Field emission device

Details Field emission device Field emission device

2000-09-01

2002-09-03

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

With luminescent solid or liquid material

Vacuum-type tube

C313S309000, C313S310000, C313S336000

Reexamination Certificate

active

06445124

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-280666, filed Sep. 30, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a field emission device, and relates, more particularly, to a field emission device having a three-electrode structure of a cathode, an anode and a gate electrode.
There have been proposed various field emission type cold cathodes. Among others, a tip emitter called a Spindt type emitter and a surface conduction emitter are representative types. In recent years, a method using a carbon nanotube that is stable with a low work function has also been proposed.
FIG. 1
shows a cross section of a tip emitter. This emitter has a sharp front end of a tip emitter
170
formed on a cathode
120
, with the front end having a curvature radius of a few nanometers to a few dozens of nanometers. The tip emitter emits cold electrons based on a strong electric field that is concentrated at the front end. In other words, an electric field is formed between the front end of the emitter
170
and a gate electrode
140
formed on a first insulation layer
130
on the cathode
120
, and electrons are emitted from the front end of the tip emitter
170
. Therefore, in order to emit electrons at a low voltage, it is ideal to set a distance between the gate electrode
140
and the emitter
170
as short as possible. The emitted electrons are drawn to a direction of an anode (not shown) disposed above the tip emitter
170
. However, each electron has an initial speed in a horizontal direction at the time of the emission, and therefore, the electron beams are spread in a lateral direction.
In order to prevent this spread of the electron beams, a control electrode
160
is disposed above the gate electrode
140
as shown in FIG.
1
. In this case, it is necessary that an aperture diameter of the gate electrode
140
and an aperture diameter of the control electrode
160
are set to have a suitable ratio. In order to install the control electrode
160
, it is necessary to install an insulation layer
150
on the gate electrode
140
and then to install the control electrode
160
on the insulation layer
150
. In order to implement this installation process, a high-precision aligner is necessary. Therefore, this has a drawback in that not only the installation process increases, but also the facility necessary for the manufacturing becomes expensive.
In the mean time, in the case of the surface conduction emitter, an electron emitter is provided on a conductive thin film that extends over a pair of electrodes (an emitter electrode and a gate electrode) that are formed on a substrate. When an electric field is applied to the electrodes on both ends of the electron emitter, electrons are drawn out in a horizontal direction from an emitter electrode, and force is applied to the gate electrode provided on the substrate. Thus, the electrons are emitted in a horizontal direction. An acceleration electrode is provided above the electron emitter, and a part of the emitted electrons fly to the acceleration electrode. However, this efficiency is low, and the electrons are emitted in a parabolic direction in stead of a vertical direction from the substrate. Therefore, the electrons that collide against the acceleration electrode are deviated from the normal line of the electron emitter. Because of this phenomenon, when the field emitter is applied to an image display unit, beams are dispersed. As a result, there occurs a leakage of beams to adjacent pixels, or a high-efficient light emission is not obtained.
FIG. 2
is a perspective view showing one example of a surface conduction emitter disclosed in Jpn. Pat. Appln. KOKAI Publication No. 8-250018. This surface conduction emitter solves the leakage of the beams to adjacent pixels by narrowing the emitted electron beams. In order to solve the above phenomenon, there are provided electrodes
122
a
and
122
b
that form an equipotential surface of approximately a U shape in a direction orthogonal with a direction of voltage application between a pair of electrodes
123
a
and
123
b
, on a surface that is defined by the direction of voltage application between the pair of electrodes
123
a
and
123
b
and a direction of an electric field application by an acceleration electrode (above the electrodes
123
a
and
123
b
not shown) that works on the emitted electrons.
However, according to the surface conduction emitter, in order to form the approximately U-shaped equipotential surface, it is necessary to set the electron emitter at the center of the device electrode, and it is also necessary to strictly adjust the device formation and the height of the wiring electrode.
In order to solve the difficulty of the above manufacturing methods, a four-electrode type field emitter has been proposed in Jpn. Pat. Appln. KOKAI Publication No. 8-293244.
FIG. 3
shows the four-electrode type field emitter. The disclosed four-electrode structure consists of a cathode
131
, a control electrode
134
, a gate electrode
133
, and an anode
136
. According to this method, neither a tip emitter nor a surface conduction emitter is used, but a material of a low work function is used as an electron emission layer
135
. A shape of electron beams is narrowed by the substrate (cathode)
131
on which the electron emission layer
135
has been formed, the beam-forming electrode (control electrode)
134
that has been formed on the electron emission layer
135
by surrounding the electron emission layer, and the gate electrode
133
that has been formed on an insulation layer
132
on the beam-forming electrode
134
.
However, according to this emitter, it is unavoidable that the process also becomes complex as it is necessary to form the control electrode in a similar manner to that of the emitter shown in FIG.
1
.
Further, Jpn. Pat. Appln. KOKAI Publication No. 9-82215 has disclosed an emitter that has a large number of field emission tips having fine sizes within the electron emission surface. Further, there has been proposed a structure that has a ratio of a distance between a gate and an emitter to an aperture diameter (short diameter) set to 1 to 2 or higher so that the large number of field emission tips can have an approximately equal opportunity of emitting electrons. Based on this structure, it has been intended to be able to drive approximately homogeneously an emitter made of a bundle of nanometer-sized wires. However, this disclosure has an object of driving approximately homogeneously the emitter made of a bundle of nanometer-sized wires. This disclosure does not intend to restrict the spreading of the orbit of electron emission. Thus, this disclosure describes that it is desirable to have a control electrode without particularly limiting the electrode structure.
As explained above, as it is difficult to control the direction of electrons emitted by the field emitter that has a three-electrode structure of a cathode, an anode and a gate electrode, it has been conventionally assumed that a four-electrode structure having a control electrode in addition to the three electrodes is necessary. However, the four-electrode structure has a complex structure around the electron emitter. Further, this structure involves a difficulty in the manufacturing aspect as the electron emitter must be installed at the center of the electric field.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a field emission device having a three-electrode structure that can be manufactured easily and that can control the direction of emitted electrons.
In order to achieve the above object, according to a first aspect of the present invention, there is provided a field emission device consisting of three electrodes, the field emission device comprising:
an emissive material formed on a cathode on a substrate;
an insulation layer formed to surround the emissive materi

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