Liquid crystal cells – elements and systems – Particular excitation of liquid crystal – Electrical excitation of liquid crystal
Reexamination Certificate
2001-11-27
2004-08-17
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular excitation of liquid crystal
Electrical excitation of liquid crystal
C349S192000
Reexamination Certificate
active
06778233
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for darkening a pixel by which a thin film transistor disposed for each pixel is used to darken a defective pixel on a display device for controlling the application of a voltage to a corresponding pixel electrode.
2. Description of the Related Art
Heretofore, as flat display devices, there have been liquid crystal displays (LCDs), which have advantages such as a low dissipation power and a thin structure, and therefore, they are widely utilized as display devices for various electrical appliances.
As these kind of LCDs, products of an active matrix type have been increasing in which a thin film transistor (TFT) is disposed corresponding to each of pixels arranged in a matrix state and which controls the display of the corresponding pixel by turning this thin film transistor ON and OFF.
However, in such an LCD of the active matrix type, if a defect, for example, leakage current, occurs in the thin film transistor during a manufacturing process, the display of this pixel is impossible. Furthermore, also owing to short circuit of a supplemental capacitive electrode and an supplemental capacitive line, the display of this pixel is impossible. At this time, a defect of one pixel unit (a point defect) occurs.
In the case of such a defect of one pixel unit, if this point is a dark point (black), it is not noticeable, but if this point is a bright point (white) and if the pixel is surrounded with black pixels, there is a problem that the defective pixel is very noticeable. Accordingly, it is required to darken the defective pixel.
In the LCD of a usual normally white mode which is the mainstream of a twisted nematic (TN) LCDs, it is necessary for the display of the operationally defect pixel to be blackened by always applying an ON voltage to a liquid crystal. Therefore, connection between the TFT and a pixel electrode is cut, and both electrodes for the supplemental capacitor for holding the applied voltage are shorted to always apply the voltage to the pixel electrode.
On the other hand, with the amplification of the display, it is required to widen a visual field angle of the display, and a vertical orientation type LCD which is less dependent on the visual field angle of the display is being developed. This vertical orientation type LCD takes the display of normally black mode. Thus, even in such an LCD of the normally black mode, it is necessary to properly repair a point defect.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for effectively darkening an operationally defect pixel in a normally black LCD.
In the present invention, a connection position between a contact and a pixel electrode is cut by a laser. Therefore, the pixel electrode can be reliably opened, whereby the application of a voltage to the pixel electrode can be prevented to darken this pixel.
Furthermore, an electrode of a thin film transistor in the vicinity of the contact can be cut by the laser, so that the thin film transistor side of the contact is also cut to completely electrically separate the contact, thereby reliably preventing the application of the voltage to the pixel electrode via the contact. Moreover, also in the case where a short occurs on an supplemental capacitive line, the voltage of supplemental capacitive line can be reliably prevented from being applied to a data line via the thin film transistor.
Furthermore, the above-mentioned display device is suitably a liquid crystal display device of the normally black type.
In addition, a liquid crystal display device according to the present invention includes a pixel darkened by the above-mentioned method.
REFERENCES:
patent: 5166085 (1992-11-01), Wakai et al.
patent: 5289174 (1994-02-01), Suzuki
patent: 5691786 (1997-11-01), Nakai
patent: 5965906 (1999-10-01), Park
patent: 6219113 (2001-04-01), Takahara
patent: 6515720 (2003-02-01), Iizuka et al.
Matsuura Yoshiaki
Segawa Yasuo
Tokunaga Masahiko
Cantor & Colburn LLP
Sanyo Electric Co,. Ltd.
Ton Toan
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