DE102012104601A1 - Microelectromechanical system acceleration sensor e.g. linear acceleration sensor, has stoppers, where distance of contact region from x-axis is different from distance of another region such that torque acts on sensor mass - Google Patents

Abstract

The sensor (1) has a sensor mass arranged on a substrate by a spring (3) and an armature (4), and stoppers (7.1-7.4) arranged on a substrate to stop movement of the sensor mass in y-direction. The mass, stoppers and spring are in contact with each other at point-shaped contact regions when movement of the mass is stopped. One of the regions is arranged at distance from a y-axis. Distance of the other contact region from an x-axis is different from the distance of the former region such that torque acts on the mass, to cause rotation of the mass in an x-y plane, during contacting the stoppers.

Description

The present invention relates to a MEMS acceleration sensor with a sensor mass, which is arranged on a substrate by means of at least one armature and a spring, wherein the spring connects the sensor mass to the armature and the sensor mass is movable in an xy plane parallel to the substrate and with at least one stopper disposed on the substrate to stop the movement of the sensor mass, and wherein the stopper and the sensor mass have a contact area where they touch when the sensor mass is stopped.

From the US 2002/0112538 A1 a micromechanical component for a MEMS acceleration sensor is known, which has a seismic mass or sensor mass which can be deflected in one plane. The sensor mass is arranged parallel to a substrate and movably connected thereto via springs and anchors. In order to avoid that the sensor mass or the springs have undesirable contacts with a deflection of the sensor mass, stoppers are provided. These stoppers avoid sticking. In the event of excessive deflection, which can be caused for example by impacts or overload, parts of the springs, for example, may touch inadmissibly and thereby stick together or even be damaged. This leads to an erroneous detection of the movement of the sensor mass or even to damage or destruction of the entire sensor. A disadvantage of this design, however, is that when contacting the stopper also the "sticking" effect can occur or it can lead to damage. Already at a contact of the springs with the stopper may lead to an adhesion, which in turn leads to a faulty measurement. This attachment happens z. B. in that the restoring force of the spring is not strong enough to avoid the adhesion of the spring to the stopper.

It is therefore an object of the present invention to provide a device with which a MEMS acceleration sensor is prevented from the "sticking" effect and damage.

The object is achieved with a MEMS acceleration sensor having the features of claim 1.

The MEMS acceleration sensor according to the invention has a sensor mass, which is arranged on a substrate by means of at least one armature and a spring. The anchor is attached to the substrate. The spring connects the sensor mass to the armature, whereby the sensor mass is movably mounted in an x-y plane parallel to the substrate. The sensor mass can move linearly along, for example, a y-axis. Of course, movements in other directions are possible. The name of the y-axis for this purpose is chosen only for ease of explanation. The corresponding coordinate system can also be defined differently.

The MEMS acceleration sensor has at least one stopper disposed on the substrate to stop the movement of the sensor mass. This stop is particularly necessary if the sensor mass is deflected too much. This happens, for example, when the sensor is exposed to shocks or the acceleration is too strong, whereby the sensor mass would be moved beyond the intended distance. The stopper prevents the sensor mass and / or the spring from being damaged in this case. In addition, the stopper prevents adhesion of individual elements of the springs and / or the sensor mass to other elements of the acceleration sensor, whereby erroneous measurements.

The stopper and the sensor masses have a Kotaktbereich where they touch when the sensor mass is stopped. The stopper may alternatively cooperate with the spring or parts of the spring, which also form a defined contact point. According to the invention, a torque is to be generated on the sensor mass when contacting the stopper, which causes a rotation of the sensor mass and thus releases additional forces, which avoids sticking of the sensor mass or the spring to the stopper. For this purpose, the at least one contact region is arranged at a distance from the y-axis. In the case of a second contact region for the same direction of movement, the distance of this second contact region from the x-axis is different from this distance of the first contact region. As a result, a torque is exerted on the sensor mass during the contacting of the stopper, which causes a rotation of the sensor mass in the x-y plane. As a result of this rotation of the sensor mass, the sensor mass is moved not only in the intended y direction, but additionally in an x direction. This additional direction of movement supports a detachment of the sensor mass or the spring from the stopper and reliably prevents sticking. The measurement accuracy of the acceleration sensor is thereby not affected, since the contact is outside the measuring range of the MEMS acceleration sensor. Other than intended for the measurement movements of the sensor mass thereby have no effect on a proper measurement of movement in the intended measuring range.

It is particularly advantageous if the contact area (s) and / or the armature (s) are not aligned with one another in the direction of movement of the sensor mass. As a result, the torque and a restoring torque is generated during the contacting of the stopper / s. In the case of an extreme deflection of the sensor mass, contact with the stopper will be effected first, and then the sensor mass will move out of the original direction of movement around the stopper in another direction, for example the x direction. By this torque introduced by the rotation of the sensor mass, the return movement of the sensor mass is supported in its starting point or in the intended range of motion without contacting the stopper. The restoring force hereby acts more strongly than if the stopper would avoid a movement of the sensor mass out of its original direction of movement.

In an advantageous embodiment of the MEMS acceleration sensor, at least one stopper and one contact area are provided for each direction of movement. Thus, a stop is created at least for the movement of the sensor mass in (+ y) direction and in (-y) direction, which causes a twisting of the sensor mass in the case of contacting and thus significantly reduces the "sticking" inclination or even completely avoided.

In order to avoid that the sensor mass is damaged in the event of a rotational movement through the stop in the y-direction or by external shocks which act on the sensor, it is advantageous if at least one further stopper for limiting the movement of the sensor mass in x-direction. Direction is provided. These stoppers may also be offset from each other as the stoppers which limit the movement in the y-direction. However, it is also possible that these stoppers are provided with the same effect in a conventional manner.

If the stoppers each have a different direction of movement of the sensor mass at a different distance from the x or y axis, the stopper, at which the sensor mass first abuts, generates a torque on the sensor mass, as a result of which the sensor mass changes from its first linear into one changed twisted movement. To avoid excessive stress on the springs or sensor mass, another stopper is provided, preferably located on the other side of the axis along which the sensor mass moves. This further stopper forms a further stop for the rotated sensor mass, so that damage to the components of the sensor is avoided.

The stoppers are particularly effective if they are arranged in the area of corners of the sensor mass on the substrate. Here are the lever arms, which act on the torque to the sensor mass greatest, and thus the inventive limitation of the extreme movement of the sensor mass is also most effective to achieve.

In order to be able to avoid the "sticking" inclination particularly effectively also in the embodiment according to the present invention, it is advantageous if the contact region is substantially point-shaped. As a result, there is almost no surface on which the moving components sensor mass or spring could "suck in" because no surfaces but only points abut each other.

It is particularly advantageous if at least one elevation is arranged in the intended contact region on the sensor mass. An optionally occurring impact on the sensor mass in a contact with the stopper is transmitted in this way at a defined, designated place on the sensor mass. Damage can be excluded. If only a single survey per contact is provided, a significant advantage is obtained in that the sensor mass is not limited in its rotational movement. The survey serves as a pivot point of the sensor mass. A harmonic, constant movement of the sensor mass due to the torque is thus generated. This also prevents damage and also causes a rapid calming of the unwanted rotational movement which deviates from the desired linear movement. The sensor mass is set back to the linear movement quickly after the rotational movement.

If the spring is softer for movement in the y-direction than for movement in the x-direction, the main direction of movement is the preferred direction of movement of the sensor mass. Only when a shock condition occurs, the sensor mass is deflected in the x direction. The normal direction of movement in the y-direction is thus the preferred direction, which is assumed even after a shock condition.

It when the sensor mass is connected to the substrate with one, preferably two anchors and one, preferably two springs at each end of the sensor mass is particularly advantageous. As a result, a particularly stable movement of the sensor mass in the main movement direction is achieved. Even when deflected in the event of shock, this is achieved evenly and the Initial state can be resumed very quickly.

If sensor elements and / or the substrate are assigned sensor elements, the deflection of the sensor mass can be detected very easily. The sensor elements are usually capacitive type, by which a change in distance is detected with electrical signals.

Further advantages of the invention are described in the following exemplary embodiments. It shows:

1 a MEMS acceleration sensor at rest and

2 the MEMS accelerometer off 1 when abutting a stopper.

In 1 is a MEMS accelerometer 1 sketched in plan view. A sensor mass 2 is parallel to a not shown, under the sensor mass 2 lying substrate. The sensor mass 2 is by means of springs 3 at anchors 4 connected to the substrate. The feathers 3 are meandering and allow movement of the sensor mass 2 essentially in the y direction. In this direction of movement B, they have a relatively low spring stiffness, whereby the mobility of the sensor mass 2 in this direction is preferred. The spring stiffness of the spring 3 In the x-direction, however, is higher, so that a deflection in this direction only in extreme cases, that is, for example, impact on the sensor 1 he follows. There are four springs in total 3 and anchor 4 two are provided at each end of the sensor mass 2 , As a result, a stable movement in the direction of movement B is achieved.

In the middle area of the sensor mass 2 There are three electrodes on each side 5 arranged. The electrodes 5 act with electrodes 6 together, which for detecting movements of the sensor mass 2 serve in the direction of movement B. The electrodes 6 are fixed on the substrate. Changes in the distance of the movable electrodes 5 from the stationary electrodes 6 cause a change of an electrical signal, from which conclusions about the movement of the sensor mass 2 and the causative acceleration can be obtained.

In the area of the corners of the sensor mass 2 are on the substrate stoppers 7 arranged. The stoppers 7 are L-shaped, so that they have a stop for the sensor mass 2 form both in the direction of movement B in the y-direction and in the x-direction. This will be a guide to the sensor mass 2 also in the case of twisting the sensor mass 2 reached from the linear movement along the y-axis. The sensor mass 2 and the springs 3 are thus better protected against damage. In the same area are at the corners of the sensor mass 2 surveys 8th arranged. The surveys 8th are hemispherical in the present embodiment and thus form a punctiform contact area with the associated stopper 7 ,

With normal movement of the sensor mass 2 in the direction of movement B in the y direction, there is no contact between the stoppers 7 and the surveys 8th instead of. Only at an acceleration which is greater than the intended maximum acceleration or in shock conditions due to external influences on the MEMS acceleration sensor 1 It may happen that the surveys 8th at the stopper 7 attacks.

In 2 is a situation of the MEMS acceleration sensor 1 out 1 shown, which is a stop of the sensor mass 2 at the stopper shown on the top left 7 shows. The sensor mass 2 is deflected maximally in (+) - y-direction and thus beats with the left upper elevation 8th at their associated stopper 7 at. This creates a torque on the sensor mass 2 which causes the sensor mass 2 from its direction of movement B swings out by an angle α until it with the corresponding survey 8th on at least one of the stoppers located on the opposite side of the y-axis 7 strikes. The feathers 3 are thereby deflected unevenly. The left of the y-axis springs 3 are less compressed or stretched than the springs shown to the right of the y-axis 3 ,

Due to the occurring torque and the different compression or elongation of the springs 3 creates an additional force, which ensures that the sensor mass 2 returns to its original position and can perform movements in the intended direction of movement B. The surveys 8th , which are arranged on the right side of the y-axis, have the top right and / or right side contact with the associated stoppers 7 , The additional force prevents the stopper in the contact areas 7 and surveys 8th an adhesion of the sensor mass 2 at the stoppers 7 reliably prevented. In addition, the forces are introduced at a defined location in the sensor mass. It is particularly advantageous that the surveys 8th at the sensor mass 2 and not at the stoppers 7 are arranged, as a result, the sensor mass 2 is better protected. The additionally occurring force due to a rotation of the sensor mass 2 The z-axis protruding from the plane of the drawing causes a force component in the x-direction, which acts in addition to the force component in the y-direction. hereby becomes a backward movement of the sensor mass 2 supported in their starting position.

The present invention is not limited to the illustrated embodiments. In particular, the type of sensor ground 2 executable differently than shown here. The invention is not limited to such acceleration sensors alone. It is also applicable to other MEMS acceleration sensors, whether accelerations of linear accelerations or rotational accelerations, at any case where a "sticking" inclination can be detected and by a one-sided stop a torque is generated, which for a active return movement of the sensor mass to its initial position provides an additional force. Also, the contact areas need not be present (only) between sensor mass and stoppers, but may also be provided on the springs, which cooperate with a stopper. The stopper need not necessarily be attached to the substrate, but it may also be provided on a part of the spring and thereby generate the torque. However, it is particularly advantageous if the stoppers are arranged stationarily on the substrate. Likewise, not the illustrated type of stopper or the elevations is decisive for the invention, but only the way how the MEMS acceleration sensor is described in claim 1.

LIST OF REFERENCE NUMBERS

1

 MEMS Accelerometer

2

 sensor mass

3

 feathers

4

 anchor

5

 electrode

6

 electrode

7

 stopper

8th

 surveys

B

 movement direction

α

 angle

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2002/0112538 A1 [0002]

Claims (11)

MEMS acceleration sensor, with a sensor mass ( 2 ) mounted on a substrate by means of at least one anchor ( 4 ) and a spring ( 3 ), the spring ( 3 ) the sensor mass ( 2 ) with the anchor ( 4 ), the sensor mass ( 2 ) is movable in an xy-plane parallel to the substrate (along a y-axis), and with at least one stopper ( 7 ), which is preferably arranged on the substrate to the movement of the sensor mass ( 2 ) stop in the y-direction, and wherein the stopper ( 7 ) and the sensor mass ( 2 ) or the spring ( 3 ) have a contact area where they touch when the sensor mass ( 2 ) is stopped, characterized in that the at least one contact region is arranged at a distance from the y-axis and in the case of a second contact region for the same direction of movement, the distance of this second contact region from the x-axis is different from this distance of the first contact region such that when contacting the stopper (s) ( 7 ) a torque on the sensor mass ( 2 ), which is a rotation of the sensor mass ( 2 ) in the xy plane. A MEMS acceleration sensor according to the preceding claim, characterized in that the contact area (s) and the armature (s) ( 4 ) in the direction of movement of the sensor mass ( 2 ) are not aligned with each other about the torque and a restoring moment in the contacting of the stopper / s ( 7 ) to create. MEMS acceleration sensor according to one or more of the preceding claims, characterized in that for each movement direction (x, y) at least one stopper ( 7 ) and a contact area is provided. MEMS acceleration sensor according to one or more of the preceding claims, characterized in that at least one further stopper ( 7 ) for limiting the movement of the sensor mass ( 2 ) is provided in the x direction. MEMS acceleration sensor according to one or more of the preceding claims, characterized in that the stoppers ( 7 ) in the region of corners of the sensor mass ( 2 ) are arranged on the substrate. MEMS acceleration sensor according to one or more of the preceding claims, characterized in that the stoppers ( 7 ) each one direction of movement of the sensor mass ( 2 ) have a different distance to the x- or y-axis. MEMS acceleration sensor according to one or more of the preceding claims, characterized in that the contact region is substantially punctiform. MEMS acceleration sensor according to one or more of the preceding claims, characterized in that in the intended contact region on the sensor mass ( 2 ) a single survey ( 8th ) is arranged. MEMS acceleration sensor according to one or more of the preceding claims, characterized in that the spring ( 3 ) is softer for a bend in the y-direction than for a movement in the x-direction. MEMS acceleration sensor according to one or more of the preceding claims, characterized in that the sensor mass ( 2 ) with the substrate with one, preferably two anchors ( 4 ) and one, preferably two spring (s) ( 3 ) at each end of the sensor mass ( 2 ) connected is. MEMS acceleration sensor according to one or more of the preceding claims, characterized in that the sensor mass ( 2 ) and / or the substrate sensor elements ( 5 . 6 ) assigned.

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