Field emission device having means for in situ feeding of hydrogen

A field emission device (100, 200) includes a cathode plate (110, 210), an anode plate (112, 212) spaced from the cathode plate (110, 210) to define an interspace region (114, 214) therebetween, a hole (144, 244) defined by the device package and in communication with the interspace region (114, 214), and a hydrogen-selective membrane (140, 240) disposed in registration with the hole (144, 244).

REFERENCE TO RELATED APPLICATION 
Related subject matter is disclosed in a co-pending, commonly assigned 
patent application entitled "Method for in Situ Cleaning of Electron 
Emitters in a Field Emission Device", Ser. No. 08/927,367, filed on even 
date herewith. 
FIELD OF THE INVENTION 
The present invention pertains to the area of field emission devices and, 
more particularly, to a field emission device having means for surface 
decontamination of the electron emitters. 
BACKGROUND OF THE INVENTION 
A typical field emission device contains electron emitters, such as Spindt 
tips, which are made from an electron-emissive metal, such as molybdenum. 
These electron emitters are susceptible to surface contamination by 
oxygen-containing and carbon-containing species. The surface oxygen and 
carbon have deleterious effects on the electron emission properties of the 
electron emitters. In particular, the presence of oxygen and carbon at the 
emissive surface increases the surface work function of the electron 
emitters. That is, a bigger electric field is required to extract 
electrons therefrom due to the contamination. Surface contaminants also 
result in emission current instability and reduced device lifetime. 
Metal field emission tips have been employed in field emission electron and 
ion microscopy. It is known to remove surface contaminants from electron 
emitters in these microscopy devices by employing high temperature 
(greater than 2000.degree. K.) flashing. However, field emission arrays 
often include glass substrates upon which the electron emitters are 
formed. These glass substrates have temperature tolerances upwards of 
700.degree.-800.degree. K. Thus, high temperature cleaning procedures 
cannot be used for decontaminating field emission electron emitters formed 
on glass substrates. 
Furthermore, the contamination of field emission electron emitters occurs 
throughout the life of the field emission device. Contaminant gaseous 
species are introduced into the vacuum of the field emission device by 
outgassing from surfaces, by electron-stimulated desorption from the 
phosphors and other surfaces that are exposed to field emitted electrons, 
by small leaks in the packaging elements, etc. 
In order to maintain constant emission characteristics over the life of the 
device, it is desirable that emitter surface contaminants be removed 
throughout the life of the device. It is also desirable that this cleaning 
process be continuous over the life of the device or be performed 
periodically at a frequency that is sufficient to prevent appreciable 
deterioration of emission characteristics. However, field emission devices 
typically have no convenient means for introducing cleaning agents into 
the device subsequent to the vacuum sealing of the device package. 
Accordingly, there exists a need for a field emission device having means 
for in situ removal of surface contaminants from field emission electron 
emitters.

It will be appreciated that for simplicity and clarity of illustration, 
elements shown in the FIGURES have not necessarily been drawn to scale. 
For example, the dimensions of some of the elements are exaggerated 
relative to each other. Further, where considered appropriate, reference 
numerals have been repeated among the FIGURES to indicate corresponding 
elements. 
DESCRIPTION 
The invention is for a field emission device having means for in situ 
feeding of hydrogen. The hydrogen supplied using said means is utilized to 
clean the electron emitters of the field emission device. The means for in 
situ feeding of hydrogen permits cleaning of the electron emitters of the 
field emission device at any time subsequent to the vacuum sealing of the 
device package. It is also compatible with the vacuum environment within 
the device. In one embodiment of the invention, a hydrogen-selective 
membrane is provided in registration with a hole/gap in the device 
package. In this embodiment, hydrogen gas is diffused into the device 
through the hydrogen-selective membrane. In another embodiment of the 
invention, a hydrogen source is disposed within the device package. The 
hydrogen source is made from a member having hydrogen entrapped therein. 
The entrapped hydrogen is controllably released from the hydrogen source 
by, for example, controlled heating of the hydrogen source. Hydrogen 
evolution is activated at a rate/frequency sufficient to remove 
contaminants from the surfaces of the electron emitters, thereby realizing 
stable electron emission over the life of the device. 
The embodiments described herein are directed to field emission display 
devices having triode configurations and employing Spindt tip electron 
emitters. However, the scope of the invention is not intended to be 
limited to display devices, to devices having a triode configuration, nor 
to devices having Spindt tip electron emitters. In general, the invention 
can be embodied in a vacuum device that employs field emission electron 
emitters, such as Spindt tips, edge emitters, wedge emitters, surface 
conduction emitters, and the like, which are made from a material that can 
be cleaned using hydrogen free-radicals. Also, the invention can be 
embodied in a field emission device having a diode configuration or a 
configuration having greater than three electrodes. 
FIG. 1 is a cross-sectional view of a first embodiment of a field emission 
device (FED) 100 configured in accordance with the invention. FED 100 
includes a cathode plate 110, which is spaced from an anode plate 112 to 
define an interspace region 114 therebetween. Cathode plate 110 includes a 
plurality of electron emitters 126. In general, during the operation of 
FED 100, electrons, indicated by a dashed line 134 in FIG. 1, are emitted 
by electron emitters 126 and are subsequently collected at anode plate 
112. 
Cathode plate 110 includes a substrate 116, which can be made from glass or 
some other hard, dielectric material. Upon substrate 116 is disposed a 
plurality of cathodes 118, which are electrodes made from a conductor, 
such as molybdenum, aluminum, and the like. A dielectric layer 120 is 
disposed on cathodes 118 and defines a plurality of emitter wells 124. 
Electron emitters 126 are disposed one each in emitter wells 124. In the 
embodiment of FIG. 1, electron emitters 126 include Spindt tips. Electron 
emitters 126 are made from a field emissive material. Exemplary field 
emissive materials include molybdenum, niobium, hafnium, tungsten, 
iridium, silicon, diamond-like carbon, and the like. In general, the field 
emissive material can be induced to emit electrons by the application of 
an electric field of appropriate strength. Also, the field emissive 
material can be conditioned/cleaned using hydrogen free radicals, which 
include atomic hydrogen and hydrogen ions. 
A plurality of gate extraction electrodes 122 is configured upon dielectric 
layer 120 for selectively addressing electron emitters 126. Gate 
extraction electrodes 122 are made from a conductive material, such as 
molybdenum, aluminum, and the like. Methods for fabricating cathode plate 
110 are known to one skilled in the art. 
Anode plate 112 includes a transparent substrate 128 made from a solid, 
transparent material, such as a glass. An anode 130 is formed on 
transparent substrate 128. Anode 130 is made from a transparent, 
conductive material, such as indium tin oxide. Anode plate 112 further 
includes a plurality of phosphors 132, which are made from a 
cathodoluminescent material. 
Between cathode plate 110 and anode plate 112, at their peripheries, is 
disposed a frame 136, which provides standoff therebetween. Frame 136 can 
be made from a glass and is affixed to cathode plate 110 with a sealant 
138. Sealant 138 can be a frit sealant, indium metal, a low temperature 
metal sealant, and the like. Cathode plate 110, anode plate 112, and frame 
136 define a device package. 
In accordance with the invention, a hydrogen-selective membrane is disposed 
in registration with a hole defined by the device package. In the 
embodiment of FIG. 1, a hydrogen-selective membrane 140 is disposed within 
a hole 144 defined by frame 136 and anode plate 112. Hydrogen-selective 
membrane 140 is made from a refractory metal, such as palladium, nickel, a 
palladium alloy, a nickel alloy, and the like, which is selectively 
permeable with respect to hydrogen. Preferably, hydrogen-selective 
membrane 140 is made from palladium. Hydrogen-selective membrane 140 has a 
thickness, in the direction of hydrogen diffusion, within a range of 
50-500 micrometers. Under the appropriate conditions of temperature and 
pressure, hydrogen gas is capable of selectively diffusing through 
hydrogen-selective membrane 140. 
The embodiment of FIG. 1 can be fabricated by first silk-screening sealant 
138 onto transparent substrate 128 at the periphery thereof. Then, 
hydrogen-selective membrane 140 is disposed on sealant 138. Refractory 
metal membranes, having thicknesses greater than about 10 micrometers, are 
available commercially. Such a refractory metal membrane can be cut into a 
suitable shape to form hydrogen-selective membrane 140. The structure is 
then heated to affix the refractory metal to sealant 138. 
Anode plate 112, having hydrogen-selective membrane 140 formed thereon, is 
assembled with cathode plate 110, having frame 136 affixed thereto, in a 
vacuum environment, so that a vacuum is realized within interspace region 
114. As illustrated in FIG. 1, hydrogen-selective membrane 140 is thus 
disposed in communication with interspace region 114. That is, hydrogen 
gas, which is indicated by an arrow 142 in FIG. 1, that diffuses through 
hydrogen-selective membrane 140 can subsequently travel into interspace 
region 114. 
Subsequent to the steps of sealing the elements of FED 100 and establishing 
a vacuum environment therein, the following steps can be used to achieve 
in situ feeding of hydrogen gas to interspace region 114. First, FED 100 
is placed in an oven having a hydrogen atmosphere. The hydrogen atmosphere 
within the oven has a hydrogen partial pressure within a range of 
milli-Torr to several atmospheres. Then, the temperature within the oven 
is elevated to within a range of about 273.degree.-450.degree. K. In 
general, the temperature and partial pressure of hydrogen within the 
hydrogen atmosphere are selected to promote diffusion of hydrogen gas 
through hydrogen-selective membrane 140. 
The diffusion of hydrogen into interspace region 114 is performed for a 
period of time sufficient to provide within interspace region 114 a 
partial pressure of hydrogen useful for cleaning electron emitters 126. 
The partial pressure of hydrogen within FED 100 is preferably within a 
range of 10.sup.-8 -10.sup.-5 Torr. 
The hydrogen content can be determined by measuring the total pressure 
within FED 100 prior to the addition of hydrogen and thereafter measuring 
the total pressure within FED 100 after the addition of hydrogen. If these 
two measurements are taken at the same temperature, the final hydrogen 
partial pressure can be derived therefrom by, for example, using the ideal 
gas law. 
In general, clean electron emitters 126 ameliorate the fluctuations in the 
emission current for a given set of conditions, including voltages and 
temperature. Thus, the level of contamination of electron emitters 126 can 
be deduced from measured fluctuations in the emission current. A partial 
pressure of hydrogen is established that provides stabilized emission 
current having fluctuations within a tolerable range. For example, it may 
be desirable to maintain current fluctuations of less than 0.5% per hour 
for a given set of conditions. 
Subsequent to the addition of hydrogen gas to interspace region 114, 
electron emitters 126 are cleaned. This is achieved by first activating 
electron emitters 126 to emit electrons. Electron emission is realized by 
applying the appropriate potentials to cathodes 118 and gate extraction 
electrodes 122, as is known to one skilled in the art. The emitted 
electrons are then attracted toward anode 130 by applying thereto an 
appropriate potential. As they travel across interspace region 114, the 
emitted electrons dissociate and ionize the hydrogen molecules present 
therein, thereby forming hydrogen free radicals within interspace region 
114. 
The hydrogen free-radicals, which include hydrogen ions and energetic 
neutral hydrogen atoms, react with the surfaces of electron emitters 126, 
which include surface contaminants, to form volatile hydrides. Exemplary 
volatile hydrides that may be produced include: H.sub.2 O, MoH.sub.x.sup.+ 
(x=1-3), MoOH.sup.+, OH.sup.+, OH, H.sup.+, CH.sub.x.sup.+ (x=1-4), and 
the like. These volatile hydrides are then removed from interspace region 
114 by gettering material (not shown) present within FED 100. 
This procedure for cleaning and conditioning electron emitters 126 can be 
performed shortly after sealing of the device package to remove surface 
contaminants, native oxides, and process residues. The cleaning procedure 
can also be performed after a period of use of FED 100, thereby 
reconditioning electron emitters 126 and removing surface contaminants 
accumulated during the operation of FED 100. In this manner, stable 
electron emission is realized over the life of FED 100. 
In general, and in accordance with the invention, the means for in situ 
feeding of hydrogen is disposed in communication with the interspace 
region of the device package. In the embodiment having a 
hydrogen-selective membrane, the hydrogen-selective membrane is configured 
in registration with a hole/gap defined by the device package. Under 
appropriate conditions of pressure and temperature, this configuration 
allows hydrogen gas to diffuse from a hydrogen atmosphere external to the 
field emission device, through the hydrogen-selective membrane, and into 
the interior of the field emission device. 
FIG. 2 is a cross-sectional view of a second embodiment of a field emission 
device (FED) 200 configured in accordance with the invention. In the 
embodiment of FIG. 2, a hole 244 is defined by a transparent substrate 228 
of an anode plate 212. Transparent substrate 228 is made from a hard, 
transparent material, such as a glass, and has affixed thereto an anode 
230 and a plurality of phosphors 232. FED 200 further includes a 
hydrogen-selective membrane 240, which overlies hole 244. 
Hydrogen-selective membrane 240 includes a membrane made from a refractory 
metal such as palladium, nickel, and the like, which is selectively 
permeable to hydrogen. The thickness of hydrogen-selective membrane is 
preferably within a range of 50-500 micrometers. 
FED 200 is fabricated by first making a cathode plate 210, in a manner 
similar to that described with reference to FIG. 1. Cathode plate 210 
includes a plurality of cathodes 218, a plurality of electron emitters 
226, and a plurality of gate extraction electrodes 222. A frame 236 is 
attached to the periphery of cathode plate 210 by using a frit sealant 
(not shown). Anode plate 212 is attached to frame 236 to define an 
interspace region 214. The step of attaching anode plate 212 can be 
performed in air because, subsequent to the sealing process, interspace 
region 214 can be evacuated through hole 244 using a vacuum pump, as is 
known to one skilled in the art. 
Hydrogen-selective membrane 240 is affixed to anode plate 212 by first 
providing a ring 246 made from an alloy having thermal expansion 
characteristics that match those of transparent substrate 228. 
Hydrogen-selective membrane 240 is brazed to ring 246, so that it covers 
the hole defined by ring 246. Then the hole defined by ring 246 is 
positioned in registration with hole 244 of transparent substrate 228. 
Ring 246 is attached to transparent substrate 228 using a frit sealant 
248. The step of attaching ring 246, having hydrogen-selective membrane 
240 affixed thereto, to transparent substrate 228 is performed subsequent 
to the evacuation of the device package. 
Subsequent to the step of attaching hydrogen-selective membrane 240 to the 
device package, a hydrogen partial pressure is established within FED 200, 
in a manner similar to that described with reference to FIG. 1. Under 
appropriate conditions of temperature and pressure, hydrogen gas, which is 
indicated by an arrow 242 in FIG. 2, is diffused through 
hydrogen-selective membrane 240 and travels into interspace region 214. 
Within interspace region 214, the hydrogen gas is converted into hydrogen 
free-radicals by electrons, which are indicated by a dashed line 234 in 
FIG. 2, that are emitted by electron emitters 226. 
FIG. 3 is a cross-sectional view of a third embodiment of a field emission 
device (FED) 300 configured in accordance with the invention and includes 
a block diagram of means for controlling the rate of hydrogen evolution 
from a hydrogen source 340. FED 300 has a cathode plate 310 and an anode 
plate 312, which define an interspace region 314. FED 300 further includes 
hydrogen source 340, which is disposed within interspace region 314. 
Hydrogen source 340 includes a solid member made from a refractory metal, 
such as palladium, nickel, a palladium alloy, a nickel alloy, and the 
like. Preferably, hydrogen source 340 is made from palladium. Hydrogen 
source 340 is secured to one of the surfaces defining interspace region 
314 by a convenient method, such as by using a frit sealant or mechanical 
means. 
Hydrogen source 340 contains hydrogen. The hydrogen is provided within by 
hydrogen source 340 by placing the metallic member in an oven having a 
hydrogen atmosphere. The temperature in the oven is elevated to induce the 
diffusion of hydrogen gas into the metallic member. After a sufficient 
amount of hydrogen has been diffused into the metallic member, the 
metallic member is cooled, thereby entrapping the hydrogen contained 
therein. 
A plurality of electron emitters 326 within FED 300 are cleaned and 
conditioned by controllably releasing hydrogen gas, which is indicated by 
an arrow 342 in FIG. 3, from hydrogen source 340. The rate/frequency of 
hydrogen evolution from hydrogen source 340 is controlled so as to provide 
within interspace region 314 a partial pressure of hydrogen that is useful 
for maintaining a stable emission current. A dashed line 334 in FIG. 3 
indicates the emission current. 
In the embodiment of FIG. 3, hydrogen gas is released from hydrogen source 
340 by heating hydrogen source 340. Hydrogen source 340 can be heated by 
passing a current directly through hydrogen source 340. Alternatively, 
hydrogen source 340 can be heated by providing a heating element, such as 
a resistive wire, and providing thermal contact between hydrogen source 
340 and the heating element. Another method for heating hydrogen source 
340 is by using an infrared laser. 
Illustrated in FIG. 3 is a block diagram of a control system useful for 
controlling the rate of hydrogen evolution from hydrogen source 340. The 
control system includes a switching circuit 354, a controller 356, a 
temperature measurement device 366, and a current measurement device 362. 
Controller 356 controls a test emission current 358 that is emitted by a 
test electron emitter 359. The characteristics of test emission current 
358 are representative of the characteristics of the emission currents 
from the remainder of electron emitters 326. Controller 356 controls test 
emission current 358 by manipulating the rate of hydrogen evolution from 
hydrogen source 340 in response to a first signal 364 from current 
measurement device 362 and a second signal 368 from temperature 
measurement device 366. 
A current measurement electrode 360 is configured on anode plate 312 to 
receive test emission current 358. Current measurement device 362 is 
connected to current measurement electrode 360 for measuring test emission 
current 358. Current measurement device 362 transmits first signal 364, 
which is related to test emission current 358, to a first input terminal 
361 of controller 356. 
Temperature measurement device 366 measures a temperature within interspace 
region 314 and transmits second signal 368, which is related to the 
temperature, to a second input terminal 363 of controller 356. The value 
of the emission current is dependent, in part, upon temperature. 
Controller 356 corrects for this temperature dependence when determining 
the status of the emission current. When the corrected value of the 
emission current drops below a predetermined level, the controller 
transmits a control signal 357 to a first input terminal 353 of switching 
circuit 354. 
Switching circuit 354 is responsive to control signal 357. Switching 
circuit 354 has an output that is connected to hydrogen source 340 for 
transmitting an activation current 350 thereto. In general, switching 
circuit 354 transmits activation current 350 to hydrogen source 340 when 
the corrected emission current drops below a predetermined value due to 
surface contamination of electron emitters 326. In the embodiment of FIG. 
3, a voltage source 352 is connected to a second input terminal 351 of 
switching circuit 354. Voltage source 352 can be included in the power 
supply of FED 300. 
Due to the heating of hydrogen source 340, the temperature within FED 300 
may increase. It is desired to maintain the temperature within FED 300 
below that which results in an excessive, catastrophic emission current at 
electron emitters 326. Controller 356 is designed to cease heating 
hydrogen source 340 when the temperature measured by temperature 
measurement device 366 reaches an upper limit. In this manner, the 
emission current is prevented from attaining a catastrophic level due to 
overheating within FED 300 caused by the heating of hydrogen source 340. 
FIG. 4 is a cross-sectional view of a fourth embodiment of a field emission 
device (FED) 400 configured in accordance with the invention and includes 
a block diagram of means for controlling the rate of hydrogen evolution 
from hydrogen source 340. FED 400 includes anode plate 112 and cathode 
plate 310, which define an interspace region 414. In the embodiment of 
FIG. 4, the system for controlling the rate of hydrogen evolution from 
hydrogen source 340 includes a current source 474 and an N-counter circuit 
472. 
FED 400 has a start-up circuit 470, which initially activates the device. 
Start-up circuit 470 is coupled to cathode plate 310 and anode plate 112 
(connections not shown) and provides the proper operating voltage for 
powering FED 400. When start-up circuit 470 is activated, it transmits a 
start-up signal 480 to an input terminal 476 of N-counter circuit 472. 
Start-up signal 480 triggers a counter. When the counter reaches N, 
N-counter circuit 472 transmits from an output terminal 477 an activation 
signal 478. Activation signal 478 is received at an input terminal 471 of 
current source 474. 
Current source 474 has an output terminal 473 that is connected to hydrogen 
source 340. Upon receipt of activation signal 478, current source 474 
transmits an activation current 475 to hydrogen source 340, resulting in 
evolution of hydrogen gas from hydrogen source 340. 
The amount of current sent to hydrogen source 340 each time N-counter 
reaches N and the value of N depend upon factors such as the size of FED 
400 and the anticipated extent of contamination during a given period of 
use of FED 400. The latter factor depends in part upon the nature of the 
materials present within FED 400. For example, different materials may 
generate contaminants at different rates. 
Another embodiment of a field emission device in accordance with the 
invention has a system for controlling the evolution of hydrogen, which 
includes a timer circuit. The configuration of this embodiment is similar 
to that of FIG. 4 in that a current source is connected to the hydrogen 
source. However, instead of an N-counter circuit, a timer circuit is used 
to generate a periodic activation signal, which is sent to the current 
source. In this manner, a predetermined amount of current can be 
periodically transmitted to the hydrogen source at predetermined 
intervals. For example, hydrogen evolution can be provided once per month 
using this configuration. 
FIG. 5 is a cross-sectional view of a fifth embodiment of a field emission 
device (FED) 500 configured in accordance with the invention. Hydrogen 
evolution into an interspace region 514 of FED 500 is realized by an 
electron-stimulated hydrogen desorption process. 
FED 500 includes a hydrogen source 540, which opposes an activation 
electron emitter 585. Hydrogen source 540 is made in the manner described 
with reference to hydrogen source 340 of FIGS. 3 and 4. A cathode plate 
510 includes activation electron emitter 585, which is one of a plurality 
of electron emitters 526 disposed within emitter wells defined by a 
dielectric layer 520. Electron emitters 526 are connected to a plurality 
of cathodes 518, which are disposed on a substrate 516. 
Hydrogen, which is indicated by an arrow 542 in FIG. 5, is evolved from 
hydrogen source 540 by impacting electrons onto hydrogen source 540. In 
the embodiment of FIG. 5, these electrons, which are generally indicated 
by a dashed line 590, are provided by selectively addressing activation 
electron emitter 585. An activation gate extraction electrode 587 is 
disposed proximate to activation electron emitter 585 and is coupled to a 
voltage source 592. Activation gate extraction electrode 587 is controlled 
independently from a plurality of gate extraction electrodes 522, which 
are used to selectively address those of electron emitters 526 that oppose 
a plurality of phosphors 532. 
Voltage source 592 is used to selectively apply an extraction voltage at 
activation gate extraction electrode 587. When hydrogen evolution from 
hydrogen source 540 is desired, voltage source 592 is used to apply the 
extraction voltage to activation gate extraction electrode 587, thereby 
realizing electron emission from activation electron emitter 585. When no 
hydrogen evolution from hydrogen source 540 is desired, voltage source 592 
is used to apply a voltage that does not result in electron emission from 
activation electron emitter 585. The output voltage of voltage source 592 
can be manipulated using one of a number of useful control methods, such 
as those described with reference to FIGS. 3 and 4. 
An electron-attracting voltage is provided at hydrogen source 540, so that 
the electrons from activation electron emitter 585 are attracted to and 
collected at hydrogen source 540. In the embodiment of FIG. 5, hydrogen 
source 540 is disposed on an anode plate 512. Anode plate 512 includes a 
transparent substrate 528, upon which is formed an anode 530. Hydrogen 
source 540 is connected to anode 530, to which the electron-attracting 
voltage is applied. Phosphors 532 are also configured on anode 530. The 
electrons collected at hydrogen source 540 stimulate hydrogen evolution 
therefrom. The hydrogen thus evolved is then ionized by electrons within 
interspace region 514, including the electrons, which are generally 
indicated by a dashed line 534, directed toward phosphors 532. 
In an alternative embodiment, the hydrogen source is not coupled to the 
anode that biases the phosphors. Rather, the hydrogen source is coupled to 
an independent voltage source, so that the voltage at the hydrogen source 
can be manipulated independently from the voltage at the phosphors. In 
this particular embodiment, the electrons for use for hydrogen evolution 
can be provided by any of the electron emitters within the device. The 
emitted electrons are directed toward the hydrogen source by selectively 
biasing it to attract the electrons. For example, subsequent to the 
sealing and evacuation of the device, some or all of the electron emitters 
are caused to emit electrons. Simultaneously, a positive, attracting 
voltage is selectively applied to the hydrogen source. After the 
decontamination steps are completed, the positive, attracting voltage is 
removed from the hydrogen source. Any subsequently emitted electrons can 
be directed toward the phosphors by selectively applying a positive, 
attracting voltage to the phosphors. 
In summary, the invention is for a field emission device having means for 
in situ feeding of hydrogen. The hydrogen supplied using said means is 
utilized to clean the electron emitters of the field emission device. The 
means for in situ feeding of hydrogen permits cleaning of the electron 
emitters at any time subsequent to the vacuum sealing of the device 
package. It is also compatible with the vacuum environment within the 
device. In the field emission device of the invention, hydrogen gas can be 
controllably introduced at a rate/frequency sufficient to remove surface 
contaminants and maintain clean electron emitters, thereby realizing 
stable electron emission over the life of the device. 
While we have shown and described specific embodiments of the present 
invention, further modifications and improvements will occur to those 
skilled in the art. We desire it to be understood, therefore, that this 
invention is not limited to the particular forms shown, and we intend in 
the appended claims to cover all modifications that do not depart from the 
spirit and scope of this invention.