Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-10-27
2002-08-06
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S141000
Reexamination Certificate
active
06429918
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a liquid crystal display having high aperture ratio and high transmittance, and more particularly to a liquid crystal display having high aperture ratio and high transmittance, that is capable of reducing light leakage.
DESCRIPTION OF THE RELATED ART
An In-plane Switching(IPS) mode liquid crystal display has been suggested to overcome the narrow viewing angle characteristic of a twisted nematic(TN) mode liquid crystal display.
In the IPS mode liquid crystal display, counter and pixel electrodes for driving liquid crystal molecules are arranged at the same substrate so as to generate an in-plane electric field. However, both counter and pixel electrodes of the IPS mode liquid crystal display are made of an opaque metal layer and arranged at pixel area, therefore the transmittance and the aperture ratio are very low.
Accordingly, a liquid crystal display using a fringe field for driving the liquid crystal molecules has been suggested to improve the transmittance and the aperture ratio of the IPS mode liquid crystal display.
The liquid crystal display using the fringe field so as to drive liquid crystal molecules has following constitutions.
The liquid crystal display having high transmittance and high aperture ratio is active matrix type that a signal from a data bus line is transmitted to a pixel electrode when a gate bus line is selected. When the display signal is applied to the pixel electrode, there is formed an electric field between the pixel electrode and the counter electrode to which a common signal is applied, thereby driving the liquid crystal molecules.
Herein, both counter and pixel electrodes for driving liquid crystal molecules are made of a transparent conductor and a distance between adjoining counter electrode and pixel electrode is narrower than the distance between upper and lower substrates.
As constituted above, all the liquid crystal molecules on and between the counter electrode and the pixel electrode are driven by the electric field formed between the counter electrode and the pixel electrode. Therefore, transmittance of the liquid crystal display is more improved.
However, a relatively high display signal is continuously applied to the data bus line though the gate bus line is not selected. Consequently, there is formed a parasitic electric field between the data bus line to which the display signal is applied and its adjoining counter electrode or the pixel electrode. Due to the parasitic electric field, liquid crystal molecules between the data bus line and its adjoining counter electrode are driven thereby leaking light when a sub-pixel not is selected. At this time, the liquid crystal display having high transmittance and high aperture ratio has a distance between the counter electrode and the data bus line that is narrower than that of the general IPS mode liquid crystal display. For this reason, the parasitic electric field of the liquid crystal display having high transmittance and high aperture ratio is generated more excessively than the IPS mode liquid crystal display.
FIG. 1
is a simulation result showing leakage light of a conventional liquid crystal display having high transmittance and high aperture ratio. Referring to
FIG. 1
, when a voltage of 6.5V is applied to the data bus line, approximately 50% of leakage light is occurred around the data bus line. More particularly, the leakage light is occurred to 9 &mgr;m of both sides of the data bus line. Herein, X portion in the drawing stands for the distribution of liquid crystal molecules and equipotential line e, and Y portion stands for the light transmittivity. When the leakage light is occurred as described above, contrast ratio of the liquid crystal display is lowered thereby degrading the display quality.
In order to prevent the leakage light that is generated through such a wide region, a method for forming a black matrix to have relatively wide size that is enough to cover a region in which the leakage light is formed. However, the black matrix decreases aperture size of the sub-pixel, therefore wanted aperture ratio can not be obtained.
SUMMARY OF THE INVENTION
Accordingly, it is the object of the present invention to provide a liquid crystal display having high transmittance and high aperture ratio, that is capable of preventing leakage light and lowering of aperture ratio.
To accomplish the object, the liquid crystal display according to the present invention comprises: a lower substrate; a gate bus line and a data bus line, both disposed in an active matrix type so as to define a sub-pixel on the lower substrate; a counter electrode formed at the sub-pixel region of the lower substrate, made of a transparent material, wherein a common signal is applied to the counter electrode; a pixel electrode formed at the sub-pixel region of the lower substrate, made of a transparent material, wherein the pixel electrode forms a fringe field with the counter electrode; a thin film transistor formed at an intersection of the gate bus line and the data bus line, wherein when the gate bus line is selected, the thin film transistor transmits a signal of the data bus line to the pixel electrode; an upper substrate opposed to the lower substrate with intervening a selected distance; a black matrix formed at an inner surface of the upper substrate and arranged so as to define the sub-pixel; a shielding electrode formed at an inner surface of the upper substrate and disposed at a location corresponding to the data bus line of the lower substrate; and a liquid crystal layer sandwiched between the upper and the lower substrates, wherein when the gate bus line is not selected, the shielding electrode forms an electric field with the data bus line.
The liquid crystal display further comprises: a lower substrate; a gate bus line and a data bus line, both disposed in an active matrix type so as to define a sub-pixel on the lower substrate; a counter electrode formed at the sub-pixel region of the lower substrate, made of a transparent material, wherein a common signal is applied to the counter electrode; a pixel electrode formed at the sub-pixel region of the lower substrate, made of a transparent material, wherein the pixel electrode forms a fringe field with the counter electrode; a thin film transistor formed at an intersection of the gate bus line and the data bus line, wherein when the gate bus line is selected, the thin film transistor transmits a signal of the data bus line to the pixel electrode; an upper substrate opposed to the lower substrate with intervening a selected distance; a black matrix formed at an inner surface of the upper substrate and arranged so as to define the sub-pixel; a shielding electrode formed at an inner surface of the upper substrate and disposed at a location corresponding to the data bus line of the lower substrate; and a liquid crystal layer sandwiched between the upper and the lower substrates, wherein the same signal as applied to the counter electrode is applied to the shielding electrode, and when the gate bus line is not selected, the shielding electrode forms an electric field with the data bus line.
The liquid crystal display still comprises: a lower substrate; a gate bus line and a data bus line, both disposed in an active matrix type so as to define a sub-pixel on the lower substrate; a counter electrode formed at the sub-pixel region of the lower substrate, made of a transparent material, wherein a common signal is applied to the counter electrode; a pixel electrode formed at the sub-pixel region of the lower substrate, made of a transparent material, wherein the pixel electrode forms a fringe field with the counter electrode; a thin film transistor formed at an intersection of the gate bus line and the data bus line, wherein when the gate bus line is selected, the thin film transistor transmits a signal of the data bus line to the pixel electrode; a first alignment layer formed on the resultant of the lower substrate; an upper substrate opposed to the lower substrate wit
An Seong Jun
Choi Woo Ho
Jeon Jong Yob
Dudek James
Hyundai Display Technology Inc.
Selitto Behr & Kim
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