Accelerometer

Abstract

An acceleration sensor (1) comprising a substrate (2) and a seismic mass (3), wherein the acceleration sensor (1) has a main extension plane and comprises a spring device (4) via which the substrate (2) and the seismic mass (3) are connected in such a way that the seismic mass (3) can be deflected in the sense of a tilting movement about a rotation axis running parallel to the main extension plane when accelerated in a detection direction running perpendicular to the main extension plane, characterized in that the seismic mass (3) is further connected to the substrate (2) via at least one first spring (11), wherein the stiffness of the first spring (11) during a deflection of the seismic mass (3) in the sense of the tilting movement in the detection direction is smaller than the stiffness of the first spring (11) during a deflection in a primary direction (P) running parallel to the main extension plane,wherein the spring device (4) transfers the seismic mass (3) into a rest position when no acceleration acts on the seismic mass (3), wherein the seismic mass (3) is arranged in the rest position substantially parallel to the main extension plane of the acceleration sensor (1), and wherein the course of the spring device divides the seismic mass (3) on both sides of the spring device into two sections with unequal partial masses.

Description

[0001] The invention relates to an acceleration sensor according to the preamble of the main claim. State of the art

[0002] Such acceleration sensors are known, for example, from the publications EP 0 244 581 A1 and EP 0 773 443 B1. The seismic mass is preferably connected to the substrate with a torsion spring such that, upon acceleration perpendicular to the main extension plane, the seismic mass is tilted about a rotational axis. Together with counter electrodes fixed to the substrate, the seismic mass typically forms a plate capacitor whose capacitance changes during the tilting movement of the seismic mass and can thus be used to quantitatively determine the acceleration. Further disclosures of acceleration sensors are known from the publications US 2004 / 0079154 A1, US 2010 / 0024554 A1, and US 2012 / 0186346 A1.

[0003] In practice, acceleration sensors are subject to stringent requirements, particularly regarding their overload resistance, meaning they should deliver plausible signals even under high mechanical overload. A known source of error in this context is the mechanical impact of the moving seismic mass. Such clipping can occur in all three spatial directions, but particularly in directions parallel to the main plane of extension (in-plane clipping). Translational movements of the seismic mass in a direction perpendicular to the axis of rotation (the tilting movement) and rotational movements of the seismic mass about an axis perpendicular to the main plane of extension are considered particularly critical with regard to clipping behavior.These two (in-plane) disturbance modes can be resonantly excited when subjected to disturbance excitation with suitable frequencies, whereby the frequencies for the two said (in-plane) disturbance modes are relatively close to the frequency used for the tilting movement. Therefore, the state of the art proposes to improve clipping behavior by increasing the frequencies for the disturbance modes, for example, by using a spring with a T-shaped cross-section as a torsion spring. While this spring can be promising for improving clipping, it also disadvantageously increases the sensitivity of the acceleration sensor to other influences. In particular, acceleration in a direction perpendicular to the axis of rotation and parallel to the main extension plane can result in a tilting movement that falsely contributes to the signal.

[0004] It is therefore an object of the present invention to provide an acceleration sensor that greatly reduces in-plane clipping without significantly increasing the sensitivity to other influences. revelation

[0005] The object is achieved by an acceleration sensor according to claim 1. This has the advantage over the prior art that an in-plane movement along the primary direction is suppressed without the deflection in the detection direction for the seismic mass being substantially restricted. This makes it possible to restrict in-plane clipping, i.e. mechanical impact of the seismic mass. Furthermore, the spring device can be arranged within the acceleration sensor such that the center of mass of the seismic mass and the axis of rotation running parallel to the main extension plane are at the same height. This advantageously ensures that an acceleration in a direction perpendicular to the axis of rotation and parallel to the main extension plane essentially leads to no tilting movement of the seismic mass.It is intended that the tilting movement takes place around a rotation axis running parallel to the main extension plane.

[0006] In a further embodiment, the seismic mass is further connected to the substrate via at least one second spring, the stiffness of which, in particular its flexural stiffness, is lower during a deflection of the seismic mass in the sense of the tilting movement in the detection direction than its stiffness during a deflection in a secondary direction running parallel to the main extension plane. It is provided that the primary direction and the secondary direction run perpendicular to each other. This embodiment has the advantage that in-plane movement along both the primary direction and the secondary direction is suppressed. This makes it possible to increase the frequency of potential spurious modes.This particularly applies to the disturbance mode associated with translational movement in a direction perpendicular to the rotation axis and parallel to the main plane of extension, and to the disturbance mode associated with rotational movement about an axis perpendicular to the main plane of extension. At the same time, the use of the first and second springs ensures that the deflection (of the seismic mass in the sense of the tilting movement) in the detection direction for the seismic mass is only slightly limited.

[0007] In a further embodiment, at least a portion of the first spring is connected to the seismic mass at a point through which the axis of rotation, running parallel to the main extension plane, passes or along which this axis of rotation extends. Substrate bending due to housing stress then leads to only slight tilting of the seismic mass, and advantageously, smaller error signals caused by the housing stress occur. The beneficial effect on in-plane clipping is retained, i.e., in-plane clipping is improved.

[0008] In a further embodiment, the seismic mass has a recess and / or a further recess in which the first spring and / or the second spring are arranged. This makes it possible, for example, to arrange the second spring such that it connects the seismic mass to the substrate as close as possible to the axis of rotation. This advantageously achieves the shortest possible lever arm, with the lever arm referring to the distance between the second spring and the axis of rotation, and the tilting movement corresponding to the associated lever movement.This positioning of the second spring with a shortened lever arm has the advantage that the stiffness of the second spring (when deflected in the sense of the tilting movement in the detection direction) influences the tilting movement less compared to a position in which a larger lever arm is assigned to the same second spring (especially if the second spring is placed at the outermost edge of the seismic mass).

[0009] If both the first and second springs are arranged within the recesses, an acceleration sensor that is particularly compact is advantageously realized.

[0010] One possibility for designing the first spring and / or the second spring so that their stiffness is sufficiently low under load or deflection along the detection direction is to meander the first and / or the second spring more strongly. While this also reduces the stiffness in the primary or secondary direction, according to the invention it remains well above the stiffness in the detection direction.

[0011] A further subject of the present invention is an acceleration sensor according to the preamble of the main claim or according to the main claim, wherein it is provided that the spring device comprises at least one component whose main extension direction runs perpendicular to the axis of rotation running parallel to the main extension plane, wherein the stiffness of the component upon deflection in the sense of the tilting movement in the detection direction is less than the stiffness of the component upon deflection in a primary direction running parallel to the main extension plane and / or upon deflection in a secondary direction running parallel to the main extension plane. It is provided that the component supports or replaces the action of a first or a second spring.The effect of the first spring is to reduce in-plane clipping along the primary direction, while the effect of the second spring is to reduce in-plane clipping along the secondary direction.

[0012] In a further embodiment, the component of the spring device replaces the first and / or the second spring, thereby advantageously providing an acceleration sensor that is as compact as possible.

[0013] In a further embodiment, it is provided that at least a part of the spring device and / or at least a part of the first spring and / or at least a part of the second spring is a component of a structurable intermediate layer, wherein the structurable intermediate layer is arranged between the substrate and the seismic mass.

[0014] In particular, the intermediate layer allows for the placement of leaf springs between the substrate and the seismic mass. The leaf spring is arranged so that its widest side runs parallel to the main extension plane of the acceleration sensor. The widest side of the leaf spring does not need to be constant along its extension. Rather, it is conceivable that the projection of the leaf spring onto a plane parallel to the main extension plane is triangular or trapezoidal.

[0015] In particular, the leaf springs are designed to suppress any movement of the seismic mass in the detection direction that does not occur in the sense of a tilting movement. This particularly refers to movements in which the entire seismic mass is displaced parallel to the main extension plane when it experiences acceleration in the detection direction. This advantageously further reduces the sensitivity of the acceleration sensor to interference.

[0016] In particular, at least a portion of the first spring and / or a portion of the second spring and / or a portion of the component of the spring device can be arranged below the seismic mass and above the substrate in the detection direction. As a result of such positioning measures, space can advantageously be saved, thus providing the most compact acceleration sensor possible. In particular, it is possible to dispense with a first and / or second recess. This results in the advantage that the total mass of the seismic mass essentially does not need to be reduced, a natural frequency for a useful mode (use frequency for the tilting movement) can therefore be kept as low as possible, and the suppression of disturbing accelerations is thus facilitated.Alternatively, it would also be possible to advantageously implement lateral damping fingers and / or fixed mechanical stops and / or spring-loaded mechanical stops above the first spring and / or the second spring.

[0017] In alternative embodiments, the acceleration sensor comprises a plurality of first and / or a plurality of second springs and / or a plurality of components of the spring device.

[0018] Advantageous embodiments and further developments of the invention can be found in the dependent claims and the description with reference to the drawings. Short description of the drawings:

[0019] It shows Fig. 1 shows a first embodiment of an acceleration sensor according to the invention, Fig. 2 shows a second embodiment of an acceleration sensor according to the invention, Fig. 3 shows a third embodiment of an acceleration sensor according to the invention, Fig. 4 shows a fourth embodiment of the acceleration sensor according to the invention, Fig. 5 shows a side view of the fourth embodiment of the acceleration sensor according to the invention, Fig. 6 shows a fifth embodiment of an acceleration sensor according to the invention, Fig. 7 shows a sixth embodiment of an acceleration sensor according to the invention Fig. 8 shows a seventh embodiment of an acceleration sensor according to the invention and Fig. 9 shows a side view of the seventh embodiment of the acceleration sensor according to the invention, Embodiments of the present invention:

[0020] In the various figures, identical parts are always provided with the same reference symbols and are therefore usually named or mentioned only once.

[0021] Fig. 1 shows a first embodiment of an acceleration sensor 1 according to the invention. The acceleration sensor 1, which has a main extension plane, comprises a substrate 2 and a seismic mass 3. The seismic mass 3 is connected to the substrate 2 via a spring device 4, preferably via one or more torsion springs. The spring device 4 is arranged such that, upon acceleration of the acceleration sensor in a direction perpendicular to the main extension plane, the seismic mass 3 can be deflected about a rotation axis running parallel to the main extension plane in the sense of a tilting movement. Furthermore, it is usually provided that the spring device 4 transfers the seismic mass 3 back to a rest position when no acceleration acts on the seismic mass 3. In the rest position, the seismic mass 3 is arranged essentially parallel to the main extension plane of the acceleration sensor 1.The reason for a rocking motion, i.e. a deflection in the sense of a tilting movement around the rotation axis, is the fact that the course of the spring device D divides the seismic mass 3 into two sections with unequal partial masses. In . Fig. 1, the smaller of the two unequal partial masses extends to the left of the path of the spring device D and the larger of the two unequal partial masses extends to the right of the path of the spring device D. During acceleration, the unequal partial masses experience different inertial forces, whereby a tilting or rocking movement moves the unequal partial masses parallel to a detection direction in opposite directions. The detection direction runs perpendicular to the main extension plane of the acceleration sensor. Typically, 2 electrodes are arranged in the substrate, with which the seismic mass 3 forms a plate capacitor. A movement of the seismic mass 3 along the detection direction then changes the capacitance of the plate capacitor and can therefore provide information about the strength of the acceleration.

[0022] According to the invention, the acceleration sensor 1 has a pair of first springs 11, which connect the seismic mass 3 to the substrate 2 on opposite sides (of the seismic mass 3). The first springs 11 are characterized in that, on the one hand, their stiffness, preferably bending stiffness, is small when subjected to a load, in particular during a deflection in the sense of a tilting movement, along the detection direction, and, on the other hand, their stiffness, preferably tensile stiffness, is large when subjected to a load along a primary direction P running parallel to the main extension plane. In other words: the first spring is designed such that, on the one hand, it does not inhibit the tilting movement of the seismic mass in the detection direction as much as, on the other hand, it inhibits a first lateral movement, i.e., the movement of the seismic mass in the primary direction P.As a result, the pair of first springs can suppress a rotational movement of the seismic mass about an axis perpendicular to the main extension plane and thereby advantageously reduce in-plane clipping.

[0023] In addition, the acceleration sensor 1 from Fig. 1 via a pair of second springs 12, which are arranged side by side (parallel to the extension of the spring device D) and connect the seismic mass 3 to the substrate 2. The second springs 11 are characterized in that, on the one hand, their stiffness, preferably bending stiffness, is low when loaded along the detection direction, and, on the other hand, their stiffness, preferably tensile stiffness, is high when loaded along a secondary direction S running parallel to the main extension plane. In other words: the second spring is designed such that, on the one hand, it does not inhibit the rocking movement of the seismic mass in the detection direction as much as, on the other hand, it inhibits a second lateral movement, i.e., the movement of the seismic mass in the secondary direction S.As a result, the pair of second springs can suppress a translational movement of the seismic mass in a direction perpendicular to the direction of the spring device and thereby advantageously further improve the in-plane clipping.

[0024] A further advantage is that, in the illustrated embodiment, the center of mass of the seismic mass and the axis of rotation around which the tilting movement can occur are essentially at the same height. This advantageously results in such an acceleration sensor generally being insensitive to accelerations that occur perpendicular to the path of the spring device D and parallel to the main extension plane.

[0025] In particular, it is intended that the first spring in the primary direction and / or the second spring in the secondary direction are meandered more strongly than in Fig. 1, whereby the stiffness of the first spring and / or the second spring is reduced when loaded along the detection direction. This also applies to all other first and / or second springs shown in the following embodiments.

[0026] The embodiments of acceleration sensors according to the invention shown in the following figures have essentially the same features as the acceleration sensor according to the first embodiment or according to a respective previously mentioned embodiment. Therefore, the description of the parts already described in Fig. 1 or in a previously mentioned embodiment. In particular, the differences from previous embodiments are highlighted.

[0027] In Fig. 2 shows a second embodiment of an acceleration sensor according to the invention, wherein the present acceleration sensor differs from the embodiment of FIG. 1 by the positioning of the first pair of springs 11 and the second pair of springs 12 with respect to the seismic mass 3. Fig. 1. It is provided that (at least) a first spring 11 is arranged in the region of the seismic mass over which the spring direction D also extends. This positions the pair of first springs 11 in close proximity to the axis of rotation. Experience has shown that substrate deflections due to housing stress are transmitted to the seismic mass 3 to a lesser extent, advantageously resulting in smaller error signals caused by the housing stress. The beneficial effect on in-plane clipping is retained.

[0028] Furthermore, the seismic mass has a recess 5 along the detection direction. In the present embodiment, the pair of second springs 12 is arranged in this recess. This moves the pair of second springs 12 closer to the rotation axis, whereby a lever arm for a tilting movement of the seismic mass about the rotation axis becomes shorter (compared to the positioning of Fig. 1). This advantageously eliminates the need to reduce the stiffness of the second spring 12 (or the pair of second springs) when loaded in the detection direction as much as would be necessary if the second spring 12 were attached to the seismic mass at the point furthest from the rotation axis. The beneficial effect on in-plane clipping is retained.

[0029] In Fig. Figure 3 shows a third embodiment of an acceleration sensor according to the invention. In this embodiment, in comparison to the embodiment of Fig. 2, the pair of first springs 11 are each replaced by a single beam spring 11, wherein the two single beam springs are arranged in a further recess 8, which extends perpendicular to the course of the spring device D. However, they are no longer opposite each other, but lie together in a line parallel to the secondary direction S. This embodiment has the advantage of being particularly compact, in particular in comparison to the embodiments of Fig. 1 and Fig. 2. The beneficial effect on in-plane clipping is maintained.

[0030] In Fig. 4 shows a fourth embodiment of an acceleration sensor according to the invention. The positions for the pair of first springs 11' and the pair of second springs 12 remain the same as in the embodiment of Fig. 3. The pair of first springs 11' and the pair of second springs 12 differ from those of Fig. 3 in that they are part of an intermediate layer, wherein the intermediate layer is arranged between the substrate 2 and the seismic mass 3. In this embodiment, the first and / or second springs 11' are preferably leaf springs. The intermediate layer is approximately a factor of 2-15 thinner than the seismic mass. This advantageously allows leaf springs to be arranged between the substrate and the seismic mass, the stiffness of which can be controlled by the thickness of the intermediate layer when loaded in the detection direction.

[0031] In Fig. Figure 5 shows a side view of an acceleration sensor according to the fourth embodiment along the section plane AB. In this illustration, it can be seen that the center of gravity of the seismic mass 3 and the axis of rotation (for the tilting movement) are not at the same height. As a result, the acceleration sensor 1 in this embodiment has a certain susceptibility to accelerations running perpendicular to the axis of rotation. However, the sensitivity to interference is advantageously low compared to that of acceleration sensors known from the prior art because the first spring 11' in the present embodiment is loaded differently than the spring with the T-shaped cross-section, in particular because a translation rather than a torsion takes place.

[0032] In Fig. Figure 6 shows a fifth embodiment of an acceleration sensor according to the invention. The fifth embodiment differs from that shown in Fig. 4 or 5 in that the cross section of the spring running parallel to the main extension plane is larger than the cross section of the spring from Fig. 4 , in particular, the first spring extends over a greater distance along the primary direction, i.e., the width of the leaf springs is increased. This increases the stiffness of the pair of first springs under load along both the primary and secondary directions to such an extent that the second pair can be advantageously dispensed with while still ensuring the improvement in in-plane clipping.

[0033] In Fig. Figure 7 shows a sixth embodiment of an acceleration sensor according to the invention. Compared to the embodiment of Fig. 6, this acceleration sensor dispenses with the spring device 4 and the recess 5. This results in the advantage of providing a particularly compact acceleration sensor.

[0034] In Fig. Figure 8 shows a seventh embodiment of an acceleration sensor according to the invention. Compared to the embodiment of Fig. 6, the further recess 8 is omitted in the acceleration sensor 1, i.e., the seismic mass 3 extends partially along the detection direction above the pair of first springs 11'. This results in the advantage that the total mass of the seismic mass does not need to be reduced substantially, a natural frequency for a useful mode (usage frequency for the rocking motion) can therefore be kept as low as possible, thus facilitating the suppression of disturbing accelerations. Alternatively, it would also be advantageous to implement lateral damping fingers and / or fixed mechanical stops and / or resilient mechanical stops above the pair of first springs.

[0035] In Fig.Figure 9 shows a side view of the acceleration sensor 1 according to the seventh embodiment along the section plane AB. Bending springs can be seen, which were created by structuring the intermediate layer and which are directly connected to the seismic mass 3 at their respective outer ends. Technically, the connection is realized via a local opening in an oxide layer between the seismic mass 3 and the intermediate layer, with the seismic mass being deposited directly onto the intermediate layer. From the areas where the seismic mass and the intermediate layer are not connected, the oxide is removed in a later manufacturing step, preferably during gas-phase etching, creating a gap 15 between the intermediate layer and the seismic mass 3.

Claims

[1] Acceleration sensor (1) with a substrate (2) and a seismic mass (3), wherein the acceleration sensor (1) has a main extension plane and comprises a spring device (4) via which the substrate (2) and the seismic mass (3) are connected in such a way that the seismic mass (3) can be deflected in the sense of a tilting movement about an axis of rotation running parallel to the main extension plane when accelerated in a detection direction running perpendicular to the main extension plane, characterized byin that the seismic mass (3) is further connected to the substrate (2) via at least one first spring (11), wherein the stiffness of the first spring (11) during a deflection of the seismic mass (3) in the sense of the tilting movement in the detection direction is smaller than the stiffness of the first spring (11) during a deflection in a primary direction (P) running parallel to the main extension plane, wherein the spring device (4) transfers the seismic mass (3) into a rest position when no acceleration acts on the seismic mass (3), wherein the seismic mass (3) is arranged in the rest position substantially parallel to the main extension plane of the acceleration sensor (1) and wherein the course of the spring device divides the seismic mass (3) on both sides of the spring device into two sections with unequal partial masses. [2] Acceleration sensor (1) according to claim 1, characterized bythat the spring device (4) comprises at least one component whose main extension direction runs perpendicular to the axis of rotation running parallel to the main extension plane, wherein the stiffness of the component during a deflection in the sense of the tilting movement in the detection direction is smaller than the stiffness of the component during a deflection in a primary direction (P) running parallel to the main extension plane and / or during a deflection in a secondary direction (S) running parallel to the main extension plane. [3] Acceleration sensor (1) according to claim 1, characterized byin that the seismic mass (3) is further connected to the substrate via at least one second spring (12), the stiffness of which spring, when the seismic mass (3) is deflected in the detection direction, is smaller than its stiffness when deflected in a secondary direction (S) running parallel to the main extension plane, the primary direction (P) and the secondary direction (S) running perpendicular to one another. [4] Acceleration sensor (1) according to one of the preceding claims, characterized by that at least a part of the first spring (11) is connected to the seismic mass (3) at a point through which the axis of rotation extending parallel to the main extension plane extends. [5] Acceleration sensor (1) according to one of the preceding claims, characterized by that the seismic mass (3) has a recess (5) and / or a further recess (6) in which the first spring (11) and / or the second spring (12) are arranged. [6] Acceleration sensor (1) according to one of the preceding claims, characterized by that at least a part of the spring device (4) and / or at least a part of the first spring (11) and / or at least a part of the second spring (12) are part of one or more structurable intermediate layers, wherein the one or more structurable intermediate layers are arranged between the substrate (2) and the seismic mass (3). [7] Acceleration sensor (1) according to one of the preceding claims, characterized by that the seismic mass (3) extends at least partially in the detection direction above the first spring (11') and / or the second spring (12').

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