Patent Description:
As is known, mobile phones are today available equipped with improved camera modules, which guarantee levels of performance by now comparable with those of professional cameras. Such modules include sensors that are progressively larger and have progressively higher performance; however, it is known how only a few solutions make it possible to implement a typical characteristic of professional cameras: a variable optical aperture.

For instance, <CIT> describes a MEMS optical shutter including a pinhole, a blade, and an actuator designed to move the blade laterally with respect to the pinhole. Said solution, however, has available only a small number of degrees of freedom for adjustment of the optical aperture; in particular, adjustment of the optical aperture is limited to a portion of the perimeter of the optical aperture.

The paper "<NPL> discloses a MEMS attenuator with a variable aperture of the iris type, which includes a substrate and a single bonded layer, which is etched so as to form a plurality of shutter blades, which are coated by a metallization. The shutter blades are driven by respective microactuators and shift in a synchronous way, so as to form a variable polygonal aperture.

The paper "<NPL>, discloses devices of the type of the micro-opto-electromechanical systems (MOEMS) based on the technology of the silicon bonded on insulator (BSOI); these devices comprise multiple-blade irises.

The aim of the present invention is thus to provide a solution that will overcome at least in part the drawbacks of the prior art.

According to the present invention a MEMS optical shutter and a related manufacturing process are provided, as defined in the annexed claims.

For a better understanding of the present invention, embodiments thereof are now described, purely by way of non-limiting example, with reference to the attached drawings, wherein:.

<FIG> shows a MEMS shutter <NUM>, which comprises a substrate <NUM> of semiconductor material (for example, silicon) and a first dielectric region <NUM>, which is arranged on the substrate <NUM> and is formed by thermal oxide.

In particular, the substrate <NUM> is delimited by a top surface Sa and a bottom surface Sb, which are parallel to a plane XY of an orthogonal reference system XYZ. The first dielectric region <NUM> extends on the top surface Sa and laterally delimits a window W, which leaves exposed a central portion of the top surface Sa; in other words, the first dielectric region <NUM> extends on a peripheral portion of the top surface Sa.

The MEMS shutter <NUM> further comprises a second dielectric region <NUM>, which is made, for example, of aluminium oxide (alumina) and extends on a peripheral portion of the first dielectric region <NUM>, leaving exposed an inner portion of the first dielectric region <NUM>, which laterally delimits the aforementioned window W.

A main aperture <NUM> extends through the substrate <NUM> starting from the bottom surface Sb and giving out onto the central portion of the top surface Sa. In what follows it is assumed, for simplicity of description and without this implying any loss of generality, that the main aperture <NUM> has its axis of symmetry that coincides with an axis of symmetry H of the MEMS shutter <NUM>, parallel to the axis Z. Furthermore, to a first approximation, the main aperture <NUM> has, for example, a frustoconical shape or a frustopyramidal shape with polygonal base, with the minor base that lies in the plane of the bottom surface Sb.

The window W communicates with the underlying main aperture <NUM> and is delimited at the bottom by a wall P, which is formed by a part of the substrate <NUM> that laterally delimits the top part of the main aperture <NUM> and has a plane and hollow shape. The wall P lies in the plane of the top surface Sa.

The MEMS shutter <NUM> further comprises a conductive layer <NUM>, which has a closed shape in top plan view (for example, polygonal or circular) so as to surround the main aperture <NUM>.

In particular, the conductive layer <NUM> has an approximately U-shaped cross-section so as to delimit a trench T.

An outer portion of the conductive layer <NUM> coats laterally and at the top the aforementioned inner portion of the first dielectric region <NUM> and further coats at the top a portion of the second dielectric region <NUM> facing the axis of symmetry H. A bottom portion of the conductive layer <NUM> coats an outer portion of the wall P; an inner portion of the conductive layer <NUM> extends in cantilever fashion from the bottom portion so as to overlie, at a distance, part of an inner portion of the wall P.

The MEMS shutter <NUM> further comprises a plurality of anchorage regions (two of which are illustrated in <FIG> and designated by <NUM>), which are made of polysilicon and extend on the second dielectric region <NUM>. In particular, the anchorage regions <NUM> are arranged at a lateral distance from the conductive layer <NUM> and are arranged on the outside of the latter.

The MEMS shutter <NUM> further comprises a first semiconductor layer <NUM> and a second semiconductor layer <NUM>, which are made of polycrystalline silicon and, as illustrated in <FIG>, form a plurality of first shielding structures <NUM> and a plurality of second shielding structures <NUM>. In connection with <FIG>, the shape of the main aperture <NUM> shown therein is just qualitative and, for simplicity of representation, is not consistent with what is illustrated in <FIG>.

Each one of the first and second shielding structures <NUM>, <NUM> is associated to a corresponding radial direction (one is illustrated in <FIG>, where it is designated by R), which is parallel to the plane XY and refers to the arrangement of the corresponding shielding structure when it is in resting conditions. As illustrated in <FIG>, in the present example it is assumed that both the first and the second shielding structures <NUM>, <NUM> are four in number. Furthermore, it is anticipated that each one of the first and second shielding structures <NUM>, <NUM> is associated to a corresponding transverse direction TR, which is perpendicular to the plane ZR; consequently, it is perpendicular to the corresponding radial direction R and also this refers to the arrangement of the corresponding shielding structure when it is in resting conditions.

In greater detail, the first semiconductor layer <NUM> forms: supporting regions <NUM>, which overlie, in direct contact, corresponding anchorage regions <NUM>; a bottom peripheral region <NUM>; and a bottom inner structure <NUM>, described in greater detail hereinafter.

The bottom peripheral region <NUM> forms a fixed bottom peripheral region <NUM>', which overlies the supporting regions <NUM>.

Furthermore, for each one of the first and second shielding structures <NUM>, <NUM>, the bottom peripheral region <NUM> forms a corresponding mobile bottom peripheral region <NUM>", which extends in cantilever fashion from the fixed bottom peripheral region <NUM>'. In particular, if we denote by Sref the top surface of the second dielectric region <NUM>, the mobile bottom peripheral region <NUM>" overlies the surface Sref at a distance.

The second semiconductor layer <NUM> forms a top peripheral region <NUM> and a top inner structure <NUM>, described in greater detail hereinafter.

The top peripheral region <NUM> comprises a fixed top peripheral region <NUM>', which overlies, in direct contact, the fixed bottom peripheral region <NUM>', with which it forms a fixed peripheral structure <NUM>.

Furthermore, for each one of the first and second shielding structures <NUM>, <NUM>, the top peripheral region <NUM> forms a corresponding mobile top peripheral region <NUM>", which extends in direct contact on the corresponding mobile bottom peripheral region <NUM>", with which it forms a corresponding cantilever structure <NUM>, which extends in cantilever fashion from the aforementioned fixed peripheral structure <NUM>.

As may be seen in <FIG>, each cantilever structure <NUM> comprises a main portion 27A and a secondary portion 27B, which are described hereinafter; the main portion 27A is visible also in <FIG>, albeit only approximately. In this connection, in general the figures are not in scale. As regards, instead, <FIG>, not shown therein is the separation between the first and second semiconductor layers <NUM>, <NUM>; on the other hand, this separation does not correspond to a physical interface, but rather represents the fact that the first and second semiconductor layers <NUM>, <NUM>, albeit made of a same material, are formed at different times, as explained hereinafter.

This having been said, and with reference to the cantilever structure <NUM> corresponding to the first shielding structure <NUM> illustrated in <FIG> and <FIG> (but said description also applies to the other cantilever structures <NUM>, also when coupled to the second shielding structures <NUM>), albeit not shown a first end of the main portion 27A is fixed with respect to a corresponding portion of the fixed peripheral structure <NUM>; the secondary portion 27B is arranged between the main portion 27A and the first shielding structure <NUM>.

In greater detail, in resting conditions, the main portion 27A has a planar shape, elongated along an axis oriented at <NUM>° with respect to the radial direction R, whereas the secondary portion 27B is elongated in a direction parallel to the radial direction R, with an approximately parallelepipedal shape. A first end of the secondary portion 27B is fixed with respect to the second end of the main portion 27A.

Without this implying any loss of generality, the main portion 27A has, in resting conditions and in top plan view, a shape tapered towards the secondary portion 27B so as to define a recess <NUM> (one of which is shown in <FIG>) having, for example, a square shape. The shape of the secondary portion 27A may, however, vary with respect to what is illustrated.

Once again with reference to <FIG>, the MEMS shutter <NUM> comprises, for each one of the first and second shielding structures <NUM>, <NUM>, a corresponding actuator <NUM> of a piezoelectric type, which extends on the main portion 27A of the corresponding cantilever structure <NUM>.

Each actuator <NUM> comprises: a first electrode <NUM>, arranged on the main portion 27A of the corresponding cantilever structure <NUM> and made, for example, of a material chosen from among: Mo, Pt, Ti, Al, TiW; a piezoelectric region <NUM>, arranged on the first electrode <NUM> and made, for example, of a material chosen from among: PZT, AlN, scandium-doped AlN; a second electrode <NUM>, arranged on the piezoelectric region <NUM> and made, for example, of a material chosen from among: Mo, Pt, Ti, Al, TiW; and a protective region <NUM>, which is made, for example, of a material chosen from among silicon oxide, silicon nitride, and aluminium nitride and extends over the second electrode <NUM>, as well as surrounding laterally the first and second electrodes <NUM>, <NUM> and the piezoelectric region <NUM> until it comes into contact with the main portion 27A of the corresponding cantilever structure <NUM>. In a per se known manner and thus not described in detail or illustrated, between the first and second electrodes <NUM>, <NUM> a voltage may be applied, for example by appropriate electrical contacts (not illustrated), which enables operation of the actuator <NUM>.

Once again with reference to the first and second shielding structures <NUM>, <NUM>, they are formed by the bottom inner structure <NUM> and the top inner structure <NUM>.

In greater detail, the first shielding structures <NUM> are the same as one another and in resting conditions are spaced at equal angular distances apart with respect to the axis of symmetry H; in particular, pairs of adjacent first shielding structures <NUM> are spaced apart at an angular distance of <NUM>°. The second shielding structures <NUM> are the same as one another and are spaced at equal angular distances apart with respect to the axis of symmetry H; in particular, pairs of adjacent second shielding structures <NUM> are spaced apart at an angular distance of <NUM>°. Furthermore, the first and second shielding structures <NUM>, <NUM> are arranged so as to alternate with one another at angular distances apart. Each first shielding structure <NUM> is thus angularly arranged between a pair of adjacent second shielding structures <NUM>, which are at a distance of <NUM>° from the first shielding structure <NUM>; likewise, each second shielding structure <NUM> is angularly arranged between a pair of adjacent first shielding structures <NUM>, which are at a distance of <NUM>° from the second shielding structure <NUM>.

In what follows, the first shielding structures <NUM> are described with reference to <FIG> and <FIG>, visible in which, as explained previously, is just one first shielding structure <NUM>.

In detail, the first shielding structure <NUM> comprises a respective top shielding region <NUM>, formed by the inner mobile portion <NUM> of the second semiconductor layer <NUM>, and an underlying bottom secondary region <NUM>, formed by the inner mobile portion <NUM> of the first semiconductor layer <NUM>.

The top shielding region <NUM> has a rectangular shape, in top plan view, and an L-shaped cross-section. In particular, the top shielding region <NUM> comprises a main portion <NUM>, which has the shape of a parallelepiped with axis parallel to the radial direction R and with ends facing, respectively, the axis of symmetry H and the top peripheral region <NUM>, and a secondary portion <NUM>, which has a parallelepipedal shape and is arranged underneath the end of the main portion <NUM> facing the top peripheral region <NUM>.

The bottom secondary region <NUM> comprises a respective main portion <NUM>, which has the shape of a parallelepiped with axis parallel to the radial direction R and with ends facing, respectively, the bottom peripheral region <NUM> and the axis of symmetry H, and a respective secondary portion <NUM>, which has a parallelepipedal shape and is arranged underneath the end of the main portion <NUM> facing the axis of symmetry H.

The secondary portion <NUM> of the top shielding region <NUM> overlies, in direct contact, the end facing the bottom peripheral region <NUM> of the main portion <NUM> of the bottom secondary region <NUM>. Extending underneath the secondary portion <NUM> of the bottom secondary region <NUM> is a suspended conductive region <NUM>, made of polysilicon.

To a first approximation, and without this implying any loss of generality, the main portions <NUM>, <NUM> and the secondary portions <NUM>, <NUM> of the top shielding region <NUM> and the bottom secondary region <NUM> have a same extension in a direction parallel to the transverse direction TR associated to the first shielding region <NUM>.

In greater detail, the main portion <NUM> of the top shielding region <NUM> and the main portion <NUM> of the bottom secondary region <NUM> extend in cantilever fashion from the secondary portion <NUM> of the top shielding region <NUM>, towards the axis of symmetry H, without intercepting it, and delimiting, at the top and at the bottom respectively, a corresponding recess <NUM>, which is laterally delimited by the secondary portion <NUM>. In addition, in the radial direction R, the main portion <NUM> of the top shielding region <NUM> has a greater extension than the main portion <NUM> of the bottom secondary region <NUM>, and is consequently at a shorter distance from the axis of symmetry H.

In resting conditions, at least part of the main portion <NUM> of the top shielding region <NUM> is suspended over the main aperture <NUM>, i.e., it projects towards the axis of symmetry H, with respect to the underlying bottom secondary region <NUM>.

Without this implying any loss of generality, the secondary portion <NUM> of the top shielding region <NUM> and the bottom secondary region <NUM> are laterally staggered with respect to the main aperture <NUM>, i.e., they overlie portions of the substrate <NUM> adjacent to the main aperture <NUM>. Albeit not illustrated, variants are, however, possible in which at least part of the bottom secondary region <NUM> is suspended over the main aperture <NUM>.

The bottom inner structure <NUM> of the first semiconductor layer <NUM> and the top inner structure <NUM> of the second semiconductor layer <NUM> further form a corresponding deformable coupling structure <NUM> for each one of the first and second shielding structures <NUM>, <NUM>, as well as a corresponding coupling body <NUM>. The deformable coupling structures <NUM>, as also the coupling bodies <NUM>, are the same as one another; for example, described in what follows are the deformable coupling structure <NUM> and the coupling body <NUM> for the first shielding structure <NUM> illustrated in <FIG> and <FIG>.

In detail, the deformable coupling structure <NUM> comprises a first elastic structure M1 and a second elastic structure M2, which in <FIG> are represented in a simplified way.

The first and second elastic structures M1, M2 are the same as, and symmetrical to, one another, with respect to a plane perpendicular to the plane XY and parallel to the radial direction R. Consequently, described in what follows is just the first elastic structure M1.

The first elastic structure M1 is an elastic transformation element of the same type as the one described in the patent application <CIT> in the name of the present applicant. Furthermore, without this implying any loss of generality, the first elastic structure M1 extends at least in part within the recess <NUM>, in order to reduce the overall dimensions.

In detail, the first elastic structure M1 comprises a first elongated structure L1 and a second elongated structure L2, a connecting arm B1 and an outer coupling region EC, which are now described with reference to the resting conditions illustrated in <FIG>. The outer coupling region EC is shared between the first and second elastic structures M1, M2.

The outer coupling region EC has approximately a parallelepipedal shape, is formed by the bottom inner structure <NUM> of the first semiconductor layer <NUM> and the top inner structure <NUM> of the second semiconductor layer <NUM>, and is fixed with respect to the second end of the secondary portion 27B of the cantilever structure <NUM>.

Without this implying any loss of generality, the first and second elongated structures L1 and L2 are the same as one another, are co-planar and are staggered in a direction parallel to the radial direction R. For this reason, just the first elongated structure L1 is described in what follows, with reference to <FIG>.

In detail, the first elongated structure L1 comprises a top elongated portion <NUM>, formed by the top inner structure <NUM> of the second semiconductor layer <NUM>, and a bottom elongated portion <NUM>, formed by the bottom inner structure <NUM> of the first semiconductor layer <NUM>.

The top elongated portion <NUM> and the bottom elongated portion <NUM> are staggered in a direction parallel to the radial direction R and have a parallelepipedal shape (for example, approximately the same shape) with axes parallel to the transverse direction TR and arranged at different heights, measured along the axis Z.

Without this implying any loss of generality, the top elongated portion <NUM> is located at a greater height than the bottom elongated portion <NUM>; furthermore, the top elongated portion <NUM> and the bottom elongated portion <NUM> are vertically separate, i.e., they don't overlap one another in side view.

The first elongated structure L1 further comprises a plurality of transverse portions <NUM> (three of which are illustrated in <FIG>), which, without this implying any loss of generality, are the same as one another, have a parallelepipedal shape with axes parallel to the axis Z and are, for example, equally spaced apart in a direction parallel to the transverse direction TR. Furthermore, the transverse portions <NUM> are arranged between the top elongated portion <NUM> and the bottom elongated portion <NUM>, which are arranged on opposite sides of each transverse portion <NUM>. In particular, a top portion of each transverse portion <NUM> laterally contacts the top elongated portion <NUM>, whereas a bottom part of the transverse portion <NUM> laterally contacts the bottom elongated portion <NUM>. The top elongated portion <NUM>, the bottom elongated portion <NUM> and the transverse portions <NUM> form a single piece of polysilicon.

The connecting arm B1 is formed by the bottom inner structure <NUM> of the first semiconductor layer <NUM> and the top inner structure <NUM> of the second semiconductor layer <NUM> and has an approximately planar shape (in particular, a parallelepipedal shape), parallel to the plane ZR. The first ends of the top elongated portion <NUM> and of the bottom elongated portion <NUM> are fixed with respect to the connecting arm B1. The second ends of the top elongated portion <NUM> and of the bottom elongated portion <NUM> are fixed with respect to the outer coupling region EC. Furthermore, the top elongated portion <NUM> and the bottom elongated portion <NUM> of the second elongated structure L2 have respective first ends, which are fixed with respect to the connecting arm B1, which is thus arranged between the first and second elongated structures L1, L2.

The second ends of the top elongated portion <NUM> and of the bottom elongated portion <NUM> of the second elongated structure L2 are fixed with respect to a first terminal portion (designated by <NUM>) of the coupling body <NUM>, which has approximately a parallelepipedal shape and is formed by the bottom inner structure <NUM> of the first semiconductor layer <NUM> and the top inner structure <NUM> of the second semiconductor layer <NUM>.

In practice, the first elastic structure M1 has the shape of a folded spring, the behaviour of which is of the type described in the aforementioned patent application <CIT> and is summarized hereinafter. Furthermore, the first elastic structure M1 is compliant along the axis Z and in a direction parallel to the radial direction R and is rigid in the transverse direction TR.

As illustrated in <FIG>, the coupling body <NUM> comprises, in addition to the aforementioned first terminal portion <NUM>, an elongated portion <NUM> and a second terminal portion <NUM>, which have parallelepipedal shapes and are formed by the inner mobile portion <NUM> of the first semiconductor layer <NUM> and by the inner mobile portion <NUM> of the second semiconductor layer <NUM>. The elongated portion <NUM> is arranged between the first and second terminal portions <NUM>, <NUM>.

In detail, in resting conditions, the first and second terminal portions <NUM>, <NUM> of the coupling body <NUM> extend in a direction parallel to the radial direction R, whereas the elongated portion <NUM> extends in a direction parallel to the transverse direction TR. Furthermore, the first and second terminal portions <NUM>, <NUM> are laterally staggered in the transverse direction TR.

The first terminal portion <NUM> has a first end, which is fixed with respect to the second elongated structures L2 of the first and second elastic structures M1, M2, and a second end, which is fixed with respect to a first end of the elongated portion <NUM>. The second terminal portion <NUM> has a first end, which is fixed with respect to the corresponding first shielding structure <NUM>, and a second end, which is fixed with respect to the second end of the elongated portion <NUM>. Furthermore, the first and second terminal portions <NUM>, <NUM> extend on opposite sides with respect to the elongated portion <NUM>, in such a way that the coupling body <NUM> is approximately Z-shaped in top plan view.

In greater detail, the first end of the second terminal portion <NUM> is fixed with respect to the top shielding region <NUM> and to the bottom secondary region <NUM> of the first shielding region <NUM>.

Furthermore, as may be seen in <FIG> and <FIG>, for each first shielding structure <NUM>, the MEMS shutter <NUM> comprises two planar springs <NUM>, which are now described, by way of example, with reference to the first shielding structure <NUM> illustrated in <FIG>.

In detail, the planar springs <NUM> are formed by the inner mobile portion <NUM> of the first semiconductor layer <NUM> and by the inner mobile portion <NUM> of the second semiconductor layer <NUM> and have an elongated shape. In resting conditions, the planar springs <NUM> are shaped like parallelepipeds elongated in a direction parallel to the radial direction R, with first ends fixed with respect to the elongated portion <NUM> of the coupling body <NUM> (at a distance from the first and second terminal portions <NUM>, <NUM>) and with second ends fixed with respect to corresponding pillar regions <NUM>. For reasons that will be clarified hereinafter, the planar springs <NUM> are rigid along the axis Z and compliant in a direction parallel to the corresponding radial direction R, and more in general in a direction parallel to the plane XY. In particular, the planar springs <NUM> function as flexural beams and, together with the first pillar regions <NUM>, form a hinge for the coupling body <NUM>.

In greater detail, the pillar regions <NUM> and the planar springs <NUM> are arranged on opposite sides of the elongated portion <NUM> of the coupling body <NUM>. Furthermore, the pillar regions <NUM> are formed both by the first and second semiconductor layers <NUM>, <NUM> (in particular, by portions of the fixed bottom peripheral region <NUM>' and by underlying supporting regions <NUM>, as well as by portions of the fixed top peripheral region <NUM>') and are anchored at the bottom to corresponding anchorage regions <NUM>.

In practice, the first shielding structure <NUM> and the coupling body <NUM> are suspended and constrained to the pillar regions <NUM> by interposition of the planar springs <NUM>.

As regards the second shielding strucutres <NUM>, they are now described with reference, by way of example, to the second shielding structure <NUM> illustrated in <FIG> and <FIG>.

In detail, the second shielding structure <NUM> comprises a respective bottom shielding region <NUM>, formed by the bottom inner structure <NUM> of the first semiconductor layer <NUM>, and an overlying top secondary region <NUM>, formed by the top inner structure <NUM> of the second semiconductor layer <NUM>.

The bottom shielding region <NUM> comprises a respective main portion <NUM>, which has the shape of a parallelepiped with axis parallel to the radial direction R associated to the second shielding structure <NUM> and with ends facing, respectively, the axis of symmetry H and the bottom peripheral region <NUM>. The bottom shielding region <NUM> further comprises a respective secondary portion <NUM>, which has a parallelepipedal shape and is arranged underneath the end of the main portion <NUM> facing the axis of symmetry H. Extending underneath the secondary portion <NUM> is a corresponding suspended conductive region <NUM>, made of polysilicon.

The top secondary region <NUM> comprises a respective main portion <NUM> and a respective secondary portion <NUM>. The main portion <NUM> has the shape of a parallelepiped with axis parallel to the radial direction R associated to the second shielding structure <NUM> and with ends facing, respectively, the top peripheral region <NUM> and the axis of symmetry H. The secondary portion <NUM> has a parallelepipedal shape, is arranged underneath the end of the main portion <NUM> facing the top peripheral region <NUM>, and further overlies, in direct contact, the end facing the bottom peripheral region <NUM> of the main portion <NUM> of the bottom shielding region <NUM>.

To a first approximation, and without this implying any loss of generality, the main portions <NUM>, <NUM> and the secondary portions <NUM>, <NUM> of the bottom shielding region <NUM> and of the top secondary region <NUM> have a same extension in the transverse direction TR associated to the second shielding region <NUM>.

Furthermore, the main portion <NUM> of the bottom shielding region <NUM> and the main portion <NUM> of the top secondary region <NUM> extend in cantilever fashion from the secondary portion <NUM> of the top secondary region <NUM>, towards the axis of symmetry H, without intercepting it, and delimiting, at the top and at the bottom respectively, a corresponding recess <NUM>, which is laterally delimited by the secondary portion <NUM> of the top secondary region <NUM>.

In addition, in the radial direction R associated to the second shielding structure <NUM>, the main portion <NUM> of the bottom shielding region <NUM> has a greater extension than the main portion <NUM> of the top secondary region <NUM>, and is consequently at a shorter distance from the axis of symmetry H. Consequently, the main portion <NUM> of the top secondary region <NUM> leaves exposed a part facing the axis of symmetry H of the main portion <NUM> of the bottom shielding region <NUM>.

In even greater detail, in resting conditions, the secondary portion <NUM> and at least part of the main portion <NUM> of the bottom shielding region <NUM> are suspended over the main aperture <NUM>. Without this implying any loss of generality, the top secondary region <NUM> is laterally staggered with respect to the underlying main aperture <NUM>, even though variants (not illustrated) are possible, in which at least part of the top secondary region <NUM> is vertically aligned with underlying portions of the main aperture <NUM>.

As illustrated in <FIG>, coupling between the second shielding structure <NUM> and the corresponding cantilever structure <NUM> is obtained thanks to the interposition of the corresponding deformable coupling structure <NUM> and of the corresponding coupling body <NUM>, in the same way as described with reference to the first shielding structure <NUM>. In particular, the first end of the second terminal portion <NUM> of the coupling body <NUM> is fixed with respect to the bottom shielding region <NUM> and to the top secondary region <NUM>.

Furthermore, for each second shielding structure <NUM>, the MEMS shutter <NUM> comprises a respective pair of planar springs <NUM>, which are mechanically coupled to the corresponding coupling body <NUM> and, respectively, to a corresponding pair of pillar regions <NUM>, in the same way as described with reference to the first shielding regions <NUM>.

All this having been said, in resting conditions the top shielding regions <NUM> of the first shielding structures <NUM> and the bottom shielding regions <NUM> of the second shielding structures <NUM> occlude partially the underlying main aperture <NUM>. In particular, when the first and second shielding structures <NUM>, <NUM> are in resting conditions, the minimum (partial) occlusion of the main aperture <NUM> is obtained; equivalently, in resting conditions the maximum optical aperture is obtained, understood as area of the main aperture <NUM> that may be traversed by a light beam that impinges with normal incidence upon the MEMS shutter <NUM>. Furthermore, each actuator <NUM> may be operated so as to rotate the corresponding first/second shielding structure <NUM>/<NUM> so as to increase occlusion of the underlying main aperture <NUM>, as described in detail hereinafter with reference to the first shielding structure <NUM> illustrated in <FIG>, even though the same considerations apply also to the second shielding structures <NUM>.

As illustrated in <FIG>, the actuator <NUM> may be operated so as to cause a translation along the axis Z of the corresponding cantilever structure <NUM>, and consequently also of the corresponding outer coupling region EC, which drags upwards the portions of the first and second elastic structures M1, M2 fixed with respect thereto. Since the portions of the first and second elastic structures M1, M2 fixed with respect to the coupling body <NUM> cannot translate along the axis Z, on account of the constraint exerted by the corresponding planar springs <NUM>, the deformable coupling structure <NUM> undergoes deformation as illustrated qualitatively in <FIG>.

In detail, the first and second elastic structures M1, M2 behave in the same way as described in the aforementioned patent application <CIT>. In particular, with reference, for example, to the first elastic structure M1, and further with reference, for example, to the first elongated structure L1, each section of the first elongated structure L1 taken in a plane parallel to the plane ZR has a pair of principal axes of inertia I<NUM>, I<NUM> (illustrated in <FIG>, which refer to <FIG>), each of which is transverse both with respect to the radial direction R and with respect to the axis Z. Consequently, a force applied to the first elongated structure L1 along the axis Z generates a so-called deviated flexure of the first elongated structure L1; in particular, said force causes a deformation along the axis Z, which leads to a consequent deformation in a direction parallel to the corresponding radial direction R of the first elongated structure L1.

In practice, whereas the portions of the first and second elastic structures M1, M2 fixed with respect to the outer coupling region EC translate to a first approximation along the axis Z, but do not undergo any movement in the plane XY, the portions of the first and second elastic structures M1, M2 fixed with respect to the coupling body <NUM> do not undergo translations along the axis Z, but translate in a direction parallel to the corresponding radial direction R, in a direction opposite to the axis of symmetry H, dragging the coupling body <NUM>, and in particular the first terminal portion <NUM> of the latter.

On account of the action of dragging exerted by the deformable coupling structure <NUM> on the first terminal portion <NUM> and of the hinge formed by the planar springs <NUM> and by the pillar regions <NUM>, the coupling body <NUM> rotates about an axis of rotation ROT (illustrated in <FIG> and <FIG>) parallel to the axis Z, without undergoing deformation and in a counterclockwise direction; to a first approximation, the axis of rotation ROT is arranged in such a way that the pillar regions <NUM> are arranged in a way symmetrical with respect thereto. Furthermore, the planar springs <NUM> undergo deformation, bending in the plane XY with curvatures opposite to one another so as to enable rotation of the coupling body <NUM> and thus also of the first shielding structure <NUM>, which forms a rigid body with the coupling body <NUM> and rotates together with the latter; in this way, the area of overlapping between the first shielding structure <NUM> and the underlying main aperture <NUM> increases.

Occlusion of the main aperture <NUM> thus increases as the rotations of the first and second shielding structures <NUM>, <NUM> increase. Furthermore, thanks to the fact that each first shielding structure <NUM> is angularly arranged between a pair of second shielding structures <NUM> and vice versa, and thanks to the fact that the top shielding regions <NUM> and the bottom shielding regions <NUM> are formed, respectively, by the second semiconductor layer <NUM> and by the first semiconductor layer <NUM> and are thus arranged on different levels, the movement of each shielding structure may take place in a way independent of the movement of the adjacent shielding structures, without there occurring any impact or limitation of the movement. In this connection, as illustrated in <FIG>, and without this implying any loss of generality, in resting conditions the end facing the axis of symmetry H of the main portion <NUM> of each top shielding region <NUM> overlies portions of the ends facing the axis of symmetry H of the main portions <NUM> of the two adjacent bottom shielding regions <NUM>.

In practice, control of occlusion of the main aperture <NUM> is performed over the entire perimeter of the main aperture <NUM> and with a large number of degrees of freedom.

Albeit not illustrated, variants are further possible where the rotations of the shielding structures about the respective axes of rotation ROT occur in a clockwise direction; for this purpose, it is, for example, possible to arrange the coupling body <NUM>, the planar springs <NUM>, the pillar regions <NUM>, the deformable coupling structure <NUM>, and the cantilever structure <NUM> so that they are symmetrical with respect to the radial direction R, according to the configuration shown in <FIG>.

According to a variant illustrated in <FIG>, the first and second shielding structures <NUM>, <NUM> are of the same type as described previously, have the same arrangement in resting conditions and have the same capacity of carrying out rotations, but the actuators (designated by <NUM>) are of an electrostatic type. This variant is now described with reference, purely by way of example, to an actuator <NUM> coupled to a first shielding structure <NUM>, but the description also applies to the actuators <NUM> coupled to the second shielding structures <NUM>.

In detail, the actuator <NUM> is of an electrostatic type and comprises, for example, a first stator region ST1 and a second stator region ST2, which are formed by corresponding portions of the fixed peripheral structure <NUM> (i.e., by corresponding portions of the fixed bottom peripheral region <NUM>' and of the fixed top peripheral region <NUM>'), as well as by underlying supporting regions <NUM> and underlying anchorage regions <NUM>. The first and second stator regions ST1, ST2 are thus fixed with respect to the underlying substrate <NUM>.

Furthermore, the first shielding structure <NUM> is operatively coupled to the actuator <NUM> through the corresponding coupling body (designated by <NUM>'), which comprises the respective elongated portion (here designated by <NUM>').

The first and second stator regions ST1, ST2 are arranged on opposite sides of the first end of the elongated portion <NUM>', from which they are electrically separate. Furthermore, the coupling body <NUM>' comprises a first set and a second set of elongated elements <NUM>, <NUM>, which have a parallelepipedal shape and extend on opposite sides of the first end of the elongated portion <NUM>', in a direction perpendicular with respect to the direction along which the elongated portion <NUM>' extends; in this connection, in resting conditions, the direction along which the elongated portion <NUM>' extends is parallel to the radial direction R (not illustrated in <FIG>) associated to the first shielding structure <NUM>.

In greater detail, the first and second sets of elongated elements <NUM>, <NUM> are formed by the bottom inner structure <NUM> of the first semiconductor layer <NUM> and the top inner structure <NUM> of the second semiconductor layer <NUM> and are laterally staggered in the direction along which the elongated portion <NUM>' extends.

The first and second stator regions ST1, ST2 comprise respective pluralities of elongated elements (designated, respectively, by <NUM> and <NUM>), which have a parallelepipedal shape and extend in a direction perpendicular with respect to the aforementioned radial direction R so as to be interdigitated with the first and second sets of elongated elements <NUM>, <NUM>, respectively.

The second end of the elongated portion <NUM>' of the coupling body <NUM>' is fixed with respect to the first shielding structure <NUM>, and in particular to the shielding top structure <NUM> and to the bottom secondary region <NUM>. Furthermore, the corresponding pair of planar springs <NUM> mechanically couples the elongated portion <NUM>' to the corresponding pair of pillar regions <NUM>, in the same way as described with reference to the previous embodiments.

In practice, the first end of the elongated portion <NUM>' of the coupling body <NUM>' forms a first capacitor and a second capacitor, respectively, with the first and second sets of elongated elements <NUM>, <NUM>, which may be controlled electronically in a per se known manner so as to generate an electrostatic force that causes a translation of the first end of the elongated portion <NUM>' of the coupling body <NUM>' alternatively towards the first or the second stator region ST1, ST2, i.e., in a direction perpendicular with respect to the radial direction R associated to the first shielding structure <NUM>. Since the planar springs <NUM> and the pillar regions <NUM> form a corresponding hinge, this leads to a rotation of the coupling body <NUM>' about the axis of rotation ROT, which is once again defined by the hinge formed by the planar springs <NUM> and by the pillar regions <NUM>. The rotation is performed alternatively in a clockwise or counterclockwise direction, as a function of the direction of translation of the first end of the elongated portion <NUM>' of the coupling body <NUM>'.

Also in this embodiment, the coupling body <NUM>' rotates without undergoing deformation, together with the first shielding structure <NUM>. Albeit not illustrated, the planar springs <NUM> undergo deformation so as to enable rotation of the coupling body <NUM>' and thus of the first shielding structure <NUM>. In this way, the area of overlapping between the first shielding structure <NUM> and the underlying main aperture <NUM> varies and, in particular, increases with respect to the resting conditions.

In practice, also the embodiment illustrated in <FIG> presents the same advantages as those described with reference to the embodiment illustrated in <FIG>. In connection with the latter embodiment, variants are possible such as to enable rotation of each shielding structure both in the clockwise direction and in the counterclockwise direction.

For instance, as illustrated in <FIG>, where for simplicity no shielding structure is illustrated, it is possible for each cantilever structure (here designated by <NUM>) to comprise, in addition to the secondary portion 27B, which is fixed with respect to the corresponding outer coupling region EC, the main portion designated by 227A.

In detail, the main portion designated by 227A has a folded shape so as to define a sort of C shape in top plan view; in particular, the main portion 227A comprises a first elongated subportion 228A and a second elongated subportion 228B and a connecting subportion 228C. For instance, the first elongated subportion 228A has the same shape as the main portion 27A of the cantilever structure <NUM> illustrated in <FIG>. Furthermore, the second elongated subportion 228B has, for example, the shape of a parallelepiped elongated in a direction parallel to the corresponding transverse direction TR; the first and second elongated subportions 228A, 228B are staggered in the radial direction R and are connected by the connecting subportion 228C.

In greater detail, the end of the first elongated subportion 228A opposite to the deformable coupling structure <NUM> is fixed with respect to the connecting subportion 228C. A first end and a second end of the second elongated subportion 228B are fixed with respect to the fixed peripheral structure <NUM> and the connecting subportion 228C, respectively.

In addition, the first elongated subportion 228A is overlaid by a corresponding first actuator, here designated by <NUM>', of the same type as the one described with reference to <FIG>, whereas the second elongated subportion 228B is overlaid by a corresponding second actuator, here designated by <NUM>", of the same type as the one described with reference to <FIG> and electrically uncoupled from the first actuator <NUM>'. In this way, by supplying voltage alternatively to the first actuator <NUM>' or the second actuator <NUM>", translations of the secondary portion 27B along the axis Z in opposite directions are obtained, with consequent translations of the corresponding shielding structure in opposite directions.

Irrespective of the type of embodiment, it is further possible for the first and second shielding structures, albeit maintaining an angularly alternating arrangement, to have a shape and/or arrangement different from what has been described, as illustrated, for example, in <FIG>, where the first and second shielding structures are, respectively, designated by <NUM> and <NUM>, and where, purely by way of example, actuation of a piezoelectric type has been assumed, even though also in this case a variant with electrostatic actuation (not illustrated) is possible. For this reason, in what follows the description is limited to the differences with respect to what has been explained in connection with the embodiment illustrated in <FIG>. Elements already present in the embodiment illustrated in <FIG> are designated by the same references, except where otherwise specified. Furthermore, in <FIG> and in the subsequent figures, the deformable coupling structures <NUM> are illustrated in a simplified way. Once again, <FIG> does not show that the first ends of the main portions 27A of the cantilever structures <NUM> are fixed with respect to corresponding portions of the fixed peripheral structure <NUM>. Furthermore, in what follows, the terms "distal" and "proximal" are used to indicate parts of the shielding structures arranged, respectively, far from or near to the corresponding deformable coupling structures <NUM>.

All this having been said, in resting conditions, each one of the first and second shielding structures <NUM>, <NUM> extends in a direction parallel to a respective direction of extension (designated, respectively, by R'). In particular, in resting conditions, both the first and the second shielding structures <NUM>, <NUM> have a same mutual arrangement with respect to the corresponding directions of extension R'.

The directions of extension R' are parallel to the plane XY, are co-planar and equidistant from the axis of symmetry H. In other words, in top plan view and in resting conditions, the directions of extension R' are to a first approximation tangential to a hypothetical circumference (not illustrated) centred on the axis of symmetry H. Furthermore, adjacent pairs of directions of extension R' form an angle equal to <NUM>° so as to be angularly distributed over <NUM>°.

Without this implying any loss of generality, for each shielding structure, the corresponding cantilever structure <NUM>, the corresponding actuator <NUM>, the corresponding deformable coupling structure <NUM> and the corresponding coupling body <NUM> have the same shapes as those described in connection with the embodiment illustrated in <FIG>, except that they refer to the corresponding direction of extension R', instead of to the aforementioned radial direction R, and except that, in top plan view, the deformable coupling structure <NUM> and the coupling body <NUM> are arranged on a side of the direction of extension R' such that the rotation of the corresponding shielding structure occurs in a clockwise direction and leads to an increase of the optical aperture.

The shape of the first shielding structures <NUM>, which are the same as one another, is now described with reference to the first shielding structure <NUM> illustrated in <FIG>; further, referred to as "transverse direction" (which is denoted by TR') is a direction perpendicular to the plane ZR'.

In detail, the main portion (designated by <NUM>) of the top shielding region (designated by <NUM>) is tapered in a direction parallel to the direction of extension R'; i.e., it has an extension in the transverse direction TR' that decreases as the distance from the respective deformable coupling structure <NUM> increases.

In top plan view, the main portion (designated by <NUM>) of the bottom secondary region (designated by <NUM>) has approximately a wedge shape and, in addition to having, in a direction parallel to the direction of extension R', a maximum dimension smaller than the maximum dimension of the main portion <NUM> of the top shielding region <NUM>, is also tapered in a direction parallel to the direction of extension R'. Furthermore, the maximum extension of the main portion <NUM> of the bottom secondary region <NUM> in a direction parallel to the transverse direction TR' is less than the maximum extension, in the same direction, of the main portion <NUM> of the top shielding region <NUM>.

The secondary portion (designated by <NUM>) of the top shielding region <NUM> has approximately the same shape, in top plan view, as the main portion <NUM> of the bottom secondary region <NUM>, except for a recess. In other words, and without this implying any loss of generality, the secondary portion <NUM> overlies a proximal part of the main portion <NUM> of the bottom secondary region <NUM>, leaving exposed a distal part of the main portion <NUM> of the bottom secondary region <NUM>.

The secondary portion of the bottom secondary region <NUM> and the underlying suspended conductive region are designated, respectively, by <NUM> and <NUM>.

In even greater detail, the main portion <NUM> of the top shielding region <NUM> extends in cantilever fashion with respect to the secondary portion <NUM> of the top shielding region <NUM> so as to project beyond the main portion <NUM> of the bottom secondary region <NUM>, not only in a direction parallel to the direction of extension R' but also in a direction parallel to the transverse direction TR' for reasons that will be clarified hereinafter. In other words, both a distal part and a proximal part of the main portion <NUM> of the top shielding region <NUM>, referred to in what follows as the projecting proximal part of the main portion <NUM>, are suspended and project laterally with respect to the underlying bottom secondary region <NUM>.

The main portion <NUM> and the secondary portion <NUM> of the top shielding region <NUM> and the main portion <NUM> of the bottom secondary region <NUM> form a coupling wall <NUM>, which is perpendicular to the direction of extension R'. Without this implying any loss of generality, the second terminal portion <NUM> of the coupling body <NUM> is fixed with respect to a portion of the coupling wall <NUM>.

As regards the second shielding structures <NUM>, which are the same as one another, their shape is now described with reference to the second shielding structure <NUM> illustrated in <FIG>.

In detail, the main portion (designated by <NUM>) of the bottom shielding region (designated by <NUM>) has approximately the same shape as the main portions <NUM> of the top shielding regions <NUM>, with respect to which it is vertically staggered.

The main portion (designated by <NUM>) and the secondary portion (designated by <NUM>) of the top secondary region (designated by <NUM>) have approximately the same wedge shapes as the main portion <NUM> of the bottom secondary region <NUM> and as the secondary portion <NUM> of the top shielding region <NUM>, respectively. Consequently, the main portion <NUM> of the top secondary region <NUM> overlies entirely the secondary portion <NUM>, but leaves exposed a distal part and a proximal part of the main portion <NUM> of the bottom shielding region <NUM> (referred to in what follows as the exposed proximal part), which project, respectively, in a direction parallel to the direction of extension R' and in a direction parallel to the transverse direction TR'.

The secondary portion of the bottom shielding region <NUM> and the underlying suspended conductive region are designated, respectively, by <NUM> and <NUM>.

The main portion <NUM> and the secondary portion <NUM> of the top secondary region <NUM> and the main portion <NUM> of the bottom shielding region <NUM> form a coupling wall <NUM>, which is perpendicular to the direction of extension R'. Without this implying any loss of generality, the second terminal portion <NUM> of the coupling body <NUM> is fixed with respect to a portion of the coupling wall <NUM>.

Thanks to the geometrical shapes of the first and second shielding structures <NUM>, <NUM>, in resting conditions what has been described hereinafter occurs.

In detail, considering any first shielding structure <NUM>, the distal part of the main portion <NUM> of the respective top shielding region <NUM> overlies, at a distance, the exposed proximal part of the main portion <NUM> of the bottom shielding region <NUM> of the second shielding structure <NUM> adjacent to the shielding structure <NUM> and arranged in a counterclockwise direction.

In addition, the projecting proximal part of the main portion <NUM> of the top shielding region <NUM> overlies, at a distance, the distal part of the main portion <NUM> of the bottom shielding region <NUM> of the second shielding structure <NUM> adjacent to the shielding structure <NUM> and arranged in a clockwise direction.

Furthermore, the first and second shielding structures <NUM>, <NUM> may rotate about the respective axes of rotation, in a clockwise direction so as to reduce occlusion of the underlying main aperture <NUM> (not illustrated in <FIG>), i.e., so as to increase the optical aperture with respect to the resting conditions. The maximum degree of the rotation is a function of the shapes of the distal parts of the main portions <NUM> of the top shielding regions <NUM> and of the exposed proximal parts of the main portions <NUM> of the bottom shielding regions <NUM>.

According to a further variant, the MEMS shutter <NUM> may be without the second shielding structures, as illustrated in <FIG>, where the first shielding structures are designated by <NUM>. Also in <FIG>, the main aperture <NUM> is not represented.

This having been said, the MEMS shutter <NUM> differs from what is illustrated in <FIG> in that it includes eight first shielding structures <NUM>, which are the same as one another and are spaced at equal angular distances apart (in resting conditions).

As illustrated in <FIG>, each first shielding structure <NUM> comprises a respective top shielding region <NUM>, formed by the top inner structure <NUM> of the second semiconductor layer <NUM>, and a respective bottom shielding region <NUM>, formed by the bottom inner structure <NUM> of the first semiconductor layer <NUM>.

The top shielding region <NUM> comprises a respective secondary portion <NUM> and a respective main portion <NUM>; the bottom shielding region <NUM> comprises a respective main portion <NUM> and a respective secondary portion <NUM>. The underlying suspended conductive region is designated by <NUM>.

A proximal part <NUM>' of the main portion <NUM> and the secondary portion <NUM> of the top shielding region <NUM> form, together with a first part <NUM>' of the main portion <NUM> of the bottom shielding region <NUM>, a main body <NUM>; the second terminal portion <NUM> of the coupling body <NUM> is fixed with respect to the main body <NUM>.

A distal part <NUM>" of the main portion <NUM> of the top shielding region <NUM> extends in cantilever fashion from the main body <NUM>, in a direction approximately parallel to the corresponding direction of extension R', projecting with respect to the underlying bottom shielding region <NUM>.

A second part <NUM>" of the main portion <NUM> of the bottom shielding region <NUM> is left exposed by the overlying top shielding region <NUM> and is laterally staggered with respect to the main body <NUM>.

Thanks to the aforementioned shape of the first shielding structures <NUM>, in resting conditions it happens that, as illustrated in <FIG>, the distal part <NUM>" of the main portion <NUM> of the top shielding region <NUM> of any first shielding structure <NUM> overlies, at a distance, the second part <NUM>" of the main portion <NUM> of the bottom shielding region <NUM> of the first shielding structure that is adjacent and arranged in a counterclockwise direction. Furthermore, the second part <NUM>" of the main portion <NUM> of the bottom shielding region <NUM> of any first shielding structure <NUM> is overlaid, at a distance, by the distal part <NUM>" of the main portion <NUM> of the top shielding region <NUM> of the first shielding structure that is adjacent and arranged in a clockwise direction.

The first shielding structures <NUM> may rotate about the respective axes of rotation ROT in the same way as described with reference to <FIG>, the maximum degree of the rotation being a function of the shapes of the distal part <NUM>' of the main portion <NUM> of the top shielding region <NUM> and of the second part <NUM>" of the main portion <NUM> of the bottom shielding region <NUM>.

Albeit not illustrated, variants are further possible where the MEMS shutter <NUM> is of the same type as that illustrated in <FIG> or <FIG>, but in which piezoelectric actuation is of a bidirectional type, as illustrated in <FIG>, or else is of an electrostatic type, in which case the shielding structures are coupled to corresponding coupling bodies <NUM>'.

The present MEMS shutter <NUM> may be manufactured using the process described hereinafter with reference, for example, to an embodiment of the type illustrated in <FIG>.

As shown in <FIG>, the present process initially envisages forming a first dielectric layer <NUM> and a second dielectric layer <NUM> on the substrate <NUM> of a semiconductor wafer <NUM>; the first and second dielectric layers <NUM>, <NUM> are made, respectively, of thermal oxide and aluminium oxide.

Next, as illustrated in <FIG>, a part of the second dielectric layer <NUM> is selectively removed so as to form a first preliminary opening WP1 through the second dielectric layer <NUM> in order to expose a part of the first dielectric layer <NUM>.

Then, as illustrated in <FIG>, portions of the exposed part of the first dielectric layer <NUM> are selectively removed so as to form, through the first dielectric layer <NUM>, a second preliminary opening WP2 and a third preliminary opening WP3, which is shaped like a trench and surrounds laterally, at a distance, the second preliminary opening WP2.

Next, as illustrated in <FIG>, polysilicon is deposited, followed by selective etching so that the residual polysilicon forms the conductive layer <NUM>, within the third preliminary opening WP3, as well as the anchorage regions <NUM> and an intermediate conductive region <NUM>, which extends in the second preliminary opening WP2, in contact with the substrate <NUM>, as well as over portions of the first dielectric layer <NUM> that laterally delimit the second preliminary opening WP2. The conductive layer <NUM> and the intermediate conductive region <NUM> are separated from one another laterally; consequently, the aforementioned operations of deposition of polysilicon and of subsequent etching leave exposed parts of the first dielectric layer <NUM>, which are laterally staggered with respect to the conductive layer <NUM> and to the intermediate conductive region <NUM>. Furthermore, portions of the second semiconductor layer <NUM> arranged on the outside of the conductive layer <NUM> and laterally staggered with respect to the anchorage regions <NUM> remain exposed.

Then, as illustrated in <FIG>, a first sacrificial region <NUM> is formed and then planarized (step not represented in detail), on the conductive layer <NUM>, on the anchorage regions <NUM>, and on the intermediate conductive region <NUM>, as well as on the exposed portions of the first and second dielectric layers <NUM>, <NUM>. In particular, the first sacrificial region <NUM> is made of TEOS oxide laid by chemical-vapour deposition.

Next, as illustrated in <FIG>, an etch is made for selective removal of portions of the first sacrificial region <NUM> arranged on the anchorage regions <NUM> and on the intermediate conductive region <NUM>. In particular, a corresponding fourth preliminary opening WP4 is formed, which traverses the first sacrificial region <NUM> and gives out onto an inner portion of the intermediate conductive region <NUM>, which is thus exposed. Without this implying any loss of generality, this inner portion of the intermediate conductive region <NUM> includes, in addition to the part of the intermediate conductive region <NUM> arranged in contact with the substrate <NUM>, also parts of the intermediate conductive region <NUM> that extend on the first dielectric layer <NUM>. Furthermore, fifth preliminary openings WP5 are formed, which traverse the first sacrificial region <NUM> and give out onto corresponding anchorage regions <NUM>.

Then, as illustrated in <FIG>, a first epitaxial growth of silicon is carried out so as to form, and then planarize (step not represented in detail), the first semiconductor layer <NUM>, which is made, as has been said, of polycrystalline silicon, and extends on the first sacrificial region <NUM>, as well as within the fourth preliminary opening WP4, in direct contact with the intermediate conductive region <NUM>, and within the fifth preliminary openings WP5, in direct contact with the anchorage regions <NUM>. In particular, the portions of the first semiconductor layer <NUM> that extend within the fifth preliminary openings WP5 form the aforementioned supporting regions <NUM>, i.e., the anchorages of the first semiconductor layer <NUM>.

Albeit not illustrated, in an optional way it is possible that, using a mask, portions of the first semiconductor layer <NUM> that are laterally staggered with respect to the anchorage regions <NUM> and to the intermediate conductive region <NUM> are subsequently removed in a selective way so as to define corresponding portions of the MEMS shutter <NUM>, such as the bottom elongated portions <NUM> of the first and second elastic structures M1, M2. In this case, optional openings are formed through the first semiconductor layer <NUM>, delimited at the bottom by the first sacrificial region <NUM>.

Next, as illustrated in <FIG>, a second sacrificial region <NUM> is formed by chemical-vapour deposition, the second sacrificial region <NUM> consisting of TEOS oxide and extending on the first semiconductor layer <NUM>, as well as possibly within the aforementioned optional openings.

Then, as illustrated in <FIG>, a selective etch is made so as to remove portions of the second sacrificial region <NUM> that are arranged on the first semiconductor layer <NUM> and are laterally staggered with respect to the intermediate conductive region <NUM> in order to expose corresponding portions of the first semiconductor layer <NUM>.

Next, as illustrated in <FIG>, a second epitaxial growth of silicon is carried out so as to form, and then planarize (step not represented in detail), the second semiconductor layer <NUM>, which is made, as has been said, of polycrystalline silicon and extends on the second sacrificial region <NUM>, as well as on the exposed portions of the first semiconductor layer <NUM>. The portions of the second semiconductor layer <NUM> that contact the first semiconductor layer <NUM> are to form the top peripheral region <NUM> and part of the deformable coupling structures <NUM>, in addition to corresponding portions of the coupling bodies <NUM>, of the planar springs <NUM> and of the pillar regions <NUM>, as well as the secondary portions <NUM> of the top shielding regions <NUM> of the first shielding structures <NUM> and the secondary portions <NUM> of the top secondary regions <NUM> of the second shielding structures <NUM>.

Then, in a per se known manner the actuators <NUM> are formed, as illustrated in <FIG>.

Next, as illustrated in <FIG>, a selective etch is performed using a mask (not illustrated) so as to remove portions of the second semiconductor layer <NUM> and form process openings <NUM>, which traverse the second semiconductor layer <NUM> and are delimited at the bottom by corresponding portions of the second sacrificial region <NUM> or else by corresponding portions of the first sacrificial region <NUM>.

In practice, the process openings <NUM> that extend as far as the first sacrificial region <NUM> laterally delimit portions of the second semiconductor layer <NUM> that form the cantilever structures <NUM>, the coupling bodies <NUM> and the planar springs <NUM>. The process openings <NUM> that extend as far as the second sacrificial region <NUM> laterally delimit portions of the second semiconductor layer <NUM> that form the main portions <NUM> of the top shielding regions <NUM> of the first shielding structures <NUM> and the main portions <NUM> of the top secondary regions <NUM> of the second shielding structures <NUM>.

Next, as illustrated in <FIG>, on the semiconductor wafer <NUM> a protection layer <NUM> is formed, for example by deposition of TEOS oxide. The protection layer <NUM> extends on the protective regions <NUM> of the actuators <NUM>, on the exposed portions of the second semiconductor layer <NUM>, and within the process openings <NUM> until it contacts portions of the first and second sacrificial regions <NUM>, <NUM>.

Next, as illustrated in <FIG>, using a respective mask (not illustrated), a backside etch of the substrate <NUM> is performed, for selective removal of portions of the substrate <NUM> that are arranged underneath the intermediate conductive region <NUM> and form the main aperture <NUM>.

In particular, the etch is of a dry type (for example, sulphur hexafluoride is used) and is guided, besides by the aforementioned mask, by the part of the intermediate conductive region <NUM> that contacts the substrate <NUM> since etching is not able to remove portions of the first dielectric layer <NUM>. Consequently, in addition to the aforementioned part of the intermediate conductive region <NUM> that contacts the substrate <NUM>, an overlying portion of the first semiconductor layer <NUM> is selectively removed. In this way, an intermediate opening <NUM> is formed, which extends through the first semiconductor layer <NUM> and the first dielectric layer <NUM> and communicates with the underlying main aperture <NUM>.

At each of the first shielding structures <NUM>, the intermediate opening <NUM> is overlaid by a portion of the second sacrificial region <NUM> arranged underneath the main portion <NUM> of the corresponding top shielding region <NUM>; this portion of the second sacrificial region <NUM> enables, in fact, a local etch stop, before the main portion <NUM> gets damaged.

Furthermore, the etching mask is such that also portions of the substrate <NUM> are removed that are laterally staggered with respect to the overlying intermediate conductive region <NUM>, said portions being delimited at the top by corresponding portions of the first dielectric layer <NUM>. In this way, the main aperture <NUM> is partially closed, at the top, by these portions of the first dielectric layer <NUM>, which are laterally staggered with respect to the part of the intermediate conductive region <NUM> in contact with the substrate <NUM>; these portions of the first dielectric layer <NUM> are in turn surrounded laterally by the conductive layer <NUM>. In practice, these portions of the first dielectric layer <NUM> partially close the top mouth of the main aperture <NUM>, understood as the area of the main aperture <NUM> in the plane of the top surface Sa of the substrate <NUM>.

In particular, for each second shielding structure <NUM>, the main aperture <NUM> is partially occluded by a corresponding portion of the first dielectric layer <NUM>, which is overlaid by a corresponding portion of the first sacrificial region <NUM> arranged underneath the main portion <NUM> of the corresponding bottom shielding region <NUM>. The aforesaid corresponding portion of the first dielectric layer <NUM> protects from etching the corresponding bottom shielding region <NUM>.

At the end of the operations illustrated in <FIG>, the remaining portions of the first semiconductor layer <NUM> form the bottom secondary regions <NUM> of the first shielding structures <NUM> and the bottom shielding regions <NUM> of the second shielding structures <NUM>. The remaining portions of the intermediate conductive region <NUM> form the suspended conductive regions <NUM>, <NUM>. In this connection, in <FIG> it may be noted how the suspended conductive regions <NUM>, <NUM> project slightly outwards, with respect to the corresponding secondary portions <NUM>, <NUM>; this detail is irrelevant for the purposes of operation of the MEMS shutter <NUM> and, for simplicity of representation, has not been illustrated in the other figures. Furthermore, the degree of the projection may be much smaller (substantially, negligible) than what is illustrated in <FIG>.

Next, an etch is made using hydrofluoric acid, which enables removal of the protection region <NUM> and the first and second sacrificial regions <NUM>, <NUM>. Furthermore, the aforementioned portions of the first dielectric layer <NUM> that in part closed at the top the main aperture <NUM> are removed. These portions of the first dielectric layer <NUM> are removed because they are not protected by the aluminium oxide of the second dielectric layer <NUM>. In this way, the first and second shielding structures <NUM>, <NUM> are released, as well as the corresponding cantilever structures <NUM> and the corresponding deformable coupling structures <NUM>, thus obtaining what is illustrated in <FIG>. The residual portions of the first and second dielectric layers <NUM>, <NUM> form, respectively, the first and second dielectric regions <NUM>, <NUM>.

In general, the manufacturing process described may be used for manufacturing also the other embodiments, as for example the embodiments with electrostatic actuation. In particular, formation of the first and second shielding structures <NUM>, <NUM> and of the coupling bodies is performed in the same way.

The advantages that the present solution afford emerge clearly from the foregoing description.

In particular, the present MEMS shutter <NUM> may be controlled electrically so as to vary the optical aperture with a large number of degrees of freedom. In fact, it is possible to shield selectively a large number of perimetral portions of the main aperture <NUM> by rotations of corresponding shielding structures. The fact that the shielding structures are patterned on two different levels enables optimization of the angular arrangement of the shielding structures themselves. In this connection, in general the effect of the movement of the shielding structures on the optical aperture also depends upon the profile of the underlying main aperture <NUM>, which represents a further degree of freedom available to the designer.

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

For instance, the shape and arrangement of the shielding structures, the fixed peripheral structure, the cantilever structures, the deformable coupling structures, the coupling bodies, and the stator regions may be different from what has been described.

The number, shape, and arrangement of the pillar regions and the planar springs may be different from what has been described. Likewise, the points of the coupling bodies to which the planar springs are fixed may also vary.

Furthermore, the alignments of the different regions during the manufacturing process may be different from what has been described, for example on account of the typical tolerances of the etching processes.

Once again with reference to the manufacturing process, the polysilicon that forms the first and second semiconductor layers <NUM>, <NUM> may be obtained in a per se known manner, for example by epitaxial growth starting from exposed portions (not illustrated) of the substrate <NUM> and of the first semiconductor layer <NUM>, respectively, in order to speed up growth thereof and increase the thicknesses of the first and second semiconductor layers <NUM>, <NUM>. In this connection, in general each one of the first and second semiconductor layers <NUM>, <NUM> may have a thickness comprised, for example, between <NUM> and <NUM>.

It is further possible for the second dielectric layer <NUM>, and thus the second dielectric region <NUM>, to be made of a material resistant to hydrofluoric acid different from aluminium oxide.

Furthermore, it is possible for the first shielding structures to be formed just by corresponding portions of the second semiconductor layer <NUM> and/or for the second shielding structures to be formed just by corresponding portions of the first semiconductor layer <NUM>, as illustrated, for example, in <FIG>, where, for instance, it is shown how each first shielding structure <NUM> is constituted by the main portion <NUM> of the top shielding region <NUM>; further, each second shielding structure <NUM> is constituted by the bottom shielding region <NUM>.

Likewise, also the coupling bodies, the deformable coupling structures, and the planar springs may be formed just by portions of one between the first and second semiconductor layers <NUM>, <NUM>; further, the cantilever structures <NUM> may be formed just by the second semiconductor layer <NUM>.

Claim 1:
A MEMS shutter comprising:
- a substrate (<NUM>) of semiconductor material traversed by a main aperture (<NUM>);
- a first semiconductor layer (<NUM>), arranged on top of the substrate (<NUM>);
- a second semiconductor layer (<NUM>), arranged on top of the first semiconductor layer (<NUM>) and forming, together with the first semiconductor layer (<NUM>), a supporting structure (<NUM>, <NUM>) fixed to the substrate (<NUM>);
- a plurality of deformable structures (<NUM>, <NUM>, <NUM>), each of which is formed by a corresponding portion of at least one of the first semiconductor layer and the second semiconductor layer;
- a plurality of actuators (<NUM>; <NUM>); and
- a plurality of shielding structures (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>), each of which is formed by a corresponding portion of at least one of the first and second semiconductor layers, the shielding structures being arranged angularly around the underlying main aperture so as to form a shielding of the main aperture, each shielding structure being further mechanically coupled to the supporting structure via a corresponding deformable structure;
and wherein each actuator is electrically controllable so as to cause a rotation of a corresponding shielding structure between a respective first position and a respective second position, thereby varying the shielding of the main aperture; and wherein said first and second positions of the shielding structures are such that, in at least one operating condition of the MEMS shutter (<NUM>), pairs of adjacent shielding structures at least partially overlap one another.