Microelectromechanical device having a structure tilted by piezoelectric actuation about two rotational axes

Abstract

The present disclosure relates to microelectromechanical devices having a structure that can be tilted by piezoelectric actuation about two rotation axes. For example, a microelectromechanical device includes: a fixed structure having a frame defining a cavity; a tiltable structure elastically suspended above the cavity and having a main extension in a horizontal plane; a piezoelectrically driven actuating structure that can be biased to cause the tiltable structure to perform a desired rotation about first and second rotation axes; and a support structure that is integrated with the fixed structure and extends from the frame into the cavity. A lever element is elastically coupled to the tiltable structure at a first end by an elastic suspension element and is coupled to the support structure at a second end by an elastic connecting element that defines the lever rotation axis. The lever elements are elastically coupled to the actuating structure so that their biasing causes the desired rotation of the tiltable structure about the first and second rotation axes.

Description

[0001] Priority Declaration

[0002] This application claims the benefit of Italian Patent Application No. 102020000022978, filed on September 29, 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 a microelectromechanical device (manufactured using MEMS - Micro-Electromechanical Systems - technology) having a structure that can be tilted by piezoelectric actuation about two rotation axes. Background Art

[0004] In the following reference will be made to a micro-electromechanical mirror device in which the tiltable structure carries a reflecting or mirror surface on its top surface, but this does not mean a loss of generality.

[0005] In a known manner, microelectromechanical mirror devices, in particular of the vector scanner type (so-called MEMS vector scanners), are used in portable devices (e.g. smartphones or tablets) for projecting images at a distance and in three-dimensional (3D) sensing applications to increase the field of view (FOV) and projection resolution or to create desired patterns. Due to their reduced size, these devices are able to meet stringent requirements regarding space usage (area and thickness).

[0006] These microelectromechanical mirror devices generally comprise a mirror structure which is manufactured starting from a body of semiconductor material and which is elastically supported above a cavity so as to be movable (e.g. by tilting or rotating movement out of a respective plane of main extension) for directing an incident light beam in a desired manner.

[0007] Typically, it is desired to deflect the incident light beam along two axes, which can be obtained by a single microelectromechanical mirror device of the dual-axis type, ie the mirror structure is tiltable about two rotation axes.

[0008] Figure 1A A mirror structure 1 of the vector scanner type is schematically shown, which projects an incident image (or dot pattern) 2 towards a screen 4 at a certain distance.

[0009] The mirror structure 1 can be driven so as to rotate about a first rotation axis and a second rotation axis designated by A1 and A2, respectively, and in particular to assume four different quasi-static positions according to said rotations, so as to direct the incident light beam 2 to a projection area 5 on the screen 4. Advantageously, said projection area 5 is four times larger than the area defined by the incident light beam 2, thus providing a projection resolution four times higher and a field of view four times larger than the characteristics of the incident light beam 2 described above.

[0010] Figure 1B A further use of the mirror structure 1 is shown, in this case for generating four simple patterns 8 on a screen, such as arrows, instructions, text with a small number of letters, etc., by reflecting an incident light beam 7 generated by a laser source 6. In this case, the mirror structure 1 can again be driven in rotation about the first and second rotation axes A1 and A2 by performing a quasi-static linear movement in order to generate the desired pattern 8 on the screen 4.

[0011] Most known micro-electromechanical mirror devices envisage either electrostatic or electromagnetic type actuation to implement the rotation of the mirror structure. Electrostatic actuation systems typically use high operating voltages, while electromagnetic actuation systems typically require high power consumption.

[0012] Therefore, methods based on piezoelectric actuation have been proposed, in particular by means of actuators made of PZT (lead zirconate titanate), and based on detecting the extent of movement of the mirror structure by means of piezoresistive (PZR) sensor elements. Piezoelectrically actuated mirror devices generally have the advantage of using lower actuation voltages and power consumption levels than electrostatic or electromagnetic actuation devices.

[0013] For example, U.S. Patent Application Publication No. 2020 / 0192199 (corresponding to European Patent No. 3,666,727 A1), the contents of which are incorporated herein by reference, discloses a microelectromechanical structure provided with a structure that can be tilted by piezoelectric actuation with improved mechanical and electrical properties.

[0014] The microelectromechanical structure includes: a fixed structure defining a cavity; a tiltable structure elastically suspended in the cavity and having a main extension in a horizontal plane; and a piezoelectrically driven actuating structure that can be biased to cause the tiltable structure to rotate about at least a first rotational axis parallel to a first horizontal axis of the horizontal plane, the actuating structure being interposed between the tiltable structure and the fixed structure. Specifically, the actuating structure includes at least a first pair of actuating arms that carry respective regions of piezoelectric material and are elastically coupled to the tiltable structure on opposite sides of the first rotational axis via respective elastic decoupling elements, wherein the elastic decoupling elements are rigid with respect to movement out of the horizontal plane and compliant with torsion about the first rotational axis.

[0015] The aforementioned microelectromechanical mirror structure is configured to rotate about a first horizontal axis using resonant movement to generate fast horizontal scanning; as described in the reference document, the tiltable structure can also be driven about a second horizontal axis using linear or quasi-static movement (i.e., at a frequency much lower than the resonant movement frequency) to generate slow vertical scanning (e.g., a sawtooth type).

[0016] Although the structure described in the above-mentioned document has several advantageous features, it is not designed for use in microelectromechanical mirror devices of the vector scanner type (so-called MEMS vector scanners) in which, as mentioned above, the mirror structure is tiltable so as to assume four different quasi-static positions.

[0017] There is a need in the art to provide a piezoelectrically actuated micro-electromechanical device that would allow overcoming the above-mentioned drawbacks of the prior art. Summary of the Invention

[0018] A microelectromechanical device is disclosed herein, comprising: a fixed structure having a frame defining a cavity; a tiltable structure elastically suspended above the cavity and having a main extension in a horizontal plane; a piezoelectrically driven actuating structure configured to bias the tiltable structure to perform a desired rotation in the horizontal plane about a first rotation axis and a second rotation axis; a support structure integral with the fixed structure and extending from the frame into the cavity; and a lever element elastically coupled to the tiltable structure at a first end via a corresponding elastic suspension element and coupled to the support structure at a second end via an elastic connection element defining a lever rotation axis. The lever element is elastically coupled to the piezoelectrically driven actuating structure such that biasing of the piezoelectrically driven actuating structure causes the desired rotation of the tiltable structure about the first rotation axis and the second rotation axis due to rotation of the lever element about the lever rotation axis.

[0019] For each lever element, the piezoelectrically driven actuation structure may include: a first pair of drive arms, elastically coupled to the lever element via a first elastic drive element; and a second pair of drive arms, elastically coupled to the lever element via a second elastic drive element, on an opposite side of the lever rotation axis relative to the first elastic drive element.

[0020] The first and second resiliently driven elements may be rigid and compliant to torsion with respect to movement out of the horizontal plane along a vertical axis orthogonal to the horizontal plane.

[0021] The first and second pairs of actuator arms can be cantilevered above the cavity, with first ends integrally coupled to the support structure and second ends resiliently coupled to the lever element. The actuator arms can carry corresponding regions of piezoelectric material on their top surfaces opposite the cavity.

[0022] The support structure may include: a first arm extending from the frame toward the tiltable structure; and a second arm having a first end elastically coupled to a corresponding lever element via a corresponding elastic connecting element and having a second end integrated with a corresponding one of the first arms; wherein the driving arms of the first pair of driving arms are arranged outside the second arm between the second arm and the frame, and the driving arms of the second pair of driving arms are arranged inside the second arm between the second arm and the corresponding lever element.

[0023] The micro-electromechanical device may have central symmetry relative to the center; wherein the first rotation axis is a first symmetry axis, and the second rotation axis is a second symmetry axis, whereby the micro-electromechanical device is divided into four quadrants relative to the center.

[0024] The drive arms of a first pair of drive arms in a given quadrant can be offset in a manner corresponding to the drive arms of a second pair of drive arms in a quadrant arranged symmetrically with respect to the center, and the drive arms of the second pair of drive arms in a given quadrant can be offset in a manner corresponding to the drive arms of the first pair of drive arms in the quadrant arranged symmetrically with respect to the center. The drive arms of the first and second pairs of drive arms can define four sets of drive electrodes that are designed to be offset to collectively define a desired rotation of the tiltable structure about the first and second rotational axes.

[0025] The four sets of drive electrodes may be designed to be biased to define four different rotations of the tiltable structure and four corresponding quasi-static drive positions.

[0026] The tiltable structure can carry a mirror surface on top of it, and the micro-electromechanical device provides a two-dimensional vector scanner mirror device.

[0027] The actuating arms of the first pair of actuating arms in each quadrant can be offset in a corresponding manner, and the actuating arms of the second pair of actuating arms in each quadrant can be offset in a corresponding manner. The actuating arms of the first and second pairs of actuating arms can be designed to be offset to limit linear movement of the tiltable structure along a vertical axis orthogonal to the horizontal plane.

[0028] Micro-electromechanical devices can provide the actuators for speaker devices.

[0029] For movement out of the horizontal plane along a vertical axis orthogonal to the horizontal plane, the elastic suspension element may be rigid and may be further configured to enable relative rotation between the tiltable structure and the lever element.

[0030] Each elastic suspension element may include a first folded portion connected to an edge portion of the tiltable structure and a second torsion portion connected between the first portion and the first end of the corresponding lever element.

[0031] The tiltable structure may be coupled to a base portion formed at the same level as the piezoelectrically driven actuating structure and the support structure via a connecting post having an extension along a vertical axis orthogonal to the horizontal plane.

[0032] The first and second rotation axes may be parallel to the first and second horizontal axes.

[0033] The first and second rotation axes may be tilted 45° relative to the first and second horizontal axes.

[0034] The elastic connecting element may be a torsionally elastic connecting element. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] For a better understanding, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0036] Figure 1A-1B is a schematic diagram of a possible use of a mirror system of a known type;

[0037] Figure 2 is a top view of the micro-electromechanical device according to the first embodiment of the present invention;

[0038] Figure 3 yes Figure 2 A top perspective view of the micro-electromechanical device when the corresponding tiltable structure undergoes rotational movement;

[0039] Figure 4 Performs rotational movement Figure 3 A schematic cross-sectional view of a portion of a microelectromechanical device;

[0040] Figure 5 It starts with SOI (Silicon on Insulator) wafers Figure 2 Schematic cross-sectional view of a possible implementation of a microelectromechanical device;

[0041] Figure 6 are cross-sectional views of various embodiments of microelectromechanical devices;

[0042] Figure 7 This is an overall block diagram of an electronic device using the micro-electromechanical device;

[0043] Figure 8 This is in the case of vertical translation of the corresponding tiltable structure Figure 2 Schematic diagram of a microelectromechanical device;

[0044] Figure 9 is a top view of a micro-electromechanical device according to another embodiment; and

[0045] Figure 10 yes Figure 9 A three-dimensional top view of the MEMS device when the corresponding tiltable structure rotates and moves. DETAILED DESCRIPTION

[0046] Figure 2 is a schematic diagram of a MEMS (Micro Electro Mechanical System) device 10 according to a first embodiment, in particular a mirror device of the vector scanner type.

[0047] The microelectromechanical device 10 is formed in a die of semiconductor material, in particular silicon, and is provided with a tiltable structure 12. This tiltable structure has a main extension in a horizontal plane XY and can be driven to rotate about a first rotation axis A1 and a second rotation axis A2, wherein the first rotation axis A1 is parallel to the first horizontal axis X of the horizontal plane XY, and the second rotation axis A2 is parallel to the second horizontal axis Y of the horizontal plane XY and defines the horizontal plane XY together with the first horizontal axis X (in the embodiment shown, the side faces of the die are also parallel to the horizontal axes X, Y).

[0048] As will be discussed below, the tiltable structure 12 may also be driven so as to move along a vertical axis Z that is orthogonal to the horizontal plane XY.

[0049] and the second rotation axis A2 represents the second symmetry axis of the same microelectromechanical device 10 , which also has central symmetry relative to the center O (also representing the center of the aforementioned tiltable structure 12 ).

[0050] Basically, the micro-electromechanical device 10 can be divided into four quadrants with respect to the aforementioned center O, which have the same arrangement and configuration.

[0051] The tiltable structure 12 is suspended above a cavity 13 obtained in the die and, in the embodiment shown, has a substantially circular shape in the horizontal plane XY. The tiltable structure 12 carries a reflecting surface 12' at the top so as to define a mirror structure.

[0052] The tiltable structure 12 is elastically coupled to a fixed structure 14 formed in the same die. Specifically, the fixed structure 14 defines a frame 14 ′ (having a substantially square shape in this example) in the horizontal plane XY, which delimits and surrounds the aforementioned cavity 13, and further includes a support structure 15 (described in more detail below) extending from the same frame 14 ′ within the cavity 13.

[0053] The tiltable structure 12 is resiliently supported above the cavity 13 and connected to a corresponding lever element 16 in each quadrant. In the illustrated embodiment, the lever elements 16 extend diagonally, inclined at 45° relative to the first and second horizontal axes x, y, from an edge of the tiltable structure 12 at a first end toward a vertex of the frame 14' at a second end. In the illustrated embodiment, the lever elements 16 have a substantially rectangular shape in the horizontal plane XY, elongated along the aforementioned diagonal direction.

[0054] Specifically, the tiltable structure 12 is elastically coupled to each lever element 16 at the first end of the lever element by a corresponding elastic suspension element 18, which has a high stiffness for movement away from the horizontal plane XY (along the orthogonal axis Z, transverse to the horizontal plane XY) and is further configured to enable relative rotation between the same tiltable structure 12 and the lever element 16.

[0055] Specifically, each elastic suspension element 18 includes: a folding-type first part 18a, connected to the above-mentioned edge part of the tiltable structure 12; and a torsional-type second part 18b, formed by straight line elements arranged in a diagonal direction and connected between the first part 18a and the first end of the lever element 16.

[0056] Each lever element 16 is further elastically coupled at its second end to the above-mentioned support structure 15, in particular by means of a corresponding elastic connecting element 20 of the torsion type, wherein, on opposite sides of the lever element 16, the elastic connecting element 20 has a straight extension that is essentially transverse to the above-mentioned diagonal direction to define a lever rotation axis L for the lever element 16.

[0057] As will be discussed below, the lever element 16 is configured to rotate about a lever rotation axis L, causing its first end (coupled to the tiltable structure 12) to move upward (and thus its second end downward) or downward (and thus its second end upward) along a vertical axis Z. In a corresponding manner, the tiltable structure 12 moves upward or downward at its edge portion coupled to the aforementioned first end of the lever rotation element 16.

[0058] In more detail, the above-mentioned support structure 15 includes: a central arm 15a, which, in the embodiment described, extends from the frame 14' towards the tiltable structure 12 along the first rotation axis A1 or the second rotation axis A2, and ends at a certain distance from the same tiltable structure 12 at the center relative to the cavity 13; and a connecting arm 15b, a first end of which is elastically coupled to the corresponding lever element 16 through the corresponding elastic connecting element 20, and a second end is fixed relative to the corresponding central arm 15a, and is connected to the corresponding central arm 15a at the corresponding first rotation axis A1 or the second rotation axis A2.

[0059] Thus, in each quadrant of the MEMS device 10 there are two connecting arms 15b extending on opposite sides relative to the corresponding lever element 16 towards a respective central arm 15a extending along the first and second rotation axes A1 , A2 , respectively.

[0060] The microelectromechanical device 10 further comprises an actuating structure 22 which is elastically coupled to the lever element 16 and is configured to cause a movement of the tiltable structure 12, in particular a rotation thereof about the first rotation axis A1 or the second rotation axis A2 (or a displacement along the vertical axis Z as will be discussed below).

[0061] In each quadrant that can be divided into microelectromechanical device 10, actuation structure 22 includes: a first pair of actuating arms 22a, arranged outside connecting arms 15b, between the same connecting arms 15b and frame 14' (separated by a portion of the aforementioned cavity 13); and a second pair of actuating arms 22b, arranged inside connecting arms 15b, between the same connecting arms 15b and corresponding lever elements 16 (separated by another portion of the aforementioned cavity 13). In the illustrated embodiment, actuating arms 22a, 22b have a generally trapezoidal (or fin) shape in horizontal plane XY.

[0062] Each driving arm 22a, 22b is suspended above the cavity 13 in a cantilever manner and carries a corresponding piezoelectric material area 23 (in particular PZT-lead zirconate titanate) on its top surface (opposite to the same cavity 13), and the piezoelectric material area has an extension in the horizontal plane XY that is basically the same as that of the driving arms 22a, 22b (for example, for the sake of simplicity, the size of each side of the piezoelectric material area 23 may be about 30 μm smaller than that of the driving arms 22a, 22b below).

[0063] In one possible embodiment, the drive arms 22 a , 22 b are shaped so as to provide substantially the same piezoelectric actuation area due to the biasing of the respective piezoelectric material areas 23 .

[0064] Each drive arm 22 a , 22 b has a respective first end fixedly coupled to a corresponding connecting arm 15 b (thus, fixed relative to the frame 14 ′) and a respective second end resiliently coupled to a corresponding lever element 16 .

[0065] Specifically, the first pair of driving arms 22a are elastically coupled to the corresponding lever elements 16 at their second ends (close to the frame 14') through a first elastic driving element 24, wherein the first elastic driving element 24 extends to the outside of the elastic connecting element 20 between the same elastic connecting element 20 and the frame 14'; and the second pair of driving arms 22b are elastically coupled to the corresponding lever elements 16 through a second elastic driving element 25, wherein the second elastic driving element 25 extends to the inside of the elastic connecting element 20 between the same elastic connecting element 20 and the tiltable structure 12.

[0066] Therefore, the first and second elastic drive elements 24, 25 extend on opposite sides of the elastic connecting element 20 relative to the lever rotation axis L and are both formed by corresponding folded elastic elements, have high stiffness for movement away from the horizontal plane XY (along the orthogonal axis Z) and are compliant with torsion (transverse to the corresponding lever element 16, around an axis of rotation parallel to its extension direction).

[0067] During operation, if another Figure 2 As is understood, the bias of the piezoelectric material region 23 carried by the first pair of drive arms 22a (for example, with a positive pressure difference ΔV) causes an upward displacement (along the vertical axis Z) of the corresponding second end elastically coupled to the corresponding lever element 16; this displacement is transmitted by the first elastic drive element 24, thereby causing an upward displacement of the second end of the lever element 16 and a rotation of the same lever element 16 around the lever rotation axis L, resulting in a corresponding downward displacement of the first end, thereby resulting in a downward displacement of the coupled edge portion of the tiltable structure 12.

[0068] This rotation of the lever element 16 is not hindered by the second elastic drive element 25 but is enabled and occurs with zero bias (eg zero voltage difference ΔV) of the piezoelectric material region 23 carried by the second pair of drive arms 22b.

[0069] Similarly, the bias of the piezoelectric material region 23 carried by the second pair of drive arms 22b (for example, again with a positive pressure difference ΔV) causes an upward displacement (along the vertical axis Z) of the corresponding second end of the corresponding lever element 16 elastically coupled; this displacement is transmitted by the second elastic drive element 25, thereby causing an upward displacement of the first end of the lever element 16 and a rotation of the same lever element 16 about the lever rotation axis L, resulting in a corresponding upward displacement of the second end, thereby causing an upward displacement of the coupled edge portion of the tiltable structure 12.

[0070] In this case, the aforementioned rotation of the lever element 16 is not hindered by the first elastically driven element 24 but is enabled and occurs, for example, with zero bias (eg zero voltage difference ΔV) of the piezoelectric material region 23 carried by the first pair of drive arms 22a.

[0071] In one possible embodiment, the piezoelectric material regions 23 of the first pair of driving arms 22 a in one of the given quadrants that divide the microelectromechanical device 20 are electrically connected (in a manner not shown, via appropriate electrical connection elements) to the piezoelectric material regions 23 of the second pair of driving arms 22 b in the quadrant of the microelectromechanical device 10 that is symmetrically arranged with respect to the center O. Similarly, the piezoelectric material regions 23 of the second pair of driving arms 22 b in one of the given quadrants that divide the microelectromechanical device 10 are electrically connected to the piezoelectric material regions 23 of the first pair of driving arms 22 a in the quadrant of the microelectromechanical device 10 that is symmetrically arranged with respect to the center O.

[0072] Through the above electrical connection, four groups of driving electrodes are obtained. Figure 2 Schematically represented in different shades of grey from darkest to lightest as: Set1, Set2, Set3 and Set4. The biasing of the drive electrode sets described above allows obtaining a desired rotation of the tiltable structure 12 about the first and second rotation axes A1, A2; in a possible non-limiting embodiment, four different rotations of the tiltable structure 12 and four corresponding quasi-static drive positions can be obtained.

[0073] In detail: applying a voltage difference ΔV (e.g., positive) to the drive electrodes of groups Set2 and Set3, and zero bias of the drive electrodes of groups Set1 and Set4 causes a negative rotation around the rotation axis A1; applying a voltage difference ΔV to the drive electrodes of groups Set1 and Set4, and zero bias of the drive electrodes of groups Set2 and Set3 causes a positive rotation around the same rotation axis A1; applying a voltage difference ΔV (e.g., positive again) to the drive electrodes of groups Set1 and Set3, and zero bias of the drive electrodes of groups Set2 and Set4 causes a negative rotation around the rotation axis A2; applying a voltage difference ΔV to the drive electrodes of groups Set2 and Set4, and zero bias of the drive electrodes of groups Set1 and Set3 causes a positive rotation around the same rotation axis A2.

[0074] As an example, Figure 3 The latter position of the tiltable structure 12 is shown, which is a positive rotation about the axis of rotation A2 and also shows the deformation of the various elastic elements involved in the same direction, as described in detail above.

[0075] As previously mentioned, in various embodiments, the biasing of the four groups of driving electrodes can enable the tiltable structure 12 to be positioned at a desired position within its range of motion.

[0076] By example, Figure 4 The micro-electromechanical device 10 is schematically shown along Figure 3 The displacement of the section IV-IV is the positive rotation around the rotation axis A2. Figure 4 In the figure, F represents the driving force due to the piezoelectric effect, which acts on the coupling point between the lever element 16 and the corresponding elastic drive element 24, 25 (in fact, it is configured to transmit the force in the direction of the vertical axis Z to the above-mentioned lever element 16), causing the lever element 16 to move around the lever rotation axis L; and θ represents the subsequent rotation angle of the tiltable structure 12 relative to the vertical axis Z.

[0077] As mentioned above Figure 2As shown schematically, the microelectromechanical device 10 also includes one or more piezoresistive (PZR) sensors 29, which are appropriately arranged to provide one or more detection signals associated with the rotation of the tiltable structure 12 about the first and second rotation axes A1, A2; these detection signals can be provided as feedback at the output from the microelectromechanical device 10, allowing the implementation of an appropriate closed control loop.

[0078] The aforementioned piezoresistive sensors 29 are obtained (for example, by surface diffusion of dopant atoms) on one or more connecting arms 15b of the connecting structure 15 (however, different arrangements of the piezoresistive sensors 29 are conceivable). Advantageously, the elastic connecting element 20 is able to transmit stresses to the connecting arms 15b and thus to the piezoresistive sensors 29, making it possible to detect the rotation of the tiltable structure 12.

[0079] In a manner not described in detail but apparent, two piezoresistive sensors 29 may be arranged in a Wheatstone bridge configuration for detecting rotation of the tiltable structure 12 about the first and second rotation axes A1 , A2 (and thus overall rotation of the tiltable structure 12 ).

[0080] Alternatively, as described in detail in the aforementioned document EP 3,666,727 A1, it is also possible to introduce a mechanical amplification structure designed to attempt, by means of an appropriate lever mechanism, to maximize the stress detected by the piezoresistive sensor 29 and thus the corresponding sensitivity.

[0081] In a manner not shown, other types of detection of the rotation of the tiltable structure 12 may also be provided, for example by piezoelectric sensors.

[0082] Figure 5 A simplified cross-sectional view of a microelectromechanical device 10 is shown, wherein some elements are omitted for simplicity and other elements are shown schematically.

[0083] In particular, the cross-sectional view shows that the frame 14 ′ is coupled at the bottom to a support wafer (so-called “handle wafer”) 31 having a groove 32 below the cavity 13 and the tiltable structure 12 for enabling the rotation of the same.

[0084] In this embodiment, similar to the actuating structure 22, the tiltable structure 12 is fabricated in the active layer 34 of the SOI wafer, with its support layer 35 separated from the active layer 34 by a dielectric layer 36 and coupled at its bottom to the aforementioned handle wafer 31. Furthermore, the tiltable structure 12 has a reinforcing element 37 at its bottom that contacts the surface opposite the reflective surface 12′ and has an extension along the vertical axis Z.

[0085] like Figure 6As shown, a possible variant embodiment is instead envisaged in which the tiltable structure 12 is formed in a stacked manner at a higher level relative to the actuating structure 22. In particular, in this case, the tiltable structure 12 is coupled in a stacked manner to a base part 40 via a connecting column 41 having an extension along the vertical axis Z, the base part 40 being formed at the same level as the actuating structure 22 (separated from the base part 40 by the cavity 13). In this case, advantageously, the lever effect implemented by the lever element 16 (not shown here) is amplified, thereby achieving a greater tilting angle of the tiltable structure 12 with a more compact and robust solution.

[0086] In this case, the tiltable structure 12 is formed in a different wafer of semiconductor material, which wafer can be coupled to the base surface 40 , for example, by wafer bonding in a front-end stage of the manufacturing process.

[0087] The advantages of the present disclosure are clear from the foregoing description.

[0088] In any case, it has to be emphasized that the described embodiments provide a robust and efficient micro-electromechanical mirror device, in particular of the two-dimensional vector scanner type (so-called MEMS vector scanner).

[0089] The described embodiment has high linearity, a wide angular aperture for mirror rotation, and a compact structure.

[0090] For example, as referenced Figure 7 As schematically shown, the microelectromechanical device 10 may advantageously be used in a projection device 40 designed to be operatively coupled to a portable electronic device 41 .

[0091] The projection device 40 comprises: a source 42 designed to generate an image 43; a micro-electromechanical device 10, acting as a reflector and designed to receive the image 43 and direct it towards a screen 45 (located outside the same projection device 40 and arranged at a certain distance); a first drive circuit 46 designed to provide a drive signal to the source 42 for generating the image 43 to be projected; a second drive circuit 48 designed to provide a drive signal to the actuating structure 22 of the micro-electromechanical device 10; and a communication interface 49 designed to receive information about the image to be projected from an external control unit 50, for example included in the portable electronic device 41, which information is for example in the form of a pixel array and is sent at the input of the source 42 for driving.

[0092] Finally, it is obvious that modifications and variations may be made to what has been described and illustrated herein without departing from the scope of the present disclosure.

[0093] In particular, the embodiments and methods may also be used to provide actuators for micro-electromechanical loudspeaker devices (so called μ-speakers) by varying the bias combination of the regions of piezoelectric material 23 carried by the first and second pairs of drive arms 22a, 22b.

[0094] In this case, the piezoelectric material regions 23 of the first pair of drive arms 22a are electrically connected together, and the piezoelectric material regions 23 of the second pair of drive arms 22b are electrically connected together.

[0095] refer to Figure 8 By applying the same voltage difference ΔV (e.g., positive) to the second pair of drive electrodes 22b, the first pair of drive electrodes 22a has zero bias, and an upward displacement along the vertical axis Z of the tiltable structure 12 is obtained. Similarly, by applying the same voltage difference ΔV to the first pair of drive electrodes 22a, the second pair of drive electrodes 22b has zero bias, and a downward displacement along the vertical axis Z of the same tiltable structure 12 is obtained.

[0096] Basically, the tiltable structure 12 realizes a piston-like displacement, whereby it can be used as an actuator, for example coupled to a suitable deformable membrane (in a manner not shown), for generating sound waves in a micro-electromechanical loudspeaker device.

[0097] Advantageously, this allows obtaining a vertical movement of the tiltable structure 12 with high linearity and excellent resistance to stresses and shocks.

[0098] Furthermore, it is obvious that variations are conceivable with regard to the shape and arrangement of the elements forming the microelectromechanical device 10 , such as for example different shapes of the tiltable structure 12 (and the corresponding reflective surface 12 ′).

[0099] Regarding this, Figure 9 A further embodiment of a microelectromechanical device 10 is shown which differs from the previously shown embodiments in that the rotation axes A1 and A2 are tilted by 45° relative to the first and second horizontal axes x and y, ie the sides of the fixing structure 14 and the frame 14 ′ of the corresponding die.

[0100] Thus, in this case, the lever element 16 is aligned with the aforementioned horizontal axes x and y, whereas the central arm 15a of the support structure 15 is oriented in a diagonal direction, ie in this case along the aforementioned rotation axes A1 and A2.

[0101] Furthermore, the tiltable structure 12 here has a substantially square shape in the horizontal plane XY, and the first portion 18 a of each elastic suspension element 18 , again of folding type, is doubled and connected to both ends of the respective side of the tiltable structure 12 .

[0102] Furthermore, in the embodiment shown, the first and second elastic decoupling elements 24 , 25 have a linear and unfolded arrangement, being in each case rigid with respect to movements out of the horizontal plane XY and compliant with respect to rotation.

[0103] In other respects, the configuration and operation of the micro-electromechanical device 10 do not differ substantially from that discussed previously with respect to the first embodiment.

[0104] For example, Figure 10 Shown Figure 9 The rotation of the tiltable structure 12 of the micro-electromechanical device 10 is a positive rotation about the first rotation axis A1 and also represents a deformation of the various elastic elements involved in the same rotation.

Claims

1. A micro-electromechanical device comprising: a fixed structure having a frame defining a cavity; a tiltable structure resiliently suspended above the cavity and having a main extension in a horizontal plane defined by a first horizontal axis and a second horizontal axis orthogonal to the first horizontal axis; a piezoelectrically driven actuation structure configured to bias the tiltable structure to cause a desired rotation about a first rotational axis and a second rotational axis in the horizontal plane; a support structure integrated with the fixed structure and extending from the frame into the cavity; as well as a lever element resiliently coupled at a first end to the tiltable structure via a respective resilient suspension element and coupled at a second end to the support structure via a resilient connection element defining an axis of rotation of the lever; wherein the lever element is elastically coupled to the piezoelectrically driven actuating structure such that a biasing of the piezoelectrically driven actuating structure causes the desired rotation of the tiltable structure about the first rotation axis and the second rotation axis due to rotation of the lever element about the lever rotation axis, wherein the first rotation axis and the second rotation axis are tilted 45° relative to the first horizontal axis and the second horizontal axis.

2. The micro-electromechanical device of claim 1 , wherein for each of the lever elements, the piezoelectrically driven actuation structure comprises: a first pair of actuating arms resiliently coupled to the lever element via a first resilient actuating element; and a second pair of drive arms resiliently coupled to the lever element on an opposite side of the lever rotation axis relative to the first resilient drive element via a second resilient drive element. 3 . The microelectromechanical device of claim 2 , wherein the first and second elastically driven elements are rigid and compliant to torsion with respect to movement out of the horizontal plane along a vertical axis orthogonal to the horizontal plane.

4. A microelectromechanical device according to claim 2, wherein the first pair of drive arms and the second pair of drive arms are suspended above the cavity in a cantilever manner, with the first end integrally coupled to the support structure and the second end elastically coupled to the lever element; and wherein the drive arms carry corresponding piezoelectric material areas on their top surfaces opposite to the cavity.

5. The micro-electromechanical device according to claim 2, wherein the support structure comprises: a first arm extending from the frame toward the tiltable structure; and a second arm having a first end resiliently coupled to a corresponding lever element via a corresponding resilient connecting element and having a second end integral with a corresponding one of the first arms; wherein the drive arm of the first pair of drive arms is arranged outside the second arm between the second arm and the frame, and The drive arms of the second pair of drive arms are arranged inside the second arm between the second arm and the corresponding lever element.

6. The micro-electromechanical device according to claim 2, wherein the micro-electromechanical device has central symmetry relative to a center; and wherein the first rotation axis is a first symmetry axis, and the second rotation axis is a second symmetry axis, the micro-electromechanical device being thereby divided into four quadrants relative to the center.

7. A microelectromechanical device according to claim 6, wherein the drive arms of the first pair of drive arms in a given quadrant are offset in a manner corresponding to the drive arms of the second pair of drive arms in a quadrant arranged symmetrically relative to the center, and the drive arms of the second pair of drive arms in the given quadrant are offset in a manner corresponding to the drive arms of the first pair of drive arms in a quadrant arranged symmetrically relative to the center; and wherein the drive arms of the first pair of drive arms and the second pair of drive arms define four groups of drive electrodes, which are designed to be offset to collectively limit the desired rotation of the tiltable structure around the first rotation axis and the second rotation axis.

8. The micro-electromechanical device of claim 7, wherein the four sets of drive electrodes are designed to be biased to define four different rotations of the tiltable structure and four corresponding quasi-static drive positions.

9. The micro-electromechanical device of claim 7, wherein the tiltable structure carries a mirror surface on top, the micro-electromechanical device being a two-dimensional vector scanner mirror device.

10. A microelectromechanical device according to claim 6, wherein the driving arms of the first pair of driving arms in each quadrant are offset in a corresponding manner, and the driving arms of the second pair of driving arms in each quadrant are offset in a corresponding corresponding manner; and wherein the driving arms of the first pair of driving arms and the second pair of driving arms are designed to be offset to limit the linear movement of the tiltable structure along a vertical axis orthogonal to the horizontal plane.

11. The micro-electromechanical device of claim 10, wherein the micro-electromechanical device provides an actuator for a speaker device.

12. The micro-electromechanical device of claim 1, wherein the elastic suspension element is rigid for movement away from the horizontal plane along a vertical axis orthogonal to the horizontal plane, and is further configured to enable relative rotation between the tiltable structure and the lever element.

13. The micro-electromechanical device of claim 12, wherein each of the elastic suspension elements comprises a first folded portion connected to an edge portion of the tiltable structure and a second torsion portion connected between the first folded portion and the first end of the corresponding lever element.

14. The microelectromechanical device according to claim 1 , wherein the tiltable structure is coupled to a base portion via a connecting post, the base portion being formed at the same level as the piezoelectrically driven actuating structure and the supporting structure, the connecting post having an extension along a vertical axis orthogonal to the horizontal plane.

15. The micro-electromechanical device of claim 1, wherein the elastic connection element comprises a torsionally elastic connection element.

16. A micro-electromechanical device comprising: a fixed structure having a frame defining a cavity; a tiltable structure resiliently suspended above the cavity and having a main extension in a horizontal plane defined by a first horizontal axis and a second horizontal axis orthogonal to the first horizontal axis; a piezoelectrically driven actuation structure configured to be biased to cause a desired rotation of the tiltable structure; a support structure integrated with the fixed structure and extending from the frame into the cavity; as well as a lever element resiliently coupled to the tiltable structure at a first end via a respective resilient suspension element and coupled to the support structure at a second end via a resilient connecting element; wherein the lever element is elastically coupled to the piezoelectrically driven actuating structure, and The piezoelectrically driven actuation structure is configured to bias the tiltable structure to perform a desired rotation in the horizontal plane about first and second rotation axes, wherein the first and second rotation axes are tilted 45° relative to the first and second horizontal axes.

17. The micro-electromechanical device of claim 16, wherein for each of the lever elements, the piezoelectrically driven actuation structure comprises: a first pair of actuating arms resiliently coupled to the lever element via a first resilient actuating element; and a second pair of drive arms resiliently coupled to the lever element at opposite sides via a second resilient drive element.

18. The micro-electromechanical device of claim 17, wherein the first and second elastically driven elements are rigid with respect to movement out of the horizontal plane and are compliant to torsion.

19. The micro-electromechanical device of claim 17, wherein the first pair of driving arms and the second pair of driving arms are suspended above the cavity in a cantilever manner, with first ends integrally coupled to the support structure and second ends elastically coupled to the lever element.

20. The microelectromechanical device of claim 19, wherein the actuating arms carry respective regions of piezoelectric material on their top surfaces opposite the cavity.

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