Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Reexamination Certificate
2000-01-12
2001-09-25
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
C349S069000, C349S159000, C428S690000
Reexamination Certificate
active
06295106
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to liquid crystal display devices, and particularly, to a novel, low-cost, energy-efficient liquid crystal display device implementing dye impregnated photoluminescent fibers.
2. Discussion of the Prior Art
Current liquid crystal display devices employing white fluorescent backlight, with diffusers, color filters and a combination of a polarizer and analyzer, result in a luminous throughput efficiency of 5% or less. As liquid crystal display pixels become smaller, the aperture ratio (the open area of the pixel relative to the total pixel area) becomes smaller because the footprint size of the thin-film transistor (TFT) device can not be reduced proportionately. Further, the fabrication process for making the color filter is complicated and increases the cost of the display.
FIG. 1
is a schematic illustration depicting a pixel
12
of a conventional full-color LCD panel. The pixel
12
has three liquid crystal cells, which corresponds to red, green and blue cells. As shown in
FIG. 1
, the panel includes an optical guide
27
, which guides white backlight
28
from a fluorescent lamp (not shown) through a polarizer
26
, transparent electrodes
25
a-
25
c
, liquid crystal material
24
, a transparent electrode
23
, and red, green and blue color filters
20
,
21
and
22
, respectively.
Colored light is finally emitted through a glass substrate
19
and an analyzer
18
. The polarization directions of polarizer
26
and analyzer
18
are aligned to obtain the designed contrast. It is understood that a diffuser element (not shown) may be placed on the light guide
27
for distributing transmitted light uniformly through the panel. A prism sheet (or a pair of prism sheets) additionally may bring the scattered light towards normal direction. It is understood that a liquid crystal cell additionally is comprised of TFT arrays and transparent electrodes (preferably comprised of Indium Tin-Oxide “ITO”).
Even in the ideal case, white visible light utilizes only ⅓ of the incident light for this configuration because of the red, green and blue color filters. Moreover, the fabrication process to make these color filters requires exacting optical lithography technology, which increases the panel cost and the manufacturing time.
Color conversion utilizing photoluminescence phenomena have been described in the prior art. For instance, the references entitled “Incorporation of Photoluminescent Polarizers into Liquid Crystal Displays,” Science 279, 835 (1998) by C. Weder, C. Sarwa, A. Montali, C. Bastiaansen, P. Smith, and “Polarizing Energy Transfer in Photoluminescent Materials for Display Applications,” Nature, 392, 261 (1998) by A. Montali, C. Bastiaansen, P. Smith, C. Weder, each describe a new type of liquid crystal display implementing a photoluminescent sheet with polarized emission. Although the devices described in these references address the prior art limitations of the conventional device, the devices are not full color devices, and only a single or two color device can be achieved.
According to the display devices implementing photoluminescence as described in these references, a fluorescent dye absorbs the incident light and either re-emits a different color of a longer wavelength or transfers the energy to a second dye which then re-emits a different color of a longer wavelength. For instance, in the above-mentioned reference entitled “Polarizing Energy Transfer in Photoluminescent Materials for Display Applications,” the ultraviolet (UV) light from the backlight is absorbed by a dye material DMC (Coumarin 1), and the energy is transferred to a stretch-aligned conjugated polymer material, EHO-OPPE, which re-emits polarized green light. When a sheet of this dye/polymer blend is placed in a liquid crystal display device it replaces both a polarizer and green color filter. This reference however, does not describe how to make a full color liquid crystal display.
It would be highly desirable to provide a full color liquid crystal display without the need for color filters and a polarizer, and further, a full color liquid crystal display that is highly efficient and can be manufactured using very low cost fabrication methods.
SUMMARY OF THE INVENTION
The present invention pertains to an improved liquid crystal display device which improves upon the display device types implementing photoluminescence.
According to one embodiment of the invention, instead of a using a sheet of color-converter material, the display device implements arrays of bulk fiber, impregnated with dye materials and other stretch-aligned polymer materials functioning to cooperatively absorb the light from the backlight and to emit blue, green and red polarized light and, replace either the polarizer or the analyzer in each fiber array. The backlight source emits ultraviolet (UV) light which is totally absorbed by either the emitting polymer or the dye material in each fiber array. For example, in one embodiment of the fiber array, the energy is first absorbed by a small molecule dye (unpolarized) and transferred to a stretch-aligned polymer which emits polarized light of longer wavelength. The dye/polymer combination is selected to give the appropriate color coordinates for blue, green, or red pixels. Each fiber array may be located behind liquid crystal light shutters within the LC cell, wherein it replaces the polarizer and only an analyzer is needed to complete the light valve. The polarized light from the fiber must be aligned with the transmitting orientation of the liquid crystal light shutter in order to obviate the need for one polarizer. In another embodiment, the fiber array may be located in front of the liquid crystal light shutters (closest to the viewer) within the LC cell and replaces or acts as the analyzer. Alternately, the PL fiber arrays may be located outside the LC cell and function as a simple color generation layer.
Alternately, in each fiber array, the energy is first absorbed in a stretch-aligned polymer and transferred to a molecule dye (unpolarized) which emits polarized light of longer wavelength. The polymer/dye combination is selected to give the appropriate color coordinates for blue, green, or red pixels.
It is further recognized that cost reduction may be achieved without the use of polarized emission. Thus, in a second alternate embodiment, the conjugated polymer emitter may be replaced with a second dye material which emits unpolarized light of selected wavelengths. In this case, materials may be used which both absorb and emit without the need for transfer. Thus, a wider range of dyes becomes available for use, especially at the red end of the spectrum.
Moreover, to obtain a full color display, each pixel is made up of a set of three sub-pixels: red, green and blue, with each sub-pixel consisting of a single emitting fiber and a liquid crystal light shutter. Thus, advantageously, known techniques of the weaving/textile/composites industry may be utilized to fabricate arrays of aligned fibers and then laminate them to the light shutter array.
REFERENCES:
patent: 5475515 (1995-12-01), Yoshinaga et al.
patent: 5966393 (1999-10-01), Hide et al.
patent: 6017584 (2000-01-01), Albert et al.
Fukuzawa Tadashi
Kohara Sayuri
Lee Victor Yee Way
Miller Robert D.
Scott John Campbell
International Business Machines - Corporation
Johnson, Esq. Daniel E.
Ngo Julie
Parker Kenneth
Scully Scott Murphy & Presser
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