Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2003-04-09
2004-12-28
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S190000
Reexamination Certificate
active
06836311
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2002-28718, filed on May 23, 2002 in Korea, which is hereby incorporated by reference for all purposes as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and more particularly, to a seal pattern for a liquid crystal display device.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices such as active matrix LCDs (AM LCDs) are widely used in devices such as notebook computers, desktop monitors, etc., due in part to their high resolution and their ability to display color and moving images. LCD devices generally include an upper substrate (i.e., an array substrate) coupled to, and spaced apart from, a lower substrate (i.e., a color filter substrate). A layer of liquid crystal material is typically disposed between the array and color filter substrates. Electrodes are provided on each of the upper and lower substrates such that electrodes of opposing substrates face each other. Anisotropic optical properties of the liquid crystal materials may be exploited by liquid crystal display devices to produce images. By varying the orientation of liquid crystal molecules in an electric field, the transmissivity of light within the layer of liquid crystal material may be selectively controlled. Liquid crystal display devices also include thin film transistors and pixel electrodes arranged in a matrix pattern.
Fabrication of LCD devices typically involves many processes including the formation of an array substrate, formation of a color filter substrate, and injection of liquid crystal material between the array and color filter substrates. Formation of array substrates includes forming switching elements and pixel electrodes. Formation of color filter substrates includes forming color filters and common electrodes.
FIG. 1
illustrates a cross-sectional view of a liquid crystal display panel used in a related art LCD device.
Referring to
FIG. 1
, an upper substrate
10
and a lower substrate
30
are coupled to, and spaced apart from each other. Liquid crystal material
50
is interposed between the upper and lower substrates
10
and
30
. A gate electrode
32
is formed on a transparent substrate
1
included within the lower substrate
30
and a gate insulator
34
is formed on the gate electrode
32
. A semiconductor layer
36
, including an active layer
36
a
and an ohmic contact layer
36
b
, is formed on the gate insulator
34
. A source electrode
38
and a drain electrode
40
are formed on the semiconductor layer
36
. A channel region “ch”, including an exposed portion of the active layer
36
a
, is formed between the source electrode
38
and the drain electrode
40
. The gate electrode
32
, the semiconductor layer
36
, the source electrode
38
, the drain electrode
40
, and the channel “ch” constitute a thin film transistor “T”. Though not shown in
FIG. 1
, a plurality of gate lines are connected to the gate electrode
32
and extend along a first direction. Further, a plurality of data lines are connected to the source electrode
38
and extend along a second direction, perpendicular to the first direction. Crossings of the gate and data lines define pixel regions “P”. A passivation layer
42
, including a drain contact hole
44
formed therein, is formed on the thin film transistor “T”. A pixel electrode
48
is formed in the pixel region “P” and is connected to the drain electrode
40
via the drain contact hole
44
. A cell area of the array substrate includes a connection portion for connecting to an external driving circuit. Accordingly, the cell area of the array substrate is wider than a corresponding cell area of the color filter substrate. A lower alignment layer
46
is formed on both the passivation layer
42
and the pixel electrode
48
in order to induce an alignment of the liquid crystal material
50
. A color filter
14
, for filtering light within a specific wavelength range, is formed beneath a transparent substrate
1
included within an upper substrate
30
at a position corresponding to the pixel electrode
48
. A black matrix
12
, for protecting light leakage and for preventing light from contacting the thin film transistor “T”, is formed in boundary areas between each color portion of the color filter
14
. A common electrode
16
, serving as an electrode with which to apply voltage to the layer of liquid crystal material
50
, is formed beneath the color filter
14
and the black matrix
12
. An upper alignment layer
18
, similar to the lower alignment layer
46
, is formed beneath the common electrode
16
. A cell gap between the upper and lower substrates
10
and
30
is sealed using a seal pattern
52
. The seal pattern
52
is provided along the edges of the substrates to prevent leakage of liquid crystal material
50
. Additionally, the seal pattern
52
maintains the upper and lower substrates
10
and
30
a predetermined distance from one another (e.g., maintains the cell gap between the upper and lower substrates
10
and
30
, respectively) and enables liquid crystal, material to be injected.
As LCD manufacturing technologies progress, LCDs are finding new applications in lap-top computers, video cameras, aviation instrument panels, other electronic devices, etc., the manufacturable size of substrates in LCDs increase, and ways of fabricating LCDs to be thinner and lighter continue to be evaluated.
Typical glass substrates used in LCDs are about 0.7 mm thick. As the size of the substrate increases, however, the weight and thickness of the substrates must be reduced through chemical (e.g., with the use of etchant such as hydrofluoric acid) or physical (e.g., grinding, polishing, etc.) processes. Through these processes, minimum substrate thicknesses of about 0.5 mm to 0.6 mm are attainable upon consideration of factors such as substrate bending and external impacts encountered during a high speed revolution spin coating processes. Physical processes are often ineffective in maintaining optimal surface roughness and substrate thickness. Accordingly, chemical processes may be employed by dipping LCD substrates in, for example, a hydrofluoric acid solution.
The fabrication of liquid crystal cells includes forming an alignment layer to align liquid crystal molecules, forming a cell gap, cutting cells, injecting liquid crystal material, and sealing an injection hole arranged between the substrates.
FIG. 2
illustrates a flow chart of a process used in fabricating liquid crystal cells of ultra-thin liquid crystal display devices. A first process step (ST
1
) includes cleaning the array and color filter substrates by removing particles on the substrate prior to formation of the alignment layer on the substrate. A second process step (ST
2
) includes forming the alignment layer by forming thin polymer film on the substrate, hardening, and rubbing the thin polymer film. A third process step (ST
3
) includes forming a seal pattern and a spacer. The seal pattern forms a cell gap allowing the injection of liquid crystal material between the substrates and preventing the injected liquid crystal material from leaking. In ultra-thin liquid crystal display devices, the seal pattern also includes a dummy-seal pattern for preventing etchants from infiltrating into the cell gap during any of the aforementioned processes. The seal pattern is fabricated using screen-printing technology, thermosetting resin, and glass fiber. The spacer is usually formed on the array substrate and uniformly maintains the gap between the two substrates. The seal pattern is typically formed on the color filter substrate to minimize error in attaching the upper and lower substrates. A fourth process step (ST
4
) includes aligning and attaching the upper and lower substrates to each other. The degree to which the upper and lower substrates may be aligned is determined by a measuring an alignment margin, usually less than a few microns, provided when the substrates are initially designed. If th
Chowdhury Tarifur R.
LG. Philips LCD Co. Ltd.
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