MEMS micro-mirror device

Abstract

A MEMS micromirror device is formed in a package comprising a housing and a cover transparent to optical radiation. The package forms a cavity that houses a tiltable platform having a reflective surface. A metastructure is formed on the cover and / or the reflective surface and comprises a plurality of diffractive optical elements.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Italian application No. 102020000016855, filed on July 10, 2020, the contents of which are incorporated herein by reference in their entirety. Technical Field

[0003] This disclosure relates to a MEMS micromirror device encapsulated in a package having a transparent surface and a tiltable platform. Background Technology

[0004] Some known MEMS devices have mirror structures obtained using semiconductor technology.

[0005] This type of MEMS micromirror device has been widely used because it can meet stringent requirements regarding volume, including both area and thickness.

[0006] Therefore, the above-mentioned devices are widely used in portable devices, such as portable computers, laptops, notebooks (including ultra-thin notebooks), PDAs, tablets, smartphones, and devices for optical applications, especially for guiding light radiation beams generated by light sources according to desired shapes.

[0007] For example, microelectromechanical systems (MEMS) reflector devices are used in microprojector modules (e.g., picoprojectors) that can project images or generate desired light patterns at a distance. Furthermore, they are very useful in augmented reality glasses and goggles, as well as in LIDAR (light detection and ranging) scanning devices.

[0008] LIDAR technology measures the distance to a target within a field of view by illuminating the target with a laser beam, detecting the reflected laser beam as a return beam using sensors, and determining the time elapsed between the laser beam's emission to the target and the reception of the returned beam ("return time"). By illuminating different targets within the field of view with a laser beam, a set of points can be constructed based on the differences in return times, forming a three-dimensional digital representation of the field of view.

[0009] Therefore, the application of LIDAR technology in fields such as geodesy, geographic information science, archaeology, geography, geology, geomorphology, seismology, forestry, atmospheric physics, laser-driven systems, ALSM (Airborne Laser Strip Mapping), and laser altimetry helps create high-resolution maps. LIDAR technology is also used for the control and navigation of autonomous vehicles, or in advanced driver assistance systems for certain vehicles.

[0010] Microelectromechanical reflector devices typically include a reflector element suspended on / inside a cavity and obtained from a semiconductor material body for mobility, typically having tilting or rotational motion, for guiding an incident beam in a desired manner.

[0011] For example, Figure 1 A microprojector 1 is schematically shown, including a light source 2, typically a laser source, that generates a combined beam 3 consisting of three monochromatic beams, one for each primary color. This combined beam is deflected by a mirror element 5 via an optical element 4, schematically shown, toward a screen 6 that generates a scan 7. In the example shown, the mirror element 5 includes two micromirrors 8 and 9 arranged sequentially along the path of the beam 3, each micromirror being rotatable about one of its axes; specifically, the first micromirror 8 is rotatable about a vertical axis A, and the second micromirror is rotatable about a horizontal axis B perpendicular to axis A. The rotation of the first micromirror 8 about the vertical axis A generates a rapid horizontal scan, such as... Figure 1 As shown. The rotation of the second micromirror 9 around the horizontal axis B produces a slow vertical scan.

[0012] In certain applications, such as augmented reality systems and the aforementioned LiDAR devices, the mirror elements or each micromirror 8, 9 are held in a low-pressure environment by a hermetically sealed package with at least one transparent side. In this way, due to the low pressure present therein, the Q-factor increases, thus enabling superior performance.

[0013] For example, Figure 2 A general-purpose micromirror 10 is shown, which achieves... Figure 1 Microscope 8 or 9.

[0014] The micromirror 10 includes a tiltable platform 11 having a reflective surface 11A and being supported by a body 12 via a support and actuation structure (not shown), such that the tiltable platform 11 can rotate at least about an axis 15. Here, the body 12 is cup-shaped and is closed at the top by a cover 16 having an outer surface 16A and a rear surface 16B.

[0015] The cover 16 is formed of or includes a transparent wall, such as glass (especially silicon oxide), which allows external incident light rays Li to reach the tiltable platform 11 and be reflected outward in an orientation related to the instantaneous angular position of the tiltable platform 11 as reflected light rays Lr.

[0016] However, in use, the cover 16 may produce artifacts due to spurious reflections caused by the cover 16. For example, external incident light Li entering the micromirror 10 is partially transmitted through the cover 16 to the tiltable platform 11 and partially reflected directly by the outer surface 16A as stray light Ls. Similar stray light (not shown) can be generated from external light Li incident on the rear surface 16B of the cover 16 and from reflected light Lr (after multiple reflections). Due to the different optical paths, these stray reflections may produce patches and noise on the target, screen, or user pointed to by the reflected light Lr and / or on certain other parameters used to detect and evaluate elapsed time or reflected light radiation.

[0017] To overcome this, various methods have been investigated, such as applying an ARC (Anti-Reflective Coating) layer to the cover 16 to eliminate any stray reflections; treating surfaces 16A and 16B to reduce their refractive index; and arranging the cover 16 (or at least a portion thereof) at an angle relative to the reflective surface 11A of the tiltable platform. For example, the latter method is shown in European Patent No. 1,748,029 (attached by reference) and allows stray rays Ls (and stray rays Ls generated on the rear surface 16B of the cover 16) to be directed in a direction quite different from the reflected rays Lr, so that they do not hit the target or are therefore undetectable.

[0018] However, the methods described above do not satisfactorily and adequately address these problems. In fact, anti-reflective layers or surface treatments are not effective enough in eliminating stray reflections, especially for visible light, where the reflective patches are large. On the other hand, the slanted arrangement of the cover or the slanted shape of a portion of the cover presents major manufacturing difficulties, and the glass wafer bonded to the wafer (the wafer forming body 12) is fragile and difficult to handle with current production equipment, resulting in high manufacturing costs, low throughput, and a large amount of production waste.

[0019] There is a need in the art to provide a micromirror that overcomes the shortcomings of the prior art. Summary of the Invention

[0020] According to this disclosure, a MEMS micromirror device includes a package comprising a housing and a cover that is transparent to light radiation. The package forms a cavity in which a tiltable platform is housed and has a reflective surface. A metastructure is formed on the package and / or the reflective surface, the metastructure including a plurality of diffractive optical elements.

[0021] The first diffraction basic unit may be formed by a first diffraction optical element among a plurality of diffraction optical elements. The first diffraction basic unit has a region extending in a plane, and the first diffraction optical elements of the first diffraction basic unit are arranged with a first variable density that is linearly variable in a variable direction belonging to the plane.

[0022] The tiltable platform can be configured to rotate about a rotation axis, and the variability direction can be perpendicular to the rotation axis.

[0023] The first diffractive optical element of the first diffractive basic unit may have a linearly variable size in the variable direction and / or be arranged with a linearly variable inter-element distance in the variable direction.

[0024] The dimensions and inter-element distances in the variable direction can be smaller than the wavelength of light radiation in the application of MEMS micromirror devices.

[0025] At least one second diffraction basic unit can be formed by a second diffraction optical element among a plurality of diffraction optical elements. The second diffraction optical elements are arranged in a first density that is linearly variable in the variable direction. The first diffraction basic unit and the second diffraction basic unit are arranged side by side with an inter-unit distance equal to a multiple of 2πλ in the variable direction, where λ is the wavelength of light radiation in the application field of the MEMS micromirror device.

[0026] The diffractive optical elements in a plurality of diffractive optical elements can be formed from pillars.

[0027] The diffractive optical element in a plurality of diffractive optical elements may be a material having a first refractive index and immersed in a medium having a second refractive index, wherein the first refractive index is greater than the second refractive index.

[0028] The diffractive optical elements in a plurality of diffractive optical elements can protrude from the support surface.

[0029] The diffractive optical elements in a plurality of diffractive optical elements can extend through the dielectric layer.

[0030] The dielectric layer can be silicon dioxide.

[0031] The diffractive optical elements in a plurality of diffractive optical elements can be formed by openings made in a dielectric layer.

[0032] The dielectric layer can be a silicon oxide layer.

[0033] The cover may be made of an optically transparent material and has an inner surface facing a tiltable platform and an outer surface opposite the inner surface, wherein the metastructure is formed on the outer surface of the cover.

[0034] A third diffractive optical element may be present among the multiple diffractive optical elements, wherein the third diffractive optical element is formed on the inner surface of the cover to form at least one third diffractive basic unit, and the third diffractive optical element is arranged with a third density that is linearly variable in a direction parallel to the variability direction, the third linearly variable density being equal to the first linearly variable density.

[0035] The tiltable platform may have a reflective surface facing the cover, and multiple diffractive optical elements are formed on the reflective surface.

[0036] The reflective surface may include a metallization layer, and the metastructure is formed directly on the metallization layer.

[0037] The reflective surface may include a metallization layer and a dielectric layer, and the metastructure may be formed on the dielectric layer.

[0038] The present invention also discloses a MEMS micromirror device, comprising: a package including a housing and a transparent cover, the package being arranged in rows to define a cavity; and a tiltable platform disposed within the cavity and having a reflective surface, wherein a metastructure is formed on the package and includes a plurality of diffractive optical elements, wherein the plurality of diffractive optical elements are formed by pillars having regions extending in a plane, and the plurality of diffractive optical elements are arranged in a variable density that is linearly variable in a variable direction belonging to the plane.

[0039] A column can be a polyhedral shape.

[0040] Columns in the shape of polyhedra can have a diameter that increases along the variable direction and can be arranged at a constant spacing.

[0041] A column can be a parallelepiped shape, having a long side parallel to the direction perpendicular to the variable direction and a diameter that increases along the variable dimension. Attached Figure Description

[0042] For better understanding, some embodiments thereof will now be described by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0043] Figure 1 This is a schematic diagram of a micro projector using one-dimensional MEMS mirror elements;

[0044] Figure 2 It is a cross-section of a known MEMS mirror element;

[0045] Figure 3 This is a cross-section of an embodiment of the MEMS micromirror device disclosed herein;

[0046] Figure 4 The effect of the structure of a metasurface with a progressive profile on the reflected wavefront of an incident beam is shown.

[0047] Figure 5 An embodiment is shown. Figure 3 A magnified view of the microscope device;

[0048] Figure 6 and Figure 7 These are top and side views of possible configurations of the elemental surface of this micromirror device;

[0049] Figure 8 and Figure 9 They are based on repetition Figure 6 and Figure 7 Top and side views of the possible configurations;

[0050] Figure 10 and Figure 11 These are top and side views of different configurations of the element surface of this micromirror device;

[0051] Figure 12 and Figure 13 These are top and side views of another configuration of the elemental surface of this micromirror device;

[0052] Figure 14 and Figure 15 yes Figure 6 and Figure 7 A top view of the variant of the configuration shown;

[0053] Figure 16 It shows Figure 3 The realization of a portion of the microscope equipment;

[0054] Figure 17 and Figure 18 Two different embodiments of a portion of this micromirror device are shown;

[0055] Figure 19 Different embodiments of this micromirror device are shown;

[0056] Figure 20 and Figure 21 It shows Figure 19 Two variations of the details of the embodiments;

[0057] Figure 22 Different embodiments of this micromirror device are shown;

[0058] Figure 23 and Figure 24 It is based on their respective variants Figure 22 A top view of the micromirror apparatus; and

[0059] Figure 25 It shows Figure 22 Another variant of the micromirror device shown. Detailed Implementation

[0060] The following disclosure enables those skilled in the art to make and use the subject matter disclosed herein. The general principles described herein can be applied to embodiments and applications other than those described in detail above, without departing from the spirit and scope of this disclosure. This disclosure is not intended to be limited to the embodiments shown, but rather to be carried out within the broadest scope consistent with the principles and features disclosed or suggested herein.

[0061] Figure 3 This is a schematic diagram of the MEMS micromirror device 20.

[0062] MEMS micromirror device 20 is uniaxial and includes a tiltable platform 21. The tiltable platform 21 has a reflective surface 21A and is supported by a body 22 via a support and an actuation structure (not shown), allowing the tiltable platform 21 to rotate about a vibration axis 25.

[0063] Here, the body 22 is cup-shaped, defining a cavity 23 for receiving the tiltable platform 21, and is closed at the top by a cover 26, which is secured to the body 22 by an adhesive layer 27. Optionally, the body 22 may have a bottom and sidewalls joined together to define the cavity 23. The body 22 may be a semiconductor material, such as silicon, and the tiltable platform 21 may be integrally formed with the body 22.

[0064] The body 22 and the cover 26 form a package 24. In the illustrated embodiment, the package 24 is sealed by an adhesive layer 27, and recesses may be present therein to obtain a high quality factor.

[0065] Here, the cover 26 is formed of a transparent planar wall, such as glass, having a first surface 26A and a second surface 26B. The first surface 26A faces the exterior of the MEMS micromirror device 20; the second surface 26B faces the interior of the MEMS micromirror device 20, toward the reflective surface 21A of the tiltable platform 21. The first surface 26A and the second surface 26B of the cover are planar and lie in a plane parallel to each other and parallel to the horizontal plane XY of the Cartesian reference frame XYZ.

[0066] In the illustrated embodiment, the vibration axis 25 of the tiltable platform 21 is parallel to the first plane and the first axis Y of the Cartesian reference frame XYZ. Furthermore, in a stationary state, the reflective surface 21A of the tiltable platform 21 is parallel to surfaces 26A and 26B of the cover 26. Therefore, the MEMS micromirror device 20 is configured to receive incident light radiation Li and generate reflected light radiation Lr, wherein the incident light radiation Li and the reflected light radiation Lr form an angle β between them, the angle β depending on the instantaneous angular position of the tiltable platform 21 and located in the vertical plane XZ of the Cartesian reference frame XYZ.

[0067] exist Figure 3 In this context, the scanning angle that can be obtained as a result of the rotation of the tiltable platform 21 is represented by γ.

[0068] according to Figure 3In the embodiment of the present invention shown, the cover 26 carries a first element structure 30 on a first surface 26A and a second element structure 31 on a second surface 26B, the second element structure 31 being configured to form a corresponding element surface.

[0069] Metasurfaces (e.g., metasurfaces formed by metastructures 30, 31) are formed by diffractive optical elements that are smaller than or comparable to the wavelength of light and are arranged in a regular manner to modify the wavefront in a desired manner in terms of phase, amplitude and polarization (see, for example, “Flat optics with designer metasurfaces”, Yu et al., February 23, 2014, Nature Materials, Vol. 13, DOI 10.1038 / NMT3839, Macmillan Publishers, which is incorporated by reference).

[0070] exist Figure 3 In the middle, the element structures 30, 31 are formed by diffractive optical elements 35, which are configured and / or arranged to have a linearly variable density so as to be equivalent to an inclined surface with respect to the light radiation reflected by the cover 26, as described below.

[0071] Specifically, the diffractive optical element 35 here has a density variable in a first extension direction given by the intersection of the horizontal plane XY and the vertical plane XZ. The first extension direction is here perpendicular to the first axis Y of the Cartesian reference frame XYZ and parallel to the second axis X, and is therefore also referred to below as the first extension direction X.

[0072] The diffractive optical elements 35 are obtained as optical thin layers (with a thickness smaller than the wavelength of light in the considered frequency range) and have a size and / or spacing smaller than the wavelength of the incident light radiation Li in the first extension direction X; in particular, their size (width) or spacing in the first extension direction X is at most equal to λ / 5, where λ is the wavelength of the incident light radiation, and the maximum height is equal to λ / 2.

[0073] The first element 30 deflects stray reflected radiation Ls on the first surface 26A of the cover 26 by an angle α relative to the incident light radiation Li in the second plane XZ. This angle differs from the angle obtainable without the element 30. In fact, the angle α of the stray reflected radiation Ls corresponds to the reflection that would exist if the first surface 26A were tilted relative to the laying plane XY. A similar deflection is caused by the second element 31 on the second surface 26B of the cover 26, as... Figure 3 The stray reflected radiation Ls' is shown in the figure.

[0074] In this way, by appropriately determining the density variations provided by the metastructures 30 and 31, as shown in the following reference... Figures 5 to 18As described in detail, stray reflected radiation Ls can be oriented in a direction that does not interfere with the target, along the propagation path of reflected light radiation LR.

[0075] In fact, as mentioned above in Yu et al.'s article "Flat optics with designer metasurfaces", the metastructures 30 and 31 cause a phase delay in stray reflected radiation Ls relative to incident radiation Li.

[0076] In this regard, please also see Figure 4 This illustrates the effect of a linear curve of phase delay Δφ with a phase delay distribution P along the second axis X, according to Huygens' principle. It can be noted that the linear phase delay causes the reflected light radiation LR to be tilted relative to the incident light radiation Li perpendicular to the second axis X.

[0077] In fact, the phase delay Δφ caused by light radiation with wavelength λ passing through a material with refractive index n along the second axis X is:

[0078]

[0079] As described above, in the MEMS mirror device 20, a linear distribution of the phase delay P is obtained through the linearly variable density arrangement of the diffractive optical elements 35 of the element structures 30 and 31. (Refer to...) Figure 5 Generally, the metastructures 30, 31 may include a plurality of basic units 40, each unit being formed by diffractive optical elements 35 arranged in a linearly variable density such that the corresponding phase retardation distribution P is arranged to form a sawtooth pattern. In one embodiment, the basic unit 40 includes at least four diffractive optical elements 35.

[0080] In addition, Figure 5 In this arrangement, the basic units 40 are arranged at a distance equal to a multiple of 2πλ, such that the interference of stray light radiation Ls is always of the constructive type.

[0081] Therefore, as a result of the configuration of the metastructures 30 and 31, the cover 26 produces tilted reflected light radiation LR.

[0082] As described below, configurations of metastructures 30 and 31 with linearly variable density can be obtained.

[0083] Figure 6 and Figure 7 Metastructures 30 and 31 are shown, which can be used... Figure 3 The MEMS micromirror device 20 is formed from a single basic unit 40. Here, the diffractive optical element 35 is formed from a column 50 having a cylindrical shape with an increased diameter in the first extending direction X.

[0084] The pillars 50 are made of a material with a high contrast refractive index relative to the medium they are immersed in (here, air). For example, the difference between the refractive index of the material of the pillars 50 and the refractive index of the medium in which they are situated (at the frequency of the light used) can be at least +0.5, for example, ≥ +1. According to one embodiment, the pillars 50 are made of a dielectric material such as amorphous silicon, silicon nitride, or titanium dioxide, and are formed directly on and protrude from the cover 26, without any material disposed between the covers 26.

[0085] exist Figure 6 and Figure 7 In one embodiment, the columns 50 are arranged in rows 51 along a first axis Y, perpendicular to a first extending direction X, and forming a second extending direction; the rows 51 are arranged at a fixed distance (with a first spacing P1) along the first extending direction X; the columns 50 in each row 51 are arranged at a fixed distance (with a second spacing P2) along the second extending direction Y; furthermore, the columns 50 in each row 51 are offset from the columns 50 in the adjacent rows 51 by a distance equal to half the second spacing P2, so as to make optimal use of the area of ​​the basic unit 40.

[0086] When the MEMS micromirror device 20 is designed to operate in visible light, the pillar 50 typically has a height H ranging from 100 to 200 nm. Figure 7 The base diameter is between 10 and 200 nm, or between 50 and 500 nm if it operates in the infrared. Furthermore, a first spacing P1 may be between 50 and 200 nm, and a second spacing P2 may be between 50 and 200 nm.

[0087] exist Figure 6 and Figure 7 In the middle, the change in the size of the pillar 50 in the first extending direction X allows for an increasing density of diffractive material from left to right; therefore, the reflected light radiation LR has an increasing phase retardation to the right, and the reflected light radiation Lr is tilted relative to the incident light radiation Li, as previously referenced. Figures 4 to 5 As stated above.

[0088] Figure 8 and Figure 9 Metastructures 30 and 31 are shown, comprising a plurality of basic units 40 arranged side by side in a first extending direction X.

[0089] Column 50 may have dimensions and a first spacing P1 and a second spacing P2, and may be as referenced. Figure 6 and Figure 7 Obtained as described in detail.

[0090] Figure 10 and Figure 11Metastructures 30, 31 comprising multiple basic units 40 are shown, wherein diffractive optical elements 35 are formed by pillars 55 having a cylindrical shape and a constant diameter, the pillars 55 being arranged at decreasing distances from each other in a first extending direction X. The pillars 55 are also arranged here at a constant distance from each other along the axis Y, and in effect form rows (again denoted as 51) arranged at a variable and linearly decreasing spacing P1. In this case, the second spacing P2 (the distance between pillars 55 in the second extending direction Y) is also constant; furthermore, here, the pillars 55 of each row 51 are also aligned in the first extending direction X.

[0091] Therefore, the first spacing P1 varies between the maximum and minimum values ​​shown above for column 55. Similarly, the second spacing P2 and the diameter D of column 55 can be shown above. Figure 6 and Figure 7 The values ​​shown in the examples vary between them.

[0092] Therefore, in the same case, an increasing density of diffractive material is obtained from left to right, so as to cause the reflected light radiation Lr to tilt relative to the incident light radiation Li. Figure 5 ).

[0093] exist Figure 12 and Figure 13 In the metastructures 30 and 31, the basic unit 40 includes a diffractive optical element 35, which is formed by pillars 60 of variable size and arranged at variable distances.

[0094] In fact, in this embodiment, both the first spacing P1 and the diameter D change along the first extending direction X. Furthermore, in this case, an increasing diffraction material density is thus obtained from left to right.

[0095] Figure 14 It shows Figure 6 A variant of the configuration. Here, the diffractive optical element 35 is formed of a column 61 having a polyhedral shape (hexagonal in the figure) with an increasing diameter in the first extending direction X, and arranged at constant spacings P1 and P2. In this embodiment, the side view is... Figure 7 same.

[0096] Figure 15 It shows Figure 6 Another variation of the configuration. Here, the diffractive optical element 35 is formed by a column 62 with a long side parallel to the second extending direction Y and a short side increasing along the first extending direction X. Here, the first spacing P1 is constant, and the side view is the same as... Figure 7 same.

[0097] Figure 16The arrangement of metastructures 30 and 31 on the two surfaces 26A and 26B of the cover 26 is shown. To achieve the same reflected light radiation tilting effect, metastructures 30 and 31 have identical structures, i.e., the same direction and degree of variation of the diffraction material density. Thus, metastructures 30 and 31 produce two equal phase retardation distributions P, and therefore...

[0098] Δφ2=Δφ1

[0099] Where Δφ2 is the phase delay on the second surface 26B, and Δφ1 is the phase delay on the first surface 26A. In particular, metastructures 30 and 31 are equal (i.e., they consist of only pillar 50 or pillar 55 or pillar 60), even though they do not necessarily have to be perpendicularly aligned with each other.

[0100] Figure 17 One embodiment is shown in which pillars 50, 55, or 60 are embedded in a dielectric layer 65 of a material with a refractive index lower than that of pillars 50, 55, or 60, such as silicon dioxide, extending on a first surface 26A and / or a second surface 26B of cap 26.

[0101] Figure 18 Different embodiments are shown, wherein the diffractive optical element is formed by a cavity or opening 66 in the diffractive layer 67, particularly through an opening, the diffractive layer 67 extending on a first surface 26A and / or a second surface 26B of the cover 26, and having a refractive index such that the difference between the refractive index of the diffractive layer 67 and that of air (at the frequency of the light used) is greater than or equal to 0.5. For example, the diffractive layer 67 may be silicon oxide.

[0102] Figure 19 Different embodiments of the MEMS micromirror device 70 are shown.

[0103] Micromirror device 70 has similar Figure 3 The structure of the MEMS micromirror device 20 is described; therefore, similar parts are designated with the same reference numerals and will not be described further.

[0104] exist Figure 19 In one embodiment, the cover, indicated by 76, has a standard planar structure. An anti-reflective layer (not shown) may be disposed on its first surface 26A or on both surfaces 76, 76B.

[0105] The third element 32 is formed on the reflective surface 21A of the tiltable platform 21.

[0106] For example, such as Figure 20 As shown, the tiltable platform 21 has a metallization layer 28, such as gold or aluminum, which forms a reflective surface 21A, and the third element structure 32 is disposed directly on the metallization layer 28.

[0107] Optionally, such as Figure 21 As shown, the metallization layer 28 is covered by a dielectric layer 29, such as silicon oxide, and a third-order structure 32 is formed on the dielectric layer 29.

[0108] The third-order structure 32 can be configured in any of the ways described above, and in Figures 6 to 18 The first element structure 30 and the second element structure 31 are shown in the diagram; therefore, it includes a plurality of diffractive optical elements 35 (e.g., pillars 50, 55, 60, 61 or 62, which are surrounded by air or by a dielectric layer 65 or Figure 16 (The opening 66 surrounds it). In addition, it can include multiple basic units 40.

[0109] Metastructures 30-32 can be fabricated using photolithography steps for processing components with dimensions smaller than the wavelength of light (see, for example, the article “Large area pixelated metasurface beam deflector on a 12-inch glass wafer for random point generation” by Nanxi Li et al. in Nano Photosonics 2019; 8(10): pp. 1855-1861, which is incorporated herein by reference). Alternatively, nanoimprint lithography can also be used.

[0110] Specifically, the MEMS micromirror devices 20 and 70 can be processed at the wafer level. In this case, the body 22 and the tiltable platform 21 can be formed in a semiconductor material wafer for multiple devices; glass wafers can be processed to form the device's metastructures 30-32. The two wafers can then be bonded and diced to obtain multiple individual MEMS micromirror devices 20 or 70.

[0111] Figure 22 Different embodiments of the MEMS micromirror device 100 are shown.

[0112] Micromirror device 100 has similar Figure 19 The structure of the MEMS micromirror device 70 is described below; therefore, similar parts are designated with the same reference numerals and will not be described further. However, unlike micromirror devices 20 and 70, there is no meta-surface (i.e., no meta-structure).

[0113] The micromirror device 100 includes an optical waveguide 102 extending between a cover 76 and a body 22, for example, facing a sidewall 24A of the package 24. Specifically, the optical waveguide 102 extends between the cover 76 and an adhesive layer 27, and is optionally integral with the cover 76. The optical waveguide 102 is made of a transparent material (e.g., glass) and is designed to guide incident light radiation Li emitted by a light source 104 outside the package 24 by allowing the light source 104 to propagate from the light source 104 to the reflective surface 21A. Specifically, the optical waveguide 102 defines the optical path of the incident light radiation Li along its main extension direction 106 (e.g., parallel to a second axis X).

[0114] Optical waveguide 102 has an input terminal 102A and an output terminal 102B that are opposite each other relative to the main extension direction 106. Input terminal 102A faces the exterior of the MEMS micromirror device 100 (i.e., the environment outside cavity 23), while output terminal 102 faces cavity 23 and therefore faces reflective surface 21A (e.g., which extends within cavity 23). In use, input terminal 102A of optical waveguide 102 is optically coupled to (e.g., facing) a light source 104 that emits incident light radiation Li; thus, incident light radiation Li enters optical waveguide 102 through input terminal 102A and is guided by optical waveguide 102 to exit optical waveguide 102 through output terminal 102B. Figure 23 As better shown in the diagram, the light source 104, the optical waveguide 102, and the tiltable platform 21 are aligned between them along the main extension direction 106.

[0115] The output terminal 102B is shaped to deflect the incident light radiation Li toward the reflective surface 21A. Specifically, the output terminal 102B is formed by a triangular tip having a deflection surface 108 that is inclined relative to the main extension direction 106. Specifically, the deflection surface 108 faces the cover 76 and forms an inclination angle θ with it (e.g., defined between the deflection surface 108 and the second surface 76B (also referred to as the bottom surface 76B) of the cover 76).

[0116] Therefore, the incident light radiating Li has a first segment and a second segment. The first segment is generally linear and extends along the main extension direction 106 in the optical waveguide 102 until it reaches the deflection surface 108. The second segment is generally linear and inclined relative to the main extension direction 106. The second segment extends from the deflection surface 108 to the reflection surface 21A in the cavity 23.

[0117] exist Figure 22In this embodiment, the tilt angle θ is designed to prevent total internal reflection (TIR) ​​at the deflection surface 108. Therefore, the incident light radiation Li is substantially unreflected through the deflection surface 108 (e.g., with minor and stray reflections due to the refractive index difference between the optical waveguide 102 and the cavity 23, and for example, less than about 4% of the incident light radiation Li; alternatively, an anti-reflective coating ARC may also be used on the deflection surface 108 to suppress these minor and stray reflections), and the anti-reflective coating is deflected toward the reflective surface 21A due to the change in refractive index experienced between the optical waveguide 102 and the cavity 23 at the deflection surface 108. This is achieved by designing the optical waveguide 102 such that the tilt angle θ is greater than a threshold tilt angle.

[0118] As a non-limiting example, when the optical waveguide 102 is made of glass, the tilt angle θ is greater than about 50° and equal to, for example, 60°. In other words, the incident light radiation Li (considered a linear beam whose propagation direction is substantially parallel to the main extension direction 106) forms an angle of incidence (not shown) on the deflection surface 108 and relative to the normal direction orthogonal to the deflection surface 108, which is complementary to the tilt angle θ with respect to known geometric properties; therefore, when the optical waveguide 102 is made of glass, the angle of incidence is less than about 40° and equal to, for example, 30°. However, these values ​​of the tilt angle θ and the angle of incidence are provided only as examples and are not intended to limit the invention, as the threshold tilt angle depends on the material used to implement the optical waveguide 102; other values ​​can be similarly considered when other materials are used to implement the optical waveguide 102 in a manner known per se. For example, if a metal layer (e.g., aluminum) is present on the deflection surface 108, the threshold tilt angle increases.

[0119] Figure 23 A top view of the micromirror device 100 in the horizontal XY plane is shown. As shown, the main extension direction 106 of the optical waveguide 102 can be perpendicular to the oscillation axis 25 (here it is exemplarily shown to be parallel to the first axis Y, while the main extension direction 106 is exemplarily shown to be parallel to the second axis X).

[0120] However, according to Figure 24 In a variation of the micromirror device 100 shown, the optical waveguide 102 can be arranged parallel to the oscillation axis 25 relative to the tiltable platform 21. In other words, the main extension direction 106 of the optical waveguide 102 can be parallel to the oscillation axis 25, and thus extend parallel to the first axis Y.

[0121] also, Figure 25Different embodiments of the micromirror device 100 are shown, wherein the tilt angle θ is designed such that total internal reflection (TIR) ​​occurs at the deflection surface 108. Therefore, incident light radiation Li traveling in the optical waveguide 102 is completely reflected at the deflection surface 108 towards the reflecting surface 21A, thus exiting the optical waveguide 102 from the bottom surface 110 facing the reflecting surface 21A (specifically, due to the refractive index difference between the optical waveguide 102 and the cavity 23). This is achieved by designing the optical waveguide 102 such that the tilt angle θ is below a threshold tilt angle.

[0122] As a non-limiting example, when the optical waveguide 102 is made of glass, the tilt angle θ is less than about 50° and equal to, for example, 40°. In other words, when the optical waveguide 102 is made of glass, the incident angle is greater than about 40° and equal to, for example, 50°.

[0123] The MEMS micromirror devices 20 and 70 described in this article have many advantages.

[0124] It solves the problem of unwanted reflected radiation at a low cost because it is able to use wafer-level processing technology, employing the usual techniques for manufacturing semiconductors from standard flat wafers, as described above.

[0125] In addition, the MEMS micromirror devices 20 and 70 have small overall dimensions, also because the covers 26 and 76 are essentially flat, and the metastructures 30-32 have a thickness that is smaller than the radiation wavelength designed for the MEMS micromirror devices 20 and 70.

[0126] Furthermore, using an optical waveguide 102 to avoid stray reflections at the cover is a simple and robust solution to manufacture. Specifically, Figure 22 The MEMS micromirror device 100 exhibits a reduced size, thereby minimizing its burden, while Figure 25 The MEMS micromirror device 100 maximizes optical efficiency by using TIR.

[0127] Finally, it is clear that modifications and variations can be made to the MEMS micromirror devices described and illustrated herein without departing from the scope of the invention as defined in the appended claims. For example, the different embodiments described can be combined to provide further solutions.

[0128] Furthermore, the MEMS micromirror device can be biaxial. In particular, when the MEMS micromirror device 20 is biaxial and is therefore configured to rotate about two axes, the metastructures 30-32 can have a linearly variable density along one of the two directions parallel to the rotation axis or along the middle direction between them.

[0129] The diffractive optical element 35 can have different shapes other than those described above.

[0130] If desired, a first element 30 and a second element 31 can be provided on the cover 26, and a third element 32 can be provided on the tiltable platform 21. Furthermore, at least the third element 32 on the tiltable platform 21 can be combined with the optical waveguide 102 to further improve the optical characteristics of the MEMS micromirror device.

[0131] Although this disclosure has been described with respect to a limited number of embodiments, those skilled in the art who benefit from this disclosure will understand that other embodiments can be conceived without departing from the scope of this disclosure. Therefore, the scope of this disclosure is limited only by the appended claims.

Claims

1. A MEMS micromirror device, comprising: An encapsulation comprising a housing and a cover transparent to light radiation, the encapsulation forming a cavity; and A tiltable platform is housed within the cavity and has a reflective surface; as well as An optical waveguide having: an input end facing the outside of the cavity and configured to be optically connected to a light source; and an output end extending within the cavity, the optical waveguide being configured to receive the light radiation emitted by the light source through the input end and to guide the light radiation to the reflective surface; The optical waveguide is integral with the cover; The accommodator includes a cup-shaped body having a bottom and sidewalls joined together to define the cavity, a cover being secured to the sidewalls by an adhesive layer, and an optical waveguide extending between the cover and the adhesive layer such that the cover covers the cavity.

2. The MEMS micromirror device of claim 1, wherein the optical waveguide extends between the cover and the housing, wherein the input end and the output end are opposite to each other along the main extension direction of the optical waveguide, and wherein the output end of the optical waveguide includes a deflection surface that is inclined relative to the main extension direction, faces the bottom surface of the cover, and forms an inclination angle θ with the bottom surface.

3. The MEMS micromirror device according to claim 2, wherein the tilt angle θ is greater than a threshold tilt angle, such that the light radiation passes through the deflection surface and is deflected on the reflective surface.

4. The MEMS micromirror device of claim 2, wherein the tilt angle θ is below a threshold tilt angle, such that the light radiation is reflected at the deflection surface for total internal reflection, and is deflected on the reflecting surface.

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