Method of growing isomeric carbon emitters onto triode...

Details Method of growing isomeric carbon emitters onto triode... Method of growing isomeric carbon emitters onto triode...

2002-08-24

2004-08-03

Ramsey, Kenneth J. (Department: 2879)

Electric lamp or space discharge component or device manufacturi

Process

With assembly or disassembly

Reexamination Certificate

active

06769945

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to a field emission display (FED), and more specifically to the growth of isomeric carbon emitters onto a triode structure of a field emission display.
BACKGROUND OF THE INVENTION
Field emission displays have been researched extensively in recent years for manufacturing large-size flat panel displays. A field emission display uses cold cathode emitter tips as electron sources instead of a hot cathode electron gun used in a conventional cathode ray tube (CRT). When a field emission display is placed in an electric field, cold cathode emitter tips aim at a phosphor-coated anode substrate fabricated in the field emission display and emit a bundle of electrons to hit the phosphor.
FIG. 1
shows a schematic diagram of a carbon nanotube field emission display with a triode structure. Electrons, being attracted by an electric field and emitted out of emitter tips
103
formed above a cathode glass substrate
101
, are accelerated by the positive voltage applied to an anode substrate
104
to hit coated phosphor
106
on the anode
105
and then produce luminescence. Carbon nanotube emitters
103
are formed within cavities of a dielectric layer
107
on a cold cathode layer
102
that is formed on the glass substrate
101
. Openings are formed at the intersections of the cathode layer
102
and a gate layer
108
for the electrons to emerge through.
FIGS. 2A-2D
illustrate a method of manufacturing the cathode plate of a carbon nanotube field emission display. A conductive paste is deposited and patterned on the surface of a transparent substrate
201
to form a cathode electrode layer
202
as shown in FIG.
2
A. The whole surface of the cathode electrode layer
202
is deposited with a layer of etchable dielectric material
203
as shown in
FIG. 2B. A
layer of conductive gate material
204
is further deposited on the dielectric layer
203
. The gate pattern is defined by a patterned photo-resist layer
205
as shown in FIG.
2
C. The gate electrode and dielectric materials are removed by sandblasting and fired in air. Finally, carbon nanotube emitter layer
206
are coated on the cathode electrode layer
202
shown in
FIG. 2D
by a screen printing process.
The carbon nanotube emitter layer
206
of the field emission displays shown in
FIG. 2
is fabricated by a screen printing method. A pre-mixed paste is applied to the surface of a pre-patterned screen and scraped using a scraper to print the pattern onto a glass substrate. Such process is repeatedly used to stack layers of patterns. The method has some drawbacks. It is difficult to increase the resolution of the printed pattern because of the limitation in the size of the screen mesh. The initial field emission voltage must be high enough to get sufficient brightness for the display. Also, the thickness of the printing film may not be uniform enough and the printed pattern may be inaccurate due to the non-uniform tension of the screen. Therefore, the distribution of the electric field is non-uniform and the alignment at post-process is difficult.
In order to overcome the drawbacks of the conventional methods and improve the quality of carbon nanotube filed emission displays, fabrication of the cathode plate using other thick-film technology has been proposed. By combining photolithography process and etching process, one method uses a photoconductive paste and an etchable dielectric material to fabricate the cathode plate of a carbon nanotube field emission display.
FIGS. 3A-3E
illustrate a method of manufacturing the cathode plate of a carbon nanotube field emission display using a thick-film technology. A conductive paste is deposited and patterned on the surface of a transparent substrate
301
to form a cathode electrode layer
302
as shown in FIG.
3
A. The whole surface of the cathode electrode layer
302
is deposited with a layer of etchable dielectric material
303
as shown in
FIG. 3B. A
layer of conductive gate material
304
is further deposited on the dielectric layer
303
. Gate patterns are then printed by a photolithography process and sintered to finish a gate electrode layer
304
as illustrated in FIG.
3
C. The gate pattern is used as a protecting film to etch a portion of the dielectric layer not covered by the protecting film in a photolithography process as shown in FIG.
3
D. Finally, a carbon nanotube emission layer
305
is filled on the cathode electrode layer to form a cathode plate structure shown in FIG.
3
E.
The fabrication of the carbon nanotube emission layer
305
can be accomplished with a photolithography method by depositing a layer of photosensitive carbon nanotube paste on the surface of the cathode plate shown in FIG.
3
D and define a pattern for the carbon nanotube emission layer
305
by alignment and exposure. It is then sintered in an nitrogen atmosphere. The carbon nanotube emission layer
305
can also be fabricated by an electrical deposition method comprising the steps of depositing a layer of positive or negative photoresist on the surface of the cathode electrode layer
302
and the gate electrode layer
304
shown in
FIG. 3D
, and using a mask to define a photoresist pattern by alignment and exposure. After the photoresist pattern is formed above the gate pattern
304
, the carbon nanotube emission layer
305
is then formed by electrically depositing a carbon nanotube paste on the cathode electrode
302
and sintering in an oven at a nitrogen atmosphere.
As described above, the fabrication process of the carbon nanotube emitter layer in the triode structure of a carbon nanotube field emission display requires rigorous alignment between the gate aperture and the pattern of the carbon nanotubes. The process is difficult and expensive. Many technical obstacles remain to be overcome for the mass production of carbon nanotube field emission displays.
Chemical vapor deposition (CVD) using catalytic metals has many advantages over other techniques and has proved to be a cheap process for large-area deposition of carbon nanotubes. However, the reaction temperature of thermal CVD is generally as high as 700-1000° C. which is well above the softening temperature 600° C. of a commonly used glass substrate of a flat panel display. Recently, the growth of carbon nanotubes on Ni catalyst coated on soda-lime glass substrate using CVD of C
2
H
2
gas at 550° C. has been reported. There is a strong need in developing an integrated thick-film process for fabricating the triode structure in combination with a low temperature CVD process for the mass production of carbon nanotube field emission displays.
SUMMARY OF THE INVENTION
This invention has been made to overcome the above-mentioned drawbacks in manufacturing conventional field emission displays. The primary object is to provide a low cost method for fabricating isomeric carbon emitters onto a triode structure of a field emission display. Accordingly, the triode structure is manufactured using a thick-film technology and then the isomeric carbon emitters are grown onto the triode structure by using CVD process.
Another object of the invention is to provide a cathode electrode layer of the triode structure on which the isomeric carbon emitters can be readily grown by using CVD process. According to the invention, a metallic catalyst is first mixed with the conductive metal powder that is used to form the cathode electrode layer. A conductive metal paste is then formed from the conductive metal powder. The cathode electrode layer is fabricated by the conductive metal paste on a transparent substrate using thick-film technology. A dielectric layer and a gate electrode layer are then deposited above the cathode electrode layer and patterned to form the triode structure. Because the cathode electrode layer comprises the metallic catalyst, the isomeric carbon emitters can be grown onto the triode structure easily.
It is also an object of the invention to provide a metallic catalyst layer in the triode structure to facilitate the growth of the isomeric carbon emitters of the

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