CA2113275A1 - Membrane light modulating systems - Google Patents
Membrane light modulating systemsInfo
- Publication number
- CA2113275A1 CA2113275A1 CA002113275A CA2113275A CA2113275A1 CA 2113275 A1 CA2113275 A1 CA 2113275A1 CA 002113275 A CA002113275 A CA 002113275A CA 2113275 A CA2113275 A CA 2113275A CA 2113275 A1 CA2113275 A1 CA 2113275A1
- Authority
- CA
- Canada
- Prior art keywords
- membrane
- pixel
- transfer plate
- conductors
- potential
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N9/00—Details of colour television systems
- H04N9/12—Picture reproducers
- H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
- H04N9/3102—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] using two-dimensional electronic spatial light modulators
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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
- G02B26/0825—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 flexible sheet or membrane, e.g. for varying the focus
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
- G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
- G09F9/30—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements
- G09F9/37—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements being movable elements
- G09F9/372—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements being movable elements the positions of the elements being controlled by the application of an electric field
Abstract
A membrane light modulator (18) comprising a charge transfer plate (30), and having a multiplicity of conductors (35) extending from the rear surface (52) to the front surface (19) of the plate (30). The conductors (35) are supported in an insulating matrix (37). The front side (19) of the transfer plate (30) has a plurality of potential wells (32) defined by insulating walls (15), each potential well (32) constituting a pixel. A plurality of conductors (35) is provided for each pixel. A deformable reflecting membrane (34, 36) comprising a metal layer (36) spans the potential wells (32). An electric potential is provided on the metal layer (36), and a source of electrons (17) is provided for impacting the rear surface (52) of the charge transfer plate (30).
Description
`W093/023~5 21i~3.27J.:.~ PCT/US92/05822 .. . ~
4 Backqround of the Invention S Spatial light modulators (SLMs) have n~merous 6 potential technical applications such as ~ultispectral 7 infrared target simulation, projection television systems, 8 and optical computer systems. First introduced by Preston 9 in 1968, deformable membrane mirror light modulators (MLMs), which incorporate a highly reflective membrane as ll the light modulating element, have generated interest 12 within the applied optics community as good candidates for 13 both adaptive optics and projection display applications.
14 Various means of addressing the two-dimensional deformable membrane mirror have been demonstrated, including electron 16 beam-addressing, optical addressing, and electrical 17~ addressing via integrated circuits. These devices have ~- ~` ;18~ ~not progressed beyond the development state, hence there 19 are no M$Ms on the commercial market. The electron beam-addressed approsch is preferred for display applicstions 2l due to the high re~olution and convenience of direct video 22 ~addressing; however, development of suitable substrates 23~ which would decouple the electron beam interaction region 24 from the reflective mirror were lacking. One method of solving this problem is by introducing the charge-transfer 26 plate (CTP) as a mesns of providing both structural 27 integrity and electrical signal transfer to the mirror 28 elements. This approach has improved the state-of-the-art 29 by yielding a device with a large number of resolution 30 lelements,~ high contrast, and low voltage operation. (see -31 U.S. patent 4,794,296 assigned to the assignee of this ~2 application) 33 Such a system is shown in Figure 18 of the above 34 referenced '296 patent and is more particularly described on column 15, lines 21 through 38 thereof. The charge 8UBSTITUTE SHEEl' WOg3/02375 PCT/US92/05822 ~3~ 2-1 transfer plate creates a two-dimensional electric field 2 which produces a local displacement of the metalized 3 reflective membrane to provide local modulation of the 4 phase output of the two-dimensional light signal reflected from the mirror. These SLMs exhibit very fast response 6 times, can be read out with high optical efficiency, and 7 in principle can incorporate a very large number of 8 resolution elemen~s. Since a deformable mirror SLM is 9 essentially a two-dimensional phase modulating element with a large phase dyna~ic range, it is well-suited to 11 adaptive optics applications such as wavefront correction, 12 laser beam steering and phase only spatial filtering.
13 With appropriate pixelization of the membrane surface, 14 intensity modulation may be accomplished via the schlieren readout schemes employed by projection display systems 16 such as the Eidophor (G.E.) and the Y-Ruticon (Xerox).
17 Recent improvements in the MLM and the system for 18 modulating the charge thereon have involved a M~M wherein 19 a membrane is deposited over an array of wells with an 20 ~addressable electrode at the bottom of each well. Thus, 21 the well and its electrode define an individual pixel.
22 The membra~e is coated with a thin light reflecting 23 electrode material held at a static potential. A pixel is 24 activated by establishing a potential difference between the well electrode and the membrane electrode, causing the 26 membrane to deform into the well region in response to 27 electrostatic forces. Hence, the pixel driving voltage 28 induces a local phase modulation on the readout wavefront 2g reflected by the membrane mirror surface. Such a system ds described in "Electron Beam Addressed Membrane Light 31 Modulator", Spatial ~ight Modulators and Applications, 32 1990 Technical Digest Series, Vol. 14, Optical Society of 33 America, Sept. 1990.
34 Brief Summary of the Invention In one preferred form of the invention a membrane ~, ; ~- 36 light modulator utilizes a charge transfer plate membrane W093/02375 2 ~ ~ 3 2 7 ~ PCT/USg2/05822 1 anode assembly. The charge transfer plate which has a 2 multiplicity of conductors extending from the rear surface 3 to the front surface of the plate. The conductors are 4 supported in an insulating matrix and the front side of the transfer plate has a plurality of reces~sed wells 6 defined by insulating walls, each recessed well 7 constituting a pixel. A plurality of conductors are 8 preferably provided for each pixel and a metal electrode 9 in the bottom of each recessed well preferably spans a plurality of the conductors. The rear surface of the 11 plate preferably includes a secondary electron-enhancing 12 coating. A deformable reflecting metal surface spans the 13 recessed wells. This metal surface can comprise a thin 14 sheet of unsupported metal, but is preferably formed of a metalized coating on a thin insulating (e.g. plastic) 16 support.
17 In another form of the invention, the anode assembly 18 is such that the support for the mirror membrane is still 19 a plurality of insulating walls defining potential wells with an electrode on tbe bottom of each potential well.
21 However, the potential wells are not part of a charge 22 transfer plate and the electron beam directly addresses 23 the mirror membrane to modify the charge thereon by either 24 electron depletion or electron accretion.
In addition to electron beam addressing of these anode 26 structures with a cathode ray tube, optical addressing by 27 means of a photocathode and microchannel plate assembly, 28 field emitter array or hard-wire addressing are also 29 possible for each of the anode structures cited herein.
31 Detailed Deacription of the Invention 32 In order to more fully comprehend the invention 33 reference should be had to the following detailed 34 description of several preferred forms of the invention taken in connection wi~h the attached drawings herein:
36 ~Figure 1 is a schematic view of an overall system 8UBSTITUTE SHEEr W093/0~75 PCT/US92/0~22 ~32~ 5 -4-1 employing an electron-addressed membrane light modulator 2 (e-MLM) in an image projection system.
3 Figure 2 is a schematic sectional view showing a 4 charge transfer plate, metalized membrane and associated S electronic and optical components which is an improvement 6 over that prior art CTP illustrated in the'cited 1990 7 technical digest.
8 Figure 3 is a schematic, partial sectional view of one 9 type of charge transfer plate.
Figure 4a is a photomicrograph of a metalized membrane 11 overlying a charge transfer plate.
12 Figure 4b is the light distribution showing the 13 sixfold svmmetry of the Fourier transform of the membrane 14 mirror of 4a.
lS Figure S is a schematic sectional view of a preferred 16 form of the invention.
17 Figure 6 is a block diagram of a comparison between 18 grid stabilized and fr~med video operation of the e-NLM.
19 Figure 7 is a diagram of an optically-addressed form of the invention, utilizing a photocathode and an electron 21 multiplier assembly a set of microchannel plates to 22 ~roduce the necessary charge image as input to the MLM
23 anode assembly.
24 Figure 8 is a form of the invention, similar to that of Figure 5, except that the electron beam-addressing side 26 of the CTP is patterned so as to realize an integrated 27 grid in registration with the readout side in order to 28 provide improved charging efficiency of the pixel . ~
29 electrodes, and reduce crosstalk between pixels.
30 i Figure 9 is a version of Figure 1 modified to 31 accommodate long-wavelength IR projection which re~uires 32 cryogenic cooling of the system.
33 Figure 10 is a form of the invention in which an 34 insulating substrate (face plate) used in lieu of a CTP.
3S~In this form, the electron beam-addressing and the optical - ~36 readout are achieved on the same face of the device.
-:~ 8UBSTITUTE SHEEr W O ~3/02375 2 1 i 3 2 7 ~ PC~r/US92/05822 1 Figure 11 is a form of the invention similar to that 2 of Figure 10, except that rather than a discontinuous 3 metal mirror coating on the membrane, a uniform dielectric 4 mirror is coated onto the membrane.
Figure 12 is a form of the invention s~imilar to Figure 6 11, except the device is addressed and re~d out on 7 opposite sides of the substrate. This is achieved by use 8 of a mirror layer embedded within the insulative well 9 structure.
Figure 13 depicts the electron gun tube enclosure and 11 readout optics which would be used with the device anode 12 architectures of Figures 10,11, or 12 in those cases where 13 the electron beam and optical readout may occur upon the 14 same surface of the well structure.
Figure 14 illustrates a form of the invention which 16 utilizes a field emitter array to produce the necessary 17 charge image oh the charge transfer plate.
8 Pigure 15 illustrates a form of the invention wherein 9 the charge transfer plate pixels are hard wired to an electronic controller.
21 Figure 16 shows the use of the electron addressed 22 membrane light modulator (e-MLM) to achieve three color 23 projection video.
24 The membrane light modulator of the present invention can be used in a number of applications. These involve 26 various~`types of high definition display techniques, such 27 as high definition television projection, infrared target 28 simulation, as well as other light modulating systems 29 wherein the spatially modulated light 11 is input to another device, for example, an optical computer. For 31 simplicity, the invention will be initially described in 32 its preferred form where it is used as an ultraviolet, 33 visible or IR image projector. This initial description 34 is noé intended to limit the scope of the invention in any way.
36 A schematic of the projector is shown in Figure 1.
.- ~
8UBSllTUl~ SHEEl-W093/0237~ PCT/USg2/0582 2 ~ ~32~ 3 -6-1 Specifically, it consists of a readout light source 10 of 2 the appropriate wavelength which can be a laser, arc lamp 3 or glowbar, for example. It also includes IR collimating 4 optics generally shown at 12, a computer 14 controlling an electron beam-source 16 addressing a membra~ne light 6 modulator anode 18. Fourier Transform (FT~ spatiàl filter 7 20 and an output device, which may be a high gain screen, 8 detector or video camera 24, are provided for viewing the 9 output image. As will be more fully described, the image is impressed onto the mirrored membrane surface 34 of the 11 e-MLM by the video signals of the scanning electron beam 12 16, and read out by the reflected light as a phase 13 modulation. The phase modulated beam is then converted to 14 a high-contrast, collimated image by the FT spatial filter 20, and displayed in projection.
16 The construction of a prior art membrane light 17 modulator (MLM) anode 18 which has been improved in 18 accordance with one preferred form of the invention is 19 shown in Figure 2. A membrane is deposited over the front surface 19 of a charge transfer plate 30 that is patterned 21 with an array of recessed wells 32 defined by insulating 22 walls 15 and having an addressable electrode 35 at the 23 bottom, each such recessed well 32 constituting a pixel.
24 Thus, the well 32 and its electrode 35 define an 25- individual pixel or resolution element as described in the 26 1990 technical digest. Additionally, a secondary electron 27 emitter enhancer coating 31 is deposited on the rear 28 surface 52 of the charge transfer plate 30 that receives 29 the electron signal. The purpose of this coating is to enhance the depletion of charge from the surface so images 31 of either positive or negative charge can be written 32 efficiently. The membrane 34 is coated with a thin 33 electrode material 36 held at a static potential. This 34 electrode material is hiqhly reflecting and also acts as a mirror. A pixel is activated by establishing a potential 36 difference between the well electrode 35 and the membrane wo g3/0237s 2 1 ~ 3 2 7 5 PCT/US92/05822 1 electrode 36, causing the membrane 34 to deform into the 2 well region 32 in response to the electrostatic force 3 created by the charge on the pin 35. Hence, the pixel 4 driving voltage induces a local phase modulation on the S readout wavefront 13 reflected by the membrane mirror 6 surface 36. Since pixel wells 32 are clo~e-packed with 7 high spatial uniformity, the membrane 36 diffracts light 8 efficiently when deformed into the wells 32. By using a 9 schlieren readout scheme 21 (e.g., low pass spatial filter that passes only the zero-order light or a band pass 11 filter that passes only the first-order light), the phase 12 object at the deformed membrane surface 34 may be 13 converted to an intensity image at the screen 24.
14 The e-MLM consists of an addressing electron beam 16 and an MLM anode assembly generally indicated at 18, as 16 illustrated in Figure 2. The anode consists of a meta~
17 mesh grid 44 before the pixelated matrix of wells 32, over 18 which~the polymeric, metalized membrane 34 is deposited.
19 The membrane 34 is environmentally protected by an hermetically sealed, IR-transmissive end window 40. For 21 use at infrared wavelengths the window material is 22 preferably zinc selenide (ZnSe) or germanium, whereas 23 materials such as glass could be used in the visible and 24 quartz in the ultraviolet. Both sides of the window 40 are anti-reflection (AR) coated to eliminate undesirable 26 light reflected by the window.
27 Referring still to Figure 2, the electron beam 16 28 writes a charge pattern onto the addressing side of the 29 CTP 30, which is transferred to the bottom of the well 32 30 Iby the electrodes 35 as a two-dimensional voltage 31 pattern. The resulting deformed mirror membrane 34,36 32 phase-modulates the reflected IR readout light 13, which 33 is converted to a projected high-contrast image by the 34 downstream schlieren optics generally shown at 21. (see 3S Figure 1) 36 ~ The heart of the anode assembly 18 is the pixelated 8UBSTlTUTi E SHEET' W O 93/02375 PC~r/US92/0582~ 2~32~ 5 -8-1 strueture, called a eharge-transfer plate CTP 30. The 2 name derives from its ability to serve as a high-density 3 multi-feedthrough vaeuum interface, transferring a two-4 dimensional charge distribution from vaeuum to air. The CTP 30, illustrated in Figure 3, is a wafer of 6 eleetrieally insulating material 37 in whie~ are imbedded 7 a regular matrix of thousands to millions of 8 longitudinally oriented conduetive pins 35. The ratio of 9 collective pin cross-seetional area to the CTP area is about 50%. Charge transfer plates 30 with 10 ym diameter 11 pins on 14 ~m eenters, and S0 ym diameter pins on 70 ym 12 centers are typical. Material may be removed from the 13 pins 35 on one side of the plate 30 so as to form a 14 regular array of recessed wells 32 a few microns deep.
lS The surface is highly polished to an optical flatness of 2A
16 across the aetive diameter. Thereafter the enhaneer 17 eoating 31 is applied to the rear surface 52 of the 18 eharge transfer plate 30 by thin film deposition 19 teehnigues.
A polymeric membrane 34 is deposited on the CTP
21 surface that eontains the wells 32 sueh that a reliable 22 bond between the two dieleetric surfaees is established 23 due to van der Waals forees. The resultant membrane 24~ pixels then assume the symmetry of the wells 32 whieh may be eireular pixels on~hexagonal elosed paeked (HCP) 26 eenters or cireular pixels on square eenters, for example.
27 Upon optieal readout of the membrane 34, this symmetry 28 (square or hexagonal) is preserved in the Fourier plane as 29 a diffraction pattern. A high-magnifieation photograph of bhe pixelated membrane surfaee with HCP symmetry and its 31 optieal Fourier transform are illustrated in Figures 4(a) ~ and 4(b), respeetively.
33 Referring again to Figure 2, we see that one means of 34 addressing of the MLM anode 18 is aeeomplished by direetly ~;~ 35 addressing the (CTP 30) with a seanning eleetron beam 16.
36 This approaeh offers the following advantages:
~: ~ 8UBSTITUTE SHEET
W093~0237~ 2 1 ~ ~ 2 7 ~i PCT/US92/0~822 _g _ 1 (1) With ~he appropriate electron gun drive 2 electronics and high-resolution te.g., vidicon-3 type) electron gun, each pixel (pin 35) of the 4 CTP anode is individually addressable;
S . ~ :
6 (2) The electron beam current of conv~ntional 7 delivery systems can be large, ranging from tens 8 of nanoamperes to hundreds of microamperes;
(3) A well-established technology standard exists for 11 scanning electron beam imaging systems, as a 12 result of the widescale development of cathode 13 ray tubes and video-based communications (e.g~, 14 television).
Electronically, the e-MLM may be viewed as a triode 16 structure, as illustrated in Figure 2. The thermionic 17 cathode 17 at Vk<0 emits a primary electron beam 16 which 18 may be intensity modulated by its video grid (not shown), 19 which strikes a pin 35 (or pins) of the CTP 30. Secondary electrons are emitted from the enhancer coating 31 21 overlying the pins 35 and collected by the qrid 44, 22 resulting in a buildup of positive charge on the pin 35 if 23 the secondary electrons are collected by the grid 44. The 24 local potential of the CTP 30 (which influences the landing energy of the primaries) is determined by the 26 membrane potential at Ym. The landing energy Ep of the 27 primaries is given by:
28 Ep - e(V~ V~.
29 The ratio of secondaries to primaries, or ~, is dictated by the particular value of Ep. In the absence of 31 an erase cycle, the throughput ~TP) of the e-M$M may be 32 gîven by:
33 TP ~pixels/sec) = is/CV, 34 where iS is the secondary current, C the pixel capacitance, and V the potential difference required to 36 deflect the membrane 34 to full-contrast modulation.
W O 93/02375 rl ~ P(~r/US92/0582~ 2~3~ -lo- : i 1 The throughput is representative of the signal rate of 2 the e-MLM for information proeessing. For example, if we 3 desire a 250x250 pixel image framed at 100 Hz, the TP
4 assoeiated with this frame rate is: TP = 250x250xlO0 =
6.25 x 106 pixels/sec. Henee, the seeondary eleetron 6 eurrent required would, given a pixel eapae'itanee of 0.5 7 pF and a full-modulation voltage of 70V, be:
8 iS=TP C V=(6.25xlO6pixels/see)(SxlO~13F/pixel)(70V)=220 ~A.
9 This level of primary eleetron eurrent is readily attainable by eonventional CRT-type eleetron guns.
11 In the framed mode, the grid 44 is grounded and a 12 potential differenee is established between the CTP pins 13 35 and the grid 44 by applying a ne~ative DC potential to 14 the membrane metalization layer 36, which drives the CTP
pins 35 to that potential by eapaeitive division. As the 16 eleetron beam 16 seans aeross a eonduetive pin 35 of the 17 CTP 30, seeondary eleetrons are emitted from the enhaneer 18 eoating 31 eovering that pin (35) and are eolleeted by the 19 grounded, planar fine mesh grid 44 held in elose proximity to the CTP surfaee. Sinee the number of seeondary 21 eleetrons emitted per ineoming primary eleetron, or ~, 22 exeeeds unity, a net positive eharge aceumulates on the 23 pin 35. If an enhaneer eoating 31 is added to the CTP 30, 24 this increases the eharging eurrent is aeeording to the inerease in ~ of the enhaneer material:
26 -- is2 ~2-28 is~
29 Where ~1 and ~2 are the seeondary eleetron emission 30 !eoeffieients without and with the enhaneer eoating 31. If 31 the eleetron beam 16 eontinues to address that pin 35, 32 eharge accumulates until the pin potential stabilizes to 33 the grid potential, ti.e. ground in this case). During 34 framed operation, the beam eurrent 16 can be eonstrained sueh that no pixel 32 is allowed to saturate to the grid 36 potential. Thus, by dynamieally varying the electron beam ~3UBSTITUl-E SHEEr ` W O 93/02375 2 1 ~ 3 2 7 ~ PC~r/US92/05822 1 current 16 at each pixel location 32, a continuously 2 varying two-dimensional charge image can be written onto 3 the conductors 35. This results in a voltage drop between 4 the membrane 34 and the pins 35 and the associated electrostatic force pulls the membrane 34 into the well 6 32. Since the pixel capacitances may be on~~he order of a 7 picofarad, charge storage times can be long (>lOOs). This 8 necessitates an erase cycle following each write cycle;
9 erasure is easily accomplished by grounding the membrane electrode 36 during electron beam addressing.
11 The device may then be read out by reflecting 12 collimated light 13 off the deformed membrane 34 at a 13 shallow (~10) angle of incidence, as indicated in Figure 14 1. Alternatively, it may be read out at normal incidence with the use of a beam splitter. The phase information 16 encoded upon the reflected wavefront is then processed by 17 Schileren optics, shown generally at 21 in Figure 1. The 18 schlieren system 21 consists of a converging lens 23, 19 field stop 25 a spatial filter 20 and a reimaging lens 22 as illustrated in Figure 1. The converging lens 23 yields 21 the Fourier transform (FT) of the phase object (i.e., the 22 deformed membrane surface) one focal length after the 23 lens. The FT is a diffraction pattern consisting of 24 bright spots of light that possess the symmetry of the CTP
30, as illustrated in Figure 4(b) for a HCP symmetry. For 26 a fully undeformed membrane surface, only the zeroth, or 27 specular, order is present in the FT plane. As pixels 32 28 are deformed, the diffraction efficiency into the higher 29 orders increases. In the preferred zeroth-order readout Ischeme an intensity-modulated image of the phase object is 31 obtained by passing only the zeroth order of the FT
32 through the spatial filter 20 before reimaging with the 33 second lens 22. This output image is both collimated and 34 parfocal, and can be displayed onto a screen 24 with varisble magnification by a subsequent projector lens. As 36 expected, the zeroth-order readout results in a contrast-SUBSTITIJTE SHEEr WOg3/02375 PCT/US92/0582~
2~3~ 12-1 reversed image, i.e., black pixels on a white field.
2 A most important aspect of manufacturing the e-MLM is 3 the fabrication of the pixel structures 32 on the readout 4 side of the MLM anode 18. As indicated in Figure 2, one - S method of forming pixel structures 32 is by etching away 6 portions of the CTP pins 35, leaving the pe'r~orated 7 insulating substrate 37 as a support structure for the 8 reflective membrane 34. While this prior art method of 9 producing the "mirror" pixels has proved satisfactory it can be improved. One method has been mentioned above when 11 the secondary emission of the electron impact surface has 12 been increased by use of the enhancer coating 31. Another 13 problem is that the periodicity of the CTP 35 pins may not 14 be perfect. Accordingly, periodicity of the membrane pixels 32 would not be perfectly periodic. This lack of 16 regularity leads to high spatial frequency, static 'noise' 17 in the reconstructed image. Another related problem is 18 that of image contrast. Since image contrast in a 19 schlieren imaging system 21 is attained by interference at the image plane, the apparent pixel fill factor is of 21 extreme importance. For example, approximately 50~ pixel 22 fill factor is necessary in order to achieve a perfect 23 intensity null in an anode 18 with HCP pattern of pixels.
24 Another issue is that of dynamic range. ~n order to modulate long-wavelength-light, membrane deflections of 26 several microns may be required. In order to enhance 27 speed, low ~oltage operation is preferable. To meet these 28 requirements, the ratio of pixel diameter to pixel well 29 depth must be large. For example, it can be shown that lthe membrane deflection can be expressed by:
31 ~ = (Eo/32) TV2 (a/D)2, 32 where ~ is the membrane deflection, ~O the permittivity of ~ 33 free space, T the membrane surface tension, V the applied ; 34 voltage, a the pixel diameter, and D the pixel well depth.
3~5 Therefore, larger deflections and/or lower operating 36 voltages will be attained by increasing the a/D ratio of :" ~
- ~ : 8UBSTITUTE SHEET
W093/0~75 2 1 ~ 3 2 7 ~ PCT/US92~0s822 .
1 the pixel geometry. In addition, the maximum deflection 2 required for deviee operation should be a fraetion (<20%) 3 of the total well depth in order to preserve the parabolic 4 shape of the deflected membrane. This represents about S half of the defleetion range of the membran,e pixel. Sinee 6 larger defleetions require deeper wells, w~ile low voltage 7 operation implies shallower wells, the optimization of 8 pixel well depth (or a/D ratio) can be determined 9 empirically. This provides the ability to continuously vary the geometry of the pixel array and achieves the 11 optimization of deviee performanee.
12 As diseussed above, a most important aspeet of 13 manufaeturing the e-MLM is the fabrication of the pixel 14 struetures 32 of the M~ anode 18. Figures 2,5,8,10,11 and 12 show a variety of different anode pixelization 16 sehemes. In the Figure 2,-for example, the prior art 17 eonstruetion pixelization is provided by the CTP 30 on 18 both the addressing side and readout side of the CTP 30.
19 The pixel well struetures 32 are formed by etehing away a few mierons of the CTP pins 35, leaving the perforated 21 insulating substrate 37 as a support strueture for the 22 membrane 34. Therefore, the strueture of the membrane 23 pixels 32 is tied to that of the CTP 30, in pixel 24 diameter, pixei piteh, periodieity, paeking density, and 25 `so on. ~ As mentioned this form of the invention ineludes 26 the improved enhaneer eoating 31.
27 Several superior arehiteetures ean be employed that 28 deeouple the pixel array from the CTP inter-pin piteh.
29 One sueh improved arehitecture is illustrated, for !examplej in Figure 5. In one sueh ease, the membrane 31 pixels 32 are ereated ~y patterning an image thereof onto ~2 a thin dieleetrie film S8 eoating the faee of the CTP 30 33 via photolithographie teehniques. In this proeess a 34 dieleetrie film 58 is deposited on the faee of the CTP 30 35 ~with~eonventional spin eoating or vaeuum-deposition 36 teehnioues. The uniformly thiek 2-10 pm eoating is 8UBSTITUTE SHEET' W093/02375 ~ 14- PCT/USg2/0582 1 overcoated with photoresist which is then exposed by UV `
2 light through a mask. After developing the photoresist, 3 the unwanted dielectric material is removed via plasma 4 etching or wet etching to produce a regular array (e.g.
S rectangular or hexagonal) of say, 100 ym diameter circular 6 pixels on a 138 ~m pitch assuming a 70 pm C~P pin pitch.
7 A layer of metal 56, 1000 angstroms thick is then 8 deposited over the remaining surface. When the 9 photoresist is stripped, the remaining metal pattern 56 defines circular pads at the bottom of each pixel 32 by 11 the metal lift-off technique.
; 12 The dielectric layer 58 has good mechanical properties 13 and provides a smooth surface for membrane attachment.
14 The immediate benefits of this process are twofold: first, the pixel periodicity and lattice geometry are of the 16 ~ighest quality due to established mask-making techniques 17 and alignment procedures. This~removes fixed-pattern 18 noise from the schlieren optics image plane. Second, the 19 pixel fill factor, pixel pitch, and well depth are adjustable in a defined fashion, allowing the structure to 21 be optimized for specific optical wavebands and various 22 applications.
~- 23 - In one preferred form of the invention of Figure 6, 26 the charge-transfer plate 30 is made according to the 27 methods described in United States Patent No. 4,863,759.
28 The plate is then polished to an optical finish and coated 1 29 with a polymer (for example polyether-imide) to obtain, i I 30 say, a 3 pm dielectric layer. The polymer is then 31 overcoated with, say, a 2 pm layer of positive 32 photoresist. The photoresist is soft-baked and exposed to 33 a collimated W beam passed through a high-contrast mask.
34 After exposure, the photoresist is developed and the CTP
30 is~placed in a ~lasma chamber. Pixel wells 32 are 36 formed by the removal of polymer material where no k~
~ ~, SUBSlTllJTE SHEEl' W0~3/02375 2 13 ~ 2 7 ~ PCT/US92/05822 1 photoresist remains. After removal from the plasma-etch 2 chamber, the CTP structure is placed in a vacuum coater 3 where a metal layer 56 is deposited by e-beam or thermal 4 evaporation. Typically 1000 angstroms of aluminum can be deposited. Upon removal from the vacuum coater, the 6 remaining photoresist is stripped, causing'the metal 7 pattern 56 to remain only in the bottom of the pixel wells 8 32.
9 The metalized membrane 34, preferably Parylene, grown by plasma polymerization by Lebow Co. for example, is 11 coated with metal 36 prior to attachment to the support 12 substrate. Silver is usually employed as the reflective 13 metal, though other environmentally-robust metals can also 14 be used. The membrane 34 is attached by slowly bringing it into contact with the substrate under 'tip/tilt' 16 control. The adhesion is due to van der Waals forces 17 which depend on materials parameters of both the substrate 18 and the membrane 34.
19 To optimize the characteristics of the membrane mirror 34, 36 including its zeroth order reflected energy content 21 in the undeflected state, the membrane 34 or underlying 22 substrate may be composed of materials that reduce the 23 tension in the membrane 34 or that reduce the rest-state 24 deflection of the membrane 34 through materials parameters such~-as Young's modulus of elongation. Alternative 26 membrane materials such as nitrocellulose, polyether-27 imide, polypropylene, PTFEP, (poly 28 [bis(trifluoroethoxy)-phospazenel), polyimide, polyimide 29 siloxane, or PET (polyethylene terephthlate) may optimize Ithe actual device performance and are compatible with the 31 process outlined here. Several substrate materials are 32 similarly compatible with this process, including:
33 polyimide, novolac resins, and PTFEP.
34 Alternative processes include direct patterning of photosensitive polymers ( W -curing adhesives, 36 photosensitive polymide, or photoresist) and similar 8UBSTITUTE SHEEl~
W093/0~7~ PCT/US92/05822 ~3~ 16~
1 patterning of vacuum-deposited (evaporated or sputtered) 2 dielectric films (such as ZnS, MgF2, SiOx, Y2O3, or 3 cryolite).
4 In summary, this improved approach for pixel construction on the MLM anodes has the following 6 advantages: ~
8 Improved contrast due to reduced rest-state 9 membrane pull-back 11 Enhanced pixel-to-pixel uniformity of response by 12 improving the uniformity of the pixel geometry.
13 Reduced or eliminated fixed-pattern noise from 14 the image by achieving a high degree of periodicity in the pixel array.
I7 Improved image contrast to at least 200:1 by 18 'tuning' the pixel fill factor.
Phase dynamic range tailored to the specific 21 waveband of interest by controlling the ratio of 22 pixel diameter to pixel well depth.
23 Due to the effi~ient charge storage characteristics of 24 the CTP 30, considerable image storage times (>103 sec) have been observed in the e-MLM. Thus, conventional video 26 operation would imply a frame erase after each video 27 fieldO Since this is wasteful of charge, and also results 28 in non-negligible image flicker, the flickerless mode of 29 operation is preferred. While the conventional video 30' addressing approach described above applies the video 31 signal to the electron gun control grid in order to 32 modulate the delivered beam current, it is also possible 33 to apply the video signal directly to the membrane 34 instead. Thus, the electron beam current will be fixed and simply scanned across the MLM anode 18 at video rates.
36 The potential difference across each pixel well 32 will SUBSTITUTE SHEEl-W093/02375 2 1 ~ 3 2 7 S PCT/US92/05822 1 thus be determined by the instantaneous potential applied 2 to the membrane 34 when the electron beam 16 is impinging 3 on that pixel 32, since the pixel pin electrode 35 4 stabilizes to the grid potential by the secondary emission process. Such a process is referred to as grid-stabilized 6 operation. A similar scheme has been suc~essfully 7 employed in the operation of the Sodern light valve to 8 eliminate flicker from the display. The differences 9 between framed operation and grid-stabilized operation are illustrated in Figure 6.
11 Apart from the absence of image flicker, the grid-12 stabilized mode of operation is more charge-efficient than 13 standard video operation by up to a factor of two.
14 In addition to the field of IR target simulation and scene generation, further developments of this class of 16 dev~ce present distinct advantages to many areas and 17 systems of significant interest to the military.
18 Important application areas of the device include: high-19 definition flîght simulator displays, infrared scene projection, laser beamsteering and wavefront correction in 21 optical communications and imaging through turbulence, 22 high-intensity large-format displays for C3I and 23 teleconferencing, robotic vision, autonomous vehicle 24 guidance, pattern recognition, parallel processing of large knowledge bases, multispectral image fusion, neural-26 network-based processing, and industrial inspection. It 27 is the unavailability of low-cost, high resolution, high 28 brightness SLMs that is impeding the development of all 29 areas of optical signal processing and other specialized 30 ! optical systems such as joint correlators and industrial 31 inspection systems. Concerning the multi-billion-dollar 32 display market, this technology can benefit the high-33 definition large-format projection displays for television 34 conference rooms, auditoriums and the home.
35~ While one embodiment of the invention has been 36 ~described above wherein an electron beam 16 is scanned 8UBSllTUTE SHEEr WOg3/0~75 PCT/US92/05822 ~ 3~ 18- ~ ~
1 across the rear of the transfer plate 30 to create an 2 image modified spatial charge on the light modulating 3 membrane 34, other methods of creating the space charge 4 image can be uti}ized as shown in Figure 7. In this case, S the write signal 63 is an image incident on a photo-6 electron emitting layer 60 carried on an i~p~ window 61.
7 This photo-electron emitting layer 60 emits an image 8 modified stream of electrons through an electron 9 multiplier assembly shown here as a set of microchannel plates (MCP) 62 which transfers the amplified stream of 11 electrons to the rear of the charge transfer plate 30 12 operating under the influence of grid 44. This anode 13 structure is preferably made in accordance with the 14 present invention. The charge is transmitted to the front thereof; the resultant electrostatic forces deform a 16 membrane 34, 36 whose image-modified deflection is read 17 through an output window 40 by suitable readout beam 13.
18 This general arrangement of elements is similar to Figure 19 18 of the above mentioned patent 4,794,296 owned by the assignee of this application.
21 Another embodiment of the present invention provides a 22 modified grid arrangement on the rear of the charge 23 transfer plate 30. As shown in Figure 8 an electron beam 24 16 strikes secondary emitting portions 70 on the rear of the charge transfer plate 30. The impacting electrons 26 cause a large emission of secondary electrons which are 27 then collected by a modified grid 44a which is formed on 28 insulated pedestals 72 created by masking techniques 29 similar to the photolithographic masking techniques discussedjabove for forming the front surface insulating 31 spacer walls 58 in Figure 5.
32 Referring now to Figure ~, in those situations where 33 the light to be modulated has a very long wave length 34 (e.g. 8-14 pm) it is necessary to provide a liquid ' 8UBSTITUTE SHEEr W093/02~75 PCT/US92/05822 1 nitrogen cooled jacket 50 to surround the whole system so 2 as to suppress background infrared radiation that could 3 interfere with and mask the IR image being processed by 4 the system. Jacket 50 in turn is surrounded by a thermal shield 71 has a port 85 for charging the jacket with 6 liquid nitrogen and a port 79 for interconn-ecting the 7 enclosure 86 to a vacuum system (not shown). A collimated 8 beam from an IR light source 81 is directed through a set 9 of baffles 78 onto the Infrared Membrane Light Modulator (IRMLM? 76. The modulated IR light is reflected onto a 11 combination of two Fourier Transform Mirrors 83 and a 12 magnetically controlled spatial-filter mirror 75 as 13 follows: the modulated IR light is first reflected to one 14 Fourier Transform Mirror 83, then onto the spatial-filter mirror, then back to a second Fourier Transform Mirror 16 from which it is directed at the system under test 74.
17 The IRMLM is directed by a controller 77.
18 In the above discussion of the preferred form of the 19 invention, the electron stream or beam 16 addresses the rear surface 52 of the charge transfer plate 30, and the 21 front of the charge transfer plate 30 carries the 22 metalized membrane mirror 34 which is selectively 23 deflected by the charge transferred through the plate.
24 In a further modification of the invention the electron beam 16 impinges directly on the metalized 26 membrane 34 of an anode structure 18 that does not 27 necessarily employ a charge transfer plate. In this case, 28 each portion of the mirror constituting an isolated pixel 29 32 is insulated from each other pixel so that an isolated 30 Icharge can be created at each pixel. This modification is 31 shown in Figure 10. where the electron beam 16 strikes the 32 metalized isolated mirror 36 overlying the pixel potential 33 wells 32~ The isolation of the mirror 36 is achieved by 34 gaps 36a in the coating 36. Secondary emission of electrons will create a static charge on the insulated ~6 mirror 36 in accordance with the intensity and energy of SUBSTll UllE SHEEl-~093/02375 PCT/USg2/05822 ~3~5 -20- .
1 the electron beam 16. This static charge will then create 2 deformation of the membrane 34 in direct accordance with 3 the charge carried thereby in the same fashion as the 4 deformation of the membrane 34 as discussed in connection with Figures 2 and 5. In this case, the struçture could 6 be essentially the same as described for F~gure S with the 7 exception that the metalized mirror 36 would have gaps 36a 8 electrically isolating each portion of the metalized 9 mirror 36 overlying the individual pixels 32.
~n Figure 10, the readout light 13 is directly 11 impinged on the mirror surface 36 through the envelope 12 surrounding the source of the electron beams 16.
13 In Figure 11, a similar embodiment of the invention is 14 shown wherein, instead of having individual metal mirror coatings 36, the reflective surface is created by a }6 dielectric mirror 90 such as a multiple alternating layer 17 stack of SiO~/TiO2. In this case, electron beam 16 18 impingement charges the dielectric mirror 90 negatively or 19 positively and concentrates the charge at the point of impact of the electron beam 16. Accordingly, the pixels 21 32 will accumulate an amount of charge depending on the 22 beam current, the dwell time of the electron beam 16, and 23 the secondary electron emission coefficient in the case of 24 positive charging. Thus the membrane 34 will be deflected into the potential wells 32 in accordance with the charge 26 carried thereon.
27 A similar system is shown in Figure 12 but in this 28 case the readout light 13 is beamed through the support 29 window 40 to the mirror 84. Note that a charge transfer plate 30 cannot be used as the membrane support since the 31 membrane substrate must be transparent. In Figure 12, a ~2 stack of two transparent insulators 80 defining the 33 potential wells 32 i5 mounted on a transparent electrode 34 82, such as an indium tin oxide layer, and mirror surfaces 84 are provided between these insulators 80. The isolated 8UBSTmJTE SHEET
WOg3/0~75 PCT/US92/05822 -21- 21i327~
.
1 mirror pixels 36 are then supported on top of the second 2 insulator stack 80 provided above the mirror surfaces 84.
3 In this case, readout light 13 is modulated in accordance 4 with the degree of deformation of the individual mirror pixels 36 into the potential wells 32. The~ contrast ratio 6 of the modulation is dependent upon the re'lative position 7 of the membrane mirror pixels 36 referenced to the mirror 8 surfaces 84 within the insulators 80.
9 In Figure 13 there is shown a schematic assembly of a readout optical system and a modified electron beam 11 addressed membrane spatial light modulator which directs 12 an image modified electron beam directly on the mirror 13 membrane anodes 36 as illustrated in Figure 10, or 11.
14 While several modifications of the invention have been described above where an electron beam cathode ray tube 16 scans the charge transfer plate 30 or the mirrored 17 membrane 36 directly, it is also possible to utilize a 18~;source of electrons from a field emitter array 64 which l9~can be elect:onically addressed. Such a field emitter array 64 is shown in the copending application Serial No.
21 07/638,317 filed January 4, 1991 and owned by the assignee 22 of the present invention. Similarly, the charge transfer 23 plate 30 can be directly wired by a suitable electronic 24 controller 65 having addressing wires 66 which directly couple to the rear surface 52 of the charge transfer plate 26 30. Examples of these two systems are shown in Figures 14 27 and 15.
28 Figure 14 shows a field emitting source 64 of 29 electrons which impact any of the anode structures of Figureæ 2,i 5, 8 or 12 of the present invention.
31 ~ In the direct wired configuration shown in Figure 15 32 an electronic controller 65 drives each of the pixels 32 33 by means of discrete metal electrodes 54 provided on the 34 rear side 52 of the charge transfer plate 30. The other (mirror) side of the charge transfer plate 30 is made in 36 accordance with the present invention.
SUBSTITUTE SHEEl~
~ 3~ 22-1 In Figure 15 the charge transfer plate anode 56 is 2 preferably made as shown in Figure 5.
3 From the above description, it should be apparent that 4 the novel charge transfer plate 30 of the present invention can be used in a wide range of applications 6 wherever spatial light modulation is desir~d. The input 7 to the membrane anode structure charge transfer plate may 8 be derived from a vast number of different types of 9 electron sources and scanning can be achieved in numerous ways as described above.
11 An improved high-definition electron-beam-addressed 12 Membrane Projection Display (MPD) System is illustrated in 13 Figure 16 as a three color projection television system.
14 It is comprised of three subsystems as shown: (a) three electron-beam-addressed Membrane Light Modulators (e-MLMs) 16 41 with their common readout light source 10 and dichroic 17 beam splitters 55, (b) a spatial filtering 20 and 18 projection optical system 43 and (c) an electronic control 19 and computer interface subsystem 45 which performs the necessary image format conversionæ and implements the 21 control functions that allow the microprocessor to control 22 the light valve.
23 In operation, white light from an arc lamp is fed into 24 the optical system consisting of the three dichroic beamsplitters (BSl, BS2, and BS3) that extract the blue 26 47, green 48, and red 49 light components, respectively, 27 for readout of the three e-MLMs 41 as shown in Figure 16.
28 Thus e-MLMl 46, for example, which is driven by the blue 29 component 47 of the electronic video signal, phase modulates only the blue component 47 of the image as it 31 reflects from the deformable membrane mirror surface 36 e-3~ MLMl 46. Similarly, the modulators e-MLM2 51 and e-MLM3 33 53 modulate the green 48 and red 49 components of the 34 readout beam 13. The modulated zero-order components of the blue, green and red light are recombined by the second 36 set of dichroic beamsplitters 55 (see Figure 16) to yield : 8UBSTITUTE SHEEl-W O 93/023?5 PC~r/US92/05822 23- 2 1 ~ 3 2 7 ~
the~p~a;se ~odulated three color signal beam 57.
2 While numerous modifications of the invention have 3 been described, many additional forms thereof will be 4 apparent to one skilled in the art and the invention is not to be limited to the specific forms shown~
-~::
`:
8UBSTITUTE SHEEl- ` ~
, ~
14 Various means of addressing the two-dimensional deformable membrane mirror have been demonstrated, including electron 16 beam-addressing, optical addressing, and electrical 17~ addressing via integrated circuits. These devices have ~- ~` ;18~ ~not progressed beyond the development state, hence there 19 are no M$Ms on the commercial market. The electron beam-addressed approsch is preferred for display applicstions 2l due to the high re~olution and convenience of direct video 22 ~addressing; however, development of suitable substrates 23~ which would decouple the electron beam interaction region 24 from the reflective mirror were lacking. One method of solving this problem is by introducing the charge-transfer 26 plate (CTP) as a mesns of providing both structural 27 integrity and electrical signal transfer to the mirror 28 elements. This approach has improved the state-of-the-art 29 by yielding a device with a large number of resolution 30 lelements,~ high contrast, and low voltage operation. (see -31 U.S. patent 4,794,296 assigned to the assignee of this ~2 application) 33 Such a system is shown in Figure 18 of the above 34 referenced '296 patent and is more particularly described on column 15, lines 21 through 38 thereof. The charge 8UBSTITUTE SHEEl' WOg3/02375 PCT/US92/05822 ~3~ 2-1 transfer plate creates a two-dimensional electric field 2 which produces a local displacement of the metalized 3 reflective membrane to provide local modulation of the 4 phase output of the two-dimensional light signal reflected from the mirror. These SLMs exhibit very fast response 6 times, can be read out with high optical efficiency, and 7 in principle can incorporate a very large number of 8 resolution elemen~s. Since a deformable mirror SLM is 9 essentially a two-dimensional phase modulating element with a large phase dyna~ic range, it is well-suited to 11 adaptive optics applications such as wavefront correction, 12 laser beam steering and phase only spatial filtering.
13 With appropriate pixelization of the membrane surface, 14 intensity modulation may be accomplished via the schlieren readout schemes employed by projection display systems 16 such as the Eidophor (G.E.) and the Y-Ruticon (Xerox).
17 Recent improvements in the MLM and the system for 18 modulating the charge thereon have involved a M~M wherein 19 a membrane is deposited over an array of wells with an 20 ~addressable electrode at the bottom of each well. Thus, 21 the well and its electrode define an individual pixel.
22 The membra~e is coated with a thin light reflecting 23 electrode material held at a static potential. A pixel is 24 activated by establishing a potential difference between the well electrode and the membrane electrode, causing the 26 membrane to deform into the well region in response to 27 electrostatic forces. Hence, the pixel driving voltage 28 induces a local phase modulation on the readout wavefront 2g reflected by the membrane mirror surface. Such a system ds described in "Electron Beam Addressed Membrane Light 31 Modulator", Spatial ~ight Modulators and Applications, 32 1990 Technical Digest Series, Vol. 14, Optical Society of 33 America, Sept. 1990.
34 Brief Summary of the Invention In one preferred form of the invention a membrane ~, ; ~- 36 light modulator utilizes a charge transfer plate membrane W093/02375 2 ~ ~ 3 2 7 ~ PCT/USg2/05822 1 anode assembly. The charge transfer plate which has a 2 multiplicity of conductors extending from the rear surface 3 to the front surface of the plate. The conductors are 4 supported in an insulating matrix and the front side of the transfer plate has a plurality of reces~sed wells 6 defined by insulating walls, each recessed well 7 constituting a pixel. A plurality of conductors are 8 preferably provided for each pixel and a metal electrode 9 in the bottom of each recessed well preferably spans a plurality of the conductors. The rear surface of the 11 plate preferably includes a secondary electron-enhancing 12 coating. A deformable reflecting metal surface spans the 13 recessed wells. This metal surface can comprise a thin 14 sheet of unsupported metal, but is preferably formed of a metalized coating on a thin insulating (e.g. plastic) 16 support.
17 In another form of the invention, the anode assembly 18 is such that the support for the mirror membrane is still 19 a plurality of insulating walls defining potential wells with an electrode on tbe bottom of each potential well.
21 However, the potential wells are not part of a charge 22 transfer plate and the electron beam directly addresses 23 the mirror membrane to modify the charge thereon by either 24 electron depletion or electron accretion.
In addition to electron beam addressing of these anode 26 structures with a cathode ray tube, optical addressing by 27 means of a photocathode and microchannel plate assembly, 28 field emitter array or hard-wire addressing are also 29 possible for each of the anode structures cited herein.
31 Detailed Deacription of the Invention 32 In order to more fully comprehend the invention 33 reference should be had to the following detailed 34 description of several preferred forms of the invention taken in connection wi~h the attached drawings herein:
36 ~Figure 1 is a schematic view of an overall system 8UBSTITUTE SHEEr W093/0~75 PCT/US92/0~22 ~32~ 5 -4-1 employing an electron-addressed membrane light modulator 2 (e-MLM) in an image projection system.
3 Figure 2 is a schematic sectional view showing a 4 charge transfer plate, metalized membrane and associated S electronic and optical components which is an improvement 6 over that prior art CTP illustrated in the'cited 1990 7 technical digest.
8 Figure 3 is a schematic, partial sectional view of one 9 type of charge transfer plate.
Figure 4a is a photomicrograph of a metalized membrane 11 overlying a charge transfer plate.
12 Figure 4b is the light distribution showing the 13 sixfold svmmetry of the Fourier transform of the membrane 14 mirror of 4a.
lS Figure S is a schematic sectional view of a preferred 16 form of the invention.
17 Figure 6 is a block diagram of a comparison between 18 grid stabilized and fr~med video operation of the e-NLM.
19 Figure 7 is a diagram of an optically-addressed form of the invention, utilizing a photocathode and an electron 21 multiplier assembly a set of microchannel plates to 22 ~roduce the necessary charge image as input to the MLM
23 anode assembly.
24 Figure 8 is a form of the invention, similar to that of Figure 5, except that the electron beam-addressing side 26 of the CTP is patterned so as to realize an integrated 27 grid in registration with the readout side in order to 28 provide improved charging efficiency of the pixel . ~
29 electrodes, and reduce crosstalk between pixels.
30 i Figure 9 is a version of Figure 1 modified to 31 accommodate long-wavelength IR projection which re~uires 32 cryogenic cooling of the system.
33 Figure 10 is a form of the invention in which an 34 insulating substrate (face plate) used in lieu of a CTP.
3S~In this form, the electron beam-addressing and the optical - ~36 readout are achieved on the same face of the device.
-:~ 8UBSTITUTE SHEEr W O ~3/02375 2 1 i 3 2 7 ~ PC~r/US92/05822 1 Figure 11 is a form of the invention similar to that 2 of Figure 10, except that rather than a discontinuous 3 metal mirror coating on the membrane, a uniform dielectric 4 mirror is coated onto the membrane.
Figure 12 is a form of the invention s~imilar to Figure 6 11, except the device is addressed and re~d out on 7 opposite sides of the substrate. This is achieved by use 8 of a mirror layer embedded within the insulative well 9 structure.
Figure 13 depicts the electron gun tube enclosure and 11 readout optics which would be used with the device anode 12 architectures of Figures 10,11, or 12 in those cases where 13 the electron beam and optical readout may occur upon the 14 same surface of the well structure.
Figure 14 illustrates a form of the invention which 16 utilizes a field emitter array to produce the necessary 17 charge image oh the charge transfer plate.
8 Pigure 15 illustrates a form of the invention wherein 9 the charge transfer plate pixels are hard wired to an electronic controller.
21 Figure 16 shows the use of the electron addressed 22 membrane light modulator (e-MLM) to achieve three color 23 projection video.
24 The membrane light modulator of the present invention can be used in a number of applications. These involve 26 various~`types of high definition display techniques, such 27 as high definition television projection, infrared target 28 simulation, as well as other light modulating systems 29 wherein the spatially modulated light 11 is input to another device, for example, an optical computer. For 31 simplicity, the invention will be initially described in 32 its preferred form where it is used as an ultraviolet, 33 visible or IR image projector. This initial description 34 is noé intended to limit the scope of the invention in any way.
36 A schematic of the projector is shown in Figure 1.
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8UBSllTUl~ SHEEl-W093/0237~ PCT/USg2/0582 2 ~ ~32~ 3 -6-1 Specifically, it consists of a readout light source 10 of 2 the appropriate wavelength which can be a laser, arc lamp 3 or glowbar, for example. It also includes IR collimating 4 optics generally shown at 12, a computer 14 controlling an electron beam-source 16 addressing a membra~ne light 6 modulator anode 18. Fourier Transform (FT~ spatiàl filter 7 20 and an output device, which may be a high gain screen, 8 detector or video camera 24, are provided for viewing the 9 output image. As will be more fully described, the image is impressed onto the mirrored membrane surface 34 of the 11 e-MLM by the video signals of the scanning electron beam 12 16, and read out by the reflected light as a phase 13 modulation. The phase modulated beam is then converted to 14 a high-contrast, collimated image by the FT spatial filter 20, and displayed in projection.
16 The construction of a prior art membrane light 17 modulator (MLM) anode 18 which has been improved in 18 accordance with one preferred form of the invention is 19 shown in Figure 2. A membrane is deposited over the front surface 19 of a charge transfer plate 30 that is patterned 21 with an array of recessed wells 32 defined by insulating 22 walls 15 and having an addressable electrode 35 at the 23 bottom, each such recessed well 32 constituting a pixel.
24 Thus, the well 32 and its electrode 35 define an 25- individual pixel or resolution element as described in the 26 1990 technical digest. Additionally, a secondary electron 27 emitter enhancer coating 31 is deposited on the rear 28 surface 52 of the charge transfer plate 30 that receives 29 the electron signal. The purpose of this coating is to enhance the depletion of charge from the surface so images 31 of either positive or negative charge can be written 32 efficiently. The membrane 34 is coated with a thin 33 electrode material 36 held at a static potential. This 34 electrode material is hiqhly reflecting and also acts as a mirror. A pixel is activated by establishing a potential 36 difference between the well electrode 35 and the membrane wo g3/0237s 2 1 ~ 3 2 7 5 PCT/US92/05822 1 electrode 36, causing the membrane 34 to deform into the 2 well region 32 in response to the electrostatic force 3 created by the charge on the pin 35. Hence, the pixel 4 driving voltage induces a local phase modulation on the S readout wavefront 13 reflected by the membrane mirror 6 surface 36. Since pixel wells 32 are clo~e-packed with 7 high spatial uniformity, the membrane 36 diffracts light 8 efficiently when deformed into the wells 32. By using a 9 schlieren readout scheme 21 (e.g., low pass spatial filter that passes only the zero-order light or a band pass 11 filter that passes only the first-order light), the phase 12 object at the deformed membrane surface 34 may be 13 converted to an intensity image at the screen 24.
14 The e-MLM consists of an addressing electron beam 16 and an MLM anode assembly generally indicated at 18, as 16 illustrated in Figure 2. The anode consists of a meta~
17 mesh grid 44 before the pixelated matrix of wells 32, over 18 which~the polymeric, metalized membrane 34 is deposited.
19 The membrane 34 is environmentally protected by an hermetically sealed, IR-transmissive end window 40. For 21 use at infrared wavelengths the window material is 22 preferably zinc selenide (ZnSe) or germanium, whereas 23 materials such as glass could be used in the visible and 24 quartz in the ultraviolet. Both sides of the window 40 are anti-reflection (AR) coated to eliminate undesirable 26 light reflected by the window.
27 Referring still to Figure 2, the electron beam 16 28 writes a charge pattern onto the addressing side of the 29 CTP 30, which is transferred to the bottom of the well 32 30 Iby the electrodes 35 as a two-dimensional voltage 31 pattern. The resulting deformed mirror membrane 34,36 32 phase-modulates the reflected IR readout light 13, which 33 is converted to a projected high-contrast image by the 34 downstream schlieren optics generally shown at 21. (see 3S Figure 1) 36 ~ The heart of the anode assembly 18 is the pixelated 8UBSTlTUTi E SHEET' W O 93/02375 PC~r/US92/0582~ 2~32~ 5 -8-1 strueture, called a eharge-transfer plate CTP 30. The 2 name derives from its ability to serve as a high-density 3 multi-feedthrough vaeuum interface, transferring a two-4 dimensional charge distribution from vaeuum to air. The CTP 30, illustrated in Figure 3, is a wafer of 6 eleetrieally insulating material 37 in whie~ are imbedded 7 a regular matrix of thousands to millions of 8 longitudinally oriented conduetive pins 35. The ratio of 9 collective pin cross-seetional area to the CTP area is about 50%. Charge transfer plates 30 with 10 ym diameter 11 pins on 14 ~m eenters, and S0 ym diameter pins on 70 ym 12 centers are typical. Material may be removed from the 13 pins 35 on one side of the plate 30 so as to form a 14 regular array of recessed wells 32 a few microns deep.
lS The surface is highly polished to an optical flatness of 2A
16 across the aetive diameter. Thereafter the enhaneer 17 eoating 31 is applied to the rear surface 52 of the 18 eharge transfer plate 30 by thin film deposition 19 teehnigues.
A polymeric membrane 34 is deposited on the CTP
21 surface that eontains the wells 32 sueh that a reliable 22 bond between the two dieleetric surfaees is established 23 due to van der Waals forees. The resultant membrane 24~ pixels then assume the symmetry of the wells 32 whieh may be eireular pixels on~hexagonal elosed paeked (HCP) 26 eenters or cireular pixels on square eenters, for example.
27 Upon optieal readout of the membrane 34, this symmetry 28 (square or hexagonal) is preserved in the Fourier plane as 29 a diffraction pattern. A high-magnifieation photograph of bhe pixelated membrane surfaee with HCP symmetry and its 31 optieal Fourier transform are illustrated in Figures 4(a) ~ and 4(b), respeetively.
33 Referring again to Figure 2, we see that one means of 34 addressing of the MLM anode 18 is aeeomplished by direetly ~;~ 35 addressing the (CTP 30) with a seanning eleetron beam 16.
36 This approaeh offers the following advantages:
~: ~ 8UBSTITUTE SHEET
W093~0237~ 2 1 ~ ~ 2 7 ~i PCT/US92/0~822 _g _ 1 (1) With ~he appropriate electron gun drive 2 electronics and high-resolution te.g., vidicon-3 type) electron gun, each pixel (pin 35) of the 4 CTP anode is individually addressable;
S . ~ :
6 (2) The electron beam current of conv~ntional 7 delivery systems can be large, ranging from tens 8 of nanoamperes to hundreds of microamperes;
(3) A well-established technology standard exists for 11 scanning electron beam imaging systems, as a 12 result of the widescale development of cathode 13 ray tubes and video-based communications (e.g~, 14 television).
Electronically, the e-MLM may be viewed as a triode 16 structure, as illustrated in Figure 2. The thermionic 17 cathode 17 at Vk<0 emits a primary electron beam 16 which 18 may be intensity modulated by its video grid (not shown), 19 which strikes a pin 35 (or pins) of the CTP 30. Secondary electrons are emitted from the enhancer coating 31 21 overlying the pins 35 and collected by the qrid 44, 22 resulting in a buildup of positive charge on the pin 35 if 23 the secondary electrons are collected by the grid 44. The 24 local potential of the CTP 30 (which influences the landing energy of the primaries) is determined by the 26 membrane potential at Ym. The landing energy Ep of the 27 primaries is given by:
28 Ep - e(V~ V~.
29 The ratio of secondaries to primaries, or ~, is dictated by the particular value of Ep. In the absence of 31 an erase cycle, the throughput ~TP) of the e-M$M may be 32 gîven by:
33 TP ~pixels/sec) = is/CV, 34 where iS is the secondary current, C the pixel capacitance, and V the potential difference required to 36 deflect the membrane 34 to full-contrast modulation.
W O 93/02375 rl ~ P(~r/US92/0582~ 2~3~ -lo- : i 1 The throughput is representative of the signal rate of 2 the e-MLM for information proeessing. For example, if we 3 desire a 250x250 pixel image framed at 100 Hz, the TP
4 assoeiated with this frame rate is: TP = 250x250xlO0 =
6.25 x 106 pixels/sec. Henee, the seeondary eleetron 6 eurrent required would, given a pixel eapae'itanee of 0.5 7 pF and a full-modulation voltage of 70V, be:
8 iS=TP C V=(6.25xlO6pixels/see)(SxlO~13F/pixel)(70V)=220 ~A.
9 This level of primary eleetron eurrent is readily attainable by eonventional CRT-type eleetron guns.
11 In the framed mode, the grid 44 is grounded and a 12 potential differenee is established between the CTP pins 13 35 and the grid 44 by applying a ne~ative DC potential to 14 the membrane metalization layer 36, which drives the CTP
pins 35 to that potential by eapaeitive division. As the 16 eleetron beam 16 seans aeross a eonduetive pin 35 of the 17 CTP 30, seeondary eleetrons are emitted from the enhaneer 18 eoating 31 eovering that pin (35) and are eolleeted by the 19 grounded, planar fine mesh grid 44 held in elose proximity to the CTP surfaee. Sinee the number of seeondary 21 eleetrons emitted per ineoming primary eleetron, or ~, 22 exeeeds unity, a net positive eharge aceumulates on the 23 pin 35. If an enhaneer eoating 31 is added to the CTP 30, 24 this increases the eharging eurrent is aeeording to the inerease in ~ of the enhaneer material:
26 -- is2 ~2-28 is~
29 Where ~1 and ~2 are the seeondary eleetron emission 30 !eoeffieients without and with the enhaneer eoating 31. If 31 the eleetron beam 16 eontinues to address that pin 35, 32 eharge accumulates until the pin potential stabilizes to 33 the grid potential, ti.e. ground in this case). During 34 framed operation, the beam eurrent 16 can be eonstrained sueh that no pixel 32 is allowed to saturate to the grid 36 potential. Thus, by dynamieally varying the electron beam ~3UBSTITUl-E SHEEr ` W O 93/02375 2 1 ~ 3 2 7 ~ PC~r/US92/05822 1 current 16 at each pixel location 32, a continuously 2 varying two-dimensional charge image can be written onto 3 the conductors 35. This results in a voltage drop between 4 the membrane 34 and the pins 35 and the associated electrostatic force pulls the membrane 34 into the well 6 32. Since the pixel capacitances may be on~~he order of a 7 picofarad, charge storage times can be long (>lOOs). This 8 necessitates an erase cycle following each write cycle;
9 erasure is easily accomplished by grounding the membrane electrode 36 during electron beam addressing.
11 The device may then be read out by reflecting 12 collimated light 13 off the deformed membrane 34 at a 13 shallow (~10) angle of incidence, as indicated in Figure 14 1. Alternatively, it may be read out at normal incidence with the use of a beam splitter. The phase information 16 encoded upon the reflected wavefront is then processed by 17 Schileren optics, shown generally at 21 in Figure 1. The 18 schlieren system 21 consists of a converging lens 23, 19 field stop 25 a spatial filter 20 and a reimaging lens 22 as illustrated in Figure 1. The converging lens 23 yields 21 the Fourier transform (FT) of the phase object (i.e., the 22 deformed membrane surface) one focal length after the 23 lens. The FT is a diffraction pattern consisting of 24 bright spots of light that possess the symmetry of the CTP
30, as illustrated in Figure 4(b) for a HCP symmetry. For 26 a fully undeformed membrane surface, only the zeroth, or 27 specular, order is present in the FT plane. As pixels 32 28 are deformed, the diffraction efficiency into the higher 29 orders increases. In the preferred zeroth-order readout Ischeme an intensity-modulated image of the phase object is 31 obtained by passing only the zeroth order of the FT
32 through the spatial filter 20 before reimaging with the 33 second lens 22. This output image is both collimated and 34 parfocal, and can be displayed onto a screen 24 with varisble magnification by a subsequent projector lens. As 36 expected, the zeroth-order readout results in a contrast-SUBSTITIJTE SHEEr WOg3/02375 PCT/US92/0582~
2~3~ 12-1 reversed image, i.e., black pixels on a white field.
2 A most important aspect of manufacturing the e-MLM is 3 the fabrication of the pixel structures 32 on the readout 4 side of the MLM anode 18. As indicated in Figure 2, one - S method of forming pixel structures 32 is by etching away 6 portions of the CTP pins 35, leaving the pe'r~orated 7 insulating substrate 37 as a support structure for the 8 reflective membrane 34. While this prior art method of 9 producing the "mirror" pixels has proved satisfactory it can be improved. One method has been mentioned above when 11 the secondary emission of the electron impact surface has 12 been increased by use of the enhancer coating 31. Another 13 problem is that the periodicity of the CTP 35 pins may not 14 be perfect. Accordingly, periodicity of the membrane pixels 32 would not be perfectly periodic. This lack of 16 regularity leads to high spatial frequency, static 'noise' 17 in the reconstructed image. Another related problem is 18 that of image contrast. Since image contrast in a 19 schlieren imaging system 21 is attained by interference at the image plane, the apparent pixel fill factor is of 21 extreme importance. For example, approximately 50~ pixel 22 fill factor is necessary in order to achieve a perfect 23 intensity null in an anode 18 with HCP pattern of pixels.
24 Another issue is that of dynamic range. ~n order to modulate long-wavelength-light, membrane deflections of 26 several microns may be required. In order to enhance 27 speed, low ~oltage operation is preferable. To meet these 28 requirements, the ratio of pixel diameter to pixel well 29 depth must be large. For example, it can be shown that lthe membrane deflection can be expressed by:
31 ~ = (Eo/32) TV2 (a/D)2, 32 where ~ is the membrane deflection, ~O the permittivity of ~ 33 free space, T the membrane surface tension, V the applied ; 34 voltage, a the pixel diameter, and D the pixel well depth.
3~5 Therefore, larger deflections and/or lower operating 36 voltages will be attained by increasing the a/D ratio of :" ~
- ~ : 8UBSTITUTE SHEET
W093/0~75 2 1 ~ 3 2 7 ~ PCT/US92~0s822 .
1 the pixel geometry. In addition, the maximum deflection 2 required for deviee operation should be a fraetion (<20%) 3 of the total well depth in order to preserve the parabolic 4 shape of the deflected membrane. This represents about S half of the defleetion range of the membran,e pixel. Sinee 6 larger defleetions require deeper wells, w~ile low voltage 7 operation implies shallower wells, the optimization of 8 pixel well depth (or a/D ratio) can be determined 9 empirically. This provides the ability to continuously vary the geometry of the pixel array and achieves the 11 optimization of deviee performanee.
12 As diseussed above, a most important aspeet of 13 manufaeturing the e-MLM is the fabrication of the pixel 14 struetures 32 of the M~ anode 18. Figures 2,5,8,10,11 and 12 show a variety of different anode pixelization 16 sehemes. In the Figure 2,-for example, the prior art 17 eonstruetion pixelization is provided by the CTP 30 on 18 both the addressing side and readout side of the CTP 30.
19 The pixel well struetures 32 are formed by etehing away a few mierons of the CTP pins 35, leaving the perforated 21 insulating substrate 37 as a support strueture for the 22 membrane 34. Therefore, the strueture of the membrane 23 pixels 32 is tied to that of the CTP 30, in pixel 24 diameter, pixei piteh, periodieity, paeking density, and 25 `so on. ~ As mentioned this form of the invention ineludes 26 the improved enhaneer eoating 31.
27 Several superior arehiteetures ean be employed that 28 deeouple the pixel array from the CTP inter-pin piteh.
29 One sueh improved arehitecture is illustrated, for !examplej in Figure 5. In one sueh ease, the membrane 31 pixels 32 are ereated ~y patterning an image thereof onto ~2 a thin dieleetrie film S8 eoating the faee of the CTP 30 33 via photolithographie teehniques. In this proeess a 34 dieleetrie film 58 is deposited on the faee of the CTP 30 35 ~with~eonventional spin eoating or vaeuum-deposition 36 teehnioues. The uniformly thiek 2-10 pm eoating is 8UBSTITUTE SHEET' W093/02375 ~ 14- PCT/USg2/0582 1 overcoated with photoresist which is then exposed by UV `
2 light through a mask. After developing the photoresist, 3 the unwanted dielectric material is removed via plasma 4 etching or wet etching to produce a regular array (e.g.
S rectangular or hexagonal) of say, 100 ym diameter circular 6 pixels on a 138 ~m pitch assuming a 70 pm C~P pin pitch.
7 A layer of metal 56, 1000 angstroms thick is then 8 deposited over the remaining surface. When the 9 photoresist is stripped, the remaining metal pattern 56 defines circular pads at the bottom of each pixel 32 by 11 the metal lift-off technique.
; 12 The dielectric layer 58 has good mechanical properties 13 and provides a smooth surface for membrane attachment.
14 The immediate benefits of this process are twofold: first, the pixel periodicity and lattice geometry are of the 16 ~ighest quality due to established mask-making techniques 17 and alignment procedures. This~removes fixed-pattern 18 noise from the schlieren optics image plane. Second, the 19 pixel fill factor, pixel pitch, and well depth are adjustable in a defined fashion, allowing the structure to 21 be optimized for specific optical wavebands and various 22 applications.
~- 23 - In one preferred form of the invention of Figure 6, 26 the charge-transfer plate 30 is made according to the 27 methods described in United States Patent No. 4,863,759.
28 The plate is then polished to an optical finish and coated 1 29 with a polymer (for example polyether-imide) to obtain, i I 30 say, a 3 pm dielectric layer. The polymer is then 31 overcoated with, say, a 2 pm layer of positive 32 photoresist. The photoresist is soft-baked and exposed to 33 a collimated W beam passed through a high-contrast mask.
34 After exposure, the photoresist is developed and the CTP
30 is~placed in a ~lasma chamber. Pixel wells 32 are 36 formed by the removal of polymer material where no k~
~ ~, SUBSlTllJTE SHEEl' W0~3/02375 2 13 ~ 2 7 ~ PCT/US92/05822 1 photoresist remains. After removal from the plasma-etch 2 chamber, the CTP structure is placed in a vacuum coater 3 where a metal layer 56 is deposited by e-beam or thermal 4 evaporation. Typically 1000 angstroms of aluminum can be deposited. Upon removal from the vacuum coater, the 6 remaining photoresist is stripped, causing'the metal 7 pattern 56 to remain only in the bottom of the pixel wells 8 32.
9 The metalized membrane 34, preferably Parylene, grown by plasma polymerization by Lebow Co. for example, is 11 coated with metal 36 prior to attachment to the support 12 substrate. Silver is usually employed as the reflective 13 metal, though other environmentally-robust metals can also 14 be used. The membrane 34 is attached by slowly bringing it into contact with the substrate under 'tip/tilt' 16 control. The adhesion is due to van der Waals forces 17 which depend on materials parameters of both the substrate 18 and the membrane 34.
19 To optimize the characteristics of the membrane mirror 34, 36 including its zeroth order reflected energy content 21 in the undeflected state, the membrane 34 or underlying 22 substrate may be composed of materials that reduce the 23 tension in the membrane 34 or that reduce the rest-state 24 deflection of the membrane 34 through materials parameters such~-as Young's modulus of elongation. Alternative 26 membrane materials such as nitrocellulose, polyether-27 imide, polypropylene, PTFEP, (poly 28 [bis(trifluoroethoxy)-phospazenel), polyimide, polyimide 29 siloxane, or PET (polyethylene terephthlate) may optimize Ithe actual device performance and are compatible with the 31 process outlined here. Several substrate materials are 32 similarly compatible with this process, including:
33 polyimide, novolac resins, and PTFEP.
34 Alternative processes include direct patterning of photosensitive polymers ( W -curing adhesives, 36 photosensitive polymide, or photoresist) and similar 8UBSTITUTE SHEEl~
W093/0~7~ PCT/US92/05822 ~3~ 16~
1 patterning of vacuum-deposited (evaporated or sputtered) 2 dielectric films (such as ZnS, MgF2, SiOx, Y2O3, or 3 cryolite).
4 In summary, this improved approach for pixel construction on the MLM anodes has the following 6 advantages: ~
8 Improved contrast due to reduced rest-state 9 membrane pull-back 11 Enhanced pixel-to-pixel uniformity of response by 12 improving the uniformity of the pixel geometry.
13 Reduced or eliminated fixed-pattern noise from 14 the image by achieving a high degree of periodicity in the pixel array.
I7 Improved image contrast to at least 200:1 by 18 'tuning' the pixel fill factor.
Phase dynamic range tailored to the specific 21 waveband of interest by controlling the ratio of 22 pixel diameter to pixel well depth.
23 Due to the effi~ient charge storage characteristics of 24 the CTP 30, considerable image storage times (>103 sec) have been observed in the e-MLM. Thus, conventional video 26 operation would imply a frame erase after each video 27 fieldO Since this is wasteful of charge, and also results 28 in non-negligible image flicker, the flickerless mode of 29 operation is preferred. While the conventional video 30' addressing approach described above applies the video 31 signal to the electron gun control grid in order to 32 modulate the delivered beam current, it is also possible 33 to apply the video signal directly to the membrane 34 instead. Thus, the electron beam current will be fixed and simply scanned across the MLM anode 18 at video rates.
36 The potential difference across each pixel well 32 will SUBSTITUTE SHEEl-W093/02375 2 1 ~ 3 2 7 S PCT/US92/05822 1 thus be determined by the instantaneous potential applied 2 to the membrane 34 when the electron beam 16 is impinging 3 on that pixel 32, since the pixel pin electrode 35 4 stabilizes to the grid potential by the secondary emission process. Such a process is referred to as grid-stabilized 6 operation. A similar scheme has been suc~essfully 7 employed in the operation of the Sodern light valve to 8 eliminate flicker from the display. The differences 9 between framed operation and grid-stabilized operation are illustrated in Figure 6.
11 Apart from the absence of image flicker, the grid-12 stabilized mode of operation is more charge-efficient than 13 standard video operation by up to a factor of two.
14 In addition to the field of IR target simulation and scene generation, further developments of this class of 16 dev~ce present distinct advantages to many areas and 17 systems of significant interest to the military.
18 Important application areas of the device include: high-19 definition flîght simulator displays, infrared scene projection, laser beamsteering and wavefront correction in 21 optical communications and imaging through turbulence, 22 high-intensity large-format displays for C3I and 23 teleconferencing, robotic vision, autonomous vehicle 24 guidance, pattern recognition, parallel processing of large knowledge bases, multispectral image fusion, neural-26 network-based processing, and industrial inspection. It 27 is the unavailability of low-cost, high resolution, high 28 brightness SLMs that is impeding the development of all 29 areas of optical signal processing and other specialized 30 ! optical systems such as joint correlators and industrial 31 inspection systems. Concerning the multi-billion-dollar 32 display market, this technology can benefit the high-33 definition large-format projection displays for television 34 conference rooms, auditoriums and the home.
35~ While one embodiment of the invention has been 36 ~described above wherein an electron beam 16 is scanned 8UBSllTUTE SHEEr WOg3/0~75 PCT/US92/05822 ~ 3~ 18- ~ ~
1 across the rear of the transfer plate 30 to create an 2 image modified spatial charge on the light modulating 3 membrane 34, other methods of creating the space charge 4 image can be uti}ized as shown in Figure 7. In this case, S the write signal 63 is an image incident on a photo-6 electron emitting layer 60 carried on an i~p~ window 61.
7 This photo-electron emitting layer 60 emits an image 8 modified stream of electrons through an electron 9 multiplier assembly shown here as a set of microchannel plates (MCP) 62 which transfers the amplified stream of 11 electrons to the rear of the charge transfer plate 30 12 operating under the influence of grid 44. This anode 13 structure is preferably made in accordance with the 14 present invention. The charge is transmitted to the front thereof; the resultant electrostatic forces deform a 16 membrane 34, 36 whose image-modified deflection is read 17 through an output window 40 by suitable readout beam 13.
18 This general arrangement of elements is similar to Figure 19 18 of the above mentioned patent 4,794,296 owned by the assignee of this application.
21 Another embodiment of the present invention provides a 22 modified grid arrangement on the rear of the charge 23 transfer plate 30. As shown in Figure 8 an electron beam 24 16 strikes secondary emitting portions 70 on the rear of the charge transfer plate 30. The impacting electrons 26 cause a large emission of secondary electrons which are 27 then collected by a modified grid 44a which is formed on 28 insulated pedestals 72 created by masking techniques 29 similar to the photolithographic masking techniques discussedjabove for forming the front surface insulating 31 spacer walls 58 in Figure 5.
32 Referring now to Figure ~, in those situations where 33 the light to be modulated has a very long wave length 34 (e.g. 8-14 pm) it is necessary to provide a liquid ' 8UBSTITUTE SHEEr W093/02~75 PCT/US92/05822 1 nitrogen cooled jacket 50 to surround the whole system so 2 as to suppress background infrared radiation that could 3 interfere with and mask the IR image being processed by 4 the system. Jacket 50 in turn is surrounded by a thermal shield 71 has a port 85 for charging the jacket with 6 liquid nitrogen and a port 79 for interconn-ecting the 7 enclosure 86 to a vacuum system (not shown). A collimated 8 beam from an IR light source 81 is directed through a set 9 of baffles 78 onto the Infrared Membrane Light Modulator (IRMLM? 76. The modulated IR light is reflected onto a 11 combination of two Fourier Transform Mirrors 83 and a 12 magnetically controlled spatial-filter mirror 75 as 13 follows: the modulated IR light is first reflected to one 14 Fourier Transform Mirror 83, then onto the spatial-filter mirror, then back to a second Fourier Transform Mirror 16 from which it is directed at the system under test 74.
17 The IRMLM is directed by a controller 77.
18 In the above discussion of the preferred form of the 19 invention, the electron stream or beam 16 addresses the rear surface 52 of the charge transfer plate 30, and the 21 front of the charge transfer plate 30 carries the 22 metalized membrane mirror 34 which is selectively 23 deflected by the charge transferred through the plate.
24 In a further modification of the invention the electron beam 16 impinges directly on the metalized 26 membrane 34 of an anode structure 18 that does not 27 necessarily employ a charge transfer plate. In this case, 28 each portion of the mirror constituting an isolated pixel 29 32 is insulated from each other pixel so that an isolated 30 Icharge can be created at each pixel. This modification is 31 shown in Figure 10. where the electron beam 16 strikes the 32 metalized isolated mirror 36 overlying the pixel potential 33 wells 32~ The isolation of the mirror 36 is achieved by 34 gaps 36a in the coating 36. Secondary emission of electrons will create a static charge on the insulated ~6 mirror 36 in accordance with the intensity and energy of SUBSTll UllE SHEEl-~093/02375 PCT/USg2/05822 ~3~5 -20- .
1 the electron beam 16. This static charge will then create 2 deformation of the membrane 34 in direct accordance with 3 the charge carried thereby in the same fashion as the 4 deformation of the membrane 34 as discussed in connection with Figures 2 and 5. In this case, the struçture could 6 be essentially the same as described for F~gure S with the 7 exception that the metalized mirror 36 would have gaps 36a 8 electrically isolating each portion of the metalized 9 mirror 36 overlying the individual pixels 32.
~n Figure 10, the readout light 13 is directly 11 impinged on the mirror surface 36 through the envelope 12 surrounding the source of the electron beams 16.
13 In Figure 11, a similar embodiment of the invention is 14 shown wherein, instead of having individual metal mirror coatings 36, the reflective surface is created by a }6 dielectric mirror 90 such as a multiple alternating layer 17 stack of SiO~/TiO2. In this case, electron beam 16 18 impingement charges the dielectric mirror 90 negatively or 19 positively and concentrates the charge at the point of impact of the electron beam 16. Accordingly, the pixels 21 32 will accumulate an amount of charge depending on the 22 beam current, the dwell time of the electron beam 16, and 23 the secondary electron emission coefficient in the case of 24 positive charging. Thus the membrane 34 will be deflected into the potential wells 32 in accordance with the charge 26 carried thereon.
27 A similar system is shown in Figure 12 but in this 28 case the readout light 13 is beamed through the support 29 window 40 to the mirror 84. Note that a charge transfer plate 30 cannot be used as the membrane support since the 31 membrane substrate must be transparent. In Figure 12, a ~2 stack of two transparent insulators 80 defining the 33 potential wells 32 i5 mounted on a transparent electrode 34 82, such as an indium tin oxide layer, and mirror surfaces 84 are provided between these insulators 80. The isolated 8UBSTmJTE SHEET
WOg3/0~75 PCT/US92/05822 -21- 21i327~
.
1 mirror pixels 36 are then supported on top of the second 2 insulator stack 80 provided above the mirror surfaces 84.
3 In this case, readout light 13 is modulated in accordance 4 with the degree of deformation of the individual mirror pixels 36 into the potential wells 32. The~ contrast ratio 6 of the modulation is dependent upon the re'lative position 7 of the membrane mirror pixels 36 referenced to the mirror 8 surfaces 84 within the insulators 80.
9 In Figure 13 there is shown a schematic assembly of a readout optical system and a modified electron beam 11 addressed membrane spatial light modulator which directs 12 an image modified electron beam directly on the mirror 13 membrane anodes 36 as illustrated in Figure 10, or 11.
14 While several modifications of the invention have been described above where an electron beam cathode ray tube 16 scans the charge transfer plate 30 or the mirrored 17 membrane 36 directly, it is also possible to utilize a 18~;source of electrons from a field emitter array 64 which l9~can be elect:onically addressed. Such a field emitter array 64 is shown in the copending application Serial No.
21 07/638,317 filed January 4, 1991 and owned by the assignee 22 of the present invention. Similarly, the charge transfer 23 plate 30 can be directly wired by a suitable electronic 24 controller 65 having addressing wires 66 which directly couple to the rear surface 52 of the charge transfer plate 26 30. Examples of these two systems are shown in Figures 14 27 and 15.
28 Figure 14 shows a field emitting source 64 of 29 electrons which impact any of the anode structures of Figureæ 2,i 5, 8 or 12 of the present invention.
31 ~ In the direct wired configuration shown in Figure 15 32 an electronic controller 65 drives each of the pixels 32 33 by means of discrete metal electrodes 54 provided on the 34 rear side 52 of the charge transfer plate 30. The other (mirror) side of the charge transfer plate 30 is made in 36 accordance with the present invention.
SUBSTITUTE SHEEl~
~ 3~ 22-1 In Figure 15 the charge transfer plate anode 56 is 2 preferably made as shown in Figure 5.
3 From the above description, it should be apparent that 4 the novel charge transfer plate 30 of the present invention can be used in a wide range of applications 6 wherever spatial light modulation is desir~d. The input 7 to the membrane anode structure charge transfer plate may 8 be derived from a vast number of different types of 9 electron sources and scanning can be achieved in numerous ways as described above.
11 An improved high-definition electron-beam-addressed 12 Membrane Projection Display (MPD) System is illustrated in 13 Figure 16 as a three color projection television system.
14 It is comprised of three subsystems as shown: (a) three electron-beam-addressed Membrane Light Modulators (e-MLMs) 16 41 with their common readout light source 10 and dichroic 17 beam splitters 55, (b) a spatial filtering 20 and 18 projection optical system 43 and (c) an electronic control 19 and computer interface subsystem 45 which performs the necessary image format conversionæ and implements the 21 control functions that allow the microprocessor to control 22 the light valve.
23 In operation, white light from an arc lamp is fed into 24 the optical system consisting of the three dichroic beamsplitters (BSl, BS2, and BS3) that extract the blue 26 47, green 48, and red 49 light components, respectively, 27 for readout of the three e-MLMs 41 as shown in Figure 16.
28 Thus e-MLMl 46, for example, which is driven by the blue 29 component 47 of the electronic video signal, phase modulates only the blue component 47 of the image as it 31 reflects from the deformable membrane mirror surface 36 e-3~ MLMl 46. Similarly, the modulators e-MLM2 51 and e-MLM3 33 53 modulate the green 48 and red 49 components of the 34 readout beam 13. The modulated zero-order components of the blue, green and red light are recombined by the second 36 set of dichroic beamsplitters 55 (see Figure 16) to yield : 8UBSTITUTE SHEEl-W O 93/023?5 PC~r/US92/05822 23- 2 1 ~ 3 2 7 ~
the~p~a;se ~odulated three color signal beam 57.
2 While numerous modifications of the invention have 3 been described, many additional forms thereof will be 4 apparent to one skilled in the art and the invention is not to be limited to the specific forms shown~
-~::
`:
8UBSTITUTE SHEEl- ` ~
, ~
Claims (15)
1. A membrane light modulator characterized by comprising, a charge transfer plate 30 having rear and front surfaces, a multiplicity of conductors 35 extending from the rear surface 52 to the front surface 19 of said plate 30, said conductors 35 being supported in an insulating matrix 37, the front surface 19 of said transfer plate 30 having thereon a plurality of potential wells 32 defined by insulating walls 15, each said potential well 32 constituting a pixel, a plurality of said multiplicity of conductors 35 being provided for each pixel, a deformable reflecting membrane 34,36 comprising a metal layer 36 spanning said potential wells 32, means providing an electric potential on said metal layer 36, means 17 providing a source of electrons 16 for impacting the rear surface 52 of said charge transfer plate 30, and means providing an image defining charge distribution to one of said last two means to provide an image defining deformation to said metal layer 36 at each pixel.
2. The membrane light modulator of claim 1, characterized in that the metal layer 36 is a thin flexible sheet of metal.
3. The membrane light modulator of claim 2, characterized in that the metal layer 36 is a metal coating on a flexible insulating substrate 34, preferably a metalized plastic.
4. The light modulator of claim 1, characterized in that said insulating walls 15 are formed from an insulating layer 72, said walls 15 being created by etching portions of said insulating layer 72 not protected by an overlying photoresist.
5. The membrane light modulator 18 of claim 1, characterized in that said means for providing a source of electrons 16 comprises an electronic controller 65 hard wired 66 to the electrode surface 54, or a photocathode and microchannel plate assembly 62, or a field emitter array 64, or a cathode ray tube 17.
6. A membrane light modulator characterized by comprising, a charge transfer plate 30 having rear and front surfaces, a multiplicity of conductors 35 extending from the rear surface 52 to the front surface 19 of said plate, said conductors 35 being supported in an insulating matrix 37, the front surface 19 of said transfer plate 30 having thereon a plurality of potential wells 32 defined by insulating walls 15, each said potential well 32 constituting a pixel, a plurality of said multiplicity of conductors 35 being provided for each pixel, a metal electrode 56 in the bottom of each potential well 32 spanning a plurality of said conductors 35, a deformable reflecting membrane 34, 36 spanning said potential wells 32, said membrane 34 comprising a metal layer 36, means providing a potential on said metal layer 36, means providing a source of electrons 17 for impacting the rear surface 52 of said charge transfer plate 30, and means providing an image defining charge distribution to said source of electrons 17 to provide an image defining deformation to said metal layer 36 at each pixel.
7. A membrane light modulator characterized by comprising, a charge transfer plate 30 having rear and front surfaces, a multiplicity of conductors 35 extending from the rear surface 52 to the front surface 19 of said plate 30, said conductors 35 being supported in an insulating matrix 37, the front surface 19 of said transfer plate 30 having thereon a plurality of potential wells 32 defined by insulating walls 15, each said potential well 32 constituting a pixel, a plurality of said multiplicity of conductors 35 being provided for each pixel, a metal electrode 56 in the bottom of each potential well 32 spanning a plurality of said conductors 35, a deformable reflecting plastic membrane 34 spanning said potential wells 32, a metal coating 36 on said plastic membrane 34 insulated from said potential wells 32, means providing a modulated stream of electrons 16 to the rear surface 52 of said charge transfer plate 30, means providing a potential on said metal coating 36, means providing an image defining charge distribution to one of said last two means to provide an image defining deformation to said sheet 34 at each pixel, and a light source 10 of predetermined wavelength impinging on said reflective membrane 34, 36 to be modified by the deformation of each pixel on said reflective membrane 34, 36.
8. A device for modulating incident light by impinging said light on a membrane mirror which can be deformed in accordance with an electric charge on individual pixel portions of the membrane mirror, the improvement characterized in that the membrane mirror 34 is supported on a plurality of insulating walls 72 which are formed on an electrode-containing surface 19 to define potential wells 32, each said potential well 32 constituting a pixel so that the bottom of each of said wells 32 has said electrode surface 56 thereon and a charge difference can be created between the electrode 56 and the portion of the membrane 34 overlying each pixel, and means for creating an image defining charge difference across said membrane 34 by addressing the structure with an image modified electron stream 16.
9. The device of claim 8, characterized by a grid 44 adjacent that side of said structure addressed by said electron stream 16.
10. The device of claim 8, characterized in that the mirror membrane 34, 36 comprises discrete mirror segments 36 overlying each pixel, and said electron stream 16 impinges on said mirror 36 and modifies the charge on each pixel by secondary electron emission from said mirror segment 36.
11. The device of claim 8, characterized in that the membrane 34, 36 comprises a dielectric coating 90 and said electron stream 16 impacts said dielectric coating 90 and modifies the charge on each pixel by accumulation or depletion of electrons thereon.
12. The device of claim 8, characterized in that the means for creating the image modified electron stream 16 comprises a matrix addressed field emitter array 64, or a photocathode and microchannel plate assembly 62, or a cathode ray tube 17.
13. The device of claim 6, further characterized by comprising a plurality of light modulators 41, a different wavelength of light 47, 48, 49 is provided to each modulator 41, and the resultant modulated light beams are combined 57 to give a multi color image.
14. A membrane light modulator characterized by comprising a charge transfer plate 30 having rear and front surfaces, a multiplicity of conductors 35 extending from the rear surface 52 to the front surface 19 of said plate 30, said conductors being supported in an insulating matrix 37, the front surface 19 of said transfer plate 30 having thereon a plurality of potential wells 32 defined by insulating walls 15, each said potential well 32 constituting a pixel; a deformable reflecting membrane 34,36 spanning said potential wells 32, a metal coating 36 on said membrane 34, means providing a potential on said metal coating 36, means providing a source of electrons 17 for impacting the rear surface 52 of said charge transfer plate 30, means providing an image defining charge distribution to one of said last two means to provide an image defining deformation to said membrane 34 at each pixel, and wherein a plurality of said multiplicity of conductors 35 are provided for each pixel and a metal electrode 56 in the bottom of each potential well 32 spans a plurality of said conductors 35.
15. A membrane light modulator characterized by comprising a charge transfer plate 30 having rear and front surfaces, a multiplicity of conductors 35 extending from the rear surface 52 to the front surface 19 of said plate 30, said conductors 35 being supported in an insulating matrix 37, the front surface 19 of said transfer plate 30 having thereon a plurality of potential wells 32 defined by insulating walls 15, each said potential well 32 constituting a pixel, a deformable reflecting membrane 34,36 spanning said potential wells 32, a metal coating 36 on said membrane 34, means providing a potential on said metal coating 36, means providing a source of electrons 17 for impacting the rear surface 52 of said charge transfer plate 30, means providing an image defining charge distribution to one of said last two means to provide an image defining deformation to said membrane 34 at each pixel, and wherein a secondary electron emitting coating 31 is applied to the rear surface 52 of said charge transfer plate 30 to increase the secondary emission of electrons therefrom and a grid electrode 44a is carried by an insulator structure 72 on the rear surface 52 of said charge transfer plate 30 and having insulating walls 15 corresponding to the insulating walls 15 defining each pixel on the front of the charge transfer plate 30.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/734,289 US5287215A (en) | 1991-07-17 | 1991-07-17 | Membrane light modulation systems |
| US07/734,289 | 1991-07-17 | ||
| PCT/US1992/005822 WO1993002375A1 (en) | 1991-07-17 | 1992-07-10 | Membrane light modulating systems |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2113275A1 true CA2113275A1 (en) | 1993-02-04 |
Family
ID=24951061
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002113275A Abandoned CA2113275A1 (en) | 1991-07-17 | 1992-07-10 | Membrane light modulating systems |
Country Status (6)
| Country | Link |
|---|---|
| US (2) | US5287215A (en) |
| EP (1) | EP0678197A1 (en) |
| JP (1) | JPH06511567A (en) |
| AU (1) | AU661501B2 (en) |
| CA (1) | CA2113275A1 (en) |
| WO (1) | WO1993002375A1 (en) |
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| US8963159B2 (en) | 2011-04-04 | 2015-02-24 | Qualcomm Mems Technologies, Inc. | Pixel via and methods of forming the same |
| US8659816B2 (en) | 2011-04-25 | 2014-02-25 | Qualcomm Mems Technologies, Inc. | Mechanical layer and methods of making the same |
| US8736939B2 (en) | 2011-11-04 | 2014-05-27 | Qualcomm Mems Technologies, Inc. | Matching layer thin-films for an electromechanical systems reflective display device |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US3385927A (en) * | 1964-08-26 | 1968-05-28 | Stromberg Carlson Corp | Display device utilizing a medium that alters the degree of refraction of light |
| US3463572A (en) * | 1966-10-21 | 1969-08-26 | Perkin Elmer Corp | Optical phase modulation apparatus |
| US3667830A (en) * | 1970-04-08 | 1972-06-06 | Stromberg Datagraphix Inc | Display system utilizing a selectively deformable light-reflecting element |
| US3701586A (en) * | 1971-04-21 | 1972-10-31 | George G Goetz | Light modulating deflectable membrane |
| US3746785A (en) * | 1971-11-26 | 1973-07-17 | Bendix Corp | Deflectable membrane optical modulator |
| US3886310A (en) * | 1973-08-22 | 1975-05-27 | Westinghouse Electric Corp | Electrostatically deflectable light valve with improved diffraction properties |
| FR2274992A1 (en) * | 1974-06-14 | 1976-01-09 | Thomson Csf | ELECTRO-OPTICAL CONVERTER AND OPTICAL RECORDING SYSTEM INCLUDING SUCH A CONVERTER |
| FR2360953A1 (en) * | 1976-04-26 | 1978-03-03 | Izon Corp | LIGHT AMPLIFIER DEVICE |
| US4087810A (en) * | 1976-06-30 | 1978-05-02 | International Business Machines Corporation | Membrane deformographic display, and method of making |
| EP0046873A1 (en) * | 1980-09-02 | 1982-03-10 | Texas Instruments Incorporated | Deformable mirror light modulator |
| EP0139991A3 (en) * | 1983-09-08 | 1986-06-25 | Texas Instruments Incorporated | Optical system for projection display using spatial light modulator (1111111) |
| GB8422262D0 (en) * | 1984-09-04 | 1984-10-10 | Green M | Variable transmission optical device |
| US4752714A (en) * | 1986-03-10 | 1988-06-21 | Tektronix, Inc. | Decelerating and scan expansion lens system for electron discharge tube incorporating a microchannel plate |
| US5214347A (en) * | 1990-06-08 | 1993-05-25 | The United States Of America As Represented By The Secretary Of The Navy | Layered thin-edged field-emitter device |
| US5237180A (en) * | 1991-12-31 | 1993-08-17 | Eastman Kodak Company | High resolution image source |
-
1991
- 1991-07-17 US US07/734,289 patent/US5287215A/en not_active Expired - Lifetime
-
1992
- 1992-07-10 CA CA002113275A patent/CA2113275A1/en not_active Abandoned
- 1992-07-10 JP JP5502875A patent/JPH06511567A/en active Pending
- 1992-07-10 WO PCT/US1992/005822 patent/WO1993002375A1/en not_active Application Discontinuation
- 1992-07-10 EP EP92915928A patent/EP0678197A1/en not_active Withdrawn
- 1992-07-10 AU AU23386/92A patent/AU661501B2/en not_active Ceased
-
1993
- 1993-12-16 US US08/168,760 patent/US5471341A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| AU661501B2 (en) | 1995-07-27 |
| US5287215A (en) | 1994-02-15 |
| EP0678197A1 (en) | 1995-10-25 |
| EP0678197A4 (en) | 1994-03-30 |
| AU2338692A (en) | 1993-02-23 |
| US5471341A (en) | 1995-11-28 |
| WO1993002375A1 (en) | 1993-02-04 |
| JPH06511567A (en) | 1994-12-22 |
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