Liquid crystal cells – elements and systems – Nominal manufacturing methods or post manufacturing... – Defect correction or compensation
Reexamination Certificate
2001-01-26
2004-11-02
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Nominal manufacturing methods or post manufacturing...
Defect correction or compensation
C349S106000
Reexamination Certificate
active
06812992
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to liquid crystal displays. More particularly, the invention relates to a technique for resolving major defects in a normally white liquid crystal display.
BACKGROUND OF THE INVENTION
Liquid crystal displays (LCDs) are used in a variety of different applications. For example, LCDs are used in laptop computers, hand-held devices, cellular phones, coordinate location systems and vehicle displays. One type of an LCD is a normally white LCD. Pixels in normally white LCDs will be non-transmissive when power is applied to the pixel when driven black. Pixels that remain transmissive when power is applied are defective and known as “electrically open” or “bright on” pixel defects. When these defects occur in quantity, there is reason for a quality rejection of the LCD.
Most users of LCDs will permit some quantity of defects. However, a “bright on” defect is considered a “major” type defect (compared to an electrically shorted pixel or partially shorted pixel, which are considered minor defects). Technology currently exists to reduce the adverse impact of a bright on pixel in a “normally black” LCD (caused by an electrical short) and, depending on the thin film transistor (TFT) structure, in some normally white LCDs. Using this technology, when electrical shorts are detected in a normally black LCD, a laser is used to isolate the circuit from the bus line on the TFT substrate. This technology, however, will not work for all normally white LCDs, and in particular will not work for normally white LCDs in which the bright on defect is caused by an open circuit. Thus, improvements are necessary to develop techniques to resolve “bright on” pixel defects in a normally white LCD.
SUMMARY OF THE INVENTION
A technique is provided to resolve “bright on” pixels defects in a normally white LCD. A laser operating with a 780-840 nm wavelength in the visible range permits the ablation of the pigmented color filter material coated or adhered to a glass substrate of the LCD without causing thermal or mechanical damage to the glass substrate. The laser is used to darken the defective pixel by focusing on a color filter of the defective pixel. After a portion of the color filter is darkened, a minor defect exists instead of a major defect.
REFERENCES:
patent: 5142386 (1992-08-01), Ishihara
patent: 5531881 (1996-07-01), Matsumura et al.
patent: 5926246 (1999-07-01), Tomita et al.
patent: 5-27111 (1993-02-01), None
patent: 09-005732 (1997-01-01), None
patent: 9-152568 (1997-06-01), None
Chowdhury Tarifur R.
Eppele Kyle
Jensen Nathan O.
Rockwell Collins
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