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 devices and electronic devices

Technical Field

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

Background Art

As is known, MEMS (“Micro Electro Mechanical System”) type inertial sensors, such as accelerometers and gyroscopes, are widely used due to their small size and high detection sensitivity.

MEMS inertial sensors are integrated into various electronic devices such as wearable devices, smart phones, notebook computers, etc.

Common applications for this type of inertial sensor include: impact monitoring, such as detecting a car accident or a person who may fall to the ground; detecting user gestures, such as the rotation of a smartphone's screen or specific types of user touches; and use as a bone conduction detector, such as as a microphone in a true wireless stereo (TWS) headset.

With specific reference to MEMS accelerometers, low-G accelerometers are currently known to detect low accelerations, for example having a full scale range (FSR) equal to 16g or 32g, while high-G sensors are used to detect high accelerations, for example 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 approach, 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 results in disadvantages, such as the need for a greater number of pads and a higher complexity of the required control circuitry (e.g., a dedicated ASIC, PCB or CPU, etc.), and more generally, a larger integration area, lower portability of the electronic device and higher manufacturing costs.

Utility Model Content

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

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 anchoring control structure. The movable structure includes a first mass, a second mass, a first elastic group, and a second elastic group. The first elastic group is mechanically coupled between the first mass and the second mass, the first elastic group is compliant along a first direction, and the first mass is configured to move relative to the substrate along the first direction. The second elastic group is mechanically coupled between the substrate and the movable structure, and the second elastic group is compliant along the first direction. The anchoring control structure is fixed 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: control the MEMS device to be in a first operating state, in which the second mass is free to move relative to the substrate along the first direction, and control the MEMS device to be in a second operating state, in which the anchoring control structure applies a pulling electrostatic force on the second mass that enables the second mass to be anchored to the anchoring structure, thereby preventing the second mass from moving relative to the substrate in response to the movement of the first mass.

In some embodiments, the anchor control structure includes a stopper fixed to the substrate, the stopper extending along a first direction at a first distance from the second proof-mass in a first operational state when at rest, and in contact with the second proof-mass in a second operational state.

In some embodiments, the anchor control structure further includes a control electrode fixed to the substrate and extending, when stationary, in the first operational state along the first direction at a second distance from the second proof-mass.

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

In some embodiments, the anchor control structure includes a control electrode, the second mass has an outer wall and a through cavity, the through cavity has an inner wall, the control electrode is arranged inside the through cavity and faces the inner wall, and the stopper faces the outer wall of the second mass.

In some embodiments, the second elastic group is coupled to the first mass block such that in a first operating state, the first mass block is coupled to the substrate via the second elastic group, and in a second operating state, the first mass block is coupled to the substrate via 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 block and the substrate.

In some embodiments, the second elastic group is coupled to the second mass block, so that in a first operating state, the first mass block is coupled to the substrate through the first elastic group and the second elastic group, the first elastic group and the second elastic group are mechanically arranged in series between the first movable mass block and the substrate, and in a second operating state, the first mass block is coupled to the substrate through the first elastic group.

In some embodiments, the movable structure further includes a third mass and a third elastic group, the third elastic group mechanically coupling the first mass to the third mass, and the third elastic group is compliant along the first direction, the second mass is arranged on a first side of the first mass, and the third mass is arranged on a second side of the first mass other than the first side, wherein the anchoring control structure is a first anchoring control structure, and the MEMS device further includes a second anchoring control structure, the second anchoring control structure is fixed to the substrate, capacitively coupled to the third mass, and is configured to: control the MEMS device to be in a third operating state, in which the third mass is free to move relative to the substrate along the first direction, and control the MEMS device to be in a fourth operating state, in which the second anchoring control structure exerts a pulling electrostatic force on the third mass that enables the third mass to be anchored to the second anchoring structure, thereby preventing the third mass from moving relative to the substrate in response to movement of the first mass.

In some embodiments, the MEMS device further includes 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, an electronic device is provided, comprising: a substrate, a first mass block including a first opening, a plurality of first electrodes, a first stopper, a second stopper, and a third mass block. The first mass block comprises a first side opposite to the second side, a third side transverse to the first side, and a fourth side opposite to the third side. The plurality of first electrodes are fixed to the substrate and in the first opening. The second stopper is spaced apart from the first stopper by the first mass block. The second mass block is coupled to the third side of the first mass block. The third mass block is coupled to the fourth side of the first mass block, and the second mass block is spaced apart from the second stopper by the third mass block and the first mass block.

In some embodiments, the plurality of second electrodes extend from the first proof-mass into the opening towards 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. The plurality of first elastic elements extend from a first side of a first mass. The plurality of second elastic elements extend from a second side of the first mass. The plurality of third elastic elements extend from a third side of the first mass and are coupled to the second mass. The 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 the plurality of second openings in the second mass.

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

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG1 shows 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 ;

FIG2 shows a top view of the MEMS device of FIG1 under operating conditions;

FIG. 2A illustrates a top view of an enlarged portion of the MEMS device of FIG. 1 under the operating conditions of FIG. 2 ;

FIG3 shows a top view of the present MEMS device according to various embodiments;

FIG4 shows a top view of the MEMS device of FIG3 under operating conditions;

FIG5 shows 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 reference frame XYZ comprising a first X axis, a second Y axis and a third Z axis.

In FIG. 1 , only elements helpful for understanding the present embodiment are shown, and elements or components irrelevant to the present disclosure, although existing in a final MEMS device, are not shown.

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

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

The MEMS device 20 includes 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 , which mechanically couple the movable structure 22 to the substrate 21 .

The movable structure 22 and the elastic supporting element 23 are formed starting from a layer of semiconductor material, for example silicon or polysilicon, and form a substantially planar structure having 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 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 detection mass 28, a first control mass 29A and a second control mass 29B, and a first elastic coupling element 30A and a second elastic coupling element 30B, which mechanically couple the first control mass 29A and the second control mass 29B to the detection mass 28, respectively.

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

The first elastic coupling element 30A and the second elastic coupling element 30B can have equal or different spring constants along the detection direction, here different and in particular greater spring constants relative to the elastic supporting element 23 .

The elastic support element 23 extends from the left and right sides of the detection mass 28, as shown in Figure 1. The first extension of the elastic support element 23 is along the first axis X. The first elastic coupling element 30A and the second elastic coupling element 30B extend from the top and bottom sides of the detection mass 28, as shown in Figure 1. These sides can be referred to as the first side and the second side (left and right) and the third side and the fourth side (top and bottom). The first extension of the second elastic 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 another support element. At each corner of the detection mass 28, each of the first elastic support element and the second elastic support element extends in a transverse direction to each other.

In detail, the first control mass 29A extends on a first side of the proof mass 28 and the second proof mass 29B extends on a second side of the proof mass 28 opposite to the first side with respect to the first axis of symmetry 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 first and second control electrodes 33A, 33B fixed to substrate 21 and capacitively coupled to first and second control masses 29A, 29B, respectively.

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

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

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

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

For each of the first through cavity 35A and the second through cavity 35B, the first inner wall 36 is arranged parallel to the second axis Y at a smaller distance from the detection mass 28 than the second inner wall 37. In other words, the first inner wall 36 is arranged toward the center of the movable structure 22, and the second inner wall 37 is arranged toward 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 both sides of the first through cavity 35A that are opposite to each other along the second axis Y.

The first control electrodes 33A are each arranged inside the corresponding first through-cavity 35A. The second control electrodes 33B are each arranged inside the 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 _d1 from the first inner wall 36 and at a distance _d2 from the second inner wall 37 .

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

For example, the distance _d1 may be greater than the stroke value of the MEMS device 20, ie, greater than the maximum displacement parallel to the second axis Y that the movable structure 22 may undergo in use.

For example, the distance _d2 may be equal to the distance _d1 plus a factor, which may be selected according to the stroke value of the MEMS device 20 depending on the specific application.

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

In detail, referring to the enlarged portion of FIG. 1A , the first stopper 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 _d3 from the wall 42 of the first stop 40A.

Relative to the distance d ₁ between the first inner wall 36 of the first through cavity 35A and the corresponding first control electrode 33A, the distance d ₃ between the first control mass 29A and the first stopper 40A may be the same as or different from the distance d 1 between the first inner wall 36 of the first through cavity 35A and the corresponding first control electrode 33A, and in particular, the distance d ₃ is smaller.

The distance _d3 may be greater than or equal to the stroke value of the MEMS device 20. In this embodiment, the distance _d3 is equal to the stroke value of the MEMS device 20, and thus defines its stroke value.

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

Although not shown in detail, what has been described with respect to 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 also includes a first voltage applying device 45A and a second voltage applying device 45B, which are only schematically presented in Figure 1. The first voltage applying device 45A and the second voltage applying device 45B respectively include a first conductive trace 46A and a second conductive trace 46B, which extend on the substrate 21 and are represented by dotted lines in Figure 1 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 provide 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 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-tooth type.

In detail, the first detection capacitor 51A and the second detection capacitor 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 embodiment shown, the cavity 60 extends through the proof mass 28 through the thickness of the proof mass 28 parallel to the third axis Z. In fact, in the embodiment shown, 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 extend toward the interior 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 can be controlled in a sensitive operating state or a low acceleration operating state, and in a high-band operating state or a high acceleration operating state, wherein the sensitive operating state or the low acceleration operating state can be used to detect low acceleration values, such as up to 16g or 32g, and the high-band operating state or the high acceleration operating state can be used to detect high acceleration values, such as up to 128g, where g represents the earth's gravity acceleration value equal to approximately 9.81m/ ^s2 .

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

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

In response to the displacement from the equilibrium position, an elastic return force acts on the movable structure 22. The elastic return force has an opposite direction with respect to the inertial force.

In the sensitive operating state, the elastic return force is applied to the movable structure 22 through the elastic support element 23. Therefore, the modulus of the elastic return force is a function of the elastic constant _k1 of the elastic support element 23.

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

As a first approximation, by neglecting the mass 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+2m, where M is the mass of the detection mass 28, and m is the mass value of the first control mass 29A and the second control mass 29B. Therefore, the MEMS device 20 has a mass of The resonant frequency f ₁ is given.

FIG. 2 shows the MEMS device 20 at equilibrium or at rest (for a zero acceleration value) in a high-band operating state.

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

Hereinafter, the operation of the MEMS device 20 in the high-frequency 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 is also applicable to the second control mass 29B, the second control electrode 33B, the second stopper 40B, and the second elastic coupling element 30B.

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

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

Voltage _Vp generates an attractive electrostatic force (arrow _Fc1 of FIG. 2) between first inner wall 36 of first movable mass 29A and first control electrode 33A. Since first control electrode 33A is fixed to substrate 21, voltage _Vp causes displacement of first control mass 29A toward first control electrode 33A.

As shown in detail in FIG. 2A , at equilibrium, in the high-band operating state, relative to the first 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 .

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 embodiment shown, the electrostatic forces F _c1 and F _c2 are equal in modulus and have opposite directions; therefore, in equilibrium, in the absence of external acceleration, the elastic support element 23 remains unchanged and the detection mass 28 does not experience a displacement relative to the rest position.

In equilibrium, first elastic coupling element 30A exerts an elastic return force (upward in FIG. 2 ) on first control mass 29A. However, since voltage _Vp is equal to or greater than the pull-in voltage, the elastic return force on first control mass 29A is lower than the electrostatic attraction force _Fc1 exerted on first control mass 29A by first control electrode 33A.

Therefore, in the high-band operation state, in the absence of external acceleration, the combined forces directed toward the first stopper 40A and the second stopper 40B, respectively, act on the first control mass 29A and the second control mass 29B. The combined force keeps the first control mass 29A and the second control mass 29B in contact with the first stopper 40A and the second stopper 40B, respectively.

In practice, in the high-band operating state, 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, voltage _Vp enables first control mass 29A and first control electrode 33A to be maintained in a pull-in condition and second control mass 29B and second control electrode 33B to be maintained in a pull-in condition even when MEMS device 20 experiences acceleration along 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.

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

For example, the MEMS device 20 may be configured to operate along the 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, referring to the first control electrode 33A and the first control mass 29A, when the MEMS device 20 is subjected to an acceleration equal to the maximum expected acceleration value in use, the detection mass 28 experiences a maximum displacement relative to the substrate 21 along the detection direction. Thus, the voltage _Vp 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 detection mass 28 and the apparent force experienced by the first control mass 29A in response to the maximum expected acceleration value of the MEMS device 20.

It can be seen from this that under the high-frequency band operating state, in the presence of acceleration, the detection mass 28 experiences an elastic return force, which is not only a function of the elastic constant _k1 of the elastic support element 23, but also a function of the elastic constant _k2 of the first elastic coupling element 30A and the second elastic coupling element 30B.

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

Therefore, in the high-band operation state, the MEMS device 20 , in particular the proof mass 28 , has an equivalent elastic constant ke _{eq ,} which is a function of the sum of the elastic constants k ₁ , k ₂ .

As a first approximation, by also neglecting here 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, ie corresponding to a single proof mass 28 .

Therefore, the MEMS device 20 has the following characteristics in the high-frequency band operation state: The resonant frequency f ₂ is given.

By appropriately selecting the _values of the spring constants k ₁ , k ₂ and the masses M, m during the design step, the values of the resonance frequencies fi ₂ of the MEMS device 20 and thus the detection properties of the MEMS device 20 in the first and second operating states may be adjusted.

In the illustrated embodiment, the resonance frequency _f2 is greater than the resonance frequency _f1 .

Therefore, in the sensitive operation state, the MEMS device 20 has a higher detection sensitivity than in the high-band operation state. In the high-band operation state, the MEMS device 20 has a larger full-scale range than in the sensitive operation state.

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

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

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

In detail, the MEMS device 120 includes a substrate 21 , a movable structure 122 , and elastic support elements, in particular, first and second elastic support elements 123A and 123B that mechanically couple the movable structure 122 to the substrate 21 .

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

In MEMS device 120, first and second elastic support elements 123A, 123B are coupled to first and second control masses 29A, 29B, respectively.

In detail, the first elastic support elements 123A each extend between a corresponding anchoring region 25A and the first control mass 29A, and the second elastic support elements 123B each extend between a corresponding 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 detection mass 28 and the substrate 21 .

The MEMS device 120 further includes first and second control electrodes 33A and 33B, first and second stoppers 40A and 40B, and a detection structure 50 .

The MEMS device 120 further comprises voltage applying means, not shown here, which allow a voltage to be applied to the first control electrode 33A and the second control electrode 33B, as discussed with reference to FIG. 1 .

Similar to what has been discussed with respect to the MEMS device 20 of FIG. 1 , the 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 and second control electrodes 33A, 33B and the first and second control masses 29A, 29B.

In the first operating state, the MEMS device 20, in particular the proof mass 28, has an equivalent spring constant _keq = _k1 · _k2 /( _k1 + _k2 ).

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

In the high-band operating state ( FIG. 4 ), voltage _Vp is applied between first control electrode 33A and first control mass 29A and between second control electrode 33B and second control mass 29B, similar to what has been discussed with reference to FIG. 2 .

In the presence of acceleration, the first control mass 29A and the second control mass 29B remain in contact with the first stop 40A and the second stop 40B, respectively; and the proof mass 28 moves relative to the equilibrium position. In fact, here too, in the pull-in condition, the first mass 29A and the second mass 29B are electrostatically fixed to the first stop 40A and the second stop 40B, respectively.

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

In fact, the equivalent spring constant _keq of the MEMS device 120 is equal to the spring constant _k2 of the first elastic coupling element 30A and the second elastic coupling element 30B.

Therefore, the MEMS device 120 has the following characteristics in the high-frequency band operation state: The resonant frequency f ₂ is given.

In fact, the MEMS device 120 may also have both high sensitivity and high full-scale range.

Figure 5 shows another embodiment of the present MEMS device, here indicated by 220. MEMS device 220 has a general structure similar to that of MEMS device 20 of Figure 1; therefore, 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 supporting element 23 .

In this embodiment, the movable structure 222 is formed by a detection mass 28 , a 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 respectively equivalent to the first control mass 29A and the first elastic coupling element 30A of the MEMS device 20 .

The MEMS device 220 further includes a plurality of control electrodes 233 and a stopper 240 , which are respectively equivalent to the first control electrode 33A and the first stopper 40A of the MEMS device 20 of FIG. 1 .

In fact, with respect to the MEMS device 20 of FIG. 1 , the 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, the MEMS device 220 is asymmetric parallel to the first X-axis.

The operation of the MEMS device 220 is similar to the operation of the MEMS device 20 of FIG. 1 and the MEMS device 120 of FIG. 3 , and therefore will not be described in further detail.

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

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

Therefore, the MEMS device 220 also has high detection versatility and can detect both high and low acceleration values.

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

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, elastic support elements, anchoring areas, stops, elastic coupling elements, through cavities for 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 include a different number of detection capacitors and/or the detection capacitors may be of different types, such as parallel plate capacitors.

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

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

Additionally or alternatively, referring to the MEMS devices 20, 120, different voltages may be applied to the first control electrode and the second control electrode depending on the specific application. For example, the pull-in voltage may be applied only to 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 along one or more directions. Alternatively, the MEMS device may include a plurality of movable structures that are appropriately configured to each detect acceleration along a corresponding 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 the movement of the movable structure.

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

A MEMS device (20; 120; 220) can be summarized as including: a substrate (21); a movable structure (22; 122; 222) suspended from the substrate and including a first mass (28); a second mass (29A, 29B; 229); and a first elastic group (30A, 30B; 230) mechanically coupled between the first mass and the second mass, the first elastic group being compliant along a first direction (Y), the first mass being configured to move relative to the substrate along the first direction; and 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. is compliant; and an anchoring control structure (33A, 40A, 33B, 40B; 233, 240) is fixed to the substrate, capacitively coupled to the second mass (29A, 29B; 129), and is configured to apply an electrostatic force on the second mass along a first direction, wherein the anchoring control structure is configured to: control the MEMS device to be in a first operating state, wherein the second mass is free to move relative to the substrate along the first direction, and control the MEMS device to be in a second operating state, wherein the anchoring control structure applies a pulling electrostatic force on the second mass that enables the second mass to be anchored to the anchoring structure, thereby preventing the second mass from moving relative to the substrate in response to movement of the first mass.

The anchor control structure may include a stopper (40A, 40B; 240) fixed to the substrate, the stopper extending at a first distance ( _d3 ) from the second mass in a first operational state along a first direction when at rest and in contact with the second mass in a second operational state.

The anchor control structure may further include a control electrode (33A, 33B; 233) fixed to the substrate (21) and extending in a first direction at a second distance ( _d1 ) from the second mass (29A, 29B) in a first operational state when at rest.

The first distance may be smaller than the second distance.

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

The second elastic group (23) can be coupled to the first mass block (28) so that in a first operating state, the first mass block is coupled to the substrate via the second elastic group, and in a second operating state, the first mass block is coupled to the substrate via the first elastic group and the second elastic group, and the first elastic group and the second elastic group are mechanically arranged in parallel between the first movable mass block and the substrate.

The second elastic group (123A, 123B) can be coupled to the second mass block (29A, 29B), so that in a first operating state, the first mass block is coupled to the substrate through the first elastic group and the second elastic group, the first elastic group and the second elastic group are mechanically arranged in series between the first movable mass block and the substrate, and in a second operating state, the first mass block is coupled to the substrate through the first elastic group.

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

The MEMS device may further include a detection structure (50) configured to detect 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) can be summarized as comprising: a substrate (21); a movable structure (22; 122; 222) suspended from the substrate and comprising a first mass (28), a second mass (29A, 29B; 229) and a first elastic group (30A, 30B; 230), the first elastic group being mechanically coupled between the first mass and the second mass, the first elastic group 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) being 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), the anchor control structure The method comprises: applying a zero voltage or a voltage lower than the pull-in voltage between the anchoring control structure and the second mass so that the MEMS device is in a first operating state in which the second mass is free to move relative to the substrate along the first direction; and applying a voltage equal to or greater than the pull-in voltage between the anchoring control structure and the second mass so that the MEMS device is in a second operating state in which the anchoring control structure applies a pull-in electrostatic force on the second mass that enables the second mass to be anchored to the anchoring structure, thereby preventing the second mass from moving 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 elastic group (30B), the third elastic group mechanically coupling the first mass (28) to the third mass, and the third elastic group is compliant along the first direction, the second mass is arranged on a first side of the first mass, and the third mass is arranged on a second side of the first mass other than the first side, wherein the anchoring control structure is a first anchoring control structure (33A, 40A), and the MEMS device may further include a second anchoring control structure (33B, 40B), the second anchoring control structure is fixed to the substrate, capacitively coupled to the third mass (29B), and is configured to apply static force on the second mass along the first direction. power, the second anchoring control structure and the second mass have a second pull-in voltage, wherein the method may further include: applying a voltage of zero or a voltage lower than the second pull-in voltage between the second anchoring control structure and the third mass, so that the MEMS device is in a third operating 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 the second pull-in voltage between the second anchoring control structure and the third mass, so 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 the third mass to be anchored to the second anchoring structure, thereby preventing the third mass from moving relative to the substrate in response to movement of the first mass.

The various embodiments described above can be combined to provide further embodiments. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide further embodiments.

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 interpreted as limiting the claims to the specific embodiments disclosed in the specification and claims, but should be interpreted as including all possible embodiments and the full range of equivalents to which these claims are entitled. Therefore, 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.