JP5799942B2 - Acceleration sensor - Google Patents

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).

  By the way, in the acceleration sensor including the fixed electrode and the movable electrode as described above, there is a possibility that a short circuit, damage, or the like may occur when the movable electrode whose position is changed by acceleration is collided with the fixed electrode. Therefore, for example, as shown in Patent Document 1, in order to prevent a collision between the movable electrode and the fixed electrode, there is one provided with a stopper for restricting the movement of the weight portion.

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

  However, a member that restricts the movement of the weight portion, such as the stopper described above, needs to be arranged at an appropriate position according to the shape and configuration of the fixed electrode and the movable electrode. In particular, in the above-described three-axis acceleration sensor, since the weight portion is provided so as to be freely movable along the plane direction, the position and inclination of the weight portion that changes from time to time according to the acceleration, etc. It was necessary to provide a stopper to function properly, and there was room for improvement.

  The technology disclosed in the present application has been proposed in view of the above problems. It is an object of the present invention to provide an acceleration sensor that can prevent a collision between a fixed electrode and a movable electrode more reliably by appropriately arranging a restricting portion that restricts movement of a weight portion with respect to a capacitance type acceleration sensor. .

  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. The distance in the detection direction relative to the movable electrode varies according to the acceleration in the detection direction parallel to the direction, and the weight swings in accordance with the acceleration. And a restriction part that restricts the movement of the part in the detection direction, and sets a rectangular frame that surrounds the entire fixed electrode in the plan view of the substrate and that each side extends along the detection direction and the direction orthogonal to the detection direction. In this case, the first straight line passing through the two points arranged along the direction orthogonal to the detection direction among the vertices of the rectangular frame is divided by the second straight line passing through the two points arranged along the detection direction. In one area, the regulating part is provided with a fixed electrode Regulating the engaging movement and the weight portion in the other four each in the region except for the region and the region adjacent to the region.

  In the acceleration sensor, the restricting portion that restricts the movement of the weight portion in the detection direction engages with the weight portion and restricts the movement in a region that does not face the fixed electrode in the detection direction and the direction orthogonal to the detection direction. More specifically, a rectangular frame that surrounds the entire fixed electrode in a plan view is set, a first straight line passing through two points arranged along a direction orthogonal to the detection direction among the vertices of the rectangular frame, and detection Nine areas defined by a second straight line passing through two points arranged in the direction are set. The restricting portion engages with the weight portion and restricts movement in each of the other four regions excluding the region where the fixed electrode is provided and the region adjacent to the region.

  In such a configuration, the position where the restricting portion engages with the weight portion is outside the position where the fixed electrode is disposed in the detection direction and the direction orthogonal to the detection direction. For example, when rotation occurs due to acceleration in the direction perpendicular to the detection direction and the direction perpendicular to the detection direction, the magnitude of displacement of the weight in the detection direction increases in proportion to the distance from the center of rotation. To do. Therefore, for example, when the rotation center of the weight portion is the center of the fixed electrode, the restriction portion engages with the weight portion at a position farther from the center of the fixed electrode than the end portion of the fixed electrode. The restricting portion engages with the weight portion at a position where the displacement amount is larger and restricts the movement. As a result, the collision between the fixed electrode and the movable electrode can be more reliably prevented. That is, it is possible to prevent the collision between the fixed electrode and the movable electrode by appropriately arranging the restricting portions.

  In the acceleration sensor according to the technique disclosed in the present application, the fixed electrode is a flat plate surface that is orthogonal to the plane of the substrate and orthogonal to the detection direction, and a plurality of fixed electrodes are arranged in parallel along the detection direction. The rectangular frame may be set along the outer periphery of the fixed electrode.

  In the acceleration sensor, the fixed electrode is configured by arranging a plurality of electrodes configured by flat plates in parallel, and the shape of the outer periphery in a plan view of the substrate is rectangular. By setting a rectangular frame on the outer periphery of the fixed electrode, the area where the fixed electrode is provided and the area adjacent to the area can be optimized and reduced. That is, the area for determining the arrangement of the restricting portion can be partitioned as large as possible.

  Further, in the acceleration sensor according to the technique disclosed in the present application, the restricting portion may be provided fixed to the substrate, and may be provided at a position that is symmetric with respect to the center of gravity of the weight portion in each of the four regions.

  In the acceleration sensor, it is possible to more reliably prevent the fixed electrode and the movable electrode from colliding by setting the restricting portion fixed to the substrate to a symmetrical position with respect to the weight portion.

  According to the technology disclosed in the present application, it is possible to more reliably prevent a collision between the fixed electrode and the movable electrode by appropriately arranging the restriction portion that restricts the movement of the weight portion with respect to the capacitance type acceleration sensor. An acceleration sensor can be provided.

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 perspective view for demonstrating the shape of a movable electrode. It is a schematic diagram for demonstrating arrangement | positioning of a stopper. It is a schematic diagram for demonstrating arrangement | positioning of the stopper in the sensor of a comparative example. It is a schematic diagram for demonstrating operation | movement of the sensor of a comparative example. It is a schematic diagram for demonstrating operation | movement of the sensor of a comparative example. (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 sensor. It is a schematic diagram for demonstrating arrangement | positioning of the stopper of another sensor. It is a schematic diagram for demonstrating the stopper of another sensor. It is a schematic diagram for demonstrating the stopper of another sensor. It is a schematic diagram for demonstrating another sensor. It is a schematic diagram for demonstrating the connection part of another sensor. It is a top view for demonstrating another sensor.

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 frame portion 23 is connected and fixed to the substrate 12 at an outer peripheral portion (not shown). 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 frame portion 23 is provided with first and second stoppers 23 </ b> A and 23 </ b> B at an inner peripheral portion that is separated from the outer peripheral portion of the weight portion 24 by a predetermined interval. The first stopper 23A is integrally formed on the inner peripheral portion of the frame portion 23 that faces the weight portion 24 in the Y direction. The second stopper 23B is integrally formed on the inner peripheral portion of the frame portion 23 facing the weight portion 24 in the X direction. The first and second stoppers 23A and 23B are formed so as to protrude inward from the inner peripheral surface of the frame portion 23, and the weight portion 24 is predetermined in either the X direction or the Y direction. It is configured to engage with the outer peripheral portion of the weight portion 24 when it is moved by this distance. The distance between the tip portions of the first and second stoppers 23A and 23B and the weight portion 24 is a width 74 (see FIG. 4) in the Y direction between first and second fixed electrodes 28 and 29 and an electrode portion 30 described later. A short distance is set. The first and second stoppers 23A and 23B have a configuration in which protruding tip portions engage with the weight portion 24, and have a shape in which the contact area with the weight portion 24 is reduced to prevent stiction. ing. The details of the positions where the first and second stoppers 23A and 23B are provided will be described later.

  In addition, as shown in FIG. 2A, the capacitance unit 27 includes first and second fixed electrodes 28 and 29 and an electrode unit 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 sets (six sets in the present embodiment) 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 a wiring (not shown) formed on the substrate 12 with a through hole 28A provided on one end side in the X direction (the upper three in the figure are the left side and the lower three are the right side). And are electrically connected. Further, the second fixed electrode 29 is provided with a through hole 29A on one end side in the X direction opposite to the first fixed electrode 28 (the upper three in the drawing are on the right side and the lower three are on the left side). It is electrically connected to the formed wiring (not shown). 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.

  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 electrode portion 30 includes an outer peripheral electrode portion 30A formed so as to surround the outer peripheral portions of the first and second fixed electrodes 28 and 29 in a plan view, and the Y direction between the first and second fixed electrodes 28 and 29. The movable electrode portion 30B is provided. The outer peripheral 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 movable 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 movable electrode portion 30 </ b> B is integrally formed with the weight portion 24 at both ends in the X direction.

  The first and second fixed electrodes 28 and 29 are disposed adjacent to each other in a region sandwiched between the movable 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 movable electrode portion 30B are flush with each other. Further, the connecting portion 29B is formed to be widened on the side of the adjacent first fixed electrode 28 so that the second fixed electrode 29 and the movable electrode portion 30B face 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 portion 30 </ b> B of the weight portion 24 and the first and second fixed electrodes 28 and 29. In the electrode portion 30 of the present embodiment, a part of the outer peripheral electrode portion 30A facing the first and second fixed electrodes 28 and 29 is the same as the movable electrode portion 30B. And function as a movable electrode constituting a capacitor. The parallel plate capacitors C1 and C2 are provided between each of the first and second fixed electrodes 28 and 29 and the movable electrode portion 30B according to the acceleration acting on the first sensor 21 in the Y direction (detection direction). 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 varies with the variation in the distance between the electrode unit 30 (movable electrode unit 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 movable 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. 14 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. 14 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 electrode portions 30 are alternately arranged along the line. Therefore, when compared with the first sensor 21A shown in FIG. 14, the first sensor 21 can be reduced in size by the number in which the connecting portions 28B and 29B are 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.

  Further, the connecting portions 28B and 29B have the same distance 74 in the Y direction (detection direction) with each electrode portion 30 (the outer peripheral electrode portion 30A and the movable electrode portion 30B). As described above, in general, in a sensor that detects acceleration using capacitance, a bridge circuit (see FIG. 3) is configured to increase the output of the difference in capacitance due to acceleration and improve sensitivity. Has been. However, the connecting portions 28B and 29B are provided at positions where the distance from the electrode portion 30 is the same, and the difference in capacitance (change amount) according to the acceleration output from the fixed electrodes 28 and 29 and the electrode portion 30. In FIG. 5, the amount of change corresponding to the output from the connection portions 28B and 29B is canceled by being output through the bridge circuit. As a result, even when such connection portions 28B and 29B face the electrode portion 30, the amount of change in capacitance effective for acceleration detection is not output and does not contribute to acceleration detection.

  On the other hand, the sensitivity of the first sensor 21 can be improved by increasing the weight of the weight portion 24 because the sensitivity correlates with the weight of the weight portion 24. Therefore, the first sensor 21 can increase the area where the weight portion 24 is formed according to the portion where the connection portions 28B and 29B are omitted, that is, the weight of the weight portion 24 can be increased. The sensitivity can be improved as compared with other acceleration sensors having a large capacitance.

  Incidentally, for example, in the first sensor 21A shown in FIG. 14, the capacitance part 27B is omitted, and the capacitance part 27A is aggregated, that is, the capacitance part 27 is aggregated at a position other than the center of the weight part 24. The structure which performs is considered. However, in such a configuration, for example, the electrode portion 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, the structure of the movable electrode part 30B of the electrode part 30 will be described in detail.
As shown in FIG. 5, the movable electrode part 30B provided in the electrostatic capacity part 27 of the first sensor 21 is formed in a substantially rectangular plate shape whose long side is along the X direction, and both ends 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 movable electrode portion 30 </ b> B 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 movable electrode portion 30B is fixed to the weight portion 24 only by one end side in the longitudinal direction, for example, only the fixed portion 81 will be described. As shown in FIG. 5, for example, the length in the longitudinal direction (X direction) of the movable 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 acceleration a (G) is applied in the detection direction to the movable electrode portion 30B in which only the fixed portion 81 is fixed, the tip of the other end side (the fixed portion 82 side) of the movable 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 movable electrode portion 30B when the acceleration a (G) is applied, and E is a Young's modulus of the material (for example, silicon) of the movable electrode portion 30B. (For example, 169 GPa (gigapascal)), I is the moment of inertia of the 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 electrode part 30 (movable electrode part 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 movable electrode portion 30B is fixed as described above, if an acceleration of a magnitude of 10,000 = 10,000 (G) is applied, the distal end portion of the movable 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 this embodiment, both ends in the longitudinal direction of each movable electrode portion 30B are connected to the weight portion 24 at the fixed portions 81 and 82. In such a configuration, when acceleration is applied to the movable electrode portion 30B, a force is applied so that the center portion in the longitudinal direction (X direction) is displaced by fixing both ends to the weight portion 24. However, in order to displace the central portion of the movable electrode portion 30B, it is necessary to deform so that the movable 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 movable 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 movable 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 an impact or the like, the movable electrode portion 30B and the first and second fixed portions are fixed. It is possible to prevent collision with the electrodes 28 and 29.

  In the first sensor 21, since the electrostatic capacitance part 27 is provided and concentrated in the center of the weight part 24, the length L in the longitudinal direction of one movable electrode part 30 </ b> B is increased to increase the electrostatic capacity. By increasing the value, sensitivity can be improved. On the other hand, as described above, when the movable electrode portion 30B is fixed only on one side, the bending corresponding to the length L occurs. Therefore, in this embodiment, since both ends of the movable electrode portion 30B are fixed to the weight portion 24 and are not easily bent, the length L of the movable electrode portion 30B is set to a desired capacitance. Even if the capacitance portion 27 is made long, it can be suitably aggregated.

  Next, the arrangement of the first and second stoppers 23A and 23B will be described in detail with reference to FIG. The arrangement of the first and second stoppers 23A and 23B of the present embodiment is determined based on the position and shape of the first and second fixed electrodes 28 and 29. More specifically, as shown in FIG. 6, first, the rectangular shape of the substrate 12 (see FIG. 1) with respect to the first and second fixed electrodes 28 and 29 having a substantially rectangular (rectangular) shape is shown. The vertices are set as end points T1 to T4. The end points T1 to T4 are set in the order of the end points T1 to T4, for example, clockwise from the upper left point in FIG. As a result, the rectangular frame connecting the end points T1 to T4 is set as a rectangular frame that surrounds the entire first and second fixed electrodes 28 and 29 in a plan view and each side extends along the X and Y directions. The Note that the positions of the end points T1 to T4 are changed as appropriate if, for example, the entire first and second fixed electrodes 28 and 29 are set within a rectangular frame connecting the end points T1 to T4. May be.

  The end points T1 and T2 are points corresponding to ends in the X direction in plan view of the substrate 12 on one end side in the Y direction (uppermost side in the drawing) of the first and second fixed electrodes 28 and 29. The end points T3 and T4 are points corresponding to the end portions in the X direction in plan view of the substrate 12 on one end side in the Y direction (the lowest side in the drawing) of the first and second fixed electrodes 28 and 29. To do. Further, the end points T1 and T4 are points corresponding to end portions in the Y direction on one end side (left side in the drawing) of the first and second fixed electrodes 28 and 29 in the X direction. Further, the end points T2 and T3 are points corresponding to end portions in the Y direction on one end side (right side in the drawing) of the first and second fixed electrodes 28 and 29 in the X direction.

  Next, a straight line passing through the two end points T1 and T2 is defined as a first straight line 85A, and a straight line passing through the end points T3 and T4 is defined as a first straight line 85B. In the first sensor 21 of the present embodiment, the first straight lines 85A and 85B are straight lines parallel to the X direction. A straight line passing through the end points T1 and T4 is referred to as a second straight line 86A, and a straight line passing through the end points T2 and T3 is referred to as a second straight line 86B. In the first sensor 21 of the present embodiment, the second straight lines 86A and 86B are straight lines parallel to the Y direction. Then, the first sensor 21 in plan view is divided into nine regions using the first straight lines 85A and 85B and the second straight lines 86A and 86B, and the respective regions are sequentially arranged (from the upper left to the lower right in the figure). ) Regions R1 to R9.

  In this case, the region R5 is a central region in plan view of the first sensor 21 in which the first and second fixed electrodes 28 and 29 are provided. Each of the regions R2 and R8 is a region adjacent to the region R5 in the Y direction. The regions R4 and R6 are adjacent to the region R5 in the X direction. The remaining four regions R1, R3, R7, and R9 are regions excluding the region R5 that is the center where the fixed electrodes 28 and 29 are provided and the regions R2, R4, R6, and R8 adjacent to the region R5. In the first sensor 21 of the present embodiment, first and second stoppers 23A and 23B are provided on a part of the frame portion 23 in the four regions R1, R3, R7, and R9. The first and second stoppers 23 </ b> A and 23 </ b> B are provided at positions that are symmetric with respect to the center of gravity of the weight portion 24. The stoppers 23 </ b> A and 23 </ b> B may be provided at positions that are asymmetric with respect to the center of gravity of the weight portion 24.

  Next, the operation when the first and second stoppers 23A, 23B are provided in the above-described regions R1, R3, R7, R9 will be described with reference to FIGS. 7 to 9 are diagrams schematically showing a sensor as a comparative example, and each member is appropriately omitted and only one fixed electrode is provided for easy understanding of the description. . The acceleration sensor 90 shown in FIG. 7 is provided with a fixed electrode 93 along the X direction and an electrode portion 94 surrounding the fixed electrode 93 at the center portion of the weight portion 91. The acceleration sensor 90 is provided with a frame portion 96 at a position facing the weight portion 91 in the Y direction. The frame portion 96 is provided with a stopper 96A at a position facing the fixed electrode 93 in the Y direction. In other words, the stopper 96A is provided within a range facing the fixed electrode 93 extending in the X direction in the Y direction.

  A distance in the Y direction between the fixed electrode 93 and the electrode portion 94 is a width 97. The width 97 is, for example, the same length as the above-described width 74 (see FIG. 4), and is preferably shortened (narrow) in order to improve sensitivity. The distance between the tip end of the stopper 96 </ b> A and the weight portion 91 is a width 98. The width 98 is a distance shorter than the width 97 in order to prevent a collision between the fixed electrode 93 and the electrode portion 94. For example, the width 98 is preferably set to a minimum length that is a processing limit in the manufacturing process, and the width 97 is set to be slightly longer than the width 98.

  Next, as shown in FIG. 8, it is assumed that acceleration in the Y direction is applied to the acceleration sensor 90 and the position of the weight portion 91 changes (changes downward in the figure). In this case, the movement of the weight portion 91 is restricted before the electrode portion 94 collides with the fixed electrode 93 by engaging the stopper 96 </ b> A with the outer peripheral portion. When the weight portion 91 is translated along the Y direction, the weight portion 91 (electrode portion 94) approaches the fixed electrode 93 to a distance excluding the width 98 from the width 97 (see FIG. 7) and stops. It will be.

  Here, when the acceleration sensor 90 is actually used, it is assumed that acceleration in other directions is applied in addition to the detection direction (in this case, the Y direction). For example, as shown in FIG. 9, when a large impact or the like is applied to the acceleration sensor 90, acceleration in the X direction is applied in addition to the Y direction, and the weight portion 91 rotates about the Z direction as a rotation axis (in the figure). Is rotated counterclockwise). In such a case, unlike the state shown in FIG. 8, the distance between the electrode portion 94 and the fixed electrode 93 in the Y direction differs depending on the position in the X direction. This is because the displacement amount with respect to the Y direction included in the movement of the weight portion 91 in the rotation direction increases in proportion to the distance from the rotation center. The center of rotation referred to here is the center of the weight portion 91 in the configuration of the acceleration sensor 90 and is the midpoint of the fixed electrode 93 in the X direction. Therefore, the distance between the electrode portion 94 and the fixed electrode 93 decreases as the displacement of the weight portion 91 in the Y direction increases as the distance from the midpoint of the fixed electrode 93 in the X direction increases.

  Further, in the acceleration sensor 90, both end portions of the fixed electrode 93 are positioned outside the stopper 96A in the X direction. For this reason, the displacement amount with respect to the Y direction of the weight portion 91 that is relatively displaced with respect to both end portions of the fixed electrode 93 is larger than the displacement amount with respect to the stopper 96A. 94 will collide.

  On the other hand, the first stopper 23A of the present embodiment shown in FIG. 6 is provided in the regions R1, R3, R7, R9 that do not face the first and second fixed electrodes 28, 29 in the Y direction. For example, in the configuration shown in FIG. 9, the position of the first stopper 23 </ b> A is the position of the stopper 99 indicated by a two-dot chain line in the drawing. The position is larger than the portion. Therefore, the stopper 99 can be engaged with the weight portion 91 before the both end portions of the fixed electrode 93 collide with the electrode portion 94, thereby preventing the collision. That is, in the first sensor 21 of the present embodiment, it is possible to more reliably prevent the collision between the first and second fixed electrodes 28 and 29 and the electrode portion 30 by optimizing the arrangement of the first stopper 23A. it can.

  Further, as a method of preventing the collision, for example, in the acceleration sensor 90 shown in FIG. 7, the distance (width 98) between the stopper 96A and the weight portion 91 is changed to the distance (width 97) between the fixed electrode 93 and the electrode portion 94. A configuration in which the length is extremely short as compared with the above can be considered. However, in such a configuration, for example, when the width 98 is set as a processing limit in the manufacturing process, it is necessary to set the width 97 to a sufficiently long distance compared to the processing limit distance, and the sensitivity is set to a desired value. It becomes difficult to improve.

  On the other hand, in the first sensor 21 of the present embodiment, for example, the distance between the first stopper 23A and the weight portion 24 (width 98 in FIG. 7) is set to the minimum length that is a processing limit in the manufacturing process, and the length On the other hand, the distance (width 97 in FIG. 7) between the first and second fixed electrodes 28 and 29 and the electrode portion 30 may be slightly increased. That is, in such a configuration, by appropriately arranging the first stopper 23A, the distance between the fixed electrode 93 and the electrode portion 94 can be narrowed close to the processing limit in the manufacturing process, and the sensitivity can be improved. It becomes possible.

  In the above description, the operation of the first stopper 23A in the Y direction has been described. However, the second stopper 23B in the X direction functions in the same manner. Similarly to the Y direction, the electrode portion 30 is relatively displaced in distance from the first and second fixed electrodes 28 and 29 in the X direction when the weight portion 24 rotates. Therefore, when the weight portion 24 is rotated as described above, the two stoppers 23B are arranged at positions outside the first and second fixed electrodes 28 and 29 in the Y direction, thereby providing both stoppers. The collision between the fixed electrode 93 and the electrode portion 94 can be more reliably prevented by 23A and 23B.

  Also in the first sensor 21A as the comparative example shown in FIG. 14 described above, the positions of the first and second stoppers 23A and 23B can be set similarly. For example, as shown in FIG. 15, with respect to the first and second fixed electrodes 28 and 29 divided in the longitudinal direction in the first sensor 21 </ b> A, rectangular vertices along the outer periphery in plan view are end points T <b> 1 to T <b> 4. Set as. Then, the first and second straight lines 85A, 85B, 86A, 86B and the regions R1 to R9 are set based on the end points T1 to T4. Even when the arrangement of the first and second stoppers 23A and 23B is determined based on the regions R1 to R9 set in this way, the first and second fixed electrodes 28 and 29 are the same as described above. And the electrode part 30 can be more reliably prevented.

Next, the structure of the spring 43 will be described.
A spring 100 illustrated in FIG. 10A 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. 10A to 10C, 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.10 (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. 10A, the number of folding times 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. 10A, 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. 11 is a graph showing the values of the spring constants Kx, Ky, Kz with respect to the folding number n. As shown in FIG. 11, 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 according to the spring constants Kx, Ky, and Kz using the graph shown in FIG. For example, the folding number n that approximates the spring constants Kx, Ky, and Kz 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 100A configured with the number of foldings n as 5 as shown in FIG. 10B. 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. 10C. 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.10 (a) of this embodiment is a spring classified into the 3rd type 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 / k x = 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, each sensor 21, 3
The sensitivity in each direction of 1 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. 12B, 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. 12C, 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. 13A, 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. 13B, 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. 13C, 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) In the first and second sensors 21 and 31, the first and second stoppers 23A and 23B for restricting the movement of the weight portion 24 are X and Y with respect to the first and second fixed electrodes 28 and 29. It is provided in the regions R1, R3, R7, R9 that do not face each other. In such a configuration, the position where the first and second stoppers 23A, 23B engage with the weight portion 24 is outside the position where the first and second fixed electrodes 28, 29 are arranged in the X and Y directions. It has become. Here, for example, in the case where rotation occurs due to acceleration in the X and Y directions with respect to the weight portion 24, the magnitude of the displacement of the weight portion 24 in each direction increases in proportion to the distance from the rotation center. To do. For this reason, the positions where the stoppers 23A and 23B engage with the weight portion 24 are located outside the positions where the fixed electrodes 28 and 29 are disposed, so that the displacement amount of the weight portion 24 is larger. Each stopper 23A, 23B engages with the weight portion 24 to restrict movement. As a result, the collision between the first and second fixed electrodes 28 and 29 and the electrode part 30 can be more reliably prevented.

(2) In the first and second sensors 21 and 31, the electrostatic capacity part 27 including the first and second fixed electrodes 28 and 29 and the electrode part 30 (movable 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) As for the 1st and 2nd sensors 21 and 31, the both ends of the longitudinal direction of each movable electrode part 30B are connected with the weight part 24 in the fixed parts 81 and 82. As shown in FIG. In such a configuration, both ends of the movable electrode portion 30B are fixed to the weight portion 24, so that even when a large acceleration is applied due to an impact or the like, the movable 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 movable electrode portion 30B are fixed to the weight portion 24 and are not easily bent, the length L (see FIG. 5) of the movable electrode portion 30B is set to obtain a desired capacitance. Even with the longer capacitance part 27, it is possible to configure an acceleration sensor with improved sensitivity while preventing a short circuit between the first and second fixed electrodes 28 and 29 and the movable 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.
Furthermore, since the springs 43 of the sensors 21 and 31 have rigidity in a direction orthogonal to the acceleration detection direction, the weight portion 24 moves in a direction different from the detection direction when a large impact or the like is applied to the sensor. Then, the rotation can be suppressed. As a result, the collision between the first and second fixed electrodes 28 and 29 and the electrode part 30 can be more reliably prevented.

(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 collision between the first and second fixed electrodes 28 and 29 and the electrode portion 30 can be prevented.

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, in the above embodiment, the first and second stoppers 23A and 23B are not opposed to the first and second fixed electrodes 28 and 29 in the regions R1, R3, R7, and R9 in the X and Y directions. However, as long as the structure engages in the region and restricts the movement of the weight portion 24, it may be appropriately changed. That is, even if the stoppers 23A and 23B themselves are not provided in each of the regions R1, R3, R7, and R9, the same effect as described above can be obtained as long as the structure engages in the region.

  Moreover, in the said embodiment, it is good also as a structure which abbreviate | omitted any one of 1st and 2nd stopper 23A, 23B. For example, the first sensor 21 may be configured to include only the first stoppers 23A (four) that face the weight portion 24 in the detection direction.

  Further, the shapes and the like of the first and second stoppers 23A and 23B in the above embodiment are merely examples, and may be changed as appropriate. For example, it is good also as a structure which provided the 1st and 2nd stopper 23A, 23B in the outer peripheral part of the weight part 24 like the 1st sensor 21B shown in FIG. The first sensor 21 </ b> B is provided so that the first and second stoppers 23 </ b> A and 23 </ b> B protrude outward toward the outer peripheral portion of the weight portion 24 and engage with the frame portion 23. Even in such a configuration, the same effect as described above can be obtained.

  The first sensor 21 </ b> B is provided at a position where the first and second stoppers 23 </ b> A and 23 </ b> B are symmetric with respect to the center of gravity of the weight portion 24. In such a configuration, the first and second stoppers 23A and 23B are positioned symmetrically with respect to the weight portion 24 that is particularly required to be symmetric in order to maintain acceleration detection accuracy. (2) The acceleration detection accuracy can be suitably maintained while preventing the collision between the fixed electrodes 28 and 29 and the electrode portion 30.

  Further, for example, as in the first sensor 21 </ b> C illustrated in FIG. 17, a stopper may be penetrated in the Z direction with respect to the weight portion 24 and may be engaged with an inner portion of the weight portion 24. The stopper 240 of the first sensor 21C is formed in a columnar shape that stands up with respect to the substrate 12 (see FIG. 1) at a position in the regions R1, R3, R7, and R9 and penetrates the weight portion 24 in the Z direction. Yes. The stopper 240 restricts the movement of the weight portion 24 by engaging with the portion of the weight portion 24 where the through hole is formed. Thereby, the collision between the first and second fixed electrodes 28 and 29 and the electrode part 30 can be prevented. Even in such a configuration, the same effect as described above can be obtained. The stopper 240 may have a configuration in which a convex portion is provided on a surface facing the weight portion 24 and a contact area with the weight portion 24 is reduced to prevent stiction.

  Moreover, in the said embodiment, although the 1st and 2nd sensors 21 and 31 were comprised as a sensor which can detect the acceleration of one direction in the plane direction of the weight part 24, the acceleration of two or more directions is detectable. It is good also as a structure. For example, the first sensor 21D shown in FIG. 18 includes a capacitance unit 232 corresponding to the acceleration in the X direction in addition to the capacitance unit 231 corresponding to the acceleration in the Y direction. In this case, the spring 43 of the first sensor 21D has, for example, a property of expanding or contracting or bending in three directions of X, Y, and Z, and the second type spring 100B shown in FIG. You may comprise as.

  For example, in the first sensor 21 </ b> D shown in FIG. 18, a rectangle along the outer periphery in plan view so as to include the entire first and second fixed electrodes 28 and 29 provided in the capacitance units 231 and 232 (see FIG. 18). You may set the vertex of a square in the structure of 18 as the end points T1-T4. Then, the first and second straight lines 85A, 85B, 86A, 86B and the regions R1 to R9 (see FIG. 6) are set based on the end points T1 to T4. The arrangement of the first and second stoppers 23A and 23B may be determined based on the regions R1 to R9 set in this way. In such a configuration, the first and second stoppers 23A and 23B are provided corresponding to each of the two detection directions of the X direction and the Y direction. The collision of the electrodes provided in the portions 231 and 232 can be prevented more reliably.

  Moreover, in the said embodiment, although connection part 28B, 29B was provided in the one end side of the longitudinal direction of the 1st and 2nd fixed electrodes 28 and 29, it is not limited to this. For example, as in the first sensor 21E shown in FIG. 19, the connection portions 28B and 29B may be provided at substantially the center in the longitudinal direction (X direction) of the first and second fixed electrodes 28 and 29. In such a configuration, the length in the X direction can be shortened by the length of the width 73, and the apparatus can be downsized.

  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. 20 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, 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 to 21E, and the second sensor 31 are examples of the acceleration sensor, and the frame portion 23 and the first and second stoppers 23A and 23B are examples of the restriction portion. The weight part 24 is an example of the weight part, the first and second fixed electrodes 28 and 29 are examples of the fixed electrode, and the electrode part 30, the outer peripheral electrode part 30A and the movable electrode part 30B are examples of the movable electrode. The regions R1 to R9 are examples of regions, and the end points T1 to T4 are examples of vertices of a rectangular frame.

DESCRIPTION OF SYMBOLS 10 Acceleration sensor, 12 board | substrates, 21,21A-21E 1st sensor, 23 frame part, 23A, 23B 1st and 2nd stopper, 24 weight part, 28 1st fixed electrode, 29 2nd fixed electrode, 30 electrode part , 30A peripheral electrode part, 30B movable electrode part, 31 second sensor, R1 to R9 region, T1 to T4 end points.

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. A fixed electrode with variable capacitance;
A regulation part that regulates movement of the weight part that swings according to the acceleration in the detection direction;
When a rectangular frame that surrounds the entire fixed electrode in plan view of the substrate and each side is set along each of the detection direction and the direction orthogonal to the detection direction is set, the vertex of the rectangular frame Of the nine regions defined by the first straight line passing through the two points aligned along the direction orthogonal to the detection direction and the second straight line passing through the two points aligned along the detection direction,
The said restriction | limiting part engages with the said weight part in each of the other 4 area | regions except the area | region where the said fixed electrode is provided, and the area | region adjacent to the said area | region, The movement sensor characterized by the above-mentioned. The fixed electrode is a flat plate surface that is orthogonal to the plane of the substrate and orthogonal to the detection direction, and a plurality of the fixed electrodes are juxtaposed along the detection direction,
The acceleration sensor according to claim 1, wherein the rectangular frame is set along an outer periphery of the fixed electrode.   The said restriction | limiting part is fixed to the said board | substrate, and exists in the position which is symmetrical with respect to the gravity center of the said weight part in each of the said 4 area | region. Acceleration sensor.

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