Electric lamp and discharge devices – Discharge devices having a multipointed or serrated edge...
Reexamination Certificate
1997-06-30
2001-03-13
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Discharge devices having a multipointed or serrated edge...
C313S336000, C313S351000
Reexamination Certificate
active
06201342
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates to the field of electron field emission cold cathodes which have atomically sharp tips and to a fabrication method for making such cathode emitters by fabrication of the gate before the field emitters.
2. Description of Prior Art
Field emission sources require sharp electron emitter structures to create electric field enhancement which promotes electron emission from the tip of the field emitter. The very sharp structures that are required for field emission cathodes have been primarily fabricated by two approaches. The first approach typically starts with a silicon wafer and uses anisotropic crystallographic etching techniques or isotropic etching techniques in combination with oxidation sharpening to form sharp field emitters. A gate structure for modulating the emission current is fabricated after the tip is created. This approach suffers from nonuniform characteristics of the sharp tip due to nonuniform etching and oxidation processes which results in poor uniformity in the tips' radius of curvature.
The second approach uses selective deposition of metals to form conical shapes. In this approach, the gate electrode is formed prior to cathode fabrication. However, following emitter material deposition, this layer of material which exists over the gate electrode is removed from atop the gate electrode. Since the emitter is formed of polycrystalline material using this technique, each emitter tip is different due to random fluctuations of the size and shape of the polycrystallites that make up the field emitter which leads to nonuniformities in the electron emission characteristics.
The Kumar U.S. Pat. No. 5,341,063 discloses cold cathode field emitters comprising an electrically conducting metal layer with diamond field emission tips protruding above the metal. Kumar's fabrication includes the steps of coating a quartz or another substrate with a film of artificial diamond 50-500 nm thick preferably with (111) orientation with a plurality of diamond tips less than about 1 micron apart; depositing a conductive metal over the diamond layer; covering the diamond tips; and etching a portion of the conductive metal to expose the diamond tips with negative electron affinity material.
OBJECTS AND SUMMARY OF INVENTION
An object of this invention is a cold cathode electron emitter characterized by a plurality of nanomesas or high-aspect ratio submicron pillars disposed on a substrate each provided with an atomically sharp self-assembled tip.
Another object of this invention pertains to fabrication of a cold cathode field emitter comprising the steps of forming spaced nanomesas on a substrate, providing a gate around each nanomesa, depositing a semiconducting material on each nanomesa and growing tips by epitaxial self-assembly on the nanomesa having tip apexes with a radius of curvature on the order of 1 nm.
It is another object of this invention to fabricate a cold cathode field emitter by fabricating the gate before the tips so that sharpness of the tips is not compromised.
It is another object of this invention to fabricate tips by epitaxial techniques which produce tips with far better uniformity and significantly smoother surface morphology than either the oxidation process or deposition of polycrystalline material.
These and other objects of this invention are accomplished by a cold cathode field emitter and fabrication thereof. The field emitter is characterized by a multitude of nanomesas on a semiconductor substrate, tips of a semiconductor material disposed on the nanomesas with apexes of the tips of about 1 nm, and a gate around the upper portion of the nanomesas for extracting electrons by field emission from the tips such that these field emitted electrons travel to the anode. The fabrication process is characterized by growing the tips on the nanomesas by self-assembled epitaxy after formation of the gate.
REFERENCES:
patent: 5341063 (1994-08-01), Kumar
patent: 5475280 (1995-12-01), Jones et al.
patent: 5627427 (1997-05-01), Das et al.
patent: 5726524 (1998-03-01), Debe
patent: 5783905 (1998-07-01), Greschner et al.
Gray Henry F.
Hobart Karl D.
Kub Francis J.
Shaw Jonathan
Thompson Phillip E.
Edelberg Barry A.
Kap George
Patel Nimeshkumar D.
The United States of America as represented by the Secretary of
Williams Joseph
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