Electric lamp or space discharge component or device manufacturi – Process – Electrode making
Reexamination Certificate
2001-05-17
2004-01-27
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
Electrode making
C445S024000, C438S020000
Reexamination Certificate
active
06682383
ABSTRACT:
TECHNICAL FIELD
The invention relates to a cathode structure for a field emission device and method of fabricating the same.
BACKGROUND OF THE INVENTION
One example of the field emission device includes a field emission display (FED) being a flat panel display. The field emission display comprises the base plate having a cathode and the face plate having phosphor, which are located in parallel positions separated by a short distance (less than 2 mm) vacuum-packaged. The field emission display is a device in which electrons emitted from the cathode in the base plate collide against a phosphor on the face plate to display image by means of a cathode luminescence of the phosphor. There has been a lot of study on a flat display that will replace a conventional cathode-ray tube (CRT).
The cathode, being one of main components of the FED, is very different in an electron emission efficiency depending on a device structure, an emitter material, the shape of an emitter, etc. At present, the structure of the field emission device is mainly classified into a diode-type structure consisting of a cathode electrode and an anode electrode, and a triode-type structure consisting of a cathode electrode, a gate electrode and an anode electrode. The emitter material may include metal, silicon, diamond, diamond-like carbon, carbon nanotube, etc. Generally, metal and silicon is used as emitter material in a cathode for a triode-type field emission device while diamond or carbon nanotube, etc. is used as emitter material in a cathode for diode-type field emission device. The diode-type field emission device mainly uses film or fiber, needle, particle or powder of diamond or carbon nanotube that has a good electron emission property in a low electric field, as the emitter material. The diode-type field emission device is disadvantageous in controllability of electron emission and a low-voltage driving, but it is advantageous in that it is simple in manufacturing process and has a high reliability of electron emission, compared to a triode-type field emission device.
Referring now to
FIG. 1
, there is shown a schematic view illustrating a conventional cathode structure for a diode-type field emission device disclosed in U.S. Pat. No. 5,900,301 issued to Brandes, etc.
A cathode
100
comprises a cathode electrode
140
on a base plate
120
, a particulate emitter
160
on the cathode electrode
140
, and a bonding material
170
for bonding the particulate emitter
160
to the cathode electrode
140
. A glass substrate is usually used as a material of the base plate
120
. The cathode electrode
140
can be fabricated by depositing metal on the glass substrate by means of sputtering process or electron beam process, etc. and then performing a selective etching process by means of photolithography process. A cathode electrode
140
usually uses metals having good electrical conductivity, which may include Cr, Ni, Nb, etc. An emitter
160
usually uses materials having a good electron emission characteristic at a low electric field, which may include materials containing carbon as the major ingredients such as diamond, diamond-like carbon, amorphous carbon, carbon nanotube, carbon nanoparticle, etc. It is preferred that the bonding material
170
uses an electrically conductive material having a high electrical conductivity since it must has the function of electrically connecting the emitter
160
to the cathode electrode
140
. The bonding material
170
must also has the function of bonding the particulate emitter
160
to the cathode electrode
140
.
The U.S. Pat. No. 5,900,301 describes that Ti, graphite, Ni or its alloy can be used as the bonding material
170
, and also describes that a technology for increasing the bonding force between the emitter
160
and the cathode electrode
140
. As another example, U.S. Pat. No. 5,948,465 issued to Blanchet-Fincher, etc. describes a metal compound as the bonding material
170
for bonding the emitter
160
to the cathode electrode
140
. The two prior arts employ AgNO
3
as the metal compound. One example for forming the bonding material
170
can be summarized as follows. A mixed solution is first prepared by adding 25 wt % AgNO
3
, 3 wt % polyvinyl alcohol (PVA), 71.9 wt % distilled water and a surface active agent of 0.1 wt % and is then coated on the cathode electrode to form a mixture film. Then, the particulate emitter material is uniformly distributed in the mixture film and then a heating step is performed. During the heating step, the mixture film is burnt, by which nonmetallic components constituting the mixed solution are thus removed to leave metal only. In case of using AgNO
3
as the metal compound, Ag is left as the bonding material, which serves to not only electrically connect the emitter and the cathode electrode but also mechanically bond them.
FIG. 2
is a schematic view illustrating a conventional cathode
200
structure for a diode-type field emission device, disclosed in U.S. Pat. No. 5,623,180 issued to Jin, etc. The cathode
200
includes a cathode electrode
240
arranged in a stripe shape on a base plate
220
, a particulate substrate
265
on the cathode electrode
240
, and an emitter
260
covering the surface of the particulate substrate
265
. It is mainly used an electrically insulator as material of the base plate
220
. The cathode electrode
240
may be fabricated by using a good electrical conductor. A metal electrode having good electrical conductivity may be used as the material of the cathode electrode, and it is mainly used some materials having a good electron emission characteristic at a low electric field as the material of the emitter
260
. Major materials of the emitter
260
may include diamond, ceramic particles such as oxide particles, nitride particles, carbon particle, etc. and semiconductor materials. As shown in
FIG. 2
, the emitter
260
bonded to the particulate substrate
265
may have a continuous phase that completely surrounds the particulate substrate
265
. However, a plurality of the emitter particles may be discontinuously bonded to the particulate substrate
265
. Some metal particles is usually used as the particulate substrate
265
, and said metal may includes a metal that easily forms carbide such as Mo or a metal having high melting point. It is required that the size of the particulate substrate
265
be in the range of 0.1 to 100 micrometer in diameter, more preferably, in the range of 0.2 to 5 micrometer.
The method of fabricating the cathode electrode
240
in
FIG. 2
is very different from that of fabricating the cathode electrode
140
in FIG.
1
. The reason is that the cathode electrode
240
in
FIG. 2
must serve to not only transfer an electrical signal to the emitter
260
but also bond the emitter
260
and the particulate substrate
265
to the cathode electrode
240
. Therefore, the method of fabricating the cathode electrode
240
in
FIG. 2
is similar to that of fabricating the bonding material
170
in FIG.
1
. The method of fabricating the cathode electrode
240
can be summarized as follows. A slurry is produced by mixing a portion of liquid such as acetone, organic binder, metal or conductive oxide particles and particulate substrate
265
bonded with the emitters
260
by a given ratio. Metal particles may employ materials using Ag as the major ingredients and the conductive oxide particles may employ CuO particle that is easily reduced at low temperature. In a subsequent heating step, organic materials are burned out. After the heating step is finished, the particulate substrate
265
bonded to the emitter
260
and metal are left as residue. As shown in
FIG. 2
, the particulate substrate
265
surrounded by the emitters
260
after the heating step has a structure in which metal films are inserted discontinuously. The metal films function as the cathode electrode
240
. In
FIG. 2
, as a portion of respective emitters
260
must have faceted edge so that it can be used as a field emission device, a surface treatment may be performed after the heating ste
Cho Kyoung-Ik
Cho Young-Rae
Hwang Chi-Sun
Jung Moon-Youn
Kang Seung-Youl
Electronics and Telecommunications Research Institute
Ramsey Kenneth J.
Seed IP Law Group PLLC
Williams Joseph
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