Electron emission device with specific island-like regions

Details Electron emission device with specific island-like regions Electron emission device with specific island-like regions

1999-09-10

2001-09-04

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

With luminescent solid or liquid material

Vacuum-type tube

C313S496000

Reexamination Certificate

active

06285123

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an electron emission device, and more particularly to an electron emission display device which has a plurality of electron emission devices arranged in an image display array, for example, in a matrix form.
2. Description of the Related Art
Conventionally, in field electron emission display apparatuses, a Field Emission Display (FED) is known as a planar emission display device equipped with an array of cold cathode electron emission sources which does not require cathode heating. The emission principle of, for example, an FED using Spindt-type cold cathodes of minute protrusions is as follows. Its emission principle is like a Cathode Ray Tube (CRT), although this FED has a cathode array of Spindt-type protrusions which is different from that of CRT. In the FED, electrons are drawn into a vacuum space by means of each gate electrode spaced apart from the Spindt-type cathode, and the electrons are made to impinge upon the fluorescent substance that is coated on a transparent anode, thereby causing light emission.
This FED, however, has a problem of low production yield because the manufacture of the minute Spindt-type emitter arrays as a cold cathode is complex and involves many processes.
There is also known an electron emission device with electron emission devices of metal-insulator-metal (MIM) structure as a planar electron emission source. The electron emission device with the MIM structure comprises an Al underlayer as a base electrode, an Al
2
O
3
insulator layer with about 10 nm thickness, and a Au overlayer, as a top electrode with about 10 nm thickness which are formed in order on the substrate. In the case that this MIM device is placed under an opposing electrode in a vacuum, when a voltage is applied between the Al underlayer and the Au overlayer and, at the same time, an acceleration voltage is applied to the opposing electrode, then some of electrons emit out of the Au overlayer and reach the opposing electrode.
However, even the electron emission device with the MIM structure does not yet provide a sufficient amount of emitted electrons.
To overcome these disadvantages of emission of the MIM device, it is conventionally considered that there is a necessity to make the Al
2
O
3
insulator layer thinner by about several nanometers and make the Al
2
O
3
insulator layer with a uniform quality so that the interface between the Al
2
O
3
insulator layer and the Au overlayer is more uniform.
To provide a thinner and more uniform insulator layer, for example, an attempt has been made to control the anodized current by using an anodization method thereby to improve the electron emission characteristics, as in the invention described in Japanese Patent Application kokai No. Hei 7-65710.
However, even an electron emission device with the MIM structure which is manufactured by this anodization method ensures an emission current of about 1×10
−5
A/cm
2
and an electron emission efficiency of about 0.1%.
The MIM type electron emission device whose insulator layer has a thickness of several tens of nanometers to several micrometers does not have a plane forming status formed uniformly resulting in a problem of bringing an unstable electron emission property of the device.
A surface conductive type electron emission device is further known. This type device is manufactured as follows. First a pair of facing electrodes are formed on a substrate of an insulative material. Subsequently a conductive thin film is bridged between the facing electrodes. The conductive thin film bridge is electrified as an electrifying process so as to form a gap or break as an electron emission portion therein. Since such a gap or break is generated by locally destroying, denaturing or modifying the conductive thin film, there are problems in that the structural homogeneity in the electron emission portion is inferior and, the re-productivity in shape of the electron emission portion is very poor. The electron emission portion is restricted in shape within a linear line.
OBJECT AND SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances, and thus an object thereof is to provide an electron emission device having an electron emitting efficiency high enough to stably emit electrons at a low voltage applied thereto, and moreover a display apparatus including a flat panel display device which employs a plurality of such electron emission devices.
To attain the above object, the present invention provides an electron emission device which comprises:
an electron-supply layer made of a semiconductor material, a metal compound or metal;
an insulator layer formed on the electron-supply layer; and
a thin-film metal electrode formed on the insulator layer,
characterized in that the insulator layer and the thin-film metal have a plurality of island-like regions where thicknesses of both the insulator layer and the thin-film metal electrode gradually decrease.
According to the electron emission device having the structure mentioned above, said island-like regions are electron emission sites.
According to the electron emission device having the structure mentioned above, said insulator layer is made of dielectric and has a film thickness of 50 nm or greater.
According to the electron emission device having the structure mentioned above, the thin-film metal electrode is terminated on the insulator layer in each of the island-like regions.
According to the electron emission device having the structure mentioned above, the insulator layer is terminated on the electron-supply layer in each of the island-like regions.
According to the electron emission device having the structure mentioned above, each of the island-like regions is a recess formed in a flat surface of the thin-film metal electrode.
According to the electron emission device having the structure mentioned above, the insulator layer and the thin-film metal are formed by a physical vapor deposition and/or chemical vapor deposition.
According to the electron emission device having the structure mentioned above, a minute particle is provided in each of the island-like regions.
According to the electron emission device having the structure mentioned above, an inverse tapered block is provided in each of the island-like regions.
According to one aspect of the present invention, there is also provided a method of manufacturing an electron emission device having a plurality of island-like regions where thicknesses of an insulator layer and a thin-film metal electrode gradually decrease, which method comprises the steps of:
forming an electron-supply layer on a substrate;
spraying a plurality of minute particles onto the electron-supply layer;
depositing an insulator material on the electron-supply layer and the minute particles, thereby forming a thin insulator layer; and
forming a thin-film metal electrode on the insulator layer and the minute particles, thereby forming island-like regions around a contact surface under the minute particles.
In an embodiment according to the invention of the method of manufacturing an electron emission device, the method further comprises a step of applying a voltage across the electron-supply layer and the thin-film metal electrode for growth of conductive paths after the thin-metal electrode forming step.
In an embodiment according to the invention of the method of manufacturing an electron emission device, the method further comprises a step of removing the minute particles from the island-like regions after the thin-metal electrode forming step.
In an embodiment according to the invention of the method of manufacturing an electron emission device, the method further comprises a step of applying a voltage across the electron-supply layer and the thin-film metal electrode for growth of conductive paths after the minute particle removing step.
According to another aspect of this invention, there is further provided a method of manufacturing an electron emission device having a

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