CA2158917C - Colour deformable mirror device having optical thin film interference colour coatings - Google Patents
Colour deformable mirror device having optical thin film interference colour coatings Download PDFInfo
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- CA2158917C CA2158917C CA002158917A CA2158917A CA2158917C CA 2158917 C CA2158917 C CA 2158917C CA 002158917 A CA002158917 A CA 002158917A CA 2158917 A CA2158917 A CA 2158917A CA 2158917 C CA2158917 C CA 2158917C
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
- G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
- G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
- G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD
- G02B26/0841—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD the reflecting element being moved or deformed by electrostatic means
Abstract
A semiconductor device comprises a plurality of coloured deformable mirrors controllable by electrical circuitry. Groups of mirrors, responsive to the electronic signals, are selectably operable to reflect incident light. The deformable mirrors are coated with an optical thin film interference colour coating having at least a layer that is substantially transparent to the visible light. As well the optical thin filminterference colour coating includes at least one further layer that is partially absorbing with respect to the visible light. The spectral reflectance and absorptance of the deformable mirror is modified in order to obtain a desired reflectance colour by the process of optical interference enhanced absorption in the optical thin film interference colour coating. The optical thin film interference colour coating has predetermined layer thicknesses and materials; the substantially transparent layer substantially determines the desired reflected colour.
Description
Colour Deformable Mirror Device ~Iaving Optical Thin Fllm Interference Colour (~o~tin~
Field of the Invention This invention is related to the field of electronic devices and more particularly S to deformable mirror devices.
R~k~round of the Invention A deforrnable mirror device (DMD) includes a plurality of electronically controllable mirrors. Each mirror is capable of a m~h~ni~l movement in response to an electrical signal and can reflect incident light in one of two predetermined 10 directions collesponding to the mirror's oriPnt~tiom DMDs can be used as light modulators for optical signal proces~ing as well as for displaying images electronically. For example, a DMD having an array of tightly spaced small mirrors or pixels in the form of rows and columns can be used in a projection display. The two orientations in which each mirror or pixel reflects light are defined as the on 15 and off" state of the mirror or pixel. Therefore this particular type of DMD may be referred to hereafter as a digital micro-mirror device. Rff~ se of its high pixel density, such a DM~ is capable of producing images co,l.~dble in resolution to cathode ray tube (CRT) displays, liquid crystal displays, etc. Advantageously, the process for manufacturing a DMD display is compatible with that used in the 20 semiconductor industry. Furthermore, the mirrors can be switched ~on or "off" in micro-seconds; hence, it is capable of displaying rapidly ch~nging images. Another advantage is that the light reflected from an "off" pixel travels along a different path and is not projected onto the image screen; hence, the display has a high contr~t Since a~lo~mately 90% of the incident light falling onto the individual on pixels 25 is reflect~ towards the image screen, this results in a more energy e-ffi~ient display com~al~d to liquid crystal projection displays.
Currently, the individual mirrors in a conv~ntion~l DMD are made of an aluminum substrate that reflects light uniformly throughout the visible spectrum;
therefore, the conventional DMD is monochrolllatic. There are several approaches to make a colour projection display system using a DMD. Two approaches involve S colour filtering the light either before or after it is refl~te~ from the DMD. In the first approach, known also as "sequential" colour, a single morloçh~omatic DMD is used. White light first passes through a rotating colour filter wheel having red (R), green (G) and blue (B) filters. The filtered white light then falls onto a monochromatic DMD and the light refle~te~ from the "on" pixels forms an image on10 a projection screen. The light reflected from the "off" pixels travels along a different path and is absorbed by a light absorber. While this sequential colour projection display system displays only one colour at a time, an observer actually perceives a colour based on the three time-inLe~ ed primary colours. This approach has certain disadvantages: a) only one colour is displayed at any given time, that reduces the 15 brightness of the display; b) synchronization between the rotating colour filter wheel and the DMD driver is required; and c) the use of a rotating colour filter wheelmakes it difficult to reduce the overall size of the display system.
In the second approach, three monochromatic DMDs are used, one for each of the three primary colours: R, G and B. Either three colour light sources or a single 20 white light source, divided into three primary colour beams by dichroic beam-splitters, can be used in the system. The three colour images from the three monochro---aLic DMDs are combined into a single image to produce the desired colour picture. The disadvantages of this system include complex chip ~lignmPnt output convergence, excessive cost and large package size of the required optical system.
A different approach for a full colour projection display system is to use a colour DMD as disclosed by W. E. Nelson in US. Pat. No. 5,168,406, issued on Dec. 1, 1992. The disclosed colour DMD has a colour filter on top of each aluminum mirror. Advantageously, no extra light splitting and combining optical components are required in the display. In Nelson's patent, the colour filters are implemented using intrin~iC absorption in dye materials. In the m~mlf~ntllring of this dye colour DMD, a dye filter mosaic or dye coating is first deposited onto a glass 5 substrate. Next, the dye filter is subsequently transferred to a DMD chip by asublimation process. In this process, the dye filter mosaic or coating is placed next to a DMD chip and is heated by a printing head. The dye m~teri~l iS vaporized and condences on the surface of the DMD. Alternatively, dye filters may be deposited by electrically charging the individual mirrors of a DMD. A dye cloud is then 10 introduced next to the DMD and condenses on the surface of the individual charged mirrors. Another method for manufacturing a colour filter for deformable mirror device has been disclosed by M. A. Mignardi et al. in US. Pat. No. 5,240,818, issued on Aug. 31, 1993. In their approach, a solution of a dye-resist ~ ure is spun uniformly onto a nearly completed DMD chip. The dye-resist coating in the 15 unwanted area is then removed by photo-lithography, i.e., by ~ Gsing the chip to W light through a mask and developing it. Different dye-resist materials can be applied in the same way to form, for example, a red, green and blue multi-colourfilter array. A transparent layer is then deposited to protect the dye-resist filters.
There are several disadvantages to all the above dye or dye-resist mixture filter 20 approaches: The stability of the dye-resist or dye filters is poor and these dye or dye-resist filters normally degrades with time. As well, their ~lroll.-al ce tends to deteriorate when exposed to heat and light sources that are present in projection display systems. Also, dye-resist and dye colours filters deposited by spinning or sublimation often have poor adhesion to the mirror subst~tP In ~ ition, the quality 25 of the dye filters can be poor, which could result in light sc~ ;ng reduçing the contrast of the display. Furthermore, the processes to apply these dyes or dye-resist ll-i~lules might not be fully compatible with current manufacturing process of the DMDs.
Object of the Invention It is an objective of the present invention to provide a more stable colour deformable mirror device having optical thin film in~elrelc;ilce colour co~ting~.
Another object of the present invention is to provide a method of depositing 5 optical thin film inlelrere,lce colour co~ting~ onto a deformable mirror device.
Summary of the Invention In accordance with the present invention there is provided, a semiconductor device comprising: circuitry for accepting electronic .~ign~l~; a plurality of deformable mirrors selectably operable to reflect inrid~nt light, responsive to the 10 electronic signals; and, a first group of said plurality of deformable mirrors being coated with an optical thin film inte,rerellce colour coating having at least a layer that is substantially tr~n~p~rent with respect to the in(i~ent light, the optical thin film intelrerence colour coating int~ (ling at least one further layer that is partially absorbing with respect to the inci~ent light, so that the spectral refl~ct~nce and 15 absorptance of the deformable mirror is modified to produce a desired reflecte~
colour by the process of optical inte:relellce enh~nce~ absorption in the optical interference colour coating, the layers being of predetermined thickn~sses and materials, wherein the thickn~ss of the subst~nti~lly tr~nsp~rent layer subst~nti~lly determines the desired reflected colour.
The optical thin film intelre~eilce colour coating in accor~lce with the presentinvention may comprise an optional high reflectance layer, at least one transparent layer on top of the high reflectance layer and at least one partially absorbing layer on top of the transparent layer. The colour deformable mirror device may comprise a25 second group of said colour mirrors that reflect a second group of wavelengths of the 215891~
incident visible light to obtain a second reflect~ colour and may further comprise a third group of said colour mirrors that reflect a third group of wavelengths of the inçident visible light to obtain a third re~flecte~ colour. The colour deformable mirror device has a first, second and third group of said colour mirrors forming three-colour S pixels. Alternatively, the colour deformable mirror device may comprise a first, second and third groups of said colour mirrors and a group of neutral mirrors forming four-colour pixels.
In accordance with yet another aspect of the present invention, there is furtherprovided, a method for the manufacture of a colour deformable mirror device having 10 a semiconductor substrate, driving electronics on the semiconductor substrate, and a plurality of deformable mirrors for reflecting inci~l~nt light, the method comprising the steps of: applying an optical thin film inte.relGnce colour coating upon a first group of the deformable mirrors by physical vapor deposition or chPmiç~l vapor deposition processes; the optical thin film in~ rc~rence colour coating being of15 predetermined thicknesses and materials and being suitable for re-flecting a first group of wavelengths of the visible light to obtain a first colour, said coating inclu(ling at least a substantially transparent layer and at least a partially absorbing layer.
One advantage of the present invention is that m~tP i~l~ typically used in the optical thin film inte-re.ence colour co~ting~ are either subst~nti~l1y tr~ncp~rent or 20 partially absorbing uniformly throughout the visible ~peCLlUlll and optical inte-re~ lce enhanced absorption is used to engine~r which particular wavel~ngthc of light are absorbed or reflected by the optical thin film illtelrelence colour coating in order to obtain a desired refl~te~ colour. Thus, the invention provides a high degree of flexibility; for example, different colours can be achieved by using the same materials 25 but with different layer thicknesces Furthermore, the colour ~lÇ~ -ance of the optical thin film inte~r~.~nce colour co~ting~ can be cle~igne~l to match most colour standards currently in use in the world such as those of the National Television 2158~17 System Committe~ (NTSC), the Phase ~ltt~rn~tion Line (PAL) and the Sequentiel Couleur avec Mémoire (SECAM). In contrast, dyes, as disclosed in the prior art, are engine~red to absorb at specific wavelengths of light and these wavelengths cannot be changed without çh~nging the dyes themcelves. Hence, the use of dyes is less flexible 5 compared to the present invention.
Another advantage of the present invention is that the optical thin film interference colour co~ting~ are made of ~ tric m~t~ri~l~ and metals that are very stable both chemic~lly and physically. Their performance can with~t~nd harsh environments and will not deteriorate with time or with high ~ e~ .~s.
Another advantage of the present invention is that the process to deposit optical thin film intelreleilce colour co~ting~ is col"palible with the process currently used to produce monochromatic deformable mirror devices. It can be easily integrated with the current process with little additional equipment.
Another advantage of the present invention is that the optical thin film 15 interference colour coating not only filters light but also acts as a protective coating for the aluminum mirrors; therefore, the colour deformable mirror device in the present invention is more stable than the conventional monoch~ullla~ic aluminum deformable mirror devices and the dye type colour deformable mirror devices.
Another advantage of the present invention is the flexibility to select the 20 available co~ting~ materials for the purpose of col~pen~ting stress in the mirror and the optical thin film inlelrel~;nce colour coating.
Another advantage of the present invention is that the optical thin film interference colour co~ting~ can be design~d so that the absorption of light outside the visible spectral region is minimi7~d As well the spectral distribution of the light 25 source and the spectral response of the optical image system and the human eye can 21~8917 be t~ken into account in the design of the optical thin film in~elrelence colour co~ting~
in order to optimize the pelrol,l,ance of the colour display and to minimi7~ therequired number of optical co"~nents.
Yet another advantage of the present invention is that the optical thin film 5 in~elrese,lce colour coatings can be desiEned to have a very high hlmin~nce reflectance for a given light source.
10 Brief Des,,;l~lion of the Drawings Exemplary embodimPnt~ of the present invention will be described in conjunction with the drawings in which:
FIG. 1 shows a portion of a cross-sectional view of a colour deformable mirror device in accol~lce with the present invention;
lS FIG. 2 shows a plan view of a colour deformable mirror device having three optical thin film in~elrelence colour co~tinEs in accoldance with the present invention;
FIG. 3 shows the calculated refl~t~nre curves of red, green and blue optical thin film intelr~,~nce colour co~ting~ of a first embodiment of the present invention;
FIG. 4 shows CE cool~inates of the red, green and blue optical thin film 20 interference colour co~tinE~ in FIG. 3 and those of standard CRT red, green and blue phosphors on a CIE chromaticity diagram;
FIG. S shows r~lcul~ted reflP~t~nce curves of red, green and blue optical thin film interference colour coatings of a second embodiment of the present invention;
FIG. 6 shows CIE coordil1ates of the red, green and blue optical thin film S interference colour co~ting~ in FIG. 5 and those of CRT phosphors and NTSC
specifi~tions on a CIE chromaticity rii~gr~m; and, FIG. 7A-7E show cross-sectional views illllctr~tive of the m~nllf~ ring steps of a colour deformable mirror device having optical thin film ill~,Çer~i~ce colour co~tin~ in accordance with the present invention.
Detailed Des~ Jlion For a better underst~n~ing of the present invention, a background knowledge of a present-day deformable mirror device is desirable, and herein, the reader is 15 referred to Spatial Light Modulator and lUethod " U.S. Pat. No. 4,662,746, L. J.
Hornbeck, issued on May 5, 1987, and Spatial Light Mod~ tor and Method," U.S.
Pat. No. 5,172,262, L. J. Hornbeck et al., issued on Dec. 15, 1992. The det~il~
description of the present invention is best illllst~ted with the aid of drawings ~;IGs.
1-7.
A colour deformable mirror device in accol~lce with the present invention comprises at least one deformable mirror that has an optical thin film inte~relci ce colour coating. The optical thin film in~relence colour coating is based on optical interference Pnh~nced light reflection and absorption as described in the follows:
Optical intelr~nce is defined as the variation of ele~;L,u.,-~gnetic wave amplitude with ~ict~nce or time, caused by the ~u~el~osiLion of two or more waves of electrom~nPtic radiation (light). These two or more waves can be the result of S reflection or tr~nsmi~ion at the interfaces of layers in an optical thin film in~-rel~nce coating, used in the present invention, provided that the thirknP-sses of the individual layers are snfficient to support optical intelrelence at the wavelengths of interest.
Intrinsic absorption of light, used in dye colour filters as described in US. Pat. No.
5,168,406, is defined as the process whereby some of the energy of electrom~gnetic 10 radiation (light) is transferred to a substance on which it is inri~lPnt or which it traverses.
It is possible to significantly Pnh~nce the amount of absorbed light in an optical thin film in~lrt;l~nce coating to obtain a desired ~lÇol-l.ance, for example, a particular refl~te~ colour, through the phenomenon of optical intelreleilce, over that 15 of intrinsic absorption alone, provided that as stated above the thirknP~ of the individual layers are sufficiçnt to support the optical in~lrerenoe at the wavelengths of interest. This phenomenon is hereinafter referred to as optical intelr~lt;nce çnh~nce~
absorption.
FIG. 1 shows a cross-sectional view of a portion of a colour deformable 20 mirror device 10, having a semiconductor ~ubsLld~e 12, a driving electronics 14 on top of the semiconductor substrate 12, and a mirror elemPnt 16 on top of the driving electronics. The mirror elçmlont 16 is comprised of the mirror ~u~pG~Liilg posts 18, the torsion hinges 20, the mirror substrate 22 and a optical thin film il~lrPrence colour coating 24. The optical thin film ill~elr~nce colour coating 24 may include 25 an optional high reflect~nc~ layer 26, a tr~n~p~rent layer 28, a partially absorbing layer 30, and, if necessary, other subsequent transparent and partially absorbing 215~917 layer(s) 32. The optical thin film intelre-ellce colour coating 24 and the mirror substrate together form a colour mirror 34. If the optional high refle~t~nr,e layer 26 is omitted, the mirror substrate 22 will act as the coating substrate for the optical thin film intelrelence colour coating 24 and will become part of the optical thin film S interference colour coating 24. Different optical thin film ih~,releilce colour co~ting~
can be deposited on top of different mirror substrates in a pre-defined way to form different colour mirrors as shown in a plan view in FIG. 2. Each colour mirror is supported by two hinges 40 and two posts 42. Three individual red 44a, green 44band blue 44c colour mirrors together form a pixel 46. Such a colour DMD can be 10 used in a full colour projection display system with only one white light source.
Without departure from the spirit of the present invention, the mirror elem~nt 16 can have other configurations as well. For PY~mrl~, the colour mirror 34 can have a different shape and can be sup~lLed by a spacer layer in a cantilever structure as described in US. Pat. No. 5,172,262. More particularly, the colour mirror 24 can 15 have only one ~uppolLing post centered in the middle, where the post sits on top of another mirror substrate suppolled by torsion hinges and posts, as described in ~Multi-level Deformable Mirror Device," US. Pat. No. 5,083,857, by L. J.
Hornbeck et al., issued on Jan. 28, 1992. This configuration ~limin~t~s the hinge and supporting area on the surface and results in a larger mirror apel~u~: that is desirable 20 in a projection display system.
Unlike the approaches disclosed in US. Pat. No. 5,168,406 and 5,240,818 that use only int-rincic absorption of light in dyes or dye-resist ~ lul~s to form colour filters, the optical thin film intelrelt;ilce colour coating 24 in the present invention uses optical in~lrel~nce enh~ncecl absorption. Therefore, the optical thin film 25 intelrt;lt;nce colour coating is much more flexible and can be ~lesigned to absorb and reflect certain wavelengths of light in the visible ~eclu~ l to obtain a desired reflected colour, as well as to reflect most of the light in the inrl~ed region to reduce heat 21S8gl7 absorption. Dyes or dye-resist mL~Llules norrnally absorb most of the infrared radiation inci~pnt upon them. In addition, to achieve a desired colour, many different thin film multilayer designs can be obtained. More i",pol~llly, with the same materials, it is possible to achieve different reflPcted colours by varying only the S thicknç~ses of the subst~nh~lly tr~n~p~rent layers. This will simplify the m~nllf~ctllre process of the optical thin film inle~fer~nce colour co~ .g~ The p.o~lLies of a practical display system can be taken into account in the optical thin film intelre.e,lce colour coating design process to obtain an optimal pelrol"-ance, i.e., the spectral distribution of the light source and the spectral response of the optical system and of 10 the human eye. As well, since the human eye is not sensitive to the red and blue parts of the visible spectral region, it is possible to design a red or a blue optical thin film interference colour coating with a relatively higher l-.. n~l~ce reflect~nce The mirror substrate 22 can be made of a corl~ucting metal, metal alloy or semiconductor, i.e., Al, Cr, Co, Cu, Au, Hf, Mo, Ni, Nb, Pt, Ag, Ta, Ti, W, Yr, 15 Zr" Si, Ge, nickel alloy such as InconelT~, etc. The optional high reflect~nce layer 26 can be made of a high reflectance metal or metal alloy, i.e., Al, Cr, Co, Cu, Au, Hf, Mo, Ni, Nb, Pt, Ag, Ta, Ti, W, Yr, Zr" Si, Ge, nickel alloy such as InconelTM, etc. The mirror substrate 22 or the optional high rçfl~t~nce layer 26 acts as the first optical layer for the subsequent layers in the optical thin film in~lÇe,eilce colour 20 coating 24. If the mirror substrate 22 is also made of a high reflect~nce m~tPri~l, such as aluminunl, then the layer 26 is not n~Pc~Ps~l ~. The transparent layer 28, and, if nece~c~ry, the subsequent transparent layer(s) 32 can made of transparent dielectric materials from the group of oxides, nitrides, fluorides, selpnic1p~ and sulfi~es, such as, sio2~ A123~ HfO2~ Nb2S~ Ta2s, TiO2, Y203, ZrO2, SiN, AlN, MgF2, CaF2, ZnSe, 25 ZnS, etc. The partially absorbing layer 20, and if n~ , the subsequent partially absorbing layer(s) 32, can be made of absorbing metals, metal alloys or semiconductors, i.e., Cr, Co, Cu, Au, Hf, Mo, Ni, Nb, Pt, Ag, Ta, Te, Ti, W, Yr,Zr, InconelTM, Si, Ge, etc.
SiO2 is a pl~f~r~d material for the transparent layer(s) in the optical thin film interference colour co~tingc in connection with the present invention; this is because it normally has low stress and is already used in a conventional DMD for other purposes. A1203 iS another ~l~felled m~tPri~l for the h~ncp~rent layer(s) because it 5 has a higher refractive index than SiO2, a good thermal conduchvity and low stress.
Nickel or nickel alloys, e.g., InconelTM, are ~l~felled absorbing materials for the partially absorbing layer(s) because they are very stable both ç~l~mic~lly and physically. They also have good thermal conductivity. ~lln,.;~ .,. is a ~l~f~ d m~teri~l for the mirror substrate 22 as well for the optional high reflect~nee layer 22;
10 this is because Al has not only good electronic and thermal con~luct;vity, but also a high reflect~nce. Other coating materials can be chosen as well, for example, m~teri~lc with opposite stress can be used to b~l~nce the total stress in the mirror elem~nts .
Several embodiments of the present invention will be described in detail in the 15 following descriptions. Without departing from the spirit of the present invention and for the purpose of a more practical demonstration, the following conditions are assumed: First, the embodiments are de-cign~d for a Xenon-arc lamp source that is currently used in a projection display system employing a convention~l monochromatic DMD. The spectral distribution of the Xenon-arc light source is 20 taken from a curve in the book Color Science: concepts and methods, quan~itative data andformulae" by G. Wyszecki et al., 2nd ed., published by Wiley in Toronto in 1982. The optical image system in the projection display is ~cc-lmPd to have a uniform spectral ~.f~,l,l,~lce in the visible spect-~l region. Third, the light is incident upon the Uon'l colour mirrors or pixels at an angle of 10 from the normal 25 incidence, which is the normal operation angle in a DMD. Fourth, the first embodiment of the optical thin film in~lrel~i-ce colour co~tingc in accordai~ce with the present invention is deci~ned to match the CIE (Commiccion Internationale deL'Eclairage) cooldinates of the current CRT red, green and blue phosphors. Fifth, the second emboflimt~nt of the optical thin film intelrereilce colour co~tin~ inaccordance with the present invention is de~ignefl to match the CIE coordinat~s of the National Television System Committ~ (NTSC) standards, that are taken from the book, Television Engineering Handbook," edited by K. B. RenCon~ published by 5 McGraw-Hill, New York, in 1992. Other colour standards can be specified as weU without departing from the spirit of the present invention.
A colour deforrnable mirror device in accordance with the present invention, comprises at least one colour mirror array having an optical thin film inlel~lei,ce colour co~ting. In the case of a full colour DMD, three optical thin film int~lr~ience 10 colour coatings providing red, green and blue colours are l~uiled. In the following descriptions, aU embo-lim~ nt~ wiU include three groups of colour mirrors while each group having a different optical thin film in~lrer~ilce primary colour coating on top of the individual mirror substrates.
FIG. 3 shows the calculated reflP~t~nce curves of the red 48a, green 48b and 15 blue 48c optical thin film interference colour co~ting~ of the first embodiment of the present invention. All three optical thin film intelrele~ ce colour co~tinp~ were d~cigned to have the same number of layers and to be made of the same materials,SiO2 and Inconel~M, but with different layer thirknP~es Although it is desirable to have as few layers and materials as possible for all the three optical thin film20 interference colour co~ting~ this is not always necP,sc~. ~r. The mirror substrate is made of aluminum that has a high reflect~nce; therefore the optional high reflect~nce layer is not lequired as the mirror substrate also acts as the first optical layer for the optical thin film inklrer~nce colour coating. The layer p~mPt~rs and calculated CIE
cooldina~es (x, y) and the lumin~nce (L) of these three primary optical thin film 25 in~lrelt;nce colour co~ting~ are listed in Table I. The CIE colour coordina~es of the above optical thin film intelrelence colour co~tinp~ and the current CRT red, green and blue phosphors are also plotted on a CIE 2 chromaticity ~ m in FIG. 4. It 215~9I 7 is obvious from FIG. 4 that the CIE coordinates of the three optical thin film interference colour co~ting~ of the first embo~iimpnt of the present invention (dark diamonds), match very well with those of the current CRT red, green and blue phosphors (circles). The red, green and blue CIE coo~.lina~s define a tri~nglP inside 5 of which all colours can be ~resented by a suitable colllhi,~t;orl of these three primary colours.
From the book, ~Color Science: concepts and methods, quar~itative data and formulae" by G. Wyszecki et al., 2nd ed., published by Wiley in Toronto, 1982, it is known that, once a light source is chosen, for each given set of CIE cooldillates (x, y) 10 there exists an optimum colour filter having a maximum hlmin~nre (L). The closer the CIE coordinates of the colour filter are to the boundary of the CIE chromaticity diagrarn, the purer the colour of the reflected or tr~n~mitt~d light. However, the colour filter also has a lower lumin~nce. The.efole, there is a trade-off between the colour purity and the l~lmin~nce of the display. In North Am~ri~, the current 15 television signals broadcast in the NTSC q~ifir~tinn~. However, if the television signals are directly applied to a monitor with the current CRT phosphors it will result in colour errors because these CRT phosphors do not match the NTSC .~pecifiç~tion~
One way to solve this problem is to incol~ldle cil~;uiL~ in a receiver to convert the NTSC signals to the signals applol liate to the used phosphors. However, this will 20 still not fully resolve the problem since some colours can not reproduced by the current CRT phosphors. Therefore, it is desirable to design a colour DMD in accordance with the present invention to match the NTSC specific~tiQn~ The second embodiment of the present invention is dP~ign~l for this pul~ose. FIG. 5 shows the calculated reflP~t~nce curves of the red 50a, green 50b and blue 50c optical thin film 25 inlelreience colour co~ting~ of the second embolliment They consist of five layers of SiO2 and InconelTM on an aluminum substrate. The layer m~tPri~l~ and thicknesses of the coatings and the calculated CIE coordinates are listed in Table II. The CIE
coordinates of the optical thin film interference colour co~ting~ (diamonds), the current CRT phosphors (circles) and the NTSC standard colour sperifit~tion~
(hi~ngles) are also ploKed on the 2 CIE chromaticity ~ gr~m in FIG. 6. From FIG.
6, it is clear that the second embodiment m~tches well with the NTSC standards and can lcplcsent more colours than the current CRT phosphors. Therefore, better colour 5 performance can be achieved in a projection system employing such a colour DMD.
This also demonstrates the flexibility of optical thin film il~Çclcnce colour co~tingc.
A prere,-cd method of fabrit~hng a colour DMD having optical thin film in~elrereilce colour coating(s), in accoç~ance with the present invention, will be explained in detail with the aid of FIGs. 7A-7E showing the cross-se~hon~l views of 10 the various steps of the fabrication process. The drawings are schPm~hc and are for the purpose of illushation only. The horizontal and vertical (lim~ncionc are not to scale. To better understand the p~ere~cd fabrication method in accordance with the present invention, knowledge of the m~mlf~rtl-ring process of the present-day conventional DMDs is required and the reader is lerellcd to Spatial Light Modulator 15 and Method," US. Pat. No. 5,172,262, I~rry. J. Hornbeck et al., issued on Dec. 15, 1992.
First, the basic shuchure 70 of the colour DMD in accordance with the present invention is fabricated by a convçntion~l process similar to that used in the present-day monochromatic DMDs. In FIG. 7A, the basic structure 70 includPs driving 20 electronics on a semiconductor substrate 72, a diplp~ r~ in~ tor layer 74, connechng elechrodes 76, a patterned thick spacer layer 78, a continUous hinge metal layer 80, a patterned hinge liplectric layer 82, and a continuous beam metal layer 84. At this stage, the optical thin film intelrclel~ce colour coating(s) in accordance with the present invention is introduced. A lift-off process is used for the deposition of the 25 first optical thin film inlclrercnce colour co~ting First, a photo-resist layer 86a is spun on the surface of the basic structure 70 and then is patterned in a pre-defined way to provide openings for the optical thin film intclrelcnce colour coating 88a as shown in FIG. 7B. A negative slope or profile of the photo-resist layer 86a is generated in order to produce a better lift-off result for the subsequent layers of the optical thin film in~lrelcnce colour coating 88a. A single layer, or, if necP~.y, a multilayer-layer photo-resist structure may be used. For example, a three layer S structure having a photo-resist layer, an anti-reflection coating and a PMMA layer, normally result in a better lift-off than a single layer photo-resist. The individual layers in the optical thin film intelreience colour coating 88a, such as described in Table I and II, are deposited by either physical vapor deposition (PVD) or çhPmir~l vapor (CVD) deposition processes. The deposition processes include evapor~tion~
10 s~ullelillg, ion plating, plasma enh~nced CVD, etc. The photo-resist layer 86a is then lifted off or removed and the coating in the open area forms the optical thin film interference colour coating 88a. If necec~ry, similar plocesses may be repeated to form a second optical thin film intelrelence colour coating 88b as shown in FIG. 7C, a third optical thin film interference colour coating 88c (FIG. 7D), etc. The second 15 88b and third 88c optical thin film intelÇele,lce colour co~tinvs can have layer materials and thicknesses as described in Table I and II. At this stage, a conventional process for the manufacture of a monochlol-latic DMD is applied to remove the hinge and beam metals in the unwanted areas in order to form each individual colour mirrors. Finally, the underlying spacer layer 78 is removed by a etching process.
20 The complete finish~ colour deformable mirror device in accordance with the present invention is shown in the cross-sectional view of FIG. 7E. The colour deformablemirror has three arrays of optical thin film intelrelcnce colour co~ting~ 88a, 88b, and 88c, where each optical thin film int~lrelc,lce colour coating is deposited on a mirror substrate 90 and is ~u~ulLt;d by two hinges 92 and two posts 94.
It is clear that, without departing from the spirit of the present invention, that other photo-lithographic patterning processes can be used to form the optical thin film intelrerence colour co~ting~ as well. For example, instead of using a lift-off process to deposit the optical thin film intel~lcnce colour co~ting~, an etching processes can 215~917 be used to pattern the optical thin film in~.rerence colour cr~tings.
A ~ignifi~nt advantage of the colour deformable mirror device in acc~r~lce with the present invention is that the m~nllf~ct~lring p-ocess is completely compatible with the processes used for the construction of a convention~l DMD. There are only 5 a few extra photo-lithographic p~ttPrning processes and deposition processes required to form the optical thin film int~.rerence colour co~ting~. This can be done easily using the existing equipment for convention~l DMDs and no e~ctra equipment is n~decl .
The colour deformable mirror devices having optical thin film in~e~rele.lce 10 colour co~ting~, in accordance with the present invention, con~i~ting of yr~felled m~tPri~l~ and being fabricated by the ylert;lled m~n~lf~c~ring methorlc, are very stable both çhemic~lly and m~h~ni~lly. Good colour perfGll--anc~ can be achievedby choosing the right thi~kn~ and m~tPri~l for each layer in the optical thin film interference colour co~tingc The colour deform~blP device has a good thermal 15 conductivity as well as low absorption in the infrared region. The optical thin film interference colour co~tings have very good ~hP~jon to the ~ .";".l.,. mirror substrate. The co~tings are of good quality with very few film defects. Therefore, the ye~ro~ ance of the optical thin film inte.re.eilce colour co~tings of the present - invention is much better than that of dyes or dye-resist Il~ixlu~S, that tend to 20 deteriorate with time and with exposure to light and heat. In ~dditir~n~ the optical thin film in~elrel~nce colour co~tings can also act as p.oteclillg co~tings for ~ "~;nll~,~
mirror substrates that usually deteriorate in the ~mbiellt atmosphere. A displaysystem employing the colour deformable mirror device in accor~ lce with the present invention can obtain full colours without the use of expP-n~ive and bulky beam 25 splitting and combining optical col-~ponents, and, therefore, is much comp~t in size and can be used in a harsh environmp-nt-Ref~ ~hCeS
1. W. E. Nelson, "Color Deformable Mirror Device and Method for M~nllf~rtllre,"
US. Pat. No. 5,168,406, issued on Dec. 1, 1992.
Field of the Invention This invention is related to the field of electronic devices and more particularly S to deformable mirror devices.
R~k~round of the Invention A deforrnable mirror device (DMD) includes a plurality of electronically controllable mirrors. Each mirror is capable of a m~h~ni~l movement in response to an electrical signal and can reflect incident light in one of two predetermined 10 directions collesponding to the mirror's oriPnt~tiom DMDs can be used as light modulators for optical signal proces~ing as well as for displaying images electronically. For example, a DMD having an array of tightly spaced small mirrors or pixels in the form of rows and columns can be used in a projection display. The two orientations in which each mirror or pixel reflects light are defined as the on 15 and off" state of the mirror or pixel. Therefore this particular type of DMD may be referred to hereafter as a digital micro-mirror device. Rff~ se of its high pixel density, such a DM~ is capable of producing images co,l.~dble in resolution to cathode ray tube (CRT) displays, liquid crystal displays, etc. Advantageously, the process for manufacturing a DMD display is compatible with that used in the 20 semiconductor industry. Furthermore, the mirrors can be switched ~on or "off" in micro-seconds; hence, it is capable of displaying rapidly ch~nging images. Another advantage is that the light reflected from an "off" pixel travels along a different path and is not projected onto the image screen; hence, the display has a high contr~t Since a~lo~mately 90% of the incident light falling onto the individual on pixels 25 is reflect~ towards the image screen, this results in a more energy e-ffi~ient display com~al~d to liquid crystal projection displays.
Currently, the individual mirrors in a conv~ntion~l DMD are made of an aluminum substrate that reflects light uniformly throughout the visible spectrum;
therefore, the conventional DMD is monochrolllatic. There are several approaches to make a colour projection display system using a DMD. Two approaches involve S colour filtering the light either before or after it is refl~te~ from the DMD. In the first approach, known also as "sequential" colour, a single morloçh~omatic DMD is used. White light first passes through a rotating colour filter wheel having red (R), green (G) and blue (B) filters. The filtered white light then falls onto a monochromatic DMD and the light refle~te~ from the "on" pixels forms an image on10 a projection screen. The light reflected from the "off" pixels travels along a different path and is absorbed by a light absorber. While this sequential colour projection display system displays only one colour at a time, an observer actually perceives a colour based on the three time-inLe~ ed primary colours. This approach has certain disadvantages: a) only one colour is displayed at any given time, that reduces the 15 brightness of the display; b) synchronization between the rotating colour filter wheel and the DMD driver is required; and c) the use of a rotating colour filter wheelmakes it difficult to reduce the overall size of the display system.
In the second approach, three monochromatic DMDs are used, one for each of the three primary colours: R, G and B. Either three colour light sources or a single 20 white light source, divided into three primary colour beams by dichroic beam-splitters, can be used in the system. The three colour images from the three monochro---aLic DMDs are combined into a single image to produce the desired colour picture. The disadvantages of this system include complex chip ~lignmPnt output convergence, excessive cost and large package size of the required optical system.
A different approach for a full colour projection display system is to use a colour DMD as disclosed by W. E. Nelson in US. Pat. No. 5,168,406, issued on Dec. 1, 1992. The disclosed colour DMD has a colour filter on top of each aluminum mirror. Advantageously, no extra light splitting and combining optical components are required in the display. In Nelson's patent, the colour filters are implemented using intrin~iC absorption in dye materials. In the m~mlf~ntllring of this dye colour DMD, a dye filter mosaic or dye coating is first deposited onto a glass 5 substrate. Next, the dye filter is subsequently transferred to a DMD chip by asublimation process. In this process, the dye filter mosaic or coating is placed next to a DMD chip and is heated by a printing head. The dye m~teri~l iS vaporized and condences on the surface of the DMD. Alternatively, dye filters may be deposited by electrically charging the individual mirrors of a DMD. A dye cloud is then 10 introduced next to the DMD and condenses on the surface of the individual charged mirrors. Another method for manufacturing a colour filter for deformable mirror device has been disclosed by M. A. Mignardi et al. in US. Pat. No. 5,240,818, issued on Aug. 31, 1993. In their approach, a solution of a dye-resist ~ ure is spun uniformly onto a nearly completed DMD chip. The dye-resist coating in the 15 unwanted area is then removed by photo-lithography, i.e., by ~ Gsing the chip to W light through a mask and developing it. Different dye-resist materials can be applied in the same way to form, for example, a red, green and blue multi-colourfilter array. A transparent layer is then deposited to protect the dye-resist filters.
There are several disadvantages to all the above dye or dye-resist mixture filter 20 approaches: The stability of the dye-resist or dye filters is poor and these dye or dye-resist filters normally degrades with time. As well, their ~lroll.-al ce tends to deteriorate when exposed to heat and light sources that are present in projection display systems. Also, dye-resist and dye colours filters deposited by spinning or sublimation often have poor adhesion to the mirror subst~tP In ~ ition, the quality 25 of the dye filters can be poor, which could result in light sc~ ;ng reduçing the contrast of the display. Furthermore, the processes to apply these dyes or dye-resist ll-i~lules might not be fully compatible with current manufacturing process of the DMDs.
Object of the Invention It is an objective of the present invention to provide a more stable colour deformable mirror device having optical thin film in~elrelc;ilce colour co~ting~.
Another object of the present invention is to provide a method of depositing 5 optical thin film inlelrere,lce colour co~ting~ onto a deformable mirror device.
Summary of the Invention In accordance with the present invention there is provided, a semiconductor device comprising: circuitry for accepting electronic .~ign~l~; a plurality of deformable mirrors selectably operable to reflect inrid~nt light, responsive to the 10 electronic signals; and, a first group of said plurality of deformable mirrors being coated with an optical thin film inte,rerellce colour coating having at least a layer that is substantially tr~n~p~rent with respect to the in(i~ent light, the optical thin film intelrerence colour coating int~ (ling at least one further layer that is partially absorbing with respect to the inci~ent light, so that the spectral refl~ct~nce and 15 absorptance of the deformable mirror is modified to produce a desired reflecte~
colour by the process of optical inte:relellce enh~nce~ absorption in the optical interference colour coating, the layers being of predetermined thickn~sses and materials, wherein the thickn~ss of the subst~nti~lly tr~nsp~rent layer subst~nti~lly determines the desired reflected colour.
The optical thin film intelre~eilce colour coating in accor~lce with the presentinvention may comprise an optional high reflectance layer, at least one transparent layer on top of the high reflectance layer and at least one partially absorbing layer on top of the transparent layer. The colour deformable mirror device may comprise a25 second group of said colour mirrors that reflect a second group of wavelengths of the 215891~
incident visible light to obtain a second reflect~ colour and may further comprise a third group of said colour mirrors that reflect a third group of wavelengths of the inçident visible light to obtain a third re~flecte~ colour. The colour deformable mirror device has a first, second and third group of said colour mirrors forming three-colour S pixels. Alternatively, the colour deformable mirror device may comprise a first, second and third groups of said colour mirrors and a group of neutral mirrors forming four-colour pixels.
In accordance with yet another aspect of the present invention, there is furtherprovided, a method for the manufacture of a colour deformable mirror device having 10 a semiconductor substrate, driving electronics on the semiconductor substrate, and a plurality of deformable mirrors for reflecting inci~l~nt light, the method comprising the steps of: applying an optical thin film inte.relGnce colour coating upon a first group of the deformable mirrors by physical vapor deposition or chPmiç~l vapor deposition processes; the optical thin film in~ rc~rence colour coating being of15 predetermined thicknesses and materials and being suitable for re-flecting a first group of wavelengths of the visible light to obtain a first colour, said coating inclu(ling at least a substantially transparent layer and at least a partially absorbing layer.
One advantage of the present invention is that m~tP i~l~ typically used in the optical thin film inte-re.ence colour co~ting~ are either subst~nti~l1y tr~ncp~rent or 20 partially absorbing uniformly throughout the visible ~peCLlUlll and optical inte-re~ lce enhanced absorption is used to engine~r which particular wavel~ngthc of light are absorbed or reflected by the optical thin film illtelrelence colour coating in order to obtain a desired refl~te~ colour. Thus, the invention provides a high degree of flexibility; for example, different colours can be achieved by using the same materials 25 but with different layer thicknesces Furthermore, the colour ~lÇ~ -ance of the optical thin film inte~r~.~nce colour co~ting~ can be cle~igne~l to match most colour standards currently in use in the world such as those of the National Television 2158~17 System Committe~ (NTSC), the Phase ~ltt~rn~tion Line (PAL) and the Sequentiel Couleur avec Mémoire (SECAM). In contrast, dyes, as disclosed in the prior art, are engine~red to absorb at specific wavelengths of light and these wavelengths cannot be changed without çh~nging the dyes themcelves. Hence, the use of dyes is less flexible 5 compared to the present invention.
Another advantage of the present invention is that the optical thin film interference colour co~ting~ are made of ~ tric m~t~ri~l~ and metals that are very stable both chemic~lly and physically. Their performance can with~t~nd harsh environments and will not deteriorate with time or with high ~ e~ .~s.
Another advantage of the present invention is that the process to deposit optical thin film intelreleilce colour co~ting~ is col"palible with the process currently used to produce monochromatic deformable mirror devices. It can be easily integrated with the current process with little additional equipment.
Another advantage of the present invention is that the optical thin film 15 interference colour coating not only filters light but also acts as a protective coating for the aluminum mirrors; therefore, the colour deformable mirror device in the present invention is more stable than the conventional monoch~ullla~ic aluminum deformable mirror devices and the dye type colour deformable mirror devices.
Another advantage of the present invention is the flexibility to select the 20 available co~ting~ materials for the purpose of col~pen~ting stress in the mirror and the optical thin film inlelrel~;nce colour coating.
Another advantage of the present invention is that the optical thin film interference colour co~ting~ can be design~d so that the absorption of light outside the visible spectral region is minimi7~d As well the spectral distribution of the light 25 source and the spectral response of the optical image system and the human eye can 21~8917 be t~ken into account in the design of the optical thin film in~elrelence colour co~ting~
in order to optimize the pelrol,l,ance of the colour display and to minimi7~ therequired number of optical co"~nents.
Yet another advantage of the present invention is that the optical thin film 5 in~elrese,lce colour coatings can be desiEned to have a very high hlmin~nce reflectance for a given light source.
10 Brief Des,,;l~lion of the Drawings Exemplary embodimPnt~ of the present invention will be described in conjunction with the drawings in which:
FIG. 1 shows a portion of a cross-sectional view of a colour deformable mirror device in accol~lce with the present invention;
lS FIG. 2 shows a plan view of a colour deformable mirror device having three optical thin film in~elrelence colour co~tinEs in accoldance with the present invention;
FIG. 3 shows the calculated refl~t~nre curves of red, green and blue optical thin film intelr~,~nce colour co~ting~ of a first embodiment of the present invention;
FIG. 4 shows CE cool~inates of the red, green and blue optical thin film 20 interference colour co~tinE~ in FIG. 3 and those of standard CRT red, green and blue phosphors on a CIE chromaticity diagram;
FIG. S shows r~lcul~ted reflP~t~nce curves of red, green and blue optical thin film interference colour coatings of a second embodiment of the present invention;
FIG. 6 shows CIE coordil1ates of the red, green and blue optical thin film S interference colour co~ting~ in FIG. 5 and those of CRT phosphors and NTSC
specifi~tions on a CIE chromaticity rii~gr~m; and, FIG. 7A-7E show cross-sectional views illllctr~tive of the m~nllf~ ring steps of a colour deformable mirror device having optical thin film ill~,Çer~i~ce colour co~tin~ in accordance with the present invention.
Detailed Des~ Jlion For a better underst~n~ing of the present invention, a background knowledge of a present-day deformable mirror device is desirable, and herein, the reader is 15 referred to Spatial Light Modulator and lUethod " U.S. Pat. No. 4,662,746, L. J.
Hornbeck, issued on May 5, 1987, and Spatial Light Mod~ tor and Method," U.S.
Pat. No. 5,172,262, L. J. Hornbeck et al., issued on Dec. 15, 1992. The det~il~
description of the present invention is best illllst~ted with the aid of drawings ~;IGs.
1-7.
A colour deformable mirror device in accol~lce with the present invention comprises at least one deformable mirror that has an optical thin film inte~relci ce colour coating. The optical thin film in~relence colour coating is based on optical interference Pnh~nced light reflection and absorption as described in the follows:
Optical intelr~nce is defined as the variation of ele~;L,u.,-~gnetic wave amplitude with ~ict~nce or time, caused by the ~u~el~osiLion of two or more waves of electrom~nPtic radiation (light). These two or more waves can be the result of S reflection or tr~nsmi~ion at the interfaces of layers in an optical thin film in~-rel~nce coating, used in the present invention, provided that the thirknP-sses of the individual layers are snfficient to support optical intelrelence at the wavelengths of interest.
Intrinsic absorption of light, used in dye colour filters as described in US. Pat. No.
5,168,406, is defined as the process whereby some of the energy of electrom~gnetic 10 radiation (light) is transferred to a substance on which it is inri~lPnt or which it traverses.
It is possible to significantly Pnh~nce the amount of absorbed light in an optical thin film in~lrt;l~nce coating to obtain a desired ~lÇol-l.ance, for example, a particular refl~te~ colour, through the phenomenon of optical intelreleilce, over that 15 of intrinsic absorption alone, provided that as stated above the thirknP~ of the individual layers are sufficiçnt to support the optical in~lrerenoe at the wavelengths of interest. This phenomenon is hereinafter referred to as optical intelr~lt;nce çnh~nce~
absorption.
FIG. 1 shows a cross-sectional view of a portion of a colour deformable 20 mirror device 10, having a semiconductor ~ubsLld~e 12, a driving electronics 14 on top of the semiconductor substrate 12, and a mirror elemPnt 16 on top of the driving electronics. The mirror elçmlont 16 is comprised of the mirror ~u~pG~Liilg posts 18, the torsion hinges 20, the mirror substrate 22 and a optical thin film il~lrPrence colour coating 24. The optical thin film ill~elr~nce colour coating 24 may include 25 an optional high reflect~nc~ layer 26, a tr~n~p~rent layer 28, a partially absorbing layer 30, and, if necessary, other subsequent transparent and partially absorbing 215~917 layer(s) 32. The optical thin film intelre-ellce colour coating 24 and the mirror substrate together form a colour mirror 34. If the optional high refle~t~nr,e layer 26 is omitted, the mirror substrate 22 will act as the coating substrate for the optical thin film intelrelence colour coating 24 and will become part of the optical thin film S interference colour coating 24. Different optical thin film ih~,releilce colour co~ting~
can be deposited on top of different mirror substrates in a pre-defined way to form different colour mirrors as shown in a plan view in FIG. 2. Each colour mirror is supported by two hinges 40 and two posts 42. Three individual red 44a, green 44band blue 44c colour mirrors together form a pixel 46. Such a colour DMD can be 10 used in a full colour projection display system with only one white light source.
Without departure from the spirit of the present invention, the mirror elem~nt 16 can have other configurations as well. For PY~mrl~, the colour mirror 34 can have a different shape and can be sup~lLed by a spacer layer in a cantilever structure as described in US. Pat. No. 5,172,262. More particularly, the colour mirror 24 can 15 have only one ~uppolLing post centered in the middle, where the post sits on top of another mirror substrate suppolled by torsion hinges and posts, as described in ~Multi-level Deformable Mirror Device," US. Pat. No. 5,083,857, by L. J.
Hornbeck et al., issued on Jan. 28, 1992. This configuration ~limin~t~s the hinge and supporting area on the surface and results in a larger mirror apel~u~: that is desirable 20 in a projection display system.
Unlike the approaches disclosed in US. Pat. No. 5,168,406 and 5,240,818 that use only int-rincic absorption of light in dyes or dye-resist ~ lul~s to form colour filters, the optical thin film intelrelt;ilce colour coating 24 in the present invention uses optical in~lrel~nce enh~ncecl absorption. Therefore, the optical thin film 25 intelrt;lt;nce colour coating is much more flexible and can be ~lesigned to absorb and reflect certain wavelengths of light in the visible ~eclu~ l to obtain a desired reflected colour, as well as to reflect most of the light in the inrl~ed region to reduce heat 21S8gl7 absorption. Dyes or dye-resist mL~Llules norrnally absorb most of the infrared radiation inci~pnt upon them. In addition, to achieve a desired colour, many different thin film multilayer designs can be obtained. More i",pol~llly, with the same materials, it is possible to achieve different reflPcted colours by varying only the S thicknç~ses of the subst~nh~lly tr~n~p~rent layers. This will simplify the m~nllf~ctllre process of the optical thin film inle~fer~nce colour co~ .g~ The p.o~lLies of a practical display system can be taken into account in the optical thin film intelre.e,lce colour coating design process to obtain an optimal pelrol"-ance, i.e., the spectral distribution of the light source and the spectral response of the optical system and of 10 the human eye. As well, since the human eye is not sensitive to the red and blue parts of the visible spectral region, it is possible to design a red or a blue optical thin film interference colour coating with a relatively higher l-.. n~l~ce reflect~nce The mirror substrate 22 can be made of a corl~ucting metal, metal alloy or semiconductor, i.e., Al, Cr, Co, Cu, Au, Hf, Mo, Ni, Nb, Pt, Ag, Ta, Ti, W, Yr, 15 Zr" Si, Ge, nickel alloy such as InconelT~, etc. The optional high reflect~nce layer 26 can be made of a high reflectance metal or metal alloy, i.e., Al, Cr, Co, Cu, Au, Hf, Mo, Ni, Nb, Pt, Ag, Ta, Ti, W, Yr, Zr" Si, Ge, nickel alloy such as InconelTM, etc. The mirror substrate 22 or the optional high rçfl~t~nce layer 26 acts as the first optical layer for the subsequent layers in the optical thin film in~lÇe,eilce colour 20 coating 24. If the mirror substrate 22 is also made of a high reflect~nce m~tPri~l, such as aluminunl, then the layer 26 is not n~Pc~Ps~l ~. The transparent layer 28, and, if nece~c~ry, the subsequent transparent layer(s) 32 can made of transparent dielectric materials from the group of oxides, nitrides, fluorides, selpnic1p~ and sulfi~es, such as, sio2~ A123~ HfO2~ Nb2S~ Ta2s, TiO2, Y203, ZrO2, SiN, AlN, MgF2, CaF2, ZnSe, 25 ZnS, etc. The partially absorbing layer 20, and if n~ , the subsequent partially absorbing layer(s) 32, can be made of absorbing metals, metal alloys or semiconductors, i.e., Cr, Co, Cu, Au, Hf, Mo, Ni, Nb, Pt, Ag, Ta, Te, Ti, W, Yr,Zr, InconelTM, Si, Ge, etc.
SiO2 is a pl~f~r~d material for the transparent layer(s) in the optical thin film interference colour co~tingc in connection with the present invention; this is because it normally has low stress and is already used in a conventional DMD for other purposes. A1203 iS another ~l~felled m~tPri~l for the h~ncp~rent layer(s) because it 5 has a higher refractive index than SiO2, a good thermal conduchvity and low stress.
Nickel or nickel alloys, e.g., InconelTM, are ~l~felled absorbing materials for the partially absorbing layer(s) because they are very stable both ç~l~mic~lly and physically. They also have good thermal conductivity. ~lln,.;~ .,. is a ~l~f~ d m~teri~l for the mirror substrate 22 as well for the optional high reflect~nee layer 22;
10 this is because Al has not only good electronic and thermal con~luct;vity, but also a high reflect~nce. Other coating materials can be chosen as well, for example, m~teri~lc with opposite stress can be used to b~l~nce the total stress in the mirror elem~nts .
Several embodiments of the present invention will be described in detail in the 15 following descriptions. Without departing from the spirit of the present invention and for the purpose of a more practical demonstration, the following conditions are assumed: First, the embodiments are de-cign~d for a Xenon-arc lamp source that is currently used in a projection display system employing a convention~l monochromatic DMD. The spectral distribution of the Xenon-arc light source is 20 taken from a curve in the book Color Science: concepts and methods, quan~itative data andformulae" by G. Wyszecki et al., 2nd ed., published by Wiley in Toronto in 1982. The optical image system in the projection display is ~cc-lmPd to have a uniform spectral ~.f~,l,l,~lce in the visible spect-~l region. Third, the light is incident upon the Uon'l colour mirrors or pixels at an angle of 10 from the normal 25 incidence, which is the normal operation angle in a DMD. Fourth, the first embodiment of the optical thin film in~lrel~i-ce colour co~tingc in accordai~ce with the present invention is deci~ned to match the CIE (Commiccion Internationale deL'Eclairage) cooldinates of the current CRT red, green and blue phosphors. Fifth, the second emboflimt~nt of the optical thin film intelrereilce colour co~tin~ inaccordance with the present invention is de~ignefl to match the CIE coordinat~s of the National Television System Committ~ (NTSC) standards, that are taken from the book, Television Engineering Handbook," edited by K. B. RenCon~ published by 5 McGraw-Hill, New York, in 1992. Other colour standards can be specified as weU without departing from the spirit of the present invention.
A colour deforrnable mirror device in accordance with the present invention, comprises at least one colour mirror array having an optical thin film inlel~lei,ce colour co~ting. In the case of a full colour DMD, three optical thin film int~lr~ience 10 colour coatings providing red, green and blue colours are l~uiled. In the following descriptions, aU embo-lim~ nt~ wiU include three groups of colour mirrors while each group having a different optical thin film in~lrer~ilce primary colour coating on top of the individual mirror substrates.
FIG. 3 shows the calculated reflP~t~nce curves of the red 48a, green 48b and 15 blue 48c optical thin film interference colour co~ting~ of the first embodiment of the present invention. All three optical thin film intelrele~ ce colour co~tinp~ were d~cigned to have the same number of layers and to be made of the same materials,SiO2 and Inconel~M, but with different layer thirknP~es Although it is desirable to have as few layers and materials as possible for all the three optical thin film20 interference colour co~ting~ this is not always necP,sc~. ~r. The mirror substrate is made of aluminum that has a high reflect~nce; therefore the optional high reflect~nce layer is not lequired as the mirror substrate also acts as the first optical layer for the optical thin film inklrer~nce colour coating. The layer p~mPt~rs and calculated CIE
cooldina~es (x, y) and the lumin~nce (L) of these three primary optical thin film 25 in~lrelt;nce colour co~ting~ are listed in Table I. The CIE colour coordina~es of the above optical thin film intelrelence colour co~tinp~ and the current CRT red, green and blue phosphors are also plotted on a CIE 2 chromaticity ~ m in FIG. 4. It 215~9I 7 is obvious from FIG. 4 that the CIE coordinates of the three optical thin film interference colour co~ting~ of the first embo~iimpnt of the present invention (dark diamonds), match very well with those of the current CRT red, green and blue phosphors (circles). The red, green and blue CIE coo~.lina~s define a tri~nglP inside 5 of which all colours can be ~resented by a suitable colllhi,~t;orl of these three primary colours.
From the book, ~Color Science: concepts and methods, quar~itative data and formulae" by G. Wyszecki et al., 2nd ed., published by Wiley in Toronto, 1982, it is known that, once a light source is chosen, for each given set of CIE cooldillates (x, y) 10 there exists an optimum colour filter having a maximum hlmin~nre (L). The closer the CIE coordinates of the colour filter are to the boundary of the CIE chromaticity diagrarn, the purer the colour of the reflected or tr~n~mitt~d light. However, the colour filter also has a lower lumin~nce. The.efole, there is a trade-off between the colour purity and the l~lmin~nce of the display. In North Am~ri~, the current 15 television signals broadcast in the NTSC q~ifir~tinn~. However, if the television signals are directly applied to a monitor with the current CRT phosphors it will result in colour errors because these CRT phosphors do not match the NTSC .~pecifiç~tion~
One way to solve this problem is to incol~ldle cil~;uiL~ in a receiver to convert the NTSC signals to the signals applol liate to the used phosphors. However, this will 20 still not fully resolve the problem since some colours can not reproduced by the current CRT phosphors. Therefore, it is desirable to design a colour DMD in accordance with the present invention to match the NTSC specific~tiQn~ The second embodiment of the present invention is dP~ign~l for this pul~ose. FIG. 5 shows the calculated reflP~t~nce curves of the red 50a, green 50b and blue 50c optical thin film 25 inlelreience colour co~ting~ of the second embolliment They consist of five layers of SiO2 and InconelTM on an aluminum substrate. The layer m~tPri~l~ and thicknesses of the coatings and the calculated CIE coordinates are listed in Table II. The CIE
coordinates of the optical thin film interference colour co~ting~ (diamonds), the current CRT phosphors (circles) and the NTSC standard colour sperifit~tion~
(hi~ngles) are also ploKed on the 2 CIE chromaticity ~ gr~m in FIG. 6. From FIG.
6, it is clear that the second embodiment m~tches well with the NTSC standards and can lcplcsent more colours than the current CRT phosphors. Therefore, better colour 5 performance can be achieved in a projection system employing such a colour DMD.
This also demonstrates the flexibility of optical thin film il~Çclcnce colour co~tingc.
A prere,-cd method of fabrit~hng a colour DMD having optical thin film in~elrereilce colour coating(s), in accoç~ance with the present invention, will be explained in detail with the aid of FIGs. 7A-7E showing the cross-se~hon~l views of 10 the various steps of the fabrication process. The drawings are schPm~hc and are for the purpose of illushation only. The horizontal and vertical (lim~ncionc are not to scale. To better understand the p~ere~cd fabrication method in accordance with the present invention, knowledge of the m~mlf~rtl-ring process of the present-day conventional DMDs is required and the reader is lerellcd to Spatial Light Modulator 15 and Method," US. Pat. No. 5,172,262, I~rry. J. Hornbeck et al., issued on Dec. 15, 1992.
First, the basic shuchure 70 of the colour DMD in accordance with the present invention is fabricated by a convçntion~l process similar to that used in the present-day monochromatic DMDs. In FIG. 7A, the basic structure 70 includPs driving 20 electronics on a semiconductor substrate 72, a diplp~ r~ in~ tor layer 74, connechng elechrodes 76, a patterned thick spacer layer 78, a continUous hinge metal layer 80, a patterned hinge liplectric layer 82, and a continuous beam metal layer 84. At this stage, the optical thin film intelrclel~ce colour coating(s) in accordance with the present invention is introduced. A lift-off process is used for the deposition of the 25 first optical thin film inlclrercnce colour co~ting First, a photo-resist layer 86a is spun on the surface of the basic structure 70 and then is patterned in a pre-defined way to provide openings for the optical thin film intclrelcnce colour coating 88a as shown in FIG. 7B. A negative slope or profile of the photo-resist layer 86a is generated in order to produce a better lift-off result for the subsequent layers of the optical thin film in~lrelcnce colour coating 88a. A single layer, or, if necP~.y, a multilayer-layer photo-resist structure may be used. For example, a three layer S structure having a photo-resist layer, an anti-reflection coating and a PMMA layer, normally result in a better lift-off than a single layer photo-resist. The individual layers in the optical thin film intelreience colour coating 88a, such as described in Table I and II, are deposited by either physical vapor deposition (PVD) or çhPmir~l vapor (CVD) deposition processes. The deposition processes include evapor~tion~
10 s~ullelillg, ion plating, plasma enh~nced CVD, etc. The photo-resist layer 86a is then lifted off or removed and the coating in the open area forms the optical thin film interference colour coating 88a. If necec~ry, similar plocesses may be repeated to form a second optical thin film intelrelence colour coating 88b as shown in FIG. 7C, a third optical thin film interference colour coating 88c (FIG. 7D), etc. The second 15 88b and third 88c optical thin film intelÇele,lce colour co~tinvs can have layer materials and thicknesses as described in Table I and II. At this stage, a conventional process for the manufacture of a monochlol-latic DMD is applied to remove the hinge and beam metals in the unwanted areas in order to form each individual colour mirrors. Finally, the underlying spacer layer 78 is removed by a etching process.
20 The complete finish~ colour deformable mirror device in accordance with the present invention is shown in the cross-sectional view of FIG. 7E. The colour deformablemirror has three arrays of optical thin film intelrelcnce colour co~ting~ 88a, 88b, and 88c, where each optical thin film int~lrelc,lce colour coating is deposited on a mirror substrate 90 and is ~u~ulLt;d by two hinges 92 and two posts 94.
It is clear that, without departing from the spirit of the present invention, that other photo-lithographic patterning processes can be used to form the optical thin film intelrerence colour co~ting~ as well. For example, instead of using a lift-off process to deposit the optical thin film intel~lcnce colour co~ting~, an etching processes can 215~917 be used to pattern the optical thin film in~.rerence colour cr~tings.
A ~ignifi~nt advantage of the colour deformable mirror device in acc~r~lce with the present invention is that the m~nllf~ct~lring p-ocess is completely compatible with the processes used for the construction of a convention~l DMD. There are only 5 a few extra photo-lithographic p~ttPrning processes and deposition processes required to form the optical thin film int~.rerence colour co~ting~. This can be done easily using the existing equipment for convention~l DMDs and no e~ctra equipment is n~decl .
The colour deformable mirror devices having optical thin film in~e~rele.lce 10 colour co~ting~, in accordance with the present invention, con~i~ting of yr~felled m~tPri~l~ and being fabricated by the ylert;lled m~n~lf~c~ring methorlc, are very stable both çhemic~lly and m~h~ni~lly. Good colour perfGll--anc~ can be achievedby choosing the right thi~kn~ and m~tPri~l for each layer in the optical thin film interference colour co~tingc The colour deform~blP device has a good thermal 15 conductivity as well as low absorption in the infrared region. The optical thin film interference colour co~tings have very good ~hP~jon to the ~ .";".l.,. mirror substrate. The co~tings are of good quality with very few film defects. Therefore, the ye~ro~ ance of the optical thin film inte.re.eilce colour co~tings of the present - invention is much better than that of dyes or dye-resist Il~ixlu~S, that tend to 20 deteriorate with time and with exposure to light and heat. In ~dditir~n~ the optical thin film in~elrel~nce colour co~tings can also act as p.oteclillg co~tings for ~ "~;nll~,~
mirror substrates that usually deteriorate in the ~mbiellt atmosphere. A displaysystem employing the colour deformable mirror device in accor~ lce with the present invention can obtain full colours without the use of expP-n~ive and bulky beam 25 splitting and combining optical col-~ponents, and, therefore, is much comp~t in size and can be used in a harsh environmp-nt-Ref~ ~hCeS
1. W. E. Nelson, "Color Deformable Mirror Device and Method for M~nllf~rtllre,"
US. Pat. No. 5,168,406, issued on Dec. 1, 1992.
2. M. A. Mignardi et al., "Method for Manuf~ctllnng a Color Filter for Deformable Mirror Device," US. Pat. No. 5,240,818, issued on Aug. 31, 1993.
3. L. J. Hornbeck, Spatial Light Modulator and Method," U.S. Pat. No.4,662,746, issued on May 5, 1987, 4. J. Hornbeck et al., "Spatial Light Mod~ t~r and M~thod " U.S. Pat. No.
5,172,262, issued on Dec. 15, 1992 10 5. G. Wyszecki et al., "Color Science: concepts and methods, quannta ive data and fo7mulae," 2nd ed., Toronto, Wiley, 1982.
6. Television Engineering Handbook, edited by K. B. Benson, McGraw-Hill, New York, 1992.
Table I - Layer ~ uncte,~ and CIE coGIJina~s of the first embo~im~nt~
Color Coating Red Green Blue Material ThicknPss Material Thickness Material Thickness (nm) (nm) (nm) Layer Sul,~llate Al 2 30 Al 2 30 Al 2 30 Structure 1 S1O 224.7 siO2 345.9 SiO2 295.6 ,_ 2 InconellM 8.5 Inconel'~ 9.1 InconellM 7.8 3 Sl02 238.6 siO2 372.6 SiO2 299.5 Medium Air Air Alr Color x=0.612 x=0.280 x=0.152 ~o CIE C.o~in~ y=0.358 y=0.587 y=0.068 c~
Coordinates L=0.187 L=0.493 L=0.066 _~
CRT x=O.~g x=0.280 x=0.152 Phosrhor y=0-350 y=0.588 y=0.064 Table II - Layer parameters and CIE coor~it~ates of the second embo-liments Color Coating Red Green Blue Material Thickness Material Thickness Material Thickness (nm) (nm) (nm) Substrate Al 2 30 Al 2 30 Al 2 30 Layer 1 SiO2 200.5 siO2 348.1 SiO2 137.6 Structure 2 InconellM 13.5 Inconel'M 10.3 InconellM 9.7 3 SiO2 232.6 SiO2 354.5 siO2 150.5 4 Inconel'M 6.0 Inconel'M 4.4 Inconel'M 3.8 S SiO2 238.5 siO2 362.7 siO2 143.3 c Medium Air Air Air Color x=~.659 x=~.211 x=0.142 ~_~
Cl~ Co~in~ y=0.324 y=0.700 y=0.084 CoorJillates L=0.123 L=0.320 L=0.087 NTSC x=0.670 x=0.210 x=0.140 Standard y=0.330 y=0.710 y=0.080
Table I - Layer ~ uncte,~ and CIE coGIJina~s of the first embo~im~nt~
Color Coating Red Green Blue Material ThicknPss Material Thickness Material Thickness (nm) (nm) (nm) Layer Sul,~llate Al 2 30 Al 2 30 Al 2 30 Structure 1 S1O 224.7 siO2 345.9 SiO2 295.6 ,_ 2 InconellM 8.5 Inconel'~ 9.1 InconellM 7.8 3 Sl02 238.6 siO2 372.6 SiO2 299.5 Medium Air Air Alr Color x=0.612 x=0.280 x=0.152 ~o CIE C.o~in~ y=0.358 y=0.587 y=0.068 c~
Coordinates L=0.187 L=0.493 L=0.066 _~
CRT x=O.~g x=0.280 x=0.152 Phosrhor y=0-350 y=0.588 y=0.064 Table II - Layer parameters and CIE coor~it~ates of the second embo-liments Color Coating Red Green Blue Material Thickness Material Thickness Material Thickness (nm) (nm) (nm) Substrate Al 2 30 Al 2 30 Al 2 30 Layer 1 SiO2 200.5 siO2 348.1 SiO2 137.6 Structure 2 InconellM 13.5 Inconel'M 10.3 InconellM 9.7 3 SiO2 232.6 SiO2 354.5 siO2 150.5 4 Inconel'M 6.0 Inconel'M 4.4 Inconel'M 3.8 S SiO2 238.5 siO2 362.7 siO2 143.3 c Medium Air Air Air Color x=~.659 x=~.211 x=0.142 ~_~
Cl~ Co~in~ y=0.324 y=0.700 y=0.084 CoorJillates L=0.123 L=0.320 L=0.087 NTSC x=0.670 x=0.210 x=0.140 Standard y=0.330 y=0.710 y=0.080
Claims (20)
1. A semiconductor device comprising:
circuitry for accepting electronic signals;
a plurality of deformable mirrors selectably operable to reflect incident light, responsive to the electronic signals; and a first group of said plurality of deformable mirrors being coated with an optical thin film interference colour coating having at least a layer that is substantially transparent with respect to the incident light, the optical thin film interference colour coating including at least one further layer that is partially absorbing with respect to the incident light, so that the spectral reflectance and absorptance of the deformable mirror is modified to produce a desired reflected colour by the process of optical interference enhanced absorption in the optical interference colour coating, the layers being of predetermined thicknesses and materials, wherein the thickness of the substantially transparent layer substantially determines the desired reflected colour.
circuitry for accepting electronic signals;
a plurality of deformable mirrors selectably operable to reflect incident light, responsive to the electronic signals; and a first group of said plurality of deformable mirrors being coated with an optical thin film interference colour coating having at least a layer that is substantially transparent with respect to the incident light, the optical thin film interference colour coating including at least one further layer that is partially absorbing with respect to the incident light, so that the spectral reflectance and absorptance of the deformable mirror is modified to produce a desired reflected colour by the process of optical interference enhanced absorption in the optical interference colour coating, the layers being of predetermined thicknesses and materials, wherein the thickness of the substantially transparent layer substantially determines the desired reflected colour.
2. A semiconductor device as defined in claim 1, wherein the deformable mirrors have a coating with a high reflectance.
3. A semiconductor device as defined in claim 1, wherein the substantially transparent layer in the optical thin film interference colour coating is between the partially absorbing layer and a reflecting surface of the deformable mirrors.
4. A semiconductor device as defined in claim 2, wherein the substantially transparent layer is between the partially absorbing layer and the coating having a high reflectance.
5. A semiconductor device as detined in claim 4, wherein the substantially transparent layer is comprised of SiOz or AlzO,.
6. A semiconductor device as defined in claim 4, wherein the partialh;
absorbing layer is comprised of an alloy of nickel.
absorbing layer is comprised of an alloy of nickel.
7. A semiconducl:or device as defined in claim 4 wherein the coating :having a high reflectance is comprised of aluminum.
8. A semiconductor device as defiled in claim 1 wherein the optical thin film interference colour coating includes a plurality of substantiahy transparent and partially absorbing alternating layers.
9. A semiconductor device as defined in claim 1, further comprising a second group of said plurality of deformable mirrors being coated with a second optical thin film interference colour coating having at least a layer that is substantially transparent with respect to the incident light, the; optical thin film interference colour coating including at least one further layer that is partially absorbing with respect to the incident light, so that the spectral reflectance and absorptance of the deformable minor is modified to produce a second desired reflected colour by the process of optical interference enhanc~:d absorption in the optical interference colour coating" the layers being of predetermined.
thicknesses and materials, wherein the thickness of the substantially transparent layer substantially determines the second desired reflected colour.
thicknesses and materials, wherein the thickness of the substantially transparent layer substantially determines the second desired reflected colour.
10. A semiconductor device as defined in claim 9, further comprising a third group of said plurality of deformable mirrors being coated with a third optical thin film interference colour coating having at least a layer that is substantially transparent with respect to the incident light, the optical thin film interference colour coating including at least one further layer that is partially absorbing with respect to the incident light, so that the spectral reflectance and absorptance of the deformable mirror is modified to produce a third desired reflected colour by the process of optical interference enhanced absorption in the optical interference colour coating, the layers being of predetermined thicknesses and materials, wherein the thickness of the substantially transparent layer substantially determines the third desired reflected colour.
11. The semiconductor device as defined in claim 10, wherein the first, second and third groups of mirrors form three-colour pixels.
12. A semiconductor device as defined in claim 1 wherein the plurality of deformable mirrors are made of a conducting metal, metal alloy, or semiconductor selected from the group consisting of Al, Cr, Co, Cu, Au, Hf, Mo, Ni, Nb, Pt, Ag, Ta, Ti, W, Yr, Zr, Si, Ge, and their alloys.
13. A semiconductor device as defined in claim 2, wherein the plurality of deformable mirrors have a coating with a high reflectance, the coating being a layer of a metal, metal alloy or semiconductor selected from the group consisting of Al, Cr, Co, Cu, Au, Hf, Mo, Ni, Nb, Pt, Ag, Ta, Ti, W, Yr, Zr, Si, Ge, and their alloys.
14. A semiconductor device as defined in claim 1 wherein the substantially transparent layer is comprised of a dielectric material selected from the group consisting of oxides, nitrides, fluorides, selenides and sulfides.
15. The semiconductor device as defined in claim 14, wherein the dielectric material is selected from the group consisting of SiO2, Al2O3, HfO2, Nb2O5, Ta2O5, TiO2, Y2O3, ZrO2, SiN, AlN, MgF2, CaF2, ZnSe, and ZnS.
16. The semiconductor device as defined in claim 1, wherein the at least partially absorbing layer is made of a material selected from the group consisting of metals, metal alloys, and semiconductors.
17. The semiconductor device as defined in claim 16, wherein the at least partially absorbing layer is made of a material selected from the group consisting of Al, Fe, Cr, Co, Cu, Au, Hf, Mo, Ni, Nb, Pt, Ag, Ta, Te, Ti, W, Yr, Z,, Si, Ge and their alloys.
18. The semiconductor device as defined in claim 1, wherein the all the deformable mirrors have only one optical thin film interference colour coating.
19. A method for the manufacture of a colour deformable mirror device having a semiconductor substrate, driving electronics on the semiconductor substrate, and a plurality of deformable mirrors for reflecting incident light, the method comprising the steps of: applying an optical thin film interference colour coating upon a first group of the deformable mirrors by physical vapor deposition or chemical vapor deposition processes; the optical thin film interference colour coating being of predetermined thicknesses and materials and being suitable for reflecting a first group of wavelengths of the visible light to obtain a first colour, said optical thin film interference colour coating including at least a substantially transparent layer and at least a partially absorbing layer.
20. The method as defined in claim 19, further comprising the step of applying a highly reflective coating to the mirrors before applying the first optical thin film interference colour coating upon the mirrors.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/314,003 | 1994-09-28 | ||
| US08/314,003 US5619059A (en) | 1994-09-28 | 1994-09-28 | Color deformable mirror device having optical thin film interference color coatings |
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| Publication Number | Publication Date |
|---|---|
| CA2158917A1 CA2158917A1 (en) | 1996-03-29 |
| CA2158917C true CA2158917C (en) | 2002-02-05 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002158917A Expired - Fee Related CA2158917C (en) | 1994-09-28 | 1995-09-20 | Colour deformable mirror device having optical thin film interference colour coatings |
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| US (1) | US5619059A (en) |
| CA (1) | CA2158917C (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5022745A (en) * | 1989-09-07 | 1991-06-11 | Massachusetts Institute Of Technology | Electrostatically deformable single crystal dielectrically coated mirror |
| US5240818A (en) * | 1991-07-31 | 1993-08-31 | Texas Instruments Incorporated | Method for manufacturing a color filter for deformable mirror device |
| US5168406A (en) * | 1991-07-31 | 1992-12-01 | Texas Instruments Incorporated | Color deformable mirror device and method for manufacture |
-
1994
- 1994-09-28 US US08/314,003 patent/US5619059A/en not_active Expired - Fee Related
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1995
- 1995-09-20 CA CA002158917A patent/CA2158917C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US5619059A (en) | 1997-04-08 |
| CA2158917A1 (en) | 1996-03-29 |
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