Ulllted States Patent [19]
`Maynard
`
`US005872880A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,872,880
`Feb. 16, 1999
`
`[54] HYBRID-OPTICAL MULTI-AXIS BEAM
`STEERING APPARATUS
`
`5,208,880
`5,325,116
`
`5/1993 RiZa et al. .
`6/1994 Sampsell
`
`...... .. 385/25
`.... .. 346/108
`
`[75] Inventor: Ronald S_ Maynard, 777 Hollenbeck
`#15 Q’ Sunnyvale’ Cahf' 94087
`
`[73] Assignee: Ronald S. Maynard, San Jose, Calif-
`
`[21] APPL NO; 695 717
`’
`Aug. 12, 1996
`
`Filed:
`
`[22]
`
`6
`[51] Int. Cl. ..................................................... .. G02B 6/36
`[52] US. Cl. ............................... .. 385/88; 385/18; 385/19;
`385/83
`[58] Field of Search .......................... .. 385/88—94, 16—23,
`
`385/25, 83
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,448,546
`
`9/1995 Pauli . . . . . . . . . . . . .
`
`. . . . .. 369/112
`
`5,504,614
`4/1996 Webb et al. .......................... .. 359/223
`FOREIGN PATENT DOCUMENTS
`
`0 331 331 A2 6/1989 European Pat. on. ........ .. G02B 6/42
`0 614 101 A2 7/1994 European Pat. Off. .
`G02B 26/08
`0 650 133 A2 4/1995 European Pat. Off. ....... .. G06K 7/10
`WO95/13638 5/1995 WIPO ........................... .. H015 3/085
`
`Primary Examiner—Hung N. Ngo
`Attorne) A em) Or Firm_W?SOn sonsini Goodrich &
`y g
`Rosa?
`
`[57]
`
`ABSTRACT
`
`.
`
`.
`
`An apparatus for precisely steering a beam of light by
`making use of a hybrid inter optical alignment precision
`Which occurs When a beam steering mechanism is micro
`machined With respect to a crystallographic orientation of a
`
`.
`
`4,505,539
`4,854,685
`4,923,745
`
`3/1985 Auracheretal. ....................... .. 385/18
`8/1989 Stanley .............. ..
`5/1990 Blonder ................................... .. 385/18
`
`Substrate‘
`
`45 Claims, 17 Drawing Sheets
`
`107
`
`100
`
`501
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 1
`
`

`
`0O03278,5
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 2
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 2 0f 17
`
`5,872,880
`
`FIG. 2
`
`I05
`
`LU
`q.
`9
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 3
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 3 0f 17
`
`5,872,880
`
`FIG. 3
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 4
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 4 0f 17
`
`5,872,880
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 5
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 5 0f 17
`
`5,872,880
`
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`Cisco Systems, Inc.
`Exhibit 1036, Page 6
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 6 0f 17
`
`5,872,880
`
`m .QI
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 7
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 7 0f 17
`
`5,872,880
`
`NOTKL
`
`.QI
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 8
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 8 0f 17
`
`5,872,880
`
`503
`
`FIG. 8
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 9
`
`

`
`0O03278,5
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 10
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 10 0f 17
`
`5,872,880
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 11
`
`

`
`Cisco Systems, Inc.
`Exhibit 1036, Page 12
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 12 0f 17
`
`5,872,880
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 13
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 13 0f 17
`
`5,872,880
`
`FIG. 13
`
`LO
`Q
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 14
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 14 0f 17
`
`5,872,880
`
`0mm
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`i
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`MOmm
`
`3 .QI
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 15
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 15 0f 17
`
`5,872,880
`
`ovm
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`
`Cisco Systems, Inc.
`Exhibit 1036, Page 16
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 16 0f 17
`
`5,872,880
`
`vom
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 17
`
`

`
`U.S. Patent
`
`Feb. 16,1999
`
`Sheet 17 0f 17
`
`5,872,880
`
`980 “1- Op?col OuTpuf
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`
`Cisco Systems, Inc.
`Exhibit 1036, Page 18
`
`

`
`1
`HYBRID-OPTICAL MULTI-AXIS BEAM
`STEERING APPARATUS
`
`5,872,880
`
`2
`describe methods of fabricating electrically controllable
`micromirrors using an additive process. The micromirrors
`may operate independently or Within a distributed array. The
`micromirrors are generally of torsion or gimbaled hinge
`design.
`An additional US. Pat. No. 5,325,116 held by TEXAS
`INSTRUMENTS describes a beam steering device used for
`Writing to and reading from an optical storage media using
`a micromachined SLM. Although the single SLM compo
`nent has the potential to greatly improve the mechanical
`dynamic response of the overall device, the surrounding
`structure Within Which the SLM resides remains bulky.
`What is needed is a faster, more precise and compact
`apparatus for steering beams of light. In particular, it Would
`be advantageous to miniaturiZe a complete optical system
`upon a single substrate, including lenses, optical ?bers,
`optical sensors, SLMs and the like. Not only Would perfor
`mance be greatly enhanced due to smaller moving masses,
`but manufacturing costs and uniformity Would also be
`improved.
`Reducing all dimensions proportionately on a given mir
`ror design results in a reduction of surface area by an inverse
`squared term and a reduction of volume and mass by an
`inverse cubed term. Thus, by diminishing the siZe of any
`object, the surface-area-to-mass-ratio Will increase linearly.
`Consequently, surface force reactions such as surface
`tension, electrostatics and Van der Waals forces, become
`more signi?cant, While gravitational and inertial forces
`becomes less of a factor in governing the static and dynamic
`equations of motion.
`The angular inertia of a rectangular plate about a center
`line lying in the plane of the plate, is linearly proportional to
`the mass of the plate. It is also proportional to the square of
`the Width of the plate Which is perpendicular to that ads.
`Therefore, if all dimensions of a plate are reduced by a factor
`of tWo, then the ?nal mass Would be the inverse cube of tWo,
`or one eighth of the original mass. The inertial mass,
`sometimes referred to as the mass moment of inertia, of the
`smaller plate Would then be one eighth times the inverse
`square of tWo or one thirty-second times the original mass.
`Since the angular acceleration of a body is directly
`proportional to an externally applied torque and inversely
`proportional to its angular inertial mass, one can conclude
`that halving all plate dimensions Will result in thirty tWo fold
`increase in angular acceleration for a given torque.
`As is commonly knoWn, electrostatic force is an effective
`means for moving small, micromachined components. The
`force produced betWeen an electrostatically charged plate
`and ground is directly proportional to the plate’s surface area
`and inversely proportional to the square of the plate-to
`ground gap for a given voltage. Thus, if all dimensions are
`again halved, the electrostatic force generated betWeen the
`plate and ground Would be equal to the initial force for a
`given voltage.
`By taking the previous dynamic and electrostatic argu
`ments into consideration, it can be surmised that by halving
`all dimensions of an electrostatically driven plate, the
`dynamic response Would be improved by a factor of thirty
`tWo for a given driving voltage. More generally, assuming
`that the driving voltage is such that electrostatic breakdoWn
`of air and insulators does not occur, then the dynamic
`response of an electrostatically driven plate Will increases as
`the inverse forth poWer of siZe reduction.
`
`BACKGROUND
`The ?eld of the present invention relates, in general, to
`methods and devices for manipulating and steering beams of
`light. More speci?cally, the ?eld of the invention relates to
`a compact, hybrid system of optical components that accept
`a beam of light from an optical element or ?ber, steer the
`beam in one or more directions, and pass the de?ected beam
`into open space or through a secondary optical element or
`?ber.
`Investigators of optical phenomenon typically rely on
`massive, vibration damped optical benches to maintain
`precise alignment betWeen optical elements during proto
`typing. Optical elements might consist of lenses, mirrors,
`beam splitters, pieZoelectric actuators, translation tables,
`prisms, screens, lasers, optical ?bers, gratings, etc. Quite
`commonly, these elements are macroscopic in siZe and can
`easily be handled and adjusted. Although suitable for most
`optical prototyping purposes, the use of macroscopic optical
`elements can have its draWbacks.
`For eXample, to precisely steer a beam of light at a high
`angular rate, one might employ a conventional pieZo motor,
`or angular galvanometer, and mirror assembly. Using tWo
`such devices at right angles to one another in the same
`optical path Would give tWo degrees of freedom for con
`trolling the path of the beam. This arrangement is commonly
`used for steering laser beams in “laser shoW” productions. In
`this application, the physiological demands of human eye
`sight require only a 30 to 60 HertZ refresh cycle of each laser
`scanned frame to provide the illusion of smooth motion.
`Given that the re?ected laser light is of adequate intensity at
`the maXimum angular sleW rate, the overall angular siZe and
`detail of a single frame Will be limited by the total path
`length traced out to form that frame. That is to say, the
`angular eXtent of a laser image is limited by the maXimum
`angular sleW rate of each steering mirror.
`One apparent solution might be to increase the torquing
`capability of the mirror driving motor. This is effective to a
`point. With increasing torque capability, the angular inertial
`mass of the rotor elements becomes ever larger. At some
`point, the mechanical dynamics of the coupled motor/mirror
`system Will suffer. UnWanted torsional de?ections Will be
`introduced that result in beam steering errors. Stiffening the
`rotor might remedy the de?ection problem, but Would again
`increase the angular inertial mass. Thus, motor siZing is not
`a complete panacea.
`Abetter solution Would be to signi?cantly reduce the siZe,
`and therefore, the mass and angular inertia of the moving
`mirror. There is no torque penalty in doing so. HoWever, care
`must be taken to insure that the stiffness of the lighter mirror
`remains high so that dynamic distortion of the mirror itself
`does not compromise optical performance.
`Beam steering devices and their functional equivalents,
`are found in a Wide variety of products including laser bar
`scanners, CD ROM heads, laser printers, optical sWitches,
`robotic vision scanners, optical choppers, optical modulators
`and display devices to name a feW.
`In the ?eld of micromechanics, a number of recent
`developments in the area of spatial light modulators (SLM),
`light valves, and deformable mirror devices (DMD) have
`resulted in a signi?cant cost reduction and a substantial
`increase in performance of beam steering devices.
`TEXAS INSTRUMENTS holds a number of DMD pat
`ents including US. Pat. Nos. 5,504,614 and 5,448,546 that
`
`10
`
`15
`
`25
`
`45
`
`55
`
`65
`
`SUMMARY
`An aspect of the invention provides a method and appa
`ratus for precisely steering a beam of light by making use of
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 19
`
`

`
`3
`a hybrid inter-optical alignment precision Which occurs
`When a beam steering mechanism is micromachined With
`respect to a crystallographic orientation of a substrate.
`That is, it has been found that an optical element such as
`a micromachined mirror may be aligned precisely in an
`optimal axis for beam propagation and steering by using
`micromachining techniques Which take advantage of the
`crystallographic orientation of a substrate.
`An aspect of the invention provides a micromachined
`mirror Which is capable of steering a beam of light With
`multiple degrees of freedom. The micromachined mirror is
`advantageously characteriZed by extremely small mass and
`high frequency response While at the same time exhibiting
`high tolerance to vibration noise.
`In another aspect of the invention, the micromirror is
`precisely steered by the application of a controlled electro
`static effect, in either a current or a voltage mode.
`These and other aspects of the invention Will be appre
`ciated from the folloWing detailed description and draWings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a perspective vieW of a hybrid ?ber optic
`multi-degree-of-freedom beam steering apparatus according
`to the present invention.
`FIG. 2 is a perspective vieW and close up of the multi
`degree-of-freedom micro-mirror shoWn in FIG. 1.
`FIG. 3 is an exploded perspective vieW of FIG. 2 shoWing
`the details of the multi-degree-of-freedom micro-mirror.
`FIG. 4 is a side vieW cross section shoWing the internal
`detail of either a torsion or cantilever hinge.
`FIG. 5 is a top vieW of FIG. 1.
`FIG. 6 is a side vieW cross section of FIG. 5 indicated by
`the section line B—B in that vieW.
`FIG. 7 is a front vieW cross section of FIG. 5 indicated by
`section line A—A in that vieW.
`FIG. 8 is an exploded perspective vieW of the hybrid ?ber
`optic multi-degree-of-freedom beam steering apparatus
`shoWn in FIG. 1.
`FIG. 9 is perspective vieW of a generaliZed double gim
`baled micromirror.
`FIG. 10 is an exploded perspective vieW of FIG. 9.
`FIG. 11 is a perspective vieW of an alternate embodiment
`FIG. 12 is a perspective vieW of another alternate embodi
`ment
`FIG. 13 is a perspective vieW of an alternate embodiment
`With an integral optical device and cover plate
`FIG. 14 is a side vieW cross section of FIG. 13
`FIG. 15 is a perspective vieW of FIG. 1 shoWing a distal
`and lateral ?ap locking means
`FIG. 16 is a side vieW cross section of FIG. 1 shoWing an
`end ?ap locking means
`FIG. 17 shoWs the functionality blocks of an embodiment
`of the invention
`
`DETAILED DESCRIPTION
`
`Referring noW to FIGS. 1, 2 and 6 a ?rst aspect of the
`present invention provides a precision micromachined
`V-groove 106 into Which an optical ?ber 105 is cemented or
`otherWise af?xed. A light Wave propagating through optical
`?ber 105 is emitted from the core in the direction of
`micromirror assembly 200. The surface normal of micro
`mirror assembly 200 is given a precise angle 508 and locked
`
`65
`
`5,872,880
`
`4
`in place With the activation of solder bars 201A and 201B.
`For the con?guration shoWn, angle 508 has a value of 45
`degrees With respect to optical axis 507 as shoWn in FIG. 6.
`Upon striking the underside of submirror 207, the light Wave
`is re?ected doWnWard through body 100 of the device.
`Electrodes 202 and 203 are in close proximity to submirror
`207 and When a voltage potential is disproportionately
`introduced on one or the other electrode With respect to
`grounded submirror 207, an unbalanced electrostatic force is
`generated. The net effect of this force is to rotate submirror
`207 about its torsional axis de?ned by torsion hinges 204A
`and 204B, thereby de?ecting the re?ected beam parallel to
`the bottom surface of the device and perpendicular to the
`axis of optical ?ber 105.
`The beam, having had its optical path 507 altered by
`submirror 207, passes doWn through the bottom of cavity
`101 and into adjoining cavity 504 as shoWn in FIG. 6. In one
`aspect of the invention, the beam passes through the bottom
`of cavity 504 and into free space. In another aspect of the
`present invention, a circular, spherical, rectangular, cylin
`drical or otherWise irregularly shaped optical element 503,
`may be precisely positioned Within cavity 504 so as to
`provide optical shaping of the emitted beam. For example,
`if a light beam traveling along optical path 507 is made to
`pass through optical element 503, it can be made to converge
`to a focal point someWhere beloW body 100 if optical
`element 503 is a converging lens, or diverge if optical
`element 503 is a diverging lens. Optical element 503 can
`take the form of a singlet lens, compound lens, achromatic
`lens, index gradient lens, micromachined lens or lens array,
`grating, prism, mirror, laser cavity, optical ?ber, optical
`ampli?er, optical sensor or any variety of optical elements
`knoWn to those skilled in the art.
`FIG. 1 shoWs one embodiment of a hybrid ?ber optic
`multi-degree-of-freedom beam steering apparatus. The
`device body 100, is preferably fabricated from a
`conventional, double side polished silicon Wafer having a
`normal to its surface coincident With the (100) crystallo
`graphic direction. After depositing and patterning all sacri
`?cial SiO2 pads, a thin ?lm 102 and 501 of silicon nitride,
`silicon carbide, silicon monoxide or the like, is deposited on
`both surfaces of substrate 100, primarily to provide an inert
`masking layer for subsequent anisotropic etchants. A
`detailed account of these and other fabrication steps Will be
`describe later. The thickness of ?lms 102 and 501 is dictated
`by the pinhole free quality of the deposit but may typically
`be on the order of 1000 angstroms. Films 102 and 501 may
`be deposited using Chemical Vapor Deposition (CVD),
`Pressure Enhanced Chemical Vapor Deposition (PECVD),
`electron beam evaporation, plasma sputtering, or other
`methods knoWn to those skilled in the art.
`Optical ?ber 105 is shoWn lying in a precision etched
`V-groove 106 Which is connected to cavity 101. V-groove
`106, cavity 504 and cavity 101 are all formed by a Wet
`anisotropic etchant such as potassium hydroxide (KOH) and
`Water, tetra-methyl ammonium hydroxide
`and
`Water, or the like. As With all such etch pro?les in silicon, the
`Walls of groove 106 and cavity 101 are de?ned by the
`crystallographic (111) planes of silicon. This is due to the
`fact that there is a dramatic difference in etch rate among the
`different plane orientations. Speci?cally, for a KOH Water
`etchant the (100):(110):(111) planes etch at a ratio of roughly
`300:150:1 respectively at 85° C.
`A signi?cant aspect of utiliZing the crystallographic
`planes of single crystal silicon to de?ne a complex inter
`connection of optical ?xturing is that the registration of
`intersecting angles from one groove or pit to the next, is
`
`15
`
`25
`
`35
`
`45
`
`55
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 20
`
`

`
`5,872,880
`
`5
`governed with atomic precision. For (100) silicon, there are
`four (111) walls that slope down 54 degrees with respect to
`the top (100) surface and they intersect one another at
`precisely 90 degrees. Further, if a square opening of width
`W is made in a KOH resistant mask, such as silicon nitride,
`and any one side of that square opening is coincident with
`a (111) plane, then the resulting etched pit will have a depth
`of exactly 0.707 times W. Such precise control of intercon-
`nected features provides a highly reliable and relatively
`inexpensive method for aligning optical components with
`great precision.
`As shown in FIG. 6, cavity 101 is connected to cavity 504
`and provides clearance for movement of micromirror assem-
`bly 200. In one embodiment of the invention, cavity 101
`may also play the role of a ground plane for the electrostatic
`actuation of one or more parts of micromirror assembly 200.
`In another embodiment of the invention, groove 106 and
`cavity 101 may be overcoated with a solderable surface such
`as a sputtered titanium/platinum/gold film approximately 0.5
`microns thick. The titanium provides for good adhesion
`between the silicon and platinum, and the platinum acts as
`a diffusion barrier to prevent excessive alloying of the gold
`and titanium and is a well know technique to those skilled
`in the art. A gold surface in groove 106 provides for the
`soldering of a metal coated optical fiber; this being but one
`method of reliably aflixing fiber 105 into groove 106. Other
`methods for securing fiber 105 into groove 106 include the
`use of adhesives such as cyanoacrylate (3M) , epoxies
`(MASTER BOND, 154 Hobart St. Hackensack, N.J.), photo
`curable adhesives (EDMUND SClJ:N'l‘lFlC, 101 E. Glouc-
`ester Pike, Barrington, N.J.), thermoplastics (DUPONT) and
`the like.
`
`A unique aspect of the invention involves an in situ
`method for assembling micromachined parts, herein referred
`to as the self—solder technique. Referring to FIG. 2, in one
`aspect of the invention, solder bars 201A and 201B are
`fabricated directly on resistive heating elements 201C and
`201D (not shown). Heating elements 201C and 201D can
`take the form of a meandering path,
`thin film conductor
`(1000 angstroms ), such as a Ti/Au film, whose resistance is
`greater than the thicker( a few microns) feed lines 104A and
`104F. As current is passed from line 104A,
`through the
`heating elements, and out
`to line 1041“,
`intense heat
`is
`conducted from heating elements 201C and 201D to solder
`bars 201A and 201B respectively, thereby causing them to /
`melt. As is the case with the present invention, if solder bars
`201A and 201B are in close proximity or intimate contact
`with a wetable surface such as a gold coated wall of cavity
`101, then the molten solder will wick between wall of cavity
`101 and mirror assembly 200 at the point of solder joint
`contact. These contact points are shown as 601 and 602 in
`FIG. 7. Removing current flow from 104A and 104F disen-
`gages the heaters and permits the joint to solidify. The
`resulting solder joint is permanent and strong.
`Solder bars 201A and 201B can be composed from a wide
`range of materials with a range or melting points from room
`temperature to 500° C., depending on the desired strength of
`the resulting solder joint and range of service temperatures.
`A higher melting point solder usually results in a stronger
`joint. Solder composition can be any variety of commonly
`known low temperature alloys such as PbSn, Pl)SbSn,
`PbSnAg, In, or higher melting point alloys composed of Sn,
`Ag, Au, Cu, Si etc. These materials may be obtained from
`companies such as the INDIUM CORPORATION OF
`AMERICA (34 Robinson Rd, Clinton N.Y.) or TECI-INICS
`(1254 Alma Ct. San Jose, Calif.). Solder bars 201A and
`201B may be formed by electroplating in the case of the Pb
`
`_
`
`6
`and In alloys, or may also be sputtered and patterned in the
`conventional manner as is known by those skilled in the art.
`It can be appreciated that
`it may also be desirable to
`incorporate a layer of flux on or within solder bars 201A and
`201B to enhance the wetability of the joined surfaces.
`A low temperature self-soldering joint can be created by
`making solder bars 201A and 201B from any of a variety of
`low melting point thermoplastics such as polyester resins,
`microcrystalline wax, polyethylene and the like. A large
`variety of thermoplastic adhesive resins are available from
`DUPONT.
`It is well known that gold alloys quite readily with silicon
`at low (400° C.) temperatures, forming an excellent silicide.
`Given suflicient heat input, it may be possible to use pure
`gold, or a eutectic gold/silicon solder (96.8% An, 3.2% Si)
`to produce a bond directly on a bare silicon surface, thereby
`simplifying the self—solder technique.
`In an alternate embodiment of the invention, it may be
`desirable to eliminate lines 104A and 104F and resistive
`heating elements 201C and 201D in lieu of placing the entire
`device on a hot plate or in an oven to directly activate solder
`bars 201A and 201B. It can be appreciated that any one of
`these method of self-soldering described in the preceding
`paragraphs, could also be used to secure fiber 105 into
`groove 106, or optical element 503 into cavity 504.
`Bar 109 provides support for bond pads 103A—103F and
`corresponding conducting lines 104A—104F as they traverse
`the underetched void created by groove 106. Bar 109 may be
`composed of a particularly thick layer of insulating material
`similar to that which makes up micromirror assembly 200.
`Another method for fabricating bar 109 would involve the
`plating of a metal such as Fe, Ni, Cu, Au or Cr that is
`subsequently overcoated with an insulator such as Si,Ny,
`Sioz, SiC or the like.
`For the embodiment shown in FIGS. 1 through 8, a light
`8 beam approaches submirror 207 from below, thus a reflec—
`tive material must be provided on the lower surface if the
`body of submirror 207 is comprised of an opaque dielectric.
`If a thin or otherwise transparent dielectric such as silicon
`nitride is used, then the rellective surface may be encapsu-
`lated within the body or reside on the upper surface of the
`mirror.
`
`A major advantage of the fabrication means disclosed
`herein, is that the critical reflective surface of a mirror may
`be sputtered directly on the surface of a freshly polished
`wafer, before any additive processing has been done.
`Because this is done first, mirrors are optically flat and
`smooth, and global planarization is not an issues.
`Details of the hinge structure employed for both torsion
`and cantilever hinges is shown in FIG. 4. Area 401 refers to
`the anchored or frame side of hinge 402, while area 403
`refers to the mirror or suspended side of the structure. As
`shown here, conductor 405 traverses hinge 402 and is made
`as thin as possible so as not to significantly contribute to
`hinge stiffness. Via pad 406 is in communication with layer
`405 and built up to prevent punch through as a plasma
`etched via is made through layer 407. Thicker lines may then
`be connected to via pad 406. In general, via pad 406 may be
`on either side of a hinge structure.
`In the preferred
`embodiment, 21 via pad 406 resides on both sides of a hinge
`structure for all lines since thicker, high current carrying
`lines are present on the cantilevered structure side.
`A general, presently preferred fabrication sequence for
`micromirror assembly 200 is as follows. Referring to FIGS.
`3 and 4, first, a thin (400 A) layer 404 of low stress IPCVD
`silicon nitride is deposited over the upper surface of sub-
`strate 100.
`
`Cisco Systems, Inc.
`Exhibit 1036, Page 21
`
`

`
`5,872,880
`
`7
`Next, a conducting layer 405 of Ti (100 A) /' Au (400 A)
`/ Ti (100 A) is sputtered or evaporated onto the surface.
`Layer 405 is patterned with a photoresist mask and a
`combination of 6:1 BOE to etch the Ti, and roon1 ten1pera-
`ture aqua regia (321 I-ICI/I-INO3) to etch the Au. All via pads
`406, may be built up by selectively electroplating these
`areas.
`
`A thicker layer 407 (i.e. 2 microns for a mirror 100
`microns wide) of low stress,
`low temperature PECVD
`silicon nitride is deposited over the surface. A second mask
`is then provided sucl1 that there are openings defining those
`areas that will be etched down to bare substrate 100.
`Specifically, those are areas that define the edges of mirror
`frame 303, submirror 207, torsion hinges 302A and 302B,
`side wall accommodating edges 304,
`the area between
`micromirror assembly 200 and the defining edges of cavity
`101, and cantilever hinge perforations sl1own as hinge group
`301 in FIG. 3. For reasons to be discussed later, a plasma
`etch of only 3000 Ais performed at this point, and is herein
`refereed to as the “head start” etch.
`
`After the old mask is removed, a third mask is provided
`having openings as previously described, but with additional
`opening over all hinge areas. Aplasma etch is done such that
`layer 407 is removed from all areas that will see a subse-
`quent Si anisotropic etch.
`This leaves a substantially thick hinge area 408, that is
`approximately equal to the thickness of the “head start” etch.
`A forth mask defines via openings down to all via pads
`406. A plasma etch is performed until all pads 406 are
`exposed.
`A sacrificial material (not shown) such as polyimide,
`PMMA, SiO2 or the like, is deposited and patterned with a
`fifth mask to form a pad above and about submirror 207 and
`extends laterally to cover those openings that define sub-
`mirror 207 while remaining within the bounds of frame 303
`and not covering pads 406. The thickness of this sacrificial
`pad defines the electrode spacing between submirror 207
`and electrodes 202 and 203.
`
`A seed layer of Ti (200 A), Au (1500 A), Ti (500 A) is
`deposited onto the substrate. A sixth mask is provided, with
`openings defining lines l04A—F and electrodes 202 and 203.
`The upper layer of Ti
`is removed with BOE,
`thereby
`exposing the Au. Au is tl1en electroplated within the open
`mask areas. After stripping of the mask, the seed layer is /
`removed with wet etchants as before.
`
`_
`
`A similar series of procedures may be used to define thin
`film heaters 201C and 201D and to electroplate or pattern the
`optional solder bars 201A and 201B.
`After electroplating, all sacrificial materials are removed.
`If polyimide is used, then a three Torr oxygen plasma is used
`to remove it. If SiO2 is used, then an extended length BOE
`wet etch is employed.
`The bare areas of substrate 100 are then subject to an 85°
`C., 25% KOH:DI etch. As cavity 101 is defined by the
`anisotropic etch, micromirror assembly 200 becomes fully
`under etched and is suspended above the cavity by hinge
`group 301. Post etch debris is removed with a 10 minute
`immersion in 121:1 HCl:H2O2:DI followed by a DI rinse.
`As previously mentioned, the cross section 408 of hinge
`group 301 is relatively thick. A thick cross section produces
`a very stiff hinge structure, thereby preventing the well know
`destructive force of surface tension from pulling micromir-
`ror assembly 200 into hard contact with the walls of cavity
`101, a condition that is irreversible.
`An overly stilf hinge, however, is undesirable for creating
`large angular deflections with moderate driving voltages.
`
`_
`
`8
`Thus, all hinges require a dry etch “tuning” to a cross
`sectional thickness 409 before being called into service.
`Depending on the thickness of layers 404 and 405, a hinge
`can be made arbitrarily thin and compliant. Because the final
`etch takes place in a dry environment, there is no danger of
`surface tension induced damage.
`Once completed, micromirror assembly 200 is electro-
`statically driven down into cavity 101 3y placing a potential
`across pads 103C and 103D. At a su icient voltage, edges
`304 of micromirror assembly 200 wi
`rest against the side
`walls of cavity 101. The predetermined geometry of micro-
`mirror assembly 200 and cavity 101 is such that when fully
`deployed to contact, micromirror assembly 200 will rest at
`a 45 degree angle with respect to the upper surface substrate
`100. While maintaining the voltage, current is momentarily
`driven through pads 104A and 104F to initiate the self
`soldering means, thereby firmly establishing micromirror
`assembly 200 within cavity 101.
`It can be appreciated that the fabrication sequence previ-
`ously suggested, can be altered significantly while attaining
`the same objectives. Thus, any permutations of sequencing
`are considered equivalent methods. In addition, other tech-
`niques such as plasma etching of the conductive layer,
`replacing dry etches with wet etches, and other substitutions
`known to those skilled in the art, are essentially equivalent
`methods to those already disclosed.
`Once deployed, a transparent or opaque cover plate 107,
`made from glass, ceramic, plastic, silicon etc., serves as a
`mechanically rigid barrier to prevent inadvertent damage of
`the delicate micromirror assembly 200. Cover plate 107 may
`be attached to body 100 with methods commonly in use
`today including, solder glass, glass frit, two part adhesives,
`thermal adhesive, UV cure adhesives, cyanoacrylate, etc. In
`order to reduce possible electrostatic interference with or to
`the environment, cover plate 107 may also have one or more
`surfaces coated with a conductor, or may itself, be electri-
`cally oonductive. If 107 is made conductive, it is apparent
`that
`it could provide the necessary ground for rotating
`submirror 207 in lieu of electrodes 202 and 203. In this
`configuration, two isolated conducting surfaces disposed on
`either side of the rotational axes defined by hinges 302A and
`302B on submirror 207, could produce an unbalanced elec-
`trostatic force by applying a voltage potential between one
`or the other of the conducting surfaces and the grounded
`surface of cover 107. Similarly,
`torsional forces can be
`produced between cavity 101 and the isolated conducting
`surfaces of submirror 207, as described previously, if cover
`107 is made non-conductive or is electrically isolated and
`cavity 101 is grounded.
`Cavity 504 is formed on the underside of body 100 in a
`five step process. First, sacrificial pad 502, preferably com-
`posed of SiO2,
`is deposited (approximately 0.5 microns
`thick) and patterned on the bottom surface of body 100.
`Secondly, a thick (1000 A10 a few microns ) underside cap
`layer 501 of Si,,N‘,, SiC or any other material that shows
`excellent resistance to I-Iydrofluoric Acid (I-IF) or Buffered
`Oxide E