Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing...
Reexamination Certificate
2001-11-27
2004-05-04
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
C349S073000, C349S040000
Reexamination Certificate
active
06731368
ABSTRACT:
This application claims the benefit of Korean Patent Application No. 2000-71013, filed on Nov. 27, 2000, which is hereby incorporated by reference as if fully set forth herein.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a method of fabricating a liquid crystal cell for a small size liquid crystal display device in which an electrical on/off inspection can be easily performed.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices having light, thin, low power consumption characteristics have been widely used in office automation (OA) equipment and video units. A typical LCD panel has upper and lower substrates and an interposed liquid crystal layer. The upper substrate, referred to as a color filter substrate, usually includes common electrodes and color filters. The lower substrate, referred to as an array substrate, includes switching elements, such as thin film transistors (TFTs), and pixel electrodes.
A brief explanation of a conventional liquid crystal cell manufacturing process and its operation will be discussed for better understanding of the present invention.
Common electrodes and pixel electrodes are formed on upper and lower substrates, respectively. A seal is then formed on the lower substrate. The upper and lower substrates are then bonded together using the seal such that the common electrodes of the upper substrate and the pixel electrodes of the lower substrate face each other, forming liquid crystal cells. Liquid crystal material is then injected into those cells through injection holes. The injection holes are then sealed. Finally, polarizing films are attached to the outer surfaces of the upper and lower substrates. The pixel and common electrodes generate electric fields that control the light passing through the liquid crystal cells. By controlling the electric fields, desired characters or images are displayed.
The liquid crystal cell process has few repeated steps compared with the TFT process or the color filter process. The whole process can be divided into the processes of forming the orientation film, forming the cell gap, injecting the liquid crystal and cutting the liquid crystal cell.
FIG. 1
is a flow chart showing a fabrication process of a typical liquid crystal cell for an LCD device.
At step ST
1
, an initial cleaning is performed after an upper substrate and a lower substrate are prepared. This step is for eliminating the impurities on the substrate before forming an orientation film.
At step ST
2
, the orientation film is formed on the upper and lower substrates. This step includes deposition and rubbing processes of the orientation film or polymer thin film. The formation of the orientation film enables the liquid crystal to operate normally by the uniform orientation of the liquid crystal molecules and is needed for the uniform display property. The most important part of this step is to deposit the orientation film uniformly over the wide area. A polymer compound of a polyimide family is widely used for the typical orientation film, and the deposited polymer compound becomes the polyimide thin film as an orientation film through the preliminary drying and the hardening process. The rubbing process scours the orientation film along one direction with the rubbing cloth and the liquid crystal molecules align along the rubbing direction.
At step ST
3
, a seal printing and a spacer deposition on the substrates are performed. The seal patterns form cell spaces that will receive the liquid crystal material and prevent the interposed liquid crystal material from leaking out of the completed liquid crystal cell. The seal patterning is a process of patterning a thermosetting plastic mixed with glass fiber. A screen-print method is widely used for this process. The next process is spraying spacers. The spacers have a definite size and act to maintain a precise and uniform space between the upper and the lower substrates. Accordingly, the spacers are placed with a uniform density on the substrate using either a wet spray method, in which the spacers are mixed in an alcohol and then sprayed, or a dry spray method, in which only the spacers are sprayed
At step ST
4
, the upper and lower substrates are aligned and attached. The alignment margin, which is less than a few micrometers, is determined by the substrate design. If the upper and lower substrates are aligned and attached beyond the alignment margin, light leaks away such that the liquid crystal cell cannot adequately perform its function.
At step ST
5
, the liquid crystal cell fabricated through the previous four steps is cut into unit liquid crystal cells. Generally, after a plurality of unit liquid crystal cells are formed on a wide glass substrate, the liquid crystal cell is divided into the plurality of unit liquid crystal cells. The cutting process typically includes a scribing process using a diamond pen to form cutting lines on the substrate, and a breaking process separating the substrate along the scribed lines by force.
At step ST
6
, a liquid crystal material is injected into the unit liquid crystal cells. Since each unit liquid crystal cell is a few square centimeters in area, but has only a few micrometers gap between substrates, a vacuum injection method using a pressure difference is effectively and widely used. Generally, since injecting the liquid crystal material into the unit liquid crystal cells takes the longest manufacturing time, for manufacturing efficiency, it is important to have optimum conditions for the vacuum injection process. In a typical vacuum injection process, after the unit liquid crystal cells and the liquid crystal material are evacuated in a vacuum apparatus, an injection hole of the unit liquid crystal cell is dipped into a vessel that contains the liquid crystal material. First, since there is no difference in pressure between the interior of the unit liquid crystal cell and the liquid crystal material, the liquid crystal material is injected into the unit liquid crystal cell by capillary forces. Later, after nitrogen gases are introduced into the vacuum apparatus, the pressure difference between the interior and exterior of the unit liquid crystal cell forces liquid crystal material into the unit liquid crystal cell.
A sealing process, which prevents the liquid crystal from leaking through the injection hole, is performed after the injection. The sealing process includes depositing an ultra violet (UV) curable resin by using a dispenser and then sealing the injection hole by irradiation of UV light. Here, since deterioration can happen from contamination of the injection hole during moving or processing, the cell should be handled carefully so as to not contact the exterior material and be exposed for a long time.
At step ST
7
, an inspection process is performed on the plurality of unit liquid crystal cells. The inspection process is performed through eye or microscope inspection by applying a voltage to the unit liquid crystal cell that has pads of a plurality of gate and data lines, each of which is connected to the pad through a shorting bar, and a common electrode. During the inspection, the quality of the unit liquid crystal cell is determined by evaluating deterioration from the impurity, a point defect from the degraded TFT, a line defect from an open of the data and gate lines, and optical property deterioration from non-uniformity of the cell gap. For simplicity, the series of the inspection process mentioned above is called an ON/OFF inspection.
At step ST
8
, a grinding process is performed after the selection of high quality cells by the ON/OFF inspection. This step includes a process of cutting the shorting bar that prevents the cell from malfunctioning due to static electricity. After the grinding process, a liquid crystal module process is performed.
Next, the fabrication process of the liquid crystal cell for small size LCD devices will be briefly explained referring to the
FIGS. 2A
to
2
E.
FIG. 2A
shows the step o
Cho Gyu-Su
Yu Hwan-Seong
LG. Philips LCD Co. Ltd.
McKenna Long & Aldridge LLP
Nguyen Hoan Chau
Ton Toan
LandOfFree
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