set to the width 73. The length in the X direction can be shortened by a length of several minutes (two widths 73). In other words, since the gap between the connection portions 28B and 29B and the weight portion 24 can be omitted in accordance with the omission of the connection portions 28B and 29B, the apparatus of the acceleration sensor using the MEMS technology particularly applied to the manufacture of a fine mechanical structure is used. It is possible to effectively reduce the size.

  Incidentally, for example, in the first sensor 21 </ b> A shown in FIG. 12, the capacitance portion 27 </ b> B is omitted and concentrated in the capacitance portion 27 </ b> A, that is, the capacitance portion 27 is concentrated at a position other than the center of the weight portion 24. The structure which performs is considered. However, in such a configuration, for example, the movable electrode 30 is formed only on one side in the X direction with respect to the weight portion 24, and the center of gravity of the weight portion 24 is shifted from the center. Therefore, when acceleration is applied, a movement in the rotational direction is generated with respect to the weight portion 24, and it becomes difficult to obtain a desired output for the acceleration in the detection direction.

  Next, an operation in which the connection portions 28B and 29B are alternately provided at different end portions with respect to the first and second fixed electrodes 28 and 29 arranged in the Y direction will be described. First, in the first sensor 21 shown in FIG. 4, the gap width between the connection portions 28 </ b> B and 29 </ b> B and the movable electrode 30 has been described using the same reference numeral as the width 73. The distance varies depending on the gap provided in each of the two. This is because the widths 73 provided on both sides in the X direction of the fixed electrodes 28 and 29 are limited due to the limit of accuracy in the manufacturing process such as position adjustment (alignment) of the photomask for forming the resist for etching and control over the etching amount. This is because it is extremely difficult to set the same distance.

  Therefore, in the following description, as shown in FIG. 5, the width 73 on one end side (left side in the figure) in the X direction is referred to as a width 73A, and the width 73 on the other end side is referred to as a width 73B. For example, the width 73A is longer than the width 73B. As shown in FIG. 5, the connecting portion 28 </ b> B has a second fixed electrode 29 adjacent on one end side of the first fixed electrode 28 so that the first fixed electrode 28 and the movable electrode 30 are flush with each other in the Y direction. It is formed to be widened. Further, the connection portion 29B is formed to be widened to the adjacent first fixed electrode 28 side at one end side of the second fixed electrode 29 so that the second fixed electrode 29 and the movable electrode 30 are flush with each other. Yes. Further, the connecting portions 28B and 29B are formed so as to be widened to positions facing the end portions of the adjacent first and second fixed electrodes 28 and 29 in the X direction. Accordingly, in the pair of first and second fixed electrodes 28 and 29, one of the connection portions 28B and 29B faces the frame-shaped electrode portion 30A at the end in the X direction.

  Here, for example, in a state where a large impact is applied to the first sensor 21 and the weight portion 24 is rotated, the widths 73A and 73B are different depending on the position in the Y direction as shown in FIG. For example, when the weight portion 24 rotates counterclockwise about the Z-axis direction as the rotation axis, the distance of the width 73A increases toward the upper side in the Y direction, while the distance of the width 73B increases in the Y direction. It becomes smaller as it goes upward. Variations in the widths 73A and 73B accompanying the rotation of the weight portion 24 cause variations in capacitance between the connection portions 28B and 29B and the frame-shaped electrode portion 30A. Since the widths 73A and 73B are different distances as described above, the variation of the capacitance due to the rotation of the weight portion 24 is different between the widths 73A and 73B, that is, both sides in the X direction.

  Therefore, in the first and second fixed electrodes 28 and 29 of the present embodiment, the positions of the end portions where the connection portions 28B and 29B are provided are alternately different from each of the fixed electrodes 28 and 29 arranged in the Y direction. It is comprised so that it may become an edge part side. As a result, the frame-shaped electrode portion 30A has a similar variation in the capacitance generated between the connection portions 28B and 29B during rotation. As a result, it is possible to eliminate the difference in fluctuation caused by the rotation with respect to the capacitance between the movable electrode 30 and each of the first and second fixed electrodes 28 and 29, and to improve the acceleration detection accuracy.

  Incidentally, in the first sensor 21 of the present embodiment, the connection portions 28B and 29B are provided at the end portions of the first and second fixed electrodes 28 and 29. On the other hand, the first sensor 21 shown in FIG. A configuration in which the connection portions 28B and 29B are provided at substantially the center in the X direction of the first and second fixed electrodes 28 and 29 as in the sensor 21B is conceivable. In such a configuration, the difference in capacitance variation during rotation between the end portions in the X direction of the first and second fixed electrodes 28 and 29 and the movable electrode 30 can be reduced, but the width of the electrodes is reduced to other portions. By providing the connection portions 28B and 29B larger than the central portion in the center portion, the distance between the fixed electrodes 28 and 29 is increased, and the region occupied by the fixed electrodes 28 and 29 with respect to the first sensor 21B is increased. Incurs an increase.

  On the other hand, in the first sensor 21 of the present embodiment, the pair of first and second fixed electrodes 28 and 29 has a frame-shaped electrode portion 30A in which one of the connection portions 28B and 29B at the end in the X direction. Is facing. And each connection part 28B and 29B from which the width | variety of an electrode becomes large is provided in the different edge part side of the fixed electrodes 28 and 29, and is arrange | positioned so that it may become alternate. Thereby, the area | region which the fixed electrodes 28 and 29 occupy can be reduced by arrange | positioning both the fixed electrodes 28 and 29 closer. As a result, it is possible to achieve both improvement in acceleration detection accuracy and downsizing of the apparatus.

Next, the structure of the plate electrode portion 30B of the movable electrode 30 will be described in detail.
As shown in FIG. 7, the plate electrode portion 30 </ b> B provided in the electrostatic capacitance portion 27 of the first sensor 21 is formed in a substantially rectangular plate shape whose long side is along the X direction, and both end portions of the long side are weights. It is fixed to the part 24. Portions (hereinafter referred to as “fixed portions”) 81 and 82 where the flat plate electrode portion 30B is fixed to the weight portion 24 are integrally formed with the weight portion 24.

Here, in order to compare with the present embodiment, a configuration in which the plate electrode portion 30B is fixed to the weight portion 24 only by one end side in the longitudinal direction, for example, the fixing portion 81 will be described. As shown in FIG. 7, for example, the length in the longitudinal direction (X direction) of the plate electrode portion 30B is L, the length in the short direction (Z direction) is h, and the thickness (length in the Y direction) is b. And When the acceleration a (G) is applied in the detection direction to the flat plate electrode portion 30B in which only the fixed portion 81 is fixed, the tip on the other end side (fixed portion 82 side) of the flat plate electrode portion 30B In such a portion, bending (displacement) represented by the following formula occurs.
v = f ₀ L ⁴ /8EI=14.7 (σaL ⁴ / Eb ² )
In the above equation, f ₀ is a load per unit length (distributed load) applied to the plate electrode portion 30B when acceleration a (G) is applied, and E is a Young's modulus of the material (for example, silicon) of the plate electrode portion 30B. (For example, 169 GPa (gigapascal)), I is the moment of inertia of the cross section, and σ is the density of the material (for example, 2330 kg / m ³ ). For example, the length L = 270 μm (micrometer), the length h = 10 μm, and the thickness b = 2 μm. In this case, when an acceleration having a magnitude of a = 10,000 (G) is applied to the sensor 21, a displacement of v = 2.7 μm occurs.

  On the other hand, the width 74 between the movable electrode 30 (the plate electrode portion 30B) and the first and second fixed electrodes 28 and 29 is such that the distance between the electrodes is reduced in order to improve the sensitivity, etching, etc. Considering the processing limit in the manufacturing process, the width 74 is about 2.0 to 2.5 μm. Therefore, in the configuration in which the one end side of the flat plate electrode portion 30B is fixed as described above, if acceleration of a magnitude of 10,000 = 10,000 (G) is applied, the tip portion of the flat plate electrode portion 30B and the first portion The first and second fixed electrodes 28 and 29 collide to cause a short circuit. Incidentally, the acceleration a = 10,000 (G) is a value that is generally within an allowable range as an acceleration applied to this type of sensor.

  On the other hand, in the first sensor 21 of the present embodiment, both ends in the longitudinal direction of each plate electrode portion 30B are connected to the weight portion 24 at the fixing portions 81 and 82. In such a configuration, when acceleration is applied to the flat plate electrode portion 30 </ b> B, a force is applied to displace the central portion in the longitudinal direction (X direction) by fixing both ends to the weight portion 24. However, in order to displace the central portion of the flat plate electrode portion 30B, it is necessary to deform so that the flat plate electrode portion 30B itself extends in addition to bending. As a result of simulation by the present inventors, the acceleration required for the central portion of the flat plate electrode portion 30B to extend and contact with the fixed electrodes 28 and 29 has a value of acceleration a = about 7.5 million (G). Therefore, in the flat plate electrode portion 30B of the present embodiment, both ends thereof are fixed to the weight portion 24, so that even when a large acceleration is applied due to impact or the like, the flat plate electrode portion 30B and the first and second fixed portions are fixed. It is possible to prevent collision with the electrodes 28 and 29.

  Moreover, since the electrostatic capacitance part 27 is provided in the center of the weight part 24 and the 1st sensor 21 is gathered, the length L of the longitudinal direction of one flat plate electrode part 30B is lengthened, and an electrostatic capacitance. By increasing the value, sensitivity can be improved. On the other hand, as described above, when the flat plate electrode portion 30B is fixed only on one side, bending corresponding to the length L occurs. Therefore, in this embodiment, since both ends of the plate electrode portion 30B are fixed to the weight portion 24 and are not easily bent, the length L of the plate electrode portion 30B is set to a desired capacitance. Even if the capacitance portion 27 is made long, it can be suitably aggregated.

  For example, a stopper that restricts the fluctuation of the weight portion 24 and the like is provided for the first sensor 21 so that the weight portion 24 fluctuates before the collision between the movable electrode 30 and the first and second fixed electrodes 28 and 29 occurs. The structure which regulates is conceivable. However, when such a stopper functions, the weight portion 24 has already fluctuated, and the width 74 between the movable electrode 30 and the first and second fixed electrodes 28 and 29 is, for example, 2. It becomes narrower than 0-2.5 micrometers, and it becomes easy to produce the collision by bending. Therefore, even in the first sensor 21 including a member such as a stopper that regulates the variation of the weight part 24, the both ends of the flat plate electrode part 30 </ b> B are fixed to the weight part 24, so that the movable electrode 30 and the first sensor 21 can be more reliably connected. It is possible to prevent collision with the first and second fixed electrodes 28 and 29.

Next, the structure of the spring 43 will be described.
A spring 100 illustrated in FIG. 8A is an example of the spring 43. As described above, the spring 100 is formed in a shape in which the short sides 111 and the long sides 112 that are perpendicular to each other are alternately connected. In the following description, as shown in FIGS. 8A to 8C, the length of the short side 111 is referred to as L1, and the length of the long side 112 is referred to as L2. Moreover, the direction shown to Fig.8 (a)-(c) has shown the direction where the springs 100, 100A, and 100B expand and contract.

  The spring 100 has a length L2 that is longer than the length L1, and a distance L3 between both ends connected to each of the weight portion 24 (see FIG. 2A) and the beam portion 41 (see FIG. 2A). It is configured to be longer than the length L2. Here, the number of times the spring 100 reciprocates in the Y direction, in other words, the number of times of folding back at one end in the Y direction (hereinafter referred to as “the number of times of folding”) is n. In the spring 100 shown in FIG. 8A, the number of times of folding n is 15. The spring 100 has a relationship in which the folding number n and the spring constants Kx, Ky, and Kz corresponding to the X, Y, and Z directions are correlated. Therefore, the present inventors have made the present invention as a result of repeated examination, simulation, and the like regarding changes in the spring constants Kx, Ky, and Kz with respect to the number n of folding of the spring 100. Specifically, as shown in FIG. 8A, for example, the area of a region S (portion surrounded by hatching in the drawing) occupied by the spring 100 in a plane orthogonal to the Z direction is constant, The spring constants Kx, Ky, Kz were examined while changing.

  FIG. 9 is a graph showing the values of the spring constants Kx, Ky, Kz with respect to the folding number n. As shown in FIG. 9, the spring constant Kx in the X direction increases as the number of folding times n increases. The graph shown by the solid line in the figure shows the result of trial calculation of the spring constant Kx, and it can be seen that as the number of foldings n increases, the rigidity in the X direction increases and the expansion and contraction is restricted.

  On the other hand, the spring constant Ky in the Y direction decreases as the number of folding times n increases. The graph shown by the broken line in the figure shows the result of the trial calculation of the spring constant Ky, and it can be seen that the rigidity in the Y direction decreases and the bending becomes easier as the number of times of folding n increases. Similarly, the spring constant Kz in the Z direction decreases as the number of folding times n increases. The graph shown by the alternate long and short dash line in the figure shows the trial calculation result of the spring constant Kz, and it can be seen that it becomes easier to flex in the Z direction as the number of folding times n increases.

  Based on the above contents, the spring 100 is classified into three types by the spring constants Kx, Ky, and Kz using the graph shown in FIG. For example, the folding number n at which the spring constants Kx, Ky, and Kz are approximate values is a reference value n1 (for example, n1 = 10), and the spring 100 in which the folding number n is smaller than the reference value n1 is the first type. . The spring 100 classified as the first type is, for example, a spring 100 </ b> A configured so that the number of times of folding n is 5 as shown in FIG. 8B. In the spring 100A, the distance L3 between both ends of the spring 100A is shorter than the length L2. The spring 100A has a characteristic that it is easily displaced in the X direction and the expansion and contraction in the Y and Z directions is restricted. That is, such a spring 100A has a characteristic of expanding and contracting in one direction, and is a spring used for a uniaxial acceleration sensor as disclosed in, for example, Japanese Patent Application Laid-Open No. 11-344507 (Patent Document 1). is there.

  Next, the spring 100 in which the respective spring constants Kx, Ky, Kz are substantially the same with the folding number n as the reference value n1 is the second type. The spring 100 classified as the second type is, for example, a spring 100B configured with the number of foldings n as 10 as shown in FIG. 8C. The spring 100B has a distance L3 between both ends of the spring 100B substantially equal to the length L2, and is displaced in the X, Y, and Z directions. In other words, this type of spring 100B has a characteristic of expanding and contracting or bending in three directions, and is used for, for example, a triaxial acceleration sensor as disclosed in JP-T-2005-534016 (Patent Document 3). Spring.

  And the spring 100 shown by Fig.8 (a) of this embodiment is a spring classified into 3rd types with the frequency | count n of folding large compared with the reference value n1, and is provided with the flexibility with respect to two directions. is there. More specifically, the spring 100 has high rigidity in the X direction in which the short side 111 and the long side 112 are connected and meanderingly extend, and is difficult to expand and contract. The spring 100 has flexibility in the Y direction perpendicular to the X direction extending in a meandering manner. The spring 100 has flexibility in the Z direction perpendicular to the plane in which the region S occupied by the spring 100 is set. Therefore, in the first sensor 21 including the spring 100 (spring 43) having such characteristics, acceleration acting in the Y direction and the Z direction is detected, while the weight portion 24 does not change in the X direction, so the X direction. It is possible to suppress the sensitivity to other axes and to improve the detection accuracy.

Next, the sensitivity of the acceleration sensor 10 configured as described above will be described.
The acceleration sensor 10 is configured to detect acceleration in the Z direction using the outputs of both the first and second sensors 21 and 31. Here, assuming that the area of the opposing electrodes is S, the distance between the electrodes is d, and the dielectric constant is ε, the capacitance C is expressed by the following equation.
C = εS / d (1)
The weight portion 24 is formed in a flat plate shape in which the plane direction is orthogonal to the Z direction, and the area S of the movable electrode that detects acceleration in the Z direction is larger than the other directions (X direction, Y direction). Can be bigger. Therefore, in the first and second sensors 21 and 31 of the present embodiment, the capacitance provided for detecting the acceleration acting in the Z direction can be larger than the other two directions. .

Further, the magnitude of the change amount ΔC of the capacitance with respect to the change amount Δd of the distance is expressed by the following equation using the above formula (1).
ΔC / Δd = εS / d ² (2)
Further, the force acting on the weight portion 24 is expressed by the following equation from the equation of motion and the law of elasticity.
F = ma = kΔd (m: mass of weight portion 24, a: acceleration, k: spring constant) (3)
From the above equations (2) and (3), the amount of change ΔC in capacitance is expressed by the following equation.
ΔC = (εS / d ² * m / k) a = (C / k * m / d) a (4)

  Therefore, from the above equation (4), in order to increase the sensitivity (capacitance change amount) to the acceleration a of the capacitive acceleration sensor 10 as in the present embodiment, the mass m of the weight portion 24 as a weight. Or increase the capacitance C of the capacitor formed by the weight portion 24 and each of the first to third fixed electrodes 28, 29, and 55, or decrease the spring constants Kx, Ky, and Kz. Can be considered. The mass m is correlated with the size of the weight portion 24. The electrostatic capacity C is correlated with the area S of the weight portion 24 in the direction orthogonal to the Z direction in the Z direction. As shown in FIG. 2A, when the acceleration sensor 10 is viewed in a plan view, the weight portion 24 occupies a large area of the plane. On the other hand, for example, a single-axis acceleration sensor (such as the acceleration sensor disclosed in the above Japanese Patent Laid-Open No. 11-344507 (Patent Document 1)) is provided corresponding to each direction of XYZ. A configuration in which they are arranged side by side on the same plane is conceivable. However, in such a configuration, when viewed in a plan view, the weight portion contributing to the Z-axis direction occupies only a partial region of the plane. That is, in the acceleration sensor 10 of the present embodiment, all the sensors (first and second sensors 21 and 31) contribute to the detection of acceleration in the Z direction. Comparing the case of configuring the acceleration sensor, the structure is excellent in miniaturization.

  In general, it is preferable that the sensitivity of the capacitive acceleration sensor be equal to each other in the XYZ directions. As shown in the above equation (4), it is conceivable to make the ratio of the capacitance C and the spring constant k in each direction equal in order to make the sensitivity in each direction comparable. For example, in the acceleration sensor 10 described above, the capacitance between the weight portion 24 of the second sensor 31 that detects acceleration in the X direction and the first and second fixed electrodes 28 and 29 is Cx, and the spring 43 Let the spring constant in the X direction be kx. Further, the capacitance between the weight 24 of the first sensor 21 that detects the acceleration in the Y direction and the first and second fixed electrodes 28 and 29 is Cy, and the spring constant of the spring 43 in the Y direction is ky. And In the present embodiment, since the first and second sensors 21 and 31 have the same structure, the capacitances Cx and Cy and the spring constants kx and ky have the same value. Further, the capacitances between the electrodes 24 and the third fixed electrode 55 for detecting the acceleration in the Z direction of the first and second sensors 21 and 31 are represented by capacitances Cz1 and Cz2, and the sensors 21. , 31 of the spring 43 in the Z direction are kz1 and kz2. In the present embodiment, since the first and second sensors 21 and 31 have the same structure, the capacitances Cz1 and Cz2 have the same value. Similarly, the spring constants kz1 and kz2 have the same value.

In this case, in order to make the ratio between the capacitance C in each direction and the spring constant k equal, it is preferable to satisfy the following equation.
2 * Cx / kz = 2 * Cy / ky = (Cz1 / kz1 + Cz2 / kz2) (5)
Therefore, by designing the value of the above formula (5) as an index, the sensitivity to acceleration in the directions of the three axes orthogonal to each other can be made equal, and the acceleration sensor 10 of this embodiment can be easily configured. It becomes possible. As shown in FIG. 3, each of the first and second sensors 21 and 31 according to the present embodiment includes a bridge circuit including capacitors C1 and C2, and a difference in capacitance between the capacitors C1 and C2. Is used to calculate the acceleration. Therefore, the sensitivity of each sensor 21 and 31 in each direction correlates with, for example, a value obtained by doubling the capacity of one of the capacitors C1 and C2. The above equation (5) takes into account the bridge circuit used in such a capacitance type acceleration sensor.

Next, an example of a method for manufacturing the first sensor 21 will be described. Note that the manufacturing method of the second sensor 31 is the same as that of the first sensor 21, and thus the description thereof is omitted.
First, the core substrate 200 shown in FIG. The core substrate 200 is a wafer made of single crystal silicon, for example. The first sensor 21 is manufactured by forming a large number of sensor elements on the core substrate 200 and then dicing into a plurality of first sensors 21.

  An insulating layer 210 is formed on the surface of the core substrate 200. The insulating layer 210 is formed by, for example, silicon nitride (SiNx) or a film obtained by stacking silicon nitride on a silicon dioxide film by using a thermal oxidation method or a deposition method. Next, a third fixed electrode 212, a pad 214, and a wiring (not shown) that are arbitrarily patterned using a photolithography technique, for example, are formed on the surface of the insulating layer 210. For the third fixed electrode 212 and the wiring (not shown), a material that is resistant to etching of the sacrificial layer 215 described later, such as polysilicon, is used. When aluminum generally used in LSI technology is used for the third fixed electrode 212 and a wiring (not shown), a silicon nitride film is laminated on the aluminum, or the insulating layer 210 described above is formed of a multilayer film. It is preferable to increase the resistance to the etching of the sacrificial layer 215 by, for example, forming and forming in it. As described above, the insulating layer 210, the third fixed electrode 212, and the wiring (not shown) may be composed of a plurality of layers. Further, the third fixed electrode 212 and the wiring (not shown) may be composed of a plurality of conductive layers.

  Next, as illustrated in FIG. 10B, a sacrificial layer 215 is formed so as to cover the insulating layer 210 and the third fixed electrode 212. The sacrificial layer 215 is formed by depositing silicon dioxide by, for example, a chemical vapor deposition (CVD) method. The thickness of the sacrificial layer 215 is, for example, 2 μm (micrometer). Next, as shown in FIG. 10C, a contact hole 216 is formed so that a part of the surface of the pad 214 is exposed to the sacrificial layer 215. The contact hole 216 is formed using, for example, a photolithography technique.

  Next, as illustrated in FIG. 11A, an electrode layer 217 is formed on the sacrificial layer 215. A part of the electrode layer 217 is filled in the contact hole 216. The electrode layer 217 is formed by depositing polysilicon by, for example, the CVD method. The thickness of the electrode layer 217 is, for example, 5 to 10 μm. Next, as shown in FIG. 11B, the electrode layer 217 is etched to form the through hole 219 and the first and second fixed electrodes 220 and 221. For the etching of the electrode layer 217, for example, a resist (not shown) formed by arbitrary patterning using a photolithography technique is formed on the electrode layer 217, and Deep− is exposed to the region exposed from the opening of the resist. Anisotropic etching is performed using RIE (Reactive Ion Etching). Although not shown, the spring 43 is formed, for example, in the same process as the first and second fixed electrodes 220 and 221 described above.

  Next, as shown in FIG. 11C, the sacrificial layer 215 is etched. For example, the sacrificial layer 215 is etched by introducing an etchant (for example, buffered hydrofluoric acid (BHF)) from the through-hole 219 or the like formed in the electrode layer 217. In this way, the first sensor 21 shown in FIG. 1 is formed.

As mentioned above, according to above-mentioned embodiment, there exist the following effects.
(1) The first and second sensors 21 and 31 included in the acceleration sensor 10 are arranged such that the positions of the end portions where the connection portions 28B and 29B are provided with respect to the first and second fixed electrodes 28 and 29 are in the Y direction. Each of the fixed electrodes 28 and 29 arranged side by side is configured to be alternately different end portions. As a result, the frame-shaped electrode portion 30A has a similar variation in the capacitance generated between the connection portions 28B and 29B during rotation. As a result, it is possible to eliminate the difference in fluctuation caused by the rotation with respect to the capacitance between the movable electrode 30 and each of the first and second fixed electrodes 28 and 29, and to improve the acceleration detection accuracy.

(2) In the first and second sensors 21 and 31, the capacitance part 27 including the first and second fixed electrodes 28 and 29 and the movable electrode 30 (plate electrode part 30B) is the central part of the weight part 24. Are provided in one line. In such a configuration, the capacitance portions 27 corresponding to one detection direction are concentrated in one place, so that the connection portions 28B and 29B that connect the first and second fixed electrodes 28 and 29 to the substrate 12 are provided. The arrangement can be optimized, and the number of connection portions 28B and 29B can be reduced to reduce the size of the apparatus. Further, in such a configuration, it is possible to increase the area where the weight portion 24 is formed in accordance with the portion where the connection portions 28B and 29B are omitted, that is, the weight of the weight portion 24 can be increased. Thus, the sensitivity can be improved as compared with other acceleration sensors having the above-mentioned capacitance.

(3) In the first sensor 21, both ends in the longitudinal direction of each plate electrode portion 30 </ b> B are connected to the weight portion 24 at the fixing portions 81 and 82. In such a configuration, since both ends of the flat plate electrode portion 30B are fixed to the weight portion 24, even when a large acceleration is applied due to an impact or the like, the flat plate electrode portion 30B and the first and second fixed electrodes 28 are provided. , 29 can be prevented from colliding.
Further, since both ends of the plate electrode portion 30B are fixed to the weight portion 24 and are not easily bent, the length L (see FIG. 7) of the plate electrode portion 30B is set to obtain a desired capacitance. Even with the elongated capacitance part 27, it is possible to configure an acceleration sensor that improves the sensitivity while preventing a short circuit between the first and second fixed electrodes 28 and 29 and the plate electrode part 30B.

(4) The first sensor 21 includes a first weight portion 24 that fluctuates in accordance with the acceleration, and the first to first portions by the spring 43 being expanded and contracted according to the acceleration in the Y and Z directions and the expansion and contraction with respect to the acceleration in the X direction being restricted. The acceleration in the Y and Z directions is detected from the change in capacitance with the third fixed electrodes 28, 29 and 55. That is, the first sensor 21 is configured as a biaxial acceleration sensor with the spring 43 having rigidity in the X direction. In the acceleration sensor 10, the second sensor 31 has the same configuration as the first sensor 21, and is configured as a three-axis acceleration sensor by detecting acceleration in the X and Z directions by the second sensor 31. Has been. In such a configuration, the spring 43 of each sensor 21, 31 has rigidity in one direction, and there is no possibility that the center of gravity of the weight portion 24 is shifted due to a defect in the manufacturing process and the rotation occurs. The acceleration sensor 10 can be configured with improved detection accuracy.

(5) The acceleration sensor 10 is configured to detect the acceleration in the Z direction using the outputs of both the first and second sensors 21 and 31. Accordingly, in the acceleration sensor 10, since all the sensors (first and second sensors 21 and 31) contribute to the detection of acceleration in the Z direction, a three-axis acceleration sensor is configured by three one-axis acceleration sensors. Compared with, it has a structure excellent in miniaturization.

(6) The spring 43 is configured such that the movable end 43B is positioned outside when the first sensor 21 is viewed in plan with respect to the fixed end 43A. In such a configuration, the influence of the rotational moment acting on the weight portion 24 is reduced, and the detection accuracy of the first sensor 21 can be improved.

Note that the present invention is not limited to the above-described embodiment, and it goes without saying that various improvements and modifications can be made without departing from the spirit of the present invention.
For example, the first sensor 21 includes an odd pair (five sets) of the pair of first and second fixed electrodes 28 and 29, but has a configuration including an even set, and the connection portions 28B and 29B are alternately different ends. It is good also as the structure made into the part side.
In the above embodiment, the first and second sensors 21 and 31 are configured as two-axis acceleration sensors capable of detecting acceleration in two directions, but are configured as one-axis acceleration sensors capable of detecting only acceleration in one direction. May be. For example, the spring 43 of the first sensor 21 may be configured as a first type of spring 100A illustrated in FIG. 8B and configured as a uniaxial acceleration sensor that detects an acceleration sensor in the Y direction. Even in such a configuration, for example, the connection portions 28B and 29B are alternately arranged on different end portions with respect to the first and second fixed electrodes 28 and 29. Can be obtained.

  In the above embodiment, the center of the capacitance part 27 is aggregated so as to coincide with the center of gravity 70 of the weight part 24. However, the capacitance part 27 is aggregated at a position that is substantially the center of the weight part 24. May be.

  Moreover, in the said embodiment, although the 1st sensor 21 was formed in planar view substantially square shape, it is not limited to this. For example, the first and second sensors 301 and 302 shown in FIG. 14 are formed in a substantially rectangular shape in plan view. The first and second sensors 301 and 302 are formed in a substantially rectangular shape in plan view with long sides extending along the X direction. The spring 311 of the first sensor 301 has a longer length in the X direction and a shorter length in the Y direction than the spring 43 of the first sensor 21 of the above embodiment. Further, the spring 312 of the second sensor 302 has a longer length in the X direction and a shorter length in the Y direction than the spring 43 of the second sensor 31 of the above embodiment. Even in such a configuration, the springs 311 and 312 have rigidity in one direction, and the first and second sensors 301 and 302 are configured as biaxial acceleration sensors. That is, according to the configuration of the first and second sensors 21 and 31 of the present embodiment, structural restrictions can be reduced and the degree of freedom in shape can be increased.

  Further, in the first and second sensors 301 and 302 shown in FIG. 14, a stopper 320 for preventing stiction between the weight portion 24 and each member is provided. The stopper 320 is formed in a column shape standing on the substrate 12 (see FIG. 1) and penetrating the weight portion 24 in the Z direction. By engaging the stopper 320 with the weight part 24, it is possible to prevent the weight part 24 from sticking to another member, for example, the first fixed electrode 28. Further, although not shown, a convex portion is provided on the surface of the stopper 320 facing the weight portion 24, and the contact area between the stopper 320 and the weight portion 24 is reduced to effectively prevent stiction. It has become. Further, such a convex portion may be provided on the surface of the other member, for example, the weight portion 24 of the anchor portion 45 facing the weight portion 24 so as to function as the stopper 320. Further, the mechanism for preventing stiction is not limited to the stopper 320, and for example, surface processing may be performed to make the end face of an arbitrary member hydrophobic.

  Further, the shape and configuration of each member is an example, and may be changed as appropriate. For example, the first sensor 21 and the second sensor 31 may have different structures.

  Incidentally, the acceleration sensor 10, the first sensors 21, 21A, 21B, 301, the second sensors 31, 302 are examples of acceleration sensors, and the weight portion 24 is an example of weight portions. The electrodes 28 and 29 are examples of fixed electrodes, the connection portions 28B and 29B are examples of first and second connection portions, and the movable electrode 30, the frame electrode portion 30A, and the plate electrode portion 30B are examples of movable electrodes. As mentioned.

DESCRIPTION OF SYMBOLS 10 Acceleration sensor, 12 board | substrate, 21,21A, 21B, 301 1st sensor, 24 weight part, 28 1st fixed electrode, 29 2nd fixed electrode, 28B, 29B connection part, 30 movable electrode, 30A frame-shaped electrode part , 30B Plate electrode part, 31, 302 Second sensor.

Claims (3)

A substrate,
A weight portion provided so as to be able to swing freely from the substrate;
A movable electrode provided on the weight portion;
The distance between the movable electrode and the movable electrode varies depending on the acceleration in the detection direction parallel to the planar direction of the substrate, and is fixed to the substrate. First and second fixed electrodes whose capacitance varies;
A first connection portion provided at one end of the first fixed electrode in a direction orthogonal to the detection direction, and connecting the first fixed electrode to the substrate;
A second connecting portion provided at the other end of the second fixed electrode opposite to the one end in the direction orthogonal to the detection direction, and connecting the second fixed electrode to the substrate;
The first and second fixed electrodes are
A pair of the first and second fixed electrodes arranged adjacent to each other in a region surrounded by the movable electrode are arranged in a plurality along with the movable electrode in the detection direction, The one end and the other end provided with the first and second connection portions are different from each other in one set of a plurality of sets and another set adjacent in the detection direction. An acceleration sensor. The first connection portion is formed to be widened at a position facing the one end portion of the adjacent second fixed electrode,
The second connection portion is formed to be widened at a position facing the other end portion of the adjacent first fixed electrode,
The pair of the first and second fixed electrodes is characterized in that, at an end portion in a direction orthogonal to the detection direction, a portion facing the movable electrode is one of the first and second connection portions. The acceleration sensor according to claim 1.   A pair of the first and second fixed electrodes and the movable electrode are arranged in a line along the detection direction in a central portion of a region surrounded by the outer peripheral edge of the weight portion in plan view of the substrate. The acceleration sensor according to claim 1, wherein the acceleration sensor is provided.

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