Electron source having first and second layers

Details Electron source having first and second layers Electron source having first and second layers

2000-07-21

2004-05-25

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

Discharge devices having a thermionic or emissive cathode

C313S309000, C313S495000

Reexamination Certificate

active

06741017

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an electron source and a process for manufacturing the same. More specifically, the present invention relates to a cold cathode electron source applicable to a back light for a liquid crystal device, various types of light sources, and a flat panel display for a computer or television, and also relates to a process for manufacturing the cold cathode electron source.
RALATED BACKGROUND ART
In a conventional electron tube, such as a cathode ray tube (CRT), a hot cathode has been used as the electron source. A hot cathode is a cathode which utilizes thermionic emission to produce electrons. Thermionic emission is a mechanism in which a cathode material is heated to 1500-2700 K to apply energy higher than the work function to free electrons in the conduction band, whereby electrons are emitted beyond the potential barrier of the surface of the cathode material. Examples of such material include pure metals and oxides. The material most frequently used today is a sintered-type material prepared by press-sintering a mixture of a barium (Ba)-based compound (e.g., 5BaO·2Al
2
O
3
·CaO) and tungsten (W) powder or an impregnated-type material prepared by impregnating porous W with a Ba-based compound in a molten state. The two types of materials have an advantage in that the electron emission density is high and, in addition, the discharge of gas generated during vacuum evacuation is small and the cathode material can be re-activated even when the cathode is exposed to the atmosphere because barium aluminate is contained in the material.
Besides thermionic emission, electron emission includes field emission, secondary electron emission, photoelectron emission and so on.
A cold cathode is a cathode which can emit electrons by field emission. In a field emission type of cathode, a high electric field (10
9
V/m) is applied in the vicinity of the surface of the cathode material to lower the potential barrier of the surface (which is the so-called “tunneling effect”), whereby electrons are emitted. This type of cathode is called a “cold cathode” because it does not require the heating of the cathode material like a hot cathode.
The current-voltage characteristic of a field emission type of cold cathode can be approximated in accordance with the Fowler-Nordheim equation. The electron-emitting section of the cold cathode is designed to have such a structure that the field enhancement factor is increased (i.e., a needle-like structure), since a high electric field is applied to the electron-emitting section while keeping the insulation state. An early type of cold cathode has a diode type structure formed by electrolytic polishing of a needle-shaped single crystal. In recent days, however, a remarkable progress has been made in the technique for manufacturing field emission type of electron sources (i.e., field emitter arrays) which can emit electrons in a high electric field by virtue of the development of micromachining techniques as used in the field of integrated circuits or thin films. In particular, a field emission type of cold cathode with a microstructure has been manufactured successfully. Such a field emission type of cold cathode is the most essential electron emitting element among the essential elements of a triode type micro-electron tube or micro-electron gun. A field emission type of cold cathode with a microstructure has an advantage in that a higher current density can be provided to a hot cathode.
A field emission display (FED) with a cold cathode is expected to be applicable to a self-emitting type of flat panel display. Under these situations, research and development of a field emission type of electron source have been aggressively made.
FIG. 14
is a sectional view showing the basic configuration of a prior art FED.
“As shown in
FIG. 14
, the FED consists mainly of a back plate
18
which effects the emission of electrons; a face plate
10
in which fluorescence-emission is effected from a luminant
11
by irradiation of an electron beam
2
from the back plate
18
, whereby an image is displayed thereon; side walls
19
for vacuum-sealing a space between the back plate
18
and the face plate
10
; and spacers
15
for supporting the gap between the back plate
18
and the face plate
10
and maintaining the strength of the structure of the FED against atmospheric pressure. The back plate
18
is provided with a gate electrode
14
via an insulator
16
. The gate electrode
14
is used for the application of an electric field to a cold cathode
13
. The cathode lines and the gate lines usually form together the X-Y matrix for addressing of pixels. When the gap between the back plate
18
and the face plate
10
is wide, a focusing electrode
17
may be required for focusing the electron beam
2
. Since the FED is a type of vacuum device like a CRT or a vacuum tube, a micropump called a “getter” is disposed in the vacuum space between the back plate
18
and the face plate
10
for the purpose of maintaining the vacuum level of the vacuum space after the vacuum-sealing thereof. The getter includes an evaporation type and a non-evaporation type. An evaporation type getter generates a fresh and active gettering surface thereon by heating evaporation or the like, on which evacuation is achieved by means of the chemical adsorption of gas onto the gettering surface. In a non-evaporation type getter, gas chemically adsorbed on the gettering surface (which has been activated by heating to a high temperature) is diffused into the getter material, whereby evacuation is achieved. If the non-evaporation type getter is made of the same material, its evacuation ability depends on the volume and the surface area thereof, and becomes higher as the volume and surface area become larger.”
In the field emission, the amount of emission current may vary 2 to 3 times for 2 to 3% of change in electric field. Therefore, when the field emission is applied to a FED, it is required to introduce a control layer, such as a ballast resistor layer.
On the other hand, there has been reported a laminate of a metal plate having through-holes and a control electrode for an electron beam to manufacture a hot cathode electron source (Japanese Patent No. 2558993).
It has been proposed to use a ceramic substrate laminate for the formation of ribs in a plasma display (Japanese Patent Application Laid-open No. 3-45565).
As the material of a field emission type of electron source for a FED, various kinds of materials have been known. Recently, a carbon nanotube (CNT) has attracted much attention as the electron emission material.
A carbon nanotube was originally developed by Iijima et al (S. Iijima, Nature, 354, 56, 1991). The carbon nanotube has a nested structure of cylindrically wound graphite layers, of which tip has a diameter of about 10 nm. The carbon nanotube is believed to be a very excellent material as an electron source array due to its properties such as high resistance against oxidation and ion bombardment. There are experimental reports on the field emission from carbon nanotubes by the research groups of R. E. Smalley et al. (A. G. Rinzler, Science, 269, 1550, 1995) and W. A. de Heer et al. (W. A. de Heer, Science, 270, 1179, 1995). The carbon nanotubes used in these experiments were casted on a metal thin plate.
The carbon nanotube has a structure having a high aspect ratio. Therefore, the electron source using carbon nanotubes is assumed to exert a higher electron emission efficiency when the carbon nanotubes are oriented in the direction of the electric field applied.
As a known electron emission element using oriented carbon nanotubes, there is mentioned a triode type one comprising carbon nanotubes which are selectively grown in small holes provided in an anode oxide film (Japanese Patent Application Laid-open No. 10-12124). In the electron emission device, the variation in properties of the electron source in each pixel is reduced and the stability of current intensity per pixel is improved.
It has been also proposed to orient carb

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