Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1997-12-22
2002-09-10
Le, Hoa T. (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C252S30140R, C313S479000, C313S483000
Reexamination Certificate
active
06447908
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for implementing a microencapsulation of phosphor particles or transparent conducting particles using a phosphor material to improve a luminous efficiency of a cathodoluminescent and a method for forming a cathodoluminescent screen using the same for a field emission display, and more particularly to a method for forming a cathodoluminescent screen provided with uniform cathodoluminescent phosphor-coated particles for a field emission display by a method such as an electrodeposition, a screen printing, or a spray by using the phosphor-coated particles.
2. Description of the Related Art
Phosphor particles are used in a variety of applications such as a flat panel display and decoration, cathode ray tube, and fluorescent lighting fixture. Luminescence or light emission from phosphor-coated particles may be stimulated by applying of heat, light, high energy radiation, or electric fields.
It has been recognized that various improvements in the performance of phosphors can be obtained if the phosphor material is coated with a protective film or pigment. Numerous attempts have been made to coat the outer surfaces of individual particles with a protective coating material.
U.S. Pat. No. 4,508,760 discloses an encapsulation technique of phosphor particles by a vacuum deposition using a certain polymer.
U.S. Pat. No. 4,515,827 is achieved by disclosing phosphor particles coated by the color modifying material while the particles are rotated in a vacuum chamber.
U.S. Pat. No. 4,585,673 discloses the formation of a continuous protective coating on phosphor particles by gas-phase chemical vapor deposition while the phosphor particles are suspended within a fluidized bed.
U.S. Pat. No. 4,515,827 discloses encapsulated cathodoluminescent phosphor particles by a vapor phase hydrolysis reaction of oxide precursor material.
U.S. Pat. No. 5,156,885 discloses encapsulated phosphor particles by a low temperature vapor phase hydrolysis reactions and deposition process.
In the above coating techniques, the movement, rotation, or vibration of the particles was necessary for a uniform film growth because it was very hard to deposit uniform, conformal continuous, and stoichiometric thin film or particles.
Also, the cathodoluminescent films of the cathodoluminescent screen of a cathode-ray tube, such as a color cathode-ray tube or a monochromatic cathode-ray tube, are formed principally by a slurry process, and the cathodoluminescent films of the cathodoluminescent screen of some cathode-ray tubes are formed by a screens printing, a spray, or an electrodeposition process.
Generally, ZnO, ZnGa
2
O
4
: Mn, ZnGa
2
O
4
: Eu, YAG: Tb, Y
2
SiO
5
: Ce, Y
2
O
3
: Eu, Y
2
O
2
S: Tb, Gd
2
O
2
S: Tb, SrS: Ce, SrTe: Ce, SrS-Sc
2
S
3
, ZnS: Ag, ZnS: Pr, SrGa
2
S
4
, ZnCdS: Cu, Al are used for cathodoluminescent materials of the cathodoluminescent screen of a field emission display.
However, in the conventional cathodoluminescent particles to form a screen of a cathode ray tube, the surfaces of the particles are continuously polished and are exposed to a dilution liquid, so that the surface of the same may be changed, thus forming a dead layer and decreasing the characteristic of the cathodoluminescence of very surface region of the particles.
Therefore, in the industry, the technique for reducing the dead layer formed on the surface of the cathodoluminescent particle becomes an important technique.
The conventional phosphor particles used in the thick film type will be explained with reference to
FIGS. 1A and 1B
.
FIGS. 1A and 1B
are cross-sectional views showing conventional phosphor particles and a cathodoluminescent screen using the same for a field emission display, respectively.
As shown in
FIG. 1B
, a transparent conductive layer
2
is formed on the transparent substrate
1
. A cathodoluminescent films
3
a
composed of phosphor particles
3
of the
FIG. 1
on the transparent conduction layer
2
is formed using phosphor-coated particles
3
of fine powder types having a diameter of less than 10 micron in average particle size by a screen printing, a spray, or an electrodeposition process.
FIG. 2
is a cross-sectional schematic drawing of a field emission display showing an electron emission tip, or field emission cathode, surrounded by the self-aligned gate structures.
Referring to
FIG. 2
, the electron emission tip
4
is integral with the single crystal semiconductor substrate
5
, and serves as a cathode conductor. Gate
8
serves as a low potential anode or grid structure for its respective cathode
4
. A dielectric insulating layer
7
is deposited on the conductive cathode layer
6
. The insulator
7
also has an opening at the field emission site location.
A field emission display employing a cold cathode is depicted. The substrate
5
can be comprised of glass, for example, or any of a variety of other suitable materials, In the preferred embodiment, a single crystal silicon layer serves as a substrate
5
onto which a conductive material layer
6
, such as doped polycrystalline silicon has been deposited. At a field emission site location, a conical micro-cathode
4
has been constructed on the top of the substrate
5
. Surrounding the micro-cathode
4
, is a low potential anode gate structure
8
. When a voltage is applied between the cathode
4
and the gate
8
, a stream of electrons
9
is emitted toward a phosphor-coated screen
1
. Screen
1
is an anode and includes cathodoluminescent material
3
on its surface. The display faceplate cover with the included cathodoluminescent layer is distantly disposed with respect to the electron emission structure. Same of emitted electrons of will impinge upon the cathodoluminescent material, and at least some of the energy of the emitted electrons is converted to photon energy as visible light. The visible light is transmitted through the transparent conduction layer
2
and the transparent substrate
1
of the display to the viewer.
The purity and intensity of light is determined by composition, uniformity and surface state of the phosphor particles. Luminous efficiency of the cathodoluminescent films formed by the thick film type is particularly determined by uniformity of the particle size and surface state of the particle. Also, the photoemission from the thin surface layer of phosphor particles becomes more important in the field emission display operated by lower acceleration voltage of electron beam.
When phosphor particles of the
FIG. 1
are formed by a conventional technique, a dead layer (non-luminescent on the particle surface is formed by continuously polishing or by exposing in the dilution with destructive state. Therefore, such conventional invention of the thick film type has been reduced luminous efficiency.
Also, if acceleration voltage of the electron beam is low, a photoemission region is thinly formed, the thinnest surface of the cathodoluminescent layer is emitted. Therefore, the surface state of the phosphor particles have influence on the luminous efficiency.
Disadvantages associated with these known methods are eliminated by the method of the present invention by which a thin phosphor film having a desired substantially uniform thickness is formed by an atomic layer deposition on the outer surface of the phosphor particles or the transparent conducting particles.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a method for coating phosphor layer on the phosphor particles and the transparent conducting particles by an atomic layer deposition to improve the luminous efficiency of the cathodoluminescent films for a field emission display and which does this while avoiding the disadvantages of the prior art.
It is another object of the present invention to provide a method for forming a cathodoluminescent screen by forming cathodoluminescent films on the inner surface of screen panel for a field emission display by a method such as a screen printing, a spray and an electrodeposition proce
Lee Joong Whan
Yun Sun Jin
Electronics and Telecommunications Research Institute
Jacobson & Holman PLLC
Le Hoa T.
LandOfFree
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