HK1259199A1 - Optical circuit switch mirror array crack protection - Google Patents

Description

Crack protection for reflector arrays in optical circuit switches

Technical Field

This application claims priority to and the benefit of U.S. Provisional Patent Application No. 62/449,429, filed on January 23, 2017, entitled “OPTICAL CIRCUIT SWITCH MIRROR ARRAY CRACK PROTECTION,” the entire contents of which are hereby incorporated by reference.

Background Art

Optical circuit switches have become increasingly prominent in data centers in recent years due to their ability to quickly convert optical data signals without first converting those signals back to the electrical domain. Some optical circuit switches are implemented using one or more single-axis or dual-axis gimbaled micro-electromechanical systems (MEMS) mirrors whose orientation can be adjusted to direct light from the switch's input port to the switch's desired output port.

Summary of the Invention

According to one aspect, the subject matter described in this disclosure relates to a microelectromechanical system (MEMS) mirror assembly comprising a mirror substrate defining an actuator, a gimbal structure, and a portion of a mirror cutout having an inner periphery. The mirror assembly includes a mirror having a reflective surface, the mirror being positioned within the mirror cutout of the mirror substrate and coupled to the mirror substrate via at least one stator. The mirror is supported by the gimbal structure. The mirror has a substantially planar surface defining a primary reflective plane of the mirror. When the primary reflective plane of the mirror is parallel to the mirror substrate, a gap separates the periphery of the mirror from the inner periphery of the mirror cutout, except at the at least one stator, substantially around the entire periphery of the mirror. The size of the gap is substantially constant around the periphery of the mirror, except for a plurality of nibbles defined in at least one of the mirror substrate and the mirror. Each kerf comprises an extension of the gap into the reflector substrate or the reflector, and each kerf has a length between about 50 microns and about 200 microns and a width between about 50 microns and about 100 microns. At least one kerf is defined in the gimbal structure and comprises an extension of the gap into the gimbal structure.

According to one aspect, the subject matter described in the present disclosure relates to a method for manufacturing a microelectromechanical system (MEMS) mirror assembly, the method comprising: defining a cavity in a base substrate; coupling a mirror substrate to a base substrate such that a first side of the mirror substrate faces the cavity in the base substrate; defining a MEMS actuator, a gimbal structure, and portions of a MEMS mirror in the mirror substrate such that the first side of the MEMS mirror faces the cavity in the base substrate and a portion of the mirror substrate is separated from the mirror by a gap; defining one or more kerfs in at least one of the mirror substrate and the mirror, wherein each kerf includes an extension of the gap into the mirror substrate or the mirror and each kerf has a length between about 50 microns and about 200 microns and a width between about 50 microns and about 100 microns; and wherein at least one kerf is defined in the mirror substrate and the mirror and includes an extension of the gap into the gimbal structure and the mirror; and disposing a reflective material on a second side of the MEMS mirror opposite the first side of the MEMS mirror.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings, which are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the invention.

1A illustrates a perspective view of a vertical comb drive actuated dual-axis mirror assembly according to an example embodiment.

FIG. 1B illustrates a plan view of the reflector assembly shown in FIG. 1A .

2 illustrates a flow chart of an example method for manufacturing a reflector assembly, such as the reflector assembly shown in FIGs. 1A and 1B .

3A-3I illustrate cross-sectional views of a portion of a reflector assembly manufactured according to the method shown in FIG. 2 .

For clarity, not every component is labeled in every figure. The drawings are not intended to be drawn to scale. Like reference numbers and names in the various drawings indicate like elements.

DETAILED DESCRIPTION

A typical MEMS mirror array includes multiple MEMS mirror assemblies. A typical MEMS mirror assembly includes a mirror supported by a gimbal structure and multiple actuators. The mirror assembly can be manufactured using a silicon-on-insulator (SOI) or double-layer silicon-on-insulator (DSOI) mirror substrate coupled to a base substrate. The base substrate provides structural stability to the mirror assembly. One or more of the actuators are actuated to tilt the mirror about a torsion beam relative to the base substrate. The structural features of a typical MEMS mirror assembly can be etched into different silicon layers using deep reactive ion etching (DRIE). However, the DRIE process can lead to an increased occurrence of thermally induced cracking of the mirror structure, which in turn reduces the yield of the mirror array. Cracking of the mirror structure can also be caused by the presence of oxides or thin films on the silicon, which can produce a bimorph structure that bends under thermal stress.

Systems and methods according to the present disclosure relate to a microelectromechanical system (MEMS) mirror assembly having crack protection features such as one or more nibs. As used herein, a "nibble" refers to a gap between two structures extending into one of the two structures. A MEMS mirror assembly according to an example embodiment enables the mirror to rotate about two rotational axes using multiple actuators and a dual-axis gimbal structure. In some embodiments, the MEMS mirror assembly includes vertical comb drive actuators, each actuator including a drive comb interleaved with a reference comb.

FIG1A illustrates a perspective view of a vertical comb drive actuated dual-axis MEMS mirror assembly 100 according to an example embodiment. FIG1B illustrates a plan view of the mirror assembly 100 shown in FIG1A . The mirror assembly 100 includes a circular mirror 105. The mirror 105 includes a mirror platform 110. The mirror platform 110 has a substantially flat reflective surface 115 that defines a primary reflective plane of the mirror 105. In some embodiments, the mirror 105 is circular with a diameter between about 100 μm and about 2 mm. In some embodiments, the mirror 105 is elliptical or oval with a major axis and a minor axis of the mirror 105 between about 500 μm and about 2 mm. In some other embodiments, the mirror 105 has a square, a rectangle, or any other geometrically regular or irregular shape.

The mirror assembly 100 is configured to rotate the mirror 105 about two rotation axes using a plurality of vertical comb drive actuators and a dual-axis gimbal structure, such as a gimbal ring 130. The gimbal ring 130 supports the mirror 105. To enable the mirror 105 to rotate about a first rotation axis, such as an inner rotation axis 155, the mirror platform 110 includes a first inner torsion beam 120a and a second inner torsion beam 120b (collectively referred to as inner torsion beams) extending outward from the mirror platform 110 and serving as torsion beams for the mirror 105 along the inner rotation axis 155.

A plurality of actuators, such as a first inner actuator, a second inner actuator, a third inner actuator, and a fourth inner actuator (collectively referred to as inner actuators), enable the reflector 105 to tilt about the inner torsion beam about the inner rotation axis 155. Each inner actuator includes a reference comb interleaved with a drive comb. The first and second inner actuators are located on either side of the first inner torsion beam 120a. The third and fourth inner actuators are located on either side of the second inner torsion beam 120b. The reference combs of the inner actuators extend outward from the inner torsion beam. The gimbal ring 130 includes a plurality of comb-like structures, such as a first inner stator 140a, a second inner stator 140b, a third inner stator 140c, and a fourth inner stator 140d. The first inner stator 140a and the second inner stator 140b serve as the drive combs for the first and second inner actuators, respectively. The third and fourth inner stators 140a and 140b serve as drive combs for the third and fourth inner actuators, respectively.

Applying a voltage to a pair of inner stators 140 (e.g., inner stators 140a and 140c or inner stators 140b and 140d) actuates their corresponding inner actuators and tilts the mirror 105 about an inner torsion beam along an inner rotation axis 155. The reference combs of the inner actuators 140 are maintained at the same potential. The first inner stator 140a and the third inner stator 140c are electrically coupled to each other. The second inner stator 140b and the fourth inner stator are electrically coupled to each other. The first inner stator 140a and the third inner stator 140c are electrically isolated from the second inner stator 140b and the fourth inner stator 140d. Applying a first voltage to the first inner stator 140a and the third inner stator 140c creates a potential difference between the first inner stator 140a and the third inner stator 140c and their corresponding reference combs, which tilts the mirror 105 in one direction about the inner rotation axis 155. Applying a second voltage to the second inner stator 140 b and the fourth inner stator 140 d generates a potential difference between the second inner stator 140 b and the fourth inner stator 140 d and their corresponding reference combs, which causes the mirror 105 to tilt in opposite directions about the inner rotation axis 155 .

The reflector assembly 100 is configured to rotate the reflector 105 about a second rotation axis, such as an outer rotation axis 150, using a plurality of vertical comb drive actuators and a gimbal ring 130. To enable the reflector 105 to rotate about the outer rotation axis 150, the gimbal ring 130 includes a first outer torsion beam 121 a and a second outer torsion beam 121 b (collectively referred to as outer torsion beams) along the outer rotation axis 150, which serve as torsion beams for the gimbal ring 130 and the reflector 105.

A plurality of vertical comb drive actuators, such as a first external actuator, a second external actuator, a third external actuator, and a fourth external actuator (collectively referred to as external actuators), enable the gimbal ring 130 and the mirror 105 to tilt about an outer rotation axis 150 about an outer torsion beam. Each external actuator includes a reference comb interleaved with a drive comb. The first and second external actuators are located on either side of the first outer torsion beam 121 a. The third and fourth external actuators are located on either side of the second outer torsion beam 121 b.

The reference combs of the external actuators of the reflector assembly 100 extend from the external torsion beam. The reflector assembly 100 includes a plurality of comb-like structures, such as a first external stator 135a, a second external stator 135b, a third external stator 135c, and a fourth external stator 135d. The first external stator 135a and the second external stator 135b serve as the drive combs for the first and second external actuators, respectively. The third external stator 135c and the fourth external stator 135d serve as the drive combs for the third and fourth external actuators, respectively.

Applying a voltage to a pair of outer stators 135 actuates the corresponding external actuators and causes the gimbal ring and mirror 105 to tilt about an outer rotation axis 150 and around an outer torsion beam. The reference combs of the external actuators are maintained at the same potential. The first and third outer stators 135a, 135c are electrically coupled to each other. The second and fourth outer stators 135b, 135d are electrically coupled to each other. The first and third outer stators 135a, 135c are electrically isolated from the second and fourth outer stators 135b, 135d. Applying a first voltage to the first and third outer stators 135a, 135c creates a potential difference between the first and third outer stators 135a, 135c and their corresponding reference combs, causing the gimbal ring 130 and mirror 105 to tilt in one direction about the outer rotation axis 150 and around the outer torsion beam. Applying a second voltage to the second outer stator 135b and the fourth outer stator 135d generates a potential difference between the second outer stator 135b and the fourth outer stator 135d and their corresponding reference combs, which causes the gimbal ring 130 and the mirror 105 to tilt in opposite directions about the outer rotation axis 150 and about the outer torsion beam. In some implementations, the inner rotation axis 155 is perpendicular to the outer rotation axis 150.

The mirror assembly 100 can be fabricated from a silicon-on-insulator (SOI) or double-layer silicon-on-insulator (DSOI) mirror substrate coupled to a base substrate. The base substrate provides structural stability to the mirror assembly. Structural features of the mirror assembly 100, such as the vertical comb drive actuator, the gimbal ring 130, and the mirror 105, including the mirror platform 110, can be etched into the silicon layer of the mirror substrate using deep reactive ion etching (DRIE). In embodiments comprising a DSOI mirror substrate, the mirror platform 110 of the mirror 105 and the reference comb of the inner actuator can be defined in the lower silicon layer of the mirror substrate, and the drive comb of the inner actuator can be defined in the upper layer of the mirror substrate. In embodiments comprising a DSOI mirror substrate, the reference comb of the outer actuator can be defined in the lower silicon layer of the mirror substrate, and the drive comb of the outer actuator can be defined in the upper layer of the mirror substrate. Similar comb structures may be located directly below the drive combs in the lower silicon layer, but these lower comb structures are electrically isolated from the actual drive combs by an intervening insulating layer.

The mirror 105 can be tilted relative to the base substrate about torsion beams (such as inner and outer torque beams) formed along rotational axes (such as inner and outer rotational axes 155 and 150). To control the position of the mirror 105, the lower silicon layer of the mirror substrate (and therefore the reference comb of the vertical comb drive actuator) and the base substrate can be maintained at ground potential. The mirror assembly 100 includes interconnects 165 that can be deposited and patterned on the upper surface of the upper silicon layer of the mirror substrate. The interconnects 165 can carry a corresponding actuation potential to the drive combs of each actuator of the mirror assembly. Applying a potential to the drive combs induces a potential difference between the portion of the drive comb formed by the upper silicon layer of the mirror substrate and its corresponding reference comb formed in the lower silicon layer of the mirror substrate, which causes the mirror platform 110 of the mirror 105 to rotate about the rotational axis (such as inner and outer rotational axes 155 and 150).

The reflector assembly 100 includes a reflector cutout and is defined in a reflector substrate of the reflector assembly 100. The reflector 105 is positioned within the reflector cutout and supported by the gimbal ring 130. As described above, the reflector 105 has a substantially flat reflective surface 115 that defines a primary reflective plane of the reflector 105. When the reflector 105 is positioned within the reflector cutout and the primary reflective plane of the reflector 105 is parallel to the reflector substrate of the reflector assembly 100, the space between the perimeter of the reflector 105 and the inner perimeter of the gimbal ring 130 forms an inner gap 145 that is constant around substantially the entire perimeter of the reflector 105, except at the inner stator. In addition, when the reflector 105 is located within the reflector cutout and the main reflection plane of the reflector 105 is parallel to the reflector substrate of the reflector assembly 100, the space between the outer periphery of the universal ring 130 and the rest of the reflector substrate forms an outer gap substantially around the entire outer periphery of the universal ring 130 except at the outer stator 135.

The reflector assembly 100 can be used in a reflector array. To allow for increased packing density of multiple reflector assemblies in the reflector array and to achieve desired mechanical properties, the spacing between the reflector 105 and the gimbal ring 130 (i.e., inner gap 145) and the spacing between the gimbal ring 130 and the rest of the reflector substrate (i.e., outer gap) are each relatively small. For example, the inner gap 145 and the outer gap can typically be on the order of about 3 μm to about 10 μm wide. In some embodiments, the inner gap 145 between the reflector 105 and the gimbal ring 130 is larger than the outer gap between the gimbal ring 130 and the upper surface of the upper silicon layer of the reflector substrate.

As described above, structural features of the mirror assembly, such as the vertical comb drive actuator, gimbal ring 130, and mirror 105, can be etched into the silicon layer using deep reactive ion etching (DRIE). Given that the inner gap 145 between the mirror 105 and the gimbal ring 130, and the outer gap (not shown) between the gimbal ring 130 and the rest of the mirror substrate, are relatively narrow relative to the thickness of the substrate and the heat released by a typical DRIE process, the mirror array may have a reduced yield due to thermally induced cracking of the mirror structure of the mirror assembly. In particular, the DRIE process may result in an increase in the occurrence of cracks where the inner stator 140 contacts the mirror 105 and the outer stator 135 contacts the gimbal ring 130.

As described above, cracks in the mirror 105 can be induced by process-related heat or by the presence of oxides or thin films on the silicon, which can create a bimorph structure that bends under thermal stress. The occurrence of cracks in the mirror 105 can be reduced in the mirror assembly 100 by introducing a plurality of kerfs at strategic locations along the perimeter of the gimbal ring 130 and/or the perimeter of the mirror 105. In Figures 1A and 1B, the size of the internal gap 145 between the mirror 105 and the gimbal ring 130 is substantially constant around the perimeter of the mirror 105, except at the inner stator 140 and the plurality of kerfs 125. The kerfs 125 are defined in at least one of the gimbal ring 130 (formed by the mirror substrate) and the mirror platform 110 of the mirror 105. Each of the plurality of kerfs 125 includes an extension of the internal gap 145 into the gimbal ring 130 and/or the mirror platform 110 of the reflector 105 and locally increases the size of the internal gap 145 between the reflector 105 and the gimbal ring 130. The reflector assembly 100 includes a plurality of kerfs 125 that extend into the mirror platform 110 of the reflector instead of extending into the gimbal ring 130. The reflector assembly 100 includes a plurality of kerfs 125 that extend into the mirror platform 110 and the gimbal ring 130. In some embodiments, the reflector assembly 100 may include a plurality of kerfs 125 that extend into the gimbal ring 130 instead of extending into the mirror platform 110.

As described above, the DRIE process may result in an increase in cracking in the event that the inner stator 140 strikes the reflector 105. Therefore, the reflector assembly 100 includes a plurality of kerfs 125 adjacent to the inner stator 140 that extend into the reflector platform 110 rather than into the gimbal ring 130. Further away from the inner stator 140, the reflector assembly 100 includes a plurality of kerfs 125 that extend into both the reflector platform 110 and the gimbal ring 130. As described above, the DRIE process may also result in an increase in cracking in the event that the outer stator 135 strikes the gimbal ring 130. In some embodiments, one or more of the kerfs 125 may be introduced around the outer periphery of the gimbal ring 130 and/or adjacent to one or both ends of the outer stator 135. In such embodiments, each kerf locally increases the size of the outer gap.

In some embodiments, the inner gap 145 is substantially constant around the perimeter of the reflector 105, except at the kerf, inner stator 140, or outer stator 135. Similarly, in some embodiments, the gap 145 is substantially constant around the outer perimeter of the gimbal ring 130, except at the location of the kerf 125 or at the inner stator 140 or outer stator 135.

In some embodiments, a plurality of kerfs 125 are positioned at regular intervals around the perimeter of the reflector 105, for example, every 90 degrees, such that a line drawn between alternate kerfs 125 (i.e., excluding those immediately adjacent to the inner stator 140) bisects the angle formed between the inner and outer rotational axes 155 and 150. In other embodiments, a plurality of kerfs 125 are positioned at 60-degree intervals or other regular intervals around the perimeter of the reflector 105. The kerfs 125 are sized such that they are larger than the smallest opening defined by the upper and lower silicon layers of the reflector assembly 100. In some embodiments, the shape of the kerfs 125 is generally elliptical. In some embodiments, the length of the kerfs 125, in a direction tangential to the perimeter of the reflector 105, can be between about 50 μm and about 200 μm. In some embodiments, the ratio of the length of the kerf 125 in a direction tangential to the perimeter of the reflector 105 to the thickness of the reflector substrate can be up to about 4:1, with the maximum kerf length being up to about 200 μm. In some embodiments, the width of the kerf 125 in the radial dimension of the reflector 105 can be between about 50 μm and about 100 μm. In some embodiments, the ratio of the width of the kerf 125 in the radial dimension of the reflector 105 to the thickness of the reflector substrate can be between about 1:1 and about 2:1, with the maximum kerf width being up to about 100 μm. Other sizes and shapes of kerfs 125 can be used without departing from the scope of the present invention.

As described above, structural features of the mirror components such as the vertical comb drive actuator, the gimbal ring 130, and the mirror 105 can be etched into the silicon layer using deep reactive ion etching (DRIE). In some embodiments, the minimum feature size of these structural components can be much smaller than the thickness of the silicon layer, for example, on the order of about 1 μm and about 10 μm. In some embodiments, the width of the teeth (or "fingers") of the vertical comb drive actuator can be between about 1.0 μm and about 10.0 μm, although other sizes are also suitable. In some embodiments, the length of the teeth (or "fingers") of the vertical comb drive actuator can be between about 10 μm and about 200 μm, although other sizes are also suitable.

In some embodiments, the reflective surface 115 can be formed by coupling a reflective coating to the uppermost surface of the reflector 105. In some embodiments, the reflective coating can be formed from a metal deposit layer, such as, but not limited to, aluminum, silver, or gold. In some embodiments, the reflective coating can be formed from a metal deposit layer and a dielectric material layer, or alternating layers of metal and dielectric material, forming a dielectric-enhanced reflector or a dielectric reflector, respectively. In other embodiments, other reflective materials can be used without departing from the scope of this disclosure.

Figure 2 illustrates a flow chart of an example method 200 of manufacturing the mirror assembly 100 of Figures 1A and 1 B. Figures 3A-3I illustrate cross-sectional views of a portion of the mirror assembly 100 of Figures 1A and 1 B at various stages of the method 200 of Figure 2 . Method 200 includes defining a cavity in a base substrate (stage 205); coupling a mirror substrate to the base substrate such that a first side of the mirror substrate faces the cavity in the base substrate (stage 210); defining a MEMS actuator and a portion of a MEMS mirror in the mirror substrate such that the first side of the MEMS mirror faces the cavity in the base substrate and a portion of the mirror substrate is separated from the mirror by a gap (stage 215); defining one or more kerfs in at least one of the mirror substrate and the mirror, wherein each kerf comprises an extension of the gap into the mirror substrate or the mirror and each kerf has a length between approximately 50 microns and 200 microns and a width between approximately 50 microns and 100 microns (stage 220); and disposing a reflective material on a second side of the MEMS mirror opposite the first side of the MEMS mirror (stage 225).

Method 200 includes defining a cavity in a base substrate (stage 205). As shown in Figures 3A and 3B, cavity 302 is defined in base substrate 305 by etching cavity 302 into base substrate 305. Method 200 includes coupling a mirror substrate to the base substrate such that a first side of the mirror substrate faces the cavity in the base substrate (stage 210). As shown in Figure 3C, DSOI stack 306 includes a silicon handle 320, a first insulating layer 310a, and a mirror substrate 308. Mirror substrate 308 includes a first silicon layer 316a, a second insulating layer 310b, and a second silicon layer 316b. A first side of first silicon layer 316a faces cavity 302 in base substrate 305.

3D , the DSOI stack 306 is coupled to the base substrate 305 by bonding the DSOI stack 306 to the base substrate 305. In some embodiments, the DSOI stack 306 is fusion bonded to the base substrate 305. After bonding, as shown in FIG3E , the silicon handle 320 and the first insulating layer 310 a are removed, leaving the mirror substrate 308 bonded to the base substrate 305.

3F, the first silicon layer 316a of the mirror substrate 308 is etched to expose the second insulating layer 310b. This etch also defines other features in the upper silicon layer such as portions of the drive combs and torsion beams.

Method 200 includes defining a MEMS actuator, a gimbal structure, and an additional portion of a MEMS mirror in a mirror substrate such that a first side of the MEMS mirror faces a cavity in the base substrate and a portion of the mirror substrate is separated from the mirror by a gap (stage 215). As shown in FIG3G , an exposed portion of a second insulating layer 310 b of the mirror substrate 308 is removed, thereby exposing a portion of a second silicon layer 316 b. As shown in FIG3H , one or more portions of the exposed portion of the second silicon layer 316 b are etched to define a mirror platform 325 of the MEMS mirror. A first side of the mirror platform 325 faces the cavity 302 in the base substrate 305. A lower portion of one or more MEMS actuators (such as a reference comb of a vertical comb drive actuator of the mirror assembly 100 in FIGS. 1A and 1B ) is also defined in the mirror substrate 308.

As mentioned above in the discussion of the mirror assembly 100 of Figures 1A and 1B, applying an electric potential to the drive comb induces a potential difference between the portion of the drive comb formed by the first silicon layer of the mirror substrate and its corresponding reference comb formed in the second silicon layer of the mirror substrate, thereby causing the mirror platform of the mirror to rotate about the rotation axis. Cavity 302 in base substrate 305 provides space for mirror platform 325 to rotate about rotation axis 335. The confined size of cavity 302 provides fluid damping of the mirror motion during actuation. Some etched portions of second silicon layer 316b also define a gap 330 between the mirror platform 325 of the mirror and a portion of the mirror substrate 308.

Method 200 includes defining one or more kerfs in at least one of a mirror substrate and a reflector, wherein each kerf comprises an extension of a gap into the mirror substrate or the reflector and each kerf has a length between approximately 50 microns and 200 microns and a width between approximately 50 microns and 100 microns (stage 220). As shown in FIG3I , a first kerf 340a and a second kerf 340b (collectively referred to as kerfs) are formed in the reflector substrate 308 and/or the reflector platform 325 of the reflector. To create the kerfs, a mask used in etching the first silicon layer 316a and the second silicon layer 310b of the reflector substrate 308 includes larger openings where the kerfs are desired. The openings in the mirror substrate 308 in the areas where the kerfs are located are larger than the openings in areas without the kerfs. During the manufacturing process, silicon exposed through the larger openings corresponding to the kerfs etches faster than silicon exposed through the narrower openings corresponding to the areas without the kerfs, thereby enabling faster completion of etching through the silicon in the areas with the kerfs. As a result, if a crack were to start elsewhere and propagate toward the location of the kerf, the lack of material at the location of the kerf may prevent the crack from progressing beyond the location of the kerf. In some embodiments, kerfs 340a, 340b, and 125 are defined as discussed above with respect to Figures 1A and 1B.

Method 200 includes disposing a reflective material on a second side of the MEMS mirror platform opposite the first side of the MEMS mirror platform (stage 225). As shown in FIG3I , the mirror platform 325 has a substantially flat surface and includes a reflective surface 350 defining a primary reflective plane of the mirror. In some embodiments, the reflective surface 350 can be formed by coupling a reflective coating to the uppermost surface of the mirror platform 325. In some embodiments, the reflective coating can be formed from a deposited layer of metal, such as, but not limited to, aluminum, silver, or gold. In some embodiments, the reflective coating can be formed from a deposited layer of metal and a layer of dielectric material, or alternating layers of metal and dielectric material, forming a dielectric-enhanced mirror or a dielectric mirror, respectively. In some other embodiments, the reflective material can be formed on the second side of the MEMS mirror platform before bonding the MEMS mirror platform to a base substrate.

Although this specification contains many specific implementation details, these should not be interpreted as limitations on the scope of any invention or the scope of protection claimed, but rather should be interpreted as descriptions of features unique to specific implementations of specific inventions. Certain features described in this specification 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 in multiple implementations separately or in any suitable subcombination. Furthermore, although features may be described above as functioning in certain combinations and even initially claimed as such, one or more features from a claimed combination may in some cases be removed from that combination, and a claimed combination may be directed to a subcombination or variations of a subcombination.

Similarly, although operations are described in a particular order in the figures, this should not be understood as requiring that such operations be performed in the particular order shown or in a sequential order, or that all illustrated operations must be performed to achieve the desired results. In certain circumstances, multitasking and parallel processing can be advantageous. Furthermore, the separation of various system components in the embodiments described above should not be understood as requiring such operation in all embodiments, and it should be understood that the components and systems can generally be integrated into a single product or packaged into multiple products.

References to "or" may be interpreted as inclusive so that any item described using "or" may indicate any one of a single, more than one, and all of the items described. The terms "first," "second," "third," and the like are not necessarily intended to indicate an order and are generally only used to distinguish identical or similar items or units. Thus, specific embodiments of the subject matter have been described. Other embodiments are within the scope of the appended claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve the desired results. In addition, the processes depicted in the accompanying drawings do not necessarily require the specific order or sequential order shown to achieve the desired results. In some embodiments, multitasking or parallel processing may be used.

Claims (20)

1. A MEMS reflector assembly, comprising: A mirror substrate defining an actuator, a gimbal structure, and a portion of a mirror cutout having an inner periphery; A reflector having a reflective surface, the reflector being located within a reflector notch on a reflector substrate and coupled to the reflector substrate via at least one stator, wherein: The reflector is supported by the gimbal structure. The reflector has a flat surface that defines the principal reflecting plane of the reflector. When the primary reflecting plane of the mirror is parallel to the mirror substrate, the periphery of the mirror and the inner periphery of the mirror cutout are separated by a gap around the entire periphery of the mirror, except at at least one stator. Except at the at least one stator and at a plurality of slits defined in at least one of the mirror substrate and the mirror, the size of the gap is constant around the periphery of the mirror, wherein each slit includes an extension of the gap between the mirror substrate and the mirror into the mirror substrate or the mirror, and each slit has a length between 50 micrometers and 200 micrometers and a width between 50 micrometers and 100 micrometers, and wherein at least one slit is defined in the gimbal structure and includes an extension of the gap into the gimbal structure. 2. The MEMS mirror assembly of claim 1, wherein at least one cutout in the mirror is defined as being adjacent to the at least one stator and includes the extension of the gap into the mirror. 3. The MEMS mirror assembly of claim 1, wherein at least one cutout is defined in the mirror and includes the extension of the gap into the mirror. 4. The MEMS mirror assembly of claim 1, wherein at least one cutout is defined in the mirror substrate and the mirror and includes the extension of the gap into the mirror substrate and the mirror. 5. The MEMS reflector assembly according to claim 1, wherein the shape of the cut is elliptical. 6. The MEMS mirror assembly according to claim 1, wherein the ratio of the length of the cutout in the direction tangent to the periphery of the mirror to the thickness of the mirror substrate is less than or equal to 4:1, and the ratio of the width of the cutout in the radial dimension of the mirror to the thickness of the mirror substrate is between 1:1 and 2:1. 7. The MEMS mirror assembly of claim 1, wherein the cutout is defined around the periphery of the mirror and each of the at least one stator is adjacent to at least one cutout. 8. The MEMS mirror assembly of claim 7, wherein the cut-off is defined around the periphery of the mirror at 90-degree intervals. 9. The MEMS mirror assembly of claim 7, wherein the cut-off is defined around the periphery of the mirror at 60-degree intervals. 10. The MEMS mirror assembly of claim 1, wherein the mirror substrate comprises an upper silicon layer and a lower silicon layer, and the size of the slits is determined such that they are larger than a minimum opening defined by the upper and lower silicon layers of the MEMS mirror assembly. 11. A method for manufacturing a MEMS mirror assembly, comprising: Define a cavity in the substrate; The mirror substrate is coupled to the substrate such that a first side of the mirror substrate faces the cavity in the substrate; A portion of a MEMS actuator, a gimbal structure, and a MEMS mirror are defined in the mirror substrate such that a first side of the MEMS mirror faces the cavity in the substrate, and a portion of the mirror substrate is spaced apart from the mirror by a gap. One or more slits are defined in at least one of the mirror substrate and the mirror, wherein each slit includes an extension of the gap between the mirror substrate and the mirror into the mirror substrate or the mirror, and each slit has a length between 50 micrometers and 200 micrometers and a width between 50 micrometers and 100 micrometers, and wherein at least one slit is defined in the mirror substrate and the mirror and includes the extension of the gap into the gimbal structure and the mirror; and A reflective material is arranged on the second side of the MEMS mirror, which is opposite to the first side of the MEMS mirror. 12. The method of claim 11, further comprising: providing a double silicon-on-insulator stack including a silicon stalk and the mirror substrate, wherein the mirror substrate includes a first silicon layer, an insulating layer, and a second silicon layer. 13. The method of claim 12, wherein defining the reflector comprises: Remove the silicon stalk of the silicon stack on the double-layer insulator; A portion of the first silicon layer of the mirror substrate is etched to expose a portion of the insulating layer of the mirror substrate; and Remove the exposed portion of the insulating layer of the reflector substrate to expose a portion of the second silicon layer. 14. The method of claim 13, wherein defining one or more cuts comprises: One or more portions of the exposed portion of the second silicon layer are etched, wherein the exposed portion of the second silicon layer defines a second side of the MEMS mirror. 15. The method of claim 13, wherein the mask used in etching the first silicon layer and removing the exposed portion of the insulating layer of the mirror substrate includes an opening in the region where the cut-out is located, wherein the opening in the region where the cut-out is located is larger than the opening in the region without the cut-out. 16. The method of claim 15, wherein the size of the gap is constant around the periphery of the mirror, except at the plurality of cutouts and the at least one stator. 17. The method of claim 15, wherein at least one cut is defined in the mirror as being adjacent to the at least one stator and includes the extension of the gap into the mirror. 18. The method of claim 15, wherein at least one cut is defined in the reflector and includes the extension of the gap into the reflector. 19. The method of claim 15, wherein the length of the cut in the direction tangent to the periphery of the mirror is less than or equal to the thickness of the mirror substrate in a ratio of 4:1, wherein the maximum cut length is 200 micrometers, and the width of the cut in the radial dimension of the mirror is between 1:1 and 2:1 in a ratio of 1:1 to the thickness of the mirror substrate in a ratio of 1:1 to 2:1, wherein the maximum cut width is 100 micrometers. 20. The method of claim 11, wherein the cut is defined around the periphery of the reflector, and each of the at least one stator is adjacent to at least one cut.