Wide-bandwidth MEMS accelerometers for vibration detection

Abstract

Various embodiments of the present disclosure relate to a wide-bandwidth MEMS accelerometer for detecting vibrations, comprising: a support structure, at least one deformable group and at least one second deformable group, the at least one deformable group and the at least one second deformable group respectively comprising a first deformable cantilever element and a second deformable cantilever element, the first deformable cantilever element and the second deformable cantilever element each having a respective first end and a respective second end, the first end being fixed to the support structure. The first deformable group and the second deformable group further comprise a first piezoelectric sensing structure and a second piezoelectric sensing structure, respectively. The MEMS accelerometer further comprises: a first moving mass and a second moving mass, each fixed to the second end of the first deformable cantilever element and the second deformable cantilever element and vertically staggered relative to the first deformable cantilever element and the second deformable cantilever element, respectively; and a first elastic structure elastically coupling the first moving mass and the second moving mass.

Description

Technical Field

[0001] The present disclosure relates to a broadband MEMS (Micro Electro Mechanical Systems) accelerometer for detecting accelerations with high frequencies, for example in the case of high frequency vibrations. Background Art

[0002] It is known that systems for monitoring vibrations are now very common and widely used, for example in the context of condition-based maintenance of machinery, in particular maintenance based on usage conditions. In fact, it is known how monitoring the vibrations to which mechanical components are subjected can, for example, detect problems and / or damage before they begin.

[0003] Typically, systems for monitoring vibrations use accelerometers to detect, for example, changes in the amplitude or frequency of a force acting on a component. More generally, it is known to use acceleration sensors with a sensitivity up to frequencies in the range of 80 kHz.

[0004] Generally speaking, sensors with different bandwidths are often used for different purposes. For example, in the case of monitoring motor shaft misalignment, an accelerometer with a small bandwidth (e.g., up to 3 kHz) is often used, while in the case of detecting fan bearing faults, an accelerometer with a large bandwidth (e.g., up to 80 kHz) is used.

[0005] In summary, it may be necessary to find a good balance between the cost and performance of the sensor. In this regard, MEMS sensors have been developed, for example, as described in F. Gerfers et al., “Sub-μg Ultra-Low-Noise MEMS Accelerometers Based on CMOS-Compatible Piezoelectric AlN Thin Films,” Transducers & Eurosensors 2007, which describes the use of a membrane structure, and in T. Kobayashi et al., “A digital output piezoelectric accelerometer using CMOS-compatible AlN thin film,” Transducers 2009, which describes the use of a structure including a cantilever element.

[0006] Typically, MEMS membrane structures are subject to residual mechanical stresses due to the presence of distributed and / or relatively numerous constraints acting on the membrane; these mechanical residual stresses lead to performance degradation. In contrast, MEMS structures with cantilever elements are less susceptible to residual mechanical stresses due to the presence of a single constraint; however, these MEMS structures are generally sensitive only to out-of-plane accelerations; that is, they are essentially uniaxial. Furthermore, when multiple cantilever elements are present, their resonant frequencies inevitably differ from one another, resulting in reduced sensitivity. Summary of the Invention

[0007] In various embodiments, the present disclosure provides accelerometers that will at least partially overcome the shortcomings of the prior art.

[0008] In at least one embodiment, the present disclosure provides a MEMS accelerometer including a support structure. A first deformable group and a second deformable group include a first deformable cantilever element and a second deformable cantilever element, respectively, the first deformable cantilever element and the second deformable cantilever element being arranged along a direction parallel to a plane and each having a respective first end and a respective second end fixed to the support structure. The first deformable group also includes a first piezoelectric detection structure mechanically coupled to the first deformable cantilever element, and the second deformable group also includes a second piezoelectric detection structure mechanically coupled to the second deformable cantilever element. A first moving mass and a second moving mass are respectively fixed to the second end of the first deformable cantilever element and the second end of the second deformable cantilever element, and are staggered relative to the first deformable cantilever element and the second deformable cantilever element in a vertical direction transverse to the plane. A first elastic structure is configured to elastically couple the first moving mass and the second moving mass.

[0009] In at least one embodiment, the present disclosure provides an apparatus comprising a support structure. A first cantilever has a deformable portion and a distal portion, and the deformable portion is secured to the support structure. A first movable mass is mechanically coupled to a first side of the deformable portion of the first cantilever. A second deformable cantilever has a deformable portion and a distal portion, and the deformable portion is secured to the support structure. The second movable mass is mechanically coupled to the first side of the deformable portion of the second cantilever. A first piezoelectric sensing structure is mechanically coupled to a second side of the first deformable cantilever element, the second side being opposite to the first side of the first deformable cantilever element. A second piezoelectric sensing structure is mechanically coupled to a second side of the second deformable cantilever element, the second side being opposite to the first side of the second deformable cantilever element. A first elastic structure is configured to elastically couple the first movable mass and the second movable mass. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] For a better understanding of the present disclosure, preferred embodiments thereof will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:

[0011] Figure 1 The accelerometer moves along Figure 2 A schematic cross-sectional view taken along section line II shown in FIG.

[0012] Figure 2 yes Figure 1 The accelerometer shown is along Figure 1 A schematic top view of a section taken along the II-II section line indicated in FIG.

[0013] Figure 3 and Figure 4 yes Figures 1 to 2 Schematic side views of parts of the accelerometer shown in different operating conditions;

[0014] Figure 5 and Figure 6 yes Figures 1 to 2 Schematic side views of parts of the accelerometer shown in different operating conditions;

[0015] Figure 7 is a schematic top view of a cross section of the accelerometer; and

[0016] Figures 8A to 8C yes Figure 7 Schematic top view of the accelerometer shown under different operating conditions. DETAILED DESCRIPTION

[0017] Figure 1 A MEMS accelerometer 1 is shown, comprising a support structure 2 defining a cavity 4 within which a sensitive structure 6 extends. Without loss of generality, the support structure 2 may have a closed shape (e.g., it may have the shape of a parallelepiped on the outside), in which case the cavity 4 is closed; i.e., it has no fluid communication with the outside. Additionally, the support structure 2 is, for example, silicon.

[0018] In more detail, assuming an orthogonal reference system XYZ, the cavity 4 is formed at the top and bottom by a top surface S parallel to the plane XY. top and bottom surface S bot In addition, the cavity 4 is parallel to the first side wall P plane YZ l1 and the second side wall P l2 and a third side wall P parallel to plane XZ l3 and the fourth side wall P l4 (exist Figure 2 (see in) laterally delimited. Top surface S top , bottom surface S botand the first side wall P l1 and the second side wall P l2 Formed by a support structure 2.

[0019] The sensitive structure 6 is constrained to the first, second, third and fourth side walls P l1 、P l2 、P l3 、P l4 , to be suspended on the bottom surface S bot Above, with the bottom surface S bot At a certain distance.

[0020] In particular, the sensitive structure 6 includes a first cantilever element 21 , a second cantilever element 22 , a third cantilever element 23 and a fourth cantilever element 24 , a first suspension group G1 , a second suspension group G2 , a third suspension group G3 and a fourth suspension group G4 , and a first spring element 41 , a second spring element 42 , a third spring element 43 and a fourth spring element 44 .

[0021] In detail, the first, second, third and fourth cantilever elements 21, 22, 23, 24 are identical to one another and are arranged in a coplanar manner in the rest state at the same height along the axis Z. In particular, the first, second, third and fourth cantilever elements 21, 22, 23, 24 have a planar shape; purely by way of example, the first, second, third and fourth cantilever elements 21, 22, 23, 24 may have a thickness (measured along the axis Z) comprised between 10 μm and 20 μm.

[0022] Furthermore, the first, second, third and fourth cantilever elements 21 , 22 , 23 , 24 are, for example, silicon.

[0023] In more detail, each of the first, second, third and fourth cantilever elements 21, 22, 23, 24 includes a corresponding deformable portion (represented by 21*, 22*, 23* and 24*, respectively) and a corresponding distal portion (represented by 21**, 22**, 23** and 24**, respectively).

[0024] The deformable portions 21 *, 22 *, 23 * and 24 * of the first, second, third and fourth cantilever elements 21 , 22 , 23 , 24 have the shape of a parallelepiped.

[0025] In particular, assuming that the first and second symmetry planes SP1 and SP2 are parallel to planes ZX and ZY, respectively, the deformable portions 21* and 22* of the first and second cantilever elements 21 and 22 are elongated in directions parallel to axis X and are arranged symmetrically with respect to the second symmetry plane SP2, at a distance from one another. More specifically, if H1 and H2 are directions in which the centroid axes of the deformable portions 21* and 22* of the first and second cantilever elements 21 and 22, respectively, extend, then directions H1 and H2 have a first approximate coincidence with axis X and are parallel to axis X. Additionally, the deformable portions 21* and 22* of the first and second cantilever elements 21 and 22 have respective first and second ends, the first ends being fixed to the first side wall P, respectively. l1 and the second side wall P l2 In practice, the first cantilever element 21 and the second cantilever element 22 are arranged opposite to each other.

[0026] The deformable portions 23*, 24* of the third cantilever element 23 and the fourth cantilever element 24 are elongated in a direction parallel to the axis Y and are arranged symmetrically with respect to the first symmetry plane SP1 at a distance from each other. In more detail, if H3 and H4 are directions in which the centroid axes of the deformable portions 23*, 24* of the third cantilever element 23 and the fourth cantilever element 24, respectively, extend to a first approximate direction, then the directions H3 and H4 are found to coincide and are parallel to the axis Y. Additionally, the deformable portions 23*, 24* of the third cantilever element 23 and the fourth cantilever element 24 have respective first ends and respective second ends, the first ends being fixed to the third side wall P, respectively. l3 and the fourth side wall P l4 In practice, the third cantilever element 23 and the fourth cantilever element 24 are arranged opposite to each other.

[0027] The first symmetry plane SP1 and the second symmetry plane SP2 intersect along an axis HX that is parallel to the axis Z. Furthermore, the distal end portions 21**, 22**, 23**, 24** of the first, second, third, and fourth cantilever elements 21, 22, 23, 24 are fixed relative to the second ends of the deformable portions 21*, 22*, 23*, 24* of the first, second, third, and fourth cantilever elements 21, 22, 23, 24, respectively, and cover the first, second, third, and fourth suspension groups G1, G2, G3, G4, respectively. As described below and without loss of generality, in top view, the distal end portions 21**, 22**, 23**, 24** of the first, second, third, and fourth cantilever elements 21, 22, 23, 24 have the same shape as the first, second, third, and fourth suspension groups G1, G2, G3, G4, respectively.

[0028] In detail, the first, second, third and fourth suspension groups G1, G2, G3, G4 are identical to one another, for example having a prism shape whose polygonal base has an axis parallel (in the static state) to the Z axis; that is, their cross section in a plane parallel to the plane XY does not change with a change in coordinate along the Z axis. In any case, the details concerning the shape of the suspension groups are irrelevant to the operational purpose of the MEMS accelerometer 1. By way of example only, in Figure 2 , the prism has a base (parallel to the plane XY) having a planar shape obtained by juxtaposing i) an isosceles trapezoid with its short base facing the axis HX, and ii) a rectangle whose long side coincides with the long base of the isosceles trapezoid. Again, without loss of generality, the base of the isosceles trapezoid defined by the first and second suspension groups G1 and G2 in top view is parallel to the Y axis, while the base of the isosceles trapezoid defined by the third and fourth suspension groups G3 and G4 in top view is parallel to the X axis.

[0029] The first, second, third and fourth suspension groups G1, G2, G3 and G4 are fixed below the distal end portions 21**, 22**, 23** and 24** of the first, second, third and fourth suspension elements 21, 22, 23 and 24 respectively.

[0030] Without loss of generality, it is assumed that each of the first, second, third and fourth suspension groups G1, G2, G3, G4 is formed by a corresponding main region of, for example, silicon (represented by 31A, 32A, 33A, 34A, respectively) and a corresponding top layer of, for example, silicon oxide (represented by 31B, 32B, 33B, 34B, respectively).

[0031] In more detail, referring to the first suspension group G1 (but the same considerations also apply to the second, third and fourth suspension groups G2, G3, G4), the corresponding top layer 31B is fixed at the top to the distal portion 21** of the first suspension element 21 and covers the underlying main region 31A. As previously mentioned and without loss of generality, the distal portion 21** of the first suspension element 21, the underlying top layer 31B and the underlying main region 31A have the same shape in top view and furthermore form a mobile mass 31 (hereinafter referred to as the first mobile mass 31). By way of example only, the top layer 31B and the underlying main region 31A have thicknesses (measured along the Z axis) ranging, for example, from 1 μm to 2 μm and from 250 μm to 500 μm, respectively. Similarly, the distal portions 22**, 23**, 24** of the second, third and fourth cantilever elements 22, 23, 24 form a second movable mass 32, a third movable mass 33 and a fourth movable mass 34, respectively, and the second movable mass 32, the third movable mass 33 and the fourth movable mass 34 respectively have lower layers of i) a top layer 32B and a main region 32A, ii) a top layer 33B and a main region 33A, and iii) a top layer 34B and a main region 34A.

[0032] In practice, the first suspended mass 31 and the second suspended mass 32 are arranged symmetrically about the second symmetry plane SP2. Similarly, the third suspended mass 33 and the fourth suspended mass 34 are arranged symmetrically about the first symmetry plane SP1. From another perspective, the first, second, third, and fourth suspended masses 31, 32, 33, 34 are arranged at the same radial distance from the axis HX and are arranged at equal angular distances of 90° from each other, so as to be arranged according to the vertices of a hypothetical rhombus.

[0033] The first, second, third and fourth spring elements 41, 42, 43, 44 each have a folded elongated shape of, for example, silicon and in the rest state may have the same thickness (along Z) as the first, second, third and fourth cantilever elements 21, 22, 23, 24 and be coplanar with them.

[0034] In more detail, each of the first, second, third, and fourth spring elements 41, 42, 43, 44 has a respective first end and a respective second end. The first ends of the first, second, third, and fourth spring elements 41, 42, 43, 44 are fixed to the distal end portions 21**, 22**, 23**, 24** of the first, second, third, and fourth spring elements 21, 22, 23, 24, respectively, thereby being in direct contact therewith and forming a single piece. The first ends of the first, second, third, and fourth spring elements 41, 42, 43, 44 are thus fixed to the first, second, third, and fourth mobile masses 31, 32, 33, 34, respectively. The second ends of the first, second, third, and fourth spring elements 41, 42, 43, 44 are fixed to one another about the axis HX to form a single cross-shaped piece.

[0035] The first spring element 41 and the second spring element 42 are rigid in a direction parallel to the axis Z and flexible in a direction parallel to the axis X, and form a first spring structure M1. The third spring element 43 and the fourth spring element 44 are rigid in a direction parallel to the axis Z and flexible in a direction parallel to the axis Y, and form a second spring structure M2.

[0036] In practice, the distal end portions 21**, 22** of the first cantilever element 21 and the second cantilever element 22 are connected to each other via a first spring structure M1, which is flexible in a direction parallel to the axis X and rigid in a direction parallel to the axis Z. Similarly, the distal end portions 23**, 24** of the third cantilever element 23 and the fourth cantilever element 24 are connected to each other via a second spring structure M2, which is flexible in a direction parallel to the axis Y and rigid in a direction parallel to the axis Z. As previously described, the first spring structure M1 and the second spring structure M2 intersect with each other and form a first arm and a second arm, respectively, of a cross-shaped structure, the first arm and the second arm being perpendicular to each other.

[0037] As mentioned above, the stiffness of the first spring structure M1 in the direction H1 (equivalently, H2) is lower than the stiffness of the deformable portions 21*, 22* of the first cantilever element 21 and the second cantilever element 22 in the direction H1. The stiffness of the second spring structure M2 in the direction H3 (equivalently, H4) is lower than the stiffness of the deformable portions 23*, 24* of the third cantilever element 23 and the fourth cantilever element 24 in the direction H3.

[0038] Additionally, the center of mass of the first mobile mass 31 and the second mobile mass 32 (in Figure 1, where they are denoted by B1 and B2, respectively) are located at a lower height (measured in a direction parallel to the Z axis). Additionally, the center of mass B1 is located at a higher coordinate value along X than the second end of the deformable portion 21* of the first cantilever element 21; and the center of mass B2 is located at a lower coordinate value along X than the second end of the deformable portion 22* of the first cantilever element 22. Equivalently, given an imaginary plane parallel to the XY plane and containing the directions H1 and H2, the centers of mass B1 and B2 of the first and second mobile masses 31 and 32 are arranged below the imaginary plane and staggered along the X axis, in the direction of the axis HX, relative to the second ends of the deformable portions of the respective cantilever elements. In other words, in the static state, the first and second mobile masses 31 and 32 are vertically and laterally staggered relative to the first and second deformable portions 21*, 22* of the first and second cantilever elements 21 and 22.

[0039] As a first approximation and without loss of generality, the centers of mass B1, B2 of the first mobile mass 31 and the second mobile mass 32 are coplanar with each other and with respect to the directions H1, H2; as a first approximation, the centers of mass B1, B2 and the directions H1, H2 lie in a first symmetry plane SP1. Similarly, although not shown, the centers of mass of the third mobile mass 33 and the fourth mobile mass 34 are located at a lower height than the directions H3, H4; as a first approximation, together with the latter directions, they lie in a second symmetry plane SP2 and are transversely staggered relative to the second ends of the deformable portions 23*, 24* of the third and fourth cantilever elements 23, 24, along the axis Y and in the direction of the axis HX.

[0040] The MEMS accelerometer 1 also includes a first piezoelectric detection structure 51, a second piezoelectric detection structure 52, a third piezoelectric detection structure 53 and a fourth piezoelectric detection structure 54, which are, for example, identical to each other and, although not shown, each include a corresponding pair of electrodes with corresponding areas of piezoelectric material (e.g., PZT) inserted between the electrode pairs.

[0041] Without loss of generality, the first, second, third and fourth piezoelectric detection structures 51, 52, 53, 54 extend over the deformable portions 21*, 22*, 23*, 24* of the first, second, third and fourth cantilever elements 21, 22, 23, 24, respectively, and are therefore laterally staggered relative to the first, second, third and fourth mobile masses 31, 32, 33, 34, respectively. Furthermore, without loss of generality, the first, second, third and fourth piezoelectric detection structures 51, 52, 53, 54 extend laterally to the first ends of the deformable portions 21*, 22*, 23*, 24* of the first, second, third and fourth cantilever elements 21, 22, 23, 24, which, as mentioned above, are fixed to the support structure 2 and represent areas subject to high deformation. Likewise, although not shown, a variant is possible in which the first, second, third and fourth piezoelectric detection structures 51 , 52 , 53 , 54 also partially extend over a portion of the support structure 2 .

[0042] In more detail, consider for example a first piezoelectric sensing structure 51 (but the same considerations apply to the other piezoelectric sensing structures), which is arranged at a distance above the centroid axis of the whole formed by the deformable portion 21* of the first cantilever element 21 and the same first piezoelectric sensing structure 51, which, as a first approximation, can be assumed to coincide with the centroid axis of the deformable portion 21* of the first cantilever element 21 and, therefore, with the above-mentioned direction H1. Furthermore, the first piezoelectric sensing structure 51 (but the same considerations apply to the other piezoelectric sensing structures and the corresponding centroid axes) has a planar shape that is symmetrical with respect to the underlying centroid axis of the deformable portion 21* of the first cantilever element 21; i.e., in top view, it is divided into two equal parts by said centroid axis.

[0043] As described above, considering the pair formed by the first cantilever element 21 and the first mobile mass 31 and temporarily ignoring the presence of the first spring structure M1 and therefore considering, for simplicity, the first mobile mass 31 to be decoupled from the second, third and fourth mobile masses 32, 33, 34, we find what is described below.

[0044] In such Figure 3In the case shown, the first mobile mass 31 is subjected to an (inertial) acceleration parallel to the axis Z (for example directed upwards, as in the case of vibrations, so that the support structure 2 is subjected to an acceleration directed along the axis Z but downwards), the deformable portion 21* of the first cantilever element 21 is subjected to a bending moment directed in a direction parallel to the axis Y, the bending moment being generated by the staggering of the first mobile mass 31 and the second end of the deformable portion 21* of the first cantilever element 21 along the axis X. This moment causes a deformation, in particular a compression, of the first piezoelectric detection structure 51 since, as previously explained, the first piezoelectric detection structure 51 is staggered vertically with respect to the neutral axis of the whole formed by the deformable portion 21* of the first cantilever element 21 and the first piezoelectric detection structure 51, which neutral axis coincides, as a first approximation, with the aforementioned centroid axis of the whole formed by the deformable portion 21* of the first cantilever element 21 and the first piezoelectric detection structure 51. The first piezoelectric detection structure 51 thus generates between its own electrodes a voltage V1 which is precisely related to the aforementioned bending moment and therefore to the amplitude of the acceleration parallel to the Z axis.

[0045] In addition, even in Figure 4 In the case shown, the first mobile mass 31 is subjected to an (inertial) acceleration parallel to and coincident with the axis X (e.g., in the case of vibrations, which subject the support structure 2 to an acceleration directed along, but not coincident with, the axis X), and the deformable portion 21* of the first cantilever element 21 is subjected to a corresponding bending moment, which is again directed in a direction parallel to the axis Y, since, as previously mentioned, the center of mass B1 of the first mobile mass 31 is located below the center of mass axis of the whole formed by the deformable portion 21* of the first cantilever element 21 and the first piezoelectric detection structure 51. This bending moment causes a deformation (in particular a compression) of the first piezoelectric detection structure 51, so that the voltage V1 is related to the bending moment itself and therefore to the amplitude of the acceleration parallel to the axis X. In the case of inertial accelerations parallel to the axis X or the axis Z, respectively, the bending moments to which the deformable portion 21* of the first cantilever element 21 is subjected are parallel and coincident with one another.

[0046] In contrast, in the event that the first mobile mass 31 is subjected to an (inertial) acceleration parallel to and coincident with the axis Y (not shown) (such as in the event of vibration, causing the support structure 2 to be subjected to an acceleration directed along the axis Y, but not coincident with it), the deformable portion 21* of the first cantilever element 21 is subjected to a torsional force about the direction H1, which causes a portion of the first piezoelectric detection structure 51 to be subjected to tension and a portion to compression, with the result that the voltage V1 is approximately zero.

[0047] Considering instead the pair formed by the second cantilever element 22 and the second mobile mass 32 , and again neglecting the presence of the first spring structure M1 , we find what is described below.

[0048] exist Figure 3 Under the conditions mentioned in , the second mobile mass 32 is subjected to an acceleration parallel to and coincident with the axis Z. The deformable portion 22* of the second cantilever element 22 is therefore subjected to a bending moment directed in a direction parallel to the axis Y and having an opposite direction with respect to the bending moment simultaneously subjected to the deformable portion 21* of the first cantilever element 31, so that the second piezoelectric structure 52 undergoes a deformation (in particular a compression) that is symmetrical with respect to the deformation undergone by the first piezoelectric structure 51. The second piezoelectric detection structure 52 therefore generates a voltage V2 between its own electrodes, which voltage V2 is indicative of the amplitude of the acceleration parallel to the axis Z. Ideally, under Figure 3 Under the conditions shown, voltage V1 and voltage V2 are equal.

[0049] exist Figure 4 Under the conditions mentioned in , the second mobile mass 32 is subjected to an acceleration parallel to and coincident with the axis X. The deformable portion 22* of the second cantilever element 22 is subjected to a corresponding bending moment, which is parallel to and coincident with the bending moment to which the deformable portion 21* of the first cantilever element 21 is simultaneously subjected. In fact, when the second ends of the first mobile mass 31 and the deformable portion 21* of the first cantilever element 21 tend to rise, the second mobile mass 32 and the deformable portion 22* of the second cantilever element 22 tend to fall. Therefore, although the deformation of the first piezoelectric detection structure 51 is of the compressive type, the second piezoelectric detection structure 52 is of the tensile type and the voltage V2 is related to the strain experienced by the second piezoelectric detection structure 52. The voltage V2 therefore has a sign opposite to that of the voltage V1. Ideally, at Figure 4 Under the conditions mentioned, voltage V1 and voltage V2 have the same magnitude and opposite signs.

[0050] By means of an electronic circuit of a type known per se and not shown here, it is thus possible, for example, to generate a signal sVZ′=V1+V2 and a signal sVX=V1−V2, which are indicative of the acceleration along Z and the acceleration along X to which the MEMS accelerometer 1 is subjected, respectively. In this regard, the bottom electrodes of the first and second piezoelectric detection structures 51, 52 can be arranged to be grounded, and the top electrodes of the first and second piezoelectric detection structures 51, 52 can be connected to generate the above-mentioned signals sVZ′ and sVX.

[0051] Similar considerations apply to the subsystems formed by the third cantilever element 23 , the third suspended mass 33 and the third piezoelectric detection structure 53 and by the fourth cantilever element 24 , the fourth suspended mass 34 and the fourth piezoelectric detection structure 54 .

[0052] In particular, if Figure 5 As shown, Figure 5 Considered with Figure 3Under the same conditions, i.e. in the presence of inertial acceleration along Z, the deformable portions 23*, 24* of the third cantilever element 23 and the fourth cantilever element 24 are subjected to parallel and opposite bending moments, which result in the same type of deformation (compression or extension, depending on the meaning of the acceleration) of the third piezoelectric detection structure 53 and the fourth piezoelectric detection structure 54. Figure 6 As shown, Figure 6 Considering the presence of inertial acceleration along the Y direction, the deformable portions 23*, 24* of the third cantilever element 23 and the fourth cantilever element 24 are subjected to parallel and consistent bending moments, which result in opposite deformation types (compression or tension) of the third piezoelectric detection structure 53 and the fourth piezoelectric detection structure 54. Therefore, if V3 and V4 are the voltages generated by the third piezoelectric detection structure 53 and the fourth piezoelectric detection structure 54, respectively, and if sVZ" and sVY are signals equal to V3+V4 and V3-V4, respectively, then the signals sVZ" and sVY indicate the acceleration along the Z direction and the acceleration along the Y direction experienced by the MEMS accelerometer 1, respectively. In addition, in the presence of acceleration along the X direction, the voltages V3 and V4 are substantially zero.

[0053] Additionally, with reference for example to the elastic coupling that exists, due to the first spring structure M1 , between the first mobile mass 31 and the second mobile mass 32 , we find what is described below.

[0054] As previously mentioned, unlike the deformable portions 21 *, 22 * ​​of the first and second cantilever elements 21, 22, the first spring structure M1 is flexible in the direction H1 and therefore in a direction parallel to the axis X. Consequently, any possible undesirable mechanical stresses acting on the support structure 2 (e.g. due to the packaging (not shown)) are compensated by the first spring structure M1 without causing any deformation of the deformable portions 21 *, 22 * ​​of the first and second deformable elements 21, 22 and therefore without changing the voltages generated by the first and second piezoelectric detection structures 51, 52.

[0055] For example, the first spring structure M1 may absorb stress caused by bonding or welding the support structure 2 to the corresponding base of the package, which stress may cause a tension or compression state of the first piezoelectric detection structure 51 and the second piezoelectric detection structure 52 .

[0056] Additionally, the deformable portions 21*, 22* of the first cantilever element 21 and the second cantilever elements 21, 22, the first movable mass 31 and the second movable mass 32, and the first spring structure M1 form a mechanical system. If the presence of the second spring structure M2 and the third cantilever element 23 and the fourth cantilever element 24 can be ignored at this time, the dimensions of the mechanical system can be determined so that the mode in which the first movable mass 31 and the second movable mass 31, 32 oscillate in phase has a desired frequency, which is lower than the frequency of the parasitic mode in which the first movable mass 31 and the second movable mass 32 oscillate in anti-phase. In this regard, without the first spring structure M1, the mechanical system formed by the deformable portion 21* of the first cantilever element 21 and the first mobile mass 31, and the mechanical system formed by the deformable portion 22* of the second cantilever element 21 and the second mobile mass 32 would be independent and have independent oscillation modes with different resonant frequencies. This would require normalization of the electrical responses provided by the first piezoelectric detection structure 51 and the second piezoelectric detection structure 52 to offset the difference caused by the different resonant frequencies of the oscillation modes of the above two independent mechanical systems. In practice, sensitivity would be reduced in any case.

[0057] The same considerations apply to the second spring structure M2 absorbing undesired stresses present on the first ends of the third and fourth cantilever elements 23 and 24 , the direction H3 and the deformable portions 23 *, 24 * of the third and fourth cantilever elements 23 and 24 .

[0058] In practice, the deformable portions 23*, 24* of the third and fourth cantilever elements 23, 24, the third and fourth mobile masses 33, 34, and the second spring structure M2 together with the deformable portions 21*, 22* of the first and second cantilever elements 21, 22, the first and second mobile masses 31, 32, and the first spring structure M1 form the aforementioned mechanical system. The dimensions of this mechanical system can thus be determined such that the so-called operating mode (i.e., the mode excited by the acceleration to be detected) is the first mode, i.e., the mode in which the first, second, third, and fourth mobile masses 31, 32, 33, 34 oscillate in phase.

[0059] Although not shown, in any case, a variant is conceivable in which, for example, the third and fourth cantilever elements 23 and 24, the third and fourth suspension groups G3 and G4, and the second spring structure M2 are absent, in which case the MEMS accelerometer 1 is insensitive to accelerations in a direction parallel to the axis Y. Similarly, a variant is possible in which the first and second cantilever elements 21 and 22, the first and second suspension groups G1 and G2, and the first spring structure M1 are absent, in which case the MEMS accelerometer 1 is insensitive to accelerations in a direction parallel to the axis X.

[0060] In practice, Figure 2 The embodiment shown makes it possible to benefit from a high elasticity with respect to the presence of undesirable mechanical stresses at the end of the cantilever element fixed to the support structure 2 , and a high sensitivity to vibrations of relatively high frequencies (eg 10 kHz to 20 kHz).

[0061] According to a different embodiment (such as Figure 7 ), wherein the MEMS accelerometer is indicated by 101, and the shape and arrangement of the moving mass and spring structure are different from those described previously, as explained in detail below, wherein, unless otherwise stated, the previously mentioned components are indicated using the same reference numerals increased by one hundred.

[0062] In detail, the first, second, third and fourth mobile masses 131, 132, 133, 134 have an approximately parallelepiped shape, are arranged at the same radial distance from the axis HX and are arranged to be spaced at equal angular distances to be arranged on the vertices of an imaginary square.

[0063] Specifically, in a static state, first, second, third, and fourth mobile masses 131, 132, 133, and 134 have a substantially parallelepipedal shape, with sidewalls alternately parallel to plane XZ or plane YZ. Furthermore, first mobile mass 131 and third mobile mass 133 are aligned parallel to axis X; similarly, second mobile mass 132 and fourth mobile mass 134 are aligned parallel to axis X. Furthermore, first mobile mass 131 and fourth mobile mass 134 are aligned parallel to axis Y; similarly, second mobile mass 132 and third mobile mass 133 are aligned parallel to axis Y.

[0064] In the static state, the deformable portions 121*, 122* of the first cantilever element 121 and the second cantilever element 121, 122 have centroid axes respectively lying in directions H1' and H2', which are parallel to the plane XY, parallel to each other and coincide, as a first approximation. In addition, the directions H1', ​​H2' are inclined by -45° with respect to the axis X. As a first approximation, the directions H1', ​​H2' also coincide with the centroid axes of the two entities respectively formed by: i) the deformable portion 121* and the first piezoelectric detection structure 151 of the first cantilever element 121, and ii) the deformable portion 122* and the second piezoelectric detection structure 152 of the second cantilever element 122, which, as a first approximation, in turn coincide with the neutral axes of the corresponding entities.

[0065] The deformable portions 123*, 124* of the third cantilever element 123 and the fourth cantilever element 124 have centroid axes respectively lying in the directions H3' and H4', which are parallel to the plane XY, parallel to each other and coincide, as a first approximation. In addition, the directions H3', H4' are inclined by +45° with respect to the axis X. As a first approximation, the directions H3', H4' also coincide with the centroid axes of the two entities respectively formed by: i) the deformable portion 123* of the third cantilever element 123 and the third piezoelectric detection structure 153, and ii) the deformable portion 124* of the fourth cantilever element 124 and the fourth piezoelectric detection structure 154, which, as a first approximation, in turn coincide with the neutral axes of the corresponding entities.

[0066] In a top view, the deformable portions 121*, 122*, 123*, 124* of the first, second, third, and fourth cantilever elements 121, 122, 123, 124 are respectively disposed between the support structure 102 and the corresponding distal portions 121**, 122**, 123**, 124**, thereby forming the first, second, third, and fourth mobile masses 131, 132, 133, 134, respectively. Furthermore, the deformable portions 121*, 122*, 123*, 124* of the first, second, third, and fourth cantilever elements 121, 122, 123, 124 are respectively covered by the first, second, third, and fourth piezoelectric detection structures 151, 152, 153, 154.

[0067] The first, second, third and fourth spring elements 141, 142, 143, 144 each have a folded elongated shape, for example of silicon, and in the static state may have the same thickness (along Z) as the first, second, third and fourth cantilever elements 121, 122, 123, 124 and be coplanar with them.

[0068] In more detail, hereinafter, F13 and F31 denote side surfaces that are parallel to and face the second symmetry plane SP2 of the first suspended mass 131 and the third suspended mass 133, respectively. Similarly, F24 and F42 denote side surfaces that are parallel to and face the second symmetry plane SP2 of the second suspended mass 132 and the fourth suspended mass 134, respectively. Additionally, F14 and F41 denote side surfaces that are parallel to and face the first symmetry plane SP1 of the first suspended mass 131 and the fourth suspended mass 134, respectively. Similarly, F23 and F32 denote side walls that are parallel to and face the first symmetry plane SP1 of the second suspended mass 132 and the third suspended mass 133, respectively.

[0069] In summary, the ends of the first spring element 141 are fixed to the side surfaces F13 and F31 of the first and third suspended masses 131 and 133 respectively to elastically couple the latter; moreover, the first spring element 141 is flexible in a direction parallel to the axis X.

[0070] The ends of the second spring element 142 are fixed to the side surfaces F24 and F42 of the second and fourth suspended masses 132 and 134 , respectively, to elastically couple the latter; moreover, the second spring element 142 is flexible in a direction parallel to the axis X.

[0071] The ends of the third spring element 143 are fixed to the side surfaces F23 and F32 of the second and third suspended masses 132 and 133, respectively, to elastically couple the latter.

[0072] The ends of the fourth spring element 144 are fixed to the side surfaces F14 and F41 of the first and fourth suspended masses 131 and 134 , respectively, to elastically couple the latter; moreover, the fourth spring element 144 is flexible in a direction parallel to the Y axis.

[0073] For the sake of simplicity, reference is made to the spring elements in contact with third mobile mass 133, and therefore to first spring element 141 and third spring element 143 (although the same considerations apply to the pairs of spring elements in contact with first, second, and fourth mobile masses 141, 142, 144), and without loss of generality, we find the following description. If VX denotes a lateral edge of third mobile mass 133 parallel to axis Z and facing axis HX, first spring element 141 and third spring element 143 respectively contact lateral surfaces F31 and F32 near edge VX, but remain at a distance from each other. Even if not shown, embodiments in which first spring element 141 and third spring element 143 are in contact with each other are possible.

[0074] In practice, the first spring element 141 and the third spring element 143, together with the third mobile mass 133, form a first branch of a first spring structure (here denoted by M1′), the first branch elastically coupling the first mobile mass 131 and the second mobile mass 132. Furthermore, the second spring element 142 and the fourth spring element 144, together with the fourth mobile mass 134, form a second branch of the first spring structure M1′, the second branch also elastically coupling the first mobile mass 131 and the second mobile mass 132 and, as a first approximation, being arranged parallel to the aforementioned first branch.

[0075] Likewise, first spring element 141 and fourth spring element 144, together with first mobile mass 131, form a first branch of a second spring structure (here denoted by M2′), which elastically couples third mobile mass 133 and fourth mobile mass 134. Additionally, second spring element 142 and third spring element 143, together with second mobile mass 132, form a second branch of second spring structure M2′, which also elastically couples third mobile mass 133 and fourth mobile mass 134 and, as a first approximation, is arranged parallel to the corresponding first branch.

[0076] The operation of the MEMS accelerometer 101 is such that, if it is subjected to an acceleration directed in a direction parallel to the axis Z, the first, second, third and fourth moving masses 131, 132, 133, 134 tend to all rise or fall together, depending on the sense of the acceleration, e.g. Figure 8A , wherein, except for mentioning the case where, for example, the mobile masses tend to rise, the classical convention is adopted to represent the tips and tails of the vectors qualitatively indicating the directions of displacement of the first, second, third and fourth mobile masses 131, 132, 133, 134 relative to their rest positions; in the subsequent Figure 8B and Figure 8C This practice is also retained in .

[0077] In the case where the MEMS accelerometer 1 is subjected to an acceleration directed towards the axis X, but with the opposite direction, it can be found Figure 8B , where arrows gx indicate the inertial acceleration experienced by the first, second, third, and fourth mobile masses 131, 132, 133, and 134. Specifically, the first mobile mass 131 and the fourth mobile mass 134 tend to rise, causing the first electrical detection structure 151 and the fourth piezoelectric detection structure 154 to compress, thereby generating voltages V1 and V4 having the same first polarity, respectively. Conversely, the second mobile mass 132 and the third mobile mass 133 tend to fall, causing the second piezoelectric detection structure 153 and the third piezoelectric detection structure 154 to stretch, thereby generating voltages V2 and V3 having the same second polarity opposite to the first polarity, respectively.

[0078] Can recall about Figures 1 to 4 and noting that the inertial acceleration gx can be decomposed into corresponding components in the direction H1' (equivalently, H2') and the direction H3' (equivalently, H4'), and noting that the first mobile mass 131 and the second mobile mass 132 and the first spring structure M1' act with respect to the components of the inertial acceleration in the directions H1' and H3', in the same manner, Figures 1 to 4 The first mobile mass 21 and the second mobile mass 22 and the first spring structure M1 of the MEMS accelerometer 1 shown in FIG act in the presence of inertial accelerations pointing in directions parallel to the axes X and Y. Furthermore, the third mobile mass 133 and the fourth mobile mass 134 and the second spring structure M2′ act in the same way with respect to the components of the inertial accelerations in the directions H1′ and H3′. Figures 1 to 4 The third and fourth moving masses 23, 24 and the second spring structure M2 of the MEMS accelerometer 1 shown in FIG. 1 act in the presence of inertial accelerations pointing in directions parallel to the X and Y axes.

[0079] In the case where the MEMS accelerometer 1 is subjected to an acceleration directed along the axis Y, it is found that Figure 8C , where arrows gy indicate the inertial acceleration experienced by the first, second, third, and fourth mobile masses 131, 132, 133, and 134. Specifically, the first and third mobile masses 131, 133 tend to descend, causing the first and third piezoelectric detection structures 151, 153 to stretch, thereby generating voltages V1 and V3 of the second polarity, respectively. Conversely, the second and fourth mobile masses 132, 134 tend to ascend, causing the second and fourth piezoelectric detection structures 152, 154 to compress, thereby generating voltages V2 and V4 of the first polarity, respectively.

[0080] By means of an electronic circuit of a type known per se and not shown here, a signal sVZ2 can thus be generated, which is for example equal to V1+V2+V3+V4 and indicates the acceleration along Z. Additionally, a signal sVX′=(V1+V4)−(V2+V3) and a signal sVY′=(V2+V4)−(V1+V3) can be generated, which respectively indicate the acceleration along X and along Y.

[0081] Figure 7 and Figures 8A to 8C The embodiments shown in the Figures 1 to 4In addition, in this case as well, a variation is possible in which, for example, the third mobile mass 133 and the fourth mobile mass 134 and the third cantilever element 123 and the fourth cantilever element 124 are not present, or a variation is possible in which, for example, the first mobile mass 131 and the second mobile mass 132 and the first cantilever element 121 and the second cantilever element 122 are not present.

[0082] In general, the advantages offered by the present accelerometer are clearly apparent from the preceding description. In particular, the present accelerometer is, for example, capable of detecting vibrations in mutually orthogonal stimulus directions with high sensitivity, these vibrations possibly having relatively high frequencies, and at the same time making it possible to benefit from a high degree of immunity to stray static effects caused by stray voltages.

[0083] Finally, it is obvious that modifications and variations may be made to what has been described and illustrated herein without departing from the scope of the present disclosure.

[0084] For example, the shapes of the cantilever element and the mobile mass and the corresponding cross-sections can differ from those described, and similarly, the shape of the piezoelectric sensing structure and its arrangement relative to the cantilever element can differ. For example, in principle, the piezoelectric sensing structure can be arranged below the deformable portion of the cantilever element.

[0085] The MEMS accelerometer can be summarized as comprising a support structure (2; 102) and at least one first deformable group (21*, 51; 121*, 151) and at least one second deformable group (22*, 52; 122*, 152), the at least one first deformable group (21*, 51; 121*, 151) and the at least one second deformable group (22*, 52; 122*, 152) respectively comprising a first deformable cantilever element (21*; 121*) and a second deformable cantilever element (22*; 122*), the first deformable cantilever element (21*; 121*) and the second deformable cantilever element (22*; 122*) being arranged in a direction parallel to a plane (XY) and each having a respective first end and a respective second end, the first end being fixed to the support structure (2; 102); the first deformable group (21*, 51; 121*, 151) further comprising:

[0086] a first piezoelectric sensing structure (51; 151) mechanically coupled to the first deformable cantilever element (21*; 121*);

[0087] The second deformable group (22*, 52; 122*, 152) further includes:

[0088] a second piezoelectric sensing structure (52; 152) mechanically coupled to the second deformable cantilever element (22*; 122*);

[0089] The MEMS accelerometer (1; 101) further comprises:

[0090] a first mobile mass (31, 131) and a second mobile mass (32, 132) fixed to the second end of the first deformable cantilever element (21*, 121*) and the second end of the first deformable cantilever element (21*, 121*), respectively, and staggered relative to the first deformable cantilever element and the second deformable cantilever element (21*, 121*; 22*, 122*), respectively, in a perpendicular direction (Z) relative to the plane (XY); and

[0091] A first elastic structure (M1, M1') is configured to elastically couple a first mobile mass and a second mobile mass (31, 131; 32, 132).

[0092] The first deformable cantilever element and the second deformable cantilever element (21*, 22*; 121*, 122*) can extend in a first detection direction (H1, H2; H1', ​​H2') and can be opposite to each other, so that when there is an acceleration pointing in a direction parallel to the first detection direction (H1, H2; H1', ​​H2'), the first deformable cantilever element and the second deformable cantilever element (21*, 22*; 121*, 122*) can undergo a first parallel and consistent bending moment.

[0093] The first deformable group and the second deformable group (21*, 51, 22*, 52; 121*, 151, 122*, 152) can respectively have a first neutral axis (H1, H1') and a second neutral axis (H2, H2') extending in the first detection direction (H1, H2; H1', ​​H2').

[0094] The first piezoelectric detection structure and the second piezoelectric detection structure (51, 52; 151, 152) can be staggered in the vertical direction (Z) relative to the first neutral axis (H1, H1') and the second neutral axis (H2, H2'), respectively, so that in the presence of the first parallel and consistent bending moment, one of the first piezoelectric detection structure and the second piezoelectric detection structure (51, 52; 151, 152) can undergo tension and the other can undergo compression.

[0095] The first and second piezoelectric detection structures (51, 52; 151, 152) may have a planar shape and be arranged symmetrically about the first neutral axis (H1, H1') and the second neutral axis (H2, H2'), respectively.

[0096] The first piezoelectric detection structure and the second piezoelectric detection structure (51, 52; 151, 152) can be arranged on the first deformable cantilever element and the second deformable cantilever element (21*, 22*; 121*, 122*), respectively; and wherein the first movable mass block and the second movable mass block (31, 131; 32, 132) can be staggered vertically downward relative to the first deformable cantilever element and the second deformable cantilever element (21*, 121*; 22*, 122*).

[0097] The first elastic structure (M1, M1') may be flexible in a direction parallel to the first detection direction (H1, H2; H1', ​​H2').

[0098] The accelerometer may further include a third deformable group (23*, 53; 123*, 153) and a fourth deformable group (24*, 54; 124*, 154), the third deformable group (23*, 53; 123*, 153) and the fourth deformable group (24*, 54; 124*, 154) may respectively include a third deformable cantilever element (23*; 123*) and a fourth deformable cantilever element (24*; 124*), the third deformable cantilever element The arm element (23*; 123*) and the fourth deformable cantilever element (24*; 124*) are arranged in a direction parallel to the plane (XY), extend in a second detection direction (H3, H4; H3', H4'), are opposite to each other and each has a respective first end and a respective second end, the first end being fixed to the support structure (2; 102); the third deformable group (23*, 53; 123*, 153) may further include:

[0099] a third piezoelectric sensing structure (53; 153) mechanically coupled to the third deformable cantilever element (23*; 123*);

[0100] The fourth deformable group (24*, 54; 124*, 154) may further include:

[0101] a fourth piezoelectric sensing structure (54; 154) mechanically coupled to the fourth deformable cantilever element (24*; 124*);

[0102] The MEMS accelerometer (1; 101) may further comprise:

[0103] a third mobile mass (33, 133) and a fourth mobile mass (34, 134) fixed to a second end of the third deformable cantilever element (23*; 123*) and a second end of the fourth deformable cantilever element (24*; 124*), respectively, and staggered in the vertical direction (Z) relative to the third deformable cantilever element and the fourth deformable cantilever element (23*, 123*; 24*, 124*), respectively, so that in the presence of an acceleration pointing in a direction parallel to the second detection direction (H3, H4; H3', H4'), the third deformable cantilever element and the fourth deformable cantilever element (23*, 123*; 24*, 124*) are subjected to a second parallel and coincident bending moment;

[0104] The accelerometer (7; 107) may further comprise a second elastic structure (M2, M2') configured to elastically couple the third and fourth mobile masses (33, 133; 34, 134).

[0105] The third deformable group and the fourth deformable group (23*, 53, 24*, 54; 123*, 153, 124*, 154) can respectively have a third neutral axis (H3, H3') and a fourth neutral axis (H4, H4') extending in the second detection direction (H3, H4; H3', H4').

[0106] The third piezoelectric detection structure and the fourth piezoelectric detection structure (53, 54; 153, 154) can be staggered in the vertical direction (Z) relative to the third neutral axis (H3, H3') and the fourth neutral axis (H4, H4'), respectively, so that in the presence of the second parallel and consistent bending moment, one of the third piezoelectric detection structure and the fourth piezoelectric detection structure (53, 54; 153, 1524) is subjected to tension and the other is subjected to compression.

[0107] The third and fourth piezoelectric detecting structures (53, 54; 153, 154) may have a planar shape, arranged in a symmetrical manner with respect to the third and fourth neutral axes (H3, H3'), respectively.

[0108] The second elastic structure ( M2 , M2 ′) may be flexible in a direction parallel to the second detection direction ( H3 , H4 ; H3 ′, H4 ′).

[0109] The first detection direction ( H1 , H2 ; H1 ′, H2 ′) and the second detection direction ( H3 , H4 ; H3 ′, H4 ′) may be perpendicular to each other and to the vertical direction (Z).

[0110] The first and second mobile masses (31, 32; 131, 132) may each have a center of mass staggered relative to a second end of the first and second deformable cantilever elements (21*, 121*; 22*, 121*) in a first detection direction (H1, H2; H1', ​​H2'), such that in the presence of an acceleration pointing in a direction parallel to the vertical direction (Z), the first and second deformable cantilever elements (21*, 121*; 22*, 121*) are subjected to third parallel and opposite bending moments; And wherein the third movable mass block and the fourth movable mass block (33, 34; 133, 134) respectively have a center of mass staggered relative to the second end of the third deformable cantilever element (23*, 123*; 24*, 124*) in the second detection direction (H3, H4; H3', H4'), so that in the presence of an acceleration pointing in a direction parallel to the vertical direction (Z), the third deformable cantilever element and the fourth deformable cantilever element (23*, 123*; 24*, 124*) are subjected to a third parallel and opposite bending moment.

[0111] The first, second, third and fourth mobile masses (131, 132, 133, 134) may be arranged in a square, so as to be arranged alternately two by two parallel to a first reference axis (X) or a second reference axis (Y), the first reference axis (X) or the second reference axis (Y) being orthogonal to each other and perpendicular to a vertical direction (Z); and wherein the first detection direction and the second detection direction (H1', H2'; H3', H4') may both be transverse to the first reference axis and the second reference axis (X, Y); wherein the accelerometer (107) may further comprise:

[0112] a first spring (141) that is flexible in a direction parallel to the first reference axis (X) and elastically couples the first mobile mass and the third mobile mass (131, 133);

[0113] a second spring (142) that is flexible in a direction parallel to the first reference axis (X) and elastically couples the second and fourth moving masses (132, 134);

[0114] a third spring (143) that is flexible in a direction parallel to the second reference axis (Y) and elastically couples the second and third mobile masses (132, 133); and

[0115] a fourth spring (144) that is flexible in a direction parallel to the second reference axis (Y) and elastically couples the first mobile mass and the fourth mobile mass (131, 134);

[0116] And wherein the first elastic structure (M1') includes a corresponding first branch and a corresponding second branch, the first branch of the first elastic structure (M1') includes a first spring and a third spring (141, 143) and a third movable mass block (133), and the second branch of the first elastic structure (M1') includes a second spring and a fourth spring (142, 144) and a fourth movable mass block (134); and wherein the second elastic structure (M2') includes a corresponding first branch and a corresponding second branch, the first branch of the second elastic structure (M2') includes a first spring and a fourth spring (141, 144) and a first movable mass block (131), and the second branch of the second elastic structure (M2') includes a second spring and a third spring (142, 143) and a second movable mass block (133).

[0117] The first, second, third and fourth moving masses (31, 32, 33, 34) may have a diamond arrangement; and wherein the first and second spring structures (M1, M2) may include first arms (41, 42) and second arms (43, 44), respectively, each of the first and second arms having a folded, elongated shape and arranged to form a cross.

[0118] The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above detailed description. Generally, 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 to include all possible embodiments claimed and the full scope of their equivalents. Therefore, the claims are not limited by the present disclosure.

Claims

1. A microelectromechanical system (MEMS) accelerometer comprising: Support structure; a first deformable group and a second deformable group, wherein the first deformable group and the second deformable group respectively include a first deformable cantilever element and a second deformable cantilever element, the first deformable cantilever element and the second deformable cantilever element being arranged in a direction parallel to a plane and each having a corresponding first end and a corresponding second end, the first end being fixed to the support structure, the first deformable group further including a first piezoelectric detection structure mechanically coupled to the first deformable cantilever element, and the second deformable group further including a second piezoelectric detection structure mechanically coupled to the second deformable cantilever element; a first movable mass and a second movable mass, the first movable mass and the second movable mass being respectively fixed to the second end of the first deformable cantilever element and the second end of the second deformable cantilever element and being staggered relative to the first deformable cantilever element and the second deformable cantilever element, respectively, in a vertical direction transverse to the plane; as well as A first elastic structure is configured to elastically couple the first moving mass and the second moving mass.

2. A MEMS accelerometer according to claim 1, wherein the first deformable cantilever element and the second deformable cantilever element extend in a first detection direction and are opposite to each other, so that in the presence of an acceleration pointing in a direction parallel to the first detection direction, the first deformable cantilever element and the second deformable cantilever element are subjected to a first parallel and consistent bending moment. 3 . The MEMS accelerometer of claim 2 , wherein the first deformable group and the second deformable group have a first neutral axis and a second neutral axis, respectively, the first neutral axis and the second neutral axis extending in the first detection direction.

4. The MEMS accelerometer of claim 3 , wherein the first piezoelectric sensing structure and the second piezoelectric sensing structure are staggered in the vertical direction relative to the first neutral axis and the second neutral axis, respectively, such that in the presence of the first parallel and consistent bending moment, one of the first piezoelectric sensing structure and the second piezoelectric sensing structure is subjected to tension while the other piezoelectric sensing structure is subjected to compression. 5 . The MEMS accelerometer according to claim 4 , wherein the first piezoelectric detection structure and the second piezoelectric detection structure have a planar shape and are arranged symmetrically with respect to the first neutral axis and the second neutral axis, respectively.

6. A MEMS accelerometer according to claim 4, wherein the first piezoelectric sensing structure and the second piezoelectric sensing structure are arranged on the first deformable cantilever element and the second deformable cantilever element, respectively, and wherein the first moving mass block and the second moving mass block are vertically staggered downward relative to the first deformable cantilever element and the second deformable cantilever element. 7 . The MEMS accelerometer of claim 2 , wherein the first elastic structure is flexible in a direction parallel to the first detection direction.

8. The MEMS accelerometer according to claim 2, further comprising: a third deformable group and a fourth deformable group, wherein the third deformable group and the fourth deformable group respectively include a third deformable cantilever element and a fourth deformable cantilever element, the third deformable cantilever element and the fourth deformable cantilever element being arranged in a direction parallel to the plane, extending in a second detection direction, facing each other, and each having a corresponding first end and a corresponding second end, the first end being fixed to the support structure, the third deformable group further including a third piezoelectric detection structure mechanically coupled to the third deformable cantilever element, and the fourth deformable group further including a fourth piezoelectric detection structure mechanically coupled to the fourth deformable cantilever element; a third mobile mass and a fourth mobile mass, the third mobile mass and the fourth mobile mass being fixed to the second end of the third deformable cantilever element and the second end of the fourth deformable cantilever element, respectively, and being staggered in the vertical direction relative to the third deformable cantilever element and the fourth deformable cantilever element, respectively, such that in the presence of an acceleration pointing in a direction parallel to the second detection direction, the third deformable cantilever element and the fourth deformable cantilever element are subjected to a second parallel and coincident bending moment; as well as The second elastic structure is configured to elastically couple the third moving mass and the fourth moving mass. 9 . The MEMS accelerometer of claim 8 , wherein the third deformable group and the fourth deformable group have a third neutral axis and a fourth neutral axis, respectively, the third neutral axis and the fourth neutral axis extending in the second detection direction.

10. The MEMS accelerometer of claim 9 , wherein the third piezoelectric sensing structure and the fourth piezoelectric sensing structure are staggered relative to the third neutral axis and the fourth neutral axis, respectively, in the vertical direction such that in the presence of the second parallel and consistent bending moment, one of the third piezoelectric sensing structure and the fourth piezoelectric sensing structure is subjected to tension while the other piezoelectric sensing structure is subjected to compression. 11 . The MEMS accelerometer according to claim 10 , wherein the third piezoelectric detection structure and the fourth piezoelectric detection structure have a planar shape and are arranged symmetrically with respect to the third neutral axis and the fourth neutral axis, respectively. 12 . The MEMS accelerometer of claim 8 , wherein the second elastic structure is flexible in a direction parallel to the second detection direction. 13 . The MEMS accelerometer of claim 8 , wherein the first detection direction and the second detection direction are perpendicular to each other and perpendicular to the vertical direction.

14. The MEMS accelerometer of claim 13 , wherein the first and second moving masses have centers of mass that are staggered relative to the second ends of the first and second deformable cantilever elements, respectively, in the first detection direction, such that in the presence of an acceleration pointing in a direction parallel to the vertical direction, the first and second deformable cantilever elements experience third parallel and opposite bending moments, and Wherein the third movable mass block and the fourth movable mass block respectively have a center of mass staggered relative to the second end of the third deformable cantilever element and the fourth deformable cantilever element in the second detection direction, so that in the presence of an acceleration pointing in a direction parallel to the vertical direction, the third deformable cantilever element and the fourth deformable cantilever element are subjected to a fourth parallel and opposite bending moment.

15. The MEMS accelerometer according to claim 13 , wherein the first mobile mass, the second mobile mass, the third mobile mass, and the fourth mobile mass are arranged in a square so as to be arranged alternately parallel to a first reference axis or a second reference axis, the first reference axis and the second reference axis being orthogonal to each other and perpendicular to the vertical direction, and wherein the first detection direction and the second detection direction are both transverse to the first reference axis and the second reference axis, the MEMS accelerometer further comprising: a first spring that is flexible in a direction parallel to the first reference axis and elastically couples the first and third moving masses; a second spring that is flexible in a direction parallel to the first reference axis and elastically couples the second mobile mass and the fourth mobile mass; a third spring that is flexible in a direction parallel to the second reference axis and elastically couples the second and third mobile masses; as well as a fourth spring that is flexible in a direction parallel to the second reference axis and elastically couples the first and fourth mobile masses, The first elastic structure includes a corresponding first branch and a corresponding second branch, the first branch of the first elastic structure includes the first spring, the third spring and the third moving mass block, the second branch of the first elastic structure includes the second spring, the fourth spring and the fourth moving mass block, and the second elastic structure includes a corresponding first branch and a corresponding second branch, the first branch of the second elastic structure includes the first spring, the fourth spring and the first moving mass block, and the second branch of the second elastic structure includes the second spring, the third spring and the second moving mass block.

16. The MEMS accelerometer of claim 13 , wherein the first moving mass, the second moving mass, the third moving mass, and the fourth moving mass have a diamond arrangement, and wherein the first elastic structure and the second elastic structure include a first arm and a second arm, respectively, each of the first arm and the second arm having a folded elongated shape and arranged to form a cross.

17. A device comprising: Support structure; a first deformable cantilever element having a deformable portion and a distal portion, the deformable portion being secured to the support structure; a first mobile mass mechanically coupled to a first side of the deformable portion of the first deformable cantilever element; a second deformable cantilever element having a deformable portion and a distal portion, the deformable portion being secured to the support structure; a second mobile mass mechanically coupled to a first side of the deformable portion of the second deformable cantilever element; a first piezoelectric sensing structure mechanically coupled to a second side of the first deformable cantilever element, the second side of the first deformable cantilever element being opposite the first side of the first deformable cantilever element; a second piezoelectric sensing structure mechanically coupled to a second side of the second deformable cantilever element, the second side of the second deformable cantilever element being opposite the first side of the second deformable cantilever element; as well as A first elastic structure is configured to elastically couple the first moving mass and the second moving mass.

18. An apparatus according to claim 17, wherein the first deformable cantilever element and the second deformable cantilever element extend in a first detection direction and are opposite to each other, and the first deformable cantilever element and the second deformable cantilever element are subjected to a first parallel and consistent bending moment in the presence of an acceleration pointing in a direction parallel to the first detection direction.

19. The device of claim 18, wherein the first resilient structure is flexible in a direction parallel to the first detection direction.

20. The apparatus of claim 17, further comprising: a third deformable cantilever element having a deformable portion and a distal portion, the deformable portion being secured to the support structure; a third mobile mass mechanically coupled to a first side of the deformable portion of the third deformable cantilever element; a fourth deformable cantilever element having a deformable portion and a distal portion, the deformable portion being secured to the support structure; a fourth mobile mass mechanically coupled to a first side of the deformable portion of the fourth deformable cantilever element; a third piezoelectric sensing structure mechanically coupled to a second side of the third deformable cantilever element, the second side of the third deformable cantilever element being opposite the first side of the third deformable cantilever element; a fourth piezoelectric sensing structure mechanically coupled to a second side of the fourth deformable cantilever element, the second side of the fourth deformable cantilever element being opposite the first side of the fourth deformable cantilever element; as well as a second elastic structure configured to elastically couple the third mobile mass and the fourth mobile mass, The first deformable cantilever element and the second deformable cantilever element are aligned with each other along a first direction, and the third deformable cantilever element and the fourth deformable cantilever element are aligned with each other along a second direction transverse to the first direction.

Images