Fabrication of gated electron-emitting devices utilizing...

Details Fabrication of gated electron-emitting devices utilizing... Fabrication of gated electron-emitting devices utilizing...

1996-06-07

2001-02-13

Lund, Jeffrie R (Department: 1763)

Semiconductor device manufacturing: process

Electron emitter manufacture

C216S023000

Reexamination Certificate

active

06187603

ABSTRACT:

FIELD OF USE
This invention relates to the fabrication of electron-emitting devices, commonly referred to as cathodes, suitable for products such as cathode-ray tube (“CRT”) displays of the flat-panel type.
BACKGROUND ART
A field-emission cathode (or field emitter) emits electrons upon being subjected to an electric field of sufficient strength. The electric field is produced by applying a suitable voltage between the cathode and an electrode, typically referred to as the anode or gate electrode, situated a short distance away from the cathode.
When a field-emission cathode is utilized in a flat-panel CRT display, electron emission from the cathode occurs across a sizable area. The electron-emitting area is commonly divided into a two-dimensional array of electron-emitting portions, each situated across from a corresponding light-emitting portion to form part or all of a picture element (pixel). The electrons emitted by each electron-emitting portion strike the corresponding light-emitting portion and cause it to emit visible light.
It is generally desirable that the illumination be uniform (constant) across the area of each light-emitting portion. One method for achieving uniform illumination is to arrange for electrons to be emitted uniformly across the area of the corresponding electron-emitting portion. This typically involves fabricating the electron-emitting portion as a large number of small, closely spaced electron-emissive elements.
Various techniques have been investigated for manufacturing electron-emitting devices that contain small, closely spaced electron-emissive elements. Spindt et al, “Research in Micron-Sized Field-Emission Tubes,”
IEEE Conf. Rec.
1966
Eighth Conf. Tube Techniques
, Sep. 20, 1966, pp. 143-147, describes how small randomly distributed spherical particles are employed to define the locations for conical electron-emissive elements in a flat field-emission cathode. The size of the spherical particles strongly controls the base diameter of the conical electron-emissive elements.
FIGS. 1
a
-
1
g
(collectively “FIG.
1
”) illustrate the sphere-based process utilized in Spindt et al to fabricate an electron-emitting diode having a thick anode. In
FIG. 1
a
, the starting point is sapphire substrate
20
. A sandwich consisting of lower molybdenum layer
22
, insulating layer
24
, and upper molybdenum layer
26
is situated on substrate
20
.
Polystyrene spheres
28
, one of which is shown in
FIG. 1
b
, are scattered across the top of molybdenum layer
26
. “Resist” is deposited to form resist layer
30
A on the uncovered part of layer
26
. See
FIG. 1
c
. Portions
30
B of the resist, typically alumina (aluminum oxide), accumulate on spherical particles
28
during the resist deposition. Spheres
28
are subsequently removed, thereby removing resist portions
30
B. Referring to
FIG. 1
d
, openings
32
extend through resist layer
30
A at the locations of removed spheres
28
.
The exposed portions of molybdenum layer
26
are etched through resist openings
32
to form openings
34
through molybdenum
26
, the remainder of which is indicated as item
26
A in
FIG. 1
e
. Similarly, the
15
exposed parts of insulating layer
24
are etched through openings
34
to form cavities
36
through remaining insulating layer
24
A. See
FIG. 1
f
. Resist layer
30
A is removed, typically during the cavity etch.
Finally, molybdenum is evaporatively deposited on top of the structure and into cavities
36
. The evaporation is performed in such a way that the openings through which the molybdenum accumulates in cavities
36
progressively close. As indicated in
FIG. 1
g
, conical molybdenum electron-emissive elements
38
A are formed in cavities
36
, while continuous molybdenum layer
38
B is formed on top of molybdenum layer
26
A. Layers
38
B and
26
A together form the anode for the diode.
Utilization of spherical particles to establish the locations, and base dimensions, of electron-emissive elements in Spindt et al is a creative approach to creating an electron-emitting device. However, the electrons emitted by elements
38
A are collected by anode
26
A/
38
B and thus are not utilized to directly activate light-emitting areas. It would be desirable to employ spherical particles to define the locations for small, closely spaced electron-emissive elements that emit electrons which can be utilized to directly activate light-emissive elements in a flat-panel device in a highly uniform manner.
GENERAL DISCLOSURE OF THE INVENTION
The present invention furnishes a set of fabrication processes in which particles, typically spherical, are so utilized in manufacturing gated electron-emitting devices. The particles define the locations, and to a large degree, the lateral areas of electron-emissive elements in the gated electron emitters. Importantly, the fabrication processes of the invention are arranged so that electrons emitted by the electron-emissive elements are available for directly activating elements such as light-emissive regions in a flat-panel device.
By appropriately adjusting the surface density and average size of the particles, the electron-emissive elements can be spaced suitably close together. Although the particles, and therefore the electron-emissive elements, are normally situated at largely random locations relative to one another, the number of electron-emissive elements per unit area is relatively uniform across the overall electron-emitting area. The surface density of the particles can readily be set at a high value. Since the particle surface density defines the surface density of the electron-emissive elements, a high surface density of electron-emissive elements can easily be attained.
Furthermore, the particles can readily be chosen to have a tight size distribution—i.e., the standard deviation in the average particle diameter is quite small. The electron-emissive elements, especially when they are conically shaped, therefore typically occupy largely equal lateral areas. By appropriately adjusting the values for certain dimensional parameters, such as certain thicknesses, the electron-emissive elements can be made to be quite similar to one another. The net result is that utilization of particles according to the manufacturing processes of the invention enables highly uniform electron emission to be achieved, thereby enabling light-emitting regions to be directly activated in a highly uniform manner.
In fabricating a gated electron emitter according to a principal aspect of the invention, a multiplicity of particles are distributed over a suitable starting structure. Importantly, the magnitude of the lateral area of the starting structure typically has little effect on the ability to distribute the particles in a relatively uniform (though largely random) manner over the starting structure. Consequently, the fabrication processes of the invention can readily be used to make electron emitters of large area.
After having been distributed over the starting structure, the particles are utilized to define corresponding locations (a) for a like multiplicity of primary openings extending through a primary layer provided over an electrically non-insulating gate layer formed over an electrically insulating layer in the structure and (b) for a like multiplicity of corresponding gate openings extending through the gate layer. As discussed below, “electrically non-insulating” means electrically conductive or electrically resistive. Each gate opening is vertically aligned to the corresponding primary opening. The primary layer typically consists of inorganic dielectric material.
The particles, preferably spherical in shape, can be distributed over the insulating layer, the gate layer, or the primary layer. Depending on which of these layers receives the particles, the particles are employed in various ways to define the gate openings.
When the particles are distributed over the insulating layer, electrically non-insulating gate material is typically provided over the insulating layer, at least in space between the particles. Suitable mat

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