Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
1999-02-18
2003-03-18
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
C445S023000
Reexamination Certificate
active
06533632
ABSTRACT:
TECHNICAL FIELD
This invention relates to flat panel displays having a baseplate used to generate an image and a faceplate through which the image is adapted to be viewed, and, more particularly, to a method of evacuating and sealing the space between the faceplate and baseplate, as well as flat panel displays and components fabricated using such method.
BACKGROUND OF THE INVENTION
Flat panel displays are commonly used for a variety of purposes, such as for notebook computer displays, display panels for electronic instruments and devices, and portable televisions and camcorders, to name a few. One commonly used flat panel display is a liquid crystal display in which an image is generated by applying signals to a baseplate to selectively modulate the transmissivity of a liquid crystal filling the space between the baseplate and a transparent faceplate. The transmissivity of the liquid crystal is modulated on a pixel-by-pixel basis to generate a monochromatic or color image that is visible through the faceplate.
Another type of flat panel display that has been proposed for use in a wide variety of applications are field emission displays. Field emissions displays employ a baseplate having a substrate containing an array of emitters or emitter sets (a group of emitters connected to each other) and an extraction grid surrounding each of the emitters. The emitters are generally biased between −30 and 0 volts, while the extraction grids are generally biased between 30 and 100 volts. When the voltage of an extraction grid is more positive by a sufficient voltage (e.g., 60 volts or more), electrons are extracted from the emitter.
The field emission display also includes a faceplate that is spaced apart from and parallel to the baseplate, thereby forming a space between the baseplate and faceplate. The surface of the faceplate facing the baseplate is coated with a layer of transparent conductive material, such as indium tin oxide (“ITO”). Finally, the transparent conductive layer is coated with a layer of a cathodoluminescent material. The cathodoluminescent material may be applied to the transparent conductive layer either uniformly or in a pattern corresponding to a desired image. Different cathodoluminescent materials also may be applied in different locations to create color images or images of multiple colors.
In operation, a large positive voltage, on the order of 1000 volts, is applied to the conductive layer coating the faceplate to draw the electrons emitted by the emitters to the conductive material. The electrons traveling to the faceplate strike the cathodoluminescent material, thereby giving up their energy thus causing the cathodoluminescent material to be illuminated and portray an image which may be viewed through the transparent faceplate. The space between the baseplate and the faceplate of field emission displays must be evacuated and remain evacuated after prolonged periods of use. Should the space between the baseplate and faceplate not be adequately evacuated, residual gases in the space, when energized by the extracted electrons, can start arcing or even glow discharge thereby seriously limiting the operating and useful life of field emission displays. The emitters must also be precisely aligned to predetermined areas of the cathodoluminescent material. A gettering agent, such as ST-122 gettering agent sold by SAES, is placed in the space between the baseplate and the faceplate to maintain the vacuum environment at times of use and storage.
As illustrated in
FIGS. 1 and 2
, a faceplate
10
is generally glass or glass/ceramic, and generally a sealing material frit, such as glass or metal, forms a bead
12
extending around the perimeter of the faceplate
10
near its periphery
14
. To assemble a field emission display, a field emission display baseplate
20
(
FIG. 2
) is placed over the faceplate
10
against an interface surface
24
formed along the upper surface of the frit bead
12
. The plates
10
,
20
are heated above a temperature at which the frit bead
12
will flow, either under the weight of one of the plates or with the application of a compressive force upon the plates
10
,
20
. The frit bead
12
is thus compressed, thereby causing the frit bead
12
to flow or extrude and adhere to the plates
10
,
20
. After the plates
10
,
20
cool, the frit bead
12
forms a seal between the plates
10
,
20
.
The above-described procedure would be entirely satisfactory if it was not necessary for the space between the plates
10
,
20
to be evacuated. However, as mentioned previously, the space between the plates
10
,
20
must be substantially evacuated. There are two primary approaches to evacuating the space between the plates
10
,
20
. In one of these approaches, a tube or other conduit (not shown) is embedded in the frit bead
12
. A hole could also be formed in one of the plates, such as by drilling. An evacuation tube would then be fritted to the plate overlying the hole during thermal processing of the plates
10
,
20
, to form a rigid, airtight seal between the plates
10
,
12
. The space between the plates
10
,
20
is evacuated by means of vacuum pumping through the tube or conduit, and the tube or conduit is thermally or resistively heated to collapse and seal itself. This approach has several disadvantages, including the expense of creating and then sealing the tube or conduit, and the potential for subsequent leakage or possible breakage. Also, this approach requires space for the tube or conduit, which may be difficult in some applications, such as in laptops, where packaging space is limited.
Another conventional approach to evacuating and sealing the space between the plates
10
,
20
is illustrated in FIG.
3
and described in U.S. Pat. Nos. 5,697,825 and 5,788,551 to Dynka et al., which are incorporated herein by reference. In this approach, frit protrusions
28
are formed at spaced apart locations along the frit bead
12
, such as at the comers of the face plate
10
. When the baseplate
20
is placed on the faceplate
10
, the protrusions
28
position the baseplate
20
above the interface surface
24
of the frit bead
12
. As a result, gaps
30
are formed between the baseplate
20
and the interface surface
24
of the frit bead
12
and provide a flow path for evacuating the space defined by the plates
10
,
20
and the frit bead
12
.
After the baseplate
20
is placed on the protrusions
28
, the plates
10
,
20
are placed in an evacuation oven (not shown). The evacuation oven heats the plates
10
,
20
in an environment of substantially zero pressure. As the pressure in the evacuation oven is reduced, residual gases, comprised mainly of air, are drawn through the gaps
30
from the space between the plates
10
,
20
. After the space between the plates
10
,
20
has been substantially evacuated, the plates
10
,
20
are heated to a temperature at which the frit bead
12
will flow. A compressive force applied to the plates
10
,
20
causes the protrusions
28
to totally collapse into the frit bead
12
and the frit bead
12
to partially compress. The frit bead
12
then bonds to the faceplate
20
so that a hermetic seal is formed between the plates
10
,
20
. The plates are allowed to cool before removing the vacuum from the evacuation oven and exposing the plates
10
,
20
to atmospheric pressure. The result of this procedure is a hermetically sealed, evacuated space between the plates
10
,
20
.
Although the above-described procedure has several advantages over the use of a tube or conduit to evacuate a space, it nevertheless can be improved. First, the need to form protrusions
28
on the frit bead
12
adds to the time and expense of manufacturing field emission displays. Second, it is difficult to ensure that all of the protrusions
28
are of exactly the same size. Yet it is possible for sized protrusions
28
to allow the frit bead
12
to compress unevenly. Although spacers (not shown) are generally used to space the faceplate
10
a fixed distance from the baseplate
20
, it is neverth
Dorsey & Whitney LLP
Micro)n Technology, Inc.
Ramsey Kenneth J.
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