Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Low workfunction layer for electron emission
Reexamination Certificate
1998-04-20
2001-06-12
Jackson. Jr., Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Low workfunction layer for electron emission
C313S309000, C313S310000, C313S336000, C313S351000
Reexamination Certificate
active
06246069
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to ungated and gated thin-film edge field emitters capable of emitting electrons of relatively low voltage and to methods for making the same.
DESCRIPTION OF THE RELATED ART
Very small localized vacuum electron sources which emit sufficiently high currents for practical applications are difficult to fabricate. This is particularly true when the sources are required to operate at reasonably low voltages. Presently available thermionic sources do not emit high current densities, but rather result in small currents being generated from small areas. In addition, thermionic sources must be heated, requiring special heating circuits and power supplies. Photo emitters have similar problems with regard to low currents and current densities.
Field emitter arrays (FEAs) are naturally small structures which provide reasonably high current densities at low voltages. FEAs typically comprise an array of conical, pyramidal or cuspshaped point, edge or wedge-shaped vertical structures which are electrically insulated from a positively charged extraction gate and which produce an electron beam that travels through an associated opening in the charged gate.
The classical field emitter includes a sharp point at the tip of the vertical structure and opposite an extraction electrode. In order to generate electrons which are not collected at the extraction electrode, but can be manipulated and collected somewhere else, a hole is created in the extraction electrode which hole is significantly larger (e.g. two orders of magnitude) than the radius of curvature of the field emitter. Thus, the extraction electrode is a flat horizontal surface containing an extraction electrode hole for the field emitter. The field emitter is centered horizontally in the extraction electrode hole and does not touch the extraction electrode, although the vertical direction of the field emitter is perpendicular to the horizontal plane of the extraction electrode. The positive charges on the edge of the extraction electrode hole surround the field emitter symmetrically so that the electric field produced between the field emitter and the extraction electrode causes the electrons to be collected on an electrode (anode) separate and distinct from the extraction electrode. A very small percentage of the electrons are intercepted by the extraction electrode. The smaller the aperture, i.e., the closer the extraction electrode is to the field emitter, the lower the voltage required to generate the electron beam.
It is difficult to create FEAs which have reproducibly small radius-of-curvature field emitter tips of conducting materials. Furthermore, it is equally difficult to gate or grid these structures where the gate-to-emitter distance is reasonably small to provide the necessary high electrostatic field at the field emitter tip with reasonably small voltages. The radius of curvature is typically 100-300 angstroms (Å) and the gate-to-emitter distance is typically 0.1-0.5 micrometers (&mgr;m).
Current methods of manufacturing FEAs include wet etching, reactive ion etching, and a variety of field emitter tip deposition techniques. Practical methods generally require the use of lithography which has a number of inherent disadvantages including the high cost of the equipment needed. Furthermore, the high degree of spatial registration required prevents parallel processing, i.e., the fabrication of a very large number of emitters at the same time in a single process.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a field emitter device which substantially eliminates the need for the use of high spatial resolution lithography in its fabrication.
It is another object of the present invention to provide a field emitter device having inherent advantages over previous electron sources, including higher emission currents, lower power requirements, less expensive fabrication costs and ease of integration with other circuitry.
It is a further object of the present invention to fabricate gated and ungated thin-film edge field emitter devices wherein the spacing between the elements is small enough to enable low voltage operation.
It is a further object of the present invention to fabricate FEAs over a large area in a manner which is inexpensive, yet results in an equal or greater degree of precision and reproducibility when compared with other prior art processes.
The above objects are accomplished by a thin-film edge field emitter device which includes a substrate having a first portion and having a protuberance extending from the first portion, the protuberance defining at least one side-wall, the side-wall constituting a second portion. An emitter layer is disposed on the substrate including the second portion, the emitter layer being selected from the group consisting of semiconductors and conductors and is a thin-film including a portion extending beyond the second portion and defining an exposed emitter edge. A pair of supportive layers is disposed on opposite sides of the emitter layer, the pair of supportive layers each being selected from the group consisting of semiconductors and conductors and each having a higher work function than the emitter layer.
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Gray Henry F.
Hsu David S.
Baumeister Bradley W.
Jackson. Jr. Jerome
Karasek John J.
Ressing Amy L.
The United States of America as represented by the Secretary of
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