Micromechanical structure with biaxial actuation and corresponding MEMS device

A reflector micromechanical structure includes a frame with a window. The frame is elastically connected to an anchorage structure by first elastic elements. An actuation structure operatively coupled to the frame is configured to generate a first actuation movement of the frame about a first actuation axis. A mobile mass is positioned within the window and elastically coupled to the frame by second elastic elements. A mass distribution is associated to the mobile mass such as to generate, by an inertial effect in response to the first actuation movement, a second actuation movement of rotation of the mobile mass about a second actuation axis.

PRIORITY CLAIM

This application claims priority from Italian Application for Patent No. 102015000078393 filed Nov. 30, 2015, the disclosure of which is incorporated by reference.

TECHNICAL FIELD

The present invention relates to a micromechanical structure with biaxial actuation and to a corresponding MEMS (Micro-Electromechanical Systems) device; in particular, the present disclosure will refer to a reflector micromechanical structure (also referred to as “micromirror”) for an optical MEMS device, for example a projector.

BACKGROUND

Reflector micromechanical structures are known, that are made, at least in part, with semiconductor materials and using MEMS technology.

These micromechanical structures may be integrated in portable electronic apparatuses, such as for example tablets, smartphones, PDAs, for optical applications, in particular for directing, with desired modalities, beams of light radiation generated by a light source, typically a laser. Thanks to the reduced dimensions, micromechanical structures enable stringent requirements to be met as regards occupation of space, in terms of area and thickness.

For instance, reflector micromechanical structures are used in miniaturized projector devices (the so-called picoprojectors), which are able to project desired images or patterns of light at a distance.

Reflector micromechanical structures generally include a mobile structure, which carries a reflecting element or mirror element (i.e. of a material having a high reflectivity for a particular wavelength, or band of wavelengths), made in a body of semiconductor material so as to be mobile, for example with a movement of inclination and/or rotation, for directing an incident light beam in a desired way by varying a direction of propagation thereof; and a supporting structure, which is also made starting from a body of semiconductor material, coupled to the mobile structure, having functions of supporting and handling. In the supporting structure, a cavity is generally formed, underneath and in a position corresponding to the mobile structure with its reflecting element, for enabling freedom of movement and rotation thereof.

Typically, the direction of propagation of the optical beam is varied in a periodic or quasi-periodic way for performing a scanning of a portion of space with the reflected optical beam. In particular, in reflector micromechanical structures of a resonant type, an actuation system causes oscillation of the reflecting element in a substantially periodic way about a resting position, the oscillation period being as close as possible to the resonance frequency in order to maximize the angular distance covered by the reflecting element during each oscillation and thus maximize the size of the scanning space portion.

Among reflector micromechanical structures, biaxial-actuation structures are known, in which the reflecting element is actuated with respect to two different mutually orthogonal actuation axes according to a so-called Lissajous scanning path.

FIG. 1illustrates in a schematic and simplified manner a reflector micromechanical structure, designated as a whole by 1.

The reflector micromechanical structure1comprises: a frame2, in the example shown having a square ring shape in a horizontal plane xy defined by a first horizontal axis x and a second horizontal axis y (and coinciding with the plane of a main surface2A of the same frame2); and a mobile mass4, in the example shown having a circular shape in the horizontal plane xy.

The frame2defines, inside it, a window5, in which the mobile mass4is housed, and is connected by first elastic elements6to an anchorage structure7, external to the same frame2, fixed with respect to a substrate8(represented schematically) of the body of semiconductor material in which the reflector micromechanical structure1is provided.

In particular, the first elastic elements6extend aligned along the first horizontal axis x, on opposite sides of the frame2, connecting respective portions of the frame2to anchoring elements7A,7B of the anchorage structure7(that are, for example, in a way herein not illustrated, vertical pillars that connect to the aforesaid substrate8).

The first elastic elements6are compliant to torsion for enabling a movement of rotation of the frame2with respect to the anchorage structure7and to the substrate8, out of the horizontal plane xy and about the first horizontal axis x.

The mobile mass4carries, at the top, a mirror element4′, of a material with high reflectivity for the light radiation to be reflected, such as, for example, aluminum or gold, and is connected to the frame2by second elastic elements9, which extend aligned along the second horizontal axis y, on opposite sides of the mobile mass4.

The second elastic elements9are compliant to torsion for enabling a movement of rotation of the mobile mass4with respect to the frame2, out of the horizontal plane xy and about the second horizontal axis y; further, the second elastic elements9are rigid with respect to bending, so that the mobile mass4is rigidly coupled to the frame2in the movement of rotation about the first horizontal axis x.

The reflector micromechanical structure1further comprises: a first actuation structure10(represented schematically) coupled to the frame2and configured to cause an actuation movement of rotation of the same frame2about the first horizontal axis x, as a function of appropriate electrical driving signals such as to generate a twisting moment Txabout the first horizontal axis x; and a second actuation structure11(which is also represented schematically), coupled to the mobile mass4and configured to cause a respective actuation movement of rotation of the same mobile mass4about the second horizontal axis y, as a function of further electrical driving signals, such as to generate a respective twisting moment Tyabout the aforesaid second horizontal axis y.

The first and second actuation structures10,11, as a function of the respective electrical driving signals, thus enable rotation of the mobile mass4, and the associated mirror element4′, about the first and second horizontal axes x, y, in this way enabling creation of a desired biaxial scanning pattern of the reflected light beam.

So far the following principles of operation have been proposed for the aforesaid first and second actuation structures10,11: electrostatic (in which respective sets of comb-fingered electrodes are coupled to the frame2and to the mobile mass4, for generation of electrostatic attraction forces and generation of the aforesaid twisting moments Tx, Ty); piezoelectric (in which piezoelectric elements are mechanically coupled to the first and second elastic elements6,9to cause torsion thereof and consequent generation of the twisting moments Tx, Ty); and electromagnetic (a coil is in this case arranged in a position corresponding to the frame2for generating, due to passage of an electric current, a magnetic field designed to generate the twisting moments Tx, Ty).

An example of a reflector micromechanical structure operating according to the electrostatic principle is, for example, described in U.S. Pat. No. 7,399,652 (incorporated by reference).

It has been noted that the solution described previously, irrespective of the principle of actuation used, is affected by certain limitations as regards the efficiency of actuation and the size of the resulting structure.

In particular, high values of the driving signals are generally to be supplied to the actuation structures to obtain the desired twisting moments Tx, Ty, for example high voltages of the order of 100 V for electrostatic actuation structures, or of 50 V for piezoelectric actuation structures, or high currents, for example of the order of 100 mA, in the case of electromagnetic actuation structures.

This problem is evidently more felt for biaxial-actuation micromechanical structures, where generally distinct driving circuits and actuation structures are required for each axis of actuation (with a consequent increase in the size and the manufacturing costs).

There is a need in the art to solve, at least in part, the above problems, which afflict micromechanical structures of a known type, and in particular to provide a structure with an improved actuation efficiency.

SUMMARY

In an embodiment, a micromechanical structure with biaxial actuation comprises: a frame including an internally defined window, said frame elastically connected by first elastic elements to an anchorage structure fixed with respect to a substrate; an actuation structure operatively coupled to said frame and configured to generate a first actuation movement of said frame with respect to a first actuation axis for said frame; a mobile mass arranged within said window and elastically coupled by second elastic elements of a torsional type to said frame and configured so that said mobile mass is rigidly coupled to said frame in said first actuation movement and further defining a second actuation axis of a torsional type for said mobile mass, and a mass distribution associated to said mobile mass and being asymmetrical at least with respect to said second actuation axis and configured to generate, by an inertial effect as a function of said first actuation movement, a second actuation movement of rotation of the mobile mass about the second actuation axis.

In an embodiment, a MEMS device of an optical type comprises: a micromechanical structure with biaxial actuation, comprising: a frame including an internally defined window, said frame elastically connected by first elastic elements to an anchorage structure fixed with respect to a substrate; an actuation structure operatively coupled to said frame and configured to generate a first actuation movement of said frame with respect to a first actuation axis for said frame; a mobile mass arranged within said window and elastically coupled by second elastic elements of a torsional type to said frame and configured so that said mobile mass is rigidly coupled to said frame in said first actuation movement and further defining a second actuation axis of a torsional type for said mobile mass, wherein said mobile mass carries a reflecting element, and a mass distribution associated to said mobile mass and being asymmetrical at least with respect to said second actuation axis and configured to generate, by an inertial effect as a function of said first actuation movement, a second actuation movement of rotation of the mobile mass about the second actuation axis; and a light source configured to generate a light beam incident on said reflecting element; wherein biaxial actuation of said mobile mass generates a movement of said reflecting element for reflection of said light beam.

In an embodiment, a micromechanical structure with biaxial actuation comprises: a frame including a window, said frame elastically connected to an anchorage structure by first elastic elements; an actuation structure operatively coupled to said frame and configured to generate a first actuation movement of said frame with respect to a first actuation axis; a mobile mass within said window and elastically coupled to said frame by second elastic elements defining a second actuation axis; a mass distribution associated to said mobile mass in an asymmetrical manner with respect to said second actuation axis and configured to generate by the inertial effect in response to said first actuation movement a second actuation movement of rotation of the mobile mass about the second actuation axis.

DETAILED DESCRIPTION

As illustrated schematically inFIG. 2A, according to one embodiment of the present solution, a micromechanical structure with biaxial actuation, in particular a reflector micromechanical structure20, has a configuration substantially equivalent to the one discussed with reference toFIG. 1, thus having: the frame2(in general, the same reference numbers are used for designating elements having a structure and a function equivalent to those of others discussed previously), elastically coupled to the anchorage structure7by the first elastic elements6; and the mobile mass4, which is arranged in the window5defined within the frame2, carries the mirror element4′ and is elastically coupled to the same frame2by the second elastic elements9.

As described previously, the first elastic elements6, of a torsional type, are configured to enable the rotation movement of the frame2with respect to the anchorage structure7and to the substrate8of the body of semiconductor material in which the reflector micromechanical structure20is made; the rotation being out of the horizontal plane xy and about the first horizontal axis x.

Furthermore, the second elastic elements9, which are also of a torsional type, are configured to enable the rotation movement of the mobile mass4with respect to the frame2, out of the horizontal plane xy and about the second horizontal axis y; the same second elastic elements9are configured to rigidly couple the mobile mass4to the frame2, in the actuation movement of rotation of the same frame2about the first horizontal axis x.

According to a particular aspect of the present solution, a distribution of mass is associated to the mobile mass4, that is specifically designed for generating, by the inertial effect, a twisting moment, again designated by Ty, about the second horizontal axis y in response to the rotation of the frame2(and of the same mobile mass4) about the first horizontal axis x.

Consequently, the reflector micromechanical structure20may comprise in this case a single actuation structure (coinciding with the first actuation structure10represented inFIG. 1, and for this reason designated by the same reference number). The actuation structure10is coupled to the frame2and configured to cause its actuation movement, in this case a movement of rotation, about the first horizontal axis x, as a function of suitable electrical driving signals, for generating the twisting moment Txabout the same first horizontal axis x.

Thanks to the aforesaid inertial coupling, it is not required (and thus it may advantageously not be present) a further and distinct actuation structure, coupled to the mobile mass4to cause rotation thereof about the second horizontal axis y (this rotation is in fact generated by inertial force coupling).

In particular, and as illustrated for example inFIGS. 2B-2C, the mass distribution of the mobile mass4is asymmetrical in the horizontal plane xy, with respect to at least one, or both, of the horizontal axes x, y (i.e., to the axes of rotation of the mobile mass4).

According to an aspect of the present solution, the mass distribution of the mobile mass4is asymmetrical with respect at least to the second horizontal axis y, i.e., to the axis of rotation of the same mobile mass4.

As illustrated schematically in the aforesaidFIGS. 2B and 2C, the mobile mass4is ideally divided, in the horizontal plane xy, into four quadrants by the horizontal axes x and y, which cross at a geometrical center O of the mobile mass4.

In a possible embodiment, additional mass portions22a,22bare associated to the mobile mass4, arranged in opposite quadrants (in the example, the second and fourth quadrants) with respect to the geometrical center O.

The above additional mass portions22a,22bhave respective centroids B, B′ arranged at a distance from the horizontal axes x, y, which are symmetrical with respect to the geometrical center O and are aligned in a diagonal direction d, inclined (for example by 45°) with respect to the horizontal axes x, y.

The additional mass portions22a,22bare, in the example, shaped like a circular-ring portion (in the example, having a 90° angular extension).

Rotation of the mobile mass4about the first horizontal axis x (as a result of the coupling to the frame2, which is suitably driven to obtain its actuation) generates an inertial force F on the same mobile mass4, which, applied at the respective centroids B, B′ (in opposite directions with respect to the horizontal plane xy), gives rise to the twisting moment Tyabout the second horizontal axis y.

The use of an asymmetrical mass distribution for the mobile mass4creates diagonal terms in the mass-coupling matrix of the mechanical system, thus creating a transfer of force between the first and second horizontal axes x, y, which are otherwise independent of one another (thus coupling, by the inertial effect, i.e. through the mass matrix, the horizontal axes x, y).

In particular, a “diagonal” mass distribution, of the type described previously, has been found to generate a greater transfer of force between the horizontal axes x, y.

In greater detail, and with reference once again toFIG. 2A, the angle of rotation of the frame2(and of the mobile mass4coupled thereto) about the first horizontal axis x is denoted by θ, the angle of rotation of the mobile mass4(and of the associated mirror element4′) about the second horizontal axis y is denoted by φ, and the angle of rotation of the frame2about the aforesaid second horizontal axis y is denoted by α.

It is considered, in fact, that the first elastic elements6are not altogether rigid to torsion with respect to the second horizontal axis y; in other words, the frame2may rotate, albeit in a limited way, due to the higher stiffness of the same first elastic elements6, also about the second horizontal axis y.

Using Lagrangian mechanical theory, it is possible to obtain the following equation of motion for the system of the reflector micromechanical structure20:

M⁢d2dt2⁢q→⁡(t)+B⁢ddt⁢q→⁡(t)+K⁢q→⁡(t)=T→⁡(t)M⁢d2dt2⁢q→⁡(t)+B⁢ddt⁢q→⁡(t)+K⁢q→⁡(t)=T→⁡(t)
where{right arrow over (q)}(t)=(θ, α, φ)Tis the vector of Lagrangian co-ordinates;M is the mass matrix of the system;B is the dissipation matrix of the system;K is the stiffness matrix of the system; and{right arrow over (T)}(t)=Tx, Ty, 0)Tis the vector of the forcing twisting moments applied to the frame2, in particular via the actuation structure10.

Applying the Laplace transform to the above equation, the following is obtained:
Ms2{right arrow over (q)}(s)+Bs{right arrow over (q)}(s)+K{right arrow over (q)}(s)={right arrow over (T)}(s)

where s=jω is the co-ordinate in the frequency domain ω (and j is the imaginary unit).

For a system with a symmetrical mass distribution for both the frame2and the mobile mass4(as in the structures according to the known art), the aforesaid equation would assume the explicit form:

From the above equation it emerges in particular that the degree of freedom θ is in this case decoupled from the other degrees of freedom, α and φ, and that, in this way, the twisting moment Txgenerates a response only on the degree of freedom θ, but not on the other degrees of freedom, α and φ.

Instead, in the present solution, with an asymmetrical mass distribution of the mobile mass4with respect to at least one, or both, of the horizontal axes x and y, the aforesaid equation assumes the form:

It is emphasized that the described coupling is of a dynamic type (i.e., it generally occurs as a result of resonant operation conditions); the presence of a resonant actuation about at least one of the horizontal axes x, y, in this case the first horizontal axis x, is thus generally required.

In the embodiment illustrated in the aforesaidFIGS. 2B, 2C, a body portion of the mobile mass4, which carries the mirror element4′, is made in a surface layer24(of the body of semiconductor material), from which the frame2and the first and second elastic elements6,9are also defined. The additional mass portions22a,22bare in this case defined starting from a structural layer25, arranged underneath the surface layer24(with respect to a vertical axis z that defines a set of three Cartesian axes with the first and second horizontal axes x, y) on the side opposite to the mirror element4′, and coupled to the body portion.

As shown inFIG. 2B, from the same structural layer25a reinforcement portion26of the frame2may further be defined, arranged underneath the frame2with respect to the vertical axis z; this reinforcement portion26has a symmetrical mass distribution in the horizontal plane xy, having a ring shape that replicates the geometry of the frame2.

It is in any case evident that the solution of inertial coupling previously discussed may be implemented with a wide range of different asymmetrical mass distributions for the mobile mass4.

For instance,FIG. 3Ashows a possible embodiment, in which just one additional mass portion is present, designated by22a(substantially C-shaped), which is asymmetrical with respect to the horizontal axes x, y extending in an incomplete circular ring over three of the four quadrants into which the mobile mass4is divided in the horizontal plane xy.

The additional mass portion22ain this case has a centroid B located in the third quadrant, where the inertial force F due to the rotation of the mobile mass4about the first horizontal axis x is applied; also in this case, the above inertial force F generates a twisting moment Tyabout the second horizontal axis y, as will be clear from an examination ofFIG. 3A.

FIG. 3Bshows a possible further embodiment, which differs as regards a different asymmetrical mass distribution for the mobile mass4.

In this case, the additional mass portions22a,22bare located in a position that is radially more external with respect to the shape of the mobile mass4in the horizontal plane xy (and as compared to the embodiment ofFIG. 2C).

This solution may have the advantage of increasing the twisting moment Tywith a same actuation force.

As shown inFIG. 3C, a further variant may envisage that the additional mass portions22a,22b, which in this case have a “quarter of a circle” conformation in the horizontal plane xy, are connected by a connecting portion22cat the geometrical center O.

A further embodiment (seeFIG. 4) envisages, instead, that the asymmetrical mass distribution of the mobile mass4is obtained by defining the same surface layer24, in which the body portion of the same mobile mass4is formed, instead of defining a structural layer underlying the surface layer24.

In this case, the additional mass portions22a,22bare defined starting from the surface layer24(thus being at the same level as the body portion of the mobile mass4), extending symmetrically with respect to the geometrical center O and parallel to the second horizontal axis y, on opposite sides of the mobile mass4with respect to the first horizontal axis x. In this case, the additional mass portions22a,22bare coupled integrally to the mobile mass4.

The above solution may offer the advantage of a simpler construction, given that it requires the processing of just one layer of semiconductor material (the aforesaid surface layer24).

Irrespective of the configuration of the asymmetrical mass distribution associated to the mobile mass4, the discussed inertial-coupling solution advantageously applies to any type of actuation envisaged to cause rotation of the frame2about the first horizontal axis x (i.e., of an electrostatic, electromagnetic, or piezoelectric type).

In this regard,FIGS. 5A and 5Bare schematic illustrations of an embodiment of the actuation structure10, coupled to the frame2, being of an electrostatic type (in particular,FIG. 5Brepresents, purely by way of example, an asymmetrical mass distribution equivalent to the one described with reference toFIG. 3C).

In this case, the actuation structure10comprises a single set of comb-fingered electrodes28coupled to the frame2, for generation of forces of electrostatic attraction such as to generate the twisting moment Txabout the first horizontal axis x.

The set of comb-fingered electrodes28comprises: mobile electrodes28acarried by the frame2, in particular by portions of the frame2parallel to the first horizontal axis x (coupled to which are the second elastic elements9); and fixed electrodes28b, carried by a fixed structure29, fixed with respect to the substrate8of the body of semiconductor material in which the reflector micromechanical structure20is obtained.

The mobile electrodes28aand the fixed electrodes28bextend parallel to one another and to the second horizontal axis y, and are comb-fingered in the horizontal plane xy and arranged at different heights along the vertical axis z.

In a per se known manner, the application of suitable driving signals to the mobile and fixed electrodes28a,28benables generation of forces of electrostatic attraction for causing rotation of the frame2(and of the mobile mass4) about the first axis x.

It is emphasized once again that, according to the present solution, just a single set of electrodes28may be used for actuation of the frame2, exploiting the inertial coupling due to the asymmetrical distribution of mass associated to the mobile mass4for generation of the twisting moment Tythat will cause rotation of the same mobile mass4about the second horizontal axis y (in other words, the present solution does not require the presence of electrodes coupled to the mobile mass4or to the second elastic elements9).

As shown inFIGS. 6A and 6B, in a different embodiment, of an electromagnetic type, the actuation structure10coupled to the frame2comprises a coil32arranged on the frame2(in the example, occupying an area having a square ring shape that extends along the entire perimeter of the same frame2).

In a per se known manner, the movement of rotation of the frame2is in this case obtained starting from the Lorenz force, generated due to passage of an appropriate electric driving current through the coil32.

With reference toFIGS. 7A and 7B, a further embodiment of the actuation structure10, this time of a piezoelectric type, envisages that the actuation structure10comprises a first thin-beam element34aand a second thin-beam element34b, which are mechanically connected to prolongations37of the frame2, which extend along the first horizontal axis x, centrally and on opposite sides with respect to the frame2.

The thin-beam elements34a,34bextend parallel to the second axis y (with a negligible extension along the vertical axis z) and carry respective piezoelectric actuators35a,35b.

In a per se known manner, application of suitable driving voltages to the aforesaid piezoelectric actuators35a,35bcauses rotation of the thin beam elements34a,34b, and consequently of the frame2, about the first horizontal axis x, with the consequent generation of the twisting moment Tx.

Also in this case, it is possible to use piezoelectric actuators35a,35bdedicated just to rotation about the first horizontal axis x, again exploiting the inertial coupling due to the asymmetrical mass distribution associated to the mobile mass4for generation of the twisting moment Tyabout the second horizontal axis y.

The advantages of the described solution emerge clearly from the foregoing discussion.

It is in any case emphasized that the inertial coupling due to the asymmetrical mass distribution associated to the mobile mass4of the reflector micromechanical structure20enables the possibility of using just one actuation structure, dedicated to the movement of the frame2, for example its rotation about the first horizontal axis x, in any case obtaining a biaxial actuation of the mobile mass4thanks to the mass coupling.

The present solution enables maximization of the efficiency of actuation of the mobile mass4by virtue of the inertial force coupling to the frame2.

It is further pointed out that the process used for the manufacture of the reflector micromechanical structure20does not envisage any substantial modifications with respect to traditional processes, envisaging the definition, with techniques that are known and already used for definition of the remaining structural elements, of a surface layer24and possibly of a structural layer25, both already present in the reflector micromechanical structure20.

The present solution may, moreover, be advantageously applied to a wide range of reflector micromechanical structures20, for example ones that operate according to the principles of electrostatic, electromagnetic, or piezoelectric actuation, in which there is preferably present at least one resonant actuation movement.

The aforesaid features render use of the micromechanical structure particularly advantageous in integrated optical devices inside portable apparatuses.

For instance,FIG. 8represents schematically use of the reflector micromechanical structure20in a projector device40of a portable apparatus43(such as, for example, a smartphone).

In particular, the reflector micromechanical structure20is operable for projecting a light beam F generated by a light source46, for example a coherent light source of a laser type, according to a desired scanning pattern.

The projector device40further comprises an electronic circuit48, for control and driving, which is able to supply appropriate driving signals both to the light source46and to the reflector micromechanical structure20for varying the position and orientation thereof according to the desired scanning pattern for the reflected light beam.

Advantageously, the electronic circuit48may be obtained in an integrated technology using semiconductor techniques, possibly in the same die in which the reflector micromechanical structure20is provided.

Finally, it is clear that modifications and variations may be made to what has been described and illustrated herein, without thereby departing from the scope of the present invention, as defined in the annexed claims.

In particular, it is clear that the actual asymmetrical mass distribution associated to the mobile mass4of the reflector micromechanical structure20may differ from what has been illustrated hitherto, possibly also according to a different movement of actuation envisaged for movement of the frame2(and of the mobile mass4, rigidly coupled to the frame2in its movement of actuation).

For instance, as shown inFIG. 9A, the frame2may be actuated by the corresponding actuation structure10(illustrated schematically) for obtaining a movement of actuation of translation along the vertical axis z (designated by Mz).

In this case, as shown inFIG. 9B, the mass distribution associated to the mobile mass4, which is asymmetrical with respect to the second horizontal axis y, may envisage a single additional mass portion22a, having a semicircular shape in the horizontal plane xy, entirely arranged along one side of the second horizontal axis y (occupying, that is, the first and the second quadrants defined previously), with its centroid B arranged at a distance from the aforesaid second horizontal axis y.

As will be evident, the translation along the vertical axis z generates, by the inertial effect, the twisting moment Tyand the consequent rotation of the mobile mass4about the second horizontal axis y.

Also for this specific embodiment, different asymmetrical mass distributions for the mobile mass4may be envisaged, provided that the single additional mass portion22ahas a centroid B arranged at a distance from the second horizontal axis y.

Furthermore, in the reflector micromechanical structure20an actuation structure for generating a movement of rotation of the mobile mass4about the second horizontal axis y may in any case be provided (in this case, the twisting moment Tygenerated as a result of the inertial coupling thus adding to this further movement of actuation, and in any case increasing the mechanical efficiency of the system).

The micromechanical structure described herein may in general be used in any MEMS device, for generating, with reduced occupation of space and high efficiency, rotation of a mobile mass about an axis of rotation following upon actuation of an actuator along, or about, an axis of actuation transverse to the same axis of rotation.