INERTIAL SENSOR AND INERTIAL MEASUREMENT UNIT

An inertia sensor detects a physical quantity based on a displacement in a Z axis when three axes orthogonal to one another are defined as an X axis, a Y axis, and the Z axis. The inertial sensor includes: a substrate; and a movable body that is fixed to the substrate, that swings around a swing axis P along the X axis, and that has two flat surfaces facing each other and a side surface connecting the two flat surfaces. The movable body includes a first extension arranged at a predetermined angle with respect to the swing axis P and a second extension arranged facing the side surface of the first extension.

The present application is based on, and claims priority from JP Application Serial Number 2021-100704, filed Jun. 17, 2021, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to an inertial sensor and an inertial measurement unit.

2. Related Art

In recent years, an inertial sensor manufactured using a micro electro mechanical systems (MEMS) technology is developed. As such an inertial sensor, for example, US Patent Application Publication No. 2015/0053002 specification discloses an inertial sensor including: a substrate; a movable body that is arranged on the substrate, that includes first and second detection electrodes, and that swings in a seesaw manner around a rotation axis; and first and second fixed electrodes that are provided on the substrate and that face the first and second detection electrodes, in which an acceleration in a vertical direction is able to be detected based on a change in capacitance generated between the first and second detection electrodes of the movable body that have different rotational moments around the rotation axis from each other and the first and second fixed electrodes that are arranged at positions facing the first and second detection electrodes, respectively.

In addition, the inertial sensor is provided with a damper having a comb structure in order to prevent an operation in an in-plane direction different from a direction in which the acceleration is detected.

However, in the inertial sensor disclosed in US Patent Application Publication No. 2015/0053002 specification, there is a problem that the operation in the in-plane direction is prevented, but an operation of rotating in the in-plane direction is difficult to be prevented.

SUMMARY

An inertia sensor that detects a physical quantity based on a displacement in a Z axis when three axes orthogonal to one another are defined as an X axis, a Y axis, and the Z axis includes: a substrate; and a movable body that is fixed to the substrate, that swings around a swing axis along the X axis, and that has two flat surfaces facing each other and a side surface connecting the two flat surfaces, in which the movable body includes a first extension arranged at a predetermined angle with respect to the swing axis and a second extension arranged facing the side surface of the first extension.

An inertial measurement unit includes: the inertial sensor described above; and a controller that performs control based on a detection signal output from the inertial sensor.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

1. First Embodiment

First, an inertial sensor1according to a first embodiment is described with reference toFIGS.1and2by taking an acceleration sensor that detects an acceleration as a physical quantity in a vertical direction as an example.

InFIG.1, for convenience of illustrating an internal configuration of the inertial sensor1, a state in which a lid body21is removed is illustrated. InFIGS.1and2, illustration of a wiring provided on a substrate11is omitted.

For convenience of description, in the following plan view, cross-sectional view, and perspective view, an X axis, a Y axis, and a Z axis are illustrated as three axes orthogonal to one another. Further, a direction along the X axis is referred to as an “X direction”, a direction along the Y axis is referred to as a “Y direction”, and a direction along the Z axis is referred to as a “Z direction”. Further, a tip end side of an arrow in each axial direction is referred to as a “plus side”, a base end side is referred to as a “minus side”, a plus side in the Z direction is referred to as “upper”, and a minus side in the Z direction is referred to as “lower”. The Z direction is along the vertical direction, and an XY plane is along a horizontal plane. In the present specification, a plus Z direction and a minus Z direction are collectively referred to as the Z direction.

The inertial sensor1shown inFIGS.1and2can detect the acceleration as the physical quantity in the Z direction, which is the vertical direction of a sensor element30. Such an inertial sensor1includes the substrate11, the sensor element30arranged on the substrate11, and the lid body21bonded to the substrate11and covering the sensor element30.

As shown inFIG.1, the substrate11has a spread in the X direction and the Y direction, and has a thickness in the Z direction. Further, as shown inFIG.2, the substrate11is formed with a recess14recessed downward from an upper surface12of the substrate11. The recess includes the sensor element30inside and is formed larger than the sensor element30in a plan view from a Z-axis direction along the Z axis. The recess14functions as a clearance for swinging the sensor element30. The substrate11includes a fixer13protruding from an inner bottom surface15of the recess14toward the sensor element30, and the sensor element30is bonded and fixed on the fixer13. Accordingly, the sensor element30can be fixed to the substrate11in a state where the sensor element30is separated from the inner bottom surface15of the recess14.

A first fixed electrode17, a second fixed electrode18, and a third fixed electrode19serving as a dummy electrode are arranged on the inner bottom surface15of the recess14. The first fixed electrode17and the second fixed electrode18have substantially the same area. Each of the first fixed electrode17and the second fixed electrode18is coupled to a QV amplifier of an external device (not shown), and a capacitance difference thereof is detected as an electric signal by a differential detection method. Therefore, it is desirable that the first fixed electrode17and the second fixed electrode18have the same area.

The substrate11is provided with coupling terminals16, which electrically couple an external device (not shown) and the first to third fixed electrodes17,18, and19, in a region on the upper surface12where the recess14is not provided.

As the substrate11, for example, a glass substrate configured with a glass material containing an alkali metal ion that is a movable ion such as Nat, for example, borosilicate glass such as Pyrex (registered trademark) glass and Tempax (registered trademark) glass can be used. However, the substrate11is not particularly limited, and, for example, a silicon substrate or a quartz substrate may be used.

Further, as the first to third fixed electrodes17,18,19and the coupling terminals16, metals such as Au, Pt, Ag, Cu and Al, alloys containing these metals, and the like can be used.

As shown inFIG.2, the lid body21is formed at a position where a recess22recessed upward overlaps with the recess14of the substrate11. The lid body21accommodates the sensor element30in the recess22and is bonded to the upper surface12of the substrate11by a glass frit6or the like. An internal space S for accommodating the sensor element30is formed in an inner side of the lid body21and the substrate11.

The internal space S is an airtight space, and is preferably filled with an inert gas such as nitrogen, helium, or argon to substantially have an atmospheric pressure at an operating temperature of about −40° C. to 125° C. However, an atmosphere of the internal space S is not particularly limited, and may be in, for example, a reduced pressure state or a pressurized state.

As the lid body21, for example, a silicon substrate can be used. However, the lid body21is not particularly limited, and, for example, a glass substrate or a quartz substrate may be used. A method of bonding the substrate11and the lid body21is not particularly limited, and may be appropriately selected depending on materials of the substrate11and the lid body21. In addition to the bonding by a bonding material such as the glass frit6, for example, anodic bonding, activation bonding for bonding surfaces activated by plasma irradiation, metal eutectic bonding for bonding metal films formed on the upper surface of the substrate11and a lower surface of the lid body21, and the like can be used.

The sensor element30is configured with a movable body31. The movable body31is orthogonal to the Z axis, and has an upper surface31aand a lower surface31bthat are two flat surfaces having a front and back relationship with each other, and side surfaces31cthat connect the upper surface31aand the lower surface31b. As shown inFIG.1, the movable body31has a rectangular shape having a long side in the Y direction in the plan view viewed from the Z direction. The movable body31includes a supporter32bonded onto the fixer13, two support beams33coupled to the supporter32and extending from the supporter32to the plus side and the minus side in the X direction, a first movable electrode38positioned on the minus side in the Y direction with respect to the support beams33, a second movable electrode39positioned on the plus side in the Y direction with respect to the support beams33, and a third movable electrode40coupled to the second movable electrode39. The first movable electrode38, the second movable electrode39, and the third movable electrode40are arranged so as to overlap the first fixed electrode17, the second fixed electrode18, and the third fixed electrode19, which are provided on the inner bottom surface15of the substrate11, in the plan view from the Z direction, respectively. Further, the first to third movable electrodes38,39, and40of the movable body31are provided with a plurality of through holes43penetrating the upper surface31aand the lower surface31b, and air resistance generated when the movable body31is displaced in the Z direction can be reduced.

A first opening36is provided between the first fixed electrode17and the second fixed electrode18, and both ends of the first movable electrode38and the second movable electrode39in the X direction are coupled by a first coupler34. The first coupler34is coupled to the support beams33at a center of the first coupler34. Therefore, when the acceleration along the Z direction is applied, the movable body31swings around a swing axis P extending along the X axis while twisting and deforming the support beams33with the support beams33as the swing axis P. Further, a second opening37is provided between the second movable electrode39and the third movable electrode40, and both ends of the second movable electrode39and the third movable electrode40in the X direction are coupled by a second coupler35.

Further, since the second movable electrode39and the third movable electrode40are coupled to each other, which are the movable body31positioned on the plus side in the Y direction with respect to the swing axis P, a length thereof in the Y direction is longer than that of the first movable electrode38, which is the movable body31positioned on the minus side in the Y direction with respect to the swing axis P. Therefore, the movable body positioned on the plus side in the Y direction with respect to the swing axis P has a larger area and a larger weight than the movable body31positioned on the minus side in the Y direction with respect to the swing axis P in the plan view from the Z direction, and thus has a larger rotational moment than the movable body31positioned on the minus side in the Y direction when the acceleration in the Z direction is applied. Due to a difference in the rotational moment, when the acceleration in the Z direction is applied, the movable body31swings in a seesaw manner around the swing axis P. The swinging in a seesaw manner means that when the first movable electrode38is displaced to the plus side in the Z direction, the second movable electrode39is displaced to the minus side in the Z direction, and conversely, when the first movable electrode38is displaced to the minus side in the Z direction, the second movable electrode39is displaced to the plus side in the Z direction.

When the inertial sensor1is driven, a drive signal is applied to the sensor element30, whereby a capacitance C1is formed between the first movable electrode38and the first fixed electrode17and a capacitance C2is formed between the movable electrode39and the second fixed electrode18. In a natural state where no acceleration is applied, capacitances C1and C2are substantially equal to each other.

When the acceleration in the Z direction is applied to the inertial sensor1, the movable body31swings around the swing axis P in a seesaw manner. Due to the swing in a seesaw manner of the movable body31, a gap between the first movable electrode38and the first fixed electrode17and a gap between the second movable electrode39and the second fixed electrode18change in opposite phases, and accordingly, the capacitances C1and C2change in the opposite phases from each other. Therefore, the inertial sensor1can detect the acceleration in the Z direction based on a difference between capacitance values of the capacitances C1and C2.

The movable body31has the first opening36between the first movable electrode38and the second movable electrode39, and the supporter32and the support beams33are arranged in the first opening36. With such a shape, a size of the sensor element30can be reduced.

In addition, in the first opening36, as shown in the plan view from the Z direction, a plurality of first extensions41extending radially from the supporter32toward outer edges of the movable body31around the supporter32are provided, and the first extensions41are arranged at predetermined angles with respect to the swing axis P, respectively. In the present embodiment, ten first extensions41extending at angles of ±30°, ±60°, and ±90° respectively with respect to the swing axis P are arranged, but the number is not limited thereto, and may be four or more. In addition, an interval between the first extensions41may not be constant.

A plurality of second extensions42extending from the first movable electrode38and the second movable electrode39of the movable body31toward the supporter32are provided in a periphery of the first opening36, and the second extensions42face the side surfaces31cof the first extensions41and are arranged at a predetermined interval. In the present embodiment, twelve second extensions42are arranged between the first extension41and the first extension41and between the first extension41and the support beams33, but the second extensions42are not limited to this, and may be arranged according to the number of the first extensions41. For example, when the number of the first extensions41is four, the number of the second extensions42is six, and when the number of the first extensions41is six, the number of the second extensions42is eight.

Since the side surfaces31cof the first extensions41, which are radially arranged around the supporter32fixed to the substrate11, face the side surfaces31cof the second extensions42and are spaced apart from the side surfaces31cof the second extensions42at a predetermined interval, when an in-plane rotation operation around the supporter32is applied, air resistance is generated between the rotationally displaced second extensions42and the fixed first extensions41, that is, the air resistance functions as a damper, and the in-plane rotation operation of the movable body31can be prevented. In addition, when an excessive in-plane rotation operation is applied, the second extensions42come into contact with the fixed first extensions41to restrict further displacement of the movable body31.

The sensor element30is formed, for example, by subjecting a conductive silicon substrate doped with an impurity of phosphorus (P), boron (B), arsenic (As) or the like to etching, particularly to vertical processing using a Bosch process that is a deep etching technique.

The inertial sensor1of the present embodiment includes the first extensions41that extend radially at the predetermined angles with respect to the swing axis P from the supporter32fixed to the substrate11, and the second extensions42whose side surfaces31cface the side surfaces31cof the first extensions41and are spaced apart from the side surfaces31cof the first extensions42at the predetermined interval. Therefore, when the in-plane rotation operation around the supporter32is applied, the air resistance is generated between the side surfaces31cof the rotationally displaced second extensions42and the side surfaces31cof the fixed first extensions41, that is, the air resistance functions as the damper, and the in-plane rotation operation of the movable body31can be prevented.

2. Second Embodiment

Next, a sensor element30aof an inertial sensor1aaccording to a second embodiment will be described with reference toFIG.3.

The inertial sensor1aof the present embodiment is the same as the inertial sensor1of the first embodiment except that a structure of a movable body311of the sensor element30ais different from that of the inertial sensor1of the first embodiment. A difference from the first embodiment described above will be mainly described, and the description of the same matters will be omitted.

As shown inFIG.3, in the sensor element30a, in the first opening36of the movable body311, first extensions41acoupled to the supporter32are arranged at a predetermined angle with respect to the swing axis P (support beams33), and third extensions44parallel to the swing axis P (support beams33) are provided at tip ends at opposite sides of the first extensions41afrom the supporter32. A plurality of second extensions42aextending from the first movable electrode38and the second movable electrode39of the movable body311toward the supporter32are provided between the first extensions41aand the third extensions44and the support beams33.

With such a configuration, the side surfaces31cof the first extensions41aand the third extensions44face the side surfaces31cof the second extensions42a, and thus the configuration functions as a damper for the in-plane rotation operation, and can obtain the same effect as obtained by the inertial sensor1of the first embodiment.

Next, a sensor element30bof an inertial sensor1baccording to a third embodiment will be described with reference toFIG.4.

The inertial sensor1bof the present embodiment is the same as the inertial sensor1of the first embodiment except that a structure of a movable body312of the sensor element30bis different from that of the inertial sensor1of the first embodiment. A difference from the first embodiment described above will be mainly described, and the description of the same matters will be omitted.

As shown inFIG.4, in the sensor element30b, in the first opening36of the movable body312, first extensions41bcoupled to a rectangular supporter32bextend orthogonally to the swing axis P from the supporter32b, and third extensions44bparallel to the swing axis P are provided at tip ends at opposite sides of the first extensions41bfrom the supporter32b. A plurality of second extensions42bextending from the first movable electrode38and the second movable electrode39of the movable body312toward the supporter32bare provided between the first extensions41band the third extensions44band the support beams33.

With such a configuration, the side surfaces31cof the first extensions41band the third extensions44bface the side surfaces31cof the second extensions42b, and thus the configuration functions as a damper for the in-plane rotation operation, and can obtain the same effect as obtained by the inertial sensor1of the first embodiment.

Next, an inertial measurement unit2000including the inertial sensors1to1baccording to a fourth embodiment will be described with reference toFIGS.5and6. In the following description, a configuration to which the inertial sensor1is applied will be described as an example.

The inertial measurement unit (IMU)2000shown inFIG.5is a device that detects an inertial motion amount of a posture, a behavior or the like of a moving body such as an automobile or a robot. The inertial measurement unit2000functions as a so-called 6-axis motion sensor including an acceleration sensor that detects accelerations Ax, Ay, and Az in directions along three axes, and angular velocity sensors that detect angular velocities ωx, ωy, and ωz around the three axes.

The inertial measurement unit2000is a rectangular parallelepiped having a substantially square planar shape. Screw holes2110as fixers are formed in the vicinity of two apexes positioned in a diagonal direction of a square. The inertial measurement unit2000can be fixed to a mounting target surface of a mounting target body such as an automobile by passing two screws through the two screw holes2110. A size of the inertial measurement unit2000can be reduced by component selection and design change so that the inertial measurement unit2000can be mounted in, for example, a smartphone or a digital camera.

The inertial measurement unit2000includes an outer case2100, a bonding member2200, and a sensor module2300, and has a configuration in which the sensor module2300is inserted inside the outer case2100with the bonding member2200interposed therebetween. The sensor module2300includes an inner case2310and a substrate2320.

Similar to an overall shape of the inertial measurement unit2000, an outer shape of the outer case2100is a rectangular parallelepiped having a substantially square planar shape, and the screw holes2110are respectively formed in the vicinity of the two apexes positioned in the diagonal direction of the square. The outer case2100has a box shape, and the sensor module2300is accommodated inside the outer case2100.

The inner case2310is a member that supports the substrate2320, and has a shape in which the inner case2310is accommodated inside the outer case2100. The inner case2310is formed with a recess2311for preventing contact with the substrate2320and an opening2312for exposing a connector2330to be described later. The inner case2310is bonded to the outer case2100via the bonding member2200. Further, the substrate2320is bonded to a lower surface of the inner case2310via an adhesive.

As shown inFIG.6, the connector2330, an angular velocity sensor2340zthat detects an angular velocity around the Z axis, an acceleration sensor unit2350that detects the acceleration in each axial direction of the X axis, the Y axis, and the Z axis, and the like are mounted on the substrate2320. Further, an angular velocity sensor2340xthat detects an angular velocity around the X axis and an angular velocity sensor2340ythat detects an angular velocity around the Y axis are mounted on side surfaces of the substrate2320.

The acceleration sensor unit2350includes at least the inertial sensor1for measuring the acceleration in the Z direction described above, and can detect the acceleration in one axial direction or accelerations in two axial directions or three axial directions as necessary. The angular velocity sensors2340x,2340y, and2340zare not particularly limited. For example, a vibration gyro sensor using a Coriolis force can be used.

Further, a control IC2360is mounted on a lower surface of the substrate2320. The control IC2360as a controller that performs control based on a detection signal output from the inertial sensor1is a micro controller unit (MCU), includes a storage including a nonvolatile memory, an A/D converter, and the like, and controls each unit of the inertial measurement unit2000. The storage stores a program defining an order and a content for detecting the acceleration and the angular velocity, a program for digitizing detection data and incorporating the digitized detection data into packet data, accompanying data, and the like. In addition, a plurality of electronic components other than components described above are mounted on the substrate2320.

Since such an inertial measurement unit2000uses the acceleration sensor unit2350including the inertial sensor1, the inertial measurement unit2000having excellent impact resistance and high reliability can be obtained.