Continuous domain in-plane switching liquid crystal display

An IPS liquid crystal display (200) of a preferred embodiment of the present invention includes a first substrate (201), a second substrate (202), and liquid crystal molecules interposed therebetween. A plurality of gate lines (211) and data lines (212) are formed at the first substrate, thereby defining a plurality of pixel regions. A pixel electrode (233), a common electrode (243) and a TFT (220) are provided in each pixel region, the pixel electrode and the common electrode having a same curved shape. Because the pixel and common electrodes of have a same curved shape with smooth bends, when a voltage is applied, disclination of the liquid crystal molecules does not occur, and the contrast ratio of the IPS LCD is unimpaired. Furthermore, the electric field generated by them is a smooth continuum of multiple domains, and the IPS LCD provides equally fine visual performance at various different viewing angles.

BACKGROUND OF THE INVENTION

1. Cross Reference to Related Application

This application is related to a co-pending application entitled “Continuous domain in-plane switch liquid crystal display,” which is assigned to the same assignee as this application.

2. Field of the Invention

The present invention relates to IPS (in-plane switching) mode LCDs (liquid crystal displays), and particularly to an IPS LCD which provides continuous domains when in a driven state.

3. General Background

A liquid crystal display utilizes the optical and electrical anisotropy of liquid crystal molecules to produce an image. The liquid crystal molecules have a particular passive orientation when no voltage is applied thereto. However, in a driven state, the liquid crystal molecules change their orientation according to the strength and direction of the driving electric field. A polarization state of incident light changes when the light transmits through the liquid crystal molecules, due to the optical anisotropy of the liquid crystal molecules. The extent of the change depends on the orientation of the liquid crystal molecules. Thus, by properly controlling the driving electric field, an orientation of the liquid crystal molecules is changed and a desired image can be produced.

The first type of LCD developed was the TN (twisted nematic) mode LCD. Even though TN mode LCDs have been put into use in many applications, they have an inherent drawback that cannot be eliminated; namely, a very narrow viewing angle. By adding compensation films on TN mode LCDs, this problem can be ameliorated to some extent. However, the cost of the TN mode LCD is increased. Therefore, a totally different driving means called IPS (in-plane switching) was proposed as early as in 1974. Then in 1993, Hitachi Corporation filed its first U.S. patent application concerning IPS LCDs, in which a particular IPS mode LCD was disclosed.

A conventional IPS mode LCD has an upper substrate, a lower substrate, and a liquid crystal layer interposed therebetween. The liquid crystal layer has a plurality of liquid crystal molecules which have a same orientation when not driven, this orientation being parallel to the substrates. Pixel electrodes and common electrodes are disposed on the lower substrate. When a voltage is applied to the electrodes, an electric field is generated between the electrodes. The electric field drives the liquid crystal molecules to rotate, so that they have a new orientation that is still parallel to the substrates. The change in orientation results in a change in light transmission. In other words, the operation of the IPS mode LCD is such that the liquid crystal molecules rotate in a plane parallel with the substrates in order to fulfill optical switching. The displayed image has the important advantage of a wide viewing angle. In basic IPS mode LCDs, the pixel electrodes and common electrodes are each comb-shaped. The electric field of these LCDs in a driven state is along a certain direction. When the displayed image is viewed at different oblique angles, an observer can notice a quite large color shift.

Referring toFIG. 5, this is a top cross-sectional view of a pixel area of an IPS liquid crystal display as disclosed in U.S. Pat. No. 6,459,465 issued on Oct. 1, 2002. The pixel area includes a gate line113arranged in a first direction, a data line115and a common line135both arranged in a second direction orthogonal to the first direction, a pixel electrode131, a common electrode133, and a TFT (thin film transistor)120positioned at an intersection of the data line115and the gate line113. The TFT120has a gate electrode121, a source electrode123and a drain electrode125, which are connected with the gate line113, the data line115and the pixel electrode131respectively. The pixel electrode131and the common electrode133are spaced apart from each other. The pixel and common electrodes131,133are each generally comb-shaped, with the teeth thereof being zigzagged. First portions of the teeth of the pixel and common electrodes131,133that are aligned in a first direction and are parallel to each other form a first sub-electrode group. Second portions of the teeth of the pixel and common electrodes131,133that are aligned in a second direction and are parallel to each other form a second sub-electrode group.

When a voltage is applied, because the pixel and common electrodes131,133have the zigzagged structures, the electric field (not shown) generated is mainly along two directions. Referring toFIG. 6, the upper portion thereof shows part of the first sub-electrode group, and the lower portion thereof shows part of the second sub-electrode group. The liquid crystal molecules130in the upper and lower portions have different orientations, and the LCD exhibits a two-domain display effect. When viewing the LCD display from any oblique angle, the color shifts generated by the two domains counteract each other, and thus the overall color shift of the display is small.

However, the two-domain electrode configuration of the LCD inherently limits the display thereof. Equally good visual performance at various different viewing angles cannot generally be attained.

What is needed is a multi-domain IPS liquid crystal display which has a high contrast ratio and improved wide viewing angle characteristics.

SUMMARY

In one embodiment, an IPS liquid crystal display includes a first substrate, a second substrate, and liquid crystal molecules interposed therebetween. The first substrate has an alignment layer positioned at an inner surface thereof, the alignment layer having a first aligning direction and a second aligning direction. A plurality of gate lines and data lines are formed at the first substrate, thereby defining a plurality of pixel regions. A pixel electrode, a common electrode and a TFT are provided in each pixel region, the pixel electrode and the common electrode having a same curved shape.

Because the pixel and common electrodes of have a same curved shape with smooth bends, when a voltage is applied, disclination of the liquid crystal molecules does not occur, and the contrast ratio of the IPS LCD is unimpaired. Furthermore, the electric field generated by them is a smooth continuum of multiple domains, and the IPS LCD provides equally fine visual performance at various different viewing angles.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring toFIG. 1andFIG. 2, an in-plane switching liquid crystal display (IPS LCD)200according to a first embodiment of the present invention includes a first substrate201, a second substrate202opposite and parallel to the first substrate201, and liquid crystal molecules203interposed between the first and second substrates201,202. An insulation layer262and a plurality of common electrodes243are disposed on an inner surface of the second substrate201, with the insulation layer262covering the common electrodes243. A passivation layer261, a plurality of pixel electrodes233, and an alignment layer204are positioned on an inner surface of the insulation layer262in that order from bottom to top, with the alignment layer204covering the pixel electrodes233. Referring toFIG. 2, a plurality of gate lines211are formed on the first substrate201, and a plurality of data lines212are disposed on the insulation layer262.

The alignment layer204has a first aligning direction and a second aligning direction (shown inFIG. 3) that are mutually perpendicular. The two aligning directions are created by one or more rubbing processes. A potential difference between each pair of the common electrodes243and pixel electrodes233defines an electric field that is substantially parallel to the first and second substrates201,202. The electric field twists liquid crystal molecules203, so as to change an optical transmission ratio of the IPS LCD200. Consequently, images are displayed by the IPS LCD200according to image signals received by the pixel electrodes233.

The gate lines211and data lines212define a plurality of pixel regions arranged in a matrix. Each pixel region includes the common electrodes243and the pixel electrodes233that are disposed on the different layers of the IPS LCD200, a common line213, and a TFT (thin film transistor)220. The TFT220has a gate electrode221connected to a gate line211, a source electrode222connected to a data line212, and a drain electrode223connected to the pixel electrodes233through a pixel line232. The common line213is connected to the common electrodes243. The pixel and common electrodes233,243are each generally comb-shaped. The teeth of the pixel and common electrodes233,243are arcuate, and are spaced a uniform distance apart from each other. That is, major portions of the teeth of the pixel and common electrodes233,243are opposite and parallel to each other. Also referring toFIG. 3, this shows the structure of the pixel electrodes233and the common electrodes243and the approximate orientation of liquid crystal molecules203when the IPS LCD200is in a driven state. Because the pixel and common electrodes233,243have the arcuate shape, the electric field generated by them is a smooth continuum of multiple domains, and the IPS LCD200provides equally fine visual performance at various different viewing angles. The pixel electrodes233and the common electrodes243can be made of a metallic material or a transparent conductive material such as ITO (indium tin oxide). The IPS LCD200has a higher aperture ratio if the electrodes233,243are transparent.

Referring toFIG. 4, an IPS LCD300according to the second embodiment of the present invention is similar to the IPS LCD200of the first embodiment. However, the IPS LCD300includes pixel electrodes333and common electrodes343whose teeth have a same wavy shape. That is, the pixel and common electrodes333,343are each generally comb-shaped, with the wavy-shaped teeth thereof being spaced a uniform distance apart from each other. Major portions of the teeth of the pixel and common electrodes333,343are opposite and parallel to each other. Liquid crystal molecules303of the IPS LCD300are divided into a first group and a second group. Aligning directions of the first group of the liquid crystal molecules303are changed according to directions of the electrodes333,343. Aligning directions of the second group of liquid crystal molecules303are also changed according to the directions of the electrodes333,343, and are perpendicular to the aligning directions of the first group of liquid crystal molecules303. Because the pixel and common electrodes333,343have the wavy shape, the electric field generated by them is a smooth continuum of multiple domains, and the IPS LCD300provides equally fine visual performance at various different viewing angles.

According to the above-described embodiments, the pixel and common electrodes have a same curved shape with smooth bends. Therefore when a voltage is applied, disclination of the liquid ceystal molecules does not occur, and the contrast radio of the IPS LCD is unimpaired. Further, the electric field generated is a smooth continuum of multiple domains. Therefore the IPS LCD200,300provides equally fine visual performance at various different viewing angles.

In alternative embodiments, the pixel electrodes233,333and common electrodes243,343may be formed on a same layer of the IPS LCD200,300, by utilizing contact holes or other suitable means. This enables a true in-plane electric field to be generated, with the efficiency of utilization of the electric field being higher.

The present invention may have further alternative embodiments, including wherein the two aligning directions are created by one or more photo alignment processes or by one or more ion beam alignment processes.