CN221764498U - MEMS device and electronic device - Google Patents

Abstract

The present disclosure relates to MEMS devices and electronic devices. The MEMS device is formed of a substrate and a movable structure suspended from the substrate. The movable structure has a first mass, a second mass, and a first elastic set mechanically coupled therebetween. The first elastic set is compliant in a first direction. The first mass is configured to move relative to the substrate in a first direction. The MEMS device further has: a second elastic set mechanically coupled between the substrate and the movable structure and compliant in the first direction; and an anchor control structure secured to the substrate, capacitively coupled to the second mass, and configured to apply an electrostatic force on the second mass in the first direction. The anchor control structure controls the MEMS device in a first operational state in which the second mass is free to move relative to the substrate in a first direction, and controls the MEMS device in a second operational state in which the anchor control structure exerts a pull-in force on the second mass that anchors the second mass to the anchor structure.

Description

MEMS device and electronic device

Technical Field

The present disclosure relates to a MEMS device having improved detection performance, and in particular, to an inertial sensor having improved detection performance.

Background

As is well known, inertial sensors of the MEMS ("microelectromechanical system") type, such as accelerometers and gyroscopes, are widely used due to their small size and high detection sensitivity.

MEMS inertial sensors are integrated into a variety of electronic devices such as wearable devices, smart phones, notebook computers, and the like.

Common applications for such inertial sensors include: impact monitoring, for example, to detect car accidents or that a person may fall to the ground; detecting a gesture of a user, such as a rotation of a screen of a smart phone or a specific type of user touch; and as a bone conduction detector, for example as a microphone in a real wireless stereo (TWS) headset.

With specific reference to MEMS accelerometers, low G accelerometers are currently known to be used to detect low accelerations, e.g., having a Full Scale Range (FSR) equal to 16G or 32G, while high G sensors are used to detect high accelerations, e.g., having a full scale range equal to 128G.

It is also known that FSR and measurement sensitivity (i.e. displacement of the movable detection structure of the inertial sensor per unit of applied acceleration) are inversely proportional to each other. Thus, a high G sensor has a high FSR but low sensitivity, and a low G sensor has a low FSR but high sensitivity.

According to one method, two movable detection structures separated from each other are integrated in the same MEMS device in order to detect both low and high accelerations.

However, the simultaneous presence of two different movable detection structures in the same MEMS device creates disadvantages such as the need for a greater number of pads and a higher complexity of the required control circuitry (e.g., dedicated ASIC, PCB or CPU, etc.), and more generally, a larger integration area, lower portability of the electronic device and higher manufacturing costs.

Disclosure of utility model

According to the present disclosure, there is thus provided a MEMS device and an electronic device.

According to a first aspect, a MEMS device is provided. The MEMS device includes a substrate; a movable structure suspended on the substrate, and an anchor control structure. The movable structure comprises a first mass block, a second mass block, a first elastic group and a second elastic group. The first spring set is mechanically coupled between the first mass and the second mass, the first spring set being compliant along a first direction, the first mass being configured to move relative to the substrate along the first direction. The second elastic set is mechanically coupled between the substrate and the movable structure, the second elastic set being compliant along the first direction. An anchor control structure is secured to the substrate, capacitively coupled to the second mass, and configured to apply an electrostatic force on the second mass along the first direction. The anchoring control structure is configured to: the MEMS device is controlled to be in a first operational state in which the second mass is free to move relative to the substrate in a first direction, and the MEMS device is controlled to be in a second operational state in which the anchor control structure exerts a pull-in electrostatic force on the second mass that enables anchoring of the second mass to the anchor structure, thereby preventing movement of the second mass relative to the substrate in response to movement of the first mass.

In some embodiments, the anchoring control structure includes a stop secured to the substrate, the stop extending along a first direction at a first distance from the second mass in a first operating state when at rest, and contacting the second mass in a second operating state.

In some embodiments, the anchor control structure further comprises a control electrode fixed to the substrate and extending at a second distance from the second mass along the first direction in the first operating state when at rest.

In some embodiments, the first distance is less than the second distance.

In some embodiments, the anchoring control structure includes a control electrode, the second mass having an outer wall and a through cavity having an inner wall, the control electrode being disposed inside the through cavity facing the inner wall, the stop facing the outer wall of the second mass.

In some embodiments, the second elastic set is coupled to the first mass such that in the first operating state the first mass is coupled to the substrate through the second elastic set and in the second operating state the first mass is coupled to the substrate through the first elastic set and the second elastic set, the first elastic set and the second elastic set being mechanically arranged in parallel between the first movable mass and the substrate.

In some embodiments, the second elastic set is coupled to the second mass such that in the first operating state the first mass is coupled to the substrate through the first elastic set and the second elastic set, the first elastic set and the second elastic set being mechanically arranged in series between the first movable mass and the substrate, and in the second operating state the first mass is coupled to the substrate through the first elastic set.

In some embodiments, the movable structure further comprises a third mass and a third spring set mechanically coupling the first mass to the third mass, and the third spring set is compliant along the first direction, the second mass is disposed on a first side of the first mass, and the third mass is disposed on a second side of the first mass other than the first side, wherein the anchor control structure is a first anchor control structure, the MEMS device further comprising a second anchor control structure secured to the substrate, capacitively coupled to the third mass, and configured to: the MEMS device is controlled to be in a third operational state in which the third mass is free to move relative to the substrate along the first direction, and the MEMS device is controlled to be in a fourth operational state in which the second anchoring control structure exerts a pull-in electrostatic force on the third mass that enables anchoring of the third mass to the second anchoring structure, thereby preventing movement of the third mass relative to the substrate in response to movement of the first mass.

In some embodiments, the MEMS device further comprises a detection structure configured to detect movement of the first mass along the first direction.

In some embodiments, the first mass is configured to move along a first direction in response to movement of the MEMS device.

According to a second aspect, there is provided an electronic device comprising: the device comprises a substrate, a first mass including a first opening, a plurality of first electrodes, a first stopper, a second stopper, and a third mass. The first mass includes a first side opposite the second side, a third side transverse to the first side, and a fourth side opposite the third side. A plurality of first electrodes are fixed to the substrate and in the first openings. The second stop is spaced apart from the first stop by the first mass. The second mass is coupled to a third side of the first mass. The third mass is coupled to the fourth side of the first mass, and the second mass is spaced apart from the second stop by the third mass and the first mass.

In some embodiments, the plurality of second electrodes extend from the first mass into the opening toward the plurality of first electrodes.

In some embodiments, the electronic device includes a plurality of first elastic elements, a plurality of second elastic elements, a plurality of third elastic elements, and a plurality of fourth elastic elements. A plurality of first elastic elements extend from a first side of the first mass. A plurality of second elastic elements extend from the second side of the first mass. A plurality of third spring elements extend from a third side of the first mass and are coupled to the second mass. A plurality of fourth elastic elements extend from a fourth side of the first mass and are coupled to the third mass.

In some embodiments, the electronic device includes a plurality of second electrodes in each of a plurality of second openings in the second mass.

In some embodiments, the electronic device includes a plurality of third electrodes in each of a plurality of third openings in the third mass.

Drawings

For a better understanding of the present disclosure, some embodiments thereof are now described, purely by way of non-limiting example, with reference to the accompanying drawings, in which:

FIG. 1 illustrates a top view of the present MEMS device according to one embodiment;

FIG. 1A shows a top view of an enlarged portion of the MEMS device of FIG. 1;

FIG. 2 shows a top view of the MEMS device of FIG. 1 in an operating condition;

FIG. 2A shows a top view of an enlarged portion of the MEMS device of FIG. 1 in the operating condition of FIG. 2;

FIG. 3 illustrates a top view of the present MEMS device in accordance with various embodiments;

FIG. 4 shows a top view of the MEMS device of FIG. 3 in an operating condition;

FIG. 5 illustrates a top view of the present MEMS device according to another embodiment; and

Fig. 6 shows a top view of the MEMS device of fig. 5 in an operating condition.

Detailed Description

Fig. 1 shows a MEMS device 20, in particular a single axis MEMS accelerometer, in a Cartesian (Cartesian) reference system XYZ comprising a first axis X, a second axis Y and a third axis Z.

In fig. 1, only elements useful for understanding the present embodiment are shown, and elements or components not relevant to the present disclosure are not shown, although present in the final MEMS device.

MEMS device 20 is formed from a body of semiconductor material (e.g., silicon) by micromachining techniques.

In the illustrated embodiment, MEMS device 20 has a first axis of symmetry a and a second axis of symmetry B that are parallel to first axis X and second axis Y, respectively.

The MEMS device 20 comprises a substrate 21, a movable structure 22 suspended on the substrate 21, and one or more elastic support elements, here four elastic support elements 23, mechanically coupling the movable structure 22 to the substrate 21.

The movable structure 22 and the elastic support element 23 are formed starting from a layer of semiconductor material, for example silicon or polysilicon, and form a substantially planar structure with a main extension in the XY-plane.

The elastic support element 23 and the movable structure 22 extend along the third axis Z at a distance from the substrate 21.

The elastic support element 23 is a folded flexure (flexure) and is configured to allow the movable structure 22 to move according to one or more degrees of freedom, here along a detection direction parallel to the second axis Y.

In detail, the elastic support elements 23 each extend between a respective anchoring region 25 fixed to the substrate 21 and the movable structure 22.

The movable structure 22 includes a proof mass (mass) 28, first and second control masses 29A and 29B, and first and second elastic coupling elements 30A and 30B, respectively, mechanically coupling the first and second control masses 29A and 29B to the proof mass 28.

The first resilient coupling element 30A and the second resilient coupling element 30B are folded flexures configured to deform in one or more directions, here parallel to the second axis Y.

The first elastic coupling element 30A and the second elastic coupling element 30B may have equal or different elastic constants along the detection direction, in which case the elastic constants are different and in particular larger with respect to the elastic support element 23.

The elastic support elements 23 extend from the left and right sides of the proof mass 28 as shown in fig. 1. The first extension of the elastic support element 23 is along the first axis X. First and second spring coupling elements 30A and 30B extend from the top and bottom sides of proof mass 28, as shown in fig. 1. These sides may be referred to as first and second sides (left and right) and third and fourth sides (top and bottom). The first extension of the second resilient coupling element is along the second axis Y. The first extension of the elastic support element 23 is transverse to the adjacent first extension from the other support element. At each corner of the proof mass 28, each of the first and second resilient support elements extends in a transverse direction to each other.

In detail, a first control mass 29A extends at a first side of the proof mass 28 and a second proof mass 29B extends at a second side of the proof mass 28 opposite the first side with respect to the first symmetry axis a.

The first elastic coupling element 30A extends parallel to the second axis Y between the first control mass 29A and the proof mass 28. The second elastic coupling element 30B extends parallel to the second axis Y between the second control mass 29B and the proof mass 28.

MEMS device 20 further includes a first control electrode 33A and a second control electrode 33B, which first control electrode 33A and second control electrode 33B are fixed to substrate 21 and capacitively coupled to first control mass 29A and second control mass 29B, respectively.

The first control electrode 33A and the second control electrode 33B are formed of a semiconductor material (e.g., silicon or polysilicon).

The first and second control electrodes 33A, 33B are configured to cause displacement of the first and second control masses 29A, 29B, respectively, along the detection direction.

In detail, three first through cavities (through-cavities) 35A extend through the thickness of the first control mass 29A along the third axis Z through the first control mass 29A, and three second through cavities 35B extend through the thickness of the second control mass 29B along the third axis Z through the second control mass 29B.

For each of the respective through cavities 35A, 35B, the first and second control masses 29A, 29B have first and second inner walls 36, 37, as shown in detail in the enlarged view of fig. 1A for the first through cavity 35A.

For each of the first and second through cavities 35A, 35B, the first inner wall 36 is arranged parallel to the second axis Y at a smaller distance from the proof mass 28 than the second inner wall 37. In other words, the first inner wall 36 is arranged towards the center of the movable structure 22, and the second inner wall 37 is arranged towards the outside of the movable structure 22.

In this embodiment, referring to the first through cavity 35A, the first inner wall 36 and the second inner wall 37 extend parallel to the first axis X on opposite sides of the first through cavity 35A from each other along the second axis Y.

The first control electrodes 33A are each disposed inside a corresponding first through cavity 35A. The second control electrodes 33B are each arranged inside a corresponding second through cavity 35B.

In detail, for simplicity, referring again to the first control mass 29A, the first control electrode 33A extends parallel to the second axis Y at a distance d ₁ from the first inner wall 36 and a distance d ₂ from the second inner wall 37.

Distance d ₁, for example comprised between 1.8m and 5m, is smaller than distance d ₂.

For example, the distance d ₁ may be greater than the stroke value of the MEMS device 20, i.e., greater than the maximum displacement that the movable structure 22 may experience in use parallel to the second axis Y.

For example, distance d ₂ may be equal to distance d ₁ plus a factor that may be selected based on the stroke value of MEMS device 20, depending on the particular application.

MEMS device 20 further comprises a first stopper 40A and a second stopper 40B, which first stopper 40A and second stopper 40B are fixed to substrate 21 and extend parallel to second axis Y at a distance from first control mass 29A and second control mass 29B, respectively. The first stop and the second stop are fixed anchoring structures.

In detail, referring to the enlarged portion of fig. 1A, the first stop 40A has a wall 42 facing an outer wall 43 of the first control mass 29A.

The outer wall 43 of the first control mass 29A extends parallel to the second axis Y at a distance d ₃ from the wall 42 of the first stop 40A.

The distance d ₃ between the first control mass 29A and the first stop 40A may be the same or different, in particular smaller here, with respect to the distance d ₁ between the first inner wall 36 of the first through cavity 35A and the respective first control electrode 33A.

The distance d ₃ may be greater than or equal to the stroke value of the MEMS device 20. In this embodiment, the distance d ₃ is equal to, and thus defines, the stroke value of the MEMS device 20.

The first stop 40A has a dimension along a first axis X that is substantially the same as the dimension of the proof mass 28 along the same first axis.

Although not shown in detail, what has been described for the first stopper 40A and the first control electrode 33A also applies to the second stopper 40B and the second control electrode 33B.

The MEMS device 20 further comprises first and second voltage applying means 45A, 45B, which are only schematically represented in fig. 1, the first and second voltage applying means 45A, 45B comprising a first and second conductive trace 46A, 46B, respectively, the first and second conductive trace 46A, 46B extending over the substrate 21 and being indicated in fig. 1 by dashed lines for simplicity.

For example, the first voltage applying device 45A and the second voltage applying device 45B may further include contact pads and bonding wires, and be configured to supply control voltages to the first control electrode 33A and the second control electrode 33B, respectively.

The MEMS device 20 further comprises a detection structure 50, which detection structure 50 is of the capacitive type and is configured to detect a movement of the proof mass 28 along a detection direction.

In the illustrated embodiment, the detection structure 50 includes a first detection capacitor 51A and a second detection capacitor 51B of a comb type.

In detail, the first and second detection capacitors 51A, 51B each include a plurality of stator electrodes 53A, 53B fixed to the substrate 21 and a plurality of rotor electrodes 54A, 54B integrated with the detection mass 28. The stator electrodes 53A, 53B are interleaved with the corresponding rotor electrodes 54A, 54B.

In the illustrated embodiment, the cavity 60 extends through the thickness of the proof mass 28 parallel to the third axis Z through the proof mass 28. Indeed, in the illustrated embodiment, the proof mass 28 has a frame shape. The stator electrodes 53A, 53B are arranged inside the cavity 60, and the rotor electrodes 54A, 54B are formed by protrusions of the proof mass 28, which protrusions extend towards the inside of the cavity 60.

In use, the MEMS device 20 is configured to detect acceleration of the same MEMS device 20 along a detection direction (here parallel to the second axis Y).

The MEMS device 20 may be controlled in a sensitive or low acceleration operating state that may be used to detect low acceleration values, such as up to 16g or 32g, and in a high-band or high acceleration operating state that may be used to detect high acceleration values, such as up to 128g, where g represents an earth gravitational acceleration value equal to about 9.81m/s ².

In the sensitive operation state, zero voltage is applied to the first control electrode 33A and the second control electrode 33B. Thus, in a sensitive operating state, the MEMS device 20 has the configuration shown in fig. 1 at equilibrium or rest (for zero acceleration values).

In the sensitive operation state, when the MEMS device 20 is subjected to acceleration in the detection direction, an inertial force parallel to the detection direction is exerted on the movable structure 22. The inertial force causes displacement of the movable structure 22 relative to the equilibrium position.

In response to displacement from the equilibrium position, a resilient return force (return force) acts on the movable structure 22. The elastic return force has an opposite direction relative to the inertial force.

In a sensitive operating condition, an elastic return force is exerted on the movable structure 22 by the elastic support element 23. The modulus of the elastic return force is thus a function of the elastic constant k ₁ of the elastic support element 23.

In fact, in a sensitive operating condition, the movable structure 22 moves as a single body along the detection direction.

As a first approximation, the movable structure 22 has a total mass equal to m+2m, where M is the mass of the proof mass 28 and M is the mass values of the first and second control masses 29A, 29B, by ignoring the masses of the first and second elastic coupling elements 30A, 30B. Accordingly, the MEMS device 20 has a differential in sensitive operating conditionsThe resonance frequency f ₁ is given.

Fig. 2 shows MEMS device 20 in equilibrium or rest (for zero acceleration values) in the high-band operating state.

In the high-band operation state, the voltage V _p is applied to the first control electrode 33A and the second control electrode 33B by the first voltage applying device 45A and the second voltage applying device 45B.

Hereinafter, the operation of the MEMS device 20 in the high-band operation state will be described with reference to the first control mass 29A, the first control electrode 33A, the first stopper 40A, and the first elastic coupling element 30A. However, what will be described also applies to the second control mass 29B, the second control electrode 33B, the second stopper 40B and the second elastic coupling element 30B.

The voltage V _p is greater than or equal to the pull-in (pull-in) voltage between the first control electrode 33A and the corresponding first inner wall 36 of the first movable mass 29A.

In effect, the first control mass 29A and the first control electrode 33A are in a pull-in condition in the high band operating state.

The voltage V _p generates an attractive electrostatic force (arrow F _c1 of fig. 2) between the first inner wall 36 of the first movable mass 29A and the first control electrode 33A. Since the first control electrode 33A is fixed to the substrate 21, the voltage V _p causes displacement of the first control mass 29A towards the first control electrode 33A.

As shown in detail in fig. 2A, at equilibrium, in the high-band operating state, the first inner wall 36 of the first through cavity 35A is at a distance d' ₁ smaller than the distance d ₁ shown in fig. 1A, relative to the first operating state.

Referring again to fig. 2, the voltage V _p also causes the second movable mass 29B, and in particular the corresponding first inner wall 36, to move towards the second control electrode 33B (electrostatic force indicated by arrow F _c2 of fig. 2).

In detail, in the illustrated embodiment, the electrostatic force F _c1 and the electrostatic force F _c2 are equal in modulus and have opposite directions; thus, at equilibrium, without external acceleration, the elastic support element 23 remains undeformed and the proof mass 28 does not undergo a displacement with respect to the rest position.

At equilibrium, the first resilient coupling element 30A exerts a resilient return force (upwards in fig. 2) on the first control mass 29A. However, since the voltage V _p is equal to or greater than the pull-in voltage, the elastic return force on the first control mass 29A is lower than the electrostatic attractive force F _c1 exerted on the first control mass 29A by the first control electrode 33A.

Thus, in the high-band operating state, the resultant forces directed towards the first and second stops 40A, 40B, respectively, act on the first and second control masses 29A, 29B in the absence of external accelerations. The resultant force keeps the first and second control masses 29A, 29B in contact with the first and second stops 40A, 40B, respectively.

In fact, in the high-band operating condition, the first control mass 29A and the second control mass 29B form further anchoring elements of the substrate 21 of the proof mass 28.

Furthermore, the voltage V _p makes it possible to maintain the first control mass 29A and the first control electrode 33A in the pull-in condition and to maintain the second control mass 29B and the second control electrode 33B in the pull-in condition even when the MEMS device 20 is subjected to acceleration in the detection direction.

Thus, when MEMS device 20 experiences such accelerations, the corresponding inertial forces applied to movable structure 22 cause only proof mass 28 to move.

In fact, even in the presence of acceleration, the first and second control masses 29A and 29B remain fixed to the first and second stops 40A and 40B, and the proof mass 28 moves relative to the first and second control masses 29A and 29B.

For example, MEMS device 20 may be configured to operate in a detection direction in the presence of an acceleration that is less than or equal to a maximum expected acceleration value (e.g., determinable during a design step depending on the particular application). By way of example, with reference to the first control electrode 33A and the first control mass 29A, when the MEMS device 20 is subjected in use to an acceleration equal to a maximum expected acceleration value, the proof mass 28 undergoes a maximum displacement relative to the substrate 21 along the detection direction. Thus, the voltage V _p may be selected such that the corresponding pull-in force exerted by the first control electrode 33A on the first control mass 29A is greater than the sum of the elastic return force exerted by the first elastic coupling element 30A on the first control mass 29A in response to the maximum displacement of the proof mass 28 and the apparent force (application force) experienced by the first control mass 29A in response to the maximum expected acceleration value of the MEMS device 20.

It follows that in the presence of acceleration, in the high-band operating state, the proof mass 28 experiences an elastic return force that is a function of not only the elastic constant k ₁ of the elastic support element 23, but also the elastic constants k ₂ of the first and second elastic coupling elements 30A and 30B.

In the high-band operating state, the first and second elastic coupling elements 30A and 30B are mechanically arranged in parallel with the elastic support element 23 between the proof mass 28 and the substrate 21.

Thus, under high-band operating conditions, MEMS device 20, and in particular proof mass 28, has an equivalent elastic constant k _eq, which is a function of the sum of elastic constants k ₁、k₂, k _eq.

As a first approximation, by here also ignoring the masses of the first elastic coupling element 30A and the second elastic coupling element 30B, the movable structure 22 has a total mass equal to M, i.e. corresponding to a unique proof mass 28.

Accordingly, the MEMS device 20 has a high-frequency band operating state defined by The resonance frequency f ₂ is given.

By appropriately selecting the value of the elastic constant k ₁、k₂ and the value of the mass M, m during the design step, the value of the resonant frequency f ₁、f₂ of the MEMS device 20 can be adjusted, and thus the detection properties of the MEMS device 20 in the first and second operating states can be adjusted.

In the illustrated embodiment, the resonant frequency f ₂ is greater than the resonant frequency f ₁.

Accordingly, in the sensitive operating state, the MEMS device 20 has a higher detection sensitivity relative to the high-band operating state. In the high-band operating state, the MEMS device 20 has a larger full-scale range relative to the sensitive operating state.

Thus, the MEMS device 20 may be used to detect both low and high acceleration values.

Furthermore, referring to fig. 1A, in MEMS device 20, at rest, the distance d ₃ between first control mass 29A and first stop 40A is smaller than the distance d ₁ between first inner wall 36 and first control electrode 33A, which fact causes first control mass 29A to be anchored to first stop 40A and not collide with first control electrode 33A in the pulled-in condition. This makes it possible to avoid a short circuit between the first wall 36 and the first electrode 33A.

Fig. 3 illustrates a different embodiment of the present MEMS device, here indicated at 120. MEMS device 120 has a general structure similar to that of MEMS device 20 of fig. 1; thus, common elements are indicated by the same reference numerals and are not further described.

In detail, the MEMS device 120 comprises a substrate 21, a movable structure 122 and an elastic support element, in particular a first elastic support element 123A and a second elastic support element 123B, which first elastic support element 123A and second elastic support element 123B mechanically couple the movable structure 122 to the substrate 21.

Also in this embodiment, the movable structure 122 includes a proof mass 28, first and second control masses 29A and 29B, and first and second elastic coupling elements 30A and 30B.

In the MEMS device 120, a first elastic support element 123A and a second elastic support element 123B are coupled to a first control mass 29A and a second control mass 29B, respectively.

In detail, the first elastic support elements 123A each extend between the respective anchoring region 25A and the first control mass 29A, and the second elastic support elements 123B each extend between the respective anchoring region 25B and the second control mass 29B.

In fact, in the MEMS device 120 of fig. 3, the first elastic support element 123A and the second elastic support element 123B are mechanically arranged in series with the first elastic coupling element 30A and the second elastic coupling element 30B, respectively, between the proof mass 28 and the substrate 21.

The MEMS device 120 further comprises a first control electrode 33A and a second control electrode 33B, a first stopper 40A and a second stopper 40B, and a detection structure 50.

MEMS device 120 also includes voltage applying means, not shown herein, that allow a voltage to be applied to first control electrode 33A and second control electrode 33B, as discussed with reference to fig. 1.

Similar to what has been discussed with respect to MEMS device 20 of fig. 1, MEMS device 120 also has a sensitive operating state configured to detect low acceleration values, and a high-band operating state configured to detect high acceleration values.

In the sensitive operating state (fig. 3), a voltage lower than the pull-in voltage, in particular a zero voltage, is applied between the first control electrode 33A and the second control electrode 33B and the first and second control masses 29A and 29B.

In the first operating state, the MEMS device 20, and in particular the proof mass 28, has an equivalent elastic constant k _eq＝k₁·k₂/(k₁+k₂).

As a first approximation, the movable structure 122 here also has a total mass equal to m+2m by ignoring the masses of the first elastic coupling element 30A and the second elastic coupling element 30B. Thus, in a sensitive operating state, the MEMS device 120 has a structure consisting of The resonance frequency f ₁ is given.

In the high-band operating state (fig. 4), a voltage V _p is applied between the first control electrode 33A and the first control mass 29A and between the second control electrode 33B and the second control mass 29B, similar to that already discussed with reference to fig. 2.

In the presence of acceleration, the first and second control masses 29A, 29B remain in contact with the first and second stops 40A, 40B, respectively; and the proof mass 28 moves relative to the equilibrium position. In fact, here as well, under the pulled-in condition, the first mass 29A and the second mass 29B are electrostatically fixed to the first stopper 40A and the second stopper 40B, respectively.

Thus, in the presence of external accelerations, only the first and second elastic coupling elements 30A, 30B exert an elastic return force on the proof mass 28.

In practice, the equivalent elastic constant k _eq of the MEMS device 120 is equal to the elastic constant k ₂ of the first elastic coupling element 30A and the second elastic coupling element 30B.

Accordingly, the MEMS device 120 has a high-band operating state consisting ofThe resonance frequency f ₂ is given.

Indeed, the MEMS device 120 may also have both high sensitivity and a high full scale range.

Fig. 5 illustrates another embodiment of the present MEMS device, indicated generally at 220. MEMS device 220 has a general structure similar to that of MEMS device 20 of fig. 1; thus, common elements are indicated by the same reference numerals and are not further described.

In detail, the MEMS device 220 includes a substrate 21, a movable structure 222, and an elastic support element 23.

In this embodiment, the movable structure 222 is formed by the proof mass 28, the control mass 229, and one or more elastic coupling elements (here, two elastic coupling elements 230).

The control mass 229 and the elastic coupling element 230 are identical to the first control mass 29A and the first elastic coupling element 30A, respectively, of the MEMS device 20.

MEMS device 220 further includes a plurality of control electrodes 233 and stops 240, the control electrodes 233 and stops 240 being equivalent to first control electrode 33A and first stops 40A, respectively, of MEMS device 20 of fig. 1.

In fact, with respect to MEMS device 20 of fig. 1, MEMS device 220 does not have a second control mass, a second elastic coupling element, a second stopper, and a second control electrode.

In other words, MEMS device 220 is asymmetric parallel to the first X-axis.

The operation of MEMS device 220 is similar to that of MEMS device 20 of fig. 1 and MEMS device 120 of fig. 3, and thus will not be described in further detail.

Fig. 6 shows MEMS device 220 in a high-band operating state, wherein control electrode 233 and control mass 229 are in a pulled-in condition.

Thus, in a sensitive operating state (fig. 5), the equivalent elastic constant of the MEMS device 220 is a function of the elastic constant of the elastic support element 23. In the high-band operating state (fig. 6), the equivalent elastic constant of MEMS device 220 is a function of the elastic constants of both elastic support element 23 and elastic coupling element 230.

Accordingly, the MEMS device 220 also has high detection versatility, and can detect both a high acceleration value and a low acceleration value.

Furthermore, MEMS device 220 has a low die area footprint and, thus, may have low manufacturing costs.

Finally, it is clear that modifications and variations may be made to the MEMS device 20, 120, 220 described and illustrated herein, without departing from the scope of the present disclosure, as defined in the appended claims.

For example, the resilient support elements, anchor regions, stops, resilient coupling elements, throughbores of the control mass, etc. may differ in number and shape from what has been described and illustrated herein.

For example, the elastic support element and the elastic coupling element may be different types of flexures, such as linear flexures.

The detection structure 50 may comprise a different number of detection capacitors and/or the detection capacitors may be of different types, e.g. parallel plate capacitors.

Alternatively, the MEMS device may be based on detection principles other than capacitive principles. For example, the detection structure 50 may be configured to detect movement of the proof mass 28 according to piezoelectric or piezoresistive detection principles.

For example, the control electrode may be used to control the MEMS device in more than two of a plurality of operating states. For example, a voltage other than zero and lower than the pull-in voltage may be applied to the control electrode, which allows the elastic constant of the elastic support element and/or the elastic constant of the elastic coupling element to be modified due to the known electrostatic softening phenomenon.

Additionally or alternatively, referring to the MEMS device 20, 120, voltages different from each other may be applied to the first and second control electrodes, depending on the particular application. For example, the pull-in voltage may be applied to only the first control electrode or the second control electrode.

For example, the present MEMS device may be a dual-axis or tri-axis accelerometer. In this case, the movable structure may be configured to move in one or more directions. Alternatively, the MEMS device may comprise a plurality of movable structures suitably configured to each detect acceleration along a respective axis.

Furthermore, the MEMS device may be an inertial sensor other than an accelerometer, such as a gyroscope or a different type of MEMS sensor, configured to detect a physical quantity based on movement of the movable structure.

Finally, the described embodiments may be combined to form further solutions.

A MEMS device (20; 120; 220) may be summarized as including: a substrate (21); a movable structure (22; 122; 222) suspended on the substrate and comprising a first mass (28); a second mass (29A, 29B; 229); and a first elastic set (30A, 30B; 230) mechanically coupled between the first mass and the second mass, the first elastic set being compliant (complexant) along a first direction (Y), the first mass being configured to move relative to the substrate along the first direction; a second elastic group (23; 123A, 123B) mechanically coupled between the substrate and the movable structure, the second elastic group being compliant along the first direction; and an anchor control structure (33A, 40A, 33B, 40B;233, 240) secured to the substrate, capacitively coupled to the second mass (29A, 29B; 129), and configured to apply an electrostatic force on the second mass along a first direction, wherein the anchor control structure is configured to: the MEMS device is controlled to be in a first operational state in which the second mass is free to move relative to the substrate in a first direction, and the MEMS device is controlled to be in a second operational state in which the anchor control structure exerts a pull-in electrostatic force on the second mass that enables anchoring of the second mass to the anchor structure, thereby preventing movement of the second mass relative to the substrate in response to movement of the first mass.

The anchoring control structure may include a stop (40A, 40B; 240) fixed to the substrate, the stop extending along a first direction at a first distance (d ₃) from the second mass in a first operating state when at rest, and being in contact with the second mass in a second operating state.

The anchoring control structure may further comprise a control electrode (33A, 33B; 233) fixed to the substrate (21) and extending at a second distance (d ₁) from the second mass (29A, 29B) in a first direction in a first operating state when stationary.

The first distance may be less than the second distance.

The anchoring control structure may comprise a control electrode (33A, 33B; 233) having an outer wall (43) and a through cavity (35A, 35B) having an inner wall (36), the control electrode being arranged inside the through cavity facing the inner wall, the stop facing the outer wall of the second mass.

The second elastic group (23) may be coupled to the first mass (28) such that in the first operating state the first mass is coupled to the substrate by the second elastic group and in the second operating state the first mass is coupled to the substrate by the first elastic group and the second elastic group, the first elastic group and the second elastic group being mechanically arranged in parallel between the first movable mass and the substrate.

The second elastic group (123A, 123B) may be coupled to the second mass (29A, 29B) such that in the first operating state the first mass is coupled to the substrate through the first elastic group and the second elastic group, the first elastic group and the second elastic group being mechanically arranged in series between the first movable mass and the substrate, and in the second operating state the first mass is coupled to the substrate through the first elastic group.

The movable structure may further include a third mass (29B) and a third spring set (30B) mechanically coupling the first mass (28) to the third mass, and the third spring set being compliant along a first direction, the second mass being arranged on a first side of the first mass, the third mass being arranged on a second side of the first mass other than the first side, wherein the anchor control structure is a first anchor control structure (33A, 40A), the MEMS device may further include a second anchor control structure (33B, 40B) fixed to the substrate, capacitively coupled to the third mass (29B), and configured to: the MEMS device is controlled to be in a third operational state in which the third mass is free to move relative to the substrate along the first direction, and the MEMS device is controlled to be in a fourth operational state in which the second anchoring control structure exerts a pull-in electrostatic force on the third mass that enables anchoring of the third mass to the second anchoring structure, thereby preventing movement of the third mass relative to the substrate in response to movement of the first mass.

The MEMS device may further comprise a detection structure (50), the detection structure (50) being configured to detect a movement of the first mass (28) along the first direction (Y).

The first mass (28) may be configured to move along a first direction in response to movement of the MEMS device.

A method for controlling a MEMS device (20; 120; 220) may be summarized as including: a substrate (21); a movable structure (22; 122; 222) suspended on the substrate and comprising a first mass (28), a second mass (29A, 29B; 229), and a first elastic set (30A, 30B; 230) mechanically coupled between the first mass and the second mass, the first elastic set being compliant along a first direction (Y) and the first mass being configured to move relative to the substrate along the first direction; a second elastic group (23; 123A, 123B) mechanically coupled between the substrate and the movable structure, the second elastic group being compliant along the first direction; and an anchor control structure (33A, 40A, 33B, 40B;233, 240) secured to the substrate, capacitively coupled to the second mass (29A, 29B; 129), and configured to apply an electrostatic force on the second mass along a first direction, the anchor control structure and the second mass having a pull-in voltage, wherein the method comprises: applying a voltage of zero or lower than the pull-in voltage between the anchor control structure and the second mass such that the MEMS device is in a first operational state, wherein the second mass is free to move relative to the substrate along a first direction; and applying a voltage equal to or greater than a pull-in voltage between the anchor control structure and the second mass such that the MEMS device is in a second operational state, wherein the anchor control structure applies a pull-in electrostatic force on the second mass that enables anchoring of the second mass to the anchor structure, thereby preventing movement of the second mass relative to the substrate in response to movement of the first mass.

The movable structure may further include a third mass (29B) and a third spring set (30B) mechanically coupling the first mass (28) to the third mass, and the third spring set being compliant along a first direction, the second mass being arranged on a first side of the first mass, the third mass being arranged on a second side of the first mass other than the first side, wherein the anchor control structure is a first anchor control structure (33A, 40A), the MEMS device may further include a second anchor control structure (33B, 40B) fixed to the substrate, capacitively coupled to the third mass (29B), and configured to apply an electrostatic force on the second mass along the first direction, the second anchor control structure and the second mass having a second pull-in voltage, wherein the method may further include: applying a voltage of zero or lower than the second pull-in voltage between the second anchoring control structure and the third mass such that the MEMS device is in a third operational state, wherein the third mass is free to move relative to the substrate along the first direction; and applying a voltage equal to or greater than a second pull-in voltage between the second anchoring control structure and the third mass such that the MEMS device is in a fourth operating state, wherein the second anchoring control structure applies a pull-in electrostatic force on the third mass that enables anchoring of the third mass to the second anchoring structure, thereby preventing movement of the third mass relative to the substrate in response to movement of the first mass.

The various embodiments described above may be combined to provide further embodiments. Modifications may be made to the aspects of the embodiments as necessary to employ the concepts of the various patents, applications and publications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of the above detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the present disclosure.

Claims (15)

1. A MEMS device, comprising:

A substrate;

A movable structure suspended on the substrate and comprising:

A first mass;

A second mass; and

A first elastic set mechanically coupled between the first mass and the second mass, the first elastic set being compliant along a first direction, the first mass being configured to move relative to the substrate along the first direction;

A second elastic set mechanically coupled between the substrate and the movable structure, the second elastic set being compliant along the first direction; and

An anchor control structure secured to the substrate, capacitively coupled to the second mass, and configured to apply an electrostatic force on the second mass along the first direction,

Wherein the anchoring control structure is configured to: controlling the MEMS device in a first operational state wherein the second mass is free to move relative to the substrate along the first direction, and controlling the MEMS device in a second operational state wherein the anchor control structure exerts a pull-in electrostatic force on the second mass that enables the second mass to be anchored to the anchor control structure, thereby preventing the second mass from moving relative to the substrate in response to movement of the first mass.

2. The MEMS device of claim 1, wherein the anchor control structure comprises a stop secured to the substrate, the stop extending along the first direction at a first distance from the second mass in the first operating state and contacting the second mass in the second operating state when at rest.

3. The MEMS device of claim 2, wherein the anchor control structure further comprises a control electrode secured to the substrate and extending at a second distance from the second mass along the first direction in the first operating state when at rest.

4. A MEMS device as claimed in claim 3, wherein the first distance is less than the second distance.

5. The MEMS device, as recited in claim 2, wherein the anchor control structure comprises a control electrode, the second mass having an outer wall and a through cavity having an inner wall, the control electrode being disposed inside the through cavity facing the inner wall, the stop facing the outer wall of the second mass.

6. The MEMS device of claim 1, wherein the second elastic set is coupled to the first mass such that in the first operational state the first mass is coupled to the substrate through the second elastic set and in the second operational state the first mass is coupled to the substrate through the first and second elastic sets, the first and second elastic sets being mechanically arranged in parallel between the first mass and the substrate.

7. The MEMS device of claim 1, wherein the second elastic set is coupled to the second proof mass such that in the first operating state the first proof mass is coupled to the substrate through the first and second elastic sets, the first and second elastic sets being mechanically arranged in series between the first proof mass and the substrate, and in the second operating state the first proof mass is coupled to the substrate through the first elastic set.

8. The MEMS device of claim 1, wherein the movable structure further comprises a third mass and a third spring set mechanically coupling the first mass to the third mass, and the third spring set is compliant along the first direction, the second mass is disposed on a first side of the first mass, and the third mass is disposed on a second side of the first mass other than the first side, wherein the anchor control structure is a first anchor control structure, the MEMS device further comprising a second anchor control structure secured to the substrate, capacitively coupled to the third mass, and configured to: controlling the MEMS device in a third operational state wherein the third mass is free to move relative to the substrate along the first direction, and controlling the MEMS device in a fourth operational state wherein the second anchoring control structure exerts a pull-in electrostatic force on the third mass that enables anchoring of the third mass to the second anchoring control structure, thereby preventing movement of the third mass relative to the substrate in response to movement of the first mass.

9. The MEMS device of claim 1, further comprising a detection structure configured to detect movement of the first mass along the first direction.

10. The MEMS device of claim 1, wherein the first mass is configured to move along the first direction in response to movement of the MEMS device.

11. An electronic device, comprising:

A substrate;

A first mass including a first opening, the first mass including a first side opposite a second side, a third side transverse to the first side, and a fourth side opposite the third side;

a plurality of first electrodes fixed to the substrate and in the first openings;

A first stopper;

a second stop spaced apart from the first stop by the first mass;

A second mass coupled to the third side of the first mass;

a third mass is coupled to the fourth side of the first mass, the second mass being spaced apart from the second stop by the third mass and the first mass.

12. The electronic device of claim 11, wherein a plurality of second electrodes extend from the first mass into the opening toward the plurality of first electrodes.

13. The electronic device of claim 11, comprising:

a plurality of first elastic elements extending from the first side of the first mass;

a plurality of second elastic elements extending from the second side of the first mass;

A plurality of third elastic elements extending from the third side of the first mass and coupled to the second mass; and

A plurality of fourth elastic elements extend from the fourth side of the first mass and are coupled to the third mass.

14. The electronic device of claim 13, comprising: a plurality of second electrodes in each of a plurality of second openings in the second mass.

15. The electronic device of claim 14, comprising: a plurality of third electrodes in each of a plurality of third openings in the third mass.