Sealing of plate structures

Details Sealing of plate structures Sealing of plate structures

2000-08-03

2002-07-09

Ramsey, Kenneth J. (Department: 2879)

Electric lamp or space discharge component or device manufacturi

Process

With assembly or disassembly

Reexamination Certificate

active

06416375

ABSTRACT:

FIELD OF USE
This invention relates to techniques for sealing structures, particularly flat-panel devices.
BACKGROUND ART
A flat-panel device contains a pair of generally flat plates connected together through an intermediate mechanism. The two plates are typically rectangular in shape. The thickness of the relatively flat-structure formed with the two plates and the intermediate connecting mechanism is small compared to the diagonal length of either plate.
When used for displaying information, a flat-panel device is typically referred to as a flat-panel display. The two plates in a flat-panel display are commonly termed the faceplate (or frontplate) and the baseplate (or backplate). The faceplate, which provides the viewing surface for the information, is part of a faceplate structure containing one or more layers formed over the faceplate. The baseplate is similarly part of a baseplate structure containing one or more layers formed over the baseplate. The faceplate structure and the baseplate structure are sealed together, typically through an outer wall, to form a sealed enclosure.
A flat-panel display utilizes mechanisms such as cathode rays (electrons), plasmas, and liquid crystals to display information on the faceplate. Flat-panel displays that employ these three mechanisms are generally referred to as cathode-ray tube (“CRT”) displays, plasma displays, and liquid-crystal displays. The constituency and arrangement of the display's faceplate structure and baseplate structure depend on the type of mechanism utilized to display information on the faceplate.
In a flat-panel CRT display, electron-emissive elements are typically provided over the interior surface of the baseplate. The electron-emissive elements are arranged in a matrix of rows and columns of picture elements (pixels). Each pixel typically contains a large number of individual electron-emissive elements. When the electron-emissive elements are appropriately excited, they emit electrons that strike phosphors arranged in corresponding pixels situated over the interior surface of the faceplate.
The faceplate in a flat-panel CRT display consists of a transparent material such as glass. Upon being struck by electrons emitted from the electron-emissive elements, the phosphors situated over the interior surface of the faceplate emit light visible on the exterior surface of the faceplate. By appropriately controlling the electron flow from the baseplate structure to the faceplate structure, a suitable image is displayed on the faceplate.
The electron-emissive elements in a flat-panel CRT display typically emit electrons according to a field-emission (cold emission) technique or a thermionic emission technique. In either case, but especially for the field-emission technique, electron emission needs to occur in a highly evacuated environment for the CRT display to operate properly and to avoid rapid degradation in performance. The enclosure formed by the faceplate structure, the baseplate structure, and the outer wall is thus fabricated in such a manner as to be at a high vacuum, typically a pressure of 10
−7
torr or less for a flat-panel CRT display of the field-emission type. One or more spacers are commonly situated between the faceplate structure and the baseplate structure to prevent outside forces, such as air pressure, from collapsing the display.
Any degradation of the vacuum can lead to various problems such as non-uniform brightness of the display caused by contaminant gases that degrade the electron-emissive elements. The contaminant gases can, for example, come from the phosphors. Degradation of the electron-emissive elements also reduces the working life of the display. It is thus critical to hermetically seal a flat-panel CRT display.
A flat-panel CRT display of the field-emission type, often referred to as a field-emission display (“FED”), is conventionally sealed in air and then evacuated through pump-out tubulation provided on the display.
FIGS. 1
a
-
1
d
(collectively “FIG.
1
”) illustrate one such conventional procedure for sealing an FED consisting of a baseplate structure
10
, a faceplate structure
12
, an outer wall
14
, and multiple spacer walls
16
.
At the point shown in
FIG. 1
a
, spacer walls
16
are mounted on the interior surface of faceplate structure
12
, and outer wall
14
is connected to the interior surface of faceplate structure
12
through frit (sealing glass)
18
provided along the faceplate edge of outer wall
14
. Frit
20
is situated along the baseplate edge of outer wall
14
. A tube
22
is sealed to the exterior surface of baseplate structure
10
through frit
24
at an opening
26
in baseplate structure
10
. A getter
28
for collecting contaminant gases is typically provided along the inside of tube
22
. The structure formed with baseplate structure
12
, outer wall
14
, and spacer
16
is physically separate from the structure formed with baseplate structure
10
, tube
22
, and getter
28
prior to sealing the display.
Structures
12
/
14
/
16
and
10
/
22
/
28
are placed in an alignment fixture
30
, aligned to each other, and brought into physical contact along frit
20
as shown in
FIG. 1
b
. Alignment fixture
30
is located in, or is placed in, an oven
32
. After being aligned and brought into contact, structures
12
/
14
/
16
and
10
/
22
/
28
are slowly heated to a sealing temperature ranging from 450° C. to greater than 600° C. Frit
20
melts, sealing structure
12
/
14
/
16
to structure
10
/
22
/
28
. The sealed FED is slowly cooled down to room temperature. The heating/sealing/cool-down process typically takes 1 hr.
After having been sealed, the FED is removed from alignment fixture
30
and oven
32
, and is placed in another oven
34
. See
FIG. 1
c
. A vacuum pumping system
36
is connected to tube
22
. With a heating element
38
placed around tube
22
, the FED is pumped down to a high vacuum level through tube
22
. The FED is then brought slowly up to a high temperature and baked for several hours to remove contaminant gases from the material of the FED. When a suitable low pressure can be maintained in the FED at the elevated temperature, the FED is cooled to room temperature, and tube
22
is heated through heating element
38
until tube
22
closes to seal the FED at a high vacuum. The FED is then removed from oven
34
and disconnected from vacuum pump
36
.
FIG. 1
d
shows the sealed FED.
The sealing process of
FIG. 1
is unsatisfactory for a number of reasons. Even though multiple FEDs can be sealed at the same time, the sealing procedure often takes too long to meet commercial needs. In addition, the entire FED is heated to a high temperature for a long period. This creates concerns relating to alignment tolerances and can degrade certain of the materials in the FED, sometimes leading to cracking. Furthermore, tube
22
protrudes out of the FED. Consequently, the FED must be handled very carefully to avoid breaking tube
22
and destroying the FED. It would be extremely beneficial to have a technique for sealing a flat-panel device, especially a flat-panel display of the field-emission CRT type, that overcomes the foregoing problems and eliminates the need for pump-out tubulation such as tube
22
.
GENERAL DISCLOSURE OF THE INVENTION
The present invention furnishes a technique for sealing portions of a structure together in such a manner that the sealed structure can readily achieve a reduced pressure state, typically a high vacuum level, without the necessity for providing the structure with an awkward pressure-reduction device, such as pump-out tubulation, that protrudes substantially beyond the remainder of the sealed structure. In the invention, sealing is effected by a gap-jumping technique in which energy is applied locally along a specified area to create the seal. The term “local” or “locally” as used here in describing an energy transfer means that the energy is directed selectively to certain material largely intended to receive the energy without being significantly transferred to nearby materia

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