Electric lamp or space discharge component or device manufacturi – Process – Electrode making
Reexamination Certificate
2001-06-12
2003-08-19
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
Electrode making
C438S020000
Reexamination Certificate
active
06607415
ABSTRACT:
TECHNICAL FIELD
The present invention relates to flat surfaces that emit electrons in localized areas to which an electrical field of threshold magnitude is applied and, in particular, to fabrication of tiny field emitter tips across the surface of a substrate that provides functionality intermediate between thin-film field emitters and field emitter tip microarrays.
BACKGROUND OF THE INVENTION
The present invention relates to design and manufacture of field emitter tips, including silicon-based field emitter tips. A brief discussion of field emission and the principles of design and operation of field emitter tips is therefore first provided in the following paragraphs, with reference to FIG.
1
.
When a wire, filament, or rod of a metallic or semiconductor material is heated, electrons of the material may gain sufficient thermal energy to escape from the material into a vacuum surrounding the material. The electrons acquire sufficient thermal energy to overcome a potential energy barrier that physically constrains the electrons to quantum states localized within the material. The potential energy barrier that constrains electrons to a material can be significantly reduced by applying an electric field to the material. When the applied electric field is relatively strong, electrons may escape from the material by quantum mechanical tunneling through a lowered potential energy barrier. The greater the magnitude of the electrical field applied to the wire, filament, or rod, the greater the current density of emitted electrons perpendicular to the wire, filament, or rod. The magnitude of the electrical field is inversely related to the radius of curvature of the wire, filament, or rod.
FIG. 1
illustrates principles of design and operation of a silicon-based field emitter tip. The field emitter tip
102
rises to a very sharp point
104
from a silicon-substrate cathode
106
, or electron source. A localized electric field is applied in the vicinity of the tip by a first anode
108
, or electron sink, having a disk-shaped aperture
110
above and around the point
104
of the field emitter tip
102
. A second cathode layer
112
is located above the first anode
108
, also with a disk-shaped aperture
114
aligned directly above the disk-shaped aperture
110
of the first anode layer
108
. This second cathode layer
112
acts as a lens, applying a repulsive electronic field to focus the emitted electrons into a narrow beam. The emitted electrons are accelerated towards a target anode
118
, impacting in a small region
120
of the target anode defined by the direction and width of the emitted electron beam
116
. Although
FIG. 1
illustrates a single field emitter tip, silicon-based field emitter tips are commonly micro-manufactured by microchip fabrication techniques as regular arrays, or grids, of field emitter tips.
Silicon-based field emitter tips can be micro-manufactured by microchip fabrication techniques as regular arrays, or grids, of field emitter tips. Uses for arrays of field emitter tips include computer display devices.
FIG. 13
illustrates a computer display device based on field emitter tip arrays. Arrays of silicon-based field emitter tips
1302
are embedded into emitters
1304
arrayed on the surface of a cathode base plate
1306
and are controlled, by selective application of voltage, to emit electrons which are accelerated towards a face plate anode
1308
coated with chemical phosphors. When the emitted electrons impact onto the phosphor, light is produced. In such applications, the individual silicon-based field emitter tips have tip radii on the order of hundreds of Angstroms and emit currents of approximately 10 nanoamperes per tip under applied electrical field strengths of around 50 Volts.
Recently, a second type of field emission display device has been proposed.
FIG. 3
illustrates operation of a field emission display device based on a thin-film, flat field emission material. In this alternative type of field emission display device, a semiconductor substrate
302
is coated with a thin film of a material
304
that emits electrons under the influence of a localized electric field. A suitable electric field is created directly below a region of the field emission material
306
with a microelectronic device fabricated within the silicon substrate
308
. Electrons emitted from the region of the thin-film field emission material
306
are accelerated in an electric field towards a phosphor-coated glass substrate
312
. Collision of an accelerated electron
314
with the phosphor produces phosphorescent emission of photons that travel through the glass substrate
312
to the retina of a viewer. Various research groups have suggested the use of nitrogen-doped, chemical vapor-deposited diamond films, amorphous carbons films, or various conjugated polymers for use as thin-film field emission materials in the flat field emission display devices, operation of which is illustrated in FIG.
3
. However, it has proved difficult to fabricate thin-film field emission materials that are long lasting and that produce acceptable current densities of emitted electrons under the influence of reasonably strong electric fields. Thus, designers and manufacturers of field emission display devices have recognized the need for a flat field emission material that can be incorporated in a semiconductor device for use in flat field emission display devices.
SUMMARY OF THE INVENTION
The present invention provides a method for fabricating a dense field of tiny, silicon-based field emitter tips across the surface of a silicon substrate. The silicon substrate is first subjected to a beam of oxygen or oxygen-containing ions to create clusters of SiO
2
within a thin surface region of the silicon substrate. The clusters of SiO
2
molecules created by ionic bombardment of the silicon substrate surface may then be coalesced, if necessary, into clusters by thermal annealing or other techniques. Finally, the surface of the silicon substrate is etched to remove the SiO
2
clusters, thereby producing a dense field of tiny silicon-based field emitter tips across the surface of the silicon substrate.
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“Fabrication Of Sub-10 nm Silicon Tips: A New Approach”; by: Huq, et al; XP 000558344; Journal Of Vacuum Science And Technology; B 13(6); Nov./Dec. 1995; pp. 2718-2721.
“Procedes de Fabrication De Micropointes En Silicium”; by: Moreau, et al; Sciences Et Techniques; XP000637302; 1996; No. 282; vol. 52; ISSN: 1266-0167; pp. 463-477.
Dunfield John Stephen
McClelland Paul H.
Milligan Donald J.
Hewlett--Packard Development Company, L.P.
Ramsey Kenneth J.
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