U.S. patent application number 10/791817 was filed with the patent office on 2004-09-02 for carbon nanotube field emission display.
This patent application is currently assigned to DELTA OPTOELECTRONICS, INC.. Invention is credited to Chen, Lai-Cheng, Fran, Yui-Shin.
Application Number | 20040169458 10/791817 |
Document ID | / |
Family ID | 21679049 |
Filed Date | 2004-09-02 |
United States Patent
Application |
20040169458 |
Kind Code |
A1 |
Fran, Yui-Shin ; et
al. |
September 2, 2004 |
Carbon nanotube field emission display
Abstract
A carbon nanotube (CNT) field emission display has a cathode
substrate having a cathode layer patterned on a glass substrate.
The surface of the cathode layer is defined as a plurality of
electron-emitting areas apart from each other, and a plurality of
CNT structures is grown on the plurality of electron-emitting areas
respectively.
Inventors: |
Fran, Yui-Shin; (Hsinchu,
TW) ; Chen, Lai-Cheng; (Hsinchu, TW) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Assignee: |
DELTA OPTOELECTRONICS, INC.
|
Family ID: |
21679049 |
Appl. No.: |
10/791817 |
Filed: |
March 4, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10791817 |
Mar 4, 2004 |
|
|
|
10011281 |
Dec 11, 2001 |
|
|
|
Current U.S.
Class: |
313/495 ;
313/309; 313/351 |
Current CPC
Class: |
H01J 1/3042 20130101;
H01J 29/085 20130101; H01J 2201/30469 20130101; B82Y 10/00
20130101; Y10S 977/952 20130101; H01J 9/025 20130101 |
Class at
Publication: |
313/495 ;
313/309; 313/351 |
International
Class: |
H01J 001/62; H01J
063/04 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 13, 2001 |
TW |
90119797 |
Claims
What is claimed is:
1. A cathode substrate of a carbon nanotube (CNT) field emission
display, comprising: a glass substrate; a cathode layer formed
overlying the glass substrate, wherein the surface of the cathode
layer is defined as a plurality of electron-emitting areas spaced
apart from each other; an insulating layer formed overlying the
glass substrate and having an opening, wherein the opening exposes
the cathode layer; a gate electrode layer formed overlying the top
of the insulating layer and exposing the cathode layer; and a CNT
structure formed overlying the cathode layer, wherein the CNT
structure comprises a plurality of sub-CNT structures arranged in
array; wherein, the sub-CNT structures are formed overlying the
plurality of electron-emitting areas respectively; and wherein, the
sub-CNT Structures are spaced apart from each other without the
insulating layer therebetween.
2. The cathode substrate according to claim 1, wherein the interval
of two adjacent electron-emitting areas is 80.about.150 .mu.m.
3. The cathode substrate according to claim 2, wherein the profile
of the electron-emitting area is quadrilateral, circular or any
other physical appearance.
4. A cathode substrate of a carbon nanotube (CNT) field emission
display, comprising: a glass substrate; a cathode layer formed
overlying the glass substrate, wherein the surface of the cathode
layer is defined as a plurality of electron-emitting areas spaced
apart from each other, and the electron-emitting areas are uniform
and arranged in array; an insulating layer formed overlying the
glass substrate and having an opening, wherein the opening exposes
the cathode layer; a gate electrode layer formed overlying the top
of the insulating layer and exposing the cathode layer; and a CNT
structure formed overlying the cathode layer, wherein the CNT
structure comprises a plurality of sub-CNT structures arranged in
array; wherein, the sub-CNT structures are formed overlying the
plurality of electron-emitting areas respectively, such that an
edge effect is formed at the periphery of each sub-CNT structures;
and wherein, the sub-CNT Structures are spaced apart from each
other without the insulating layer therebetween.
5. The cathode substrate according to claim 4, wherein the profile
of the electron-emitting area is quadrilateral, circular or any
other physical appearance.
Description
[0001] This application is a Continuation of co-pending application
Ser. No. 10/011,281, filed on Dec. 11, 2001, the entire contents of
which are hereby incorporated by reference and for which priority
is claimed under 35 U.S.C. .sctn. 120; and this application claims
priority of Application No. 090119797 filed in Taiwan, R.O.C. on
Aug. 13, 2001 under 35 U.S.C. .sctn. 119.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a field emission display
(FED) and, more particularly, to a carbon nanotube field emission
display (CNT-FED).
[0004] 2. Description of the Related Art
[0005] Filed emission display (FED), having competitiveness in the
panel display market, is a high-voltage display with a triode
structure consisting of anode, cathode and gate electrode to
achieve high illumination by applying a high voltage and a low
current. FED has advantages of light weight and thin profile, like
liquid crystal display (LCD), and advantages of high brightness and
self luminescence, like cathode ray tube (CRT). In conventional FED
processing, fluorescent material is formed on an anode substrate,
an electron-emitting source with a discharge tip is formed on a
cathode substrate, and a gate electrode is formed to surround the
discharge tip. Thus, applying a high electric field generated from
the gate electrode, electrons are released from the discharge tip
and then the electrons are accelerated by applied high voltage to
strike the fluorescent material, resulting in emitted cathode
fluorescence. With regard to the fabrication of the
electron-emitting source, molybdenum (Mo) metal is employed to form
a micro-tip shape, despite attendant problems of complex process,
expensive equipment cost and low throughput.
[0006] Recently, carbon nanotube (CNT) materials, having high
mechanical strength and great electrical performance, have been
used to form the electron-emitting source of FED. Since simple and
low cost technologies, such as screen printing, chemical vapor
deposition (CVD) and coating, are applied to coat/grow carbon
nanotubes within an electron-emitting area, the product, CNT-FED,
has high throughput and may be formed as a large-size display. FIG.
1 is a sectional diagram showing a primitive CNT-FED 10. The
CNT-FED 10 has a cathode substrate 12, an anode substrate 14 over
and parallel to the cathode substrate 12, a spacer 16 disposed in
the vacuum space between the two substrates 12 and 14 for
maintaining a predetermined vertical distance and resisting
atmosphere pressure. The anode substrate 14 has a glass substrate
18, a plurality of fluorescent layers 20 patterned on predetermined
regions of the glass substrate 18, and planarized Al film 22 formed
on the exposed regions of the glass substrate 18. The first purpose
of the Al film 22 is to serve as a conductive layer of the anode
substrate 14, the second purpose is to serve as a reflective layer
of the fluorescent layer 20, and the third purpose is to serve as a
protective layer for protecting the fluorescent layer 20 from ion
bombardment and electric-filed attraction. The cathode substrate 12
has a glass substrate 24, a plurality of cathode layers 26
patterned on predetermined regions of the glass substrate 24, a
plurality of CNT structures 34 grown on each electron-emitting area
of the cathode layer 26, an insulating layer 28 formed on
peripheral region of the glass substrate 24, and a net-shaped metal
layer 32 glued on the insulating layer 28 by frit. In addition,
each opening 32a of the net-shaped metal layer 32 corresponds to
each electron-emitting area of the cathode layer 26, thus the metal
material of the net-shaped metal layer 32 surrounding the cathode
layer 26 serves as a gate electrode 32b.
[0007] However, the CNT-FED 10 has disadvantages. First, edge
effect is found at the outer carbon nanotubes that surround the
electron-emitting area, thus each fluorescent layer 20 emits a
comparatively brighter light at periphery and a comparatively
darker light at the center. This causes non-uniform luminescence
and decreases luminescent property of the CNT-FED 10. Second, since
only the edge of the net-shaped metal layer 32 is glued to the
insulating layer 28 that is formed on the peripheral region of the
cathode substrate 12, most of the gate electrodes 32b are suspended
over the cathode substrate 12. As the size of the net-shaped metal
layer 32 is increased, the center area of the net-shaped metal
layer 32 easily droops and become uneven. This causes electrons to
bombard the gate electrode 32 and forms non-uniform electric
fields, which may vibrate the gate electrode 32 or even peel the
net-shaped metal layer 32. Third, when removing organic materials
at high temperature, preferably at 450-500.degree. C., part of the
Al film 22 may be oxidized to become aluminum oxide, resulting in a
decreased conductivity of the Al film 22. This leads to an
accumulation of charges when electrons are emitted to bombard the
anode substrate 14. Also, when the charges are accumulated to reach
a critical amount, an arc phenomenon is formed in order to deplete
the accumulated charges, and thus the brightness on the anode
substrate 14 is burned out. Moreover, the accumulated charges may
generate a repellent electric field that makes the subsequently
emitted electrons unable to bombard the anode substrate 14. This
decreases the electron quantities that bombard the anode substrate
14 and degrades the brightness that is emitted from the fluorescent
layer 20. Fourth, no matter whether the electron-emitting source
employs a metal tip or the CNT structure 34, a divergent phenomenon
of the electrons is always found to cause cross-talk on the anode
substrate 14. Furthermore, as the amount of emitted electrons is
greater, the excessive electrons directly bombard the anode
substrate 14 to generate a spark. Thus, a novel structure of the
CNT-FED and an improved process of forming the same to solve the
aforementioned problems are called for.
SUMMARY OF THE INVENTION
[0008] The present invention provides a CNT-FED with a novel
cathode substrate and a novel anode substrate to solve the problems
caused by prior art.
[0009] The carbon nanotube (CNT) field emission display has a
cathode substrate having a cathode layer patterned on a glass
substrate. The surface of the cathode layer is defined as a
plurality of electron-emitting areas apart from each other, and a
plurality of CNT structures is grown on the plurality of
electron-emitting areas respectively.
[0010] A method of forming a cathode substrate comprises: providing
a glass substrate on which a plurality of cathode layers are
patterned; forming a plurality of ribs in each space between
adjacent cathode layers, wherein the rib protrudes from the top of
the cathode layer to reach a predetermined height; printing to form
a net-shaped gate electrode layer on the plurality of ribs; and
performing high-temperature baking.
[0011] The CNT-FED has an anode substrate with a plurality of
fluorescent layers patterned on a glass substrate. A planarized Al
film covers the fluorescent layers, and a metal sheet covers the Al
film. The metal sheet has a plurality of openings, wherein the
openings are corresponding to the fluorescent layers
respectively.
[0012] The CNT-FED has a cathode substrate with a plurality of
cathode layers patterned on a glass substrate, wherein each cathode
layer has an electron-emitting area on which a CNT structure is
formed. A plurality of ribs fills each space between adjacent
cathode layers and each rib protrudes from the top of the cathode
layer to reach a predetermined height. A net-shaped gate electrode
layer is formed on the plurality of ribs, and a metal cap covers
the gate electrode layer. The metal cap has a plurality of
apertures, wherein the plurality of apertures is corresponding to
the electron-emitting areas respectively.
[0013] Accordingly, it is a principle object of the invention to
provide the metal sheet to prevent arc phenomenon.
[0014] It is another object of the invention to protect the gate
electrode layer from vibrating and peeling.
[0015] Yet another object of the invention is to increase the
luminescent uniformity and luminescent efficiency of the
CNT-FED.
[0016] It is a further object of the invention to provide the metal
cap to avoid cross-talk on the anode substrate.
[0017] Still another object of the invention is to provide the
apertures on the metal cap to limit the emitting space of the
direct-emitting electrons; thereby decreasing the amount of
accumulated electrons is decreased to eliminate arcing.
[0018] These and other objects of the present invention will become
readily apparent upon further review of the following specification
and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a sectional diagram showing a primitive
CNT-FED.
[0020] FIG. 2A is a sectional diagram showing a cathode substrate
of CNT-FED according to the first embodiment of the present
invention.
[0021] FIG. 2B is a top view showing an electron-emitting area
according the prior art.
[0022] FIGS. 2C and 2D are top views showing an electron-emitting
area according to the first embodiment of the present
invention.
[0023] FIGS. 3A to 3C are sectional diagrams showing a method of
forming a gate electrode layer according to the second embodiment
of the present invention.
[0024] FIGS. 4A and 4B are sectional diagrams showing an anode
substrate of CNT-FED according to the third embodiment of the
present invention.
[0025] FIG. 5A is a sectional diagram showing a cathode substrate
according to the fourth embodiment of the present invention.
[0026] FIGS. 5B to 5D are three-dimensional diagrams showing a
metal cap according to the fourth embodiment of the present
invention.
[0027] FIG. 6 is a sectional diagram showing a CNT-FED according to
the fifth embodiment of the present invention.
[0028] Similar reference characters denote corresponding features
consistently throughout the attached drawings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] [First Embodiment]
[0030] Please refer to FIGS. 2A to 2D. FIG. 2A is a sectional
diagram showing a cathode substrate of CNT-FED according to the
first embodiment of the present invention. FIG. 2B is a top view
showing an electron-emitting area according to the prior art. FIGS.
2C and 2D are top views showing an electron-emitting area according
to the first embodiment of the present invention. As shown in FIG.
2A, in the first embodiment of CNT-FED, a cathode substrate 40
comprises a glass substrate 41, a plurality of cathode layers 42
patterned on predetermined regions of the glass substrate 41, an
insulating layer 44 formed in the space between adjacent cathode
layers 42, a plurality of openings 45 passing through the
insulating layer 44 to expose each cathode layer 42, a net-shaped
gate electrode layer 46 formed on the insulating layer 44 without
covering the openings 45, and a plurality of CNT structures 48.
Each of the CNT structures 48 is grown on an electron-emitting area
of each cathode layer 42, and each CNT structure 48 has a plurality
of sub-CNT structures 481, 482 and 483 that are apart from each
other and arranged in array. It is noted that the sub-CNT
structures 481, 482 and 483 are spaced apart from each other
without forming an insulating layer therebetween.
[0031] As shown in FIG. 2B, in the prior art, an electron-emitting
area A is filled with carbon nanotubes and thus some of the carbon
nanotubes grown at the periphery of the area A always cause edge
effect, decreasing the luminescent uniformity of the CNT-FED. In
order to solve this problem, in the first embodiment, the
electron-emitting area A is divided into a plurality of sub-areas
on which each sub-CNT structure is grown. As shown in FIGS. 2C and
2D, the area A is divided into sub-areas A1, A2 and A3 that are
uniform and apart from each other and arranged in array, and the
sub-CNT structures 481, 482 and 483 are grown on the sub-areas A1,
A2 and A3 respectively. It is noted that the sub-areas A1, A2 and
A3 are spaced apart from each other without forming an insulating
layer therebetween. Since edge effect is formed at the periphery of
each sub-area A1, A2 and A3, the combination of all edge effects
can improve the luminescent uniformity of the CNT-FED. Also, as the
size of the sub-area is decreased, the interval between adjacent
sub-areas is reduced, and the distribution of the sub-areas is
denser, the brightness and luminescent uniformity of the CNT-FED
are increased.
[0032] In addition, depending on process requirements and
limitations, the profile of the sub-areas A1, A2 and A3 is a design
choice. Preferably, the profile of the sub-area may be
quadrilateral, circular or any other physical appearance. In
fabricating the CNT structure 48, printing is preferred used to
coat CNT materials on the sub-areas A1, A2 and A3. Preferably, the
interval between adjacent sub-areas is 80.about.150 .mu.m, and the
size of the sub-area is 200.times.200 m.sup.2.
[0033] [Second Embodiment]
[0034] FIGS. 3A to 3C are sectional diagrams showing a method of
forming a gate electrode layer according to the second embodiment
of the present invention. The second embodiment provides a method
of forming a gate electrode layer on a cathode substrate 50 of
CNT-FED. As shown in FIG. 3A, using deposition and
photolithography/printing, a plurality of cathode layers 52 is
patterned on a glass substrate 51. The cathode layer 52 is selected
from Ag, Cu or other conductive metal materials. Then, as shown in
FIG. 3B, using deposition and photolithography/printing, a
plurality of ribs 54 is formed to fill the space between adjacent
cathode layers 52 and protrude the top of the cathode layers 52,
resulting in a plurality of cavities 57 over the cathode layers 52
respectively. Preferably, the thickness of the rib 54 is
30.about.100 .mu.m. Next, as shown in FIG. 3C, using printing, a
plurality of gate electrode layers 56 is formed on each top of the
ribs 54. The gate electrode layer 56 is selected from Ag, Cu or
other conductive metal materials. Thereafter, high-temperature
baking is used for the rib 54 and the gate electrode layers 56.
[0035] Compared with the prior method of forming a net-shaped metal
layer, each of the gate electrode layers 56 formed on each top of
the ribs 54 cannot droop or become uneven. This prevents the gate
electrode layer 56 from vibrating and peeling, and thus improves
the luminescent uniformity and luminescent efficiency of the
CNT-FED. In addition, in the subsequent process of forming a CNT
structure on the cathode layer 52, the CNT structure can be formed
on the whole electron-emitting area A by using CVD as shown in FIG.
2B. Alternatively, coordinating the first embodiment, sub-CNT
structures can be formed on each sub-area A1, A2 and A3 as shown in
FIGS. 2C and 2D. In another case, the CNT structure can be printed
before the formation of the ribs 54 by using screen printing, and
then the gate electrode layers 56 are formed on the ribs 54 by
using printing. Next, high-temperature baking can be used for the
multilayer.
[0036] [Third Embodiment]
[0037] FIGS. 4A and 4B are sectional diagrams showing an anode
substrate of CNT-FED according to the third embodiment of the
present invention. In the third embodiment, an anode substrate 60
is provided with a glass substrate 61, a plurality of fluorescent
layers 62 patterned on predetermined regions of the glass substrate
61, and a planarized Al film 64 covering the fluorescent layers 62
and the exposed glass substrate 61. In addition, a metal sheet 66
glued to the glass substrate 61 by frit covers the Al film 64 and
has a potential the same as the Al film 64. Preferably, the metal
sheet 66 and the Al film 64 are spaced out a predetermined distance
apart. In order to make electrons bombard the fluorescent layers,
the metal sheet 66 has a plurality of openings 67 corresponding to
the fluorescent layers respectively. Also, in order to block the
scattering electrons, two metal feet 68 bent outside the opening 67
are provided, as shown in FIG. 4A. This leads electrons to directly
bombard the fluorescent layer 62 to prevent cross-talk on the anode
substrate 60.
[0038] Although part of the Al film 64 may be oxidized when
removing organic materials at high temperature
(450.about.500.degree. C.), the metal sheet 66 can compensate
conductivity for the Al film 64 to prevent an arc phenomenon
generated by the accumulated of electrons.
[0039] [Fourth Embodiment]
[0040] In order to prevent the divergent phenomenon from causing
cross-talk on the anode substrate, the fourth embodiment provides a
metal cap to cover the completed cathode substrate for blocking
scattering electrons. FIG. 5A is a sectional diagram showing a
cathode substrate according to the fourth embodiment of the present
invention. FIGS. 5B to 5D are three-dimensional diagrams showing a
metal cap according to the fourth embodiment of the present
invention. As shown in FIG. 5A, using the cathode substrate 50 on
which the gate electrode layers 56 are formed according to the
second embodiment, the CNT structures are formed on the cathode
layers 52 respectively and a metal cap 58 is employed to mask the
surface of the cathode substrate 50. The metal cap 58 has a
plurality of apertures 59 corresponding to the electron-emitting
areas respectively and corresponding to the fluorescent layers
respectively. The metal cap 58 and the gate electrode layer 56 have
an equal potential and are spaced out a predetermined distance
apart, preferably 0.1.about.1 mm. The gate electrode layer 56 is
used to attract emitted electrons, and the metal cap 58 is used to
focus the electron beam. Since an electric field generated by the
metal cap 58 is smaller than another electric field generated by
the gate electrode layer 56, the excessive electrons cannot bombard
the metal cap 58 to cause vibration. Also, since the scattering
electrons are blocked and guided outside by the metal cap 58, the
cross-talk on the anode substrate is avoided. Furthermore, the
apertures 59 limit the emitting space of the direct-emitting
electrons, therefore the amount of the accumulated electrons is
decreased to eliminate arc phenomenon.
[0041] Preferably, the diameter of the aperture 59 is 300.about.600
.mu.m, and the distance between adjacent apertures 59 is
100.about.200 .mu.m. The profile of the aperture 59 is a design
choice. As the size of the aperture 59 is increased, the current of
the direct-emitting electrons is increased. Preferably, the profile
of the aperture 59 is circular as shown in FIG. 5B, quadrilateral
as shown in FIG. 5C, or hexagon as shown in FIG. 5D that achieves
the lager size.
[0042] [Fifth Embodiment]
[0043] FIG. 6 is a sectional diagram showing a CNT-FED according to
the fifth embodiment of the present invention. The fifth embodiment
provides a CNT-FED that is the combination of the anode substrate
60 shown in FIG. 4A and the cathode substrate 50 shown in FIG. 5A.
Using the metal foot 68 and the apertures 59, the CNT-FED can
further prevent the cross-talk on the anode substrate 60.
[0044] It is to be understood that the present invention is not
limited to the embodiments described above, but encompasses any and
all embodiments within the scope of the following claims.
* * * * *