MEMS sensor with high robustness against static friction phenomena

Abstract

The invention relates to a MEMS sensor with high robustness against static friction phenomena. The MEMS sensor is configured to measure a physical quantity and has a substrate and a movable mass suspended at a distance from the substrate in a direction and coupled to the substrate. The MEMS sensor also has a contact sensing structure coupled to the substrate and extending at a distance from the movable mass in a sensing direction when stationary; and at least one stator electrode coupled to the substrate and configured to form, with the movable mass, at least one capacitor having a capacitance that is variable according to movement of the movable mass. The control circuit is configured to: sense a voltage difference between the movable mass and the stator electrode; sensing a contact between the movable mass and the contact sensing structure; and in response to sensing the contact between the movable mass and the contact sensing structure, modifying the induced voltage difference to reduce an electrostatic force applied on the movable mass.

Description

Technical Field

[0001] The present disclosure relates to MEMS ("Micro-Electro-Mechanical Systems") sensors that are highly robust against the phenomenon of static friction. In particular, the present disclosure relates to inertial sensors, such as accelerometers. Background Art

[0002] It is well known that the phenomenon of static friction can cause MEMS sensors to malfunction based on the movement of a movable mass.

[0003] For example, a known type of MEMS accelerometer has a movable mass that is suspended above a substrate and is free to move relative to the substrate depending on an external acceleration. The movable mass is coupled to the substrate by means of a coupling elastic element.

[0004] It is also known to provide a MEMS accelerometer with a travel-end mechanical element (stop) that is fixed to the substrate and, at rest, is arranged at a certain distance from the movable mass. The stop determines the maximum displacement that the movable mass may experience during use.

[0005] In the presence of a high acceleration, the movable mass may experience a large displacement, such as causing contact between the movable mass and the stop. In response to the contact between the movable mass and the stop, an attractive adhesion force may be established between the movable mass and the stop.

[0006] When the high acceleration ends, if the adhesion force cannot be exceeded by the return force exerted by the coupling elastic element, the movable mass does not return to the rest position. In other words, in this case, the movable mass is affected by the phenomenon of static friction and remains stuck. Consequently, the movable mass can no longer move depending on the external acceleration, leading to a sensing failure of the accelerometer.

[0007] According to one method, the coupling elastic element is designed to have a high stiffness. In this way, the coupling elastic element exerts a high elastic return force, thus reducing the risk of the static friction phenomenon. However, this method may result in higher sensing noise and lower sensor stability.

[0008] According to another method, the stop can have an anti-static friction layer configured to reduce the adhesion force that may be established between the movable mass and the stop. However, this method requires higher manufacturing complexity, additional manufacturing steps, and thus high manufacturing costs.

[0009] According to other methods, the sensor may have a dedicated electrode configured to apply an electrostatic force on the movable mass in a direction opposite to the direction of the adhesion force. However, the applicant has observed that the electrostatic force required to detach the movable mass from the stopper may cause the movable mass to move, such as to cause the movable mass to collide with other stoppers arranged on the opposite side of the movable mass, thereby causing other static friction situations. In practice, this method also cannot effectively return the sensor to the operating state.

[0010] The object of the present disclosure is to overcome at least in part the disadvantages of the prior art. Summary of the Invention

[0011] According to the present disclosure, there is thus provided a MEMS sensor and a method for controlling a MEMS sensor. Brief Description of the Drawings

[0012] To better understand the present disclosure, reference is now made to the accompanying drawings, which describe embodiments of the present disclosure by way of non-limiting examples only, in which:

[0013] Figure 1 A schematic diagram of a MEMS accelerometer according to one embodiment is shown;

[0014] Figure 2 Shows Figure 1 a part of the MEMS accelerometer under a first use condition;

[0015] Figure 3 Shows Figure 2 a part of the MEMS accelerometer under a second use condition;

[0016] Figure 4 Shows Figure 2 a part of the MEMS accelerometer under a third use condition;

[0017] Figure 5 A schematic cross-section of the MEMS accelerometer at rest according to different embodiments is shown; and

[0018] Figure 6 Shows Figure 5 the MEMS accelerometer in use. Detailed Description of the Embodiments

[0019] Figure 1 A MEMS sensor is shown, specifically a MEMS accelerometer 1, which includes a sensing body 3 and a control circuit 5.

[0020] The sensing body 3 will be described below with reference to a Cartesian reference system XYZ having a first axis X, a second axis Y, and a third axis Z.

[0021] The MEMS accelerometer 1 can be formed starting from one or more bodies of semiconductor material (e.g., silicon) by using micro / nano processing techniques.

[0022] For example, the sensing body 3 and the control circuit 5 can be formed on the same die or on different dies.

[0023] The MEMS accelerometer 1 includes a substrate 10 and a movable mass 12 suspended on the substrate 10. The movable mass 12 extends along the third axis Z at a certain distance from the substrate 10.

[0024] The movable mass 12 can be wholly or partly of a suitably doped semiconductor material (e.g., silicon or polysilicon).

[0025] The movable mass 12 is coupled to the substrate 10 to undergo an in-plane movement relative to the substrate 10 along the sensing direction S (here parallel to the second axis Y) in response to an external acceleration experienced by the MEMS accelerometer 1.

[0026] Specifically, in this embodiment, the movable mass 12 is configured to undergo a movement along the sensing direction S in response to an acceleration along the sensing direction S.

[0027] In detail, the MEMS accelerometer 10 includes: an anchoring region 14 fixed to the substrate 10; and a coupling elastic element (spring) 16 extending between the anchoring region 14 and the movable mass 12. The coupling elastic element 16 holds the movable mass 12 suspended on the substrate 10.

[0028] The anchoring region 14 and / or the coupling elastic element 16 can be wholly or partly of a suitably doped semiconductor material (e.g., silicon or polysilicon).

[0029] The coupling elastic element 16 is configured to allow the movable mass 12 to move relative to the substrate 10 parallel to the sensing direction S. Specifically, the coupling elastic element 16 is configured to respond to an acceleration of the MEMS accelerometer 1 along the sensing direction S such that the movable mass 12 moves along the sensing direction S.

[0030] The MEMS accelerometer 10 includes two stator electrodes 18A, 18B mechanically coupled to the substrate 10 and arranged at a certain distance from the movable mass 12 along the sensing direction S.

[0031] The stator electrodes 18A, 18B are carried by the substrate 10 and, in particular, are fixed to the substrate 10.

[0032] The stator electrodes 18A, 18B are capacitively coupled to the movable mass 12. For example, the stator electrodes 18A, 18B can be of a suitably doped semiconductor material (e.g., silicon or polysilicon).

[0033] In this embodiment, the movable mass 12 has a through cavity 20 that extends through the movable mass 12 along the third axis Z through the thickness of the movable mass 12. The stator electrodes 18A, 18B are disposed inside the through cavity 20.

[0034] In detail, the movable mass 12 has a first inner wall 21A and a second inner wall 21B. The first inner wall 21A defines the through cavity 20 on a first side, and the second inner wall 21B defines the through cavity 20 on a second side that is opposite the first side along the sensing direction S.

[0035] The stator electrode 18A faces the first inner wall 21A. The stator electrode 18B faces the second inner wall 21B.

[0036] The first inner wall 21A and the second inner wall 21B form rotor electrodes that are integral with the movable mass 12 and are each capacitively coupled to the respective stator electrodes 18A, 18B. In other words, the movable mass 12 includes the rotor electrodes 21A, 21B.

[0037] In practice, the inner walls 21A, 21B and the stator electrodes 18A, 18B form respective capacitors that have a variable capacitance depending on the movement of the movable mass 12.

[0038] The stator electrodes 18A, 18B each extend at a distance g el along the sensing direction S from the respective inner walls 21A, 21B.

[0039] The distance g el can be between, for example, 2 μm and 3 μm.

[0040] In this embodiment, the stator electrodes 18A, 18B are at the same distance g el from the respective inner walls 21A, 21B. However, the stator electrodes 18A, 18B can extend at different distances from the respective inner walls 21A, 21B.

[0041] The sensing body 3 further includes a travel end region (stop) 25 that, at rest, extends at a distance g max along the sensing direction S from the movable mass 12.

[0042] The stop region 25 is configured to determine the maximum movement that the movable mass 12 can experience parallel to the sensing direction S.

[0043] The stop region 25 can be wholly or partly of a suitably doped semiconductor material (e.g., silicon or polysilicon).

[0044] Distance g max can be between, for example, 1.5 μm and 2.8 μm.

[0045] Distance g max can be shorter than distance g el Short.

[0046] In this way, the stop region 25 can prevent the movable mass 12 from colliding with the stator electrodes 18A, 18B during use. In other words, the maximum movement that the movable mass 12 can experience is less than the movement along the sensing direction S that would cause the movable mass 12 to contact the stator electrodes 18A, 18B.

[0047] Specifically, in this embodiment, the stop region 25 extends at a certain distance from the outer wall 26 of the movable mass 12 when at rest.

[0048] The stop region 25 is carried by the substrate 10 and can be integrally coupled (fixed) to the substrate 10.

[0049] In detail, the stop region 25 includes an anchoring region 27 and a protruding region 28, the anchoring region 27 being fixed to the substrate 10 and the protruding region 28 extending from the anchoring region 27 towards the outer wall 26 of the movable mass 12.

[0050] The protruding region 28 extends at a distance g max from the outer wall 26 of the movable mass 12.

[0051] The sensing body 3 further includes a contact sensing structure 30, the contact sensing structure 30 being mechanically coupled to the substrate 10 and extending at a distance g SW from the movable mass 12 along the sensing direction S when at rest.

[0052] In practice, the contact sensing structure 30 is carried by the substrate 10.

[0053] The contact sensing structure 30 can be wholly or partly of a suitably doped semiconductor material (e.g., silicon or polysilicon).

[0054] Distance g SW can be between, for example, 1.2 μm and 2.5 μm.

[0055] Distance g SW can be shorter than distance gmax Short. In this way, in use, the movable mass 12 can contact the contact sensing structure 30 before the stop region 25 during movement along the sensing direction S.

[0056] Specifically, in this embodiment, when the contact sensing structure 30 is at rest, it extends at a distance g from the outer wall 26 of the movable mass 12. SW extending.

[0057] In detail, the contact sensing structure 30 includes an anchoring region 32, a deformable region 33, and a bumper portion 34. The anchoring region 32 is fixed to the substrate 10. The deformable region 33 extends from the anchoring region 32. The bumper portion 34 is configured to contact the movable mass 12 during the movement of the movable mass 12 along the sensing direction S.

[0058] The deformable region 33 is also configured to undergo elastic deformation in response to a collision between the movable mass 12 and the contact sensing structure 30.

[0059] In this embodiment, the deformable region 33 has a main extension that is transverse to the sensing direction S, specifically parallel to the first axis X here.

[0060] For example, the deformable region 33 can be suspended on the substrate 10 at a certain distance from the substrate 10 along the third axis Z. For example, the deformable region 33 can be a cantilever.

[0061] The deformable region 33 faces the movable mass 12 partially along the sensing direction S; specifically, it faces the outer wall 26.

[0062] In Figure 1 the embodiment, the bumper portion 34 faces the movable mass 12 along the sensing direction S and extends from the deformable region 33 towards the movable mass 12 along the sensing direction S.

[0063] The bumper portion 34 determines the distance g SW .

[0064] The bumper portion 34 has a contact surface that is configured to contact the movable mass 12 in response to the movement of the movable mass 12 along the sensing direction S (upward in Figure 1 ). The contact surface can be smaller than the surface of the outer wall 26; this can allow for a reduction in the adhesion force that may be established between the movable mass 12 and the bumper portion 34. For example, the contact surface of the bumper portion 34 can have an in-plane extension (e.g., in the plane XY) between 0.2 μm and 10 μm. For example, the contact surface of the bumper portion 34 can extend along the third axis Z through the thickness of the movable mass 12.

[0065] The MEMS accelerometer 1 further includes means for sensing the electrical connection between the body 3 and the control circuit 5, such as, for example, the conductive rails, contact pads, etc., schematically illustrated only in Figure 1 the figure.

[0066] In detail, the MEMS accelerometer 1 includes: connection means 37 for the electrical connection of the movable mass 12; connection means 38 for the electrical connection of the stator electrodes 18A, 18B; and connection means 39 for the electrical connection of the contact sensing structure 30.

[0067] Specifically, for example, if the movable mass 12 is of a suitably doped semiconductor material, the movable mass 12 can have an electrical behavior of the conductive / metal type; thus, hereinafter, for simplicity, the electrical connection of the movable mass 12 also means the electrical connection of the inner walls (rotor electrodes) 21A, 21B and the outer wall 26, or more generally, the electrical connection of the entire movable mass 12 as a whole. In practice, hereinafter, for simplicity, it can be assumed that the movable mass 12, the rotor electrodes 21A, 21B and the outer wall 26 are substantially at the same potential.

[0068] Similarly, for example, if the contact sensing structure 30 is of a suitably doped semiconductor material, the contact sensing structure 30 can also have an electrical behavior of the conductive / metal type; thus, hereinafter, for simplicity, the electrical connection of the contact sensing structure 30 refers to the electrical connection of the buffer portion 34, or more generally, the electrical connection of the entire contact sensing structure 30.

[0069] The control circuit 5 includes: drive (bias) circuit means 45, which is electrically coupled to the movable mass 12 and the stator electrodes 18A, 18B; and contact sensing circuit means 46, which is electrically coupled to the contact sensing structure 30.

[0070] The drive circuit means 45 is configured to bias the movable mass 12 and / or the stator electrodes 18A, 18B so as to be able to sense the capacitance change between the movable mass 12 and the stator electrodes 18A, 18B in response to the movement of the movable mass 12. In other words, the drive circuit means 45 is configured to sense the voltage difference between the movable mass 12 and the stator electrodes 18A, 18B to sense the capacitance change between the movable mass 12 and the stator electrodes 18A, 18B.

[0071] The contact sensing circuit means 46 is configured to sense the contact between the movable mass 12 and the buffer portion 34 of the contact sensing structure 30.

[0072] The control circuit 5 further includes an acceleration sensing circuit device 47 which is coupled to the sensing body 3 and one or more of the drive circuit device 45 and the contact sensing circuit device 46 in a manner not shown herein, and is configured to sense external acceleration in a manner known per se and will not be discussed further in detail herein. For example, the acceleration sensing circuit device 47 may be configured to measure the capacitance change between the rotor (the movable mass 12) and the stator (the electrodes 18A, 18B).

[0073] Figure 2 Shown is the MEMS accelerometer 1 in use, under normal operating conditions, where the MEMS accelerometer 1 has experienced a low external acceleration, such as an external acceleration below the maximum acceleration value a detectable by the MEMS accelerometer 1 max . For example, in Figure 2 the normal operating conditions, the external acceleration may be zero, or may cause, for example, the movable mass 12 to move M along the sensing direction S relative to Figure 1 its rest position by an amount M less than the distance g SW .

[0074] By way of example only, in Figure 2 the movable mass 12 moves upward, i.e., towards the buffer portion 34 of the contact sensing structure 30.

[0075] Under normal operating conditions, in order to sense the external acceleration experienced by the MEMS accelerometer 1, the drive circuit device 45 biases the movable mass 12 and the stator electrodes 18A, 18B. In other words, the drive circuit device 45 senses the voltage difference between the movable mass 12 and the stator electrodes 18A, 18B. In this way, the capacitance change between the rotor electrodes 21A, 21B and the stator electrodes 18A, 18B can be sensed, which is caused by the movable mass 12 in response to the acceleration of the MEMS accelerometer 1.

[0076] Specifically, the drive circuit device 45 applies the rotor voltage V ROT to the rotor electrodes 21A, 21B and applies a stator voltage V ROT different from the rotor voltage V STAT to the stator electrodes 18A, 18B.

[0077] In this embodiment, the stator voltage V STAT is a DC voltage equal to V cm and the rotor voltage V ROT is a time-varying voltage.

[0078] Specifically, the rotor voltage V ROTIt can oscillate between a minimum value and a maximum value, for example, with a constant or variable frequency.

[0079] Voltage V ROT can be a varying voltage around the stator voltage V STAT = V cm of.

[0080] Specifically, the rotor voltage V ROT can have a time-varying average value, and the average value is equal to the stator voltage V STAT .

[0081] In Figure 2 the example of, the rotor voltage V ROT is a square wave between 0V and 2V CM .

[0082] Relative to Figure 1 the stationary position of, the movement M of the movable mass 12 causes the inner wall 21B to move towards the stator electrode 18B and the inner wall 21A to move away from the stator electrode 18A. The resulting capacitance change can be sensed by the acceleration sensing circuit device 47.

[0083] In practice, in response to the movement M of the movable mass 12, the distance along the sensing direction S between the movable mass 12 and the stator electrode 18B is shorter than the distance between the movable mass 12 and the stator electrode 18A. Therefore, a net electrostatic force F el (upward in Figure 2 the example of) is applied to the movable mass 12.

[0084] At the same time, the coupling elastic element 16 undergoes deformation (elongation in Figure 2 the example of) in response to Figure 2 the movement M of the movable mass 12 of. Therefore, in response to the movement M of the movable mass 12, the coupling elastic element 16 applies an elastic return force F el in the sensing direction S and in the direction opposite to the net electrostatic force F Figure 2 (i.e., downward in mec the example of) on the movable mass 12.

[0085] Under normal operating conditions, the MEMS accelerometer 1 is configured such that when the external acceleration ends, the elastic return force F mec returns the movable mass 12 to Figure 1 the equilibrium position of.

[0086] During normal operating conditions, the contact sensing circuit device 46 senses the voltage difference between the contact sensing structure 30 and the movable mass 12.

[0087] Specifically, in this embodiment, the contact sensing circuit device 46 applies a DC voltage V to the contact sensing structure 30 SW . The DC voltage V SW may be different from the average value of the rotor voltage V ROT ; specifically, it may be a lower voltage.

[0088] Specifically, in Figure 2 the embodiment, V SW = V cm - Δ.

[0089] The contact sensing circuit device 46 is further configured to sense a contact current I between the movable mass 12 and the contact sensing structure 30 C .

[0090] Specifically, the contact sensing circuit device 46 may be configured to sense the DC component of the contact current I C .

[0091] During normal operating conditions in which the movable mass 12 undergoes movement, such as to remain at a certain distance from the contact sensing structure 30, the contact current I C is zero.

[0092] Figure 3 FIG. shows the MEMS accelerometer 1 under first shock operating conditions during use, where the MEMS accelerometer 1 has experienced a high external acceleration, the high external acceleration being, for example, equal to or greater than the maximum acceleration value a detectable by the MEMS accelerometer 1 max . For example, in Figure 3 the operating conditions, the external acceleration is such that it causes a movement M' of the movable mass 12 relative to Figure 1 the rest position along the sensing direction S, the movement M' being equal to or greater than the distance g SW .

[0093] In practice, the movement M' of the movable mass 12 is such that the movable mass 12 contacts the buffer portion 34 of the contact sensing structure 30.

[0094] In response to the contact of the movable mass 12 with the buffer portion 34, the contact sensing circuit device 46 senses a contact current I different from zero C . In fact, in response to the contact, the contact current I C is a function of the voltage difference between the rotor voltage V ROT and the voltage V SW .

[0095] For example, the contact sensing circuit device 46 may be configured to at the contact current I CSense when exceeding a threshold value, the threshold value being equal to or different from zero, and the threshold value can be selected during a design or calibration step.

[0096] In response to sensing a contact current I different from zero C , the contact sensing circuit device 46 generates a contact sensing signal S C .

[0097] The drive circuit device 45 receives the contact sensing signal S C , and in response, modifies the bias of the stator electrodes 18A, 18B and / or the movable mass 12 as Figure 2 described, to reduce the electrostatic force exerted on the movable mass 12 by the stator electrodes 18A, 18B.

[0098] In other words, the drive circuit device 45 can modify the induced voltage difference between the stator electrodes 18A, 18B and the movable mass 12 to sense capacitance changes.

[0099] For example, the drive circuit device 45 can reduce the amplitude of the rotor voltage V ROT .

[0100] In this embodiment, the drive circuit device 45, in response to receiving the contact sensing signal S C , applies the rotor voltage V ROT , and the rotor voltage V ROT is a DC voltage equal to the stator voltage V STAT = V cm .

[0101] The drive circuit device 45 can hold the rotor voltage V ROT at a new value during a time interval Δt (where V ROT = V cm is maintained here), the time interval Δt being greater than 5 ms, for example between 5 ms and 30 ms, especially about 10 ms; this can help reduce the risk of static friction of the movable mass against the buffer portion 34.

[0102] At the end of the time interval Δt, the MEMS accelerometer 1 can return to the normal operating conditions as Figure 2 described above to sense a new external acceleration experienced by the MEMS accelerometer 1.

[0103] In response to contact between the movable mass 12 and the buffer portion 34, the buffer portion 34 can apply an adhesion force F Figure 3 in the sensing direction S (upward in the example of adh ) on the movable mass 12.

[0104] At the same time, the coupling elastic element 16 undergoes deformation in response to the movement M' (Figure 3 Therefore, the coupling elastic element 16 exerts an elastic return force F′ on the movable mass block 12 along the sensing direction S and in the direction opposite to the adhesion force. mec .

[0105] Reducing the potential difference between the movable mass 12 and the stator electrodes 18A, 18B so that the stator electrodes 18A, 18B exert a low net electrostatic force F′ on the movable mass 12 el ; i.e., low net electrostatic force F' el Below will be Figure 2 The net electrostatic force applied under the operating conditions (i.e., if the rotor voltage V ROT Keep as reference Figure 2 as described).

[0106] By reducing the electrostatic force contribution induced by the stator electrodes 18A, 18B on the movable mass 12, the risk of the movable mass 12 remaining stuck on the buffer portion 34 may be reduced. The MEMS accelerometer 1 may thus have a high robustness against stiction phenomena.

[0107] Specifically, in the illustrated embodiment, the voltage difference between the movable mass 12 and the stator electrodes 18A, 18B is zeroed (V ROT =V STAT =V cm ). Therefore, the electrostatic contribution F' exerted by the stator electrodes 18A, 18B on the movable mass 12 is el This allows the robustness of the MEMS accelerometer 1 against stiction phenomena to be further improved.

[0108] The present MEMS accelerometer can therefore have high reliability.

[0109] The potential difference between the movable mass 12 and the contact sensing structure 30 may induce an electrostatic force contribution along the sensing direction S and opposing the elastic return force (ie, at Figure 2 and Figure 3 center upward).

[0110] However, the fact that the bumper portion 34 may have a lower contact area with the movable mass 12 helps to reduce the risk of stiction of the movable mass 12 against the bumper portion 34 .

[0111] Additionally or alternatively, V SW With V ROT The fact that the voltage difference between is low helps to reduce this electrostatic contribution.

[0112] Figure 4Shows the MEMS accelerometer 1 in use, under second shock operating conditions, where the MEMS accelerometer 1 has experienced a high external acceleration, the high external acceleration being, for example, equal to or greater than the maximum acceleration value a detectable by the MEMS accelerometer 1 max .

[0113] Specifically, under the operating conditions of Figure 4 , the external acceleration is such that it causes a movement M” of the movable mass 12 relative to the Figure 1 rest position along the sensing direction S, the movement M” being greater than the distance g SW .

[0114] In practice, the movement M” of the movable mass 12 is such that the movable mass 12 contacts the buffer portion 34 of the contact sensing structure 30 and the deformable region 33 of the contact sensing structure 30 deforms.

[0115] Specifically, in Figure 4 , the movement M” of the movable mass 12 is such that the movable mass 12 contacts the stop region 25.

[0116] The content described with reference to the contact of the movable mass 12 with the buffer portion 34 also applies to the Figure 3 operating conditions of Figure 4 .

[0117] Furthermore, the fact that the deformable region 33 deforms along the sensing direction S in response to a collision with the movable mass 12 causes the deformable region 33 to apply a corresponding elastic return force F mec in the same direction as the elastic return force F” of the coupling elastic element 16 on the movable mass 12 mec,2 . Thus, the deformable region 33 provides an additional force contribution in a direction opposite to the adhesion force.

[0118] In other words, the fact that the contact sensing structure 30 is deformable in response to contact with the movable mass 12 can contribute to further improving the robustness of the MEMS accelerometer 1 against the phenomenon of static friction, and thus increasing its sensing reliability.

[0119] Figure 5 Different embodiments of the MEMS accelerometer 100 at rest are shown in a Cartesian reference system XYZ. Only the corresponding sensing body 103 of the MEMS accelerometer 100 is shown, limited to the parts useful for understanding the present disclosure.

[0120] The MEMS accelerometer 100 further includes Figure 1 a control circuit 5 in

[0121] The MEMS accelerometer 100 is an out-of-plane MEMS accelerometer configured to sense acceleration along an out-of-plane sensing direction S' parallel to the third axis Z.

[0122] The MEMS accelerometer 100 includes a substrate 10 and a movable mass 112 suspended on the substrate 10. The movable mass 112 extends at a distance from the substrate 10 along the third axis Z.

[0123] In this embodiment, the movable mass 112 is coupled to the substrate 10 such that in response to an external acceleration of the MEMS accelerometer 10 along the third axis Z, it undergoes an out-of-plane movement (i.e., having a component along the third axis Z) relative to the substrate 10.

[0124] The MEMS accelerometer 100 includes an anchoring region 114 and at least one coupling elastic element 116 (schematically shown only in Figure 5 ), the anchoring region 114 is fixed to the substrate 10, and the at least one coupling elastic element 116 couples the movable mass 112 to the anchoring region 114. The coupling elastic element 116 holds the movable mass 112 suspended on the substrate 10 at rest.

[0125] The coupling elastic element 116 is configured to allow an out-of-plane movement of the movable mass 112 in response to the acceleration experienced by the MEMS accelerometer 100 along the third axis Z.

[0126] Specifically, in this embodiment, the MEMS accelerometer 100 has a seesaw structure.

[0127] In practice, the movable mass 112 has a center of gravity G and the coupling elastic element 116 couples the movable mass 112 to the anchoring region 114 at a fulcrum F that is offset with respect to the center of gravity G of the movable mass 112.

[0128] The coupling elastic element 116 is a torsional elastic element configured to allow the movable mass 112 to rotate about a rotation axis (not shown here) passing through the fulcrum F and parallel to the first axis X.

[0129] In other words, the rotation axis is a non-centroidal axis, i.e., it does not pass through the center of gravity G of the movable mass 112.

[0130] The MEMS accelerometer 100 includes stator electrodes 118A, 118B fixed to the substrate 10 and arranged at a distance from the movable mass 112 along the third axis Z.

[0131] Similar to what has been done for Figure 1Description of the MEMS accelerometer 1 therein, the stator electrodes 118A, 118B are capacitively coupled to the movable mass 112, which thus forms the rotor electrode.

[0132] The MEMS accelerometer 100 further includes a contact sensing structure 130, the contact sensing structure 130 is fixed to the substrate 10, and is configured to contact the movable mass 112 before the movable mass 112 contacts the stator electrodes 118A, 118B in response to a high acceleration (impact) of the MEMS accelerometer 100.

[0133] Specifically, to ensure that the movable mass 112 contacts the contact sensing structure 130 before contacting the stator electrodes 118A, 118B, the contact sensing structure 130 is arranged to face the end of the movable mass 112.

[0134] Specifically, in this embodiment, the movable mass 112 includes: a main region 112A, the main region 112A faces the stator electrodes 118A, 118B; and a deformable region 133, the deformable region 133 is configured to undergo elastic deformation in response to the contact between the movable mass 112 and the contact sensing structure 130.

[0135] For example, the deformable region 133 may have a different size relative to the main region 112A such that it undergoes elastic deformation in response to a collision with the contact sensing structure 130. For example, depending on the specific manufacturing steps and specific applications used, the deformable region 133 may have a thickness smaller than the thickness of the main region 112A along the third axis Z, or the deformable region 133 may have the same thickness as the main region 112A along the third axis Z and have a suitable in-plane geometry (layout).

[0136] When at rest, the deformable region 133 faces the contact sensing structure 130 along the third axis Z, at a certain distance from the contact sensing structure 130.

[0137] Specifically, in this embodiment, the deformable region 133 forms an extension of the movable mass 112 in a direction parallel to the axis Y.

[0138] The deformable region 133 extends from one end (outer wall) of the main region 112A.

[0139] The MEMS accelerometer 100 may also have a protrusion 135, the protrusion 135 extends from the deformable region 133 toward the substrate 10 along the third axis Z and faces (when at rest) the contact sensing structure 130. In practice, in this embodiment, the protrusion 135 serves as the contact portion between the movable mass 112 and the contact sensing structure 130.

[0140] As Figure 5 shown in the embodiment of Figure 5 , the main region 112A of the movable mass 112 may also include other protrusions 137 facing above the contact sensing structure 130. Specifically, the other protrusions 137 extend along the third axis Z from the main region 112A towards the contact sensing structure 130.

[0141] In practice, the protrusion 137 is arranged at a certain distance along the axis Y from the fulcrum F, and this distance is shorter than the distance of the protrusion 135 along the axis Y from the fulcrum F. Therefore, in response to the rotation of the movable mass 112, the protrusion 135 may contact the contact sensing structure 130 before the protrusion 137. This allows the protrusion 137 and the contact sensing structure 130 to act as a stop region of the MEMS accelerometer 100.

[0142] The MEMS accelerometer 100 also includes connection means 37, 38 and 39 for electrically connecting the movable mass 112, the stator electrodes 118A, 118B and the contact sensing structure 130 respectively, as discussed with reference to MEMS accelerometer 1.

[0143] In use, as shown for example Figure 6 in Figure 6 , the MEMS accelerometer 100 has a similar function to the MEMS accelerometer 1 described in references Figure 2 and Figure 3 and will not be described in further detail herein.

[0144] In practice, the contact sensing circuit means 46 is configured to sense the contact between the movable mass 112 and the contact sensing structure 130, and in response, modify the bias between the movable mass 112 and the stator electrodes 118A, 118B to reduce (specifically to zero) the electrostatic force between the movable mass 112 and the stator electrodes 118A, 118B.

[0145] In this way, even in the case where there is an adhesion force between the movable mass 112 and the contact sensing structure 130, the torque T applied by the coupling elastic element 116 on the movable mass 112 mec can bring the movable mass 112 back to the equilibrium position.

[0146] In practice, the MEMS accelerometer 100 may also have high robustness against the static friction phenomenon of the movable mass 112.

[0147] Furthermore, also in this embodiment, similar to what has been discussed with reference to the deformable region 33 of the MEMS accelerometer 1, the presence of the deformable region 133 helps to further improve the robustness of the MEMS accelerometer 100 against the static friction phenomenon.

[0148] Finally, it is clear that the MEMS accelerometers described and illustrated herein can be modified and varied without thereby departing from the scope of the disclosure as defined in the appended claims.

[0149] The MEMS accelerometers 1, 100 can have a shape different from the shapes shown and described.

[0150] For example, the number and arrangement of the coupling elastic elements, stator electrodes, stop regions, etc. can be different.

[0151] For example, referring Figure 1 to the MEMS accelerometer 1 of, the stator electrodes 18A, 18B can be coupled to the outer walls of the movable mass 12. For example, the movable mass 12 can not have a through cavity 20.

[0152] For example, the stop region 25 can be absent and the contact sensing structure 30 can act as a stop region.

[0153] The MEMS accelerometer 1 can, for example, have other stop regions on the side facing the anchoring region 14.

[0154] For example, depending on the specific design requirements, the movable mass 12 can have a shape different from the shape shown, for example, not rectangular or quadrilateral, but having a different number of sides, or having a regular or irregular shape.

[0155] For example, the stop region 25 and the contact sensing structure 130 can be configured to contact a portion, surface, wall, or face of the movable mass 12 that is different from and / or different from each other than those shown, depending on the specific shape of the movable mass 12.

[0156] For example, the movable mass 12 can have a plurality of openings 150 that are different from each other, the plurality of openings 150 extending through the movable mass 12 along a third axis Z, through the thickness of the movable mass 12. Alternatively, the openings 150 can be absent.

[0157] For example, the MEMS accelerometer 100 can have a structure different from the seesaw structure, that is, a structure in which the movable mass 112 is coupled to the substrate 10 to undergo an out-of-plane movement (e.g., translation) different from rotation in response to an acceleration of the MEMS accelerometer in the out-of-plane direction (Z).

[0158] The MEMS accelerometer 100 can have a seesaw structure, but a shape different from the shapes shown and described.

[0159] For example, the coupling elastic elements 16, 116 may be configured to move the movable masses 12, 112 along the sensing directions S, S' in response to an acceleration in a direction transverse to the sensing directions S, S'.

[0160] For example, the MEMS accelerometers 1, 100 may be biaxial or triaxial accelerometers, i.e., configured to sense accelerations along two or more sensing directions transverse to each other.

[0161] For example, the rotor V ROT voltage and the stator V STAT voltages may be opposite to each other. For example, in order to reduce or zero the electrostatic force between the movable mass and the stator electrodes, the stator voltage V STAT may be additionally or alternatively modified to the rotor voltage V ROT .

[0162] For example, the contact sensing circuitry 46 may be configured to sense the contact between the movable mass and the contact sensing structure in a manner different from that described; for example, by sensing an alternating current or using other methods that do not contemplate monitoring the current.

[0163] For example, the stator electrodes 18A, 18B and the outer wall 26 may be biased independently of each other, for example, in the case where the movable mass 12 includes an insulating region. For example, the rotor electrodes 21A, 21B may be formed by different structures (e.g., protrusions) integrally coupled to the movable mass 12.

[0164] The applicant has verified that MEMS accelerometers can be more sensitive to the phenomena of static friction and electrostatic contributions compared to other MEMS sensors; thus, the present disclosure has been described above with reference to MEMS accelerometers. However, the present disclosure may refer to different types of MEMS sensors, such as inertial sensors, such as, for example, gyroscopes configured to measure the rotation of the MEMS sensor, or non-inertial MEMS sensors for measuring different physical quantities, wherein the MEMS sensor has a movable mass suspended on a substrate and configured to undergo movement relative to the substrate depending on the physical quantity to be measured, and wherein the measurement of the physical quantity is based on capacitive sensing, i.e., by applying a voltage difference between the movable mass (e.g., a rotor electrode integral therewith) and the stator electrodes (integral with the substrate) and sensing the change in capacitance between the movable mass and the stator electrodes.

[0165] Finally, the different embodiments described above may be combined to provide other solutions.

[0166] A MEMS sensor (1; 100) configured to measure a physical quantity can generally be summarized as including: a substrate (10); a movable mass (12; 112), the movable mass (12; 112) being suspended at a distance from the substrate along a first direction (Z), the movable mass being coupled to the substrate to undergo a movement (M, M′, M″) relative to the substrate along a sensing direction (S; S′) according to the physical quantity to be measured; a contact sensing structure (30; 130), the contact sensing structure (30; 130) being coupled to the substrate and, at rest, extending at a first distance (g SW ) from the movable mass along the sensing direction; at least one stator electrode (18A, 18B; 118A, 118B), the at least one stator electrode (18A, 18B; 118A, 118B) being coupled to the substrate and configured to form at least one capacitor with the movable mass, the at least one capacitor having a variable capacitance according to the movement of the movable mass; and a control circuit (5), wherein the control circuit is configured to: sense a voltage difference between the movable mass (12; 112) and the at least one stator electrode (18A, 18B; 118A, 118B) for sensing a change in capacitance between the movable mass and the at least one stator electrode; sense contact between the movable mass (12; 112) and the contact sensing structure (30; 130); and in response to sensing contact between the movable mass and the contact sensing structure, modify the sensed voltage difference between the movable mass (12; 112) and the at least one stator electrode (18A, 18B; 118A, 118B) to reduce the electrostatic force exerted on the movable mass by the at least one stator electrode.

[0167] The control circuit may be configured to modify the voltage difference to zero the electrostatic force exerted on the movable mass by the at least one stator electrode.

[0168] The control circuit may be configured to modify the voltage difference between the movable mass and the at least one stator electrode within a time interval greater than 5 ms, specifically between 5 ms and 30 ms.

[0169] The control circuit (5) may be configured to apply a rotor voltage (V ROT ) to the movable mass and a stator voltage (V STAT ) different from the rotor voltage to the at least one stator electrode in order to sense the voltage difference between the movable mass (12; 112) and the at least one stator electrode (18A, 18B; 118A, 118B).

[0170] One of the rotor voltage and the stator voltage may be a first value (V cm) and the other of the rotor voltage and the stator voltage may be a varying voltage.

[0171] The control circuit (5) may be configured to apply a voltage difference between the movable mass (12; 112) and the contact sensing structure (30) and monitor the contact current (I C ) between the movable mass and the contact sensing structure in order to sense the contact between the movable mass and the contact sensing structure.

[0172] The contact sensing structure (30; 130) may extend at least partially facing the movable mass (12; 112) parallel to the sensing direction (S; S').

[0173] At least one of the contact sensing structure (30) and the movable mass (112) may include a deformable region (33; 133) configured to undergo elastic deformation along the sensing direction (S; S') in response to the contact between the movable mass and the contact sensing structure.

[0174] The MEMS sensor is configured such that the movable mass (12; 112) may contact the contact sensing structure (30; 130) before contacting at least one stator electrode in response to movement along the sensing direction (S; S'). For example, at least one stator electrode (18A, 18B) may extend at a second distance (g el ) from the movable mass along the sensing direction when at rest, and the second distance (g el ) is greater than the first distance (g SW ).

[0175] The MEMS sensor may further include a stop region (25; 130, 137) configured to determine the maximum movement of the movable mass (12; 112) along the sensing direction (S; S'), and the maximum movement is less than the movement along the sensing direction that would cause the movable mass to contact at least one stator electrode.

[0176] The MEMS sensor may be configured such that the movable mass (12; 112) contacts the contact sensing structure (30; 130) in response to movement along the sensing direction (S; S') that is less than the maximum movement.

[0177] The MEMS sensor may be an inertial sensor and the quantity to be measured may be the acceleration or rotation of the MEMS sensor. Specifically, the MEMS sensor may be a MEMS accelerometer and the physical quantity to be measured may be the acceleration of the MEMS sensor.

[0178] The MEMS sensor can be an in-plane MEMS accelerometer (1) or an out-of-plane MEMS accelerometer (100). The in-plane MEMS accelerometer (1) is configured to sense acceleration along a second direction (Y), which is transverse to a first direction (Z). The out-of-plane MEMS accelerometer (100) is configured to sense acceleration along the first direction (Z).

[0179] A method for controlling a MEMS sensor configured to measure a physical quantity, the MEMS sensor can be generally summarized as including: a substrate (10); a movable mass (12; 112) suspended at a distance from the substrate along a first direction (Z), wherein the movable mass is coupled to the substrate to experience a movement (M, M′, M″) relative to the substrate along a sensing direction (S; S′) according to the physical quantity to be measured; a contact sensing structure (30; 130) coupled to the substrate and extending at a first distance (g SW ) from the movable mass along the sensing direction when at rest; and at least one stator electrode (18A, 18B; 118A, 118B) coupled to the substrate and configured to form at least one capacitor with the movable mass, the at least one capacitor having a capacitance variable according to the movement of the movable mass; the method includes, by a control circuit of the MEMS sensor: inducing a voltage difference between the movable mass (12; 112) and the at least one stator electrode (18A, 18B; 118A, 118B) for sensing a change in capacitance between the movable mass and the at least one stator electrode; sensing a contact between the movable mass (12; 112) and the contact sensing structure (30; 130); and in response to sensing the contact between the movable mass and the contact sensing structure, modifying the voltage difference between the movable mass (12; 112) and the at least one stator electrode (18A, 18B; 118A, 118B) to reduce the electrostatic force applied by the at least one stator electrode on the movable mass.

[0180] The various embodiments described above can be combined to provide other embodiments. Aspects of the embodiments can be modified as needed to incorporate concepts from various patents, applications, and publications to provide other embodiments.

[0181] These and other changes can be made to the embodiments in light of the above detailed description. In general, in the appended claims, the terms used should not be construed as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be construed to include all possible embodiments and the full scope of equivalents to such claims. Thus, the claims are not limited by the present disclosure.

Claims

1. A MEMS sensor configured to measure a physical quantity, the MEMS sensor comprising: A substrate; A movable mass suspended at a distance from the substrate in a first direction, the movable mass being coupled to the substrate to undergo movement relative to the substrate in a sensing direction in accordance with the physical quantity to be measured; A contact sensing structure coupled to the substrate and, at rest, extending at a first distance from the movable mass in the sensing direction; At least one stator electrode coupled to the substrate and configured to form at least one capacitor with the movable mass, the at least one capacitor having a variable capacitance in accordance with the movement of the movable mass; And A control circuit, Wherein the control circuit is configured to: Sense a voltage difference between the movable mass and the at least one stator electrode for sensing a change in capacitance between the movable mass and the at least one stator electrode; Sense contact between the movable mass and the contact sensing structure; In response to sensing the contact between the movable mass and the contact sensing structure, modify the sensed voltage difference between the movable mass and the at least one stator electrode to reduce the electrostatic force applied by the at least one stator electrode on the movable mass towards zero.

2. The MEMS sensor according to claim 1, wherein the control circuit is configured to modify the voltage difference to zero the electrostatic force applied by the at least one stator electrode on the movable mass.

3. The MEMS sensor according to claim 1, wherein the control circuit is configured to modify the voltage difference between the movable mass and the at least one stator electrode within a time interval greater than 5 ms, the time interval being specifically between 5 ms and 30 ms.

4. The MEMS sensor according to claim 1, wherein, in order to sense the voltage difference between the movable mass and the at least one stator electrode, the control circuit is configured to apply a rotor voltage to the movable mass and a stator voltage to the at least one stator electrode, the stator voltage being different from the rotor voltage.

5. The MEMS sensor according to claim 4, wherein one of the rotor voltage and the stator voltage is a DC voltage having a first value, and the other of the rotor voltage and the stator voltage is a varying voltage.

6. The MEMS sensor according to claim 1, wherein, in order to sense contact between the movable mass and the contact sensing structure, the control circuit is configured to apply the voltage difference between the movable mass and the contact sensing structure and monitor the contact current between the movable mass and the contact sensing structure.

7. The MEMS sensor according to claim 1, wherein the contact sensing structure extends at least partially towards the movable mass parallel to the sensing direction.

8. The MEMS sensor according to claim 1, wherein at least one of the contact sensing structure and the movable mass includes a deformable region configured to undergo elastic deformation along the sensing direction in response to the contact of the movable mass with the contact sensing structure.

9. The MEMS sensor according to claim 1, configured such that the movable mass contacts the contact sensing structure before contacting the at least one stator electrode in response to movement along the sensing direction, the at least one stator electrode extending at a second distance from the movable mass along the sensing direction at rest, the second distance being greater than the first distance.

10. The MEMS sensor according to claim 1, further comprising a stop region configured to determine a maximum movement of the movable mass along the sensing direction, the maximum movement being less than the movement along the sensing direction that would cause the movable mass to contact the at least one stator electrode.

11. The MEMS sensor according to claim 10, configured such that the movable mass contacts the contact sensing structure in response to movement along the sensing direction that is less than the maximum movement.

12. The MEMS sensor according to claim 1, wherein the MEMS sensor is an inertial sensor, and wherein the quantity to be measured is the acceleration or rotation of the MEMS sensor, specifically wherein the MEMS sensor is a MEMS accelerometer and the physical quantity to be measured is the acceleration of the MEMS sensor.

13. The MEMS sensor according to claim 12, wherein the MEMS sensor is: an in-plane MEMS accelerometer configured to sense acceleration along a second direction transverse to the first direction; or an out-of-plane MEMS accelerometer configured to sense acceleration along the first direction.

14. A method for controlling a MEMS sensor configured to measure a physical quantity, the method comprising: The MEMS sensor includes: a substrate; a movable mass suspended at a distance from the substrate along a first direction, wherein the movable mass is coupled to the substrate to undergo movement relative to the substrate along a sensing direction according to the physical quantity to be measured; a contact sensing structure coupled to the substrate and extending at a first distance from the movable mass along the sensing direction at rest; and At least one stator electrode, the at least one stator electrode being coupled to the substrate and configured to form at least one capacitor with the movable mass, the at least one capacitor having a capacitance that can vary according to the movement of the movable mass; Controlling the MEMS sensor using a control circuit, and controlling the MEMS sensor using a control circuit includes: Inducing a voltage difference between the movable mass and the at least one stator electrode for sensing a change in capacitance between the movable mass and the at least one stator electrode; Sensing contact between the movable mass and the contact sensing structure; In response to sensing the contact between the movable mass and the contact sensing structure, modifying the voltage difference between the movable mass and the at least one stator electrode to zero the electrostatic force applied by the at least one stator electrode on the movable mass.

15. The method according to claim 14 further comprises: Moving the movable mass away from a rest position, at which the at least one stator electrode extends at a second distance from the movable mass along the sensing direction, the second distance being greater than the first distance.

16. The method according to claim 15, further comprising: Bringing a stop region into contact with the movable mass; Determining a maximum movement of the movable mass along the sensing direction, the maximum movement being less than a movement along the sensing direction that would cause the movable mass to contact the at least one stator electrode.

17. An apparatus, comprising: A substrate; A movable mass suspended at a distance from the substrate along a first direction, the movable mass being coupled to the substrate to undergo movement along a sensing direction according to a physical quantity to be measured; A contact sensing structure coupled to the substrate, the contact sensing structure being spaced apart from the movable mass by a first distance when the movable mass is in a rest position; At least one stator electrode coupled to the substrate and configured to form at least one capacitor with the movable mass, the at least one capacitor having a variable capacitance according to the movement of the movable mass, the at least one stator electrode being spaced apart from the movable mass by a second distance when the movable mass is in the rest position, the second distance being greater than the first distance; And A stop region coupled to the substrate and configured to stop the movable mass at a maximum position, the stop region being spaced apart from the movable mass by a third distance when the movable mass is in the rest position, the third distance being greater than the first distance and less than the second distance; A control circuit configured to: Induce a voltage difference between the movable mass and the at least one stator electrode; Sense contact between the movable mass and the contact sensing structure; Modify the induced voltage difference between the movable mass and the at least one stator electrode to zero the electrostatic force applied by the at least one stator electrode on the movable mass.

18. The apparatus according to claim 17, wherein the contact sensing structure is configured to elastically deflect by a deflection distance equal to the difference between the first distance and the third distance.

19. The apparatus according to claim 17, wherein the movable mass is elastically coupled to the anchoring region by a coupling elastic element.

20. The apparatus according to claim 17, wherein the movable mass includes a central opening, and the at least one stator electrode is within the central opening of the movable mass.

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