U.S. patent application number 09/749813 was filed with the patent office on 2001-07-05 for triode structure field emission device.
Invention is credited to Choi, Jun-hee, Choi, Yong-soo, Kim, Jong-min, Lee, Nae-sung.
Application Number | 20010006232 09/749813 |
Document ID | / |
Family ID | 19633183 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006232 |
Kind Code |
A1 |
Choi, Yong-soo ; et
al. |
July 5, 2001 |
Triode structure field emission device
Abstract
A triode field emission device using a field emission material
and a driving method thereof are provided. In this device, gate
electrodes serving to take electrons out of a field emission
material on cathodes are installed on a substrate below the
cathodes, so that the manufacture of the device is easy. Also,
electrons emitted from the field emission material are controlled
by controlling gate voltage.
Inventors: |
Choi, Yong-soo; (Seoul,
KR) ; Choi, Jun-hee; (Kyungki-do, KR) ; Lee,
Nae-sung; (Seoul, KR) ; Kim, Jong-min;
(Kyungki-do, KR) |
Correspondence
Address: |
BURNS DOANE SWECKER & MATHIS L L P
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Family ID: |
19633183 |
Appl. No.: |
09/749813 |
Filed: |
December 28, 2000 |
Current U.S.
Class: |
257/10 ; 257/11;
313/310; 313/311; 313/351 |
Current CPC
Class: |
H01J 3/022 20130101;
H01J 21/105 20130101 |
Class at
Publication: |
257/10 ; 257/11;
313/310; 313/311; 313/351 |
International
Class: |
H01L 029/06; H01L
029/12 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 30, 1999 |
KR |
99-66031 |
Claims
What is claimed is:
1. A triode field emission device comprising: a rear substrate and
a front substrate which face each other at a predetermined gap;
spacers for vacuum sealing the space formed by the two substrates
while maintaining the gap between the two substrates; cathodes and
anodes arranged in strips on the facing surfaces of the two
substrates so that the cathodes cross with the anodes; electron
emission sources formed on the portions of the cathodes at the
intersections of the cathodes and the anodes; and gates for
controlling electrons emitted from the electron emission sources,
wherein the gates are arranged on the rear substrate under the
cathodes, and an insulative layer for electrical insulation is
formed between the gates and the cathodes.
2. The triode field emission device of claim 1, wherein the gates
are arranged in strips on the rear substrate to cross with the
cathodes so that the gates are located straightly over the
anodes.
3. The triode field emission device of claim 1, wherein the
electron emission sources are formed of at least one material
selected from the group consisting of a metal, diamond and
graphite, on the cathodes at the intersections of the cathodes and
anodes.
4. The triode field emission device of claim 1, wherein the
electron emission sources are formed of a mixture of a conductive
material, a dielectric material or an insulative material, and at
least one material selected from the group consisting of carbon
nanotube, a metal, diamond and graphite, on the cathodes at the
intersections of the cathodes and the gates.
5. The triode field emission device of claim 3, wherein the
electron emission sources are formed straight on the entire surface
or one edge of cathodes at the intersections of the cathodes and
gates.
6. The triode field emission device of claim 3, wherein the
electron emission, sources are formed around at least one hole
pierced in the cathodes at the intersections of the cathodes and
gates.
7. The triode field emission device of claim 3, wherein the
electron emission sources are formed by a method among a printing
method, an electrophoretic method and a vapor deposition
method.
8. The triode field emission device of claim 6, wherein, when three
or more holes are formed, a middle hole is formed as large as
possible, and a field emission material is formed around the outer
circumference of each of the holes, so that the uniformity of
emission current within a pixel is increased.
9. The triode field emission device of claim 1, wherein the
insulative layer is formed in a blanket or linearly formed along
the lines of the cathodes.
10. A method of driving a triode field emission device including: a
rear substrate and a front substrate which face each other at a
predetermined gap; spacers for vacuum sealing the space formed by
the two substrates while maintaining the gap between the two
substrates; cathodes and anodes arranged in strips on the facing
surfaces of the two substrates so that the cathodes cross with the
anodes; electron emission sources formed on the portions of the
cathodes at the intersections of the cathodes and the anodes, to
serve as electron emission sources; and gates for controlling
electrons emitted from the electron emission sources, wherein the
gates are arranged on the rear substrate under the cathodes to
cross with the cathodes so that the gates are located straightly
over the anodes, and an insulative layer for electrical insulation
is formed between the gates and the cathodes, the method comprising
controlling current flowing between the cathodes and the anodes by
controlling the gate voltage.
11. The method of claim 10, wherein the electron emission sources
are formed of at least one material selected from the group
consisting of carbon nanotube, a metal, diamond and graphite, on
the cathodes at the intersections of the cathodes and gates.
12. The method of claim 10, wherein the electron emission sources
are formed of a mixture of a conductive material, a dielectric
material or an insulative material, and at least one material
selected from the group consisting of carbon nanotube, a metal,
diamond and graphite, on the cathodes at the intersections of the
cathodes and the gates.
13. The method of claim 10, wherein the insulative layer is formed
in a blanket or linearly formed along the lines of the
cathodes.
14. The method of claim 11, wherein the electron emission sources
are formed straight on the entire surface or one edge of cathodes
at the intersections of the cathodes and gates.
15. The method of claim 11, wherein the electron emission sources
are formed around at least one hole pierced in the cathodes at the
intersections of the cathodes and anodes.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a triode structure field
emission device using carbon nanotubes that is a low voltage field
emission material and a driving method thereof.
[0003] 2. Description of the Related Art
[0004] FIG. 1 is a cross-sectional view schematically illustrating
the structure of a conventional triode field emission device using
a field emission material. As shown in FIG. 1, the conventional
triode field emission device includes a rear substrate 1 and a
front substrate 10 which face each other having an interval of the
length of a spacer 6. Cathodes 2 on each of which a field emission
material 5 is formed, gates 3 and anodes 4 are included as electron
emission sources between the two substrates. The cathodes 2 are
disposed on the rear substrate 1 in parallel strips, and the anodes
4 are disposed on the front substrate 10 in parallel strips to
cross with the cathodes 2. The gates 3 are disposed in parallel
strips to cross with the cathodes 2 so that they are arranged
straightly over the anodes 4. A field emission material 5 and an
aperture 3a are formed at places where the cathodes 2 cross with
the gates 3. That is, the electron emission materials 5 are coated
on the intersections on the cathodes 2, and apertures 3a are formed
at the intersections on the gates 3, that is, at the positions on
the gates 3 which correspond to the field emission materials, such
that electrons emitted from the field emission materials 5 flow
into the anodes 4.
[0005] As described above, field emission devices have a diode
structure made up of cathodes and anodes, or a triode structure in
which gates are interposed between cathodes and anodes, such that
the amount of electron emitted from the cathodes is controlled.
Structures in which carbon nanotubes rather than existing metal
tips are applied as electron emission sources formed on cathodes
have been recently attempted due to the advent of carbon nanotubes,
which serve as a new field emission material. Carbon nanotubes have
a large aspect ratio (which is greater than 100), electrical
characteristics having conductivity such as conductors, and stable
mechanical characteristics, so that they are receiving much
attention of research institutions to employ them as the electron
emission sources for field emission devices. Diode structure field
emission devices using carbon nanotubes can be manufactured by a
typical method. However, diode structure field emission devices
have a trouble in controlling emitted current, in spite of the
easiness of the manufacture, so that it is difficult to realize
moving pictures or gray-scale images. Triode structure field
emission devices using carbon nanotubes can be manufactured in
consideration of installation of gate electrodes right on cathodes
and installation of a grid-shaped metal sheet. The former field
emission devices has difficulty in coupling carbon nanotubes to
cathodes because of the arrangement of gates. The latter field
emission devices have problems in that the manufacture is
complicated, and control voltage increases.
SUMMARY OF THE INVENTION
[0006] To solve the above problems, an objective of the present
invention is to provide a triode field emission device in which
location of gate electrodes under cathodes facilitates the control
of emitted current, and it is easy to coat the cathodes with a
field emission material, and a driving method thereof.
[0007] To achieve the above objective, the present invention
provides a triode field emission device including: a rear substrate
and a front substrate which face each other at a predetermined gap;
spacers for vacuum sealing the space formed by the two substrates
while maintaining the gap between the two substrates; cathodes and
anodes arranged in strips on the facing surfaces of the two
substrates so that the cathodes cross with the anodes; electron
emission sources formed on the portions of the cathodes at the
intersections of the cathodes and the anodes; and gates for
controlling electrons emitted from the electron emission sources,
wherein the gates are arranged on the rear substrate under the
cathodes, and an insulative layer for electrical insulation is
formed between the gates and the cathodes.
[0008] Preferably, the gates are formed like a full surface or
disposed as parallel strips on the rear substrate to cross with the
cathodes so that the gates are located straightly over the
anodes.
[0009] It is preferable that the electron emission sources are
formed on the cathodes at the intersections of the cathodes and
anodes, of at least one material selected from the group consisting
of a metal, diamond and graphite, or a mixture of the selected
material with a conductive material, a dielectric material or an
insulative material.
[0010] Preferably, the electron emission sources are formed
straight on the entire surface or one edge of cathodes at the
intersections of the cathodes and gates, and the electron emission
sources are formed around at least one hole pierced in the cathodes
at the intersections of the cathodes and gates.
[0011] In the present invention, the electron emission sources are
formed by a method among a printing method, an electrophoretic
method and a vapor deposition method. It is also preferable that,
when three or more holes are formed, a middle hole is formed to a
dominant size, and a field emission material is formed around the
outer circumference of each of the holes, so that the uniformity of
emission current within a pixel is increased.
[0012] To achieve the above objective, the present invention
provides a method of driving a triode field emission device
including: a rear substrate and a front substrate which face each
other at a predetermined gap; spacers for vacuum sealing the space
formed by the two substrates while maintaining the gap between the
two substrates; cathodes and anodes arranged in strips on the
facing surfaces of the two substrates so that the cathodes cross
with the anodes; electron emission sources formed on the portions
of the cathodes at the intersections of the cathodes and the
anodes; and gates for controlling electrons emitted from the
electron emission sources, wherein the gates are arranged on the
rear substrate under the cathodes to cross with the cathodes so
that the gates are located straightly over the anodes, and an
insulative layer for electrical insulation is formed between the
gates and the cathodes, the method including controlling current
flowing between the cathodes and the anodes by controlling the gate
voltage.
[0013] Preferably, the electron emission sources are formed of at
least one material selected from the group consisting of carbon
nanotube, a metal, diamond and graphite, on the cathodes at the
intersections of the cathodes and gates. Alternatively, the
electron emission sources are formed of a mixture of a conductive
material, a dielectric material or an insulative material with at
least one material selected from the group consisting of carbon
nanotube, a metal, diamond and graphite, on the cathodes at the
intersections of the cathodes and the gates.
[0014] It is preferable that the electron emission sources are
formed straight on the entire surface or one edge of cathodes at
the intersections of the cathodes and gates.
[0015] Alternatively, it is preferable that the electron emission
sources are formed around at least one hole pierced in the cathodes
at the intersections of the cathodes and anodes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The above objective and advantage of the present invention
will become more apparent by describing in detail a preferred
embodiment thereof with reference to the attached drawings in
which:
[0017] FIG. 1 is a vertical cross-sectional view schematically
illustrating the structure of a triode field emission device using
a conventional field emission material;
[0018] FIG. 2 is a vertical cross-sectional view schematically
illustrating the structure of a triode field emission device using
a field emission material according to the present invention;
[0019] FIG. 3 is a view illustrating an embodiment of the triode
field emission device using a field emission material of FIG. 2, in
which the field emission material is formed on the edge of cathodes
at the intersections of the cathodes and gates;
[0020] FIGS. 4A through 4D are views illustrating embodiments of
the triode field emission device using a field emission material of
FIG. 2, in which the field emission material is formed around at
least one hole pierced on the edge of cathodes at the intersections
of the cathodes and gates;
[0021] FIGS. 5A and 5B are curves illustrating an equipotential
line distribution and a field distribution with respect to a gate
voltage in the field emission device of FIG. 2 in which the gap
between cathodes is 60 .mu.m, an anode voltage is 500 V, the gap
between a cathode and an anode is 200 .mu.m, and the gaps (h)
between cathodes and gates are identical;
[0022] FIGS. 6A and 6B are graphs showing variations in edge field
strength and deviation, respectively, with respect to voltages
applied to gates in the field emission device of FIG. 2 in three
cases of the gap (h) between a cathode and a gate being 5 .mu.m, 10
.mu.m and 15 .mu.m with the gap between cathodes of 60 .mu.m, an
anode voltage 500 V, and the gap between a cathode and an anode of
200 .mu.m;
[0023] FIGS. 7 through 9 show the electrical characteristics with
respect to variations in gate voltage when an anode voltage is 400
V, in an embodiment of the field emission device of FIG. 2
manufactured so that the gap between a cathode and an anode is 1.1
mm, wherein FIGS. 7 and 8 are graphs showing the anode current and
the Fowler-Nordheim plot value, respectively, with respect to
variations in gate voltage, and FIG. 9 is a picture of the
brightness of the above actually-manufactured field emission device
when half of a substrate is gated on while the remaining half is
gated off;
[0024] FIGS. 10A through 11B are graphs and pictures with respect
to a field emission device in which the gap between a cathode and
an anode is 200 .mu.m, and cathodes are coated with a paste
obtained by mixing Ag and carbon nanotubes;
[0025] FIG. 12 is a picture with respect to a triode field emission
device in which the gap between a cathode and an anode is 1.1 mm,
and cathodes are coated with a paste obtained by mixing glass and
carbon nanotubes; and
[0026] FIGS. 13A and 13B are pictures of the brightness of a triode
field emission device in two cases, that is, when insulative layers
between gates and cathodes are formed in strips along the cathodes,
and when the insulative layer is formed in the form of a plane,
respectively.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0027] FIG. 2 is a cross-sectional view schematically illustrating
the structure of a triode field emission device using carbon
nanotubes according to the present invention. As shown in FIG. 2,
the triode field emission device according to the present invention
includes a rear substrate 11 and a front substrate 20 which face
each other at the interval corresponding to the length of a spacer
16. Anodes 4 and cathodes 12 on each of which an electron emission
source 15 made of carbon nanotube, metal, diamond or graphite is
partially formed, and anodes 14, are formed as electron emission
sources between the two substrates. Gates 13 are formed below an
insulative layer 17 formed below the cathodes 12. The gates 13 are
formed like a full surface on the rear substrate 11 or disposed in
parallel strips thereon. The insulative layer 17 is formed on the
rear substrate 11 on which the gates 13 are formed. When the gates
13 are formed in strips not like a full surface, the cathodes 12
are disposed in parallel strips in the direction of crossing with
the gates 13. The anodes 14 are disposed in parallel strips on the
cathode-facing surface of the front substrate 20 so that they cross
with the anodes 12, that is, so that they are arranged in parallel
with the gates 13 straightly over the gates 13. Electron emission
sources 15 made of carbon nanotube, metal, diamond or graphite are
formed on the cathodes 12 at the intersections of the cathodes 12
and the gates 13.
[0028] The electron emission sources 15 can be locally formed on
the edge of the cathodes 12 at the intersections with the gates 13
(or anodes), as shown in FIG. 3, or formed on the entire surface of
the cathodes 12. Alternatively, as shown in FIGS. 4A through 4D,
the electron emission sources 15 can be locally formed around at
least one hole pierced in the cathodes 12 at the intersections with
the gates 13 (or anodes). As described above, the electron emission
sources 15 can be formed at any positions on the cathodes at the
intersections with the gates. However, the formation of the
electron emission sources 15 on the edge of the cathodes has an
advantage in that the strongest field is experimentally formed at
the edge thereof. The electron emission sources 15 formed on the
cathodes 12 can have any width compared to the line width of the
cathodes 12.
[0029] FIG. 3 illustrates the case where a field emission material
15 is linearly coated on one edge of a cathode 12 at the
intersection with a gate 13. FIGS. 4A through 4D illustrate the
four cases where one, two, three and four holes are pierced in a
cathode 12 at the intersection with a gate 13, respectively,
wherein an electron emission source 15 is circularly formed around
each of the holes. Here, the electron emission source 15 can also
be formed in different shapes. In particular, when three or more
holes are formed, a hole to be positioned in the middle is formed
to a dominant size, and, preferably, a field emission material is
formed around the outer circumference of each of the holes, so that
the uniformity of emission current within a pixel is increased. The
number of circular or different-shaped field emission material
figures is controlled to obtain the maximum uniform electron
emission effect at the minimum power, according to all of the
conditions such as the standards such as the gap between cathodes,
the gap between a cathode and a gate, and the gap between a cathode
and an anode, the material of an insulative layer, and a voltage
applied to each electrode.
[0030] The insulative layer 17, which insulates the gate electrode
13 from the cathode 12, can be formed in a plane or in lines along
the lines of the cathodes 12. Here, when the insulative layer 17 is
linearly formed, the line width of the insulative layer 17 can be
equal to or larger than that of the cathode 12.
[0031] As described above, in the field emission device according
to the present invention having a triode structure by which emitted
current is easily controlled, gate electrodes are placed under
cathodes in order to easily form electron emission materials
serving as electron emission sources on the cathodes. Also, emitted
current can be controlled with low voltage by field emission at the
edge of cathodes, and the uniformity of emitted current can be
improved by the formation of various patterns.
[0032] Furthermore, the gate electrodes are formed below an
insulative layer formed below the cathodes, so that, if an
appropriate amount of voltage is applied to the gate electrodes, an
electrical field caused by the gate voltage transmits the
insulative layer, and thus a strong electrical field is formed in
electron emission sources. Thus, electrons are emitted by the field
emission. The emitted electrons are moved toward anodes by an
additional electrical field formed by an anode voltage, and serve
as their functions. Curves representing an equipotential line
distribution and a field distribution (an electron emission path)
with respect to a gate voltage are shown FIGS. 5A and 5B. The
curves are the results obtained by simulating the case that the gap
between cathodes is 60 .mu.m, an anode voltage is 500 V, the gap
between a cathode and an anode is 200 .mu.m, and the gaps (h)
between cathodes and gates are identical. Here, FIG. 5A refers to
the case when 0 V is applied to gates, and FIG. 5B refers to the
case when 80 V is applied to the gates. Referring to the
equipotential line distribution, when the gate voltage is high,
that is, when 80 V is applied to the gates, the gap between
equipotential lines is more narrow near cathodes than at the other
portions, which means that the field strength around the cathodes
is higher than that in the other portions. This infers that a
greater number of electrons are emitted near the cathodes than at
the other portions, as can be seen from the simulation results
shown in FIGS. 6A and 6B.
[0033] FIGS. 6A and 6B are graphs showing variations in edge field
strength and horizontal deviation of emitted electrons from
emission points, respectively, with respect to voltages applied to
gates, in three cases of the gap (h) between a cathode and a gate
being 5 .mu.m, 10 .mu.m and 15 .mu.m with the gap between cathodes
of 60 .mu.m, an anode voltage 500 V, and the gap between a cathode
and an anode of 200 .mu.m as described above. As shown in FIG. 6A,
the edge field strength increases as the gate voltage increases.
FIG. 6B is a graph showing a deviation of electrons emitted from
the edge of cathodes, with variations in gate voltage, the
deviation measured from a position over anodes.
[0034] <First embodiment>
[0035] FIGS. 7 through 9 show the electrical characteristics with
respect to variations in gate voltage when an anode voltage is 400
V, in a field emission device according to the present invention
manufactured so that the gap between a cathode and an anode is 1.1
mm. Here, FIGS. 7 and 8 are graphs showing the anode current and
the Fowler-Nordheim plot value, respectively, with respect to
variations in gate voltage, and FIG. 9 is a picture of the
brightness of the above actually-manufactured field emission device
when half of a substrate is gated on while the remaining half is
gated off. In FIG. 7, RHS denotes the right hand side, and LHS
denotes the left hand side. FIG. 7 refers to the case when only the
right half of a substrate is gated on and the case when only the
left half of a substrate is gated on. In FIG. 8, which shows the
Fowler-Norheim plot of FIG. 7, measured current is interpreted as
current generated by field emission if data points exist on a
line.
[0036] <Second embodiment>
[0037] FIGS. 10A through 11B are graphs and pictures with respect
to a field emission device according to the present invention
manufactured so that the gap between a cathode and an anode is 200
.mu.m, in which a paste obtained by mixing Ag and carbon nanotubes
is printed on cathodes to serve as electron emission sources. Here,
FIG. 10A shows the intensity of anode current with variations in
gate voltage, and FIG. 10B is a graph showing the Fowler-Norheim
plot of FIG. 7. FIG. 11A is a picture of the brightness of a diode
field emission device when an anode voltage is 500 V, and FIG. 11B
is a picture of the brightness of a triode field emission device at
a gate voltage of 120 V, when anodes are biased by 250 V.
[0038] <Third embodiment>
[0039] FIG. 12 is a picture with respect to a triode field emission
device according to the present invention manufactured so that the
gap between a cathode and an anode is 1.1 mm, in which a paste
obtained by mixing glass and carbon nanotubes is printed on the
cathodes to serve as electron emission sources. Here, an anode
voltage is DC 700 V, and a gate voltage is AC 300 V (130 Hz,
{fraction (1/100)}duty). FIG. 12 refers to the case when only the
left half of a substrate is gated on.
[0040] <Fourth embodiment>
[0041] FIGS. 13A and 13B are pictures of the brightness of a triode
field emission device in two cases, that is, when insulative layers
between gates and cathodes are formed in strips along the cathodes,
and when the insulative layer is formed in a plane, respectively.
In the two cases, an anode voltage is DC 500 V. As shown in FIG.
13A, in the case when the insulative layer is linearly formed, the
uniformity of field emission is improved, and an operation voltage
(which is 160 V in the case of linear formation of the insulative
layer, or 240 V in the case of blanket formation of the insulative
layer) increases.
[0042] In the manufacture of this field emission device, first,
gate electrode lines in strips are formed on a substrate, and then
an insulating material having a constant thickness (about several
to several tens of .mu.m) is entirely or locally coated on the gate
electrode lines. Next, cathode lines are formed on the insulative
layer to cross with the gate electrodes. Then, carbon nanotubes are
coupled to the edge of each of the cathodes at the dot area where
the gate electrodes are overlapped by the cathodes, by a printing
method, an electrophoretic method or a vapor deposition method.
Alternatively, carbon nanotubes are formed around holes pierced in
the dot area where the gate electrodes are overlapped by the
cathodes. Thereafter, anodes and the resultant substrate are vacuum
sealed using spacers by a typical method.
[0043] As described above, in a triode field emission device using
carbon nanotubes according to the present invention, gate
electrodes serving to take electrons out of carbon nanotubes on
cathodes are installed below the cathodes on a substrate, so that
the manufacture of the devices is easy. However, in all existing
triode electron emission devices, gate electrodes are interposed
between cathodes and anodes. In the present invention, the gate
electrodes are formed below an insulative layer formed below the
cathodes, so that, if an appropriate amount of voltage is applied
to the gate electrodes, an electrical field caused by the gate
voltage transmits the insulative layer, and thus a strong
electrical field is formed in carbon nanotubes. Thus, the carbon
nanotubes can control the emission of electrons due to the field
emission. The emitted electrons are moved toward anodes by an
additional electrical field formed by an anode voltage, and serve
as their functions. Field emission devices having such a structure
can be simply manufactured by present techniques, and driven at low
voltage and enlarged because of the use of carbon nanotubes as
electron emission sources. Therefore, these field emission devices
receive much attention for their potential to serve as
next-generation flat display devices.
* * * * *