WO2003048848A1 - Realisation d'ecrans aclma monolithiques ou de type monolithique, robustes et de grande taille avec large angle de vue - Google Patents

Realisation d'ecrans aclma monolithiques ou de type monolithique, robustes et de grande taille avec large angle de vue Download PDF

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Publication number
WO2003048848A1
WO2003048848A1 PCT/US2001/045234 US0145234W WO03048848A1 WO 2003048848 A1 WO2003048848 A1 WO 2003048848A1 US 0145234 W US0145234 W US 0145234W WO 03048848 A1 WO03048848 A1 WO 03048848A1
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WIPO (PCT)
Prior art keywords
monolithic
amlcd
luminance
chromaticity
display
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PCT/US2001/045234
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English (en)
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WO2003048848A8 (fr
Inventor
Raymond G. Greene
J. Peter Krusius
Donald P. Seraphim
Dean W. Skinner
Boris Yost
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Rainbow Displays Inc
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Application filed by Rainbow Displays Inc filed Critical Rainbow Displays Inc
Priority to PCT/US2001/045234 priority Critical patent/WO2003048848A1/fr
Priority to EP01993194A priority patent/EP1346254A1/fr
Priority to CN01806754A priority patent/CN1418324A/zh
Priority to KR10-2003-7003152A priority patent/KR20040043088A/ko
Publication of WO2003048848A1 publication Critical patent/WO2003048848A1/fr
Publication of WO2003048848A8 publication Critical patent/WO2003048848A8/fr

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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133504—Diffusing, scattering, diffracting elements
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/13336—Combining plural substrates to produce large-area displays, e.g. tiled displays

Definitions

  • This invention pertains to the design and manufacture of large flat-panel electronic displays and, more particularly, to the manufacture of AMLCD type, flat -panel displays assembled in a single monolithic or monolithic-like assembly, strengthened for structural integrity, corrected for brightness and hue variations due to optical or electro-optical aberrations and structural non- uniformities, equipped with lighting means and optical means that provide large view angles while improving acuity and contrast, and thin film wiring in said display that is designed to avoid or compensate for non-uniformities in pixel response, brightness, and chromaticity .
  • AMLCD active matrix liquid crystal display
  • the present invention describes unique designs and methods for fabricating or operating large monolithic, or monolithic- like, AMLCDs of both color and gray-scale types using many of the techniques developed for large tiled flat-panel displays (FPDs) .
  • FPDs large tiled flat-panel displays
  • this invention describes most of the techniques and methods in the context of AMLCDs, many of them can be applied to other transparent, light-valve type FPDs.
  • Characteristic of such displays is that light from a uniform, back light source is transmitted through the display assembly towards the viewer located on the front side.
  • the light valves control the amount of primary light rays transmitted through the apertures of the sub-pixels.
  • the transmitted light from the sub-pixels mixes to form all desired brightness and hue combinations (color space) before it reaches the viewer located at the predefined viewing distance from the display.
  • Robust display glass laminates can be made using adhesive films with a preferred thickness in the range from 25 to 250 ⁇ m, and optimized in compliance.
  • the monolithic display panel can, for example, be laminated between glass cover and back plates without stressing the birefringent AMLCD glass and deforming the LC cell gap.
  • Patent 5,867,236 "CONSTRUCTION AND SEALING OF TILED FLAT-PANEL DISPLAYS", copending United States Patent Application Serial No. 09/490,776, United States Patent Application Serial Nos. 09/368,921 and 09/369,465 show laminate structures which accomplish the desired result.
  • Laminate structures for a prototype 800x600 SVGA 38.6" diagonal tiled display are also shown in copending United States Patent Application Serial No.
  • the laminate is designed with a symmetry about the image creation plane in the AMLCD glass sandwich (LC layer) , which contains the weakest link to shear or bending.
  • This link is formed by a narrow adhesive seal, typically about 5 ⁇ m thick, that joins the thin-film-transistor (TFT) substrate to the color-filter (CF) substrate around the perimeter.
  • the width of this seal may be as narrow as 1 mm, or less, and it may be the only mechanical link, other than surface tension of the LC liquid layer, that holds the substrates together during handling, assembly, and field use induced stresses.
  • An external full face seal material in dry film form, of a preferred thickness range, is used to bond the robust glass cover and back plates on both sides of the AMLCD sandwich to increase the bending strength.
  • This preferred design provides a substantially increased resistance to bending, and thereby decreasing the impact of any unintentional stresses exerted on the narrow seal.
  • the preferred thickness of the adhesive films between cover and back plates and the AMLCD sandwich are dependent on whether or not a mask is used on the back plate to set the light collimation angles. The relationships of these angles are shown in detail in United States Patent Application Serial No. 09/396,142 and Serial No. 60/153,962, filed Sept. 15, 1999, and United States Patent Application Serial No. 09/322,047, filed May 28, 1999.
  • aperture masks are not needed to keep light rays away from the seams in monolithic displays, the thickness requirement for the adhesive may be relaxed for the monolithic display laminates. Aperture masks may still be desirable in monolithic displays to optimize the acuity and contract of displayed images. Alternatively, they may be removed from the display stack, if other light collimation means are preferred.
  • Back or cover plates may be made of standard glass, such as Corning 1737 that is commonly used in the AMLCD industry.
  • Today's glass sheet thicknesses have been standardized to 0.5, 0.7 and 1.1 mm. Any of these glass thicknesses may be used in display assembly lamination. Small glass thicknesses allow a smaller radius to be used in an adhesive extrusion process. This translates into a smaller probability for trapping bubble defects.
  • Lamination produces a robust assembly with a continuous refractive index and a well matched thermal expansion compared to the conventional display glass substrates.
  • the robustness is improved by increasing the cross-sectional inertia to bending stresses, it is also important to maintain the neutral axis in the LC image plane, in which the epoxy seal joins TFT and CF substrates. This can be accomplished by making the thickness of the adhesive films between the cover and back plates and the AMLCD sandwich equal. For this reason, the laminate is designed to be approximately symmetrical around the LC plane. Consequently, the thickness of both the glass cover and the plates is chosen to lie in the range of 1.1 mm (or greater) .
  • the transparent regions in the sub-pixel compared the total area (aperture ratio) are substantially larger in monolithic AMLCDs (60-80%) compared to tiled FPDs (30-50%) due to the space required by the seam. This has been described in Patent Application Serial No. 60/153,072.
  • the viewing angles in monolithic displays are generally not as wide as desired, and the image acuity is highly dependent on the back light, which is normally diffuse.
  • One published method under development for improving the viewing angles is discussed in the following reference (Information Display Magazine Feb. 1999 by Joel Pollock "Sharp Microelectronics' Approach to New-Generation AMLCDs").
  • Monolithic flat-panel displays made in accordance with known liquid crystal display (LCD) technologies for applications in portable computers (notebook) and desktop monitors are limited in size due to manufacturing yields and cost. This limitation arises partly from the trends towards ever higher resolutions, rather than optimizing the designs and manufacturing or inexpensive, larger, consumer TV displays with diagonal sizes between 20 and 50". Assembly tolerance requirements for tiled displays are stringent and will become more severe with the reducing size of the displays. The practical range of sizes for tiled displays at acceptable resolutions is currently estimated to be at about 30" or larger. Thus the range of interest for application of direct view monolithic AMLCDs to consumer TVs spans from less than 20" to about 30". Monolithic display sizes much beyond 30" are likely to be too expensive for mass productions. At such sizes they will be in direct competition with projection displays, direct view plasma FPDs, and tiled AMLCD FPDs.
  • flat-panel digital TVs in the 24 to 40" size range with resolutions from SDTV (480 lines) to HDTV (720 to 1080 lines) are chosen as illustrations for the preferred invented design elements.
  • T-V curve determines luminance of each sub-pixel light valve via the discretized voltage across the pixel, the LC cell in an AMLCD. Color is produced by having the light rays pass through color filter layers placed on top of the sub-pixel apertures. Three separate color filters for the red, blue and green (RGB) primary colors are the most common choice. Additive mixing of the primaries, properly weighed, produces all brightness and hue combinations in the color space. Unless otherwise noted, the T-V curve for each sub-pixel is here considered to be an effective relationship that includes the entire display system response from the electronic drive signal to the resulting luminance.
  • the flat-panel display structures targeted in this invention include monolithic and monolithic-like units in which pixels are addressed in a matrix fashion but accessed from two edges, a single edge, or more than two edges of the array. While two-edge accessing is most common, other alternatives may be preferable for specific applications. Generally these different access configurations give rise to interconnect lines with a different length and cross-over count depending on the location of the pixel within the array. These differences alter the electrical characteristics of the pixels, for example through the most significant impact is on the kick-down effect that changes the LC cell voltage after charging from the column line via the local coupling capacitance between the cell and the row line.
  • both the cross over capacitance between the row and column lines and the gate-to-drain capacitance of the TFT contribute to this coupling.
  • this kick-down voltage may be as large as 2V, i.e., a significant fraction of the column voltages range. It is possible correct for the kick-down voltage by adjusting the pixel drive signals, if this effect is uniform over the array. If the kick-down voltage varies as a function of pixel location, for example because of array accessing, these corrections will become much more difficult . Techniques that work for such conditions will be described in this invention.
  • ⁇ for designing large, robust monolithic and monolithic- like displays having good brightness and contrast over a wide range of viewing angles.
  • These techniques include controlling the layout of the pixel array and its access circuits that modify the electrical characteristics in order to minimize undesirable optical, electro-optical, and ambient light aberrations and any electronic anomalies creating visually perceptible discontinuities or boundaries. These artifacts are reduced to levels that allow for better color correction.
  • optical components such as collimators, light enhancing films, diffusers, screens, polarizers and masks are described.
  • the resulting displays present luminance and chromaticity outputs from areas of originally varying optical response that become uniform within the tolerances of the human visual system.
  • an object of this invention to provide compensating means for correcting for the effects induced by any other optical, electro-optical, mechanical, or structure related anomalies in large monolithic or monolithic-like LC displays.
  • These include, for example, the variations in the cell gap, which is determined by the size and placement distribution of spacer balls or fiber and by stresses generated within the assembly. Chromaticity and luminance variations at the boundaries will either be corrected or smoothed over a predetermined width, so that residual variations are thus suppressed and boundaries or seams will become visually imperceptible.
  • the final object of this invention is the electronic correction of the brightness of all pixels across the interior of the pixel array, whether tiled or monolithic, so that the display presents a visually uniform luminance and chromaticity to the viewer. Such corrections are made for each display assembly and are unique to that display.
  • FIGURE 1 displays a cross-sectional schematic view of a portion of a large, monolithic, AMLCD, flat-panel display with a robust structure, optical enhancements, and lighting means for consumer applications;
  • FIGURE 2 shows a cross-sectional schematic view of the preferred embodiment of the light collimating illumination source with the associated monolithic, flat-panel display assembly superimposed on the top;
  • FIGURE 3 is a plan view of three embodiments of light collimating lattice geometries: (a), (b) and (c) for square, triangular, and hexagonal geometry, respectively;
  • FIGURE 4 is a diagram showing the light collimating characteristics, relative light intensity as a function of the off-normal angle, for various light collimating elements: lattice collimator, an optical collimator, and a diffuser being shown;
  • FIGURE 5 shows the calculated light transmission efficiency as a function of the off-normal angle for light collimation by a cylindrical lattice with a varying angular efficiency resulting from absorbing lattice surfaces with various height to radius ratios, the insert showing the lattice cell geometry and its geometrical parameter values;
  • FIGURE 6 shows the calculated angular light transmission efficiency as a function of the off-normal angle for a variety of lattice collimator designs of interest to large monolithic-like displays, the insert showing the lattice cell geometry and its geometrical parameter values;
  • FIGURE 7 illustrates a cross-sectional schematic view of an alternative embodiment of a large monolithic-like AMLCD in contrast to the design shown in FIGURE 1;
  • FIGURE 8 presents a topographical map of typical color shifts and color graduation variations resulting from a variety of mechanisms in a large monolithic-like, AMLCD, flat-panel display assembly;
  • FIGURE 9 illustrates access wiring from two edges of the matrix addressed pixel array in a monolithic AMLCD, column lines being accessed from the top and row lines from the bottom using special row access lines;
  • FIGURES 10a and 10b illustrate pixel array access wiring from a single edge of the matrix addressed pixel array in a monolithic AMLCD, FIGURE 10a showing continuous column lines with row access lines connected at tap points to row lines, and FIGURE 10b showing continuous row lines and continuous common lines with column access lines connected at tap points to column lines;
  • FIGURE 11 shows an equivalent circuit model for a liquid crystal cell within a sub-pixel for a typical AMLCD
  • FIGURE 12 shows the result of a simulation of the kick-down voltage effect in the liquid crystal cell after the turn-off of the TFT due to coupling capacitance between the cell row and column lines in a typical AMLCD with a 1 mm pixel pitch
  • FIGURE 13a shows the simulated data voltage for pixels subject to a given excitation level after the voltage kick-down effect as a function of the distance from the driver circuit connected to one edge of the row line;
  • FIGURE 13b shows the simulated data voltage for pixels subject to a given excitation level after the kick-down effect as a function of the location of the pixel with respect to the row line tap point located in the middle of the row line;
  • FIGURE 14 illustrates the layout of a field shield electrode placed between the liquid crystal cell electrode and thin film wiring in order to equalize capacitive coupling of all LC cells;
  • FIGURE 15 illustrates distributed or discrete capacitance along column interconnections in order to equalize the apparent capacitance seen by the liquid crystal cells
  • FIGURE 16 illustrates distributed or discrete capacitance along a row in order to equalize the apparent capacitance seen by the liquid crystal cells
  • FIGURE 17 illustrates distributed or discrete capacitance along column fan-out lines in order to equalize the apparent capacitance seen by the liquid crystal cells
  • FIGURE 18 illustrates distributed or discrete capacitance along row access lines in order to equalize the apparent capacitance seen by the liquid crystal cells
  • FIGURE 19 illustrates the adjustment of row-to-liquid crystal cell coupling capacitance in order to control kick-down voltage variation for pixels along said row line
  • FIGURE 20 depicts a system level circuit diagram for two AMLCD cells with single edge addressing for use in circuit simulation of equalization of cell voltage levels and waveforms;
  • FIGURE 21 shows the normalized transmission (proportional to luminance) of liquid crystal cell as a function of cell gap for typical red, green, and blue light;
  • FIGURE 22 depicts the normalized luminance of a typical LC cell as a function of the cell gap height-to-wavelength ratio
  • FIGURE 23 illustrates a normalized effective T-V for an LC cell in a typical AMLCD
  • FIGURES 24a-24c show the normalized brightness data values for a row of pixels, FIGURE 24a for a row of RGB sub-pixels for uncorrected data, FIGURE 24b for a row of RGB sub-pixels for corrected data and FIGURE 24c for a row of RGB sub-pixels corrected for uniform luminance; and
  • FIGURE 25 illustrates a block diagram of one embodiment of a luminance and chromaticity correction circuit controlled by pixel correction control unit for a single pixel, sets of pixels, or all pixel corrections.
  • the present invention pertains to the manufacturing and assembly of large monolithic, monolithic-like, or tiled AMLCD flat-panel displays with diagonal sizes from about 20" to 40", and more specifically to: hardware structures; assembly designs; optical enhancements; control, drive and correction electronics; and back light systems that facilitate wide view angles in consumer electronic SDTV or HDTV applications.
  • the present invention also describes corrective means for brightness and color discontinuities and their topographical variations that are objectionable to the viewer and that require special optical designs and the ability to correct the display with unique algorithms and control electronics .
  • FIGURE 1 A cross section of the embodiment of an assembled robust laminated large monolithic AMLCD is shown in FIGURE 1.
  • the cover plate 102 contains a mask 104a on one side and polarizer 106a on the opposite side.
  • a screen 108 is adhesively bonded to the polarizer 106a.
  • a back plate 110 contains a second mask 104b on one side and a polarizer 106b on the opposite side.
  • the display 100 is sandwiched between the cover plate 102 and the back plate 110 and is adhesively bonded over the full face with compliant polymer films, 114 and 116 respectively.
  • the light box 118 also contains a light collimating mechanism 120, a light enhancing film 122, and a light diffuser 124.
  • a specific light box and light collimation mechanism are described in copending United States Patent Applications RDI-125, RDI-126, RDI-127, and RDI- 112, respectively that are herein included by reference.
  • FIGURE 2 a cross-sectional view of a monolithic flat-panel display assembly is shown, generally at reference numeral 130.
  • This assembly also contains the inventive collimating lattice 120.
  • the assembly 130 utilizes a conventional light box 118 in conjunction with the collimating lattice 120 and the robust laminated structure 113 (FIGURE 1) .
  • a conventional light source for an LCD display normally consists of the following four elements: a light box 118 housing with one or more fluorescent lamps 132, a diffuser sheet 120, and an optical collimator (brightness enhancing film) 122 and a reflecting cavity (not shown) .
  • a fifth element is added to the light source in this invention: a unique collimating lattice 120.
  • the light collimating lattice 120 is used to efficiently produce the collimated light that is needed in order to generate a sharp image at wide view angles on the large flat-panel display.
  • H and D and choices for their values will be discussed in detail hereinbelow.
  • FIGURE 3 plan views of three geometric shapes of light collimating lattice assemblies are shown. These are desirable embodiments of the method described in the current invention.
  • the upper, middle and lower sections of FIGURE 3 show a lattice of square cells 136, triangular cells 140, and hexagonal or honeycomb cells 150, respectively.
  • the lattice cells 136, 140, and 150 can be characterized by their typical width W of about 3-5 mm, 132, 142, and 152, respectively.
  • the lattices 136, 140, 150 may be constructed from any material that is thin compared to the size of the pixel. Such materials include plastic, paper, aluminum, or other metals.
  • the interior surfaces of the cells in the lattice may be plated, dyed, painted, or treated in any other way to produce surfaces with a uniform but low specular and diffuse reflectivity for all wavelengths contained in the visible spectrum of light originating from the light source.
  • the material itself can be non-reflective.
  • the thickness of the cell wall in the lattice, that is now shown in FIGURE 3, should be minimized to permit as much light as possible to pass through the lattice 136, 140, 150.
  • a commercially available aluminum honeycomb lattice is spray or dip painted with the preferred paint.
  • FIGURE 4 there is shown a graph 160 of the relative collimating efficiencies of various light collimating elements of the light source shown in FIGURE 2: diffuser 124, optical collimator, 122, and lattice collimator 120.
  • an ideal diffuser 124 disperses the light from the lamps 132 forward in all directions, at a uniform brightness. Light intensity should be constant at all angles measured with respect to line 134 normal to the front or rear surface planes of the diffuser 124. Light of this nature is referred to as Lambertian.
  • the light from the lamps 132 first passes through diffuser 124 and then passes through optical collimators or brightness enhancing film 122.
  • An improved lattice collimator with a substantially increased light can be achieved by treating the internal cell internal surfaces in the lower section (closer to the light source) with a highly specular reflective material, while keeping the low specular and diffuse reflectivities in the upper section.
  • the angular intensity factors are shown in FIGURE 6 for a variety of light collimator lattice designs varying the reflective and non-reflective sections of the lattice cell walls.
  • a preferred light collimation design may be chosen that balances light intensity with good visual image acuity or sharpness at desired view angles.
  • the inventive designs project more light forward by virtue of the reflective portion of the lattice cells, but can also achieve desired sharply cut-off angular distribution for application in tiled FPD's, in which wide angle light rays should be kept away from seams.
  • a highly efficient light recirculation mechanism within the light box is preferable for this collimation technique .
  • FIGURE 7 An alternative effective optical stack is shown in FIGURE 7.
  • a third polarizer 160 has been inserted on the viewer's side of the screen 108 in order to adjust and counteract the ambient light passed into the optical stack from the outside and being reflected back from various interfaces within the optical stack. This undesirable reflective light would otherwise reach the viewer superimposed on the displayed image and therefore degrade the image modulation and contrast.
  • the mask 104b (FIGURE 1) on the back plate 110 (FIGURE l) is not employed in the design shown in FIGURE 7, because light collimation has been optimized tailoring the lattice light collimation mechanism 120 placed within the light box 118.
  • FIGURE 7 An additional embodiment, not shown in FIGURE 7, is identical to this design except that it has no masks (104a, 104b) on either plate (102, 110) . If masks are used on the cover plate, a slight misregistration of the pixels with respect to the mask 104a will cause color shifts in a tiled display due to the slight variations in the position of sub-pixel and mask apertures. Such color shifts will be smaller in the image view plane of a monolithic AMLCD' s, but any small angular variations in lighting in the assembly cross section may still produce visually disturbing artifacts.
  • FIGURES 1 and 7 also feature a light box 118 that provides the assembled FPD laminate structure 113 with a desired uniform distribution of light and light collimating angles, both of which can be optimized for the chosen pixel size and optical stack height.
  • a light box 118 that provides the assembled FPD laminate structure 113 with a desired uniform distribution of light and light collimating angles, both of which can be optimized for the chosen pixel size and optical stack height.
  • the dark space between pixels will generally be much smaller. Therefore if a mask is used, the mask stripe dimensions can be chosen to be very small. Consequently the mask will have only a minimum impact on the light-power efficiency.
  • light collimating angles in the back light can be designed to optimize the visual acuity, brightness, and contrast for wide view angles using a screen 108 that is chosen for a monolithic display without physical seams.
  • FIGURE 8 There are other mechanisms other than physical or electronic seams that may degrade the image. This is illustrated in FIGURE 8.
  • One of them is local stress that can change the cell gap. Stress variations are likely to occur near the perimeter of the display, where panel 170 is attached to the frame 172.
  • Another potential location is near an imposed stress or deformation induced by a fastener, such as a screw 171. If the cell gap is decreased in any area that area will display a blue gray color tint. Alternatively if the cell gap is increased over a surrounding area that area becomes brownish in color.
  • the polymer films encasing and sandwiching the monolithic AMLCD panel should have a very low elastic modulus, preferably in the range of 1,000 PSI, be thick and fludic enough during the encasing process, so that the display panel 112 can uniformly relax to a low stress level .
  • This encasing process and design of the cross section allows the as manufactured AMLCD panels to carry a small bend or warp or have a slightly out-of-flat surface. Flatness and the stress issues at the seal generally increase with the size of the display panel. Therefore increasing the robustness of the cross section of the laminate with cover and back plates is essential for large monolithic AMLCD FPDs in order to stabilize their mechanical cross section and especially the cell gap.
  • the residual impact of stresses in the constrained areas of the AMLCD laminate can be corrected by the methods disclosed in RDI-118 and our copending United States Patent Application Serial No. 08/649,240 filed May 14, 1996, if they cause small residual brightness or hue shifts.
  • the non- uniform cell gap locally alters the color space formed by the set of all possible tristimulus values.
  • a uniform gray scale response for all primaries and their luminance levels is the preferred goal .
  • the same material and thickness should be used in the perimeter outside the pixel array in order to precisely control the cell gap in an AMLCD.
  • This combination of a single thickest color filter layer together with the diameter distribution of spacer balls or fibers determines the cell gap and the cell gap uniformity.
  • This design determines that the thin-film-transistor (TFT) and the color filter (CF) substrates will be substantially parallel to each other, thus determining a substantially uniform cell gap over the entire pixel array of the display.
  • TFT thin-film-transistor
  • CF color filter
  • FIGURE 8 Also illustrated in FIGURE 8 is a stress effect induced by combination of the polarizer and cover plate glass. This may cause visible optical birefringence effects 174, when the AMLCD is operated in the dark state. Large streaky white areas superimposed on the desired image and spread over broad regions of the FPD are the visual impact on this effect. These large area effects are caused by the non-uniform stresses in the glass that are thought to arise from the directionality of the cooling, when the glass sheet is manufactured. These stresses will be optically enhanced, when the polarizer is attached. The brightness variations of these regions areas can be corrected and smoothed using the software and electronics.
  • FIGURE 8 Still another effect demonstrated in FIGURE 8 is the effect of spacer balls clustering 176 on light transmission. This type of defect increases with the panel size and with decreasing panel glass thickness.
  • the layout design of the cell is also impacted by this effect.
  • the flexibility of the large glass sheets and ability of the liquid crystal material to flow across a large monolithic panel allows the spacers to relocate and collect into clusters during manufacturing as well as in field use.
  • the thick cover and back plates decrease the flexibility by approximately a factor of 8 with the lamination of thicker cover and back plates into the assembly (e.g., 1.1 mm thickness).
  • this invention covers a cell design with a single thickest color filter in all dark space areas to make the TFT and CF glass plates parallel.
  • spacer balls are then only free to move within the aperture of a sub-pixel, which greatly minimizes clustering spacer ball or fiber clustering despite the larger pixel pitch.
  • the spacer balls in the color filter area will be pinned down by the stiff laminate assembly and thus unable to migrate into clusters.
  • FIGURE 8 Finally shown in FIGURE 8 are seam like boundaries 178 that arise from the impact of small electronic variations on brightness and hue over the pixel array.
  • a variety of mechanisms can cause electronic discontinuities over large monolithic AMLCD panels. The most probable of these to be visible are brightness and hue shifts at the boundary 178 between two pixel array regions driven by different row or column driver chips. Therefore either a column driver boundary (usually vertical) or a row driver boundary (usually horizontal) within the pixel array may appear.
  • Brightness and hue differences especially if they appear in a recognizable static pattern, can be induced by data voltage differences as small as 5-10mV. Larger pixel drive voltage differences arising from dynamic charge effects on row and column lines will be tolerable, if the displayed images change rapidly.
  • Display designs that access the matrix addressed pixel from opposite edges of the array as shown in FIGURE 9, or with access from a single edge, as diagramed in FIGURE 10 will show electronic artifacts in particularly disturbing ways. Since the interconnect layout and distances from the driver chips to individual pixels vary much more than in conventional matrix addressed displays with array access from two adjacent edges, pixel drive signal delays and waveforms may vary significantly from pixel to pixel. Row pulse variations have less impact on pixels because row lines generally select pixels rather than provide the data that sets the light valve to one of its discrete levels, usually to a precision of 8 bits or 256 levels. Column pulse levels must be controlled to the precision of the least significant bit in the given timing window.
  • the least significant bit is about 20 mV for uniformly spaced levels.
  • pixel data voltage waveforms are affected by local capacitances within each pixel and distributed global capacitances in the column and row circuits (FIGURE 11) .
  • One of the most significant capacitive coupling effects produces the so-called data voltage "kick-back" or “kick-down” effect. It reduces the voltage stored into the cell that will be stored for the entire frame time until the next data voltage is written.
  • the magnitude of the kick-down voltage is determined by the design of the display, and it may in a typical AMLCD be as large as 2V. If these capacitive coupling effects on LC cell voltages are substantially uniform over the entire pixel array, they can easily be compensated for by adjusting data voltages, common voltages, or reference voltages that are used by the digital-to- analog (D/A) converters to produce the actual row column voltage waveforms.
  • D/A digital-to- analog
  • the global distributed capacitance may vary significantly even if local intra-cell capacitances are uniform.
  • the resulting pixel drive voltage levels and waveforms will produce luminance and chromaticity over the pixel array. If such variations would occur smoothly over many pixel pitches they will not be as readily visible as in cases where adjacent pixels are affected or patterns emerge. Because of the regular layout of row and column lines, and any access lines from driver chips to row and column lines present regular patterns, most unconventional array access configurations are likely to produce visible patterns in the brightness and the hue of the display that are objectionable to the viewer.
  • the kick-down voltage in an AMLCD is used as the illustrative example.
  • the kick-down voltage is determined by the ratio of the coupling capacitance and the cell capacitance and multiplied by the magnitude of the voltage swing between the row and column lines, all of which are quantities local to the pixel in question (FIGURE 12) .
  • the kick-down voltage also depends on the impedance of the row and column drive circuits as seen by the pixel in question. This impedance is dominated by the distributed capacitance of the row and column lines.
  • Capacitances arise from metal interconnect interactions with other metal interconnect lines on the same or different level, all of which are located on the TFT substrate, or from interactions with the conductive but transparent indium-tin-oxide (ITO) electrodes, one of which is located on the TFT substrate and the other on the CF substrate.
  • ITO indium-tin-oxide
  • the magnitude of the kick-down voltage of an LC cell increases with the distance of said pixel from the row and column driver chips in a conventional matrix addressed AMLCD with access from two orthogonal edges (FIGURE 13a) .
  • the magnitude of the kick-down voltage also depends on the distance of the pixel from the row or column tap point (FIGURE 13b) .
  • the kick- down voltage is largest in LC cells at the tap points, while increasing with distance for other pixels.
  • Typical amounts for the kick-down voltage variations in today's AMLCD ' s are below 50 mV. While such variations for conventional two-edge matrix addressing are gradual over the pixel array and therefore not necessarily visible, patterns in the magnitude of the kick-down voltages will be introduced for unconventional access wiring. Such patterns may become clearly visible during normal drive voltage uniformities in today's AMLCD ' s . Resistive and inductive line effects have much less impact. Therefore any compensation or equalization is best done by adjusting the capacitances in the row and column drive circuits from the driver chips to the pixels.
  • metal-to-metal or metal -to- ITO overlap capacitances on the same substrate are about 30 times larger than metal-to-ITO capacitance with conductor located on opposite substrates.
  • the former types of capacitances are thus more effective in adjusting capacitances.
  • each sub-pixel aperture such that its capacitive interactions with other conductive materials becomes essentially equal. This can be accomplished rearranging the layout of the sub-pixel, adjusting distances to proximate conductors, and inserting grounded or floating field shields between the sub-pixel and adjacent conductive structures (FIGURE 14) .
  • each sub-pixel Design the layout of each sub-pixel such that the total cell capacitance, including the LC capacitance and any storage capacitors used to stabilize the cell voltage, as well as the cell to row line coupling capacitance, including TFT gate-to- drain and gate-to-source capacitance, as applicable, are equal in all pixels. The best way to achieve this is to make all cell layouts identical.
  • These capacitances include line body components, fringing fields, and overlap capacitances that depend on the layout of said access lines. While such fan-out lines generally have a very simply layout with few, if any crossovers, in FPD's with two-sided or four-sided pixel array access, layouts especially for single sided access are very complex. Both line lengths and the number and geometry of line-to-line crossovers varies greatly. As a consequence the total distributed line capacitance also will vary. Equalization can be done by adjusting the width of the line, adjusting the line spacing, and adding additional overlap capacitance over the length of the line. Metal -to-metal overlaps provide the most area efficient adder.
  • Each row access line shall then be connected to one row line at a tap point within the pixel array.
  • row access line lengths will vary from zero to the full height of the pixel array.
  • Equalization can be done by extending row or column lines beyond the tap points, adjusting line width, adjusting the line spacing, and adding additional overlap capacitances over the length of the line either in discrete chunks or as a continuous structure. Equalization should be done such that the row or column drive circuit impedance from the pixels connected to that row or column line become closely matched.
  • the first order goal is to match the total capacitance in said row or column drive circuit.
  • the refinements into the amount of added capacitance is its best distribution can be determined using circuit simulation. Metal - to-metal overlaps provide the most area efficient adder.
  • the final design technique for controlling pixel voltage level and waveform uniformities in large monolithic and tiled displays is based on adjusting the pixel layout as a means for compensation.
  • the magnitude of the kick-down voltage in the LC cell decreases with the distance to the tap point or the output lead of the driver chip, whichever is directly connected to the row line.
  • the magnitude of the kick-down voltage is proportional to the coupling capacitance between the LC cell and the row line. Therefore a reduction of the kick-down voltage with position can be compensated for by increasing the coupling capacitance monotonically with distance from the tap point or driver chip output lead (FIGURE 19) .
  • the coupling capacitance can be decreased as a function of cell location thus reducing the magnitude of the kick-down voltages.
  • the holding voltage curve can also be rigidly moved up or down, if the same amount of capacitance is deducted or added from the coupling capacitance of the sub-pixels along a chosen row line.
  • the easiest way to enhance or lower the coupling capacitance is to increase or decrease, respectively, the area of the overlap between the row and column lines serving the sub-pixel in question.
  • the gate-to-drain overlap capacitance can be used to adjust coupling capacitance or additional overlap capacitances can be placed into the dark areas of the sub-pixels. Whichever way is chosen, all of them lead to relatively simple changes in the layout of the sub-pixel or pixel .
  • a preferable approach to deciding which of the above capacitive equalization techniques to implement is best determined by circuit simulation.
  • a typical circuit diagram for these simulations is given in FIGURE 20. Simulations can predict drive voltage level and waveform variations and the emergence of any electronic gradients, steps, boundaries, or patterns over the pixel array.
  • the circuit simulator in combination with measured electrical data for the display, or alternatively simulated electrical data derived from two- dimensional electromagnetic field or device simulations, can be used to evaluate and fine-tune each of the above capacitive equalization techniques for the large monolithic or tiled FPDs in question.
  • the required circuit, electromagnetic field, and device simulation tools are well known to those familiar with modern integrated circuit design techniques.
  • the above non-uniformities originating from the details of the underlying electronic circuits are all second order effects that may, or may not be fully suppressed below the visual threshold of a critical viewer. It may be desirable to use additional luminance and chromaticity correction techniques and algorithms as disclosed in RDI-118 for smoothing visual artifacts in order to reach the final image quality level in a large monolithic or tiled display. A conservative approach is to make the correction data memory so large that every pixel can be corrected. This may still be economical for SDTV consumer applications with 852 x 480 pixels, and become impractical in HDTV AMLCDs with pixel array sizes of 1280 x 768, or larger. Hence, it will be advantageous to implement many of the above capacitive equalization techniques, so that the amount of brightness and color correction electronic circuitry and corrective computations required don't exceed cost budget allocated for these functions.
  • the typical simulated normalized luminances of the sub-pixels in an LCD cell are plotted as functions of the optical length of the cell gap for red 140, green 142 and blue 143 light with wavelengths of approximately 612, 542, and 487 nm, respectively.
  • the optical length was determined by the ratio of cell gap and the wavelength of light. This is the fundamental parameter that locally determines the optical retardation of light rays passing through the color valves and the light flux emanating from the cell . Therefore the balance between the primary color fluxes (color balance) changes spacially as the cell gap varies.
  • the typical simulated normalized luminances of the sub-pixels in a LCD cell are plotted as a function of the optical length of the cell gap for red 140, green 142 and blue 144 light with wavelengths of 612, 542, and 487 nm respectively.
  • the optical length was determined by the ratio of the cell gap and the wavelength of light.
  • T-V transmission-voltage
  • an effective T-V curve, or the difference between two effective T-V curves can therefore be described or approximated by dividing the domain of the function (or input code range) into finite pieces, and then describing each piece in a simple manner that is easy to compute in real time. Because of the smoothness and the generally small deviations from the nominal, one possibility is to describe each piece by a linear function (piece-wise linear approximation) . Then only the slope and offset would need to be stored to describe each piece. Consequently, the inverse transfer function (correction) for each piece would also be a linear function for each pixel or set of essentially identical pixels on the large monolithic display.
  • FIGURE 24a depicts the relative brightness values of RGB sub-pixels in a row of pixels from a boundary of an area of color non-uniformity in a large monolithic display.
  • a uniform gray scale combination defines the input signals to the primary color sub-pixels.
  • the boundary 34 is positioned to the left of the pixel row 60 in this figure and for example may be a contour line 48, 49, 174 in FIGURE 8.
  • the relative brightness values have been normalized into the usual 8 bit range, i.e., 0-255.
  • the RGB signal values in the interior of the area of color non- uniformity, 70/99/62 respectively, correspond to the nominal drive signal values for this sample gray scale field.
  • No corrections have been applied to the pixels in FIGURE 24a. The corrections will be applied in two steps: first considering hue and second brightness.
  • Electronic controls in color displays typically allow for 8 bit or 256 levels of "gray" for each primary color.
  • the corrections should be done to the frame buffer onto the frame data presented to the display. This eliminates boundaries related to hue variations or non-uniformities over the large display.
  • FIGURE 24c shows the relative brightness values of all the sub-pixels after they have been corrected for uniform luminance level everywhere.
  • This correction can be achieved by applying a correction bit map image (not shown in this figure) to each incoming frame before the latter is sent to the data drivers (usually column) of the display. All pixel data will then be changed in accordance with the teachings of this invention. Sub-pixel data is adjusted such that the spectral output from the display is that of the desired hue and brightness uniformly across the entire pixel array of the display.
  • the incoming video data is first temporarily stored in an input frame buffer memory.
  • the video data is read from the input frame buffer and correction data from the correction data memory under the control of the pixel correction control unit into the pixel data processor.
  • the correction data memory should be composed of nonvolatile memory, or of volatile memory initialized to values stored in auxiliary non-volatile memory, or be initialized with values calculated from values stored in non-volatile memory.
  • both incoming and corrected video data for each sub-pixel is comprised of a single n-bit integer number (usually 8-bit) , all pixel data processing only needs be done to n bit precision.
  • pixel data Once pixel data has been corrected, it can be sent directly into the display.
  • the pixel correction control unit is merged with the pixel data processing unit.
  • corrected pixel data is collected into an output frame buffer memory before it will be sent to the display.
  • Sub-pixel data corrections can be accomplished in many ways.
  • sub-pixels are grouped according to their effective T-V curve response and then each group is assigned a previously stored response function specific to that group.
  • Groups could, for example, include interior area sub-pixels for each bounded substantially uniform area, and edge pixels for each inner and outer edge of each boundary. As long as the number of groups is reasonable the amount of data for the response functions that must be stored in the correction data memory will be acceptable.

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Abstract

la présente invention concerne des techniques permettant de concevoir des écrans monolithiques ou de type monolithique, robustes et de grande taille (100) caractérisés par une grande luminosité, un bon contraste et une vaste éventail d'angles de visionnement. Ces techniques consistent à maîtriser l'agencement du réseau de pixels et ses circuits d'accès qui modifient les caractéristiques électriques dans le but de réduire les aberrations optiques, électro-optiques et de lumière ambiante indésirables, ainsi que toute anomalie électronique produisant des discontinuités ou limites visuellement perceptibles. Ces artéfacts sont ramenés à des niveaux autorisant une meilleure correction des couleurs. Est également décrite l'utilisation de composants optiques tels que collimateurs (120), films accentuateurs de lumière (122), diffuseurs (124), écrans (108), polariseurs (106a, 106b) et masques (104a, 104b).
PCT/US2001/045234 2001-12-03 2001-12-03 Realisation d'ecrans aclma monolithiques ou de type monolithique, robustes et de grande taille avec large angle de vue WO2003048848A1 (fr)

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EP01993194A EP1346254A1 (fr) 2001-12-03 2001-12-03 Realisation d'ecrans aclma monolithiques ou de type monolithique, robustes et de grande taille avec large angle de vue
CN01806754A CN1418324A (zh) 2001-12-03 2001-12-03 宽视角的大型的坚固的单片和单片状的amlcd显示器的结构
KR10-2003-7003152A KR20040043088A (ko) 2001-12-03 2001-12-03 넓은 시야각을 지닌 견고한 대형 모놀리식 및 모롤리식형ａｍｌｃｄ 디스플레이 장치 제작

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US5691788A (en) * 1995-01-06 1997-11-25 Samsung Electronics Co., Ltd. LCD having a polarization or diffusion plate with an irregularly coated first opaque material and a black matrix of a second opaque material
US6356322B1 (en) * 1996-09-30 2002-03-12 Fuji Photo Film Co., Ltd. Liquid crystal display system with improved contrast and less dependence on visual angle

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5691788A (en) * 1995-01-06 1997-11-25 Samsung Electronics Co., Ltd. LCD having a polarization or diffusion plate with an irregularly coated first opaque material and a black matrix of a second opaque material
US6356322B1 (en) * 1996-09-30 2002-03-12 Fuji Photo Film Co., Ltd. Liquid crystal display system with improved contrast and less dependence on visual angle

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