Field emission device and method of operation

Details Field emission device and method of operation Field emission device and method of operation

1999-09-07

2003-05-20

Patel, Vip (Department: 2879)

Electric lamp and discharge devices

With luminescent solid or liquid material

Vacuum-type tube

C313S496000, C313S309000, C315S169100

Reexamination Certificate

active

06566804

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates, in general, to field emission devices, and, more particularly, to methods for operating field emission devices.
BACKGROUND OF THE INVENTION
High voltage field emission devices (FED's) are known in the art. A high voltage FED, is characterized by the application to an anode of the device of a potential greater than about 600 volts, typically more than 1000 volts. Illustrated in
FIG. 1
is a partial, cross-sectional view of a prior an high voltage FED
100
.
FED
100
includes a cathode plate
110
, an anode plate
120
), and a sealant
130
, which are configured to provide a thin envelope. Cathode plate
110
is spaced apart from anode plate
120
to define an interspace region
111
. Interspace region
111
is typically evacuated to a pressure of about 10% Torr. A separation distance, d, between anode plate
120
and cathode plate
110
is on the order of one millimeter.
Cathode plate
110
Includes a back plate
112
, which is typically made from glass or silicon. Back plate
112
defines a proximate surface
155
and a distal surface
146
. A cathode
113
is disposed on proximate surface
155
. Cathode
113
is partially defined by a ballast resistor
114
, which is a semiconductive layer. Cathode
113
also includes conductive portions, which are connected by ballast resistor
114
. Cathode
113
is connected to an electron emitter
118
at one of the conductive portions, thereby operably coupling ballast resistor
111
to electron emitter
118
. Cathode
113
supplies electrons to electron emitter
118
. Ballast resistor
114
is useful for controlling the flow of electrons to electron emitter
119
.
The distance between electron emitter
119
and distal surface
146
is greater than the distance between electron emitter
118
and proximate surface
155
. That is, proximate surface
155
is proximately disposed with respect to electron emitter
118
, and distal surface
196
is distally disposed with respect to electron emitter
110
.
Cathode plate
110
further includes a dielectric layer
116
, which is disposed on cathode
113
and defines an emitter well
117
. Electron emitter
118
is disposed within emitter well
117
. Dielectric layer
116
further defines a surface
140
. A gate extraction electrode
119
is disposed upon a portion of surface
140
of dielectric layer
116
.
Anode plate
120
is disposed to receive electrons emitted by election emitter
118
. Anode plate
120
includes a transparent substrate
122
, which is typically made from a glass. Transparent substrate
122
defines a proximate surface
153
and a distal surface
159
, which are spaced apart from one another. Proximate surface
153
of transparent substrate
122
partially defines interspace region
111
.
An anode
124
is disposed on a portion of proximate surface
153
of transparent substrate
122
. Anode
124
is typically made from a transparent conductive material, such as indium tin oxide. A phosphor
126
is disposed upon anode
124
. Phosphor
126
is cathodoluminescent and emits light upon activation by electrons.
As further illustrated in
FIG. 1
, a first voltage source
132
is connected to cathode
113
, for applying a cathode voltage thereto; a second voltage source
134
is connected to gate extraction electrode
115
, for applying a gate voltage thereto; and a third voltage source
136
is connected to anode
124
, for applying an anode voltage thereto. During the operation of FED
100
, the cathode voltage, the gate voltage, and the anode voltage are elected to cause and control an electron current
138
from electron emitter
118
and to attract the electrons toward phosphor
116
. Electron current
138
can cause ionization of gaseous species that exist within interspace region
111
, thereby creating a plurality of ionized species
142
.
However, during the operation of prior art FED
100
, several forces operate to undesirably change the electrical characteristics of FED
100
. The undesirable changes are due at least in part to the presence of mobile electric charges within the components of FED
100
.
For example, transparent substrate
122
contains a plurality of mobile charges
150
. Because FED
100
is a high voltage device, the anode voltage is a high positive potential, which can be greater than 1000 volts. The high anode voltage causes positive charge within transparent substrate
122
to be repelled away from anode
124
and toward an edge
148
of transparent substrate
122
. A build up of positive charge at edge
148
creates the risk of establishing a potential at proximate surface
153
which is sufficient to cause electric arcing over the surface of sealant
130
within interspace region
111
. The risk of electric arcing is further exacerbated by the fact that the separation distance between anode plate
120
and cathode plate
110
is very small.
As a further example, back plate
112
has a plurality of mobile charges
144
, which are also redistributed during the operation of FED
100
. A force, which can cause this change in the distribution of charge, is the electrostatic force due to the accumulation of ionized species
142
at surface
140
of dielectric layer
116
. Mobile charges
144
are repelled from proximate surface
155
. A change in the charge distribution at proximate surface
155
causes a change in the conductivity of ballast resistor
114
. Because ballast resistor
114
is a semiconductor the change in charge distribution at the underlying surface Because charges in the properties of the conductive channel of, ballast resistor
114
. An uncontrolled change in the conductivity of ballast resistor
114
causes an undesirable change in the magnitude of electron current
138
.
Accordingly, there exists a need for an improved field emission device, which overcomes at least these shortcomings of the prior art.


REFERENCES:
patent: 3998678 (1976-12-01), Fukase et al.
patent: 5982082 (1999-11-01), Janning
patent: 6100628 (2000-08-01), Coll et al.
patent: 6147445 (2000-11-01), Jager et al.

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