Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS20070018065 A1
Publication typeApplication
Application numberUS 11/187,054
Publication dateJan 25, 2007
Filing dateJul 21, 2005
Priority dateJul 21, 2005
Also published asWO2007015747A2, WO2007015747A3
Publication number11187054, 187054, US 2007/0018065 A1, US 2007/018065 A1, US 20070018065 A1, US 20070018065A1, US 2007018065 A1, US 2007018065A1, US-A1-20070018065, US-A1-2007018065, US2007/0018065A1, US2007/018065A1, US20070018065 A1, US20070018065A1, US2007018065 A1, US2007018065A1
InventorsJeffrey DeNatale, Xiaobin Li
Original AssigneeRockwell Scientific Licensing, Llc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Electrically controlled tiltable microstructures
US 20070018065 A1
Abstract
A support structure extends upwards from a substrate and supports a tiltable platform, the upper surface of which can be a mirror, by means of spaced flexible couplings that enable the platform to tilt relative to the support structure. Respective electrodes associated with the substrate and platform control the platform tilt in response to applied signals. The platform electrodes are preferably spaced below and tilt with the platform, with the platform extending laterally from the support structure further than the platform electrodes. The platform is preferably bulk micromachined, and the support structure surface micromachined.
Images(7)
Previous page
Next page
Claims(31)
1. An electrically controlled microstructure, comprising:
a tiltable platform,
a substrate,
a support structure extending upward from said substrate,
a plurality of spaced flexible couplings supporting said platform with respect to said support structure and enabling the platform to tilt relative to the support structure, and
respective electrodes associated with said substrate and with said platform controlling the platform tilt in response to applied electrical signals.
2. The microstructure of claim 1, wherein said couplings comprising flexible beams.
3. The microstructure of claim 2, wherein said electrodes associated with said platform are coupled to respective flexible beams on opposite sides of said support structure by respective torsion arms.
4. The microstructure of claim 3, said flexible beams and torsion arms enabling 2-axis tip/tilt motions for said platform.
5. The microstructure of claim 2, wherein said platform and mounting structure extend laterally beyond opposite sides of said support structure.
6. The microstructure of claim 5, said mounting structure comprising a pair of said platform electrodes, said platform electrodes aligned with corresponding substrate electrodes, and said platforms spaced above said platform electrodes.
7. The microstructure of claim 6, wherein said platform extends laterally from said support structure further than said platform electrodes.
8. The microstructure of claim 1, said electrodes having an interdigiated comb structure.
9. The microstructure of claim 1, wherein said electrodes are coupled to said support structure and to said platform to produce a piston movement of the platform in response to the application of common electrical signals between said electrodes associated with said substrate, and said electrodes associated with said platform.
10. The microstructure of claim 1, wherein said platform comprises a bulk micromachined structure, and said support structure comprises a surface micromachined structure.
11. The microstructure of claim 1, said platform comprising silicon.
12. The microstructure of claim 1, said platform comprising a mirror.
13. The microstructure of claim 12, further comprising an operating system, with said mirror performing a light directing function within said operating system.
14. The microstructure of claim 13, said operating system comprising an optical cross-coupler, a projector, an optical alternator or an atmospheric compensator.
15. The microstructure of claim 1, further comprising a drive circuit for said electrodes, electrical connections to said electrodes which extend to the underside of said substrate, and electromechanical connectors on the underside of said substrate between said drive circuit and said electrical connections.
16. An electrically controlled microstructure, comprising:
a substrate,
a support structure extending upward from the substrate,
tilt electrodes extending laterally out from opposite sides of said support structure and coupled to said support structure to tilt relative to said support structure and substrate,
lower electrodes carried by said substrate spaced from and in alignment with respective ones of said tilt electrodes, and
a platform carried above and tilting with said tilt electrodes, said platform extending laterally out beyond and spaced above said tilt electrodes so that it has a greater tilt angle range than if it were at the level of said tilt electrodes.
17. The microstructure of claim 16, wherein said tilt electrodes are coupled to said support structure by flexible beams which flex to enable tilting of said tilt electrodes.
18. The microstructure of claim 17, wherein said tilt electrodes are coupled to respective flexible beams by respective torsion arms.
19. The microstructure of claim 16, wherein said platform comprises a bulk micromachined structure, and said support structure comprises a surface micromachined structure.
20. The microstructure of claim 16, said platform comprising silicon.
21. The microstructure of claim 16, said platform comprising a mirror.
22. The microstructure of claim 21, further comprising an operating system, with said mirror performing a light directing function within said operating system.
23. The microstructure of claim 22, said operating system comprising an optical cross-coupler, a projector, an optical alternator or an atmospheric compensator.
24. The microstructure of claim 16, further comprising a drive circuit for said electrodes, electrical connections to said electrodes which extend to the underside of said substrate, and electromechanical connectors on the underside of said substrate between said drive circuit and said electrical connections.
25. The microstructure of claim 24, wherein said electrical connectors comprise indium, solder or Au-alloy conductive adhesives.
26. A microstructure, comprising:
a substrate,
a surface micromachined support structure extending upward from said substrate, and
a bulk micromachined mirror carried by said support structure to tilt relative to said substrate.
27. The microstructure of claim 26, further comprising tilt electrodes interfacing between said support structure and said mirror, said tilt electrodes being tiltable with respect to said support structure and substrate, said mirror carried above and tilting with said tilt electrodes, and substrate electrodes carried by said substrate in alignment with and spaced from said tilt electrodes.
28. The microstructure of claim 27, said mirror extending laterally out beyond said tilt electrodes so that it has a greater tilt angle range than if it were at the level of said tilt electrodes.
29. The microstructure of claim 26, further comprising an operating system, with said mirror performing a light directing function within said operating system.
30. The microstructure of claim 29, said operating system comprising an optical cross-coupler, a projector, an optical alternator or an atmospheric compensator.
31. The microstructure of claim 9, further comprising a drive circuit for said electrodes, electrical connections to said electrodes which extend to the underside of said substrate, and electromechanical connectors on the underside of said substrate between said drive circuit and said electrical connections.
Description
    BACKGROUND OF THE INVENTION
  • [0001]
    1. Field of the Invention
  • [0002]
    This invention relates to electrically controlled microstructures with tiltable platforms, and has particular application to micromirrors.
  • [0003]
    2. Description of the Related Art
  • [0004]
    There are various applications for micromirror arrays with tilting capabilities, such as optical cross-couplers, projection displays, optical attenuators and laser beam scanning and pointing systems. It is desirable that the micromirrors have a large tilt angle, to maximize the contrast between “on” and “off” states, and good mirror surface quality to reduce non-specular scatter that degrades image contrast. Achieving both qualities in micromachined devices has proven to be very difficult.
  • [0005]
    In one approach, micromirrors formed from thin metal films that are monolithically integrated onto the control circuitry have been used for projector displays. The mirrors are co-fabricated with the circuitry, leading to temperature and material limitations such as difficulty in achieving a flat mirror surface, especially when coatings have applied to it, scaling the mirrors in size, optical power and reflectivity limitations, and the proximity of the mirrors to the supporting substrate surface which limits their tilt angle.
  • [0006]
    Another approach employs micromirrors that are fabricated on a stressed support structure, which releases and allows the mirror to pop up after fabrication has been completed to increase the tilt angle. However, all connections are made along the side of the device, which limits its scalability to large scale 2-dimensional arrays, and it has a low fill factor (percentage of total array area occupied by mirror surfaces). While the mirrors can be used to point a beam among different reception optical fibers, the relatively large spacing between mirrors makes the array unusable for quality display purposes.
  • [0007]
    A different approach employs a single crystal silicon mirror with a polysilicon actuator bonded to it that enables a piston-like up and down motion, but not a tilting motion. Only an individual device is disclosed, which is generally not scalable to a full array.
  • SUMMARY OF THE INVENTION
  • [0008]
    The present invention provides an electrically controlled microstructure that can be capable of relatively large angle tilts, with a smooth and sturdy surface for mirror or other applications, a capacity for a large fill factor, and applications for tilting, tilting and tipping (tilting about two different axes), and tilting combined with a piston motion.
  • [0009]
    In one aspect of the invention, a support structure extends upwards from a substrate and supports a tiltable platform, the upper surface of which can be a mirror, by means of spaced flexible couplings that enable the platform to tilt relative to the support structure. Respective electrodes associated with the substrate and platform control the platform tilt in response to applied electrical signals.
  • [0010]
    In one embodiment, the platform electrodes are spaced below and tilt with the platform, with the platform extending laterally from the support structure further than the platform electrodes. This makes it possible to achieve a desired balance between tilt angle and the voltage magnitudes required to operate the device.
  • [0011]
    The platform is preferably bulk micromachined, and the support structure surface micromachined. The flexible couplings and electrodes can be designed to provide combined tip/tilt and tilt/piston movements in a variety of applications.
  • [0012]
    These and other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • [0013]
    FIGS. 1 and 2 are perspective views illustrating one embodiment of the invention;
  • [0014]
    FIG. 3 is a fragmentary perspective view of an electrode support mechanism for the embodiment of FIGS. 1 and 2;
  • [0015]
    FIG. 4 is a plan view of segmented lower electrodes that can be used with the embodiment of FIGS. 1 and 2;
  • [0016]
    FIGS. 5-7 are sectional views illustrating successive stages in the fabrication of a tiltable mirror;
  • [0017]
    FIGS. 8 a and 8 b are perspective views of the device illustrated in FIGS. 1 and 2 performing left and right tilts;
  • [0018]
    FIG. 8 c is a perspective view of the device illustrated in FIGS. 1, 2 and 4 performing a backward tip;
  • [0019]
    FIG. 9 is a graph of platform tilt angle as a function of applied voltage between the platform and substrate electrodes for the device shown in FIG. 3;
  • [0020]
    FIG. 10 is an exploded perspective view of a micromirror array conceptually illustrating flip-chip bump connections to underlying addressing circuitry;
  • [0021]
    FIG. 11 is a perspective view of a vertical comb drive embodiment of the invention;
  • [0022]
    FIG. 12 is a fragmentary perspective view of an electrode support mechanism for the embodiment of FIG. 11; and
  • [0023]
    FIGS. 13, 14, 15 and 16 are respectively block diagrams of cross-coupler, projector, optical attenuator and atmospheric compensation applications for the invention.
  • DETAILED DESCRIPTION
  • [0024]
    An illustrative microstructure device which supports a tiltable platform in accordance with the invention is illustrated in FIGS. 1 and 2. As used herein, the term “platform” includes a mirror but is not limited to mirror applications; it can also provide a base for other functions such as filters, gratings, and non-optical applications.
  • [0025]
    Although not required by the invention, the fabrication preferably employs a hybrid micromachining approach that combines bulk and surface micromachine techniques. This approach to forming a microstructure is disclosed in U.S. Pat. No. 6,587,613 by the present inventor, issued Jul. 1, 2003, the contents of which are incorporated by reference herein. It involves the formation of a support structure for a bulk micromachined element by fabricating the support structure on the element using surface micromachining techniques. One implementation uses a 5-level surface micromachining technology that allows for the fabrication of complex movable components on translatable stages that can engage and interact with other subassemblies. This technology is commonly referred to as the Sandia Ultra-planar Multi-level MEMS Technology V (SUMMiT V). [M. S. Rogers and J. J. Snigegowski, Designing Microelectromechanical Systems-On-AChip in a 5-level Surface Micromachine Technology, 2nd Annual Int. Conf. on Engineering Design and Automation (August 1998), and M. S. Rogers and J. J. Sniegowski, 5-Level Polysilicon Surface Micromachining Technology Application to Complex Mechanical Systems, Proc. 1998 Solid State Sensor and Actuator Workshop, Pg. 144 (June 1998, Hilton Head, S.C.)]. Other multi-level MEMS surface micromachining processes may also be used within the scope of the invention.
  • [0026]
    In the context of a micromirror, this approach reverses the traditional technique of first fabricating a support structure, and then emplacing a mirror element on that structure. Instead, a relatively thick and sturdy bulk micromachined mirror element has a support structure built up on one surface by surface micromachining, forming layers of active support structure and sacrificial material on the mirror element, and then dissolving away the layers of sacrificial material. The resulting micro electromechanical system (MEMS) device is capable of high quality optical surfaces and complex support structures. In the U.S. Pat. No. 6,587,613 patent, the mirror element is supported in a manner that allows it to move in a piston motion relative to a substrate for the support structure. A voltage is applied across a central electrode below the mirror element and the mirror element itself, to produce an electrostatic attraction between the two. The mirror element is preferably implemented as the device layer of a silicon-on-insulator (SOI) structure, with a doped silicon mirror supported by an insulative layer and thick handle layer that are removed towards the end of the fabrication sequence. The support structure is preferably formed from polysilicon together with sacrificial oxide material.
  • [0027]
    A microstructure device in accordance with the invention is shown in FIG. 1 with a tiltable mirror removed, and in FIG. 2 with the mirror 2 in place. The structure is preferably fabricated with a hybrid micromachining approach as described above. In practice the mirror 2 is fabricated by bulk micromachining, while the remainder of the structure is fabricated upon the mirror with a surface micromachining technique such as SUMMiT V. Thus, although in FIG. 2 the mirror 2 is shown at the top of the structure, the structure is actually constructed using the bulk mirror as a starting point and fabricating successive layers in the downward direction from the mirror as seen in FIG. 2.
  • [0028]
    Although the mirror is typically supported in an upright position, the device can actually be used in any desired orientation. Successive layers are surface micromachined, beginning from the bulk micromachined mirror 2. The first layer from the mirror, seen only in FIG. 1, is patterned into a pair of upstanding posts 6 a and 6 b which support the mirror and space it above the next layer. This layer includes a pair of polysilicon upper electrodes 8 a and 8 b on opposite sides of a central hollow, generally rectangular frame consisting of a pair of stiffly flexible beams 10 a and 10 b, and frame ends 12 a and 12 b connected the ends of beams 10 a and 10 b. Electrodes 8 a and 8 b are parallel to beams 10 a and 10 b, with electrode 8 a connected to and spaced from beam 10 a by a central torsion arm 14 a, and electrode 8 b connected to and spaced from beam 10 b by a similar central torsion arm 14 b. Posts 6 a and 6 b sit upon torsion arms 14 a and 14 b, respectively.
  • [0029]
    The upper electrodes 8 a and 8 b are spaced above and separated from a corresponding pair of lower electrodes 16 a and 16 b, respectively, by two additional SUMMiT V layers 18 and 20 which extend between the frame ends 12 a, 12 b and a central portion 16 c of the lower electrode layer between lower electrodes 16 a and 16 b.
  • [0030]
    A framework linking structure 22 may be provided on the underside of the lower electrode layer in a manner similar to that described in U.S. Pat. No. 6,587,613. This is a continuous structure across an array of MEMs devices and is built up on the devices after they have been individually fabricated. The structure 22 links the individual MEMs devices in an array. Electrical contacts to the MEMs devices can be deposited on the linking framework structure 22 using known metallization processes, or on the lower electrode layer if no linking framework is provided.
  • [0031]
    FIG. 3 provides an enlarged view illustrating the relationship between upper electrode 8 a, beam 10 a and torsion arm 14 a. There is a similar relationship between upper electrode 8 b, beam 10 b and torsion arm 14 b. This relationship allows for three degrees of freedom in the movement of electrode 8 a in response to an applied electrostatic voltage between the upper and lower electrodes 8 a and 16 a, which are aligned with each other on one side of the device. First, an electrostatic attraction or repulsion between upper and lower electrodes 8 a and 16 a can cause beam 10 a to flex downward or upward, respectively, as upper electrode 8 a is drawn down toward or repulsed up away from the lower electrode 16 a. This is indicated by the flex axis 24 for the beam and by the (exaggerated) upwardly flexed beam position indicated by dashed lines 10 a′.
  • [0032]
    Second, torsion arm 14 a can undergo a cantilever flexing that allows upper electrode 8 a to move somewhat up or down in response to electrostatic repulsion or attraction, respectively, between the upper and lower electrodes 8 a and 16 a. This is indicated by the flex arrow 26.
  • [0033]
    Third, if either the upper or the lower electrodes, or both, are segmented into forward and rear sections that are electrically isolated from each other, a torsional twisting force can be applied to arm 14 a by applying an electrostatic attraction or repulsion force between the upper and lower forward electrodes and an opposite electrostatic force between the upper and lower rear electrodes. This causes the upper electrode 8 a to pivot forward or rearward around torsion arm 14 a, as indicated by pivot arrow 28. It is normally easier to divide the lower electrodes into electrically isolated forward and rear sections, than to divide the upper electrodes. For example, gaps 24 may be left in lower electrode 16 a and 16 b to divide them each into two sections. This is illustrated in FIG. 4, which shows only the lower electrode layer for this embodiment. Lower electrodes 16 a and 16 b are divided into forward sections 16 aF, 16 bF and rear sections 16 aR, 16 bR. The upper silicon electrodes would normally both be grounded and electrically tied together. In response to an applied electrostatic attraction between the upper electrodes and forward sections of the lower electrodes, and/or an applied electrostatic repulsion between the upper electrodes and rear sections of the lower electrodes, the upper electrodes will tip forward about their torsion arms; they tip rearwards when the electrostatic forces are reversed.
  • [0034]
    Referring back to FIGS. 1 and 2, it can be seen that, since mirror 2 rides on posts 6 a and 6 b, which in turn ride on torsion arms 14 a and 14 b, movements of the upper electrodes and torsion arms will be translated into corresponding mirror movements. As described in more detail below, this allows for a greater range of mirror movement than would be the case if the upper electrodes were provided directly on the mirror.
  • [0035]
    FIGS. 5-7 illustrate successive stages in the preferred fabrication technique for the device of FIGS. 1-4. Since the general fabrication technique is generally similar to that described in incorporated U.S. Pat. No. 6,587,613, it will not be described in great detail. In FIG. 5 an SOI (silicon on insulator) wafer 30 includes a relative thin silicon layer 2 anchored to a handle layer 32 by an oxide layer 34. The handle layer 32 is generally thicker than the silicon layer 2, with a suitable thickness of about 500 microns. The silicon layer 2 serves as the MEMs device's micromirror and is preferably on the order of 100 microns thick, although other thicknesses can also work. If it is too thick its movement can become too slow, while if it is too thin it can lose rigidity. The surface micromachined layers fabricated on the mirror layer 2 are preferably on the order of 5 microns thick silicon.
  • [0036]
    The handle layer 32 provides a convenient mechanism for holding and flipping the device during fabrication, and is then removed. The surface machined elements of the device, indicated by the same reference numbers as in FIGS. 1-3, are formed from polysilicon structural material and are built up with oxide sacrificial material 36 (indicated by stippling) occupying areas that will become voids in later stages of the fabrication. Electrical contacts 38 are provided on the underside of the framework linking structure 22. The device can be flipped over once the framework linking structure has been emplaced, and electrically and mechanically bonded to a substrate 40 via flip-chip bond contacts 38.
  • [0037]
    FIG. 6 shows the device with the handle layer 32 removed after the device has been flip-chip bonded to substrate 40. It can be removed mechanically, such as by grinding, or the oxide layer 34 can be dissolved by chemical etching to release the handle layer. In FIG. 7 the remaining oxide sacrificial material has been dissolved by a chemical etch. Separate control signals would be applied to the contacts 38 for each of the lower electrodes 16 a and 16 b, while the upper electrodes 8 a and 8 b would preferably be grounded. The silicon preferred for the structure would normally be sufficiently conductive to transmit these signals, although if desired it could be doped to increase its conductivity.
  • [0038]
    FIGS. 8 a and 8 b are simplified perspective views illustrating the structure of FIGS. 1 and 2 performing left and right tilts. The substrate upon which the support structure is mounted is not shown for simplification. In FIG. 8 a, a voltage has been applied across the left hand upper (mirror) and lower (substrate) electrodes 8 a and 16 a, drawing them towards each other by electrostatic force and thus causing the mirror 2, which moves with the mirror electrodes 8 a, 8 b, to tilt to the left. In this movement the left hand flex beam 10 a flexes downward, while the right hand beam 10 b flexes upward. In the figure the mirror 2 is shown at its maximum tilt angle, with the left mirror electrode 8 a bottomed out upon the left substrate 16 a electrode; this defines the maximum tilt angle. Similarly, in FIG. 8 b a voltage has been applied across the right hand mirror and substrate electrodes, 8 b, 16 b, causing them to move together and thus tilt the mirror 2 to the right. Left hand beam 10 a flexes upward, and right hand beam 10 b downward.
  • [0039]
    FIG. 8 c illustrates the 2-axis movement capability of the segmented electrode embodiment illustrated in FIG. 4. In response to an electrostatic repulsion between the forward electrode segments and/or an electrostatic attraction between the rear electrode segments, the mirror tips backward as shown. This version is also capable of left and right tilting.
  • [0040]
    A degree of up/down piston action for the mirror 2 can also be achieved by applying a common voltage signal to both of the lower electrodes 16 a and 16 b, so that both of the upper electrodes 8 a and 8 b are either attracted to or repulsed from the lower electrodes. The amount of piston movement available depends primarily upon the flexibility of the beams 10 a and 10 b.
  • [0041]
    The electrostatic force of attraction between the mirror and substrate electrodes is a function of the voltage applied across these electrodes. However, the tilt angle-voltage relationship is not linear. FIG. 9 illustrates the characteristics of one microstructure, showing that the required voltage to produce a given tilt angle increases at a greater rate than the angle. The results shown in FIG. 9 were achieved with a mirror that was 100 microns long and 5 microns thick, with a gap of 3.75 microns between the mirror and the mirror electrodes.
  • [0042]
    Spacing the mirror electrodes 8 a, 8 b below the bottom surface of the mirror element 2, rather than forming them directly on that surface, reduces the spacing between the mirror and substrate electrodes, thus enabling the application of lower voltages, especially for higher tilt angles. Since the mirror 2 itself extends laterally away from the support structure by a greater distance than the mirror electrodes, 8 a, 8 b, the mirror electrodes will not bottom out until a greater tilt angle has been reached than would be the case if the electrodes extended the full extent of the mirror length. Thus, in addition to lower operating voltages, the illustrated structure enables greater tilt angles.
  • [0043]
    FIG. 10 illustrates an array of micromirrors 42 of the type shown in FIGS. 1 and 2, connected to electronic drive circuitry 44, typically an addressing ASIC, by means of flip-chip mounting in which indium “bumps” or solder balls 46 on the upper surface of the addressing electronics and the lower surface of the array provide electrical and mechanical connections between the array and the electronics substrate (the array bumps are not shown). Although only a single bump is illustrated on the addressing circuit for each microelement, in practice a common ground bump would be used for all of the substrate electrodes, and a separate bump for each element electrode. This enables the entire array to be transferred to pixel-level drive electronics, eliminating planar interconnects that would otherwise be required. The resulting array has a large fill factor which provides high optical quality, is scalable to large array formats, exhibits system level simplicity and uses the mature and reliable bump contact technology. If desired, the array can be fabricated on a large scale wafer which is then segmented into individual pixels by a deep anisotropic etch. Such bonding can be accomplished by a range of different processes known to those skilled in the art, such as indium, solder or Au/Au thermocompression bonding.
  • [0044]
    The microstructures would preferably be flip-chip mounted to a drive circuit which multiplexes the actuation signals in order to address desired pixels or sets of pixels. Typically, each pixel would correspond to a unique combination of addressing rows and columns, with a particular pixel or set of pixels addressed by activating its corresponding row and column via the multiplexer.
  • [0045]
    In the context of micromirror arrays, the invention offers a highly flexible approach to the manipulation of light, including adaptive optics, beam steering, projection displays and fiber switching, with a high fill factor. The device structure of FIGS. 1 and 2 can be adapted to provide 2-axis tip/tilt operation with the mechanical arms or flexors 14 a, 14 b to accommodate torsional deformation about the second axis and, by segmenting the two substrate electrodes into four, allowing a second axis tilt to be accomplished. Other designs to implement 2-axis tilt using the hybrid micromachining process will be evident to those skilled in the art, and are within the spirit of the invention. This also enables piston motion with all electrodes actuated.
  • [0046]
    Similarly, the flexibility afforded by the hybrid micromachining process enables designs incorporating other electrostatic electrode concepts, such as vertical comb drivers. Such an approach is illustrated in FIG. 11, which is similar to the embodiment of FIG. 1 but in which interdigitated upper 48 a, 48 b and lower 50 a, 50 b “comb” electrodes are substituted for the planar electrodes 8 a, 8 b, 16 a, 16 b of FIG. 1. The upper electrode fingers 52 a, 52 b extend outward at their upper inner edges from respective stiffly flexible beams 54 a, 54 b, respectively, while the lower electrode fingers 56 a, 56 b extend inward from respective support beams 58 a, 58 b on the framework linking structure 22. The mirror 2 (not shown) is supported on respective posts 60 a, 60 b which extend upward from beams 54 a, 54 b, respectively.
  • [0047]
    FIG. 12 is an enlarged fragmentary view of the upper electrode 48 a; the other upper electrode 48 b has a mirror image structure. As with the planar electrode embodiment, an electrostatic attraction or repulsion between the upper and lower electrodes 48 a and 50 a causes beam 54 a to flex downward or upward. This is indicated by the flex axis 62 for the beam and by the (exaggerated) upwardly flexed beam position indicated by dashed lines 54 a′. The beam 54 a will tend to be somewhat less flexible than beam 10 a in the planar electrode embodiment because of the electrode fingers 52 a distributed along the length of beam 54 a.
  • [0048]
    An interdigitated comb structures as in FIGS. 11 and 12 tends to provide a greater degree of electrostatic stability than does the planar electrode structure described above. The planar electrodes tend to snap together once the gap between the upper and lower electrodes has been closed by more than roughly ⅓, but this does not occur with an interdigitated comb structure. On the other hand, the illustrated comb structure tends to have a somewhat lesser piston movement capability than the planar electrode version, due to the reduced flexibility of its flex beams 54 a and 54 b. While the upper and lower combs overlap somewhat, electrostatic attraction and repulsion forces are still generated because the center of mass of the upper comb will remain above that of the lower comb.
  • [0049]
    The invention is capable of at least +/−10 of tilt, and actuation speeds in excess of 50 kHz. Its preferred embodiment is highly manufacturable due to its use of a mature polysilicon processing technology, while the employment of a hybrid bulk and surface micromachining assembly process enables flexibility in its attachment to high voltage drive circuitry. With the drive circuitry provided directly below the MEMS device as illustrated, very compact systems integrating the electronics and MEMS are possible. The use of a thick, preferably dielectric platform is particularly useful for high optical power applications such as projectors.
  • [0050]
    There are numerous applications for the new microstructure, particularly in its micromirror array form. One such application, an optical cross-coupler, is illustrated conceptually in FIG. 13. Optical signals propagated through an array of input optical fibers 64 are directed in a desired pattern to corresponding fibers 66 in an output fiber array. The input light signals are processed through whatever input optics 68 may be required to direct them onto respective tiltable mirrors in a mirror array 70 constructed in accordance with the invention. The tilt angles, and also the tip angles if desired, of individual mirrors within the array 70 are controlled by a drive signal 72 so that each input signal is delivered to a desired fiber in the output array 66. An array of lenses 74 will generally be provided, with one lens for each output fiber, to focus the signals onto the desired fibers. By adjusting the angle of the individual micromirrors, the input light signals can be distributed among the output fibers in a desired fashion.
  • [0051]
    FIG. 14 illustrates the application of the invention to a color projector. A lamp 76, which includes appropriate optics, directs a white light beam onto a tiltable mirror array 78 in accordance with the invention. The individual mirrors within the array are controlled by a drive signal 80 so that they are directed onto desired portions of a color wheel 82, with a timing signal input 84 applied to the mirror array and color wheel to keep them in synchronism. The resulting color light array is processed by projection optics 86 which output a projected image.
  • [0052]
    An optical attenuator embodiment is illustrated in FIG. 15. Incoming light in an input optical fiber 88 is directed onto a mirror array 90 by appropriate optics 92. An output optical fiber 94 is provided downstream from the mirror array, with appropriate optics 96 such as a lens array interfacing between the mirror array 90 and output fiber 94. A drive and control signal 98 is applied to the mirror array 90 to steer the output optical signal array so that a desired portion of the light is incident on the output optics 96 and reaches the output fiber 94, with the remainder of the light lost to the system. In this application the mirrors will commonly be operated in tandem with each other, but this is not necessary. The degree of attenuation is controlled by the drive and control signal 98, which controls how much of the input light reaches the output fiber 94.
  • [0053]
    FIG. 16 illustrates a system which compensates for atmospheric interference to a light signal. An input optical wavefront 100 which has been transmitted through a portion of the atmosphere is processed by input optics 102, which input the signal onto a mirror array 104 in accordance with the invention. The optical beam array reflected from the mirror array is transmitted through an optical sampler 106 to output optics 108, which form the light signals into an image 110. The signal samples obtained by sampler 106 are delivered to a wavefront sensor 112, which stores an impression of how a wavefront would appear in the absence of atmospheric interference, and compares it with the beam samples to determine the degree and nature of the atmospheric aberrations experienced by the input wavefront. The wavefront sensor 112 produces a drive and control output signal 114 that is transmitted to the mirror array 104 and adjusts the mirror angular orientations to compensate for the atmospheric interference. The mirror array 104, sampler 106 and wavefront sensor 112 form an active feedback loop that continually updates the compensation as the atmospheric interference changes.
  • [0054]
    Numerous other applications for the invention can also be visualized. The term “light” as used above is not limited to visible light, but rather covers all regions of the electromagnetic spectrum capable of being directed by a mirror array as discussed herein. While particular embodiments of the invention have been shown and described, numerous alternate embodiments will be apparent to those skilled in the art. Accordingly, it is intended that the invention be limited only in terms of the appended claims.
Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1591824 *Jun 13, 1924Jul 6, 1926John H HeroldPotato picker
US5212582 *Mar 4, 1992May 18, 1993Texas Instruments IncorporatedElectrostatically controlled beam steering device and method
US6028689 *Jan 24, 1997Feb 22, 2000The United States Of America As Represented By The Secretary Of The Air ForceMulti-motion micromirror
US6587613 *Jul 24, 2001Jul 1, 2003Innovative Technology Licensing, LlcHybrid MEMS fabrication method and new optical MEMS device
US20040184132 *Mar 22, 2003Sep 23, 2004Novotny Vlad J.Spatial light modulator with hidden comb actuator
US20050094242 *Nov 1, 2003May 5, 2005Fusao IshiiVacuum packaged micromirror arrays and methods of manufacturing the same
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US7466476 *Aug 2, 2006Dec 16, 2008Texas Instruments IncorporatedSloped cantilever beam electrode for a MEMS device
US7764418Dec 16, 2008Jul 27, 2010Texas Instruments IncorporatedSloped cantilever beam electrode for a MEMS device
US20080030840 *Aug 2, 2006Feb 7, 2008Texas Instruments IncorporatedSloped cantilever beam electrode for a MEMS device
US20090097091 *Dec 16, 2008Apr 16, 2009Texas Instruments IncorporatedSloped Cantilever Beam Electrode for a MEMS Device
Classifications
U.S. Classification248/281.11
International ClassificationA47F5/00
Cooperative ClassificationG02B26/0841, B81B3/0062, B81B2201/033, B81B2201/042, B81B2203/058, B81B2203/053
European ClassificationB81B3/00P, G02B26/08M4E
Legal Events
DateCodeEventDescription
Jul 21, 2005ASAssignment
Owner name: ROCKWELL SCIENTIFIC LICENSING, LLC, CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:DENATALE, JEFF;LI, XIAOBIN;REEL/FRAME:016802/0007;SIGNING DATES FROM 20050714 TO 20050719
Dec 5, 2006ASAssignment
Owner name: TELEDYNE LICENSING, LLC,CALIFORNIA
Free format text: CHANGE OF NAME;ASSIGNOR:ROCKWELL SCIENTIFIC LICENSING, LLC;REEL/FRAME:018583/0159
Effective date: 20060918