Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
2000-12-12
2004-05-25
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S310000
Reexamination Certificate
active
06741026
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a field emission display, and more particularly, to a field emission display which has a stable driving voltage and an excellent productivity, and a method for fabricating the same.
2. Background of the Related Art
Referring to
FIG. 1
, a related art Spindt type FED(Field Emission Display) is provided with an anode part
10
, a cathode part
20
, and a spacer
9
connected between the anode part and the cathode part. The anode part
10
has a face plate
1
which is a glass substrate, an anode
2
which is an ITO (Indium Tin Oxide) thin film electrode formed thereon, and R, G, B stripes
8
of fluorescent materials coated thereon. The cathode part
20
has a base plate
3
of a nonconductive material, an orthogonal matrix of cathode electrode
4
rows and gate electrode
5
columns, FEA(Field Emission Array) emitters
6
matrix addressed between adjacent row electrode and column electrode for emission of electrodes, and an approx. 1 &mgr;m thick insulator
7
between adjacent emitters. The spacer
9
is inserted between the anode part
10
and the cathode part
20
, to maintain a 20~400 &mgr;m gap between the face plate
1
and the base plate
3
, with the two plates sealed with frit glass to maintain a cavity formed thereby to be 10
−7
torr. The cathode electrode
4
, the row electrode of the cathode part
20
, is negative electrode, and for stable operation by reducing current from the emitter
6
, electrons from 1000~10000 the emitters are designed to be directed toward one pixel formed on a screen of the face plate.
The related art FED display forms an image as an electric field is provided to the cathode electrode
4
, to boost a voltage on the gate electrode
5
, that causes the emitter
6
to emit electrons, which are accelerated toward the anode
2
until the electrons hit onto the fluorescent surface
8
on the anode
2
that causes the fluorescent surface emits light, to form the image. If an intense field are provided to a surface of a metal and the like having a work function, which makes a potential barrier thinner, electrons overcome the barrier and are emitted out of the surface(tunneling). The more intense the field become, the thinner the potential barrier become, for easier emission of the electron. And, in order to maximize the field under the same voltage, a structure with a sharp end, such as a tip, is formed. Accordingly, the Spindt type emitters are used in the related art. The Spindt type emitters are disclosed in Japanese Patent Publications H10-12166, H11-111160, H10-69867.
In the meantime, according to Fowler-Nordheim theory, an emission current is heavily dependent on a work function of an emissive substance, wherein Fowler and Nordheim found an equation for calculating a current density ‘J’ which can be obtained when a field emission is occurred by application of a field to the substance in 1928. This is a calculation of a flow of electrons (current) emitted from a free electron metal with a work function &phgr;, which has a step barrier on a surface thereof and is applied of an electric field. The above theory can be expressed as the following equations (1) and (2).
⟨
MARGIN
⟩
⟨
TR
⟩
⟨
P
⟩
⟨
CHAR
⟩
J
=
A
β
2
V
2
Φ
Exp
-
(
B
Φ
3
2
β
v
)
(
1
)
⟨
/
CHAR
⟩
⟨
/
P
⟩
⟨
P
⟩
⟨
CHAR
⟩
Ln
(
I
V
2
)
=
Ln
(
a
)
-
(
b
V
)
⟨
/
CHAR
⟩
<
/
P
&AutoLeftMatch;
⟩
(
2
)
where, J denotes an emission current density A/cm
2
, V denotes an electric field applied to a metal surface V/cm, <MARGIN><TR><P><CHAR>&phgr;=<CHAR></P> work function of a metal eV, A, and B denote constants, &bgr; denotes an electric field multiplication coefficient: an electrode gap, Tip sharpness. A graph drawn taking 1/V as an X-axis and ln(1/v2) as a Y-axis in the equation (1) is called as a Fowler-Nordheim Plot(or FN plot), which is an important method for determining characteristics of field emission electrons. A straight portion of the graph with a negative slop is a current region caused by the field emission.
According to the equation (2), the work function is required to be small for effective electron emission. However, with the work function between 4~5, the Spindt tip emitter requires much energy for the electron emission. And, in fabrication of the FED, because an E-beam is used, screen size can not be any larger than 20″, fabrication of the FED takes much time, and product cost is high.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a field emission display and a method for fabricating the same that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a field emission display and a method for fabricating the same, which is suitable to form a large sized display with easy.
Another object of the present invention is to provide a field emission display and a method for fabricating the same, which makes a driving voltage stable, has a uniform field emission characteristic, low cost, and an excellent productivity.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the field emission display including a cathode array having a cathode electrode formed on a substrate, insulating layers and carbon nanotube films for use as emitter electrodes formed alternately on the cathode electrode, and a gate electrode formed on the insulating layer.
In another aspect of the present invention, there is provided a method for fabricating a field emission display, including the steps of (1) forming a cathode electrode, an insulating layer, and a gate electrode on a substrate in succession, (2) etching the gate electrode and the insulating layer into a cathode array pattern, to form an emitter region, (3) forming a sacrificial layer on the gate electrode which is not etched, (4) depositing a carbon nanotube film on the cathode electrode in the emitter region, to form an emitter, and (5) etching the sacrificial layer for removing the carbon nanotube formed on the sacrificial layer, to form a cathode array.
In further aspect of the present invention, there is provided a method for fabricating a field emission display, including the steps of (1) forming a cathode electrode, an insulating layer, a gate electrode, and a sacrificial layer on a substrate in succession, (2) etching the sacrificial layer, the gate electrode, and the insulating layer into a cathode array pattern, to form an emitter region, (3) forming a carbon nanotube film as an emitter on the cathode electrode in an etched emitter region, and (4) etching the sacrificial layer not etched in the step (2) for removing the carbon nanotube formed on the sacrificial layer, to form a cathode array.
Thus, the present invention can fabricate a large sized cathode plate at a low cost because the film is formed by screen printing and exposure, which can reduce the cumbersome steps in fabrication of the related art Spindt emitter tip. And, as the carbon nanotube film used as the emitter has a low work functi
Han Si Wook
Kim Sang Mun
Fleshner & Kim LLP
LG Electronics Inc.
Patel Ashok
Williams Joseph
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