Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Screen other than for cathode-ray tube
Reexamination Certificate
1999-07-30
2001-11-27
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Screen other than for cathode-ray tube
C430S321000, C445S024000
Reexamination Certificate
active
06322937
ABSTRACT:
FIELD OF THE INVENTION
The present claimed invention relates to the field of flat panel displays. More particularly, the present claimed invention relates to the fabrication of a color filter layer on a flat panel display screen structure.
BACKGROUND ART
Flat panel displays have become popular for use in outdoors due in large part to their portability. However, bright lights, and sunlight in particular, have been a persistent source of problem for the flat panel color display screens. Even a modest sunlight may reduce the contrast, or “wash out” a display so as to make it practically unreadable.
Bright lights wash out displays by reflecting off of a display screen. These reflections occur at all wavelengths of the visible light hitting the screen. At the same time, light is being transmitted to the screen for the viewer. This light also has certain wavelengths corresponding to its color. The bright sunlight washes out the displays by obscuring the desired color of light emitted from the display.
Conventional display screens have attempted to address the washing out problem by applying color pigment crystals into a pixel structure on the display screens. These color pigment crystals form a color filter to absorb unwanted light and transmit light of a desired color (i.e. wavelength). Specifically, color pigment crystals have been deposited into the sub-pixels of display screens in various arrangements. The color of the pigment crystals so deposited corresponds to the color of the light assigned to a sub-pixel. The conventional methods then used photolithographic process to cure the color pigment crystals into the pixels on the display. Schematic side sectional views depicting conventional steps used in depositing color pigment crystal on the pixels are shown in Prior Art
FIGS. 1A through 1G
.
Prior Art
FIG. 1A
illustrates a top view of a black matrix
102
defining a pixel structure. Black matrix
102
is disposed on the interior surface of a display screen
100
, typically comprised of glass. The pixel structure is further divided into sub-pixels, typically shown as
104
, of three primary light colors: red (R), green (G), and blue (B).
A side sectional view of display screen
100
with black matrix
102
disposed on it interior surface is depicted in Prior Art FIG.
1
B.
Prior Art
FIG. 1C
illustrates a side sectional view of black matrix
102
disposed on top of display screen
100
with colored phosphors
106
disposed thereon. On the interior surface of display screen
100
, plurality of sub-pixels are disposed. Phosphors
106
are first coated with color pigment crystals
104
of red, green, or blue color. Subsequently, phosphors of single color, for example red, are deposited on the display screen with a photomask. The color coated phosphors are then cured into the sub-pixels of corresponding color on the display screen. Finally, the phosphors deposited into sub-pixels of different color are removed. This process repeats until all three colors of phosphors are cured in the pixels.
With reference to Prior Art
FIG. 1D
, phosphors
106
coated with color pigment crystals are then cured into corresponding pixels on the interior surface by an ultra-violet (UV) light
108
illuminated from the interior side of the display screen
100
. During the UV exposure process, a photomask is used to ensure curing of color pigment crystals in desired sub-pixels only. That is, the material must not be cured along the top or the edge of black matrix
102
.
However, coating individual phosphor particles with color pigment crystals produces unwanted side effects. The main function of the phosphors is to generate light when a beam of electrons bombard them. With an added coat of color pigment crystals, some electrons of lower kinetic energy may no longer be able to penetrate the added color coating. Moreover, even if the electrons make it through the coated crystals, they may not have sufficient kinetic energy left to enable phosphor particles to generate light. Hence, phosphors do not generate as much light as they would without the coating. Such electron impedance translates directly into reduced brightness of the display screen images. As a result, coated phosphors require higher kinetic energy electron requiring higher voltage emitters. Consequently, coated phosphor methods have not been suitable for a low voltage class of display structures.
With reference to Prior Art
FIG. 1E
, a side sectional view of another display screen
100
is illustrated. On its interior surface, a black matrix
102
, defining a plurality of sub-pixels corresponding to red, green, and blue colors is disposed. Color pigment crystals
104
, for example red, are then deposited into the sub-pixels of matching colors with a photomask. The color pigment crystals are then cured into the sub-pixels of corresponding color on the display screen. Finally, the color pigment crystals deposited into sub-pixels of different color are removed. This process repeats until all three colors of pigment crystals are cured in the pixels.
As illustrated in Prior Art
FIG. 1F
, the color crystal pigments
104
are then cured into the pixels on the interior surface by UV light
108
illuminated from the interior side of the display screen
100
. Phosphors are then deposited into the sub-pixels on top of the color crystal pigments by a well known photolithographic process. During the UV exposure process, a photomask is used to ensure curing of color pigment crystals in desired sub-pixels only. That is, the material must not be cured along the top or the edge of black matrix
102
.
Consequently, conventional methods of curing color pigment crystals require precision in mask alignment and thus are error prone. For example, a slight misalignment of a photomask leads to curing of color pigment crystals in unwanted areas such as along the top or the edge black matrix
102
. Prior Art
FIG. 1F
illustrates portions
109
of color pigment crystals
104
on top of black matrix
102
, which should not be cured.
Those skilled in the art will no doubt appreciate that a good adhesion of the color pigment crystals to the surface of a display screen is important for reducing reflection of unwanted lights and increasing transmission of phosphor lights. That is, a tightly bound interface is far more efficient than a poorly-bound interface surface in reflecting and transmitting light. Without a satisfactory adhesion of the color pigment crystals to display screens, reflectivity and transmission properties of a display screen may be adversely affected.
Unfortunately, under the conventional method shown in
FIG. 1F
, the color pigment crystals are often not adequately cured onto display screens due to their intrinsic nanocrystalline properties. For instance, as illustrated in Prior Art
FIG. 1G
, when color pigment crystals
104
are subjected to a UV light
108
, a cross-linking depicted by structure
110
may occur in the crystals at the top of the layer. The color pigment crystals
104
at the top of the color crystal layer bond to each other before the color pigment crystals
104
below can satisfactorily adhere to display screen
100
. Hence under conventional methods, a strong adhesion of color pigment crystals
104
to display screen
100
is not easily obtainable.
Furthermore, the cross-linking of color pigment crystals means that the exposure to an UV light must proceed at a relatively slow pace. That is, rapid exposure to UV light enhances the detrimental cross-linking effect at the top of the layer of color pigment crystals.
Thus, a need exists for a method to create a color filter on a display screen which improves readability of display screens by reducing reflection of ambient light and by increasing transmission of phosphor light of desired wavelength without reducing generation of light by phosphors. A further need exists to achieve the above-mentioned color filter in a way that provides a more efficient adhesion of color pigment crystals to the screen display structure while improving precision in curing process.
SUMMARY OF INVENTION
Drumm Paul M.
Mackey Bob L.
Candescent Technologies Corporation
McPherson John A.
Wagner , Murabito & Hao LLP
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