Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing...
Reexamination Certificate
2001-11-28
2003-10-28
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
C349S139000, C349S073000
Reexamination Certificate
active
06639646
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-71353, filed in Korea on Nov. 28, 2000, which is hereby incorporated by reference.
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 manufacturing process of liquid crystal cells for small sized liquid crystal display devices.
2. Discussion of the Related Art
A conventional liquid crystal display (LCD) panel has upper and lower substrates and a liquid crystal layer interposed therebetween. The upper substrate includes common electrodes, and the lower substrate includes switching elements, such as thin film transistors (TFTs), and pixel electrodes. The common electrodes and pixel electrodes are formed on upper and lower substrates, respectively, and a seal is formed on the lower substrate. The upper and lower substrates are then bonded together using a sealing material so that the common electrodes of the upper substrate and the pixel electrodes of the lower substrate come face to face with each other. A liquid crystal material is injected through injection holes of the seal into a gap formed between the upper and lower substrates through injection holes, and the injection holes are sealed. Polarizing films are attached to outer surfaces of the upper and lower substrates.
During operation of the liquid crystal panel, light passing through the liquid crystal panel is controlled by electric fields. The electric fields are applied by the pixel and common electrodes. By controlling the electric fields, image data (characters) are displayed on the liquid crystal panel.
Fabrication processes of various components of the liquid crystal display device, such as the thin film transistors and color filters, conventionally require numerous manufacturing steps.
FIG. 1
is a flow chart illustrating a fabricating sequence of the liquid crystal cell for a conventional liquid crystal display device.
In
FIG. 1
, a first step ST
1
involves cleaning the upper and lower substrates, commonly referred to as a color filter substrate and an array substrate, respectively. The first step ST
1
removes impurities that may exist on the substrates and on one or more of the cells that have been previously formed on the upper and lower substrates.
In
FIG. 1
, a second step ST
2
involves formation of alignment layers on the common and pixel electrodes previously formed on the upper and lower substrates, respectively. The second step ST
2
also includes processes for coating, hardening, and rubbing of the alignment layers. A polyimide-based resin is conventionally selected for forming the alignment layers because it demonstrates excellent alignment characteristics with various liquid crystal materials. A surface of the hardened alignment layers is rubbed by a fabric to create surface scratches along a uniform direction. The rubbing process is necessary to form uniform alignment of the liquid crystal molecules in the liquid crystal layer, thereby ensuring uniform display. Accordingly, it is very important to uniformly form the alignment layers on a large surface of the common and pixel electrodes.
In
FIG. 1
, a third step ST
3
involves printing a seal pattern and spacers on one, or both of the substrates. When the upper and lower substrates are attached, the seal pattern forms cell gaps between the upper and lower substrates that will receive the liquid crystal material. The seal pattern prevents the liquid crystal material from escaping out of the completed liquid crystal cell. A thermosetting resin that includes glass fibers, and a screen-print process are conventionally used to fabricate the seal pattern. The seal pattern includes an injection hole, and is formed along edge portions of a display area of each liquid crystal cell. After the seal pattern is printed, spacers are formed to maintain an accurate and uniform cell gap between the upper and lower substrates. Accordingly, the spacers must be formed on one, or both of the substrates with a uniform density. Presently, there are two processes for forming the spacers. A first process includes a wet dispensing method for spraying a mixture of alcohol and the spacers. A second process includes a dry dispensing method for spraying only the spacers.
In
FIG. 1
, a fourth step ST
4
involves aligning and attaching the upper and lower substrates to each other. Accordingly, an aligning error margin in the fourth step ST
4
is less than a few micrometers. If the upper and lower substrates are aligned and attached with an aligning margin larger than the aligning error margin less than a few micrometers, display quality of the display panel deteriorates due to leakage of light during operation of the liquid crystal cell.
In
FIG. 1
, a fifth step ST
5
involves cutting the liquid crystal cell fabricated in the steps ST
1
-ST
4
into individual liquid crystal cells. The cutting process includes a step of scribing the substrates to form cutting lines, and a step of severing the substrates along the scribed lines to form the individual liquid crystal cells.
In
FIG. 1
, a sixth step ST
6
involves injecting the liquid crystal material into the individual liquid crystal cells. Since each individual liquid crystal cell has a gap ratio of only a few micrometers per hundreds of square centimeters in substrate surface area, a vacuum injection process utilizing a pressure difference is conventionally used for the liquid crystal cell. Since the vacuum injection process requires a significant amount of time in addition to the many other different fabrication processes for forming the liquid crystal display device, it is important to set an optimum condition for the vacuum injection process to increase fabrication yield. However, since there is no pressure difference between an interior of the liquid crystal cell and the liquid crystal material at the beginning of injection process, the liquid crystal material is injected by capillary action. When the liquid crystal material is injected into the liquid crystal cell, nitrogen gas or air is supplied to a vacuum chamber, thereby creating a pressure difference between the interior of the liquid crystal cell and an interior of the vacuum chamber. Accordingly, the liquid crystal material is injected into the liquid crystal cell as a result of the pressure difference. After the liquid crystal material is injected into the liquid crystal cell through an injection hole, the injection hole is sealed. The injection hole is conventionally sealed by forming an ultraviolet curable resin plug in the injection hole using a dispenser, and irradiating the plug with ultraviolet light to cure the resin and seal the hole. However, since the liquid crystal cell may become contaminated when exposed to air, the unsealed liquid crystal cell must be protected from the air and must not be allowed to be exposed to the air for a long period of time.
In
FIG. 1
, a seventh step ST
7
involves inspecting the liquid crystal cell. A plurality of data lines and a plurality of gate lines of a unit cell are connected to a data pad and a gate pad, respectively, via shorting bars disposed in a marginal space of the liquid crystal cell. The marginal space includes a common voltage pad for applying a common voltage to the common electrode of the unit cell. The inspection is conducted by applying a voltage to the liquid crystal cell and observing an image displayed on the liquid crystal cell with a naked eye or with a microscope. In the inspection process, various qualities may be inspected. An existence of contaminates in the liquid crystal cell, point defects caused by the thin film transistors, line defects caused by discontinuities of the gate and data lines, and a optical defect properties caused by a differences of cell thickness, for example, may be inspected. Two inspection methods may be performed that include an ON-OFF inspection process, and an auto probe inspection process. The ON-OFF inspection process is performed by applying a direct current voltage using an ON-OFF apparat
Duong Tai
LG. Philips LCD Co. Ltd.
Morgan & Lewis & Bockius, LLP
Ton Toan
LandOfFree
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