Cold cathode element

Details Cold cathode element Cold cathode element

1999-01-27

2001-07-31

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

Discharge devices having a thermionic or emissive cathode

C313S311000, C313S309000, C313S351000

Reexamination Certificate

active

06268686

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cold cathode element, which emits electrons on application of an electric field.
2. Description of Related Art
A hot cathode element and a cold cathode element have been known as elements for emitting electrons.
A hot cathode element is used in the field represented by a vacuum tube, but has a problem in that it is difficult to be integrated with other components due to the heat generated. On the other hand, a cold cathode element is expected to be used in elements, such as a flat panel display, a voltage amplification element and a high frequency amplification element, since it does not use heat and can be integrated with other components.
SUMMARY OF THE INVENTION
An object of the invention is to provide a highly practical cold cathode element that can sufficiently emit electrons even by application of low voltage.
In order to attain the object, the invention provides a cold cathode element which emits electrons on application of an electric field, the element comprising a diamond carbon film having a half width Hw of a photoelectron spectrum of a C
1S
electron using X-ray photoelectron spectroscopy of 1.72 eV or more.
The term “diamond carbon film” used herein means a carbon film having characteristics close to a diamond although its crystalline structure is not a diamond single crystal structure.
By setting the half width Hw to the above range for the diamond carbon film, the diamond characteristic, i.e., electric insulating property, of the diamond carbon film is weakened, but the graphite characteristic, i.e., conductivity, is enhanced. Accordingly, the emission electric field of the cold cathode element is lowered to make it possible that electrons are sufficiently emitted even by applying a low voltage.
If the half width Hw is less than 1.72 eV, the diamond characteristic of the diamond carbon film becomes too strong, and the emission electric field is too high.
The invention also provides a cold cathode element for emitting electrons on application of an electric field, the element comprising a diamond carbon film including Cs (cesium) in an amount of from 0.1 to 0.5 atomic %.
The diamond carbon film functions as a cold cathode element by itself. By adding the above-specified amount of Cs to the diamond carbon film, however, turbulence is generated in the structure of the film due to the difference in atomic radius between C (carbon) and Cs, and the electric insulating property of the film is weakened but the conductivity is enhanced. Cs in the film also lowers the work function of C. The emission electric field of the cold cathode element is thus lowered to make it possible that an electron is sufficiently emitted even by applying a low voltage.
If the content of Cs is less than 0.1 atomic %, the effect of the addition of Cs is nil. If the content of Cs is more than 5.0 atomic %, the turbulence in the film becomes large to reduce the SP
3
characteristic of the film, and the field emission by the negative electron affinity of the film cannot be expected. In this case, when the amount of Cs becomes more than 1.8 atomic %, the Cs amount at the surface of the film is excessive, and oxidation of Cs rapidly proceeds due to exposure of the film to the air, which results in possible formation of cracks in the film. Therefore, the cold cathode element having a Cs content of more than 1.8 atomic % but not more than 5.0 atomic % must be produced and used in vacuum. In other words, the cold cathode element that is possibly exposed to the air, preferably has a Cs content of 1.8 atomic % or less.
The diamond carbon film may be used singly, or may be used as a material constituting a surface covering layer of a cold cathode element comprising Si, for example, to enhance the performance of the element.
The above and other objects, characteristic features and advantages of the invention will be apparent from the following detailed description with respect to preferred embodiments according to the attached drawings.


REFERENCES:
patent: 5650201 (1997-07-01), Tompa
patent: 5760536 (1998-06-01), Susukida et al.
patent: 5852303 (1998-12-01), Cuomo et al.

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