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. This 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 nonlimiting 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>, this refers to the embodiment illustrated in <FIG>, which differs from the embodiment illustrated in <FIG> for the shape of the main aperture <NUM>. In what follows, the description will be limited to the embodiment illustrated in <FIG>, except where otherwise specified; references to <FIG> will, however, be made, to the extent where they are applicable also to the embodiment 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. 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.

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 this description also applies to the other cantilever structures <NUM> even when they are coupled to the second shielding structures <NUM>), a first end of the main portion 27A is fixed with respect to a corresponding portion of the fixed peripheral structure <NUM> (just one of which is illustrated in <FIG>); 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 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 triangular 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 on 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 through 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 first adjacent 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 second adjacent 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 second adjacent 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 first adjacent 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>, where, as explained previously, just one first shielding structure <NUM> is visible.

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 the axis of symmetry H and the top peripheral region <NUM>, respectively, 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 the bottom peripheral region <NUM> and the axis of symmetry H, respectively, 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 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 an extension greater 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, also part of the main portion <NUM> of the bottom secondary region <NUM> is suspended, together with the corresponding secondary portion <NUM>, over the main aperture <NUM>, albeit at a greater distance from the axis of symmetry H as compared to the aforementioned part of the main portion <NUM> of the top shielding region <NUM>. Without this implying any loss of generality, the secondary portion <NUM> of the top shielding region <NUM> is at least in part laterally staggered with respect to the main aperture <NUM>, even though variants are possible, in which, for example, the entire first shielding structure <NUM> is arranged on top of the main aperture <NUM>, or else variants in which the entire bottom secondary region <NUM> is laterally staggered with respect to the main aperture <NUM>, as illustrated, for example, in <FIG>.

In top plan view, the area of overlapping between the main portion <NUM> of the top shielding region <NUM> and the main aperture <NUM> is greater than the area of overlapping between the main portion <NUM> of the bottom secondary region <NUM> and the main aperture <NUM> since, as explained previously, the main portion <NUM> of the top shielding region <NUM> has a radial extension greater than the main portion <NUM> of the bottom secondary region <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>. The deformable coupling structures <NUM> are the same as one another; for example, described in what follows is the deformable coupling structure <NUM> for the first shielding structure <NUM> illustrated in <FIG> and <FIG>.

In detail, as shown in <FIG>, the deformable coupling structure <NUM> comprises a first elastic structure M1 and a second elastic structure M2, which in <FIG> are illustrated 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, a second elongated structure L2, and a third elongated structure L3, a first connecting arm B1 and a second connecting arm B2, an outer coupling region EC and an inner coupling region IC, which are now described with reference to the resting conditions illustrated in <FIG>.

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, second, and third elongated structures L1, L2, L3 are the same as one another, co-planar and 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 first 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 first 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 first 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 the second connecting arm B2, which has to a first approximation the same shape as the first connecting arm B1.

The first ends of the top elongated portion <NUM> and of the bottom elongated portion <NUM> of the third elongated structure L3 are fixed with respect to the inner coupling region IC, which 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>, has an approximately parallelepipedal shape and extends in cantilever fashion starting (for example) from an angular portion of the first shielding structure <NUM>, with respect to which it is fixed. In particular, the inner coupling region IC is fixed with respect to portions of the top shielding region <NUM> and the bottom secondary region <NUM>.

The second ends of the top elongated portion <NUM> and of the bottom elongated portion <NUM> of the third elongated structure L3 are fixed with respect to the second connecting arm B2, which is thus arranged between the second and third elongated structures L2, L3.

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 the radial direction R and is rigid in the transverse direction TR.

As may be seen in <FIG> and <FIG>, for each first shielding structure <NUM>, the MEMS shutter <NUM> further comprises four first 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 first planar springs <NUM> are formed by the inner mobile portion <NUM> of the second semiconductor layer <NUM> and have an elongated shape. In particular, in resting conditions, the first planar springs <NUM> are shaped like parallelepipeds elongated in a direction parallel to the transverse direction TR, with first ends fixed with respect to the main portion <NUM> of the top shielding region <NUM> and with second ends fixed with respect to corresponding first pillar regions <NUM>. For reasons that will be clarified hereinafter, the first 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 greater detail, the first planar springs <NUM> are arranged two by two on opposite sides of the main portion <NUM> of the top shielding region <NUM>, in a way symmetrical with respect to a plane of symmetry parallel to the plane RZ. Furthermore, the first 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>.

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 an extension greater 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 secondary portion <NUM> of the top secondary region <NUM> is at least in part laterally staggered with respect to the main aperture <NUM>, even though variants are possible, in which, for example, the entire second shielding structure <NUM> is arranged on top of the main aperture <NUM>, or else variants in which the entire top secondary region <NUM> is laterally staggered with respect to the main aperture <NUM>, as illustrated, for example, in <FIG>. Furthermore, in top plan view, the area of overlapping between the main portion <NUM> of the bottom shielding region <NUM> and the main aperture <NUM> is greater than the area of overlapping between the main portion <NUM> of the top secondary region <NUM> and the main aperture <NUM> since, as explained previously, the main portion <NUM> of the bottom shielding region <NUM> has an extension in the radial direction R greater than the extension of the main portion <NUM> of the top secondary region <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>, in the same way as described with reference to the first shielding structure <NUM>. In particular, for each of the corresponding first and second elastic structures M1, M2, the corresponding inner coupling region IC extends in cantilever fashion starting (for example) from an angular portion of the second shielding structure <NUM>, with respect to which it is fixed. In particular, the inner coupling region IC is fixed with respect to portions of the bottom shielding region <NUM> and of the top secondary region <NUM>.

For each second shielding structure <NUM>, the MEMS shutter <NUM> further comprises four second planar springs <NUM>, which are now described, by way of example, with reference to the second shielding structure <NUM> illustrated in <FIG>.

In detail, the second planar springs <NUM> are formed by the bottom inner structure <NUM> of the first semiconductor layer <NUM> and have an elongated shape. In particular, in resting conditions the second planar springs <NUM> are shaped like parallelepipeds elongated in a direction perpendicular with respect to the corresponding radial direction R (i.e., in a direction parallel to the corresponding transverse direction TR), with first ends fixed with respect to the main portion <NUM> of the bottom shielding region <NUM> and with second ends fixed with respect to corresponding second pillar regions <NUM>. For reasons that will be clarified hereinafter, the second 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 greater detail, the second planar springs <NUM> are arranged two by two on opposite sides of the main portion <NUM> of the bottom shielding region <NUM>, in a way symmetrical with respect to a plane of symmetry parallel to the plane RZ. Furthermore, the second pillar regions <NUM> are formed by the first semiconductor layer <NUM> (in particular, by portions of the fixed bottom peripheral region <NUM>' and by underlying supporting regions <NUM>) and are anchored, at the bottom, to corresponding anchorage 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 only partially the underlying main aperture <NUM>. In particular, when the first and second shielding structures <NUM>, <NUM> are in resting conditions, the maximum (partial) occlusion of the main aperture <NUM> is obtained; equivalently, in resting conditions there occurs the minimum optical aperture, 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 move in the respective radial direction R the corresponding first/second shielding structure <NUM>/<NUM>, in a direction opposite to the axis of symmetry H, thus reducing 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 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, via the inner coupling region IC, with respect to the first shielding structure <NUM> may not translate along the axis Z, on account of the constraint exerted by the first 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 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 inner coupling region IC do not undergo translations along the axis Z, but translate in the corresponding radial direction R, in a direction opposite to the axis of symmetry H, dragging the first shielding structure <NUM> and reducing the area of overlapping between the latter and the underlying main aperture <NUM>. On account of this dragging action, the first planar springs <NUM> curve, in top plan view.

Occlusion of the main aperture <NUM> decreases as the first and second shielding structures <NUM>, <NUM> move away from the axis of symmetry H. 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.

According to a variant illustrated in <FIG> (where, for simplicity, the main aperture <NUM> is not illustrated), 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 translations in the respective radial directions R, but the actuators (designated by <NUM>) are of an electrostatic type. This variant is now described, purely by way of example, with reference to the actuator <NUM> coupled to the first shielding structure <NUM> illustrated in <FIG>, 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 pair of first stator regions ST1 and a pair of second stator regions 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 by 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 a coupling body <NUM>, which is approximately T-shaped in top plan view.

In particular, as illustrated in <FIG>, the coupling body <NUM> 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>. Furthermore, the coupling body <NUM> comprises an elongated portion <NUM> with a parallelepipedal shape, which extends in a direction parallel to the radial direction R, and a transverse portion <NUM>, which in turn comprises a supporting portion <NUM>, which has a shape elongated in a direction parallel to the transverse direction TR, and a plurality of coupling portions <NUM>, which are arranged on two opposite sides of the supporting portion <NUM> and are staggered in the transverse direction TR, each coupling portion <NUM> departing from the respective side of the supporting portion <NUM>, in a direction parallel to the radial direction R.

The elongated portion <NUM> has a first end fixed with respect to the first shielding structure <NUM> and a second end fixed with respect to the supporting portion <NUM> of the transverse portion <NUM>, which functions, together with the coupling portions <NUM>, as rotor region.

The first and second stator regions ST1, ST2 extend on opposite sides of the transverse portion <NUM> and form corresponding pluralities of elements elongated in the radial direction R (designated, respectively, by <NUM> and <NUM>). The elongated elements <NUM> of each first stator region ST1 are laterally staggered in a direction parallel to the transverse direction TR so as to be interdigitated with respect to a corresponding set of coupling portions <NUM>. Likewise, the elongated elements <NUM> of each second stator region ST2 are laterally staggered in a direction parallel to the transverse direction TR so as to be interdigitated with respect to a corresponding set of coupling portions <NUM>.

Two pairs of third pillar regions <NUM> extend on opposite sides of the elongated portion <NUM> of the coupling body <NUM> and have the same structure as the first pillar regions 71and are thus anchored at the bottom to corresponding anchorage regions <NUM>. Each third pillar portion <NUM> is mechanically coupled to the elongated portion <NUM> of the coupling body <NUM> by interposition of a corresponding third planar spring <NUM>, which has, for example, a folded 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 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 practice, the first shielding structure <NUM> and the coupling body <NUM> are suspended and constrained to the third pillar regions <NUM> by interposition of the third planar springs <NUM>. Albeit not illustrated, variants are, however, possible in which the third planar springs <NUM> have ends fixed to the first shielding structure <NUM>, instead of to the coupling body <NUM>.

In use, by applying voltages between the first and second stator regions ST1, ST2 and the rotor region, the coupling body <NUM> is subjected to a force of an electrostatic nature, which causes a translation of the coupling body <NUM> with respect to the first and second stator regions ST1, ST2, in the corresponding radial direction R; said translation may take place in either direction. The first shielding structure <NUM> translates in a way fixed with respect to the coupling body <NUM> in the corresponding radial direction R, with consequent variation of occlusion of the underlying main aperture <NUM>.

The advantages afforded by arranging first and second shielding structures <NUM>, <NUM> that form shields in different semiconductor layers are thus obtained also with this variant. Furthermore, according to this variant, the shielding structures may be subject, with respect to the positions assumed in the resting conditions, to both positive and negative movements, measured with respect to the respective radial directions R.

Positive and negative displacements with respect to the positions of rest may be obtained also in the case of use of piezoelectric actuators, as illustrated with reference to <FIG>, which is now described limitedly to the differences with respect to what is illustrated in <FIG>.

In detail, the cantilever structure (here designated by <NUM>) comprises the secondary portion 27B, which is coupled to the corresponding shielding structure in the same way as described previously; in this connection, in <FIG> reference is made, by way of example, to a first shielding structure <NUM>.

The main portion (here designated by 227A) of the cantilever structure <NUM> 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> and <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 <FIG> and electrically uncoupled from the first actuator <NUM>'. In this way, by supplying voltage alternatively to the first actuator <NUM>' or to the second actuator <NUM>", translations of the secondary portion 27B are obtained along the axis Z in opposite directions, 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> (not illustrated in <FIG>). In addition, for simplicity, <FIG> does not illustrate the couplings between the first and second shielding structures <NUM>, <NUM> and, respectively, the first and second pillar regions, through the first and second planar springs. Finally, 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, 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', 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>°.

For each shielding structure, the corresponding cantilever structure <NUM>, the corresponding deformable coupling structure <NUM> and the corresponding actuator <NUM> have the same shapes and arrangements 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.

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 from 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>, which is 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 first and second elastic structures M1, M2 of the corresponding deformable coupling structure <NUM> are fixed with respect to portions 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 the direction of extension R' and in 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 first and second elastic structures M1, M2 of the corresponding deformable coupling structure <NUM> are fixed with respect to portions of the coupling wall <NUM>.

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

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 translate in the respective directions of extension R', in the same way as described with reference to the previous embodiments, so as to reduce the area of overlapping between the shielding structures, and thus reduce occlusion of the underlying main aperture <NUM> (not illustrated in <FIG>).

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 illustrated. Not shown, for simplicity, are further the couplings between the first shielding structures <NUM> and corresponding pillar regions, provided by corresponding planar springs of the same type as described previously and formed indifferently by the first semiconductor layer <NUM> and/or by the second semiconductor layer <NUM>.

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 first and second elastic structures M1, M2 of the deformable coupling structure <NUM> are 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>, approximately in 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, as shown 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. In these conditions, occlusion of the underlying main aperture <NUM> is maximum since, in top plan view, there is no solution of continuity between the first shielding structures.

The first shielding structures <NUM> may translate in the respective directions of extension R' so as that the distal parts <NUM>" of the main portions <NUM> of the top shielding region <NUM> become laterally separate from, i.e., no longer overlying, the adjacent shielding structures. In other words, in top plan view, there is solution of continuity between the first shielding structures <NUM>; i.e., occlusion of the underlying main aperture <NUM> decreases.

Albeit not illustrated, variants are further possible where the MEMS shutter <NUM> is of the same type as what is illustrated in <FIG> or <FIG>, but where the piezoelectric actuation is of a bidirectional type, as shown in <FIG>, or else is of an electrostatic type, in which case the shielding structures are coupled to corresponding coupling bodies. For instance, with reference to the variant illustrated in <FIG>, <FIG>, the coupling bodies may be fixed with respect to the aforementioned coupling walls <NUM>, in the case of the first shielding structures <NUM>, and to the aforementioned coupling walls <NUM>, in the case of the second shielding structures <NUM>.

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

As illustrated 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 on 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.

Next, 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.

Then, as illustrated in <FIG>, an etch is made for selective removal of portions of the first sacrificial region <NUM> that are arranged on the anchorage regions <NUM> and on the intermediate conductive region <NUM>. In particular, a corresponding fourth preliminary opening WP4 is formed, which passes through the first sacrificial region <NUM> and gives out onto an inner portion of the intermediate conductive region <NUM>, which is 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 pass through the first sacrificial region <NUM> and give out onto corresponding anchorage regions <NUM>.

Next, 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>.

As illustrated in <FIG>, using a mask (not illustrated) 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 then removed in a selective way so as to form a plurality of first process openings <NUM>, which pass through the first semiconductor layer <NUM> and are delimited at the bottom by corresponding portions of the first sacrificial region <NUM>.

The first process openings <NUM> laterally delimit the portions of the first semiconductor layer <NUM> that form the bottom peripheral region <NUM> and the deformable coupling structures <NUM> (in particular, the bottom elongated portions <NUM> of the elongated structures of the elastic structures).

Next, as illustrated in <FIG>, a second sacrificial region <NUM> is formed by chemical-vapour deposition, the second sacrificial region <NUM> being formed by TEOS oxide and extending on the first semiconductor layer <NUM>, as well as within the first process openings <NUM> until it comes into contact with the portions of the first sacrificial region <NUM> that delimit at the bottom the first process openings <NUM>.

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 thus laterally staggered with respect to the first process openings <NUM>. In particular, anchorage openings <NUM> are formed, which are delimited at the bottom by 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 within the anchorage openings <NUM> so as to contact the portions of the first semiconductor layer <NUM> that delimit at the bottom the anchorage openings <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 particular, part of the transverse portions <NUM> of the elongated structures of the elastic structures), in addition to 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 second 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>.

In practice, the second process openings <NUM> laterally delimit the portions of the second semiconductor layer <NUM> that form the top peripheral region <NUM> and the top elongated portions <NUM> of the elongated structures of the elastic structures. Furthermore, the second process openings <NUM> laterally delimit 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 second process openings <NUM> until it comes into contact with the portions of the second sacrificial region <NUM> that delimit at the bottom the second process openings <NUM>.

Then, 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> arranged underneath the intermediate conductive region <NUM> and forming the main aperture <NUM>.

In particular, the etch is of a dry type (for example, sulphur hexafluoride is used) and is guided, as well as 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>, which are in contact with one another. 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 also for the manufacture of the other embodiments, as for example the embodiments with electrostatic actuation. In this connection, with reference, for example, to the embodiment illustrated in <FIG>, formation of the first and second shielding structures <NUM>, <NUM> is performed in the same way as described previously. In addition, formation of the first sacrificial region <NUM> and the subsequent formation of the first process openings <NUM> through the first semiconductor layer <NUM> enables definition of the parts of the third planar springs <NUM> and of the coupling body <NUM> formed by the first semiconductor layer <NUM>, in addition to the parts of the first and second stator regions ST1, ST2 formed by the first semiconductor layer <NUM>. Formation of the second process openings <NUM> through the second semiconductor layer <NUM> enables definition of the parts of the third planar springs <NUM> and of the coupling body <NUM> formed by the second semiconductor layer <NUM>, in addition to the parts of the first and second stator regions ST1, ST2 formed by the second semiconductor layer <NUM>.

Further possible variants are where, for example, etching of the first semiconductor layer <NUM>, mentioned previously with reference to <FIG>, with formation of the first process openings <NUM>, does not entail definition of (for example) the bottom peripheral region <NUM>, as illustrated in <FIG>. In this case, the bottom peripheral region <NUM> may be defined during the subsequent etching of the second semiconductor layer <NUM>, which is performed so as to cause also removal of underlying portions of the first semiconductor layer <NUM>. For this purpose, as illustrated in <FIG>, patterning of the second sacrificial region <NUM>, described previously with reference to <FIG>, and the mask (not illustrated and mentioned with reference to <FIG>) used during selective etching of the second semiconductor layer <NUM> are such that the latter etching causes formation, not only of the second process openings <NUM>, but also of deep openings <NUM>*, which traverse both the first semiconductor layer <NUM> and the second semiconductor layer <NUM> and are delimited at the bottom by the first sacrificial region <NUM>. Furthermore, albeit not illustrated, in the case of the variants where etching of the second semiconductor layer <NUM> also involves removal of underlying portions of the first semiconductor layer <NUM>, until portions of the first sacrificial region <NUM> are exposed, the protection layer <NUM> may extend within the deep openings <NUM>* until it comes into contact with the aforesaid portions of the first sacrificial region <NUM>. In addition, in general, the deep openings <NUM>* may be used to define parts of the MEMS shutter <NUM> formed both by the first semiconductor layer <NUM> and by the second semiconductor layer <NUM>, such as the aforementioned transverse portions <NUM>.

The advantages that the present solution affords 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 translations 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 of the shielding structures, the fixed peripheral structure, the cantilever structures, the deformable coupling structures (in the case of piezoelectric actuation), and the coupling bodies and stator regions (in the case of electrostatic actuation) may be different from what has been described. For instance, the stator regions may in turn include cantilever portions.

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, such as the ones that lead to formation of the anchorage openings <NUM>, illustrated in <FIG>. It is thus, for example, possible for there be obtained what is illustrated in <FIG>, which regards the same step of the manufacturing process as that shown in <FIG>.

In detail, if by top surface Stop is designated the top surface of the second sacrificial region <NUM>, the parts of the top peripheral region <NUM> and of the top inner structure <NUM> (formed by the second semiconductor layer <NUM>) that are located on the top surface Stop protrude slightly from the respective underlying portions arranged between the top surface Stop and the surface (designated by Sint) that geometrically separates the first and second semiconductor layers <NUM>, <NUM>.

Once again with reference to the manufacturing process, the polysilicon that forms the first and second semiconductor layers <NUM>, <NUM> may be formed in a per se known manner, for example by epitaxial growth starting from exposed portions (not illustrated) of the substrate <NUM> and, respectively, of the first semiconductor layer <NUM>, 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, both the first semiconductor layer <NUM> and the second semiconductor layer <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 (for example, silicon nitride).

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

Finally, 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 <NUM> and the deformable coupling structures <NUM> may be formed just by portions of one of the first semiconductor layer <NUM> and the second semiconductor layer <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>, <NUM>; <NUM>, <NUM>) fixed to the substrate (<NUM>);
- a plurality of deformable 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;
- 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 translation 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.