Mirror assembly of a microelectromechanical system and method for manufacturing a mirror arrangement of a microelectromechanical system

Abstract

Mirror assembly of a microelectromechanical system (MEMS) comprising: a base substrate (315; 415; 515; 800) that defines a cavity (340; 440; 540; 802) and several first features (804) that extend upwards from a floor of the cavity (340; 440; 540; 802); a mirror substrate (310; 410; 510; 822) coupled to the base substrate (315; 415; 515; 800) and defining a first MEMS actuator and a MEMS mirror platform (305; 405; 505; 824), wherein the mirror substrate (310; 410; 510; 822) defines a gimbal suspension (210) positioned above the cavity (340; 440; 540; 802), wherein the gimbal suspension (210) defines a second MEMS actuator and a cutout containing the MEMS mirror platform (305; 405; 505; 824), wherein the first and second MEMS actuators are vertical comb drive actuators, each driving a first and have a second section; wherein actuation of the first MEMS actuator moves the MEMS mirror platform (305; 405; 505; 824) from a first position state to a second position state and the MEMS mirror platform (305; 405; 505; 824) defines several second features (818) on one side of the MEMS mirror platform (305; 405; 505; 824) facing the base substrate (315; 415; 515; 800), which are dimensioned, shaped and positioned such that the several second features (818) extend into the spaces separating the several first features (804) when the MEMS mirror platform (305; 405; 505; 824) is in the second position state; wherein the actuation of the first MEMS actuator rotates the MEMS mirror platform (305; 405; 505; 824) about a first axis and the actuation of the second MEMS actuator rotates the gimbal suspension (210) and the MEMS mirror platform (305; 405; 505; 824) about a second axis which is substantially orthogonal to the first axis; and a reflective material (828) arranged on one side of the MEMS mirror platform (305; 405; 505; 824) facing away from the base substrate (315; 415; 515; 800).

Description

BACKGROUND

[0001] The mirrors of microelectromechanical systems (MEMS) have widespread applications in beam guidance devices. Applying a voltage and / or current can control the position of the MEMS mirror and consequently direct a beam in a desired direction. However, when the mirror is repositioned, it may "ring" for a period of time before settling into its new position.

[0002] US Patent 6,392,220 B1 discloses a monolithically fabricated micromechanical structure that couples a reference frame to a dynamic plate or a second frame to rotate the plate or second frame relative to the reference frame. The performance of torsional oscillators or scanners is significantly improved by coupling the frame to the plate or second frame with torsional-bending hinges instead of torsion bars. Attachments, retaining straps, or an improved drive circuit enhance the electrostatic drive stability of torsional oscillators. Wide and thin torsional-bending hinges and isotopically pure silicon improve thermal conductivity between the plate and the frame.

[0003] EP 1 479 647 A2 discloses a microelectromechanical (MEMS) mirror device for use in an optical switch. A "piano-style" MEM device comprises an elongated platform pivotally mounted near its center by a torsion joint. The central part of the platform and the torsion joint together have a width smaller than the width of the rest of the platform, allowing several of these "piano-style" MEM devices to be positioned side by side, pivotally about the same axis with only a relatively small air gap between them.

[0004] US Patent 8,274,722 B2 discloses a multilayer concealed hinge and actuator structure for a biaxial, high-fill-factor MEMS mirror array for wavelength-selective switches (WSS) based on a silicon-on-insulator (SOI) process with wafer bonding and coarsely aligned orthogonal vertical comb and / or parallel-plate actuators. The disclosure relates to a micromirror in a linear MEMS micromirror array comprising a micromirror layer, a hinge layer, and an electrode / substrate layer. The structure is fabricated by separately manufacturing the layers in an SOI structure and then joining them together.

[0005] JP 2000-147419 A addresses the problem of how to manufacture a light deflector that oscillates at high speed and a large deflection angle even with low drive power, while simultaneously featuring a reflecting mirror element with very high stiffness. The proposed solution involves designing the reflecting mirror element of the deflector such that it can pivot freely on a base by means of a pair of support elements and a pair of fixed electrodes. The mirror element is then arranged on the base by applying a voltage to the space between the electrodes and the mirror element, causing it to pivot about a pivoting axis by means of an electrostatic force.

[0006] US 2007 / 0127146 A1 discloses a vibration-type tilting device according to an embodiment of the disclosure, comprising a mirror holder that carries a mirror on one side which tilts together with the mirror such that the mirror periodically tilts light along a light path at a tiny angle; a mounting support that carries the mirror holder; a drive element that supplies the mirror holder with driving force; and a damping element that is arranged between the mirror holder and the mounting element to reduce overshoot of the mirror holder, which can improve the vibration performance of the tilting device to achieve a smoother and clearer image quality. SUMMARY

[0007] At least one aspect is directed towards a mirror assembly of a microelectromechanical system (MEMS) according to claim 1.

[0008] At least one aspect is directed to a method for manufacturing a mirror arrangement of a microelectromechanical system (MEMS) according to claim 9.

[0009] These and other aspects and implementations are discussed in detail below. The preceding information and the following detailed description contain illustrative examples of the various aspects and implementations and provide an overview or framework for understanding the nature and character of the claimed aspects and implementations. The drawings provide an illustration and further understanding of the various aspects and implementations, and are incorporated into and form part of this description. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The accompanying drawings are not intended to be drawn to scale. Identical reference symbols and labels in the various drawings refer to the same elements. For clarity, not every component is labeled in every drawing. The drawings include: Fig. Figure 1 is a block diagram of an optical circuit switch (OCS) according to an illustrative implementation; Fig. Figure 2A is a graphical representation of a mirror of a microelectromechanical system (MEMS) according to an illustrative implementation; Fig. Figure 2B is a graphical representation of a MEMS mirror arrangement according to an illustrative implementation; Fig. Figure 3 is a graphical representation of a cross-section of a MEMS mirror according to an illustrative implementation; Fig. 4 its graphical representation of a cross-section of a MEMS mirror with the mirror platform features and the base substrate features nested when the mirror platform is at rest, according to an illustrative implementation; Fig. Figure 5 is a graphical representation of a cross-section of a MEMS mirror with base substrate features that have different heights with respect to the bottom of a cavity defined in the base substrate, according to an illustrative implementation; Fig. 6A-6C are graphical representations of exemplary mirror platform features and base substrate features according to illustrative implementations; Fig. 7A-7D are flowcharts of exemplary procedures for fabricating a MEMS mirror array according to illustrative implementations; and Fig. Figure 8A-81 shows steps of an exemplary process for manufacturing a MEMS mirror assembly according to an illustrative implementation. DETAILED DESCRIPTION

[0011] This disclosure generally relates to dampers for mirrors of microelectromechanical systems (MEMS) used for beam steering. Beam steering by MEMS mirrors is useful, for example, in an optical line switch (OCS). An OCS is a fully optical 3D switching matrix that, in some implementations, can direct light from any input fiber N to any output fiber M by changing the positions of the mirrors in two-dimensional MEMS mirror arrays. OCSs enable switching in the optical domain without converting optical signals to electrical signals and back again. This reduces latency, improves traffic safety, and makes switching agnostic with respect to coding and data rates.

[0012] A MEMS mirror in the OCS can direct optical signals by rotating under the control of analog voltages applied to actuators coupled to the mirror. The mirror position is non-binary; however, after actuation, the mirror tends to "ring" for a period that depends on the resonant frequency of the mirror and its supports, and the amount of mechanical and fluid damping around the actuator and the mirror. During the ringing period, the mirror may be unable to direct the optical signal to its intended destination. The ringing therefore causes a switching delay, during which the switch cannot transmit an optical signal via the ringing mirror. The magnitude of the ringing depends on the quality factor (Q) of the device, with a high Q correlating with more ringing. A Q greater than 10 is typical for the MEMS mirrors currently used in OCSs.By incorporating a damper according to this disclosure, the Q can be significantly reduced in some implementations. In some cases, the Q can be reduced by an order of magnitude. In some cases, the Q can be brought below 10.

[0013] The MEMS mirrors can contain a mirror platform above a base. The dampers can take the form of complementary features on the bottom of the mirror platform and on the top of the base. These complementary features can be nested together, so that a fluid, such as dry air, is compressed in the gaps of one surface, while the prongs or pillars on the opposite surface move into the gaps. As the fluid is forced past the features to exit the gap, it generates a shear force along the edges of the features that is phase-shifted from the intended direction of actuation, thereby producing a large damping force.

[0014] The complementary features can take on various forms depending on the desired amount of damping. Certain shapes can provide additional advantages. For example, a densely packed structure of pedestal- or cavity-like features etched into the underside of the mirror platform can reduce the mirror's mass. The reduced mass of the mirror platform can increase the resonant frequency and the effectiveness of any existing fluid damping mechanisms.

[0015] A significantly underdamped MEMS mirror (with a high Q) can ring for many cycles (10 s to 100 s) before it has oscillated sufficiently to allow transmission of the optical signal. Adding dampers according to this disclosure can reduce the ringing to only a few cycles in some implementations, allowing for faster switching. Additionally, the dampers can reduce the mirror's sensitivity to movement caused by external excitation events, such as shocks or vibrations.

[0016] Fig. Figure 1 is a block diagram of an optical circuit switch (OCS) 100 according to an illustrative implementation. In some implementations, the OCS 100 can route the optical signals from any input fiber N to any output fiber M. The OCS 100 includes the collimators 105a and 105b (collectively the "Collimators 105"), the mirror assemblies 110a and 110b (collectively the "Mirror Assemblies 110"), the mirrors 115a-115c (collectively the "Mirrors 115"), the injectors 120a and 120b (collectively the "Injectors 120"), and the cameras 130a and 130b (collectively the "Cameras 130"). The OCS 100 can receive signals from fiber optic cables 125a and 125b (collectively referred to as "fiber optic cables 125"). The functions of the OCS 100 can be controlled by a Controller 140.

[0017] The OCS 100 can be a non-directional switch, meaning it can route optical signals in both directions between cables 125a and 125b, including bidirectional connections where optical signals travel in both directions within a single optical fiber. Descriptions of the OCS 100's operation that include directional terms such as "input," "output," "enter," or "exit" are for illustrative purposes only and are not intended to be restrictive.

[0018] In an exemplary operation, an optical signal 135 can enter the OCS 100 via a first fiber optic cable 125a. A first collimator 105a can receive the optical signal 135 from the first fiber optic cable 125a and direct it through a first mirror 115a to a first MEMS mirror array 110a. In some implementations, each mirror of the first MEMS mirror array 110a can correspond to a specific optical fiber of the first fiber optic cable 125a, with the first collimator 105a serving to direct the optical signal 135 from the optical fiber to the corresponding mirror of the first MEMS mirror array 110a.

[0019] The first MEMS mirror assembly 110a can transmit the optical signal 135 from a second mirror 115b to a second MEMS mirror assembly 110b. The second MEMS mirror assembly 110b can transmit the optical signal 135 from a third mirror 115c to a second collimator 105b. The second collimator 105b can then transmit the optical signal to the second cable 125b.

[0020] The OCS 100 can include self-monitoring and self-diagnostic capabilities. The OCS 100 can include injectors 120 and cameras 130 for monitoring the condition of the mirror assemblies 110. The injectors 120 can direct a laser 145 at the mirror assemblies 110. The cameras 130 can receive the reflected laser 145 and determine the position of each mirror in the mirror assemblies 110. The cameras 130 can detect whether a mirror is still ringing after being repositioned. Based on the mirror condition information from the injectors 120 and the cameras 130, the controller 140 can control the routing of the optical signals. The controller 140 can maintain information regarding the condition of each mirror and each signal path. The controller 140 can monitor for ringing mirrors, malfunctioning mirrors, or other signal path obstructions.The Controller 140 can send alarm signals containing messages to interrupt traffic in a special fiber optic cable until the switching path is stable or until another switching path can be established.

[0021] Fig. Figure 2A is a graphical representation of a mirror assembly 200 of a microelectromechanical system (MEMS) according to an illustrative implementation. The MEMS mirror assembly 110 can contain many MEMS mirror assemblies 200. The MEMS mirror assembly 200 contains three main components: a mirror platform 205, a gimbal suspension 210, and a mirror substrate 215. The mirror platform 205, the gimbal suspension 210, and the mirror substrate 215 are arranged above a base substrate (not shown). The mirror platform 205 has a reflective surface on its upper surface. The MEMS mirror assembly 200 contains actuators for moving the components. In the Fig. In the implementation shown in Figure 2A, the MEMS mirror assembly 200 can be actuated in two dimensions. The actuators 220a and 220b (collectively the “actuators 200”) can move the mirror platform 205 relative to the gimbal suspension 210, while the actuators 225a and 225b (collectively the “actuators 225”) can move the gimbal suspension 210 and the mirror platform 205 relative to the mirror substrate 215.

[0022] In some implementations, actuators 220 and 225 can exert a torque on their inner component. For example, actuators 220 can exert a torque to rotate the mirror platform 205 to cause a rotation in the XZ plane (i.e., about the Y-axis), while actuators 225 can exert a torque to rotate the gimbal suspension 210 to cause a rotation in the YZ plane (i.e., about the X-axis). In this way, actuators 220 and 225 can move the mirror platform 205 about a first axis and a second axis, respectively, with the axes being essentially orthogonal to each other. In some implementations, actuators 220 and 225 can exert a vertical force (in the Z-direction) on their inner component. Actuators 220 can, for example, B. the mirror platform 205 can rotate in the YZ plane, while the actuators 225 can rotate the gimbal suspension 210 in the XZ plane.In these implementations, the mirror platform 205 can be positioned in two dimensions.

[0023] In some implementations, actuators 220 and 225 can be vertical electrostatic comb drive actuators. Each actuator 220 and 225 can have a first section and a second section; for example, actuators 220 can have a left side and a right side, while actuators 225 can have a top and a bottom, as oriented in the drawing. A first voltage applied to the first section of the actuator can cause the actuator to move the mirror platform 205 in a first direction. In some implementations, the first direction can be a rotation about an axis of movement of the mirror platform 205. A second voltage applied to the second section of the actuator can cause the actuator to move the mirror platform in a second direction opposite to the first. The first voltage can be, for example,The first voltage causes the mirror platform 205 to move clockwise around the axis, while the second voltage can cause the mirror platform 205 to move counterclockwise around the axis.

[0024] In some implementations, the actuators 220 and 225 and the moving components (i.e., the mirror platform 205 and the gimbal suspension 210) of the MEMS mirror assembly 200 can behave like a spring-mass system. The MEMS mirror assembly 200 may exhibit some intrinsic damping due to the material properties of the elastic mounts or supports that hold the moving components and any fluid, such as a gas or liquid, surrounding the moving components. However, the system may be underdamped, so that after a disturbance, such as a physical shock or vibration, or after repositioning of the mirror platform 205 during normal operation, the moving components may oscillate or ring.This unwanted movement of the mirror platform 205 can render the MEMS mirror assembly 200 unusable for guiding an optical signal until the movement subsides and the mirror platform 205 reaches equilibrium. Therefore, it can be advantageous to increase the damping of the system until it is closer to critical damping, so that the mirror platform 205 oscillates for only a few cycles before reaching equilibrium. In some implementations, the MEMS mirror assembly 200 may be critically damped or overdamped. The implementation of the dampers for damping the MEMS mirror assembly 200 is described below with respect to the... Fig. 3-5 and the Fig. 6A-6C described in more detail.

[0025] Fig. Figure 2B is a graphical representation of a MEMS mirror array 110 according to an illustrative implementation. The MEMS mirror array 110 can contain multiple MEMS mirror assemblies 200a-200c (collectively, the "MEMS mirror assemblies 200"). In some implementations, the MEMS mirrors can be arranged in an offset grid, as shown in Figure 2B. Fig. As shown in Figure 2B, the MEMS mirror assemblies 200 may be arranged in a square grid or a pattern of concentric circles or spirals. In some implementations, the distribution of the MEMS mirror assemblies 200 in the MEMS mirror assembly 110 corresponds to the configuration of the collimators 105, such that each optical signal beam entering or leaving the collimator 105 is directed to or from a corresponding MEMS mirror assembly 200 of the MEMS mirror assembly 110. In some implementations, the MEMS mirror assembly 110 may include (not shown) signal traces made of copper or another conductive material that transmit the switching voltages to the actuators 200 and 225. The switching voltage can originate from the controller 140 or from a digital-to-analog converter assigned to the controller 140, which can convert the switching commands from the controller 140 into analog voltages for actuating the MEMS mirror assemblies 200.In some implementations, the MEMS mirror assembly 110 can contain four signal paths for each MEMS mirror assembly 200. The four signal paths can include a first signal path that transmits a voltage to the actuators 220a and 220b to move the mirror platform 205 about a first axis in a first direction, a second signal path that transmits a voltage to the actuators 220a and 220b to move the mirror platform 205 about the first axis in a second direction, a third signal path that transmits a voltage to the actuators 225a and 225b to move the mirror platform 205 and the gimbal suspension 210 about a second axis in a third direction, and a fourth signal path that transmits a voltage to the actuators 225a and 225b to move the mirror platform 205 and the gimbal suspension 210 about the second axis in a fourth direction.

[0026] In some implementations, the mirror platform 205, the gimbal suspension 210, and the mirror substrate 215 of each MEMS mirror assembly 200 can be fabricated from a combination of the mirror substrate 215 (e.g., a double silicon-on-insulator (DSOI) wafer) bonded to a base substrate (i.e., a second silicon wafer). An exemplary method for fabricating a MEMS mirror assembly 200 is described below with respect to the Fig. 7A-7D described. Exemplary steps of a process for manufacturing a MEMS mirror assembly 200 are described below with regard to the Fig. 8A-81 described.

[0027] Fig. Figure 3 is a graphical representation of a cross-section of a MEMS mirror assembly 300 according to an illustrative implementation. The MEMS mirror assembly 300 is made from a mirror substrate 310 bonded to a base substrate 315. The mirror platform 305 is made from the mirror substrate 310 and is detached from the mirror substrate 310 so that it can rotate about an axis 325. The mirror platform 305 has a reflective surface 320 that is deposited or otherwise applied to a top surface.

[0028] The base substrate 315 defines a cavity 340 and an array of features 345 extending upward from a floor of the cavity 340. A floor surface of the mirror platform 305 defines an array of cavities 330 and an array of features 335. The array of features 335 is dimensioned, shaped, and positioned such that the array of features 345 can extend into the spaces separating the array of features 335 when the mirror platform 305 moves from its rest state. In some implementations, the array of features 335 defines an array of cavities 330 into which the array of features 345 extends when the mirror platform 305 moves from its rest state. In some implementations, the arrangement of features 345 defines an arrangement of cavities 330 into which the arrangement of features 335 extends when the mirror platform 305 moves from its rest state.

[0029] When features 335 and 345 are nested, the fluid between the mirror platform 305 and the base substrate 315 must be forced past features 335 and 345. The friction of the fluid against the side faces of features 335 and 345 generates a shear force along the side faces of the features, which is phase-shifted from the direction of actuation of the mirror platform 305. This generates a damping force. The shear force can further dampen the movement of the mirror platform 305 during any subsequent belling motion. A gap between features 335 and 345 can be configured to promote the desired amount of friction while allowing sufficient clearance to prevent mechanical disturbance due to manufacturing tolerances and / or during the rotation of the mirror platform 305.In some implementations, the gap can be approximately 0.1–20 µm, measured between adjacent sides of features 335 and 345 in a direction parallel to a top surface of the base substrate 315, when the MEMS mirror platform 305 is in a resting state. In other implementations, the gap can be approximately 5–10 µm. The gap can vary depending on the positional state of the MEMS mirror platform 305.

[0030] In some implementations, the presence of the cavities 330 in the mirror platform 305 can reduce the rotational mass of the mirror platform 305 and consequently increase the resonance frequency of the MEMS mirror assembly 300 system. The increase in the resonance frequency enhances the effect of the fluid damping mechanisms.

[0031] In some implementations, the mirror platform 305 can be mounted on a gimbal. The gimbal can facilitate rotational motion in two dimensions. In this configuration, the mirror platform can rotate independently of the gimbal in a first dimension, but in accordance with the gimbal in a second dimension. Consequently, the system can exhibit a moment of inertia that is greater for motion in one dimension than the other. In some implementations, the damping characteristics can be distributed to provide as much damping as is practical for each dimension of rotation. In some implementations, the damping characteristics can be distributed to provide more resistance in a dimension where the system has greater stiffness or a larger moment of inertia, thereby approximating equal damping in both dimensions.In some implementations, additional features may be defined in the underside of the gimbal suspension and in the base substrate area below the gimbal suspension.

[0032] Exemplary configurations of the features of the mirror platform 305 and the base substrate 305 are described below with regard to the Fig. 6A-6C described.

[0033] Fig. Figure 4 is a graphical representation of a cross-section of a MEMS mirror assembly 400 with mirror platform features 435 and base substrate features 445a and 445b (collectively the “base substrate features 445”), which are nested when the mirror platform 405 is at rest, according to an exemplary implementation. The MEMS mirror assembly 400 is similar to the MEMS mirror assembly 300 described above, except that one or more of the mirror platform features 435 or the base substrate features 445 are extended with respect to the interface 450 between the mirror substrate 410 and the base substrate 415. In this configuration, the MEMS mirror assembly 400 can experience more damping when the mirror platform 405 moves between positions close to its rest position.

[0034] In some implementations, the substrate features 445 can contain a first subset of features 445a and a second subset of features 445b. The first subset of features 445a can extend into the spaces separating the mirror platform features 435 at least when the mirror platform 405 is in a first position state. The second subset of features 445b can extend into the spaces separating the mirror platform features 435 at least when the mirror platform 405 is in a second position state. In this way, at least a fraction of the features 445 in each position state of the mirror platform 405 extends into the spaces separating the mirror platform features 435.

[0035] Fig. Figure 5 is a graphical representation of a cross-section of a MEMS mirror assembly 500 with base substrate features 545a and 545b (collectively the "features 545"), which have different heights relative to the bottom of a cavity 540 defined in the base substrate 515, according to an illustrative implementation. The MEMS mirror assembly 500 is similar to the MEMS mirror assembly 300 described above, except that the respective heights of features 545a and 545b can be configured relative to each other to allow a greater range of rotation of the mirror platform 505.In some implementations, the first subset of features 545a is located at a first distance from the axis of rotation 535 of the mirror platform 505, the second subset of features 545b is located at a second distance, greater than the first distance, from the axis of rotation 535 of the mirror platform 505, and the first subset of features 545a extends further upwards from the bottom of the cavity 540 than the second subset of features 545b. This configuration can allow more clearance before the top of a feature 545b comes into contact with the bottom of a cavity 530 in the mirror platform 505.

[0036] The Fig. Figures 6A-6C are graphical representations of exemplary features of the mirror platforms 605, 635, and 665 and the features of the base substrates 620, 650, and 680 according to illustrative implementations. In each graphical representation, white represents the areas recessed relative to the viewing perspective, such as the bottom of a cavity, while black represents the areas of the component raised relative to the viewing perspective, such as the top of a feature or the bottom surface of a mirror platform. In some implementations, the patterns may be reversed; for example, with protrusions on the mirror platforms 605, 635, and 665 and cavities in the base substrates 620, 650, and 680.

[0037] Fig. Figure 6A shows a graphical representation of an exemplary mirror platform 605 and an exemplary base substrate 620. The features of the mirror platform 605 include walls that surround an array of triangular cavities 610. The cavities 610 extend into the base surface 615 of the mirror platform 605. In some implementations, the array of cavities 610 can form a densely packed structure. A densely packed structure of this type allows for the removal of a relatively large amount of mass while leaving behind a grid of walls that maintains the structural integrity of the mirror platform 605. This type of structure also creates a large surface area of ​​the features of the mirror platform 605 for interaction with the features of the base substrate 620.

[0038] The base substrate features an arrangement of triangular projections 625 extending upwards from the bottom of a cavity 630 in the base substrate 620. The projections 625 and the cavities 610 are configured to allow each to interlock with the other as the mirror platform 605 moves relative to the base substrate 620. The dimensions of the cavities 610 and the projections 625 can be configured to generate the desired amount of damping from fluid friction while providing sufficient clearance to allow the desired amount of movement of the mirror platform 605.

[0039] Fig. Figure 6B shows a graphical representation of an exemplary mirror platform 635 and an exemplary base substrate 650. The features of the mirror platform 635 include walls that surround an array of circular or cylindrical cavities 640. The cavities 640 extend into the base surface 645 of the mirror platform 635. In some implementations, the array of cavities 640 can form a densely packed structure. A densely packed structure of this type allows for the removal of a relatively large amount of mass while leaving behind a grid of walls that maintains the structural integrity of the mirror platform 635. This type of structure also creates a large surface area of ​​the features of the mirror platform 635 for interaction with the features of the base substrate 650.

[0040] The base substrate features an arrangement of cylindrical projections 655 extending upwards from the bottom of a cavity 660 in the base substrate 650. The projections 655 and the cavities 640 are configured to allow each to interlock with the other as the mirror platform 635 moves relative to the base substrate 650. The dimensions of the cavities 640 and the projections 655 can be configured to generate the desired amount of damping from fluid friction while providing sufficient clearance to allow the desired amount of movement of the mirror platform 635.

[0041] Fig. Figure 6C shows a graphical representation of an exemplary mirror platform 665 and an exemplary base substrate 680. The features of the mirror platform 665 include walls that surround an array of rectangular cavities 670. The cavities 670 extend into the base surface 675 of the mirror platform 665. In some implementations, the array of cavities 670 can form rectangles that extend lengthwise in two different dimensions. This configuration can create damping in each dimension that is approximately equivalent to the damping in the other dimension. This configuration also creates a large surface area of ​​the features of the mirror platform 665 for interaction with the features of the base substrate 680.

[0042] The base substrate features an arrangement of rectangular projections 685 extending upwards from the bottom of a cavity 690 in the base substrate 680. The projections 685 and the cavities 670 are configured to allow each to interlock with the other as the mirror platform 665 moves relative to the base substrate 680. The dimensions of the cavities 670 and the projections 685 can be configured to generate the desired amount of damping from fluid friction while providing sufficient clearance to allow the desired amount of movement of the mirror platform 665.

[0043] In some implementations, the mirror platform features can form a matrix or grid over substantially all of the bottom surface of the mirror platform 605, 635, and / or 665, except for a fixed-width edge or boundary. The base substrate 620, 650, and / or 680 can contain base substrate features configured to be nested with the mirror platform features during rotation of the mirror platform. However, the base substrate 620, 650, and / or 680 cannot contain features nested with any mirror platform features that have an irregular shape due to bumping against the edge or boundary.

[0044] The Fig. Figures 7A-7D are flowcharts of an exemplary procedure 700 for manufacturing a MEMS mirror assembly, while the Fig. 8A-81 shows the steps of an exemplary process for manufacturing a MEMS mirror array using Method 700 according to illustrative implementations. Method 700 is described below with reference to and concurrently with the manufacturing steps according to the Fig. 8A-81 described. Method 700 includes providing a base substrate that defines an array of cavities, each cavity having several first features extending upward from a floor of the cavity (stage 710). The method includes providing a mirror substrate that defines an array of MEMS actuators and MEMS mirror platforms, each MEMS mirror platform defining several second features on a first side of the MEMS mirror platform, which are sized, shaped, and positioned such that the several second features can fit into the spaces separating the several first features extending upward from a corresponding cavity in the base substrate (stage 720).Method 700 includes coupling the mirror substrate to the base substrate such that the first side of each MEMS mirror platform faces a corresponding cavity in the base substrate, and activation of each MEMS actuator moves the corresponding MEMS mirror platform from a first position state to a second position state, the multiple second features in the second position state extending into the spaces separating the multiple first features (stage 730). Method 700 includes providing a reflective material on a second side of each MEMS mirror platform, opposite the first side of the MEMS mirror platform (stage 740). In some implementations, Method 700 may include providing conductive traces on the mirror substrate for the purpose of supplying actuation voltages to the actuators of each MEMS mirror assembly of the MEMS mirror array (stage 750).

[0045] Method 700 includes the provision of a base substrate that defines an arrangement of cavities, each cavity having several first features extending upwards from a floor of the cavity (stage 710). The base substrate may have a configuration corresponding to one or a combination of base substrates 315, 415, 515, 620, 650 and / or 680, which are described in the Fig. 3, Fig. 4, Fig. 5, Fig. 6A, Fig. 6B and 6C are similar. In some implementations, level 710 can be the one shown in Fig. The additional stages shown in 7B are included. As shown in Fig. As shown in Figure 7B, stage 710 can provide a base substrate 800, as shown in Figure 7B. Fig. 8A is shown, included (stage 711). Stage 710 may include the etching of a cavity 802 into the base substrate 800 (stage 712). The cavity 802 is etched to leave behind an array of first features 804 extending upwards from a bottom of the cavity 802, as shown in Fig. Figure 8B is shown. In some implementations, the etching process may include a reactive ion deep etching (DRIE) process. In some implementations, the height of features 804 is such that they are nested with the features of a mirror substrate when the mirror substrate is in a rest position, as in the one shown above. Fig. 4 described base substrate 415. In some implementations, the raised features 804 can be produced by adding another layer to the lower SOI stack and then using an etching process that stops for the areas below this layer, except for the raised features 804. In some implementations, etching with potassium hydroxide or with tetraethylammonium hydroxide can be used to form a sequence of steps that become the raised features 804, which may be nested with the features of the mirror substrate. In some implementations, the base substrate 800 can be etched such that some of the features 804 have different heights, as in the one described above. Fig. 5 described basic substrate 515. In some implementations, the height difference between the features 804 can be generated by performing one or more additional etching steps, during which only a subset of the features 804 is masked.

[0046] Method 700 includes providing a mirror substrate that defines an arrangement of MEMS actuators and MEMS mirror platforms, each MEMS mirror platform defining multiple second features on a first side of the MEMS mirror platform, which are dimensioned, shaped, and positioned such that the multiple second features can fit into the spaces separating the multiple first features extending upward from a corresponding cavity in the base substrate (step 720). The mirror substrate can have a configuration corresponding to one or more of the mirror substrates 310, 410, and / or 510 described in the Fig. 3, Fig. 4 or 5 are shown, is similar, and can have a mirror platform having a configuration corresponding to one of, or a combination of, mirror platforms 305, 405, 505, 605, 635 and / or 665 shown in the Fig. 3, Fig. 4, Fig. 5, Fig. 6A, Fig. 6B and 6C are similar. In some implementations, level 720 may include the additional levels shown in Fig. 7C are shown. As in Fig. As shown in Figure 7C, step 710 can include the provision of a double silicon-on-insulator (DSOI) stack 806 containing a retaining layer 816, as shown in Figure 7C. Fig. Figure 8C (stage 721) shows that the DSOI stack 806 can contain multiple layers, including an actuator layer 808, a first insulator layer 810, a mirror layer 812, a second insulator layer 814, and a holder layer 816. In some implementations, the actuator layer 808, the mirror layer 812, and the holder layer 816 can contain silicon. The silicon in these layers can be intrinsic or doped, crystalline or amorphous. In some implementations, the holder layer 816 can contain glass. In some implementations, the insulator layers 810 and 814 can be silicon oxide or another dielectric oxide. In some implementations, the insulator layers 810 and 814 can contain organic or polymeric materials, such as polyimide, Kapton, or a protective lacquer. Stage 720 may include the etching of the actuator layer 808 of the DSOI stack 806 to define the arrangement of the second features 818 (stage 722).In some implementations, the second features 818 may include one or a combination of the features and / or cavities of the mirror platforms 305, 405, 505, 605, 635, and / or 665. In some implementations, etching stage 722 may include additional steps to increase or decrease the height of some or all of the features 818.

[0047] Method 700 involves coupling the mirror substrate to the base substrate such that the first side of each MEMS mirror platform faces a corresponding cavity in the base substrate, and the activation of each MEMS actuator moves the corresponding MEMS mirror platform from a first position state to a second position state, with the multiple second features in the second position state extending into the spaces separating the multiple first features (stage 730). In some implementations, stage 730 can be the one described in Fig. The additional levels shown in 7D are included. As shown in Fig. As shown in Figure 7C, stage 730 can contain the fusion bond of the DSOI stack 806, which contains the mirror substrate, with the base substrate 800, which contains the base substrate, as shown in Figure 7C. Fig. Figure 8D shows (step 731). The DSOI stack 806 and the base substrate 800 are joined such that the features 804 are aligned with the spaces between the features 818. In some implementations, a silicon-silicon fusion process or plasma-initiated bonding may be used to create a bond between the DSOI stack 806 and the base substrate 800 at the interface 820. In some implementations, an anodic bond may be used to join substrate materials other than silicon. Step 730 may include the removal of the retainer layer 816 and the second insulator layer 814, as shown in Figure 8D. Fig. Figure 8E (step 732) shows that removing the holder layer 816 and the second insulator layer 814 exposes the mirror layer 812, leaving the mirror substrate 823 still bonded to the base substrate 800. In some implementations, the holder layer 816 and the second insulator layer 814 are removed using one or more etching steps. In some implementations, the holder layer 816 and the second insulator layer 814 are removed using one or more machining or planing steps. In some implementations, a combination or sequence of several processes can be used to remove these layers. For example, a grinding and polishing operation could reduce the layer to a thickness that can be more easily etched using a potassium hydroxide or tetraethylammonium hydroxide wet process. The advantage of this multi-step process is that it can be used on multiple wafers simultaneously.In some implementations, a DRIE-based process could be used. However, a DRIE process may only be practical for implementing it on a single wafer at a time. Stage 730 may include etching the fixture features of the top layer, as shown in [reference missing]. Fig. 8F is shown (stage 733). This stage exposes the first insulator layer 810 and begins the process of removing the actuator sections, the gimbal suspension, and the mirror platform. Stage 730 may include etching the first insulator layer 810 to expose the actuator layer 808, as shown in Fig. 8G is shown (stage 734). Stage 730 can include etching through the mirror layer 812, the first insulator layer 810, and the actuator layer 808 around the mirror platform 824, as shown in Fig. 8H is shown (stage 735). This stage can complete the release of the actuators, the gimbal suspension, and the mirror platform 824. In some implementations, when released, the mirror platform 824 is free to rotate about an axis 826. As the mirror platform 824 rotates about the axis 826, the features 804 can fit into the spaces separating the features 818 to achieve the desired damping of the mirror platform 824's movement.

[0048] Method 700 includes providing a reflective material 828 arranged on a second side of each MEMS mirror platform 824, opposite the first side of the MEMS mirror platform, as shown in Fig.8I is shown (level 740). In some implementations, the reflective material 828 may contain a pure metal or alloy including gold, nickel, aluminum, chromium, titanium, or any combination thereof. In some implementations, the reflective material 828 may contain a dielectric-based film tuned to reflect one or more target wavelengths. The reflective material 828 may be deposited using sputtering, thin-film, or thick-film deposition techniques.

[0049] In some implementations, Method 700 may include providing conductive traces on the mirror substrate for the purpose of supplying actuation voltages to the actuators of each MEMS mirror assembly of the MEMS mirror array (stage 750). Each MEMS actuator may include a first section and a second section. Method 700 may include providing multiple first conductive traces on the mirror substrate. Each first conductive trace may be configured to carry a first actuation voltage to a corresponding first section of the MEMS actuator to move a corresponding MEMS mirror platform in a first direction. Method 700 may include providing multiple second conductive traces on the mirror substrate.Every second conductive track can be configured to carry a second actuation voltage to a corresponding second section of the MEMS actuator to move the corresponding MEMS mirror platform in a second direction opposite to the first direction.

[0050] While this description contains many specific implementation details, these should not be interpreted as limitations on the scope of protection of any inventions or on what can be claimed, but rather as descriptions of features specific to particular implementations of the particular inventions. Certain features described in this description in the context of separate implementations may also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation may also be implemented separately in multiple implementations or in any suitable subcombination.Although the features described above may be effective in certain combinations and may even initially be claimed as such, in addition, one or more features from a claimed combination may in some cases be removed from the combination and the claimed combination may be directed to a subcombination or a variation of a subcombination.

[0051] While the operations in the drawings are depicted in a specific order, this should not be interpreted as requiring that such operations be performed in the specific order shown, or in any sequential order, or that all illustrated operations be performed to achieve the desired results. Multitasking and parallel processing can be advantageous under certain circumstances. Furthermore, the separation of the various system components in the implementations described above should not be interpreted as requiring such separation in all implementations. It should be recognized that the described program components and systems can generally be integrated into a single software product or packaged across multiple software products.

[0052] References to "or" may be interpreted inclusively, so that any terms described using "or" may refer to any of a single described term, more than one described term, or all of the described terms. The designations "first," "second," "third," etc., are not necessarily intended to indicate an order, being generally used simply to distinguish between identical or similar details or elements.

[0053] For those skilled in the art, various modifications to the implementations described in this disclosure may be readily apparent, and the generic principles defined herein can be applied to other implementations without departing from the inventive concept or scope of protection of this disclosure. Consequently, the claims are not intended to be limited to the implementations shown herein, but rather to correspond to the broadest scope of protection consistent with this disclosure, the principles, and the novel features disclosed herein.

[0054] A mirror assembly of a microelectromechanical system (MEMS) includes a base substrate that defines a cavity and several first features extending upward from the bottom of the cavity. The MEMS mirror assembly includes a mirror substrate coupled to the base substrate and defines a MEMS actuator and a MEMS mirror platform. Actuation of the MEMS actuator moves the MEMS mirror platform from a first position state to a second position state. The MEMS mirror platform defines several second features on one side of the MEMS mirror platform facing the base substrate. These second features are dimensioned, shaped, and positioned such that, when the mirror platform is in the second position state, they extend into the spaces separating the first features.The MEMS mirror assembly contains a reflective material that is located on one side of the MEMS mirror platform facing away from the base substrate.

Claims

[1] Mirror assembly of a microelectromechanical system (MEMS) comprising: a base substrate (315; 415; 515; 800) that defines a cavity (340; 440; 540; 802) and several first features (804) that extend upwards from a floor of the cavity (340; 440; 540; 802); a mirror substrate (310; 410; 510; 822) coupled to the base substrate (315; 415; 515; 800) and defining a first MEMS actuator and a MEMS mirror platform (305; 405; 505; 824), wherein the mirror substrate (310; 410; 510; 822) defines a gimbal suspension (210) positioned above the cavity (340; 440; 540; 802), wherein the gimbal suspension (210) defines a second MEMS actuator and a cutout containing the MEMS mirror platform (305; 405; 505; 824), wherein the first and second MEMS actuators are vertical comb drive actuators, each driving a first and have a second section; wherein actuation of the first MEMS actuator moves the MEMS mirror platform (305; 405; 505; 824) from a first position state to a second position state and the MEMS mirror platform (305; 405; 505; 824) defines several second features (818) on one side of the MEMS mirror platform (305; 405; 505; 824) facing the base substrate (315; 415; 515; 800), which are dimensioned, shaped and positioned such that the several second features (818) extend into the spaces separating the several first features (804) when the MEMS mirror platform (305; 405; 505; 824) is in the second position state; wherein the actuation of the first MEMS actuator rotates the MEMS mirror platform (305; 405; 505; 824) about a first axis and the actuation of the second MEMS actuator rotates the gimbal suspension (210) and the MEMS mirror platform (305; 405; 505; 824) about a second axis which is substantially orthogonal to the first axis; and a reflective material (828) arranged on one side of the MEMS mirror platform (305; 405; 505; 824) facing away from the base substrate (315; 415; 515; 800). [2] MEMS mirror assembly according to claim 1, wherein: the first MEMS actuator rotates the MEMS mirror platform (305; 405; 505; 824) around the first axis to reach the first position state and the second position state. [3] MEMS mirror assembly according to claim 1 or claim 2, wherein: the multiple second features (818) form multiple walls that define openings into which the multiple first features (804) can extend when the MEMS mirror platform (305; 405; 505; 824) is in the second position state. [4] MEMS mirror assembly according to claim 3, wherein: the mirror platform moves from the first position state to the second position state by rotating around the first axis, the several first features (804) include a first subset of features located at a first distance from the first axis and a second subset of features located at a second distance from the first axis that is greater than the first distance and the first subset of features extends further from the bottom of the cavity (340; 440; 540; 802) than the second subset of features. [5] MEMS mirror assembly according to any one of claims 1 to 4, wherein: the first several features (804) extend to a height greater than the depth of the cavity (340; 440; 540; 802). [6] MEMS mirror assembly according to any one of claims 1 to 5, wherein: a first subset of the first set of several features extends into spaces that separate a first subset of the second set of several features when the mirror platform (305; 405; 505; 824) is in the first position state; and a second subset of the first multiple features extends into spaces separating a second subset of the second multiple features when the mirror platform (305; 405; 505; 824) is in the second position state. [7] MEMS mirror assembly according to any one of claims 1 to 6, comprising: a fluid surrounding the MEMS mirror platform (305; 405; 505; 824), the multiple first features (804) and the multiple second features (818), wherein: a gap between the multiple first features (804) and the multiple second features (818) between 5 and 10 µm, measured in a direction parallel to a top surface of the base substrate (315; 415; 515; 800) when the MEMS mirror platform (305; 405; 505; 824) is in a resting state. [8] MEMS mirror assembly according to any one of claims 1 to 7, wherein: A first voltage applied across the first section of the first MEMS actuator moves the MEMS mirror platform (305; 405; 505; 824) in a first direction and A second voltage applied across the second section of the first MEMS actuator moves the MEMS mirror platform (305; 405; 505; 824) in a second direction opposite to the first direction. [9] Method for fabricating a mirror arrangement of a microelectromechanical system (MEMS) comprising: Providing a base substrate (315; 415; 515; 800) defining an arrangement of cavities (340; 440; 540; 802), each cavity (340; 440; 540; 802) having several first features (804) extending upwards from a floor of the cavity (340; 440; 540; 802); Providing a mirror substrate (310; 410; 510; 822) defining an arrangement of a first MEMS actuator and a first MEMS mirror platform (305; 405; 505; 824), wherein the mirror substrate (310; 410; 510; 822) further defines an arrangement of gimbal suspensions (210) positioned above the cavities (340; 440; 540; 802), each gimbal suspension (210) defining a second MEMS actuator (225) and a cutout containing a corresponding MEMS mirror platform (305; 405; 505; 824) of the arrangement of MEMS mirror platforms (305; 405; 505; 824), each first and second MEMS actuator having vertical Comb drive actuators are those that each have a first and a second section; wherein each MEMS mirror platform (305; 405; 505; 824) defines several second features on a first side of the MEMS mirror platform (305; 405; 505; 824) which are dimensioned, shaped and positioned such that the several second features (818) can fit into the spaces separating the several first features (804) which extend upward from a corresponding cavity (340; 440; 540; 802) in the base substrate (315; 415; 515; 800); Coupling the mirror substrate (310; 410; 510; 822) to the base substrate (315; 415; 515; 800), such that the first side of each MEMS mirror platform (305; 405; 505; 824) faces a corresponding cavity (340; 440; 540; 802) in the base substrate (315; 415; 515; 800) and the activation of the first MEMS actuator moves the corresponding MEMS mirror platform (310; 410; 510; 822) from a first position state to a second position state, wherein the multiple second features (818) in the second position state extend into spaces that separate the multiple first features (804); wherein actuation of the first MEMS actuator rotates the corresponding MEMS mirror platform (305; 405; 505; 824) about a first axis, and actuation of the second MEMS actuator rotates the corresponding gimbal suspension (210) and the corresponding MEMS mirror platform (305; 405; 505; 824) about a second axis that is substantially orthogonal to the first axis; and Providing a reflective material (828) arranged on a second side of each MEMS mirror platform (305; 405; 505; 824) opposite the first side of the MEMS mirror platform (305; 405; 505; 824). [10] Method according to claim 9, wherein the first MEMS actuator is configured to rotate the MEMS mirror platform (305; 405; 505; 824) about the first axis to reach the first position state and the second position state. [11] Method according to claim 9 or claim 10, wherein: the multiple second features (818) form multiple walls that define openings into which the multiple first features (804) can extend when the MEMS mirror platform (305; 405; 505; 824) is in the second position state. [12] Method according to claim 11, wherein: Each MEMS mirror platform (305; 405; 505; 824) is configured to move from the first position state to the second position state by rotating around the first axis, the several first features (804) include a first subset of features located at a first distance from the first axis, and a second subset of features located at a second distance from the first axis that is greater than the first distance, and the first subset of features extends further from the bottom of the cavity (340; 440; 540; 802) than the second subset of features. [13] Method according to any one of claims 9 to 12, wherein: the first several features (804) extend to a height greater than the depth of the cavity (340; 440; 540; 802). [14] Method according to any one of claims 9 to 13, wherein: a first subset of the first multiple features extends into spaces separating a first subset of the second multiple features when the MEMS mirror platform (305; 405; 505; 824) is in the first position state; and a second subset of the first multiple features extends into spaces separating a second subset of the second multiple features when the mirror platform (305; 405; 505; 824) is in the second position state. [15] Method according to any one of claims 9 to 14, comprising: Providing a fluid surrounding the MEMS mirror platform (305; 405; 505; 824), the multiple first features (804) and the multiple second features (818), wherein: a gap between the multiple first features (804) and the multiple second features (818) between 5 and 10 µm, measured in a direction parallel to a top surface of the base substrate (315; 415; 515; 800) when the MEMS mirror platform (305; 405; 505; 824) is in a resting state. [16] Method according to any one of claims 9 to 15, wherein the method comprises: Providing several first conductive tracks on the mirror substrate (310; 410; 510; 822), each first conductive track being configured to convey a first actuation voltage to a corresponding first section of the first MEMS actuator to move the MEMS mirror platform (305; 405; 505; 824) in the first direction, and Providing several second conductive tracks on the mirror substrate (310; 410; 510; 822), each second conductive track being configured to convey a second actuation voltage to a corresponding second section of the first MEMS actuator to move a corresponding MEMS mirror platform (305; 405; 505; 824) in a second direction opposite to the first direction.

Images