Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-05-17
2003-06-03
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S098000
Reexamination Certificate
active
06573961
ABSTRACT:
BACKGROUND OF INVENTION
1. Technical Field
The present invention relates to a high-brightness color liquid crystal display (LCD) panel with improved image contrast employing non-absorptive spectral filtering, light recycling among neighboring subpixels and ambient glare reduction, and also to methods and apparatus for manufacturing the same.
2. Brief Description of the Prior Art
Without question, there is a great need for flat display panels capable of displaying video imagery in both direct and projection modes of viewing. Examples of equipment requiring such display structures for direct viewing include notebook computers, laptop computers, a and palmtop computers, and equipment requiring such display structures for projection viewing include LCD projection panels and LCD image projectors.
In general, prior art color LCD display panels have essentially the same basic construction in that each comprises the following basic components, namely: a backlighting structure for producing a plane of uniform intensity backlighting; an electrically-addressable array of spatial intensity modulating elements for modulating the spatial intensity of the plane of backlight transmitted therethrough; and an array of color filtering elements in registration with the array of spatial intensity modulating elements, for spectral filtering the intensity modulated light rays transmitted therethrough, to form a color image for either direct or projection viewing. Examples of such prior art LCD panel systems are described in “A Systems Approach to Color Filters for Flat-Panel Displays” by J. Hunninghake, et al, published in SID 94 DIGEST (pages 407-410), incorporated herein by reference.
In color LCD panel design, the goal is to maximize the percentage of light transmitted from the backlighting structure through the color filtering array. However, using prior art design techniques, it has been impossible to achieve this design goal due to significant losses in light transmission caused by the following factors, namely: absorption of light energy due to absorption-type polarizers used in the LCD panels;—absorption of light reflected off thin-film transistors (TFTs) and wiring of the pixelated spatial intensity modulation arrays used in the LCD panels; absorption of light by pigments used in the spectral filters of the LCD panels; absorption of light energy by the black-matrix used to spatially separate the subpixel filters in the LCD panel in order to enhance image contrast; and Fresnel losses due to the mismatching of refractive indices between layers within the LCD panels. As a result of such design factors, the light transmission efficiency of prior art color LCD panels is typically no more than 5%. Consequently, up to 95% of the light produced by the backlighting structure is converted into heat across the LCD panel. Thus, it is impossible to produce high brightness images from prior art color LCD panels used in either direct or projection display systems without using ultra-high intensity backlighting sources which require high power supplies, and produce great amounts of heat necessitating cooling measures and the like.
The light transmission efficiency of prior art LCD panels has been severely degraded as a result of the following factors: absorption of light energy due to absorption-type polarizers used in the LCD panels; absorption of light reflected off thin-film transistors (TFTs) and wiring of the pixelated spatial intensity modulation arrays used in the LCD panels; absorption of light by pigments used in the spectral filters of the LCD panels; absorption of light energy by the black-matrix used to spatially separate the subpixel filters in the LCD panel in order to enhance image contrast; and Fresnel losses due to the mismatching of refractive indices between layers within the LCD panels. As a result of such light energy losses, it has been virtually impossible to improve the light transmission efficiency of prior art LCD panels beyond about 5%.
In response to the shortcomings and drawbacks of prior art color LCD panel designs, several alternative approaches have been proposed in order to improve the light transmission efficiency of the panel and thus the brightness of images produced therefrom.
For example, U.S. Pat. No. 5,822,029 entitled “Illumination System and Display Device” discloses a LCD panel construction comprising a broad-band CLC reflective polarizer (
32
) disposed between the backlighting structure (
10
,
12
,
30
and
34
) and a reflective color filtering structure (
18
in
FIG. 1A
) made from a pair of cholesteric liquid crystal (CLC) film layers, as shown in
FIGS. 1A and 1B
of the accompanying Drawings which are identical to
FIGS. 5 and 6
in U.S. Pat. No. 5,822,029. As shown in
FIG. 1A
, the reflective color filter structure (
18
in
FIG. 1A
) has a first layer with portions which reflect red, green and blue light while transmitting other colors ,and a second layer identical to the first layer but out of alignment therewith so that each region of the spectral filter transmits only one color of light from the light source of backlighting structure (illustrated in FIG.
1
C), while all other colors are reflected back towards the backlighting structure. During operation, the spectral components which are not transmitted through its respective subpixel structure, are reflected back through the broad-band CLC reflective polarizer (
32
) and recycled within the backlighting structure, after polarization state conversion in order to improve the light transmission efficiency of the LCD panel and thus the output brightness thereof.
In order to recycle light striking the TFT areas and wiring regions associated with each subpixel region on the LCD panel, U.S. Pat. No. 5,822,029 discloses the use of a reflective-type black matrix about the transmission apertures of the subpixels, realized placing a reflective material and a quarter-wave film (
36
and
38
in
FIG. 1B
) on a substrate attached to the layers of CLC reflective material.
In order to improve the viewing angle of the LCD panel, U.S. Pat. No. 5,822,029 also discloses in Col. 4, at lines 29-50 thereof, that a collimated light source m ay be used so that light emitted by the light source will fall within the angular acceptance bandwidth of the broadband CLC polarizer (
32
),
While U.S. Pat. No. 5,822,029 discloses an LCD panel construction having the above-described improvements, this prior art LCD panel system nevertheless suffers from a number of significant shortcomings and drawbacks. For example, the manufacturing of CLC layers having three color regions or sections is quite difficult because of the limited dynamic range in color tuning afforded by the CLC manufacturing techniques disclosed in U.S. Pat. No. 5,822,029 and other prior art references.
Adding the reflective-type black matrix pattern to the CLC spectral filter structure increases the complexity of the display system and adds to the overall cost of the display which must be minimized for low-cost consumer product applications.
While recommending the use of light collimation techniques to ensure that the incident upon the spectral filter falls within the angular acceptance bandwidth of its CLC material, U.S. Pat. No. 5,822,029 fails to disclose, teach or suggest practical ways of achieving this requirement of CLC material, nor even recognizes in the slightest way the fact that non-collimated light falling on the broad-band CLC reflective polarizer (
32
) results in significant polarization distortion, as illustrated in FIGS. ID through
1
H.
While U.S. Pat. No. 5,822,029 discloses the use of CLC-based spectral filters for improved light recycling within a LCD panel, the methods taught therein necessarily result in CLC films having narrow bandwidths which limited their usefulness in creating practical color (i.e. spectral) filter structures for use in LCD panels. While U.S. Pat. No. 5,822,029 discloses a technique of increasing the bandwidth of the cholesteric liquid crystal material by providing a plurality of different pitches in each portion of the
Faris Sadeg M.
Galabova Hristina
Hochbaum Aharon
Jiang Yingqiu
Li Le
Brill Gerow D.
Perkowski Esq. P.C. Thomas J.
Reveo Inc.
Ton Toan
LandOfFree
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