Scanning mirror system and method of manufacture

Abstract

Scanning micromirror devices, methods of manufacturing scanning micromirror devices, two-dimensional optical scanning systems including scanning micromirror devices, and methods of projecting light and images using two-dimensional optical scanning systems are described. The disclosed two-dimensional optical scanning systems can include a first scanning micromirror device oscillating at a relatively higher frequency that directs reflected light to a second scanning micromirror device oscillating at a relatively lower frequency that directs the reflected light for projection.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit and priority of U.S. Provisional Application No. 62 / 962,168, filed January 16, 2020, and U.S. Provisional Application No. 63 / 058,384, filed July 29, 2020, which are incorporated herein by reference in their entirety. Background Technology

[0003] Digital micromirror devices have been used in image projection systems. For example, U.S. Patent 6,856,446 describes a micromirror array in which a number of individually hinged and controllable micromirror elements can be used to control the direction of reflected light to project an array of digital pixels. These devices typically require the use of a color wheel or three separate pixel arrays for different colors to project a full-color image and often employ large, high-intensity light sources, which limits the compactness of the projection system. Summary of the Invention

[0004] This disclosure relates to a two-dimensional scanning micromirror system and its use in image projection systems and methods. The disclosed two-dimensional scanning micromirror system is advantageously used to drive reflected light in two directions and can be more robust and compact than other reflective scanning systems. The disclosed two-dimensional scanning micromirror system can utilize two separate uniaxial micromirror devices to scan the beam in orthogonal directions.

[0005] In a first aspect, an optical scanning system is disclosed. The optical scanning system may include one or more scanning micromirror devices for projecting and scanning a light beam. In some cases, two scanning micromirror devices may be used sequentially, a first scanning micromirror device for scanning along a first direction, and a second scanning micromirror device in optical communication with the first scanning micromirror device for scanning along a second direction. Optionally, an hermetically sealed enclosure may be used to maintain a lower pressure inside the hermetically sealed enclosure at the scanning micromirror device than outside the hermetically sealed enclosure. In some embodiments, an optical repeater may be used to provide optical communication between the first and second scanning micromirror devices. Exemplary optical repeaters include, but are not limited to, the optical repeater described in U.S. Provisional Application No. 62 / 964,508, filed January 22, 2020, which is incorporated herein by reference. The optical scanning system may include a light source arranged to direct emitted light to a first reflector of the first scanning micromirror device. The light source may be modulated to allow control of color and / or intensity based on time and / or the projection position of light reflected from the scanning micromirror device to allow image display.

[0006] An example scanning micromirror device includes: a first platform coupled to a first base via a plurality of first support flexures, for example, wherein the first platform is oscillable about a first axis; a stress-relief layer located on a first side of the first platform; a first reflector located on the first side of the first platform, for example, wherein the stress-relief layer is located between the first reflector and the first platform; a first conductive coil located on a second side of the first platform opposite to the first side of the first platform, the first conductive coil being arranged to apply a magnetic force to the first platform about the first axis; and a first magnetic field source arranged to apply a first magnetic field to the first platform. Useful scanning micromirror devices include, but are not limited to, scanning micromirror devices with inherent resonant frequencies in the range of 1 kHz to 10 MHz.

[0007] In some cases, a thick platform can be used in scanning micromirror devices of this type. Although other components are included in the thick platform, it allows the reflector of the micromirror device to be robust and have good flatness. In some examples, the first platform can have a thickness between 100 μm and 500 μm. The use of a stress-relief layer can also improve the flatness of the reflector by allowing stresses on different sides of the platform to cancel each other out, resulting in good flatness of the reflector. In some examples, the stress-relief layer provides a first stress distribution on the first side of the first platform, while the first conductive coil provides a second stress distribution on the second side of the first platform. Therefore, the first stress distribution and the second stress distribution can be opposite to each other and result in at least partial cancellation. In some cases, the first conductive coil can be embedded in the second side of the first platform (e.g., positioned in one or more trenches on the first platform), or it can be located above and supported by the second side of the first platform (e.g., as a partial overlay).

[0008] Electromagnetic actuation can be used to actuate the scanning micromirror device, for example, in which current through a conductive coil interacts with a magnetic field and where the current is inherently oscillating to drive an oscillating force and / or oscillation of the platform. For example, a first magnetic field source can be arranged to provide a first magnetic field orthogonally oriented to a first axis. The scanning micromirror device may also include multiple conductive traces located on the plurality of support flexures, for example, to provide electrical communication with the conductive coils. In some cases, the conductive traces can apply strain to the support flexures, thus requiring the conductive traces to be arranged in a configuration on the plurality of support flexures to apply opposing stresses on different sides of the plurality of first support flexures, which may help avoid, reduce, or limit nonlinear effects.

[0009] In some cases, the scanning micromirror device may include additional components, such as actuation components or sensor components. In one example, the scanning micromirror device may also include one or more piezoelectric actuators arranged to apply force to cause the first platform to oscillate about the first axis or to sense the oscillation or position of the first platform about the first axis.

[0010] Another example scanning micromirror device includes: a first frame coupled to a second base via a plurality of second supporting flexible members, for example, wherein the first frame is oscillable about a second axis; a second platform coupled to the first frame, for example, wherein the second platform is oscillable together with the first frame about the second axis; a second reflector located on the second platform; a second conductive coil located on the first frame, the second conductive coil being arranged to apply a magnetic force to the first frame about the second axis; and a second magnetic field source arranged to apply a second magnetic field to the first frame. Useful scanning micromirror devices include, but are not limited to, scanning micromirror devices with inherent resonant frequencies in the range of 15 Hz to 2 kHz.

[0011] In some examples, the scanning micromirror device may further include a second frame coupled between the first frame and the second platform, for example, wherein the second frame is coupled to the first frame via a plurality of third support flexures, and wherein the second frame is oscillable about a second axis together with the first frame and the second platform. In some examples, such an intermediate frame may include other components, such as sensors or actuators. For example, in some embodiments, the scanning micromirror device may further include a temperature sensor contained within the second frame. Optionally, the second scanning micromirror device may further include a strain sensor contained within the second frame. Optionally, the second scanning micromirror device may further include a plurality of piezoelectric actuators contained within the second frame, such as piezoelectric actuators arranged to change or sense the position of the second platform about a third axis orthogonal to the second axis or to change or sense the curvature of the second platform.

[0012] This document also describes methods for projecting images. One example method includes: providing a two-dimensional optical scanning system, such as a two-dimensional optical scanning system comprising a first scanning micromirror device and a second scanning micromirror device in optical communication with the first scanning micromirror device; inducing a first oscillation of the first scanning micromirror device at a first frequency; inducing a second oscillation of the second scanning micromirror device at a second frequency, for example, wherein the second frequency is optionally less than the first frequency; and illuminating a first reflector of the first scanning micromirror device with a light source to generate reflected light, the reflected light being directed to the second scanning micromirror device and reflected by a second reflector of the second scanning micromirror device to generate output reflected light. The first and second scanning micromirror devices may independently correspond to different scanning micromirror devices described herein. Optionally, this aspect of the method may further include directing the output reflected light from the second scanning micromirror device to an eyepiece. This aspect of the method may also include synchronously controlling the oscillation of the first scanning micromirror device, the oscillation of the second scanning micromirror device, and the output color and / or intensity of the light from the light source. Such a configuration may be useful for plotting images or image domains and sequences of images or image domains.

[0013] The disclosed scanning micromirror device and projection method can be advantageously used in head-mounted display systems. An example head-mounted display system may include a two-dimensional optical scanning system; and an eyepiece comprising one or more optical components configured to receive light reflected or output from the two-dimensional optical scanning system and redirect it to one or both eyes of a user. A head-mounted display system may include control circuitry operatively coupled to a light source and the scanning micromirror device of the two-dimensional optical scanning system to allow the display of an image. For example, the control circuitry may be configured to display one or more images by synchronously performing the following operations: controlling the light source to emit light corresponding to pixels of the one or more images; controlling the flow of current in a first conductive coil of a first scanning micromirror device to cause oscillation of the first scanning micromirror device or its platform; and controlling the flow of current in a second conductive coil of a second scanning micromirror device to cause oscillation of the second scanning micromirror device or its platform.

[0014] On the other hand, a method for fabricating a scanning micromirror device using microfabrication techniques is disclosed. Specific example methods are described below in the detailed description and accompanying drawings. Further, additional features, benefits, and embodiments are described below in the detailed description, accompanying drawings, and claims. Attached Figure Description

[0015] Figure 1 A schematic diagram of an example image projection system is provided.

[0016] Figure 2AA schematic diagram of the bottom surface of an example scanning micromirror device is shown. Figure 2B A schematic cross-sectional view of an example scanning micromirror device is shown. Figure 2C A schematic cross-sectional view of an example scanning micromirror device in hermetically sealed or vacuum-sealed packaging is shown.

[0017] Figure 3A A schematic diagram of the top surface of an example scanning micromirror device is shown. Figure 3B A cross-sectional schematic diagram of an example scanning micromirror device is shown. Figure 3C and 3D A schematic diagram of an example scanning micromirror device is provided to illustrate additional features.

[0018] Figure 4 An overview of example methods for projecting images using a two-dimensional scanning micromirror device is provided.

[0019] Figure 5A , Figure 5B , Figure 5C , Figure 5D , Figure 5E , Figure 5F and Figure 5G Schematic diagrams are provided at various points in the manufacturing process for the example scanning micromirror device.

[0020] Figure 6A , Figure 6B , Figure 6C , Figure 6D , Figure 6E , Figure 6F , Figure 6G and Figure 6H Schematic diagrams are provided of various points in the manufacturing process for another example scanning micromirror device.

[0021] Figure 7A , Figure 7B , Figure 7C , Figure 7D , Figure 7E , Figure 7F and Figure 7G Schematic diagrams are provided of various points in the example manufacturing / assembly process of vacuum packaging of scanning micromirror devices. Detailed Implementation

[0022] This document describes a scanning micromirror device, a method for manufacturing a scanning micromirror device, a two-dimensional optical scanning system including a scanning micromirror device, and a method for projecting light and images using the two-dimensional optical scanning system. The disclosed two-dimensional optical scanning system may include a first scanning micromirror device oscillating at a relatively high frequency, which guides reflected light to a second scanning micromirror device oscillating at a relatively low frequency, which guides the reflected light for projection.

[0023] The disclosed scanning micromirror devices exhibit features that provide benefits for two-dimensional optical scanning and image projection. For example, some scanning micromirror devices are configured to achieve a high degree of flatness of the reflective elements of the scanning mirror while allowing good or precise control over the oscillations of the scanning micromirror. Some scanning micromirror devices may include sensor elements and control elements to allow monitoring of conditions such as temperature, strain, or position. Some scanning micromirror devices may include actuators, for example, for changing the relative position of the reflective elements or altering or achieving a high or even higher degree of flatness. The disclosed scanning micromirror devices may employ electromagnetic actuation, wherein a conductive coil is located on the platform of the scanning micromirror device to apply a magnetic force, thereby causing the scanning micromirror device to oscillate.

[0024] In some cases, the disclosed scanning micromirror apparatus can be very thick, for example, thicker than conventional scanning micromirror apparatuses. This allows for improved flatness of the reflector on the platform of the scanning micromirror apparatus. In some examples, the thickness of the platform of the scanning micromirror apparatus can be between 100 μm and 500 μm, for example, within the ranges of 100 μm to 150 μm, 150 μm to 200 μm, 200 μm to 250 μm, 250 μm to 300 μm, 300 μm to 350 μm, 350 μm to 400 μm, 400 μm to 450 μm, 450 μm to 500 μm, or any value between specified ranges. In some cases, a thicker platform can increase the power requirements for driving oscillations, although operation under natural resonance limits the power requirements. However, the increased power requirements can be offset by the ability to maintain the flatness of the reflector, which would otherwise result in undesirable images or projection artifacts.

[0025] The disclosed scanning micromirror device can be used for image projection, such as projecting light for a user to view. In some cases, the disclosed scanning micromirror device and image projection system can be used in head-mounted display devices, for example, because they are compact and capable of projecting high-quality images using low-power operation.

[0026] Figure 1A schematic diagram of an example image projection system 100 is provided. The image projection system 100 includes a first scanning micromirror device 105, which includes a first reflector 110; and a second scanning micromirror device 115, which includes a second reflector 120. The image projection system 100 also includes a light source 125 arranged in optical communication with the first reflector 110 to guide light 130 from the light source 125 to the first reflector 110, wherein the light is reflected toward the second reflector 120, and from there, is output for projection. The movement of the first scanning micromirror device 105 and the second scanning micromirror device 115 can be driven in such a way as to guide the output reflected light 130 to a projection plane 135. By utilizing the oscillating motion of the first scanning micromirror device 105 and the second scanning micromirror device 115 to control the color, intensity, and timing of the light 130 output by the light source 125, the output light 140 can generate an image at the projection plane 135. By repeated scanning, images and / or video sequences can be projected.

[0027] In some examples, the first scanning micromirror device 105 can oscillate about a first axis, such that the output reflected light 140 can form a series of horizontal (from left to right and from right to left) passes, while the second scanning micromirror device 115 can oscillate about a second axis, such that the output reflected light 140 can also oscillate vertically across the projection plane 135 from top to bottom and / or from bottom to top. The oscillation frequency along the horizontal direction can be very fast, such as, for example, in the range of 1 kHz to 10 MHz. Some projection systems can use a sawtooth or triangular oscillation pattern along the vertical direction, which may be useful for creating regularly spaced horizontal passes in a vertical direction (e.g., from top to bottom), although a sinusoidal oscillation pattern can also be used. The oscillation frequency along the vertical direction can be slower, such as, for example, in the range of 15 Hz to 2 kHz. If only repeated projection from top to bottom is desired, a blanking period can be used during which the light source 125 does not generate light, and the second scanning micromirror device 115 oscillates in the upward direction. However, in some cases, both top-to-bottom and bottom-to-top projection can be used. The blanking period can also be used at the extremes of horizontal dimensions to avoid projection at the side edges of the projection plane 135.

[0028] It will be understood that references to the horizontal (or left-to-right and right-to-left) and vertical (or bottom-to-top and top-to-bottom) directions are merely references. Figure 1 An example of the orientation markings of the projection plane 135 is shown. Other configurations, such as switching between horizontal and vertical markings or using other markings, are contemplated within the scope of this disclosure.

[0029] Image projection system 100 may be a component of an optical projector, for example, an optical projector used to project still images or video images onto a projection plane. In some cases, image projection system 100 may be a component of a head-mounted display device and / or for coupling the projected light to an eyepiece, such as the eyepiece of a head-mounted display device. In some examples, projection plane 135 may correspond to the eyepiece or the user's retina. Image projection system 100 may optionally include projection optics, such as mirrors, lenses, collimators, filters, gratings, etc., which in... Figure 1 Not shown, but may be located, for example, in the optical path between light source 125 and projection plane 135. In some cases, an optical repeater 145, including multiple reflecting and / or focusing elements, may be used between the first scanning micromirror device 105 and the second scanning micromirror device 115 to guide light reflected from the first mirror 110 onto the second mirror 120. Light source 125 may be a monochromatic or multicolor light source and may include, for example, a light-emitting diode or a laser source, which may output switchable or modulated light at high rates (e.g., up to 100 MHz). Optionally, light source 125 may include or correspond to multiple individually modulated light sources, such as outputting different colors (e.g., red, green, blue).

[0030] Figure 2A A schematic diagram of an example scanning micromirror device 200 is provided. The scanning micromirror device 200 may include silicon or other materials, thereby allowing patterning and fabrication according to known microfabrication techniques. The scanning micromirror device 200 includes a base 205 and a platform 210, the platform 210 being coupled to the base 205 via a plurality of support flexures 215. The support flexures 215 are configured and arranged to allow the platform 210 to oscillate about an axis 220, as schematically shown by arrow 245. Figure 2A The specific configuration of the supporting flexible elements 215 shown can, in some cases, be referred to as torsion beams because they support the oscillation of the platform 210 about axis 220 through partial rotation relative to the base 205. Although the base 205 is... Figure 2A The image shows a frame surrounding other components, but the base 205 may extend in other directions or be positioned differently relative to the platform 210, for example, below the first platform 210. The reflector 225 may be positioned on the opposite surface of the platform 210, such as... Figure 2A As shown.

[0031] The scanning micromirror device 200 also includes a conductive trace 230 that forms a conductive coil 235 at the platform 210. The conductive coil 235 can be used to apply a force (e.g., magnetic / electromagnetic force) to the platform 210 to cause the platform 210 to oscillate about the axis 220. The conductive coil 235 can have any suitable number of turns. In some cases, the conductive trace 230, which transmits current from a current source via contact 240 to the conductive coil 235, can increase the stiffness of the support flexibility 215. Since the support flexibility 215 can bend and / or move during the oscillation as the support flexibility 215 rotates, the additional stiffness imparted by the conductive trace 230 is time-dependent, as the additional stiffness depends on the scanning angle, which can lead to some nonlinearity in the oscillation of the platform 210 about the axis 220. Narrower and / or thinner conductive traces 230 can offset or minimize this nonlinearity; however, smaller or thinner conductive traces 230 may increase the resistance and power consumption of the device. Therefore, in some embodiments, increasing the width of the conductive traces 230 may be advantageous, for example, by occupying as much of the surface of the supporting flexible element 215 as possible (i.e., up to the entire width). Furthermore, the conductive traces 230 may simultaneously be located on one side of the scanning micromirror device 200 (e.g., ...). Figure 2A (As shown) and the opposite side, to counteract disturbances. In addition to electromagnetic actuation implemented using conductive coil 235, other actuators, such as piezoelectric actuators, electrostatic actuators, etc., can be used. In some cases, piezoelectric actuators or electrostatic actuators can be used to sense the position, scanning angle, or oscillation of the sensing platform 210.

[0032] Figure 2B A schematic cross-sectional view of an example scanning micromirror device 200 is shown. It should be understood that... Figure 2A and 2B The configuration shown is for illustrative purposes only and may not be drawn to scale. Figure 2B In the diagram, axis 220 extends into and out of the plane, and the oscillation of platform 210 is schematically shown by arrow 245. A magnetic source 250 is shown, positioned to provide a magnetic field at platform 210. The magnetic field can interact with a current flowing through conductive coil 235 to impart a force on platform 210 to induce oscillation, for example, by passing alternating current through conductive coil 235. Other forms of actuators, such as piezoelectric or electrostatic actuators, can be used as a complement or alternative to electromagnetic actuation. Reflector 225 is shown located on the opposite side of platform 210. For example, reflector 225 may comprise a metallic reflector or a dielectric reflector, or a combination thereof.

[0033] The presence of the conductive coil 235 applies stress to the platform 210, which interferes with the flatness of the reflector 225. To counteract the effects of the stress imposed by the conductive coil 235, a stress-relief layer 255 may be positioned between the reflector 225 and the platform 210. The stress-relief layer 255 may apply a stress to the platform 210 opposite to that imposed by the conductive coil 235. The stress-relief layer 255 and the conductive coil 235 may be made of the same material and / or may have the same volume on the platform 210 to minimize or reduce the total applied stress and limit interference with the flatness of the reflector 225.

[0034] The scanning micromirror device 200 is configured for relatively high-frequency oscillations, for example, in the range of 1 kHz to 10 MHz. To reduce the power consumed by actuation and oscillation of the driving platform 210, the device can operate at its resonant frequency, which generates a quality factor (Q) that amplifies the displacement achieved by actuation. Therefore, the inherent resonant frequency of the platform 210 oscillating about axis 220 is in the range of 1 kHz to 10 MHz.

[0035] In some cases, further improvements in quality factor can be achieved by using vacuum or hermetically sealed packaging. Figure 2C A schematic cross-sectional view of a scanning micromirror device 200 including a vacuum-encapsulated package is shown. The vacuum package may include a transparent top component 260 and a bottom component 265. The top component 260 may be transparent to allow light to pass through and may optionally include an anti-reflective coating on one or more surfaces to minimize surface reflection. Example materials for the top component 260 may include glass or a crystalline material. The bottom component 265 may be positioned adjacent to a magnetic source 250 and may include a transparent or opaque material. In some examples, the bottom component 265 may include silicon. The top component 260 and the bottom component 265 may be sealed relative to a base 205, for example, using frit paste.

[0036] Figure 3A and Figure 3BTop and cross-sectional schematics of another example scanning micromirror device 300 are provided. The scanning micromirror device 300 may include silicon or other materials, allowing for patterning and fabrication according to known microfabrication techniques. The scanning micromirror device 300 includes a base 305 and a first frame 310 coupled to the base 305 via a plurality of support flexures 315. The support flexures 315 are configured and arranged to allow oscillation of the first frame 310 and internal or associated components about an axis 320, as schematically indicated by arrow 345. The scanning micromirror device 300 also includes a platform 325 and a second frame 330 located between the platform 325 and the first frame 310. A conductive coil 335 is shown located on the first frame 310, and a reflector 340 is shown located on the platform 325. Conductive traces (not shown) may pass through the support flexures 315 to provide current to and / or provide current from the conductive coil 335. The conductive coil 335 may have any suitable number of turns.

[0037] A magnetic source 350 is shown, positioned to provide a magnetic field at the first frame 310. This magnetic field can interact with a current flowing through a conductive coil 335 to impart a force on the first frame 310, causing the first frame 310, second frame 330, and platform 325 to oscillate about an axis 320, for example, by passing alternating current through the conductive coil 335. Other forms of actuators, such as piezoelectric or electrostatic actuators, can be used as a complement or alternative to electromagnetic actuation.

[0038] Reflector 340 is shown positioned on platform 325. For example, reflector 225 may include a metallic reflector or a dielectric reflector, or a combination thereof. Figure 3A In the configuration shown, reflector 340 has a length in a direction parallel to axis 320, which is greater than the length in a direction perpendicular to axis 320. This configuration can be used to allow light received at reflector 340 to oscillate along axis 320, which may occur when light received at reflector 340 comes from another scanning micromirror device, thus causing the light to oscillate.

[0039] The scanning micromirror device 300 is configured for relatively low-frequency oscillations, for example, in the range of 15 Hz to 2 kHz. To reduce the power consumed by actuation and oscillation of the driving platform 325, the device can operate at its resonant frequency, which generates a quality factor (Q) that amplifies the displacement achieved by actuation. Therefore, the inherent resonant frequencies of the first frame 310, the second frame 330, and the platform 325 about axis 320 are in the range of 15 Hz to 2 kHz. The supporting flexible element 315 can be configured to support this oscillating operation.

[0040] The use of a second frame 330 between the first frame 310 and the platform 325 allows for the inclusion of additional components in the scanning micromirror device 300. For example, such as... Figure 3C As shown, resistor 355 can be located on the second frame 330. Such resistor 355 can be used to evaluate the temperature of the scanning micromirror device 300, for example, by using resistor 355 whose resistance is a function of temperature (i.e., a thermistor). Conductive access lines for electrical communication with resistor 355 are not shown. Figure 3C As shown in the image.

[0041] In another example, the piezoelectric actuator 360 can be located on the second frame 330, such as Figure 3D As shown. Furthermore, the conductive access line used for electrical communication with the piezoelectric actuator 360 is not in... Figure 3D As shown in the diagram, the piezoelectric actuator 360 can be used to sense and / or control the flatness and / or position of the platform 325 about the second axis 365. The piezoelectric actuator 360 can be used as a strain sensor to sense the position of the second frame 330. For example, if the second frame 330 and the platform 325 deform relative to the axis 365, the piezoelectric actuator 360 can generate a voltage, thereby providing a way to detect position or flatness. A voltage can be applied to the piezoelectric actuator 360 to change the tilt of the second frame and the platform 325 relative to the axis 365, for example, in the case where the piezoelectric actuator 360 causes deformation, which results in a deflection about the axis 365 in a corresponding direction (e.g., causing one end of the frame 330 to tilt upwards and the other end of the frame 330 to tilt downwards). Alternatively, a voltage can be applied to the piezoelectric actuator 360 to change the curvature of the second frame and platform 325 relative to the axis 365, for example, in the case where the piezoelectric actuator 360 causes deformation on opposite sides of the axis 365, which results in a coordinated deflection about the axis 365 (e.g., causing one end of the frame 330 to tilt upwards, and the other end of the frame 330 to tilt upwards as well).

[0042] In some cases, the scanning micromirror device 300 can be encapsulated in a vacuum or hermetically sealed package, similar to that described above with respect to the scanning micromirror device 200. Since the scanning micromirror device 300 can be configured for relatively low-frequency operation, such encapsulation is optional and not preferred for all embodiments.

[0043] Next turn Figure 4An overview of example method 400 is shown. Method 400 corresponds, for example, to a method of projecting an image using multiple scanning micromirror devices. At block 402, a two-dimensional optical scanning system is provided, such as a two-dimensional optical scanning system including a first scanning micromirror device and a second scanning micromirror device (e.g., like image projection system 100). The scanning micromirror devices may include, for example, one or more of scanning micromirror device 200 or scanning micromirror device 300, or one of scanning micromirror device 200 and scanning micromirror device 300.

[0044] Method 400 includes steps 404 and 406, wherein different resonant oscillations are induced in the scanning micromirror device. Although steps 404 and 406 are instructed to induce oscillations in the first scanning micromirror device and then inducing oscillations in the second scanning micromirror device, the oscillations of the scanning micromirror devices can be induced in any order or simultaneously. Inducing oscillations in the scanning micromirror device may include passing current (e.g., alternating current) through a conductive coil of the scanning micromirror device.

[0045] At box 408, a controllable light source, such as a multicolor light source, is used to illuminate the reflector of the first scanning micromirror device. The reflector of the first scanning micromirror device can reflect light from the light source to generate reflected light, which is directed to the reflector of the second scanning micromirror device. An optical repeater may be positioned between the first and second scanning micromirror devices to provide optical communication, for example, in a folded beam configuration, which is useful for reducing or minimizing the size of the optical scanning system. The reflector of the second scanning micromirror device can reflect light from the first scanning micromirror device to generate output reflected light.

[0046] At frame 410, the output reflected light can be guided to an eyepiece, such as the eyepiece of a head-mounted image display device. Output optics can be included between the eyepiece and the second scanning micromirror device. Example optics include lenses, reflectors, filters, diffraction gratings, prisms, etc.

[0047] Some aspects of the invention can be further understood through the following non-limiting examples.

[0048] Example 1: Fabrication of a scanning micromirror device with an intermediate frame

[0049] This example provides an overview of a manufacturing scheme for a scanning micromirror device. The various details described in this example will allow those skilled in the art to understand an example process for manufacturing scanning micromirror devices used in the image projection systems, head-mounted display systems, and two-dimensional scanning systems described herein. It should be understood that conventional processes may be used for some manufacturing steps. Not all manufacturing steps are described in detail in this example to avoid obscuring other disclosed aspects. It should be understood that the accompanying drawings described in this example are for illustrative purposes and may not be drawn to scale.

[0050] Figure 5A-5G A schematic diagram of various points in the fabrication process for a scanning micromirror device is provided. In this example, the fabrication process begins with a silicon-on-insulator (SOI) wafer 500, such as... Figure 5A As shown. As a first step, a photolithography process is used to establish the location of the conductive coil, which indicates the position where the conductive coil will be embedded in the SOI wafer 500 within the platform of the resulting scanning micromirror device. After the photolithography step, silicon can be etched to create recessed locations for the conductive coil, and then any photoresist can be stripped. The wafer can undergo a dry oxidation process, followed by the deposition of a silicon nitride (SiN) layer, for example, using low-pressure chemical vapor deposition, to create an insulator separating the conductive coil from the silicon wafer. For example, a metal seed layer 510 (such as a tantalum / copper seed layer) can be deposited into the recesses via a sputtering process. At this point, the wafer appears similar to Figure 5A As shown, the SOI wafer is identified by reference numeral 500, the recess is identified by reference numeral 505, and the metal seed layer is identified by reference numeral 510.

[0051] Following this, a copper layer is deposited on the metal seed layer using, for example, an electrochemical deposition process to form the majority of the conductive coil. Excess copper and the metal seed layer can be removed using chemical mechanical polishing or planarization processes, creating a flat surface for the device, thus filling the recess with copper. At this point, the wafer appears similar to... Figure 5B As shown, the recess filled with copper is identified by reference numeral 515.

[0052] The surface can be passivated using plasma-enhanced chemical vapor deposition (PECVD) to create a silicon nitride / silicon oxide layer. Vias 520 can be created using photolithography to provide access points for electrical contacts to conductive coils, followed by etching the vias and stripping away any remaining photoresist. At this point, the wafer appears similar to... Figure 5C As shown, the vias are identified by reference numeral 520.

[0053] To provide conductivity, a second metal layer 525, such as a titanium / molybdenum layer, can be deposited. The second metal layer can provide electrical connections to conductive coils at vias 520 created thereon. The second metal layer 525 can be subjected to photolithography to define the locations where the second metal layer 525 will remain, followed by an etching process (e.g., a wet etching process) and a photoresist stripping process. Another passivation layer 530 (e.g., silicon oxide) can be formed, for example, using a plasma-enhanced chemical vapor deposition process. At this point, the wafer appears similar to... Figure 5D As shown, the second metal layer is identified by reference numeral 525, and the passivation layer is identified by reference numeral 530.

[0054] The platform of the scanning micromirror device can be positioned using photolithography, and the top passivation layer can be thinned or removed using etching, and any remaining photoresist can be stripped. For the reflector of the scanning micromirror device, a reflective layer 535, such as an aluminum layer, can be deposited and patterned using a series of deposition, photolithography, etching, and photoresist stripping processes. The passivation layer 530 can then be formed again (e.g., by plasma-enhanced chemical vapor deposition). At this point, the wafer appears similar to... Figure 5E As shown, the reflector is identified by reference numeral 535, and the passivation layer is identified by reference numeral 540.

[0055] A photolithography process can be used to define a second via 540 for connection to the second metal layer, for example, to allow wiring bonding. The via can be etched, and then any residual photoresist can be stripped away. Another photolithography process can be used to define the area between and around the platform, support flexibility, and frame (if any) of the scanning micromirror device located between the base and the platform. The recess can be created by one or more etching processes and photoresist stripping processes. At this point, the wafer looks similar to Figure 5F As shown, the vias used for the second metal layer are identified by reference numeral 545.

[0056] A protective layer, such as parylene, can be deposited on the device and then stripped from the back side to allow processing of the bottom side of the device while protecting the top side. In this example, the back side can undergo a photolithography process, followed by one or more etching processes to remove the silicon oxide layer, silicon nitride layer, processed wafer, and buried oxide layer. Parylene and any residual photoresist layers can be stripped. Finally, the wafer can be diced, for example, by stealth or laser dicing processes. The resulting wafer 550 has an appearance similar to Figure 5G As shown, the scanning micromirror platform is identified by reference numeral 555.

[0057] It should be understood that the steps outlined in this example are merely one example of the process for manufacturing components of a scanning micromirror device, and other processes or step sequences may be used.

[0058] Example 2: Fabrication of scanning micromirror devices, conductive coils, and stress relief layers

[0059] This example provides an overview of a manufacturing scheme for fabricating a scanning micromirror device. The various details described in this example will allow those skilled in the art to understand an example process for fabricating a scanning micromirror device used in the image projection systems, head-mounted display systems, and two-dimensional scanning systems described herein. It should be understood that conventional processes may be used for some manufacturing steps. Not all manufacturing steps are described in detail in this example to avoid obscuring other disclosed aspects. It should be understood that the accompanying drawings described in this example are for illustrative purposes and may not be drawn to scale.

[0060] Figures 6A-6H Schematic diagrams are provided of various points in the fabrication process for a scanning micromirror device. In this example, the fabrication process begins with a silicon wafer 600 polished on both sides. As a first step, a photolithography process is used to establish the positions of conductive coils, which indicates the location of the wafer in which the conductive coils will be embedded in the resulting scanning micromirror device platform. After the photolithography step, the silicon can be etched to create recessed locations for the conductive coils, and then any photoresist is removed. The wafer can undergo a dry oxidation process, followed by the deposition of a silicon nitride (SiN) layer, for example, using low-pressure chemical vapor deposition, to create an insulator separating the conductive coils from the silicon wafer. For example, a metal seed layer 610 (such as a tantalum / copper seed layer) can be deposited into the recesses by a sputtering process. At this point, the wafer looks similar to that shown in 6A, where the silicon wafer is identified by reference numeral 600, the recesses by reference numeral 605, and the metal seed layer by reference numeral 610.

[0061] Following this, a copper layer is deposited on the metal seed layer using, for example, an electrochemical deposition process to form most of the conductive coil. Excess copper and the metal seed layer can be removed using chemical mechanical polishing or planarization processes, forming a flat surface of the device, thus filling the recess 605 with copper. At this point, the wafer appears similar to... Figure 6B As shown, the recess filled with copper is identified by reference numeral 615.

[0062] The surface can be passivated using plasma-enhanced chemical vapor deposition (PECVD) to form a silicon nitride / silicon oxide layer. Vias can be created using photolithography, providing access points for electrical contacts to conductive coils. The vias are then etched, and any remaining photoresist is removed. At this point, the wafer appears similar to... Figure 6C As shown, the vias are identified by reference numeral 620.

[0063] To provide conductivity, a second metal layer 625, such as a titanium / molybdenum layer, can be deposited. The second metal layer can provide electrical connections to conductive coils at vias created thereon. The second metal layer 625 can be subjected to photolithography to define the locations where the second metal layer 625 will remain, followed by an etching process (e.g., a wet etching process) and a photoresist stripping process. Another passivation layer 630 (e.g., silicon oxide) can be formed, for example, using a plasma-enhanced chemical vapor deposition process. At this point, the wafer appears similar to... Figure 6D As shown, the second metal layer is identified by reference numeral 625 and the passivation layer is identified by reference numeral 630.

[0064] like Figures 6A-6D As shown, the above steps can all be used to form conductive coils on the back side of a silicon wafer. It should be understood that the references to back side and front side, or top side and bottom side, are merely examples describing opposing sides of the wafer and these terms are not intended to be limiting. It will also be understood that the outlined steps are merely one example of a process for manufacturing components of a scanning micromirror device, and other processes or sequences of steps may be used.

[0065] A stress-relief layer 635, such as a copper layer, and a reflective layer 640, such as an aluminum layer, can be deposited on the front side of the wafer, for example, through photolithography, etching, and photoresist stripping processes, to define the positions of the stress-relief layer 635, the reflective layer 640, and the platform. Optionally, passivation processes (e.g., silicon oxide and / or silicon nitride layer deposition via plasma-enhanced chemical vapor deposition) can be used to isolate the stress-relief layer and the reflective layer from each other and from the silicon wafer. At this point, the wafer appears similar to... Figure 6E As shown, the stress relief layer is identified by reference numeral 635, and the reflective layer is identified by reference numeral 640.

[0066] A second via for connecting to the second metal layer can be defined using photolithography. The via can be etched, and any remaining photoresist can be stripped away. A third metal layer 645, such as aluminum, can be deposited in the via, where it is patterned using photolithography, etching, and photoresist stripping. At this point, the wafer looks similar to... Figure 6F As shown, the third metal layer is identified by reference numeral 645.

[0067] The overall shape of the scanning micromirror platform can be established by identifying passivation layer regions on the back side of the device, selectively removing them by photolithographically patterning the back side and etching the passivation layer, then stripping away any excess photoresist. In this case, the passivation layer on the back side may be quite thick, making it difficult to remove from the front side by etching; therefore, it is selectively removed from the back side as needed at this stage. A protective layer, such as parylene, can be deposited on the device, and then stripped from the front side to prepare for full etching of the silicon wafer. At this point, the wafer looks similar to... Figure 6G As shown, the parylene protective layer is identified by reference numeral 650.

[0068] Finally, the overall shape of the scanning micromirror platform can be established from the front of the device by photolithographically patterning and etching the passivation layer, then etching silicon down to the parylene layer, followed by stripping the parylene layer. Finally, the wafer is diced as needed, for example by stealth or laser dicing processes. The resulting wafer 660 can have a shape similar to... Figure 6H The features shown. In some cases, the wafer can be cut later, such as after assembling a vacuum package, as described below in Example 3.

[0069] Example 3: Hermetic or vacuum sealing of scanning micromirror devices

[0070] This example provides an overview of the vacuum packaging process for manufacturing scanning micromirror devices. The various details described in this example will allow those skilled in the art to understand the example process used to manufacture scanning micromirror devices for use in the image projection systems, head-mounted display systems, and 2D scanning systems described herein. It should be understood that conventional processes may be used for some manufacturing steps. Not all manufacturing steps are described in detail in this example to avoid obscuring other aspects of the disclosure. It should be understood that the accompanying drawings described in this example are for illustrative purposes and may not be drawn to scale.

[0071] Figures 7A-7G A schematic diagram of various points in the fabrication / assembly process of a vacuum package for a scanning micromirror device is provided. In this example, the fabrication of the top package begins with a silicon wafer polished on both sides. As a first step, the wafer may be drilled and / or machined to form holes and recesses necessary to accommodate the scanning micromirror device and its movement. A cleaning process can be used to prepare for the next part of the process. At this point, the top package wafer looks similar to Figure 7A As shown, the silicon wafer is identified by reference numeral 700, the via is identified by reference numeral 705, and the recess is identified by reference numeral 710.

[0072] Glass molten paste can be screen-printed onto the top of a silicon wafer to bond and seal a transparent cap, such as glass (e.g., borosilicate glass) or a crystal cap. In this case, the top encapsulation looks similar to... Figure 7B As shown, the transparent cover is identified by reference numeral 715 and the molten glass paste is identified by reference numeral 720. One or both sides of the transparent cover may be coated with an anti-reflective coating.

[0073] The fabrication of the bottom package can similarly begin with a silicon wafer 725 that has been polished on both sides. The top surface recess 730 can be photolithographically patterned and etched, and then any excess photoresist can be stripped away. The locations of the holes on the bottom surface can also be patterned via photolithography. At this point, the bottom package wafer looks similar to... Figure 7C As shown, the silicon wafer is identified by reference numeral 725, the top surface recess is identified by reference numeral 730, and the patterned photoresist on the back surface is identified by reference numeral 735.

[0074] The bottom surface can be partially etched to form recesses for holes that will be fully etched later, and then any excess photoresist can be stripped away. The device can be protected, for example, by a parylene protective layer 745, which can be removed from the front side for further processing. At this point, the bottom package wafer looks similar to... Figure 7D As shown, some of the etching is identified by reference numeral 740 and the protective layer is identified by reference numeral 745.

[0075] The top surface can be photolithographically patterned to define the location of the deeper recess 750 and the hole 755 partially etched from the bottom surface in a previous step. The wafer can then be etched to form the second recess 750 and complete the hole 755, after which any excess photoresist and protective layer material can be stripped. For example, the second recess 750 can be used to accommodate the movement of a platform for a scanning micromirror device. At this point, the bottom package wafer appears similar to... Figure 7E As shown, the deeper depressions are identified by reference numeral 750 and the holes by reference numeral 755.

[0076] The top and bottom packages can be assembled into, for example, a scanning micromirror device prepared according to Example 2 above. For the top surface, glass molten paste 770 can be screen-printed onto the bottom surface of the top package 765 for bonding to the top surface of the scanning micromirror device 760. At this point, the assembly looks similar to... Figure 7F As shown, the scanning micromirror device is identified by reference numeral 760, the top encapsulation is identified by reference numeral 765, and the glass molten paste is identified by reference numeral 770.

[0077] For the bottom surface, glass molten paste 780 can be screen-printed onto the top surface of the bottom package 775 for bonding to the bottom surface of the scanning micromirror device 760. The assembled vacuum-packaged scanning micromirror device resembles... Figure 7G As shown, the scanning micromirror device is identified by reference numeral 760, the top package by reference numeral 765, the bottom package by reference numeral 775, and the molten glass paste by reference numeral 780. As shown, the hole in the bottom package is positioned to align with the third metal layer on the bottom surface of the scanning micromirror device.

[0078] While the above description of manufacturing a vacuum-encapsulated scanning micromirror device refers to the scanning micromirror device prepared according to Example 2 above, other scanning micromirror devices can also benefit from and be positioned within the vacuum encapsulation according to this example. For example, U.S. Provisional Patent Application No. 63 / 034,884, filed June 4, 2020 and incorporated herein by reference, describes a two-dimensional microelectromechanical system mirror with electromagnetic drive, and these micromirror devices can be encapsulated similarly using the vacuum encapsulation components and techniques described above. Such a system can utilize a single micromirror device for two-dimensional scanning, in contrast to other systems described herein that employ a first scanning mirror device for oscillation along a first direction and a second scanning mirror device for oscillation along a second direction perpendicular to the first direction. In a specific example, the scanning micromirror device 760 may include: a two-dimensional microelectromechanical system mirror including a base, a first platform coupled to the base via a plurality of first support flexible elements, and a second platform coupled to the first platform via a plurality of second support flexible elements, the second platform including a reflector. The first platform may be oscillable about a first axis, which is useful for controlling the oscillation of reflected light in the first direction. The second platform can be oscillating about a second axis orthogonal to the first axis, which is useful for controlling the oscillation of reflected light in a second direction, which can be orthogonal (e.g., perpendicular) to the first direction. The first platform, the second platform, and the plurality of second supporting flexible elements together can exhibit a first resonance with a first resonant frequency, wherein the first resonance corresponds to the oscillating motion of at least the first platform, the second platform, and the plurality of second supporting flexible elements about the first axis. The first platform, the second platform, and the plurality of second supporting flexible elements together can exhibit or further exhibit a second resonance with a second resonant frequency, wherein the second frequency is greater than the first frequency, and the second resonance corresponds to the oscillating motion of at least the second platform about the second axis. The first platform, the second platform, and the plurality of second supporting flexible elements together can exhibit or further exhibit a third resonance with a third resonant frequency, wherein the third frequency is twice the second frequency, and the third resonance corresponds to the oscillating motion of at least the second platform about the first axis.

[0079] Computing device components

[0080] The computing device may be incorporated as part of the previously described systems, such as image projection systems, head-mounted display systems, and two-dimensional scanning systems. The computing device may be useful for performing aspects of the previously described methods and systems. For example, the computing device may be useful for controlling the modulation of a light beam. The computing device may also be useful for controlling the orientation and / or oscillation of a scanning mirror. The computing device may also be useful for controlling the application of voltage or current. Example computing devices include hardware elements that can be electrically coupled (or otherwise communicated) via a bus. The hardware elements may include one or more processors, including but not limited to one or more general-purpose processors and / or one or more special-purpose processors (such as digital signal processing chips, graphics accelerators, video decoders, and / or the like); one or more input devices, which may include, but are not limited to, a mouse, a touchscreen, a keyboard, a remote control, voice input, and / or the like; and one or more output devices, which may include, but are not limited to, a display device, a printer, a speaker, a server, a linear actuator, a rotary actuator, etc.

[0081] The computing device may also include one or more non-transitory storage devices (and / or devices that can communicate with them), which may include, but are not limited to, local and / or network access storage, and / or may include, but are not limited to, disk drives, drive arrays, optical storage devices, solid-state storage devices such as solid-state drives (“SSDs”), random access memory (“RAM”), and / or read-only memory (“ROM”), which may be programmable, flash-updatable, and / or the like. Such storage devices may be configured to implement any suitable data storage, including but not limited to various file systems, database structures, and / or the like.

[0082] The computing device may also include a communication subsystem, including but not limited to a modem, a network card (wireless or wired), an infrared communication device, a wireless communication device, and / or a chipset (such as a Bluetooth device, Bluetooth Low Energy or BLE device, 802.11 device, 802.15.4 device, WiFi device, WiMax device, cellular communication device, etc.), a G.hn device, and / or the like. The communication subsystem may allow data exchange with networks, other computer systems, and / or any other device described herein. In many embodiments, the computing device will further include working memory, which may include RAM or ROM devices as described above.

[0083] The computing device may also include software elements, shown as currently residing in working memory, including operating systems, device drivers, executable libraries, and / or other code, such as one or more applications, which may include computer programs provided by various embodiments, and / or may be designed to implement methods, and / or configure systems provided by other embodiments, as described above. By way of example only, one or more programs described with respect to the methods discussed above may be implemented as code and / or instructions executable by a computer (and / or a processor within a computer); in this respect, such code and / or instructions may then be used to configure and / or adapt a computer (or other device) to perform one or more operations according to the described methods or for the operation of the described device and system.

[0084] These sets of instructions and / or code may be stored on a non-transitory computer-readable storage medium, such as the non-transitory storage device described above. In some cases, the storage medium may be incorporated into a computer system, such as a computing device described above. In other embodiments, the storage medium may be separable from the computer system (e.g., a removable medium, such as an optical disc, or a cloud or network-based storage system), and / or provided in an installation package such that the storage medium can be used to program, configure, and / or adapt a computer using the instructions / code stored thereon. These instructions may take the form of executable code executable by a computing device or its components and / or may take the form of source code and / or installable code, which, when compiled and / or installed on the computing device (e.g., using any of a variety of generally available compilers, installers, compression / decompression utilities, etc.), then take the form of executable code.

[0085] It will be apparent to those skilled in the art that substantial modifications can be made to suit specific requirements. For example, custom hardware may also be used, and / or specific components may be implemented in hardware, software (including portable software such as applets), or both. Furthermore, connections to other computing devices, such as network input / output devices, may be employed.

[0086] As mentioned above, in one aspect, some embodiments may employ a computing device to perform methods according to various embodiments. According to one set of embodiments, some or all of the procedures of such a method are executed by a computing device in response to a processor executing one or more sequences of one or more instructions contained in working memory (which may be contained in an operating system and / or other code, such as an application). Such instructions may be read into working memory from another computer-readable medium (such as one or more non-transitory storage devices). By way of example only, execution of a sequence of instructions contained in working memory can cause a processor to perform one or more procedures of the methods described herein.

[0087] As used herein, the terms “machine-readable medium,” “computer-readable storage medium,” and “computer-readable medium” refer to any medium that participates in providing data that causes a machine to operate in a particular manner. These media can be non-transitory. In embodiments implemented using computing devices, various computer-readable media can relate to providing instructions / code to a processor for execution and / or being usable for storing and / or carrying such instructions / code. In many embodiments, computer-readable media are physical and / or tangible storage media. Such media can take the form of non-volatile or volatile media. Non-volatile media include, for example, optical discs and / or magnetic disks, such as non-transitory storage devices. Volatile media include, but are not limited to, dynamic memory, such as working memory.

[0088] Common forms of physical and / or tangible computer-readable media include, for example, floppy disks, hard disks, magnetic tapes, or any other magnetic media, CD-ROMs, any other optical media, any other physical media with marked patterns, RAM, PROMs, EPROMs, FLASH-EPROMs, any other memory chips or tape cassettes, or any other media from which a computer can read instructions and / or code. Network-based and cloud-based storage systems can also be useful forms of computer-readable media.

[0089] Various forms of computer-readable media can involve carrying one or more sequences of one or more instructions to a processor for execution. By way of example only, instructions may initially be carried on a disk and / or optical disk of a remote computer. The remote computer may load the instructions into its dynamic memory and transmit them as signals via a transmission medium for reception and / or execution by a computing device.

[0090] The communication subsystem (and / or its components) typically receives signals, and the bus can then carry the signals (and / or the data, instructions, etc. carried by the signals) to working memory, from which the processor retrieves and executes the instructions. Instructions received from the working memory may optionally be stored on non-transitory storage devices before or after execution by the processor.

[0091] It should be further understood that the components of a computing device can be distributed. For example, some processing may be executed at one location using a first processor, while other processing may be executed by another processor remotely located from the first processor. Alternatively, the system described herein may include multiple independent processors that can exchange instructions or issue commands or provide data to each other. Other components of the computing device can be similarly distributed. Therefore, a computing device can be interpreted as a distributed computing system that performs processing at multiple locations. In some instances, depending on the context, a computing device can be interpreted as a single computing device, such as different laptop computers, desktop computers, etc.

[0092] Although preferred embodiments of the invention have been described and illustrated, it will be clear that the invention is not limited to these embodiments. Many modifications, alterations, variations, substitutions, and equivalents will be apparent to those skilled in the art without departing from the spirit and scope of the invention as described in the claims.

Claims

1. A two-dimensional optical scanning system, comprising: A first scanning micromirror device, wherein the first scanning micromirror device comprises: A first platform is coupled to a first base via a plurality of first supporting flexible elements, wherein the first platform is oscillating about a first axis; A stress relief layer is located on a first side of the first platform, wherein the stress relief layer provides a first stress distribution on the first side of the first platform; A first reflector is located on the first side of the first platform, wherein the stress relief layer is located between the first reflector and the first platform; A first conductive coil, located on a second side of the first platform opposite to the first side of the first platform, is arranged to apply a magnetic force to the first platform around the first axis and provide a second stress distribution on the second side of the first platform, wherein the first stress distribution is opposite to the second stress distribution; and A first magnetic field source is configured to apply a first magnetic field to the first platform; and A second scanning micromirror device, which is in optical communication with the first scanning micromirror device, wherein the second scanning micromirror device includes: A first frame is coupled to a second base via a plurality of second supporting flexible elements, wherein the first frame is oscillating about a second axis; A second platform coupled to the first frame, wherein the second platform is oscillating about the second axis together with the first frame; A second reflector is located on the second platform; A second conductive coil, located on the first frame, is arranged to apply a magnetic force to the first frame about the second axis; and A second magnetic field source is arranged to apply a second magnetic field to the first frame.

2. The two-dimensional optical scanning system according to claim 1, wherein, The first platform has a thickness between 100µm and 500µm.

3. The two-dimensional optical scanning system according to claim 1, wherein, The first conductive coil is embedded in the second side of the first platform.

4. The two-dimensional optical scanning system according to claim 1, wherein, The first magnetic field source is arranged to provide the first magnetic field orthogonally oriented to the first axis.

5. The two-dimensional optical scanning system according to claim 1, wherein, The first scanning micromirror device further includes one or more piezoelectric actuators arranged to apply force to cause the first platform to oscillate about the first axis or to sense the oscillation or position of the first platform about the first axis.

6. The two-dimensional optical scanning system according to claim 1, wherein, The first scanning micromirror device further includes: a plurality of conductive traces located on the plurality of first support flexible members for providing electrical communication with the first conductive coil, wherein the plurality of conductive traces are configured to be arranged on the plurality of first support flexible members to apply opposite stresses on different sides of the plurality of first support flexible members.

7. The two-dimensional optical scanning system according to claim 1, further comprising: An hermetically sealed device is provided to maintain a lower pressure inside the hermetically sealed device at the first scanning micromirror device than outside the hermetically sealed device.

8. The two-dimensional optical scanning system according to claim 1, wherein, The second scanning micromirror device further includes: a second frame coupled between the first frame and the second platform, wherein the second frame is coupled to the first frame via a plurality of third support flexible members, and wherein the second frame is oscillable about a second axis together with the first frame and the second platform.

9. The two-dimensional optical scanning system according to claim 8, wherein, The second scanning micromirror device further includes a temperature sensor contained within the second frame.

10. The two-dimensional optical scanning system according to claim 8, wherein, The second scanning micromirror device further includes a strain sensor contained within the second frame.

11. The two-dimensional optical scanning system according to claim 8, wherein, The second scanning micromirror device further includes a plurality of piezoelectric actuators contained in the second frame, wherein the plurality of piezoelectric actuators are arranged to change the position of the second platform about a third axis orthogonal to the second axis, or to change the curvature of the second platform.

12. The two-dimensional optical scanning system according to claim 1, wherein, The first scanning micromirror device has a first intrinsic resonant frequency of 1 kHz to 10 MHz, and the second scanning micromirror device has a second intrinsic resonant frequency of 15 Hz to 2 kHz.

13. The two-dimensional optical scanning system according to claim 1, further comprising: An optical repeater that provides optical communication between the first scanning micromirror device and the second scanning micromirror device.

14. The two-dimensional optical scanning system according to claim 1, further comprising: A light source is arranged to direct emitted light to the first reflector.

15. A method for projecting an image, the method comprising: A two-dimensional optical scanning system is provided, the two-dimensional optical scanning system comprising: A first scanning micromirror device, wherein the first scanning micromirror device comprises: A first platform is coupled to a first base via a plurality of first supporting flexible elements, wherein the first platform is oscillating about a first axis; A stress relief layer is located on a first side of the first platform, wherein the stress relief layer provides a first stress distribution on the first side of the first platform; A first reflector is located on the first side of the first platform, wherein the stress relief layer is located between the first reflector and the first platform; A first conductive coil, located on a second side of the first platform opposite to the first side of the first platform, is arranged to apply a magnetic force to the first platform around the first axis and provide a second stress distribution on the second side of the first platform, wherein the first stress distribution is opposite to the second stress distribution; and A first magnetic field source is configured to apply a first magnetic field to the first platform; and A second scanning micromirror device, which is in optical communication with the first scanning micromirror device, wherein the second scanning micromirror device includes: A first frame is coupled to a second base via a plurality of second supporting flexible elements, wherein the first frame is oscillating about a second axis; A second platform coupled to the first frame, wherein the second platform is oscillating about the second axis together with the first frame; A second reflector is located on the second platform; A second conductive coil, located on the first frame, is arranged to apply a magnetic force to the first frame about the second axis; and A second magnetic field source is arranged to apply a second magnetic field to the first frame; The first oscillation of the first scanning micromirror device is caused at a first frequency; A second oscillation of the second scanning micromirror device is caused at a second frequency, wherein the second frequency is less than the first frequency; and The first reflector of the first scanning micromirror device is illuminated by a light source to generate reflected light, which is then guided to the second scanning micromirror device and reflected by the second reflector of the second scanning micromirror device to generate output reflected light.

16. The method of claim 15, further comprising: The output reflected light from the second scanning micromirror device is guided to the eyepiece.

17. The method of claim 15, further comprising: The oscillations of the first scanning micromirror device, the oscillations of the second scanning micromirror device, and the output color and / or intensity of the light from the light source are controlled synchronously.

18. The method according to claim 15, wherein, The two-dimensional optical scanning system includes the two-dimensional optical scanning system according to any one of claims 1-14.

19. A head-mounted display system, comprising: The two-dimensional optical scanning system according to any one of claims 1-14; as well as An eyepiece, comprising one or more optical components configured to receive light reflected by the second scanning micromirror device and redirect it to one or both of the user's eyes.

20. The head-mounted display system according to claim 19, further comprising: A control circuit, operatively coupled to a light source and the first and second scanning micromirror devices, wherein the control circuit is configured to display one or more images by synchronously performing the following operations: Control the light source to emit light corresponding to pixels of the one or more images; Control the current flow in the first conductive coil to cause the first platform to oscillate around the first axis; as well as The current flow in the second conductive coil is controlled to cause the second platform to oscillate around the second axis.

Images