Cold cathode field emission device and display

Details Cold cathode field emission device and display Cold cathode field emission device and display

1999-12-03

2002-10-15

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

Discharge devices having a multipointed or serrated edge...

C313S495000

Reexamination Certificate

active

06465941

ABSTRACT:

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a cold cathode field emission device, a process for the production thereof and a cold cathode field emission display. More specifically, it relates to a cold cathode field emission device of which the tip portion has a conical form, a process for the production thereof and a flat panel type cold cathode field emission display having the above cold cathode field emission devices arranged in a two-dimensional matrix form.
Various flat panel type displays are studied for substitutes for currently main-stream cathode ray tubes (CRT). The flat type displays include a liquid crystal display (LCD), an electroluminescence display (ELD) and a plasma display (PDP). Further, a cold cathode field emission type display which can emit electrons from a solid into vacuum without relying on thermal excitation, that is, a so-called field emission display (FED) is proposed as well, and it attracts attention from the viewpoints of brightness on a screen and low power consumption.
A cold cathode field emission type display (to be sometimes simply referred to as “display” hereinafter) generally has a structure in which a cathode panel having electron emitting portions so as to correspond to pixels arranged in a two-dimensional matrix form and an anode panel having a fluorescent layer which emits light when excited by colliding with electrons emitted from the electron emitting portions face each other through a vacuum layer. In each pixel on the cathode panel, generally, a plurality of electron emitting portions are formed, and further, gate electrodes are also formed for extracting electrons from the electron emitting portions. A portion having the above electron emitting portion and the above gate electrode will be referred to as an field emission device hereinafter.
For attaining a large emitted electron current at a low driving voltage in the above structure, it is required to form a top end of the electron emitting portion so as to have an acutely sharpened form, it is required to increase the density of electron emitting portions that can exist in a section corresponding to one pixel by finely forming the electron emitting portions, and it is also required to decrease the distance between the top end of the electron emitting portion and the gate electrode. For materializing these, therefore, there have been already proposed field emission devices having a variety of structures.
As one of typical examples of field emission devices used in the above conventional displays, there is known a so-called Spindt type field emission device of which the electron emitting portion is composed of a conical conductive material.
FIG. 51
schematically shows the above Spindt type display. The Spindt type field emission device formed in a cathode panel CP comprises a cathode electrode
201
formed on a support
200
, an insulating layer
202
, a gate electrode
203
formed on the insulating layer
202
, and a conical electron emitting portion
205
formed in an opening portion
204
which is provided so as to penetrate the gate electrode
203
and the insulating layer
202
. A predetermined number of the electron emitting portions
205
are arranged in a two-dimensional matrix form to form one pixel. An anode panel AP has a structure in which a fluorescence layer
211
having a predetermined pattern is formed on a transparent substrate
210
and the fluorescence layer
211
is covered with an anode electrode
212
.
When a voltage is applied between the electron emitting portion
205
and the gate electrode
203
, electrons “e” are extracted from the top end of the electron emitting portion
205
due to a consequently generated electric field. These electrons “e” are attracted to the anode electrode
212
of the anode panel AP to collide with the fluorescence layer
211
which is a light-emitting layer formed between the anode electrode
212
and the transparent substrate
210
. As a result, the fluorescence layer
211
is excited to emit light, and a desired image can be obtained. The performance of the above field emission device is basically controlled by a voltage to be applied to the gate electrode
203
.
The method of producing a field emission device of the above display will be outlined with reference to
FIGS. 52A
,
52
B,
53
A and
53
B hereinafter. This production method is basically a method in which the conical electron emitting portion
205
is formed by vertical vapor deposition of a metal material. That is, vaporized particles comes in perpendicularly to the opening portion
204
. A shielding effect of an overhanged deposit formed in the vicinities of an opening end portion of the gate electrode
203
is utilized to gradually decrease the amount of the vaporized particles which reach a bottom portion of the opening portion
204
, and the electron emitting portion
205
which is a conical deposit is formed in a self-aligned manner. For facilitating the removal of an unnecessary overhanged deposit, a peeling-off layer
206
is formed on the gate electrode
203
beforehand, and the method including the formation of the peeling-off layer will be explained below.
[Step-
10
]
First, the cathode electrode
201
of niobium (Nb) is formed on the support
200
which is formed of, for example, glass substrate. Then, the insulating layer
202
of SiO
2
and the gate electrode
203
of an electrically conductive material are consecutively formed thereon. Then, the gate electrode
203
and the insulating layer
202
are patterned to form the opening portion
204
(see FIG.
52
A).
[Step-
20
]
Then, as shown in
FIG. 52B
, aluminum is deposited on the gate electrode
203
and the insulating layer
202
by oblique vapor deposition to form the peeling-off layer
206
. In this case, a sufficiently large incidence angle of vaporized particles with regard to the normal of the support
200
is selected, whereby the peeling-off layer
206
can be formed on the gate electrode
203
and the insulating layer
202
with depositing almost no aluminum on the bottom of the opening portion
204
. The peeling-off layer
206
is overhanged in the form of eaves from an upper end portion of the opening portion
204
, and the diameter of the opening portion
204
is substantially decreased.
[Step-
30
]
Then, an electrically conductive material such as molybdenum (Mo) is deposited on the entire surface by vertical vapor deposition. In this case, as shown in
FIG. 53A
, as a conductive material layer
205
A having an overhanged form grows on the peeling-off layer
206
, the substantial diameter of the opening portion
204
is decreased, so that vaporized particles which serve to form a deposit on the bottom of the opening portion
204
gradually comes to be limited to vaporized particles which pass a central area of the opening portion
204
. As a result, a conical deposit is formed on the bottom portion of the opening portion
204
, and the conical deposit works as the electron emitting portion
205
.
[Step-
40
]
Then, as shown in
FIG. 53B
, the peeling-off layer
206
is removed from the surface of the gate electrode
203
by an electrochemical process and a wet process, whereby the conductive material layer
205
A above the gate electrode
203
is selectively removed.
Meanwhile, the electron emitting characteristic of the field emission device having the structure shown in
FIG. 53B
is greatly dependent upon a distance from an edge portion
203
A of the gate electrode
203
constituting the upper end portion of the opening portion
204
to a tip portion of the electron emitting portion
205
. And, the above distance is greatly dependent upon the formation accuracy of the opening portion
204
, the dimensional accuracy of diameter of the opening portion
204
, the thickness accuracy and coverage (step coverage) of the conductive material layer
205
A formed in [Step-
30
] and, further, the formation accuracy of the peeling-off layer
206
which is a kind of an undercoat thereof.
For producin

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