Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
1999-10-14
2002-05-07
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S038000, C349S039000, C349S192000
Reexamination Certificate
active
06384878
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a liquid crystal display (referred to as an LCD hereinafter), more particularly, to an LCD having an electrostatic protection circuit.
(b) Description of the Related Art
A liquid crystal display (LCD), which is one type of flat panel displays (FPDs), includes two substrates having transparent electrodes and a liquid crystal layer interposed between the substrates. In the LCD, light transmittance is controlled by varying the voltages applied to the liquid crystal layer. The LCD is increasingly used because of its low driving voltage and low power consumption.
Most of the LCD manufacturing process is performed on a glass substrate. Since the glass substrate is nonconductive, electric charges, which are abruptly generated on the substrate, cannot be dispersed. This may shorten or disconnect metal lines formed on the substrate, or damage the insulating films or TFTs by the electrostatic discharge. Most of such defects, which can not be repaired, decrease the yields. In addition, it requires various limitations in manufacturing process and a specialized equipment and environment to overcome the limitations, increasing overall manufacturing costs.
In a conventional LCD, a plurality of gate lines and a plurality of data lines are formed in a display area for displaying visual images. The gate lines and the data lines cross each other to define a plurality of pixels. A thin film transistor (TFT) is formed in each of the pixels, and a gate terminal and a source terminal of the TFT are respectively connected to one of the gate lines and one of the data lines. Moreover, a storage capacitor is formed between a drain terminal of the TFT and a previous gate line for the pixel. And the drain terminal is also connected to a liquid crystal capacitor. Electric charges in the pixel when the TFT is turned ON are maintained by the two capacitors even after the TFT is turned off. The gate lines and the data lines are extended outside the display area, pads are formed at ends of the gate and data lines, and an electrostatic charge shorting bar that links all the lines is formed outside the pads.
In the LCD manufacturing process, the shorting bar is removed by grinding edge portions of the substrate along grinding lines after attaching a polarizer to the substrate. In the grinding process, the polarizer is also very often ground and damaged, which limits the size of the polarizer and the substrate edge area. Accordingly, it is preferable to attach the polarizer after the grinding step. However, since the shorting bar is removed after grinding, it is not possible to protect the device from the electrostatic charges generated when attaching the polarizer.
An electrostatic charge dispersing circuit is disclosed in a currently pending application, application Ser. No. 09/172,130 filed Oct. 14, 1998, entitled “LIQUID CRYSTAL DISPLAYS AND MANUFACTURING METHODS THEREOF”, by inventors Joo-Hyung LEE, Dong-Gyu KIM and Woon-Yong PARK. This application is hereby incorporated by reference.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a liquid crystal display having an electrostatic protection circuit that effectively prevents the electrostatic damage.
It is another object of the present invention to provide a liquid crystal display that minimizes limitations placed on the LCD manufacturing process.
To achieve the above objects, the present invention provides a liquid crystal display including a plurality of first wires and a plurality of second wires intersecting the first wires. A plurality of pixels are respectively defined by the first wire and the second wire and each pixel has a liquid crystal capacitor, a thin film transistor and a storage capacitor. A plurality of dummy wires are located outside a display area defined by the plurality of pixels and intersect the first wires. A plurality of dummy TFTs are formed outside the display area, and a source terminal and a drain terminal of the dummy TFT are respectively connected to the first wire and the dummy wire. Electrodes of a dummy storage capacitor are respectively connected to the drain terminal of the dummy TFT and the dummy wire. In this structure, a ratio of a storage capacitance of the storage capacitor located in the display area to a storage capacitance of the dummy storage capacitor located outside the display area is no higher than 2.23.
Meanwhile, it is possible that the ratio of the storage capacitance of the storage capacitor to the storage capacitance of the dummy storage capacitor is no higher than 1.95. Moreover, more than two dummy storage capacitors may be coupled to one another.
It is also possible that a transparent electrode is located opposite the drain terminal of the dummy TFT, and a storage capacitor is formed by the electrode and the drain terminal overlapping the electrode via a passivation film.
In the LCD, it is possible to avoid defects arising from electrostatic charges without limiting the storage capacitance, which is an inherent design parameter for a display device, inside the display area.
REFERENCES:
patent: 5606340 (1997-02-01), Suzuki et al.
patent: 5930607 (1999-07-01), Satou
patent: 6088073 (2000-07-01), Hioki et al.
patent: 6104449 (2000-08-01), Takahashi et al.
patent: 6175394 (2001-01-01), Wu et al.
Chung David
Parker Kenneth
Samsung Electronics,Co., Ltd.
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