Methods of electrophoretic deposition of phosphor molecules

Details Methods of electrophoretic deposition of phosphor molecules Methods of electrophoretic deposition of phosphor molecules

2000-10-10

2002-09-17

Nguyen, Nam (Department: 1741)

Chemistry: electrical and wave energy

Processes and products

Electrophoresis or electro-osmosis processes and electrolyte...

Reexamination Certificate

active

06451190

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
The invention pertains to methods of fabricating display screens. In particular embodiments, the invention pertains to methods of reducing precipitate formation in a phosphor-containing solution during electrophoretic deposition of phosphor, and to methods of depositing phosphor over selected regions of a substrate.
2. Description of the Related Art
Phosphor-containing display devices have numerous applications, including, for example, utilization as TV screens and computer monitors. Phosphor-containing display devices generally utilize one or more components to project electrons against a phosphor to cause one or both of fluorescence or phosphorescence, and to thereby cause an image to be displayed. Exemplary components which can be utilized to generate electrons are cathode ray tubes, and cathode emitter arrays.
An exemplary phosphor-containing display device
40
is described with reference to FIG.
1
. Device
40
is a field emission display (FED) device comprising a plurality of phosphor molecules
33
(only some of which are labeled) coated over a conductive layer
34
, which in turn is over a transparent display screen
35
. The phosphor molecules can also be referred to as “phosphor”. Conductive layer
34
can comprise, for example, indium tin oxide, and transparent screen
35
can comprise, for example, glass. Screen
35
can be referred to as a face plate. Device
40
further comprises a base plate
12
spaced from face plate
35
, and which can also comprise glass. A conductive layer
14
is over base plate
12
, and can comprise, for example, conductively-doped semiconductive material.
Emitters
26
are formed over and in electrical connection with conductive material
14
. Dielectric regions
28
(only some of which are labeled) and an emitter grid
30
(only some of which is labeled) are formed over layer
14
and proximate emitters
26
. Insulative spacers
32
are provided to support face plate
35
in a spaced relation relative to base plate
12
. A power source
37
is provided to supply a voltage differential between conductive layer
34
, conductive layer
14
, and emitter grid
30
.
In operation, cathode emitters
26
are electrically stimulated to cause electrons
36
(shown as dashed lines, and only some of which are labeled) to be ejected from emitters
26
and against phosphor molecules
33
. The electrons then cause one of both of phosphorescence and fluorescence by phosphor molecules
33
to result in an image being displayed. Such image can be viewed by a user looking through transparent face plate
35
.
The individual phosphor molecules
33
can all comprise a single uniform color (such as, for example, green) or can comprise a multitude of colors, depending on the application. Frequently, three colors of phosphor molecules
33
(for instance, red, green and blue) are provided. Each of the three colors is formed in a specific region separate from the others of the three colors, and the specific regions are surrounded by black regions.
Methodology for forming phosphor-coated face plate
35
is described with reference to an electrophoretic deposition system
70
illustrated in FIG.
2
. System
70
comprises an electrophoretic deposition bath
50
contained within a vessel
51
. Glass plate
35
, having conductive layer
34
formed thereover, is placed within electrophoretic deposition bath
50
. Conductive material
34
is utilized as a first electrode within bath
50
, and a second electrode
52
is also provided within bath
50
. A power source
53
is provided to electrically charge electrodes
34
and
52
, with electrode
34
being charged as a negative electrode and electrode
52
being charged as a positive electrode.
Bath
50
typically comprises a mixture of isopropyl alcohol, glycerol and water, within which phosphor particles and metal complexes are dissolved. Additional electrolyte ions, besides the phosphor particles and metal ions of the metal complexes, can also be dissolved within solution
50
. An exemplary solution
50
comprises 80 milligrams of isopropyl alcohol (99.5% pure), 0.35 grams of phosphor, 0.2 grams of glycerol (100% pure), and 0.025 grams of one or both of In(NO
3
)
2
and Ce(NO
3
)
3
.H
2
O.
In operation, power applied from source
53
generates a negative potential at conductive layer
34
which attracts positively charged ions
63
to a surface of conductive layer
34
. The positively charge ions comprise phosphor molecule ions and metal ions. The negative potential at conductive layer
34
also causes hydrolysis of water to form hydroxide ions adjacent the surface of conductive layer
34
. The hydroxide ions and metal ions interact with the phosphor particle surface to form a complex which adheres to surface
34
.
In particular applications, conductive material
34
can be formed in a pattern over face plate
35
as shown in FIG.
3
. Such pattern leaves some portions
37
of face plate
35
uncovered with conductive material
34
. Since the phosphor molecule ions selectively deposit on conductive material
34
, the patterning of conductive material
34
shown in
FIG. 3
can result in the phosphor molecules being deposited in a pattern corresponding to the pattern of conductive material
34
over face plate
35
. Portions
37
of glass plate
35
between regions of conductive material
34
can be either covered with a protective layer (such as, for example, photoresist) prior to the electrophoretic deposition of phosphor molecules, or left exposed to the deposition conditions.
After the electrophoretic deposition described with reference to
FIG. 2
, face plate
35
is removed from deposition bath
50
and rinsed with isopropyl alcohol. Such rinsing preferably leaves the complexes of phosphor molecule ions, metal ions and hydroxide ion over conductive material
34
, while removing phosphor particles from regions where the particles are unintended to be deposited.
After the rinsing, face plate
35
is dried by, for example, thermal dehydration or infrared radiation dehydration.
In embodiments in which multiple colors of phosphor molecules are to be deposited over a single face plate, the electrophoretic deposition and rinsing will be repeated for each color of phosphor molecule that is to be deposited. For instance, if red, green and blue phosphor molecules are to be deposited on a glass substrate, a first lithography, first electrophoretic deposition and subsequent isopropyl rinse will be done with one of the three colors of phosphor molecules, and subsequently a second and third lithography, electrophoretic deposition and isopropyl rinse will be done with each of the remaining two colors of phosphor molecules.
The processing described above with reference to
FIGS. 2 and 3
has difficulties associated therewith. For instance, a precipitate forms over time within electrophoretic deposition bath
50
which complicates repeated utilization of the deposition bath. Further, it is found that phosphor molecules deposited over conductive material
34
will occasionally be displaced by the isopropyl alcohol rinse to cause bleeding of phosphor colors and to reduce a total amount of phosphor ultimately formed over conductive material
34
. It would be desirable to develop methodologies which overcome one or both of the above-described difficulties.
SUMMARY OF THE INVENTION
In one aspect, the invention encompasses a method of fabricating a display screen. Phosphor molecules are electrophoretically deposited onto a substrate in a first solution having a first concentration of hydroxide ions. The deposited phosphor molecules are then rinsed with a second solution having a second concentration of hydroxide ions greater than the first concentration of hydroxide ions.
In another aspect, the invention encompasses a method of depositing phosphor molecules over selected regions of a substrate. Conductive regions are formed over portions of a substrate while non-conductive regions are left over other portions of the substrate. Phosphor molecules are electrophoretically deposited onto t

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