Electric lamp and discharge devices – Discharge devices having a thermionic or emissive cathode
Patent
1997-11-06
1999-10-26
O'Shea, Sandra
Electric lamp and discharge devices
Discharge devices having a thermionic or emissive cathode
445 6, H01J 105, H01J 900
Patent
active
059734469
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a field emission cathode to be used in light sources and similar devices, such as display panels, cathode-ray tubes, etc., and to methods in the production of such a field emission cathode.
BACKGROUND OF THE INVENTION
In order for field emission illuminating devices to become useful, there is a need for a field emission cathode with a higher efficiency than known cathodes. Once a field emission cathode is achieved with a low work function, high durability, non-polluting composition and low production cost, it will be possible to replace a great variety of light sources with light sources including a field emission means in combination with a fluorescent surface for emission of visible light.
For example, great efforts are made today for reducing problems with commonly used fluorescent tubes, which require complicated external electrical devices and contain material with negative environmental effects. In present fluorescent tubes, gas discharge is employed for emitting radiation onto a fluorescent material that emits visible light in turn. A new type of emission means is desired for eliminating drawbacks of present fluorescent tubes.
PRIOR ART
U.S. Pat. No. 4,728,851 discloses a field emission cathode in an emitting device with a memory function, consisting of one carbon fibre with a diameter in the order of two micrometers with an emitting end sharpened by corona discharge to a diameter of approximately 0.2 micrometers.
U.S. Pat. No. 4,272,699 discloses a field emission cathode in an electron impact ion source device consisting of a bundle of carbon fibres with diameters in the order of two to ten micrometers with emitting ends, which are cut off and not sharpened by any refinishing operation.
The above-mentioned documents are incorporated by reference.
SUMMARY OF THE INVENTION
An object of the invention is to provide a method in the production of a field emission cathode, wherein the cathode is provided with a surface geometry that facilitates the achievement of local high electric field strengths for electron field emission. Another object is to provide a method in the production of a field emission cathode, wherein the cathode has a high mechanical and electrical durability. Another object is to provide a method in the production of a field emission cathode, wherein the cathode has a low work function. Another object is to provide a method in the production of a field emission cathode, wnerein negative environmental effects of an illuminating device including the cathode are minimized. Another object is to provide a method in the production of a field emission cathode, wnerein the cathode has an advantageous geometrical configuration. Another object is to provide a method in the production of a field emission cathode, wherein the cathode gives a very short switching time in the electron emission.
Another object of the invention is to provide a field emission cathode for elect-on field emission with a surface geometry adapted for high intensity local electric fields. Further objects of a field emission cathode of the invention are to attain a field emission cathode with an emitting surface having irregular topography facilitating electron field emission, a high mechanical durability, a high electrical durability of cathode, preferably a low electron work function, as well as a long life in use, a high emission of energy per unit area of cathode, a very short switching time it the electron emission, and minimized negative environmental effects of an illuminating device including the cathode.
A further object of the invention is to improve an illuminating device, or other electron field emission devices, the operating principles of which are known per se, by employing at least one field emission cathode with features set fourth above.
The above objects are attained by the features set fourth in the appended claims.
In a method of the invention, a field emission cathode constituted by at least one body, preferably purified to contain essenti
REFERENCES:
patent: 4272699 (1981-06-01), Faubel et al.
patent: 4728851 (1988-03-01), Lambe
patent: 5588893 (1996-12-01), Kaftanov et al.
Kaftanov Vitaly Sergeevich
Sheshin Evgenij Pavlovich
Suvorov Alexander Leonidovich
Lightlab AB
O'shea Sandra
Smith Michael J.
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