Angular piezoelectric actuator for MEMS shutter and manufacturing method thereof

Abstract

Various embodiments of the present disclosure relate to angular piezoelectric actuators for MEMS shutters and methods for manufacturing the same. A MEMS actuator comprises a body having a central portion and a peripheral portion, the central portion being capable of being coupled to a substrate, the peripheral portion being suspended above the substrate when the central portion is coupled to the substrate. The peripheral portion has a deformable structure extending around the central portion and forming a continuously arranged membrane. The MEMS actuator comprises a supporting structure and a corresponding piezoelectric actuator. The supporting structure is fixed to the deformable structure at the top of the supporting structure and laterally defines corresponding cavities, each cavity having a lateral opening facing the central portion of the body and closed by a membrane at the top. The fixed section of the membrane is fixed to the underlying supporting structure, and the suspended section is laterally offset relative to the underlying supporting structure. The piezoelectric actuator is controllable to cause deformation of the corresponding membrane and rotation of the supporting structure around the central portion of the body.

Description

[0001] Priority claim

[0002] This application claims the benefit of priority from Italian Patent Application No. 102020000015775, filed on June 30, 2020, the contents of which are incorporated herein by reference in their entirety to the maximum extent permitted by law. Technical Field

[0003] The present disclosure relates to an angular piezoelectric actuator for a MEMS (micro-electromechanical system) shutter and a method of manufacturing a MEMS shutter. Background Art

[0004] As is well known, an angular actuator is a device that is able to rotate the structure to which it is connected.

[0005] For example, an angular actuator can be used to control a shutter.

[0006] A shutter is a device comprising a blocking structure that lies in a plane and is constrained to an angular actuator and is coupled to a light beam, such as a laser beam.

[0007] Typically, when stationary, the blocking structure is arranged to intercept the light beam and thereby prevent it from passing through. During use, the angular actuator is controlled to cause the blocking structure to rotate within a plane, thereby freeing the path of the light beam. For example, the blocking structure can be actuated to modify the size and intensity of the light beam or to modulate the intensity of the light beam, for example at a frequency in the kilohertz range.

[0008] Angular actuators manufactured using MEMS technology are known and have actuation systems of the electromagnetic, electrostatic or bulk piezoelectric type.

[0009] However, these known MEMS angular actuators have disadvantages. They are characterized by high energy consumption due to high actuation voltages, often hundreds of volts, particularly in electrostatic actuation systems. Furthermore, in bulk piezoelectric actuation systems, MEMS angular actuators are characterized by low actuation speeds and large dimensions, with thicknesses of several millimeters. Therefore, further development of this technology is desired. Summary of the Invention

[0010] This article discloses a MEMS angular actuator, a manufacturing method thereof, and an optical shutter.

[0011] Specifically, a microelectromechanical (MEMS) actuator is described herein, comprising a body including a central portion and a peripheral portion, wherein the central portion is capable of being coupled to a substrate. When the central portion is coupled to the substrate, the peripheral portion is suspended above the substrate. The peripheral portion includes a deformable structure that extends around the central portion and forms a plurality of membranes arranged in a continuous manner, wherein the peripheral portion has a spiral planar shape when at rest.

[0012] The MEMS actuator further includes a plurality of support structures, each of which is secured to the deformable structure at a top portion of the support structure and laterally defines a corresponding cavity. The corresponding cavity has a lateral opening facing the central portion of the body and is enclosed at its top by a corresponding membrane. The corresponding membrane has a fixed section secured to the underlying support structure and a suspended section laterally offset relative to the underlying support structure and defining the lateral opening of the cavity.

[0013] Each support structure has a corresponding piezoelectric actuator associated with it. The piezoelectric actuator is electrically controllable to cause deformation of the corresponding membrane, the deformation including upward bending of a portion of the suspension segment, the upward bending of the portion of the suspension segment of the membrane causing the support structure to rotate about the central portion of the body.

[0014] The support structure may have a spiral shape and extend below the deformable structure. Each bearing structure may include a corresponding portion of the support structure and a pair of reinforcing structures that, when at rest, extend from corresponding ends of the corresponding portion of the support structure in corresponding radial directions toward the central portion of the body. The fixed section of each membrane may be fixed to the corresponding pair of reinforcing structures and to the corresponding portion of the support structure.

[0015] The upward bending of the portion of the suspended section of the membrane may cause an increase in the curvature of each portion of the support structure, with consequent increase in the angular extension of the support structure and a rotational translation of the reinforcement structure, said rotational translation comprising a rotation about the central portion of the body.

[0016] Each reinforcement structure may have a first end and a second end, the first end being integral with a corresponding portion of the support structure. The overhanging segment of each membrane may include a corresponding edge extending between the second end of the corresponding reinforcement structure and covering a corresponding transverse opening laterally bounded by the second end of the corresponding reinforcement structure. Upward bending of the portion of the overhanging segment of each membrane may cause the corresponding edge to bend upward, with the concave surface facing downward.

[0017] The membrane may have an angularly constant dimension along the radial direction.

[0018] At least a section of the support structure can have an angularly constant dimension in the radial direction.

[0019] The deformable structure may have a thickness that is less than a thickness of the reinforcement structure and less than a thickness of the support structure.

[0020] Each piezoelectric actuator may include a piezoelectric region extending over a suspended section of a corresponding membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] For a better understanding, embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:

[0022] Figure 1 is a schematic perspective view of a MEMS angular actuator disclosed herein;

[0023] Figure 2 yes Figure 1 A schematic perspective view from above of a detail of a MEMS angular actuator;

[0024] Figure 3 yes Figure 2 A schematic perspective view from below of a detail of a MEMS angular actuator;

[0025] Figure 4 yes Figure 2 Schematic top view of details of the MEMS angular actuator;

[0026] Figure 5 It is along Figure 4 A schematic cross-section of the MEMS angular actuator disclosed herein, taken along section line VV;

[0027] Figure 6 It is along Figure 4 A schematic cross section of the MEMS angular actuator disclosed herein taken along the line VI-VI;

[0028] Figure 7 and Figure 8 They are Figure 2 Schematic perspective views of details of a MEMS angular actuator at rest and in use;

[0029] Figure 9 yes Figure 8 a schematic top view of a detail of , wherein the rest position is indicated by a dashed line;

[0030] Figure 10 yes Figure 4 A schematic top view of a detail in use, wherein the rotation relative to the rest position is indicated by a dotted line;

[0031] Figure 11is a simplified perspective view of an optical shutter incorporating the MEMS angle actuator disclosed herein at rest;

[0032] Figure 12 yes Figure 11 A simplified perspective illustration of an optical shutter in use; and

[0033] Figures 13 to 18 is a schematic cross-section of the MEMS angular actuator disclosed herein in successive manufacturing steps. DETAILED DESCRIPTION

[0034] Described below is an angular actuator 10 (hereinafter also referred to as actuator 10 ) made of piezoelectric thin film MEMS technology, which is capable of applying a torque about the Z axis of a Cartesian reference system having X, Y, and Z axes.

[0035] like Figure 1 As shown, the actuator 10 comprises a substrate 11 of a semiconductor material, such as silicon, and a layered structure 13 formed by a layer stack 17 .

[0036] In detail, in this embodiment and as Figure 5 and Figure 6 As shown, the layer stack 17 is formed successively along the Z axis and from bottom to top by: a first insulating layer 20, for example formed of silicon oxide or tetraethyl orthosilicate (TEOS); a structural layer 21, formed of a semiconductor material such as silicon, having a large thickness comprised, for example, between 50 μm and 500 μm (for example, approximately 300 μm); a second insulating layer 22, for example formed of silicon oxide or tetraethyl orthosilicate (TEOS); a membrane layer 23, formed of a semiconductor material such as polycrystalline silicon, having a thickness comprised, for example, between 0.2 μm and 50 μm (for example, approximately 0.7 μm); and a third insulating layer 24, for example formed of silicon oxide or tetraethyl orthosilicate (TEOS).

[0037] The layer stack 17 is formed on the top and bottom by a top surface S top and bottom surface S bot Defined, top surface S top and bottom surface S bot They are respectively formed by the third insulating layer 24 and the first insulating layer 20 and are parallel to the XY plane.

[0038] like Figures 2 to 4 As shown, the layered structure 13 is formed by the gap 99 so as to form a body 15, which includes a central portion 29A and a peripheral portion 29B, the central portion 29A having an approximately cylindrical shape with an axis OH parallel to the Z axis, and the peripheral portion 29B having a spiral shape and extending around the central portion 29A and therefore extending around the axis OH.

[0039] like Figure 5 and Figure 6 As shown, the actuator 10 further includes a pin 14, which is formed on the bottom surface S bot Extending below and in particular below central portion 29A, and having a cylindrical shape with an axis coinciding with axis OH; moreover, pin 14 has a first end bonded to substrate 11 and a second end fixed to central portion 29A.

[0040] Specifically, pin 14 is formed of a first portion 28A of a semiconductor material (e.g., polysilicon) and a second portion 28B of an insulating material (e.g., silicon oxide or tetraethyl orthosilicate (TEOS)). First portion 28A of pin 14 is disposed below and in direct contact with a portion of first insulating layer 20 forming central portion 29A; second portion 28B of pin 14 is disposed between first portion 28A and substrate 11, in direct contact with substrate 11.

[0041] In fact, due to the presence of the pins 14 , the peripheral portion 29B of the body 15 is suspended above the substrate 11 at a certain distance from the substrate 11 .

[0042] As previously mentioned, peripheral portion 29B of body 15 has a spiral shape comprising a plurality of windings 30 extending concentrically from and around central portion 29A, and therefore around axis OH. Body 15 has a static dimension D when at rest and in a direction parallel to axis Y. In particular, assuming a cylindrical reference system centered on axis OH and having radial coordinates R and angular coordinates θ, each winding 30 is formed by a corresponding segment of peripheral portion 29B of body 15 having an extension equal to 360° relative to angular coordinate θ.

[0043] Furthermore, as described in more detail below, the windings 30 have the same width along the radial coordinate R; furthermore, adjacent pairs of windings are separated from each other by the same distance; in other words, the peripheral portion 29B of the body 15 forms an Archimedean spiral.

[0044] In more detail, the windings 30 of the peripheral portion 29B of the body 15 are supported by the support structure 38. * and is formed of a plurality of deformable cells 31 which are arranged consecutively so as to form a single piece starting from a central portion 29A up to a final deformable cell 31A which is at a maximum distance (in radial direction and in angular direction) from the central portion 29A.

[0045] Each deformable unit 31 comprises a membrane 35 suspended above a corresponding cavity 37; a support structure 38 * and a pair of reinforcing structures 39.

[0046] In more detail, in each deformable unit 31, the membrane 35 is formed by corresponding portions of the second insulating layer 22, the membrane layer 23, and the third insulating layer 24. In addition, the support structure 38 is formed by corresponding portions of the first insulating layer 20 and the structural layer 21. * and strengthening structures39.

[0047] The cavity 37 is bounded at the top by the membrane 35 and partially by the supported structure 38 * The corresponding portion 38 and the reinforcing structure 39 are laterally delimited, open at the bottom in the direction of the underlying substrate 11 and via a lateral opening AP (at Figure 7 (as can be seen in the figure) opens laterally in the direction of the axis OH.

[0048] like Figure 5 As shown, the support structure 38 * By the inner wall P oriented toward the axis OH i and the outer wall P directed outwards e Define horizontally.

[0049] Inner wall P i and outer wall P e It is wound around the axis OH and is curved, with a single concave surface oriented toward the axis OH. i At each point on the inner wall P i The plane tangent to and passing through this point is parallel to the Z axis; the same considerations apply to the outer wall P e point.

[0050] To a first approximation, and at rest, the support structure 38 * The portions 38 of each have, in plan view, a substantially annular sector shape; their cross-sections perpendicular to the Z axis are therefore invariant to translations along the Z axis. Furthermore, to a first approximation, the outer wall P e and inner wall P i The support structure 38 is defined * The corresponding portion 38 of each portion has a corresponding single radius of curvature, the outer wall P e The curvature radius of this part is greater than the inner wall P i The radius of curvature of this part.

[0051] The two reinforcement structures 39 have the same shape.

[0052] In particular, each reinforcement structure 39 has the shape of a parallelepiped having a shape fixed to the support structure 38 * The first end portion of the corresponding end portion 38 (at Figure 6The shape is parallel to the direction of the radial coordinate and extends from the first end to the second end toward the axis OH. In other words, the second end of the reinforcing structure 39 is arranged at a shorter distance from the axis OH than the corresponding first end.

[0053] The membranes 35 each cover the support structure 38 * on both the corresponding portion 38 and the corresponding pair of reinforcing structures 39, thereby forming a single piece with them.

[0054] Each membrane 35 comprises a fixed section 35A fixed to a support structure 38 and a hanging section 35B. * The suspension segments 35B cover the corresponding cavities 37 on the corresponding lower portions 38 and the corresponding lower reinforcement structures 39 .

[0055] In particular, if Figure 7 As can also be seen in the figure, each membrane 35 has a rectangular shape in a top view with curved long sides, the two short sides of the rectangular shape and the long side of the rectangular shape away from the axis OH forming a fixing section 35A and being fixed to the two reinforcing structures 39 and to the supporting structure 38 respectively. * , while the long sides closer to the axis OH are not constrained and form an edge 36 extending between the second ends of the corresponding reinforcing structures 39, which edge laterally delimits the hanging section 35B of the membrane 35 and the lateral opening AP of the corresponding cavity 37 at the top.

[0056] The membrane 35 of the deformable unit 31 forms a single planar structure 35 without any interruptions. * .

[0057] Without loss of generality, in addition to having a cross-section that is invariant with respect to translation along the Z axis, except for a possible variation in width near the central portion 29A, i.e. for values ​​of θ below, for example, 270°, the planar structure 35 * It also has a width measured along the radial coordinate R that is constant with respect to the angular coordinate θ (and therefore also independent of the winding 30 under consideration). * From the inner surface S facing the axis OH mi and an outwardly oriented outer surface S me Laterally defined. Inner surface S mi and outer surface S me Around the axis OH. In addition, on the inner surface S mi At each point of the inner surface S mi The plane that is tangent to and passes through this point is parallel to the Z axis; the same considerations apply to the outer surface S me point.

[0058] Therefore, each membrane 35 consists of a planar structure 35 * Part of the formation.

[0059] In more detail, the outer wall P e With plane structure 35 * The outer surface Sme of the outer wall P is aligned vertically. In other words, the outer wall P e With the outer surface S me Shared bus.

[0060] Furthermore, considering any pair formed by a first winding 30 and a second winding 30 adjacent to each other, wherein the first winding 30 is arranged on the outside of the second winding 30, the outer surface S of the second winding 30 me and the inner surface S of the first winding 30 mi The parts are separated from each other by a distance d (in Figure 5 , for example, equal to 145 μm), and laterally delimits a corresponding portion of gap 99 which, as previously described, has a spiral shape in top view and is arranged between adjacent winding pairs. Furthermore, each cavity 37 is laterally offset outward relative to the portion of gap 99 that delimits the corresponding membrane 35. Cavities 37 are in fluid communication with gap 99 because they open laterally toward axis OH.

[0061] The deformable units 31 are arranged successively along the helical profile so as to form the winding 30 of the body 15 as previously described.

[0062] In detail, the pair of reinforcement structures 39 of the final deformable unit 31A comprises a final reinforcement structure 39A having an angular and radial maximum distance relative to the axis OH.

[0063] In addition, if Figure 6 As shown, and without loss of generality, the reinforcement structure 39 has the same width in the radial direction, which width, without loss of generality, is equal to the width of the membrane 35 and therefore represents the width of the winding 30 .

[0064] A continuous plurality of first units (eg, nine in this embodiment) of the deformable units 31 arranged starting from the central portion 29A of the body 15 may have a shape and size different from the remaining deformable units 31 .

[0065] In particular, in this embodiment, the membrane 35 and the reinforcement structure 39 of the first unit in the succession of deformable units 31 have a smaller width relative to the remaining deformable units 31 .

[0066] Additionally, pairs of adjacent deformable units 31 share corresponding reinforcement structures 39 .

[0067] Referring again to the reinforcement structures 39, and without loss of generality, at rest, the reinforcement structures are angularly distributed along twelve radial directions, angularly equally spaced, hereinafter referred to as shared radial directions. In other words, with the exception of the aforementioned first deformable element 31, the reinforcement structures 39 of each winding 30 extend along a corresponding shared radial direction. Thus, the reinforcement structures 39 can be grouped into a plurality of groups, each associated with a corresponding shared radial direction, and each winding 30 includes the reinforcement structures 39 of the winding 30 extending in the corresponding shared radial direction.

[0068] The actuator 10 also includes a plurality of actuating elements 40, each of which is formed by a stack comprising a bottom electrode 42 of a metal material such as platinum, an actuating region 43 of a piezoelectric material (such as lead zirconate titanate (PZT), BaTiO3, KNN (sodium and potassium niobate), PbTiO2 or PbNb2O6 and having a thickness between 1 μm and 3 μm, in particular 2 μm), and a top electrode 44 of a metal material such as a titanium-tungsten alloy; the actuating region 43 is arranged to be in direct contact between the bottom electrode 42 and the top electrode 44.

[0069] Each actuating element 40 is arranged on the corresponding deformable unit 31, and in particular on the portion of the third insulating layer 24 forming the corresponding membrane 35, so that the corresponding bottom electrode 42 contacts the portion of the third insulating layer 24. Thus, the actuating element 40 and the corresponding cavity 37 are arranged on opposite sides of the corresponding membrane 35.

[0070] In detail, without loss of generality, each actuating element 40 covers the suspended section 35B of the corresponding membrane 35 .

[0071] Alternatively, an embodiment (not shown) is also possible in which the actuating element 40 also covers a part of the fixing section 35A of the respective membrane 35 .

[0072] In more detail, in this embodiment, segments of the deformable unit 31 support corresponding actuating elements 40. In particular, the first preceding unit of the deformable unit 31 lacks a corresponding actuating element 40. However, embodiments are possible in which all deformable units 31 support corresponding actuating elements 40.

[0073] Each actuating element 40 is also coated with a passivation region 45 of an insulating material, such as aluminum nitride, silicon nitride, undoped silicate glass (USG), hafnium oxide (HfO 2 ), or a dry polymer film.

[0074] Alternatively, the passivation region 45 may be formed by stacking a plurality of insulating layers.

[0075] Furthermore, the top electrodes 44 of the plurality of actuator elements 40 are connected together by corresponding metal traces (not visible here), which also enable connection to contact pads (not visible) for electrical connection to an external electrical bias circuit. Similarly, the bottom electrodes 42 of the plurality of actuator elements 40 are connected together by corresponding metal traces (not visible here), which also enable connection to contact pads for electrical connection to a suitable potential, such as ground.

[0076] For example, the contact pads may be arranged on the central portion 29A of the body 15 .

[0077] In use, a bias voltage is applied between the top electrode 44 and the bottom electrode 42 of each actuator element 40. In particular, the bias voltage may be a direct current voltage or an alternating current voltage, depending on the desired application.

[0078] In each actuating element 40 , the bias voltage causes deformation of the piezoelectric region 43 ; therefore, each membrane 35 integral with respect to the corresponding actuating element 40 undergoes deformation.

[0079] In particular, if Figure 8 As shown (wherein, for the sake of clarity, the value of the deformation has been magnified a hundred times), the fixed section 35A and the support structure 38 * Starting from the portion of the membrane 35 which overlaps the corresponding portion 38 and moving in the radial direction towards the axis OH, the following can be observed. The hanging section 35B of the membrane 35 is initially bent towards the cavity 37, slightly below the corresponding rest position, so as to form a first concave surface C facing upwards. U , and then bends so as to rise significantly above the corresponding rest position, thus in a direction opposite to the cavity 37, so as to form a second concave surface C facing downwards D ; Furthermore, the edge 36 is curved and presents a profile with a corresponding concavity, facing the cavity 37 below.

[0080] In detail, such as Figure 9 As shown in a plan view of FIG, wherein the rest position is highlighted by a dotted line and the deformed position is highlighted by a solid line, the deformation of the membrane 35 causes the corresponding reinforcement structure 39 and the support structure 38 to * The corresponding portion 38 is substantially rotated and translated in a direction parallel to the XY plane, the support structure 38 * The corresponding portion 38 also undergoes deformation.

[0081] More specifically, the reinforcing structures 39 rotate, each of which rotates about its own axis parallel to the Z axis, so that the second ends of the reinforcing structures 39 of each deformable cell 31 move closer to each other; to a first approximation, this rotation is negligible. Furthermore, the reinforcing structures 39 of each deformable cell 31 translate toward the central portion 29A of the body 15. Furthermore, the reinforcing structures 39 of each deformable cell 31 rotate integrally with each other about the central portion 29A of the central body 15 in a direction opposite to the direction of winding of the peripheral portions 29B, which is considered to be a direction starting from the final deformable cell 31A and toward the central portion 29A.

[0082] Support structure 38 * The deformation of each portion 38 causes the inner wall P i and outer wall P e Defining the support structure 38 * The radius of curvature of each portion 38 of the support structure 38 is reduced compared to the rest position. In other words, the local curvature of each portion 38 of the support structure 38 is increased, resulting in the support structure 38 * The angular extension increases.

[0083] Thus, each deformable element 31 undergoes a rotation about the axis OH, the extent of this rotation increasing as the distance of the deformable element 31 from the central portion 29A increases; ultimately, the deformable element 31A thus undergoes the rotation having the greatest extent.

[0084] In particular, the final reinforcing structure 39A undergoes a maximum rotation about the axis OH relative to the rest position.

[0085] In addition, the main body 15 is compressed in a direction parallel to the XY plane, so that the main body 15 assumes a working dimension D measured parallel to the Y axis. * , the working dimension is smaller than the static dimension D.

[0086] In particular, with a bias voltage of 40 V applied to the actuating element 40, the resulting reinforcement structure 39A can undergo a rotation of up to 8° about the axis OH (e.g., Figure 10 , shown by dashed lines relative to the rest position).

[0087] Furthermore, the body 15, and in particular the final deformable unit 31A, undergoes a small out-of-plane displacement parallel to the Z-axis. In this embodiment, as verified by simulations, the out-of-plane displacement of the final reinforcement structure 39A may be approximately 0.2% of its own displacement parallel to the XY plane. In detail, due to the thickness of each membrane 35, the support structure 38 * This reduced out-of-plane displacement is achieved due to the greater thickness of the reinforcement structure 39.

[0088] like Figure 11 As shown, the actuator 10 may be used in an optical shutter 100 .

[0089] In addition to the actuator 10 , the optical shutter 100 includes an arm 101 and a blocking structure 102 .

[0090] The arm 101 is formed in one piece with the layered structure 13 and the barrier structure 102 is formed in one piece with the arm 101. Thus, the arm 101 and the barrier structure 102 are formed by corresponding parts of the layer stack 17.

[0091] In detail, the arm 101 has the shape of a parallelepiped with a thickness along the Z axis, which is equal to the thickness of the layer stack 17 , and a horizontal extension parallel to the XY plane, which is relatively large, for example of the order of a few millimeters.

[0092] The barrier structure 102 here has a cylindrical shape, for example with a diameter of 1 mm and a thickness parallel to the Z axis that is equal to the layer stack 17 .

[0093] The blocking structure 102 also includes a top surface 104 coated with a material that absorbs or reflects electromagnetic radiation, such as a metal, for example gold or aluminum.

[0094] In this embodiment, the arm 101 is constrained at a first end 101A to the final reinforcement structure 39A and the support structure 38 of the final deformable element 31A. * further, the second end portion 101B of the arm 101 is fixed to a portion of the side surface of the blocking structure 102 .

[0095] Optical shutter 100 is arranged along the optical path of light beam 105 (eg, laser beam) generated by light source 106 .

[0096] Without loss of generality, the optical shutter 100 is arranged such that when stationary, the blocking structure 102 intercepts the light beam 105 , completely blocking the light path. In particular, the light beam 105 can be completely reflected or absorbed by the top surface 104 of the blocking structure 102 .

[0097] In use, the bias voltage may cause rotation of the actuator 10 as previously described.

[0098] Therefore, if Figure 12 As shown, the blocking structure 102 is positioned relative to the rest position (at Figure 12 highlighted with a dotted line in the figure).

[0099] In particular, the blocking structure 102 undergoes a rotation having an arc with a linear length proportional to the angle of rotation of the resulting reinforcing structure 39A and the length of the arm 101 .

[0100] Therefore, the blocking structure 102 releases the optical path of the light beam 105 .

[0101] A bias voltage may be applied to fully or partially free the optical path of the light beam 105 , for example to modify the size and intensity of the light beam 105 .

[0102] Alternatively, the bias voltage may have a frequency component capable of modulating the intensity of the light beam 105 in time.

[0103] Advantageously, the actuator 10 allows obtaining an optical shutter that has small dimensions, operates at a low bias voltage, is efficient from the point of view of power consumption, and has a small out-of-plane displacement of the blocking structure 102 .

[0104] The following describes the process for making Figure 1 In particular, for clarity, Figures 13 to 18 The manufacturing steps are shown with respect to a cross section taken along the line of section VV.

[0105] Figure 13 A cross section of a wafer 150 that has undergone a first manufacturing step is shown. In detail, the wafer 150 comprises a working substrate 151 (for forming the structural layer 21 of the layer stack 17) of a semiconductor material (e.g., silicon) having a first surface 151A and a second surface 151B. The working substrate 151 has been ground and polished, for example by chemical mechanical polishing (CMP), to a thickness of, for example, 300 μm.

[0106] A first dielectric layer 152 (forming the second insulating layer 22 of the layer stack 17 ), for example formed from deposited tetraethyl orthosilicate (TEOS) and having a thickness of, for example, at least 1 μm, here 1 μm, extends over the first surface 151A of the working substrate 151 .

[0107] A passivation layer 153 (for forming the membrane layer 22 of the layer stack 17 ), which is formed from a semiconductor material (eg polysilicon) and here has a thickness of 700 nm, extends over the first dielectric layer 152 .

[0108] A second dielectric layer 154 (for forming the third insulating layer 24 of the layer stack 17 ), for example formed by depositing TEOS and having a thickness of, for example, 0.5 μm, extends over the passivation layer 153 .

[0109] A first patterned layer 155 (for forming the first insulating layer 20 of the layer stack 17), for example formed of TEOS and having a thickness of, for example, 1 μm, extends above the second surface 151B of the working substrate 151; a bonding layer 156 is formed of a semiconductor material (for example, polycrystalline silicon) and having a thickness of, for example, 50 μm, extending below the first patterned layer 155 and in direct contact with the first patterned layer.

[0110] Next, refer to Figure 14 , a first metal layer 160 formed, for example, of platinum is deposited on the second dielectric layer 154; an actuation layer 161, formed of a piezoelectric material such as lead zirconate titanate (PZT), BaTiO3, KNN (sodium and potassium niobate), PbTiO2 or PbNb2O6 and having a thickness between 1 μm and 3 μm, in particular 2 μm, is deposited on the first metal layer 160; and a second metal layer 162, for example formed of a tungsten-titanium alloy, is deposited on the actuation layer 161 to form a stack of actuation layers.

[0111] The stack of actuation layers thus obtained is defined by photolithographic steps and selective chemical etching in order to form a plurality of actuation elements 40 .

[0112] In particular, for each actuating element 40 , first metal layer 160 forms bottom electrode 42 , actuating layer 161 forms actuating region 43 , and second metal layer 162 forms top electrode 44 .

[0113] In addition, the first metal layer 160 also forms corresponding metal traces (not shown here) for electrical connection with each other and with the corresponding contact pads of each bottom electrode 42 of the actuator element 40 .

[0114] In addition, a passivation layer 163 formed of an insulating material such as aluminum nitride, silicon nitride, undoped silica glass (USG), hafnium oxide (HfO2) or a dry polymer film is deposited to completely cover and surround the actuating elements 40 and is photolithographically defined to form a passivation region 45 for each actuating element 40.

[0115] Next, in a manner not shown, a through hole is formed in each passivation area 45, and another metal layer is deposited and defined on the actuating element 40 so as to form corresponding metal traces, not shown here, for electrical connection to each other and to the corresponding contact pad of each top electrode 44.

[0116] like Figure 15As shown, the wafer 150 then undergoes a selective chemical etching sequence from the second dielectric layer 154 to the first surface 151A of the working substrate 151 to form a trench 165 and expose a section of the working substrate 151. The trench 165 extends along the Z axis through the second dielectric layer 154, the passivation layer 153 and the first dielectric layer 152 to the first surface 151A of the working substrate 151; in a top view, the trench 165 has a spiral shape and is designed to form the gap 99. In particular, as shown in FIG. Figure 15 As can be seen in FIG, the groove 165 is laterally offset relative to each actuating element 40.

[0117] Then, if Figure 16 As shown, the bonding layer 156 undergoes grinding and chemical mechanical polishing to obtain a thickness of, for example, 4 μm.

[0118] A second patterned layer 170 is then deposited over the bonding layer 156 and photolithographically defined to form a window 171. The window 171 extends through the patterned layer 170 to expose a section of the bonding layer 156. A portion 172 remains from the second patterned layer 170, which is approximately shaped like a cylinder having an axis OH and is used to form the second portion 28B of the pin 14.

[0119] Then, if Figure 17 As shown, selective chemical etching is performed on the second surface 151B of the working substrate 151 using a portion 172 of the second patterned layer 170 to form the cavity 37 and the body 15 .

[0120] In detail, the window 171 is used to selectively remove a section of the bonding layer 156 , with a portion of the section remaining, disposed on top of the portion 172 of the second insulating layer and used to form the first portion 28A of the pin 14 .

[0121] Next, first patterned layer 155 is photolithographically defined to form a portion disposed on top of the remaining portion of bonding layer 156 (for forming second portion 28B of pin 14) and a plurality of portions 173 that are laterally offset to leave exposed portions of second surface 151B of working substrate 151. Next, using portion 172 of second patterned layer 170 and portions 173 of first patterned layer 155 as masks, portions of working substrate 151 are selectively removed from the exposed portions of second surface 151B until first surface 151A of working substrate 151 is removed to form corresponding cavities 37 that communicate with trench 165.

[0122] Thus, in addition to the cavity 37, the pin 14 and the support structure 38 are formed. * , membrane 35 and reinforcement structure 39 of each deformable unit 31 .

[0123] Next, if Figure 18 As shown, portion 172 of second patterned layer 170 is bonded to a support wafer 180 formed of a semiconductor material, such as silicon.

[0124] Finally, in a manner not shown, the set 200 formed by the wafer 150 and the support wafer 180 is cut so that, after the packaging and electrical connection operations, each die forms Figure 1 The actuator 10 is configured as follows. In detail, the support wafer 180 forms the substrate 11.

[0125] The methods described herein can be extended to fabricate optical shutter 100 from wafer 150 , arm 101 , and blocking structure 102 .

[0126] Finally, it is clear that modifications and variations may be made to the actuator 10 , the optical shutter 100 and the manufacturing method described and illustrated herein without departing from the scope of the present disclosure as defined in the accompanying claims.

[0127] For example, the windings of the outer portion of the body formed by the layered structure can be spaced at a variable distance, for example to form a logarithmic spiral. However, given the same performance of the MEMS angular actuator, the variable distance between the windings may involve the use of a larger area of ​​material.

[0128] For example, the number of windings, the size of the windings, the number of deformable units, the number of actuating elements and the thickness of each layer of the layer stack may be modified and selected based on the desired mechanical properties of the MEMS angular actuator.

[0129] For example, the reinforcement structure may extend outwards from a corresponding portion of the support structure, ie moved away from the central portion of the body, such that the cavity and the lateral opening of the deformable unit are directed outwards and not towards the central portion of the body.

[0130] For example, the actuating element may partially extend over parts of the support structure and / or at least sections of a pair of reinforcement structures of each deformable unit.

[0131] For example, each deformable unit may have a corresponding pair of reinforcing structures that is different from the pair of reinforcing structures of an adjacent deformable unit.

[0132] For example, the arms of the shutter may be constrained to any reinforcing structure or part of the supporting structure of any deformable unit.

[0133] Furthermore, it is obvious to a person skilled in the art that the peripheral portion of the central body may have portions for smaller values ​​of the angular coordinate θ and therefore near the central portion of the body, having shapes and dimensions that differ from the shapes and dimensions of corresponding portions for larger values ​​of the angular coordinate θ, taking into account specific manufacturing requirements.

Claims

1. A micro-electromechanical actuator comprising: a body comprising a central portion and a peripheral portion, the central portion being coupleable to a substrate, wherein the peripheral portion is suspended above the substrate when the central portion is coupled to the substrate, and wherein the peripheral portion comprises a deformable structure extending around the central portion and forming a plurality of membranes arranged in series, the peripheral portion having a helical planar shape when at rest; and a plurality of load-bearing structures, each of which is fixed to the deformable structure at a top portion thereof and laterally delimits a corresponding cavity, the corresponding cavity having a lateral opening facing the central portion of the body and being closed at the top portion of the corresponding cavity by a corresponding membrane, the corresponding membrane comprising a fixed section and a hanging section, the fixed section being attached to an underlying load-bearing structure, the hanging section being laterally offset relative to the underlying load-bearing structure and delimiting the lateral opening of the cavity; Each load-bearing structure has a corresponding piezoelectric actuator associated with the load-bearing structure; and wherein the piezoelectric actuator is electrically controllable so as to cause deformation of the corresponding membrane, the deformation comprising an upward bending of a portion of the suspension segment, the upward bending of the portion of the suspension segment of the membrane causing rotation of the supporting structure around the central portion of the body.

2. The micro-electromechanical actuator according to claim 1, further comprising a support structure having a spiral shape and extending below the deformable structure; And among them, Each load-bearing structure includes: a corresponding portion of the support structure; and a pair of reinforcing structures extending from respective ends of the respective portions of the support structure in respective radial directions toward the central portion of the body when at rest; wherein the fixing section of each membrane is fixed to a corresponding pair of reinforcement structures and to the corresponding portion of the support structure; and wherein the upward bending of the portion of the suspended section of the membrane causes an increase in the curvature of each portion of the support structure, which in turn causes an increase in the angular extension of the support structure and a rotational translation of the reinforcement structure, the rotational translation comprising a rotation around the central portion of the body.

3. The micro-electromechanical actuator according to claim 2, wherein: Each reinforcement structure has a first end and a second end, the first end being integral with the corresponding portion of the support structure; and wherein the hanging section of each membrane includes a respective edge, the respective edge extending between the second ends of the respective reinforcement structures and covering a respective lateral opening, the lateral opening being laterally delimited by the second ends of the respective reinforcement structures; and wherein an upward bending of the portion of the hanging section of each membrane causes an upward bending of the respective edge, with the concave surface facing downwards.

4. The micro-electromechanical actuator according to claim 3, wherein: The membrane has an angularly constant dimension along the radial direction.

5. The micro-electromechanical actuator according to claim 3, wherein: At least a section of the support structure has an angularly constant dimension along the radial direction.

6. The micro-electromechanical actuator according to claim 2, wherein: The deformable structure has a thickness that is less than a thickness of the reinforcement structure and less than a thickness of the support structure.

7. The micro-electromechanical actuator according to claim 1, wherein: Each piezoelectric actuator includes a piezoelectric region extending over the suspended section of the corresponding membrane.

8. An optical shutter comprising: MEMS actuators, including: a body comprising a central portion and a peripheral portion, the central portion being coupleable to a substrate, wherein the peripheral portion is suspended above the substrate when the central portion is coupled to the substrate, and wherein the peripheral portion comprises a deformable structure extending around the central portion and forming a plurality of membranes arranged in series, the peripheral portion having a helical planar shape when at rest; a plurality of load-bearing structures, each of which is fixed to the deformable structure at a top portion thereof and laterally delimits a corresponding cavity, the corresponding cavity having a lateral opening facing the central portion of the body and being closed at the top portion of the corresponding cavity by a corresponding membrane, the corresponding membrane comprising a fixed section and a hanging section, the fixed section being attached to an underlying load-bearing structure, the hanging section being laterally offset relative to the underlying load-bearing structure and delimiting the lateral opening of the cavity; Each load-bearing structure has a corresponding piezoelectric actuator associated with the load-bearing structure; wherein the piezoelectric actuator is electrically controllable so as to cause deformation of the corresponding membrane, the deformation comprising an upward bending of a portion of the suspension segment, the bending of the portion of the suspension segment of the membrane causing rotation of the support structure about the central portion of the body; an arm having a first end and a second end, the first end being constrained to one of the load-bearing structures; and A blocking structure is constrained to the second end of the arm and is configured to reflect or absorb electromagnetic radiation.

9. The optical shutter according to claim 8, wherein: The arms are constrained to a load-bearing structure farthest from the central portion of the body.

10. The optical shutter of claim 8, further comprising a support structure having a spiral shape and extending below the deformable structure; And among them, Each load-bearing structure includes: a corresponding portion of the support structure; and a pair of reinforcing structures extending from respective ends of the respective portions of the support structure in respective radial directions toward the central portion of the body when at rest; wherein the fixing section of each membrane is fixed to a corresponding pair of reinforcing structures and to the corresponding portion of the support structure; and wherein the upward bending of the portion of the suspended section of the membrane causes an increase in the curvature of each portion of the support structure, which in turn causes an increase in the angular extension of the support structure, and a rotational translation of the reinforcement structure, the rotational translation comprising a rotation around the central portion of the body.

11. The optical shutter according to claim 10, wherein: Each reinforcement structure has a first end and a second end, the first end being integral with a corresponding portion of the support structure; and wherein the hanging section of each membrane includes a respective edge, the respective edge extending between the second end of the corresponding reinforcement structure and covering a corresponding lateral opening, the lateral opening being laterally delimited by the second end of the corresponding reinforcement structure; and wherein the upward bending of the portion of the hanging section of each membrane causes an upward bending of the corresponding edge, with the concave surface facing downwards.

12. The optical shutter according to claim 11, wherein: The membrane has an angularly constant dimension along the radial direction.

13. The optical shutter according to claim 11, wherein: At least a section of the support structure has an angularly constant dimension along the radial direction.

14. The optical shutter according to claim 10, wherein: The deformable structure has a thickness that is less than a thickness of the reinforcement structure and less than a thickness of the support structure.

15. The optical shutter according to claim 8, wherein Each piezoelectric actuator comprises a piezoelectric region extending over the suspended section of the corresponding membrane.

16. An electronic system comprising: Optical shutter, including: MEMS actuators, including: a body comprising a central portion and a peripheral portion, the central portion being coupleable to a substrate, wherein the peripheral portion is suspended above the substrate when the central portion is coupled to the substrate, and wherein the peripheral portion comprises a deformable structure extending around the central portion and forming a plurality of membranes arranged in series, the peripheral portion having a helical planar shape when at rest; a plurality of load-bearing structures, each of which is fixed to the deformable structure at a top portion thereof and laterally delimits a corresponding cavity, the corresponding cavity having a lateral opening facing the central portion of the body and being closed at the top portion of the corresponding cavity by a corresponding membrane, the corresponding membrane comprising a fixed section and a hanging section, the fixed section being attached to an underlying load-bearing structure, the hanging section being laterally offset relative to the underlying load-bearing structure and delimiting the lateral opening of the cavity; Each load-bearing structure has a corresponding piezoelectric actuator associated with the load-bearing structure; wherein the piezoelectric actuator is electrically controllable so as to cause deformation of the corresponding membrane, the deformation comprising an upward bending of a portion of the suspension segment, the bending of the portion of the suspension segment of the membrane causing rotation of the support structure about the central portion of the body; an arm having a first end and a second end, the first end being constrained to one of the load-bearing structures; and a blocking structure constrained to the second end of the arm and configured to reflect or absorb electromagnetic radiation; and a light source configured to generate a light beam; The optical shutter is configured to operate alternately under the following conditions: a first operating condition in which the light beam impinges on the blocking structure; and A second operating condition in which the light beam is at least partially displaced laterally relative to the blocking structure.

17. The electronic system according to claim 16, wherein: The arms are constrained to a load-bearing structure farthest from the central portion of the body.

18. The electronic system according to claim 16, wherein: The optical shutter further includes a support structure having a spiral shape and extending below the deformable structure; And wherein each bearing structure comprises: a corresponding portion of the support structure; and a pair of reinforcing structures extending from respective ends of the respective portions of the support structure in respective radial directions toward the central portion of the body when at rest; wherein the fixing section of each membrane is fixed to a corresponding pair of reinforcing structures and to the corresponding portion of the support structure; and wherein the upward bending of the portion of the suspended section of the membrane causes an increase in the curvature of each portion of the support structure, which in turn causes an increase in the angular extension of the support structure, and a rotational translation of the reinforcement structure, the rotational translation comprising a rotation around the central portion of the body.

19. The electronic system according to claim 18, wherein: Each reinforcement structure has a first end and a second end, the first end being integral with a corresponding portion of the support structure; and wherein the hanging section of each membrane includes a respective edge, the respective edge extending between the second end of the respective reinforcement structure and covering a respective lateral opening, the lateral opening being laterally delimited by the second end of the respective reinforcement structure; and wherein the upward bending of the portion of the hanging section of each membrane causes an upward bending of the respective edge, with the concave surface facing downwardly.

20. The electronic system according to claim 19, wherein The membrane has an angularly constant dimension along the radial direction.

21. The electronic system according to claim 19, wherein: At least a section of the support structure has an angularly constant dimension along the radial direction.

22. The electronic system according to claim 18, wherein: The deformable structure has a thickness that is less than a thickness of the reinforcement structure and less than a thickness of the support structure.

23. The electronic system according to claim 16, wherein: Each piezoelectric actuator comprises a piezoelectric region extending over the suspended section of the corresponding membrane.

24. A method for manufacturing a micro-electromechanical actuator, comprising: forming a body comprising a central portion and a peripheral portion, the central portion being coupleable to a substrate, the peripheral portion being suspended from the substrate when the central portion is coupled to the substrate and comprising a deformable structure, wherein the deformable structure extends around the central portion and forms a plurality of membranes arranged in series, the deformable structure having a helical planar shape when at rest; forming a plurality of load-bearing structures, each of which is fixed at a top portion of the load-bearing structure to the deformable structure and laterally delimits a corresponding cavity, the corresponding cavity having a lateral opening facing the central portion of the body and being closed at the top portion of the corresponding cavity by a corresponding membrane, the corresponding membrane comprising a fixed section and a hanging section, the fixed section being attached to an underlying load-bearing structure, the hanging section being laterally offset relative to the underlying load-bearing structure and delimiting the lateral opening of the cavity; and For each supporting structure, a corresponding piezoelectric actuator is formed, each piezoelectric actuator being electrically controllable so as to cause deformation of the corresponding membrane, the deformation comprising an upward bending of a portion of the suspension segment, the upward bending of the portion of the suspension segment of the membrane causing the corresponding supporting structure to rotate around the central portion of the body.

25. The method according to claim 24, further comprising: forming a support structure to have a spiral shape and to extend below the deformable structure; And wherein forming the plurality of bearing structures comprises: forming each load-bearing structure so as to include a corresponding portion of the support structure; and forming, for each load-bearing structure, a pair of reinforcing structures, said pair of reinforcing structures extending from respective ends of said respective portions of said support structure in respective radial directions towards said central portion of said body when at rest; wherein the formation of the body enables the fixed section of each membrane to be fixed to a corresponding pair of reinforcing structures, and to the corresponding part of the support structure, so that bending of the part of the suspension section of the membrane causes an increase in the curvature of each part of the support structure, which in turn causes an increase in the angular extension of the support structure, and a rotational translation of the reinforcing structure, the rotational translation comprising a rotation around the central part of the body.

26. The method according to claim 25, wherein Forming the main body includes: forming a multilayer dielectric structure on a semiconductor substrate defined by a front surface and a back surface; subsequently forming a piezoelectric actuator on the multilayer dielectric structure; selectively removing a portion of the multilayer dielectric structure that is laterally offset relative to the piezoelectric actuator to form a trench having a spiral shape, the trench facing the semiconductor substrate and laterally delimiting the deformable structure; Wherein, forming the plurality of supporting structures includes selectively removing a portion of the semiconductor substrate from the back side so that the cavity is connected to the trench.

27. The method according to claim 26, further comprising: After selectively removing portions of the semiconductor substrate, the central portion of the body is secured to a semiconductor wafer such that the peripheral portion of the body is suspended above the semiconductor wafer.

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